Because of high contents of pesticides and micro-organisms in IJssel Lake water N.V. PWN Water Supply Company North Holland (PWN) was compelled to implement multiple barriers against these contaminants at their surface water treatment plants at Heemskerk and Andijk. For degradation of pesticides advanced oxidation was pursued. After thorough studies O3/H2O2-treatment was rejected in view of bromate formation. Subsequently application of UV/H2O2-treatment was pursued.
UV-photolysis shows a selective pesticide degradation. Conversion using an electric energy of 1 kWh/m3 varies from 18% for trichloroacetic acid to 70% for atrazine. UV/H2O2-treatment gives a much more aselective pesticide degradation. For a combination of an electric energy of 1 kWh/m3 and 15 g/m3 H2O2 most pesticides can be degraded by more than 80%. Formation of harmful by-products proved to be insignificant. In the range of 0.1-2.5 kWh/m3 electric energy and 0-25 g/m3 H2O2 bromate formation is absent, while metabolite formation is insignificant. AOC-formation is found up to 140 μg/l. Therefore AOC and residual H2O2 must be removed in a following treatment step. GAC-filtration showed very reliable results.
Application of UV/H2O2-treatment for pesticide control with an electric energy of 1 kWh/m3 goes together with an average UV-dose of 2,000 mJ/cm2. This dose is about 50 times as high as applied in conventional UV-disinfection. As expected E. coli and (after spiking) spores of sulphite reducing Clostridia are inactivated completely. In addition orientating experiments have been carried out with an UV-dose of 100 mJ/cm2. Inactivation of MS-2 phages amounted to 2.7 log, Bacillus spores inactivation to 3.4 log, while Cryptosporidium inactivation was complete (>3 log). Additional data are gathered together with the University of Alberta.
In view of the very promising results, application of UV/H2O2-treatment will be pursued for full scale application at both the Heemskerk plant for organic contaminant control and the Andijk plant for both organic contaminant control and disinfection.
- pesticide degradation
- protozoan inactivation
- © IWA Publishing 2002