Glossary of Water Treatment Terms & Definitions - U

Ultrafiltration

A membrane type system that removes small colloids and large molecules from solutions. Ultrafiltration removes particles in size range between 0.002 to 0.1 micron range. The process falls between reverse osmosis and microfiltration as far as the size of particles removed is concerned.

Ultrapure Water

No standards exist describing ultrapure water though it is not considered to be sterile. It is water that has been deionized and provides high resistivity and contains no organics.

Ultraviolet Light

Radiation having a wave length shorter than 4000 angstroms (visible light) down to 100 angstroms on the border of the x-ray region. Ultraviolet light is used as a disinfectant.

Upflow

The operation of an ion exchange unit in which solutions are passed in at the bottom and out at the top of the container.

Uranium

A radioactive metallic element found naturally in combination with other materials. Uranium 238 is the most common form.