Building Science Concepts: Rubbish

Explore the science concepts that underpin knowledge and understanding about rubbish, how we identify and classify it.

The New Zealand Ministry of Education’s Building Science Concepts (BSC) series presents sets of interlinking concepts that build stage by stage towards overarching science concepts or big ideas. A big idea shows how a fully developed understanding of the concept might look, but recognises that such an understanding might not be achieved until New Zealand Curriculum level 7 or 8.

This resource is a partial replication of Rubbish: How Do We Deal with It? The background information on this page, combined with the information in the interactive, covers the science notes provided in the original BSC book. The overarching science concepts (big ideas) and how they may be scaffolded in sequence are illustrated in the interactive below.

The context of rubbish (rāpihi) is well known to students, and investigations into the ways items are classified (whakarōpū) as rubbish can be explored in classroom and school contexts. Classification is one of the big ideas in science so it is a useful concept to develop in this context. In grouping rubbish, its physical and chemical properties (āhuatanga) are explored. These activities can act as an introduction to work on Recycling: New Uses for Rubbish, Book 61 of the Building Science Concepts series .

What is rubbish?

Rubbish is simply something that is unwanted. However, we can also consider a range of types of rubbish. Waste (toenga, para) is something that is superfluous or a byproduct – for example, trimmings of fabric that are too small to be useful or bark that is removed from timber to be used for building. Rubbish is something that has lost some quality that made it useful – for example, rubber bands that are no longer flexible or paper products soiled by food.

Properties of rubbish

Something may be considered rubbish if it has:

• an issue that prevent its ongoing use

• a missing component

• lost some element of its component’s properties – for example, clothing losing its colour due to fading or where the fibres lose strength due to being stretched, worn or torn.

Ways of sorting rubbish

People use a range of ways to sort rubbish. One way is by using our senses. We discard food that:

• smells bad

• tastes peculiar

• feels hard and stale (bread) or soft and pulpy (fruit and vegetables)

• looks rotten, contaminated or mouldy

• sounds mushy or hollow.

Rubbish is also sorted by its physical properties. Organic materials like food waste and garden waste may be collected separately for composting rather than being sent to a landfill. Items that have properties that allow them to be remade into new products are also collected separately. For example, glass, aluminium, tins, paper and some plastics are recycled rather than disposed of.

Waste managers have developed a classification system based on the physical properties of rubbish. Rubbish sorting that happens before collection is known as source separation. After collection, a further sort happens to separate similar things but with different properties – such as plastics with RIC numbers 1 and 2.

Disposing of rubbish

Methods of disposal that used to be common, such as burning, have been re-examined to check for environmental impacts. There is new technology being investigated that looks at burning to generate energy but also closely monitors and manages all outputs such as gases produced by burning and remaining ash.

In Aotearoa New Zealand, we still bury some of our rubbish, but we’ve moved to closed landfill systems that capture and collect leachate and gases.

Binning bad habits

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Households, businesses and schools are encouraged to consider what they put in the rubbish. Composting and recycling are two ways to divert a lot of material from the landfill.

This graphic was produced from an audit of kerbside rubbish bags in the Thames-Coromandel District in 2021 – what do you think a similar audit in your town might reveal?

Rights: Thames Coromandel District Council

Reduce, reuse, recycle

We produce millions of tonnes of rubbish, and this figure is growing. The problem is how to deal with this mass . There are three approaches used – reduce the amount of rubbish, reuse whatever we can and the third option is to recycle.

Reducing the amount of rubbish generated includes:

• only buying what we need

• replacing things we buy with items that last longer, have a lower environmental cost, can be more easily reused or recycled with fewer contaminants and have less packaging.

Reusing items rather than disposing of them includes:

• altering or mending clothing

• cleaning containers for reuse

• removing contaminants from solids or liquids – for example, filtering used car oil

• using containers instead of plastic wrap for food storage.

Recycling items by:

• using some parts to make new products – for example, making craft items from fabric scraps or old blankets

• putting materials through a chemical process to make them into a new yet similar form (such as making playground mats from discarded tyres), to change them into a different product (such as making fleece fabric from recycled plastic bottles) or to use them to create a different new product (such as making compost to grow plants).

Playground safety surfaces

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The soft matting found in playgrounds is often made of recycled materials.

Rights: Public domain

Te ao Māori connections

Māori have a holistic and interconnected relationship with the natural world and its resources. Values of kaitiakitanga and care of Papatūānuku and Ranginui are foremost. Kuputaka Māori mo para (te reo Māori words associated with rubbish and recycling) is available in a downloadable Word format.

Alternative conceptions

Students may think that rubbish is worthless. However, rubbish may have value in another context or to another user. For example, old newspapers are useful as a weed mat when planting a garden.

Students may think that rubbish means untidiness, especially in the domestic context. In reality, rubbish can be neat and contained – for example, stacked and crushed car bodies or bagged household rubbish.

Students may consider that rubbish means organic detritus that no longer has a purpose, like fallen leaves and seaweed on the beach. However, dead or decomposing organic matter can be composted or laid on top of the soil providing additional nutrients for plants.

Students may think that rubbish can be got rid of (made to disappear) by burning or flushing down a toilet. The principle of conservation of matter means that nothing ever vanishes completely. Burning produces carbon dioxide and other gases. Flushing something away simply moves it somewhere else even if it is in smaller particles.

Smoking bonfire

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Burning material causes air pollution. The smoke from a fire releases particulates into the environment, which can have a detrimental effect on people’s health.

Rights: Tomasz Sienicki, CC BY-SA 3.0

Supporting resources

Two downloadable Word documents provide useful information and content vocabulary:

• Physical properties of rubbish of rubbish lists material properties such as colour and texture, and how changes to these properties turn materials from useful to ‘rubbish’.

• Waste classification splits common wastes into categories, with primary and secondary classifications. For example, paper is a primary classification, but is split into secondary classifications such as newsprint, magazines and cardboard.

The article Seagull Centre – reducing, reusing and recycling tells of a community response to the growing waste issue in Thames. It is an excellent example of how individuals and groups can take action to solve environmental problems and create change.