ABSTRACT
Several mathematical models are available in the literature that attempt to describe the mechanism of transport through membranes. Although the op erating techniques of microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) are similar, the latter two are almost certainly not separation merely by size alone. Microfiltration and ultrafiltration, on the other hand, due to their relatively large pores, have most frequently been vi sualized as sieve filtration. The approach taken in this chapter is to briefly describe typical models and possible mechanisms of flow through the mem brane and to illustrate how several important operating variables can affect flux. Only cross-flow operations are considered: dead-end filtration, especially when used with large (>1 /z) particles and/or with MF membranes, can ad equately be described by well-known cake-filtration models and are not dis cussed here.
