Influence of carbonate on the ozone/hydrogen peroxide based advanced oxidation process for drinking water treatment

The influence of carbonate on the ozone/hydrogen peroxide process has been investigated. Carbonate radicals, which are formed from the reaction of bicarbonate/carbonate with OH radicals, act as a chain carrier for ozone decomposition due to their reaction with hydrogen peroxide. The efficiency of bicarbonate/carbonate as a promoter for the radical-based chain reaction in presence of hydrogen peroxide has been calibrated and compared to a well-known chain promoter (methanol) and an inhibitor (tert-butanol). Relative to tert-butanol, the hydrogen peroxide induced ozone decomposition is accelerated by bicarbonate/carbonate. Relative to methanol, bicarbonate/carbonate in presence of hydrogen peroxide is less effective as a promoter under comparable experimental conditions. In the O-3/H2O2 process, the consumption of hydrogen peroxide is proportional to the fraction by which bicarbonate+carbonate contributes to the total rate of OH radical scavenging. In drinking water treatment this is important if the organic matter content of the water is low (less than or equal to 1 mgn). The overall OH radical oxidation capacity is not affected by the reaction of carbonate radicals with H2O2. The OH radical oxidation capacity depends only on the overall scavenging rate. However, the rate of the oxidation of a micropollutant can be significantly increased in presence of H2O2 if the bicarbonate/carbonate fraction on the overall scavenging gets more important. The rate of ozone decomposition increases in such conditions, resulting in a smaller ozone oxidation capacity and less disinfection. The experimental findings (ozone decomposition, OH radical oxidation capacity and hydrogen peroxide consumption) could be reproduced by kinetic modeling using a standard set of rate constants from the literature. This further supports our proposed mechanism for the processes in the Advanced Oxidation Process (AOP) O-3/H2O2 in presence of bicarbonate/carbonate.