Biosurfactant-enhanced bioremediation of petroleum sludge: Unveiling the potential of Enterobacter cloacae AR-IASST (01)

Petroleum sludge is accidentally released in oil fields and refineries, which can harm the environment because it contains emerging contaminants such as PAHs, BTEX components, heavy metals, and asphaltenes. This study developed a method to eliminate petroleum sludge-related emerging contaminants using a novel bacterium, AR-IASST (01), which can produce biosurfactants (surface tension reduced to 26.4 mN/m). The potential bacterium was Gram-negative, and molecular characterization revealed that the bacterium belongs to Enterobacter cloacae with positive oxidase, catalase, gelatin, hemolytic, and negative glucose fermentation tests. After five days of culture incubation, a degradation of 86.9% was achieved, and biosurfactant production was also observed during the sludge degradation process. The peak numbers in the GC-MS analysis were reduced from 184 to 13 in the treated sample, indicating complete degradation of PAHs in the sludge. The biosurfactant was identified as a rhamnolipid in nature. The biosurfactant was emulsified well with several oils, and an E24 of 100% was achieved against crude oil. The biosurfactant was stable across a wide temperature and salt concentration range, though it was sensitive in highly acidic conditions. Furthermore, the bacterial treatment was found to remove heavy metals viz. nickel (Ni), zinc (Zn), lead (Pb), iron (Fe), chromium (Cr), and copper (Cu) from the sludge sample. Thus, the current study demonstrates that the novel bacterium is highly potent and can be widely used to restore petroleum sludge-contaminated sites.