絮体老化与调节对回流进水及混凝的影响机制

为探索絮体老化与pH值调节对回流进水颗粒组成及混凝的影响，采用激光粒度仪进行了絮体粒径分析并通过Al （OH）₃胶体（Al-gel）的老化实验探究了老化与pH值调节对絮体形态及性质的内在影响机制.结果表明，原水颗粒物粒径呈现单峰分布，絮体回流进水颗粒物粒径呈现双峰分布，并且回流进水颗粒d₅₀随着絮体老化时间的增加而减小；由于絮体回流提高了颗粒物与混凝剂接触机率和碰撞效率，因此加快了絮体的生长；絮体在pH=5的环境下老化12h后进行回流混凝的絮体粒径生长速率最高（1.16 μm/s）并且生成的絮体具有较大的分形维数（2.35）.Al-gel的老化实验结果表明，絮体老化过程会涉及羟桥反应和结晶反应并导致絮体的表面活性基团数量减少，从而不利于与原水颗粒物的相互作用.pH值调节对絮体产生不同的影响，pH=5的条件下进行老化会加速絮体的羟桥反应和结晶反应，而pH=9的条件下进行老化则会涉及溶解-沉淀-结晶反应.

Mechanism on the effects of floc aging and pH adjustment on reflux feed water and coagulation

Effects of floc aging and pH adjustment on the particle composition and coagulation of the reflux water were investigated using laser particle size analyzer, and the mechanisms of aging and pH adjustment on floc properties were explored by the aging experiments of Al(OH)₃ gel (Al-gel). The results showed that the particle size of raw water displayed a unimodal distribution, and the particle size of the influent flocs presented a bimodal distribution. Meanwhile, there was a decrease of the particle d₅₀ of reflux water with the increase of aging time. The growth rate of the flocs increased as the reflux flocs that were subjected to reflux coagulation after being aged at pH=5 for 12h had the highest floc d₅₀ growth rate (1.16μm/s) and produced the flocs with a higher fractal dimension (2.35). The results of Al-gel aging experiment demonstrated that hydroxyl-bridging and crystallization reactions occurred during aging, leading to a reduction in the number of reactive groups on the floc surfaces, which was not conducive to the interaction with raw water particles. The pH adjustment had different effects on the flocs. For example, the aging at pH=5accelerated the hydroxyl-bridging and crystallization reactions, while the aging at pH=9 may involve dissolution-precipitation-crystallization interactions.