Rejection of organic matters by RO/NF membrane

Abstract

Isolated organics fractions were obtained by column chromatography fractionation process from a secondary effluent. Results from the preliminary study revealed that hydrophobicity, charges of solute molecules and membrane materials, and interactions among organic fractions were the three major factors. Two adsorption models were modified and applied to describe the rate of organics adsorption. In continuous-flow experiments using neutral fractions, the membrane rejection varied with the significance of adsorption (indicated by i??). Rejections of acid/base fractions were found to be among the worst at pH 4, better at pH 7 and the best at pH 9, suggested a combined effect of hydrophobicity of the organics fraction, variation of membrane charge and tightness, and the extent of dissociation of organics fractions. Ionic strength showed less significant effect than pH. With the presence of acid/neutral fractions, the rejections for target base fractions were improved by 9-35%, due to neutralization reactions or frictional coupling.