A comparative study of microfiltration and ultrafiltration of activated sludge-lagoon effluent T. Nguyen, L. Fan, F.A. Roddick*, J.L. Harris School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476V, Melbourne, Australia 3001 email: felicity.roddick@rmit.edu.au Received 30 June 2007; revised accepted 7 October 2007 Abstract Melbourne’s Western Treatment Plant is unusual in that it employs a sequential activated sludge-lagoon (AS-lagoon) system to treat municipal wastewater. Reuse of the treated water is limited for some applications due to salt content, and membrane pre-treatment prior to reverse osmosis is under consideration. The use of micro- filtration (MF) and ultrafiltration (UF) for improving the quality of water prior to reverse osmosis was investi- gated. The organic components of the feed water (AS-lagoon effluent), permeates and foulant layers were characterised using three-dimensional excitation-emission-matrix (EEM) spectroscopy, attenuated total reflec- tion-Fourier transform infrared spectroscopy (ATR-FTIR), dissolved organic carbon (DOC) determination, size exclusion chromatography (SEC) and ultraviolet (UV) absorbance. DOC removal was 28% for UF and 2% for MF. MF removed mostly non-UV absorbing molecules of AMW 40–70 kDa, whereas UF removed molecules in this size range, a high proportion of which were UV-absorbing, as well as some organic compounds in the 3–8 kDa range, some of which were UV-absorbing. The organic compounds removed by UF had hydrophobic, hydrophilic and transphilic character, and were shown to comprise humic-like matter, soluble microbial products and protein-like extracellular matter. Fulvic-like matter largely passed through the UF membrane. ATR-FTIR analysis of fouled MF and UF membranes showed that polysaccharides, polysaccharide-like compounds and pro- teins were the prominent components in the fouling layer. Keywords: Activated sludge; Lagoon; Microfiltration; Ultrafiltration; Organic fouling; Organic matter *Corresponding author. Presented at the International Membrane Science and Technology Conference, IMSTEC 07, 5–9 November 2007, Sydney, Australia 0011-9164/09/$– See front matter # 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.0000.00.000 Desalination 236 (2009) 208–215