Fuels can be made by fermentation of
natural products. Waste products can
often be used. Fermentation is when
bacteria or yeast break sugars down by
anaerobic respiration
Ethanol is made by anaerobic fermentation of
sugar. Yeast make ethanol when they break down
glucose by anaerobic respiration. Glucose = ethanol
+ CO2 + energy. Sugar cane juices can be used or
glucose can be derived from maize starch by the
action of carbohydrase (an enzyme) The ethanol is
distilled to seperate it from the yeastand reamining
glucose before it's used. In some countries, cars are
adapted to run on a mixture of ethanol and petrol -
gasohol.
Biogas is made by anaerobic fermentation of waste material.
Biogas is usually about 70% methane and 30% CO2. Lots of
different microorganisms are used to produce biogas. They
ferment plant and animal waste which contains carbohydrates.
Sludge waste from eg sewage works is used to make biogas on a
large scale, Biogas generators need to be kept at a constant temp
to keep the microorganisms respiring away.
There are 2 types of biogas
generators- batch generators and
continuous generators. Biogas
can't be stored as a liquid (needs
too high a pressure) so it has to be
used straight away for
heating/cooking/lighting/power
turbines to generate electricity
Fuel production can happen on a large or small
scale. Large scale biogas generators are now being
set up in a number of countries. In some counties,
small biogas generators are used to make enough
gas for a village or a family to use their cooking
stoves and for heating and lighting.
Human waste, waste from keepig pigs and
food race, can be digested by bacteria to
produce biogas. By - products are used to
fertilise crops and gardens.