Biological Denitrification Process Research Articles

Nitrate Upcycling Mediated by Organonickel Catalysis

AbstractNitrogen oxides (NOx) are major environmental pollutants and to neutralize this long‐term environmental threat, new catalytic methods are needed. Although there are biological denitrification processes involving four different enzymatic reactions to convert nitrate (NO3−) into dinitrogen (N2), it is unfortunately difficult to apply in industry due to the complexity of the processes. In particular, nitrate is difficult to functionalize because of its chemical stability. Thus, there is no organometallic catalysis to convert nitrate into useful chemicals. Herein, we present a nickel pincer complex that is effective as a bifunctional catalyst to stepwise deoxygenate NO3− by carbonylation and further through C−N coupling. By using this nickel catalysis, nitrate salts can be selectively transformed into various oximes (>20 substrates) with excellent conversion (>90 %). Here, we demonstrate for the first time that the highly inert nitrate ion can be functionalized to produce useful chemicals by a new organonickel catalysis. Our results show that the NOx conversion and utilization (NCU) technology is a successful pathway for environmental restoration coupled with value‐added chemical generation.

Nitrate Upcycling Mediated by Organonickel Catalysis.

Nitrogen oxides (NOx) are major environmental pollutants and to neutralize this long-term environmental threat, new catalytic methods are needed. Although there are biological denitrification processes involving four different enzymatic reactions to convert nitrate (NO3 -) into dinitrogen (N2), it is unfortunately difficult to apply in industry due to the complexity of the processes. In particular, nitrate is difficult to functionalize because of its chemical stability. Thus, there is no organometallic catalysis to convert nitrate into useful chemicals. Herein, we present a nickel pincer complex that is effective as a bifunctional catalyst to stepwise deoxygenate NO3 - by carbonylation and further through C-N coupling. By using this nickel catalysis, nitrate salts can be selectively transformed into various oximes (>20 substrates) with excellent conversion (>90 %). Here, we demonstrate for the first time that the highly inert nitrate ion can be functionalized to produce useful chemicals by a new organonickel catalysis. Our results show that the NOx conversion and utilization (NCU) technology is a successful pathway for environmental restoration coupled with value-added chemical generation.

Effects and mechanisms of oxytetracycline and norfloxacin on microbial extracellular polymeric substances (EPS) in biological denitrification of aquaculture wastewater

The direct equalizing ray method was employed to design three groups of mixtures of oxytetracycline(OTC) and norfloxacin(NOR) with varying proportions(Group R1 had a higher proportion of OTC, while R2 had similar concentrations of both antibiotics, and R3 had a higher proportion of NOR).The effects of these mixtures on the content and properties of extracellular polymeric substances (EPS) in the biological denitrification process were investigated using an sequencing batch reactor activated sludge reactor (SBR). The results revealed that the removal rates of ammonia nitrogen(NH3-N) decreased in all three groups with the addition of antibiotics. As the antibiotic concentration increased, the EPS content decreased by 68.46%, 55.53%, and 65.03% in R1, R2, and R3, respectively. To understand the interaction mechanism of mixed antibiotics on EPS in activated sludge, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) techniques were employed. The findings demonstrated significant effects of mixed antibiotics on functional groups such as C-O, CO, and C-O-C. Specifically, hydrogen bonding was found to be the primary influencing factor in the R1 ratio, while Π-Π conjugation played a major role in the R3 ratio.

Prediction of nitrous oxide emission of a municipal wastewater treatment plant using LSTM-based deep learning models.

Accurate assessment of greenhouse gas emissions from wastewater treatment plants is crucial for mitigating climate change. N2O is a potent greenhouse gas that is emitted from wastewater treatment plants during the biological denitrification process. In this study, we developed and evaluated deep learning models for predicting N2O emissions from a WWTP in Switzerland. Six key parameters were selected to obtain the optimal LSTM model by adjusting experimental parameter conditions. The optimal parameter condition was achieved with 150 neurons, the tanh activation function, the RMSprop optimization algorithm, a learning rate of 0.001, no dropout regularization, and a batch size of 128. Under the same conditions, we compared the performance of recurrent neural networks (RNNs) and Long Short-Term Memory (LSTM) networks. We found that LSTM models outperformed RNN models in predicting N2O emissions. The optimal LSTM model achieved a 36% improvement in mean absolute error (MAE), a 19% improvement in root mean squared error (RMSE), and a 6.92% improvement in R2 score compared to the RNN model. Additionally, LSTM models demonstrated better resilience to sudden changes in the target sequence, exhibiting a 9.54% higher percentage of explained variance compared to RNNs. These results highlight the potential of LSTM models for accurate and robust prediction of N2O emissions from wastewater treatment plants, contributing to effective greenhouse gas mitigation strategies.

Characterization of simultaneous ammonium and nitrate removal and microbial communities in airlift reactor using 3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) as carbon source and biofilm carrier

As a novel trend, solid carbon sources are applied to act as electron donors and biofilm carrier in biological denitrification process. In this study, simultaneous nitrate and ammonium removal process in an airlift sequencing batch reactor using 3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) as carbon source and biofilm carrier under intermittent aeration conditions was established to treat effluent of synthetic marine recirculating aquaculture system. The results showed that maximum nitrate and ammonia nitrogen removal rates of 0.45 and 0.09 kg m−3 d−1 were achieved. No significant nitrite accumulation was found during 200-day operation, while effluent dissolved organic carbon accumulation and particle size reduction significantly increased. Microbial community analysis and batch tests illuminate that the generated sludge and attached biofilm played important roles in nitrogen removal. This study demonstrates the potential mechanism for the nitrogen removal process mediated by 3-hydroxybutyrate-co-3-hydroxyvalerate and provide a new idea for the alternative solutions of solid carbon sources.

Comparative Analysis of Greenhouse Gas Emissions from Domestic Wastewater Treatment Processes by Modeling: Existing Estimation Methods vs Modeling

This study examined the existing methodologies and the applicability of process modeling concerning the estimation of nitrous oxide (N<sub>2</sub>O) emissions from wastewater treatment processes. The method of extimating N<sub>2</sub>O emissions from wastewater occurring during biological nitrification and denitrification processes can be divided into those before and after legal nitrogen effluent quality enhancement for domestic wastewater treatment plant. Initial IPCC guidelines such as IPCC 1996 GL, GPG 2000, and IPCC 2006 GL, provided methods for estimating N<sub>2</sub>O emissions throughout domestic wastewater, while the revised version, IPCC 2019 RF, proposed methods for estimating each N<sub>2</sub>O emission by distinguishing wastewater treatment and effluent after the advancement of wastewater treatment plants. The National Greenhouse Gas Inventory Report (NIR) in Korea adopted the methodology of GPG 2000, and the Emissions Trading System (ETS) applies the estimation method of IPCC 2006 GL in the wastewater treatment plants. This study utilized process modeling to consider the process characteristics and operating conditions of wastewater treatment plants. IPCC, NIR, and ETS estimate N<sub>2</sub>O emissions based on nitrogen behavior activity data and emissions factors. On the other hand, process modeling estimates N<sub>2</sub>O emissions in each unit process of the wastewater treatment plant using a 4-step AOB nitrification/4-step denitrification model and a liquid/gas transfer model. The estimation results of N<sub>2</sub>O emissions from modeling method were compared with the estimation results of IPCC, NIR, and ETS to analyze the suitability of the estimation method. Through this, it was evaluated how appropriate process modeling is for estimating N<sub>2</sub>O emissions in domestic wastewater treatment plants.

Study on the mechanism of enhanced anaerobic ammonia oxidation performance by extracellular electron acceptor biochar

ABSTRACT Anaerobic ammonia oxidation process has the advantages of energy and cost reduction, therefore, it has been considered as one of the main alternatives to conventional biological denitrification process in recent years. Biochar has been applied in the anammox process for nitrogen removal efficiency. But, due to its extracellular electron transfer capacity and abundance of redox-specific functional groups, which served as extracellular electron acceptor to anaerobically oxidize NH4 + is still controversy. In this study, the anaerobic ammonia oxidation was investigated when biochar was used as electron acceptor in the wastewater. According to the optimal process variables determined in the batch tests, when the influent NH4 +-N concentration in the anaerobic ammonia oxidation reaction was 30–50 mg/L and the biochar dosing was at 10 g/L, it showed some promotion in the long-term experiments. The anaerobic ammonia oxidation process with biochar as the electron acceptor reached more than 60% NH4 +-N removal efficiency in the system, and the ΔNO3 --N/ΔNH4 +-N ratio reached 0.19 which tended to the theoretical value. After 20 days, the voltage in the system keeps fluctuating about 4 mV, indicated that the functional bacteria using biochar as the electron acceptor gradually dominated the system. In addition, the abundance of norank_f__norank_o__SBR1031 in the Chloroflexi phylum has increased significantly at 29.92%, while the abundance of the major genus Candidatus_Kuenenia in AnAOB has decreased slightly at 11.47%.

Granular biomass technology for providing drinking water: microbial versatility and nitrate performance in response to carbon source

The aerobic granular biomass technology was optimized for treating nitrate-polluted groundwater based on the biological denitrification processes in order to provide drinking water. Reactors inoculated with granular biomass were operated at progressively lower C/N rate using acetate and methanol to encourage heterotrophic denitrification, in order to meet the recommended requirements described by European Drinking Water Framework Directive. The granulation and long-term stability of granular biomass under low C/N were successful for all stages, demonstrated compactness of granules and absence of filamentous microorganisms. The nitrate removal was similar in methanol- and acetate-fed reactors, occurring in both cases nitrate removal ratios > 80%, and fact allows the selection of one of both depending groundwater polluted case. Also, feeding reactors with 2 C/N ratio showed nitrate removal values of ≥ 95%, treating highly polluted groundwater (100 mg·L−1). The microbial diversity was higher in the methanol-fed reactor with representative phylotypes as Flavobacterium, Cytophagaceae, NS9 marine group, while species richness was higher in the acetate-fed reactor, which was mainly represented by Flavobacterium genus. Statistical analyses revealed the higher resilience of bacterial population on granules fed with acetate, showing more resistance under drop C/N ratio. Oscillating pollution in groundwater during seasonal periods should be treated using acetate as carbon source for denitrification carried out by granular biomass, while stable pollution concentrations over time allow the use of methanol as a carbon source since the greater microbial diversity allows the elimination of other contaminants present in groundwater.

Effects of freeze-thaw intensities on N2O release from subsurface wastewater infiltration system

Subsurface wastewater infiltration system (SWIS) is a low-investment and cost-effective wastewater treatment technology. Nitrous oxide (N2O), an important greenhouse and ozone-depleting gas, is a major by-product of biological denitrification processes within SWIS. Although SWIS has been widely applied in varying zones, until now, whether and how periodical freeze-thaw cycles (FTCs) occurring in aerobic layers affect N2O release still remain unclear? In this study, two runs were arranged, which covered two freeze-thaw (FT) intensities of − 5 °C/5 °C and − 15 °C/5 °C, respectively. An in-situ simulation system of SWIS was carried out to monitor N2O release and microbial community structure in different profiles. The result revealed that raising FT intensity decreased the rate of nitrogen removal of SWIS. Average removal rate of TN under strong FTCs was 88.65–88.97%, which was 1.32–2.47% lower than that under weak FTCs conditions. In addition, a positive correlation was found between FT numbers and N2O release. The contribution of anaerobic zone increased from 29.24% to 75.16% with extending the FT cycles from 1 to 9. High-throughput sequencing results showed that different FT intensities had distinct effects on microbial communities. Euryarchaeota abundance increased significantly under strong FT treatment, while Proteobacteria abundance sharply decreased from 49.5% to 7.6% at day 27 of stable operation. PCA analysis shows that bacterial community composition of samples treated with weak FT and CK is similar. While significant differences in sample composition were found between strong and weak FT treatments, which was the main reason resulting in different N2O release patterns.

Improvement of nitrate-dependent anaerobic ferrous oxidation by EDTA-2Na addition: An effective way for dealing with iron crusts

The nitrate-dependent anaerobic ferrous oxidation (NAFO) is a newly discovered biological denitrification process. However, the formation of iron crusts on the surface of microorganisms by residual ferric iron poses a significant challenge to the maintenance of NAFO performance. To solve the aforementioned issue, this study set up two continuous NAFO systems with (R2) and without EDTA-2Na (R1), and investigated the impact of EDTA-2Na on nitrate removal and microbial community. After 91 days of operation, EDTA-2Na demonstrated the ability to improve the ferrous utilization rate in NAFO process, and the average effluent ferrous concentration was 15.71 mg/L in R2, which was superior to the 50.03 mg/L of R1. Compared with the conventional system, R2 increased nitrate removal by 17 % and stabilized the growth of microorganisms by mitigating iron crusts in the long-term operation. Batch experiments indicated that the optimal nitrate removal efficiency was achieved at an initial Fe/N of 3.24 and a pH of 6.42. High-throughput analysis implied that the reactor with EDTA-2Na contained numerous nitrogen removal pathways. This study provided a practical method for the long-term stable operation of a NAFO system.

Influence of Cellulose on the Anoxic Treatment of Domestic Wastewater in Septic Tanks: Statistical Analysis of the Chemical and Physico-Chemical Parameters

Cellulose is a very common polymer in domestic wastewater (WW), representing a not negligible part of the organic substance contained in sewage. To date, many studies have highlighted the feasibility of reusing this compound in several ways (e.g., building sector, wastewater treatment, energy production, etc.) after its separation from domestic WW. However, studies about the impact of the absence of cellulose on the chemical and physico-chemical parameters of a biological process are still lacking. In this work, two pilot-scale plants were used to simulate an anoxic treatment of WW in septic tanks, with and without cellulose (CWW and NCWW, respectively), for three months. The results of the monitoring highlighted that T, pH, and electrical conductivity (EC) remained almost constants, in both cases. The Spearman correlation coefficients (SCC) for turbidity (TUR), total suspended solids (TSS), and color (COL) indicated a higher removal in the case of CWW (65%, 66%, and 56%, respectively). Organic substance and nitrogen forms showed a similar behavior with and without cellulose, but in the case of CWW, N-NH3 was highly negatively correlated with TUR (SCC: −0.54), TSS (−0.49), and COL (−0.39). A biological denitrification process was highlighted in both cases. Despite these differences, when statistically analyzing the trends of the chemical and physico-chemical parameters for CWW and NCWW, a significant difference due to the absence of cellulose was excluded. These results will be useful to the scientific community, as they exclude that the operational parameters of anoxic treatments and the effectiveness on pollutants removal can be affected in the case of preliminary cellulose separation from domestic WW for recovery/reuse purposes.

Long-Term Operation of a Pilot-Scale Sulfur-Based Autotrophic Denitrification System for Deep Nitrogen Removal

Sulfur-based autotrophic denitrification is a novel biological denitrification process characterized by the absence of an organic carbon source, a short reaction time, a high denitrification rate, a low treatment cost, and a small footprint. However, the technique is facing challenges with respect to engineering applications. In this study, a pilot-scale sulfur-based autotrophic denitrification system was established with an optimal hydraulic retention time (HRT) of 0.21 h, which achieved the highest denitrification load of 1158 mg/(L·d) and a denitrification rate of 164 gNO3−-N/(m3·h). Effective backwashing is the basis for the long-term stable and efficient nitrogen removal performance, which recovered its normal nitrogen removal performance within 0.5 h. In addition, the operation cost is merely 0.013 $/t, indicating that the sulfur-based autotrophic denitrification process presents good economic applicability, and the relatively low operation cost will lay a foundation for practical application.

An enriched ammonia-oxidizing microbiota enables high removal efficiency of ammonia in antibiotic production wastewater

High ammonia concentration hinders the efficient treatment of antibiotic production wastewater (APW). Developing effective ammonia oxidation wastewater treatment strategies is an ideal approach for facilitating APW treatment. Compared with traditional nitrification strategies, the partial nitrification process is more eco-friendly, less energy-intensive, and less excess sludge. The primary limiting factor of the partial nitrification process is increasing ammonia-oxidizing bacteria (AOB) while decreasing nitrite-oxidizing bacteria (NOB). In this study, an efficient AOB microbiota (named AF2) was obtained via enrichment of an aerobic activated sludge (AS0) collected from a pharmaceutical wastewater treatment plant. After a 52-day enrichment of AS0 in 250 mL flasks, the microbiota AE1 with 69.18% Nitrosomonas microorganisms was obtained. Subsequent scaled-up cultivation in a 10 L fermenter led to the AF2 microbiota with 59.22% Nitrosomonas. Low concentration of free ammonia (FA, < 42.01 mg L−1) had a negligible effect on the activity of AF2, and the nitrite-nitrogen accumulation rate (NAR) of AF2 was 98% when FA concentration was 42.01 mg L−1. The specific ammonia oxidation rates (SAORs) at 30 °C and 15 °C were 3.64 kg NH4+-N·kg MLVSS−1·d−1 and 1.43 kg NH4+-N·kg MLVSS−1·d−1 (MLVSS: mixed liquor volatile suspended solids). The SAOR was 0.52 kg NH4+-N·kg MLVSS−1·d−1 when the NaCl concentration was increased from 0 to 20 g L−1, showing that AF2 functioning was stable in a high-level salt environment. The ammonia oxidation performance of AF2 was verified by treating abamectin and lincomycin production wastewater. The NARs of AF2 used for abamectin and lincomycin production wastewater treatment were >90% and the SAORs were 2.39 kg NH4+-N·kg MLVSS−1·d−1 and 0.54 kg NH4+-N·kg MLVSS−1·d−1, respectively, which was higher than the traditional biological denitrification process. In summary, AF2 was effective for APW treatment via enhanced ammonia removal efficiency, demonstrating great potential for future industrial wastewater treatment.

Evaluating the efficacy of slow-releasing carbon source tablets for in situ biological heterotrophic denitrification of groundwater.

Slow-releasing precipitating tablets (SRPTs) and slow-releasing floating tablets (SRFTs) were formulated to release fumarate as a carbon source (CS) and/or electron donor (ED) in an in situ biological heterotrophic denitrification system. These tablets were prepared using pharmaceutical manufacturing. Soil column tests were conducted to evaluate nitrate denitrification efficacy, microbial population changes, and mass balance of fumarate and potential electron acceptors. Significant and simultaneous consumption of both fumarate and nitrate, and the production and consumption of nitrite were observed in both SRPT-treated and SRFT-treated soil columns. These results suggest that SRPT and SRFT releasing fumarate, induce heterotrophic biological denitrification. In the SRPT- and SRFT-treated columns, 65% and 73% of fumarate were associated with heterotrophic denitrification, respectively. Particularly, surplus citric acid, originally designed to serve as a floating agent, was utilized for 36% and 28% for SRFT flotation and denitrification, respectively. The results of 16s RNA analyses revealed that a bacterium that shared 99% 16s rRNA sequence similarity with those of Azoarcus sp. AN9, and Pseudogulbenkiania sp. NH8B, a facultative heterotrophic denitrifier, was detected in the column effluent. This study confirms that SRPT and SRFT can effectively operate long-term in situ biological denitrification processes, because it is possible to supply detailed CS and/or ED uniformly by applying both SRPT and SRFT in the well.

The mechanism of nitrate-Cr(VI) remediation in aquifers stimulated with emulsified vegetable oil: Pathways, microbial communities and functional genes

Nitrate and hexavalent chromium (Cr(VI)) cocontamination in groundwater has become a serious challenge for environmental health. Emulsified vegetable oil in situ technology could simultaneously remediate nitrate and Cr(VI) in groundwater, but the remediation pathways and mechanisms are still unclear. In this research, the biological denitrification processes for nitrate and the reduction and biogenic mineralization processes for Cr(VI) in a cocontaminated aquifer were studied, and the remediation mechanisms were speculated. The results indicated that the addition of emulsified vegetable oil can directionally stimulate the growth of indigenous functional microorganisms and effectively remediate nitrate and Cr(VI) in groundwater. Nitrate in groundwater could be completely reduced to nitrogen gas through biological denitrification without a short circuit. And the remediation processes of Cr(VI) can be divided into two steps: 1) Cr(VI) was reduced to trivalent chromium (Cr(III)) by microbial secondary Fe(II), 2) the reduced Cr(III) was entrapped into aquifer medium in residuals speciation through biogenic mineralization.

Evaluation on applying Condensate from Food Waste Dry Process as External Carbon Source to Biological Denitrification Process

Objectives:In this study, the applicability of dry condensate generated from food waste dry feed conversion process was evaluated as an external carbon source to increase the efficiency of the biological denitrification process.Methods:The experiment was carried out in the form of a batch test, and dry condensate was injected into each reactor according to the COD and T/N ratio (C/N ratio). Then, the reactor was operated under anoxic conditions for 5 hours, and nitrate nitrogen was analyzed at intervals of 1 hour.Results and Discussion:The dry condensate from food waste showed a low nitrogen content (T-N 220 mg/L) compared to a high organic matter content (TCOD 21,863 mg/L), and was analyzed to satisfy the conditions of an external carbon source in the denitrification process. And as a result of the experiment, it was found that the nitrate nitrogen removal efficiency was up to 76% after 5 hours at a C/N ratio 7.50:1, which was significantly increased compared to the control which was without condensed water (removal efficiency 4%). Moreover, the removal efficiency of 28% was exhibited even at the C/N ratio 0.95:1, which exhibited the lowest efficiency. In addition, as a result of calculating the specific denitrification rate (SDNR) for each C/N ratio, 7.50:1 was found to be as 0.0726 mg NO3-/mg VSS/d, which was significantly increased than that of control as 0.0038mg NO3-/mg VSS/d.Conclusion:Based on these results, it is judged that it is possible to utilize the dried condensate of food waste as an external carbon source in the denitrification process.

Application of aerobic denitrifier for simultaneous removal of nitrogen, zinc, and bisphenol A from wastewater

High concentrations of heavy metals and other pollutants affect microbial activity in the wastewater treatment system and impede biological denitrification process. In this study, a novel Zn(II)-resistant aerobic denitrifier (Pseudomonas stutzeri KY-37) was isolated with potential in Bisphenol A (BPA) biodegradation and removal. The capability of this denitrifier in removing nitrogen, zinc, and BPA was tested. Using 56 mg/L nitrate as the sole nitrogen source, its removal efficiency achieved 98.5% in 12 h. This novel denitrifier had a strong auto-aggregation (maximum 65.8%), a high hydrophobicity rate (maximum 88.2%), and a massive amount (maximum 41.1 mg/g cell dry weight) of extracellular polymeric substances (EPS) production. Moreover, Zn(II) removal efficiency reached more than 95% with the initial high concentrations of 200 mg/L. The maximum BPA removal efficiency reached 88.8% with initial 10 mg/L. The removal mechanism of BPA was further explored in terms of microbial degradation, EPS adsorption, and intermediate degradation products.

Nitrate removal from drinking water using different reactor/membrane types: A comprehensive review

Nitrate is considered one of the key contaminants in drinking water sources, particularly groundwater. This could be a result of excessive human activities. Numerous studies have been successfully developed and are still developing eco-friendly and cost-effective treatment techniques for highly efficient nitrate removal from drinking water. Although most of the nitrate removal techniques are physically and chemically based, for example, ion exchange and reverse osmosis, biological treatment is an equally potent approach applied in full scale through autotrophic and heterotrophic denitrification. However, many studies are trying to reduce some of the disadvantages of the biological treatment, such as the need for further treatment for microbial or organic carbon removal. This paper addresses some of the conventional nitrate removal approaches and reviews the biological denitrification processes, highlighting the advantages and disadvantages of the following methods: (i) conventional nitrate removal techniques, (ii) biological denitrification via bioreactor membrane techniques, (iii) membrane bioreactor (MBR), (iv) membrane biofilm-reactor (MBfR), (v) ion exchange membrane bioreactor (IEMBR), and (vi) biofilm-electrode reactor (BER).

Nitrogen Removal from Mature Landfill Leachate via Anammox Based Processes: A Review

Mature landfill leachate is a complex and highly polluted effluent with a large amount of ammonia nitrogen, toxic components and low biodegradability. Its COD/N and BOD5/COD ratios are low, which is not suitable for traditional nitrification and denitrification processes. Anaerobic ammonia oxidation (anammox) is an innovative biological denitrification process, relying on anammox bacteria to form stable biofilms or granules. It has been extensively used in nitrogen removal of mature landfill leachate due to its high efficiency, low cost and sludge yield. This paper reviewed recent advances of anammox based processes for mature landfill leachate treatment. The state of the art anammox process for mature landfill leachate is systematically described, mainly including partial nitrification–anammox, partial nitrification–anammox coupled denitrification. At the same time, the microbiological analysis of the process operation was given. Anaerobic ammonium oxidation (anammox) has the merit of saving the carbon source and aeration energy, while its practical application is mainly limited by an unstable influent condition, operational control and seasonal temperature variation. To improve process efficiency, it is suggested to develop some novel denitrification processes coupled with anammox to reduce the inhibition of anammox bacteria by mature landfill leachate, and to find cheap new carbon sources (methane, waste fruits) to improve the biological denitrification efficiency of the anammox system.

Aerobic Denitrification Is Enhanced Using Biocathode of SMFC in Low-Organic Matter Wastewater

Nitrate (NO3−) in wastewater is a rising global threat to ecological and health safety. A sufficient carbon source, as the electron donor, is essential in the conventional biological denitrification process. It is not appropriate to add extra carbon sources into specific water bodies in terms of material cost and secondary pollution. Thus, innovative NO3− removal technologies that are independent of carbon sources, are urgently needed. This study constructed sediment microbial fuel cells (SMFCs) for aerobic denitrification in low-organic matter wastewater and explored the key factors affecting denitrification efficiencies. The SMFC treatments removed 72–91% NO3− through two main denitrifying stages which were driven by carbon sources (COD) and generated electrons, respectively. After COD was fully consumed, denitrification efficiencies were enhanced in SMFC treatments by 24–47% using the generated electrons within 3 days. In this stage, the NO3− removal efficiencies were positively correlated with external current intensities (p &lt; 0.05). The improved denitrification efficiencies were attributed to two enriched phyla in the SMFC cathode. The dominant genera also demonstrated the heterotrophic denitrifying capacity of the SMFC biocathode. Furthermore, electrical characteristics could be used to monitor or regulate the denitrification process in the SMFC system. In conclusion, this study presents an innovative treatment strategy that is economical and eco-friendly compared with conventional physicochemical methods.