STASIS - A UNIFIED METHOD IN THE PROGRAM AREA FOR TREATMENT OF SULFIDE SOILS
The STASIS project is a collaboration between Novia University of Applied Sciences and Vaasa University of Applies Sciences in Finland, and Dåva Deponi och Avfallscenter i Umeå AB, Luleå University of Technology and Linnaeus University in Sweden.
The main goal of the project is a unified and cost-effective method in the Botnia-Atlantica area for treatment of intermediate sulfide soil, shaft bottom surfaces, deposited sulfide soil and deposited dredged materials rich in sulfides. The project aim is to minimize the risk of acidified and metal contaminated watercourses. Via the method it is estimated that large volumes of sulfide soils can be managed at a lower cost, while the negative environmental consequences are mitigated.
Background - sulfide rich sediments and oxidation
Large coastal areas surrounding Kvarken and the Bothnian Bay in both Sweden and Finland have emerged from the sea due to land uplift.
These old marine sediments are rich in sulfides and will slowly become oxidized when exposed to atmospheric oxygen that (among other products) generates sulfuric acid. The oxidation process is intensified when the groundwater table is lowered due to artificial drainage, or when large volumes of sulfide-rich material are excavated or dredged and deposited without proper precautions.
In consequence, water emanating from the oxidized soil materials and dredged sediments is both acidic and rich in metals. As this drainage water reaches nearby streams and rivers, negative consequences in the form of large-scale fish die-offs are possible.
Treatment of large volumes of materials rich in sulfide
In connection with the construction of infrastructure, large volumes of sulfide-rich material need to be rapidly treated in order to prevent oxidation.
This is presently achieved by either depositing the material below water or by mixing sufficient lime with the material to neutralize its complete acidification potential. Both alternatives are costly, and capacity is limited especially for depositing below water.
In this project, improved methods will be developed for on-site treatments, intermediate storage and depositing techniques for materials rich in sulfide. The use of ultrafine-grained limestone will be compared with mechanical in-mixing of traditional coarser liming materials. In addition, surface treatments or injection of suspensions of ultrafine-grained limestone will be tested. Biochar and peat will also be used for retention of leached metals. Peat can also function as an antioxidant as well as a source of energy and carbon for sulfate-reducing bacteria.
Since the problem is common on both the Swedish and the Finnish side of the Baltic Sea, the prospect of successfully combining existing competences and skills across the border is excellent.
The project allows us to further our common knowledge base, to develop common systems for the protection of coastal water streams and to disseminate our results to stakeholders in both Finland and Sweden. In the project, a significant activity will therefore be the two-way dialogue with the stakeholders that will be maintained by virtual and when possible physical meetings, seminars and workshops held in both Finland and Sweden throughout the whole project period.
The project area Botnia-Atlantica
Boxes with sediment in the laboratory in Technobothnia