Wastewater Words

Glossary of wastewater treatment descriptions, terms and acronyms associated with wastewater reclamation and sewage treatment.

Activated Sludge Process (ASP)

A biological wastewater treatment process that promotes waste decomposition in the treated wastewater.


An aquatic environment that has dissolved oxygen added.


A condition in which the aquatic environment is free of dissolved and chemically bound oxygen.


A condition in which the aquatic environment does not contain dissolved oxygen. Generally, it contains chemically bound oxygen such as nitrate.


The modified Bardenpho process is a biological process that provides conditions for both nitrogen and phosphorous removal. This system consists of five distinct reactor basins, which are respectively: anaerobic basin, first anoxic basin, aerobic basin, second anoxic basin, and reaeration basin.

Biochemical Oxygen Demand (BOD)

The rate at which organisms use the oxygen in water or wastewater while stabilizing decomposable organic matter under aerobic conditions.  In decomposition, organic matter serves as food for the bacteria, and energy results from its oxidation.  BOD is used as a way to measure the strength of wastewater.

Biological Nutrient Removal (BNR)

Removes total nitrogen and phosphorus from wastewater through the use of microorganisms under different environmental conditions in the treatment process.

Biological Phosphorus Removal (Bio P)

Removes phosphorus from waste through the use of microorganisms under different environmental conditions, within each basin, in the treatment process without using chemicals.

Bugs (Micro Organisms)

An industry-wide term used when referring to micro organisms in the mixed liquor.

Class A+ Water

The highest quality of reclaimed water permitted by the Arizona Department of Environmental Quality.


An anoxic process occurs when nitrate ions are reduced to nitrogen gas.  The nitrogen gas is released into the atmosphere.


A process that removes or separates a portion of water present in the waste-activated sludge is removed.

Dissolved Oxygen (DO)

Molecular oxygen dissolved in wastewater.

Glycogen Accumulating Organisms (GAO)

A group of bacteria that compete for the same food resources as Phosphorus Accumulating Organisms.

Grit Chamber

The Grit Chamber at GVW is a circular basin with a rotating agitator in the middle that forces the heavier grit against the outer walls by centrifugal force.  This heavier settles to the bottom of the chamber to get removed.

Inorganic Material

Materials such as sand, salt, iron, calcium, coffee grounds, eggshells, and other materials that are only slightly affected by the action of organisms.  Also referred to as nonvolatile


Living organisms that are seen individually with the aid of a microscope.

Mixed Liquor Suspended Solids (MLSS)

The amount (measured in mg/L) of suspended solids in the mixed liquor of an aeration tank.

Mixed Liquor

When Return Activated Sludge is mixed with raw wastewater, this mixture is referred to as mixed liquor.


An inorganic chemical that is a product of Nitrifying ammonium.  It is easily broken down in an anoxic zone.


A stage of decomposition occurs in biological treatment processes when aerobic bacteria, using dissolved oxygen, change ammonia into oxidized nitrogen.


A chemical compound that is an intermediate product of the oxidation of ammonium to Nitrate


Nephelometric turbidity units.

Organic Material

Material that comes from animal waste or plant sources.  It can generally be consumed by bacteria and other tiny organisms. Also referred to as volatile.

Phosphorus Accumulating Organisms (PAO)

A group of bacteria that, under certain conditions, facilitate the removal of phosphorus from wastewater.

Plant Process Water

It is the water reclamation facility’s A+ reuse water that gets used onsite instead of using Town of Payson Potable Water.


A long-chain molecule formed by the union of many monomers.  Polymer is used as a coagulant to aid in the binding of small suspended particles to form larger flocs to aid with the removal of water.


Non-biodegradable materials such as paper towels, “flushable” wipes, clothing, towels, and other similar items.

Raw Influent

Untreated water flowing into the treatment plant.


An aquatic environment that has been reintroduced to dissolved oxygen.

Return Activated Sludge (RAS)

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


All the materials that get removed from the influent with the step screen.  These are materials that should not be coming to the water reclamation facility.

Sludge Retention Time (SRT)

A measure of the length of time a microorganism has been retained in the activated sludge process.  SRT is operationally optimized for the water reclamation facility conditions.


The cloudy appearance of water caused by the presence of suspended and colloidal matter.  It is used to measure the clarity of the water.

Volatile Fatty Acids (VFA)

Water-soluble acids are formed when BOD is fermented.

Waste Activated Sludge (WAS)

Settled activated sludge that is collected in the secondary clarifier and sent to a thickener, digester, or dewatering equipment.