Effects Of AO~4 Process On The Removal Capacity Of Antibiotics And Antibiotic Resistance Genes In Swine Wastewater

Due to the abuse of antibiotics in pig-feeding industry,residual antibiotics and antibiotic resistance genes(ARGs)as emerging contaminants have been existed in swine wastewater extensively.Traditional swine wastewater treatment technologies could significantly reduce the conventional contaminants such as COD,NH4+-N,TN and TP,but these technologies could not effectively remove antibiotics,and even accelerate the emergence and distribution of ARGs.The novel process for swine wastewater treatment,anoxic and four-stage micro oxygen aerated sequence coupled with a coagulation process(AO4)could effectively remove the conventional contaminants,while removal efficiency and removal mechanism of antibiotics and ARGs by the AO4 process need to be studied in depth.In this study,the liquid chromatography-electrospray ionization tandem mass spectrometry(LC-ESI-MS/MS)and quantitative polymerase chain reaction(qPCR)were used to quantify the concentrations of eight antibiotics and the abundance of ARGs.The main conclusions are summarized as follows:(1)The AO4 process could remove the COD,NH4+-N,TN and TP effectively,significant reductions of COD,NH4+-N,TN and TP were observed to be more than 98.48%,99.32%,96.81%and 96.36%in the final effluent,respectively,which could meet the standard of the second exposure draft of the "Discharge standard of pollutants for livestock and poultry breeding".(2)The AO4 process could effectively remove the targeted antibiotics in swine wastewater.The AO4 process could increase the concentration of sludge,which could accelerate the adsorption and degradation of antibiotics,resulting in better antibiotics reduction than that of traditional swine wastewater treatment technologies.According to the quantification of targeted antibiotics,tetracyclines(TCs),sulfonamides(SAs)and quinolones(QLs)were observed to be 99.34%,98.71%and 88.52%in the effluent.Sludge sorption was the dominant pathway for TCs and QLs,and the SAs removal mainly relied on the biodegradation of activated sludge.(3)The AO4 process could remove the targeted antibiotics effectively,4-6 orders magnitude reductions of the ARGs copy numbers were achieved in the final effluent.The long-term low DO operational condition played a significant role in decreasing the relative abundance of ARGs.Long-term low DO operational condition could reduce the bacterial endogenous decay rate and increase the total bacterial population size,simultaneously,long-term low DO operational condition could inhibit the emergence and distributions of ARGs via enhancing the metabolic burden of plasmid reproduction.,which resulted in the decrease of relative abundance of ARGs in swine wastewater.