Siltbuster Deployed on the Thames Tideway Tunnel Project
Siltbuster has helped CVB – the joint venture between Costain, Vinci Construction Grands Projets and Bachy Soletanche – treat the wastewaters generated during construction of the East section of the Thames Tideway Tunnel. The Siltbuster solution has saved precious space on site, reduced man hours, eliminated the need for expensive stabilising agents, and over the next six months will save CVB over £200,000.
CVB is building the main drive shaft at Chambers Street, for tunnelling on the East portion of the project. The construction and grouting works for this create 36 m3 of Bentonite slurry waste each day, with a very high pH level. Prior to Siltbuster getting involved, CVB was using stabilising agents to solidify the slurry. However, such agents are more suited to small volumes and with the amount of slurry being generated this method proved very expensive.
“We were using three pallets of stabilising agent per day, that’s 120 bags. With each bag costing £45 we were spending £5,400 a day on the agent alone,” says Mick Brown, Supervisor, Geotechnical Works, Bachy Soletanche.
As a time-consuming, manual process it also created a backlog, with a lagoon having to be built and six to eight holding tanks of slurry having to be stored on site during treatment – a real issue as space is very limited. Mick Brown elaborates:
“We had to build up a big lagoon, use a digger to add the agent, move the muck around, have two tankers on site each day to remove the slurry and then once it was off site pay for it to be dewatered so it could be disposed of as dry waste. This all took up a huge amount of time, space, money and manpower, so we turned to Siltbuster.”
Siltbuster specialises in treating construction site wastewaters and has worked on some of the world’s biggest construction projects. Through tests Siltbuster’s experts recognised that the effluent would not quickly settle in a settlement tank. So Siltbuster devised a special filter press system with a cycle time fast enough to cope with dewatering the large volumes of slurry. The press connects to a Siltbuster PMPU20 unit which provides a two-stage continuous pH treatment for the residual water. This includes an initial pH adjustment, a clarification stage for the recovery of settled solids, followed by a final pH correction using carbon dioxide. During the treatment process the dry solids are recovered for off-site disposal. The remaining water’s alkalinity is reduced from 12, which is the equivalent of bleach or oven cleaner, to a neutral 7 – making it compliant with Thames Water and safe to discharge to the sewer.
The solution, which has been operational since July and will be in place for a minimum period of six months, not only means the huge volumes of slurry are being safely treated and the best environmental standards are being met, but it has eliminated the use of expensive, labour intensive, stabilising agents and freed up precious space on the site as Chris Radegonde, Siltbuster’s Technical Sales Engineer for London and the South East explains:
“As always, with this project we’ve focused on the two things which really matter – helping our client meet the environmental standards required to stay compliant, and delivering a system which works at a very practical level. For instance, our solution is incredibly space efficient; it occupies a very small footprint on the site, and because the press has a very high treatment capacity, the lagoon and many storage skips which were previously being used to hold the slurry are no longer required on site. Added to this, the agent costs have been eliminated and there are far fewer man hours now involved in dealing with the slurry.”
Mick Brown throws further light on the man hours being saved: “Before we got in Siltbuster we had five men in every Saturday for eight hours sorting the slurry out – now we just have the Siltbuster system. It’s total solution. It’s practical, easy to operate and most importantly, it works. Allowing for the cost of the system, I’d say on this one site alone it’s saving us £8,000 per week – which if we use it for 6 months will amount to a £208,000 saving.”
Mick Brown has been so impressed that he’s just commissioned another Siltbuster system to be used at Greenwich on the Tideway project.