Mineralization of sorbed and NAPL-phase hexadecane by catalyzed hydrogen peroxide

The oxidation and mineralization of hexadecane in silica sand slurries was investigated using aggressive Fenton,like reactions [high concentrations of hydrogen peroxide and an iron (II) catalyst]. When spiked with 0.1 mmol kg (-1) hexadecane, 56% of the hydrocarbon was sorbed to the silica sand and m ost of the remaining hexadecane was found as nonaqueous phase liquid (NAPL) . Gas-purge methodology documented that hexadecane desorption from the sili ca sand slurries was negligible over 72 h. Three process variables [hydroge n peroxide concentration, slurry volume and soluble iron (II) amendment] we re studied to determine their effects on hexadecane oxidation. A central co mposite rotatable experimental design was used to determine the most effect ive oxidation conditions as well as possible interactions between variables . In addition to investigating the oxidation of the parent compound, parall el experiments were conducted using C-14-hexadecane to evaluate its mineral ization. The recovery of C-14-CO2 confirmed that under the most effective c onditions (high concentrations of hydrogen peroxide and low slurry volumes) , 83% of the sorbed and NAPL-phase hexadecane was mineralized to CO2 and H2 O. The iron (II) concentration had a negligible effect on parent compound d egradation within the range investigated (5 to 25 mM) but was a significant variable in promoting the mineralization of hexadecane. The results show t hat under aggressive Fenton-like conditions, even a highly hydrophobic comp ound that is sorbed and in a NAPL-phase can be oxidized to its thermodynami c endpoints. (C) 1999 Elsevier Science Ltd. All rights reserved.