French pump rental company Telstar and Siltbuster, a UK provider of water treatment solutions for the construction industry, are partnering to treat wastewater generated on the €23 billion Grand Paris Express (GPE) rail expansion scheme. The GPE subway project includes the construction of 68 stations and over 120 miles of new track to improve the public transport network across the city.
Telstar is supplying pumps to Bachy Soletanche for use on a section of the project which involves the construction of new tunnel shafts at Vitry-Sur-Seine, Paris. During the grouting of the GPE shafts and tunnel faces, excess waste grout is pumped to an above ground centrifuge and filter press. Here it is dewatered, enabling its disposal in landfill. However, the wastewater created as a by-product of the dewatering process contains very small grout particulates and has an elevated alkaline pH level of around 12-13, which is harmful to aquatic life.
Bachy Soletanche asked Telstar for advice about treating the up to 40 m3 per hour of these sediment-rich waters generated. Telstar recommended calling in Siltbuster, which advised the waters be collected in a storage tank where a small submersible transfer pump forwards them to a Siltbuster modular chemical dosing system comprising a mixing tank and a lamella clarifier. The mix tank with integrated pH probe and controller monitors the pH level of the water as it enters the system. When the alkaline level detected exceeds an upper user-defined limit, the system automatically introduces carbon dioxide (CO2) into a stirred reaction tank to neutralise the water. A coagulant and flocculant are then added to the wastewater to ensure any slow-settling solids can be removed. The remaining pH-neutral water is then discharged to an adjacent sewer. The first Siltbuster modular three-stage chemical dosing system was installed in August this year. A further eight systems are on order for the project.