Effect of Ionic Strength and Flow Rate on the Transport of Colloidal Activated Carbon in Saturated Porous Media
Open AccessIt is necessary to use ex-situ remediation technology and in-situ remediation technology to clean up the PFAS-contaminated area. Otherwise, people would be at risk of exposure due to PFAS entering the groundwater. Compared to ex-situ remediation, in-situ remediation is more cost-effective and energy saving. Our study mainly focuses on the colloidal activated carbon (CAC) In-situ remediation which works by injecting colloid activated carbon into the aquifer and coating the soil particles in a thin layer of activated carbon, creating a purifying filter to which PFAS is adsorbed. However, after the CAC is emplaced, a change of ionic strength will cause the remobilization of the CAC particles from the aquifer materials. This remobilization will reduce the long-term effectiveness of the remediation and may also make it easier for the PFAS plume to migrate in groundwater.Bare CAC particles without surface modification are extremely unstable and tend to aggregate in aqueous solution. To solve this problem, polymers are used as stabilizers to enhance the dispersion and colloidal stability of CAC particles in the remediation processes. Based on electrostatic stabilization and/or steric stabilization, polymer coating can improve the stability and mobility of CAC particles in subsurface environments, which is a prerequisite for in situ remediation via direct injection of CAC Suspensions. In our experiments, to make the CAC particles more stable and prevent to aggregate in aqueous, we used the carboxymethyl cellulose (CMC) as the stabilizers to enhance the dispersion and colloidal stability of the CAC particles. These enhancements make CAC a suitable injection material for in-situ PFAS remediation. According to the DLVO theory, the change of ionic strength has significant effects on colloid stability. We believe that in coastal areas, the tidal pumping processes that cause variations in groundwater and sea water would result in a continuous change in ionic strength that would affect the stability of the emplaced colloid activated carbon. In summary, our research questions include two aspects. First, to what extent and how fast would emplaced CMC-CAC get released upon changing of groundwater ionic strength? Second, to what extent and how fast would emplaced CMC-CAC get released upon changing of groundwater flow?
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