In situ bioremediation of pentachlorophenol
Abstract
The first known attempt to implement in situ anaerobic bioremediation of pentachlorophenol (PCP) was successfully initiated at a former wood treatment site located in Tippecanoe County, Indiana, USA. The objective of this study was to determine factors limiting PCP biodegradation in the field. This is the first detailed examination of the effect of soil mass to solution volume (m/V) ratio on PCP toxicity. It was possible to reduce the aqueous concentration and toxicity of PCP to anaerobic PCP degrading microorganisms by reducing the m/V ratio. PCP biodegradation is controlled by the aqueous PCP concentration. Aqueous PCP concentrations greater than 70 uM inhibited anaerobic dechlorination of PCP, while PCP concentrations greater than 25 uM inhibited degradation of a primary metabolite, 3-monochlorophenol (3-MCP). Since 3-MCP dechlorinating microorganisms are the most sensitive to PCP toxicity, 3-MCP may accumulate during PCP biodegradation. PCP also inhibited methanogenesis. PCP toxicity may explain why others observe accumulation of metabolites and a lack of complete dechlorination of PCP. Glucose or methanol were effective electron donors and significantly increased the extent of dechlorination when compared to not adding substrate. PCP dechlorination ceased when the aqueous concentration fell below 0.20 uM. Inducing PCP dechlorination with pentabromophenol, which is debrominated without a lag-time, reduced the degradation endpoint of PCP in contaminated soils. This suggests that environmentally safe “dechlorination inducers” could result in significant improvements in bioremediation clean-up levels. In situ anaerobic bioremediation was initiated at the contaminated site under investigation in this study by adding a glucose solution to the contaminated soil via an infiltration drainage system. Water was recirculated through the contaminated soil using recovery wells placed around the perimeter of the infiltration system. Ex situ aerobic treatment was utilized in aerated tanks to biodegrade PCP which was desorbed into the recirculation water. Since initiating bioremediation, new dechlorination products have been detected in the well water and the molar percent of PCP of the total chlorophenols present in well water has been decreasing, while the molar percent of dechlorination products in well water has been increasing. Anaerobic in situ biotreatment can be an effective remediation technology at PCP contaminated sites.
Degree
Ph.D.
Advisors
Nies, Purdue University.
Subject Area
Environmental engineering
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