a
    primer
      on
waste water
    treatment
II, S. DEPARTMENT OF THE INTERIOR • FEDERAL WATER POLLUTION CONTROL ADMINISTRATION

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           WALTER J. HICKEL
         Secretary of the Interior
            CARL L.  KLEIN
    Assistant Secretary for Water Quality
             and Research
          DAVID D. DOMINICK
    Commissioner, Federal Water Pollution
          Control Administration
                           CONTENTS

         Collecting and treating wastes    1
                   Primary treatment    3
                 Secondary treatment    4
             Lagoons and septic tanks    7
The need for further treatment of wastes    9
               The types of pollutants   10
   Advanced methods of treating wastes   14
            Coagulation-sedimentation   15
                         Adsorption   15
                      Electrodiaiysis   17
         The blending of treated water   17
    New challenges for waste treatment   19
                   Chemical oxidation   20
               Polymers  and pollution   20
         The problem of waste disposal   21
 Common sewage treatment terminology   24
  CWA-12
October  1969
   For sale by the Superintendent of Documents,
        U.S. Government Printing Office
     Washington, D.C. 20402 - Price 55 cents
                               Thousands of waste treatment plants will be constructed
                                or expanded across the Nation during the years ahead
                           to control or prevent water pollution.

                           This increased construction activity  is the result of the
                           passage of the Water Quality Act of 1965 which called for
                           the  establishment of water quality standards  for all the
                           interstate streams, coastal waters, and lakes, and the Clean
                           Water Restoration Act of 1966 which increased Federal
                           financial aid to cities to help build these needed plants.

                           Communities across  the land will be planning, financing,
                           and building the facilities to meet the water quality stand-
                           ards.  Some cities will be  constructing plants where none
                           existed  before.  Others  will   be  expanding  inadequate
                           facilities while  some communities will be adding more ad-
                           vanced methods to handle new types  of wastes.

                           It won't happen overnight. From drawiing board to opera-
                           tion takes time.  In some cases,  projects will be built  in
                           stages.  Consequently,  more  and  more people will be
                           watching this developing  progress  toward cleaner water.
                           They  will need to know more about waste treatment.

                           In this primer,  the methods used now and processes being
                           developed for the future to treat wastes are explained.



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                                                 primer
                                                        on
                                       waste   water
                                            treatment
                     The 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 indus-
                  tries 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 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  separated 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, part of the water,
including varying amounts of raw sewage,
is allowed to bypass directly into the re-
ceiving streams. The rest of the wastes
are sent to the treatment plant. If part of
the increased load of water were not di-
verted, the waste treatment plant would
be overloaded and the purifying processes
would not function properly. (A special
research program  is  under way on the
problem of storm and combined sewers.)

Interceptor sewers are also used in sani-
tary sewer systems as collectors of flow
from main sewers and trunks, but do not
normally include provisions for bypassing.
Untreated sewage pours into stream from combined storm-sanitary sewer.

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STREET-DRAIN
A waste treatment plant's 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.

When the sewage  of previous years was
dumped into waterways, the natural  proc-
ess of purification began. First, the  sheer
volume  of  clean water in the  stream di-
luted 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 ac-
quires  this all-important oxygen by  ab-
sorbing it from the air and from  plants
that grow in the water itself.  These plants
   OVERFLOW CONTROL'
                          FEWER  SYSTEM

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use sunlight  to  turn the carbon  dioxide
present in water into oxygen.

The life and  death of any body of water
depends mainly  upon its ability to main-
tain 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 and
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 prob-
lems of pollution have become more com-
plex.  The increased amounts  of wastes
and the larger  demands for water have
reduced the capacity of running water to
purify itself.  Consequently, cities and in-
dustry have had to begin thinking about
removing  as  much  as  possible  of  the
oxygen-demanding pollutants from  their
sewage.

Adequate  treatment of wastes along with
providing  a  sufficient  supply  of clean
water has  become a major concern.
PRIMARY TREATMENT

At present,  there are two basic ways of
treating wastes.  They are called primary
and  secondary.   In primary  treatment,
solids are allowed  to settle and  are  re-
moved from the water.  Secondary treat-
ment, a further step in purifying waste
water, uses biological processes.

As  sewage  enters  a plant for primary
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 up-
stream surface of the screen can be raked
off manually or mechanically.

Some plants use a device known as a com-
minutor 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 pulver-
ized 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.

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SCREEN
                     In some plants, another screen is placed
                     after the grit  chamber to remove any
                     further material that might damage equip-
                     ment or interfere with later processes.
                     With the screening completed and the grit
                     removed, the sewage  still contains sus-
                     pended solids.  These are 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 re-
                     duced, the  suspended  solids will grad-
                     ually 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 dis-
                     posal.

                     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  continu-
                     ously while others  remove it at intervals.
                      To  complete the primary treatment, the
                      effluent  with  the sludge  removed leaves
                     the  sedimentation  tank for chlorination
before being discharged into a stream or
river.  Chlorine gas is fed into the water
to kill disease-causing bacteria.  It  also
helps to reduce odors.
Although 30 percent of the municipalities
in the United States give only primary
treatment to their sewage, this process by
itself is considered entirely inadequate for
most needs.
Today's cities and industry, faced with in-
creased amounts of wastes and wastes that
are more difficult to remove from water,
have turned to secondary and even  ad-
vanced waste treatment.
   SECONDARY TREATMENT
   Secondary treatment removes  up to 90
   percent of the organic matter in sewage by
   making use of the bacteria in it. The two
   principal types of secondary treatment are
   trickling niters and the activated-sludge
   process.
   After the  effluent leaves the sedimenta-
   tion tank in the primary stage of treat-
   ment, 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 ten 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 con-
   sists  of distributing the  effluent inter-
   mittently  through  a network of pipes laid
   on or beneath the surface of the stones.

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Attached to these pipes are smaller, verti-
cal 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.
The trend today is toward the use of the
activated sludge process instead of trick-
ling 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
primary treatment,  it is  pumped to an
aeration tank where it is mixed with air
and  sludge loaded  with  bacteria and al-
lowed to remain for several hours. During
this  time, the  bacteria break down  the
organic matter.
From the aeration tank,  the sewage, now
called   mixed  liquor,  flows to  another
sedimentation tank to remove the solids.
Chlorination of the effluent completes the
basic secondary treatment.
The sludge, now  activated WiMl aodi-
tional millions of bacteria and  other tiny
organisms, can be used again by returaiBg"
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 lim-
itations.  The size  of the units necessary
for this  treatment  is small, thereby re-
quiring  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 difficult industrial wastes.
An adequate supply of oxygen is neces-
sary for the activated sludge  process to
be  effective. Air is mixed with  sewage
and biologically active sludge in the aera-
tion tanks by three different methods.
The first, mechanical aeration,  is  accom-
plished  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.

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In the second method, large amounts  of
air under pressure are piped  down into
the sewage and forced out through open-
ings in  the pipe.  The third method is  a
combination  of  mechanical  aeration and
the forced air method.
The final phase of the secondary treatment
consists  of the  addition  of  chlorine  to
the effluent coming from the  trickling
filter  or  the  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.
                                           Aeration unit in sewage treatment plant mixes
                                           oxygen from  the air  with  waste water to
                                           help bacteria break down organic compounds.

                                           Slowly  revolving  pipes  in  trickling  filter
                                           spray  waste  water over  beds  of  stones
                                           where  bacteria  consume   organic  matter.

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                         LAGOONS AND  SEPTIC TANKS
                         There  are many well-populated areas in
                         the United  States  that are  not  served
                         by any sewer systems or waste treatment
                         plants. Lagoons and septic tanks are the
                         usual  alternatives in such situations.

                         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 bac-
                         teria in the sewage  break down the or-
                         ganic 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  is a safe and effective means  of
                         disposing of strictly domestic wastes. Sep-
                         tic tanks should always  be located  so that
                         none of the effluent can seep into wells
                           ed for drinking.

                         Lagoons or, as they are sometimes called,
                         stabilization or oxidation ponds also have
several  advantages  when used correctly.

They can give sewage primary and sec-
ondary  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 equal to or
better than effluent from secondary treat-
ment. Changes in the weather  affect how
well a lagoon will break down the sewage.

When  used with  other  waste treatment
processes, lagoons  can be very effective.
A good example  of this is the Santee,
California,  water  reclamation  project.
After conventional primary and secondary
treatment by activated sludge,  the town's
waste water is kept in  a lagoon for  30
days.  Then the effluent, after chlorina-
tion, 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 qual-
ity, the residents of the area  can  swim,
boat, and fish in  the lake water.
                           Sunlight, algae, oxygen work together to purify waste water in a lagoon or oxidation pond.
DIAGRAM OF A SEPTIC TANK

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Industrial   concentrations  can  cause
gross pollution  without adequate treat-
ment.  Note  sewers dumping  wastes.
Activated carbon is tested in tanks as an
improved method of removing organic
matter  by  adsorption.  Organic  com-
pounds cling  to carbon  and settle out.

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                           '•v
               •v  /—f
  In the past,  pollution control was con-
   cerned 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 techno-
logical developments, changing land prac-
tices,  and  many other factors.

The  increased production  of goods  has
greatly  increased  the  amounts  of com-
mon industrial wastes. New  processes in
manufacturing are producing new, com-
plex  wastes that sometimes defy present
pollution  control   technology.  The  in-
creased application of commercial fertil-
izers and the development and widespread
use of a vast array of  new pesticides are
resulting in  a host of new pollution prob-
lems 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 situa-
tion.

Long  stretches   of  both  interstate  and
intrastate streams are subjected to pollu-
tion which ruins or reduces the use of
the water for many purposes.  Conven-
tional  biological waste treatment  proces-
ses 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 pack-
ing our  central  cities  but spreading  out
farther and farther into suburbia and ex-
urbia.  Across the country, new satellite
communities  are being born almost daily.
The construction or extension  of sewer
lines has  not matched either  the  growth
rate or its movements. Sea water intrusion
is a growing  problem in coastal areas. It
is usually caused by the excessive pump-
ing of  fresh water from the ground which
lowers the water level, allowing salt water
to  flow into the ground  water area.

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THE TYPES OF POLLUTANTS
Present-day problems  that  must be met
by  sewage  treatment  plants   can  be
summed up in the eight types of pollutants
affecting our waters.

The eight general categories are: common
sewage   and   other   oxygen-demanding
wastes;  disease-causing agents; plant nu-
trients;  synthetic organic chemicals; inor-
ganic chemicals and  other  mineral  sub-
stances; sediment; radioactive substances;
and heat.

Oxygen-demanding wastes—  These are
the traditional organic wastes contributed
by domestic sewage and industrial wastes
of plant and animal origin. Besides human
sewage,  such  wastes  result  from  food
processing,  paper mill  production, tan-
ning,  and other manufacturing processes.
These wastes  are usually  destroyed  by
bacteria if there is sufficient oxygen pres-
ent 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 in-
cludes  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 disin-
fection  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.  Nitrogen and
phosphorus  are the  two chief nutrients
present in small amounts in natural water,
but much larger amounts are  contributed
Common sewage from homes,  businesses
depletes  oxygen   supply  in  the  water.
              • y
Blood and grease  turn water  brown
at drain  from  meat packing  plant.


Floating algae create unsightly conditions.


10

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            Chemicals  in water from factory
            turn  stream   into   bubbling
            mess and are difficult to remove.
   by sewage, certain industrial wastes, and
   drainage from fertilized lands. Biological
   waste treatment processes do not remove
   the  nutrients—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-stimu-
   lates 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 man-
   ufacture.  Many of these substances are
   toxic to  fish and aquatic life and possibly
   harmful to  humans.  They  cause  taste
   and  odor problems, and resist conven-
Acid forms  in  water draining from abandoned mine,
tional waste treatment.  Some are known
to be highly poisonous at very low con-
centrations.  What the  long-term effects
of small doses of  toxic substances may
be is not yet known.

 Inorganic  chemicals  and  mineral  sub-
stances—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 opera-
 tions,  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.

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        R «$>
..   -         -     ,

                            Dirt from soil erosion 'pollutes water, reduces stream bed.
    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
    Thousands  of  fish are killed
    each year by wastes  in water
    that reduce oxygen supplies.
hardness  of  water supplies; corrode  ex-
pensive water treatment equipment;  in-
crease 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.  Sedi-
ments  fill  stream channels and harbors,
requiring  expensive  dredging,  and they
fill  reservoirs, reducing their  capacities
and  useful life. They erode power  tur-
bines and pumping equipment, and reduce
fish and shellfish  populations by blanket-
ing fish nests and food supplies.

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        Steaming  hot  water  pollutes  river.
More importantly, sediments reduce  the
amount of sunlight penetrating the water.
The sunlight is required by green aquatic
plants  which produce the oxygen neces-
sary 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 pol-
lution results from the mining and proces-
sing of radioactive ores; from the use of
refined radioactive materials in power re-
actors and for industrial, medical, and re-
search purposes; and from fallout follow-
ing  nuclear weapons  testing.  Increased
use of these substances poses a potential
public health problem. Since radiation ac-
cumulates in humans, control of this type
of pollution must take into consideration
total exposure in the human environment
—water, air, food, occupation, and medi-
cal  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.

Water in lakes or stored in impoundments
can be greatly affected by heat.  Summer
temperatures heat  up the surfaces, caus-
ing  the water to form into layers, with the
cooler water forming the deeper  layers.
Decomposing vegetative matter  from nat-
ural 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 dis-
charged  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 pollu-
tion.
To complicate matters, most of our wastes
are a mixture of the eight types of pollu-
tion,  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 drain-
age may contain radioactive substances
and pollutants washed from the sky, vege-
tation, buildings,  and streets  during rain-
fall.
                                                                                13

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    These  new problems  of a  modern  so-
    ciety have placed additional burdens
upon  our waste treatment systems.  To-
day's  pollutants  are more difficult to  re-
move  from the water.  And  increased
demands upon our water supply  aggra-
vate the problem. During the dry season,
the flow of rivers decreases  to such  an
extent that they  have difficulty  in assimi-
lating the effluent  from waste  treatment
plants.
In the future, these problems will be met
through better and more complete meth-
ods 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 prob-
lems is the widespread application of  ex-
isting  waste treatment  methods.  Many
cities  that  have only primary  treatment
need  secondary  treatment.  Many  other
cities  need  enlarged or modernized pri-
mary  and secondary systems.

But this is only  a  temporary solution.
The  discharge   of  oxygen-consuming
wastes will increase despite the universal
application  of  the most  efficient waste
treatment processes now available. And
these  are the simplest wastes to dispose of.
Conventional treatment processes are al-
ready  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 in 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 meth-
ods for removing pollutants are being de-
veloped.  The advanced waste treatment
techniques under investigation range from
extensions  of biological treatment capa-
ble of removing nitrogen and phosphorus
nutrients to physical-chemical separation
techniques such as adsorption,  distillation,
and reverse osmosis.

These  new processes can achieve any de-
gree 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."

Such water  can  be deliberately and  di-
rectly  reused for agricultural, industrial,
recreational,  or even drinking water sup-
plies.  This  complete  water  renovation
will mean  complete pollution  control and
at  the  same time  more water for the
Nation.
14

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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 sys-
      tems  will no  doubt replace the  modern
      facilities of today.
The process known as coagulation-sedi-
mentation  may  be used to increase the
removal of solids from effluent after pri-
mary and  secondary treatment.  Besides
removing  essentially all of the settleable
solids, this method can, with proper con-
trol  and sufficient addition of chemicals,
reduce the concentration of phosphate by
over 90 percent.

In this process, alum or lime is added to
effluent as it comes from the secondary
treatment.  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  treat-
ment, coagulation-sedimentation is classi-
fied 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

           After the removal of most of the solids,
           the  next problem  facing  the advanced
           waste treatment system is to get rid of the
           dissolved refractory organics. As the word
           indicates, this is the stubborn  organic
           matter which persists in water and resists
           normal biological treatment.
                                                                                                15

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The effects of the organics are not too well
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 gran-
ules 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.

An improvement of the process through
the use  of powdered  carbon is  under
study.  Rather than  pass the  effluent
through a bed  of granules, the powdered
carbon is put directly into the stream. The
organics stick to the carbon and then the
carbon is removed from the  effluent  by
using coagulating chemicals and allowing
the coagulated  carbon particles to settle
in a tank.

As would be expected, this finely ground
carbon will take out even more of the re-
fractory, or stubborn, organics.  The po-
tential  widespread  use  of  powdered
carbon adsorption depends largely on the
effectiveness  of regenerating  the  carbon
for use again.

Except for the  salts added during the use
of water,  municipal waste water that has
gone through the previous advanced proc-
esses  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.
16

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ELECTRODIALYSIS

Electrodialysis  is a  rather  complicated
process by  which electricity and  mem-
branes 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  an example, the two parts of common
table salt are sodium and chlorine.  When
these two elements separate  as salt  dis-
solves  in water, the sodium and chlorine
particles are called  ions.  Sodium ions
have a positive charge while chlorine ions
have a negative charge.

When the effluent passes through the elec-
trodialysis cell, the positive  sodium ions
are  attracted through a membrane to a
pole  or  electrode   that  is negatively
charged. The negatively charged chlorine
ions are pulled out of the water  through
another membrane toward  an electrode
with a positive charge.
With the salts  removed by the action of
the two electrodes, the clean  water flows
out of the electrodialysis cell for reuse or
discharge  into a river or stream.

When  a  typical  city  uses its water  the
amount of  salts  in  the  water  doubles.
Fortunately,  electrodialysis  can  reduce
the  amount  of salts by about one-half or
more.  In other  words, this process returns
the   salt  content  of  the  water  back 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 meth-
ods 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
treatment removes the material that  will
readily settle or float; the secondary bio-
logical step  takes care of the decompos-
able  impurities;  coagulation-sedimenta-
tion,  the   third  step,  eliminates  the
suspended solids; carbon adsorption re-
moves  the  remaining dissolved  organic
matter; electrodialysis returns the level of
the salts  to  what it was before the water
was  used; and, finally,  chlorination pro-
vides 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  primary and secondary treat-
ment but then is divided. Part of the ef-
fluent  passes  through  the   coagulation-
sedimentation and adsorption processes
which remove the organic  matter.  The
other half  of the sewage  is treated by
evaporation  and adsorption  to remove all
impurities including the minerals.

After  going  separate  ways, the   two
                                                                                            17

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     FILTER AND ADSORPTION
                             MIX
                                                             streams  are  mixed together,  chlorinated,
                                                             and then are ready for reuse or discharge
                                                             into a stream.  Splitting the effluent into
                                                             two streams and then reblending helps re-
                                                             duce the cost of waste treatment  for  a
                                                             more expensive process such as distilla-
                                                             tion.

                                                             Distillation or evaporation basically con-
                                                             sists 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. The
                                                             unwanted minerals and other  impurities
                                                             remain in the original chamber.

                                                             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 distilla-
                                                             tion process  is used on only part of the
                                                             effluent, and the rest of the waste water is
                                                             treated by the less  costly procedures.
                                                                                                  *•••«#»
18

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   So far, the most readily available proc-
    esses 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 reason-
able cost.

One such possible process under study is
reverse osmosis. When liquids with differ-
ent concentrations of mineral  salts  are
separated by a membrane, molecules of
  PRESSURE
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,
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—bac-
teria, detergents, nitrates.

Tests have shown that the theory  works
well, resulting in water good enough to
drink.  Efforts are now under way  to de-
velop large  membranes with long life.
Also,  the process and equipment need to
be tested on a large scale.

Many other techniques  to improve  waste
                                                                               19

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treatment  are  under  development  in
laboratories and in the field.

For  example, special  microscopic orga-
nisms are being tested for removing ni-
trates from  waste  water by reducing the
nitrates to elemental nitrogen.
CHEMICAL OXIDATION

Municipal  waste  waters  contain  many
organic materials only partially removed
by  the  conventional treatment  methods.
Detergents are a good example.  Oxidants
such  as ozone and chlorine  have been
used for many years to improve the taste
and odor qualities or to disinfect munici-
pal drinking water.  They  improve  the
quality of the water by destroying or alter-
ing 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 pre-
vented  the  use of this  process in  the
treating of wastes.  Now, improvements in
the production  and application of ozone
and pure oxygen  may  reduce costs suffi-
ciently  to  make  their use  practicable.
When operated in conjunction with other
processes, oxidation could become an ef-
fective weapon in eliminating wastes re-
sistant to other processes.
 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 time. Sludge must be
dried so that it can be more easily dis-
posed  of. By introducing  polymers into
the  sludge,  the  physical  and chemical
bonds  between the solids  are  tightened.
When this happens, Ihe water can be ex-
tracted more rapidly.

Wider use of polymers is  now being in-
vestigated.   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 arid  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.
POLYMERS  AND  POLLUTION

In discussing  the coagulation-sedimenta-
tion  process,  mention was made  of  the
use of alum or lime  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.
20

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                No 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 burned, buried, or disposed of in some
            manner.

            It is  a twofold  problem.  The sludge or
            other matter must be disposed  of to com-
            plete a city's or industry's waste treat-
            ment. And it must be disposed of in a
            manner not to add to or 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 at-
            mosphere.   This would  only  create  an
            additional  burden for our  already over-
burdened air to cope with. And air pollu-
tants by the action of rain and wind have
a habit of returning to the water, compli-
cating the waste treatment problem rather
than helping it.
There  are  many methods and processes
for dealing with the  disposal problem,
which  is  sometimes referred to as  the
problem  of ultimate disposal. The most
common method for disposing of sludge
and other waste concentrates consists of
digestion followed by filtration  and  in-
cineration.
The  digestion  of  sludge  takes  place in
heated tanks where the material  can  de-
compose 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
Sludge, solid matter left
after treatment, is spread
over  the  land  to  dry.


-------
the drum rotates in the sludge, the water
is  pulled through the filter and the resi-
dues 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,  conse-
quently, will  be  easier  to dispose of on
land or in water.

Incineration consists of burning the dried
sludge to reduce the residues to  a safe,
non-burnable ash.  The ash can  be dis-
posed  of by filling unused land  or  by
dumping it well out into the ocean. Since
most of the pollutants have been removed
by the  burning,  the ash will cause very
little change  in the quality of the water.
A very promising new method of sludge
disposal gets rid of the unwanted sludge
and helps restore a ravaged countryside.
In many areas of the country, tops of hills
and mountains were sliced away to get at
the coal beneath.  This strip mining left
ugly gashes and scars in otherwise beauti-
ful valleys of many States.  It would take
nature many years to restore the denuded
areas.

With  the  new  disposal  idea,  digested
sludge in semi-liquid form is piped to the
spoiled  areas.   The  slurry,  containing
many nutrients from the wastes, is spread
over the land to give nature a hand in re-
turning grass,  trees, and flowers to the
barren hilltops.

Restoration of the  countryside will also
help in the control of acids that drain from
mines  into streams and rivers, endanger-
ing the  fish and other aquatic life and
adding to the  difficulty in reusing the
        Countryside  restored  after  strip mining by  using  sludge  as  ft

-------
 water.  Acids are formed when pyrite con-
 taining iron and sulfur is exposed  to the
 air.

 Sludge  or other waste concentrates  are
 not always costly burdens. By drying and
 other processes, some cities have pro-
 duced fertilizers that are sold to help pay
 for part of the cost of treating wastes. If
 not sold to the public, some municipalities
 use the  soil enrichers on parks, road park-
 ways, and other public areas.
Some industries have found they can re-
claim  certain  chemicals  during  waste
treatment and reuse them in manufactur-
ing or refining processes. Other firms have
developed saleable by-products from resi-
dues in waste treatment.

More studies are going on to find greater
use for  sludge to  help solve the disposal
problem and to help offset the  cost  of
waste treatment.
                                                   Sludge from paper mill removed  from  waste  stream
                                                   and  dried  to  prevent  pollution  of  nearby river.
           Revolving drum filters water  from sludge
           so residues can be disposed of more easily.

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Common sewage  treatment terminology
Activated Sludge process removes
organic matter from sewage by sat-
urating it with air and biologically
active sludge.
Adsorption is an advanced way of
treating wastes in which carbon re-
moves  organic matter not respon-
sive  to clarification  or  biological
treatment.
Aeration Tank serves  as a chamber
for injecting air  into  water.

Algae are plants  which grow in sun-
lit waters. They are a food for fish
and small aquatic animals and, like
all plants, put oxygen in the water.

Bacteria are the  smallest living or-
ganisms which literally eat the or-
ganic parts of sewage.
BOD,  or  biochemical oxygen de-
mand,  is  the  amount of  oxygen
necessary  in the  water for bacteria
who  consume  the organic sewage.
It  is used as a  measure  in telling
how  well a sewage treatment  plant
is working.
Chlorinator  is a device for adding
chlorine gas to sewage to kill  infec-
tious germs.

Coagulation is  the  clumping  to-
gether  of solids to make them settle
out of  the sewage faster.  Coagula-
tion  of solids is brought about with
the use of certain  chemicals such
as lime, alum, or polyelectrolytes.
Combined Sewer carries  both sew-
age  and storm  water run-off.

Comminutor is  a  device  for the
catching and  shredding  of heavy
solid matter in the primary stage of
waste treatment.

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 pipe and escapes
out through holes  in the  side of
the pipe.

Digestion of sludge takes place in
heated   tanks  where  the  material
can  decompose  naturally and the
odors can be  controlled.

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 concen-
trated residue.
Effluent is the liquid that comes out
of a treatment plant after comple-
tion of the treatment  process.

Electrodialysis  is  a   process  by
which  electricity attracts  or draws
the mineral salts from sewage.

Floe is a clump of solids formed in
sewage when certain chemicals are
added.

Flocculation is the process by which
certain chemicals form clumps  of
solids in sewage.

Incineration consists of burning the
sludge to remove the water and re-
duce  the remaining  residues to a
safe,  non-burnable  ash.  The ash
can then be disposed of  safely on
land,  in some waters, or into  caves
or other underground  locations.

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 re-
ceiving stream.  This protects the
treatment plant  from  being  over-
loaded in case  of a sudden  surge
of  water  into  the  sewers.   Inter-
ceptors 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 process.

Lateral  sewers  are  the pipes that
run under the streets of a city and
into which empty the sewers from
homes or businesses.

Lagoons   are  scientifically   con-
structed ponds  in which sunlight,
algae, and  oxygen interact  to re-
store  water to  a quality equal  to
effluent from a secondary treatment
plant.

Mechanical  Aeration  begins  by
forcing the sewage up through a
pipe in a tank.  Then it is  sprayed
over the surface  of tank,  causing
the waste stream to absorb oxygen
from the atmosphere.

Microbes are minute living things,
either plant or animal. In  sewage,
microbes may be germs that  cause
disease.
Mixed Liquor is the name given the
effluent that  comes from the aera-
tion tank after the sewage has been
mixed with  activated sludge  and
air.
Molecule is the smallest particle of
an element or compound that can
remain in a free state and still keep
the characteristics of the  element
or compound.

Organic Matter is the waste from
homes or  industry of plant or ani-
mal origin.

Oxidation is  the  consuming   or
breaking down of organic wastes or
chemicals in  sewage by  bacteria
and chemical oxidants.
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 oxi-
dation pond is basically the same as
a sewage lagoon.
Primary  Treatment  removes  the
material that  floats or will settle in
sewage. It is accomplished by  us-
ing screens  to catch the  floating
objects and  tanks for  the heavy
matter to settle in.
Pollution results when something—
animal, vegetable,  or   mineral—
reaches water, making it more diffi-
cult or dangerous to use  for drink-
ing, recreation, agriculture, indus-
try, or wildlife.
Polyelectrolytes are synthetic chem-
icals used to  speed the removal of
solids from sewage. The  chemicals
cause  the solids  to  coagulate   or
clump together more rapidly than
chemicals like alum  or lime.

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   Filter  removes the  organic
wastes from sewage. The waste
water  is trickled over the bed of
sand.  Air and bacteria decompose
the wastes filtering through the sand.
The clean water flows out  through
drains in the bottom of the bed.
24

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The sludge accumulating at the sur-
face 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 trick-
ling  filters or  in  the  activated
sludge process.
Sedimentation  Tanks help remove
solids from sewage. The waste wa-
ter is  pumped to the  tanks where
the solids  settle  to the bottom or
float on top as scum. The scum  is
skimmed off the  top, and solids on
the bottom  are pumped  out to
sludge digestion  tanks.
Septic Tanks are used to treat do-
mestic  wastes.  The  underground
tanks  receive  the waste water di-
rectly  from the  home.  The  bac-
teria in the sewage decomposes the
organic waste  and  the sludge set-
tles on the bottom  of the tank.
The effluent flows out of the tank
into the ground through drains. The
sludge is pumped out of the tanks,
usually by commercial firms, at reg-
ular 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 set-
tles to the  bottom of sedimentation
tanks  and  must be disposed of by
digestion or other methods to com-
plete  waste treatment.
Storm  Sewers are a separate system
of  pipes  that  carry  only runoffs
from  buildings and land  during  a
storm.
Suspended Solids  are the wastes that
will not  sink  or settle in sewage.
Trickling  Filter is a bed of rocks
or stones.  The sewage is trickled
over the bed  so the  bacteria  can
break  down  the organic wastes.
The bacteria collect on the stones
through repeated use of the filter.
Waste  Treatment Plant is a series
of tanks, screens, filters, and other
processes  by which pollutants are
removed from water.


Sprawling waste treatment plant that serves part of Chicago.
                                     As the Nation's
                                     principal conservation agency,
                                     the Department of
                                     the Interior has
                                     basic responsibilities for
                                     water, fish, wildlife,
                                     mineral, land, park,
                                     and recreational resources.
                                     Indian and
                                     Territorial affairs
                                     are other major concerns
                                     of America's "Department
                                     of Natural Resources."
                                     The Department works
                                     to assure the wisest
                                     choice in managing
                                     all our resources
                                     so each will make
                                     its full contribution
                                     to a better United States—
                                     now
                                     and in the future.
                                          A publication prepared by the Office of Public Information
                                              Federal Water Pollution Control Administration

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    the  fight
U.S. DEPARTMENT OF THE INTERIOR • FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
                    US. GOVERNMENT PRINTING OFFICE • I96» 0—335-309

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