The Wattrelos wastewater treatment plant is the second largest in the Lille metropolitan area, with a capacity of 350,000 population equivalents and a nominal flow rate of 3.3m3/s. It is fed by a combined collection system with flows ranging from 1m3/s in dry weather to more than 50m3/s in wet
weather.
Its discharges and load shedding account for 100% of the flow into the direct receiving environment. The objectives of the project are to :
o adapting effluent treatment to the requirements of improving surface water quality, with the insertion of primary decantation upstream of biological treatment and tertiary treatment by filtration,
o improve the handling of the first rainfall effluents by building a buffer basin at the head of the system, which will enable biological treatment to be mobilised for these effluents by staggered discharge.
o limit direct discharges for all rainfall events by building a primary treatment line for rainy weather (pretreatment, clarifloculation).
o build the supply works needed to increase the flows taken on.
o completely rebuild the sludge process with energy recovery (biogas).
The project management mission entrusted to the Merlin-Setec consortium includes preliminary feasibility studies and pre-definition of the processes, preparation of environmental files, preparation of tender documents, evaluation of bids, and assistance with monitoring studies and works.
A complicated system :
The future supply to the plant will have to handle and distribute flows in excess of 15m3/s, before discharge, which will require a complete overhaul of the supply works. As early as the preliminary studies, setec implemented 3D hydraulic modelling known as “CFD” using ANSYS software to describe, in various possible cases of incidental flows, the conditions of supply and discharge, the risks of deposits, and the requirements for hydrometry to meet self-monitoring obligations. This approach made it possible to identify the main design issues to be addressed to contractors.