PAC-改性淀粉复合混凝剂对铜绿微囊藻的去除

Effects of composite coagulant with modified starch and PAC on the removal of Microcystis aeruginosa

利用阳离子型淀粉复合聚合氯化铝(PAC)制得的混凝剂对铜绿微囊藻进行处理,并进行多因素影响下的比较分析。Zeta电位、扫描电镜等结果表明,相比传统PAC,复合混凝剂所带正电荷量升高,它对藻细胞的电中和作用是对蓝藻重要的去除机理,而PAC水解产物和改性淀粉的吸附架桥和网捕卷扫作用也有重要作用。在所选范围内,复合混凝剂在弱酸性(pH=5.5)和中性条件下(pH=7.5)的去除效果较好,最佳去除率能超过80%。不同pH下复合混凝剂对蓝藻的去除存在最佳投加量,投加量过高时它对蓝藻的去除率发生下降。当达到最佳去除率时,延滞期蓝藻所需复合混凝剂投加量最低,稳定生长期蓝藻需要的投加量最高,蓝藻生长过程中产生的胞外物质是导致该结果的重要原因,具体表现为:蓝藻的胞外多糖(EPS)会增加混凝剂的消耗量,但一定量EPS也有助于混凝剂的作用效果。随着初始藻密度提高(1×10^(5)-5×10^(6)cells·mL^(−1)),复合混凝剂对蓝藻的处理效果逐渐发生下降。由于搅拌是为了使混凝剂与藻细胞充分混匀并形成尺寸较大且结构稳定的絮体,因此快搅拌速率不宜过高或过低,快搅拌速率在300 r·min^(−1)时蓝藻的去除效果更好;慢搅拌速率为40 r·min^(−1)且搅拌时间为20 min时蓝藻去除率最高。

The composite coagulant with modified starch and polymeric aluminium chloride(PAC)was used to deal with Microcystis aeruginosa under different conditions.Confirmed by results such as Zeta potential and scanning electron microscope(SEM)images,the amount of positive charges carried by composite coagulant increased compared with that of original PAC,and charge neutralization of cells played an important role on the removal of M.aeruginosa.Besides,the adsorption bridging and sweeping by the hydrolysate of PAC and modified starch were also involved in the removal process.Within the selected pH range,the removal rate of M.aeruginosa was higher under weak acidity conditions(pH=5.5)and neutral conditions(pH=7.5)by the composite coagulant,when more than 80%of M.aeruginosa could be removed.Moreover,there was an optimal dosage for the composite coagulant at different pH,and the removal rate decreased when coagulant dosage was too high.At the best removal rate,the required dosage of composite coagulant was lowest for M.aeruginosa at the lag phase and highest for M.aeruginosa at stationary growth,which could be mainly caused by the extracellular substances produced by algae.The extracellular polysaccharide(EPS)produced by M.aeruginosa increased the consumption of coagulant,while certain amount of EPS could also contribute to the coagulation performance.For the initial densities of M.aeruginosa ranging from 1×10^(5)-5×10^(6) cells·mL^(−1),the removal efficiency of composite coagulant decreased with increasing algal densities.Since agitation was used to thoroughly mix the coagulant and cells and to form the large size flocs with stable structure,the speed of fast-stirring should not be too high nor too low.The removal rate of M.aeruginosa was better at 300 r·min^(−1) of fast−stirring.Meanwhile,the removal rate of M.aeruginosa was highest at 40 r·min^(−1) of slow−stirring for 20 min.