Environmental applications of the biosurfactant produced by Candida sphaerica cultivated in low-cost substrates

• The biosurfactant produced in bioreactor reduced the surface tension for 27 mN/m.
• The biosurfactant yield was 8 and 21 g/L in flasks and bioreactor, respectively.
• The biosurfactant demulsified 40% of motor oil in seawater.
• The crude biosurfactant dispersed 90% of oil droplets in seawater.
• The biosurfactant proved to be non-toxic to indigenous marine microbiota.

Surfactants are amphipathic molecules that accumulate at interfaces, decrease interfacial tensions, and form aggregate structures such as micelles. Biosurfactants constitute one of the main classes of natural surfactants produced by microorganisms, being classified in accordance with their chemical composition or microbial origin. These polymers had attracted, in the last few years, considerable interest due to biodegradable nature, low toxicity and diversity of applications. In this paper the biosurfactant from Candida sphaerica UCP 0995 grown in distilled water supplemented with 9% ground-nut oil refinery residue plus and 9% corn steep liquor was first produced in shake flasks and in a bioreactor. The biosurfactant decreased the surface tension of water from 72 to 25 mN/m with a yield of 8.0 g/L when produced in shake flasks while the biosurfactant produced in the bioreactor reduced the surface tension for 27 mN/m with a yield of 21 g/L after 144 h. The biosurfactant was then tested for demulsification of motor oil emulsions, showing values around 40%. The crude biosurfactant was capable of dispersing approximately 90% of oil droplets in seawater and proved to be non-toxic to indigenous marine microbiota. The biosurfactant acted as a solubilizer of motor oil in sea water as demonstrated by the acceleration and growth of the indigenous microorganisms throughout the 30 days of cultivation. The present findings indicate the application potential of the biosurfactant produced by C. sphaerica in the oil industry as a complement to remediation processes involving contaminated water.

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