Chemical oxidation of chlorinated non-aqueous phase liquid by hydrogen peroxide in natural sand systems

摘要

This study explored the Fenton-like oxidation of trichloroethylene (TCE) existing as dense non-aqueous phase liquid (DNAPL) in natural silica sand (iron = 0.04 g/kg) and the sand from an aquifer (iron = 2.01 g/kg). Glass bead containing no iron mineral was used as the control. Batch oxidation experiments were conducted to assess interactions between oxidant and TCE DNAPL. Column experiments were performed to evaluate dynamics of TCE and H2O2 during oxidation. The pH was not altered. In the batch system, a single application of 3% H_2O_2 to the aquifer sand oxidized 40% of the added TCE DNAPL in 1 h, which was four times of that by dissolution with the gas purge procedure. This demonstrated the ability of mineral-catalyzed Fenton-like reaction to directly oxidize TCE in non-aqueous liquid. In the column experiments, after passing 7 pore volumes (PVs) of 1.5 and 3% H2O2 solution, the residual TCE in aquifer sand column was 12.0 and 2.6% of the initial added, respectively. On the other hand, 28.4% of the added TCE still remained in the silica sand column by 7 PVs of 3% H_2O_2. The distribution of TCE in column and effluent indicated the occurring of direct oxidation of TCE DNAPL and the increased solubilization, which probably due to size reduction of DNAPL droplets, followed by water-phased TCE oxidation.