Impact of Redox Potential on Biofilms and Water Quality in Managed Aquifer Recharge Lab System

Soil aquifer treatment (SAT) is operated by flooding and drying cycles, thus swiftly changing topsoil redox conditions. Currently, the links between the redox conditions, biofilm activity, and contaminants removal in SAT topsoil are not well understood. Here, two extreme-redox potentials (governed by oxic conditions) were evaluated while flooding occurred during two seasons. All tests were performed in 30 cm columns packed with SAT topsoil and flooded with artificial secondary wastewater. Redox conditions and removal efficiency of ammonia, ibuprofen, and bacteriophage, alongside bacterial activity and diversity, were determined. Biofilm activity was more intensive under aerobic than under anaerobic conditions during summer and winter (83 and 155%, respectively). Similarly, the removal of ammonia and ibuprofen was higher under aerobic conditions (82 and 54%, respectively). Differently, bacteriophage reduction was not affected by the redox conditions, as the main removal mechanism was adsorption. Additionally, biofilm richness was highly adaptive within 48 h of flooding (Shannon index: 4.7 ± 0.1) yet less diverse under anaerobic conditions. These results stress the importance of measuring and controlling the redox potential within the SAT topsoil. Moreso, continuous monitoring of the oxic conditions in the subsurface could optimize the tillage intervals as well as the wetting and drying cycles without sacrificing water quality.