Biodegradation residual of 4-octylphenoxyacetic acid in laboratory columnsunder groundwater recharge conditions

The biodegradation of 4-octylphenoxyacetic acid (OP1EC) was studied in labo ratory columns to determine the residual concentration that can persist dur ing groundwater recharge or transport. Biofilm models predict residual conc entrations 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 biode gradable dissolved organic carbon (DOC) and groundwater (GW) containing no biodegradable DOG. The feedwater was amended with OP1EC first at high (1 mg /L) and then at low (50 mu g L-1) concentration. To simulate mixing of rech arged 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 OP 1EC concentration was 1000 mu g/L the residual concentrations in the LW and GW trains ranged from 0.3 to 3 and 0.8 to 3 mu g L-1, respectively. When t he feed concentrations were decreased to 50 mu g L-1, the residual concentr ation in the LW decreased to below the detection limit (<0.1 mu g L-1) but stayed above 0.2 mu g L-1 in the GW train effluent. Mixing the two LW and G W column effluents stimulated addition al (up to 11%) dissolved organic car bon (DOC) removal but no additional OP1EC degradation.