Modeling for size distributions of flocculating yeast cell flocs during continuous ethanol fermentation
The focused beam reflectance measurement probe (FBRM) was directly inserted into a stirred fermentor, and the size distributions of self-flocculating yeast strain SPSC01, a fusant from Saccharomyces cerevisiae and Schizosaccharomyces pombe for ethanol fermentation, was online monitored.In a simulated system composed of the floc-buffer suspensions, it was found that the floc size distributions could be characterized by a lognormal function.The characteristic parameter,M,could be correlated with the stirring speed of fermentor,r, by a logarithmic function.Therefore, the designated size distributions of the flocs could be achieved by controlling the stirred speed. Interference by CO_2 bubbles generated during cell metabolism was observed in a real yeast floc ethanol fermentation system.The floc chord length distribution was measured with the FBRM for intrinsic kinetics investigation during which the floc size needed to be controlled at a level of micrometer scale to eliminate inner mass transfer limitations. Using the established model, the CO_2 bubbles interference was climinated by data processing to give the floc size distributions.