- 3,800 Tons Soil
- 30,800 ppm Crude Oil
- 97% Removal on Coarse Fraction, 95% Removal on Fines
- Additional Biodegradation Achieved Additional 60% Reduction Without Benefit of Additional Microbe Nutrient
BioGenesis demonstrated its soil washing process at full scale at a Midwestern refinery by washing 3,800 tons of soil contaminated with 30,800 ppm of crude oil. Using Wentworth Classification, the soil had an effective grain size of about 50 microns (10% smaller, 90% larger). Samples of washed soil were tested to establish a baseline concentration value, then degradation of the crude oil residual in the soil was monitored for four months.
After washing, and a short adaptation period (<40 days), degradation proceeded at a steady rate until 120 days when it slowed. At 120 days, effectiveness ranged from 50% to 60% additional removal beyond the level after washing.
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Significantly, no nutrient or moisture was added to the soil during the observation period. This was done to isolate just the degradation effect of the washing chemical. In normal field use of the process, degradation is monitored and additional nutrients are added to maintain the oil degrading microbe population and its activity. Such additions increase both the degradation rate and its duration so that very low residual levels in complete compliance are achieved.
Based on an initial contamination level of 30,800 ppm, extraction effectiveness for the washing alone was 85-90 percent, with subsequent biodegradation raising that to an overall effectiveness of 95 to 98 percent. As was expected, after initial washing, greater extraction (91%) was achieved on the larger fraction than on the smaller particle sizes. Even so, for the fines fraction, washing achieved 85 percent extraction. Direct conclusions drawn include the validity of the chemical enhancement to subsequent biodegradation. In addition, the process proved to be effective on weathered, heavy oil from soils with an effective grain size of 50 microns.
The equipment's relatively small size, mobility, negligible undesirable by- products, high processing rates, the absence of air pollution, and elimination of the necessity to transport contaminated material off-site all point to reduced cost and increased acceptability by regulatory authorities, public interest and environmental groups.
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