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The terms contained within this glossary are general definitions and are accurate as they relate to water analysis, water treatment and Hach® Company products. They are for reference only and are not intended to be applied outside the scope of these areas. All trademarks or product names mentioned are the property of their respective owners.
acid
any substance capable of giving up a proton; a substance that ionizes in solution to give the positive ion of the solvent; a solution with a pH measurement less than 7.
acidity
the quantitative capacity of aqueous solutions to react with hydroxyl ions. It is measured by titration with a standard solution of base to a specified end point.
acre-foot
the volume of water, 43,560 cubic feet, that will cover an area of one acre to a depth of one foot; a term used in sewage treatment in measuring the volume of material in a trickling filter.
activated sludge process
removes organic matter from sewage by saturating it with air and microbial organisms
activation
treatment of a substance by heat, radiation, or activating reagent to produce a more complete or rapid chemical or physical change.
advanced waste treatment
any treatment method or process employed following biological treatment (1) to reduce pollution load (2) to remove substances that may be harmful to receiving waters or the environment (3) to produce a high-quality effluent suitable for reuse in any specific manner or for discharge under critical conditions. The term tertiary treatment is commonly used to denote advanced waste treatment methods.
adsorption
the adhesion of an extremely thin layer solid, liquid, or vapor molecules to the surface of a solid or liquid
aerobic
living or occurring only in the presence of oxygen
aerobic biological oxidation
any waste treatment process or other process utilizing aerobic organisms, in the presence of air or oxygen, as the agent for reducing pollution load, oxygen demand, or the amount of organic substance in waste. The term is used in reference to secondary treatment of wastes
alcohol
Any class of organic compounds containing the hydroxyl group, OH. Specifically, the term is applied to ethyl alcohol (C2H5OH).
algaecide
chemical agent added to water to destroy algae.
alkalinity
the capacity of water to neutralize acids, a property imparted by the water's content of carbonate, bicarbonate, hydroxide, and on occasion borate, silicate, and phosphate. It is expressed in milligrams per liter of equivalent calcium carbonate (mg/l CaCO3). Learn more about alkalinity.
alternating current (ac)
current that reverses its direction at regular intervals, such as a common 115 volt circuit.
alum
technically, a double sulfate of ammonium or a univalent or trivalent metal but commonly used to denote aluminum sulfate (Al2(SO4)3.
amines
a class of organic compounds of nitrogen that may be considered as derived from ammonia (NH3) by replacing one or more of the hydrogen atoms by organic radicals, such as CH3 or C6H5, as in methylamine and aniline. The former is a gas at ordinary temperature and pressure, but other amines are liquids or solids. All amines are basic in nature and usually combine readily with hydrochloric or other strong acids to form salts.
anaerobic
living or occurring only in the absence of free oxygen.
anaerobic biological treatment
any waste treatment process utilizing anaerobic or facultative organisms in the absence of air to reduce the organic matter in water.
anaerobic waste treatment
(sludge processing) waste stabilization brought about through the action of microorganisms in the absence of air or elemental oxygen.
anhydrous
a term meaning without water.
angstrom
a unit of length, used especially in expressing the length of light waves, equal to one ten-thousandth of a micron, or one hundredth-millionth of a centimeter (1 x 10E-8 cm).
anion
ion having a negative charge; an atom with extra electrons. Atoms of non-metals, in solution, become anions.
aquifer
a subsurface geological structure that contains water.
atom
the smallest particle of an element which can exist alone or enter into a chemical combination.
atomic absorption
quantitative chemical method used for the analysis of elemental constituents.
atomic mass
the mass of an atom expressed in atomic mass units (amu); the total number of protons and neutrons in the nucleus.
atomic mass unit (amu)
a unit of mass equal to 1/12 the mass of the carbon isotope with mass number 12, approximately 1.6604 x 10E-24 gram.
atomic number
the number of protons in the nucleus of an atom.
atomic weight
the average weight of an atom of an element, usually expressed relative to one atom of the carbon isotope taken to have a standard weight of 12.
autooxidation
oxidation caused by the atmosphere; an oxidation reaction that is self-catalyzed and spontaneous; an oxidation reaction begun only by an inductor.
backflow prevention
a system designed to protect potable water from wastewater contamination which could occur if wastewater pressure exceeds potable water pressure over a cross-connection where one or more check valves fail.
backsiphonage
the backflow of contaminated or polluted water, from a plumbing fixture or cross-connection into a water supply line, due to a lowering of the pressure in the line.
backwashing
the process of cleaning a rapid sand or mechanical filter by reversing the flow of water.
bacteria
any of numerous unicellular microorganisms of the class Schizomycetes, occurring in a wide variety of forms, existing either as free-living organisms or parasites, and having a wide range of biochemical, often pathogenic properties. Some bacteria are capable of causing human, animal or plant diseases; others are essential in pollution control because they break-down organic matter in air and water.
bacterial examination
the examination of water and wastewater to determine the presence, number, and identification of bacteria. Also called bacterial analysis.
banks, sludge
accumulations of solid, sewage, or industrial waste deposits on the bed of a waterway.
base
any substance which contains hydroxyl (OH) groups and furnishes hydroxide ions in solution; a molecular or ionic substance capable of combining with a proton to form a new substance; a substance that provides a pair of electrons for a covalent bond with an acid; a solution with a pH of greater than 7.
bioassay
an assay method using a change in biological activity as a qualitative or quantitative means of analyzing a material response to industrial waste and other wastewater by using viable organisms or live fish as test organisms.
biochemical oxygen demand (BOD)
the quantity of oxygen used in the biochemical oxidation of organic matter in a specified time, at a specified temperature, and under specified conditions; standard test used in assessing wastewater biological oxygen demand. Learn more about biochemical oxygen demand (BOD).
biocides
chemical agents with the capacity to kill biological life forms. Bactericides, insecticides, pesticides, etc. are examples.
biodegradability
the susceptibility of a substance to decomposition by microorganisms; specifically, the rate at which compounds may be chemically broken down by bacteria and/or natural environmental factors.
biological wastewater treatment
forms of wastewater treatment in which bacterial or biochemical action is intensified to stabilize, oxidize, and nitrify the unstable organic matter present. Intermittent sand filters, contact beds, trickling filters, and activated sludge processes are examples.
biomonitoring
the use of living organisms to test the suitability of effluent for discharge into receiving waters and to test the quality of such waters downstream from a discharge.
blowdown
removal of liquids and/or solids from a process vessel or storage vessel or line by the use of pressure; often used to remove materials which, in high concentrations, could cause damage to the vessel or line, or exceed limits established by best engineering practices.
blowoff
a controlled outlet on a pipeline, tank, or conduit which is used to discharge water or accumulations of material carried by the water.
breakdown
failure of insulator or insulating medium to prevent discharge or current flow.
british thermal unit (btu)
the quantity of heat necessary to raise the temperature of 1 pound of water by 1oF.
buffer
a solution selected or prepared to minimize changes in hydrogen ion concentration which would otherwise occur as a result of a chemical reaction.
bulking agent
a fine, solid material which is sometimes added to a wastewater stream to produce clarification or coagulation by adding bulk to the solids.
cake, sludge
the material resulting from air drying or dehydrating sludge.
calibration
the checking, adjusting, or systematic standardizing of the graduations of a quantitative measuring instrument.
calorie
the quantity of heat necessary to raise the temperature of 1 gram of water 1 oC at 1 atmosphere pressure.
catalyst
a substance that alters the velocity of a chemical reaction and may be recovered essentially unaltered in form and amount at the end of the reaction.
cation
a positively charged atom or group of atoms, or a radical which moves to the negative pole (cathode) during electrolysis.
caustic
capable of destroying or eating away by chemical action; a hydroxide of a light metal.
caustic soda
sodium hydroxide, NaOH.
chemical analysis
the use of a standard chemical analytical procedures to determine the concentration of a specific analyte in a sample, or qualitatively or quantitatively measure a specific parameter of a sample.
chemical coagulation
the destabilization and initial aggregation of colloidal and finely divided suspended matter by the addition of a floc-forming chemical.
chemical oxygen demand
the amount of oxygen required for the chemical oxidation of organics in a liquid; a chemical test that determines the oxygen equivalent of the amount of organic matter oxidizable by potassium dichromate in a 50% sulfuric acid solution. Learn more about chemical oxygen demand.
chemical precipitation
(1) the process of utilizing chemicals to produce a separable solid phase within a liquid medium; in analytical chemistry, precipitation is used to separate a solid phase in an aqueous solution. (2) the process of softening water by the addition of lime and soda ash as the precipitants.
chlorination
the addition of chlorine to water or wastewater, generally for the purpose of disinfecting, but frequently done to achieve other biological or chemical results. Learn more about chlorination.
chlorination break point
the addition of chlorine to water, sewage, or industrial waste containing free ammonia to the point where free residual chlorine is available.
chlorination, free residual
the addition of chlorine to water, sewage or industrial wastes to produce, directly or through the destruction of ammonia or certain organic nitrogenous compounds, a free available chlorine residual.
chlorine, available
the quantity of chlorine released by a bleaching powder when treated with acid.
chlorine, combined available residual
that portion of the total residual chlorine remaining in water, sewage or industrial waste at the end of a specified contact period, which will react chemically and biologically as chloramines or organic chloramines.
chlorine demand
the quantity of chlorine absorbed by wastewater (or water) in a given length of time.
chlorine, total residual
free residual chlorine plus combined residual chlorine.
circuit
a path through which an electrical current can flow when the path is complete.
clarification
the composite wastewater treatment process consisting of flash mixing of coagulants, pH adjusting chemicals, and/or polyelectrolytes, flocculation, and sedimentation.
clarifier
a unit which provides for settling and removal of solids from wastewater.
coagulation
the clumping of particles in order to settle out impurities; often induced by chemicals such as lime or alum.
coliform organisms
any of a number of organisms whose presence in wastewater is an indicator of pollution and of potentially dangerous bacterial contamination.
complexing
the use of chelating or sequestering agents to form relatively loose chemical bonding as a means of treating certain pollutants such as nickel, copper, and cobalt.
compound
two of more elements combined; a substance having different properties than of the elements used.
concentrated
being of full strength, or undiluted.
concentration
in solutions, the mass, volume, or number of moles of solute present in proportion to the amount of solvent or total solution Common measures are: molarity, normality, percent, molality, and by specific gravity scales.
condensate
water obtained by evaporation or a product that has changed from a gaseous or vaporous form to a liquid form.
conductance
a measure of the conducting power of a solution equal to the reciprocal of the resistance. The resistance is expressed in ohms.
conductivity
ability of a material to carry current or heat.
contact coagulation
a water clarification process which involves the addition of a coagulant with appropriate mixing for the purpose of floc formation within a filter media, which will be periodically back-flushed to permit the separation of the resulting solids from the main wastewater stream.
contamination
a general term signifying the introduction into water of microorganisms, chemicals, wastes or sewage which renders the water unfit for its intended use.
cooling tower
a device for cooling water through a combination of sensing and evaporative heat transfer. Water passes over a number a wooden or plastic racks known as “fill”, that act as a heat-transfer surface.
current
a movement of electrons through a conductor. Measured in amperes.
decant
to remove the liquid portion of a settled mixture without disturbing the sediment.
dechlorination process
a process by which excess chlorine is removed from water to a desired level. Usually accomplished by chemical reduction, by passage through carbon beds or by aeration at a suitable pH.
degradable
that which can be reduced, broken down or chemically separated.
degreasing
the process of removing greases and oils from sewage, waste, and sludge.
demineralization
removal from water of mineral contaminants. Methods include ion exchange, flash distillation, electrodialysis, or reverse osmosis.
detention time
the time allowed for solids to collect in a settling tank. Theoretically detention time is equal to the volume of the tank divided by the flow rate.
dew point
the temperature at which the condensation of a vapor begins; the term is usually applied to condensation of moisture from the water vapor in the atmosphere.
dialysis
the separation of a colloid from a substance in solution by allowing the solution to diffuse through a semipermeable membrane.
diatomaceous earth
a filter medium used for filtration of effluents from secondary and tertiary treatments, particularly when a very high grade of water for reuse in certain industrial purposes is required; used as an absorbant for oils and oily emulsions in some wastewater treatment designs; also used historically in preparing standard suspensions for turbidity measurements.
digestion
the biochemical decomposition of organic matter which results in the formation of mineral compounds and simple organic compounds.
DI water
deionized water, having had all the ions removed.
diluent
the thinning agent used to dilute a fluid, usually water.
dilute
to thin out, or having been thinned out; less than full strength.
diode
a component that readily passes current in one direction but opposes current flow in the opposite direction.
direct current (dc)
a non-oscillating current that flows continually in one direction through a circuit
disinfection
effective killing by chemical or physical processes of all organisms capable of causing infectious disease. Chlorination is the disinfection method commonly employed in sewage-treatment processes.
dissolved oxygen (DO)
the oxygen dissolved in sewage, water, or other liquid, usually expressed in milligrams per liter or percent of saturation. It is the test used in BOD determination. dissolved solids: the total amount of dissolved material, organic and inorganic, contained in water or wastewater. Excessive dissolved solids make water unpalatable for drinking and unsuitable for industrial use. Measurements are expressed as ppm or mg/L. Learn more about dissolved oxygen (DO).
distillation
the process of heating a liquid to its boiling point, removing the vapors through a cooling and condensing apparatus, and finally collecting the condensed liquid in a separate receiver. It is commonly used for the separation of two or more liquids in a mixture, or for the separation of the solvent from dissolved substances.
distilled water
water that has been purified by distillation (boiling the water off as steam and condensing it back to a liquid, leaving the impurities behind). Having been boiled, it is also sterile.
edta titration (edta)
ethylenediaminetetraacetic acid (or its salts). A standard method of measuring the hardness of a solution
effluent
a liquid that has passed through a processing operation.
effluent limitation
any restriction (including schedules of compliance) established by a state or EPA on quantities, rates, and concentrations of chemical, physical, biological, and other constituents which are discharged from point sources into navigable water, the waters of the contiguous zone, or the ocean.
electron
the sub-atomic particle, with a negative charge, that orbits the nucleus of an atom.
element
a substance that cannot be resolved into two or more other substances; a substance made up of atoms with the same atomic number.
emulsion
a liquid system in which one liquid is finely dispersed in another liquid in such a manner that the two will not separate through the action of gravity alone.
end point
that stage in the titration at which an effect, such as a color change, occurs, indicating that a desired point in the titration has been reached.
enrichment
the addition of nitrogen, phosphorous, and carbonaceous compounds, or other nutrients into a lake or other waterway that greatly increases the growth potential for algae and other aquatic plants. Most frequently, enrichment results from the inflow of sewage effluents or from agricultural runoff.
facultative
having the power to live under different conditions either with or without oxygen.
fats (wastes)
triglyceride-esters of fatty acids. Erroneously used as synonymous with grease.
filtration
the process of separating solids from a liquid by means of a porous substance through which only the liquid can pass.
filter backwash
the reversal of flow though a filter to wash clogged material out of the filter medium and reduce conditions causing loss in flow through the filter.
floatation
the process of removing finely divided particles from a liquid suspension by agitating the liquid with gas bubbles thus increasing the buoyancy of the particles, and concentrating them at the surface of the liquid medium.
floc
a very fine, fluffy mass formed by the aggregation of fine suspended particles.
flocculation
the process of separating suspended solids from wastewater by chemical creation of a coagulated, or flocculent masses.
flowrate
usually expressed as liters/minute (gallons/minute) or liters/day. Design flowrate is that used to size the wastewater treatment process. Peak flowrate is 1.5 to 2.5 times design and relates to the hydraulic flow limit and is specified for each plant.
fluid
a substance which yields readily to any force which tends to alter its shape; fluids possess no definite shape; the term includes both liquids and gases.
flux
a material used to promote joining of metals in soldering.
formazin
a polymer suspension used as the standard for turbidity.
formazin nephelometric unit (FNU)
an industry standard unit measurement used in the European Union, equivalent to NTU.
formazin turbidity unit (FTU)
a measure of water turbidity equivalent, but not equal, to Jackson Turbidity Units (JTU).
formula
an expression of chemical composition, using symbols and figures.
FNU
see formazin nephelometric unit.
FTU
see formazin turbidity unit.
fuse
a protective device containing a short piece of wire that melts and breaks when current through it exceeds a rated value, thus de-energizing the circuit.
gas
a fluid having neither independent shape nor volume, but tending to expand indefinitely. The word is often used to denote anesthetics, combustibles (gasoline), poisonous materials, etc., whether liquid or solids at ordinary temperatures.
grab sample
a single sample of wastewater taken at neither set time nor flow.
group
a family of elements with similar chemical properties, represented by a vertical column in the periodic table.
ground wire
a conductor leading from electrical equipment to a low resistance connection with the earth.
hardness
a characteristic of water, imparted by salts of calcium, magnesium, and iron, such as bicarbonates, carbonates, sulfates, chlorides, and nitrates that cause curdling of soap, deposition of scale in boilers, damage in some industrial process, and sometimes objectionable taste. It may be determined by a standard laboratory procedure or computed from the amounts of calcium and magnesium as well as iron, aluminum, manganese, barium, strontium, and zinc; expressed as equivalent parts per million of calcium carbonate. Learn more about hardness.
heavy metals
a general term given to the ions of metallic elements such as copper, zinc, chromium, and aluminum. They are removed from wastewater by forming an insoluble precipitate (usually a metallic hydroxide).
hertz (Hz)
in electrical/electronic applications with alternating current, a unit of frequency where 1 Hz equals one cycle per second.
hot (circuit)
connected, alive, energized.
hydrocarbon
a chemical compound containing only hydrogen and carbon; the largest source of hydrocarbons comes from petroleum crude oil.
hydrogenation
the infusing of unsaturated or impure hydrocarbons with hydrogen gas at controlled temperatures and pressures for the purpose of obtaining saturated hydrocarbons and/or removing various impurities such as sulfur and nitrogen.
hydrogen ion concentration
the normality of a solution with respect to hydrogen ions, H+; it is related to acidity measurements in most cases by the equation pH= log 1/2[1/(H+)] where H+ is the hydrogen ion concentration in gram equivalents per liter of solution.
hydroxyl radical
an oxygen and hydrogen atom occurring as a group (OH-).
impedance
total opposition to flow of current, measured in ohms; combined effort of resistance, inductance, and capacitance.
incineration
the combustion of organic matter in wastewater sludge solids after water evaporation from the solids.
indicator
a compound that changes color at a particular pH, or over a particular narrow range of pH, used to show titration end points.
influent
sewage, water or other liquid, either raw or partly treated, flowing into a reservoir basin, or treatment plant or any part thereof.
ion
an isolated electron or positron; an atom or molecule which by loss or gain of one or more electrons has acquired a net electric charge.
ion exchange
a chemical reaction in which mobile hydrated ions of a solid are exchanged, equivalent for equivalent, for ions of like charge in solution. The process can be used to remove ionic pollutants from wastewater.
ionization
a process by which a neutral atom or molecule loses or gains electrons, thereby acquiring a net charge and becoming an ion; occurs as the result of the dissociation of the atoms of a molecule in solution or of a gas in an electric field.
isomer
chemical compound that has the same number, and kinds of atoms as another compound, but a different structural arrangement of the atoms.
jackson turbidity unit (JTU)
a measure of the turbidity of water, proportional to the ppm silica, where 100 ppm silica equals 21.5 JTU. This method was the standard for turbidity for many years; it applied the use of a candle, measuring tube, and the human eye for determining the value. This method has since been replaced by the use of a known turbidity standard, Formazin, and the use of analytical instruments that will detect forward-scattered light and light scattered at 90 degrees.
JTU
see jackson turbidity unit.
lagoon
in wastewater treatment, a shallow pond where sunlight, bacterial action, and oxygen interact to restore wastewater to a reasonable state of purity.
lime
any of a family of chemicals consisting essentially of calcium hydroxide made from limestone (calcite) which is composed mostly of calcium carbonate or a mixture of calcium carbonate and magnesium carbonate.
limnology
the study of the physical, chemical, meteorological and biological aspects of fresh water.
manometer
an instrument for measuring pressure liquids and gasses. It usually consists of a U-shaped tube containing a liquid, the surface of which is in one end of the tube; moves proportionally with changes in pressure on the liquid in the other end. Also, a tube type differential pressure gauge.
mass
the quantity of matter in a body as measured by its resistance to a change in acceleration; different but proportional to weight.
mass number
the total number of protons and neutrons in an atomic nucleus.
meniscus
the curved upper surface of a non-turbulent liquid in a container; it is concave (curves upward) if it wets the container walls, and convex (curves downward) if it does not. For accurate measurements, readings should be taken at the flat center of the meniscus.
micro
a prefix meaning one-millionth of a unit.
microorganism
organisms (microbes) observable only through a microscope; larger, visible types are called macroorganisms.
milligrams per liter (mg/l)
this is a weight per volume designation used in water and wastewater analysis. 1mg/L = 1ppm.
molal
a solution concentration having a mole of solute per 1,000 grams of solvent, usually water.
molality
a measure of solution concentration expressed in moles of solute per 1,000 grams of solvent.
molar
a solution concentration having one mole of solute per liter of solution.
molarity
a measure of solution concentration expressed in moles of solute per liter of solution.
mole
an amount of a substance weighing the number of grams equal to the total atomic weight in one molecule (or atom). Equivalent to gram-atomic, gram-molecular, and gram-formula weights.
molecular weight
the sum of the atomic weights of all the atoms in a molecule.
molecule
the simplest structural unit of a substance that retains the properties of the substance, and is composed of one or more atoms.
most probable number (MPN)
that number of organisms per unit volume that, in accordance with statistical theory, would be more likely than any other number to be yielded with the greatest frequency in a specific test. Expressed as density of organisms per 100 ml. Results are computed from the number of positive findings of coliform-group organisms resulting from multiple-portion decimal-dilution plantings.
nephelometer
an instrument that measures scattered light in a liquid.
nephelometric turbidity unit (NTU)
a standard unit of turbidity measurement, equivalent to FNU.
neutralization
chemical addition of either acid or base to a solution such that the pH is adjusted to 7.
neutron
an uncharged sub-atomic particle, with a mass nearly equal to that of a proton. Present in the nucleus of all atoms except hydrogen.
nitrification
the conversion of nitrogenous matter or free nitrogen into nitrates and ammonia by bacteria.
non-ionic surfactants
a general family of surfactants so called because in solution the entire molecule remains associated. Non-ionic molecules orient themselves at surfaces not by an electrical charge, but through separate grease-solublizing and water-soluble groups within the molecule.
nonsettleable matter
the suspended matter which neither settles nor floats to the surface of water in a period of one hour.
nonsettleable solids
wastewater matter that will stay in suspension for an extended period of time. Such period may be arbitrarily taken for testing purposes as one hour.
normal
a solution concentration of one gram equivalent per liter of solution.
normality
a measure of solution concentration expressed in equivalent weights of solute per liter of solution.
NTU
see nephelometric turbidity unit.
nutrients
materials which are considered essential to the support of biological life.
ohm
a unit of electrical resistance equal to that of a conductor in which a current of one ampere is produced by a potential of one volt across its terminals.
organic matter
chemical compounds based on carbon chains or rings, and also containing hydrogen with or without oxygen, nitrogen, or other compounds.
organic nitrogen
nitrogen combined in organic molecules such as protein, amines, and amino acids.
orthophosphate
an acid or salt containing phosphorus as PO4, such as K3PO4 (potassium phosphate).
oxidant
a chemical agent that oxidizes.
oxidation
in a broad sense oxidation is the increase in positive valence of any element in a substance. On the basis of the electron theory, oxidation is a process in which an element loses electrons. In a narrow sense, oxidation means the chemical addition of oxygen to a substance.
ozone
oxygen in molecular form with three atoms of oxygen forming each molecule (O3). Atmospheric oxygen is molecular in form but each molecule contains only two atoms of oxygen. Ozone is formed by passing high voltage electric charges through dry air. The third atom of oxygen in each molecule of ozone is loosely bound and is easily released, thus making it a powerful oxidant; used to purify water and treat industrial wastes.
parts per million (ppm)
the unit commonly used to represent the degree of pollutant concentration where the concentrations are small. Larger concentrations are given in percentages. 1ppm = 1mg/L. In BOD analysis, the results are expressed in ppm, whereas in the suspended solids test, the values are expressed in percents. In air, ppm is usually a volume/volume ratio; in water, ppm represents a weight/volume ratio.
pathogenic bacteria
bacteria which may cause disease in the organisms by their parasitic growth.
period
a series of elements, arranged in order of atomic number represented by a horizontal row on the Periodic Table.
periodic table
a table in which the elements are commonly arranged in order of increasing atomic number. Elements of similar properties are placed one under the other, yielding eight families or groups of elements. Within each group there is a gradation of chemical and physical properties, but in general a similarity of chemical behavior. From group to group, however, there is a progressive shift of chemical behavior from one end of the table to the other.
pH
the negative logarithm of the hydrogen ion concentration (-log10[H+]) where H+ is the hydrogen-ion concentration in moles per liter. Neutral water has a pH value of 7. Learn more about pH.
pH adjustment
a means of maintaining the optimum pH through the use of chemical additives.
phenolphthalein alkalinity
a measure of the hydroxides plus one-half of the normal carbonates in aqueous suspension. Measured by the amount of sulfuric acid required to bring the water to a pH value of 8.3, as indicated by a change in color of phenolphthalein. It is expressed in ppm of calcium carbonate (CaCO3).
potable water
water suitable for drinking or cooking purposes from both health and aesthetic considerations.
prechlorination
chlorination of water prior to filtration, or chlorination of sewage prior to treatment.
precipitant
a chemical or chemicals that cause a precipitate to form when added to a solution.
precipitate
the discrete particles of material separate from the liquid solution.
precipitation, chemical
to cause a solid substance to be separated (precipitate out) of a solution by the addition of chemical additives; the process of softening water by the addition of lime and soda ash as the precipitants.
pretreatment
any wastewater treatment process used to partially reduce pollution load before the wastewater is introduced into a main sewer system or delivered to a treatment plant; a substantial reduction of the pollution load.
process, biological
the process by which the life activities of bacteria, and other microorganisms in the search for food, break down complex organic material into simple, more stable substances. Self-purification of sewage, polluted streams, sludge digestion, and all so-called secondary sewage treatments result from this process. Also called biochemical process.
process, oxidation
any method of sewage treatment for the oxidation of the decomposable organic matter that brings about the decomposition of such matter. The usual methods are biological filtration, and activated sludge processes.
proton
a sub-atomic particle, positively charged, in the nucleus of atoms.
putrefaction
biological decomposition of organic matter accompanied by the production of a foul smell associated with anaerobic condition.
quantitative analysis
chemical determination of the amounts or proportions of constituents in a substance.
radical
an atom or group of atoms with at least one unpaired electron.
reagent
a chemical substance used to cause a reaction for the purpose of chemical analysis.
recorder
a device that makes a graph or other automatic record of the stage, pressure, depth, velocity, or the movement or position of water controlling devices, usually as a function of time.
reduction
chemical reaction in which an atom or molecule gains an electron; decrease in positive valence; addition of hydrogen to a molecule.
reduction treatment
the opposite of oxidation treatment wherein a reductant is used to lower the valence state of a pollutant to a less toxic form; e.g. the use of SO2 to reduce Cr6+ to Cr3+ in an acidic solution.
residual chlorine
chlorine remaining in water or wastewater at the end of specified contact period as combined or free chlorine.
resistance
the opposition which a device or material offers to the flow of current; measured in ohms.
resistor
a component of an electrical circuit intended to offer resistance to electrical current flow.
salinity
(1) the relative concentration of salts, usually sodium chloride, in a given water. It is usually expressed in terms of the number of ppm of chloride. (2) a measure of the concentration of dissolved mineral substances in water.
salt
any compound formed by combination of any negative ion (except hydroxide) with any positive ion (except hydrogen or hydronium); the precipitate produced as the result of neutralization of an acid with a base.
saturated
(1) in organics, a chemical compound with all carbon bonds satisfied; it does not contain double or triple bonds and thus cannot add elements or compounds. (2) in liquids, a solution that contains enough of a dissolved solid, liquid, or gas so that no more will dissolve into the solution at a given temperature and pressure.
scale
the precipitate that forms on surfaces in contact with water as the results of a physical or chemical change, often due to the presence of calcium carbonate (CaCO3) or magnesium carbonate (MgCO3).
sedimentation
the deposition of suspended matter carried by water, wastewater, or other liquids, by gravity. It is usually accomplished by reducing the velocity of the liquid below the point at which it can transport the suspended material. Also called settling.
settleable solids
particles of debris and fine matter heavy enough to settle out of wastewater.
sewage
the total of organic waste and wastewater generated by residential and commercial establishments.
sewage, combined
a sewage containing both sanitary sewage and surface or storm water with or without industrial wastes.
sewage, dilute
sewage containing less than 150 ppm of suspended solids and BOD (weak sewage).
sewage, industrial
sewage in which industrial wastes predominate.
sewage, raw
sewage prior to receiving any treatment.
sewage, settled
sewage from which most of the settleable solids have been removed by sedimentation.
sewage, storm
liquid flowing in sewers during or following a period of heavy rainfall.
sludge
the solids (and accompanying water and organic matter) which are separated from sewage or industrial wastewater in treatment plant facilities. Sludge separation and disposal is one of the major expenses in wastewater treatment operations.
sludge conditioning
a process employed to prepare sludge for final disposal, e.g., thickening, digesting, heat treatment or other procedures.
sludge digestion
the process by which organic or volatile matter in sludge is gasified, liquefied, mineralized, or converted into more stable organic matter through the activities of either anaerobic or aerobic organisms.
sludge disposal
the final disposal of solid wastes including the use of sewage sludge as fertilizers and soil builders, and fill for low-lying lands.
sludge thickening
the increase in solids concentrations of sludge in the sedimentation of digestion tank.
slurry
a watery mixture or suspension of solids.
soda ash
a common water treating chemical, sodium carbonate.
softening
the removal of hardness—calcium and magnesium—from water.
solder
an alloy of lead/tin used for making permanent electrical connections between parts and wire.
solute
the substance that is dissolved to form a solution.
solution
a liquid (solvent) that contains a dissolved substance (solute).
solvent
a liquid used to dissolve another substance.
specific gravity
a comparison by weight to an equal volume of pure water, at a standard temperature.
standard (or standardized solution)
a solution containing a known, precise concentration of an element or chemical compound, often used to calibrate analytical chemistry measurement devices.
surface tension
the property, due to molecular forces in the surface film, that tends to contract the liquid into a form having the least surface/volume ratio.
surfactant
a surface-active substance, such as a detergent or soap, that lowers the surface tension of a solvent (usually water).
suspended matter
(1) solids in suspension in water, wastewater or effluent. (2) solids in suspension that can be removed readily by standard filtering procedures in a laboratory.
suspended solids
(1) solids that either float on the surface of, or are in suspension in, water, wastewater, or other liquids, and which are largely removable by laboratory filtering. (2) the quantity of material removed from wastewater in a laboratory test, as prescribed in “Standard Methods” and referred to as nonfilterable residue.
tertiary treatment
process utilized to remove practically all solids and organic matter from wastewater. Granular activated carbon filtration is a tertiary treatment process. Phosphate removal by chemical coagulation is also regarded as a step in tertiary treatment.
thermistor
a semiconductor whose resistance will vary with temperature.
titration
a method of analyzing the composition of a solution by adding known amounts of a standardized solution until a given reaction (color change, precipitation, or conductivity change) is produced.
tracer
(1) a foreign substance mixed with or attached to a given substance for the determination of the location or distribution of the substance. (2) an element or compound that has been made radioactive so that it can be easily followed (traced) in biological and industrial processes. Radiation emitted by the radioisotope pinpoints its location.
treatment efficiency
usually refers to the percentage reduction of a specific or group of pollutants by a specific wastewater treatment step or treatment plant.
turbidimeter
an instrument for measurement of turbidity in which a standard suspension is used for reference.
turbidity
(1) a condition in water or wastewater caused by the presence of suspended matter, resulting in the scattering and absorption of light rays. (2) a measure of fine suspended matter in liquids. (3) an analytical quantity usually reported in turbidity units (NTU/FNU, FTU, JTU) determined by measurements of light diffraction. Learn more about turbidity.
unsaturated
any chemical compound with more than one bond between adjacent atoms, usually carbon, and thus reactive toward the addition of other atoms at that point; for example: olefins, diolefins, and unsaturated fatty acids.
valence
the relative ability of a biological substance to react or combine; a positive number that characterizes the combining power of an element for other elements, as measured by the number of bonds to other atoms which one atom of the given element forms upon chemical combination – hydrogen is assigned valence 1, and the valence is the number of hydrogen atoms, or their equivalent, with which an atom of the given element combines.
viscosity
the resistance offered by a fluid (liquid or gas) to flow. The viscosity is a characteristic property and is a measure of the combined effects of adhesion and cohesion.
volatile solids
the quantity of solid in water, wastewater or other liquids, lost on ignition of the dry solids at 600 oC.
voltage
the electrical pressure (electromotive force) that makes current flow through a conductor.
volume
the space occupied in three dimensions.
washdown
water resulting from cleaning of equipment, walls, floors, etc., within a plant.
watt
the practical unit of electrical power.
wire gauge
wire size, measured in diameter.