Impacts of a non-ionic surfactant on the remediation of NAPL-associated and soil sorbed pentachlorophenol

Pentachlorophenol (PCP) is a common hydrophobic organic contaminant in soil resulting from use as a wood preservative and pesticide. In-situ biodegradation of PCP may be slow due to poor bioavailability of soil-sorbed and nonaqueous phase liquid (NAPL)-associated PCP. Therefore, other treatment strategies able to enhance the speed and effectiveness of PCP remediation are of interest. This work explored fundamental aspects of surfactant-enhanced remediation of PCP-contaminated soil with and without NAPLs.; The use of the non-ionic surfactant Tergitol NP-10 (TNP10) to remediate PCP-contaminated soil was investigated. Batch tests were used to determine the effects of pH, ionic strength, and soil type on TNP10 and PCP sorption to soil. Significant amounts of surfactant sorbed to soil solids with increasing TNP10 sorption to soil at concentrations far above the critical micelle concentration (CMC). TNP10 sorption was described by a Langmuir isotherm. Approximately 40–45 times more TNP10 and 20–30 times more PCP sorbed to a soil with higher organic matter content and smaller average grain size. Aqueous TNP10 concentrations well above the CMC (≥5,500 mg/L) were needed to enhance PCP desorption from soil. Low TNP10 doses actually increased PCP sorption to the soil, and PCP appeared to have a greater affinity for sorbed TNP10 than natural soil organic matter. Less TNP10 and PCP sorption to soil occurred at higher solution pH. Lower ionic strength increased PCP desorption from soil.; The effect of TNP10 on the partitioning of PCP out of a heavy mineral oil NAPL was studied in batch tests at various pH and ionic strength. A significant fraction of the surfactant partitioned into the NAPL. Enhanced PCP dissolution into water was achieved at aqueous TNP10 concentrations of ≥200 mg/L, well above the CMC. The surfactant had a greater influence on PCP dissolution at lower pH. Higher ionic strength decreased the amount of PCP that dissolved out of the NAPL into water.; To extend understanding beyond the basic equilibrium partitioning behavior of surfactants and PCP, column studies with simulated groundwater flow were conducted. Results indicated that effluent surfactant concentrations at ≥200 mg/L TNP10 significantly increased the effluent PCP concentration from soil columns containing NAPL. The seeded bacteria did not significantly reduce effluent PCP concentrations from soil columns, with negligible effects at high surfactant concentrations (≥3,850 mg/L). Of the soil-sorbed surfactant, 70 to 80% was removed from the column during 25 pore volumes of clean water flushing, indicating that the surfactant adsorption is reversible. The results indicate the conditions under which surfactant addition will aid the removal of PCP-contaminated sites.