New insights in oxidation and disinfection processes – Effect of organic matter and formation of secondary oxidants

Oxidative water treatment is a very important step for disinfection and pollutant degradation. Worldwide the most often used oxidant is chlorine as it is easy to apply and a very good disinfectant. However, all oxidation processes change the chemical composition of the water matrix. E.g. reactions of oxidants with organic matter often lead to the formation of undesired by-products but also to further (secondary) oxidizing agents. This largely increases the complexity of these processes as intrinsically formed oxidants themselves can form undesired by-products and have an effect on disinfection and pollutant degradation. The most prominent example is the formation of highly reactive hydroxyl radicals in ozone-based processes which contribute to pollutant degradation. Recent results have shown that the reaction of chlorine dioxide (ClO2) with organic matter forms hypochlorous acid as a secondary oxidant. This results in an additional set of undesired by-products but also effects pollutant degradation and disinfection processes. The intrinsic formation of secondary oxidants is also important for intracellular reactions. The formation of hypochlorous acid in the endoplasm of pathogens may largely increase cell damage and may thus, improve the ClO2 based disinfection process.
These examples show that the natural and bacterial organic matter has far more influence on oxidation processes than a sole consumption of an oxidizing agent. Due to complexity of the NOM-structure these reactions are yet, not well understood. A better understanding of these processes will be become more important in the future, since the quality of water resources is changing, as one of the consequences of climate change.
In the seminar new mechanistic insights of oxidant reactions with natural and bacterial organic matter and the formation of secondary oxidants will be discussed.