Fate of organics during column studies of soil aquifer treatment

Soil column experiments were performed to differentiate between abiotic and biological mechanisms for removal of residual organics from chlorinated municipal effluent during soil aquifer treatment (SAT) and to relate SAT efficiency to degree of wastewater treatment. Three water-quality parameters were examined: dissolved organic carbon (DOC), ultraviolet (UV) absorbance at 254 nm (UVA₂₅₄), and adsorbable organic halide (AOX). Secondary and tertiary-treated effluents were applied to 1-m unsaturated columns containing soils from the Sweetwater Underground Storage and Recovery Facility, Tucson, Ariz. DOC was removed primarily by biological activity during SAT. Through-column removal using chlorinated secondary effluent averaged 48%. UVA₂₅₄ reductions were dependent on biological and abiotic removal mechanisms. Aerobic biological activity did not contribute significantly to AOX removal. Through-column reductions for UVA₂₅₄ and AOX from secondary effluent averaged 30% and 17%, respectively. Forty-four percent of the through-column DOC removal and 57% of UVA₂₅₄ attenuation occurred in the top 8 cm of soil. The post-SAT organic quality of secondary and tertiary (dual-media filtered) effluents was essentially equivalent.