The mechanisms by which Pseudonionas putidu causes fouling on a microfiltration membrane have been studied. For an initial P. putidu concentration of 0.77 g/L (5.1 x 10(8) cfu/mL) stirred dead-end tests indicated that approximately 70% of the permeability was lost during the first minute of filtration and only 15% more was lost during the following 24 min. SEM observations showed the presence of aggregates within the most external part of the membrane pores, partially blocking these pores and leading to more or less regular surface deposits and consequently, an intermediate blocking model was proposed and successfully fitted. The analysis of fouling resistance-in-series indicated that the selection of a high TMP during the microfiltration of P. putida had no effect on the final permeate flux but provoked an increase in external in comparison to internal fouling. On the other hand, the selection of a lower TMP led to a low rate of accumulation of P. putida on the membrane, reducing the total membrane resistance and allowing a deeper penetration of the bacteria into the pore. Studies on the cleanability of the membrane using sonication showed how this technique was more effective when membrane was fouled at higher TMP, achieving permeability recoveries of around 80% in the best cases. (C) 2014 Elsevier B.V. All rights reserved.