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Denitrifying anaerobic methane oxidation (DAMO) process uses methane as electron donor to reduce nitrate/nitrite to dinitrogen, which is a potentially efficient, low-cost and clean biological nitrogen removal technology. However, slow microbial growth rate severely limits the application of this promising process. In this study, a series hollow-fiber membrane biofilm reactor (HfMBR) was operated for 90 days to achieve rapid enrichment of these denitrifying methanotrophs. Finally, the highest relative abundance of denitrifying methanotrophic archaea and bacteria (DAMO archaea and bacteria) reached 47.5% and 11.3%, respectively. And the average abundance of DAMO archaea and bacteria increased 92.9 and 136.6 times respectively during the 90-day enrichment. High growth rate of DAMO archaea with a doubling time of 11.6 days was achieved in the second HfMBR according to quantitative PCR results. The results implied that dissolved oxygen would inhibit the growth of DAMO archaea, but the series HfMBR could effectively counteract this unfavorable factor. This work provided theoretical guidance for the rapid enrichment of denitrifying methanotrophs and contributed to the application of methane-dependent denitrification process., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

This study focused on the nitrous oxide (N 2 O) generation from the biological nitrogen removal process under different pH levels. To explore a pH optimum, the online N 2 O emission and the bacterial composition and function in the anoxic-oxic process were investigated. The mean gaseous N 2 O emission accounted for 0.329%, 0.103%, 0.085%, and 0.793% of the influent total nitrogen at pH of 5, 6, 8, and 9, respectively. Incomplete oxidation in oxic tanks was the primary source of N 2 O, while N 2 O in the anoxic tank was mainly generated by nitrifier denitrification. No direct correlations were observed between N 2 O emission and potential nitrifiers and denitrifiers. The impacts of pH on N 2 O generation were more likely related to the response of bacterial enzymes and nitrogen compounds, rather than the feedback of bacterial community structure itself. Above all, an influent pH range of 6-8 is recommended for nitrogen removal and N 2 O mitigation in anoxic-oxic process., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Aerobic denitrification is a novel biological nitrogen removal technology, which has been widely investigated as an alternative to the conventional denitrification and for its unique advantages. To fully comprehend aerobic denitrification, it is essential to clarify the regulatory mechanisms of intracellular electron transfer during aerobic denitrification. However, reports on intracellular electron transfer during aerobic denitrification are rather limited. Thus, the purpose of this review is to discuss the molecular mechanism of aerobic denitrification from the perspective of electron transfer, by summarizing the advancements in current research on electron transfer based on conventional denitrification. Firstly, the implication of aerobic denitrification is briefly discussed, and the status of current research on aerobic denitrification is summarized. Then, the occurring foundation and significance of aerobic denitrification are discussed based on a brief review of the key components involved in the electron transfer of denitrifying enzymes. Moreover, a strategy for enhancing the efficiency of aerobic denitrification is proposed on the basis of the regulatory mechanisms of denitrification enzymes. Finally, scientific outlooks are given for further investigation on aerobic denitrification in the future. This review could help clarify the mechanism of aerobic denitrification from the perspective of electron transfer., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The C/N ratio in wastewater differs in place and time and affects the nitrogen removal performance of wastewater treatment. However, studies have focused only on the direct relationship between C/N and nitrogen removal efficiency but disregarded the significant role of soluble microbial products (SMPs) as an intermediate electron station. In this work, the contribution of SMPs to TN removal for treating wastewater with different C/N in a sequencing batch reactor (SBR) was investigated to extend relevance from C/N-TN removal to C/N-SMP-TN removal. TN removal efficiency was improved by increasing the influent C/N. The relative contribution of SMPs increased from 15% (C/N = 2) to 54% (C/N = 8), including 25.5% via utilization-associated product (UAP)-dependent denitrification and 28.5% via biomass-associated product (BAP)-dependent denitrification. The direct contribution of influent organic substrates dramatically decreased from 85.1% to 46%. In addition, providing an anoxic phase effectively enhanced BAP-dependent denitrification and achieved an increment of the SMP absolute contribution from 20.3% to 43% at C/N = 8 with 6.7 mg/L of TN additionally removed. This work clarified the significant contribution of SMPs to the nitrogen removal process, particularly in treating wastewater with high C/N. It also presented a new strategy for improving nitrogen removal performance via SMP reclamation., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Nitrite-dependent anaerobic methane oxidation (N-DAMO) is a newly discovered bioprocess which uses methane as electron donor to reduce nitrite into dinitrogen. It is a promising clean bioprocess for denitrification in wastewater treatment. However, the low reaction rate and slow growth rate of N-DAMO bacteria within NC10 phylum limit the application of the process. In this study, we chose vitamin, heme, nucleobase and betaine to investigate their short- and long-term effects on N-DAMO bacteria. The concentrations of the growth factors of medium were improved according to the short-term experiments. The results were subsequently verified via long-term inoculations and were applied in a magnetically stirred gas lift reactor (MSGLR). The results indicated that nucleobase and betaine (5.0 and 200 μg L -1 , respectively) significantly stimulated the N-DAMO activity, whereas vitamin and heme had no significant effects in the tested concentration ranges. During the long-term incubation, N-DAMO bacteria continuously increased and finally achieved a relative abundance of 14.4% on day 300. Notably, larger aggregates of N-DAMO bacteria were observed at the end of the long-term incubation. And the nitrogen removal rate of the MSGLR increased to 70 mg N L -1 day -1 , with the total nitrogen removal efficiency over 99.0%. However, the addition of betaine introduced methyl into the reactors and this made methylotrophs account a considerable part of the bacterial community, which limited the enrichment degree of N-DAMO bacteria. This work will contribute to the engineering application and enrichment of N-DAMO bacteria., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Tourmaline is a ring borosilicate with unique pyro-electricity and piezoelectricity values. Non-gem tourmaline is usually used as an environmental material. The short-term effects of ultrafine tourmaline particles on nitrogen removal performs microbial population dynamics. Key functional species in a sequencing batch reactor were investigated at 9 ± 1 °C. The investigation results showed that 1 g·L −1 ultrafine tourmaline particles could resist the effect of temperature shock on the metabolism of NH₄⁺-N and were beneficial to the restoration of the metabolism capacity of NH₄⁺-N. 1 g·L −1 ultrafine tourmaline particles, which increased the oxidation rate of NH₄⁺-N in the aerobic phase, the formation rate of NO₃ − -N in the aerobic phase, and the denitrification rate in the hypoxia phase at low temperatures. However, the community richness or diversities were not changed after short-term exposure to 1 g·L −1 ultrafine tourmaline particles at low temperatures and 1 g·L −1 ultrafine tourmaline particles could not change the relative abundances of functional microbes except nitrite oxidizing bacteria.

Combined bioelectrochemical and sulfur autotrophic denitrification (CBSAD) system had proven to be feasible for nitrate removal at low temperature. This system obtained excellent denitrification efficiency 96.55% at 10 ± 2 °C long term operation. Nitrate removal efficiency presented increased tendency with applied current increased from 50 to 200 mA and then decreased when the applied current was further increased to 300 mA. The CBSAD system owned the most abundant and rich communities at current 200 mA, and the community structures of the microbial samples at different current conditions were clearly different from each other. Phyla Firmicutes, Proteobacteria and classes Epsilonproteobacteria, Gammaproteobacteria, Betaproteobacteria, Clostridia dominated in all the communities in the system. The largest genus at current 50 mA was Arcobacter, whereas Pseudomonas was the most dominant genus at current 100-300 mA condition, suggesting that high current changed the bacterial structure in this CBSAD reactor., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The present study investigated effect of ammonium utilization on aerobic denitrification by Pseudomonas stutzeri T13. Per nitrogen balance calculation, all consumed ammonium was utilized as nitrogen source for cell propagation by assimilation rather than heterotrophic nitrification. Total organic carbon (TOC) and ammonium were necessary substrates to sustain heterotrophic propagation of P. stutzeri T13 at optimum proportion equal to seven. Under aerobic condition, nitrate was utilized as substitute nitrogen source when ammonium was completely exhausted. Biomass production effectively increased with increasing initial ammonium from 0mg/L to 100mg/L. Owing to enlarged biomass, average nitrate reduction rate increased from 7.36mgL -1 h -1 to 11.95mgL -1 h -1 . Such process also successfully reduced nitrite accumulation from 121.8mg/L to 66.16mg/L during aerobic denitrification. As important accessory during aerobic denitrification, ammonium assimilation efficiently doubled total nitrogen (TN) removal from 54.97mg/L (no ammonium provided) to 113.1mg/L (100mg/L ammonium involved)., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

An aerobic denitrification system, initially bioaugmented with Pseudomonas strain T13, was established to treat coal-based ethylene glycol industry wastewater, which contained 3219 ± 86 mg/L total nitrogen (TN) and 1978 ± 14 mg/L NO 3 -N. In the current study, a stable denitrification efficiency of 53.7 ± 4.7% and nitrite removal efficiency of 40.1 ± 2.7% were achieved at different diluted influent concentrations. Toxicity evaluation showed that a lower toxicity of effluent was achieved when industry wastewater was treated by stuffing biofilm communities compared to suspended communities. Relatively high TN removal (~50%) and chemical oxygen demand removal percentages (>65%) were obtained when the influent concentration was controlled at below 50% of the raw industry wastewater. However, a further increased concentration led to a 20-30% decrease in nitrate and nitrite removal. Microbial network evaluation showed that a reduction in Pseudomonas abundance was induced during the succession of the microbial community. The napA gene analysis indicated that the decrease in nitrate and nitrite removal happened when abundance of Pseudomonas was reduced to less than 10% of the overall stuffing biofilm communities. Meanwhile, other denitrifying bacteria, such as Paracoccus, Brevundimonas, and Brucella, were subsequently enriched through symbiosis in the whole microbial network.- -N. In the current study, a stable denitrification efficiency of 53.7 ± 4.7% and nitrite removal efficiency of 40.1 ± 2.7% were achieved at different diluted influent concentrations. Toxicity evaluation showed that a lower toxicity of effluent was achieved when industry wastewater was treated by stuffing biofilm communities compared to suspended communities. Relatively high TN removal (~50%) and chemical oxygen demand removal percentages (>65%) were obtained when the influent concentration was controlled at below 50% of the raw industry wastewater. However, a further increased concentration led to a 20-30% decrease in nitrate and nitrite removal. Microbial network evaluation showed that a reduction in Pseudomonas abundance was induced during the succession of the microbial community. The napA gene analysis indicated that the decrease in nitrate and nitrite removal happened when abundance of Pseudomonas was reduced to less than 10% of the overall stuffing biofilm communities. Meanwhile, other denitrifying bacteria, such as Paracoccus, Brevundimonas, and Brucella, were subsequently enriched through symbiosis in the whole microbial network.

A novel aerobic denitrification and biomineralization strain H36 was isolated from the Qu Jiang artificial lake. Based on phylogenetic characteristics, the isolated strain was identified as Acinetobacter species. Strain H36 was confirmed to have the ability to perform simultaneous denitrification and biomineralization. Results showed the strain H36 had the capability to completely reduce 96.29% of NO 3 - -N and 78.59% of Ca 2+ over 112h under aerobic condition. Response surface methodology (RSM) analysis demonstrated the highest removal ratio of Ca 2+ was 74.24% with hardness concentration of 350mg/L, pH of 8.5, organic concentration of 0.75g/L and inoculum size of 15%. The highest removal ratio of nitrate was 77.00% with hardness concentration of 350mg/L, pH of 7.5, organic concentration of 0.75g/L and inoculum size of 10%. Besides, X-ray diffraction (XRD) analysis showed calcium carbonate could be formed in the process of biomineralization., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Sulfur/dolomite and pyrite/dolomite autotrophic denitrification reactors were applied to treat the secondary effluent of wastewater treatment plant to explore the removal effect, the changes of microbial community, and recovery time of reactors after starvation period. It was shown in the results that after 30 d non-water starvation endurance, the effluent concentrations of NO 3 - -N in sulfur/dolomite and pyrite/dolomite reactors increased from 1.78 mg·L -1 , 11.32 mg·L -1 to 27.87 mg·L -1 , 26.56 mg·L -1 respectively at the low temperature of 12-14℃. In addition, sulfur/dolomite and pyrite/dolomite reactors recovered within 5 d and 11 d since restarted and could maintain a good effect of nitrogen removal at low temperature. MiSeq high throughput sequencing results showed that the abundance and diversity of the bacterial communities in starvation period in both reactors were lower than those in recovery period. The dominating phylum was Proteobacteria in both reactors while the dominating class was β was identified as the main genus for denitrification in sulfur/dolomite reactor.Thiobacillus was identified as the main genus for denitrification in sulfur/dolomite reactor.

A novel aerobic denitrification and biomineralization strain CN86 was isolated from the Qu Jiang artificial lake. Based on phylogenetic characteristics, the isolated strain was identified as Acinetobacter species. Strain CN86 was confirmed to have the ability to perform simultaneous denitrification and biomineralization. Exponential decay equation was used for the matching of kinetic processes on denitrification and biomineralization. A highest nitrate removal rate was achieved at the pH7.0, organic concentration of 1.5g/L and temperature of 30°C. An optimal hardness removal rate was obtained at the pH9.0, organic concentration of 2.0g/L and temperature of 30°C. Strain CN86 is a suitable candidate for the simultaneous removal of nitrate and hardness in groundwater treatment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Acinetobacter sp. J25 exhibited good denitrification and high algicidal activity against toxic Microcystis aeruginosa. Response surface methodology (RSM) experiments showed that the maximum algicidal ratio occurred under the following conditions: temperature, 30.46°C; M. aeruginosa density, 960,000cellsmL(-1); and inoculum, 23.75% (v/v). Of these, inoculum produced the maximum effect. In the eutrophic landscape water experiment, 10% bacterial culture was infected with M. aeruginosa cells in the landscape water. After 24days, the removal ratios of nitrate and chlorophyll-a were high, 100% and 87.86%, respectively. The denitrification rate was approximately 0.118mgNO3(-)-N·L(-1)·h(-1). Moreover, the high-throughput sequencing result showed that Acinetobacter sp. J25 was obviously beneficial for chlorophyll-a and nitrate removal performance in the eutrophic landscape water treatment. Therefore, strain J25 is promising for the simultaneous removal of chlorophyll-a and nitrate in the eutrophic landscape water treatment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The role of electron donors (Fe(2+) and Mn(2+)) in the autotrophic denitrification of contaminated groundwater by bacterial strain SY6 was characterized based on empirical laboratory-scale analysis. Strain SY6 can utilize Fe(2+) more efficiently than Mn(2+) as an electron donor. This study has shown that the highest nitrate removal ratio, observed with Fe(2+) as the electron donor, was approximately 88.89%. An immobilized biological filter reactor was tested by using three levels of influent nitrate (10, 30, and 50 mg/L), three pH levels (6, 7, and 8), and three levels of hydraulic retention time (HRT; 6, 8, and 12 h), respectively. An optimal nitrate removal ratio of about 95% was achieved at pH 6.0 using a nitrate concentration of 50 mg/L and HRT of 12 h with Fe(2+) as an electron donor. The study showed that 90% of Fe(2+) and 75.52% removal of Mn(2+) were achieved at pH 8.0 with a nitrate concentration of 50 mg/L and a HRT of 12 h. Removal ratio of Fe(2+) and Mn(2+) is higher with higher influent nitrate and HRT. A weakly alkaline environment assisted the removal of Fe(2+) and Mn(2+).

A newly aerobic denitrifying bacterial strain, Pseudomonas sp. X31, which was isolated from activated sludge, was added to a newly developed aerobic denitrification bio-ceramsite reactor as an inoculum to treat nitrate-polluted water and the denitrification activities of this system under different air-water ratio, hydraulic loading, and C/N (carbon/nitrogen ratio) conditions were investigated. It demonstrated excellent capability for denitrification in the bio-ceramsite reactor at air-water ratios that varied from 6.5:1 to 8:1. The optimal hydraulic loading for the bio-ceramsite reactor was 0.75 m/h with the optimum denitrification efficiency of 95.18%. The optimal C/N was 4.5:1 with a maximum nitrate removal efficiency of 98.48%. COD could be completely removed under the most appropriate condition (air-water ratio 6.5:1-8:1, hydraulic loading 0.75 m/h, and C/N 4.5:1). The quantity of the biomass in the reactor decreased along with flow, which was in accordance with the variety of the available substrate concentrations in the water. However, the biofilm activity was not proportional to the biomass in the bio-ceramsite reactor, but increased with the quantity of the biomass up to a peak value and then decreased.

A novel indigenous bacterium, strain JM10, isolated from the oligotrophic Hei He reservoir was characterized and showed aerobic denitrification ability. JM10 was identified as Bacillus sp. by phylogenetic analysis of its 16S rRNA gene sequence. Strain JM10 displayed very high levels of activity in aerobic conditions, consuming over 94.3% NO3(-)-N (approximately 3.06 mg L(-1)) with a maximum reduction rate of 0.108 mg NO3(-)-N L(-1) h(-1). Full-factorial Box-Behnken design and response surface methodology were employed to investigate the optimal nitrate degradation conditions. The optimum conditions for nitrate degradation, at a rate of 0.140 mg L(-1) h(-1), were found to be an inoculum size of 16.3% v/v, initial pH of 7.6, C/N ratio of 7.4, and temperature of 27.4 °C, and the C/N ratio and temperature had the largest effect on the nitrate degradation rate. Strain JM10 was added into the water samples from Hei He reservoir and the total nitrogen and nitrate removal rates of the strain reached 66.5% and 100%, respectively. Therefore, our results demonstrate that the strain JM10 favored the bioremediation of the oligotrophic reservoir.

The short-cut nitrification and denitrification process of a polyurethane biofilm reactor was studied at four different carbon to nitrogen ratios (C/N ratios) (C/N =15:1, 10:1, 5:1 and 1.8:1) with focus on reactor performance and microbial community composition. Results showed that when the influent carbon/nitrogen ratio decreased from 15 to 10, 5 and 1.8, the nitrite accumulation rate was increased from 56.1% to 62.3%, 72.3% and 83.2% after 100 d operation. System achieved the optimal removal efficiency at an influent carbon/nitrogen ratio of 10 with 99.1% of ammonia removal and 91.0% of total nitrogen removal. Simultaneous nitrification and denitrification occurred in the polyurethane biofilm system at different influent carbon/nitrogen ratio. As the influent carbon/nitrogen ratio decreased from 15 to 10, 5 and 1.8, the efficiency of simultaneous nitrification and denitrification was gradually reduced. The microbial biofilm analysis indicated that the microbial diversity of biofilm with an influent carbon/nitrogen ratio of 15 was significantly higher than that in other conditions. The predominant ammonia oxidizing bacteria and nitrite oxidizing bacteria were Nitrosospira sp. and Nitrospira sp., respectively, and the predominant denitrifying bacteria were Pseudomonas sp.

A denitrifying polyphosphate-accumulating organism (DPAO) was isolated and identified, and the denitrifying functional genes were investigated. The strain ZQN2 was isolated using denitrifying medium. It was distinguished as DPAO by tests of aerobic phosphorus uptake, nitrate reduction, metachromatic granules and PHB (poly-beta-hydroxybutyrate) granules dyeing. Test of anaerobic phosphorus release/anoxic phosphorus uptake showed that strain ZQN2 released phosphorus and synthesized PHB at the anaerobic phase and used NO3- as acceptor to oxidize PHB during the anoxic phase with luxury phosphorus uptake, performing the function of simultaneous denitrifying phosphorus removal. The 16S rRNA gene sequence of strain ZQN2 was used for homology analysis and construction of phylogenetic trees. The results suggested that the 16S rRNA gene sequence of ZQN2 had up to 99% homology with those of many strains of Bacillus cereus strains in GenBank database. With physiological and biochemical reactions, the strain ZQN2 was identified as Bacillus cereus. The result of denitrifying functional gene study suggested that strain ZQN2 was the type of nirS+ and nirK-, which confirmed its denitrifying function from molecular biology point of view. Moreover, the phylogenetic analysis of nirS gene of ZQN2 showed that it was closely related to many strains of Pseadomonas aeruginosa, which was different from the analysis results of the 16S rRNA.

The performance of a sequencing batch reactor for simultaneous nitrification and denitrification (SBR-SND) was investigated under 5-30°C and strategies against temperature influences were proposed. Aeration of 8, 7, 7 and 6h were sufficient for 5±2, 10±2, 20±2 and 30±2°C, respectively. Further extension was insubstantial, only increased the aeration cost. The adjustment of C/N ratio to offset the temperature impacts was not remarkable. Prolonged sludge retention time lessened the influences of low temperature but deteriorated the system at high temperature. The oxidation reduction potential, the dissolved oxygen concentration, the sludge volume index and the extracellular polymeric substances amount changed with temperature alterations and thus affected the system performance. In conclusion, measures should be taken for temperature oscillations and the regulation and control of the operational parameters could alleviate the influences of temperature on the performances of the SBR-SND system., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The effects of dissolved oxygen on simultaneous nitrification and denitrification were evaluated in polyurethane foam contact oxidation reactors in a municipal wastewater treatment process. It was observed that nitrate could be removed at low dissolved oxygen levels, but the removal rate was gradually reduced as the dissolved oxygen concentration increased to a higher level of 6.0 mg/L. Nitrogen removal remained optimal within the dissolved oxygen range of 0.5 to 1.0 mg/L. Denaturing gradient gel electrophoresis (DGGE) analysis revealed that the diversity of the microbial community changed accompanying dissolved oxygen values of 0.5 to 1.0 mg/L, 2.5 to 3.5 mg/L, 6.0 to 6.5 mg/L, and 10.0 to 12.0 mg/L, in turn, which was supported by the Shannon-Wiener index of 1.56, 1.71, 1.43, and 1.56, accordingly. Both DGGE profiling and phylogenetic analysis confirmed that the nitrifiers in reactors that are responsible for nitrification during the experiment include Nitrosospira sp., Nitrosomonas sp., and Nitrospira sp.

A sequencing batch biofilm reactor (SBBR) filled with polyurethane (PU) was operated in low dissolved oxygen (DO) (0.1-0.9 mg/L) at three different carbon to nitrogen ratios (C/N ratios) (C/N = 1.8:1, 5.0:1 and 10.5:1) with focus on reactor performance and microbial community composition of nitrifying and denitrifying bacteria. Meanwhile, the ammonium, nitrite, nitrate, pH and dissolved oxygen were analyzed to monitor the process of nitrification-denitrification. The reactor had a steady ammonium removal in spite of a large variation in the initial ammonium loading (the ammonium removal efficiency was 87.2% at C/N 1.8:1, 92.9% at C/N 5.0:1, 88.4% at C/N 10.5:1). However, the total nitrogen (TN) removal was strongly affected by the initial organic loading (the TN removal efficiency was 55.2% at C/N 1.8:1, 74.3% at C/N 5.0:1, 79.0% at C/N 10.5:1). It was indicated that higher organic load promoted denitrification. The real-time quantitative polymerase chain reaction (real-time qPCR) analysis shown that Beta-proteobacteria occupied over 35% numerically. As for the Nitrosomonas sp., Nitrosospira sp. and Nitrospira sp. gene copy numbers, their abundance was generally in the order of magnitude of 10(10). The Nitrosospira sp. fluctuated significantly in the range of 3.1-9.8% at different C/N ratios, while the Nitrosomonas sp. just changed a little.

Kinetics of low nitrate and ammonia concentration removal by oligotrophic Acinetobacter sp. SYF26 were examined in this study. Heterotrophic nitrification-aerobic denitrification followed first-order reaction kinetics. The maximum removal rate was achieved under pH = 7.0, 30°C, and a carbon-to-nitrogen ratio (C/N) = 7.5. In a landscape water experiment, strain SYF26 was capable of both heterotrophic nitrification and aerobic denitrification and exhibited no nitrite accumulation during the whole process. Both three-dimensional excitation-emission matrix fluorescence spectroscopy and Fourier transform near-infrared spectroscopy assessments of landscape water illustrated that strain SYF26 could use protein-like compounds and humus as carbon sources for heterotrophic nitrification-aerobic denitrification. Results illustrated that strain SYF26 is a suitable candidate for the bioremediation of landscape water. [ABSTRACT FROM AUTHOR]

The effect of nitrite on autotrophic denitrification was tested using mixed electron donors of Mn(II) and Fe(II) with Pseudomonas sp. SZF15. In batch experiments, nitrate and nitrite were completely depleted without ammonia production (denitrification rate of 0.151 mg-NO3−-N·L−1·h−1 and 0.104 mg-NO2−-N·L−1·h−1, respectively), suggesting that denitrification occurred by strain SZF15 via nitrite reductase. A maximum denitrification rate of 0.097 mg-NOX−-N·L−1·h−1 was found at an n(NO3−-N):n(NO2−-N) ratio of 5:5. Edwards and Aiba models were used to describe the denitrification inhibition caused by nitrite, and the kinetic parameters determined from the Edwards model were rmax of 2.148 mg-NO2−-N·g-VSS−1·h−1, KS of 6.225 mg-NO2−-N·L−1, and KI of 25.152 mg-NO2−-N·L−1. These results provide useful information for optimization of the autotrophic denitrification process by avoiding inhibition to obtain higher denitrification efficiencies. In addition, strain SZF15 showed excellent denitrification performance for groundwater treatment. [ABSTRACT FROM AUTHOR]

Strain H117 was isolated from the Tang Yu reservoir. Based on the phylogenetic characteristics, strain H117, which was identified as Pseudomonas sp. strain H117, had the capability to utilize bicarbonate and sodium acetate as a carbon source under anaerobic conditions. Furthermore, the strain could grow on both autotrophic and heterotrophic media, and could perform both autotrophic and heterotrophic denitrification in the medium. Response surface methodology analysis demonstrated that the maximum degradation ratio of nitrate-occurred under the following conditions in the autotrophic medium: initial pH of 6.00, C/N ratio of 4.68 and temperature of 31.33°C. The maximum degradation ratio of nitrate occurred under the following conditions in the heterotrophic medium: initial pH of 6.16, C/N ratio of 8.23 and temperature of 28.48°C. Finally, the denitrification performance of strain H117 was evaluated under the optimum conditions. These results suggest that strain H117 has potential applications for the bioremediation of polluted groundwater. [ABSTRACT FROM AUTHOR]

Coupled autotrophic denitrification with iron cycle is an important but poorly understood process. A newly bacterium Enterobacter sp. CC76 exhibits an efficient autotrophic denitrification ability with a maximum nitrate removal rate of 0.24 mg/L•h coupling with iron cycle under the anaerobic conditions. The presence of the nirS gene and meteorological chromatography analysis suggest that N 2 is produced as an end product by sequence amplification identified. Meanwhile, response surface methodology (RSM) experiments show that the maximum removal ratio of nitrate can reach to approximately 100% under the following conditions: pH of 5.58, temperature of 28.69 °C, C/N ratio of 5.09, Fe (III) concentration of 28.05 mg/L. And, a potential pathway of nitrate removal with iron cycle for strain CC76 is proposed. Moreover, a nitrate removal rate of 0.96 mg/L•h from iron cycle is achieved with immobilization of strain CC76 in the groundwater. [ABSTRACT FROM AUTHOR]

A novel bacterium, strain SZ28, identified asAcinetobactersp., showed anaerobic denitrification ability using Mn(II) as the electron donor. Nitrate-nitrogen concentration decreased from nearly 16.52–mg L−1to 4.4–mg L−1, without accumulation of nitrite as an intermediate, with a maximum of 0.063–mg NO3−-N L−1h−1, reaching a peak of 0.085–mg NO3−-N L−1h−1in sodium acetate. The nitrate removal rate reached 0.067–mg NO3−-N L−1h−1, 0.059–mg NO3−-N L−1h−1, and 0.078 mg NO3−-N L−1h−1using Mn(II), S(II), and Fe(II) as electron donors, respectively. The optimum pH was 6.0, with a removal rate of 0.063–mg NO3−-N L−1h−1 [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) could be deemed hazardous materials in aquatic environment. Microcystis aeruginosa is a toxic HAB causing alga, which causes serious economic losses and health problems. In this study, a strain J25 with the high algicidal activity isolated from an eutrophic Qu Jiang Lake, was identified as Acinetobacter sp. based on its morphological features and phylogenetic analysis by sequencing of 16S rDNA. Its algae-lysing characteristics on M. aeruginosa , was tested under the different conditions. The results showed that the strain J25 had good tolerance of acid and alkali, and full illumination played a positive role in the algae removal. Furthermore, this was the first report about the relationship between algicidal and denitrification activities. The maximum denitrification rate (1.62 mg NO 3 − –N L −1 h −1 ) was observed within 6 days at 15% of inoculum. [ABSTRACT FROM AUTHOR]

The excellent removal efficiency of nitrate by the aerobic denitrifier, Pseudomonas stutzeri T13, was achieved in free cells system. However, poor nitrite reduction prevents efficient aerobic denitrification because of the nitrite accumulation. This problem could be conquered by immobilizing the cells on supports. In this study, strain T13 was immobilized by mycelial pellets (MPs), polyurethane foam cubes (PFCs) and sodium alginate beads (SABs). Higher removal percentages of TN in MP (43.78%), PFC (42.31%) and SAB (57.25%) systems were achieved compared with the free cell system (29.7%). Furthermore, the optimal condition for immobilized cell systems was as follows: 30 °C, 100 rpm shaking speed and pH 7. The shock-resistance of SAB system was relatively poor, which could collapse under either alkaline (pH = 9) or high rotating (200 rpm) conditions. The recycling experiments demonstrated that the high steady TN removal rate could be maintained for seven cycles in both MP and PFC systems. [ABSTRACT FROM AUTHOR]

To investigate the effect of different environmental factors on the efficiency of denitrifying phosphorus removal bacteria (DPB), anaerobic/oxic/anoxic reactor (A!O/A- SBR) was used to culture the granular sludge. By designing the orthogonal test, the overall investigation of the biological nitrogen and phosphorus removal efficiency of DPB under various carbon source, carbon concentration, inlet water temperature and pH value was carried out. The results show that: when carbon source is sodium propionate, COD concentration is 400 mgiL, inlet water temperature is 25 °C, and pH value is 7, the COD degradation efficiency of DPB is the highest; when carbon source is sodium propionate, COD concentration is 400 mg/L, inlet water temperature is 15 °C, pH value is 7, the nitrogen removal efficiency of DPB is the highest; when carbon source is sodium acetate, COD concentration is 400 mg/L, inlet water temperature is 25 °C, pH value is 8, the removal efficiency of soluble P is best. Temperature is the most influential factor for the COD and nitrogen removal, while the influence of pH is the minimum. The most influential factor for phosphorus removal of DPB is pH, and carbon source affects the minimum. [ABSTRACT FROM AUTHOR]

In this paper, 16 denitrifying phosphate --accumulating organisms (DNPAOs) were isolated in the special medium from the anaerobic/aerobic/anoxic SBR reactor, and the most efficient DNPAOs called Q -- hrb05, was screened by a phosphate uptake experiment, where nitrates were denitrified to gas and through inspection of the poly -- P. Strain Q -- hrb05 was identified by 16S rDNA gene analysis, and the accession number of 16 S rDNA gene sequence of strain Q -- hrb05 in GenBank was GU214826. The result showed that the strain Q -- hrb05 belonged to Bacillus sp, of which the homology could reach to 99%, that also corresponded to the result of biochemical features. The average phosphorus uptake rate of strain Q -- hrb05 was at 85% within 12 hours, and it had the denitrification capacity in the aerobic condition. It could be found that the phosphorus uptake rate was related to the content change of PHB. Under anaerobic condition, the maximal P -- release rate was 66%, which could reach to 12% of the dry cell weight. The P -- uptake rate was 92% with the decreasing of PHB content. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of simultaneous nitrification and denitrification (SND) and promote the efficiency of SND system, by using the domesticated efficient SND sludge, the effects of organism, DO and temperature on the SBR reactor were studied. The experiment results showed that, when the temperature was 25 -30 and pH was 7 -9, the nitrate -nitrogen removal was preferably; when C/N rate varied between 1:1 - 8: 1, COD concentration, ammonia nitrogen removal rate and TN removal rate decrease with the increasing of C/N rate. Dosing organic compounds in twice can enhance the aerobic denitrification effect. When aeration volume varied from 0. 12 to 0.80 L ⋅ min -1 , ammonia nitrogen removal rate increased first and then kept approximate constant with the increase of aeration volume, finally became stable at 99.8%. TN removal rate increased first to the highest at 95.52%, then decreased, when aeration volume was 0. 2 L ⋅ min -1, and COD was stable above 91%. The influence of aeration rate on the COD removal is not distinct. The best effect will be achieved if the system temperature is 25 -30 ° C, C/N rate is 1.5: 1, aeration volume is 0.2 L ⋅ min-1 , pH is 7 -9 and the dosing of organic compounds is in twice. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of denitrifying phosphorus removal and provide functional strains for nitrogen and phosphorus removal, denitrifying phosphorus removal bacteria (DPB) were enriched and isolated from A2SBR. This study made use of controlling the inflow water operation mode of A2SBR for DPB enrichment and screening. The isolated DPB were complex formulated for construction of nitrogen and phosphorus removal functional bacteria. Two-stage inflow water operating mode and high inflow water rate enabled DPB to become rapidly dominant in the reactor. Five DPB strains were isolated and identified by the microbial identification system with fatty acids. The DPB strain and phosphorus accumulating organisms or denitrobacteria were complex formulated, the results showed that the best combination was b204 and 16. Its phosphorus removal rate was 85.78% and its denitrification efficiency was 75.02%, better than the single strains removal rate. Experimental results also showed that DPB could become dominant populations quickly with optimum cultivation conditions :rod appropriate influent. [ABSTRACT FROM AUTHOR]

This paper discusses the mechanism and application of denitrification inhibition to the activity of sulfate - reducing bacteria in wastewater treatment of domestic and overseas oilfields. All factors affecting this process and shortcomings in the process were reviewed as well. It is suggested that the study on protein structure and environmental gene is important for the mechanism research, particularly for studying the effect of addition of inhibiting agents, such as nitrate and denitrifying bacteria, on the gene and protein structure of sulfate - reducing bacteria as well as the metabolism process. It is critical to investigate this process from the view of microbial molecular ecology. The case application has also been studied for Daqing Oilfield. [ABSTRACT FROM AUTHOR]

To improve the growth and efficiency of aerobic denitrifying bacteria, by adding different dose of magnetic powder (within 0.5 - 3.0 g/L, 0. 5 g/L for a gradient) and after 24 h, the growth absorbency, nitrate removal rate and dehydrogenase activity were determinated. Results show that the growth increases, and the nitrogen removal efficiency and dehydrogenase activity of T13 first increase and then decrease with increasing of magnetic powder dosage. The magnetic powder promotes the aerobic denitrifying bacteria growth and efficiency, and 2.0 g/L of magnetic powder is the optimal dosing quantity, under which the dehydrogenase activity and denitration nitrogen removal of T13 go to the maximum 73.9 µ/( mL⋅ h) and 100% respectively. [ABSTRACT FROM AUTHOR]

Microcystis aeruginosa is a cyanobacterium that can cause harmful algal blooms (HABs) in freshwater bodies. In this study, the bacterium Raoultella sp. R11 was evaluated for its ability to control the growth of M. aeruginosa . Algal growth, denitrification activity, and toxin production were measured in the presence of various concentrations of Raoultella sp. R11. The algicidal effects of Raoultella sp. R11 were studied by measuring the zeta potential (surface charge), the activity of superoxide dismutase (SOD), and the concentrations of chlorophyll-a, dissolved organic matter, and microcystin-LR in algal cultures. The results suggested that chlorophyll-a removal, which indicates algal death, was correlated with the dose of Raoultella sp. R11. The zeta potential and denitrification activity decreased in the presence of bacteria in a dose-dependent manner. SOD activity was correlated with the inoculation dosage of Raoultella sp. R11. Using a 30% (v/v) dose of bacterial culture, the removal efficiency of chlorophyll-a was as high as 94.28% after 6 days. In addition, dissolved microbial metabolites and humic acid were detected in high quantities whereas low quantities of protein-like substances and fulvic acid were found. Furthermore, toxic microcystin-LR produced by the algae was eliminated at up to 92.21% efficiency. A high denitrification rate (1.57 mg NO 3 - -N L −1 h −1 ) and chlorophyll-a removal efficiency (73.12%) were observed within 6 days at an inoculation dosage of 20% (v/v) of bacterial culture. Our findings indicated that Raoultella sp. R11 has a high potential for applications in simultaneously controlling M. aeruginosa and facilitating denitrification in freshwater bodies. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Simultaneous denitrification and chromium reduction was achieved in a BES. • The BES could achieve satisfied removal abilities under the selected pH range, and optimum pH was occurred at 7.0. • Key functional groups for denitrification and chromium reduction were identified. • Pseudomonas , Halomonas and Thauera enriched in the BES and facilitated the denitrification and Cr (VI) reduction process. Abstract A novel bioelectrochemical system (BES) was established to investigate the feasibility of simultaneous autotrophic denitrification and chromium removal under different pH conditions in terms of the removal performance and dominant microbial community. Reliable nitrate and hexavalent chromium (Cr (VI)) removal was obtained, and the optimum pH was 7.0 with the highest removal efficiencies of 97.21 and 72.65%, respectively. The bacterial communities exhibited highly selective and concentrated as revealed by the alpha-diversity indices and the Pareto–Lorenz (PL) evenness curves. The highest community richness was achieved under neutral environment, while increasing pH strengthen the species diversity. The predominant phylum Proteobacteria and class Gammaproteobacteria might act as the main contributors, accounting for 95.21–98.47% and 64.49–88.84% of the classified sequences. Key functional groups in terms of the denitrifying bacteria (DNB) and Cr reduction bacteria (CRB) were identified at the genus level. The similar total number of DNB and CRB indicated a good adaptability to pH. The stable removal ability was ascribed to the presences of Pseudomonas , Halomonas and Thauera , which facilitated the combined autohydrogenotrophic denitrification and Cr (VI) reduction process. This study provides a more in-depth understanding of application of BES for simultaneous denitrification and Cr (VI) reduction process. [ABSTRACT FROM AUTHOR]

Soluble microbial products (SMP) cause major soluble chemical oxygen demands (sCOD) in secondary effluent and significantly affect effluent quality. However, SMP can be also treated as new organic carbon resource, which can provide electrons for denitrification under anoxic conditions. This work investigated contribution of SMP as electron donors during denitrification under different conditions (feast, feast–famine, and famine). Only fraction of utilization-associated products could be adopted as electron donors for denitrification in feast condition because of sufficient organic carbon supply. Most biomass-associated products remained in water. In feast-famine condition, the nitrogen (nitrate and nitrite) reduction using influent TOC and SMP as electron donors were 86.4 and 55.2 mg N/L respectively. SMP accounted for 33.6% and 39.0% of total nitrogen (TN) removal and total nitrogen (nitrate and nitrite) reduction, respectively. Only SMP can be adopted as sole electron donors in famine condition. Approximately 128.7 mg N/L of nitrogen (nitrate and nitrite) reduction was calculated. Nitrate and TN removal were 91.4% and 51.7%, respectively. As electron acceptors under anoxic conditions, nitrate or nitrite can stimulate SMP generation from hydrolysis of extracellular polymeric substances. [ABSTRACT FROM AUTHOR]

In this study, Mn(II) as electron donor was tested for the effects on denitrification in the MBBR under the conditions of initial nitrate concentration (10 mg L −1 , 30 mg L −1 , 50 mg L −1 ), pH (5, 6, 7) and hydraulic retention time (HRT) (4 h, 8 h, 12 h) which conducted by response surface methodology (RSM), the results demonstrated that the highest nitrate removal efficiency was occurred under the conditions of initial nitrate concentration of 47.64 mg L −1 , HRT of 11.96 h and pH 5.21. Analysis of SEM and flow cytometry suggested that microorganisms were immobilized on the Yu Long plastic carrier media successfully before the reactor began to operate. Furthermore, high-throughput sequencing was employed to characterize and compare the community compositions and structures of MBBR under the optimum conditions, the results showed that Pseudomonas sp. SZF15 was the dominant contributor for effective removal of nitrate in the MBBR. [ABSTRACT FROM AUTHOR]

Acinetobacter sp. SZ28 exhibited efficient autotrophic denitrification ability using Mn 2+ as an electron donor. Sequence amplification identified the presence of the nirS gene. Meteorological chromatography analysis showed that N 2 was produced as an end product. Response surface methodology experiments showed that the maximum removal of nitrate occurred under the following conditions: Mn 2+ concentration of 143.56 mg/L, C/N ratio of 6.82, initial pH of 5.17, and temperature of 34.26 °C, where the initial Mn 2+ concentration produced the largest effect. In the groundwater experiment, nitrate levels decreased from 1.63 mg/L to 0 mg/L. Three-dimensional fluorescence analysis showed a decrease in the peak intensity of the original humus. Humus and the small-molecule amino acid tryptophan were detected. These results demonstrated that strain SZ28 is a suitable candidate for the simultaneous removal of nitrogen and Mn 2+ in groundwater treatment. [ABSTRACT FROM AUTHOR]