H60 Emulsified Vegetable Oil Substrate (EVOS)™

There are three different techniques for in situ biological transformation of chlorinated contaminants: Natural Attenuation; Passive Accelerated Anaerobic Bioremediation; and Accelerated Anaerobic Bioremediation.  Depending on site conditions, economics, and treatment goals one or more of these techniques can be used at the site.

Natural Attenuation: Involves the use of unenhanced natural processes as part of a site remediation strategy. These processes which can transform contaminants to less harmful forms or immobilize them to reduce risks result from biological, chemical, and physical reactions that take place in the subsurface. The dominant attenuation process for chlorinated organics is biotransformation.

Passive Accelerated Anaerobic Bioremediation: Using DPT methods, pumping into existing wells or advanced injection methods a slow release substrate such as an edible oil or edible oil emulsion is injected into the formation to generate reducing conditions and provide the native micro flora with sufficient carbon to conduct reductive dechlorination. Although a number of factors impact the speed of the biological process, the technique most likely will require less than half the time required for Natural Attenuation.

Accelerated Anaerobic Bioremediation: Using a recirculating groundwater system as the transport mechanism, a quick release substrate such as sodium lactate is continuously added and moved throughout the formation. Depending on site conditions, this technique can be expected to remediate a site in a time frame of six months to 5 years.

The accelerated anaerobic bioremediation process uses either native or introduced microorganisms to degrade chlorinated solvents such as PCE to innocuous end products including ethene and ethane. An organic substrate must be added to the groundwater to generate reducing conditions and provide the necessary carbon to support biodegradation of the chlorinated solvents. The organic substrate can be soluble compounds such as benzoate, lactate, molasses, acetate, or methanol. These soluble substrates must be added periodically at either high batch dosages or continuously at low dosages to provide the necessary carbon. Groundwater recirculation is generally necessary to distribute the dissolved organics throughout the contaminated site. Another option for the substrate would be to use a relatively insoluble compound such as edible oil (i.e. soybean oil) which would be added to the groundwater periodically (probably every two to ten years) and usually does not require the groundwater recirculation system. Additional nutrients such as nitrogen, phosphorus, trace elements, and vitamins are also needed.

The approach for stimulating in situ reductive dehalogenation dramatically reduces both the initial capital and long-term O&M costs of treating chlorinated solvent impacted formations. An injection of a low solubility, slowly biodegradable food-grade edible oil (EVOS™) is made through a direct push technology or temporary injection wells. Depending on site-specific conditions, a mixture of several different oils and soluble substrates may be required. The soluble substrates are used to induce rapid, initial biodegradation of the chlorinated solvents in the more bioavailable regions (sand layers). Over time, the oils slowly dissolve and are degraded providing a steady release of dissolved organic carbon to degrade any contaminants that slowly bleed out of low permeability zones.

The key to successful implementation of an in situ bioremediation project is cost-effective distribution of electron donors. Shown below is an evaluation of several commonly used substrates: molasses, corn syrup, lactate, polylactate ester, and EVOS™. Molasses, corn syrup, lactate and other soluble substrates can be dissolved in water and flushed through the treatment zone to very effectively treat the high permeability zones. However these substrates are very rapidly degraded so they must be frequently replenished. Molasses and corn syrup are available quickly and may lead to inhibitory, low pH conditions as organic acids are rapidly released. The polylactate ester has some advantages since it can last six months or more.

  1. Distance indicates expected radial distribution away from injection point
  2. Prices reflect those obtainable for bulk chemicals in 2001.  Price per pound is based upon weight of actual electron donor.  Where present, weight of water or viscosity reducing agents is factored out of cost calculation.
  3. Harkness, M. 2000. “Economic Considerations In Enhanced Anaerobic Bioremediation”  In The Second International Conference on Remediation of Chlorinated and Recalcitrant Compounds: Vol. 4.  Battelle Press, Columbus, OH.  pp. 9-14.

Packaging Options

Packaging
  • 55-gallon poly drums
  • 275-gallon IBC containers
  • 3,000 - 5,000 gallon tankers