Persulfate treatments of phenanthrene-contaminated soil: Effect of the application parameters

The aim of this work was to study the effects of the parameters involved in persulfate (PS) application, namely, the cation counterion, mode of persulfate addition and soil-moisture content, to optimize the use of low doses of PS coupled with bioremediation technologies. Soil microcosms were contaminated with 110 +/- 20 mg of phenanthrene per kilogram of dry soil. The efficiency of each treatment in phenanthrene elimination was evaluated. Additionally, the impact on cultivable autochthonous heterotrophic bacteria populations was examined. The addition of sodium persulfate in successive doses (14.9 g/kg(DS)) showed the greatest efficiency in phenanthrene elimination (36%) after 7 days of treatment, but inhibited further bioremediation. Sodium persulfate was more efficient than ammonium. Increased moisture enhanced the bioremediation but inhibited the oxidative treatment. The persulfate-ion decomposition rate decreased at high moisture levels, possibly through diluting activators within the soil. The results suggest that, for oxidative treatments of contaminated soil, the application of low doses of sodium PS at low soil-moisture levels is the most effective option for an elimination of phenanthrene that is compatible with bioremediation.