Anaerobic digestion plants and planning requirements
Anaerobic Digestion (AD) is a natural process which uses bacteria in tanks to break down effluent.
It produces 'bio-gas' (primarily methane), heat and 'digestate' (residue).
Benefits of AD
AD requires the right balance and 'bio-energy crops' are necessary as well as effluent, but where this is achievable
sustainability and the environmental benefits of AD outweigh most concerns.
- Biogas can power a turbine to input electricity to the grid.
- Final carbon dioxide output is 20 times less powerful than methane as a greenhouse gas .
- Biogas may also be exported direct to the gas grid at certain sites.
- Heat can be used locally for poultry units, greenhouses, neighbouring homes and businesses.
- Digestate starts as a slurry, separated to liquid and dry compost. Both are spread on land as fertiliser.
- Digestate is much less odorous than raw effluent; the process removes much of the nitrate and ammonia, reducing requirements for mineral fertilisers and their transportation.
Planning policies and permission for AD
National and local planning policies support proposals for AD in particular, on appropriate sites and subject to high environmental standards. Farmers are also using managed woodland waste as biomass for heating poultry and dairy units. This can be used in conjunction with an AD plant for kiln-drying biomass which is regarded as 'waste' if it would otherwise be shipped off-site.
AD plants normally also require an Environmental Permit to regulate operational matters.