03-10-2012, 05:05 PM
Filtration Process used in Fermentation Industries
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Filtration: INTRODUCTION
Filtration is a mechanical or physical operation by which solid particles are separated from a fluid-solid mixture by forcing the fluid through a filter medium or filter cloth.
It is one of the most common processes used at all scales of operation to separate suspended particles from a liquid or gas through a porous substance called “filter”.
Example(s):Fine particles, Microbes, Polymer molecules, Mist, Aerosol, etc.
FILTRATIONS DEPENDS UPON:
Viscosity and density of the fluid: Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Unit: Pa-s (N·m−2·s)
The nature of the solid particles, particularly their size and shape distribution
Aseptic conditions: Aseptic conditions is essential to avoid undue contamination and degradation of labile (becoming inactive when subjected to heat or radiation) products.
Cake Filtration
A filter cake is formed by the substances that are retained on a filter. The filter cake grows in the course of filtration, becomes "thicker" as particulate matter is being retained.
Due to the deposition of solids, the thickness of filter cake is increased and so it make a constraint to further filtration.
When filter cake is deposited heavily, it is removed from the filter by back flushing.
This is essential to avoid disruption because when the flow resistance of the filter cake gets too high, then too little of the mixture is filtered through the filter cake and the filter plugs.
Filter Aid
“Filter Aids” is a group of inert materials that can be used in filtration pretreatment.
Filter aids are used when filtering bacteria or other fine or gelatinous substances which prove slow to filter or particularly block a filter.
Filter aids such as diatomaceous earth have found widespread use in the fermentation industry to improve the efficiency of filtration.
factors of filtration
Filtration efficiency: Filtration efficiency is the ratio of the upstream suspended solids concentration compared to the downstream suspended solid concentration which has passed through the filter.
Flow rate: The flow rate is the volume or weight of the fluid which has passed through the filter at the unit area at the unit time.
Filtration life: The life of the filter is the time it takes until the filter becomes clogged with particles and other suspended matter so that it can no longer function at a certain flow volume.
Filter media
There are three main types of filter media employed in the filtration process:
Surface filtration: This filtration mechanism mainly retains particulate matter from the fluid on the surface of the filter.
Depth filtration: This filtration mechanism retains particulate matter not only on the surface of the filter but also at the inside of the filter.
Cake filtration: By this filtration mechanism, the cake accumulated on the surface of the filter is itself used as a filter.