Optimisation of pre-treatment at WWTP

The Gramat WWTP in France has significantly improved its pre-treatment process by installing a Lackeby Roto-Sieve® drum screen. The plant, with a capacity of 9,500 PE, processes an average of 60 m³ of influent per hour and experiences peak loads of up to 110 m³ per hour during rainy periods.
Previously, the installation struggled with frequent maintenance problems due to the limited performance of the existing channel screen with a mesh size of 6 mm. The high supply of sand and dirt from waste water and rainwater caused regular malfunctions. This meant that blockages had to be removed manually every two weeks.
In 2021, it was decided to replace the channel grate with a Lackeby Roto-Sieve® drum screen with a perforation of 2.5 mm. To this end, the platform above the grease trap was modified so that the drum screen could be placed above the channel and the screened water could be collected directly.
After commissioning, the volume of screened material tripled from approximately 150 to 450 litres per week, indicating more efficient removal of solids in the pre-treatment stage. Whereas previously reactive measures had to be taken in the event of overflow, the tanks are now cleaned preventively once every six months. In addition, the maintenance regime has been simplified: whereas the old screen had to be completely dismantled every two years, no components have been replaced after two years of operation with the Roto-Sieve®.
Clear effects are also visible downstream. The annual production of thickened sludge, which is transported externally for composting, fell from approximately 405 tonnes to 275 tonnes. According to the operator, the installation of the drum screen has resulted in a demonstrable improvement in performance and substantial operational benefits for the WWTP.