Impact of enhanced coagulation ways on flocs properties and membrane fouling: Increasing dosage and applying new composite coagulant

Increasing dosage and applying new composite coagulants were common ways to enhance coagulation in removing natural organic matter (NOM). The role of increasing dosage and applying new composite coagulant on flocs properties and ultrafiltration membrane fouling were investigated by examining flocs aggregation process and membrane permeate flux variation of polyferric chloride (PFC) and polyferric chloride–polydimethyldiallylammonium chloride (PFC–PDMDAAC) in traditional and enhanced coagulation regions. The results showed that when PFC dosage was increased to 82 mg/L (the second enhanced region), the removal efficiency of DOC was increased by 70%. The application of PFC–PDMDAAC could get 85% UV254 removal efficiency in the traditional coagulation region, which was higher than PFC. The flocs size and fractal dimension of PFC–PDMDAAC was 462 um and 2.35 in traditional coagulation region respectively, which were higher than those of PFC. And increasing PFC dosage would result in flocs size decreasing from 414 um to 166 um, although fractal dimension increased when PFC dosage increased to the first enhanced coagulation region. Membrane fouling index (MFI) of PFC decreased in the following order: the first enhanced coagulation > traditional coagulation > the second enhanced coagulation. And MFI of PFC–PDMDAAC was significantly higher than that of PFC.

► Increasing dosage and applying PFC–PDMDAAC could improve the coagulation.
► Flocs size and fractal dimension of PFC–PDMDAAC were higher than those of PFC.
► The first enhanced coagulation induced the most severe membrane fouling for PFC.
► MFI of PFC–PDMDAAC was significantly higher than that of PFC.