Calcium phosphate could be accumulated in aerobic granules, which attracts attention recently for phosphorus removal and recovery from wastewater. In this study, partial nitrifying granules with high calcium precipitate content were sorted into different size groups for characterization and evaluation to reveal the dynamic balance of granules at stead state and relevant calcium phosphate precipitation and accumulation mechanism. It was found that light yellow small granules without calcium precipitates but high microbial activity co-existed with deep brown granules with calcium precipitate of around 91% and low microbial activity. Characterization with specific oxygen uptake rates, specific ammonium oxidation rates, calcium and phosphate removal rates from solution, EPS contents, elemental compositions by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and scanning electron microscopy (SEM) for different size groups of granules enabled a proposal of a new hypothesized mechanism for calcium precipitation and accumulation. With this proposed mechanism, it is believed that sufficient granule retention time in reactors was critical for the accumulation of calcium precipitates followed by a slow microbial growth rate of biomass due to mass transfer resistance. The co-precipitation of calcium carbonate and calcium phosphate mainly occurred in granules with a size less than 710 µm while calcium phosphate dominant minerals were accumulated in granules larger than 710 µm. The results and conclusions in this study shed light on the mechanisms of calcium phosphate accumulation in granules, which could be used to better operate and control aerobic granular sludge with calcium phosphates for phosphorus removal and recovery.

磷酸钙可以在好氧颗粒中积累，最近它在废水中的除磷和回收方面引起了人们的关注。本研究将钙沉淀含量高的部分硝化颗粒分为不同大小的组进行表征和评价，以揭示稳态颗粒的动态平衡以及相关的磷酸钙沉淀和积累机制。发现浅黄色小颗粒无钙沉淀但微生物活性高，与深棕色颗粒共存，钙沉淀约91%，微生物活性低。通过能量色散 X 射线光谱 (EDX) 表征特定的氧气吸收率、特定的铵氧化速率、从溶液中去除钙和磷酸盐的速率、EPS 含量、元素组成，X 射线衍射 (XRD) 和扫描电子显微镜 (SEM) 对不同尺寸的颗粒组提出了一种新的钙沉淀和积累的假设机制。使用这种提出的机制，据信在反应器中足够的颗粒停留时间对于钙沉淀的积累至关重要，随后由于传质阻力导致生物质的微生物生长速度缓慢。碳酸钙和磷酸钙的共沉淀主要发生在小于 710 µm 的颗粒中，而磷酸钙优势矿物在大于 710 µm 的颗粒中积累。本研究的结果和结论阐明了磷酸钙在颗粒中积累的机制，