Maximum Oil Retention

Design emulsified oil injections for optimal performance at a minimal cost

Chlorinated solvents including tetrachloroethene (PCE) and trichloroethene (TCE) have been widely used in a variety of industrial/commercial applications and are now prominent groundwater contaminants.  Under anaerobic conditions, PCE and TCE are susceptible to biological reductive dechlorination through the daughter products cis-dichloroethene and vinyl chloride to ethene, an innocuous end product.  While monitored natural attenuation (MNA) can be an effective remedial approach, reductive dechlorination can be hindered by a lack of electron donors under MNA conditions.  Therefore, biostimulation by subsurface injection of a suitable electron donor such as an edible oil emulsion is often performed to promote biological reductive dechlorination and enhance anaerobic bioremediation.

Although a wide variety of site-specific variables including contaminant area, saturated zone thickness, and injection point spacing must be considered, one of the most fundamental design parameters when evaluating biostimulation as a treatment technology is the amount of emulsified oil required.

  • If the injected mass is too low, the oil will be rapidly depleted and long-term performance will be limited.
  • Conversely, overestimation of the edible oil mass required leads to increased costs with little improvement of overall treatment.

Thus, the amount of emulsified oil injected should be optimized to permit effective treatment at the lowest possible capital cost.

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The amount of emulsified oil required is a function of the maximum amount of oil retained per unit mass of aquifer material (ORM) in addition to the treatment zone dimensions.  Typically, the ORM (g oil/g aquifer material) is estimated based on the sediment type.  However, reported ORM values range from as low as 0.0004 g/g for coarse grained sands and gravel to as high as 0.01 g/g for fine, clayey sands containing kaolinite.  Considering that underestimation or overestimation of ORM can dramatically impact treatment efficiency and capital costs, determine a site specific ORM is a cost-effective measure to optimize biostimulation as a remedial action.

 

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