Nothing
is a waste until it is wasted. Waste generated from one process can be an
important input to another process. This is an idea behind zero-waste
agriculture. Wastes used to generate useful energy such as biogas are biodegradable
in nature; examples include, Animal dung, Poultry waste, Plant residue (duckweed
or rice straw), Vegetable waste, Wheat offal, Cassava Peels, Human Waste, Meat
Processing waste, etc. Biogas is an important gas for cooking and generation of
electricity. Many homes in countries like India, China, Kenya, Australia, etc. have
been using biogas generated from their wastes for cooking thereby reducing
their cost on other energy sources. Biodegradable wastes are being generated on
a daily basis from households, Livestock farms, Crop farms, food and fruit processing
factory, etc. Many unused wastes are major contributors to environmental pollution
and green house effect. However, it is important that we maximize our wastes
effectively and efficiently in order to save our cost on energy and of course
create a clean and safe environment for ourselves.
Biogas
Production
Biogas
is mixture of gases which is generated when biomass (organic matter) are
fermented in the absence of air/oxygen (Anaerobic Fermentation). This gas
mixture is mainly made of carbon dioxide (CO2) and methane (CH4).
Methane is a combustible gas, which means it can be burned. It can be used as a
fuel for cooking and lighting. Methane is produced artificially in a container
called Digester. During digestion, 30-60% of the digestible solids are
converted into biogas. Feedstock (biomass used) for the production of biogas
includes: livestock effluents, meat processing waste, organic components of
landfills, any other source of biomass (e.g. wastewater treatment sludge or food
and beverage industry wastes), and household waste. On average, biogas
contains: 55-80% methane (CH4); 20-40% carbon dioxide (CO2);
trace gases, including toxic hydrogen sulphide and nitrous oxide.
Digester
comprises the inlet, the fermentation chamber, the gas, the gas storage bag or
tank, and the outlet and the exit pipe through which the gas is removed.
Organic matter (biomass) is brought into the fermentation chamber through the
inlet. The process of anaerobic fermentation will take place here to generate biogas.
It will also produce a substrate rich in nutrients which can be used as organic
fertilizer or fish feed. The processing of manure, organic rubbish and
wastewater in the plant helps to keep the environment clean. There is no longer
any bad smell from sewage or livestock manure. Cooking by biogas is much
cleaner than cooking over a wood fire, and there is no smoke to cause lung
problems and eye diseases.
Begin
by loading the fermentation chamber with the materials to be fermented (manure
or other wastes). You should begin with an initial load of 300 - 500 kg of
materials for each cubic meter of the fermentation chamber. This needs
to be supplemented by an additional 8- 10 kg each day for each cubic meter of
the fermentation chamber. The gas output will be 250 - 400 liters for each
cubic meter of the chamber. Expressed another way, 1 kg of manure will
have a gas yield of 30 - 60 liters/day, for several days. The gas yield from 1
kg of water hyacinth will be 40 - 50 liters/day, for several days. One
cubic meter of gas (= 1000 liters) is enough to cook the day's food for a 6 - 7
member family, or provide lighting for 4 - 5 hours. It could replace one liter
of petrol to operate a 400W electric generator for two hours.