Chlorinated solvents have been widely used in industries for decades and caused serious problem in groundwater contamination.  Some of the most commonly found in groundwater are perchloroethylene, trichloroethylene (TCE), 1,1,1-trichloroethane (1,1,1-TCA), carbon tetrachloride. Bioremediation by anaerobic reductive dechlorination has become a popular option for remediation of these contaminated aquifers.  This approach requires a good electron donor amendment to stimulate the indigenous microorganism to degrade the chlorinated contaminants.  Currently, most commercially available bioremediation enhancers are either in solid form or as an emulsion with oil droplet size larger than 500 nm.  Here, we focused on formulating vegetable oil nanoemulsion with an initial oil droplet size less than 100 nm that has shown much better transport characteristics than those traditional enhancers.  To prove the feasibility, a pilot study is undertaken at a site contaminated with 1,1-dichloroethylene and TCE in the southwestern part of Taiwan.  Two tests were conducted and the second one did not start until the value of total organic carbon (TOC) dropped to baseline.  In the second test, by adding about 1,350 liter of this emulsion, the degradation of TCE is quite fast with a first-order rate constant at 0.272 d<sup>-1</sup> (R<sup>2 </sup>= 0.9998).  The half-life of TCE is about 2.55 d that is quite short comparing to the values reported in literature.  Through the measurement of TOC, it is estimated that the emulsion existed as a slow releasing compound good for at least 150 d.  The influence range was more than 5.0 meter downstream within 14 d.  The main reasons for this fast degradation rate could be (1) the acclimation of indigenous microorganisms during the first test; (2) higher groundwater temperature in tropical area (most halorespiring microbes are more active at temperature between 30-35°C); (3) ample supply of electrons through this emulsion formulation (this can effectively depleted other competitive electron acceptors) ; (4) smaller oil droplet size rendering higher specific surface area for contact of microbes and contaminants; and (5) higher emulsion stability eliminating pore clogging problems.

Pilot study on bioremediation of chlorinated solvent-contaminated aquifer using vegetable oil nanoemulsion

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.