Production of biosurfactant by Bacillus subtilis LB5a on a pilot scale using cassava wastewater as substrate

Abstract

The main characteristic of biosurfactants is their property of reducing the superficial and interfacial tension between two immiscible liquids of different polarities. The main obstacle to the application of biosurfactants is the high production costs, the use of alternative substrates being indicated to solve this problem. This work report the production of biosurfactant by Bacillus subtilis LB5a on a pilot scale using cassava wastewater as the substrate, and the study of the parameters related to its production. The cassava wastewater was heated, centrifuged and poured into a 40-liter batch pilot bioreactor adapted for simultaneous foam collection during the fermentative process. The temperature was maintained at 35 degrees C, agitation at 150 rpm and aeration 0.38 vvm during the first 12 h, and 0.63 vvm for the rest of the process. Samples of liquid fermentate were collected at regular intervals for the analysis of total carbohydrates, reducing sugars, pH, CFU/mL count and superficial tension. The foam was centrifuged and the biosurfactant purified. The kinetic data of the process showed that both the microbial population, which reached a maximum after about 24 h, and the foam production of 10.6 L, peaked between 24 and 36 h, coinciding with the greatest production of biosurfactant. The yield of semi-purified surfactant in the foam was 2.4 g/L. The superficial tension of the medium was reduced from 51 to 27 mN/m and the critical micellar concentration was 11 mg/L, which, in principle, characterizes it as a good tensoactive agent. As a function of its composition and productivity, cassava wastewater was identified as a good substrate for the production of the biosurfactant.