Filtration Sterilization – Pharmaceutical Microbiology Third Semester PDF Notes

Filtration Sterilization


• Principle of filtration sterilization

• Advantages and limitations of filtration sterilization

• Depth and screen filters

• Method of filtration sterilization

• Advantages and disadvantages

• Types of bacteriological filters

• Advantages and disadvantages of each type of filter


At the end of this lecture, the student will be able to:

• Explain the principle of filtration sterilization

• List the advantages and limitations of filtration

• Differentiate between depth filters and screen filters

• Describe the mechanism of different classes of filters

• Explain the steps involved in filtration sterilization

• List different types of bacteriological filters

• Explain the advantages and disadvantages of different
types of filters


• Filtration removes, rather than destroying the

• It is capable of preventing the passage of both viable and
nonviable particles

• Used for both the clarification and sterilization of
liquids and gases


• Sterilization of heat-sensitive injections, ophthalmic
solutions and biological products

• Filtration of air and other gases for supply to aseptic

• As a part of venting systems on fermentors, centrifuges, autoclaves
and freeze driers

• Used in sterility testing

of filtration sterilization

• Major mechanisms of filtration are sieving, adsorption and
trapping within the matrix of the filter material

Types of

1. Surface

In surface filtration the medium is used to support the
captured solids which deposit onto the medium (called septum, membranes, cloth
etc) during operation.

Removal of solids is effected by the previously deposited
solids or cake.

As the cake builds so does the resistance to flow

2. Depth Filtration:

In depth filtration the suspended particles enter into the
porous medium (called grains) and move to the grain surface for attachment or
re-entry into the fluid, repeating this procedure through the filter column

sterilization of liquids

• Membrane filters of 0.2 – 0.22mm nominal pore diameter are
chiefly used

• Sintered filters are used only in restricted
circumstances, i.e. for the processing of corrosive liquids, viscous fluids or
organic solvents

• Filtration sterilization is an aseptic process and careful
monitoring of filter integrity is necessary as well as final product sterility

• Filtration under pressure – filling at high flow rates
directly into the final containers without problems of foaming, solvent
evaporation or air leaks

• Membrane filters are often used in combination with a
coarse-grade fibreglass depth prefilter to improve their dirt-handling capacity

Filtration sterilization

• To increase the filtration area, and hence process
volumes, several filter discs can be used in parallel in multiple-plate
filtration systems

• Alternatively, membrane filters can be fabricated into
plain or pleated cylinders and installed in cartridges

sterilization of gases


• Filtration sterilization of gases is in the provision of
sterile air to

– Aseptic manufacturing suites

– Hospital isolation units

– Operating theatres

Efficiency Particulate Air (HEPA) filters

• Filters employed generally consist of pleated sheets of
glass microfibers separated and supported by corrugated sheets of Kraft paper
or aluminium

• HEPA filters can remove up to 99.997% of particles
>0.3mm in diameter and thus are acting as depth filters

• Air is forced through HEPA filters by blower fans, and
prefilters are used to remove larger particles to extend the lifetime of the
HEPA filter

Other applications
of filters

• Sterilization of venting or displacement air in tissue and
microbiological culture (carbon filters and hydrophobic membrane filters)

• Decontamination of air in mechanical ventilators (glass
fibre filters)

• Treatment of exhausted air from microbiological safety
cabinets (HEPA filters)

• Clarification and sterilization of medical gases (glass
wool depth filters and hydrophobic membrane filters)

filter – Candle filter

glass and metal filters

Membrane filters

sterilization process

1. Passage of the solution to be sterilized through a
previously sterilized filter unit

2. Aseptic transfer of the filtrate to sterile containers

3. Aseptic sealing of the containers

4. Sterility testing

• Since filtration is very slow through bacteriological

• To enhance filtration rate, two methods are used:

– Positive pressure type – solution forced through using
compressed air

– Negative pressure type (vacuum) – solution is sucked
through the filter

of filtration sterilization

1. Ideal for thermolabile substances like blood products,
insulin and enzymes

2. Useful for large volume solutions

3. Both clarification and filtration achieved

4. Filtered organisms can be further cultured

5. All bacteria, living and dead are removed

6. Rapid supply of small volume parenteral in emergency

of filtration sterilization

1. Sterility testing required

2. Virus, filterable forms off bacteria and bacterial
products like toxins and pyrogens are not removed

3. Filter may break down suddenly or gradual faults may not
be dectected

4. Clogging

5. Adsorption

6. Cannot be used for suspensions

7. Shedding of fibers

8. Suitable only for solutions


• Also called filter candles

• Made up of porcelain or kieselguhr

• Available in a range of pore sizes

• Numbered according to pore size

Examples: Berkefeld filters and Mandler filters


• Made up of unglazed porcelain or kieselguhr

• Hollow cylinder candles mounted of metal joints

• Candles can be sterilized by moist heat

• Clogging can be cleaned by scrubling the exterior with a
nail brush or soft brush


• Relatively inexpensive

• Can be used for thermolabile substances

• Various porosities are available


• May get clogged

• Requires cleaning after every process

• Leaks occur at nozzle joints

• Difficult to fill into filter units

• Relatively high pressure needle for filtration

filter/ fibrous pad filter

• 3mm thick

• Consists of two parts

• Lower part holds perforated disc

• On top of it is a compressed filter sheets composed mainly
of asbestos fiber with other fibrous material such as wood cellulose to give
adequate porosity

glass filter

metal filter



• Filtration removes, rather than destroys, microorganism

• Used in the sterilization of heat-sensitive liquids

• It also clarifies along with filtration

• Filtration is also used for sterilization of air and other
gases for supply to aseptic areas

• Filtration requires aseptic procedures

• Materials sterilized by filtration requires sterility

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