Viral RNA and antibiotic resistance genes associations in a full-scale activated sludge wastewater treatment plant

Wastewater Treatment Plants (WWTPs) based on activated sludge (AS) processes have demonstrated moderate capacity to remove viruses from wastewater. However, few studies have systematically assessed viruses along water and sludge treatment lines and their associations with Antibiotic-Resistant Genes (ARGs). In this work, the fate, distribution and possible interactions of RNA from SARS-CoV-2 and coliphage MS2 with ARGs in a full-scale AS WWTP were investigated. Total reductions of SARS-CoV-2 and MS2 RNA (2.5 and 2.4 log 10 units, respectively) were achieved mainly in the water treatment line. In contrast, lower total reductions (0.7 to 1.5 log 10 units) of 16S rRNA, class 1 integron-integrase ( intI 1), sulfonamide-resistant dihydropteroate synthase (sul 1 ) and tetracycline resistance protein ( tetO ) were mainly achieved during sludge treatment. Along with the water treatment line, sludge stabilisation was a critical barrier to controlling viral RNA and ARGs in the outflows. Amplification of intI 1 and sul 1 seemed to occur in the AS reactors, likely enhanced by viral activity supported by MS2 RNA in these units. Thus, the participation of bacteriophages in the amplification of ARGs in AS systems should not be ruled out. RNA viruses and ARGs should be more frequently determined in WWTPs to assess and prevent phage-mediated amplification of ARGs. • Activated sludge (AS) removed up to 2 log 10 of viral RNA, 16S rRNA, intI 1 and ARGs • Viral RNA and sul 1 were removed mainly in the water treatment line • 16S rRNA, intI 1 and tet O were removed mainly in the sludge treatment line (STL) • intI 1 and sul 1 were amplified in the AS but intI 1 was further removed in the STL • Bacteriophage-mediated ARG´s amplification may be occurring in AS systems