Problem
Ethanol is a renewable fuel made from various plant materials such as grains, tubers, and lignocellulosic residues collectively known as “biomass.” More than 97% of U.S. gasoline contains ethanol, typically E10 (10% Ethanol, 90% Gasoline), to oxygenate the fuel and reduce air pollution.
There are several steps involved in making ethanol available as a vehicle fuel:
- Feed stocks containing starch are milled wet or dry to form slurry containing pure starch or starch with other plant biomaterials such as proteins, fatty acids, and non-starch polymers.
- This slurry is heated to liquefy the starch in presence of amylase enzyme (PLUTO-ZYME ENHANCE©) to control viscosity and make the starch soluble.
- This slurry containing starch and dextrin are hydrolyzed to simple sugars such as glucose by an enzyme called glucoamylase (PLUTO-ZYME BRAVO©).
- Ethanol production starts simultaneously after addition of suitable yeast.
- The final mash is distilled and dehydrated to make fuel grade ethanol at a production facility and then transported to a fuel terminal or end-user by rail, truck, or barge.
- Ethanol is blended with gasoline to make E10, E15, or E85, and then distributed.
In the process of slurry formation, apart from process water, certain recycle streams are also added to save freshwater usage, such as thin slops, process condensate, etc. The quality of the feedstock and these process streams bring along various types of microbial load in the process which leads to production of various volatile acids and organic acids which are inhibitory to yeast. Further, these contaminating bacteria thrive on the sugars released in the process. The overall effect is a loss of ethanol yield and the requirement for extra energy input to purify the final product during distillation.