腐殖酸絮凝体形成过程中初期搅拌条件对其形态结构的影响

以腐殖酸为研究对象,采用硫酸铝为混凝剂进行混凝杯罐实验,借助PDA在线监测系统、图像解析法及粒子图像测速技术分析评价絮凝体的构造特征,着重探讨了混凝过程中初期快速搅拌条件对絮凝体形态结构的影响.结果表明,快速搅拌条件对腐殖酸絮凝体的形成过程及形态结构有着显著影响.最佳快速搅拌条件为:搅拌历时l min,搅拌强度300 r·min-,此时形成的絮凝体结构密实,抗剪切能力强,整体性能最优,絮凝体分形维数、强度及平均粒径分别为1.8842、0.164 N·m-2、0.43 mm.腐殖酸絮凝体的形成包括不溶性微粒的产生及初期颗粒的形成与结合等过程,其中,不溶性微粒的形成及初期颗粒的致密化过程是决定最终絮凝体形态构造的重要环节,而快速搅拌条件影响着混凝剂扩散混合效果和初期颗粒的形成速率与致密化程度,这也是初期快速搅拌条件对于腐殖酸混凝过程有显著影响的一个重要因素.

Effects of initial stirring conditions on humic floc morphological structure during coagulation process

The coagulation jar tests, with aluminum sulfate as the coagulant and humic acid as the research object, were conducted under different initial stirring conditions. Based on analyzing and evaluating the floc structure characteristics through PDA online monitoring, image analysis and particle image velocimetry, effects of initial stirring conditions on floc morphological structure was discussed. The results show that stirring conditions have a significant impact on floc forming process and its morphological characteristics. The optimum fast mixing condition is stirring 1min with 300 r·min^-1. This indicates that flocs formed under this condition (1 min, 300 r·min^-1) have a compact structure, a strong resisting shearing ability, and the optimal overall properties, with floc fractal dimension of 1.8842, strength of 0.164 N·m^-2, and size of 0.43 mm. Formation of humic flocs includes the precipitation of insoluble particles and the production and combination of primary particles, in which the precipitation of insoluble particles and the densification of initial grain are the most important steps that influence floc structure. However, the initial fast stirring condition affects the diffusion mixed effect of coagulant, the formation rate and densification degree of primary particles. This is the key factor of the significant influence of initial stirring condition on humic acid coagulation process.