Biological Treatment Methods

It appears that petroleum-degrading microorganisms are encountered wherever petroleum is found in freezing and frozen soils (Aislabie 1997; Braddock et al. 1997; Margesin and Schinner 1998; Mohn and Stewart 2000; Whyte et al. 2002; Margesin et al. 2003). However, low temperatures (and other factors) limit microbial activity and therefore bioremediation potential (Delille et al. 2007; Rike et al. 2008). Environmental practitioners working in cold regions have developed enhanced remediation techniques to overcome cold-climate limitations in the treatment of petroleum-contaminated soils. Examples of enhanced remediation schemes include soil vapor extraction combined with air sparging to simultaneously treat the vadose zone and underlying groundwater, and bioventing at low flow rates to treat unsaturated petroleum-contaminated soils at sub-Arctic sites. Most recently, micro-bioventing with small air-injection rods embedded in saturated peaty soil was tri-aled on sub-Antarctic Macquerie Island (Rayner et al. 2007). Yielding petroleum-hydrocarbon biodegradation rates of ~10-20 mg kg-1 per day, this method may be amenable to wet contaminated tundra sites.

Landfarming and composting, which are similar treatment methods, provide enhanced bioremediation without the use of mechanized systems. They are prepared-bed type treatments that require proper management of aeration, soil moisture and pH, nutrients, and temperature to affect biodegradation of organic contaminants in soil. Landfarming is an open-air process whereby petroleum-contaminated soil is amended with nutrients and then tilled in a lined biocell. A compost pile(s) can be constructed as a closed and insulated soil pile that is amended with a bulking agent (e.g., wood chips or sawdust) to enhance mixing and oxygenation, forced-air aeration, and nutrients over a smaller footprint. One treata-bility study for composting uses two or three small test piles of the soil to be treated, each amended with raw organic waste material (Savage et al. 1985). Once viable microbial populations are established in the seed piles, seed material is then blended with the target soil as compost piles to stimulate biodegradation. Where landfarming's biological processes are highly dependent on environmental conditions, composting offers greater control of important environmental conditions (Riser-Roberts 1998), and a closed and insulated compost pile generates heat that can potentially extend the period of annual treatment. Landfarming is now well-developed for cold regions and offers low-cost treatment of petroleum-contaminated soil in sizable biocells (Walworth et al. 2008). Ironically, composting is little used and has not yet been fully developed for use with petroleum-contaminated soils in polar regions.

Engineered bioremediation implies use of mechanized systems (e.g., forced aeration with pipe networks, heating and insulation systems, irrigation for nutrient delivery) coupled to increase biodegradation rates and improve overall bioremedia-tion efficiency. An advantage of engineered bioremediation with a heating component for Arctic or Antarctic use is a longer annual treatment season. Environmental engineers have demonstrated that with engineered bioremediation, large volumes of petroleum-contaminated soils can be remediated to cleanup standards within two to three treatment seasons in Alaska (Filler et al. 2008a). Nevertheless, a treatability study should precede any cold-region bioremediation project. Engineered bioreme-diation efficiency is dependent on optimization of mechanized systems and biodegradation parameters in soil. The nominal Arctic bioremediation season is June-September, but can be enhanced by 3 months (May-November) with thermally enhanced bioremediation. Engineered bioremediation for use at remote Arctic sites is being considered, and will likely require an innovative energy scheme (e.g., hydrogen fuel cell, solar, or co-generated power) for implementation. A hybrid engineered bioremediation scheme is planned for use at Casey Station, Antarctica (Filler et al. 2006).

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