•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.
•A new Fe-dosing strategy proposes centralized dosage into returned sludge than sewage.•Centralized Fe-dosing acidifies sludge and resulted in free nitrous acid accumulation.•The new strategy ...achieves less biomass production and shortcut nitrogen removal.•The new strategy still provides the same benefits as common mainstream Fe-dosing.
Iron salts (i.e. FeCl3) are the most used chemicals in the urban wastewater system. Iron is commonly dosed into sewage or the mainstream system, which provides multiple benefits such as enhanced phosphorus removal and improved sludge settleability/dewaterability. This study reported and demonstrated a new approach that dosed FeCl3 into returned sludge in order to bring two more benefits to wastewater management: short-cut nitrogen removal via the nitrite pathway and less biomass production. This approach is achieved based on our findings that with similar amount of FeCl3, centralized iron dosing into a sidestream sludge unit generated iron concentration two orders of magnitude higher than the common mainstream dosing (e.g. 10–40 mg Fe/L-wastewater), leading to sludge acidification (pH = 2.1) with Fe (III) hydrolysis. Together with accumulated nitrite in the supernatant of the sludge, ppm-level of free nitrous acid was generated and thus enabled sludge disintegration, cell lysis, and selective elimination of nitrite-oxidizing bacteria (NOB). Long-term effects on nitrifying bacteria and overall reactor performance were evaluated using two laboratory reactor experiments for over one year. The experimental reactor showed stable nitrite accumulation with an average NO2−/(NO2− + NO3−) ratio above 80% and ∼30% observed biomass yield reduction compared to those in control reactors. In addition, the centralized sludge dosing strategy still provided benefits such as improved settleability and dewaterability of sludge and enhanced phosphorus removal.
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•High-salinity treatment as an ex situ NOB inactivation strategy was first proposed.•High salinity presented greater inactivation of NOB than AOB.•NAR was above 33% during nitrification after one ...high-salinity treatment.•Sludge characteristics remained almost unchanged after inhibition.•A novel process for achieving mainstream PN was proposed and evaluated.
The difficulty in achieving stable partial nitritation (PN) is a challenge that limits the application of mainstream anaerobic ammonium oxidation (anammox). This study proposes high-salinity treatment as a novel strategy for inactivating nitrite-oxidising bacteria (NOB). The study indicated that NOB are more sensitive to high salinity than ammonia-oxidising bacteria (AOB). The inhibitory effect on the nitrifier gradually increased with increasing salinity from 0 to 100 g NaCl/L. After 24 h and 35 g NaCl/L inhibition, the AOB and NOB activities were 36.65% and 7.15% of their original activities, respectively. After one high-salinity treatment, nitrite accumulation rate (NAR) was above 33% during nitrification. Moreover, the sludge characteristics remained almost unchanged after suppression. A novel process for achieving mainstream PN was proposed and evaluated based on the results. An energy consumption analysis showed that mainstream PN/anammox based on the ex situ high-salinity treatment can achieve higher energy self-sufficiency compared with activated sludge.
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•Variable N2H4 concentration dosage make mainstream deammonification process stable.•The inhibit effect of N2H4 on AnAOB and AnAOB self-regulate mechanism was found.•Variable N2H4 ...concentration dosage was beneficial for most microorganisms.
In this study, an expanded granular sludge blanket reactor (EGSB) was proposed to achieve stable mainstream deammonification process by adding hydrazine (N2H4). Two N2H4 addition methods consisted of constant concentration (strategy A) and variable concentration (strategy B) both can inhibit nitrite oxidizing bacteria. A efficient performance was achieved with higher total nitrogen removal efficiency (82 ± 6%) and nitrogen removal rate (0.32 ± 0.02 kg N/(m3·d)) under strategy B. For strategy A, anaerobic ammonia oxidizing bacteria (AnAOB) in-situ activity was decreased from 2.76 to 0.68 mg N/(g VSS·h) at 42 mg/L NH4+-N. Candidatus Brocadia abundance increase from 14.62% to 20.07% under the strategy may indicated the self-regulate mechanism of AnAOB. Aerobic ammonia oxidizing bacteria (AOB, mainly Nitrosomonas) and AnAOB (mainly Candidatus Brocadia) were always dominated under two strategies. Strategy B provided better environment for most microorganisms (mainly Chloroflexri, Planctomycetes, Proteobacteria and Chlorobi).