Wastewater management specialist Siltbuster has developed a new system to capture and treat the high pH water that is generated by washing down concrete truck delivery chutes on construction sites.
Despite clear guidance in the Environment Agency’s pollution prevention guidelines (PPG5), and pressure to deliver environmental improvement, many contractors have resorted to capturing washwater in polyethylene-lined skips, and then dispose of it without treatment.
Siltbuster’s patented roadside concrete washwater (RCW) system combines solids removal and automatic pH adjustment in a single unit that comes with its own battery-powered automatic control system.
After offloading, trucks reverse up to the RCW and wash off the delivery chute as normal, directly into the front end of the unit. Washwater enters one of two specialist dewatering bags, where surplus concrete solids are captured and allowed to hydrate ahead of disposal.
Bleed water from the concrete washwater then seeps through the dewatering bag fabric into the main treatment unit for pH adjustment.
On reaching a preset level, the water is treated using a process in which CO2 vapour is pumped into the water, adjusting its pH level from highly alkaline (about pH13) to neutral (pH6 to pH8). Precipitated solids are allowed to settle, and then the water can be released for discharge off-site or for re-use.
Reuse on site
Once they are full, the dewatering bags are removed and the concrete solids can be re-used on site, or taken off site for further treatment or disposal.
Siltbuster managing director Dr Richard Coulton said using CO2 reduces health and safety concerns, as plant operators do not have to work with strong acids to adjust pH levels. “Dosing with CO2 is intrinsically safe as it can’t be overdosed and it’s readily available from various industrial gas suppliers across the country,” he added.
The firm says the RCW can handle the washwater from 25 to 30 trucks a day. Standard units are now available for hire or purchase, and Siltbuster is also developing alternative battery charging options, such as solar panels and wind turbines, along with continuous data-logging and printed data outputs.