Intensive mining of non-renewable groundwater supplies to meet our growing water demands is unsustainable. Alternative water resources like treated wastewater need to be considered so as to alleviate water scarcity concerns. Prior to reuse, wastewaters have to go through proper treatment to remove majority of the contaminants. However, many studies have shown that the conventional wastewater treatment plants (WWTPs) do not achieve full removal of antibiotic resistant bacteria (ARB) along with their resistance genes. In certain instances, WWTPs may be selectively enriching for ARB. Furthermore, most WWTPs rely on chlorine as a final disinfection step to inactivate remnant bacteria. Chlorination results in the formation of disinfection byproducts (DBPs) which are carcinogenic and mutagenic micropollutants. Bacteria inactivated by chlorine can release extracellular DNA, which together with the DBPs, can promote for horizontal gene transfer via natural transformation. In our study, the stimulatory effects of DBPs over natural transformation was observed in a dose-response manner. Using transcriptomics, the mechanism leading to the transformation induction was further described. Given this phenomenon, sole reliance on chlorine to disinfect our treated waters may not be a wise choice. Other disinfection strategies that impose different biocidal mechanisms compared with chlorine (e.g. UV<sub>254nm</sub> or sunlight) should also be evaluated for their inactivation efficiencies as well as stimulatory effects on natural transformation. Our findings suggest that UV<sub>254nm</sub> was able to achieve high inactivation efficiencies with no induction on natural transformation. However, UV disinfection is less effective in turbid waters, and should only be used to disinfect effluent obtained after membrane filtration. As we explore the use of alternative water resources, it is important to note that century old treatment processes may have to be reassessed for their efficacies in removing emerging contaminants, and if needed, should be retrofitted with advanced technologies to ensure safe reclaimed waters.

Understanding and mitigating the emerging microbial-associated threats in our treated wastewaters

2019 Spring National Meeting

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