The role of interactions between extracellular organic matter and humic substances on coagulation-ultrafiltration process

Abstract

Removals of extracellular organic matter (EOM) derived from cyanobacterium M. aeruginosa and humic acid (HA) in single-component and bi-component systems and the interactions during the coagulation-ultrafiltration (C–UF) process were investigated in this study. In a single-component system, only 23% EOM could be removed by alum at dose as high as 6 mg/L, which induced serious membrane fouling in the following UF process. Interestingly, higher EOM removal efficiency was achieved (increase by about 20%) with the existence of HA and EOM-HA achieved less decline of permeate flux compared with individual EOM C–UF process. Zeta potential and Fourier transform infrared spectroscopy analysis indicated that the interactions of HA and EOM can strengthen charge neutralization and reduce CH2 chemical bonds, which had a positive effect on the coagulation process. In addition, EOM-HA floc had a more open and looser structure than EOM floc, which was more favorable in the UF process. The extended Derjaguin–Landau–Verwey–Overbeek theory indicated that the acid–base interaction energy was mainly reduced, thereby alleviating membrane fouling. The study showed this beneficial interaction between the HA and EOM would enhance the EOM removal efficacy by coagulation and release the membrane fouling caused by EOM.