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Dissimilatory nitrate reduction to ammonium (DNRA) received more attention for its ability to recover ammonium. This study investigated the possibility of low-frequency infrared electromagnetic field (IR-EMF) to improve DNRA. The optimal IR-EMF intensity of 0.04 μT could effectively improve DNRA activity of nonwoven fabric membrane bioreactors. In the long-term operation, the average ammonium conversion efficiency was enhanced by 117.7% and 62.5% under 0.04 μT and 0.06 μT IR-EMF, respectively. The highest nrfA-gene abundance and potential DNRA rate were obtained under 0.04 μT IR-EMF exposure. Bacteroidetes fragilis, Shewanelle oneidensis MR-1, and Thauera sp. RT1901 were selected to investigate the dynamic response of nitrogen transformation and energy metabolism to IR-EMF. The transcriptome sequencing and RT-qPCR results suggested that IR-EMF could enhance both denitrification and DNRA process, mainly by improving ATP synthesis to boost metabolic activity. This study provided an efficient method for the nitrogen recovery via DNRA process by applying IR-EMF. [ABSTRACT FROM AUTHOR]

The integrated fixed‐film activated sludge (IFAS) process is considered one of the cutting‐edge solutions to the traditional wastewater treatment challenges, allowing suspended sludge and attached biofilm to grow in the same system. In addition, the coupling of IFAS with anaerobic ammonium oxidation (Anammox) can further improve the efficiency of biological denitrification. This paper summarises the research progress of IFAS coupled with the anammox process, including partial nitrification anammox, simultaneous partial nitrification anammox and denitrification, and partial denitrification anammox technologies, and describes the factors that limit the development of related processes. The effects of dissolved oxygen, influent carbon source, sludge retention time, temperature, microbial community, and nitrite‐oxidising bacteria inhibition methods on the anammox of IFAS are presented. At the same time, this paper gives an outlook on future research focus and engineering practice direction of the process. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effects of salinity on elemental sulfur-driven autotrophic denitrification (SAD) efficiency, and microbial communities. The results revealed that when the salinity was≤6 g/L, the nitrate removal efficiency in SAD increased with the increasing salinity reaching 95.53% at 6 g/L salinity. Above this salt concentration, the performance of SAD gradually decreased, and the nitrate removal efficiency decreased to 33.63% at 25 g/L salinity. Approximately 5mg/L of the hazardous nitrite was detectable at 15 g/L salinity, but decreased at 25 g/L salinity, accompanied by the generation of ammonium. When the salinity was ≥15 g/L, the abundance of the salt-tolerant microorganisms, Thiobacillus and Sulfurimonas, increased, while that of other microbial species decreased. This study provides support for the practical application of elemental sulfur-driven autotrophic denitrification in saline nitrate wastewater. [ABSTRACT FROM AUTHOR]

The California current system (CCS) hosts one of the largest oxygen minimum zones (OMZs) in the world: the Eastern North Pacific (ENP) OMZ, which is dissociated into a subtropical and tropical region (i.e., the ESTNP and ETNP). In the modern ENP OMZ, bioavailable nitrogen (N) is lost via denitrification and anaerobic ammonium oxidation (anammox). Even so, paleo-reconstructions of N-loss have focused solely on denitrification. Fluctuations in bulk sedimentary δ15N over glacial-interglacial cycles have been interpreted to reflect variations in denitrification rates in response to ETNP OMZ intensity changes. This δ15N signal is thought to be transported northwards to the ESTNP OMZ. Here, we present the first CCS sedimentary record of ladderane lipids, biomarkers for anammox, located within the ESTNP OMZ (32° N; 118° W). Over the last two glacial terminations (~160 cal ka BP), ladderane concentrations were analysed in combination with the index of ladderanes with five cyclobutane moieties (NL5), short-chain (SC) ladderane degradation products, and productivity proxies. This shows that: 1) ladderanes derived from anammox bacteria living within the ESTNP OMZ water column; 2) ladderanes were continuously present, with relatively high concentrations during both glacial- and interglacial-periods, showcasing the ESTNP OMZ must have retained an anoxic core in which N-loss occurred; and 3) anammox abundance appears to have been driven both by OM-remineralization and advection changes, which regulated nutrient and oxygen levels. Our study shows that anammox was an important feature in the CCS and provides a more holistic picture of N-loss dynamics and the development of the ESTNP OMZ over glacial-interglacial cycles. Lastly, ladderanes were also detected in 160–500 cal ka BP sediments (15.7–37.5 mbsf; analysed at a low temporal resolution), highlighting their potential as anammox biomarkers in relatively deeper buried sediments for future studies. [ABSTRACT FROM AUTHOR]

The California current system (CCS) hosts one of the largest oxygen minimum zones (OMZs) in the world: the Eastern North Pacific (ENP) OMZ, which is dissociated into a subtropical and tropical region (i.e., the ESTNP and ETNP). In the modern ENP OMZ, bioavailable nitrogen (N) is lost via denitrification and anaerobic ammonium oxidation (anammox). Even so, paleo-reconstructions of N-loss have focused solely on denitrification. Fluctuations in bulk sedimentary δ15N over glacial-interglacial cycles have been interpreted to reflect variations in denitrification rates in response to ETNP OMZ intensity changes. This δ15N signal is thought to be transported northwards to the ESTNP OMZ. Here, we present the first CCS sedimentary record of ladderane lipids, biomarkers for anammox, located within the ESTNP OMZ (32°N; 118°W). Over the last two glacial terminations (~160 cal ka BP), ladderane concentrations were analysed in combination with the index of ladderanes with five cyclobutane moieties (NL5), short-chain (SC) ladderane degradation products, and productivity proxies. This shows that: 1) ladderanes derived from anammox bacteria living within the ESTNP OMZ water column; 2) ladderanes were continuously present, with relatively high concentrations during both glacial- and interglacial-periods, showcasing the ESTNP OMZ must have retained an anoxic core in which N-loss occurred; and 3) anammox abundance appears to have been driven both by OM-remineralization and advection changes, which regulated nutrient and oxygen levels. Our study shows that anammox was an important feature in the CCS and provides a more holistic picture of N-loss dynamics and the development of the ESTNP OMZ over glacial-interglacial cycles. Lastly, ladderanes were also detected in 160-500 cal ka BP sediments (15.7-37.5 mbsf; analysed at a low temporal resolution), highlighting their potential as anammox biomarkers in relatively deeper buried sediments for future studies. [ABSTRACT FROM AUTHOR]

BACKGROUND: Dissolved oxygen (DO) and aeration on/off time are the determining parameters for simultaneous carbon and nitrogen removal in biological treatment processes. The most effective way to decide the optimum operational conditions, e.g. aeration on/off time or DO concentration during the aeration period, is to determine specific nitrification/denitrification rates. For this purpose, the effects of DO (6 and 3 mg L−1) and aeration on/off time (from 2/2 to 90/360 min) on the specific ammonium oxidation and denitritation/denitrification rates in a membrane bioreactor (MBR) treating real textile wastewater were deeply investigated. RESULTS: The highest specific ammonium oxidation, denitritation and denitrification rates were obtained as 5.4, 3.8, and 5.3 mg N g−1 volatile suspended solids h−1, respectively, at an aeration on/off time of 90/360 min, which corresponded to the increase in specific ammonium oxidation rates by 1.8 and 2.1 times compared to continuous aeration conditions where DO was 6 and 3 mg L−1, respectively. CONCLUSION: Higher specific ammonium oxidation and denitrification rates can be achieved with the intermittent aeration compared to continuous aeration. Hence existing treatment plants can be retrofitted for higher performance with reduced energy requirements. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Aerobic denitrifier Alcaligenes faecalis No. 4 removes ammonium-nitrogen to nitrogen gas via denitrification in a single aerobic condition. In our previous studies, factors such as ammonium removal rate, denitrification ratio, and cell growth were tested in various conditions. The removal pathway from ammonium to nitrogen gas still needs to be determined in detail. To clarify this pathway of Alcaligenes faecalis No. 4, we in this study investigated the effects of several factors on ammonium removal, such as foam-recycle, initial pH, initial ammonium concentration, and airflow rate. Denitrification ratio was improved by up to 23% through foam-recycle. The improvement of the denitrification ratio was resulted by the higher enzyme activity of hydroxylamine oxidoreductase (HAO) in the produced foam, which was about 28 times higher than that in the culture broth (i.e., without foam-recycle). The stripped ammonia was significantly high (above pH 9). The initial ammonium concentration and airflow rate also influenced the denitrification ratio. [ABSTRACT FROM AUTHOR]

The aftermath of mining weathered crust elution-deposited rare earth ore produces a large amount of residual ammonium leaching solution, which causes ammonia and nitrogen pollution to the mine site. Recently, denitrification by heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria has attracted much attention. However, limited studies exist regarding the denitrification process of HN-AD bacteria. In this study, we combined four strains of HN-AD bacteria, Pseudomonas fulva K3, Pseudomonas mosselii K17, Klebsiella oxytoca A12, and Enterobacter hormaechei A16, obtained from rare earth element leaching sites, to select the best microbial consortium for ammonia nitrogen removal. We designed an ammonia removal process applicable to HN-AD bacteria to directly remove ammonia nitrogen from acidic leaching solutions. The experimental results demonstrated that the most efficient microbial consortium for ammonia nitrogen removal to be K3 + K17 + A16, with a removal efficiency of 89.68% for 8 h. In this process, considering the influencing factors of the ammonia removal process, the larger the influent flow rate and influent ammonia nitrogen concentration, the greater the ammonia nitrogen accumulation and pH decrease in the reactor. In consecutive multi-batch experiments, the ammonia removal process was used to remove ammonia nitrogen, at concentrations of 100–600 mg/L, from the simulated leaching solution at pH 4–7, whereby the effluent ammonia nitrogen concentration was lower than 15 mg/L. The results demonstrate that the ammonia removal process is highly feasible and stable. These findings will provide new ideas for the application of HN-AD bacteria and new methods for the removal of ammonia nitrogen from acidic leaching solutions. [ABSTRACT FROM AUTHOR]

Pseudomonas otitidis YM-01, which was isolated from swine wastewater, showed efficient simultaneous nitrification and denitrification ability by effectively using a single nitrogen source and a mixed nitrogen source. A high concentration of free ammonia (FA) can decompose EPS (extracellular polymeric substances), which makes the ammonia monooxygenase (AMO), hydroxylamine oxidase (HAO), periplasmic nitrate reductase (Nap), and nitrite reductase (NIR) lose the protective activity of EPS, resulting in the deterioration of the denitrification performance of the strain. For high-strength ammonium wastewater (500 mg/L and 1000 mg/L) with FA concentrations of 55 mg/L and 209 mg/L, the removal rates of strain YM-01 were 70.24% and 27.84%, respectively. The results indicate that strain YM-01 has the potential for application in high-strength ammonium wastewater. [ABSTRACT FROM AUTHOR]

Electrocatalytic nitrate reduction into ammonia is promising for its restricted activity and selectivity in wastewater treatment, however, it remains challenging. In this work, Co3O4 nanosheet electrodes with rich oxygen vacancies (OVs) (Co3O4−x/NF) are prepared and then applied as efficient catalysts for selective electrocatalytic reduction of nitrate to ammonia. The resulting Co3O4−x/NF electrodes exhibit high NO3−-N removal efficiency and NH4+-N selectivity, at 93.7% and 85.4%, respectively. X-Ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectra (EPR) results clearly reveal the formation of OVs in Co3O4−x/NF. The electrochemical characterization results confirm that OVs can effectively improve electron transfer as well as the electrochemically active area. The Co2+/Co3+ ratio of Co3O4−x/NF increases after the electrocatalytic reduction of nitrate, highlighting the crucial role played by Co2+ in mediating ammonia production via the Co2+/Co3+ cycle. These findings offer valuable guidelines for the development of more efficient and sustainable approaches for nitrate-contaminated wastewater treatment and ammonia synthesis. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) has shown success in past years for the treatment of municipal and industrial wastewater containing inorganic nutrients (i.e., nitrogen). However, the increase in polycyclic aromatic hydrocarbon (PAH)-contaminated matrices calls for new strategies for efficient and environmentally sustainable remediation. Therefore, the present review examined the literature on the connection between the anammox process and PAHs using VOSviewer to shed light on the mechanisms involved during PAH biodegradation and the key factors affecting anammox bacteria. The scientific literature thoroughly discussed here shows that PAHs can be involved in nitrogen removal by acting as electron donors, and their presence does not adversely affect the anammox bacteria. Anammox activity can be improved by regulating the operating parameters (e.g., organic load, dissolved oxygen, carbon-to-nitrogen ratio) and external supplementation (i.e., calcium nitrate) that promote changes in the microbial community (e.g., Candidatus Jettenia), favoring PAH degradation. The onset of a synergistic dissimilatory nitrate reduction to ammonium and partial denitrification can be beneficial for PAH and nitrogen removal. [ABSTRACT FROM AUTHOR]

The electrolysis of nitrate reduction to ammonia (NRA) is promising for obtaining value-added chemicals and mitigating environmental concerns. Recently, catalysts with high-performance ammonia synthesis from nitrate has been achieved under alkaline or acidic conditions. However, NRA in neutral solution still suffers from the low yield rate and selectivity of ammonia due to the low binding affinity and nucleophilicity of NO3-. Here, we confirmed that the in-situ-generated Fe(II) ions existed as specifically adsorbed cations in the inner Helmholtz plane (IHP) with a low redox potential. Inspired by this, a strategy (Fe-IHP strategy) was proposed to enhance NRA activity by tuning the affinity of the electrode--electrolyte interface. The specifically adsorbed Fe(II) ions [SA-Fe(II)] greatly alleviated the electrostatic repulsion around the interfac-eresulting in a 10-fold lower in the adsorption-free energy of NO3- when compared to the case without SA-Fe(II). Meanwhile, the modulated interface accelerated the kinetic mass transfer process by 25 folds compared to the control. Under neutral conditions, a Faraday efficiency of 99.6%, a selectivity of 99%, and an extremely high NH3 yield rate of 485.8 mmol h-1 g-1 FeOOH were achieved. Theoretical calculations and in-situ Raman spectroscopy confirmed the electron-rich state of the SA-Fe(II) donated to p orbitals of N atom and favored the hydrogenation of *NO to *NOH for promoting the formation of high-selectivity ammonia. In sum, these findings complement the textbook on the specific adsorption of cations and provide insights into the design of low-cost NRA catalysts with efficient ammonia synthesis. [ABSTRACT FROM AUTHOR]

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Peatlands are an important source of nitrous oxide (N2O) emissions, which is a potent greenhouse gas and is also involved in the depletion of stratospheric ozone. Due to the large number of N2O production and consumption processes, it is challenging to trace N2O emissions to an individual process. We investigated the effect of different water regimes (dry, intermediate and flooded) on N2O emissions via 15N tracing in a microcosm study with well-decomposed nitrogen-rich alluvial fen peat. The isotopic composition of the peat and emitted N2O gas was analysed in combination with qPCR analysis of abundances and diversity of N-cycle functional genes. Bacterial denitrification was the predominant source of N2O emission, followed by nitrification (ammonia oxidation). This was identified by a close relationship between 15N-N2O and 15N-NO3− under flooded (anoxic) and intermediate (sub-oxic) treatments and concomitant increases in nirK, nirS and nosZ after the flooding. The site preference and δ18O values fell within the previously observed range indicating multiple overlapping processes and bacterial denitrification as the dominant process. Although the combination of isotopic and microbial analyses indicates that bacterial denitrification is the primary process under intermediate and flooded treatments, the high abundance of amoA indicates that nitrification via comammox was present. High archaeal amoA and bacterial amoA gene copy numbers and second highest N2O emissions under the intermediate and flooded peats indicated that ammonia oxidation was, secondary to denitrification, also a source for N2O. The increase in emissions with nrfA gene copies also showed that dissimilatory nitrate reduction to ammonium (DNRA) potentially contributed to N2O emission under flooded treatment. [ABSTRACT FROM AUTHOR]

Anammox has received increased attention due to its enhanced and cost-efficient approach to nitrogen removal. However, its practical application is complicated by strict influent NO 2 −-N to NH 4 +-N ratio demands and an 11% nitrate production from the anammox process. This study was the first known research to propose and verify a system of zeolite integrated with partial denitrification and anammox (Z-PDA) in an up-flow anaerobic sludge bed (UASB) reactor. The enhanced and robust nitrogen removal resulted in an ultra-high nitrogen removal efficiency (NRE, 93.0 ± 2.0%). Zeolite adsorption and biological desorption of ammonium contributed to robust nitrogen removal with fluctuating influent NO 2 −-N to NH 4 +-N ratios. Applying 16S rRNA gene sequencing found that Candidatus Brocadia and Thauera were the key bacteria responsible for anammox and partial denitrification (PD), respectively. Zeolite also acted as a biological carrier. This significantly enriched anammox bacteria with a higher relative abundance of Candidatus Brocadia , reaching 49.2%. Metagenomic analysis demonstrated that the multiple functional genes related to nitrogen removal (nrfA/H, narG/H/I) and the metabolic pathways (Biosynthesis of cofactors, the Two-component system, the Biosynthesis of nucleotide sugars, and Purine metabolism) ensured the resilience of the Z-PDA system despite influent fluctuations. Overall, this study provided novel insights into the impacts of zeolite in the PDA system. It described the fundamental mechanism of zeolite based on adsorption and biological desorption, and demonstrated a meaningful application of the anammox process in sewage treatment. [Display omitted] • Zeolite integrated with partial denitrification and anammox (Z-PDA) system is proposed. • An ultra-high and enhanced nitrogen removal efficiency (93.0 ± 2.0%) was achieved. • Zeolite played dual role as biological carrier and ammonium reservoir. • Zeolite adsorption and biological desorption of ammonium improved nitrogen removal. • Candidatus Brocadia (49.2%) was highly enriched on the zeolite biofilm. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultra-high nitrogen removal efficiency (NRE) of 95.5% at C/N of 2.7 was achieved. • Lower NAR (range 40 %∼70 %) instead resulted in better anammox contribution and NRE. • High-efficiency EPDA with less NO X - loss dominated in ammonium removal than PN/A. • Enriching NOB and GAOs in PN/A process instead favored co-metabolism stability. • The nitrate introduction effectively attenuated the competition of ED for nitrite. Higher nitrite accumulation, which is challenging to achieve reliably, is always sought to obtain better nitrogen removal performance in traditional partial nitritation-anammox (PN/A) process. This study developed a modified PN/A process by introducing nitrite-oxidizing bacteria and endogenous metabolism. Advanced nitrogen removal performance of 95.5 % was achieved at a low C/N ratio of 2.7 under nitrite accumulation ratio (NAR) fluctuations. Higher nitrate accumulation at lower NAR (70 ∼ 40 %) resulted in superior anammox contribution (60 ∼ 75 %) and nitrogen removal performance (93 ∼ 98 %). This was attributed to the higher nitrogen removal efficiency of the post-anoxic endogenous partial denitrification coupling anammox process, although the PN/A process occurring first possessed a faster anammox rate of 2.0 mg NH 4 +-N /(g VSS⋅h). The introduction of nitrate allowed more nitrite flow to anammox, promoting a high enrichment of anammox bacteria (Ca. Brocadia, 0.3 % to 2.8 %). This study provides new insights into the practical application of the PN/A process. [ABSTRACT FROM AUTHOR]

Elevated nitrate concentrations in groundwater and surface water supplies can negatively impact the quality of the environment and human health. Recent studies have examined the use of zero-valent iron technology to treat nitrate-contaminated groundwater. Mechanistic aspects of nitrate reduction by zero-valent iron are unresolved. This project investigated the kinetics and mechanism of nitrate reduction by zero-valent iron under anoxic conditions and under oxic conditions. Stirred-batch reactions were studied over environmentally relevant ranges of reactant concentration, pH, and temperature. A complex rate expression was derived with a 1.8 order dependence on nitrate, a 1.4 order dependence on zero-valent iron, and a fractional order (0.8) dependence on proton concentrations under anoxic conditions. An apparent activation energy of 35 kJ mol−1 was observed indicating that nitrate reduction was diffusion controlled under our conditions. Furthermore, the calculated entropy of activation value of −162 J mol−1K−1 indicates that this reaction occurred by an associative mechanism. Under oxic conditions, there was a lag period in nitrate reduction where oxygen was preferentially utilized, leading to a slower rate of nitrate reduction when compared with anoxic conditions. These rate data can be used in predicting nitrate disappearance in nitrate-contaminated groundwater and wastewater treated with zero-valent iron. [ABSTRACT FROM AUTHOR]

In aquatic ecosystems, nitrogen (N) loading is mitigated in redox transition zones principally through the processes of denitrification and anaerobic oxidation of ammonium (anammox). Here, we investigate the N cycling processes in the water column of a seasonal stratified lake influenced by benthic processes in Southern Germany (Fohnsee) during the development of the vertical redox stratification between April and September. Concentration profiles and stable isotope compositions of NO3− and NH4+ together with numerical modeling and quantification of the hydrazine synthase gene (hzsB) and nitrite reductase (nirK and nirS) genes were used to identify the predominant nitrogen‐transformation processes at lake Fohnsee throughout the spring and summer periods. Water chemistry data, quantitative polymerase chain reaction analysis and increases of δ15N and δ18O values of nitrate from 7.0‰ to 41.0‰ and 2.0‰ to 28.0‰, respectively, showed that nitrate reduction to nitrite and NO occurs in an upward moving zone of the water column from June to September following the displacement of the oxycline caused by thermal stratification. We also observed an increase in δ15N of ammonium from 15‰ to 28‰ in the anoxic water column. Modeling results suggest that this shift in δ15N‐NH4+ is predominantly controlled by mixing between ammonium stemming from the oxic water column with δ15N values of 25‰ and ammonium that is likely formed in the lake sediments by oxidation of organic matter with δ15N values of 11‰. Observed gene abundances (hzsB, nirK, and nirS) in lake water samples collected in June and July indicated the co‐occurrence of nitrate reduction and low rates of anammox, while the presence of sulfide in August and September may have inhibited the activity of anammox bacteria near the sulfate‐reduction zone at the lake bottom. This study revealed temporal and spatial (e.g., depth dependent) variations in the dominant N‐transformation processes in the investigated lake. [ABSTRACT FROM AUTHOR]

• Fe(III) induced ammonium formation via DNRA during nitrate dependent AOM. • N 2 O was produced during simultaneous Fe(III) and nitrate dependent AOM. • The Nrf bypass and reverse HURM-Cyt P460 pathways contributed to N 2 O production. • ' Ca. M. nitroreducens' producing N 2 O may offset its greenhouse gas reduction potential. ' Candidatus Methanoperedens nitroreducens' is an archaeal methanotroph with global importance that links carbon and nitrogen cycles and great potential for sustainable operation of wastewater treatment. It has been reported to mediate the anaerobic oxidation of methane through a reverse methanogenesis pathway while reducing nitrate to nitrite. Here, we demonstrate that ' Ca. M. nitroreducens' reduces ferric iron forming ammonium (23.1 %) and nitrous oxide (N 2 O, 46.5 %) from nitrate. These results are supported with the upregulation of genes coding for proteins responsible for dissimilatory nitrate reduction to ammonium (nrfA), N 2 O formation (norV, cyt P460), and multiple multiheme c-type cytochromes for ferric iron reduction. Concomitantly, an increase in the N 2 O-reducing SJA-28 lineage and a decrease in the nitrite-reducing ' Candidatus Methylomirabilis oxyfera' are consistent with the changes in ' Ca. M. nitroreducens' end products. These findings demonstrate the highly flexible physiology of ' Ca. M. nitroreducens' in anaerobic ecosystems with diverse electron acceptor conditions, and further reveals its roles in linking methane oxidation to global biogeochemical cycles. ' Ca. M. nitroreducens' could significantly affect the bioavailability of nitrogen sources as well as the emission of greenhouse gas in natural ecosystems and wastewater treatment plants. [Display omitted] [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition has a significant impact on terrestrial N cycling. However, it has not been well understood how external inorganic N addition affects the dynamics of soil organic N (SON) that supports long-term plant productivity and carbon (C) sequestration. Here, we added six levels of ammonium (NH 4 +-N) or nitrate (NO 3 −-N) to a temperate grassland soil to reveal the mechanisms of SON responses to inorganic N addition. Results showed that the SON content decreased by 7% ± 2%–15% ± 1%, which corresponded with the increase in the abundance of functional gene related to SON mineralization (i.e., chiA) by both NH 4 +-N and NO 3 −-N. The inorganic N addition stimulated gaseous losses from the native soil N, leading to at least 6% ± 2%–12% ± 1% of the initial SON lost at different N addition levels (i.e., N-priming). However, the responses of nitrification- and denitrification-related functional genes to NH 4 +-N and NO 3 −-N treatments varied remarkably. The positive responses of nitrification- and denitrification-related functional genes (i.e., hao , nirS , and narG) to NO 3 −-N addition contributed to gaseous N losses. The negative responses of some denitrification-related functional genes (i.e., nirK , narG , and napA) to NH 4 +-N addition resulted in less gaseous N losses by NH 4 +-N compared with that by NO 3 −-N addition. Additionally, the release of H+ by NH 4 +-N addition may liberate organic matter from associated minerals, showing a decrease in mineral-associated organic matter (MAOM) but an increase in extractable Fe. These findings provide direct evidence that the addition of inorganic N results in a net native SON loss through microbe-mediated mineralization and gaseous emissions. The study also emphasizes the different mechanisms of reduced and oxidized N additions in affecting SON mineralization and gaseous N losses. [Display omitted] • Inorganic nitrogen addition decreased soil organic nitrogen (SON) content by 7% ± 2%–15% ± 1%. • Both NH 4 +-N and NO 3 −-N increased the abundance of chiA , a key gene in SON mineralization. • Inorganic nitrogen addition stimulated gaseous losses, resulting in at least 6% ± 2%–12% ± 1% initial SON loss (N-priming). • Gaseous N losses caused by NH 4 +-N was less than that by NO 3 −-N addition. • The release of H+ by NH 4 +-N addition may liberate organic matter from associated minerals. [ABSTRACT FROM AUTHOR]

[Display omitted] • Competitive DNRA vs. DEN partitioning and simultaneous fermentation were determined. • Moderate COD/N ratio and readily available COD favored DNRA. • A kinetic model to include DNRA and DEN for nitrogen conversion was developed. • Limited COD, high NO 3 − input, and low sludge concentration triggered N 2 O emissions. • VFA composition shifted from mixed type to acetic acid in the presence of nitrate. The complex interaction between nitrate (NO 3 −) reduction and fermentation is poorly understood when high levels of NO 3 − are introduced into anaerobic systems. This study investigated the competitive distribution between conventional denitrification (DEN) and dissimilatory nitrate reduction to ammonium (DNRA) during simultaneous denitrification and fermentation in arrested methanogenesis. Up to 62% of initial NO 3 − (200 mg-N/L) was retained as ammonium through DNRA at a chemical oxygen demand (COD)/N ratio of 25. Significant N 2 O emission occurred (1.7 – 8.0% of the initial NO 3 −) with limited carbon supply (≤1600 mg COD/L) and sludge concentration (≤3000 mg COD/L). VFA composition shifted predominantly towards acetic acid (>50%) in the presence of nitrate. A novel kinetic model was developed to predict DNRA vs. DEN partitioning and NO 2 − accumulation. Overall, NO 3 − input, organic loading, and carbon source characteristics independently and collectively controlled competitive DNRA vs. DEN partitioning. [ABSTRACT FROM AUTHOR]

• Rapid and high efficiency of nitrite accumulation was achieved via a novel feast-famine strategy. • Genes expression for nitrate reductase jumped to much higher levels without carbon. • Extracellular metabolites facilitated functional bacterial survival at famine stage. • Selective genes expression and microbial cross-feeding were key reason for rapid PD. Nitrite production via denitrification has been regarded as a key approach for survival of anaerobic ammonium oxidation (anammox) bacteria. Despite the important carbon substrate, little is known about the role of differential genes expression and extracellular metabolite regulation among diverse microbial communities. In this study, a novel alternating feast-famine strategy was proposed and demonstrated to efficiently accumulate nitrite in a low-nitrogen loading rate (NLR) (0.2∼0.8 kg N/m3/d) denitrification system. Highly selective expression of denitrifying genes was revealed as key regulators. Interestingly, in absence of carbon source (ACS) condition, the expression of narG and narI/V genes responsible for reduction of nitrate to nitrite jumped to 2.5 and 5.1 times higher than that in presence of carbon source (PCS) condition with carbon to nitrate ratio of 3.0. This fortunately facilitated a rapid nitrite accumulation once acetate was added, despite a significantly down-regulated narG and narI/narV and up-regulated nirS / nirK. This strategy selected Thauera as the most dominant denitrifier (50.2 %) with the highest contribution to narG and narI/narV genes, responsible for the high nitrite accumulation. Additionally, extracellular xylose, pyruvate, and glucose jointly promoted carbon-central metabolic pathway of key denitrifiers in ACS stage, playing an important role in the process of self-growth and selective enrichment of functional bacteria. The relatively rapid establishment and robust performance obtained in this study shows an engineering-feasible and economically-favorable solution for the regulation of partial denitrification in practical application. [Display omitted] [ABSTRACT FROM AUTHOR]

A microfluidic paper-based analytical device (μPAD) utilizing gas-diffusion separation and solid-phase reduction was developed for the first time for the determination of both ammonium and nitrate, which are the dominant inorganic nitrogen species in environmental waters. The device consists of 3 filter paper layers accommodating the sample, reagent and detection zones. The reagent zone is separated from the detection zone by a semipermeable hydrophobic membrane and acts as a solid-phase reactor where nitrate is reduced to ammonia by Devarda's alloy microparticles, integrated into a μPAD for the first time. The detection zone incorporates the acid-base indicators bromothymol blue (BTB) or nitrazine yellow (NY) and changes colour in two steps. Initially the colour change is caused by ammonia generated by the reaction of ammonium and sodium hydroxide in the sample zone. This colour change is followed by a subsequent colour change as a result of the ammonia produced by the reduction of nitrate by the Devarda's alloy microparticles. The corresponding reflectance value changes are used for the quantification of the two inorganic nitrogen species in the ranges 6.5–100.0 or 2.1–15.0 mg N L−1 for ammonium and 18.2–100.0 or 4.2–15.0 mg N L−1 for nitrate when BTB or NY are used, respectively. Under optimal conditions the limits of quantification of ammonium and nitrate in the case of BTB were determined as 6.5 and 18.2 mg N L−1, respectively, while the corresponding values in the case of NY were found to be 2.1 and 4.2 mg N L−1. The newly developed μPAD was stable for 62 days when stored in a freezer and 1 day at ambient temperature. It was validated with a certified reference material and successfully applied to the determination of ammonium and nitrate in spiked environmental water samples and soil extracts. [Display omitted] • A microfluidic paper-based analytical device (μPAD) for inorganic N is proposed. • NH 4 + and NO 3 − are determined as NH 3 ; NO 3 − is reduced to NH 3 by Devarda's alloy. • NH 3 is separated across a Teflon membrane by a gas-diffusion approach. • Detection is based on colour change of bromothymol blue or nitrazine yellow. • The μPAD is validated with a certified reference material and spiked water samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • Micro-oxygen combined with applied voltage promote total nitrogen removal. • Electrode regulates the spatial distribution of functional microorganisms. • Applied voltage regulates function gene abundance and enzyme activity. • Hydroxylamine oxidation peaks and up-regulation hao gene are demonstrated. Anodic ammonium oxidation catalyzed by microorganisms holds great potential as an effective anaerobic approach for ammonium and total nitrogen removal. However, the application of this approach is constrained by a low rate of ammonium oxidation, limiting the efficiency of total nitrogen removal. To overcome this limitation, a small amount of oxygen was introduced into a single-chamber microbial electrolysis cell to initiate the production of hydroxylamine through ammonium oxidation. Enhanced efficiency of overall nitrogen removal was obtained by the combined regulation of micro-oxygen and microbial electrode catalysis for ammonium oxidation and denitrification. According to the ammonium oxidation amount, the total oxidized nitrogen removal efficiency reached 67.87 ± 0.25 % and total nitrogen removal amount was 202.9 ± 0.5 mg/L, showing a high performance for treating high ammonium-contained wastewater. The oxidation peaks of hydroxylamine were determined at 0.43 V (vs. Ag/AgCl) for revealing the possible process of anodic hydroxylamine oxidation coupling to cathodic denitrification. In addition, microbial community analysis revealed that increasing the applied voltage regulated the abundance of nitrifying and denitrifying functional microbial communities both in the solution and on electrodes, and the key functional genes including hydroxylamine oxidation (hao), nitrate reduction (narG , narH , narI , napA , napB), nitrite reduce (nirK, nirS), and nitric oxide reduce (norB , norC), increased significantly at the applied voltage of 0.9 V, which accompanied by an obvious enhancement of enzyme activity compared to anaerobic and open circuit voltage. This work revealed the enhanced performance and mechanism on synergistic regulation by micro-oxygen and applied voltage for ammonium oxidation and denitrification, and provided new insights and feasible enhancing measures for treating high ammonium-nitrogen wastewater with low C/N ratio. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is an ideal carbon-free power source in the future sustainable hydrogen economy for growing energy demand. The electrochemical nitrate reduction reaction (NO3-RR) is a promising approach for nitrate removal and NH3 production at ambient conditions, but efficient electrocatalysts are lacking. Here, we present a metal-organic framework (MOF)-derived cobalt-doped Fe@Fe2O3 (Co-Fe@Fe2O3) NO3-RR catalyst for electrochemical energy production. This catalyst has a nitrate removal capacity of 100.8 mg N gcat-1 h-1 and an ammonium selectivity of 99.0 ± 0.1%, which was the highest among all reported research. In addition, NH3 was produced at a rate of 1,505.9 µg h-1 cm-2, and the maximum faradaic efficiency was 85.2 ± 0.6%. Experimental and computational results reveal that the high performance of Co-Fe@Fe2O3 results from cobalt doping, which tunes the Fe d-band center, enabling the adsorption energies for intermediates to be modulated and suppressing hydrogen production. Thus, this study provides a strategy in the design of electrocatalysts in electrochemical nitrate reduction. [ABSTRACT FROM AUTHOR]

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) both require low oxygen and high organic carbon conditions common in wetland ecosystems. Denitrification permanently removes nitrogen from the ecosystem as a gas while DNRA recycles nitrogen within the ecosystem via production of ammonium. The relative prevalence of denitrification versus DNRA has implications for the fate of nitrate in ecosystems. Unplanned and unmanaged urban accidental wetlands in the Salt River channel near downtown Phoenix, Arizona, USA receive high nitrate relative to non‐urban wetlands and have a high capacity for denitrification, but unknown capacity for DNRA. We conducted in‐situ push‐pull tests with isotopically labeled nitrate to measure denitrification and DNRA rates in three of the dominant vegetative patch types in these urban accidental wetlands. DNRA accounted for between 2% and 40% of nitrate reduction (DNRA plus denitrification) with the highest rates measured in patches of Ludwigia peploides compared to Typha spp. and non‐vegetated patches. The wetland patches were similar with respect to dissolved organic carbon concentration but may have differed in carbon lability or strength of reducing conditions due to a combination of litter decomposition and oxygen supply via diffusion and aerenchyma. The ratio of DNRA to denitrification was negatively correlated with nitrate concentration, indicating that DNRA may become a more important pathway for nitrate attenuation at low nitrate concentration. Although DNRA was generally lower than denitrification, this pathway was an important component of nitrate attenuation within certain patches in these unmanaged urban accidental wetlands. Plain Language Summary: Urban waterways commonly have higher nitrogen concentrations relative to non‐urban systems, which can damage ecosystems. Wetlands support microbes that can carry out denitrification, which removes a deleterious form of nitrogen, and dissimilatory nitrate reduction to ammonium (DNRA), transforming to a less mobile but still potentially deleterious form of nitrogen, thus recycling the nitrogen in the system. We measured these two transformations in urban accidental wetlands in Phoenix, Arizona, USA. We found DNRA was ubiquitous and could account for as much as 40% of the combined rates. Both denitrification and DNRA were higher in places covered by certain plant species than in other wetland areas. These plants may create conditions more favorable for microbes because the plant produces substances that are easily consumed by the microbes or because they regulate oxygen conditions through roots. Overall, we found that DNRA was a small yet substantial pathway for nitrogen recycling in these urban wetland ecosystems. Key Points: Dissimilatory nitrate reduction to ammonium (DNRA) accounted for up to 40% of nitrate reduction (DNRA plus denitrification) in the urban accidental wetlands in Phoenix, Arizona, USADNRA rates differed among wetland patches with unique plant species and these differences were not driven by dissolved organic carbonPerennial accidental wetlands have a high capacity to attenuate nitrate loading through both DNRA and denitrification [ABSTRACT FROM AUTHOR]

Realizing the smallest nitrogen loss is a challenge in the nitrate reduction process. Dissimilatory nitrate reduction to ammonium (DNRA) and nitrate assimilation play crucial roles in nitrogen retention. In this study, the effects of the carbon source, C/N ratio, pH, and dissolved oxygen on the multiple nitrate reduction pathways conducted by Pseudomonas putida Y-9 are explored. Strain Y-9 efficiently removed nitrate (up to 89.79%) with glucose as the sole carbon source, and the nitrogen loss in this system was 15.43%. The total nitrogen decrease and ammonium accumulation at a C/N ratio of 9 were lower than that at 12 and higher than that at 15, respectively (P < 0.05). Besides, neutral and alkaline conditions (pH 7–9) favored nitrate reduction. Largest nitrate removal (81.78%) and minimum nitrogen loss (10.63%) were observed at pH 7. The nitrate removal and ammonium production efficiencies of strain Y-9 increased due to an increased shaking speed. The expression patterns of nirBD (the gene that controls nitrate assimilation and DNRA) in strain Y-9 were similar to ammonium patterns of the tested incubation conditions. In summary, the following conditions facilitated nitrate assimilation and DNRA by strain Y-9, while reducing the denitrification: glucose as the carbon source, a C/N ratio of 9, a pH of 7, and a shaking speed of 150 rpm. Under these conditions, nitrate removal was substantial, and nitrogen loss from the system was minimal. [ABSTRACT FROM AUTHOR]

ABSTRAK Saat ini kualitas badan air semakin menurun akibat pembuangan limbah domestik dan industri secara langsung pada aliran sungai. Kualitas air sungai dengan beban nutrien dan organik yang tinggi mempersulit pengolahan air minum di salah satu industri DKI Jakarta. Salah satu dampak dari memburuknya beban nutrien air baku adalah tingginya kandungan parameter amonium yang berakibat tidak efisiennya proses klorinasi. Hal ini membuat dibangunnya unit MBBR aerob, dengan tujuan menyisihkan kandungan amonium. Akan tetapi, unit MBBR aerob ini tidak berfungsi secara optimal. Masalah ini akan diatasi dengan mengalihfungsikan unit pra-sedimentasi yang ada menjadi unit MBBR anaerob secara pre-anoxik, sehingga dapat melengkapi proses penyisihan amonium yang terdiri dari nitrifikasi dan denitrifikasi. Tujuan dari modifikasi ini adalah mendapatkan efisiensi penyisihan amonium sebesar 90%. Metode yang digunakan pada perancangan ini dimulai dengan mengumpulkan data sekunder, lalu dilakukan perhitungan perancangan unit MBBR anaerob. Hasil perancangan menunjukkan bahwa dimensi yang dibutuhkan untuk unit MBBR anaerob ini adalah dengan ukuran panjang 18 m, lebar 7 m, dan kedalaman 9.5 m. Dengan efisiensi akhir diharapkan sebesar 90% untuk MBBR anaerob dengan konsentrasi akhir amonium diharapkan sebesar 1.05 mg.L-1. Kata kunci: amonium, denitrifikasi, MBBR, nitrifikasi, pre-anoksik ABSTRACT At present the quality of water bodies is decreasing due to the disposal of domestic and industrial waste directly in the river flow. River water quality with high nutrients and organic load is difficult to drinking water treatment in one of the industries in DKI Jakarta. One of the effects of the worsening raw water nutrient load is the high content of ammonium parameters which results in inefficient chlorination processes. The declining raw water condition makes build an MBBR aerobic unit, with the aim to remove the ammonium content. However, the existing MBBR aerob unit does not function optimally. This problem can be overcome by changing the pre-sedimentation unit into an anaerobic MBBR unit pre-Anoxikally, so as to complete the ammonium removal process consisting of nitrification and denitrification. The purpose of this modification is to obtain an ammonium removal efficiency of 90%. The method used in this design is to collect secondary data. Then, anaerobic MBBR unit design is calculated. The results of the design show that the dimensions needed for this anaerobic MBBR unit are 18 m long, 7 m wide, and 9.5 m height. With a final efficiency expected of 90% for anaerobic MBBR with an ammonium final concentration expected to be 1.05 mg.L-1. Keywords: ammonium, denitrification, MBBR, nitrification, pre-Anoxic

While the emissions of methane (CH4) by natural systems have been widely investigated, CH4 aquatic sinks are still poorly constrained. Here, we investigated the CH4 cycle and its interactions with nitrogen (N), iron (Fe) and manganese (Mn) cycles in the oxic-anoxic interface and deep anoxic waters of a small, meromictic and eutrophic lake, during two summertime sampling campaigns. Anaerobic CH4 oxidation (AOM) was measured from the temporal decrease of CH4 concentrations, with the addition of three potential electron acceptors (NO3–, iron oxides (Fe(OH)3) and manganese oxides (MnO2)). Experiments with the addition of either 15N-labeled nitrate (15N-NO3–) or 15N-NO3– combined with sulfide (H2S), to measure denitrification, chemolithotrophic denitrification and anaerobic ammonium oxidation (anammox) rates, were also performed. Measurements showed AOM rates up to 3.8 µmol CH4 L–1 d–1 that strongly increased with the addition of NO3– and moderately increased with the addition of Fe(OH)3. No stimulation was observed with MnO2 added. Potential denitrification and anammox rates up to 63 and 0.27 µmol N2 L–1 d–1, respectively, were measured when only 15N-NO3– was added. When H2S was added, both denitrification and anammox rates increased. Altogether, these results suggest that prokaryote communities in the redoxcline are able to efficiently use the most available substrates. [ABSTRACT FROM AUTHOR]

Nitrogen is removed during municipal wastewater treatment to reduce eutrophication of waterways and preserve drinking water quality. Nitrification-denitrification and sidestream partial nitrification-anammox are state-of-the-art municipal N removal technologies, but they require energy for aeration and can release nitrous oxide as a fugitive greenhouse gas. An emerging sidestream electrodialysis technology is intended to both remove and recover N as ammonium-based fertilizer. This midpoint life cycle assessment compiles literature values to compare the state-of-the-art technologies of municipal wastewater nitrogen removal to the new electrodialysis nitrogen removal and recovery technology, accounting for the offset of Haber-Bosch-derived ammonia. Electrodialysis is projected to be environmentally favorable compared to the state-of-the-art, predicting electricity savings similar to anammox and, with the offset of industrial ammonia manufacture, net negative emissions in five of ten midpoint environmental impact categories, including global warming potential.

Copyright of Vatten is the property of Foreningen Vatten and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Methionine is one of the many amino acids in the soil. In order to study the role of methionine in acidic forest soil, the effect of methionine (Met) was compared with control together with addition of ammonium (Met + A), nitrite (Met + N), and glucose (Met + C) under 60% or 90% water holding capacity (WHC), because ammonium and nitrite are important factors in nitrification, and glucose affect the heterotrophic nitrification and nitrogen immobilization. We found that methionine addition significantly reduced NO3− concentration in acidic forest soil. Compared to Met, Met + A and Met + N treatments non-significantly enhanced nitrification; however, Met + C treatment decreased NH4+ concentration which suggested that soil autotrophic and heterotrophic nitrification were limited in the presence of methionine at 60% WHC. Further, our findings of 15N-labeled treatment showed the impact and priming effect of methionine was negative for NO3− concentration and positive for N2O emission, which were observed mainly from the soil N source rather than methionine. At 90% WHC, Met + C treatment significantly lessened concentrations of NH4+ and NO3−, nonetheless improved N2O compared to Met treatment. Therefore, besides the denitrification and dissimilatory NO3− reduction to ammonia, the immobilization might be the key factor to explain this decrease in NO3− concentration at 90% WHC, while these processes were induced with the C addition. This study indicated that the positive role of amino acids in soil N cycling might be overrated. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Display omitted] • Electrocatalytic nitrate reduction reaction was done using Cu foils as an electrocatalyst. • The effects of nitrate concentrations, pHs of electrolytes and temperatures were studied. • The products of NRR were determined and correlated with the reaction mechanisms. • The effects of oxalic ions on the activity and product selectivity were explored. Nitrate reduction reaction (NO 3 -RR), an emerging technology for clean and efficient nitrate removal, is of great significance to reduce water pollution. In this study, NO 3 -RR activity was assessed on the copper foils, and the effects of various variables including initial pHs, temperatures, and nitrate concentrations on the NO 3 -RR were investigated. The copper foils displayed excellent NO 3 -RR activity with a high ammonium selectivity of 45% at pH = 1 and a conversion rate of 55% at pH = 13. The conversion of nitrate to nitrite was the rate determining step at pH = 7 and pH = 13. Oxalic ions displayed significant inhibition effects on NO 3 -RR by copper foils in the acidic and alkaline electrolytes. In particular, the inhibition effect of oxalate ions on NO 3 -RR approached to 50% with a nitrate/oxalate ratio of 2:1 in acidic media, which is likely attributed to the formation of complexes between oxalate ions and the copper surface. Such an inhibition effect is not noted in the neutral electrolyte. Structural characterizations including atomic force microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy elucidated that the oxalate ions occupied a large number of the copper sites on the surface of copper foil to form competitive adsorption with nitrate. The experimental parameters for NO 3 -RR by copper foils were comprehensively analyzed, affording new insights on the complex interactions between the copper, nitrate, and oxalate. [ABSTRACT FROM AUTHOR]

Anaerobic secondary treatment is promising for energy-positive operation but creates ammonium- and sulfide-rich effluent. Here, we investigated a lab-scale membrane aerated biofilm reactor (MABR) incorporating silicon tubes as gas permeable membranes for simultaneous removal of ammonium and sulfide from synthetic mainstream anaerobic secondary effluent. At an ammonium loading rate of 2.06 g NH 4 +-N/m2/d and sulfide loading rate of 0.44 g S/m2/d, the MABR removed approximately 80 % of influent ammonium and >99 % of influent sulfide. A decrease in the ammonium loading rate to 1.18 g NH 4 +-N/m2/d and a stepwise increase in the sulfide loading rate to 0.88 and 1.77 g S/m2/d resulted in an average total nitrogen removal efficiency of 77 %. Sulfide removal efficiency consistently remained >99 %, but sulfate recovery had a wide variation due to elemental sulfur accumulation within biomass. Community analysis from 16s rRNA gene sequencing and mass balance data suggested that ammonium was primarily oxidized to nitrate by Nitrospira and was subsequently removed by denitrification with sulfide (Thiobacillus) or heterotrophically (Rhodocylaceae). We conclude that silicone tubes could be used gas permeable membranes to enable simultaneous ammonia and sulfide removal in anaerobic secondary effluent. More research is needed to maintain optimal biofilm thickness and control elemental sulfur accumulation in the reactor. • Silicone tubes were used as gas permeable membranes in a lab-scale MABR. • The MABR enabled simultaneous ammonium and sulfide removal. • The MABR produced high-quality effluent. • Sulfide-based denitrification completed total nitrogen removal. • Elemental sulfur accumulation was observed in biofilm. [ABSTRACT FROM AUTHOR]

In this study, a multi-storey bio-electrochemical reactor equipped with a pump-around system has been developed to adjust pH at desired value during treatment of synthetic ammonium-rich wastewater. The efficiency of the reactor to remove a high concentration of ammonium has been evaluated at various C/N ratios. The results demonstrated that a multi-storey reactor had high potential to remove ammonium within the function of an extensive operational range of C/N ratio (0.5--4), which is three times higher than the twin-chamber up-flow bio-electrochemical reactor. The accumulation of nitrite in the anode at the highest C/N ratio of 4 was less than other applied ratios, with 64% ammonium removal. [ABSTRACT FROM AUTHOR]

A novel strain AL-6, which was identified as Acinetobacter baumannii , presented an efficient ability to remove ammonium. Nitrogen balance indicates that 55.8% of the initial NH 4 +–N was ultimately converted to N 2 through heterotrophic nitrification and aerobic denitrification, while 30.6% was contributed to assimilation. More interestingly, efficient ammonium removal could be achieved in the presence of Cr(VI) of 0–10 mg L−1 by strain AL-6. Meanwhile, Cr(VI) reduction was observed. The Cr(VI) was mainly reduced to less toxic Cr(III) by strain AL-6 in the culture, while a small part of Cr(VI) might be accumulated in bacterial cells in the formation of Cr(III). The optimal conditions for ammonium removal as well as Cr(VI) reduction was pH of 7 and C/N ratio of 10–15. This study provided a potential prospect for the treatment of Cr(VI)-containing ammonium wastewater. [ABSTRACT FROM AUTHOR]

Background: Achieving nitrogen (N) and phosphorus (P) control in sediment remediation projects by adding natural materials is receiving increasing attention. In this study, different natural materials, including iron-rich clay minerals, calcite, kaoline, sugarcane bagasse and Phragmites detritus, were applied to test their effects on N and P in a mesocosm experiment. Results: Iron-rich clay minerals and Phragmites detritus had obvious advantages for P control; they resulted in almost undetectable levels of soluble reactive phosphorus (SRP) in the water column throughout the experiment. This finding can be explained by their strong P adsorption ability. The high level of available organic carbon in the sediment and water column after sugarcane bagasse addition provided enough electron donors for denitrification and dissimilatory nitrate reduction to ammonium (DNRA), which caused nitrate (NO3−-N) deficiency and ammonium (NH4+-N) accumulation in the water column. Additionally, this resulted in anaerobic conditions, further fuelling the release of P from iron-bound P induced by anoxia. Thus, the amount of sugarcane bagasse applied should be considered carefully in order to balance denitrification and DNRA as well as P releases. Calcite and Phragmites detritus are recommended as remediation materials for N removal based on their significant promotion of denitrification and limitation of DNRA, which resulted in low NO3−-N and NH4+-N levels. These results can be explained by the shifts in the functional microbial community composition and abundance after the addition of natural materials. Conclusions: Iron-rich clay minerals and Phragmites detritus are promising sediment remediation materials for P immobilization due to their strong P adsorption ability. Taken together, the selection of sediment remediation materials should consider the N and P coupling relationship, to prevent NO3−-N removal from causing P leaching or NH4+-N accumulation. [ABSTRACT FROM AUTHOR]

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]

A heterotrophic nitrification-aerobic denitrification (HN-AD) mixed culture was established as a simulated aquatic ecosystem to investigate the simultaneous removal of aniline and ammonium, as well as the succession of bacterial community. Aniline and ammonium were found to be simultaneously transformed, with maximum removal efficiencies of 99.98% and 89.87%, respectively. The presence of aniline at lower concentrations (0 to 100 mg/L) slightly inhibited ammonium oxidation, whereas further increasing the aniline concentration (from 100 to 500 mg/L) yielded an apparent enhancement effect, increasing the ammonium-N removal rate from 0.33 to 1.26 mg/L/day. In contrast, ammonium-N concentrations of 100 mg/L were able to facilitate aniline removal. Ammonium was the preferred nitrogen source for aniline removal when compared with nitrification metabolites such as nitrate or nitrite. The analysis of microbial community succession using high-throughput sequencing revealed that the microbial diversity generally decreased throughout the aniline and ammonium removal process. Proteobacteria is observed to increase at the climax stage, and the average relative abundances of Pseudomonas, Massilia, and Bacillus were highest at the climax stage and were positively related to the removal rate of aniline and ammonium-N. Surprisingly, the abundance of these microbes at the end stage was almost equal to that observed at the initial stage. This study demonstrated that polluted aquatic ecosystems hold potential for simultaneous removal of pollutants (hazardous organic carbon and ammonium), and have excellent self-rehabilitation abilities. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions from a nitrifying biofilm reactor were investigated with N2O isotopocules. The nitrogen isotopomer site preference of N2O (15N -SP) indicated the contribution of producing and consuming pathways in response to changes in oxygenation level (from 0 % to 21 % O2 in the gas mix), temperature (from 13.5 to 22.3 ∘ C) and ammonium concentrations (from 6.2 to 62.1 mg N L -1). Nitrite reduction, either nitrifier denitrification or heterotrophic denitrification, was the main N2O -producing pathway under the tested conditions. Difference between oxidative and reductive rates of nitrite consumption was discussed in relation to NO2- concentrations and N2O emissions. Hence, nitrite oxidation rates seem to decrease as compared to ammonium oxidation rates at temperatures above 20 ∘ C and under oxygen-depleted atmosphere, increasing N2O production by the nitrite reduction pathway. Below 20 ∘ C, a difference in temperature sensitivity between hydroxylamine and ammonium oxidation rates is most likely responsible for an increase in N2O production via the hydroxylamine oxidation pathway (nitrification). A negative correlation between the reaction kinetics and the apparent isotope fractionation was additionally shown from the variations of δ15N and δ18O values of N2O produced from ammonium. The approach and results obtained here, for a nitrifying biofilm reactor under variable environmental conditions, should allow for application and extrapolation of N2O emissions from other systems such as lakes, soils and sediments. [ABSTRACT FROM AUTHOR]

Biological ammonium removal via heterotrophic nitrification/aerobic denitrification (HN/AD) presents several advantages in relation to conventional removal processes, but little is known about the microorganisms and metabolic pathways involved in this process. In this study, Pseudomonas stutzeri UFV5 was isolated from an activated sludge sample from oil wastewater treatment station and its ammonium removal via HN/AD was investigated by physicochemical and molecular approaches to better understand this process and optimize the biological ammonium removal in wastewater treatment plants. Results showed that P. stutzeri UFV5 removed all the ammonium in 48–72 hours using pyruvate, acetate, citrate or sodium succinate as carbon sources, C/N ratios 6, 8, 10 and 12, 3–6% salinities, pH 7–9 and temperatures of 20–40 °C. Comparative genomics and PCR revealed that genes encoding the enzymes involved in anaerobic denitrification process are present in P. stutzeri genome, but no gene that encodes enzymes involved in autotrophic nitrification was found. Furthermore, transcriptomics showed that none of the known enzymes of autotrophic nitrification and anaerobic denitrification had their expression differentiated and an upregulation of the biosynthesis machinery and protein translation was observed, besides several genes with unknown function, indicating a non-conventional mechanism involved in HN/AD process. [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]

Microbe-mediated anaerobic degradation is a practical method for remediation of the hazardous monoaromatic hydrocarbons (BTEX, including benzene, toluene, ethylbenzene and xylenes) under electron-deficient contaminated sites. However, how do the anaerobic functional microbes adapt to oxygen exposure and flexibly catabolize BTEX remain poorly understood. We investigated the switches of substrate spectrum and bacterial community upon oxygen perturbation in a nitrate-amended anaerobic toluene-degrading microbiota which was dominated by Aromatoleum species. DNA-stable isotope probing demonstrated that Aromatoleum species was involved in anaerobic mineralization of toluene. Metagenome-assembled genome of Aromatoleum species harbored both the nirBD -type genes for nitrate reduction to ammonium coupled with toluene oxidation and the additional meta- cleavage pathway for aerobic benzene catabolism. Once the anaerobic microbiota was fully exposed to oxygen and benzene, 1.05 ± 0.06% of Diaphorobacter species rapidly replaced Aromatoleum species and flourished to 96.72 ± 0.01%. Diaphorobacter sp. ZM was isolated, which was not only able to utilize benzene as the sole carbon source for aerobic growth and but also innovatively reduce nitrate to ammonium with citrate/lactate/glucose as the carbon source under anaerobic conditions. This study expands our understanding of the adaptive mechanism of microbiota for environmental redox disturbance and provides theoretical guidance for the bioremediation of BTEX-contaminated sites. [Display omitted] • A microbiota flexible for monoaromatic hydrocarbons degradation was obtained. • Aromatoleum sp. MAG1 was identified as the anaerobic toluene degrader. • Genus Aromatoleum harbored nirBD -type gene for nitrate reduction to ammonium. • Diaphorobacter sp. ZM was isolated as an aerobic benzene degrader. • Diaphorobacter sp. ZM reduced nitrate under anaerobic conditions via DNRA. [ABSTRACT FROM AUTHOR]

Enrichment of anaerobic ammonium oxidizing bacteria (AnAOB) in the anaerobic ammonium oxidation (anammox) process remains a challenge in engineering applications. In this study, for faster enrichment of AnAOB, red mud-based carriers were positively charged with FeCl 3 and microbial promoters. The experimental results showed that the average nitrogen removal rates of the red mud-based carriers (RMGA), FeCl 3 -modified red mud-based carriers (RMGA-Fe), and microbial promoter-modified red mud-based carriers (RMGA-MA) increased by 24.4%–175% compared with the commercially available K3 carriers. Combining the results of SEM and laser confocal microscope, electrostatic attraction played a leading role on loading AnAOB. The increase in the surface roughness and specific area of the carriers after the attachment and the presence of Fe2+, Ca2+, and Mg2+ plasma were necessary for the subsequent growth of AnAOB, while the leaching of Cr(VI) promoted the nitrogen removal effect of AnAOB. [Display omitted] • Red mud can be used as hazardous waste. • Red mud-based carriers positively charged can well load anaerobic ammonia oxidizing bacteria. • The average nitrogen removal rates increased by 24.4%–175% compared with the commercially available K3 carriers. [ABSTRACT FROM AUTHOR]

[Display omitted] • The deficient inorganic N, P, and C sources induced decline in S0AD efficiency. • Specific thresholds for inorganic N, P, and C to robust S0AD were established. • Substantial reduction in SOBs occurred under deficient inorganic nutrients. • External supplying mitigated nutrient constraints in a pilot-scale S0PB bioreactor. Elemental sulfur packed-bed (S0PB) bioreactors are increasingly employed to treat secondary effluents from wastewater treatment plants. Limited availability of inorganic nutrients, such as ammonium, phosphate, and inorganic carbon, significantly determines the growth of autotrophic microorganisms and the denitrification efficiency. This study investigated the constraining thresholds of inorganic nutrients on the elemental sulfur autotrophic denitrification process. In the absence of ammonium, phosphate, and bicarbonate, the denitrification rate decreased. Specifically, the ammonium assimilation process could be replaced by nitrate assimilation pathways, resulting in a 29.5 % decline in denitrification efficiency when the ammonium-N feed was reduced from 2.0 to 0 mg-N/L. However, the absence of phosphate-P and bicarbonate-C led to substantial drops in denitrification efficiency by 66.7 % and 77.5 %, respectively. This was primarily attributed to diminished biomass yield, as evidenced by reductions of 77.8–82.6 % in ATP and 35.7–44.3 % in protein content, along with a 12.4 %–14.7 % decrease in the relative abundances of dominant sulfur-oxidizing bacteria. Correlation analyses established specific thresholds for desired nitrate removal amounts: 0.131 for ammonium-N, 0.053 for phosphate-P, and 0.597 for bicarbonate-C. These thresholds provided valuable guidance for adjusting real-life wastewater through external supplementation when employing a pilot-scale S0PB bioreactor, leading to a significant enhancement of denitrification efficiency. This study emphasizes the significance of considering the concentrations of inorganic nutrients in wastewater when implementing S0PB bioreactors, which is a context that frequently neglects potential negative consequences. [ABSTRACT FROM AUTHOR]

Thiocyanate (SCN−)-based autotrophic denitrification (AD) has recently been demonstrated as a promising technology that could be integrated with anaerobic ammonium oxidation (Anammox) to achieve simultaneous removal of nitrogen and SCN−. However, there is still a lack of a complete SCN−-based AD model, and the potential microbial competition/synergy between AD bacteria and Anammox bacteria under different operating conditions remains unknown, which significantly hinders the possible application of coupling SCN−-based AD with Anammox. To this end, a complete SCN−-based AD model was firstly developed and reliably calibrated/validated using experimental datasets. The obtained SCN−-based AD model was then integrated with the well-established Anammox model and satisfactorily verified with experimental data from a system coupling AD with Anammox. The integrated model was lastly applied to investigate the impacts of influent NH 4 +-N/NO 2 −-N ratio and SCN− concentration on the steady-state microbial composition as well as the removal of nitrogen and SCN−. The results showed that the NH 4 +-N/NO 2 −-N ratio in the presence of a certain SCN− level should be controlled at a proper value so that the maximum synergy between AD bacteria and Anammox bacteria could be achieved while their competition for NO 2 − would be minimized. For the simultaneous maximum removal (>95%) of nitrogen and SCN−, there existed a negative relationship between the influent SCN− concentration and the optimal NH 4 +-N/NO 2 −-N ratio needed. Image 1 • A complete thiocyanate-based autotrophic denitrification (AD) model was developed. • Thiocyanate-based AD model was evaluated with integration of Anammox model. • Relationship between thiocyanate and NH 4 +-N/NO 2 −-N for maximum removal was studied. High-level (>95%) simultaneous removal of nitrogen and thiocyanate could be achieved through combining thiocyanate-based autotrophic denitrification and Anammox. [ABSTRACT FROM AUTHOR]