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A new bacterium capable of heterotrophic nitrogen removal was isolated and identified as Oligella sp. XS68. The strain exhibited efficient heterotrophic nitrogen removal capabilities, with a low accumulation of nitrification products. Single-factor experiments indicated that efficient nitrogen removal and growth of the strain XS68 occurred with sodium succinate as the carbon source, C/N ratio 15, pH 6.0-9.0, temperature 30-37 °C, and shaking speed 160-200 rpm. The removal efficiency of ammonium nitrogen could achieve 98 % within 96 h when the initial nitrogen concentration was 421.3 mg L-1. These findings demonstrate that XS68 is a promising candidate for nitrogen removal in wastewater treatments. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox), a promising technology for bio-nitrogen removal, has been a research hotspot in the field of leachate treatment. However, the inhibitory effect of organic matter and high-strength nitrogen on anammox bacteria and the limitation of the theoretical total nitrogen removal efficiency of anammox (<90%) are obstacles to its wider application. The mechanisms of the inhibitory effects of organic matter, ammonium, and nitrite on anammox bacteria, and the corresponding control strategies are summaries. The anammox-based processes developed for advanced nitrogen removal (ANR) in recent years, including anammox-based heterotrophic denitrification, anammox-based partial denitrification, and anammox-based constructed wetlands are systematically discussed. An integrated anaerobic system of simultaneous denitrification and methanogenesis (anaerobic membrane bioreactor) + anammox-based processes was proposed for the ANR and optimal energy recovery from leachate. This process showed a 16% increase in biogas yield, a 64% decrease in aeration energy consumption, and the decrease in the external carbon source is expected to be 100% compared to conventional leachate treatment processes such as anoxic/oxic-membrane bioreactors. Finally, a few research perspectives on leachate treatment using anammox-based processes are reviewed. The conclusions drawn from the studies presented herein provide guidance for further research and engineering applications in the field of leachate treatment. AnMBR pretreatment is proposed for energy recovery and elimination of inhibition of anammox bacteria by organics. Anammox-based heterotrophic denitrification, partial denitrification, and anammox-based constructed wetlands are discussed for ANR. SDM is proposed for ANR from leachate via anammox effluent recirculation. An SDM(AnMBR)+anammox based process is proposed for energy saving and recovery. [ABSTRACT FROM AUTHOR]

• Denitrification alone does not govern N removal in woodchip and coconut husk bioreactors. • Substantial N removal can be achieved via the anammox pathway. • Relative contributions of denitrification and anammox vary between media types used. • Anammox becomes more dominant when denitrification is carbon limited. Denitrification has been considered the main pathway converting nitrate (NO 3 –) to dinitrogen gas (N 2) in denitrifying bioreactors. Here, the importance of an alternative nitrogen (N) removal process, namely anaerobic ammonium oxidation (anammox), was assessed by monitoring the removal of N species from partially nitrified municipal wastewater passing through fifteen mesocosm scale (∼700 L) bioreactors containing woodchip, coconut husk or gravel during their initial and eighth year of operation. Additionally, lab experiments using a 15N isotope-pairing technique were performed to partition production of N 2 to these different microbial processes. The effective removal of both NO 3 – and ammonium (NH 4 +) and the formation of hybrid N 2 (i.e. 29N 2) observed in this study demonstrated that, along with denitrification, anammox was an effective pathway for N removal when both NO 3 – and NH 4 + were present. Anammox removal rates ranged from 0.6 to 3.8 g N per m3 per day, while denitrification rates ranged from 0.7 to 2.6 g N per m3 per day. The contributions of anammox to N removal was dependent on media, with anammox becoming more dominant in bioreactors where denitrification was carbon limited. Designing denitrifying bioreactors to support both denitrification and anammox expands the utility of these passive approaches for improving treatment of wastewater. [ABSTRACT FROM AUTHOR]

A dynamic analysis approach for determining nitrite production and consumption rates was established to systematically investigate the characteristics of nitrogen transformation and N 2 O emission of the completely autotrophic nitrogen removal over nitrite (CANON) process coupled with denitrification using a sequencing batch biofilm reactor (SBBR). The results indicate that anaerobic ammonium-oxidizing bacteria was not inhibited significantly by low C/N ratios. There were no obvious differences in the nitrite production rate, nitrite consumption rate or nitrogen removal among reactors operated with C/N ratios of 0, 0.67 and 1.00, which suggested that the certain carbon source did not significantly affect the nitrite conversion and nitrogen removal in the process. More than 60% of total N 2 O emission is generated during the initial phase of each period in the SBBR. More than 94.5% of N 2 O was generated by NO 2 −-N consumption via denitrification in the process. Interestingly, total N 2 O production drops by 16.7%, when the C/N ratio increases from 0 to 1. This phenomenon may be caused by the inhibition of N 2 O production via AOB denitrification. Therefore, an appropriate carbon source (C/N = 1.00) has the beneficial effect of reducing N 2 O emission by CANON coupled with denitrification. The results of this study provide an important empirical foundation for the mitigation of N 2 O emission in the CANON process coupled with denitrification. Image 1 • N conversion and N 2 O emission were investigated in a CANON coupled with DN process. • AOB and AnAOB were not inhibited significantly by low C/N ratios. • Low C/N ratios did not evidently affect nitrite conversion and nitrogen removal. • More than 94.5% of N 2 O was generated by NO 2 −-N consumption via denitrification. • The C/N ratio should be maintained at 1.00 for the N 2 O emission reduction. [ABSTRACT FROM AUTHOR]

• Both SMX and N-SMX exposure inhibited denitrification and DNRA rates in a short time. • Denitrification and DNRA rates recovered under SMX/N-SMX exposure in a long time. • The removal of nitrogen, SMX, and N-SMX can be achieved simultaneously. • Nitrogen-reducing bacteria that also degrade antibiotics were detected. Constructed wetlands (CWs) are increasingly used to treat complex pollution such as nitrogen and emerging organic micropollutants from anthropogenic sources. In this study, the denitrification, anaerobic ammonium oxidation, dissimilatory nitrate reduction to ammonium, and nitrous oxide release rates following exposure to the frequently detected sulfonamides sulfamethoxazole (SMX) and its human metabolite, N-acetylsulfamethoxazole (N-SMX), were investigated in lab-scale CWs. Over a period of 190 d, the denitrification rates were noticeably inhibited in the SMX and N-SMX groups at week 5. Subsequently, the denitrification rates recovered, accompanied by an increase in the relevant nitrogen reduction and antibiotic resistance genes (ARGs). The composition of the microbial community also changed during this process. After the denitrification rates recovered, Burkholderia _ Paraburkholderia and Gordonia exhibited a significant positive correlation with SMX exposure, which simultaneously reduced nitrate concentrations and degraded antibiotics. Burkholderia _ Paraburkholderia is a key carrier of ARGs. Finally, nitrogen reduction (> 90%) and antibiotic removal (> 80%) also recovered in both SMX- and N-SMX-exposed lab-scale CWs during the operation, which revealed the interaction of SMX or N-SMX removal and nitrogen reduction. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Isolated a bacterial consortium to enable P recovery. • Nitrate is participate in phosphorus bio-recovery process. • Different N species has little influence on the characteristics of products. • Acinetobacter genus dominates phosphorus recovery in different nitrogen species. Recovering finite and non-substitutable phosphorus from liquid waste streams through bio-mediated techniques has attracted increasing interest, but current approaches are incredibly dependent on ammonium. Herein, a process to recover phosphorus from wastewater under multiple nitrogen species conditions was developed. This study compared the effects of nitrogen species on the recovery of phosphorus resources by a bacterial consortium. It found that the consortium could not only efficiently utilize ammonium to enable phosphorus recovery but also utilize nitrate via dissimilatory nitrate reduction to ammonium (DNRA) to recover phosphorus. The characteristics of the generated phosphorus-bearing minerals, including magnesium phosphate and struvite, were evaluated. Furthermore, nitrogen loading positively influenced the stability of the bacterial community structure. The genus Acinetobacter was dominant under nitrate and ammonium conditions, with a relatively stable abundance of 89.01% and 88.54%, respectively. The finding may provide new insights into nutrient biorecovery from phosphorus-containing wastewater contaminated with multiple nitrogen species. [ABSTRACT FROM AUTHOR]

Dissimilatory nitrate reduction to ammonium (DNRA), denitrification, anaerobic ammonium oxidation (anammox) and biological N2 fixation (BNF) can influence the nitrogen (N) use efficiency of rice production. Whilst the effect of N application on BNF is known, little is known about its effect on NO3 - partitioning between DNRA, denitrification and anammox. Here, we investigated the effect of N application on DNRA, denitrification, anammox and BNF, and on the abundance of relevant genes in three paddy soils in Australia. Rice was grown in the glasshouse with (150 kg N ha-1 ) and without N-fertiliser for 75 days, and the rhizosphere and bulk soils were collected separately for laboratory incubation and quantitative PCR analysis. Nitrogen application reduced DNRA rates by >16% in all the soils regardless of the rhizospheric zone but it did not affect the nrfA gene abundance. Without N, the amount and proportion of NO3 - reduced by DNRA (0.42-0.52 µg g-1 soil day-1 , 45-55%) was similar or higher than that by denitrification. However, with N the amount of NO3 - reduced by DNRA (0.32-0.40 µg g-1 soil day-1 ) was 40-50% lower than the NO3 - reduced by denitrification. Denitrification loss increased by >20% with N addition, and was affected by the rhizospheric zones. Nitrogen loss was minimal through anammox, while BNF added 0.02-0.25 µg N g-1 soil day-1. We found that DNRA plays significant positive role in paddy soil N retention as it accounts for up to 55% of the total NO3 - reduction, but this is reduced by N application. [ABSTRACT FROM AUTHOR]

The availability of nitrogen (N) can alter vegetation species composition and diversity in degraded ecosystems. A comprehensive understanding of the dynamic fate of ammonium (NH 4 + -N) and nitrate (NO 3 − -N) processing and the underlying mechanisms are still lacking, particularly in arid to semi-arid degraded ecosystems. We compared and quantified the changes in the rates of net ammonification (R a ), nitrification (R n ) and total mineralization (R m ) and the abundance of bacteria, archaea, and microbial genes related to N transformation on the northern Loess Plateau of China across a 40-year chronosequence of farmland undergoing spontaneous restoration. We found that R a , R n , and R m decreased in grassland soils (0–30-y sites) of different ages and exhibited significant increases at the 40-y sites. The capabilities of the soil to deliver NH 4 + -N and NO 3 − -N were not a limiting factor during the growing season after 40 years of vegetation recovery. Soil mineral nitrogen may be not suitable for predicting and assessing the long-term (approximately 40 years) restoration success and progress. The abundance of functional N genes showed differences in sensitivity to natural vegetation recovery of abandoned farmland, which likely reflects the fact that the multi-pathways driven by N functional microbial communities had a large influence on the dynamic fate of NH 4 + -N and NO 3 − -N. Quantitative response relationships between net N transformation rates and microbial genes related to N transformation were established, and these relationships confirmed that different N transformation processes were strongly linked with certain N functional genes, and collaboratively contributed to N transformation as vegetation recovery progressed. Specifically, R a was controlled by AOA- amoA , AOB- amoA , and nxrA ; R n was governed by napA , narG , nirK , nirS , and nosZ ; and R m was controlled by nifH , apr , AOA- amoA , AOB- amoA , nirS , and nirK . [ABSTRACT FROM AUTHOR]

[Display omitted] • An aerobic-heterotrophic nitrogen removal strain was isolated from saltern sediment. • The strain removed nitrogen from high-salinity (2–10% (w/v) NaCl) wastewater. • Nitrogen removal occurred via ammonium assimilation and HN-AD processes. • The complete genome of the strain was sequenced. • A complex nitrogen metabolism network was proposed. Nitrogen (N) removal from high-salinity wastewater is a major challenge. The aerobic-heterotrophic nitrogen removal (AHNR) process has been demonstrated to be feasible for treating hypersaline wastewater. In this study, Halomonas venusta SND-01, a halophilic strain capable of performing AHNR, was isolated from saltern sediment. The strain achieved ammonium, nitrite, and nitrate removal efficiencies of 98%, 81%, and 100%, respectively. The N balance experiment suggests that this isolate removes N mainly via assimilation. Various functional genes related to N metabolism were found in the genome of the strain, establishing a complex AHNR pathway that includes ammonium assimilation, heterotrophic nitrification-aerobic denitrification, and assimilatory nitrate reduction. Four key enzymes in the N removal process were successfully expressed. The strain exhibited high-adaptability under C/N ratios of 5–15, salinities of 2%−10% (m/v), and pH of 6.5–9.5. Therefore, the strain shows high potential for treating saline wastewater with different inorganic N compositions. [ABSTRACT FROM AUTHOR]

Mechanisms through which microorganisms are impacted by surface application of ground cover and nutrient source in organic orchard management are not fully understood. Twelve ground cover (compost, wood chips, paper mulch, or mow-and-blow) by fertilizer (poultry litter, organic commercial, or a no-fertilizer control) treatment combinations were applied annually in April beginning in 2006, with soil collected in March 2007 and 2013 to determine the 1-year and 7-year effects of treatments on soil chemical and biological properties. Organic matter (OM) increased through time regardless of ground cover treatment averaged across fertilizers, with the greatest increase occurring with compost addition. Soil water content, microbial biomass N, ammonium-N, and nitrate-N were greater in 2013 than in 2007 at the 0–10 cm depth. Denaturing gradient gel electrophoresis analysis of denitrifying ( nirK) communities revealed that fertilizers did not have a significant main effect or interaction with ground covers. Greater nirK richness and diversity coincided with clustering of the nirK community composition within compost treatments, and greater dissolved organic carbon concentrations with compost compared to wood chip or mow-and-blow treatments in 2007. By 2013 nirK communities in wood chip and compost ground covers tended to cluster together. Furthermore, soil nirK richness increased significantly from 2007 to 2013 in compost and wood chip treatments and was greatest in 2013 under those two ground covers. Diversity with wood chip addition increased from among the least in 2007 to among the greatest in 2013. Greater richness and diversity and community composition in the nirK community within a year of compost additions and gradually over time with wood chip addition indicate potential for enhanced denitrification in low OM, organic apple orchard soil receiving compost and wood chips mulches. [ABSTRACT FROM AUTHOR]

Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer-reviewed papers and conducted a meta-analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil NH4+ (12%) and soil total N (210%), although it decreased soil NO3− (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil N2O fluxes as well as hydrological NH4+ and NO2− fluxes more than threefold, although it decreased the hydrological dissolved organic nitrogen ( DON) flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta-analysis. Overall, this meta-analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro-ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro-ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized. [ABSTRACT FROM AUTHOR]

Removal of biologically available nitrogen (N) by the microbially mediated processes denitrification and anaerobic ammonium oxidation (anammox) affects ecosystem N availability. Although few studies have examined temperature responses of denitrification and anammox, previous work suggests that denitrification could become more important than anammox in response to climate warming. To test this hypothesis, we determined whether temperature responses of denitrification and anammox differed in shelf and estuarine sediments from coastal Rhode Island over a seasonal cycle. The influence of temperature and organic C availability was further assessed in a 12-week laboratory microcosm experiment. Temperature responses, as characterized by thermal optima ( Topt) and apparent activation energy ( Ea), were determined by measuring potential rates of denitrification and anammox at 31 discrete temperatures ranging from 3 to 59 °C. With a few exceptions, Topt and Ea of denitrification and anammox did not differ in Rhode Island sediments over the seasonal cycle. In microcosm sediments, Ea was somewhat lower for anammox compared to denitrification across all treatments. However, Topt did not differ between processes, and neither Ea nor Topt changed with warming or carbon addition. Thus, the two processes behaved similarly in terms of temperature responses, and these responses were not influenced by warming. This led us to reject the hypothesis that anammox is more cold-adapted than denitrification in our study system. Overall, our study suggests that temperature responses of both processes can be accurately modeled for temperate regions in the future using a single set of parameters, which are likely not to change over the next century as a result of predicted climate warming. We further conclude that climate warming will not directly alter the partitioning of N flow through anammox and denitrification. [ABSTRACT FROM AUTHOR]

High organic loadings to constructed wetlands can result in water quality issues such as low dissolved oxygen and high ammonium concentrations, with artificial aeration a potential mitigation option. This study compared baseline (no aeration – NA), continuous aeration (CA), and intermittent aeration (IA) conditions to improve water quality in a tertiary treatment free water surface constructed wetland (FWS CW) with night time hypoxia/anoxia, and high nutrient concentrations. The response variables included dissolved oxygen (DO), total nitrogen (TN), ammonium nitrogen (NH 4 +-N), nitrate nitrogen (NO 3 −-N), total phosphorus (TP), phosphate (PO 4 3–-P), and dissolved organic carbon (DOC). In situ aeration and monitoring was performed from April to June 2021 in a large, field-scale FWS CW, the Laratinga wetlands Mount Barker, South Australia. The results demonstrated that DO increased by an average 2.11 mg L−1 from NA to CA during the night and 1.26 mg L−1 and 1.84 mg L−1 from NA to IA during the night and day respectively when averaging over the basins. The C/N ratio was very low and there was no significant influence of DO on DOC concentrations. There was no significant difference in TN concentrations with the application of aeration aside from a decrease in the channel at night from NA to IA, and an increase in NH 4 +-N resulted under IA compared with NA in Basin 1 and 2 during the day. This implies that the N loadings exceeded the wetland's ability to complete nutrient conversions at a rate that aligns with input rate. The concentrations of NO 3 −-N increased at night under CA and IA treatments suggesting that some nitrification was promoted, or there was inhibition of dissimilatory nitrate reduction to ammonium. The concentrations of TP and PO 4 3–-P significantly increased with the aeration compared with no aeration, however there was no difference between the aeration treatments. This suggested that increased sediment resuspension during aeration increased P in the water. There was no change in DOC with the application of aeration. Overall, the DO increased with aeration application and may be able to better support the wetland ecology; however, the Laratinga wetland is overloaded and the capacity of the wetland to effectively transform and remove nutrients is inhibited, even with the application of artificial aeration. • Dissolved oxygen increased with the application of continuous and intermittent aeration. • There was no change in total nitrogen with aeration and ammonium levels remained high. • There was a small increase in nitrate, and total and soluble phosphorus with aeration. • Despite near-neutral pH values, unionised ammonia was calculated to be at toxic levels. • Using aeration to manage systems with high nutrient loadings is challenging. [ABSTRACT FROM AUTHOR]

Ammonium (NH 4 +) enrichment of riverbank filtration (RBF) systems is gaining popularity. However, most previous research has concentrated on NO 3 − removal efficiencies, while the mechanisms of NH 4 + enrichment remain unknown. A nitrogen biogeochemical process model was developed for the quantitative analysis of NH 4 + enrichment in the Kaladian well field in northwest Songyuan City, NE China. Data from laboratory experiments and in-situ monitoring were used to determine initial values and calibrate the thermodynamic/kinetic parameters representing nitrogen (N) biogeochemical reactions. (1) The NO 3 − from river was subjected to denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) within 10–14 m of the shore, whereas the NH 4 + in groundwater was caused by DNRA, organic nitrogen mineralization (MIN), and mixing with laterally recharged high NH 4 + groundwater. (2) DNF and DNRA were regulated by hydrodynamic processes, with the ranges of these processes being more significant in the wet season due to a higher hydraulic gradient. MIN occurred widely throughout the water flow path, with temperature primarily controlling the rates of the three reactions. (3) DNRA activity was relatively higher in the wet season when the water temperature was higher within 10–14 m of the shore. In the wet season, DNRA contributed 25%–30% to NO 3 − reduction, which was higher than in the dry season (5%–10%). DNRA contributed at least 40% and 15% to NH 4 + enrichment in the wet and dry seasons, respectively. (4). Organic N in media gradually released NH 4 + into groundwater via MIN and desorption across the entire flow path, with contributions to NH 4 + enrichment reaching 75% and 85%, respectively, in the wet and dry seasons. • Spatiotemporal variations of N biogeochemical reactions in RBF were identified. • Conditions for denitrification, DNRA, and mineralization in RBF were identified. • Simulation parameters were refined through multi-environmental N experiments. • Contributions of DNRA to NO 3 − reduction and NH 4 + enrichment were quantified. • Introduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • The coupling of Feammox and NDFO is novel and cost-effective. • The comparison between this process and other denitrification technologies is summarized. • The main factors affecting the coupling process and the research of the process are analyzed. • The transformation forms of iron and nitrogen are two key issues in the coupling process. [ABSTRACT FROM AUTHOR]

The oxidation of ammonium (NH 4 + ) under iron reducing conditions, also referred to as Feammox, has been described in recent years by several investigators. The environmental characteristics in which the Feammox process occurs need to be understood in order to determine its contribution to the nitrogen cycle. In this study, through extensive field sampling at various locations in the US (mostly New Jersey) and South China, soil chemical analyses, serial incubation experiments, analysis of microbial communities, and using canonical correspondence analyses, it was determined that the soil pH, as well as its Fe(III) and NH 4 + concentration were the most important factors controlling the distribution of Acidimicrobiaceae , which have been linked to the Feammox reaction. Under the conditions that favored the presence of Feammox bacteria and their oxidation of NH 4 + under iron reducing conditions, denitrification bacteria were also abundant. However, the presence of known nitrous oxide (N 2 O) reducers was limited under these conditions, implying that at locations where the Feammox process is active, conditions might favor a higher N 2 O:N 2 ratio for the nitrogen (N) end products. To determine the effect of dissolved oxygen (DO) on NH 4 + oxidation under iron reducing conditions, incubations were conducted at two different DO levels. In incubations with DO < 0.02 mg/L, and when NH 4 + oxidation was noticeable, the proportion of Acidimicrobiaceae with respect to total bacteria increased, while the proportion of other known NH 4 + oxidizing bacteria (aerobic ammonia-oxidizing bacteria and anammox bacteria) decreased. In incubations of the same soil but with DO = 0.8–1.0 mg/L the opposite trend was observed, indicating that Feammox favored very low or no DO in these incubations. [ABSTRACT FROM AUTHOR]

Acinetobacter junii YB was found to exhibit efficient heterotrophic nitrification and aerobic denitrification ability, with the maximum ammonium, nitrite and nitrate removal rate of 8.82, 8.45 and 7.98 mg/L/h, respectively. Meanwhile, ammonium was found to be removed preferentially in the process of simultaneous nitrification and denitrification in mixed N-sources. The successful PCR amplification of hao , nap A and nir S genes further provided additional evidence of heterotrophic nitrification and aerobic denitrification by strain YB. In addition, orthogonal test showed that dissolved oxygen was the most important determinant of nitrite removal, and the optimal conditions were C/N 15, pH 7.0, 37 °C and 200 rpm. Furthermore, stable nitrogen and organics removal were achieved by one-time dosing of enriched bacteria in a sequencing batch reactor. The inoculation of strain YB significantly improved the denitrification efficiency with minimal accumulation of nitrified products, which demonstrated high potential of the isolate for future practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Continuous aeration in membrane-aerated biofilms resulted in full nitrification. • Intermittent aeration suppressed nitrite oxidation and supported anammox process. • Biofilm pH presented periodic upshifts with aeration switches. • Free ammonia speciation likely caused the inhibition of nitrite-oxidizing bacteria. • Heterotrophs established nitrous oxide-reduction zones under intermittent aeration. Membrane-aerated biofilm reactors (MABR) are being applied for autotrophic nitrogen removal, yet control of nitrogen turnover remains challenging in MABR counter-diffusion biofilms. In this study, we regulated microbial activities in two lab-scale MABRs by providing continuous versus intermittent aeration. Nitrogen consumption by different functional microbial groups was estimated from bulk measurements via a mass balance approach. Nitrite-oxidizing bacteria (NOB) proliferated under continuous aeration while they were significantly suppressed under intermittent aeration, and NOB suppression activated anaerobic ammonium oxidation. Nitritation performance in the MABR was studied through long-term bulk measurements and in situ biofilm microprofiles of dissolved oxygen (DO) and pH. During intermittent aeration pH effects rather than DO effects determined nitritation success, especially ammonia speciation, which serves as substrate and inhibitor in nitrification processes. Biofilm transition phases were monitored upon aeration switches. Canonical correspondence analysis suggested that the relative transition after anoxia and aeration intermittency were less decisive for biofilm performance than the relative aeration duration. Heterotrophic bacteria displayed minor denitrification rates with aeration control, but contributed to mitigation of nitrous oxide (N 2 O) emissions. N 2 O production hotspots were identified at the top of the anoxic biofilm zone under continuous aeration. Instead, under intermittent aeration an anoxic N 2 O reduction zone was established. Our observations support intermittent aeration control of MABRs as a simple strategy for energy-efficient nitrogen removal with low N 2 O emission.. [ABSTRACT FROM AUTHOR]

• A novel dPAO from aquaculture sediment was isolated. • Strain K14 could utilize ammonium through assimilation rather than nitrification. • The strain can effectively remove phosphorus during ammonium assimilation. • The napA , nirS , norB , nosZ , and ppk genes coexisted in strain K14. 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. [ABSTRACT FROM AUTHOR]

A combination of anaerobic ammonium oxidation (anammox) with sulfur-autotrophic denitrification is a promising alternative for complete nitrogen removal. Herein, a novel anammox coupled with sulfite-driven autotrophic denitrification (ASDAD) is firstly proposed. The influence of pH (8.5–6.5) on nitrogen removal and N 2 O emission is investigated in an anaerobic sequencing batch biofilm reactor fed with low-nitrogen wastewater containing sulfite. Long-term operation demonstrates that a maximum nitrogen removal of 94.5% occurred at a pH of 7.5 and that the contribution of autotrophic denitrification to nitrogen removal increased as the pH declined. Cyclic and batch experiments verify that anammox and sulfite-autotrophic denitrification simultaneously participates in nitrogen removal, and the stoichiometry for sulfite-driven autotrophic denitrification is firstly proposed. Furthermore, N 2 O accumulation is also highly correlated with the pH. The N 2 O emission peaks at a pH of 6.5 due to the inactivated anammox and incomplete autotrophic denitrification of nitrite at such a low pH. High-throughput sequencing reveals the coexistence of anammox (Candidatus Brocadia and Candidatus Kuenenia) and sulfur-oxidizing species (Thiobacillus). Finally, the schema for nitrogen conversion and N 2 O formation of ASDAD is elucidated based on metagenomic metabolism. This study offers a cost-effective and environment-friendly completely autotrophic nitrogen removal process for municipal wastewater with a low carbon-to-nitrogen ratio in practice. [Display omitted] • A novel anammox-sulfite autotrophic denitrification (ASDAD) process was developed. • Optimal pH for maximum nitrogen removal of ASDAD was 7.5 • N 2 O emission factor was the highest as 0.71% at a pH of 6.5 • Co-existence of C. Brocadia , C. Kuenenia and Thiobacillus promoted ASDAD. • Schema for nitrogen conversion and N 2 O formation was elucidated. [ABSTRACT FROM AUTHOR]

As water flows from the North Pacific Ocean to the Arctic Ocean, it passes through the shallow eastern shelf of the Bering Sea which serves as a major sink of inorganic nitrogen. This study explores the physical and biological factors that influence the spatiotemporal variability of this sink. A regional relationship of dissolved inorganic nitrogen to inorganic phosphorus (DIN:P) was established for waters entering the shelf. Residuals from this relationship (termed N∗∗) are a measure of the nitrogen deficit and were determined for bottom waters on the shelf using nutrient data collected on 52 hydrographic cruises spanning 2003 – 2018. Spatial variability in N∗∗ was related to advection, cross-shelf and vertical mixing, and residence time (using simulated ages of bottom water over the middle shelf). On average, this deficit accounted for approximately one-third of the inorganic nitrogen that enters the shelf, and the highest deficits (>8 ​μM DIN) were observed on the middle shelf between 60°N and St. Lawrence Island (63°N). Temporal variability in N∗∗ was examined over the middle shelf, and higher nitrogen deficits that occurred in colder years were hypothesized to result from weaker flow and increased export of organic matter in the presence of sea ice. On the southern middle shelf, the volume integrated (40 ​m to bottom) seasonal change in N∗∗ was equivalent to a denitrification rate of 0.7 ​± ​0.3 ​mmol ​N m-2 d-1. Rates of nitrogen loss were also estimated by combining N∗∗ with the simulated residence time of water on the shelf and found to be 0.20 ​± ​0.02 ​mmol ​N m-2 d-1. These rates were comparable to prior measurements of denitrification/anammox reported on the shelf. The nitrogen deficit could not be wholly ascribed to denitrification/anammox as the N:P stoichiometric ratio in particulate matter is known to be lower at higher latitudes, and a lower ratio was observed when dissolved organic matter was measured in a small number of samples. It remains unclear how future reductions in sea ice might impact the extent of nitrogen loss in the Bering Sea. • Bottom water nitrogen deficit was determined using 15 years of hydrographic data. • The northern middle shelf had the highest deficits and longest residence times. • Seasonal and interannual variability was associated with variability of sea-ice. [ABSTRACT FROM AUTHOR]

Influence of anammox process on autotrophic denitrification was investigated in this study, during simultaneous ammonium, nitrate and sulfide treatment. Elemental sulfur production and nitrogen removal by sulfide-dependent denitrifier (S-den) and mixed culture (S-den-anammox) were compared. Accumulation of nitrite (100%) and elemental sulfur (46.3%) was achieved at pH 7.0 and 30 °C with S 2 O 3 2−/NO 3 − ratio of 1:1 by autotrophic denitrifier. Enhanced elemental sulfur production (56.5%–99.5%) by autotrophic denitrifier was obtained after coupling with anammox process. Total nitrogen removal increased to 80.5% in mixed culture reactor, which was 72.0% in anammox reactor. N 2 O emission in anammox reactor was not affected (<0.5% gaseous nitrogen) after coupling with autotrophic denitrification. Therefore, this study demonstrated enhanced elemental sulfur recovery and nitrogen removal through coupling of sulfide-dependent denitrification and anammox processes, which might be a potential technology for water eutrophication and corrosion control, and atmospheric acid rain, PM 2.5 and global warming control. Image 1 • Removal of NO 3 −, S2− and NH 4 + was achieved in sulfide-dependent DEAMOX process. • Elemental sulfur production was enhanced 26.8% after cooperation with anammox. • TN removal increased about 10% in sulfide-dependent DEAMOX reactor. • NO x was lower than 0.5% gaseous nitrogen in sulfide-dependent DEAMOX reactor. [ABSTRACT FROM AUTHOR]

• A red yeast capable of heterotrophic nitrifying-aerobic denitrifying was isolated. • The yeast tolerated high concentrations (140 mg·L-1) of NH 4 +-N, NO 2 −-N and NO 3 −-N. • The maximum NH 4 +-N removal percentage reached 99.85% at 36 h. • The yeast exhibited optimal growth and nitrogen removal efficiency on glucose. • The functional genes nirK, napA and amoA were successfully amplified. Heterotrophic nitrification and aerobic denitrification (HN-AD), which is primarily performed by bacteria rather than fungi, is an attractive approach for nitrogen removal. In this study, a red yeast, Sporidiobolus pararoseus Y1, was isolated and shown to exhibit optimal growth and nitrogen removal efficiency on glucose, followed by citrate, sucrose, acetate and starch. The nitrogen removal efficiency increased with increasing initial concentrations of NH 4 +-N, NO 2 −-N and NO 3 −-N from 14 to 140 mg·L-1. At an initial nitrogen concentration of 140 mg·L-1, the maximum removal efficiencies of NH 4 +-N, NO 2 −-N and NO 3 −-N were 98.67%, 97.13% and 83.51% after 72 h incubation, while those of corresponding total nitrogen were 88.89%, 81.31% and 70.18%, respectively. The nitrification (amoA) and denitrification genes (nirK and napA) were amplified from Y1. These results suggest that yeast are also capable of HN-AD, which can be used to remove nitrogen in wastewater systems. [ABSTRACT FROM AUTHOR]

• Denitrification and assimilatory nitrate reduction contributed to N management. • Excessive nitrogen loss was averted during the N removal processes. • In-situ eliminated NO 2 − and NH 4 + without adding external carbon sources. • YL28 showed the great potential to be used as the safe probiotics. 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. [ABSTRACT FROM AUTHOR]