School of Environmental Science and Engineering, Shandong University, No. 27 Shanda Nan Road, Jinan 250100, PR China.
Water Res. 2011 Nov 15;45(18):6181-8. doi: 10.1016/j.watres.2011.09.019. Epub 2011 Sep 16.
The adjustment of pH is an important way to enhance removal efficiency in coagulation units, and in this process, the floc size, strength and structure can be changed, influencing the subsequent solid/liquid separation effect. In this study, an inorganic polymer coagulant, polyferric chloride (PFC) was used in a low dissolved organic carbon (DOC) and high alkalinity surface water treatment. The influence of coagulation pH on removal efficiency, floc growth, strength, re-growth capability and fractal dimension was examined. The optimum dosage was predetermined as 0.150 mmol/L, and excellent particle and organic matter removal appeared in the pH range of 5.50-5.75. The structure characteristics of flocs formed under four pH conditions were investigated through the analysis of floc size, effect of shear and particle scattering properties by a laser scattering instrument. The results indicated that flocs formed at neutral pH condition gave the largest floc size and the highest growth rate. During the coagulation period, the fractal dimension of floc aggregates increased in the first minutes and then decreased and larger flocs generally had smaller fractal dimensions. The floc strength, which was assessed by the relationship of floc diameter and velocity gradient, decreased with the increase of coagulation pH. Flocs formed at pH 4.00 had better recovery capability when exposed to lower shear forces, while flocs formed at neutral and alkaline conditions had better performance under higher shear forces.
pH 值的调节是增强混凝单元去除效率的一种重要方式，在此过程中，絮体的大小、强度和结构会发生变化，从而影响后续的固液分离效果。本研究采用无机高分子混凝剂聚合氯化铁（PFC）处理低溶解有机碳（DOC）和高碱度地表水。考察了混凝 pH 值对去除效率、絮体生长、强度、再生长能力和分形维数的影响。确定最佳投加量为 0.150mmol/L，在 pH 值为 5.50-5.75 的范围内，表现出优异的颗粒和有机物去除效果。通过分析激光散射仪测量的絮体大小、剪切效应和颗粒散射特性，研究了四种 pH 值条件下形成的絮体的结构特征。结果表明，在中性 pH 值条件下形成的絮体具有最大的絮体尺寸和最高的生长速率。在混凝过程中，絮体聚集体的分形维数在最初的几分钟内增加，然后降低，较大的絮体通常具有较小的分形维数。通过絮体直径与速度梯度的关系评估的絮体强度随混凝 pH 值的增加而降低。在较低剪切力下，pH 值为 4.00 时形成的絮体具有更好的恢复能力，而在中性和碱性条件下形成的絮体在较高剪切力下具有更好的性能。
