Abstract:
Pseudomonas aeruginosa SP4, which was isolated from a petroleum-contaminated soil in Thailand, was used to produce rhamnolipid-type biosurfactants in this study. This research was performed by using two identical units of continuous sequencing batch reactors (SBRs), which were operated on a fill-and-draw basis at a constant temperature of 37°C under aseptic conditions with 1,500 ml working volume, 500 ml feeding volume, and 500 ml decanting volume. Palm oil and a mineral medium were used the sole carbon source and nutrient source, respectively. The effect of cycle time on biosurfactant production performance was investigated at an oil loading rate of 2 kg/m³d. The results showed that 2 d/cycle was the optimum cycle time for biosurfactant production to provide the highest surface tension reduction of 59% and the lowest surface tension of 28.82 mN/m with a critical micelle concentration of 1.05 times CMC, corresponding to the highest COD and oil removal of 89.8% and 96.7%, respectively. Moreover, this cycle time also gave a stable and suitable pH for microbial growth, which was found to be around 6.04. The C/N ratio (16/0.57, 16/1 and 16/3) was found to significantly affect on biomass, pH and biosurfactant production. Nevertheless, the C/N ratio of 16/1 was an optimum ratio for the biosurfactant production by the strain SP4.
