Anaerobic Reductive Dechlorination
PCE and TCE contaminants in ground water can be biodegraded by naturally occurring anaerobic bacteria by a process known as reductive dechlorination. This occurs when anaerobic bacteria take electrons from small organic compounds (the "electron donors") and produce H2. The dechlorinating bacteria use the electrons in the H2 to replace a chlorine atom in TCE/PCE.
If the site soil and ground water contain organic electron donors, this process can proceed until all of the chlorine atoms are removed, and TCE is dechlorinated completely via dichloroethene (DCE) and chloroethene (VC) to ethylene gas, a harmless end-product. Other solvents, such as 1,1,1-TCA and Carbon Tetrachloride, can also be degraded by reductive dechlorination.
At many sites, organic electron donors have been consumed, resulting in lack of biodegradation or accumulation of intermediates such as DCE and VC.