Column Studies on Methanotrophic Degradation of Trichloroethene and 1,2‐Dichloroethane

The potential for and variables affecting enhanced aerobic biodegradation of 14 C‐labeled trichloroethene (TCE) and 1,2‐dichloroethane (1,2‐DC A) were evaluated using laboratory columns packed with fully saturated sandy aquifer material. The column fluids were exchanged weekly to simulate the growth of native microorganisms capable of biotransforming halogenated aliphatics. The exchange solutions for seven columns, one of which served as a control, contained dissolved oxygen as the electron acceptor. The electron donor, or primary substrate, for another column was dissolved propane, and the remaining five columns were fed varying concentrations of dissolved methane. Propane was not consumed, and TCE degradation did not occur in this column. However, methane was utilized in other columns, and the resulting stimulated populations mineralized both TCE and 1,2‐DCA to CO 2 . Little or no TCE degradation occurred when the methane concentration was 4.5 mg/1, but when the methane was reduced to 1.5 mg/1, degradation occurred. TCE degradation was greatest when either a low methane concentration (1.5 mg/1) or an alternating pulse of methane (4.5 mg/1 or 1.5 mg/1) with oxygen one week followed by oxygen only the next was used. Nutrient supplements (NH 4 + and PO4 2‐ ) did not conclusively enhance TCE degradation. When TCE addition was stopped and methanotrophic bacteria stimulation was continued, half of the 14 C from previously sorbed TCE that was subsequently eluted by exchange was present as nonvolatile compounds and CO 2 , and the other half as TCE. With a caution that the results obtained are site‐specific, they do suggest that the addition of methane and oxygen to water circulated through a ground‐water system to remove TCE by aboveground treatment can, in some cases at least, result in a doubling of the rate of removal and affect mineralization of about one‐half of the TCE removed.