Viruses filtration processes

Bearing in mind the previous discussion, there are basic official or unofficial sterilization procedures, all of which are overkills, designed to kill or get rid of the very last and most resistant organism in the system being treated. Filtration is, of course, designed to physically remove all bacteria present. It does not usually remove viruses or mycoplasms and, as noted above, some of the assumptions made during a filtration process need to be very carefully evaluated by the operator. 

An understanding of the properties and behavior of soil systems is essential if we are to understand and predict the behavior of contaminant species released into and on soils. A variety of physical, geochemical, and biological processes operate in soils. Soils can physically filter out particulate contaminants, including bacteria and viruses. Filtration is most effective in A, E, and B horizons. 

For the clearance of enveloped and non-enveloped viruses, today s requirements ask for an orthogonal combination of methods that are based on the different physical principles of removal and inactivation, and are complementary to each other [165]. Virus filtration and solvent/de-tergent treatment are state of the art for removal and inactivation [166, 167]. Partitioning steps are considered less robust, as they are somewhat influenced by the actual process conditions. In any case, scaled-down models must be designed... 

Whenever possible, products should be sterilized in the final container, preferably by heat sterilization. Certain solutions and liquids that cannot be sterilized in the final container can be filtered through a sterile fitter of nominal pore size 0.22pm (or less), or with at least equivalent microorganism-retaining properties, into a previously sterilized container. Such filters can remove bacteria and moulds, but not all viruses or mycoplasmas. Consideration should be given to complementing the filtration process with some degree of heat treatment. 

The DLVO-Lifshitz theory should be regarded as a principal mechanism governing the adsorption of viruses on various inorganic surfaces. This finding has direct application to problems concerning transport of viruses in aquatic systems and soils. It is possible that it could lead to the design and optimization of adsorption-filtration processes for removing viruses and other particulates from contaminated water. 

In summary, it is worth noting that the selection of an inactivation procedure will depend on the type/complexity of the material to be obtained (for instance, enveloped viruses are more difficult to inactivate than those non enveloped), as well as its compatibility with other processing steps. If the final product is not consumed during the processing steps, spontaneous inactivation due to mechanical stress or other phenomena could also be observed (for example, filtration processes involving change of phase - liquid to solid - may be traumatic for the vims particle). In this situation, an individual inactivation step would not be necessary, resulting in cost reductions. 

In this treatment process, unit operations such as chemical coagulation, flocculation, and sedimentation followed by filtration, activated carbon, ion exchange, and reverse osmosis are employed to remove significant amounts of nitrogen, phosphorus, heavy metals, organic matters, bacteria, and viruses present in wastewater.2 It is always the last process step in the wastewater treatment plant that finally renders the treated wastewater reusable and disposable into the environment without any adverse effect (Figure 22.1). 

The Producing System. The questions of particular concern here are the nature of the system used to manufacture the desired substance, and the precision with which it is controlled. If the system consists of prokaryotic cells, then how well-defined is their provenance and how is their consistency demonstrated If mammalian cells are employed, their lineage must be considered. In both instances, it is important to ensure that extraneous virus, infections, DNA and less well-defined factors such as slow viruses are excluded by the origins and history of the producer strain, or because the physical (e.g., filtration) or chemical (pH, solvents, affinity separation) nature of the production process can be relied upon to exclude passage of an infectious agent. 

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