Enhanced heterogeneous photo-Fenton-like degradation of tetracycline over CuFeO2/biochar catalyst through accelerating electron transfer under visible light.

The visible-light induced heterogeneous photo-Fenton-like (HPF-like) process is regarded as a promising technique for organic pollutants degradation due to its efficient utilization of solar energy and high H2O2 activation activity. This study prepared the CuFeO2/biochar catalysts via hydrothermal technique at no extra reductant and systematically investigated their band structure and photoelectric properties. The dispersed distribution of CuFeO2 particles in CuFeO2/biochar composites narrowed bandgap of CuFeO2 and promoted electron transport of CuFeO2. Compared with CuFeO2, the CuFeO2/biochar containing 1.0 g biochar in the preparation (CuFeO2/biochar-1.0) possessed higher carrier density and longer photoelectron lifetime, which is beneficial to higher catalytic performance. The apparent rate constant for tetracycline as target pollutant degradation by CuFeO2/biochar-1.0 was 2.0 times higher than that by CuFeO2. The acquired optimum conditions for tetracycline degradation were 220 mg L-1 CuFeO2/BC-1.0, 22 mM H2O2 and pH 6.4 using response surface methodology. The quenching experiments and ESR analysis revealed that OH was the predominant active species, and photoelectron and O2- were auxiliary species. The photoelectron could promote in-situ recycling of Cu2+ to Cu+ and Fe3+ to Fe2+, which significantly improved H2O2 activation by CuFeO2. The possible pathway of tetracycline was proposed according to intermediates identified by HPLC/MS. The toxicity analysis demonstrated that the overall toxicity of the identified intermediates was reduced in HPF-like system.

Photoelectrocatalytic degradation of p-chloronitrobenzene by g-C3N4/TiO2 nanotube arrays photoelectrodes under visible light irradiation.

As a typical refractory pollutant, p-chloronitrobenzene (p-CNB) from industrial wastewater poses a serious threat to the aquatic environment safety and human health. The photoelectrocatalytic (PEC) technology is regarded as a promising and cleaner approach for p-CNB removal. Therefore, the graphitic carbon nitride (g-C3N4) modified TiO2 nanotube arrays (g-C3N4/TNAs) were prepared as the photoelectrodes for p-CNB degradation. The PEC degradation efficiency for p-CNB by g-C3N4/TNAs (0.00484 min-1) was much higher than that by bare TNAs (0.00135 min-1) under visible light. The g-C3N4/TNAs photoelectrodes exhibited excellent visible-light response, efficient charges separation and high redox potentials of electron/hole, which was favorable for p-CNB degradation. The radical scavenging experiments indicated that both reductive electrons and oxidized species (holes and ·OH) played crucial roles simultaneously during the dechlorination process, whereas the mineralization of p-CNB mainly depended on the photo-generated holes and ·OH. The degradation pathways of p-CNB were proposed through GC/MS spectra. The acute toxicity, bioaccumulation factor and mutagenicity of identified intermediates were reduced after PEC degradation by g-C3N4/TNAs photoelectrodes. The Z-scheme g-C3N4/TNAs provided an efficient approach for simultaneous dechlorination and mineralization of refractory pollutants.

Effects of aluminum oxide nanoparticles on the performance, extracellular polymeric substances, microbial community and enzymatic activity of sequencing batch reactor.

The performance, pollutant removal rate, microbial community and enzymatic activity of a sequencing batch reactor (SBR) were investigated under oxide nanoparticles (Al2O3 NPs) stress. Al2O3 NPs at 0-50 mg/L showed no evident impact on the COD and NH4 + removals of SBR. The oxygen-uptake rate, nitrifying rate and nitrite-reducing rate slightly diminished with the increase of Al2O3 NPs concentration. Compared with 0 mg/L Al2O3 NPs, the dehydrogenase activity declined by 23.52% at 50 mg/L Al2O3 NPs. The activities of ammonia monooxygenase, nitrite oxidoreductase and nitrite reductase decreased with the increase of Al2O3 NPs concentration from 0 to 50 mg/L Al2O3 NPs. However, the nitrate reductase (NR) activity slightly increased at 5 and 15 mg/L Al2O3 NPs and declined at 30 and 50 mg/L Al2O3 NPs. The microbial reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release merely raised 14.80% and 20.72% at 50 mg/L Al2O3 NPs by contrast with 0 mg/L Al2O3 NPs, respectively. Al2O3 NPs enhanced the production, protein content and polysaccharide content of extracellular polymeric substances owing to preventing the microbes from Al2O3 NPs biotoxicity. The existence of Al2O3 NPs led to the variations of microbial richness and diversity in the SBR due to their biotoxicity.

Single and combined effects of divalent copper and hexavalent chromium on the performance, microbial community and enzymatic activity of sequencing batch reactor.

Divalent copper (Cu2+) and hexavalent chromium (Cr6+) are often encountered in industrial wastewater and municipal wastewater, the effect of combined Cu2+ and Cr6+ on biological wastewater treatment systems has cause wide concern. In the present research, the performance, microbial community and enzymatic activity of sequencing batch reactors (SBRs) were compared under the single and combined Cu2+ at 20 mg/L and Cr6+ at 10 mg/L. The chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) removal efficiencies under the combined Cu2+ and Cr6+ were less than those under the single Cu2+ and Cr6+. The combined Cu2+ and Cr6+ displayed more inhibition effects on the oxygen uptake rate, nitrification rate and denitrification rate of activated sludge than the single Cu2+ and Cr6+. The inhibitory effects of the combined Cu2+ and Cr6+ on the activities of dehydrogenase, ammonia monooxygenase, nitrite oxidoreductase, nitrite reductase and nitrate reductase showed significant increases by comparison with the single Cr6+. However, the combined Cu2+ and Cr6+ had a little more inhibitory effects on the enzymatic activities than the single Cu2+. The microbial richness and diversity displayed some obvious changes under the single and combined Cu2+ and Cr6+ by comparison the absence of Cu2+ and Cr6+. The relative abundances of nitrifying genera (e.g. Nitrosomonas and Nitrospira) under the combined Cu2+ and Cr6+ was less than those under the single Cu2+ and Cr6+. These findings will be helpful to better understand the combined effects of multiple heavy metals on biological wastewater treatment systems.

Insights into the effects of single and combined divalent copper and humic acid on the performance, microbial community and enzymatic activity of activated sludge from sequencing batch reactor.

The performance, microbial community and enzymatic activity of activated sludge from four identical sequencing batch reactors (SBRs) were compared by treating synthetic wastewater under the single and combined divalent copper (Cu2+) at 20 mg/L and humic acid (HA) at 20 mg/L. Compared with the absence of Cu2+ and HA, the single HA slightly enhanced the oxygen uptake rate (OUR), the nitrification and denitrification rates and the activities of dehydrogenase, nitrifying enzymes and denitrifying enzymes, whereas the single Cu2+ had the opposite results. The combined Cu2+ and HA inhibited the OUR, nitrogen removal rate and enzymatic activity of activated sludge almost the same as the single Cu2+. The single HA had no obvious effect on the balance between the microbial oxidative stress and antioxidant activity. However, the variations of microbial reactive oxygen species production, peroxidase activity, catalase activity, superoxide dismutase activity, and lactate dehydrogenase release demonstrated that the combined Cu2+ and HA and single Cu2+ produced obvious toxicity to microorganisms in activated sludge. The microbial richness and diversity had some obvious changes under the single and combined Cu2+ and HA. The relative abundances of Nitrosomonas, Nitrospira and some denitrifying genera (e.g. Zoogloea, Dokdonella, Denitratisoma, Flavobacterium and Thermomonas) under the combined Cu2+ and HA were less than those under the single Cu2+.

Effects of transient 3-chloroaniline shock loading on the performance, microbial community and enzymatic activity of sequencing batch reactor.

Chloroanilines from industrial wastewater can produce adverse effects on biological wastewater treatment systems due to their potential biotoxicity. The performance, nitrogen removal rate, microbial community and enzymatic activity of a sequencing batch reactor (SBR) were evaluated under transient 3-chloroaniline shock loading. After 40 mg/L 3-chloroaniline shock loading of 24 h on day 9, the chemical oxygen demand (COD) removal efficiency decreased from 90.71% on day 8 to 80.57% on day 11, and the NH4+-N removal efficiency reduced from 98.96% on day 8 to 35.51% on day 12. Subsequently, the COD and NH4+-N removal efficiencies gradually recovered to normal value. Compared with the absence of 3-chloroaniline shock loading, the ammonia-oxidizing rate (SAOR), nitrite-oxidizing rate (SNOR), nitrite-reducing rate (SNIRR) and nitrate-reducing rate (SNRR) decreased by 66.19%, 14.49%, 16.20% and 49.38% on day 11, respectively, and then they gradually recovered to normal value. The SAOR, SNOR, SNIRR and SNRR displayed the similar varying trends to the activities of ammonia monooxygenase, nitrite oxidoreductase, nitrite reductase and nitrate reductase, respectively. The appearance of 3-chloroaniline promoted the microbial reactive oxygen species production and lactate dehydrogenase release. The transient 3-chloroaniline shock loading distinctly impacted the microbial richness and diversity. The present research results can provide theoretical basis and technical support for evaluating the effects of transient 3-chloroaniline shock on biological wastewater treatment systems, which is beneficial to take reasonable preventable measures to decrease the adverse effects on the bioreactor performance.

Size-dependent effects of ZnO nanoparticles on performance, microbial enzymatic activity and extracellular polymeric substances in sequencing batch reactor.

ZnO nanoparticles (NPs) have been detected in various wastewater treatment plants. It is widely assumed that size has a crucial effect on the NPs toxicity. Concerns have been raised over probable size-dependent toxicity of ZnO NPs to activated sludge, which could eventually affect the treatment efficiencies of wastewater treatment facilities. The size-dependent influences of ZnO NPs on performance, microbial activities, and extracellular polymeric substances (EPS) from activated sludge were examined in sequencing batch reactor (SBR) in present study. Three different sizes (15, 50, and 90 nm) and five concentrations (2, 5, 10, 30, and 60 mg L-1) were trialled. The inhibitions on COD and nitrogen removal were determined by the particle size, and smaller ZnO NPs (15 nm) showed higher inhibition effect than those of 50 and 90 nm, whereas the ZnO NPs with size of 50 nm showed maximum inhibition effect on phosphorus removal among three sizes of ZnO NPs. After exposure to different sized ZnO NPs, microbial enzymatic activities and removal rates of activated sludge represented the same trend, consistent with the nitrogen and phosphorus removal efficiency. In addition, apparent size- and concentration-dependent effects on EPS contents and components were also observed. Compared with the absence of ZnO NPs, 60 mg L-1 ZnO NPs with sizes of 15, 50, and 90 nm increased the EPS contents from 92.5, 92.4, and 92.0 mg g-1 VSS to 277.5, 196.8, and 178.2 mg g-1 VSS (p < 0.05), respectively. The protein and polysaccharide contents increased with the decreasing particle sizes and increasing ZnO NPs concentrations, and the content of protein was always higher than that of polysaccharide.

Long-term effect of different Cu(II) concentrations on the performance, microbial enzymatic activity and microbial community of sequencing batch reactor.

The performance, microbial community and enzymatic activity of sequencing batch reactors (SBRs) were investigated under 75-day exposure of different Cu(II) concentrations. Cu(II) at 0-5 mg/L had no distinct impact on the chemical oxygen demand (COD) and nitrogen removal, oxygen-uptake rate (OUR), nitrification and denitrification rate, and microbial enzymatic activity. The inhibitory effects of Cu(II) at 10 and 30 mg/L on the nitrogen removal rate, OUR, and microbial enzymatic activity of SBR increased with an increment in operation time due to the Cu(II) biotoxicity and the Cu(II) accumulation in activated sludge. The changes of microbial reactive oxygen species production, lactate dehydrogenase release, catalase activity and superoxide dismutase activity demonstrated that Cu(II) at 10 and 30 mg/L broke the equilibrium between the oxidation and antioxidation processes in microbial cells and also damaged the cytomembrance integrity, which could affect the COD and nitrogen removal performance and change normal microbial cell morphology. The Cu(II) in the influent could be removed by the microbial absorption and accumulated in the activated sludge under long-term exposure. The microbial community displayed some distinct changes from 0 to 30 mg/L Cu(II). In contrast with 0 mg/L Cu(II), Nitrosomonas, Nitrospira and some denitrifying bacteria obviously decreased in relative abundance under long-term exposure of 10 and 30 mg/L Cu(II).

Insights into long-term effects of amino-functionalized multi-walled carbon nanotubes (MWCNTs-NH2) on the performance, enzymatic activity and microbial community of sequencing batch reactor.

Carbon nanotubes (CNTs) inevitably enter domestic sewage and industrial wastewater with the continuous increase of their production and application field. The potential effect of CNTs on biological wastewater treatment processes has raised wide concerns due to their biotoxicity. In the present study, the performance, microbial community and enzymatic activity of sequencing batch reactors (SBRs) were evaluated under 148-day exposure of amino-functionalized multi-walled CNTs (MWCNTs-NH2) at 10 and 30 mg/L. The COD removal efficiency at 10 and 30 mg/L MWCNTs-NH2 gradually reduced from 91.03% and 90.43% on day to 89.11% and 86.70% on day 148, respectively. The NH4+-N removal efficiency at 10 and 30 mg/L MWCNTs-NH2 gradually reduced from 98.98% and 98.46% on day 1 to 96.65% and 63.39% on day 148, respectively. Compared to 0 mg/L MWCNTs-NH2, the oxygen-utilizing rate, ammonia-oxidizing rate, nitrite-oxidizing rate, nitrite-reducing rate and nitrate-reducing rate at 30 mg/L MWCNTs-NH2 were decreased by 52.35%, 60.58%, 55.12%, 56.56% and 57.42% on day 148, respectively. The microbial reactive oxygen species and lactate dehydrogenase release on day 148 was increased by 59.71% and 55.28% at 30 mg/L MWCNTs-NH2, respectively. The key microbial enzymatic activity related to nitrogen removal decreased with the increase of operation time under MWCNTs-NH2 stress. The relative abundances of Nitrosomonas, Nitrosospira, Nitrospira and some denitrifying bacteria at 10 mg/L MWCNTs-NH2 gradually reduced with an increment in operation time. The changes of nitrogen removal rate, microbial community and enzymatic activity of SBR were related to the time-cumulative nonlinear inhibition effect under long-term exposure.

Insights into the effect of nickel (Ni(II)) on the performance, microbial enzymatic activity and extracellular polymeric substances of activated sludge.

The performance, nitrogen removal rate, microbial enzymatic activity and extracellular polymeric substances (EPS) of activated sludge were assessed under nickel (Ni(II)) stress. The organic matter and NH4+-N removal efficiencies were stable at less than 10 mg/L Ni(II) and subsequently decreased with the increment of Ni(II) concentration from 10 to 30 mg/L. The specific oxygen uptake rate and dehydrogenase activity kept stable at less than 5 mg/L Ni(II) and then declined at 5-30 mg/L Ni(II). Both specific ammonia-oxidizing rate (SAOR) and specific nitrite-oxidizing rate (SNOR) decreased with the increment of Ni(II) concentration. The changing trends of ammonia monooxygenase and nitrite oxidoreductase activities were matched those of SAOR and SNOR, respectively. The nitrite-reducing rate and nitrate-reducing rate illustrated a similar variation tendency to the nitrite reductase activity and nitrate reductase activity, respectively. Ni(II) impacted on the production, chemical composition and functional group of EPS. The relation between the sludge volume index and the EPS production exhibited a better linear function with a negative slope, demonstrating that Ni(II) improved the sludge settleability despite of the increase of EPS production.

Long-term impacts of carboxyl functionalized multi-walled carbon nanotubes on the performance, microbial enzymatic activity and microbial community of sequencing batch reactor.

The performance, microbial community and enzymatic activity of sequencing batch reactors (SBRs) were evaluated under long-term exposure of 0, 10 and 30 mg/L carboxyl functionalized multi-walled carbon nanotubes (MWCNTs-COOH). The presence of 10 mg/L MWCNTs-COOH displayed no adverse impacts on the COD and NH4+-N removal of SBR, whereas 30 mg/L MWCNTs-COOH declined the COD and NH4+-N removal. MWCNTs-COOH inhibited the denitrifying process and led to the accumulation of effluent NO2--N concentration. The inhibition of MWCNTs-COOH on the oxygen utilization rate, nitrogen removal rate and enzymatic activity of activated sludge gradually enhanced with the increase of operating time and influent MWCNTs-COOH concentration. MWCNTs-COOH stimulated more reactive oxygen species production and lactate dehydrogenase release, which might affect the microbial physiological functions and morphology. The microbial diversity and richness was declined evidently after long-term exposure of MWCNTs-COOH. The relative abundance of nitrifying and denitrifying bacteria showed some changes under MWCNTs-COOH stress.

Impact of ampicillin on the nitrogen removal, microbial community and enzymatic activity of activated sludge.

The performance, nitrogen removal rate, extracellular polymeric substances (EPS), microbial community and enzymatic activity of activated sludge have been assessed in a sequencing batch reactor under ampicillin stress. The chemical oxygen demand and ammonia removal kept relatively stable at 0-30 mg/L ampicillin. No obvious nitrite and nitrate accumulation was found in the effluent. However, the oxygen utilization rate, nitrification rate and denitrification rate declined with the increment of ampicillin concentration. The activities of dehydrogenase and microbial enzymes relating to nitrogen removal were inhibited under ampicillin stress. Ampicillin at 20 and 30 mg/L heightened the microbial lactate dehydrogenase release and reactive oxygen species production. Ampicillin promoted the production of EPS, loosely bound EPS and tightly bound EPS and affected their chemical composition. Additionally, the protein/polysaccharide ratios in the EPS and the sludge settleability reduced with the increment of ampicillin concentration. Ampicillin obviously affected the relative abundance of nitrifying- and denitrifying bacteria.

Effect of magnesium oxide nanoparticles on microbial diversity and removal performance of sequencing batch reactor.

The performance, microbial enzymatic activity and microbial community of a sequencing batch reactor (SBR) have been explored under magnesium oxide nanoparticles (MgO NPs) stress. The NH4+-N removal efficiency kept relatively stable during the whole operational process. The MgO NPs at 30-60 mg/L slightly restrained the removal of chemical oxygen demand (COD), and the presence of MgO NPs also affected the denitrification and phosphorus removal. The specific oxygen uptake rate, nitrifying and denitrifying rates, phosphorus removal rate, and microbial enzymatic activities distinctly varied with the increase of MgO NPs concentration. The appearance of MgO NPs promoted more reactive oxygen species generation and lactate dehydrogenase leakage from activated sludge, suggesting that MgO NPs had obvious toxicity to activated sludge in the SBR. The protein and polysaccharide contents of extracellular polymeric substances from activated sludge increased with the increase of MgO NPs concentration. The microbial richness and diversity at different MgO NPs concentrations obviously varied at the phylum, class and genus levels due to the biological toxicity of MgO NPs.

Performance evaluation and microbial community shift of a sequencing batch reactor under silica nanoparticles stress.

The performance, microbial community and enzymatic activity of a sequencing batch reactor (SBR) were evaluated at different silica nanoparticles (SiO2 NPs) concentrations. SiO2 NPs concentration at 5-30mg/L had a slight inhibitory impact on the nitrogen and COD removals, whereas the phosphorus removal was obviously inhibited at 30mg/L SiO2 NPs. The rates of nitrification, nitrite reduction and phosphorus removal decreased with the increase of SiO2 NPs concentration. The nitrate reduction rate decreased at less than 5mg/L SiO2 NPs and subsequently showed an increase at 10-30mg/L SiO2 NPs. The organic matter, nitrogen and phosphorus removal rates had similar varying tendencies to the corresponding microbial enzymatic activities under SiO2 NPs stress. Some SiO2 NPs were firstly absorbed on sludge surface and subsequently entered the interior of the microbial cells, which could exert the biological toxicity to activated sludge. The microbial community showed some obvious variations under SiO2 NPs stress.

Impacts of silver nanoparticles on performance and microbial community and enzymatic activity of a sequencing batch reactor.

The performance, microbial community and enzymatic activity of a sequencing batch reactor (SBR) were evaluated under silver nanoparticles (Ag NPs) stress. Over 5 mg/L Ag NPs inhibited the COD and phosphorus removals, whereas the NH4+ removal kept stable during the whole operational period. The organic matter, nitrogen and phosphorus removal rates were obviously inhibited under Ag NPs stress, which showed similar varying trends with the corresponding microbial enzymatic activities. The change of Ag content in the activated sludge indicated that some Ag NPs were absorbed by the sludge. The presence of Ag NPs promoted the increase of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) of microorganism due to the microbial response to the Ag NPs toxicity, which could impact on the microbial morphology and physiological functions. The presence of Ag NPs could produce some evident changes in the microbial community.

Long-term impacts of titanium dioxide nanoparticles (TiO2 NPs) on performance and microbial community of activated sludge.

The long-term impacts of titanium dioxide nanoparticles (TiO2 NPs) on the performance and microbial community of activated sludge were evaluated in a sequencing batch reactor (SBR). TiO2 NPs impacted the COD and phosphorus removals of activated sludge, whereas the NH4+-N removal efficiency had no distinct change at 0-60mg/L TiO2 NPs. The presence of TiO2 NPs obviously inhibited the organic matter and nitrogen removal rates of activated sludge. The phosphorus removal rate gradually reduced at 0-5mg/L TiO2 NPs and then increased at 10-60mg/L TiO2 NPs. The removal rates of organic matter, nitrogen and phosphorus had the similar varying trends to the corresponding microbial enzymatic activities. High TiO2 NPs concentration promoted more reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release of activated sludge. The microbial richness and diversity of activated sludge were obviously affected at the phyla, class and genus levels.

Magnetic Fe3O4 nanoparticles induced effects on performance and microbial community of activated sludge from a sequencing batch reactor under long-term exposure.

The performance and microbial community of activated sludge from a sequencing batch reactor (SBR) were investigated under long-term exposure of magnetic Fe3O4 nanoparticles (Fe3O4 NPs). The COD removal showed a slight decrease at 5-60mg/L Fe3O4 NPs compared to 0mg/L Fe3O4 NPs, whereas the NH4+-N removal had no obvious variation at 0-60mg/L Fe3O4 NPs. It was found that 10-60mg/L Fe3O4 NPs improved the denitrification process and phosphorus removal of activated sludge. The microbial enzymatic activities of activated sludge could be affected by Fe3O4 NPs, which had similar variation trends to the nitrogen and phosphorus removal rates of activated sludge. The reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release demonstrated that Fe3O4 NPs led to the toxicity to activated sludge and destroyed the integrity of microbial cytomembrane. High throughput sequencing indicated that Fe3O4 NPs could obviously affect the microbial richness and diversity of activated sludge.

Long-term effects of cupric oxide nanoparticles (CuO NPs) on the performance, microbial community and enzymatic activity of activated sludge in a sequencing batch reactor.

The long-term effects of cupric oxide nanoparticles (CuO NPs) on the performance, microbial activity and microbial community of activated sludge were investigated in a sequencing batch reactor (SBR). The SBR performance had no evident change at 0-10 mg/L CuO NPs, whereas the CuO NPs concentration at 30-60 mg/L affected the COD, NH4+-N and soluble orthophosphate (SOP) removal, nitrogen and phosphorus removal rate and microbial enzymatic activity of activated sludge. Some CuO NPs might be absorbed on the surface of activated sludge or penetrate the microbial cytomembrane into the microbial cell interior of activated sludge. Compared to 0 mg/L CuO NPs, the reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release increased by 43.6% and 56.4% at 60 mg/L CuO NPs, respectively. The variations of ROS production and LDH release demonstrated that CuO NPs could induce the toxicity towards the microorganisms and destroy the integrity of microbial cytomembrane in the activated sludge. High throughput sequencing of 16S rDNA indicated that CuO NPs could evidently impact on the microbial richness, diversity and composition of activated sludge in the SBR.

Long-term effects of nickel oxide nanoparticles on performance, microbial enzymatic activity, and microbial community of a sequencing batch reactor.

The nitrogen and phosphorus removal, microbial enzymatic activity, and microbial community of a sequencing batch reactor (SBR) were evaluated under long-term exposure to nickel oxide nanoparticles (NiO NPs). High NiO NP concentration (over 5 mg L-1) affected the removal of chemical oxygen demand, nitrogen, and phosphorus. The presence of NiO NP inhibited the microbial enzymatic activities and reduced the nitrogen and phosphorus removal rates of activated sludge. The microbial enzymatic activities of the activated sludge showed a similar variation trend to the nitrogen and phosphorus removal rates with the increase in NiO NP concentration from 0 to 60 mg L-1. The Ni content in the effluent and activated sludge showed an increasing trend with the increase in NiO NP concentration. Some NiO NPs were absorbed on the sludge surface or penetrate the cell membrane into the interior of microbial cells in the activated sludge. NiO NP facilitated the increase in reactive oxygen species by disturbing the balance between the oxidation and anti-oxidation processes, and the variation in lactate dehydrogenase demonstrated that NiO NP could destroy the cytomembrane and cause variations in the microbial morphology and physiological function. High-throughput sequencing demonstrated that the microbial community of SBR had some obvious changes at 0-60 mg L-1 NiO NPs at the phyla, class and genus levels.