The Fate Of Antibiotics During Sludge Pretreatment And Anaerobic Digestion Processes

Currently,the study on the fate of antibiotics during sludge pretreatment and anaerobic digestion is very limited.Deep study in this field is conducive to understanding the pathway and level of antibiotics outputting to the environment.In this study,three common pretreatment methods were selected,including low power density ultrasonic pretreatment(0.15W/m L,0~60min),alkaline pretreatment(0.04 gNaOH /g TS,24h)and thermal hydrolysis pretreatment(120 ℃,60min).Mesophilic anaerobic digestion test was carried out after the pretreatment to investigate the solid-liquid distribution and degradation of antibiotics before and after sludge pretreatment,and compare the effects of different pretreatment methods on the fate of antibiotics during anaerobic digestion.The pretreatment of sludge had significant solubilization effect on antibiotics,and the solubilization percentage after ultrasonic,alkaline and thermal hydrolysis pretreatments were 233~1981%,58~1896% and 64~49859%,respectively.The pretreatment methods had similar effects on the solubilization of antibiotics and soluble COD,with the effectiveness in order of thermal hydrolysis > alkaline pretreatment > ultrasonic pretreatment.Antibiotics are prevalent within the sludge cells and the distribution is affected by the antibiotic class.Ultrasonic and alkaline pretreatments mainly play the role of floc dispersion and dissolution of extracellular polymers,and will not damage the molecular structure of antibiotics,so the total amount of antibiotics before and after pretreatment was unchanged.After thermal hydrolysis,the total amount of quinolones,dehydration erythromycin and roxithromycin increased,while sulfonamides,tetracycline and azithromycin decreased.There are two dynamic processes during the thermal hydrolysis pretreatment,release of intracellular antibiotics with the disruption of cells,and the decomposition of antibiotics.The removal efficiency of antibiotics in sludge pretreatment-anaerobic digestion was 12.1~100%,and the biodegradation easiness followed the order of tetracycline >macrolide > quinolone.Compared with the single anaerobic digestion process,the degradation efficiencies of quinolones and macrolides decreased by 2~27% in pretreatment-anaerobic digestion.The removal efficiency of tetracycline was highest in the process of thermal hydrolysis-anaerobic digestion,with an increase of 3~13% compared to others.At the end of anaerobic digestion,the dissolved concentration of antibiotics increased and the accumulation of dissolved antibiotics inhibited the further desorption of adsorbed antibiotics.Thus the limiting step for antibiotics degradation is biodegradation,but not desorption and dissolution process of antibiotics.Ultrasonic and alkaline pretreatments had no distinct effect on the solid-liquid distribution of antibiotics after anaerobic digestion.Thermal hydrolysis enhanced the concentration of dissolved antibiotics after anaerobic digestion,and had a negative effect on the degradation of adsorbed quinolones and macrolide antibiotics.