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Bioremediation - Effectiveness of Bioremediation

 

Effectiveness of Bioremediation

 

Removal of various types of organic contaminants has been successful and unsuccessful at a number of sites (USEPA, 2001a). This is simply a list showing examples of sites where various methods have been either successful or unsuccessful, further details can be found in "Use of Bioremediation at Superfund Sites" (USEPA, 2001a).

 

PAHs

 

Burlington Northern Superfund Site, Minnesota. PAHs were reduced from 70,633 mg/kg to 800mg/kg. A reduction of around 99%. The cleanup goal was 8,632 mg/kg. The contaminated material consisted on soil and sludge and was treated using land farming techniques. The additives used included lime and cattle manure. Bonneville Power Administration Ross Complex. Removal was at 90% but targets were not achieved. The initial PAH concentration was around 150mg/kg, this was reduced to 6.76-21.83 mg/kg. The cleanup goal was 1 mg/kg. In this case only soil was treated using land treatment and UV oxidation as part of a technology demonstration. Peroxide and ethanol were used as amendments.

 

Chlorinated VOCs

 

Groundwater at the Avco Lycoming site was contaminated with TCE at 67μg/L and was reduced to 6.7μg/L. The required level was actually 5μg/L and so the project was considered unsuccessful. The method employed was direct injection under anaerobic conditions. The amendment was molasses. The project was actually a pilot study and one of the first to establish clean up goals (USEPA, 2001a). It was probably unsuccessful because the molasses was unable to mix fully with the contaminated water. Another project at the US Department of Energy (DOE) site at Savannah River, South Carolina was successful. Groundwater contamined with TCE (10-1,031μg/L) and PCE (3-124μg/L) was treated using a recirculating cell with amendments of nitrogen, phosporus and methane. Concentrations of both contaminants was reduced to <5μg/L as required. Success is attributed to the fact that the recirculating cell ensured a good mix of contaminated water and amendments.

 

Pesticides/Herbicides

 

Navajo Indian Reservation. Toxaphene was at 4000mg/kg and reduced to 180mg/kg using anaerobic slurry-phase bioremediation. Removal being at 95%. At the Stauffer Chemical Company site, a cocktail of 6 chemicals including DDT (88.4 mg/kg) was present. A composting method known as Xenorem™ was used as part of a demonstration and DDT concentrations were lowered to 8.91 mg/kg. Target removal levels not achieved were not achieved at the end of the 64 day trial period, however. It has been suggested that a longer test period may have reduced concentrations futher.

 

Explosives

 

Removal of explosives can vary greatly. The Joliet Army Ammunition Plant was contaminated with trinitrotoluene (TNT) and tetryl. Two pilot tests achieved removal of removal of TNT at 31% and 97% and tetryl at 3% and 100%, respectively (USEPA, 2001a). The 'unsuccessful' approach mixed compacted soil with potato waste. Then a blend of aerobic and anaerobic bacteria were added and then nutrients were sprayed onto the soil once every two weeks. The 'successful' approach made use of powdered iron and a proprietary organic amendment (DARAMEND®) mixed with the soil. The amendment alters the physical and chemical properties of the contaminated soil to support microbial life and promote biodegradation. Throughout the treatment conditions cycled between aerobic and anaerobic conditions. From these and other similar projects it has been suggested that the addition of proprietary amendments such as DARAMEND® lead to greater removal of explosive contaminants.

 

 

 

 

 

 

 

 

 

 

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