LAUSR

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.