Study On The Removal Efficiency Of Antibiotics In Wastewater By A/O-MBR

The main source of antibiotics in wastewater is the hospital.In this paper,the concentration of antibiotics in hospital wastewater is taken as the research background.Hospital wastewater contains a large amount of active ingredients,and antibiotics are an important part of the active ingredients.Hospital wastewater is discharged into the urban sewage treatment plant though the municipal pipe network,which would result in serious penetration of antibiotics in the wastewater plant and the emergence and transmission of resistance genes,leading to a high environmental risk.Therefore,the reduction of antibiotics in hospital wastewater is very important to achieve good antibiotic removal at the source.In this study,we selected four kinds of antibiotics as the representative target substances to study the effect of antibiotics on the operation of A/O-MBR and the migration and transformation of antibiotics in the reactor.In this paper,two sets of laboratory-scale A/O-MBR devices were used to investigate the removal of the conventional pollutants(COD,Ammonia nitrogen,TN,TP)and antibiotics,and the changes of sludge activities at different levels of antibiotics.The results are as follows: Low concentration of antibiotics(50ug / L)had little effect on A/O-MBR operation,and the removal effect of conventional pollutants did not change compared with that before antibiotics addition.While sludge activities were inhibited at high concentration(mg/L)of antibiotics,which influenced COD,TN,TP removal except ammonia.However,the removal efficiency of COD and TN did not change with the antibiotics concentration increasing.While TP removal deteriorated gradually due to that bacteria releasing phosphorus was inhibited by antibiotics.The removal mechanisms of the four antibiotics in the reactors were different.The removal efficiencies of penicillin(PEN)and chlortetracycline(CTC)maintained more than98% and 94% respectively because of hudrolysis.After short-term acclimation of antibiotics,the activated sludge in reactors was able to degrade sulfamethoxazole(SMX),leading to SMX removal rate increasing.The removal rate of SMX in the two reactors maintained at 98%(under high concentration)and 84%(under low concentration),respectively.The removal rate of norfloxacin(NOR)was high during the initial operation,which mainly depended on adsorption.With the adsorption of sludge saturated,the removal rate eventually maintained between 30% and 40%.In addition,the mechanism of adsorption of antibiotics and the factors affecting antibiotics biodegradation in the A/O-MBR process were studied by batch experiment,which provided the theoretical basis for the removal of antibiotics.The results are as follows:The higher the sludge concentration,the higher the adsorption capacity of antibiotics was,leading to the higher initial adsorption rate and the shorter equilibriumtime.However,the adsorption capacity of activated sludge per unit mass decrease.The increase of pH would affect the presence of antibiotics in water,the surface charge of sludge and the content of organic matter in the sludge,which could inhibit the adsorption rate and adsorption capacity of activated sludge on antibiotics.The increase of temperature will reduce the equilibrated adsorption capacity.The kinetic analysis showed that the adsorption process on antibiotics was in accordance with the pseudo-second-order kinetics equation,indicating that the adsorption was mainly chemical adsorption.From the thermodynamic analysis,the adsorption process was spontaneous exothermic reaction.But the adsorption process of NOR in low concentration lead to increasing in entropy,while decreasing in entropy in high concerntration.The SMX adsorption was entropy reduction process.Analysis of the factors affecting antibiotics biodegradation showed that aerobic conditions played a major role in the removal of antibiotics.SMX and NOR can be degraded as the sole substrate under aerobic conditions.The addition of additional carbon and nitrogen sources inhibited the removal process of SMX,but promoted the removal of NOR.Under anoxic condition,SMX was removed with a small amount though denitrification,however NOR was nearly not removed in the anoxic condition.