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The Acinetobacter indicus strain ZJB20129 isolated from an urban sewage treatment plant demonstrated the heterotrophic nitrification-aerobic denitrification (HN-AD) ability. Stain ZJB20129 could remove 98.73% of ammonium-N, 97.26% of nitrite-N and 96.55% of nitrate-N, and the maximum removal rate was 3.66, 4.62 and 5.21 mg/L/h, respectively. Ammonium was preferentially used during simultaneous nitrification and denitrification. Strain ZJB20129 exhibited highest ammonium removal capability when carbon source was sodium succinate, C/N ratio was 15, pH was 8.0, and temperature was 35 ℃. Key enzymes involved in HN-AD including hydroxylamine oxidase, periplasmic nitrate reductase and nitrite reductase as well as their encoding genes were detected, and the metabolic pathway of HN-AD was subsequently predicted. Our results suggested that Acinetobacter indicus ZJB20129 displayed superior nitrogen removal performance on actual wastewater and thus made it have a good application prospect in wastewater biological treatment.

In this study, the fluctuating profiles of physicochemical and microbial characterizations along different filling heights of continuously up-flow solid-phase denitrification (SPD) columns packed with polycaprolactone (PCL) were investigated. It was found both the PCL filling area and non-filling area made significant contributions to treatment performance and denitrification mainly occurred near the bottom of the filling column. Nitrate displayed a high proportional removal (≥98.7%) among all the cases except the one with the lowest filling ratio (FR30) and highest NLR (3.99 ± 0.12 gN/(L·d)), while nitrite and ammonium displayed a weak accumulation in final effluents (nitrite ≤ 0.40 mg/L; ammonium ≤ 0.98 mg/L). The intensity of PCL hydrolysis in the top substrate was stronger than those in the middle or bottom. Both dissimilatory nitrate reduction to ammonium (DNRA) and microbial lysis contributed to ammonium accumulation, and nitrate was mainly removed via traditional denitrification and DNRA. JGI_0000069-P22_unclassified and Gracilibacteria_unclassified might contribute to denitrification.

This study presented a novel simultaneous partial nitritation (PN), denitratation and anammox (SPNDA) process for treating ammonium and nitrate wastewater. Results indicated that SPNDA could achieve a great total nitrogen (TN) removal of 97.6 ± 0.5%, leading to effluent TN concentration of only 3.4 mg/L. Mass balance indicated that nitrogen removal rates via anammox, simultaneous nitrification and denitrification were 96.7% and 3.3%, respectively. Extended aerobic duration (12 h) and low dissolved oxygen (DO) concentration (0.15 mg/L) could improve ammonia-oxidizing bacteria (AOB) activity and maintain PN stability. The stable suppression of nitrite-oxidizing bacteria activity was attributed to the low DO (0.15 mg/L) and high free ammonia (3.63 mg/L) in SPND. Besides, the nitrogen conversion mechanisms for SPNDA were revealed based on a typical operational cycle. Microbial analysis showed that AOB (Nitrosomonas) and partial denitrifying bacteria (Thauera and Denitratisoma) coexisted with anammox bacteria (Candidatus Brocadia and Candidatus Anammoxoglobus) in the mixotrophic bio-community.

The nitrogen metabolic pathways of Pseudomonas taiwanensis J488 have not been confirmed from genomic function analysis and its divalent metal ion resistance remains poorly understood. In this study, the key denitrifying gene of Pseudomonas taiwanensis J488, nirB, was determined by draft genome sequencing. The nitrification of ammonium was insensitive to high concentrations of Ca(II), Mn(II), Zn(II), and Cd(II). Similarly, complete nitrite removal was achieved despite Mn(II) and Zn(II) reaching concentrations up to 30 mg/L. Furthermore, the efficiency of nitrate removal was significantly enhanced by 1.33%, 3.33%, 5.99%, and 1.53% with the addition of 0.5 mg/L Ca(II), 20 mg/L Mn(II), 5 mg/L Zn(II), and 2 mg/L Cd(II), respectively, comparison with the control. The bacterial growth in both nitrifying and denitrifying processes was substantially promoted by various dosages of divalent metal ions. These results indicate that divalent metal ions would not severely limit the capacity of strain J488 to purify nitrogen-polluted wastewater.

The one-stage partial nitritation and anammox process with the hydroxyapatite (HAP)-based syntrophic granules was studied for the ammonium nitrogen removal from the effluents of a self-agitated anaerobic baffled reactor treating the fish processing wastewater. When the ammonium in the influent was 1140 mg N·L-1, a high nitrogen removal rate and nitrogen removal efficiency of 1.51 ± 0.10 kg N·m−3·d-1 and 88.2% were obtained, respectively. Anammox bacteria of Candidatus Kuenenia stuttgartiensis and ammonium oxidizing bacteria of Nitrosomonas were the two most predominant bacteria, while nitrite oxidizing bacteria activity was low and could be neglected during the treatment. The inorganic element properties of the sludge were analyzed by several methods to confirm the existence of HAP granules. Optical microscopic observation and scanning electron microscopy analysis revealed the structure of the granular sludge. This study supports the feasibility and potential of this process for high-efficiency nitrogen removal from fish processing wastewater.

Heterotrophic nitrifying and aerobic denitrifying bacteria (HNADB) are important for partial nitrification treatment of high strength ammonium leachate. However, conditions for their optimal performance in mixed reactor systems have yet to be determined. In this study, optimal parameters were identified and included free ammonia (FA) concentrations below 40 mg/L, a dissolved oxygen concentration of 1.2 mg/L, a carbon to nitrogen ratio of 5 and a reflux ratio of 4. These conditions were applied to a continuous anoxic/oxic membrane moving biofilm reactor treating raw incineration leachate with high total ammonium nitrogen (TAN = 1400 mg/L). Ammonium conversion and nitrogen removal efficiencies of 99% and 86% were achieved. Autotrophic ammonia oxidizing bacteria were inhibited at FA concentrations above 25 mg/L. HNADB, particularly Paracoccus species, contributed to ammonium conversion at high FA (25–40 mg/L). These results show that leachate with high TAN and FA can be treated using parameters that support the growth of HNADB.

A novel bacterial strain that exhibited a high capacity for the simultaneous degradation and removal of tylosin and ammonia nitrogen, respectively, was isolated from tylosin fermentation dregs (TFDs) and identified as Klebsiella pneumoniae TN-1. The removal efficiencies of tylosin and ammonia nitrogen reached 95.31% and 83.26%, respectively, at initial concentrations of 300 mg/L for both. Three identified intermediates with less toxicity indicated that de-sugarization and hydrolysis were the proposed biodegradation pathways. The results also suggested that strain TN-1 could reduce nitrogen loss by transforming ammonium into nitrate nitrogen according to the transcriptional expression of nitrogen transformation-related genes and the activities of functional enzymes. Moreover, strain TN-1 effectively reduced ammonia volatilization by 65.20% and facilitated tylosin degradation, with a maximum removal efficiency of 57.35% in the simulated fermentation process of TFDs. This work provides an efficient bioaugmentation for simultaneous antibiotic degradation and nitrogen conservation during the composting process.

Pseudomonas stutzeri strain XL-2 presented efficient ammonium removal due to heterotrophic nitrification-aerobic denitrification. The modified walnut shell biochar also showed ammonium adsorption due to chemical interaction. The complex of modified biochar and strain XL-2 exhibited excellent synergistic effects on ammonium removal, especially in unfavorable environment. The maximum average ammonium removal rate of the complex was 4.40 mg·L−1·h−1, which was 3.01 times higher than that of pure bacteria and 5.57 times higher than that of biochar. A large number of irregular pores and hydrophilic functional groups promoted the immobilization of strain XL-2 on biochar. Adsorption of ammonium, high specific surface area and release of Mg2+ by biochar enhanced biodegradation of strain XL-2. Approximately 96.34%−98.73% of ammonium was removed in a sequencing batch reactor (SBR) inoculating with the complex of strain XL-2 and biochar, which was much higher than the treatment efficiency of free bacteria in SBR.

Partial nitritation-anaerobic ammonium oxidation (PN-Anammox) was successfully applied for high-strength ammonium iron oxide red wastewater (IORW) treatment based on stable PN performance of zeolite-biological aerated filter (ZBAF). By separating Na2CO3 dosage avoid the high free ammonia (FA) inhibited nitritation, two-stage ZBAF was applied for achieving efficient PN with Na2CO3 as the alkalinity donor and saving about 40.0% of the alkalinity cost compared to NaHCO3. Moreover, Anammox was used for further nitrogen removal from IORW and stable total nitrogen (TN) removal was obtained at the influent NH 4 + -N concentration of 567 mg/L and TN removal efficiency kept above 70.0% after 100 days operation. High throughput sequencing-based approaches showed that Nitrosomoadaceae (AOB) and Kuenenia was dominance in two-stage ZBAF and Anammox samples respectively, while Nitrospire and Nitrobacter (NOB) undetected. The combined process should have advantages for similar high-strength ammonium wastewater treatment.

A new acid-resistant bacterium Acinetobacter sp. JR1 was isolated, and its feasibility in nitrogen removal was investigated under acidic condition. Results show that JR1 indicated excellent ammonium and nitrate removal abilities with no accumulation of intermediates, and the maximum ammonium and nitrate removal efficiencies were 98.5% and 91.1%, respectively. Further experiments demonstrated that JR1 preferred to use ammonium with ammonium and nitrate as the mixed N-sources. For JR1, ammonium was assimilated directly as nutrients into cells and also converted into N2 through heterotrophic nitrification-aerobic denitrification. Under acidic condition, JR1 performed comparable nitrogen removal abilities to other strains under neutral or weak alkaline environment, and the efficient removal of ammonium occurred at pH 4.5–10, C/N 12–24, 20–40 °C, DO ≥4.72 mg/L, 0–1.5% of salinity, 10 mg/L Zn2+ or 20 mg/L Mn2+. All these make JR1 a promising candidate for treating acidic wastewater containing nitrogen.

An aerobic heterotrophic nitrogen removal bacterium strain, B1, was isolated from aquaculture water and identified as Pannonibacter phragmitetus (99% similarity) by 16S rRNA sequencing analysis. When ammonium, nitrite or nitrate was the sole nitrogen source, with an initial nitrogen concentration of 14 mg/L, the nitrogen removal efficiencies were 98.66%, 99.96% and 98.73%, respectively, and the corresponding maximum removal rates reached as high as 1.16, 0.77 and 0.81 mg/L/h, respectively. In the presence of NH4+-N, the removal efficiency of 56 mg/L NO2−-N within 27 h increased by 83.50%, and the corresponding removal rate reached as high as 1.72 mg/L/h. Additionally, different carbon sources ( dl -malic acid, sucrose, sodium citrate, and glucose) could be utilized in nitrogen removal. Sequence amplification indicates that the denitrification genes nirK, norB and narG are present in strain B1. All results demonstrate that strain B1 has high promise for future applications of removing inorganic nitrogen from wastewater.

Pseudomonas stutzeri XL-2, with the capability of heterotrophic nitrification-aerobic denitrification and biofilm-forming, was applied in a sequencing batch biofilm reactor (SBBR) for bioaugmented treatment of ammonium-rich wastewater. The bioaugmented system SBBR 1 showed a rapid development of biofilm and relatively shorter time for biofilm hanging compared with the control system SBBR 2 without strain XL-2 inoculation. At different NH4+-N loads of 100, 200 and 300 mg/L, the effluent TN removal ratios ranged in 88.7–97.0%, 85.1–93.5% and 87.8–92.5% respectively in SBBR 1, while only ranged in 77.4–85.4%, 77.1–84.3% and 79.8–85.0% in SBBR 2. Less accumulation of NO2−-N and NO3−-N resulted in the better performance on TN removal in SBBR 1. Microbial community structure analysis revealed that strain XL-2 successfully proliferated in SBBR 1 and contributed to the less accumulation of NO2−-N and NO3−-N as well as biofilm formation.

Stable nitritation for low-strength ammonium wastewater was the key obstacle for cost-effective and low-carbon biological nitrogen removal. A zeolite biological fixed bed (ZBFB) and an anoxic sequencing batch reactor (ASBR) were successfully applied for achieving nitritation-denitrification of low-strength ammonium wastewater by adsorption, biological desorption and denitrification. Based on free ammonia inhibition on biofilm, stable nitrite accumulation could be realized with suitable operational time and aeration in biological desorption. During cycle operation, adsorption effluent NH4+-N kept at 3.0–4.0 mg/L, biological desorption effluent NO2−-N maintained at 226.8–243.2 mg/L with average nitrite accumulation ratio of 97.18%, and nitrite removal rate was about 0.628–0.672 kg NO2−-N·m−3·day−1, revealing obvious feasibility of ZBFB and ASBR for low-strength ammonium wastewater treatment. High-throughput sequencing analysis results further presented significant microbial community variations happened after cycle operation, with ammonia oxidizing bacteria enrichment and nitrite oxidizing bacteria inhibition in ZBFB and dominance of denitrifiers in ASBR.

© 2018 Elsevier Ltd A comprehensive mathematical model was constructed to evaluate the complex substrate and microbial interaction in algal-bacterial photo sequencing batch reactors (PSBR). The kinetics of metabolite, growth and endogenous respiration of ammonia oxidizing bacteria, nitrite oxidizing bacteria and heterotrophic bacteria were coupled to those of microalgae and then embedded into widely-used activated sludge model series. The impact of light intensity was considered for microalgae growth, while the effect of inorganic carbon was considered for each microorganism. The integrated model framework was assessed using experimental data from algal-bacterial consortia performing sidestream nitritation/denitritation. The validity of the model was further evaluated based on dataset from PSBR performing mainstream nitrification. The developed model could satisfactorily capture the dynamics of microbial populations and substrates under different operational conditions (i.e. feeding, carbon dosing and illuminating mode, light intensity, influent ammonium concentration), which might serve as a powerful tool for optimizing the novel algal-bacterial nitrogen removal processes.

The ability of cyanobacterium Arthrospira sp. to assimilate waste nitrogen sources (ammonium and urea) makes it an important candidate for wastewater management. The aim of this work was to evaluate a cultivation approach based on continuous-transitional-feeding regime (nitrate-ammonium-nitrate) in a photobioreactor to assess the effects of ammonium salts on Arthrospira sp. PCC 8005 metabolism. Using a comprehensive biochemical, proteomic and stoichiometric profiling of biomass, this study demonstrated that the proposed cultivation approach could increase the proteins and pigments yields by 20-30%, compared to the respective yields obtained from wild-type Arthrospira sp. strain A light-energy-transfer model was used to predict the biomass and oxygen productivities of Arthrospira sp. cultivated under transitional-feeding regime. 95 ± 2% match was observed between the experimental and simulated productivities. This study thus opened new avenues for use of ammonium rich wastewater for commercial production of high value pigments, biofuel and bioplastics using Arthrospira sp.

This study investigated a novel bioreactor configuration coupled with a side-stream dynamic membrane (DM) for Anammox enrichment as an alternative for conventional membrane. Bioreactor was fed with synthetic feed and seeded with a mix of anaerobic and aerobic sludge. In situ mechanical cleaning was employed for DM cleaning. DM development and performance was analysed over two polyamide-nylon meshes (200 and 52 µm). Solid-liquid separation of 52 µm mesh outperformed 200 µm with an average effluent turbidity of 2.4 ± 0.1 NTU. The system was operated at a maximum nitrogen loading rate of 696 mg-N L−1 d−1 and achieved a maximum nitrogen removal rate of 611.6 mg-N L−1 d−1. At steady state, the average ammonium, nitrite and total nitrogen removal efficiencies were 87 ± 0.6%, 98.5 ± 0.15% and 87.5 ± 0.56% respectively. Digital realtime PCR Sequence analysis showed that Planctomycetales belonging to ascertained Anammox-specific genera progressively increased their presence in the reactor consistently with its nitrogen removal performance. © 2018 Elsevier Ltd

The single-stage nitrogen removal using anammox and partial nitritation (SNAP) is a promising alternative for low-cost ammonium removal from wastewaters. This study aimed to evaluate the anammox biomass enrichment and SNAP process start-up in a laboratory-scale membrane-aerated biofilm reactor (MABR) at nitrogen loading rates of 50 g N.m−3.d−1 (period 1) and 100 g N.m−3.d−1 (period 2). Anammox activity was observed after 48 days, and the SNAP process was stable after 80 days. In period 1, the average total nitrogen (TN) removal was 78 ± 6%, and the maximum removal was 84%. In period 2, the average TN removal was 61 ± 5%, and the maximum was 69%. Higher dissolved oxygen levels may have caused imbalances in the microbial community in period 2, decreasing the reactor performance. These results demonstrated the potential of the MABR for the fast implementation of the single-stage partial nitritation and anammox processes.

The effect of phosphate on marine anammox bacteria (MAB)-dominated anammox process in nitrogen-laden saline wastewater was first investigated. The activity of MAB was enhanced by dosing low concentrations of phosphate (5–30 mg/L PO43−-P), and the time of complete ammonium removal was shortened by 0.5 h. When PO43−-P exceeded 160 mg/L, the calcium magnesium phosphate precipitation was formed in the reactor. The contact between substrates and biomass was hindered by the sediments, and the nitrogen removal performance of MAB was also worsened. At 400 mg/L PO43−-P, the ammonium removal rate and nitrite removal rate decreased to 0.45 and 0.43 kg/(m3⋅d), respectively. During the 158-day operation, MAB was still the dominant strain, but its relative abundance decreased by 15.4% at 400 mg/L PO43−-P. Besides, the presence of sediments stimulated the production of extracellular polymeric substances and the maximum yield reached 11.25 mg/g⋅wet weight at 200 mg/L PO43−-P.

The removal efficacy of biological nitrogen removal process is inhibited by low temperatures. Herein, a psychrotrophic bacterium strain, Bacillus simplex H-b, was isolated and identified with the potential to conduct heterotrophic nitrification and aerobic denitrification in the temperature range from 5 to 37 °C. At 10 °C, the removal efficiencies of initial nitrate–N (63 mg/L), nitrite–N (10 mg/L) and ammonium–N (60 mg/L) were 67.29%, 78.69% and 82.16%, with the maximum removal rate of 0.56, 0.18 and 0.74 mg/L/h, respectively. Additionally, both the accumulation level of ATP (adenosine triphosphate) and the formation of extracellular polymeric substances was found to increase with the decrease of temperature from 37 °C to 10 °C, indicating strain H-b might resist low temperature stress through its cellular extreme environment resistant mechanism and further suggesting the newly isolated strain could serve as a promising candidate for nitrogen contaminated wastewater treatment, especially under low-temperature condition.

The efficient removal of ammonium nitrogen (NH4+-N) is vital to eliminating black and odorous water bodies. In this work, tidal flow constructed wetlands with gravel (TFCW-G) and with a mixture of zeolite and gravel (TFCW-Z) were set up to treat black and odorous water bodies at different hydraulic loading rates (HLRs). Results showed that zeolite significantly enhanced nitrogen removal, and the maximum NH4+-N removal efficiency of 96.69% was achieved in TFCW-Z at HLR of 3 m·d−1 with a flooding and drying cycle of 2 h. Zeolite addition changed the microbial community structure and the abundance of nitrification genes. Comammox Nitrospira was the only enriched strain accounting for NH4+-N removal in TFCW-G, while the co-occurrence of comammox Nitrospira and the canonical and potential ammonia-oxidizing bacteria were identified in TFCW-Z. Summarily, high performance, together with low footprint and low maintenance cost, are characteristics that make the TFCW-Z a promising and competitive alternative.

A single up-flow thiosulfate-driven nitrate denitratation coupled with the sulfurized Anammox (TDSA) with the core–shell structure (S0@ Anammox granules) provided a chemical/energy-saving way for the removal of high-content ammonium with nitrate as electron acceptor. Approximately 83.66% total nitrogen removal efficiency (TNRE) could be achieved by the sulfurized Anammox encrusted by S0/Sn2− at a high loading rate (2.6 kg-N/(m3·d)) via resisting high concentration of free ammonia (FA) (22.35 mg/L), mainly through S2O32−, S0/Sn2− -driven partial denitrification-Anammox (PDN-Anammox) process. Moreover, S0/Sn2−-PDN-Anammox was largely restricted when intermittently aerated, but still resulting in 74.47% TNRE due to the partial nitrification-Anammox (PN-Anammox). The sequencing analysis revealed that Anammox bacterium (Candidatus_Kuenenia) and sulfur-oxidizing bacterium (Thiobacillus) coexisted, in which Anammox process occurred mainly via NO instead of NH2OH. This study provided a new perspective for high concentration nitrogen wastewater removal in engineering applications.

Pseudomonas chloritidismutans K14, a novel phosphate-accumulating organism with the capacity to perform ammonium assimilation, aerobic denitrification, and phosphorus removal, was isolated from aquaculture sediments. It produced no hemolysin, and showed susceptibility to most antibiotics. Optimum conditions were achieved with sodium pyruvate as a carbon source, a C/N ratio of 10, pH of 7.5, temperature of 27 °C, P/N ratio of 0.26, and shaking at 140 rpm. Under optimum conditions, the highest removal efficiencies of ammonium, nitrite, and nitrate were 99.82%, 99.11%, and 99.78%, respectively; the corresponding removal rates were 6.27, 4.51, and 4.99 mg/L/h. The strain removed over 98% of phosphorus, and over 87% of chemical oxygen demand. The highest biomass nitrogen during ammonium assimilation was 99.18 mg/L; no gaseous nitrogen was produced. The genes involved in nitrogen and phosphorus removal were amplified by PCR. This study demonstrated the potential application prospects of strain K14 for nitrogen and phosphorus removal.

The feasibility of in situ start-up of mainstream anammox process was investigated in three parallel sequencing batch biofilm reactors (SBBRs) inoculated with nitrification sludge, partial nitrification sludge, and denitrifying phosphorus removal sludge, respectively. The SBBRs were operated under alternate anaerobic/aerobic/anoxic pattern at ambient temperature (16.5–26.8 °C). The influent organic and nitrogen loading rates were increased stepwise. Anammox bacteria grew exponentially with relative abundance and overall bacterial activity increasing from 0 to 0.004% to 0.29–0.40% and ‘not detected’ to 6–7 mg N/L/h, respectively. Desirable nitrogen removal efficiency of about 86% was obtained in 3–4 months for the influent nitrogen of 40.5–73.6 mg N/L. Anammox was the primary nitrogen transformation pathway. For the anammox bacterial enrichment, biofilm, alternate anaerobic/aerobic/anoxic pattern, and limited aeration played important roles. Seed sludge with high ammonium oxidizing bacterial activity further promoted the start-up of anammox process. The in situ start-up strategy could promote the full-scale application of mainstream anammox.

In this study, a partially-saturated vertical-flow constructed wetland (VFCW) with continuous-feed was operated to investigate nutrients transformation and possible pathways in unsaturated and saturated zones. Effect of temperature on nutrients removal and microbial community was also evaluated. The variation of temperature barely affected removal of NH4+-N and COD, achieving removal efficiencies of 99.5–100.0% and 96.8–100.0% at effluent temperature of 14.9–27.7 °C. The removal of COD, NH4+-N, total inorganic nitrogen (TIN) and total phosphorus mainly occurred in unsaturated zone, achieving much higher removal rates than saturated zone. Nitrification process in the VFCW was associated with autotrophic/heterotrophic ammonia oxidizing bacteria and nitrite oxidizing bacteria. Denitrification process relied on both autotrophic and heterotrophic denitrifiers. Anaerobic ammonium oxidizing bacteria was also detected, contributing to TIN removal. All of the groups for nutrients removal exhibited higher abundance in unsaturated zone. Diverse pathways co-existed for nitrogen removal, while the main metabolic pathways were different along the depth.

Anaerobic ammonium oxidation (anammox) is an autotrophic denitrification process that has broad application potential for treating coking wastewaters. The present study estimated the effects of thiocyanate (SCN−), a common pollutant in coking wastewaters, on anammox processes and microbial communities in anammox reactors for over two years of continuous exposure. The addition of SCN− (from 50 to 200 mg L−1) showed negative effects on the denitrification performance of the anammox reactors. In SCN−-dosed reactors, increased effluent ammonium concentrations indicated the occurrence of SCN−-based biodegradation processes. Microbial analysis revealed that the anammox species almost disappeared in the reactor dosed with SCN− at over 100 mg L−1. Instead, an abundance of chemolithoautotrophic bacteria belonging to the Thiobacillus genus demonstrated a linear increase with SCN− addition. The competition between anammox species and SCN−-degrading microorganisms was expected to dominate the inhibition effects of SCN− addition on the performance of anammox reactors.

The performance of nitrogen and organic carbon removal in a single reactor (R1) operating with A. faecalis strain NR aerobically was assessed. Under 150 mg/L influent NH4+-N, 91.3%, 71.4% and 90.9% of NH4+-N, TN and TOC were removed, presenting much higher efficiency than a control bioreactor inoculating activated sludge (R0). The amoA gene expression from strain NR in R1 was 7.8 times higher than that from activated sludge in R0, demonstrating the role of strain NR in removing NH4+. The analysis of microbial community composition revealed that strain NR was the dominant species and outcompeted ammonium oxidizing bacterium (AOB) under high organic carbon as well as ammonium. Simultaneous ammonium and organic carbon removal still maintained for a long-term operation with NH4+-N loadings of 300 and 450 mg/L in R1. Nitrogen balance showed that stripped NH3 only occupied a few percentages and aerobic denitrification played a significant role in nitrogen removal.

This study presents a novel denitratation/anammox biofilter (DABF) for nitrate removal from secondary effluent, where denitratation (NO3–→NO2–) is coupled with anammox (NO2– +NH4+→N2) instead of denitritation (NO2–→N2). Total nitrogen (TN) was removed by 81.90% in this DABF when the average effluent TN concentration was 7.82 mg/L. Meanwhile, organic carbon source consumption and backwash sludge production in the DABF were reduced by 63% and 70%, respectively, compared to conventional denitrifying biofilter (DNBF). Nitrogen banlance analysis indicates that 93% of the nitrogen gas produced in DABF was via anammox. Batch tests confirmed that the DABF biofilm reduced nitrite using ammonium as the electron donor, and accumulated nitrite during denitratation, thus providing nitrite for the anammox bacteria. Moreover, high-throughput sequencing approach also revealed that the anammox bacteria Candidatus Brocadia dominated the community, which could also be responsible for the stable processes in DABF by interacting with the other denitrifying bacteria.

A set of constructed wetlands (CWs) under different biochar addition ratios (0%, 10%, 20%, and 30%) was established to analyze the pollutant removal performance enhancement and nitrous oxide (N2O) emission reduction from various angles, including microbial community structure, functional genes and enzyme activity. Results revealed that the average removal efficiencies of ammonium (NH4+-N) and total nitrogen (TN) were improved by 2.6%-5.2% and 2.5%-7.0%. Meanwhile, N2O emissions were reduced by 56.0%-67.5% after biochar addition. Increased nitrogen removal efficiency and decreased N2O emissions resulted from the increase of biochar addition ratio. Biochar addition changed the microbial community diversity and similarity. The relative abundance of functional microorganisms such as Nitrosomonas, Nitrospira, Thauera and Pseudomonas, increased due to biochar addition, which promoted the nitrogen cycle and N2O emission reduction. High gene copy number and enzyme activity involved in nitrification and denitrification process were obtained in biochar CWs, moderating N2O emission.

This study aimed at assessing the influence of aeration mode and influent COD/N ratio on nitrogen removal in constructed wetlands (CWs). The results showed that a simultaneous partial nitrification, anammox and denitrification (SNAD) process was established in the intermittent aerated V1. While nitrogen removal pathway gradually changed from partial nitrification-denitrification to complete nitrification-denitrification along with reducing COD/N ratio in the continuous limited aerated V2. Effective inhibition of NOBs under intermittent aeration conditions, good retention of anammox bacteria biomass and much faster depletion of COD prior to substantial NH4+-N conversion jointly led to the successful achievement of stable SNDA process with elevated influent COD/N ratios in V1. Furthermore, the presence of SNAD ensured a robust ammonium (84-92%) and TN (80-91%) removal efficiency in V1 under varying COD loading rates. In contrast, the TN removal efficiency decreased rapidly along with the reducing influent COD/N ratios in V2.

Partial oxidation of ammonium to nitrite is a pre- and crucial step to achieve shortcut biological nitrogen removal from ammonium-rich wastewater. In the present study, a nitritation granular reactor using activated sludge as inoculum was started up in a sequencing batch reactor (SBR) at a fixed influent C/N ratio of 2:1. Variations in the reactor performance, functional bacteria activities, sludge morphology and bacterial community structure were investigated. Results showed the formation of compact granules was achieved in 55 days, and a stable nitrite accumulation rate of 0.68 kg N·m−3·d−1 was maintained in the following period. With a rapid growth of granular size, the total nitrogen removal by simultaneous nitritation/denitritation was progressively increased to 50%. In sludge granulation, the significant enrichment of r-strategist ammonium oxidizing bacteria (Nitrosomonas) was identified. Additionally, both high free ammonia concentration and extra nitrite competition by heterotrophic denitrifiers were critical to suppress nitrite oxidizing bacteria effectively.

To enhance nutrient removal more cost-efficiently in microaerobic process treating piggery wastewater characterized by high ammonium (NH4+-N) and low chemical oxygen demand (COD) to total nitrogen (TN) ratio, a novel upflow microaerobic biofilm reactor (UMBR) was constructed and the efficiency in nutrient removal was evaluated with various influent COD/TN ratios and reflux ratios. The results showed that the biofilm on the carriers had increased the biomass in the UMBR and enhanced the enrichment of slow-growth-rate bacteria such as nitrifiers, denitrifiers and anammox bacteria. The packed bed allowed the microaerobic biofilm process perform well at a low reflux ratio of 35 with a NH4+-N and TN removal as high as 93.1% and 89.9%, respectively. Compared with the previously developed upflow microaerobic sludge reactor, the UMBR had not changed the dominant anammox approach to nitrogen removal, but was more cost-efficiently in treating organic wastewater with high NH4+-N and low COD/TN ratio.

This study compared two anammox sequencing batch reactors (SBR) for one year. SBRconstantT was kept at 30 degrees C while temperature in SBRloweringT was decreased step-wise from 30 degrees C to 20 degrees C and 15 degrees C followed by over 140 days at 12.5 degrees C and 10 degrees C. High retention of anammox bacteria (AnAOB) and minimization of competition with AnAOB were key. 5-L anoxic reactors with the same inoculum were fed synthetic influent containing 25.9 mg NH4+-N/L and 34.1 mg NO2--N/L (no COD). Specific ammonium removal rates continuously increased in SBRconstantT, reaching 785 mg NH4+-N/gVSS/d, and were maintained in SBRloweringT, reaching 82.2 and 91.8 mg NH4+-N/gVSS/d at 12.5 and 10 degrees C respectively. AnAOB enrichment (increasing hzsA and 16S rDNA gene concentrations) and adaptation (shift from Ca. Brocadia to Ca. Kuenenia in SBRloweringT) contributed to these high rates. Rapidly settling granules developed, with average diameters of 1.2 (SBRconstantT) and 1.6 mm (SBRloweringT). Results reinforce the potential of anammox for mainstream applications.

The utilization of halophilic bioresources is limited due to a lack of isolation and characterization work. A halophilic bacterium strain SND-01 of Exiguobacterium mexicanum was isolated in this study, which is the first report on its novel function in heterotrophic nitrification-aerobic denitrification (HN-AD). The strain SND-01 is slightly halophilic, surviving at 0 up to 9% (w/v) salinity. When utilizing ammonium, nitrate or nitrite as the sole nitrogen source in aerobic conditions, the isolated strain showed the maximum nitrogen removal rate of 2.24 ± 0.14 mg/(L·h), 3.63 ± 0.21 mg/(L·h) and 2.30 ± 0.23 mg/(L·h), respectively. Functional genes and key enzymes involved in heterotrophic-aerobic nitrogen transformations were characterized, establishing the pathway of HN-AD. The nitrogen removal via HN-AD is dependent on the C/N ratio, salinity and temperature. The halophilic Exiguobacterium mexicanum strain SND-01 shows a significant potential in biotreatment of saline wastewater in an easy and cost-effective way.

The effect of glucose on nitrogen removal and microbial communities in the anammox-denitrification systems was investigated. The optimal nitrogen removal could be achieved when the influent glucose concentration was 56.4mgL-1. The influent nitrite to ammonium ratio of 0.95-1.40 would not obviously affect the nitrogen removal due to the coexistence of anammox, denitrification and partial denitrification. The anammox activity was deteriorated with increasing glucose concentration. When the influent glucose concentration was increased to 374.9mgL-1, the average ammonium removal efficiency decreased from 97% to around 10% and anammox activity was seriously inhibited. The anammox activity quickly recovered with decreasing influent glucose and increasing influent nitrite. High-throughput sequencing analysis suggested that the predominant genus changed from Candidatus Kuenenia to Diaphorobacter with the addition of glucose and then changed to Hydrogenophaga with the decrease of glucose. It indicated that organics concentration had an effect on the microbial communities.

The performance of an autotrophic nitrogen removal process to treat digested piggery wastewater (DPW) was investigated by gradually shortening the HRT and enhancing the DPW concentration during 390 days of operation. The results showed that the total nitrogen removal rate and efficiency reached 3.9 kg-N m −3 day −1 and 73%, which were significantly higher than the levels reported previously. A high relative abundance of Nitrosomonas (4.2%) and functional microbes (12.15%) resulted in a high aerobic ammonium oxidizing activity (1.25 ± 0.1 g-N g VSS −1 d −1 ), and a good settling ability (SVI, 78.42 mL g −1 SS) resulted in a high sludge concentration (VSS, 11.01 g L −1 ), which laid a solid foundation for the excellent performance. High-throughput pyrosequencing indicated that, compared with synthetic wastewater, the DPW decreased the relative abundances of every functional group of nitrogen removal microbes, and increased relative abundances of anaerobes (15.7%), sulfur-oxidizing bacteria (9.4%) and methanogens (40.8%).

The ability of Arthrobacter arilaitensis Y-10 for nitrogen removal from simulated wastewater was studied. Results showed that ammonium was the best inorganic nitrogen for strain Y-10’s cell growth, which could also promote nitrate reduction. Approximately 100.0% of ammonium was removed in the nitrogen removal experiments. The nitrate removal efficiency was 73.3% with nitrate as sole nitrogen source, and then the nitrate efficiency was increased to 85.3% and 100.0% with ammonium and nitrate (both about 5 or 100 mg/L) as the mixed nitrogen sources. Nitrite accumulation was observed in presence of ammonium and nitrate. When the concentration of sole nitrite nitrogen was 10.31 mg/L, the nitrite removal efficiency was 100.0%. Neither ammonium nor nitrate was accumulated during the whole experimental process. All experimental results indicated that A. arilaitensis Y-10 could remove ammonium, nitrate and nitrite at 15 °C from wastewater, and could also perform simultaneous nitrification and denitrification under aerobic condition.

This study tested the feasibility of plug-flow integrated fixed-film activated sludge (IFAS) reactor in applying sewage partial nitritation/anammox (PN/A) process. The IFAS reactor was fed with real pre-treated sewage (C/N ratio = 1.3) and operated for 200 days. High nitrogen removal efficiency of 82% was achieved with nitrogen removal rates of 0.097 ± 0.019 kg N/(m3·d). Therefore, plug-flow IFAS reactor could be an alternative to applying sewage PN/A process. Besides, it was found that the stability of sewage PN/A process was significantly affected by residual ammonium. Nitrate accumulated in effluent and PN/A performance deteriorated when residual ammonium was below 1 mg/L. On the contrary, long-term stable PN/A operation was achieved when residual ammonium was over 3 mg/L.

Heterotrophic bacterium, Enterobacter cloacae CF-S27 exhibited simultaneous nitrification and aerobic denitrification in presence of high concentration of hydroxylamine. With the initial nitrogen concentration of 100 mg L−1 h−1, ammonium, nitrate and nitrite removal efficiencies were 81%, 99.9% and 92.8%, while the corresponding maximum removal rates reached as high as 11.6, 15.1 and 11.2 mg L−1 h−1 respectively. Quantitative amplification by real time PCR and enzyme assay demonstrated that hydroxylamine reductase gene (hao) is actively involved in hetrotrophic nitrification and aerobic denitrification process of Enterobacter cloacae CF-S27. PCR primers were designed targeting amplification of hao gene from diversified environmental soil DNA. The strain Enterobacter cloacae CF-S27 significantly maintained the undetectable amount of dissolved nitrogen throughout 60 days of zero water exchange fish culture experiment in domestic wastewater.

This work demonstrates the feasibility of simultaneous nitrogen removal and external waste activated sludge (WAS) reutilization/reduction by using the synergy of sludge fermentation, denitrification and anammox processes in up-flow reactors (SFDA). Pre-treated domestic wastewater and synthetic wastewater (containing nitrite ∼20mg/L, ammonium ∼10mg/L in both) were fed to 1# and 2# SFDA, respectively. Long-term operation of 1# SFDA was investigated with achieving the peak ammonium removal rate of 0.021 and nitrite removal rate of 0.081kgN/(m(3)d) as nitrogen loading rate elevated from 0.075 to 0.106kgN/(m(3)d). Negative effect of dissolved oxygen on anammox or fermentation in the 2# SFDA was demonstrated negligible due to rapid depletion by microorganisms. Furthermore, a "net" sludge reduction of 38.8% was obtained due to sludge decay and organics consumption by denitrification. The SFDA process was expected to potentially be used for nitrogen removal and WAS reutilization/reduction in full-scale application.

A novel hybrid anaerobic-aerobic baffled reactor (HAOBR) with four compartments was constructed to treat manure-free piggery wastewater with an average COD/TN ratio as low as 0.98, without any supplement of external carbon source. Inoculated with aerobic activated sludge and operated at hydraulic retention time 36 h, 32 °C and reflux ratio 2.0, the reactor could perform steadily within 24 days. The removal of COD, NH4+-N and TN within the 21-days steady phase averaged 87.0%, 100% and 91.3%, respectively. Analysis of stoichiometry and results of high-throughput pyrosequencing revealed that the excellent nitrogen removal in the HAOBR was achieved by the cooperation of heterotrophic and autotrophic denitrification with anammox as the dominant approach. Compared with the previously developed microaerobic treatment processes and the recently reported modified A/O process, the HAOBR was more cost-efficient in treating manure-free piggery wastewater because of the less energy consumption, rapid startup process and efficient nutrients removal.

A novel strain DQ01 capable of simultaneous removal of nitrate and ammonium under the aerobic condition was isolated from the landfill leachate and identified as Stenotrophomonas maltophilia. The result showed that S. maltophilia had carbon selection for the nitrogen removal pathway, and preferred to utilize carboxylate rather than carbohydrate, as carboxylate could directly participate in TCA cycle without Embden Meyerhof Parmas (EMP). Nitrogen and carbon balances confirmed that the ammonium assimilation was the main or even sole removal pathway for S. maltophilia, and carboxylate was more conducive to heterotrophic nitrification-aerobic denitrification (HN-AD) process due to the serious self-alkalization and higher reduction potential of carboxylate, which followed: NH4+ → NO2− → NO3− → NO2− → NO due to the lack of nor and nos. Meanwhile, the higher C/N and nitrate could generate a more powerful ion transport driving force to accelerate the electron transfer in the denitrifying respiratory chain.

Nitrogen pollution in aquaculture needs the efficient and cost-effective in-situ technology. This study aims to apply Marichromatium gracile YL28 to in-situ bioremediation and test its ability to maintain the nitrogen balance in aquaculture. In laboratory aquaculture system, approximately 99.96% of nitrite (1 mg/L) was removed within 7 d through denitrification coupled with assimilatory nitrate reduction. Ammonium (3.5 mg/L) of 95.6% was directly assimilated by YL28 within 7 d. Moreover, in zero exchange water from shrimp (Penaeus vannamei) aquaculture field trials (20 days), YL28 significantly reduced the ammonium accumulation (0.6 mg/L) and 99.3% of nitrite (1.25 mg/L). Toxicological studies with the Institute of Cancer Research (ICR) mice and Oryzias melastigma indicated that M. gracile YL28 can be safely applied in aquatic ecosystems. All results demonstrate that strain YL28 has high promise for future applications of removing inorganic nitrogen and maintaining the nitrogen balance from in-situ aquaculture.

A spontaneous development of full-scale anaerobic ammonium oxidation (anammox) process was seldom reported, and its operational parameters could supply references in actual applications. This engineered case indicated that anammox process was suitable for treating relatively high-strength ammonium and organics wastewater due to niche differentiation of biofilm. Results of isotope labelling showed that anammox contributed approximately 40% to N-loss in aerobic unit, but this value increased to 78.3% in anoxic tank. Mass balance showed that N-removal via anammox and denitrification pathways were 38.1 and 23.9 g m−3 d−1, and anammox rate was 1.6 times higher than denitrifiaction. The wild-type anammox granules had a high purity, with anammox accounting for 92.2%. Candidatus Brocadia was the predominant species. Mixing sludge had a higher oxygen tolerance compared with granules, although the latter had a higher anammox activity under anaerobic conditions. Moreover, physicochemical precipitation on the surface of granules may be related to granulation mechanism.

A novel strain NP5 with efficient heterotrophic nitrification, aerobic denitrification and phosphorus accumulation ability was isolated and identified as Pseudomonas putida strain NP5. The removed ammonium and phosphate were mainly converted into intracellular components by assimilation, and negligible nitrification intermediates and N2O were accumulated during heterotrophic nitrification. In addition, the optimal conditions for nutrient removal were: succinate as carbon source, C/N 10, P/N 0.2, temperature 30 °C, salinity 0% and shaking speed 160 rpm. Besides, strain NP5 possessed an exceptional heavy metal and nanoparticles resistance. Cr6+ was found to be the most toxic among the tested metals, and it could be removed simultaneously. Moreover, an obvious phosphorus release was observed under anaerobic condition, and repeated exposure to the anaerobic/aerobic conditions could significantly improve the nutrient removal. Furthermore, the successful expression of key enzymes for nitrogen and phosphorous removal provided additional evidence for possibility of simultaneous nitrification, denitrification and phosphorus removal.

For municipal wastewater with low temperature and ammonium, conventional oxygen-limited have difficulty achieving long-term stable inhibition of nitrite oxidizing bacteria (NOB) and stable nitritation. So a partial nitrification-anaerobic ammonium oxidation integrated reactor with independent partitions was used to investigate the feasibility of adding an auto-recycling system to promote low exposure of nitrite in the aerobic zone and to inhibit the NOB activity. The results showed that nitrite produced in the aerobic zone could be timely transported to the anaerobic zone for Anammox utilization, and the nitrite nitrogen concentration was diluted to keep within 1 mg/L in the aerobic zone by the effluent recycling. NOB growth was inhibited by nitrite deficiency. The maximum nitrogen removal rate of the reactor was 0.29 kg/(m3·d), and the nitrate nitrogen production rate of NOB was controlled within 0.04 kg/(m3·d). Nitrosomonas and Candidatus Kuenenia were found as functional species of ammonia-oxidizing bacteria and Anammox bacteria, respectively.

Recently, a flocculent-granular hybrid reactor was reported as a novel nitrogen removal system; however, the mechanisms of stable operation in the system remain unclear. In this study, the mechanisms of the stable nitrogen removal performance in a flocculent-granular hybrid system were investigated with temperature reduction. The operational period was divided into three phases with different temperatures ranges. In phase I, the nitrogen removal efficiency was stabilized at about 90% with nitrogen removal load maintained at approximately 0.28 kg N/(m3·day). In phase II, while decreasing the temperature to 20 °C, the activities of key enzymes were reduced immediately and were then maintained at a certain level. The relative abundances of aerobic ammonium-oxidizing bacteria and anaerobic ammonium-oxidizing bacteria gradually increased at this phase. In phase III, after the temperature dropped to 15 °C, the activities of key enzymes gradually increased due to adaptation to low temperature, boosting the nitrogen removal efficiency to 83%.