Fouling mechanisms in nanofiltration membranes used for surface water treatment
In this study, the influence of calcium concentration on flux decline and fouling mechanisms in NF90 membrane used for filtration of constant high DOC in synthetic water was observed and analyzed. The synthetic water was composed of sodium alginate (17 mg/L as DOC) and calcium chloride (50, 200, and 350 mg/L as CaCO3). Several fouling models, resistance-in-series model and Atomic Force Microscopy (AFM) were used to analyze the flux decline curves, hydraulic resistances due to various fouling mechanisms and membrane surface morphology, respectively. Results of fouling experiments identified that reversibility of fouling increased with increasing calcium concentration due to increase in cohesive forces between calcium and alginate molecules. However, the flux decline and total hydraulic resistance was highly dependent on the concentration of both calcium and alginate in feed water forming Ca-alginate complexes. Also, at high calcium concentrations, gel layer formation becomes the dominant fouling mechanism offering maximum hydraulic resistance.
Nanofiltration, Surface water, DOC, Hardness, Ca-Alginate complexation, Fouling mechanisms, Gel layer