The ultrafiltration membrane is a micro porous filter membrane with uniform pore size and rated aperture range of 0.001-0.02 microns (i.e., 1 -- 20 nm). With the appropriate pressure on the side of the membrane, the solutes smaller than the pore size can be screened out, and the particles with the molecular weight greater than 500 Dalton and the particle size greater than 2 ~ 20 nanometers.
The size of the bacteria varies greatly depending on the species, and the size of the coccid is expressed in diameter. It is indicated by length and width of the bacteria. The length of the helicoid is generally calculated by the distance between the two ends of the fungus, but the true length of the helicoid is calculated by the diameter and winding number of the spiral. Measurement of bacterial size is usually measured with a microscope, and the commonly used units are micrometer (micrometer, mu m, 1 mu = 10-3mm). The smallest bacteria are only 0.2 microns, the largest can be up to 80 microns, but the most common bacteria are: 0.5 ~ 1 micron, 0.2 ~ 1.0 x 0.7 ~ 3 micron, and 0.3 ~ 10 x 1.0 ~ 50 microns.
Viruses are much smaller than bacteria. The diameter is between 20 and 40 nanometers. Large pox viruses, 200 by 250-350 nm, are similar to small bacteria. Small as the mouth of the disease, only 22 nanometers in diameter.