The Project

To make traveling through Gothenburg easier, Västlänken is being constructed - a railway connection through the central parts of the city that is eight kilometers long, with six kilometers in a tunnel.

Due to the construction, some existing pipeline tunnels must be redirected. Therefore, the core and hammer drills, the general contractor Besab, operate from an establishment in central Gothenburg. The company started the work in the spring of 2017, and it is expected to continue until 2019.

The challenge

Drilling and wire sawing in rock are cooled with water, resulting in drilling sludge. This consists of fine-grained stone flour, gravel, and water. Stormwater flows into the Göta River, which is a Natura 2000 area, where cloudy water could cause significant damage to the aquatic ecosystem. The ecosystem includes many fish, bottom-dwelling animals, and plants dependent on light. Additionally, drilling sludge can clog stormwater pipes.

To treat the cloudy water with traditional methods, such as sedimentation, would have been very expensive since it would have required a large sedimentation basin. Moreover, the space at the establishment is very limited, and therefore the project needs a compact treatment plant.

The solution

After hearing a presentation about Swedish Hydro Solutions' solutions, Emma Sundberg, responsible environmental consultant at engineering consulting firm Tyréns, suggested that Besab should use Swedish Hydro Solutions' treatment technology with passive flocculation, where particles are settled using the biodegradable flocculating agent chitosan.

– The common solutions on the market require handling unpleasant chemicals for flocculation and constant monitoring. Swedish Hydro Solutions' solution is compact, simple, and quite self-sufficient. It's enough to check it once a day, says Emma Sundberg.

After flocculation, the remaining particles and any metals are filtered out using the passive Biomedia filtration.

– Swedish Hydro Solutions installed the entire system in one day, and it took another day to fine-tune the system. Then, the contractor could manage the system himself. If there's anything at all, you just call the company – they have been helpful in every way. The entire solution is above ground, where the cloudy water is pumped from the tunnel drilling.

The result

After treatment, the water quality exceeds the requirements set by the City of Gothenburg.

– The treatment technology is extremely effective for particles, so we are super satisfied. I haven't worked with drilling sludge before, but compared to surface water, it is clearly much, much more efficient than other methods, Emma says.

– With many other methods, such as sedimentation basins, the water is often still cloudy after treatment. With chitosan flocculation combined with Biomedia filtration, the water becomes completely clear. We've only had to replace the filter media in the Biomedia filter once, and then it started working again.

– Additionally, chitosan is a product produced from waste – a more sustainable method than using hazardous chemicals. And it's easy to manage; you don't need an employee to handle the treatment, as you do with other methods.

A new standard for particle separation

– This is a new standard for particle separation. Here in Gothenburg, there is a lot of clay that many claim cannot be removed from water. But now you can't say that anymore. Now it is possible – in a quite easy way, says Emma Sundberg.

– We are super satisfied, and I can recommend Swedish Hydro Solutions' treatment technology to everyone. It's a simple but really effective system that requires little space and supervision while being based on more sustainable products.