Waste Decomposition Times

Waste Decomposition Times

Waste Decomposition Times

The break-down of waste depends on a number of factors including the availability of air, moisture, light and microorganisms, and the type of waste. Biodegradable, or organic waste, typically originates from plant or animal products and includes food scraps, garden waste and paper. Organic waste generally breaks down quite quickly into naturally occurring substances if air, light and moisture are present.

Non-biodegradable or inorganic waste includesman-made products, such as plastic or glass, that take a lot longer to break down. Non-biodegradable waste is generally made from non-renewable sources such as minerals and oil. This waste is not broken down by microorganisms into naturally-occurring organic products, but will eventually break down into smaller and smaller pieces over time.

The following image shows the time it takes for litter items to break down naturally. These times are based on the assumption that items are exposed to air, light, moisture and microorganisms.

Note that, even though plastic bags, bottles and six-pack holders, and polystyrene cups break down in the times indicated, they are still petrochemical products and will always remain in the environment.

This picture shows the waste decomposition times for various household items Banana skins take three to four weeks to break down Paper bags take one month to break down Carboard takes two months to break down A wool sock takes one year to break down An orange peel takes up to two years to break down Chewing gum takes up to five years to break down Cigarette butts take up to tweleve years to break down Plastic bags take up to twenty years to break down Polyfilm or clingwrap takes up to twenty five years to break down Leather shoes take up to forty five years to break down Tin cans take between fifty and seventy five years to break down A plastic bottle takes four hundred and fifty years to break down Plastic six pack holders and disposable nappies take up to five hundred years to break down Polystyrene cups take more than five hundred years to break down Aluminium cans take more than one million years to break down if at all Glass takes between one and two million years to break down Note that even though plastic bags bottles and six pack holders and polystyrene cups break down in the times indicated they are still petrochemical products and will always remain in the environment

1 Image showing list of litter items and the time it take for these to break down.

Did you know?

It is estimated that Australians use more than 6 billion plastic bags a year. Worldwide it is estimated that more than 500 billion are thrown away each year.1

Decomposition in landfill

In a landfill, where the waste is compacted and buried, there is very little air, moisture or microbes. Under these conditions, rubbish breaks downsvery slowly. An archaeological dig of a landfill in America, fifty years after waste was buried, found perfectly-preserved heads of lettuce, 40-year-old hot dogs, and completely legible 50 year old newspapers.2These items are all organic and would normally break down in less than 6 months if exposed to all the elements needed for decomposition

When organic waste is buried in landfill, decomposition occurs in anaerobically, that is in an environment free of oxygen. This process creates landfill gas made up of methane and carbon dioxide, which is captured using pipes and either flared off or converted to electricity. This process occurs so slowly that old landfill sites need to be monitored for landfill gas at least thirty years after dumping has stopped.

Plastic, metals, glass and other non-organic waste will remain buried in landfill indefinitely. At this stage, it is not known how long these materials will take to start to decay, or even if items like glass jars will ever decay.

Did you know?

Every disposable nappy buried at Rochedale Landfill may have only just started to break down, if at all, and may never break down completely.

1 Australian Conservation Foundtion2011

2 William Rathje, Rubbish: The Archaeology of garbage, 1992

Image source: Queensland Beautiful

Brisbane City Council

Rethink Your Rubbish Fact Sheet: Decomposition times

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