Tarmac Site Recycles Grey Site Water for Dust Suppression Thanks to EnviroHub and Senteos
Tarmac Banbury is a dual site, housing their own road asphalt plant and ready-mix concrete batching, plus distributing to other aggregate companies in the area. It’s served by a railhead for thousands of tons of bulk aggregate delivery and processing every day.
A highly productive and busy site, Tarmac Banbury has recently undergone a major refurbishment to meet additional demand locally, including the London to Birmingham HS2 line.
The existing batching plant was dismantled, and a larger one was built which increased productivity and made better use of the site’s space.
With multiple rail deliveries and many truck movements every day, sites like this are prone to flooding with dirty surface water in wet weather, and airborne dust issues during dryer spells.
De-watering and Dust Control
Previously, existing sumps collected the surface run-off water to prevent it from running into the public drains and neighbouring land. When dust suppression was needed, the site staff did their best with mobile water tanks deployed across the yard. However, these took time to fill and manage – and even prompted a question from a passer by as to “what chemical was being disposed” of. A fair question considering the sensitivity of the nearby Grimsbury Nature Reserve, river network and a Thames Water reservoir in the vicinity.
Dirty Water Management Improvements
Controlling surface water run-off and keeping the financial and carbon costs of dirty water management in check was the priority, following refurbishment of the plant. Tarmac is relentlessly pursuing its “ACT” sustainability strategy, with goals on climate action, environmental stewardship, and the circular economy. A ‘best practice’ water management plan was needed to match Tarmac’s ACT purpose and help continue its success on this ambitious journey.
Consulting with Atlantic Pumps regarding EnviroHub, the water treatment and recycling system, it soon became apparent that the most sustainable approach would be to join up the site’s water needs wherever possible.
Sustainable Dust Suppression
Any dust suppression system is obviously a water consumer. If EnviroHub could be proven to clarify the yard runoff water to the required quality, it would be possible to recycle the dirty water on site for this purpose.
A controlled water spray is often the simplest way to prevent dust being generated from vehicle movements onsite. A damp ground-surface prevents particles becoming airborne and helps ‘lay’ any airborne dust that enters the area from elsewhere. Having a bespoke dust suppression system installed is a big time-saver compared to manual ‘hose-down’, which tends to be all or nothing, with patchy over-or-under wetting across the site.
Not only does recycling site water reduce consumption, but it also dramatically reduces the emissions and cost of transporting wastewater off-site, traditionally done by road tanker removal. The clarified water exiting the EnviroHub system is clean enough for licensed regular direct discharge, should there be an excess after on-site re-use is covered.
EnviroHub is a modular system that is engineered to meet the requirements of the particular site’s contaminated water treatment needs.
The system installed at Tarmac Banbury consists of silt settlement and pH treatment modules to clean the water, even from any cementitious alkaline contamination.
A New Site Water Treatment Process at Tarmac Banbury
Run-off water collects in wedge pits as before and is then pumped via underground ducts to storage tanks prior to being fed into the EnviroHub system. High/low and low/high level sensors control the movement from pit to tank to smooth the supply and demand.
The first stage of EnviroHub water treatment uses CO2 to neutralise the water to pH 7. This water is then pumped to an EnviroHub Treatment Tank (TT) where it is accurately dosed with coagulant and flocculent. This is where the first stage of separation occurs via sweep flocculation before it goes to an HL20 lamella settlement tank. Here the heavier clumped solids are pumped away by a peristaltic sludge pump, whilst the clean water runs off the top, into a dust suppression buffer tank. If this tank is full, the excess overflows into a ground discharge point which is continuously monitored via Senteos®, an online environmental management software, crucially controlling for flow and daily volume limits in addition to pH level.
At various stages, intelligent sensors monitor the live parameters of the water, including pH, clarity and viscosity. These trigger the transfer of water to the next step when specified readings are met, rather than on a fixed time.
On applications like this, the amount of treatment time or dosing needed can vary a lot from week to week so it’s impossible to calculate set treatment requirements based on a sampled average. EnviroHub is programmed to auto-adjust the treatment regime for consistent quality of output and efficiency, based on live measurement of actual properties. This significantly reduces wastage of time, energy and treatment media.
Circular surface-water to dust suppression
The new water recycling program at Tarmac Banbury clearly supports their ACT sustainability programme. Namely, the safety and well-being of staff and site visitors, further improving their supply-chain by reduction of fresh water consumption, and protecting the neighbouring community from dust and run-off contamination.
Adjoining the site is wet pastureland, grazed part of the year, and teaming with wildlife. It demonstrates the harmony that Tarmac have achieved by working with and alongside nature and the local community. Recently, the site manager even had a fox brush past him onsite, as they both went about their early morning work!
Controlled Dust Control System
The new dust suppression system consists of eleven high-power sprinkler heads that cover the length of the driveway and truck manoeuvring areas. These sprinklers are fed by a booster pump with a variable frequency drive (VFD) and can be individually isolated or the whole system can be turned on or off by remote control. The VFD inverter ensures that a consistent spray is delivered, regardless of the number of heads in operation. It also means that there is capacity for additional heads to be added, future-proofing the installation without increasing running costs in the meantime.
Water Data Visibility and Control
Bringing all water data and flow control together, Tarmac’s management can view historical and real-time water treatment and discharge data via the Senteos portal. They can also specify email and text alerts for early warning of a potential quality issue, enabling timely invention. As a safety backup, the system stops dispensing if a hard limit is reached, such as maximum permitted pH variance or discharge amount per day.
Hydrocarbon sensors ensure that the water flowing into the system is non-contaminated, again it is programmed to stop the feed pump should a problem be flagged.
Banbury’s site supervisor, Scott Sowerby is satisfied that Tarmac’s investment has been rewarded by enhanced control over dust, water discharge and operational costs. It has strengthened their environmental stewardship and relationship with neighbours and regulators, which ultimately stands to reduce the cost and timescales of future permit applications.
“It's surprising how far the flocculant goes, we’ve not had to top it up yet” says Scott, as a testament to the waste avoidance that’s inherent in EnviroHub’s design methodology.
Despite the challenge of overhead power lines, the installation was quick and trouble-free “The EnviroHub system was delivered as pre-assembled modules and Ed and his team got the pipework done really quickly” Scott said, allowing production to continue uninterrupted.
It doesn’t stop at installation – Atlantic Pumps are committed to long-term relationships and after-sales service. “Anything pump-related, I know I can call Atlantic Pumps” said Scott, citing an experience when Mike, one of Atlantic’s field engineers, fixed an issue onsite within a couple of hours of a phone call. “If I’ve got a problem with a pump, Atlantic are the first people I call. If they can’t get out same day, they’ll give me a date when they can…the guys are always on-time and efficient” he explained.
When asked about the potential for other sites to adopt EnviroHub, Scott believes multi-purpose aggregate plants and quarry sites have the greatest to benefit. The installation takes a certain space and budget but works trouble-free and is highly effective, making EnviroHub’s long lifetime and operational payback attractive.
Concrete Water Supply
With EnviroHub’s pH correction and silt removal, there is scope for future gains by linking up the water recycling system to the concrete batching plant onsite. This is another use of EnviroHub that is being used successfully to recycle grey water and concrete washout for clean concrete production.
To explore site water treatment, water recycling and sustainable discharge opportunities in your operations, contact the EnviroHub technical sales team at Atlantic Pumps.