Broad Overview of AD Approaches
Anaerobic digestion is a process in which biodegradable materials (feedstocks) are decomposed in anaerobic digesters by bacteria in the absence of oxygen, under carefully managed conditions (e.g. temperature control).
Feedstocks that can be digested include the following; Agricultural manures and slurries, sewage sludge, catering waste, commercial and industrial organic wastes, source segregated or centrally separated municipal waste, silage and crops grown specifically for AD e.g. maize, wheat and grass. The biodegradable materials are ultimately converted into biogas and a whole digestate.
The methane rich biogas can be used to produce heat and electricity. It can also be upgraded and used as a vehicle fuel or directly injected into natural gas pipelines.
Digestates are a rich source of nutrients (e.g. nitrogen, phosphorus and potassium) and can be used as an alternative to chemical fertilisers. The publication of the Quality protocol (PAS 110) for anaerobic digestates and the Anaerobic Digestate Quality Protocol (ADQP) has helped clarify whether digestate is considered a waste or a valuable product that can be used as a biofertiliser. Complying with these standards allows the digestate not to be treated as a waste.
AD is widely deployed in many countries. The water industry in the UK already has a well established system of AD plants which treat approximately 66% of the country’s sewage sludge.
AD is a unique technology in that it represents an opportunity to divert biodegradable municipal waste from landfill, generate renewable energy, and produce an agriculturally beneficial soil conditioner (depending on the quality of the feedstock). AD is therefore able to aid achieving multiple government targets by producing a secure supply of renewable energy and non-fossil fuel fertiliser, whilst at the same time reducing waste and agricultural related methane emissions.
For further information on the different types of anaerobic systems available and on the utilisation of biogas and digestate please use the links below.