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waste water

           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

         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
                      E/ectrodia/ysis   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
                         October  1969
    For sale by the Superintendent of Documents,
        U.S. Government Printing Office
      Washington, D.C. 20402 - Price 65 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 drawing 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.

                     COLLECT! WO
                  TIRE ATI WO  WASTES
                         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.

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


                          {EWER  SYSTEM

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

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

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-
minuter 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 hi 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.

                GRIT CHAMBER
              "\  v-Jfc&.v.  n
                     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-

                     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 filters  and the activated-sludge
                                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.


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 with  addi-
tional millions of bacteria 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 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

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.

                          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
                           ink 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
                          used 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.


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.

FURTHER                                      OF
                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-

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.


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.
Blood and grease turn water brown
at drain  from meat packing plant.
Floating algae create unsightly conditions.

            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

   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.

                         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.

        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-

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-

              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

           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


      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.


                                                            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.
                     •• ••

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.



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
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.
               TREATED WATER

Properly designed and applied, the meth-
ods that have been explained will be able
to supply any  quality of water  for any

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

                                                              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-

                                                              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.

            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

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
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


 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.

 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

 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, the 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 and secondary  stages.
And this method of removing solids can
be  applied immediately without lengthy
and expensive  addition  of buildings or
new facilities.

The chemicals  also hold  promise  as a
means  of  speeding the  flow of  waste
waters through  sewer systems,  thus, in
effect, increasing  the capacity of  existing

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.

         THE  PROBLEM
                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

            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-
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
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
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  fertilizer for plants.

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

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.

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
 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

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

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

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
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
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

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.

The sludge accumulating at the sur-
face must be removed  from the bed
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 decompose-; 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
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
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—
                                     and in the future.
                                            publication prepared by the Office of Public Information
                                               Federal Water Pollution Control Administration