Determination of potassium permanganate demand variation with depth for oxidation-remediation of soils from a PAHs-contaminated coking plant.

Bench-scale experiments were conducted to investigate the potassium permanganate demand, a key parameter for in situ chemical oxidation (ISCO) system design, and its variation with depth in PAHs-contaminated site of a coking plant. The concentrations of permanganate decreased rapidly during the first 8 d of the reaction process. The reaction follows first order kinetics, with rate constant ranging from 0.01 to 0.3/h. The total oxidant demand (TOD) is significantly higher for clayey silt fill than for soils of other lithology. The typical TOD is about 50 g MnO(4)(-)/kg soil for clayey silt fill, 20-40 g MnO(4)(-)/kg soil for silt, silty clay and 1-7 g MnO(4)(-)/kg soil for fine sand. Statistical analysis revealed that TOD was positively correlated with total organic carbon (TOC) content, clay content and PAHs concentrations, besides sand content, meanwhile TOC was the parameter with the strongest influence on oxidant demand. After 32 d duration of oxidation, PAHs in all tested soils were effectively removed, with total removal percent ranging from 78% to 99%, and small molecular weight PAHs were removed to a greater extent than high molecular weight PAHs. Parameters obtained in this study, combined with soil bulk density, soil porosity and soil moisture, can be used for full-scale ISCO system design and application in coking contaminated site.