Sustainable emulsion treatment by volatilization enhanced by temperature and alkaline conditions in the remediation of a polluted landfill with lindane production wastes

Abstract

This study investigates the sustainable treatment of actual contaminated emulsions resulting from the injection of a non-ionic surfactant (Surfactant-Enhanced Aquifer Remediation, SEAR) in a landfill highly contaminated with residual dense non-aqueous phase liquid (DNAPL) from lindane wastes. Located in Bailin, Sabiñanigo, this landfill underwent SEAR treatment as part of the LIFE SURFING project in 2022. The DNAPL is a complex mixture, encompassing approximately 28 chlorinated organic compounds (COCs), including both aromatic (chlorobenzenes) and non-aromatic components (Hexachlorocyclohexanes, HCHs, and Heptachlorocyclohexanes, HeptaCHs). Notably, the non-aromatic compounds exhibit higher density and lower volatility than chlorobenzenes. SEAR-polluted emulsion can be treated by pollutant separation through volatilisation with an airstream. However, this method is limited to compounds with high-moderate volatility. Additionally, a decrease in vapour pressure is observed with increasing surfactant concentration. To overcome these limitations, simultaneous dehydrochlorination of HCHs and HeptaCHs, volatilisation of chlorobenzenes and emulsion breakage were carried out under alkaline conditions enhanced by temperature at a pilot scale using two real polluted emulsions from LIFE SURFING project. The intensified process demonstrated remarkable efficiency, eliminating over 90 % of COCs from the emulsion within 25 h of treatment. Furthermore, the pilot-scale results were used to validate a kinetic model developed here, predicting the hydrolysis rate of HCHs and HeptaCHs as a function of surfactant (1–10 g L–1) and COCs (500–2500 mg L–1) concentrations, temperature (25–60 ºC), and alkali concentration (90–190 mM). This model and the previously established volatilisation kinetic model yield a good agreement between experimental and predicted data. The model constructed holds the potential to optimise treatment times and conditions for various pollutant and surfactant concentrations in emulsions during remediation.