Activated carbon adsorption of chloroacetanilide herbicides and their degradation products from surface water supplies

A recent (1995-2001) 175-site surface drinking water monitoring programme in the United States showed that one community water system (Nashville, Illinois) was particularly successful at removing chloroacetanilide herbicides and their degradation products from source water. Nashville adds powdered activated carbon (PAC) just prior to a clarifier in which settled solids are recirculated, increasing the PAC residence time. We conducted bench-scale studies to quantify the effects of PAC dose and contact time on removal efficiency. Results indicate that 90% of the parent herbicides and 40-45% of the acetanilide degradation products are removed for a contact time of 60 min and a PAC dose of 20 mg/l, from Nashville, IL, source water. Removal of these compounds by the same PAC dose and contact time was even higher in three other US water sources (Idaho, Kansas, Missouri) and a European (Dutch) water source, generally 60-80% for the degradation products and over 95% for the parent compounds. Removal percentages substantially increased with higher PAC dose and contact time, fell slightly with decreasing pH or higher NOM, but remained constant when the inlet concentration was raised from 2 to 10 mug/l.