Ultrasonically assisted Fermentation to Bioethanol0 pages

Ultrasonically-Assisted Fermentation for Bioethanol Production
by Kathrin Hielscher, Hielscher Ultrasonics, Germany
www.hielscher.com; info@hielscher.com

1. Fermentation
Fermentation can be an aerobic (= oxidative fermentation) or anaerobic process,
which is used for biotechnological applications to convert organic material by
bacterial, fungal or other biological cell cultures or by enzymes. By fermentation,
energy is extracted from the oxidation of organic compounds, e.g. carbohydrates.
Sugar is the most common substrate of fermentation, resulting after fermentation in
products such as lactic acid, lactose, ethanol and hydrogen. Ethanol – especially for
use as fuel, but also for alcoholic beverages - is produced by fermentation. When
certain yeast strains, such as Saccharomyces cerevisiae metabolize sugar, the yeast
cells convert the starting material into ethanol and carbon dioxide.
The chemical equations below summarize the conversion:
C6H12O6 → 2 CH3CH2OH + 2 CO2
C12H22O11 + H2O → 4 CH3CH2OH + 4 CO2
If the starting material is starch, e.g. from corn, firstly the starch must be converted
into sugar. For bioethanol used as fuel, hydrolysis for the starch conversion is
required. Typically, the hydrolysis is speeded up by acidic or enzymatic treatment or
by combination of both. Normally, fermentation is carried out at around 35–40 °C.
Overview over various fermentation processes:
Biogas/ ethanol: - improvement of biogas/ bioethanol production from biomass
- biogas production from sewage sludge
Food:

- production & preservation
- dairy (lactic acid fermentation), e.g. yogurt, buttermilk, kefir
- lactic fermented vegetables, e.g. kimchi, miso, natto, tsukemono,
sauerkraut
- development of aromatics, e.g. soy sauce
- decomposition of tanning agents, e.g. tea, cocoa, coffee, tobacco
- alcoholic beverages, e.g. beer, wine, whiskey

Drugs:

- production of medical compounds, e.g. insulin, hyaluronic acid

Various research papers and tests in bench-top and pilot size have shown that
ultrasound improves the fermentation process by making more biomass available for
the enzymatic fermentation. In the following section, the effects of ultrasound in a
liquid will be elaborated.
2. Effects of Ultrasonic Liquid Processing
By high-power/ low-frequency ultrasound high amplitudes can be generated.
Thereby, high-power/ low-frequency ultrasound can be used for the processing of
liquids such as mixing, emulsifying, dispersing and deagglomeration, or milling.
When sonicating liquids at high intensities, the sound waves that propagate into the

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