To assist you in choosing the appropriate porosity for your filtration needs, Sterlitech is pleased to share with you The Filtration Spectrum, a guide that was designed by GE Osmonics to display the size range of particles and what types of filtration are used for each range, on a relative and absolute scale. The spectrum is broken down in five major particle ranges and filter process ranges: Macro & Micro Range (Particle Filtration), Macro Molecular Range (Microfiltration), Molecular Range (Ultrafiltration (UF) & Nanofiltration (NF)), and Ionic Range (Reverse Osmosis (RO)).
Sterlitech Corporation primarily offers filtration products in the Microfiltration Range, as well as a few products in the UF, NF, & RO process ranges.
MACRO/MICRO PARTICLE RANGE (Particle Filtration) Macro particles are visible to the naked eye and range in size from 20 micrometers (µm) to 1 mm. Examples of particles in this size range include: beach sand, granular activated carbon, human hair, mist, pollen and milled flour. Filters that are designed for particle filtration are usually screen, sand, bag, plate and frame, activated carbon, and depth filters.
MICRO/ MACRO MOLECULAR PARTICLE RANGE (Microfiltration) Micro particles are not visible to the naked eye; an optical microscope is needed. These particles range in size from about 50 nanometers (nm) to over 1 µm and include some of the following: giardia cyst, yeast cells, bacteria, coal dust, red blood cells, blue indigo dye, asbestos, and latex/emulsion.
Sterlitech offers a wide range of microfiltration products to filter particles of this size, including all of our Membrane Disc Filters, syringe filters and pressure and vacuum filter holders.
MOLECULAR RANGE (Ultrafiltration, Nanofiltration) Submicron particles, 0.5 nm to 0.1 µm, are only visible with a scanning electron microscope (SEM) or a Scanning Tunneling (ST) microscope. Particles of this size are filtered using crossflow membrane technology - reverse osmosis (RO) nanofiltration (NF) and ultrafiltration (UF). RO, NF, and UF are the finest forms of filtration presently known, with reverse osmosis permitting only pure water through the membrane, nanofiltration allowing some salts through the membrane and ultrafiltration allowing passage of nearly all salts and medium molecular weight particles.
Typically, ultrafiltration is used when the only issues are fine filtration and removal of most organic contaminants. Examples of particles in this size range include: carbon black particles, viruses, gelatin, colloidal silica, proteins, tannins and lignins (color components found in surface waters).
Nanofiltration is used for particles in the molecular range (80 nm to 8 nm). These size particles are only visible with an SEM. Sugar, synthetic dye, endotoxins and pyrogens are molecules rejected within this range as well as smaller particles of gelatin, viruses and larger charged ions such as hardness. Nanofiltration covers an area in-between with organic rejections of 300-1000 mw (or Daltons) and salt passages of 15 - 90%. Several different types of nanofiltration membranes cover the entire spectrum of the area between RO and UF.
IONIC RANGE (Reverse Osmosis) The ionic range consists of particles that are only visible with a ST microscope. These particles range in size from 12 nm and below. Particles in this size range include aqueous salt, metal ion, carbohydrate molecules, and small pesticides and herbicides. To filter particles of this size or to reduce inorganic salts (e.g. sodium, alkalinity), reverse osmosis membranes are used.
Sterlitech offers a range of UF, NF, and RO membranes for bench scale testing. The membranes are available from us in sheets or cut to the size you need. Sterlitech manufactures bench scale cross flow filtration units including the HP4750 stirred cell, the CF042 cross flow cell, and the Sepa CF membrane cell system.
