Thermally activated persulfate for the chemical oxidation of chlorinated organic compounds in groundwater.

Chlorinated pesticides were extensively produced in the XX century, generating high amounts of toxic wastes often dumped in the surroundings of the production sites, resulting in hot points of soil and groundwater pollution worldwide. This is the case of Bailín landfill, located in Sabiñánigo (Spain), where groundwater is highly polluted with chlorobenzenes (mono, di, tri and tetra) and hexachlorocyclohexanes. This study addresses the abatement of chlorinated organic compounds (COCs) present in the groundwater coming from the Bailín landfill by thermally activated persulfate, PS (TAP). The influence of temperature (30-50 °C) and oxidant concentration (2-40 g L-1) on the efficiency of COCs (initial concentration of COCs = 57.53 mg L-1, determined by the solubility of the pollutants in water) degradation has been investigated. Raising the reaction temperature and PS concentration the degradation of COCs significantly accelerates, as a result of higher production of sulfate radicals. The thermal activation of PS implies side reactions, involving the unproductive decomposition of this oxidant. The activation energy calculated for this reaction (128.48 kJ mol-1) reveals that is slightly more favored by temperature than the oxidation of COCs by sulfate radicals (102.4-115.72 kJ mol-1). At the selected operating conditions (PS = 10 g L-1, 40 °C), the almost complete conversion of COCs and a dechlorination and mineralization degree above 80% were obtained at 168 h reaction time. A kinetic model, able to adequately predict the experimental concentration of COCs when operating at different temperatures and initial concentration of PS has been proposed.