Structure of landfills

We all throw away rubbish, we all produce waste – items we decide we cannot use any more. This may be anything from food wrappers to clothes and furniture.

In New Zealand, there is a strong sustainability network of people, communities and industries working towards a different system – a system that has a focus on the end life of products produced and ensuring the life cycles of materials are maximised. We call this system a circular economy. It provides a different way of thinking about the production of products and services. Most products produced presently are part of a ‘take-make-waste’ linear model.

One person's trash is another person's treasure.

Even in a circular economy, waste streams are inevitable – so what happens to the ‘stuff’ that has come to the end of its usable life?

Landfill waste

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Eventually, items we cannot use any more become waste. Most waste items end up in a landfill.

Rights: Petro Perutdkyi, 123RF Ltd

Landfills

New Zealand generates almost 2.5 million tonnes of waste each year that is buried in landfill sites. Decades ago, landfills were large open holes in the ground, normally on the outskirts of urban areas. People would take their rubbish to these sites and dump it. When landfill sites reached capacity, they were covered with soil and reinstated into vegetation. In some cases, historical landfill sites now have extensive urban housing development on them.

Now local refuse stations are where we take the waste that is not picked up by roadside collections. From there, it is sorted, and what cannot be repurposed is trucked to a landfill along with the roadside collected rubbish.

The problem with old landfill designs

Over the last 30 years, landfills have undergone major advancements in design, management and monitoring. We’ve moved from an open landfill system to using closed systems.

When it rains on open landfills, water percolates through the waste. As it moves through, it becomes contaminated with suspended and dissolved material, forming leachate. If this is not contained, it can contaminate groundwater.

Old landfills are not contained and are considered a hazard Many of these are scattered across New Zealand, and events such as flooding or earthquakes can compromise them and cause significant environmental damage. Examples of these events include the Fox Glacier landfill in 2019 and a landfill near Te Araroa in 2020.

South Westland landfill breach

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Flooding washed a large amount of rubbish from the long-disused Fox Glacier landfill down the Fox River and along the coast, prompting a major clean-up by locals.

Rights: DOC, CC BY 4.0

Regulations now require waste to be sorted into four main waste streams of:

• cleanfill

• municipal – household solid waste landfill

• industrial waste landfill

• hazardous waste landfill or hazardous waste containment facility.

This system ensures the management of the waste is matched to the waste stream held in specific landfill sites.

New municipal landfill sites containing our general household waste are now regulated to be closed systems. This system ensures new landfill sites use impermeable liners, made up of a thick compacted sub-base of clay overlayed with a geosynthetic clay liner and then lined with a synthetic flexible membrane. They also have collection systems to contain and capture leachate. Once a landfill site or cell is full, it is sealed off to prevent rainwater from moving through the landfill and forming leachate. The ground around landfills must be tested for leachate to ensure any breaches of the liner are identified, and action is taken to prevent pollutants from contaminating groundwater.

General waste landfill gases

New general waste landfills have larger air-filled spaces between objects. Oxygen in the air space is used by microorganisms in a cellular process called respiration, and carbon dioxide is released. The microorganisms break down organic matter, like food or paper. As the landfill gets fuller and more compacted, oxygen is used up and the deeper sections of the landfill become anaerobic (without oxygen). Some microorganisms are able to respire in anaerobic conditions and continue to break down organic matter. This anaerobic process produces the methane that is found in mature landfill gas. This gas is able to be captured and used to fuel numerous other innovative initiatives.

Gas production from landfill

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Microorganisms decompose landfill organic waste. The composition of the gas produced changes over time. There are two main environmental processes producing gas in a landfill. The first is aerobic respiration, and as time increases, this changes to anaerobic respiration.

Rights: The University of Waikato Te Whare Wānanga o Waikato