Effect of ballasted floc morphology on membrane fouling during shortened ultrafiltration process
HE Wei-peng1,2, ZHENG Sa1,2, WU Hui-ying1,2, LI Bo3, XU Shi-rong1,2
1. Key Laboratory of Building Safety and Energy Efficiency, Ministry of Education, Hunan University, Changsha 410082, China; 2. College of Civil Engineering, Hunan University, Changsha 410082, China; 3. Changsha Planning & Design Institute Co., Ltd., Changsha 410007, China
Abstract：Synthetic water samples containing kaolin, humic acid and antimony(Ⅲ) were purified by combined process of ballasted flocculation and ultrafiltration with using polymeric ferric sulfate (PFS) as coagulant and microsand as ballasting agent. The effects of PFS and microsand dosages on ballasted floc morphological characteristics, ultrafiltration membrane flux decline, fouling reversibility and purified water quality were systematically investigated. Also, the mechanisms of membrane fouling were explored in details. The results showed that the PFS dosage had a significant effect on floc morphology, membrane filtration efficiency and fouling properties; and especially, negative influence could be observed at PFS dosages both lower and higher than 30mg/L. With injecting a certain amount of microsand (1~6g/L), the formation of larger and relatively looser flocs would weaken irreversible membrane fouling and produce quite stable purified-water quality after ultrafiltration. Membrane specific flux and floc average size had a very strongly positive correlation (R2=0.8774), but for floc fractal dimension, a weaker negative correlation (R2=0.5760) was established, possibly due to distinct roles of those particles with higher fractal dimension on ultrafiltration.
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