Glossary of Terms - V
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A mechanical device which automatically vents a water line to the atmosphere when subjected to a partial vacuum, thus preventing backflow. (See Backflow, Air Gap, Backflow Preventer)
Distillation that occurs at a pressure somewhat below atmospheric pressure. Lowering the pressure also lowers the boiling point of water, thus conserving energy by requiring less heat to bring about distillation.
The filtration process in which a partial vacuum is applied to increase the rate of filtration by causing the water to be sucked through the filter medium.
This is one of the oldest mechanical dewatering techniques in continuous use.
In municipal softening, this process is used to separate water from the lime sludge for sludge disposal.
A form of desalination using a vacuum to help cool and fast freeze high TDS source water which separates the solids by concentrating them in the portion of the water that doesn't freeze, or that freezes last in a similar manner to what occurs in the cloudy centers of ice cubes.
An airtight container used to produce granulated water softener salt using a process involving the evaporation of brine-turned-to-steam in a partial vacuum.
A pumping apparatus which exhausts gas or air from an enclosed space to achieve a desired degree of vacuum.
A small positive or negative whole number, which indicates the net number of electrons gained or lost in the formation of an ion, and thus the numbers of each kind of ion necessary for a balanced chemical reaction. For example, two hydrogen ions (each with a valence of + 1) must be present for each ion of oxygen (-2) to form a molecule of water (H2O).
1. (water treatment industry) Determination upon testing that a representative sample of a water treatment equipment model has met the requirements of a specified standard.
2. (pharmaceutical industry) The requirement of certain quality control testing and record keeping procedures to ensure compliance not only with a specific quality but also with a specific means to achieve and ensure that quality.
Weak attractive forces acting between molecules.
These forces are somewhat weaker than hydrogen bonds and far weaker than interatomic valences.
The gaseous form of any substance whose usual form is a liquid or a solid. Visible particles of moisture suspended in air, such as mist or fog.
The pressure, often expressed in millimeters of mercury (mm Hg), at which a vapor is in a state of balance with its liquid or solid form.
Input costs that change as the nature of the production activity of its circumstances change; for example, as production levels vary.
A State with primary enforcement responsibility under the Safe Drinking Water Act may relieve a public water system from a requirement respecting an MCL by granting a variance if certain conditions exist. These are:
1. The system cannot meet the MCL in spite of the application of best available treatment technology, treatment techniques, or other means (taking costs into consideration), due to the characteristics of the raw water sources which are reasonably available to the system; and the variance will not result in an unreasonable public health risk.
2. A system may also be granted a variance from a specified treatment technique if it can show that, due to the nature of the system's raw water source, such treatment is not necessary to public health.
Nonpoint source pollution control practices that involve plants (vegetative cover) to reduce erosion and minimize the loss of pollutants.
As relates to general water treatment, the time measurement of linear motion (flow) in a given direction. For example, water flowing 60 feet in a conduit each minute has a velocity of 60 feet per minute (fpm) or one foot per second (1 fps).
The relationship between the velocity of fluid flowing adjacent to the conduit wall or membrane surface and that flowing at a distance from the wall or surface.
A tube with a narrow throat (a constriction) that increases the velocity and decreases the pressure of the liquid passing through it, creating a partial vacuum immediately after the constriction in the tube.
The vacuum created has a sucking effect (eduction), and a venturi is commonly used to introduce a liquid (such as a regenerant) or gas (such as air) into a flowing water stream.
See Also: Voltage Back Siphonage Backwash Continous Flow Operation Cross Connection Intermittent Flow Normal Flow Filtration Cross flow filtration
A chemical substance used in water analysis for water hardness or with an indicator to colorimetrically measure hardness quality.
Alive and capable of continued life.
A water or waste water treatment process capable of accomplishing the desired water quality.
Degree of ability to cause disease.
The smallest form of life known to be capable of producng disease or infection, ususally considered to be of large molecular size. They multiply by assembly of component fragments in living cells, rather than by cell division, as do most bacteria.
The resistance of fluids to flow, due to internal forces and friction between molecules.
The volume of the pores or spaces between particles of ion exchanger, filter media, or other granular material, often expressed as a percentage of the total volume occupied by the material.
Capable of vaporization at a relatively low temperature.
Acids produced during digestion.
Fatty acids which are soluble in water and can be steam-distilled at atmospheric pressure. Also called organic acids.
Volatile acids are commonly reported as equivalent to acetic acid.
Liquids which easily vaporize or evaporate at room temperatures.
Organic chemicals that turn into vapor at relatively low temperatures.
Matter which remains as a residue after evaporation at 105 or 180oC, but which is lost after ignition at 600oC. Includes most forms of organic matter.
Loss of a substance through evaporation.
Referring to measurement by volume rahter than weight.
A revolving mass of water which forms a whirlpool. This whirlpool is caused by water flowing out of a small opening in the bottom of a basin or reservoir. A funnel-shaped opening is created downward from the water surface.