pH对混凝超滤组合工艺性能的影响

在聚合氯化铝(PACl)投加量为4 mg/L条件下,通过调节原水的初始pH值,考察pH条件对混凝超滤组合工艺的净水性能及膜污染的影响。结果表明:当pH为7.5时,组合工艺对CODMn、UV254、DOC的去除率分别为40.2%、35.4%和36.1%;当pH降至4.5时,对应的去除率分别增加至52.9%、52.1%和42.0%。酸性条件下,膜池内絮体的分形维数大,絮体结构密实,膜污染速率较快;当pH等于4.5时,絮体分形维数为1.75±0.15,尺寸大于500 μm的絮体数占总絮体数的9%。中性及偏碱性条件下,絮体分形维数小,絮体结构松散多枝,膜污染速率缓慢;当pH等于7.5时,絮体分形维数为1.37±0.05,尺寸大于500 μm的絮体占65%。针对该水库的水质状况,控制原水pH为7.5有利于混凝超滤膜组合装置的运行。

Effects of pH on performance of combined process of coagulation and ultrafiltration

The effects of pH on the purification performance and membrane fouling of a combined coagulation-ultrafiltration process were investigated by adjusting the pH of raw water to different values under the polyaluminum chloride (PACl) dosage of 4 mg/L.The experimental results showed that the removal rates of chemical oxygen demand (CODMn), UV254, and dissolved organic carbon (DOC) from raw water at a pH of 7.5 were 40.2%, 35.4%, and 36.1%, respectively.These removal rates for raw water at a pH of 4.5 increased to 52.9%, 52.1%, and 42.0%, respectively.The fractal dimensions of flocs were relatively high, the structures were dense, and the membrane fouling was quick under the acidic conditions of raw water.The fractal dimensions of flocs were 1.75±0.15 and the percent of flocs with a size range over 500 μm was 9% under a pH of 4.5.Yet the fractal dimensions of flocs were low, the structures were highly-branched and loosely-bound, and the membrane fouling was relatively slow under neutral and alkaline conditions.The fractal dimensions of flocs were 1.37±0.05 and the percent of flocs with a size range over 500 μm was 65% under a pH of 7.5.According to the water quality conditions of the reservoir, it is beneficial to the operation of the combined coagulation-ultrafiltration system to control the pH of raw water at a level of 7.5.