Many advanced oxidation processes involve addition of hydrogen peroxide (H 2O 2) with the aim of generating hydroxyl radicals to oxidize organic contaminants in water. However, chemical oxygen demand, a common measure of gross residual organic contamination, is subject to interference from residual H 2O 2 in the treated water. A new method, involving catalytic decomposition of H 2O 2 with addition of heat and sodium carbonate (Na2CO3), is proposed in this work to address this problem. The method is demonstrated experimentally, and modeled kinetically. Results for 5 mM H 2O 2 in deionized (DI) water included reduction to below the COD detection limit after 60 min heating (90°C) with addition of 20 g/L Na2CO3 concentrated solution, whereas 900 min were required in treated municipal wastewater. An approximate second order rate constant of 11.331 M -1min -1 at Na 2CO 3 dosage of 20 g/L was found for the tested wastewater. However, kinetic modeling indicated a two-step reaction mechanism, with formation of peroxocarbonate (CO 4 2-) and ultimate decomposition to H 2O and O 2 in pure H 2O 2 solution. A similar mechanism is apparent in wastewater at high catalyst concentrations, whereas at low Na 2CO 3 addition rates, the catalytic effects of other constituents appear important.
ASJC Scopus subject areas
- Environmental Chemistry