Thermal conversion of fish bones into fertilizers and biostimulants for plant growth-A low tech valorization process for the development of circular economy in least developed countries

Local food production systems of least developed countries (LDCs) are more vulnerable to environmental factors, such as climate change, with respect to those of developed ones. Hence, the development of low-tech processes to empower LDCs adaptive capacity through a circular economy approach is very promising. Here, we report on a straightforward process for potential application in LDCs contexts based on the thermal conversion of fishery by-products (fish bone) into calcium phosphate-based materials with application as fertilizers and biostimulants. Sardinella aurita bones collected from artisanal ports in Senegal were calcined in air at 300 °C, 600 °C and 900 °C. The sample obtained at 300 °C was a composite material made of an organic part, deriving from the uncomplete combustion of fish bone collagen and fatty acid, and an inorganic part made of very poorly crystalline hydroxyapatite. The other two samples obtained at 600 °C and 900 °C had a negligible content of organic matter, and consisted of hydroxyapatite and β-TCP. Materials phytotoxicity was tested against Lepidium sativum seed, and their bio-stimulation activity was assayed on Zea mais seedlings and coleoptiles. All the materials showed promising results in terms of seed germination, plant fertilization and corn coleoptile biostimulation. Finally, we briefly analyzed the environmental impacts and economic cost of the proposed low-tech thermal process to confirm its large-scale applicability in LDCs for the conversion of fish bones into valuable products.