Biodegradation Residual of 4-Octylphenoxyacetic Acid in Laboratory Columns under Groundwater Recharge Conditions

The biodegradation of 4-octylphenoxyacetic acid (OP1EC) was studied in laboratory columns to determine the residual concentration that can persist during groundwater recharge or transport. Biofilm models predict residual concentrations are independent of the initial concentration and residence time. Two column trains, constructed with glass beads and providing a residence time of 280 min were fed continuously with lake water (LW) containing biodegradable dissolved organic carbon (DOC) and groundwater (GW) containing no biodegradable DOC. The feedwater was amended with OP1EC first at high (1 mg/ L) and then at low (50 μg L-1) concentration. To simulate mixing of recharged LW and regional GW, the effluents of the GW and LW train were blended and fed to a column (BW) with 114 min residence time. When the influent OP1EC concentration was 1000 μg/L the residual concentrations in the LW and GW trains ranged from 0.3 to 3 and 0.8 to 3 μg L-1, respectively. When the feed concentrations were decreased to 50 μg L-1, the residual concentration in the LW decreased to below the detection limit (<0.1 μg L-1) but stayed above 0.2 μg L-1 in the GW train effluent. Mixing the two LW and GW column effluents stimulated additional (up to 11%) dissolved organic carbon (DOC) removal but no additional OP1EC degradation.