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Organic Waste and Landfill Gases

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When organic waste breaks down in a landfill it makes leachate and greenhouse gases such as methane and carbon dioxide. At Kate Valley Landfill, this methane is used to create electricity.

Organic waste and landfills

What is organic waste?

Organic waste is anything that was once living, such as:

  • food
  • garden and lawn clippings
  • animals and animal waste
  • paper
  • cardboard
  • timber.

Organic waste and landfills - like a big biodigester!

A biodigester is like a mechanical stomach that is fed with organic waste. The waste is broken down (decomposed) by micro-organisms (bacteria) in an oxygen-free environment. The same thing happens when organic waste is put into a landfill.

This process creates a liquid called leachate, and biogas (methane and carbon dioxide). Both of these are greenhouse gases.

The carbon cycle

Carbon from the atmosphere gets locked up by plants and released back into the atmosphere either quickly or slowly. Methane is one of the carriers of carbon from organic material to the atmosphere so it’s part of the natural carbon cycle.

Carbon naturally moves from one part of the Earth to another through the carbon cycle. However, human activity is adding carbon to the air (in the form of carbon dioxide and methane) faster than it can be removed. This is causing the earth to warm and the climate to change.

This diagram of the carbon cycle shows how carbon moves between the air, oceans, ground and living things:

Greenhouses gases and the greenhouse effect

Greenhouse gases are found naturally in the air and keep our Earth warm enough to support life. They include water vapour, CO2, methane and some others.

The Earth gets energy from the Sun in the form of sunlight and heats up. When the Earth cools down it gives off a different form of energy called infrared radiation. Greenhouse gases in the air hold on to some of this radiation, which makes the air warmer - a bit like a greenhouse.

Planets without greenhouse gases get very hot when the sun shines on them but very cold at night time.

The Earth needs some greenhouse gases to trap heat but if these gases increase too much the air will keep getting warmer.

There are different types of greenhouse gases. Carbon dioxide is the greenhouse gas you hear people talk about the most. That is because we produce more carbon dioxide than any other greenhouse gas and it causes most of the warming.

Greenhouse gases come from all sorts of everyday activities, such as:

  • heating our homes
  • driving cars and trucks.

The graph below shows the main greenhouse gases:


Another important greenhouse gas is methane (CH4). Methane is made when organic matter rots. You might think landfills make a lot of methane - and they do!

Methane is an interesting (but bad) gas:

  • It is more harmful than carbon dioxide as a greenhouse gas.
  • It can kill you if you breathe it.
  • It is very explosive.

Methane is also valuable because it has lots of energy. At Kate Valley the methane is collected through a network of pipes. The pipes take this gas to large generators that make electricity.

Closing the loop

Kate Valley Landfill controls the gas that comes from organic waste. Not only does it stop harm to the air, it also makes electricity from the gas. 

The electricity created by organic waste at the landfill is being used to fuel new electric vehicles that collect waste - how cool is that!

Audio Māori keywords: 

Challenge: Create a diagram that shows how the collection of gas at Kate Valley Landfill reduces harm to the environment.

Innovation at Kate Valley

Kate Valley Biodiversity Project


Organic waste is anything that was once living or made from something that was living. What happens when organic waste is put into a modern, engineered landfill? Image: Creative Commons.

The greenhouse effect keeps the Earth warm. What will cause Earth to get warmer? Image: Public Domain.

Wells are placed down into the rubbish to collect gas. The gas is then piped to a generation plant that makes electricity. I wonder how the gas is made to travel through the pipes. Image: Andrew Penny, LEARNZ.

This is where the gas is first comes to from the landfill. What might the big chimney stack be for? Image: Andrew Penny, LEARNZ.

These four large generators make electricity at Kate Valley Landfill. What is the main gas used as fuel for the generators? Image: CWS.