Biomass
Growing energy and smart ways with waste
What is biomass?
Biomass is the name given to all plants and animals (including humans) on earth. Energy from biomass refers to ways of using plants and animals as energy sources.
How do we get energy from biomass?
Biomass can be converted to energy in two ways:
- directly by producing electricity, normally done by burning the biomass (e.g. wood or waste products) in steam generators.
- indirectly by converting it into a liquid or gas fuel.
People have always used plants and animals as renewable energy.
Burning wood for cooking and heating is as old as fire itself. Domesticated animals, such as horses, buffalo and elephants, have long been used to provide power for transportation and work like ploughing.
Oils from plants and animals were also used to provide fuel for cooking and lighting. Oil from the blubber of giant sperm whales was used widely in lamps and candles for lighting before electric light was widely available.
But the whales of the world can relax because modern biofuels come mostly from crops and the world’s tiniest organisms!
Many crops that are grown for food can also be used to make biofuels.
Corn, sugar cane and sugar beet are used to make ethanol because of their high sucrose content. Tiny organisms feed off the sucrose and convert it to a form of alcohol called ethanol. Ethanol is a flammable liquid that can be used to run cars or be added to petrol.
Other crops are processed for their oils, to be used as a fuel. This includes a wide variety of seed crops like linseed, rapeseed, soy bean and jojoba. These oils are used as biodiesel in engines.
Another way of getting energy from plants is by capturing the gases produced as the plant matter decomposes. As plants decay, microbes that live on the decomposing material give off methane gas. If this gas can be collected it can be used as a fuel.
Rubbish dumps, containing such things as household waste or kitchen scraps, produce methane gas. Some local councils collect this gas and burn it to generate electricity that is fed back into the grid. One council uses the gas from an old tip to help heat the local swimming pool5.
Capturing methane gas is very important because it is a potent greenhouse gas. When methane gas is burned for energy, the CO2 created has less greenhouse impact plus we get to use the power created. Methane is 21 times worse than CO2 for its greenhouse gases content, so converting methane into CO2 is a good thing.
Waste not, want not
Sugar cane provides energy for more than the human body. After sugar cane has been processed, the crushed cane is often burned to make electricity for the sugar mill.
The electricity used by the sugar mill is fed into the electricity grid – so some of the electricity used by consumers comes from sugar cane waste.
The left over crushed sugar cane is called bagasse.
In Queensland, some sugar mills are experimenting with storing the crushed cane (bagasse) for use throughout the year. This means the supply of power from the sugar mills is spread all year round and not just in the harvesting season6.
Timber mills are another industry that commonly uses waste, in their case burning off-cuts and shavings to provide energy.
Using waste products for energy solves the waste problem and creates energy. If it is not burnt it rots and gives off methane which is worse than burning and creating CO2.
Gases collected from human sewerage are also being used to create energy. In the Sydney suburb of Cronulla, the water authority is capturing methane from treated sewerage waste and using it to generate electricity. Similar plants operate in other major treatment works across Australia7.
Biomass and greenhouse gases
While using biomass fuels creates greenhouse gases, it is estimated that their impact is ‘greenhouse neutral’. Why would this be so? Because plants absorb greenhouse gases as they grow – just like trees do.
Energy buzz word
Biofuels and biogas are energy sources produced by microbes and enzymes – tiny living creatures whose natural processes create fuels or gases that we can use.
Biomass pros and cons
Biomass energy sources like wood, biofuels and biogases are important sources of renewable energy. In many ways they have a ‘head start’ because they come from crops that are already widely grown for food – like sugar cane and corn.
They are also suitable for existing technologies like petrol and diesel engines. Using waste for energy solves two problems – it reduces waste and it creates useable energy. However, a lot of land and water are required to grow many of the crops and burning wood for fuel creates smoke pollution.
| For | Against |
|---|---|
| Greenhouse gas neutral, i.e. carbon dioxide produced when the fuels are burned is balanced by the carbon dioxide taken in when the plants grow | Bio fuel crops need a lot of land and water |
| Renewable | Burning wood creates pollution, e.g. smoke |
| Used to supplement other fuels | Bio crops are vulnerable to climate variations |
| Stops methane reaching the atmosphere |
Discover other renewable sources: Wind
energy, Hydro
5
http://www.greenhouse.gov.au/local/publications/pubs/e20.pdf
6
http://www.greenhouse.gov.au/renewable/recp/biomass/eight.html
7
http://www.bcse.org.au/default.asp?id=107&articleid=43