Anaerobic Ammonium Oxidation Reactor Research Articles

Magnetite addition reduces nitrite requirement for efficient anaerobic ammonium oxidation by facilitating mutualism of ANAMMOX and FEAMMOX bacteria

Partial nitrification (PN) is crucial for anaerobic ammonium oxidation (ANAMMOX), but faces challenges such as high energy demands and process control. Recent research has highlighted additives like magnetite as potential alternatives to conventional electron acceptors (O₂ and NO₂−) for enhancing ammonium (NH4+) oxidation with lower energy consumption. This study investigated the effect of adding 50 mg/L of magnetite to ANAMMOX reactors, resulting in improved nitrogen (N) removal efficiency. The magnetite-added ANAMMOX (M-ANA) reactor yielded N removal efficiencies of 71 %, 66 %, and 57 % for NH4+:NO2− molar ratios of 1:1.3, 1:0.8, and 1:0.5, respectively. The M-ANA reactor operated under a 0.5 mol lower NO2− concentration achieved similar performance to the control ANAMMOX (C-ANA) reactor operated with a theoretical amount of NO2−. Moreover, the M-ANA reactor showed the potential to remove NH4+ by 56 % without any NO2− supplementation. Metagenomic analysis showed that the addition of magnetite significantly improved the relative abundance of microorganisms involved in the FEAMMOX reaction, such as Fimbriimonas ginsengisoli and Pseudomonas stutzeri. It also facilitated positive mutualism between ANAMMOX and FEAMMOX reactions. In addition, M-ANA granules exhibited a dense and compact structure compared with C-ANA, and the presence of magnetite facilitated the formation of resilient granules. Notably, the useful protein (Heme C) concentration and specific microbial activity in the M-ANA reactor were 1.3 and 2.2 times higher than those in the C-ANA reactor. Overall, the results demonstrate that an appropriate amount of magnetite can enhance the N removal efficiency while reducing the energy input requirements and associated carbon emissions. These findings can guide the future development of carbon- and energy-neutral N removal processes.

Harnessing the Potential of Extracellular Polymeric Substances in Enhancing ANAMMOX Processes: Mechanisms, Strategies, and Perspectives

Anaerobic ammonium oxidation (ANAMMOX) has emerged as a promising sustainable nitrogen removal technology that offers significant advantages over conventional nitrification–denitrification processes, such as reduced energy consumption, a 60% reduction in oxygen demand, and a 90% reduction in sludge production. However, the practical application of ANAMMOX is hindered by several challenges, including the slow growth of ANAMMOX bacteria, long start-up periods, and high sensitivity to environmental disturbances. Recent studies have highlighted the crucial role of extracellular polymeric substances (EPSs) in the formation, activity, and stability of ANAMMOX biofilms and granules. An EPS is a complex mixture of high-molecular-weight polymers secreted by microorganisms, mainly composed of polysaccharides, proteins, nucleic acids, and lipids. The diverse physicochemical properties and functional groups of EPSs enable them to serve as a structural scaffold, protective barrier, sorption site, electron shuttle, and nutrient source for ANAMMOX bacteria. This review aims to provide an overview of the latest research progress on harnessing the potential of EPSs to enhance the ANAMMOX process. The characteristics, compositions, and extraction methods of ANAMMOX-derived EPSs are summarized. The mechanisms of how EPSs facilitate the enrichment, immobilization, aggregation, and adaptation of ANAMMOX bacteria are elucidated. The strategies and effects of EPS supplementation on improving the performance and robustness of ANAMMOX reactors under various stresses are critically reviewed. The challenges and future perspectives of the EPS-mediated optimization of the ANAMMOX process are also discussed. This review sheds new light on exploiting EPSs as a renewable bioresource to develop more efficient and stable ANAMMOX applications for sustainable wastewater treatment.

The long-term effect of glutaraldehyde on the bacterial community in anaerobic ammonium oxidation reactor

A 160-day incubation was performed with two anammox reactors (GA and CK) to investigate the effect of glutaraldehyde. The results indicated that anammox bacteria were very sensitive when glutaraldehyde in GA reactor increased to 40 mg/L, the nitrogen removal efficiency sharply decreased to 11%, only one-quarter of CK. Glutaraldehyde changed spatial distribution of exopolysaccharides, caused anammox bacteria (Brocadia CK_gra75) to disassociate from granules (24.70% of the reads in CK but only 14.09% in GA granules). Metagenome analysis indicated glutaraldehyde led to the denitrifier community succession from strains without nir (nitrite reductase) and nor (nitric oxide reductases) genes to those with them, and the rapid growth of denitrifiers with NodT (an outer membrane factor)-related efflux pumps replacing those with another TolC -related ones. Meanwhile, Brocadia CK_gra75 lacks the NodT proteins. This study provides important insight into community adaptation and potential resistance mechanism in an active anammox community after exposure to disinfectant.

Study on Long-term Effect of Oxytetracycline on ANAMMOX Nitrogen Removal Performance in the Treatment of Salt-containing Wastewater

The effects of oxytetracycline on anaerobic ammonium oxidation (ANAMMOX) were analyzed in this study. Meanwhile, the change of specific ANAMMOX activity (SAA) and the content of heme c were also revealed. The performance of ANAMMOX reactor decreased gradually when the increase of OTC concentration from 2mg/L to 10mg/L under 10‰ salinity. The nitrogen removal performance almost collapsed until the elevation to 10 mg/L OTC, observed with a huge decrease of SAA of 77.71% and heme c content of 88.04%. After no addition of OTC into the ANAMMOX reactor, the system performance recovered within 20 days. At the end of this phase, NH4+-N was completely removed, NO2--N was removed above 99%, and total nitrogen removal efficiency recovered to 85.33%.

Alleviation of substrate inhibition in an anaerobic ammonia oxidation reactor: Recovery process performance and microbial community

Substrate inhibition is one of the key factors that threatens the stability of anaerobic ammonia oxidation (anammox) reactors. Most of the current studies have focused on the inhibition of anammox by substrates; however, little attention has been given to the recovery process and microbial community changes in anammox reactors after inhibition. To remediate the damage substrate inhibition can do to anammox systems, the study investigated the recovery process of an anammox reactor that was inhibited by high substrate concentrations. The results showed that a reduction in the ratio of influent NO2−-N to NH4+-N from the theoretical stoichiometric ratio of 1.32 to 0.5 was conducive to the rapid recovery of anammox system performance. The analysis of the microbial community structure indicated that the relative abundance of the primary anammox bacteria on the biofilm carriers and mixed sludge was 19.51 % and 9.92 %, respectively, after reactor recovery. Biofilms played an important role in resisting reactor destabilization.

Start-up of Anammox and Effect of Fe2+ on Nitrogen Removal Rate

Anammox reaction was started by inoculating sewage plant digested sludge, and the change of N element in the reactor was detected. It was found that Anammox needed to go through three parts: hydrolysis period, activity lag period and activity increase period. The effect of different Fe2+ concentrations on the denitrification rate was investigated with the well-run Anammox sludge as the inoculation sludge. The results showed that Fe2+ had a positive effect on the anaerobic ammonium oxidation reaction within a certain concentration range, while the denitrification effect would be inhibited if the concentration was too high. When the concentration of Fe2+ was 0.08mmol/L, Fe2+ on Anammox had the best denitrification effect.

Advanced nitrogen removal in a fixed-bed anaerobic ammonia oxidation reactor following an anoxic/oxic reactor: Nitrogen removal contributions and mechanisms

This study demonstrated the feasibility of anaerobic ammonia oxidation (anammox) served as tertiary nitrogen removal process. An upflow fixed-bed reactor (UFBR) pre-inoculated with anammox bacteria (AnAOB) followed an anoxic/oxic (A/O) reactor treating magnetic-coagulation pretreated municipal wastewater. When bypassing 15% of influent into UFBR, UFBR removed 5.37 mg-TN/L contributing to 23.4% on total TN removal, in which the combination of partial nitritation and partial denitrification with anammox was main nitrogen removal pathway. Relatively low concentrations of NH4+-N and anaerobic environment promoted the growth of ammonia oxidizing archaea (AOA) in the inner-layer of biofilm in UFBR. The cooperation of AOA and ammonia-oxidizing bacteria (AOB) with AnAOB was achieved, with AOA, AOB, and AnAOB abundances of 0.01–0.32%, 0.25–0.44%, and 0.77–2.18% on the biofilm, respectively. Metagenomic analysis found that although AOB was the main NH4+-N oxidizer, archaeal amo gene on biofilm increased threefold during 90 days’ treatment.

Domestic Sewage Treatment Using a One-Stage ANAMMOX Process

A one-stage anaerobic ammonium oxidation (ANAMMOX) reactor can be quickly started within 40 days by mixing partial nitrifying sludge with ANAMMOX granular sludge with an average temperature of 30 °C. After 70 days of nitrogen load acclimation, Acinetobacter, including Candidatus Kuenenia, became the dominant strain of the system within the reactor, which exhibited high efficiency and a stable nitrogen removal performance. At an influent chemical oxygen demand (COD), NH4+-N content, total nitrogen (TN) content, hydraulic retention time (HRT), temperature, and reactor dissolved oxygen (DO) content of 100, 60, and 70 mg/L, 6 h, 30 ± 1 °C, and below 0.6 mg/L, respectively, the one-stage ANAMMOX reactor could effectively treat domestic sewage on campus. The removal rates of COD, NH4+-N, and TN were approximately 89%, 96.7%, and 70%, respectively.

Partial nitritation and anaerobic ammonium oxidation in biofilter reactors treating low ammonium strength wastewater

Partial nitritation (PN) and anaerobic ammonium oxidation (ANAMMOX) were applied in biofilter reactors to treat low ammonium strength wastewater. The removal efficiency and contribution of PN-ANAMMOX process to CODcr, BOD5, NH3-N, TN and TP were investigated. The results showed that the average removal rates of CODcr, BOD5, NH3-N, TN and TP via PN-ANAMMOX process were 91.9%, 96.7%, 98.9%, 92.8% and 93.3% respectively when hydraulic load was 1.0 m/d. The effluent CODcr, BOD5, NH3-N, TN and TP concentrations were lower than 13.8, 4.8, 0.76, 4.4 and 0.28 mg/L, respectively. The PN-ANAMMOX process showed high efficiency and stability in removing C, N and P pollutants from wastewater. PN reactor played a major role in the removal of CODcr, BOD5, NH3-N and TP. ANAMMOX reactor played a leading role in TN removal.

Nitrogen Removal from Mature Landfill Leachate via Denitrification-Partial Nitritation-ANAMMOX Based on a Zeolite Biological Aerated Filter

A combined process of denitrification-partial nitritation-ANAMMOX based on a zeolite biological aerated filter (ZBAF) was applied to treat mature landfill leachate. We investigate the partial nitritation characteristics of the ZBAF and the nitrogen removal performance as well as the carbon removal performance of the combined process. Results showed that, based on the selective inhibition of nitrite oxidizing bacteria (NOB) by free ammonia (FA), the ZBAF could successfully achieve stable and efficient partial nitrification of mature landfill leachate, with an average nitrite accumulation rate (NAR) of 93.8% and a maximum nitrite production rate (NPR) of 1.659 kg·(m3·d)-1. After adding 700 mg·L-1 glucose to the influent, due to the synergistic effect of denitrification and anammoxidation, the combined process achieved its best nitrogen removal performance at a reflux ratio of 2.0 and hydraulic retention time (HRT) of 2.2 days. The average ammonia removal efficiency (ARE), total nitrogen removal efficiency (NRE), total nitrogen removal loading rate (NRR), and average chemical oxygen demand (COD) removal efficiency were 97.2%, 90.0%, 0.585 kg·(m3·d)-1, and 45.3%, respectively. Furthermore, the NRR of the anaerobic ammonium oxidation (ANAMMOX) process (NRRANA) reached 1.268 kg·(m3·d)-1. High-throughput sequencing technology was used to analyze the microbial community structure in each device. Results showed that denitrifiers (Paracoccus and Comamonas), ammonia-oxidizing bacteria (AOB) (Nitrosomonas), and ANAMMOX bacteria (Candidatus Kuenenia and Candidatus Anammoxoglobus) were the dominant bacteria in the UASB, ZBAF, and ANAMMOX reactor, respectively, which corresponded to the stable nitrogen removal performance of the combined process.

Treatment of anaerobically digested effluent from kitchen waste using combined processes of anaerobic digestion-complete nitritation-ANAMMOX based on reflux dilution.

In this study, an anaerobically digested effluent from kitchen waste with high concentrations of chemical oxygen demand (COD) and ammonia nitrogen was treated using combined processes of anaerobic digestion (AD), complete nitritation (CN), and anaerobic ammonium oxidation (ANAMMOX). The COD and nitrogen removal efficiency of each treatment unit were investigated. The feasibility of using the final treatment effluent to dilute the original wastewater was also discussed. Findings showed that as a pretreatment step, AD resulted in the decline in biodegradability and increase in concentration. CN was successfully and stably achieved for 106days with an average nitritation rate of 95% by maintaining the dissolved oxygen at 2-3mg/L and hydraulic retention time of 24hr under 30±1°C. High and . removal efficiencies of over 88% and 96% were attained in the following ANAMMOX reactor. The reflux of ANAMMOX-treated effluent for the dilution of raw wastewater or an influent of CN and ANAMMOX ensured the stable operation of the combined system. PRACTITIONER POINTS: Anaerobic digestion effluent of kitchen waste had low COD/ ratio and poor biodegradability. Stable and efficient nitritation was realized by controlling DO, HRT and TEMP. High and removal efficiency were obtained by ANAMMOX process. Average nitrogen removal rate of 0.94kgN/m3 /day were obtained by ANAMMOX. Reflux dilution with the effluent guaranteed the system's successful operation.

Setup and Microbial Community Analysis of ANAMMOX System for Landfill Leachate Treatment Coupling Partial Nitrification-Denitrification Process

In order to upgrade the current shortcut nitrification and denitrification process for landfill leachate treatment and to stimulate nitrification-denitrification coupled with anaerobic ammonia oxidation (ANAMMOX) at a landfill, an ANAMMOX process was started using an up-flow anaerobic sludge bed (UASB) reactor seeded with nitrification and denitrification sludge. The performances of the reactor were investigated, including the nitrogen loading and nitrogen removal rates. Moreover, Illumina Miseq sequencing was conducted to analyze the microbial community dynamics under long-term operation on a molecular level. The results showed that the ANAMMOX reactor was successfully started in 149 days. The total nitrogen loading rate reached 4000.00 mg·(L·d)-1, and the total nitrogen removal rate reached 3885.76 mg·(L·d)-1 after stable operation. The average ammonium and nitrite removal efficiencies were more than 95%. In 250 days, the Planctomycetes in the reactor experienced rapid growth, and its abundance reached 54.94%. The abundance of Candidatus Kuenenia reached 49.66%. The upgrading process of landfill leachate treatment by coupling ANAMMOX based on short-cut nitrification and denitrification was confirmed to be feasible.

Low energy treatment of landfill leachate using simultaneous partial nitrification and partial denitrification with anaerobic ammonia oxidation

An up-flow anaerobic sludge blanket reactor (UASB), anoxic/oxic (A/O)–anaerobic ammonia oxidation reactor (ANAOR or anammox reactor), and anaerobic sequencing batch reactor (ASBR) were employed in the treatment of landfill leachate with partial nitrification-anammox and half-denitrification-anammox. The Chemical Oxygen Demand (COD) concentration, ammonium nitrogen (NH4+-N) concentration, and total nitrogen (TN) concentration of the basal leachate was 2200–2500 mg/L, 1200–1300 mg/L, and 1300–1400 mg/L, respectively. After a 1:2 dilution using domestic sewage, the COD, NH4+-N, and TN concentrations in the influent were 800–1000 mg/L, 400–430 mg/L, and 420–440 mg/L, respectively. After treatment, the final COD, NH4+-N, and TN were decreased to 90–100 mg/L, 13–14 mg/L, and 35–38 mg/L, respectively. In the ASBR, organic carbon sources in sewage-diluted landfill leachate were introduced for the conversion of nitrate nitrogen (NO3−-N) into nitrite nitrogen (NO2−-N). This enabled the continued reaction of NO2−-N with NH4+-N from the newly introduced sewage-diluted landfill leachate via anammox. As a result, complete TN removal was achieved in the system. Microbial diversity analysis indicated that the relative abundance of ammonia-oxidizing bacteria (AOB) was four to five times greater than nitrite-oxidizing bacteria (NOB) in the A/O reactor, showing that partial nitrification was prevalent. The relative abundance of the anammox bacterium Candidatus Kuenenia gradually increased in each reactor, reaching a maximum of 1.17%–1.39%. Using this set-up, we achieved advanced, efficient, and economical, COD reduction and nitrogen removal. Taken together, the findings provide important insights into the optimal operation of landfill leachate treatments.

Ecotoxicological study of landfill leachate treated in the ANAMMOX process

Abstract The exacerbated production of solid residues represents a major problem in the management and handling of urban wastes. The by-product of stored municipal and industrial solid waste production is landfill leachate. Leachate is characterized by a high concentration of organic compounds, ammonia, and the presence of heavy metals. Because of its composition, this kind of wastewater can cause serious environmental pollution and should be treated to reduce its toxic effects. Increasingly, the interest is directed to the application of the ANAMMOX (anaerobic ammonium oxidation) process for the landfill leachate treatment. In this study, for the first time, the effect of treatment with the ANAMMOX process on the toxicity of leachate was investigated. Based on the research performed in this study, it could be stated that the untreated landfill leachate from the municipal landfill and the influent of the ANAMMOX reactor present phytotoxicity to Lemna minor, due to a correlation of high concentrations of organic compounds, heavy metals, such as Cd2+, Cu2+, Zn2+, and the presence of an unionized form of ammonia (NH3). The results of the Allium cepa test demonstrated that the treatment was not efficient in eliminating the genotoxic substances that are responsible for the mutagenic potential in the effluent. This article has been made Open Access thanks to the kind support of CAWQ/ACQE (https://www.cawq.ca).

A holistic analysis of ANAMMOX process in response to salinity: From adaptation to collapse

The application of anaerobic ammonium oxidation (ANAMMOX) process to industrial wastewater treatment usually faces the challenge of high salinity. However, most of the current ANAMMOX sludge was enriched from low-salinity water, resulting in the critical gap between the inoculum and saline wastewater. In this work, an ANAMMOX reactor fed with inoculum enriched from low-salinity water successfully adapted to saline wastewater (500 mmol/L NaCl, 2.92%) after a long-term stepwise acclimatization. The nitrogen removal rate and total nitrogen removal efficiency reached 9.72 kg·m−3·d−1 and 80.90%, respectively. However, further salinity increase to 600 mmol/L caused a collapse of reactor performance. The proportion of inorganic matters improved along with the increase of salinity, which might be attributed to the compact particles observed in the microstructure of ANAMMOX sludge. A microbial community succession occurred in response to the increase of salinity. When the salinity increased to 160 mmol/L, the dominant functional bacteria shifted from Candidatus Kuenenia to unclassified Brocadiaceae, which was supposed to be salt-tolerant. The up and down regulations of polysaccharides and ζ potential in EPS were positive strategies for salinity adaptation of ANAMMOX bacteria. However, the barrier of seawater salinity (3–5%) could not be overcome. The present work would provide a holistic view for the enrichment of salt-tolerant ANAMMOX bacteria and help in the selection of seeding sludge for the treatment of saline wastewater by ANAMMOX process.

Successful start-up of pilot-scale single-stage ANAMMOX reactor through cultivation of ammonia oxidizing and ANAMMOX bacteria

The lack of seed sludges for Ammonium Oxidizing Bacteria (AOB) and slow-growing ANaerobic AMMonium OXidation (ANAMMOX) bacteria is one of the major problem for large-scale application. In this study, 24m3 of single-stage SBR (Sequencing Batch Reactor) was operated to remove nitrogen from reject water using AOB and ANAMMOX bacteria cultivated from activated sludge in the field. The ANAMMOX activity was found after 44 days of cultivation in the ANAMMOX cultivation reactor, and then 0.66 kg N/m3/d of the nitrogen removal rate was achieved at 0.78 kg N/m3/d of the nitrogen loading rate at 153 days of cultivation. The AOB cultivation reactor showed 0.2 kg N/m3/d of nitrite production rate at 0.4 kg N/m3/d of nitrogen loading rate after 36 days of operation. The cultivated ANAMMOX bacteria and AOB was mixed into the single-stage SBR. The feed distribution was applied to remove total nitrogen stably in the single-stage SBR. The nitrogen removal rate in the single-stage SBR was gradually enhanced with an increase of specific activities of both AOB and ANAMMOX bacteria by showing 0.49 kg N/m3/d of the nitrogen removal rate at 0.56 kg N/m3/d of the nitrogen loading rate at 54 days of operation.

The microbial community structure change of an anaerobic ammonia oxidation reactor in response to decreasing temperatures.

In anaerobic ammonium oxidation (anammox) systems, temperature may regulate the activity of functional bacteria (e.g., anammox bacteria) and the composition of the microbial population, ultimately determining the performance of the anammox reactor. Knowledge of the dynamic changes in nitrogen removal rates and the microbial anammox community at low and/or ambient temperature is still limited. This study explored the response of an anammox sequencing batch reactor (SBR) to a gradient of decreasing temperature (33, 25, 20, 15, 10°C), followed by recovery to 22°C, over 360days. Particularly, the specific anammox activity (SAA) and microbial community were assessed. The anammox reaction in the SBR remained stable and efficient at 20-33°C, with a total nitrogen removal load of 0.4g-NL-1day-1 and an SAA of > 0.32g-Ng-VSS-1day-1; 10°C was the turning point for the anammox bacterial metabolic activity, at which the SAA decreased by 91% compared with that at 33°C. After the temperature was returned to 22°C, the anammox activity recovered to 0.24g-Ng-VSS-1day-1. The apparent activation energy for the anammox reaction was 68.4kJmol-1 at 10-33°C and 152.9kJmol-1 at 10-20°C. High-throughput sequencing results revealed that Kuenenia was the dominant species of anammox bacteria, and Kuenenia had a higher tolerance to low temperature than Candidatus Brocadia and Candidatus Jettenia. This study clearly shows the effectiveness of anammox bioreactors for treatment of wastewater at ambient temperatures of 15-33°C.

Effect of HRT on Nitrogen Removal Using ANAMMOX and Heterotrophic Denitrification

Real domestic sewage was first treated in SBR and partial nitrification was achieved. When average concentrations of NH4+-N, NO2--N, and COD were 37.27, 39.97, and 120 mg·L-1, respectively, the effluent was delivered as influent of an anaerobic ammonia oxidation reactor (ASBR). The effect of different HRTs (36 h, 33 h, 30 h, 27 h) on nitrogen removal of ANAMMOX and heterotrophic denitrification were investigated under conditions of temperature of 24℃ and pH of 7.2±0.2. Results showed that 1 nitrogen removal efficiency was optimum with HRT of 33 h. The average total nitrogen load rate(TNLR)and total nitrogen removal rate(TNRR)were 0.056 kg·(m3·d)-1and 0.050 kg·(m3·d)-1, respectively. The average effluent concentrations of NH4+-N, NO2--N, and COD were 1.36, 0.47, and 49.79 mg·L-1, and removal rates were 96.30%, 98.83%, and 56.17%, respectively. △NO2--N/△NH4+-N and △NO3--N/△NH4+-N were 1.17 and 0.15, 0.15 and 0.11 less than theoretical ANAMMOX values (1.32, 0.26) due to heterotrophic denitrification. 2 The contribution of ANAMMOX to nitrogen removal decreased; however, the contribution of heterotrophic denitrification to nitrogen removal gradually increased with decreasing HRT. This provides a point of reference for ANAMMOX in engineering applications.

Influence of Tourmaline on the Activity of ANAMMOX Bacteria and ANAMMOX Reaction

AbstractThe performance of the anaerobic ammonium oxidation (ANAMMOX) process was investigated in two identical sequencing batch reactors (SBRs) [designated as SBR1 (tourmaline addition) and SBR2 (...

Effect of Seeding Single/Mixed Sludge on Rapid Start-up of an ANAMMOX Reactor

The experiment explored the effect of different seeding sludge on the rapid start-up of an anaerobic ammonium oxidation (ANAMMOX) reactor by seeding a single type of denitrified granular sludge and a mixed sludge composed of denitrified granular sludge and aerobic nitrification sludge (the volume ratio of the mixed sludge was 2:1) in two sequencing batch reactors (SBR), R0 and R1, respectively. The results indicated that R0 was started up successfully on day 64 with a nitrogen removal rate (NRR) of 0.26 kg·(m3·d)-1, while R1 was started up by day 47 with a NRR of 0.30 kg·(m3·d)-1, which was shorter than R0 by 17 d. In the enrichment stage, reddish sludge appeared in R1, and the characteristics of anaerobic ammonium oxidation of the system were more obvious than in R0. After the reactor was started up successfully, the stoichiometric ratio of R0 was 1.20 and 0.34, respectively, and the stoichiometric ratio of R1 was 1.26 and 0.21, which was closer to the theoretical values of 1.32 and 0.26. The mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) of R0 were restored to 51% (4.2 g·L-1) and 38% (2.3 g·L-1)of the initial seeding sludge, respectively, while the MLSS and MLVSS of R1 were restored to 54% (4.4 g·L-1) and 42% (2.6 g·L-1),which was higher than R0. It can be speculated that the proliferation rate of AnAOB in R1 was faster than in R0. Seeding mixed sludge can accelerate the start-up process of anaerobic ammonium oxidation with more stable N-removal performance.