Buffering agent for pH control during in situ bioremediation of chlorinated solvent source zones

Chloroethenes such as tetrachloroethene (PCE) and trichloroethene (TCE) are among the most prevalent contaminants in groundwater. Because of their low aqueous solubility, PCE and TCE are often present as dense non aqueous phase liquid (DNAPL) that can act as a long term source of groundwater contamination. In situ enhanced bioremediation is an attractive technology for removal of PCE and TCE. It relies on a process called dehalorespiration in which dehalogenating bacteria reduce PCE to ethene, which is a harmless compound for the environment. Enhanced bioremediation is achieved by stimulating the activity of these specialized bacteria through the addition of an electron donor. This method has been widely used for remediation of chlorinated ethene plumes for more than thirty years and recent studies have indicated that it is a promising technology for bioremediation of source zone. However, application of source zone bioremediation is still a significant technical challenge. One of the main issues is groundwater acidification due to dechlorination and fermentation processes thereby inhibiting activity of dehalogenating micro-organisms. Objective of this project is to develop an efficient buffering strategy for source zone remediation. Utilisation of silicate mineral as buffering agent has been investigated through geochemical modeling and batch experiment. A methodology to select appropriate silicate minerals for pH control based on their kinetics properties and field characteristics has also been developed. A geochemical model, done with the chemical speciation code Phreeqc, including transport phenomena has been implemented to assess the influence of silicate dissolution on acidity. Preliminary results have demonstrated that certain minerals belonging to aluminosilicate (nepheline) and magnesium iron silicate (olivine) present kinetics fast enough to neutralize acidity typically produced during bioremediation of DNAPL source zone. Experimental studies including mineral dissolution and reductive dechlorination by bacterial culture are currently performed to validate the results of this model.

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David Andrew Barry, Christof Holliger, Elsa Marina Lacroix
2010
Poster talk

Abstract

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https://infoscience.epfl.ch/record/147465?ln=en

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Related concepts (4)

Silicate mineral

Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually considered a silicate mineral. Silica is found in nature as the mineral quartz, and its polymorphs. On Earth, a wide variety of silicate minerals occur in an even wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years.

Bioremediation

Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings. The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment.

Groundwater

Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table.