Chemical oxidation of cable insulating oil contaminated soil

Abstract

Leaking cable insulating oil is a common source of soil contamination of high-voltage underground electricity cables in many European countries. In situ remediation of these contaminations is very difficult, due to the nature of the contamination and the high concentrations present. Chemical oxidation leads to partial removal of highly contaminated soil, therefore chemical oxidation was investigated and optimized aiming at a subsequent bioremediation treatment. Chemical oxidation of cable oil was studied with liquid H 2O 2 and solid CaO 2 as well as permanganate at pH 1.8, 3.0 and 7.5. Liquid H 2O 2 most effectively removed cable oil at pH 7.5 (24%). At pH 7.5 poor oil removal of below 5% was observed with solid CaO 2 and permanganate within 2 d contact time, whereas 18% and 29% was removed at pH 1.8, respectively. A prolonged contact time of 7 d showed an increased oil removal for permanganate to 19%, such improvement was not observed for CaO 2. Liquid H 2O 2 treatment at pH 7.5 was most effective with a low acid use and was best fit to a subsequent bioremediation treatment. To further optimize in situ chemical oxidation with subsequent bioremediation the effect of the addition of the iron catalyst and a stepwise liquid H 2O 2 addition was performed. Optimization led to a maximum of 46% cable oil removal with 1469 mM of H 2O 2, and 6.98 mM Fe(II) chelated with citric acid (H 2O 2:FeSO 4 = 210:1 (mol mol −1). The optimum delivery method was a one step addition of the iron catalyst followed by step wise addition of H 2O 2.