United States	Office of Water	July 1980
Environmental Protection	Programs Operations (WH-547)	MCD-65
Agency	Washington DC 20460
&EPA Primer
for Wastewater
Treatment

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Contents
Collecting ft Treating Wastes	3
Basic Treatment	4
Primary Stage
Secondary Stage
Wastewater Treatment Ponds
Land Application
Irrigation
Rapid Infiltration
Overland Flow
Small Onsite Systems
Septic Tanks
Aerobic Units
Absorption Field
Modified Absorption Fields
Mound Systems
Evapotranspiration System
Alternative Systems
Pressure Sewers
Waterless Systems
Operation and Maintenance
The Need for Further Treatment of Wastes 10
Types of Pollutants
Oxygen-demanding wastes
Disease Causing Agents
Plant Nutrients
Synthetic Organic Chemicals
Inorganic Chemicals and Mineral Substances
Sediments
Radioactive Substances
Heat
Advanced Methods of Treating Wastes 13
Nitrogen Control
Coagulation-Sedimentation
Adsorption
Electrodialysis
New Challenges for Waste Treatment 16
Reverse Osmosis
Chemical Oxidation
Polymers and Pollution
The Use or Disposal of Wastewater
Treatment Residues	17
Common Sewage Treatment Terminology 19

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Under the 1972 Amendments to
the Federal Water Pollution
Control Act (Public Law 92-500)
and the more recent Clean Water
Act of 1977 (Public Law 95-217),
enacted in December 1977, thou-
sands of municipal waste treat-
ment plants are being constructed
or expanded across the Nation to
control or prevent water pollution.
The 1972 law authorized grants
totaling $18 billion and the 1977
law authorized an additional
$24.5 billion; all to help towns
and cities to construct waste
treatment facilities. An additional
$1,480 billion was made available
under other laws. The grants
under the 1972 Act funded 75
percent of the eligible cost of
facilities.
The law also established the
National Pollution Discharge
Elimination System which calls
for limitations on the amount
and quality of effluents and re-
quires all municipal and industrial
dischargers to obtain permits.
The permits include effluent
clean-up dates which are en-
forceable by State or Federal
Government. Further, the 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 watch-
ing this progress. And they want
to know more about wastewater
treatment.
This primer explains the meth-
ods used now and processes
being developed for the future to
treat wastewater discharges and
to give the Nation clean water.
1

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2

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Collecting
and Treating
Wastes
The most common form of pol-
lution control in the United
States consists of a system of
sewers and waste treatment
plants. The sewers collect the
wastewater from homes, busi-
nesses, and many industries and
deliver it to the plants for treat-
ment to make it fit for discharge
into streams or for reuse.
There are two kinds of sewer
systems — combined and sepa-
rate. 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 sys-
tem 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 com-
mon or lateral sewer beneath a
nearby street. Lateral sewers
connect with larger sewers called
trunk or main sewers. In a com-
bined sewer system, these trunk
or main sewers discharge into a
larger sewer called an inter-
ceptor. The interceptor is de-
signed 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 wastewater,
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. (These large "slugs"
of combined raw sewage and
storm water discharged to
streams can be damaging to
water quality and efforts are
underway to control them.)
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 run-
off of rainwater polluted by dirt
and other contaminants.)
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 indus-
try grew to their present size.
However, these natural proc-
esses, even though accelerated
in a waste treatment plant, are
not sufficient to remove other
contaminants such as disease-
causing germs, excessive nutri-
ents such as phosphates and
nitrates and chemicals and trace
elements.
When the sewage of previous
years was dumped into water-
ways, the natural process of pu-
rification 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 diox-
ide, and other products.
But the bacteria normally pres-
ent in water must have oxygen
to do their part in breaking down
the sewage. Water acquires this
all-important oxygen by absorb-
ing it from the air and from
plants that grow in the water
itself. These plants use sunlight
to turn the carbon dioxide pres-
ent 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 af-
fected and the bacteria can do
their work; the stream can quick-
ly 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 demand placed on the natu-
ral supply of dissolved oxygen is
used as a measure in telling how
well a sewage treatment plant is
working. This measuring device
is called biochemical oxygen de-
mand, or BOD. If the effluent or
the end-product from a treat-
ment plant has a high content of
organic pollutants, the effluent
will have a high BOD. In other
words, it will demand more oxy-
gen from the water to break
down the sewage and conse-
quently will leave the water with
less oxygen (and more pollutants).
With the growth of the Nation,
the problems of pollution have
become more complex. The in-
creased amounts of wastes and
the larger demands for water
have reduced the capacity of
running water to absorb waste
water and purify itself. Conse-
quently, 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 sec-
ondary. 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
wastewater even further. In
some cases, the two stages may
be combined into one basic
operation.
Separate systems . . . storm
sewer outfall
3

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Basic
T reatment
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 in-
clined position to the flow of the
sewage to make cleaning easier.
The debris caught on the up-
stream surface of the screen can
be raked off manually or me-
chanically.
Some plants use a device
known as a comminutor which
combines the functions of a
screen and a grinder. These de-
vices 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 sew-
age still contains dissolved or-
ganic and inorganic matter along
with suspended solids. The latter
Basic treatment. . . primary stage
Sedimentation tanks
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
usually disinfected with chlorine
before being discharged into a
stream or river. Chlorine is fed
into the water to kill and reduce
the number of disease-causing
bacteria. Chlorination also helps
to reduce objectionable odors.
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 inade-
quate 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.
4

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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 filters 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. More recently, interlock-
ing sheets of corrugated plastic
or other types of synthetic media
have also been used for trickling
filter beds. 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 principle
ways. One method consists of
distributing the effluent intermit-
tently through a network of
pipes laid on or beneath the sur-
face of the stones.
Attached to these pipes are
small, 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 sedi-
mentation tank to remove the
bacteria. Disinfection of the ef-
fluent with chlorine is generally
used to complete the secondary
stage of basic treatment.
The trend today is toward the
use of the activated sludge proc-
ess instead of trickling filters.
There is, however, a renewed
interest in trickling filters because
of their relative ease of operation
and efficient use of energy. The
activated sludge 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 bac-
teria break down the organic
matter.
The sludge, now activated
with additional millions of bac-
teria and 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 the
process is free of flies and odors.
But it is more costly to operate
than the trickling filter, and the
activated sludge process some-
times loses its effectiveness
when faced with complex indus-
trial 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 oxy-
gen 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 meth-
od. Relatively pure oxygen which
can be produced by means of a
number of different manufactur-
ing processes has also been used
to provide oxygen to the sewage.
From the aeration tank, the
sewage flows to another sedi-
mentation tank to remove the
bacteria.
There are some recent devel-
opments in biological secondary
treatment processes which are
essentially variations or combina-
tions of the trickling filter and
activated sludge methods of
treatment. These include the use
of synthetic discs in place of sta-
tionary media in trickling filters.
In this case the discs are rotated
through the sewage to contact
the bacteria with the organic
matter in the sewage. There are
also variations of the activated
sludge process which have been
Secondary stage . . . activated sludge process
5

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Aeration tank
Trickling filter
Wastewater
Treatment Ponds
Lagoons, or as they are usually
called, wastewater treatment
ponds also have several advan-
tages 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.
Treatment ponds, predominantly
in smaller communities, account
for more than one-fourth of the
municipal wastewater treatment
facilities in this country.
A treatment pond is a scientif-
ically constructed pond usually
three to five feet deep, in which
sunlight, algae, and oxygen in-
adapted for smaller and moderate-
sized communities. These sys-
tems provide longer contact of
the sewage with the bacteria to
facilitate easier operation. Con-
ventional rectangular and circular
tanks or racetrack shaped basins
have both been used in these
systems.
The final step again generally
consists of the addition of chlo-
rine — the most common method
of disinfection — to the effluent
coming from the trickling filter or
activated sludge process. Chlo-
rine 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.
Some municipalities are now
manufacturing chlorine solution
on site to avoid the necessity of
transporting and storing large
amounts of chlorine gas. Alter-
nates to chlorine disinfection,
such as ozone, are also being
used in a number of situations
where chlorine in sewage efflu-
ents can be harmful to fish and
other aquatic life.

6

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Land Application
Sewage treatment lagoons
teract to restore water to a qual-
ity that is often equal to effluent
from the secondary treatment
stage. Changes in the weather
may change the effectiveness of
lagoons.
Ponds also can be used with
other basic waste treatment proc-
esses. A good example of this is
the Santee, California, water
reclamation project. After con-
ventional 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 waters.
Land application can provide
basic treatment as well as ad-
vanced wastewater treatment
(described later in this publica-
tion). Land application systems
can remove pollutants not re-
moved in other basic treatment,
and in many cases, reuse or ren-
ovate the wastewater. Three
techniques are used: crop irriga-
tion, rapid infiltration, and over-
land flow, or a combination of all
three.
In the arid western States,
municipal wastewater has been
used for a number of years to
irrigate crops. In recent years,
land application and crop irriga-
tion has spread to all sections of
the country. Land application of
many types of industrial waste-
water is also common.
EVAPORATION
Irrigation
In the case of crop irrigation (or
slow rate infiltration) the waste-
water penetrates into the ground
where the natural filtering and
straining action of the soil re-
moves most of the pollutants.
Part of the water evaporates or
is absorbed by plants. The re-
mainder is either collected under-
ground for surface discharge or
is allowed to percolate to the
groundwater.
Crop irrigation is the most
commonly used land application
technique. It not only reuses the
water, but the minerals and nu-
trients in it. The wastewater is
sometimes disinfected before
use, depending on the end use
of the crop and the irrigation
method. The wastewater is ap-
plied to the land by spraying,
flooding, or ridge and furrow
irrigation. The 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. Phosphorus 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
wastewater for reuse. Since the
rapid infiltration process is the
simplest land application tech-
nique, and is effective in cold or
wet weather, it has been used
frequently in the northeastern
States.
Large amounts of wastewater
are applied to a limited land area
and allowed to infiltrate the
ground surface and percolate
through the soil below. If the
water is to be reused, it can be
recovered by drilling wells to
draw it to the surface. Normally,
however, the water will seep
downward to the ground water.
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.

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Small
Onsite Systems
Overland Flow
This method has been used suc-
cessfully in the food-processing
industries to remove bacteria and
nutrients from wastewater. And
it has been used to a limited ex-
tent in treating municipal waste-
water for many years.
The wastewater 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 re-
use. The remainder evaporates.
This process is well suited to
clay or clay-type soils with little
or no adsorption capacity.
Whatever method is used,
land appliction may be an eco-
nomic alternative, particularly
when compared to more costly
advanced treatment plants. Re-
search is also being conducted
to determine what levels of nu-
trients and trace elements can be
allowed to build up in the soil
without harming agricultural
plants, or posing health hazards
when the crops may enter the
human food chain.
Septic Tanks
A septic tank is simply a tank
buried in the ground to treat the
sewage from a home.
Wastewater from the home
flows into the tank where bac-
teria 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 can be a
reasonable means of disposing
of strictly domestic wastes.
Septic tanks should always be
located so that none of the efflu-
ent can pollute the ground
water used as a drinking water
source.
mixed with the wastewater in
the tank. Aerobic bacteria
(utilize oxygen) consume
organic substances in the
sewage and liquefy most of
the solids. The liquid
discharges to an absorption
field where treatment
continues as it leaches into
soils.
Absorption Field
Soil conditions permitting, the
most common method of dispos-
ing of septic tank or aerobic
system effluent is by means of
the absorption field. It consists
mainly of a series of
perforated parallel pipes laid in
gravel or crushed stone. The
effluent drains through the stone
and into the soil which becomes
an aerobic treatment medium.
Granular filtration occurs as
treated effluent flows through
a ground level or buried sand
pit. Liquid enters a perforated
pipe at the top and filters
through sand and gravel to a
pipe in the bottom of the pit.
The bottom pipe conducts the
liquid to a disinfection tank
before discharge to a stream
or ditch.
Modified Absorption Fields
If proper soil for the installation
of a regular absorption field is
not available, other methods can
be utilized to dispose of the ef-
fluent. They are:
Granular Filtration
Aerobic Units
These are similar to septic
tanks, but air is introduced and
EVAPORATION
RUNOFF
COLLECTION
ROOF TERMINAL
PLUMBING FIXTURES
TO BE PROPERLY
TRAPPED AND
VENTED
STACK
HOUSE SEWER
i- TO BE LAID ON WELL
COMPACT ED EARTH
SEPTIC TANK
, /COMPACT EARTH
AROUNDTANK^
NON-PERFORAFED PIPE
ABSORPTION
FIELD
-GRAVEL $
|R CRUSHED
STONE-—"
PERFORATED
PIPE
8

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Mound System
PERFORATED PVC PIPE
CLAY FILL OR TOPSOIL
FROM
HOUSI
TOPSOIL
1.	Mound System
This system is used in conjunc-
tion with the septic tank or
aerobic unit. The absorption
field is located above natural
ground. The tile drainage
system is laid in a mound of
sand. The liquid goes from the
septic tank into a pumping
chamber. Here it is stored until
there is sufficient liquid to pump.
Once this level is reached the
liquid is pumped to the mound
where it is spread evenly. The
liquid moves laterally until it is
absorbed by the less permeable
soils below.
2.	Evapotranspiration System
This system is similar to the ab-
sorption field with the difference
that no liquid is allowed to enter
the undisturbed earth beneath
the system. The treated effluent
is disposed of by evaporation
into the atmosphere and by
transpiration through plants. This
system depends to some extent
on the climatic conditions of the
area.
Other Alternative Systems
1. Pressure Sewers
A pressure sewer is a small-
diameter plastic pipe that
transports wastewater under
pressure. When soil conditions
do not permit the use of an
absorption field to dispose of
the wastewater, pressure
sewers can be utilized to carry
wastewater to a central or
alternative treatment and
disposal system.
Two major pressure sewer
systems are the "grinder
pump" (GP) and the "septic
tank effluent pump" (STEP). In
the GP system, a grinder pump
housed in an underground
storage tank that receives raw
sewage directly from the
building grinds the raw
sewage and pumps it directly
into the pressure sewer.
In the STEP system,
wastewater flows from a
septic tank to a storage tank
that contains an effluent
pump. The pump then forces
the partially treated
wastewater into the small-
diameter pressure sewer
which carries it to an alternate
treatment and disposal system.
The sludge remains in the
septic tank or aerobic unit and
must be removed every 2 to 3
years.
2. Recirculating Toilets
Recirculating toilets utilize a
closed loop water system to
transport black water (carrying
Evapotranspiration System
urine and fecal material) to a
complete treatment center
usually housed in the
basement of the building.
There the wastewater is
cleansed and recirculated back
to the toilet tank to be used
again.
3. Waterless Systems
There are other individual
systems for the handling of
domestic wastewater that do
not utilize water for transport
of wastes. These include:
a)	composting toilets
b)	recirculating oil flush toilets
c)	incinerating toilets
d)	chemical toilets
Operation
and
Maintenance
Wastewater treatment plants,
septic tanks and other alternative
systems 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. A common
reason for this failure is poor
operation and maintenance. A
sufficient number of well-trained
operators and maintenance peo-
ple and a well-equipped water-
testing laboratory will contribute
to satisfactory reduction of
pollutants.
The failure of septic tanks and
other onsite systems is mainly
due to improper design, construc-
tion or maintenance. If proper care
is exercised during construction
and the system is properly main-
tained the system can outlive the
residence or facility it was de-
signed to serve.

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The Need For
Further Treatment
of Wastes
The Types of
Pollutants
In the past, pollution control was
concerned primarily with prob-
lems caused by domestic waste
and the simpler wastes of indus-
try. Control was aimed principally
towards protecting downstream
public water supplies and stop-
ping or preventing nuisance
conditions.
Pollution problems were prin-
cipally 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 tech-
nological developments, chang-
ing land use, and many other
factors.
The increased production of
goods has greatly increased the
amounts of common industrial
wastes. New processes in manu-
facturing are producing new,
complex wastes that sometimes
defy present pollution control
technology. The increased appli-
cation of commercial fertilizers
and the development and wide-
spread 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 radio-
active materials foreshadow still
another complicating and poten-
tially serious water pollution
situation.
Long stretches of both inter-
state and intrastate streams are
subjected to pollution which
ruins or reduces the use of the
water for many purposes. Con-
ventional, biological waste treat-
ment 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 al-
most daily. The construction of
facilities to handle the wastes
generated in these communities
has sometimes not matched
either the growth rate or changes
in growth patterns.
Sea water intrusion may be a
growing problem in coastal areas.
It is usually caused by the exces-
sive pumping of fresh water
from the ground which lowers
the water level, allowing salt
water to flow into the ground
water area.
Present day problems that must
be met by sewage treatment
facilities can be summed up in
eight types of pollutants affect-
ing 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 sub-
stances; and heat.
Oxygen-demanding wastes -
These are the traditional organic
wastes and ammonia contributed
by (1) domestic sewage, and
(2) industrial wastes of plant and
animal origin. In the latter case,
such wastes result from food
processing, paper mill produc-
tion, tanning, and other manu-
facturing processes. These
wastes are usually destroyed by
bacteria if there is sufficient oxy-
gen present in the water. Since
fish and other aquatic life de-
pend on oxygen for life, the
oxygen-demanding wastes must
be controlled, or the fish die.
Disease-causing agents - This
category includes infectious or-
ganisms which are carried into
surface and ground water by
sewage from cities and institu-
tions, and by certain kinds of
industrial wastes, such as tan-
ning 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 dis-
infection 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 life, such as algae and
water weeds, which support and
stimulate their growth. Carbon,
Domestic sewage
10

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Algae
Chemicals
nitrogen and phosphorus are the
three chief nutrients present in
natural water. Large amounts of
these nutrients are present in
sewage, certain industrial
wastes, and drainage from ferti-
lized land. Biological waste treat-
ment 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 nutri-
ents overstimulates the growth
of water plants, causing unsight-
ly conditions, interfering with
water treatment processes, and
causing unpleasant and disagree-
able tastes and odors in the
water.
Synthetic organic chemicals -
Included in this category are
detergents and other household
aids, all the new synthetic or-
ganic pesticides, synthetic indus-
trial 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 treat-
ment. Some are known to be
highly poisonous at very low
concentrations. The long-term
effects, if any, of small doses of
toxic substances is not yet
known.
Inorganic chemicals and mineral
substances - A vast array of
metal salts, acids, solid matter,
and many other chemical com-
pounds are included in this
group. They reach our waters
from mining and manufacturing
processes, oil field operations,
agricultural practices, and natural
11
Acid drainage	Sediment

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Thermal pollution
sources. Water used in irrigation
picks up large amounts of min-
erals as it filters down through
the soil on its way to the nearest
stream. A wide variety of acids
are discharged as waste by in-
dustry, but the largest single
source of acid in our water
comes from mining operations
and mines that have been aban-
doned.
Many of these types of chem-
icals are being created each year.
They interfere with natural stream
purification; destroy fish and
other aquatic life; cause exces-
sive hardness of water supplies;
corrode expensive water treat-
ment equipment; increase com-
mercial and recreational boat
maintenance costs; and boost
the cost of waste treatment.
Sediments - These are the par-
ticles of soil, sand, and minerals
washed into the water from the
land and from paved areas of
communities. Construction proj-
ects are often large sediment
producers. While not as invidious
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 capac-
ity and useful life. They erode
power turbines and pumping
equipment, and reduce fish and
shellfish populations by blanket-
ing fish nests and food supplies.
More importantly, sediments
reduce the amount of sunlight
penetrating the water. The sun-
light is required by the green
aquatic plants which produce the
oxygen necessary to normal
stream balance. Sediments
greatly increase the treatment
costs for municipal and industrial
water supplies and for sewage
treatment where combined
sewers are in use.
Radioactive substances - Radio-
active pollution results from the
mining and processing of radio-
active ores; from the use of re-
fined radioactive materials in
power reactors and for industrial,
medical, and research purposes;
and from fallout following nu-
clear 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 consid-
eration total exposure in the
human environment — water,
air, food, occupation, and med-
ical treatment.
Heat - Heat reduces the capacity
of water to absorb oxygen. Tre-
mendous volumes of water are
used by power plants and indus-
try 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 dis-
charges of waste heat can seri-
ously 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 tem-
peratures 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 pol-
lutants 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 down-
stream fish life and reduce the
ability of the stream to assimilate
downstream pollution.
To complicate matters, many
of our wastes are a mixture of
the eight types of pollution,
making the problems of treat-
ment and control that much
more difficult.
Municipal wastes usually con-
tain 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 sub-
stances and pollutants washed
from the sky, vegetation, build-
ings, and streets during rainfall.
12

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Advanced Methods
of Treating
Wastes
New pollution problems of a
modern society have placed ad-
ditional burdens upon our waste
treatment systems. Today's pol-
lutants are more difficult to
remove from the water. In-
creased 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.
These problems are beginning
to be met through better and
more complete methods of
removing pollutants at treatment
plants or better means for
preventing some wastes from
even entering the sewer system.
Pretreatment of industrial waste,
for example, removes many
troublesome pollutants at the
source.
The best immediate answer to
these problems is the widespread
application of available 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 wastewater at the sec-
ondary stage. With nationwide
provision of secondary treat-
ment only, discharge of oxygen
consuming materials would
still degrade water quality and
inhibit aquatic life. Further
treatment, land treatment, or
wastewater reuse providing for
removal of more pollutants will
therefore be required in many
cases.
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 con-
sideration 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 processes in various
combinations can achieve any
degree of pollution control
desired and, as waste effluents
are purified to higher and
higher degrees by such treat-
ment, the point is reached
where effluents become "too
good to throw away."
Such water can be
deliberately and directly reused
for agricultural, industrial,
recreational, or possibly even
drinking water supplies. Com-
plete water renovation will
mean complete pollution con-
trol and at the same time more
water for the Nation.
Nitrogen Control
Nitrogen in one form or another
is present in all municipal
wastewater and is not removed
by secondary treatment. It can
be harmful if discharged into
lakes and streams. Nitrogen in
the form of ammonia can place a
direct demand on oxygen in cer-
tain surface waters or can
stimulate the excessive growth
of aquatic algae. As overgrowths
of algae die and decompose, the
process can deplete the supply
of life-supporting oxygen in the
water. Algae as well as the am-
monia in wastewater effluent can
also be directly toxic to fish in
certain instances.
By providing additional
biological treatment beyond the
secondary stage, bacteria pres-
ent in wastewater treatment can
biologically change ammonia to
nitrate in a process known as
nitrification. In some instances
where ammonia nitrogen is a
concern because of oxygen
demand or toxicity nitrification
is sufficient to protect the
environment. However, nitro-
gen in the form of nitrate is
also a nutrient which can
contribute to the excessive
growth of aquatic algae.
In those instances where
nitrogen must be completely
removed from the effluent, an
additional biological process can
be added to the system to
change the nitrate to nitrogen
gas. Nitrogen gas of course
comprises almost 80% of our air
and causes no environmental
harm when released into the at-
mosphere. As is the case with
the other biological treatment
processes, conversion of nitrate
to nitrogen gas is done by
bacteria in a process known as
denitrification.
There are also methods of
treating wastewater with
chemicals to directly remove
Advanced wastewater treatment plant
13

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Coagulation-
Sedimentation
Adsorption
Electrodialysis
the ammonia. However, this
has had only limited use in the
municipal wastewater field to
date, and can be very
expensive.
As discussed in a previous
section of this publication, land
application is a promising
method which can provide
both basic treatment and
advanced wastewater
treatment. The plants and soil
bacteria utilize phosphorus and
nitrogen and in so doing
remove it from the
wastewater. The application of
advanced techniques for waste
treatment begins where
primary and secondary
treatment ends.
The process known as coagula-
tion-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 suf-
ficient addition of chemicals,
reduce the concentration of
phosphate by over 95 percent.
In the process, alum, lime, or
iron salts are added to the
wastewater either during or after
the secondary treatment stage.
When the chemicals are added
after the secondary treatment
stage, the flow then passes
through flocculation 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, coagula-
tion-sedimentation is classified as
an advanced process because it
had not previously been routinely
applied to the treatment of
municipal wastes. In many
cases, the process is a necessary
pre-treatment for some of the
other advanced techniques.
Technology has also been
developed to remove refractory
organic materials. This is organic
matter which stubbornly resists
removal by 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 ac-
tivated carbon granules which
will remove more than 98 per-
cent of the organics. To cut
down the cost of the procedure,
the carbon granules can be
cleaned by heat and used again.
With the exception of added
salts, municipal waste water that
has gone through the advanced
treatment processes will be
restored to a chemical quality
almost the same as before it was
used.
In waste treatment language,
salt is not limited to common
table salt. Salts include 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 is a rather com-
plicated process by which elec-
tricity 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 in-
creases by 300-400 milligrams per
liter. Fortunately, electrodialysis
can remove this buildup.
In fact, the process of elec-
trodialysis can reduce the salt
content of water to the level it
was before the city received the
water, or even lower.

CHEMICAL
14

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Properly designed and applied,
the preceeding wastewater treat-
ment methods are capable of
providing treated water of any
desired degree of purity for any
desired reuse from irrigation to
drinking water.
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 mak-
ing 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 most of the decom-
posable impurities; coagula-
tion-sedimentation, the third
step, eliminates most of the
suspended solids; carbon ad-
sorption can remove the
remaining dissolved organic
matter; electrodialysis can
return the level of the salts to
what it was before the water
was used; and, finally, dis-
infection provides a barrier
against most disease-carrying
organisms.
Wastewater filtration unit in the coagulation-sedimentation process
Denitrification plants remove excess nitrogen in advanced treatment
15
SECONDARY
EVAPO-
RATION
FILTER ¦
, AND ^
kABSORP-
V TION
PRIMARY
CHLORINEl

-------
Polymers
and Pollution
Chemical Oxidation
Reverse Osmosis
In discussing the coagulation-
sedimentation process, mention
was made of the use of chemi-
cals to force suspended solids in-
to 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 polyelec-
trolytes 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 ex-
tracted more rapidly.
If polymers are put into raw
sewage, waste treatment plants
may be able to combine a
chemical process with the stan-
dard primary and secondary
stages. This method of removing
solids could be applied im-
mediately without adding expen-
sive new facilities.
However the volume of
sludge generated will greatly
increase and methods of utili-
zation or disposal of this
additional sludge must be
considered.
Polymer chemicals also hold
promise as a means of speeding
the flow of wastewaters through
sewer systems, thus, in effect,
increasing the capacity of ex-
isting systems.
Chlorine and oxidants such as
ozone have been used for many
years to improve the taste and
odor or to disinfect municipal
drinking water. Such materials
improve the quality of water by
destroying or altering the struc-
ture 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 con-
junction with other processes,
however, oxidation could
become an effective weapon in
eliminating wastes resistant to
other processes.
When liquids with different con-
centrations of mineral salts are
separated by a membrane,
molecules of pure water tend to
pass by osmosis from the more
concentrated to the less concen-
trated 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, the natural force
reverses itself, causing the
molecules of pure water to flow
out of the compartment contain-
ing a high salt concentration.
This means that perfectly pure
water is being taken out of the
waste, rather than taking
pollutants out of water in the
traditional way. And this process
takes clean water away from
everything — bacteria, deter-
gents, nitrates.
Tests have shown that the
theory works well, resulting in
water good enough to drink. Ef-
forts are now underway to
develop large, long life mem-
branes, along with matching
processes and equipment for
testing on a large scale,
Reserve osmosis
16

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The Use or Disposal
of Wastewater Treatment
Residues
When conventional treatment
techniques are used, there is
always something left over. It
may be the rags and sticks
caught on the screens at the
very beginning of primary treat-
ment. 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 wastewater
process is not completed until all
waste is used or disposed in a
way that does not harm the en-
vironment.
The utilization and disposal of
sludge is being jointly addressed
under the Clean Water Act and
the Resource Conservation and
Recovery Act. Both of these
Federal laws emphasize the need
to employ environmentally sound
sludge management techniques
and to beneficially use sludge
whenever possible. At the same
time, the national requirements
for improved wastewater treat-
ment 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 per-
cent of the construction grant
funds for individual treatment
plants provided under the Clean
Water Act may be required to
build adequate sludge manage-
ment facilities. In addition, the
permits required for effluent
discharge from sewage treatment
plants will be affected by and
contain provisions related to the
sludge management techniques
employed by the facilities.
Until recently all but about 20
percent of the Nation's sludge
had been burned (incinerated),
landfilled, or dumped into the
ocean. Currently, much more at-
tention is being given to sludge
utilization by application to land
as a soil conditioner or fertilizer
and to combustion with or with-
out solid waste in facilities
designed to recover energy.
Prior to utilization or disposal,
sludge may be stabilized to con-
trol odors and reduce the
number of disease-causing
organisms. The sludge may also
be dewatered to reduce volumes
to be transported or to prepare it
for final processing.
Digestion of sludge takes place
in heated tanks where the
material can decompose naturally
and the odors can be controlled.
Anaerobic sludge digestion
(without air) has the added
benefit of producing methane
gas which is usable as fuel.
Stabilization of sludge may also
be accomplished by the addition
of lime or by heating it under
pressure. After stabilization the
sludge can be spread on land as
a liquid (2-10% solids) or addi-
tional water can be removed by
use of dewatering processes
such as pressure or vacuum
filtration or centrifugation.
Liquid digested sludge has
been used successfully as a fer-
tilizer and for restoring areas
disrupted by strip mining. Under
this sludge management ap-
proach, digested sludge in semi-
liquid form is transported to the
spoiled areas. The slurry, con-
taining nutrients from the
wastes, is spread over the land
to give nature a hand in return-
ing grass, trees, and flowers to
barren land. Restoration of the
countryside will also help control
the flow of acids that drain from
Sludge drying beds
mines into streams and rivers,
endangering fish and other
aquatic life and adding to the
difficulty of reusing the water.
In some areas liquid sewage
sludges are now being marketed
to farmers as fertilizer. Liquid
sludge is a good source of
nitrogen and phosphorus which
are nutrient elements required by
plants.
Dewatering of sludge is often
necessary prior to utilization or
disposal. The liquid sludge,
which contains 90-98% water,
can be partially dewatered by a
number of processes.
One such process, vacuum fil-
tration, makes use of a slowly
rotating filter drum and suction.
As the drum rotates, the water is
filtered out of the sludge and the
residues are peeled off for utiliza-
17

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Treated sludge may be used as fertilizer for some agricultural crops
tion or disposal. For more effec-
tive dewatering, the sludge can
be first treated with a coagulant
chemical such as lime or ferric
chloride to produce larger solid
particles before the sludge
reaches the filter. Centrifugation
is a comparable process which
relies on the principle of high
speed rotation to "spin" the
water out of the sludge.
After dewatering the sludge
can be spread directly on the
land as a soil conditioner if it has
been previously stabilized. Un-
digested sludge can be further
processed by appropriate stabili-
zation techniques such as com-
posting or drying, or it can be
directly incinerated.
Composting of sewage sludge
is a promising, new approach to
sludge management that is being
adopted by a number of cities.
Sludge is transformed micro-
biologically in the presence of air
to a dry peat-like form. The com-
post product has shown par-
ticular promise for use in produc-
tion of soil for revegetation of
top soil depleted areas, and as a
potting amendment.
Incineration consists of burn-
ing the dried sludge to reduce
the residues to a non-burnable
ash. The ash can be disposed of
by filling unused land. Because
of the increasing premium placed
on our fuel supplies, sludge in-
cinerators now being considered
make provisions for minimum
dependence on auxiliary fuels
and often include heat recovery
features. Undigested sewage
sludge has some fuel
value as a result of its high
organic content. However, to
take advantage of the fuel poten-
tial of the sludge, the water con-
tent of the sludge must be less
than that achieved by traditional
dewatering processes. For this
reason newer pressure filtration
techniques are being used to ob-
tain sludges which are suffi-
ciently dry to burn without con-
tinual reliance on auxiliary fuels.
In some cities sludge will also be
mixed with refuse or refuse-
derived fuel prior to burning.
Generally, heat will be recovered
to provide the greatest amount
of energy efficiency.
The law now requires that dis-
posal of sludge into the ocean
be phased out by 1981. In the
meantime interim permits are be-
ing issued to cities by EPA for
ocean dumping provided that an
active plan is being followed for
cessation of this form of
disposal.
The problem of how to best
manage sludge can be lessened
by pretreatment of industrial
sewage wastes to prevent un-
wanted toxicants such as certain
heavy metals and persistent
organic metals from contami-
nating the sludge. Regulations to
foster pretreatment have been
developed in accordance with
provisions of the Clean Water
Act. The problem of what to do
with sludge can be reduced even
more by shifting from conven-
tional forms of wastewater treat-
ment to land treatment systems
which produce only small quan-
tities of sludge.
As this discussion shows,
sludge or other waste concen-
trates are not always costly
burdens. By drying and other
processes, some cities have pro-
duced 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 park-
ways, and other public areas.
Some industries have found
they can reclaim certain
chemicals during waste treat-
ment processes and reuse them.
Other firms have developed sale-
able byproducts 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 in-
creasing volumes of wastewater
treatment residuals — and to
help offset the cost of waste
treatment.
18

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Common
Waste Treatment
Terminology
Activated Sludge: A process
for removing organic matter from
sewage by saturating it with air
and adding biologically active
sludge.
Adsorption is an advanced way
of treating wastes in which ac-
tivated carbon removes organic
matter from wastewater.
Aeration Tank serves as a
chamber for injecting air into
water.
Aerobic refers to a life or
process that occurs in the
presence of oxygen.
Algae are plants which grow in
sunlit waters and release oxygen
into the water. They are a food
for fish and small aquatic
animals.
Alternative Systems: A system
utilized in lieu of a conventional
system.
Anaerobic refers to a life or
process that occurs in the
absence of oxygen.
Bacteria are small living
organisms which often consume
the organic constituents of
sewage.
Black Water is the term given
to any water that carries animal,
human or food wastes.
BOD (Biochemical Oxygen De-
mand) is the dissolved oxygen
required by organisms for the
aerobic decomposition of organic
matter present in water. It is
used as a measure in determin-
ing the efficiency of a sewage
treatment plant or ot determine
the potential of an effluent to
degrade a stream.
Chlorinator is a device for add-
ing chlorine gas to sewage to kill
infectious germs.
Coagulation is the clumping
together of solids to make them
settle out of the sewage faster.
Coagulation of solids is brought
about with the use of certain
chemicals such as lime, alum
and iron salts.
Combined Sewers carry both
sewage and stormwater runoff.
Comminutor is a device for the
catching and shredding of heavy
solid matter in the primary stage
of waste treatment.
Composting is the natural
biological decomposition of
organic material in the presence
of air to form a humus-like
material.
Conventional Systems are
systems that have been tradi-
tionally used to collect municipal
wastewater in gravity sewers and
convey it to a central primary or
secondary treatment plant prior
to discharge to surface waters.
Diffused Air is a technique by
which air under pressure is
forced into sewage in an aeration
tank. The air is pumped down
into the sewage through a per-
forated pipe and bubbled
through the sewage.
Digestion of sludge takes place
in tanks when the materials
decompose, resulting in partial
gasification, liquefaction, and
mineralization of pollutants.
Distillation in waste treatment
consists 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 re-
main in the concentrated
residue.
Eligible Costs are those
wastewater treatment works
construction costs upon which
Federal participation is based.
EPA grants are awarded for 75%
or 85% of the eligible cost
depending on the project.
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 com-
pletely terrestrial state and disap-
pears. During eutrophication the
lake becomes so rich in nutritive
compounds, especially nitrogen
and phosphorus, that algae and
other microscopic plant life
become super-abundant, thereby
"choking" the lake, and causing
it eventually to dry up. Eutro-
phication may be accelerated by
many human activities.
Evapotranspiration is the loss
of water from the soil both by
evaporation and by transpiration
from the plants growing thereon.
Floe is a clump of solids formed
in sewage by biological or chemi-
cal 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.
Gray Water is the term given
to domestic wastewater com-
posed of washwater from
sinks, kitchen sinks, bathroom
sinks and tubs and laundry
tubs.
Grinder Pump is a mechanical
device which shreds solids and
raises the fluid to a higher eleva-
tion through pressure sewers.
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 sur-
face into sub-surface soil or the
penetration of water from the
soil into a pipe.
Infiltration/Percolation is a
land application technique where
large volumes of waste water are
applied to land, allowed to
penetrate the surface and per-
colate through the underlying
soil.
Influent is the term given to
identify water, wastewater or
other liquid flowing into a reser-
voir, basin or treatment plant, or
any unit thereof.
Interceptors are larger sewer
lines that, 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
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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 electrodialysis proc-
ess.
Irrigation is a land application
technique wherein wastewater is
applied 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 receive the sewers from
homes or businesses.
Mechanical Aeration uses
mechanical 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.
Mixed Liquor is a mixture of ac-
tivated sludge and waters con-
taining organic matter undergo-
ing activated sludge treatment in
the aeration tank.
Nitrogeneous Wastes: Wastes
of animal or plant origin that
contain a significant concentra-
tion of nitrogen.
Nutrients: Elements or com-
pounds essential as raw materials
for organism growth and devel-
opment; for example, carbon,
oxygen, nitrogen and phospho-
rous.
Organic Matter is the car-
bonaceous waste contained in
plant or animal matter and
originating from domestic or in-
dustrial sources.
Overland Flow is a land applica-
tion technique that cleanses
wastewater by allowing it to flow
over a sloped surface. As the
water flows over the surface, the
contaminants are removed and
the water is collected at the bot-
tom of the slope for reuse.
Oxidation is the addition of oxy-
gen 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 fre-
quently with other waste treat-
ment processes. An oxidation
pond is basically the same as a
sewage lagoon.
Percolation is the movement of
water through sub-surface soil
layers, usually continuing
downward to the groundwater.
Phosphorous: An element that
while essential to life, con-
tributes to the eutrophication of
lakes and other bodies of water.
Pollution results when animal,
vegetable, mineral or heat
wastes or discharges reach
water, making it less desirable
for domestic, recreation, in-
dustry, or wildlife uses.
Polyelectrolytes are synthetic
chemicals used to speed the
removal of solids from sewage.
The chemicals cause the solids
to flocculate or clump together
more rapidly than chemicals like
alum or lime.
Pressure Sewers is a system of
pipes in which the water, waste-
water or other liquid is trans-
ported to a higher elevation by
applying a pumping force behind
it.
Primary Treatment is a stage in
basic treatment of sewage that
removes material that floats or
will settle. Screens remove
floating objects, settling tanks
remove heavy material.
Pump is a mechanical device for
causing flow, for raising or lifting
water or other fluid, or for apply-
ing pressure to fluids.
Receiving Waters are rivers,
lakes, oceans, or other water
courses that receive treated or
untreated wastewaters.
Salts are the minerals that water
picks up as it passes through the
air, over and under the ground,
and as the water is used by
households and industry.
Sand Filters physically remove
some suspended solids from
sewage. Air and bacteria decom-
pose additional wastes filtering
through the sand. Cleaner water
drains from the bed. The sludge
accumulating at the surface must
be removed from the bed period-
ically.
Sanitary Sewers, in a separate
system, are pipes in a city that
carry only domestic wastewater.
The stormwater runoff is taken
care of by a separate system of
pipes.
Secondary Treatment is the
second step in most waste treat-
ment systems in which bacteria
consume the organic parts of the
wastes. It is accomplished by
bringing together waste, bacteria
and oxygen in trickling filters or
in the activated sludge process.
Sedimentation Tanks help
remove solids from sewage. The
wastewater 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 bot-
tom are pumped to incineration,
digestion, filtration or other
means of final disposal.
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Seepage is defined as the slow
movement of water through
small cracks or pores of a
material, through the soil, or into
or out of a body of surface or
subsurface water.
Septic Tanks are used for
domestic wastes when a sewer
line is not available to carry them
to a treatment plant. The wastes
are piped to underground tanks
directly from the home or
homes. The bacteria in the
wastes decompose the organic
waste and the sludge settles on
the bottom of the tank. The ef-
fluent flows out of the tank into
the ground through drains. The
sludge is pumped out of the
tanks, usually by commercial
firms, at regular intervals.
Sewers are a system of pipes
that collect and deliver waste-
water to treatment plants or
receiving streams.
Sludge is the solid matter that
settles to the bottom, floats, or
becomes suspended in the sedi-
mentation tanks and must be
disposed of by filtration and in-
cineration or by transport to ap-
propriate disposal sites.
Soil Absorption Field is a sub-
surface area containing a trench
or bed which has a minimum
depth of 12 inches of clean
stones and a system of distribu-
tion piping through which
treated sewage may seep into
the surrounding soil for further
treatment and disposal.
Sterilization is the destruction
of all living organisms. In con-
trast, disinfection is the destruc-
tion of most of the living
organisms.
Storm Sewers are a separate
system of pipes that carry only
runoffs from buildings and land
during a storm.
Sump Pump is a mechanism
used for removing water or
wastewater from a sump or wet
well. It may be energized by air,
water, steam or electric motors.
Suspended Solids are the small
particles of solid pollutants
which are present in sewage and
which resist separation from the
water by conventional means.
Transpiration is the process by
which water vapor is lost to the
atmosphere from living plants.
The term can be also applied to
the quantity of water thus
dissipated.
Trickling Filter is a support
media for bacterial growth,
usually a bed of rocks or stones
The sewage is trickled over the
bed so the bacteria can break
down the organic wastes.
Waste Treatment Plant is a
series of tanks, screens, filters,
and other processes by which
pollutants are removed from
water.
Virus is the smallest form of
microorganism capable of caus-
ing disease.

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