| The extensive pentachlorophenol (PCP) contamination and its increasing treatment costs motivate the search for a more competitive treatment alternative. Anaerobic sludge handling at a wastewater treatment plant comprises some commonly-used bioprocesses for organics destruction and biosolids application. Its availability and effectiveness make anaerobic sludge handling a potential technology to treat PCP-contaminated soil.; The technical feasibility of using anaerobic sludge bioprocesses was studied by treating PCP soil in pilot digesters to represent primary sludge digestion, in serum bottles to represent post-sludge digestion, and in glass pans to represent on-site sludge application. For primary digestion, up to 0.98 and 0.6 mM of chemical and soil PCP were treated at nearly 100% and 97.5% efficiencies. PCP degradation followed two major pathways: PCP to 2,3,4,5-TeCP to 2,3,5- or 3,4,5-TCP to 3,5-DCP to 3-MCP; PCP to 2,3,5,6-TeCP to 2,3,5-TCP to 3,5,-DCP to 3-MCP. The PCP was transformed 95% to 3-MCP, 4.5% to 3,4-DCP, and 0.5% to 3,5-DCP. A system of first-order differential equations was sufficient to model a batch-mode PCP degradation system. For post digestion, 100% pure chemical PCP and greater than 95% soil PCP were removed in less than 6 months. Complete removal of PCP by-products makes this process a good soil cleanup method. For on-site treatment, PCP was efficiently treated by multiple sludge application.; Currently, soil treatment is regulated by the cleanup standard, a risk-based value, that defines a site as nonhazardous and Land Disposal Restriction standard that allows putting the treated soil back to its original site if soil PCP is less than 74 mg/kg or treatment efficiency is greater than 90%. All three anaerobic sludge bioprocesses showed that they were capable of degrading soil PCP, demonstrating their potential use in PCP-contaminated site remediation. Sludge acclimation resulted in better PCP treatment efficiencies with all three processes. More mass PCP per unit sludge per day was processed using primary sludge digestion than with on-site soil treatment or post-sludge digestion. |
