Vapor phase treatment of PCE in a soil column by lab-scale anaerobic bioventing

Abstract

Microbial destruction of highly chlorinated organic compounds must be initiated by anaerobic followed by aerobic dechlorination. In-situ dechlorination of vadose zone soil contaminated with these compounds requires, among other factors, the establishment of highly reductive anaerobic conditions in the unsaturated subsurface. Such conditions may be established by delivering appropriate gas mixtures to the subsurface, i.e., “anaerobic bioventing”. The gas must include an electron donor. This study was conducted as a feasibility study for anaerobic bioventing, using tetrachloroethene (PCE) as a test contaminant and H 2 as the electron donor. Using a soil column inoculated with anaerobic dechlorinating bacteria, to simulate the vadose zone, experimental results showed that by passing a gas composed of 1% H 2 and >0.1% CO 2 in N 2, methanogenic conditions were established and that PCE (fed as a vapor in the gas stream) was rapidly converted with terminal products vinyl chloride (VC) and trans-dichloroethene ( trans-DCE). PCE half life in the column was 7 min, while parameter estimation yielded a first order PCE degradation rate k PCE, of 0.098 min −1. Intermediate products detected but not accumulated in the column were trichloroethylene (TCE) and cis-dichloroethene ( cis-DCE). The high dechlorination rates observed for PCE make anaerobic bioventing an attractive method that can potentially be integrated in an in-situ remediation process to treat contaminated soils in the unsaturated zone.