Ethyl Alcohol Produciton by Microbiological Processes

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Ethyl Alcohol Produciton by Microbiological Processes

	Ethyl Alcohol Production by Microbiological Processes - Production of ethyl alcohol from sugary materials is one of the oldest known microbiological processes. Alcohol is an important solvent and raw material used in a variety of chemical industries. Although to day industrial alcohol is also produced synthetically from ethylene, production of alcohol by fermentation of cheap sugary materials such as molasses by yeast, is still an important industry.
For ethyl alcohol production, selected strains of Saccharomyces cerevisiae are employed since all the strains are not equally efficient. The alcohol tolerance and sugar tolerance are important criteria used in the selection of yeast strains. Strains tolerant to high sugar and alcohol concentration are desired. The raw material generally used is either crude cane molasses or best molasses which contain about 50 per cent fermentable sugars
The production process involves the dilution of molasses to a suitable sugar concentration (15-16 per cent sugars), addition of a small quantity of nitrogen source (urea, ammonium sulfate or ammonium phosphate), adjustment of pH to about 5.0, and the, addition of an actively growing yeast culture. The fermentation is .carried out in big deep tanks of steel or stainless steel. The fermentation is allowed to continue for about 24-36 hours at 25°C-30°C after which the cells are allowed to settle. The fermented mash is then distilled and passed through rectifying columns to recover ethyl alcohol.
A large amount of carbon dioxide is also produced during the fermentation which is purified and compressed. The yield of ethyl alcohol is about 50 per cent of the fermentable sugar concentration. Further purification of the ethyl alcohol is done by fractional distillation. In Some distilleries, the yeast is recovered and used as animal feed while in most, it is discarded into the effluents, a procedure that is very undesirable
	In recent years because of the possibility of using ethyl alcohol as a fuel supplement and a chemical feed stock, there is increased interest in increasing production but at a cheaper and economical rate. For this, a variety of improvements in the traditional batch fermentation have been described in literature. Among these, the one that has attracted attention is the cell recycle technique which does not involve much additional expenditure.

Basically, the technique involves the reuse of cell mass that is produced during the fermentation. It has been found that by doing so, about 5-10 per cent of the substrate which would have been otherwise used for cell growth is saved ill addition to a great saving in the cost of inoculum and time. By using recycling technology, fermentation time has been drastically reduced from 24-36 hours in a batch fermentation to as low as 5-6 hours.

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