Wastewater Terminology And Definitions

If you wish to converse with me, define your terms.



To learn wastewater treatment operations (or any other technology for that matter), you must master the language associated with the technology. Each technology has its own terms with definitions. Many of the terms used in wastewater treatment are unique; others combine words from many different technologies and professions. One thing is certain: Wastewater operators without a clear understanding of the terms related to their profession are ill equipped to perform their duties in the manner required. Usually, a handbook or text like this one includes a glossary of terms at the end of the work. In this handbook, however, we list and define many of the terms used right upfront. Experience has shown that an early introduction to keywords is a benefit to readers. An upfront introduction to key terms facilitates a more orderly, logical, systematic learning activity. Those terms not defined in this section are defined as they appear in the text. A short quiz on many of the following terms follows at the end of this chapter.

Absorb—To take in. Many things absorb water.

Acid, rain—The acidic rainfall that results when rain combines with sulfur oxides emissions from combustion of fossil fuels (coal, for example).

Acre-feet (acre-foot)—An expression of water quantity. One acre-foot will cover 1 acre of ground 1 foot deep. An acre-foot contains 43,560 cubic feet, 1233 cubic meters, or 325,829 gallons (U.S). Also abbreviated as ac-ft.

Activated carbon—Derived from vegetable or animal materials by roasting in a vacuum furnace. Its porous nature gives it a very high surface area per unit mass—as much as 1000 square meters per gram, which is 10 million times the surface area of 1 gram of water in an open container. Used in adsorption (see definition), activated carbon adsorbs substances that are not or are only slightly adsorbed by other methods.

Activated sludge—The solids formed when microorganisms are used to treat wastewater using the activated sludge treatment process. It includes organisms, accumulated food materials, and waste products from the aerobic decomposition process.

Adsorption—The adhesion of a substance to the surface of a solid or liquid. Adsorption is often used to extract pollutants by causing them to attach to such adsorbents as activated carbon or silica gel. Hydrophobic (water-repulsing) adsorbents are used to extract oil from waterways in oil spills.

Advanced wastewater treatment—Treatment technology to produce an extremely high-quality discharge.

Aeration—The process of bubbling air through a solution, sometimes cleaning water of impurities by exposure to air.

Aerobic—Conditions in which free, elemental oxygen is present. Also used to describe organisms, biological activity, or treatment processes that require free oxygen.

Agglomeration—Floc particles colliding and gathering into a larger settleable mass.

Air gap—The air space between the free-flowing discharge end of a supply pipe and an unpressurized receiving vessel.

Algae bloom—A phenomenon whereby excessive nutrients within a river, stream, or lake causes an explosion of plant life that results in the depletion of the oxygen in the water needed by fish and other aquatic life. Algae bloom is usually the result of urban runoff (of lawn fertilizers, etc.). The potential tragedy is that of a "fish kill," where the stream life dies in one mass execution.

Alum—Aluminum sulfate, a standard coagulant used in water treatment.

Ambient—The expected natural conditions that occur in water unaffected or uninfluenced by human activities.

Anaerobic—Conditions in which no oxygen (free or combined) is available. Also used to describe organisms, biological activity, or treatment processes that function in the absence of oxygen.

Anoxic—Conditions in which no free, elemental oxygen is present. The only source of oxygen is combined oxygen, such as that found in nitrate compounds. Also used to describe biological activity of treatment processes that function only in the presence of combined oxygen.

Aquifer—A water-bearing stratum of permeable rock, sand, or gravel.

Aquifer system—A heterogeneous body of introduced permeable and less permeable material that acts as a water-yielding hydraulic unit of regional extent.

Artesian water—A well tapping a confined or artesian aquifer in which the static water level stands above the top of the aquifer. The term is sometimes used to include all wells tapping confined water. Wells with water level above the water table are said to have positive artesian head (pressure), and those with water level below the water table negative artesian head.

Average monthly discharge limitation—The highest allowable discharge over a calendar month.

Average weekly discharge limitation—The highest allowable discharge over a calendar week.

Backflow—Reversal of flow when pressure in a service connection exceeds the pressure in the distribution main.

Backwash—Fluidizing filter media with water, air, or a combination of the two so individual grains can be cleaned of the material that has accumulated during the filter run.

Bacteria—Any of a number of one-celled organisms, some of which cause disease.

Bar screen—A series of bars formed into a grid used to screen out large debris from influent flow.

Base—A substance that has a pH value between 7 and 14.

Basin—A groundwater reservoir defined by the overlying land surface and underlying aquifers that contain water stored in the reservoir.

Beneficial use of water—The use of water for any beneficial purpose. Such uses include domestic, irrigation, recreation, fish and wildlife, fire protection, navigation, power, and industrial uses, among others. The benefit varies from one location to another and by custom. What constitutes beneficial use is often defined by statute or court decisions.

Biochemical oxygen demand (BOD5)—The oxygen used in meeting the metabolic needs of aerobic microorganisms in water rich in organic matter.

Biosolids*— Solid organic matter recovered from a sewage treatment process and used especially as fertilizer or soil amendment; usually

* In this text, the term biosolids is used in many places to replace the standard term sludge (activated sludge being the exception). It is the opinion of the author that the term sludge is an ugly four-letter world inappropriate for describing biosolids. Biosolids are a product that can be reused; they have some value. Because biosolids have value, they certainly should not be classified as a waste product, and when the topic of biosolids for beneficial reuse is addressed, it is made clear that they are not a waste product.

referred to in the plural (Merriam-Webster's Collegiate Dictionary, 10th ed., 1998).

Biota—All the species of plants and animals indigenous to a certain area.

Boiling point—The temperature at which a liquid boils. The temperature at which the vapor pressure of a liquid equals the pressure on its surface. If the pressure of the liquid varies, the actual boiling point varies. The boiling point of water is 212° Fahrenheit or 100° Celsius.

Breakpoint—Point at which chlorine dosage satisfies chlorine demand.

Breakthrough—In filtering, when unwanted materials start to pass through the filter.

Buffer—A substance or solution that resists changes in pH.

Calcium carbonate—Compound that is principally responsible for hardness.

Calcium hardness—Portion of total hardness caused by calcium compounds.

Carbonaceous biochemical oxygen demand (CBOD)—The amount of biochemical oxygen demand that can be attributed to carbonaceous material.

Carbonate hardness—Caused primarily by compounds containing carbonate.

Chemical oxygen demand (COD)—The amount of chemically oxidiz-able materials present in the wastewater.

Chlorination—Disinfection of water using chlorine as the oxidizing agent.

Clarifier—A device designed to permit solids to settle or rise and be separated from the flow. Also known as a settling tank or sedimentation basin.

Coagulation—Neutralization of the charges of colloidal matter.

Coliform—A type of bacteria used to indicate possible human or animal contamination of water.

Combined sewer—A collection system that carries both wastewater and stormwater flows.

Comminution—A process to shred solids into smaller, less harmful particles.

Composite sample—A combination of individual samples taken in proportion to flow.

Connate water—Pressurized water trapped in the pore spaces of sedimentary rock at the time it was deposited. It is usually highly mineralized.

Consumptive use—(1) The quantity of water absorbed by crops and transpired or used directly in the building of plant tissue, together with the water evaporated from the cropped area. (2) The quantity of water transpired and evaporated from a cropped area or the normal loss of water from the soil by evaporation and plant transpiration. (3) The quantity of water discharged to the atmosphere or incorporated in the products of the process in connection with vegetative growth, food processing, or an industrial process.

Contamination (water)—Damage to the quality of water sources by sewage, industrial waste, or other material.

Cross-connection—A connection between a storm-drain system and a sanitary collection system, a connection between two sections of a collection system to handle anticipated overloads of one system, or a connection between drinking (potable) water and an unsafe water supply or sanitary collection system.

Daily discharge—The discharge of a pollutant measured during a calendar day or any 24-hour period that reasonably represents a calendar day for the purposes of sampling. Limitations expressed as weight are total mass (weight) discharged over the day; limitations expressed in other units are average measurement of the day.

Daily maximum discharge—The highest allowable values for a daily discharge.

Darcy's law—An equation for the computation of the quantity of water flowing through porous media. Darcy's law assumes that the flow is laminar and that inertia can be neglected. The law states that the rate of viscous flow of homogeneous fluids through isotropic porous media is proportional to, and in the direction of, the hydraulic gradient.

Detention time—The theoretical time water remains in a tank at a given flow rate.

Dewatering—The removal or separation of a portion of water present in a sludge or slurry.

Diffusion—The process by which both ionic and molecular species dissolved in water move from areas of higher concentration to areas of lower concentration.

Discharge monitoring report (DMR)—The monthly report required by the treatment plant's National Pollutant Discharge Elimination System (NPDES) discharge permit.

Disinfection—Water treatment process that kills pathogenic organisms.

Disinfection byproducts (DBPs)—Chemical compounds formed by the reaction of disinfectants with organic compounds in water.

Dissolved oxygen (DO)—The amount of oxygen dissolved in water or sewage. Concentrations of less than 5 parts per million (ppm) can limit aquatic life or cause offensive odors. Excessive organic matter present in water because of inadequate waste treatment and runoff from agricultural or urban land generally causes low DO.

Dissolved solids—The total amount of dissolved inorganic material contained in water or wastes. Excessive dissolved solids make water unsuitable for drinking or industrial uses.

Domestic consumption (use)—Water used for household purposes such as washing, food preparation, and showers. The quantity (or quantity per capita) of water consumed in a municipality or district for domestic uses or purposes during a given period, it sometimes encompasses all uses, including the quantity wasted, lost, or otherwise unaccounted for.

Drawdown—Lowering the water level by pumping. It is measured in feet for a given quantity of water pumped during a specified period, or after the pumping level has become constant.

Drinking water standards—Established by state agencies, the U.S. Public Health Service, and the Environmental Protection Agency (EPA) for drinking water in the United States.

Effluent—Something that flows out, usually a polluting gas or liquid discharge.

Effluent limitation—Any restriction imposed by the regulatory agency on quantities, discharge rates, or concentrations of pollutants discharged from point sources into state waters.

Energy—In scientific terms, the ability or capacity of doing work. Various forms of energy include kinetic, potential, thermal, nuclear, rotational, and electromagnetic. One form of energy may be changed to another, as when coal is burned to produce steam to drive a turbine, which produces electric energy.

Erosion—The wearing away of the land surface by wind, water, ice, or other geologic agents. Erosion occurs naturally from weather or runoff but is often intensified by human land-use practices.

Eutrophication—The process of enrichment of water bodies by nutrients. Eutrophication of a lake normally contributes to its slow evolution into a bog or marsh and ultimately to dry land. Eutrophication may be accelerated by human activities, thereby speeding up the aging process.

Evaporation—The process by which water becomes a vapor at a temperature below the boiling point.

Facultative— Organisms that can survive and function in the presence or absence of free, elemental oxygen.

Fecal coliform—The portion of the coliform bacteria group that is present in the intestinal tracts and feces of warm-blooded animals.

Field capacity—The capacity of soil to hold water. It is measured as the ratio of the weight of water retained by the soil to the weight of the dry soil.

Filtration—The mechanical process that removes particulate matter by separating water from solid material, usually by passing it through sand.

Floc—Solids that join to form larger particles that will settle better.

Flocculation—Slow mixing process in which particles are brought into contact, with the intent of promoting their agglomeration.

Flume—A flow rate measurement device.

Fluoridation—Chemical addition to water to reduce incidence of dental caries in children.

Food-to-microorganisms (F/M) ratio—An activated sludge process control calculation based on the amount of food (BODs or COD) available per pound of mixed liquor volatile suspended solids.

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

Grab sample—An individual sample collected at a randomly selected time.

Graywater—Water that has been used for showering, clothes washing, and faucet uses. Kitchen sink and toilet water is excluded. This water has excellent potential for reuse as irrigation for yards.

Grit—Heavy inorganic solids, such as sand, gravel, eggshells, or metal filings.

Groundwater—The supply of freshwater found beneath the Earth's surface (usually in aquifers) often used for supplying wells and springs. Because groundwater is a major source of drinking water, concern is growing over areas where leaching agricultural or industrial pollutants or substances from leaking underground storage tanks (USTs) are contaminating groundwater.

Groundwater hydrology—The branch of hydrology that deals with groundwater: its occurrence and movements, its replenishment and depletion, the properties of rocks that control groundwater movement and storage, and the methods of investigation and use of groundwater.

Groundwater recharge—The inflow to a groundwater reservoir.

Groundwater runoff—A portion of runoff that has passed into the ground, has become groundwater, and has been discharged into a stream channel as spring or seepage water.

Hardness—The concentration of calcium and magnesium salts in water.

Head loss—Amount of energy used by water in moving from one point to another.

Heavy metals—Metallic elements with high atomic weights, such as mercury, chromium, cadmium, arsenic, and lead. They can damage living things at low concentrations and tend to accumulate in the food chain.

Holding pond—A small basin or pond designed to hold sediment-laden or contaminated water until it can be treated to meet water quality standards or used in some other way.

Hydraulic cleaning—Cleaning pipe with water under enough pressure to produce high water velocities.

Hydraulic gradient—A measure of the change in groundwater head over a given distance.

Hydraulic head—The height above a specific datum (generally sea level) that water will rise in a well.

Hydrologic cycle (water cycle)—The cycle of water movement from the atmosphere to the Earth and back to the atmosphere through various processes. These processes include precipitation, infiltration, percolation, storage, evaporation, transpiration, and condensation.

Hydrology—The science dealing with the properties, distribution, and circulation of water.

Impoundment—A body of water, such as a pond confined by a dam, dike, floodgate, or other barrier, that is used to collect and store water for future use.

Industrial wastewater—Wastes associated with industrial manufacturing processes.

Infiltration—The gradual downward flow of water from the surface into soil material.

Infiltration/inflow—Extraneous flows in sewers; simply, inflow is water discharged into sewer pipes or service connections from such sources as foundation drains, roof leaders, cellar and yard area drains, cooling water from air conditioners, and other clean-water discharges from commercial and industrial establishments. Defined by Metcalf & Eddy (2003) as follows:

Delayed inflow—Stormwater requiring several days or more to drain through the sewer system. This category can include the discharge of sump pumps from cellar drainage as well as the slowed entry of surface water through manholes in ponded areas.

Direct flow—Those types of inflow that have a direct stormwater runoff connection to the sanitary sewer and cause an almost immediate increase in wastewater flows. Possible sources are roof leaders, yard and areaway drains, manhole covers, cross-connections from storm drains and catch basins, and combined sewers.

Infiltration—Water entering the collection system through cracks, joints, or breaks.

Steady inflow—Water discharged from cellar and foundation drains, cooling water discharges, and drains from springs and swampy areas. This type of inflow is steady and is identified and measured along with infiltration.

Total inflow—The sum of the direct inflow at any point in the system plus any flow discharged from the system upstream through overflows, pumping station bypasses, and the like.

Influent—Wastewater entering a tank, channel, or treatment process.

Inorganic chemical/compounds—Chemical substances of mineral origin, not of carbon structure. These include metals such as lead, iron (ferric chloride), and cadmium.

Ion exchange process—Used to remove hardness from water.

Jar test—Laboratory procedure used to estimate proper coagulant dosage.

Langelier saturation index (LI)—A numerical index that indicates whether calcium carbonate will be deposited or dissolved in a distribution system.

Leaching—The process by which soluble materials in the soil such as nutrients, pesticide chemicals, or contaminants are washed into a lower layer of soil or are dissolved and carried away by water.

License—A certificate issued by the State Board of Waterworks/ Wastewater Works Operators authorizing the holder to perform the duties of a wastewater treatment plant operator.

Lift station—A wastewater pumping station designed to "lift" the wastewater to a higher elevation. A lift station normally employs pumps or other mechanical devices to pump the wastewater and discharges into a pressure pipe called a force main.

Maximum contaminant level (MCL)—An enforceable standard for protection of human health.

Mean cell residence time (MCRT)—The average length of time a mixed liquor suspended solids particle remains in the activated sludge process. May also be known as sludge retention time.

Mechanical cleaning—Clearing pipe by using equipment (bucket machines, power rodders, or hand rods) that scrapes, cuts, pulls, or pushes the material out of the pipe.

Membrane process—A process that draws a measured volume of water through a filter membrane with small enough openings to take out contaminants.

Metering pump—A chemical solution feed pump that adds a measured amount of solution with each stroke or rotation of the pump.

Milligrams per liter (mg/L)—A measure of concentration equivalent to parts per million (ppm).

Mixed liquor suspended solids—The suspended solids concentration of the mixed liquor.

Mixed liquor volatile suspended solids (MLVSS)—The concentration of organic matter in the mixed liquor suspended solids.

Nephelometric turbidity unit (NTU)—Indicates amount of turbidity in a water sample.

Nitrogenous oxygen demand (NoD)—A measure of the amount of oxygen required to biologically oxidize nitrogen compounds under specified conditions of time and temperature.

Nonpoint-source (NPS) pollution—Forms of pollution caused by sediment, nutrients, and organic and toxic substances originating from land-use activities that are carried to lakes and streams by surface runoff. Nonpoint-source pollution occurs when the rate of materials entering these water bodies exceeds natural levels.

NPDES permit—National Pollutant Discharge Elimination System permit, which authorizes the discharge of treated wastes and specifies the conditions that must be met for discharge.

Nutrients—Substances required to support living organisms. Usually refers to nitrogen, phosphorus, iron, and other trace metals.

Organic chemicals/compounds—Animal- or plant-produced substances containing mainly carbon, hydrogen, and oxygen, such as benzene and toluene.

Parts per million (ppm)—The number of parts by weight of a substance per million parts of water. This unit is commonly used to represent pollutant concentrations. Large concentrations are expressed in percentages.

Pathogenic—Disease causing. A pathogenic organism is capable of causing illness.

Percolation—The movement of water through the subsurface soil layers, usually continuing downward to the groundwater or water table reservoirs.

pH—A way of expressing both acidity and alkalinity on a scale of 0 to 14, with 7 representing neutrality; numbers less than 7 indicate increasing acidity, and numbers greater than 7 indicate increasing alkalinity.

Photosynthesis—A process in green plants in which water, carbon dioxide, and sunlight combine to form sugar.

Piezometric surface—An imaginary surface that coincides with the hydrostatic pressure level of water in an aquifer.

Point-source pollution—A type of water pollution resulting from discharges into receiving waters from easily identifiable points. Common point sources of pollution are discharges from factories and municipal sewage treatment plants.

Pollution—The alteration of the physical, thermal, chemical, or biological quality of, or the contamination of, any water in the state that renders the water harmful, detrimental, or injurious to humans, animal life, vegetation, property or public health, safety, or welfare, or impairs the usefulness or the public enjoyment of the water for any lawful or reasonable purpose.

Porosity—That part of a rock that contains pore spaces without regard to size, shape, interconnection, or arrangement of openings. It is expressed as percentage of total volume occupied by spaces.

Potable water—Water satisfactorily safe for drinking purposes from the standpoint of its chemical, physical, and biological characteristics.

Precipitate—A deposit on the Earth of hail, rain, mist, sleet, or snow; the common process by which atmospheric water becomes surface or subsurface water. The term precipitation is also commonly used to designate the quantity of water precipitated.

Preventive maintenance (PM)—Regularly scheduled servicing of machinery or other equipment using appropriate tools, tests, and lubricants. This type of maintenance can prolong the useful life of equipment and machinery and increase its efficiency by detecting and correcting problems before they cause a breakdown of the equipment.

Purveyor—An agency or person that supplies potable water.

Radon—A radioactive, colorless, odorless gas that occurs naturally in the earth. When trapped in buildings, concentrations build up and can cause health hazards such as lung cancer.

Recharge—The addition of water into a groundwater system.

Reservoir—A pond, lake, tank, or basin (natural or human made) where water is collected and used for storage. Large bodies of groundwa-ter are called groundwater reservoirs; water behind a dam is also called a reservoir of water.

Reverse osmosis—Process in which almost pure water is passed through a semipermeable membrane.

Return activated sludge solids (RASS)—The concentration of suspended solids in the sludge flow being returned from the settling tank to the head of the aeration tank.

River basin—A term used to designate the area drained by a river and its tributaries.

Sanitary wastewater—Wastes discharged from residences and from commercial, institutional, and similar facilities that include both sewage and industrial wastes.

Schmutzdecke—Layer of solids and biological growth that forms on top of a slow sand filter, allowing the filter to remove turbidity effectively without chemical coagulation.

Scum—The mixture of floatable solids and water removed from the surface of the settling tank.

Sediment—Transported and deposited particles derived from rocks, soil, or biological material.

Sedimentation—A process that reduces the velocity of water in basins so suspended material can settle out by gravity.

Seepage—The appearance and disappearance of water at the ground surface. Seepage designates movement of water in saturated material. It differs from percolation, which is predominantly the movement of water in unsaturated material.

Septic tanks—Used to hold domestic wastes when a sewer line is not available to carry them to a treatment plant. The wastes are piped to underground tanks directly from a home or homes. Bacteria in the wastes decompose some of the organic matter, the sludge settles on the bottom of the tank, and the effluent flows out of the tank into the ground through drains.

Settleability—A process control test used to evaluate the settling characteristics of the activated sludge. Readings taken at 30 to 60 minutes are used to calculate the settled sludge volume (SSV) and the sludge volume index (SVI).

Settled sludge volume (SSV)—The volume (in percent) occupied by an activated sludge sample after 30 to 60 minutes of settling; normally written as SSV with a subscript to indicate the time of the reading used for calculation (SSV60 or SSV30).

Sludge—The mixture of settleable solids and water removed from the bottom of the settling tank.

Sludge retention time (SRT)—See mean cell residence time.

Sludge volume index (SVI)—A process control calculation used to evaluate the settling quality of the activated sludge; requires the SSV30 and mixed liquor suspended solids test results to calculate.

Soil moisture (soil water)—Water diffused in the soil. It is found in the upper part of the zone of aeration from which water is discharged by transpiration from plants or by soil evaporation.

Specific heat—The heat capacity of a material per unit mass. The amount of heat (in calories) required to raise the temperature of 1 gram of a substance 1°C; the specific heat of water is 1 calorie.

Storm sewer—A collection system designed to carry only stormwater runoff.

Stormwater—Runoff resulting from rainfall and snowmelt.

Stream—A general term for a body of flowing water. In hydrology, the term is generally applied to the water flowing in a natural channel as distinct from a canal. More generally, it is applied to the water flowing in any channel, natural or artificial. Some types of streams include: (1) ephemeral, a stream that flows only in direct response to precipitation and whose channel is at all times above the water table; (2) intermittent or seasonal, a stream that flows only at certain times of the year when it receives water from springs, rainfall, or surface sources such as melting snow; (3) perennial, a stream that flows continuously; (4) gaining, an effluent stream or reach of a stream that receives water from the zone of saturation; (5) insulated, a stream or reach of a stream that is separated from the zones of saturation by an impermeable bed so it neither contributes water to the zone of saturation nor receives water from it; (6) losing, an influent stream or reach of a stream that contributes water to the zone of saturation; and (7) perched, either a losing stream or an insulated stream that is separated from the underlying groundwater by a zone of aeration.

Supernatant—The liquid standing above a sediment or precipitate.

Surface tension—The free energy produced in a liquid surface by the unbalanced inward pull exerted by molecules underlying the layer of surface molecules.

Surface water—Lakes, bays, ponds, impounding reservoirs, springs, rivers, streams, creeks, estuaries, wetlands, marshes, inlets, canals, gulfs inside the territorial limits of the state, and all other bodies of surface water, natural or artificial, inland or coastal, fresh or salt, navigable or nonnavigable, and including the beds and banks of all watercourses and bodies of surface water that are wholly or partially inside or bordering the state or subject to the jurisdiction of the state; except that waters in treatment systems which are authorized by state or federal law, regulation, or permit, and which are created for the purpose of water treatment, are not considered to be waters in the state.

Thermal pollution—The degradation of water quality by the introduction of a heated effluent. Primarily the result of the discharge of cooling waters from industrial processes (particularly from electrical power generation); waste heat eventually results from virtually every energy conversion.

Titrant—A solution of known strength of concentration; used in titration.

Titration—A process whereby a solution of known strength (titrant) is added to a certain volume of treated sample containing an indicator. A color change shows when the reaction is complete.

Titrator—An instrument, usually a calibrated cylinder (tube-form), used in titration to measure the amount of titrant being added to the sample.

Total dissolved solids—The amount of material (inorganic salts and small amounts of organic material) dissolved in water and commonly expressed as a concentration in terms of milligrams per liter.

Total suspended solids (TSS)—Total suspended solids in water, commonly expressed as a concentration in terms of milligrams per liter.

Toxicity—The occurrence of lethal or sublethal adverse effects on representative sensitive organisms due to exposure to toxic materials. Adverse effects caused by conditions of temperature, dissolved oxygen, or nontoxic dissolved substances are excluded from the definition of toxicity.

Transpiration—The process by which water vapor escapes from the living plant, principally the leaves, and enters the atmosphere.

Vaporization—The change of a substance from a liquid or solid state to a gaseous state.

Volatile organic compound (VOC)—Any organic compound that participates in atmospheric photochemical reactions except for those designated by the EPA Administrator as having negligible photochemical reactivity.

Waste activated sludge solids (WASS)—The concentration of suspended solids in the sludge being removed from the activated sludge process.

Wastewater—The water supply of a community after it has been soiled by use. Wastewater can also be defined as a community's spent water. Wastewater contains the impurities that were present when the water was obtained (water picks up impurities as it travels) and any impurities added through human uses. The term sewage is often used to refer to wastewater but is more properly applied to domestic or household wastewater. As mentioned, raw wastewa-ter entering a treatment plant (or unit process) is referred to as influent. The treated water discharged from a wastewater treatment plant (or unit process) is known as effluent.

Water cycle—The process by which water travels in a sequence from the air (condensation) to the Earth (precipitation) and returns to the atmosphere (evaporation). It is also referred to as the hydro-logic cycle.

Water quality—A term used to describe the chemical, physical, and biological characteristics of water with respect to its suitability for a particular use.

Water quality standard—A plan for water quality management containing four major elements: water use, criteria to protect users, implementation plans, and enforcement plans. An antidegradation statement is sometimes prepared to protect existing high-quality waters.

Water supply—Any quantity of available water.

Waterborne disease—A disease caused by a microorganism that is carried from one person or animal to another by water.

Watershed—The area of land that contributes surface runoff to a given point in a drainage system.

Weir—A device used to measure wastewater flow.

Zone of aeration—A region in the Earth above the water table. Water in the zone of aeration is under atmospheric pressure and would not flow into a well.

Zoogleal slime—The biological slime that forms on fixed-film treatment devices. It contains a wide variety of organisms essential to the treatment process.

2.2 CHAPTER REviEW Questions Matching Exercise

Match the definitions listed in Part A with the terms listed in Part B by placing the correct letter in the blank.

Note: After completing this exercise, compare your answers to those provided in Appendix A.

Part A

1. A nonchemical turbidity removal layer in a slow sand filter _

2. Region in Earth (soil) above the water table _

3. Compound associated with photochemical reaction _

4. Oxygen used in water-rich inorganic matter _

5. A stream that receives water from the zone of saturation

6. The addition of water into a groundwater system

7. The natural water cycle

8. Present in intestinal tracts and feces of animals and humans

9. Discharge from a factory or municipal sewage treatment plant

10. Common to fixed-film treatment devices

11. Water that is identified as safe to drink

12. The capacity of soil to hold water

13. Used to measure acidity and alkalinity

14. Rain mixed with sulfur oxides

15. Enrichment of water bodies by nutrients

16. A solution of known strength or concentration

17. Water lost by foliage

18. Another name for a wastewater pumping station

19. Plants and animals indigenous to an area

20. The amount of oxygen dissolved in water

21. A stream that flows continuously

22. A result of excessive nutrients within a water body

23. Change in groundwater head over a given distance

24. Water trapped in sedimentary rocks

25. Heat capacity of a material per unit mass

26. A compound derived from material that once lived

Part B




Algae bloom


Zone of aeration


Hydrological cycle


Point-source pollution






Connate water


Fecal coliform




Field capacity






Specific heat






Zoogleal slime










Acid rain




Lift station




Hydraulic gradient


Metcalf & Eddy, Inc. (2003). Wastewater Engineering: Treatment, Disposal, Reuse, 4th ed. New York: McGraw-Hill.

Pearce, F. (2006). When the Rivers Run Dry. Boston, MA: Beacon Press. Pielou, E.C. (1998). Fresh Water. Chicago, IL: University of Chicago.


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