Abstract
Wood ash recycling to forests after logging residues harvest is important to ensure long-term sustainable forest management, however, it is not recycled in Sweden at the level required to compensate for current logging residue out-take. A problem in this context is wood ash contamination through co-incineration of waste wood with forest fuels, a practice driven by the political goal of a circular bioenergy system. We performed a case study of co-incineration at a typical Swedish district heating (DH) plant, which showed that the forest fuel ash alone could be recycled to forests due to high nutrient levels. Co-incineration with waste wood resulted however in such high levels of contaminants that the ash was landfilled as hazardous waste. Our assessment of the Swedish DH sector showed that wood ash contamination through co-incineration is common, and that only a minor proportion of the ash from forest fuels is recycled to the forest. It also revealed a lack of reliable data regarding ash production and management, making implementation and evaluation of effective countermeasures difficult. Practical measures to enable wood ash recycling, such as removal of waste wood from the fuel mix, incineration of separate fuels, and ash after-treatment, are hampered by technical and economic barriers. Furthermore, no comprehensive policy tools currently exist on either a national or EU level that facilitate wood ash recycling. Thus, we conclude that comprehensive and efficient policy tools are urgently needed to overcome current barriers, and stimulate large-scale recycling of wood ash for long-term sustainable forest fuel utilisation.
Highlights
Sweden uses a large proportion of bioenergy (33% in 2016), mainly for heating [1]
Wood ash recycling to forests after logging residues harvest is important to ensure long-term sustainable forest management, it is not recycled in Sweden at the level required to compensate for current logging residue out-take
The findings of this study show that co-incineration of forest fuels and waste wood leads to contaminated wood ash, and that coincineration is common in the Swedish district heating (DH) sector
Summary
Sweden uses a large proportion of bioenergy (33% in 2016), mainly for heating [1]. In line with the political goal of a biobased economy, logging residues have the potential to satisfy a substantial part of the demand for bio energy in Sweden, which is projected to increase over the coming de cades [3]. This expansion has been promoted by various economic incentives such as a carbon dioxide tax on fossil fuels (introduced in 1991) and green certificates for renewable electricity production (introduced in 2003). The availability of wood ash with suitable quality is currently low, and logging residues are removed from larger areas than are compensated for with wood ash recycling [4]
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