Remediation of Perfluoroalkyl Contaminated Aquifers Using an In-situ Two-layer Barrier: Laboratory Batch and Column Study

Abstract : This ER-2127 project is a Limited Scope SEED project with a fixed budget of $150K, starting in June 2011 and scheduled to complete in May 2014 after no cost extension. The project is proof of concept in nature, which was designed to investigate the feasibility of a novel scheme for the remediation of groundwater contaminated by perfluoroalkyl chemicals (PFCs). This approach is derived from our previous finding that PFCs can be effectively transformed during enzyme-catalyzed humification reactions in the presence of phenolic substrates as mediators (Colosi et al. 2009). The phenolic mediators generate highly reactive radical intermediates under the enzyme catalysis which in turn initiate fortuitous secondary reactions of PFCs, leading to their degradation. The primary objective of this study is to verify the feasibility of using a permeable reactive barrier system to induce effective enzyme-catalyzed humification reactions for in-situ remediation of groundwater PFC contamination. PFCs, such as perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), have extremely high thermal and chemical stability, stemming from their unique structural features in which all hydrogens on carbon are replaced with fluorines. Carbon-fluorine bond is strong because fluorine has strong electronegativity that induces a partial positive charge on carbon and a negative charge on fluorine atoms, leading to electrostatic attraction that makes the bond shorter and stronger. Fluorine is the most electronegative element having a reduction potential of 3.6 V (Wardman 1989). It is thus thermodynamically unfavorable to oxidatively replace the fluorine atom with any other atom. In addition, the fluorine atoms, which are much larger than hydrogen in size, form a dense hydrophobic layer in PFOX (X=S or X=A) surrounding carbon-carbon bonds, which shields them from attack by oxidative reagents.