Role of Humic Substances on the Removal of Haloacetic Acids from Swimming Pool Water by Nanofiltration

Abstract

Given the ubiquitous presence of humic substances (HS) in swimming pool waters (SPWs) and its potential impact on haloacetic acids (HAAs) removal, this study made a systematic investigation on their potential interaction during nanofiltration (NF) process. The water flux decreased by 26.6% and 11.1% for NF90 and NF270, respectively, after 24 h exposure to 30 mg/L HS, whereas the rejections of NaCl increased by 8.9% and 14.6%, HAAs by 6.9% and 20.5%, and boron by 2.6% and 7.1%. Fulvic acid features the smallest particle size and the strongest hydrophobicity of all HS fractions tested, therefore showing the highest potential of depositing on the surfaces and/or into the pore channels of membranes with loose structures, and serving as the main component of HS responsible for the variations of membrane performance. The decreased hydrophilicity and pore size of membrane surface were jointly responsible for the reduced water flux. The enhanced size exclusion effect either competed against the weakened charge repulsion effect, which happened for NF270, or cooperated with the strengthened charge repulsion effect, which happened for NF90, leading to overall increased rejections of charged HAA and NaCl. For neutral compound boron, the reduced pore size was likely the main factor leading to its increased rejection. By exploring underlying interaction mechanism among trace contaminants, HS, and membranes, this study provides novel theoretical insights for the assessment of NF process.

Keywords: nanofiltration membrane, haloacetic acids, humic substances, swimming pool water, rejection mechanism