Try this: Compost in a bottle
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| You will need these materials. |
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| Cut the bottle to make a flip-top lid. |
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| Chop the scraps into small pieces. Tear the newspaper into small squares. |
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| Fill the bottle with layers of soil, scraps, newspaper and leaves. Use the table as a guide. |
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| Seal the bottle and leave in a warm place to decompose. |
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Safety: This activity involves a knife. See the CSIRO Education safety page for more information.
You will need
- 2 L plastic bottle
- Fruit and vegetable scraps, such as banana peels and apple cores
- Garden soil
- Newspaper
- Dried leaves or lawn clippings
- Water in a spray bottle
- Scissors
- Chopping board
- Small knife
- Tape
What to do
- Remove the label from the bottle, but leave the lid on. Use the scissors to cut the bottle a quarter of the way down to make a flip-top lid. Don't cut the top completely off.
- Use the knife to cut the fruit and vegetable scraps into small pieces on the chopping board.
- Tear the newspaper into small squares.
- Add the following layers to the bottle:
| Material | Depth (cm) |
| Soil | 2-3 |
| Food scraps | 2-3 |
| Soil | 1 |
| Lawn clippings or leaves | 3 |
| Soil | 1 |
| Newspaper | 3 |
| Soil | 1 |
| Food scraps | 3 |
| Soil | 1 |
If the soil is dry, spray each soil layer with water from the bottle. - Close the lid and secure with a small piece of tape. Wash your hands with soap and water.
- Place the bottle in a warm, sunny area and observe every few days. If the mixture looks too dry, open the bottle and spray the mixture with a bit of water. If it looks too moist, leave the top open to dry out. If you notice a bad smell or see furry green mould, place the bottle into a plastic bag and dispose of it in the waste.
- Continue until all the organic material has decayed away. This will take a number of weeks. When your compost is finished you can spread it onto your garden
What's happening?
In this activity, microbes in the soil feed on the food scraps, lawn clippings, leaves and newspaper, and break them down. Different types of microbes thrive under different conditions.
Some of these microbes need oxygen to flourish, and like carbon-rich food, such as newspaper. These microbes are described as aerobic. Aerobically respiring microbes generate large amounts of heat, carbon dioxide and water.
Microbes that respire anaerobically thrive in low-oxygen environments, and like nitrogen-rich food, such as fruit and vegetable scraps. Anaerobically respiring microbes don't produce as much heat. They release gases such as methane, hydrogen sulfide (which smells of rotten eggs) and ammonia.
When these microbes are breaking down your compost, decomposition is taking place. Both aerobic and anaerobic decomposition can occur. If your compost looks a bit slimy and has a bad odour, then you have anaerobic decomposition. If your compost is warm, not too wet and doesn't have a bad smell, then aerobic decomposition is taking place. Aerobic decomposition happens faster than anaerobic decomposition.
Applications
Usually, when making compost, aerobic decomposition is preferred. Although carbon dioxide is a greenhouse gas, the methane produced by anaerobic decomposition is much more potent.
Much of the food waste thrown out in garbage ends up as landfill. This is often buried, meaning there is a lack of oxygen, which leads to anaerobic decomposition. The methane and other gases produced seep up through the surface and into the atmosphere.
Composting your green waste in a way that promotes aerobic decomposition reduces the amount of organic matter that goes into landfill. This reduces the amount of methane produced by household waste.
By Patrick Mahony
More information
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