Is landfill part of the ‘Circular’ Economy? – AustraliaPosted on February 18, 2021 by DrRossH in Landfills and Disposal
The Circular Economy is where materials are reclaimed from end-of- life products and recycled or re-used back into the same product. This is claimed to be the way of the future and the best approach to a sustainable economy. Avoidance of waste going to landfill is a key part of the Circular Economy.
In this paper I make a case for landfill itself to be a circular economy for organic wastes and one that is linked into the natural carbon cycle.
What is a Circular Economy?
In contrast to the ‘take-make-waste’ linear model, a circular economy is regenerative by design and aims to gradually decouple growth from the consumption of finite resources. However, it meets headwinds if you consider Australia imports most of its consumer goods and mines and grows far more resources than we can consume.
Co-operation in our circular economy is a very big ask. Nevertheless, WMRR and others keeps pushing the concept as the solution to waste in Australia.
The carbon cycle
Nature has quite a few ‘circular economies’ such as the water cycle, the nitrogen cycle and one I will expand on the carbon cycle. The biogenic carbon cycle illustrated below. Biogenic means produced by living organisms and refers to the short-term carbon cycle. Fossil fuels contain carbon derived from living organisms that died millions of years ago and the carbon cycle was disrupted by formation of coal, oil and gas deposits.
The biogenic carbon cycle circulates carbon through the atmosphere as carbon dioxide and then into plants by photosynthesis and into animals and other invertebrates by digestion of the plants. The plants and animals die and degrade back into carbon dioxide and circular carbon economy continues.
There is no market to satisfy, no industrial processes to perform. It is all done by living plants, animals and importantly bacteria.
Carbon cycle with landfill
If the plant and animal waste is deposited in landfill a different carbon cycle occurs as shown below. The first part of the carbon cycle is the same as before, but instead of letting the animal and plant material degrade naturally, it is placed in a landfill.
There the carbon undergoes a series of complex changes by bacterial action, the last of which is methanogenesis. 50 per cent of the organic carbon is resistant to the bacteria in landfill and is stored for many 100’s of years thereby taking that carbon out of the biogenic carbon cycle.
The other 50 per cent is split into methane and carbon dioxide called landfill gas. The methane is burned in an engine to generate renewable electricity that offsets fossil fuelled electricity generation. The methane will be converted to carbon dioxide and water by combustion and be released into the biogenic carbon cycle as though it never entered the landfill.
A portion of the landfill gas will escape into the atmosphere directly and the methane part of that is a greenhouse gas which causes climate change. The carbon dioxide that escapes is part of the carbon cycle and does not cause climate change.
Carbon Cycle with Landfill carbon dioxide greenhouse gas methane carbon dioxide (photosysthesis) carbohydrates (eating) air (atmosphere) animals plants landfill carbon storage Renewable electricity
The only part of the landfill carbon cycle that is not the same as the basic carbon cycle is the release of methane into the atmosphere. Methane is a powerful greenhouse gas 25 times more harmful than carbon dioxide.
The greenhouse emissions are offset by the carbon storage and by the renewable electricity. Carbon storage is a natural effect due to lignin in the waste. Lignin will not break down in anaerobic conditions. An example is timber which is preserved in landfill and basically unaltered after being buried for decades. The renewable electricity offset depends on how the grid electricity is generated.
In Victoria brown coal fuelled electricity generation has a high offset, whereas in other states it would be less. The only negative effect of landfill is the release of methane and this is subject to strong regulation in all States. With modern landfills that are built in cells that fill in two years or less, the waste does not reach full methanogenesis before the cell is completed.
If extraction bores are drilled within two years of starting the cell most of the methane is captured and collection efficiencies of more than 80 per cent can be reliably achieved. Capping with an impermeable membrane helps to maintain the high collection efficiency. Small leaks in the cap can be oxidised by methane oxidising bacteria in the cover soils with the use of biofilters.
In the very long term, methane oxidation will eliminate residual methane emissions when the cap might have deteriorated. All these benefits of methanogenesis allowing renewable electricity generation, carbon storage and methane oxidation happen naturally by some of the oldest types of bacteria on earth, that have developed amazing capabilities to utilise the waste for its energy source with no additions from humankind.
The reliability of landfill gas electricity generation is well known in the industry with availability greater than 98 per cent. It uses no other fuel and burns a very small amount of lubricating oil in comparison to its electrical output.
In fact, taking everything into account landfills are greenhouse sinks and the only waste management technology that is reducing biogenic and fossil carbon dioxide in the atmosphere.
How does landfill circular economy compare with other treatments for organic wastes?
Alternative waste such as mechanical/ biological treatment and composting all have considerable energy inputs in the way of electricity and diesel fuel to power the waste handling and air blowing machinery. Anaerobic digestion can generate biogas that is used for electricity generation, but experience has shown that little is exported and most is used in plant.
Aerobic processes have no energy offset but may have an offset benefit from substitution for fertilizers. The compost produced by alternative treatment has to find a market and this has been difficult from a mixed waste feedstock. Compost itself is a valuable commodity but only if made from carefully controlled feedstocks.
Landfill has no market to satisfy except the natural carbon cycle. If it emits carbon dioxide into the atmosphere it is part of the carbon cycle and there is no limit on that market.
The critical component of the landfill carbon cycle is the amount of methane that escapes into the atmosphere. Comparative studies often use very low collection efficiencies below 50 per cent. This is simply not realistic. Modern landfills with electricity generation on-site can easily collect 60 per cent and more. If they follow best practice this increases to 80 per cent and more. With the offsets available for renewable electricity and carbon storage landfill can easily achieve net carbon storage.
If the proponents of the circular economy looked at landfills as part of the natural carbon cycle they would be encouraging best practice and the disposal of organic waste to landfill. It is so much closer to the ideal of “a circular economy as a systemic approach to economic development designed to benefit businesses, society, and the environment” than any of the alternatives.
Indeed it is the only way some material is going to get recycled. With anaerobic biodegradation producing Methane this is the last way we can get some useful energy from the waste. That company Biogone has been pushing this for a few years now.