Culture media disposal methods

The most common collection methods rely on impaction, the same process as described in Section 5.5 for nonbioaerosols. Slit impactors impact particles directly onto a culture medium. For bacteria and fungal spores, the culture medium, called agar, is a semisolid material containing water and nutrients that foster the growth of the viable particles that are collected. For viruses, cell or tissue culture media are used. Typically, the agar fills a 100-mm or 150-mm disposable petri dish, called a culture plate, that is slowly rotated under the slit to provide a history of bioaerosol concentration. Rotating slit impactors have flow rates of 28-50 L/min and cutoff diameters of about 0.5 pm. 

The most important technique for perfusion culture methods is to separate the concentrated cells and conditioned medium from the suspended culture broth. As noted above, the separation methods chiefly used are filtration with tubular and flat membranes as well as ceramic macroporous filters. These membrane reactors can be employed for both anchorage-dependent and suspension growing cells. Static maintenance type systems are commercially available for disposable reactors, and small size unit reactors from 80 ml to 1 liter are used for continuous production of monoclonal antibodies with hybridoma cells. The maintainable cell densities are about 10 -10 cells/ ml which is essentially mouse ascites level. However, in these systems, the cell numbers cannot be counted directly because the cells adhere to membranes or hollow fibers. Therefore, the measurement of cell density must use indirect methods. Such indirect methods include the assaying of the quantities of glucose consumption and the accumulation of lactate. The parameters of scale-up have not yet been established for these static methods. 

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