Non-ionic surfactant flushing of pentachlorophenol from NAPL-contaminated soil.

Column studies were conducted to assess the suitability of a non-ionic surfactant Tergitol NP-10 (TNP10) for washing pentachlorophenol (PCP) from soil and non-aqueous phase liquids (NAPLs). Flushing of 50 and 200 pore volumes of 5 g/L TNP10 was required to exhaust the surfactant sorption capacity of the soil and soil plus NAPL, respectively. The sorption of surfactant to the soil in the columns was four times greater than the quantity previously observed in batch tests. Flushing with 5 g/L TNP10 removed 71-79% of the 200mg/kg soil-sorbed PCP after 160 pore volumes compared to 0.7-2% PCP removal without surfactant. In columns additionally containing 0.2% and 0.4% PCP-contaminated heavy oil NAPL, the PCP removal efficiency after flushing 200 pore volumes of 5g/L TNP10 was nearly 100%. Therefore, removal of the PCP was more efficient in the NAPL-containing columns, potentially due to competition of the NAPL for PCP sorption sites. Rate-limited desorption of PCP and TNP10 likely occurred.

Aqueous chemistry and interactive effects on non-ionic surfactant and pentachlorophenol sorption to soil.

Non-ionic surfactant addition was investigated as a method to remediate pentachlorophenol (PCP) contaminated soil. The goal was to quantify surfactant (Tergitol NP-10 (TNP10)) and PCP sorption to soil and their interactive effects under varying pH, ionic strength, and soil conditions. Up to 16,700 mg/kg of TNP10 partitioned to soil, with increasing sorption far above the critical micelle concentration (CMC) and with greater amounts of PCP present. Approximately 40-45 times more TNP10 and 20-30 times more PCP sorbed to the finer soil with higher organic matter content. Aqueous TNP10 concentrations well above the CMC (>/=5500 mg/L) were required to enhance PCP desorption from the soil. As pH increased by 0.5-0.85 units, TNP10 sorption decreased by 14-25% and PCP sorption as measured by the log of the equilibrium partition coefficient decreased by 1-1.5. A lower ionic strength of 0.03 versus 0.112 M increased PCP desorption from contaminated soil by 5-17% in the presence of TNP10. This work is relevant to designing ex situ soil washing or surfactant-aided PCP remediation.

Equilibrium partitioning of a non-ionic surfactant and pentachlorophenol between water and a non-aqueous phase liquid.

The partitioning of the non-ionic surfactant Tergitol NP-10 (TNP10) and pentachlorophenol (PCP) into a mineral oil light non-aqueous phase liquid (NAPL) were quantified in batch tests. Due to the ionizable nature of PCP, the effects of pH and ionic strength (micro) on the equilibrium partitioning were evaluated. NAPL:water partition coefficients (K(n:w)) of TNP10 ranged from 3 to 7 l(water)/l(NAPL). Enhanced PCP dissolution into water from the NAPL was achieved at aqueous TNP10 concentrations > or =200mg/l. Surfactant addition of 1200 mg/l TNP10 increased the aqueous PCP concentrations by 14-fold at pH 5 versus 2 to 3-fold at pH 7 as compared to PCP aqueous solubility. The more significant response at the lower pH is likely due to the greater hydrophobicity of PCP at the lower pH, which is approaching PCP's pK(a) of 4.7. Higher ionic strength (micro 0.11 versus 0.001 M) increased K(n:w) of PCP by 10-33% without surfactant, compared to a more than 150% increase with a dose of 4000 mg/l TNP10. This work contributes information relevant to the application of surfactants to remediate sites contaminated with NAPLs.