水样pH对不同碱度含藻水混凝性能的影响

Effects of pH on the coagulation performance of algae-laden water with different alkalinity

为探明碱度对混凝去除藻细胞及其分泌有机物的影响,保证饮用水水质。以铜绿微囊藻为研究对象,选用氯化铝(AlCl3·6H2O)作为混凝剂进行混凝实验,考察了不同碱度的含藻水样在pH为6.0~9.0条件下的混凝性能、絮体特性和出水余铝。结果表明:当水样pH=6.0时,相对于低碱度(95、175和245 mg·L^(-1))水样,碱度较高(330 mg·L^(-1)和415 mg·L^(-1))的水样Zeta电位趋近于0,可有效降低颗粒间的排斥力,藻细胞的去除率达到74.45%以上(低碱度水样藻细胞去除率在31.64%以下),出水余铝最低为0.0036 mg·L^(-1)(低碱度时为0.0889 mg·L^(-1));当水样pH≥6.5时,碱度较低的水样依靠吸附架桥和网捕卷扫协同作用,使得藻细胞去除率最高达到94.31%,出水余铝可降低至0.0353 mg·L^(-1);随着碱度的增加,铝盐水解生成的Al(OH)3胶状沉淀逐渐转变为Al(OH)4^(-),使得网捕卷扫作用减弱,藻细胞去除率有所下降;当水样pH=7.5时,随着碱度增加,平衡时絮体粒径从811.02μm降低至540.62μm,絮体强度因子从35.97%降低至24.79%,恢复因子从35.31%增加至47.88%,分形维数从1.586减小到1.372。通过调节水样pH,可有效缓解碱度对含藻水混凝过程的影响,提高藻细胞的去除率。

In order to investigate the influence of alkalinity on the removal of algal cells and the organic substances secreted by algal cells by coagulation and ensure the drinking water quality,aluminum chloride(AlCl3·6 H2O)was used as a coagulant to conduct coagulation test for Microcystis aeruginosa removal.The coagulation performance,floc properties and residual aluminum in effluent were investigated during the treatment of algae-laden water with different basicity.The results showed that when the pHs of water samples were adjusted to 6.0,in comparison with water samples with low alkalinity(95,175 and 245 mg·L^(-1)),the Zeta potentials of water samples with high alkalinity(330 mg·L^(-1) and 415 mg·L^(-1))approached 0 mV,and the repulsive force between particles decreased effectively.The removal rates for algae cells could reach over74.45%(below 31.64%for water samples with low alkalinity),the lowest residual aluminum in effluent was0.0036 mg·L^(-1)(0.0889 mg·L^(-1) for water samples with low alkalinity).When the pH of water sample was above6.5,the removal rate for algae cells was up to 94.31%during the treatment of water sample with lower alkalinity due to the synergistic effects of bridging effects and sweep coagulation,and the residual aluminum in effluent decreased to 0.0353 mg·L^(-1).With increasing the alkalinity,the colloidal precipitation of Al(OH)3 generated in the solution gradually changed to Al(OH)4^(-),the effects of sweep coagulation decreased and the removal rate for algae cells decreased accordingly.When the pH of water sample was 7.5,the stable floc size decreased from 811.02μm to 540.62μm with the increase of alkalinity,its strength factor for decreased from 35.97%to24.79%,its recovery factor increased from 35.31%to 47.88%,and its fractal dimension decreased from 1.586 to1.372.The results indicated that pH regulation could alleviate the effect of alkalinity on the coagulation process of algae-laden water and increase the removal rate of algal cells.