The soaking up of one
substance into the body of another substance.
An accumulator is a device which can be attached to a valve to
dissipate the energy released when the valve is shut off abruptly.
A setup used to feed liquid fluoride directly into the water
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 is used to remove inorganic elements, such as
arsenic, from water.
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
The primary types of activated carbon are powdered activated carbon and
granular activated carbon.
|Activated Carbon - Types
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 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 is the intimate exposure of water to air. It is
a method used to treat a variety of problems in water.
Aerators are machines used to add air to water.
Air binding occurs
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
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 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.
A negatively charged particle.
A ring-shaped space between two pipes or between a pipe and a
The negatively charged portion of an electrolytic cell. The anode
gives up electrons.
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 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 is the time between each backwashing.
Bacteriology is the science that deals with the study of bacteria and
their relations to medicine, industry, agriculture, and water
A chart which shows the relationship between pH,
alkalinity, and water
During backwashing, the water pushes
the media up until it is suspended
in the water. The height to which the media rises during
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 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 is the process in coagulation that binds small particles
together into larger, heavier clumps which settle out relatively
An ion with a charge of +2.
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.
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
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
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.
|Calcium Carbonate Equivalent
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
|Calibration - Calibration Chart
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.
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
A catalyst is any substance that encourages a reaction without
being consumed in the process.
A cathode is the positively charged portion of an electrolytic
cell. The cathode accepts electrons.
introduction of a different electrical circuit into the pipe to
A positively charged particle.
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
Every chemical reaction results in a change of energy. The
reactive components may gain energy as they change into the product or
Every chemical compound has a certain amount of energy available for
release. The CRC Handbook lists the activity level of common
compounds and elements.
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
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.
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 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
for each of these chemicals has been achieved.
The chemistry of disinfection with chlorine depends on the form of
chlorine used and on whether or not the operator is practicing
The efficiency of chlorination is primarily dependent on the contact
time and on the concentration of chlorine residual.
|Chlorination - Efficiency
The equipment used during chlorination can include hypochlorinators,
chlorinators, and chlorine cylinders.
|Chlorination - Equipment
Chlorinators are machines which use liquid chlorine supplied in steel
cylinders to chlorinate water. They are most economical
in large systems.
The total amount of chlorine which is used up in
reactions with compounds in the water.
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 (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
2NaClO2 + Cl2
In addition to use as disinfectant, sodium chlorine is
used for taste and odor control.
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
system in order to prevent contamination.
A chlorine residual consisting of chlorine combined with nitrogen to
form a chloramine. Combined chlorine residuals are sometimes used
to disinfect water.
|Combined Chlorine Residual
The body of laws of a state or nation regulating ordinary private
matters, as distinct from laws regulating criminal, political, or
A square or circular sedimentation basin with horizontal flow. A
specific kind of clarifier, known as a solids-contact
solids-contact clarifier, or upflow
combines coagulation, flocculation, and sedimentation within a single
basin. Solids-contact clarifiers are often found in packaged
and in cold climates where sedimentation must occur indoors. This
clarifier is also often used in softening operations.
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 refers to the proximity of reactive components. This is
one of the four requirements for a chemical reaction.
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 include primary coagulants and coagulant
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.
|Coagulants - Primary
Coagulation is a step in the water treatment process in which the
particles in water are clumped together into larger particles, called
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
coliforms per hundred milliliters of water sampled.
Colloidal, or nonsettleable, solids do
not dissolve in water although they are electrically
charged. Still, the particles are so small that they will not
of the water even after several years and they cannot be removed by
filtration alone. Colloidal solids range between 1 and 500 Mu in
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
|Colloidal (Nonsettleable) Solids
Concentration of a chemical is the amount of the chemical in relation
to the volume of a container.
Treating the sludge to aid in thickening. The treatment may
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 is a measure of the ability of a solution to carry an
Provided by, in accordance with, or not prohibited by, 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
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
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 can be any substance considered undesirable in water and
are divided into two types, organic and inorganic.
The treatment of water to prevent corrosion in the pipes. This
often involves removing and/or neutralizing the free carbon
dioxide in the water.
The gradual deterioration of a substance or material by chemical or
electrochemical action which often results from exposure to moisture,
chemicals, or other agents.
Many characteristics influence the corrosiveness of water. These
include primary water characteristics, secondary water characteristics,
physical water characteristics, and bacteria.
|Corrosion - Causes
Corrosion results from an electrochemical reaction in the corrosion
|Corrosion - Chemistry
Testing for corrosion can involve noticing indicators such as red water
or carrying out long-term or short-term monitoring.
|Corrosion - Testing
Treatment for corrosion can include chemical treatment or physical
|Corrosion - Treatment
The various types of corrosion include internal, external,
electrolysis, oxygen concentration cell, and galvanic corrosion.
|Corrosion - Types
A coupon is a small section of metal inserted in a water line to test
for corrosion or scaling rate of a water system.
The laws of a state or country dealing with criminal offenses and their
Cryptosporidium is a parasite often found in the intestines of
livestock which contaminates water when the feces from the animal
with a water source.
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)
The Clean Water Act (CWA) constitutes the basic federal water pollution
control statute for the United States.
Density is the mass of a substance divided by the volume of the
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- 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
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.
|Deposition or Corrosion in Accordance with pH and
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:
Dewatering, or thickening, sludge is a drying process which makes the
sludge easier to transport away from the plant for disposal.
ceramic, or other non-conductive sections placed between two
different types of metal in a pipe. Since electrons cannot flow
dielectric coupling, it breaks the circuit and prevents
Filtration that follows
coagulation and flocculation, without sedimentation. This method
can be used when raw water has low turbidity.
Disease is a pathological or morbid condition, which exhibits certain
signs, symptoms, and clinical findings.
The process of selectively destroying or inactivating
pathogenic organisms in water, usually by chemical means.
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 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.
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.
Equipment used to feed dry chemicals into water.
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
Efficiency is the condition of being adequate in performance with a
minimum of waste or effort.
A trough which
collects the water flowing out of the sedimentation basin and directs
it to the effluent piping.
Electric charges on particles in water include electricity and van der
waal's forces. These charges will influence coagulation and
|Electric Charges on Particles
A softening process which involves
passing water between two plates with opposite electrical
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
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.
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.
which causes an electric current to flow. For example, a battery,
or a corrosion cell in a pipe.
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
|Empty Bed Contact Time
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
or stop extinction abroad.
|Endangered Species Act
An endothermic reaction is a chemical reaction in which energy is
An exothermic reaction is a chemical reaction in which energy is
Feed rate is the amount of chemical applied to a given system per unit
Seeding is the amount of microbes that are needed to metabolize a
certain amount of food.
|Feed Rates - Seeding
Cleaning a filter involves backwashing and surface washing.
Regulates flow rates of water through the rapid sand filter. Also
known as a controller.
|Filter Control System
The layers of materials in a filter which remove particles from the
water. Typical filter media include sand, anthracite, and
The length of time between each backwashing of a filter.
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.
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 - Efficiency
Four mechanisms remove particles from water during
filtration - biological action, adsorption, absorption, and
|Filtering - Mechanisms
Rapid sand filters, pressure filters, and slow sand filters are types
of filters which are used in different situations.
Fish eyes are large clumps of polymer which result from
inadequate flash mixing.
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.
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
|Flavor Profile Analysis
Floc are clumps of bacteria and other solids in water which have come
together to form a cluster.
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.
Water flows from the flash mix chamber into the flocculation
basin, where it is gently agitated to promote the formation of floc.
A flocculation chart predicts the amount of lime, alum, and /or polymer
floc in accordance with turbidity for a specific system or watershed.
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.
Channel flow uses the velocity of the water in the channel multiplied
by the cross sectional area to give the total flow:
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 - Container/Time
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.
|Flows - Differential Pressure
Flow from a pipe can be estimated using a few simple measurements.
|Flow - Estimating
There are many ways to measure flow. All flow is expressed in a
The Parshall flume can be used to measure flow in an open channel.
|Flow - Parshall Flume
Method of measuring flow in a pipe.
|Flow - Pressure Differential Meter
An ultrasonic flow meter uses sound waves to measure the resistance of
|Flows - Ultrasonic
A weir is an obstruction built across an open channel or
pipe over which the flow must pass.
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.
Dry feeders are used to feed dry chemicals into water. For
fluoridation, but volumetric and gravimetric feeders can be used.
|Fluoridation - Dry Feeders
Operation of a fluoridation system involves monitoring the system,
troubleshooting when problems arise, and ensuring that safety
procedures are followed.
|Fluoridation - Operation
Solution feeders are used to feed liquids into water. For
fluoridation, a variety of equipment may be associated with solution
|Fluoridation - Solution Feeders
Mottled brown stains on teeth resulting from excess fluoride
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.
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.
|Free Chlorine Residual
A type of corrosion caused by two dissimilar metals coming in contact
with each other.
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.
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.
|Granular Activated Carbon
Grates are mechanical devices designed to filter large objects
and prevent such objects from entering pipes and drain channels.
Gravimetric feeders feed dry chemicals by weight.
Water which contains a high concentration of calcium and magnesium
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
by water as it flows through a pipe or channel.
The organic part
of the soil which results from the decay of plant matter.
A chemical used in the lime softening process. Also known as
Ca(OH)2, calcium hydroxide, and slaked lime.
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 (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.
Hypochlorinators are used to feed hypochlorite solutions into water in
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, HOCl, is formed from the reaction of chlorine gas
with water. It is the most effective form of free chlorine
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.
An Imhoff cone is a clear, cone-shaped container used to measure the
volume of settleable solids in a specific volume of water.
Chemicals used to physically prevent corrosion by forming thin
protective films on pipe walls.
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
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
must be mixed with hard water to prevent softness problems in the
distributed water. The process is also known as zeolite
|Ion Exchange Softening
Nature is always treating water. Along streams there are
holding chambers that reduce the flow velocity and allows for
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
and water. Nature is continually renewing this precious resource.
An electrically charged particle.
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 tests are used to test the concentration of coagulant chemicals
added in the flash mix chamber.
A small-volume storage pond used to thicken sludge.
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.
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.
A model used to understand adsorption under a variety of
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 (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.
A pipe joining chlorine cylinders together
so that chlorine gas is drawn from several
cylinders at once.
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.
A metering pump feeds a wet solution
(a liquid) into the water by pumping a volume of solution with each
stroke or rotation.
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.
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
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
loss of filter capacity, since water will not pass through the mudballs
and must flow around them.
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.
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 problems are caused by external conditions such as
flooding, temperature change, icy conditions, pollution, and drought.
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 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
A type of corrosion caused by varying oxygen concentration in the
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.
|Oxygen Concentration Cell
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.
|Overview of Water Treatment
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.
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 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.
|Paddle Mixers(Propeller Flocculators)
Particle counters can be used to
count the number of particles in the filter effluent which are within
range of Giardia and Cryptosporidium to determine how
efficiently the filter has removed these microorganisms.
Pathogens are disease-causing organisms.
Very small floc which can be produced in low turbidity water and
removed by filtration.
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
Chemicals added to the filter influent to improve the
quality of the
effluent water by helping
the floc get caught in the filter.
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
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 is the
application of chlorine after water has been treated but before the
water reaches the distribution system. At this stage,
to kill pathogens and to provide a chlorine residual in the
distribution system. Postchlorination is nearly always part of
treatment process, either used in combination with prechlorination or
used as the sole disinfection process.
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.
|Powdered Activated Carbon
Power is defined as the amount of work done or energy transferred per
unit time. Power can be determined using the following equation:
Pressure × Flow
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
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.
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.
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.
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, 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.
Problems can be solved logically by following the problem-solving
Pumps are mechanical devices that are designed to transfer a non-solid
material (liquid, gas, or powder) from one location to another.
are used in solution feeders to feed a measured volume of a liquid
chemical during a specific time period. They have several
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.
|Pumps - Positive Displacement
A chemical which must be slaked before it is used in the lime softening
process. Also known as CaO, calcium oxide, or unslaked lime.
Radioactive substances which can be found in water.
A radioactive gas which may enter homes or water through the
The rate of a reaction is how fast a reaction occurs. The rate
depends on temperature, pressure, concentration, catalyst, and
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 are substances which have some ability or potential
for a reaction.
A reactor is any housing which contains a reaction. Reactors
isolate the reaction and optimize the conditions for the reaction.
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.
An external direct current source used in some cathodic protection
"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 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.
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 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.
Each pipe has a resistance value which refers to the roughness
of the interior of the pipe.
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
A type of softening process in which water is forced through a
Calcium, magnesium, and dissolved solids are captured while the
softened water is passed through the membrane.
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.
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
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
Stable compounds formed from the combination of cations with
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
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 are used to remove debris before water enters the treatment
One of the methods used by aerators to physically remove unwanted
components from water. Scrubbing action is caused by turbulence
between water and air.
A sedimentation basin is a basin or tank in which water is retained to
allow settleable matter, such as floc, to settle by gravity.
Efficiency of a sedimentation basin is influenced by many factors
including floc characteristics and short-circuiting.
|Sedimentation Basin - Efficiency
Each sedimentation basin has four zones - inlet, settling, outlet, and
|Sedimentation Basin - Zones
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.
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
send electrical pulse duration. Electronic controls use direct
current in either milliamps or voltage with 4 to 20 milliamps
being the most common.
|Signals - Types and Control
A process of converting quicklime to hydrated lime by adding water, as
Calcium oxide + Water
CaO + H2O →Ca (OH)2
Slaking requires specialized equipment.
The floc which settles to the bottom of the sedimentation basin and
must be removed as waste.
A mixture of PAC and water.
Soda ash is sodium carbonate (Na2CO3). Soda
ash is a chemical which acts as a buffer, neutralizing the pH of water.
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 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
A fluoridation chemical. Also known as
sodium fluorosilicate and characterized by the formula Na2SiF6. It has
solubility which makes it difficult to dissolve and use.
A type of filter used for ion exchange softening.
The process of removing hardness from water.
Ion exchange softening uses a softener to remove hardness from
|Softening - Ion Exchange
Lime softening uses lime and sometimes soda ash to change the calcium
magnesium compounds in water into calcium carbonate and magnesium
hydroxide, both of which will settle out of water.
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.
Equipment used to feed liquid chemicals into water.
Stabilization is the process of stabilizing water so that it is neither
corrosive nor scale-forming.
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
Standard Operating Procedures, or SOP's, are written
lists of the steps that should be followed in various circumstances to
problems in water treatment plants.
|Standard Operating Procedures
Sterilization is the complete
destruction of all organisms found in water. Sterilization is
usually expensive and unnecessary. Most water is disinfected, not
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
particles from water by passing the water through a filter in which the
pores are smaller than the particles to be removed.
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.
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
|Streaming Current Monitor
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 uses spray to release particles trapped at the surface of
the sand during backwash of a filter.
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.
|Suspended (Settleable) Solids
Suspension velocity is the aggregation of particulate material
in a two-step sequential process.
Taste and odor in water are not usually hazardous to health, but cause
numerous complaints and must be controlled.
Treatment of taste and odor can include optimizing plant processes, ion
exchange, air stripping, oxidation, or adsorption.
|Taste and Odor - Treatment
Temperature is a measure of average random energy.
Water quality is tested at various stages in the treatment process.
Alkalinity testing is used to measure the ability of water to buffer an
|Testing - Alkalinity
Carbon dioxide testing uses a base to absorb carbon dioxide in
ground water. Determination is made by titrimetric method of
carbonate or sodium hydroxide to form sodium bicarbonate. A
reaction is indicated by color change of phenolphthalein at the
pH of 8.3.
There are two methods for DO analysis available for use, the Winkler or
iodometric and the electrometric using membrane electrodes.
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.
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.
|Testing - Turbidity
Used to determine the amount of odor found in water. During the
procedure, the water being tested is diluted with odor-free water and
smelled. The dilutions continue until no odor can be
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.
|Threshold Odor Test
Time plays an important role in every chemical reaction.
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 is the capacity of water to neutralize acids. It
depends on the concentration of various buffers in the water.
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, or TOC, is the amount of carbon bound in organic
in a water sample.
|Total Organic Carbon
Toxins are regulated by the Clean Water Act and include carcinogenic
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
compounds of chloroform, bromodichloromethane, dibromochloromethane,
and bromoform. Trihalomethanes are suspected of being
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.
production of mounds of rust on the inside of the pipe as a result of
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, or UV, light is light
outside the range usually detectable by the human eye. UV light
can be used to disinfect water.
|Ultraviolet (UV) Light
Valves are devices in hydraulic systems that are used to restrict
and/or allow movement of a liquid.
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.
|Van Der Waal's Forces
A measurement of the
intensity of mixing in
the flocculation or flash mix chamber.
The resistance of water
to flow due to internal molecular forces.
A volatile material is one
capable of being evaporated or changed to vapor at relatively low
temperatures, meaning that it has a low boiling point.
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.
Equipment which feed a
measured volume of dry chemical into water within a given time interval.
Anything unused, unproductive, or not properly utilized;
anything left over or superfluous, as excess material or by products;
has no value.
Walls preventing water
from flowing uncontrolled into the launder of a sedimentation
basin. The weirs serve
to skim the water evenly off the tank.
Finger weirs are an
launders which extend out into the settling basin.
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
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
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.