Nanocomposite membranes (NCMs) of sodium alginate/poly(vinyl pyrrolidone) blend polymers incorporated with varying concentrations of phosphotungstic acid (H3PW12O40) (PWA) nanoparticles have been prepared and used in ethanol dehydration by the pervaporation (PV) technique. Effects of filler concentration, temperature and feed water composition have been investigated to understand the PV performance of the membranes in terms of separation factor and flux. Surface morphology/energy, free volume, collective and complex range of interactions between the permeants and membranes as well as membrane swelling were studied. Arrhenius activation parameters for diffusion and permeation have been estimated. Membranes were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and environmental emission scanning electron microscopy (ESEM). Size of the PWA nanoparticles was determined by a particle size analyzer. Surface free energies calculated from contact angles as well as free volume and fractional free volume parameters obtained from positron annihilation lifetime spectroscopy (PALS) have been used to understand the membrane transport phenomenon in terms of membrane-permeate interactions. Published by Elsevier B.V.