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Definition of Terms - T

tangible assets
Permanent property of a physical nature, such as lands, buildings, mineral deposits, wells, reservoirs, plant equipment of all kinds, utensils, furnishings, rolling stock, merchandise, intended for immediate use and permanent improvements. Also called physical assets.
tank
A structure or container for containing water or wastewater for such purposes as aeration, disinfection, equalization, holding, sedimentation, treatment or for mixing dilution, feeding or other handling of chemical additives.
tapered aeration
The method of supplying varying amounts of air into the different parts of an aeration tank in the activated sludge process, more at the inlet, less near the outlet, in approximate proportion to the oxygen demand of the mixed liquor under aeration.
terminal manhole
The first manhole at the upper end of a branch sewer line.
terminal settling velocity
The maximum rate of sedimentation of a suspended particle that is not hindered in any way.
tertiary effluent
The liquid portion of wastewater leaving tertiary treatment.
tertiary treatment
The treatment of wastewater beyond the secondary or biological stage. Term normally implies the removal of nutrients, such as phosphorus and nitrogen, and of a high percentage of suspended solids. Term now being replaced by the preferable term, advanced waste treatment.
thermophilic digestion
Digestion carried on at a temperature approaching or within the thermophilic range, generally between 43 and 60 °C (110 and 140 °F).
thickener
Any process equipment or process which increases the concentration of solids in sludges, with or without the use of chemical flocculants.
threshold odor
The minimum odor of the 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 yields a definitely perceptible odor.
tile field
A system of open-jointed tile, usually laid on a rock fill, used for dispersing wastewater effluent into the ground.
tile wastewater-disposal lines
Lines of unglazed open-joint tile placed beneath the ground surface, through which wastewater is dispersed by subsurface disposal.
time & materials (T&M;) contract
A contract form used where it is impossible to define the amount of work to be done, or to estimate the costs in advance. The contractor is paid for all labor costs and all materials used. The major difference between T&M; and other types of cost reimbursable contracts is that there are no fees or burdens paid on materials. Materials are billed to the buyer at actual invoice cost to the contractor.
topographic map
A map showing the various topographic features of a given area, such as hills, valleys, mountains and slope of the land surfaces, usually by means of contours or lines connecting points of equal elevation and including other pertinent information.
total carbon (TC)
A quantitative measure of both total inorganic and organic carbon (mg/L) in water or wastewater, as determined instrumentally by chemical oxidation to CO2 and subsequent infrared detection in a carbon analyzer.
total dissolved solids (TDS)
The sum of all dissolved solids (volatile and non-volatile) in a sample of water or wastewater, measured in mg/L.
total dynamic head (TDH)
The difference between the elevation corresponding to the pressure at the discharge flange of a pump and the elevation corresponding to the vacuum or pressure at the suction flange of the pump, corrected to the same datum plane, plus the velocity head at the discharge flange of the pump, minus the velocity head at the suction flange of the pump.
total head
(1) The sum of the pressure, velocity and position heads above a datum. The height of the energy line above a datum. (2) The difference in elevation between the surface of water at the source of supply and the elevation of the water at the outlet, plus velocity head and lost head. (3) The high distance of the energy line above the datum; energy head. (4) In open channel flow, the depth plus the velocity head.
total Kjeldahl nitrogen (TKN)
The total concentration of nitrogen, both organic and ammoniac, in a wastewater sample; determined by the standard Kjeldahl nitrogen test..
total liabilities
The total of all current and long-term liabilities.
total maximum daily load (TMDL)
The maximum amount of a given pollutant that a receiving water can assimilate without violating water quality standards.
total organic carbon (TOC)
The amount of carbon bound in organic compounds in a sample of water or watewater, measured in mg/L. Because all organic compounds have carbon as the common element, total organic carbon measurements provide a fundamental means of accessing the degree of organic pollution.
total oxygen demand (TOD)
A quantitative measure of all oxidizable material in a sample water or wastewater as determined instrumentally by measuring the depletion of oxygen after high-temperature combustion.
total solids
The sum of dissolved and suspended solid constituents in water or wastewater.
toxic
Poisonous.
toxicant
A substance that kills or injures an organism through chemical, physical, or biological action. Examples include cyanides, pesticides, and heavy metals.
toxic hot spot
An area where the concentration of air toxics is significantly higher than background levels, and where individuals may be exposed to an elevated risk of adverse health effects. Toxic hot spot sources can include landfills, sewage treatment plants, refineries, and numerous other operations.
toxicity
The adverse effect which a biologically active substance has, at some concentration, on a test organism.
toxic wastes
Wastes which, when they come in contact with a living organism, cause an adverse response.
trace element
Any element in water or wastewater that, for reasons associated with natural distribution, industrial use, solubility or other factor, is present at very low concentrations.
trace gases
All other organic or inorganic compounds or elements, measured at less than one percent by volume, found together with the principal gases in landfill gas, and may include vinyl chloride, benzene, hydrogen sulfide, carbon monoxide, hydrogen, mercury, etc.
trade wastes
The liquid wastes from industrial processes, as distinct from domestic or sanitary wastes. Also called industrial wastes.
transdermal exposure
Exposure through the skin.
transmissivity
The rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of the aquifer under a unit hydraulic gradient.
trap
(1) A device used to prevent a material flowing or carried through a conduit from reversing its direction of flow or movement or from passing a given point. (2) A device to prevent the escape of air from sewers through a plumbing fixture or catch basin.
trash
Debris that may be removed from reservoirs, combined sewers, and storm sewers by coarse racks.
trash rack
A grid or screen placed across a waterway to catch flowing debris.
trash screen
A screen installed or constructed in a waterway to collect and prevent the passage of trash.
tray aerator
An aerator in which the water enters the top tray of a series of perforated trays of equal area and falls in distinct drops through the air into successively lower trays or collectors.
treated wastewater
Wastewater that has received partial or complete treatment.
treatment
Any method, technique, or process designed to change the physical, chemical, or biological characteristics of waste so as to render it less harmful to the quality of the waters of the state, safer to handle, or easier to contain or manage.
treatment zone
A soil area of unsaturated zone of a land treatment unit within which constituents of concern are degraded, transformed, or immobilized.
trench
(1) An excavation made for installing pipes, masonry walls and for other purposes. A trench is distinguished from a ditch in that the opening is temporary and eventually backfilled. (2) A relatively long but narrow structural or erosional feature of the earth's surface or the ocean floor.
trickling filter
A biological treatment process in which wastewater (usually downstream of primary treatment) is distributed over a porous rock or synthetic medium where BOD and nutrients are removed by microorganisms growing on the medium. This is an aerobic process and air moves upward through the medium either by natural flow or forced ventilation. See also biofilter.
trickling filter media
Rocks or other durable materials that make up the body of the filter. Synthetic (manufactured) media have been used successfully.
trihalomethanes
Derivatives of methane in which any combination of three halogen atoms (chlorine, bromine, or iodine) are substituted individually or in combination for three of the four hydrogen atoms.
trunk sewer
A sewer that receives flow from many tributary branches and serves a large territory.
tuberculation
The formation of tubercles in pipe, resulting in an increase in friction coefficient.
tubercle
(1) A small knob or button of rust formed on the inside of an iron pipe. (2) An attached deposit of metallic salts in pipes.
tube settler
A series of tubes, about 2 inches in diameter or 2 inches square, placed in a sedimentation tank for improving the efficiency of solids removal. Similar to lamella settlers and plate settlers.
turbidity
(1) A condition in water or wastewater caused by the presence of suspended matter, resulting in the scattering and absorption of light. (2) Any suspended solids imparting a visible haze or cloudiness to water which can be removed by filtration. (3) An analytical quantity usually reported in turbidity units determined by measurements of light scattering.
turnkey
An expansion of design-build services that may involve additional services such as financing, site selection, permitting, startup, and in certain cases, an initial period of operation and maintenance. In some cases, title to the facilities may be held by the turnkey contractor until the fully operational facilities are turned over to the owner.
two-stage digestion
The biological decomposition of organic matter in sludge followed by solids-liquid separation of the digested sludge. Two-stage digestion uses two compartments or two tanks to separate the initial digestion period from the slower final period to enhance both the digestion and the solid-liquid separation after digestion.
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