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Bioprocessing refers to the production of biologically active therapeutic and diagnostic proteins that are expressed by mammalian or bacterial cells. A series of unit operations isolates and purifies the products of fermentation. A schematic drawing showing the various unit operations involved in a typical bioprocessing activity is given in Figure 4.28 .
In most cell culture and fermentation processes, air and liquid nutrient feed streams are clarified and sterile filtered to eliminate particulate and microbiological contamination of the fermenter. Serum and culture media feeds are sterile filtered
with membrane cartridges to remove contaminating micro-organisms. Hydrophobic filters provide sterile filtration of inlet fermentation air.
Cell separation in the downstream processing stage recovers the product from the fermentation broth. Initial clarification steps separate the biomass from the desired product in solution. Depth filtration can provide effective, economical cell separation for removing cells, cell debris, endotoxin and contaminating host cell DNA. Cartridge systems can offer advantages over competitive technologies such as plate and frame filter presses.
Concentration and purification in downstream processing is dependent on the nature of the product to be recovered. Chromatographic columns should be protected with prefilters, and chromatography buffers should be membrane filtered.
Sterilizing grade membrane filters provide sterility of the final parenteral product just prior to filling operations. Prefilters provide high contaminant-holding capacity while protecting downstream filters. Hydrophobic tank vent cartridges maintain a sterile environment in product holding tanks.
Chemicals and solvents used in biological manufacturing include alcohol, acetone, methylene chloride and numerous other aggressive materials. Filters required for chemical and solvent filtration include coarse prefilters, fine prefilters, membrane prefilters, final sterile filters and tank vent filters.
Air and gas systems requiring filtration include sterile filtration of inlet fermenter air, pressure sources for tank to tank transfers and cooling media for holding tanks after sterilization. For sterile manufacturing processes, gases coming into contact with the product are always sterile filtered. Typically, 0.2m filters provide reliable sterile filtration of air and gas in bioprocess manufacturing environments. Biological treatment of wastewater streams range from municipal and industrial to landfill run-off wastewater filtration. Biological treatment reduces and decomposes water pollutants into nitrogen, carbon dioxide and water. Disc and decanter centrifuges and sludge separators are normally used to separate biomass from the reactor outlet stream. Tubular and multi-tubular membranes can also offer advantages in complete biomass rejection.
The effective removal of grease and fats, and the frequent occurrence of a poor settling biological sludge, have often been problems for the dairy industry. A process for dealing with the latter problem when treating wastewater by the activated
sludge process has been developed. It is still an activated sludge process, but differs from the conventional system by employing dissolved air flotation as the liquidsolid separation system for both primary and secondary stages.