Electrolysis catalyzed ozonation for advanced wastewater treatment

Abstract

The prohibitive cost of advanced oxidation processes (AOPs) necessitates the development of innovative variations to increase their applicability. This investigation evaluated the combination of ozonation and electrolysis using iron electrodes as a catalytic ozonation AOP for the mineralization of organic compounds in water. The operating parameters of initial pH and current density were optimized using response surface methodology (RSM) to maximize total organic carbon (TOC) removal from a dextrose based synthetic wastewater. The process was most effective for TOC removal in alkaline conditions (initial pH of 9), although performance compared to ozonation alone was more significantly enhanced in acidic conditions (initial pH of 3). TOC removal was found to increase as current density increased from 4 to 12 mA/cm2, regardless of initial pH, primarily due to the increased rate of catalyst addition from the sacrificial anode. It was determined that the initial pH of the system presented a more statistically significant effect on TOC removal than current density, although both parameters were determined to be relevant. Under optimal conditions of 12 mA/cm2 and an initial pH of 9, 63% TOC removal was achieved after 60 min of treatment. Catalyst dosage using electrochemical and chemical approaches was compared, finding that electrochemical catalyst dosage was preferred for TOC removal, illustrated by the pseudo-first order rate constant of observed TOC removal, which was 51–76% higher using the electrochemical approach. Using an indirect measurement method involving tert-Butyl alcohol, hydroxyl radicals were detected during the combined ozonation and electrolysis treatment. Radical production was found to be linked to the conditions which favoured TOC removal. The results of this study have demonstrated the ability of an electrochemical catalytic ozonation process to enhance the removal of organic contaminants in wastewater compared to ozonation alone, established the advantages of harnessing an electrochemically generated catalyst, and characterized the effect of key operating parameters on TOC removal performance and hydroxyl radical production.