Abstract:
The growing demand for high-quality water requires sustainable strategies to promote reuse and recycling. Managed Aquifer Recharge strategies, particularly Soil-Aquifer Treatment systems, have demonstrated effectiveness in improving water quality by reducing contaminants through biodegradation, retention, and sorption.

The coexistence of solid, liquid, and gas phases in the unsaturated zone enhances adsorption and retention of pathogens and colloids, while the availability of organic carbon and terminal electron acceptors sustains this zone as critical for biodegradation processes. During recharge, soil heterogeneity causes water to infiltrate through preferential pathways, gradually hydrating the surrounding medium. This behavior is influenced by system management (recharge strategy, applied flow rate, and installation of reactive barriers), which also promotes biofilm development that facilitates water retention and acts as localized microreactors for contaminant biodegradation.

We investigate the influence of recharge strategies (pulsed versus continuous) and the presence of a reactive barrier on the hydration-drainage front and biofilm development in two Soil-Aquifer Treatment systems using cross-hole electrical resistivity tomography and extracellular polymeric substances quantification.The study compares a fine sand system and another incorporating a reactive barrier composed of sand, woodchips, compost, biochar, zeolites, and clay, under continuous and pulsed flow with the same average rate.

Results show infiltration through preferential pathways, creating significant heterogeneity in water content. The reactive barrier enhanced water retention during dry periods, supporting biofilm development, while pulsed recharge promoted biofilm growth more effectively than continuous recharge. These findings provide insight into optimizing recharge strategies and media composition to enhance contaminant removal in Soil-Aquifer Treatment systems.