Study On Removal Characteristics Of Of Loxacin By A/O-MBR Process

The antibiotics residue in the environment, as one of pharmaceutically active substances(PhACs),has been paid more and more attention, due to their inverse effect on ecosystems andhuman health. Ofloxacin (OFL), one of the representatives of fluoroquinolone drug, is widelyused as a broad-spectrum antimicrobial agents.The residue OFL in the environment is one of theantibiotics which have the highest risk to the environment. Since ammonia oxidizing bacteria(AOB) in nitrification activated sludge (NAS) can produce ammonia monooxygenase (AMO) anddegrade some recalcitrant PhACs by cometabolism. In this paper, the short term effect of OFL onthe activity of NAS enriched by A/O-MBR reactor and the adsorption and degradation of OFL bythe NAS was investigated. And the removal of OFL in A/O-MBR at of different HRTconditions and the effect of OFL microbial communities in A/O-MBR was investigated.The enrichment of nitrifying activated sludge (NAS) was achieved by gradually increasingthe influent ammonia concentration of an A/O-MBR system at first. The results showed that theammonia oxidation rate of the enriched NAS could reach to20mg/gSS/h.Then the short term effect of OFL on the activity of NAS and the degradation and adsorptionof ofloxacin by NAS was investigated by batch test. The results showed that the activity of NASdid not change significantly when the concentration of OFL was500μgg/L and was inhibitedwhen the concentration of OFL was increased to500mg/L. MLSS, pH and temperature affectedthe adsorption of OFL by NAS significantly.The higher the concentration of MLSS was, the lowerthe adsorption of OFL by NAS was. But the total removal rate increased. The higher the pH was,the lower adsorption capcity of NAS was.This indicated that the high pH was adverse to theremoval of OFL.The higher the temperature was,the lower the adsorption capcity of NAS.Thisindicated that the adsorption of NAS on OFL is an exothermic reaction. Adsorption isotherms showed that the adsorption of OFL by NASfitted well with Freundlich model.The NAS had asignificant degradation of OFL. There was no obvious effect of COD on the removal of OFL whenthe allylthiourea (ATU) was added. Increasing the initial ammonia concentration and the ammoniaoxidation rate of NAS could increase the degradation amount of OFL. The degradation amount ofOFL increased from67.26μg/g to82.11μg/g with the increaseof the initial ammonia concentrationfrom50mg/L to150mg/L and ranged from30.71μg/g to75.16μg/g with the increase in theammonia oxidation rate from less than2.5mg/gSS/h to more than20mg/gSS/h.Finally, the effect of HRT on the removal of OFL and the effect of OFL on the microbialcommunities in the A/O-MBR was investigated. The results showed that the rejection ofmembrane and the biodegradation of OFL by NAS at anoxic condition can be neglected. Thehigher the HRT was, the lower the removal of OFL with the discharge of residual activated sludgeand the degradation rate was. The amount of the degradation of OFL in oxic tank was the highestwhen HRT was8h. Microbial communities in both MBR-control and the MBR-OFL reactormainly were Proteobacteria, Bacteroidetes at phylum level. The proportion of Nitrosomonas,Azohydromonas, Azospira, Aeromonas, Bdellovibrio, Nitrospira, Ferruginibacter, Pasteuria,Rhodopirellula, Planctomyces in the MBR-OFL reduced compared with the MBR-control at thegenus level.Diversity of microbial community in MBR-OFL is lower than that of MBR-control.