Chlorinated ethenes (CEs) are used mainly in industry as degreasing agent, in dry cleaning, and in plastic manufacturing. Mismanagement of their use and improper elimination of mainly PCE and TCE during the 20th century, caused their massive dispersal into the environment. CEs can be fully degraded anaerobically by a biological reductive dechlorination process, during which chlorine atoms are sequentially replaced by hydrogen atoms until the final production of the harmless ethene molecule, in a process called reductive dechlorination. Several bacterial species have been isolated that can couple the reductive dechlorination of CEs to energy conservation. These bacteria differ in their electron donor requirements, kinetics, endpoints of dechlorination, and the maximum tolerated concentrations of chlorinated solvent.
This dechlorination process occurs in contaminated sites (often aquifers) naturally, but the process is slow and often incomplete. Experiences have shown that the degree of CE attenuation is influenced by background concentrations of aqueous and solid phase electron acceptors (not only CEs) in different redox conditions as well as the amounts of potential sources of organic carbon.
From an ecological point of view, aquifers can be considered heterogeneous assemblages of discrete macro- and micro-scale habitats that provide a variety of living conditions, which influence the heterogeneous distribution of the microbial community structures and their inherent activities. Thus, our research activities focus on the relationships and correlations between the living and inert parts of the aquifer, i.e. how the microbes interact with their habitat. They involve research and evaluation of specific actors responsible for the degradation of CEs as well as analysis of bacterial community structures (metagenomes and amplicon sequencing).
Our research activities focus on the developing of statistic tools derived from the field of numerical ecology. Statistical tools were adapted to the analysis of the physico-chemical status of the contaminated aquifers as well as the composition of the bacterial communities and the presence of the bacteria involved in CEs reduction. The conclusions drawn from this analysis contribute for instance to the unambiguous identification of the reasons for which the natural attenuation of CEs cannot be attained fully and to the evaluation of of potential solutions.
Research partners
Christof Holliger : Laboratory for Environmental Biotechnology, EPFL, Lausanne
Sonia Tarnawski : eOde Sàrl, Neuchâtel, Switzerland