Membrane filtration
- Slovak term: Slovenský termín
- 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).
References
- 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
