Biogas
Biogas is a mixture comprising mainly methane and carbon dioxide. It is produced when organic matter decomposes in the absence of oxygen. This can take place in a landfill site to give landfill gas or in an anaerobic digester to give biogas. Sewage gas is biogas produced by the digestion of sewage sludge.
An anaerobic digester produces conditions that encourage the natural breakdown of organic matter by bacteria in the absence of air, so that the biomass breaks down much faster than usual.
Anaerobic digestion is a method for turning residues from livestock farming and food processing industries into biogas, fibre and a liquid called 'digestate'. The outputs from the digestion process are:
Biogas – a mixture of 60% methane, 40% carbon dioxide and traces of other gases. Biogas can be burnt to produce either heat or energy. The biogas is burnt in the same was as natural gas, and the resultant heat can either be used for space heating, hot water systems, or to generate electricity or as a road fuel.
Digestate – an inert and sterile wet product containing valuable plant nutrients and organic humus which can be applied to land as a soil conditioner and biofertilizer.
Benefits of AD for Farmers
As well as the production of heat, power and biofertilizer from the digestion process there are other benefits from on farm biogas production including:
Odour control – AD can reduce smell from slurries by up to 80%
Handling – digestate flows more easily than raw slurry and requires less mixing before spreading
Grazing – cattle are less likely to reject grass spread with digestate than grass spread with untreated slurry
Weed control – the AD process kills many weed seeds and thus may reduce the need for herbicides.
Policy Incentives:
The AD industry benefits from the implementation of a number of UK policies aimed at a range of environmental initiatives:
The Renewables Obligation (RO) – Energy generated by burning biogas is eligible to receive Renewable Energy Certificates (ROCs). AD may be eligible for double ROCs under the proposed banding system from ROCs due to come into force in April 2009
Climate Change Levy
Landfill Directive – European legislation setting targets for reduction in landfilling for member states. The UK is required to reduce the amount sent to landfill to 75% of 1995 values by 2010, 50% by 2013 and 35% by 2020.
Landfill Tax Regulations - Landfill tax is £32 per tonne for 2008-09. This is set to rise by £8 next year and every year after that until 2010-11. AD plants can charge gate fees to receive source separated green waste diverted from landfill
The Nitrates Directive
Animal By-products Order - Sets stringent minimum treatment standards for any waste containing material of animal origin. The Order splits waste into 3 categories according to risk and identifies AD as a suitable method to treat some category 2 and all category 3 material including kitchen waste
For more information:
Greenfinch is “the UK's anaerobic digestion & biogas specialists”
www.greenfinch.co.uk
Further detailed documents about Anaerobic Digestion can be found on the BioenergyWM Library page:
http://www.bioenergywm.co.uk/library.aspx?cat=7&linktitle=Anaerobic%20Digestion
Presentations from the Bioenergy West Midlands Anaerobic Digestion Seminar on 5th August 2008 can be downloaded at:
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