Tangential Flow Filtration

See Cross Flow Filtration.

Tannic Acid

See Tannin.


Any of a group of water soluble, natural organic phenolic compounds that are produced by metabolism in trees andplants, and are part of the degredation-resistant fulvic acid materials formed during the decomposition of vegetation.     Tannins occur in water in almost any location where large quantities of vegetation have decayed. Tannins can impart a faintly yellowish to brown color to water.     Tannin molecules tend to form anions in water above pH 6 and can then be treated with anion exchange resins. Below pH 5, tannins are better treated with activated carbon.


The ability of water to trasmit or convey ultraviolet energy

Taste Threshold

The minimum concentration of a chemical or biological substance which can just be tasted.


Total Dissolved Solids.

TDS Creep

The appearance of salt in RO product water which sometimes occurs as a result of the reduction of differential pressure across the membrane as can occur when the RO unit has been shut down for a period of time.     Water flow will cease to permeate through the membrane when there is insufficient differential water pressure across the membrane.     However TDS permeates through the membrane as a function of the TDS concentration difference across the membrane.


Trade name for a high temperature industrial plastic material used in cookware finishes, bearings, lubricating, plumbing sealants, and a practically inert coating on metal and glass surfaces.


The electrical link between the transmitter and the receiver. Telephone lines are commonly used to serve as the electrical line.

Temperature Sensor

A device that opens and closes a switch in response to changes in the temperature. This device might be a metal contact, or a thermocouple that generates minute electrical current proportional to the difference in heat, or a variable resistor whose value changes in response to changes in temperature.     Also called a heat sensor.

Temporary Hardness

See Carbonate Hardness.


1. Electric potential or voltage. The term usually is used to mean high voltage, as in "high tension transformer" or "high tension lines." <br>  2. Stretched to stiffness or tautness.


The introduction of nonhereditary congential malformations (birth defects) in a developing fetus by exogenous factors acting in the womb; interference with normal embryonic development.


The capacity of a physical or chemical agent to cause teratogenesis in offspring.


A broad channel, bench, or embankment constructed across the slope to intercept runoff and detain or channel it to protected outlets, thereby reducing erosion from agricultural areas.

Tertiary Treatment

The third stage of treatment that brings water to a high degree of refinement or conditioning following the reduction of substances in the primary and secondary stages of treatment.


Thin-film Composite.


Total Hardness.

Therapeutic Index

The ratio of the dose required to produce toxic or lethal effect to dose required to produce nonadverse or therapeutic response.

Thermal Conductivity

The ability of a substance to conduct heat.  Mathematically, the ratio of the rate of heat flow to the rate of temperature change in the particular substance.

Thermal Ozone Destructor

A unit in an ozonation system that employs high temperature to destroy excess ozone.

Thermal Stratification

The formation of layers of different temperatures in a lake or reservoir.


The layer in a lake which divides the warm upper current-mixed zone (epilimnion) from the colder lower deep-water stagnant zone (hypolimnion).     During the warm summertime, the thermocline is the middle layer of the lake. Lying between the two layers, the thermocline loses heat rapidly.     Also called the metalimnion.


A heat-sensing device made of two conductors of different metals joined at their ends.   An electric current is produced when there is a difference in temperature between the ends.


Materials such as certain synthetic resins and plastics that soften or fuse when heated and harden and become rigid when cooled, and that can usually be remelted and cooled time after time with no appreciable chemical change.


Certain plastics and synthetic resins that once solidified will not resoften or fuse when heated. Thermoset materials may decompose at high temperature, but will not soften or melt.

Thin-Film Composite Membrane

A class of reverse osmosis membranes made with polyamide-based polymer and fabricated with different materials in the separation and support layers.


A genus of bacteria that obtain their energy from oxidation of sulfides, thiosulfates, or sulfur, forming sulfur, persulfates, sulfuric acid, and sulfates.


A genus of bacteria that obtain their energy from oxidation of sulfides, thiosulfates, or sulfur, forming sulfur, persulfates, sulfuric acid, and sulfates.

THM Precursor

See Precursor.


See Trihalomethanes.


The lowest dose of a chemical at which a specified measurable effect is observed and below which it is not observed.

Threshold Odor

The minimum odor of a water sample that can just be detected after successive dilutions with odorless water.     Also called odor threshold.

Threshold Odor Number

The greatest dilution of a sample with odor-free water that still yields a just-detectable odor.

Threshold Substance

See Trace Substance.

Throughput Volume

The amount in gallons or liters of water passed through an ion exchange resin bed or water treatment system before exhaustion of the exchanger or system is reached.

Thrust Block

A mass of concrete of similar material appropriately placed around a pipe to prevent movement when the pipe is carrying water. Usually placed at bends and valve structures.


Plowing, seedbed preparation, and cultivation practices.

Time Lag

The time required for processes and control system to respond to a signal or to reach a desired level.

Time Weighted Average

The average value of a parameter (e.g., concentration of a chemical in air) that varies over time.


A device for automatically starting or stopping a machine or other device at a given time.


A group of similar cells.


To titrate a sample, a chemical solution of known strength is added on a drop-by-drop basis until a certain color change, precipitate, or pH change in the sample is observed (endpoint).     Titration is the process of adding the chemical reagent in increments until completion of the reaction, as signaled by the endpoint.


An analytical technique for determining how much of a certain substance (concentration) is present in a solution (such as a water sample) by measuring how much of another substance (of known concentration) must be added to produce a given reaction (often color change in the solution).     Titration is used for determining the level of concentration of a substance in solution. This procedure is widely used in water testing.


See Transient Water System.


Total Organic Carbon.

Too Numerous to Count

The total number of bacterial colonies exceeds 200 on a 47mm diameter membrane filter used for coliform detection.


The arrangement of hills and valleys in a geographic area.

Tortuous Path

Water flow through channels which are constricted and marked by repeated twists, bends and winding turns. In an electrodialysis system, water flow in which spacers, turbulence promoters or cross traps are used to produce turbulence in the flow stream.

Total Acidity

The total of all forms of acidity in a solution, including mineral acidity, carbon dioxide, and acid salts.

Total Alkalinity

See Alkalinity.

Total Capacity

See Rated Capacity.

Total Chlorine

The total concentration of the chlorine in a water, including the combined available chlorine and the free available chlorine.

Total Chlorine Residual

The total amount of chlorine residual present in a water sample, without regard to type.

Total Dissolved Phosphorus

Total phosphorus content of material that will pass through a filter of a specific size.

Total Dissolved Solids (TDS)

The total weight of the solids that are dissolved in the water, give in ppm per unit volume of water. TDS is determined by filtering a given volume of water (usually through a 0.45 micron filter), evaporating it at a defined temperature (usually 103-105 degrees Celsius), and then weighing the residue.     Note: A test measuring the electrical conductivity of the water provides only an estimate of the TDS present, as conductivity is not precisely proportional to the weight of an ion and nonconductive substances cannot be measured by electrical tests.

Total Dynamic Head (TDH)

When a pump is lifting or pumping water, the vertical distance (in feet) from the elevation of the energy grade line on the suction side of the pump to the elevation of the energy grade line on the discharge side of the pump.

Total Hardness (TH)

The total of the amounts of divalent metallic cations, principally calcium hardness and magnesium hardness, expressed in terms of calcium carbonate equivalent.

Total Matter

The sum of all suspended and dissolved matter in a water sample.

Total Nitrogen

The sum of all nitrogen forms.

Total Organic Carbon (TOC)

The amount of carbon covalently bound in organic compounds in a water sample. TOC is measured by the amount of carbon dioxide produced when a water sample is atomized in a combustion chamber.

Total Ozone Demand

The total amount of ozone gas which must be mixed with a liquid (water), solid, or gas in order to satisfy all the ozone oxidation requirements.

Total Particulate Phosphorus

Total phosphorus content of material retained on a filter of a specific size.

Total Phosphorus

The sum of all phosphorus forms.

Total Residual Chlorine

The amount of available chlorine remaining after a given contact time. The sum of the combined available residual chlorine and the free available residual chlorine.

Total Solids (TS)

The weight of all organic and inorganic solids, both dissolved and suspended, per unit volume of water. The weight of total solids in a solution is generally determined by evaporation of a measured volume of water at 105 degrees C in a preweighed dish.

Total Suspended Solids

The particles which can be removed from a solution by filtration, usually specified as the matter which will not pass through a 0.45 micron pore-diameter filter.

Total Trihalomethanes (TTHMs)

The sum of the concentration, in milligrams per liter, of the trihalomethane compounds [trichloromethane (chloroform), dibromochloromethane, bromodichloromethane, and tribromomethane (bromoform)], rounded to two significant figures.


A device that tallies and indicates the total quantity of flow through a measuring device.     Also called an integrator.


A chemical that causes adverse health effects in domestic water supplies and also is toxic to freshwater and marine aquatic life.


Poisonous (to living organisms); capable of producing disease or otherwise harmful to human health when taken into the body.

Toxic Substances

Chemical elements and compounds, such as lead, radon, benzene, dioxin, and numerous others, that have toxic properties by either ingestion, inhalation, or absorption into the human body.     There is considerable variation in the degree of toxicity among the various toxic substances and in the exposure level that induces toxicity.


A harmful substance or agent that may injure an exposed organism.


The quality of being toxic.

Toxicity Assessment

Characterization of the toxicological properties and effects of a chemical, including all aspects of its absorption, metabolism, excretion, and mechanism of action, with special emphasis on establishment of dose-response characteristics.


The science and study of poisons control.

Trace Element

An element essential to plant and/or animal nutrition in trace concentration of one percent or less.     For example, iron, manganese, zinc, copper, potassium, sodium, etc. Such elements are also called micronutrients.

Trace Substance (or Trace)

A substance which is found during water analysis in a very small concentration high enough to be detected, but too low to be quantified accurately by standard testing methods.     Sometimes referred to as a threshold substance.


A device which senses some varying condition and converts it to an electrical signal for transmission to some other device (a receiver) for processing or decision-making.


Acquisition by a cell of the property of uncontrolled growth.

Transient Water System

A noncommunity water system that does not serve 25 of the same nonresident persons per day for more than six months per year. Also called a transient noncommunity water system (TNCWS).

Transmission Lines

Pipelines that transport raw water from its source to a water treatment plant. After treatment, water is usually pumped into pipelines (transmission lines) that are connected to a distribution grid system.

Transmission of Ultraviolet

The percentage of light wave length at 2537 angstrom units transmitted through water.


The ability of an aquifer to transmit water


The ability of water to transmit or convey ultraviolet energy.


The ability of water to transmit or convey ultraviolet energy.


The process by which water vapor is released to the atmosphere by living plants.

Treated Waste Water

Waste water that has been subjected to one or more physical, chemical, and biological processes to reduce its pollution of health hazard.


A device used to place concrete or grout under water.

Trichloroethylene (TCE)

A toxic volatile organic compound often used as a solvent.

Trigger Point

A stage in a demand initiated regeneration (DIR) water softener or valve control cycle when the unit is ready for regeneration.

Trihalomethanes (THMs)

A group of organic chemicals, suspected of being carcinogenic, which are formed in water when chlorine being used as a disinfectant reacts with natural organic matter such as humic acids from decayed vegetation.     Humic acids are present in all natural water used as sources of drinking water supplies.     Chloroform is one of the most common THMs formed in this type of reaction.


Having a valence of three.

Trophic Status

The ability of a lake to support plant growth as measured by phosphorus content, algae abundance, and depth of light penetration.


Total solids


Total suspended solids

Tube Settler

A device that uses bundles of small bore (2 to 3 inches or 50 to 75 mm) tubes installed on an incline as an aid to sedimentation. The tubes may come in a variety of shapes including circular and rectangular. As water rises within the tubes, settling solids fall to the tube surface. As the sludge (from the settled solids) in the tube gains weight, it moves down the tubes and settles to the bottom of the basin for removal by conventional sludge collection means.     Tube settlers are sometimes installed in sedimentation basins and clarifiers to improve particle removal.


A protective crust of corrosion products (rust) which builds up over a pit caused by the loss of metal due to corrosion.


The development or formation of small mounds of corrosion products (rust) on the inside of iron pipe. These mounds (tubercules) increase the roughness of the inside of the pipe, thus increasing resistance to water flow (decreases the C factor).

Tumor Incidence

Fraction of animals having a tumor of a certain type.


Having a cloudy or muddy appearance.


A device that measures the amount of light scattered by suspended solids in a liquid.


The amount of small particles of solid matter suspended in water as measured by the amount of scattering and absorption of light rays caused by the particles.     Turbidity blocks light rays and makes the water opaque. Turbidity is measured in nephelometric turbidity units (NTU). Potable water should not exceed 0.5 NTU.     Turbidity cannot be directly equated to suspended solids because white particles reflect more light than dark-colored particles and many small particles will reflect more light than an equivalent large particle.


A pattern of water flow characterized by cross currents and eddies which mix the water (as opposed to a streamlined or laminar flow pattern). Turbulence may be caused by excessive flow rates, curves or rough surfaces in the flow channel, or by turbulence promoters (such as baffles) purposely created to mix the water.     Turbulence significantly increases pressure drop in a system.

Turbulence Promoter

Devices which are inserted into the feedwater channel or the product water channel to increase the turbulence and improve the mixing characteristics of the fluid flow.     Typical turbulence promoters include baffles, spiral wires, balls, spacers, and static kinetic-type mixers.

Turbulent Flow

See Turbulence.


The mixing of the lower and upper layers of a lake, generally occurring in the spring and the fall, caused by temperature change and density equalization.     Also called overturn.


A pairing of cation and anion exchange tanks and typically operating in series. It is best used for the deionization of relatively high volumes of water and is capable of producing product water with resistivity of up to one megohm-centimeter.

Type 1 Resin

A strong base polystyrene/divinylbenzene anion exchange resin in which the exchange site is a trimethylamine [-N(CH<sub>3</sub>)<sub>3</sub>].     Type 1 resins are inherently more stable both chemically and thermally than type 2 resins, especially in the hydroxide form. They, therefore, typically have a longer life potential and can be regenerated at higher temperatures (e.g., for low silica effluents).     However, type 1 resins have a lower affinity for hydroxide ion relative to other anions than does type 2 resin. It typically has lower operating capacity, lower regeneration efficiency, and lower organic fouling resistance than type 2 resin.     Type 1 resins sometimes emit a very fishy odor.

Type 2 Resin

A strong base polystyrene/divinylbenzene anion exchange resin in which the exchange site is a dimethylethanol amine [-N(CH<sub>3</sub>)<sub>2</sub>(CH<sub>2</sub><sup>-</sup>CH<sub>2</sub>OH)], i.e., an alcohol takes the place of one of the methyl groups on the type 1 resin.     The alcohol can sometimes be cleaved off the amine group during operations leaving a weak base exchange site on the type 2 resin and imparting a characteristic alcohol-like odor.     Resins also typically require longer rinse times as they lose strong base capacity. The type 2 resin is not as stable as its type 1 counterpart, but because of its higher affinity for the hydroxide ion relative to other anions, it has a higher operating capacity, a higher regeneration efficiency, and is much more resistant to organic fouling.

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Updated on Mon, 22 Jun 2020 by Jonathan

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