Monday, April 30, 2007

Oxygen controlled biosurfactant production in a bench scale bioreactor

Frederico A. Kronemberger Sr.1, Lídia M. Santa Anna2, Luiz Fernando D. Tavares3, Ana Carolina L. B. Fernandes3, Cristiano P. Borges1, and Denise M. G. Freire3. (1) Chemical Engineering Program, COPPE / UFRJ, Av. Horácio Macedo, 2030 - Centro de Tecnologia - Bloco G - Sala G-115, CEP: 21941-914, Caixa postal 68502 - Cidade Universitária / Ilha do Fundão, Rio de Janeiro, Brazil, (2) Petrobras Research Center (CENPES), Petrobras, (3) Instituto de Química, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos 149, Centro de Tecnologia, bloco A, sala 549-1 - Cidade Universitária, Rio de Janeiro, Brazil

The rhamnolipids have been pointed out as promising biosurfactants. The most studied microorganisms for the aerobic production of this molecules are the bacteria of the genus Pseudomonas. The aim of this work was to produce rhamnolipid type biosurfactant in a bench scale bioreactor by one strain of Pseudomonas aeruginosa isolated from oil environments. In order to study the microorganism growth and production dependency on oxygen, a programmable logic controller (PLC) was used to set the dissolved oxygen concentration in a constant value. Using the data stored in a computer connected to the PLC and the predetermined characteristics of the oxygenation device, it was possible to evaluate the oxygen uptake rate (OUR) and the specific oxygen uptake rate (SOUR) of this microorganism. This rates, obtained for some different dissolved oxygen concentrations, were than compared to the bacterial growth, to the carbon source consumption and to the rhamnolipid and other virulence factors production. In the studied cases, the SOUR presented an initial value of about 60,0 mgO2.(gDW.h)-1. When the exponential growth phase begins, there is a linear rise in this rate, which varies between 9,0 and 14,0 mgO2.(gDW.h)-1 per hour. This rise last until the end of the exponential growth phase. After that, the SOUR reduces to 25,0 mgO2.(gDW.h)-1, remaining constant until the end of the fermentation. The carbon source consumption is linear during the whole process and the rhamnolipid production becomes linear during the exponential phase.