ABSTRACT
Pressure-driven membrane processes are being increasingly integrated into existing reaction, isolation, and recovery schemes for the biological production of valuable molecules. These processes can be distinguished by their increasing volumetric permeation rates and have been called reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. They are commonly used to retain all ions, bivalent from univalent ions, macromolecules, and suspended colloids and particles, respectively. Membrane systems are being used for both upstream (involving the bioreactor) and downstream (involving product recovery) processing, taking advantage of their permselectivity, high surface area per unit volume, and their potential for controlling the level of contact and/or mixing between two phases. These processes are now commonly being used to concentrate proteins, exchange buffers, clarify suspensions for cell harvesting, and sterile filter liquids to remove viruses and bacteria [1].
