Oxidation of dissolved organic matter in the effluent of a sewage treatment plant using ozone combined with hydrogen peroxide (O3/H2O2)

The effluent from the secondary clarifier of an Urban Sewage Treatment Plant was oxidized by the combined and simultaneous use of ozone and hydrogen peroxide. The purpose was to increase the wastewater's reuse potential by improving water quality. The removal of dissolved organic chemicals was enhanced by adding periodic pulses of hydrogen peroxide while keeping pH above 8.0 throughout the runs. These conditions led to almost complete mineralization in less than 1 h. Under similar conditions, without the addition of hydrogen peroxide, the removal of total organic carbon (TOC) was no higher than 35%. The evolution of TOC was related to the concentration of hydroxyl radicals using a second-order kinetic model in which the exposure to hydroxyl radical was included by assuming a quasi-steady-state approximation. The concentration of hydroxyl radical was computed using the experimental data from ozone and hydrogen peroxide. The kinetic constants for the hydroxyl-mediated mineralization process were determined for wastewaters collected during a 1-year sampling campaign. The results showed that the mineralization process takes place in two periods whose rate constants were linked to the chemical oxygen demand (COD) to biochemical oxygen demand (BOD) ratio and to the chloride content of wastewaters. During the first part of the runs, the specific rate of mineralization was high, before subsequently decreasing after a period of 5–15 min by an average factor of 6.4 whose 95% confidence interval was in the 3.4–9.3 range. The moles of TOC removed per mole of ozone consumed were in the range of 9.2–17.7 mg O3/mg TOC measured at maximum ozone efficiency, which always occurred within the first 10 min.