Soil-Aquifer Treatment (SAT) systems are managed aquifers for water storage and treatment. Considering the high energy requirements of traditional wastewater treatment processes, SAT is appealing due to its low requirements. The SAT functionality comes from microbial communities that metabolize organic carbon, nitrogen species, and organic contaminants from the water infiltrating the permeable aquifer. SAT systems are limited by bioclogging, as microbial biomass fills the pore space and limits the infiltration capacity. In infiltration ponds, bioclogging is evident near the soil surface, where conditions for heterotrophic respiration are optimal. Drying periods are operational strategies to reverse bioclogging by interrupting nutrient delivery and desiccating biofilms. The downside is that the volume of water that ends up being treated is considerably diminished, which can prove threatening for water-scarce communities that rely on SATs for water storage. Our work focuses on the numerical modeling of the intersection between biogeochemistry and groundwater hydraulics to inform SAT operation. Earlier work in this area has focused on biochemical optimization regarding organic carbon, oxygen, and nitrogen but has not considered the role of microbial clogging. Our goal is to identify the operational strategy that optimizes both nutrient transformation and water infiltration in SAT systems. For this, we present a 3-D finite-volume modeling framework that couples the relationship between unsaturated flow, nutrients’ reactive transport, and microbial growth with changes in the hydraulic conductivity field due to bioclogging. We show results from the model compared to unsaturated-flow column experiments and then simulated combinations of drying and flooding periods.
