i-263 315
:EPA
United States
Environmental Protection
Agency
Office of Public Affairs (A-107)
Washington, D C 20460
July 1976
A Primer
on Wastewater
Treatment
OOOK76001
U.S. Environmental Protection Agency
Region 5 Library (PL-12J)
77 West Jackson Blvd., 12th Roor
Chicago, IL 60604-3590
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TJnder the 1972 amendments to the
Federal Water Pollution Control
Act (Public Law 92-500), thousands of
municipal waste treatment plants are
being constructed or expanded across
the Nation to control or prevent water
pollution.
The 1972 law authorizes grants
totalling $18 billion to help towns and
cities construct waste treatment
facilities. The grants, which cover 75
percent of the cost of the facilities, were
to be awarded by September, 1977.
The law also established the National
Pollution Discharge Elimination
System which calls for limitations on
the amount and quality of effluents
and requires all municipal and
industrial dischargers to obtain
permits. The permits include effluent
clean-up dates which are enforceable
by State or Federal Government.
Further, the new law sets this goal:
water clean enough for swimming,
boating, and protection of fish,
shellfish, and wildlife by 1983.
Construction of the needed municipal
treatment plants won't happen
overnight. From drawing board to
operation takes time. But progress is
being made, and more and more
people are watching this progress. And
they want to know more about
wastewater treatment.
This primer explains the methods used
now and processes being developed for
the future to treat waste water
discharges and to give the Nation clean
water.
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COMBINED SYSTEM
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Collecting
and Treating Wastes
most common form of pollution
control in the United States consists
of a system of sewers and waste
treatment plants. The sewers collect
the waste water from homes,
businesses, and many industries and
deliver it to the plants for treatment to
make it fit for discharge into streams
or for reuse.
There are two kinds of sewer
systems—combined and separate.
Combined sewers carry away both
water polluted by human use and
water polluted as it drains off homes,
streets, or land during a storm.
In a separate system, one system of
sewers, usually called sanitary, carries
only sewage. Another system of storm
sewers takes care of the large volumes
of water from rain or melting snow.
Each home has a sewer or pipe which
connects to the common or lateral
sewer beneath a nearby street. Lateral
sewers connect with larger sewers
called trunk or main sewers. In a
combined sewer system, these trunk or
main sewers discharge into a larger
sewer called an interceptor. The
interceptor is designed to carry several
times the dry-weather flow of the
system feeding into it.
During dry weather when the sewers
are handling only the normal amount
of waste water, all of it is carried to the
waste treatment plant. During a storm
when the amount of water in the sewer
system is much greater, it may be
necessary to allow part of the water—
including varying amounts of raw
sewage—to bypass directly into the
receiving streams. The rest of the
wastes are sent to the treatment plant.
If part of the increased load of water
were not diverted, the waste treatment
plant would be overloaded and the
purifying processes would not function
properly. (Technology has been
developed that will, when applied,
control and treat the storm water
discharges and the general runoff of
rainwater polluted by dirt and other
contaminants.)
Separate system . . . storm sewer outfall
Interceptor sewers are also used in
sanitary sewer systems as collectors of
flow from main sewers and trunks, but
do not normally include provisions for
bypassing.
A waste treatment works' basic
function is to speed up the natural
processes by which water purifies itself.
In many cases, Nature's treatment
process in streams and lakes was
adequate before our population and
industry grew to their present size.
However, these natural processes, even
though accelerated in a waste
treatment plant, are not sufficient to
remove other contaminants such as
disease-causing germs, excessive
nutrients such as phosphates and
nitrates, and chemicals and trace
elements.
When the sewage of previous years
was dumped into waterways, the
natural process of purification began.
First, the sheer volume of clean water
in the stream diluted the small amount
of wastes. Bacteria and other small
organisms in the water consumed the
sewage or other organic matter,
turning it into new bacterial cells,
carbon dioxide, and other products.
But the bacteria normally present in
water must have oxygen to do their
part in breaking down the sewage.
Water acquires this all-important
oxygen by absorbing it from the air
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Basic Treatment
and from plants that grow in the water
itself. These plants use sunlight to turn
the carbon dioxide present in water
into oxygen.
The life and death of any body of
water depend mainly upon its ability
to maintain a certain amount of
dissolved oxygen. This dissolved
oxygen—or DO—is what fish breathe.
Without it they suffocate. If only a
small amount of sewage is dumped
into a stream, fish are not affected and
the bacteria can do their work; the
stream can quickly restore its oxygen
loss from the atmosphere and from
plants. Trouble begins when the
sewage load is excessive. The sewage
will decay and the water will begin to
give off odors. If carried to the
extreme, the water could lose all of its
oxygen, resulting in the death of fish
and beneficial plant life.
Since dissolved oxygen is the key
element in the life of water, the
demands on it are used as a measure in
telling how well a sewage treatment
plant is working. This measuring
device is called biochemical oxygen
demand, or BOD. If the effluent or the
end-product from a treatment plant
has a high content of organic
pollutants, the effluent will have a high
BOD. In other words, it will demand
more oxygen from the water to break
down the sewage and consequently will
leave the water with less oxygen (and
also dirtier).
With the growth of the Nation, the
problems of pollution have become
more complex. The increased amounts
of wastes and the larger demands for
water have reduced the capacity of
running water to absorb waste water
and purify itself. Consequently, cities
and industries have had to begin to
remove as much as possible of the
oxygen-demanding and other
pollutants from their sewage.
Adequate treatment of wastes along
with providing a sufficient supply of
clean water has become a major
concern.
At present there are two basic stages
in the treatment of wastes. They are
called primary and secondary. In the
primary stage of treatment, solids are
allowed to settle and are removed from
the water. The secondary stage uses
biological processes to purify the
waste water even further. In some
cases, the two stages may be combined
into one basic operation.
Primary Stage
As sewage enters a plant for treatment,
it flows through a screen. The screen
removes large floating objects such as
rags and sticks that may clog pumps
and small pipes. The screens vary from
coarse to fine—from those with
parallel steel or iron bars with
openings of about half an inch or more
to screens with much smaller openings.
Screens are generally placed in a
chamber or channel in an inclined
position to the flow of the sewage to
make cleaning easier. The debris
caught on the upstream surface of the
screen can be raked off manually or
mechanically.
Sedimentation tank
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Some plants use a device known as a
comminutor which combines the
functions of a screen and a grinder.
These devices catch and then cut or
shred the heavy solid material. In the
process, the pulverized matter remains
in the sewage flow to be removed later
in a settling tank.
After the sewage has been screened, it
passes into what is called a grit
chamber where sand, grit, cinders, and
small stones are allowed to settle to the
bottom. A grit chamber is highly
important for cities with combined
sewer systems because it will remove
the grit or gravel that washes off
streets or land during a storm and ends
up at treatment plants.
The unwanted grit or gravel from this
process is usually disposed of by filling
land near a treatment plant.
In some plants, another screen is
placed after the grit chamber to
remove any further material that might
damage equipment or interfere with
later processes.
With the screening completed and the
grit removed, the sewage still contains
dissolved organic and inorganic matter
along with suspended solids. The latter
consist of minute particles of matter
that can be removed from the sewage
by treatment in a sedimentation tank.
When the speed of the flow of sewage
through one of these tanks is reduced,
the suspended solids will gradually
sink to the bottom. This mass of solids
is called raw sludge.
Various methods have been devised for
removing sludge from the tanks.
In older plants, sludge removal was
done by hand. After a tank had been
in service for several days or weeks,
the sewage flow was diverted to
another tank. The sludge in the
bottom of the out-of-service tank was
pushed or flushed with water to a pit
near the tank, and then removed,
usually by pumping, for further
treatment or disposal.
Almost all plants built within the past
30 years have had a mechanical means
for removing the sludge from
sedimentation tanks. Some plants
remove it continuously while others
remove it at intervals.
To complete the primary treatment,
the effluent from the sedimentation
tank is chlorinated before being
discharged into a stream or river.
Chlorine gas is fed into the water to
kill and reduce the number of disease-
causing bacteria. Chlorination also
helps to reduce objectionable odors.
Basic treatment. . . primary stage
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In the past, 30 percent of the
municipalities in the United States did
not treat their sewage beyond the
primary stage. This amount of
treatment alone was inadequate to
meet today's water quality
requirements. To meet these
requirements, cities and industries will
have to remove even more
contaminants at the secondary stage,
and in some cases, use advanced
treatment.
Secondary Stage
The secondary stage of treatment
removes up to 90 percent of the
organic matter in sewage by making
use of the bacteria in it. The two
principal techniques used in the
secondary stage are trickling niters and
the activated sludge process.
After the effluent leaves the
sedimentation tank in the primary
stage of treatment, it flows or is
pumped to a facility using one or the
other of these processes. A trickling
filter is simply a bed of stones from
three to six feet deep through which
the sewage passes. Bacteria gather and
multiply on these stones until they can
consume most of the organic matter in
the sewage. The cleaner water trickles
out through pipes in the bottom of the
filter for further treatment.
The sewage is applied to the bed of
stones in two principal ways. One
method consists of distributing the
effluent intermittently through a
network of pipes laid on or beneath
the surface of the stones.
Attached to these pipes are smaller,
vertical pipes which spray the sewage
over the stones.
Another much-used method consists of
a vertical pipe in the center of the filter
connected to rotating horizontal pipes
which spray the sewage continuously
upon the stones.
From the trickling filter, the sewage
flows to another sedimentation tank to
remove the bacteria. Chlorination of
the effluent completes the secondary
stage of basic treatment.
The trend today is toward the use of
the activated sludge process instead of
trickling filters. This process speeds up
the work of the bacteria by bringing
air and sludge heavily laden with
bacteria into close contact with the
sewage.
After the sewage leaves the settling
tank in the primary stage, it is pumped
to an aeration tank where it is mixed
with air and sludge loaded with
bacteria and allowed to remain for
several hours. During this time, the
bacteria break down the organic
matter.
The sludge, now activated with
additional millions of bacteria and
AIR
Secondary stage . . . activated sludge process
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other tiny organisms, can be used again
by returning it to an aeration tank for
mixing with new sewage and ample
amounts of air.
The activated sludge process, like most
other techniques, has advantages and
limitations. The size of the units
necessary for this treatment is small,
thereby requiring less land space and
Trickling filter
Aeration tank
the process is free of flies and odors.
But it is more costly to operate than
the trickling filter, and the activated
sludge process sometimes loses its
effectiveness when faced with complex
industrial wastes.
An adequate supply of oxygen is
necessary for the activated sludge
process to be effective. Air is mixed
with sewage and biologically active
sludge in the aeration tanks by three
different methods.
The first, mechanical aeration, is
accomplished by drawing the sewage
from the bottom of the tank and
spraying it over the surface, thus
causing the sewage to absorb large
amounts of oxygen from the
atmosphere.
In the second method, large amounts
of air under pressure are piped down
into the sewage and forced out
through openings in the pipe. The
third method is a combination of
mechanical aeration and the forced air
method.
From the aeration tank, the sewage
flows to another sedimentation tank to
remove the bacteria.
The final step again consists of the
addition of chlorine—the most
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common method of disinfection—to
the effluent coming from the trickling
filter or activated sludge process.
Chlorine is usually purchased in liquid
form, converted to a gas, and injected
into the effluent 15 to 30 minutes
before the treated water is discharged
into a water course. If done properly,
chlorination will kill more than 99
percent of the harmful bacteria in an
effluent.
Lagoons
Lagoons, or as they are sometimes
called, stabilization or oxidation ponds
also have several advantages when
used correctly.
They can be used to treat sewage to the
secondary stage of treatment or they
can be used to supplement other
processes.
A lagoon is a scientifically constructed
pond usually three to five feet deep, in
which sunlight, algae, and oxygen
interact to restore water to a quality
that is often equal to effluent from the
secondary treatment stage. Changes in
the weather may change the
effectiveness of lagoons.
When used with other basic waste
treatment processes, lagoons can be
very effective. A good example of this
is the Santee, California, water
reclamation project. After
conventional basic treatment by
activated sludge, the town's waste
water is kept in a lagoon for 30 days.
Then the effluent, after chlorination, is
pumped to land immediately above a
series of lakes and allowed to trickle
down through sandy soil into the
lakes. The resulting water is of such
good quality, the residents of the area
can swim, boat, and fish in the lake
water.
Sewage treatment lagoons
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Septic Tanks
A septic tank is simply a tank buried
in the ground to treat the sewage from
an individual home. Waste water from
the home flows into the tank where
bacteria in the sewage may break
down the organic matter and the
cleaner water flows out of the tank
into the ground through sub-surface
drains. Periodically the sludge or solid
matter in the bottom of the tank must
be removed and disposed of.
In a rural setting, with the right kind
of soil and the proper location, the
septic tank may be a reasonable and
temporary means of disposing of
strictly domestic wastes. Septic tanks
should always be located so that none
of the effluent can seep into sources
used for drinking.
Operation and Maintenance
Wastewater treatment plants can clean
the Nation's waters and prevent
pollution. But to accomplish this
purpose, they must be maintained and
operated efficiently.
EPA studies have shown that many
wastewater treatment plants are not
meeting water quality requirements.
The most common reason for this
failure is poor operation and
maintenance. A sufficient number of
well-trained operators and
maintenance people and a well-
equipped water-testing laboratory will
assure an efficient operation and a
satisfactory reduction of pollutants.
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The Need
for Further Treatment
of Wastes
Tn the past, pollution control was
concerned primarily with problems
caused by domestic and the simpler
wastes of industry. Control was aimed
principally towards protecting
downstream public water supplies and
stopping or preventing nuisance
conditions.
Pollution problems were principally
local in extent and their control a local
matter.
This is no longer true. National growth
and change have altered this picture.
Progress in abating pollution has been
outdistanced by population growth,
the speed of industrial progress and
technological developments, changing
land practices, and many other factors.
The increased production of goods has
greatly increased the amounts of
common industrial wastes. New
processes in manufacturing are
producing new, complex wastes that
sometimes defy present pollution
control technology. The increased
application of commercial fertilizers
and the development and widespread
use of a vast array of new pesticides
are resulting in a host of new pollution
problems from water draining off land.
The growth of the nuclear energy field
and the use of radioactive materials
foreshadow still another complicating
and potentially serious water pollution
situation.
Long stretches of both interstate and
intrastate streams are subjected to
pollution which ruins or reduces the
use of the water for many purposes.
Conventional biological waste
treatment processes are hard-pressed
to hold the pollution line and for a
growing number of our larger cities
these processes are no longer adequate.
Our growing population not only is
packing our central cities but
spreading out farther and farther into
suburbia and exurbia. Across the
country, new satellite communities are
being born almost daily. The
construction or extension of sewer
lines has sometimes not matched either
the growth rate or changes in growth
patterns. Sea water intrusion is a
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growing problem in coastal areas. It is
usually caused by the excessive
pumping of fresh water from the
ground which lowers the water level,
allowing salt water to flow into the
ground water area.
The Types of Pollutants
Present day problems that must be met
by sewage treatment plants can be
summed up in eight types of pollutants
affecting our waters.
The eight general categories are:
common sewage and other oxygen-
demanding wastes; disease-causing
agents; plant nutrients; synthetic
organic chemicals; inorganic chemicals
and other mineral substances;
sediments; radioactive substances; and
heat.
Oxygen-demanding wastes — These are
the traditional organic wastes and
ammonia contributed by domestic
sewage and industrial wastes of plant
and animal orgin. Besides human
sewage, such wastes result from food
processing, paper mill production,
tanning, and other manufacturing
processes. These wastes are usually
destroyed by bacteria if there is
sufficient oxygen present in the water.
Since fish and other aquatic life
depend on oxygen for life, the oxygen-
demanding wastes must be controlled,
or the fish die.
Disease-causing agents —This category
includes infectious organisms which
are carried into surface and ground
water by sewage from cities and
institutions, and by certain kinds of
industrial wastes, such as tanning and
meat packing plants. Man or animals
come in contact with these microbes
either by drinking the water or
through swimming, fishing, or other
activities. Although modern
disinfection techniques have greatly
reduced the danger of this type of
pollutant, the problem must be
watched constantly.
Plant nutrients —These are the
substances in the food chain of aquatic
Industrial wastes
Domestic sewage
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Algae
Chemicals
Acid drainage
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Sediment
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life, such as algae and water weeds,
which support and stimulate their
growth. Carbon, nitrogen and
phosphorus are the three chief
nutrients present in natural water.
Large amounts of these nutrients are
produced by sewage, certain industrial
wastes, and drainage from fertilized
lands. Biological waste treatment
processes do not remove the
phosphorus and nitrogen to any
substantial extent—in fact, they
convert the organic forms of these
substances into mineral form, making
them more usable by plant life. The
problem starts when an excess of these
nutrients over-stimulates the growth of
water plants which cause unsightly
conditions, interfere with treatment
processes, and cause unpleasant and
disagreeable tastes and odors in the
water.
Synthetic organic chemicals—Included
in this category are detergents and
other household aids, all the new
synthetic organic pesticides, synthetic
industrial chemicals, and the wastes
from their manufacture. Many of these
substances are toxic to fish and aquatic
life and possibly harmful to humans.
They cause taste and odor problems,
and resist conventional waste
treatment. Some are known to be
highly poisonous at very low
concentrations. What the long-term
effects of small doses of toxic
substances may be is not yet known.
Inorganic chemicals and mineral
substances—A vast array of metal
salts, acids, solid matter, and many
other chemical compounds are
included in this group. They reach our
waters from mining and
manufacturing processes, oil field
operations, agricultural practices, and
natural sources. Water used in
irrigation picks up large amounts of
minerals as it filters down through the
soil on its way to the nearest stream.
Acids of a wide variety are discharged
as wastes by industry, but the largest
single source of acid in our water
comes from mining operations and
mines that have been abandoned.
Many of these types of chemicals are
being created each year. They interfere
with natural stream purification;
destroy fish and other aquatic life;
cause excessive hardness of water
supplies; corrode expensive water
treatment equipment; increase
commercial and recreational boat
maintenance costs; and boost the cost
of waste treatment.
Sediments—These are the particles of
soils, sands, and minerals washed from
the land and paved areas of
communities into the water.
Construction projects are often large
sediment producers. While not as
insidious as some other types of
pollution, sediments are a major
problem because of the sheer
magnitude of the amount reaching our
waterways. Sediments fill stream
channels and harbors, requiring
expensive dredging, and they fill
reservoirs, reducing their capacities
and useful life. They erode power
turbines and pumping equipment, and
reduce fish and shellfish populations
by blanketing fish nests and food
supplies.
More importantly, sediments reduce
the amount of sunlight penetrating the
water. The sunlight is required by
green aquatic plants which produce the
oxygen necessary to normal stream
balance. Sediments greatly increase the
treatment costs for municipal and
industrial water supply and for sewage
treatment where combined sewers are
in use.
Radioactive substances— Radioactive
pollution results from the mining and
processing of radioactive ores; from
the use of refined radioactive materials
in power reactors and for industrial,
medical, and research purposes; and
from fallout following nuclear
weapons testing. Increased use of these
substances poses a potential public
health problem. Since radiation
accumulates in humans, control of this
type of pollution must take into
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consideration total exposure in the
human environment—water, air, food,
occupation, and medical treatment,
Heat—Heat reduces the capacity of
water to absorb oxygen. Tremendous
volumes of water are used by power
plants and industry for cooling. Most
of the water, with the added heat, is
returned to streams, raising their
temperatures. With less oxygen, the
water is not as efficient in assimilating
oxygen-consuming wastes and in
supporting fish and aquatic life.
Unchecked waste heat discharges can
seriously alter the ecology of a lake, a
stream, or even part of the sea.
Water in lakes or stored in
impoundments can be greatly affected
by heat. Summer temperatures heat up
the surfaces, causing the water to form
into layers, with the cooler water
forming the deeper layers.
Decomposing vegetative matter from
natural and man-made pollutants
deplete the oxygen from these cooler
lower layers with harmful effects on
the aquatic life. When the oxygen-
deficient water is discharged from the
lower gates of a dam, it may have
serious effects on downstream fish life
and reduce the ability of the stream to
assimilate downstream pollution.
To complicate matters, most of our
wastes are a mixture of the eight types
of pollution, making the problems of
treatment and control that much more
difficult.
Municipal wastes usually contain
oxygen-consuming pollutants,
synthetic organic chemicals such as
detergents, sediments, and other types
of pollutants. The same is true of
many industrial wastes which may
contain, in addition, substantial
amounts of heat from cooling
processes. Water that drains off the
land usually contains great amounts of
organic matter in addition to sediment.
Also, land drainage may contain
radioactive substances and pollutants
washed from the sky, vegetation,
buildings, and streets during rainfall.
Thermal pollution
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Advanced Methods
of Treating
Wastes
These new problems of a modern
society have placed additional
burdens upon our waste treatment
systems. Today's pollutants are more
difficult to remove from the water.
And increased demands upon our
water supply aggravate the problem.
During the dry season, the flow of
rivers decreases to such an extent that
they have difficulty in assimilating the
effluent from waste treatment plants.
In the future, these problems will be
met through better and more complete
methods of removing pollutants from
water and better means for preventing
some wastes from even reaching our
streams in the first place.
The best immediate answer to these
problems is the widespread application
of existing waste treatment methods.
Many cities still do not treat their
sewage beyond the primary treatment
stage. Many other cities need enlarged
or modernized systems to treat
waste water at the secondary stage. But
this only a temporary solution. The
discharge of oxygen consuming wastes
will increase despite the nationwide
addition of the secondary stage of
wastewater treatment. And these are
the simplest wastes to dispose of.
Conventional treatment processes are
already losing the battle against the
modern-day, tougher wastes.
The increasing need to reuse water
now calls for better and better waste
treatment. Every use of water—
whether at home, in the factory, or on
the farm—results in some change in its
quality.
To return water of more usable quality
to receiving lakes and streams, new
methods for removing pollutants are
being developed. The advanced waste
treatment techniques under
investigation range from extensions of
biological treatment capable of
removing nitrogen and phosphorus
nutrients to physical-chemical
separation techniques such as
adsorption, distillation, and reverse
osmosis.
These new processes can achieve any
degree of pollution control desired
and, as waste effluents are purified to
higher and higher degrees by such
treatment, the point is reached where
effluents become "too good to throw
away."
Advanced wastewater treatment plant
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Such water can be deliberately and
directly reused for agricultural,
industrial, recreational, or even
drinking water supplies. This complete
water renovation will mean complete
pollution control and at the same time
more water for the Nation.
Land Application
Land application is one method of
advanced wastewater treatment that
can remove pollutants not removed in
basic treatment, and in some cases,
reuse or renovate the waste water.
Municipal waste water has been used to
irrigate crops around the country, but
primarily in the arid western states.
Land application of industrial
waste water has also been tried but
mainly in a few eastern states. In land
application three techniques are used:
crop irrigation, rapid infiltration,
overland flow, or a combination of the
three.
Irrigation
In the case of crop irrigation (or slow
rate infiltration) the wastewater
penetrates into the ground where the
natural filtering and straining action of
the soil removes most of the
pollutants. The water eventually
percolates to the groundwater,
evaporates, or is absorbed by plants.
Crop irrigation is one land application
method that reuses the water, and the
minerals and nutrients in it. It is the
most commonly used land application
technique. The waste water is
sometimes disinfected before being
used for crop irrigation, depending on
the end use of the crop. The
waste water is applied to the land by
spraying, flooding, or ridge and furrow
irrigation, to supply water and
nutrients to the crops. The irrigation
method selected depends on cost
considerations, terrain, and the crops
grown. Much of the water and most of
the nitrogen are absorbed by the
plants. The remaining water
evaporates or percolates to the
groundwater. Phosphorous and trace
elements are removed to the soil by
adsorption.
Rapid-Infiltration
Unlike slow rate systems, the rapid
infiltration process is used mainly to
treat and recover waste water for reuse.
Since the rapid infiltration process is
the simplest land application
technique, and is effective in cold or
wet weather, it has been used
frequently in the northeastern states.
Large amounts of waste water are
applied to a limited land area and
allowed to infiltrate the ground's
surface and percolate through the soil
below. If the water is to be reused, it
EVAPORATION
SPRAY OR VVNN
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Flood irrigation
Spray irrigation
Ridge and furrow irrigation
can be recovered by drilling wells to
draw it to the surface. Normally,
however, the water will seep
downward to the goundwater. Because
this process depends on the soil's
ability to absorb a large amount of
water quickly and efficiently, good soil
drainage is important. Impervious soils
may be better suited to the overland
flow process.
Overland Flow
This method has been used
successfully in the food processing
industries to remove bacteria and
nutrients from waste water. And it has
been used to a limited extent in
treating municipal waste water for
many years.
The waste water is allowed to flow
down a sloped surface that is planted
with vegetation to control runoff and
erosion. As the water runs down the
slope, the soil and its micro-organisms
remove the bacteria and nutrients.
Most of the water is recovered at the
bottom of the slope for reuse. The
remainder evaporates. This process is
well suited to clay or clay-type soils
with little or no absorption capacity.
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Whatever method is used, land
application may be an economic
alternative to more costly advanced
treatment plants. Further study is
underway to evaluate the costs more
accurately. Research is also being
conducted to determine what levels of
nutrients and trace elements can be
allowed to build up in the soil without
harming agricultural plants, or posing
health hazards where the crops may
enter the human food chain.
EVAPORATION
SPRAY OR
SURFACE
APPLICATION
Coagulation—Sedimentation
The application of advanced
techniques for waste treatment, at least
in the next several years, will most
likely take up where primary and
secondary treatment leave off.
Ultimately, entirely new systems will
no doubt replace the modern facilities
of today.
The process known as coagulation-
sedimentation may be used to increase
the removal of solids from effluent
after primary and secondary
treatment. Besides removing essentially
all of the settleable solids, this method
can, with proper control and sufficient
addition of chemicals, reduce the
concentration of phosphate by over 95
percent.
In this process, alum, lime, or iron
salts are added to effluent as it comes
from the secondary treatment. The
flow then passes through flocculation
CHEMICAL
Overland flow
EVAPORATION
Coagulation-Sedimentation
Rapid infiltration
16
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tanks where the chemicals cause the
smaller particles to floe or bunch
together into large masses.
The larger masses of particles or lumps
will settle faster when the effluent
reaches the next step—the
sedimentation tank.
Although used for years in the
treatment of industrial wastes and in
water treatment, coagulation-
sedimentation is classified as an
advanced process because it is not
usually applied to the treatment of
municipal wastes. In many cases, the
process is a necessary pre-treatment
for some of the other advanced
techniques.
Adsorption
Technology has also been developed to
effect the removal of refractory organic
materials. These materials are the
Adsorption
stubborn organic matter which persists
in water and resists normal biological
treatment.
The effects of the organics are not
completely understood, but taste and
odor problems in water, tainting of
fish flesh, foaming of water, and fish
kills have been attributed to such
materials.
Adsorption consists of passing the
effluent through a bed of activated
carbon granules which will remove
more than 98 percent of the organics.
To cut down the cost of the procedure,
the carbon granules can be cleaned by
heat and used again.
Except for the salts added during the
use of water, municipal waste water
that has gone through the previous
advanced processes will be restored to
a chemical quality almost the same as
before it was used.
When talking of salts in water, salt is
not limited to the common kind that is
used in the home for seasoning food.
In waste treatment language, salts
mean the many minerals dissolved by
water, as it passes through the air as
rainfall, as it trickles through the soil
and over rocks, and as it is used in the
home and factory.
Electrodialysis
Electrodialysis is a rather complicated
process by which electricity and
membranes are used to remove salts
from an effluent. A membrane is
usually made of chemically treated
plastic. The salts are forced out of the
water by the action of an electric field.
When a mineral salt is placed in water
it has a tendency to break down into
ions. An ion is an atom or a small
group of atoms having an electrical
charge.
As a city uses its water, the amount of
salts in the water increases by 300-400
milligrams per liter. Fortunately,
electrodialysis can remove this buildup
of salts.
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Electrodialysis
Blending water
In other words, this process returns the
salt content of the water to where it
was or even better than when the city
first received the water.
The Blending of Treated Water
Properly designed and applied, the
methods that have been explained will
be able to supply any quality of water
for any reuse.
But none of these processes will stand
alone. They must be used in a series or
a parallel plan. In a series, all the
sewage passes through all the
processes, one after another, each
process making a particular
contribution toward improving the
water. For example, the conventional
primary stage of treatment removes
the material that will readily settle or
float; the secondary biological step
takes care of the decomposable
impurities; coagulation-sedimentation,
the third step, eliminates the
suspended solids; carbon adsorption
removes the remaining dissolved
organic matter; electrodialysis returns
the level of the salts to what it was
before the water was used; and, finally,
chlorination provides the health safety
barrier against disease carriers.
Basically the same result can be
achieved by separating the effluent into
two streams. In this instance, all of the
waste receives the basic treatment and
then passes through the coagulation-
sedimentation and adsorption
processes which remove the organic
matter. Half of the sewage is then
treated by evaporation and adsorption
to remove all impurities including the
minerals. This effluent, when blended
with the other half, can provide water
with the desired level of minerals.
After chlorination, the water can be
reused for industrial purposes.
Almost any degree of water quality
can be achieved by varying the flow of
the two streams. This technique
reduces the treatment cost, since only a
fraction of the flow requires treatment
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with the more expensive unit
processes, such as distillation.
Distillation or evaporation basically
consists of bringing the effluent to the
boiling point. The steam or vapor
produced is piped to another chamber
where it is cooled, changing it back to
a liquid. Most of the unwanted
polluting impurities remain in the
original chamber. However, some
volatile substances may distill along
with the water and carry along foreign
materials that contribute objectionable
taste.
As most people have discovered,
distilled water has a flat, disagreeable
taste caused by the absence of minerals
and air. But by blending this pure
water with water that still contains
some minerals, a clean, better tasting
water results. And just as importantly,
the more expensive distillation process
is used on only part of the effluent, and
the rest of the waste water is treated by
the less costly procedures.
Denitrification plants can remove
excess nitrogen in advanced treatment
Wastewater filtration unit in the coagulation-sedimentation process
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New Challenges
for Waste Treatment
Co far, the most readily available
processes that will solve most
current pollution problems have been
covered. But the future holds many
new challenges. Scientists are still
looking for the ultimate system that
will do the complete job of cleaning up
water, simply and at a reasonable cost.
One such possible process under study
is reverse osmosis. When liquids with
different concentrations of mineral
salts are separated by a membrane,
molecules of pure water tend to pass
by osmosis from the more
concentrated to the less concentrated
side until both liquids have the same
mineral content.
Scientists are now exploring ways to
take advantage of the natural
phenomena of osmosis, but in reverse.
When pressure is exerted on the side
with the most minerals, this natural
force reverses itself, causing the
molecules of pure water to flow out of
the compartment containing a high
salt concentration.
This means that perfectly pure water is
being taken out of the waste, rather
than taking pollutants out of water as
is the traditional way. And this process
takes clean water away from
everything—bacteria, detergents,
nitrates.
Tests have shown that the theory
works well, resulting in water good
enough to drink. Efforts are now
under way to develop large membranes
with long life. Also, the process and
equipment need to be tested on a large
scale.
Many other techniques to improve
waste treatment are under
development in laboratories and in the
field.
For example, in denitriflcation, special
microscopic organisms are being
tested for removing nitrates from
waste water by reducing the nitrates
to elemental nitrogen.
Reverse osmosis
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Chemical Oxidation
Municipal waste waters contain many
organic materials only partially
removed by the conventional
treatment methods. Oxidants such as
ozone and chlorine have been used for
many years to improve the taste and
odor qualities or to disinfect municipal
drinking water. They improve the
quality of water by destroying or
altering the structure of the chemicals
in the water.
However, the concentration of the
organic materials in drinking water
supplies is much less than it is in the
waste-bearing waters reaching
treatment plants. Until recently, the
cost of the oxidants has prevented the
use of this process in the treating of
wastes. When operated in
conjunction with other processes,
oxidation could become an effective
weapon in eliminating wastes resistant
to other processes.
Polymers and Pollution
In discussing the coagulation-
sedimentation process, mention was
made of the use of chemicals to force
suspended solids into larger masses.
The clumping together helps speed up
one of the key steps in waste
treatment—the separation of solids
and liquids.
During the past 10 to 15 years, the
chemical industry has been working on
synthetic organic chemicals, known as
polyelectrolytes or polymers, to further
improve the separation step.
Formerly, polymers have proved
effective when used at a later stage of
treatment—the sludge disposal step.
Sludge must be dewatered so that it
can be more easily disposed of. By
introducing polymers into the sludge,
the physical and chemical bonds
between the solids are tightened. When
this happens, the water can be
extracted more rapidly.
Wider use of polymers is now being
investigated. By putting polymers into
streams or rivers, it may be possible to
capture silt at specified locations so
that it can be removed in quantity.
If polymers are put into raw sewage,
waste treatment plants may be able to
combine a chemical process with the
standard primary and secondary
stages. And this method of removing
solids can be applied immediately
without lengthy and expensive
addition of buildings or new facilities.
The chemicals also hold promise as a
means of speeding the flow of waste
waters through sewer systems, thus, in
effect, increasing the capacity of
existing systems.
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The Use or Disposal
of Wastewater Treatment
Residues
"Mlo matter how good the treatment of
wastes, there is always something
left over. It may be the rags and sticks
that were caught on the screens at the
very beginning of the primary
treatment. It could be brine or it could
be sludge—that part of the sewage
that settles to the bottom in
sedimentation tanks. Whatever it is,
there is always something that must be
reused, burned, buried, or disposed of
in some manner.
The management of these wastewater
treatment residuals is a twofold
problem. The sludge or other matter
must be disposed of to complete a
city's or industry's waste treatment
efforts. And it must be done in a
manner not to upset the rest of the
environment.
If it is burned, it must be done in a
way not to add to the pollution of the
atmosphere. This would only create an
additional burden for our already
over-burdened air to cope with. And
air pollutants by the action of rain and
wind have a habit of returning to the
water, further complicating the waste
treatment problem.
The requirements of the Federal Water
Pollution Control Act Amendments of
1972 (PL 92-500) emphasize the need
to employ environmentally sound
sludge management techniques. At the
same time, the national requirements
for improved wastewater treatment
will result in the production of a
greater quantity of residuals. And
possibly more concentrated forms of
contaminants will be present in these
residuals than ever before. As much as
40 percent of the construction grant
funds for individual treatment plants
provided under PL 92-500 may be
required to build adequate sludge
management facilities. In addition, the
permits required for effluent discharge
from sewage treatment plants can in
some cases be affected by the sludge
management techniques employed by
the facilities.
There are many methods and processes
for dealing with the "ultimate
disposal" of wastewater treatment
residuals. In general, the various
techniques involve either direct
resource recovery from or beneficial
uses of the residuals.
One of the most common disposal
methods consists of digestion followed
by filtration and incineration. The
Sludge drying beds
22
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digestion of sludge takes place in
heated tanks where the material can
decompose naturally and the odors
can be controlled. As digested sludge
consists of 90 to 95 percent water, the
next step in disposal must be the
removal of as much of the water as
possible.
Water can be removed from sludge by
use of a rotating filter drum and
suction. As the drum rotates, the water
is filtered out of the sludge and the
residues are peeled off for disposal.
For more effective dewatering, the
sludge can be first treated with a
coagulant chemical such as lime or
ferric chloride to produce larger solids
before the sludge reaches the filter.
Drying beds which are usually made of
layers of sand and gravel can be used
to remove water from sludge. The
sludge is spread over the bed and
allowed to dry. After a week or two of
drying, the residue will be reduced in
volume and, consequently, will be
easier to dispose of.
Incineration consists of burning the
dried sludge to reduce the residues to a
non-burnable ash. The ash can be
disposed of by filling unused land.
Since most of the pollutants have been
removed by the burning, the ash
should cause very little nuisance.
In 1974, 5,676,000 tons of sewage
sludge were disposed in the oceans.
The Marine Protection, Research, and
Sanctuaries Act of 1972 authorized
EPA to regulate this kind of ocean
disposal. Accordingly, EPA
implemented a permit program in late
1973 to limit the amounts and kinds of
wastes that can be dumped at sea.
A very promising new approach to
sludge management gets rid of the
unwanted sludge and helps restore
ravaged countrysides, where tops of
hills and mountains were sliced away
to get at the coal beneath. This strip
'mining left ugly gashes and scars in
otherwise beautiful areas of some
Municipal sludge may be composted
for use as a soil enricher
Rotating drum filter
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Treated sludge may be used as fertilizer for some agricultural crops
States. It would take nature many
years to repair the damage.
Under a new sludge management
approach, digested sludge in semi-
liquid form is piped to the spoiled
areas. The slurry, containing nutrients
from the wastes, is spread over the
land to give nature a hand in returning
grass, trees, and flowers to barren
land.
Restoration of the countryside will
also help control the flow of acids that
drain from mines into streams and
rivers, endangering fish and other
aquatic life and adding to the difficulty
of reusing the water.
Sludge or other waste concentrates are
not always costly burdens. By drying
and other processes, some cities have
produced fertilizers from sludge which
are sold to help pay part of the cost of
treating wastes. Some municipalities
use the soil enrichers on parks, road
parkways, and other public areas.
Some industries have found they can
reclaim certain chemicals during waste
treatment processes and reuse them.
Other firms have developed saleable
by-products from residues of waste
treatment.
More studies are underway to find
other beneficial uses for sludge and to
help solve the problem of what to do
with increasing volumes of wastewater
treatment residuals—and to help offset
the cost of waste treatment.
24
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jmmon Waste
eatment
jrminology
tivated Sludge process removes
,anic matter from sewage by
uratmg it with air and adding
ilogically active sludge.
sorption is an advanced way of
atmg wastes in which activated
•bon removes organic matter from
ste water.
ration Tank serves as a chamber
• injecting air into water.
gae are plants which grow in sunlit
ters. They are a food for fish and
iall aquatic animals and, like all
mts, put oxygen in the water
cteria are small living organisms
uch often consume the organic
nstituents of sewage.
ID, or biochemical oxygen de-
ind, is the dissolved oxygen
uired by organisms for the aerob-
decomposition of organic matter
;sent in water It is used as a
:asure in determining the efficiency
a sewage treatment plant or to
termme the potential of an effluent
degrade a stream.
ilorinator is a device for adding
lorine gas to sewage to kill
'ectious germs
jagulation is the clumping together
solids to make them settle out of
e sewage faster. Coagulation of
lids is brought about with the use
certain chemicals such as lime,
um and iron salts.
mibined Sewer carries both sewage
id storm water run-off.
smminutor is a device for the
tchmg and shredding of heavy
lid matter in the primary stage of
aste treatment.
iffused Air is a technique by which
r under pressure is forced into
•wage in an aeration tank. The air is
umped down into the sewage
irough a pipe and escapes out
irough holes in the side of the pipe.
Digestion of sludge takes place in
tanks when the materials decompose,
resulting in partial gasification,
liquefaction, and mineralization of
pollutants.
Distillation in waste treatment con-
sists of heating the effluent and then
removing the vapor or steam. When
the steam is returned to a liquid it is
almost pure water. The pollutants
remain in the concentrated residue.
Effluent is the liquid that comes out
of a treatment plant after completion
of the treatment process.
Eutrophication: The normally slow
aging process by which a lake evolves
into a bog or marsh and ultimately
assumes a completely terrestrial state
and disappears During eutrophica-
tion the lake becomes so rich in
nutritive compounds, especially ni-
trogen and phosphorus, that algae
and other microscopic plant life
become super-abundant, thereby
"choking" the lake, and causing it
eventually to dry up Eutrophication
may be accelerated by many human
activities
Floe is a clump of solids formed in
sewage by biological or chemical
action
Flocculation is the process by which
clumps of solids in sewage are made
to increase in size by chemical,
physical, or biological action.
Fungi are small, non-chlorophyll-
bearing plants which may play a
useful role in trickling filter treat-
ment operations.
Groundwater is the body of water
beneath the surface of the ground. It
is made up primarily of the water
that has seeped down from the
surface.
Incineration consists of burning the
sludge to remove the water and
reduce the remaining residues to a
safe, non-burnable ash The ash can
be disposed of safely on land, in
some waters, or into caves or other
underground locations
Infiltration is the penetration of
water through the ground's surface
into sub-surface soil.
Infiltration/Percolation is a land
application technique where large
volumes of waste water are applied to
land, allowed to penetrate the sur-
face and percolate through the
underlying soil.
Interceptor sewers in a combined
system control the flow of the sewage
to the treatment plant In a storm,
they allow some of the sewage to
flow directly into a receiving stream.
This protects the treatment plant
from being overloaded in case of a
sudden surge of water into the
sewers. Interceptors are also used in
separate sanitation systems to collect
the flows from main and trunk
sewers and carry them to the points
of treatment.
Ion is an electrically charged atom or
group of atoms which can be drawn
from waste water during the electro-
dialysis process.
Irrigation is a land application
technique where waste water is appli-
ed to the land to supply the water
and nutrient needs of plants
Land Application—the discharge of
waste water onto the ground for
treatment or reuse
Lateral sewers are the pipes that run
under the streets of a city and into
which empty the sewers from homes
or businesses
Mechanical Aeration uses mechani-
cal energy to inject air into water,
causing the waste stream to absorb
oxygen from the atmosphere.
Microbes are minute plant or animal
life. Some microbes which may cause
disease exist in sewage.
25
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Mixed Liquor is a mixture of Polyelectrolytes are synthetic^hem'i-
activated sludge and waters contain- cals used to speed the removal of
ing organic matter undergoing acti- solids from sewage. The -Jfiemicals
vated sludge treatment in the aera- cause the solids to flocculate or
tion tank. clump together more rapidly than
chemicals like alum or lime.
Nitrogenous wastes: Wastes of ani-
mal or plant origin that contain a
significant concentration of nitro-
gen.
Nutrients: Elements or compounds
essential as raw materials for orga-
nism growth and development, for
example, carbon, oxygen, nitrogen
and phosphorus.
Organic Matter is the carbonaceous
waste contained in plant or animal
matter and originating from domes-
tic or industrial sources
Overland Flow is a land application
technique that cleanses waste water
by allowing it to flow over a sloped
surface. As the water flows over the
surface, the contaminants are re-
moved and the water is collected at
the bottom of the slope for reuse.
Oxidation is the addition of oxygen
which breaks down organic wastes or
chemicals in sewage by bacterial and
chemical means.
Oxidation Pond is a man-made lake
or body of water in which wastes are
consumed by bacteria. It is used
most frequently with other waste
treatment processes. An oxidation
pond is basically the same as a
sewage lagoon.
Percolation is the movement of
water through sub-surface soil lay-
ers, usually continuing downward to
the ground-water.
Phosphorus: An element that while
essential to life, contributes to the
eutrophication of lakes and other
bodies of water.
Pollution results when animal, veg-
etable, mineral or heat wastes or
discharges reach water, making it
less desirable for domestic, recrea-
tion, industry, or wildlife uses.
Primary treatment is the stage in
basic treatment that removes the
material that floats or will settle in
sewage. It is accomplished by using
screens to catch the floating objects
and tanks for the heavy matter to
settle in.
Receiving Waters are rivers, lakes,
oceans, or other water courses that
receive treated or untreated waste
waters.
Salts are the minerals that water
picks up as it passes through the air,
over and under the ground, and
through household and industrial
uses.
Sand Filters remove some sus-
pended solids from sewage. Air and
bacteria decompose additional
wastes filtering through the sand.
Cleaner water drains from the bed.
The sludge accumulating at the
surface must be removed from the
bed periodically.
Sanitary Sewers, in a separate sys-
tem, are pipes in a city that carry
only domestic waste water. The
storm water runoff is taken care of
by a separate system of pipes.
Secondary Treatment is the second
step in most waste treatment sys-
tems in which bacteria consume the
organic parts of the wastes. It is
accomplished by bringing the sew-
age and bacteria together in trickling
filters or in the activated sludge
process.
Sedimentation Tanks help remove
solids from sewage. The waste water
is pumped to the tanks where the
solids settle to the bottom or float on
the top as scum. The scum is
skimmed off the top, and solids on
the bottom are pumped to incinera-
tion, digestion, filtration or other
means of final disposal
Septic Tanks are used for domes
wastes when a sewer line is i
available to carry them to a tre
ment plant. The wastes are piped
underground tanks directly from I
home or homes. The bacteria in I
wastes decompose the organic wa
and the sludge settles on the botti
of the tank The effluent flows out
the tank into the ground throu
drains. The sludge is pumped out
the tanks, usually by commerc
firms, at regular intervals.
Sewers are a system of pipes th
collect and deliver waste water
treatment plants or receivi
streams
Sludge is the solid matter that sett
to the bottom, floats, or becorr
suspended in the sedimentati
tanks and must be disposed of
filtration and incineration or
transport to appropriate dispoi
sites.
Sterilization is the destruction of
living organisms. In contrast, disi
fection is the destruction of most
the living organisms
Storm Sewers are a separate syste
of pipes that carry only runoffs fro
buildings and land during a storn
Suspended Solids are the smi
particles of solid pollutants whu
are present in sewage and whi<
resist separation from the water
conventional means.
Trickling Filter is a support med
for bacterial growth, usually a bed
rocks or stones The sewage
trickled over the bed so the bacter
can break down the organic waste
The bacteria collect on the stem
through repeated use of the filter.
Waste Treatment Plant is a series (
tanks, screens, filters, and othc
processes by which pollutants ai
removed from water.
Virus is the smallest form of micrt
organism capable of causing diseasi
26
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U.S. Environmental Protection Agency
Region 5 Library (PL-12J)
77 West Jackson Blvd., 12th Floor
Chicago, IL 60604-3590
Expansion of Blue Plains waste treatment plant
-------
Office of Public Affairs (A-107)
U.S. Environmental Protection Agency
Washington, D.C. 20460
Official Business
Penalty for Private Use $300
Postage and Fees Paid
Environmental Protection Agency
EPA 335
Third Class Bulk Rate
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