The UK currently has the disposal problem of two million tonnes of sewage sludge per year, much of which is used as agricultural fertiliser. In a bid to help to reduce the sludge mountain, Lafarge is trying out the use of sewage sludge as alternative fuel in its cement production process. The pellets have two-thirds the heat value of coal and could replace up to 20,000t of coal annually if the green light is given to use them as a permanent fuel. An added benefit is that the use of sewage pellets will also reduce nitrogen oxide emissions.
After being given permission by the Environment Agency in February, the company started trials of burning processed sewage pellets, following experiences in Switzerland and Japan. The trial, monitored by the Environment Agency, will run till August, after which a consultation period will take place before the Environment Agency will make its decision.
The pellets are supplied by a Teesside sewage plant, the only place to provide the required specification, according to Ian Mycock, Cauldon works manager. The sewage sludge is heat treated to 500 ˚C, making it safe as garden soil. After pelletisation, it is transported to the works in closed lorries. The cement plant has invested in £2m closed plant and equipment to handle the pellets.