Decentralized Wastewater Glossary

Average of daily measurements over a 30-d period, calculated as the sum of all daily measurements taken during a 30-d period divided by the number of daily measurements taken during that 30-d period. Each new 30-d average begins on the day following the end of the previous average

Type of average, calculated as the nth root of the product of n values (daily measurements) taken over a 30-d period. Each new 30-d geometric mean begins on the day following the end of the previous geometric mean

Average of daily measurements over a 7-d period, calculated as the sum of all daily measurements taken during a 7-d period divided by the number of daily measurements taken during that 7-d period. Each new 7-d average begins on the day following the end of the previous average

Discontinued use of a system component or components by removing them or rendering them inaccessible and inoperable.

Soil treatment area designed and installed such that all or part of the infiltrative surface is located at or above original ground elevation using appropriate imported material; cover of suitable soil stabilizes the final grade, supports vegetative growth and sheds runoff; includes mounds and elevated systems; see also at-grade and below-grade.

Process of incorporation or assimilation by which one substance is physically taken into and included with another substance; for example, plant roots assimilating nutrients from the soil.

Design parameter described by the square footage of an absorptive surface that is associated with the hydraulic acceptance of effluent; see also absorptive surface; basal area; and infiltrative surface.

Plane of native soil where hydraulic properties change.

Condition in which a component is performing its intended purpose and is in an operable state; see also, unacceptable.

Infiltration of effluent into a designated media expressed as a rate (e.g., cm/day); see also long-term acceptance rate.

Requirements which are compatible with standards of practice required of a registered professional engineer.

Conduit facilitating access to subsurface components of a wastewater treatment system.

Conversion of volatile fatty acids to acetic acid, hydrogen gas and carbon dioxide.

Conversion of fatty acids to volatile fatty acids and sugars to acetic acid, hydrogen gas and carbon dioxide.

Device filled with a porous form of carbon that is used to decolorize liquids, recover solvents, and remove toxins and odors from water and air.

Highly concentrated mass of live organisms in a suspended growth aerated and mixed environment.

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.

Process of introducing air via either mechanical means or diffused aeration; see also aeration, passive.

Product added to a sewage treatment system and marketed to improve performance.

Adhesion of a substance to the surface of solid bodies or liquids with which it is in contact.

Level of treatment that achieves 95% reduction in BOD and TSS, generally to levels below 10 mg/L.

Any post-sedimentation treatment process or sequential treatment processes that reduce contaminants to specified target levels prior to conveyance to a final treatment and dispersal component, reuse or recycling; often, this treatment is designed to meet advanced secondary, tertiary, and/or disinfection treatment standards.

Process of introducing air into a treatment component or process

Chamber or tank in which wastewater is brought into contact with air to facilitate biological degradation such as in (but not limited to) the activated sludge process.

Piping, diffusers, air source, vents, and all other necessary devices for an active aeration process.

Tank or compartment in which wastewater is brought into contact with air to facilitate biological degradation such as in (but not limited to) the activated sludge process.

Mechanical device used to introduce air into a treatment component or process.

Having molecular oxygen (O₂) as a part of the environment, or a biological process that occurs only in the presence of molecular oxygen; see also anaerobic and anoxic.

Bacteria that can metabolize only in the presence of molecular oxygen.

Digestion of organic matter in an environment containing molecular (or dissolved) oxygen (O₂).

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.

1. Primary soil particles that cohere to each other more strongly than other surrounding particles; 2. naturally-occurring inorganic material (crushed rock or gravel) screened to sizes for various uses; see also distribution media; and treatment media.

See soil structure.

Colorless, odorless, and tasteless gaseous mixture of nitrogen (78%), oxygen (21%) and trace amounts of other gases.

Device that uses a fan to deliver air to a component; does not substantially compress air.

Device that delivers pressurized air to a component.

Piping that conveys air from the source to the point of diffusion.

1. Condition in a pressurized distribution system where the presence of air or other gases prevents flow; 2. condition where air or other gases collect at a high point in a gravity distribution system and prevent or restrict flow.

Allowing air to escape during pressurization of a distribution system using an air/vacuum relief valve.

Process of venting air from a component.       

Device which supplies air to a treatment process.

valve that allows air in the lines to be purged during pressurizing flow and allows air to enter during depressurized flow.

Device that provides information on the status of a component using a visual and/or audible device; can either be on site or remotely located.

Volume between ‘pump on’ level and ‘alarm on’ level in a demand dosing configuration.

Device used to record the number of times an alarm has been activated.

Pertaining to processes or materials associated with transportation or deposition of sediment by water.

1. Soil developing from sediments (alluvium) recently deposited by running water of streams and rivers and exhibiting essentially no horizon development or modification of the recently deposited materials; 2. wWhen capitalized, it refers to a great soil group of the azonal order consisting of soils with little or no modification of the recent sediment in which they are forming.

Uncosolidated sediments deposited by running water of streams and rivers; may occur on terraces well above present streams, on the present flood plains or deltas, or as a fan at the base of a slope; see also colluvium

Modification of a wastewater treatment system on the basis of: an increase in the volume of permitted flow; a change in the nature of permitted influent; a change from the planning materials approved by the permitting authority; a change in construction; or an increase, lengthening, or expansion of the treatment or dispersal system.

See alternating soil treatment area (STA).

Final treatment and dispersal component that is comprised of multiple soil treatment areas which are independently dosed.

See switching valve.

Onsite wastewater treatment system that is not a conventional system as described by local regulatory code.

System of piping and other appurtenances consisting of service lines, small diameter variable grade effluent sewers (STEG or STEP), pressure sewers (grinder basins or ejector pumps) and vacuum sewers that receive and convey wastewater.

Pre-engineered shoring system comprised of aluminum hydraulic cylinders (cross braces) used in conjunction with vertical rails (uprights) or horizontal rails (wales); designed specifically to support the sidewalls of an excavation and prevent cave-ins.

Engineered treatment and dispersal system in which native material is excavated and replaced with media targeting removal of specific contaminants.

Non-ionized form of reduced nitrogen.

Biochemical process whereby ammonium nitrogen (NH₄⁺) is release from nitrogen-containing compounds.

Ionized form of reduced nitrogen usable by plants.

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.                         

Absence of molecular oxygen (O₂) as a 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 (NO₃^-) sulfate (SO₄⁺) and carbon dioxide (CO₂); see also aerobic and anoxic.

Bacteria that can metabolize in the absence of molecular oxygen.

Dgestion of organic matter in an environment without molecular (or dissolved) oxygen (O₂).

Media filter through which wastewater flows from a lower to a higher elevation; usually characterized by an anaerobic environment.

See blocky.

Condition of low dissolved molecular oxygen (anaerobic) with presence of bound oxygen in nitrate form; conditions in a septic tank are generally anaerobic, but not anoxic; see also aerobic, anaerobic and denitrification.

Variation of episaturation associated with controlled flooding, which causes a reduced environment in a soil layer and oxidation of mobilized iron and manganese in a deeper unsaturated subsoil; see also endosaturation and episaturation.

Variation of episaturation associated with controlled flooding, which causes a reduced environment in a soil layer and oxidation of mobilized iron and manganese in a deeper unsaturated subsoil; see also endosaturation and episaturation.

Devices, machinery, appliances, or auxilliary structures attached to a main structure to enable it to function but not considered an integral part of it.

Continuous or periodic saturation and reduction indicated by redoximorphic features and verified by measuring saturation and reduction of the soil.

Soil moisture regime nearly free of dissolved oxygen due to saturation by groundwater or its capillary fringe and occurring during periods when the soil temperature 50 cm (20 inches) below the surface is greater than 5°c (41°f).

Geologic formation, group of formations, or part of a formation that is saturated and sufficiently permeable to transmit water.

Quantity of liquid applied to the footprint of the soil treatment area (or the absorption area of an above-grade soil treatment area) in a time interval, expressed as volume per unit time per unit area, e.g., gallons per day per square foot (gpd/ft²).

Construction document that is the approved design with red-line notations by the installer that reflect all modifications, substitutions and deviations made during the construction process. See also record drawing.

Device which moves fluid (liquid or gas) by developing a vacuum.

Donversion of absorbed wastewater constituents into living tissue.

Temporary benchmark used as a reference; typically assigned an elevation of 100.00 feet.

American Society for Testing and Materials

Published standard from the American Society for Testing and Materials that provides specifications for clean sand used in various engineering and construction applications.

Above-grade soil treatment area designed and installed such that some part of the infiltrative surface is located at the original ground elevation using suitable imported soil material for fill; excavation is 0 to 6” into native soil; utilizes gravity, pressure-dosed gravity or low-pressure distribution with the orifices of the distribution pipe above the original ground elevation; cover of suitable soil stabilizes the final grade, supports vegetative growth and sheds runoff; see also above-grade, below-grade and trench, shallow.

See fixed-film process.

Approval to begin the system installation process.

Sum of individual measurements taken during a given period divided by the total number of measurements taken during the same period.

Average volume of wastewater in a 24-hour period; calculated from values measured over a period (e.g., week, month, year, etc.).

Volume dosed within a 24-hour period using a flow-equalization configuration.

Centrifugal pump that incorporates an impeller that resembles a propeller and is used for pumping treated effluent or clean water; less useful for raw wastewater or sludge because the tight tolerances of the impellers cannot easily handle solids or stringy material.

Form of backflow which occurs because of negative pressure; see also backflow; anti-siphon device.

The hillslope position that forms the steepest, and generally linear, middle portion of the slope. In profile, backslopes are bounded by a convex shoulder above and a concave footslope below; may or may not include cliff segments (i.e., free faces).

1. Material placed in an excavation; 2. To place material in an excavation; 3. portion of an excavation above the haunch zone; for straight-walled tanks or structures, that portion of an excavation above the bedding.

Reverse direction of flow, with liquid returning to the source.

Any device, method, or configuration used to prevent a reversal of flow.

To reverse the direction of flow to clean laterals; see also backwash.

Rod reading taken on a point of known or assumed elevation (where establishing the first benchmark, usually assumed as 100.00); the backsight reading is added to the elevation to determine the height of instrument (HI); see also height of instrument (HI).

To reverse the direction of flow through a filter, ion exchange column, or membrane for cleaning purposes; see also backflush.

Unicellular microorganisms that are ubiquitous, living in the human gut as well as aquatic and terrestrial habitats; beneficial species aid in human digestion and biological wastewater treatment; pathogenic species are a constituent of concern in biological wastewater treatment systems.