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[Display omitted] • Nitrogen removal efficiencies by zeolite wetland was better than ceramists and lava. • Selective inhibition of amo B and hao gene abundance on different substrates. • Denitrification is a key pathway for nitrate removal in constructed wetland (CW) • Dissimilatory nitrate reduction process was enhanced in CW- zeolite. This study conducted an analysis of the variations in nitrogen metabolism pathways within constructed wetlands (CWs) using zeolite (CW-Z), ceramsite (CW-C), and lava (CW-L) under high concentration sulfamethoxazole (SMX) stress. The introduction of SMX hindered the formation of hydrogen bonds on the substrate surfaces; however, these surfaces still maintained a dense and thick biofilm. CW-Z exhibited superior removal efficiencies for ammonium nitrogen (NH 4 +-N) and nitrate nitrogen (NO 3 –-N) compared to CW-C and CW-L, with removal rates of 92.54 ± 2.88 % and 89.39 ± 6.74 %, respectively. Interestingly, the proportion of genes involved in nitrification, denitrification and nitrate reduction genes in CW-C (36.05 %) were higher than that in CW-C (29.81 %) and CW-L (29.70 %) but the interactions among nitrogen functional bacteria in CW-Z were much more complex. Further analysis of the nitrogen metabolism pathway indicated that under CW-Z enhanced dissimilatory nitrate reduction SMX stress, while CW-L enhanced assimilatory nitrate reduction process compared to CW-C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Significant removal capability of inorganic N was detected in strain DN3. • N assimilation dominated the NH 4 +-N, NO 3 −-N, and NO 2 −-N removal process. • Hetertrophic nitrification pathway of DN3 was revealed: NH 4 + → NH 2 OH → NO → N 2 O → N 2. • N eliminating assays under various conditions showed bacterial potential application. • A candidate for treatment of mariculture wastewater was provided by this work. Recently, the functional microorganisms capable of eliminating nitrogenous waste have been applied in mariculture systems. As a potential candidate for treating mariculture wastewater, strain DN3 eliminated 100% of ammonia and nitrate and 96.61%–100% of nitrite within 72 h, when single nitrogen sources at concentrations of 0–50 mg/L. Strain DN3 also exhibited the efficient removal performance of mixed-form nitrogen (ammonia, nitrate, and nitrite) at salinity 30 ‰, C/N ratio 20, and 180 rpm. The nitrogen assimilation pathway dominated inorganic nitrogen metabolism, with less nitrogen (14.23%-25.02% of TN) lost into the air via nitrification and denitrification, based on nitrogen balance analysis. Moreover, the bacterial nitrification pathway was explored by enzymatic assays and inhibition assays. These complex nitrogen assimilation and dissimilation processes were further revealed by bacterial genome analysis. These results provide important insight into nitrogen metabolism of Halomonas sp. and theoretical support for treating mariculture wastewater with strain DN3. [ABSTRACT FROM AUTHOR]

To solve the nitrate accumulation phenomenon in recirculating aquaculture system (RAS). This study aimed to provide a sufficient organic carbon source, denitrifying bacteria, and a suitable microenvironment for denitrification in RAS. Denitrifying capsules were prepared using the encapsulation method, the morphology, microbial community and influencing factors for nitrogen removal efficiency of the denitrifying capsules in synthetic RAS wastewater were investigated. The denitrifying capsules had a porous, rough, and loose structure, with a diameter of approximately 6 mm and a density of approximately 1.05 g per cubic centimeter. The effect of a low ratio of solid-to-liquid (10:1) and temperature (15 °C) on nitrate removal was significant during the initial acclimation period (1-10d). After the enclosed denitrifying bacteria activity was recovered, the influence was not significant. At the end of the test, the nitrate removal rate could reach more than 80% even at a lower ratio of solid-to-liquid (10:1) or at 15 °C. The capsule exhibited a short adaptation time for diverse types of substrates and adapted well to the substrate concentration. Under low influent nitrate or nitrite loading, the removal rate reached 80% on the 6th day, which was earlier than with high influent nitrate loading. The denitrification rate experiment showed that the nitrate removal rate could reach 80.14% at 14 h and finally stabilize at approximately 81.89%. The capsule-supported denitrification process was a zero-order reaction and the denitrification rate of the capsule was calculated to be 109.0 mg N/L-capsule·h. The longtime evaluation indicated that until the semen litchi powder was exhausted, the capsule could retain a high nitrate removal rate. Functional enzyme analysis reveals the nitrogen conversion pathway in the capsule included denitrification, dissimilatory nitrate reduction and nitrogenfixation. The porous structure and good adaptability to environmental conditions of the denitrifying capsule would help to achieve denitrification and reduce the nitrate content on the present RAS, without increasing infrastructure investment. • Core-shell structure denitrifying capsule was designed for denitrification in RAS. • The capsule adapted well to substrate concentrations and temperature. • Afther a short activation time the nitrate removal rate could reach 96.6%. • Denitrification prosess in RAS may achieve easily with the denitrifying capsule. [ABSTRACT FROM AUTHOR]

Aerobic denitrification is a feasible and sustainable process for nitrogen removal in environmental protection. The C/N ratio was the vital one that has a significant impact on the performance. However, comprehension of the C/N ratio effect on this bioprocess was not well clarified. In this study, the response of an aerobic denitrifier (Pseudomonas balearica strain RAD-17) to the C/N ratio was investigated from a view of metabolism. It was found that a high total nitrogen (TN) removal efficiency of about 95% was achieved with the dosing C/N ratio of 7.5, while only a slight increase when the dosing C/N ratios were further increased to a high range of 10–30. The carbon validity was out of sync with TN removal and a balance between the two was realizable at a dosing C/N ratio of 7.5 based on the economic consideration. Moreover, weakened assimilation while enhanced respiration along with the increased C/N ratios was revealed, evidenced by the decreased net intracellular nitrogen and increased nitrogenous gas proportions in nitrogen balance analysis. The growth characteristics in terms of cell number and OD 600 showed a division for the high flux of nitrate and organics directed to assimilation and respiration, respectively. The expression levels of carbon and nitrate metabolism-related function genes in P. balearica supported the results above. The C/N ratio of 5.0–7.5 was supposed to be the turning region for the metabolism division between assimilation and respiration in aerobic denitrifying. The results are expected to offer a guideline for the decision made for organics supply for the aerobic denitrification process and support its sustainable application. [Display omitted] • C/N ratio of 7.5 was the threshold value to achieve TN removal of over 95%. • The carbon validity and nitrogen removal efficiency had an inverse relationship. • Nitrogen balance and growth property of P. balearica showed a metabolic division. • Expression levels of nitrate and carbon related functional genes were investigated. • Turning region of C/N ratio for microbial assimilation and respiration was 5.0–7.5. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrification-denitrification existed in AD systems and contributed to TAN removal. • Biogas circulation and AC addition lowered the TAN by 6% and 2%, respectively. • Both strategies enriched nitrification-/denitrification-related bacteria or genes. • Their combination had a synergetic effect on enrichment of specific bacteria/genes. • Combined strategy led to a 24% lower TAN level and a 44% higher CH 4 yield. This study investigated the biological nitrogen removal mechanisms during the anaerobic digestion of swine manure and the effects of biogas circulation and activated carbon (AC) addition. Biogas circulation, AC addition, and their combination increased the methane yield by 25.9%, 22.3%, and 44.1%, respectively, when compared to the control. Nitrogen species analysis and metagenomic results indicated that nitrification–denitrification was the dominant ammonia removal pathway in all digesters with little oxygen, while anammox did not occur. Biogas circulation could promote mass transfer and induce air infiltration to enrich nitrification- and denitrification-related bacteria and functional genes. And AC might act as an electron shuttle to facilitate ammonia removal. The combined strategies showed a synergetic effect on the enrichment of nitrification and denitrification bacteria and functional genes, significantly lowering the total ammonia nitrogen by 23.6%. A single digester with biogas circulation and AC addition could enhance methanogenesis and ammonia removal via nitrification and denitrification. [ABSTRACT FROM AUTHOR]

The mainstream anaerobic ammonium oxidation (anammox) has attracted extensive attention recently, particularly due to its potential of transforming current wastewater treatment plants from energy consuming to energy neutral or positive. However, the presence of biodegradable chemical oxygen demanding (COD, 20–80 mg COD L −1 ) in the mainstream anammox reactor stimulates the growth of heterotrophic bacteria, which would compete for oxygen with ammonia-oxidizing bacteria (AOB) and for nitrite with anammox bacteria, thus interfering with the autotrophic nitrogen removal process. In the present work, with consideration of granule size distribution, a one-dimensional model describing the mainstream simultaneous partial nitrification, anammox and denitrification (SNAD) in a granule-based reactor was established, calibrated and validated, based on the long-term experimental results. Through applying the verified model, simulation studies were conducted and the results showed that the effluent total nitrogen concentration of <5 mg N L −1 could be achieved at C/N ratio of 0.2–0.6, DO concentration of 0.2–0.4 mg L −1 and granule radius of 300–600 μm. The combined effects indicated that the SNAD process with TN removal efficiency >90% was obtained at C/N ratio and DO concentration of 0.2–1.0 and 0.2–0.4 mg O 2 L −1 respectively. Finally, the various granule size distribution patterns were simulated, which confirmed that the size distribution needed to be incorporated in the model to accurately describe the granular anammox system, considering a model based on a uniform granule size does not reflect the real situations. These results provide guides to optimize the operation of mainstream granular autotrophic nitrogen removal process. [ABSTRACT FROM AUTHOR]

This study cultivated denitrifying granular sludge in three UASB reactors by the semi-starvation fluctuation C/N ratio strategy (reactor 1 (R1): constant C/N ratio; R2: regular fluctuation C/N ratio; and R3: semi-starvation fluctuation C/N ratio (SSF)). Microbial aggregates appeared in R1, R2 and R3 on days 28, 14 and 6, respectively. Compared with the results in R1 and R2, the guanosine tetraphosphate (ppGpp) concentration was highest, the acyl homoserine lactones (AHLs) concentration quickly reached a certain threshold, and more protein (PN) of extracellular polymeric substances (EPS) secretion resulted in the rapid formation of denitrifying granular sludge in R3. The SSF strategy enhances microbial diversity, and denitrifying granular sludge has a better nitrogen removal performance. The result demonstrates that ppGpp, AHLs, EPS and the denitrifying sludge granulation process are associated. A mechanism for denitrifying sludge granulation with SSF strategy was proposed from the aspect of quorum sensing (QS). [ABSTRACT FROM AUTHOR]

Swine wastewater was treated using an integrated ion exchange and bioelectrochemical system. This system contains three chambers separated by a cation exchange membrane (CEM) and an anion exchange membrane (AEM). Each chamber acted as a bioanode chamber, an aerated biocathode chamber, and a denitrification chamber. To accelerate the ammonium transportation through CEM, a bioelectrochemical system was installed between bioanode and aerated biocathode. The current was provided by a programmable DC power supply. The average chemical oxygen demand (COD) removal efficiencies at applied voltages of 0, 1 and 3 V were 65.6%, 75.4% and 80.6%, respectively. Unlike the COD removal, the total nitrogen removal was proportional to the ammonium flux through the CEM. The average total nitrogen removal efficiencies at the applied voltages of 0, 1 and 3 V were 37.0%, 63.1% and 70.5%, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient MBBR was operated for simultaneous removal of N, P, and COD. • Nitrogen balance was evaluated throughout the MBBR operation phase. • EPS, ETSA, and enzyme activity were used to evaluate biofilm performance. • Proteobacteria and Gammaproteobacteria were identified as the dominant PAO. • A new synchronous N and P removal pathway was proposed at various C/N ratios. The long-term moving bed biofilm reactor (MBBR) with carrier-attached biofilm was successfully operated for simultaneous removal of nitrogen, phosphorus, and COD at various C/N ratios. Results indicated that 99.60%, 63.58%, 78.94%, and 59.64% of NH 4 +-N, NO 3 –-N, TN, and TP were removed at C/N ratio, hydraulic retention time (HRT), and carrier film amount of 5, 40 h, and 1.2 mg·g−1. Nitrogen balance analysis showed that more than 89% of nitrogen (C/N = 20, 15, 10, 5) was converted to gas products. Extracellular polymeric substances (EPS), electron transport system activity (ETSA), and enzyme activity of biofilm were evaluated. Protein (PN)/polysaccharose (PS) values and ETSA decreased with the decrease of C/N ratios. Metagenomics sequencing further revealed that the prominent phyla for nitrogen and phosphorus removal were identified including Proteobacteria , Acidobacteria , Nitrospirae , and Chloroflexi. Proteobacteria and Gammaproteobacteria were identified as the dominant denitrifying phosphate accumulating organisms (PAO) at the phylum and class level, respectively. [ABSTRACT FROM AUTHOR]

• Actinomycetes strains M5 and M6 were identified as Streptomyces sp. • The TOC and NO 3 –-N removal efficiency of strains was higher than 97.02% and 95.44%. • Strains M5 and M6 had higher utilization performance for esters, amino acids. • Network model exhibited interaction of metabolic activity and fingerprinting. • The TN removal efficiency in raw water was ranged from 68.63% to 85.59%. The denitrification characteristics of actinomyetes in aquatic ecosystem under aerobic conditions are not well known. Here, two actinomyetes strains M5 and M6 were separated and annotated as Streptomyces sp. Strains M5 and M6 could reduce 95.02% and 96.84 % of total nitrogen, 98.14 % and 97.02 % of total organic carbon under aerobic condition. Nitrogen balance analysis indicated that 78.60 % and 83.01 % of nitrogen was translated into gaseous, with 13.48 % and 10.77 % of nitrogen was assimilated into biomass for strains M5 and M6. The highest removal efficiency of nitrate of strains M5 and M6 in micro-polluted water bodies were 88.61 % and 82.53 %, respectively. Moreover, strains M5 and M6 exhibited remarkable carbon metabolic capacity, especially for esters. Altogether, this study provides a new perspective for understanding the performance of actinomyetes in aerobic denitrification and micro-polluted water reparation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The major N 2 O production pathway varied at different composting stages. • The bioelectrochemical assistance reduced N 2 O emission by 28.5–75.5%. • The mitigation mechanism was ammonia oxidation repression. • Heterotrophs outcompeted Nitrosomonadaceae for oxygen under an electric potential. • The bioelectrochemical assistance was proposed as a nitrification inhibitor. Targeted options to reduce nitrous oxide (N 2 O) emission from composting is scarce due to challenges in disentangling the complex N 2 O production pathways. Here, combined approaches of nitrogen form analysis, isotopocule mapping, quantitative PCR, and Illumina MiSeq sequencing were used to differentiate N 2 O production pathways and decipher the underlying biochemical mechanisms. Results suggested that most N 2 O was produced at the latter stage through nitrifier denitrification. The bioelectrochemical assistance through applying an electric potential reduced N 2 O emissions by 28.5–75.5%, and the underlying mitigation mechanism was ammonia oxidation repression, as evidenced by the observed reduction in the proportion of the amoA containing family Nitrosomonadaceae from 99% to 83% at the lower voltage and to a negligible level at the higher voltage assessed, which was attributed to their depressed competitiveness for oxygen with heterotrophs. The findings provide evidence that the bioelectrochemical assistance could function as a nitrification inhibitor to minimize compost derived N 2 O emissions. [ABSTRACT FROM AUTHOR]

• Phosphorus content and removal efficiency should be considered to evaluate PAOs. • A novel highly-efficient strain C-13 with SNDPR ability was isolated. • A convenient way for nitrogen balance analysis was adopted to assess the HNAD. • Ammonium would be the optimal nitrogen source for assimilation and HNAD. Strain C-13, identified as an Acinetobacter sp. by homology searches, exhibited efficient simultaneous heterotrophic nitrification-aerobic denitrification phosphorus removal (SNDPR) abilities by nitrogen balance analysis and further confirmation of successful amplification of functional genes ppk , napA , and nirS. In addition, strain C-13 could utilize NH 4 +-N, NO 3 –-N, and NO 2 –-N as nitrogen sources, among which NH 4 +-N was indicated to be an excellent nitrogen source for assimilation and heterotrophic nitrification. Besides, the optimum conditions for nutrient removal were determined as follows: sodium acetate as the sole carbon source, C/N/P ratio of 100/10/2, pH = 7.5, and temperature of 30 °C. Meanwhile, the strain also showed the traditional features, such as release and the excess uptake of phosphate under anaerobic/aerobic conditions, with the highest phosphorus content of 5.01% after cultivation. Strain C-13 presents promising prospects for application in biological nutrient removal in wastewater treatment. [ABSTRACT FROM AUTHOR]

• Acinetobacter sp. YS2 was isolated from petrochemical wastewater treatment process. • Nitrifying and denitrifying enzyme genes were amplified successfully. • The proportion of aerobic denitrifiers reached 87.44% in the microbial community. • YS2 has potential application in the SND treatment for petrochemical wastewater. The ecological niche of aerobic denitrifiers in activated sludge is little studied, but this determines the performance of these bacteria in reactors. Acinetobacter sp. YS2 isolated from a treatment process for petrochemical wastewater and showed excellent nitrogen removal performance. In the nitrification and denitrification process, the removal efficiencies of NH 4 +-N and NO 3 −-N were 87.81% and 88.20% at 24 h, respectively, and nitrogen balance analysis indicated that the proportions of nitrogen removal by gaseous nitrogen were 37.58% and 46.45%, respectively. During simultaneous nitrification and denitrification (SND) treatment of synthetic petrochemical wastewater in a sequencing batch reactor (SBR), aerobic denitrifiers became the dominant species and the proportion reached 87.44% in the microbial community. The removal efficiencies of NH 4 +-N and TN were 99.46% and 80.36% over 5 days, respectively. This research has shown that aerobic denitrifiers can become the dominant species in the applications of SND treatment for petrochemical wastewater. [ABSTRACT FROM AUTHOR]