Production and application of nano-bonechar for immobilizing fluoride in naturally contaminated soil and it’s potential towards climate smart agriculture

Abstract

Fluoride ion (F-) is one of the major geogenic contaminants in water and soil. Excessive consumption of F- poses serious health impacts on humans and plants. In this study, a novel carbonaceous material, nano-bonechar (NBC), was synthesized from cow bones and applied as a soil amendment to remediate and revitalize naturally F--contaminated soil. The incubation experiments conducted revealed that NBC significantly reduced the mobility and bioavailability of F- by 90% in the contaminated soil, and improved the soil quality by increasing the soil water holding capacity, soil organic matter, and the bioavailable contents of PO43-, Ca2+ , and Na+. Subsequently, the pot experiment results showed a significant reduction in the uptake of F- by 93% in Zea mays plants. The F--immobilization in soil was mainly due to the presence of hydroxyapatite [Ca10(PO4)6(OH)2] mineral in the NBC. Ion exchange between OH- (of NBC) and F- (of soil), and the formation of insoluble fluorite (CaF2) contributed to the attenuation of F- mobility in the soil. To test the potential of NBC towards climate smart agriculture (CSA), a pot experiment was done under deficit irrigation, and the efflux of CO2-C was measured using an incubation experiment. The experiment was conducted with three different irrigation rates (40%, 70%, and 100%), and 0 – 2% NBC application rates. Results revealed that NBC increases plant productivity and yield, and water retention capacity. The NBC application improved the plant's growth as indicated by the higher fresh and dry weights, root and shoot lengths, and total content of PO43-, Ca2+ , and K+ than those of un-amended soil. However, CO2-C emissions remain higher in amended soil than in un amended soil. This may be a result of high organic matter in the NBC that increased microbial activity in the soil. The findings indicate that NBC was not only beneficial for plant yield, but also for water conservation. Pot experiment showed the significant increment in fresh and dry weight, root an shoot length and total content of P, Ca and K in plants grown in NBC amended soil. The study concluded that the use of NBC is a natural waste management treatment for eliminating F- from the soil, and a sustainable method for CSA. Moreover, due to its size and enrichment in hydroxyapatite, NBC could successfully be utilized for the rapid remediation and revitalization of F--contaminated agricultural soil.