Membrane filtration
Definition
Filtration technique based on a physical barrier (a membrane) with specific pore sizes that
traps contaminants larger than the pore size on the top surface of the membrane (WHO
2006).
Membrane filtration is a process of a fluid passing through a semi permeable membrane
into a solution where its concentration is lower (World Plumbing Council Working Group
2008).
Membrane filtration is a process where a fluid passes through a porous partition, which can
remove unwanted matter from a pre-determined selective membrane separation wall.
Certain substances can pass through the membrane, while others have their concentration
lowered (Macquarie Library, University New South Wales 1985).
Explanation
Contaminants smaller than the specified pore size may pass through the membrane or may
be captured within the membrane by some other mechanism (WHO 2006).
Membrane filtration employs a semi-permeable membrane to separate materials according
to their physical and chemical properties when a pressure differential or electrical
potential difference is applied across the membrane. Pressure driven processes can be
broadly classified according to the membrane pore size and size of particles removed. They
are microfiltration, ultra-filtration, nanofiltration and reverse osmosis (Twort et al. 2000). Example
Membrane types in common drinking water use include ultrafiltration, microfiltration,
nanofiltration and reverse osmosis. Immersed membrane systems are used in wastewater
treatment. Membrane filtration has functional designed levels of porosity of the membrane
filter. The higher the filtering performance the higher the pressure required to make it
work. With known technology, when salts for example, need to be removed from water, a
reverse osmosis process is applied. The pressure required to perform reverse osmosis is
much higher than the pressure required for basic micro filtration. As the pressure raises
the productivity the through put is lowed. As the pressure rises, the energy required to
drive the filtration process increases substantially (World Plumbing Council Working Group
2008).
Reference for Definition
(c) World Health Organisation
www.who.int/thelexicon
Macquarie Library, University New South Wales (1985) The Macquarie Dictionary Revised
Edition
Twort, A.C., Ratnayaka, D.D., and Brandt, J.J. (2000) Water Supply, Fifth Edition. Internatonal Water Association. WHO (2006) Guidelines for the safe use of wastewater, excreta and greywater
Useful Links
(c) World Health Organisation
www.who.int/thelexicon