Abstract:

Chlorinated solvents are common groundwater contaminants. They are denser than water and are typically found in anaerobic groundwater. These compounds are biodegradable by different organisms, e.g., bacteria in the genus Dehalococcoides. Such dehalorespiring bacteria rely on an electron donor such as dissolved molecular hydrogen (H_2) to provide electrons in a process that replaces a Cl atom in the chlorinated solvent with hydrogen, at the same time releasing another hydrogen ion as well as chloride into the groundwater. This process thus produces HCl. For this well-studied degradation pathway, the lack of molecular hydrogen is typically the limiting factor in natural biodegradation of chlorinated solvents. In enhanced remediation schemes, the aim is to produce H_2 via fermentation of injected organic matter. However, the HCl produced eventually acidifies the groundwater (and halts biodegradation for pH < 6) unless buffering is provided, either naturally or otherwise. In addition, fermentation produces organic acids. In this talk, two modelling approaches that account for the acid production and buffering occurring in groundwater systems are presented. Because the models are mechanistic, they can aid the design of enhanced remediation schemes either through the addition of buffering agents or through control of groundwater flow rates.