吸附架桥机理主导下APAM的多级絮凝效能

对吸附架桥机理主导下阴离子聚丙烯酰胺(APAM)的絮凝过程进行了研究,通过改变絮凝剂投加工况,对比分析常规絮凝与多级絮凝在污染物去除效果、絮体性能、絮体生长动力学与污泥调理能耗等方面的差异。结果表明,相同投药量下,两级絮凝的出水浊度低于三级絮凝和常规絮凝,两级絮凝在最少的APAM投加量(2 mg/L)下达到最低的出水浊度(19.53 NTU);与常规絮凝相比,两级絮凝的絮体成长速率、平均粒径和沉降速率分别增加12.67%、30μm、36.74%。两级絮凝在投加间隔为240 s、投配比为1∶1条件下絮凝效能最优,出水浊度为15.34 NTU,絮体沉降速率为1.1 NTU/s,絮体密度达到1.123 4 g/cm³。絮体破碎再絮凝过程中,两级絮凝与常规絮凝破碎后均能恢复至破碎前水平,但破碎后均出现不可逆的絮体结构破损,粒径在0~100μm的絮体颗粒增多,粒径>400μm的絮体减少,破碎后两级絮凝的絮体强度因子(68.15%)高于常规絮凝(41.63%),两级絮凝的絮体强度和抗破碎剪切能力更高。在剩余污泥调理方面,两级絮凝产生的污泥只需要投加40mg/L的APAM就可以达到最低的滤饼含水率(75.5%)。因此,两级絮凝可以显著提升除浊效能与絮体性能,是强化絮凝的发展方向。

Multi-stage Flocculation Efficiency of APAM Led by Adsorption and Bridging Mechanism

Flocculation process of anionic polyacrylamide(APAM) led by adsorption and bridging mechanism was explored.The differences between conventional flocculation and multi-stage flocculation in pollutants removal,flocculation performance,flocculation growth kinetics and sludge conditioning energy consumption were compared and analyzed by changing flocculant dosing conditions.Under the same dosage,the effluent turbidity of the two-stage flocculation was the lowest,followed by the three-stage flocculation and the conventional flocculation.The two-stage flocculation achieved the lowest turbidity of19.53 NTU in the effluent at the minimum dosage of APAM(2 mg/L).Compared with conventional flocculation,the growth rate of floc,average particle size and sedimentation velocity of two-stage flocculation increased by 12.67%,30 μm and 36.74%,respectively.The best flocculation performance of the two-stage flocculation was obtained under the condition of dosing interval of 240 s and dosage ratio of1∶1,and the effluent turbidity was 15.34 NTU,the floc sedimentation velocity was 1.1 NTU/s and the floc density reached 1.123 4 g/cm³.In the process of floc breakage and re-growth,both the two-stage flocculation and the conventional flocculation could recover to the level before breakage.However,irreversible damage of the floc structure occurred after breakage.Proportion of flocs with sizes of 0-100μm increased,and proportion of flocs with sizes more than 400 μm decreased.In addition,the strength factor of the two-stage flocculation(68.15%) after breaking was higher than that of the conventional flocculation(41.63%),and flocs produced by the two-stage flocculation had higher strength and stronger shear resistance.In terms of excess sludge conditioning,the lowest water content of filter cake(75.5%)could be achieved by only adding 40 mg/L APAM for the sludge produced by two-stage flocculation.Therefore,two-stage flocculation can significantly improve the turbidity removal efficiency and flocculation performance,which is a promising direction of enhanced flocculation.