Treatment of heavy petroleum hydrocarbons polluted soil leachates by ultrafiltration and oxidation for surfactant recovery

Surfactant technology can improve the remediation of soils polluted by semivolatile hydrophobic contaminants, like polycyclic aromatic hydrocarbons (PAHs), by enhancing their solubility in water. However, the recovery of surfactant from soil-leachates is critical for the economic feasibility of this treatment technology. To tackle this issue, ultrafiltration (UF) and its combination with permanganate, is reported for the selective recovery of surfactant from wastewater contaminated by a complex mixture of heavy hydrocarbons mainly composed of PAHs. The overall performance of the process including the successive steps of contaminant mobilization in leachates and surfactant recovery from wastewater was investigated at lab-and field-scales, considering aged mixtures of pollutants in pure liquid phase and trapped in soil. Surfactant loss during contaminant extraction, separation and affecting factors including surfactant concentration and nature (anionc, zwitterionic and nonionic), hydrocarbon concentration were studied. Regardless of the nature of surfactant and concentrations, wastewater were effectively treated using UF, with hydrocarbon removals higher than 90%, but with strong variations in surfactant recovery. Surfactant adsorption occurred with a deleterious effect on surfactant recovery and permeate flux, stressing the interest of hydrophilic membranes. Hydrophilic zwitterionic surfactants were adsorbed moderately to the contaminated interfaces and to the UF-membrane. Lauryl betaine concentration between 0.15 and 0.5% (w/w) was found to be optimal for the overall process of contaminants mobilization and surfactant recovery by UF. Surfactant recovery and permeate flux were improved by 5-times and 20%, respectively, through the preferential removal of the emulsified hydrocarbons using small amounts of permanganate as a selective precipitant.