This is a unit operation note

1. What is Filtration?
Filtration is technically defined as the process of separating suspended solid matter from a liquid,
by causing the latter to pass through the pores of a membrane, called a filter. The most common
example is making tea. While preparing tea, a filter or a sieve is used to separate tea leaves from
the water. Through the sieve pores, only water will pass. The liquid which has obtained after
filtration is called the filtrate; in this case, water is the filtrate. The filter can be a paper, cloth,
cotton-wool, asbestos, slag- or glass-wool, unglazed earthenware, sand, or any other porous
material. Filtration is used in water treatment and sewage treatment. (Thomas and Robert,
2015).
Types of Filtration
Vacuum Filtration: In order to swiftly pull fluid through a filter, vacuum filtration uses a
vacuum pump.
Centrifugal Filtration: The material to be filtered is spun at a high speed during this
filtration process.
Gravity filtration: It is a method for purifying liquids by utilizing gravity to move the
liquid through a filter as it passes.
Various Filtration techniques
I. Depth filtration
II. Surface filtration
III. Cross-flow filtration
IV. Centrifugal filtration
V. Micro-filtration

2. VI. Ultrafiltration
VII. Nano-filtration
VIII. Dialysis
I. Depth filtration: This is a type of filtration which uses a thick filter medium to capture
impurities in the liquid. This technique uses a filter medium that has many small pores, which
allows the liquid to pass through while trapping the solids. The filter medium can be made of
materials like paper, cotton, or synthetic fibers. Depth filtration is often used in the early stages of
a filtration process, before the liquid is sent through a more refined filtration process.
II. Surface filtration: This is a type of filtration Which uses a thin filter medium that only
allows the liquid to pass through the surface. The filter medium has pores that are just large
enough to let the liquid pass through, but small enough to trap any solids. The filter medium is
often made of a materiallikepolypropylene, polytetrafluoroethylene(PTFE) or polyvinylidene
fluoride (PVDF). Surface filtration is often used for removing fine particles or micro organisms
from liquids.
III. Cross-flow filtration:This is a type of filtration in which the liquid being filtered flows in a
direction that is perpendicular to the direction of the filter. In other words, the liquid flows at a
90-degree angle to the filter, rather than directly through it. This type of filtration is often used in
food processing because it allows for continuous filtration, which can be more efficient than
other types of filtration. (Shuler and maginn 2019).
IV.Centrifugal filtration: This is a type of filtration that uses centrifugal force to separate solids
from liquids. The liquid is spun at high speeds in a centrifuge, which forces the solids to move to
the outside of the centrifuge and the liquid to move to the center. This type of filtration is often
used for separating solids from liquid foods, such as fruit juices or milk.
Micro-filtration: This is a type of filtration that uses a membrane with very small pores to
separate solids from liquids. Micro-filtration is often used to remove bacteria, viruses, and other
microorganisms from liquids. In food processing, micro-filtration is often used to purify water or
milk.
VI. Nano-filtration: This is a type of filtration that uses a membrane with extremely small pores.
Nano-filtration can separate molecules that are as small as one nanometer in size. In food
processing, nano-filtration is often used to remove salts and organic compounds from liquids.
Various filtration techniques.
VII. Reverse osmosis is a type of filtration that uses pressure to force water through a
semi-permeable membrane.The water molecules pass through the membrane, but the salts and
other impurities are left behind. Reverse osmosis is often used to purify water, including in the
production of bottled water and soft drinks.
VIII. Dialysis: This is a type of filtration that uses a semi-permeable membrane to remove waste
products from the blood. Dialysis is often used to treat people with kidney failure, as it helps to
remove toxins and excess fluid from the body.

3. Reference
Thomas R.Adams and Robert A.j. Briggs, 2015 " principle of unit operation in food processing".
www.ift.org/science/food-filtration-separations
Maginn leo and shuler l Ronald.2019 " food engineering operations".