Biodegradation-transformation Rules Of Typical Pharmaceutical Pollutants In Municipal Sewage At Anaerobic,Anoxic And Aerobic Conditions

Pharmaceutical pollutants, existing in aquatic environment as trace contaminants with characteristics of environmental stability, refractory and bioaccumulation, can cause potential irreversible hazards to ecological environment and human health while long-term exposure of humans and animals. Municipal sewage treatment plants, as the "sink" of urban sewage and potential pollutant "source" of aqueous environment, play very important roles in the removal of common pollutants. Reversed A2/O (anoxic-anaerobic-aerobic) process, as a common process in the activated sludge treatment system, is used widely in sewage treatment plants because of consise technological process and good removal efficiency of pollutants. However, the research work for the removal of pharmaceutical contaminants in the sewage has just begun. Therefore, it is necessary to establish a sewage treatment process with good removal results for pharmaceutical pollutants and conventional contaminants simultaneously.The subject selects four prevalent pharmaceutical pollutants in urban sewage, phenacetin, gemfibrozil, caffeine, and diclofenac acid as the objectives, and uses the real wastewater coming from our university as the influent to examine biodegradable rules of the target compounds under anoxic, anaerobic and aerobic conditions through a simulated reversed A2/O process laboratory setup. Key factors about microbial degradation of pharmaceutical pollutants could be found through the parameters experiments of hydraulic retention time (HRT), temperature (℃), sludge recycle ratio (%) and initial concentration (mg/L) of the pharmaceuticals, and also optimize the biological treatment process conditions to improve biodegradation efficiency of pharmaceutical pollutants in urban sewage. Moreover, the subject carries out batch experiments to examine the biological removal pathway of four target drugs.Experimental study proved that phenacetin was most likely to be microbial degradation in four medical pollutants. When hydraulic retention time was16h, average removal rate of phenacetin by microorganism was more than90%, and the average removal of caffeine reached85%. Biodegradations of phenacetin and caffeine were fitted with first order reaction kinetics with the change of initial pharmaceutical concentrations. Removal of gemfibrozil was main sludge adsorption and also had biodegradation, and dynamic adsorption-desorption existed in the sewage. Diclofenac as the most difficult target to remove, its average removal was56%. Compared with50%of sludge recycle ratio, removal rates of phenacetin and caffeine improved10%under100%of the sludge recycle ratio. The study also showed that phenacetin, caffeine and diclofenac had the best removal efficiencies under aerobic condition, and gemfibrozil had the best removal under anaerobic condition.The study could provide theoretical and practical basis for the better utilization of microorganism in removing pharmaceutical contaminants in urban sewage, and further reduce the risk and potential harm of pharmaceutical pollutants to human health and water environment.