In large-scale manufacture of proteins, filter applications that utilize micro-and ultrafiltration membranes play a key role in many processing stages. The capabil ity of membrane filtration such as ultrafiltration has been well recognized and generally secured as a full-scale industrial process for many years [1,2]. The unit operation offers benefits such as low energy requirements, continuous flow, ease of operation, reproducibility, scalability, and gentleness to the product. The filtra tion system can be divided, on the basis of membrane geometry, into four com monly known modules: parallel plate, spiral, hollow-fiber, and tubular. Much of the methodology on these systems has been evaluated  and reduced to practice in the plasma fractionation industry . Previous work using mostly hollow-fiber systems has not only established and refined the technique but has also elucidated factors affecting process recovery and process efficiency. Once the membrane with the proper pore size is determined, differences in product recovery among the different filtration modules are generally not substantial. The selection of one type over another for a specific application may be dependent on other factors. For example, one system could be more favorable than the others in regard to size, cost, process time, and ease of availability. There are a large number of commercial units available; therefore we decided to limit our present investiga tion to the parallel-plate module which allows scaleup by adding modules in
parallel. This chapter will discuss our experience using parallel plates in the fol lowing areas:
Tangential flow cell separation of tissue culture fluid Tangential flow filtration and dead end filtration as applied to tissue culture
fluid Concentration of cell-free filtrate Ultrafiltration/diafiltration in downstream processing Nanofiltration
II. TANGENTIAL FLOW CELL SEPARATION OF TISSUE CULTURE FLUID
Clarification of tissue culture fluid removes DNA-containing cells and cell debris. The operation could be achieved with centrifugation which carries the potential for heat generation, aerosol formation, and labor-intensive assembly. In the pres ent study, we investigated a plate-and-frame unit for tangential flow cell separa tion. Tissue culture fluid derived from large scaled fermentors was used. The system, Sartocon II, was purchased (Sartorius Corp., Bohemia, NY). The mem brane was a 0.45-p.m microfilter with an area of 0.6 m2. Recirculation was achieved with a Watson-Marlowe 701 S/R manual control peristaltic pump (Bacon Technical Industries, Concord, MA). The module, pump, and pressure gauges were mounted on a mobile trolley, which was stationed conveniently close to the fermentors. Figure 1 depicts the equipment arrangement in the experiment.