Wastewater treatment plants as reservoirs and sources for antibiotic resistance genes: A review on occurrence, transmission and removal

Antibiotic resistance genes (ARGs), carried by antibiotic resistant bacteria (ARB) have been present in large numbers in wastewater. Wastewater treatment plants (WWTPs) are regarded as reservoirs and sources for a wide variety of ARGs. A large number of mobile genetic elements (MGEs), heavy metals and emerging pollutants (e.g., microplastics, nanomaterials, pharmaceuticals and personal care products and quorum sensing inhibitors) detected in WWTPs can impact the proliferation of ARGs. Moreover, the removal efficiency of ARGs is limited in wastewater treatment processes. Therefore, it is of significance to summarize the research status of ARGs in WWTPs. This paper reviewed the occurrence and transmission of ARGs. The problem of multiple drug resistance and elimination of ARB were assessed in WWTPs. Also, the effects of heavy metals and emerging pollutants on ARGs in WWTPs were summarized. Furthermore, physical treatment and advanced oxidation processes for ARGs removal were critically discussed. Future research prospects were proposed with the ultimate goal to reduce the potential harm of ARGs to ecological environments and to provide guidance for practical applications.