Filtration is commonly the mechanical or physical operation which is used for the separation of products like solids from fluids by interposing a medium through which only the fluid can pass.

1. FILTRATION
Tapeshwar
Yadav
(Lecturer)
BMLT, DNHE,
M.Sc. Medical

2. Introduction
 Filtration is commonly the mechanical or physical operation
which is used for the separation of products like solids from
fluids by interposing a medium through which only the fluid
can pass.
 The fluid that passes through is called a filtrate.
 Filtration is the best established and most versatile method for
removing insoluble from dilute streams like fermentation
broths.

3. FILTERATION
The separation of solids from a suspension in a
liquid by means of a porous medium or screen
which retains the solids and allows the liquid to
pass is termed filtration.

4. Filtration
In the laboratory, the suspension is
poured into a conical funnel fitted with
a filter paper.
In the industrial equivalent, difficulties
are encountered in the mechanical
handling of much larger quantities of
suspension and solids. A thicker layer
of solids has to form and, in order to
achieve a high rate of passage of
liquid through the solids, higher
pressures are needed, and a far
greater area has to be provided.

5. Steps involved in
filtration
1. Draining the liquor
2. Filtration
3. Filling with wash water
4. Washing
5. Draining the wash water
6. Opening, dumping and reassembling
7. Filling with slurry.

6. Principle of filtration

7. Principle of Filtration
Since the filter medium is permeable only to the fluid, it retains the
solid particles and permits only the fluid to pass through which is
collected as the filtrate. The volume of filtrate collected per unit
time (dV/dt) is termed as the rate of filtration.
As the filtration proceeds, solid particle accumulate on the filter
medium forming a packed bed of solids, called filter cake.
As the thickness of the cake increases
 resistance to flow of filtrate increases
 rate of filtration gradually decreases.
If rate is maintained to be constant then
pressure difference driving force (-P) will
increase.
Therefore, a batch filter is operated either at constant pressure or at constant rate.

8. Constant rate and Pressure Filtration

9.  Darcy's law is a phenomenological derived constitutive
equation that describes the flow of a fluid through
a porous medium.
 Darcy's law is a simple proportional relationship between the
instantaneous discharge rate through a porous medium,
the viscosity of the fluid and the pressure drop over a given
distance.
The total discharge, Q (units of volume per time, e.g., m3/s) is equal to the product of the
intrinsic permeability of the medium, k (m2), the cross-sectional area to flow, A (units of
area, e.g., m2), and the pressure drop (Pb - Pa), (Pascals), all divided by
the viscosity, μ (Pa·s) and the length over which the pressure drop is taking place (m).
General theory of filtration

10. Types of filtration equipment
The industrial filtration equipment differs from laboratory
filtration equipment only in the amount of material handled and
in the necessity for low-cost operation.
Fig. Simple laboratory filtration apparatus

11.  Filters can also be classified by operating cycle. Filters can be
operated as batch, where the cake is removed after a run, or
continuous, where the cake is removed continuously.
 In another classification, filters can be of the gravity type,
where the liquid simply flows by means of a hydrostatic head,
or pressure or vacuum can be used to increase the flow rates.

13. Some of the most important types of
filters:
1. Bed filter
2. Plate-and-frame-filter
3. Leaf Filters
4. Continuous rotary filters
a. Continuous rotary vacuum-drum filter
b. Continuous rotary disk filter
c. Continuous rotary horizontal filter

14.  Such filters are useful mainly in cases where relatively small
amounts of solids are to be removed from large amounts of
water in clarifying the liquid.
Fig. Bed Filter
1. BED FILTER

15. 2. PLATE-AND-FRAME-FILTER
The feed slurry is pumped which flows through the duct.
The filtrate flows through the filter cloth and the solids
build up as a cake on the frame side of the cloth. The
filtrate flows between the filter cloth and the face of the
plate through the channels to the outlet.
Fig. Plate-and-frame-filter press

16. 3. Leaf Filters
This filter is useful for many purposes but is not economical
for handling large quantities of sludge or for washing with a
small amount of fresh water. The wash water often channels in
the cake and large volumes of wash water may be needed.
Fig. Leaf Filter

17. 4. Continuous rotary filters
A number of such filters are as follows:
a. Continuous rotary vacuum-drum filter
b. Continuous rotary disk filter
c. Continuous rotary horizontal filter

18. A. CONTINUOUS ROTARY VACUUM-
DRUM FILTER
Fig. Continuous rotary Vacuum drum
filter

19. B. CONTINUOUS ROTARY DISK FILTER
The filter consist of concentric vertical disks mounted on a
horizontal rotating shaft. The filter operates on the same
principle as the vacuum rotary-drum filter. Each disk in hollow
and covered with a filter cloth and is partly submerged in the
slurry.
C. CONTINUOUS ROTARY HORIZONTAL
FILTER
This type is a vacuum filter with the rotating annular filtering
surface divided into sectors. As the horizontal filter rotates, it
successively receives slurry, is washed, is dried, and the cake is
scraped off.

20. Removal of Insoluble Products

21. Rotary Vacuum Filtration
slurry is pumped into the trough
The vacuum draws liquid and air through the filter media and out the shaft hence
forming a layer of cake
An agitator is used to regulate the slurry if the texture is coarse and it is settling rapidly
Solids that are trapped on the surface of the drum
washed and dried, removing all the free moisture

22. Microfiltration/ Ultra filtration
Microfiltration usually serves as a pre-treatment for other
separation processes such as ultrafiltration, and a post-
treatment for granular media filtration.
 The typical particle size used for microfiltration ranges from
about 0.1 to 10 µm.
 In terms of approximate molecular weight these membranes
can separate macromolecules generally less than 100,000
g/mol.

23.  The filters used in the microfiltration process are specially
designed to prevent particles such as, sediment,
algae, protozoa or large bacteria from passing through a
specially designed filter.
 More microscopic, atomic or ionic materials such as water
(H2O), monovalent species such as Sodium (Na+) or Chloride
(Cl-) ions, dissolved or natural organic matter, and
small colloids and viruses will still be able to pass through the
filter.

24. Microfiltration
 Separates soluble contaminants remaining within
the supernatant
 Supernatant may include:
Other proteins
Bio-molecules
Un-used growth media
Microfiltration image from:
http://www.aaflow.de/filtertech/index.html

25. How does Microfiltration work?
 Pressure driven process
 Separates:
Components in a
solution or suspension
based on molecular size
Particles size range:
10mm
(starches) to aprx.
0.04mm (DNA,
Viruses, and globular
proteins)
Microfiltration image from:
http://www.faireymicrofiltrex.com/Vokes%20Mi
crofiltration/media/images/e-fluor.gif

26. Ultrafiltration
Usually used to
further separate any
contaminants able to
pass through the
microfiltration
membrane using a
pressure gradient
Ultrafiltration image from:
http://www.awatec.ch/produkte/ultrafiltration.jpg

27. How does Ultrafiltration work?
Separates:
Particle size range:
0.1mm to 0.001mm
Usually based on
molecular weight
Typical range:
200 to 300,000 g/mole
Ultrafiltration image from:
http://www.toltecint.com/how_dialysis_works/how_hemodial
ysis_works.htm

28. Microfiltration vs. Ultrafiltration
Microfiltration:
Proteins act as the
permeate
Ultrafiltration
Proteins act as the
retentate
Images from:
http://www.geafil
tration.com/html/
technology/ftech
nology.html

29. Microfiltration vs. Ultrafiltration
Microfiltration:
Separates larger
particles
For example-
Colloids
Fat globules
Cells
Located upstream to
reduce load and
fouling capacity on
ultrafiltration
membrane
downstream
 Ultrafiltration
 Separates smaller
particles
 For example-
 Macromolecules
However,
processes are
basically identical

30. Applications of Filtration:
 Filtration methods are used in the home, in research
laboratories, in industrial processes, and in
controlling environmental pollution. For example, a
coffee filter is used to separate brewed coffee from
the grounds, and HEPA filters are used in air
conditioners and vacuum cleaners. Some filters are
used to clean ambient air by removing dust from the
atmosphere.
 In kidneys :The kidney works by filtration of blood in
the glomerulus, followed by selectively reabsorbing
many substances essential for the body.

31. Applications of Filtration:
 Chemists often use filtration to separate
materials from mixtures of different chemical
compositions.
 On an industrial scale, filtration is used by the oil,
gas, food and beverage, and pharmaceutical
industries, among others. Municipalities use
filtration techniques when treating sewage and
purifying water.
 Filtration cleans up river streams or other water
streams. Furnaces use filtration to prevent the
furnace elements from fouling with particulates.

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