Identifier

etd-11102007-154707

Degree

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Document Type

Dissertation

Abstract

The discharge of hydrophobic organic chemicals (HOCs) and other hazardous substances from anthropogenic sources to surface waters and the atmosphere has led to the widespread contamination of bottom sediments throughout the world. HOCs collect in sediments due to their affinity for organic matter and other sorbents present on and within their solid matrices. There is interest in the movement of HOCs from historically contaminated, resuspended sediments to surface waters due to the connection between chemical desorption and bioavailability. Quantitatively accurate predictions of contaminant concentrations in environmental media are needed for reliable risk assessment and to develop strategies for protection of environmental quality. To fully describe the processes relevant to HOC transport between sediment and water, several scales must be understood. These include the molecular, intraparticle, particle, and operational scales of chemical transport. The understanding of particle-scale processes is an evolving area of environmental science and engineering research but suffers from a lack of information regarding the role of particle structure and organic matter arrangement at the intraparticle scale. Using insights from studies of sediment and soil surface properties and empirical measurements of contaminant release rates, a particle-scale model of contaminant desorption has been developed that provides some insight into the nature of biphasic chemical desorption. HOC release in the environment is a serious problem that can be exacerbated in the short term by the implementation of remediation technologies. Environmental dredging is a commonly employed remediation option, often for the practical purpose of maintaining waterways. During dredging operations significant quantities of sediment are resuspended and move offsite. To date, it has been assumed that the impact of this material is greatest at the point of dredging, but this has not been tested either experimentally or using a robust chemodynamic modeling approach. A mechanistic model incorporating the relevant transport processes for introduction and removal of dissolved chemical in the water column originating from suspended sediment was developed and simulations using field data forecast a maximum soluble chemical concentration far downstream from the point-of-dredging. This contradicts the equilibrium partitioning assumption often used to estimate the impact of remedial dredging.

Date

2007

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Louis J. Thibodeaux

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