Research On Membrane Fouling Control Technology Of Enhanced Coagulation-ultra Filtration System

Using enhanced coagulation-ultra filtration system to treat drinking water has been widely studied, but the impact of coagulation process on the membrane performance in the combined process is still the pivotal issue. In this paper, the humic acid-kaolin simulation water samples treated by eight kinds of screened flocculants were performed in order to research the impact of coagulation on the membrane performance and investigate the membrane fouling mechanism, by comparing the different water quality of coagulation and ultra filtration process.The result shows that, in the coagulation-Ultra filtration (UF) hybrid process, the optimum coagulant dosage and pH value are 3mg/L and pH = 6, respectively. At the optimum condition, the removal efficiency of UV₂₅₄ and turbidity are 79.30% and 99.70%, respectively. At dosage of 0.5 and 8 mg/L, the removal efficiency of turbidity by coagulation are poor, especially, the phenomenon of return turbidity appears at the dosage of 8mg/L, and the streaming current turns into a positive value, meanwhile causing the largest membrane fouling.The effect of ionic strength changes on the results of coagulation is not obvious, but can change the particle size distribution, thus affecting the membrane. The particle sizes are mainly distributed between 1 and 10μm at the ionic strength of 0.05mmol/L and 0.25mmol/L, while around 100μm at the ionic strength of 0.15mmol/L causing minimal membrane fouling.With the increase of hardness, the removal efficiency of UV₂₅₄ appears to increase substantially. When the concentration of CaCl₂ is 8mmol/L, the removal efficiency of UV₂₅₄ reaches to 86.67%, which is better than the effect of raw water treatment without Ca²⁺. It indicates that the solution containing a small amount of Ca2 + is beneficial to the removal of organic matter. The membrane flux is degressive as the hardness increasing. When the concentration of CaCl₂ is 1mmol/L, The particle sizes are mainly distributed between 1 and 10μm, the decline of membrane flux is the fastest.Three kinds of flocculants AlCl₃,PAC and PAC-JY01 were comparatively studied, AlCl₃ on membrane fouling is the most serious, and the decline of membrane flux is the fastest ; the median particle size of PAC is the smallest, and its against shear Crushing capacity is also the strongest, but the ability to recover after it is broken is worse; PAC-JY01 has the largest particle size, the ability of recovery after fragmentation is strong, after recovery, the median particle size is the highest, the decline in flux is the smallest.