Nitrate Chemodenitrification by Iron Sulfides to Ammonium under Mild Conditions and Transformation Mechanism.

Autotrophic denitrification utilizing iron sulfides as electron donors has been well studied, but the occurrence and mechanism of abiotic nitrate (NO3-) chemodenitrification by iron sulfides have not yet been thoroughly investigated. In this study, NO3- chemodenitrification by three types of iron sulfides (FeS, FeS2, and pyrrhotite) at pH 6.37 and ambient temperature of 30 °C was investigated. FeS chemically reduced NO3- to ammonium (NH4+), with a high reduction efficiency of 97.5% and NH4+ formation selectivity of 82.6%, but FeS2 and pyrrhotite did not reduce NO3- abiotically. Electrochemical Tafel characterization confirmed that the electron release rate from FeS was higher than that from FeS2 and pyrrhotite. Quenching experiments and density functional theory calculations further elucidated the heterogeneous chemodenitrification mechanism of NO3- by FeS. Fe(II) on the FeS surface was the primary site for NO3- reduction. FeS possessing sulfur vacancies can selectively adsorb oxygen atoms from NO3- and water molecules and promote water dissociation to form adsorbed hydrogen, thereby forming NH4+. Collectively, these findings suggest that the NO3- chemodenitrification by iron sulfides cannot be ignored, which has great implications for the nitrogen, sulfur, and iron cycles in soil and water ecosystems.

Enhancing Roxarsone Degradation and In Situ Arsenic Immobilization Using a Sulfate-Mediated Bioelectrochemical System.

Roxarsone (ROX) is widely used in animal farms, thereby producing organoarsenic-bearing manure/wastewater. ROX cannot be completely degraded and nor can its arsenical metabolites be effectively immobilized during anaerobic digestion, potentially causing arsenic contamination upon discharge to the environment. Herein, we designed and tested a sulfate-mediated bioelectrochemical system (BES) to enhance ROX degradation and in situ immobilization of the released inorganic arsenic. Using our BES (0.5 V voltage and 350 µM sulfate), ROX and its metabolite, 4-hydroxy-3-amino-phenylarsonic acid (HAPA), were completely degraded within 13-22 days. In contrast, the degradation efficiency of ROX and HAPA was <85% during 32-day anaerobic digestion. In a sulfate-mediated BES, 75.0-83.2% of the total arsenic was immobilized in the sludge, significantly more compared to the anaerobic digestion (34.1-57.3%). Our results demonstrate that the combination of sulfate amendment and voltage application exerted a synergetic effect on enhancing HAPA degradation and sulfide-driven arsenic precipitation. This finding was further verified using real swine wastewater. A double-cell BES experiment indicated that As(V) and sulfate were transported from the anode to the cathode chamber and coprecipitated as crystalline alacranite in the cathode chamber. These findings suggest that the sulfate-mediated BES is a promising technique for enhanced arsenic decontamination of organoarsenic-bearing manure/wastewater.

Effects of Sludge Retention Time on the Performance of Anaerobic Ceramic Membrane Bioreactor Treating High-Strength Phenol Wastewater.

Anaerobic ceramic membrane bioreactor (AnCMBR) is an attractive alternative for the treatment of high-strength phenol wastewater, but the effects of sludge retention time (SRT) on the performance and membrane fouling are still unclear. The results indicated that the AnCMBR was successfully employed to treat high-strength wastewater containing 5 g phenol L-1. The removal efficiencies of phenol and chemical oxygen demand (COD) reached over 99.5% and 99%, respectively, with long SRT and short SRT. SRT had no obvious effect on the performance of the AnCMBR treating high-strength phenol wastewater with long time operation. The strong performance robustness of AnCMBR benefited from the enrichment of hydrogenotrophic methanogens and syntrophic phenol-degrading bacteria. However, the decline of SRT led to a more severe membrane fouling in the AnCMBR, which was caused by the small size of sludge flocs and high concentration of protein in the biopolymers. Therefore, this work presented a comprehensive insight to the feasibility and robustness of the AnCMBR for treating high-strength phenol wastewater.

Effects of loading rate and aeration on nitrogen removal and N2O emissions in intermittently aerated sequencing batch reactors treating slaughterhouse wastewater at 11 °C.

This study aimed to find optimal operation conditions for nitrogen removal from high strength slaughterhouse wastewater at 11 °C using the intermittently aerated sequencing batch reactors (IASBRs) so as to provide an engineering control strategy for the IASBR technology. Two operational parameters were examined: (1) loading rates and (2) aeration rates. Both the two parameters affected variation of DO concentrations in the IASBR operation cycles. It was found that to achieve efficient nitrogen removal via partial nitrification-denitrification (PND), "DO elbow" point must appear at the end of the last aeration period. There was a correlation between the ammonium oxidizing bacteria (AOB)/nitrite oxidizing bacteria (NOB) ratio and the average DO concentrations in the last aeration periods; when the average DO concentrations in the last aeration periods were lower than 4.86 mg/L, AOB became the dominant nitrifier population, which benefited nitrogen removal via PND. Both the nitrogen loading rate and the aeration rate influenced the population sizes of AOB and NOB. To accomplish efficient nitrogen removal via PND, the optimum aeration rate (A, L air/min) applied can be predicted according to the average organic loading rates based on mathematical equations developed in this study. The research shows that the amount of N2O generation in the aeration period was reduced with increasing the aeration rate; however, the highest N2O generation in the non-aeration period was observed at the optimum aeration rates.

Electrochemical stimulation of microbial roxarsone degradation under anaerobic conditions.

Roxarsone (4-hydroxy-3-nitrophenylarsonic acid) has been commonly used in animal feed as an organoarsenic additive, most of which is excreted in manure. Roxarsone is easily biodegraded to 4-hydroxy-3-aminophenylarsonic acid (HAPA) under anaerobic conditions, but HAPA persists for long periods in the environment, increasing the risk of arsenic contamination through diffusion. We investigated the electrochemical stimulation of the microbial degradation of roxarsone under anaerobic conditions. After the carbon sources in the substrate were depleted, HAPA was slowly degraded to form arsenite under anaerobic conditions. The degradation rate of HAPA was significantly increased when 0.5 V was applied without adding a carbon source. The two-cell membrane reactor assays reveal that the HAPA was degraded in the anode chambers, confirming that the anode enhanced the electron transfer process by acting as an electron acceptor. The degradation product formed with electrochemical stimulation was arsenate, which facilitates the removal of arsenic from wastewater. Based on the high performance liquid chromatography-ultraviolet-hydride generation-atomic fluorescence spectrometry (HPLC-UV-HG-AFS) and gas chromatography-mass spectrometry (GC-MS) data, the pathway for the biodegradation of roxarsone and the mechanisms for the electrochemically stimulated degradation are proposed. This method provides a potential solution for the removal of arsenic from organoarsenic-contaminated wastewater.

Resource availability shapes microbial motility and mediates early-stage formation of microbial clusters in biological wastewater treatment processes.

Microbial cluster functions as a key unit in biological wastewater treatment. Mechanistic understanding of early-stage microbial clustering, including kinetics of microbial cluster formation and the driving forces, remains largely unclear. We report an experimental observation of resource availability, in terms of dissolved oxygen, carbon, and nitrogen sources, mediating early-stage formation of microbial clusters. We proposed a simple model for quantifying the role of microbial motility mediated by resources availability in early-stage microbial clustering processes. Simulation results reflected that limited resource availability promotes early-stage microbial cluster formation through enhanced microbial motility essential for sufficient foraging. The results indicate that microorganisms prefer a relative clustering growth pattern to disperse mode in resource-limited environment for survival. It provides new insights on early-stage microbial cluster formation and its dynamics that may improve future design and operations in biological wastewater treatment.

Controlling carbon dioxide-to-hydrogen ratio to improve hydrogen utilization and denitrification rates of hydrogenotrophic autotrophic denitrification through homoacetogenesis-heterotrophic denitrification pathway.

Hydrogenotrophic denitrification, an environment-friendly process for organic-free influents, is limited due to poor hydrogen mass transfer efficiency and significant pH fluctuations. In this study, we manipulated the carbon dioxide-to-hydrogen ratio to improve hydrogenotrophic denitrification. When carbon dioxide-to-hydrogen ratio was 1:1 (carbon dioxide, 200 ml: hydrogen, 200 ml), the hydrogen utilization and denitrification rates were 2.4 times and 3.0 times that when carbon dioxide-to-hydrogen ratio was 0:1 (carbon dioxide, 0 ml: hydrogen, 200 ml), respectively. The pH fluctuation decreased from 3.1±0.3 to 0.2±0.1. Furthermore, the hydrogenotrophic denitrification, acetoclastic denitrification, homoacetogenic, and electron transfer activities of the sludge were improved. A high carbon dioxide-to-hydrogen ratio augmented the acid-producing and heterotrophic denitrifying microorganism populations. By maintaining a high carbon dioxide-to-hydrogen ratio, the dominant hydrogenotrophic autotrophic denitrification pathway was transformed into a homoacetogenesis-heterotrophic denitrification pathway, thereby achieving higher hydrogen utilization and denitrification rates.

Integration of anaerobic digestion and electrodialysis for methane yield promotion and in-situ ammonium recovery.

Ammonia inhibition is a common issue encountered in anaerobic digestion (AD) when treating nitrogen-rich substrates. This study proposed a novel approach, the electrodialysis-integrated AD (ADED) system, for in-situ recovery of ammonium (NH4+) while simultaneously enhancing AD performance. The ADED reactor was operated at two different NH4+-N concentrations (5,000 mg/L and 10,000 mg/L) to evaluate its performance against a conventional AD reactor. The results indicate that the ADED technology effectively reduced the NH4+-N concentration to below 2,000 mg/L, achieving this with a competitive energy consumption. Moreover, the ADED reactor demonstrated a 1.43-fold improvement in methane production when the influent NH4+-N was 5,000 mg/L, and it effectively prevented complete inhibition of methane production at the influent NH4+-N of 10,000 mg/L. The life cycle impact assessment reveals that ADED technology offers a more environmentally friendly alternative by recovering valuable fertilizer from the AD system.

Unacclimated activated sludge improved nitrate reduction and N2 selectivity in iron filling/biochar systems.

Iron (Fe)-based denitrification is a proven technology for removing nitrate from water, yet challenges such as limited pH preference range and low N2 selectivity (reduction of nitrate to N2) persist. Adding biochar (BC) can improve the pH preference range but not N2 selectivity. This study aimed to improve nitrate reduction and N2 selectivity in iron filling/biochar (Fe/BC) systems with a simplified approach by coupling unacclimated microbes (M) in the system. Factors such as initial pH, Fe/BC ratio, and Fe/BC dosage on nitrate removal efficiency and N2 selectivity were evaluated. Results show that the introduction of microbes significantly enhanced nitrate removal and N2 selectivity, achieving 100 % nitrate removal and 79 % N2 selectivity. The Fe/BC/M system exhibited efficient nitrate reduction at pH of 2-10. Moreover, the Fe/BC/M system demonstrated an improved electrochemical active surface area (ECSA), lower electron transfer resistance and lower corrosion potential, leading to enhanced nitrate reduction. The high i0 value in Fe/BC/M system means more Hads could be generated, thus improving the N2 selectivity. This study provides valuable insights into a novel approach for effective nitrate removal, offering a potential solution to the environmental challenges posed by excessive nitrate in wastewater, surface water and ground water.

Assessment of nitrogen and phosphorus removal in an intermittently aerated sequencing batch reactor (IASBR) and a sequencing batch reactor (SBR).

Biological nitrogen and phosphorus removal was investigated in an intermittently aerated sequencing batch reactor (IASBR) and a sequencing batch reactor (SBR). The removal efficiencies of ammonium-nitrogen (NH4(+)-N) were 100% in both reactors in steady operation state. The total nitrogen (TN) removal efficiencies were 90.4% in the IASBR and 79.3% in the SBR, while the total phosphorus (TP) removal efficiencies were 88.8% in the IASBR and 82.3% in the SBR. The efficiencies of simultaneous nitrification and denitrification (SND) were 90.4% in the IASBR and 79.3% in the SBR, indicating that the IASBR was more efficient than the SBR in SND. The sludge in the IASBR had a P release capability of 16.6 mg P/g VSS (volatile suspended solids) but only 7.5 mg P/g VSS in the SBR.

Adsorption removal of tetracycline from aqueous solution by anaerobic granular sludge: equilibrium and kinetic studies.

High concentration animal wastewater is often contaminated by tetracycline and an upflow anaerobic sludge bioreactor (UASB) with granular sludge is often used to treat the wastewater. The investigation of the adsorption process of tetracycline on anaerobic granular sludge during anaerobic digestion of animal wastewater will increase the understanding of antibiotics behavior in the UASB reactor. In this study, the effects of initial pH, humic acid concentration, and temperature on the removal of tetracycline by anaerobic granular sludge from aqueous solution were investigated using the batch adsorption technique in 100 mL flasks with 75 mL of work volume. The results show that the highest removal efficiency of 93.0% was achieved around pH 3.0 and the removal efficiency at the neutral pH range (pH 6.0-8.0) is about 91.5%. The thermodynamic analysis indicates that the adsorption is a spontaneous and endothermic process. The adsorption kinetics followed the pseudo-second-order equation. The adsorption isotherms analysis indicates that the Langmuir model is better than the Freundlich model for the description of the adsorption process and confirms the result of thermodynamics analysis. The maximum adsorption capacities were 2.984, 4.108 and 4.618 mg/g at 25, 35 and 45 °C, respectively. These results provide useful information for understanding the fate and transformation of tetracycline in a UASB digestion system and improving the management of tetracycline contaminated animal wastewater.

Nutrient removal from separated pig manure digestate liquid using hybrid biofilters.

In this study, laboratory-scale hybrid biofilters were set up to treat the separated pig manure digestate liquid at two loading rates of 0.12 and 0.07 kg N m(-3) per day. The hybrid biofilters were operated with a sequencing batch reactor mode. Over the operation of 136 days, 84% and 88% of total nitrogen was removed on average in addition with complete nitrification at the high loading rate and low loading rate, respectively. In the anoxic phase, the nitrate reduction rates were 0.31 and 0.24 mg L(-1) min(-1); and in the aerobic phase, nitrification rates were 0.29 and 0.18 mg L(-1) min(-1) at the high loading rate and low loading rate, respectively. It was found that in the hybrid biofilters, biofilm biomass had much higher nitrification and denitrification activities than suspended growth biomass. Phosphorus removals achieved were up to 88%. The results show the hybrid biofilter technology is valid for high nutrient pig manure digestate liquid treatment.

Performance of anaerobic digestion of phenol using exogenous hydrogen and granular activated carbon and analysis of microbial community.

Anaerobic conversion rate of phenol to methane was low due to its biological toxicity. In this study, the coupling of granular activated carbon (GAC) and exogenous hydrogen (EH) could enhance greatly methane production of phenol anaerobic digestion, and the metagenomic was firstly used to analyze its potential mechanism. The results indicated that a mass of syntrophic acetate-oxidizing bacteria and hydrogen-utilizing methanogens were enriched on the GAC surface, and SAO-HM pathway has become the dominant pathway. The energy transfer analysis implied that the abundance of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NADH) oxidase increased. Furthermore, direct interspecies electron transfer (DIET) was formed by promoting type IV e-pili between Methanobacterium and Syntrophus, thereby improving the interspecies electron transfer efficiency. The dominant SAO-HM pathway was induced and DIET was formed, which was the internal mechanism of the coupling of GAC and EH to enhance anaerobic biotransformation of phenol.

Mechanism insights into enhanced treatment of wasted activated sludge by hydrogen-mediated anaerobic digestion.

In the current study, different forms of added gas including H2, CO2, and mixed gas (VH2:VCO2 = 4:1), as well as different hydrogen partial pressures (0.10, 0.30, and 0.50 atm) were investigated for the influence on anaerobic performance in waste activated sludge (WAS) treatment. The mixed gas significantly improved methane production by over 20%, which positively correlated with the hydrogen partial pressure. However, pure H2 (0.5 atm) heavily inhibited methane production by 76.5%. Combined with the microbial metabolic activity study, H2 accelerated the hydrolysis process. Afterward, mixing with CO2 accelerated H2 and organic consumption, thus promoting WAS degradation and methane production. Based on the most extra release of organics, the mixed group exerted the superior performance with hydrogen partial pressure at 0.3 atm. The microbial community analysis evidenced that mixed gas enriched proteolytic and homoacetogenic bacteria and hybrid-trophic methanogens. By metagenomics study, hydrolysis, acetogenic, and methanogenesis pathways were all enhanced via the exogenous addition of H2 and CO2, sustainably transforming WAS towards CH4. This study discovered the mechanism of the enhanced conversion from WAS to CH4 by exogenous H2 and provided a promising approach for WAS reduction and energy recovery.

Ca(ClO)2 pretreatment enhancing suspended solids removal through flocculation from digested dairy wastewater and its mechanisms.

Intensive animal farming produces large volume of digested liquid, and overdose application often causes the pollution of surface water and groundwater. Therefore, post-treatment is very necessary for the discharging of surplus digested liquid, but the removal of high concentrations of suspended solids (SS) in the digested liquid is a challenge. In this study, the effect of Ca(ClO)2 pretreatment on SS flocculation removal of digested dairy wastewater was investigated. The results showed that, without Ca(ClO)2 pretreatment, the flocculation by polyacrylamide (PAM), polyferric sulfate (PFS) or polymeric aluminum chloride (PAC) only removed 42.6 %-50.4 % SS from anaerobic digested liquid. With the combination of Ca(ClO)2 pretreatment and PAC flocculation together, the SS removal efficiency can reach 80 %. The total chemical oxygen demand (TCOD) removal had a similar trend with SS removal, but soluble chemical oxygen demand (SCOD) removal was less affected by the pretreatment and flocculation. More than 75 % of orthophosphate (SRP) and total soluble phosphorus (TSP) was removed after Ca(ClO)2 pretreatment and flocculation with PFS or PAC. Ca(ClO)2 pretreatment also effectively inactivated fecal bacteria. The mechanisms of Ca(ClO)2 pretreatment enhancing SS flocculation removal were further elucidated. The SS removal was the action of ClO- and Ca2+ together. The function of ClO- was to break down suspended particles, change the surface, and decrease the absolute Zeta potential, while the function of Ca2+ was to form precipitation. This result indicates that Ca(ClO)2 pretreatment can effectively enhance the SS flocculation removal of anaerobic digested liquid.

Repurposing of spent lithium-ion battery separator as a green reductant for efficiently refining the cathode metals.

Developing green and high-efficient pyrometallurgy processes to recycle precious metals from spent lithium-ion batteries (LIBs) is of great importance for resource sustainability and environmental protection. Herein, a novel reduction roasting approach relying on spent LIB separator to refine the spent cathode is proposed. The efficiency of repurposing separator as a reductant for roasting the spent LiCoO2 cathode and the underlying mechanisms were investigated. After the separator-mediated roasting at 500 °C for 2 h, Li+ leaching efficiency of the cathode reached 93.2 %, >2.6 times higher than those after roasting without reductant (25.2 %) or with benchmark reductant graphite (26.1 %). Under the separator-added roasting condition, the cathode was converted to the desired products, CoO and Li2CO3. Based on the analysis of in-situ reaction using thermogravimetric/differential scanning calorimetry and pyrolysis gas species identification, the separator-mediated reduction roasting of cathode was composed of two stages, i.e., reducing gas generation due to separator pyrolysis, followed by the reducing gas mediated LiCoO2 reduction. During the process, the generated C2H4 and CO dominated the reduction. The use of co-existing separator to recover precious metals from spent LIBs is an effective and sustainable strategy to maximize the utilization of spent LIBs.

Modification of fluorescence staining method for small-sized microplastic quantification: Focus on the interference exclusion and exposure time optimization.

Microplastics are an emerging pollutant of global concern, and fluorescence staining as an efficient method for small-sized microplastic qualification often undergoes the serious interference from external environments. The key steps affecting the accuracy of fluorescent staining and the corresponding quality assurance measures were rarely known. Therefore, this study took the Nile Red/DAPI co-staining method as an example to explore the key factors affecting its accuracy and effective measures to avoid interference. High background microplastic contamination in typical lab waters (up to 1115 MP/L), glass fiber filter membrane and glassware were identified as dominant factors affecting microplastic quantification. The background microplastics in lab waters mainly originated from the process of water production and storage. A simple filtration process removed 99% of the background microplastic in the lab waters. After burning at 500 °C for 1 h, the microplastic contamination in the filter membrane and glassware was completely eliminated. H2O2 pretreatment and exposure time caused erroneous microplastic size assessment, and were suggested to be set at 48 h and 10 ms, respectively. During the extraction process, the residue in beakers reached ~ 20% and > 50% for 5 µm and 20 µm sized microplastics, respectively, greatly contributing to the microplastic loss. The comprehensive modified measures caused microplastic concentrations in the three typical samples detected by Nile Red/DAPI co-staining method to decrease by 65.7 - 92.2% and to approach the micro-Raman results. This study clarified the reasons for interfering with quantitative microplastics by fluorescent staining and the effective measures to avoid interference, which were conducive to improving the accuracy of quantitative methods of microplastics.

Modification of TiO2 by Er3+ and rGO enhancing visible photocatalytic degradation of arsanilic acid.

As a typical wide band gap photocatalyst, titania (TiO2) cannot use the visible light and has fast recombination rate of photogenerated electron-hole pairs. Simultaneous introduction of erbium ion (Er3+) and graphene oxide (rGO) into TiO2 might overcome these two drawbacks. In this study, Er3+ and rGO were co-doped on TiO2 to synthesize Er3+-rGO/TiO2 photocatalyst through a two-step sol-gel method. Based on the UV-visible diffuse reflectance spectra and photoluminescence spectrum, the introduction of Er3+ and rGO increased the visible light absorption efficiency and enhanced the migration of photogenerated electron. Pure TiO2 has almost no photocatalytic activity for arsanilic acid (p-ASA) degradation under visible light irradiation. However, while doping with 2.0 mol% Er3+ and 10.0 mol% rGO, the p-ASA could be completely degraded within 50 min by the Er3+-rGO/TiO2 photocatalyst under visible light irradiation, and most of produced inorganic arsenic was in situ removed by adsorption from the solution. The reactive oxygen species (ROS) reacting with p-ASA was determined and superoxide radical (O2•-) and singlet oxygen (1O2) were the dominant ROS for the oxidation of p-ASA and arsenite. This work provides an approach of introducing Er3+ and rGO to enhance the visible light photocatalytic efficiency of TiO2.

Role of suspended solids on the co-precipitation of pathogenic indicators and antibiotic resistance genes with struvite from digested swine wastewater.

Struvite recovered from wastewater contains high concentration of fecal indicator bacteria (FIB), porcine adenoviruses (PAdV) and antibiotic resistance genes (ARGs), becoming potential resources of these microbial hazards. Understanding the precipitation behavior of pathogenic indicators and ARGs with suspended solids (SS) will provide the possible strategy for the control of co-precipitation. In this study, SS was divided into high-density SS (separated by centrifugation) and low-density SS (further separated by filtration), and the role of SS on the co-precipitation of FIB, PAdV and ARGs was investigated. The distribution analysis showed that 35.5-73.0% FIB, 79.6% PAdV and 64.5-94.8% ARGs existed in high-density SS, while the corresponding values were 26.9-64.4%, 11.7% and 3.5-24.3% in low-density SS. During struvite generation, 82.7-96.9% FIB, 75.5% PAdV and 56.3-86.5% ARGs were co-precipitated into struvite. High-density SS contributed 20.7-68.5% FIB, 63.9% PAdV and 38.7-87.2% ARGs co-precipitation, and the corresponding contribution of low-density SS was 31.4-79.2%, 3.9% and 6.2-54.7%. Moreover, the precipitated SS in struvite obviously decreased inactivation efficiency of FIB and ARGs in drying process. These results provide a potential way to control the co-precipitation and inactivation of FIB, PAdV and ARGs in struvite through removing high-density SS prior to struvite recovery.

Co-precipitation of heavy metals with struvite from digested swine wastewater: Role of suspended solids.

Struvite production can recover ammonia and phosphorous from digested wastewater as fertilizer. During struvite generation, most of the heavy metals was co-precipitated with ammonia and phosphorous into struvite. Understanding the precipitation behavior of heavy metals with suspended solids (SS) might provide the possible strategy for the control of co-precipitation. In this study, the distribution of heavy metals in SS and their role on the co-precipitation during struvite recovery from digested swine wastewater were investigated. The results showed that the concentration of heavy metal (including Mn, Zn, Cu, Ni, Cr, Pb and As) ranged from 0.05 to 17.05 mg/L in the digested swine wastewater. The distribution analysis showed that SS with particles > 50 µm harbored most of individual heavy metal (41.3-55.6%), followed by particles 0.45-50 µm (20.9-43.3%), and SS-removed filtrate (5.2-32.9%). During struvite generation, 56.9-80.3% of individual heavy metal was co-precipitated into struvite. The contributions of SS with particles > 50 µm, 0.45-50 µm, and SS-removed filtrate on the individual heavy metal co-precipitation were 40.9-64.3%, 25.3-48.3% and 1.9-22.9%, respectively. These finding provides potential way for controlling the co-precipitation of heavy metals in struvite.