Absorption
More...
The soaking up of one substance into the body of another substance.


 
Accumulator
More...
An accumulator is a device which can be attached to a valve to dissipate the energy released when the valve is shut off abruptly.


 
Acid Feed System
More...
A setup used to feed liquid fluoride directly into the water main.  The hydrofluosilicic acid begins in the shipping container, which is placed on a scales to measure the remaining liquid in the container.  A pump pulls acid from the shipping container into a physical break box.  From the break box, the fluoride flows to the other side of the pump and is pumped to the water line. 


 
Activated Alumina
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Activated alumina is used to remove inorganic elements, such as arsenic, from water.


 
Activated Carbon
More...
Activated carbon is a material produced by heating coal or wood in such a way as to yield a porous structure, creating a very large internal surface area.


Activated Carbon - Types
More...
The primary types of activated carbon are powdered activated carbon and granular activated carbon. 

 

Administration
More...
Any group entrusted with executive or administrative powers; The executive branch of the U.S. government as headed by the President and in power during his or her term of office.

 

Adsorption
More...
Adsorption is the process of adhering to a surface by a combination of complex physical forces and chemical action.  Filters and activated carbon pull substances out of the water by the process of adsorption.

 

Aeration
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Aeration is the intimate exposure of water to air.  It is a method used to treat a variety of problems in water.

 

Aerators
More...
Aerators are machines used to add air to water.


 
Agency Laws
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Air Binding
More...
Air binding occurs when excess oxygen comes out of solution in the filter, resulting in air bubbles which harm both the filtration and backwash process by clogging filters, pipes, or pumps.  Air binding happens when air is released into water due to a decrease in water pressure (negative head) or when excess air is added to water during aeration. 

 

Alkalinity
More...
Alkalinity is the capacity of the water to neutralize acids, based on the water's content of carbonate, bicarbonate, hydroxide, borate, silicate, and phosphate.  Water with a high alkalinity is preferred for coagulation since it tends to have more positively charged ions to interact with the negatively charged colloids. 


 
Alum
More...
Alum is the common name for aluminum sulfate Al2 (SO4) 3, which is often used as a coagulant in water treatment.  Alum is a white crystalline compound and is also used in papermaking, sanitation, and tanning.


Anion
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A negatively charged particle. 


Annular Space
More...
A ring-shaped space between two pipes or between a pipe and a pipe lining.


Anode
More...
The negatively charged portion of an electrolytic cell.  The anode gives up electrons. 


Baffle
More...
A flat board or plate, deflector, guide, or similar device placed in flowing water to cause more uniform flow, to absorb energy, and to divert, guide, or agitate liquids.


 
Backwash
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Backwash is the reversal of flow through a filter to remove the material trapped on and between the grains of filter media.  This is a way of cleaning a filter.


 
Backwash Interval
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Backwash interval is the time between each backwashing.


 
Bacteriology
More...
Bacteriology is the science that deals with the study of bacteria and their relations to medicine, industry, agriculture, and water purification.


Baylis Curve
More...
A chart which shows the relationship between pH, alkalinity, and water stability.


Bed Expansion
More...
During backwashing, the water pushes the media up until it is suspended in the water.  The height to which the media rises during backwashing is known as the bed expansion.  For example, if the filter media is 2 feet deep, it may rise up to 3 feet deep during backwashing.  This is a 50% bed expansion


Bentonite
More...
Bentonite is a type of clay used as a coagulant aid in water high in color and low in turbidity and mineral content.  This type of water usually would not form floc large enough to settle out of the water.  The bentonite joins with the small floc, making the floc heavier and thus making it settle more quickly. 


 
Binding
More...
Binding is the process in coagulation that binds small particles together into larger, heavier clumps which settle out relatively quickly.


Bivalent Ion
More...
An ion with a charge of +2. 


Break Box
More...
Break boxes are used to prevent overfeeding fluoride into water.  Fluoride flows into the box through an inlet at the top and out through an outlet at the bottom.  If excess fluoride is pumped into the breakbox, the extra flows out of the box through an overflow pipe rather than through the outlet. 


Breakpoint Chlorination
More...
A method of chlorination in which chlorine is added to water until the chlorine demand has been completed satisfied (the breakpoint.)  Chlorine is added past the breakpoint to create free chlorine residual. 


 
Breakthrough
More...
A breakthrough is a crack or break in a filter bed which allows the water to pass through without contacting the filter and being cleaned.  Breakthroughs can be caused by not cleaning filters in a timely manner.


Calcium Carbonate Equivalent
More...
A measurement of hardness which is an expression of the concentration of hardness ions in water in terms of their equivalent value of calcium carbonate. 


 
Calibration - Calibration Chart
More...
Calibration involves adjusting a measuring device such as a pH meter to a known value or standard to increase the accuracy of measurements.  A calibration chart is the graphical representation of the measured or observed values of the instrument opposed to the established or set values of the standard.  A calibration chart is used for determining data when an instrument consistently reads different from the standard values.

 

Carbon Dioxide
More...
Carbon dioxide is a gas which can dissolve in water, making the water acidic.  The acidic water will attack metal pipes and cause iron rust in water unless it is neutralized.  Carbon dioxide is removed from water through two techniques: aeration and addition of an alkali.

 

Carbonate Hardness
More...
Hardness caused by metals combined with a form of alkalinity.  Carbonate hardness is the most common type of hardness and is responsible for the deposition of calcium carbonate scale in pipes and equipment.  It is sometimes known as "temporary hardness" since it can be removed by boiling the water. 


 
Catalyst
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A catalyst is any substance that encourages a reaction without being consumed in the process.


Cathode
More...
A cathode is the positively charged portion of an electrolytic cell.  The cathode accepts electrons. 


Cathodic Protection
More...
The introduction of a different electrical circuit into the pipe to prevent  corrosion. 


Cation
More...
A positively charged particle. 


Caustic Soda
More...
A chemical which is sometimes used to replace soda ash and some of the lime in the lime softening process.  Also known as NaOH, or sodium hydroxide. 

 

Change of Energy
More...
Every chemical reaction results in a change of energy.  The reactive components may gain energy as they change into the product or lose energy.

 

Chemical Activity
More...
Every chemical compound has a certain amount of energy available for release.  The CRC Handbook lists the activity level of common compounds and elements. 


 
Chemical Limits
More...
In water and wastewater treatment, local and federal agencies pose restrictions on the amount of chemicals, which can be added or removed from water.  Usually limits are specified in parts per million or milligrams per liter.  Limits have been set for chlorine, ammonia, fluoride, and other minor contaminants that pertain to public health.


Chemical Precipitation
More...
A type of softening process which is similar to removal of turbidity by coagulation, flocculation, and sedimentation.  There are many variations, but the typical process involves adding lime to raise the pH of water until it is high enough for reactions to occur which prompt hardness compounds to settle out of the water. 


Chloramines
More...
Chemicals combining chlorine and nitrogen.  Chloramines are formed by first adding chlorine gas or hypochlorite to water and then adding ammonia.  Chloramines are a form of combined chlorine residual which can be used to disinfect water.  They are weaker than chlorine gas, but are more stable, so they are often used as the disinfectant in the distribution lines of water treatment systems. 


 
Chlorination
More...
Chlorination is the destruction of waterborne pathogens through disinfection with various forms of chlorine (e.g. sodium hypochlorite (NaOCl), Calcium hypochlorite (Ca (O Cl2) * 4 H2O), chlorine gas, chloramines, and chlorine dioxide.  Design of feed facilities for each of these chemicals has been achieved.


Chlorination Chemistry
More...
The chemistry of disinfection with chlorine depends on the form of chlorine used and on whether or not the operator is practicing breakpoint chlorination. 


Chlorination  - Efficiency
More...
The efficiency of chlorination is primarily dependent on the contact time and on the concentration of chlorine residual.


Chlorination  - Equipment
More...
The equipment used during chlorination can include hypochlorinators, chlorinators, and chlorine cylinders. 

 

Chlorinator
More...
Chlorinators are machines which use liquid chlorine supplied in steel cylinders to chlorinate water.  They are most economical in large systems.  


Chlorine Demand
More...
The total amount of chlorine which is used up in reactions with compounds in the water.  A sufficient quantity of chlorine must be added to the water so that, after the chlorine demand is met, there is still some chlorine left to kill microorganisms in the water.


 
Chlorine Dioxide
More...
Chlorine Dioxide (ClO2) has been used in a somewhat limited application in the U.S. for the past fifty years.  Mixing solutions of sodium chlorite and chlorine in controlled proportions forms chlorine dioxide:

2NaClO2  + Cl2 = 2ClO  + 2NaCl. 

In addition to use as disinfectant, sodium chlorine is used for taste and odor control.


 
Chlorine Residual
More...
After treatment, a certain amount of chlorine will remain in the water.  This amount is the chlorine residual.  The chlorine residual must be maintained at a certain level throughout the distribution system in order to prevent contamination.


Combined Chlorine Residual
More...
A chlorine residual consisting of chlorine combined with nitrogen to form a chloramine.  Combined chlorine residuals are sometimes used to disinfect water. 


 
Civil Laws
More...
The body of laws of a state or nation regulating ordinary private matters, as distinct from laws regulating criminal, political, or military matters.


Clarifier
More...
A square or circular sedimentation basin with horizontal flow.  A specific kind of clarifier, known as a solids-contact clarifier, upflow solids-contact clarifier, or upflow sludge-blanket clarifier combines coagulation, flocculation, and sedimentation within a single basin.  Solids-contact clarifiers are often found in packaged plants and in cold climates where sedimentation must occur indoors.  This type of clarifier is also often used in softening operations. 


 
Clear Well
More...
A clear well is a reservoir containing potable water which has been previously treated before entering the distribution lines.  Chlorine, fluorine, and Calgon are added to the water in the clear well and are given sufficient contact time before the water is pumped to the customers.  The clear well should also have adequate volume to provide backwash water for the filters. 

 

Closeness
More...
Closeness refers to the proximity of reactive components.  This is one of the four requirements for a chemical reaction.  

 

Coagulant Aid
More...
Coagulant aids are chemicals added to water to promote coagulation.  They add density to slow-settling flocs and add toughness so that the floc will not break up while settling out of the water.  Polymers are one type of coagulant aid.

 

Coagulant Chemicals
More...
Coagulant chemicals include primary coagulants and coagulant aids. 

 

Coagulants - Primary
More...
Primary coagulants are added to water to promote coagulation.  These chemicals neutralize the electrical charges of the particles suspended in the water and cause them to begin clumping together.  Alum is one type of primary coagulant.

 

Coagulation
More...
Coagulation is a step in the water treatment process in which the particles in water are clumped together into larger particles, called floc. 

 

Coliform Bacteria
More...
Coliform bacteria are a type of bacteria which often grow in the guts of warm-blooded animals such as humans, but can also be found in plants, soil, water, or air.  These bacteria are used as indicator species when testing water for human consumption.  If coliform bacteria are present in the water, then other microorganisms which cause disease are also likely to be present.  After chlorination, water should have 0 coliforms per hundred milliliters of water sampled. 

 

Colloidal (Nonsettleable) Solids
More...
Colloidal, or nonsettleable, solids do not dissolve in water although they are electrically charged.  Still, the particles are so small that they will not settle out of the water even after several years and they cannot be removed by filtration alone.  Colloidal solids range between 1 and 500 Mu in size and can be seen only with a high-powered microscope.  Examples include bacteria, fine clays, and silts.  Colloidal solids often cause colored water, such as the "tea color" of swamp water. 

 

Concentration
More...
Concentration of a chemical is the amount of the chemical in relation to the volume of a container.  

 

Conditioning
More...
Treating the sludge to aid in thickening.  The treatment may include the addition of polymers to aid in the dewatering process or the sludge can be heated or frozen and thawed to increase the solids concentration.


 
Conductivity
More...
Conductivity is a measure of the ability of a solution to carry an electrical current.


 
Constitutional Laws
More...
Provided by, in accordance with, or not prohibited by, the Constitution.

 

Contact Time
More...
The amount of time which the chlorine has to react with the microorganisms in the water, which will equal the time between the moment when chlorine is added to the water and the moment when that water is used by the customer.  The longer the contact time, the more efficient the disinfection process is.  When using chlorine for disinfection a minimum contact time of 30 minutes is required for adequate disinfection. 

 

Contactor
More...
A separate filter containing GAC and used to remove taste, odor, and trihalomethane precursors.  The contactor is placed downstream of the filter so that turbidity won't clog the contactor. 


 
Contaminants
More...
Contaminants can be any substance considered undesirable in water and are divided into two types, organic and inorganic.

 

Corrective Treatment
More...
The treatment of water to prevent corrosion in the pipes.  This often involves removing and/or neutralizing the free carbon dioxide in the water.


 
Corrosion
More...
The gradual deterioration of a substance or material by chemical or electrochemical action which often results from exposure to moisture, chemicals, or other agents.


Corrosion - Causes
More...
Many characteristics influence the corrosiveness of water.  These include primary water characteristics, secondary water characteristics, physical water characteristics, and bacteria. 


Corrosion - Chemistry
More...
Corrosion results from an electrochemical reaction in the corrosion cell.

 

Corrosion - Testing
More...
Testing for corrosion can involve noticing indicators such as red water or carrying out long-term or short-term monitoring.

 

Corrosion - Treatment
More...
Treatment for corrosion can include chemical treatment or physical protection. 

 

Corrosion - Types
More...
The various types of corrosion include internal, external, electrolysis, oxygen concentration cell, and galvanic corrosion. 


 
Coupons
More...
A coupon is a small section of metal inserted in a water line to test for corrosion or scaling rate of a water system.


 
Criminal Laws
More...
The laws of a state or country dealing with criminal offenses and their punishments.


 
Cryptosporidium
More...
Cryptosporidium is a parasite often found in the intestines of livestock which contaminates water when the feces from the animal interacts with a water source.


CT Value
More...
Used as a measurement of the degree of pathogen inactivation due to chlorination.  The CT value is calculated as follows:

CT = (Chlorine residual, mg/L) (Contact time, minutes)


 
CWA
More...
The Clean Water Act (CWA) constitutes the basic federal water pollution control statute for the United States.


 
Density
More...
Density is the mass of a substance divided by the volume of the substance:


Depolarization
More...
Depolarization occurs during corrosion when dissolved oxygen in the water reacts with the hydrogen gas surrounding the cathode.  This speeds up the corrosion process. 


 
Deposition or Corrosion in Accordance with pH and Hardness
More...
Deposition or corrosion in accordance with pH and hardness- Pipes in a water system may either corrode or develop a build up of scale; both situations to the extreme causes problems.  Hardness refers to a characteristic of water primarily caused by calcium and magnesium salts.  Corrosion is a chemical destruction of a pipe The Baylis curve shows the relationship between the pH and the alkalinity of the water and provides a tool for establishing chemical feed rates in order to avoid deposition and corrosion.


Detention Time
More...
The time required for a small amount of water to pass through a tank at a given flow rate.  Mathematically, detention time is given by the following formula in which "t" is detention time, "V" is tank volume, and "Q" is flow:

Formula for detention time.


Dewatering
More...
Dewatering, or thickening, sludge is a drying process which makes the sludge easier to transport away from the plant for disposal. 


Dielectric Couplings
More...
Plastic, ceramic, or other non-conductive sections placed between two different types of metal in a pipe.  Since electrons cannot flow through the dielectric coupling, it breaks the circuit and prevents corrosion. 


Direct Filtration
More...
Filtration that follows coagulation and flocculation, without sedimentation.  This method can be used when raw water has low turbidity.


 
Diseases
More...
Disease is a pathological or morbid condition, which exhibits certain signs, symptoms, and clinical findings.


Disinfection
More...
The process of selectively destroying or inactivating pathogenic organisms in water, usually by chemical means. 


Distillation
More...
A process used to purify water.  The water is heated until it becomes water vapor, leaving all impurities behind.  Then it is cooled to produce distilled water. 


 
Drift
More...
Drift is a change in an instrument reading over a change in time.  All measuring instruments have drift and must be re-calibrated in accordance with time to a standard to provide reliable results.


 
Drop Test
More...
A drop test refers to a method of measuring the flow of a filter bed in a water treatment facility by closing the influent valve and observing the volume loss in a specified time.


Dry Feeders
More...
Equipment used to feed dry chemicals into water. 


Drying Bed
More...
Used to thicken sludge destined for a landfill more quickly than the sludge would be thickened in a lagoon.  Sludge is applied on top of layers of sand and gravel, allowing the water to drain away in as little as a few days or weeks. 


 
Efficiency
More...
Efficiency is the condition of being adequate in performance with a minimum of waste or effort.


Effluent Launder
More...
A trough which collects the water flowing out of the sedimentation basin and directs it to the effluent piping.


Electric Charges on Particles
More...
Electric charges on particles in water include electricity and van der waal's forces.  These charges will influence coagulation and flocculation. 


Electrodialysis
More...
A softening process which involves passing water between two plates with opposite electrical charges.  The metals in the water are attracted to the plate with the negative charge while the non-metals are attracted to the plate with the positive charge.  Both types of ions can be removed from the plates and discarded.


Electrolysis
More...
A type of corrosion caused when a D.C. electric current enters a metal pipe and causes flow of electrons through the pipe and to the ground.  The pipe, fueled by the electric current, becomes the anode while the soil becomes the cathode.  The outside of the pipe corrodes, with the metal from the pipe plating out in the surrounding soil. 


Electrolyte
More...
A conducting solution in the electrolytic cell which accepts electrons from the cathode.  In a corrosion cell in a pipe, the electrolyte is the water within the pipe with its dissolved salts.


Electrolytic Cell
More...
A device which causes an electric current to flow.  For example, a battery, or a corrosion cell in a pipe. 


Empty Bed Contact Time
More...
A calculation used to ensure that water in a contactor has adequate contact time with the filter media.  Calculated as the volume of the contactor divided by the flow rate.  The calculation is called "empty bed contact time" (or EBCT) because the volume taken up by the media in the contactor is not taken into account.  Empty bed contact time should be about ten minutes. 


 
Endangered Species Act
More...
This act was passed by Congress in 1973; it's main goal was to stop the extinction of wildlife species in the United States, and to slow or stop extinction abroad.


 
Endothermic Reaction
More...
An endothermic reaction is a chemical reaction in which energy is absorbed.

 

Exothermic Reaction
More...
An exothermic reaction is a chemical reaction in which energy is released.

Feed Rates
More...
Feed rate is the amount of chemical applied to a given system per unit of time.


 
Feed Rates - Seeding
More...
Seeding is the amount of microbes that are needed to metabolize a certain amount of food.

Filter Cleaning
More...
Cleaning a filter involves backwashing and surface washing. 


Filter Control System
More...
Regulates flow rates of water through the rapid sand filter.  Also known as a controller. 


Filter Media
More...
The layers of materials in a filter which remove particles from the water.  Typical filter media include sand, anthracite, and garnet. 


Filter Run
More...
The length of time between each backwashing of a filter. 


 
Filtering
More...
Filtering is a mechanical means of removing impurities and floc from the water being treated.  In general, filtration consists of passing the water through sand and gravel or some other filter.  The floc and impurities get stuck in the sand while the water passes through.  Filtration is usually one of the last steps in the water treatment process. 


Filtering - Efficiency
More...
The efficiency of a filter depends on a variety of factors including chemical characteristics of the water, type and degree of previous treatment, and the operation of the filter. 


Filtering - Mechanisms
More...
Four mechanisms remove particles from water during filtration - biological action, adsorption, absorption, and straining. 


 
Filters - Types
More...
Rapid sand filters, pressure filters, and slow sand filters are types of filters which are used in different situations.  


Fish Eyes
More...
Fish eyes are large clumps of polymer which result from inadequate flash mixing. 


 
Flash Mixer
More...
A flash mixer is a chamber that contains mechanical stirrers, which is designed to assure fast, thorough, mixing of lime and alum for the purpose of creating floc.

 

Flavor Profile Analysis
More...
Used to determine which tastes and odors are present in water.  This test uses a panel of trained judges who taste the water and list which tastes they can detect.  Since the tastes present are described carefully, the Flavor Profile Analysis can be helpful in determining which chemicals are at the root of the problem. 

 

Floc
More...
Floc are clumps of bacteria and other solids in water which have come together to form a cluster.

 

Floc - Pinpoint
More...
Pinpoint floc is a condition in which low turbidity in water causes the formation of very small floc. Pinpoint floc does not settle out of the water in the sedimentation basin but is removed in the filters.

 

Flocculation Basin
More...
Water flows from the flash mix chamber into the  flocculation basin, where it is gently agitated to promote the formation of floc.


 
Flocculation Chart
More...
A flocculation chart predicts the amount of lime, alum, and /or polymer floc in accordance with turbidity for a specific system or watershed.

 

Flow
More...
Flow is the rate of water discharged from a source, given in volume with respect to time.  Flow is usually measured in gallons per minute, cubic feet per second, or million gallons per day.  By measuring the rate at which water flows into the water treatment plant, the operator is able to adjust chemical feed rates, calculate detention times, and monitor the amount of water being treated.


 
Flows - Channel
More...
Channel flow uses the velocity of the water in the channel multiplied by the cross sectional area to give the total flow:


 
Flows - Container/Time
More...
One of the simplest ways to measure flow when a tank or other volume is known, is by the volume of the container divided by the time required to fill the volume:


 
Flows - Differential Pressure
More...
The flow of water through any pipe or any other device loses pressure due to the water molecules rubbing the sides of the pipe.  This pressure can be correlated to give the flow measure in the pipe or device.  The most common head differential flow measurement device for waste treatment is the venturi meter.


 
Flow - Estimating
More...
Flow from a pipe can be estimated using a few simple measurements.


 
Flow - Other
More...
There are many ways to measure flow.  All flow is expressed in a quantity/time unit.

 

Flow - Parshall Flume
More...
The Parshall flume can be used to measure flow in an open channel.

 

Flow - Pressure Differential Meter
More...
Method of measuring flow in a pipe.


 
Flows - Ultrasonic
More...
An ultrasonic flow meter uses sound waves to measure the resistance of a flow


 
Flows - Weirs
More...
 A weir is an obstruction built across an open channel or pipe over which the flow must pass.


 
Fluoridation
More...
Fluoride is a naturally occurring element, which is added to drinking water to increase the concentration of fluoride ions to an optimum level.  The purpose of fluoridation is to reduce the incidence of dental cavities in children.


Fluoridation - Dry Feeders
More...
Dry feeders are used to feed dry chemicals into water.  For fluoridation, but volumetric and gravimetric feeders can be used. 


Fluoridation - Operation
More...
Operation of a fluoridation system involves monitoring the system, troubleshooting when problems arise, and ensuring that safety procedures are followed. 


Fluoridation - Solution Feeders
More...
Solution feeders are used to feed liquids into water.  For fluoridation, a variety of equipment may be associated with solution feeding. 


Fluorosis
More...
Mottled brown stains on teeth resulting from excess fluoride consumption.  Fluorosis results from fluoride concentrations of 2 to 13 ppm in drinking water.  Although fluorosis is only an aesthetic problem, treatment plants strive to prevent fluorosis by setting the recommended fluoride level at about 1 ppm. 


Free Chlorine Residual
More...
After chlorine is added to water, some chlorine is used up by reacting with the water and with chemicals in the water.  The free chlorine residual is the chlorine available to kill microorganisms in the water after these reactions.


Galvanic Corrosion
More...
A type of corrosion caused by two dissimilar metals coming in contact with each other. 


Galvanic Series
More...
A list which arranges metals according to their tendency to corrode.  From most active to least active, some of the common metals are: magnesium, zinc, aluminum (2S), cadmium, aluminum (175T), steel or iron, cast iron, lead, nickel, brass, copper, bronze, stainless steel (304), monel metal, stainless steel (316), silver, graphite, and gold. 


Granular Activated Carbon
More...
Also known as GAC.  A type of activated carbon with a larger particle size than PAC.  GAC is used as a filter medium to remove tastes, odors, and trihalomethane precursors. 


 
Grates
More...
Grates are mechanical devices designed to filter large objects and prevent such objects from entering pipes and drain channels.


Gravimetric Feeder
More...
Gravimetric feeders feed dry chemicals by weight.


Hard Water
More...
Water which contains a high concentration of calcium and magnesium ions.

 

Head Loss
More...
Head loss is the difference in the amount of pressure needed to force water through a filter when it is clean compared to when it is dirty.  A large head loss means that a filter needs to be cleaned.  Head loss can also be used more generally to mean the pressure lost by water as it flows through a pipe or channel.

 

Humic Substances
More...
The organic part of the soil which results from the decay of plant matter.

 

Hydrated Lime
More...
A chemical used in the lime softening process.  Also known as Ca(OH)2, calcium  hydroxide, and slaked lime.

 

Hydrofluosilicic Acid
More...
The most commonly used fluoridating chemical.  This acid, also known as fluorosilicic acid, hexafluosilicic acid, and silicofluoric acid, is a liquid with the formula H2SiF6.  The liquid may be fed directly into the raw water or may be diluted.  Hydrofluosilicic acid is a popular choice in many water treatment plants because it is usually the least expensive fluoridation chemical and is the easiest to feed.  However, it can be expensive to ship since it is a liquid and is heavier than the other fluoridation chemicals.

 

Hydrogen Sulfide
More...
Hydrogen sulfide (H2S) is a gas which can dissolve in water and turn into hydrosulfuric acid.  Although hydrosulfuric acid is weak, it is highly corrosive, eating up electrical contacts, causing a rotten egg odor, and resulting in "black water" complaints.  Hydrogen sulfide in water is treated with aeration, oxidation with chlorine, or by treatment with ozone.  

 

Hypochlorinator
More...
Hypochlorinators are used to feed hypochlorite solutions into water in treatment plants.


Hypochlorite
More...
Hypochlorites are a liquid form of chlorine, also known as bleach.  Hypochlorites are less pure than chlorine gas, which means that they are also less dangerous.  However, they have the major disadvantage that they decompose in strength over time while in storage.  There are three types of hypochlorites - sodium hypochlorite, calcium hypochlorite, and commercial bleach.


Hypochlorous Acid
More...
Hypochlorous acid, HOCl, is formed from the reaction of chlorine gas with water.  It is the most effective form of free chlorine residual. 


 
Hysteresis
More...
Hysteresis is the phenomena of having two different readings, as opposed to the standard or known, in the same instrument when the values are measured from opposing ends on a scale.


 
Ice-Safety
More...


 
Imhoff Cones
More...
An Imhoff cone is a clear, cone-shaped container used to measure the volume of settleable solids in a specific volume of water.


Inhibitors
More...
Chemicals used to physically prevent corrosion by forming thin protective films on pipe walls.


In-line Filtration
More...
Filtration without flocculation or sedimentation.  A coagulant chemical is added to the water just before filtration and coagulation occurs in the filter.  In-line filtration is often used with pressure filters, but is not as efficient with variable turbidity and bacteria levels as conventional filtration is. 


Ion Exchange Softening
More...
A type of softening process which passes water through a softener containing resin granules.  In the softener, calcium and magnesium in the water are exchanged for sodium from the resin granules.  The resulting water has a hardness of 0 mg/L and must be mixed with hard water to prevent softness problems in the distributed water.  The process is also known as zeolite softening. 


 
Introduction
More...
Nature is always treating water.  Along streams there are holding chambers that reduce the flow velocity and allows for bacteriological treatment.  Ozone, which is produced during thunderstorms, serves to disinfect rainwater and soil filters ground water.  Sunlight kills bacteria and surface waters are aerated by the interface of atmosphere and water.  Nature is continually renewing this precious resource.


Ion
More...
An electrically charged particle. 


 
Iron
More...
Iron (Fe) is a very troublesome mineral when found in water.  It stains porcelain and laundry, causes tea and coffee to be cloudy and unpalatable, and causes diarrhea.  Iron is removed from water by changing the pH of the water or through aeration.  Both treatment options oxidize the mineral and cause it to drop out of the water.    


 
Jar Test
More...
Jar tests are used to test the concentration of coagulant chemicals added in the flash mix chamber.  


Lagoon
More...
A small-volume storage pond used to thicken sludge. 


Lamella Plates
More...
Lamella plates are used to increase settling efficiency and speed in sedimentation basins, especially where space is limited.  As water flows up between the slanted plates, floc settles out and drifts back down into the lower portions of the sedimentation basin.


Langelier Index
More...
A laboratory test used to determine the degree of calcium carbonate saturation in water.  This is a way of testing whether the water will be corrosive, stable, or scale-forming. 


Langmuir Isotherm
More...
A model used to understand adsorption under a variety of circumstances.


 
Lime
More...
The chemical formula for limestone is CaCO3 and upon burning forms calcium oxide (CaO), which is known as burnt lime.   Calcium oxide, when mixed with water, forms calcium hydroxide (Ca(OH)2).  Calcium hydroxide is used to treat water as a coagulation aid along with aluminum sulfate.  It can also be used as an alkali to remove iron and carbon dioxide from water.


 
Manganese
More...
Manganese (Mn) is a very troublesome mineral when found in water.  It stains porcelain and laundry, causes tea and coffee to be cloudy and unpalatable, and causes diarrhea.  Manganese is removed from water by changing the pH of the water or through aeration.  Both treatment options oxidize the mineral and cause it to drop out of the water.


Manifold
More...
A pipe joining chlorine cylinders together so that chlorine gas is drawn from several cylinders at once. 


Marble Test
More...
A laboratory test used to determine the degree of calcium carbonate saturation in water.  This is a way of testing whether the water will be corrosive, stable, or scale-forming. 


Metering Pump
More...
A metering pump feeds a wet solution (a liquid) into the water by pumping a volume of solution with each stroke or rotation. 


 
Mixing
More...
For any substantial reaction to occur, thorough mixing of components must take place.   In order for floc to form in a water treatment plant, the alum and lime must be mixed at the right time and at the right velocity for a good floc to form.


Mudballs
More...
Approximately round conglomerations of filter material, ranging in size from pea-sized to two inches or more in diameter.  Mudballs form on the surface of filters when adhesive materials cause particles out of the water and media grains to stick together.  If the filter is not properly backwashed and surface washed, mudballs will continue accumulating material and will grow larger, eventually sinking down into the filter media.  Mudballs in the media result in shortened filter runs and in loss of filter capacity, since water will not pass through the mudballs and must flow around them. 

Noncarbonate Hardness
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Hardness caused when metals combine with anything other than alkalinity.  Noncarbonate hardness is responsible for soap scum.  This type of hardness is sometimes called "permanent hardness" because it is not destroyed by boiling. 

Oils
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Any of a large class of substances typically unctuous, viscous, combustible, liquid at ordinary temperatures, and soluble in ether or alcohol, but not in water.


 
Operational Problem
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Operational problems are caused by external conditions such as flooding, temperature change, icy conditions, pollution, and drought.


Overflow Rate
More...
A property of a sedimentation basin also known as surface loading or surface overflow rate.  It is equal to the settling velocity of the smallest particle which the basin will remove and is calculated by dividing the flow by the surface area of the tank.  Overflow rate should usually be less than 1,000 gal/day-ft.2


Oxidation
More...
Oxidation is the addition of oxygen, the removal of hydrogen, or the removal of electrons from an element or compound.  Oxidation is the part of the aeration process which causes iron and manganese to fall out of solution in the water.  Oxidation also forms rust from iron during corrosion. 


Oxygen Concentration Cell
More...
A type of corrosion caused by varying oxygen concentration in the water.  The portion of the pipe touching water with a low oxygen concentration becomes the anode while the part of the pipe in contact with a high oxygen concentration becomes the cathode.  This is the most common cause of corrosion in pipes. 

 

Overview of Water Treatment
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In a water plant, the treatment process usually begins with aeration, continues through flash mixing, coagulation and flocculation, sedimentation, filtration, and ends in the clear well.  


 
Ozone (O3)
More...
Ozone is a naturally occurring gas found in the upper atmosphere that protects the earth from most of the sun's harmful rays.  Ozone can be used to disinfect water. 


Pacing Meter
More...
A type of flow meter called a pacing meter can be be used to match the feed rate of fluoride to the flow rate of the water being treated.  Pacing meters measure the total water flow rate and then produce a signal which allows for automatic adjustment of the fluoride feed rate.  


 
Paddle Mixers(Propeller Flocculators)
More...
Paddle mixers are large propellers or blades, which are slowly driven by electromechanical energy.  The large paddles are rotated with the least amount of energy so as not to shear the floc, and allow the components enough mixing for the floc to form.  The rpm of the motor is around l whereas the rpm of the flash mixer is around 100 rpm.


Particle Counters
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Particle counters can be used to count the number of particles in the filter effluent which are within the size range of Giardia and Cryptosporidium to determine how efficiently the filter has removed these microorganisms. 


Pathogens
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Pathogens are disease-causing organisms.


Pinpoint Floc
More...
Very small floc which can be produced in low turbidity water and removed by filtration. 


Polarization
More...
Part of the corrosion process in which hydrogen gas coats the cathode and separates it from the water.  Polarization breaks the connection between the cathode and the electrolyte and slows corrosion.


Polymer Aids
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Chemicals added to the filter influent to improve the quality of the effluent water by helping the floc get caught in the filter. 


Polymers
More...
A polymer is a man-made organic compound made up of a long chain of smaller molecules called monomers.  In water and wastewater treatment processes, polymers are also referred to as Polyelectrolytes.


 
Polymer Floc
More...
Polymer floc is the term used when referring to the material created during coagulation that enables contaminants within the water to collect together and fall out of water.


Postchlorination
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Postchlorination is the application of chlorine after water has been treated but before the water reaches the distribution system.  At this stage, chlorination is meant to kill pathogens and to provide a chlorine residual in the distribution system.  Postchlorination is nearly always part of the treatment process, either used in combination with prechlorination or used as the sole disinfection process. 


Powdered Activated Carbon
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Also known as PAC.  A form of activated carbon with a very small particle size.  Treatment involves adding PAC to water, allowing the PAC to interact with contaminants in the water, then removing the PAC by sedimentation or filtration. 

 

Power
More...
Power is defined as the amount of work done or energy transferred per unit time.  Power can be determined using the following equation:

            Power = Pressure × Flow



 
PPM
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PPM is the abbreviation for "parts per million", a measurement of concentration.  A part per million is equal to a milligram per liter.   Parts per million refers to a ratio of weights.  For example, one part per million is one pound in a million pounds, one ounce in a million ounces, one gram in a million grams, etc.


 
Pre-chlorination
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Prechlorination is the act of adding chlorine to the raw water.  The residual chlorine is useful in several stages of the treatment process - aiding in coagulation, controlling algae problems in basins, reducing odor problems, and controlling mudball formation.  In addition, the chlorine has a much longer contact time when added at the beginning of the treatment process, so prechlorination increases safety in disinfecting heavily contaminated water.  However, the long contact time allows the chlorine to react with the organics in the water and create trihalomethanes, so prechlorination is becoming less common. 


 
Pre-sedimentation
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If the intake is very high in turbidity then a presedimentation basin is used to settle out most of the turbidity before primary water treatment begins.  This makes later chemical treatment of the water more efficient.  Also known as plain sedimentation because the process depends merely on gravity and includes no coagulation and flocculation. 


 
Presumptive Test
More...
The presumptive test is used to test for coliform bacteria.  Water samples are incubated in a lactose or lauryl tryptose broth.  If no gas is produced, then there are no coliforms present.  If gas is produced, then the confirmed test is used to determine how many coliforms are present.    

 

Pretreatment
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Pretreatment, or preliminary treatment, is any physical, chemical or mechanical process used on water before it undergoes the main treatment process.  This may include screening, presedimentation, chemical addition, flow measurement, and aeration.

 

Problem-Solving
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Problems can be solved logically by following the problem-solving pathway. 


 
Pumps
More...
Pumps are mechanical devices that are designed to transfer a non-solid material (liquid, gas, or powder) from one location to another.

 

Pumps - Positive Displacement
More...
Positive displacement pumps are used in solution feeders to feed a measured volume of a liquid chemical during a specific time period.  They have several advantages over other types of pumps, being accurate and capable of feeding a solution against pressure into a pipe or tank of water as well as into open tanks of water. 

 

Quicklime
More...
A chemical which must be slaked before it is used in the lime softening process.  Also known as CaO, calcium oxide, or unslaked lime.

 

Radionuclides
More...
Radioactive substances which can be found in water. 

 

Radon
More...
A radioactive gas which may enter homes or water through the soil. 

 

Rate
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The rate of a reaction is how fast a reaction occurs.  The rate depends on temperature, pressure, concentration, catalyst, and chemical activity.

 

Reactions
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Substantial, planned chemical reactions require: reactive components, closeness, thorough mixing, and a change of energy.  Time also plays an important role within a reaction.

 

Reactive Components
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Reactive components are substances which have some ability or potential for a reaction.

 

Reactors
More...
A reactor is any housing which contains a reaction.  Reactors isolate the reaction and optimize the conditions for the reaction.  

 

Recarbonation
More...
The process of stabilizing the water by lowering the pH and precipitating out excess lime and calcium carbonate.  Recarbonation is a step in the lime softening process. 

 

Rectifier
More...
An external direct current source used in some cathodic protection systems. 

 

Red Water
More...
"Red water" results from iron in the water.  The iron may have been present in the source water or may have entered the water through corrosion of iron pipes.  


 
Regulations
More...
Regulations for water and wastewater are administered by the Clean Water Act, Health Department, Department of Environmental Quality, and the Environmental Protection Agency.  These regulations are for the benefit of all.


 
Reporting
More...
The Health Department and the Department of Environmental Quality require water and wastewater facilities to report at certain intervals to show compliance with regulations.


Resins
More...
Resins are substances found in softeners.  They are insoluble solids with attached cations or anions capable of reversible exchange with mobile ions of the opposite sign in the solutions in which they are brought in contact.  Zeolite resin is one type commonly used in softening. 


 
Resistance Values
More...
Each pipe has a resistance value which refers to the roughness of the interior of the pipe.


 
Retention Times
More...
In order for water to be treated, it must be contained for an adequate amount of time.  The retention time of a tank or other holding facility can be found by dividing the flow (in gallons per minute or million gallons per day) into the tank volume:

                RT = V
                         Q


Reverse-osmosis Softening
More...
A type of softening process in which water is forced through a semi-permeable membrane.  Calcium, magnesium, and dissolved solids are captured while the softened water is passed through the membrane.


 
Rewash
More...
Rewash refers to the short period of time after the filter is washed and before the bed has completely settled.  The water that enters from the flocculation chamber is mixed with the remaining water from the clearwell that was used to wash the filter and is wasted to prevent the contamination of the filter bed.


Sacrificial Anode
More...
A piece of very active metal (usually zinc or magnesium) which is more galvanically active than any other metal in the system.  The sacrificial anode will be the only metal corroded, and even previously active anodes on the pipe wall will become cathodes and will thus be protected.


Safety
More...
Most accidents at water treatment plants occur during maintenance, slips or falls, and material handling.  Operators can prevent many accidents by being alert, wearing appropriate safety equipment, using mechanical aids for lifting, and by using basic caution.


Salts
More...
Stable compounds formed from the combination of cations with anions.   


Saturator
More...
A device used in fluoride feed systems which produces a fluoride solution.  The saturator dissolves dry fluoride chemicals so that they may be fed into the water line using a solution feeder. 


Schmutzdecke
More...
A layer of dirt, debris, and microorganisms that builds up on the top of the sand in a slow sand filter.  The schmutzdecke breaks down organic particles in the water biologically, and is also very effective in straining out even very small inorganic particles from water.

 

Screens
More...
Screens are used to remove debris before water enters the treatment plant. 

 

Scrubbing Action
More...
One of the methods used by aerators to physically remove unwanted components from water.  Scrubbing action is caused by turbulence between water and air.


 
Sedimentation Basin
More...
A sedimentation basin is a basin or tank in which water is retained to allow settleable matter, such as floc, to settle by gravity.


Sedimentation Basin - Efficiency
More...
Efficiency of a sedimentation basin is influenced by many factors including floc characteristics and short-circuiting.


Sedimentation Basin - Zones
More...
Each sedimentation basin has four zones - inlet, settling, outlet, and sludge. 


Short-circuiting
More...
A problem in sedimentation basins in which water bypasses the normal flow path through the basin and reaches the outlet in less than the normal detention time.


 
Signals - Types and Control
More...
A signal is an indicator that serves as a means of communication.  Mechanical types of controls are operated by media via floats, pulleys, and levers.  Hydraulic controls are operated by fluid, valve, and variable speed drives for pressure or flow control.  Pneumatic controls send electrical pulse duration.  Electronic controls use direct current in either milliamps or  voltage with 4 to 20 milliamps being the most common.


Slaking
More...
A process of converting quicklime to hydrated lime by adding water, as shown below:

Calcium oxide + Water Hydrated lime
CaO + H2O Ca (OH)2


Slaking requires specialized equipment.


Sludge
More...
The floc which settles to the bottom of the sedimentation basin and must be removed as waste. 

 

Slurry
More...
A mixture of PAC and water.

 

Soda Ash
More...
Soda ash is sodium carbonate (Na2CO3).  Soda ash is a chemical which acts as a buffer, neutralizing the pH of water.  

 

Sodium Fluoride
More...
A fluoridation chemical.  Sodium fluoride, or NaF, is a dry chemical which is easier to feed than other powdered fluoridation chemicals because it is more soluble in water.  Sodium fluoride was the first chemical used for fluoridation and is still used in small installations, but it is not generally used in large plants because of the high cost of chemicals and bulky saturators. 


 
Sodium Hexametaphosphate
More...
Sodium hexametaphosphate is a chemical also known as glassy phosphate, Calgon, and Sodium Polyphos. It is used in corrective treatment to form a protective coating on iron pipes, but may cause corrosion of copper pipes. 


Sodium Silicofluoride
More...
A fluoridation chemical.  Also known as sodium fluorosilicate and characterized by the formula Na2SiF6.  It has limited solubility which makes it difficult to dissolve and use.


Softener
More...
A type of filter used for ion exchange softening. 


Softening
More...
The process of removing hardness from water. 


Softening - Ion Exchange
More...
Ion exchange softening uses a softener to remove hardness from water. 


Softening - Lime
More...
Lime softening uses lime and sometimes soda ash to change the calcium and magnesium compounds in water into calcium carbonate and magnesium hydroxide, both of which will settle out of water. 


Solution
More...
A chemical in solution is completely dissolved in the water.  It is completely stable and will never settle out of the water.  Chemicals in solution are not visible, either using the naked eye or using a microscope, and are less than 1 Mu in size.  An example of a chemical in solution is sugar in water. 


Solution Feeders
More...
Equipment used to feed liquid chemicals into water. 


Stabilization
More...
Stabilization is the process of stabilizing water so that it is neither corrosive nor scale-forming. 


Stable Water
More...
Water in chemical balance, containing the concentration of calcium carbonate in which it will neither tend to precipitate out of the water (causing scale) nor dissolve into the water (causing corrosion.) 


Standard Operating Procedures
More...
Standard Operating Procedures, or SOP's, are written lists of the steps that should be followed in various circumstances to solve problems in water treatment plants. 


Sterilization
More...
Sterilization is the complete destruction of all organisms found in water.  Sterilization is usually expensive and unnecessary.  Most water is disinfected, not sterilized. 


Stilling Wall
More...
A type of sedimentation basin inlet which spans the entire basin from top to bottom and from side to side.  Water leaves the inlet and enters the settling zone of the sedimentation basin by flowing through the holes evenly spaced across the stilling wall.  Also known as a perforated baffle wall. 


Straining
More...
The removal of particles from water by passing the water through a filter in which the pores are smaller than the particles to be removed.


Stratification
More...
A problem in sedimentation basins which can cause short-circuiting.  Stratification occurs when the water in the basin separates into bands having different temperatures.  Incoming water will tend to flow through the band of water which corresponds to its own temperature, and will not spread throughout the rest of the basin. 


Streaming Current Monitor
More...
A streaming current monitor (SCM) is used to determine the appropriate dosage of coagulants to use.  The SCM uses an electric sensor to determine when charge neutralization has been reached in a suspension.


Superchlorination
More...
Adding a larger dosage of chlorine to water than is required for disinfection in order to oxidize taste and odor causing compounds.  Superchlorination can deal with fishy, grassy, or flowery odors and with iron and hydrogen sulfide but makes other problems worse and increases trihalomethane concentration. 


 
Surface Wash
More...
Surface wash uses spray to release particles trapped at the surface of the sand during backwash of a filter.


Suspended (Settleable) Solids
More...
Suspended, or settleable, solids will settle out of water over time, though this may be so slow that it is impractical to merely allow the particles to settle out in a water treatment plant.  The particles are more than 1,000 Mu in size and can be seen with a microscope or, sometimes, with the naked eye.  Examples of suspended solids include sand and heavy silts. 


 
Suspension Velocity
More...
Suspension velocity is the aggregation of particulate material in a two-step sequential process.


Taste and Odor
More...
Taste and odor in water are not usually hazardous to health, but cause numerous complaints and must be controlled. 


Taste and Odor - Treatment
More...
Treatment of taste and odor can include optimizing plant processes, ion exchange, air stripping, oxidation, or adsorption. 


 
Temperature
More...
Temperature is a measure of average random energy.


 
Testing
More...
Water quality is tested at various stages in the treatment process.  


 
Testing - Alkalinity
More...
Alkalinity testing is used to measure the ability of water to buffer an acid.


 
Testing - CO2
More...
Carbon dioxide testing uses a base to absorb carbon dioxide in ground water.  Determination is made by titrimetric method of sodium carbonate or sodium hydroxide to form sodium bicarbonate.  A completed reaction is indicated by color change of phenolphthalein at the equivalent pH of 8.3.


 
Testing - DO
More...
There are two methods for DO analysis available for use, the Winkler or iodometric and the electrometric using membrane electrodes.


 
Testing - pH
More...
pH is defined as the negative logarithm of the hydrogen ion concentration or activity, and it covers the acidity and alkalinity of solutions over a range of 0-14.


 
Testing - Turbidity
More...
Turbidity testing is based on a comparison of the intensity of light scattered by a standard reference suspension under the same conditions.  According to Standard Methods, the higher the intensity of scattered light, the higher the turbidity.


Threshold Odor Test
More...
Used to determine the amount of odor found in water.  During the procedure, the water being tested is diluted with odor-free water and is smelled.  The dilutions continue until no odor can be discerned.  The last dilution at which odor is detected determines the Threshold Odor Number (TON), which is a measure of the amount of odor in the water.

 

Time 
More...
Time plays an important role in every chemical reaction.


 
Time To Treat
More...
In order for water or sludge to receive treatment, it must be held for a certain amount of time.  Retention time refers to water treatment and detention time refers to sewage treatment.  Both are calculated the same way using the container/flow formula.


 
Total Alkalinity
More...
Total alkalinity is the capacity of water to neutralize acids.  It depends on the concentration of various buffers in the water. 


Total Hardness
More...
The sum of all hardness compounds in water, expressed as a calcium carbonate equivalent.  Total hardness includes both temporary and permanent hardness caused by calcium and magnesium compounds. 


Total Organic Carbon
More...
Total organic carbon, or TOC, is the amount of carbon bound in organic compounds in a water sample.


 
Toxins
More...
Toxins are regulated by the Clean Water Act and include carcinogenic compounds.


 
Trihalomethanes
More...
Trihalomethanes are compounds formed when natural organic substances from decaying vegetation and soil, such as humic and fulvic acids, react with chlorine.  The subsequent substances typically include the compounds of chloroform, bromodichloromethane, dibromochloromethane, and bromoform.  Trihalomethanes are suspected of being carcinogenic to humans.


Tube Settlers
More...
Tube settlers are used to increase settling efficiency and speed in sedimentation basins, especially where space is limited.  As water flows up through the slanted tubes, floc settles out and drifts back down into the lower portions of the sedimentation basin. 


Tuberculation
More...
The production of mounds of rust on the inside of the pipe as a result of corrosion. 


 
Turbidity
More...
Turbidity is the cloudy appearance of water caused by small particles suspended in the water.  Turbidity is treated with coagulation, flocculation, and then filtration.


Ultraviolet (UV) Light
More...
Ultraviolet, or UV, light is light outside the range usually detectable by the human eye.  UV light can be used to disinfect water. 


 
Valves
More...
Valves are devices in hydraulic systems that are used to restrict and/or allow movement of a liquid.


Van Der Waal's Forces
More...
The tendency of particles in nature to attract each other weakly if they have no charge.  Once coagulants neutralize the repellent forces between particles in water, Van der Waal's forces pull the particles together into floc. 


Velocity Gradient
More...
A measurement of the intensity of mixing in the flocculation or flash mix chamber.


Viscosity
More...
The resistance of water to flow due to internal molecular forces. 


Volatile
More...
A volatile material is one that is capable of being evaporated or changed to vapor at relatively low temperatures, meaning that it has a low boiling point.


 
Volume
More...
Volume is calculated using three dimensions; length, width, and height.  Volume units are given in cubes such as cubic feet or cubic meters.  One cubic foot is equal to 7.481 gallons.


Volumetric Feeders
More...
Equipment which feed a measured volume of dry chemical into water within a given time interval.


 
Waste
More...
Anything unused, unproductive, or not properly utilized;  anything left over or superfluous, as excess material or by products; has no value.


Weirs
More...
Walls preventing water from flowing uncontrolled into the launder of a sedimentation basin.   The weirs serve to skim the water evenly off the tank.


Weirs - Finger
More...
Finger weirs are an arrangement of launders which extend out into the settling basin.


Weirs - Loading
More...
Weir loading, also known as weir overflow rate, is the number of gallons of water passing over a foot of weir per day.  The standard weir overflow rate is 10,000 to 14,000 gpd/ft and should be less than 20,000 gpd/ft.  Longer weirs allow more water to flow out of the sedimentation basin without exceeding the recommended water velocity.


 
Zeta Potential
More...
Zeta potential is a measurement of the magnitude of electrical charge surrounding colloidal particles.  You can think of the zeta potential as the amount of repulsive force which keeps the particles in the water.  The more negative the zeta potential, the stronger the particle charge and the repelling force between particles and the more coagulants will be needed to produce floc.