Re-examining energy from waste

RECOVERING energy from waste immediately raises the spectre of dirty, polluting mass-burn incinerators. But it is actually much "greener" than simply burying waste materials. By MATTHEW WARNKEN
Re-examining energy from waste Re-examining energy from waste Re-examining energy from waste Re-examining energy from waste Re-examining energy from waste

by putting waste into 'mass-dump' landfill we are losing the opportunity to recover about 10 million tonnes of black coal equivalent energy and directly save 26.2 million tonnes of CO2 equivalent in greenhouse gas emissions. We need to rethink the value proposition of energy from waste.

How to recover energy from waste

There are two key opportunities to recover energy from waste.

The first is through use as a fuel where the calorific content is accessed through direct burning, combustion or thermal oxidation, depending on your predilection for terminology.

It is also possible to anaerobically digest food waste and soft garden organics for biogas that can also be used as an energy source.

The second option is to recover embodied energy. Embodied energy is a measure of the amount of energy used to transform raw materials into a final product or material.

The recycling of materials with high embodied energy reduces the amount of energy used to manufacture commodities, thus preventing associated environmental impacts from the original energy use.

How much energy could be recovered?

On a yearly basis we are generating about 40 million tonnes of waste in Australia, with nearly 23 million tonnes landfilled.

These wastes comprise a mixture of materials including: food and other organics; paper and cardboard; garden organics; wood/timber; plastic; glass and metals.

In order to determine the potential for solid fuel usage, I used estimates of the energy content of paper, garden, wood and plastic materials to calculate the energy content of wastes being landfilled, and assumed that 50% of paper and plastic would be recovered for use as fuel and that 50% would be recycled.

This gives an estimate of 7.8 million tonnes of potential fuel and 2.1 million tonnes of high embodied energy recycling (including glass and metals), with an additional 3.6 million tonnes of food waste that could be used for anaerobic digestion.

The energy content of the potential solid fuel is equivalent to 4.5 million tonnes of washed black coal (at 27 gigajoules per tonne), which is a loss of 120 petajoules of energy to the economy.

The energy savings that could be realised through recycling (derived by subtracting the embodied energy of recycled commodities from the virgin material embodied energy) equate to around 4.8 million tonnes of black coal equivalent, which is 130 petajoules of energy.

Add to these two totals the 633,000 tonnes of black coal equivalent that could be recovered through the anaerobic digestion of food waste (18 petajoules) and we see that energy from waste could displace the equivalent of 10 million tonnes of black coal in Australia.

If this energy was used to generate electricity it would create 25 million MW/hr per year, which is enough for three million households, or nearly 40% of Australian households. This is not an insignificant amount of energy to the Australian economy just to be wasted on an annual basis as inappropriate fill of land.

There are also the greenhouse benefits to consider from the displaced fossil fuel energy (where the energy recovered is renewable) and the greenhouse savings from recycling high embodied energy materials.

Combined, this represents approximately 26.2 million tonnes of CO2e emissions.

Furthermore, this does not take into account the greenhouse benefit from avoided landfilling of degradable organic carbon, which would prevent methane generation in landfill and lead to additional comparable savings in greenhouse gas emissions.

Need for change

The recovery of energy from waste in Australia would displace the use of primary fossil fuels and also prevent materials with degradable organic carbon from being landfilled, while at the same time maximising opportunities for the recycling of high embodied energy materials: a triple dividend of carbon abatement and a compelling sustainability argument for re-examining community opposition to energy from waste.

Part of the pathway forward involves avoiding mass burn incineration in favour of a fuel preparation approach that ensures only suitable materials are used for energy.

There is also a need for supporting infrastructure to detoxify the residual waste stream and create the opportunity to recover embodied energy from the waste stream.

For municipal waste this could be provided through reverse logistic centres that support Extended Producer Responsibility (EPR) across brands and products, including reverse vending machines for containers and drop offs for household hazardous waste.

In a decarbonising economy there is no room for landfilling of biogenic carbon (or other calorific value), or for lost opportunities to save embodied energy through recycling.

Sustainable energy from waste, far from being an oxymoron, is an essential component of a sustainable and biomimetic economy.

Matthew Warnken is a sustainable business and research consultant with Crucible Carbon. Contact at matthew.warnken@cruciblecarbon.com

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