Volatilization of Contaminants from Suspended Sediment in a Water Column during Dredging

Abstract

Remedial dredging of contaminated bed sediments in rivers and lakes results in the suspension of sediment solids in the water column, which can potentially be a source for evaporation of hydrophobic organic compounds (HOCs) associated with the sediment solids. Laboratory experiments were conducted in an oscillating grid chamber to simulate the suspension of contaminated sediments and flux to air from the surface of the water column. A contaminated field sediment from Indiana Harbor Canal (IHC) and a laboratory-inoculated University Lake (UL) sediment, Baton Rouge, LA, were used in the experiments, where water and solids concentration and particle size distribution were measured in addition to contaminant fluxes to air. A transient model that takes into account contaminant desorption from sediment to water and evaporation from the water column was used to simulate water and sediment concentrations and air fluxes from the solids suspension. In experiments with both sediments, the total suspended solids (TSS) concentration and the average particle diameter of the suspended solids decreased with time. As expected, the evaporative losses were higher for compounds with higher vapor pressure and lower hydrophobicity. For the laboratory-inoculated sediment (UL), the water concentrations and air fluxes were high initially and decreased steadily implying that contaminant release to the water column from the suspended solids was rapid, followed by evaporative decay. For the field sediments (IHC), the fluxes and water concentrations increased initially and subsequently decreased steadily. This implied that the initial desorption to water was slow and that perhaps the presence of oil and grease and aging influenced the contaminant release. Comparison of the model and experimental data suggested that a realistic determination of the TSS concentration that can be input into the model was the most critical parameter for predicting air emission rates.

Contaminated Sediments

“…Pore water concentrations of ammonium, nitrates, organic nitrogen, phosphate, and silicate were found to decrease immediately after dredging activity. Release of hydrophobic organic compounds to the water phase and subsequent volatilization into the air were studied in a laboratory oscillating grid chamber (Ravikrishna et al, 2003) 2174 for field sediments that the contaminant fluxes and water concentrations increased initially and subsequently decreased steadily. Linkov et al (2002) studied the interactions among foraging behavior, habitat preferences, site characteristics, and contaminant spatial distribution to develop accurate PCB exposure estimates for winter flounder at a hypothetical open water dredge material disposal site.…”

Evaluation of a sustainable remediation option: Beneficial reuse of petroleum-contaminated sediment as an energy source

“…Capping requires an additional energy cost to produce and/or mine capping materials. Dredging does not often result in complete removal of contaminated sediments, but it accomplishes the removal of highly contaminated hot spots and is successful in decreasing the mass transfer and bioaccumulation to benthic organisms and the water column (Ravikrishna et al, 2002). If dredging and subsequent land disposal is chosen as an option, there is the potential for direct contact by humans, as well as uptake by plants and animals and bioaccumulation up the food web, posing risk to wildlife and to humans that may eat organisms in this food web (Hyötyläinen and Oikari, 2004;Meudec et al, 2006).…”

Cultivating river sediments into efficient denitrifying sludge for treating municipal wastewater

“…[7,8], which has great economic value and can be effectively used [9]. At present, the disposal of sediments mainly includes dredging [10] and landfill [11][12][13] which can easily cause secondary pollution [14,15] and are high in cost [16][17][18]. Therefore, advanced and environment-friendly methods that can effectively dispose of sediments are urgently needed.…”