Enhanced bioremediation for treatment of chlorinated solvent residual source areas

Recent studies have demonstrated enhanced mass transfer of chlorinated solvents from the nonaqueous phase to the aqueous phase during bioremediation. In addition to two previously identified mechanisms for enhanced mass transfer, a third mechanism observed during studies at the Idaho National Engineering and Enviromnental Laboratory is described. Laboratory measurements demonstrated that sodium lactate (used as an electron donor for biostimulation) can decrease interfacial tension with nonaqueous TCE by 26% when the concentration is increased from 0.1% to 3% by weight, and by 47% when the concentration is increased to 30%. A field study showed sodium lactate injection resulted in a factor of 23 increase in trichloroethene (TCE) concentrations due to enhanced mass transfer. The TCE was then stoichiometrically converted to cis-1,2-dichloroethene and ultimately was completely biologically reduced to ethene.