Thames Water has begun drying sludge at Slough Sewage Works in Berkshire to produce a new renewable fuel that burns like wood chip.
Thames Water said the £1.5M sewage sludge dryer at Slough will reduce its carbon emissions by more than 500t annually and bring up to £300,000 a year of operational cost benefits. The cost saving comes from reducing use of non-renewable gas from the grid, additional government Rewewable Obligation Certificate (ROC) feed-ins and reducing the volumes of leftover sludge that need to be trucked to spread on agricultural land as fertiliser.
Some 20% of the solids left over from the treatment process at the Slough works — about 5t a day of sludge — are being put through the new dryer. The resulting “sludge flakes” are then transported to Crossness sewage works in Bexley, east London, where they are fed into a sludge-powered generator to generate renewable electricity.
Using more sludge flakes — which are 95% dry and thus more readily combustible than more traditional sludge cake which is only 25% dry — will reduce the generator’s reliance on non-renewable gas from the grid to keep the fire going in the machine.