Calcium accumulation characterization in the aerobic granules cultivated in a continuous-flow airlift bioreactor

Limited work has been done on the accumulation characterization of Ca(2+) in aerobic granules that are cultivated in a continuous-flow bioreactor. In this work, the contribution of Ca(2+) to the biogranulation in a continuous flow airlift fluidized bed (CAFB) reactor has been studied. The spatial distribution and form of calcium in the granules were investigated by scanning electron microscopy-mapping, energy dispersive X-ray and X-ray diffraction (XRD). Calcium was located throughout the Ca-rich granules, rather than accumulating in the center of the granules of the sequencing batch reactor. Furthermore, CaCO3 was detected as the main crystalline mineral form of the calcium. Calcium augmentation of the inflow promoted the accumulation of magnesium in the granules in the CAFB. The magnesium was presented as Ca7Mg2P6O24 according to XRD analyses.