In Australia, we are one of the highest waste producers in the world and almost half of our household waste goes directly from kerbsides to landfill. Per year, that’s over 21 million tonnes of waste rotting in landfills which generates greenhouse gases like methane and can leach toxins into the surrounding land and waterways.
Today’s problem will become a larger and uglier one in the future, as our waste production increases and finding suitable landfill sites becomes more difficult. Meanwhile our cities are missing out on an opportunity to generate reliable power using this waste, which includes a large component of renewable energy as a significant proportion can be used as fuel is from biomass (such as wood or food scraps).
Based on population growth forecasts from the Australian Bureau of Statistics, we could produce up to 74 million tonnes of waste every year by 2060 unless current behaviour and waste management policy changes significantly.
Wasted Opportunity
Waste-to-energy plants use household waste, known as municipal solid waste or MSW, as fuel to create electricity and/or heat. Council collection trucks drive waste to a plant where the operator is paid to receive it and then uses the waste as fuel. This is contrary to the current Australian waste arrangements where councils – and taxpayers – pay landfill operators levies to dispose of waste in the ground.
The technology for waste-to-energy has been around for decades and has been thoroughly road-tested in thousands of plants around the world. Europe and Asia, currently have approximately 450 and over 1500 waste-to-energy plants respectively.
Most plants process the waste in a furnace, creating steam that drives a steam turbine to generate electricity (see Figure 1). In cold climates, the residual heat in the steam exhausted from the turbine can be used for district heating schemes.
Given the unpredictable composition of waste, regulators around the globe require strict control of the quality of the flue gas (combustion products) released to the atmosphere. The emissions limits specified by the European Union’s Waste Incineration Directive are the most commonly referenced benchmark.
To meet these limits, a range of treatment processes are implemented including urea injection for NOx gas reduction, caustic scrubbing to remove acid gases, activated carbon injection to adsorb volatile metals and organic compounds, particulate matter collection using bag filters, and control of flue gas temperature to limit the formation of dioxins.
So where are the large-scale MSW energy-to-waste facilities in Australia today? Most experts attribute this to an historical abundance of landfill sites with very low or non-existent state-based landfill levies and the public perception that incineration is a harmful process. This is not surprising since air pollution concerns ultimately led to the banning of the iconic Aussie backyard incinerator.
Today, with rising population density in our major cities, the reduction in suitable landfill sites and significant improvements in combustion processes and environmental control technologies, the balance is strongly swinging in favour of a change to our past practises – and the advantages of converting waste to energy are increasingly outweighing the disadvantages (see Table 1).