Persulfate oxidation activated by peroxide with and without iron for remediation of soil contaminated by heavy fuel oil

Laboratory and pilot-scale experiments were used to evaluate and optimize the chemical oxidation process at a power plant in Penghu County, Taiwan. Prior to pilot test, bench scale tests were performed in the laboratory and analytical results indicated that persulfate oxidation achieved 90% removal of fuel oil while Fenton-like oxidation achieved only 41% removal of fuel oil within three days of testing period. Persulfate oxidation coupled with Fenton-like reaction was then used in a pilot test to treat the contaminated soil onsite. The Fenton-like reaction served the first stage of oxidation which formed hydroxyl radicals to break down fuel oil. The excess ferrous ions and heat resulted from Fenton´s reaction would then activate persulfate oxidation which, in turn, produced sulfate radicals for continual brake-down of fuel oil. Result of soil pilot test indicated that the concentration of fuel oil was reduced to below the regulated standard within one week. Of the treated soil, there are 71.7% of fuel oil oxidized by chemical oxidation, 23.5% of fuel oil recovered as free product, and 4.8% of fuel oil remained in soil. Because the soil onsite was rich in heavy metals, leachate collected from the treatment cells was identified to contain heavy metals as nickel and chromium at concentrations exceeding the regulatory standards and could pose threat of secondary contamination to ambient environment if in-situ soil persulfate oxidation was implemented.