Critical review of ARGs reduction behavior in various sludge and sewage treatment processes in wastewater treatment plants

It is becoming clear that the wastewater treatment plants (WWTPs) is a key repository for antibiotic resistance genes (ARGs), and WWTPs also represent an important node for limiting ARGs spreading via altering the magnitude and distribution of ARGs in environment. This review provides an overview of the ARGs degradation performance both in sewage sludge and wastewater in WWTPs. The ARGs reduction behaviors during sludge treatment processes including anaerobic digestion (AD), composting, aerobic digestion, bio-drying and air-drying were reviewed, and parameters affecting ARGs reducing efficiency and the probable mechanisms were concluded. In particular, pretreatment approaches such as microwave, thermal hydrolysis and ozone before sludge AD are found to provide the extra benefits for ARGs removal. Additionally, ARGs fates and reduction mechanisms during sewage biological treatments such as anaerobic, aerobic, anaerobic combined with aerobic process and physical-chemical treatment including coagulation, advanced oxidation and disinfection processes were appraised. Furthermore, problems or doubts of previous study are proposed, and some in-depth mechanism researches are anticipated to elucidate the ARGs decay in sewage and sludge treatment process. This can help further enhance the ARGs removal efficiency in WWTPs.