Cometabolism of trichloroethylene: concepts, limitations and available strategies for sustained biodegradation

Due to its toxicity and persistence in the environment, trichloroethylene (TCE) has become a major soil and groundwater contaminant in many countries. A group of aliphatic- and aromatic-degrading bacteria expressing nonspecific oxygenases have been reported to transform TCE through aerobic cometabolism in the presence of primary substrate such as methane, ammonia, propane, phenol, toluene or cumene. This paper reviews the fundamentals and results of TCE cometabolism from laboratory and field studies. The limitations associated with TCE cometabolism including the causes and effects of substrate and/or inducer utilization rate and depletion, enzyme inhibition and inactivation, and cytotoxicity during TCE oxidation among various TCE-degrading bacteria and enzymes are discussed. In addition, the potential strategies e.g. addition of primary substrate/inducer or external energy substrate, use of a two-stage reactor and application of cell immobilization for sustained TCE degradation are highlighted. The review summarizes important information on TCE cometabolism, which is necessary for developing efficient TCE bioremediation approaches.