Degradation of trichloroethene by siderite-catalyzed hydrogen peroxide and persulfate: Investigation of reaction mechanisms and degradation products.

A binary catalytic system, siderite-catalyzed hydrogen peroxide (HO) coupled with persulfate (SO), was investigated for the remediation of trichloroethene (TCE) contamination. Batch experiments were conducted to investigate reaction mechanisms, oxidant decomposition rates, and degradation products. By using high performance liquid chromatography (HPLC) coupled with electron paramagnetic resonance (EPR), we identified four radicals (hydroxyl (HO·), sulfate (SO·), hydroperoxyl (HO·), and superoxide (O·)) in the siderite-catalyzed HO-SO system. In the absence of SO (i.e., siderite-catalyzed HO), a majority of HO was decomposed in the first hour of the experiment, resulting in the waste of HO·. The addition of SO moderated the HO decomposition rate, producing a more sustainable release of hydroxyl radicals that improved the treatment efficiency. Furthermore, the heat released by HO decomposition accelerated the activation of SO, and the resultant SO· was the primary oxidative agent during the first two hours of the reaction. Dichloroacetic acid was firstly detected by ion chromatography (IC). The results of this study indicate a new insight to the reaction mechanism for the catalytic binary HO-SO oxidant system, and the delineation of radicals and the discovery of the chlorinated byproduct provide useful information for efficient treatment of chlorinated-solvent contamination in groundwater.