Valorization of animal bone into phosphorus biofertilizer: effects of animal species, thermal processing method, and production temperature on phosphorus availability
Milkiyas Ahmed, Abebe Nigussie, Solomon Addisu, Berhanu Belay, Shinjiro Sato
Abstract
Thermal processing has been promoted to recycle phosphorus (P) contained within animal bone. There is a dearth of information on the mechanisms that control P solubility and availability from thermally treated bones. Chemical extraction, XRD, and FTIR were used to elucidate P solubility, and incubation and pot experiments to evaluate P bioavailability from different animal bones, thermal processing methods (pyrolysis vs. combustion), and production temperatures. Pyrolysis resulted in higher formic P than combustion, particularly at temperatures >500°C. Chicken bone showed the highest water-soluble P content (p< 0.001), irrespective of processing methods and temperatures. In contrast, pig bone exhibited the lowest water-soluble P despite its high total P content. The XRD and FTIR studies confirmed higher degree of crystallization for those produced from pig bone, combustion, and higher temperatures (>700°C). Infrared splitting factor and width at 85% of the height of the 604 cm−1 peak were used to assess bioapatite crystallinity, and confirmed a negative correlation between crystallinity and P availability (p< 0.001), indicating the attribution of bioapatite crystallization for low soluble P during combustion and higher temperatures. In low pH soil (pH~4), the addition of thermally treated bones increased Olsen-P and plant P uptake by two- to five-folds compared with unamended soils; however, no significant variation was observed in higher pH soil (pH~7). The finding suggested processing bones below temperatures of 700°C resulted in less crystallinity, thus higher P solubility. The P-fertilizing value of thermally treated bones was more pronounced in lower pH soil.