Denitrification Of Wastewater Research Articles

Carbon Source in Tertiary Denitrification Regulates Dissolved Organic Nitrogen in Wastewater Effluent.

With global eutrophication and increasingly stringent nitrogen discharge restrictions, dissolved organic nitrogen (DON) holds considerable potential to upgrade advanced wastewater denitrification because of its large contribution to low-nitrogen effluents and stronger stimulation effect for algae. Here, we show that DON from the postdenitrification systems dominates effluent eutrophication potential under different carbon sources. Methanol resulted in significantly lower DON concentrations (0.84 ± 0.03 mg/L) compared with the total nitrogen removal-preferred acetate (1.11 ± 0.02 mg/L) (p < 0.05, ANOVA). With our well-developed mathematical model (R2 = 0.867-0.958), produced DON instead of shared (persist in both influent and effluent) and/or removed DON was identified as the key component for effluent DON variation (Pearson r = 0.992, p < 0.01). The partial least-squares path modeling analysis showed that it is the microbial community (r = 0.947, p < 0.01) rather than the predicted metabolic functions (r = 0.040, p > 0.1) that affected produced DON. Carbon sources rebuild the microorganism-DON interaction by affecting the structure of microbial communities with different abilities to generate and recapture produced DON to finally regulate effluent DON. This study revalues the importance of carbon source selection and overturns the current rationality of pursuing only the total nitrogen removal efficiency by emphasizing DON.

Highly efficient electrochemical ammonia synthesis via nitrate reduction over metallic Cu phase coupling sulfion oxidation.

Electrochemical nitrate reduction reaction (NO3RR) is a promising technology for ammonia production and denitrification of wastewater. Its application is seriously restricted by the development of the highly active and selective electrocatalyst and a rational electrolysis system. Here, we constructed an efficient electrochemical ammonia production process via nitrate reduction on the metallic Cu electrocatalyst when coupled with anodic sulfion oxidation reaction (SOR). The synthesized Cu catalyst delivers an excellent NH3 Faradaic efficiency of 96.0 % and a NH3 yield of 0.391 mmol h-1 cm-2 at -0.2 V vs. reversible hydrogen electrode, which mainly stem from the more favorable conversion of NO2 - to NH3 on Cu0. Importantly, the well-designed electrolysis system with cathodic NO3RR and anodic SOR achieves a dramatically reduced cell voltage of 0.8 V at 50 mA cm-2 in comparison with the one with anodic oxygen evolution reaction (OER) of 1.9 V. This work presents an effective strategy for the energy-saving ammonia production via constructing effective nitrate reduction catalyst and replacing the OER with SOR while removing the pollutants including nitrate and sulfion.

Tourmaline mediated enhanced autotrophic denitrification: The mechanisms of electron transfer and Paracoccus enrichment

Autotrophic denitrification (AD) without carbon source is an inevitable choice for denitrification of municipal wastewater under the carbon peaking and carbon neutrality goals. This study first employed sulfur-tourmaline-AD (STAD) as an innovative nitrate removal trial technique in wastewater. STAD demonstrated a 2.23-fold increase in nitrate‑nitrogen (NO3−-N) removal rate with reduced nitrite‑nitrogen (NO2−-N) accumulation, effectively removing 99 % of nitrogen pollutants compared to sulfur denitrification. Some denitrifiers microorganisms that could secrete tyrosine, tryptophan, and aromatic protein (extracellular polymeric substances (EPS)). Moreover, according to the EPS composition and characteristics analysis, the secretion of loosely bound extracellular polymeric substances (LB-EPS) that bound to the bacterial endogenous respiration and enriched microbial abundance, was produced more in the STAD system, further improving the system stability. Furthermore, the addition of tourmaline (Tm) facilitated the discovery of a new genus (Paracoccus) that enhanced nitrate decomposition. Applying optimal electron donors through metabolic pathways and the microbial community helps to strengthen the AD process and treat low carbon/nitrogen ratio wastewater efficiently.

The track, hotspot and frontier of anammox technology in wastewater treatment 2001–2022

Anaerobic ammonia oxidation (anammox) technology is gaining traction as a promising solution for wastewater denitrification due to its ability to reduce investment, and minimize operational costs and sludge production. As a result, it has become a hot research topic of wastewater treatment, with a growing body of literature exploring its potential applications. However, despite the increasing interest in this field, there is a lack of comprehensive analysis that provides a clear overview of the development context and quantitative research on the overall trends of anammox technology in wastewater treatment. To manage this gap, this article conducted a systematic bibliometric analysis of global application research of anammox technology in wastewater treatment using VOSviewer, CiteSpace, and Bibliometric for the core collection database of Web of Science. The study included drawing a collaborative map of countries, institutions, and researchers to display the distribution of research forces and scientific research cooperation in this field. Moreover, the article employed software co-occurrence analysis to obtain the hot scientific fields in anammox wastewater treatment. Finally, valuable insights into the future direction of research in this field were provided through the use of a keyword co-occurrence network atlas and literature co-citation network atlas, which were employed to analyze research hotspots, research frontiers, and development trends.

Removal of Nitrate Nitrogen from Municipal Wastewater Using Autotrophic Denitrification Based on Magnetic Pyrite

As the problem of eutrophication of water bodies and nitrate pollution of surface and groundwater is becoming more and more prominent, deep denitrification of wastewater can effectively reduce the amount of nitrate nitrogen (NO3−-N) discharged into natural water bodies. To solve this problem, in this research, the autotrophic denitrifying bacteria were incorporated in an autotrophic denitrification simulator equipped with magnetic pyrite to remove NO3−-N and total nitrogen (TN) from wastewater. The purified strains were inoculated into municipal sewage. When the ratio of magnetic pyrite to quartz sand was 1:1 and the particle size of the filler was 0.5–1 mm, the removal rate of NO3−-N and TN was optimized, at 93.52% and 83.22%, respectively. Sulphate (SO42−) concentrations will level off during stable system operation, and SO42− concentrations show a positive correlation with NO3−-N and TN removal. The 16s rDNA sequencing analysis of the screened sludge showed that the main phyla in the screened and purified sludge were Epsilonbacteraeota and Proteobacteria, with an abundance of 65.83% and 26.88%, and the final enriched products were dominated by Sulfurimonas and Thiobacillus, with an abundance of 64.91% and 9.32%, respectively. The results showed that autotrophic denitrifying bacteria could be screened and purified using thiosulfate as a substrate, and that the use of magneto pyrite as an electron donor reduced most of the NO3−-N to N2, while reducing the TN content.

Environmental proteomics as a useful methodology for early-stage detection of stress in anammox engineered systems

Anammox bacteria are widely applied worldwide for denitrification of urban wastewater. Differently, their application in the case of industrial effluents has been more limited. Those frequently present high loads of contaminants, demanding an individual evaluation of their treatability by anammox technologies. Bioreactors setting up and recovery after contaminants-derived perturbations are slow. Also, toxicity is frequently not acute but cumulative, which causes negative macroscopic effects to appear only after medium or long-term operations. All these particularities lead to relevant economic and time losses. We hypothesized that contaminants cause changes at anammox proteome level before perturbations in the engineered systems are detectable by macroscopic analyses. In this study, we explored the usefulness of short-batch tests combined with environmental proteomics for the early detection of those changes. Copper was used as a model of stressor contaminant, and anammox granules were exposed to increasing copper concentrations including previously reported IC50 values. The proteomic results revealed that specific anammox proteins involved in stress response (bacterioferritin, universal stress protein, or superoxide dismutase) were overexpressed in as short a time as 28 h at the higher copper concentrations. Consequently, EPS production was also increased, as indicated by the alginate export family protein, polysaccharide biosynthesis protein, and sulfotransferase increased expression. The described workflow can be applied to detect early-stage stress biomarkers of the negative effect of other metals, organics, or even changes in physical-chemical parameters such as pH or temperature on anammox-engineered systems. On an industrial level, it can be of great value for decision-making, especially before dealing with new effluents on facilities, deriving important economic and time savings.

Mechanisms of nanoscale zero-valent iron mediating aerobic denitrification in Pseudomonas stutzeri by promoting electron transfer and gene expression

Aerobic denitrification and its mechanism by P. stutzeri was investigated in the presence of nanoscale zero-valent iron (nZVI). The removal of nitrate and ammonia was accelerated and the nitrite nitrogen accumulation was reduced by nZVI. The particle size and dosage of nZVI were key factors for enhancing aerobic denitrification. nZVI reduced the negative effects of low carbon/nitrogen, heavy metals, surfactants and salts to aerobic denitrification. nZVI and its dissolved irons were adsorbed into the bacteria cells, enhancing the transfer of electrons from nicotinamide adenine dinucleotide (NADH) to nitrate reductase. Moreover, the activities of NADH-ubiquinone reductase involved in the respiratory system, and the denitrifying enzymes were increased. The expression of denitrifying enzyme genes napA and nirS, as well as the iron metabolism gene fur, were promoted in the presence of nZVI. This work provides a strategy for enhancing the biological denitrification of wastewater using the bio-stimulation of nanomaterials.

Denitrification using a novel Ni-CNF/g-C3N4 catalyst and nitrate-enriched wastewater-resourced Achromobacter denitirificans

This study presents a novel hybrid approach combining heterogeneous catalytic chemical reaction with biological intervention to denitrify wastewater. A graphitic carbon nitride (g-C3N4)-supported Ni-carbon nanofiber (CNF) is used as the catalyst, while Achromobacter denitirificans, isolated from an effluent of a sewage treatment plant, is used as the denitrifying bacteria. g-C3N4 acts as an artificial electron elicitor for biological regulation. Ni enhances the activity of key enzymes which are involved in bacterial denitrification, while the CNF surface immobilizes the bacteria. The catalyst and bacterial cells are characterized and identified using spectroscopic techniques and 16S rRNA sequencing, respectively. The data reveal approximately 99% removal of nitrates from water in 24h at the nitrate concentration of 150 mg/L at the catalyst and bacterial dose of 0.025 g/L and 1% (v/v) with 107 CFU/mL, respectively. Spent water can be recycled and reused. This study provides a new strategy for the denitrification of wastewater.

Simultaneous nitrification and denitrification of real domestic wastewater using novel biodegradable Cocos Nucifera fibre as biofilter media and carbon source: Performances and microbial community composition

The simultaneous nitrification and denitrification (SND) performances in biofiltration system are largely governed by the filter media material and also the operating conditions. Moreover, a significant gap exists regarding the influence of different operating conditions on the SND performances in using plant-based waste materials as the biofilter media. Thus, in this study, long-term SND and organic pollutants removal were investigated in a continuous-flow biofiltration system filled with novel biodegradable Cocos nucifera fibre media operating under different dissolved oxygen (DO) concentrations, HRT and backwash intensity. Under best operating conditions of DO 1.5 mg/L, HRT 16.0 h, and airflow and water flow rate of 1.0 L/m2/s, the biofiltration system was able to remove an average of 70.7 % of NH3-N, 98.5 % of NO2-N, 90.3 % of COD, 86.9 % of soluble COD (sCOD), 98.7 % of TSS, 70.4 % of TN and achieved 94.3 % of SND efficiencies. The coexistence of enriched functional microorganisms such as nitrifiers (Nitrosomonas, Nitrospira) and denitrifiers (Dechloromonas, Zoogloea, Acidovorax) were believed to be responsible for the efficient performance of the system working under best operating conditions.

Optimizing waste molasses utilization to enhance electron transfer via micromagnetic carriers: Mechanisms and high-nitrate wastewater denitrification performance

The biological denitrification of high-nitrate wastewater (HNW) is primarily hindered by insufficient carbon sources and excessive nitrite accumulation. In this study, micromagnetic carriers with varying micromagnetic field (MMF) strengths (0.0, 0.3, 0.6, 0.9 mT) were employed to enhance the denitrification of HNW using waste molasses (WMs) as a carbon source. The results revealed that 0.6 mT MMF significantly improved the total nitrogen removal (TN) efficiency at 96.3%. A high nitrate (NO3−-N) removal efficiency at 99.3% with a low nitrite (NO2−-N) accumulation at 25.5 mg/L was achieved at 0.6 mT MMF. The application of MMF facilitated the synthesis of adenosine triphosphate (ATP) and stimulated denitrifying enzymes (e.g., nitrate reductase (NAR), nitrite reductase (NIR), and nitric oxide reductase (NOR)), which thereby promoting denitrification. Moreover, the effluent chemical oxygen demand (COD), tryptophan and fulvic-like substances exhibited their lowest levels at 0.6 mT MMF. Analysis through 16S ribosomal ribonucleic acid gene sequencing indicated a significant enrichment of denitrifying bacteria including Castellaniella Klebsiella under the influence of MMF. Besides, the proliferation of Acholeplasma, Klebsiella and Proteiniphilum at 0.6 mT MMF promoted the hydrolysis and acidification of WMs. This study offers new insights into the enhanced utilization of WMs and the denitrification of HNW through the application of MMF.

Nitrate removal from industrial wastewater using six newly isolated strains of aerobic heterotrophic denitrifiers in an attached growth

ABSTRACTBackgroundThe objective of this study was to isolate specific heterotrophic aerobic denitrifying bacteria from a wastewater treatment plant and employ them in an attached growth system for wastewater denitrification.MethodsTo isolate and screen aerobic denitrifiers, Denitrifying Medium (DM) and Screen Medium (GN) were utilized. The Polymerase Chain Reaction (PCR) technique and 16S rDNA sequencing were used to identify the isolates. The formation of biofilms by selected isolates on ceramic media was examined using a Scanning Electron Microscope (SEM). This study also investigated various variables for nitrate removal, including temperature, Carbon/Nitrogen ratio (C/N), and the carbon source. A series of experiments were conducted to gauge nitrate removal under optimal variable values.ResultsSix purified strains exhibited the highest denitrification efficiency in less than 30 h. Pseudomonas species were chosen for additional experiments. Denitrification efficiencies ranged from a low of 71.4% (at a temperature of 30 °C, C/N ratio of 17, and citrate as the carbon source) to a high of 98.9% (at a temperature of 33 °C, C/N ratio of 8, and citrate as the carbon source). The average denitrification efficiency was 84.02%. Optimal nitrate removal occurred at temperatures around 30–31 °C and C/N ratios of approximately 5.8–6.5.ConclusionThis study demonstrates that aerobic denitrifying bacteria can effectively remove nitrate from aqueous solutions.

Optimization of nitrogen removal conditions based on response surface methodology and nitrogen removal pathway of Paracoccus sp. QD-19

The strain Paracoccus sp. QD-19 was isolated from the sludge-water mixture of aerobic tanks at the southern wastewater treatment plant in Shenyang, China. The optimal nitrogen removal conditions for strain QD-19 were determined using the Plackett–Burman design, path of steepest ascent method, and response surface methodology (RSM). The optimum nitrogen removal conditions were C/N 12.93, temperature 37 °C, and shaking speed 175.50 r/min. Strain QD-19 achieved 83.82 ± 0.80 % nitrogen removal efficiency at 10 h under optimum conditions. Functional enzyme-encodinge genes amplified via 16S rRNA sequence analysis included amoA, hao, napA, nirS, nirK, norB, and nosZ. The results revealed that NH4+-N → NH2OH → NO2−-N → NO3‐-N → NO2−-N → NO → N2O → N2 was the pathway for heterotrophic nitrification - aerobic denitrification. The strain was used to treat wastewater from a sewage treatment plant under optimal response surface methodology conditions. As a result, the TN removal efficiency was 77.11 %. The findings demonstrated that strain QD-19 exhibits favorable potential for heterotrophic nitrification and aerobic denitrification (HN-AD) of actual wastewater, presenting a promising application for biological wastewater treatment.

Study on denitrification of hydroponic wastewater reverse osmosis concentrate using sulfur-autotrophic denitrification

Hydroponic agriculture is one of the sectors that generate the highest amounts of nitrogen-containing wastewater. Sulfur-autotrophic denitrification is considered a promising technology due to its stable and excellent denitrification performance, cost-effectiveness, and operational advantages. In order to investigate the denitrification performance and the contribution of the filter layer under high NO3--N concentration (600 mg·L−1), this experiment designed a denitrification system using Na2S2O3 as an electron donor. The results showed that the reactor achieved the highest denitrification efficiency with a hydraulic retention time of 12 h, pH of 7, and sulfur to nitrogen ratio of 2, maintaining a stable NO3--N removal efficiency of 99%. The majority of NO3--N was removed by the bottom filter layer (0–300 mm), accounting for 86% of the total denitrification. The microbial community in the lower part of the filter column was dominated by Proteobacteria, with relatively high abundances of the genera Chryseobacterium, Thiobacillus, and Sulfurimonas. Similarly, the microbial community structure in the upper filter layer was dominated by Proteobacteria, with an increased abundance of the genus Chryseobacterium and a significant reduction in the abundance of Sulfurimonas. The study indicates that SAD can achieve stable and efficient denitrification of wastewater from hydroponic reverse osmosis concentrate. Moreover, higher NO3--N concentrations can influence the bacterial community structure within the reactor.

Research progress of novel bio-denitrification technology in deep wastewater treatment.

Excessive nitrogen emissions are a major contributor to water pollution, posing a threat not only to the environment but also to human health. Therefore, achieving deep denitrification of wastewater is of significant importance. Traditional biological denitrification methods have some drawbacks, including long processing times, substantial land requirements, high energy consumption, and high investment and operational costs. In contrast, the novel bio-denitrification technology reduces the traditional processing time and lowers operational and maintenance costs while improving denitrification efficiency. This technology falls within the category of environmentally friendly, low-energy deep denitrification methods. This paper introduces several innovative bio-denitrification technologies and their combinations, conducts a comparative analysis of their denitrification efficiency across various wastewater types, and concludes by outlining the future prospects for the development of these novel bio-denitrification technologies.

Partial denitrification in domestic sewage and nitrate wastewater: study of the initiation, influencing factors and operational performance

AbstractBACKGROUNDPractical application of the anaerobic ammonium oxidation (anammox) process has been limited by the difficulty of obtaining a stable supply of NO2−–N. In this study, partial denitrification was utilized as a novel approach to obtain nitrite for anammox, investigating the initiation, influencing factors and performance of partial denitrification in the simultaneous treatment of domestic sewage and nitrate wastewater.RESULTSWhen the influent concentration of NO3−–N was 40 mg L−1 and the chemical oxygen demand to nitrate (COD/NO3−–N) ratio was 2.7, the NO2−–N accumulation rate exceeded 80%, with an effluent NO2−–N concentration of 35.64 mg L−1. Furthermore, the partial denitrification performance was good. When the volume ratio of domestic sewage and nitrate wastewater was adjusted to 2:3 and sodium acetate was added to form a COD/NO3−–N ratio of 3.6, the effluent NO2−–N/NH4+–N ratio was 1.24 and the effluent NO2−–N concentration and average NO2−–N accumulation rate reached &gt;31.24 mg L−1 and 83.38%, respectively, effectively ensuring influent requirements for anammox.CONCLUSIONThe NO3−–N reduction rate, NO3−–N removal rate and NO2−–N accumulation rate were positively correlated with the influent nitrate concentration when ranging between 15 and 40 mg L−1. An appropriate increase in the influent COD/NO3−–N ratio was conducive to a reduction in the time required for maximum levels of NO2−–N accumulation to occur, with an influent NO3−–N concentration of 40 mg L−1. The partial denitrification system could simultaneously treat domestic sewage and nitrate wastewater, effectively ensuring that the generated effluent met the influent requirements for subsequent anammox. © 2023 Society of Chemical Industry.

Chemical deposition from a liquid crystal template: A highly active mesoporous nickel phosphate electrocatalyst for hydrogen green production via urea electro-oxidation in an alkaline solution

Recently the urea and urinated wastewater electrolysis process has shown promising technology for hydrogen fuel green production in addition to denitrification of wastewater. However, to make the process economically valuable, the electrocatalysts nanoarchitecture, nanometer size, shape, facets, and composition need to be engineered to boost the urea oxidation reaction (UOR). This work demonstrates a simple and novel approach to the synthesis of mesoporous nickel phosphate nanoparticles (meso-NiPO) via chemical deposition from a surfactant liquid crystal template. Typically, the nickel ions dissolved in the aqueous domain of the hexagonal liquid crystalline phase of the Brij®78 template were chemically reacted with the sodium phosphate solution to precipitate the mesoporous nickel phosphate nanoarchitecture after washing up the surfactant. The physicochemical characterizations show the meso-NiPO exhibits an amorphous highly mesoporous structure with a higher specific surface area (43.50 m2/g) compared to the bare nickel phosphate (bare-NiPO, 4.26 m2/g) prepared in the absence of surfactant. The electrochemical performance of meso-NiPO electrocatalyst for the urea oxidation reaction in alkaline solution exhibits superior activity including a lower oxidation onset potential (0.30 V vs. Ag/AgCl), charge transfer resistance (3.35 O) and mass activity of 700.7 mA/cm2 mg at the oxidation potential of 0.6 V vs. Ag/AgCl. Moreover, the meso-NiPO reveals long-term stability, and 97.5% of the steady-state oxidation current was maintained after the 3-hour urea electrolysis test. Using an H-shape urea electrolyzer, the corresponding cathodic hydrogen production rate reached 415 µmol/h and a Faradic efficiency of 96.8 % at an applied bias of 2.0 V. The electroactivity high performance of the mesoporous nickel phosphate is ascribed to the high specific surface area and mesoporous architecture that provide efficient charge transfer, as well as mass transport of the electroactive species. The chemical deposition from a surfactant liquid crystal template has the advantages of a one-pot template, applicable to the synthesis of a wide range of nanomaterials with various compositions and nanoarchitectures at room temperature for application in electrochemical energy production and storage systems.

Preparation of Self-Releasing Carbon Biofilm Carrier Based on Corncob and Denitrification Properties

Wastewater with a low carbon/nitrogen (C/N) ratio is widespread and difficult to treat. The addition of an external carbon source is an effective method for treating such wastewater. Therefore, we aimed to prepare a self-releasing carbon biofilm carrier using agricultural waste (corncobs), polyvinyl alcohol, and sponge iron in various ratios to provide a carbon source that would facilitate denitrification, providing an optimal environment for microorganisms. We found that the carbon release of the MAC biofilm carrier that accumulated over 60 d was 116.139 mg of chemical oxygen demand (COD)·g−1, whereas the accumulated total nitrogen release was approximately 0 mg·(g·d)−1. The NO3−-N removal rate after 24 h reached 98.1%, whereas the theoretical use rate of the carbon source (in terms of COD) was stable at 90.34%. In addition, the sum of the abundances of the denitrifying and cellulose-degrading bacteria was 49.89%. Furthermore, biofilm carriers are used as functional carriers that contribute to cellulose degradation, a process in which sponge iron produces Fe2+ to provide electron donors and shuttles for denitrifying bacteria and forms the iron cycle, thereby inducing an increase in microbial abundance; this increase then facilitates the microbial degradation of cellulose and synergistic denitrification through interspecific bacterial cooperation. This study provides a new and effective method for enhancing the denitrification of wastewater with low C/N ratios.

Sodium hydroxide or tetramethylammonium hydroxide modified corncob combined with biodegradable polymers to prepare slow-release carbon source for wastewater denitrification

This study proposed a method to improve the bioavailability of artificially prepared carbon sources for the purpose of wastewater denitrification. This carbon source (named SPC) was prepared by mixing corncobs with poly(3-hydroxybutyrate-3-hydroxyvalerate) (PHBV), where the corncobs were pretreated by NaOH or TMAOH. The results of compositional analysis and FTIR showed that both NaOH and TMAOH degraded lignin, hemicellulose and their connection bonds in corncob, thus increased the cellulose content from 39% to 53% and 55%, respectively. The cumulative carbon release from SPC was about 9.3 mg/g and was consistent with both the first-order kinetic and Ritger-Peppas equation. The released organic matters contained low concentration of refractory components. Correspondingly, it showed excellent denitrification performance in simulated wastewater, and the total nitrogen (TN) removal rate was above 95% (influent NO3−-N was 40 mg/L) and effluent residual chemical oxygen demand (COD) was less than 50 mg/L.

Enhanced electron recovery by optimizing sandwich structure agricultural waste corncob filled anode in microbial electrochemical system to facilitate wastewater denitrification

Microbial electrochemical system autotrophic denitrification has attracted much attention due to its cost-efficiency and clean advantages. The autotrophic denitrification rate highly depends on the input electrons to the cathode. In this study, agricultural waste corncob was filled into sandwich structure anode as low-cost carbon source for electron production. The COMSOL software was used to guide the construction of sandwich structure anode to control carbon source release and enhance electron collection, including suitable pore size (4 mm) and current collector arrangement (five branches). Optimized sandwich structure anode system with the help of 3D printing obtained a higher denitrification efficiency (21.79 ± 0.22 gNO3--N/m3d) than anodic systems without pore and current collector. Statistical analysis showed that enhanced autotrophic denitrification efficiency was the responsible for enhanced denitrification performance of the optimized anode system. This study provides a strategy to improve the autotrophic denitrification performance of the microbial electrochemical system by optimizing the anode structure.

Efficient ammonia removal promoted in a bifunctional system constructed with NiCu–S/DSA electrodes

Currently, the treatment of ammonia in wastewater, one of the main causes of eutrophication in water bodies, has received widespread attention. In this work, a novel electrocatalytic bifunctional system was constructed to achieve efficient degradation of ammonia. It consists of Ni1Cu0.25-S/DSA electrodes with both anode and cathode, which is prepared by a combination of electrodeposition and electrochemical tuning strategies. The crystalline phases and oxidation states of the nano-textured particulate metal oxides were determined by using a series of physical characterizations. The Ni1Cu0.25-S/DSA electrode with the best electrocatalytic performance was screened by electrochemical analysis, which has good stability and reliability when processing ammonia nitrogen. The efficiency of electrodes for ammonia removal was verified by running denitrification of synthetic and real wastewater. The results showed that the NH4+-N removal efficiency could approach up to 99%. Kinetically, compared with the monofunctional system, the bifunctional system obtained a higher NH4+-N degradation rate of 45.5 mg L−1 h−1, increased the rate of N2 generation by more than 10 times, and reduced the rate of NO3−-N and NO2−-N generation by one-third on average. The possible reaction mechanism of anodic ammonia oxidation and cathodic nitrate reduction in the bifunctional system was proposed.