An analysis can be conducted for anaerobic digestion in a similar manner to the previously used technique to estimate the potential of generating electricity by using all the UK's available waste. There is about 90Mt of waste produced in the UK each year. 62% of this waste stream is said to be biodegradable (DETR, Limiting Landfill, 1999). This biodegradable waste will produce about 150m3/tonne of biogas at 60% methane concentration (Warmer Information Sheet, 1998). Using a 70% process efficiency, 70% load factor, and the known 37GJ/tonne energy content for methane, an estimate can be produced. After accounting for the 20-40% of energy needed to maintain the digestion is accounted for, anaerobic digestion could provide the UK with about 1.4GW. This represents about 1.9% of the UK's installed capacity.
Comparing to the other processes anaerobic digestion solely for the purpose of electricity generation is about twice as productive as total landfill gas power, but only a third as efficient as mass burn, and only a fifth as fruitful as gasification.
From an ecological point of view it is quite a sound process. Impacts related to visual intrusion, pests and noise will be similar to other waste management options and with proper planning can be minimised to acceptable levels. The input of waste, seen as a liability, can be reduced to a saleable soil conditioner. All the greenhouse gas generated is burnt for energy recovery rather than letting some of it escape to the atmosphere as would occur in landfill. CO2 is emitted but as it comes from organic material this has a short carbon cycle and so has no overall environmental impact. However, as this waste management option only deals with part of the waste stream, it is not on it's own going to solve the sustainable waste management dilemma.
Anaerobic digestion has not taken off as a waste treatment and disposal option in the UK mainly due to the lack of market for the produced soil conditioner.
At www.anaerobic-digestion.com we think that there are more reasons for AD not already being a commonly adopted process, than the lack of a market for the soils conditioner, indeed, is this still true?
BUT, this web site will soon need updating, in our opinion as "AD takes off" given the recent activity and Welsh support for AD recently announced.