低温条件下絮体破碎再絮凝去除水中颗粒的研究

Removal of particles through floc breakage and re-growth at low temperature

为了了解低温条件下絮体的形成/破碎/再絮凝过程在适当条件下对絮凝去除水中颗粒物的强化效果,采用PDA2000透光率脉动检测仪对絮凝破碎再絮凝过程进行了在线监测.研究结果表明,当电中和机理占主导作用时(混凝剂投加量小于0.1mmo.lL-1),絮体破碎后能重新絮凝,絮体大小能恢复到破碎之前;而当网捕卷扫机理占主导作用时(混凝剂投加量大于0.2mmol.L-1),絮体的恢复情况不如电中和条件,再絮凝能力降低.投加适量的腐殖酸会增加絮体破碎前后的分形维数,但过量的腐殖酸则会降低破碎前后絮体的分形维数.絮体破碎再絮凝后其分形维数比破碎前高.腐殖酸的投加量并不会明显影响絮凝和破碎后再絮凝的FI指数.电中和絮体破碎前初始絮凝时间越长破碎后沉后水浊度越低,破碎后其浊度会比破碎前显著减小.较低投量的铝盐就能使得沉后水浊度降到很低,因此可以降低混凝剂投量而达到更好的水处理效果.

The efficiency of coagulation and flocculation can be significantly improved through floc breakage and re-growth under appropriate conditions. At low temperature, the formation, breakage, and re-growth of floes formed by kaolin with aluminum sulfate （alum＇） were investigated with PDA 2000 to explore the reversibility of broken floes. There was a full re-growth of floes when they were coagulated by charge neutralization; but when coagulated by sweep coagulation, the floc break-up process was distinctly irreversible. The presence of humie acid in water facilitated the re-growth of floes. Proper quantities of humic acid in water could improve the fractal dimension of floes, but excessive humie acid decreased the fraetal dimension. The fractal dimension of floes after re-growth was a little higher than that before breakage. At low temperature, humie acid did not influence the flocculation index （FI） dramatically. More importantly, the residual turbidity after re-growth of broken floes decreased as the original coagulation time increased, and was significantly lower than that before floc breakage under charge neutralization conditions, which could reduce the dosage of coagulant required to reach similar residual turbidity.