Ultra Filtration

One of the most advanced methods of professional water filtration is the process of ultra filtration, a highly technical procedure that utilizes various types of filters comprised of semi-permeable membranes. These membranes remove minute particles that are suspended within the water, and can capture even smaller particles than are filtered out by microfiltration systems.

Ultrafiltration (UF) involves pressure-driven separation of materials from a feed solution. The technology is used to remove particulate and microbial contaminants, but it does not remove ions and small molecules. Pressure drives the process, which typically operates with a feed pressure of 4 to 100 psig. UF plants are automated and have low operational labor requirements. These systems, however, can require frequent cleaning. UF membranes have a service life of three to five years or longer, which is comparable to reverse osmosis membranes. UF modules are commercially available in tubular, hollow-fiber, plate and frame, and spiral wound configurations.

UF membranes reject solutes ranging in size from 0.03 microns and larger. The UF membrane process separates molecules in solution on the basis of size. The pore size and molecular weight cut-off (MWCO) are often used to characterize a membrane. The pore size is the nominal diameter of the openings or micro pores in the membrane expressed in microns. The MWCO is the molecular mass or weight of a solute that rejects greater than 90 percent. The unit of measurement for MWCO is the Dalton (D).


The usefulness of ultra-filtered or ultrapure water has increased over the years, as more applications for this extremely pure and clean standard of water have emerged. Although water may be potable, for example, and purified with agents such as chlorine, it may still contain harmful organisms such as giardia that happen to be resistant to chlorine treatments. But ultra filtration or UF technology is almost entirely effective at even removing these particles, so many municipal water treatment facilities, for example, rely upon UF treatment to guard against contamination from cryptosporidium, giardia, and other organisms that could cause serious illness if ingested.


These same water treatment systems often depend on ultra filtration and microfiltration for the effective removal of foreign particles that may also clog or foul the extremely small pores within reverse osmosis membranes. For the same reasons, for example, an ultra filtration membrane may be used to minimize the density of silt in water, or as a preliminary step in a phased process of treating water that will late be run through another level of purification.


UF treatment is also highly valuable to private sector companies and industries, and ultra filtering is used in many areas of the pharmaceutical and medical industry, for instance. Kidney dialysis is an area of health care that depends upon modern microfiltration and ultra filtration equipment and technology, for instance. Ultrafiltration is also used in the biotech and semiconductor manufacturing industries. In the making of semiconductors, for example, even microscopic particles of contaminants can compromise the integrity and performance of the semiconductor wafers, so they must be created in an ultra-pure environment. Standard metrics and guidelines for ultra filtering of water are set by various governing bodies, agencies, and regulatory authorities. Purity standards for ultrapure water include those set by a number of organizations, such as the USP, ASTM, CAP, NCCLS, ANSI and AAMI. .

The process of analyzing or certifying this unique and special grade of ultra-purified water involves scientific sampling, study, and analysis by trained researchers, engineers, and other experts. The goal of their scrutiny of water samples is to reveal any and all potential contaminants such as chemical additives, suspended solids, dissolved particles of contaminants, the presence of organic carbon, dissolved gases, or biological organisms such as pyrogens, bacteria, or viruses living within the water.