Key Takeaways & Executive Findings
- •• • ZnCl₂ modification of biogas residue biochar increased specific surface area, adsorption capacity, capacitance, and conductivity, leading to superior electrochemical performance compared to unmodified biochar. • • In simulated digestate, FCDI with 7.5% modified biochar achieved 47.7% NH₄⁺-N and 55.2% RP removal over 12 h, demonstrating effective nutrient recovery potential. • • In actual anaerobic digestion filtrate, maximum removals were 32.2% for NH₄⁺-N and 26.2% for RP, indicating a 15.5% and 29.0% reduction compared to simulated conditions due to membrane fouling. • • Membrane fouling by peptides and amino acids in real digestate increased membrane resistance and blocked ion transport, underscoring the need for anti-fouling strategies in FCDI scale-up.
Abstract
The digestate from anaerobic digestion of food waste is separated into solid residue and liquid filtrate. The filtrate retains high nutrient and carbon content, making it a viable resource for recovery. This study prepared biochar from food waste digestate residue and employed it as an electrode active material in a flow-electrode capacitive deionization (FCDI) system, with activated carbon as a control, to assess nitrogen and phosphorus removal from kitchen waste biogas slurry. ZnCl₂ modification significantly enhanced the biochar's specific surface area, adsorption capacity, capacitance, and conductivity. The optimal mass fraction of modified biochar in the electrode liquid was 7.5%. In simulated digestate, the FCDI system achieved removal efficiencies of 47.7% for NH₄⁺-N and 55.2% for reactive phosphorus (RP) over 12 hours. Performance ranking of electrode materials was activated carbon > ZnCl₂-modified biochar > unmodified biochar. In continuous operation with actual anaerobic digestion filtrate, maximum removal efficiencies were 32.2% for NH₄⁺-N and 26.2% for RP. The reduced performance in real digestate is attributed to organic foulants such as peptides and amino acids, which block ion-exchange membrane channels, increase membrane resistance, and impede ion transfer and charge transport, thereby diminishing deionization efficiency.
1. Introduction
Kitchen waste generation in China is projected to reach 170 million tons by 2025, posing significant environmental and public health risks if improperly managed. Anaerobic digestion is a preferred treatment due to its resource recovery and low energy footprint, yet the resulting biogas slurry contains high concentrations of ammonia nitrogen, phosphate, and organic matter, necessitating effective nutrient removal before discharge. Conventional biological processes such as SBR, A²/O, MBR, and anammox suffer from long process chains, high operational costs, and secondary pollution, while often failing to meet stringent discharge standards.
Flow-electrode capacitive deionization (FCDI) has emerged as a promising alternative for nutrient recovery, but its performance is hindered by electrode material limitations and membrane fouling. This study addresses these bottlenecks by employing ZnCl₂-modified biogas residue biochar as a low-cost, high-performance electrode material. The modification enhances surface area and electrochemical properties, improving nitrogen and phosphorus removal. However, real digestate introduces organic foulants that compromise membrane integrity, highlighting the need for robust anti-fouling strategies. This research provides critical performance data and identifies future directions for biochar modification and membrane development in FCDI systems.
Loading authentic research manuscript (Pages 1–5)...
SUN Huimin, WU Yubiao, HUANG Shengjie, ZHANG Xuedong (2026). Nitrogen and phosphorus removal from kitchen waste biogas slurry by ZnCl₂-modified biogas residue biochar in FCDI. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202605021
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the optimal mass fraction of ZnCl₂-modified biochar in the electrode liquid, and how does it affect FCDI performance?
The optimal mass fraction was determined to be 7.5%. At this concentration, the FCDI system achieved 47.7% NH₄⁺-N and 55.2% RP removal in simulated digestate over 12 hours. Lower fractions likely reduce active sites, while higher fractions may increase viscosity and hinder ion transport.
How does the performance of ZnCl₂-modified biochar compare to activated carbon and unmodified biochar in FCDI?
Activated carbon exhibited the highest ion separation performance, followed by ZnCl₂-modified biochar, with unmodified biochar showing the lowest. Specifically, modified biochar achieved 47.7% NH₄⁺-N and 55.2% RP removal, whereas unmodified biochar performed significantly worse, indicating that ZnCl₂ modification enhances electrochemical properties but does not surpass activated carbon.
What are the main causes of reduced nitrogen and phosphorus removal in actual digestate compared to simulated conditions?
The presence of organic foulants such as peptides and amino acids in actual digestate leads to membrane fouling. These foulants block ion-exchange membrane channels and increase membrane resistance, which impedes ion transfer and charge transport, thereby reducing the deionization performance. This resulted in lower maximum removal efficiencies of 32.2% for NH₄⁺-N and 26.2% for RP.
What are the implications of membrane fouling for the scalability of FCDI systems treating real wastewater?
Membrane fouling is a critical bottleneck for industrial application. The study indicates that fouling reduces nutrient removal efficiency by up to 29% for RP. To scale up, anti-fouling strategies such as periodic cleaning, membrane surface modification, or pre-treatment of digestate to remove organic foulants are necessary to maintain long-term performance and economic viability.
What future research directions are suggested by this study for improving FCDI performance?
The study highlights the need for further investigation into the stability of modified biochar in flow electrodes and the development of anti-fouling anion-exchange membranes. Additionally, optimizing biochar modification methods and exploring alternative low-cost materials could enhance nutrient recovery efficiency and reduce operational costs for pilot-scale and full-scale applications.
Related Chinese Research & Cross-Citations
Synergistic Regulation by Long- and Short-Chain Quorum Sensing Signaling Molecules Enhances Sulfamethoxazole Metabolism in Electroactive Biofilms within a Microbial Electrolysis Cell Coupled Anaerobic Digestion System
High-strength sulfamethoxazole (SMX) wastewater severely inhibits anaerobic microorganisms, reducing organic degradation and methane yield. This study investigated the effects of short-chain (C6-HSL) and long-chain (C12-HSL) N-acyl-homoserine lactone (AHL) signaling molecules, individually and in combination, on the construction, performance, and antibiotic resistance gene (ARG) profiles of anaerobic electroactive biofilms within a microbial electrolysis cell coupled anaerobic digestion (MEC-AD) system. Compared to the control (no AHLs), SMX removal efficiency increased by 9.26%, 7.44%, and 10.67% for C6-HSL (T1), C12-HSL (T2), and combined (T3) treatments, respectively. Methane production rates rose by 20.4%, 16.9%, and 23.1% for T1, T2, and T3, respectively. AHLs promoted extracellular polymeric substance secretion, enhancing electroactive microbe attachment to the anode. Microbial community analysis revealed increased diversity and modulated key functional genera. Notably, Georgenia abundance increased by 16.77% (T1) and 36.47% (T3) but decreased by 15.99% (T2). ARG analysis showed that single AHLs elevated intI1, sul1, and sul2 abundances, whereas combined AHLs (T3) exhibited a milder response, with sul2 abundance reduced by 4.92% relative to control. This suggests synergistic AHLs suppress ARG host proliferation. This study first demonstrates that combined short- and long-chain AHLs enhance electroactive biofilm formation, maintain microbial community stability, and modulate ARG dissemination risk, offering a quorum sensing-based strategy for antibiotic wastewater treatment and risk management.
Preparation of Solid-Phase Carbon Sources with Different Ratios and Their Carbon Release Properties
Low C/N ratios in wastewater treatment plant effluent necessitate external carbon sources for denitrification, but conventional liquid carbon sources are costly and unstable. This study prepared nine composite solid-phase carbon sources by combining PHBV with natural cellulose materials (straw, sawdust, corncob) at different mass ratios. Dynamic release experiments, DOC analysis, UV-Vis spectroscopy, and EEM fluorescence were employed to characterize carbon release. Results showed that increasing cellulose proportion in corncob-based sources led to release patterns opposite to those of straw- and sawdust-based sources. For straw and sawdust, higher cellulose ratios accelerated release rates, increased total release and duration, reduced aromaticity and molecular weight of released DOM, and promoted protein-like components (tryptophan, tyrosine), indicating enhanced bioavailability. Under identical ratios, corncob-based sources exhibited moderate total release, release durations exceeding 134 h, lower DOM aromaticity and molecular weight, and lower humic substance proportion, indicating superior bioavailability and engineering potential. Among the nine sources, JG5, MX5, and CC4 (PHBV:cellulose mass ratios of 4:5, 4:5, and 1:1, respectively) showed optimal comprehensive performance with low theoretical maximum release, long release periods, and high mass transfer coefficients. EEM-PARAFAC identified three DOM components (protein-like C1, C2; humic-like C3), with protein-like components dominating. This study validates the relationship between cellulose proportion and release kinetics and reveals synergistic regulation of DOM components, offering guidance for designing effective solid-phase carbon sources.
Enhancement of Anaerobic Digestion Operational Efficiency for Guar Gum Production Wastewater Using a Microaerobic-Biochar Coupled System
Guar gum production wastewater contains 1,2-propanediol, which in conventional anaerobic treatment causes propionate accumulation and microbial inhibition. Microaerobic conditions foster fermentative bacterial metabolism, enhancing organic substrate conversion, while biochar promotes anaerobic microbial aggregation and oxygen tolerance. This study treated actual guar gum wastewater using three configurations: blank control, anaerobic, and microaerobic-biochar (O2/BC) coupled systems. Under mesophilic conditions (37 °C), with micro-aeration at 0.2 mL/(g VS·d) and biochar dosage of 15 g/L, the O2/BC system achieved a COD removal efficiency of 90%, 10.6 percentage points higher than the anaerobic control. Effluent COD and propionate concentrations dropped to 3800 mg/L and 0.15 g/L, respectively, representing reductions of 49.6% and 98.4% versus the control. Biogas production was 1.64 times that of the control, with a maximum methane concentration of 77.2%. Fourier transform infrared spectroscopy (FT-IR) indicated increased abundance of –OH, –CH2–, and C–O functional groups on sludge surfaces, revealing biochar's adsorption enhancement. Scanning electron microscopy (SEM) showed dense microbial aggregates dominated by long bacilli, distinct from conventional anaerobic sludge. Microbial community analysis revealed increased abundance of Clostridium and Comamonas, modulating the propionate-to-acetate ratio and optimizing acidification efficiency, thereby promoting complex organic degradation. This study provides a novel technical pathway for biological treatment of alcohol-rich organic wastewater.
Occurrence Characteristics, Source Apportionment, and Ecological Risk Assessment of Pesticides in Plateau Lakes: A Case Study of Dianchi Lake
This study systematically investigated the occurrence, spatial distribution, sources, and ecological risks of 160 pesticides in Dianchi Lake, a typical plateau lake impacted by agricultural activities. A total of 37 pesticides were detected in the water, with total concentrations ranging from 64.2 to 1132.8 ng/L (average 610.0 ng/L). Fungicides, including boscalid (BOS), fluopicolide (FPC), and dimethomorph (DMM), were dominant, contributing up to 65.0% of the total concentration. Spatially, the southern lake region exhibited significantly higher concentrations (672.5 ng/L) than the north, attributed to intensive facility agriculture. Highly hydrophobic pesticides, such as penconazole (PEN), showed a tendency to enrich in bottom layers. Source apportionment identified inflowing rivers and wastewater treatment plant effluents as primary input sources, with average concentrations 7 and 9 times higher than lake water, respectively. Ecological risk assessment revealed that pesticides posed the highest risk to algae, followed by daphnia and fish. Prometryn (PMT) was identified as a high-risk factor for algae, while profenofos (PFF) and carbendazim (CBD) posed potential threats to higher trophic levels. These findings provide fundamental data and technical support for understanding pesticide pollution in plateau lake ecosystems.
Microbiome Mechanisms of Composite Carbon Sources for Enhancing Denitrification and Reducing N2O Emissions
Biological nitrogen removal in wastewater treatment plants (WWTPs) is often limited by insufficient influent carbon sources, necessitating external carbon addition to enhance denitrification. Conventional single carbon sources, such as sodium acetate, frequently fail to meet the metabolic demands of complex microbial communities, compromising nitrogen removal efficiency and stability. Composite carbon sources, by providing multiple electron donors, can improve metabolic cooperation among microorganisms, yet their underlying microbial mechanisms remain insufficiently understood. In this study, activated sludge from a municipal WWTP was used to investigate the microbial mechanisms of composite carbon sources during denitrification. Batch denitrification experiments were conducted in combination with metagenomic and metatranscriptomic analyses to systematically characterize microbial community structure and functional gene expression under different carbon source conditions. Results showed that, compared with sodium acetate as the single carbon source, the composite carbon source system (sodium acetate: sodium succinate: ethanol = 2:1:3) increased the denitrification rate from (6.822 ± 0.141) mg/(L·h) to (8.370 ± 0.186) mg/(L·h), representing a 22.7% improvement, while reducing N2O accumulation by approximately 55%. Metagenomic analysis revealed that Ottowia, Rubrivivax, Thauera, and Zoogloea were the dominant denitrifying genera. Metatranscriptomic results further demonstrated that the composite carbon sources significantly upregulated the transcription of key denitrification genes, with nirS, norB, and nosZ increasing by 37.8%, 27.4%, and 48.6%, respectively. In addition, the composite carbon sources promoted complementary carbon metabolic strategies among different microbial communities, enhancing electron donor supply and improving denitrification efficiency. These findings indicate that composite carbon sources synergistically enhance denitrification performance through regulation of functional gene transcription in complex microbial communities, providing a theoretical basis for carbon source optimization in WWTPs.
Key Environmental Behaviors and Pollution Control Strategies of Tire Wear Particles in Aquatic Environments
Tire wear particles (TWPs) are emerging pollutants and constitute the dominant type of microplastics (MPs) in urban stormwater runoff, accounting for up to 90% of MPs in some cases. They are characterized by small size, high mobility, complex composition, and significant toxicity. Current research on TWPs remains fragmented, lacking a comprehensive understanding of their environmental behaviors and pollution control in aquatic systems. This review systematically analyzes the enrichment and vectoring roles of TWPs for coexisting pollutants, and their environmental fate, including ecotoxicological impacts, detection methodologies, release of intrinsic additives, and aggregation and sedimentation behaviors. Drawing on insights from other microplastic studies, the paper explores control technologies across the pollution pathway—source, transport, and terminal treatment—and proposes feasible management strategies. Key findings indicate that TWPs can adsorb heavy metals and organic contaminants, with adsorption capacities influenced by aging processes. Their aggregation is governed by solution chemistry, with critical coagulation concentrations varying with ionic strength and pH. The release of additives such as zinc and benzothiazoles is significant, posing ecological risks. Future research should focus on real-water aggregation mechanisms, additive release under natural conditions, long-term performance of treatment facilities like constructed wetlands under TWPs stress, enzymatic degradation pathways, and integration of AI, big data, and IoT for cost-effective detection and risk modeling. This review provides a scientific basis for developing targeted pollution control measures for TWPs in aquatic environments.