Generalized model of pentachlorophenol distribution in amended soil-water systems

This paper describes laboratory experiments and subsequent statistical data analysis performed to reevaluate the overall effect of soil characteristics and liquid-phase composition on the extent of pentachlorophenol (PCP) adsorption in complex soil-water systems. The PCP adsorption isotherms were first generated for eight soils of varying physical and chemical properties. Binding tests were then performed in the presence of different additives (surfactant, oil, etc.) and conditions (temperature and pH) based on a fractional factorial design. Statistical analysis of data showed strong interdependencies among several of the soil parameters, but confirmed that organic carbon content (foc) and pH of the soils were the best predictors of the adsorption constant of PCP (Kd) for nonamended soil-water systems. It was determined that the effect on Kd of a 0.2 unit decrease in soil pH was approximately the same as increasing foc by 1%. From studying the effect of the amendments, two interactions (surfactant-pH and surfactant-oil) and two primary effects (surfactant and oil) have been detected. The effectiveness of the surfactant in decreasing Kd varied depending on the pH and oil content of the soil. A generalized nonlinear model expressing Kd as a function of pH, foc, oil content of soil, and surfactant dose was developed for the range of conditions studied. The proposed model and modeling approach can be adapted to other types of contaminants or variables for specific natural and engineered systems.