Microwave-alkali co-activated persulfate enables minute-scale fertilization of food waste with high fulvic-like acid yield

Microwave-alkali co-activated persulfate enables minute-scale fertilization of food waste with high fulvic-like acid yield | 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 Article Microwave-alkali co-activated persulfate enables minute-scale fertilization of food waste with high fulvic-like acid yield Dongqing Cai, Yanping Zhu, Yi Qiao, Dongfang Wang, Shihu Shu, and 9 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6923064/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 13 Jan, 2026 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract This study demonstrated rapid humification of waste potato (WP), as a model food waste, into fulvic-like acid (FLA) fertilizer (15wt% FLA and 7.6wt% K + ) using microwave-triggered KOH/persulfate (MW/KOH/PS) process. Under synergistic MW irradiation (180 W) and KOH (2wt%), PS (2wt%) was activated to generate •OH and •SO 4 - . This process simultaneously dissolved organic matter and elevated system temperature, inducing humification of organic components within 10 minutes. Compositional analyses revealed Maillard reactions and amidation during humification. Compared to KOH/PS, microwave intensification reduced chemical consumption by 75%, while achieving comparable FLA yields and significantly lowering cost by 62.4%. Pot experiments validated the plant-growth promotion and soil-amendment capabilities of the humified product. Scale-up trials confirmed the efficacy for practical vegetable residues and cooked food waste. Unlike composting (20-60 d), this process completed in 10 min without requiring optimal C/N ratio or moisture content, exhibited only 20.1% carbon loss (WP system), and operated in scalable reactor, thus enabling same-day waste valorization into fertilizer. Earth and environmental sciences/Environmental sciences/Environmental chemistry/Pollution remediation Earth and environmental sciences/Biogeochemistry/Carbon cycle Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Globally, approximately 1.3 billion tons of food wastes were generated in 2023, accounting for 30-50% of total municipal solid waste 1 . Conventional disposal methods such as landfill and incineration posed substantial environmental risks, necessitating urgent advancements in sustainable resource recovery technologies 2-4 . While anaerobic digestion and aerobic composting currently dominated waste valorization strategies 5 , their widespread adoption was constrained by prolonged processing periods (20-60 days) and extensive land requirements 6 . For instance, microbial-mediated composting usually converted perishable organics into stabilized humic-like acid (HLA) and fulvic-like acid (FLA), yet suffered from inherently slow metabolic rates and poor directional control, contributing to relatively high carbon loss (i.e. 30-50%) and low water-soluble HLA (<15%) and FLA (<2%) yields 7,8 . In our recent study 9 , radicals generated in KOH/persulfate (PS) enabled waste milk rapid conversion into HLA/FLA via degradation-polymerization, achieving remarkable HLA and FLA yields of 18.9 and 25.5wt% within 1 hour, respectively. Nevertheless, high PS and KOH inputs (8wt% each) remained a practical limitation. More importantly, the heterogeneous composition and high viscosity of food wastes may impede mass transfer and reaction kinetics compared to homogeneous milk 10 , thus the applicability of this approach required further systematic investigation. Microwave-assisted advanced oxidation processes (MW-AOPs) had been investigated in wastewater remediation due to its unique advantages of uniform heating, enhanced mass transfer, and oxidant activation 11,12 . To explore its potential in chemical-saving and humification efficiency improvement, this work employed microwave and KOH co-activated PS (MW/KOH/PS) in humification of waste potato, a model food waste, and compared with KOH/PS. The process efficiency, humification mechanism, product components, and HLA/FLA yields were systematically investigated as well as product’s fertilizer efficacy. Furthermore, its efficacy towards practical food wastes was verified using vegetable residue and cooked food waste. This work highlighted a time (minute-scale) and chemical-efficient (4wt%, saving 75% chemicals) method for converting food wastes into FLA fertilizer, promoting their onsite and spontaneous recycling (Fig. 1). Results Robust humification of WP induced by MW/KOH/PS and condition optimization As shown in Fig. 2, during the humification of WP, the dynamic evolution of soluble fluorescent components was monitored using three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy. The 3D-EEM spectrum was generally divided into five regions 13,14 : regions I and II were typically associated with simple aromatic proteins and amino acids, region IV referred to soluble microbial byproducts (SMP), regions III and V corresponded to humic-like acid (HLA) and fulvic-like acid (FLA). In WP (Fig. 2A), intense fluorescence signals were observed in regions I, II, and IV, suggesting that proteins/amino acids and SMP dominated its fluorescent components. Isolated treatments with KOH or MW (Figs. 2B and E) exhibited negligible alteration in fluorescence distribution compared to WP, indicating their insignificant effects used alone. In contrast, 2wt%PS treatment (Fig. 2C) induced a marked reduction in fluorescence intensities across regions I, II, and IV, likely attributed to PS-driven oxidative degradation of proteins/amino acids and SMP 15 . After treatment by 2%KOH/2%PS without MW (Fig. 2D) or MW/2%PS (Fig. 2F), florescence intensities in regions I, II and IV decreased, while those in regions III and V slightly elevated, implying their slight humification effects. This shift aligned with the generation of reactive radicals during KOH or MW activated PS processes, which may promote oxidative degradation and subsequent humification. Similarly, combined MW and 2wt%KOH treatment (MW/KOH) (Fig. 2G) induced a slight fluorescence intensity increase in regions III and V, potentially reflecting base-thermal synergistic effects on humification 16 . Notably, the most pronounced transformation occurred under the combined MW/KOH/PS treatment (Fig. 2H), where fluorescence signals completely migrated from regions I, II, and IV to regions III and V. Fluorescence region integral (FRI) analysis (Table S1, according to the method described in Text S1) revealed that the cumulative fluorescence contribution of regions III and V (P III+V ) surged from 10.59% in WP (Fig. 2A) to 67.09% after MW/KOH/PS treatment (Fig. 2H). These findings proved the synergistic role of MW/KOH/PS in driving robust humification of WP, likely through synergistic mechanisms of thermal/KOH activation, radical oxidation, and base/heat hydrolysis 17-20 . To optimize the humification efficiency of WP by MW/KOH/PS, the dosages of PS and KOH were evaluated within the range of 1-3wt%. With the increase of their dosages, the fluorescence intensities (Fig. 2I-L, Fig. S1A and B) and P III+V (Table S1) increased initially (from 1 to 2wt%) and then decreased (from 2 to 3wt%), achieving the maximum at 2%KOH/2%PS. Therein, the decrease trend at overdoses (above 2wt%) of PS and KOH was consistent with our prior results in waste milk’s humification 21 , likely due to radical self-quenching at excessive oxidant conditions or accelerated decomposition of humification precursors/products. Besides, the MW dose was optimized through adjusting the reaction time. As shown in Fig. 2M-P and Fig. S1 C, the fluorescence intensity increased with MW exposure time and plateaued after 10 min, consistent with the similar P III+V values of Fig. 2H and 2P in Table S1. Therefore, the optimal humification conditions were chosen at dosages of 2%KOH/2%PS and microwave exposure time of 10 min through their synergistic effect. Besides, the EEM spectra of the product remain unchanged in 7 d (Fig. S2), reflecting the high stability of the product. Advantages of MW/KOH/PS humification compared to KOH/PS The role of MW during WP’s humification was investigated on chemical consumption reduction and efficiency elevation. 3D-EEM spectra revealed that the florescence signals shifted from protein and SMP (Fig. 2A) to HLA/FLA regions after treated by KOH/PS at 2-8wt% each for 60 min (Fig. 3A-C and Fig. S1 D), with stronger intensities at higher dosages (8wt% each). Notably, treatments of 8%KOH/8%PS (in 60 min) resulted in comparable FRI distributions in HLA/FLA regions (65.7%) compared to MW/2%KOH/2%PS (67.1% in 10 min) shown in Table S1, along with the slightly lower FLA content in the humified product (Fig. 3D). These results showed that the involvement of MW could substantially reduce the chemical input by 75% as well as shortening reaction duration by 83%. Besides, Fig. 3E showed that systems treated with 8%KOH/8%PS and MW/2%KOH/2%PS exhibited rapid temperature rise from ambient conditions (20°C) to peak values of 80.3 °C (5 min) and 92.1 °C (10 min), respectively, significantly higher than that of 2%KOH/2%PS (38.4 o C). These results indicated that the maximum temperature of the system without MW increased with dosages of KOH and PS, attributed to radical-involved exothermic reactions 15 . In comparison, MW/2%KOH/2%PS may activate PS through exogenous heating and direct MW attack besides KOH 22,23 , accelerating radical formation and finally realizing similar humification effects to 8%KOH/8%PS. Critically, Fig. 3F showed that the carbon loss during the humification induced through MW/2%KOH/2%PS and 8%KOH/8%PS were 20.1% and 43.4%, respectively. That is, MW/2%KOH/2%PS could significantly reduce the carbon loss by 53.7% compared to 8%KOH/8%PS, likely attributable to abbreviated reaction duration and thus minimized oxidative decomposition. This highlighted its potential in enhancing carbon retention besides concurrent resource efficiency (chemical/time savings), positioning it as a sustainable strategy for rapid fertilization of food wastes 24,25 . Fig. 3G showed a preliminary techno-economic comparison between MW/2%KOH/2%PS and 8%KOH/8%PS. The total production cost for FLA fertilizer derived from per ton of WP was calculated by integrating costs of chemical consumption, electricity, equipment depreciation, and labor 26,27 . The analysis revealed that MW/2%KOH/2%PS incurred a total cost of 320 RMB/ton, whereas the conventional 8%KOH/8%PS process required 850 RMB/ton. Notably, the MW-integrated approach achieved a 62.4% reduction in overall costs, primarily attributed to the minimized chemical usage. Humification product characterization The components of the product were characterized comprehensively in Fig. 4. As shown in Fig. 4A, peaks of N-H (713 cm -1 ), aromatic C-O (1027 cm -1 ), C-N (1152 cm -1 ), carboxyl -OH (1578 cm -1 ), and aromatic C=C (1670 cm -1 ) became stronger after humification. These variations indicated the occurrence of aromatization, carboxylation, and amidation 28,29 . Meanwhile, the groups of aromatic C-O and C=C, amide N-H, and carboxyl C-O were consistently observed in standard FA (SFA), indicating the formation of FLA 30 . Similarly, the solid-state 13 C NMR spectra in Fig. 4B showed that peaks belong to regions of oxygenated aliphatic carbon (50-100 ppm), aromatic carbon (100-160 ppm), and carboxyl C=O (160-220 ppm) become stronger after humification, align with the peaks in the spectra of SFA 31 . XPS C1s results in Fig. 4C showed that C1s peak in WP could be deconvoluted into peaks located at 284.5, 285.5, 285.9 and 287.8 eV, corresponding to C-C, C-O, C=O, and Π-Π. After humification, Fig. 4D showed that peaks representing C-C/C=C, C=O, and Π-Π were strengthened, while C-O was weakened. Meanwhile, the peaks in O1s spectra (Fig. 4E and F) also observed the strengthened C=O peak and weakened C-O peak in the product compared with WP. These results consistently reflected the occurrence of aromatization and carboxylation 32,33 . Thermo gravimetric analysis (TGA) spectra showed that the product possessed a higher thermal stability compared with WP (Fig. 4G), likely related to the conversion of perishable organics (proteins/amino acids) and SMP into HLA/FLA with higher thermal stability besides introduction of K 2 SO 4 . Besides, the main contents in Fig. 4H showed that a total of 10.5 g dry matter was contained in 50 g WP, corresponding to a moisture of 79%. Therein, contents of organic matter (OM) and dissolved organic carbon (DOC) accounted for 9.6 g and 0.6 g, respectively. Besides, WP also contained 1.5 g K + , 0.6 g FLA, and 0.15 g SO 4 2- . After humification, OM content decreased to 8.7 g, corresponding to a loss of 9.4%. While DOC content increased to 6.5 g likely due to the formation of dissolving OM during humification. K + and SO 4 2- contents increased to 3.8 and 0.2 g in the product respectively. XRD spectra in Fig. 4I showed the emerged peaks of K 2 SO 4 in the product due to the decomposition of PS, consistent with the result in Fig. 4H. To be noted, K + was an important inorganic fertilizer for plant, making the product like a kind of compound fertilizer 34 . MW/KOH/PS-induced humification mechanism Fig. 5A showed the electron paramagnetic resonance (EPR) spectra during WP’s humification. Both •OH and •SO 4 - radicals were detected at 2 min, with weakened signals at 6 min and disappeared at 10 min, indicating their possible involvement in the humification. With the addition of TBA as the •OH quencher to MW/KOH/PS humification system (Fig. 5B) 23 , the 3D-EEM spectrum showed slightly weakened signals in protein/amino acids regions compared with WP (Fig. 2A), with insignificant variation in HLA/FLA regions. This result indicated the key contribution of •OH in degradation of protein/amino acids and HLA/FLA formation. Similarly, in the presence of EtOH, quenchers of both •OH and •SO 4 - 35 , the florescence peaks were almost unchanged, verifying the key role of •SO 4 - besides •OH in WP humification (Fig. 5C). Furthermore, Fig. 5D showed that the UV absorbance at 250-270 nm, representing the aromatization degree 36 , was significantly increased after humification, while the peaks were suppressed after addition of radical quenchers especially EtOH. Therefore, these quenchers inhibited the aromatization and humification, which were consistent with our previous observations in waste milk and glucose humification systems 15 . Fig. 5E showed an initial (0-4 min) fast then (4-10 min) slow PS decomposition trend with time, reaching a 100% PS consumption in 10 min, which was consistent with the time-dependent variation of radical signals and humification process. Besides, the Gel permeation chromatography (GPC) results in Fig. 4E showed that the molecular distribution of dissolved organics in WP was mainly between 300-7370 Da, with the most distributed around 1141 Da. While after humification, that of the product increased to a range of 300-15000 Da, with the most distributed around 1405 Da, indicating that radical-induced polymerization likely occurred, which was considered as a characteristic reaction of humification 37,38 . Since the general molecular weights of FA and HA were distributed in the ranges of 600-1500 and 10000-100000 Da respectively 39,40 , the GPC distribution of the product also suggested the formation of FLA and HLA. As shown in Fig. 5G-I, the FTIR spectra variation of treated WP were analyzed within 10 min through two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS). According to synchronous 2DCOS in Fig. 5H, overall structural variation mainly distributed at 1578, 1400, 1100 and 1020 cm -1 , corresponding to aromatic C=C, carboxyl O-H, aromatic C-O and C-N, respectively. These peaks consistently showed a gradually strengthened trend (Fig. 5G). Asynchronous maps in Fig. 5I showed that the groups variation followed the order of aromatic C-O > carboxyl O-H> aromatic C=C > C-N (Table S2). Collectively, this humification was mainly induced through radical-involved aromatization, carboxylation, and amidation (i.e. characteristic Mallard reactions) 41 . Preparation and nutrient release behavior of product-based slow-release fertilizer As shown in Fig. 6A, the product was conveniently granulated into FLA and K + slow-release fertilizer after mixing with ATP at a weight ratio of 1:1. Fig. 6B demonstrated that the SRF granules remained intact throughout a 30-day water immersion period, indicating a good water resistance. Concurrently, the aqueous solution gradually transitioned from colorless to brown. This color change was consistent with the progressively intensified fluorescence signals in the HLA/FLA regions observed over 30 days (Fig. 6B), suggesting the slow release of HLA/FLA. The release profiles of FLA and K⁺, presented in Fig. 6C and 6D respectively, confirmed their time-dependent release behavior, reaching release ratios of 98.15% and 97.7% after 30 days. FTIR spectra (Fig. 6E) revealed a significant weakening of peaks corresponding to amide N-H, aromatic C=C, C-O, aliphatic C-H, and O-H bonds after 30-day immersion, likely attributable to FLA release. SEM analysis (Fig. 6F) showed a dense surface morphology for SRF, suggesting successful loading of the product in ATP with a nanonetwork structure 42 . However, post-immersion, the surface exhibited substantial rod-like structures, presumably resulting from the release of loaded contents from the ATP nanonetwork. Furthermore, XRD analysis (Fig. 6G) showed strong characteristic peaks of K 2 SO 4 in the fresh SRF, which almost disappeared after 30-day release. This finding aligned with the significantly weakened distribution signals observed in the SEM-mapping results (Fig. S3). In a word, these results confirmed the successful synthesis of SRF based on WP’s humified product. The synthesized SRF exhibited favorable slow-release properties for both FLA and K⁺ over a 30-day period. Fertilization effect of WP-derived product in pot experiment As shown in Fig. 7, the fertilization effect of the product on Shanghai Cabbage’ growth was compared with WP and K 2 SO 4 through pot tests. After 21 d cultivation, the overall plant growth parameters (fresh weight, plant height, root length, germination rate, dry weight, chlorophyll content) showed an order of SRF>Product>K 2 SO 4 >Blank>WP (Fig. 7A-7H). Therein, the fresh weight (actually the yield) of Product group was 5.2 g, 163.1%, 425.3% and 45.8% higher than the Blank, WP, and K 2 SO 4 group respectively. The decreased fresh weight of WP group than Blank group was likely owing to the negative effect of labile organic matter (proteins) in WP on plant growth. The positive effects of the Product indicated the effectiveness of the humification process in converting WP into a functional fertilizer. The superior performance of the Product over K 2 SO 4 demonstrated the significant contribution of HLA/FLA. Notably, SRF treatment further amplified the fertilization effect, resulting in better overall growth (including a 17.4% higher fresh weight) compared to the Product. Therefore, the slow-release of FLA and K⁺ likely enhanced their absorption and utilization efficiency by plants 43 . Key soil indexes were also measured after harvest and shown in Fig. 7I. The soil organic matter (SOM) content showed an order of Product>SRF>WP>Blank. The higher SOM content in the Product group than WP indicated effective conversion of labile organic carbon into stable humic fractions during humification. Similarly, total and available nitrogen (TN and AN) consistently increased in WP and Product groups compared with Blank likely due to their inherent high nitrogen contents in WP. Notably, total and available potassium (TK and AK) in Product group surged by 17.4% and 150.8% compared with WP, primarily due to external K + supplementation during the humification process. The slightly lower values of these soil indexes in the SRF group compared to the Product group may be associated with the slow-release characteristics. Besides, the biosafety of the product was monitored with earthworm as a kind of bioindicator (Fig. S4). After 7-d cultivation, the survival rate and weight gain rate in different groups followed an order of Product>Blank>WP, indicating that the Product with a good biosafety may favor the growth of earthworms. These findings validated the dual functionality of the humification product: (i) as a high-efficiency fertilizer through K + and HLA/FLA-mediated plant growth promotion, and (ii) as a soil conditioner via carbon sequestration and nutrient reservoir construction. MW/PS/KOH induced scaling-up humification of practical food wastes The application feasibility of MW/PS/KOH was explored in scaling-up experiments (1 kg) using practical vegetable residue (VR) and cooked kitchen waste (CKW). Fig. 8A showed that the color of the VR changed from green into brown after MW/KOH/PS treatment, likely a visual sign of humification. Meanwhile, Fig. 8B and 8C illustrated that the 3D-EEM spectra showed significant florescence shifts from regions I, II, and IV to region V, confirming the conversion of labile organic matter (proteins, amino acids, and SMP) into stabilized humic substances (HLA/FLA). After humification, a significant enhancement of UV absorbance at 250-270 nm appeared, suggesting the occurrence of aromatization (Fig. 8D). Besides, Fig. 8H showed a dramatic FLA content increase from 2.3wt% (VR) and 2.6wt% (CKW) to 32.3wt% and 28.4wt% after treatment, verifying the dramatic occurrence of humification. Notably, similar humification phenomenon was observed in both WP and CKW systems (Fig. 6D-H and Fig. S5). Besides, Fig. S6 showed that the growth of amaranth followed an order of VR-Product>CKW-Product>K 2 SO 4 >Blank>CKW>VR in field tests, indicating the fertilization of derived products from VR and CKW. These findings validated the universal applicability of MW/PS/KOH treatment in inducing scaling-up humification of diverse practical food wastes (i.e. VR and CKW). Fig. 8I showed that the MW/PS/KOH process enabled on-site fertilizer production from food waste at both household and park scales. The integrated procedure comprised three sequential stages: pretreatment, humification, and fertilizer recycling. During pretreatment, food waste underwent sorting (manually or via magnetic separation) and pulping (using household or industrial-grade mechanical pulpers), converting raw waste into biodegradable slurry (particle diameter <1 mm, impurity content <3%). Subsequently, the humification of slurry could be realized in a microwave oven (household or industrial scale) after KOH and PS addition within 10 min. The derived humified product could be directly applied as fertilizer for adjacent green spaces (e.g., residential gardens or urban parks). This process demonstrated advantages of ultra-low chemical consumption, equipment versatility, rapid treatment efficiency, and closed-loop resource utilization. The designed application modes favored the efficient recycling of food waste, alleviating the potential pollution from storage and long-term composting. Discussion MW/KOH/PS treatment enabled rapid conversion of food wastes (i.e. waste potatoes, vegetable residues, and cooked food wastes) into fertilizer rich in FLA (15wt%) and K⁺ (7.6wt%). The involvement of microwave could significantly reduce chemical consumption by 75%, and shorten the reaction period from 60 to 10 min, thus reducing processing cost and carbon loss by 20.1% and 43.4%, respectively. This offered distinct advantages in both cost-effectiveness and carbon emission reduction. The inherent flexibility and low cost of microwave equipment further facilitated its significant potential for the efficient humification of food waste. Table 1 Technical comparison between this work and conventional composting Duration FLA yield (%) Cost (RMB/t) C loss (%) C/N ratio T max ( o C) Sterilization (%) This work 6-10 min 10.9-15 250-320 a 21 No need 90-95 >99 Composting 20-60 d 44-46 1-2 47 200-300 48,49 30-60 50 20-30 50,51 60-80 31 - a The cost was calculated based on the value in WP’s small-scale tests in Fig. 3G, the range was considering that treatment duration could be shorten in scaling-up tests, saving corresponding electricity cost. In contrast to traditional composting (Table 1), this technology featured drastically shortened duration (10 min vs. 20-60 d), higher FLA yield (10.9-15% vs. 1-2%), lower carbon loss (21% vs. 30-60%), ultrahigh sterilization rate (>99%) (Fig. S7 and Table S3), and elimination of C/N ratio adjustment. These advantages supported "generate-and-recycle within hours" for food waste across diverse scales, from households to commercial entities. Consequently, this approach saved substantial transportation and storage costs and effectively mitigated the risk of secondary pollution during processing, exhibiting high application potential in food waste recycling. Methods Reagents and materials All reagents used in this study were of analytical grade. Potassium persulfate (K 2 S 2 O 8 , purity≥99.5%), potassium hydroxide (KOH, purity≥95%), hydrochloric acid (HCl, 36.0-38.0%), anhydrous ethanol (EtOH, C 2 H 6 O, 99.5%), tert-butanol (TBA, C 4 H 10 O, ≥99%) and 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Attapulgite (ATP) and aminosilicone oil (ASO) were supplied by Fufeng Biotechnology Co., Ltd. (Inner Mongolia, China). A microwave oven (Midea PM20A1, 800 W, 2450 MHz) and industrial microwave oven (LY-40KW, 5800*1060*1700mm, Shanghai Longyu Microwave Equipment Co., Ltd.) were employed for microwave-involved processes. Shanghai cabbage seeds (Fast-growing 605) were obtained from Shanghai Vegetable Seed Company. Cooked food waste (diameter<0.5 mm, 80% moisture content) was obtained from China Everbright Environment Group Limited. Adult earthworms (Eisenia fetida) were provided by Ruizhou Fishing Tackle Co., Ltd. (Jiangsu Province, China). Potatoes (Longdan No.1) was provided by Chunzhengsheng Co., Ltd. (Shanxi Province, China). Deionized water was used for all experiments, except for pot test where tap water was applied. Humification of WP, vegetable residues and cooked food wastes Prior to humification, waste potatoes and vegetable residues (weight ratio of potatoes: spinach: tomatoes = 5:2.5:2.5) were pulped into slurry using a crusher. The moisture contents of WP and VR were around 89.5% and 90.2%, respectively. In small scale test, solid KOH and PS at dosages of 0-4 g were added simultaneously to 50 g WP slurry with stirring (150 rpm). Then the mixture was subjected to the microwave oven (160 W, 0-15 min) to achieve humification. In scaling-up test, solid KOH and PS with 20 g each were added to 1 kg slurry of WP, VR or CK under stirring (150 rpm). Then the mixture was placed individually on the conveyor belt of the industrial microwave oven and treated at a power of 3 kW for 6 minutes. Radical identification Radicals (•OH and •SO 4 - ) produced during the process were determined on an electron paramagnetic resonance (EPR) spectrometer using DMPO as the spin-trapping agent 52,53 . Additionally, quenching experiments were carried out by adding 6 mol/L EtOH and TBA (higher than 10 times of PS and KOH dosages) to 50 g WP before PS and KOH to obtain the contributions of those radicals. Extraction and quantitative analyses of HLA and FLA in product The quantitative analysis of HLA/FLA was conducted according to alkali dissolution and acid precipitation method detailed in BS ISO 19822-20182843. First, the product was adjusted to pH of approximately 10.5 and then shaken at 300 rpm for 1 hour. Subsequently, the product was centrifuged at 12,000 rpm for 20 minutes at 4℃. The insoluble substances (precipitate 1) were separated from the soluble humic acid (SHA) in the supernatant. Next, the pH of the supernatant was adjusted to 1 with hydrochloric acid and stand overnight at room temperature. Then, the supernatant (FLA) was separated from precipitate 2 (HLA) after centrifugation at 12,000rpm for 20 minutes. Finally, the product (around 50 g), precipitate 1, and precipitate 2 were weighed after freeze drying. The yields of HLA and FLA could be calculated according to formulas (1)-(4). Wherein m SHA , m product , m FLA , and m HLA represented the dry weights of SHA, product, FLA and HLA respectively. m 1 and m 2 represented the dry weight of precipitate 1 and weight of K 2 SO 4 calculated according to the stoichiometric method under the condition that PS has completely decomposed. Fabrication of SRF and nutrient release behavior The humification product derived from 50 g of WP under optimized conditions (1 g PS, 1 g KOH, 160 W MW irradiation for 10 min) was mixed with 50 g of ATP. The mixture was then granulated to produce spherical fertilizer particles approximately 5 mm in diameter. Subsequently, these particles were soaked in 25 mL of ASO for 5 min. SRF was obtained after air-drying. For slow-release test, SRF (30 g) was immersed in 1 L of deionized water. Solution aliquots (5 mL) were collected at given intervals to determine the FLA content in the aqueous system. The released FLA content was determined using UV-vis spectrophotometry at its maximum absorbing wavelengths of 270 nm. Pot experiment with Shanghai cabbage and biosafety evaluation To evaluate the fertilization of WP’s humification product and SRF, pot experiment was conducted with five treatments in triplicate: (A) 300 g soil (Blank), (B) 300 g soil + 7.8 g WP (WP), (C) 300 g soil + 3.2 g K 2 SO 4 (K 2 SO 4 , corresponding to the K + dosage in 7.8 g Product), (D) 300 g soil + 7.8 g Product (Product), and (E) 300 g soil + 15.6 g SRF (SRF). In each pot (top width and length of 9.8 cm, bottom width and length of 7.5 cm, height of 10.5 cm), 10 Shanghai cabbage seeds were sprayed evenly in soil at depth of around 1 cm, and the pots were put in an incubator (humidity of 60%, 22 o C). After harvest in 14 d, plant parameters and rhizosphere soil were collected for analysis. Besides, earthworm was used as a bioindicator to evaluate the biological safety of Product and SRF. All the experiments were carried out with three replicates for each treatment. The detailed procedure was provided in Text S2. Characterizations After filtration through a 0.45-μm membrane, the components of WP, VR and CKW during humification were preliminarily analyzed by a 3D-EEM fluorescence spectroscopy (F-7000, Hitachi High Technologies Co., Japan) and UV-vis spectrometry (UV-1900i, SHIMADZU Co., Ltd. of Japan). TOC and DOC were measured using a TOC analyzer (Muti N/C 210, Germany). Molecular weight distribution was measured using a GPC (LC-20A HPLC, SHIMADZU Co., Ltd. of Japan). K + was measured with an inductively coupled plasma optical emission spectroscopy (ICP-MS, iCAP™TQ, Thermo Fisher). Radicals were identified via an EPR spectrometer (Magnettech MS5000, Germany). The structural components of the freeze-dried samples were analyzed through the X-ray Photoelectron Spectroscopy (ESCALAB 250, Thermo-VG Scientific Co., USA), Fourier Transform Infrared spectroscopy (NEXUS-670, Nicolet Co., USA), X-ray Diffraction (D/max-2550VB/PC, Rigaku Co., Japan), and solid state 13 C Nuclear Magnetic Resonance (Bruker AVANCE III 600 M). Thermal stability was analyzed with a Thermal Gravimetric Analyzer (TGA, TG-209F1, NETZSCH Germany). The soil indexes including SOM, TN, TP, TK, AN, AP, and AK were measured according to the procedures previously reported 54 . The surface morphology of the SRF was measured with Scanning Electron Microscopy (SU8010, Hitachi Japan). Statistical analysis Experiments were conducted at least in triplicate throughout the study, with data presented as mean ± standard deviation. Data analysis was conducted with Microsoft Excel (Microsoft CoWPoration) and Origin Pro 2021 (OriginLab Co, Northampton, MA). Statistical analysis was conducted using SPSS (Inc., Chicago, IL) based on one-way analysis of variance (ANOVA). Data availability The authors declare that all data of this study are available within the article and the supplementary information. Source data are provided with this paper. Any additional data can be obtained from the corresponding author upon reasonable request. Declarations Competing interests The authors declare no competing interest. Author contributions Y.Z., D.W. and D.C. designed the experiments. Y.Q., Y.Y. and W.L. conducted the experiments and prepared the manuscript. S.S., P.Z., L.L. and J.S. supervised the study. W.Z., K.Z., and R.Z. provided constructive suggestions for the manuscript revision. Acknowledgements This work was supported by Key R&D Program of Shandong Province (2022SFGC0302), Jiangxi Province Agriculture Key Core Technology Project (JXNK202307-04-05), the National Natural Science Foundation of China (No. 52370129), the Key R&D Program of Guangxi Province (No. Guike AB23026061), Natural Science Foundation of Shanghai (No. 24ZR1403700), Fundamental Research Funds for the Central Universities (22D111317 and 2232020D-22), Science and Technology Service Program of Chinese Academy of Science (KFJ-STS-QYZD-199), Key R&D Program of Inner Mongolia Autonomous Region (2021GG0300), Key Program (Achievement Transformation) of “Revitalizing the City by Science and Technology” of Hulun Buir (2022HZZX008), the Plan for Anhui Major Provincial Science and Technology Project (202203a06020001), and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA0450000). References Lahiri, A. et al. 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Improved performance indicators and institutional setup for more viable compost production from municipal solid waste in Sri Lanka. Manage . 3 , 100217 (2025). Tian, P. et al. LCA as a decision support tool for the environmental improvement of organic fraction of municipal solid waste composting in China. J. Cleaner Prod. 495 ,145068 (2025). Zhang, W. et al. Increased abundance of nitrogen transforming bacteria by higher C/N ratio reduces the total losses of N and C in chicken manure and corn stover mix composting. Bioresour. Technol. 297 , 122410 (2020). Nguyen, V. et al. Effects of C/N ratios and turning frequencies on the composting process of food waste and dry leaves. Bioresour. Technol. Rep. 11 , 100527 (2020). Makino, K. et al. Cautionary note for DMPO spin trapping in the presence of iron ion. Biochem. Biophys. Res. Commun. 172 , 1073-1080 (1990). Chen, Z. et al. Understanding the selectivity trend of water and sulfate (SO 4 2− ) oxidation on metal oxides: On-site synthesis of persulfate, H 2 O 2 for wastewater treatment. Chem. Eng. J. 431 , 134332 (2022). Yang, B. et al. Air heating-alkaline hydrothermal production of artificial humic acid: Rapid and efficient humification of waste biomass. J. Environ. Chem. Eng. 13 ，116770 (2025). Additional Declarations There is NO Competing Interest. Supplementary Files SIv5.docx Microwave-alkali co-activated persulfate enables minute-scale fertilization of food waste with high fulvic-like acid yield Cite Share Download PDF Status: Published Journal Publication published 13 Jan, 2026 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6923064","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":480219161,"identity":"e3566d19-e741-4b4d-9442-38810b153d6a","order_by":0,"name":"Dongqing 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fertilizer\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/4f7806f959ee7692a687fab9.png"},{"id":86124820,"identity":"11ab09d0-9707-4d30-a124-bb0327612d6a","added_by":"auto","created_at":"2025-07-07 05:08:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":992813,"visible":true,"origin":"","legend":"\u003cp\u003eThree-dimensional excitation-emission matrix fluorescence\u003cstrong\u003e (\u003c/strong\u003e3D-EEM) spectra of waste potatoes (WP) treated by microwave/KOH/persulfate (MW/KOH/PS) under different conditions: \u003cstrong\u003e(A-H) \u003c/strong\u003esynergistic effect of PS and KOH, effect of \u003cstrong\u003e(I-L) \u003c/strong\u003eKOH/PS dosage and \u003cstrong\u003e(M-P) \u003c/strong\u003emicrowave time. Conditions: WP=50 g, KOH or PS dosage=0-3wt% and microwave time=0-15 min, ambient temperature=22±1\u003csup\u003eo\u003c/sup\u003eC. Each experiment was performed three times independently with similar results.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/aba6a4d60872e569c36e7d0f.png"},{"id":86124508,"identity":"a75cfbe1-5e42-4ca6-a789-2cdaa3cd3e2b","added_by":"auto","created_at":"2025-07-07 05:00:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":354546,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEfficiency and cost comparison between KOH/PS and MW/KOH/PS for WP humification. \u003c/strong\u003e3D-EEM fluorescence spectra of WP treated by \u003cstrong\u003e(A)\u003c/strong\u003e 2%KOH/2%PS, \u003cstrong\u003e(B)\u003c/strong\u003e 6%KOH/6%PS and \u003cstrong\u003e(C)\u003c/strong\u003e 8%KOH/8%PS for 60 min without MW. \u003cstrong\u003e(D)\u003c/strong\u003e FLA content of WP and the product after MW/2%KOH/2%PS and 8%KOH/8%PS treatment. \u003cstrong\u003e(E)\u003c/strong\u003e Temperature variation of the reaction system under different treatment conditions. \u003cstrong\u003e(F)\u003c/strong\u003e TOC loss and \u003cstrong\u003e(G) \u003c/strong\u003efertilizer production cost comparison between MW/2%KOH/2%PS and 8%KOH/8%PS treatment. Conditions: WP=50 g, KOH or PS dosage=2-8wt%, ambient temperature=22±1\u003csup\u003eo\u003c/sup\u003eC. Each experiment was performed three times independently with similar results.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/77c6b6983e17c86cbc343932.png"},{"id":86124506,"identity":"47cdfd58-abed-4fb2-bdc7-148b7d8ad64c","added_by":"auto","created_at":"2025-07-07 05:00:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":212655,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComponents characterization of WP and Product under optimal humification conditions (MW/2%KOH/2%PS). (A)\u003c/strong\u003e Fourier Transform Infrared Spectrometer (FTIR) spectra and \u003cstrong\u003e(B) \u003c/strong\u003eSolid-state \u003csup\u003e13\u003c/sup\u003eC Nuclear Magnetic Resonance (\u003csup\u003e13\u003c/sup\u003eC-NMR) spectra of SFA, Product and WP. X-ray Photoelectron Spectroscopy (XPS) spectra of \u003cstrong\u003e(C, D) \u003c/strong\u003eC1s, \u003cstrong\u003e(E, F) \u003c/strong\u003eO1s for WP and Product. \u003cstrong\u003e(G)\u003c/strong\u003e Thermo gravimetric analysis (TGA) spectra of WP and Product under nitrogen condition. \u003cstrong\u003e(H) \u003c/strong\u003eX-ray Diffraction (XRD) spectra of WP and Product. \u003cstrong\u003e(I) \u003c/strong\u003eMain contents in WP and Product.\u003cstrong\u003e \u003c/strong\u003eConditions: WP=50 g, KOH or PS dosage=2wt%, microwave time=10 min, ambient temperature=22±1\u003csup\u003eo\u003c/sup\u003eC. Each experiment was performed three times independently with similar results. ND in Fig. 4(H) referred to not detected.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/01abd3668a8cffb716d4a2af.png"},{"id":86124509,"identity":"729f9c70-48ce-4053-b6bd-2ac3fc060b2c","added_by":"auto","created_at":"2025-07-07 05:00:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":425741,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eHumification mechanism elucidation under optimum conditions (MW/2%KOH/2%PS). (A)\u003c/strong\u003e Electron paramagnetic resonance (EPR) spectra of •OH and •SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e during the humification of WP.\u003cstrong\u003e (B, C) \u003c/strong\u003e3D-EEM spectra of MW/2%KOH/2%PS -treated WP in the presence of tert-butanol (TBA) and ethanol anhydrous (EtOH). \u003cstrong\u003e(D) \u003c/strong\u003eUV-vis absorbance spectra of treated WP in different systems \u003cstrong\u003e(E) \u003c/strong\u003ePS decomposition rate of WP during humification. \u003cstrong\u003e(F) \u003c/strong\u003eGel permeation chromatography (GPC) spectra of WP and Product.\u003cstrong\u003e (G)\u003c/strong\u003e FTIR spectra of treated WP at different intervals (0, 2, 6 and 10 min). \u003cstrong\u003e(H)\u003c/strong\u003e Synchronous and \u003cstrong\u003e(I) \u003c/strong\u003easynchronous FTIR two-dimensional correlation spectra (2D-COS) of treated WP during humification. Conditions: WP=50 g, KOH or PS dosage=2wt%, microwave time=10 min, ambient temperature=22±1\u003csup\u003eo\u003c/sup\u003eC, TBA=10 mol/L, EtOH=10 mol/L. Each experiment was performed three times independently with similar results.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/4c8d3ff01bff063379c2a692.png"},{"id":86124514,"identity":"b35052a1-16c7-46c7-92af-e5725eb9c55b","added_by":"auto","created_at":"2025-07-07 05:00:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":877611,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSlow-release fertilizer (SRF) preparation and nutrient release behavior.\u003c/strong\u003e (A) Preparation flowchart of granular SRF using the Product and ATP. (B) Digital images of SRF in water immersion system and time-dependent 3D-EEM spectra variation of the aqueous solution within 30 d. Release curve of (C) FLA and (D) K\u003csup\u003e+\u003c/sup\u003e during 30 d water immersion of SRF.\u0026nbsp; (E) FTIR spectra, (F) scanning electron microscopy (SEM) images, and (G) XRD spectra of SRF before and after slow-release.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/2cd0ff32e7f81257fb097200.png"},{"id":86124512,"identity":"71b88da2-0a85-4efb-95b7-8520ab9a005a","added_by":"auto","created_at":"2025-07-07 05:00:23","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":931338,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFertilization of product derived under optimal humification conditions (MW/2%KOH/2%PS). (A, B)\u003c/strong\u003e Digital images, \u003cstrong\u003e(C) \u003c/strong\u003efresh weight, \u003cstrong\u003e(D)\u003c/strong\u003e plant height,\u003cstrong\u003e (E)\u003c/strong\u003e root length, \u003cstrong\u003e(F)\u003c/strong\u003e germination rate, \u003cstrong\u003e(G)\u003c/strong\u003e dry weight, \u003cstrong\u003e(H)\u003c/strong\u003e chlorophyll content of Shanghai Cabbage and \u003cstrong\u003e(I)\u003c/strong\u003e soil parameters with different treatments: Blank, WP, K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, Product, and SRF referred to 300 g soil alone, 300 g soil+7.8 WP, 300 g soil + 3.2 g K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, 300 g soil+7.8 g product, and 300 g soil+15.6 g SRF respectively. Each pot contained 10 Shanghai Cabbage seeds. Each group was in triplicates and error bars represent the standard deviations. n\u003csub\u003epot\u003c/sub\u003e indicated the number of pots selected for analysis, and n\u003csub\u003eplant\u003c/sub\u003e referred to the number of plants selected in each group for analysis. Comparison among results of different treatments were via one-way ANOVA analysis, and different letters refer to significant differences with Tukey’s t test at p\u0026lt;0.05 (n=3).\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/b328c140d5e01467ae29d18e.png"},{"id":86124829,"identity":"456b971c-a53f-4721-bb03-b07508a28ce1","added_by":"auto","created_at":"2025-07-07 05:08:23","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":884592,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScaling-up efficacy of MW/KOH/PS induced humification in practical food waste systems. \u003c/strong\u003eDigital images\u003cstrong\u003e of (A)\u003c/strong\u003e vegetable residue (VR, weight ratio of potatoes: spinach: tomatoes = 5:2.5:2.5) and \u003cstrong\u003e(E)\u003c/strong\u003e cooked kitchen waste (CKW) before and after humification. 3D-EEM spectra of \u003cstrong\u003e(B, C) \u003c/strong\u003eVR and \u003cstrong\u003e(F, G) \u003c/strong\u003eCKW before and after treatment. \u003cstrong\u003e(D)\u003c/strong\u003e UV-vis absorbance spectra and \u003cstrong\u003e(H)\u003c/strong\u003e FLA contents of VR and CKW before and after treatment. \u003cstrong\u003e(I) \u003c/strong\u003eProposed food waste fertilization modes in household and park scales.\u003cstrong\u003e \u003c/strong\u003eConditions: VR or CKW=1000 g, KOH or PS dosage=2wt%, microwave time=6 min, ambient temperature=22±1\u003csup\u003eo\u003c/sup\u003eC, MW power=2 KW. Each experiment was performed three times independently with similar results.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/881cfd9eb79853605ae315f7.png"},{"id":102575534,"identity":"749dbef8-a22e-4659-bf77-8a90d916f3b7","added_by":"auto","created_at":"2026-02-13 08:11:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6049429,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/9b467ab2-1c09-47f7-b826-3d4aac17597a.pdf"},{"id":86124825,"identity":"c80156e7-dda1-4a90-ba48-b61f5294fa26","added_by":"auto","created_at":"2025-07-07 05:08:23","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":7510959,"visible":true,"origin":"","legend":"Microwave-alkali co-activated persulfate enables minute-scale fertilization of food waste with high fulvic-like acid yield","description":"","filename":"SIv5.docx","url":"https://assets-eu.researchsquare.com/files/rs-6923064/v1/5e584f17d9a1a7a35769e71e.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Microwave-alkali co-activated persulfate enables minute-scale fertilization of food waste with high fulvic-like acid yield","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGlobally, approximately 1.3 billion tons of food wastes were generated in 2023, accounting for 30-50% of total municipal solid waste\u003csup\u003e1\u003c/sup\u003e. Conventional disposal methods such as\u0026nbsp;landfill and incineration posed substantial environmental risks, necessitating urgent advancements in sustainable resource recovery technologies\u003csup\u003e2-4\u003c/sup\u003e. While anaerobic digestion and aerobic composting currently dominated waste valorization strategies\u003csup\u003e5\u003c/sup\u003e, their widespread adoption was constrained by prolonged processing periods (20-60 days) and extensive land requirements\u003csup\u003e6\u003c/sup\u003e. For instance, microbial-mediated composting usually converted perishable organics into stabilized humic-like acid (HLA) and fulvic-like acid (FLA), yet suffered from inherently slow metabolic rates and poor directional control, contributing to relatively high carbon loss (i.e. 30-50%) and low water-soluble HLA (\u0026lt;15%) and FLA (\u0026lt;2%) yields\u003csup\u003e7,8\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eIn our recent study\u003csup\u003e9\u003c/sup\u003e, radicals generated in KOH/persulfate (PS) enabled waste milk rapid conversion into HLA/FLA via degradation-polymerization, achieving remarkable HLA and FLA yields of 18.9 and 25.5wt% within 1 hour, respectively. Nevertheless, high PS and KOH inputs (8wt% each) remained a practical limitation. More importantly, the heterogeneous composition and high viscosity of food wastes may impede mass transfer and reaction kinetics compared to homogeneous milk\u003csup\u003e10\u003c/sup\u003e, thus the applicability of this approach required further systematic investigation.\u003c/p\u003e\n\u003cp\u003eMicrowave-assisted advanced oxidation processes (MW-AOPs) had been investigated in wastewater remediation due to its unique advantages of uniform heating, enhanced mass transfer, and oxidant activation\u003csup\u003e11,12\u003c/sup\u003e. To explore its potential in chemical-saving and humification efficiency improvement, this work employed microwave and KOH co-activated PS (MW/KOH/PS) in humification of waste potato, a model food waste, and compared with KOH/PS. The process efficiency, humification mechanism, product components, and HLA/FLA yields were systematically investigated as well as product\u0026rsquo;s fertilizer efficacy. Furthermore, its efficacy towards practical food wastes was verified using vegetable residue and cooked food waste. This work highlighted a time (minute-scale) and chemical-efficient (4wt%, saving 75% chemicals) method for converting food wastes into FLA fertilizer, promoting their onsite and spontaneous recycling (Fig. 1).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eRobust humification of WP induced by MW/KOH/PS and condition optimization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAs shown in Fig. 2, during the humification of WP, the dynamic evolution of soluble fluorescent components was monitored using three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy. The 3D-EEM spectrum was generally divided into five regions\u003csup\u003e13,14\u003c/sup\u003e: regions I and II were typically associated with simple aromatic proteins and amino acids, region IV referred to soluble microbial byproducts (SMP), regions III and V corresponded to humic-like acid (HLA) and fulvic-like acid (FLA).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn WP (Fig. 2A), intense fluorescence signals were observed in regions I, II, and IV, suggesting that proteins/amino acids and SMP dominated its fluorescent components. Isolated treatments with KOH or MW (Figs. 2B and E) exhibited negligible alteration in fluorescence distribution compared to WP, indicating their insignificant effects used alone. In contrast, 2wt%PS treatment (Fig. 2C) induced a marked reduction in fluorescence intensities across regions I, II, and IV, likely attributed to PS-driven oxidative degradation of proteins/amino acids and SMP\u003csup\u003e15\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAfter treatment by 2%KOH/2%PS without MW (Fig. 2D) or MW/2%PS (Fig. 2F), florescence intensities in regions I, II and IV decreased, while those in regions III and V slightly elevated, implying their slight humification effects. This shift aligned with the generation of reactive radicals during KOH or MW activated PS processes, which may promote oxidative degradation and subsequent humification. Similarly, combined MW and 2wt%KOH treatment (MW/KOH) (Fig. 2G) induced a slight fluorescence intensity increase in regions III and V, potentially reflecting base-thermal synergistic effects on humification\u003csup\u003e16\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNotably, the most pronounced transformation occurred under the combined MW/KOH/PS treatment (Fig. 2H), where fluorescence signals completely migrated from regions I, II, and IV to regions III and V. Fluorescence region integral (FRI) analysis (Table S1, according to the method described in Text S1) revealed that the cumulative fluorescence contribution of regions III and V (P\u003csub\u003eIII+V\u003c/sub\u003e) surged from\u0026nbsp;10.59%\u0026nbsp;in WP (Fig. 2A) to\u0026nbsp;67.09%\u0026nbsp;after MW/KOH/PS treatment (Fig. 2H). These findings proved the synergistic role of MW/KOH/PS in driving robust humification of WP, likely through synergistic mechanisms of thermal/KOH activation, radical oxidation, and base/heat hydrolysis\u003csup\u003e17-20\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eTo optimize the humification efficiency of WP by MW/KOH/PS, the dosages of PS and KOH were evaluated within the range of 1-3wt%. With the increase of their dosages, the fluorescence intensities (Fig. 2I-L, Fig. S1A and B) and P\u003csub\u003eIII+V\u003c/sub\u003e (Table S1) increased initially (from 1 to 2wt%) and then decreased (from 2 to 3wt%), achieving the maximum at 2%KOH/2%PS. Therein, the decrease trend at overdoses (above 2wt%) of PS and KOH was consistent with our prior results in waste milk\u0026rsquo;s humification\u003csup\u003e21\u003c/sup\u003e, likely due to radical self-quenching at excessive oxidant conditions or accelerated decomposition of humification precursors/products.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBesides, the MW dose was optimized through adjusting the reaction time. As shown in Fig. 2M-P and Fig. S1 C, the fluorescence intensity increased with MW exposure time and plateaued after 10 min, consistent with the similar P\u003csub\u003eIII+V\u0026nbsp;\u003c/sub\u003evalues of Fig. 2H and 2P in Table S1. Therefore, the optimal humification conditions were chosen at dosages of 2%KOH/2%PS and microwave exposure time of 10 min through their synergistic effect. Besides, the EEM spectra of the product remain unchanged in 7 d (Fig. S2), reflecting the high stability of the product.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdvantages of MW/KOH/PS humification compared to KOH/PS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe role of MW during WP\u0026rsquo;s humification was investigated on chemical consumption reduction and efficiency elevation. 3D-EEM spectra revealed that the florescence signals shifted from protein and SMP (Fig. 2A) to HLA/FLA regions after treated by KOH/PS at 2-8wt% each for 60 min (Fig. 3A-C and Fig. S1 D), with stronger intensities at higher dosages (8wt% each). Notably, treatments of 8%KOH/8%PS (in 60 min) resulted in comparable FRI distributions in HLA/FLA regions (65.7%) compared to MW/2%KOH/2%PS (67.1% in 10 min) shown in Table S1, along with the slightly lower FLA content in the humified product (Fig. 3D). These results showed that the involvement of MW could substantially reduce the chemical input by 75% as well as shortening reaction duration by 83%.\u003c/p\u003e\n\u003cp\u003eBesides, Fig. 3E showed that systems treated with 8%KOH/8%PS and MW/2%KOH/2%PS exhibited rapid temperature rise from ambient conditions (20\u0026deg;C) to peak values of 80.3 \u0026deg;C (5 min) and 92.1 \u0026deg;C (10 min), respectively, significantly higher than that of 2%KOH/2%PS (38.4 \u003csup\u003eo\u003c/sup\u003eC). These results indicated that the maximum temperature of the system without MW increased with dosages of KOH and PS, attributed to radical-involved exothermic reactions\u003csup\u003e15\u003c/sup\u003e. In comparison, MW/2%KOH/2%PS may activate PS through exogenous heating and direct MW attack besides KOH\u003csup\u003e22,23\u003c/sup\u003e , accelerating radical formation and finally realizing similar humification effects to 8%KOH/8%PS.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCritically, Fig. 3F showed that the carbon loss during the humification induced through MW/2%KOH/2%PS and 8%KOH/8%PS were 20.1% and 43.4%, respectively. That is, MW/2%KOH/2%PS could significantly reduce the carbon loss by 53.7% compared to 8%KOH/8%PS, likely attributable to abbreviated reaction duration and thus minimized oxidative decomposition. This highlighted its potential in enhancing carbon retention besides concurrent resource efficiency (chemical/time savings), positioning it as a sustainable strategy for rapid fertilization of food wastes\u003csup\u003e24,25\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFig. 3G showed a preliminary techno-economic comparison between\u0026nbsp;MW/2%KOH/2%PS\u0026nbsp;and\u0026nbsp;8%KOH/8%PS. The total production cost for FLA fertilizer derived from per ton of WP was calculated by integrating costs of chemical consumption,\u0026nbsp;electricity,\u0026nbsp;equipment depreciation, and\u0026nbsp;labor\u003csup\u003e26,27\u003c/sup\u003e. The analysis revealed that MW/2%KOH/2%PS incurred a total cost of 320 RMB/ton, whereas the conventional 8%KOH/8%PS process required 850 RMB/ton. Notably, the MW-integrated approach achieved a 62.4% reduction in overall costs, primarily attributed to the minimized chemical usage.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHumification product characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe components of the product were characterized comprehensively in Fig. 4. As shown in Fig. 4A, peaks of N-H (713 cm\u003csup\u003e-1\u003c/sup\u003e), aromatic C-O (1027 cm\u003csup\u003e-1\u003c/sup\u003e), C-N (1152 cm\u003csup\u003e-1\u003c/sup\u003e), carboxyl -OH (1578 cm\u003csup\u003e-1\u003c/sup\u003e), and aromatic C=C (1670\u0026nbsp;cm\u003csup\u003e-1\u003c/sup\u003e) became stronger after humification. These variations indicated the occurrence of aromatization, carboxylation, and amidation\u003csup\u003e28,29\u003c/sup\u003e. Meanwhile, the groups of aromatic C-O and C=C, amide N-H, and carboxyl C-O were consistently observed in standard FA (SFA), indicating the formation of FLA\u003csup\u003e30\u003c/sup\u003e. Similarly, the solid-state \u003csup\u003e13\u003c/sup\u003eC NMR spectra in Fig. 4B showed that peaks belong to regions of oxygenated aliphatic carbon (50-100 ppm), aromatic carbon (100-160 ppm), and carboxyl C=O (160-220 ppm) become stronger after humification, align with the peaks in the spectra of SFA\u003csup\u003e31\u003c/sup\u003e. XPS C1s results in Fig. 4C showed that C1s peak in WP could be deconvoluted into peaks located at 284.5, 285.5, 285.9 and 287.8 eV, corresponding to C-C, C-O, C=O, and \u0026Pi;-\u0026Pi;. After humification, Fig. 4D showed that peaks representing C-C/C=C, C=O, and \u0026Pi;-\u0026Pi; were strengthened, while C-O was weakened. Meanwhile, the peaks in O1s spectra (Fig. 4E and F) also observed the strengthened C=O peak and weakened C-O peak in the product compared with WP. These results consistently reflected the occurrence of aromatization and carboxylation\u003csup\u003e32,33\u003c/sup\u003e. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThermo gravimetric analysis (TGA) spectra showed that the product possessed a higher thermal stability compared with WP (Fig. 4G), likely related to the conversion of perishable organics (proteins/amino acids) and SMP into HLA/FLA with higher thermal stability besides introduction of K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. Besides, the main contents in Fig. 4H showed that a total of 10.5 g dry matter was contained in 50 g WP, corresponding to a moisture of 79%. Therein, contents of organic matter (OM) and dissolved organic carbon (DOC) accounted for 9.6 g and 0.6 g, respectively. Besides, WP also contained 1.5 g K\u003csup\u003e+\u003c/sup\u003e, 0.6 g FLA, and 0.15 g SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e. After humification, OM content decreased to 8.7 g, corresponding to a loss of 9.4%. While DOC content increased to 6.5 g likely due to the formation of dissolving OM during humification. K\u003csup\u003e+\u003c/sup\u003e and SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e contents increased to 3.8 and 0.2 g in the product respectively. XRD spectra in Fig. 4I showed the emerged peaks of K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in the product due to the decomposition of PS, consistent with the result in Fig. 4H. To be noted, K\u003csup\u003e+\u003c/sup\u003e was an important inorganic fertilizer for plant, making the product like a kind of compound fertilizer\u003csup\u003e34\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMW/KOH/PS-induced humification mechanism\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFig. 5A showed the electron paramagnetic resonance (EPR) spectra during WP\u0026rsquo;s humification. Both \u0026bull;OH and \u0026bull;SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e radicals were detected at 2 min, with weakened signals at 6 min and disappeared at 10 min, indicating their possible involvement in the humification. With the addition of TBA as the \u0026bull;OH quencher to MW/KOH/PS humification system (Fig. 5B)\u003csup\u003e23\u003c/sup\u003e, the 3D-EEM spectrum showed slightly weakened signals in protein/amino acids regions compared with WP (Fig. 2A), with insignificant variation in HLA/FLA regions. This result indicated the key contribution of \u0026bull;OH in degradation of protein/amino acids and HLA/FLA formation. Similarly, in the presence of EtOH, quenchers of both \u0026bull;OH and \u0026bull;SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e35\u003c/sup\u003e, the florescence peaks were almost unchanged, verifying the key role of\u0026nbsp;\u0026bull;SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e besides \u0026bull;OH in WP humification (Fig. 5C). Furthermore, Fig. 5D showed that the UV absorbance at 250-270 nm, representing the aromatization degree\u003csup\u003e36\u003c/sup\u003e, was significantly increased after humification, while the peaks were suppressed after addition of radical quenchers especially EtOH. Therefore, these quenchers inhibited the aromatization and humification, which were consistent with our previous observations in waste milk and glucose humification systems\u003csup\u003e15\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFig. 5E showed an initial (0-4 min) fast then (4-10 min) slow PS decomposition trend with time, reaching a 100% PS consumption in 10 min, which was consistent with the time-dependent variation of radical signals and humification process. Besides, the Gel permeation chromatography (GPC) results in Fig. 4E showed that the molecular distribution of dissolved organics in WP was mainly between 300-7370 Da, with the most distributed around 1141 Da. While after humification, that of the product increased to a range of 300-15000 Da, with the most distributed around 1405 Da, indicating that radical-induced polymerization likely occurred, which was considered as a characteristic reaction of humification\u003csup\u003e37,38\u003c/sup\u003e. Since the general molecular weights of FA and HA were distributed in the ranges of 600-1500 and 10000-100000 Da respectively \u003csup\u003e39,40\u003c/sup\u003e , the GPC distribution of the product also suggested the formation of FLA and HLA.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig. 5G-I, the FTIR spectra variation of treated WP were analyzed within 10 min through two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS). According to synchronous 2DCOS in Fig. 5H, overall structural variation mainly distributed at 1578, 1400, 1100 and 1020 cm\u003csup\u003e-1\u003c/sup\u003e, corresponding to aromatic C=C, carboxyl O-H, aromatic C-O and C-N, respectively. These peaks consistently showed a gradually strengthened trend (Fig. 5G). Asynchronous maps in Fig. 5I showed that the groups variation followed the order of aromatic C-O \u0026gt; carboxyl O-H\u0026gt; aromatic C=C \u0026gt; C-N\u0026nbsp;(Table S2).\u0026nbsp;Collectively, this humification\u0026nbsp;was mainly induced through radical-involved aromatization, carboxylation, and amidation (i.e. characteristic Mallard reactions)\u003csup\u003e41\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePreparation and nutrient release behavior of product-based slow-release fertilizer\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAs shown in Fig. 6A, the product was conveniently granulated into FLA and K\u003csup\u003e+\u003c/sup\u003e slow-release fertilizer after mixing with ATP at a weight ratio of 1:1. Fig. 6B demonstrated that the SRF granules remained intact throughout a 30-day water immersion period, indicating a good water resistance. Concurrently, the aqueous solution gradually transitioned from colorless to brown. This color change was consistent with the progressively intensified fluorescence signals in the HLA/FLA regions observed over 30 days (Fig. 6B), suggesting the slow release of HLA/FLA. The release profiles of FLA and K⁺, presented in Fig. 6C and 6D respectively, confirmed their time-dependent release behavior, reaching release ratios of 98.15% and 97.7% after 30 days.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFTIR spectra (Fig. 6E) revealed a significant weakening of peaks corresponding to amide N-H, aromatic C=C, C-O, aliphatic C-H, and O-H bonds after 30-day immersion, likely attributable to FLA release. SEM analysis (Fig. 6F) showed a dense surface morphology for SRF, suggesting successful loading of the product in ATP with a nanonetwork structure\u003csup\u003e42\u003c/sup\u003e. However, post-immersion, the surface exhibited substantial rod-like structures,\u0026nbsp;presumably resulting from\u0026nbsp;the release of loaded contents from the ATP nanonetwork.\u0026nbsp;Furthermore, XRD analysis\u0026nbsp;(Fig. 6G) showed strong characteristic peaks of K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in the fresh SRF, which almost disappeared after 30-day release. This finding aligned with the significantly weakened distribution signals observed in the SEM-mapping results (Fig. S3). In a word, these results confirmed the successful synthesis of SRF based on WP\u0026rsquo;s humified product. The synthesized SRF exhibited favorable slow-release properties for both FLA and K⁺ over a 30-day period.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFertilization effect of WP-derived product in pot experiment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAs shown in Fig. 7, the fertilization effect of the product on Shanghai Cabbage\u0026rsquo; growth was compared with WP and K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e through pot tests. \u0026nbsp;After 21 d cultivation, the overall plant growth parameters (fresh weight, plant height, root length, germination rate, dry weight, chlorophyll content) showed an order of SRF\u0026gt;Product\u0026gt;K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u0026gt;Blank\u0026gt;WP (Fig. 7A-7H). Therein, the fresh weight (actually the yield) of Product group was 5.2 g, 163.1%, 425.3% and 45.8% higher than the Blank, WP, and K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e group respectively. The decreased fresh weight of WP group than Blank group was likely owing to the negative effect of labile organic matter (proteins) in WP on plant growth. The positive effects of the Product indicated the effectiveness of the humification process in converting WP into a functional fertilizer. The superior performance of the Product over K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e demonstrated the significant contribution of HLA/FLA. Notably, SRF treatment further amplified the fertilization effect, resulting in better overall growth (including a 17.4% higher fresh weight) compared to the Product. Therefore, the slow-release of FLA and K⁺ likely enhanced their absorption and utilization efficiency by plants\u003csup\u003e43\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eKey soil indexes were also measured after harvest and shown in Fig. 7I. The soil organic matter (SOM) content showed an order of Product\u0026gt;SRF\u0026gt;WP\u0026gt;Blank. The higher SOM content in the Product group than WP indicated effective conversion of labile organic carbon into stable humic fractions during humification. Similarly, total and available nitrogen (TN and AN) consistently increased in WP and Product groups compared with Blank likely due to their inherent high nitrogen contents in WP. Notably, total and available potassium (TK and AK) in Product group surged by 17.4% and 150.8% compared with WP, primarily due to external K\u003csup\u003e+\u003c/sup\u003e supplementation during the humification process. \u0026nbsp;The slightly lower values of these soil indexes in the SRF group compared to the Product group may be associated with the slow-release characteristics.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBesides, the biosafety of the product was monitored with earthworm as a kind of bioindicator (Fig. S4). After 7-d cultivation, the survival rate and weight gain rate in different groups followed an order of Product\u0026gt;Blank\u0026gt;WP, indicating that the Product with a good biosafety may favor the growth of earthworms. These findings validated the dual functionality of the humification product: (i) as a high-efficiency fertilizer through K\u003csup\u003e+\u003c/sup\u003e and HLA/FLA-mediated plant growth promotion, and (ii) as a soil conditioner via carbon sequestration and nutrient reservoir construction.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMW/PS/KOH induced scaling-up humification of practical food wastes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe application feasibility of MW/PS/KOH was explored in scaling-up experiments (1 kg) using practical vegetable residue (VR) and cooked kitchen waste (CKW). Fig. 8A showed that the color of the VR changed from green into brown after MW/KOH/PS treatment, likely a visual sign of humification. Meanwhile, Fig. 8B and 8C illustrated that the 3D-EEM spectra showed significant florescence shifts from regions I, II, and IV to region V, confirming the conversion of labile organic matter (proteins, amino acids, and SMP) into stabilized humic substances (HLA/FLA). After humification, a significant enhancement of UV absorbance at 250-270 nm appeared, suggesting the occurrence of aromatization (Fig. 8D). Besides, Fig. 8H showed a dramatic FLA content increase from 2.3wt% (VR) and 2.6wt% (CKW) to 32.3wt% and 28.4wt% after treatment, verifying the dramatic occurrence of humification. Notably, similar humification phenomenon was observed in both WP and CKW systems (Fig. 6D-H and Fig. S5). Besides, Fig. S6 showed that the growth of amaranth followed an order of VR-Product\u0026gt;CKW-Product\u0026gt;K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u0026gt;Blank\u0026gt;CKW\u0026gt;VR in field tests, indicating the fertilization of derived products from VR and CKW. These findings validated the universal applicability of MW/PS/KOH treatment in inducing scaling-up humification of diverse practical food wastes (i.e. VR and CKW).\u003c/p\u003e\n\u003cp\u003eFig. 8I showed that the MW/PS/KOH process enabled on-site fertilizer production from food waste at both household and park scales. The integrated procedure comprised three sequential stages: pretreatment, humification, and fertilizer recycling. During pretreatment, food waste underwent sorting (manually or via magnetic separation) and pulping (using household or industrial-grade mechanical pulpers), converting raw waste into biodegradable slurry (particle diameter \u0026lt;1 mm, impurity content \u0026lt;3%). Subsequently, the humification of slurry could be realized in a microwave oven (household or industrial scale) after KOH and PS addition within 10 min. The derived humified product could be directly applied as fertilizer for adjacent green spaces (e.g., residential gardens or urban parks). This process demonstrated advantages of ultra-low chemical consumption, equipment versatility, rapid treatment efficiency, and closed-loop resource utilization. The designed application modes favored the efficient recycling of food waste, alleviating the potential pollution from storage and long-term composting.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eMW/KOH/PS treatment enabled rapid conversion of food wastes (i.e. waste potatoes, vegetable residues, and cooked food wastes) into fertilizer rich in FLA (15wt%) and K⁺ (7.6wt%). The involvement of microwave could\u0026nbsp;significantly reduce chemical consumption by 75%, and shorten the reaction period from 60 to 10 min, thus reducing processing cost and carbon loss by 20.1% and 43.4%, respectively. This offered distinct advantages in both cost-effectiveness and carbon emission reduction. The inherent flexibility and low cost of microwave equipment further facilitated its significant potential for the efficient humification of food waste.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1 Technical comparison between this work and conventional composting\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"558\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 16.9643%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.5714%;\"\u003e\n \u003cp\u003eDuration\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003eFLA yield\u003c/p\u003e\n \u003cp\u003e(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.7857%;\"\u003e\n \u003cp\u003eCost (RMB/t)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003eC loss (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003eC/N ratio\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003eT\u003csub\u003emax\u003c/sub\u003e (\u003csup\u003eo\u003c/sup\u003eC)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.9643%;\"\u003e\n \u003cp\u003eSterilization (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 16.9643%;\"\u003e\n \u003cp\u003eThis work\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.5714%;\"\u003e\n \u003cp\u003e6-10 min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003e10.9-15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.7857%;\"\u003e\n \u003cp\u003e250-320\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003eNo need\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003e90-95\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.9643%;\"\u003e\n \u003cp\u003e\u0026gt;99\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 16.9643%;\"\u003e\n \u003cp\u003eComposting\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.5714%;\"\u003e\n \u003cp\u003e20-60 d\u003csup\u003e44-46\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003e1-2\u003csup\u003e47\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.7857%;\"\u003e\n \u003cp\u003e200-300\u003csup\u003e48,49\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003e30-60\u003csup\u003e50\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003e20-30\u003csup\u003e50,51\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.1786%;\"\u003e\n \u003cp\u003e60-80\u003csup\u003e31\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16.9643%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003e The cost was calculated based on the value in WP\u0026rsquo;s small-scale tests in Fig. 3G, the range was considering that treatment duration could be shorten in scaling-up tests, saving corresponding electricity cost.\u003c/p\u003e\n\u003cp\u003eIn contrast to traditional composting (Table 1), this technology featured drastically shortened duration (10 min \u003cem\u003evs.\u003c/em\u003e 20-60 d), higher FLA yield (10.9-15%\u003cem\u003e\u0026nbsp;vs.\u003c/em\u003e 1-2%), lower carbon loss (21% \u003cem\u003evs.\u003c/em\u003e 30-60%), ultrahigh sterilization rate (\u0026gt;99%) (Fig. S7 and Table S3), and elimination of C/N ratio adjustment. These advantages supported \u0026quot;generate-and-recycle within hours\u0026quot; for food waste across diverse scales, from households to commercial entities. Consequently, this approach saved substantial transportation and storage costs and effectively mitigated the risk of secondary pollution during processing, exhibiting high application potential in food waste recycling.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eReagents and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll reagents used in this study were of analytical grade. Potassium persulfate (K\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e, purity\u0026ge;99.5%), potassium hydroxide (KOH, purity\u0026ge;95%), hydrochloric acid (HCl, 36.0-38.0%), anhydrous ethanol (EtOH, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO, 99.5%), tert-butanol (TBA, C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eO,\u0026nbsp;\u0026ge;99%) and 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Attapulgite (ATP) and aminosilicone oil (ASO) were supplied by Fufeng Biotechnology Co., Ltd. (Inner Mongolia, China). A microwave oven (Midea PM20A1, 800 W, 2450 MHz) and industrial microwave oven (LY-40KW, 5800*1060*1700mm, Shanghai Longyu Microwave Equipment Co., Ltd.) were employed for microwave-involved processes. Shanghai cabbage seeds (Fast-growing 605) were obtained from Shanghai Vegetable Seed Company. Cooked food waste (diameter\u0026lt;0.5 mm, 80% moisture content) was obtained from China Everbright Environment Group Limited. Adult earthworms (Eisenia fetida) were provided by Ruizhou Fishing Tackle Co., Ltd. (Jiangsu Province, China). Potatoes (Longdan No.1) was provided by Chunzhengsheng Co., Ltd. (Shanxi Province, China). Deionized water was used for all experiments, except for pot test where tap water was applied.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHumification of WP, vegetable residues and cooked food wastes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePrior to humification, waste potatoes and vegetable residues (weight ratio of potatoes: spinach: tomatoes = 5:2.5:2.5)\u0026nbsp;were pulped into slurry using a crusher. The moisture contents of WP and VR were around 89.5% and 90.2%, respectively.\u003c/p\u003e\n\u003cp\u003eIn small scale test, solid KOH and PS at dosages of 0-4 g were added simultaneously to 50 g WP slurry with stirring (150 rpm). Then the mixture was subjected to the microwave oven (160 W, 0-15 min) to achieve humification.\u003c/p\u003e\n\u003cp\u003eIn scaling-up test, solid KOH and PS with 20 g each were added to 1 kg slurry of WP, VR or CK under stirring (150 rpm). Then the mixture was placed individually on the conveyor belt of the industrial microwave oven and treated at a power of 3 kW for 6 minutes.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRadical identification\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRadicals (\u0026bull;OH and \u0026bull;SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e) produced during the process were determined on an electron paramagnetic resonance (EPR) spectrometer using DMPO as the spin-trapping agent\u003csup\u003e52,53\u003c/sup\u003e. Additionally, quenching experiments were carried out by adding 6 mol/L EtOH and TBA (higher than 10 times of PS and KOH dosages) to 50 g WP before PS and KOH to obtain the contributions of those radicals.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eExtraction and quantitative analyses of HLA and FLA in product\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe quantitative analysis of HLA/FLA was conducted according to alkali dissolution and acid precipitation method detailed in BS ISO 19822-20182843. First, the product was adjusted to pH of approximately 10.5 and then shaken at 300 rpm for 1 hour. Subsequently, the product was centrifuged at 12,000 rpm for 20 minutes at 4℃. The insoluble substances (precipitate 1) were separated from the soluble humic acid (SHA) in the supernatant. Next, the pH of the supernatant was adjusted to 1 with hydrochloric acid and stand overnight at room temperature. Then, the supernatant (FLA) was separated from precipitate 2 (HLA) after centrifugation at 12,000rpm for 20 minutes. Finally, the product (around 50 g), precipitate 1, and precipitate 2 were weighed after freeze drying. The yields of HLA and FLA could be calculated according to formulas (1)-(4).\u003c/p\u003e\n\u003cp\u003eWherein m\u003csub\u003eSHA\u003c/sub\u003e, m\u003csub\u003eproduct\u003c/sub\u003e, m\u003csub\u003eFLA\u003c/sub\u003e, and m\u003csub\u003eHLA\u003c/sub\u003e represented the dry weights of SHA, product, FLA and HLA respectively. m\u003csub\u003e1\u003c/sub\u003e and m\u003csub\u003e2\u003c/sub\u003e represented the dry weight of precipitate 1 and weight of K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e calculated according to the stoichiometric method under the condition that PS has completely decomposed.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/58895_8739fc6c57c1c19a/58895_custom_files/img1751863748.png\" width=\"623\" height=\"256\"\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFabrication of SRF and nutrient release behavior\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe humification product derived from 50 g of WP under optimized conditions (1 g PS, 1 g KOH, 160 W MW irradiation for 10 min) was mixed with 50 g of ATP. The mixture was then granulated to produce spherical fertilizer particles approximately 5 mm in diameter. Subsequently, these particles were soaked in 25 mL of ASO for 5 min. SRF was obtained after air-drying.\u003c/p\u003e\n\u003cp\u003eFor slow-release test, SRF (30 g) was immersed in 1 L of deionized water. Solution aliquots (5 mL) were collected at given intervals to determine the FLA content in the aqueous system. The released FLA content was determined using UV-vis spectrophotometry at its maximum absorbing wavelengths of 270 nm.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePot experiment with Shanghai cabbage and biosafety evaluation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo evaluate the fertilization of WP\u0026rsquo;s humification product and SRF, pot experiment was conducted with five treatments in triplicate: (A) 300 g soil (Blank), (B) 300 g soil + 7.8 g WP (WP), (C) 300 g soil + 3.2 g K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e (K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, corresponding to the K\u003csup\u003e+\u003c/sup\u003e dosage in 7.8 g Product), (D) 300 g soil + 7.8 g Product (Product), and (E) 300 g soil + 15.6 g SRF (SRF). In each pot (top width and length of 9.8 cm, bottom width and length of 7.5 cm, height of 10.5 cm), 10 Shanghai cabbage seeds were sprayed evenly in soil at depth of around 1 cm, and the pots were put in an incubator (humidity of 60%, 22\u003csup\u003eo\u003c/sup\u003eC). After harvest in 14 d, plant parameters and rhizosphere soil were collected for analysis.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBesides, earthworm was used as a bioindicator to evaluate the biological safety of Product and SRF. All the experiments were carried out with three replicates for each treatment. The detailed procedure was provided in Text S2.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterizations \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter filtration through a 0.45-\u0026mu;m membrane, the components of WP, VR and CKW during humification were preliminarily analyzed by a 3D-EEM fluorescence spectroscopy (F-7000, Hitachi High Technologies Co., Japan) and UV-vis spectrometry (UV-1900i, SHIMADZU Co., Ltd. of Japan). TOC and DOC were measured using a TOC analyzer (Muti N/C 210, Germany). Molecular weight distribution was measured using a GPC (LC-20A HPLC, SHIMADZU Co., Ltd. of Japan). K\u003csup\u003e+\u003c/sup\u003e was measured with an inductively coupled plasma optical emission spectroscopy (ICP-MS, iCAP\u0026trade;TQ, Thermo Fisher). Radicals were identified via an EPR spectrometer (Magnettech MS5000, Germany).\u003c/p\u003e\n\u003cp\u003eThe structural components of the freeze-dried samples were analyzed through the X-ray Photoelectron Spectroscopy (ESCALAB 250, Thermo-VG Scientific Co., USA), \u0026nbsp; Fourier Transform Infrared spectroscopy (NEXUS-670, Nicolet Co., USA), X-ray Diffraction (D/max-2550VB/PC, Rigaku Co., Japan), and solid state \u003csup\u003e13\u003c/sup\u003eC Nuclear Magnetic Resonance (Bruker AVANCE III 600 M). Thermal stability was analyzed with a Thermal Gravimetric Analyzer (TGA, TG-209F1, NETZSCH Germany). The soil indexes including SOM, TN, TP, TK, AN, AP, and AK were measured according to the procedures previously reported\u003csup\u003e54\u003c/sup\u003e. The surface morphology of the SRF was measured with Scanning Electron Microscopy (SU8010, Hitachi Japan).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eExperiments were conducted at least in triplicate throughout the study, with data presented as mean \u0026plusmn; standard deviation. Data analysis was conducted with Microsoft Excel (Microsoft CoWPoration) and Origin Pro 2021 (OriginLab Co, Northampton, MA). Statistical analysis was conducted using SPSS (Inc., Chicago, IL) based on one-way analysis of variance (ANOVA).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that all data of this study are available within the article and the supplementary information. Source data are provided with this paper. Any additional data can be obtained from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eCompeting interests\u003c/h2\u003e\u003cp\u003eThe authors declare no competing interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e\u003cp\u003eY.Z., D.W. and D.C. designed the experiments. Y.Q., Y.Y. and W.L. conducted the experiments and prepared the manuscript. S.S., P.Z., L.L. and J.S. supervised the study. W.Z., K.Z., and R.Z. provided constructive suggestions for the manuscript revision.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThis work was supported by Key R\u0026amp;D Program of Shandong Province (2022SFGC0302), Jiangxi Province Agriculture Key Core Technology Project (JXNK202307-04-05), the National Natural Science Foundation of China (No. 52370129), the Key R\u0026amp;D Program of Guangxi Province (No. Guike AB23026061), Natural Science Foundation of Shanghai (No. 24ZR1403700), Fundamental Research Funds for the Central Universities (22D111317 and 2232020D-22), Science and Technology Service Program of Chinese Academy of Science (KFJ-STS-QYZD-199), Key R\u0026amp;D Program of Inner Mongolia Autonomous Region (2021GG0300), Key Program (Achievement Transformation) of \u0026ldquo;Revitalizing the City by Science and Technology\u0026rdquo; of Hulun Buir (2022HZZX008), the Plan for Anhui Major Provincial Science and Technology Project (202203a06020001), and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA0450000).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLahiri, A.\u003cem\u003e et al.\u003c/em\u003e A critical review on food waste management for the production of materials and biofuel. \u003cem\u003eJ. 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Eng. \u003c/em\u003e\u003cstrong\u003e13\u003c/strong\u003e，116770 (2025).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6923064/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6923064/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study demonstrated rapid humification of waste potato (WP), as a model food waste, into fulvic-like acid (FLA) fertilizer (15wt% FLA and 7.6wt% K\u003csup\u003e+\u003c/sup\u003e) using microwave-triggered KOH/persulfate (MW/KOH/PS) process. Under synergistic MW irradiation (180 W) and KOH (2wt%), PS (2wt%) was activated to generate •OH and •SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e. This process simultaneously dissolved organic matter and elevated system temperature, inducing humification of organic components within 10 minutes. Compositional analyses revealed Maillard reactions and amidation during humification. Compared to KOH/PS, microwave intensification reduced chemical consumption by 75%, while achieving comparable FLA yields and significantly lowering cost by 62.4%. Pot experiments validated the plant-growth promotion and soil-amendment capabilities of the humified product. Scale-up trials confirmed the efficacy for practical vegetable residues and cooked food waste. Unlike composting (20-60 d), this process completed in 10 min without requiring optimal C/N ratio or moisture content, exhibited only 20.1% carbon loss (WP system), and operated in scalable reactor, thus enabling same-day waste valorization into fertilizer.\u003c/p\u003e","manuscriptTitle":"Microwave-alkali co-activated persulfate enables minute-scale fertilization of food waste with high fulvic-like acid yield","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-07 05:00:18","doi":"10.21203/rs.3.rs-6923064/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"c26da7a3-4276-42cc-8022-2e5d1016221f","owner":[],"postedDate":"July 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":50997957,"name":"Earth and environmental sciences/Environmental sciences/Environmental chemistry/Pollution remediation"},{"id":50997958,"name":"Earth and environmental sciences/Biogeochemistry/Carbon cycle"}],"tags":[],"updatedAt":"2026-02-13T08:10:49+00:00","versionOfRecord":{"articleIdentity":"rs-6923064","link":"https://doi.org/10.1038/s41467-026-68295-6","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2026-01-13 05:00:00","publishedOnDateReadable":"January 13th, 2026"},"versionCreatedAt":"2025-07-07 05:00:18","video":"","vorDoi":"10.1038/s41467-026-68295-6","vorDoiUrl":"https://doi.org/10.1038/s41467-026-68295-6","workflowStages":[]},"version":"v1","identity":"rs-6923064","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6923064","identity":"rs-6923064","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}