Fate and persistence of sulfamethoxazole resistant bacteria and resistance genes in a multi-barrier treatment facility for direct potable reuse

Abstract

Direct potable reuse has become a promising option to overcome sever lack of potable water in arid regions. However, the growing awareness of the presence of ARB and ARG in waste and drinking water has led to new safety concerns. Knowledge of the effect of advanced water treatment technologies on these water contaminants is limited, especially in the context of direct potable reuse. This study investigated the fate of ARB and ARG after each treatment step of an advanced water treatment facility in Windhoek, Namibia. The New Goreangab Water Reclamation plant (NGWRP) produces drinking water from domestic secondary effluent and thus directly provides for roughly a third of Windhoek’s potable water demand. The plant applies a multi-barrier treatment train that consists of eight advanced water treatment technologies in consecutive order. Procedures to study resistance determinants were based on molecular biology and culture-based microbiological methods. Selective culture media were used to enumerate microbial indicators growing in the presence and in the absence of the antibiotic to provide an estimate of viable ARB. TaqMan Real-Time PCR was employed to detect and quantify intracellular as well as extracellular sulfamethoxazole resistance gene, sul1. The NGWRP reduced the amount of both culturable bacterial indicators as well as the sul1 resistance gene to levels below the limit of detection in the final product. The main ozonation and the ultrafiltration had the highest removal efficiencies on both resistance determinants.