The lab-scale system combined bioelectrochemical and sulfur autotrophic denitrification (CBSAD) was established to evaluate the effects of currents (50–300 mA) on both the performances and microbial ...communities. Results showed that the nitrate removal rate increased significantly when the current increased from 50 to 200 mA, while it slightly decreased with higher currents. Mass balance results revealed that hydrogen autotrophic denitrification contributed almost three times (70.25–78.62%) to denitrification compared with that of the sulfur part (21.38–29.75%). Illumina MiSeq sequencing showed that the currents changed the bacterial richness and diversity in this system. Phylum Firmicutes and class Clostridia predominated >50% under each condition. And multiple key bacteria capable of denitrification such as Proteiniclasticum, Thauera and Family_XI_uncultured were identified and found in higher proportions when the current was 200 mA. Therefore, this study helps revealing the mechanisms of accelerating nitrate-reduction through applied currents in the CBSAD systems.
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•The CBSAD system obtained the best denitrification efficiency at current 200 mA.•Hydrogen autotrophic denitrification was the primary contribution to denitrification.•Currents changed the bacterial richness and diversity in this CBSAD system.•Key genus Proteiniclasticum contributed to better denitrification performances.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The traditional biological nitrogen removal technology consists of two steps: nitrification by autotrophs in aerobic circumstances and denitrification by heterotrophs in anaerobic situations; ...however, this technology requires a huge area and stringent environmental conditions. Researchers reached the conclusion that the denitrification process could also be carried out in aerobic circumstances with the discovery of aerobic denitrification. The aerobic denitrification process is carried out by aerobic denitrifying bacteria (ADB), most of which are heterotrophic bacteria that can metabolize various forms of nitrogen compounds under aerobic conditions and directly convert ammonia nitrogen to N2 for discharge from the system. Despite the fact that there is no universal agreement on the mechanism of aerobic denitrification, this article reviewed four current explanations for the denitrification mechanism of ADB, including the microenvironment theory, theory of enzyme, electron transport bottlenecks theory, and omics study, and summarized the parameters affecting the denitrification efficiency of ADB in terms of carbon source, temperature, dissolved oxygen (DO), and pH. It also discussed the current status of the application of aerobic denitrification in practical processes. Following the review, the difficulties of present aerobic denitrification technology are outlined and future research options are highlighted. This review may help to improve the design of current wastewater treatment facilities by utilizing ADB for effective nitrogen removal and provide the engineers with relevant references.
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•Aerobic denitrifying bacteria (ADB) are reviewed in light of water treatment.•Currently known mechanisms of nitrogen removal by ADB are summarized.•The effect of environmental conditions on ADB performance is discussed.•The process application of ADB in water treatment is discussed.•Limitations in molecular techniques and future research directions were highlighted.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Food wastes were used for anaerobic fermentation to prepare carbon sources for enhancing nitrogen removal in wastewater treatment. Under anaerobic conditions without pH adjustment, the fermentation ...liquid from food wastes (FLFW) with a high organic acid content was produced at room temperature (25 °C) and initial solid concentration of 13%. Using FLFW as the sole carbon source of artificial wastewater for biological treatment by sequence batch operation, maximized denitrification (with a denitrification rate of VDN = 12.89mg/gVSS h and a denitrification potential of PDN = 0.174 gN/gCOD) could be achieved at a COD/TN ratio of 6. The readily biodegradable fraction in the FLFW was evaluated as 58.35%. By comparing FLFW with glucose and sodium acetate, two commonly used chemical carbon sources, FLFW showed a denitrification result similar to sodium acetate but much better than glucose in terms of total nitrogen removal, VDN, PDN, organic matter consumption rate (VCOD) and heterotrophy anoxic yield coefficient (YH).
•Food waste was used for anaerobic fermentation to prepare carbon sources.•Fermentation liquid of high organic acid was used for enhancing denitrification.•High denitrification rate and potential were gained with fermentation liquid.•Fermentation liquid showed similar denitrification result as sodium acetate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Nitrate groundwater contamination is a worldwide concern. In this study, a novel 2-stage, sequential biocathodic denitrification system was tested to perform autotrophic denitrification of synthetic ...groundwater. The system was operated at different nitrate loading rates (66–301 gNO3−-N m−3NCC d−1) at constant NO3−-N concentration (40 mgNO3−-N L−1), by varying hydraulic retention time (HRT) during different trials from about 14 to 3 h. The system was able to achieve almost complete removal of nitrate (>95%) and Total Nitrogen (TN) (>92%) at NO3− loading rates between 66 and 200 gNO3−-N m−3NCC d−1. The first stage reactor achieved lower values of effluent nitrate and nitrite than WHO guidelines for drinking water quality (<11.3 mg NO3−-N L−1, and 0.9 mgNO2−-N L−1, respectively) up to a nitrate loading rate of 167 gNO3−-N m−3NCC d−1; in these conditions the second stage acted mainly as polishing step. From a loading rate of 200 gNO3−-N m−3NCC d−1 on, N2O accumulation was observed in the first stage reactor, afterwards successfully removed in the second stage. Maximum nitrate removal rate of the 2-step process was 259.83 gNO3−-N m−3NCC at HRT of 3.19 h. The specific energy consumption of the system (SEC) decreased with decreasing HRT, both in terms of mass of nitrate removed (SECN) and volume treated (SECV). The described combination of two bioelectrochemical systems system hence proved to be effective for groundwater denitrification.
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•A 2-stage controlled biocathodic denitrification (CBD) system was built and operated.•The system was run at increasing nitrate loading rates (and decreasing HRT).•The system showed increasing nitrate removal rates, up to 259.83 gNO3−-N m−3NCC d−1.•The specific energy consumption (SEC) decreased at the decrease of HRT.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Wastewater from households wastewater treatment plants (HWWTP) is discharged to the ground or to the surface waters. Special consideration should be given to the improvement of HWWTP effectiveness, ...particularly in relation to nutrients. The addition of biodegradable carbon sources to biofilm reactor, can enhance microbial activity but may also lead to filling clogging. The study aimed to compare 3 different organic substrates: acetic acid (commonly applied)and two untypical - citric acid and waste beer, under the same operational conditions in a post-denitrification biofilm reactor. The study investigated the impact of a type of organic substrate, low pH and time on: (1) biofilm growth, (2) the characteristics of extracellular polymeric substances (EPS), (3) the kinetics of nutrients removal and (4) reactor clogging. Results were referred to (5) the effectiveness of nutrients removal. The study demonstrated that low pH assured the development of a thinbiofilm. Citric acid ensured the lowest biomass volume, being by 53% lower than in the reactor with acetic acid and by as much as 61% lower than in the reactor with waste beer. The soluble EPS fraction prevailed in the total EPS in all reactors. The content of the tightly bound EPS fraction ranged from 26.93% (citric acid) to 36.32% (waste beer). Investigations showed also a high ratio of exoproteins to polysaccharide in all fractions, which indicated a significant role of proteins in developing a highly-proliferating biofilm. The treated wastewater met requirements of Polish regulations concerning COD and nitrogen concentrations.
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•The exoproteins were responsible for the amount of biofilm in the reactor.•The biofilm growth in the reactor depended on the type of substrate applied.•An external organic substrate ensured effective post-denitrification at SBBR.•Citric acid may counteract clogging of biofilm reactors.•Abundant biofilm and high rate of denitrification caused accumulation of nitrites.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•A novel Cu0/Cu2O-PANI-CNTs photocatalyst was prepared.•At neutral pH, 100% NO3− removal efficiency and 100 % N2 selectivity were achieved.•No additional hole scavengers were used in ...the selective photoreduction of NO3−.•Cu0/Cu2O-PANI-CNTs showed excellent practicality and stability.
The selective photoreduction of nitrate (NO3−) to nitrogen (N2) has emerged as an energy-efficient and environmentally friendly NO3− removal route under mild conditions. However, NO3− photoreduction often suffers low NO3− removal efficiency in the absence of hole scavengers at neutral pH, the generation of undesired side products (nitrite (NO2−), ammonium (NH4+), nitrogen oxides (NOx), etc.) and poor photocatalyst stability. In this study, a novel copper/copper(I) oxide-polyaniline-carbon nanotubes (Cu0/Cu2O-PANI-CNTs) photocatalyst was prepared through a combination of in situ polymerization and liquid phase reduction processes and used to reduce NO3− to N2. In the Cu0/Cu2O-PANI-CNTs/hv system, NO3− was reduced to NO2− by photogenerated electrons (ecb−) on the surface of Cu0/Cu2O, and the generated NO2− was further reduced to N2 by PANI, resulting in high N2 selectivity. –NH– in PANI acted as photogenerated hole (hvb+) capture centres, leading to NO3− photoreduction without additional hole scavengers. Given the interaction between Cu0, ecb− and PANI, Cu0/Cu2O-PANI-CNTs show excellent repeatability. A 100% NO3− removal efficiency and 100 % N2 selectivity could be achieved by the Cu0/Cu2O-PANI-CNTs/hv system at neutral pH. With river water, secondary effluent and the fourth reuse of the catalyst, the NO3− removal efficiencies were as high as 93.0%, 91.2% and 84.4%, respectively, with 100 % N2 selectivity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•The stoichiometric coefficients of aerobic denitrification by T13 were obtained.•The kinetic constants of aerobic denitrification by T13 were obtained.•Accumulated nitrite was ...simulated with a two-step denitrification model.•The validity of the stoichiometric coefficients and kinetic constants was tested.
The mechanism of total nitrogen (TN) removal at aerobic condition in wastewater treatment plants (WWTPs) has been one of the most popular research fields. However, the role of aerobic denitrification in TN removal was unclear because of the lack of stoichiometric coefficients and kinetic constants of aerobic denitrification bacterium. Thus, this study aimed to investigate the stoichiometry and kinetics of aerobic denitrification by using Pseudomonas stutzeri T13 as a model aerobic denitrification bacterium. Results indicated that strain T13 obtained the maximum yield coefficient (0.1098 mol biomass-N/mol COD) when using NH4+-N as the sole nitrogen source. This value decreased slightly (0.1077 mol biomass-N/mol COD) during aerobic denitrification, but was still higher than that of conventional denitrification. The half-saturation constants for ammonium, nitrate and nitrite (KNH4+, KNO3- and KNO2-) of strain T13 were fitted based on the experimental data and were 2.72, 18.33 and 209.07 mg/L, respectively. The validity of the stoichiometric coefficients and kinetic constants was tested at two extra conditions and perfect fitting results were obtained. To our knowledge, this is the first time to report the stoichiometric coefficients and kinetic constants of aerobic denitrification. These parameters will be useful in modelling nitrogen removal performance in systems inoculated with aerobic denitrification bacterium. Moreover, this study could provide an experimental basis for further clarifying the mechanism of aerobic denitrification from a quantitative perspective.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
An ex-situ
15
N–
18
O tracing experiment with soils collected from the valley and slope, respectively, of a subtropical secondary karst forest with three N addition levels, i.e., 0, 50, and ...100 kg N ha
−1
year
−1
for each topographic position to investigate N
2
O production pathways. Autotrophic nitrification pathways (ammonia oxidation, nitrifier denitrification, and nitrification-coupled denitrification) accounted for > 70% of total N
2
O production, but denitrification pathways (heterotrophic denitrification and co-denitrification) were the minor source of N
2
O at both topographic positions. In the valley, chronic N addition stimulated ammonia oxidation-derived N
2
O, which was paralleled by increased ammonia-oxidizing archaea (AOA)
amoA
gene transcript abundance, but inhibited nitrifier denitrification- and nitrification-coupled denitrification–derived N
2
O along with suppressed ammonia-oxidizing bacteria (AOB)
amoA
gene transcript abundance and stimulated
nosZ
II gene transcript abundance, respectively. On the slope, chronic N addition stimulated ammonia oxidation-derived N
2
O along with increased AOB
amoA
gene transcript abundance, and enhanced nitrifier denitrification-derived N
2
O congruent with increased AOB
amoA
and decreased
nirK
gene transcript abundances. In addition, chronic N addition reduced the relative contribution of heterotrophic denitrification to N
2
O production but had no significant influence on heterotrophic denitrification-derived N
2
O on the slope. Overall, our results provide a comprehensive view in terms of how topography-driven soil properties regulate N
2
O production and its pathways in a subtropical forest.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Compared with Fe0-mediated autotrophic denitrification (ADN), mixotrophic denitrification (MDN) can alleviate the problem of reduced denitrification efficiency due to Fe0 passivation. In this study, ...carbon fiber (CF) was added as an additional cathode material to Fe0-mediated MDN to promote Fe0 corrosion and advanced denitrification of secondary effluent with low chemical oxygen demand (COD) to nitrogen (C/N) ratio. The results showed that the average removal efficiencies of total nitrogen (TN) and nitrate nitrogen (NO3--N) in the experimental group with CF coupling Fe0 (CF/Fe0) were achieved as high as 80.08 % and 79.79 % in Phase VI (C/N ratio = 3, hydraulic retention time (HRT) = 48 h), respectively. Mechanistic investigation showed that part of Fe0 corroded during the reaction process and the reaction products (Fe3+, Fe2+) were adsorbed on CF surface, sustaining the reaction of NO3--N conversion and promoting denitrification performance. Furthermore, the iron ions attached to the CF surface will further stimulate the generation of extracellular polymeric substance (EPS) containing redox-active components such as flavins and Cytochrome c (Cyt c). Consequently, the activity of the electron transport system was promoted. CF dosing resulted in a high enrichment of dominant denitrifying bacteria such as Acinetobacter, Comamonas and Pseudomonas in MDN, and expression of narG, napA, nosZ and other microbial metabolic function genes. Based on the above, the efficiency and mechanism of CF enhanced Fe0-mediated MDN was elucidated, which is favorable for enhancing the nitrogen removal in secondary effluent containing NO3--N with low C/N ratio based on Fe0-mediated MDN.
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•An advanced denitrification by CF enhanced Fe0-mediated MDN is proposed.•The enhancement of CF on Fe0-mediated MDN is demonstrated and elucidated.•The problem of the electron donor loss caused by the Fe0 passivation is dissolved.•The promotion effect of CF on the enrichment denitrifying bacteria is elaborated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► Heterotrophic nitrification–aerobic denitrification of Bacillus methylotrophicus. ► Transform NH3 to N2O and NO2- to N2 for G+ bacteria were never described. ► Nitrite other than nitrate was ...employed as denitrification substrate. ► GC–MS and GC–IRMS revealed a different gaseous nitrogen compound emitting pattern.
Bacillus methylotrophicus strain L7, exhibited efficient heterotrophic nitrification–aerobic denitrification ability, with maximum NH4+-N and NO2--N removal rate of 51.58mg/L/d and 5.81mg/L/d, respectively. Strain L7 showed different gaseous emitting patterns from those strains ever described. When 15NH4Cl, or Na15NO2, or K15NO3 was used, results of GC–MS indicated that N2O was emitted as the intermediate of heterotrophic nitrification or aerobic denitrification, while GC–IRMS results showed that N2 was produced as end product when nitrite was used. Single factor experiments suggested that the optimal conditions for heterotrophic nitrification were sodium succinate as carbon source, C/N 6, pH 7–8, 0g/L NaCl, 37°C and a wide range of NH4+-N from 80 to 1000mg/L. Orthogonal tests showed that the optimal conditions for aerobic denitrification were C/N 20, pH 7–8, 10g/L NaCl and DO 4.82mg/L (shaking speed 50r/min) when nitrite was served as substrate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
