Monday, May 5, 2008
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Modeling oxygen uptake rates in a rhamnolipid type biosurfactant production

Frederico A. Kronemberger Sr.1, Lídia Maria Melo Santa Anna2, Ana Carolina L. B. Fernandes3, Cristiano P. Borges1, and Denise M. G. Freire4. (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) Chemical Institute, IQ/ UFRJ, Av. Athos da Silveira Ramos,149 - Centro de Tecnologia - Bloco A, Sala 549-2, CEP: 21941-909 - Cidade Universitária / Ilha do Fundão, Rio de Janeiro, Brazil, (4) 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 actual work was to evaluate and model the oxygen uptake rates during the rhamnolipid type biosurfactant production in a bench scale bioreactor by one strain of Pseudomonas aeruginosa isolated from oil environments. In a previous work, a non dispersive oxygenation device was developed. In order to study the microorganism 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. These rates, obtained for some different dissolved oxygen concentrations, were than compared to the theoretical ones. 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 20,0 mgO2.(gDW.h)-1, remaining constant until the end of the fermentation. The simulation results were close to the experimental ones. Thus, they can be used to estimate the total oxygen demand in a fermentation for the rhamnolipid production.

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