Impact of carbon/nitrogen ratio on the performance and microbial community of sequencing batch biofilm reactor treating synthetic mariculture wastewater.

The differences of cultured organism species, aquaculture model and supervisor mode lead to different carbon/nitrogen ratios in mariculture wastewater. Therefore, the performance, microbial community and enzymatic activity of sequencing batch biofilm reactor were compared in treating synthetic mariculture wastewater at different chemical oxygen demand/nitrogen (COD/N) ratios. Compared with COD/N ratio of 6, the ammonia-oxidizing rate and nitrite-oxidizing rate at COD/N ratio of 5, 4 and 3 increased by 3.66 % and 3.08 %, 11.19 % and 14.95 %, and 24.50 % and 32.54 %, respectively. Similarly, the ammonia monooxygenase and nitrite oxidoreductase activities increased by 3.50 % and 6.76 %, 11.09 % and 16.22 %, and 25.43 % and 39.19 % at COD/N ratio at 5, 4 and 3, respectively. However, the denitrifying rate and denitrification enzymatic activity declined with the decrease of C/N ratio from 6 to 3. The production, protein content and polysaccharide content of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) reduced with the decrease of COD/N ratio from 6 to 3. The abundance of nitrifying genera increased with the decrease of COD/N ratio from 6 to 3, whereas most of denitrification genera displayed a decreasing trend. The microbial co-occurrence pattern, keystone taxa and significant difference were altered with the decrease of COD/N ratio. Among the keystone taxa, Thauera, Denitromonas, Nitrosomonas and Denitratisoma had a close link with nitrogen transformation. The present results can provide some theoretical basis for evaluating the effect of carbon/nitrogen ratio on the nitrogen removal of biological wastewater treatment systems.

Effect of aerobic/anoxic duration on the performance, microbial activity and microbial community of sequencing batch biofilm reactor treating synthetic mariculture wastewater.

The effect of aerobic/anoxic duration on the performance, microbial community and enzymatic activity of sequencing batch biofilm reactor (SBBR) were investigated in treating mariculture wastewater. The microbial oxygen uptake rate and nitrifying rate gradually decreased with the aerobic/anoxic duration from 120/210 to 30/300 min, whereas the nitrite reducing rate and nitrate reducing rate had the opposite results. The activities of dehydrogenase, ammonia monooxygenase and nitrite oxidoreductase gradually decreased with the aerobic/anoxic duration from 120/210 to 30/300 min, but the activities of nitrate reductase and nitrite reductase had a gradual increment. The microbial nitrogen removal rates had similar changing trends to their corresponding enzymatic activities at different aerobic/anoxic duration. The variation of aerobic/anoxic duration obviously affected the microbial richness and diversity of SBBR. The co-occurrence, keystone taxa and significant difference of microbial community had some changes with the aerobic/anoxic duration from 120/210 to 30/300 min.

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 impacts of nickel and cadmium on the performance, microbial community and enzymatic activity of sequencing batch reactors.

The performance, microbial enzymatic activities and the microbial community of sequencing batch reactors (SBRs) were evaluated under the single and combined nickel (Ni2+) at 20 mg/L and cadmium (Cd2+) at 10 mg/L. The single and combined Ni2+ and Cd2+ had no adverse impacts on the COD removal, whereas the NH4+-N removal efficiency declined sharply from about 99% to 34.42% and 42.67% under the single Ni2+ and combined Ni2+ and Cd2+. Compared with the absence of Ni2+ or Cd2+, the specific oxygen uptake rate (SOUR), ammonia-oxidizing rate (SAOR), nitrite-oxidizing rate (SNOR), nitrite-reducing rate (SNIRR) and nitrate-reducing rate (SNRR) declined by 24.09%, 56.63%, 51.50%, 58.01% and 52.09% under the combined Ni2+ and Cd2+, which were slower than the sum of those under single Ni2+ and Cd2+. The dehydrogenase, ammonia monooxygenase, nitrite oxidoreductase, nitrate reductase and nitrite reductase activities showed the similar varying trends to the SOUR, SAOR, SNOR, SNIRR and SNRR, suggesting that the combined Ni2+ and Cd2+ displayed antagonistic inhibition on the nitrogen removal rates and microbial enzyme activities. The combined Ni2+ and Cd2+ declined the microbial diversity and richness less than the sum of those under single Ni2+ and Cd2+. The relative abundance of Nitrosomonas, Nitrospira and identified denitrifying bacteria displayed some changes under single and combined Ni2+ and Cd2+. These findings would contribute to better understand the combined impacts of multiple heavy metals on biological wastewater treatment systems.

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.

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.