Removal of pesticides during the drinking water treatment process at Florence water supply, Italy

Removal of pesticides from surface water during drinking water treatment processing was evaluated at two full-scale treatment plants that employed prechlorination with chlorine dioxide, powdered activated carbon (PAC) adsorption, flocc-sedimentation, sand filtration, ozonation, biological GAC filtration, and postchlorination. A two year-investigation showed that the conventional treatment process was ineffective in removing metolachlor and terbutylazine from the water. The effectiveness of an ozonation or biological GAC filtration process has proved to be very limited for complying with the EC drinking water standard of 0.1 μg/L for individual pesticides. The removal efficiency of the PAC treatment was dependent on the PAC dosage, as well as the type of flocc-sedimentation system employed. PAC combined with Pulsator flocc-sedimentation proved to be more effective for removing pesticides than PAC combined with Dorr flocc-sedimentation. An effective treatment option for removing the seasonal occurrence of pesticide pollution in surface water appears to be PAC adsorption followed by Pulsator flocc-sedimentation and ozonation.