Evaluation of a microbial consortium for crude oil spill bioremediation and its potential uses in enhanced oil recovery

Abstract

Abstract Microbial enhanced oil recovery (MEOR) process utilizes reservoir microorganisms (in situ) or specially selected bacteria to use their metabolic products (ex-situ) for extra oil recovery from depleted oil reservoirs. Biodegradation of crude oil and simultaneous production of bioemulsifiers by a mixed culture consisting of Ochrobactrum pseudintermedium C1 and Bacillus cereus K1 have been investigated in this study along with the potential ex-situ application of bioemulsifier in MEOR process. The culture parameters namely pH, temperature, aeration rate and agitation rate have been optimized in a lab scale bioreactor using Taguchi's L9 orthogonal array approach to increase the rate of biodegradation of crude oil. At optimized culture condition (pH 8.0, temperature 35 °C, aeration rate 1.5Nl/min and agitation rate 150 rpm), the bacterial consortium degrade up to 70.54% of total petroleum hydrocarbons (TPH) after 72 h incubation using crude oil (4% v/v) as the sole source of carbon and produced two different exopolysaccharides (EPS), which showed very good emulsification activity (EI) towards crude oil up to 80.5% and also reduced the interfacial tension of crude-oil water system from 46 mN/m to 14.5 mN/m. FT-IR, NMR and chemical analyses revealed that EPS formed by C1 contained 61.5% (w/w) carbohydrates, 29.2% protein and 9.3% lipid whereas, the EPS formed by K1 comprises of 43.6% (w/w) carbohydrates, 51.7% lipids and 6.3% protein. The crude bioemulsifier mixture was found to be pseudoplastic, Non-Newtonian in nature and was stable at a wide range of pH (2−10), temperature (40–121 °C) and salinity (0–15% w/v), hence signifies its applicability in MEOR process. The results of the sand pack column flooding tests at simulated reservoir conditions demonstrated that the additional oil recovery efficiency due to the ex-situ injection of the cell-free bioemulsifier solution was 40.93% and 46.85% at 40 °C and 70 °C temperatures respectively. The mixed culture presented a great potential application in bioremediation of oil polluted sites owing to its degradation ability to crude oil and also in enhanced oil recovery process using the crude bioemulsifier having combined surface and emulsification activity.