In-situ generation of both hydroxyl radical and adsorptive flocs in electro-coagulation process with air breathing cathode

Abstract

In order to achieve considerable generation of free radicals during electro-coagulation (EC) process, EC with air breathing cathode (EC-ABC) was designed to allow for the coexistence of electro-Fenton (EF) and EC functions. This EC-EF-ABC synergetic system allows for both in-situ free radicals and adsorptive flocs generation in an undivided electrolytic cell. The yield of hydroxyl radicals and adsorptive flocs were quantified for accurate mechanism analysis. The control mechanism of the transition from EF to EC function during EC-ABC system was investigated. The air cathode material was studied and optimized to obtain high hydroxyl radical generation. The influences of both dissolved oxygen (DO) and pH condition on hydroxyl radical and flocs generation were studied. Whiles the latter was found to dominate the successive EF and EC functions, and further controls the hydroxyl radicals and flocs yield, the former only has a dominant effect on the hydroxyl radical yield. The adsorptive iron (oxy)hydroxide flocs’ structure was also found to be fully depend on the DO condition. The control mechanism of initial pH and DO condition on radical and flocs generation was simplified as a ‘Sudoku-like’ relationship. The optimized initial pH and DO condition was studied to maximize the generation of hydroxyl radicals and adsorptive flocs. The design of EC-ABC process could have both advanced oxidation and adsorption abilities for wastewater pollutant removal.