Glossary of Terms
Commonly Used in Wastewater Treatment

A

Activated Sludge:
Sludge floc produced in raw or settled wastewater by the growth of zoogleal bacteria and other organisms in the presence of dissolved oxygen.
Sludge particles produced by the growth of micro organisms in aerated tanks as a
part of the activated sludge process to treat wastewater.

Aeration:
Exposing to circulating air; adds oxygen to the wastewater and allows other gases trapped in the wastewater to escape (the first step in secondary treatment via activated sludge process).

Aerobic Bacteria:
Bacteria that require free elemental oxygen for their growth.

Alkalinity:
Alkalinity is a measure of a wastewater's capacity to neutralize acids. The bicarbonate, carbonate, and hydroxide ions are the primary contributors to alkalinity. However, borates, silicates, and phosphates may also contribute.
The determination of alkalinity levels at various points in a plant will be an aid to the proper understanding and interpretation of the treatment process. For example, if chemical addition is used to coagulate a wastewater for solids removal, hydrogen ions may be released and cause the pH to decrease. Alkalinity will tend to neutralize ("buffer") the acids formed and permit coagulation to proceed in the proper pH range. Some other pH-dependent processes are disinfection, digestion, and sludge preparation/conditioning.

Anaerobic:
A biological environment that is deficient in all forms of oxygen, especially molecular oxygen, nitrates, and nitrites.

Anaerobic Bacteria:
Bacteria that grow only in the absence of free elemental oxygen.

Anoxic:
A biological environment that is deficient in molecular oxygen, but may contain chemically bound oxygen, such as nitrates and nitrites.

B

Bacteria:
A group of universally distributed, rigid, essentially unicellular, microscopic organisms lacking chlorophyll. Characterized as spheroids, rod-like, or curved entities, but occasionally appearing as sheets, chains, or branched filaments.

Biochemical Oxygen Demand (BOD):
A laboratory measurement of wastewater that is one of the main indicators of the quantity of pollutants present; a parameter used to measure the amount of oxygen that will be consumed by micro organisms during the biological reaction of oxygen with organic material.
The total milligrams of oxygen required over a 5-day test period to biologically assimilate the organic contaminants in 1 litre of wastewater maintained at 20°C.
The BOD5 of a wastewater is widely used as an indicator of the fraction of organic matter that may be degraded by microbial action in a given time period at a temperature of 20°C. BOD5 is a measure of the pollutional strength of a wastewater and the test is related to the oxygen that would be required to stabilize the waste after discharge to a receiving body of water. The BOD5 test has been widely used by regulatory agencies to gauge overall treatment plant performance. The BOD5 of domestic wastewater plant influent in the U.S. typically ranges form 100 to 300 mg/.
The traditional measurement of BOD5 of the plant influent, primary tank effluent, and final effluent gives the most common measure of treatment plant efficiency. The drop in BOD5 from raw influent to final effluent is usually used in calculating the solids growth rate in the aeration tank. This test is too slow to provide timely information to the operator for control purposes. It can, however, provide the operator with the historic results of previous operating decisions. Tests for BOD5 are to be made on composite samples daily. BOD tests run for at least 20 days should also be made on the effluent periodically to determine the oxygen requirements of the nitrogen compounds present in the effluent.
COD measurements are preferred for a mixed domestic-industrial wastewater or where a more rapid determination of the load is desired. The COD test will record the oxygen demand for certain industrial wastes that cannot be used readily as food by the treatment plant organisms. The COD test may be run in several hours, giving the operator a more timely measurement of what is entering the plant and how the plant is performing.

Biosolids:
Sludge that is intended for beneficial use. Biosolids must meet certain government specified criteria depending on its use (e.g., fertilizer or soil amendment).

BOD:
BOD is the biochemical oxygen demand of the wastewater (mg/l). The BOD is obtained from closed batch tests which operate for a number of days.

C

Chemical Oxygen Demand (COD):
The milligrams of oxygen required to chemically oxidize, using chromic acid, the organic contaminants in 1 litre of wastewater.
COD is another means of measuring the pollutional strength of a wastewater. By using this method, most oxidizable organic compounds present in the wastewater sample are measured rather than only the more easily oxidizable ones measured using the BOD5 test. Generally, COD values will be higher than those determined with the BOD text. The reason for this difference is that the BOD5 test measures only the quantity of organic material capable of being oxidized by microbial action, while the COD test represents a more complete oxidation.
The COD test has a major advantage over the BOD analysis because of the short time required - a few hours as opposed to 5 days for the standard BOD test. This advantage permits more responsive operational control of the treatment process. Typical COD values for domestic wastewater range from 200 to 500 mg/l. As the industrial content of the wastewater increases, the ratio of COD to BOD5 typically also increases.

COD:
See Chemical oxygen demand - the amount of oxygen in mg/l required to oxidize both organic and oxidizable inorganic compounds.

Coliform-Group Bacteria:
A group of bacteria predominantly inhabiting the intestines of man or animal, but also occasionally found elsewhere. In includes all aerobic and facultative anaerobic Gram-negative, nonspore-forming bacilli that ferment lactose with production of gas. Also included are all bacteria that produce a dark, purplish-green colony with a metallic sheen by the membrane-filter technique used for coliform identification. The two groups are not always identical, but they are generally of equal sanitary significance.

D

Decomposition:
The process of breaking down into constituent parts or elements.

Denitrification:
A biological process by which nitrate is converted to nitrogen gas.

Detention Time:
The theoretical time required to displace the contents of a tank or unit at a given rate of discharge.

Digestion:
The biological decomposition of organic matter in sludge resulting in partial gasification, liquefaction, and mineralization of putrescible and offensive solids.

Dissolved Oxygen (DO):
The oxygen dissolved in water, wastewater, or other liquid; usually expressed in milligrams per litre, parts per million, or percent of saturation.

Diurnal:
The cyclic characteristics of wastewater composition and waste stream flow during a 24-hour period.

Domestic Wastewater:
Wastewater that comes primarily from individuals, and does not generally
include industrial or agricultural wastewater.
Wastewater derived principally from dwellings, business buildings, institutions, and the like. It may or may not contain groundwater, surface water, or storm water.
 

E

Effluent:
Treated wastewater, flowing from a lagoon, tank, treatment process, or treatment plant.

Enzyme:
A catalyst produced by living cells. All enzymes are proteins, but not all proteins are enzymes.

EPS:
Extra cellular polymeric substances (extra cellular polsaccharide, exocellular polysaccharide), many micro organisms do produce an "overcoat" of polymers outside of the cell. These polymers bind water and various chemicals to form protective and storage functions.

Equalizing Basin:
A holding basin in which variations in flows and waste composition are averaged. Such basins are used to provide a flow of a reasonably uniform nature to a downstream treatment unit. The basin is sometimes called a balancing waste reservoir.

Escherichia Coli (E. Coli):
One of the species of bacteria in the coliform group. Its presence is considered indicative of fresh fecal contamination.

Eutrophic Lake:
A lake or other contained water body that is rich in nutrients. Characterized by a large quantity of planktonic algae, low water transparency with high dissolved oxygen in upper layer, zero dissolved oxygen in deep layers during summer months, and large organic deposits colour brown or black. Hydrogen sulphide is often present in water and deposits.

Excess Activated Sludge:
The quantity of sludge, surpassing that needed for proper operation, which is removed from the activated sludge system for ultimate disposal.

Extended Aeration:
A modification of the activated sludge process which provides for aerobic sludge digestion within the aeration system. The concept envisages the stabilization of organic matter under aerobic conditions and disposal of the end products into the air as gases and with the plant effluent as finely divided suspended matter and soluble matter.

F

Facultative Anaerobic Bacteria:
Bacteria which can adapt themselves to growth in the presence, as well as in the absence, of oxygen. Sometimes referred to simply as facultative bacteria.

Fats (Wastes):
Triglyceride esters of fatty acids. Erroneously used as synonymous with grease.

First-Stage Biochemical Oxygen Demand:
That part of oxygen demand associated with biochemical oxidation of carbonaceous, as distinct from nitrogenous, material. Usually, the greater part, if not all, of the carbonaceous material is oxidized before the second stage, or substantial oxidation of the nitrogenous material takes place. Nearly always, at least a portion of the carbonaceous material is oxidized before oxidation of nitrogenous material even starts.

Floc:
Small gelatinous masses formed in a liquid by the reaction of a coagulant added thereto, through biochemical processes, or by agglomeration.

Flocculation:
In water and wastewater treatment, agglomeration of colloidal and finely divided suspended matter after coagulation by gentle stirring by either mechanical or hydraulic means. In biological wastewater treatment where coagulation is not used, agglomeration may be accomplished biologically.

Flocculation Agent:
A coagulating substance which, when added to water, forms a flocculent precipitate that will entrain suspended matter and expedite sedimentation. Examples are alum, ferrous sulphate, and lime.

Foam:
(1) A collection of minute bubbles formed on the surface of a liquid by agitation, fermentation, and so on.

(2) The frothy substance composed of an aggregation of bubbles on the surface of liquids and created by violent agitation or by the admission of air bubbles to liquid containing surface-active materials, solid particles, or both.
 

G

Gasification:
The transformation of soluble and suspended organic materials into gas during waste decomposition.

Grease:
In wastewater, a group of substances including fats, waxes, free fatty acids, calcium and magnesium soaps, mineral oils, and certain other nonfatty materials.

Grease Skimmer:
A device for removing floating grease or scum from the surface of wastewater in a tank.

Grit chamber:
A chamber or tank used in primary treatment where wastewater slows down and
heavy, large solids (grit) settle out and are removed.
 

H

Heterotrophic Organisms:
Bacteria that thrive only on organic materials for energy and growth.

I

Infiltration:
1. The flow or movement of water through the interstices or pores of a soil or other porous medium.

2. The quantity of groundwater that leaks into a pipe through joints, porous walls, or breaks.

3. The entrance of water from the ground into a gallery.

4. The absorption of liquid by the soil, either as it falls as precipitation or from a stream flowing over the surface.

Influent:
Wastewater flowing into a treatment plant.

Internal Recycle:
A nitrified mixed liquor stream that is pumped from the oxic section of the reactor to the anoxic section of the reactor for the purpose of denitrification.

Inverse Sludge Index:
Properly called sludge density index. It is the reciprocal of the sludge volume index multiplied by 100.

Ion-Exchange Treatment:
The use of ion-exchange materials such as resin or zeolites to remove undesirable ions from a liquid and substitute acceptable ions.

J

Jar Test:
A laboratory procedure for evaluating coagulation, flocculation, and sedimentation processes in a series of  parallel comparisons.

Jet Aeration:
A method of adding dissolved oxygen to mixed liquor by injecting an air-water mixture through nozzles into the reactor.

K

Kjeldahl Nitrogen:
The combined amount of organic and ammonia nitrogen. Also called total Kjeldahl nitrogen (TKN).

Kraus Process:
A modification of the activated-sludge process in which aerobically conditioned supernatant liquor from anaerobic digesters is added to activated sludge biological reactors to improve the settling characteristics of the sludge and to add an oxygen resource in the form of nitrates.

L

Lagoon (oxidation ponds or stabilization ponds):
A pond containing raw or partially treated wastewater in which aerobic or anaerobic stabilization occurs.
A wastewater treatment method that uses ponds to treat wastewater. Algae grow within the lagoons and utilize sunlight to produce oxygen, which is in turn used by micro organisms in the lagoon to break down organic material in the wastewater. Wastewater solids settle in the lagoon, resulting in effluent that is relatively well treated, although it does contain algae.

M

Mechanical Aeration:
1. The mixing, by mechanical means, of wastewater and activated sludge in the aeration tank of the activated sludge process to bring fresh surfaces of liquid into contact with the atmosphere.

2. The introduction of atmospheric oxygen into a liquid by the mechanical action of paddle, paddle wheel, spray, or turbine mechanisms.

MGD:
Million Gallons per Day - 694.4 gallons per minute.

Microbial Activity:
Chemical changes resulting from the metabolism of living organisms. Biochemical action.

Milligrams Per Litre:
A unit of concentration of water or a wastewater constituent. It is 0.001 g of the constituent in 1,000 ml of water. It has replaced the unit formerly used commonly, parts per million, to which it is approximately equivalent, in reporting the results of water and wastewater analysis.

Mixed Liquor (ML):
The mixture of activated sludge, wastewater, and oxygen, wherein biological assimilation occurs.

Mixed Liquid Suspended Solids (MLSS):
The milligrams of suspended solids (filtered and dries at 103°C) contained in one litre of the mixed liquor.

Mixed Liquor Volatile Suspended Solids (MLVSS):
The milligrams of suspended solids per litre of mixed liquor that are combustible at 550°C.

Municipal:
Of or relating to a municipality (city, town, etc.). Municipal wastewater is primarily
domestic wastewater.

N

Nephelometer:
An instrument for comparing turbidities of solutions by passing a beam of light through a transparent tube and measuring the ratio of the intensity of the scattered light to that of the incident light.

Nitrification:
The conversion of nitrogen matter into nitrates by bacteria.

Nitrobacter:
A genus of bacteria that oxidizes nitrite to nitrate.

Nitrogen:
Nitrogen appears in organic wastes in various forms. In wastewater, four species of nitrogen are commonly determined:
1. Organic nitrogen;
2. Ammonia nitrogen, including both ammonium ion and free ammonia;
3. Nitrite nitrogen; and
4. Nitrate nitrogen.
These different forms constitute the total nitrogen content. Fresh, cold wastewater is usually relatively high in organic nitrogen and low in ammonia nitrogen. A stale, warm wastewater is usually relatively high in ammonia nitrogen and low in organic nitrogen. Nitrates and nitrites may be present in fresh domestic wastewater, but always in very low concentrations. In treated wastewater, their concentrations usually will be higher. Nitrites are not stable, however, and will be either reduced to ammonia or oxidized to nitrates.

Nitrosomonas:
A genus of bacteria that oxidizes ammonia to nitrite.

O

Oligotriphic Lake:
Lake or other contained water body poor in nutrients. Characterized by low quantity of planktonic algae, high water transparency with high dissolved oxygen in upper layer, adequate dissolved oxygen in deep layers, low organic deposits coloured shades of brown, and absence of hydrogen sulphide in water and deposits.

Organic Nitrogen:
Nitrogen combined in organic molecules such as proteins, amines, and amino acids.

Orthophosphate:
A simple compound of phosphorus and oxygen that is soluble in water: PO4-3.

Oxic:
A biological environment which contain molecular oxygen; aerobic.

Oxidation Pond:
A basin used for retention of wastewater before final disposal, in which biological oxidation of organic material is effected by natural or artificially accelerated transfer of oxygen to the water from the air.

Oxygenation Capacity:
In treatment processes, a measure of the ability of an aerator to supply oxygen to a liquid.

Oxygen Balance:
1. The dissolved oxygen level at any point in a stream, resulting from the opposing forces of deoxygenation and reaeration.

2. The relation between the biochemical oxygen demand of a wastewater or treatment plant effluent and the oxygen available in the diluting water.

Oxygen Saturation:
The maximum quantity of dissolved oxygen that liquid of given chemical characteristics, in equilibrium with the atmosphere, can contain at a given temperature and pressure.
 

P

Parshall Flume:
A calibrated device developed by Parshall for measuring the flow of liquid in an open conduit. It consists essentially of a contracting length, a throat, and an expanding length. At the throat is a sill over which the flow passes at Belanger's critical depth. The upper and lower heads are each measured at a definite distance from the sill. The lower head need not be measured unless the sill is submerged more than about 67 percent.

Peak Demand:
The maximum momentary load placed on a water or wastewater plant or pumping station. This is usually the maximum average load in one hour or less, but may be specified as instantaneous, or with some other defined short time period.

pH:
pH is a method of expressing the acid condition (hydrogen ion concentration) of a wastewater. The pH scale ranges from 1 to approximately 14, with a pH of 1 to 7 considered the acid range and 7 to 14, the basic range. A pH of 7 is defined as neutral. pH is a vital tool for the wastewater treatment plant operator when evaluating unit operations. It is important that the plant operator becomes thoroughly familiar with this measurement and its specific application as a process control tool.

Phosphorus:
Phosphorus is an essential element in the metabolism of biological organisms. A minimal concentration is necessary to achieve optimum operation of biological treatment systems. Because it has been implicated as a contributing factor in the development of noxious algal blooms, more emphasis is being placed on controlling the amount of phosphorus discharged in the treatment plant effluent.
Phosphorus may exist in many different forms in aqueous solution. These forms may be classified as [a] orthophosphate, [b] pyro-, poly-, and metaphosphate (condensed phosphates), and [c] organic phosphorus. The orthophosphates are of most concern because they are freely available for biological metabolism.

Polymer:
A large molecule formed by polymerisation of monomeric units. Synthetic organic compounds with high molecular weights and composed of repeating chemical units (monomers). Polymers may be polyelectrolytes (such as water-soluble flocculants or water-insoluble ion-exchange resins) or insoluble uncharged materials, such as those
used for plastic or plastic-lined pipe and plastic trickling filter media. Liquid polymers are used as flocculation aids.

Polyphosphate:
A large compound formed by connecting several orthophosphate molecules by phosphate-storing micro organisms.

Population Equivalent:
A means of expressing the strength of organic material in wastewater. Domestic wastewater consumes, on an average, 0.17 lb of oxygen per capita per day, as measured by the standard BOD test. This figure has been used to measure the strength of organic industrial discharges 1,000 pounds of BOD per day, its waste is equivalent to the domestic wastewater from 6,000 persons (1,000 ¸ 0.17 = 6000).

Preaeration:
A preparatory treatment of wastewater consisting of aeration to remove gases, add oxygen, promote flotation of grease, and aid coagulation.

Primary Settling Tank:
The first settling tank for the removal of settle able soils through which wastewater is passed in a treatment works.

Primary treatment:
The first stage of wastewater treatment that removes settle able or floating solids
only; generally removes 40% of the suspended solids and 30-40% of the BOD in the
wastewater.

Protein:
1. Any of the complex nitrogenous compounds formed in living organisms that consist of amino acids bound together by the peptide linkage.

2. Any of a group of nitrogenous organic compounds of high molecular weight synthesized by plants and animals that, upon hydrolysis by enzymes, yield amino acids and that are required for all life processes in animal metabolism.

Protozoa:
Small one-celled animals including amoeba, ciliates, and flagellates.

Q

Quantitative Analysis:
Chemical determination of the amounts or proportions of constituents in a substance.

R

Raw Wastewater:
Wastewater before it receives any treatment.

Reactor:
A tank where a wastewater stream is mixed with bacterial sludge and biochemical reactions occur.

Returned Sludge:
Settled activated sludge returned to mix with incoming raw or primary settled wastewater.

Return Activated Sludge (RAS):
A concentrated sludge for recycling.

Rotifera:
Minute, many-celled aquatic animals.

Roughing Filter:
A wastewater filter of relatively coarse material operated at a high rate to afford preliminary treatment.

S

Sampler:
A device used with or without flow measurement to obtain an aliquot portion of water or waste for analytical purposes. May be designed for taking single sample (grab), composite sample, continuous sample, or periodic sample.

Sanitary Sewer:
A sewer that carries liquid and water-carried wastes from residences, commercial buildings, industrial plants, and institutions; together with minor quantities of ground, storm, and surface waters that are not admitted intentionally.

Screening:
The removal of relatively coarse floating and suspended solids by straining through racks or screens.

Scum Collector:
A mechanical device for skimming and removing scum from the surface of a settling tank.

Secondary Settling Tank:
A tank through which effluent from some prior treatment process flows for the purpose of removing settle able solids.

Secondary Wastewater Treatment:
The treatment of wastewater by biological methods after primary treatment by sedimentation.
A type of wastewater treatment used to convert dissolved and suspended pollutants into a form that can be removed, producing a relatively highly treated effluent.
Secondary treatment normally utilizes biological treatment processes (activated sludge, trickling filters, etc.) followed by settling tanks and will remove approximately 85% of the BOD and TSS in wastewater. Secondary treatment for municipal wastewater is the minimum level of treatment required by the Clean Water Act.

Second Stage Biochemical Oxygen Demand:
The part of the oxygen demand associated with the biochemical oxidation of nitrogenous material. As the term implies, the oxidation of the nitrogenous materials usually does not start until a portion of the carbonaceous material has been oxidized during the first stage.

Sedimentation:
The process used in both primary and secondary wastewater treatment, that takes
place when gravity pulls particles to the bottom of a tank (also called settling).

Settling tank (sedimentation tank or clarifier):
A vessel in which solids settle out of water by gravity during wastewater or drinking water treatment processes.

Sewage:
The spend water of a community. This term is now being replaced in technical usage by the preferable term wastewater.

Sludge:
Any solid, semisolid, or liquid waste that settles to the bottom of sedimentation tanks (in wastewater treatment plants or drinking water treatment plants) or septic tanks.

Sludge Age:
In the activated sludge process, a measure of the length of time a particle of suspended solids has been undergoing aeration, expressed in days. It is usually computed by dividing the weight of the suspended solids in the aeration tank by the weight of excess activated sludge discharged from the system per day.

Sludge Bulking:
A phenomenon that occurs in activated sludge plants whereby the sludge occupies excessive volumes and will not concentrate readily.

Sludge Cake:
The sludge that has been dewatered by a treatment process to a moisture content of 60-85 percent, depending on type of sludge and manner of treatment.

Sludge Index:
Properly called sludge volume index (SVI). It is the volume in millimetres occupied by 1 g of activated sludge after settling of the aerated liquid for 30 minutes.

Sludge Reaeration:
The continuous aeration of sludge after its initial aeration for the purpose of improving or maintaining its condition.

Solids:
The determinations of various forms of residue are useful in the control of a wastewater treatment plant. Total Solids (TS), Suspended Solids (SS) and Dissolved Solids (DS), and their volatile and fixed fractions, may be used to assess wastewater strength, process efficiency, and unit loadings. Measurements of the various residue concentrations are necessary to establish and assure satisfactory operational control. It is important that the operator develop sufficient knowledge of these measurements and their interpretation so that they become routine daily procedures.

Sparger:
An air diffuser designed to give large bubbles, used singly or in combination with mechanical aeration devices.

Specific Oxygen Uptake Rate:
The rate at which oxygen is consumed in the activated sludge process relative to the dry weight concentration of volatile suspended matter. Units are milligrams of oxygen per gram MLVSS per hour.

Sphaerotilus Bulking:
A type of sludge bulking that occurs when a genus of filamentous bacteria, Sphaerotilus, is present in large numbers.

Splitting Box:
1. A division box that splits the incoming flow into two or more streams.

2. A device for splitting and directing discharge from the head box to two separate points of application.

Standard Methods:
Methods for the examination of water and wastewater published jointly by the American Public Health Association. The American Water Works Association and the Water Pollution Control Federation.

Storm Sewer:
A sewer that carries storm water and surface water, street wash and other wash waters, or drainage, but excludes domestic wastewater and industrial wastes.

Supernatant:
The liquid standing above a sediment or precipitate.

T

Temperature:
Temperature is indicative of the relative "hotness" of wastewater. It is usually measured with the familiar mercury glass thermometer marked in either Fahrenheit or Celsius degrees. Other instruments, however, such as bimetallic thermometers, thermistors, and thermo-couples also may be used.

Tertiary treatment:
Any level of treatment beyond secondary treatment, which could include
filtration, nutrient removal (removal of nitrogen and phosphorus) and removal of toxic chemicals or metals; also called “advanced treatment” when nutrient removal is included.

Total Dissolved Solids (TDS):
The sum of the inorganic and organic materials dissolved in water. Total Suspended Solids (TSS): The sum of all insoluble particles suspended in a water.

Total Organic Carbon (TOC):
The need for rapid determination of wastewater strength has led to the development of organic carbon analysers and their use in some treatment plant laboratories. All of the available instruments measure the organic carbon content of aqueous samples, although there are several methods by which this is accomplished. Because a number of organic compounds may not be oxidized in the analysis, the TOC values will generally be somewhat less than COD values. Typical values of TOC for a domestic waste in the U.S. range form 100 to 300 mg/l.
TOC measurements have been used as a method for determining wastewater strength for many years. The organic carbon determination is free of many of the variables that plague the COD and BOD analyses, with somewhat more reliable and reproducible data being the net result.
The TOC concentration often may be correlated with COD and occasionally with BOD values. Because the analysis time using the carbon analyser is only several minutes, usable control results may be obtained quickly if a reliable TOC-BOC or TOC-COD correlation can be established.

Total Oxygen Demand (TOD):
Another instrumental method of measuring organic matter present in a wastewater is the TOD test, whereby the sample is oxidized to stable end products in a platinum-catalyzed combustion chamber. TOD is determined by measuring the oxygen content of the inert carrier gas, nitrogen. The results obtained generally will be equivalent to those obtained in the COD test.
TOD measurements are becoming more popular because of the quickness in determining what is entering the plant and how the plant is responding. Analysis time is approximately 5 min.

Total Solids (TS):
TS, is a term applied to the weight of material per unit volume of sample remaining in a previously weighed crucible after evaporation of the sample at a temperature of 103° to 105°C. TS is equivalent to the sum of filterable residue (the portion of TS that would have been retained if the sample were filtered before evaporation) and nonfilterable residue. In wastewater work, the term "suspended solids" is taken to correspond to filterable residue. The term "dissolved solids" is taken to correspond to the nonfilterable residue.

Total Suspended Solids (TSS):
A laboratory measurement of the quantity of suspended solids present
in wastewater that is one of the main indicators of the quantity of pollutants present.

Trickling Filter:
A filter consisting of an artificial bed of coarse material, such as broken stone, clinkers, slate slats, brush, or plastic materials, over which wastewater is distributed or applied in drops, films, or spray from troughs, drippers, moving distributors, or fixed nozzles, and through which it trickles to the under drains, giving opportunity for the formation of zoogleal slimes which clarify and oxidize the wastewater.

Trickling Filter Process:
A biological treatment process that uses coarse media (usually rock or plastic) contained in a tank that serves as a surface on which microbiological growth occurs.
Wastewater trickles over the media and micro organisms remove the pollutants (BOD and TSS). Trickling filters are followed by settling tanks to remove micro organisms that wash off or pass through the trickling filter media.

Turbidity:
The cloudy or muddy appearance of a naturally clear liquid caused by the suspension of particulate matter.
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 arbitrary turbidity units determined by measurements of light diffraction.
 

U

Ultimate Biochemical Oxygen Demand:
1. Commonly, the total quantity of oxygen required to satisfy completely the first-stage biochemical oxygen demand.

2. More strictly, the quantity of oxygen required to satisfy completely both the first-stage and the second-stage biochemical oxygen demands.

V

Volatile Acids:
Fatty acids containing six or less carbon atoms, which are soluble in water and which can be steam-distilled at atmospheric pressure. Volatile acids are commonly reported as equivalent to acetic acid.

W

Waste Activated Sludge (WAS):
Excess activated sludge removed from the treatment process to maintain the micro-organism population in balance with the sewage inflow.

Wuhrmann Process:
Developed in the 1960's, this process was a post denitrification process using an unaerated zone after the aeration basin of a conventional activated sludge plant. Denitrification was inefficient due to the low (endogenous) denitrification rate. This plant has become the basis for some plants using external carbon (methanol) addition to manage denitrification.

X

Xenobiotic:
A chemical compound which does not occur naturally, but is completely synthetic.

Y

Yeasts:
Unicellular fungi.

Z

Zone Settling Velocity (ZSV):
The maximum rate at which agglomerated sludge particles or floc settle toward the bottom of a specified vessel under the influent of gravity.

Zooglea:
A jelly-like matrix developed by bacteria. A major part of activated sludge floc and of trickling filter slimes.