Insight into the combined colloidal-humic acid fouling on the hybrid coagulation microfiltration membrane process: The importance of aluminum

The hybrid coagulation–microfiltration process has been used for water treatment plants. However, membrane fouling is still the major barrier for its application. In this study, the impact of interactions between natural organic matter and particles on fouling has been investigated. The model substances were kaolin, humic acid and aluminum as the coagulant. The results demonstrated that flux was almost kept constant for humic acid due to its linear structure. However, the flux of the synthetic solution decline was substantial. More interesting, the addition of aluminum with different dosages played a significant role in membrane filtration. With the low dosage of AlCl3 as 0.06 mmol/L, there were no visible flocs, but the flux of the synthetic solution showed a noticeable decreasing due to the complexation of humic acid and aluminum. With the increase of aluminum, the flux was apparently improved for the flocs formed. It indicated that the dosage of coagulant was a key parameter to decide the effect of filtration since coagulation had both positive and negative effects on membrane fouling. Additionally, the experimental results also revealed that the floc structure and pore blocking might take the major responsibility for the flux decline.