Biomethane

About biomethane

Biomethane has the same composition as methane derived from fossil fuels and can be used as a substitute for natural gas.

Biomethane is produced at Bristol sewage treatment works by upgrading biogas produced from anaerobic digestion - a completely natural process in which micro-organisms break down biodegradable material in the absence of oxygen.

Gas to grid

Gas to grid plant

The gas to grid plant at Bristol sewage treatment works is the first and largest of its kind. The plant produces up to 1,900m3/hr of enriched biomethane by cleaning and upgrading methane-rich biogas produced from the anaerobic digestion of waste.

Biomethane is used as a renewably sourced and sustainable substitute for natural gas in our local distribution network across Bristol. We supply the national grid with enough gas to supply thousands of local homes and ensure our sewage treatment works is energy self-sufficient.  

How it works

1. Sewage sludge and food waste is treated and pumped into a series of anaerobic digesters. The waste is heated to 32 - 42°C and kept in the digesters for 12 to 18 days. During this time, micro-organisms break down the biodegradable material in the absence of oxygen to produce methane rich biogas. At this point, the biogas contains around 60% methane.
2. The biogas produced from the digesters then enters the gas to grid plant. The first stage upgrades the biogas to biomethane (~98%; 1.5% nitrogen).
3. A bioscrubber removes gaseous impurities, such as carbon dioxide and hydrogen sulphide. Meanwhile the carbon filters produce virtually odour free emissions to the air.
4. A small volume of propane is injected into the biomethane. This enriches the gas to natural gas quality and calorific value.
5. The end product, enriched biomethane, is analysed and undergoes strict quality controls before being fed into the local gas distribution network.

Green Gas Certificates

GENeco's gas to grid facility is registered with the Green Gas Certification Scheme (GGCS), a system that tracks biomethane, or 'green gas', through the supply chain to provide certainty for those that buy it.

Each unit of biomethane injected into the grid displaces a unit of conventional gas. Each kWh of biomethane is labelled electronically with a unique identifier known as a Renewable Gas Guarantee of Origin (RGGO). This identifier contains information about where, when and how the green gas was produced. When consumers buy green gas the RGGO is their guarantee that the gas is authentic and has not been sold to anyone else. It ensures there is no double-counting from production to end use.

The globally-recognised GHG Protocol has recently recognised that Green Gas Certificates, issued by the Green Gas Certification Scheme (GGCS), can support a business's reporting of onsite GHG emissions, and lead to near-zero greenhouse gas emissions reporting.

If you wish to discuss any aspect of GENeco's Green Gas Certificates, please get in touch.