Natural organic matter (NOM) fouling of low-pressure (MF and UF) membranes: Identification of foulants, fouling mechanisms, and evaluation of pretreatment.

摘要

An understanding of NOM characteristics as a foulant, the behavior of NOM components in membrane fouling, and application of appropriate pretreatment are needed to provide a basis for appropriate selection of membrane technology for drinking water treatment and optimal operating conditions in accordance with increased attention of low pressure membrane application (MF/UF).; Based on water quality profiles in terms of SUVA, XAD-8/-4 fractionation, and HPSEC-DOC/UV of bulk natural waters, significant flux decline trends were associated with a low SUVA value, a high HPI content and high molecular weight peak of SEC. The hydrophilic fraction (HPI) of natural waters, based on DOC distribution by XAD-8/-4 fractionation, contains colloidal organic matter and macromolecules, and natural waters with a high content of HPI resulted in more significant flux decline.; The depth of clean membranes displays a narrow distribution due to a homogeneous distribution of pores around the membrane surface whereas fouled membranes exhibit a wider distribution by irregular distribution of pores on the membrane surface due to pore blockage or an extensively developed surface coverage, or narrower distribution due to heavy fouling with the difference of elevation between membrane surface and the top of the foulant than a clean membrane.; Backwashing experiments also support the notion that fouling of the UF membranes is more likely affected by cake layer formation while MF membrane fouling is more likely attributed to pore blockage. In comparing flux decline with different pre-filtration methods (0.45 μm vs. 1 μm), a high flux decline was attributed to the presence of DOM (0.45 μm) formed a much denser cake/gel layer on the membrane surface and/or blocked pores.; MIEX adsorption achieved a high removal of DOC (∼82%) over a very short contact time (∼10 minutes) and a low dose (5∼10ml/L) compared to other chemicals/materials used in hybrid membrane systems, PAC and coagulants. The removal of MIEX adsorption can be depended on MW and charge density (acidity). The results of XAD-8/-4 fractionation before and after MIEX treatment demonstrated a significant removal of the transphilic (TPI) fraction and hydrophilic (HPI) fraction as well as hydrophobic (HPO) fraction. (Abstract shortened by UMI.)