Microfiltration (MF) and ultrafiltration (UF) membranes, widely used for pre-treatment of reverse osmosis (RO) processes in wastewater recovery, are nonetheless subject to fouling which considerably reduces the process throughput. In this study, reversible and irreversible fouling of a pilot MF process treating secondary wastewater effluent were measured over an 18 month period and data pertaining to common feedwater quality determinants collated. Fouling rates were quantified as a function of the key operating parameters (flux and backwash interval) and water quality determinants (turbidity and temperature). Fouling was found to increase exponentially with turbidity. Irreversible fouling was promoted only by increased flux and backwash interval, while reversible fouling rate depended on flux, turbidity and temperature. Some residual fouling, following the same exponential or power relationship with the flux as that manifested at different turbidities, was observed at zero turbidity. Operation above the so-called critical flux was sustained through appropriate backflushing. It was concluded that the sustainable flux concept was a more appropriate basis for process control and optimisation than critical flux, since the latter does not take into account process economics. (C) 2012 Elsevier B.V. All rights reserved.