Bioremediation of petroleum sludge using bacterial consortium with biosurfactant

Petroleum hydrocarbon continues to be used as the principle source of energy and hence an important global environmental pollutant. Apart from accidental contamination of the ecosystem, the vast amounts of oil sludge, generated in refineries from water oil separation systems and accumulation of waste oily materials in crude oil storage tank bottoms, pose great problems because of the expensive disposal methods (Ferrari et al. 1996; Vasudevan and Rajaram 2001). Despite decades of research, successful bioremediation of petroleum hydrocarbon contaminated soil remains a challenge. Petroleum is a complex mixture of non-aqueous and hydrophobic components like n-alkane, aromatics, resins and asphaltenes. Bioavailability might be the limiting factor in the biodegradation of such compounds. Biosurfactants are amphiphilic compounds that reduce surface and interfacial tensions by accumulating at the interface of immiscible fluids or of a fluid and a solid and increase the surface areas of insoluble compounds leading to increased mobility, bioavailability and subsequent biodegradation. They are produced by many bacterial strains that can degrade or transform the components of petroleum products. They are non-toxic, non-hazardous, biodegradable and environmentally friendly compounds (Banat et al. 2000), which may be produced cost effectively under ex-situ conditions, while in-situ production may be stimulated at the site of contamination and can be recovered and recycled (Moran et al. 2000). There have been recent successful reports on using them in enhanced oil recovery and in the release of bitumen from tar sands (Mulligan et al. 2001). Hence, reclamation of petroleum hydrocarbon polluted sites can be carried out by the bioremediation, which is an enhanced natural process of biodegradation, using biosurfactant producing and oil degrading bacterial cultures. Bioremediation technologies generally aim at providing favourable conditions of aeration, temperature and nutrients to enhance biological hydrocarbon breakdown (Rahman et al. 2002a,b). In the present study, we investigated the effect of rhamnolipid biosurfactant (RL) produced by a Pseudomanas aeruginosa strain and addition of nutrients, such as nitrogen, phosphorus and potassium (NPK) and a bacterial consortium (BC) to augment natural fertility of the polluted site on the bioremediation of crude oil tank bottom sludge (TBS).