GLOSSARY WASTEWATER TERMS
Sludge that has undergone flocculation forming a bacterial culture typically carried out in tanks.
Can be extended with aeration.
Advanced Primary Treatment
The use of special additives to raw wastewater to cause flocculation or clumping to help settling
before the primary treatment such as screening.
Advanced Wastewater Treatment
Any advanced process used above and beyond the defacto typical minimum primary and
secondary wastewater treatment.
Aerobic Wastewater Treatment
Oxygen dependent wastewater treatment requiring the presence of oxygen for aerobic bacterial
breakdown of waste.
A measure of a substances ability to neutralize acid. Water containing carbonates, bicarbonates,
hydroxides, and occasionally borates, silicates, and phosphates can be alkaline. Alkaline
substances have a pH value over 7
Anaerobic Wastewater Treatment
Wastewater treatment in the absence of oxygen, anaerobic bacteria breakdown waste.
Single cell microscopic living organisms lacking chlorophyll, which digest many organic and
inorganic substances. An essential part of the ecosystem including within human beings.
The use of living plants as part of the system, be it wastewater treatment, erosion control, water
polishing, habitat repair and on.
Rich organic material leftover from aerobic wastewater treatment, essentially dewatered sludge
that can be re-used.
BOD - Biochemical Oxygen Demand
Since oxygen is required in the breakdown or decomposition process of wastewater, its
"demand" or BOD, is a measure of the concentration of organics in the wastewater.
A piece of wastewater treatment equipment used to "clarify" the wastewater, usually some sort of
holding tank that allows settling. Used when solids have a specific gravity greater than 1.
COD - Chemical Oxygen Demand
The amount of chemical oxidant required to breakdown the wastes, also an indicator of the
concentration of organics.
Cold Climate Limitations
The limitations of various wastewater treatment options caused by severe cold and its incidents
such as ice, snow, very low temperatures and so on.
Combining the municipal sewer systems with storm drainage. Risks overpowering the system in
large rain events. The benefit is that pollutants from storm drainage get treated,
Combined Sewer Overflow (CSO)
When a combined sewer system is overpowered by storm drainage and overflows.
An artificially created wetland usually with a waterproof lining for wastewater purification.
Detention, flow rates, types of plants and other parameters are controlled to improve BOD, SS
and N removal. Typical riparian plants like cattails and reeds are used to provide bacteria with an
oxygenating root zone.
Detention Time - Retention Time, Residence Time
How long on average wastewater undergoes the wastewater treatment process. Time vary greatly
across various types of wastewater treatment, from minutes to weeks.
The sludge after it's been dewatered, also know as sludge cake.
Dewatered Sludge Cake
The sludge after dewatering that is cake like, compressed. The lower the water content the better
for wastewater treatment purposes.
Removing water from sludge or other solids.
The breaking down of sludge and other waste biologically by microorganisms. Results in
byproducts such as methane gas, carbon dioxide, sludge solids and water. Aerobic digestion
requires oxygen, anaerobic digestion the absence of oxygen.
Biologically removing nitrate converting it to nitrogen gas.
The use of chemicals to kill any disease causing organisms in the polished wastewater. UV light
can also be used.
Dissolved Oxygen (DO)
The amount of oxygen dissolved in the water. Measured in milligrams per liter.
Systems designs that are considered to be "sustainable", that is with the aim of having little to no
impact on earth's ecology. See Industrial Ecology.
The final output flow of a wastewater treatment plant.
An aeration system that adds aerobic sludge digestion to the activated sludge process.
Wastewater ponds with some form of aeration for oxygen replenishment. Can also use algae and
other plants for oxygen replenishment.
Particulate and or bacterial clumps forming wooly looking clusters in wastewater. In biological
processes such as extended aeration or activated sludge and others the floc contains aerobic or
anaerobic microorganisms. For industrial applications flocculants are used.
The process whereby a chemical or other substance is added to wastewater to trap or attract the
particulate suspended solids into clusters or clumps of floc or flocculent, wooly looking masses.
The flocculant or chemical used to cause flocculation.
Same as flocculating agent, the catalyst substance that causes the chemical reaction with TSS to
form flocculent many times encapsulating the solids.
The "floc" or wooly mass of clusters that is formed in flocculation. Many times used
interchangeably with "flocculant" however truly refers to the floc mass and not the catalyst
Free Water Surface Wetland (FWS)
A constructed wetland or other shallow wastewater treatment pond where the shallow water is
exposed directly to the air.
Fats, soaps, oils, waxes and etc. in wastewater.
Usually in municipal wastewater treatment, a chamber or tank in which primary influent is
slowed down so heavy typically inorganic solids can drop out, such as metals and plastics.
The beginning of the treatment plant where the influent begins treatment.
Industrial Ecology (IE) focuses on combining perpetually desirable outcomes in environment,
economy and technology sustainably. The primary tenet is that all systems mimic nature and are
thus closed loop, continuous, circular. In wastewater treatment industrial ecology would mean
that all so called "waste" is re-input into the same or other process. For example, biosolids as
fertilizer can be considered a use of sludge consistent with industrial ecology. Recycling
wastewater into the treatment plant, manufacturing or other process is another example.
Industrial Wastewater Treatment
Wastewater treatment for industries such as manufacturing, food processing, corrugators,
printing and so on. Paper and pulp mills' treatment of wastewater is an example of industrial
wastewater treatment. Municipal wastewater treatment would be an example not considered to
The untreated wastewater or raw sewage coming into a wastewater treatment plant.
Screens used to remove large inorganic solids from the waste stream.
Innovative and Alternative (I&A)
An EPA term for wastewater treatment systems that reuse all or part of the wastewater.
Liquid Solids Separation
The process of separating the liquids and solids in a given wastewater. Liquid/solids separation
comes in one of 3 processes:
1. If the solids sink (specific gravity greater than 1) use a clarifier
2. If the solids float (specific gravity less than 1) use a floatation unit (DAF)
3. If neither sink or float (specific gravity is 1) try using a screen (rotary or parabolic)
Million Gallons per Day - 694.4 gallons per minute.
Modified Permit, Waiver
EPA variances or waivers granted.
The measure of nitrogen usually as ammonia and nitrate present in various wastewaters.
Wastewater treatment systems usually biological with a minimum of mechanical components or
processes, for example, constructed wetlands.
Wastewater treatment at the point of production typically associated with residential systems
such as septic tanks. Onsite treatment plants are also common in hotels, schools, small
communities and manufacturing plants. Onsite treatment can reduce the costs of concentrating
wastewaters into one huge treatment plant.
Overland Flow Land Treatment
Grassy slopes used to treat wastewater. Leftover water is captured at the bottom.
A measure of acidity or alkalinity of water, or any given substance. The scale is 1 to 14 with 7
being neutral. Over 7 is alkaline or caustic, under 7 is acid or base.
The measure of Phosphorus present in wastewater.
Primary Wastewater Treatment
The first process usually associated with municipal wastewater treatment to remove the large
inorganic solids and settle out sand and grit.
Untreated sanitary wastewater.
Reusable wastewater from wastewater treatment such as tertiary treatment of wastewater in
biological and other systems.
Storm flows that aren't absorbed and flow off the land and streets.
Sanitary Wastewater (domestic)
Wastewater from human domestic water use.
Usually fatty material in wastewater that floats.
Secondary Wastewater Treatment
Second biological process of digestion with bacteria.
Sewage (or wastewater)
The used water and added waste of a community which is carried away by drains and sewers.
A system of sewers; the removal of waste materials by means of a sewer system.
The solid waste material which settles out in the wastewater treatment process, sometimes
biosolids. Can be dewatered and reused or disposed.
Removing the remaining water from sludge for reuse and to lighten the sludge for reuse or
Storm Water Run-Off (SRO)
The pulse of surface water following a rainstorm. The water carries sediment, gas, oil, animal
feces, glass and other waste from the watershed to receiving waters creating a difficult
urban/suburban wastewater problem.
A pipeline or channel system that carries surface water and/or runoff to public waters, but does
not feed into sewer system.
Subsurface Flow Wetland (SF)
A type of constructed wetland in which primarily treated waste flows through deep gravel or
other porous substrate planted with wetland vegetation. The water is not exposed to the air,
avoiding problems with odor and direct contact.
TDS - Total Dissolved Solids
Total Dissolved Solids (TDS) is the combined total of all dissolved solids in wastewater, both
organic and inorganic and very fine, such as colloidal minerals. Generally particles must be
smaller than two micrometers to be considered a dissolved solid. For example, salt dissolved in
water is a dissolved solid. Therefore TDS will "survive" screening or other coarse filtration.
Tertiary Wastewater Treatment (Advanced)
Biological or chemical polishing of wastewater to remove organics, solids and nutrients. Tertiary
wastewater effluent limits are generally 10 mg/1 BOD5 and 10 mg/1 TSS.
The use of filtration to remove microscopic particles from wastewater that has already been
treated to a Secondary Level. Anthracite coal is the filter medium used by the MWWD.
How treatable a water sample is with a given substance.
TSS - Total Suspended Solids
As the name implies, the total solid particles that are suspended (as opposed to dissolved) in the
wastewater. TSS must be filtered out, flocculated, digested and so on for removal in the
treatment of wastewater. Though not necessarily pollutants TSS is considered to be a measure of
pollutants in water by the EPA in the US.
A measure of how clear water is in Nephelometric Turbidity Unit (NTU), invisible to the average
naked eye until readings in excess of 100 are reached, typically determined by shining light
through a sample placed in a turbidimeter.
Ultraviolet Disinfection (UV)
The use of ultraviolet light to kills bacteria and other microorganisms in water and wastewater.
Typically a final treatment step.
Wastewater is "used" water, the water leftover after its use in numerous application such as
industrial, agricultural, municipal, domestic and on.