A biological wastewater treatment plant

Built in 1991, the current wastewater treatment plant treats urban wastewater from several neighbouring municipalities as well as wastewater from the airport. But after more than three decades in service, it has reached its maximum capacity.

Faced with demographic change and growing needs, Sidest has decided to double the plant's treatment capacity, from 35,000 to 122,000 population equivalents.

The project, entrusted to Félix Giorgetti, involves the construction of an imposing infrastructure: 146 metres long, 65 metres wide and 13 metres high, including basins and technical premises. The work will be carried out in an enclosure that has been excavated and reinforced beforehand, at a depth of 15 metres.

For example, the clean concrete covers an area of 9,500 m² and is 15 cm high. The invert is a good one metre thick.

"The main challenge was the high rate of reinforcement and concreting. The site was divided into 15 zones to optimise the schedule, explains Mathieu Repplinger, site manager. That's why we're pre-assembling the columns and walls."

In fact, some sections of the site already have columns and walls, while on others Ferrac workers are still weaving the imposing skeletons of the invert.

Around a hundred lorries were needed to ensure a continuous supply of sulphate-resistant concrete. In all, 1,000 m³ of concrete were poured by double pumping.