Bioremediation has been recognized as an effective method to treat petroleum hydrocarbon pollutants. However, the biodegradation of crude oil contaminated sludge could be a time-consuming and low-efficiency process. One of the reasons is that petroleum hydrocarbons in the sludge are unavailable for utilization by microorganisms. Surfactants have the potential to increase the bioavailability of such pollutants due to their capability of reducing the surface and interfacial tension and increasing the solubility of hydrocarbons in water. In this study, the production of biological surfactants during sludge bioremediation was observed using surface tension measurement method, and this would provide valuable information for developing an effective bioremediation process. The addition of two different chemical surfactants (Igepal CO-630 and Cedephos FA-600) and a biosurfactant (Rhamnolipids) were tested using a laboratory respirometer, and the effects of such surfactants on the biodegradation of total petroleum hydrocarbons (TPH) in the oil refinery sludge were investigated. All surfactants were found to be effective for improving microbial growth at low concentration. Igepal CO-630 at 400 mg/kg, Cedephos FA-600 at 400 mg/kg and Rhamnolipids at 200 mg/kg were found most effective in improving the reduction of TPH (C10-C50) compared to the control sample without any addition of surfactants. Better oxygen availability to soils contaminated with hydrocarbon sludge enhances both microbial growth and TPH reduction in the samples when surfactant concentrations were optimized. --P.i.
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