Glossary of Water & Wastewater Terms

Abatement (uh-BAIT-ment)

Putting an end to an undesirable or unlawful condition affecting the wastewater collection system. A property owner found to have inflow sources connected to the collection system may be issued a notice of abatement. Such notices will usually describe the violation, suggest corrective measures, and grant a period of time for compliance. 


Alkyl Benzene Sulfonate. A type of surfactant, or surface active agent, present in synthetic detergents in the United States before 1965. ABS was especially troublesome because it caused foaming and resisted breakdown by biological treatment processes. ABS has been replaced in detergents by linear alkyl sulfonate (LAS), which is biodegradable.

Absorption Rate

The speed at which a measured amount of solid material can absorb a measured amount of liquid. Under pressure, water can infiltrate a given volume of gravel very rapidly. The water will penetrate (or be absorbed by) sand more slowly and will take even longer to saturate the same amount of clay.

Activated Sludge

The activated sludge process is a process for treating sewage and industrial wastewaters using air and a biological floc composed of bacteria and protozoa.

Advanced Sewage Treatment

Advanced treatment involves the removal of nutrients such as nitrogen and phosphate from the sewage by special biological processes with the aid of chemicals or filtration processes.

Advanced Waste Treatment

Any process of water renovation that upgrades treated wastewater to meet specific reuse requirements. May include general cleanup of water or removal of specific parts of wastes insufficiently removed by conventional treatment processes. Typical processes include chemical treatment and pressure filtration. Also called tertiary treatment.

Aeration Control Valve

Valves which allow for proper regulation at wide aperture, resulting in energy efficient wastewater treatment operation. Fixed throttling apertures and imprecise regulation methods cause unnecessary pressure losses and high energy costs.

Aeration Tank (air-a-shun)

The tank where raw or settled wastewater is mixed with return sludge and aerated. The same as aeration bay, aerator, or reactor.

Aerobic Treatment System

An aerobic treatment system or ATS, often called (incorrectly) an aerobic septic system, is a small scale sewage treatment system similar to a septic tank system, but which uses an aerobic process for digestion rather than just the anaerobic process used in septic systems.

Aging Infrastructure

An aging water and sewer infrastructure lying beneath city streets, including pipes, pumps, valves and other vital equipment - some sections are nearly a century old or more - is in constant need of repairs and upgrades.

Air Binding

The clogging of a filter, pipe, or pump due to the presence of air released from water. Air entering the filter media is harmful to both the filtration and backwash processes. Air can prevent the passage of water during the filtration process and can cause the loss of filter media during the backwash process.

Air Blower

A device used to ventilate manholes and lift stations.

Air Gap

An open, vertical drop, or vertical empty space, between a drinking (potable) water supply and potentially contaminated water. This gap prevents the contamination of drinking water by backsiphonage because there is no way potentially contaminated water can reach the drinking water supply.

Air Lift Pump

A special type of pump consisting of a vertical riser pipe submerged in the wastewater or sludge to be pumped. Compressed air is injected into a tail piece at the bottom of the 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 in the discharge pipe to the outlet.

Air Padding

Pumping dry air (dew point –40ÅãF (–40ÅãC)) into a container to assist with the withdrawal of a liquid or to force a liquefied gas such as chlorine or sulfur dioxide out of a container.

Air Release

A type of valve used to allow air caught in high spots in pipes to escape.

Air Stripping

A physical treatment process used to remove volatile substances from water or wastestreams. The process uses large volumes of air to transfer volatile pollutants from a high concentration in the water or wastestream into a lower concentration in an air stream.

Air Test

A method of inspecting a sewer pipe for leaks. Inflatable or similar plugs are placed in the line and the space between these plugs is pressurized with air. A drop in pressure indicates the line or run being tested has leaks.

Alignment (uh-LINE-ment)

The proper positioning of parts in a system. The alignment of a pipeline or other line refers to its location and direction.

Alkali (AL-kuh-lie)

Any of certain soluble salts, principally of sodium, potassium, magnesium, and calcium, that have the property of combining with acids to form neutral salts and may be used in chemical processes such as water or wastewater treatment.

Alkalinity (al-kuh-lin-it-tee)

The capacity of water or wastewater to neutralize acids. This capacity is caused by the water’s content of carbonate, bicarbonate, hydroxide, and occasionally borate, silicate, and phosphate. Alkalinity is expressed in milligrams per liter of equivalent calcium carbonate. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have a high alkalinity. Alkalinity is a measure of how much acid must be added to a liquid to lower the pH to 4.5.

Alternating Current (AC)

An electric current that reverses its direction (positive/negative values) at regular intervals.

Altitude Valve

A valve that automatically shuts off the flow into an elevated tank when the water level in the tank reaches a predetermined level. The valve automatically opens when the pressure in the distribution system drops below the pressure in the tank.

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.


The maximum strength of an alternating current during its cycle, as distinguished from the mean or effective strength.


The continuously variable signal type sent to an analog instrument (for example, 4–20 mA).

Anaerobic Wastewater Treatment

Processes that are widely applied in the treatment of industrial wastewaters and biological sludge. Some wastewater may be highly treated and reused as reclaimed water.


A device that conducts a periodic or continuous measurement of turbidity or some factor such as chlorine or fluoride concentration. Analyzers operate by any of several methods including photocells, conductivity, or complex instrumentation.

Angstrom (ANG-strem)

A unit of length equal to one-tenth of a nanometer or one-tenbillionth of a meter (1 Angstrom = 0.000 000 000 1 meter). One Angstrom is the approximate diameter of an atom.


An electrochemical process that deposits a coating of an insoluble oxide on a metal surface. Aluminum is the most frequently anodized material.

Apparent Color

Color of the water that includes not only the color due to substances in the water but suspended matter, as well.

Aquifer (ACK-wi-fer)

A natural, underground layer of porous, waterbearing materials (sand, gravel) usually capable of yielding a large amount or supply of water.


  1. The curved top of a sewer pipe or conduit.
  2. A bridge or arch of hardened or caked chemical that will prevent the flow of the chemical.

Artesian (are-TEE-zhun)

Pertaining to groundwater, a well, or underground basin where the water is under a pressure greater than atmospheric and will rise above the level of its upper confining surface if given an opportunity to do so.

Artificial Groundwater Table

A groundwater table that is changed by artificial means. Examples of activities that artificially raise the level of a groundwater table include agricultural irrigation, dams, and excessive sewer line exfiltration. A groundwater table can be artificially lowered by sewer line infiltration, water wells, and similar drainage methods.

Aspirate (AS-per-rate)

Use of a hydraulic device (aspirator or eductor) to create a negative pressure (suction) by forcing a liquid through a restriction, such as a Venturi tube. An aspirator may be used in the laboratory in place of a vacuum pump; sometimes used instead of a sump pump.


The abbreviation for atmosphere. One atmosphere is equal to 14.7 psi or 100 kPa.

Attached Growth Processes

Wastewater treatment processes in which the microorganisms and bacteria treating the wastes are attached to the media in the reactor. The wastes being treated flow over the media. Trickling filters and rotating biological contactors are attached growth reactors. These reactors can be used for BOD removal, nitrification, and denitrification.

Auger (AW-grr)

A sharp tool used to go through and break up or remove various materials that become lodged in sewers.

Automatic Meter Reading (AMR)

Technology that automatically collects usage, diagnostic, and status data from water metering devices and transfers that data to a central database for billing, troubleshooting, and analyzing.

Axial to Impeller

The direction in which material being pumped flows around the impeller or flows parallel to the impeller shaft.

Back Pressure

A pressure that can cause water to backflow into the water supply when a user’s water system is at a higher pressure than the public water system.


  1. Material used to fill in a trench or excavation.
  2. The material placed over a pipe up to the ground surface. This consists of initial and final backfill.
  3. The act of filling a trench or excavation, usually after a pipe or some type of structure has been placed in the trench or excavation.


A reverse flow condition, created by a difference in water pressures, that causes water to flow back into the distribution pipes of a potable water supply from any source or sources other than an intended source.


A procedure used to wash settled waste matter off upstream structures to prevent odors from developing after a main line stoppage has been cleared.

Backwater Gate

A gate installed at the end of a drain or outlet pipe to prevent the backward flow of water or wastewater. Generally used on storm sewer outlets into streams to prevent backward flow during times of flood or high tide. Also called a tide gate.


A flat board or plate, deflector, guide, or similar device constructed or placed in flowing water, wastewater, or slurry systems to cause more uniform flow velocities, to absorb energy, and to divert, guide, or agitate liquids (water, chemical solutions, slurry).

Bailer (BAY-ler)

A length of pipe equipped with a valve at the lower end used to remove slurry from the bottom or the side of a well as it is being drilled.


A type of transformer that is used to limit the current to an ultraviolet (UV) lamp.


A method of hydraulically cleaning a sewer or storm drain by using the pressure of a water head to create a high cleansing velocity of water around a sewer-cleaning ball. In normal operation, the ball is restrained by a cable while water washes past the ball at high velocity. Special sewer-cleaning balls have an outside tread that causes them to spin or rotate, resulting in a scrubbing action of the flowing water along the pipe wall.

Ball Valve

A ball valve is a form of quarter-turn valve which uses a hollow, perforated and pivoting ball (called a “floating ball”) to control flow through it. It is open when the ball’s hole is in line with the flow and closed when it is pivoted 90-degrees by the valve handle.


  1. A substance that takes up or accepts protons.
  2. A substance that dissociates (separates) in aqueous solution to yield hydroxyl ions (OH–).
  3. A substance containing hydroxyl ions that reacts with an acid to form a salt or that may react with metals to form precipitates.

Base Metal

A metal (such as iron) that reacts with dilute hydrochloric acid to form hydrogen.

Baseline Monitoring Report (BMR)

All industrial users subject to categorical pretreatment standards must submit a baseline monitoring report (BMR) to the control authority (POTW, state, or EPA). The purpose of the BMR is to provide information to the control authority to document the industrial user’s current compliance status with a categorical pretreatment standard.

Batch Process

A treatment process in which a tank or reactor is filled, the water (or wastewater or other solution) is treated or a chemical solution is prepared, and the tank is emptied. The tank may then be filled and the process repeated. Batch processes are also used to cleanse, stabilize, or condition chemical solutions for use in industrial manufacturing and treatment processes.


The prepared base or bottom of a trench or excavation on which a pipe or other underground structure is supported.


  1. In a pipe fitting, the enlarged female end of a pipe into which the male end fits. Also called a hub.
  2. In plumbing, the expanded female end of a wiped joint.

Bell-and-Spigot Joint

A form of joint used on pipes that have an enlarged diameter or bell at one end and a spigot at the other that fits into and is laid in the bell. The joint is then made tight by lead, cement, rubber O-ring, or other jointing compounds or materials.

Bench-Scale Analysis (Test)

A method of studying different ways or chemical doses for treating water or wastewater and solids on a

small scale in a laboratory.

Bioassay (BUY-o-AS-say)

  1. A way of showing or measuring the effect of biological treatment on a particular substance or waste.
  2. A method of determining the relative toxicity of a test sample of industrial wastes or other wastes by using live test organisms, such as fish.


The addition of bacterial cultures to speed up the breakdown of grease and other organic materials. Bioaugmentation is used to clean sewers and, on a preventive basis, to remove deposits in sewers. This method is also used to prevent grease buildup in lift station wet wells.

Biodegradable (BUY-o-dee-GRADE-able)

Organic matter that can be broken down by bacteria to more stable forms that will not create a nuisance or give off foul odors is considered biodegradable.


The process of filtering water through a filter medium that has been allowed to develop a microbial biofilm that assists in the removal of fine particulate matter and dissolved organic materials. Also called biological filtration.

Bioflocculation (BUY-o-flock-yoo-LAY-shun)

The clumping together of fine, dispersed organic particles by the action of certain bacteria and algae. This results in faster and more complete settling of the organic solids in wastewater.


A biofuel is a fuel that is produced through contemporary biological processes, such as agriculture and anaerobic digestion, rather than a fuel produced by geological processes such as those involved in the formation of fossil fuels, such as coal and petroleum, from prehistoric biological matter.

Biological Sewage Treatment

Uses microorganisms to dissolve organic substances and break down nitrogen compounds. Technical processes further enhance these biological self purification processes. They take place in primary clarifiers, activated sludge tanks, and secondary clarifiers. Biological sewage treatment processes produce different sludge types:

  1. Primary sludge. Sludge from sedimentation tanks.
  2. Secondary sludge. Sludge from biological sewage treatment.
  3. Tertiary sludge. Sludge from the third stage of sewage treatment.
  4. Mixed sludge. Combination of the above sludge types.
  5. External sludge. Sludge hauled to the sewage treatment plant from other sources.

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.


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.


The clogging of the filtering medium of a microscreen or a vacuum filter when the holes or spaces in the media become clogged or sealed off due to a buildup of grease or the material being filtered.


Any incident in which a sewer is partially or completely blocked, causing a backup, a service interruption, or an overflow. Also called stoppage.


A device used to ventilate manholes and lift stations.

BOD (pronounce as separate letters)

Biochemical Oxygen Demand. A measure of the amount of dissolved oxygen consumed (exertion) by aerobic organisms while stabilizing decomposable organic matter under aerobic conditions. The BOD value is commonly expressed as BOD5 and refers to the milligrams of oxygen consumed per liter of water during a 5-day incubation period at 20ÅãC. In decomposition, organic matter serves as food for the organisms and energy results from its oxidation. BOD measurements are used as a measure of the organic strength of wastes in water.

Boiler Feed Pump

A boiler feedwater pump is a specific type of pump used to pump feedwater into a steam boiler. The water may be freshly supplied or returning condensate produced as a result of the condensation of the steam produced by the boiler. These pumps are normally high pressure units that take suction from a condensate return system and can be of the centrifugal pump type or positive displacement type.

Bonnet (BON-it)

The cover on a gate valve.

Bound Water

Water contained within the cell mass of sludges or strongly held on the surface of colloidal particles. One of the causes of bulking sludge in the activated sludge process.

Bowl, Pump

The submerged pumping unit in a well, including the shaft, impellers, and housing.

Brake Horsepower

  1. The horsepower required at the top or end of a pump shaft (input to a pump).
  2. The energy provided by a motor or other power source.

Branch Manhole

A sewer or drain manhole that has more than one pipe feeding into it. A standard manhole will have one outlet and one inlet. A branch manhole will have one outlet and two or more inlets.

Branch Sewer

A sewer that receives wastewater from a relatively small area and discharges into a main sewer serving more than one branch sewer area.


A fracture or opening in a pipe, manhole, or other structure due to structural failure or defect.

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 that is directly proportional to the amount of chlorine added beyond the breakpoint.


A crack or break in a filter bed allowing the passage of floc or particulate matter through a filter. This will cause an increase in filter effluent turbidity. A breakthrough can occur (1) when a filter is first placed in service, (2) when the effluent valve suddenly opens or closes, and (3) during periods of excessive head loss through the filter (including when the filter is exposed to negative heads).

Brinelling (bruh-NEL-ing)

Tiny indentations (dents) high on the shoulder of the bearing race or bearing. A type of bearing failure.

BTU (pronounce as separate letters)

British Thermal Unit. The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

Buchner Funnel

A special funnel used to separate solids (sludge) from a mixture. A perforated plate or a filter paper is placed in the lower portion of the funnel to hold the mixture (wet sludge). The funnel is placed in a filter flask and a vacuum is applied to remove the liquid (dewater the sludge).


  1. A special device designed to be pulled along a sewer for the removal of debris from the sewer. The bucket has one end open with the opposite end having a set of jaws. When pulled from the jaw end, the jaws are automatically opened. When pulled from the other end, the jaws close. In operation, the bucket is pulled into the debris from the jaw end and to a point where some of the debris has been forced into the bucket. The bucket is then pulled out of the sewer from the other end, causing the jaws to close and retain the debris. Once removed from the manhole, the bucket is emptied and the process repeated.
  2. A conventional pail or bucket used in BUCKETING OUT and also for lowering and raising tools and materials from manholes and excavations.

Bucket Machine

A powered winch machine designed for operation over a manhole. The machine controls the travel of buckets used to clean sewers.

Bucketing Out

An expression used to describe removal of debris from a manhole with a pail or bucket on a rope. In balling or high-velocity cleaning of sewers, debris is washed into the downstream manhole. Removal of this debris by scooping it into pails and hauling it out is called bucketing out.


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 or bound water.


A term used to describe what happens when billowing solids are swept by the water up and out over the effluent weirs in the discharged effluent. Billowing solids result when the settling tank sludge blanket becomes too deep (occupies too much volume in the bottom of the tank).

Butterfly Control Valve

A butterfly valve is used for regulating or isolating flow by using a rotatable disc. Butterfly valves are usually low in cost and weight.


  1. A pipe, valve, gate, weir, trench, or other device designed to permit all or part of a wastewater flow to be diverted from usual channels or flow. Sometimes refers to a special line that carries the flow around a facility or device that needs maintenance or repair.
  2. The diversion of all or part of a flow from its usual channels or sewers to storm drains or surface waters.


The act of causing all or part of a flow to be diverted from its usual channels. In a wastewater treatment plant, overload flows should be bypassed into a holding pond for future treatment.


Sludge handling methods are designed to destroy harmful organisms and remove water. The end product of the sludge handling process is a relatively dry material known as “cake.” It can be applied to agricultural land as a soil conditioner, placed in landfills, or cleanly burned. At some plants, sludge serves as a fuel to produce energy.

Catch Basin

A chamber or well used with storm or combined sewers as a means of removing grit that might otherwise enter and be deposited in sewers.

Categorical Standards (Limits)

Industrial waste discharge standards (limits) developed by EPA that are applied to the effluent from any industry in any category anywhere in the United States that discharges to a Publicly Owned Treatment Works (POTW). These are standards based on the technology available to treat the waste streams from the processes of the specific industrial category and normally are measured at the point of discharge from the regulated process. The standards are listed in the Code of Federal Regulations.

Cathodic Protection (kath-ODD-ick)

An electrical system for prevention of rust, corrosion, and pitting of metal surfaces that are in contact with water, wastewater, or soil. A low-voltage current is made to flow through a liquid (water) or a soil in contact with the metal in such a manner that the external electromotive force renders the metal structure cathodic. This concentrates corrosion on auxiliary anodic parts, which are deliberately allowed to corrode instead of letting the structure corrode.

Cavitation (kav-uh-TAY-shun)

The formation and collapse of a gas pocket or bubble on the blade of an impeller or the gate of a valve. The collapse of this gas pocket or bubble drives water into the impeller or gate with a terrific force that can knock metal particles off and cause pitting on the impeller or gate surface. Cavitation is accompanied by loud noises that sound like someone is pounding on the impeller or gate with a hammer.


  1. A spontaneous, electrochemical process that involves the reduction of a more electropositive (noble) species, for example, copper, silver, mercury, or cadmium, by electronegative (sacrificial) metals, such as iron, zinc, or aluminum. This process is used to purify spent electrolytic solutions and for the treatment of wastewaters, leachates, and sludges bearing heavy metals. Also called electrolytic recovery.
  2. The process of heating two substances that are placed in contact with each other for the purpose of bringing about some change in one of them, such as changing iron to steel by surrounding it with charcoal and then heating it.

Centralized Waste Treatment (CWT) Facility

A facility designed to properly handle treatment of specific hazardous wastes from industries with similar wastestreams. The wastewaters containing the hazardous substances are transported to the facility for proper storage, treatment, and disposal. Different facilities treat different types of hazardous wastes.


The water leaving a centrifuge after most of the solids have been removed.

Centrifugal Pump (sen-TRIF-uh-gull)

A pump consisting of an impeller fixed on a rotating shaft that is enclosed in a casing, and having an inlet and discharge connection. As the rotating impeller whirls the liquid around, centrifugal force builds up enough pressure to force the water through the discharge outlet.


A mechanical device that uses centrifugal or rotational forces to separate solids from liquids.


Comprehensive Environmental Response, Compensation, and Liability Act of 1980. This act was passed primarily to correct past mistakes in industrial waste management. The focus of the act is to locate hazardous waste disposal sites that are creating problems through pollution of the environment and, by proper funding and implementation of study and corrective activities, eliminate the problem from these sites. Current users of CERCLA-identified substances must report releases of these substances to the environment when they take place (not just historic ones). This act is also called the Superfund Act.

Certification Examination

An examination administered by a state agency or professional association that operators take to indicate a level of professional competence. In the United States, certification of operators of water treatment plants, wastewater treatment plants, water distribution systems, and small water supply systems is mandatory. In many states, certification of wastewater collection system operators, industrial wastewater treatment plant operators, pretreatment facility inspectors, and small wastewater system operators is voluntary; however, current trends indicate that more states, provinces, and employers will require these operators to be certified in the future. Operator certification is mandatory in the United States for the Chief Operators of water treatment plants, water distribution systems, and wastewater treatment plants.


A lined or partially lined excavation or pit for dumping raw household wastewater for natural decomposition and percolation into the soil.


Cubic Feet Per Second. A measure of flow rate.

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.

Chemical Precipitation

Chemical precipitation is a method of wastewater treatment. Wastewater treatment chemicals are added to form particles which settle and remove contaminants. The treated water is then decanted and appropriately disposed of or reused. The resultant sludge can be dewatered to reduce volume and must be appropriately disposed of. Chemical precipitation can be used to remove metals, fats, oils and greases (FOG), suspended solids and some organics. It can also to be used to remove phosphorus, fluoride, ferrocyanide and other inorganics.

Chlorination (klor-uh-NAY-shun)

The application of chlorine to water or wastewater, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results-aiding coagulation and controlling tastes and odors in drinking water, or controlling odors or sludge bulking in wastewater.

Circle of Influence

The circular outer edge of a depression produced in the water table by the pumping of water from a well.


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. The device can be manually reset.


Clarifiers are settling tanks built with mechanical means for continuous removal of solids being deposited by sedimentation. A clarifier is generally used to remove solid particulates or suspended solids from liquid for clarification and (or) thickening.

Clean Water Act 1972

The primary federal law in the United States governing water pollution. Its objective is to restore and maintain the chemical, physical, and biological integrity of the nation’s waters by preventing point and nonpoint pollution sources, providing assistance to publicly owned treatment works for the improvement of wastewater treatment, and maintaining the integrity of wetlands. It is one of the United States’ first and most influential modern environmental laws. As with many other major U.S. federal environmental statutes, it is administered by the U.S. Environmental Protection Agency (EPA), in coordination with state governments.

Clean Water Restoration Act 1966

Extended federal grants for plant construction.

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 (pronounce as separate letters)

Chemical Oxygen Demand. A measure of the oxygen-consuming capacity of organic matter present in wastewater. COD is expressed as the amount of oxygen consumed from a chemical oxidant in mg/L during a specific test. Results are not necessarily related to the biochemical oxygen demand (BOD) because the chemical oxidant may react with substances that bacteria do not stabilize.

Collection System

A network of pipes, manholes, cleanouts, traps, siphons, lift stations, and other structures used to collect all wastewater and wastewater-carried wastes of an area and transport them to a treatment plant. The collection system includes land, wastewater lines and appurtenances, pumping stations, and general property.

Combined Sewer

A sewer designed to carry both sanitary wastewaters and stormwater or surface water runoff.

Combined- or Separate-Stage Nitrification and Denitrification

A certain amount of nitrogen removal (20-30%) occurs in conventional activated sludge systems. Nitrogen removal ranging from 70 to 90 % can be obtained by use of nitrification-denitrification method in plants based on activated sludge and other suspended growth systems. Biological denitrification requires prior nitrification of all ammonia and organic nitrogen in the incoming waste.

Combined Wastewater

A mixture of stormwater or surface water runoff and other wastewater, such as domestic or industrial wastewater.

Commercial Contribution

Liquid and liquid-carried wastes dumped by commercial establishments into the wastewater collection system. Used in this context, commercial contributions are distinct from domestic and industrial sources of wastewater contributions. Examples of high-yield commercial sources are laundries, restaurants, and hotels.

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.


The procedures used by a utility agency to inspect, test, train staff, start up, operate, and ultimately accept a new facility.

Compatible Pollutants

Those pollutants that are normally removed by the POTW treatment system. Biochemical oxygen demand (BOD), suspended solids (SS), and ammonia are considered compatible pollutants.

Complete Treatment

A method of treating water that consists of the addition of coagulant chemicals, flash mixing, coagulation-flocculation, sedimentation, and filtration. Also called conventional filtration.

Computed Collection System Contribution

The part of a collection system flow computed to be actual domestic and industrial wastewater. Applied to infiltration/inflow research, the computed domestic and industrial wastewater contribution is subtracted from a total flow to determine infiltration/inflow amounts.

Computed Facility Contribution

The computed liquid-waste discharge from a single facility based on the sources of waste flows in the facility.


Pretreatment of sludge to facilitate removal of water in subsequent treatment processes.


A rapid method of estimating the total dissolved solids content of a water supply. The measurement indicates the capacity of a sample of water to carry an electric current, which is related to the concentration of ionized substances in the water. Also called specific conductance.


Any artificial or natural duct, either open or closed, for carrying fluids from one point to another. An electrical conduit carries electricity.

Conservative Pollutant

A pollutant found in wastewater that is not changed while passing through the treatment processes in a conventional wastewater treatment plant. This type of pollutant may be removed by the treatment processes and retained in the plant’s sludges or it may leave in the plant effluent. Heavy metals such as cadmium and lead are conservative pollutants.

Continuous Process

A treatment process in which water is treated continuously in a tank or reactor. The water being treated continuously flows into the tank at one end, is treated as it flows through the tank, and flows out the opposite end as treated water.


Waters, wastewaters, or liquid-carried wastes entering a wastewater collection system.

Control Loop

The combination of one or more interconnected instrumentation devices that are arranged to measure, display, and control a process variable. Also called a loop.

Control System

An instrumentation system that senses and controls its own operation on a close, continuous basis in what is called proportional (or modulating) control.


A device that controls the starting, stopping, or operation of a device or piece of equipment.

Conventional Filtration

A method of treating water that consists of the addition of coagulant chemicals, flash mixing, coagulation-flocculation, sedimentation, and filtration. Also called complete treatment.

Conventional Treatment

  1. The common wastewater treatment processes such as preliminary treatment, sedimentation, flotation, trickling filter, rotating biological contactor, activated sludge, and chlorination wastewater treatment processes used by POTWs.
  2. The hydroxide precipitation of metals processes used by pretreatment facilities.


A treatment process that occurs when ferrous iron is added to water or metallic wastestreams and subsequently oxidized in an aerator. The oxidized iron, which is insoluble, precipitates along with other metallic contaminants present in the water or wastestream, thereby enhancing metals removal.


The gradual decomposition or destruction of a material by chemical action, often due to an electrochemical reaction. Corrosion may be caused by (1) stray current electrolysis, (2) galvanic corrosion caused by dissimilar metals, or (3) differentialconcentration cells. Corrosion starts at the surface of a material and moves inward.


  1. A threaded sleeve used to connect two pipes.
  2. A device used to connect two adjacent parts, such as a pipe coupling, hose coupling, or drive coupling.


A steel specimen inserted into water or wastewater to measure corrosiveness. The rate of corrosion is measured as the loss of weight of the coupon or change in its physical characteristics. Measure the weight loss (in milligrams) per surface area (in square decimeters) exposed to the water or wastewater per day. 1 meter = 10 decimeters = 100 centimeters.

CPK Standardized Chemical Pump

A particularly powerful standardized pump for the chemical and petrochemical industry, and many other fields of application. This standardized pump offers particular flexibility and suitability for numerous applications, and can be easily adapted to local conditions.

Cradle to Grave

A term used to describe a hazardous waste manifest system used by regulatory agencies to track a hazardous waste from the point of generation to the hauler and then to the ultimate disposal site.


  1. A connection between drinking (potable) water and an unapproved water supply.
  2. A connection between a storm drain system and a sanitary collection system.
  3. Less frequently used to mean a connection between two sections of a collection system to handle anticipated overloads of one system.

Cross-Flow Filtration

A type of membrane filtration where the water being filtered flows across the surface of the membrane to keep the particle buildup and fouling to a minimum. The flow that is not filtered becomes concentrated and flows out the end of the membrane fiber as a wastestream.


Combined Sewer Overflow. Wastewater that flows out of a combined sewer (or lift station) as a result of flows exceeding the hydraulic capacity of the sewer or stoppages in the sewer. CSOs exceeding the hydraulic capacity usually occur during periods of heavy precipitation or high levels of runoff from snow melt or other runoff sources.

CT Value

Residual concentration of a given disinfectant in mg/L times the disinfectant’s contact time in minutes.

Curb Inlet

A chamber or well built at the curbline of a street to admit gutter flow to the stormwater drainage system.

Curb Stop

A water service shutoff valve located in a water service pipe near the curb and between the water main and the building. This valve is usually operated by a wrench or valve key and is used to start or stop flows in the water service line to a building. Also called a curb cock.

Dateometer (day-TOM-uh-ter)

A small calendar disk attached to motors and equipment to indicate the year in which the last maintenance service was performed.

Datum Line

A line from which heights and depths are calculated or measured. Also called a datum plane or a datum level.


A process in which ammonia is removed mostly from return streams and can result in a 60 percent energy savings compared to nitrification/denitrification. The two-step process involves anaerobic ammonia oxidation (Anammox), which reduces the amount of energy required for aeration. Deployment is common in Europe with a number of pilots at various plants. Full-scale plants are either planned or under construction in Washington, D.C., Chicago and at the Hampton Roads Sanitation District in Virginia.

Dead-End Filtration

A type of membrane filtration where the water being filtered flows through the membrane, but there is no wastestream from the system. All solids accumulate on the membrane during filtration and are removed during backwash.

Dead-End Manhole

A manhole located at the upstream end of a sewer and having no inlet pipe. Also called a terminal manhole.

Debris (de-BREE)

Any material in wastewater found floating, suspended, settled, or moving along the bottom of a sewer. This material may cause stoppages by getting hung up on roots or settling out in a sewer. Debris includes grit, paper, plastic, rubber, silt, and all materials except liquids.

Decant Water (de-KANT)

Water that has separated from sludge and is removed from the layer of water above the sludge.

Desalinization (DEE-SAY-lin-uh-ZAY-shun)

The removal of dissolved salts (such as sodium chloride, NaCl) from water by natural means (leaching) or by specific water treatment processes.

Detritus (dee-TRY-tus)

The heavy material present in wastewater such as sand, coffee grounds, eggshells, gravel, and cinders. Also called grit.


  1. To remove or separate a portion of the water present in a sludge or slurry. To dry sludge so it can be handled and disposed of.
  2. To remove or drain the water from a tank or a trench. A structure may be dewatered so that it can be inspected or repaired


A point in a sewer pipe where a drain grade defect results in a puddle of standing water when there is no flow. If the grade defect is severe enough to cause the standing water to fill the pipe at any point (preventing passage of air through the pipe), it is called a trap dip, full dip, or filled dip.

Direct Filtration

A method of treating water that consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration. The flocculation facilities may be omitted, but the physical-chemical reactions will occur to some extent. The sedimentation process is omitted.

Direct Potable Reuse

Direct Potable Reuse can be defined as either the injection of recycled water directly into the potable water supply distribution system downstream of the water treatment plant, or into the raw water supply immediately upstream of the water treatment plant. Injection could either be into a service reservoir or directly into a water pipeline. Therefore, the water used by consumers could be either undiluted, or slightly diluted recycled water. In this definition, the key distinction with indirect potable reuse is that there is no temporal or spatial separation between the recycled water introduction and its distribution to consumers.

Direct Runoff

Water that flows over the ground surface directly into streams, rivers, or lakes. Also called storm runoff.


Discharge, or effluent, in the artificial sense is in general considered to be water pollution, such as the outflow from a sewage treatment facility or the wastewater discharge from industrial facilities. An effluent sump pump, for instance, pumps waste from toilets installed below a main sewage line.

Discharge Head

The pressure (in pounds per square inch (psi) or kilopascals (kPa) measured at the centerline of a pump discharge and very close to the discharge flange, converted into feet or meters. The pressure is measured from the centerline of the pump to the hydraulic grade line of the water in the discharge pipe.

Discharge Head, ft = (Discharge Pressure, psi)(2.31 ft/psi)


Discharge Head, m =(Discharge Pressure, kPa)(1 m/9.8 kPa)

Discharge Pressure

Discharge pressure (also called high side pressure or head pressure) is the pressure generated on the output side of a gas compressor in a refrigeration or air conditioning system. The discharge pressure is affected by several factors: size and speed of the condenser fan, condition and cleanliness of the condenser coil, and the size of the discharge line.

Disinfection (dis-in-FECT-shun)

The process designed to kill or inactivate most microorganisms in water or wastewater, including essentially all pathogenic (disease-causing) bacteria. There are several ways to disinfect, with chlorination being the most frequently used in water and wastewater treatment plants.

Dissolved Oxygen (DO)

Molecular oxygen dissolved in water or wastewater.


The rotating mechanism that distributes the wastewater evenly over the surface of a trickling filter or other process unit.

DO (pronounce as separate letters)

Dissolved Oxygen. DO is the molecular oxygen dissolved in water or wastewater.

Drain Field

Septic drain fields, also called leach fields or leach drains are used to remove contaminants and impurities from the liquid that emerges from the septic tank. A septic tank, the septic drain field, and the associated piping compose a complete septic system. The septic drain field is effective for disposal of organic materials readily catabolized by a microbial ecosystem.

Dry Well

A dry room or compartment in a lift station, near or below the water level, where the pumps are located, usually next to the wet well.

Dynamic Head

When a pump is operating, the vertical distance (in feet or meters) from a point to the energy grade line.

Dynamic Pressure

When a pump is operating, pressure resulting from the dynamic head.

Dynamic Pressure, psi = (Dynamic Head, ft)(0.433 psi/ft)


Dynamic Pressure, kPa = (Dynamic Head, m)(9.8 kPa/m)


Legal right to use the property of others for a specific purpose. For example, a utility company may have a five-foot (1.5 m) easement along the property line of a home. This gives the utility the legal right to install and maintain a sewer line within the easement.

Eductor (e-DUCK-ter)

A hydraulic device used to create a negative pressure (suction) by forcing a liquid through a restriction, such as a Venturi. An eductor or aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump. As an injector, it is used to produce vacuum for chlorinators. Sometimes used instead of a suction pump.

Effective Range

That portion of the design range (usually from 10 to 90+ percent) in which an instrument has acceptable accuracy. Also see RANGE and SPAN.

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.

Effluent Disinfection

Disinfection of effluent from water reclamation facilities (WRFs) is required to decrease the disease risks associated with the discharge of wastewaters containing human pathogens (disease-causing organisms) into receiving waters. These microorganisms are present in large numbers in wastewater.

Elutriation (e-LOO-tree-A-shun)

The washing of digested sludge with either fresh water, plant effluent, or other wastewater. The objective is to remove (wash out) fine particulates or the alkalinity in sludge. This process reduces the demand for conditioning chemicals and improves settling or filtering characteristics of the solids.

End Bells

Devices used to hold the rotor and stator of a motor in position.

End Point

The completion of a desired chemical reaction. Samples of water or wastewater are titrated to the end point. This means that a chemical is added, drop by drop, to a sample until a certain color change (blue to clear, for example) occurs. This is called the end point of the titration. In addition to a color change, an end point may be reached by the formation of a precipitate or the reaching of a specified pH. An end point may be detected by the use of an electronic device, such as a pH meter.

Enhanced Biological Phosphorus Removal (EBPR)

A sewage treatment configuration applied to activated sludge systems for the removal of phosphate.

Estimated Flow

A rough guess of the amount of flow in a collection system. When greater accuracy is needed, flow could be computed using average or typical flow quantities. Even greater accuracy would result from metering or otherwise measuring the actual flow.

European Foundation for Quality Management (EFQM)

EFQM brings together organizations striving for sustainable excellence. Through its network of members comprising private and public organizations of every size and sector, many active around the world, EFQM applies its know-how and extracts outstanding approaches by engaging with executives and front-line managers.

Exfiltration (EX-fill-TRAY-shun)

Liquid wastes and liquid-carried wastes that unintentionally leak out of a sewer pipe system and into the environment.

External Sludge

Sludge hauled to the sewage treatment plant from other sources.

Extremely Hazardous Waste

Any hazardous waste or mixture of hazardous wastes that, if any human exposure should occur, may likely result in death, disabling personal injury, or illness during, or as a proximate result of, any disposal of such waste or mixture of wastes because of its quantity, concentration, or chemical characteristics.

Federal Water Pollution Control Act of 1948

Primarily for the provision of federal funds for water quality surveys and construction of collection and treatment plants. Amended in 1972.


The water that is fed to a treatment process; the water that is going to be treated.


The process of passing water through a porous bed of fine granular material to remove suspended matter from the water. The suspended matter is mainly particles of floc, soil, and debris; but it also includes living organisms such as algae, bacteria, viruses, and protozoa.

Final Clarifiers

Once the flow has passed through the aeration tanks, it moves to the final clarifiers. Here the velocity is slowed to allow the sludge to settle.

Finished Water

Water that has passed through a water treatment plant. All the treatment processes are completed or finished. This water is the product from the water treatment plant and is ready to be delivered to consumers. Also called product water.


Scraper boards, made from redwood or other rotresistant woods or plastic, used to collect and move settled sludge or floating scum.

Float (Control)

A device used to measure the elevation of the surface of water. The float rests on the surface of the water and rises or falls with it. The elevation of the water surface is measured by a rod, chain, rope, or tape attached to the float.

Float on the System

A method of operating a water storage facility. Daily flow into the facility is approximately equal to the average daily demand for water. When consumer demands for water are low, the storage facility will be filling. During periods of high demand, the facility will be emptying.


Aluminium, iron, and calcium salts, which form poorly soluble compounds in the water.

Flocculation (flock-yoo-LAY-shun)

The gathering together of fine particles after coagulation to form larger particles by a process of gentle mixing. This clumping together makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.

Fluidized (FLOO-id-i-zd)

A mass of solid particles that is made to flow like a liquid by injection of water or gas is said to have been fluidized. In water and wastewater treatment, a bed of filter media is fluidized by backwashing water through the filter.


The removal of deposits of material that have lodged in water distribution lines or sewers because of inadequate velocity of flows. Water is discharged into the lines at such rates that the larger flow and higher velocities are sufficient to remove the material.

Foot Valve

A special type of check valve located at the bottom end of the suction pipe on a pump. This valve opens when the pump operates to allow water to enter the suction pipe but closes when the pump shuts off to prevent water from flowing out of the suction pipe.

Force Main

A pipe that carries wastewater under pressure from the discharge side of a pump to a point of gravity flow downstream.

Friction Loss

The head, pressure, or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, or restrictions caused by fittings. Water flowing in a pipe loses head, pressure, or energy as a result of friction. Also called head loss.

Gate Valve

A gate valve, also known as a sluice valve, is a valve that opens by lifting a round or rectangular gate wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar, so gate valves are often used when a straight-line flow of fluid and minimum restriction is desired.


A device for checking or measuring a particular dimension of something, using specific standardized units. For example, a gauge might measure the elevation of a water surface, the velocity of flowing water, the pressure of water, the amount or intensity of precipitation, or the depth of snowfall. Gauges also are used to determine the location or position of equipment during installation and after operation.

Gauge Pressure

The pressure within a closed container or pipe as measured with a gauge. In contrast, absolute pressure is the sum of atmospheric pressure (14.7 lbs/sq in (1.0 atm.)) PLUS pressure within a vessel (as measured with a gauge). Most pressure gauges read in “gauge pressure” or psig (pounds per square inch gauge pressure or kilopascals).

Geological Log

A detailed description of all underground features discovered during the drilling of a well (depth, thickness, and type of formations).

Globe Valve

A globe valve, different from ball valve, is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body.

Granular Activated Sludge

Activated sludge is also the name given to the active biological material produced by activated sludge plants. Excess sludge is called “surplus activated sludge” or “waste activated sludge” and is removed from the treatment process to keep the ratio of biomass to food supplied in the wastewater in balance.

Gravity Flow

Water or wastewater flowing from a higher elevation to a lower elevation due to the force of gravity. The water does not flow due to energy provided by a pump. Wherever possible, wastewater collection systems are designed to use the force of gravity to carry waste liquids and solids.

Grinder Pump

A small, submersible, centrifugal pump with an impeller, designed to grind solids into small pieces before they enter the collection system.


The heavy material present in wastewater such as sand, coffee grounds, eggshells, gravel, and cinders. Also called detritus.


Subsurface water in the saturation zone from which wells and springs are fed. In a strict sense the term applies only to water below the water table. Also called phreatic water and plerotic water.

Hard Water

Water having a high concentration of calcium and magnesium ions. A water may be considered hard if it has a hardness greater than the typical hardness of water from the region. Some textbooks define hard water as a water with a hardness of more than 100 mg/L as calcium carbonate.


The vertical distance, height, or energy of water above a reference point. A head of water may be measured in either height (feet or meters) or pressure (pounds per square inch or kilograms per square centimeter).

Head Loss

  1. For water: The head, pressure, or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, or restrictions caused by fittings. Water flowing in a pipe loses head, pressure, or energy as a result of friction. The head loss through a filter is due to friction caused by material building up on the surface or by the water flowing through the filter media.
  2. For wastewater: The head, pressure, or energy (they are the same) lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of the pipe, channel walls, or restrictions caused by fittings. Water flowing in a pipe loses head, pressure, or energy as a result of friction. The head loss through a comminutor is due to friction caused by the cutters or shredders as the water passes through them and by the roughness of the comminutor walls conveying the flow through the comminutor. Also called friction loss.


The facilities where wastewater enters a wastewater treatment plant. The headworks may consist of bar racks or bar screens, comminutors, a wet well, and pumps.

Hertz (Hz)

The number of complete electromagnetic cycles or waves in one second of an electric or electronic circuit. Also called the frequency of the current.

Hindered Solids Separation

Solids settling in a thickening rather than in a clarifying mode. Suspended solids settling (clarifying) velocities are strongly influenced by the applied solids concentration. The greater the applied solids concentration, the greater the opportunity for thickening (hindered) solids settling.

Hot Tap

Tapping into a sewer line under pressure, such as a force main or a small-diameter sewer under pressure.

Hydraulic Loading

Hydraulic loading refers to the flows (MGD or cum/day) to a treatment plant or treatment process. Detention times, surface loadings, and weir overflow rates are directly influenced by flows.

Hydraulic Population Equivalent

A flow of 100 gallons (378 liters) per day is the hydraulic or flow equivalent to the contribution or flow from one person. Population equivalent = 100 GPCD or gallons per capita per day (378 LPCD or liters per capita per day).

Hydrologic Cycle (HI-dro-LOJ-ick)

The process of evaporation of water into the air and its return to earth by precipitation (rain or snow). This process also includes transpiration from plants, groundwater movement, and runoff into rivers, streams, and the ocean. Also called the water cycle.

Hydrostatic Pressure (hi-dro-STAT-ick)

  1. The pressure at a specific elevation exerted by a body of water at rest.
  2. In the case of groundwater, the pressure at a specific elevation due to the weight of water at higher levels in the same zone of saturation.

Hydrostatic System (hi-dro-STAT-ick)

In a hydrostatic sludge removal system, the surface of the water in the clarifier is higher than the surface of the water in the sludge well or hopper. This difference in pressure head forces sludge from the bottom of the clarifier to flow through pipes to the sludge well or hopper.

Imhoff Tank

The Imhoff tank, named for German engineer Karl Imhoff (1876–1965), is a chamber suitable for the reception and processing of sewage. It may be used for the clarification of sewage by simple settling and sedimentation, along with anaerobic digestion of the extracted sludge.


A rotating set of vanes in a pump or compressor designed to pump or move water or air.


The conversion of dewatered wastewater solids by combustion (burning) to ash, carbon dioxide, and water vapor.

Indirect Potable Reuse

The reclamation and treatment of water from wastewater (usually sewage effluent) and the eventual returning of it into the current/natural water cycle well upstream of the drinking water treatment plant. Planned reuse indicates that there is an intent to reuse the water for potable use.

Industrial Wastewater

Liquid wastes originating from industrial processing. Because industries have peculiar liquid waste characteristics requiring special consideration, these sources are usually handled and treated separately before being discharged to a wastewater collection system.

Industrial Water Processes

Separated into two market segments—water treatment and wastewater treatment. Water treatment refers to the processes used to make city or reclaimed water acceptable for an intended use through the reduction or removal of contaminants. Wastewater treatment refers to the processes used to treat waters that have been contaminated by industrial or commercial activity prior to reuse or release to the environment.

Infiltration (in-fill-TRAY-shun)

The seepage of groundwater into a sewer system, including service connections. Seepage frequently occurs through defective or cracked pipes, pipe joints and connections, interceptor access risers and covers, or manhole walls.

Infiltration Head

The distance from a point of infiltration leaking into a collection system to the water table elevation. This is the pressure of the water being forced through the leak in the collection system.


Water discharged into a sewer system and service connections from such sources as, but not limited to, roof leaders, cellars, yard and area drains, foundation drains, cooling water discharges, drains from springs and swampy areas, around manhole covers or through holes in the covers, cross-connections from storm and combined sewer systems, catch basins, stormwaters, surface runoff, street wash waters, or drainage. Inflow differs from infiltration in that it is a direct discharge into the sewer rather than a leak in the sewer itself.


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


The basic physical and organizational structures and facilities (e.g., buildings, roads, and power supplies) needed for the operation of a society or enterprise.


Interference with the operation of wastewater treatment processes by the introduction of pollutants into publicly owned treatment works (POTWs).


  1. A surface connection to a drain pipe.
  2. A chamber for collecting stormwater with no well below the outlet pipe for collecting grit. Often connected to a CATCH BASIN or a basin manhole (cleanout manhole) with a grit chamber.

Input Horsepower

The total power used in operating a pump and motor.

Integrated Facility (Integrated Plant)

Plants that, prior to treatment or discharge, combine the metal finishing wastewaters with significant quantities (more than 10 percent of total volume) of wastewaters not covered by the metal finishing category. Also refers to any facilities covered by any of the industrial pretreatment categories and various combinations of categories.


A septic tank or other holding tank that serves as a temporary wastewater storage reservoir for a septic tank effluent pump (STEP) system.

Interceptor (Intercepting) Sewer

A large sewer that receives flow from a number of sewers and conducts the wastewater to a treatment plant. Often called an interceptor. The term interceptor is sometimes used in small communities to describe a septic tank or other holding tank that serves as a temporary wastewater storage reservoir for a septic tank effluent pump (STEP) system.

Internal Inflow

Nonsanitary or industrial wastewaters generated inside a domestic, commercial, or industrial facility and being discharged into the sewer system. Examples are cooling tower waters, basement sump pump discharge waters, continuous-flow drinking fountains, and defective or leaking plumbing fixtures.

Inverted Siphon

A pressure pipeline used to carry wastewater flowing in a gravity collection system under a depression, such as a valley or roadway, or under a structure, such as a building. Also called a depressed sewer.

Ion Exchange

A water or wastewater treatment process involving the reversible interchange (switching) of ions between the water being treated and the solid resin contained within an ion exchange unit. Undesirable ions are exchanged with acceptable ions on the resin or recoverable ions in the water being treated are exchanged with other acceptable ions on the resin.

Ion Exchange Resins

Insoluble polymers, used in water or wastewater treatment, that are capable of exchanging (switching or giving) acceptable cations or anions to the water being treated for less desirable ions or for ions to be recovered.


O-rings or gaskets used with piston pumps to provide a seal between the piston and the side wall.

Lift Station

A wastewater pumping station that lifts the wastewater to a higher elevation when continuing the sewer at reasonable slopes would involve excessive depths of trench. Also, an installation of pumps that raise wastewater from areas too low to drain into available sewers. Lift stations may be equipped with air-operated ejectors or centrifugal pumps. Sometimes called a pump station, but this term is usually reserved for a similar type of facility that is discharging into a long FORCE MAIN, while a lift station has a discharge line or force main only up to the downstream gravity sewer. Throughout these manuals when we refer to lift stations, we intend to include pump stations.


Limewater is the common name for a diluted solution of calcium hydroxide. Calcium hydroxide, Ca(OH)2, is sparsely soluble in water. Pure limewater is clear and colorless, with a slight earthy smell and an alkaline bitter taste of calcium hydroxide. The term lime refers to the alkaline mineral, and is unrelated to the acidic fruit.

Liquefaction (lick-we-FACK-shun)

The conversion of large, solid particles of sludge into very fine particles that either dissolve or remain suspended in wastewater.

Lubriflushing (LOOB-rah-flush-ing)

A method of lubricating bearings with grease. Remove the relief plug and apply the proper lubricant to the bearing at the lubrication fitting. Run the pump to expel excess lubricant.

Main Line

Branch or lateral sewers that collect wastewater from building sewers and service lines.

Main Sewer

A sewer line that receives wastewater from many tributary branches and sewer lines and serves as an outlet for a large territory or is used to feed an intercepting sewer. Also called trunk sewer.

Manning’s Formula

A mathematical formula for calculating wastewater flows in sewers. n Q means flow in cubic feet per second (CFS) (cubic meters per second (m3/s)). n n means the Manning pipe or channel roughness factor. 

A means the cross-sectional area of the flow in square feet (sq ft) (square meters (m2)).

R means the hydraulic radius in feet (meters) where R equals A/P. P is the wetted perimeter of the channel or pipe in feet (meters).

S means the slope of the channel or energy grade line in feet per foot (ft/ft) (meters per meter (m/m)).

Manometer (man-NAH-mut-ter)

An instrument for measuring pressure. Usually, a manometer is a glass tube filled with a liquid that is used to measure the difference in pressure across a flow measuring device, such as an orifice or a Venturi meter. The instrument used to measure blood pressure is a type of manometer.


Membrane Bioreactor. A wastewater treatment process that uses a suspended growth bioreactor (typically found in activated sludge treatment processes) coupled with a membrane filtration process like microfiltration or ultrafiltration.

MED (Multiple Effect Distillation)

Multiple-effect distillation (MED) is a distillation process often used for seawater desalination. It consists of multiple stages or “effects”. In each stage the feed water is heated by steam in tubes. Some of the water evaporates, and this steam flows into the tubes of the next stage, heating and evaporating more water. Each stage essentially reuses the energy from the previous stage.

Membrane Bioreactor (MBR)

A wastewater treatment process that uses a suspended growth bioreactor (typically found in activated sludge treatment processes) coupled with a membrane filtration process like microfiltration or ultrafiltration.

Microfiltration (MF)

A pressure-driven membrane filtration process that separates particles down to approximately 0.1 μm diameter from influent water using a sieving process.

Milligrams per Liter (mg/L)

A measure of the concentration by weight of a substance per unit volume in water or wastewater. In reporting the results of water and wastewater analysis, mg/L is preferred to the unit parts per million (ppm), to which it is approximately equivalent.

Million Gallons

A unit of measurement used in wastewater treatment plant design and collection system capacities or performances. One million gallons of water is approximately equivalent to these units of measurement:

13,690 Cubic Feet

3.07 Acre-Feet

8,340,000 Pounds of Weight

4,170 Tons of Weight

3,785 Cubic Meters

Mine Drainage Pump

Used in mines for maintenance of a normal water level and (as a part of dewatering plants) for pumping accumulated water above ground.

Mixed Liquor

When the activated sludge in an aeration tank is mixed with primary effluent or the raw wastewater and return sludge, this mixture is then referred to as mixed liquor as long as it is in the aeration tank. Mixed liquor also may refer to the contents of mixed aerobic or anaerobic digesters.

Mixed Sludge

A combination of primary, secondary, and tertiary sludges.


Mixed Liquor Suspended Solids. The amount (mg/L) of suspended solids in the mixed liquor of an aeration tank.

Motor Efficiency

The ratio of energy delivered by a motor to the energy supplied to it during a fixed period or cycle. Motor efficiency ratings will vary depending on motor manufacturer and usually will be near 90.0 percent.

MSF (multi-stage flash)

Multi-stage flash distillation (MSF) is a water desalination process that distills seawater by flashing a portion of the water into steam in multiple stages of what are essentially countercurrent heat exchangers.

Multistage Pump

A pump that has more than one impeller. A singlestage pump has one impeller.

Municipal wastewater (also called sewage)

Usually conveyed in a combined sewer or sanitary sewer, and treated at a wastewater treatment plant.


A municipality is usually an urban administrative division having corporate status and powers of self government or jurisdiction. The term municipality is also used to mean the governing, ruling body of a municipality. A municipality is a general-purpose administrative subdivision, as opposed to a special purpose district.

National Pollutant Discharge Elimination System(NPDES)

The U.S. Environmental Protection Agency (EPA) developed the federal National Pollutant Discharge Elimination System (NPDES) stormwater permitting program in two phases. Phase I, promulgated in 1990, addresses the following sources:

“Large” and “medium” municipal separate storm sewer systems (MS4s) located in incorporated places and counties with populations of 100,000 or more, and

Eleven categories of industrial activity, one of which is large construction activity that disturbs 5 or more acres of land.

Phase II, promulgated in 1999, addresses additional sources, including MS4s not regulated under Phase I, and small construction activity disturbing between 1 and 5 acres.

In October 2000, EPA authorized the Florida Department of Environmental Protection (DEP) to implement the NPDES stormwater permitting program in the State of Florida (in all areas except Indian Country lands). DEP’s authority to administer the NPDES program is set forth in Section 403.0885, Florida Statutes (F.S.). The NPDES stormwater program regulates point source discharges of stormwater into surface waters of the State of Florida from certain municipal, industrial and construction activities. As the NPDES stormwater permitting authority, DEP is responsible for promulgating rules and issuing permits, managing and reviewing permit applications, and performing compliance and enforcement activities.

Nanofiltration (NF)

A pressure-driven membrane filtration process that separates particles down to approximately 0.002 to 0.005 μm diameter from influent water using a sieving process.

Net Wastewater Contribution

In a wastewater collection system, the net wastewater contribution consists of the liquid wastes and liquid-carried wastes transported by the pipelines or received by the pipelines. This value would be the only wastewater found in a collection system if all sources of infiltration, inflow, and exfiltration were eliminated.

Net Wastewater Flow

The actual wastewater flow from a collection system that reaches a wastewater treatment plant. The net wastewater flow includes the net wastewater contribution, infiltration, and inflow and does not include losses through exfiltration.

Nitrification (NYE-truh-fuh-KAY-shun)

An aerobic process in which bacteria change the ammonia and organic nitrogen in water or wastewater into oxidized nitrogen (usually nitrate).

Nitrogen Removal

High levels of nitrogen in water resources create hazard to human health and the environment. In many watersheds nitrogen from wastewater contributes 40 to 80 percent of total nitrogen loads (Lombardo, 2007). When Designing wastewater treatment system, nitrogen removal is the main concern. There are different methods used to remove nitrogen in the wastewater. Nitrogen in the ammonia form is toxic to certain aquatic organism (USEPA, 2002). According to USEPA (2002), Organic and inorganic forms of nitrogen may cause eutrophicaion (i.e., high productivity of algae) problems in nitrogenlimited freshwater lakes and in estuarine and coastal water.

Nonintegrated Facility

Plants that produce wastewaters from different pretreatment categorical processes but do not combine the wastestreams prior to pretreatment or discharge to sewers.


Any solid object in or protruding into a wastewater flow in a collection line that prevents a smooth or even passage of the wastewater.

Operating Pressure Differential

The operating pressure range for a hydropneumatic system. For example, when the pressure drops below 40 psi in a system designed to operate between 40 psi and 60 psi, the pump will come on and stay on until the pressure builds up to 60 psi. When the pressure reaches 60 psi the pump will shut off. The operating pressure differential in this example is 20 psi.

ORP (pronounce as separate letters)

Oxidation-Reduction Potential. The electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element (the reductant); used as a qualitative measure of the state of oxidation in water and wastewater treatment systems. ORP is measured in millivolts, with negative values indicating a tendency to reduce compounds or elements and positive values indicating a tendency to oxidize compounds or elements.

Osmosis (oz-MOE-sis)

The passage of a liquid from a weak solution to a more concentrated solution across a semipermeable membrane. The membrane allows the passage of the water (solvent) but not the dissolved solids (solutes). This process tends to equalize the conditions on either side of the membrane.

Outfall Sewer

A sewer that receives wastewater from a collection system or from a wastewater treatment plant and carries it to a point of ultimate or final discharge in the environment.

Overall Efficiency, Pump

The combined efficiency of a pump and motor together. Also called the wire-to-wire efficiency.

Overflow Rate

One of the guidelines for the design of settling tanks and clarifiers in treatment plants. Used by operators to determine if tanks and clarifiers are hydraulically (flow) over- or underloaded. Also called surface loading.


Oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound; in the environment and in wastewater treatment processes, organic matter is oxidized to more stable substances.

Ozonation (O-zoe-NAY-shun)

The application of ozone to water, wastewater, or air, generally for the purposes of disinfection or odor control.

Package Treatment Plant

A small wastewater treatment plant often fabricated at the manufacturer’s factory, hauled to the site, and installed as one facility. The package may be either a small primary or a secondary wastewater treatment plant.

Packing Ring

A ring made of asbestos or metal, which may be lubricated with Teflon or graphite, that forms a seal between the pump shaft and its casing.

Parallel Operation

Wastewater being treated is split and a portion flows to one treatment unit while the remainder flows to another similar treatment unit.

Parts Per Million (PPM)

Parts per million parts, a measurement of concentration on a weight or volume basis. This term is equivalent to milligrams per liter (mg/L), which is the preferred term.

Peristaltic Pump (PAIR-uh-STALL-tick)

A type of positive displacement pump also commonly referred to as a “hose pump”.

Phosphorus Recovery

While phosphorus recovery in the United States is still opportunistic and voluntary, Sweden’s Committee on Environmental Objectives studying sustainable development proposed a goal for returning 75 percent of waste- and wastewaterborne phosphorus to the ecosystem. The Swedish Environmental Protection Agency further refined the goal, proposing that at least 60 percent of wastewater phosphorus be restored to productive soil – half of which should be returned to arable land – by 2015. A goal of 70 percent recovery is now set for other plants in Europe.

Physical Waste Treatment Process

Physical wastewater treatment processes include use of racks, screens, comminutors, clarifiers (sedimentation and flotation), and filtration. Chemical or biological reactions are important treatment processes, but not part of a physical treatment process.

Pilot-Scale Study

A method of studying different ways of treating water or wastewater and solids or to obtain design criteria on a small scale in the field.

Plant Hydraulic Capacity

The flow or load, in millions of gallons per day (or portion thereof), that a treatment plant is designed to handle.


Programmable logic controller. A microcomputer-based control device containing programmable software; used to control process variables.

Plunger Pump

A plunger pump is a type of positive displacement pump where the high-pressure seal is stationary and a smooth cylindrical plunger slides through the seal. This makes them different from piston pumps and allows them to be used at higher pressures. This type of pump is often used to transfer municipal and industrial sewage.

Pneumatic Ejector (noo-MAT-tik ee-JECK-tor)

A device for raising wastewater, sludge, or other liquid by compressed air. The liquid is alternately admitted through an inward-swinging check valve into the bottom of an airtight pot. When the pot is filled, compressed air is applied to the top of the liquid. The compressed air forces the inlet valve closed and forces the liquid in the pot through an outward-swinging check valve, thus emptying the pot.

Positive Displacement Pump

A type of piston, diaphragm, gear, or screw pump that delivers a constant volume with each stroke. Positive displacement pumps are used as chemical solution feeders.

Positive Pressure

A positive pressure is a pressure greater than atmospheric. It is measured as pounds per square inch (psi) or as inches of water column. A negative pressure (vacuum) is less than atmospheric and is sometimes measured in inches of mercury. In the metric system, pressures are measured in kg/sq m, kg/sq cm, or pascals (1 psi = 6,895 Pa = 6.895 kN/sq m).


Publicly Owned Treatment Works. A treatment works that is owned by a state, municipality, city, town, special sewer district, or other publicly owned and financed entity as opposed to a privately (industrial) owned treatment facility. This definition includes any devices and systems used in the storage, treatment, recycling, and reclamation of municipal sewage (wastewater) or industrial wastes of a liquid nature. It also includes sewers, pipes, and other conveyances only if they carry wastewater to a POTW treatment plant. The term also means the municipality (public entity) that has jurisdiction over the indirect discharges to and the discharges from such a treatment works.


The addition of air at the initial stages of treatment to freshen the wastewater, remove gases, add oxygen, promote flotation of grease, and aid coagulation.

Pressure Control

A switch that operates on changes in pressure. Usually this is a diaphragm pressing against a spring. When the force on the diaphragm overcomes the spring pressure, the switch is activated.

Pressure Head

The vertical distance (in feet or meters) equal to the pressure (in psi or kPa) at a specific point. The pressure head is equal to the pressure in psi (or kPa) times 2.31 ft/psi (or 1.0 m/9.81 kPa).

Pretreatment Facility

Industrial wastewater treatment plant consisting of one or more treatment devices designed to remove sufficient pollutants from wastewaters to allow an industry to comply with effluent limits established by the US EPA General and Categorical Pretreatment Regulations or locally derived prohibited discharge requirements and local effluent limits. Compliance with effluent limits allows for a legal discharge to a POTW.

Primary Clarifiers

Primary clarifiers are most commonly used in “municipal” wastewater treatment systems even though many municipal wastewater plants have a significant industrial flow contribution. In an “industrial” wastewater treatment plant primary clarifiers are used less frequently. The reason has to do with the generally higher suspended solids concentration in a municipal wastewater influent than what is often found in many industrial wastewater streams which makes gravity settling in relatively large primary clarifiers a very effective unit process. In a municipal wastewater plant, the primary clarifier also helps provide “equalization” to the potentially high strength recycle flows that are generated from sludge thickening, sludge treatment, and sludge dewatering processes.

Primary Sludge

Sludge from sedimentation tanks.

Primary Treatment

A wastewater treatment process that takes place in a rectangular or circular tank and allows those substances in wastewater that readily settle or float to be separated from the wastewater being treated. A septic tank is also considered primary treatment.

Private Water Utilities

Professional water service providers that own regulated water and wastewater utilities, partner with municipalities in a form of public-private partnership, or operate systems as a contracted service provider. These companies may be privately owned or publicly traded.


Pounds per Square Inch Gauge pressure. The pressure within a closed container or pipe measured with a gauge in pounds per square inch.

Public Water Utilities

A public utility is an organization that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Public utilities are subject to forms of public control and regulation ranging from local community-based groups to statewide government monopolies.

Publicly Owned Treatment Works (POTWs)

A publicly owned treatment works (POTW) is a term used in the United States for a sewage treatment plant that is owned, and usually operated, by a government agency. In the U.S., POTWs are typically owned by local government agencies, and are usually designed to treat domestic sewage and not industrial wastewater.

Public-Private Partnership (PPP)

A public–private partnership (PPP or 3P or P3) is a government service of government and one or more private sector companies. PPP involves a contract between a public sector authority and a private party, in which the private party provides a public service or project and assumes substantial financial, technical and operational risk in the project.


Evenly spaced, parallel metal bars or rods located in the influent channel to remove rags, rocks, and cans from wastewater.

RAS (pronounce as separate letters, or RAZZ)

Return Activated Sludge. Settled activated sludge that is collected in the secondary clarifier or the membrane basin and returned to the aeration basin to mix with incoming raw or primary settled wastewater.

Raw Wastewater

Plant influent or wastewater before any treatment.

Receiving Water

A stream, river, lake, ocean, or other surface or groundwaters into which treated or untreated wastewater is discharged.


A constituent of wastewater or surface waters that uses either free (O2) or combined oxygen in the process of stabilization.

Resource Recovery

The selective extraction of disposed materials for a specific next use, such as recycling, composting or energy generation in order to extract the maximum benefits from products, delay the consumption of virgin resources, and reduce the amount of waste generated.

Return Activated Sludge (RAS)

Settled activated sludge that is collected in the secondary clarifier or the membrane basin and returned to the aeration basin to mix with incoming raw or primary settled wastewater.

Reverse Osmosis (RO) (oz-MOE-sis)

The application of pressure to a concentrated solution, which causes the passage of a liquid from the concentrated solution to a weaker solution across a semipermeable membrane. The membrane allows the passage of the water (solvent) but not the dissolved solids (solutes). In the reverse osmosis process, two liquids are produced: (1) the reject (containing high concentrations of dissolved solids), and (2) the permeate (containing low concentrations). The clean water (permeate) is not always considered to be demineralized.

Rivers and Harbors Appropriations (“Refuse Act”)1899

The first federal regulation of sewage, it prohibited the discharge of solids to navigational waters without a permit from U.S. Army Corps of Engineers

Rotary Pump

A type of displacement pump consisting essentially of elements rotating in a close-fitting pump case. The rotation of these elements alternately draws in and discharges the water being pumped. Such pumps act with neither suction nor discharge valves, operate at almost any speed, and do not depend on centrifugal forces to lift the water.


The rotating part of a machine. The rotor is surrounded by the stationary (nonmoving) parts (stator) of the machine.


That part of rain or other precipitation that runs off the surface of a drainage area and does not enter the soil or the sewer system as inflow.

SCADA System (SKAY-dah)

Supervisory Control And Data Acquisition system. A computer-monitored alarm, response, control, and data acquisition system used to monitor and adjust treatment processes and facilities.


Standard Cubic Feet per Minute. Cubic feet of air per minute at standard conditions of temperature, pressure, and humidity (0ÅãC, 14.7 psia, and 50 percent relative humidity).

Seawater Desalination

Desalination or desalinization is a process that removes minerals from saline water. More generally, desalination may also refer to the removal of salts and minerals, as in soil desalination, which also happens to be a major issue for agricultural production.

Secondary Clarifier

A wastewater treatment device consisting of a rectangular or circular tank that allows separation of substances that settle or float not removed by previous treatment processes.

Secondary Sludge

Sludge from biological sewage treatment.

Secondary Treatment

A wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the water being treated. Usually, the process follows primary treatment using sedimentation. The process commonly is a type of biological treatment followed by secondary clarifiers that allow the solids to settle out from the water being treated.


Sedimentation is a physical water treatment process using gravity to remove suspended solids from water. Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans. Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation.

Seed Sludge

In wastewater treatment, seed, seed culture, or seed sludge refer to a mass of sludge that contains populations of microorganisms. When a seed sludge is mixed with wastewater or sludge being treated, the process of biological decomposition takes place more rapidly.

Septic Tank

A septic tank is a key component of a septic system, a small-scale sewage treatment system common in areas that lack connection to main sewage pipes provided by local governments or private corporations.

Septic Tank Effluent Filter System (STEF)

A facility in which effluent flows from a septic tank into a gravity flow collection system that flows into a gravity sewer, treatment plant, or subsurface leaching system. The gravity flow pipeline is called an effluent drain.

Septic Tank Effluent Pump System (STEP)

A facility in which effluent is pumped from a septic tank into a pressurized collection system that may flow into a gravity sewer, treatment plant, or subsurface leaching system.

Septicity (sep-TIS-uh-tee)

The condition in which organic matter decomposes to form foul-smelling products associated with the absence of free oxygen. If severe, the wastewater produces hydrogen sulfide, turns black, gives off foul odors, contains little or no dissolved oxygen, and the wastewater has a high oxygen demand.

Sequencing Batch Reactor (SBR)

A type of activated sludge system that is specifically designed and automated to mix/aerate untreated wastewater and allow solids flocculation/separation to occur as a batch treatment process.


A type of wastewater that comprises domestic wastewater and is therefore contaminated with feces or urine from people’s toilets, but the term sewage is also used to mean any type of wastewater.

Sewage Lifting Unit

Sewage lifting units are complete drainage systems which operate automatically. Water level sensors are integrated in the collecting tank to monitor and control the pumps in combination with a control system. The pumps are started and stopped as a function of the water level. Single-pump or dual-pump sewage lifting units are used in buildings, including hotels and hospitals, to dispose of domestic waste water and sewage from below the flood level, where it will not run off following a natural gradient


The physical infrastructure, including pipes, pumps, screens, channels, etc., used to convey sewage from its origin to the point of eventual treatment or disposal.

Shock Load

1. The arrival at a water treatment plant of raw water containing unusual amounts of algae, colloidal matter, color, suspended solids, turbidity, or other pollutants.

2. The arrival at a waste treatment facility of a waste that is toxic to organisms in sufficient quantity or strength to cause operating problems. Possible problems include odors and sloughing off of the growth or slime on trickling filter media, or bulking sludge, which will result in a high loss of solids from the secondary clarifiers into the plant effluent and a biological process upset. Organic or hydraulic overloads also can cause a shock load.


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

Shut-Off Valve

When this type of valve is tripped, the flow is quickly stopped and an indicator disc tells the operator that the electrical circuit has been opened by a failure somewhere in the system. When the system failure has been corrected so that the circuit is again closed, the valve can be opened by the action of the hand lever.


Wastewater flows that develop from other storage or treatment facilities. This wastewater may or may not need additional treatment.

Single-Stage Pump

A pump that has only one impeller. A multistage pump has more than one impeller.

Slow Sand Filtration

Slow sand filters are used in water purification for treating raw water to produce a potable product. They are typically 1 to 2 meters deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water.

Sludge (SLUJ)

  1. The settleable solids separated from liquids during processing.
  2. The deposits of foreign materials on the bottoms of streams or other bodies of water or on the bottoms and edges of wastewater collection lines and appurtenances.

Sludge Homogenization

To obtain a conveyable medium.

Sludge Treatment

Solids removed in the sewage treatment process are rendered harmless by means of digestion, composting or pasteurization and are eliminated by sintering or incineration.

Sludge Volume Index (SVI)

A calculation that indicates the tendency of activated sludge solids (aerated solids) to thicken or to become concentrated during the sedimentation/thickening process. SVI is calculated in the following manner: (1) allow a mixed liquor sample from the aeration basin to settle for 30 minutes; (2) determine the suspended solids concentration for a sample of the same mixed liquor; (3) calculate SVI by dividing the measured (or observed) wet volume (mL/L) of the settled sludge by the dry weight concentration of MLSS in grams/L.

Sludge Volume Ratio (S/V)

The volume of sludge blanket divided by the daily volume of sludge pumped from the thickener.


A watery mixture or suspension of insoluble (not dissolved) matter; a thin, watery mud or any substance resembling it (such as a grit slurry or a lime slurry).

Slurry Pump

A slurry pump is a type of centrifugal pump, lobe pump or peristaltic hose pump in physics principle that increases the pressure of liquid and solid particle mixture (aka slurry), through centrifugal force (a rotating impeller) and converts electrical energy into slurry potential and kinetic energy.

Small-Diameter Gravity Sewer System (SDGS)

A type of collection system in which a series of septic tanks discharge effluent by gravity, pump, or siphon to a small-diameter wastewater collection main. The wastewater flows by gravity to a lift station, a manhole in a conventional gravity collection system, or directly to a wastewater treatment plant.

Solids Separation System

This innovative technology temporarily prevents solids and other sewage content from reaching the pump while allowing the pump to handle the complete content afterward. This process enables the hydraulic to use smaller free passages without clogging, leading to higher efficiency and a less limited head.

Specific Gravity

  1. Weight of a particle, substance, or chemical solution in relation to the weight of an equal volume of water. Water has a specific gravity of 1.000 at 4C (39F). Particulates with specific gravity less than 1.0 float to the surface and particulates with specific gravity greater than 1.0 sink. Wastewater particles or substances usually have a specific gravity of 0.5 to 2.5.
  2. Weight of a particular gas in relation to the weight of an equal volume of air at the same temperature and pressure (air has a specific gravity of 1.0). Chlorine gas has a specific gravity of 2.5.

Static Head

When water is not moving, the vertical distance (in feet or meters) from a reference point to the water surface is the static head.

Static Lift

Vertical distance water is lifted from upstream water surface to downstream water surface (which is at a higher elevation) when no water is being pumped.

Static Pressure

When water is not moving, the vertical distance (in feet or meters) from a specific point to the water surface is the static head. The static pressure in psi (or kPa) is the static head in feet times 0.433 psi/ft (or meters 9.81 kPa/m).

Static Water Head

Elevation or surface of water that is not being pumped.

Steeter Phelps DO Sag Curve

Model for streams to predict BOD assimilation capacity.

Storm Runoff

Water that flows over the ground surface directly into streams, rivers, or lakes. Also called direct runoff.

Storm Sewer

A separate pipe, conduit, or open channel (sewer) that carries runoff from storms, surface drainage, and street wash, but does not include domestic and industrial wastes. Storm sewers are often the recipients of hazardous or toxic substances due to the illegal dumping of hazardous wastes or spills caused by accidents involving vehicles transporting these substances.


The excess water running off from the surface of a drainage area during and immediately after a period of rain.

Stormwater Lift Station

Stormwater Pump Stations are constructed for the removal of surface water from areas lacking drainage or for control of storm water run off. These pump stations are similar to Sanitary Lift Stations in many respects, except they often do not include the valve vault. In these cases the control valves are installed in the pump station or in small cast iron valve boxes. Stormwater Pump Stations can be designed with submersible pumps or with other style pumps, such as vertical turbine pumps or propeller pumps, where high flows are encountered.

Submersible Mixer

A mechanical device that is used to mix sludge tanks and other liquid volumes. Submersible mixers are often used in sewage treatment plants to keep solids in suspension in the various process tanks and/or sludge holding tanks.

Submersible Motor

Municipal and industrial wastewater markets use submersible motors for both wet and dry pit applications. These are totally enclosed, nonventilated motors. Wet pit motors use the effluent for cooling and are designed to run continuously while submerged.

Submersible Pump

A device which has a hermetically sealed motor closecoupled to the pump body. The whole assembly is submerged in the fluid to be pumped.[4] The main advantage of this type of pump is that it prevents pump cavitation, a problem associated with a high elevation difference between pump and the fluid surface. Submersible pumps push fluid to the surface as opposed to jet pumps having to pull fluids. Submersibles are more efficient than jet pumps.

Suction Head

The positive pressure in feet (meters) of water or pounds per square inch (kilograms per square centimeter) of mercury vacuum on the suction side of a pump. The pressure can be measured from the centerline of the pump up to the elevation of the hydraulic grade line on the suction side of the pump.

Suction Lift

The negative pressure [in feet (meters) of water or inches (centimeters) of mercury vacuum] on the suction side of a pump. The pressure can be measured from the centerline of the pump down to (lift) the elevation of the hydraulic grade line on the suction side of the pump.


This term refers to a facility or structure that connects an industrial discharger to a public sewer. The sump could be a sample box, a clarifier, or an intercepting sewer.

Surface Loading

One of the guidelines for the design of settling tanks and clarifiers in treatment plants. Used by operators to determine if tanks and clarifiers are hydraulically (flow) over- or underloaded. Also called overflow rate.

Surge Chamber

A chamber or tank connected to a pipe and located at or near a valve that may quickly open or close or a pump that may suddenly start or stop. When the flow of water in a pipe starts or stops quickly, the surge chamber allows water to flow into or out of the pipe and minimize any sudden positive or negative pressure waves or surges in the pipe.


Sustainability is the property of biological systems to remain diverse and productive indefinitely.


Sludge Volume Index. A calculation that indicates the tendency of activated sludge solids (aerated solids) to thicken or to become concentrated during the sedimentation/thickening process. SVI is calculated in the following manner: (1) allow a mixed liquor sample from the aeration basin to settle for 30 minutes; (2) determine the suspended solids concentration for a sample of the same mixed liquor; (3) calculate SVI by dividing the measured (or observed) wet volume (mL/L) of the settled sludge by the dry weight concentration of MLSS in grams/L.

SWPA (Submersible Wastewater Pump Association)

A national trade association representing and serving the manufacturers of submersible pumps for municipal and industrial wastewater applications. Founded in 1976, the associations primary focus is on industry guidelines, education, and promotion.

10 States Standards from the Great Lakes-Upper Mississippi River Board

The Great Lakes-Upper Mississippi River Board of State and Provincial Public Health and Environmental Managers in 1950 created a Water Supply Committee consisting of one associate from each state represented on the Board. A representative from the Province of Ontario was added in 1978. The Committee was assigned the responsibility for reviewing existing water works practices, policies, and procedures, and reporting its findings to the Board. The report of the Water Supply Committee was first published in 1953, and subsequently has been revised and published in 1962, 1968, 1976, 1982, 1987, 1992, 1997, 2003, 2007, and 2012.

Tertiary Sludge

Sludge from the third stage of sewage treatment.

Tertiary Treatment (TER-she-air-ee)

Any process of water renovation that upgrades treated wastewater to meet specific reuse requirements. May include general cleanup of water or removal of specific parts of wastes insufficiently removed by conventional treatment processes. Typical processes include chemical treatment and pressure filtration. Also called advanced waste treatment.


Treatment to remove water from the sludge mass to reduce the volume that must be handled.

Total Dynamic Head (TDH)

When a pump is lifting or pumping water, the vertical distance (in feet or meters) from the elevation of the energy grade line on the suction side of the pump to the elevation of the energy grade line on the discharge side of the pump. The total dynamic head is the static head plus pipe friction losses.

Total Flow

The total flow passing a selected point of measurement in the collection system during a specified period of time.

Transducer (trans-DUE-sir)

A device that senses some varying condition measured by a primary sensor and converts it to an electrical or other signal for transmission to some other device (a receiver) for processing or decision making.

Trickling Filter

A trickling filter is a type of wastewater treatment system first used by Dibden and Clowes It consists of a fixed bed of rocks, lava, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media.

U.S. Army Corps of Engineers

The U.S. Army Corps of Engineers has approximately 37,000 dedicated civilians and soldiers delivering engineering services to customers in more than 130 countries worldwide. With environmental sustainability as a guiding principle, the disciplined Corps team works diligently to strengthen U.S. security by building and maintaining America’s infrastructure and providing military facilities where service members train, work and live.

Vacuum Filter

A device that removes all visible oil mist from vacuum pump exhaust, even when it is saturated with oil. The exhaust gas may be recycled to the process or the pumps may exhaust into a clean work area, eliminating the need to run ductwork and exhaust pipes outside.

Variable Frequency Drive

A control system that allows the frequency of the current applied to a motor to be varied. The motor is connected to a low-frequency source while standing still; the frequency is then increased gradually until the motor and pump (or other driven machine) are operating at the desired speed.

Velocity Head

The energy in flowing water as determined by a vertical height (in feet or meters) equal to the square of the velocity of flowing water divided by twice the acceleration due to gravity (V2/2g).

Viscosity (vis-KOSS-uh-tee)

A property of water, or any other fluid, that resists efforts to change its shape or flow. Syrup is more viscous (has a higher viscosity) than water. The viscosity of water increases significantly as temperatures decrease. Motor oil is rated by how thick (viscous) it is; 20 weight oil is considered relatively thin while 50 weight oil is relatively thick or viscous.

Volute (vol-LOOT)

The spiral-shaped casing that surrounds a pump, blower, or turbine impeller and collects the liquid or gas discharged by the impeller.


A community’s used water and water-carried solids (including used water from industrial processes) that flow to a treatment plant. Stormwater, surface water, and groundwater infiltration also may be included in the wastewater that enters a wastewater treatment plant. The term sewage usually refers to household wastes, but this word is being replaced by the term wastewater.

Wastewater Collection System

The pipe system for collecting and carrying water and water-carried wastes from domestic and industrial sources to a wastewater treatment plant.

Wastewater Lift Station

Sewage lift/pump stations are used for pumping wastewater or sewage from a lower to higher elevation, particularly where the elevation of the source is not sufficient for gravity flow and/or when the use of gravity conveyance will result in excessive excavation and higher construction costs.

Wastewater Treatment

Refers to the physical, chemical, and biological processes used to remove pollutants from wastewater before discharging it into a water body.

Wastewater Treatment

Refers to the physical, chemical, and biological processes used to remove pollutants from wastewater before discharging it into a water body. The major aim of wastewater treatment is to remove as much of the suspended solids as possible before the remaining water, called effluent, is discharged back to the environment. As solid material decays, it uses up oxygen, which is needed by the plants and animals living in the water.

Water Conditioning

Private water supplies typically require treatment for undesirable properties that are present from the water source. Disinfection is necessary around the world to provide biologically safe drinking water to prevent waterborne diseases such as cholera, typhoid and dysentery. To prevent corrosion and the pitting of pipes and appliances, pH adjustment or control is often necessary. Water containing excessive levels of iron, manganese or hydrogen sulfide can stain appliances, foul filters or cause an unpleasant rotten egg odor and requires treatment.

Water Environment Federation (WEF)

The Water Environment Federation is an organization of engineers and industry related to wastewater, water, and water reuse. WEF, founded in 1928, was formerly known as the Federation of Sewage Works Associations and later as the Water Pollution Control Federation.

Water Hammer

What occurs when a valve is opened or closed very rapidly. When a valve position is changed quickly, the water pressure in a pipe will increase and decrease back and forth very quickly. This rise and fall in pressures can cause serious damage to the system.


The region or land area that contributes to the drainage or catchment area above a specific point on a stream or river.

Water Quality Act of 1987 (EPA)

A bill to amend the Federal Water Pollution Control Act to provide for the renewal of the quality of the Nation’s waters, and for other purposes.

Wellhead Protection Area (WHPA)

The surface and subsurface area surrounding a public water system water well or well field, through which contaminants are reasonably likely to move toward and reach such water well or well field.

Wet Well

A compartment or tank in which wastewater is collected. The suction pipe of a pump may be connected to the wet well or a submersible pump may be located in the wet well.


The quantity of water (expressed as a rate of flow— GPM, GPH, GPD, cu m/day, ML/day, or total quantity per year) that can be collected for a given use from surface or groundwater sources. The yield may vary with the use proposed, with the plan of development, and also with economic considerations.

Zone of Saturation

1. The soil or rock located below the top of the groundwater table. By definition, the zone of saturation is saturated with water.

2. Where raw wastewater is exfiltrating from a sewer pipe, the area of soil that is moistened around the leak point is often called the zone of saturation.




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