Removal of precursors for disinfection by-products (DBPs) - differences between ozone- and OH-radical-induced oxidation

Pre-oxidation is often applied to reduce the formation of disinfection by-p roducts (DBPs). The aim of preoxidation is to remove the centers of natural organic matter (NOM) which are responsible for the formation of DBPs. In t his paper, the differences between ozone- and OH-radical-induced oxidation to remove DBP-precursors are compared. The experiments were done with water of the River Ruhr (Germany) with a concentration of dissolved organic carb on (DOC) of 2 mg/l. Ozonation was able to remove DBP precursors selectively . After application of an absorbed ozone mass of 1.5 mg/mg DOG, a reduction in the formation potential for (THM-FP) and in the formation potential for organic halogen adsorbable on activated carbon (AOX-FP) down to 68 and 73% of the initial concentration was achieved, respectively. A removal of NOM was not achieved using absorbed ozone masses between 0.5 and 1.5 mg/mg DOG. In the hydrogen peroxide/UV process, in which OH-radicals are the reactive species, an increase in the THM concentration was measured after applicati on of this process with short irradiation times. The maximum value of the T HM-FP was 20% higher than the initial THM-FP. After an irradiation time of 1050 min and a hydrogen peroxide consumption of 5.6 mg/l, the THM-FP and AO X-FP decreased to 75 and 71% of the initial formation potential, respective ly. There was no selective removal of DBP precursors because the DOC concen tration decreased also to 75% of the initial DOC-concentration after 1050 m in of irradiation. (C) 2000 Elsevier Science B.V. All rights reserved.