Processes of microbial pesticide degradation in rapid sand filters for treatment of drinking water

Aerobic rapid sand filters for treatment of groundwater at waterworks were investigated for the ability to remove pesticides. The potential, kinetics and mechanisms of microbial pesticide removal was investigated in microcosms consisting of filter sand, treated water and pesticides in initial concentrations of 0.04-2.4 μg/L. The pesticides were removed from the water in microcosms with filter sand from all three investigated sand filters. Within the experimental periode of six to 13 days, 65-85% of the bentazone, 86-93% of the glyphosate, 97-99% of the p-nitrophenol was removed from the water phase. Investigations of the removal kinetics of bentazone at Sjælsø waterworks Plant II revealed that more than 50% of bentazone was removed within 30 minutes (initial concentrations 0.1-2.4 μg/L). Ammonium and methane is oxidized by bacteria in rapid sand filters, and these are known to degrade xenobiotics by cometabolic processes. It was investigated if addition of ammonium affected bentazone removal or if removal was affected by addition of allylthiourea, which inhibits ammonium oxidizing bacteria. Preliminary results indicated that addition of ammonium as well as allylthiourea affected the removal of bentazone.