Distribution, Dissemination and Fate of Antibiotic Resistance Genes During Sewage Sludge Processing-a Review

Sewage sludge, a common by-product of wastewater treatment plants, is one important repository of antibiotic resistance genes (ARGs). The growing demands of sewage sludge reclamation, such as land application, increase the possibility of introducing ARGs into the environment and even the further dissemination of antibiotic resistance. Previous studies have paid much attention to the removal efficiencies of conventional pollutants such as heavy metals and pathogenic microorganisms during the sludge treatment processes. However, the effects on the abundance and diversity of ARGs got great concerns only recently. This paper mainly focuses on the enrichment and transmission modes of ARGs in sludge and the effects of representative sludge treatment technologies on ARG distributions in sludge. It seems that most physical and chemical techniques such as microwave, alkali treatment, and coagulation are ineffective in ARG reduction. The impacts of biological sludge treatment technologies on ARGs are varied, probably because of the diverse microbial community structures, operational parameters, and even environmental factors such as rainwater. Therefore, the sensitivities of potential hosts of specific ARG to the sludge treatments should determine the abundance of ARG before and after treatment. In addition, a reasonable combination of different sludge process techniques is usually a better choice than the single one for ARGs' removal due to its better ability to efficiently damage the embedded cells and directly degrade the released ARGs. In summary, the appropriate treatment techniques should be applied on the excess sewage sludge to help mitigate the release of ARGs to the environment.