COLLOIDAL AND NON-COLLOIDAL NOM FOULING OF UF MEMBRANES

Membrane fouling of ultrafiltration membranes by natural organic matter (NOM) has become an important concern in advanced water treatment applications. Surface water, after pre-filtration with a 0.45μm filter, was separated into colloidal and non-colloidal NOM through dialysis with two types of dialysate (deionized water and a synthetic surface water solution). Filtration experiments were conducted at constant flux (138.5 L/m.hr) running 10 filtration cycles of 30min, followed by immediate backwashing with permeate water. Results of dialysis showed that circa 33-40 % of the total DOC (~17mg/L) of pre-filtered surface water was colloidal NOM, in the size range 1.3nm-0.45μm; and ca. 60-67 % was non-colloidal NOM (<1.3nm). Colloidal NOM was composed mainly of polysaccharides and humics. However, the inorganic colloidal concentration was assumed to be below 0.5mg/L (total silica content measured by ICP). The non-colloidal NOM comprised humics, building blocks, neutral amphiphilics and low molecular weight acids. Results of UF filtration tests of pre-filtered 0.45μm and colloidal NOM revealed that colloidal NOM was responsible for the major increase in transmembrane pressure (TMP) during ultrafiltration. LC-OCD analyses identified polysaccharides as foulants that were backwashable. UF filtration test of non-colloidal NOM with a DOC concentration of 5mg/L, also resulted in an increase in TMP over time. Simulations of surface water fouling were made using the normalized non-colloidal NOM (~11mg/L) and colloidal NOM (~6mg/L) fouling results, and the simulated increase in TMP matched the surface water quite well