Anaerobic Biodegradation of Chlorinated Aliphatic Solvents

The anaerobic biodegradation of chlorinated aliphatic hydrocarbons (CAH) including carbontetrachloride (CT) and trichloroethylene (TCE) under various electron acceptor conditions was investigated using enrichment cultures developed from the anaerobic digester sludge of Thibodaux sewage treatment plant. The results indicated that CT was biotransformed under sulfate-reducing, methanogenic, nitrate-reducing, iron-reducing, fermenting, and mixed electron acceptor conditions. However, the rates of CT removal varied among the conditions studied. The fastest removal of CT (100% removal in 12 days) was observed under mixed electron acceptor conditions followed in order by sulfate-reducing, methanogenic, fermenting, iron-reducing, and nitrate-reducing conditions. Similar results were observed for TCE. Under mixed electron acceptor conditions, the CT was converted to methyl chlorides, which was further metabolized. Under sulfate, iron, nitrate-reducing, and methanogenic conditions, the major metabolite produced from CT metabolism was chloroform (CF). Under fermenting conditions, methylene chloride was produced from CT metabolism. This study showed evidence for CT and TCE metabolism in a mixed microbial population system similar to any contaminated field sites, where heterogeneous microbial population exists.