Date of Award

1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Kalliat T. Valsaraj

Second Advisor

Danny D. Reible

Abstract

Contaminated sediments that become exposed to the air as a result of dredging or water receding are potential sources of emissions of toxic compounds to the atmosphere. Exposure models are currently being developed to assess the risk associated with this pathway of contaminant release and to design efficient remediation techniques. A critical parameter in these emission models is the equilibrium partition coefficient of the contaminant between the sediment and the air. In this study, the sediment-air equilibrium partitioning of a polymiclear aromatic hydrocarbon (phenanthrene) and a heterocyclic aromatic hydrocarbon (dibenzofuran) was investigated. Both classes of compounds are commonly found in contaminated sediments and are known carcinogens. A gas saturation technique was used to study the influence of ambient temperature and sediment moisture content on the partition coefficient of the contaminants. The primary factor affecting the partitioning is the sediment moisture content (mc). Its variation from about 0% to 6% causes the partition coefficient to decrease by up to three orders of magnitude. Determination of phenanthrene's heat of sorption in dry (mc = 0.3%) and wet (mc > 6.0%) sediments indicates that different mechanisms of sorption exist in each moisture range. In the dry range, the contaminant is mainly adsorbed on the mineral surfaces of the sediment. When the moisture content increases, the competitive adsorption of water progressively displaces the contaminant from the mineral adsorption sites. Finally, in the wet range, the contaminant is mainly associated with the sediment organic matter. In addition, the physical state of water in the sediment as a function of moisture content was characterized by comparing the isotherm of water sorption to the pore-volume distribution. This permitted the estimation of the respective contributions of the various sorption mechanisms to the overall sediment-air partitioning process. A model of the sediment-air partition coefficient is proposed that accurately accounts for the observed variations resulting from changes in sediment moisture content.

ISBN

9780599252295

Pages

252

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