Process stability in expanded granular sludge bed bioreactors enhances resistance to organic load shocks.

Environmental perturbations such as changes in organic loading rate (OLR) can have deleterious effects on the anaerobic digestion process, leading to VFA accumulation and process failure. However, the operational history of a reactor, such as prior exposure to VFA build up, can impact a reactor's resistance to shock loads. In the present study, the effects of long term (>100 days) bioreactor (un)stability on OLR shock resistance were assessed. Three 4 L EGSB bioreactors were subjected to varying levels of process stability. Operational conditions such as OLR, temperature and pH were maintained stable in R1; R2 was subjected to a series of minor OLR perturbations and R3 was subjected to a series of non-OLR perturbations, including ammonium, temperature, pH and sulfide. The effect of these different operational histories on each reactor's resistance to a sudden 8-fold increase in OLR were assessed by monitoring COD removal efficiency and biogas production. The microbial communities of each reactor were monitored using 16S rRNA gene sequencing to understand the relationship between microbial diversity and reactor stability. It was determined that the stable (un-perturbed) reactor performed best in terms of its resistance to a large OLR shock, despite its lower microbial community diversity.

Influence of microbial spatial distribution and activity in an EGSB reactor under high- and low-loading denitrification desulfurization.

To characterize the impact of reactor configuration and influent loading on elemental sulphur (S0) recovery during denitrification desulfurization, a laboratory-scale expanded granular sludge bed (EGSB) reactor was established under two influent acetate/nitrate/sulphide loadings; the water flow velocity, microbial community, and functional genes at different heights were investigated. There was no S0 generated when acetate/nitrate/sulphide loadings were set to 0.95/0.60/1.05 kg/m3.d (low-loading). Furthermore, there were no typical denitrifying sulphide oxidizing bacteria under this condition, and Syntrophobacter, Anaerolineaceae genera were predominant in the reactor. As the influent loading was doubled (high-loading), S0 recovery increased to 87%; the bacterial distribution was relatively homogeneous with sulphide oxidation genera (Thauera) being predominant. Neither nirK nor sqr genes were detected in the low-loading sample at a height of 50 cm. The sqr/sox ratios of low-loading stage were 2.50 (10 cm), 0.94 (30 cm), and 0 (50 cm), and the ratios of the high-loading stage were 1.38 (10 cm), 1.33 (30 cm), and 1.08 (50 cm). A hydrodynamics analysis indicated that the water flow velocity was homogenous throughout the reactor. Appropriate reactor configuration and operation parameters play an important role in the efficient regulation of S0 recovery during denitrification desulfurization.

Microbial community and molecular ecological network in the EGSB reactor treating antibiotic wastewater: Response to environmental factors.

In this study, one lab-scale EGSB reactor (1.47 L volume) was designed to treat the antibiotic wastewater under different environmental factors, including the addition of cephalexin (CFX), Temperature (T) and Hydraulic Retention Time (HRT). The microbial community structure in EGSB reactor was analyzed with high-throughput sequencing technology to investigate their response to environmental factors changes, and then the random-matrix-theory (RMT)-based network analysis was used to investigate the microbial community's molecular ecological network in EGSB systems treating antibiotics wastewater. Moreover, the explanatory value of each environmental factor on the change of microbial community structure was obtained through the result of redundancy analysis (RDA). The results showed that the addition of cephalexin (CFX), decline of T and decline of HRT (8 h) would decrease the removal efficiency of COD decreasing. And the removal efficiency of CFX would not be affected by decline of T and HRT, except the producing and degrading process of CFX by-products was changed obviously. The result of RDA analysis suggested the environmental factors mainly affected bacterial and fungal microbial community structure but not archaeal ones. The result of high-throughput sequencing showed the relative abundance (RA) of Firmicutes had been obviously affected by T and HRT, which might be main reason leading to the decrease of COD removal efficiency. In addition, molecular ecological network analysis showed the growth of Bacteroidetes occupied the niche of functional microorganism and led to the unstable operation of EGSB when T declined. What's more, the molecular ecological network analysis revealed that Exophiala which belonged to fungi Ascomycota phylum was the hub genus to degrade complex refractory organic pollutants, and Aceticlastic methanogens Methanosaeta was the core functional archaea genus.

Characteristics of microbial community in EGSB system treating with oxytetracycline production wastewater.

In order to realize the efficient and stable operation of anaerobic digestion for oxytetracycline (OTC) production wastewater which contains high concentration refractory organic matters and antibiotic residues, two laboratory-scale EGSB reactors (the experimental reactor and the control reactor) were constructed for pre-treating OTC production wastewater and the complex characteristics and connections among anaerobic fermentative bacteria, methanogens and fungi were analyzed. The experimental reactor gradually increased OTC doses of 0-200 mg/L by four phases compared with the control reactor which was fed without OTC addition during 280 days' operation. The average COD removal efficiency of 91.44% with the average OTC removal efficiency of 27.90% was achieved at OTC concentration of 200 mg/L. The addition of OTC did not affect the preponderant methanogen type, and Methanosaeta, a strict aceticlastic methanogen genus, was dominant both in working and controlling reactors on day 280. Redundancy analysis revealed that OTC and VFAs were the main environmental factors affecting the microbial communities and molecular ecological networks analysis indicated that the key genera principally belonged to Methanosaeta, Proteobacteria and Apiotrichum. Additionally, the fungi genus Apiotrichum might be related to the degradation of complex organic contaminants in OTC production wastewater treatment system.

Recirculation ratio regulates denitrifying sulfide removal and elemental sulfur recovery by altering sludge characteristics and microbial community composition in an EGSB reactor.

Expanded granular sludge blanket (EGSB) is regarded as a promising reactor to carry out denitrifying sulfide removal (DSR) and elemental sulfur (S0) recovery. Although the recirculation ratio is an essential parameter for EGSB reactors, how it impacts the DSR process remains poorly understood. Here, three lab-scale DSR-EGSB reactors were established with the different recirculation ratios (3:1, 6:1 and 9:1) to evaluate the corresponding variations in pollutant removal, S0 recovery, anaerobic granular sludge (AGS) characteristics and microbial community composition. It was found that an intermediate recirculation ratio (6:1) could facilitate long-term reactor stability. Adequate recirculation ratio could enhance S0 recovery, but an excessive recirculation ratio (9:1) was likely to cause AGS fragmentation and biomass loss. The S0 desorbed more from sludge at higher recirculation ratios, probably due to the enhanced hydraulic disturbance caused by the increased recirculation ratios. At the low recirculation ratio (3:1), S0 accumulation as inorganic suspended solids in AGS led to a decrease in VSS/TSS ratio and mass transfer efficiency. Although typical denitrifying and sulfide-oxidizing bacteria (e.g., Azoarcus, Thauera and Arcobacter) were predominant in all conditions, facultative and heterotrophic functional bacteria (e.g., Azoarcus and Thauera) were more adaptable to higher recirculation ratios than autotrophs (e.g., Arcobacter, Thiobacillus and Vulcanibacillus), which was conducive to the formation of bacterial aggregates to response to the increased recirculation ratio. The study revealed recirculation ratio regulation significantly impacted the DSR-EGSB reactor performance by altering AGS characteristics and microbial community composition, which provides a novel strategy to improve DSR performance and S0 recovery.

Insight into effect of high-level cephalexin on fate and driver mechanism of antibiotics resistance genes in antibiotic wastewater treatment system.

In the study, antibiotic resistance genes (ARGs) were examined in wastewater and sludge samples to explore the effect of cephalexin (CFX) on the spreading and removal of ARGs in the Expanded Granular Sludge Bed (EGSB) reactor treating antibiotics wastewater. The result showed that the addition of CFX in the wastewater affected the removal amount of ß-lactam ARGs and other types ARGs. Besides, the addition of CFX in the wastewater had no obviously effect on total concentration of targeted ARGs in the sludge, but it was related to the accumulation of some typical ARGs. Based on gene cassette array libraries analysis, the diversity of gene cassettes carried by intI1 gene was increased by the addition of CFX in the wastewater. Furthermore, the co-occurrence patterns between ARGs and bacterial genus were also investigated. The results showed the CFX in the wastewater not only affected the number of potential host bacteria of ARGs, but also changed the types of potential host bacteria of ARGs. The correlation analysis of ARG in influent, effluent and sludge showed that, for blaCTX-M, sul2, qnrS and AmpC genes, their removal amount in EGSB reactor treating antibiotic wastewater system might be enhanced by reducing their concentration in the sludge.

The co-existence of anammox genera in an expanded granular sludge bed reactor with biomass carriers for nitrogen removal.

Anaerobic ammonium oxidation (anammox)-based nitrogen removal saves aeration energy and organic carbon costs, attributed to its anaerobic and autotrophic nature. However, due to the slow growth of anaerobic ammonium oxidation bacteria (AnAOB), drawbacks including long startup time and sensitivity to toxins still hamper the application of anammox-based processes. To cope with the slow growth of AnAOB, various bioreactor configurations have been investigated for the capability of retaining anammox biomass, among which, the expanded granular sludge bed (EGSB) reactor is a promising option. In this study, two laboratory-scale EGSB reactors were used to gain insights of microbial population and their response to amending biofilm-carriers, aiming to enhance the biomass retention of AnAOB. The respective ammonium and nitrite removal efficiencies were up to over 90%, and the overall nitrogen removal efficiency (NRE) was stable at over 70%, in the EGSB reactor amended with carriers (CEGSB). Compared to the control EGSB, CEGSB's observed performance was more stable during the 236-day operational period. The abundance of AnAOB reached 22% in the EGSB and 49% in the CEGSB. It was also observed that Ca. Brocadia (14.25%) and Asahi BRW2 (33.19%) coexisted in the CEGSB. The dynamics of major metabolisms and functional genes involved in nitrogen conversion were further observed by FAPROTAX based on the taxonomic data, providing more insights into the functions of the microbial communities.

Strategies of anaerobic sludge granulation in an EGSB reactor.

Anaerobic sludge granulation was evaluated in an expanded granular sludge bed (EGSB) reactor based on the increases in the specific organic loading rate (SOLR). The effect of precursor substances (calcium chloride, sodium chloride, and tannin) on the development of granular sludge was also investigated in batch reactors. The reactors were fed with synthetic sewage and operated in mesophilic conditions. The EGSB was operated with a variable hydraulic retention time (HRT) and the batch reactors, with cycles of 8 h and 16 h. The increase of SOLR from 17.4 ±â€¯7.4 to 104.6 ±â€¯66.7 mgCOD gVSS-1 d-1 in the EGSB resulted in an increase on the average granules diameter from 344.3 to 1583.3 µm. These conditions also favored the reduction rates of chemical oxygen demand (COD) and volatile fatty acids (VFAs) concentration in the reactor. When the upflow velocity suffered an abrupt increase (from 0.06 L h-1 to 0.25 L h-1), the granules size began to decrease and lose their settleability characteristics. Considering this, it is proposed to start the biomass granulation process without effluent recirculation, and, after the granules reach the desired size and settleability capacity, the normal operation of EGSB reactor starts. The results showed that calcium chloride was more efficient for granulation. CaCl2 addition can be performed only during the reactor's start-up, improving granulation and reducing start-up time. Thus, these results have practical implications as granules maintenance is the key to the proper EGSB operation.

High-rate anaerobic treatment of wastewater from soft drink industry: Methods, performance and experiences.

At an Austrian soft drink company, an expanded granular sludge bed reactor for anaerobic wastewater treatment was inoculated with sludge from paper and food industries. Detailed online monitoring and laboratory examinations were carried out during startup and subsequent phases, which included a period of inhibition after ca. 80 days during which reactor degradative performance diminished suddenly, following a period of increased effluent VFA. After dosing iron chloride (FeCl2) and micronutrients and reducing organic loading to startup levels, the reactor eventually reached efficient operation (>85% COD degradation) after a gradual recovery phase. In this work performance data both at lab and full scale are elaborated along startup, adaptation, pre-inhibition, recovery and stable phases, and correlated between scales. High rate anaerobic treatment of soft drink industry wastewater was successful in terms of COD removal efficiency and final effluent COD (∼300 mg l-1), with a startup period (including inhibition) of ca. 5 months.

Amoxicillin effects on functional microbial community and spread of antibiotic resistance genes in amoxicillin manufacture wastewater treatment system.

This study aimed to reveal how amoxicillin (AMX) affected the microbial community and the spread mechanism of antibiotic resistance genes (ARGs) in the AMX manufacture wastewater treatment system. For this purpose, a 1.47 L expanded granular sludge bed (EGSB) reactor was designed and run for 241days treating artificial AMX manufacture wastewater. 454 pyrosequencing was applied to analyze functional microorganisms in the system. The antibiotic genes OXA-1, OXA-2, OXA-10, TEM-1, CTX-M-1, class I integrons (intI1) and 16S rRNA genes were also examined in sludge samples. The results showed that the genera Ignavibacterium, Phocoenobacter, Spirochaeta, Aminobacterium and Cloacibacillus contributed to the degradation of different organic compounds (such as various sugars and amines). And the relative quantification of each ß-lactam resistance gene in the study was changed with the increasing of AMX concentration. Furthermore the vertical gene transfer was the main driver for the spread of ARGs rather than horizontal transfer pathways in the system.

Effects of the support material addition on the hydrodynamic behavior of an anaerobic expanded granular sludge bed reactor.

As a support material, zeolite can be used to promote the granulation process due to its high settable property and the ability to retain biomass on its surface. The present paper reports on the influence of zeolite addition on the hydrodynamic behavior of an expanded granular sludge bed reactor (EGSB). Different models were applied to fit the flow pattern and to compare EGSB hydrodynamic performance with and without the addition of zeolite. The experimental data fit the tanks in a series model for zeolite bed height of 5cm and upflow velocity of 6m/hr. Higher axial dispersion degree (D/uL) was obtained at lower heights of zeolite. The real hydraulic retention time (HRTr) was increased with both increased zeolite bed height and increased upflow velocity. The short-circuit results for 5cm of zeolite bed and 6, 8 and 10m/hr upflow velocity were 0.3, 0.24 and 0.19 respectively, demonstrating the feasibility of using zeolite for a proper hydrodynamic environment to operate the EGSB reactor. The presence of zeolite resulted in the higher percentage values of dead zones, ranging from 12% to 24%. Zeolite addition exerted a positive effect on the hydrodynamics pattern for this technology being advantageous for the anaerobic process because of its possible contribution to better biofilm agglomeration, granule formation and substrate-microorganism contact.

Simultaneous biological removal of phenol, sulfide, and nitrate using expanded granular sludge bed reactor.

Biological removal of sulfide, nitrate, and phenol at loading rates of 600 g S/(m(3) day), 900 g N/(m(3) day), and 450 g C/(m(3) day), respectively, from synthetic wastewaters was achieved in an expanded granular sludge bed (EGSB) reactor, whose rates are much higher than literature works and are considered feasible for handling high-strength petrochemical wastewaters without dilution. Effects of C/S ratio (2-2.5:1) on EGSB performance were noted insignificantly. The strains Bacillus sp., Thauera sp., and Pseudomonas sp. were the heterotrophic denitrifiers and the strains Thiobacillus sp., Azoarcus sp., and Sulfurovum sp. were the autotrophic denitrifiers in the EGSB granules. The EGSB reactor experienced biological breakdown at loadings higher than 1200 g S/(m(3) day), 1800 g N/(m(3) day), and 900 g C/(m(3) day) by the following mechanism: high sulfide first inhibits heterotrophic denitrifies (Bacillus sp. and Pseudomonas sp.), thereby accumulating nitrite in the system; then, the accumulated nitrite inhibits autotrophic denitrifiers (Thiobacillus sp., Azoarcus sp., and Sulfurovum sp.) to complete breakdown of the system.

Denitrifying sulfide removal process on high-salinity wastewaters in the presence of Halomonas sp.

Biological conversion of sulfide, acetate, and nitrate to, respectively, elemental sulfur (S(0)), carbon dioxide, and nitrogen-containing gas (such as N2) at NaCl concentration of 35-70 g/L was achieved in an expanded granular sludge bed (EGSB) reactor. A C/N ratio of 1:1 was noted to achieve high sulfide removal and S(0) conversion rate at high salinity. The extracellular polymeric substance (EPS) quantities were increased with NaCl concentration, being 11.4-mg/g volatile-suspended solids at 70 mg/L NaCl. The denitrifying sulfide removal (DSR) consortium incorporated Thauera sp. and Halomonas sp. as the heterotrophs and Azoarcus sp. being the autotrophs at high salinity condition. Halomonas sp. correlates with the enhanced DSR performance at high salinity.

Complete reduction of highly concentrated contaminants in piggery waste by a novel process scheme with an algal-bacterial symbiotic photobioreactor.

The complete reduction of highly concentrated contaminants in piggery waste was achieved with an innovative process scheme consecutively combining autothermal thermophilic aerobic digestion (ATAD), an expanded granular sludge bed (EGSB) and a microalgal-bacterial symbiotic vertical photobioreactor (VPBR), followed by biomass recycling for effluent polishing. Contaminants in piggery waste, such as high organic and inorganic matter, total nitrogen (TN), and total phosphorus (TP) contents, were successfully reduced in the newly implemented system. The concentrations of volatile solids (VS) and the chemical oxygen demand (COD) for organic matter in the feed were reduced by approximately 99.3% and 99.7%, respectively, in the innovative system. The overall reduction efficiencies in TN, ammoniacal nitrogen, and TP were 98.8, 98.4, and 93.5%, respectively, through ammonia gas emission, coagulated sludge disposal, and the algal-bacterial symbiotic polishing process. Fecal coliform density was decreased to <1.7 × 10(4) CFU g(-1) total solids. Biogas and CH4 in the EGSB were generated in the range of 0.36-0.79 and 0.18-0.44 L g(-1) [VS removed], respectively, and contained 245 ± 19 ppm (v/v) [H2S].

Evaluation of anionic surfactant removal in anaerobic reactor with Fe(III) supplementation.

The objective of this study was to evaluate the removal of linear alkylbenzene sulfonate (LAS) associated with Fe(III) supplementation using an expanded granular sludge bed (EGSB) reactor. The reactor was inoculated with a granular sludge and fed with synthetic wastewater containing a specific LAS load rate (SLLR) of 1.5 mg gVS-1 d-1 (∼16.4 mgLAS L-1 influent) and supplied with 7276 µMol L-1 of Fe(III). The biomasses from the inoculum and at the end of the EGSB-Fe operation (127 days) were characterized using 16S rRNA Ion Tag sequencing. An increase of 20% in the removal efficiency was observed compared to reactors without Fe(III) supplementation that was reported in the literature, and the LAS removal was approximately 84%. The Fe(III) reduction was dissimilatory (the total iron concentration in the influent and effluent were similar) and reached approximately 64%. The higher Fe(III) reduction and LAS removal were corroborated by the enrichment of genera, such as Shewanella (only EGSB-Fe - 0.5%) and Geobacter (1% - inoculum; 18% - EGSB-Fe). Furthermore, the enrichment of genera that degrade LAS and/or aromatic compounds (3.8% - inoculum; 29.6% - EGSB-Fe of relative abundance) was observed for a total of 20 different genera.

Anaerobic removal of 1-methoxy-2-propanol under ambient temperature in an EGSB reactor.

Two laboratory-scale expanded granular sludge bed (EGSB) reactors were operated at 18 and 25 °C, respectively, for the treatment of synthetic wastewater composed of ethanol and 1-methoxy-2-propanol (M2P) in a mass ratio of 4:1. Reactors were operated first with continuous wastewater supply and after with discontinuous substrate supply (5 days a week, 16 h a day) to simulate shift working conditions. Under continuous wastewater supply chemical oxygen demand (COD), removal efficiency higher than 95 % was achieved at the end of the trial applying organic loading rates (OLR) of 29 and 43 kg COD m(-3) day(-1) at 18 and 25 °C; thus, corresponding to M2P OLR of 6.4 and 9.3 kg COD m(-3) day(-1), respectively. During intermittent supply of substrate, good performance was recorded at both temperatures with an OLR of 30 kg COD m(-3) day(-1) (M2P OLR of 6.6 kg COD m(-3) day(-1)). After 56 h without substrate supply, a decline in methane yield of 15-30 % was observed due to the deactivation of the biomass. Specific methanogenic activity (SMA) assays were carried out at the end of the experiments. SMA values using 1-methoxy-2-propanol as substrate were 24.3 and 7.8 ml CH4 gVSS(-1) day(-1) at 25 °C and at 18 °C, respectively. This is the first attempt to investigate the removal of 1-methoxy-2-propanol by EGSB reactors.

Performance and microbial diversity of an expanded granular sludge bed reactor for high sulfate and nitrate waste brine treatment.

The disposal of waste brines has become a major challenge that hinders the wide application of ion-exchange resins in the water industry in recent decades. In this study, high sulfate removal efficiency (80%-90%) was achieved at the influent sulfate concentration of 3600 mg/L and 3% NaCl after 145 days in an expanded granular sludge bed (EGSB) reactor. Furthermore, the feasibility of treating synthetic waste brine containing high levels of sulfate and nitrate was investigated in a single EGSB reactor during an operation period of 261 days. The highest nitrate and sulfate loading rate reached 6.38 and 5.78 kg/(m(3)·day) at SO(2-)4-S/NO(-)3-N mass ratio of 4/3, and the corresponding removal efficiency was 99.97% and 82.26% at 3% NaCl, respectively. Meanwhile, 454-pyrosequencing technology was used to analyze the bacterial diversity of the sludge on the 240th day for stable operation of phase X. Results showed that a total of 9194 sequences were obtained, which could be affiliated to 14 phyla, including Proteobacteria, Firmicutes, Chlorobi, Bacteroidetes, Synergistetes and so on. Proteobacteria (77.66%) was the dominant microbial population, followed by Firmicutes (12.23%) and Chlorobi (2.71%).

Anaerobic granular sludge performance in an expanded granular sludge bed reactor treating calcium-rich wastewater by adjusting CaCO3 crystallization: Effect of upflow velocity and Ca2+ concentration.

The role of upflow velocity and Ca2+ concentration in controlling the type and rate of CaCO3 crystallization and their impacts on the anaerobic granular sludge (AnGS) formation and performance in an expanded granular sludge bed (EGSB) reactor were studied. The results showed that an improved upflow velocity could promote metastable CaCO3 crystals and achieve the optimized portion of vaterite with a value of 84 % at 10 m/h with a small amount of aragonite, thus limiting the scaling in the reactor. The removal efficiency of Ca2+ was to some extent positively correlated to the influent Ca2+ concentration, but declined when Ca2+ exceeded a specific threshold. Vaterite was dominant with the increase of Ca2+ concentrations of the influent. Compared with granules in R1 (Ca2+ 10 mg/L) and R2 (Ca2+ 100 mg/L), granules cultivated in R3 (Ca2+ 800 mg/L) revealed maximum amount of biomass with biggest particle size distribution and fastest average settling rate, with relative stable COD removal efficiency and the fast optimized reactor capacity at OLR of 16 kgCOD/m3d. A low upflow velocity and a higher Ca2+ concentration promoted nucleus formation and granules growth at the initial cultivation stage of the EGSB reactor. The Ca2+ concentration had a significant impact on the bacterial community and favoured the growth of Tolumonas and Anaeromousa Anaeroarcus. Archaea, rather than bacteria, was strengthened to contribute more to methane production at a relatively high Ca2+ concentration.

Long-term evaluating the strengthening effects of iron-carbon mediator for coking wastewater treatment in EGSB reactor.

Coking wastewater (CWW) treatment is difficult due to its complex composition and high biological toxicity. Iron-carbon mediators was used to enhance the treatment of CWW through iron-carbon microelectrolysis (ICME). The results indicated that the removal rate of COD and phenolic compounds were enhanced by 24.1 % and 23.5 %, while biogas production and methane content were promoted by 50 % and 7 %. Microbial community analysis indicated that iron-carbon mediators had a transformative impact on the reactor's performance and dependability by enriching microorganisms involved in direct and indirect electron transfer, such as Anaerolineae and Methanothrix. The mediator also produced noteworthy gains in LB-EPS and TB-EPS, increasing by roughly 109.3 % and 211.6 %, respectively. PICRISt analysis demonstrated that iron-carbon mediators effectively augment the abundance of functional genes associated with metabolism, Citrate cycle, and EET pathway. This study provides a new approach for CWW treatment.

Sequential bio-treatment of ammonia-rich wastewater from Chinese medicine residue utilization: Regulation of dissolved oxygen.

To effectively treat actual ammonia-rich Chinese medicine residue (CMR) resource utilization wastewater, we optimized an anaerobic-microaerobic two-stage expanded granular sludge bed (EGSB) and moving bed sequencing batch reactor (MBSBR) combined process. By controlling dissolved oxygen (DO) levels, impressive removal efficiencies were achieved. Microaeration, contrasting with anaerobic conditions, bolstered dehydrogenase activity, enhanced electron transfer, and enriched the functional microorganism community. The increased relative abundance of Synergistetes and Proteobacteria facilitated hydrolytic acidification and fostered nitrogen and phosphorus removal. Furthermore, we examined the impact of DO concentration in MBSBR on pollutant removal and microbial metabolic activity, pinpointing 2.5 mg/L as the optimal DO concentration for superior removal performance and energy conservation.