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Södra closes forest biomass to forest bio-ash loop

Södra has developed a bio-ash that comprises of nutrients from forest raw materials and can be produced at the company’s own pulp mills. The material will be used to return nutrients to the forest to close the ecosystem and ensure long-term production capacity.

Södra has developed a bio-ash that comprises nutrients from forest raw materials and can be produced at the company’s own pulp mills (photo courtesy Södra).

Södra has developed a bio-ash that comprises nutrients from forest raw materials and can be produced at the company’s own pulp mills (photo courtesy Södra).

A concern when increasing the use of logging residues, such as tops and branches, as biomass fuel is that the amount of nutrients extracted from the forest also increases. This is because the nutrients are primarily found in the needles and leaves, which under typical cut-to-length harvesting operations are left behind in the forest. Biomass ash recovery and returning the mineral nutrients back to the forest has thus been subject of research in Sweden since 2002.

No signs of nutrient depletion

Addressing this issue, Swedish forest owners association Södra has revealed that it has developed a bio-ash that comprises of nutrients from forest raw materials and can be produced at the company’s own pulp mills. The material will be used to return nutrients to the forest in order to close the ecosystem and ensure long-term production capacity.

– There are currently no signs of nutrient depletion, but we must think about the long term and ensure we have a system in place that will enable nutrients to be returned to the forest for many years to come. Research suggests that – if executed effectively – returning nutrients to healthy forest land could result in increased forest growth for at least ten years after the bio-ash is spread. On fertile land, this could mean an additional 15 m³fo per hectare, said Hedvig Johansson, Project Manager at Södra Skog, the forestry arm of the association.

Bark ash and digester nutrients

At the pulp mill in Mönsterås, Södra has developed its own spreadable ash mix, which has been approved by the Swedish Forest Agency as a means of returning nutrients to the forest. The bio-ash is produced by mixing the ash from the pulp mill’s bark boiler with nutrients extracted from wood raw material in the digester. Södra’s bio-ash contains nutrients such as magnesium and potassium as well as a high proportion of calcium, which helps to achieve a lower rate of acidification in the forest.

So far, Södra has spread this newly developed bio-ash on 600 hectares (ha) of member forest land in the Sweden’s eastern Småland region, achieving a positive result. The initiative is now being scaled up and the bio-ash will be spread on approximately 1 200 ha of forest land by autumn 2017.

According to Hedvig Johansson, Södra has all the pieces in place to soon be able offer an effective and cost-efficient service for nutrient recycling.

– We have a complete chain in place – from the forest to industry and back to the forest – and a clean and effective production process. This is a true forestry ecosystem. The challenge now is to scale up the system for all of our forest owners, said Hedvig Johansson.

Södra is Sweden’s largest forest-owner association, with over 50 000 forest owners as its members. Södra is also an international forest industry group, with pulp and sawmill operations based on processing its members’ forest products.

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