Organic waste in schools

Only about 14% of school waste is rubbish – the rest can be recycled or composted. Organic waste (which includes food scraps and garden waste) in landfill produces methane, which is a powerful greenhouse gas – 25 times more potent than carbon dioxide.

Collecting organic waste and turning it into compost is a great way your school can take climate action. You can use the compost to fertilise your school’s gardens or offer it to your community.

Before you start

To decide on the most appropriate composting system for your school, consider:

• how much organic waste your school produces by doing a waste audit (talk to us about assessing your general food scraps from students/staff and from the canteen)
• where you will collect the organic waste
• how much space you have
• who will collect it
• who will maintain the system
• how much time you plan to spend managing organic waste.

Composting systems

Open heap or bay

This is the easiest, cheapest and most flexible system.

The minimum heap size is about 1m³. Build a 1 x 1 metre enclosure/bay directly on top of the earth using star pickets and chicken wire or pallets. Contact with the earth is the source of helpful microorganisms and composting critters. Cover the earth with brown, carbon-rich organic matter such as straw or dead leaves.

Add food scraps in a layer. Then add another layer of the brown material. Keep adding layers. Cover the heap with a piece of shade cloth to keep it cool and moist. Worms will come so this is essentially a worm farm, not a hot compost. In Canberra, it can take up to 6 months for everything to break down with this method. Turning the heap is not essential but may speed up the rate of decomposition.

Ideally, you’ll have more than one enclosure/bay. When one is full, cover it and start using the next bay. If you want to make hot compost, search for a recipe online, collect all the materials, then build the heap. This takes more effort and you need space to store the materials.

Closed system

Non-insulated tumblers compost very slowly in Canberra. Bins that sit on the ground can be used in the same way as the open heap and may be somewhat rodent-proof.

Large, insulated tumblers designed for use in very cold climates work well in Canberra. They are rodent-proof and stay warm and moist so organic waste ‘hot composts’ quickly. You will either need:

• 2 tumblers
• one tumbler with 2 compartments.

When one is full, close it off and start on the next one. This is a more expensive system and it may limit the number of scraps you can compost.

Bokashi bins

Bokashi bins are used to collect all organic waste including meat, bones and dairy. A mixture containing helpful microorganisms is added to accelerate composting and prevent smells. The waste breaks down in the bucket and is then buried in a shallow hole or added to an existing compost system.

Worm farms

Compost worms break down organic waste to produce worm juice and castings which are valuable fertilisers. There are numerous designs to build your own, you can purchase one or hire an organic waste recycler to design one for your school.

It is important to have a system that can manage the volume of waste you are producing. The worms graze on the microorganisms growing on the food scraps. This system may limit the types of scraps you can collect, given worms prefer not to eat citrus, onions, dairy and meat. This can make sorting organic waste a bit more difficult, although commercial worm farmers say worms eventually eat everything organic!

Organic waste collection service

Organic waste collection services collect organic waste for their large-scale worm farms. There are a range of options and prices for the service.

Give it away

Someone might like to collect your organic waste for themselves, their chickens or their community.

See what other schools are doing to make sustainable and cost saving choices.

Successful composting

Many things can be composted. This includes meat, fish, bones, dairy and citrus. Some things take longer to break down than others.

For your compost to work effectively, it should have the right ratio of carbon (60%) to nitrogen (40%).

Green stuff is high in nitrogen, such as:

• food scraps
• fresh lawn clippings
• manure (avoid dog and cat poo due to possible parasites)
• coffee grounds
• weeds (though be careful of seeds not breaking down, which could spread once the compost is used).

Brown stuff is high in carbon, such as:

• straw
• dead leaves
• shredded paper (please avoid glitter and glue)
• shredded cardboard.

Compost needs warmth and moisture. The compost should feel moist in your hand. If it is dry, sprinkle it with water. If it is wet, add more brown stuff. Find out more about what you can and can’t compost, or check the Recyclopaedia.

Pests in your compost

Any open heap containing food may attract rodents. Locate and design your system with this in mind.

Maggots in your compost are most likely black soldier fly larvae, which eat large amounts of food scraps and convert them into compost.

Flies in your compost are likely vinegar flies, which love fermenting fruit and vegetable scraps. Cover fresh scraps with brown stuff and cover the heap.

Get your students involved in identifying all the organisms that live in compost.

Smelly compost

Compost that is too wet or does not have enough air may produce a strong smell. Turn the heap to aerate it and mix in more brown stuff. You can also poke holes in the heap or insert some tubes with holes in them to help with aeration.

Find out more

Read more about recycling and waste.

You can find out about taking climate action through the Sustainable Schools Program.

Meet our Schools Award winners.