Filtering effectiveness: It’s all about microns!
The micrometer or micron (μm) is unit of length equalling 1×10−6 metre, which is one millionth of a meter or one thousandth of a millimeter. Here are examples of some micron sizes:
- A red blood cell is typically 8 μm.
- A width of a strand of spider web silk is typically 3 – 8 μm.
- A white blood cell is typically 25 μm.
- A human hair is on average 70 μm.
- A grain of table salt is approximately 100 μm.
A micron rating for a water filter indicates the ability of the filter to remove contaminants by the size of the contaminant’s particles. The higher the micron number the larger the filtration pores.
Bacteria range in size from 0.2 to 2 microns in width or diameter and from 1 to 10 microns in length for the non-spherical specie. The common Escherichia coli (E. coli) is a rod-shaped bacterium where each bacterium measures approximately 0.5 μm in width by 2 μm in length. Vibrio cholerae (Cholera) is also a rod-shaped bacterium, measuring 0.3 μm in width and 1.3 μm in length. Viruses are typically 0.02 to 0.4 microns in size, which makes them much smaller than bacteria.
Bearing this in mind, one should seek a filter with a smaller micron number for better filtering capability; the larger the micron number, the less effective the filter in removing health threatening contaminants.
The highly recommended Sydney 905 Filters ® prove to be one of the fastest, easiest, highly effective and most cost efficient ways to get safe water. These water filters use hollow fibre (Polysulfone) membranes.
There are two types of filters available:
- With the 0.1 micron (absolute) pore size filter, it is impossible for any bacteria, protozoa or cysts to pass through this microfiltration filter. This is the company’s standard filter. It has been tested by Umgeni Water which is SANAS accredited. Membrane area is 0.5m (nominal value).
As the pores of the membranes within the Sydney 905 Filter are 0.1 microns in size, this means 700 pores can fit, side by side, in a width of a single human hair or approximately 10 000 will fit into a millimeter.
- If viruses are an issue, then with the 0.01 micron (absolute) pore size purifier, it is impossible for viruses in addition to bacteria, protozoa and cysts to pass through this ultrafiltration purifier. This is the company’s premium filter. This purifier is known to block even the smallest know virus to man which is the MS2 virus. However, the flow through this membrane is slow due to this absolute pore size and thus it is recommended to be configured within a pressurised system. Membrane area is 0.61m (nominal value).
As the pores of the membranes within the Sydney 905 Purifier are 0.01 microns in size, this means 7000 pores can fit, side by side, in a width of a single human hair or approximately 100 000 will fit into a millimeter.