Enhanced mineralization of 2,4-dichlorophenol by ozone in the presence of trace permanganate: effect of pH

Ozonation of 2,4-dichlorophenol (DCP) in the presence of permanganate has been investigated at various levels of pH. Compared with only 40% in single ozonation, by catalytic ozonation the total organic carbon removal efficiency reached almost 95%. It has been shown that the addition of 0.5 mg L-1 MnO4- (based on manganese content) greatly accelerated the mineralization of DCP when the initial pH was below 8.5. Under these conditions MnO4- was reduced to Mn2+, which enabled homogeneous catalysis to take place. When the initial pH was above 10.1, the MnO4- was reduced to MnO2, which did not promote mineralization of DCP by ozone under either neutral or alkaline conditions. Under acidic conditions, however, the addition of MnO2 greatly enhanced DCP mineralization, the mechanism being that MnO2 was reduced to Mn2+ which is a highly effective homogeneous catalyst for ozonation.