(PICTURE TAKEN FROM COLEPARMER.COM)
With the exception of mixed culture and open fermentations, there is the need for filters in most types of fermentations. The need for filtration is even more extreme and demanding in cases of highly aseptic fermentations such as in pharmaceutical fermentations.
The main purpose of these filters is either to sterilize the incoming fluids or the containment of microorganisms from being released to the surrounding environment from the fermentor. In between these functions are the maintenance of aseptic integrity of the fermentor throughout the fermentation process.
There are many types of filters used for different function of the fermentor. The common function is the exclusion of microscopic particles or microorganisms such as bacteria, spores and other solids by being excluded entrance through the pores of the filters. The physical exclusion of microbial contaminants is achieved either through size exclusion of the particles that exceed the pore size of the filters or by the adsorption of the particles on the filtering media through electrostatic interactions between the filter and the particles.
Filters are essential in the maintenance of a successful fermentation process but at the same time it got to be admitted that filters used in the fermentation process are subjected to a lot of physical and chemical stresses such as high heat, pressure and chemicals. It is also in certain cases subjected to biofouling by microorganisms.
The use of filters is subjected to its life span. Intense and extreme exposure to various stress will result in the rapid deterioration of the filter function. In such situations and as filters are expensive it is very important that the life span of the filters must be extended as long as possible. However, in the process of extending the life span of filters it is not worth the cost of fermentation failures due to the malfunctioning filters. Thus filters need to be examined periodically to avoid failed fermentation which could be disastrous especially at the production scale.
In order to prolong the life span and the filtration efficiency of the filters it is common to introduce prefilters before the filters used. These prefilters are really filters but they are more coarser and durable and will help remove significant load of particles to be filtered by the filters after the prefilters
In most filters used in the fermentation process,various types of fluids are pumped through the filters
PROBLEM OF AIR FILTERS
In discussing air filtration in any fermentation system we must see it from the perspective of air inlet and air outlet. The inlet and outlet air have different physical, chemical and microbiological characteristics and particle loads.
The objective of filtration of air in the inlet line is more the towards the prevention of entry of particles, spores and microorganisms that would interfere the fermentation process. Whereas in the case of the outlet air it is more towards the prevention or escape of microorganisms from the internal environment of the fermentor to the surrounding environment. This is more the problem of microbial containment especially in fermentations involved with the cultivation of pathogenic microorganisms
While on a small laboratory scale fermentation the use of millipore type membrane filters is suitable, in large scale fermentations sartridge or even ceramic filters are more applicable.
In membrane filters usually the filter membrane is hydrophobic material to prevent the filter from getting wet and affect the filtration process. However at times, even such filters could be affected by the formation of droplets of water on the membrane surface which interfere in the filtration efficiency.
PROBLEM OF LIQUID FILTERS
Liquid filtration are normally carried out in very sensitive filtration such as pharmaceutical fermentation. Under such conditions the fermentor are often sterilized before the media or nutrient are added . Conventional heat sterilization is not applicable as it could denature the components before the process of fermentation is carried out.
Further in pharmaceutical fermentations the scale of fermentation is small and not as big as in most industrial fermentations
Under such situations the filtration load is drastically reduced by using pure fine grade chemicals as its fermentation media. This will eliminate solids and sources of impurities to be faced by the liquid filters. Additionally the use of various units of prefilters helped in extending the efficiency and life of the filters.
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