The membrane plant dimension and fouling control strategy of an integrated batch UF and NF membranes-in-series process is addressed for the simultaneous treatment of the two main effluents generated in olive mills operating with the two-phase technology, in particular wastewater derived from the washing of the olives (OWW) and from the olive oil washing during the vertical centrifugation (OOW). Beforehand, the raw effluent, that is, 1:1 v/v mixture of OWW and OOW, called OWMW2, was pretreated by pH-temperature flocculation stand-alone or followed by photocatalysis with TiO2 nanoparticles under UV irradiation. The proposed model is able to predict the permeate flux performance of the selected membranes at a given time as a function of the applied pressure and organic matter load of the feedstock accurately. Moreover, working upon threshold conditions provides significant and stable fluxes, 15.5 Lh(-1)m(-2) on the UF membrane and 22.2 Lh(-1)m(-2) on the NF one, minor fouling build up (28.6-33.3% reduction) as well as required membrane area, 170.3 and 61 m(2), respectively. Finally, the treatment line just comprising OF preceded by pH-T flocculation and UV/TiO2 photocatalysis provides an effluent compatible for irrigation and permits the minimum membrane plant dimension (only 6 total modules). (C) 2014 Elsevier B.V. All rights reserved.