The water company, which serves eight million people across the Midlands and Wales, says the power generated will be enough to heat more than 8,000 homes for a year.
The equipment and processes are already up and running at Strongford Sewage Treatment Works in Stoke and at Stoke Bardolph Sewage Treatment Works in Nottingham.
Spondon Sewage Treatment Works in Derby is due to become operational next year.
Each of the constantly operating plants will produce up to 500 cubic metres of biomethane an hour and this fuel is suitable for use in homes, industry or vehicles.
Martyn Lightfoot, Renewable Energy Development Engineer at Severn Trent, said: “This investment is all part of our programme to self-generate the equivalent of half of the energy we use by 2020.
“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.”