Effect of anaerobic digestion and pyrolysis on nutrient composition, heavy metals, and phosphorus recovery in manure and sewage sludge biochar

Effect of anaerobic digestion and pyrolysis on nutrient composition, heavy metals, and phosphorus recovery in manure and sewage sludge biochar | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effect of anaerobic digestion and pyrolysis on nutrient composition, heavy metals, and phosphorus recovery in manure and sewage sludge biochar Merkeb Woldu Bezabeh, Maria M. Estevez, Renata Tomczak Wandzel, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8242369/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Recycling nutrients from organic residues is key to circular agriculture, but contaminant limits restrict their reuse. This study examined how anaerobic digestion (AD) and pyrolysis influence nutrient enrichment and regulatory compliance in biochar derived from six feedstocks: raw and digested manures (RM, DM) and biologically or chemically treated raw and digested sewage sludges (BTRSS, CTRSS, BTDSS, CTDSS). Samples were analyzed for pH, dry matter (DM), loss on ignition (LOI), total C and N, macro-/micronutrients, and trace elements, and evaluated against Norway’s 2025 fertilizer regulation using concentration classes and P: metal ratio thresholds. AD reduced DM, LOI, and total C but increased pH, Ca, and Mg; it enhanced P in manures but lowered it in sludges. Pyrolysis produced stable, alkaline biochar (DM > 97%) enriched in P, K, Ca, and Mg, while N and S decreased. Micronutrients (Fe, Mn, B, Mo) and heavy metals became concentrated, with Zn and Cu as key regulatory constraints, whereas Cd, Pb, Hg, and As remained below limits. Chemically treated sludges showed high Al due to coagulants. Overall, digested manure biochar at 400 °C met both P and heavy metal criteria, while most sludge-derived biochar failed eligibility, except for chemically treated raw sludge at 400 °C. anaerobic digestion pyrolysis nutrient enrichment phosphorus recovery heavy metals Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. INTRODUCTION Nutrient recycling from organic residues is increasingly recognized as essential for sustainable agriculture and for the development of circular bioeconomy strategies. Phosphorus (P) is a central element in this context, given its irreplaceable role in plant growth, energy transfer, and root development (Bhat et al., 2024 ; Malhotra et al., 2018 ; Srivastava et al., 2018 ). However, global phosphate rock reserves are finite, geographically concentrated, and subject to market volatility (Chowdhury et al., 2017 ; Dhillon et al., 2017 ; Edixhoven et al., 2014 ; Illakwahhi et al., 2024 ). At the same time, animal manure and sewage sludge represent large, underutilized nutrient streams rich in both macronutrients and micronutrients. Direct application of these residues can supply nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), and Sulphur (S) (Dadrasnia et al., 2021 ; Dridi et al., 2020 ; Gobbi et al., 2000 ; Saikumar & Rao, 2017 ) as well as micronutrients, which are essential for plant metabolism. However, their use is constrained by environmental risks, including nutrient leaching, eutrophication, greenhouse gas emissions, and the accumulation of potentially toxic elements such as cadmium (Cd), lead (Pb), mercury (Hg), nickel (Ni), and chromium (Cr). Biochar production through pyrolysis has emerged as a promising pathway to stabilize carbon (Altıkat et al., 2024 ; Zhu et al., 2022 ), inactivate pathogens (Abdullah et al., 2023 ; Li et al., 2022 ), and concentrate nutrients in a solid matrix (Abdullah et al., 2023 ; Khater et al., 2024 ; Sahoo et al., 2021 ). Moreover, biochar can serve as a source of micronutrients (e.g., Zn, Fe, Mn, Cu), though their bioavailability depends strongly on feedstock type and pyrolysis conditions. Nevertheless, concerns persist regarding elevated heavy metal concentrations, particularly in biochar derived from sewage sludge. (Jin, J. et al., 2016 ; Lu et al., 2016 ; Zhao et al., 2021 ), which may limit their agricultural application under current regulatory frameworks. Anaerobic digestion (AD) is widely used before land application or thermal processing of organic wastes, primarily for biogas production and stabilizing easily degradable organic matter. (Khalid et al., 2011 ; Yadav et al., 2021 ; Zamri et al., 2021 ). AD modifies feedstock chemistry by increasing pH, altering carbon-to-nitrogen ratios, and transforming nutrient pools. For example, NH 4 + -N becomes more dominant, organic matter is partly mineralized, and the relative concentrations of P, K, Ca, and Mg often increase in the solid fraction (Jiang et al., 2019 ; Nyang’au et al., 2024 ; Thakur et al., 2023 ). These shifts are expected to influence the thermal conversion process and the resulting nutrient and heavy metal profiles of digestate-derived biochar. However, systematic evidence on how AD pre-treatment affects macronutrient retention, micronutrient enrichment, heavy metal concentrations, and P recovery in biochar remains limited. This whole study addresses this knowledge gap by comparing biochar produced from raw and anaerobically digested manure and sewage sludge. The objectives were to: (I) assess the effect of AD and pyrolysis on nutrient composition, (II) quantify heavy metal concentrations relative to Norwegian and EU fertilizer regulations, and (III) evaluate phosphorus recovery and classify the P-to-heavy metal ratio (Norwegian 2025 regulation) for agricultural use. The research was based on biochar produced from small-scale pyrolysis trials at 400°C and 600°C across all feedstocks, and on the characterization of raw and anaerobically digested feedstocks and their respective biochar samples. We hypothesized that AD and pyrolysis would (a) concentrate P, Ca, and Mg, and select micronutrients in the solid fraction, thereby increasing their retention in biochar; (b) reduce N and S contents due to enhanced mineralization and volatilization; and (c) influence heavy metal concentrations and P recovery pathways by modifying feedstock chemistry before pyrolysis. 2. MATERIALS AND METHODS 2.1 Feedstock and biochar samples Six different feedstocks were used in the pyrolysis trials: raw manure (RM), digested manure (DM), biologically treated raw sewage sludge (BTRSS), biologically treated digested sewage sludge (BTDSS), chemically treated raw sewage sludge (CTRSS), and chemically treated digested sewage sludge (CTDSS). Samples of BTRSS and BTDSS were sourced from western Norway, provided by the regional wastewater treatment plant (WWTP). Nord Jæren (SNJ), in Mekjarvik, operated by the inter-municipal water and wastewater organization for the Stavanger region, IVAR IKS. SNJ WWTP runs a process that focuses on enhanced biological phosphorus removal (EBPR), a well–established technology for phosphorus removal from wastewater that can be combined with activated sludge, as in the case of SNJ, to remove P without the use of chemicals. The process utilizes Polyphosphate–Accumulating Organisms (PAOs) in the biomass, which remove P from the liquid phase through cellular growth. It has been reported that the PAOs are altered between anaerobic and aerobic conditions. After wastewater treatment, the generated sludge undergoes mesophilic (36 ± 1°C) AD with an organic loading rate (OLR) of 2 kg VS/m3/day and a hydraulic retention time (HRT) of 19 days. CTRSS samples were provided by Åse WWTP, managed by ÅRIM AS (today Attvin AS), the inter-municipal waste and wastewater organization for the Ålesund region. At the Åse plant, wastewater is chemically treated with polyaluminum chloride (PAX 33) to remove phosphorus and organic matter. The CTDSS samples were from the biogas plant at Rådalen, operated by Bergen Municipality. This last plant treats municipal sludge generated at all the wastewater treatment plants in the Bergen area, with a pre-hygienisation process (70°C for 1 hour) before running thermophilic (54 ± 1°C) AD with an OLR of 3–4 Kg VS/m3.day and an HRT of 12 days. The sludge samples were dewatered to achieve dry matter (DM) concentrations of 25%-32%, followed by oven drying to a final DM content of 85%–95%. Additionally, cattle manure samples were collected from the farm at Kalnes Agricultural School in Sarpsborg. Solid manure, rich in fibres from straw, sawdust, cow and horse manure, was directly used as a feedstock for biochar production. Digested manure was provided by Aquateam COWI, after continuous mesophilic AD in two laboratory bench-scale reactors (Belach Bioteknik AB, Sweden) with a working volume of 20 L (OLR: 2 g VS/L.day, HRT: 20 days) of the manure fraction obtained from Kalnes farm. Pyrolysis trials The pyrolysis trials were performed by WAI Environmental Solutions AS (Tonsberg, Norway). A small-scale pyrolysis unit was employed, consisting of a rotatory tube furnace with a 2 L working volume, 3.5 kW installed power, and N2 as the carrier gas (flow: 3 L/min). The trials run at 400°C and 600°C with a residence time of 60 minutes. Feedstocks and Biochar Laboratory Analysis Total C and N in feedstocks and biochar were measured in dried and crushed samples by dry combustion (Nelson & Sommers, 1982 ). At 1050°C, using a Leco CHN1000 instrument (St. Joseph, Michigan, USA) according to the Dumas method (Bremner & Mulvaney, 1982 ), and the pH was measured from a 1:5 biochar and (feedstock) to water ratio. The main element (K, Mg, Ca, Fe, P, S and Mo, B, Mn) and trace element (As, Cd, Co, Cr, Cu, Ni, Pb, Hg and Zn) contents in feedstocks and biochar’s were determined by sample digestion with HNO 3 (conc.) at 260°C in an Ultraclave microwave digestion system (Milestone) for two and a half hours, with subsequent dilution up to 50 mL and analysis with a Triple QQQ 8800 ICP-MS (Agilent Technologies) with a reaction-collision cell (B, As, Cd, Co, Cr, Cu, Mo, Ni, Pb, and Hg ) and a 5100 SVDV ICP-OES (Agilent Technologies) for determination of Ca, Fe, K, Mg, Mn, P, Al, S and Zn. 3. RESULTS 3.1. Impact of anaerobic digestion and pyrolysis on dry matter, loss on ignition, carbon, and macronutrient composition of manure and sewage sludge-derived biochar’s AD and pyrolysis markedly influenced the physicochemical properties of manure and sludge-derived materials. Across all feedstocks, AD consistently reduced dry matter (Fig. 1 B), with the most drastic reduction observed in biologically treated sludge (–15%). At the same time, pyrolysis generally counteracted this effect, producing highly stable biochar with dry matter values above 97%, except in the case of CTDSS, where no improvement was observed. Loss on ignition (LOI) (Fig. 1 C) followed a similar pattern. Raw manure (RM) had the highest LOI (89.99%), which decreased after AD (77.81%) and fell further with pyrolysis to 60.31% (raw, 600°C) and 59.76% (digestate, 400°C). In BTRSS, LOI declined from 79.65% (raw) to 69.35% (digestate), and further to 59.76% (raw, 400°C) and 45.31% (digestate, 600°C) after pyrolysis. CTRSS showed 69.35% LOI in the raw form, decreasing to 46.22% and 37.54% after pyrolysis at 400°C and 600°C, respectively. The CTDSS already had a relatively low LOI (58.8%), which remained unchanged after pyrolysis, indicating a limited response due to its high mineral content. The pH of feedstock and biochar varied with both AD and pyrolysis (Fig. 1 D). Raw manure was slightly alkaline (7.34), increasing modestly after AD (7.70) and strongly after pyrolysis (10.3–10.4). Digested manure’s (DM) biochar reached 9.7 at 400°C. Raw, biologically treated sludge was acidic (5.9), but it became more acidic after AD (6.9) and pyrolysis (7.2–9.9). The chemically treated sludge was near neutral (pH 6.6–7.5), although pyrolysis at 400°C reduced the pH, reflecting the sludge's mineral-rich composition and its buffering effect. Overall, AD raised pH in manure and biological sludge, while pyrolysis generally enhanced alkalinity, especially at 600°C. Total carbon (C) decreased after AD across all feedstocks (Fig. 1 A). In manure, pyrolysis concentrated C (53% in raw manure biochar), whereas in sludges it declined, most notably in CTRSS (41% in feedstock vs. 27% after 400°C). P concentrations increased strongly after pyrolysis in all feedstocks (Fig. 2 B). Manure P rose from 4.1 g kg⁻¹ in raw feedstock to 8.5 g kg⁻¹ at 600°C, while digestate manure reached 29 g kg⁻¹ at 400°C. BTSS increased from 17 to 37 g kg⁻¹ (feedstock to 600°C biochar), while biologically treated digestate sludge rose from 14 to 25 g kg⁻¹. CTRSS showed the highest enrichment (42.5 to 84.5 g kg⁻¹ at 400°C). AD concentrated P in manure but reduced it in sludges. Nitrogen (N) dynamics contrast between feedstocks (Fig. 2 A). AD increased N in manures (1.85–2.36%) and chemical sludge but reduced it in biological sludge. Pyrolysis consistently decreased N levels, especially at 600°C, due to volatilisation losses. Potassium (K) (Fig. 2 C), magnesium (Mg) (Fig. 2 E), and calcium (Ca) (Fig. 2 D) were all affected differently by AD and pyrolysis. AD generally reduced K concentrations (e.g., raw manure 20 to 13.7 g kg⁻¹; raw biological 4.2 to 2.9 g kg⁻¹), but increased Mg and Ca. DM contained higher Mg (10.6 vs. 2.4 g kg⁻¹ in raw) and Ca (21.7 vs. 6.2 g kg⁻¹), while BTDSS also showed enrichment (Mg 5.5 vs. 4.7 g kg⁻¹; Ca 21 vs. 10 g kg⁻¹). Pyrolysis consistently concentrated these minerals: manure-derived biochar showed substantial increases, with K rising to 32 g kg⁻¹ and Ca to 17 g kg⁻¹ at 600°C, while digestate manure biochar was particularly enriched, with Ca increasing to 43.3 g kg⁻¹ and K to 29.3 g kg⁻¹ at 400°C, and Mg reaching 19.8 g kg⁻¹. In sludges, enrichment was also pronounced, with Ca in digestate biological sludge rising to 51 g kg⁻¹ at 600°C. Sulfur (S) (Fig. 2 F) generally decreased with pyrolysis. In manure, S dropped from 2.3 g kg⁻¹ in raw feedstock to 1.6 g kg⁻¹ at 400°C. In biologically treated raw sludge, S declined sharply from 9.1 to 1.3 g kg⁻¹ (feedstock to 600°C biochar), while in biologically treated digestate sludge it decreased from 10 to 3.8 g kg⁻¹. The exception was digestate chemical sludge, where S remained stable (11 g kg⁻¹). AD increased S in most feedstocks, particularly manure and chemical sludge. Overall, AD tended to raise pH and enrich Mg and Ca (while reducing K), but lowered C and P in sludges. Pyrolysis enriched P, K, Mg, and Ca across all materials, but consistently reduced N and S. 3.2 Impact of anaerobic digestion and pyrolysis on micronutrients (Fe, Mo, Mn, B), Se and Al composition of manure and sewage sludge-derived biochar’s The concentrations of micronutrients (Fe, Mo, Mn, B), selenium, and aluminum varied substantially among feedstocks and were strongly modified by AD and pyrolysis (Figs. 3 A, 3 B, 3 C, 3 D, 3 E, and 3 F). Iron (Fe) (Figs. 3 A) was generally low in manure (1.1 g kg⁻¹) but increased after pyrolysis (up to 6 g kg⁻¹ at 400°C). In comparison, DM showed higher initial levels (2.16 g kg⁻¹) and remained enriched in biochar. BTRSS contained moderate Fe (8.5 g kg⁻¹ in raw), with insignificant effect of AD, but pyrolysis caused slight increases at 400°C and reductions at 600°C. In contrast, chemical-treated sewage sludges contained far higher Fe levels, particularly under digestate conditions (37 g kg⁻¹ in feedstock, 60 g kg⁻¹ at 400°C), highlighting a strong enrichment effect of AD and pyrolysis. Molybdenum (Mo) (Figs. 3 C) followed a similar trend, being lowest in manure (< 2 mg kg⁻¹) but enriched by AD and pyrolysis (digestate manure: 3.4 increased to 7.8 mg kg⁻¹ at 400°C). Biologically treated sewage sludges contained higher Mo (4.9–5.9 mg kg⁻¹), which increased by more than 2.5 times after pyrolysis (up to 12 mg kg⁻¹). At the same time, chemical sludges also increased sharply, with raw sludge rising from 3.3 to 8.4 mg kg⁻¹ at 400°C. Manganese (Mn) (Fig. 3 B) was low in manures (0.16 g kg⁻¹ raw) but concentrated after pyrolysis (0.35 g kg⁻¹ at 600°C), with AD enhancing levels before charring. Biological sludge showed the most substantial enrichment, with digestate material rising from 0.37 g kg⁻¹ to 0.83 g kg⁻¹ after pyrolysis at 600°C. In contrast, chemical sludge remained lower overall but showed consistent AD-driven enrichment. B (Figs. 3 D) exhibited a similar pattern, being modest in raw manure (8.8 mg kg⁻¹) but increasing sharply after AD (23.3 mg kg⁻¹ in digestate) and pyrolysis (up to 49.8 mg kg⁻¹ at 400°C). Biological sludges also displayed strong B enrichment (9.7–25 mg kg⁻¹), whereas chemical sludges contained less but still increased steadily, with digestates showing higher initial concentrations and greater retention in biochar. Aluminum (Al) (Figs. 3 E) concentrations varied strongly between feedstocks, with apparent effects of both AD and pyrolysis. In manures (RM, DM), Al remained very low (< 2 g kg⁻¹) and was unaffected by either treatment, indicating that manure is not a significant source of Al. In biologically treated sewage sludges, Al was moderate in the raw material (8 g kg⁻¹) and increased after AD to 9.1 g kg⁻¹. Pyrolysis also significantly increased to (18–21 g kg⁻¹) in row biologically treated sewage sludges and (16–19 g kg⁻¹) in digestate biologically treated sewage sludges. AD consistently raised Al concentrations across feedstocks but decreased in chemically treated sludge (from 54 g kg⁻¹ to 40 g kg⁻¹) and increased in pyrolysis. Selenium (Se) (Fig. 3 F) displayed contrasting behaviors. It was shallow in manure (0.23 mg kg⁻¹), enriched by AD (1.4 mg kg⁻¹), but reduced again after pyrolysis due to volatilization. Biological sludge contained the highest Se concentration among feedstocks (2.5 mg kg⁻¹), but pyrolysis reduced these concentrations, confirming Se's sensitivity to thermal treatment. In contrast, digestate chemical sludge exhibited the highest Se levels overall (2.9 mg kg⁻¹), which further increased after pyrolysis (3.35 mg kg⁻¹), suggesting strong stabilization of Se in this mineral-rich matrix. 3.3. Effects of anaerobic digestion and pyrolysis on heavy metal enrichment and regulatory classification of manure- and sludge-derived biochar Heavy metal concentrations showed significant differences between feedstocks and varied in response to AD and pyrolysis (Table 1 ). In manure, AD reduced Cu slightly (21 to 15 mg kg⁻¹) but increased concentrated Zn (96 to 137 mg kg⁻¹), while pyrolysis further enriched both elements, particularly in digested manure biochar at 400°C (Cu 123 mg kg⁻¹; Zn 543 mg kg⁻¹). Raw manure biochar showed more moderate increments due to up-concentration (Cu 34–48 mg kg⁻¹; Zn 165–195 mg kg⁻¹). In BTRSS, AD did not affect Cu (250 mg kg⁻¹) but increased concentrated Zn (680 to 790 mg kg⁻¹). Pyrolysis caused strong enrichment, with Cu rising to 580–690 mg kg⁻¹ in raw sludge biochar and 470–540 mg kg⁻¹ in digestate sludge biochar, while Zn doubled to 1500–1900 mg kg⁻¹. Ni also increased consistently (15–21 → 36–48 mg kg⁻¹), and Cd rose modestly after AD (0.75 → 0.96 mg kg⁻¹) and further with pyrolysis (up to 1.8 mg kg⁻¹). CTRSS showed a higher content of Cu (150 → 260 mg kg⁻¹), Zn (285 → 610 mg kg⁻¹), and Ni (12 → 18 mg kg⁻¹) after AD, while pyrolysis further concentrated Cu (220–390 mg kg⁻¹), Zn (580–925 mg kg⁻¹), and Cr (from 24.5–39.5 to 63–66.5 mg kg⁻¹). Cd also increased steadily, from 0.25 mg kg⁻¹ in the raw feedstock to 0.85 mg kg⁻¹ after AD and up to 1.25 mg kg⁻¹ after pyrolysis. Table 1 Effect of anaerobic digestion and pyrolysis temperature on heavy metals composition Treatments Type of material Cu Cr Zn Ni Cd Pb Hg [As] mg/kg RM Feedstock 21 3.8 96 2.7 0.09 0.7 0.01 0.18 RM Biochar (400C °) 34 7.1 165 6.7 0.20 2.4 0.01 0.33 RM Biochar (600C °) 48 8 195 6.7 0.03 1.8 0.01 0.51 DM Feedstock 15 5.4 137 3.4 0.10 2.7 < 0.01 0.30 DM Biochar (400C °) 123 11.3 543 15.7 0.30 5.2 < 0.01 0.50 BTRSS Feedstock 250 19 680 15 0.75 18 0.36 4.20 BTRSS Biochar (400C °) 580 41 1600 36 1.80 41 < 0.01 3.80 BTRSS Biochar (600C °) 690 47 1900 43 1.80 49 < 0.01 4.10 BTDSS Feedstock 250 27 790 21 0.96 21 0.51 3.80 BTDSS Biochar (400C °) 470 49 1500 39 1.80 40 < 0.01 4.00 BTDSS Biochar (600C °) 540 57 1700 48 1.50 0 < 0.01 4.70 CTRSS Feedstock 150 24.5 285 12 0.25 7.2 0.60 0.63 CTRSS Biochar (400C °) 220 66.5 580 36 0.47 12 0.13 0.89 CTDSS Feedstock 260 39.5 610 18 0.85 30 0.52 2.55 CTDSS Biochar (400C °) 390 63 925 27.5 1.25 45 0.019 3.15 Where RM, Raw manure; DM, Digestate manure ; BTRSS, biologically treated raw sewage sludge , BTDSS, biologically treated digestate sewage sludge; CTRSS, chemically treated raw sewage sludge , CTDSS, chemically treated digestate sewage sludge. The biochar and feedstocks were also further classified according to the recently updated Norwegian fertilizer regulation (LMD, 2025 ) (Fig. 4 ), which confirmed these trends. Manure-derived feedstocks and biochar (RM, DM) remained within Class 0–II, with all metals well below regulatory thresholds, indicating negligible contamination risk. In contrast, sewage sludge-derived materials were associated with greater regulatory concerns. In biologically treated sludge and digestate (BTRSS, BTDSS), Zn exceeded Class III after pyrolysis at both 400°C and 600°C, while Cu reached Class III in the 600°C biochar. Cr and Cd generally remained within Class II–III. In chemically treated sludge and digestate (CTRSS, CTDSS), AD moderately increased Zn, and pyrolysis further concentrated it to Class III levels at 400°C. In contrast, other metals (Cr, Ni, Cd, Pb, Hg, As) remained within Class I–II. Overall, AD elevated heavy metal concentrations in sewage sludge feedstocks, while pyrolysis consistently intensified this effect, especially for Zn and Cu. In contrast, manure-derived materials maintained low contaminant levels and remained fully compliant with the national fertilizer regulation. 3.4 Effects of anaerobic digestion and pyrolysis on phosphorus enrichment and regulatory eligibility of biochar The relationship between phosphorus content and P: metal ratios revealed contrasting impacts of AD and pyrolysis across different feedstocks (Figs. 5 and 6 ). AD increased P% in manure (DM) and in sludge digestates (BTDSS, CTDSS), thereby improving P: metal ratios for Cu and Cr (Fig. 5 ). Pyrolysis further increased P concentrations, shifting materials to the right on the P% axis; however, this enrichment was often offset by lower P: metal ratios due to heavy-metal accumulation, particularly Zn. Manure-derived biochar, especially DM biochar at 400°C, achieved both higher P% (exceeding the eligibility threshold of 1.5%) and favorable P: Cu, P: Cr, and P: Ni ratios, all well above the regulatory limits (24, 155, and 310, respectively). In contrast, sludge-derived biochar consistently showed Zn as the limiting factor. Despite pyrolysis increasing their P content above the eligibility threshold, their P: Zn ratios remained close to or below the threshold (19), with BTRSS and BTDSS biochar at 400–600°C particularly constrained by excessive Zn accumulation. By comparison, Cu, Cr, and Ni ratios were consistently above their thresholds across all treatments, confirming they are not critical for compliance. For Cd, Pb, Hg, and As (Fig. 6 ), all feedstocks and biochar-maintained P: metal ratios far exceeding their respective regulatory thresholds (7,750, 194, 5,167, and 780, respectively), regardless of treatment. Cd and Hg, commonly highlighted as critical contaminants in sewage sludge, posed no limitation here, with ratios remaining orders of magnitude above the thresholds. Pb and As, while enriched in chemically treated sludge (CTRSS, CTDSS), also maintained safe margins well above the regulatory limits. The phosphorus eligibility threshold (P% ≥ 1.5%) remained decisive: raw manure (RM) and untreated digestates, which exhibited favorable P: metal ratios, were excluded due to insufficient phosphorus concentration. Overall, the analysis demonstrates that Cd, Pb, Hg, and As are not limiting factors under the 2025–2028 Norwegian regulation. The regulatory classification of feedstocks and their corresponding biochar (Fig. 7 ) revealed apparent differences in eligibility under the updated Norwegian fertilizer regulation. Manure-derived materials (RM and DM) were essentially not eligible because of their low phosphorus content (P < 1.5%), except for digestate manure biochar at 400°C, which complied with all heavy-metal thresholds and was therefore fully eligible for agricultural use. In contrast, sewage sludge-derived materials were more constrained by heavy metals, particularly zinc and copper. Biologically treated raw sludge (BTRSS) was initially eligible as a feedstock; however, its biochar exceeded the Zn Class IV and Cu Class III thresholds, rendering it ineligible. BTDSS was an eligible feedstock. Still, the 400°C biochar was restricted to non-cultivated uses due to Zn Class III, while the 600°C biochar exceeded Zn Class IV and was not permitted. Among chemically treated sludge materials, CTRSS was consistently eligible as both a feedstock and a biochar, whereas CTDSS was eligible as a feedstock but restricted to non-cultivated areas at 400°C (Zn Class III). Overall, these results demonstrate that pyrolysis increases phosphorus concentration, which can improve the eligibility of manure biochar; however, it also concentrates heavy metals in sewage sludge biochar, particularly zinc, thereby limiting their use primarily to non-food or non-cultivated land applications. 4. DISCUSSION 4.1 Impact of anaerobic digestion and pyrolysis on dry matter, loss on ignition, carbon, and macronutrient composition of manure and sewage sludge-derived biochar’s AD and pyrolysis induced contrasting but complementary effects on the stability and nutrient composition of manure and sewage sludge. Across all feedstocks, AD reduced dry matter (DM), loss on ignition (LOI), and total carbon (C) contents, confirming the microbial decomposition of labile organics and their conversion into biogas (Aguirre-Villegas et al., 2019 ; Wang et al., 2020 ; Wang et al., 2023 ). This reduction was particularly pronounced in biologically treated sewage sludge, which lost nearly one-fifth of its DM, while manures and chemically treated sludge were less affected. At the same time, AD raised the pH in manure and sewage sludges, most likely through the accumulation of ammonia and carbonate salts (Chen et al., 2024 ; Demirbaş et al., 2016 ; Kang et al., 2017 ), and increased concentrations of some nutrients, such as N, Mg, Ca, and S, reflecting the mineralization and redistribution of organic matter during digestion (Adani et al., 2020 ; Weimers et al., 2022 ). Pyrolysis, on the other hand, largely counteracted the loss of stability caused by AD, producing biochar with very high DM (> 97%) and low LOI, while also shifting the chemical composition towards a more mineral-rich and alkaline material (Basinas et al., 2023 ; Opatokun et al., 2017 ; Petrovič et al., 2021 ). These changes illustrate the role of pyrolysis as a stabilization step that fixes the remaining carbon into aromatic structures while concentrating on the inorganic fraction (Opatokun et al., 2017 ). Nutrient dynamics differed strongly between elements and feedstocks. Phosphorus (P) was consistently enriched after pyrolysis, especially in chemically treated sewage sludge, where concentrations doubled beyond 80 g kg⁻¹ due to the retention of Fe-, Al-, and Ca-bound phosphates after organic matter volatilization. (Feng et al., 2024 ; Filho et al., 2024 ; Frišták et al., 2018 ; Robinson et al., 2017 ). Nitrogen (N), by contrast, declined markedly with pyrolysis as volatile compounds such as ammonia (NH₃), hydrogen cyanide (HCN), and nitrogen oxides (NOx) were released (Cao et al., 2013 ; Chen, G. et al., 2020 ; Chen et al., 2012 ; Chen et al., 2017 ; Wang, Y. et al., 2019 ). However, AD increased N in manure and chemically treated sludge by concentrating ammoniacal N as organic matter degraded. Potassium (K), calcium (Ca), and magnesium (Mg) were strongly enriched in all biochar, with the greatest increase observed in digestate manure and sludge, confirming their thermal stability and accumulation in the ash fraction. (Khater et al., 2024 ; Liu et al., 2023 ; Shen & Yuan, 2021 ; Shi et al., 2023 ). Sulfur (S) showed the opposite trend, with significant reductions during pyrolysis due to volatilization as SO₂ and H₂S (Hou et al., 2018 ; Xu et al., 2021 ; Zhang et al., 2017 ), except in digestate chemical sludge, where mineral sulfates or sulfides likely stabilized S this is related to materials rich in mineral content, where sulfur can be stabilized as mineral sulfates or sulfides (Cao et al., 2022 ; Huang et al., 2020 ; Xing et al., 2024 ). 4.2 Impact of anaerobic digestion and pyrolysis on micronutrient composition of manure and sewage sludge-derived biochar’s AD and pyrolysis substantially influenced the concentrations and distribution of micronutrients (Fe, Mo, Mn, B, Al, and Se) across manure- and sewage sludge-derived feedstocks. Iron (Fe) was particularly enriched in chemically treated sewage sludges, where concentrations increased from 6.3 g kg⁻¹ in the raw feedstock to > 12 g kg⁻¹ in biochar, and further to 60 g kg⁻¹ in digestate chemical sludge after pyrolysis. This strong enrichment reflects the influence of Fe-based coagulants commonly used during chemical sludge treatment, which persist and concentrate during AD and thermal processing (Geng et al., 2022 ; Wang, R. et al., 2019 ; Xiao et al., 2017 ). In contrast, manure and biological sludge contained lower Fe levels, with AD exerting only modest effects and pyrolysis leading to moderate concentration. Molybdenum (Mo) was found in low levels in manure. Still, it was enriched substantially in sludge-derived biochar, with concentrations more than doubling during pyrolysis, particularly in biological sludge (from 5 mg kg⁻¹ to > 12 mg kg⁻¹). AD enhanced Mo concentrations in both manure and sludge feedstocks, likely due to organic matter breakdown and concentration of trace elements, with pyrolysis further amplifying this effect (Cai et al., 2022 ). These trends suggest that Mo is largely conserved under pyrolytic conditions and that AD acts as a pre-concentrating step. Manganese (Mn) also showed consistent enrichment, with the highest values recorded in digestate biological sludge biochar (> 0.8 g kg⁻¹). AD increased Mn in all feedstocks, likely through mineralization and solubilization processes, while pyrolysis concentrated Mn further into the ash fraction (Rodríguez et al., 2020 ). Boron (B) concentrations followed a similar pattern: AD raised B levels in manure and sludge feedstocks, and pyrolysis further enriched them, with digestate manure biochar at 400°C containing nearly six times more B than raw manure. The stability of B during pyrolysis contrasts with that of more volatile nutrients such as N and S (Cao et al., 2022 ; Hong et al., 2022 ), highlighting its potential retention in biochar as a micronutrient source (Cao et al., 2022 ; Dong et al., 2022 ; Gao et al., 2015 ). Aluminum (Al) showed the most pronounced enrichment in chemically treated sludges, with pyrolysis nearly doubling its concentration (from ~ 54 to 105 g kg⁻¹). This reflects the widespread use of Al-based chemicals in wastewater treatment, which persist through AD and concentrate strongly in biochar (Barakwan et al., 2019 ; Basri et al., 2019 ; Muisa et al., 2020 ). In contrast, selenium (Se) exhibited different behavior across digestion and pyrolysis, revealing a strong influence of volatilization and matrix stabilization. In most feedstocks, AD led to an increase in Se (via concentration in residual solids), but pyrolysis at 400–600°C induced marked decreases in Se content, consistent with the volatilization of Se as SeO₂ or elemental Se vapor (Ruiqing, 2013 ; Sugawara et al., 2002 ; Wang & Jia, 2024 ; Wang et al., 2025 ). However, the anomalous enrichment observed in chemically digested sludge (CDRSS) suggests that metal coagulants used in sludge treatment (e.g., Fe/Al) may form intense binding phases or capture volatilized Se, thereby retaining it in the solid fraction. This aligns with documented capture of Se by metal oxides in gasification systems (Yu et al., 2022 ) and supports that the presence of reactive metal phases can mitigate Se loss under high-temperature conditions. 4.3. Heavy metal classification, phosphorus enrichment, and regulatory eligibility of feedstocks and biochar Heavy metal enrichment and phosphorus metal ratios The contrasting responses of heavy metals to AD and pyrolysis reflect the interplay between organic matter degradation, mineral composition, and thermal stability. In manures, AD caused relatively minor changes, with Cu levels decreasing slightly and Zn levels increasing in the digestate compared to raw manure. This suggests that mineralization during AD can mobilize certain metals (e.g., Zn) into more concentrated forms, while others (e.g., Cu) may be redistributed or partly lost through the liquid phase. After pyrolysis, both raw and digestate manures showed enrichment of Cu and Zn. Still, the effect was more substantial in the digestate, likely because the lower organic matter content after AD reduced dilution and enhanced concentration during thermal treatment. In sewage sludges, however, the effects were more pronounced. AD consistently increased heavy metal concentrations relative to raw sludges by removing volatile and labile organics and leaving metals enriched in the solid fraction (Aguirre-Villegas et al., 2019 ; Suanon et al., 2016 ; Zhang et al., 2016 ). Pyrolysis then focused on metals, with Zn and Cu showing the most significant increases, particularly in biologically treated sludges. Zn reached up to 1900 mg kg⁻¹ in biochar, consistent with its non-volatility and association with stable mineral phases (Qian et al., 2016 ). Cu also accumulated strongly, especially at 600°C, reflecting its persistence in oxide and sulfide forms (Krunks et al., 1997 ). Cr, Ni, and Cd were less enriched but followed the same pattern. Chemically treated sludge exhibited the most pronounced AD concentration effect, followed by further enrichment during pyrolysis, consistent with the immobilization of metals in Fe- and Al-based precipitates during wastewater treatment (Cui et al., 2022 ; Giwa et al., 2023 ; Xiao et al., 2024 ). These findings highlight the contrasting impacts of AD and pyrolysis on the agronomic value and regulatory compliance of organic residuals. In manure-derived materials, AD enhanced P concentrations while maintaining low heavy metal contents, consistent with earlier reports that nutrient retention in manures after AD is largely preserved, with reductions mainly in organic matter and volatile components (Eghball et al., 2002 ; Li et al., 2016 ). Pyrolysis further concentrated and stabilized phosphorus. (Hadroug et al., 2021 ; Jin, Y. et al., 2016 ; Keskinen et al., 2019 ) without causing problematic heavy metal enrichment (Liu et al., 2024 ). As a result, manure-derived biochar, mainly that derived from digestate, has strong potential as a sustainable phosphorus fertilizer, combining high nutrient value with negligible contamination. These findings highlight the contrasting impacts of AD and pyrolysis on the agronomic value and regulatory compliance of organic residuals. In manure-derived materials, AD increased P concentrations while maintaining low heavy metal contents, consistent with earlier reports that nutrient retention in manures after AD is largely preserved, with reductions mainly in organic matter and volatile components. Pyrolysis further concentrated and stabilized phosphorus without causing problematic heavy-metal enrichment. As a result, manure-derived biochar, especially that from digestate, shows strong potential as a sustainable phosphorus fertilizer, combining high nutrient value with minimal contamination risks. In sewage sludge-derived materials, however, AD decreased total P concentrations in both biologically and chemically treated sludges, likely due to solubilization and mobilization losses during digestion, as observed in previous sludge management studies (Alvarenga et al., 2017 ; Chen, Y. et al., 2020 ; Smith et al., 2006 ). Analytical factors may also contribute, as incomplete recovery of refractory P forms during nitric acid digestion can lead to a slight underestimation of total P in AD-treated samples, particularly when P is firmly bound to Fe- and Al-rich phases. Pyrolysis then reconcentrated P in the solid fraction, enhancing apparent fertilizer value, but simultaneously intensified heavy metal accumulation (Hosseinian et al., 2024 ; Rangabhashiyam et al., 2021 ; Schlederer et al., 2024 ). This dual effect shifted sludge-derived biochar toward higher P% but at the expense of lower P:metal ratios. Among the metals, Zn consistently represented the most critical limiting element, with ratios near or below the threshold, followed by Cu in certain digestate and chemically treated sludges (Fig. 5 ). Similar findings have been reported elsewhere, where Zn and Cu were identified as the dominant contaminants restricting the agricultural reuse of sludge-derived biochar (Krueger et al., 2019 ); in contrast, Cr and Ni did not pose restrictions, with P: metal ratios far above threshold values. The extended assessment of Cd, Pb, Hg, and As (Fig. 6 ) shows a markedly different picture. Across all feedstocks and treatments, the P: Cd, P: Pb, P: Hg, and P: As ratios were several orders of magnitude higher than the regulatory thresholds (7750, 194, 5167, and 780, respectively). Even after pyrolysis at 600°C, no treatment approached these critical limits. This suggests that these metals are not limited to agricultural applications, unlike Zn and Cu. Taken together, the results highlight that the regulatory bottleneck for sludge-derived biochar lies primarily in Zn (and secondarily Cu), while Cd, Pb, Hg, and As remain well within safe limits. From a management perspective, this means that while digestate manure biochar is suitable for agronomic use without restriction, raw manure biochar is restricted because its P% is below the threshold. Sludge-derived biochar requires targeted mitigation strategies (e.g., blending, co-pyrolysis, chemical pretreatment) to meet the Norwegian 2025 fertilizer regulation. Regulatory eligibility of feedstocks and biochar The regulatory eligibility analysis (Fig. 7 ) further clarifies these dynamics. Raw manure (RM) was consistently classified as not eligible due to phosphorus levels below the 1.5% threshold, despite safe P: metal ratios. In contrast, digestate manure (DM) became eligible after pyrolysis, confirming its suitability as a compliant fertilizer with both agronomic value and low contamination risk. For sewage sludge-derived materials, outcomes varied. Biologically treated raw and digestate sludges (BTRSS and BDRSS) were eligible as feedstocks. Still, they were downgraded after pyrolysis because of zinc enrichment to Class III–IV levels and, in some cases, copper accumulation. Chemically digested sludge (CDRSS) was also eligible as a feedstock; however, its biochar was restricted at 400°C (Zn Class III) and became fully non-eligible at 600°C (Zn Class IV). Conversely, chemically treated raw sludge (CTRSS) behaved differently from the other sludge types, remaining fully eligible both as a feedstock and after pyrolysis at 400°C, with phosphorus concentrations exceeding the agronomic threshold and P: metal ratios consistently within safe limits. Overall, these results show that digestate manure biochar (DM) is agronomically valuable and fully compliant with regulatory standards, making it a viable alternative to mineral phosphorus fertilizers. Meanwhile, raw manure biochar (RM) is limited by its low phosphorus content, despite favorable heavy metal levels. Among the sludge-derived materials, CTRSS is a clear exception, retaining eligibility across all treatments. In contrast, BTRSS, BDRSS, and CDRSS become increasingly restricted or fully non-eligible after pyrolysis due to zinc accumulation, with copper also contributing in some cases. Thus, while pyrolysis increases phosphorus concentrations, zinc and, to a lesser extent, copper remain the critical bottlenecks for most sludge-derived biochar, highlighting the need for mitigation strategies such as blending, co-pyrolysis, or chemical pre-treatments to enable safe agricultural use under Norwegian and EU regulatory frameworks. 5. CONCLUSION Anaerobic digestion and pyrolysis served as complementary treatments that reshaped the nutrient and contaminant profiles of manure- and sludge-derived residues. AD reduced C and dry matter while raising pH and enriching Ca, Mg, and, in some cases, Se, whereas pyrolysis produced stable, alkaline biochar with intensely concentrated P, K, Ca, and Mg but losses of N and S. Micronutrients (Fe, Mn, B, Mo) were retained and enriched. At the same time, Se was mostly volatilized except in Fe/Al-rich digestate chemical sludge, where retention was enhanced. Heavy metals, particularly Zn and Cu, concentrated intensely after pyrolysis and represented the main regulatory bottlenecks, while Cd, Pb, Hg, and As remained far below thresholds. According to the Norwegian 2025 fertilizer regulation, digestate manure biochar at 400°C fully met the P and heavy-metal criteria, making it suitable as a compliant P fertilizer. Raw manure remained ineligible due to insufficient P. Among sewage sludge-derived biochar’s, most were excluded by Zn enrichment, except for chemically treated raw sludge biochar at 400°C, which retained eligibility. 6. FUTURE WORK AND TAKE-HOME MESSAGE Future Work Further research should address three primary areas. First, selenium dynamics: while AD increased Se levels, pyrolysis often led to volatilization, except in Fe/Al-rich digestate chemical sludge, where retention was enhanced. Future studies should clarify the role of mineral phases in stabilizing Se and assess its plant availability. Second, heavy metal mitigation: Zn and Cu enrichment remain the dominant barriers to regulatory compliance for sludge-derived biochar. Strategies such as blending low-metal feedstocks, co-pyrolysis with sorbents, or chemical pretreatments should be explored. Third, aluminum accumulation: Al was negligible in manures but strongly enriched in chemically treated sludges due to Al-based coagulants. Although not regulated under current fertilizer laws, its long-term agronomic and environmental effects need evaluation. Finally, agronomic trials should test the actual availability of P, Se, and other micronutrients to crops, ensuring laboratory findings align with field performance. Take-Home Message The combined AD pyrolysis pathway improves stability and P recovery in organic residues. Under the 2025 Norwegian fertilizer regulation, digestate manure biochar at 400°C is fully compliant and represents a promising circular P fertilizer. Raw manure remains ineligible due to low P. Most sludge-derived biochar is excluded by Zn (and sometimes Cu), except chemically treated raw sludge biochar at 400°C, which retained eligibility. Thus, while manure-derived biochar can safely substitute for mineral fertilizers, sludge-derived biochar requires targeted innovations to reduce Zn/Cu enrichment and to assess the implications of Al and Se for sustainable agricultural use. Declarations COMPETING INTERESTS “The authors have no relevant financial or non-financial interests to disclose.” DATA AVAILABILITY “The datasets generated during and/or analyzed during the current study are not publicly available due to [DATA ARE STORED INTERNALLY AT NMBU DATA DRIVE AND SHARED AMONG THE PARTNERS, NOT PUBLIC] but are available from the corresponding author on reasonable request.” ACKNOWLEDGEMENT This work was supported by the Research Council of Norway through the RenCARBio project (Grant No. 326914). References Abdullah, N., Taib, R., Aziz, N. S. M., Omar, M. R. & Disa, N. M. (2023). Banana pseudo-stem biochar derived from the slow and fast pyrolysis processes. Heliyon , 9. doi: 10.1016/j.heliyon.2023.e12940. Adani, F., D’Imporzano, G., Tambone, F., Riva, C., Boccasile, G. & Orzi, V. (2020). Anaerobic Digestion and Renewable Fertilisers. 215–229. doi: 10.1002/9781118921487.ch5-2. Aguirre-Villegas, H., Larson, R., & Sharara, M. (2019). Anaerobic digestion, solid-liquid separation, and drying of dairy manure: Measuring constituents and modelling emission. Science of The Total Environment , 696: 134059. doi: 10.1016/J.SCITOTENV.2019.134059. Altıkat, A., Alma, M., Altikat, A., Bilgili, M. & Altıkat, S. (2024). A Comprehensive Study of Biochar Yield and Quality Concerning Pyrolysis Conditions: A Multifaceted Approach. Sustainability . Doi: 10.3390/su16020937. Alvarenga, E., Øgaard, A. & Vråle, L. (2017). Effect of anaerobic digestion and liming on plant availability of phosphorus in iron- and aluminium-precipitated sewage sludge from primary wastewater treatment plants. Water science and technology : a journal of the International Association on Water Pollution Research , 75 7-8: 1743-1752. doi: 10.2166/wst.2017.056. Barakwan, R., Trihadiningrum, Y. & Bagastyo, A. (2019). Characterisation of Alum Sludge from Surabaya Water Treatment Plant, Indonesia. Journal of Ecological Engineering . Doi: 10.12911/22998993/104619. Basinas, P., Rusín, J., Chamrádová, K. & Kaldis, S. (2023). Pyrolysis of the anaerobic digestion solid by-product: Characterisation of digestate decomposition and screening of the biochar use as soil amendment and as an additive in anaerobic digestion. Energy Conversion and Management . Doi: 10.1016/j.enconman.2023.116658. Basri, M. H., Don, N. M., Kasmuri, N., Hamzah, N., Alias, S. & Azizan, F. (2019). Aluminium recovery from water treatment sludge under different dosages of sulphuric acid. Journal of Physics: Conference Series , 1349. doi: 10.1088/1742-6596/1349/1/012005. Bhat, M. A., Mishra, A., Shah, S. N., Bhat, M., Jan, S., Rahman, S., Baek, K.-H. & Jan, A. T. (2024). Soil and Mineral Nutrients in Plant Health: A Prospective Study of Iron and Phosphorus in the Growth and Development of Plants. Current Issues in Molecular Biology , 46: 5194–5222. doi: 10.3390/cimb46060312. Bremner, J. M. & Mulvaney, C. (1982). Nitrogen—total. Methods of soil analysis: part 2 chemical and microbiological properties , 9: 595–624. Cai, Y., Janke, L., Meng, X., Zheng, Z., Zhao, X., Pröter, J. and Schäfer, F. 2022. The absolute concentration and bioavailability of trace elements: two vital parameters affecting anaerobic digestion performance of chicken manure leachate. Bioresource technology : 126909. doi: 10.1016/j.biortech.2022.126909. Cao, C.-Y., Cheng, Y., Hu, H., Wang, H., Liu, S., Hu, M., Li, X., & Yao, H. (2022). Products distribution and sulfur fixation during the pyrolysis of CaO conditioned textile dyeing sludge: Effects of pyrolysis temperature and heating rate. Waste management , 153: 367–375. doi: 10.1016/j.wasman.2022.09.027. Cao, J., Li, L., Morishita, K., Xiao, X., Zhao, X.-Y., Wei, X. & Takarada, T. (2013). Nitrogen transformations during fast pyrolysis of sewage sludge. Fuel , 104: 1–6. doi: 10.1016/J.FUEL.2010.08.015. Chen, G., Li, J., Li, K., Lin, F., Tian, W., Che, L., Yan, B., Wenchao & Song, Y. (2020). Nitrogen, sulfur, chlorine containing pollutants releasing characteristics during pyrolysis and combustion of oily sludge. Fuel , 273: 117772. doi: 10.1016/j.fuel.2020.117772. Chen, H., Wang, Y., Xu, G. & Yoshikawa, K. (2012). Fuel-N Evolution during the Pyrolysis of Industrial Biomass Wastes with High Nitrogen Content. Energies , 5: 5418–5438. doi: 10.3390/EN5125418. Chen, W., Yang, H., Chen, Y., Xia, M., Chen, X., & Chen, H. (2017). Transformation of Nitrogen and Evolution of N-Containing Species during Algae Pyrolysis. Environmental science & technology , 51 11: 6570–6579. doi: 10.1021/acs.est.7b00434. Chen, Y., Sun, R., Sun, T., Chen, P., Yu, Z., Ding, L., Jiang, Y., Wang, X., Dai, C., & Sun, B. (2020). Evidence for involvement of keystone fungal taxa in organic phosphorus mineralisation in subtropical soil and the impact of labile carbon. Soil Biology and Biochemistry , 148: 107900. Chen, Y., Ding, W., Bai, Y., Wang, X., Shen, N., Li, L., Lu, D. & Zhou, Y. (2024). Phosphorus release and realignment in anaerobic digestion of thermal hydrolysis pretreatment sludge - Masking effects from high ammonium. Water research , 255: 121488. doi: 10.1016/j.watres.2024.121488. Chowdhury, R., Moore, G., Weatherley, A. & Arora, M. (2017). Key sustainability challenges for the global phosphorus resource, their implications for global food security, and options for mitigation. Journal of Cleaner Production , 140: 945–963. doi: 10.1016/J.JCLEPRO.2016.07.012. Cui, Z., Xu, G.-R., Ormeci, B., Liu, H.-W. & Zhang, Z. (2022). Transformation and stabilisation of heavy metals during pyrolysis of organic and inorganic-dominated sewage sludges and their mechanisms. Waste management , 150: 57–65. doi: 10.1016/j.wasman.2022.06.023. Dadrasnia, A., Muñoz, I., Yáñez, E., Lamkaddam, I. U., Mora, M., Ponsá, S., Ahmed, M., Argelaguet, L., Williams, P. & Oatley-Radcliffe, D. (2021). Sustainable nutrient recovery from animal manure: A review of current best practice technology and the potential for freeze concentration. Journal of Cleaner Production , 315: 128106. doi: 10.1016/J.JCLEPRO.2021.128106. Demirbaş, A., Taylan, O. & Kaya, D. (2016). Biogas production from municipal sewage sludge (MSS). Energy Sources, Part A: Recovery, Utilisation, and Environmental Effects , 38: 3027-3033. doi: 10.1080/15567036.2015.1124944. Dhillon, J., Torres, G., Driver, E., Figueiredo, B., & Raun, W. (2017). World Phosphorus Use Efficiency in Cereal Crops. Agronomy Journal , 109: 1670–1677. doi: 10.2134/AGRONJ2016.08.0483. Dong, Z., Yang, H., Liu, Z., Chen, P., Chen, Y., Wang, X., Chen, H. and Wang, S. 2022. Pyrolysis of boron-crosslinked lignin: influence on lignin softening and product properties. Bioresource technology : 127218. doi: 10.1016/j.biortech.2022.127218. Dridi, N., Romdhane, L., Ferreira, R. & Sleimi, N. (2020). Fertiliser effect of composted sewage sludge and cattle manure on Pelargonium growth. Journal of Water, Sanitation, and Hygiene for Development . doi: 10.2166/washdev. 2020.082. Edixhoven, J., Gupta, J. & Savenije, H. (2014). Recent revisions of phosphate rock reserves and resources: a critique. Earth System Dynamics Discussions , 5: 491-507. doi: 10.5194/ESD-5-491-2014. Eghball, B., Wienhold, B., Gilley, J. & Eigenberg, R. (2002). Mineralisation of manure nutrients. Journal of Soil and Water Conservation . Doi: 10.1080/00224561.2002.12457480. Feng, H., Zhou, S., Guan, W., Zhu, L., Li, R., & Wang, S. (2024). Enhancement of Apatite-Phosphorus-Rich Biochar Production from Sewage Sludge Pyrolysis Assisted by Carbide Slag. Process Safety and Environmental Protection . doi: 10.1016/j.psep.2024.10.031. Filho, J. F. L., Da Silva Rodrigues Viana, R., Melo, L. C. A. & De Figueiredo, C. C. (2024). Changes in phosphorus due to pyrolysis and in the soil-plant system amended with sewage sludge biochar compared to conventional P fertilisers: a global meta-analysis. Chemosphere : 144055. doi: 10.1016/j.chemosphere.2024.144055. Frišták, V., Pipíška, M. & Soja, G. (2018). Pyrolysis treatment of sewage sludge: A promising way to produce phosphorus fertiliser. Journal of Cleaner Production , 172: 1772-1778. doi: 10.1016/J.JCLEPRO.2017.12.015. Gao, N., Jiang, X. & Liu, Y. (2015). Dipropargyl ether bisphenol A-based boron-containing polymer: synthesis, characterisation and molecular dynamics simulations of the resulting pyrolysis and carbonisation. RSC Advances , 5: 3390–3398. doi: 10.1039/C4RA12694G. Geng, N., Wang, Y., Zhang, D., Fan, X., Li, E., Han, Z. & Zhao, X. (2022). An electro-peroxone oxidation-Fe(III) coagulation sequential conditioning process for enhanced waste-activated sludge dewatering: bound water release and multivariate changes in organics. The Science of the total environment : 155272. doi: 10.1016/j.scitotenv.2022.155272. Giwa, A., Maurice, N. J., Ai, L., Liu, X., Yang, Y. & Hong, Z. (2023). Advances in sewage sludge application and treatment: Process integration of plasma pyrolysis and anaerobic digestion with the resource recovery. Heliyon , 9. doi: 10.1016/j.heliyon.2023.e19765. Gobbi, M., Pigozzo, A. T. J., Lenzi, E. & Luchese, E. (2000). Effects of the application of sewage sludge and fowl manure on soils of Paraná state in maize plants (Zea mays L.) as a macro-nutrient source. Brazilian Archives of Biology and Technology , 43: 151–157. doi: 10.1590/S1516-89132000000200003. Hadroug, S., Jellali, S., Jeguirim, M., Kwapinska, M., Hamdi, H., Leahy, J., & Kwapinski, W. (2021). Static and Dynamic Investigations on Leaching/Retention of Nutrients from Raw Poultry Manure Biochars and Amended Agricultural Soil. Sustainability . Doi: 10.3390/SU13031212. Hong, Y.-K., Qu, G., Du, Y., Yuan, T., Hao, S., Yang, W. & Dai, Z. (2022). Experimental Investigations into the Pyrolysis Mechanism and Composition of Ceramic Precursors Containing Boron and Nitrides with Different Boron Contents. Materials , 15. doi: 10.3390/ma15238390. Hosseinian, A., Brancoli, P., Vali, N., Ylä-Mella, J., Pettersson, A. & Pongrácz, E. (2024). Life Cycle Assessment of Sewage Sludge Treatment: Comparison of pyrolysis with traditional methods in two Swedish municipalities. Journal of Cleaner Production . Doi: 10.1016/j.jclepro.2024.142375. Hou, J., Yue, Li, S., Shi, J., He, L. & Li, J. (2018). Transformation of sulfur and nitrogen during Shenmu coal pyrolysis. Fuel . doi: 10.1016/J.FUEL.2018.05.046. Huang, R., Tang, Y. & Luo, L. (2020). Thermochemistry of sulfur during pyrolysis and hydrothermal carbonisation of sewage sludges. Waste management , 121: 276–285. doi: 10.1016/j.wasman.2020.12.004. Illakwahhi, D., Vegi, M. & Srivastava, B. (2024). Phosphorus' future insecurity, the horror of depletion, and sustainability measures. International Journal of Environmental Science and Technology . Doi: 10.1007/s13762-024-05664-y. Jiang, Y., McAdam, E., Zhang, Y., Heaven, S., Banks, C. & Longhurst, P. (2019). Ammonia inhibition and toxicity in anaerobic digestion: A critical review. Journal of Water Process Engineering . doi: 10.1016/J.JWPE.2019.100899. Jin, J., Li, Y., Zhang, J., Wu, S., Cao, Y., Liang, P., Zhang, J., Wong, M., Wang, M., Shan, S., et al. (2016). Influence of pyrolysis temperature on properties and environmental safety of heavy metals in biochars derived from municipal sewage sludge. Journal of hazardous materials , 320: 417–426. doi: 10.1016/j.jhazmat.2016.08.050. Jin, Y., Liang, X., He, M., Liu, Y., Tian, G. & Shi, J. (2016). Manure biochar influence upon soil properties, phosphorus distribution and phosphatase activities: A microcosm incubation study. Chemosphere , 142: 128–135. doi: 10.1016/j.chemosphere.2015.07.015. Kang, J., Kwon, G., Nam, J., Kim, Y. & Jahng, D. (2017). Carbon dioxide stripping from anaerobic digestate of food waste using two types of aerators. International Journal of Environmental Science and Technology , 14: 1397–1408. doi: 10.1007/s13762-017-1250-1. Keskinen, R., Hyväluoma, J., Sohlo, L., Help, H. & Rasa, K. (2019). Fertiliser and soil conditioner value of broiler manure biochars. Biochar , 1: 259-270. doi: 10.1007/s42773-019-00020-7. Khalid, A., Arshad, M., Anjum, M., Mahmood, T. & Dawson, L. (2011). The anaerobic digestion of solid organic waste. Waste management , 31 8: 1737-1744. doi: 10.1016/j.wasman.2011.03.021. Khater, E.-S., Bahnasawy, A., Hamouda, R., Sabahy, A., Abbas, W. & Morsy, O. (2024). Biochar production under different pyrolysis temperatures with different types of agricultural wastes. Scientific Reports , 14. doi: 10.1038/s41598-024-52336-5. Krueger, B., Fowler, G., Templeton, M. & Moya, B. (2019). Resource recovery and biochar characteristics from full-scale faecal sludge treatment and co-treatment with agricultural waste. Water Research , 169. doi: 10.1016/j.watres.2019.115253. Krunks, M., Mellikov, E. & Bijakina, O. (1997). Copper sulfides by chemical spray pyrolysis process. Physica Scripta , 69: 189-192. doi: 10.1088/0031-8949/1997/T69/037. Li, H., Tan, F., Ke, L., Xia, D., Wang, Y., He, N., Zheng, Y. & Li, Q. (2016). Mass balances and distributions of C, N, and P in the anaerobic digestion of different substrates and relationships between products and substrates. Chemical Engineering Journal , 287: 329-336. doi: 10.1016/J.CEJ.2015.11.003. Li, Y., Gupta, R., Zhang, Q. & You, S. (2022). Review of Biochar Production via Crop Residue Pyrolysis: Development and Perspectives. Bioresource technology : 128423. doi: 10.1016/j.biortech.2022.128423. Liu, T., Shao, T., Jiang, J., Wen, Y., Feng, R., Dong, D., Wang, Y., Bai, T. & Xu, Y. (2024). Influence of potassium addition on phosphorus availability and heavy metals immobility of biochar derived from swine manure. Scientific Reports , 14. doi: 10.1038/s41598-024-69761-1. Liu, Z., Yuan, D., Qin, X., He, P. & Fu, Y. (2023). Effect of Mg-Modified Waste Straw Biochar on the Chemical and Biological Properties of Acidic Soils. Molecules , 28. doi: 10.3390/molecules28135225. LMD. (2025). Forskrift om lagring og bruk av gjødsel mv (gjødselbrukforskriften) [FOR-2025-01-29-115] : Lovdata. Lu, T., Yuan, H., Wang, Y., Huang, H. & Chen, Y. (2016). Characteristic of heavy metals in biochar derived from sewage sludge. Journal of Material Cycles and Waste Management , 18: 725-733. doi: 10.1007/S10163-015-0366-Y. Malhotra, H., Vandana, Sharma, S. & Pandey, R. (2018). Phosphorus Nutrition: Plant Growth in Response to Deficiency and Excess. 171-190. doi: 10.1007/978-981-10-9044-8_7. Muisa, N., Nhapi, I., Ruziwa, W. & Manyuchi, M. (2020). Utilization of alum sludge as adsorbent for phosphorus removal in municipal wastewater: A review. Journal of Water Process Engineering . doi: 10.1016/j.jwpe.2020.101187. Nelson, D. W. & Sommers, L. E. (1982). Total carbon, organic carbon, and organic matter. Methods of soil analysis: Part 2 chemical and microbiological properties , 9: 539-579. Nyang’au, J., Mahdi, J. E., Møller, H. & Sørensen, P. (2024). Unlocking higher methane yields and digestate nitrogen availability in soil through thermal treatment of feedstocks in a two-step anaerobic digestion. Chemical and Biological Technologies in Agriculture . doi: 10.1186/s40538-024-00694-7. Opatokun, S. A., Yousef, L. & Strezov, V. (2017). Agronomic assessment of pyrolysed food waste digestate for sandy soil management. Journal of environmental management , 187: 24-30. doi: 10.1016/j.jenvman.2016.11.030. Petrovič, A., Vohl, S., Predikaka, T. C., Bedoić, R., Simonič, M., Ban, I. & Čuček, L. (2021). Pyrolysis of Solid Digestate from Sewage Sludge and Lignocellulosic Biomass: Kinetic and Thermodynamic Analysis, Characterization of Biochar. Sustainability . doi: 10.3390/su13179642. Qian, T., Wang, Y., Fan, T., Fang, G. & Zhou, D.-M. (2016). A new insight into the immobilization mechanism of Zn on biochar: the role of anions dissolved from ash. Scientific Reports , 6. doi: 10.1038/srep33630. Rangabhashiyam, S., Lins, P., Oliveira, L., Sepúlveda, P., Ighalo, J., Rajapaksha, A. & Meili, L. (2021). Sewage sludge-derived biochar for the adsorptive removal of wastewater pollutants: A critical review. Environmental pollution : 118581. doi: 10.1016/j.envpol.2021.118581. Robinson, J., Baumann, K., Hu, Y., Hagemann, P., Kebelmann, L. & Leinweber, P. (2017). Phosphorus transformations in plant-based and bio-waste materials induced by pyrolysis. Ambio , 47: 73-82. doi: 10.1007/s13280-017-0990-y. Rodríguez, J., Filho, J., Melo, L., Assis, I. & Oliveira, T. (2020). Influence of pyrolysis temperature and feedstock on the properties of biochars produced from agricultural and industrial wastes. Journal of Analytical and Applied Pyrolysis , 149: 104839. doi: 10.1016/j.jaap.2020.104839. Ruiqing, L. (2013). Influence of minerals and mineral ions on selenium release behaviors during coal pyrolysis. Environmental Chemistry . Sahoo, S., Vijay, V., Chandra, R. & Kumar, H. (2021). Production and characterisation of biochar produced from slow pyrolysis of pigeon pea stalk and bamboo. Cleaner Engineering and Technology . doi: 10.1016/J.CLET.2021.100101. Saikumar, R. & Rao, K. (2017). Effect of Sewage Sludge, Urban Compost, Poultry Manure and Chemical Fertilisers on Soil Heavy Metal Status in Brinjal-Cauliflower Cropping System. International Journal of Current Microbiology and Applied Sciences , 6: 1087-1094. doi: 10.20546/IJCMAS.2017.606.126. Schlederer, F., Martín-Hernández, E. & Vaneeckhaute, C. (2024). Ensuring safety standards in sewage sludge-derived biochar: Impact of pyrolysis process temperature and carrier gas on micropollutant removal. Journal of environmental management , 352: 119964. doi: 10.1016/j.jenvman.2023.119964. Shen, Y. & Yuan, R. (2021). Pyrolysis of agroforestry bio-wastes with Calcium/Magnesium oxides or carbonates – Focusing on biochar as soil conditioner. Biomass and Bioenergy . Doi: 10.1016/j.biombioe.2021.106277. Shi, W., Lian, W., Tian, S., Gong, X.-M., Yu, Q.-H., Guo, Z., Zhang, X., Biao, Bian, R., Zheng, J., et al. (2023). A review of agronomic and environmental properties of inorganic compounds in biochars. Current Research in Environmental Sustainability . Doi: 10.1016/j.crsust.2023.100226. Smith, M., Cade‐Menun, B. & Tibbett, M. (2006). Soil phosphorus dynamics and phytoavailability from sewage sludge at different stages in a treatment stream. Biology and Fertility of Soils , 42: 186-197. doi: 10.1007/s00374-005-0014-0. Srivastava, S., Upadhyay, M., Srivastava, A., Abdelrahman, M., Suprasanna, P., and Tran, L. 2018. Cellular and Subcellular Phosphate Transport Machinery in Plants. International Journal of Molecular Sciences , 19. doi: 10.3390/ijms19071914. Suanon, F., Sun, Q., Mama, D., Li, J., Dimon, B., & Yu, C. (2016). Effect of nanoscale zero-valent iron and magnetite (Fe3O4) on the fate of metals during anaerobic digestion of sludge. Water research , 88: 897–903. doi: 10.1016/j.watres.2015.11.014. Sugawara, K., Enda, Y., Inoue, H., Sugawara, T. & Shirai, M. (2002). Dynamic behaviour of trace elements during pyrolysis of coals. Fuel , 81: 1439–1443. doi: 10.1016/S0016-2361(02)00063-7. Thakur, N., Sharma, M., Alghamdi, H., Zheng, Y., Xue, W., Jeon, B.-H., Salama, E.-S., & Li, X. (2023). A recent trend in anaerobic digestion (AD): Enhancement of microbiome and digestibility of feedstocks via abiotic stress factors for biomethanation. Chemical Engineering Journal . doi: 10.1016/j.cej.2023.145047. Wang, R., Wilfert, P., Dugulan, I., Goubitz, K., Korving, L., Witkamp, G.-J. & van Loosdrecht, M. C. (2019). Fe (III) reduction and vivianite formation in activated sludge. Separation and Purification Technology , 220: 126–135. Wang, X. & Jia, W. (2024). Se-Pair Search for Deciphering Selenium-Encoded Peptide and a Pyrolysis-Thermolysis Dietary Model for Minimising Loss of "KKSe(M)R" during Processing. Journal of agricultural and food chemistry . doi: 10.1021/acs.jafc.4c01638. Wang, X., Jia, W., Zhang, R., Shi, L. & He, B. (2025). Pyro-Thermolysis Pattern Analysis of Selenopeptide in Selenium-Enriched Rice Based on Two-Dimensional Dietary Kinetics Evolution. Journal of agricultural and food chemistry . Doi: 10.1021/acs.jafc.4c07303. Wang, Y., Dong, B., Fan, Y., Hu, Y., Zhai, X., Deng, C., Xu, Y., Shen, D. & Dai, X. (2019). Nitrogen transformation during pyrolysis of oilfield sludge with high polymer content. Chemosphere , 219: 383-389. doi: 10.1016/j.chemosphere.2018.11.171. Wang, Z., Jiang, Y., Wang, S., Zhang, Y., Hu, Y., Hu, Z.-H., Wu, G. & Zhan, X. (2020). Impact of total solids content on anaerobic co-digestion of pig manure and food waste: Insights into shifting of the methanogenic pathway. Waste management , 114: 96–106. doi: 10.1016/j.wasman.2020.06.048. Wang, Z., Hu, Y., Wang, S., Wu, G., & Zhan, X. (2023). A critical review on dry anaerobic digestion of organic waste: Characteristics, operational conditions, and improvement strategies. Renewable and Sustainable Energy Reviews . Doi: 10.1016/j.rser.2023.113208. Weimers, K., Bergstrand, K., Hultberg, M. & Asp, H. (2022). Liquid Anaerobic Digestate as Sole Nutrient Source in Soilless Horticulture—Or Spiked With Mineral Nutrients for Improved Plant Growth. Frontiers in Plant Science , 13. doi: 10.3389/fpls.2022.770179. Xiao, K., Chen, Y., Jiang, X., Yang, Q., Seow, W., Zhu, W. & Zhou, Y. (2017). Variations in physical, chemical and biological properties in relation to sludge dewaterability under Fe (II) - Oxone conditioning. Water research , 109: 13–23. doi: 10.1016/j.watres.2016.11.034. Xiao, Y., Yan, T., Yao, P., Xiang, W., Wu, Y. & Li, J. (2024). Co-pyrolysis of sewage sludge and phosphate tailings: Synergistically enhancing heavy metal immobilisation and phosphorus availability. Waste management , 181: 44–56. doi: 10.1016/j.wasman.2024.04.003. Xing, Y., Huang, J., Wang, Z., Hu, W., Xu, M. & Qiao, Y. (2024). Transformation and control of organic sulfur during pyrolysis of sludge under conditions relevant to smouldering combustion: Role of oxygen and CaO. Energy . doi: 10.1016/j.energy.2024.133143. Xu, F., Chu, M., Chang, Z., Gu, Z. & Sun, X. (2021). Sulfur release and transformation during the pyrolysis of lignite with different particle sizes—Journal of Analytical and Applied Pyrolysis , 156: 105162. doi: 10.1016/J.JAAP.2021.105162. Yadav, M., Joshi, C., Paritosh, K., Thakur, J., Pareek, N., Masakapalli, S., & Vivekanand, V. (2021). Organic waste conversion through anaerobic digestion: A critical insight into the metabolic pathways and microbial interactions. Metabolic engineering . doi: 10.1016/j.ymben.2021.11.014. Yu, Y., Li, X., Zhao, R., Liu, H., & Chen, J. (2022). Gaseous selenium removal by metal oxide sorbent: Experimental and density functional theory study. Fuel . Doi: 10.1016/j.fuel.2022.124904. Zamri, M. F. M. A., Hasmady, S., Akhiar, A., Ideris, F., Shamsuddin, A., Mofijur, M., Fattah, I., & Mahlia, T. (2021). A comprehensive review on anaerobic digestion of organic fraction of municipal solid waste. Renewable and Sustainable Energy Reviews . Doi: 10.1016/j.rser.2020.110637. Zhang, J., Zuo, W., Tian, Y., Chen, L., Yin, L. & Zhang, J. (2017). Sulfur Transformation during Microwave and Conventional Pyrolysis of Sewage Sludge. Environmental science & technology , 51 1: 709–717. doi: 10.1021/acs.est.6b03784. Zhang, M., Yang, C., Jing, Y. & Li, J. (2016). Effect of energy grass on methane production and heavy metal fractionation during anaerobic digestion of sewage sludge. Waste management , 58: 316–323. doi: 10.1016/j.wasman.2016.09.040. Zhao, J., Qiu, C., Fan, X., Zheng, J., Liu, N., Wang, C., Wang, D. & Wang, S. (2021). Chemical speciation and risk assessment of heavy metals in biochars derived from sewage sludge and anaerobically digested sludge. Water science and technology : a journal of the International Association on Water Pollution Research , 84 5: 1079–1089. doi: 10.2166/wst.2021.305. Zhu, X., Labianca, C., He, M., Luo, Z., Wu, C., You, S., & Tsang, D. (2022). Life-cycle assessment of pyrolysis processes for sustainable production of biochar from agro-residues. Bioresource technology : 127601. doi: 10.1016/j.biortech.2022.127601. 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1","display":"","copyAsset":false,"role":"figure","size":122070,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Total carbon (%); (B) Dry matter (%); (C) Loss on ignition (%); and (D) pH of feedstocks and biochars produced at 400 °C and 600 °C.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eWhere\u003c/strong\u003e\u003c/em\u003e: \u003cem\u003eMR, Raw manure; DM, Digestate manure; BTRSS, Biological treated raw sewage sludge; BDRSS, Biological digested sewage sludge; CTRSS, Chemical treated raw sewage sludge; CDRSS, Chemical digested sewage sludge\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/2aa57914221919fec1e65729.png"},{"id":97668850,"identity":"88545d15-1465-42f7-9dfe-476bc626c468","added_by":"auto","created_at":"2025-12-08 09:26:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":178308,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Nitrogen (%); (B) Phosphorus (g kg⁻¹); (C) Potassium (g kg⁻¹); (D) Calcium (g kg⁻¹); (E) Magnesium (g kg⁻¹); and (F) Sulfur (g kg⁻¹) concentrations in feedstocks and biochars produced at 400 °C and 600 °C.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eW\u003c/em\u003e\u003cem\u003e\u003cstrong\u003ehere\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e:\u003c/em\u003e \u003cem\u003eMR, Raw manure; DM, Digestate manure; BTRSS, Biological treated raw sewage sludge; BDRSS, Biological digested sewage sludge; CTRSS, Chemical treated raw sewage sludge; CDRSS, Chemical digested sewage sludge\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/376a145c771f88652067c8ad.png"},{"id":97668202,"identity":"57ba6022-0da7-4a85-b473-e055b56c63df","added_by":"auto","created_at":"2025-12-08 09:25:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":163120,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Iron (g kg⁻¹); (B) Manganese (g kg⁻¹); (C) Molybdenum (mg kg⁻¹); (D) Boron (mg kg⁻¹); (E) Aluminum (g kg⁻¹); and (F) Selenium (mg kg⁻¹) concentrations in feedstocks and biochars produced at 400 °C and 600 °C\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eW\u003c/em\u003e\u003cem\u003e\u003cstrong\u003ehere\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e:\u003c/em\u003e \u003cem\u003eMR, Raw manure; DM, Digestate manure; BTRSS, Biological treated raw sewage sludge; BDRSS, Biological digested sewage sludge; CTRSS, Chemical treated raw sewage sludge; CDRSS, Chemical digested sewage sludge\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/c9eb49ab8c94908ccee90a7d.png"},{"id":97459773,"identity":"e48d4d07-e6d4-4ceb-9497-17bbe41171e0","added_by":"auto","created_at":"2025-12-04 15:14:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":288618,"visible":true,"origin":"","legend":"\u003cp\u003eHeavy metal classification of feedstocks and biochars (400 °C and 600 °C) according to the Norwegian fertilizer regulation (2025).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eWhere: MR, Raw manure; DM, Digestate manure; BTRSS, Biological treated raw sewage sludge; BDRSS, Biological digested sewage sludge; CTRSS, Chemical treated raw sewage sludge; CDRSS, Chemical digested sewage sludge\u003c/em\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/a09f41eb5e166c1597eba2f5.png"},{"id":97668806,"identity":"50459169-a43e-41c1-8888-f3cf00a16a60","added_by":"auto","created_at":"2025-12-08 09:26:17","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":138989,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between phosphorus content (P%) and P: metal ratios in feedstocks and biochar’s produced at 400 °C and 600 °C. (A) P: Cu ratio; (B) P: Cr ratio; (C) P: Zn ratio; and (D) P: Ni ratio. Vertical green dashed line indicates the P% threshold of 1.5, and horizontal red dashed lines indicate Norwegian regulatory thresholds (2025).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eWhere\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e: MR, Raw manure; DM, Digestate manure; BTRSS, Biological treated raw sewage sludge; BDRSS, Biological digested sewage sludge; CTRSS, Chemical treated raw sewage sludge; CDRSS, Chemical digested sewage sludge\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/e4868f80bd1582c9e92387b8.png"},{"id":97669713,"identity":"bbef8200-62b1-4b9d-b991-8bb1e4ceeff8","added_by":"auto","created_at":"2025-12-08 09:28:46","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":150755,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between phosphorus content (P%) and P: metal ratios in feedstocks and biochar’s produced at 400 °C and 600 °C. (A) P: Cd ratio; (B) P: Pb ratio; (C) P: Hg ratio; and (D) P: As ratio. Vertical green dashed line indicates the P% threshold of 1.5, and horizontal red dashed lines indicate Norwegian regulatory thresholds (2025): Cd = 7750, Pb = 194, Hg = 5167, As = 780 (mg mg⁻¹ P)\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eWhere\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e: MR, Raw manure; DM, Digestate manure; BTRSS, Biological treated raw sewage sludge; BDRSS, Biological digested sewage sludge; CTRSS, Chemical treated raw sewage sludge; CDRSS, Chemical digested sewage sludge\u003c/em\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/ee79f96902930ee1b337f209.png"},{"id":97667897,"identity":"93ff235e-0149-466d-836c-60a91f2be2b0","added_by":"auto","created_at":"2025-12-08 09:24:27","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":148405,"visible":true,"origin":"","legend":"\u003cp\u003eRegulatory eligibility of feedstocks and biochar’s (400 °C and 600 °C) for agricultural use under the Norwegian fertiliser regulation (2025). Status categories: 0 = not eligible (P \u0026lt; 1.5%); 1 = not eligible due to heavy metals exceeding class III; 2 = restricted (eligible only for non-cultivated areas); and 3 = eligible.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eWhere\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e: MR, Raw manure; DM, Digestate manure; BTRSS, Biological treated raw sewage sludge; BDRSS, Biological digested sewage sludge; CTRSS, Chemical treated raw sewage sludge; CDRSS, Chemical digested sewage sludge\u003c/em\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/450627881a9371dacb917412.png"},{"id":105564299,"identity":"e38e807c-9b83-457b-8987-ecedf88565c8","added_by":"auto","created_at":"2026-03-27 12:49:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2369377,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/caa908bf-7d20-448c-ba9f-ad8493dceb6d.pdf"},{"id":97667921,"identity":"b1f8351c-1937-4cbc-bb00-019fc8edef2e","added_by":"auto","created_at":"2025-12-08 09:24:29","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":314707,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstruct.docx","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/de8b1387c980b7f44c48260e.docx"},{"id":97459769,"identity":"2edd4270-cea0-4805-ba1a-59e0c27566ac","added_by":"auto","created_at":"2025-12-04 15:14:33","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":16485,"visible":true,"origin":"","legend":"","description":"","filename":"Highlight.docx","url":"https://assets-eu.researchsquare.com/files/rs-8242369/v1/6e4fe16d96ac127a90d0e355.docx"}],"financialInterests":"","formattedTitle":"\u003cp\u003eEffect of anaerobic digestion and pyrolysis on nutrient composition, heavy metals, and phosphorus recovery in manure and sewage sludge biochar\u003c/p\u003e","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eNutrient recycling from organic residues is increasingly recognized as essential for sustainable agriculture and for the development of circular bioeconomy strategies. Phosphorus (P) is a central element in this context, given its irreplaceable role in plant growth, energy transfer, and root development (Bhat et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Malhotra et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Srivastava et al., \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). However, global phosphate rock reserves are finite, geographically concentrated, and subject to market volatility (Chowdhury et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Dhillon et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Edixhoven et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Illakwahhi et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). At the same time, animal manure and sewage sludge represent large, underutilized nutrient streams rich in both macronutrients and micronutrients. Direct application of these residues can supply nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), and Sulphur (S) (Dadrasnia et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Dridi et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Gobbi et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Saikumar \u0026amp; Rao, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) as well as micronutrients, which are essential for plant metabolism. However, their use is constrained by environmental risks, including nutrient leaching, eutrophication, greenhouse gas emissions, and the accumulation of potentially toxic elements such as cadmium (Cd), lead (Pb), mercury (Hg), nickel (Ni), and chromium (Cr).\u003c/p\u003e\u003cp\u003eBiochar production through pyrolysis has emerged as a promising pathway to stabilize carbon (Altıkat et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Zhu et al., \u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), inactivate pathogens (Abdullah et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), and concentrate nutrients in a solid matrix (Abdullah et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Khater et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Sahoo et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Moreover, biochar can serve as a source of micronutrients (e.g., Zn, Fe, Mn, Cu), though their bioavailability depends strongly on feedstock type and pyrolysis conditions. Nevertheless, concerns persist regarding elevated heavy metal concentrations, particularly in biochar derived from sewage sludge. (Jin, J. et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Lu et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Zhao et al., \u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which may limit their agricultural application under current regulatory frameworks.\u003c/p\u003e\u003cp\u003eAnaerobic digestion (AD) is widely used before land application or thermal processing of organic wastes, primarily for biogas production and stabilizing easily degradable organic matter. (Khalid et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Yadav et al., \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Zamri et al., \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). AD modifies feedstock chemistry by increasing pH, altering carbon-to-nitrogen ratios, and transforming nutrient pools. For example, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N becomes more dominant, organic matter is partly mineralized, and the relative concentrations of P, K, Ca, and Mg often increase in the solid fraction (Jiang et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Nyang\u0026rsquo;au et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Thakur et al., \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). These shifts are expected to influence the thermal conversion process and the resulting nutrient and heavy metal profiles of digestate-derived biochar. However, systematic evidence on how AD pre-treatment affects macronutrient retention, micronutrient enrichment, heavy metal concentrations, and P recovery in biochar remains limited.\u003c/p\u003e\u003cp\u003eThis whole study addresses this knowledge gap by comparing biochar produced from raw and anaerobically digested manure and sewage sludge. The objectives were to: (I) assess the effect of AD and pyrolysis on nutrient composition, (II) quantify heavy metal concentrations relative to Norwegian and EU fertilizer regulations, and (III) evaluate phosphorus recovery and classify the P-to-heavy metal ratio (Norwegian 2025 regulation) for agricultural use.\u003c/p\u003e\u003cp\u003eThe research was based on biochar produced from small-scale pyrolysis trials at 400\u0026deg;C and 600\u0026deg;C across all feedstocks, and on the characterization of raw and anaerobically digested feedstocks and their respective biochar samples.\u003c/p\u003e\u003cp\u003eWe hypothesized that AD and pyrolysis would (a) concentrate P, Ca, and Mg, and select micronutrients in the solid fraction, thereby increasing their retention in biochar; (b) reduce N and S contents due to enhanced mineralization and volatilization; and (c) influence heavy metal concentrations and P recovery pathways by modifying feedstock chemistry before pyrolysis.\u003c/p\u003e"},{"header":"2. MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Feedstock and biochar samples\u003c/h2\u003e\u003cp\u003eSix different feedstocks were used in the pyrolysis trials: raw manure (RM), digested manure (DM), biologically treated raw sewage sludge (BTRSS), biologically treated digested sewage sludge (BTDSS), chemically treated raw sewage sludge (CTRSS), and chemically treated digested sewage sludge (CTDSS). Samples of BTRSS and BTDSS were sourced from western Norway, provided by the regional wastewater treatment plant (WWTP). Nord J\u0026aelig;ren (SNJ), in Mekjarvik, operated by the inter-municipal water and wastewater organization for the Stavanger region, IVAR IKS. SNJ WWTP runs a process that focuses on enhanced biological phosphorus removal (EBPR), a well\u0026ndash;established technology for phosphorus removal from wastewater that can be combined with activated sludge, as in the case of SNJ, to remove P without the use of chemicals. The process utilizes Polyphosphate\u0026ndash;Accumulating Organisms (PAOs) in the biomass, which remove P from the liquid phase through cellular growth. It has been reported that the PAOs are altered between anaerobic and aerobic conditions. After wastewater treatment, the generated sludge undergoes mesophilic (36\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C) AD with an organic loading rate (OLR) of 2 kg VS/m3/day and a hydraulic retention time (HRT) of 19 days.\u003c/p\u003e\u003cp\u003eCTRSS samples were provided by \u0026Aring;se WWTP, managed by \u0026Aring;RIM AS (today Attvin AS), the inter-municipal waste and wastewater organization for the \u0026Aring;lesund region. At the \u0026Aring;se plant, wastewater is chemically treated with polyaluminum chloride (PAX 33) to remove phosphorus and organic matter. The CTDSS samples were from the biogas plant at R\u0026aring;dalen, operated by Bergen Municipality. This last plant treats municipal sludge generated at all the wastewater treatment plants in the Bergen area, with a pre-hygienisation process (70\u0026deg;C for 1 hour) before running thermophilic (54\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C) AD with an OLR of 3\u0026ndash;4 Kg VS/m3.day and an HRT of 12 days. The sludge samples were dewatered to achieve dry matter (DM) concentrations of 25%-32%, followed by oven drying to a final DM content of 85%\u0026ndash;95%. Additionally, cattle manure samples were collected from the farm at Kalnes Agricultural School in Sarpsborg. Solid manure, rich in fibres from straw, sawdust, cow and horse manure, was directly used as a feedstock for biochar production. Digested manure was provided by Aquateam COWI, after continuous mesophilic AD in two laboratory bench-scale reactors (Belach Bioteknik AB, Sweden) with a working volume of 20 L (OLR: 2 g VS/L.day, HRT: 20 days) of the manure fraction obtained from Kalnes farm.\u003c/p\u003e\u003cp\u003e\u003cb\u003ePyrolysis trials\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe pyrolysis trials were performed by WAI Environmental Solutions AS (Tonsberg, Norway). A small-scale pyrolysis unit was employed, consisting of a rotatory tube furnace with a 2 L working volume, 3.5 kW installed power, and N2 as the carrier gas (flow: 3 L/min). The trials run at 400\u0026deg;C and 600\u0026deg;C with a residence time of 60 minutes.\u003c/p\u003e\u003cp\u003e\u003cb\u003eFeedstocks and Biochar Laboratory Analysis\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTotal C and N in feedstocks and biochar were measured in dried and crushed samples by dry combustion (Nelson \u0026amp; Sommers, \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1982\u003c/span\u003e). At 1050\u0026deg;C, using a Leco CHN1000 instrument (St. Joseph, Michigan, USA) according to the Dumas method (Bremner \u0026amp; Mulvaney, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1982\u003c/span\u003e), and the pH was measured from a 1:5 biochar and (feedstock) to water ratio. The main element (K, Mg, Ca, Fe, P, S and Mo, B, Mn) and trace element (As, Cd, Co, Cr, Cu, Ni, Pb, Hg and Zn) contents in feedstocks and biochar\u0026rsquo;s were determined by sample digestion with HNO\u003csub\u003e3\u003c/sub\u003e (conc.) at 260\u0026deg;C in an Ultraclave microwave digestion system (Milestone) for two and a half hours, with subsequent dilution up to 50 mL and analysis with a Triple QQQ 8800 ICP-MS (Agilent Technologies) with a reaction-collision cell (B, As, Cd, Co, Cr, Cu, Mo, Ni, Pb, and Hg ) and a 5100 SVDV ICP-OES (Agilent Technologies) for determination of Ca, Fe, K, Mg, Mn, P, Al, S and Zn.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. RESULTS","content":"\u003cp\u003e\u003cb\u003e3.1. Impact of anaerobic digestion and pyrolysis on dry matter, loss on ignition, carbon, and macronutrient composition of manure and sewage sludge-derived biochar\u0026rsquo;s\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAD and pyrolysis markedly influenced the physicochemical properties of manure and sludge-derived materials. Across all feedstocks, AD consistently reduced dry matter (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB), with the most drastic reduction observed in biologically treated sludge (\u0026ndash;15%). At the same time, pyrolysis generally counteracted this effect, producing highly stable biochar with dry matter values above 97%, except in the case of CTDSS, where no improvement was observed. Loss on ignition (LOI) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC) followed a similar pattern. Raw manure (RM) had the highest LOI (89.99%), which decreased after AD (77.81%) and fell further with pyrolysis to 60.31% (raw, 600\u0026deg;C) and 59.76% (digestate, 400\u0026deg;C). In BTRSS, LOI declined from 79.65% (raw) to 69.35% (digestate), and further to 59.76% (raw, 400\u0026deg;C) and 45.31% (digestate, 600\u0026deg;C) after pyrolysis. CTRSS showed 69.35% LOI in the raw form, decreasing to 46.22% and 37.54% after pyrolysis at 400\u0026deg;C and 600\u0026deg;C, respectively. The CTDSS already had a relatively low LOI (58.8%), which remained unchanged after pyrolysis, indicating a limited response due to its high mineral content.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe pH of feedstock and biochar varied with both AD and pyrolysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD). Raw manure was slightly alkaline (7.34), increasing modestly after AD (7.70) and strongly after pyrolysis (10.3\u0026ndash;10.4). Digested manure\u0026rsquo;s (DM) biochar reached 9.7 at 400\u0026deg;C. Raw, biologically treated sludge was acidic (5.9), but it became more acidic after AD (6.9) and pyrolysis (7.2\u0026ndash;9.9). The chemically treated sludge was near neutral (pH 6.6\u0026ndash;7.5), although pyrolysis at 400\u0026deg;C reduced the pH, reflecting the sludge's mineral-rich composition and its buffering effect. Overall, AD raised pH in manure and biological sludge, while pyrolysis generally enhanced alkalinity, especially at 600\u0026deg;C. Total carbon (C) decreased after AD across all feedstocks (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). In manure, pyrolysis concentrated C (53% in raw manure biochar), whereas in sludges it declined, most notably in CTRSS (41% in feedstock vs. 27% after 400\u0026deg;C). P concentrations increased strongly after pyrolysis in all feedstocks (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). Manure P rose from 4.1 g kg⁻\u0026sup1; in raw feedstock to 8.5 g kg⁻\u0026sup1; at 600\u0026deg;C, while digestate manure reached 29 g kg⁻\u0026sup1; at 400\u0026deg;C. BTSS increased from 17 to 37 g kg⁻\u0026sup1; (feedstock to 600\u0026deg;C biochar), while biologically treated digestate sludge rose from 14 to 25 g kg⁻\u0026sup1;. CTRSS showed the highest enrichment (42.5 to 84.5 g kg⁻\u0026sup1; at 400\u0026deg;C). AD concentrated P in manure but reduced it in sludges. Nitrogen (N) dynamics contrast between feedstocks (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). AD increased N in manures (1.85\u0026ndash;2.36%) and chemical sludge but reduced it in biological sludge. Pyrolysis consistently decreased N levels, especially at 600\u0026deg;C, due to volatilisation losses. Potassium (K) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC), magnesium (Mg) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE), and calcium (Ca) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD) were all affected differently by AD and pyrolysis. AD generally reduced K concentrations (e.g., raw manure 20 to 13.7 g kg⁻\u0026sup1;; raw biological 4.2 to 2.9 g kg⁻\u0026sup1;), but increased Mg and Ca. DM contained higher Mg (10.6 vs. 2.4 g kg⁻\u0026sup1; in raw) and Ca (21.7 vs. 6.2 g kg⁻\u0026sup1;), while BTDSS also showed enrichment (Mg 5.5 vs. 4.7 g kg⁻\u0026sup1;; Ca 21 vs. 10 g kg⁻\u0026sup1;). Pyrolysis consistently concentrated these minerals: manure-derived biochar showed substantial increases, with K rising to 32 g kg⁻\u0026sup1; and Ca to 17 g kg⁻\u0026sup1; at 600\u0026deg;C, while digestate manure biochar was particularly enriched, with Ca increasing to 43.3 g kg⁻\u0026sup1; and K to 29.3 g kg⁻\u0026sup1; at 400\u0026deg;C, and Mg reaching 19.8 g kg⁻\u0026sup1;. In sludges, enrichment was also pronounced, with Ca in digestate biological sludge rising to 51 g kg⁻\u0026sup1; at 600\u0026deg;C. Sulfur (S) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF) generally decreased with pyrolysis. In manure, S dropped from 2.3 g kg⁻\u0026sup1; in raw feedstock to 1.6 g kg⁻\u0026sup1; at 400\u0026deg;C. In biologically treated raw sludge, S declined sharply from 9.1 to 1.3 g kg⁻\u0026sup1; (feedstock to 600\u0026deg;C biochar), while in biologically treated digestate sludge it decreased from 10 to 3.8 g kg⁻\u0026sup1;. The exception was digestate chemical sludge, where S remained stable (11 g kg⁻\u0026sup1;). AD increased S in most feedstocks, particularly manure and chemical sludge. Overall, AD tended to raise pH and enrich Mg and Ca (while reducing K), but lowered C and P in sludges. Pyrolysis enriched P, K, Mg, and Ca across all materials, but consistently reduced N and S.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003e3.2 Impact of anaerobic digestion and pyrolysis on micronutrients (Fe, Mo, Mn, B), Se and Al composition of manure and sewage sludge-derived biochar\u0026rsquo;s\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe concentrations of micronutrients (Fe, Mo, Mn, B), selenium, and aluminum varied substantially among feedstocks and were strongly modified by AD and pyrolysis (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE, and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF). Iron (Fe) (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA) was generally low in manure (1.1 g kg⁻\u0026sup1;) but increased after pyrolysis (up to 6 g kg⁻\u0026sup1; at 400\u0026deg;C). In comparison, DM showed higher initial levels (2.16 g kg⁻\u0026sup1;) and remained enriched in biochar. BTRSS contained moderate Fe (8.5 g kg⁻\u0026sup1; in raw), with insignificant effect of AD, but pyrolysis caused slight increases at 400\u0026deg;C and reductions at 600\u0026deg;C. In contrast, chemical-treated sewage sludges contained far higher Fe levels, particularly under digestate conditions (37 g kg⁻\u0026sup1; in feedstock, 60 g kg⁻\u0026sup1; at 400\u0026deg;C), highlighting a strong enrichment effect of AD and pyrolysis. Molybdenum (Mo) (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC) followed a similar trend, being lowest in manure (\u0026lt;\u0026thinsp;2 mg kg⁻\u0026sup1;) but enriched by AD and pyrolysis (digestate manure: 3.4 increased to 7.8 mg kg⁻\u0026sup1; at 400\u0026deg;C). Biologically treated sewage sludges contained higher Mo (4.9\u0026ndash;5.9 mg kg⁻\u0026sup1;), which increased by more than 2.5 times after pyrolysis (up to 12 mg kg⁻\u0026sup1;). At the same time, chemical sludges also increased sharply, with raw sludge rising from 3.3 to 8.4 mg kg⁻\u0026sup1; at 400\u0026deg;C. Manganese (Mn) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB) was low in manures (0.16 g kg⁻\u0026sup1; raw) but concentrated after pyrolysis (0.35 g kg⁻\u0026sup1; at 600\u0026deg;C), with AD enhancing levels before charring. Biological sludge showed the most substantial enrichment, with digestate material rising from 0.37 g kg⁻\u0026sup1; to 0.83 g kg⁻\u0026sup1; after pyrolysis at 600\u0026deg;C. In contrast, chemical sludge remained lower overall but showed consistent AD-driven enrichment. B (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD) exhibited a similar pattern, being modest in raw manure (8.8 mg kg⁻\u0026sup1;) but increasing sharply after AD (23.3 mg kg⁻\u0026sup1; in digestate) and pyrolysis (up to 49.8 mg kg⁻\u0026sup1; at 400\u0026deg;C). Biological sludges also displayed strong B enrichment (9.7\u0026ndash;25 mg kg⁻\u0026sup1;), whereas chemical sludges contained less but still increased steadily, with digestates showing higher initial concentrations and greater retention in biochar.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAluminum (Al) (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE) concentrations varied strongly between feedstocks, with apparent effects of both AD and pyrolysis. In manures (RM, DM), Al remained very low (\u0026lt;\u0026thinsp;2 g kg⁻\u0026sup1;) and was unaffected by either treatment, indicating that manure is not a significant source of Al. In biologically treated sewage sludges, Al was moderate in the raw material (8 g kg⁻\u0026sup1;) and increased after AD to 9.1 g kg⁻\u0026sup1;. Pyrolysis also significantly increased to (18\u0026ndash;21 g kg⁻\u0026sup1;) in row biologically treated sewage sludges and (16\u0026ndash;19 g kg⁻\u0026sup1;) in digestate biologically treated sewage sludges. AD consistently raised Al concentrations across feedstocks but decreased in chemically treated sludge (from 54 g kg⁻\u0026sup1; to 40 g kg⁻\u0026sup1;) and increased in pyrolysis.\u003c/p\u003e\u003cp\u003eSelenium (Se) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF) displayed contrasting behaviors. It was shallow in manure (0.23 mg kg⁻\u0026sup1;), enriched by AD (1.4 mg kg⁻\u0026sup1;), but reduced again after pyrolysis due to volatilization. Biological sludge contained the highest Se concentration among feedstocks (2.5 mg kg⁻\u0026sup1;), but pyrolysis reduced these concentrations, confirming Se's sensitivity to thermal treatment. In contrast, digestate chemical sludge exhibited the highest Se levels overall (2.9 mg kg⁻\u0026sup1;), which further increased after pyrolysis (3.35 mg kg⁻\u0026sup1;), suggesting strong stabilization of Se in this mineral-rich matrix.\u003c/p\u003e\u003cp\u003e\u003cb\u003e3.3. Effects of anaerobic digestion and pyrolysis on heavy metal enrichment and regulatory classification of manure- and sludge-derived biochar\u003c/b\u003e\u003c/p\u003e\u003cp\u003eHeavy metal concentrations showed significant differences between feedstocks and varied in response to AD and pyrolysis (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In manure, AD reduced Cu slightly (21 to 15 mg kg⁻\u0026sup1;) but increased concentrated Zn (96 to 137 mg kg⁻\u0026sup1;), while pyrolysis further enriched both elements, particularly in digested manure biochar at 400\u0026deg;C (Cu 123 mg kg⁻\u0026sup1;; Zn 543 mg kg⁻\u0026sup1;). Raw manure biochar showed more moderate increments due to up-concentration (Cu 34\u0026ndash;48 mg kg⁻\u0026sup1;; Zn 165\u0026ndash;195 mg kg⁻\u0026sup1;). In BTRSS, AD did not affect Cu (250 mg kg⁻\u0026sup1;) but increased concentrated Zn (680 to 790 mg kg⁻\u0026sup1;). Pyrolysis caused strong enrichment, with Cu rising to 580\u0026ndash;690 mg kg⁻\u0026sup1; in raw sludge biochar and 470\u0026ndash;540 mg kg⁻\u0026sup1; in digestate sludge biochar, while Zn doubled to 1500\u0026ndash;1900 mg kg⁻\u0026sup1;. Ni also increased consistently (15\u0026ndash;21 \u0026rarr; 36\u0026ndash;48 mg kg⁻\u0026sup1;), and Cd rose modestly after AD (0.75 \u0026rarr; 0.96 mg kg⁻\u0026sup1;) and further with pyrolysis (up to 1.8 mg kg⁻\u0026sup1;). CTRSS showed a higher content of Cu (150 \u0026rarr; 260 mg kg⁻\u0026sup1;), Zn (285 \u0026rarr; 610 mg kg⁻\u0026sup1;), and Ni (12 \u0026rarr; 18 mg kg⁻\u0026sup1;) after AD, while pyrolysis further concentrated Cu (220\u0026ndash;390 mg kg⁻\u0026sup1;), Zn (580\u0026ndash;925 mg kg⁻\u0026sup1;), and Cr (from 24.5\u0026ndash;39.5 to 63\u0026ndash;66.5 mg kg⁻\u0026sup1;). Cd also increased steadily, from 0.25 mg kg⁻\u0026sup1; in the raw feedstock to 0.85 mg kg⁻\u0026sup1; after AD and up to 1.25 mg kg⁻\u0026sup1; after pyrolysis.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eEffect of anaerobic digestion and pyrolysis temperature on heavy metals composition\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"10\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTreatments\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eType of material\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCu\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCr\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eZn\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eNi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eCd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003ePb\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eHg\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003e[As]\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"7\" nameend=\"c9\" namest=\"c3\"\u003e\u003cp\u003emg/kg\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eRM\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eFeedstock\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.18\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eRM\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (400C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e7.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e165\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e6.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e2.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.33\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eRM\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (600C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e195\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e6.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.51\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eDM\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eFeedstock\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e137\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e2.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.30\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eDM\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (400C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e123\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e11.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e543\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e15.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e5.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.50\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eBTRSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eFeedstock\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e680\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e4.20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eBTRSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (400C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e580\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1600\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e3.80\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eBTRSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (600C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e690\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1900\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e4.10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eBTDSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eFeedstock\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e790\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e3.80\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eBTDSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (400C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e470\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e4.00\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eBTDSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (600C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e540\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1700\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e4.70\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eCTRSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eFeedstock\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e150\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e24.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e285\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e7.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.63\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eCTRSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (400C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e220\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e66.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e580\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.89\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eCTDSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eFeedstock\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e260\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e39.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e610\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.85\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e2.55\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eCTDSS\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eBiochar (400C \u0026deg;)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e390\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e925\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e27.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.019\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e3.15\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"10\"\u003e\u003cb\u003eWhere\u003c/b\u003e \u003cem\u003eRM, Raw manure; DM, Digestate manure\u003c/em\u003e; \u003cem\u003eBTRSS, biologically treated raw sewage sludge\u003c/em\u003e, \u003cem\u003eBTDSS, biologically treated digestate sewage sludge; CTRSS, chemically treated raw sewage sludge\u003c/em\u003e, \u003cem\u003eCTDSS, chemically treated digestate sewage sludge.\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe biochar and feedstocks were also further classified according to the recently updated Norwegian fertilizer regulation (LMD, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), which confirmed these trends. Manure-derived feedstocks and biochar (RM, DM) remained within Class 0\u0026ndash;II, with all metals well below regulatory thresholds, indicating negligible contamination risk. In contrast, sewage sludge-derived materials were associated with greater regulatory concerns. In biologically treated sludge and digestate (BTRSS, BTDSS), Zn exceeded Class III after pyrolysis at both 400\u0026deg;C and 600\u0026deg;C, while Cu reached Class III in the 600\u0026deg;C biochar. Cr and Cd generally remained within Class II\u0026ndash;III. In chemically treated sludge and digestate (CTRSS, CTDSS), AD moderately increased Zn, and pyrolysis further concentrated it to Class III levels at 400\u0026deg;C. In contrast, other metals (Cr, Ni, Cd, Pb, Hg, As) remained within Class I\u0026ndash;II. Overall, AD elevated heavy metal concentrations in sewage sludge feedstocks, while pyrolysis consistently intensified this effect, especially for Zn and Cu. In contrast, manure-derived materials maintained low contaminant levels and remained fully compliant with the national fertilizer regulation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Effects of anaerobic digestion and pyrolysis on phosphorus enrichment and regulatory eligibility of biochar\u003c/h2\u003e\u003cp\u003eThe relationship between phosphorus content and P: metal ratios revealed contrasting impacts of AD and pyrolysis across different feedstocks (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). AD increased P% in manure (DM) and in sludge digestates (BTDSS, CTDSS), thereby improving P: metal ratios for Cu and Cr (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Pyrolysis further increased P concentrations, shifting materials to the right on the P% axis; however, this enrichment was often offset by lower P: metal ratios due to heavy-metal accumulation, particularly Zn. Manure-derived biochar, especially DM biochar at 400\u0026deg;C, achieved both higher P% (exceeding the eligibility threshold of 1.5%) and favorable P: Cu, P: Cr, and P: Ni ratios, all well above the regulatory limits (24, 155, and 310, respectively). In contrast, sludge-derived biochar consistently showed Zn as the limiting factor. Despite pyrolysis increasing their P content above the eligibility threshold, their P: Zn ratios remained close to or below the threshold (19), with BTRSS and BTDSS biochar at 400\u0026ndash;600\u0026deg;C particularly constrained by excessive Zn accumulation. By comparison, Cu, Cr, and Ni ratios were consistently above their thresholds across all treatments, confirming they are not critical for compliance. For Cd, Pb, Hg, and As (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), all feedstocks and biochar-maintained P: metal ratios far exceeding their respective regulatory thresholds (7,750, 194, 5,167, and 780, respectively), regardless of treatment. Cd and Hg, commonly highlighted as critical contaminants in sewage sludge, posed no limitation here, with ratios remaining orders of magnitude above the thresholds. Pb and As, while enriched in chemically treated sludge (CTRSS, CTDSS), also maintained safe margins well above the regulatory limits. The phosphorus eligibility threshold (P% \u0026ge; 1.5%) remained decisive: raw manure (RM) and untreated digestates, which exhibited favorable P: metal ratios, were excluded due to insufficient phosphorus concentration. Overall, the analysis demonstrates that Cd, Pb, Hg, and As are not limiting factors under the 2025\u0026ndash;2028 Norwegian regulation. The regulatory classification of feedstocks and their corresponding biochar (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) revealed apparent differences in eligibility under the updated Norwegian fertilizer regulation. Manure-derived materials (RM and DM) were essentially not eligible because of their low phosphorus content (P\u0026thinsp;\u0026lt;\u0026thinsp;1.5%), except for digestate manure biochar at 400\u0026deg;C, which complied with all heavy-metal thresholds and was therefore fully eligible for agricultural use. In contrast, sewage sludge-derived materials were more constrained by heavy metals, particularly zinc and copper. Biologically treated raw sludge (BTRSS) was initially eligible as a feedstock; however, its biochar exceeded the Zn Class IV and Cu Class III thresholds, rendering it ineligible. BTDSS was an eligible feedstock. Still, the 400\u0026deg;C biochar was restricted to non-cultivated uses due to Zn Class III, while the 600\u0026deg;C biochar exceeded Zn Class IV and was not permitted. Among chemically treated sludge materials, CTRSS was consistently eligible as both a feedstock and a biochar, whereas CTDSS was eligible as a feedstock but restricted to non-cultivated areas at 400\u0026deg;C (Zn Class III). Overall, these results demonstrate that pyrolysis increases phosphorus concentration, which can improve the eligibility of manure biochar; however, it also concentrates heavy metals in sewage sludge biochar, particularly zinc, thereby limiting their use primarily to non-food or non-cultivated land applications.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. DISCUSSION","content":"\u003cp\u003e\u003cb\u003e4.1 Impact of anaerobic digestion and pyrolysis on dry matter, loss on ignition, carbon, and macronutrient composition of manure and sewage sludge-derived biochar\u0026rsquo;s\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAD and pyrolysis induced contrasting but complementary effects on the stability and nutrient composition of manure and sewage sludge. Across all feedstocks, AD reduced dry matter (DM), loss on ignition (LOI), and total carbon (C) contents, confirming the microbial decomposition of labile organics and their conversion into biogas (Aguirre-Villegas et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This reduction was particularly pronounced in biologically treated sewage sludge, which lost nearly one-fifth of its DM, while manures and chemically treated sludge were less affected. At the same time, AD raised the pH in manure and sewage sludges, most likely through the accumulation of ammonia and carbonate salts (Chen et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Demirbaş et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Kang et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), and increased concentrations of some nutrients, such as N, Mg, Ca, and S, reflecting the mineralization and redistribution of organic matter during digestion (Adani et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Weimers et al., \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Pyrolysis, on the other hand, largely counteracted the loss of stability caused by AD, producing biochar with very high DM (\u0026gt;\u0026thinsp;97%) and low LOI, while also shifting the chemical composition towards a more mineral-rich and alkaline material (Basinas et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Opatokun et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Petrovič et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These changes illustrate the role of pyrolysis as a stabilization step that fixes the remaining carbon into aromatic structures while concentrating on the inorganic fraction (Opatokun et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eNutrient dynamics differed strongly between elements and feedstocks. Phosphorus (P) was consistently enriched after pyrolysis, especially in chemically treated sewage sludge, where concentrations doubled beyond 80 g kg⁻\u0026sup1; due to the retention of Fe-, Al-, and Ca-bound phosphates after organic matter volatilization. (Feng et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Filho et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Frišt\u0026aacute;k et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Robinson et al., \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Nitrogen (N), by contrast, declined markedly with pyrolysis as volatile compounds such as ammonia (NH₃), hydrogen cyanide (HCN), and nitrogen oxides (NOx) were released (Cao et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Chen, G. et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Wang, Y. et al., \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, AD increased N in manure and chemically treated sludge by concentrating ammoniacal N as organic matter degraded. Potassium (K), calcium (Ca), and magnesium (Mg) were strongly enriched in all biochar, with the greatest increase observed in digestate manure and sludge, confirming their thermal stability and accumulation in the ash fraction. (Khater et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Shen \u0026amp; Yuan, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Shi et al., \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Sulfur (S) showed the opposite trend, with significant reductions during pyrolysis due to volatilization as SO₂ and H₂S (Hou et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Xu et al., \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), except in digestate chemical sludge, where mineral sulfates or sulfides likely stabilized S this is related to materials rich in mineral content, where sulfur can be stabilized as mineral sulfates or sulfides (Cao et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Huang et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Xing et al., \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e4.2 Impact of anaerobic digestion and pyrolysis on micronutrient composition of manure and sewage sludge-derived biochar\u0026rsquo;s\u003c/h2\u003e\u003cp\u003eAD and pyrolysis substantially influenced the concentrations and distribution of micronutrients (Fe, Mo, Mn, B, Al, and Se) across manure- and sewage sludge-derived feedstocks. Iron (Fe) was particularly enriched in chemically treated sewage sludges, where concentrations increased from 6.3 g kg⁻\u0026sup1; in the raw feedstock to \u0026gt;\u0026thinsp;12 g kg⁻\u0026sup1; in biochar, and further to 60 g kg⁻\u0026sup1; in digestate chemical sludge after pyrolysis. This strong enrichment reflects the influence of Fe-based coagulants commonly used during chemical sludge treatment, which persist and concentrate during AD and thermal processing (Geng et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Wang, R. et al., \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Xiao et al., \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In contrast, manure and biological sludge contained lower Fe levels, with AD exerting only modest effects and pyrolysis leading to moderate concentration. Molybdenum (Mo) was found in low levels in manure. Still, it was enriched substantially in sludge-derived biochar, with concentrations more than doubling during pyrolysis, particularly in biological sludge (from 5 mg kg⁻\u0026sup1; to \u0026gt;\u0026thinsp;12 mg kg⁻\u0026sup1;). AD enhanced Mo concentrations in both manure and sludge feedstocks, likely due to organic matter breakdown and concentration of trace elements, with pyrolysis further amplifying this effect (Cai et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These trends suggest that Mo is largely conserved under pyrolytic conditions and that AD acts as a pre-concentrating step.\u003c/p\u003e\u003cp\u003eManganese (Mn) also showed consistent enrichment, with the highest values recorded in digestate biological sludge biochar (\u0026gt;\u0026thinsp;0.8 g kg⁻\u0026sup1;). AD increased Mn in all feedstocks, likely through mineralization and solubilization processes, while pyrolysis concentrated Mn further into the ash fraction (Rodr\u0026iacute;guez et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Boron (B) concentrations followed a similar pattern: AD raised B levels in manure and sludge feedstocks, and pyrolysis further enriched them, with digestate manure biochar at 400\u0026deg;C containing nearly six times more B than raw manure. The stability of B during pyrolysis contrasts with that of more volatile nutrients such as N and S (Cao et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Hong et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), highlighting its potential retention in biochar as a micronutrient source (Cao et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Dong et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Gao et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Aluminum (Al) showed the most pronounced enrichment in chemically treated sludges, with pyrolysis nearly doubling its concentration (from ~\u0026thinsp;54 to 105 g kg⁻\u0026sup1;). This reflects the widespread use of Al-based chemicals in wastewater treatment, which persist through AD and concentrate strongly in biochar (Barakwan et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Basri et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Muisa et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn contrast, selenium (Se) exhibited different behavior across digestion and pyrolysis, revealing a strong influence of volatilization and matrix stabilization. In most feedstocks, AD led to an increase in Se (via concentration in residual solids), but pyrolysis at 400\u0026ndash;600\u0026deg;C induced marked decreases in Se content, consistent with the volatilization of Se as SeO₂ or elemental Se vapor (Ruiqing, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Sugawara et al., \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Wang \u0026amp; Jia, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). However, the anomalous enrichment observed in chemically digested sludge (CDRSS) suggests that metal coagulants used in sludge treatment (e.g., Fe/Al) may form intense binding phases or capture volatilized Se, thereby retaining it in the solid fraction. This aligns with documented capture of Se by metal oxides in gasification systems (Yu et al., \u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) and supports that the presence of reactive metal phases can mitigate Se loss under high-temperature conditions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e4.3. Heavy metal classification, phosphorus enrichment, and regulatory eligibility of feedstocks and biochar\u003c/h2\u003e\u003cp\u003e\u003cb\u003eHeavy metal enrichment and phosphorus metal ratios\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe contrasting responses of heavy metals to AD and pyrolysis reflect the interplay between organic matter degradation, mineral composition, and thermal stability. In manures, AD caused relatively minor changes, with Cu levels decreasing slightly and Zn levels increasing in the digestate compared to raw manure. This suggests that mineralization during AD can mobilize certain metals (e.g., Zn) into more concentrated forms, while others (e.g., Cu) may be redistributed or partly lost through the liquid phase. After pyrolysis, both raw and digestate manures showed enrichment of Cu and Zn. Still, the effect was more substantial in the digestate, likely because the lower organic matter content after AD reduced dilution and enhanced concentration during thermal treatment. In sewage sludges, however, the effects were more pronounced. AD consistently increased heavy metal concentrations relative to raw sludges by removing volatile and labile organics and leaving metals enriched in the solid fraction (Aguirre-Villegas et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Suanon et al., \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Pyrolysis then focused on metals, with Zn and Cu showing the most significant increases, particularly in biologically treated sludges. Zn reached up to 1900 mg kg⁻\u0026sup1; in biochar, consistent with its non-volatility and association with stable mineral phases (Qian et al., \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Cu also accumulated strongly, especially at 600\u0026deg;C, reflecting its persistence in oxide and sulfide forms (Krunks et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). Cr, Ni, and Cd were less enriched but followed the same pattern. Chemically treated sludge exhibited the most pronounced AD concentration effect, followed by further enrichment during pyrolysis, consistent with the immobilization of metals in Fe- and Al-based precipitates during wastewater treatment (Cui et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Giwa et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Xiao et al., \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThese findings highlight the contrasting impacts of AD and pyrolysis on the agronomic value and regulatory compliance of organic residuals. In manure-derived materials, AD enhanced P concentrations while maintaining low heavy metal contents, consistent with earlier reports that nutrient retention in manures after AD is largely preserved, with reductions mainly in organic matter and volatile components (Eghball et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Pyrolysis further concentrated and stabilized phosphorus. (Hadroug et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Jin, Y. et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Keskinen et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) without causing problematic heavy metal enrichment (Liu et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). As a result, manure-derived biochar, mainly that derived from digestate, has strong potential as a sustainable phosphorus fertilizer, combining high nutrient value with negligible contamination. These findings highlight the contrasting impacts of AD and pyrolysis on the agronomic value and regulatory compliance of organic residuals. In manure-derived materials, AD increased P concentrations while maintaining low heavy metal contents, consistent with earlier reports that nutrient retention in manures after AD is largely preserved, with reductions mainly in organic matter and volatile components.\u003c/p\u003e\u003cp\u003ePyrolysis further concentrated and stabilized phosphorus without causing problematic heavy-metal enrichment. As a result, manure-derived biochar, especially that from digestate, shows strong potential as a sustainable phosphorus fertilizer, combining high nutrient value with minimal contamination risks.\u003c/p\u003e\u003cp\u003eIn sewage sludge-derived materials, however, AD decreased total P concentrations in both biologically and chemically treated sludges, likely due to solubilization and mobilization losses during digestion, as observed in previous sludge management studies (Alvarenga et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Chen, Y. et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Smith et al., \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Analytical factors may also contribute, as incomplete recovery of refractory P forms during nitric acid digestion can lead to a slight underestimation of total P in AD-treated samples, particularly when P is firmly bound to Fe- and Al-rich phases. Pyrolysis then reconcentrated P in the solid fraction, enhancing apparent fertilizer value, but simultaneously intensified heavy metal accumulation (Hosseinian et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Rangabhashiyam et al., \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Schlederer et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This dual effect shifted sludge-derived biochar toward higher P% but at the expense of lower P:metal ratios. Among the metals, Zn consistently represented the most critical limiting element, with ratios near or below the threshold, followed by Cu in certain digestate and chemically treated sludges (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Similar findings have been reported elsewhere, where Zn and Cu were identified as the dominant contaminants restricting the agricultural reuse of sludge-derived biochar (Krueger et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); in contrast, Cr and Ni did not pose restrictions, with P: metal ratios far above threshold values.\u003c/p\u003e\u003cp\u003eThe extended assessment of Cd, Pb, Hg, and As (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) shows a markedly different picture. Across all feedstocks and treatments, the P: Cd, P: Pb, P: Hg, and P: As ratios were several orders of magnitude higher than the regulatory thresholds (7750, 194, 5167, and 780, respectively). Even after pyrolysis at 600\u0026deg;C, no treatment approached these critical limits. This suggests that these metals are not limited to agricultural applications, unlike Zn and Cu. Taken together, the results highlight that the regulatory bottleneck for sludge-derived biochar lies primarily in Zn (and secondarily Cu), while Cd, Pb, Hg, and As remain well within safe limits. From a management perspective, this means that while digestate manure biochar is suitable for agronomic use without restriction, raw manure biochar is restricted because its P% is below the threshold. Sludge-derived biochar requires targeted mitigation strategies (e.g., blending, co-pyrolysis, chemical pretreatment) to meet the Norwegian 2025 fertilizer regulation.\u003c/p\u003e\u003cp\u003e\u003cb\u003eRegulatory eligibility of feedstocks and biochar\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe regulatory eligibility analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) further clarifies these dynamics. Raw manure (RM) was consistently classified as not eligible due to phosphorus levels below the 1.5% threshold, despite safe P: metal ratios. In contrast, digestate manure (DM) became eligible after pyrolysis, confirming its suitability as a compliant fertilizer with both agronomic value and low contamination risk. For sewage sludge-derived materials, outcomes varied. Biologically treated raw and digestate sludges (BTRSS and BDRSS) were eligible as feedstocks. Still, they were downgraded after pyrolysis because of zinc enrichment to Class III\u0026ndash;IV levels and, in some cases, copper accumulation. Chemically digested sludge (CDRSS) was also eligible as a feedstock; however, its biochar was restricted at 400\u0026deg;C (Zn Class III) and became fully non-eligible at 600\u0026deg;C (Zn Class IV). Conversely, chemically treated raw sludge (CTRSS) behaved differently from the other sludge types, remaining fully eligible both as a feedstock and after pyrolysis at 400\u0026deg;C, with phosphorus concentrations exceeding the agronomic threshold and P: metal ratios consistently within safe limits. Overall, these results show that digestate manure biochar (DM) is agronomically valuable and fully compliant with regulatory standards, making it a viable alternative to mineral phosphorus fertilizers. Meanwhile, raw manure biochar (RM) is limited by its low phosphorus content, despite favorable heavy metal levels. Among the sludge-derived materials, CTRSS is a clear exception, retaining eligibility across all treatments. In contrast, BTRSS, BDRSS, and CDRSS become increasingly restricted or fully non-eligible after pyrolysis due to zinc accumulation, with copper also contributing in some cases. Thus, while pyrolysis increases phosphorus concentrations, zinc and, to a lesser extent, copper remain the critical bottlenecks for most sludge-derived biochar, highlighting the need for mitigation strategies such as blending, co-pyrolysis, or chemical pre-treatments to enable safe agricultural use under Norwegian and EU regulatory frameworks.\u003c/p\u003e\u003c/div\u003e"},{"header":"5. CONCLUSION","content":"\u003cp\u003eAnaerobic digestion and pyrolysis served as complementary treatments that reshaped the nutrient and contaminant profiles of manure- and sludge-derived residues. AD reduced C and dry matter while raising pH and enriching Ca, Mg, and, in some cases, Se, whereas pyrolysis produced stable, alkaline biochar with intensely concentrated P, K, Ca, and Mg but losses of N and S. Micronutrients (Fe, Mn, B, Mo) were retained and enriched. At the same time, Se was mostly volatilized except in Fe/Al-rich digestate chemical sludge, where retention was enhanced. Heavy metals, particularly Zn and Cu, concentrated intensely after pyrolysis and represented the main regulatory bottlenecks, while Cd, Pb, Hg, and As remained far below thresholds. According to the Norwegian 2025 fertilizer regulation, digestate manure biochar at 400\u0026deg;C fully met the P and heavy-metal criteria, making it suitable as a compliant P fertilizer. Raw manure remained ineligible due to insufficient P. Among sewage sludge-derived biochar\u0026rsquo;s, most were excluded by Zn enrichment, except for chemically treated raw sludge biochar at 400\u0026deg;C, which retained eligibility.\u003c/p\u003e"},{"header":"6. FUTURE WORK AND TAKE-HOME MESSAGE","content":"\u003cp\u003e\u003cb\u003eFuture Work\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFurther research should address three primary areas. First, selenium dynamics: while AD increased Se levels, pyrolysis often led to volatilization, except in Fe/Al-rich digestate chemical sludge, where retention was enhanced. Future studies should clarify the role of mineral phases in stabilizing Se and assess its plant availability. Second, heavy metal mitigation: Zn and Cu enrichment remain the dominant barriers to regulatory compliance for sludge-derived biochar. Strategies such as blending low-metal feedstocks, co-pyrolysis with sorbents, or chemical pretreatments should be explored. Third, aluminum accumulation: Al was negligible in manures but strongly enriched in chemically treated sludges due to Al-based coagulants. Although not regulated under current fertilizer laws, its long-term agronomic and environmental effects need evaluation. Finally, agronomic trials should test the actual availability of P, Se, and other micronutrients to crops, ensuring laboratory findings align with field performance.\u003c/p\u003e\u003cp\u003e\u003cb\u003eTake-Home Message\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe combined AD pyrolysis pathway improves stability and P recovery in organic residues. Under the 2025 Norwegian fertilizer regulation, digestate manure biochar at 400\u0026deg;C is fully compliant and represents a promising circular P fertilizer. Raw manure remains ineligible due to low P. Most sludge-derived biochar is excluded by Zn (and sometimes Cu), except chemically treated raw sludge biochar at 400\u0026deg;C, which retained eligibility. Thus, while manure-derived biochar can safely substitute for mineral fertilizers, sludge-derived biochar requires targeted innovations to reduce Zn/Cu enrichment and to assess the implications of Al and Se for sustainable agricultural use.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCOMPETING INTERESTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e“The authors have no relevant financial or non-financial interests to disclose.”\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDATA AVAILABILITY\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e“The datasets generated during and/or analyzed during the current study are not publicly available due to \u003cstrong\u003e[DATA ARE STORED INTERNALLY AT NMBU DATA DRIVE AND SHARED AMONG THE PARTNERS, NOT PUBLIC]\u003c/strong\u003e but are available from the corresponding author on reasonable request.”\u003c/em\u003e\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eACKNOWLEDGEMENT\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eThis work was supported by the Research Council of Norway through the RenCARBio project (Grant No. 326914).\u003c/em\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAbdullah, N., Taib, R., Aziz, N. S. M., Omar, M. R. \u0026amp; Disa, N. M. (2023). Banana pseudo-stem biochar derived from the slow and fast pyrolysis processes. \u003cem\u003eHeliyon\u003c/em\u003e, 9. doi: 10.1016/j.heliyon.2023.e12940.\u003c/li\u003e\n \u003cli\u003eAdani, F., D\u0026rsquo;Imporzano, G., Tambone, F., Riva, C., Boccasile, G. \u0026amp; Orzi, V. (2020). Anaerobic Digestion and Renewable Fertilisers. 215\u0026ndash;229. doi: 10.1002/9781118921487.ch5-2.\u003c/li\u003e\n \u003cli\u003eAguirre-Villegas, H., Larson, R., \u0026amp; Sharara, M. (2019). Anaerobic digestion, solid-liquid separation, and drying of dairy manure: Measuring constituents and modelling emission. \u003cem\u003eScience of The Total Environment\u003c/em\u003e, 696: 134059. doi: 10.1016/J.SCITOTENV.2019.134059.\u003c/li\u003e\n \u003cli\u003eAltıkat, A., Alma, M., Altikat, A., Bilgili, M. \u0026amp; Altıkat, S. (2024). A Comprehensive Study of Biochar Yield and Quality Concerning Pyrolysis Conditions: A Multifaceted Approach. \u003cem\u003eSustainability\u003c/em\u003e. Doi: 10.3390/su16020937.\u003c/li\u003e\n \u003cli\u003eAlvarenga, E., \u0026Oslash;gaard, A. \u0026amp; Vr\u0026aring;le, L. (2017). Effect of anaerobic digestion and liming on plant availability of phosphorus in iron- and aluminium-precipitated sewage sludge from primary wastewater treatment plants. \u003cem\u003eWater science and technology : a journal of the International Association on Water Pollution Research\u003c/em\u003e, 75 7-8: 1743-1752. doi: 10.2166/wst.2017.056.\u003c/li\u003e\n \u003cli\u003eBarakwan, R., Trihadiningrum, Y. \u0026amp; Bagastyo, A. (2019). Characterisation of Alum Sludge from Surabaya Water Treatment Plant, Indonesia. \u003cem\u003eJournal of Ecological Engineering\u003c/em\u003e. Doi: 10.12911/22998993/104619.\u003c/li\u003e\n \u003cli\u003eBasinas, P., Rus\u0026iacute;n, J., Chamr\u0026aacute;dov\u0026aacute;, K. \u0026amp; Kaldis, S. (2023). Pyrolysis of the anaerobic digestion solid by-product: Characterisation of digestate decomposition and screening of the biochar use as soil amendment and as an additive in anaerobic digestion. \u003cem\u003eEnergy Conversion and Management\u003c/em\u003e. Doi: 10.1016/j.enconman.2023.116658.\u003c/li\u003e\n \u003cli\u003eBasri, M. H., Don, N. M., Kasmuri, N., Hamzah, N., Alias, S. \u0026amp; Azizan, F. (2019). Aluminium recovery from water treatment sludge under different dosages of sulphuric acid. \u003cem\u003eJournal of Physics: Conference Series\u003c/em\u003e, 1349. doi: 10.1088/1742-6596/1349/1/012005.\u003c/li\u003e\n \u003cli\u003eBhat, M. A., Mishra, A., Shah, S. N., Bhat, M., Jan, S., Rahman, S., Baek, K.-H. \u0026amp; Jan, A. T. (2024). Soil and Mineral Nutrients in Plant Health: A Prospective Study of Iron and Phosphorus in the Growth and Development of Plants. \u003cem\u003eCurrent Issues in Molecular Biology\u003c/em\u003e, 46: 5194\u0026ndash;5222. doi: 10.3390/cimb46060312.\u003c/li\u003e\n \u003cli\u003eBremner, J. M. \u0026amp; Mulvaney, C. (1982). Nitrogen\u0026mdash;total. \u003cem\u003eMethods of soil analysis: part 2 chemical and microbiological properties\u003c/em\u003e, 9: 595\u0026ndash;624.\u003c/li\u003e\n \u003cli\u003eCai, Y., Janke, L., Meng, X., Zheng, Z., Zhao, X., Pr\u0026ouml;ter, J. and Sch\u0026auml;fer, F. 2022. The absolute concentration and bioavailability of trace elements: two vital parameters affecting anaerobic digestion performance of chicken manure leachate. \u003cem\u003eBioresource technology\u003c/em\u003e: 126909. doi: 10.1016/j.biortech.2022.126909.\u003c/li\u003e\n \u003cli\u003eCao, C.-Y., Cheng, Y., Hu, H., Wang, H., Liu, S., Hu, M., Li, X., \u0026amp; Yao, H. (2022). Products distribution and sulfur fixation during the pyrolysis of CaO conditioned textile dyeing sludge: Effects of pyrolysis temperature and heating rate. \u003cem\u003eWaste management\u003c/em\u003e, 153: 367\u0026ndash;375. doi: 10.1016/j.wasman.2022.09.027.\u003c/li\u003e\n \u003cli\u003eCao, J., Li, L., Morishita, K., Xiao, X., Zhao, X.-Y., Wei, X. \u0026amp; Takarada, T. (2013). Nitrogen transformations during fast pyrolysis of sewage sludge. \u003cem\u003eFuel\u003c/em\u003e, 104: 1\u0026ndash;6. doi: 10.1016/J.FUEL.2010.08.015.\u003c/li\u003e\n \u003cli\u003eChen, G., Li, J., Li, K., Lin, F., Tian, W., Che, L., Yan, B., Wenchao \u0026amp; Song, Y. (2020). Nitrogen, sulfur, chlorine containing pollutants releasing characteristics during pyrolysis and combustion of oily sludge. \u003cem\u003eFuel\u003c/em\u003e, 273: 117772. doi: 10.1016/j.fuel.2020.117772.\u003c/li\u003e\n \u003cli\u003eChen, H., Wang, Y., Xu, G. \u0026amp; Yoshikawa, K. (2012). Fuel-N Evolution during the Pyrolysis of Industrial Biomass Wastes with High Nitrogen Content. \u003cem\u003eEnergies\u003c/em\u003e, 5: 5418\u0026ndash;5438. doi: 10.3390/EN5125418.\u003c/li\u003e\n \u003cli\u003eChen, W., Yang, H., Chen, Y., Xia, M., Chen, X., \u0026amp; Chen, H. (2017). Transformation of Nitrogen and Evolution of N-Containing Species during Algae Pyrolysis. \u003cem\u003eEnvironmental science \u0026amp; technology\u003c/em\u003e, 51 11: 6570\u0026ndash;6579. doi: 10.1021/acs.est.7b00434.\u003c/li\u003e\n \u003cli\u003eChen, Y., Sun, R., Sun, T., Chen, P., Yu, Z., Ding, L., Jiang, Y., Wang, X., Dai, C., \u0026amp; Sun, B. (2020). Evidence for involvement of keystone fungal taxa in organic phosphorus mineralisation in subtropical soil and the impact of labile carbon. \u003cem\u003eSoil Biology and Biochemistry\u003c/em\u003e, 148: 107900.\u003c/li\u003e\n \u003cli\u003eChen, Y., Ding, W., Bai, Y., Wang, X., Shen, N., Li, L., Lu, D. \u0026amp; Zhou, Y. (2024). Phosphorus release and realignment in anaerobic digestion of thermal hydrolysis pretreatment sludge - Masking effects from high ammonium. \u003cem\u003eWater research\u003c/em\u003e, 255: 121488. doi: 10.1016/j.watres.2024.121488.\u003c/li\u003e\n \u003cli\u003eChowdhury, R., Moore, G., Weatherley, A. \u0026amp; Arora, M. (2017). Key sustainability challenges for the global phosphorus resource, their implications for global food security, and options for mitigation. \u003cem\u003eJournal of Cleaner Production\u003c/em\u003e, 140: 945\u0026ndash;963. doi: 10.1016/J.JCLEPRO.2016.07.012.\u003c/li\u003e\n \u003cli\u003eCui, Z., Xu, G.-R., Ormeci, B., Liu, H.-W. \u0026amp; Zhang, Z. (2022). Transformation and stabilisation of heavy metals during pyrolysis of organic and inorganic-dominated sewage sludges and their mechanisms. \u003cem\u003eWaste management\u003c/em\u003e, 150: 57\u0026ndash;65. doi: 10.1016/j.wasman.2022.06.023.\u003c/li\u003e\n \u003cli\u003eDadrasnia, A., Mu\u0026ntilde;oz, I., Y\u0026aacute;\u0026ntilde;ez, E., Lamkaddam, I. U., Mora, M., Pons\u0026aacute;, S., Ahmed, M., Argelaguet, L., Williams, P. \u0026amp; Oatley-Radcliffe, D. (2021). Sustainable nutrient recovery from animal manure: A review of current best practice technology and the potential for freeze concentration. \u003cem\u003eJournal of Cleaner Production\u003c/em\u003e, 315: 128106. doi: 10.1016/J.JCLEPRO.2021.128106.\u003c/li\u003e\n \u003cli\u003eDemirbaş, A., Taylan, O. \u0026amp; Kaya, D. (2016). Biogas production from municipal sewage sludge (MSS). \u003cem\u003eEnergy Sources, Part A: Recovery, Utilisation, and Environmental Effects\u003c/em\u003e, 38: 3027-3033. doi: 10.1080/15567036.2015.1124944.\u003c/li\u003e\n \u003cli\u003eDhillon, J., Torres, G., Driver, E., Figueiredo, B., \u0026amp; Raun, W. (2017). World Phosphorus Use Efficiency in Cereal Crops. \u003cem\u003eAgronomy Journal\u003c/em\u003e, 109: 1670\u0026ndash;1677. doi: 10.2134/AGRONJ2016.08.0483.\u003c/li\u003e\n \u003cli\u003eDong, Z., Yang, H., Liu, Z., Chen, P., Chen, Y., Wang, X., Chen, H. and Wang, S. 2022. Pyrolysis of boron-crosslinked lignin: influence on lignin softening and product properties. \u003cem\u003eBioresource technology\u003c/em\u003e: 127218. doi: 10.1016/j.biortech.2022.127218.\u003c/li\u003e\n \u003cli\u003eDridi, N., Romdhane, L., Ferreira, R. \u0026amp; Sleimi, N. (2020). Fertiliser effect of composted sewage sludge and cattle manure on Pelargonium growth. \u003cem\u003eJournal of Water, Sanitation, and Hygiene for Development\u003c/em\u003e. doi: 10.2166/washdev. 2020.082.\u003c/li\u003e\n \u003cli\u003eEdixhoven, J., Gupta, J. \u0026amp; Savenije, H. (2014). Recent revisions of phosphate rock reserves and resources: a critique. \u003cem\u003eEarth System Dynamics Discussions\u003c/em\u003e, 5: 491-507. doi: 10.5194/ESD-5-491-2014.\u003c/li\u003e\n \u003cli\u003eEghball, B., Wienhold, B., Gilley, J. \u0026amp; Eigenberg, R. (2002). Mineralisation of manure nutrients. \u003cem\u003eJournal of Soil and Water Conservation\u003c/em\u003e. Doi: 10.1080/00224561.2002.12457480.\u003c/li\u003e\n \u003cli\u003eFeng, H., Zhou, S., Guan, W., Zhu, L., Li, R., \u0026amp; Wang, S. (2024). Enhancement of Apatite-Phosphorus-Rich Biochar Production from Sewage Sludge Pyrolysis Assisted by Carbide Slag.\u0026nbsp;\u003cem\u003eProcess Safety and Environmental Protection\u003c/em\u003e. doi: 10.1016/j.psep.2024.10.031.\u003c/li\u003e\n \u003cli\u003eFilho, J. F. L., Da Silva Rodrigues Viana, R., Melo, L. C. A. \u0026amp; De Figueiredo, C. C. (2024). Changes in phosphorus due to pyrolysis and in the soil-plant system amended with sewage sludge biochar compared to conventional P fertilisers: a global meta-analysis. \u003cem\u003eChemosphere\u003c/em\u003e: 144055. doi: 10.1016/j.chemosphere.2024.144055.\u003c/li\u003e\n \u003cli\u003eFri\u0026scaron;t\u0026aacute;k, V., Pip\u0026iacute;\u0026scaron;ka, M. \u0026amp; Soja, G. (2018). Pyrolysis treatment of sewage sludge: A promising way to produce phosphorus fertiliser. \u003cem\u003eJournal of Cleaner Production\u003c/em\u003e, 172: 1772-1778. doi: 10.1016/J.JCLEPRO.2017.12.015.\u003c/li\u003e\n \u003cli\u003eGao, N., Jiang, X. \u0026amp; Liu, Y. (2015). Dipropargyl ether bisphenol A-based boron-containing polymer: synthesis, characterisation and molecular dynamics simulations of the resulting pyrolysis and carbonisation. \u003cem\u003eRSC Advances\u003c/em\u003e, 5: 3390\u0026ndash;3398. doi: 10.1039/C4RA12694G.\u003c/li\u003e\n \u003cli\u003eGeng, N., Wang, Y., Zhang, D., Fan, X., Li, E., Han, Z. \u0026amp; Zhao, X. (2022). An electro-peroxone oxidation-Fe(III) coagulation sequential conditioning process for enhanced waste-activated sludge dewatering: bound water release and multivariate changes in organics. \u003cem\u003eThe Science of the total environment\u003c/em\u003e: 155272. doi: 10.1016/j.scitotenv.2022.155272.\u003c/li\u003e\n \u003cli\u003eGiwa, A., Maurice, N. J., Ai, L., Liu, X., Yang, Y. \u0026amp; Hong, Z. (2023). Advances in sewage sludge application and treatment: Process integration of plasma pyrolysis and anaerobic digestion with the resource recovery. \u003cem\u003eHeliyon\u003c/em\u003e, 9. doi: 10.1016/j.heliyon.2023.e19765.\u003c/li\u003e\n \u003cli\u003eGobbi, M., Pigozzo, A. T. J., Lenzi, E. \u0026amp; Luchese, E. (2000). Effects of the application of sewage sludge and fowl manure on soils of Paran\u0026aacute; state in maize plants (Zea mays L.) as a macro-nutrient source. \u003cem\u003eBrazilian Archives of Biology and Technology\u003c/em\u003e, 43: 151\u0026ndash;157. doi: 10.1590/S1516-89132000000200003.\u003c/li\u003e\n \u003cli\u003eHadroug, S., Jellali, S., Jeguirim, M., Kwapinska, M., Hamdi, H., Leahy, J., \u0026amp; Kwapinski, W. (2021). Static and Dynamic Investigations on Leaching/Retention of Nutrients from Raw Poultry Manure Biochars and Amended Agricultural Soil. \u003cem\u003eSustainability\u003c/em\u003e. Doi: 10.3390/SU13031212.\u003c/li\u003e\n \u003cli\u003eHong, Y.-K., Qu, G., Du, Y., Yuan, T., Hao, S., Yang, W. \u0026amp; Dai, Z. (2022). Experimental Investigations into the Pyrolysis Mechanism and Composition of Ceramic Precursors Containing Boron and Nitrides with Different Boron Contents. \u003cem\u003eMaterials\u003c/em\u003e, 15. doi: 10.3390/ma15238390.\u003c/li\u003e\n \u003cli\u003eHosseinian, A., Brancoli, P., Vali, N., Yl\u0026auml;-Mella, J., Pettersson, A. \u0026amp; Pongr\u0026aacute;cz, E. (2024). Life Cycle Assessment of Sewage Sludge Treatment: Comparison of pyrolysis with traditional methods in two Swedish municipalities. \u003cem\u003eJournal of Cleaner Production\u003c/em\u003e. Doi: 10.1016/j.jclepro.2024.142375.\u003c/li\u003e\n \u003cli\u003eHou, J., Yue, Li, S., Shi, J., He, L. \u0026amp; Li, J. (2018). Transformation of sulfur and nitrogen during Shenmu coal pyrolysis.\u0026nbsp;\u003cem\u003eFuel\u003c/em\u003e. doi: 10.1016/J.FUEL.2018.05.046.\u003c/li\u003e\n \u003cli\u003eHuang, R., Tang, Y. \u0026amp; Luo, L. (2020). Thermochemistry of sulfur during pyrolysis and hydrothermal carbonisation of sewage sludges. \u003cem\u003eWaste management\u003c/em\u003e, 121: 276\u0026ndash;285. doi: 10.1016/j.wasman.2020.12.004.\u003c/li\u003e\n \u003cli\u003eIllakwahhi, D., Vegi, M. \u0026amp; Srivastava, B. (2024). Phosphorus\u0026apos; future insecurity, the horror of depletion, and sustainability measures. \u003cem\u003eInternational Journal of Environmental Science and Technology\u003c/em\u003e. Doi: 10.1007/s13762-024-05664-y.\u003c/li\u003e\n \u003cli\u003eJiang, Y., McAdam, E., Zhang, Y., Heaven, S., Banks, C. \u0026amp; Longhurst, P. (2019). Ammonia inhibition and toxicity in anaerobic digestion: A critical review. \u003cem\u003eJournal of Water Process Engineering\u003c/em\u003e. doi: 10.1016/J.JWPE.2019.100899.\u003c/li\u003e\n \u003cli\u003eJin, J., Li, Y., Zhang, J., Wu, S., Cao, Y., Liang, P., Zhang, J., Wong, M., Wang, M., Shan, S., et al. (2016). Influence of pyrolysis temperature on properties and environmental safety of heavy metals in biochars derived from municipal sewage sludge. \u003cem\u003eJournal of hazardous materials\u003c/em\u003e, 320: 417\u0026ndash;426. doi: 10.1016/j.jhazmat.2016.08.050.\u003c/li\u003e\n \u003cli\u003eJin, Y., Liang, X., He, M., Liu, Y., Tian, G. \u0026amp; Shi, J. (2016). Manure biochar influence upon soil properties, phosphorus distribution and phosphatase activities: A microcosm incubation study. \u003cem\u003eChemosphere\u003c/em\u003e, 142: 128\u0026ndash;135. doi: 10.1016/j.chemosphere.2015.07.015.\u003c/li\u003e\n \u003cli\u003eKang, J., Kwon, G., Nam, J., Kim, Y. \u0026amp; Jahng, D. (2017). Carbon dioxide stripping from anaerobic digestate of food waste using two types of aerators. \u003cem\u003eInternational Journal of Environmental Science and Technology\u003c/em\u003e, 14: 1397\u0026ndash;1408. doi: 10.1007/s13762-017-1250-1.\u003c/li\u003e\n \u003cli\u003eKeskinen, R., Hyv\u0026auml;luoma, J., Sohlo, L., Help, H. \u0026amp; Rasa, K. (2019). Fertiliser and soil conditioner value of broiler manure biochars. \u003cem\u003eBiochar\u003c/em\u003e, 1: 259-270. doi: 10.1007/s42773-019-00020-7.\u003c/li\u003e\n \u003cli\u003eKhalid, A., Arshad, M., Anjum, M., Mahmood, T. \u0026amp; Dawson, L. (2011). The anaerobic digestion of solid organic waste. \u003cem\u003eWaste management\u003c/em\u003e, 31 8: 1737-1744. doi: 10.1016/j.wasman.2011.03.021.\u003c/li\u003e\n \u003cli\u003eKhater, E.-S., Bahnasawy, A., Hamouda, R., Sabahy, A., Abbas, W. \u0026amp; Morsy, O. (2024). Biochar production under different pyrolysis temperatures with different types of agricultural wastes. \u003cem\u003eScientific Reports\u003c/em\u003e, 14. doi: 10.1038/s41598-024-52336-5.\u003c/li\u003e\n \u003cli\u003eKrueger, B., Fowler, G., Templeton, M. \u0026amp; Moya, B. (2019). Resource recovery and biochar characteristics from full-scale faecal sludge treatment and co-treatment with agricultural waste. \u003cem\u003eWater Research\u003c/em\u003e, 169. doi: 10.1016/j.watres.2019.115253.\u003c/li\u003e\n \u003cli\u003eKrunks, M., Mellikov, E. \u0026amp; Bijakina, O. (1997). Copper sulfides by chemical spray pyrolysis process. \u003cem\u003ePhysica Scripta\u003c/em\u003e, 69: 189-192. doi: 10.1088/0031-8949/1997/T69/037.\u003c/li\u003e\n \u003cli\u003eLi, H., Tan, F., Ke, L., Xia, D., Wang, Y., He, N., Zheng, Y. \u0026amp; Li, Q. (2016). Mass balances and distributions of C, N, and P in the anaerobic digestion of different substrates and relationships between products and substrates. \u003cem\u003eChemical Engineering Journal\u003c/em\u003e, 287: 329-336. doi: 10.1016/J.CEJ.2015.11.003.\u003c/li\u003e\n \u003cli\u003eLi, Y., Gupta, R., Zhang, Q. \u0026amp; You, S. (2022). Review of Biochar Production via Crop Residue Pyrolysis: Development and Perspectives. \u003cem\u003eBioresource technology\u003c/em\u003e: 128423. doi: 10.1016/j.biortech.2022.128423.\u003c/li\u003e\n \u003cli\u003eLiu, T., Shao, T., Jiang, J., Wen, Y., Feng, R., Dong, D., Wang, Y., Bai, T. \u0026amp; Xu, Y. (2024). Influence of potassium addition on phosphorus availability and heavy metals immobility of biochar derived from swine manure. \u003cem\u003eScientific Reports\u003c/em\u003e, 14. doi: 10.1038/s41598-024-69761-1.\u003c/li\u003e\n \u003cli\u003eLiu, Z., Yuan, D., Qin, X., He, P. \u0026amp; Fu, Y. (2023). Effect of Mg-Modified Waste Straw Biochar on the Chemical and Biological Properties of Acidic Soils.\u0026nbsp;\u003cem\u003eMolecules\u003c/em\u003e, 28. doi: 10.3390/molecules28135225.\u003c/li\u003e\n \u003cli\u003eLMD. (2025). \u003cem\u003eForskrift om lagring og bruk av gj\u0026oslash;dsel mv (gj\u0026oslash;dselbrukforskriften) [FOR-2025-01-29-115]\u003c/em\u003e: Lovdata.\u003c/li\u003e\n \u003cli\u003eLu, T., Yuan, H., Wang, Y., Huang, H. \u0026amp; Chen, Y. (2016). Characteristic of heavy metals in biochar derived from sewage sludge. \u003cem\u003eJournal of Material Cycles and Waste Management\u003c/em\u003e, 18: 725-733. doi: 10.1007/S10163-015-0366-Y.\u003c/li\u003e\n \u003cli\u003eMalhotra, H., Vandana, Sharma, S. \u0026amp; Pandey, R. (2018). Phosphorus Nutrition: Plant Growth in Response to Deficiency and Excess. 171-190. doi: 10.1007/978-981-10-9044-8_7.\u003c/li\u003e\n \u003cli\u003eMuisa, N., Nhapi, I., Ruziwa, W. \u0026amp; Manyuchi, M. (2020). Utilization of alum sludge as adsorbent for phosphorus removal in municipal wastewater: A review. \u003cem\u003eJournal of Water Process Engineering\u003c/em\u003e. doi: 10.1016/j.jwpe.2020.101187.\u003c/li\u003e\n \u003cli\u003eNelson, D. W. \u0026amp; Sommers, L. E. (1982). Total carbon, organic carbon, and organic matter. \u003cem\u003eMethods of soil analysis: Part 2 chemical and microbiological properties\u003c/em\u003e, 9: 539-579.\u003c/li\u003e\n \u003cli\u003eNyang\u0026rsquo;au, J., Mahdi, J. E., M\u0026oslash;ller, H. \u0026amp; S\u0026oslash;rensen, P. (2024). Unlocking higher methane yields and digestate nitrogen availability in soil through thermal treatment of feedstocks in a two-step anaerobic digestion. \u003cem\u003eChemical and Biological Technologies in Agriculture\u003c/em\u003e. doi: 10.1186/s40538-024-00694-7.\u003c/li\u003e\n \u003cli\u003eOpatokun, S. A., Yousef, L. \u0026amp; Strezov, V. (2017). Agronomic assessment of pyrolysed food waste digestate for sandy soil management. \u003cem\u003eJournal of environmental management\u003c/em\u003e, 187: 24-30. doi: 10.1016/j.jenvman.2016.11.030.\u003c/li\u003e\n \u003cli\u003ePetrovič, A., Vohl, S., Predikaka, T. C., Bedoić, R., Simonič, M., Ban, I. \u0026amp; Čuček, L. (2021). Pyrolysis of Solid Digestate from Sewage Sludge and Lignocellulosic Biomass: Kinetic and Thermodynamic Analysis, Characterization of Biochar. \u003cem\u003eSustainability\u003c/em\u003e. doi: 10.3390/su13179642.\u003c/li\u003e\n \u003cli\u003eQian, T., Wang, Y., Fan, T., Fang, G. \u0026amp; Zhou, D.-M. (2016). A new insight into the immobilization mechanism of Zn on biochar: the role of anions dissolved from ash.\u0026nbsp;\u003cem\u003eScientific Reports\u003c/em\u003e, 6. doi: 10.1038/srep33630.\u003c/li\u003e\n \u003cli\u003eRangabhashiyam, S., Lins, P., Oliveira, L., Sep\u0026uacute;lveda, P., Ighalo, J., Rajapaksha, A. \u0026amp; Meili, L. (2021). Sewage sludge-derived biochar for the adsorptive removal of wastewater pollutants: A critical review. \u003cem\u003eEnvironmental pollution\u003c/em\u003e: 118581. doi: 10.1016/j.envpol.2021.118581.\u003c/li\u003e\n \u003cli\u003eRobinson, J., Baumann, K., Hu, Y., Hagemann, P., Kebelmann, L. \u0026amp; Leinweber, P. (2017). Phosphorus transformations in plant-based and bio-waste materials induced by pyrolysis.\u0026nbsp;\u003cem\u003eAmbio\u003c/em\u003e, 47: 73-82. doi: 10.1007/s13280-017-0990-y.\u003c/li\u003e\n \u003cli\u003eRodr\u0026iacute;guez, J., Filho, J., Melo, L., Assis, I. \u0026amp; Oliveira, T. (2020). Influence of pyrolysis temperature and feedstock on the properties of biochars produced from agricultural and industrial wastes. \u003cem\u003eJournal of Analytical and Applied Pyrolysis\u003c/em\u003e, 149: 104839. doi: 10.1016/j.jaap.2020.104839.\u003c/li\u003e\n \u003cli\u003eRuiqing, L. (2013). Influence of minerals and mineral ions on selenium release behaviors during coal pyrolysis. \u003cem\u003eEnvironmental Chemistry\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003eSahoo, S., Vijay, V., Chandra, R. \u0026amp; Kumar, H. (2021). Production and characterisation of biochar produced from slow pyrolysis of pigeon pea stalk and bamboo. \u003cem\u003eCleaner Engineering and Technology\u003c/em\u003e. doi: 10.1016/J.CLET.2021.100101.\u003c/li\u003e\n \u003cli\u003eSaikumar, R. \u0026amp; Rao, K. (2017). Effect of Sewage Sludge, Urban Compost, Poultry Manure and Chemical Fertilisers on Soil Heavy Metal Status in Brinjal-Cauliflower Cropping System. \u003cem\u003eInternational Journal of Current Microbiology and Applied Sciences\u003c/em\u003e, 6: 1087-1094. doi: 10.20546/IJCMAS.2017.606.126.\u003c/li\u003e\n \u003cli\u003eSchlederer, F., Mart\u0026iacute;n-Hern\u0026aacute;ndez, E. \u0026amp; Vaneeckhaute, C. (2024). Ensuring safety standards in sewage sludge-derived biochar: Impact of pyrolysis process temperature and carrier gas on micropollutant removal. \u003cem\u003eJournal of environmental management\u003c/em\u003e, 352: 119964. doi: 10.1016/j.jenvman.2023.119964.\u003c/li\u003e\n \u003cli\u003eShen, Y. \u0026amp; Yuan, R. (2021). Pyrolysis of agroforestry bio-wastes with Calcium/Magnesium oxides or carbonates \u0026ndash; Focusing on biochar as soil conditioner. \u003cem\u003eBiomass and Bioenergy\u003c/em\u003e. Doi: 10.1016/j.biombioe.2021.106277.\u003c/li\u003e\n \u003cli\u003eShi, W., Lian, W., Tian, S., Gong, X.-M., Yu, Q.-H., Guo, Z., Zhang, X., Biao, Bian, R., Zheng, J., et al. (2023). A review of agronomic and environmental properties of inorganic compounds in biochars. \u003cem\u003eCurrent Research in Environmental Sustainability\u003c/em\u003e. Doi: 10.1016/j.crsust.2023.100226.\u003c/li\u003e\n \u003cli\u003eSmith, M., Cade‐Menun, B. \u0026amp; Tibbett, M. (2006). Soil phosphorus dynamics and phytoavailability from sewage sludge at different stages in a treatment stream. \u003cem\u003eBiology and Fertility of Soils\u003c/em\u003e, 42: 186-197. doi: 10.1007/s00374-005-0014-0.\u003c/li\u003e\n \u003cli\u003eSrivastava, S., Upadhyay, M., Srivastava, A., Abdelrahman, M., Suprasanna, P., and Tran, L. 2018. Cellular and Subcellular Phosphate Transport Machinery in Plants. \u003cem\u003eInternational Journal of Molecular Sciences\u003c/em\u003e, 19. doi: 10.3390/ijms19071914.\u003c/li\u003e\n \u003cli\u003eSuanon, F., Sun, Q., Mama, D., Li, J., Dimon, B., \u0026amp; Yu, C. (2016). Effect of nanoscale zero-valent iron and magnetite (Fe3O4) on the fate of metals during anaerobic digestion of sludge. \u003cem\u003eWater research\u003c/em\u003e, 88: 897\u0026ndash;903. doi: 10.1016/j.watres.2015.11.014.\u003c/li\u003e\n \u003cli\u003eSugawara, K., Enda, Y., Inoue, H., Sugawara, T. \u0026amp; Shirai, M. (2002). Dynamic behaviour of trace elements during pyrolysis of coals.\u0026nbsp;\u003cem\u003eFuel\u003c/em\u003e, 81: 1439\u0026ndash;1443. doi: 10.1016/S0016-2361(02)00063-7.\u003c/li\u003e\n \u003cli\u003eThakur, N., Sharma, M., Alghamdi, H., Zheng, Y., Xue, W., Jeon, B.-H., Salama, E.-S., \u0026amp; Li, X. (2023). A recent trend in anaerobic digestion (AD): Enhancement of microbiome and digestibility of feedstocks via abiotic stress factors for biomethanation. \u003cem\u003eChemical Engineering Journal\u003c/em\u003e. doi: 10.1016/j.cej.2023.145047.\u003c/li\u003e\n \u003cli\u003eWang, R., Wilfert, P., Dugulan, I., Goubitz, K., Korving, L., Witkamp, G.-J. \u0026amp; van Loosdrecht, M. C. (2019). Fe (III) reduction and vivianite formation in activated sludge. \u003cem\u003eSeparation and Purification Technology\u003c/em\u003e, 220: 126\u0026ndash;135.\u003c/li\u003e\n \u003cli\u003eWang, X. \u0026amp; Jia, W. (2024). Se-Pair Search for Deciphering Selenium-Encoded Peptide and a Pyrolysis-Thermolysis Dietary Model for Minimising Loss of \u0026quot;KKSe(M)R\u0026quot; during Processing. \u003cem\u003eJournal of agricultural and food chemistry\u003c/em\u003e. doi: 10.1021/acs.jafc.4c01638.\u003c/li\u003e\n \u003cli\u003eWang, X., Jia, W., Zhang, R., Shi, L. \u0026amp; He, B. (2025). Pyro-Thermolysis Pattern Analysis of Selenopeptide in Selenium-Enriched Rice Based on Two-Dimensional Dietary Kinetics Evolution. \u003cem\u003eJournal of agricultural and food chemistry\u003c/em\u003e. Doi: 10.1021/acs.jafc.4c07303.\u003c/li\u003e\n \u003cli\u003eWang, Y., Dong, B., Fan, Y., Hu, Y., Zhai, X., Deng, C., Xu, Y., Shen, D. \u0026amp; Dai, X. (2019). Nitrogen transformation during pyrolysis of oilfield sludge with high polymer content. \u003cem\u003eChemosphere\u003c/em\u003e, 219: 383-389. doi: 10.1016/j.chemosphere.2018.11.171.\u003c/li\u003e\n \u003cli\u003eWang, Z., Jiang, Y., Wang, S., Zhang, Y., Hu, Y., Hu, Z.-H., Wu, G. \u0026amp; Zhan, X. (2020). Impact of total solids content on anaerobic co-digestion of pig manure and food waste: Insights into shifting of the methanogenic pathway. \u003cem\u003eWaste management\u003c/em\u003e, 114: 96\u0026ndash;106. doi: 10.1016/j.wasman.2020.06.048.\u003c/li\u003e\n \u003cli\u003eWang, Z., Hu, Y., Wang, S., Wu, G., \u0026amp; Zhan, X. (2023). A critical review on dry anaerobic digestion of organic waste: Characteristics, operational conditions, and improvement strategies. \u003cem\u003eRenewable and Sustainable Energy Reviews\u003c/em\u003e. Doi: 10.1016/j.rser.2023.113208.\u003c/li\u003e\n \u003cli\u003eWeimers, K., Bergstrand, K., Hultberg, M. \u0026amp; Asp, H. (2022). Liquid Anaerobic Digestate as Sole Nutrient Source in Soilless Horticulture\u0026mdash;Or Spiked With Mineral Nutrients for Improved Plant Growth. \u003cem\u003eFrontiers in Plant Science\u003c/em\u003e, 13. doi: 10.3389/fpls.2022.770179.\u003c/li\u003e\n \u003cli\u003eXiao, K., Chen, Y., Jiang, X., Yang, Q., Seow, W., Zhu, W. \u0026amp; Zhou, Y. (2017). Variations in physical, chemical and biological properties in relation to sludge dewaterability under Fe (II) - Oxone conditioning. \u003cem\u003eWater research\u003c/em\u003e, 109: 13\u0026ndash;23. doi: 10.1016/j.watres.2016.11.034.\u003c/li\u003e\n \u003cli\u003eXiao, Y., Yan, T., Yao, P., Xiang, W., Wu, Y. \u0026amp; Li, J. (2024). Co-pyrolysis of sewage sludge and phosphate tailings: Synergistically enhancing heavy metal immobilisation and phosphorus availability. \u003cem\u003eWaste management\u003c/em\u003e, 181: 44\u0026ndash;56. doi: 10.1016/j.wasman.2024.04.003.\u003c/li\u003e\n \u003cli\u003eXing, Y., Huang, J., Wang, Z., Hu, W., Xu, M. \u0026amp; Qiao, Y. (2024). Transformation and control of organic sulfur during pyrolysis of sludge under conditions relevant to smouldering combustion: Role of oxygen and CaO. \u003cem\u003eEnergy\u003c/em\u003e. doi: 10.1016/j.energy.2024.133143.\u003c/li\u003e\n \u003cli\u003eXu, F., Chu, M., Chang, Z., Gu, Z. \u0026amp; Sun, X. (2021). Sulfur release and transformation during the pyrolysis of lignite with different particle sizes\u0026mdash;Journal\u003cem\u003e\u0026nbsp;of Analytical and Applied Pyrolysis\u003c/em\u003e, 156: 105162. doi: 10.1016/J.JAAP.2021.105162.\u003c/li\u003e\n \u003cli\u003eYadav, M., Joshi, C., Paritosh, K., Thakur, J., Pareek, N., Masakapalli, S., \u0026amp; Vivekanand, V. (2021). Organic waste conversion through anaerobic digestion: A critical insight into the metabolic pathways and microbial interactions. \u003cem\u003eMetabolic engineering\u003c/em\u003e. doi: 10.1016/j.ymben.2021.11.014.\u003c/li\u003e\n \u003cli\u003eYu, Y., Li, X., Zhao, R., Liu, H., \u0026amp; Chen, J. (2022). Gaseous selenium removal by metal oxide sorbent: Experimental and density functional theory study. \u003cem\u003eFuel\u003c/em\u003e. Doi: 10.1016/j.fuel.2022.124904.\u003c/li\u003e\n \u003cli\u003eZamri, M. F. M. A., Hasmady, S., Akhiar, A., Ideris, F., Shamsuddin, A., Mofijur, M., Fattah, I., \u0026amp; Mahlia, T. (2021). A comprehensive review on anaerobic digestion of organic fraction of municipal solid waste. \u003cem\u003eRenewable and Sustainable Energy Reviews\u003c/em\u003e. Doi: 10.1016/j.rser.2020.110637.\u003c/li\u003e\n \u003cli\u003eZhang, J., Zuo, W., Tian, Y., Chen, L., Yin, L. \u0026amp; Zhang, J. (2017). Sulfur Transformation during Microwave and Conventional Pyrolysis of Sewage Sludge. \u003cem\u003eEnvironmental science \u0026amp; technology\u003c/em\u003e, 51 1: 709\u0026ndash;717. doi: 10.1021/acs.est.6b03784.\u003c/li\u003e\n \u003cli\u003eZhang, M., Yang, C., Jing, Y. \u0026amp; Li, J. (2016). Effect of energy grass on methane production and heavy metal fractionation during anaerobic digestion of sewage sludge. \u003cem\u003eWaste management\u003c/em\u003e, 58: 316\u0026ndash;323. doi: 10.1016/j.wasman.2016.09.040.\u003c/li\u003e\n \u003cli\u003eZhao, J., Qiu, C., Fan, X., Zheng, J., Liu, N., Wang, C., Wang, D. \u0026amp; Wang, S. (2021). Chemical speciation and risk assessment of heavy metals in biochars derived from sewage sludge and anaerobically digested sludge. \u003cem\u003eWater science and technology : a journal of the International Association on Water Pollution Research\u003c/em\u003e, 84 5: 1079\u0026ndash;1089. doi: 10.2166/wst.2021.305.\u003c/li\u003e\n \u003cli\u003eZhu, X., Labianca, C., He, M., Luo, Z., Wu, C., You, S., \u0026amp; Tsang, D. (2022). Life-cycle assessment of pyrolysis processes for sustainable production of biochar from agro-residues. \u003cem\u003eBioresource technology\u003c/em\u003e: 127601. doi: 10.1016/j.biortech.2022.127601.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"anaerobic digestion, pyrolysis, nutrient enrichment, phosphorus recovery, heavy metals","lastPublishedDoi":"10.21203/rs.3.rs-8242369/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8242369/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRecycling nutrients from organic residues is key to circular agriculture, but contaminant limits restrict their reuse. This study examined how anaerobic digestion (AD) and pyrolysis influence nutrient enrichment and regulatory compliance in biochar derived from six feedstocks: raw and digested manures (RM, DM) and biologically or chemically treated raw and digested sewage sludges (BTRSS, CTRSS, BTDSS, CTDSS). Samples were analyzed for pH, dry matter (DM), loss on ignition (LOI), total C and N, macro-/micronutrients, and trace elements, and evaluated against Norway’s 2025 fertilizer regulation using concentration classes and P: metal ratio thresholds. AD reduced DM, LOI, and total C but increased pH, Ca, and Mg; it enhanced P in manures but lowered it in sludges. Pyrolysis produced stable, alkaline biochar (DM \u0026gt; 97%) enriched in P, K, Ca, and Mg, while N and S decreased. Micronutrients (Fe, Mn, B, Mo) and heavy metals became concentrated, with Zn and Cu as key regulatory constraints, whereas Cd, Pb, Hg, and As remained below limits. Chemically treated sludges showed high Al due to coagulants. Overall, digested manure biochar at 400 °C met both P and heavy metal criteria, while most sludge-derived biochar failed eligibility, except for chemically treated raw sludge at 400 °C.\u003c/p\u003e","manuscriptTitle":"Effect of anaerobic digestion and pyrolysis on nutrient composition, heavy metals, and phosphorus recovery in manure and sewage sludge biochar","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-04 15:14:28","doi":"10.21203/rs.3.rs-8242369/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"fb0cf6d2-d0ea-4952-961d-25b2f3da26e7","owner":[],"postedDate":"December 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-23T13:59:14+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-04 15:14:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8242369","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8242369","identity":"rs-8242369","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}