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•A novel three-stage process, comprising PN/A, acidic PN, and anammox, is proposed.•The PN/A unit requires residual ammonium to suppress nitrite-oxidizing bacteria (NOB).•The acidic ...PN unit provides stable nitrite sources to the anammox unit.•The anammox unit removes the residual ammonium and nitrite from the PN/A and the acidic PN units.•The overall nitrogen removal efficiency is higher than 90% based on model simulation.
Sewage treatment with partial nitritation and anammox (PN/A, also termed as deammonification) has gained widespread attentions over the past decade, driven by the need of establishing energy-neutral/positive sewage treatment plants (STPs). However, a key challenge for the mainstream deammonification is to achieve stable suppression of nitrite-oxidizing bacteria (NOB). Deammonification can be configured in either one reactor or two reactors (where PN and anammox are separated), known as one-stage and two-stage configurations, respectively. This study first analyses the current bottlenecks in one-stage and two-stage deammonification. To address these issues, a new, three-stage configuration is proposed. Three-stage deammonification comprises three components, including a PN/A reactor, an acidic PN reactor, and an anammox reactor. The majority of sewage is allocated to the PN/A reactor, which produces an effluent with an elevated level of residual ammonium (2–40 mg N L−1), as required for NOB suppression in this reactor. The residual ammonium is removed in the anammox reactor, using the nitrite supplied from the acidic PN reactor. The acidic PN reactor is fed with a mixture of sewage and anaerobic digestion liquor with a ratio that allows the attainment of a low pH (<6.0) and NOB suppression. This three-stage process was shown applicable to a wide range of municipal wastewaters which have a HCO3–/ NH4+ mole ratio of 1.17–2.41, based on mass balance. Further, simulation indicates that this three-stage process can deliver a stable and high-quality effluent, with the total nitrogen < 10 mg N L−1 and the nitrogen removal efficiency > 90%.
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•Aerobic granules SNDPR used for hypersaline wastewater treatment.•Reliable nitrogen removal efficiency was achieved at elevated salinity.•EBPR was deteriorated with 2 % (w/v) ...salinity stress.•Salinity induced changes in granular community structure.•Halophilic and non-halophilic bacteria were recognized.
Hypersaline wastewater may pose threats to biological wastewater treatment processes. An aerobic granular sludge-based sequencing batch reactor (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR) was evaluated with increased salinity from 1 to 2 % (w/v). Nitrogen removal performance was unaffected by salinity up to 20 g/L in terms of reliable and efficient nitrification and denitrification. Enhanced biological phosphorus removal (EBPR) process was completely deteriorated at salinity up to 2 %, in contrast to excellent phosphorus removal at 1 %. Profiles of phosphorus over one cycle demonstrated that higher salinity not only inhibited anaerobic phosphorus release but also impeded aerobic/anoxic phosphorus uptake. Illumina MiSeq sequencing revealed multiple halophilic and non-halophilic bacteria within aerobic granules with family Anaerolineaceae being the predominant potential salt adapter. Besides, ammonia oxidizing bacteria (AOB), glycogen accumulating organisms (GAOs) were more tolerant to salt than nitrite oxidizing bacteria (NOB) and phosphorus accumulating organisms (PAOs) and denitrifying PAOs (DNPAOs). These results deciphered the resilience of aerobic granular sludge-based biological nitrogen and phosphorus removal processes to hypersaline stress.
The accumulation of nitrite is frequently overlooked, despite the fact that nitrification is the most essential phase of the entire nitrogen (N) cycle and that nitrifying bacteria play a significant ...role in nitrification. At present, the effects of different N application rates on soil nitrite-oxidizing bacteria (NOB) abundance, community composition, diversity, and its main influencing factors are still unclear. In this study, five N fertilizer application rates under film mulching and a drip irrigation system were studied in the semi-arid area of Northeast China. The treatments were 0 kg ha−1 (N0), 90 kg ha−1 (N1), 150 kg ha−1 (N2), 210 kg ha−1 (N3), and 270 kg ha−1 (N4). Fluorescent quantitative PCR and Illumina Miseq sequencing were used to analyze the abundance and community structure of NOB under different amounts of N application. The results showed that the increase in amounts of N application was strongly accompanied by an increase in the content of soil organic matter (SOM), total nitrogen (TN), nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N), while the pH significantly reduced with an increase in N fertilization. N fertilization significantly increased soil nitrite oxidoreductase (NXR) activity, soil nitrification potential (PNR), and soil nitrite oxidation potential (PNO). A high N application rate significantly heightened the abundance of Nitrospira- and Nitrobacter-like NOB. N fertilizer considerably raised the Shannon index of Nitrospira-like NOB. The N application amount was the key factor affecting the community structure of Nitrospira-like NOB, and available nitrogen (AN) had the dominant influence on the community structure of Nitrospira-like NOB. N fertilizer can cause soil acidification, which affects NOB abundance and diversity. Nitrospira-like NOB may promote nitrite oxidation in different N application rates under a mulched fertigation system. The findings offered a crucial scientific foundation for further investigation into how nitrite-oxidizing bacteria respond to N fertilizer management strategies in farmland soil under film mulching drip irrigation in Northeast China.
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•PN/A-EPD/A process was developed in an IFAS-SBR treating real municipal wastewater.•High NRE of 90.1% was achieved under aerobic HRT of 8 h and DO of 0.4 ± 0.1 mg/L.•89.9% of TN was ...removed by anammox pathway in typical cycle.•Relative abundance of Candidatus Brocadia rose from 0% to 0.79% in suspended sludge.
In this study, an innovative partial nitrification-anammox (PN/A) and endogenous partial denitrification-anammox (EPD/A) process was developed in a single-stage integrated fixed film activated sludge sequencing batch reactor (IFAS-SBR) treating real municipal wastewater with C/N ratio below 3.2. Enhanced efficiency of total nitrogen (TN) removal reached 90.1% with low HRT of 12 h and DO of 0.4 ± 0.1 mg/L. Detailed nitrogen removal mechanism analysis of typical cycle revealed that 89.9% of TN was eliminated through anammox pathway. Anammox bacteria (Candidatus Brocadia) and endogenous denitrifying bacteria (Candidatus Competibacter) were abundant both in biofilms and suspended sludge, meanwhile ammonium-oxidizing bacteria has outcompeted nitrite-oxidizing bacteria, which all favored the synergistic effect of anammox with PN and EPD and contributed to the improvement of nitrogen removal. Overall, the above results confirmed that combined PN/A and EPD/A process is a reliable and efficient alternative for mainstream anammox process.
•Balancing AOB and AnAOB rates is the key factor for mainstream PNA at μM DO.•Stable PNA after temperature decrease from 25 to 15 °C without acclimation.•Heterotrophs growth on dissolved organic ...carbon from cell lysis decreases effluent NO3−.•Nitrospira was the only NOB and their control was assisted by AnAOB activity.•Candidatus Kuenenia was the predominant AnAOB throughout the study.
This study aimed at assessing the performance and microbial community in a granular one-stage partial nitritation-anammox sequencing batch reactor (PNA-SBR) subjected to temperature transition from 25 to 15 °C without biomass acclimation. The PNA-SBR was operated by controlling the oxygen transfer rate (OTR) according to the ammonium loading rate (ALR), which resulted in micromolar (µM) bulk dissolved oxygen (DO) concentration. The applied strategy proved to be feasible to operate the one-stage PNA-SBR at mainstream conditions because it was possible to control nitritation according to anammox rate. Nitrogen removal rate (NRR) of 330.24 ± 25.36 mg N·L−1·d−1 was achieved at 25 °C. Nitratation control by µM bulk DO limited the NO3−production:NH4+removed at 0.28 ± 0.04. No instability was experienced by decreasing the temperature to 15 °C, but removal rates were adapted to the resulting anammox activity, which decreased at low temperature. After temperature transition, nitratation was kept controlled and the NO3−production:NH4+removed molar ratio remained at 0.33 ± 0.05, although anammox activity deteriorated and higher nitrate production was obtained. Sequencing analysis revealed the dominant bacterial groups in the microbial community that clustered within the phyla Planctomycetes, Proteobacteria, Chloroflexi, and Bacteroidetes. Temperature drop only affected bacterial abundance, but the main bacteria involved in nitrification and anammox processes did not change during the study. Candidatus Kuenenia was the main anammox genus. Moreover, the presence of bacterial groups associated with heterotrophic metabolism indicates denitrification might be supported by the release of dissolved organic carbon due to bacterial lysis, and lower nitrate effluent concentration could be reached in PNA reactors.
The mainstream partial nitritation/anammox (PN/A) process has been intensively studied but its stability remains a key challenge. It is shown here that biofilm thickness can exhibit a critical role ...in controlling the process stability of mainstream PN/A against dissolved oxygen (DO) variation. In a laboratory moving bed biofilm reactor (MBBR), PN/A performance was initially established in 200 days by controlling a low DO of 0.13 ± 0.07 mg O2/L in the bulk liquid, which deteriorated with an increase of DO (0.35 ± 0.13 mg O2/L) for over two months, and then rapidly recovered in a month with the initial low DO level re-applied. Biofilm thickness of PN/A carriers was measured during the experiment, which became significantly thinner (367 ± 146 μm) at mainstream conditions. The thin thickness primarily decreased the in-situ consumption rate of nitrite, rather than ammonium, when DO increased from 0.1 to 0.4 mg O2/L, due to that the thin thickness can only restrict anammox capacity. These results illustrated the role of biofilm thickness in regulating PN/A performance and microbial activities. Further investigation using an established model revealed the joint contribution of biofilm thickness and DO concentration to PN/A process, while particularly, the biofilm thickness can determine the optimal DO level for maximizing the nitrogen removal efficiency and system robustness against DO variation. These results highlight the need of considering biofilm thickness in PN/A process optimization and stability improvement in low-strength wastewater treatment.
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•N-removal efficiency >80% is achieved via PN/A in a mainstream MBBR.•The mainstream PN/A is stably realized at DO concentration of 0.13 ± 0.07 mgO2/L.•Biofilm thickness controls the maximal capacity of anammox rather than AOB or NOB.•A narrow DO range (0.15-0.20 mgO2/L) is required for high N-removal in thin biofilm.
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•Manure application significantly increased both PAO and PNO.•Manure fertilization augmented nitrifier abundance.•Soil NH4+-N and TC are good indicators for NOB and comammox ...community.•Community composition of NOB and comammox was affected by both soil type and manure fertilizer.•Manure fertilizer made nitrifier community more closely linked and stimulated the function performance of nitrifiers.
Nitrification plays an important role in the soil nitrogen cycle. Here, we conducted an experiment in three different soil types (red soil, black soil, and alluvial soil) to evaluate the response of nitrifiers and nitrification to manure fertilizers. We found that long-term manure fertilization altered the soil physicochemical properties, increased soil organic matter and NO3－-N concentrations, and decreased NH4+-N concentrations. Both ammonia and nitrite oxidation potential were higher in the manured soils than those in the control soils. Long-term manure fertilization markedely increased the abundance of nitrifiers and the abundance of the complete ammonia oxidation (comammox) amoA gene copy number ranged from 0.78 × 106 to 2.18 × 106 g−1 dry soil, which was lower than that of canonical nitrifiers including ammonia‐oxidizing archaea, ammonia‐oxidizing bacteria, and nitrite‐oxidizing bacteria (NOB). The community composition of NOB and comammox was affected by both soil type and manure fertilizer. Soil NH4+-N concentration and total carbon content were the factors that were most strongly correlated with the microbial community composition. Manure fertilizers promoted the coupling linkages among soil Nitrobacter, Nitrospira, and comammox communities and created a more closely linked microbial community. The results suggest that long-term inputs of manure to agricultural soils influence the structure of NOB and increase nitrification rates.
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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.
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•A unique feature of the SNAD in this study was using suspended activated sludge.•Only 1.02 mg/L of nitrate was detected in the effluent treating real domestic sewage.•TN removal ...efficiency of 86.1% was achieved in the SNAD system.•Micro-aeration saved energy as well as maintained the efficiency of the system.•Quantity of Candidatus Brocadia and Thauera increased in the SNAD system.
Bottleneck issues such as difficult biofilm culturing, time-consuming granular formation and excessive nitrate production, always limited the application of anammox processes. By using the common but meaningful suspended activated sludge instead of biofilm or granule activated sludge, a combined anammox process, simultaneous partial nitrification, anammox and denitrification (SNAD), was established in a sequencing batch reactor (SBR) in this study to treat real domestic sewage and was operated for 300 days. Results indicated that a high ammonia removal rate and nitrogen removal rate (1.1 and 1.03 (kgN/(m3·d)), respectively) were achieved during the baseline phase treating high ammonia wastewater (350–550 mg/L). During the experimental phase treating domestic sewage with a C/N of 3–3.5, 86.1% of total nitrogen removal efficiency was achieved and only 1.02 mg/L of nitrate concentration was detected in the effluent with an averagely 64.6 mg/L of ammonium in the influent. Nitrogen mass balance analysis demonstrated that about 89% of total nitrogen (TN) was removed by anammox and the remaining 11% of TN was removed by denitrification. Bacterial abundance of Candidatus Brocadia and Thauera increased from 0.02% to 0.5% and 0.39% to 2.24% (from baseline phase to experimental phase), respectively, which made an essential contribution to the nitrogen removal. The advanced nitrogen removal performance reached in the SNAD process showed the possibility of using suspended sludge as a substitute of biofilm and granule sludge concerning anammox, and the process could treat real domestic sewage with a C/N of 3–3.5 without pretreatment of chemical oxygen demand (COD).
