Destruction of a Carbon Tetrachloride Dense Nonaqueous Phase Liquid by Modified Fentons Reagent

Destruction of a dense nonaqueous phase liquid (DNAPL) by soluble iron (III)-catalyzed and pyrolusite ((beta)-MnO2)-catalyzed Fentonʹs reactions (hydrogen peroxide and transition metal catalysts) was investigated using carbon tetrachloride (CT) as a model contaminant. In the system amended with 5 mM soluble iron (III), 24% of the CT DNAPL was destroyed after 3 h while CT dissolution in parallel fill-and-draw systems was minimal, indicating that CT was degraded more rapidly than it dissolved into the aqueous phase. Fentonʹs reactions catalyzed by the naturally occurring manganese oxide pyrolusite were even more effective in destroying CT DNAPLs, with 53% degradation after 3 h. Although Fentonʹs reactions are characterized by hydroxyl radical generation, carbon tetrachloride is unreactive with hydroxyl radicals; therefore, a transient oxygen species other than hydroxyl radicals formed through Fentonʹs propagation reactions was likely responsible for CT destruction. These results demonstrate that Fenton-like reactions in which nonhydroxyl radical species are generated may provide an effective method for the in situ treatment of DNAPLs.