Wastewater Terms

Acid

A proton (H+) donor.

Acidic (uh-SID-ick)

The condition of water or soil that contains a sufficient amount of acid substances to lower the pH below 7.0.

Acre-foot

A volume of water that covers one acre to a depth of one foot.

Activated Sludge

Sludge particles produced in raw or settled wastewater by the growth of organisms in aeration tanks in the presence of dissolved oxygen.

Aeration (air-A-shun)

The process of adding air to water.

Aeration Tank (air-a-shun)

The tank where activated wastewater is aerated. The same as aeration bay, aerator, or reactor.

Aerobic (air-O-bick)

A condition in which atmospheric or dissolved oxygen is present in the aquatic (water) environment.

Aerobic Bacteria (air-O-bick)

Bacteria that will live and reproduce only in an environment containing oxygen that is available for their respiration (breathing), namely atmospheric oxygen or oxygen dissolved in water.

Air Lift Pump

Compressed air is injected into a tail piece at the bottom of a pipe. Fine air bubbles mix with the wastewater or sludge to form a mixture lighter than the surrounding water, which causes the mixture to rise.

Algae (AL-jee)

Microscopic plants containing chlorophyll that live floating or suspended in water. They also may be attached to structures, rocks, or other submerged surfaces.

Algal Bloom (al-gull)

Sudden, massive growths of microscopic and macroscopic plant life, such as green or blue-green algae, which can, under the proper conditions, develop in lakes, reservoirs, and ponds.

Alkali (AL-kuh-lie)

Soluble salts, principally of sodium, potassium, magnesium, and calcium, that have the property of combining with acids to form neutral salts.

Alkaline (AL-kuh-line)

The condition of water or soil that contains a sufficient amount of alkali substances to raise the pH above 7.0.

Alkalinity

The capacity of water or wastewater to neutralize acids. Alkalinity is not the same as pH but rather it's a buffer. Alkalinity is a measure of how much acid must be added to a liquid to lower the pH to 4.5.

Ammonification

The decomposion of organic material creates ammonia as a byproduct.

Amperage (AM-purr-age)

The strength of an electric current measured in amperes. The amount of electric current flow, similar to the flow of water in gallons per minute.

Ampere (AM-peer)

The unit used to measure current strength. The current produced by an electromotive force of one volt acting through a resistance of one ohm.

Anabolism

Cells break compounds down into smaller groupings of atoms, and then recombine the atoms into new structures needed by the cell.

Anaerobic (AN-air-O-bick)

A condition in which atmospheric or dissolved oxygen (DO) is NOT present in the aquatic (water) environment.

Anaerobic Bacteria (AN-air-O-bick)

Bacteria that live and reproduce in an environment containing no free or dissolved oxygen. Anaerobic bacteria obtain their oxygen supply by breaking down chemical compounds that contain oxygen, such as sulfate.

Anaerobic Digester (AN-air-O-bick)

A wastewater solids treatment device in which the solids and water (about 5 percent solids, 95 percent water) are placed in a large tank where bacteria decompose the solids in the absence of dissolved oxygen.

Anaerobic Digestion (AN-air-O-bick)

A treatment process in which wastewater solids and water (about 5 percent solids, 95 percent water) are placed in a large tank (the digester) where bacteria decompose the solids in the absence of dissolved oxygen.

Anion

Ions with a negative charge due to the gain of electrons.

Anionic Polymer (AN-eye-ON-ick)

A polymer having negatively charged groups of ions; often used as a filter aid and for dewatering sludges.

Anoxic (an-OX-ick)

A condition in which the aquatic (water) environment does not contain dissolved oxygen (DO). Generally refers to an environment in which chemically bound oxygen, such as in nitrate, is present.

Area (Formula)

Rectangle: Length x Width. Circle: (0.785) x Diameter squared.

Ashing

Formation of an activated sludge floc in a clarifier effluent that is well oxidized and floats on the water surface (has the appearance of gray ash).

Atom

The atom is the smallest part of matter that represents a particular element.

Atomic Number

The number of protons in a particular atom.

Autotrophic (auto-TROF-ick)

Describes organisms (plants and some bacteria) that use inorganic materials for energy and growth.

Backwashing

The process of reversing the flow of water back through the filter media to remove the entrapped solids.

Bar Rack

A screen composed of parallel bars, either vertical or inclined, placed in a sewer or other waterway to catch debris. Also called a bar screen.

Base

A proton (H+) acceptor.

Batch Process

A treatment process in which a tank or reactor is filled, the water is treated or a chemical solution is prepared, and the tank is emptied.

Biomass (BUY-o-mass)

A mass or clump of organic material consisting of living organisms feeding on the wastes in wastewater, dead organisms, and other debris.

Biosolids

A primarily organic solid product produced by wastewater treatment processes that can be beneficially recycled. The word biosolids is replacing the word sludge when referring to treated waste.

BOD

Biochemical Oxygen Demand. The rate at which organisms use the oxygen in water or wastewater while stabilizing decomposable organic matter under aerobic conditions.

BOD (Test)

A procedure that measures the rate of oxygen use under controlled conditions of time and temperature. Standard test conditions include dark incubation at 20°C for a specified time (usually five days).

Brake Horsepower

The energy provided by a motor or other power source.

Breakpoint Chlorination

Addition of chlorine to water or wastewater until the chlorine demand has been satisfied. At this point, further additions of chlorine will result in a free chlorine residual.

Buchner Funnel

A special funnel used to separate solids from a mixture. A filter paper is placed in the lower portion of the funnel to hold the mixture. The funnel is placed in a filter flask and a vacuum is applied to remove the liquid.

Buffer

A buffer solution resists changes in pH from the effects of acids or bases. Buffer solutions maintain pH because they're switch hitters — they can either release hydrogen ions into a solution or remove them.

Buffer Capacity

A measure of the capacity of a solution or liquid to neutralize acids or bases. This is a measure of the capacity of water or wastewater for offering a resistance to changes in pH.

Bulking

Clouds of billowing sludge that occur throughout secondary clarifiers and sludge thickeners when the sludge does not settle properly. In the activated sludge process, bulking is usually caused by filamentous bacteria.

Burping

Billowing solids are swept up by the water and flow out over the effluent weirs in the discharged effluent. Billowing solids result when the settling tank sludge blanket becomes too deep.

CAS

Conventional Activated Sludge. The basic most common activated sludge wastewater system. Gravity Fed. In contrast to MBR and SBR.

Catabolsim

Cells transfer energy from food by breaking large molecules into small ones.

Catalyst (KAT-uh-list)

A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction.

Cation

Ions that have a positive charge due to the loss of electrons.

Cationic Polymer

A polymer having positively charged groups of ions; often used as a coagulant aid.

Cellular Respiration

A metabolic pathway that, through a series of small steps, rearranges the atoms in the food molecules, making their stored energy available to the cell.

Centrifugal Pump

A pump consisting of an impeller fixed on a rotating shaft that is enclosed in a casing. As the rotating impeller whirls the liquid around, centrifugal force builds up enough pressure to force the water out.

Check Valve

A special valve with a hinged disk or flap that opens in the direction of normal flow and is forced shut when flows go in the reverse or opposite direction of normal flows.

Chlorination (klor-uh-NAY-shun)

The application of chlorine to water or wastewater, generally for the purpose of disinfection.

Chlorinator (KLOR-uh-nay-ter)

A metering device that is used to add chlorine to water.

Chlorine Contact Chamber

A baffled basin that provides sufficient detention time of chlorine contact with wastewater for disinfection to occur. The minimum contact time is usually 30 minutes.

Chlorine Residual

The concentration of chlorine present in water after the chlorine demand has been satisfied.

Ciliates (SILLY-ates)

A class of protozoans distinguished by short hairs on all or part of their bodies.

Circuit

The complete path of an electric current, including the generating apparatus or other source; or, a specific segment or section of the complete path.

Circuit Breaker

A safety device in an electric circuit that automatically shuts off the circuit when it becomes overloaded.

Cl2

Chlorine is a chemical element with symbol Cl and is used for disinfection.

Clarifier (KLAIR-uh-fire)

A tank or basin in which wastewater is held for a period of time during which the heavier solids settle to the bottom and lighter elements, like water, float to the surface.

Clear Well

A reservoir for the storage of filtered water of sufficient capacity to prevent the need to vary the filtration rate with variations in demand.

CO2

Carbon Dioxide

Coagulant (ko-AGG-yoo-lent)

A chemical that causes very fine particles to clump (floc) together into larger particles. This makes it easier to separate the solids from the liquids by settling, skimming, draining, or filtering.

COD

Chemical Oxygen Demand. A measure of the oxygen-consuming capacity of organic matter present in wastewater. Chemical oxidants can may react with substances that bacteria do not stabilize.

Coliform (KOAL-i-form)

A group of bacteria found in the intestines of warm-blooded animals. The presence of coliform bacteria is an indication that the water is polluted and may contain pathogenic organisms.

Colloids (KALL-loids)

Very small, finely divided solids that remain dispersed in a liquid for a long time due to their small size and electrical charge.

Comminution (kom-mih-NEW-shun)

A mechanical treatment process that cuts large pieces of wastes into smaller pieces so they will not plug pipes or damage equipment. Comminution and shredding usually mean the same thing.

Compounds

A compound is composed of two or more elements in a specific ratio. For example, water (H2O) is a compound made up of two elements, hydrogen (H) and oxygen (O).

Conductivity

A measure of the ability of a solution (water) to carry an electric current.

Covalent Bond

A chemical bond that comes from the sharing of one or more electron pairs between two atoms.

Current

A movement or flow of electricity. Electric current is measured by the number of coulombs per second flowing past a certain point in a conductor.

Decant (de-KANT)

To draw off the upper layer of liquid (water) after the heavier material (a solid or another liquid) has settled.

Dechlorination (DEE-klor-uh-NAY-shun)

The deliberate removal of chlorine from water. The partial or complete reduction of residual chlorine by any chemical or physical process.

Decomposition

The conversion of chemically unstable materials to more stable forms by chemical or biological action.

Denitrification (dee-NYE-truh-fuh-KAY-shun)

An anoxic process that occurs when nitrite or nitrate ions are reduced to nitrogen gas.

Density

A measure of how heavy a substance is for its size. Density is expressed in terms of weight per unit volume.

Detention Time

The theoretical (calculated) time required for a given amount of water or wastewater to pass through a tank at a given rate of flow.

Detention Time (Formula)

Tank Volume x 24 Hours / Influent Flow.

Diffuser

A device (porous plate, tube, bag) used to break the air stream from the blower system into fine bubbles in an aeration tank or reactor.

Digester (dye-JEST-er)

A tank in which sludge is placed to allow decomposition by microorganisms. Digestion may occur under anaerobic (more common) or aerobic conditions.

Dissolved Organic Carbon (DOC)

That portion of the organic carbon in water that passes through a 0.45 µm pore-diameter filter.

Dissolved Oxygen

Molecular oxygen dissolved in water or wastewater, usually abbreviated DO.

Effluent (EF-loo-ent)

Water or other liquid—raw (untreated), partially treated, or completely treated—flowing from a reservoir, basin, treatment process, or treatment plant.

Electron

Subatomic Particle. Have a negative electrical charge (-1), have virtually no mass, and orbit the nucleus of the atom.

Electron Acceptor

A molecule that receives or accepts electrons from another molecule during a redox reaction.

Electron Carrier

A molecule capable of accepting one (or more than one) electrons from another molecule (electron donor), and then ferry these electrons to donate to another during the process of electron transport.

Electronegativity

The strength an atom has to attract a bonding pair of electrons to itself.

Element

An element is composed of a single kind of atom.

Endogenous Respiration (en-DODGE-en-us)

A situation in which living organisms oxidize some of their own cellular mass instead of new organic matter they adsorb or absorb from their environment.

Energy

Something you need to do work.

Enzymes (EN-zimes)

Organic substances that cause or speed up chemical reactions.

EPS

Extracellular Polymeric Substances. EPS is a general term for various types macromolecules found outside the cell surface, most commonly carbohydrates and proteins which are sticky polymers.

Equalizing Basin

A holding basin in which variations in flow and composition of a liquid are averaged. Such basins are used to provide a flow of reasonably uniform volume and composition to a treatment unit.

Eutrophication (YOO-tro-fi-KAY-shun)

The increase in the nutrient levels of a lake or other body of water; this usually causes an increase in the growth of aquatic animal and plant life.

F/M Ratio

Food to microorganism ratio. A measure of food provided to bacteria in an aeration tank in relation to the quantity of microorganisms in the tank.

F/M Ratio (Formula)

Lbs of Influent BOD / Lbs of MLSS in Aerator.

Facultative Bacteria (FACK-ul-tay-tive)

Facultative bacteria can use either dissolved oxygen or oxygen obtained from food materials such as sulfate or nitrate ions. In other words, facultative bacteria can live under aerobic, anoxic, or anaerobic conditions.

Filamentous Organisms (fill-uh-MEN-tuss)

Organisms that grow in a thread or scaffolding array, capable of suspending solids and preventing settleability.