Influence of soil–water ratio on the performance of slurry phase bioreactor treating herbicide contaminated soil

The influence of soil–water ratio was studied on the performance of the slurry phase bioreactor operated in sequencing batch mode (anoxic–aerobic–anoxic microenvironments) during the bioremediation of soil contaminated with pendimethalin. The performance of the reactors was evaluated at different soil–water ratios (1:5–1:25; at soil loading rate (60 kg of soil/cum-day to 12 kg of soil/cum-day)) keeping the loading rate of pendimethalin constant (133.2 g/kg of soil-day) in six reactors and variable (66.6 g/kg of soil-day to 166.6 g/kg of soil-day) in other four reactors. At 1:20 soil–water ratio, the slurry phase system showed enhanced degradation of substrate (629 μg pendimethalin/g soil). The removal efficiency of pendimethalin in the reactors was dependent on the mass-transfer rates of the substrate from the soil to the aqueous phase. Soil–water ratio and substrate loading rates showed significant influence on the substrate portioning, substrate degradation efficiency and substrate desorption rate.