The “Yellow Line” is the working name of a new metro line in the city of Stockholm, which will be completed by the end of the present decade. In order to facilitate the building of the main tunnel on this new route, a so-called work tunnel first has to be excavated; a project managed by the construction company Implenia.

The work tunnel as well as the main tunnel are treated as two individual projects, but both share the same need to treat the drainage water generated during tunnel excavation. The client, the regional authority of Stockholm, therefore required that the water treatment equipment is purchased by the first project – in order for it to be handed over to the subsequent project thereafter. For Implenia, this requirement created a golden opportunity. They wanted to test the treatment equipment they already had used with great success in the Johannelund project – equipment from Swedish Hydro Solutions – on their own and on a larger scale.

In the Johannelund project, Swedish Hydro Solutions’ technology was first used as a complement solution to Implenia’s existing treatment system. Implenia’s own systems treat water using sedimentation, but do not handle dissolved metals, which the systems from Swedish Hydro Solutions can do. And in the Hagalund Tunneling Project, they wanted to see how the technology would perform when acting completely independent.

– We are function testing the whole system to see if Swedish Hydro Solutions’ technology is suitable for our operations. We excavate tunnels, which is different from earth excavation, as we mostly remove crushed rock, says Daniel Zetterman, Machinery Manager at Implenia.

To meet the client’s requirement that the water treatment technology can be transferred to the main tunnel project, Implenia purchased a complete mobile water treatment system from Swedish Hydro Solutions instead of just renting one. This is the first time Swedish Hydro Solutions has ever agreed to sell a complete system. Implenia simultaneously signed a service agreement with Swedish Hydro Solutions when purchasing the system.

Before installation, Swedish Hydro Solutions conducted a pre-study to dimension the system that would be needed, based on calculated flows and what pollutants had to be taken care of. The result of the prestudy was the installation of a system consisting of a container dosing chitosan and other additional precipitation agents to flocculate suspended materials and precipitate dissolved metals. The system also included pH control, dosing of RedOx3 to reduce chromium VI to chromium III, sedimentation containers, automatic and online water quality monitoring, and an automatic sampler.

– After the start-up period, the water treatment works well. Once the project has been completed and we can compile the costs, we will evaluate the economics of the costs per cubic meter of water.

Is there any advantage to buying a system rather than renting?

– It is always an advantage to own. Then you are more familiar with how the system works and there is more own commitment in the operation in terms of performance monitoring and maintenance.

Excavation of the Hagalund Tunneling Project began in January 2020, and Swedish Hydro Solutions set up the system in December 2020. The project will run well into 2022.