Effect of Fe (III) species in polyferric chloride on floc properties and membrane fouling in coagulation-ultrafiltration process

Impacts of Fe (III) species on floc properties and membrane fouling in coagulation-ultrafiltration (C-UF) hybrid process were investigated. Fulvic acid (FA)-kaolin synthetized water was used to simulate the actual surface water coagulated by polyferric chloride (PFC) with four different basicity (B) values. Four PFC coagulants with B values of 0.5, 1.0, 1.5 and 2.0 were denoted as PFC05, PFC10, PFC15 and PFC20, respectively. The distribution of Fe (III) species in PFC was determined by a timed complexation spectroscopy method. The results implied that the sum of monomeric and polymeric species (Fe-a and Fe-b) in PFC decreased as B values of PFC increased. PFC with higher Fe-a and Fe-b had better dissolved organic carbon (DOC) removal efficiency and higher zeta potential, which made charge neturalization stronger. Fe-a and Fe-b in PFC were beneficial to form larger and looser flocs. The permeate fluxes of PFC with different B values decreased in the following order: PFC05 > PFC20 > PFC10 = PFC15 and membrane fouling index (MFI) had opposite order. PFC05 displayed a flux advantage due to larger and looser flocs formed by it. In addition, cake resistance (Rc) relative to the total resistance was in the order of PFC20 < PFC05 < PFC10 < PFC15. (C) 2013 Elsevier B.V. All rights reserved.