Effect of organic molecular weight distribution on membrane fouling in an ultrafiltration system with ozone oxidation from the perspective of interaction energy

Abstract

Herein, the effect of molecular weight (MW) distribution on ultrafiltration (UF) membrane fouling was investigated using humic acids, and the mechanism was explored by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. The short-range acid–base (AB) interaction energy was found dominant, followed by van der Waals (LW) energy, whereas electrostatic (EL) interaction energy was negligible. Organic colloid fractions with MW >100 kDa contributed mainly to transmembrane pressure (TMP) increase, whereas the fractions with MW <1 kDa had less influence on membrane fouling due to their strong hydrophilicity, oleophobicity, and polarity. However, no relationship was observed between MW size and its contribution to the TMP increase; this indicated that the total interaction energy between organic colloids and membrane material was a better predictor of membrane fouling than other characteristics of organics. Water from Yangtze River was ozonized prior to UF for fouling control. With the addition of ozone, the proportion of the organic fraction with MW <1 kDa increased, causing decreased absolute value of AB interaction energy between colloid and membrane. The inflection point of interaction energy variation was attained at a 0.8 mg L⁻¹ ozone dosage, corresponding to a slow increase in TMP with the increasing ozone dosage, whereas the least influent organic matter was attained at a 1.2 mg L⁻¹ ozone dosage. This indicated that it was more feasible to optimize ozone dosage according to the interaction energy rather than according to the concentration of the influent organic matter.