Siltbuster, a UK provider of water treatment solutions for the construction industry, is partnering with French pump rental company Telstar 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. “Historically when faced with waters like these, French construction sites have relied on conventional methods such as baffle tanks, but that old-fashioned approach doesn’t properly limit the pollution potential of such waters," Dr Richard Coulton, Siltbuster’s CEO, explains. "In today’s more highly regulated, environmentally aware construction industry, companies are looking for a much more effective solution.” With up to 40 m3 per hour of these alkaline, sediment-rich waters to deal with, Bachy Soletanche asked Telstar for advice. 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 has an integrated pH probe and controller to monitor 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 similar systems are on order for the project.