DECHLORINATION OF CHLORINATED BENZENES BY AN ANAEROBIC MICROBIAL CONSORTIUM THAT SELECTIVELY MEDIATES THE THERMODYNAMIC MOST FAVORABLE REACTIONS

A chlorinated benzene dechlorinating anaerobic microbial consortium was obtained by selective enrichment with hexachlorobenzene (HCB) and lactate from a freshwater sediment sample that originated from an area with proven in situ HCB dechlorination. The consortium was used to determine compound selectivity and relative dechlorination rates by incubation with the individual chlorinated benzenes under methanogenic conditions. The dechlorinating activity was restricted to benzenes with at least three adjacent chlorines, except for a relative slow transformation of 1,2,4,5-tetrachlorobenzene to 1,2,4-trichlorobenzene. Optimal temperature for dechlorination was around 30 degrees C, significant dechlorinating activity was still observed at a temperature of 3 degrees C. The selectivity of the enrichment culture showed an interesting correlation with the thermodynamics of the various dechlorination steps: from the 19 dechlorination reactions possible with benzenes that contain at least two chlorines, only the seven reactions with the highest energy release took place.