Resource quality of wood waste: The importance of physical and chemical impurities in wood waste for recycling

Recycling of post-consumer wood waste into particleboard may be hindered by the presence of physical and chemical impurities in the waste stream, therefore calling for increased attention on the quality of wood waste. However, wood waste comprises several uses/types of wood, along with different levels of contamination. This study provides the detailed sampling and characterisation of wood waste according to its source, type and resource quality grade. Eight tonnes of wood waste, intended for recycling and collected at three Danish recycling centres, were subdivided into 34 individual material fractions and characterised with respect to the presence of three classes of physical impurities (misplacements, interfering materials and low-quality wood waste) as well as chemical concentrations of more than hundred chemical elements and persistent organic pollutants (POPs). The results demonstrated that contaminant and concentration levels vary significantly according to wood waste type and source, thus emphasising that wood waste should not be viewed as a single material flow but rather be understood and managed according to the presence of individual fractions. Including only clean wood waste fractions at the three recycling centres, 41–87% of the collected wood waste per weight could be recycled – the rest being physical impurities. The results showed that chemical contamination was significantly higher for low-quality wood waste, thus clearly indicating that improvements in separate collection, sorting and handling of wood waste may improve the resource quality of wood waste and potentially achieve cleaner recycling practices.