Thermodynamic mechanism insights into the dynamic evolution of nanofiltration membrane fouling: Effect of calcium ion on organic fouling

Abstract

To better control nanofiltration (NF) membrane fouling during mine water treatment, an accurate elaboration of the fouling mechanisms of anionic polyacrylamide (APAM) coexisted with Ca2+ and fulvic acid (FA) is vital. An attractive phenomenon was observed during the membrane fouling tests: When Ca2+ and FA coexist with APAM, increasing Ca2+ concentration at high Ca2+ concentration will alleviate membrane fouling. The degree of membrane fouling is determined by the interaction of the foulant with the membrane and is closely related to the Lewis acid-base (AB) interaction energy. At the shortest separation distance, the AB interaction energy decreased from 3608 kT to −17,386 kT when the Ca2+ concentration was increased from 0 mM to 2 mM, then increased to −14,385 kT when the Ca2+ concentration was further increased to 6 mM. The change in AB interaction energy explains the dynamic evolution of the membrane fouling phenomenon. This work elucidates the effects of high Ca2+ concentrations on organic fouling and will benefit the better understanding of the efficient NF processes when multiple pollutants coexist.