(Waste Treatment Technology News) Nov 2002 - Solutions Industrial &Environmental Services, Inc. (Bob Borden, 3722 Benson Dr., Raleigh, NC27609; Tel: 919/873-1060, Fax: 919/873-1074) and Terra Systems, Inc. (1035Philadelphia Pike, Suite E, Wilmington, DE 19809; Tel: 302/798-9553) havedeveloped a simple, cost-effective method for enhancing the in-situbiodegradation of chlorinated solvents. In the Edible Oil Substrate (EOS)process, food-grade oils are emulsified and injected into contaminatedaquifers to stimulate reductive dechlorination.Chlorinated solvent contamination is a common and expensive cleanupproblem existing at industrial sites, military bases and dry cleaners.Standard "pump and treat" processes can control plume migration, but areexpensive to operate long-term. Newer remediation techniques such assurfactant and solvent flushing can remove solvents from highlycontaminated source areas, but have high capital costs and are notsuitable for light contamination or at sites where the pollution source isill defined.Researchers have long known that naturally occurring bacteria cananaerobically biodegrade chlorinated solvents to non-toxic end productsthrough reductive dechlorination. In the EOS process, which received U.S.Patent 6,398,960 in July, a site-appropriate edible oil is selected anddistributed throughout the contaminated zone, providing good contactbetween the oil and the chlorinated solvent. The oil slowly dissolves overseveral years providing a carbon and energy source to accelerate theanaerobic biodegradation of contaminants. All materials used in theprocess are food-grade substances, which eases regulatory approval for in-situ application. The oil may be added to the treatment zone throughconventional wells or using direct push technology to reduce costs.In reductive dechlorination, naturally occurring bacteria gain energy forcell metabolism and growth by removing chlorine atoms from chlorinatedpollutants and replacing them with hydrogen. Chlorinated solvents amenableto reductive dechlorination include tetrachloroethene (PCE),trichloroethene (TCE), cis-1,2- dichloroethene (cis-DCE), vinyl chloride(VC), 1,1,1- trichloroethane, 1,1,2-trichloroethane, 1,2-dichloroethane,carbon tetrachloride and chloroform.A variety of organic substrates including acetate, butyrate, glucose,lactate, methanol and molasses can be used to provide hydrogen forreductive dechlorination. But such substances are rapidly degraded andmust be continuously replenished or biodegradation will cease. Equipment,materials and labor required for continuous injection greatly increasecapital and O&M costs. Properly applied, common vegetable oil can providea long-lasting and less expensive carbon source for reductivedechlorination.In laboratory tests, company researchers constructed microcosms usingaquifer material from a chlorinated solvent contaminated site that wasamended with 500 mg/L of soybean oil. TCE and DCE were completelyeliminated from all microcosm bottles within 50 days. Produced vinylchloride was fully transformed to ethene after about 90 days. Aftersitting idle for one year, the microcosms were repeatedly respiked withPCE, but no more soybean oil was added. Immediately after the fifthrespike with 20 mg/L PCE, the PCE concentration dropped to about 2.2 mg/Las it sorbed to the vegetable oil. The dissolved and sorbed PCE thenrapidly transformed to TCE, then DCE, then VC and eventually to ethene.All of the chlorinated compounds were degraded to below detection limitsin each microcosm within 50 days of respiking. More than 3 years after thelast soybean oil addition, the chlorinated solvents still continue tobiodegrade.The companies have also completed pilot and full-scale applications of EOStechnology at military and commercial sites in New York, Delaware, NorthCarolina, Virginia, Oklahoma and California. After a recent application inOklahoma, TCE and cis- DCE declined in wells used to install the EOSbarrier immediately after injection. In a monitor well located immediatelydown gradient of the barrier, TCE declined more slowly with a temporaryaccumulation of VC. Within four months of EOS injection, however, TCE haddeclined by more than 90% and VC was degraded to below detection.The developers expect life cycle costs for EOS barriers to be much lowerthan competing technologies such as pump and treat or zero valent ironpermeable reactive barriers (PRBs). In a comparative analysis that modeledcosts over a 30-year period for a 600-ft- wide by 80-ft-deep chlorinatedsolvent plume, installation of an EOS barrier was much less expensive thanpump and treat or an iron PRB. Costs include engineering design,permitting, installation, materials, operation and maintenance, andmonitoring for 30 years. The EOS barrier cost assumes reinjection of oilevery five years and monitoring expenses similar to an iron PRB. Monitorednatural attenuation (MNA) proved less expensive than all other remediationapproaches, including construction of an EOS barrier, but, in many cases,regulators will not approve corrective action plans based on MNA alone.Laboratory studies are underway to evaluate the use of EOS for treatmentof a wide variety of other pollutants including nitrate, perchlorate,chromium, radionuclides such as uranium and technetium and acid minedrainage.