DEVELOPMENT AND CHARACTERIZATION OF CONTROLLED-RELEASE PERMANGANATE GEL FOR GROUNDWATER REMEDIATION

Dense Non-Aqueous Phase Liquids (DNAPL) contamination of aquifers, particularly by chlorinated solvents, is widespread and difficult to treat. A large number of issues associated with in-situ oxidant flushing of DNAPLs can be avoided through the introduction of controlled-release potassium permanganate (KMnO₄). To develop an effective treatment system, the behavior of materials to be injected into groundwater must be investigated in terms of emplacement and oxidant release. This study investigates colloidal silica as a primary delivery system through the conduction of gelation and release tests.

Batch gelation tests were conducted to monitor the increase in viscosity through time, due to the sol-gel process. This process resulted in a solidified gel to provide a vehicle for diffusional release of oxidant. Gels were modified in terms of ionic strength in order to achieve extended gelation time that would allow for increased emplacement area within an aquifer. Column tests were conducted to determine mass flux and kinetics of release of the controlled-release gel. Once characterized in the absence of media, the tests were replicated in the presence of flowing water and porous media to represent aquifer conditions.

Data obtained from tests was used to identify a suitable solution that will gel in three days’ time and release over a sustained period. Observed gelation times ranged from 1 hour to 15 days. Results indicated that gelation time as related to ionic strength was not a constant or linear relationship. Gel saturation with respect to potassium permanganate was observed as a dominant factor in gelation time. Column test results indicated rapid release of oxidant followed by an immediate decrease in flux, with little to no sustained release phase. Gel forms were observed to be exhausted within 24 hours, suggesting the need to further extend release kinetics. Results suggest the new approach using the KMnO₄ gel solution could provide a long term, cost-effective remedial option for large or dilute plumes of chlorinated solvents in groundwater.