Did you know sewage is much more than a waste product? Biogas is a by-product of the sewage treatment process, and helps us to power our treatment plants with renewable energy.
What is biogas?
When sewage breaks down in an anaerobic (oxygen-free) environment, it releases biogas made up of mostly methane and carbon dioxide.
Capturing biogas and converting it into energy is beneficial for the environmental because it:
- turns a by-product of the sewage treatment process into a useful resource
- reduces direct greenhouse gas emissions created by the sewage treatment process
- produces renewable electricity
- help us to reach our target of net zero emissions by 2030.
How we use biogas
We capture biogas at the Western Treatment Plant and the Eastern Treatment Plant. Biogas is captured in anaerobic digesters and from covered anaerobic treatment lagoons. The gases are then transferred to on-site power stations, where they are combusted. This releases energy that spins a turbine connected to a power generator – converting the energy in biogas into electricity.
Western Treatment Plant
The Western Treatment Plant uses biogas to meet about 80% of its electricity needs.
It generates 70,000 megawatt hours of renewable electricity every year, equal to about 7,000 households’ worth (based an average of 10MWh per household).
Sometimes the plant produces more energy than it uses. The excess is exported to the electricity grid to offset usage at our other sites.
Eastern Treatment Plant
The Eastern Treatment Plant uses biogas to power about 30% of its electricity usage.
The plant’s seven power generators can run solely on biogas, which is supplemented with natural gas as needed.
Second power station at the Western Treatment Plant
We’ve built a second power station (power station B) at our Western Treatment Plant to enable us to turn most of the biogas the site produces into electricity.
The exact amount produced depends on the time of year and volume of incoming sewage, with summer being the peak time for methane production.
Once complete, biogas power stations A and B are expected to generate over 100% of Western Treatment Plant’s electricity needs (on average, based on the site’s existing electricity demand).
The construction of power station B was completed in October 2022 and is currently awaiting commission.