A series of pilot-scale filtration experiments were performed systematically under various operating conditions to investigate the fouling behavior of ultrafiltration (UF) membranes to treat tertiary wastewater for resuse. All experiments were conducted using a pilot system, which consisted of six inside-out capillary polyether sulfone UF membrane modules (molecular-weight cutoff = 150,000 Da), arranged in parallel configuration. The pilot unit was operated in dead-end filtration mode and the membranes were frequently backwashed with chlorinated water. Results of this research clearly indicated that the productivity of the UF membranes, measured by the specific water flux (K-w), declined much faster as operating flux increased. This observation was attributed to enhanced solid and organic loading to the membrane surface at higher operating fluxes. Furthermore, the analysis of K-w variation against filtrate volume showed larger productivity reduction per foulant mass loading during operation at high flux rates, suggesting the formation of more compact cake layers which were not easily removed during backwashing. Pilot study results also demonstrated that increasing backwashing with chlorine addition significantly improved membrane productivity, primarily due to enhanced foulant removal by organic oxidation and biogrowth control. In addition, flux enhancement per backwashing volume increased with decreasing time between backwashing events. Ferric chloride pretreatment also markedly enhanced membrane productivity by increasing particle floc size, which led to decreased pore plugging, reduced cake layer resistance, and enhanced backwashing efficiency.