Biologically enhanced dissolution of tetrachloroethene DNAPL

One major problem with tetrachloroethene (PCE) contamination of aquifers is its ability to form dense, nonaqueous-phase liquids (DNAPL), which can act as a persistent contamination source for decades. Batch studies were performed to determine the potential for biological reductive PCE dehalogenation at high concentration and the effect on competing microorganisms, including methanogens and homoacetogens. Results show that PCE dehalogenation can be obtained at saturation concentration (>0.9 mM). Also, trichloroethene was dehalogenated up to 2.26 mM, and no apparent inhibitory effect on dehalogenation was found with cis-1,2-dich- loroethene (cDCE) and ethene at the highest tested levels of 0.66 and 1.05 mM, respectively. However, such high concentrations of PCE, cDCE, and ethene were inhibitory to methanogens, and high concentrations of PCE were inhibitory to homoacetogens. Such inhibition is highly beneficial as it greatly diminished the competition by methanogens and homoacetogens for added electron donors, including hydrogen, resulting in highly efficient substrate utilization for dehalogenation. PCE DNAPL dehalogenation in a column study required less than 1 g of the electron donor pentanol to dehalogenate 1 g of PCE to cDCE (<2 mol of pentanol/mol of PCE). Additionally, DNAPL dissolution rate was significantly enhanced when directly coupled with biological dehalogenation.