Table 1.

Summary of anaerobic and aerobic processes involved in dechlorination/degradation of chlorinated ethenes.

	Oxidation processes		Co-metabolic processes
	Anaerobic (energy yielding)	Aerobic (oxygen dependent, energy yielding)	Anaerobic reduction	Aerobic oxidation	Chlororespiration: anaerobic (energy-yielding reduction)
Metabolic group(s)	Fe(III) reducers Mn(IV) reducers Humic acid reducers	Mycobacterium spp. Nocardioides spp. Pseudomonas spp. Polaromonas sp.	Sulfidogens Methanogens Acetogens	Organisms with broad range oxygenases	Chlororespirers
Relative dechlorination/degradation rates	Unknown	++	+	++a	++++
Frequency of active organisms in nature	Unknown	VC oxidizers widely distributed in aerobic environments	High in anaerobic environments	High in aerobic environments	Not rare in anaerobic environments
Favorable site conditions	Fe(III) reducing Mn(IV) reducing	Aerobic	Anaerobic, not e− donor or e− acceptor limited	Aerobic, primary substrate present	Anaerobic, appropriate e− donor present, no interfering TEAPs

Abbreviations: e⁻, electron; TEAP, terminal electron-accepting process; +, slow rate; ++, moderate rate; +++, fast rate; ++++, very fast rate.

^aDechlorination rates are often not sustained because of accumulation of toxic intermediates.