(173a) Bioethanol Production by Fermentation of Starch Particles Using a Novel, Inexpensive Media

An efficient method for conversion of biomass into fuel is by ethanol production because ethanol is an economical as well as environment friendly liquid fuel. Ethanol has the advantages of being renewable, cleaner burning and producing no net greenhouse gases. Yeast cells (Saccharomyces cerevisiae) are facultative anaerobes and under anaerobic conditions can ferment glucose to ethanol. Saccharomyces yeasts are ideal for ethanol production due to several properties including fast growth rates, efficient glucose repression, efficient ethanol production and a tolerance for environmental stresses, such as high ethanol concentration and low oxygen levels. Glucose is broken down to form pyruvate in most organisms via the glycolytic pathway and this pyruvate can result in ethanol under anaerobic conditions. The energy for growth of cells during ethanol production is provided by the glycolytic and fermentation pathways. But glucose is expensive for industrial applications and therefore, starch is an economical alternative.

Although sugarcane is the most widely used raw material for ethanol production via fermentation, starch based raw materials are more abundant. In the USA and Eastern Canada, corn is used for ethanol production, but in Western Canada, wheat starch is more readily available. Approximately 25 million tones of wheat are grown every year in Canada, 50% of which is produced in Saskatchewan. The starch content of this wheat is approximately 65% based on a dry mass basis. Starch, a macromolecular polymer of glucose units, is a significant component of domestic and commercial waste and a useful resource that can be converted into ethanol. Yeast cells are unable to consume raw starch directly and hence, the starch must first be broken down into simple sugars. This task is achieved by two enzymes: alpha amylase, which hydrolyzes alpha-1, 6 linkages and glucoamylase, which hydrolyzes alpha-1, 4 linkages in starch molecules. In industrial processes, starch is first cooked at high temperatures to solubilize it, followed by high temperature enzymatic liquefaction (á-amylase) and saccharification (glucoamylase). The use of starch particles for bioethanol production by fermentation is economical because it avoids this cooking process and saves time and energy. However, developing a cost-effective fermentation process for starch particles with high efficiency of ethanol production still remains an outstanding challenge.

In this work, simultaneous cold starch hydrolysis and fermentation was investigated as a way of ethanol production from pure wheat starch. With a view to minimize process costs while maintaining a satisfactory ethanol yield, a novel, inexpensive media was formulated and tested for its fermentation capacity.

A New Brunswick Scientific Bioflo III bioreactor was used to carry out batch fermentation runs using three different substrate concentrations of 20 g/L, 100 g/L and 200 g/L starch particles. Correct proportions of the novel media components of this inexpensive media were used for fermentation. The yeast used was Muntons active dry yeast. The temperature and pH were optimized to improve productivity. The results, including growth rates, ethanol yields, biokinetic models and economics will be presented. The new media formulation and bioreactor operating conditions are shown to significantly improve the economics of bioethanol production from raw starches.