Appraisal, attenuation, and remediation of intracellular antibiotic resistance genes in wastewater and drinking water treatment plants

Antibiotics are pivotal in diseases and infections control. Yet increased consumption and widespread misuse have proliferated resistance determinants, as up to 90% of antibiotics are excreted unmetabolized or unconjugated. This promotes untreatable infections and increases mortality rates, especially in the developing world. Conventional water and wastewater treatment plants struggle with antibiotic resistance genes (ARGs) removal, as these have not been designed for the removal of contaminants of emerging concern (CEC). Here, the occurrence and persistence of intracellular ARGs (iARGs) was monitored through municipal wastewater and drinking water treatment in South Africa. In total, 21 iARGs were monitored, although only tetA, ermB, and sul1 were prevalent in the influent water, likely reflecting the local antibiotic usage patterns and the prevailing microbial community structure within the catchment areas of these treatment plants. These genes infer resistance to the antibiotic classes macrolide (ermB), tetracycline (tetA) and sulfonamide (sul1). ARGs were mostly removed in primary wastewater treatment, suggesting that sewage sludge is a sink and reservoir for ARGs. The drinking water treatment plant effectively eliminated ermB resistance gene (∼100% reduction) but could only reduce sul1 by 60%, while tetA levels increased. Wastewater treatment with 10 mg/L ferrate (Fe(VI)) (10 min contact time) practically removed (≥98%) ermB, sul1, and tetA, with advanced oxidation and coagulation (e.g., precipitation with ferric hydroxides) being the main removal mechanisms. Therefore, the combination of oxidative DNA damage with enhanced coagulation in a single treatment-step render ferrate a novel green biocide for water and wastewater treatment.