KINETICS OF ALACHLOR AND ATRAZINE BIOTRANSFORMATION UNDER VARIOUS ELECTRON-ACCEPTOR CONDITIONS

Second-order rate constants were developed for the biotransformation o f the herbicides atrazine and alachlor under aerobic, nitrate-reducing , sulfate-reducing, and methanogenic conditions. Batch-reactor techniq ues were used, with seed cultures taken from acclimated biofilm column s. The reactors were fed acetate as a primary substrate. Pesticide bio transformation appeared to depend upon the continued presence of the p rimary substrate, indicating co-metabolic transformations. All four el ectron acceptor conditions tested resulted in some biotransformation o f both pesticides. Rate constants for alachlor ranged from 6.25 x 10(- 5) to 1.60 x 10(-4) L/mg volatile suspended solids (VSS).h, with the h ighest rate constant occurring under sulfate-reducing conditions, and the lowest under methanogenic conditions. Rate constants for atrazine ranged from 1.04 x 10(-5) to 3.32 x 10(-5) L/mg VSS.h, although differ ences among the four electron acceptor conditions were not statistical ly significant.