What is anaerobic digestion?
Anaerobic digestion is the natural breakdown of organic matter in an atmosphere with little or no oxygen. This process produces a combustible gas (biogas) and a nutrient rich organic by-product (digestate). There are many different types of feedstock which can be used to create energy and in many cases wastes such as food and animal slurry can be utilised. Anaerobic digestion systems take advantage of this naturally occurring process to capture the combustible gas preventing it from escaping to the atmosphere.
Why use anaerobic digestion?
Every year millions of tonnes of biomass waste need to be disposed of. Anaerobic digestion is one method that can be used to reduce the amount of waste going to landfill. AS large volumes of greenhouse gases are released from Landfill, the capture of these gases via an anaerobic digestion process is undoubtedly beneficial. The UK government has committed to reducing emissions by 80% by 2050 and anaerobic digestion has been recognised in its Low Carbon Transition Plan.
In addition if digestate is used efficiently it can reduce the amount of synthetic fertiliser created which can also reduce greenhouse gas emissions.
Income can be made from anaerobic digestion through the Renewable Feed-In Tariff (FIT), Renewable Heat Incentive (RHI), ROCS, and charging gate fees for waste which is accepted.
What is digestate?
Digestate is the byproduct of biogas production via anaerobic digestion and the substance with which the BCS is concerned. It is a nutrient rich substance which can either be applied directly to land as whole digestate or be separated into components; liquor which is nitrogen rich and fibrous phosphate soil conditioner.
Digestate is the left over indigestible material and dead micro-organisms which remain in the digester after biogas production. As biogas does not contain nitrogen, potassium or phosphorous all of these remain within the digestate. Digestates differ from untreated slurries as they have more readily available nitrogen levels and they have a lower pathogen and weed seed load especially when pasteurised. Thus, digestate can be used as replacement or partial replacement for synthetic fertilisers. It should always be remembered however that the properties of digestate will differ depending on the feedstock used in the AD process.
All digestates should be applied to land in accordance with the PEPFAA code and NVZ regulations (where appropriate). Farm assurance bodies should be contacted prior to use as many have restrictions on when and where digestate can be used.