Microbial nitrite oxidation is the primary pathway that generates nitrate in wastewater treatment systems and can be performed by a variety of microbes: namely, nitrite-oxidizing bacteria (NOB). ...Since NOB were first isolated 130 years ago, the understanding of the phylogenetical and physiological diversities of NOB has been gradually deepened. In recent endeavors of advanced biological nitrogen removal, NOB have been more considered as a troublesome disruptor, and strategies on NOB suppression often fail in practice after long-term operation due to the growth of specific NOB that are able to adapt to even harsh conditions. In line with a review of the history of currently known NOB genera, a phylogenetic tree is constructed to exhibit a wide range of NOB in different phyla. In addition, the growth behavior and metabolic performance of different NOB strains are summarized. These specific features of various NOB (e.g., high oxygen affinity of Nitrospira, tolerance to chemical inhibitors of Nitrobacter and Candidatus Nitrotoga, and preference to high temperature of Nitrolancea) highlight the differentiation of the NOB ecological niche in biological nitrogen processes and potentially support their adaptation to different suppression strategies (e.g., low dissolved oxygen, chemical treatment, and high temperature). This review implicates the acquired physiological characteristics of NOB to their emergence from a genomic and ecological perspective and emphasizes the importance of understanding physiological characterization and genomic information in future wastewater treatment studies.
The interaction of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) is of considerable importance in nitrification process. Ecophysiological interactions between the communities ...of AOB and NOB were investigated by monitoring NO
2
−
as the intermediate compound in an organic carbon-depleted nitrifying activated sludge fed only NH
4
+
as a nitrogen source (40 mg/L). The presence of boom and bust (feast and famine) cycle successfully indicates the activity cycles of AOB and NOB through cultivation-dependent method. The maximum growth rate and yield for AOB in nitritation-dominant period were (0.67 day
−1
, 0.17 gVSS gN
−1
) and for NOB in nitratation-dominant period were (0.71 day
−1
, 0.072 gVSS gN
−1
). Soluble microbial products (SMP) and extracellular polymeric substances (EPS) generated by AOB were 1.2 and 1.8 mg/L, respectively, while NOB produced 0.6 mg/L of SMP and 1 mg/L of EPS. While NOB were low in utilization-associated products (UAP) (0.07 mg/L) and biomass-associated products (BAP) (0.12 mg/L), AOB were higher in UAP (0.15 mg/L) and BAP (0.3 mg/L). The continuation presence of zero C/N ratio, in either inlet ratio or net available ratio for the microbial community, can prolong and enhance nitratation process. NOB enrichment and nitratation intensification strategy through zero C/N ratio are able to reduce remarkably microbial metabolites 50% lower than conventional process and enhance nitrification efficiency in activated sludge-involved processes.
•Intermittent ultrasonic treatment is an effective way to establish nitrite pathway.•Population of nitrite-oxidizing bacteria is successfully suppressed.•Sludge treatment ratio (RS) is identified to ...be an important operational parameter.
Achieving mainstream nitrogen removal via the nitrite pathway (NH4+ → NO2− → N2) is highly beneficial for energy neutral/positive wastewater treatment. Our previous batch assays revealed that ultrasonic treatment can suppress nitrite-oxidizing bacteria (NOB) while enhancing the activity of ammonia-oxidizing bacteria (AOB). Based on this concept, this study investigated the feasibility of applying ultrasonication to achieve the nitrite pathway in mainstream wastewater treatment. Two lab-scale sequencing batch reactors were set-up in parallel and fed with real municipal wastewater. With 100% of the sludge treated every 12 h at a treatment energy input of 0.066 kJ per mg mixed liquor suspended solids, the nitrite pathway was rapidly (within two weeks) established in the experimental reactor with stable effluent nitrite accumulation ratio (NO2−/(NO2− + NO3−)) of above 80% and significantly decreased NOB population. In comparison, the control reactor always possessed the conventional nitrification and denitrification pathway. Economic analysis indicated that energy consumption is too high for practical applications. However, this technology may be used in conjunction with other technologies, whereby this ultrasonic treatment can be used infrequently (e.g. once every few months) when the nitrite pathway becomes unstable.
Constructed wetlands are multi-functional systems that can effectively store and transform pollutants primarily through natural processes. However, the removal of nitrogen pollutant by wetlands is ...highly variable, likely due to a combination of factors such as plant species-specific assimilation behavior, the effects of soil microbial diversity, and variable nitrogen inputs. In this study, the effects of plant species richness (i.e., number of plant species in a system) and seasonal nutrient loading (i.e., nitrogen fertilization) on the microbial community responsible for regulating nitrogen turnover in wetland mesocosm soils was investigated. Digital polymerase chain reaction was used to quantify bacterial abundance. Principal component analysis was employed to identify dominant patterns within the data, and resampling-based analysis of variance was used to assess statistical significance of any observed differences caused by fertilization, season, and/or plant species richness. Results indicated that fertilization or season, which was convolved with fertilization, was the dominant factor influencing the microbial community in the study environment. The effects of plant species richness were more nuanced. Its greater richness significantly impacted the abundance of only a subset of bacterial groups (i.e., the ammonia oxidizing bacteria, Nitrospira spp. of nitrite-oxidizing bacteria, and comammox, but not the denitrifying bacteria).
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•Microbial community involved in nitrogen turnover was investigated.•Digital polymerase chain reaction was used to quantify bacterial abundance.•Principal component analysis was employed to identify dominant patterns.•Seasonal fertilization was the dominant factor influencing the microbial community.•Plant species richness level only impacted a subset of bacterial groups.
•Effects of light irradiation on the activities of nitrifiers were investigated.•Irradiation power affects nitrifiers more over irradiation time and sludge concentration.•Light irradiation with ...appropriate energy densities stimulates AOB activity.•Photostimulation might be related to enhanced electronic transport and energy utilization.•Metabolic disorders and lipid peroxidation probably contribute to photoinhibition.
Microalgal-bacterial consortium (MBC) process has been proposed as an alternative to conventional activated sludge process for nitrogen removal from wastewater. As one of the most influencing parameters, light irradiation effects on microalgae have been extensively investigated. However, light influence on the performance of nitrifiers in activated sludge and its mechanism remains unclear. In this study, the effects of three factors (light irradiation power, irradiation time and sludge concentration) on activities and physiological characteristics of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were systematically studied through both the Design of Experiments driven response surface methodology (RSM) approach and light-nitrification kinetic modeling. Results indicated that light irradiation with the specific light energy density (Es) at 0.0203–0.1571 kJ·mg−1 VSS (80–160 W/400–1000 μmol·m−2·s−1, 2.0–5.0 h and 2750–4250 mg·L−1) stimulated the relative AOB activities (rAOB) by 120.0%. This was supported by the increased electron transport system activity, key enzyme activity (AMO) , gene expression (amoA) and energy generation (ATP consumption) in the light treatment. Moreover, further Es increasing up to 0.18 kJ·mg−1 VSS inhibited both AOB and NOB activities. The inhibition was ascribed to the joint light responses of metabolic disorders and lipid peroxidation. The findings enhance our understanding of nitrifiers’ physiological responses to short-term light irradiation, and promote the development of MBC as a sustainable approach for wastewater treatment.
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•Stable nitritation was achieved at low SRT and high NH4+ concentration.•High NH4+ concentration triggered the high AOB activity.•SRT was critical for the competition outcome of r and K strategist ...AOB.•NOB repression was achieved at low SRT and high NH4+ concentration.
The enrichment of r-strategist ammonium oxidizing bacteria (r-AOB) to enhance nitritation and effective nitrogen removal was studied. A lab-scale three-compartment reactor system removing nitrogen from synthetic wastewater containing ammonium and COD (NH4+:COD ratio at ca. 1:8) was used. A stable nitritation-denitritation process was achieved. The first compartment was anoxic for denitrification and the last two compartments were aerobic to oxidize ammonium into nitrite (nitritation). Recirculation between last and first compartment allowed for effective denitrification. Nitritation was achieved by enhancing the growth of fast growing r-AOB and setting a high NH4+ concentrations in the first of the two aerobic compartments (named as r-AOB selector). The sludge was wasted adaptively to maintain NH4+ concentration between 10 and 20mgN/L in the r-AOB selector. The adaptive sludge wastage resulted in a short sludge retention time (SRT) of 4.2days that led to full nitritation within 100days of operation. Kinetic parameter estimation indicated that the maximum specific growth rate for AOB increased from 0.39 to 1.45d−1, while the NH4+ half saturation constant increased from 0.51 to 5.23mgN/L, indicating the transition from K-AOB (slower growing K-strategist AOB) to r-AOB. Mathematical simulation indicated that the SRT and NH4+ concentration were the main factors determining the outcome of nitrifying species competition.
Due to the key role of nitrite in novel nitrogen removal systems, nitrite oxidizing bacteria (NOB) have been receiving increasing attention. In this study, the coexistence and interactions of ...nitrifying bacteria were explored at decreasing solids retention times (SRTs). Four 5-week washout experiments were carried out in laboratory-scale (V = 10 L) sequencing batch reactors (SBRs) with mixed liquor from two full-scale activated sludge systems (continuous flow vs SBR). During the experiments, the SRT was gradually reduced from the initial value of 4.0 d to approximately 1.0 d. The reactors were operated under limited dissolved oxygen conditions (set point of 0.6 mg O2/L) and two process temperatures: 12 °C (winter) and 20 °C (summer). At both temperatures, the progressive SRT reduction was inefficient for the out-selection of both canonical NOB and comammox Nitrospira. However, the dominant NOB switched from Nitrospira to Ca. Nitrotoga, whereas the dominant AOB was always Nitrosomonas. The results of this study are important for optimizing NOB suppression strategies in the novel N removal processes, which are based on nitrite accumulation.
•Higher NH4+-N load led to higher oxygen transfer rate and lower NOB activity.•NOB was inhibited by low DO concentration in the limited space of aerobic biofilm.•Closed-end aeration mode favored ...Nitrosomonas and inhibited Nitrospira.•A strategy was proposed for quick start-up and stable mainstream PN in MABR.
The proliferation of nitrite oxidizing bacteria (NOB) still remains as a major challenge for nitrogen removal in mainstream wastewater treatment process based on partial nitrification (PN). This study investigated different operational conditions to establish mainstream PN for the fast start-up of membrane aerated biofilm reactor (MABR) systems. Different oxygen controlling strategies were adopted by employing different influent NH4+-N loads and oxygen supply strategies to inhibit NOB. We indicated the essential for NOB suppression was to reduce the oxygen concentration of the inner biofilm and the thickness of aerobic biofilm. A higher NH4+-N load (7.4 g-N/(m2·d)) induced higher oxygen utilization rate (14.4 g-O2/(m2·d)) and steeper gradient of oxygen concentration, which reduced the thickness of aerobic biofilm. Employing closed-end oxygen supply mode exhibited the minimum concentration of oxygen to realize PN, which was over 46% reduction of the normal open-end oxygen mode. Under the conditions of high NH4+-N load and closed-end oxygen supply mode, the microbial community exhibited a comparative advantage of ammonium oxidizing bacteria over NOB in the aerobic biofilm, with a relative abundance of Nitrosomonas of 30–40% and no detection of Nitrospira. The optimal fast start-up strategy was proposed with open-end aeration mode in the first 10 days and closed-end mode subsequently under high NH4+-N load. The results revealed the mechanism of NOB inhibition on the biofilm and provided strategies for a quick start-up and stable mainstream PN simultaneously, which poses great significance for the future application of MABR.
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Nitrite-oxidizing bacteria (NOB) catalyze the second step of nitrification by oxidizing nitrite to nitrate, which is a key process in the biogeochemical nitrogen cycling. However, little is known ...about the co-occurrence patterns and assembly processes of NOB communities in agricultural soils with different salinities. Here, we explored the effects of salinity on Nitrobacter and Nitrospira community using high-throughput sequencing and multivariate statistical analyses. Our results showed that high salinity significantly inhibited the nitrite oxidation rates and decreased the abundance of Nitrobacter and Nitrospira. Extreme salty conditions significantly altered the diversity and composition of Nitrospira community but had little effect on Nitrobacter community. Nitrobacter network in high salinity soils was more closely connected while the connectivity of Nitrospira network became weak. Nitrobacter and Nitrospira community exhibited distinct assembly processes at different salinity levels. Stochastic processes were dominant in the Nitrobacter community assembly in both low and high salinity soils. Interestingly, the assembly of Nitrospira community was governed by stochastic and deterministic processes in low and high salinity soils, respectively. To our knowledge, our study provides the first description of the co-occurrence patterns and assembly processes of NOB communities in agricultural soils with different salinities. These results can help us understand the NOB ecological roles and improve the nitrite oxidation activity in a high salinity environment.
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•Potential nitrite oxidation (PNO) was inhibited in high salinity habitats.•High salinity decreased the diversity of Nitrospira more than Nitrobacter.•High salinity greatly weakened the Nitrospira co-occurrence network.•Modules of Nitrobacter network positively correlated with PNO.•Assembly processes in saline soils differed between Nitrobacter and Nitrospira.
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