Experimental Investigation of Sophorolipid Biosurfactants Produced by Candida and Pleurotus Species Using Waste Oils and Rice Bran and Their Oilfield Benefits

Abstract

Conventional chemical surfactants applications usually linked with environmental unfriendliness and toxicity are associated with high production costs resulting from fluctuations in oil prices and thermal energy requirements. Sophorolipid biosurfactants can potentially be implemented with a remarkably low operating cost. Besides economic interest, sophorolipids and their derivatives have shown promise as emulsifiers, antimicrobials, surfactants and a source of specialty chemicals possessing both hydrophilic and hydrophobic structural moieties that impart surface tension reduction capacities, thus, facilitating microbial hydrocarbon and heavy metal emulsification and uptake. In this study, sophorolipids produced by Candida and Pleurotus species respectively isolated and harvested from oil contaminated soils from Ukwa West LGA of Abia State were investigated. Mineral salt media supplemented with different hydrophilic (rice bran, spent mushroom substrate and cassava peels) and hydrophobic (food industry waste oil) renewable wastes as sources of carbon were tested on nine (9) of the potential isolates to select the best medium and organism that maximized sophorolipids production. This was supported by the emulsification index after 24 hours (E24), FT-IR and GC-MS analysis. All isolates were subjected to biosurfactants production screening, to find the best sophorolipid producer among the available strains. Results showed that isolate CP1SP6c, a hydrocarbon utilizing fungi (HUF) exhibiting β-haemolysis and 92.4% microbial adhesion to hydrocarbon (MATH), gave the maximum E24 of 69.2%, within 6 days of incubation on media fortified with rice bran and food industry waste oil in a rotary shaker. Further studies on CP1SP6c were carried out to assess the interaction of the produced sophorolipids with porous media in core flooding experiments as a tertiary recovery technique. The results showed high promises of using this bio-product in hydrocarbon recovery, where 12.3% of crude oil was recovered after injecting the culture supernatant. An additional recovery of 15.7% of residual oil was observed after concentrating the sophorolipid solution.