Microfiltration membranes, cross-flow transport mechanisms and fouling studies

Abstract

Microfiltration membranes have been used, in dead-end mode, in gas purification, wine clarification and medical-product sterilization applications. The same types of membrane have been tested even in the cross-flow mode of operation (CFMF), but with less success. Especially a great effort has been made to apply CFMF in the downstream processing of biotechnological applications, like cell harvesting and cell-debris removal. It is recognized that a great deal remains to be done in developing membranes suitable for the cross-flow mode of operation, in such a way that biofouling, seeming to be the main reason hindering the progress of the method, will be minimized. In this paper we will present a literature review we have carried out about the state of the art of microfiltration membranes; their types, methods of preparation and characterization, commercial and potential applications, and theoretical models. Understanding the mechanisms of the transport as well as the phenomena leading to fouling seems to be another prerequisite for the further development of cross-flow microfiltration. This need addresses to the necessity of carrying out studies at a basic level, using well characterized membranes and testing substances. In this paper, we will also present and discuss results, which we have until now obtained, about the performance of selected commercial microfiltration membranes in terms of flux decline and retention properties under varying experimental conditions of transmembrane pressure and circulation velocity. The feed is a model dispersion containing two kind of components: typical biopolymer like BSA protein and silica particles of a size 600-800 nm. These particles were used in order to simulate microorganism, as providing, the size apart, the possibility of varying surface modification. Besides flux decline and pure water flux recovery data, electron microscopy is used in order to study the prevailing fouling mechanisms.