Isolation and comparison of biosurfactants produced by Bacillus subtilis PT2 and Pseudomonas aeruginosa SP4 for microbial surfactant-enhanced oil recovery

In this present study, two types of biosurfactant-producing microorganisms, Bacillus subtilis PT2 and Pseudomonas aeruginosa SP4, were isolated from sludge oil and petroleum-contaminated soil in Thailand, respectively. The biosurfactant production was done by using a nutrient broth with palm oil as the carbon source. The microbial growths were investigated, and the best cultivation times for the biosurfactant production by B. subtilis PT2 and P. aeruginosa SP4 were found to be 51 and 48 h, respectively. After the microbial cultivations at 37 °C under the optimum conditions, the biosurfactants produced by B. subtilis PT2 and P. aeruginosa SP4 were found to reduce the surface tension of pure water to 26.4 and 28.3 mN/m with the critical micelle concentrations (CMCs) of about 25 and 120 mg/l, respectively. From the results of the oil recovery tests, the biosurfactant produced by B. subtilis PT2 exhibited oil recovery efficiency higher than that produced by P. aeruginosa SP4. Moreover, it was found that both biosurfactants could recover oil more effectively than three synthetic surfactants, including polyoxyethylene sorbitan monooleate (Tween 80), sodium dodecyl benzene sulfonate (SDBS), and sodium alkyl polypropylene oxide sulfate (Alfoterra 145-5PO).