Chlorinated Solvent Biodegradation by Methanotrophs in Unsaturated Soils

Chlorinated aliphatic solvents arc common contaminants of unsaturated soils. This research focuses on the feasibility of treatment by in situ bioremediation with indigenous methanotrophs. Batch biodegradation experiments are conducted with three unsaturated soils in which indigenous methanotrophs are stimulated by exposure to a methane/air atmosphere. Of the three chlorinated solvents tested, 1,2‐dichloroethane is degraded the fastest, followed by trichloroethylene, and finally chloroform. Zero‐order rate constants for conversion to ${\mathrm{CO}}_2$ range from 0.05 to 1.4 μg solvent/g dry soil‐day. Assuming contaminant concentrations on the order of 100 μg/g soil, these rates imply that in situ bioremediation would require several months to several years for completion. Depending upon the particular chlorinated solvent and soil, microbial activity produces, in addition to ${\mathrm{CO}}_2\text{,}$ significant quantities of nonvolatile products. The products represent disappearance of the parent chlorinated solvent, but may or may not represent acceptable bioremediation depending upon the nature of the products and the treatment goals. Availability of nutrients also significantly affects degradation rates.