Clarification and Filtration PDF Notes

 Clarification and Filtration


It is defined as the removal of solids in very less concentration and filtrate is the required product.


• Filtration is defined as the removal of solid particles or suspended matter from the liquid or gas by passing it through a porous medium which retains the solid particles but allows the fluid to pass is known as Filtration.


• Filtration may be defined as the separation of intracellular liquid from solid by the use of pressure on semi permeable membrane.

• The pores medium used to retain the solids is known as filter media. The solids which get collected on the filter is called filter cake. The spear liquid passing through the filter is known as filterate.

Theory of filtration.

• The theory of integration give an idea about the factor influence the rate of interaction through the filtering media rather than the mechanism by which the particles in retained.

• The factor affecting the rate of filtration where is studies by a scientist name darey and he expressed it in he from of an equation which is known as “Darcy’s Low” The equation is

This is also known as Darcy’s Law where

V = Volume of filtrate

t = Time of filtrations

dV/dt= Rate of change of volume with time or flow rate with time k = Constants for the filter medium and filter cake

A = Area of filter medium

ΔP = Pressure difference above the filter medium and below the filter medium

µ = Viscosity of the filtrate

l = Thickness of the filter cake & filter medium.

The above equation makes it clear that the rate of filtration depend not only on the nature of liquid undergoing filtration but also on so many other factors.

Factor affecting the rate of filtration:

1. Pressure: – The rate of filtration is directly proportional to the pressure difference between the filter medium and filter cake.

2. Viscosity: The rate of filtration is inversely proportional to the viscosity of the liquid undergoing Filtration.

3. Surface area of filter medium: The rate of filtration is directly proportional to the surface area of filter media.

4. Temperature liquid to filtered

5. Particle size

6. Pore size of filter media

7. Thickness of cake

8. Nature of solid material.

Filter Medium:-

The surface of medium used for filtration for the separation the solid particles from a liquid or gas is known as filter medium.

Ideal properties of filter media

      It should not absorb amount of the ingredients of the product to be filtered.

      It should be chemically inert.

      It should good power to retain the solid particles.

      It should give a free passage to the liquid.

Some Filter media used in Laboratories:

1. Filter Paper: It is used as filter medium For small scale filtration. They are available in different size of pores like Coarse, fine.

2. Filter cloth: cotton clothes & synthetic clothes are commonly used as filter medium for largest scale filtrations. Synthetic clothes are preferred over cotton clothes because synthetic cloth has less absorbing properties.

3. Glass Wool: It is used for filtering corrosive chemicals such as strong alkalies, strong oxidizing agent etc. Glass wool consists of fine fibers of glass. It is used to remove the coarse particles from strong acids, strong alkalies, etc.

4. Asbestos: It is also used for filtering the corrosive liquids.

5. Cotton Wool: Cotton wool is commonly used as filter media for coarse particles.

Filter Aids:

Filter aids are substances which increase the rate of filtration by reducing the resistance of the filtrate and added externally to the process of filtration.

Ideal properties of Filter Aids

1. It should be chemically inert.

2. It should be free from impurities.

3. It should be insoluble in the liquid to be filtered.

4. It should form a porous cake.

5. It should be readily recoverable from liquid.

Filter Press:

The plate and frame press is widely used for filtrations in pharmaceutical industries.

Construction of Filter Press:

• It consists of plates and frames. Plates have grooved surface to support the filter cloth and a free passage to the filtrate. The frames are open with an inlet for the liquid to be filtered.

• Filter cloth is fixed on each side of the plate.

• The plates and frames are placed alternatively and filtered in an outer frame of the press. Each plate works as a filtration unit. The outlet of each plate is attached to a common outlet pipe.

Working of Filter Press:

The liquid to be filtered is allowed to enter the frame under pressure. The filtrate Presses through filter medium on to the surface of the plate. The filtrate is collected in the plates. The cake is deposited in the frames. The process of filtration is continued until the frame is filled with filter cake. Thickness of filter cake depends on the solid contents present in the filtering liquid.

Advantage of Filter Press:

1. It requires less space

2. Filter medium can be used repeatedly.

3. Operation & handling easy

4. Filter medium can be used repeatedly.

Disadvantage of Filter Press:

1. It is a batch process.

2. It is suitable only for those products which contain about 5% or less solids.

3. The filter press is quite costly and labour cost involved in replacement of Filter cloth and washing.

Sintered filter:

It sintered glass filters. The filter medium is made up of glass particles. The fusion is done by heating the glass particles to a temperature at which different particles adhere together without melting.

Sintered glass filters are designed primarily for vacuum filtration and are available in different pore sizes.

The porosity of the filter depends on the size of granules used in its preparation


Grade No

Pore Size




Coarse material



Filtrations of fine ppt.


Upto 2 microns

Bacterial filtration.

Sintered glass filters should be washed with hot HCL or HNO3 and then rinsed thoroughly with water.

Filter candles:-

• Filter candle for ceramic fiber or sintered ceramics.

• They are made up of porcelain or Kieselguhr.

• Kieselguhr candle are more permeable than porcelain candles.

• One side of the candle is closed and the other side has an opening which is connected to vacuum pump for reducing the pressure under it during the filtration process.

• The candle is placed in the solution to be filtered and the vacuum is applied.

• The filtration takes place from outside to inner side from where it is removed when candle is filled.

• The inter candle get blocked with continuous use the candle is washed by passing water in the opposite direction from inner side to outer side This candles are used for sterilisation of solution.

Meta filters:-

• America filter consists of grooved drainage rod on which a metal ring made from stainless steel are packed.

• These rings have a thickness of 0.8 mm, 15mm inside diameter and 22 mm outer diameter.

• These rings are packed on the rod. The opening between the rings vary from 25 μm.

• The filtration is carried out by applying vacuum.

• The filter is placed in the slurry to be filtered and the filtration takes place from outside to inner side.

• These filters may filtration takes place with a steam jacket for the filtration of very viscous liquids such as Syrups or Oily Substances.

Uses of Metafilters:

• It is used for filtration of coarse particles.

• It is used as a Strainer.

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