What is “Waste to Energy”?
‘Waste to energy’ is a term commonly used to describe the process of generating energy—such as electricity, heat or fuels—from waste.
Benefits of Waste to Energy Facilities
Recovering energy from waste can deliver positive outcomes for the community and the environment as part of an integrated waste system. Generating energy from waste provides the opportunity to extract value from waste that would otherwise be landfilled. This helps reduce reliance on landfills and prolongs landfill capacity. It also helps reduce greenhouse gas emissions and environmental impacts through the diversion of organic material going to landfill and reduces transport of waste where waste to energy facilities are established near the production of the feedstock. Waste to energy facilities can help provide economic and regional development through investment and job creation.
Regional Waste to Energy Facilities
There are several waste to energy facilities operating in the Grampians Region. These include anerobic digesters at Berrybank Farm Piggery and Triggs Dairy, and wood combustion boilers at Beaufort Hospital and Meredith Dairy.
Establishing a Waste to Energy project
There are four key components to consider when establishing a waste to energy project. These are the feedstock, the site, the offtake and the technology
- The feedstock is the first consideration. A wide variety of waste feedstocks can be used in waste to energy facilities, though some waste to energy technologies prefer certain types of feedstock over others. Its important to secure the feedstock, understand the availability, volume, composition, calorific value and cost.
- The site – a location with appropriate buffers, permits, licences and community acceptance to establish the facility is critical.
- The offtake – It’s important to establish an ongoing use and commitment for the energy produced from the facility.
- The technology – Once the above three items are established the appropriate technology and size can be selected.
Waste to energy technologies generally fall into two broad categories – the thermal treatment of residual waste or the biological processing of biodegradable waste. The main technologies for each category are described below.
- Combustion: The process of burning wastes to produce heat and steam, which can be converted into electricity. Combustion is a mature technology used globally and is capable of processing large amounts of unsorted waste. This process produces residues of ‘bottom ash’ and ‘fly ash’ and requires treatment of residual gas particulates to avoid airborne pollutants in the environment.
- Gasification: The process of heating waste in a low-oxygen environment to produce synthetic gas or ‘syngas’ (a mixture of carbon monoxide and hydrogen), which can be used to generate heat and electricity.
- Plasma gasification is another form of gasification which uses an arc gasifier to create temperatures of up to 8000 degrees Celsius. This can convert approximately 99% of solid waste into syngas and melt ash into a stabilised slag.
- Pyrolysis: The process of heating waste in the absence of oxygen to create liquid fuels or gaseous products. These fuels can be used for heat and energy generation, or to synthesise chemicals. It works best on a small scale using a homogenous feedstock (such as plastic or tyres) and is unsuitable for processing unsorted waste. A carbon char (biochar) is left after pyrolysis which may be used later to produce heat and energy. Char may have other commercial value as a soil improvement, metallurgical reduction and carbon sequestration product.
- Anaerobic Digestion: The process of decomposing organic waste in the absence of oxygen to produce biogas (a mixture of methane and carbon dioxide) and digestate (a nutrient-rich sludge). Biogas can be used to produce heat or electricity. It requires a homogenous feedstock of wet organic waste such as sewage sludge or wet agricultural waste and cannot process dry organics like timber or unsorted waste streams.
- Mechanical Biological Treatment (MBT): The combination of several processes which include a mechanical component such as sorting, shredding, milling, separating or screening; and a biological component such as biodrying, composting or anaerobic digestion to create a solid recovered fuel (SRF) or refuse derived fuel (RDF) which often comes in the form of fuel pellets or briquettes. SRF/RDF can then be used as feedstock in thermal waste to energy facilities or can act as a partial replacement to fossil fuels in traditional fossil fuel depending facilities.