Study On The Treatment Of Simulated Benzothiazole Contaminated Wastewater By An Anaerobic Granular Sludge Membrane Bioreactor

Benzothiazole(BTH)is a polar heterocyclic compound that contains a benzene ring and a thiazole ring,which is the leading skeleton and mother of organic compounds.Due to the high biological activity,BTH is widespread used in the fields of medicine,pesticide and industry.The limited biodegradability,the potential danger of toxicities and mutagenic effects of BTH could inhibite the activity of microbe,and then influence the efficiency of wastewater treatment.The treatment of BTH wastewater by anaerobic membrane bioreactors can not only generate a large number of energy gas methane,but also reduce the antibiotics resistance bacteria and antibiotics resistance genes which transferred to other water bodies.In this study,an improved anaerobic granular sludge membrane bioreactor was used to treat synthetic benzothiazole contaminated wastewater.This study investigated the impact of acclimation process,the change of hydraulic retention time(HRT)and temperature on the performance,membrane fouling and microbial community structures.The removal pathway and removal kinetics of BTH were investigated by batch experiment.In order to improve the efficiency of organics,the start-up and acclimation phases were completed at the condition of chemical oxygen demand(COD)of 3151±162 mg/L,HRT of 24 h at 35°C.After the operation of 58 d,the bioreactor had been successfully start-up.The COD removal efficiency was 95.6±0.4%.The accumulation of total volatile fatty acids(t VFAs)was 10.86±2.09 mg/L.The biogas production was 12.74±0.40 L/d and the methane content was 69.3±0.9%.The cycle of membrane fouling was 5.9 d.The sludge was acclimated by gradually increasing the concentration of BTH.After the operation of 127 d,the removal efficiencies of COD and BTH were 93.6±0.6% and 97.6±0.5%.The accumulation of t VFAs was 57.83±13.81 mg/L.The biogas production was 10.74±0.40 L/d and the methane content was 70.9±0.7%.The cycle of membrane fouling was 5.3 d.The batch experiment showed that the biological removal was the main removal pathway of BTH,and the removal dynamics abided by the first-order kinetics model(R2=0.9898).The biological removal efficiency of BTH increased from 27.8% to 98.1% by the acclimation process.After start-up and acclimation phases,the effects of different HRTs(24 h,18 h and 12 h)and temperature(35°C,25°C and 15°C)on the performance and membrane fouling were investigated.The optimum operating parameter of the reactor was found.The results showed that the performance was the best when HRT was 24 h and the temperature was 35°C.The shortening HRT had obvious effects on BTH removal efficiency and the cycle of membrane fouling,and the effect on methane yield was little.With the decreasing HRT,the COD removal efficiency dropped from 93.6±0.6% to 90.9±0.9%.The BTH removal efficiency decreased from 97.6±0.5% to 82.3±3.7%.The accumulation of t VFAs increased from 57.83±13.81 mg/L to 171.05±10.89 mg/L.The biogas production increased from 10.74±0.40 L/d to 21.49±1.26 L/d.The methane content fluctuated from 69.3±1.6% to 73.5±2.1%,and the methane yields were at 0.309±0.014 m3CH4/kg CODremoval to 0.327±0.028 m3CH4/kg CODremoval.The cycle of membrane fouling decreased from 5.3 d to 3.2 d.The drop of temperature had adverse effects on the performance and membrane fouling.With the decreasing temperature,the COD removal efficiency dropped from 93.4±0.9% to 86.0±1.5%,and the BTH removal efficiency dropped from 97.6±0.5% to 48.4±4.0%.The accumulation of t VFAs increased from 57.57±11.11 mg/L to 283.23±27.96 mg/L.The biogas production decreased from 11.24±0.83 L/d to 7.64±0.76 L/d.The methane content decreased from 72.4±1.7% to 48.2±4.1%,and the methane yields decreased from 0.302±0.026 m3CH4/kg CODremoval to 0.184±0.024 m3CH4/kg CODremoval.The cycle of membrane fouling decreased from 5.2 d to 2.5 d.According to the different phases of the reactor,microbial community structures were compared.The microbial community structures had obvious differences in the start-up phase and acclimation phase.The dominant phylum of bacteria in start-up phase and acclimation phase was Firmicutes,and the relative abundance were 67.3% and 41.4%.The dominant genera of bacteria changed from Trichococcus(43.1%)to Clostridium(23.9%).The dominant genus of archaea was Methanosaeta,and the relative abundance were 90.3% and 80.8%.In the different conditions of HRTs,the dominant phylum of bacteria was Firmicutes in proportion of 41.4%(HRT 24 h),27.8%(HRT 18 h)and 28.5%(HRT 12 h).The dominant genus of bacteria was Clostridium in proportion of 23.9%(HRT 24 h),16.4%(HRT 18 h)and 15.3%(HRT 12 h).The dominant genus of archaea was Methanosaeta in proportion of 80.6%(HRT 24 h),91.9%(HRT 18 h)and 91.2%(HRT 12 h).The microbial community structures had large influences by the change of temperature.Under the conditions of 35°C and 25°C,the dominant phylum of bacteria was Firmicutes in proportion of 33.4% and 49.5%.The dominant phylum of bacteria was Chloroflexi(26.6%)at 25°C.The dominant genera were Clostridium(35°C),Levilinea(25°C)and Lactococcus(15°C)in proportion of 10.8%,15.2% and 17.9%.The dominant genus of archaea was Methanosaeta in proportions of 94.2%(35 °C),83.1%(25 °C)and 98.3%(15 °C).