earticle

영어

Ethanol, as a typical primary metabolite of yeast cells, its production is tightly coupled with the growth of yeast cells. Theoretically, the immobilization of yeast cells by supporting materials, particularly by gel entrapments, is not desirable for ethanol production, because not only is the growth of yeast cells restrained, but also the slowly growing yeast cells are difficult to be removed from the systems. Moreover, the additional cost from the consumption of the supporting materials, the contamination of the supporting materials to the co-product of ethanol production such as animal feed, and the difficulty in the microbial contamination control all make the immobilized yeast cells economically unacceptable by the industry. In contrast, the self-immobilization of yeast cells through their self-flocculating can effectively overcome those drawbacks. Based on this idea, a yeast strain was bred by the protoplast fusion technique from the two parent yeast strains: Saccharomyces cerevisiae K2, an industrial strain with excellent ethanol fermentation performance and used by the Chinese ethanol fermentation industry, and Schizosaccharomyces pombe, a laboratory strain with a good self-flocculating ability. Then, a prototype suspended-bed fermentor was developed, through which the self-flocculating yeast cells were effectively retained and immobilized. Kinetics, both intrinsic and observed, was investigated for the self-flocculating yeast cells, and the process optimization was achieved by establishing a cascade fermentation system through which ethanol inhibition was effectively alleviated. The engineering scale-up of the suspended-bed fermentor was further developed through the pilot plant test in which four suspended-bed fermentors, each with a working volume of 10 m3, were designed and operated in a cascade mode, with an etahnol production capacity of 33 tons per day. Finally, this new ethanol fermentation technology was successfully commercialized with the establishment of a large plant with its fuel ethanol production capacity of 200, 000 tons per year.