The impact of the particle size of meat and bone meal (MBM) incineration ash on phosphate precipitation and phosphorus recovery

Abstract

Meat and bone meal (MBM) ash was characterized and used for phosphate wastewater treatment and phosphorus recovery. The bottom ash (MBM-BA) with size >250 µm accounted for ~80% and distributed evenly in the >1000 µm, 500–1000 µm, and 250–500 µm fractions, while air pollution control residue (MBM-APCr) distributed evenly among the 250–500 µm, 125–250 µm, and <125 µm fractions. The P content in ash ranged 7.9–15.6% depending on particle size, and P content in MBM-BA (14.33%) was higher than MBM-APCr (9.28%). P in both MBM-BA and MBM-APCr was mainly hydroxyapatite (HAP) as analysed by X-ray powder diffraction (XRD). Decreased HAP and increased Ca(OH)2 were observed with decreasing particle size of MBM-BA. NaCl and Na2SO4·3K2SO4 were found with high content in the MBM-APCr, and increased as decreasing size. Ash type, pH, and particle size had significant effects on phosphate removal from synthetic wastewater. Phosphate removal capacities of 13.5–279 and 13.5–36.6 mg PO43–/g ash were obtained using MBM-BA and MBM-APCr, respectively. Phosphate removal capacities were particle size-dependent; the smaller the size, the higher the capacity: those for MBM-BA of size >1000 µm and <63 µm were 13.5 and 279 mg/g, respectively. Equilibrium pH > 8 was favorable to P removal. Based on the compositions of the solid phases, extracts before and after treatment, and Ca/P ratio 1.22–1.73, the phosphate removal mechanisms were dominated by HAP crystallization/precipitation. Using MBM-BA for wastewater treatment increased its P content to 16.30%. Depending on particle size, the acid consumption for P recovery of 84% from MBM-BA was 2.6–3.0 mM H+/mM P. Strategies for management and utilization of MBMA according to these findings were proposed.