Development of cell carrier for improved productivity of continuous ethanol fermentation by Saccharomyces cerevisiae

Abstract

The production of a renewable energy from biomass, such as ethanol by fermentation, has received special attention as a consequence of the world energy crisis. Nowadays, gasohol E-10, a mixture of 10% ethanol and 90% gasoline has been widely used in vehicles in Thailand and there is an attempt to promote the use of E-20 or E-85 in the vehicles in the near future. Ethanol fermentation by conventional batch suffers from various constrains such as, low cell density and rather time consuming. Although continuous fermentation by suspended cell culture can be used to speed up the process, it is more difficult to operate and maintain it free of microbial contamination. Immobilized cell technology has been suggested as an effective mean for improved fermentation. The immobilization of cells leads to a high productivity, and good operational stability. The main advantages in the use of immobilized cells in comparison with suspended cells are the retention in a reactor of higher cell concentration, protection of cells against toxic substances and elimination of costly processes of cell recovery and cell recycle. However, the major problems of using immobilization technique in industrial scale are mass transfer limitation and instability in long term operation. For improved performance of immobilized cell carriers, three new types of the cell carriers for ethanol fermentation were developed in the current study, namely, 1) Loofa reinforced alginate carriers 2) Alumina doped alginate gel carrier and 3) Thin shell silk cocoon. These cell carriers were applied for the immobilization of Saccharomyces cerevisiae M30 in ethanol fermentation using sugar cane molasses as a C-source. The developed cell carriers provided many advantage characteristics such as, good mechanical strength, high stability and high immobilization yield. The ethanol productivities of 1.3-1.5 and 8.0-19.0 g/(L h) were achieved by using the immobilized cultures in batch and continuous modes of operation, respectively. The ethanol fermentations in a continuous packed-bed reactor using the immobilized cultures worked efficiently and were stable over 30 days. The results demonstrated the potential use of the cell carriers in an ethanol fermentation system for a long period of time. In extending this work, biomaterial development and characterization for tissue engineering and membrane separation were carried out. Based on this research, we can produce 8 international research articles, 2 Thai patents, 4 international conference proceedings, 3 national conference proceedings and support research activities for 7 master degree students and 1 doctoral degree student.