How do we get energy from sewage?
Sewage sludge is loaded into airtight tanks called anaerobic digesters. Here it is kept at 35°C and mixed with bacteria to break it down. As the bacteria digest the sewage methane (a natural gas) is produced, as well as a fertilizer by-product. The methane is piped into large engines which produce heat and electricity. Electricity can be used on site or exported to the National Grid, whilst the heat is used to keep the digesters at the right temperature. Re-using the heat makes this a very efficient process. We currently have 56 engines across 34 sites.
What does the future hold for this process?
We’re always looking to refine the technologies involved in generating electricity from sewage and as part of this we’re starting to replace older gas engines with newer models. We’re also looking at ways to increase the amount of methane produced in the digesters, perhaps by adding fats, oils and greases which build up in the sewage treatment process. If these can be broken down, they will release large amounts of energy as gas which we can use to produce even more power.