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Activated Sludge

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.


Combined Sewer

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.


Constructed Wetland

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.


Dewatered Sludge

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.


Ecological Engineering

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.


Extended Aeration

An aeration system that adds aerobic sludge digestion to the activated sludge process. 


Facultative Ponds

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.


Flocculating Agent

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

flocculating agent.


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.


Grit Chamber

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

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

be industrial.



The untreated wastewater or raw sewage coming into a wastewater treatment plant.


Influent Screens

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.


N: Nitrogen

The measure of nitrogen usually as ammonia and nitrate present in various wastewaters.


Natural Systems

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.


P: Phosphorus

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.


Raw Sewage

Untreated sanitary wastewater.


Reclaimed Water

Reusable wastewater from wastewater treatment such as tertiary treatment of wastewater in

biological and other systems.


Run Off

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.


Sludge Dewatering

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.


Storm Drain

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.


Tertiary Treatment

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.

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