Anaerobic Digestion (AD) is a naturally occurring process where biomass is broken down by micro-organisms in the absence of air. This process is utilised by AD plants, with waste material placed in a large digester under specific temperature conditions producing a methane rich 'bio gas'. This page will provide a brief introduction to the technology and provide links for community groups to learn more about the technology and how it could be potentially developed into a community project.
What are the benefits?
- AD can be used to treat wastewater, domestic and commercial food waste, manures and biofuel crops.
- The biogas can be used to generate renewable heat and power, helping cut carbon emissions and offsetting the use of natural gas.
- The remaining material (digestate) is rich in nutrients and can be spread on land as a fertiliser.
- AD offers a cost effective way of dealing with large quantities of waste, turning it from a liability to an income stream.
- AD is eligible for the feed-in tariff, renewable obligation certificates and the renewable heat incentive. This can provide a reliable, long-term income stream.
Types of AD plant
There are many different types of AD depending on the type of feedstock to be treated. The main difference is the temperature and speed at which the waste is treated. For high solid materials such as garden and food waste, high temperatures are used and the waste is treated in batches. Lower solid materials such as animal slurry are more likely to be treated at a lower temperature using a continuous process.
Community Owned AD plants
Due to the capital intensive nature of AD plants, planning and developing a community owned installation is a significant undertaking and very few community AD plants exist.
However, case studies have shown that AD plants can be profitable, second only to wind turbines in the UK. Two important points to consider are that you must have an end user for the heat and that feedstock supply contracts must be long-term to ensure viability. The links provided below provide a good starting point for community groups who think AD might be a suitable technology.
Severn Wye Energy Agency have produced a detailed guide to AD in England and Wales including several case studies.
Community Pathways have an example approach to developing a community owned AD plant.
NNFCC have produced an AD factsheet providing an overview, benefits and drivers, biogas yields from different feedstocks and an overview of the economics.
The NNFCC have mapped all operational AD plants in the UK and these can be filtered to show community plants.
Isabel have produced a report “Region-Specific Social Innovation and Community Energy Approaches with an Application Potential in Biogas”