A novel photoelectro-peroxone process for the degradation and mineralization of substituted benzenes in water

A novel photoelectro-peroxone (PEP) process was developed by combining conventional ozonation, UV irradiation, and electrolysis process to treat substituted benzene (nitrobenzene, chlorobenzene, and benzaldehyde) solutions. The PEP process involves electrochemically generating H2O2 from O-2 in the sparged ozone generator effluent (O-2 and O-3 gas mixture) at a carbon-based cathode. The in-situ generated H2O2 then undergoes UV-induced photolysis and reacts with the sparged O-3 to yield (OH)-O-center dot, which can rapidly and non-selectively oxidize most organic pollutants. Thanks to the enhanced (OH)-O-center dot production, the PEP process considerably increased the pseudo-first order rate constants for the degradation of the three substituted benzenes to similar to 4.7-8.4 times of the simple linear combination of the individual ozonation, UV, and electrolysis processes. In addition, the PEP process was capable of removing 98% total organic carbon (TOC) from the substituted benzene solution in 15 min with a specific energy consumption (SEC) of 0.66 kWh (g TOCremoved)(-1). In comparison, UV/O-3 and electro-peroxone (EP, i.e., ozonation in combination with electro-generation of H2O2) processes took similar to 90 min to remove the same amount of TOC with SEC of 156 and 1.07 kWh (g TOCremoved)(-1), respectively. Furthermore, the presence of Fe2+/Fe3+ did not negatively affect TOC removal by the PEP process, whereas it decreased the efficiency of the EP process considerably. The results indicate that the PEP process can significantly improve the kinetics and energy efficiency for substituted benzene mineralization compared with conventional ozonation, UV photolysis, electrolysis, and their combined processes (UV/O-3 and EP) that have been previously investigated, and may thus offer a highly effective and energy-efficient alternative for wastewater treatment. (C) 2015 Elsevier B.V. All rights reserved.