Treating Soil PCP at Optimal Conditions Using Heme and Peroxide Shyi-Tien Chen 1 ; David K. Stevens 2 ; Guyoung Kang 3 ; and M.-J. Hsieh 4 Abstract: The environmental impact of pentachlorophenol PCP has been the subject of extensive research in recent years. Investiga- tions of PCP degradation using both biotic and abiotic methods are extensively reported in literature. Based on some preliminary tests not shown, an abiotic method was found for oxidative PCP degradation in soil under unsaturated conditions and a neutral pH. Reagents used were heme a catalyst and peroxide an oxidant. From two screening tests not shown, the heme and peroxide were identified as the most important factors on PCP degradation in highly PCP-contaminated soil. The objective of this study was to determine the optimum doses of heme and peroxide for PCP degradation in soil. Using a statistical method, known as response surface methodology, a quadratic function was fit to the data and used to estimate the optimum doses of heme and peroxide at 0.035 g/2 g-soil and 0.105 g/2 g-soil, respectively, in treating PCP-contaminated soil. The model also was used to determine the region in which the response was within the 95% confidence region of the optimum. The lowest heme and peroxide doses required to achieve a response within the 95% confidence region of the optimum were found to be 0.017 g/2 g-soil and 0.095 g/2 g-soil, respectively. Based on the results of the optimization studies, kinetic studies were conducted to examine the rate and extent of PCP degradation in soil over time. The results showed that about 50% of PCP was degraded within the first 30 min, and up to 80% of PCP was degraded within 4 h. DOI: 10.1061/ASCE0733-93722006132:7704 CE Database subject headings: Oxidation; Environmental impacts; Degradation; Soil pollution; Soil treatment. Introduction There has been a recent renewal of interest in in situ chemical processes for the destruction of xenobiotic chemicals in soil at waste disposal sites. Among those xenobiotic chemicals, pen- tachlorophenol PCP is known as one of the recalcitrant toxins to microorganisms. Oxidation of phenolics using the hydroxyl radi- cal has been demonstrated to a limited degree by several research- ers using variants of the well-known Fenton’s reagent that uses the oxidation of transition metals, such as ironII to generate the hydroxide radical from hydrogen peroxide Eisenhaur 1964; Bowers et al. 1989; Watts et al. 1990; Chen et al. 2001; Neyens and Baeyens 2003. Application of Fenton’s reagent for destruc- tion of xenobiotics in slurry systems required large amounts of peroxide Sedlak and Andren 1991; Teel and Watts 2002, and the generated hydroxyl radical is extremely reactive and highly toxic to microorganisms. Leaching problems and hydroxyl radical tox- icity are two major difficulties in using Fenton’s reagent on site. In addition to Fenton’s reagent, the oxidation of various or- ganic compounds in peroxidase systems is well known Danner et al. 1973; Umezawa and Higuchi 1989. Hemoprotein iron oxi- dation in peroxidase enzymes by hydrogen peroxide has been reported in literature Danner et al. 1973; Ator et al. 1987.A wide range of unsaturated lipids and fatty acids is catalytically oxidized by heme and heme proteins Tappel 1955; Rice et al. 1983; Tappel 1953. Peroxidases generally serve as protective en- zymatic systems; however, they can catalyze a peroxide- dependent binding process which may result in cellular genetic damage. In this system active oxygen species, such as a free radical and singlet oxygen, are produced. The macromolecules or tissue, near those active oxygen species can be damaged Rice et al. 1983. Based on an analogy to this and the peroxidase system, Chen et al. 1999 postulated a mechanism of heme catalyzed degrada- tion of PCP given in Fig. 1. It is believed that the active oxygen species may result in the cleavage of the PCP ring. The reaction cycle will not stop until either the electron donors, such as PCP, are completely oxidized, or the system runs out of the oxidizing source—the peroxide. Fig. 1 shows that heme loses two electrons due to the presence of peroxide and becomes an activated heme radical. The highly oxidized heme radical can obtain an electron from the chlorinated organic compound, such as PCP, and be- comes the activated heme group that may obtain another electron from other chlorinated compounds and return to its original form. In the postulated cycle, peroxide that gains two electrons is known as an oxidant, the heme that has no electron change is a catalyst, and the chlorinated compounds that lose electrons are the 1 Dept. of Safety, Health and Environmental Engineering, National Kaohsiung First Univ. of Science and Technology, No. 2 Juoyue Rd., Nantsu, Kaohsiung 811, Taiwan corresponding author. E-mail: shyitien@ccms.nkfust.edu.tw 2 Dept. of Civil and Environmental Engineering, Utah State Univ., Logan, UT 84322-4110. 3 Dept. of Environmental Studies, Hankuk Univ. of Foreign Studies, 89 Wangsan-Ri Mohyun-Myun Yongin-Kun, Kyungki-do 449-791, South Korea. 4 Dept. of Safety, Health and Environmental Engineering, National Kaohsiung First Univ. of Science and Technology, No. 2 Juoyue Rd., Nantsu, Kaohsiung 811, Taiwan. Note. Discussion open until December 1, 2006. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and pos- sible publication on March 23, 2005; approved on September 6, 2005. This paper is part of the Journal of Environmental Engineering, Vol. 132, No. 7, July 1, 2006. ©ASCE, ISSN 0733-9372/2006/7-704–708/ $25.00. 704 / JOURNAL OF ENVIRONMENTAL ENGINEERING © ASCE / JULY 2006