Electrodialysis (ED) is one of a number of attractive options in the desalination of secondary effluent, but membrane fouling is still an issue that needs to be resolved. This study investigated potential foulants and the fouling control of ED during desalination. Cation and anion exchange membranes were found to be fouled with different components in secondary effluent. Protein and calcium ion were the most responsible for the fouling of anion and cation exchange membranes, respectively. Pretreatment using iron oxide particles (IOPs) as an adsorbent contributed greatly to the reduction of irreversible fouling caused by organic matter present in the secondary effluent. IOP pretreatment also improved the quality of the treated water significantly.