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What is Anaerobic Digestion? |
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Anaerobic Digestion ( AD) is the process where plant and animal material ( biomass) is converted into useful products by micro-organisms in the absence of air. Biomass is put inside sealed tanks and naturally occurring micro-organisms digest it, releasing methane that can be used to provide heat and power. This means AD can help reduce fossil fuel use and reduce greenhouse gas emissions. The material left over at the end of the process is rich in nutrients so it can be used as fertiliser.
AD is not a new technology - it has actually been used in the UK since the 1800s - and there are a growing number of AD plants in the UK processing our waste and producing energy.
Almost any biomass can be processed in AD; food waste, energy crops, slurry, crop residues, etc. AD can accept waste from our homes, supermarkets, industry and farms, meaning less waste goes to landfill. However, woody biomass cannot be used in AD because the micro-organisms can't breakdown the lignin, the compound that gives wood its strength.
The products of AD are referred to as biogas and digestate. Biogas is a mixture of 60% methane, 40% carbon dioxide and traces of other contaminant gases. Biogas can be combusted to provide heat, electricity or both. Alternatively, the biogas can be cleaned up and the pure methane injected into the mains gas grid or used as a road fuel. Digestate is made from left over indigestible material and dead micro-organisms. It contains valuable plant nutrients like nitrogen and potassium. It can be used as a fertiliser and soil conditioner. If you want to know more, read this brochure from Severn Wye Energy.
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