In situ chemical oxidation (ISCO) is an attractive approach for the remediation of recalcitrant contaminants, due to the fact that target compounds are degraded in place. However, field applications of ISCO approaches have been plagued by “rebound” of contaminant concentrations in groundwater after treatment. The cause of rebound is associated with back-diffusion from finer grained, low permeability units or the presence of non-aqueous phase liquids (NAPLs). Modifications to ISCO methods have been proposed to overcome these challenges, including the use of shear-thinning polymers to improve delivery of oxidants to low permeability units and the addition of surfactants to improve dissolution of contaminants from NAPLs. In this work, we investigate the application of these approaches to the oxidation of manufactured gas plant (MGP) tars—NAPLs composed primarily of polycyclic aromatic hydrocarbons (PAHs). We conducted experiments to determine the impact of each chemical component on the physical and chemical properties of the overall system. Experiments were designed to: determine the kinetics and overall effectiveness of contaminant-oxidant reactions for multiple oxidant-activator combinations; screen several common surfactants in terms of their ability to increase MGP tar solubility and their compatibility with oxidant systems; measure the impact of oxidants and surfactants on the rheology of polymer additives, including xanthan gum, guar gum, hydroxyethyl cellulose, and carboxymethyl cellulose, and; assess the effect of surfactants and polymers on the consumption of oxidants/activators and on the kinetics of contaminant-oxidant reactions. The results of this work provide insight into the chemical and physical mechanisms associated with enhanced ISCO approaches.
Sina Sadeghi– Graduate Student, California State University, Northridge, Calabasas