BIOAUGMENTATION FOR IN SITU TREATMENT OF CHLORINATED ETHENES

The complete reductive dechlorination of chlorinated solvents such a tetrachloroethene (PCE) and trichloroethene (TCE) to ethene is the holy grail of any enhanced in situ bioremediation (EISB) systems. Most practitioners and research has focused on the selection and delivery of appropriate nutrients (e.g., electron donors such as molasses, edible oils, lactate, hydrogen) to promote reductive dechlorination. Recent laboratory and field research is showing that the presence of Dehalococcoides ethenogenes-like species is required to cause complete dechlorination. Unfortunately, D. ethenogenes does not appear to be ubiquitous, and therefore limits the ability to implement EISB at every site.

Phylogenetic relatives of D. ethenogenes have been shown to be present in dechlorinating cultures, and their addition to sites deficient of these microorganisms has resulted in the complete dechlorination of PCE/TCE where this activity otherwise does not occur. A laboratory microcosm study and a pilot scale field test were conducted to evaluate biostimulation and bioaugmentation to dechlorinate PCE to ethene at Kelly Air Force Base, TX. Only partial dechlorination of PCE was observed in laboratory and field studies when various electron donors were used. Following the addition of a dechlorinating enrichment culture, called KB-1, the chlorinated ethenes in the microcosms and in the field were completely converted to ethene. The maximum rates of dechlorination estimated from field data were rapid (half lives of a few hours). Use of Dehalococcoides-specific PCR assay and 16S rDNA sequence information conclusively demonstrated that Dehalococcoides species in the KB-1 culture had progressively increased in abundance and spread downgradient from their point of introduction, and where responsible for complete conversion of PCE to ethene.