Energy From Waste (Biological)
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Biological treatments of waste include anaerobic digestion (without oxygen) and aerobic digestion (in presence of oxygen) . Only biodegradable waste such as green (e.g. garden), food waste, animal slurry etc can be treated with these processes. In anaerobic digestion, biodegradable material is converted into methane and carbon dioxide (biogas) and water, leaving a wet organic mixture known as “digestate”. The gas can be burned to generate heat and electricity, or used as transport fuel. The digestate can be applied on to land as a soil conditioner with some treatment.
Types
- Medium to large scale, eg community use, sewage treatment works or on a farm. Min 5,000 tonnes a year.
Other components
- CHP engine or boilers to convert biogas to heat and/or power
- Fuel and digestate storage and transportation
- Communal energy centre to house large scale plant
- District heat network
Typical saving
Scheme-dependent. By diverting waste from landfill, substantial quantities of greenhouse gases such as methane and carbon dioxide that would have otherwise been emitted to the atmosphere are controlled and used to displace demand for fossil fuels.
Indicative cost
A large 1MWe anaerobic digester would be £3 to £4 millions, with an operational and maintenance cost of 3% of the capital cost per annum.
Main issues affecting feasibility
- Heat and power demand: Most efficient if heat can be used, so year round heat demand ideal.
- Consistency of waste: Consistent quality of the feedstock and sufficient pre-treatment (i.e. segregation) to ensure a “clean” organic stream are crucial for the optimum performance of the process .
- Traffic: from waste deliveries
- Pollution and health: including odours, bio-aerosols, dust, noise, vermin
- Visual impact and public perception
