A Rotterdam refinery is treating 10,000 metric tons of petroleum-contaminated soils in aboveground bioremediation cells equipped with vapor-extraction systems.
The treatment process, designed bar Groundwater Technology Inc., Norwood, Mass., the refinery's remediation consultant, is degrading the hydrocarbons to meet strict butch standards. Project completion is expected by Spring, requiring a total of only about 9 months.
The contamination was accumulated in more than 25 years of refining operations at the site. As part of the construction of a new hydrocracker, the refinery was required to remediate the soils and take measures to reduce groundwater contamination.
PILOT TEST
Aboveground bioremediation involves placing soils in engineered treatment cells or "biopiles." These biopiles contain manifolded piping systems for oxygenation, nutrient addition, process control, and monitoring.
The nutrients and increased oxygen stimulate growth of naturally occurring bacteria that degrade the hydrocarbons to carbon dioxide and water. The process is controlled by air-pumping equipment, which regulates air flow, and vapor systems, which treat off-gases.
The treatment cells are contained within an impermeable base, and protective sheeting prevents runoff and traps heat during cold periods.
To obtain regulatory approval for using the process, a pilot study was conducted to demonstrate the applicability of the process to site conditions. For this purpose, the refinery provided 800 metric tons of contaminated soil: 500 tons containing medium-to-heavy oil (heavier than diesel) and 300 tons containing very heavy oil (similar to crude oil,).
The soils were placed in a single engineered treatment cell. Within 8 months, the concentration of the lighter oil was reduced to less than the regulatory limit and substantial progress had been made in reducing concentrations of the heavy product.
Within 13 months, the lighter oil concentration was less than the detection limit and the heavy product concentration had reached low residual levels (Fig. 1).
Based on the pilot test results, the refinery was given permission to treat and reuse larger quantities of soil on site.
PROJECT SCALE-UP
In preparing for construction of the hydrocracker, about 15,000 metric tons of soils were excavated from the site. Extensive testing showed that only 10,000 metric tons of the excavated soils required treatment.
The soils are being treated in four engineered treatment cells, each capable of handling batches of 2,500 tons (Fig. 2). Excellent results were achieved after the first 75 days of treatment.
Contamination remaining beneath the site will be treated by an in situ bioremediation and groundwater extraction system. The system is being installed concurrently with the hydrocracker construction and will be integrated into the hydrocracker design. The groundwater extraction and treatment system will include 23 pumping wells and 11 monitoring wells.
According to project manager Yvo Veenis of Groundwater Technology, "Treating soils on site will be accomplished at about half the cost of off site treatment alternatives. In addition, the refinery will avoid the liability of transporting contaminated soils on public roads and the limited applications for soils treated by destructive processes."
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