Nutrient recycling of fly ashes from fast pyrolysis as an innovative treatment for organic waste

Fast pyrolysis is a promising approach for the production of renewable energy (bio-oil, fast pyrolysis bio-oil (FPBO)) from different biomass sources. Side-products emerging from the process include low calorific gases and charcoal. Both are further combusted to generate energy for the process with the subsequent production of fly ashes (FAs). To assure the sustainability of FPBO technology, it is of utmost importance to properly manage the resulting FAs so as to avoid potential negative environmental impacts. Their use as a nutrient supplement in agriculture and/or the forestry sector seems to be an optimal option for their recycling, helping to both counteract acidification and correct nutrient deficiency in soil; however, there is still scarce information about the potential usefulness of FPBO-ashes as a soil amendment. Therefore, the purpose of this chapter is to compare and provide a detailed characterisation of FPBO-FAs derived from different waste streams and an overview of their potential effects on soil properties and plant growth. Legal aspects of the use of ashes in the fields of waste management and fertilizer production in four member states of the European Union will also be addressed.