Coagulation efficiency, floc properties and membrane fouling of polyaluminum chloride in coagulation–ultrafiltration system: The role of magnesium

Zhao, Shuang; Gao, Baoyu; Sun, Shenglei; Yue, Qinyan; Dong, Hongyu; Song, Wen

Coagulation efficiency, floc properties and membrane fouling of polyaluminum chloride in coagulation–ultrafiltration system: The role of magnesium

2015

The influence of magnesium on coagulation–ultrafiltration process was investigated regarding coagulation efficiency, floc properties and the subsequent impact on membrane fouling. PACl with different basicity values (B, OH/Al3+molar ratio) were used as coagulants. Fulvic acid (FA) water and high hardness FA water (containing magnesium) were used as original water in this study. Floc characteristics were investigated using a laser diffraction particle sizing device while membrane fouling was evaluated by a dead-end ultrafiltration batch unit. The results showed that PACl with higher OH/Al3+ value was more efficient for FA removal. Moreover, the addition of magnesium could improve its coagulation efficiency. Flocs generated in FA-magnesium water was smaller than that of FA water and showed a lower Df value, which indicated that these flocs had open structures. Results of ultrafiltration test showed that membrane fouling became severe as OH/Al3+ value increasing in FA water, but could be reduced apparently when magnesium was added. In addition, the permeate pH increased as OH/Al3+ values growing whereas the permeate pH of FA-magnesium solution was higher than that of FA solution regardless of the original pH and coagulants.

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