Down near Dax, the small town of Castets plans to position itself as the new surfing El Dorado by playing host to a tourist complex, complete with a giant wave pool.
This project and the population growth it will entail mean the town’s WWTP’s capacity needs to be doubled in advance. The Les Landes SYDEC (Departmental Municipal Equipment Authority) has selected SADE (head of consortium) and its partner Gallego for this mission.
The goal, is to design and build the new infrastructure and partially modify the existing systems to boost treatment capacity from 2,750 PE to 5,500 PE, as well as adding a new sludge treatment line, without suspending services. This doubling will mean the activated sludge WWTP can handle an average dry weather flow rate of 50m3/h and a peak flow rate of 90m3/h. Designed by SIng and the Bordeaux Regional Division, this project is a genuine technical challenge, and therefore right up SADE’s street!
The core of the worksite
Doubling the plant’s capacities firstly requires the construction of two imposing concrete basins. The first, an aeration basin, has an internal diameter of 12m. It is a 6m-high, semi-inground structure featuring 3 fine-bubble aerators and 2 agitators. The second, a clarifying basin, is used to separate effluent from activated sludge floc. It has an internal diameter of 14m and its tapered bottom varies its height from the centre to its edges from 4.90m to 3.30m. This top-notch facility is equipped with a radial scraper bridge including both bottom and surface blades.
Ancillary? More like essential.
Adding an extra treatment section and creating a new sludge treatment section, as well as maintaining continuous service requires not only inch-perfect organisation, but also the construction of so-called ancillary facilities, which are actually essential to ensure the whole system works properly. Of course, this includes new systems and a partial overhaul of existing equipment, as well as high-pressure air generating sets, a deaerator, electrical systems, automated systems, etc.
Delivered on time
Previously a T&M project, the WWTP was taken under SYDEC’s wing in January 2020, and the contract awarded to the SADE/Gallego consortium. Following modification of the project on request from the new project owner, work began on the site in September 2020 after 2 months of preparation and will be completed by the end of April 2021. An even more impressive feat when you consider that this change of management came against the backdrop of the current sanitary crisis.
Once the project has been completed, the plant’s sludge will be compacted and dehydrated in a specific unit, then sent in pellet form to a SYDEC repurposing centre in Thalie. Once there, it will go through a proven, secure process to repurpose wastewater treatment sludge for agricultural use. This is a fine example of the local circular economic network to which SADE is proud to contribute.