Generally alcohol produced from starch based feedstock by fermentation comprises hydrolysis, fermentation and separation, the main product and by product of the process are ethanol and carbon dioxide respectively.
a) Alcohol from grains
Grain is milled (ground) and then mixed with water to form slurry. The grain slurry is cooked to boiling, and special enzymes and/or acids added to make the starch soluble. Additional water is then added and a different enzyme used to convert the solubilized starch to sugar.
b) Alcohol from potatoes
The potato is Sliced and crushed then water is added, heated and PH adjusted, the slurry is then treated with several enzymes, the first reduces starch to dextrin then the mash is cooled and treated with a second enzyme to reduce the dextrin into sugar.
The mixture (mash) is cooled to and placed in large fermentation vats. Yeast is added and fermentation takes place over about three days during which the sugar is mostly converted to alcohol and carbon dioxide. Heat produced during fermentation is removed by external cooling; cooling is necessary for good yields.
Most factories discharge the carbon dioxide to the atmosphere. However, it is economical to manufacture dry ice or liquid carbon dioxide from this gas.
Alcohol is removed from the fermentation mash with steam and further purified, and all water removed by distillation. The still bottoms (slop-containing unfermented byproducts and water) are fed to animals wet or processed to dried distiller's grains for animal feeds.
The system can be designed to process alcohol from potatoes. But, also grains can be processed with modification to the feed handling system on the milling/grinding step and with minor changes required in the operating parameters of the cooking section. Since the by product i.e. still bottoms is used as animal feed the plant will have no adverse impact on the environment. Any liquid waste to be generated in the factory will be collected in a concrete made containment for the water to be evaporated and the solid will be collected and disposed as solid waste. The concrete containment cost is treated in the machinery and equipment cost.