Multiscale modelling of protein fouling in ultrafiltration

Fouling can be considered as the major drawback of membrane operations. Many different studies dealing with membrane fouling as determined by colloids or proteins were carried out. As far as the theoretical analyses are concerned, most of the available models are based on a set of transport equations written with reference to micro- or macro- space-time scale. In these models, the used physical-chemical properties of the solutes were seldom evaluated by ab-initio calculations; rather, they were obtained by fitting available experimental data. Although, the characteristic molecular features could be evaluated by atomistic computational approaches, up to date, literature exhibits a significant lack of information concerning the use of proper computational methodologies in conjunction with the micro- and macro- theoretical models. In addition, theoretical works combining the sub-nano scale properties with a set of equations typical of larger space-time scale cannot be found. The present study is intended to fill such a gap. With reference to the Bovine Serum Albumin (BSA), some sub-nano and nano quantities, namely the atomic charges and the molecular surface, respectively, have been preliminarily calculated by accurate quantum and molecular approaches. These quantities have been then exploited to define the input parameter (zeta potential) necessary to formulate, on a micro-scale, a balance of the forces acting on each BSA particle. In this way, the additional resistance due to membrane fouling has been determined. Finally, a transport model describing the unsteady-state transfer of both momentum and mass has been formulated so as to predict, on the basis of the results of the above calculations, the permeate flux decay occurring during BSA ultrafiltration.