Forest biofuel removes nutrients. To complete the natural cycle, nutrients that remain in the ash from the burnt biomass should be returned to the forest. Askungen Vital AB serves as the link between energy producers and forestry, managing the entire chain from ash output until the carefully analyzed ashes are spread.

”The harvest of bio-fuels removes important nutrient from the forest’s eco-system.  Nitrogen is consumed in the combustion at a thermal plant, but nutrients such as magnesium, phosphorus, potassium and calcium still remain in the ash. These nutrients promote tree growth and mitigate soil acidification. The Forestry Board recommends ash recycling, but there is neither binding regulation nor strong economic incentives to close the nutrient cycle. Nevertheless, a lot of ash is recycled, and we are one of the key players”, says Henrik Pedersen, CEO of Askungen Vital.

Nutrient recycling promotes development

To promote wood ash recycling, better regulation, improved knowledge and method development and stronger economic incentives should be pursued, according to Henrik Pedersen. Photo: Askungen Vital

Every year, the Swedish energy companies produce 1.7 million tonnes of ash as a residue. There is no data available on the amount of unpolluted ash available for ash recycling. Considering the amount of harvest residues (branches and tops) used as biofuel in Sweden, 200 000 tonnes of ash should be a reasonable estimate of production from combustion of pure wood pulp. As long as the fuel has not been mixed with contaminated waste, this ash is suitable for distribution in the woodland. Currently, approximately 40 000 tonnes of ash is returned to the forest, mostly in the counties of Västra Götaland, Skåne and Kalmar. These are ashes that meet the Forest Board recommendations specifying minimum and maximum levels of substances such as heavy metals in the product.

”A thermal plant that uses biofuel will be left with an ash residue after combustion, between one and three percent of the original volume. This adds up to large amounts, and somehow, the energy producer has to find a way to get rid of the ash. There are a number of ways to go about this. Much is deposited on landfills as a covering material, or incorporated as a binder component in cement. Some is sold as garden soil amendment. These alternatives may appear less costly than ash recycling if only the management cost is taken into account. But in the long term, such usage will deplete forest soils of nutrients, resulting in lowered wood production, increased soil and water acidification, and substantial social cost”, Henrik Pedersen says.

”Our business concept is to provide the missing link between sustainable forestry and high energy production, in a cost-efficient fashion. To achieve that, we will need an acknowledgement of the importance of ash recycling from energy companies, and a demand for the ash from landowners. There is a market demand, and we are handling 25 000 – 30 000 tonnes of ash every year – but that is far less than it would be if everyone followed the Forestry Board’s recommendations. We estimate that there is an annual production of 200 000 tonnes of suitable ash. For the biofuel to truly be considered renewable, ash recycling should be mandatory. And that would benefit both our business and the forest”.

Sustainable forestry with special care for sensitive areas

”We can return ash to most forests, both deciduos and coniferous, as long as there are tracks where our spreading machines can get through. Dissemination can be done from after the first thinning until about two years before harvest. We can also spread ash on clear-cut areas, both before and after replanting, if there is some vegetation present”, Henrik says.

”We want to do good work that benefits the forest without causing damage to land or trees. Our drivers are Green Card certified, with good knowledge about careful forestry practices. The ashes are beneficial virtually everywhere, but are not  spread in proximity to lakes and streams or on wetlands, formally protected land, key biotopes or certain locations with especially sensitive nature or cultural values.”

The entire chain from energy producer to forestry

”Askungen Vital manages the entire chain from ash output until the ashes are out in the woods. The ash is taken from the thermal plant or sawmill to one of our storages, where it is stored for at least 3 months in order to harden. During this process the ash becomes less alkaline. When the ashes are hardened, they are crushed and sieved so that the dissolution rate of the grains in the forest soil is optimal. The ash should dissolve slowly to prevent initial negative effects. Ash that is insufficiently hardened may cause damage to plants and animals, and increase the risk of nutrient leaching. The aim is for the ash to dissolve over a period of 5 – 25 years”, Henrik Pedersen says.

”This ash spreader is a rebuilt forwarder, designed with a tub and a disseminator. The machine, equipped with computer and GPS, is unique. Eight wheels keep it balanced and distribute the load, but the fuel-efficient machine is still nimble enough to navigate the forest tracks”, says Henrik Pedersen, Askungen Vital. Photo: Askungen Vital.

”Dissemination is planned in cooperation with the Forestry Board. The areas are mapped and the treatment method and the volume of material is determined. Once the permits and documentation is in order, the application begins. Analysis of the chemical composition is important; obviously, contaminated ash may not be transported to the forest. The ash is treated to make sure that the grain fraction and water content is suitable for spreading”.

”Once the chemical composition is confirmed to be within the recommendations, the treated ashes are loaded on swap cargo beds and transported out to the forests. The ash spreader will meet up with the swap cargo beds at the place were the ashes are unloaded, before driving further into the forest, where the truck fails to get through. Then we spread it with one of our spreading machines. Normal amount of spread is 3 tonnes of ash per hectare. The spreading is documented on the map. There is no dust from spreading and since the ash is brownish it is not visible after a couple of days. The vehicles are small and distribution is handled with care for nature”.

Contributing to Sweden’s environmental objectives

Biobased energy sources represent almost one third of the Swedish energy mix, and the harvest of wood fuels is on the rise. Forest biomass is an important resource, reducing the climate impact from energy production and contributing to the transformation to a circular economy. According to Askungen Vital, the safe return of pH-elevating and nutritious ashes is the missing piece of the puzzle.

”To meet the growing demand for wood chips, more and more branches and tops are recovered. In the past, such fractions were left to decompose, re-circulating much of the nutrients to the soil. In today’s forestry, even stumps are removed. If too much is harvested without recycling, soils become depleted of nutrients. Askungen Vital’s business idea is to increase the amount of recycled ash to close the nutrient cycle, promote vitality and development and maintain a viable, environmentally sound Swedish forestry. It makes sense to return the nutrients we have borrowed to cover our energy needs. Our work also contributes towards several of Sweden’s environmental objectives: Natural Acidification Only, Sustainable Forests, Flourishing Lakes and Streams and A Non-Toxic Environment”, Henrik Pedersen says.

The article was published in May 2017.