Ultrafiltration and microfiltration can be highly efficient methods for secondary-effluent polishing. Nevertheless, their use is limited by their main operational problem - colloidal fouling. In this work colloidal fouling mitigation by pretreatment of iron-based electrocoagulation (electroflocculation), prior to secondary effluents microfiltration and ultrafiltration, was investigated. Without electrocoagulation pretreatment, severe fouling was observed. The flux reduction from fouling was higher in microfiltration than ultrafiltration. This observation demonstrated the importance of the ratio between clean membrane resistance and additional fouling resistance, rather than only the latter, with regard to fouling effect on flux. Electrocoagulation pretreatment significantly mitigated fouling (up to 36-fold reduction in filtration time) for all three types of secondary effluent examined. In general, fouling mitigation was much higher in microfiltration than in ultrafiltration, also attributed to the ratio between clean membrane resistance and the additional fouling resistance. Comparing 10 KDa ultrafiltration, 100 KDa ultrafiltration and microfiltration of 0.75 L of effluent without electrocoagulation pretreatment, the shortest filtration time was observed with the 100 KDa ultrafiltration membrane. However, with the electrocoagulation pretreatment, the microfiltration filtration time was much shorter than that with the ultrafiltration membranes. (C) 2011 Elsevier B.V. All rights reserved.