Kinetics of alachlor and atrazine biotransformation under various electron acceptor conditions

Second-order rate constants were developed for the biotransformation of the herbicides atrazine and alachlor under aerobic, nitrate-reducing, sulfate-reducing, and methanogenic conditions. Batch-reactor techniques were used, with seed cultures taken from acclimated biofilm columns. The reactors were fed acetate as a primary substrate. Pesticide biotransformation appeared to depend upon the continued presence of the primary substrate, indicating co-metabolic transformations. All four electron acceptor conditions tested resulted in some biotransformation of both pesticides. Rate constants for alachlor ranged from 6.25 × 10−5 to 1.60 × 10−4 L/mg volatile suspended solids (VSS)·h, with the highest rate constant occurring under sulfate-reducing conditions, and the lowest under methanogenic conditions. Rate constants for atrazine ranged from 1.04 × 10−5 to 3.32 × 10−5 L/mg VSS·h, although differences among the four electron acceptor conditions were not statistically significant.