3-15: Determination of inhibition kinetic mechanism of acetic acid on yeast growth during alcoholic fermentation with cell recycle

Monday, April 29, 2013
Exhibit Hall
Elmer Ccopa Rivera1, Celina Kiyomi Yamakawa2, Antonio Bonomi1, Rubens Maciel Filho3 and Carlos Eduardo Vaz Rossell2, (1)Technological Assessment Program, Brazilian Bioethanol Science and Technology Laboratory, Campinas, Brazil, (2)Industrial Program, Brazilian Bioethanol Science and Technology Laboratory, Campinas, Brazil, (3)School of Chemical Engineering, State University of Campinas (UNICAMP), Campinas, Brazil
Besides furfural and phenolic compounds, acetic acid is among the main inhibitors of the alcoholic fermentation. The presence of this compound can have opposite effects; at low concentrations, it stimulates cell growth while at high concentrations; there has been a reduction in microbial growth which leads to an increased production of ethanol. Some studies have pointed to a complete inhibition of yeast growth, in presence of acetic acid. Hence, a detailed description of an inhibition term for acetic acid on cell growth is essential for a reliable kinetic modeling study. The insertion of this term inhibition in a fermentation kinetic model requires the description of a transient profile of the acetic acid concentration. It means that it is necessary the inclusion of an additional differential equation to the system of equations describing cell growth, ethanol formation and substrate consumption. For the estimation of the kinetic parameters of the inhibition term, the system of differential equations was integrated numerically while parameters estimation was formulated as an non-linear optimization problem. The parameters were adjusted by minimizing a performance criteria using a hybrid optimization method, coupling Genetic Algorithm and Quasi-Newton method, which intuitively made the estimation procedure to be significantly quicker. Results showed that this approach allowed an accurate description of the behavior of the alcoholic fermentation with cell recycle. Besides, this tool was applied to explore the impact of several strategies on the process behavior which is an important issue to lead the process to be operated at high level of performance.