Monitoring and Management > 5. Water >
Describe the design and composition of microscopic membrane filters and explain how they purify contaminated water
- Membrane Filter: A thin film of synthetic polymer through which there are pores of reasonably uniform size.
- Membrane filters are commonly made of:
- Polypropylene.
- Polyvinylchloride (PVC).
- Polycarbonate.
- Polyester.
- Polysulfone.
- Polytetrafluoroethylene.
- There are two main types of membrane filters:
- A sheet of porous material folded around a central rigid porous core.
- Particles are trapped on the outside, while clean water flows through.
- Forms a cartridge that can be placed in a suitable housing mounted in a water pipe.
- Porous material formed into hollow capillaries.
- Particles are trapped on the outside, while clean water flows through.
- Large numbers of capillaries are bundled together to form a filtering unit with a large surface area.
- A sheet of porous material folded around a central rigid porous core.
- Membrane filters are classified according to the size of their pores:
- Nanometre (nm): One billionth of a metre.
- Microfiltration (MF) membranes remove particles of 200-500 nm, such as microscopic parasites, viruses, and fine colloidal particles.
- Ultrafiltration (UF) membrandes remove particles of 2-100 nm, such as paint particles and large organic molecules.
- Nanofiltration (NF) membranes remove particles of less than 1 nm, such as metal ions and small molecules.
- Many membrane filters can be cleaned by blowing air from the clean side to dislodge trapped particle on the other side, and can therefore be reused.
- Membrane filters can be used for:
- Filtering drinking water.
- Treating waste-water.