Influences Of Roxithromycin And Chlortetracycline On Volatile Fatty Acids Production In Anaerobic Fermentation Of Waste Activated Sludge

Wastewater treatement plant is an important way for antibiotic's removel,but the potential role of residual antibiotics in the disposal of waste activated sludge?WAS?has not been clearly understood,which made uncertain factors to the resourceful treatment of sludge.In this study,the effects of roxithromycin?ROX?and chlortetracycline?CTC?on volatile fatty acid production?VFAs?during WAS anaerobic fermentation were investigated by comparing the changes of VFA concentrations during WAS anaerobic fermentation under different concentrations?0,10,50 and 100 mg/kg TSS?of ROX and CTC.And then the mechanisms of ROX and CTC on VFA production were investigated via analyzing the changes of solubilization,hydrolysis,acidification,methanogenesis process,COD mass balance and key enzyme activities.The experimental results showed that both ROX and CTC can promote the production of VFAs during sludge fermentation.With the increase of ROX dosages from 0 to 100 mg/kg TSS,the maximum accumulation of VFAs increased from 295 to610 mg COD/L.The concentration of ROX below 50 mg/kg TSS mainly promoted the increase of acetic acid,while 100 mg/kg TSS ROX increased the concentrations of individual VFAs except n-valeric acid.In addition,the degradation of ROX did not produce VFAs.Mechanism studies revealed that ROX promoted the solubilization of WAS by facilitating the disruption of extracellular polymeric substances?EPS?.And the hydrolysis was inhibited by reducing the activities of?-glucosidase,the accumulation of acetic acid was promoted by increasing acetate kinase's activity and inhibiting methanogenesis by decreasing the activity of coenzyme F₄₂₀.ROX was found to have a stronger inhibition on methanogenesis than hydrolysis process,thus increasing the accumulation of VFAs.Differ from ROX,when the content of CTC was 10 mg/kg TSS,the maximum VFA production increased from 508 to 615 mg COD/L,but further increase of CTC leads to the decrease of VFAs.And CTC improved VFA accumulation mainly by increasing the yield of acetic acid and propionic acid.Mechanism exploration shows that CTC stimulates the secretion of EPS,thereby cultivating an enabling environment for anaerobes to produce VFAs.In addition,the degradation of CTC has no contribution to the production of VFAs from WAS anaerobic fermentation.CTC had no significant effect on the solubilization and hydrolysis,and enhanced the accumulation of VFAs by promoting acidification and inhibiting methanogenesis.This study revealed the effects and mechanisms of ROX and CTC on anaerobic fermentation of WAS.These findings provide important references for understanding the potential impact of residual antibiotics on activated sludge systems and has certain theoretical and practical values to the optimal design of sludge anaerobic fermentation.