FATE OF ORGANICS DURING COLUMN STUDIES OF SOIL AQUIFER TREATMENT

Soil column experiments were performed to differentiate between abioti c and biological mechanisms for removal of residual organics from chlo rinated municipal effluent during soil aquifer treatment (SAT) and to relate SAT efficiency to degree of wastewater treatment. Three water-q uality parameters were examined: dissolved organic carbon (DOC), ultra violet (UV) absorbance at 254 nm (UVA(254)), and adsorbable organic ha lide (AOX). Secondary and tertiary-treated effluents were applied to 1 -m unsaturated columns containing soils from the Sweetwater Undergroun d Storage and Recovery Facility, Tucson, Ariz. DOC was removed primari ly by biological activity during SAT. Through-column removal using chl orinated secondary effluent averaged 48%. UVA(254) reductions were dep endent on biological and abiotic removal mechanisms. Aerobic biologica l activity did not contribute significantly to AOX removal. Through-co lumn reductions for UVA(254) and AOX from secondary effluent averaged 30% and 17%, respectively. Forty-four percent of the through-column DO C removal and 57% of UVA(254) attenuation occurred in the top 8 cm of soil. The post-SAT organic quality of secondary and tertiary (dual-med ia filtered) effluents was essentially equivalent.