Launched in 2017, the Chartres Métropole conurbation wastewater treatment plant in Mainvilliers (28) has twice the capacity of the old plant at Lèves. This new installation, which today receives wastewater from the conurbation’s twelve municipalities, operates with a capacity of 160’000 population equivalents, with the possibility to be adjusted as the area develops and the potential to increase treatment capacity by a further 25%.

The plant’s equipment has been designed to limit the smell and noise nuisance as well as to allow the adaptation of energy consumption to the actual needs.

The challenge

In aeration basins, the air generation consumes the most energy. Indeed, air compressing accounts for close to a third of the entire system’s total energy consumption.

The Chartres Métropole treatment plant is separated into two parallel and identical biological treatment lines, each consisting of a succession of one anaerobic basin and two activated sludge basins, making a total of four aeration basins equipped with air diffusers.

“The production of air represents a very substantial part of the site’s energy consumption. In 2018, it represented 27% of the annual total of 6.8 MWh,” says Mr Fabien Monmousseau, Sanitation operations manager at Aqualter.

Being keen to keep energy consumption to a minimum and greatly reduce the plant’s energy bill, Mr Monmousseau turned to equipment suitable for applications which simultaneously require constant pressure and substantial variations in output.

The solution

After careful consultation, Aqualter opted for Sulzer’s offer with HST turbocompressors, which offer outstanding energy performance and a low level of noise.

“The initial project plan provided for a traditional compressor, but switching to a turbocompressor has allowed us to reduce energy consumption by 20%,” Mr Monmousseau observes.

The result is that each of the four basins at the Chartres plant has been aerated by a dedicated HST 20 turbocompressor since 2017, while a fifth unit ensures backup for any of the others.

“A performance study based on the produced airflow was conducted on each basin to optimize the machines’ settings. The result is an operating time that is slightly greater than was initially foreseen, for lower total consumption,” Mr Monmousseau adds.

The HST turbocompressor range sets the standard today for energy efficiency, thanks in particular to the high-speed permanent magnet motor, driven by a variable frequency drive and magnetic bearings which reduce the need for maintenance.