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Bench-Scale Evaluation of Gas Ebullition On The Release of Contaminants From Sediments
Citation:
Chattopadhyay, S., T. LYONS, V. Lal, AND E. Foote. Bench-Scale Evaluation of Gas Ebullition On The Release of Contaminants From Sediments. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-10/062, 2010.
Impact/Purpose:
To describe the performance of a microcosm and bench-scale column studies to understand and quantify the release of contaminants of concern (COCs) from uncapped and capped sediments.
Description:
The release of gas bubbles from sediments into overlying water (ebullition) is a major mechanism for the discharge of biogenic and geogenic gases into the water body. Microbial breakdown of sedimentary organic matter produces gas bubbles which are inherently hydrophobic and tend to accumulate both hydrophobic organic contaminants and colloids from porewater. Through this mechanism the ebullition of CH4 and CO2 in contaminated sediments may contribute to the release of COCs from the sediment-water interface and into the water column. With the formation of gas bubbles in the sediment, a three phase benthic system exists: solid sediment particles, water and gas. Organic compounds present in sediment will partition between the solid sediment particles and liquid porewater based on the sorptive characteristics of the sediment and physicochemical properties of the COCs. Partitioning of the organic contaminant between the gas and water phase is determined by the gas-water partition coefficient of individual components of the COC. The transport of contaminants would therefore occur when gas bubbles, containing volatilized organic compounds, are ejected from the sediment and transported directly to the atmosphere. Transfer of organic contaminants from the gas bubbles to the overlying water may occur during transit through the water column as a result of gas to water partitioning. Microbial breakdown of sedimentary organic matter produces gases, which tend to migrate out of sediments into overlying water and are eventually vented to the atmosphere. Gas generation indicates that microorganisms are able to break down sedimentary organic matter for energy and nutrients. The duration of gas production is still unknown, since gas production is still occurring. No systematic column studies have explored the phenomenon of gas ebullition in sediments on the stability and effectiveness of the cap and consequently to the release of sediment/cap bound contaminants to overlying water. This report describes the performance of microcosm and a bench-scale column studies to attempt to understand and quantify the release of COCs from uncapped and capped sediments. The gas ebullition through the sediment bed was simulated by sparging mixed anaerobic gas at two flow rates (6.5 and 18.5 mL/min).
URLs/Downloads:
BENCH-SCALE EVALUATION OF GAS EBULLITION ON THE RELEASE OF CONTAMINANTS FROM SEDIMENTSAbstract
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