SOIL WASHING AND BIOTREATMENT OF PETROLEUM-CONTAMINATED SOILS

Soil washing was evaluated in combination with biological treatment as a decontamination technology for petroleum-contaminated soils. The bench-scale soil washing system utilized to clean the soils also fractionated the bulk soil into sand, silt, and clay fractions. With tap water as the carrier, the petroleum removal efficiencies varied from 44% to 55% for three soils. The postwash hydrocarbon levels were in the range of 145-905 mg/kg for sands, 2,000-5,000 mg/kg for silts, and greater than 14,000 mg/kg for clays. Biological degradation was evaluated as a secondary treatment to reduce the contaminant levels on each fraction to desired levels. Simulated composting lowered hydrocarbon levels on sands to below 50 mg/kg. Slurry treatment of silt and clay fractions reduced hydrocarbon levels to near 100 mg/kg for silt and in the range of 500 to 1,000 mg/kg for clays. It was found that composting and slurry treatment effectively met the suggested target-treatment level of 100 mg/kg for the sand and silt fractions. For the clays, slow desorption of the hydrocarbons and long treatment periods made slurry treatment an uneconomical alternative.