KL a Evaluation during the course of fermentation using data reconciliation techniques

Abstract

The oxygen mass transfer coef®cient often serves to compare the ef®ciency of bioreactors and their mixing devices as well as being an important scale-up factor. In submerged fermentation, four methods are available to estimate the overall oxygen mass transfer coef®cient (K L a): the dynamic method, the stationary method based on a previous determination of the oxygen uptake rate (Q O 2 X), the gaseous oxygen balance and the carbon dioxide balance. Each method provides a distinct estimation of the value of K L a. Data reconciliation was used to obtain a more probable value of K L a during the production of Saccharomyces cerevisiae, performed in 22.5-l fed-batch bioreactor. The estimate of K L a is obtained by minimising an objective function that includes measurement terms and oxygen conservation models, each being weighted according to their level of con®dence. Weighting factors of measurement terms were taken as their respective inverse variance whereas weighting factors of oxygen conservation models were obtained using Monte Carlo simulations. Results show that more coherent and precise estimations of K L a are obtained.List of symbols C L dissolved oxygen concentration, mol/m 3 C 0 L pseudo-steady-state dissolved oxygen concentration recorded at the initiation of the dynamic method, mol/m 3 C Ã L dissolved oxygen concentration in equilibrium with mean gaseous oxygen concentration, mol/m 3 C P dissolved oxygen concentration recorded by the probe, mol/m 3 K L a overall oxygen mass transfer coef®cient, s À1 J objective function P pressure, Pa Q G gas¯ow rate, m 3 /s Q O 2 X oxygen uptake rate, mol/m 3 s R gas constant, 8.306 Pa m 3 /(mol K) S substrate, mol/m 3 RQ respiratory quotient T temperature, K V L liquid volume in the fermenter, m 3 y gaseous mole fractionGreek letters a weighting factor associated to each term in the objective function b relative weighting factor between measurements and conservation models s P time constant of the dissolved oxygen probe, s

Influence of agitation and aeration on growth and antibiotic production by Xenorhabdus nematophila

“…Oxygen mass transfer coefficient K L a was measured before inoculation following the dynamic method (Pouliot et al 2000;Rainer 1990) .…”

Avaliação Da Influência Das Células De Bacillus Megaterium Na Determinação Do Coeficiente De Transferência De Oxigênio Em Cultivo Submerso

“…A técnica original envolve a breve interrupção da aeração e da agitação no biorreator. Empregando-se a modificação descrita por Pouliot et al (2000), a agitação foi reduzida a 50 rpm e não totalmente interrompida, a fim de impedir a decantação das células e, assim, garantir a obtenção de medidas corretas pelo eletrodo de oxigênio. A taxa específica de respiração (q O2 ) foi determinada pela razão entre a OUR e biomassa.…”

“…A partir de 9 h, o metabolismo pareceu restabelecer seu comportamento típico. De fato, conforme Pouliot et al (2000), se a atividade da reação bioquímica for alta o suficiente para reduzir significativamente os níveis de oxigênio dissolvido no cultivo, a determinação pelo método dinâmico torna-se inviável, devendo-se utilizar determinações baseadas em balanço de gás. Da mesma forma, Borzani et al (2001) afirmam que para aplicação do método dinâmico, deve-se contar com uma concentração de oxigênio dissolvido relativamente alta, evitando o risco de que ela caia abaixo da crítica, de modo a manter constante o valor de q O2 das células.…”

“…A Figura 3 apresenta os resultados obtidos para o k L a. Foram desconsiderados os valores a 7 h e 8 h devido aos aspectos discutidos na seção anterior e à dificuldade de obtenção de um valor confiável nesses tempos. Pouliot et al (2000). Para esses autores, mantendo-se as demais condições experimentais constantes durante a fermentação, o k L a permanece relativamente inalterado para cultivos de baixa viscosidade, caso de Saccharomyces cervisiae e de B. megaterium.…”

Optimization of lipase production by Staphylococcus warneri EX17 using the polydimethylsiloxanes artificial oxygen carriers

“…The optimized temperature and pH were 37°C and 7.0, respectively [20]. The tested values of the oxygen volumetric mass transfer coefficient, k L a, were determined by the dynamic gassing-out method [15]. The agitation and aeration rates were set at different values, characterizing five different oxygen transfer conditions.…”