Efficient removal of antibiotic resistance genes and of enteric bacteria from reclaimed wastewater by enhanced Soil Aquifer Treatments

: Soil Aquifer Treatment (SAT) is a robust technology to increase groundwater recharge and to improve reclaimed water quality. SAT reduces dissolved organic carbon, contaminants of emerging concern, nutrients, and colloidal matter, including pathogen indicators, but little is known about its ability to reduce loads of antibiotic resistance genes (ARGs) from reclaimed waters. Here we test six pilot SAT systems to eliminate various biological hazards from the secondary effluents of a wastewater treatment plant (WWTP), equipped with reactive barriers (RBs) including different sorptive materials. Using flow cytometry, qPCR and 16S rRNA gene amplicon sequencing methods, we determined that all six SAT systems reduced total loads of bacteria by 80 to 95 % and of clinically relevant ARGs by 85 to 99.9 %. These efficiencies are similar to those reported for UV/oxidation or membrane-based tertiary treatments, which require much more energy and resources. The presence and composition of reactive barriers, the season of sampling (June 2020, October 2020, and September 2021), or the flow regime (continuous versus pulsating) did not affect ARG removal efficiency, although they did alter the microbial community composition. This suggests that an adequate design of the SAT reactive barriers may significantly increase their performance. Under a mechanistic point of view, we observed an ecological succession of bacterial groups, linked to the changing physical-chemical conditions along the SAT, and likely correlated to the removal of ARGs. We concluded that SAT is as cost-efficient technology able to dramatically reduce ARG loads and other biological hazards from WWTP secondary effluents.