阳离子型聚合物对低温低浊水的絮凝效果与形态学特性

Flocculation efficiencies and morphological properties of cationic polymers in the treatment of low temperature and low turbidity raw water

采用微絮凝-深床直接过滤工艺,以西安市曲江水厂低温低浊水质为原水(水温低于10℃,初始浊度低于10NTU),投加阳离子型聚合物(简称CP)作主混凝剂或助凝剂,借助分形数学理论与图像分析技术,对滤料粒径、原水浊度、原水温度、药剂种类、聚合物分子量及投加量、混合强度等因素对处理效果的影响进行了研究,分析探讨了不同药剂处理低温低浊水的作用机理、絮凝形态学特征以及絮体结构的分形特性.结果表明,①当温度低于4℃、初始浊度小于4NTU时,不宜单独采用Al2(SO4)3或PAC作为絮凝剂;当温度为4～10℃、初始浊度小于10NTU时,如果只投加Al2(SO4)3或PAC作为絮凝剂,宜用细砂滤料过滤;低温低浊条件下,无机混凝剂形成的絮体粒径小、结构松散脆弱、有效质量密度低、沉速慢,但表征絮体分形特性的分维值较高.②CP作絮凝剂能显著改善低温低浊水的絮凝效果与过滤性能,但混合强度需增大,宜用粗砂滤料过滤;③单独用CP作絮凝剂时,宜投加分子量较低的弱阳性聚合物或投加低剂量较高分子量的强阳性聚合物;CP用作助凝剂时,能显著减少主混凝剂用量,但宜投加强阳性聚合物或增加弱阳性聚合物的剂量.④CP兼备电性中和与吸附架桥絮凝作用,能形成粒径较大、吸附性能与过滤性能良好的网状絮体构型,其有效质量密度高,产生的污泥量少,污泥沉降速度快,脱水效果好,但分维值低.⑤各种水处理药剂的处理效果为:Al2(SO4)3(或PAC)+CP>CP>PAC>Al2(SO4)3,这种差别由絮体的形态学特性与构型特征各异引起.

Effects of addition of cationic high molecular weight polymers （CP） as a primary flocculant or coagulant aid, ,on the treatment efficiencies for raw water with low temperature （ T 〈 10℃ ） and low turbidity （ C0 〈 10 NTU） were measured. The raw water was obtained from the Qujiang water treatment plant in Xi＇an, China and investigated using a micro-flocculation depth-bed direct filtration process. Fractal mathematics and image analysis were used to analyze the effects of the following factors on treatment efficiencies： filter medium; raw water turbidity and temperature; chemical type, molecular weight and dosage of polymer; and mixing strength. The flocculation mechanism, floe morphologies and the fractal properties of floc structures were also Compared after adding different flocculants. Five important results were obtained ： ① It is not suitable to use Al2（SO4）3（AS） or polyaluminium chloride （PAC） alone when T 〈 4℃ , C0 〈 4 NTU. Fine sand filter medium should be used if Al2（SO4）3 or PAC is added alone under the conditions 4℃ 〈 T〈 10℃, C0 〈 10 NTU. For raw water with low temperature and turbidity, the flocs formed from inorganic coagulants are small, loose and fragile structures, with low efficient mass density and settling rate, but high fractal dimension. ②A coarse sand filter markedly improved CP flocculation efficiencies of raw water with low temperature and turbidity; but the mixing strength should be increased due to high viscosity of CP; ③It is appropriate to use low molecular weight polymers with weakly cationic properties or a lower dosage of CP with strong cationic properties if CP serves as a primary flocculant. When CP is used as a coagulant aid, the dosage of the primary coagulant can be greatly decreased, but it is better to use high molecular weight polymers with strong cationic properties or to increase the dosage of CP with weak cationic properties. ④The flocculation mechanisms of CP are charge neutralization, adsorption and bridging. Flocs formed from CP have have large network configurations, which lead to reduced sludge volumes and increased sludge settling rates as well as good dewatering behavior, but have a lower fractal dimension than inorganic flocs. ⑤ The treatment efficiencies of all tested flocculants are as follows ： Al2（SO4）3（or PAC） ＋ CP 〉 CP 〉 PAC 〉 Al2（SO4）3.