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Downloaded by UNIV OF MISSOURI COLUMBIA on October 7, 2013 | http://pubs.acs.org Publication Date: January 8, 1985 | doi: 10.1021/bk-1985-0271.ch003
Practical Aspects of Tangential Flow Filtration in Cell Separations JOSEPH Z A H K A and T I M O T H Y J . L E A H Y Millipore Corporation, Bedford, M A 01730
Tangential flow filtration is an effective method for performing the separation of cells from a suspending liquid. Cell separation is the unit process of concentrating biomass that has grown during a fermentation. It typically represents the first step in the extraction and purification of product. There are two advantages of using tangential flow filtration over other unit processes to separate cells and products from fermentors. These are the ability: (l) to work in a closed system without generating aerosols; and (2) to effect a more complete removal of the cells from the fermentor effluent. In addition, Tangential Flow Filtration allows for convenient cell washing after concentration in the same system. The theory of tangential flow Filtration as it applies to cell separations is discussed. Major emphasis, however, is placed on presenting the relationship of experimental results to theoretical performance. Topics highlighted are: flux decay with time, effects of operating pressures and flow, membrane fouling, prefiltration requirements and filter geometries . In most fermentation processes, the fermentation is only the first step in the long process train which includes product formation, recovery, and purification. Commonly the step following fermentation is the separation of the cells from the soluble components in the growth medium. This paper discusses an alternative technique for achieving such a solid/liquid separation. In the case of extracellular products, emphasis is on the treatment of the product-containing broth. Cells, in this instance, are by-products of the fermentation. The processing of the cells is only important in terms of the potential loss of product with the discarded cells. The primary concern is the clarification of soluble product to increase the efficiency of such operations as product isolation and modification. Intracellular products, on the 0097-6156/ 85/0271 -0051 $06.00/0 © 1985 American Chemical Society In Purification of Fermentation Products; LeRoith, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
Downloaded by UNIV OF MISSOURI COLUMBIA on October 7, 2013 | http://pubs.acs.org Publication Date: January 8, 1985 | doi: 10.1021/bk-1985-0271.ch003
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PURIFICATION OF FERMENTATION PRODUCTS
o t h e r hand, r e q u i r e t h e c o n c e n t r a t i o n o f p r o d u c t - c o n t a i n i n g c e l l s ; t h e suspending l i q u i d i s d i s c a r d e d . T y p i c a l l y , t h e c o n c e n t r a t e d c e l l mass i s t h e n p r o c e s s e d t o f a c i l i t a t e r e l e a s e o f t h e p r o d u c t . The d e s i r e d c o n c e n t r a t i o n o f c e l l s i s o f t e n a f u n c t i o n o f how t h e c e l l s w i l l be p r o c e s s e d . F o r example, c e l l r u p t u r e by s o n i c a t i o n i s most e f f e c t i v e i n a narrow c e l l c o n c e n t r a t i o n range. S e v e r a l t e c h n i q u e s a r e used t o s e p a r a t e c e l l s from t h e ferment a t i o n b r o t h . The most common ones used i n l a r g e s c a l e f e r m e n t a t i o n s a r e continuous f l o w c e n t r i f u g a t i o n , f i l t e r p r e s s e s and r o t a r y drum vacuum f i l t r a t i o n . T a n g e n t i a l ( o r c r o s s ) f l o w f i l t r a t i o n (TFF) has been proposed as a f o u r t h a l t e r n a t i v e {2). I t i s w i d e l y used t o p r o c e s s s m a l l f e r m e n t a t i o n b a t c h e s (
