Treatment Of Low-strength Wastewater Research Articles

Simultaneously autotrophic denitrification and organics degradation in low-strength coal gasification wastewater (LSCGW) treatment via microelectrolysis-triggered Fe(II)/Fe(III) cycle

The autotrophic iron-depended denitrification (AIDD), triggered by microelectrolysis, was established in the microelectrolysis-assistant up-flow anaerobic sludge blanket (MEA-UASB) with the purpose of low-strength coal gasification wastewater (LSCGW) treatment while control UASB operated in parallel. The results revealed that chemical oxygen demand (COD) removal efficiency and total nitrogen (TN) removal load at optimum current (2.5 A/m3) in MEA-UASB (83.2 ± 2.6% and 0.220 ± 0.010 kg N/m3·d) were 1.42-fold and 1.57-fold higher than those (58.5 ± 2.1% and 0.139 ± 0.011 kg N/m3·d) in UASB, verifying that AIDD and following dissimilatory iron reduction (DIR) process could offer the novel pathway to solve the electron donor-deficient and traditionally denitrification-infeasible problems. High-throughput 16S rRNA gene pyrosequencing shown that iron-oxidizing denitrifiers (Thiobacillus and Acidovorax species) and iron reducing bacteria (Geothrix and Ignavibacterium speices), acted as microbial iron cycle of contributors, were specially enriched at optimum operating condition. Additionally, the activities of microbial electron transfer chain, electron transporters (complex I, II, III and cytochrome c) and abundance of genes encoding important enzymes (narG, nirK/S, norB and nosZ) were remarkably promoted, suggesting that electron transport and consumption capacities were stimulated during denitrification process. This study could shed light on better understanding about microelectrolysis-triggered AIDD for treatment of refractory LSCGW and further widen its application potential in the future.

Reactor performance and microbial community structure of single-stage partial nitritation anammox membrane bioreactors inoculated with Brocadia and Scalindua enrichment cultures

Partial nitritation combined with anaerobic ammonium oxidation (anammox), hereafter referred to as PNA, is a promising biological nitrogen-removal process for ammonia-rich wastewater; however, the PNA application process to low-strength ammonia wastewater (i.e., mainstream anammox) remains challenging. In this study, two single-stage PNA processes using a membrane bioreactor (MBR) inoculated with the anammox enrichment culture of Candidatus Brocadia sinica (Brocadia-MBR) or Candidatus Scalindua sp. (Scalindua-MBR) were operated for low-strength ammonia wastewater treatment. Single-stage PNA process was established in both MBRs, showing rates of total nitrogen (TN) removal from 0.58 g-N L−1 day−1 to 0.66 g-N L−1 day−1, and 81%–89% TN-removal efficiency under optimal dissolved oxygen. Microbial community analysis showed that three ammonia-oxidizing bacteria (AOB), one nitrite-oxidizing bacteria (NOB), one Candidatus Brocadia were detected in the Brocadia-MBR, whereas one AOB, no NOB, and one Candidatus Scalindua were detected in Scalindua-MBR. The operational conditions in this study resulted in the outcompetition of anammox bacteria in both MBRs.

Effect of voltage intensity on the nutrient removal performance and microbial community in the iron electrolysis-integrated aerobic granular sludge system.

The effects of voltage intensity on the nutrient removal performance and microbial community in the iron electrolysis-integrated aerobic granular sludge (AGS) system were investigated over a period of 15 weeks. Results revealed that the application outcomes of iron electrolysis for AGS systems relied on voltage intensity. When a constant voltage of 1.5V was applied, the sludge granulation was most obviously accelerated with a specific growth rate of the sludge diameter of 0.078 day-1, and the removal efficiencies of total nitrogen (TN) and total phosphorus (TP) increased by 14.1% and 20.2%, respectively, compared to the control reactor (without the iron electrolysis-integration). Moreover, the AGS developed at different voltages included different microbial communities, whose shifts were driven by the Fe content and the average diameter of AGS. Both heterotrophic nitrifiers and mixotrophic denitrifiers were significantly enriched in the AGS developed at 1.5V, which effectively enhanced TN removal. Together with the response of the functional genes involved in Fe, N, and P metabolism, the electrolytic iron-driven nutrient degradation pathway was further elaborated. Overall, this study clarified the optimum voltage condition when iron electrolysis was integrated into the AGS system, and revealed the enhancement mechanism of this coupling technology on nutrient removal during the treatment of low-strength municipal wastewater.

Conversion of full nitritation to partial nitritation/anammox in a continuous granular reactor for low-strength ammonium wastewater treatment at 20°C.

The feasibility of converting full nitritation to partial nitritation/anammox (PN/A) at ambient temperature (20°C) was investigated in a continuous granular reactor. The process was conducted without anammox bacteria inoculation for the treatment of 70mgL-1 of low-strength ammonium nitrogen wastewater. Following the stepwise increase of the nitrogen loading rate from 0.84 to 1.30kgNm-3d-1 in 320days of operation, the removal efficiency of total inorganic nitrogen (TIN) exceeded 80% under oxygen-limiting conditions. The mature PN/A granules, which had a compact structure and abundant biomass, exhibited a specific TIN removal rate of 0.11gNg-1 VSSd-1 and a settling velocity of 70.2mh-1. This was comparable with that obtained at above 30°C in previous reports. High-throughput pyrosequencing results revealed that the co-enrichment of aerobic and anaerobic ammonium-oxidizing bacteria identified as genera Nitrosomonas and Candidatus Kuenenia, which prompted a hybrid competition for oxygen and nitrite with nitrite-oxidizing bacteria (NOB). However, the overgrowth of novel NOB Candidatus Nitrotoga adapted to low temperatures and low nitrite concentration could potentially deteriorate the one-stage PN/A process by exhausting residual bulk ammonium under long-term excessive aeration.

Characteristics and formation mechanism of hollow Anammox granular sludge in low-strength ammonia sewage treatment

• Hollow Anammox granular sludge formed in low-strength ammonia wastewater. • TN removal efficiency was 80% with NRR 0.93 kg N m −3 d −1 under a short HRT (1.8 h). • Tryptophan or protein-like was the active component of PN as the main part of EPS. • Candidatus Kuenenia lived and coexisted with other bacteria under EPS shield. • The formation of bubble cavitation was one of the key steps of regranulation. Hollow anaerobic ammonium oxidation (Anammox) granular sludge formed and became the main part in the treatment of low-strength ammonia wastewater. The characteristics and formation mechanism of hollow Anammox granular sludge were investigated in a continuous stirred tank reactor (CSTR) at room temperature. Granular sludge was found to be cavitated, and Candidatus Kuenenia was the dominant bacteria that lived and coexisted with other bacteria in walls under an extracellular polymeric substance (EPS) shield. The EEM-PARAFAC analysis was applied to characterize the EPS, while EPS secretion was the expression of specific Anammox activity. Tryptophan or protein-like was the active component of proteins (PN) as the main part of EPS in granules. These results confirm that hollow Anammox granular sludge is suitable for low-strength ammonia sewage. Finally, a conceptual model of hollow Anammox granules growth and breakage was developed, and cavitation was a key step of regranulation.

Probing the key foulants and membrane fouling under increasing salinity in anaerobic osmotic membrane bioreactors for low-strength wastewater treatment

Anaerobic osmotic membrane bioreactors (AnOMBRs) have attracted much attention in recent years due to their ability to produce high-quality effluent with low energy demand. Here, the performance of a thin film composite (TFC) forward osmosis (FO) membrane in an AnOMBR system is evaluated, and the key membrane foulants are examined by analyzing the characteristics of the mixed liquor and the fouling layer. As the experiment progressed, the water flux declined due to membrane fouling and salt accumulation in the bioreactor, and reached approximately 3.5 LMH by the end of each operating cycle where membrane cleaning was adopted. The conductivity increased from 3.3 mS/cm to 23.6 mS/cm over the 28-day treatment. The contaminant rejection rates of total organic carbon, total phosphorous and ammonia-nitrogen were more than 93%, 98% and 60%, respectively. Results also suggested that extracellular polymeric substances (EPS) was the major contributor to membrane fouling, and the increase of EPS in the mixed liquor with salinity was primarily composed of polysaccharides. The comprehensive characterization of the fouling layer via X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and confocal laser scanning microcopy (CLSM) revealed the coexistence of biofouling and organic fouling. The CLSM images further demonstrated the prevalence of β polysaccharides, proteins and microorganisms on the fouled TFC FO membrane surface. In addition, the flow cytometric analysis indicated that the foulant sample was “bacterial viable”, the large number of bacteria in suspension (96.61% live cells) maybe corresponded to the high EPS content in the bulk mixed liquor.

Autotrophic nitrogen removal by partial nitrification-anammox process in two-stage sequencing batch constructed wetlands for low-strength ammonium wastewater

In this study, partial nitrification-anammox process was established in two-stage sequencing batch constructed wetlands (SBCWs) to achieve autotrophic nitrogen removal for low-strength ammonium wastewater treatment. The operational parameters of the partial nitrification process were investigated and optimized, for the subsequent anammox process. The results indicated idle time and reaction time had significant influences to partial nitrification SBCW (WPN). In the WPN with optimal condition (idle time = 7.5 h, reaction time = 16 h), the effluent nitrite to ammonium ratio (NO2−-N/NH4+-N) remained stable at 1.24 ± 0.09, which favored the anammox process. The anammox SBCW (WAmx) was established rapidly within 61 d. The two-stage SBCWs showed high-efficient nitrogen removal capacity, with effluent total nitrogen (TN) concentration of 3.89 ± 0.62 mg/L and TN removal rate of 81.11 ± 2.92 %. Moreover, high-throughput sequencing revealed that Nitrosomonas (37.5 %) was dominant under optimal condition in WPN and responsible for partial nitrification process. Candidatus Brocadia (26.5 %) was enriched in WAmx, undertaking anammox process with synergism of flanking bacteria. This study provides a sustainable alternative for low-strength wastewater treatment.

Anaerobic Sequencing Biofilter (AnSBio): A novel approach for high-quality biogas production from low-strength wastewaters at ambient temperature

The Anaerobic Sequencing Biofilter (AnSBio) treating municipal sewage was operated for 370-days at ambient temperature with an organic loading rate (OLR) of 0.4–0.7 kgCOD/m3·d. Temperature did not affect soluble chemical oxygen demand (CODsol) removal efficiency (RE), which averaged 89 ± 3%, whereas, total COD (CODtot) RE, ranging 82 ± 5%, exhibited an unclear profile due to suspended solids (SS) loss under cooler temperatures. The inherent filtering capacity resulted in reduced bed porosity under psychrophilic temperatures, manifested as head loss increase (348 ± 34 and 314 ± 19 cm during first and second winter, respectively). Hydrolysis of particulate matter at mesophilic temperatures caused head loss decrease (271 ± 58 cm). Biogas yields were 124 and 315 NmL/gCODremoved at the lowest (14 °C) and the highest (35 °C) reactor operating temperature, respectively. Biogas methane content was 85 ± 4%. The AnSBio is a valid alternative for low-strength wastewater treatment at ambient temperature.

Effects of phenol on extracellular polymeric substances and microbial communities from aerobic granular sludge treating low strength and salinity wastewater

The effects of phenol on aerobic granular sludge including extracellular polymeric substances (EPS) and microbial community were investigated for low strength and salinity wastewater treatment. Elevated phenol over 20 mg/L stimulated biological phosphorus removal mainly via co-metabolism with nearly complete phenol degradation, whereas resulted in significant accumulation of nitrate around 4 mg/L. Aerobic granules kept structural stability via enhancing production of extracellular polymeric substances (EPS), especially folds of polysaccharides (PS) and varying functional groups identified through EEM, FTIR and XPS spectral characterizations at increasing phenol loads. Illumina MiSeq sequencing results indicated that elevated phenol decreased the bacterial diversity and richness, and caused remarkable variations in structural and compositions of microbial population. Multiple halophilic bacteria including Stappia, Luteococcus, and Formosa laid the biological basis for stability of aerobic granules and efficient biological nutrients and phenol removal. Redundancy analysis (RDA) suggested the key role of phenol in shaping the relative abundances and predominant genera. This study proved that aerobic granular sludge was feasible for low-saline and phenol-laden low-strength wastewater treatment.

A mathematical approach to predict the solids concentration in anaerobic membrane bioreactos (AnMBR): Evaluation of the volatile solids solubilization

Anaerobic Membrane Bioreactors (AnMBR) are gaining attention as a suitable approach for sustainable low-strength wastewater treatment, as they bring together the advantages of both anaerobic treatments and membrane bioreactors. However, increasing the sludge retention time (SRT) necessary to favor hydrolysis increases the suspended solids concentration potentially leading to decreased permeate flux. Therefore, the availability of a mathematical approach to predict the solids concentration within an AnMBR can be very useful. In this work, a mathematical model describing the volatile solids concentration within the reactor as a function of the operating parameters and the influent characteristics is developed. The solubilization of organic particulates was clearly influenced by temperature and the SRT, whereas the hydraulic retention time influence was negligible. Furthermore, the activation energy value of about 20 kJ mol−1 confirms the idea that diffusion of hydrolytic enzymes from the bulk solution to the particle surface is the rate-limiting step of hydrolysis.

The use of pure oxygen for aeration in aerobic wastewater treatment: A review of its potential and limitations

In aerobic wastewater treatment, aeration is the most critical element of the treatment system. It supplies microorganisms with the required dissolved oxygen, maintains solids in suspension and, in membrane bioreactors, it controls fouling. However, conventional activated sludge is limited to the treatment of low strength wastewaters, as higher loadings require both higher biomass and higher dissolved oxygen concentrations. By replacing air with pure oxygen, oxygen transfer rates increase at lower flowrates. In this work, the potential and limitations of pure oxygen aeration are reviewed. The effect of the system’s operational parameters and the mixed liquor characteristics on oxygen transfer, and vice versa, are determined. Pure oxygen treats higher loadings without compromising effluent quality. Fine bubbles are more efficient in oxygen transfer due to their increased contact area. However, pure oxygen is not always essential, so it is recommended to be restricted to applications where air is not adequate.

Performance and microbial community of a novel combined anaerobic bioreactor integrating anaerobic baffling and anaerobic filtration process for low-strength rural wastewater treatment

A novel combined bioreactor integrating anaerobic baffling and anaerobic filtration process was developed and operated for 210days to treat low-strength rural wastewater. The effects of hydraulic residence time (HRT) and organic loading rate (OLR) on chemical oxygen demand (COD) removal and methane (CH4) production of the combined bioreactor were investigated. The combined bioreactor can start up successfully in 25days and achieve enhanced performance. The COD removal rate and CH4 yield were influenced significantly by HRT and OLR. The influent COD was removed effectively through the synergistic effects of the anaerobic baffling and anaerobic filtration. The baffle zone played the main role in the degradation of the pollutants, and the filter zone mainly contributed to improve the resistance to shock loading. High-throughput sequencing technology was used to analyze the bacterial and archaeal community structure and diversity. Clostridium_sensu_stricto, Longilinea, Acetoanaerobium, Arcobacter, and Acinetobacter were found to be the dominant bacteria. While Methanothrix and Methanoregula were the dominant archaea, which were responsible for methane generation. This study not only highlights the good energy recovery and resource utilization potential of the combined bioreactor but also presents significant guidance for the application of the combined anaerobic process for low-strength rural wastewater treatment.

Use of a low-cost and energy-efficient device for treating low-strength wastewater at low temperatures focusing on nitrogen removal and microbial community

Treating wastewater at low temperatures has always been challenging. In this study, an anoxic filter (ANF)/multi-stage waterwheel driving rotating biological contactors (ms-wdRBCs) device was investigated as a potential solution for treatment of low-strength domestic wastewater at low temperatures (6–18 °C). Parameters, including the recirculation ratio (RR) and hydraulic retention time (HRT), were regulated to identify the optimum operating conditions. Using the optimum parameters of 200% RR, 10.67 h HRTANF, and 1.33 h HRTwdRBC, 75.37% ± 4.43% COD, 44.81% ± 3.67% TN, 75.05% ±1.86% NH4+-N, and 35.46% ± 4.87% TP were removed. The microbial communities in eight different sections of the device were investigated through the 16s rRNA analysis. The microbial results helped to explain the device performance. Denitrification-related bacteria were present in great abundance in both the ANF and the ms-wdRBCs. Anammox-related bacteria were also in significant abundance in ANF and some parts of ms-wdRBCs, which suggested a potential solution for improving the device performance by expanding the role of these anammox bacteria. Considering both the pollutant removal efficiency and investment costs, this device is acceptable as part of a low-strength domestic wastewater treatment solution at low temperatures.

Limited simultaneous nitrification-denitrification (SND) in aerobic granular sludge systems treating municipal wastewater: Mechanisms and practical implications

Simultaneous nitrification-denitrification (SND) is, in theory, a key advantage of aerobic granular sludge systems over conventional activated sludge systems. But practical experience and literature suggests that SND and thus total nitrogen removal are limited during treatment of municipal wastewater using AGS systems. This study thus aims at quantifying the extent and understanding the mechanisms of SND during treatment of municipal wastewater with aerobic granular sludge (AGS) systems. Experiments (long-term and batch-tests) as well as mathematical modelling were performed. Our experimental results demonstrate that SND is significantly limited during treatment of low-strength municipal wastewater with AGS systems (14–39%), while almost full SND is observed when treating synthetic influent containing only diffusible substrate (90%). Our simulations demonstrate that the main mechanisms behind limited SND are (1) the dynamics of anoxic zone formation inside the granule, (2) the diffusibility and availability of electron-donors in those zones and (3) the aeration mode. The development of anoxic zones is driven by the utilisation of oxygen in the upper layers of the granule leading to transport limitations of oxygen inside the granule; this effect is closely linked to granule size and wastewater composition. Development of anoxic zones during the aerobic phase is limited for small granules at constant aeration at bulk dissolved oxygen (DO) concentration of 2 mgO2 L−1, and anoxic zones only develop during a brief period of the aerated phase for large granules. Modelling results further indicate that a large fraction of electron-donors are actually utilised in aerobic rather than anoxic redox zones – in the bulk or at the granule surface. Thus, full SND cannot be achieved with AGS treating low strength municipal wastewater if a constant DO is maintained during the aeration phase. Optimised aeration strategies are therefore required. 2-step and alternating aeration are tested successfully using mathematical modelling and increase TN removal to 40–79%, without compromising nitrification, and by shifting electron-donor utilisation towards anoxic redox conditions.

Treatment of low-strength ammonia wastewater by single-stage partial nitritation and anammox using upflow dual-bed gel-carrier reactor (UDGR)

This study investigated the single-stage partial nitritation and anammox (S-PNA) treatment of low-strength ammonia wastewater (≤140 mg NH4+-N/L). Upflow dual-bed gel-carrier reactor (UDGR) with polyvinyl alcohol cryogel biocarriers, developed in this study, was employed for the anammox biomass enrichment from conventional activated sludge and subsequent S-PNA experiments. Anammox biomass was successfully enriched from conventional activated sludge. The enriched anammox carriers were inoculated together with gel carriers containing nitrifying sludge into the S-PNA reactors. S-PNA activity developed rapidly, and the nitrogen removal efficiency and rate reached up to 90.1% (with complete ammonia removal) and 0.15 kg N/m3⋅d, respectively, under low nitrogen loading conditions (0.10–0.17 kg N/m3⋅d). The microbial community structure changed significantly while adapting to anammox and S-PNA conditions. Anammox was likely driven solely by a Candidatus Jettenia population accounting for ≤49.4% of bacterial 16S rRNA genes. The results demonstrate that the UDGR-based S-PNA is suitable for treating low-strength wastewater.

Enhance the treatment of low strength wastewater at low temperature with the coexistence system of AnAOB and heterotrophic bacteria: Performance and bacterial community

The application of anammox process in mainstream wastewater treatment process is still facing challenges especially at the low temperature. To resolve this problem, the coexistence system of anaerobic ammonia-oxidizing bacteria (AnAOB) and heterotrophic bacteria (HB) was built in this study. The nitrogen removal efficiency mainly maintained at above 90% during the process of temperature reducing from 35 °C to 10 °C. The nitrogen removal rate were 0.30 g N·L−1·d−1 at both 25 and 15 °C and 0.10 g N·L−1·d−1 at 10 °C, respectively. Analysis of 16S rRNA genus sequencing revealed that as the temperature reduced to 10 °C, the Denutrotisoma genera presented a downward trend but Comamonadaceae genera showed an upward trend. At 10 °C, the contrast of anammox activities between granular and flocculent sludge in the system revealed that although the abundance of anammox genera was much lower in flocculent sludge than that in granular sludge, the anammox activities showed no significant discrepancy. And the abundance of Comamonadaceae and Chloroflexales genera were much higher in flocculent sludge than those in granular sludge, presenting their key roles to anammox activity at low temperature. The Circos diagram and Cluster of orthologous Group of protein functional predication showed that the functional abundance related to interaction among microbial communities were higher in flocculent sludge but those related to self-growth was higher in granular sludge. This result indicated the significance of the interactions based on the microbial diversity in the application of annamox process at low temperature.

Optimizing induced struvite crystallization in a fluidized bed reactor for low-strength ammonium wastewater treatment

Optimizing induced struvite crystallization in a fluidized bed reactor for low-strength ammonium wastewater treatment

Influence of hydraulic retention time and temperature on the performance of an anaerobic ammonium oxidation fluidized bed membrane bioreactor for low-strength ammonia wastewater treatment

The feasibility of anaerobic ammonium oxidation (Anammox) process with a fluidized bed membrane bioreactor (Anammox-FMBR) was evaluated for 561 days treating synthetic wastewater containing 35 mg/L of NO2−-N and 25 mg/L of NH4+-N. During start-up periods, higher nitrogen loading rate (NLR) induced faster stabilization than the low NLR. Total nitrogen (TN) removal efficiency was over 82% even with short hydraulic retention time (HRT) of 0.75 h at 25 °C conditions but decreased to below 30% at 15 °C. Pronounced effect of operating temperature at lower range was supported by high activation energy (Ea) value. The membrane fouling was controlled well, as evidenced from negligible fouling rates when the systems were operated at less than 13 L/m2/h flux with granular activated carbon (GAC) fluidization as cleaning media. With the estimated low energy requirements of 0.0005 kWh/kg Nremoved, the Anammox-FMBR could be successfully applied in mainstream operation for the energy efficient treatment of low ammonia wastewater.

Promising carbon utilization for nitrogen recovery in low strength wastewater treatment: Ammonia nitrogen assimilation, protein production and microbial community structure

Acetic acid and sodium acetate are generally supplied to wastewater treatment plants (WWTPs) in China to improve total nitrogen (TN) and total phosphorus (TP) removal, and the addition of carbon source also facilitates to increase sludge growth rate and further provides material basis for the extraction of proteins and amino acids from activated sludge. To recycle ammonia nitrogen resources, a system that combined adsorption and anaerobic–anoxic–oxic (A/AAO) process for treating low strength wastewater was established. Experimental results showed that by the addition of carbon substrate from a mixture of anaerobically fermented adsorption sludge, the average removal efficiency of chemical oxygen demand (COD), ammonia nitrogen, TN, and TP were 88%, 96.9%, 93.9%, and 92.1%, respectively, and the ratio of nitrogen assimilation to nitrogen dissimilation significantly increased by a factor of 2.5. Through energy analysis (based on adenosine triphosphate, ATP), sludge flocculation capacity and settling property, it was found that the AAO process sludge presented the logarithmic growth characteristics. The respective sludge protein and amino acids contents increased by over 11.4% and 40.3%, and the synthetic products of glutamic acid, alanine and aspartate increased through the assimilation of ammonia nitrogen, thereby indicating that replenishing the carbon substrate could markedly enhance protein and amino acids contents in AAO process sludge. Moreover, the diversity of the microbial community in adsorption process was relatively rich, the diversity in the adsorption process sludge was the highest, while the diversity of the AAO process sludge evidently decreased. The microbial community in each process was similarly based on 16S rDNA gene sequence analysis, microflora was prominent in the AAO process, with Dechloromonas, Flavobacterium, Zoogloea, Unclassified_Rhodocyclaceae and Thauera as the dominant species. Promising carbon utilization facilitates contaminants removal in low strength wastewater treatment and is conducive to protein production through ammonia nitrogen assimilation.

Response of FANIR system to starvation stress: “Dormancy”

Anaerobic ammonium oxidation (Anammox) process has been successfully applied in the nitrogen removal from high-strength wastewaters. However, little information is available for its treatment of low-strength wastewaters. In this study, a Famine Anammox NItrogen Removal (FANIR) system was developed to investigate the effect of long-term substrate starvation at the low nitrogen concentration (the influent total nitrogen was set at ∼1 mg/L). The results showed that the response of FANIR system to the starvation stress took on two phases: the functional decline phase (0–54 day) and the functional stabilization phase (62–116 day). Over the two phases, the Nitrogen Removal Rate (NRR) of anammox reactor firstly dropped sharply; and then came to a constant level. The activity and settleability of Anammox Granular Sludge (AnGS) firstly deteriorated seriously, and then stayed in a stable range. The relative abundance of Anaerobic Ammonium Oxidation Bacteria (AnAOB) firstly decreased markedly, and then approached a steady state with the change of dominant genus from Candidatus Brocadia to Candidatus Kuenenia. The abundance of 16S rRNA gene and hzs gene of AnAOB and their transcription level firstly declined largely as well, and then became stable with the 16S rRNA gene, hzs gene, 16S rRNA and hzs-mRNA of AnAOB at 23.9%, 9.1%, 1.2% and 1.0% of the initial value, respectively. To our delight, the behavior of FANIR system in the functional stabilization phase was proved indeed consistent with the feature for AnAOB to enter the dormancy state. These findings are helpful to understand the physiology of AnAOB over the starvation stress and to promote the extension of anammox process to the treatment of low-strength wastewaters.