Nakagawa, H.; Yamaguchi, E. (2012) 14th Asia Pacific Confederation of Chemical Engineering Congress, pp. 274
Fenton reaction that produces an active oxidant through the reaction between ferrous ion and hydrogen peroxide has been believed to be effective for degrading organic pollutants in the wastewater. However, it is also well known that a significant amount of degraded organic compounds remains in the treated water. To enhance the degree of mineralization, irradiation of UV light during Fenton reaction, which so-called photo-assisted Fenton reaction, has been proposed and successive results have been reported. Mineralization mechanism on the photo-assisted Fenton reaction is not, however, understood well. In this study, the effect of reaction condition on the degree of mineralization of phenol and mineralization mechanism is examined through the analysis of organic compounds remaining in the treated water.
A fairly large amount of oxalic acid was found to be formed through the degradation of phenol with Fenton reagent. The yield of oxalic acid reached as high as 0.50 on the carbon basis. It was confirmed that oxalic acid is very stable against the Fenton reagent, indicating that it is one of the main organic compounds remaining in the treated water. UV irradiation could decompose Fe(III)-oxalate to produce Fe(II) and CO2 and mineralization degree reached 0.95 for 4 h. The reduction rate of TOC was almost consistent with the reduction rate of oxalic acid on the carbon basis. Therefore, decomposition of Fe(III)-oxalate mainly contributes to the mineralization. Irradiation time to achieve 0.95 in mineralization degree was independent of initial Fe(II) concentration. This result indicates that almost UV light is absorbed to Fe(III)-oxalate because of its high absorbability and an appropriate light intensity has to be required for the effective mineralization of organic compounds in the wastewater.