The following is a layman's guide to the abbreviations and terminology used in the waste water treatment industry, compiled for your convenience from a multitude of sources.


BOD5 - The Biological oxygen demand of effluent, measured continuously over a five day period

CBOD5 - Carbonaceous Biochemical oxygen demand

COD - Chemical oxygen demand, typically 5 times CBOD

ES - Extended storage. Refers to the process by which solid materials are recirculated thru the processing chambers to reduce solid accumulation and extend the period before the treatment system must be serviced.

NSF - National Standards Foundation, a government organization in the USA which certifies the suitability of a product for a particular purpose. The Canadian equivalent is CSA (Canadian standards association) certification.

NTU - Nephelometric Turbidity Units, measured by passing ultraviolet light thru the sample and measuring the dispersion of the output. Pure water has a turbidity of 0.02 NTU.

ORP - Oxygen Reduction Potential, as measured by a probe that measures electrical flow in the effluent, which is directly proportional to the amount of chlorine residue. Used to determine if the dechlorination is working properly.

pH - A characteristic of liquids on a scale from 0 to 14 varying from extremely acidic to totally basic. Neutral liquids such as pure water have a pH level of 7. Values in the 6 to 8 range qualify as safe for drinking water.

PLC - Programmable logic controller, a monitoring device that can adjust various parameters. For water treatment systems that may include the amount of aeration and the flow rate through the system.

Sludge Filter Press - A device to compact sludge (solid materials) in a treatment system, used to reduce the volume and mass of the solids that need to be removed mechanically.

SM - Sludge Management, including recycling, burning or pressing.

SRT - Solid retention time, usually measured in the clarifier chamber, when solid materials settle to the bottom.

SS - Suspended solids

SVI - Sludge Volume Index, measured as the amount of water / volume of biosolids

TKN - Total Kjeldahl Nitrogen - NH3 and NH4 (ammonia)

TOC - Total Organic Carbon

TSS - Total Suspended solids


Activated Sludge - The process by which healthy bacteria (the activated sludge solids) act to digest sewage. Where a Fixed or floating media (see below) are used, bacteria that falls off the media is returned to the treatment system by aeration from below.

Aeration - The process of aiding oxygen to a water treatment system, which can be done either from below with a blower or by spraying the wastewater through the air in an aeration chamber.

Aerobic Bacteria - Bacteria that require free dissolved oxygen for their growth.

Aerobic Degradation Potential - Measures the ability of a water treatment system to create aerobic bacteria to process the incoming water. Certain chemicals, particularly those containing chlorine, present in the water to be treated may inhibit the bacteria growth. In that case bacteria from another treatment system may be added, either during the start up period of a system or continuously, to increase the aerobic degradation potential.

Anaerobic Bacteria - are bacteria that grow only in the absence of free dissolved oxygen

Anoxic - free of dissolved oxygen. Normally the influent from a home or plant is anoxic, allowing for denitrification.

Attached growth - The technology by which a media is included in the sewage chamber to which the microorganisms that process the sewage attach themselves (see fixed and floating media). The advantage of the technology include better mixing and variation of the bacteria, and reduction of solids.

Biological reactor - Refers to the complete water treatment system, that acts to stimulate the biological decay of the influent.

Chlorination - The addition of chlorine to the effluent after treatment to remove fecal coliform. Often done by addition of calcium hypochlorite tablets. It may take up to 90 minutes to completely disinfect the effluent. Dechlorination by the addition of injection of another chemical such as sodium thiosulphite is necessary if the water is intended for irrigation or drinking water.

Coagulation/Flocculation - The process of adding reagents to facilitate the removal of suspended solids and colloidal particles(less than 1 micron). It is used in the final stage of solids-liquids separation for large water treatment systems ,either via settling, flotation or filtration. The coagulant is the reagent that destabilized the solids and causes them to flocculate (come together and grow till they are heavy enough to sink).

Effluent - The output or discharge from a water treatment system

Fecal coliform - A type of bacteria that occurs in human feces. Although not normally disease causing in themselves, high levels may indicate the presence of more harmful bacteria which can cause hepatitis and dysentery. Removal of fecal coliform is done by chlorination in water systems. Measurement of fecal coliform can be done by incubating the water sample in a fermentation tube and measuring the gas production. The unit of measurement is MPN (most probable number) of coliform present in a 100 milliliter sample. This is equivalent to CPU (colony producing units) per 100 ml. Where there is likely to be human contact with the effluent, levels of less than 200 CPU are required, rising to 2000 CPU for private dispersal fields. See http://bcn.boulder.co.us/basin/data/FECAL/info/FColi.html.

Fixed media - A gridwork, often in layers, typically of PVC plastic, which is fixed in place the water processing chambers. The microorganisms(bacteria) tend to attach themselves to the media and grow there, a process somewhat akin to coral reef growth.

Floating media - Can take the form of sponges, cylinders or plastic tubes with a narrow top. Depending on the design, they may float or be partially submerged in the treatment chamber. Advantages as opposed to fixed media are reduced chance of blockage and easier to service or replace.

Granular Activated Carbon Filter - A type of filter made from bituminous coal providing large particle size and high surface area, as well as strength, for chemical purification of water. It can be used in anything from a home aquarium to a municipal water treatment plant.

Influent - The input to a water treatment system

Nitrification/Denitrification - Nitrification is the process of conversion of nitrogen compounds (primarily ammonia) to nitrates and nitrites (from NH3 to NO or NO2). This occurs naturally in water treatment systems. Denitrification is the process of converting the nitrate/nitrite to free oxygen. It can be accomplished in water treatment by recycling the effluent to the first chamber which is oxygen poor, with the releases of oxygen and nitrogen as gases. The nitrate/nitrite compounds are not normally harmful but in high concentrations they can be harmful to fish.

Pathogenic organisms - Illness or disease causing organisms that may be present in a water supply (see fecal coliform).

Percolation Rate - The rate at which liquids introduced at surface sink thru the subsoil, measured in time per vertical distance. If the percolation is too slow, the effluent may accumulate at surface creating a pond. If the percolation is too fast, the effluent may reach a water well or property boundary without sufficient dilution. A percolation test is normally required prior to installation of a water treatment system, and special regulations may apply for the location of the discharge area.

Polishing - The final treatment of the effluent, often by percolation thru a sand or gravel media.

Superchlorination - When small amounts of chlorine are introduced into water containing nitrogen, various compounds known as chloramines form. In a swimming pool these are the compounds that cause your eyes to burn. Superchlorination is the addition of high quantities of chlorine (typically ten times the ammonia present) which effectively prevents the chloramines from forming. Instead the ammonia is converted to a gas that is released in the air.

Total nitrogen - The total of ammonia-nitrogen, nitrite and nitrate in a liquid solution

Trickling filter - The process of having the wastewater pass thru a filter to hold back and digest any remaining solid materials or paper. This protects the drainage filed or dispersal site from accumulation of solids and prevents clogging of the drain pipes.

Turbidity - The measure of the clarity of a liquid measured in NTU units. Minimum turbidity standards are common in most water regulation acts, especially if the water is to recycled for irrigation purposes.

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