Glossary of Terms - U
A B C D E F G H I J K L M N O P Q R S T U V W Z
ultra-filtration - A method of cross flow filtration (similar to reverse osmosis but using lower pressures) which uses a membrane to separate small colloids and large molecules from water and other liquids. The ultra-filtration process falls between reverse osmosis and micro-filtration in terms of the size of particles removed, with ultra-filtration removing particles in the 0.002 to 0.1 micron range, and typically rejecting organics over 1,000 molecular weight while passing ions and smaller organics.
ultraviolet (UV) - Pertaining to ultraviolet light.
ultraviolet chamber - The area where the water is irradiated with ultraviolet rays.
ultraviolet demand - The amount of ultraviolet rays required to inactivate certain microorganisms.
ultraviolet dosage - The amount of disinfectant ultraviolet rays delivered to the organisms in the water being disinfected. Dosage is a combination of UV intensity times the contact time and is measured in watt-seconds per square centimeter.
unaccounted-for water - A term used in municipal water systems to describe the difference between the water produced and that metered and sold. It usually includes losses due to leakage, water used for fire fighting, public sprinkling and other municipal purposes, and usually ranges from 10 to 35 percent of the water produced.
uniformity coefficient - The measure of the variation in particle sizes of filter and ion exchange media. The uniformity coefficient is defined as the ratio of the sieve size that will permit passage of 60 percent of the media material by weight to the sieve size that will permit passage of 10 percent of the media material by weight. A uniformity coefficient of 1.00 denotes a material having particle grains all the same size; numbers increasingly greater than one denote increasingly less uniformity.
up-flow - A pattern of water flow in which a solution (water or regenerant usually) enters at the bottom of the vessel or column and flows out at the top of the vessel or column during any phase of the treatment unit's operating cycle. The term is used to describe ion exchange system flow patterns or water flow through filter media. A system can have up-flow during the treatment cycle and down-flow during regeneration. Up-flow is also called counter current flow.
Countercurrent flow means regeneration flows and service flows are in the opposite directions.
up-flow brining - Is a means of forcing the brine solution upward through the cation exchanger for regenerating the resin. Where the softening flow is downward and the regenerating brine flow is upward, the mode is also called countercurrent flow. Countercurrent flow means regeneration flows and service flows are in the opposite directions.
up-flow softening - A pattern of water flow used in softeners in which the service water flows upward through the ion exchange bed; the media is restricted in movement, usually because of a packed bed. The regeneration brine usually flows downward in such systems. Up-flow softening is normally used to achieve higher operating efficiency.
USEPA - United States Environmental Protection Agency. (www.epa.gov)
USPHS - United States Public Health Service. (www.usphs.gov)