Maximisation of oil recovery from an oil-water separator sludge: Influence of type, concentration, and application ratio of surfactants

• Published in: Waste management (Elmsford) 2018-12, Vol.82, p.100-110
• Main Authors: Ramirez, Diego, Collins, Chris D.
• Format: Article
• Language: English
• Subjects: Micelles; Octoxynol; Oil recovery; Oil sludge; Oil sludge washing (OSW); Sewage; Sodium Dodecyl Sulfate; Surface-Active Agents; Surfactants; Taguchi experimental design
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2018.10.016

[Display omitted] •Surfactants were used to wash an oil-water separator sludge.•Surfactant type, concentration and application ratio to sludge were analysed.•Surface activity and micelle size could predict the oil recovery performance.•Triton X100, X114, rhamnolipid had higher oil recovery rates than Tween 80 and SDS.•The highest oil recovery rates were found at low surfactant application ratios. Worldwide the generation of oil sludges is approximately 160 million metric tonnes per annum. The washing of oil sludge with surfactant solutions can be used to recover the oil and reused as a feedstock for fuel production. There is a need to establish the influence of the surfactant type, concentration, and application (surfactant to oil sludge, S/OS) ratio to oil sludge for the maximisation of oil recovery. This study presented the oil recovery rates from the washing of an oil-water separator sludge using surfactants, Triton X-100, sodium dodecyl sulphate (SDS), Tween 80, rhamnolipid, and Triton X-114. The surfactants were characterised by critical micelle concentration (CMC), micelle size, and surface activity. A Taguchi experimental design was applied to reduce the number of experimental runs. In general, Triton X-100 and X-114, and rhamnolipid had higher micelle sizes and surfactant activities which resulted in higher oil recoveries. The key role of the surfactants in the washing was evidenced because the ORR values with the surfactants were significantly higher than the value with the control with no surfactant solution. The S/OS ratio was the factor with the largest effect on the Taguchi signal-to-noise ratio (an indicator of variation) of the oil recovery rate. The levels with the maximum recovery rate were 1:1 S/OS, 2CMC of surfactant concentration and Triton X-100 (32% ± 5), Triton X-114 (30% ± 7), and rhamnolipid (29% ± 8). In conclusion, less surfactant solution (1:1 S/OS) and low surfactant concentration (≤2CMC) provided the maximum oil recovery from this type of oil sludge. To our knowledge, no previous study with surfactants has reported low oil recovery values at high S/OS ratios in the oil sludge washing.