Field application of palladized iron for the dechlorination of trichloroethene

Palladized iron (Pd/Fe) has been tested under field conditions for the dech lorination of trichloroethene (TCE) in groundwater. Contaminated water was pumped from aquifers in Ohio (similar to0.7- 1.5 mg/l TCE) and Missouri (2- 9 mg/l TCE and 1,2-dichloroethene) and passed through columns of Pd/Fe. The experiments demonstrated that the dechlorination reaction occurs efficient ly until the surface of the Pd/Fe becomes fouled. Regeneration of the surfa ce with dilute (1M) hydrochloric acid is easily accomplished under laborato ry conditions, but initially was unsuccessful in the field. Further experim ents indicated, that reduced sulfur species, although not naturally present in the groundwater being treated, were permanently poisoning the palladium . Apparently, sulfur-reducing bacteria utilize the hydrogen produced by the Pd/Fe process and reduce the sulfate that is present. An anion exchange co lumn was used to remove sulfate (similar to 20 mg/l) from groundwater at th e Kansas City Plant in order to test this theory. Under these conditions, a column of Pd/Fe was repetitively regenerated for a 4-week period. A second column, not protected by sulfate removal, could not be regenerated. The re sults demonstrated that Pd/Fe could be used in a long-term field process if a material with more resistance to Fe and Pd losses is developed. (C) 2000 Elsevier Science Ltd. All rights reserved.