Use of an Anaerobic Sludge Digestion Process to Treat Pentachlorophenol-(PCP-) Contaminated Soil

Extensive pentachlorophenol (PCP) contamination and its increasing treatment costs motivate the search for better treatment alternatives. In this study, the feasibility and effectiveness of an anaerobic sludge digestion process was evaluated. Two laboratory-scale digesters mimicking the commonly used anaerobic sludge digester in a municipal wastewater treatment plant were operated to treat PCP. Results showed that up to 0.98 mM of chemical PCP dissolved in acetone and 0.6 mM soil PCP from a contaminated site were treated at nearly 100 and 97.3% efficiencies, respectively. PCP dechlorination followed two major pathways: PCP to 2,3,4,5-TeCP to 2,3,5- or 3,4,5-TCP to 3,5-DCP and PCP to 2,3,5,6-TeCP to 2,3,5-TCP to 3,5-DCP to 3-MCP. The 3-MCP was not present until 26 days after the first addition of PCP, which also concluded the end of the sludge acclimation process to PCP. Microbial acclimation reduced chlorophenol toxicity and enhanced degradation of chlorophenol. Without acclimation the gas production and chlorophenol degradation were both significantly hindered. 95% of the added PCP was transformed to 3-MCP, 4.5% to 3,4-DCP, and 0.5% to 3,5-DCP, and about 20% of the PCP by-products remained in liquid and the rest adsorbed on sludge solids. Results of this study suggested the potential use of an anaerobic sludge digestion process for PCP-contaminated soil remediation.