Biomass Conditioning - Degradation of Biomass during the Storage of Woodchips

Abstract

One big problem of energy production by combustion of woodchips is the storage related loss of biomass. Wood­destroying fungi metabolizing cellulose, hemicellulose and lignin are able to cause economic relevant material losses. Beside water content, particle size, height and shape of woodchip piles are important factors that have to be considered. On the basis of two test set­ups and laboratory analyses, the project aims to find an optimized storage and pre­treatment method for woodchips. Biomass loss analysis showed a monthly substance loss of 1% up to 4% depending on biomass quality, water content and temperature. Standard woodchips showed lowest biomass losses and a low microbiological growth. Bark woodchips and forest residues tend to be more susceptible for fungal growth and highest biomass loss could be proved for bark woodchips. Field tests revealed that woodchip piles consist of at least three main layers. An outer layer called “weather belt” staying in direct contact to ambient conditions, an aerobic layer and in some cases an anaerobic central part. These layers offer different growth conditions for microorganisms. Therefore the determination of an overall degree of degradation for one woodchip quality or even woodchip pile shows big difficulties and further studies have to be conducted.