Ozonation and UV254Â nm radiation for the removal of microorganisms and antibiotic resistance genes from urban wastewater

The abundance of the different microbiological parameters per volume of wastewater was reduced by ∼ 2 log units for cultivable fungi and 16S rRNA and intI1 genes, by ∼3-4 log units, for total heterotrophs, enterobacteria and enterococci, and to values close or below the limits of quantification for ARG, for both processes, after a contact time of 30 min. Yet, most of the cultivable populations, the 16S rRNA and intI1 genes as well as the ARG, except qnrS after ozonation, reached pre-treatment levels after 3 days storage, suggesting a transitory rather than permanent microbial inactivation. Noticeably, normalization per 16S rRNA gene evidenced an increase of the ARG and intI1 prevalence, mainly after UV254 nm treatment. The results suggest that these tertiary treatments may be selecting for ARB&ARG populations.