Microemulsion formation of surfactant/oily wastewater system and relation to clean-up by froth flotation

Abstract

Froth flotation is one of the surfactant based separation processes which is suitable for treating diluted wastewaters containing oil and/or colloidal particles. In this technique, there are several advantages such as low space requirement, high removal efficiency, flexibility for various pollutants at various scales, and low cost. In this work, batch mode of froth flotation was focused as technique to remove emulsified oil from wastewater. From the previous work, high oil removal was achieved in a Winsor type III microemulsion region. Therefore, microemulsion concept was combined with froth flotation technique to achieve high separation efficiency. Dihexyl sulfosuccinate (Aerosal MA or AMA) was used to prepare microemulsion solutions with ethylbenzene while branched alcohol propoxylate sulfate sodium salt with 14-15 carbon number and 4 propylene oxide groups (Alfoterra 145-4PO) was utilized to form microemulsion with diesel. Interfacial tension (IFT), which is one of the important characteristics in Winsor type III microemulsions, was investigated as a function of separation efficiency. In addition, performance of froth flotation as a function of foam characteristics was also elucidated. In froth flotation experiments, various parameters such as surfactant concentration, salinity, oil to water ratio, air flow rate, and equilibration condition were studied in order to correlate the oil removal efficiency with IFT value and foam characteristics. From the results, there are conditions of the diesel system where no separation occurs even though IFT value is in the ultra-low range (i.e. 10⁻² mN/m) because the foam characteristics are extremely low. Therefore, both IFT and the foam characteristics influence the efficiency of oil removal in the froth flotation process. Moreover, the oil removal is not significantly affected by oil to water ratio. In froth flotation operation, air flow rate should be optimized to achieve high removal efficiency. Ultimately, equilibrium condition always yields the highest separation efficiency in froth flotation operation.