Effects of recycling flocculation membrane filtration on drinking water treatment

Recycling flocculation membrane filtration (RF-MF) and coagulation membrane filtration (C-MF) were investigated for removal of natural organic matter (NOM) from Luan river in this study. The effectiveness of recycling flocculation pretreatment on both NOM removal and membrane filtration were assessed under different concentrations of coagulant and reflux flocs. Under the conditions of coagulant dosage of 6 mg/L and reflux flocs of 10 mg/L, the removal of dissolved organic carbon (DOC) was 48.4 and 48.2% by coagulation and membrane filtration, respectively. Compared to C-MF, floc recycling benefited the removal of DOC in the coagulation stage. A unified membrane filtration index (UMFI) was used to analyze the membrane fouling, and it was observed that the lowest value was 0.0004 m²/L at 6 mg/L coagulant and 10 mg/L reflux flocs. According to the results of NOM removal and membrane fouling, it can be concluded that DOC was the main reason for membrane fouling. In addition, the RF-MF contributed to small flocs aggregating into larger flocs with a denser structure. The maximal values of average floc size and the fractal dimension were 588.42 μm and 1.356, under the combination of 6 mg/L coagulant and 10 mg/L reflux flocs.