ABSTRACT
A membrane is a selective barrier that allows some species to permeate the barrier while retaining others. In food and biotechnology applications, the goal is typically to concentrate, recover, or remove particles, macromolecules, or low-molecular-weight solutes from an aqueous feed stream. Membrane filtration can be categorized into four major pressure-driven membrane processes: microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and direct osmotic concentration where chemical potential is the driving force. There are two modes of membrane operation: dead-end and crossflow. The original mode of operation for membrane processes was dead-end, where the feed stream is normal to the membrane. The applied pressure across the membrane causes the liquid portion of the feed to permeate. In crossflow operation, the feed stream flows tangentially across the surface of the membrane. Membrane processes have been used industrially for half a century and the majority of physical phenomena connected with the processes are understood.
