Microscopic Membrane Filters

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.
  • 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.