Glossary of Industry Definitions

Most industrial processes include water at some point. There is terminology that is unique to the water industry, plus there are many terms unique to industries we serve. 


This Glossary contains many definitions for frequently-used words and phrases found on this site and by the industries we serve.

We hope this resource helps you to get the most from our website, but it's far from comprehensive. Please let us know if you encounter terminology that you think should be added to this section.

316SS: 316 grade stainless steel is the second most common austenite steel. Also called marine grade stainless, it is used primarily for its increased resistance to corrosion. Low-carbon versions, for example 316L or 304L, are used to avoid corrosion problems caused by welding. The "L" means that the carbon content of the alloy is below 0.03%, which reduces the sensitization effect (precipitation of chromium carbides at grain boundaries) caused by the high temperatures involved in welding.

ABAC: See - Ammonia-based aeration control

Absorption: The sponge-like process of taking up a substance into another physical structure without a chemical reaction.

In chemistry, absorption is a physical or chemical phenomenon or a process in which atoms, molecules or ions enter into a liquid or solid material. See also adsorption.

adsorption: The adhesion of atoms, ions or molecules to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid (the absorbate) is dissolved by or permeates a liquid or solid (the absorbent). Adsorption is a surface phenomenon, while absorption involves the whole volume of the material, although adsorption does often precede absorption. The term sorption encompasses both processes, while desorption is the reverse of it.

Activated Sludge: Sewage mixed with bacteria and protozoa that thrive and multiply in it and lead to its oxidation (see biological oxygen demand).

Adenosine triphosphate (ATP): Adenosine Triphosphate (ATP) is the primary energy carrier in all living organisms on earth. Microorganisms capture and store energy metabolized from food and light sources in the form of ATP.

When the cell requires energy, ATP is broken down through hydrolysis. The high energy bond is broken and a phosphoryl group is removed. The energy released from this process is used to drive various cellular processes.

In wastewater treatment, ATP can directly quantify active biomass, which is key to providing secondary treatment. Two of the many potential uses for ATP in a wastewater treatment plant are aeration and solids optimization and toxicity monitoring and identification.

Aerobe: a microorganism which grows in the presence of air or requires oxygen for growth.

Aerobic: relating to, involving, or requiring free oxygen.

Aerobic Wastewater Treatment: Aerobic wastewater treatment is a biological treatment process that takes place in the presence of oxygen. Aerobic biomass converts organics in the wastewater into carbon dioxide and water, or new biomass and heat.

Ag: See "Silver".

Aircraft Deicing Fluid (ADF): Deicing of aircraft is commonly performed in both commercial and general aviation. The chemicals used in this operation are called deicing or anti-icing fluids. These fluids are typically referred to as ADF (Aircraft Deicing Fluid), ADAF (Aircraft Deicer and Anti-icer Fluid) or AAF (Aircraft Anti-icing Fluid).

The most common deicing fluids are composed of ethylene glycol (EG) or propylene glycol (PG), plus thickening agents, surfactants (wetting agents), corrosion inhibitors, colors, and UV-sensitive dye. Propylene glycol-based fluid is less toxic than ethylene glycol.

Both ethylene glycol and propylene glycol exert high biochemical oxygen demand (BOD) during degradation in surface waters or during wastewater treatment. Dissolved oxygen (DO) is consumed by microbes to decompose the deicer. In surface waters this can deprive aquatic life of needed oxygen, while in wastewater treatment it places a costly burden on the blowers that provide oxygen to the basins. Deicing programs are regulated by the FAA (14 CFR § 121.629), and subsequent deicer runoff is regulated by the EPA (40 CFR Part 449) as part of an airfield's NPDES permit.

Aliquot: a portion of a larger whole, especially a sample taken for chemical analysis or other treatment. "an aliquot was examined daily for the appearance of cholesterol monohydrate crystals"

Alum: Aluminum sulfate. Iron free Aluminum Sulfate (Alum) is most widely used in municipal drinking water and wastewater treatment systems. In potable water applications, alum functions as an excellent primary coagulant. Through charge neutralization and flocculation in raw water, alum removes turbidity.

American Society of Civil Engineers (ASCE): American Society of Civil Engineers

The American Society of Civil Engineers is a tax-exempt professional body founded in 1852 to represent members of the civil engineering profession worldwide. Headquartered in Reston, Virginia, it is the oldest national engineering society in the United States.

American Society for Microbiology (ASM): American Society for Microbiology

American Society for Testing and Materials (ASTM): American Society for Testing and Materials

Ammonia-based Aeration Control: (ABAC) is a cascade control concept for controlling total ammonia nitrogen (NHx-N) in the activated sludge process. Its main goals are to tailor the aeration intensity to the NHx-N loading and to maintain consistent nitrification, to meet effluent limits but minimize energy consumption.

Amperometric: Pertaining to or involving the measurement of an electric current.

Anaerobe: an organism that grows without air, or requires oxygen-free conditions to live.

Anaerobic: relating to, involving, or requiring an absence of free oxygen. "anaerobic bacteria".

Anaerobic wastewater treatment: is a biological process where microorganisms degrade organic contaminants in the absence of oxygen. In a basic anaerobic treatment cycle, wastewater enters a bioreactor receptacle. The bioreactor contains a thick, semi-solid substance known as sludge, which is comprised of anaerobic bacteria and other microorganisms. These anaerobic microorganisms, or “anaerobes,” digest the biodegradable matter present in the wastewater, resulting in an effluent with lower biological oxygen demand (BOD), chemical oxygen demand (COD), and/or total suspended solids (TSS), as well as biogas byproducts.

ASCE: See: American Society of Civil Engineers

ASM: See: American Society for Microbiology

ASTM: See: American Society for Testing and Materials

ASTM D6238 - 98 (2017): Standard Test Method for Total Oxygen Demand (TOD) in Water TOD offers a rapid alternative to BOD and COD tests. Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) analyzers have long time cycles and in the case of COD analyzers use corrosive reagents (with inherent disposal problems).

Total Oxygen Demand analysis is faster, approximately three minutes, and uses thermal oxidation rather than chemical reagents for a chemical-free analysis.

TOD can be correlated to both COD and BOD, providing effective online analysis and control.

TOD offers several features which make it a more attractive measurement than carbon monitoring using total carbon (TC) or total organic carbon (TOC) analyzers. TOD is unaffected by the presence of inorganic carbon. TOD analysis will also indicate non-carbonaceous materials that consume or contribute oxygen. For example, the oxygen demand of ammonia, sulfite and sulfides will be reflected in the TOD measurement. Also, since the actual measurement is oxygen consumption, TOD reflects the oxidation state of the chemical compound (that is, urea and formic acid have the same number of carbon atoms, yet urea has five times the oxygen demand of formic acid).

The Total Oxygen Demand (TOD) measurement is achieved by continuous analysis of the concentration of oxygen in a combustion process gas effluent. The decrease in oxygen resulting from introduction of the sample into the combustion zone is a measure of oxygen demand.

Principle of Operation: The oxidizable components in a liquid sample introduced into a carrier gas stream containing a fixed amount of oxygen flowing through a combustion reactor are converted to their stable oxides. The momentary reduction in the oxygen concentration in the carrier gas is detected by an oxygen sensor. Results can be displayed and/or recorded. The TOD for the sample is obtained by comparing the area of a calibration curve to the area of a curve derived from the combustion of a sample.

The TOD for the standard solution is based on experimentally observed reactions in which carbon is converted to carbon dioxide, hydrogen to water, combined nitrogen (including ammonia) to nitric oxide, and elemental or organic sulfur to sulfur dioxide. Sample injection is achieved by means of automated injection into the combustion reactor, thus providing unattended sequencial batch monitoring in the laboratory or on-line.

Analyte: a substance whose chemical constituents are being identified and measured.

ATP: See Adenosine triphosphate

Autotroph: An organism capable of synthesizing its own food from inorganic substances, using light or chemical energy. Green plants, algae, and certain bacteria are autotrophs. In wastewater treatment, autotrophs are responsible for the removal of ammonia by converting first to nitrite, then to nitrate. This work is performed primarily by two species; nitrobacter and nitrosomonas.

Black Liquor: In industrial chemistry, black liquor is the by-product from the kraft process when digesting pulpwood into paper pulp by removing lignin, hemicelluloses and other extractives from the wood to free the cellulose fibers.

Biological Nutrient Removal (BNR): In wastewater treatment, biological Nutrient Removal reduces nitrogen and phosphorus from wastewater before it is discharged to surface or ground water. BNR is necessary since nitrogen and phosphorus are nutrients. In discharge they contribute to algal blooms, which can lead to eutrofication.

Biochemical Oxygen Demand (BOD): is the amount of dissolved oxygen needed (i.e. demanded) by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. The BOD value is most commonly expressed in milligrams of oxygen consumed per liter of sample during 5 days of incubation at 20 °C and is often used as a surrogate for the degree of organic pollution in water.

BOD reduction is used as a gauge of the effectiveness of wastewater treatment plants. BOD of wastewater effluents is used to indicate the short-term impact on the oxygen levels of the receiving water.

Biomass: the total mass of organisms in a given area or volume. In biological wastewater treatment, biomass refers to the microorganisms (catalyzers), also known as sludge in the secondary treatment stage. Substrate refers to the organic matter in the influent that is degraded, (metabolized), by the biomass. See also F/M Ratio.

BOD20: Twenty-day Biochemical Oxygen Demand. The amount of dissolved oxygen consumed in twenty days by biological processes breaking down organic matter.

BOD5: Five-day Biochemical Oxygen Demand. The amount of dissolved oxygen consumed in five days by biological processes breaking down organic matter. Found on

°C Degrees centigrade.

CaCO3 Calcium carbonate

Cd: Cadmium

Ce: Effluent concentration of the specified analyte

CERCLA: Comprehensive Environmental Response, Compensation, and Liability Act

CFR: Code of Federal Regulations

Chromium (Cr): the chemical element of atomic number 24, a hard white metal used in stainless steel and other alloys. Trivalent chromium, or chromium(III), is essential to human health. Hexavalent chromium, or chromium(VI), is toxic. Chromium(VI) is hemotoxic, genotoxic, and carcinogenic. When hexavalent chromium enters the bloodstream, it damages blood cells by causing oxidation reactions. This oxidative damage can lead to hemolysis and, ultimately, kidney and liver failure.

Ci: See Influent concentration

CO2: Carbon dioxide: In TOC measurement, organic compounds are oxidized to CO2. For an accurate measurement, inorganic carbon must first be removed.

COC: Chain-of-custody

COD: Chemical oxygen demand. In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution which in SI units is milligrams per litre (mg/L). A COD test can be used to easily quantify the amount of organics in water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g. lakes and rivers) or wastewater. COD is useful in terms of water quality by providing a metric to determine the effect an effluent will have on the receiving body, much like biochemical oxygen demand (BOD).
For information on the laboratory potassium dichromate method, please see also, EPA Standard Method 410.4, Revision 2.0: The Determination of Chemical Oxygen Demand by SemiAutomated Colorimetry

Cr: Chromium

CuSO4: Copper sulfate

cu ft/lb: Cubic feet per pound

CV: Coefficient of variation: The Coefficient of Variation (CV), also known as Relative Standard Deviation (RSD), is a standardized measure of dispersion of a probability distribution or frequency distribution. It is often expressed as a percentage, and is defined as the ratio of the standard deviation to the mean (or its absolute value).

CWA: Clean Water Act

DPD Method: An analytical method for determining chlorine residual utilizing the reagent DPD (n-diethyl-e-phenylenediamine). This is the most commonly and officially recognized test for free chlorine residual.

DMR: Discharge monitoring report

DO: Dissolved Oxygen

EC50: In aerobic wastewater treatement, the median Effective Concentration (EC50) is the concentration of a toxic substance in a known volume of activated sludge expected to produce a 50% reduction in oxygen uptake (toxicity) by a sample of activated sludge. The EC50 is an indicator of the toxicity of a compound to a sludge plant's biomass.

ECOTOX: Ecotoxicology Database Retrieval System

EDTA: Ethylenediaminetetraacetate

Effluent: Effluent is an outflowing of water or gas to a natural body of water, from a structure such as a wastewater treatment plant, sewer pipe, or industrial outfall. Effluent, in engineering, is the stream exiting a chemical reactor.

Effluent is defined by the US EPA as "wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers to wastes discharged into surface waters". The Compact Oxford English Dictionary defines effluent as "liquid waste or sewage discharged into a river or the sea".

In the context of wastewater treatment plants, effluent that has been treated is sometimes called secondary effluent, or treated effluent. This cleaner effluent is then used to feed the bacteria in biofilters.

Ethylene Glycol: An organic compound with the formula (CH₂OH)₂. It is mainly used for two purposes, as a raw material in the manufacture of polyester fibers and for antifreeze formulations. It is an odorless, colorless, sweet-tasting, viscous liquid.

Eutrophication: Eutrophication is the over-enrichment of a body of water with minerals and nutrients which induce excessive growth of algae. Left unchecked, this process results in oxygen depletion of the water body after the bacterial degradation of algae or great increase of phytoplankton in a pond, lake, river or coastal zone as a response to increased levels of nutrients. Eutrophication is often induced by the discharge of nitrate or phosphate-containing detergents, fertilizers, or sewage into an aquatic system.

EPA: Environmental Protection Agency
Please see US Environmental Protection Agency

F/M: Food to microorganism ratio

Free Chlorine: When sodium hypochlorite (NaOCl) is dissolved in water it produces hypochlorous acid and hypochlorite ion. The hypochlorite ions are called free chlorine.

Floc: Particles that clump together to form a cluster because of the actions of bacteria (biological floc) or coagulants (chemical floc).

g/L: Grams per liter

glycol: Any of a class of organic compounds belonging to the alcohol family; in the molecule of a glycol, two hydroxyl (―OH) groups are attached to different carbon atoms. See also: ethylene glycol and propylene glycol.

gpd/sq ft: Gallons per day per square foot

gpm/sf: Gallons per minute per square foot

GAC: Granular activated carbon

H and S: Health and Safety

H₂O₂: Hydrogen Peroxide. A colorless, viscous, unstable liquid with strong oxidizing properties, commonly used in diluted form in disinfectants and bleaches. Hydrogen peroxide works by producing destructive hydroxyl free radicals that can attack membrane lipids, DNA, and other essential cell components.

Heterotroph: An organism that cannot synthesize its own food (organic carbon compounds) and is dependent on complex organic substances for nutrition.

Hg: See "Mercury"

HNO₃: Nitric acid

HPLC: High-performance liquid chromatography

HRT: See: "Hydraulic Retention Time"

Hydraulic Retention Time (HRT):
The Hydraulic retention time (HRT) or t (tau) is a measure of the average length of time that a soluable compound remains in a constructed bioreactor. The volume of the aeration tank divided by the influent flowrate is τ (tau), the hyraulic retention time.

Hydrophilic: having a tendency to easily mix with, dissolve in, or be wetted by water.

A hydrophilic molecule or portion of a molecule is one whose interactions with water and other polar substances are more thermodynamically favorable than their interactions with oil or other hydrophobic solvents. They are typically charge-polarized and capable of hydrogen bonding. This makes these molecules soluble not only in water but also in other polar solvents.

Hydrophobic: Literally - "Fear of Water". In chemistry, the term "hydrophobic" refers to a substance (hydrophobe) that seemingly repels water. Water droplets on hydrophobic surfaces will exhibit a high contact angle.

Examples of hydrophobic molecules include alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar substances from polar compounds.

By contrast, a hydrophile is a substance that is attracted to water.

Inductive conductivity measurement: Using a coil to induce a current in the secondary coil. Since both coils have no direct contact to the media this method is sometimes called non-contacting conductivity or - due to the "doughnut" shape of the coils - torroidal conductivity. This method makes it possible to measure in concentrated acids, alkalis, and aqueous solutions with high solids content.

Influent concentration (Ci): Influent concentration for a specified analyte

ICp: ICp Inhibition concentration causing a percent effect (p) in the test species (e.g., IC25, IC50)

Ion-selective electrode: An ion-selective electrode, (ISE), also known as a specific ion electrode, is a transducer that converts the activity of a specific ion dissolved in a solution into an electrical potential. The voltage is theoretically dependent on the logarithm of the ionic activity, according to the Nernst equation.

Junction Box: An electrical junction box is an enclosure housing electrical connections.
Junction boxes protect the electrical connections from the weather, as well as prevent people from accidental electric shocks.

KHP:See Potassium Hydrogen Phthalate.

L: Liter

Lead (Pb): Lead is a chemical element with the symbol Pb and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead is silvery with a hint of blue; it tarnishes to a dull gray color when exposed to air.

EPA and the Centers for Disease Control and Prevention (CDC) agree that there is no known safe level of lead in a child's blood. Lead is harmful to health, especially for children.

The most common sources of lead in drinking water are lead pipes, faucets, and plumbing fixtures. Certain pipes that carry drinking water from the water source to the home may contain lead. Household plumbing fixtures, welding solder, and pipe fittings made prior to 1986 may also contain lead.

LC50: Lethal concentration causing a 50% mortality in exposed test organisms

MCRT: See Mean cell residence time

Mean cell residence time (MCRT): The mean cell residence time or MCRT is the amount of time, in days, that solids or bacteria are maintained in the activated sludge process. The MCRT is known also as the solids retention time (SRT).

mg/L: Milligram per liter

Mercury (Hg): Mercury is a chemical element with the symbol Hg and atomic number 80. Mercury becomes a solid at -38.83°C and a gas at 356.7°C.

Concerns about the element's toxicity have led to restricted use of mercury in commercial goods, although mercury remains in use in scientific research applications and in amalgam for dental restoration in some locales. It is also used in fluorescent lighting.

Mercury poisoning can result from exposure to water-soluble forms of mercury (such as mercuric chloride or methylmercury), by inhalation of mercury vapor, or by ingesting any form of mercury.

In the United States, the Environmental Protection Agency is charged with regulating and managing mercury contamination. Several laws give the EPA this authority, including the Clean Air Act, the Clean Water Act, the Resource Conservation and Recovery Act, and the Safe Drinking Water Act.

Method 410.4: Method 410.4, The Determination of Chemical Oxygen Demand by SemiAutomated Colorimetry

In Method 410.4, sample, blanks, and standards in sealed tubes are heated in an oven or block digestor in the presence of dichromate at 150°C. After two hours, the tubes are removed from the oven or digester, cooled, and measured spectrophotometrically at 600 nm. The colorimetric determination may also be performed manually.

Reduced volume versions of this method that use the same reagents and molar ratios are acceptable provided they meet the quality control and performance requirements stated in the method.

Method 5210 B (5-day BOD Test): This EPA Standard Method consists of filling with sample, to overflowing, an airtight bottle of the specified size and incubating it at the specified temperature for 5 d. Dissolved oxygen is measured initially and after incubation, and the BOD is computed from the difference between initial and final DO.

mg O2/hr/g: Milligram dissolved oxygen per hour per gram

mL: Milliliter

mixed liquor: Mixed liquor suspended solids (MLSS) is the concentration of suspended solids, in an aeration tank during the activated sludge process, which occurs during the treatment of waste water. The units MLSS is primarily measured in milligram per litre (mg/L), but for activated sludge its mostly measured in gram per litre [g/L] which is equal to kilogram per cubic metre [kg/m3]. Mixed liquor is a combination of raw or unsettled wastewater or pre-settled wastewater and activated sludge within an aeration tank. MLSS consists mostly of microorganisms and non-biodegradable suspended matter. MLSS is an important part of the activated sludge process to ensure that there is a sufficient quantity of active biomass available to consume the applied quantity of organic pollutant at any time. This is known as the food to microorganism ratio, more commonly notated as the F/M ratio. By maintaining this ratio at the appropriate level the biomass will consume high percentages of the food. This minimizes the loss of residual food in the treated effluent. In simple terms, the more the biomass consumes the lower the biochemical oxygen demand (BOD) will be in the discharge. It is important that MLSS removes COD and BOD in order to purify water for clean surface waters, and subsequently clean drinking water and hygiene. Raw sewage enters in the water treatment process with a concentration of sometimes several hundred mg/L of BOD. Upon being treated by screening, pre-settling, activated sludge processes or other methods of treatment, the concentration of BOD in water can be lowered to less than 2 mg/L, which is considered to be clean, safe to discharge to surface waters or to reuse water. The total weight of MLSS within an aeration tank can be calculated by multiplying the concentration of MLSS (kg/m3) in the aeration tank by the tank volume (m3).

MLE: See - Modified Ludzack-Ettinger

MLSS: Mixed liquor suspended solids

MLVSS: Mixed liquor volatile suspended solids

Modified Ludzack-Ettinger (MLE): The MLE process employs both an anoxic and aerobic zone for the combined removal of BOD, ammonia, and nitrate/nitrite. The MLE process can achieve a 6 to 8 mg/l Total Nitrogen discharge, depending upon the wastewater influent characteristics.

MS: Mass spectrometry

MSDS: Material safety data sheet

MGD: Million Gallons per Day

Na2HPO4: Disodium phosphate

NaCl: Sodium chloride

NaH2PO4: Monosodium phosphate

NDIR Detector: a Non-dispersive Infrared Detector.

NEMA: National Electrical Manufacturers Association. An example of NEMA is a rating that is used as a standard to define the types of environments where an electrical device can be used; a NEMA rating.

NETAC: USEPA’s National Effluent Toxicity Assessment Center

NH3: Un-ionized ammonia

NH4+: Ammonium ion

NH3-N: Total ammonia as nitrogen

Ni: Nickel

Nitrification: Nitrification reduces nutrients in wastewater prior to discharge. Nitrification is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate. The transformation of ammonia to nitrogen is principally accomplished by two bacteria; nitrosomonas and nitrobacter. Nitrobacter oxidizes ammonia to nitrite, then nitrisomonas oxidizes the nitrite to nitrate. The transformation of ammonia to nitrite is usually the rate limiting step of nitrification.

NO3-N: Nitrate as nitrogen

Non-purgeable Organic Carbon: The carbon compounds that remain after purgeable inorganic carbon is removed through acidification. After the inorganic carbon has been removed, NPOC is a measure of Total Organic Carbon.

NPDES: The National Pollutant Discharge Elimination System (NPDES) is a permit program implemented by authorized state governments and the Environmental Protection Agency (EPA) under the Clean Water Act.
The NPDES permit program addresses water pollution by regulating point sources that discharge pollutants to waters of the United States.
Created in 1972 by the Clean Water Act, the NPDES permit program is authorized to state governments by EPA to perform many permitting, administrative, and enforcement aspects of the program.

NPO: Non-polar organic

NTIS: National Technical Information Service

O2: Oxygen molecule. In the secondary stage of wastewater treatment, oxygen is a critical control parameter, and maintaining the optimal oxygen level directly impacts the treatment efficiency and capacity of the plant.

Organic Compounds: Prior to 1824, it was generally believed that organic compounds could only be created by living organisms, hence the term "organic". Modern chemitry defines organic compounds as those containing carbon, with the exception of inorganic carbon compounds, which include carbides, carbonates (excluding carbonate esters), simple oxides of carbon (for example, CO and CO2), and cyanides.

ORP: Reduction potential (also known as redox potential, oxidation / reduction potential, ORP, pE, ε, or E_{h}) is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts (V), or millivolts (mV). Each species has its own intrinsic reduction potential; the more positive the potential, the greater the species' affinity for electrons and tendency to be reduced. ORP is a common measurement for water quality.

OUR: Oxygen Uptake Rate
The oxygen uptake test measures the respiration rate of the organisms in the activated sludge process. Since it measures the oxygen used in the process, it is a useful tool in the evaluation of process performance, aeration equipment and biodegradability of the waste. See also: Specific Oxygen Uptake Rate (SOUR)

Oxygen Demand: Oxygen demand is an environmental chemistry term that may refer to:
▲ Biochemical oxygen demand (BOD), the amount of oxygen needed by organisms to break down organic material present in a water sample
▲ Carbonaceous biochemical oxygen demand (CBOD), the amount of oxygen needed to break down carbon compounds, excluding nitrogen compounds
▲ Chemical and biological oxygen demand, the combination of biochemical (BOD) and chemical oxygen demand (COD)
▲ Chemical oxygen demand (COD), a test commonly used to indirectly measure the amount of organic compounds in a water sample
▲ Nitrogenous oxygen demand (NOD), the amount of oxygen required to break down nitrogenous compounds in a water sample, like ammonia
▲ Theoretical oxygen demand (ThOD), the calculated amount of oxygen required to oxidize a compound to its final oxidation products

Ozone (O3): Ozone (O3) is a colorless unstable toxic gas with a pungent odor and powerful oxidizing properties, formed from oxygen by electrical discharges or ultraviolet light. It differs from normal oxygen (O2) in having three atoms in its molecule. Ozone is produced when oxygen molecules are dissociated by an energy source into oxygen atoms and subsequently collide with an oxygen molecule to form an unstable gas, ozone , which is used to disinfect wastewater. Wastewater treatment plants that use ozone for dissinfection generate ozone by imposing a high voltage alternating current (6 to 20 kilovolts) across a dielectric discharge gap that contains an oxygen-bearing gas. Ozone is generated onsite because it decomposes to elemental oxygen in a short amount of time.

P: See Phosphorus.

PAC: See Powdered Activated Carbon

Peracetic acid (PAA):

Peracetic acid (C₂H₄O₃) is a mixture of acetic acid (CH₃CO₂H) and hydrogen peroxide (H₂O₂) in water. Peracetic acid is produced by a reaction between hydrogen peroxide and acetic acid:

CH₃-C-OH + H₂O₂ → CH₃C-O-OH + H₂O

acetic acid + hydrogen peroxide → peracetic acid

When peracetic acid dissolves in water, it disintegrates to hydrogen peroxide and acetic acid, which will further dissociate to water, oxygen and carbon dioxide. Peracetic acid degradation products are non-toxic and can easily dissolve in water.

Peracetic acid has a stronger oxidation potential than chlorine or chlorine dioxide.


FOOD INDUSTRY: Peracetic acid is applied as a cleanser and disinfectant for fruits and vegetables, and to disinfect recycled rinse water for foodstuffs. MEDICINE: Disinfection of medical supplies PULP AND PAPER: Prevent biofilm formation and as a disinfectant for plumbing disinfection. COOLING TOWERS: Peracetic acid prevents biofilm and disinfects against Legionella bacteria.

Powdered activated carbon (PAC): Powdered activated carbon

Pb: See "Lead"

PBO: Piperonyl butoxide
A metabolic blocking agent used to detect the presence of organophosphate insecticides

Persulfate: A strong oxidant used as a reagent in some analytical methods for determination of TOC. To enhance the efficiency of the oxidation, the method may also include exposure to ultraviolet light, heat, or both.

Perfluoroalkyl Substances (PFAS): Perfluoroalkyl substances (PFAS) are very stable manmade chemicals that have properties that allow them to repel both water and oil. The different PFAS have different lengths and/or differ in their properties at one end, which can change the toxicity of the chemicals.

pH: A measure of acidity and alkalinity of a solution that is a number on a scale on which a value of 7 represents neutrality and lower numbers indicate increasing acidity and higher numbers increasing alkalinity and on which each unit of change represents a tenfold change in acidity or alkalinity and that is the negative logarithm of the effective hydrogen-ion concentration or hydrogen-ion activity in gram equivalents per liter of the solution; also : the condition represented by a pH number.

Phosphorus (P): Phosphorus - In wastewater treatment, phosphorus is a control parameter. When present in discharge, phosphorus (a nutrient) contributes to eutrification. The element phosphorus (atomic number 15) is a poisonous, combustible non-metal. The two most common allotropic forms are white phosphorus, a yellowish waxy solid which ignites spontaneously in air and glows in the dark, and red phosphorus, a less reactive form used in making matches. As a major ingredient in fertilizers and detergents, municipal wastewaters may contain from 5 to 20 mg/l of phosphorus, of which 1-5 mg/l is organic and the rest is inorganic.

PO4-P: Orthophosphate as phosphorus

Potassium Dichromate Method: Chemical Oxygen Demand (COD) is determined in the laboratory using chemicals to accelerate oxidation. The most prevalent laboratory COD tests are variations of the potassium dichromate method, also known as Method 410.4. Using this method, sealed tubes containing sample, blanks, and standards are heated in the presence of dichromate at 150°C to digest the organic load. After two hours, the tubes are cooled and results are indirectly measured colorimetrically at 600nm. Limitations of the Method
▲ Two hours required
▲ Hazardous Residue (chromic acid, mercury sulphate, sulphuric acid and titration reagents)
▲ Poor accuracy
▲ Limited to mmeasurements bellow 900 ppm

Potassium hydrogen phthalate: (KHP), is an acidic salt compound. In TOC analysis, KHP is often used as a calibration standard.

POTW: Publicly Owned Treatment Works

propylene glycol: Propylene glycol is a viscous, colorless liquid, which is nearly odorless but possesses a faintly sweet taste. Its chemical formula is CH₃CHCH₂OH. Containing two alcohol groups, it is classed as a diol. It is miscible with a broad range of solvents, including water, acetone, and chloroform.

PP: Polypropolene

PPCR: Pretreatment program chemical review

Primary Treatment: In wastewater, primary treatment includes mechanical filters and gravity thickeners

PTFE: Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best known brand name of PTFE is Teflon by DuPont Co.

PTFE is a fluorocarbon solid, as it is a high-molecular-weight compound consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine. PTFE has one of the lowest coefficients of friction against any solid.

PP: Plypropolene

Teflon: See PTFE

Quartz Wool: In TOC measurement, quartz wool provides a salt trap that protects the NDIR detector. Quartz wool features the same chemical and physical properties as other fused quartz products. Fused quartz wool has good resistance to high temperatures and chemical corrosions Fused quartz wool fibers are non-flammable and non-combustible.

RAS: Return activated sludge

RBC: Rotating Biological Contactor

RCRA: Resource Conservation and Recovery Act

Residual Chlorine: The goal of infrastructure-based (piped) water treatment systems is effective disinfection at the endpoints (i.e., water taps) of the system: defined by the WHO (1993) as: “a residual concentration of free chlorine of greater than or equal to 0.5 mg/L (0.5 ppm or parts per million) after at least 30 minutes contact time at pH less than 8.0.”

Respirometry: Monitoring Sludge Health and Toxicity

In wastewater treatment, respirometry is a technology used to measure and interpret oxygen consumption in the biomass as total consumption or rate of consumption in a biological wastewater treatment plant.

Measuring the Oxygen uptake rate of aerobic organisms is a simple way to determine the activity level of the biomass. Under controlled conditions, oxygen consumption is a fundamental measure of biomass health. Conversely, reduced respiration can easily identify and quantify toxicity. For Activated Sludge Bacteria a Resprirometer can be used to measure:

* Respiration rate, which measures the rate of biodegradation by sludge bacteria
* Toxicity of influents for both Carbonaceous and Nitrifying bacteria.
* Respiration rate measurements are used for both toxicity management and process optimisation.

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

SBOD5: Five-day soluble biochemical oxygen demand

Secondary Treatment: In wastewater treatment, secondary treatment is aerobic biological treatment. In secondary treatment microbes constitute a biomass, maintained in aeration lanes, that oxidizes organic compounds as a carbonaceous food source.

Silver (Ag): Silver is a chemical element with the symbol Ag and atomic number 47. Silver is a soft, white, lustrous transition metal. It exhibits high electrical conductivity, thermal conductivity, and reflectivity. The metal is found in the Earth's crust in the pure, free elemental form ("native silver"), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining. Silver nanoparticles (AgNPs, nanosilver) are used as an antimicrobial agent in many consumer products. These nanoparticles are often released during washing and eventually enter wastewater treatment plants, where bacteria, and especially nitrifying bacteria, are especially susceptible to inhibition by silver nanoparticles. The accumulation of silver in activated sludge can have a detrimental effect on wastewater treatment if the concentration reaches threshold levels.

SCOD: Soluble Chemical Oxygen Demand

SIC: Standard Industrial Classification

Sludge Volume Index: (SVI) Sludge Volume Index is used to describe the settling characteristics of sludge in the aeration tank in Activated Sludge Process. It is a process control parameter to determine the recycle rate of sludge.

SNH3-N: Soluble ammonia – nitrogen

SO2: Sulfur Dioxide

SOUR: Specific Oxygen Uptake Rate. In aerobic wastewater treatment, SOUR is a calculation that adjusts an OUR measurement for the amount of Total Solids present. Since biological concentration directly impacts the rate of oxygen uptake, adjusting for solids concentration is necessary and has been formalized by the EPA as METHOD 1683: Specific Oxygen Uptake Rate in Biosolids

SP: Soluble phosphorus

SRT: Sludge Retention Time

Suspended Solids (SS): is the dry-weight of suspended particles larger than 2 microns that are not dissolved in a sample of water, and that can be trapped by a 1.5-micron filter that is then analyzed using a filtration apparatus. It is used as one indicator of water quality, and is typically measured in grams per liter (g/L).

SVI: Sludge Volume Index

TBOD5: Total five-day Biochemical Oxygen Demand

TDS: Total Dissolved Solids

TIE: Toxicity Identification Evaluation

TKN: Total Kjeldahl Nitrogen - The Kjeldahl method or Kjeldahl digestion (Danish pronunciation: [ˈkʰelˌtɛˀl]) in analytical chemistry is a method for the quantitative determination of nitrogen contained in organic substances plus the nitrogen contained in the inorganic compounds ammonia and ammonium (NH3/NH4+). Without modification, other forms of inorganic nitrogen, for instance nitrate, are not included in this measurement. Using an empirical relation between Kjeldahl nitrogen content and protein content it is an important method for analyzing proteins. This method was developed by Johan Kjeldahl in 1883.

TMP: Toxicity management program

Total Bonded Nitrogen (TNb): Total Bonded Nitrogen

TOC: See Total Organic Carbon

Total Oxygen Demand (TOD): Total Oxygen Demand is a reliable and reproducable method for the measurement of oxygen demand in water.

TOD correlates easily to COD and, therefore, is a rapid alternative to laboratory COD measurement. Moreover, it is suitable for online measurement and process control. TOD is has been standardized as ASTM D6238.

Torroidal Conductivity: See Inductive Conductivity

Total Organic Carbon: Total Organic Carbon (TOC): is the amount of carbon found in an organic compound and is often used as a non-specific indicator of organic contaminants in water.

TOC can be measured as (1) TOC-by-Difference or (2) TOC-Direct:

(1) TOC-by-Difference - First oxidize the total carbon compounds (TC), measuring the resulting CO2 with an NDIR detector, then subjecting a sample to an acid sparge to drive out the inorganic carbon (IC) as CO2 and also measuring this with an NDIR detector. Finally, subtracting the Inorganic Carbon from the Total Carbon yields Total Organic Carbon as the remainder (TC-IC=TOC).

(2) TOC-Direct - First use an acid sparge to remove all inorganic carbon from a sample, and vent the inorganic carbon to atmosphere. Next oxidize the IC-free sample. The only remaining carbon is organic, and the resulting CO2 measurement is representative of the Total Organic Carbon. This method is also called non-purgeable organic carbon (NPOC).

Related parameters include Total Carbon (TC), Total Inorganic Carbon (TIC), Disolved Organic Carbon (DOC), Particulate Organic Carbon (POC), and Volatile Organic Carbon (VOC).

TP: Total phosphorus

TRC: Total Residual Chlorine

TSS: Total Suspended Solids

Turbidity: Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the eye. The measurement of turbidity is a key test of water quality. Fluids can contain suspended solid matter consisting of particles of many different sizes. While some suspended material will be large enough and heavy enough to settle rapidly to the bottom of the container if a liquid sample is left to stand (the settable solids), very small particles will settle only very slowly or not at all if the sample is regularly agitated or the particles are colloidal. These small solid particles cause the liquid to appear turbid. The most widely used measurement unit for turbidity is the Formazin Turbidity Unit (FTU). ISO refers to its units as FNU (Formazin Nephelometric Units).

µg/L: Microgram per liter

µm: Micron

US Pharmacopoeia: USP is the only independent, not-for-profit, nongovernmental pharmacopeia in the world. USP sets quality, purity, strength, and identity standards for medicines, food ingredients, and dietary supplements. USP publishes standards (also known as monographs) in primary reference text, the USP-NF, and by developing USP Reference Standards (also known as physical standards)— used by manufacturers to test their products against USP standards to ensure they meet published specifications.


United States Environmental Protection Agency The US Environmental Protection Agency is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on December 2, 1970, after Nixon signed an executive order.

Ultraviolet (UV): Ultraviolet electromagnetic radiation with wavelength from 10 nm[1] (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. In water analytics, UV light is sometimes used to oxidize samples. In water treatment, UV Light can be used to disinfect.


Measuring TOC using Ultraviolet-enhanced persulfate oxidation The UV/Persulfate method measures TOC by oxidizing organic compounds and measuring the resulting CO2 using an NDIR detector. Oxidation is accomplished using UV light to enhance the oxidizing efficacy of a chemical oxidant (persulfate solution). The UV–chemical oxidation method offers a relatively low maintenance, high sensitivity method for a wide range of applications. However, there are oxidation limitations of this method. Limitations include the inaccuracies associated with the addition of any foreign substance into the analyte and samples with high amounts of particulates. Performing "System Blank" analysis, which is to analyze then subtract the amount of carbon contributed by the chemical additive, inaccuracies are lowered. However, analyses of levels below 200 ppb TOC are still difficult.

UV-VIS: Ultraviolet – visible spectrophotometer

Vital Force Theory: According to vital force theory, (vitalism) organic compounds must have their origin in living organisms and consequently could never be synthesized from inorganic material. This theory was disproven in 1828, when Friedrich Wöhler synthesized urea from ammonium cyanate (The Wöhler synthesis). This event is often cited as founding modern organic chemistry.

VOC: Volatile organic compound (VOC) are organic chemicals that have a high vapor pressure at room temperature. High vapor pressure correlates with a low boiling point, which relates to the number of the sample's molecules in the surrounding air, a trait known as volatility.

VSS: Volatile suspended solids

WAS: Waste Activated Sludge. The excess quantity (mg/L) of microorganisms that must be removed from the process to keep the biological system in balance.

Wastewater Treatment:

Wastewater Treatment is a process used to remove contaminants from wastewater or sewage and convert it into an effluent that can be returned to the water cycle with acceptable impact on the environment, or reused for various purposes (called water reclamation).

Zn: Zinc