Siltbuster has launched a new machine designed to treat concrete washwater so it can be safely disposed.
The Siltbuster RCW is a two-stage setup that uses CO2 to bring alkaline water back to a neutral pH so it can be safely poured away without damaging local soil.
Siltbuster director George Anderson explains that the system was originally conceived for use in the civils market but is suitable for other concrete applications.
“The original concept came from contractors working by the side of the road and having a very constrained space to wash out their concrete trucks,” he says. “Traditionally to this would require the use of a plastic lined skip, into which you’d tip the washwater.”
The RCW system instead is a batch type process. Once the concrete has been offloaded, each truck reverses up to the RCW and washes off the rear end of the truck directly into the front end of the RCW unit, which contains two de-watering bags. The concrete solids are captured in the bags, which are porous, so the water filters through into the main treatment unit.
This bleed water is highly alkaline, so through an automated process, CO2 gas is pumped into the unit until the water has been neutralised. The end result is water with a pH of 6-9, as required by the Environment Agency.
With now-common discussions about reducing carbon foot prints, carbon dioxide might be regarded as something to be avoided but Mr Anderson points out that using CO2 in this way is safe and can be sustainable. “The health and safety issues associated with using an acid can be horrendous, so using CO2 is much safer. Furthermore, the CO2 required for the system can be recycled from waste products created by other industrial processes,” he says.
Morgan Sindall has been an early adopter of the equipment, having used the Siltbuster RCW on the construction of a wing manufacturing unit for Airbus in Flintshire. The 52,000 sq m site has high-level groundwater issues and allowing high pH water to seep into the ground would pollute the groundwater system. With an average of 60 deliveries of concrete per day and over 53,000 cu m of concrete required, there was a considerable volume of concrete washwater that had to be dealt with on site.
Four RCW units were used on site as deliveries peaked at 283 concrete trucks for one weekend. According to Siltbuster, the units have been able to treat 177,000 litres of washwater and reincorporate 192 cu m of concrete into works on site. One of the supply chain firms has estimated the units negated the need for 15 skips for traditional storage treatment.
This reduction has led to the system getting recognition within the industry. The Airbus project won the Constructing Excellence Wales Award for Innovation this year, as a result of using the RCW system.