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•Achieving PN in domestic wastewater controlled by aeration time.•AOB and NOB activities eliminated entirely during simultaneous elimination period.•Prolonged aeration time led to AOB ...quickly recovery, on the contrary to NOB.•Stable PN maintained for 205 days with high NAR (96%) and ARE (94.3%).•Without additional chemical agents and infrastructure costs for this strategy.
This study developed a novel strategy for rapidly achieving partial nitrification (PN) without additional chemical agents, and infrastructure costs, only by controlling aeration time to selectively enrich ammonium oxidizing bacteria (AOB) after simultaneously eliminating AOB and nitrite oxidizing bacteria (NOB). Shorter aeration time and sludge retention time (10 days) were implemented to simultaneously eliminate AOB and NOB, the bioactivities drastically decreased to 13 and 0%, respectively. Subsequently, a gradually prolonged aeration time selectively enriched AOB and resulted in PN. The amoA abundances increased to 1.9 × 1010 copies gVSS−1, whereas Nitrospira and Nitrobacter abundances remained stable (3.2 × 109 and 3.1 × 109 copies gVSS−1). A nitrite accumulation rate above 96% was achieved and maintained for 205 days over the entire temperature range (28.5–17.9 °C). The effluent contained 1.9 mg N L−1 of ammonium, 25.3 mg N L−1 of nitrite, and less than 1.0 mg N L−1 of nitrate, facilitating mainstream wastewater anammox.
Membrane aerated biofilm reactor (MABR) and shortcut nitrogen removal are two types of solutions to reduce energy consumption in wastewater treatment, with the former improving the aeration ...efficiency and the latter reducing the oxygen demand. However, integrating these two solutions, i.e., achieving shortcut nitrogen removal in MABR, is challenging due to the difficulty in suppressing nitrite-oxidizing bacteria (NOB). In this study, four MABRs were established to demonstrate the feasibility of initiating, maintaining, and restoring NOB suppression using low dissolved oxygen (DO) control, in the presence and absence of anammox bacteria, respectively. Long-term results revealed that the strict low DO (< 0.1 mg/L) in MABR could initiate and maintain stable NOB suppression for more than five months with nitrite accumulation ratio above 90 %, but it was unable to re-suppress NOB once they prevailed. Moreover, the presence of anammox bacteria increased the threshold of DO level to maintain NOB suppression in MABRs, but it was still incapable to restore the deteriorated NOB suppression in conjunction with low DO control. Mathematical modelling confirmed the experimental results and further explored the differences of NOB suppression in conventional biofilms and MABR biofilms. Simulation results showed that it is more challenging to maintain stable NOB suppression in MABRs compared to conventional biofilms, regardless of biofilm thickness or influent nitrogen concentration. Kinetic mechanisms for NOB suppression in different types of biofilms were proposed, suggesting that it is difficult to wash out NOB developed in the innermost layer of MABR biofilms because of the high oxygen level and low sludge wasting rate. In summary, this study systematically demonstrated the challenges of NOB suppression in MABRs through both experiments and mathematical modelling. These findings provide valuable insights into the applications of MABRs and call for more studies in developing effective strategies to achieve stable shortcut nitrogen removal in this energy-efficient configuration.
Nitrification is a vital ecosystem function in the open ocean that regenerates inorganic nitrogen and promotes primary production. Recent studies have shown that the ecology and physiology of ...nitrifying organisms is more complex than previously postulated. The distribution of these organisms in the remote oligotrophic ocean and their interactions with the physicochemical environment are relatively understudied. In this work, we aimed to evaluate the depth profile of nitrifying archaea and bacteria in the Eastern North Pacific Subtropical Front, an area with limited biological surveys but with intense trophic transferences and physicochemical gradients. Furthermore, we investigated the dominant physicochemical and biological relationships within and between ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) as well as with the overall prokaryotic community. We used a 16S rRNA gene sequencing approach to identify and characterize the nitrifying groups within the first 500 m of the water column and to analyze their abiotic and biotic interactions. The water column was characterized mainly by two contrasting environments, warm O
-rich surface waters with low dissolved inorganic nitrogen (DIN) and a cold O
-deficient mesopelagic layer with high concentrations of nitrate (NO
). Thaumarcheotal AOA and bacterial NOB were highly abundant below the deep chlorophyll maximum (DCM) and in the mesopelagic. In the mesopelagic, AOA and NOB represented up to 25 and 3% of the total prokaryotic community, respectively. Interestingly, the AOA community in the mesopelagic was dominated by unclassified genera that may constitute a novel group of AOA highly adapted to the conditions observed at those depths. Several of these unclassified amplicon sequence variants (ASVs) were positively correlated with NO
concentrations and negatively correlated with temperature and O
, whereas known thaumarcheotal genera exhibited the opposite behavior. Additionally, we found a large network of positive interactions within and between putative nitrifying ASVs and other prokaryotic groups, including 13230 significant correlations and 23 sub-communities of AOA, AOB, NOB, irrespective of their taxonomic classification. This study provides new insights into our understanding of the roles that AOA may play in recycling inorganic nitrogen in the oligotrophic ocean, with potential consequences to primary production in these remote ecosystems.
The development of new wastewater treatment processes can assist in reducing the impact of wastewater treatment on the environment. The recently developed partial nitritation anammox (PNA) process, ...for example, consumes less energy for aeration and reduces nitrate in the effluent without requiring additional organic carbon. However, achieving stable nitritation (ammonium oxidation; NH4+ → NO2−) at mainstream conditions (T = 10–25 °C, C:N > 10, influent ammonium < 50 mgNH4-N/L and effluent < 1 mgNH4-N/L) remains challenging. This study explores the potential and mechanism of nitrite-oxidizing bacteria (NOB) suppression in a bottom-fed sequencing batch reactor (SBR). Two bench-scale (11 L) reactors and a pilot-scale reactor (8 m3) were operated for over a year and were fed with organic substrate depleted municipal wastewater. Initially, nitratation (nitrite oxidation; NO2− → NO3−) occurred occasionally until an anaerobic phase was integrated into the operating cycle. The introduction of the anaerobic phase effectively suppressed the regrowth of NOB while nitritation was stable over 300 days, down to 8 °C and at ammonium influent concentrations < 25 mgNH4-N/L. Batch experiments and process data revealed that parameters typically affecting NOB growth (e.g., dissolved oxygen, alkalinity, trace elements, lag-phase after anoxia, free nitrous acid (FNA), free ammonia (FA), pH, sulfide, or solids retention time (SRT)) could not fully explain the suppression of nitratation. Experiments in which fresh nitrifying microbial biomass was added to the nitritation system indicated that NOB inactivation explained NOB suppression better than NOB washout at high SRT. This study concludes that bottom-fed SBRs with anaerobic phases allow for stable nitritation over a broad range of operational parameters. Coupling this type of SBR to an anammox reactor can enable efficient mainstream anammox-based wastewater treatment.
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•Nitritation was stable in municipal wastewater, even at low temperatures (8 °C).•A one-hour anaerobic phase, after reactor filling, rapidly established nitritation.•Bottom-feeding was used for a 90% volume exchange each SBR cycle.•NOB suppression is driven by NOB inactivation rather than washout.•Up-scaling of nitritation to an 8 m3 reactor was successful.
•Higher external mass transfer resistance favours NOB repression.•IFAS has reduced operating conditions range despite achieving higher removal rates.•AOB seeding from biofilm is crucial for stability ...of IFAS systems.•Anammox nitrite sink is strongly affected by the inhibition of anammox by oxygen.
A model-based study was developed to analyse the behaviour of Moving Bed Biofilm Reactor (MBBR) and Integrated Fixed-Film Activated Sludge (IFAS) reactor configurations for the removal of nitrogen in the main water line of municipal wastewater treatment plants via partial nitritation/anammox (PN/AMX). The basic principles and underlying mechanisms linking operating conditions to process performance were investigated, with particular focus on nitrite oxidizing bacteria (NOB) repression and resulting volumetric conversion rates. The external mass transfer resistance is a major factor differentiating granular sludge PN/AMX processes from MBBR or IFAS systems. The external mass transfer resistance was found to promote the metabolic coupling between anammox (AMX) and ammonia oxidizing bacteria (AOB), crucial for NOB repression in the biofilm. Operation at low bulk DO prevents NOB proliferation in the flocs of IFAS systems as AMX activity limits nitrite availability (the so-called AMX nitrite sink). Importantly, the effectiveness of the AMX nitrite sink strongly depends on the AMX sensitivity to oxygen. Also, over a broad range of operational conditions, the seeding of AOB from the biofilm played a crucial role in maintaining their activity in the flocs. From a practical perspective, while low DO promotes NOB repression, lower nitrogen loads have to be applied to maintain the same effluent quality. Thus, a trade-off between NOB repression and volumetric conversion capacity needs to be defined. To this end, IFAS allow for higher volumetric rates, but the window of operating conditions with effective NOB repression is smaller than that for MBBR. Ultimately, this study identified the principles controlling NOB in MBBR and IFAS systems and the key differences with granular reactors, allowing for the interpretation of (seemingly contradictory) published experimental results.
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•A novel PN/Anammox system with low ammonia and no temperature control was developed.•Low sludge is advantageous for the suppression of NOB activity by light.•Stable nitrification was ...achieved by light irradiation under mainstream conditions.•Ellin6067 of light-resistant AOB bacteria enhances nitrification system performance.•PN/Anammox achieves a total nitrogen removal rate of > 90 % under mainstream conditions.
PN/Anammox, as an economical and effective nitrogen removal process, is of great significance for reducing carbon emission in municipal wastewater treatment. However, municipal wastewater has mainstream characterized of low temperature and low NH4+-N concentration, and NOB activity is difficult to inhibit, so achieving a stable PN process is the biggest challenge in the application of PN/Anammox to mainstream wastewater. This study developed a method for stable and efficient PN/Anammox based on very low sludge volume (MLVSS = 65 mg/L). Even when the temperature dropped to 15℃ or there was exogenous nitrite-oxidizing bacteria (NOB) interference, the system still had good inhibition of NOB activity. The total stable operation time was 386 days, and the NO2–-N accumulation efficiency could reach more than 90 %. Ellin6067, Nitrosomonas and Candidatus_Brocadia were the dominant functional microorganisms in the system. Nitrospira was the dominant genera of NOB with very low relative abundance (<0.04 %). The mechanism of the long-term stable mainstream PN/Anammox system showed that low sludge content was beneficial to light irradiation on microorganisms in the reactor, while nxrA, the functional gene of NOB, had weak light resistance and oxidation resistance, which makes the system had strong inhibition effect on NOB. The construction of this new system which does not depend on activated sludge volume and complex NOB activity inhibition strategy can better promote the practical application of PN/Anammox under mainstream conditions.
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•Mainstream PN was quickly established by sludge treatment using high salinity.•High NAR (95.69 ± 2.65 %) was maintained stable in the mainstream CSTR.•Salinity increased the relative ...abundance of Nitrosomonas from 5.98% to 38.08%.•NOB activity was almost undetectable after sludge treatment using high salinity.•The absolute activity change of NOB should be given attention for sludge treatment.
The difficulty of the start-up and maintenance the stability of partial nitritation (PN) was considered as a key challenge for mainstream anammox. This study demonstrated a novel approach for achieving rapid start-up of mainstream PN by sludge treatment using high salinity based on the phenomenon which high salinity is far more biocidal to nitrite-oxidising bacteria (NOB) than to ammonia-oxidising bacteria (AOB) in short-term (within 24 h). In this study, one-third of the nitrifying sludge from the continuous stirred tank reactor (CSTR) fed by mainstream wastewater was suppressed at 70 g NaCl/L for 24 h every day. The treated nitrifying sludge was afterwards returned back to the CSTR. Mainstream PN with high nitrite accumulation ratio (NAR) was rapidly established (in 14 d) after optimizing the suppression conditions and maintained stable (NAR = 95.69 ± 2.65 %) more than 45 days in the mainstream reactor, indicating the establishment of PN process. After long-term high salinity treatment, NOB activity in the reactor was almost undetectable, while AOB activity significantly increased. Microbial community analysis revealed that the sludge treatment using high salinity could significantly reduce Nitrospira abundance while the relative abundance of Nitrosomonas increased by an order of magnitude. Moreover, the relationship between the absolute activity change of nitrifying sludge and inhibition strength was explored based on the activity batch assays and quantitative polymerase chain reaction assays analysis. The approach of achieving mainstream PN by sludge treatment using high salinity is economically and environmentally attractive because salt is an easily obtainable substance.
Sidestream sludge treatment approaches have been developed in recent years to achieve mainstream nitrite shunt or partial nitritation, where NOB are selectively inactivated by biocidal factors such ...as free nitrous acid (FNA) or free ammonium (FA) in a sidestream reactor. The existence of NOB in raw wastewater has been increasingly realized and could pose critical challenge to stable NOB suppressions in those systems. This study, for the first time, evaluated the impact of influent NOB on the NOB suppressions in a mainstream nitrite shunt system achieved through sidestream sludge treatment. An over 500-day sequential batch reactor operation with six experimental phases rigorously demonstrated the negative effects of influent NOB on mainstream NOB control. Continuously seeding of NOB contained in influent stimulated NOB community shifts, leading to different extents of ineffective NOB suppression. The role of primary wastewater treatment in NOB removal from raw wastewater was also investigated. Results suggest primary settling and High Rate Activated Sludge system could remove a large part of NOB contained in raw wastewater. Primary treatment for raw wastewater is necessary for ensuring stable mainstream NOB suppressions.
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•Influent NOB challenge NOB suppression by stimulating community shift and resistance.•Primary settling substantially reduces NOB in raw wastewater.•High-rate activated sludge treatment substantially reduces NOB in raw wastewater.•This study expanded the current knowledge of mainstream NOB suppression.
•A continuous flow reactor for treating actual municipal wastewater was studied•Nitritation was quickly initiated in 15 d via UL-SRT during seasonal warming•Stable nitritation could be achieved by ...using joint UL-SRT and tapered aeration•The AOB (amoA) abundance increased approximately 50 times after nitritation
Rapid achievement of nitritation of mainstream municipal wastewater in a continuous-flow process is attractive since it favors the involvement of the anammox process and reduces the operational costs. In this study, a feasible and economical strategy is proposed to rapidly achieve the nitritation of municipal wastewater. By aggressively discharging excess sludge during the seasonal warming period (temperature increasing from 18°C to 22°C), nitritation was established in 15 days with a nitrite accumulation ratio of 85.09% in a continuous-flow anaerobic/oxic (An/O) reactor. Meanwhile, qPCR results revealed that amoA abundance increased from (1.78±0.10) × 108 copies/(g VSS) to (1.05±0.11) × 1010 copies/(g VSS) while the abundance of nitrite-oxidizing bacteria decreased from (1.1±0.02) × 1010 copies/(g VSS) to (5.01±0.02) × 108 copies/(g VSS). The temperature gradually stabilized at 26°C during the following operational period and stable nitritation was maintained with a nitrite accumulation ratio above 90%, which was mainly attributed to a short sludge retention time (SRT) of 4.3 days and a low dissolved oxygen of 0.86 ± 0.5 mg/L. Falling temperature negatively impacted the stability of nitritation, but nitritation could be restarted by aggressively discharging excess sludge during another temperature increase period. Overall, this study provides a feasible strategy to start-up nitritation that has great potential applications for municipal wastewater treatment.
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