Glossary

Compiled from a list by: The Consortium of Institutes for Decentralized Wastewater Treatment

 

TERM	DEFINITION
Activated-sludge process	Wastewater treatment process that uses activated sludge to biologically convert non-settleable (suspended, dissolved, and colloidal) organic materials to a settleable product using aerobic and facultative microorganisms; typically followed by clarification and sludge return.
Aeration system	Piping, diffusers, air source, vents, and all other necessary devices for an active aeration process.
Aerobic	Having molecular oxygen as part of the environment, or a biological process that occurs only in the presence of molecular oxygen; See also anaerobic and anoxic.
Aerobic treatment unit (ATU)	1. Treatment component that utilizes oxygen to degrade or decompose wastewater, with or without mechanical means; 2. Term traditionally used to describe proprietary devices that use direct introduction of air into wastewater by mechanical means to maintain aerobic conditions within the pretreatment component.
Anaerobic	Absence of molecular oxygen as part of the environment, or a biological process that occurs in the absence of molecular oxygen; bound oxygen is present in other molecules, such as nitrate, sulfate and carbon dioxide; See also aerobic and anoxic.
Anoxic	Condition in which all constituents are in their reduced form (no oxidants present); conditions in a septic tank are generally anaerobic, but not anoxic; see also aerobic and anaerobic.
Attached-growth process	Configuration wherein the microorganisms responsible for treatment colonize a fixed medium; see also suspended growth process.
Baffle	Physical barrier placed in a component to dissipate energy, direct flow, retain solids and FOG, and/or draw water from a specific depth.
Biochemical oxygen demand, five-day (BOD5)	Quantitative measure of the amount of oxygen consumed by bacteria while stabilizing, digesting, or treating biodegradable organic matter under aerobic conditions over a five-day incubation period; expressed in milligrams per liter (mg/L).
Biofilter	Media filter in which the media used is biological in origin (i.e., peat or coir).
Blackwater	Portion of the wastewater stream that originates from toilet fixtures, dishwashers, and food preparation sinks; see also graywater.
Clarifier	Component or tank that uses separation to remove suspended solids from wastewater.
Constructed wetland	Pretreatment component that incorporates appropriate moisture tolerant vegetation and consists of one or more lined basins where wastewater undergoes some combination of physical, chemical, and/or biological treatment; configurations include free surface and submerged flow configurations.
Control panel	Component that contains electrical devices that provide information on system operation and may allow adjustment of settings for operation of electrical devices.
Decant	Act of transferring effluent slowly so as to separate liquid from solid after a previous settling process.
Denitrification	Biochemical reduction of nitrate or nitrite to gaseous molecular nitrogen or an oxide of nitrogen.
Detention time	Average length of time a unit volume of wastewater or suspended particle remains in a tank or chamber; mathematically, it is the volume of water in the tank divided by the flow rate through the tank (assuming ideal hydraulic conditions).
Diffuser	Part or device that injects air under pressure into wastewater (e.g., submerged porous plate, perforated pipe, or orifice).
Disinfection	Process used to destroy or inactivate pathogenic microorganisms in wastewater to render them non-infectious; see also disinfection, chlorine; disinfection, ozone; and disinfection, ultraviolet.
Dissolved oxygen (DO)	Amount of molecular oxygen dissolved in water, wastewater, or other liquid; commonly expressed as a concentration in milligrams per liter (mg/L), parts per million (ppm), or a percent of saturation.
Drip field	Above or below grade soil treatment area where final treatment and dispersal occurs via application of effluent to the infiltrative surface via pressurized drip tubing utilizing emitters; see also drip field, surface; drip field, subsurface; and drip tubing.
Effluent	Liquid flowing out of a component or device.
FOG (fats, oils, and grease)	Constituent of sewage typically originating from foodstuffs (animal fats or vegetable oils) or consisting of compounds of alcohol or glycerol with fatty acids (soaps and lotions), typically measured in mg/L.
Filter, media	Device that uses materials designed to treat effluent by reducing BOD and/or removing suspended solids in an unsaturated environment; biological treatment is facilitated via microbial growth on the surface of the media.
Filter, peat	Media filter that uses appropriate organic fibric material (peat) as the media; typically packaged as prefabricated modular units with the media in a container; a type of biofilter.
Filter, sand	Media filter which uses sand of particular specifications as the media.
Filter, textile	Type of media filter which uses non-rigid, synthetic material of varying shapes and configurations; typically packaged as pre-fabricated modular units.
Filter, trickling	Type of media filter which uses a variety of media such as rigid plastics of varying shapes, stone, or tire chips; includes a clarifier in its configuration and may include a recirculation mode.
Flow, daily design	Estimated volume of wastewater for any 24-hour period; parameter used to size systems.
Flow, peak	Highest flow occurring within a specified time (minutes, hours, days, etc.); may be further expressed as peak hourly flow, peak daily flow, peak monthly flow, peak seasonal flow, etc.
Flow, surge	Flow of effluent that occurs in a short enough period of time that it upsets the function of one or more components of the treatment train.
Force main	Part of a collection system consisting of the piping that conveys sewage under pressure from a lift station to a location where gravity flow can again be utilized.
Graywater	Water captured from non-food preparation sinks, showers, baths, spa baths, clothes washing machines, and laundry tubs; see also blackwater.
Grease trap	Relatively large device similar to a septic tank located outside a facility that generates commercial food service wastewater and is designed to intercept, congeal, and retain or remove fats, oils, and grease (FOGs); see also grease interceptor.
Grinder pump	Pump that shreds solids in a waste stream and conveys the resulting mixture under pressure to a subsequent system component.
Holding tank sewage system	System which combines or utilizes a holding tank with alarm, the services of a sewage pumper/hauler, and off-site treatment of the collected sewage.
I and I	Infiltration and inflow; term used to describe the combined undesirable entry of extraneous water into a system component; see also infiltration and inflow.
Impermeable	Not permitting the passage of fluid through pores; in practical terms, some small level of hydraulic conductivity may occur, but at so low a level that it is considered to be negligible.
Influent	Liquid entering a component or device.
Lagoon	Constructed basin lined with either soils with very low permeability or a synthetic material, surrounded with berms and which contains at least three feet of wastewater which utilizes sunlight, wind or mechanical aeration, and natural bacteria to break down waste via physical, chemical, and biological processes.
Land application	Process in which biosolids or liquid waste treatment residuals are spread over, sprayed onto, or injected into the soil.
Mixed liquor	Suspended mixture of activated sludge, dissolved gasses (e.g. DO) and wastewater undergoing treatment in the activated-sludge process; energy is required to maintain the condition.
Nitrification	Biological oxidation of ammonium to nitrite and nitrate, or a biologically induced increase in the oxidations state of nitrogen.
Nitrogen, total	Measure of the complete nitrogen content in wastewater including nitrate, nitrite, ammonia, ammonium, and organic nitrogen, expressed as mg/L of N; all of these forms of nitrogen, (as well as nitrogen gas), can be biochemically converted from one form to another and are constituents of the nitrogen cycle.
Nitrogen, total Kjeldahl (TKN)	Measure of the total concentration of organic nitrogen, ammonia, and ammonium nitrogen.
Orifice	Discharge hole in a distribution system.
Package plant	Term commonly used to describe a modular aerobic treatment system unit serving multiple dwellings or establishments with relatively large flows (greater than 1,500 gallons per day).
Pathogenic	Capable of causing disease; commonly applied to organisms that cause infectious diseases.
Percolation test	Usually called a "perk test"; measurement of the drop in water level in a boring as water moves into the surrounding soil material.
pH	Measure of the acid or base quality of water that is the negative log of the hydrogen ion concentration; the scale ranges form 1-14, with a pH of 7.0 equal to neutral, 14.0 being strongly alkaline (basic), and 1.0 being strongly acidic.
Pumper	Service provider who removes septage from a wastewater treatment component and disposes of it according to specific regulatory parameters.
Rotating biological contractor (RBC)	Type of attached growth pretreatment component consisting of disks mounted on a drive shaft which rotates; microorganisms attached to the discs are alternately exposed to free oxygen in the atmosphere and the wastewater.
Scum	Layer of floating material on a liquid surface.
Septic tank effluent gravity (STEG)	Collection system that uses septic tanks to separate solids and allow gravity flow of effluent to a subsequent component.
Septic tank effluent pump (STEP)	Collection system that uses a septic tank to separate solids and incorporates a pump vault, pump and associated devices to convey effluent under pressure to a subsequent component.
Sequencing batch reactor (SBR)	Component in which batch type suspended growth (activated sludge) processes are carried out in the same tank in stepwise order (e.g. fill, treat, settle, decant, and draw).
Sludge	Accumulated solids and associated entrained water within a pretreatment component, generated during the biological, physical, or chemical treatment; coagulation; or clarification of wastewater.
Solids, total suspended (TSS)	Measure of all suspended solids in a liquid, typically expressed in mg/L; to measure, a well-mixed sample is filtered through a standard glass fiber filter and the residue retained on the filter is dried to a constant weight at 217 to 221 degrees F (103 to 105 degrees C); the increase in the weight of the filter represents the amount of total suspended solids.
Suspended-growth process	Configuration wherein the microorganisms responsible for treatment are maintained in suspension within a liquid; see also attached-growth process.
Tank, flow equalization	Dosing tank that provides storage of effluent and uses timed dosing to allow for uniform delivery to a subsequent component over time, usually a day or more; also known as a surge tank.
Treatment, primary	Physical treatment processes involving removal of particles, typically by settling and flotation with or without the use of coagulants; (e.g. a grease interceptor or a septic tank provides primary treatment); see also treatment, physical.
Treatment, secondary	Biological and chemical treatment processes designed to remove organic matter; a typical standard for secondary effluent is BOD and TSS less than or equal to 20 mg/L each on a 30-day average basis.
Treatment, tertiary	Advanced treatment of wastewater for enhanced organic matter removal, pathogen reduction, and nutrient removal; typical standards for tertiary effluent vary according to regulatory requirements.
Valve, flush	Valve used to control the expelling of effluent and accumulated materials from a distribution system.
Wastewater, high-strength	1. Influent having BOD5 greater than 300 mg/L; and/or TSS greater than 200 mg/L; and/or fates, oils, and grease greater than 50 mg/L entering a pretreatment component (as defined by NSF Standard 40 testing protocol); 2. Effluent form a septic tank or other pretreatment component that has BOD 5 greater than 170 mg/L; and/or TSS greater than 60 mg/L; and/or fats, oils, and grease greater than 25 mg/L and is applied to an infiltrative surface.
Wastewater, residential strength	Effluent from a septic tank or other treatment device with a BOD5 less than or equal to 170 mg/L; TSS less than or equal to 60 mg/L; and fats, oils, and grease less than or equal to 25 mg/L.
Wetlands	Areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil condition; wetlands generally include swamps, marshes, bogs, and similar areas; constructed wetlands used in wastewater treatment are purposely excluded.

 

• FastFact

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