Bioashes and their potential for reuse to sustain ecosystem services and underpin circular economy

Global promotion of decarbonisation by using sustainable bio-renewables is associated with generation of ash residues whose amounts have increased exponentially in the last decades. Bioashes are physicochemically complex, ultra-alkaline, and potentially hazardous solids, but with a huge potential to become (co)products with environmental/economic value. Their diverse nature lends itself to a wide range of uses in land remediation, wastewater treatment, civil and bio-tech engineering, end even medicine. However, there are issues hindering the usage of bioashes as valuable resources: i) large variation among specific fractions and types, ii) strong and long-lasting reactivity and potential toxicity, and iii) an incoherent, often non-existent, legislative and regulatory framework for management of specific bio-wastes. Overcoming these obstacles and uncertainties regarding the ecological and economic benefits vs. negative side-effects is a significant challenge. The research and implementation work is urgently needed to i) elucidate dosage-dependent biological outcomes of bioash amendments, especially those related to soil and aquatic microbiomes as the primary living barriers/biofilters for most substances released from bioashes, and ii) transform finely powdered matrices to easy-to-apply forms (from nano/micro-to mm-sized agglomerates) to reduce human health implications. The continued progress in material sciences and nanotechnology offers a fascinating array of solutions for re-purposing bioashes; however, given the stringent quality-demanding criteria, the separation and concentration of targeted submatrices (e.g. aluminosilicates) from the bulk bioashes are yet to be achieved on the lab to industrial scales. Meanwhile, a significant reuse potential of bioashes will remain under-exploited and compounded by the adverse environmental issues arising from landfill disposal.