NOVEL USE OF OXIDIZING BIOCIDES TO INCREASE ETHANOL YIELD By Reed Semenza
In ethanol production, yeast (Saccaromyces cerevisiae) is used to convert sugar into ethanol. Other microorganisms can compete with yeast for the sugars. These microorganisms include but are not limited to lactic acid and acetic acid bacteria. When acid bacteria grow, they compete with the supply of sugar resulting in less sugar for ethanol production. Also, acid-forming bacteria can create low pH conditions that tend to inhibit the growth of ethanol producing yeast. To control the growth of acid producing bacteria, many ethanol plants add antibiotics to the fermentation tanks. The antibiotics kill much of the acid bacteria, but the antibiotics apparently do not harm the yeast. The current method calls for 3 to 5 pounds of antibiotic, usually Virginiamycin, per 500,000 gallons of corn mash in the fermenter. Actual dose of antibiotics is determined by the level of lactic acid in the corn mash during the first 30 hours of fermentation. Antibiotics, though generally effective, have several major disadvantages. The main disadvantage of antibiotics is that they only work in the fermenter. Biofilms that grow in the mash cooler and consume sugars are not arrested and, as a result, ethanol yield is compromised. A second disadvantage of antibiotics is that acid bacteria can become resistant over time rendering the use of antibiotics less effective, resulting in ethanol production losses.
In order to further improve ethanol yield, DeLasan CMT, a patented system comprised of 22% peracetic acid (PAA), distributed by DeLaval, and hydrogen peroxide (HP) were blended in line and added to the fermenter via the mash cooler. The primary objective of the study was to determine the most economical dose of DeLasan CMT and to determine the relationship between lactic and acetic bacteria reduction, ethanol yield improvement, and dose. Secondary objectives included measure-
ment of residual levels of PAA, HP, and stabilizers in the distillers grains. Background The ethanol plant in the study is a 55 MMgy continuous plant located in Illinois. The facility’s management desired to improve ethanol yield, save money on their antimicrobial program and produce distillers grains that are free of antibiotics. The plant process flow is shown in Figure 1.
FIGURE 1
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36 | ETHANOL PRODUCER MAGAZINE | JANUARY 2022
