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

A chlorinated benzene dechlorinating anaerobic microbial consortium wa s obtained by selective enrichment with hexachlorobenzene (HCB) and la ctate from a freshwater sediment sample that originated from an area w ith proven in situ HCB dechlorination. The consortium was used to dete rmine compound selectivity and relative dechlorination rates by incuba tion with the individual chlorinated benzenes under methanogenic condi tions. The dechlorinating activity was restricted to benzenes with at least three adjacent chlorines, except for a relative slow transformat ion of 1,2,4,5-tetrachlorobenzene to 1,2,4-trichlorobenzene. Optimal t emperature for dechlorination was around 30 degrees C, significant dec hlorinating activity was still observed at a temperature of 3 degrees C. The selectivity of the enrichment culture showed an interesting cor relation with the thermodynamics of the various dechlorination steps: from the 19 dechlorination reactions possible with benzenes that conta in at least two chlorines, only the seven reactions with the highest e nergy release took place.