Algal organic matter (AOM) released from Microcystis aeruginosa has high potential to cause fouling of water treatment membranes. The role of AOM components in the fouling of a commercial tubular ceramic microfiltration (MF) membrane (ZrO2-TiO2, 0.1 mu m) was investigated. The organic matter extracted from the three operationally-defined fouling layers (i.e., outer, middle and inner layer detached from the membrane using cross-flow flush, backwash and chemical cleaning, respectively) was characterised to gain an understanding of the fouling mechanism. The majority of the flux decline in the MF of the AOM solution was attributed to the large amount of organic matter (51% of total DOC of Iced, primarily very high molecular weight (MW) hydrophobic molecules) deposited on the ceramic membrane surface to form a thick and dense outer layer. The middle layer contained a very small amount of organics (3%), mainly very high MW hydrophilic molecules, and contributed very little to the flux decline. The inner layer (22% of total DOC), which was responsible for the hydraulically irreversible fouling, was dominated by the high and low MW hydrophilic compounds. These molecules reached the membrane inner pores due to their hydrophilic nature, leading to pore restriction by adsorptive fouling. (c) 2013 Elsevier B.V. All rights reserved