Diesel removal by continuous froth flotation: effects of ultralow interfacial tension and foam characteristics

Froth flotation if one of surfactant-based separation processes which is suitable for treating dilute oily wastewaters. The objective of this study was to investigate the relationship between the ultra-low IFT and the efficiency of diesel removal from water by using continuous froth flotation technique. Branched alcohol propoxylate sulfate, sodium salt (Alfoterra 145-5PO) and sodium dodecyl sulfate (SDS) were used for both microemulsion formation and froth flotation studies. Surfactant concentration, salinity, and oil to water ratio were varied in the microemulsion formation experiment in order to determine the compositions required to obtain ultra-low IFT. The effects of surfactant concentration, salinity, oil to water ratio, foam height, air flow rate, and HRT on the oil removal were investigated. From the results, the oil removal efficiency of the froth flotation process did not correspond to the minimum IFT of the system indicating that the ultra low IFT alone cannot be used as a sole criteria for froth flotation operation. Foam stability was revealed to be another crucial factor in the froth flotation operation. The system with 0.1 wt% Alfoterra, 0.5 wt% SDS, 4 wt% NaCl, 1:19 oil:water ratio, 0.15 L/min air flow rate, 26 cm foam height, and 49 min HRT gave the maximum oil removal (90.37%).