Kinetics of Pentachlorophenol Degradation in Soil Using Heme and Peroxide

Kinetics of an abiotic method for oxidative pentachlorophenol (PCP) degradation in soil under unsaturated conditions and a neutral pH has been studied. Reagents used were heme as the catalyst and peroxide as the oxidant. Our previous results showed that the heme and peroxide degraded PCP efficiently with two optimum doses of heme and peroxide: one was the optimum point derived from the quadratic model fitting with heme of 0.035 g∕2 g soil and peroxide of 0.105 g∕2 g soil; the other had lower doses of heme ( 0.017 g∕2 g soil) and peroxide ( 0.095 g∕2 g soil) derived from the calculation of 95% confidence interval of the optimum point. Based on these results, the purpose of this study was to examine the kinetics of soil PCP degradation in terms of the rate and extent of PCP destruction at the optimal dosages determined. The results showed that PCP degradation at both optimal dosages looked similar, which showed about 70% of PCP destruction within the first 2 h of reaction and up to 80% of PCP destruction within 1 day after the heme/peroxide treatment. Use of the radio-labeled C14 PCP revealed that 17% of the soil PCP was mineralized to carbon dioxide. Moreover a scaled-up experiment with soil pretreated with ethanol was conducted. The results showed about 70% degradation of PCP which agreed well with the results of the laboratory-scale runs. However the addition of ethanol showed little help in PCP oxidation. Finally a pseudofirst-order kinetic model was employed to describe the trend of the PCP degradation over time, and the outcomes were satisfactory.