Biomass is biological material derived from living or recently living organisms. The term is generally applied to plant tissue, including material from agricultural crops, forestry, and trees growing in parks, gardens and along streets. Large quantities of biomass – in the form of food waste, paper, cardboard and wood waste – are disposed of in landfill each year. These resources could be used to displace fossil fuels in power- and heat-generating projects and, provided they come from sustainably managed sources, have the potential to reduce greenhouse gas emissions and pressure on conventional waste management services.
Trees growing in the urban landscape are carefully managed to ensure they remain healthy and continue to provide benefit to local communities. Branches removed from trees, together with trees that are blown over or damaged in storms, can be processed to provide fuel to local renewable heat and power projects. This material is often referred to as ‘arboricultural arisings’.
As well as offering potential economic benefits, using arboricultural arisings in urban-based heat- and power-generating projects can highlight issues such as climate change, environmental pollution, energy security and renewable energy to a large audience from a variety of backgrounds. Using this fuel source can also help councils and local businesses to increase their use of renewable energy and decrease carbon emissions and reliance on fossil fuels. Ensuring that arboricultural arisings are used as a fuel could reduce waste management costs incurred by the council, and may reduce fossil fuel bills.
On the downside, as with many other fuel types, poorly chosen or badly installed and maintained boilers that use arboricultural arisings could have a detrimental effect on local air quality.
There is a lot of interest in using biomass fuels, and numerous grants are available to help meet some of the capital costs associated with installing biomass boilers. Other grants are available to those looking to establish local biomass fuel-supply chains. These businesses typically take in arboricultural arisings and convert them into high-quality woodchips suitable for use in modern high-efficiency boilers.
Care must be taken to ensure projects using arboricultural arisings and other biomass fuels do not have a negative effect on local air quality. Boilers and other conversion systems using arboricultural arisings must comply with air-quality regulations such as the Clean Air Act and should be equipped with abatement systems designed to minimise emissions of PM10 and PM2.5 pollutants (particles <10 and <2.5 μm in diameter). Further information on emissions is available from the Biomass Energy Centre. Using a single boiler to supply heat to several buildings is generally a more efficient way to use biomass, and helps minimise emissions per kWh of heat delivered. This type of installation is often known as a district heating system.
There are a number of projects using woodfuel produced from trees growing in the urban environment:
- Bristol City Council (PDF-291K) installed woodfuel boilers at two locations; a 400 kW woodfuel boiler at Blaise Nursery and a 700kW woodfuel boiler at a social housing tower in South Bristol. The boilers are fuelled by wood chips produced from arboricultural arisings generated by council and tree surgery activity.
- The Croydon TreeStation, established by BioRegional, produces around 8000 tonnes of woodfuel each year. The raw material for this fuel is provided from arboricultural arisings produced during the management of Croydon’s trees. This offers the Council significant reductions in its green waste management bill, as well as potentially saving thousands of tonnes of greenhouse gas emissions.
- Thames Valley Energy created the Tree Station that converts arboricultural arisings and other material into woodfuel, reducing the volume going to the region’s landfill sites or being burned on site.
Forest Research has been studying and developing systems associated with the production, processing and end use of biomass and woodfuel for over two decades. This research track record, combined with a proven technology-transfer capability, ensures that Forest Research is well placed to develop a ‘national focus of knowledge and analysis on biomass energy’, as recommended to Government by the Biomass Task Force in October 2005.
As part of Government’s response to these recommendations, the Biomass Energy Centre was launched in April 2006. Managed by Forest Research on behalf of the Forestry Commission and Defra, the Biomass Energy Centre:
- Has provided impartial, up-to-date advice and guidance in response to thousands of enquiries and requests for information in its first year
- Has played an important part in initiatives aimed at developing a sustainable biomass sector, and is integral to the Woodfuel Strategy published by Forestry Commission England in March 2007
- Also works with woodfuel officers employed by Forestry Commission Scotland and the Wood Energy Business Scheme team in Wales
- Continues to develop links and information-delivery mechanisms with regional bodies and local organisations across the UK.
More information on the production and use of biomass: