Fermentation using bacteria
Limitations of conventional yeast
Yeast is very good at converting glucose, and other six-carbon sugars into ethanol. Unfortunately, a significant proportion of waste biomass consists of complex natural polymers made from sugars that are not "digested" readily by yeast enzymes.
These include hemicellulose, which on hydrolysis produces a range of sugars including: mannose, xylose, arabinose and galactose, depending on the original source.

diagram: xylose sugar molecule

Commercial Development

The BC International Corporation is attempting to develop this approach commercially in the United States, focusing on:

  • areas where legislation prohibits burning of agricultural waste
  • conventional ethanol plants suitable for conversion and refurbishment
Diagram: Ethanol from waste biomass

A genetically modified bacterium, developed by the microbiologist Lonnie Ingram in 1987, has enabled these sugars to be converted to ethanol. The bacterium, referred to as KO11, would normally produce acids, but the modification means ethanol is produced instead.

The advantage over yeast is that a wider range of sugars can be processed, enabling the utilisation of biomass waste such as wood waste, corn stalks, rice hulls, and other organic waste, which would otherwise require disposal by some other method, or which could only be partially utilised by conventional fermentation methods, making them uneconomic.

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