GLOSSARY OF COMMONLY USED TERMS IN WATER AND SEWAGE POLLUTION CONTROL
Activated Sludge: The particles produced by the growth of microorganisms in the biological treatment of wastewater. See TWISTER aerator.
Activated Sludge Process: Discovered in Britain in 1913, the process refers to the treatment of wastewater using microorganisms, that break down organic materials into water, carbon dioxide, and other compounds that can easily settle in the water. See TWISTER aerator.
Aeration: The process of dissolving air in water or wastewater. This is achieved by increasing the water air interface in order to promote the absorption of the air by the water. In wastewater treatment, aeration increases oxygen content in the water. Oxygen is needed by bacteria to break down dissolved or suspended organic materials. In water treatment, aeration helps oxidize certain compounds into a form that settle in the water which can then be filtered out. Aeration can help in the removal of gases in water, a process known as air stripping.
Aeration Methods: Aeration can be performed either by introducing air into the water or by introducing water into the air. In the air-to-water method, small air bubbles are forced into the water, such as in diffused air systems or aspirating aerators. In the water-to-air method, small water droplets or thin sheets of water contact the air, such as in fountains or cascading flowing creeks.
Aeration Tank: Any water or wastewater compartment (basin, cell lagoon, pond, reactor, tank, etc.) where aeration is performed. See biological reactor.
Aerator: A device that brings air into intimate contact with water and wastewater.
Aerator, Directional: An aerator that directs the water in a certain direction to enhance mixing and aeration.
Aerator, Fixed: Fixed aerators are designed to be permanently mounted on a bridge, platform, wall, or at bottom of the aeration tank. Generally, they can be manually adjusted for relatively small water level variations.
Aerator, Floating: A floating aerator is designed to float on water. The obvious benefit is the fact that the aerator goes up and down with the water level. Floating aerators are generally more expensive than fixed ones, due to the added cost of the float and anchoring system, however, they are generally easier to install and remove from the water.
Aerator, High Speed: An aerator in which the speed of the rotor/propeller/impeller is the same or almost the same as that of the motor. Generally, no gear reducer is used and speed is typically above 900 rpm.
Aerator, Horizontal: An aerator in which the axis of rotation is horizontal. See MONSOON Aerator.
Aerator, Low Speed: An aerator that uses a low speed rotor/propeller to perform aeration and mixing. Generally, a gearbox is used to reduce speed to around one tenth to one thirtieth the speed of the motor. See TWISTER Aerator.
Aerator, Submerged: Submerged aerators perform aeration at the bottom of the water. This is accomplished in several different ways.
(1) In diffused air systems air diffusers are placed at the bottom of the aeration tank. Blowers placed outside the aeration tank supply air to the diffusers air through air pipes.
(2) Submersible aerators consist of a completely submerged motor and diffusers placed at the bottom of the tank. An air draft tube that extends slightly above the water surface bring air to the bottom by aspiration or by blowers placed above the water. See HURRICANE Aerator.
Aerator,Sub-Surface: Sub-Surface aerators perform aeration just below the surface of the water. A rotating propeller creats a vacuum that forces air through a draft tube and into the water. The rotating propeller ensures that the air gets through the water. Sub-Surface aerators eliminate the problems associated with mist and odors.
Aerator, Surface: Surface aerators perform aeration at the surface of the water. It is acheived either by spraying or pumping thin sheets of water into the air just above the surface and/or pushing air into the water. Depending on the design, vigorous agitation and mixing spread the absorbed oxygen into other parts of the water. See TORNADO Aerator.
Aerator, Vertical: An aerator in which the axis of rotation is vertical.
Aerobic: A condition in which free oxygen is present in the wastewater.
Aerobic Bacteria: Bacteria that require free oxygen to break down organic pollutants in water.
Aerobic Digestion: Aerobic and facultative bacteria use oxygen to break down organic matter into carbon dioxide, water, and other compounds. The resulting sludge is stable and can be disposed of without concern over odor problems.
Air Stripping: The process of removing undesired gases in water by injecting large amounts of air. See BREEZE.
Anaerobic: A condition in which oxygen is not present in the wastewater.
Anaerobic Digestion: In anaerobic digestion, facultative and strict anaerobic bacteria break down organic matter into carbon dioxide, water, methane, and other compounds. The remaining sludge becomes stable and therefore can be disposed of without concern over odor problems.
Anoxic: A condition in which oxygen is not present as free and dissolved in the water, but rather chemically combined with other elements.
Bacteria: Microscopic organisms that perform a variety of functions in the treatment of wastewater.
Biochemical Oxygen Demand (BOD5): A measure of the quantity of oxygen consumed in the oxidation of organic matter during a 5-day period at a temperature of 20ºC.
Biological Reactor: A tank in which microorganisms convert organic materials in the water from an undesired form into a preferred one.
Clarifier: A circular or rectangular tank used to remove solids in water or wastewater.
Complete Mix Reactor: An activated sludge reactor in which the wastewater is rapidly and continuously mixed to create homogeneity throughout the reactor.
Denitrification: The biological conversion of nitrate nitrogen to nitrogen gas in the absence of oxygen (anaerobic conditions).
Detention Time : The period of time that flowing water or wastewater is retained in a tank, lagoon, or basin. It is calculated by dividing the average daily flow rate by the water volume in the tank.
Dissolved Oxygen (DO): The oxygen dissolved in water or wastewater. Its concentration is typically measured in milligrams per liter (mg/l) or in percent saturation.
Dissolved Solids: Solids that are in solution in the water.
Effluent: Water or wastewater exiting a tank, basin, lagoon after treatment.
Equalization Basin : A tank that serves to create a more uniform water body thus eliminating wild variations in the composition and flows of the incoming water.
Extended Aeration : A variation of the activated sludge process in which long aeration periods enhance aerobic digestion. See TWISTER aerator.
Facultative Bacteria: Bacteria that can survive with or without the presence of free oxygen.
Five-Day Biochemical Oxygen Demand (BOD5) : See BOD. A measure of the oxygen consumed at a temperature of 20ºC during a 5 day period.
Influent: Water or wastewater flowing into a tank, basin, lagoon for treatment.
Lagoon: A large earthen basin or pond used as a holding tank for aeration, sedimentation, or some other purpose while treating water and wastewater. See TORNADO Aerator.
Nitrification: The biological conversion (oxidation) of ammonia nitrogen into nitrate nitrogen in the presence of oxygen (aerobic condition).
Post-Aeration : The process of increasing the oxygen concentration of wastewater that has already been treated.
Pre-Aeration: The addition of air into the wastewater as an initial step in the treatment process to remove gases, oils, and greases, improve coagulation, or simply to increase oxygen concentration.
Retention Time: See detention time.
Return Activated Sludge (RAS): A portion of the sludge in the clarifier that is returned to mix with influent wastewater.
Screen: A mechanical device used to remove solids in a flow stream.
Sedimentation: Also called settling. The process of separating solids in water or wastewater depending on gravity.
Sludge: Any solids that have settled or have been separated from water or wastewater during a treatment process, such as sedimentation, flotation, and agglomeration.
Suspended Solids: Particles not soluble in water and are floating or hanging in the water..
Waste Activated Sludge: A portion of the sludge in a clarifier that is disposed of to reduce the build-up of solids in the activated sludge process.
Wastewater: Any water used by people in cities and towns, by industrial and commercial, and government. Such water contains dissolved solids and suspended matter. It cannot be reused or discharged without some treatment.
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