Remediation of petroleum-contaminated loess soil by surfactant-enhanced flushing technique

A laboratory study was carried out to evaluate the feasibility of in situ remediation of a loess soil site contaminated with diesel oil. Six nonionic and anionic surfactants were selected and compared. In experiments of diesel oil desorption using the anionic surfactants LAS and SDS, it was shown that diesel oil solubilization increased linearly with surfactant dose at bulk aqueous concentrations of the two surfactants in excess of the relative CMC. The slope of the organic compound concentration in the micellar phase versus the concentration in the aqueous phase was used to determine the molar solubilization ratio and the diesel oil mole fraction micelle-phase/aqueous-phase partition coefficient K-m. The Km values calculated by an empirical model with diesel oil octanol-water partition were very similar to that derived using the curve slope approach. Aliphatic polyethenoxy ether (AEO(9)) and sodium alcohol polyethoxylated ether sulfate (AES) were chosen for soil flushing. Through column tests in the laboratory, the washing effectiveness of the two selected surfactants and the relevant optimal operation conditions were examined. The results showed that AEO(9) was more effective than AES in the flushing of diesel oil from contaminated loess soil, whereas AES was still more than 10 times as effective than fresh water alone. A mixed surfactant solution of 0.8% (v/v) AEO(9) and 0.1% (v/v) AES could significantly increase the removal efficiency by 10% when compared with that using AEO(9) alone. It was estimated that using an amount of the mixed surfactant solution equal to 60 pore volumes would be able to remove 60% of the petroleum residue remaining in the contaminated unsaturated zone within 9 days. This laboratory study provided a suitable model for a safe remediation alternative in the contaminated loess soil field.