Reductive dehalogenation of chlorinated ethenes with elemental iron: The role of microorganisms

Trichloroethene (TCE) transformation and the product distribution in an aqu eous medium containing zero-valent iron (Fe(0)) was investigated in the pre sence of an anaerobic mixed culture to assess the potential role of microor ganisms in permeable iron barriers. The presence of the culture increased t he rate of TCE disappearance and changed the product distribution. Rapid fo rmation and degradation of cis-dichloroethene (cis-DCE) was observed in rea ctors containing cells plus Fe(0) or H-2 as a bulk reducing agent. High lev els of vinyl chloride (VC) were formed and very similar profiles were obtai ned in the Fc(0) plus cell and H2 plus cell reactors, but not in Fe(0)-only reactors. The similar trends observed in Fe(0)-cell and H-cell reactors su ggest that most cis-DCE and VC in the Fe(0)-cell reactors were produced and transformed biologically rather than abiotically. Accumulation of methane in the Fe(0)-cell system indicates that hydrogen gas generated during anaer obic iron corrosion could support a methanogenic culture. Digital confocal images showed that the microorganisms were able to colonize the iron surfac e. The results suggest that potential development of dechlorinating populat ions in Fe(0) barriers may alter the TCE reduction pathway and produce VC, which would have significant impact on the performance of Fe(0) barriers. ( C) 2001 Published by Elsevier Science Ltd.