DEGRADATION OF PESTICIDES BY OZONATION AND ADVANCED OXIDATION

In the Netherlands many water supply companies are upgrading their sur face water treatment plants in order to guarantee the water supply and water quality in the coming years. The Water Supply Company North Wes t Brabant (WNWB) has plans to upgrade their treatment plant at Zevenbe rgen. In the retrofit plant chlorination will be abandoned and probabl y ozonation will be the major barrier against microorganisms. Pesticid e concentrations will be decreased by three barriers: storage, ozonati on and activated carbon filtration. If the ozone dosage is restricted just to reach the required disinfection level at pH 7.2, ozonation is a poor barrier against pesticides. Out of 23 selected pesticides, only 6 were effectively degraded: dimethoate, chlortoluron, diuron, isopro turon, metoxuron and vinclozolin (O-2/DOC = 0.55 g/g). Application of an (O-3/DOC ratio of 1.0 g/g results in an effective barrier for rough ly 50% of the tested pesticides (also for diazinon, parathion-methyl, linuron, methabenzthiazuron, metobromuron, MCPA and MCPP). Pesticides were degraded more effectively at high pH and high temperature. For ad ditional degradation of high concentrations of persistent pesticides, advanced oxidation may be applied. Atrazine, propazine, simazine, chlo rfenvinphos, tetrachlorvinphos, 2,4-D, 2,4-DP and 2,4,5-T were degrade d by O-3/DOC = 1.4 g/g and H2O2/O-3 = 0.5 g/g. Dicamba and dikegulac w ere most persistent. pH has a minor effect on the degradation of pesti cides by advanced oxidation. Higher hydrogen peroxide dosages showed n o improvement in degradation. After ozonation and advanced oxidation, about 50% of totally reacted atrazine and propazine was converted into desethylatrazine. No desisopropylatrazine formation was observed.