Enhanced nitrogen removal from low COD/TIN mainstream wastewater in a continuous plug-flow reactor via partial nitrification, simultaneous anammox and endogenous denitrification (PN-SAED) process

Robustness of the anammox process at low temperatures and low dissolved oxygen for low C/N municipal wastewater treatment

Low water temperatures and ammonium concentrations pose challenges for anammox applications in the treatment of low C/N municipal wastewater. In this study, a 10 L-water bath sequencing batch reactor combing biofilm and suspended sludge was designed for low C/N municipal wastewater treatment. The nitrogen removal performance via partial nitrification anammox-(endogenous) denitrification anammox process was investigated with anaerobic-aerobic-anoxic mode at low temperatures and dissolved oxygen (DO). The results showed that with the decrease of temperature from 30 to 15℃, the influent and effluent nitrogen concentrations and nitrogen removal efficiencies were 73.7 ± 6.5 mg/L, 7.8 ± 2.8 mg/L, and 89.4 %, respectively, with aerobic hydraulic retention time of only 6 h and DO concentration of 0.2-0.5 mg/L. Among that, the stable anammox process compensated for the inhibitory effects of the low temperatures on the nitrification and denitrification processes. Notably, from 30 to 15℃, the anammox activity and relative abundance of the dominant Brocadia genus were increased from 39.7 to 45.5 mgN/gVSS/d and 7.3 to 12.0 %, respectively; the single gene expression level of the biofilm increased 9.0 times. The anammox bacteria showed a good adaptation to temperatures reduction. However, nitrogen removal by anammox was not improved by increasing DO (≥ 4 mg/L) at 8-4℃. Overall, the results of this study demonstrate the feasibility of the mainstream anammox process at low temperatures.

Efficient nitrogen removal from real municipal wastewater and mature landfill leachate using partial nitrification-simultaneous anammox and partial denitrification process

Anaerobic ammonia oxidation (anammox) of municipal wastewater is a research focus, especially the combined treatment with mature landfill leachate is a current research hotspot. In this study, municipal wastewater was treated by partial nitrification via sequencing batch reactor (SBR), and its effluent and mature landfill leachate were then mixed into an up-flow anaerobic sludge blanket (UASB) for simultaneous anammox and partial denitrification reaction. Through partial nitrification, a high nitrite accumulation rate (93.0 ± 3.8 %) was achieved by low dissolved oxygen (0.5-1.6 mg/L) and controlled aerobic time (3.5 h) in SBR. The UASB system was responsible for 78.8 ± 2.1 % nitrogen removal of the entire system with a hydraulic reaction time (HRT) of 3.8 h, accompanied by the anammox contribution up to 89.4 ± 6.0 %. The overall partial nitrification-simultaneous anammox and partial denitrification (PN-SAPD) system was controlled at a total COD/TIN of 2.8 ± 0.3 and a total HRT of only 10.2 h, achieving the nitrogen removal efficiency and effluent TIN were 95.2 ± 2.2 % and 3.4 ± 1.5 mg/L, respectively. The qPCR results showed functional genes (hzsA(B), hdh) associated with anaerobic ammonia-oxidizing bacteria (AnAOB), whose high gene copy abundance and transcription expression ensured the removal of major nitrogen from municipal wastewater and mature landfill leachate. 16S amplicon sequencing showed that the Ca. Brocadia (9.72-12.6 %) was further enrichment after sodium acetate was added, and the transcription expression of Thauera (0.5-7.0 %) caused nitrate to nitrite. The high abundance of related enzymes (hao, hzs, hdh, narGHI) involved in anammox and partial denitrification processes were found in the macrogenomic sequencing, and only Ca. Brocadia was involved in multi-pathway nitrogen metabolism in AnAOB. Based on the efficient nitrogen removal by AnAOB and denitrifying bacteria, this modified PN-SAPD process provides a new option for the co-treatment of mature landfill leachate in municipal wastewater treatment plants.

Achieving synchronous and highly efficient removal of nitrogen and phosphorus by rapid enrichment and cultivation denitrifying phosphorus accumulating organisms in anaerobic-oxic-anoxic operation mode

Realizing the quick enrichment and development of denitrifying phosphorus accumulating organisms (DPAOs) in actual household wastewater and industrial nitrate wastewater has significant research significance. In this study, a novel operation mode of anaerobic-oxic-anoxic (AOA) was adopted to successfully realize the enrichment and cultivation of DPAOs in urban domestic wastewater. Adjusting influent COD to PO43--P ratio, shortening the aerobic time and decreasing the aeration volume were conducive to select DPAOs in microbial populations. The system was operated for 180 days and the DPAOs were well enriched during the stable operation with the percentage of Dechloromonas increased to 5.1 %. Accordingly, the effluent PO43--P was < 0.3 mg P/L, the removal efficiency of phosphorus was 96.9 % and the removal efficiency of nitrate was 92.5 %. Above all, DPR can be successfully applied to AOA systems with good phosphorus removal performance.

Tracing and utilizing nitrogen loss in wastewater treatment: The trade-off between performance improvement, energy saving, and carbon footprint reduction

Biological nitrogen removal is widely applied to reduce the discharge of inorganic nitrogen and mitigate the eutrophication of receiving water. However, nitrogen loss is frequently observed in wastewater treatment systems, yet the underlying principle and potential enlightenment is still lacking a comprehensive discussion. With the development and application of novel biological technologies, there are increasing achievement in the deep understanding and mechanisms of nitrogen loss processes. This article reviews the potential and novel pathways of nitrogen loss, occurrence mechanisms, influential factors, and control strategies. A survey of recent literature showed that 3%∼73% of nitrogen loss beyond the nitrogen budget can be ascribed to the unintentional presence of simultaneous nitrification/denitrification, partial nitrification/anammox, and endogenous denitrification processes, under low dissolved oxygen (DO) and limited available organic carbon source at aerobic conditions. Key influential parameters, including DO, aeration strategies, solid retention time (SRT), hydraulic retention time (HRT), temperature and pH, significantly affect both the potential pathways of nitrogen loss and its quantitative contribution. Notably, the widespread and spontaneous growth of anammox bacteria is an important reason for ammonia escape at anaerobic/anoxic conditions, leading to 7%∼78% of nitrogen loss through anammox pathway. Moreover, the unwanted nitrous oxide (N2O) emission should also be considered as a key pathway in nitrogen loss. Future development of new nitrogen removal technologies is proposed to suppress the generation of harmful nitrogen losses and reduce the carbon footprint of wastewater treatment by controlling key influential parameters. Transforming "unintentional observation" to "intentional action" as high-efficiency and energy-efficient nitrogen removal process provides a new approach for the development of wastewater treatment.

Efficient nitrogen removal in a total floc sludge system from domestic wastewater with low C/N: High anammox nitrogen removal contribution driven by endogenous partial denitrification

Since unsustainable partial nitrification prone to unstable nitrogen removal rates, cultivation and enrichment of AnAOB, further improve autotrophic nitrogen removal contribution have been challenges in the mainstream anammox process. This study proposed a new strategy to enrich AnAOB motivated by endogenous partial denitrification (EPD) in total floc sludge system through the AOA process with sustainable nitrification. The results showed that in the presence of NH₄⁺ and NO₃^- at the anoxic stage of N-EPDA, Ca. Brocadia was enriched (0.005%→0.92%) in floc sludge via internal carbon source metabolism of EPD. The C/N and temperature of N-EPDA were also optimized to achieve higher activities of EPD and anammox. The N-EPDA was operated at low C/N ratio (3.1) with anammox nitrogen removal contribution of 78% during the anoxic stage, Eff.TIN of 8.3 mg/L and NRE of 83.5% during phase III, achieved efficient autotrophic nitrogen removal and AnAOB enrichment in the absence of partial nitrification.

Elucidating performance failure in the use of an Anaerobic-Oxic-Anoxic (AOA) plug-flow system for biological nutrient removal

The Anaerobic-oxic-anoxic (AOA) process is a carbon-saving and high-efficiency way to treat municipal wastewater and gets more attention. Recent reports suggest that in the AOA process, well-performed endogenous denitrification (ED), conducted by glycogen accumulating organisms (GAOs), is crucial to advanced nutrient removal. However, the consensuses about starting up and optimizing AOA, and in-situ enriching GAOs, are still lacking. Hence, this study tried to verify whether AOA could be established in an ongoing anaerobic-oxic (AO) system. For this aim, a lab-scale plug-flow reactor (working volume of 40 L) previously operated under AO mode for 150 days, during that 97.87 % of ammonium was oxidized to nitrate and 44.4 % of orthophosphate was absorbed. Contrary to expectations, under AOA mode, little nitrate reduction (only 6.3 mg/L within 5.33 h) indicated the failure of ED. According to high-throughput sequencing analysis, GAOs (Candidatus_Competibacter and Defluviicoccus) were enriched within the AO period (14.27 % and 3 %) and then still dominated during the AOA period (13.9 % and 10.07 %) but contributed little to ED. Although apparent alternate orthophosphate variations existed in this reactor, no typical phosphorus accumulating organisms were abundant (< 2 %). More than that, within the long-term AOA operation (109 days), the nitrification weakened (merely 40.11 % of ammonium been oxidized) since the dual effects of low dissolved oxygen and long unaerated duration. This work reveals the necessity of developing practical strategies for starting and optimizing AOA, and then three aspects in future studying are pointed out.

Balancing denitrifying phosphorus-accumulating organisms and denitrifying glycogen-accumulating organisms for advanced nitrogen and phosphorus removal from municipal wastewater

Given the carbon limitation of municipal wastewater, the balance of biological nitrogen and phosphorus removal remains a challenging task. In this study, an anaerobic-anoxic-oxic combining with biological contact oxidation (A²/O-BCO) system treating real municipal wastewater was operated for 205 days, and COD-to-PO₄^3--P ratio was confirmed as the key parameter for balancing denitrifying phosphorus-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) to enhance N and P removal. When DPAOs dominated in nutrients removal, the increase in COD/P from 17.1 to 38.1 caused the deterioration in nitrogen removal performance decreasing to 71.8 %. As COD/P ratio decreased from 81.3 to 46.8, Ca.Competibacter proliferated from 3.11 % to 6.00 %, contributing to 58.9 % of nitrogen removal. The nitrogen and phosphorus removal efficiency reached up to 79.3 % and 95.2 %. Overall, establishing DGAOs-DPAOs balance by strengthening the effect of DGAOs could enhance the nutrients removal performance and accordingly improve the stability and efficiency of the system.

Double anammox process in the AOAO process of treating real low C/N sewage: Validation, enhancement, and quantification of the contribution of anammox in the oxic zone

Enhancement of anaerobic ammonium oxidation (anammox) process and enrichment of anammox bacteria in the oxic zone of mainstream sewage treatments are complex. Also, quantification of the anammox contribution for nitrogen removal in the oxic zone is hindered owing to the simultaneous occurrence of anammox and nitrification. An alternating anaerobic/oxic/anoxic/oxic bioreactor whose oxic zone boosted partial nitrification coupling anammox (PN/A) and anoxic zone boosted partial denitrification coupling anammox (PD/A), respectively, was operated to treat real sewage for >380 days. Desirable nitrogen removal (effluent total inorganic nitrogen (TIN) of 4.7 ± 1.9 mg N/L) was obtained from low carbon/nitrogen (3.6 ± 0.5) sewage with ammonium concentration of 52.5 ± 2.2 mg N/L in the influent. Under the condition of dissolved oxygen (DO) of 1.5-3 mg/L, anammox bacteria was still enriched within the aerobic biofilms, with the relative abundance increasing to 8.2 % (day 345) from 0 % (no biomass on day 1), which was higher than the value in the flocculent sludge (0.03 %) (P < 0.001). PN driven by flocculent sludge with high activity of ammonium oxidized bacteria (AOB) ensured sufficient nitrite supply for the anammox process with the existence of continuous DO. During the steady operation period, the maximum anammox contribution in the oxic zone was quantified to be 10.6 % by withdrawing aerobic biofilms from the system.

Excellent anammox performance driven by stable partial denitrification when encountering seasonal decreasing temperature

Effluent quality deterioration caused by seasonal temperature reductions in wastewater treatment systems using partial anammox technology is a challenge that cannot be ignored. Here, relationships of denitrification and anammox under decreasing temperature were investigated in an anoxic moving bed biofilm reactor (MBBR). Compared with stable partial-denitrification (NO3- → NO2-), the NO2- reduction to N2 was considerably inhibited when the temperature decreased, conversely helping to the competition of NO2- for anammox. Namely, this transformation provided sufficient substrates for anammox bacteria. Although the TIN removal decreased slightly, anammox contribution was robustly maintained at 91.3 ± 6.6 %, even increased. High-throughput sequencing results revealed that anammox bacteria were enriched (0.56 % to 1.22 %). Moreover, qPCR results showed that increased ratio of hzsB/(nirK + nirS) further supported anammox gained an enhancement. This study demonstrated partial-denitrification/anammox process using anoxic MBBR could maintain stable autotrophic nitrogen removal contribution when encountering temperature decrease, providing a new perspective on the application of mainstream anammox.

Enhanced nitrogen removal from municipal wastewater via a novel combined process driven by partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A) with an ultra-low hydraulic retention time (HRT)

Anaerobic ammonia oxidation (Anammox) is a highly productive research area in municipal wastewater treatment. A novel combined process driven by partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A) was established in this paper using a sequencing batch reactor (SBR) and two up-flow sludge beds (USBs). Municipal wastewater after carbon removal pretreatment in SBR entered PN/A-USB. PN/A process was initiated and enhanced by optimizing the intermittent aeration mode under low dissolved oxygen (DO). After enhancing and stabilizing the PD/A process, PN/A effluent entered the PD/A-USB along with raw municipal wastewater at a ratio of 4:1 and the combined system was established. Through this, this study achieved a nitrogen removal efficiency (NRE) of 84.9 % from municipal wastewater at an ultra-low total hydraulic residence time (HRT) of 3.9 h. Candidatus Brocadia (1.8 % in PN/A, 1.0 % in PD/A) was the only functional anammox bacterium in the combined process.

A review on upgrading of the anammox-based nitrogen removal processes: Performance, stability, and control strategies

The anaerobic ammonia oxidation (anammox) process is a promising biological nitrogen removal technology. However, owing to the sensitivity and slow cell growth of anammox bacteria, long startup time and initially low nitrogen removal rate (NRR) are still limiting factors of practical applications of anammox process. Moreover, nitrogen removal efficiency (NRE) is often lower than 88 %. This review summarizes the most common methods for improving NRR by increasing microorganism concentration, and modifying reactor configuration. Recent integrated anammox-based systems were evaluated, including hydroxyapatite (HAP)-enhanced one-stage partial nitritation/anammox (PNA) process for a high NRR of over 2 kg N/m3/d at 25 °C, partial denitrification/anammox (PDA) process, and simultaneous partial nitrification, anammox, and denitrification process for a high NRE of up to 100 %. After discussing the challenges for the application of these systems critically, a combined system of anaerobic digestion, HAP-enhanced one-stage PNA and PDA is proposed in order to achieve a high NRR, high NRE, and phosphorus removal simultaneously.

Establishment and optimization of partial nitrification/anammox/partial nitrification/anammox (PN/A/PN/A) process based on multi-stage ammonia oxidation: Using response surface method as a tool

The presence of nitrite-oxidizing bacteria (NOB) when treating low-strength ammonia wastewater was a challenge in the application of the PN/A process. The partial nitrification/ANAMMOX/partial nitrification/ANAMMOX (PN/A/PN/A) process based on multiple oxidations of ammonia was proposed to solve this problem. The influence of independent variables such as nitrite concentration was analyzed based on the response surface method (RSM). The model showed that nitrite concentration has an adverse impact on ammonia removal efficiency and nitrite accumulation rate. The model provided optimal parameters for the PN/A/PN/A process: the dissolved oxygen concentration was 0.60 mg/L, and the cycle duration was 90 min. Advanced nitrogen removal was achieved by maintaining the nitrite concentration below 10.0 mg/L. The nitrogen removal efficiency was 81.44 ± 4.15 %, and the nitrogen removal rate was 0.18 ± 0.02 kg N/(m³⋅d). Potential functions of microorganisms were analyzed by functional annotation of prokaryotic taxa (FAPROTAX) and the correlation network analysis was performed.

Stable nitrogen removal in the novel continuous flow anammox system under deteriorated partial nitrification: Significance and superiority of the anaerobic-oxic-anoxic-oxic operation mode

The collapse of mainstream anammox system caused by deterioration of partial nitrification (PN) is easy to occur and it is vital to quickly restore the stable nitrogen elimination performance. Herein, a novel continuous push-flow anaerobic-oxic-anoxic-oxic (AOAO) process treating sewage was used to restore the nitrogen elimination performance rapidly under deteriorated PN. The increased abundances of Nitrospira and Candidatus Nitrotoga was responsible for the deterioration of PN. Effluent total inorganic nitrogen of 8.7 mg N/L and a stable nitrogen removal rate of 0.083 kg N/m³·d were obtained with the aerobic hydraulic retention time (HRT) of 3.75 h even PN deteriorated. Endogenous partial denitrification coupled anammox in the anoxic zone was essential to maintain stable nitrogen removal under the deterioration of PN and the anammox contribution increased from 17.2 % to 23.6 %. The AOAO system shows robustness on nitrogen removal even PN deteriorated under the decrease of HRT from 16 to 12 h.

Mutual boost of granulation and enrichment of anammox bacteria in an anaerobic/oxic/anoxic system as the temperature decreases when treating municipal wastewater

Low temperature is an important factor affecting the municipal wastewater treatment systems. The aim of this study was tracking the variations in the abundance of anammox bacteria (AnAOB) and the sludge form as the temperature decreased. Mutual boost of granulation and enrichment of AnAOB was achieved even though the temperature dropped from 20.4 °C to 12.9 °C. The average particle size of the sludge increased from 128.5 μm to 245.6 μm. With low dissolved oxygen (DO) aeration (0.2-0.5 mg/L) and short oxic hydraulic retention time (HRT) (5 h), nitritation in the anaerobic/oxic/anoxic (AOA) system was stable enough to provide NO₂^- for AnAOB. Ca. Brocadia, a type of typical AnAOB, was enriched from 0.03% to 0.24% in the suspended sludge and reached 16.09% in the granular sludge. Overall, this study presents the prospects of anammox and granule technologies when treating municipal wastewater at a low temperature.

Synergistic simultaneous endogenous partial denitrification/anammox (EPDA) and denitrifying dephosphatation for advanced nitrogen and phosphorus removal in a complete biofilm system

To achieve simultaneous biological nitrogen and phosphorus removal from municipal wastewater, the endogenous partial denitrification/anammox (EPDA) was combined with denitrifying dephosphatation in a complete biofilm reactor. Advanced nitrogen and phosphorus removal were achieved with effluent total nitrogen (TN) and PO₄^3--P concentrations of 7.77 ± 0.33 mg/L and 0.35 ± 0.10 mg/L, respectively. Anammox took a major role in the system, accounting for 76 ± 7% of nitrogen removal. 16S rRNA high-throughput sequencing results showed that the anammox bacteria co-existed with the denitrifying glycogen accumulating organisms (DGAOs) and the denitrifying phosphorus accumulating organisms (DPAOs). Anammox bacteria were mainly distributed in the inner layer, while DGAOs and DPAOs existed in the outer layer of EPDA biofilms. Furthermore, based on the EPDA biofilm system, a promising advanced nitrogen and phosphorus removal process was suggested to achieve lower requirements for energy and reagent consumption.

Enhanced simultaneous partial nitrification and denitrification performance of aerobic granular sludge via tapered aeration in sequencing batch reactor for treating low strength and low COD/TN ratio municipal wastewater

The aerobic granular sludge simultaneous partial nitrification, denitrification and phosphorus removal (AGS-SPNDPR) process was carried out via tapered aeration in sequencing batch reactor (SBR) for treating low strength and low COD/TN ratio municipal wastewater. The results showed that aerobic granular sludge was successfully cultivated with good sedimentation performance when treating the municipal wastewater. Meanwhile, the median granule size increased to 270 (R1) and 257 (R2) μm on day 80. The excellent removal performance of COD (92%) and NH₄⁺-N (95%) were achieved under different aeration modes, while the higher TN removal efficiency (76%) was achieved by tapered aeration. The accumulation of NO₂^--N in R2 indicated that the tapered aeration was beneficial to achieve simultaneously partial nitrification and denitrification. Meanwhile, the high-efficiency phosphorus (95%) removal was realized via additional carbon source, and SPNDPR process was formed under tapered aeration. The bacterial community analysis indicated denitrifying glycogen-accumulating organisms (DGAOs) Candidatus_Competibacter and ammonia-oxidizing bacteria (AOB) Nitrosomonas were more effectively enriched via tapered aeration, while phosphorus-accumulating organisms (PAOs) Candidatus_Accumulibacter were effectively enriched under additional organic carbon. AOB, denitrifying bacteria and PAOs were simultaneously enriched by tapered aeration and additional carbon source, which was beneficial to nutrients removal. This study might be conducive to the application of AGS-SPNDPR system for treating low strength and low COD/TN ratio municipal wastewater under tapered aeration.

Biological nutrients removal performance under starvation stress: Efficacy deterioration and recovery

Biological nutrients removal performance affected by starvation stress was investigated via the addition of pre-anoxic stage to SBR. COD removal efficiency maintained at around 90% regardless of the starvation stress. Starvation stress presented significant impact on nitrogen and phosphorus removal, with noticeable reduction of TN removal and remarkable deterioration of TP removal as prolonging the pre-anoxic time, which was mainly attributed to the integrative effect of carbon source competition, depression of denitrification and invalid P release as well as the variation of microbial community. It was notable that starvation stress exerted distinct evolution on microbial community. The improvement in relative abundance of the certain genera relating to denitrification was the main reason for the partial recovery of nitrogen removal after eliminating stress starvation. The promotion of P uptake capacity accompanied with the relief of invalid P release and the enriched DPAOs accounted for the complete recovery of phosphorus removal.

Enhanced nutrient removal from mainstream sewage via denitrifying dephosphatation, endogenous denitrification and anammox in a novel continuous flow process

It is a challenging subject to realize nitrogen and phosphorus elimination synchronously from limited-carbon sewage through conventional biological processes. Herein, a novel continuous flow anaerobic/oxic/anoxic/oxic (AOA-O) process, which integrated denitrifying dephosphatation, endogenous denitrification and anammox in the anoxic zone, was developed to enhance nutrient elimination from low carbon/nitrogen sewage (3.4 in average). After the long-term operation (280 days), a satisfactory nutrient removal performance (effluent PO43--P: 0.2 mg P/L, total inorganic nitrogen (TIN):8.9 mg N/L) was obtained. Mass balance indicated that anammox contributed to 26.1% TIN removal and denitrifying dephosphatation contributed to 25.6% phosphorus removal, respectively. The cooperation of anammox bacteria retained in biofilms and endogenous denitrifying bacteria in flocculent sludge was responsible for the enhanced nutrient removal in the anoxic zone. Dechloromonas carried out phosphorus uptake both under oxic conditions and anoxic conditions. This study can broaden the application prospect of mainstream anammox.

Critical review on negative emerging contaminant removal efficiency of wastewater treatment systems: Concept, consistency and consequences

Emerging contaminants (ECs) are not completely removed by wastewater treatment owing to their capabilities of making complexes, toxic derivatives, byproduct formation, and dynamic partitioning. Negative contaminant removal i.e., higher concentrations (up to 5731%) of these ECs in the effluent with respect to the influent sampled on the same occasions, is globally prevalent in almost all types of treatment systems. Conventional WWTPs showed the highest negative removal (NR) for Carbamazepine, and Carbadox. Conjugation-deconjugation, types of WWTPs, transformations, leaching, operational parameters, sampling schemes, and nature of substance governs the NR efficiencies. Among the various categories of micropollutants, pesticides and beta-blockers are reported to exhibit the maximum percentage of NR, posing threat to human and the environment. With > 200% of NR for beta-blockers, low blood-pressure related symptoms may likely to get more prevalent in the near future. Study red-flags this phenomenon of negative removal that needs urgent attention.

A novel control strategy to strengthen nitrogen removal from domestic wastewater through eliminating nitrite oxidizing bacteria in a plug-flow process

In this study, intermittent aeration strategy was investigated in a plug-flow reactor on real municipal wastewater. Over 200 days of operation, the total inorganic nitrogen (TIN) removal efficiency of 72.43 ± 7.56% was achieved with a total aerobic hydraulic retention time in the range 2.4-3.0 h under a low C/N ratio of 3.19. The batch tests showed that the activity of nitrite oxidizing bacteria (NOB) was effectively inhibited, and simultaneous nitrification and denitrification via nitrite were observed under double intermittent aeration mode. The Illumina MiSep sequencing revealed that the relative abundance of the Nitrospira as the only detected NOB, decreased from 2.22% (day 0) to 0.91% (day 207) at the genus level. Overall, this study provides a new strategy for NOB suppression to strengthen nitrogen removal from low C/N domestic wastewater through the continuous process.