Solar photo-Fenton mediated by alternative oxidants for MWWTP effluent quality improvement: Impact on microbial community, priority pathogens and removal of antibiotic-resistant genes

Municipal wastewater treatment plant effluent (MWWTPE) contains thousands of resistant strains which carry numerous genes and their variants. Avoiding the spread of these contaminants to the environment is a public health concern. Although solar photo-Fenton has been proved an effective complementary method for the control of antimicrobial resistance in MWWTPE, the use of persulfate (PS) as an oxidant for the elimination of antimicrobial-resistant bacteria and genes in the photo-Fenton treatment is still underexplored. This study aimed to investigate PS-mediated solar photo-Fenton (solar/Fe2+/S2O82-), and a combined oxidant system (solar/Fe2+/H2O2 + S2O82-) for the removal of ARB and ARGs from MWWTPE. Solar/Fe2+/S2O82- reached the lowest richness and diversity of microbial community, along with effective removal of the main phyla originally present in MWWTPE (88% of Proteobacteria, 99% of Bacteroidetes, and complete removal of Chlroflexi), 44% removal of total ARGs, and 99% removal of M. tuberculosis. Yet, it led to a 35-fold enrichment for Firmicutes. Hence, it is critical to investigate tolerance mechanisms pertaining to this group. In contrast, the combined oxidant system did not significantly impact alpha diversity of microbial community originally present in MWWTPE (p-value > 0.1), so being less efficient for ARB elimination than the solar/Fe2+/S2O82-. This was not expected as co-occurring reactions in this system should lead to a higher number of reactive radicals (SO4 center dot- and HO center dot). Furthermore, it also caused positive selection of Firmicutes (>8-fold) and Proteobacteria (>2-fold). Nonetheless, the combined oxidant system resulted in total DNA fragmentation. Thus, it is important to promote further investigation of mechanisms involved in bacteria inactivation and DNA damage in the combined oxidant system.