Testing biochar for water treatment

In collaboration with Ålands Vatten's and the regional government's project Rent Vatten 2030, we initiated a pilot to test biochar for water treatment in Stallhaga träsk, located in Finström municipality, Åland. The aim of the biochar pilot at Stallhaga träsk is to test if biochar could help in remediating the eutrophic condition of the small lake. Similar projects with the same biochar have yielded good results in the USA.

Karl-Johan Henriksson from Brändö Lax, Patricia Wiklund from Invenire and Ann Nedergård from Ålands Vatten with the biochar sacks floating in the background.

In the Stallhaga träsk pilot test, approximately 56 kg of premium quality biochar made of wood was loaded into 130 cm long sacks made of tight mesh material. Eight of the sacks were placed in Stallhaga träsk and anchored to hold them in place. Additional couple of sacks were placed in two ditches running into Stallhaga träsk.

Because of its porous structure, one gram of the biochar used in the Stallhaga träsk pilot has an astounding surface area of 400 square meters. This means that the surface area of the biochar placed into Stallhaga träsk covers the lake's surface area approximately 1600 times. Initially, the sacks stay afloat, but they will sink underwater once they've adsorbed enough water.

The biochar along with the mesh sacks and anchoring were provided by fish farming company Brändö Lax, and they were also responsible for placing the biochar sacks into Stallhaga träsk. Ålands Vatten will collect and analyse regular water samples over the next year from Stallhaga träsk to see if any changes in the nutrient levels and other key parameters can be detected.

Watch the video below to see what the sacks look like and how they were placed into Stallhaga träsk.

Background on Stallhaga träsk

Stallhaga träsk is a small and shallow lake, with a maximum depth of 2 m and an estimated area of 1,4 ha. It's located within the water protection area for lakes Markusbölefjärden and Långsjön, which are the main drinking water sources of Åland. The catchment area of Stallhaga träsk collects its water from the surrounding agricultural area of ​​approximately 298 ha. Brewery and gastropub Stallhagen is located right next to Stallhaga träsk on its eastern shore.

Stallhaga träsk is quite heavily eutrophic. According to a survey conducted 2023 and 2024 by Ålands Vatten, Stallhaga träsk can be classified as being of unsatisfactory status when it comes to total nitrogen and of poor status for total phosphorus. According to the regional government's action plan for Markusbölefjärden and Långsjön (Åtgärdsplan Markusbölefjärden och Långsjön) approximately 10 % of the phosphorus loading into Långsjön originates from Stallhaga träsk.

The video below shows an aerial of the main ditch running into Stallhaga träsk and from there onwards into the nearby lake Långsjön.