Conversion of biowastes to biomaterial: An innovative waste management approach

The study suggests that biowastes (eggshells and urine) can be potentially used as precursors to produce hydroxyapatite (HAp) biomaterial in a simple chemical process. A batch reactor was used in this work to produce HAp powder from eggshells and synthetic urine (SU). Fine powder of calcined eggshells was dissolved in water to produce aqueous calcium hydroxide. The solution was then mixed with concentrated SU in stoichiometric amounts corresponding to HAp (Ca/P molar ratio∼1.67). The initial pH of the solution was alkaline (pH∼8.5) and particles formed rapidly with slight mixing. Stirring the turbid solution for a longer period (72h) did not show any visual change, but the particle size decreased slightly. When the pH of the solution was adjusted to 5, the solution was initially clear, but particle formation was apparent after 48h stirring. It was noticed that at a slow stirring speed (100rpm), film formation occurred on the solution, whereas at a higher stirring speed (500rpm) no such film formation was observed. X-ray diffraction (XRD) analysis confirmed that the particles (formed at 500rpm) were an amorphous calcium phosphate (CaP). Alkaline treatment at 80°C for 2h converted the amorphous CaP into HAp. Inductively coupled plasma mass spectrometry (ICP-MS) analysis of the particles (formed at 500rpm) suggested that they are calcium-deficient HAp (Ca/P molar ratio 1.58).