Phenanthrene sorption/desorption mechanisms and rapid prediction of long-term desorption rates using superheated water

Hydrophobic organic contaminants (HOCs) in subsurface systems pose carcinogenic threats to drinking water supplies, but remediation is limited by sorption to and slow desorption from soils and sediments. Thus, in order to predict associated risk and plan effective remediation strategies, HOC sorption and desorption processes must be understood in a predictable manner.;Soil and sediment organic matter (SOM) is typically the dominant sorption domain of HOCs. It has been hypothesized that sorption capacity and isotherm nonlinearity are a function of the degree of condensation and aromatization of SOM resulting from natural diagenetic processes, but this has not been directly tested because natural diagenesis occurs over extremely long time scales. To overcome the barrier of geologic time, a method for artificially inducing SOM diagenesis through superheated water extraction and reaction was developed. Subsequent phenanthrene sorption equilibria for artificially aged samples provide direct evidence that sorption capacity and isotherm nonlinearity both increase with increasing degree of SOM condensation and aromatization.;Desorption of HOCs from soils and sediments into interstitial water can take months or years to reach an endpoint. This study improved current experimental techniques and characterized long-term phenanthrene desorption as a function of soil and sediment organic matter type, loading level, and aging time.;Rate limiting mechanisms responsible for slow HOC desorption from soils and sediments are poorly understood and actively debated in the scientific literature. Through determining apparent activation energies of phenanthrene desorption from soils and sediments and identification of an isokinetic temperature, this study supports the theory that intraorganic matter diffusion is a dominant rate limiting mechanism for slow desorption.;A laboratory technique for rapidly predicting the long-term HOC desorption behavior in a contaminated soil or sediment would be invaluable for engineers and scientists planning remediation. Schemes and/or grappling with difficult alternative remediation endpoint decisions. Therefore, this study also developed a superheated water extraction technique for rapid prediction of long-term phenanthrene desorption. Proposed methodologies have great practical significance because desorption at ambient temperatures requires months or years, while high temperature experiments are accomplished in hours or days.