Wastewater stabilisation lagoons frequently suffer from cyanobacterial blooms which can negatively impact subsequent water reclamation clue to fouling of membranes by the resultant algal organic matter (AOM). Biological activated carbon (BAC) was investigated as a pre-treatment for reducing the fouling in the microfiltration (0.1 mu m PVDF) of biologically treated secondary effluent (BTSE) to which AOM had been added. The AOM was extracted from Microcystis aentginosa in stationary phase which had been grown in either MLA growth medium or BTSE and so had different organic composition. Although the DOC concentration was the same, the feedwater containing AOM from the MLA culture led to a greater flux decline than the AOM from the BTSE culture due to its higher biopolymer content (MW >= 20,000 Da). BAC treatment substantially reduced the fouling potential of the BTSE (with and without the added AOM) due to biodegradation of biopolymers by the microorganisms and adsorption of humic substances by the activated carbon. When the BTSE was spiked with the cyanotoxin microcystin-LR, the BAC treatment gave a microcystin reduction of more than 90%. This study demonstrated the potential of BAC for mitigating the impact of AOM and removing cyanotoxin when treating cyanobacterially impacted secondary effluent using low pressure membranes. (C) 2015 Elsevier B.V. All rights reserved.