Effect Of Al Species In Polyaluminium Silicate Chloride Coagulant (PASiC) On Its Coagulation Performance

The relative importance of three different Al species of polyaluminum silicate chloride (PASiC) in coagulation was investigated. Polyaluminum silicate chlorides with the dominant components of different Al species were prepared and the differences in the treatment of humic acid-kaolin clay (HA-Kaolin) synthetic solution were compared. The experimental results showed that the PASiC with the dominant components of Alb and Alc performed well in removing turbidity, DOC and UV254. Then, PASiCb and PASiCc with different Al/Si ratio were prepared to examine the coagulation effect and floc aggregation. Thirdly, the relative importance of Al species in polyaluminum silicate chloride (PASiC) was investigated in treating Yellow River diversion reservoir water. The main conclusions are as follows:(1) When the pH increased from4to9, the turbidity removal efficiency by PASiCa, PASiCb and PASiCc increased with the increase in pH, while the UV254and DOC removal efficiency corresponding to three coagulants all increased first and decreased subsequently, and reached the peak at pH of6. The turbidity and DOC removal efficiency by PASiCb was higher than that by PASiCa and PASiCc in all pH range investigated. In terms of UV254removal, PASiCc was the most efficient coagulant followed by PASiCb and PASiCa within the entire pH range tested.(2) The average floc size of PASiCa in the steady phase was the largest followed by that of PASiCb and PASiCc in descending order in different coagulant dosage conditions. But the fractal dimension of PASiCa was the minimum which indicated that the floc was the loosest. The floc equivalent diameters of PASiCb were invariable with the change in pH, meanwhile the strength factors and recovery factors of PASiCc were larger than those of PASiCa and PASiCb at all pH values investigated. The fractal dimension of PASiC20was largest at the pH of6and9.(3) The compound coagulant mixed by Alb and PSi was better than pure Alb at moving turbidity. The UV254removal efficiency by PASiCb (20:1) was highest and could reach82%at the dosage of4mg Al/L. PASiCb (5:1) was effective in removing DOC and the DOC removal efficiency was the highest (35%) at the dosage of8mg/L(4) PASiCb (10:1) performed best in the floc formation with the largest floc size and the same form speed as the others. But it performed badly in resisting broken and the ability to resume the broken.(5) The turbidity removal efficiency by PACc、PASiCc(5:1)、PASiCc(10:1)、 PASiCc(20:1) increased with the increasing of pH and reached up to90%when the pH was higher than6. In the condition of different dosage and pH, PASiCc (5:1) was most effective in removing DOC and the DOC removal efficiency reached44%at the dosage of8mg/L. In different pH condition researched, the UV254removal efficiency order was as follows:PASiCc(20:1)>PASiCc(10:1)>PACc> PASiCc(5:1).(6) When the dosage was2mg/L and4mg/L, the fractal dimension of PASiCc (5:1) was largest, so the floc was the most compact. But at the dosage of8mg/L, the Df of PACc was largest. The Df of PASiCc (5:1) was largest to be1.96at pH of6and9.(7) PASiCb was thought to be most efficient in treating the Yellow River diversion reservoir water with the comprehensive consideration of turbidity removal, UV254removal and DOC removal, and the most efficient pH was confirmed to be6.