COLLOIDAL AND NON-COLLOIDAL NOM FOULING OF UF MEMBRANES Maria D. Kennedy a , Victor Yangali-Quintanilla a , Bas G.J. Heijman b,c , Gary Amy a,c and Jan C. Schippers a a UNESCO-IHE Institute for Water Education, PO Box 3015, 2601 DA Delft, The Netherlands b Kiwa Water Research, Groningenhaven 7, 3430 BB Nieuwegein, The Netherlands c Delft University of Technology, The Netherlands Abstract 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/m².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. Keywords: ultrafiltration, NOM, fouling, colloidal, cleaning 1. Introduction Advanced membrane water treatment of surface water containing Natural Organic Matter (NOM) faces as main problem fouling of membranes in micorfiltration and ultrafiltration applications. The study of membrane fouling by natural organic matter has kept the scientific attention since the beginning of the 90s. However, even at the present time not all contributions of fouling by NOM are well understood. Different studies have demonstrated that NOM, composed of humic as well as non-humic substances, in natural water is a membrane foulant (Howe and Clark, 2002; Lin et al., 2000, 2001; Carrol et al., 2000; Yuan and Zydney, 1999a, 2000; Cho et al. 1999). Nevertheless the complexity of NOM has not allowed identification of the fraction or part of NOM that exactly causes membrane fouling. So far, both the hydrophobic