Science & Technology in Action

4th Edition

Enzymes and Biofuels

Enterprise Ireland

The development of enzymes that could break down cellulose has the potential to make alternative fuels economically attractive and simultaneously reduce organic waste.
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Lesson excerpt

Biofuels may be loosely defined as fuels derived from plant and animal sources. For many years their use was uneconomic owing to the easy availability of fossil fuels. Environmental concerns and increasing demand for oil have led to a need for alternative fuel sources. Among the biofuels in use or under consideration for future use are ethanol,biodiesel, biogas, hydrogen, butanol and ethers.

Ethanol, pure or blended with petrol, has been used as motor fuel since the 1970s oil crises. Its basic production method involves enzymatic hydrolysis of starchstarch from plant sources byamylases – enzymes that break down starch. The product sugars, mainly glucose, are subsequently fermented by yeasts to yield ethanol that is then isolated and purified. Glucose and other sugars (including 5-carbon sugars such as xylose) can be fermented by other organisms to butanol – a superior fuel toethanol.

Fuel crops (e.g. sugar cane, cassava, corn and rapeseed) are now being widely grown. There are serious concerns that their wide cultivation, which is expected to increase, is already affecting food supply and the environment.

Much of a plant’s glucose is tied up in cellulose. For more efficient fuel production this source must be unlocked. Using cellulosewould also mean that many currently uncommercial plants (e.g.; switchgrass, bent, dog’s mercury) and forestry plantations could theoretically be exploited. So too could compost and municipal waste (paper, clothing).

True or False?

  1. Ethanol is the only alcohol that can be used as a biofuel. false
  2. Lignin has long been used as a fuel. true
  3. Non-food plants are potential sources of fuel. true
  4. Compared with other processes, enzymes can work under milder conditions, are more specific and give good yields. true
  5. It can be difficult to maintain optimal conditions for cellulase-producing organisms. true
  6. Starch and cellulose are built of glucose units. true
  7. All sugars are easily metabolised to alcohol. false
  8. GM technology may be a useful complement to enzymes in biofuel production. true
  9. The costs and availability of labour, fuel, fertilisers, pest control are factors involved in growing fuel crops. true
  10. Cellulose-to-ethanol conversion is now a proven commercial technology. false