Energy can be recovered from waste by various (very different) technologies. It is important that recyclable material is removed first, and that energy is recovered from what remains from the residual waste. And the energy from waste technologies are shown below:
1. Combustion, in which the residual waste is burned at 850 C and the energy recovered as electricity or heat;
2. Pyrolysis and gasification, where the fuel is heated with little or no oxygen to produce “syngas” which can be used to generate energy or as a feedstock for producing methane, chemicals, biofuels, or hydrogen;
3. Anaerobic digestion,which uses microorganisms to convert organic waste into a methane-rich biogas that can be combusted to generate electricity and heat or converted to biomethane. This technology is most suitable for wet organic wastes or food waste. The other output is a biofertiliser.It is also possible to harness energy from waste after it has been disposed of in a landfill.
As the UK has traditionally landfilled much of its waste, we are currently exploiting this legacy at many landfills, by capturing landfill gas produced as waste decomposes. Landfill gas contains methane, which is a powerful greenhouse gas. Capturing it prevents it from polluting the atmosphere. The production of landfill gas will slowly decline as we move towards more sustainable and efficient practices of waste management.
Harnessing energy from waste has many benefits:
a. It helps the UK reduce its dependency on energy imports;
b. It contributes towards reducing carbon emissions and meeting renewable energy targets When used for electricity generation, these technologies have a steady and controllable output, sometimes referred to as providing “baseload” power;
c. It has very good sustainability and greenhouse gas saving characteristics, as it makes further use of materials that have already been discarded. This is reflected in the methodology used under the Renewable Energy Directive for assessing carbon and sustainability characteristics.