Effects of Permeate Flux in Adsorption/Coagulation-Membrane Filtration System for Removing Turbid Matter and Humic Acid from River Water

Natural organic matter (NOM) and turbid matters (colloids, microplastics) in river water used for drinking can foul filtration membranes. This study explores the effects of permeate flux in adsorption/coagulation membrane filtration (MF) system characteristics on the treatment of water, specifically synthetic water containing turbid matter (< 70 ntu) and total organic carbon (TOC, < 8 mg/L). The experiments involved adsorption using powdered activated carbon (PAC), coagulation using a jar test with alum (< 5 mg/L) as a coagulant, and MF process using a stirred dead-cell filter. When appling 10-30 L/m2.h in permeate flux, both coagulation and MF significantly reduced turbid matter but not TOC, while PAC adsorption achieved a 70% higher reduction in TOC than coagulation and MF. The normalized permeate flux (J/Jo) of MF was reduced with increasing filtration time. Experiments with PAC adsorption and coagulation achieved a 30-50% higher permeate flux than those without PAC and coagulation. In particular, the permeate flux of MF coupled with PAC adsorption was similar to that of the coagulation/MF system. The results indicate that humic acid, PAC, and alum play a role in aggregating a particle in the water. However, residual PAC and alum after adsorption and coagulation play a role in increasing membrane fouling. Thus, driven pressure should be lower and the stirring strength higher to increase permeate flux with an appropriate PAC and coagulant dosage.