Near-Complete Phosphorus Recovery from Challenging Water Matrices Using Multiuse Ceramsite Made from Water Treatment Residual (WTR)

Near-Complete Phosphorus Recovery from Challenging Water Matrices Using Multiuse Ceramsite Made from Water Treatment Residual (WTR) | 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 Near-Complete Phosphorus Recovery from Challenging Water Matrices Using Multiuse Ceramsite Made from Water Treatment Residual (WTR) Jinkai Xue, Jianfei Chen, Jinyong Liu, Seyed Hesam-Aldin Samaei, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4558561/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Water treatment residual (WTR) is a burden for many water treatment plants due to the large volumes and associated management costs. Here, we transform aluminum-salt WTR (Al-WTR) into ceramsite (ASC) to recover phosphate from challenging waters. ASC showed remarkably higher specific surface area (SSA, 70.53 m 2 /g) and phosphate adsorption capacity (calculated 47.2 mg P/g) compared with previously reported ceramsite materials (< 40 m 2 /g SSA and 94.9% phosphate over a wide pH range (3 – 11) and generally sustained > 90% of its phosphate recovery at high concentrations of competing anions (i.e., Cl - , F - , SO 4 2- , or HCO 3 - ) or humic acid (HA). We challenged the material with real municipal wastewater at 10℃ and achieved simultaneous phosphate (>97.1%) and COD removal (71.2%). Once saturated with phosphate, ASC can be repurposed for landscaping or soil amendment. Economic analysis indicates that ASC can be a competitive alternative to natural clay-based ceramsite, biochar, or other useful materials. Therefore, ASC is an eco-friendly, cost-effective adsorbent for phosphate recovery from complex waters, shedding light upon a circular economy in the water sector. Synopsis: Ceramsite made from aluminum-salt water treatment residual exhibited great capability of recovering phosphate from waters under challenging conditions. Physical sciences/Engineering/Civil engineering Physical sciences/Engineering/Chemical engineering eutrophication circular economy sludge valorization waste valorization water treatment adsorbent Sips isotherm nutrient recovery Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The large quantities of water treatment residual (WTR) produced in the coagulation process at drinking water treatment plants (DWTPs) are a challenge to the utilities and local environment. Because aluminum salts (e.g., alum and polyaluminum chloride (PACl)) are widely used coagulants, sustainable management of aluminum salt-based WTR (Al-WTR) is particularly interesting to the industry. Traditionally, Al-WTR has been disposed of at local landfills, which is a financial and environmental burden. Transforming this waste into ceramsite can be promising. Ceramsite is traditionally made from clay or shale and can be used as lightweight aggregate, landscaping mulch, etc. 1 Al-WTR contains both skeleton materials (i.e., Al 2 O 3 and SiO 2 ) and flux materials (e.g., Na 2 O, CaO, Fe 2 O 3 , and K 2 O) that are critical to ceramsite. In addition, Al-WTR contains a higher content of organic matter (pore-forming), 2 making it a better raw material for ceramsite than clay. Therefore, transforming Al-WTR into ceramsite can help the water sector reduce operating costs and environmental footprint, generate more revenue, and assist the ceramsite industry in addressing environmental and land use concerns. Hence, a circular economy can be achieved. To date, few studies have used Al-WTR for ceramsite fabrication. Al-WTR-based ceramsite (termed ASC ) can find many beneficial uses as an adsorbent, construction material, landscaping mulch, etc. In particular, given its abundant di-/tri-valent metal content (e.g., Al), ASC can be a promising adsorbent for phosphate and holds great potential to recover the precious P resource from eutrophic water and wastewater. 3, 4 Due to the non-renewable nature of the geologic P deposits, a global shortfall of phosphorus (P) for industrial and agricultural needs is predicted by 2035. 5 ASC offers an opportunity to obliterate the unbalanced distribution of P and facilitate sustainable development. Herein, we developed an ASC adsorbent and used it to recover phosphate from various challenging water matrices. The ASC exhibited substantially higher specific surface area (SSA) and phosphate adsorption capacity than all previously reported ceramsite materials. It is robust in adsorbing phosphate at various initial concentrations (< 50 mg PO 4 3- /L) under the effect of competing anions or humic acids (HA), or even in real municipal wastewater at a low temperature (10℃). Mechanistic insights on phosphate adsorption onto the ASC were elucidated based on model fitting and X-ray photoelectron spectroscopy (XPS). Experimental and theoretical analyses indicate that this material can be a cost-effective solution to tackle the phosphate challenge in eutrophic waterbodies such as agricultural ponds. Economic analyses suggest that ASC can be a more affordable alternative to several commercial products such as clay ceramsite, tire crumb, and lightweight aggregate. Transforming WTR into ceramsite can help water treatment plants: 1) reduce operating costs and environmental impact, 2) create new revenue opportunities, and 3) achieve a circular economy. ASC is an exceptional adsorbent for phosphate ASC demonstrated exceptional performance compared to previously reported ceramsite materials. Its SSA and total pore volume were 70.53 m 2 /g and 0.23 cm 3 /g, respectively (Figure 1A and Figure S2A&B). Its pore size distribution was between 2 and 50 nm (Figure 1A), with a peak at 7.7 nm (Figure S2B). In contrast, Wang et al.’s ceramsite made from WTR and bentonite (7:3 wt) had an SSA of 45.4 m 2 /g, 6 and the modified commercial ceramsite in Wu, et al. 7 had a pore size of 7.7 to 14.8 nm and a pore volume of 0.067 – 0.151 cm 3 /g. Benchmarking against previously reported ceramsite materials (made from red mud, slag, clay, etc. 4, 7-11 ) with a large SSA and high phosphate adsorption capacity, we found ASC in this study had the largest SSA (Figure 1B&C and Table S7). A large SSA results in a high number of adsorption sites. Isotherm experiments (Figure S4D) proved an experimentally determined maximum phosphate adsorption capacity of 42.9 mg PO 4 3- /g (or 14.3 mg P/g) of ASC, and the Sips model predicted a maximum absorption capacity at 10℃ to be 141.7 mg PO 4 3- /g (or 47.23 mg P/g), making this WTR-derived ceramsite the best performer in both Figure 1B&C. Adsorption experiments for kinetic analysis were conducted using three initial phosphate concentrations (i.e., 5, 30, and 50 mg PO 4 3- /L)(Figure S4A). These were very high concentrations in relation to environmental P levels. In Canada, water bodies with a total phosphorus (TP) concentration of 0.035 – 0.100 mg P/L (equivalent to 0.107 – 0.306 mg PO 4 3- /L) are categorized as eutrophic, and waters with [TP] > 0.100 mg P/L (or > 0.306 mg PO 4 3- /L) is hyper-eutrophic. 12 At 10℃, after around 11 hrs, adsorption stabilized at 0.74, 4.22, and 8.13 mg PO 4 3- /g, corresponding to a phosphate recovery rate of 97.6, 93.9, and 91.9%, respectively (Figure S4A). The kinetic and XPS analyses suggest that the phosphateadsorption onto ASC was primarily driven by strong chemical adsorption between surface active sites (e.g., Al 3+ , Ca 2+ ) and functional groups (SI Text S6). 8, 13 On the other hand, the surface of ASC was among the least active, as indicated by the ratio of phosphate adsorption capacity (either experimentally determined or model-predicted) and SSA in Figure 1D. We anticipate that our ASC can be further enhanced by increasing the density of active sites on the surface. XRD analysis (Figure S2D) showed that the main crystalline phases of ASC were quartz (SiO 2 ), muscovite (KAl 2 Si 3 AlO 10 (OH) 2 ), albite (NaAlSi 3 O 8 ), sanidine (KAlSi 3 AlO 8 ), and a small amount of calcite (CaCO 3 ), which help explain the good phosphate adsorption by ASC and implicate possible opportunities to improve it. A few strategies can be explored: 1) adjust the fabrication conditions, 2) add certain auxiliary materials (e.g., eggshell) to the recipe, or 3) modify the surface after sintering by incorporating lanthanum, iron, or other hard acid metals. 4, 14, 15 Regardless of future improvement, the high phosphate adsorption capacity achieved in this study inspires us to envision ASC’s potential application for remediating eutrophic waterbodies, such as agricultural ponds for livestock (dugouts) and stormwater ponds. For a small dugout with a volume of one million Imperial gallons (4.5 million litres), which is typical in Western Canada,16, 17 if the phosphate concentration is 0.1 mg P/L (highly eutrophic12), merely 10 kg of ASC will be needed to recover the phosphorus from the polluted water. For an extremely large dugout of 30 million litres of water,17 63 kg of ASC will be enough. Each tonne of ASC will be able to recover 141.6 kg of phosphate. If we are conservative and use the phosphate adsorption capacity of 14.3 mg P/g achieved in our experiments, the 4.5-million-litre and 30-million-litre dugouts will require 32 and 210 kg of ASC, respectively. But real waters are complex, will this material robustly recover phosphate under the influence of various factors? What will impact phosphate adsorption onto ASC? We examined several factors that may influence phosphate adsorption onto ASC, which were ASC dosage, pH, temperature, co-existing anions and NOM, and regeneration cycles. Effect of ASC dosage The effect of adsorbent dosage on phosphate adsorption was evaluated (Fig. 2A). With the adsorbent dosage increased from 2 to 10 g/L, the removal significantly increased from ~ 78 to 100%, obviously owing to the increased total surface area and the number of adsorption sites. However, the equilibrium adsorption capacity decreased from 3.68 to 0.91 mg PO 4 3− /g as the dosage increased, suggesting abundant, unoccupied sites. The phosphate removal exceeded 95% with an ASC dosage of 6 g/L, while a further increase in adsorbent dosage provided marginal improvement. Hence, an ASC dosage of 6 g/L was selected for subsequent experiments. Effect of pH pH affects the speciation of the adsorbate in this study (Figure S6), which, in turn, may affect the adsorption efficiency. We studied the adsorption of (total) phosphate (the sum of H 3 PO 4 , H 2 PO 4 − , HPO 4 2− , and PO 4 3− ) by ASC over a wide range of pH (3.0–11.0)(Fig. 2B). In this pH range, H 2 PO 4 − and HPO 4 2− are the main species (Figure S6). 18 pH influences the surface charge of the adsorbent, which further influences phosphate adsorption. The pH pzc of ASC was close to 8.2 (Figure S2C), indicating that the adsorbent surface was positively charged at pH < 8.2. Figure 2B indicates stable, excellent phosphate adsorption (94.9–97.0%) across all tested pH levels at low phosphate levels (10 mg PO 4 3− /L). It follows that at pH < pH pzc , the ceramsite surface underwent protonation, allowing for electrostatic attraction between the positively charged ceramsite surface and PO 4 3− . The nonetheless high phosphate adsorption (94.9%) by ASC at pH = 11.0 was due to the stronger affinity between phosphate ions and di-/tri-valent metals on ASC surface. Compared with OH − ions, PO 4 3− ions have a higher charge density and smaller ionic radius. The same reason allowed phosphate ions to replace the alkaline species (e.g., OH − ) that had been initially bound to the di-/trivalent metals of the pristine ceramsite surfaces. 19 It was this ligand exchange phenomenon that resulted in a substantial pH increase in all the systems after phosphate adsorption (Fig. 2B). In addition, other mechanisms might also play a role in phosphate adsorption onto ASC. For instance, calcite (the XRD result in Figure S2D) can adsorb phosphate. In conclusion, ASC showed near-complete phosphate adsorption across a broad pH range at a low temperature, and the effect of pH was negligible. Effect of temperature Adsorption experiments were performed with three initial phosphate concentrations (10, 50, and 100 mg PO 4 3− /L) at three temperatures (10, 20, and 30℃)(Fig. 2C). For 10 mg PO 4 3− /L, the effect of temperature was negligible, whereas higher temperature appeared to slightly benefit phosphate adsorption at an initial concentration of 50 and 100 mg PO 4 3− /L. The van’t Hoff equation was used to compute Gibbs free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) for phosphate adsorption (Fig. 2D and Table S6). As indicated by the negative values of ΔG, the adsorption process is spontaneous and favoured at higher temperatures. The positive ΔS values suggest a strong affinity between ASC and phosphate and an increased randomness index at the solid/liquid interface during adsorption at a higher temperature. 20 Effect of co-existing anions Anions in water may influence phosphate adsorption due to their competition for active sites (Fig. 3 A). However, the co-existing anions in our experiments only slightly impacted phosphate recovery, with an order of Cl − < SO 4 2− < F − 90% phosphate recovery in the presence of competing anions with only two exceptions (at 30 mM F − or HCO 3 − ). In the presence of 15 mM Cl − or SO 4 2− , ASC achieved 96.7 and 95.3% phosphate removal, respectively. When the concentrations of these anions were doubled (30 mM), the inhibition of phosphate adsorption increased slightly (e.g., from 4.7 to 5.7% by SO 4 2− ). This confirmed the formation of inner-sphere mono-dentate or bi-dentate complexes during phosphate adsorption. 21 Among all the tested anions, HCO 3 − exhibited the most significant impact on phosphate adsorption by reducing it from 96.5% (at 0 mM HCO 3− ) to 90.4% (at 15 mM HCO 3− ) and further to 85.2% (at 30 mM HCO 3− ). The results were similar to those of a previous study using katoite adsorbent. 22 Due to the similarity of HCO 3 − and H 2 PO 4 − , the anions are readily adsorbed via inner/outer-sphere complexation, which is crucial for understanding their competitive interaction on adsorbent surfaces. 23 Moreover, F − led to a notable decrease in phosphate removal (e.g., from 97.4% at 0 mM to 86.5% at 30 mM F − ), which can be attributed to its strong affinity towards metal-active sites. 24 Metallic-modified (e.g., La 3+ , Al 3+ , and Fe 3+ ) adsorbents are commonly inhibited by background pollutants in water despite their Lewis acid-base interaction-induced high selectivity for phosphate. 25 Such inhibition was also observed when natural zeolite or clay modified with calcium hydroxide was used as an adsorbent. 26 The slight inhibition of phosphate adsorption observed in our experiments is, therefore, not unexpected and should not be a significant deterrent for the application of ASC. Overall, ASC showed excellent phosphate selectivity by maintaining over 85% (generally over 90%) of its adsorption capacity at high concentrations of competing anions. This suggests phosphate adsorption on ASC was primarily driven by chemisorption (as presumed in Section 3.1) rather than outer-sphere complexation via electrostatic attraction. The impact of water hardness (i.e., Mg 2+ and Ca 2+ ) was not investigated in the present study, which commonly promotes phosphate adsorption according to the literature. 9, 27 Effect of co-existing natural organic matter (NOM) NOM may also impact phosphate adsorption in natural water systems. Contrary to expectations, 15 our experiments showed a negligible impact of HA (representing NOM) on phosphate adsorption (Fig. 3 A), which was similar to recent studies using magnesium-stirred biochar and lanthanum-modified bio-ceramsite. 11, 28 In contrast, Liu, Wang, et al. 11 observed significantly inhibited phosphate adsorption by 50 and 100 mg/L of HA. Such high concentrations of HA, however, are less environmentally relevant. Comparative experiments indicated that phosphate interfered with HA adsorption onto ACS (Fig. 3 B and Figure S1 B). Such interference was the most significant when the HA concentration was low (1 mg/L) and became almost negligible when the latter increased to 20 mg/L. This pseudo-unilateral impact of phosphate on HA in competing for adsorption sites on ceramsite suggests that the HA adsorbed on the ceramsite offered adsorption sites for phosphate, perhaps through electrostatic attraction between amine groups of HA and phosphate ions. Considering the di- or tri-valent cations that could be released from the ceramsite, bridging and complexation could also play a role in facilitating phosphate adsorption onto HA-loaded ceramsite. Further experimental and modelling studies may help unveil the interaction between HA and phosphate on the ceramsite surface in greater detail. Regardless, ASC has shown its potential for phosphate recovery from complex water matrices under cold conditions. Effect of regeneration Two solutions (1.0 M NaOH or HCl) and RO water were tested to desorb phosphate from spent ASC. After desorption for 12 hrs, 94.2 ± 1.4% of the adsorbed phosphate was removed from ASC by 1.0 M NaOH, which was more effective than what 1.0 M HCl achieved. Therefore, NaOH was chosen as the regeneration agent. 29 After four cycles of reuse, the removal declined from 98.7 (pristine) to 80.6% (Fig. 3 D). This decline can be attributed to multiple reasons, such as leaching loss of active elements such as Al and Ca under strongly alkaline conditions, depletion of active sites due to chemical precipitation between phosphate ions and di- or tri-valent metals on the ASC surface, or phosphate ions trapped in deep pores (which makes it hard to wash adsorbed phosphate out in the desorption process). The phosphate-rich eluent can be used to produce fertilizers such as struvite. 30 Further investigation is warranted to minimize the use of strong eluent and reduce contact times in regenerating spent ASC. Although our ASC exhibited good reusability, it may not need regeneration at all. Instead, the spent ceramsite can be repurposed, such as being used as a nutrient-rich landscaping mulch that is a safe, inexpensive alternative to wood chips or toxic tire shreds, 31 offering additional environmental and economic benefits (more discussion in Section 3.3). Phosphate recovery from municipal wastewater under cold conditions? ASC was used to recover phosphate from real municipal wastewater (Fig. 3 D). After the suspended solids were removed, the wastewater’s pH (7.5) and initial phosphate concentration (35.5 mg PO 4 3− /L) were determined. Over 97.1% of phosphate and 71.2% of COD of the real wastewater were simultaneously removed by 6 g/L ASC at 10℃, resulting in a final phosphate concentration of 0.34 mg P/L (Fig. 3 B and Table S8). Hence, ASC is promising for recovering phosphate from actual wastewater under cold conditions or polishing treated wastewater (Fig. 4 ). To meet the stringent discharge limits (0.05–0.3 mg P/L), 32 slightly increasing the adsorbent dosage or raising the operating temperature should help. This requires validation by running real water in a pilot-scale system to determine the optimal operating conditions. Therefore, ASC can be an extraordinary adsorbent to recover phosphate from various water matrices, such as municipal wastewater, lagoons, and dugouts (Fig. 4 ). It offers municipalities, agricultural producers, and industries an inexpensive and facile approach to tackling phosphate pollution. The spent ASC can also be a valuable product for beneficial uses. ASC enriched in phosphate can be used for landscaping or soil amendment, relocating phosphate from polluted waters to where it is desired (Fig. 4 ). Moreover, ASC can also find applications in stormwater management as a bioretention cell medium or storage medium, or in the construction industry as a lightweight aggregate. The question is -- Is this material economically affordable? Economic analysis of ASC A preliminary cost analysis is conducted herein based on the framework described previously. 33 Each tonne of ASC required 15.9 tonnes of raw WTR (10wt% solids) and 0.4 tonnes of clay. The direct production cost of each tonne of ASC is broken down in Table 1 . The most important cost results from the dewatering and drying process, which accounts for 82.8% of the total cost. This cost can be further reduced by using adequate freeze-thaw and air-drying. It is assumed that the other costs associated with ASC production, such as labour and equipment, are comparable to the total direct production cost, 34 making the total production cost for ASC CA $ 171.5 × 2 = CA $ 343 per tonne. Considering the service fee paid by the DWTP for sludge disposal and potential subsidies and incentives from the federal and provincial governments, the actual cost of ASC can be lower. Given that ASC can be a good material for water filtration and landscaping mulch, we collected the prices of the common materials for these purposes on the Canadian market by web searching, emailing, or calling the vendors (Fig. 5 ). ASC is advantageous to many of these materials, including biochar, commercial ceramsite made from clay, and tire crumb. In particular, we found that natural clay-based lightweight aggregate (essentially ceramsite) is priced at ~ CA $ 600 per tonne. ASC will offer good profitability if priced at < CA $ 600. Moreover, if intended as landscaping mulch or soil amendment, each tonne of ASC can be used to recover up to 141.6 kg of phosphate from eutrophic waters prior to the final use, providing additional environmental and economic benefits. Environmental and Industrial Implications Al-WTR-based ceramsite (ASC) is a promising adsorbent for phosphate recovery and eutrophication control. It demonstrated broad pH adaptability and strong phosphate selectivity in complex water matrices, even at low temperatures. The adsorption experiments and Sips isotherm model suggested a theoretical maximal phosphate adsorption capacity of 141.7 mg PO 4 3- /g under cold conditions. The excellent phosphate adsorption of ASC in complex waters under cold conditions has solid implications for phosphorus recovery or pollutant removal from engineered (e.g., WWTPs, stormwater ponds, and dugouts) and natural water systems (e.g., lakes). What makes this waste-derived product more appealing is that it does not need to be regenerated once saturated with non-hazardous pollutants such as phosphate and NOM. Instead, the spent ceramsite can subsequently be repurposed for other beneficial applications, such as lightweight concrete aggregate and safe, fertilizing landscaping mulch to replace tire shreds (toxic) or wood chips. Multiple sectors can be interested in this material. For instance, municipalities can incorporate ceramsite filters into their WWTP to remove nutrients, microplastics, and emerging pollutants. Furthermore, other wastes that are rich in silica (e.g., glass waste) can be used to replace the clay used in this study, further bettering the environmental and social benefits. The adsorption capability and mechanical strength of the material may also have substantial implications in other sectors, such as the energy and construction industries. More research is needed to explore such possibilities and further improve the material’s performance. This study showcases the practicality of repurposing Al-WTR for beneficial uses. It sheds light on building a circular economy in the water sector and promotes the industry’s sustainability. Methods Materials The Al-WTR was collected from the Buffalo Pound Water Treatment Plant (BPWTP), which uses PACl as the primary coagulant. The wastewater (primary influent) was collected from the local wastewater treatment plant (WWTP). All chemicals were purchased from either Fisher Scientific or VWR. Details are shown in Supporting Information (SI) Text S1. Fabrication of ceramsite The raw material (RM) was Al-WTR, and the auxiliary material (AM) was bentonite clay (clay). Approximately 90.8 ± 1.1wt% of the raw Al-WTR was water, while the solid content had a higher volatile fraction (61.9wt% organics) than the fixed (38.1wt% inorganics). The clay ensured sufficient formation of the liquid phase and easy mouldability. 35 The main mineral compositions of the raw materials are in Table 2. Al-WTR and clay were dried at 105℃ for 72 hrs and then ground to pass through Mesh #100 sieves (pore size equivalent to 0.15 mm). The completely mixed raw meal was gradually poured into a granulator to prepare raw granules with particle sizes of < 3 mm. RO water was sprayed during the granulation process. Raw meals made with a range of Al-WTR: clay mass ratios were used. The obtained granules were then pre-dried at 105°C for 12 hrs before they were transferred into a muffle furnace for sintering (Figure 6). To efficiently improve the fabrication process, Taguchi Experimental Design method was used. The fabricating factors were Al-WTR : clay mass ratio (wt%, C 1 ), preheating time (min, C 2 ), preheating temperature (℃, C 3 ), sintering time (min, C 4 ), sintering temperature (℃, C 5 , between 800 and 1200℃), and heating rate (℃/min, C 6 ). Each factor was examined at three levels, creating an L27 (6 3 ) orthogonal design. The Brunauer-Emmett-Teller specific surface area (BET-SSA) of the ceramsite was used as the evaluation index given by its direct impact on adsorption. Minitab 20 software was used for data analyses. Details in SI Text S4. Through the Taguchi Experiments, the ceramsite with batch ID ASC#25 had the largest SSA and could be the best adsorbent among all the tested batches. To assess the heavy metal leaching risk of ASC, leaching experiments were conducted at pH = 2.0 (Table S3). ASC met the limits specified by the US EPA. 36 Adsorption experiments The ceramsite granules were first rinsed with RO water (3 – 5 times) to remove impurities, followed by 20-min shaking for further purification, then dried at 105°C for 24 hrs before being used for adsorption. Dried ceramsite was stored in a sealed desiccator. Adsorption experiments were conducted in an incubator shaker (HNY-2102C, Honour Instrument Co., Ltd., China) at 150 ± 1 rpm, and the pH of the synthetic solution was adjusted with 1.0 M HCl or NaOH solutions as appropriate. At every predetermined time point, the suspension was collected and filtered through a pre-rinsed syringe filter (0.45-μm mixed cellulose esters). The total phosphate (TP) concentration was measured by a pre-calibrated spectrophotometer (HACH DR 3900), using the PhosVer®3 kit. Phosphate concentrations of all suspension samples were measured in duplicates. The detailed measurement methods of chemical oxygen demand (COD), ammonia (NH 4 + ), nitrate (NO 3 - ), and HA are summarized in Text S2. The adsorption of phosphate and HA onto the container walls was experimentally determined to be negligible (Figure S1). Adsorption kinetics were studied with different initial phosphate concentrations (i.e., 5, 30, and 50 mg/L) at 10℃ for 72 hrs (pH = 7.5 and S/L ratio = 6.0 g/L). Samples were taken at different times (0 – 72 hrs) for model fitting. For the adsorption isotherms, approximately 0.18 g of the adsorbent was added into 30 mL of phosphate solution (i.e., S/L ratio = 6 g/L) with initial phosphate concentrations ranging from 5 to 900 mg PO 4 3- /L in polypropylene bottles at 10℃ and shaken at 150 rpm for 72 hrs. The pH of the solution was adjusted to 7.50 ± 0.02. Four adsorption kinetics (i.e., pseudo-first order, PFO; pseudo-second-order, PSO; Elovich; and intra-particle diffusion, IPD), three adsorption isotherms (i.e., Langmuir, Freundlich, and Sips), and adsorption thermodynamics were employed. Subsequent adsorption experiments were conducted with different pH values (3.0 – 11.0 with 2-unit increments), solid : liquid ratios (S/L ratio, 2.0 – 10.0, 2-unit increments), temperatures (10, 20, and 30℃), contact times (0 – 72 hrs), and initial concentrations of phosphate (10, 50, and 100 mg PO 4 3- /L). Additionally, the effects of coexisting anions (i.e., Cl - , F - , SO 4 2- , or HCO 3 - ) and natural organic matter (NOM, i.e., humic acid, HA) on phosphate adsorption were examined. The concentrations were set at 0, 15, or 30 mM for anions and 1, 5, or 20 mg/L for HA. The details are shown in Text S3. Adsorbent regeneration A series of four-cycle adsorption-desorption experiments were conducted. ASC (0.18 g) was dosed into 30 mL of phosphate solution (10 mg PO 4 3- /L) for 48 hrs at pH = 7.5 and 10°C. For desorption, the exhausted adsorbent was regenerated using 30 mL of 1.0 M HCl or NaOH solution, followed by RO water rinsing. After regeneration, the adsorption and desorption processes were repeated under the same operating conditions. Material characterization The ceramsite was characterized for its morphology, surface charge, crystalline composition, and phosphate adsorption. Details on BET, pH PZC , X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), XPS, and scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDS) are provided in SI Text S5. Declarations Acknowledgements This study was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through the NSERC Discovery Grant, NSERC Alliance Grant, NSERC Alliance International Catalyst Grant, Mitacs Accelerate Grant, Canada Foundation for Innovation (CFI) - John R. Evans Leaders Fund (JELF), Prairies Economic Development Canada (PrairiesCan) Regional Innovation Ecosystems (RIE) program, Innovation Saskatchewan, and the University of Regina (UofR) Vice President Research Discretionary Funds. We thank Buffalo Pound Water Treatment Corporation (BPWTC) for their generous funding support and field support. We thank the City of Regina and EPCOR for providing us with wastewater samples for our experiments. We thank Mr. Ben Lichtenwald, the Lab Instructor in Environmental Systems Engineering, for his invaluable support during sample preparation. S. S. and J. 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Additional Declarations There is NO Competing Interest. Supplementary Files GraphicalAbstract.png ASCPO4SIinfo.doc Cite Share Download PDF Status: Posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4558561","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":313232189,"identity":"a23bbd6e-0a4f-46b8-8e74-a424b768b33c","order_by":0,"name":"Jinkai Xue","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7klEQVRIiWNgGAWjYBACxmYGZgYGAxCT+QCI5CFFC1sCcVpApkNpHgPiHMbcznvY4EcBQ+KG4z3fpCsqamXM2Q8wfviB12F8yYk9BgzGBmfObpM8c+Y4j2VPArNkD14tPMYHgE6SM7iRu02yse0Yj8GBBDa8PgJpOfjHAOiR+2+eSTb+A2o5/4CN8Q8BLckQW3jYJBsbangMbiSwMROyxVjGQMJY8kyasWXDMaAjbzxslpbBo8Ww/4yx5Js/Nol9xw8/vNlQU2dvcD754Mc3+LQ0gCkJGP8wyOYGPBoYGOTR+HV4VY+CUTAKRsHIBADrAEdkCxYTAQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-8824-1495","institution":"University of Regina","correspondingAuthor":true,"prefix":"","firstName":"Jinkai","middleName":"","lastName":"Xue","suffix":""},{"id":313232190,"identity":"71cf0779-ca30-4649-a4dd-5cf1e8e54976","order_by":1,"name":"Jianfei Chen","email":"","orcid":"","institution":"University of Regina","correspondingAuthor":false,"prefix":"","firstName":"Jianfei","middleName":"","lastName":"Chen","suffix":""},{"id":313232191,"identity":"47eddbc0-4941-45be-ac05-a9e3490f3e48","order_by":2,"name":"Jinyong Liu","email":"","orcid":"https://orcid.org/0000-0003-1473-5377","institution":"University of California, Riverside","correspondingAuthor":false,"prefix":"","firstName":"Jinyong","middleName":"","lastName":"Liu","suffix":""},{"id":313232192,"identity":"e0a5708f-7059-43fa-823d-b55adba21853","order_by":3,"name":"Seyed Hesam-Aldin Samaei","email":"","orcid":"","institution":"University of Regina","correspondingAuthor":false,"prefix":"","firstName":"Seyed","middleName":"Hesam-Aldin","lastName":"Samaei","suffix":""},{"id":313232193,"identity":"7f2e10af-89c4-4dc9-804f-b16498d71aca","order_by":4,"name":"Leslie Robbins","email":"","orcid":"https://orcid.org/0000-0002-6931-5743","institution":"University of Regina","correspondingAuthor":false,"prefix":"","firstName":"Leslie","middleName":"","lastName":"Robbins","suffix":""}],"badges":[],"createdAt":"2024-06-10 14:11:40","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4558561/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4558561/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":58181394,"identity":"991db8ab-64b6-4c9a-bc0b-b6ae9ce03058","added_by":"auto","created_at":"2024-06-12 06:18:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":422660,"visible":true,"origin":"","legend":"\u003cp\u003eProperties of the ASC (A) and benchmarking its SSA and phosphate adsorption against ceramsite materials in the literature: experimentally determined maximum phosphate adsorption capacity and SSA (B), model predicted maximum phosphate adsorption capacity and SSA (C), and the ratio of phosphate adsorption capacity to SSA (D).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/a59f35a57015865c085469a2.png"},{"id":58180328,"identity":"70bfbda4-32c2-4a90-aa48-5eb5c8c1b2b1","added_by":"auto","created_at":"2024-06-12 06:02:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":22275,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of ASC dosage (A), pH (B), temperature on phosphate adsorption onto ASC (C), and van’t Hoff plot for phosphate adsorption onto ASC with different initial phosphate concentrations (D).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/1e7bd0fc64998b10da289a25.png"},{"id":58180785,"identity":"d45e00b4-9a78-49e5-ae1d-ec8d4976fd8b","added_by":"auto","created_at":"2024-06-12 06:10:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":24418,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of co-existing anions and NOM on phosphate adsorption by ASC (A); the HA removal (%) by ASC with and without phosphate (10 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/L, 10℃, 6 g ASC/L, pH=7.5, @150 rpm for 72 hrs)(B); regeneration of ASC using 1.0 M NaOH (C); and ASC for real municipal wastewater treatment (6 g ASC/L, pH = 7.5, at 10℃, @150 rpm for 72 hrs) (D).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/1dd91bad8c03fd049ae9a443.png"},{"id":58180330,"identity":"e830a2cc-3509-4a11-97ee-b58baee02967","added_by":"auto","created_at":"2024-06-12 06:02:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":331753,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of ASC’s versatility.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/10851937aaae1de8d29e210f.png"},{"id":58180329,"identity":"ee295a00-ad09-4517-9eba-7b4181ad9f65","added_by":"auto","created_at":"2024-06-12 06:02:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":45897,"visible":true,"origin":"","legend":"\u003cp\u003ePrices of materials that may be replaced with ASC on the Canadian market as of April 2024 (*estimated break-even price, CA$343).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/66e442ee7ddadfec17fac1cf.png"},{"id":58180334,"identity":"f69d4dfc-3997-4b58-a49b-24ef9acc0fe7","added_by":"auto","created_at":"2024-06-12 06:02:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":224335,"visible":true,"origin":"","legend":"\u003cp\u003eThe workflow of the ACS fabrication.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/465a5c9c63144706bd09c3a9.png"},{"id":61889248,"identity":"3a0d251e-ef5a-4b8d-bf91-3806fec29f4c","added_by":"auto","created_at":"2024-08-06 17:48:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1711761,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/c29232e2-f0f2-4a2f-bcdc-63a58daf0f7b.pdf"},{"id":58180333,"identity":"82c0f7c4-7d09-4103-a61f-51f24ec612d6","added_by":"auto","created_at":"2024-06-12 06:02:34","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":162051,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.png","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/878e74326cbfe1897c3e0048.png"},{"id":58180335,"identity":"e65f608c-874c-4eb4-99be-02f5c39afd01","added_by":"auto","created_at":"2024-06-12 06:02:34","extension":"doc","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":2250752,"visible":true,"origin":"","legend":"","description":"","filename":"ASCPO4SIinfo.doc","url":"https://assets-eu.researchsquare.com/files/rs-4558561/v1/9893d8b44b3bde5d74a008f2.doc"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Near-Complete Phosphorus Recovery from Challenging Water Matrices Using Multiuse Ceramsite Made from Water Treatment Residual (WTR)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe large quantities of water treatment residual (WTR) produced in the coagulation process at drinking water treatment plants (DWTPs) are a challenge to the utilities and local environment. Because aluminum salts (e.g., alum and polyaluminum chloride (PACl)) are widely used coagulants, sustainable management of aluminum salt-based WTR (Al-WTR) is particularly interesting to the industry. Traditionally, Al-WTR has been disposed of at local landfills, which is a financial and environmental burden. Transforming this waste into ceramsite can be promising.\u003c/p\u003e\n\u003cp\u003eCeramsite is traditionally\u0026nbsp;made from clay or shale and can be used as lightweight aggregate, landscaping mulch, etc.\u003csup\u003e1\u003c/sup\u003e Al-WTR contains both skeleton materials (i.e., Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e) and flux materials (e.g., Na\u003csub\u003e2\u003c/sub\u003eO, CaO, Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and K\u003csub\u003e2\u003c/sub\u003eO) that are critical to ceramsite. In addition, Al-WTR contains a higher content of organic matter (pore-forming),\u003csup\u003e2\u003c/sup\u003e making it a better raw material for ceramsite than clay. Therefore, transforming Al-WTR into ceramsite can help the water sector reduce operating costs and environmental footprint, generate more revenue, and assist the ceramsite industry in addressing environmental and land use concerns. Hence, a circular economy can be achieved. To date, few studies have used Al-WTR for ceramsite fabrication. Al-WTR-based ceramsite (termed \u003cstrong\u003eASC\u003c/strong\u003e) can find many beneficial uses as an adsorbent, construction material, landscaping mulch, etc. In particular, given its abundant di-/tri-valent metal content (e.g., Al), ASC can be a promising adsorbent for phosphate and holds great potential to recover the precious P resource from eutrophic water and wastewater.\u003csup\u003e3, 4\u003c/sup\u003e Due to the non-renewable nature of the geologic P deposits, a global shortfall of phosphorus (P) for industrial and agricultural needs is predicted by 2035.\u003csup\u003e5\u003c/sup\u003e ASC offers an opportunity to obliterate the unbalanced distribution of P and facilitate sustainable development.\u003c/p\u003e\n\u003cp\u003eHerein, we developed an ASC adsorbent and used it to recover phosphate from various challenging water matrices. The ASC exhibited substantially higher specific surface area (SSA) and phosphate adsorption capacity than all previously reported ceramsite materials. It is robust in adsorbing phosphate at various initial concentrations (\u0026lt; 50 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/L) under the effect of competing anions or humic acids (HA), or even in real municipal wastewater at a low temperature (10℃). Mechanistic insights on phosphate adsorption onto the ASC were elucidated based on model fitting and X-ray photoelectron spectroscopy (XPS). Experimental and theoretical analyses indicate that this material can be a cost-effective solution to tackle the phosphate challenge in eutrophic waterbodies such as agricultural ponds. Economic analyses suggest that ASC can be a more affordable alternative to several commercial products such as clay ceramsite, tire crumb, and lightweight aggregate. Transforming WTR into ceramsite can help water treatment plants: 1) reduce operating costs and environmental impact, 2) create new revenue opportunities, and 3) achieve a circular economy.\u003c/p\u003e\n\u003ch3\u003eASC is an exceptional adsorbent for phosphate\u003c/h3\u003e\n\u003cp\u003eASC demonstrated exceptional performance compared to previously reported ceramsite materials. Its SSA and total pore volume were 70.53 m\u003csup\u003e2\u003c/sup\u003e/g and 0.23 cm\u003csup\u003e3\u003c/sup\u003e/g, respectively (Figure 1A and Figure S2A\u0026amp;B). Its pore size distribution was between 2 and 50 nm (Figure 1A), with a peak at 7.7 nm (Figure S2B). In contrast, Wang et al.\u0026rsquo;s ceramsite made from WTR and bentonite (7:3 wt) had an SSA of 45.4 m\u003csup\u003e2\u003c/sup\u003e/g,\u003csup\u003e6\u003c/sup\u003e and the modified commercial ceramsite in\u0026nbsp;Wu, et al. \u003csup\u003e7\u003c/sup\u003e had a pore size of 7.7 to 14.8 nm and a pore volume of 0.067 \u0026ndash; 0.151 cm\u003csup\u003e3\u003c/sup\u003e/g. Benchmarking against previously reported ceramsite materials (made from\u0026nbsp;red mud, slag, clay, etc.\u003csup\u003e4, 7-11\u003c/sup\u003e) with a large SSA and high phosphate adsorption capacity, we found\u0026nbsp;ASC in this study had the largest SSA (Figure 1B\u0026amp;C and Table S7). A large SSA results in a high number of adsorption sites. Isotherm experiments (Figure S4D) proved an experimentally determined maximum phosphate adsorption capacity of 42.9 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/g (or 14.3 mg P/g) of ASC, and the Sips model predicted a maximum absorption capacity at 10℃ to be 141.7 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/g (or 47.23 mg P/g), making this WTR-derived ceramsite the best performer in both Figure 1B\u0026amp;C. Adsorption experiments for kinetic analysis were conducted using three initial phosphate concentrations (i.e., 5, 30, and 50 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/L)(Figure S4A). These were very high concentrations in relation to environmental P levels. In Canada, water bodies with a total phosphorus (TP) concentration of 0.035 \u0026ndash; 0.100 mg P/L (equivalent to 0.107 \u0026ndash; 0.306 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/L) are categorized as eutrophic, and waters with [TP] \u0026gt; 0.100 mg P/L (or \u0026gt; 0.306 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/L) is hyper-eutrophic.\u003csup\u003e12\u003c/sup\u003e At 10℃, after around 11 hrs, adsorption stabilized at 0.74, 4.22, and 8.13 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/g, corresponding to a phosphate recovery rate of 97.6, 93.9, and 91.9%, respectively (Figure S4A). The kinetic and XPS analyses suggest that the phosphateadsorption onto ASC was primarily driven by strong chemical adsorption between surface active sites (e.g., Al\u003csup\u003e3+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e) and functional groups (SI Text S6).\u003csup\u003e8, 13\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eOn the other hand, the surface of ASC was among the least active, as indicated by the ratio of phosphate adsorption capacity (either experimentally determined or model-predicted) and SSA in Figure 1D. We anticipate that our ASC can be further enhanced by increasing the density of active sites on the surface. XRD analysis (Figure S2D) showed that the main crystalline phases of ASC were quartz (SiO\u003csub\u003e2\u003c/sub\u003e), muscovite (KAl\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e3\u003c/sub\u003eAlO\u003csub\u003e10\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e), albite (NaAlSi\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e), sanidine (KAlSi\u003csub\u003e3\u003c/sub\u003eAlO\u003csub\u003e8\u003c/sub\u003e), and a small amount of calcite (CaCO\u003csub\u003e3\u003c/sub\u003e), which help explain the good phosphate adsorption by ASC and implicate possible opportunities to improve it. A few strategies can be explored: 1) adjust the fabrication conditions, 2) add certain auxiliary materials (e.g., eggshell) to the recipe, or 3) modify the surface after sintering by incorporating lanthanum, iron, or other hard acid metals.\u003csup\u003e4, 14, 15\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eRegardless of future improvement, the high phosphate adsorption capacity achieved in this study inspires us to envision ASC\u0026rsquo;s potential application for remediating eutrophic waterbodies, such as agricultural ponds for livestock (dugouts) and stormwater ponds. For a small dugout with a volume of one million Imperial gallons (4.5 million litres), which is typical in Western Canada,16, 17 if the phosphate concentration is 0.1 mg P/L (highly eutrophic12), merely 10 kg of ASC will be needed to recover the phosphorus from the polluted water. For an extremely large dugout of 30 million litres of water,17 63 kg of ASC will be enough. Each tonne of ASC will be able to recover 141.6 kg of phosphate. If we are conservative and use the phosphate adsorption capacity of 14.3 mg P/g achieved in our experiments, the 4.5-million-litre and 30-million-litre dugouts will require 32 and 210 kg of ASC, respectively. But real waters are complex, will this material robustly recover phosphate under the influence of various factors?\u003c/p\u003e\n\u003ch3\u003eWhat will impact phosphate adsorption onto ASC?\u003c/h3\u003e\n\u003cp\u003eWe examined several factors that may influence phosphate adsorption onto ASC, which were ASC dosage, pH, temperature, co-existing anions and NOM, and regeneration cycles.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of ASC dosage\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe effect of adsorbent dosage on phosphate adsorption was evaluated (Fig.\u0026nbsp;2A). With the adsorbent dosage increased from 2 to 10 g/L, the removal significantly increased from ~\u0026thinsp;78 to 100%, obviously owing to the increased total surface area and the number of adsorption sites. However, the equilibrium adsorption capacity decreased from 3.68 to 0.91 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e/g as the dosage increased, suggesting abundant, unoccupied sites. The phosphate removal exceeded 95% with an ASC dosage of 6 g/L, while a further increase in adsorbent dosage provided marginal improvement. Hence, an ASC dosage of 6 g/L was selected for subsequent experiments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of pH\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003epH affects the speciation of the adsorbate in this study (Figure S6), which, in turn, may affect the adsorption efficiency. We studied the adsorption of (total) phosphate (the sum of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, H\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, HPO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e, and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e) by ASC over a wide range of pH (3.0\u0026ndash;11.0)(Fig.\u0026nbsp;2B). In this pH range, H\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e and HPO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e are the main species (Figure S6).\u003csup\u003e18\u003c/sup\u003e pH influences the surface charge of the adsorbent, which further influences phosphate adsorption. The pH\u003csub\u003epzc\u003c/sub\u003e of ASC was close to 8.2 (Figure S2C), indicating that the adsorbent surface was positively charged at pH\u0026thinsp;\u0026lt;\u0026thinsp;8.2. Figure 2B indicates stable, excellent phosphate adsorption (94.9\u0026ndash;97.0%) across all tested pH levels at low phosphate levels (10 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e/L). It follows that at pH\u0026thinsp;\u0026lt;\u0026thinsp;pH\u003csub\u003epzc\u003c/sub\u003e, the ceramsite surface underwent protonation, allowing for electrostatic attraction between the positively charged ceramsite surface and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e. The nonetheless high phosphate adsorption (94.9%) by ASC at pH\u0026thinsp;=\u0026thinsp;11.0 was due to the stronger affinity between phosphate ions and di-/tri-valent metals on ASC surface. Compared with OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions, PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e ions have a higher charge density and smaller ionic radius. The same reason allowed phosphate ions to replace the alkaline species (e.g., OH\u003csup\u003e\u0026minus;\u003c/sup\u003e) that had been initially bound to the di-/trivalent metals of the pristine ceramsite surfaces.\u003csup\u003e19\u003c/sup\u003e It was this ligand exchange phenomenon that resulted in a substantial pH increase in all the systems after phosphate adsorption (Fig. 2B). In addition, other mechanisms might also play a role in phosphate adsorption onto ASC. For instance, calcite (the XRD result in Figure S2D) can adsorb phosphate. In conclusion, ASC showed near-complete phosphate adsorption across a broad pH range at a low temperature, and the effect of pH was negligible.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of temperature\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAdsorption experiments were performed with three initial phosphate concentrations (10, 50, and 100 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e/L) at three temperatures (10, 20, and 30℃)(Fig.\u0026nbsp;2C). For 10 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e/L, the effect of temperature was negligible, whereas higher temperature appeared to slightly benefit phosphate adsorption at an initial concentration of 50 and 100 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e/L. The van\u0026rsquo;t Hoff equation was used to compute Gibbs free energy change (\u0026Delta;G), enthalpy change (\u0026Delta;H), and entropy change (\u0026Delta;S) for phosphate adsorption (Fig.\u0026nbsp;2D and Table S6). As indicated by the negative values of \u0026Delta;G, the adsorption process is spontaneous and favoured at higher temperatures. The positive \u0026Delta;S values suggest a strong affinity between ASC and phosphate and an increased randomness index at the solid/liquid interface during adsorption at a higher temperature.\u003csup\u003e20\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of co-existing anions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnions in water may influence phosphate adsorption due to their competition for active sites (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA). However, the co-existing anions in our experiments only slightly impacted phosphate recovery, with an order of Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026lt; SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e \u0026lt; F\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026lt; HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e. ASC generally maintained\u0026thinsp;\u0026gt;\u0026thinsp;90% phosphate recovery in the presence of competing anions with only two exceptions (at 30 mM F\u003csup\u003e\u0026minus;\u003c/sup\u003e or HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e). In the presence of 15 mM Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e or SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e, ASC achieved 96.7 and 95.3% phosphate removal, respectively. When the concentrations of these anions were doubled (30 mM), the inhibition of phosphate adsorption increased slightly (e.g., from 4.7 to 5.7% by SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e). This confirmed the formation of inner-sphere mono-dentate or bi-dentate complexes during phosphate adsorption.\u003csup\u003e21\u003c/sup\u003e Among all the tested anions, HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e exhibited the most significant impact on phosphate adsorption by reducing it from 96.5% (at 0 mM HCO\u003csup\u003e3\u0026minus;\u003c/sup\u003e) to 90.4% (at 15 mM HCO\u003csup\u003e3\u0026minus;\u003c/sup\u003e) and further to 85.2% (at 30 mM HCO\u003csup\u003e3\u0026minus;\u003c/sup\u003e). The results were similar to those of a previous study using katoite adsorbent.\u003csup\u003e22\u003c/sup\u003e Due to the similarity of HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e and H\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, the anions are readily adsorbed via inner/outer-sphere complexation, which is crucial for understanding their competitive interaction on adsorbent surfaces.\u003csup\u003e23\u003c/sup\u003e Moreover, F\u003csup\u003e\u0026minus;\u003c/sup\u003e led to a notable decrease in phosphate removal (e.g., from 97.4% at 0 mM to 86.5% at 30 mM F\u003csup\u003e\u0026minus;\u003c/sup\u003e), which can be attributed to its strong affinity towards metal-active sites.\u003csup\u003e24\u003c/sup\u003e Metallic-modified (e.g., La\u003csup\u003e3+\u003c/sup\u003e, Al\u003csup\u003e3+\u003c/sup\u003e, and Fe\u003csup\u003e3+\u003c/sup\u003e) adsorbents are commonly inhibited by background pollutants in water despite their Lewis acid-base interaction-induced high selectivity for phosphate.\u003csup\u003e25\u003c/sup\u003e Such inhibition was also observed when natural zeolite or clay modified with calcium hydroxide was used as an adsorbent.\u003csup\u003e26\u003c/sup\u003e The slight inhibition of phosphate adsorption observed in our experiments is, therefore, not unexpected and should not be a significant deterrent for the application of ASC. Overall, ASC showed excellent phosphate selectivity by maintaining over 85% (generally over 90%) of its adsorption capacity at high concentrations of competing anions. This suggests phosphate adsorption on ASC was primarily driven by chemisorption (as presumed in Section 3.1) rather than outer-sphere complexation via electrostatic attraction. The impact of water hardness (i.e., Mg\u003csup\u003e2+\u003c/sup\u003e and Ca\u003csup\u003e2+\u003c/sup\u003e) was not investigated in the present study, which commonly promotes phosphate adsorption according to the literature.\u003csup\u003e9, 27\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of co-existing natural organic matter (NOM)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNOM may also impact phosphate adsorption in natural water systems. Contrary to expectations,\u003csup\u003e15\u003c/sup\u003e our experiments showed a negligible impact of HA (representing NOM) on phosphate adsorption (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eA), which was similar to recent studies using magnesium-stirred biochar and lanthanum-modified bio-ceramsite.\u003csup\u003e11, 28\u003c/sup\u003e In contrast, Liu, Wang, et al. \u003csup\u003e11\u003c/sup\u003e observed significantly inhibited phosphate adsorption by 50 and 100 mg/L of HA. Such high concentrations of HA, however, are less environmentally relevant. Comparative experiments indicated that phosphate interfered with HA adsorption onto ACS (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB and Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003eB). Such interference was the most significant when the HA concentration was low (1 mg/L) and became almost negligible when the latter increased to 20 mg/L. This pseudo-unilateral impact of phosphate on HA in competing for adsorption sites on ceramsite suggests that the HA adsorbed on the ceramsite offered adsorption sites for phosphate, perhaps through electrostatic attraction between amine groups of HA and phosphate ions. Considering the di- or tri-valent cations that could be released from the ceramsite, bridging and complexation could also play a role in facilitating phosphate adsorption onto HA-loaded ceramsite. Further experimental and modelling studies may help unveil the interaction between HA and phosphate on the ceramsite surface in greater detail. Regardless, ASC has shown its potential for phosphate recovery from complex water matrices under cold conditions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEffect of regeneration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTwo solutions (1.0 M NaOH or HCl) and RO water were tested to desorb phosphate from spent ASC. After desorption for 12 hrs, 94.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4% of the adsorbed phosphate was removed from ASC by 1.0 M NaOH, which was more effective than what 1.0 M HCl achieved. Therefore, NaOH was chosen as the regeneration agent.\u003csup\u003e29\u003c/sup\u003e After four cycles of reuse, the removal declined from 98.7 (pristine) to 80.6% (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eD). This decline can be attributed to multiple reasons, such as leaching loss of active elements such as Al and Ca under strongly alkaline conditions, depletion of active sites due to chemical precipitation between phosphate ions and di- or tri-valent metals on the ASC surface, or phosphate ions trapped in deep pores (which makes it hard to wash adsorbed phosphate out in the desorption process). The phosphate-rich eluent can be used to produce fertilizers such as struvite.\u003csup\u003e30\u003c/sup\u003e Further investigation is warranted to minimize the use of strong eluent and reduce contact times in regenerating spent ASC. Although our ASC exhibited good reusability, it may not need regeneration at all. Instead, the spent ceramsite can be repurposed, such as being used as a nutrient-rich landscaping mulch that is a safe, inexpensive alternative to wood chips or toxic tire shreds,\u003csup\u003e31\u003c/sup\u003e offering additional environmental and economic benefits (more discussion in Section 3.3).\u003c/p\u003e\n\u003ch3\u003ePhosphate recovery from municipal wastewater under cold conditions?\u003c/h3\u003e\n\u003cp\u003eASC was used to recover phosphate from real municipal wastewater (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eD). After the suspended solids were removed, the wastewater\u0026rsquo;s pH (7.5) and initial phosphate concentration (35.5 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e/L) were determined. Over 97.1% of phosphate and 71.2% of COD of the real wastewater were simultaneously removed by 6 g/L ASC at 10℃, resulting in a final phosphate concentration of 0.34 mg P/L (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eB and Table S8). Hence, ASC is promising for recovering phosphate from actual wastewater under cold conditions or polishing treated wastewater (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). To meet the stringent discharge limits (0.05\u0026ndash;0.3 mg P/L),\u003csup\u003e32\u003c/sup\u003e slightly increasing the adsorbent dosage or raising the operating temperature should help. This requires validation by running real water in a pilot-scale system to determine the optimal operating conditions.\u003c/p\u003e\n\u003cp\u003eTherefore, ASC can be an extraordinary adsorbent to recover phosphate from various water matrices, such as municipal wastewater, lagoons, and dugouts (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). It offers municipalities, agricultural producers, and industries an inexpensive and facile approach to tackling phosphate pollution. The spent ASC can also be a valuable product for beneficial uses. ASC enriched in phosphate can be used for landscaping or soil amendment, relocating phosphate from polluted waters to where it is desired (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Moreover, ASC can also find applications in stormwater management as a bioretention cell medium or storage medium, or in the construction industry as a lightweight aggregate. The question is -- Is this material economically affordable?\u003c/p\u003e\n\u003ch3\u003eEconomic analysis of ASC\u003c/h3\u003e\n\u003cp\u003eA preliminary cost analysis is conducted herein based on the framework described previously.\u003csup\u003e33\u003c/sup\u003e Each tonne of ASC required 15.9 tonnes of raw WTR (10wt% solids) and 0.4 tonnes of clay. The direct production cost of each tonne of ASC is broken down in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The most important cost results from the dewatering and drying process, which accounts for 82.8% of the total cost. This cost can be further reduced by using adequate freeze-thaw and air-drying. It is assumed that the other costs associated with ASC production, such as labour and equipment, are comparable to the total direct production cost,\u003csup\u003e34\u003c/sup\u003e making the total production cost for ASC CA\u003cspan\u003e$\u003c/span\u003e171.5 \u0026times; 2\u0026thinsp;=\u0026thinsp;CA\u003cspan\u003e$\u003c/span\u003e343 per tonne. Considering the service fee paid by the DWTP for sludge disposal and potential subsidies and incentives from the federal and provincial governments, the actual cost of ASC can be lower. Given that ASC can be a good material for water filtration and landscaping mulch, we collected the prices of the common materials for these purposes on the Canadian market by web searching, emailing, or calling the vendors (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). ASC is advantageous to many of these materials, including biochar, commercial ceramsite made from clay, and tire crumb. In particular, we found that natural clay-based lightweight aggregate (essentially ceramsite) is priced at ~\u0026thinsp;CA\u003cspan\u003e$\u003c/span\u003e600 per tonne. ASC will offer good profitability if priced at \u0026lt;\u0026thinsp;CA\u003cspan\u003e$\u003c/span\u003e600. Moreover, if intended as landscaping mulch or soil amendment, each tonne of ASC can be used to recover up to 141.6 kg of phosphate from eutrophic waters prior to the final use, providing additional environmental and economic benefits.\u003c/p\u003e\n\u003ch3\u003eEnvironmental and Industrial Implications\u003c/h3\u003e\n\u003cp\u003eAl-WTR-based ceramsite (ASC) is a promising adsorbent for phosphate recovery and eutrophication control. It demonstrated broad pH adaptability and strong phosphate selectivity in complex water matrices, even at low temperatures. The adsorption experiments and Sips isotherm model suggested a theoretical maximal phosphate adsorption capacity of 141.7 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/g under cold conditions. The excellent phosphate adsorption of ASC in complex waters under cold conditions has solid implications for phosphorus recovery or pollutant removal from engineered (e.g., WWTPs, stormwater ponds, and dugouts) and natural water systems (e.g., lakes). What makes this waste-derived product more appealing is that it does not need to be regenerated once saturated with non-hazardous pollutants such as phosphate and NOM. Instead, the spent ceramsite can subsequently be repurposed for other beneficial applications, such as lightweight concrete aggregate and safe, fertilizing landscaping mulch to replace tire shreds (toxic) or wood chips. Multiple sectors can be interested in this material. For instance, municipalities can incorporate ceramsite filters into their WWTP to remove nutrients, microplastics, and emerging pollutants. Furthermore, other wastes that are rich in silica (e.g., glass waste) can be used to replace the clay used in this study, further bettering the environmental and social benefits. The adsorption capability and mechanical strength of the material may also have substantial implications in other sectors, such as the energy and construction industries. More research is needed to explore such possibilities and further improve the material\u0026rsquo;s performance. This study showcases the practicality of repurposing Al-WTR for beneficial uses. It sheds light on building a circular economy in the water sector and promotes the industry\u0026rsquo;s sustainability.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch2\u003e\u003cstrong\u003eMaterials\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe Al-WTR was collected from the Buffalo Pound Water Treatment Plant (BPWTP), which uses PACl as the primary coagulant. The wastewater (primary influent) was collected from the local wastewater treatment plant (WWTP). All chemicals were purchased from either Fisher Scientific or VWR. Details are shown in Supporting Information (SI) Text S1.\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eFabrication of ceramsite\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe raw material (RM) was Al-WTR, and the auxiliary material (AM) was bentonite clay (clay). Approximately 90.8 \u0026plusmn; 1.1wt% of the raw Al-WTR was water, while the solid content had a higher volatile fraction (61.9wt% organics) than the fixed (38.1wt% inorganics). The clay ensured sufficient formation of the liquid phase and easy mouldability.\u003csup\u003e35\u003c/sup\u003e The main mineral compositions of the raw materials are in Table 2. Al-WTR and clay were dried at 105℃ for 72 hrs and then ground to pass through Mesh #100 sieves (pore size equivalent to 0.15 mm). The completely mixed raw meal was gradually poured into a granulator to prepare raw granules with particle sizes of \u0026lt; 3 mm. RO water was sprayed during the granulation process. Raw meals made with a range of Al-WTR: clay mass ratios were used. The obtained granules were then pre-dried at 105\u0026deg;C for 12 hrs before they were transferred into a muffle furnace for sintering (Figure 6).\u003c/p\u003e\n\u003cp\u003eTo efficiently improve the fabrication process, Taguchi Experimental Design method was used. The fabricating factors were Al-WTR : clay mass ratio (wt%, C\u003csub\u003e1\u003c/sub\u003e), preheating time (min, C\u003csub\u003e2\u003c/sub\u003e), preheating temperature (℃, C\u003csub\u003e3\u003c/sub\u003e), sintering time (min, C\u003csub\u003e4\u003c/sub\u003e), sintering temperature (℃, C\u003csub\u003e5\u003c/sub\u003e, between 800 and 1200℃), and heating rate (℃/min, C\u003csub\u003e6\u003c/sub\u003e). Each factor was examined at three levels, creating an L27 (6\u003csup\u003e3\u003c/sup\u003e) orthogonal design. The Brunauer-Emmett-Teller specific surface area (BET-SSA) of the ceramsite was used as the evaluation index given by its direct impact on adsorption. Minitab 20 software was used for data analyses. Details in SI Text S4. Through the Taguchi Experiments, the ceramsite with batch ID ASC#25 had the largest SSA and could be the best adsorbent among all the tested batches.\u0026nbsp;To assess the heavy metal leaching risk of ASC, leaching experiments were conducted at pH = 2.0 (Table S3). ASC met the limits specified by the US EPA.\u003csup\u003e36\u003c/sup\u003e\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eAdsorption experiments\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe ceramsite granules were first rinsed with RO water (3 \u0026ndash; 5 times) to remove impurities, followed by 20-min shaking for further purification, then dried at 105\u0026deg;C for 24 hrs before being used for adsorption. Dried ceramsite was stored in a sealed desiccator. Adsorption experiments were conducted in an incubator shaker (HNY-2102C, Honour Instrument Co., Ltd., China) at 150 \u0026plusmn; 1 rpm, and the pH of the synthetic solution was adjusted with 1.0 M HCl or NaOH solutions as appropriate.\u0026nbsp;At every predetermined time point, the suspension was collected and filtered through a pre-rinsed syringe filter (0.45-\u0026mu;m mixed cellulose esters). The total phosphate (TP) concentration was measured by a pre-calibrated spectrophotometer (HACH DR 3900), using the PhosVer\u0026reg;3 kit. Phosphate\u003csup\u003e\u0026nbsp;\u003c/sup\u003econcentrations of all suspension samples were measured in duplicates.\u0026nbsp;The detailed measurement methods of chemical oxygen demand (COD), ammonia (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e), nitrate (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e), and HA are summarized in Text S2. The adsorption of phosphate and HA onto the container walls was experimentally determined to be negligible (Figure S1).\u003c/p\u003e\n\u003cp\u003eAdsorption kinetics were studied with different initial phosphate\u003csup\u003e\u0026nbsp;\u003c/sup\u003econcentrations (i.e., 5, 30, and 50 mg/L) at 10℃ for 72 hrs (pH = 7.5 and S/L ratio = 6.0 g/L). Samples were taken at different times (0 \u0026ndash; 72 hrs) for model fitting. For the adsorption isotherms, approximately 0.18 g of the adsorbent was added into 30 mL of phosphate solution (i.e., S/L ratio = 6 g/L) with initial phosphate concentrations ranging from 5 to 900 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/L in polypropylene bottles at 10℃ and shaken at 150 rpm for 72 hrs. The pH of the solution was adjusted to 7.50 \u0026plusmn; 0.02. Four adsorption kinetics (i.e., pseudo-first order, PFO; pseudo-second-order, PSO; Elovich; and intra-particle diffusion, IPD), three adsorption isotherms (i.e., Langmuir, Freundlich, and Sips), and adsorption thermodynamics were employed. Subsequent adsorption experiments were conducted with different pH values (3.0 \u0026ndash; 11.0 with 2-unit increments), solid : liquid ratios (S/L ratio, 2.0 \u0026ndash; 10.0, 2-unit increments), temperatures (10, 20, and 30℃), contact times (0 \u0026ndash; 72 hrs), and initial concentrations of phosphate (10, 50, and 100 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/L). Additionally, the effects of coexisting anions (i.e., Cl\u003csup\u003e-\u003c/sup\u003e, F\u003csup\u003e-\u003c/sup\u003e, SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e, or HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e) and natural organic matter (NOM, i.e., humic acid, HA) on phosphate adsorption were examined. The concentrations were set at 0, 15, or 30 mM for anions and 1, 5, or 20 mg/L for HA. The details are shown in Text S3.\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eAdsorbent regeneration\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eA series of four-cycle adsorption-desorption experiments were conducted. ASC (0.18 g) was dosed into 30 mL of phosphate solution (10 mg PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e/L) for 48 hrs at pH = 7.5 and 10\u0026deg;C. For desorption, the exhausted adsorbent was regenerated using 30 mL of 1.0 M HCl or NaOH solution, followed by RO water rinsing. After regeneration, the adsorption and desorption processes were repeated under the same operating conditions.\u003c/p\u003e\n\u003ch2\u003e\u003cstrong\u003eMaterial characterization\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe ceramsite was characterized for its morphology, surface charge, crystalline composition, and phosphate adsorption. Details on BET, pH\u003csub\u003ePZC\u003c/sub\u003e, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), XPS, and scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDS) are provided in SI Text S5.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis study was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through the NSERC Discovery Grant, NSERC Alliance Grant, NSERC Alliance International Catalyst Grant, Mitacs Accelerate Grant, Canada Foundation for Innovation (CFI) - John R. Evans Leaders Fund (JELF), Prairies Economic Development Canada (PrairiesCan) Regional Innovation Ecosystems (RIE) program, Innovation Saskatchewan, and the University of Regina (UofR) Vice President Research Discretionary Funds. We thank Buffalo Pound Water Treatment Corporation (BPWTC) for their generous funding support and field support. We thank the City of Regina and EPCOR for providing us with wastewater samples for our experiments. We thank Mr. Ben Lichtenwald, the Lab Instructor in Environmental Systems Engineering, for his invaluable support during sample preparation. S. S. and J. C. would thank the Saskatchewan Innovation and Excellence Graduate Scholarship and the UofR Faculty of Graduate Studies and Research (FGSR) Graduate Teaching Assistantship Award. J. C. thanks the UofR FGSR Asia Pacific Studies Scholarship. A natural language artificial intelligence (AI) chatbot, ChatGPT (Version 4.0, OpenAI), has been used to polish the language of this paper. We also acknowledge the edits made by CRWRRL\u0026rsquo;s students Ms. Parnian Mojahednia and Ms. Lin Zhang, PDF Dr. Bin Wang, and Mr. Blair Kardash from BPWTC.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eLiu, S.; Yang, C.; Liu, W.; Yi, L.; Qin, W. A novel approach to preparing ultra-lightweight ceramsite with a large amount of fly ash. \u003cem\u003eFrontiers of environmental science \u0026amp; engineering\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e2020\u003c/strong\u003e, \u003cem\u003e14\u003c/em\u003e, 1-11.\u003c/li\u003e\n \u003cli\u003eHuang, C.; Yuan, N.; He, X.; Wang, C. Ceramsite made from drinking water treatment residue for water treatment: a critical review in association with typical ceramsite making. \u003cem\u003eJournal of Environmental Management\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e2023\u003c/strong\u003e, \u003cem\u003e328\u003c/em\u003e, 117000.\u003c/li\u003e\n \u003cli\u003eWang, H.; Xu, J.; Liu, Y.; Sheng, L. 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In \u003cem\u003eU S Environmental Protection Agency, Washington DC\u003c/em\u003e, 2004.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"eutrophication, circular economy, sludge valorization, waste valorization, water treatment, adsorbent, Sips isotherm, nutrient recovery","lastPublishedDoi":"10.21203/rs.3.rs-4558561/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4558561/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWater treatment residual (WTR) is a burden for many water treatment plants due to the large volumes and associated management costs. Here, we transform aluminum-salt WTR (Al-WTR) into ceramsite (ASC) to recover phosphate from challenging waters. ASC showed remarkably higher specific surface area (SSA, 70.53 m\u003csup\u003e2\u003c/sup\u003e/g) and phosphate adsorption capacity (calculated 47.2 mg P/g) compared with previously reported ceramsite materials (\u0026lt; 40 m\u003csup\u003e2\u003c/sup\u003e/g SSA and \u0026lt; 20 mg P/g). ASC recovered \u0026gt; 94.9% phosphate over a wide pH range (3 – 11) and generally sustained \u0026gt; 90% of its phosphate recovery at high concentrations of competing anions (i.e., Cl\u003csup\u003e-\u003c/sup\u003e, F\u003csup\u003e-\u003c/sup\u003e, SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e, or HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e) or humic acid (HA). We challenged the material with real municipal wastewater at 10℃ and achieved simultaneous phosphate (\u0026gt;97.1%) and COD removal (71.2%). Once saturated with phosphate, ASC can be repurposed for landscaping or soil amendment. Economic analysis indicates that ASC can be a competitive alternative to natural clay-based ceramsite, biochar, or other useful materials. Therefore, ASC is an eco-friendly, cost-effective adsorbent for phosphate recovery from complex waters, shedding light upon a circular economy in the water sector.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSynopsis: \u003c/strong\u003eCeramsite made from\u003cstrong\u003e \u003c/strong\u003ealuminum-salt\u003cstrong\u003e \u003c/strong\u003ewater treatment residual exhibited great capability of recovering phosphate from waters under challenging conditions.\u003c/p\u003e","manuscriptTitle":"Near-Complete Phosphorus Recovery from Challenging Water Matrices Using Multiuse Ceramsite Made from Water Treatment Residual (WTR)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-12 06:02:29","doi":"10.21203/rs.3.rs-4558561/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d80b0249-b579-41ed-8ad7-bd7eb5a46bd2","owner":[],"postedDate":"June 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":33116570,"name":"Physical sciences/Engineering/Civil engineering"},{"id":33116571,"name":"Physical sciences/Engineering/Chemical engineering"}],"tags":[],"updatedAt":"2024-08-06T17:40:14+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-12 06:02:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4558561","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4558561","identity":"rs-4558561","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}