UV/H_2O_2-TREATMENT FOR INACTIVATION OF PATHOGENIC MICRO-ORGANISMS AND PESTICIDE DEGRADATION: FROM CHALLENGE TO FULL SCALE APPLICATION

摘要

Caused by high contents of micro-organisms and pesticides in IJssel Lake water N.V. PWN Water Supply Company North Holland (PWN) has decided to implement UV/H_2O_2-treatment at their surface water treatment plant at Andijk.rnIn collimated beam experiments both Giardia muris and Cryptosporidium parvum proved to be veryrnsusceptible to UV-radiation. UV doses as low as 20 mJ/cm~2 resulted in a 2 and 3 log inactivationrnrespectively.rnBoth Bacillus subtilis endospores and MS2 phages were shown to be more resistant to UV. MS2rnphages showed the greatest resistance, UV doses as high as 105 mJ/cm~2 were needed for 3.5 log-unitrninactivation. The results were confirmed by pilot plant data.rnAt a dose of 105 mJ/cm~2 there was no evidence of reactivation. However there was evidence thatrnGiardia muris cyst reactivation may occur at an UV-exposure lower than 25 mJ/cm~2.rnThe data demonstrate that medium pressure UV-radiation effectively inactivated the microbialrnpathogens and indicator organisms for a UV dose of 105 mJ/cm~2.rnUV-photolysis showed a selective pesticide degradation. Conversion using an electric energy of 1 kWh/m~3 varied from 18 % for trichloroacetic acid to 70 % for atrazine. UV/H_2O_2-treatment gave a much more aselective pesticide degradation. For a broad range of combination of electric energy (< 1 kWh/m~3) and H_2O_2 dose (< 15 g/m~3 H_2O_2) all pesticides can be degraded for more than 80 %. This UV dose of 1 kWh/m~3 (1200 mJ/cm~2) is much higher than needed for disinfection.rnFormation of harmful by-products proved to be insignificant. In the range of 0.1 - 2.5 kWh/m~3 electric energy and 0-25 g/m~3 H_2O_2 bromate formation was absent, while primary metabolite formation was insignificant. AOC-formation was found up to 140 μg/l. Therefore AOC and residual H_2O_2 must be removed in a following treatment step. GAC-filtration showed very reliable results.rnIn view of the very promising results application of UV/H_2O_2-treatment will be implemented in the Andijk plant for both organic contaminant control and disinfection.