Mott MacDonald has been appointed detailed civil engineering designer for Thames Water's Long Reach Sewage Treatment Works upgrade, by a joint venture of Galliford Try and Biwater.

The £40million Thames Water project will provide additional treatment processes at the works in Dartford, Kent, to improve the quality of treated effluent returned to the River Thames and to meet new Environment Agency standards. The improvements will also enable the plant to generate more renewable energy from the sewage treatment process - enough to power over half the site.

Works will include the construction of a new covered and odour controlled building for the storage of limed sludge prior to use for agriculture. Four new aeration lanes will be installed and a new final settling tank, along with a new sludge thickening plant and returned activated sludge pumping station. In addition, mechanical and electrical control equipment will be upgraded.

Mott MacDonald will manage the detailed civil, structural and geotechnical design for the construction stage of the project. The works is situated close to the tidal stretches of the River Thames. With ground water close to the surface and pressure in the water table varying with the tide, work on this project is expected to be challenging, requiring expertise and careful planning.

Mott MacDonald project director, David Thomas, said: 'We are delighted to take on such an important role in this significant project. Mott MacDonald has extensive experience in structural design as well as providing safe, innovative and sustainable solutions for all aspects of wastes and resources management.'

Steve Shine, Thames Water's chief operating officer, said: 'These improvements will help clean up the River Thames for all those who use and enjoy it, as well as improving conditions for fish by increasing oxygen levels. This upgrade is part of a £675million Thames Water programme to modernise and extend London's five major sewage treatment works to increase the amount of sewage each site can treat, and improve the standards to which we treat it.'

The Long Reach project is due for completion in 2012.