Performance of adsorption pretreatment in mitigating humic acid fouling of ultrafiltration membrane under environmentally relevant ionic conditions

This study comprehensively investigated humic acid (HA) fouling of ultrafiltration (UF) membrane and the efficiency of adsorption pretreatment in its control under environmentally relevant ionic conditions. Two types of adsorbents, mesoporous adsorbent resin (MAR) and powdered activated carbon (PAC), were examined, and the ionic conditions investigated included ionic strength varying from 1 mM to 500 mM and different ionic composition at three ionic strength levels. HA fouling decreased at first and increased afterwards as the ionic strength rose, and the influence of ionic composition varied between different levels of ionic strength. Moreover, the efficiency of physical cleaning (imposing surface shear stress and backwashing) decreased with the elevation of ionic strength and calcium ions because of the intensification of the HA-membrane and HA-HA interactions. With the increase of ionic strength and calcium concentration, HA removal efficiency of MAR pretreatment increased more rapidly than that of PAC pretreatment. Meanwhile, due to the characteristics of the adsorbents' pore structure, MAR pretreatment efficiently removed HA that would deposit on/within the membrane while PAC pretreatment preferentially adsorbed HA that would pass through the membrane. Therefore, MAR pretreatment significantly outperformed PAC pretreatment in HA fouling control under most environmentally relevant ionic conditions.