Abstract：
Calcium-induced agglomeration of anaerobic granular sludge bed (AGSB) has become a critical factor in performance decline of calcified anaerobic reactors. However, the agglomeration process of AGSB and the underlying mechanisms remain unclear and elusive. This study delved into the evolution of calcified AGSB, and four typical states of normal AGSB (Nor-AGSB), calcified dispersed AGSB (Dis-AGSB), calcified dimeric AGSB (Dim-AGSB), and calcified polymeric AGSB (Pol-AGSB) were characterized. It was found that the minimum transport velocity of Dis-AGSB was 3.14-3.79 times higher than that of Nor-AGSB, and surpassed both the superficial velocity and the bubble-induced wake velocity. This led to the sedimentation of AGS at the bottom of reactor, resulting in stable contacts with each other. Solid fillers between AGS, namely cement, were observed within Dim-AGSB and Pol-AGSB, and could be classified as tightly- and loosely- bonded cement (T- and L-cement). Further analysis revealed that T-cement was rich in extracellular polymeric substances and intertwining pili/flagella, serving as the primary driving force for robust inter-AGS adhesion. While the L-cement was primarily in the form of calcite precipitation, and blocked the convective mass transfer pathways in Pol-AGSB, leading to the decreased convective mass transfer capacity. The critical distance between calcite and AGS was further revealed as 5.33 nm to form stable initial adhesion. Consequently, the agglomeration mechanism involving the evolution of AGSB was proposed as calcium-induced sedimentation, calcium-induced adhesion, and calcium-induced stasis in order. This study is expected to offer deep insight into the calcium-induced agglomeration especially from the overlooked perspective of AGSB, and provides feasible control strategies to manage the pressing calcification issues in engineering applications.
摘要：
钙诱导的厌氧颗粒污泥床（AGSB）的团聚已成为钙化厌氧反应器性能下降的关键因素。然而,AGSB的聚集过程和潜在机制仍不清楚和难以捉摸。本研究探讨了钙化AGSB的演化，和正常AGSB(Nor-AGSB)的四种典型状态，钙化分散AGSB（Dis-AGSB），钙化二聚体AGSB（Dim-AGSB），和钙化聚合物AGSB（Pol-AGSB）进行了表征。发现Dis-AGSB的最小传输速度是Nor-AGSB的3.14-3.79倍，并超过了表面速度和气泡诱导的尾流速度。这导致了AGS在反应器底部的沉淀,导致彼此稳定的接触。AGS之间的固体填料，即水泥,在Dim-AGSB和Pol-AGSB中观察到，并且可以分类为紧密粘结水泥和松散粘结水泥(T-和L-水泥)。进一步分析表明，T-水泥富含胞外聚合物，并缠绕菌毛/鞭毛，作为AGS间牢固附着力的主要驱动力。虽然L-水泥主要是方解石沉淀的形式，并阻断了Pol-AGSB中的对流传质途径，导致对流传质能力下降。方解石和AGS之间的临界距离进一步显示为5.33nm以形成稳定的初始粘附。因此,提出了涉及AGSB演化的团聚机制为钙诱导沉降，钙诱导的粘附，和钙诱导的淤滞。这项研究有望为钙诱导的团聚提供深刻的见解，特别是从AGSB被忽视的角度来看，并提供了可行的控制策略来管理工程应用中紧迫的钙化问题。
