Knoll Environmental, LLC (Knoll)

Probiological Remediation Technology (PRT) Services

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Bioremediation is a dynamic biological process that provides for the remediation of ground water through the acceleration and enhancement of natural biodegradation. The process involves stimulation of the resident microbial population by providing nutrients such as oxygen, nitrogen and phosphorus. The nutrient-enhanced bacteria feed directly on the contaminants. The desired end result of the overall process is the conversion of the contaminant into carbon dioxide and water. Nutrient introduction is commonly accomplished by in-situ injection through wells and surface vessel mixing. The method selected is a function of site specific considerations such as; hydrology, type and concentration of contaminants present; media impacted (soil and/or ground water) and level of cleanup required.

In-Situ Reductive Dechlorination

The contaminant PCE and TCE are common ground water contaminants from dry cleaner sites and are technically difficult and costly to remediate. Knoll has successfully implemented in-situ reductive chlorination at several sites in Massachusetts.

Reductive dechlorination is a biological process where anaerobic microorganisms indigenous to the aquifer use hydrogen to remove the chlorine atoms form the organic molecule resulting in non-toxic end products such as ethane/ethene. Anaerobic microorganisms substitute hydrogen (H+) for chlorine on the PCE/TCE chlorinated hydrocarbons.

Through this process, the chlorinated hydrocarbons can be degraded to form vinyl chloride, and even ethene, as depicted below.

The concept of in-situ reductive dechlorination using natural anaerobic microbial communities for the destruction of chlorinated contaminants in the ground water and soil relies on the principle that the indigenous microbial community in the subsurface will metabolize the contaminants to harmless byproduct compounds. However, only a few selective anaerobic microorganisms have the capacity for complete dechlorination of PCE to non-toxic products, such as ethene. Therefore, in addition to an efficient food source for the microorganisms, Knoll identifies and measures the bacterium, the Dehalococcoides group organisms (Dhc), capable of complete dechlorination of chloroethenes (i.e., tetrachloroethene, trichloroethene, cis-dichloroethene, vinyl chloride to non-toxic ethene).

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