Severn Trent expands green gas to grid capacity

Stoke Bardolph STW
Stoke Bardolph sewage treatment works is one of three sites used by Severn Trent to process biomethane for the grid

Midlands-based water and waste water utility Severn Trent has invested £15 million to build three biomethane plants that will turn the gas produced in the digestion of sewage sludge, energy crops from contaminated land and food waste into a gas that can be injected into the national gas network.

The water industry uses large amounts of energy every day for pumping, water treatment and waste management. Severn Trent is aiming to self-generate the equivalent of half of the energy it uses by 2020 and these three biomethane plants will play a significant role in achieving that goal. Severn Trent recently revealed it produces the equivalent of 38 per cent of the energy it uses, so it is well on its way to meeting the 50 per cent target

The process that takes place at the plants produces biomethane, a renewable gas that can be injected directly into the grid or used in nearby homes and businesses.

Strongford sewage treatment works (STW) in Stoke-on-Trent and Stoke Bardolph STW in Nottingham already have equipment and processes up and running, while Spondon STW is due to become operational next year. A food waste digestion plant is currently under construction at the Derby site.

Stoke Bardolph team
L-R: Martyn Lightfoot, Ian Middleton, Baz Corbett and Craig Meese all from Severn Trent at Stoke Bardolph STW

Martyn Lightfoot, renewable energy development engineer at Severn Trent, explains: “These new plants will help us save around £3 million a year on our energy bills, and that saving will be passed on to our customers who already pay less than £1 a day for their clean and waste water services.”

Severn Trent serves eight million people across the Midlands and into north and mid-Wales. The green gas generated at all three sites would be enough to heat more than 8,000 homes for a year.

Each plant will produce up to 500m³ an hour of biomethane from 1,000m³ of biogas. They will operate 365 days a year and 24 hours a day.

The gas is ‘washed’ at high pressure and then ‘squashed’ so it is at the same pressure as natural gas before being tested for quality. An odour is then added so it smells like normal gas and once that has been done, it is finally injected into the gas supply network.

Martyn continues: “We’ve been experts in anaerobic digestion for more than 60 years, and creating sustainable and clean energy is now a huge part of our business.

“It’s an area where we’re continuing to develop our knowledge and skills to make sure we continue to operate as a sustainable business long into the future.”