Selective removal of chlorinated organic compounds from lindane wastes by combination of nonionic surfactant soil flushing and Fenton oxidation

Abstract

The extensive use of the organochlorine pesticide lindane in the second half of the 20th century generated large volumes of wastes over the world. Among these wastes, a dense non-aqueous phase liquid (DNAPL), mainly composed of chlorobenzenes, hexachlorocyclohexanes and heptachlorocyclohexanes, was dumped in insecure landfills remaining in the subsurface and contaminating the groundwater. A coupled process, combining soil flushing (with a nonionic surfactant) and Fenton oxidation, was proposed to deal with this problem. A commercial surfactant (E-Mulse 3 ®) was used to extract most of the residual DNAPL in soil at column conditions. The resulting surfactant flushing solution (SFS) presented high concentration of chlorinated organic compounds (COCs = 3693 mg L−1). In order to recover the surfactant and abate the COCs, the SFS was treated by Fenton process using three doses of hydrogen peroxide (200%, 100% and 50% of the theoretical stoichiometric amount for the complete mineralization of COCs; maintaining a molar ratio of H2O2:Fe = 32). Conversions of COCs above 80% were obtained when H2O2 doses of 100% and 200% of the stoichiometric amount were used at 144 h and 48 h, respectively. Non-aromatic compounds resulted to be less prone to oxidation by hydroxyl radicals than chlorobenzenes. The oxidation of the surfactant was significantly lower than that of the pollutants; therefore the surfactant capacity was maintained after the oxidation treatment and it could be reused in further flushing steps, improving the economy of the process.