Viral and Microbial Pathogens, Indicator Microorganisms, Microbial Source Tracking Indicators, and Antibiotic Resistance Genes in a Confined Managed Effluent Recharge System

A large-scale comprehensive survey of indicator bacteria, pathogen viruses, coliphages, microbial source tracking (MST) indicators, and antibiotic resistance genes was carried out in the Shafdan soil aquifer treatment (SAT) of the Tel Aviv, Israel area. The study reveals complete elimination of pathogen viruses - enterovirus, adenovirus, norovirus, parechovirus, and coliphage - and of the bacterial indicators total and fecal coliforms, fecal streptococcus, and microbial source tracking (MST) Bacteroides already in the vadose zone below the percolation basins. Trace levels of antibiotic resistance genes (ARGs) were detected in the recovery wells, but these were also detected in wells not impacted by effluent, suggesting that these genes are associated with native aquifer bacterial communities. This is the first comprehensive survey describing four types of microbial indicators - bacteria, pathogenic viruses, coliphages, and MST - for SAT research, and the first to address the occurrence of antibiotic resistance genes in SAT systems. The results should provide guidance to regulatory agencies regarding the attainable efficiency of optimally designed and operated SAT systems and the monitoring point locations. Most of the pathogen removal occurs in the vadose zone underneath the basins, which can be monitored more rapidly than the water quality in the recovery wells.