[Comparison of the effect of solution environment on humic acid removal behavior with charged and traditional neutral ultrafiltration membranes].

Experiments were performed to evaluate the effect of solution environment (pH value, ionic strength and Ca2+) on humic acid removal and membrane fouling during filtration of humic acid through charge-modified regenerated (RC) ultrafiltration (UF) membrane and traditional unmodified neutral RC UF membrane. Results showed that: (1) the pH value changed the net charge on humic acid molecule and charged membrane through protonation effect, which further influenced the ultrafiltration behavior. When the solution pH value decreased from 7.5 to 3.5, the rejection coefficient of HA decreased from 92% to 79%, and the flux decline increased from 26% to 36% at 4 h filtration time on charged UF membrane; (23) the ionic strength influenced the ultrafiltration behavior through the change of humic acid molecule property and electrostatic shielding effect. In each solution with ionic strength of 0 mmol/L, 3 mmol/L and 100 mmol/L, the rejection coefficient decreased with the value of 92%, 87% and 48% respectively, and the flux decline increased with the value of 26%, 35% and 63% respectively at 4 h filtration time on charged membranes; (3) the effect of Ca2+ concentration on ultrafiltration behavior was due to the complementary effects of electrostatic shielding, Ca2+ bridge and the compact property of the cake layer. (4) the effect of pH value, ionic strength and Ca2+ concentration on the neutral membrane was similar to that on the charged membrane, but in different degrees. Results provide important guidance on the choice of appropriate solution environment when using charged ultrafiltration technology.