S98: Contamination management in fuel ethanol plants: A review and strategies for success

Microbial contamination is a common problem in the fuel ethanol industry.  Contaminant microorganisms enter the plant from a variety of sources, including feed stock, process water, plant personnel, recycle streams, and process equipment, among other sources. These contaminants reduce overall fermentation efficiency by competing with inoculants for available nutrients, and produce metabolites other than ethanol, thus reducing overall efficiency and causing significant economic losses.  In fuel ethanol plants, the majority of these contaminants are lactic acid bacteria. The bacteria produce organic acids, predominantly lactic and acetic acids, diverting glucose from ethanol production, and directly inhibiting yeast growth and performance.  Most plants employ a combination of methods to minimize the effects of contamination, such as rigorous Clean-in-Place (CIP) procedures, temperature management, pH adjustment, and a wide variety of antimicrobials.  Despite these efforts, many facilities continue to experience periodic contamination due to a variety of factors.  These factors, as well as sources of contamination in fuel ethanol plants, and strategies for managing the negative effects of contaminant microorganisms will be reviewed.