Comparison of Reducing Agents for Dechlorination in a Simulated Aquifer (PDF)

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A simulated aquifer system (Aquifer Simulation Vessel – ASV) was used to study the efficacy of various reducing agents to assist microbial dechlorination. The soil samples are homogenized and the soil is packed into 6.0-foot long tubes with an internal diameter of 5.75 inches. Flow rates can be calibrated for flow at 0.1 to 2.0 feet/day. The system has a volume of 2025.44 in3.  A solution of TCE and water is held in a reservoir at the beginning of the tube and connected to a nitrogen tank under slight positive pressure to retard volatilization of TCE. The TCE concentration in the reservoir is maintained at 20 ppm.  This system has been used for several years and found to be quite reproducible in determining gradient profiles of contaminants as they are bioremediated with an active soil and reducing agent. Lactate released from a polylactate ester was compared to vegetable oil and molasses for efficacy of bioremediation of the TCE. Vegetable oil and molasses were not able to maintain a profile of reducing agent along the tube. Controlling the location of the reducing agent appears critical in order to obtain consistent results. The efficacy of a reducing agent as well as the economics of use should consider the total amount of material that is needed to maintain contact with the bioremediation zone as well as the cost and timing of application. With the polylactate ester the source of the agent remains stationary and only the released lactate migrates with the water flow while with oil and molasses the entire reducing agent plume moves away from the treatment zone over time.

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