Performance And Mechanism Of Mesophilic Anaerobic Sequencing Batch Reactor For Cefotaxime Sodium Pharmaceutical Wastewater Treatment

Antibiotic pharmaceutical wastewater contains high concentrations of residual antibiotics in addition to high concentrations of conventional organic pollutants,which may induce the production of antibiotic resistance genes（ARG）and resistant bacteria（ARB）in its biological treatment and after discharge to the environment,which in turn may lead to novel contamination.Anaerobic sequencing batch reactor（AnSBR）has the characteristics of complete mixing in space,push flow in time,flexible operation,methane energy recovery,and methanogenic bacteria,such as archaea,have the potential advantage of toleratingβ-lactam antibiotics because their cell wall structure is significantly different from that of bacteria.Therefore,this study focused on the mesophilic AnSBR process to treat cefotaxime sodium（CTS,a third-generation semi-syntheticβ-lactam antibiotic）pharmaceutical wastewater,firstly to investigate the interaction mechanism between CTS and anaerobic activated sludge through short-term anaerobic batch tests,and then to investigate the efficacy of mesophilic AnSBR in treating simulated CTS pharmaceutical wastewater and the recovery of inhibited anaerobic sludge by granular activated carbon in long-term tests.Finally,macrogenomic analysis of the anaerobic sludge was carried out to analyze the distribution of microflora and ARG.The main research results were obtained as follows.The short-term anaerobic batch test showed that the hydrolysis of CTS in pure water was by quasi primary kinetics,and the hydrolysis rate was positively correlated with temperature,suspended matter,organic matter,and inorganic salts.After 36 h of exposure at 35°C and different solution environments,the CTS removal rate in the anaerobic activated sludge group reached 94.4%,which was significantly higher than that in the inactivated sludge group;the CTS removal rate in the inactivated sludge group was higher than that in the simulated water distribution group due to the high concentration of suspended matter;the CTS removal rate in the simulated water distribution containing organic matter and inorganic salts was higher than that in the pure water.CTS at 10 mg/L～1000mg/L had a negative effect on anaerobic sludge activity,and the methane production was 47.0%～91.0%of that of the control group without CTS,respectively.Fe₃O₄ powder can effectively enhance the anaerobic digestion process,and the higher the concentration the better the enhancement effect,but it is not suitable for AnSBR because it is difficult to settle and cannot be retained in the reactor for a long time.Granular activated carbon at 1 g/L increased the methane production of anaerobic sludge inhibited by CTS by 9.4%～55.7%on average,but failed to fully restore the anaerobic sludge activity in the short term.The long-term operation test of the mesophilic AnSBR pilot showed that the treatment efficiency was not significantly affected by the addition of 10 mg/L CTS.The COD removal rate at the end of each stage gradually decreased after the sequential injection of 50 mg/L,100 mg/L,200 mg/L,and 500 mg/L CTS;the methane conversion rate could be restored to about 70%after different degrees of influence,and the equivalent COD percentage of effluent VFAs was below 10%,which showed that the low and medium concentrations of CTS mainly inhibited the methanogenic process indirectly by directly inhibiting acid-producing bacteria.CTS at 800 mg/L and 1000 mg/L had a destructive effect on the methanogenic process of AnSBR,and the COD removal rate and methane conversion rate decreased to 30.59%and 2.10%at the lowest,and the equivalent COD of effluent VFAs reached 20%～55%,indicating that the activity of methanogenic bacteria was also inhibited under the high concentration of CTS.The CTS concentration in the AnSBR effluent was lower than the detection limit after the addition of 10mg/L～100 mg/L CTS.The CTS removal rate could reach more than 97.8%at the stage of 200 mg/L～1000 mg/L.The COD removal rate and methane conversion rate in the AnSBR,which was destructively affected by 1000 mg/L CTS,were partially restored by the addition of 1 g/L granular activated carbon,but the microbial activity was not completely restored in the short term.Macrogenomic analysis of AnSBR inoculated sludge,domesticated sludge,and sludge at the end of stage VII showed that the domestication stage contributed to the enrichment of the main functional microflora for anaerobic digestion.CTS was more effective in inhibiting Bacteroides and Gram-negative bacteria and less effective in inhibiting Archaea and Gram-positive bacteria,which is consistent with the inhibition of the hydrolytic acidification process in AnSBR at low and medium concentrations of CTS.This is consistent with the inhibition of the hydrolytic acidification process of AnSBR at a low concentration of CTS.The microbial diversity,total ARG,and ARG subtype species of the domesticated sludge increased compared to the inoculated sludge,while the stage VII end sludge decreased compared to the domesticated sludge,and the efflux pump was the main antibiotic resistance mechanism of the anaerobic sludge.Moreβ-lactam ARG isoforms were induced in sludge after CTS dosing.Methanogenic bacteria as archaea became the dominant genus at stage VII with 18.234%.