Background Antibiotic Resistance and Microbial Communities Dominate Effects of Advanced Purified Water Recharge to an Urban Aquifer

The growing need for potable reuse of wastewater has led to significant development and implementation of advanced treatment processes. However, the emergence of new safety concerns (e.g., antibiotic resistance) necessitates an ongoing evaluation of current and future reuse schemes to demonstrate both water security and public safety. This study elucidates the microbial community and antibiotic resistance gene (ARG) profiles of a 100 million gallon per day (MGD) advanced water treatment facility (AWTF). A concurrent evaluation of the groundwater aquifer that is recharged with AWTF product water was also performed to determine the fate of specific microbial targets in the downstream environment. Results indicated that the AWTF reduced nearly all targeted ARGs to below detection limits (<50 copies/L). In groundwater samples, however, a ubiquitous presence of ARGs conferring resistance to sulfonamides (sul1 and sul2) and β-lactams (oxa-1) was observed (104–106 copies/L) in both AWTF-recharged locations and control locations. Microbial community analysis via 16S rRNA gene sequencing further showed that the AWTF treatment train effectively excluded any upstream wastewater microbial community characteristics from the product water. Groundwater receiving AWTF recharge through percolation basins was greatly influenced by its proximity to a river that is known to receive conventional wastewater treatment plant effluents.