WATER POLLUTION CONTROL RESEARCH SERIES  17090 EHX 07/71
Waste Treatment  Lagoons-
I     State of the  Art
   U.S. ENVIRONMENTAL PROTECTION AGENCY

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          WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes the
results and progress in the control and abatement of pollution
in our Nation's waters.  They provide a central source of
information on the research, development and demonstration
activities in the Environmental Protection Agency, through
inhouse research and grants and contracts with Federal, State,
and local agenciefs, research institutions, and industrial
organizations.

Inquiries pertaining to VJater Pollution Control Research
Reports should be directed to the Chief, Publications Branch
(Water), Research Information Division, R&M, Environmental
Protection Agency, Washington, B.C. 20^-60.

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    WASTE  TREATMENT  LAGOONS -  STATE  OF THE ART
                           by
    Missouri Basin  Engineering  Health Council
                  State Office  Building
                    Cheyenne, Wyoming
                        for  the
            Office of Research and Monitoring
           ENVIRONMENTAL PROTECTION AGENCY
                  Project  #17090  EHX
                       July,  1971
For sale by the Superintendent of Documents, U.S. Government Printing OlEce, Washington, D.C. 20402 - Price $1.25

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                  EPA Review Notice
This report has been reviewed by the Environmental Protection
Agency and approved for publication.  Approval does not
signify that the contents necessarily reflect the views and
policies of the Environmental Protection Agency nor does
mention of trade names or commercial products constitute
endorsement or recommendation for use.
                        ii

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                       ABSTRACT

Waste treatment lagoons have found extensive use in the
United States with over 3500 units in operation.  For con-
venience, it was possible to break down waste treatment
lagoons into three groups:  (1)  oxidation ponds,  (2) aerated
lagoons and  (3) anaerobic lagoons.

Oxidation ponds are relatively shallow lagoons with a long
retention period.  Operating data indicate that oxidation
ponds do not produce a high quality effluent all of the time.
The effluent quality problem is created by algae which are
discharged in the effluent.  Multicell series ponds improve
effluent quality significantly.  Various types of simple
filters may be of value but further research is needed.

Aerated lagoons were developed to meet overloaded oxidation
ponds by supplying oxygen mechanically.  The aerated lagoons
have developed as short retention time, completely mixed acti-
vated sludge systems and as large, incompletely mixed systems.
The CMAS aerated lagoons lend themselves to mathematical
evaluation and more precise design whereas incompletely aer-
ated lagoons defy simple evaluation.  Aerated lagoons must
be modified to obtain maximum solids removal if a high
quality effluent is to be obtained.

Anaerobic lagoons are heavily loaded systems which depend
on anaerobic metabolism to produce up to 80% BOD reduction.
The key to good anaerobic systems lie in adequate mixing
below the surface, surface scum, warm temperature, sufficient
retention  time, and a uniform rate of feeding.  To date best
results with anaerobic lagoons have been obtained with meat
packing wastes.  Aerobic treatment must follow anaerobic
lagoons in order to produce a high quality effluent.

The future of wastewater lagoons lies with their proper
design and operation.  There is no reason to believe lagoons
cannot meet water quality criteria with minor modifications.

This report was submitted in fulfillment of Project # 1T090EHK
under the sponsorship of the Environmental Protection Agency.
                          ill

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                     CONTENTS
Section




  I.        Conclusions




  II.        Recommendations




  III.      Introduction




  IV.        Oxidation Ponds




  V.        Aerated Lagoons




  VI.        Anaerobic Lagoons




  VII.      Acknowledgements




  VIII.     Glossary
Page




   1




   3




   5




   7




  73




 115




 147




 148
                           v

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                         TABLES

No.                                                  Page
 1.   Fayette, Mo., Oxidation Pond Operational        24
      Data, 1957-58.

 2.   Fayette, Mo., Oxidation Pond Operational        25
      Data, 1958-59.

 3.   BOD Data Collected at Five California           28
      Oxidation Ponds

 4.   Median Values for Industrial Oxidation          29
      Ponds

 5.   Criteria Used for the Design of Anaerobic      118
      Lagoons Treating Meat Wastes

 6.   Manure Stabilization Pond Loading Rates        120

 7.   Summary of Loading and Performance Data        124
      for Anaerobic Lagoons Treating Municipal
      Wastewater in Australia

 8.   Operation Data for Anaerobic Lagoons           127
      Treating Industrial Wastewaters

 9.   Required Conditions or Levels of Indicated     135
      Biological Reaction in Ponds.
                            VI

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                        SECTION I
                       CONCLUSIONS

 1.  Operational data from oxidation ponds indicates that
    effluent quality will not meet current Water Quality
    Criteria all of the time.

 2.  Effluent quality from oxidation ponds is determined by
    the concentration of algae in the effluent.

 3.  Single cell ponds are not as efficient as multicell
    ponds in reducing the 'suspended algae concentration.

 4.  Chemical precipitation can be used to remove the excess
    algae from the effluent but is expensive.

 5.  Research indicates a rock filter may assist in removal of
    algae.                           '

 6.  Coliform reductions in oxidation ponds are the result of
    starvation rather than from toxic materials or from un-
    usual predation.

 7-  Aerated lagoons are basically useful for partial BOD
    removal.

 8.  High quality aerated lagoon effluents can be produced
    only if the microbial solids are removed from the ef-
    fluents.

 9.  Low temperatures adversely affect floating aerators in
    aerated lagoons with ice build up changing the operating
    characteristics.

10.  Diffused aeration systems have worked better than mech-
    anical systems in cold climates.

11.  Completely mixed aerated lagoons require short term aera-
    tion time for economical operation.

12.  Facultative aerated lagoons are designed with enough
    aeration to supply the oxygen demand but not enough to
    keep the solids in suspension.

13.  Performance criteria cannot be predicted for facultative
    aerated lagoons prior to actual operation.

14.  Aerated oxidation ponds are overloaded oxidation ponds
    to which diffused air was added to increase algae growth.

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15. Anaerobic lagoons are useful in reducing the BOD up to
    80% with concentrated organic wastes.

16. Anaerobic lagoons must be followed by aerobic treatment
    for a high quality effluent.

17. Anaerobic lagoons have been most successful in treating
    meat packing wastes.

18. The future of all types of lagoons depends upon proper
    design and operation  in relationship with the fundamental
    biochemistry of the microbes in the various systems.

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                       SECTION II

                    RECOMMENDATIONS

This study was designed to review the current state of
knowledge concerning wastewater lagoons and to summarize
the existing information on design and operation as well
as indicating future needs in order to improve these
systems.

One of the primary needs for all three wastewater lagoon
systems is for a concerted field data gathering and evalua-
tion program.  The simplicity of wastewater lagoons has
resulted in little operational data of value for proper
engineering evaluation.  Long term data collection is an
urgent need that should be started immediately if informa-
tion is to be obtained in the forseeable future.

Solids separation studies should be begun immediately since
the primary cause of poor effluent quality is directly
related to the microbial solids in the effluent.  Multi-
cell ponds and rock filters offer two possible methods for
removing the solids to a reasonable level.

Wastewater lagoons have been an important part of the waste
treatment package, especially for small municipalities and
industries.  It is apparent that current design criteria
for wastewater lagoons are not adequate to meet the water
quality criteria currently being established.  As a net
result, there is some effort being made to discard waste-
water  lagoons from future consideration.  Fundamental con-
cepts  discussed in this study point to a number of ways
wastewater lagoon designs can be modified to produce the
desired effluent quality.  The value of wastewater lagoons
far outweighs their disadvantages, making it essential that
efforts be directed to demonstrating how the different
lagoons systems can be modified  to produce the desired re-
sults .

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                      SECTION III

                      INTRODUCTION

Although waste treatment .lagoons were first used in the mid-
twenties, it was not until the last two decades that waste
treatment lagoons achieved popularity.   Currently,  there are
over 3500 waste treatment lagoons handling domestic sewage in
the United States and more are being constructed each day.
In spite of their widespread use, there is limited  data as to
the operational characteristics of waste treatment  lagoons.
Engineers have not bothered to make scienfific evaluations to
correlate operational conditions with original design criter-
ia.  Only in a few instances has there  been the development
of basic data sufficient to produce sound design criteria.
While there has been a large number of  studies in waste treat-
ment lagoons, most of these studies have been  fragmented and
lacking in sufficient depth to have real meaning.   If we
are to continue to design and construct waste  treatment la-
goons, it is important that we have proper design criteria
that will result in the production of the desired effluent
quality.  The purpose of this state of  the art review is to
bring as much information as is available together  to develop
sound design and operational criteria.   It is  hoped that this
review will be of value to all engineers concerned  with waste
treatment lagoons.

One of the problems with waste treatment lagoons  is that of
semantics.  Over the years a number of  terms have been used
to designate waste treatment lagoons.   Each person  selected
the term that was used in his area.   The net result has been
a certain amount of confusion.   To compound the  problem,  two
additional modifications of the original waste treatment la-
goon have been developed with conflicting terminology.   in
order to eliminate some of the confusion with  regard to nom-
enclature, it was decided to use the following terms to des-
cribe the different waste treatment lagoons:

    1.  Oxidation Ponds:  the original waste treatment lagoon
                        utilizing bacteria-algae  symbiosis
                        and sedimentation for  treatment.

    2.  Aerated Lagoons:  waste treatment  lagoons  having a
                        mechanical aeration device  to supply
                        the oxygen needed by the bacteria
                        for stabilization.

    3.  Anaerobic Lagoons:  waste  treatment lagoons devoid of
                        oxygen,  utilizing methane bacteria
                        for stabilizing  the organic matter
                        in the wastes.

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These definitions were not meant to be all inclusive; but
rather were designed to define the three basic modifications
of waste treatment lagoons in simple terms that could be
meaningful to engineers concerned with their design and oper-
ation.

Each of the three basic waste treatment lagoon systems has
their own distinctive characteristics even though they all
operate on the same fundamental biochemical concepts.  In
order to minimize confusion, it was decided to divide the
State of the Art review into three distinct sections, one for
each of the three basic lagoon systems.  This organizational
scheme resulted in some overlap of fundamental ideas; but it
was felt that this limited redundancy would help reinforce
the fundamental concepts.  In view of the different back-
grounds of the authors, the approaches to each section repre-
sent three ways of looking at waste treatment lagoons.  At
the same time it should be recognized that the senior author
exercised his prerogative of assisting the junior authors
with their sections.  Most of all one should understand that
this State of the Art review was not prepared by three uni-
versity professors from a purely academic point of view.  All
three of the authors have been actively involved in field
studies as well as in laboratory studies.  This State of the
Art reflects their professional experience both directly and
indirectly through interpretation of other investigators re-
search results.  The value of this review lies in the fact
that it is more than just a compilation of published informa-
tion, it is a professional interpretation and critical evalu-
ation of the available literature.  Judgement has been used
in selecting the references from the tremendous number of
reports and publications.  Some information was missed by
oversight; while other information was omitted for lack of
specific value.  In any case, the authors recognize that some
people will disagree with their selection and interpretation.
For this the authors offer no apology as no personal slight
was intended.  Each of us has assumed full professional re-
sponsibility for what we have written and we believe that we
have shown that waste treatment lagoons have just begun to
find their place in preserving our environment from pollution.
At the same time, we recognize the need for modification of
existing engineering practice if we are to achieve the maxi-
mum capabilities of waste treatment lagoons.  We have attempt-
ed to point out the areas where changes are needed and we have
made specific recommendations.  Ours was not just the role of
the critic, but that of the innovator as well.  We hope that
you will find this State of the Art of real value.  If you
do, then our efforts will have been well spent.

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                        SECTION IV

                     OXIDATION PONDS

Oxidation ponds grew out of the concept of natural purifica-
tion.  It was observed that the discharge of wastewaters in-
to streams and rivers resulted in the purification of the
organic contaminants by the microorganisms living within the
streams *   Only a short time of flow was required to stabilize
relatively large quantities of organic pollutants.  Not only
was the organic matter stabilized but the enteric pathogens
died off, making the water safe for reuse downstream.  As the
need for wastewater treatment increased, it was recognized
that simple systems requiring little operational skills were
needed for small communities, shopping centers, motels, sub-
divisions, and individual homes.  Existing wastewater treat-
ment systems utilized the principles of natural purification
but required considerable equipment and close operational
controls.  Since the basic problem in the stabilization of
organic wastes was the transfer of oxygen from the atmosphere
into the wastewaters, it was only natural to create a shallow
lake to permit rapid transfer of oxygen for the microorgan-
isms .  The large surface area permitted oxygen to penetrate
the shallow liquid depth, thereby stimulating aerobic bacter-
ia and preventing odor nuisances from developing.  It was
soon observed that these shallow sewage ponds stimulated the
growth of algae during warm weather with the production of
tremendous quantities of oxygen.  It was soon concluded that
the bacteria and algae in the oxidation ponds formed a sym-
biotic relationship which accelerated the treatment of waste-
waters.  The bacteria aerobically stabilized the organic
matter with the release of carbon dioxide which was taken up
by the algae in the presence of sunlight with the production
of more algae and the release of oxygen for the bacteria.
Together the bacteria and the algae produced a combined re-
action that neither produced alone.  The resulting effluent
from these sewage ponds showed a definite BOD reduction and
contained only dispersed green algae.  Thus, the oxidation
pond found application as the simplest biological treatment
system to design, construct, and operate; as long as land was
available.

Initially, oxidation ponds were used after primary sediment-
ation to remove gross solids; but it was soon learned that
raw sewage could be added directly to the oxidation pond
without any problems.  Design of oxidation ponds was largely
a matter of trial and error.  Data learned from existing
plants were incorporated into the design of new plants.  As
additional experience was gained in the field, the design of
oxidation ponds became more sophisticated.  California and

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Texas were the first states to develop design criteria for
oxidation ponds.  World War II showed the results that could
be obtained in treating sewage from military camps and furn-
ished the impetus to look at oxidation ponds more seriously.
Slowly but surely, sound design criteria were developed which
could be applied almost everywhere in the United States.

                       DESIGN CRITERIA

Originally, the design criteria for oxidation ponds was re-
latively simple.  Domestic sewage oxidation ponds were design-
ed for 20 to 25 days retention based on settled effluent.  Us-
ing 100 gpcd flow rates and a 3 ft. depth, loading rates up to
400 people per acre of 45 Ibs BOD/acre/day were allowed.
Two or more ponds were recommended.  These criteria were the
basis of design of oxidation ponds in California by Caldwell
(1) .

Today, most state health departments have more detailed
design criteria.  By and large these design criteria have
been developed from the Committee Report of the Missouri
Basin Engineering Health Council (2), approved on January 21,
1960.  The Recommended Standards for Sewage Works, Great
Lakes-Upper Mississippi River Board of State Sanitary Engine-
ers, 1969 Edition, represents the typical design criteria
currently being employed by engineers in the design of oxida-
tion ponds.  The following design criteria was reproduced
from material submitted by the South Dakota State Department
of Health.

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           WASTE STABILIZATION PONDS (Lagoons)

A. Supplement to Engineer's Report

The engineer's report shall contain pertinent information
on location, geology, soil conditions,  area for expansion,
and any other factors that will affect the feasibility and
acceptability of the proposed treatment.

The following information must be submitted in addition to
that required in Section I, engineer's report.

1. Supplementary Field Survey Data

   a. The looation and direction of all residences, commercial
      development, and water supplies within 1/2 mile of the
      proposed pond.

   b. Soil borings to determine surface and subsurface soil
      characteristics of the immediate area and their effect
      on the construction and operation of a pond located on
      the site.

   c. Data demonstrating anticipated percolation rates at
      the elevation of the proposed pond bottom.

   d. A description, including maps showing elevations and
      contours  of the site and adjacent area suitable for
      expansion.

   e. Sulfate content of the basic water supply.

B. Basis of Design

1. Area and Loadings

One acre of water surface  should be provided  for each 100
design_population or population equivalent.   In terms of  BOD,
a loading of 0.4 pounds per day per 1,000  square feet should
not be exceeded.  Higher design loadings will be judged
after review of material contained  in  the  engineer's report
and after a field investigation of  the proposed site by  the
reviewing authority.

Due consideration will be  given to  possible future  municipal
expansion and/or additional sources of wastes when  the origin-
al land acquisition  is made.   Suitable land should  be avail-
able at the site  for increasing the size  of the original con-
struction.

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 2.  Industrial Wastes

 Due consideration will  be  given  to  the  type  and  effects  of
 industrial wastes on  the treatment  process.

 3.  Multiple Units

 Multiple cells designed to permit both  series  and  parallel
 operation are recommended  for  all except  small installations
 (3  acres or less).  All future stabilization pond  designs
 should specify two-cell units  or, on  small installations,
 two-level bottoms.  This flexibility  is desirable  when load-
 ings are light or when  a community  is installing a new sewer
 system,  since in  the  period preceding substantial  connections
 the entire discharge  can be put  into a  single  cell,  thus fac-
 ilitating the maintenance  of satisfactory water  levels.  In
 addition, when a  low  algae content  in the effluent is desired,
 the cells may be  advantageously  operated  in  parallel during
 fall,  winter,  and spring when  algae development  is less  in-
 tensive  and in series during the summer months.  Series  oper-
 ation is also beneficial where a high level  of BOD or coli-
 form removal is important.

 Where a  greater degree  of  treatment is necessary or  desirable,
 1 or more cells in each series may be added  to the primary
 cell.   In series  operation, the  primary cell shall have  a
 surface  area equal to that set forth in Section  B.I.

 4.  Pretreatment

 When ponds are used to  provide additional treatment  for  ef-
 fluents  from existing or new primary or secondary  sewage
 treatment works,  the reviewing authority will, upon  request,
 establish BOD  loadings  for  the pond after due  consideration
 of  the efficiencies of  the  preceding treatment units.

 5.  Pond  Shape

 The  shape of all  cells  should be such that there are no
 narrow or elongated portions.   Round, square,  or rectangular
 ponds  with a  length not exceeding 3 times the  width  are  con-
 sidered  most desirable.   No islands, peninsulas, or  coves
 should be  permitted.   Dikes should be rounded  at corners to
 minimize  accumulations of  floating materials.

 C. Location

 1. Distance From Habitation

A pond site should be as far as practicable from habitation


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or any area which may be built uj6 within a reasonable future
period.

2. Prevailing Winds

If practicable, ponds should be located so that local prevail-
ing winds will be in the direction of uninhabited areas. Pre-
ference should be given sites which will permit an unobstruct-
ed wind sweep across the ponds, especially in the direction
of the local prevailing winds.

3. Surface Runoff

Location of ponds in watersheds receiving significant amounts
of runoff water is discouraged unless adequate provisions are
made to divert storm water around the ponds and otherwise
protect pond embankments.

4. Ground Water Pollution

Proximity of ponds to water supplies and other facilities
subject to contamination and location in areas of porous soils
and fissured rock formations should be critically evaluated
to avoid creation of health hazards or other undesirable con-
ditions.  The possibility of chemical pollution may merit
appropriate consideration.

D. Pond Construction Details

1. Embankments and Dikes

  a. Material

     Embankments and dikes shall be constructed of relatively
     imprevious materials and compacted sufficiently to
     form a stable structure.  Vegetation should be removed
     from the area upon which the embankment is to be placed.

  b. Top Width

     The minimum embankment top width should be 8 feet to
     permit access of maintenance vehicles.  Lesser top widths
     will be considered for very small installations, 1 acre
     or less.

  c. Maximum slopes

     Embankment slopes should not be steeper than:

      (1)  Inner
          3 horizontal to 1 vertical
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   (2)  Outer
        3 horizontal to 1 vertical.

d. Minimum Slopes

   Embankment slopes should not be flatter than:

    (1) Inner
        6 horizontal to 1 vertical.  Flatter slopes are
        sometimes specified for larger installations be-
        cause of wave action but have the disadvantage of
        added shallow areas conducive to emergent vegeta-
        tion.

    (2) Outer
        Not applicable, except significant volumes of
        surface water should not enter the ponds.

e. Freeboard

   Minimum freeboard shall be 3 feet except for very small
   installations, 1 acre or less.

f. Minimum Depth

   The minimum normal liquid depth should be 2 feet.

g. Maximum Depth

   Maximum normal liquid depth should be 5 feet.

h. Seeding

   Embankments shall be seeded from the outside toe to 1
   foot above the high water line on the dikes, measured on
   the slope.  Perennial type, low growing, spreading
   grasses that withstand errosion and can be kept mowed
   are most satisfactory for seeding of embankments.  In
   general, alfalfa and other long-rooted crops should
   not be used in seeding, since the roots of this type
   plant are apt to impair the water holding efficiency of
   the dikes.  The County Agricultural Extension Agent
   can usually advise as to hardy, locally suited permanent
   grasses which would be satisfactory for embankment seed-
   ing.  Additional protection for embankments  (riprap) may
   be necessary where the dikes are subject to erosion due
   to severe flooding of an adjacent watercourse or severe
   wave action.
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   i.  Vegetation Control

    A method shall be specified which will prevent vegetation
    growth over the bottom of the lagoon and up to 1 foot
    above the water line on the dikes.

2.  Pond Bottom

   a.  Uniformity

    The pond bottom should be as level as possible at all
    points.  Finished elevations should not be more than 3
    inches from the average elevation of the bottom.  Shallow
    or feathering fringe areas usually result in locally un-
    satisfactory conditions.

   b.  Vegetation

    The bottom shall be cleared of vegetation and debris.  Or-
    ganic material thus removed shall not be used in the dike
    core construction.  However, suitable topsoil relatively
    free of debris may be used as cover material on the outer
    slopes of the embankment.

   c.  Soil Formation

    The soil formation or structure of the bottom should be
    relatively tight to avoid excessive liquid loss due to
    percolation or seepage.  Soil borings and tests to deter-
    mine the characteristics of surface soil and subsoil shall
    be made a part of preliminary surveys to select pond sites.
    Gravel and limestone areas must be avoided.

   d.  Percolation

    The ability to maintain a satisfactory water level in the
    ponds is one of the most important aspects of design.  Re-
    moval of porous topsoil and proper compaction of subsoil
    improve the waterholding characteristics of the bottom.
    Removal of porous areas, as gravel or sandy pockets,
    and replacement with well-compacted clay or other suitable
    material may be indicated.  Where excessive percolation
    is anticipated, sealing of the bottom with a clay blanket,
    bentonite, or other sealing material should be given
    consideration.

3.  Influent Lines

   a.  Material

    Any generally accepted material for underground sewer


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  construction will be given consideration for the influent
  line to the pond.  The material selected should be adapt-
  ed to local conditions.  Special consideration must be
  given to the character of the wastes,  possibility of
  septicity,  exceptionally heavy external loadings,
  abrasion, the necessity of reducing the number of joints,
  soft foundations, and similar problems.  Surcharging of
  the sewer upstream from the inlet manhole is not permit-
  ted.
b. Manholes

  A manhole shall be installed at the terminus of the out-
  fall line or the force main and shall be located as close
  to the dike as topography permits and its invert should
  be at least 6 inches above the maximum operating level
  of the pond to provide sufficient hydraulic head without
  surcharging the manhole.

c. Influent Lines

  Influent lines should be  located along the bottom of the
  pond so that the top of the pipe is just below the aver-
  age elevation of the pond bottom.  This line can be placed
  at zero grade.  The use of an exposed dike to carry the
  influent line to the discharge points is prohibited, as
  such a structure will impede circulation.

d. Point of Discharge

  The influent line to a single celled pond should be es-
  sentially center discharging.  Each cell of a multiple
  celled pond operated in parallel shall have its own near
  center inlet but this does not apply to those cells
  following the primary cell when series operation alone is
  used.  Influent lines or  interconnecting piping to second-
  ary cells of multiple celled ponds operated in series
  may consist of pipes through the separating dikes.
  (Section D.4.c.)   Influent lines to rectangular ponds
  should terminate at approximately the third point farther-
  est from the outlet structure.  Influent and effluent
  piping should be located  to minimize short-circuiting
  within the pond.

e. Inlets

  The inlet line shall discharge horizontally into a shallow,
  saucer-shaped depression  which should extend below the
  pond bottom not more than the diameter of the influent
  pipe plus 1 foot.


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  f.  Discharge Apron

    The end of the discharge line should rest on a suitable
    concrete apron with a minimum size of 4 feet square.

4. Overflow Structures and Interconnecting Piping

  a.  Material

    Interconnecting piping and overflows should be of cast
    iron pipe or corrugated metal pipe of ample size.

  b.  Overflow Structure

    Overflow structures should consist of a manhole or box
    equipped with multiple-valved pond drawoff lines or an
    adjustable overflow device so that the liquid level of
    the pond can be adjusted to permit operation at depths
    of 2 to 5 feet.  The lowest of the drawoff lines to such
    structure should be 12 inches off the bottom to control
    eroding velocities and avoid pickup of bottom deposits.
    The overflow from the pond during ice-free periods
    should be taken near, but below, the water surface to
    release the best effluent and insure retention of float-
    ing solids.  The structure should also have provisions
    for draining the ponds.  A locking device should be
    provided to prevent unauthorized access to the level con-
    trol facilities.  When possible the outlet structure
    should be located on the windward side to prevent short-
    circuiting.  Consideration must be given in the design of
    all structures to protect against freezing or ice damage
    under winter conditions.

  c.  Interconnecting Piping

    Interconnecting piping for multiple unit installations
    operated in series should be valved or provided with
    other arrangements to regulate flow between structures
    and permit flexible depth control.  The interconnecting
    pipe to the secondary cell should discharge horizontally
    near the lagoon bottom to minimize need for erosion con-
    trol measures and should be located as near the dividing
    dike as construction permits.

E. Miscellaneous

  1.  Fencing

    The pond area shall be enclosed with a suitable fence to
    exclude livestock and discourage trespassing.  A vehicle
    access gate of minimum 8 foot width to accomodate mowing
    equipment should be provided.  All access gates should

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   be provided with locks.

2.  Warning Signs

   Appropriate signs should be provided along the fence
   around the pond to designate the nature of the facility
   and advise against trespassing.   A minimum size of 20"
   by 12" with a minimum size letter of 2" is recommended.

3.  Flow Measurement

   Provisions for flow measurement  shall be provided on the
   inlet and outlet.

4.  Liquid Depth Operation

   Optimum liquid depth is  influenced to some extent by
   lagoon area since circulation in larger installations
   permits greater liquid depth. The basic plan of opera-
   tion may also influence  depth.   Facilities to permit
   operation at selected depths between 2 and 5 feet are
   recommended for operational flexibility.
                         16

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Intrepretation of Criteria

Oxidation ponds have been considered as the equivalent to
other secondary treatment systems.  Operational data have
indicated 99 percent MPN coliform reduction and BOD reductions
from "70 percent in the winter under ice cover to 99 percent in
the summer.  This degree of treatment combined with their
simplicity has been responsible for the widespread use of oxi-
dation ponds.

Loading

Because of the importance of light for the growth of algae and
the concept of bacteria-algae symbiosis, loading criteria have
been based on the needs of the algae.  Oxidation ponds have
large surface areas to give maximum exposure to the sunlight.
The loading factors have been given in terms of population per
acre or in terms of BOD per acre per day.  The previous design
criteria indicated one acre of oxidation pond surface for
each 100 population.  Further south in Oklahoma the loading
rate can be increased to one acre per 200 population.  The
use of population loadirig rates is based on typical domestic
sewage where BOD data are not available.  The BOD loading was
0.4 lbs/1000 sq.ft./day or 17.4 Ibs/acre/day.  Further south
in Missouri the BOD loading can be 45 Ibs/acre/day.  While
it may seem that these surface loadings are rather arbitrary,
there is a definite basis for these loadings utilizing the
available  light for photosynthesis.  Oswald and Gotaas (3)
discussed  the relationship between bacterial oxygen demand
and photosynthesis meeting this demand.  They indicated that
photosynthetic efficiencies of only 10 percent were possible
in sewage  oxidation ponds.  Neel et al_   (4) suggested 1.5
langleys  (1 langley = 1 gm cal. peF cm2)/day/lb BOD/acre was
required for proper operation of oxidation ponds where ice was
not a factor in the winter months.  Winter loadings cannot
be evaluated from a light viewpoint and must be based on ex-
perience.  They found that 20 Ibs BOD/acre/day was the prac-
tical winter loading rate.  Although light was believed to
be a critical design factor, engineers were unable to utilize
the design equations employing light variations effectively.
Since light and load conditions were interrelated, BOD loading
factors could be employed more easily with decreasing loading
rates as one progressed from south to north.

Number of  Ponds.

Multiple ponds have been recommended from  the very beginning.
Two ponds  in series were considered  as  minimum.   In  Sweden,
Wennstrom  (6) constructed a system in  1934 with three oxidation
ponds in series and added the fourth pond  in  1939.   During  the
                              17

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summer  months microscopic  animals  developed which ate
the excess  algae in Pond  4.   Even  without the development
of microscopic animals, multiple cell oxidation ponds produc-
ed an effluent with less  algae  than  single cell ponds.  Un-
fortunately,  engineers  have  tended to ignore the value of
multiple cell ponds and have constructed single cell ponds.
The report  of the Missouri Basin Engineering Health Council
(2) may have  contributed  to  the shift to single cell ponds
by stating  that single  cell  ponds  were better for small in-
stallations.   Since single cell ponds were easier to construct
than multiple cell ponds,  most  oxidation pond installations
were considered small.  The  net result has been that a large
number  of oxidation ponds  are not  producing the effluent
quality that  they should  be  producing.  A short time ago
Oswald  et al   (7) developed  an  integrated oxidation pond
system  wTth~sound subdivision planning in which he recommend-
eded six ponds in series.  The  effluent quality in the last
pond was such that it could  be  used  in a park without danger.

Shape

It is  interesting to note  that  shape is important in the
design  of oxidation ponds.  The suggested design criteria
recommend round, square,  or  slightly rectangular ponds.
The purpose of this design is to permit distribution of the
incoming load throughout  the pond, depending upon wind
direction.   The shape of  the oxidation pond probably is not
as important  as originally thought.  A study in Israel (8)
has shown that it is possible to have a long narrow oxidation
pond  to create plug flow  characteristics.  It was found that
the long narrow type pond  gave  the same results as the square
type  pond.  As long as  reasonable  attention is paid to the
prevailing winds and their effect  on pond mixing, the shape
of the  pond is not critical.

Location

The location  of oxidation  ponds should be as far from houses
as possible so that odor  nuisances do not create problems.
It should be  recognized that future  growth will encroach on
any waste treatment plant.  There  is no way to design a treat-
ment  plant that will remain  isolated forever.  This is one
of the  reasons why conservative design criteria should be
employed to minimize the  possibility of odor nuisances.  Care
should  be made that the prevailing winds blow away from the
community served as they  pass over the oxidation pond.  This
will minimize the public  complaints  about the sewage treat-
ment plant.  It is also important  that the pond surface be
free  of obstructions so that the wind produces maximum mix-
ing.   Surrounding the oxidation pond by tall trees may hide
                            18

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the pond from view as might location in a ravine; but wind
action will be diverted above the pond and mixing" will be
minimized.  Without adequate mixing, the oxidation pond will
not function properly.  It is necessary to divert surface
runoff from entering the treatment plant.  Too much surface
runoff will reduce the retention time below desirable levels.
It is relatively simple to divert surface drainage around the
pond into the final effluent.  Care should be taken to insure
that ground waters near the ponds are not contaminated.  Soil
percolation tests can show the ability of the soil to hold
the water.  Neel and Hopkins  (9) documented an excellent
example of an oxidation pond built in porous soil.  Seepage
was so great that the pond was filled with difficulty and
nearby water wells became contaminated with synthetic deter-
gents.  This study clearly demonstrated the value of sealing
ponds prior to operation.  Clay has been used to seal ponds
as has plastic lining.  The organics in the wastewaters can-
not be counted on to seal the pond as there is simply not
enough organic matter for a complete seal for many years in
most raw sewage oxidation ponds.  Evaporation is important in
some areas of the United States.  Where a zero effluent dis-
charge system is desired, evaporation and percolation must
balance the influent flow and precipitation.  In arid areas,
evaporation may necessitate deeper pond depths during the
driest period of the year.  Because of evaporation and perco-
lation it is desirable to provide flow measuring devices at
the influent as well as at the effluent.  Too few plants have
provided even the simplest measuring devices, preventing any
reasonable evaluation of the treatment plant operations.

Depth

The liquid depth control in oxidation ponds should be variable
between a minimum of 2 ft and a maximum of 5 ft, except in
special circumstances where evaporation is very high.  Normal
pond depth is 4 ft.  This permits reasonable mixing of the
oxygenated upper layer of water with the deoxygenated lower
water layers so that aerobic conditions can be maintained in
the pond.  Where winter conditions are severe, the oxidation
pond merely becomes a sewage storage tank until warm weather
arrives.  At low temperatures biological activity is reduced
to a minimum and the sewage remains essentially untreated
until spring.  For this reason the ponds are normally drawn
down to 2 ft after the first frost has killed the algae.  The
effluent of the pond volume without any water quality problems.
This leaves 3 ft of pond depth for storage of sewage during
the winter months before any discharge occurs.  Discharge can
be made in the spring when effluent quality meets water quality
criteria.  The shallow pond then yields maximum treatment as
the liquid warms and normal depth can be reset without serious
problems.  Where severe winters are not a problem, the depth
                           19

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of the pond is kept constant at all times, adjustable water
depths are not of real value,under these conditions and can
be ignored.

The operation of oxidation ponds is affected by many factors
such as the waste characteristics, available light, tempera-
ture, wind, depth, retention time, and microbial predomina-
tion.  The design criteria established to date attempts to
produce the optimum system.  The success or failure of the
design criteria is determined by the quality of the effluent
produced daily in the field.  In order to evaluate existing
design criteria it is necessary to examine the field experi-
ences that have been reported for oxidation ponds and to
determine the critical variations effecting design.

                  OPERATING EXPERIENCES

Domestic Sewage

In the early part of the 1950s oxidation ponds were beginning
to see extensive use in the Missouri River Basin for the
treatment of domestic sewage except that little real informa-
tion was available as to a scientific evaluation of their
operations.  In 1954 the Conference of State and Territorial
Health Officers requested that the USPHS make detailed studies
on oxidation ponds so that sound design and operational data
could be developed.  Prior to this request, the primary data
on oxidation ponds came from Caldwell (1.) .  In working with
oxidation ponds Caldwell had developed some definite design
and operational concepts.  He believed that only settled sew-
age should be used in oxidation ponds.  With settled sewage
satisfactory treatment could be obtained in only 25 days re-
tention.  With a minimum depth of three feet the normal
design flow resulted in a load factor of 400 population/acre.
Considering the BOD load, it was 45 Ibs/acre/day or 15, Ibs/
acre-ft/day.  Caldwell recommended the use of two or more
ponds.  Operationally, Caldwell observed that the effluents
from oxidation ponds were very green with lots of algae.  The
conventional sewage tests for BOD and suspended solids were
found to be of little value in plant evaluation since they
were rather high.  There was a definite difference in the raw
waste characteristics and the final effluent characteristics.
While both contained BOD and suspended solids, the effluent
did not create obnoxious conditions on standing as did the
raw wastes.  This fact made Caldwell question the value of
these parameters in evaluating oxidation pond operations.  He
indicated that there was little of the original sewage in
the treated effluent, only suspended algae.  Caldwell was one
of the first to recognize that the quantity of organic matter
discharged in the effluent as algae cells could exceed the
quantity of organic matter entering the pond in the raw wastes
                           20

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This simple observation is of extreme importance in under-
standing oxidation pond operations, especially in view of
increasing stream quality regulations.  It was observed that
coliform bacteria were quickly destroyed in the presence of
algae but the mechanism of destruction was not known.  When
periodic odors did arise, Caldwell recommended use of nitrates.
While Caldwell supplied the best operational information to
date, there was definitely a need for more information from
field operations.

In 1956 Towne et al  (10) presented a report on cooperative
studies that the USPHS had undertaken with the state health
departments.  Their studies were divided into three areas:
1. basic data collection, 2. field studies, and 3. controlled
experimental studies.  The basic data collection was designed
to gather all of the information available about existing
ponds.  Approximately 350 were in operation in the Southwest
and the Midwest when this study was started.  The field
studies included the examination in depth of 5 oxidation ponds
in North and South Dakota and of 34 ponds in Texas and Okla-
homa.  The controlled experimental studies were designed to
produce fundamental data on the process mechanism.  The pri-
mary field results were summarized in this report.  The
North and South Dakota ponds were from 4 to 27 acres with
depths from 1.2 to 5.4 ft.  The BOD loadings ranged from 7 to
17 pounds/acre/day.  Four of the ponds were single cell ponds
while the fifth pond had five cells.  It was found that coli-
form bacteria reductions reached 99% more than 50% of the
time.  BOD reductions unfiltered samples were from 43% to
98%.  In the winter the suspended solids were reduced by 80
to 84% but in the summer there were priodic increases to as
much as 258%.  Sulfides were generally present under ice cover
but were absent in the summer.  These latter two items re-
flected upon the action or lack of action of the algae.
Scenedesmus was the predominant algae in the winter; while
Euglena was dominant in the warm weather.  Light penetration
was reduced by ice cover to 0.5% to 15% of that reaching the
surface.  In the summer 99% of the light was absorbed in the
upper 24 inches of the pond.  Diurnal variations in photo-
synthesis caused the dissolved oxygen to vary from 4 to 6
mg/1 at night to 38 mg/1 in the late afternoon.  The Texas
and Oklahoma plants treated primary or secondary effluents
in contrast to the raw sewage ponds in North and South Dakota.
Only two ponds studied in Texas and Oklahoma treated raw sew-
age.  The ponds averaged 3 ft depth and varied considerably
in size, shape, and loading.  The BOD loadings ranged from
12 to 225 Ibs/acre/day.  Operations were quite good with
little impact from temperature variations such as were observ-
ed in the Dakotas.  Thus, efforts were underway to develop
the information needed for proper evaluation of oxidation ponds
                            21

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These efforts culminated in a symposium on waste stabiliza-
tion lagoons in Kansas City, Missouri, in August, 1960.

While studies were underway in the United States, Wennstrom
(6) presented extensive operational data on oxidation pond
systems in Sweden.  This plant employed four ponds in series
after primary sedimentation.  With a retention period of
under 17 days, Wennstrom observed a BOD reduction from 159
mg/1 to 20 mg/1.  One innovation in these ponds was recircul-
ation of the pond contents to produce better mixing and equal-
ization of the material in the ponds.  Extensive biological
studies were carried out in this system of ponds yielding
the most extensive zooplankton studies on oxidation ponds.
Wennstrom clearly demonstrated the value of oxidation ponds
in treating domestic sewage and the results to be expected
in each pond operating in series, one with the other.  Un-
fortunately, Wennstrom?s study had limited circulation in the
United States and went unnoticed for the most part.

In Australia Parker et_ a_l (12) utilized anaerobic ponds ahead
of oxidation ponds for" the treatment of wastewaters.  The
anaerobic lagoons were capable of removing 80% of the BOD
with 5 days retention at 64F.  BOD loadings recommended
were 600 Ibs BOD/acre/day without any problems.  They found
that algae in the effluent greatly influenced the final BOD
and suspended solids.  The oxidation pond removed all of the
sewage contaminants so that the algae were the cause of both
the BOD and the suspended solids in the effluent.  The final
BOD ranged from 20 to 50 mg/1.  Parker questioned the desir-
ability of discharging the algae in the effluent even though
Caldwell  (1) had indicated it was not a problem.

 Neel and Hopkins  (9) reported on extensive tests carried
out at Kearney, Nebraska, from May, 1954 to July, 1955.  The
value of this study was limited by the fact that the Kearney
oxidation pond was constructed in very porous soil and tended
to leak excessively.  Approximately 75% of the wastes added
to the oxidation pond were lost by evaporation and percola-
tion.  The Kearney oxidation pond had a surface area of 10
acres and was designed as an experimental unit for determin-
ing the feasibility of using oxidation ponds for treating
all of the sewage from Kearney.  This latter fact accounted
for the large amount of data collected.  Examination of the
data indicated that the pond temperature ranged from 1 C to
34 C.  The turbidity in the oxidation pond was created by
algae and varied with the seasons of the year, reaching a
maximum in the summer.  These algae showed very little ten-
dency to settle.  Odors were unnoticeable as long as there
was adequate oxygen in the pond.  When anaerobic conditions
developed during the winter, odors were quite offensive.  Ice
cover on the lagoon acted as a lid and kept the odors within


                            22

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the pond until the spring thaw.  Floating solids created de-
finite operational problems and odors.  Wind action was re-
sponsible for mixing in the pond.  The wind action was suf-
ficient to cause a definite difference in elevations in the
pond and to induce a strong backflow along the bottom of the
pond.  Currents of 0.3 to 0.7 fps were measured along the
shore.  In spite of the wind action, normal waves were not
formed.  It was believed that synthetic detergents prevented
proper wave formation.  One thing for certain, the observation
reported by Caldwell  (1) that surface characteristics could be
used to determine treatment efficiency was confirmed in this
study.  When the organic wastes are stabilized in the pond,
a light wind will create definite waves which are visible on
the surface.  When organic matter remains untreated, the sur-
face of the pond is glassy smooth even with a light breeze.
The dissolved oxygen concentration in the pond ranged from
0 mg/1 to 36 mg/1.  Wind action was responsible for mixing
so that the dissolved oxygen or lack of dissolved oxygen
occurred at all depths.  The average BOD in the sewage was
149 mg/1.  The effluent BOD ranged from 18 mg/1 to 94 mg/1.
Neel and Hopkins were also faced with the fact that oxidation
pond effluent BOD values did not represent the stabilization
of the domestic sewage; but reflected the growth of algae.
Examination of other data indicates the difficulties that
arise in evaluating oxidation ponds operations on a simple
influent-effluent relationship.  The influent can show con-
siderable daily variation in waste characteristics while the
pond effluent is unaffected by these variations.  This is most
clearly shown in the chloride data where some data indicated
more chlorides entering the pond than leaving.  The pond
operated as a large surge basin for leveling out waste vari-
ations.  Real data evaluation for oxidation ponds requires
extensive data collection to determine average influent and
effluent values.

With loss of pond water by percolation,tests were run on
the chemical quality of water in nearby wells.  Chlorides
and synthetic detergent analyses definitely showed that the
ground water was being contaminated by the seepage from the
oxidation pond.  The reduction of coliform bacteria averaged
83%.  The predominant algae were Chlamydomonas, Microactinium,
and Euglena.  Algal growth and dissolved oxygen concentrations
in the oxidation pond were correlated generally with the avail-
able light.  Ciliated protozoa and rotifers were the primary
forms of zooplankton observed in the pond.  The loss of the
pond contents by percolation and contamination of the ground
water forced cessation  of the Kearney study and prompted
the search for another site for evaluating oxidation ponds.

The next test site for the USPHS was at Fayette, Missouri
(4,13).  A 15 acre oxidation pond system was constructed with
                             23

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five one acre test ponds and one 10 acre pond.  This system
was tested for 13 months in 1957-58 in one series and then
changed for a second 10 month series in 1958-59.  In the
1957-58 tests all units operated with 2.5 ft water depth ex-
cept the large unit which had 3.0 ft water depth.  The load on
each cell was adjusted to a BOD/acre/day basis as follows:
20, 40, 60, 80, and 100 Ibs BOD/acre/day.  The large cell had
a 15 Ibs BOD/acre/day load.  The average data for the first
series of test is given in Table 1.

                         Table 1

    Fayette, Mo., Oxidation Pond Operational Data, 1957-58



Total


Alkalin-



Unit


Raw Sewage
1
2
3
4
5
6
. 20
. 40
. 60
. 80
. 100
. 15
Ib/A/dy
Ib/A/dy
Ib/A/dy
Ib/A/dy
Ib/A/dy
Ib/A/dy
ity
(mg/1)
255
174
178
187
199
191
175
Oxygen
(mg/1)
_
16
15
14
11
11
13
BOD
(mg/1)
267
34
38
48
49
47
30


Total
P04

(mg/1)
42
8
9
13
12
12
8
.7
.2
.7
.8
.8
.8
.7

Total
N



(mg/1)
160.
11.
13.
18.
17.
17.
11.
6
4
8
4
4
1
6
Coli-
forms
(MPN/
100 ml)
40xl06
13xl03
20xl03
28xl03
34x103
64xl03
15xl03
These data reflect sufficient data to permit reasonable con-
clusions to be drawn.  The impact of increasing the organic
load and reducing the hydraulic retention time is shown in
these results.  The 100 Ibs BOD/acre/day loading rate produced
a 17 day retention period which was one-fifth that in the
20 Ibs BOD/acre/day unit.  Of all of the data the coliform
count reflected the effect of the detention period.  Essenti-
ally, the effluent coliform count was a function of retention
period in the pond, reflecting a linear die away relationship.
Effluent quality was essentially related to the algal growth
with load and retention period having only a slight effect
on algal growth.  Maximum reduction in alkalinity and maxi-
mum oxygen production occurred in the long retention period
system.  As the retention period decreased, the alkalinity
rose and the oxygen produced fell.  The effluent BOD increas-
ed as did total phosphate and total nitrogen.  The 160 mg/1
of total nitrogen is abnormal for domestic sewage and was
essentially organic nitrogen that was in the form of suspend-
ed solids which could be easily removed by sedimentation in
the ponds.   It was concluded from the first phase that 40 Ibs
BOD/acre/day was probably the best load for this area of
the country because of winter operations and ice cover.  Two
cells were considered better than one cell so that one cell
                           24

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could be operated in the summer and both cells could be
operated in the winter.  Winter operations with ice coyer
confirmed the 2Q Ibs BOD/acre/day as .maximum loading to keep
anaerobic conditions from developing.  A two cell system oper*
ating at an average of 40 Ibs BOD/acre/day could have a
6Q lb BOD/acre/day load on the first cell and a 20 Ib BOD/
acre/day load on the second cell.  Where ice cover is not
a problem, design can be based on 3 langleys/lb BOD during
the minimum light month.

In the second series the plant operation was changed with
cell 1 being loaded at 120 Ibs BOD/acre/day.  Cell 3 was
loaded at 100 Ibs/acre/day with cell 2 taking the effluent
from cell 3 for series operation.  Cell 4 was loaded at 60
Ibs BOD/acre/day with an increase in water depth to 5 ft.
Cell 5 was also loaded at 60 Ibs BOD/acre/day with the depth
remaining at 2.5 ft.  The loading on cell 6 was only 8 Ibs
BOD/acre/day.  The average sewage flow over the 10 month
operating period was 216,000 gpd, the same as in the first
period.  The operational data are shown in Table 2.

                         Table 2
    Fayette, Mo. Oxidation Pond Operational Data, 1958-59
Total
Alkalin-

Unit
Raw
1.
2.
3.
4.
5.
6.


ity

(mg/1)
Sewage
120
100

60
60
8
Ib/A/dy
Ib/A/dy
	

Ib/A/dy
Ib/A/dy
Ib/A/dy
281
192
187
172
184
184
155
Oxygen
(mg/1)
_
8.2
7.7
10.6
7.2
8.8
9.6
BOD
(mg/1)
268
53
50
26
40
44
30
Total
P04

(mg/1)
44
10.
8.
3.
6.
6.
4.

8
0
2
9
6
6
Total
N


(mg/1)
152
12.
10.
4.
9.
9.
6.

9
8
8
6
9
7
Coli-
f orms
(MPN/
100 ml)
ISOxlO6
31xl03
33xl03
6xl03
22xl03
17xl03
7xl03
These data followed similar trends as before with higher
loadings reflecting poorer effluent quality.  The importance
of series operation was clearly demonstrated with cells 2 and
3.  In effect all of the waste stabilization had occurred in
cell 3 with cell 2 merely permitting algae to grow and die.
The algae growth increased the dissolved oxygen while decreas-
ing the alkalinity, the phosphate and the nitrogen.  the low-
er BOD in the effluent reflects the fact that some of the al-
gae settled out in the pond and were not lost in the effluent.
Further algae separation would have produced even better ef-
fluent quality.  The two cells loaded at the same rate but
with different water depths produced almost identical results.
The shallower cell produced more oxygen and more algae and
gave a higher BOD in the effluent.  Detailed evaluation of
                             25

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these two units showed that stratification definitely occured
in both units.  Stratification was most apparent in the 5 ft
cell.  The lower layer was anaerobic while the upper layer
was aerobic.  This fact reinforced the importance of mixing
to produce good oxygen distribution.  The small one acre
cell made mixing difficult and produced conditions that would
not occur on large oxidation ponds.  Care must be employed in
translating the results of these small cells to large plants.
The hydraulic differences that are produced are significant.
Samples taken of the bottom by coring indicated that the
oxidation pond accumulated solids at the rate of one foot
every 25 years so that solids accumulation is not an import-
ant consideration in oxidation ponds except over very long
time periods.

The next major study was made by the USPHS at Lebanon, Ohio
 (14).  Two ponds, one 0.32 acres and the other 0.27 acres,
were studied as to the fate of pathogenic bacteria at high
loading rates.  Pond I was loaded from 49 to 82 Ibs BOD/acre/
day and Pond III was loaded at 117 to 194 Ibs BOD/acre/day.
The retention time in Pond I was 45 days while the retention
time in Pond III was 15 days.  Concentrated testing was
carried out for a period of 10 consecutive days during each
of the four seasons of the year.  The total coliforms in the
raw sewage were normally around 3.3 x 106/100 ml.  Pond I
effluent contained around 300 x 103/100 ml and Pond III ef-
fluent contained around 600 x 10^/100 ml.  Fecal coliforms
were around 0.9 x 10^ in the raw sewage and around 60 x 10^
in Pond I and 170 x 10^ in Pond III.  The fecal streptococci
were 3.1 x  10" in the raw sewage and around 52 x 1Q3 in Pond
 I and 200 x 103 in Pond III.  The raw sewage BOD was 276 mg/1
with an effluent of 57 mg/1 in Pond I and 97 mg/1 in Pond III.
A special study of photosynthesis showed the relationship
between oxygen demand and oxygen production.  On one day
 there was an oxygen deficit while on the other day there was
 an excess of oxygen.  It is important that oxygen resources
balance the oxygen demand.  It was demonstrated that the
 effluent could be treated with 10 mg/1 chlorine and 15 min-
 utes contact to achieve reasonable coliform reductions.

A shallow lagoon system, operating depths of 0 to 1.87 ft.,
was  studied by Nemerow and Bryson  (15) at Hancock Air Force
 Base near Syracuse, New York.  The primary cell of 1.7 acres,
 loaded at 130 Ibs BOD/acre/day, showed 69 percent removal of
 BOD  and the secondary cell of 6.5 acres, loaded at 10.9 Ibs
 BOD/acre/day, showed 88 percent removal of BOD.  This lagoon
 also reduced phosphates to 3 to 4 mg/1.  Much of the liquid
 in the cells was lost to percolation and evaporation, approxi-
 mately 30 percent of total, so that during seven of the twelve
 operating months no discharge was realized.  This study re-
 lates the difficulties in attempting to operate lagoons of


                            26

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shallow depths, apparently due to lack of compaction or  seal-
ing of the constructed cells.  Growth of excess vegetation  in
and around the lagoon resulted with cat tails, marsh grass,
small, trees and weeds being evident in the'cells.  Mosquitoes
were prevalent during the summer months and rats and muskrats
caused extensive damage to the banks and dikes.  Since opera-
tion bf the lagoon resulted in sludge build-up, and since op-
erating depths were shallow, it,is expected that methane
fermehtation did not occur as one would expect in deeper ponds
where anaerobiasis would be expected at the mud phase.  Al-
though the authors of this study did not indicate presence
of gas formation in the lagoon, and since, sludge build-up was
a problem, it is assumed that methanogenic organisms were
not present in large numbers.

Middlebrooks et al  (16) examined the problem of solids accumu-
lation in oxicTatTon ponds.  Core samples were collected from
15 oxidation ponds in Mississippi loaded at around 25 Ibs BOD
/acre/day.  Solids were found to accumulate around the oxida-
tion pond inlet.  Mathematical evaluation of the data on the
IBM 1620 computer led to an equation that predicted the rate
of sludge accumulation at one foot'every 27.6 years.  This
agreed closely with the data of Clare et al. (13) .

In 1967 Williford and Middlebrooks (17) studied two experi-
mental oxidation ponds at Mississippi State University.  The*
first oxidation pond had 0.74 acres of surface area with a
5 ft water depth while the second oxidation pond had a sur-
face of 68 acres with a 3 ft water depth.  The study covered
a 14 month period.  The raw sewage had a BOD of 188 mg/1.
Both oxidation ponds were loaded at 100 Ibs BOD/acre/day.
The effluent from the 5 ft pond had 45 mg/1 BOD while the
effluent from the 3 ft pond had 55 mg/1 BOD.  These data are
very close to those obtained at Fayette, Missouri (4,13).
As expected, the pH was the highest in the summer during day-
light hours.  Maximum pH recorded in August was 10.8.  Normal
variations showed a range from 8.3 just before dawn to 9.9 in
the late afternoon.  The carbon dioxide concentration in the
pond was a maximum at night and a minimum in the day, reflect-
ing endogenous respiration'of the algae in the dark and their
metabolism of carbon dioxide in the daylight.  The 3 ft
pond averaged 6.1 mg/1 DO at thessurface and 1.8 mg/1 at the
bottom.  The 5 ft pond had 5.8 mg/1 DO at the surface and
0.95 jng/1 at the bottom.  During the summer the ponds were
devoid of oxygen at the bottom.  Mixing again is the key to
oxygen distribution.

Although California was a leader in developing the oxidation
pond, it was slow to utilize the raw sewage oxidation pond.
In order to develop a better understanding of the operation
of these systems a ,study  (18) was made of 20 oxidation ponds
within the state of California.  Odors were noticeable at


                             27

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six of the ponds while complaints have been received at five
ponds.  Sodium nitrate was the only material used to reduce
odor nuisances.  Most of the oxidation ponds were located
downwind from the community they served and 3/4 of the plants
had clear windsweeps.  Based on results of the initial visit-
ations five oxidation ponds were selected for detailed study.
Of necessity the tests were short term, one week in the winter
and one week in the summer.  The Woodland oxidation pond sy-
stem consisted of 12 two acre oxidation ponds with only five
units in operation, all in parallel.  The Esparto oxidation
pond system has 5 two acre ponds.  Two ponds act as primary
units in parallel with their effluent being discharged to
the final three ponds which all operate in series.  The last
pond is actually a percolation pond.  The Shastina Sanitary
District oxidation pond consists of four ponds in series.
The Los Banos oxidation pond system consists of two ponds in
series.  Each pond has an area of 85 acres.  The Orland
oxidation pond system has two 10 acre oxidation ponds and two
15 acre ponds.  The 10 acre ponds operate in parallel as pri-
mary oxidation ponds with the effluent discharging to the 15
acre ponds.  Olive brine wastes presented a special problem
in this pond.  The BOD data are given in Table 3.

                         Table 3

    BOD Data Collected at Five California Oxidation Ponds

                    BOD Load      BOD Influent  BOD Effluent
Pond             (Ibs/acre/day)      (mg/1)        (mg/1)

Woodland
  Winter               29              125            42
  Summer               25               67            26

Esparto
  Winter               16              119            11
  Summer               15              165            25

Shastina Sanitary District
  Winter               50               85            19
  Summer              161              135             2

Los Banos
  Winter               77              295            38
  Summer               78              265            26

Orland
  Winter               17              145            20
                            28

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These data showed a wide variety of results with little
correlation between effluent quality and BOD loading.  The
most important aspect was the use of series ponds.  There
was no doubt that multiple ponds produced better effluent
quality than the single cell pond.  The removal of algae was
the important difference.

Although experience with oxidation ponds in sufficient depth
to be meaningful is limited, the data have tended to follow
the same trends.  There is enough data that it is possible to
state certain definite design and operating principles.
Proper application of these principles should produce better
oxidation ponds for domestic sewage.  Since industrial wastes
merely contain a different form of organic matter than domes-
tic sewage, the same principles should be derived by examin-
ing operating data from industrail waste oxidation ponds.

Industrial Wastes

In 1963 Forges  (18) reported that 827 ponds were being used
by industry in the United States in 1962.  Of these 827 ponds
the canning industry had 29% and the meat and poultry industry
had 20%.  There were 239 oxidation ponds of which 142 were
single cell ponds and 77 were series ponds.  There was not much
experimental data to permit complete evaluation of the oxida-
tion ponds but some data were presented.  Table 4 shows the
median values of the BOD loading and removal' as well as depth
and retention period.

                         Table 4

        Median Values for Industrial Oxidation Ponds

               BOD Loading       %BOD     Retention    Depth
Industry       (Ibs/acre/day)   Reduction Time  (days)   (feet)

Canning             139           98         38         5.8

Meat & Poultry       72           80         70         3.0
Petroleum            28           76         25         5.0

Dairy                22           95         98         5.0
Paper               105           80         30         5.0

Rendering            36           76         48         4.2


Industrial oxidation ponds have been loaded greater than con-
ventional domestic sewage oxidation ponds in an effort to keep
the land requirements low.  The net result has been a tendency
to overload industrial ponds more than domestic sewage ponds.
                              29

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The data are quite normal except for canning wastes.  It is
highly improbable that canning ponds produce 98% BOD reduction.
Of the 38 oxidation ponds reporting serious odor problems, 18
were canning ponds.  Odor nuisances occur only when the oxida-
tion pond is overloaded and is not producing satisfactory
treatment.  The other data seem normal considering the waste
characteristics.  The majority of industrial waste systems
have wastes with a high BOD concentration.  Without satisfact-
ory mixing for distribution of wastes, the concentrated organ-
ics create anaerobic pockets and produce unsatisfactory re-
sults.  A few industrial wastes have high suspended solids
that are quickly removed by sedimentation in oxidation ponds.

The canning industry waste disposal situation was recently
reviewed by Canham  (19).  He indicated that oxidation ponds
were used primarily as holding ponds.  The short canning
season results in the production of wastes over a few months
period.  The oxidation ponds are sized to hold the entire pro-
duction of one seasons canning.  Because of odor production
sodium nitrate has been used extensively by the canning in-
dustry to act as a supplemental source of oxygen for the bac-
teria stabilizing the wastes.  The soluble sugars in canning
wastes permit rapid bacteria metabolism and create adverse
environmental conditions.  Recent use of spray irrigation has
been tried in a number of instances as have experiments with
aerated lagoons.  Few if any canning ponds have been loaded
at BOD rates acceptable for oxidation pond operations.  The
high concentration of BOD does not permit distribution of the
load properly thoughout the needed liquid volume for good
operation.

The meat packing industry has made extensive use of oxidation
ponds.  The high suspended solids and high BOD of packinghouse
wastes makes them suitable for anaerobic lagoon treatment a-
head of oxidation ponds.  Thus it is that the oxidation pond
has assumed primarily a role as a secondary treatment unit.
Steffen  (20) reported that loadings ranged from 50 Ibs BOD/
acre/day in South Dakota to 214 Ibs/acre/day in Delaware.
With the first anaerobic-aerobic system constructed in Moultrie,
Georgia, in 1955, the  meatpacking industry was embarked on
the concept of anaerobic lagoons followed by oxidation ponds.
The data presented by Sollo  (21) for 1959 indicated a raw
waste BOD of 1060 mg/1.  The effluent from the anaerobic
lagoon was 163 mg/1, 85% reduction.  The effluent from the
oxidation pond averaged 58 mg/1.  The total treatment plant
BOD reduction was 94% while the BOD reduction within the single
cell oxidation pond was 64%.  These results are typical of
the data reported for other meat packing plants.

Cooper et al.(22) investigated the treatment of organic in-
dustriaTT~wastes in California by ponding.  A rendering plant
                             30

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waste was discharged to an anaerobic lagoon with an average
load of 228 Ibs BOD/acre/day for a retention period of 160
days.  The raw wastes had a BOD of 1870 mg/1.  Approximately,
88 percent BOD reduction was obtained in the aerobic pond.
The oxidation pond following the anaerobic pond was loaded
at 15 Ibs/acre/day.  The BOD reduction in the oxidation pond
averaged 78 percent while the overall plant reduction appro-
ached 98 percent.  A petroleum refinery had 144 acres of
oxidation ponds with a 4-5 ft depth and a waste flow varying
from  4 to 20 MGD.  The average BOD loading was 54 Ibs/acre/
day with an influent BOD of 77 mg/1.  The effluent BOD aver-
aged 45 mg/1 for only 38% reduction.  Examination of the
phenol reduction indicated 88.5%.  This difference in BOD
reduction and phenol reduction clearly shows the impact of
the algae in the effluent.  It would appear that this refin-
ery pond had an algal population quite similar to that of
domestic sewage.  Even with industrial wastes the effluent
BOD is determined by the algae when loading rates are employ-
ed with weak wastes.

Nemerow  (23) showed 92% BOD reduction in a two stage pond
system receiving poultry wastes.  The first pond was loaded
at 935 Ibs BOD/acre/day with a 7.4 day retention period.
This second pond was operated as an oxidation pond at 79 Ibs
BOD/acre/day with a 2 ft depth.  With the algae in the ef-
fluent the BOD reduction was only 9.2%; but with removal of
the algae the BOD reduction was 70%.  Once again the import-
ance of algae in the effluent quality was clearly demonstra-
ted.

Oxidation ponds have been used for canning and poultry pro-
cessing wastes by the Campbell Soup Company  (24).  A plant
in Listowel, Canada, has 69 acres of oxidation ponds in two
cells.  The BOD loading was 67 Ibs/acre/day-  The first cell
had a BOD of 41 mg/1 in the effluent.  Filtering out the
algae dropped the BOD to 4 mg/1.  The second cell dropped
the BOD to 35 mg/1 with 7.9 mg/1 remaining after the algae
were filtered out.  Once again the oxidation pond with wastes
similar to domestic sewage reacted the same.  Industrial
wastes in themselves pose no special problems or represent
any unusual set of conditons that require a different set of
design and operational criteria.  At Tecumseh, Nebraska, a
3 pond system of 15 acres each was originally designed for
50 Ibs BOD/acre/day; but actual operational data indicated
a loading in excess of 100 Ibs BOD/acre/day.  In an effort
to reduce the load prior to the oxidation ponds, an anaerobic
lagoon was constructed with a 15 ft depth and was loaded at
12 Ibs BOD/1000 cf/day.  The raw waste BOD averaged 900 mg/1.
The anaerobic lagoon had an effluent with 310 mg/1 BOD;
while the oxidation pond effluent averaged 90 mg/1.
                              31

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The addition of whey wastes to a domestic sewage oxidation
pond system in El Centro, California, was reported (25)  to have
created serious operational problems.  The readily degradable
organics in the whey produced an excessive amount of organics
in the oxidation ponds.  The El Centro treatment system con-
sisted of primary sedimentation with three parallel oxidation
ponds covering 50 acres.  With a settled BOD of 210 mg/1
the BOD loading on the oxidation ponds ranged from 50 to 70
Ibs/acre/day.  The whey wastes stimulated sulfate reducing
bacteria with the production of hydrogen sulfide.  The hydro-
gen sulfide was partially lost into the atmosphere with the
creation of odor nuisances and was partially precipitated
by the iron in the sewage.  The addition of nitrates helped
to control the odor nuisances but considerable quantities
of nitrates were needed to supply the oxygen demanded by
the microbes metabolising the whey wastes.  A dilution of
whey of 1:360 was required if the oxidation ponds were to
operate satisfactorily.

Extended collection of data by industries on oxidation pond
treatment has been rather limited.  Few industries have been
willing to present their data to the public since the ef-
fluents were usually not as good as they had hoped.  The
strong BOD concentration of most industrial wastes and ttie
high solubility of some industrial wastes requires some basic
modifications in the design and operation of oxidation ponds
over that used for conventional domestic sewage.  In spite
of these differences the operational data from properly de-
signed and operated oxidation ponds treating a variety of
industrial wastes are identical to the results obtained from
domestic sewage systems.

                  WATER QUALITY CRITERIA

The purpose of any wastewater treatment process is the
production of an effluent which can be discharged back into
the environment without creating further pollution.  In rec-
cent years concern over water pollution has increased.  The
net effect of this concern for water pollution has been the
establishment of stringent water quality criteria.  The 1965
Water Quality Act required each State in the United States
to establish satisfactory water quality criteria that met
with Federal approval.  In effect, a national set of water
quality criteria were being requested with the forced coop-
eration of each State.  The Water Quality Act permitted the
Federal government to establish criteria if it disagreed
with the criteria adopted by the States.  Currently, efforts
are underway to establish national effluent standards with-
out regard to the receiving stream.  There are definite ad-
vantages to effluent standards and there is every reason to
believe that national effluent standards will be adopted


                            32

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within the next few years.  Thus, when one honestly looks
at the use of oxidation ponds for wastewater treatment
systems, one must examine the effluent quality very carefully.

Recently, Middleton and Bunch, C26) raised the question as to
whether or not oxidation ponds were going to find continued
use for wastewater treatment.  They recognized that oxidation
ponds had grown in popularity during the decade of the six-
ties; but they were concerned if the effluent quality being
produced by oxidation ponds was adequate for future condi-
tions.  Currently, high quality treated wastes were expected
to have BOD values under 30 mg/1, COD values under 75 mg/1,
and suspended solids values under 25 mg/1 at least 90 percent
of the time with 24 hr composite samples.  The fecal coliforms
were expected to be under 200/100 ml samples.  In effect,
Middleton and Bunch were suggesting an effluent standard for
oxidation ponds.  Examination of existing oxidation ponds in-
dicated a higher BOD than that suggested.  Algae seemed to
be responsible for both the high BOD and the high suspended
solids in the effluent.  The spectre of ultimate BOD in con-
trast to BOD5 was raised briefly.  They felt that there were
no known methods for easily removing the algae from the
effluents.  It was also indicated in their report that the
current effluents probably could not meet the desired fecal
coliform level.  While they did not condemn the oxidation
pond as a method for treating wastewaters, Middleton and
Bunch definitely expressed serious doubts as to its continued
use in the future.

Reservations as to the future of oxidation ponds has been
expressed more emphatically by Barsom and Ryckman (27).
They felt that oxidation ponds have created a number of
problems, such as odors, a highly colored effluent, high
suspended solids effluent, mosquito and insect problems, and
noxious weeds.  In order to examine oxidation ponds Barsom
and Ryckman developed an arbitrary failure scale based on BOD
and suspended solids in the effluent.  They felt that first
degree failure occurred when the effluent BOD exceeded 20 mg/1
and the suspened solids exceeded 25 mg/1.  A second degree
failure occurred at BOD values above 30 mg/1 and suspended
solids values above 35 mg/1.  The third degree failure oc-
curred when the BOD exceeded 40 mg/1 and the suspended
solids exceeded 45 mg/1.  Examination of published data on
oxidation pond operations indicated that of 20 ponds studied,
16 ponds exceeded third degree failures for BOD and the re-
maining 5 ponds exceeded second degree failures.  With regard
to suspended solids data 15 plants were studied and all showed
third degree failures.  It was not surprising to note that
Barsom and Ryckman concluded that "continued use of oxidation
ponds as presently designed and operated will not enhance,
restore, or maintain the quality of the receiving stream."
                             33

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There was no doubt in their minds that oxidation ponds had no
place in the future of wastewater treatment.

There is no doubt that a review of the operational data al-
ready presented earlier together with the review by
Fitzgerald and Rohlich (28) confirms the fact that oxidation
ponds have not produced a high quality effluent consistently.
The quality of the oxidation pond effluent is primarily de-
pendent upon the algae discharged.  The algae make up the
suspended solids and create the major fraction of the carbon-
aceous BOD.  It has been shown many times over that  if the
algae are removed, a very high quality effluent can  be pro-
duced.  The problem is how to remove the dispersed algae.  A
number of methods have been proposed for removing the algae
but none have proven satisfactory to date.  Microscreening,
sand filtration, and chemical precipitation have proven too
complex and too expensive for routine use.

Early investigations indicated that algae did not create
problems in the receiving waters and that it was not fair to
use the dark bottle BOD test as a measure of the impact of
the algae on the stream.  Unfortunately, there is no easy
way to evaluate the impact of the oxidation pond effluents
except to examine the receiving streams.  Few investigators
have made downstream evaluations of oxidation pond discharges,
Two recent studies have been made which contribute signifi-
cant information to this problem.  King et a_l  (29) carried
out a study on Bear Creek in Columbia, Mri~souri, where two
oxidation ponds discharge their effluents.  The stream flow
averaged 0.88 cfs below the oxidation ponds with the ponds
making up 25% of the flow.  They found that the algae in the
lagoon effluent had a detrimental effect on the receiving
stream.  The oxygen generated by algae in the stream can be
used by the other organisms but it cannot be considered as
free oxygen and must be paid off when the algae settle to
the bottom of the stream and undergo respiration.  They felt
that the stream must be considered as part of the treatment
system with atmospheric reaeration satisfying the ultimate
oxygen demand.  Long term BOD tests revealed that the efflu-
ent BOD was only 20% of the ultimate BOD.  The ultimate BOD
was 90 to 95% of the effluent COD.  It appeared that nitri-
fication played an important part in the long term BOD data.

Bain e_t a_l  (30) studied the impact of the effluent from
oxidation ponds at Stockton, California on the estuary of
the San Joaquin River.  Their data showed that the algae
from the oxidation pond settled in the estuary and demanded
more oxygen than was produced.  The zooplankton population
showed a definite increase below the oxidation pond  dis-
charge over the area above the discharge.  They too, found
that 5 day BOD was approximately 20% of the ultimate BOD.
                            34

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Thus, it was shown that the algae have to be considered in
evaluating stream quality.  Once again, nitrification posed
a serious problem in the receiving stream the same as the
algae.  Part of the nitrification problem was related to
the algae but part of it was related to the excess nitrogen
in the treated sewage.

The data obtained from these two field studies together
with the multitude of data on the effluent characteristics
from oxidation ponds clearly points to the fact that the dis-
charge of algae clearly poses a problem in meeting current
water quality criteria^.  Filtered BOD data showed that removal
of the algae resulted in an effluent that could meet current
water quality criteria with regards to BOD.  The solution
to the water quality dilemma of excessive BOD in the oxida-
tion pond effluent would be simply to remove the algae prior
to final discharge of the effluent into the receiving stream.

A number of investigators have tackled the problem of algae
removal.  Oswald et ai_ (31,32) found that centrifugation or
chemical flocculatTon were the most effective methods for
removing the algae from the oxidation pond effluent.  In high
rate oxidation ponds, designed primarily for rapid algae
growth, the BOD was reduced from 121 mg/1 to 2.1 mg/1 with
only 3 days retention when the algae were removed by chemical
flocculation.  Van Duuren and Van Duuren (33) developed a
complex system for algae removal from a maturation pond
effluent in South West Africa.  They used primary sedimenta-
tion with alum followed by lime and chlorine, a second sedi-
mentation tank, a sand filter, a carbon filter and final
chlorination.  The results were excellent at 125-170 mg/1 alum
with 25 to 40 mg/1 suspended solids.  Further studies by
McGary  (34) showed that alum and cationic polyelectrolytes
could be used to remove algae from high rate oxidation ponds.
Golueke and Oswald (35) reported on the use of cationic re-
sins for removing algae.   ,The algae were removed by the resin
and could be regenerated by backwashing with water.  The
algae tended to aggregate around the resin beads and remained
aggregated in the backwashing process.  The chemical regener-
ation of the resins made this process too expensive.  A simple
concept that was proposed by Martin  (36) has been success-
fully tried on oxidation pond effluent in the laboratory.  A
shallow rock filter operating on an upflow basis removed 80
to 90% of the algae when operated at the rate of 12.5 gal/sf/
day.  It appeared that 20 cf of rock would be required for
each per capita design basis.  The simplicity of the rock
filter and the laboratory data to date makes further testing
in the field most desirable.  If the rock filter could effect
at least 50 percent reduction in algae, most effluents would
be able to meet current water quality criteria as well as the
                             35

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arbitrary standards of Barsom and Ryckman (27).  Removal of
algae is definitely a high priority research item in view of
the widespread use of oxidation ponds at the present time.
Removal of the algae would not only produce a satisfactory
BOD quality but it would also produce a satisfactory suspend-
ed solids quality.

The survival of pathogenic microorganisms has always been
a major concern in sewage treatment.  One of the objectives
of wastewater treatment is the reduction of harmful micro-
organisms.  While direct isolation and study of pathogenic
microorganisms is most difficult, treatment plant evaluation
is generally based on the reduction in coliform bacteria.
Neel et al  (4)  found that the coliform survival was related
to fluid retention time in the oxidation ponds.  While 99-99
percent coliform reduction was possible in their ponds, the
effluent still had an average of 14.7 x 10J/100 ml.  This
linear rate relationship for the survival of coliforms was
noted by Meron et aJL  (8) .  They calculated that an 80 day re-
tention period was "necessary to produce an MPN of 2.

Fitzgerald and Rohlich  (28) felt that oxidation ponds could
reduce fecal coliforms down below 100/ml, an MPN of 10,000.
An extensive study by Parker  (37)in Australia utilized 8
ponds in series.  The fecal coliform bacteria decreased from
an MPN of 6 x 107/100 ml to 13 during the summer with 38.5
days retention.  Enumeration of S. faecalis showed a drop
from 1 x 10^/ml to 0.09/ml.  In the winter only 6 ponds were
in use.  The fecal coliforms decreased from a MPN of 5.4 x
107/100 ml to 4.4 x 104 in 30.5 days retention.  The S. fae-
calis count dropped from 4.8 x 104/ml to 43/ml.  The bacteria
reductions were related to retention and temperature as
would be expected from fundamentals.

Cody and Tischer  (38) attempted to isolate Salmonella and
Shigella from oxidation ponds.  While they were able to
isolate Salmonella occassionally; they were unable to isolate
any Shigella.  The Salmonella were found in samples collected
near the waste influent to the pond and were not found in the
effluent from the oxidation pond.  They concluded that the
coliform reductions through oxidation ponds gave a good in-
dicator of the reduction of enteric pathogenic bacteria.  It
was concluded that oxidation ponds should not pose a hazard
from bacterial pathogens.  Hok (39) and Hsu and Kruse  (40)
reported that Salmonella abortus equi did not survive long
when added to an oxidation pond.It was recovered on the
third day but was lost on the fourth day.  The environment
in the oxidation pond is definitely not suited for the sur-
vival of pathogenic bacteria.

Slanetz e_t a_l (41) studied three oxidation ponds treating


                             36

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domestic sewage for reductions in. coliforms, Salmonella, and
enteric viruses.  They found that three ponds in series gave
95 to 99 percent reduction in coliforms and fecal strepto-
cocci..  Most samples, examined for Salmonella were negative
while many of the virus samples were positive.  Survival
of enteric microorganisms were greater in the winter than in
the summer, reinforcing the temperature factor.  Little ejt al
(42) examined 9 oxidation ponds in the Southeastern part of
the United States for fecal coliforms.  There was no correla-
tion between fecal coliforms and BOD loading on the oxidation
ponds; although there appeared to be a correlation between
fecal coliforms and retention time.  The longer the fluid re-
tention time in the oxidation pond, the lower the number of
fecal coliforms surviving were observed.  The use of multi-
cell ponds gave better results than single cell ponds as a
result of less short circuiting and better retention of the
wastes flowing through the ponds.  They believed that efflu-
ent chlorination could be used effectively in single cell
ponds to reduce the coliform population.

Horn  (43) examined the chlorination of an oxidation pond
effluent treating domestic sewage from Concord, California.
He found that with 5 mg/1 chlorine he was able to obtain
99.99 percent reduction in coliforms with 30 minutes contact
time.  Increasing the chlorine concentration resulted in better
coliform reductons; but the algae were also killed and lysed,
increasing the BOD of the chlorinated effluent.  Thus, it was
necessary to chlorinate carefully to kill the coliforms with-
out damaging too many algae.  The effluent quality from the
Concord oxidation pond was better than most effluent, a BOD
under 20 mg/1 and suspended solids of 30 mg/1.  The effluent
coliform concentration was 2.2 x 10^/100 ml, considerably
higher than most of the previous data reported.  Since inform-
ation concerning the oxidation pond design and operation
were not included, it was difficult to evaluate the applica-
bility of these results to other situations.

Chlorination of oxidation pond effluents poses a number of
problems.  First, the high concentrationof algae tend to
react with the chlorine in much the same way that bacteria
do.  Death of the algae would result in the release of
organics and create a definite BOD.  The immediate impact
of the dead algae on the receiving stream would be greater
than if the algae were alive.  Second, the chlorine reacts
readily with ammonia and other chemical compounds to form
chlorinated compounds.  Chloramines are not as effective bact-
ericidal agents as chlorine.  The addition of chlorine to
organic cbmpounds results in the formation of chlorinated
hydrocarbons which can be toxic to biological life in the
receiving stream.  Often, the chlorinated hydrocarbons are
toxic to the bacteria in the BOD bottle, giving the impression
                             37

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that the chlorine oxidized the organic matter when all that
really happened was that the chlorine formed toxic chlorina-
ted hydrocarbons.  This fact explains why early research on
sewage chlorination gave high values for BOD reductions for
relatively low chlorine doses.  Oxidation of organic matter
requires a high chlorine dose.  Virus, being pure organic
material, require partial oxidation to produce irreversible
reactons.  Considerable study is needed before chlorination
of oxidation pond effluents directly is recommended as
standard practice.

One question that no one raised was the required effluent
quality as compared to the desired effluent quality.  If
it were possible, a bacteria free and a virus free effluent
would be desired.  There could be no disease transmission if
there were no microbes to transmit them.  Since it is not
possible to achieve the desired effluent quality, what should
the required effluent quality be?  Currently, there is no
correlation between existing water quality criteria for fecal
coliforms and enteric disease in the United States.  One of
the prime purposes of wastewater treatment is the protection
of public health by prevention of the transmission of patho-
genic microorganisms through water.  There is a need to be
safe in selecting water quality criteria but there is a limit
on the practical degree of treatment needed to be safe.  Cur-
rently, water quality criteria have been established arbit-
rarily without regard to disease transmission.  In view of
the economics of chlorination and the potential dangers from
chlorinated hydrocarbons, it is essential that sound bacterio-
logical water quality criteria be established.  Further re-
search in this vital area is definitely needed.

It has been well demonstrated that pathogenic microbes de-
crease with increasing retention time in ponds.  Storage has
long been considered as the simplest and most effective
method for decontaminating water.  Originally, oxidation
ponds were designed with relatively long retention periods,
90 to 120 days, and multiple cells were recommended to maxi-
mize the flow through time.  As experience showed that oxi-
dation  ponds could handle heavier organic loads than origin-
ally anticipated, the retention time decreased proportionate-
ly.  The multiple ponds were shifted to single ponds since
high quality effluents were not too critical in most oxi-
dation pond installations.  The net effect was that oxida-
tion ponds shifted from being capable of producing high
quality effluents without effort to producing marginal ef-
fluents without effort to producing marginal effluents.  It
appears that bacteriological quality suffered the most.  Ex-
perience also indicates that marginal oxidation pond effluents
can be shifted to high quality effluents with a minimum of
effort and without loss of existing treatment investments.


                            38

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As water quality criteria become more severe, oxidation
ponds will have to meet new challenges.  In some areas phos-
phate removal could pose a new condition.  Nitrogen removal
or total nitrification has also been suggested for some
streams and lakes.  It will be interesting to see how oxi-
dation ponds meet the ever changing water quality criteria.

                 OXIDATION POND CONCEPTS

Oxidation ponds have, more often than not, been built on the
basis of past experience with little regard to basic concepts
of biological treatment.  If oxidation ponds are to be de-
signed and operated at their optimum level, it is essential
that the design engineer understand the fundamental micro-
biology and biochemistry of the oxidation pond system.  With-
out the microbes, there could be no chemical reactions to
produce ultimate stabilization.  Some of the microbes produce
desirable chemical reactions and some of the microbes produce
undesirable chemical reactions.  In the past the engineer had
no idea of which group of microbes would grow and to what
extent.  His experience was basically one of a continuous
series of surprises that were never tied together into any
meaningful fabric that could be used in future designs.  The
microbial reactions in oxidation ponds follow specific patterns
and are entirely predictable and reproducible.  Careful
application of these microbial fundamentals can be used to
design oxidation ponds that can meet any desired effluent
criteria currently in effect or that might be adopted in the
future.

Microorganisms

It was recognized very early that oxidation ponds operated
on a bacteria-algae symbiosis in which the bacteria aero-
bically stabilized the organic matter while the algae grew
autotrophically on the stable end products of bacteria meta-
bolism and produced excess oxygen for the bacteria to use.
The algae were the microroganisms that seemed to make the
difference in the oxidation ponds. The most common algae re-
ported in oxidation ponds include:

         Euglena  (44) (45) (4) (5) (8) (9) (10) (46) (37)
         Chlamydomonas  (45)(4)(5)(9)(46)
         Chlorogonium  (4)(46)
         Microactinium  (4)(9)(37)
         Ankistrodesmus  (4)
         Scenedesmus (4) (5) (10) (46)  (35) (37)
         ChlorellaT45) (4)  (5)  (8)  (46) (35) (37) (43) (47)
         Qscillatoria  (4) (46)  (47)
         Anabaena(4)
                             39

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         Carteria (46)
         Phormidium (46)
         Navicula~T37)
         Closteri'um (37)
         Anacystis (47)

The above list of algae is not intended as a complete list
of algae that are found in oxidation ponds; but rather re-
presents large growths  as reported in various articles in the
literature.  Examination of these organisms indicates that
the algae belong in three general groups;  the motile algae,
the non-motile small algae, and the filamentous algae.  The
motile algae have the ability to move and compensate for
varying light conditions.  Euglena and Chiamydomonas are the
most frequent motile algae in oxidation ponds.Chlorella and
Scendesmus are small, non-motile algae that present a large
surface area to mass ratio so that they remain suspended
with very slight fluid motion.  The primary filamentous algae
found in oxidation ponds is the blue green algae, Oscilla-
toria.  The filamentous algae tend to form floating mats
that are undesirable in oxidation ponds as they block light
transfer, mixing, and surface reaeration.

In contrast to the large amount of information available on
the algae in oxidation ponds the amount of information related
to the bacteria is very sparce.  No real detailed bacterio-
logical studies have been made on them.  Gann et al (48)
made a laboratory study of the bacteriology of oxITdation
ponds and found Achromobacter, Pseudomonas, Flavobacterium,
Bacillus, and coliforms.   Approximately, 9"0-95% of the bac-
teria belong to Achrombacter, Pseudomonas, and Flavobacterium.
They found that the coliforms died off as  the BOD wasreduced.
Most of the primary bacteria activity occurred around the
influent where the organic matter was being added to the
ponds.

Observations of existing ponds and biochemical data would
indicate that the normal soil and enteric bacteria are
carried into the pond.   The overall environment determines
which bacteria grow and to what extent.  It appears that ana-
erobic bacteria grow where the organic solids have settled
near the influent.  Methane production in highly loaded
ponds indicates that methane bacteria are present.  In
heavily loaded oxidation ponds, the presence of hydrogen
sulfide could mean the presence of the Desulfovibrio, sulfate
reducing bacteria.  The lack of nitrates in the oxidation
pond effluents would indicate the presence of very few, if
any, nitrifying bacteria.  Most oxidation ponds show denitri-
fication where nitrates are present in the influent.  The
prime concern with the bacteriology of oxidation ponds has
been more related to the survival of enteric bacteria and
                            40

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potential survival of pathogenic bacteria.  This public
health aspect of oxidation' pond bacteriology has overshadowed
the microbiology concerned with waste stabilization.  In all
probability the bacteriology of oxidation ponds is similar
to the bacteriology of other aerobic and anaerobic waste
treatment systems.

Fungi are related to bacteria and are found in soil.  It
would be reasonable to expect fungi to be present in oxidation
ponds,but the question could be raised as to their signific-
ance.  Cooke and Matsuura (49) made a study of the oxidation
pond near Lebanon, Ohio.  Yeast were the primary group of
fungi in the liquid phase with some filamentous fungi in
pond sludges and floating scum.  The difficulty in determin-
ing quantitative counts with fungi makes evaluation of the
role of fungi difficult.  While fungi are able to grow in
oxidation ponds, there is no information available to indi-
cate that fungi play a significant role in stabilizing the
organic matter in oxidation ponds.  Their role is secondary
to the bacteria.

Viruses have stimulated interest from their possible public
health standpoint like the enteric bacteria.  Few studies
have been made with virus because of their extreme specificity
and the difficulty in quantitative measurements.  In 1966
Christie (50) reported on a study with polio virus.  It
was demonstrated that oxidation ponds were capable of reducing
the polio virus.  Mixing the virus with raw sewage or with a
pure culture of Chlorella showed that these materials were
not toxic to the virus.  Nupen (51) carried out extensive
viral studies at the Windhoek treatment plant in South West
Africa.  Polio virus was also used in this study.  Matura-
tion ponds showed better than 95% virus reduction with only
14 days retention.  Chlorination was definitely able to pro-
duce a viral free water after tertiary treatment (33).

Microscopic animals also occur in oxidation ponds.   As in
other waste treatment systems, the microscopic animals play
a secondary role, feeding on the bacteria and the algae.
Wennstrom (8) reported extensively on the microscopic animals
in his 4 pond system.  The protozoa predominated from October
to March during the cool weather.  Multicelular animals grew
readily during the remainder of the year.  Vorticella was the
major stalked form of protozoa while Paramecium was the pri-
mary free swimming ciliated protozoa.  Glaucoma and Euplotes
were present in large numbers as was Colpidium.  Rotifers
and the crustacean, Daphnia, were very active in the summer
months.  At times the Daphnia ate most of the algae in the
final pond, producing an effluent essentiall free of algae.
The crustaceans also received the attention of Loedolff  (52)
at Pretoria, South Africa.  The Cladocera, Moina, was found

                             41

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to remove E. coli at a faster rate than Daphnia. While these
crustaceans were able to remove bacteria from wastewater
systems, it was felt that the protozoa and rotifers were
more efficient and hence, more significant.  Daphnia  appear
to feed on algae when long retention periods are available
for their growth.  Usually, the Daphnia are able to clarify
the pond of algae provided the food level is low.  The
Daphnia will not remove all of the algae in primary ponds
where the algae have enough food for rapid growth.  There is
no doubt that the microscopic animals can play an important
role in reducing the algae population in the final effluent.
The study by Wennstrom (8) showed that when the Daphnia pre-
dominated in the final pond, an effluent BOD of essentially
zero was produced.  To date, the design of oxidation ponds
in the United States have not attempted to utilize the algae
removal capabilities of these crustaceans.  Their growths
have been noted from time to time as an example of a strange,
uncontrolled, biological growth.  In isolated areas where
land was readily available, Daphnia could produce a high
quality effluent without any special operational requirements,
especially in the warmer sections of the United States.

A highly specialized group of microorganisms that are some-
times found in oxidation ponds are the purple sulfur bacteria.
The purple sulfur bacteria are photosynthetic bacteria that
grow similar to algae.  In the presence of sunlight, carbon
dioxide and hydrogen sulfide the purple sulfur bacteria are
able to grow and oxidize the hydrogen sulfide.  Needless
to say, these highly colored bacteria will occur only at
the surface of very heavily loaded oxidation ponds.  This
is the reason why the purple sulfur bacteria are treated
separately from the normal bacteria in oxidation ponds.  Be-
cause of their unusual color, the purple sulfur bacteria
have attracted considerable attention.  Cooper et al  (22)
found Thiopedia in a pond treating rendering wastei~"and
Chromatium in another pond treating petroleum wastes.  Parker
 (37)also found Chromatium in an oxidation pond loaded in
excess of 1000 Ibs BOD/acre/day.  Holm and Vennes  (53) ident-
ified three genera of purple sulfur bacteria in North Dakota
lagoons receiving potato processing wastes together with do-
mestic sewage.  Thiocapsa was the predominant organisms when
acetate in the lagoon reached 1000 mg/1.  Over 90% BOD re-
duction was obtained during the period when the purple sulfur
bacteria predominated.  Normally, the purple sulfur bacteria
do not grow in properly designed and operated oxidation
ponds; but it is important to recognize that their presence
in an oxidation pond is definite evidence of overloading and
the production of hydrogen sulfide.

The microorganisms that grow in any oxidation pond are a
function of the organic matter in the wastes, the retention
time, mixing, and other environmental factors.  The success

                            42

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or failure of the oxidation pond as. a waste treatment device
depends upon the biochemical reactions that the microorgan-
isms produce.  For this reason it is important not only to
know which microorganisms occur but also to know the re-
actions that each group of microorganisms produce.

Biochemical Reactions;

There are two primary biochemical reactions and one second-
ary biochemical reaction in normal oxidation ponds.  As
shown by Oswald and Gotaas  (3) the bacteria metabolise the
organic matter with the production of bacteria and stable
end products.  With adequate oxygen the end products are
carbon dioxide, water, ammonia, and phosphates.  The algae
can utilize these end products of bacterial metabolism in the
presence of sunlight to synthesize more algae with the re-
lease of the excess oxygen.  The bacteria derive their energy
for cellular synthesis from the oxidation of a portion of
the organic matter in the wastes and conversion of the re-
mainder of the organic matter to new cells.  On the other
hand, the algae use light energy to reduce the oxidized end
products of bacterial metabolism to cellular protoplasm.
The reduction reaction results in a release of oxygen which
can be used by the bacteria.  This general reaction formed
the basis for oxidation pond operation for many years with
little regard to the quantitative aspects of any of the bio-
chemical reactions.

Oswald et al (54) attempted to put quantitative relation-
ships onto the algae-bacteria symbiosis that occurred in
oxidation ponds.  The maximum bacteria population occurred
in domestic sewage at 1.5 days, approximately 108/ml.  Euglena
was the algae used since it occurred in most oxidation ponds.
It was found that optimum growth of Euglena occurred at 400
ft-candles of light although there was little variation up to
1200 ft-candles.  Chemical analyses of Euglena gave an empiri-
cal formula of Cj^g2H8.082.53N1.0-  Tne metabolic equation
for algae growth was set forth:

1.0NH4+ + 7.62C02 + 2.53 ^0 	> C7.62H8.082.53N1.0 +

                                   7.6202 + 1.0H+

The ratio of carbon dioxide consumed to oxygen produced was
1.0.  This was similar to that reported in the literature
with algae grown in pure culture on simple substrates.  The
growth of algae followed the growth of the bacteria since
the algae used the carbon dioxide produced by the bacteria.
One significant factor that has been overlooked by many
engineers was the fact that carbon was the limiting factor
in the growth of algae in sewage oxidation ponds.
                             43

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Studies summarizing the metabolism of algae have been report-
ed by Fogg  (55).  He stated that the algae metabolism was  as
follows:

        C02 + 2H20 	  CCH 0) + H20 + 02

Fogg felt that the algae used  free carbon dioxide only  and
produced carbohydrates which were further metabolised to
form algae protoplasm.  He, too, analysed algae and pre-
sented the following metabolic equation for the growth  of
algae:

1.0 NH^ + 5.7 CO- + 3.4 H-0 	> C. ^HQ B0- -N + 6.25  02
      j         2.        2.         D./y.oZ.j          *

The quantity of oxygen produced by this equation is actually
greater than the carbon dioxide consumed, giving an increase
in oxygen production over that normally expected.  The  weight
of oxygen produced per unit weight of protoplasm produced
was 1.55 gm 02/gm vol. algae mass by Oswald et al  (54).  Yet,
there was a definite difference in the formulation  of  the
algae.  A recent study by Richardson e_t al  (56) on Oocystis
and Chlorella found the empirical formulation of two pure
culture analyses averaged Cc,_3Hg^402.yN.  It would appear
that the formula originally presented in Fogg  (55) is the
probable empirical formula for algae grown in oxidation ponds.
Richardson e_t al^ (56) found the caloric value of 5.9 Kcal/gm
vol. algae mass~for Chlorella  and 6.2 Kcal/gm vol. algae
mass for Oocystis.   This checks quite close to the caloric
value for bacteria reported by Payne (57).

Oswald et. al_ (58) observed that 3.68 calories of energy
were required by algae to produce 1.0 mg/1 of oxygen.   This
value was confirmed by Richardson et a.1  (56).  It has been
indicated that algae can convert approximately 10 percent
of the light energy into the creation of new cells.  Since
the growth of algae and the resultant oxygen production are
related to the use of light energy, more oxygen will be
produced in the summer than in the winter in odixdation ponds.

A study of the biochemical reactions as they exist in field
ponds was carried out by Bartsch and Allum  (59) in South
Dakota.   They used light and dark bottle studies to examine
the oxygen production and respiration as it actually occurs
in oxidation ponds.  The growth of algae results in suspend-
ed solids that block the light and prevents its penetration.
Thus, the more algae that grow, the less light there is for
further growth.  It also means that growth is pushed closer
to the surface of the pond.  In July, 1955, 99% of the  light
reaching the surface of the oxidation pond at Kodaka, South
Dakota,  was absorbed in the top 15 inches.  At Leitunon,  South
Dakota,  99% light absorbance occurred at 32 inches.  They


                            44

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found that the Lemmon oxidation pond produced 2.9 mg/1 02/hr
at 1050 ft-candles of light, 0.4 mg/1 02/hr at 167 ft-candles,
0.1 mg/1 02/hr at 27 f t-candles, and 0.04 mg/l/hr at 3.8 f t--
candles.  Stabilization of the sewage added to the oxidation
pond produced a uniform oxygen demand rate of 0.04 gm/m2/hr.
The total microbial respiration rate was 0.7 gm/m^/hr.  Thus
it was that the algae created an endogenous respiration oxygen
demand 17 times greater than the microbial oxygen demand for
stabilizing the sewage.  This clearly indicated that the algae
growth was related to something more than stabilized sewage.

Towne et al (60) commented further on the data collected in
the previous study (59).  They indicated that wind action
across the surface of the oxidation pond is important in
carrying the oxygenated water to the lower depths; but this
same wind action accelerated the loss of oxygen to the atmo-
sphere.  Supersaturation of the surface of the oxidation pond
with oxygen reached as high as 43 mg/1.  Loss of this oxygen
to the atmosphere meant that some algae would not have enough
oxygen for complete endogenous respiraton.  Bartsch (61)  in-
dicated that the production of 1.6 pounds of oxygen in the oxi-
dation pond resulted in the creation of 1.0 pound of volatile
algae mass.  Thus, lots of algae were produced for every pound
of BOD stabilized in the oxidation pond.  These algae had an
oxygen demand that had to be satisfied.  In effect, he re-
cognized that the oxidation pond was transforming the organ-
ics from their original form in sewage to a new form as algal
cells.  The question was raised as to the desirability of such
a conversion.

Research into the algae metabolism by Stoltenberg (62) in-
dicated that Chlorella  could produce 1.22 moles Cu/mole
CO- utilized at low carbon dioxide concentrations.  On the
otner hand, endogenous respiration produced one mole C02/mole
02 utilized.  The rate of endogenous respiration was 11.2
mg/l/hr/1000 mg/1 algae at 25C, approximately the same as
bacteria.  The data indicated that approximately 18 percent
of the algae mass was not biodegraded by endogenous respira-
tion.  Nelson (63) examined the endogenous respiration of the
algae bacteria mixture in greater depth and found that the
endogenous respiration rate was related to the metabolism of
carbohydrates first and proteins second.  The overall endog-
enous rate for the protein fraction was 1.8%/hr while the
carbohydrate fraction was metabolised at a faster rate.  The
rate of oxygen production was found to occur from 14 to 60
times as fast as the endogenous respiration rate.  Algae have
the ability to produce oxygen very rapidly and can use both
bicarbonates and carbonates as sources of carbon as well as
carbon dioxide.   In the light algae use the carbon dioxide
from the endogenous respiration as fast as it is given off;
but in the dark the algae can exert a large oxygen demand
                             45

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rate.  Nelson demonstrated that the algae definitely had an
inert organic cell mass residual that was not metabolised the
same as bacteria.

While the symbiosis between the bacteria and algae was
recognized, the concepts of oxidation ponds were still look-
ed at as a simple  aerobic system in which the aerobic bacter-
ia stabilized the  organic matter and the algae produced the
oxygen needed for  the aerobic reaction.  Few engineers
recognized that the suspended solids in raw sewage settled
out close to the inlet, creating a sludge blanket.  Most of
the early concern  for settleable solids was with loss of
oxidation pond capacity.  Little concern was shown for meta-
bolism of those settled solids.  It was just assumed that
these settled solids underwent aerobic matabolism until data
were collected to  show that the oxygen concentration at the
bottom of most oxidation ponds were devoid of oxygen essent-
ially all of the time.  This meant simply that the settled
solids were undergoing anaerobic metabolism rather than aero-
bic metabolism. Oswald  (64) recognized that anaerobic con-
ditions developed  in normal oxidation ponds and resulted
in removal of some of the BOD load.  He indicated that at
low temperature, 4C, or at low pH, under 5.5, the biological
metabolism ceased.  Thus, during the winter months in the
northern states the settled organic matter is stored until
the weather warms  up.  This is a very important reaction in
oxidation ponds located in cold weather regions.  When the
bacteria degrade the organic solids anaerobically, organic
acids are produced which diffuse slowly into the liquid
layer above the settled solids.  If the organic acids build
up too much the pH will drop and stop further metabolism.
If sulfates are present in the water around the solids, sul-
fate reducing bacteria can grow up with the production of hy-
drogen sulfide that diffuses into the upper layer of water
in the pond.  If excess organic matter still remains methane
bacteria can buildup and produce considerable quantities of
methane that is lost to the atmosphere. Oswald et 
-------
bacteria protoplasm and found that the empirical formula for
bacteria was C5H702N.  A number of other empirical formula
have been proposed but .they generally represent materials
other than living bacteria.  Eckenfelder and 0'Conner  (66)
reported that the caloric value of activated sludge grown on
skim milk was 5.7 Kcal/gm.  By and large efforts to develop
simple thermodynamic data on the metabolic reactions of
bacteria in wastewater have not been too successful. Endog-
enous respiration has produced a secondary reaction that
made determination of the synthesis reaction difficult.
McKinney (67) followed up earlier work that showed a relation-
ship between BOD and cellular synthesis and developed a
basic metabolic concept.  He postulated that 1/3 of the
energy contained in the organic matter being metabolised
would be oxidized to yield the energy to convert the re-
maining 2/3 to cell mass.  This was the synthesis reaction.
Endogenous respiration resulted in oxidation of the remain-
ing cellular energy.  In terms of maximum synthesis 0.47 gm
dry weight vol. bacteria mass would be produced for each gm
of ultimate BOD metabolised by the bacteria.  Payne (57)
reported 62% of the enthalphy was conserved as cell mass in
comparison to 67% as indicated by McKinney.  Servizi and
Bogan  (68) disputed the validity of the 1/3-2/3 relationship
and related synthesis to the free energy of oxidation.  They
followed up with data  (69) to show that activated sludge
systems had a synthesis yield of 0.39 gm dry weight vol.
bacteria mass for each gm of COD metabolised as carbohydrates
and 0.35 gm vol. mass/gm COD as aromatics and aliphatic acids.
Since Bogan and Servizi failed to consider endogenous respira-
tion as a factor in evaluating their data, their synthesis-
energy values are low.  The complexity of the energy relation-
ships as proposed in the current literature is such that
engineers concerned with biological treatment plant design
have ignored most of the relationships as they cannot measure
the basic parameters.  The exact 1/3-2/3 relationship pro-
posed by McKinney may not be absolutely precise but is within
experimental error for treatment plant design and makes a
useful tool.  In terms of 5 day BOD the synthesis reaction
requires a minimum of 0.5 Ib 02 for the production of 0.7 Ib
vol. mass from 1.0 Ib BOD.  Endogenous respiration increases
the oxygen demand and reduces the cell mass proportionally
as time proceeds.  In oxidation ponds the retention period is
very long so that endogenous respiration becomes significant.

Kountz and Forney (70) studied endogenous respiration in bio-
logical systems and found approximately 20% of the activated
sludge produced was non-biodegradable.  The fact that 1/5 of
the vol. mass does not undergo oxidation means that only 4/5
can be oxidized.  The net result is that only 87% of the ulti-
mate BOD can be exerted in a biotreatment system.  The remaining
                             47

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13% of the ultimate BOD is essentially inert in the aqueous
environment.  It probably is degraded very slowly, too
slowly to be significant in treatment plant design or opera-
tion.  In effect, the maximum amount of oxygen required by
the BOD in domestic sewage would be 1.3 Ibs/lb of BOD stab-
ilized.  This is the amount of oxygen which the algae must
produce unless some of the BOD is removed by sedimentation
and methane fermentation.  With domestic sewage approxi-
mately 50% of the BOD is in the form os suspended solids
which will settle out in an oxidation pond.

The settleable solids in domestic sewage are only partially
degradable.  Approximately, 40% of the volatile suspended
solids fraction is non-biodegradable.  Couple this non-
biodegr-dable organic fraction with the inorganic fraction
and you have essentially 50% of the settleable solids that
can undergo decomposition even under favorable conditions.
It is not surprising to note that the settled solids in
oxidation ponds do not undergo rapid metabolism.  These s
solids settle out close to the inlet structure with each new
load of solids settling over the previous solids.  The new
solids act as a blanket that retards further metabolism of
the settled solids.  In an effort to examine the oxygen de-
mand rate of settled sludge, samples were studied in the
Laboratory by McKinney and Benjes (71) to determine some of
the basic factors affecting metabolism.  As expected, the
rate of metabolism was found to be a function of diffusion
of anaerobic end products into the aerobic upper layer where
they could be oxidized.  As the rate of fluid flow over the
top of the sludge increased, the rate of oxygen demand in-
creased.  Thus, mixing becomes very important in stabiliza-
tion of the settled solids.  Since most oxidation ponds
have little movement of water over the surface of the settled
sludge, the rate of metabolism becomes limited by that water
movement and simple molecular diffusion.  One could expect
10-20% of the settled BOD to be exerted in lightly loaded
oxidation ponds and less in more heavily loaded ponds.  The
remaining organic matter will be preserved by the low pH of
the organic acids or converted to methane.  Some sulfate
reduction could take place but it would be limited to the
available sulfates trapped in the water with the solids.
It appears that most oxidation ponds will require only 0.8 Ib
oxygen/lb BOD when the raw wastes are domestic sewage.
Soluble industrial wastes can be expected to demand the full
oxygen load of 1.3 Ib 02/lb BOD.

It has been indicated the algae use the carbon dioxide pro-
duced by the bacteria for metabolism.  Examination of the
characteristics of domestic sewage indicates that 87% of
the oxygen utilized is for the oxidation of carbon while the
remaining 13% of the oxygen required is for oxidation of
                           48

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hydrogen.  This means that the bacteria are going to demand
more oxygen than will be released by the algae if the algae
have an RQ of 1.0 as indicated in the literature.  It has
been suggested that the extra oxygen could be supplied by
surface aeration.  Examination of field data indicates that
a significant quantity of the oxygen produced by the algae
is actually lost to the atmosphere, making the situation
even worse.  It appears that the algae metabolise the bicar-
bonate alkalinity in the water as well as the carbon dioxide
produced by the bacteria.

Normal domestic sewage will contain close to 300 mg/1 bicar-
bonate ions together with approximately 30 mg/1 carbon diox-
ide.  The carbon dioxide will be metabolised by the algae
first and then the bicarbonate will be metabolised.  As the
bicarbonate is metabolised, the pH increases and a portion
of the bicarbonate is converted to carbonate.  As the pH rises
to the point where significant hydroxide alkalinity is formed,
toxic conditions result and further metabolism ceases.  It
appears that approximately 10 mg/1 hydroxide alkalinity is
toxic to the algae, making pH of 10.3 about maximum.  In hard
water the calcium ions will precipitate and remove the car-
bonate ion concentration down to 30 to 40 mg/1  At pH 10.3
there would be approximately 27 mg/1 bicarbonate left un-
metabolised.  The 270 mg/1 of, bicarbonate that was removed
was converted to carbon dioxide and carbonates.  There would
have been 135 mg/1 carbonate formed.  Approximately 100 mg/1
of the carbonate ion would have been precipitated with 67 mg/1
calcium.  There would still be 25 mg/1 of calcium left in
solution.  Since phosphate tends to precipitate at pH values
above 9.0, an additional 25 mg/1 of calcium would have been
removed with the phosphate precipitate.  Few sewages have
120 mg/1 calcium for maximum precipitation.  The net result
is that some of the carbonate will remain unprecipitated as
will some of the phosphate.

With normal domestic sewage one can expect that 52 mg/1 of
carbon would be released as carbon dioxide from the stabiliza-
tion of the BOD.  Maximum utilization of the bicarbonate car-
bon as indicated in the previous section would yield an
additional 27 mg/1 of carbon.  If the algae were able to
metabolise all this carbon, they would form approximately
160 mg/1 VSS of new algae and release 210 mg/1 of oxygen.
Since the bacteria only need 160 mg/1 of oxygen for stabil-
ization, there is an apparent surplus of oxygen.  But it
must be recognized that the algae formed have a potential
oxygen demand of their own that must be satisfied.  If the
algae were completely metabolised, approximately 20% of
the cell mass would remain unmetabolised the same as bacteria.
The 160 mg/1 VSS of algae would need 180 mg/1 for endogenous
respiraton.  Since only 50 mg/1 of oxygen is available,

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there would be a deficit of 130 mg/1 of oxygen.  This oxygen
deficit is currently being satisfied by one of two methods,
sedimentation of algae prior to complete endogenous respira-
tion or discharge in the effluent.  The high effluent sus-
pended solids in some oxidation ponds indicates that a con-
siderable quantity of the algae is being lost to the receiv-
ing stream and the oxygen burden is being transferred to
downstream areas.  With multiple ponds the algae are retained
in the oxidation pond system through sedimentation and a
satisfactory effluent quality is produced.

The rate of metabolism becomes a very important factor in
the oxidation pond the same as in any biotreatment system.
In effect, the oxidation pond operates in the same fashion
as the BOD bottle.  The bacteria are essentially maintained
in a dilute, dispersed condition and are limited in their
ability to obtain organic matter.  It can be expected that
all of the soluble organic matter in the raw sewage would be
oxidized within 20 days at 20C.  This would mean that the
bacteria converted all of the organic matter to new cell
tissue in 2 to 3 days with endogenous respiration and pre-
dation by protozoa, rotifers and crustaceans accounting for
the remaining oxygen use over the next 18 days.  Increasing
the temperature to 30C would permit stabilization in 10
days instead of 20 days while a decrease in temperature to
10C would require 40 days and to near 0C would require 80
days.

The response of the algae is similar to the bacteria except
that the algae can continue to grow in the light and recycle
their carbon as fast as it is released by endogenous respira-
tion.  It appears that the rate of endogenous respiration
will be around 1.0-2.0%/hr on a uniform basis at 20C.  The
inert organic matter related to the algae will accumulate
at the rate of approximately 5% per day so that the turnover
time of the algae will be around 20 days.  The accumulation
of the inert fraction of algae reduces the ultimate oxygen
demand on the receiving stream.  Thus, it is then that long-
er retention period oxidation ponds not only permit the algae
to settle but also allow the algae to recycle adequately to
accumulate enough inert organic matter to yield an excess
of oxygen for the stabilization reaction in the oxidation
pond.  Since the carbon dioxide from the algae can be reused,
it follows that the maximum crop of 160 mg/1 VSS of algae
would be reduced to 128 mg/1 in 20 days, 102 mg/1 in 40 days,
82 mg/1 in 60 days, 66 mg/1 in 80 days, 53 mg/1 in 100 days
and 42 mg/1 in 120 days by endogenous respiration alone with-
out any sedimentation.  At temperatures lower than 20C
the rate of endogenous respiration decreases.  The temperature
factor decreases by two for each 10C temperature drop.  it
follows that the effluent BOD from the oxidation pond system
                            50

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will be related to the endogenous respiration of the algae
mass discharged.  It can be estimated that the BOD of the
algae will be 0.75 mg/1 for each 1.0 mg/1 living cell mass,
VSS.  It can easily be seen that without some form of algae
separation, a high quality effluent in terms of BOD or
suspended solids could not be produced from an oxidation pond.

The previous evaluation was based on complete metabolism of
available carbon.  It must be recognized that all of the
carbon is not available for photosynthesis.  Without mixing
the algae would build up at the surface of the oxidation
pond and block light penetration.  It appaers that the upper
10 to 15 inches in the pond will be actively photosynthesiz-
ing if the data presented by Oswald (64) is correct.  If it
is assumed that only the top foot of the oxidation pond is
active photosynthetically, the algae production in a 4 ft
pond would be reduced by a factor of four without mixing.
Since algae production is essential for adequate oxygen,
mixing is a must.  Wind action is responsible for mixing
in most ponds.  Where the pond detention time is long enough,
60 days or more, wind action is adequate.  In oxidation
ponds having short detention times, wind mixing may not be
adequate and some form of mechanical nixing may be necessary
to produce maximum algae production.  Care must be taken with
mechanical mixing devices as too much agitation at the sur-
face will result in loss of oxygen to the atmosphere rather
than retention for the microbial reactions.

Thus, tha primary biological reactions occurring in the
oxidation pond are the bacteria stabilizing the organic
matter and then undergoing endogenous respiration and the al-
gae producing oxygen and algae from inorganic carbon sources
and undergoing endogenous respiration.  The bacteria are not
light dependent but the algae are.  These facts tell the en-
gineer why proper lighting and mixing are so important to
the proper functioning of the oxidation pond.  The secondary
biological reactor is the consumption of bacteria and algae
by protozoa, rotifers, and crustaceans.  These microscopic
animals are strict aerobes and will grow best in the upper
layers where the algae have produced a good food source and
adequate oxygen.  The bacteria and the algae grow more rapid-
ly than the microscopic animals, permitting maintenance of
all forms when mixing is adequate.  Occasionally, the crusta-
ceans have metabolised all of the algae in the final cell of
multicell ponds when mixing is minimal.  Normally, metabol-
ism of the available algae will result in loss of the avail-
able food supply for the crustaceans and they will soon die
off and the algae will reappear.  To date, it has not been
possible to design oxidation ponds to take advantage of the
ability of the crustaceans to remove the excess algae from
the oxidation pond effluent.  While the crustaceans would


                             51

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have removed the algae, they in turn would exert a BOD which
would have to be satisfied eventually.

Design Relationships

The basic biochemical reactions form a basis for the develop-
ment of sound design relationships.  It can be seen that the
bacteria stabilize the organic matter very rapidly, 1-2 days
in the summer and 8-10 days in the winter, provided they have
adequate oxygen for metabolism.  The bacteria then undergo
slow endogenous respiration.  In effect, the bacteria then
would be completely stabilized in 20 days at 20 C under
aerobic conditions.  Atmospheric diffusion could be expected
to meet the oxygen demand of the bacteria with a retention
period of 80 days with little mixing and in a shorter period
with good mixing.  The growth of algae precludes the con-
struction of a simple bacteria pond.  The algae respond to
the environment created by the bacteria and the wastes and
grow.  Normal domestic sewage will permit synthesis of 160
mg/1 VSS as algae provided there is good mixing.  With poor
mixing only the upper 12 inches of the oxidation pond will
have 160 mg/1 algal mass.  Diluting this algae with the total
effluent would give an algae concentration of only 40 mg/1.
Wind mixing normally permits the algae synthesis in the pond
to be between 40 mg/1 and 160 mg/1.  Synthesis of 100 mg/1 of
algae would meet the oxygen demand of the bacteria.  Most
oxidation ponds can produce algae as fast as the carbon di-
oxide becomes available from the bacteria.  Theoretically, a
20 day retention period pond with a depth of 4 ft could satis-
fy the oxygen demand of the bacteria.  The only problem is
separating the algae from the liquid.  Endogenous respira-
tion and protozoa predation are needed to reduce the algae
concentration to a reasonable level.  A 20 day retention
period for normal domestic sewage would give a BOD load of
108 Ibs/acre/day.  Research at Fayette, Mo. (11) demonstrate
that a BOD loading of 120 Ibs/acre/day produced adequate
algae growth to maintain dissolved oxygen except at low tem-
peratures when ice covered the ponds.  Based on BOD loadings
and changes in the alkalinity the daily oxygen demand of
200 mg/1 in the summer was satisfied by the production of
220 mg/1 oxygen from the daily growth of 170 mg/1 algae.  At
20C the average algae mass in the oxidation pond would have
been 137 mg/1 with 20 days retention and the effluent BOD
would have been approximately 100 mg/1.  The actual BOD was
lower than this as the result of algae settling in the pond.
Examination of the organic nitrogen data indicated that 83%
of the algae had been removed by sedimentation.  If this were
the case, the expected BOD would have been 18 mg/1.  The
measured BOD in July was 23 mg/1.  It appeared from the
Fayette data that the theoretical BOD relationship with
regard to organic nitrogen in algae cells checked very close
                            52

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to 8.6 mg/1 BOD for 1.0 mg/1 organic nitrogen.  The 10
month average organic nitrogen concentration in the heavily
loaded pond from the Fayette study was 6.6 mg/1, giving a
predicted BOD of 57 mg/1 against an average measured BOD of
53 mg/1.  This indicates that the organic matter in the wast-
es were stabilized by the algae in accordance with the bio-
chemical concepts presented in the previous section and that
the effluent quality was strictly a function of algae separa-
tion.  The second oxidation pond in series received only the
algae from the first pond.  Endogenous respiration and sedi-
mentation reduced the organic nitrogen in the effluent to
2.4 mg/1, giving a predicted effluent BOD of 21 mg/1 against
a measured average of 26 mg/1.  Closer results cannot be
expected from field data.

The problem in oxidation pond design lies in algae separa-
tion and temperature effects.  As long as ice is not a
factor to block the algae from obtaining adequate light, a
20 day retention period is adequate for waste stabilization
of domestic sewage even in cold weather.  Ice formation
blocks the light from reaching the algae and prevents develop-
ment of adequate oxygen for the bacteria to continue metab-
olism until the algae return.  As long as the ice covers the
oxidation pond, the anaerobic end products that create the
obnoxious odors are held in the liquid and can only be lost
in the effluent.  When the ice melts and spring winds create
rapid mixing, the anaerobic end products which have been
produced are released to create nuisance conditions in the
immediate vicinity of the oxidation, pond.  These nuisances
persist until the algae create enough additional oxygen to
satisfy the extra demand.  This explains why the more heavily
loaded oxidation ponds take longer to recover from winter
operations than lightly loaded oxidation ponds.  Artifical
aeration during the winter months can satisfy the oxygen de-
mand under the ice if odor nuisances are critical problems.
When the ice melts and the algae have returned to a satis-
factory level, the artificial aeration system can be discon-
tinued until the ice cover returns.  During winter opera-
tions bacteria can stabilize the organic matter easily within
the 20 day retention period but complete endogenous respira-
tion of the bacteria would require almost 80 days at 0C.
The effluent quality in the winter period is related then to
both anaerobic end products and the bacteria remaining.
Where a high quality effluent must be produced in the winter
months, artificial aeration will be a necessity.  Even with
artificial aeration, bacteria separation will be required
the same as algae separation is required during the remainder
of the year.

Very little research has been carried on for algae separa-
tion in small ponds with a minimum of operational skills and


                             53

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equipment.  For the most part it has been shown that centri-
fugation and chemical precipitation can remove the algae
and produce a quality effluent.  Unfortunately, both are
far boo complex to use in the majority of oxidation pond
installations.  The best method to date for algae separation
in the field appears to be multicell ponds.  Not only do
multicell ponds reduce the short circuiting of wastewater
flow through the oxidation pond; but they permit some effect-
ive seaparation of algae by the use of subsurface drawoffs.
The important aspect of multicell design is the outlet struc-
ture.  The outlet structure is designed to draw final efflu-
ent from below the surface of the oxidation pond.  In this
way the heavy algae growth at the pond surface is avoided.
In the past the multicell ponds have been designed on the
basis of total pond voluem as the treatment unit.  Actually,
the first pond is the treatment unit and the remaining cells
are merely solids separation ponds.  If maximum solids sep-
aration is to be desired, minimum mixing is desired.  Since
mixing is important in the treatment unit, it can be seen
that a single cell oxidation pond is a poor design as far as
treatment is concerned.  In the bacterial reactor there is a
need for limited mixing to keep the oxygen and the bacteria
together with the soluble organics to be metabolised.  Actu-
ally, the mixing should not be such that the heavy solids
in the raw wastes are kept in suspension.  This intermediate
degree of mixing is difficult to achieve when natural wind
action is the basis for mixing.  In the other ponds, mixing
is not needed and is undesirable.

If multicell ponds are to be used for algae separation, it
appears that the first cell should be designed for 20 days
retention on an average flow rate to permit variations in
organic load to be easily absorbed and to permit good opera-
tion in the winter period under ice cover.  The first pond
should be designed with a 4 ft normal depth to give maximum
surface area for photosynthesis.  The inlet should be design-
ed to give a circular, deeper, sludge storage zone below
the bottom of the normal pond.  This will allow maximum wind
mixing to occur without stirring up the settled solids.  The
sludge storage section should have a maximum diameter of
100-200 ft with a center depth of 4 to 6 ft.  The taw waste
inlet pipe should be located in the center of the sludge
storage section so that the raw wastes enter the pond in a
radial fashion to distribute the load around the inlet pipe
in the same fashion that inlet structures are designed for
circular clarifiers except that all of the baffles in the
oxidation pond should be submerged.  This will permit the
heavy solids to remain around the inlet and undergo anaerobic
decomposition with a minimum oxygen demand.  The outlet from
the first cell should have the capacity to change the depth
from 3 to 5 ft in 6 inch increments to give operational
                            54

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flexibility as well as a drain for the entire pond.  The out-
let structure should be designed to minimize fluid velocities
at a single point.  In small plants a large pipe outlet with
adjustable sections is adequate.  In large plants an adjust-
able weir will be required.  There should be three sets of
baffles concentrically around the effluent structure.  The
first baffle should be designed to extend around the outlet
structure 3-5 ft with the baffle extending at least 6 inches
to one ft above the highest water level and down to within
one foot of the bottom of the pond.  Thus, the effluent will
be drawn from the bottom of the pond.  The second concentric
baffle rises from the bottom of the pond to within 6 inches
of the surface at the lowest possible level.  The third con-
centric baffle is the same as the first, rising above the
maximum surface and dropping to within one foot of the bottom
of the pond.  These baffles are designed to give an up and
over type baffle with a bottom drawoff to minimize removal of
algae from the active zone and to allow the algae to congre-
gate at the surface within a quiescent ring that is not
affected by wind action.  In effect, a stilling basin is
created which encourages the algae to accumulate at the
light surface and minimizes mixing to interfere with sedi-
mentation.  The addition of 1-2 inch rock to a depth of two
feet around the outlet structure out to the second baffle
will give filtering surfaces that will increase the algae re-
moval even further.

The second pond should be designed for algae removal.  Mixing
dur to wind action should be minimized.  The small particle
size and the low specific gravity of algae prevent rapid re-
moval.  The size of the pond depends on the extent of endog-
enous respiraton desired.  The reuse of carbon dioxide pro-
duced by endogenous respiration limits the size of the second
ponds or additional ponds.  To produce a quality effluent from
endogenous respiration alone, the ponds would need a total
retention period of 120 to 160 days.  A small second pond can
be used as easily as a large second pond or a series of ponds,
if the algae can be removed.  Use of a small second cell re-
quires that the algae be removed by rock filtration as
suggested by Martin (36) or possibly killed with chlorine
and allowed to settle or chemically precipitated.  Further
research is need on this  topic.  There appears to be limit-
ed benefit from more than three cells in series although the
wastewater flow through time will be better in multicell units
than in a single unit.  This is very important in coliform
reductons.

Coliform reductions and pathogenic bacteria reduction does
not result from a toxic environment or any unusual predation.
The die-off of coliforms and any bacteria follow the same
general patterns.  As indicated by theory, the organic
matter is essentially removed in 2 days so that there is

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limited food for the microbes to metabolise and to stay
alive.  The net result is that the bacteria die off.  The
bacteriological data collected to date (8,37,41,42) con-
firms the coliform dieoff follows expected patterns with
detention period being the predominant factor and temperature
a secondary factor.  The coliform dieoff appears to follow
normal endogenous respiration rates with slower metabolism
at the lower temperature and hence greater survival rate.  At
20C the dieoff of coliforms and the enteric bacterial patho-
gens should give 99% reduction in 20 days, 99.99% reduction
in 40 days, and 99.9999% reduction in 60 days provided
there is no short circuiting.  A single cell pond will show
considerable short circuiting, depending upon the wind mixing.
To maximize the dieoff of bacteria a large number of cells
with minimum mixing is required.  Needless to say, it is
not possible to achieve a high degree of bacteria removal
with retention periods under 100 days with conventional two
cell ponds.  Chlorination will be required to produce a
high degree of bacterial reduction.  If chlorination is to
be used in oxidation ponds,  it might as well be used to kill
the algae as well as the bacteria as some kill will result.
By constructing a small cell with the oxidation pond or by
a separate pond having two days retention and surface baffles
to retard mixing, it is possible to chlorinate the algae-
bacteria mixture and kill both the algae and the bacteria.
The two day retention perbd pond will allow the algae to
settle and will produce a satisfactory effluent.  The dead
algae will be allowed to accumulate in the small pond and will
not exert as great a BOD in the receiving stream as would
be the case if the algae are chlorinated as the eflfuent
leaves the oxidation pond.  The rock filter would also bfe
of value in removing the dead algae in the chlorination pond.

There is no doubt that oxidation ponds as currently designed
will not meet future water  quality criteria.  In this the
critics are right.  But examination of the fundamental micro-
biology and biochemistry together with engineering concepts
indicates that there are solutions to the oxidation pond
effluent quality problem without major changes in concepts.
Short time pond systems are possible if the algae are re-
moved.  Long retention periods are required if a high quality
effluent is to be produced naturally.  A number of design
modifications were suggested based on limited small scale
research or on extrapolation of available field data and the
fundamentals.  These concepts should be tried in demonstra-
tion projects as soon as possible so that the value of these
modifications can be ascertained.  It is essential that
every effort be made to obtain the maximum capability from
the oxidation pond systems.   They remain on the simplest
wastewater treatment systems to design, construct, and oper-
ate.  In view of limited skills for the future in the area of


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wastewater technology, oxidation ponds must be kept as simple
as possible while attaining the deisred results.
                               tT'
In recent years researchers and engineers have attempted
to mathematically evaluate oxidation ponds so that a series
of design equations could be available to the engineer.
For the most part these design equations were developed from
laboratory models or field data without careful examination
of the fundamental reactions occurring within the ponds.
The net result was that the various design models fitted the
data at hand but differed from each other and tended to create
confusion rather than clarity in the minds of the design en-
gineers.  It is not surprising that engineers have ignored
these design models in favor of the simplified design cri-
teria based on field experience.  Field experience has worked
reasonably well.  With the additional fundamental concepts
to help the design engineer understand what is happening in
oxidation ponds, it should be possible for the engineer to
design oxidation ponds to produce any desired result.

                DESIGN EXAMPLE

A domestic sewage has the following characteristics:

   BOD = 200 mg/1
   Suspended solids = 240 mg/1
   Flow = 100 gpcd
   Population = 10,000 people

Design an oxidation system to produce an effluent of 20 mg/1
BOD and 20 mg/1 suspended solids with (a)  a minimum of mech-
anical equipment and with (b) mechanical equipment needed to
minimize the pond size.

(a) Minimum Mechanical Equipment

It must be recognized that the 20 mg/1 BOD is carbonaceous
BOD only.  It is assumed that the receiving stream has the
ability to absorb the nitrogenous BOD.  Since mechanical equip-
ment is to be minimized, the pond retention period must be
maximized.  All of the effluent BOD and suspended solids
will be related to the algae in the system.  Actually the
effluent suspended solids will control the design in this
case.

The algae have 90% volatile matter in their cells,

   Effluent VSS =0.9 (20) = 18 mg/1
   Effluent BOD =0.75 (18)  = 14 mg/1
   Influent load:  BOD5 = 1670 Ibs/day
                   SS   = 2000 Ibs/day
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Design the system in multicell units having a 20 day
  retention each.

   Cell volume = 20(1,000,000) = 20 x 106 gallons each
                               = 2.65 x 106 cf each
   Cell depth = 4 ft.

Design the cell so that it is square.

   Bottom length = 800 ft.
   Top length = 824 ft.
   Surface area = 680,000 sq. ft.
                =15.7 acres

Organic load on 1st cell = 1670/15.7 = 106 Ibs BOD5/acre/day
   This BOD load is not excessive for the first cell.

Design a sludge retention section around the raw waste inlet.
   Use a 200 ft diameter section 4 ft deep located in one
     corner.
   Assume 95% suspended solids settling in this section.
   Solids accumulation = 0.95(2000) = 1900 Ibs/day.
   Assume 6% solids concentration.
   Solids volume = 500 cu ft/day
   Sludge retention section volume = 125,000 cu ft.
   Sludge retention without metabolism = 250 days.

Needless to say, the sludge retention period is too short
for effective storage.  The volume must be increased signi-
ficantly.  Because of the heavy solids load on the first
cell, consider deepening the entire cell another 4 ft. for
sludge storage.

   Sludge retention volume = 2,470,000 cu ft.
   Sludge retention without metabolism = 4,950 days
                                       = 13.5 years
   Assume 20% metabolism of biodegradable fraction of
    settled solids.
   Expected sludge retention = approximately 15 years.

At the end of 15 years operation the sludge retention section
should be full of sludge and should be removed and returned
to the land.  Additional anaerobic metabolism could reduce
the solids and extend the life of the sludge retention section.
Concentration of solids to 10% would extend the life of the
sludge retention section to 25 years.
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Influent pipe: Locate inlet pipe approximately 300 ft along
               the diagonal across the corners at the bottom.
               The inlet pipe should rest firmly on the
               bottom of the pond or should be below ground.
               The influent pipe should be attached to a
               concrete slab or anchor at end with a verti-
               cal riser above the pond surface approxi-
               mately one ft and topped with a removable
               cap for cleaning.  The discharge points from
               the influent pipe shall consist of a series
               of vertical slots, 6 inches long and 2 inches
               wide, around the pipe.  The top of the slots
               shall be located 4 ft below the normal water
               surface, giving a discharge in the horizontal
               plane.  The heavy solids would be expected
               to settle out within a radius of 100 ft.  of
               the inlet.  It may be necessary to periodi-
               cally check the area immediately around the
               inlet for solids accumulation.

Effluent pipe: The effluent pipe between the first and se-
               cond cells should be located near the oppos-
               ite corner from the inlet pipe.  The efflu-
               ent pipe should be at least 24 inches in
               diameter and laid horizontally between the
               two ponds at a depth of 4 ft so that the
               pipe invert enters at the floor of the
               second cell.  A 4 ft diameter circular steel
               baffle should be placed around the outlet
               pipe, going from the ground to one ft below
               normal water level.  A second circular steel
               baffle 8 ft in diameter is placed around the
               4 ft diameter baffle.  The 8 ft diameter
               baffle should extend 2 ft above normal water
               level and extend into the ground.   A single
               12 inch diameter hole located 4 ft below the
               normal water surface permits the water to
               flow from the oxidation pond into the stilling
               area and over the 4 ft baffle and down to
               the effluent pipe.  The baffles will retain
               all heavy solids while allowing the microbes
               to be transferred to the second cell.  A
               vertical sampling pipe should be located
               near the top edge of the dike so that a
               sample bottle can be lowered to obtain samp-
               les of the material flowing between the two
               ponds.
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Oxygen Requirements:  With separation of the settleable solids
                the oxygen requirement will be 0.8 Ib/lb
                BOD.
                Daily oxygen demand = 0.8(1670) = 1340 Ibs/day.
                                    = 160 mg/l/day

Algae Producton: 1.5 Ib oxygen produced/lb of VSS of algae
                 mass produced
                 Required algae production: 1340/1.5 = 890
                   Ibs/day VSS
                 Carbon dioxide produced from BOD stabiliza-
                   tion = 0.87 (1340) (44/32)
                   1580 Ibs/day
                 Carbon available from BOD stabilization =
                    (12/44)(1580)  = 430 Ibs/day
                   52 mg/l/day
                 Alkalinity in domestic sewage: 250 mg/1 as
                   CaC03
                   approximately 300 mg/1 as HC03
                 Total carbon in HC03 = (12/61)(300)= 59 mg/1
                 Carbon dioxide in domestic sewage: 50 mg/1
                  at pH 7 and 250 mg/1 alkalinity
                 Carbon in C02 = (12/44)(50) = 14 mg/1
                 Assume raising pH to 8.3 with only the
                   carbon dioxide and the carbon from the
                   BOD stabilization being used.
                 Carbon used = 52 + 14 = 66 mg/1
                 Oxygen released by algae synthesis =
                   1.1 (66)(32/12)  = 195 mg/l/day
                   1620 Ibs/day
                 This is more than adequate oxygen and re-
                 presents normal levels of operation for
                 domestic sewage oxidation ponds.
                 Expected algae production: 130 mg/l/day VSS
                   = 1090 Ibs/day VSS

                 Normally, the algae at the surface will
                 raise the pH while the bacteria in the
                 settled sludge will lower the pH.  The
                 normal mixing will produce a pH around 8.3
                 as an average.  With shallower ponds the
                 pH will increase and the algae will use
                 some of the alkalinity for their carbon.
                 In deeper ponds the pH will not rise as
                 high.  The carbon dioxide-alkalinity-calcium
                 relationships must be carefully evaluated
                 for each design to determine the full extent
                 of algae production.
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Effluent quality:
                   BOD = 79 mg/1
                   Suspended solids = 110 mg/1
Second Cell:
              Construct the 2nd cell for 20 days retention.
                   Bottom length = 800 ft.
                   Top Length = 824 ft.
                   Surface area = 680,000 sq ft.
                                = 15.7 acres
                   Depth = 4 ft.
                   Effluent pipe is a horizontal pipe set on
                   the floor of the second cell to the third
                   cell without baffles.  A sample pipe rises
                   to the top of the dike near the edge to
                   permit sampling of the material moving
                   between ponds.

Effluent quality:  The only reaction is endogenous respira-
                   tion of the algae which will decrease
                   the active mass 20% in 20 days at 20C.
                   Location of the effluent at the bottom
                   of the pond will permit a further reduction
                   of 25% so that total reduction of algae
                   for each cell after the 1st cell will be
                   40%.

                   BOD =61 mg/1
                   Suspended solids = 90 mg/1

Series Ponds:  In all a total of six ponds with a total of
                   120 days retention will be required to
                   produce a satisfactory effluent from a
                   BOD and suspended solids standpoint.

Final Effluent Quality:  BOD = 8 mg/1
                   Suspended solids = 11 mg/1
                   Fecal coliforms - under 200/100 ml

Special Conditions:  As the temperature decreases sharply in
                   the Fall of the year, the algae will die
                   and settle.  The final effluent will be
                   very good during this period.  The algae
                   will return rapidly in Cell 1 since the
                   environment is more conducive to growth.
                   The algae will return more slowly in the
                   5 remaining cells.  When the ponds freeze,
                   algae action will be limited and the good
                   quality effluent will be displaced slowly
                   by the incoming sewage.  The retention
                   period should be long enough that the
                   effluent quality will remain satisfactory
                   until the spring thaw and the algae
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                   explode in all ponds.   The quality of th
                   effluent at this time  will depend upon
                   the efficiency of the  algae to congregate
                   at the surface.   For a few weeks the
                   effluent may not meet  the 20-20 require-
                   ments; but this  generally will occur
                   during periods of spring thaw and rapid
                   runoff permitting a greater discharge
                   without problemsinn the receiving stream.
                   In dry areas the rate  of evaporation will
                   exceed the inflow and  no discharge will
                   result.  In these areas the pond design
                   must be adjusted accordingly.

(b)  With Mechanical Equipment

The first cell can be designed the  same as without mechani-
cal equipment.  The first cell will function normally during
the summer period but will have problems  when the algae
die off in the fall and when ice covers the pond.  The aera-
tion equipment should probably be diffused aeration with
plastic tubing diffusers placed over the  entire area of the
pond at mid-depth to prevent disturbing the settled solids
and to prevent clogging during the  non-winter period.  The
aeration equipment must be able to  transfer all of the re-
quired oxygen for bacterial metabolism without assistance
from the algae.   When the ice melts the aeration equipment
should continue to be run until the algae have grown enough
to produce the oxygen.  Normally, this will take one or two
weeks after the ice melts.

Aeration Equipment:  Diffused aeration as recommended by
                   manufacturer.
                   Oxygen transfer  = 1340 Ibs/day
                                   = 160  mg/l/day
                                   = 6.7  mg/l/hr

Effluent Quality:  The effluent will be high in algae and
                   bacteria and will need further treatment
                   prior to discharge.

Second Cell:  The second cell should have 20 days retention
                   also and be similar in shape as the second
                   cell in the previous design with a 4 ft.
                   depth and 17.5 acre surface.  In order
                   to remove the algae as quickly as possible,
                   7 baffles are run across the second cell to
                   divide the cell  into 8 sections approxi-
                   mately 100 ft wide. A single hole, 12
                   inches in diameter shall be located at
                   alternating ends of the baffles at the


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Final Subcell:
                   bottom to create 8 subcells operating in
                   a definite flow through pattern to mini-
                   mize short circuiting.  The baffles are
                   designed to minimize mixing and maximize
                   retention of the algae.

                The final subcell is modified to have a 24
                   inch diameter pipe laid along the bottom
                   of the pond next to the baffle for the full
                   800 ft. length.  A continuously operating
                   chlorinator will add 20 to 24 mg/1 chlorine
                   at the entrance to this pipe for disin-
                   fection and destruction of the residual
                   algae.  The 800 ft. length will give
                   almost 30 minutes contact time prior to
                   discharge into the final subcell with a
                   2.5 day retention peirod.  A series of 7
                   cross baffles will further divide this
                   last subcell into 8 chambers for the dead
                   algae to settle out.  It is expected
                   that the final effluent should meet the
                   required effluent quality at all times.
                   The mechanical aerators, the baffle walls,
                   and the chlorinator are relatively simple
                   changes to replace the four large cells.

Research Needs: There is a need to demonstrate the design
                   criteria proposed in this evaluation study.
                   the  proposed design criteria represent
                   The best concepts available at the present
                   time but they have not been studied
                   thoroughly in a single system.  It is
                   equally important to demonstrate modifi-
                   cation of existing oxidation ponds to
                   obtain high quality effluents.

                    Specifically, studies should be carried
                   out in the field to demonstrate the value
                   of a submerged rock filter in removing
                   algae from the treated effluent.  Labor-
                   atory studies have demonstrated that
                   rock filters could assist in the removal
                   of algae which are kept in suspension by
                   wind action.  Other forms of algae filters
                   with minimum operational requirements
                   should also be evaluated when available.
                   The key to a quality effluent lies in
                   removal of the algae.

                   Additional research is needed on the
                             63

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conversion of large oxidation ponds into
multicell ponds to demonstrate the value
of multicell units as a means of re-
ducing the algae.   Care should be given
to the design of the outlet structure
from each pond to minimize suspension of
the algae.

It appears that chlorination can be used
to kill algae as well as bacteria.  In
fact, disinfection with chlorine results
in destruction of the algae more easily
than the bacteria.  Studies should be
made on the construction of a chlori-
nation chamber ahead of a short term sedi-
mentation pond to permit the dead algae
to settle out.  Surface baffles will be
needed in areas having surface winds if
mixing is to be prevented.

Since chlorine reacts more readily with
the organic matter in algae to form
chlorinated hydrocarbons than to com-
pletely oxidize the organic matter, re-
search should be carried out as the
impact of these chlorinated organics on
higher forms of aquatic life which might
feed on the chlorinated algae in the
receiving stream.   Basic studies should
be carried out on the identification of
the chlorinated organic compounds in view
of the persistence and the potential
hazards created by the uncontrolled dis-
charge of chlorinated organics into the
environment.

Fundamental studies on the growth of algae
in domestic sewage would assist in under-
standing the basic problems in the micro-
biology of oxidation ponds.  Such studies
would include the effect of endogenous
respiration on the synthesis of new
algae and key nutrient elements affect-
ing algae growth.

Studies should be made to demonstrate
proper evaluation of pond effluent
quality to pond influent loading.  The
day to day efficiency based on influent
and effluent for that day is not a valid
method for evaluating oxidation pond
         64

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efficiency.  There is a need to develop
a sound evaluation procedure so that
engineers can anticipate the effluent
quality to be produced from a given set
of loading conditions.

Oxidation pond research needs to be
oriented to field installations.  The
laboratory studies in the past have con-
tributed significantly to a general
understanding of oxidation pond reactions
but have not fully demonstrated the re-
sults obtained in the field.  It should
be recognized that significant field data
will take considerable time.  Approxi-
mately one year of continuous sampling
and analysis will be required to obtain
a base set of data to evaluate new con-
cepts.  A second year of continuous
sampling and analysis will be required to
examine any one plant modification.  By
comparison with other forms of biotreat-
ment research on oxidation ponds is slow
and difficult.  It is important to realize
that research results cannot be obtained
quickly without increasing the chances
of significant error.  The size of the
ponds are also important in view of the
importance of wind mixing.

Oxidation ponds have been a valuable
part of the biotreatment complex.  The
simplicity and the low cost of oxidation
ponds have made them attractive for small
communities.  Unfortunately, these same
characteristics which made oxidation
ponds attractive to small communities
have restricted research and have limited
operational data.  The net result is a
serious gap in adequate information con-
cerning existing oxidation ponds.  Since
oxidation ponds will continue to have
use in the future, it is important that
efforts are directed to obtain the
necessary data to permit improvement of
effluent quality at minimum cost.  This
is the challenge for research on oxi-
dation ponds.
          65

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                       BIBLIOGRAPHY

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                              67

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25.  Maloney,  T.E.,  Ludwig, H.F., Harmon, J.A.,  and McClintock,
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                           68

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26. Middle-ton, F.M. and Bunch, R.L. , "Challenge for Waste
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27. Bersem, G.M. and Ryckman, D.W., "Evaluation of Lagoon
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28. Fitzgerald, G.P. and Rehlich, G.A.,  "An Evaluation of
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              ;                       i
29. King, D.L., Tolmseff, A.J., and Atherton, M.J., "Effect
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30. Bain, R.C., McCarty, P.L., Robertson, J.A., and Pierce,
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    (1970) .                       ;

31. Oswald, W.J., Golueke, C.G., Cooper, R.C., Gee, H.K, and
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    Conf. on Water Poll. Research, 2^, 119-157, Pergamon Press
    (1964) .                     ~

32. Golueke, C.G., and Oswald, W.J., "Harvesting and Process-
    ing Sewage Grown Planktonic Algae",  Jour. Water Poll. Con.
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33. Van Duuren, L.R.J. and Van Duuren, F.A., "Removal of Algae
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34. McGarry, M.G., "Algal Flocculation with Aluminum Sulfate
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35. Golueke,.C.G. and Oswald, W.J., "Surface Properties and
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36. Martin, D.M., "Several Methods of Algae Removal in
    Municipal Oxidation Ponds", MS Thesis, Univ. of Kansas
    (Dec. 1970).
                             69

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37.  Parker,  C.D.,  "Microbiological Aspects of Lagoon Treat-
    ment" Jour.  Water Poll.  Con.  Fed.,  34, 2, 149-161(1962).

38.  Cody, R.M.  and Tischer,  R.G.,  "Isolation and Frequency of
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39.  Hok,  J.T.,  "Die-Away of  Salmonella  abortus equi in Oxi-
    dation Ponds", Presented at Conference on Waste Treatment
    by Oxidation Ponds at Nagpur,  India, Oct. 29-30, 1963.

40.  Hsu,  Y.C. and Kruse,  C.W., "Survival of S. typhi in Sewage
    Oxidation Ponds", Jour.  San.  Engr.  Div., ASCE,  93, SA1,
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41.  Slanetz,  L.W., Hartley,  C.H.,  Metcalf, T.G., and Nesman,R.
    "Survival of Eneteric Bacteria and  Viruses in Municipal
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    ment  Lagoons,  Kansas City, Mo.,  132-141 (June,  1970) .

42.  Little,  J.A.,  Carroll, B.J.,  and Gentry, R.E.,  "Bacteria
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    Treatment Lagoons, Kansas  City,  Mo., 141-151(June,1970).

43.  Horn,  L.W.,  "Chlorination of Waste Pond Effluents", Proc.
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    Mo.,  151-159 (June, 1970).

44.  Ludwig,  H.F.,  Oswald, W.J., Gotaas, H.B., and Lynch,  V.,
    "Algae Symbiosis  in Oxidation Ponds I. Growth Character-
    istics of Euglena gracilis Cultured in Sewage," Sewage
    and Ind.  Wastes,  23,  11, 1337-1355  (1951).

45.  Merz, R.C.,  Merrell,  J.C., and Stone, R., "Investigation
    of Primary Lagoon Treatment at Mojave, California",  Sew.
    and Ind.  Wastes,  29_,  2,  115-123 (1957) .

46.  Silva,  P.C.  and Papenfuss, G.F.,  "A Systematic Study of
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47.  McKinney, R.E.,  "Overloaded Oxidation Ponds - Two Case
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48.  Gann, J.D.,  Collier,  R.E.  and Lawrence, C.H. "Aerobic
    Bacteriology of Waste Stabilization Ponds", Jour. Water
    Poll. Con.  Fed.,  40,  2,  185-191 (1968).              ~
                           70

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49. Cooke, W.B. and Matsuura, G.S., "Distribution of Fungi
    in a Waste-Stabilization Pond System", Ecology, 50, 4,
    689-694 (1969).

50. Christie,  A.E., "Virus Reduction in the Waste Stabiliza-
    tion Pond", Ontario Water Resources Commission Publ.  #9,
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51. Nupen, E.M., "Virus Studies on the Windhoek Wastewater
    Reclamation Plant  (South-West Africa)", Water Research
    4_, 661-672  (1970).

52. Loedolff,  C.J.,."The Function of 'Cladocera in Oxidation
    Ponds", Proc.  2nd Inter. Conf. on Water Poll. Research,
    1, 307-325, Pergamon Press (1965).

53. Holm, H.W. and Vennes, J.W.,  "Studies on the Occurrence
    of Purple Sulfur Bacteria in a Sewage Treatment Lagoon",
    Appl. Microbiol. , 1_9, 988-996  (1970).

54. Oswald, W.J.,  Gotaas, H.B., Ludwig, H.F., and Lynch,  V-,
    "Algae Symbiosis in Oxidation Ponds III.  Photosynthetic
    Oxygenation",  Sew. & Ind. Wastes, 25, 6, 692-705 (1953).

55. Fogg, G.E., The Metabolism of Algae, John Wiley & Sons,
55. New York,   (1953).

56. Richardson, B., Orcutt, D.M.  Schwertner, H.A.,  Martinez,
    C.L. and Wickline, H.E., "Effects of Nitrogen Limitations
    on the Growth and Composition of Unicellular Algae in
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    (1969).

57. Payne, W.J., "Energy Yields and Growth of Heterotrophs",
    Ann. Review of Microbiol., 24, 17-52 (1970).

58. Oswald, W.J.,  Gotaas, H.B., Golueke, C.G., and Kellen,
    W.R., "Algae in Waste Treatment", Sew. & Ind. Wastes, 29,
    4, 437-455  (1957).
                     l    ^
59. Bartsch, A.F.  and Allum, M.O., "Biological Factors in
    Treatment of Raw Sewage in Artifical Ponds", Limnology
    & Oceanography, II, 2, 77-84 (1957).

60. Towne, W.W., Bartsch, A.F., and Davis, W.H., "Raw Sewage
    Stabilization Ponds in the Dakotas", Sew. & Ind. Wastes,
    29, 4, 377-396  (1957).

61. Bartsch, A.F.,  "Algae as a Source of Oxygen in Waste
    Treatment, Jour. Water Poll.  Con. Fed., 33, 3, 239-249
    (1961).       ~"
                             71

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62. Stoltenberg,  D.H.   "Algal Metabolism as Related to the
    Theory of Oxidation Ponds",  MS Thesis, University of
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63. Nelson,  E.W., "Manometric Observations of Algal Endogenous
    Metabolism",  MS Thesis,  Univ.  of Kansas (Feb., 1964).

64. Oswald,  W.J., "Stabilization Pond Research and Installa-
    tion Experiences in California", Proc. Sym. on Waste
    Stabilization Lagoons,  Kansas  City^  Mo. 41-50  (1960) .

65. Hoover,  S.R.  and Porges,  N.,  "Assimilation of Dairy
    Wastes by Activated Sludge II.  The  Equation of Synthesis
    and Rate of Oxygen Utilization", Sew. & Ind. Wastes, 24,
    306-312  (1952).

66. Eckenfelder,  W.W.  and  O'Conner,  D.J., Biological Waste
    Treatment, Macmillan Co., New  York (1961).

67. McKinney,  R.E., "Mathematics  of  Complete-Mixing Activated
    Sludge", Jour.  San. Engr. Div.,  ASCE, 88,  SA3, 87-113,
    (1962).

68. Servizi, J.A. and  Bogan,  R.H., "Free Energy as a Para-
    meter in Biological Treatment",  Jour. San.  Engr. Div.,
    ASCE, 8_9,  SA 3, 17-40  (1963).

69. Servizi, J.A. and  Bogan,  R.H., "Thermodynamic Aspects of
    Biological Oxidation and  Synthesis",  Jour.  Water Poll.
    Con. Fed. , 3_6,  607-618  (1964).

70. Lountz,  R.R.  and Forney,  C.,  "Metabolic Energy Balances
    in a Total Oxidation Activated Sludge System", Jour.
    Water Poll. Con. Fed.,  31., 7,  819-826 (1959).

71. McKinney,  R.E.  and Benjes, H.H., Jr., "Evaluation of Two
    Aerated  Lagoons",  Jour.  San.  Engr. Div.,  ASCE, 91, SA6,
    43-55,  (1965) .
                            72

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                        SECTION V

                     AERATED LAGOONS

As the need for improved waste treatment became a necessity,
engineers began to look to new treatment concepts.  There was
a need for a treatment process which produced an intermediate
level of treatment between primary treatment and conventional
secondary treatment.  Industry provided the incentive for de-
velopment of the aerated lagoon.  During the past decade aer-
ated lagoons have found extensive use in both industrial
waste treatment and municipal waste treatment.

INITIAL STUDIES

In 1957 (1) the Glatfelder Company of Spring Grove, Pa.,
began carrying out studies on biological treatment of the
process wastes from the manufacture of paper.  Initially,
a large scale activated sludge system was constructed to study
the effect of conventional activated sludge as well as con-
tact stabilization activated sludge.  It was estimated that
72% BOD reduction was required at a waste flow of 10 MGD
and 78% BOD reduction at 20 MGD.  The pilot study showed
that activated sludge would treat the waste satisfactorily
but the cost was quite high.

Fundamental concepts developed by Weston and Stack (2) in-
dicated that an aeration only system could produce a satis-
factory effluent.  It was believed that several ponds in ser-
ies would produce as high a degree of treatment.  In order
to test the aerated lagoon concept, laboratory units were
set up on a batch basis.  The results indicated 76%  BOD
reduction with 2.5 days aeration for a waste with 225 mg/1
BOD.  Because of the good results, a large scale pilot plant
was constructed with a capacity of 98,900 gallons.  Diffused
aeration was used in this pilot unit.  Tests were carried out
with 3 and 4 days aeration.  The BOD reduction was 55% at
3 days and 68% at 4 days.

It was decided to construct a large scale treatment plant
to treat 2.5 MGD of wastes.  The treatment plant was con-
structed with two aeration cells, 110 ft. wide, 12 ft. deep
and 703 ft. long.  The size of the aeration cells required
a different type of aeration system than the diffused aera-
tion system used in the pilot plant.  Infilco helped develop
a turbine type surface aerator.  Mechanical aeration equip-
ment had little use in the United States prior to this time.
Three 60 HP Vortair, turbine aerators were placed in each aer-
ator.  The cost of the treatment plant was $480,000.  Unfor-
tunately, the treatment facility was placed into operation in
                             73

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January, 1959.   January is a bad time to start a biological
treatment plant because of the low temperature.  It was found
that the treatability of the wastewaters had changed.  More
importantly, it was observed that two ponds in series did not
remove the same percentage of BOD as anticipated.  The second
pond removed much less BOD than the first pond.  Thus, it was
demonstrated that series ponds could not produce the BOD re-
duction expected from theoretical analyses of biological
treatment.  Few people have recognized the importance of this
field scale study.  It demonstrated that the subsequent ponds
were not functioning at the same rate as the first pond.
Strangely, this fact has been ignored in the fundamental,
mathematical analyses made after this study.

Cost data indicated that aerated lagoons were more expensive
than activated sludge.  Contract stabilization proved to be
the most economical form of biological waste treatment.  In
March, 1961 the full scale contact stabilization plant got
underway.

Aerated lagoons looked like an easy solution to industrial
waste problems.  Eckenfelder and 0'Conner (3)  applied the
aerated lagoon concept to cannery wastes.  They applied the
fundamental concepts of biological waste treatmemt to aerated
lagoon design.   Unfortunately, the mathematics were for a
completely mixed system.  Their laboratory models were com-
pletely mixed but their field scale systems were not complete-
ly mixed.  The mathematics were not directed towards real
system but no one really recognized this essential fact.  It
suffices to say, the idea worked.

Eckenfelder (4) saw the aerated lagoon as a modification of
the activated sludge process.  The oxygen requirements ranged
from 0.9 to 1.2 Ibs 02/lb. 5 day BOD.  Approximately 25% of
the oxygen transfer was through the surface.  The aerator
transferred 2.5 to 3.5 Ibs 02/HP-hr. with 4-7 days aeration.
The cost of the aerated lagoon was only 2/3 the cost of a con-
ventional activated sludge system.  The problem with the aera-
ted lagoon was the high loss of suspended solids.

Aerated lagoons were connected to industrial wastes until
September 1960 when a special study was begun on the treat-
ment of domestic sewage.  This study was the result of the
imagination and the engineering concepts of Ansel Mitchell
and Les Webb.   Les Webb believed that aerated lagoons had a
broader application than for industrial wastes only.  Ansel
Mitchell agreed with this basic concept and designed the
first aerated lagoon to treat domestic sewage.  The Univer-
sity of Kansas was asked to test this unit.  McKinney and
Edde  (5) carried out extensive studies on the 65 ft. diameter
aerated lagoon which was aerated with a 3 HP Vortair
                            74

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mechanical aerator.  It was found that 76% BOD reduction
occurred with 6.4 days aeration.  Removal of the suspended
solids produced 92% BOD reduction.  The aerator transferred
2.0 Ibs 02 HP/hr at 1.0 mg/1 D.O..  This study demonstrated
that the aerated lagoon was a new concept for domestic sewage
as well.

Aerated lagoons were suddenly a major factor in wastewater
treatment.  Overloaded oxidation ponds plus the need for
partial treatment stimulated application of aerated lagoons.
Examination of fundamentals (5a) showed that temperature,
mixing, 02 transfer, retention time, and microbes were all
important factors in BOD reduction.  It was observed that
few aerated lagoons were truly completely mixed systems.
The problem was a lack of adequate mixing.  Aerated lagoons
were affected primarily  by oxygen transfer and mixing.  The
initial studies indicate that mechanical aeration equipment
could transfer 1.5 Ibs 02 HP.hr..  With 24 hours aeration
50% BOD removal was expected.  For the first time the engine-
er was furnished with design data for aerated lagoon to
treat either domestic sewage or industrial wastes.

Red Bridge furnished a fruitful area for research.  A second
aerated lagoon was designed to demonstrate the feasibility
of the aerobic-anaerobic concept.  A 10 ft. deep aerated
lagoon was constructed in hopes that the bottom 5 ft. would
be anaerobic while the upper 5 ft. would be aerobic.  The
hydraulic mixing concepts changed the operational character-
istics of the system.  The entire area around the mechanical
mixer remained aerobic while the area further out was ana-
erobic.  Evaluation of both aerated lagoon systems  (6) show-
ed 1 . 8 Ibs 02 HP. hr.  Mixing was a problem for both units.
It was felt that 1/5 to 1/4 HP was required/100 cf of aeration
volume.  Adequate power was needed to keep the solids in sus-
pension.  The BOD reduction was 63% for 1.7 days aeration and
78% for 7.1 days aeration.  The primary cause of the residual
BOD was unflocculated microbial solids.  Placing an oxidation
pond following the aerated lagoon resulted in removal of the
suspended solids but permitted algae to grow up.  Operational
data showed that the effluent BOD from the oxidation pond
was essentially the same before and after construction of the
aerated lagoon.  The effluent BOD was created by algae and
averaged 30 mg/1.

Mancini and Barnhart (7) applied fundamental concepts to the
design of aerated lagoons for industrial wastes.  Their
equatbns were developed for complete mixing systems.  Sawyer
(8) felt that aerated lagoons should be operated as complete
mixing systems.  He preferred mechanical surface aeration
over diffused aeration because of mixing and power require-
ments.  Aerated lagoons produced 0.5 pounds suspended solids


                            75

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per pound of BOD stabilized and requires from 0.8 to 1.2
pounds of oxygen per pound of BOD.  Caution was urged for
aerators over 25 HP as there was a tendency to create too
much localized mixing and not enough mixing for the entire
tank.

The conversion of overloaded oxidation ponds to aerated la-
goons  became a standard practice for increasing the load on
ponds.  Typical was the conversion of the oxidation ponds at
Travis Air Force Base (9).   Laboratory studies showed that
sedimentation ponds following the aerated lagoons would pro-
duce an effluent of 10 mg/1 BOD.  The aerated lagoons for 2
MGD of wastes were designed with 9-15 HP mechanical aerators
spaced 70 ft. apart.

Aerated lagoons have also been used for tertiary treatment
(10).   Peak flow periods caused loss of solids from a contact
stabilization activated sludge plant in East Windsor, New
Jersey.  A 3.11 acre aerated lagoon using diffused aeration
was placed in operation after the activated sludge plant.
The influent BOD and SS was 80 mg/1 at peak flows.  The ef-
fluent BOD and SS were from 12-15 mg/1.

Examination of 10 years experience with aerated lagoons by
Benjes  (11) indicated that there were three basic types of
aerated lagoons: 1. the complete mixing aerated lagoon where
all contents of the aeration cell were held in suspension;
2. facultative aerated lagoons where some solids settle out
due to incomplete mixing; and 3. aerated oxidation ponds
where there is little mixing.  Examination of theoretical de-
sign equations by Eckenfelder, McKinney and Monod revealed
slight differences in approach but no serious differences.
Mixing and aeration was of primary concern.  Turbine type
aerators were more efficient than propeller type aerators as
far as pumping fluid was concerned.  It was indicated that
pumpage was only 2,000 gpm/HP and oxygen transfer was 2
pounds oxygen/HP/hr.  When aerated lagoons have less than
24 hours retention the power for oxygen transfer controls
the design.  Above 24 hours retention the power for mixing
controls.

A simplified kinetic theory for aerated lagoon design was
developed by Marais and Capri  (12).  It was felt that sever-
al ponds in series could achieve more efficient BOD reduction
than one single pond.  The key lay in the fact that metabol-
ism progressed at the same rate in all ponds.  Unfortunately,
the earlier studies of Rice and Weston  (1) had shown that the
kinetic rate of metabolism was not the same in all series
ponds.  Basically, metabolism will convert all the organics
of microbes in the first pond provided there is adequate mix-
ing and oxygen.  The other ponds will primarily be concerned
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with stabilization of cells.  This points to the need to
combine mathematical concepts with biological concepts to
develop sound design criteria.

INDUSTRIAL WASTES

Industry provided the initial impetus for the development
of aerated lagoons and furnished much of the early design
and operational information.

Pulp and Paper;

The pulp and paper industry has found extensive use for
aerated lagoons.  Eckenfelder (13) examined the need for
additional nutrients such as nitrogen and phosphorus for tre-
ating pulp and paper wastewaters.  He showed that the prime
problem with the lack of nitrients was a slower rate of BOD
removal.  Basically, nutrients are exchangeable with aeration
time provided there is at least a minimum level of nitrients
in the wastewater.

Gehm (14) felt that aerated lagoons did not offer any advan-
tages over activated sludge and could not produce as good
an effluent.  It was felt that a high degree of treatment
was needed for pulp and paper wastes and it could not be pro-
vided for by aerated lagoons.

Yet, there was a need to build wastewater treatment plants as
economical as possible.  The aerated lagoon offered an econo-
mical method for meeting the needs of a number of pulp and
paper plants.  Weyerhaeuser Company (15) built aerated lagoon
systems at its Springfield, Oregon, and Cosmopolis, Washing-
ton plants.  The Springfield aerated lagoon covered 21 acres
with a depth of 10 ft.  The wastewaters and an 8 day detention
time with an influent BOD of 200 mg/1 and an effluent BOD of
16 mg/1.  Aeration was designed to transfer 20,000 pounds of
oxygen a day with 5-75 Yeoman surface aerators with a 20 HP
Infilco aerator as a spare.  The Cosmopolis aerated lagoon
system consisted of two parallel lagoons each with 5.5
million gallons capacity and 8-75 Yeoman aerators.  The re-
tention period was 5 days.  The avearge BOD of the wastewaters
was 4,000 mg/1.  BOD reductions from 83 to 95% were achieved.
The Kamloops Pulp and Paper Company in Kamloops, British
Columbia, had 23 acres of aerated lagoons, 10 to 12 feet deep.
The retention period was 7 days at 13 MGD flow.  There were
4-60 HP fixed aerators and 5-15 HP floating aerators.  One of
problems was icing of the aerators during the winter.  Low
temperatures definitely reduced BOD reduction.  Fortunately,
the raw wastes were able to keep the temperature around 60F.
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The Packaging Corporation of America plant at Rittman, Ohio
(16) had a waste flow of 3 MGD.  Primary treatment removed
90% suspended solids and 25% BOD.  The settled effluent was
treated in four earthen aerated lagoons.  Two units were 200
ft. by 500 ft. with 8 ft. depth.  There were 3-30 HP
aerators in each of these lagoons.  The other two units were
240 ft. by 310 ft.  with 8 ft. depth.  The units had 3-40 HP
aerators.  After 11 days aeration the effluent had 69 mg/1
BOD.  A 7 day sedimentation period after aeration only lowered
the BOD to 63 mg/1.  Post aeration with a 20 HP floating
Aqualator in an 80,000 gallon basin raised the effluent D.O.
to 3.8 mg/1 with a BOD of 56 mg/1.  The treatment operations
cost $0.64/MG.  The primary operational problem was the gear
boxes on the aerators.  Overall the BOD reduction was 86%.

The Riegel Paper Company plant  (17) in Riegelwood, North
Carolina had 230 acres of ponds to handle the wastes from
200 tons of bleached kraft pulp per day.  Originally, 14-60
HP floating aerators were added to the ponds.  It was anti-
cipated that the aerators would transfer 3.3 pounds oxygen/
HP/hour.  It was necessary to operate the aerators only in
the summer.  The aerators cost $155,000 with a power cost of
$40,000/year.  The current BOD load was 108,000 pounds per
day with an effluent of 18,000 pounds per day.  An additional
15-20 HP aerators were added to give additional oxygen.

The Moraine Division plant of Kimberly Clark at West Carroll-
ton, Ohio  (18) produces 5.5 MGD.  The heavy suspended solids
load required primary sedimentation prior to the aerated
lagoons.  Two aerated lagoons were employed 1400 ft. long
by 145 ft. wide and 14 ft. deep.  The aeration capacity gave
a 6 day retention with 3-60 HP floating aerators in each cell.
The influent BOD to the aerated lagoon was 375 mg/1 and the
effluent BOD was 50 mg/1.  The change in suspended solids
was from 100 mg/1 to 60 mg/1.  The major operating problem
was ice on the aerators.

Summarizing industry activity, Gellman and Berger  (19)
reported that there were 11 installations treating 150 MGD.
By and large evaluation of aerated lagoons in the pulp and
paper industry was with equations presented either by Ecken-
felder or McKinney.  It was apparent that aerated lagoons
were of major importance to the pulp and paper industry.

Textile:

Cotton textile wastes pose problems similar to pulp and paper
wastes.  They are generally high in carbohydrates and low in
nutrients.  In addition the pH is generally high, above 9.5.
Studies at Mooresville Mills in Mooresville, North Carolina
(20) indicated that aerated lagoons could be used to treat
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cotton textile wastes. 'Two concrete tanks, 254 ft. long,
112 ft. wide and 12 ft. deep, were constructed to give a
48 hour aeration to a flow of 2 MGD.  Four 25 HP mechanical
aerators were selected for aeration.  The aerated lagoon was
followed by a settling lagoon 122 ft. long, 68 ft. wide, and
12 ft. deep.  The sedimentation time was 12 hours at average
flow.  The estimated construction cost was $234,000 with
$7,400/year in operation costs.

Dye wastes present a problem of color in addition to
the soluble organics.  The wastewaters from the United Piece
Dye Works in Bluefield, Virginia, (21) had a pH of 6.8,
85 mg/1 SS, 325 mg/1 BOD, and 750 mg/1 COD.  Chemical treat-
ment was necessary to remove the color.  Lime plus an anionic
polyelectrolyte was used to flocculate the wastes prior to
neutralization and biotreatment.  The aerated lagoon system
consisted of four lagoons in series with a total of 5 days
retention.  The first lagoon had 100 HP mechanical aeration
with 2 days retention.  The second lagoon had a 20HP floating
Aqualator.  The third lagoon had 2-20 HP Aqualators and the
fourth lagoon had a 20 HP Aqualator.  During summer months
the system gave 90% BOD reduction with 20 mg/1 BOD in the
effluent.  The BOD reduction in the winter was only 50% with
an effluent having 160 mg/1 BOD.

Refinery;

Oxidation ponds have had extensive use in treating process
wastes from refineries.  It was only natural that aerated
lagoons would be used where land was limited or to increase
the capacity of existing systems.  The American Oil Company
refinery located at Sugar Creek, Missouri, was faced with
limited land for waste treatment facilities and constructed
a four cell treatment system.  The first cell was designed
as an oil skimming unit.  The next two cells were aerated
lagoons.  The final cell was a sedimentation cell.  The first
aerated lagoon was 120 ft. by 713 ft. by 10 ft. with 3-60 HP
Vortair mechanical aerators.  The second lagoon was the same
size but contained only 3-15 HP Vortair mechanical aeration.
Two studies on this system  (22)(23)  at a flow of 8 MGD
showed 89% reduction in oil; 197 mg/1 to 22 mg/1; 94% re-
duction in phenol, 7.4 mg/1 to 0.4 mg/1; 69% reduction in COD
467 mg/1 to 146 mg/1; and 76% BOD reduction, 175 mg/1 to 42
mg/1.  It was apparent from the results that oxygen transfer
was limiting the treatment efficiency.  The oxygen demand
at the first aerator demonstrated the hydraulic effect of a
plug flow type aerator.  Additional floating aerators have
since been added to try to meet the oxygen demand.

The Humble Oil and Refining Company plant at Houston, Texas
(24) had a dry weather flow of 15 to 18 MGD.  The wastewaters
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have 976 mg/1 COD, 227 mg/1 BOD, 54 mg/1 NH3-N, and 2.5 mg/1
PO4-  The aerated lagoon covered 7.75 acres with 16-60 HP
mechanical aerators at 80-150 ft. spacings.  Unfortunately,
the data indicated a lack of sufficient mixing and dissolved
oxygen for good treatment.  This illustrates one of the major
problems facing aerated lagoons, too much volume of lagoon
and not enough mixing.

Chemical;

Chemical wastes are similar to refinery wastes being primar-
ily soluble hydrocarbons.  The 3M Company wastes (25) had
237 mg/1 BOD, 15 mg/1 phenol, and a pH of 6.1.  An aerated
lagoon 47 ft. by 26 ft by 5 ft., 38,000 gallons, was con-
structed to treat these wastes.   With 4.6 days retention at
71F the unit showed 90% BOD reduction.  At 51F the BOD re-
duction dropped to 25%.  This illustrates the impact of
temperature on aerated lagoons.   Tests on phenol removal
showed that phenol and BOD removal followed the same pattern,
indicating that phenol was easily removed by microorganisms.

One of the largest aerated lagoons for synthetic chemicals
was constructed by Union Carbide (26) to treat 50,000 Ibs
BOD/day.  The aerated lagoon facility cost $900,000 and was
designed to treat 5.3 MGD wastes having a BOD of 2,100 mg/1.
An initial laboratory study showed 98-94% BOD reduction with
5 to 15 days aeration at 23C.  At 9C the BOD reduction was
83-87% with 5-8 days aeration and 63-71% with 2.5-5 days aer-
ation.  The treatment system had 66 hours aeration and 4
hours sedimentation.  Operational data during the summer
showed 35C, 0 mg/1 D.O., 54% BOD removal at 46 Ibs BOD/
1000 cf/day with 2.9 days aeration time.  Winter operations
with 2.3 days aeration time and 15C showed 2.0 mg/1 D.O. at
56 Ibs BOD/1000 cf/day and 40% BOD removal.  The oxygen trans-
fer characteristics of the Yeoman type mechanical aerators
were measured at 2.68 Ibs 02/HP/hr at 20C and zero D.O.
The BOD removal rates were 25 lbs/1000 cf/day at 24-36C and
27 lbs/1000 cf/day at 15C.  The microbial cells resulting
from metabolism were quite dispersed and did not settle in
the sedimentation pond.  This system was limited by oxygen
transfer characteristics as were many aerated lagoon systems,
especially large systems.

Roofing:

A small asphalt roofing shingle manufacturer utilized waste
paper and rags for roofing felt.  The Tamko Asphalt Pro-
ducts Plant  (27) in Joplin, Missouri, produced 150,000 gpd
wastes 7 days a week.  The wastes were discharged to a series
of ponds but the ponds were full of solids.  It was decided
to use aerated lagoons as pretreatment prior to discharge to
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the municipal sewerage system.  The aerated lagoon system
consisted of an equalization basin with 1.4 days retention,
an aerated lagoon with 0.9 days retention, and polishing
ponds with 3.6 days retention.  The operating data showed
the raw wastes had a BOD of 975 mg/1.  The influent to the
aerated lagoon had 900 mg/1 BOD and the effluent had 340 mg/1,
The polishing ponds reduced the BOD to 275 mg/1 prior to
discharge to the sanitary sewer.  The suspended solids were
reduced from 990 mg/1 to 145 mg/1.  The basic metabolic re-
action was limited by oxygen transfer as only one of the
three mechanical aerators was initially placed in service.
In spite of the oxygen deficiency, the system met the per-
formance requirements for discharge to the sanitary sewer.

Food Processing;

Food processing plants produce strong wastes that are largely
soluble or colloidal.  The initial use of oxidation ponds for
food processing wastes led to overloaded conditions and the
need for aeration.  Typical of this problem was the Sandwich
West Township (28) that had a dairy supplying 80% of the flow.
A 2 1/2 day aerated lagoon was constructed ahead of a 3 month
retention oxidation pond.  The aerated lagoon was 8 feet deep
with 221,000 Imp. gallons capacity and had a 20 HP Simcar
mechanical aerator.  The oxidation pond had a 4 ft depth and
a surface area of 6.8 acres.  The influent BOD was 370 Ibs/
day, and the effluent BOD was 253 Ibs/day.  The oxygen uptake
rate was 5.7 mg/1 hour.  The high pH of the wastes, 9-10,
appeared to retard biological activity in the aerated lagoon.

Park River, North Dakota, (29) had a small potato flake plant
which discharged its wastes to the sanitary sewer.  In order
to provide additional treatment, a single cell aerated
lagoon one acre in size, 8 ft. deep, was constructed.  The
retention period was,6-14 days during maximum load.  A single
25 HP Vortair aerator was used to provide proper oxygen trans-
fer.  It was found that 90% BOD reduction could be obtained
at a loading of 300 Ibs BOD/acre/day.

Potato processing wastes in Idaho were studied quite exten-
sively (30) over a two year period in 3 pilot lagoons.  One
system employed an aerated lagoon following primary sediment-
ation while the other system used one lagoon as an anaerobic
lagoon followed by an aerated lagoon.  The test ponds were
40 ft. square and 10 ft. deep.  The aerated lagoon following
primary sedimentation had a 10 HP Eimco surface aerator
while the aerated lagoon after the anaerobic lagoon had a
5 HP Welles floating aerator.  The aerated lagoon only show-
ed 55% BOD reduction at 24 Ibs BOD/1000 cf/day with 4.2 days
retention.  The BOD reduction increased to 81% at 11.3 Ibs
BOD/1000 cf/day and 7.8 days aeration.  The aerated lagoon
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following the anaerobic lagoon showed 83% BOD reduction at
20 Ibs BOD/1000 cf/day.  Increasing the load to 44 Ibs BOD/
1000 cf/day reduced the BOD removal to 50% oxygen transfer
was the limiting factor in treatment efficiency.

Pea processing wastes at Ferndale, Washington,  (31), were
treated in a 1.75 acre aerated lagoon, 10 ft deep.  The
aeration equipment consisted of four 50 HP surface aerators.
The effluent from the aerated lagoon went to a J.35,000 gallon
polishing pond.  During pea processing 96,000 to 180,000 Ibs
of peas were processed with 3,500 gallons of wastes produced
per 1000 pounds of peas processed.  The influent BOD averaged
820 mg/1.  The aerated lagoon effluent had 196 mg/1 BOD and
the final effluent had 182 mg/1 BOD.  The soluble BOD was
only 35 mg/1.  Microscopic examination of the activated
sludge showed predomination of Sphaerotilus and flaggellated
protozoa.  The high BOD load created less than optimum con-
ditions .

Fruit processing wastes at Yakima, Washington were treated
in a 6 MG aerated lagoon, 280 ft. square and 12.5 ft. depth.
Four 60 HP surface aerators were used to treat 20,000 BOD/day
in 1967.   The aerated lagoon gave 70% BOD removal but pro-
duced excessive quantities of suspended solids.  In 1968
a 150 HP surface aerator was added as was a 90 ft diameter
final clarifier.  The complete mixing concept provided ade-
quate treatment as long as nutrients are added.  The mechanic-
al aerator provided 0.3 HP/1000 cf for mixing and 2 Ibs 02/
HP-hour.  Material balances indicated that 0.46 Ibs 02 were
used for each pound of BOD removed.  Destruction of volatile
suspended solids required 1.2 pounds of oxygen per pound of
VSS destroyed.  The cost of treatment was $0.041/pound BOD
removed.  (32).

Mink food manufacturing at Midvale, Utah, resulted in wastes
that were treated in two aerated lagoons operating in series.
The aeration equipment consisted of a 10 HP 146 SCFM air
blower to 5,000 ft of aeration tubing in the primary lagoon
and 2,500 ft. of aeration tubing in the secondary lagoon. The
retention time was 30 days with 90% BOD reduction. The secon-
dary lagoon showed very profuse algae growth.  The aeration
tubing tended to clog but were cleaned by the use of HCL gas.
Approximately 20 minutes cleaning time was required at a cost
of under $20/month. (33).

Packinghouse and Animal Wastes;

As the aerated lagoon began to show promise as a simple sy-
stem for treating wastewaters, it was only natural to try aera-
ted lagoons for animal wastes.  Unfortunately, animal wastes
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are very concentrated and are not easily treated aerobically.
Two schemes were developed for treating animal wastes.  One
scheme employed anaerobic lagoons ahead of the aerated
lagoons and the other scheme employed dilution with treated
wastes.

Research at the University of Kansas during the early part
of the 1960 decade, resulted in a demonstration project em-
ploying the anaerobic-aerated lagoon concept for cattle
manure (34).  This project operated over a 3 year period from
1966 to 1969 and demonstrated the problems of this system for
treating manure from a beef cattle feedlot.  At the same time
parallel studies were being carried out on aerobic treatment
of hog manure in confined buildings.  In January, 1966, the
first full scale aerated lagoon for hog manure treatment
within a building was placed into operation near Lawrence,
Kansas.  A study  (35) by the University of Kansas demonstrat-
ed that the self contained, aerated lagoon could readily con-
vert, odorous hog manure into microbial solids which were
easily applied to agricultural lands.

The University of Illinois also carried out tests (36) on
aerated lagoon treatment of hog manure in confined buildings.
The BOD of the hog manure was reduced from 35,000 mg/1 to
approximately 3,000 mg/1.  The retention period of the manure
in the aerated lagoon was approximately 50 days.  By 1969
there were over 100 confined hog manure aerated lagoons in
operation.

Studies on dairy cattle manure treatment in a conventional
aerated lagoon employing a floating, mechanical aerator (37)
found that 0.10 HP was needed per cow as well as 1400 cu. ft.
of lagoon volume per cow.  Hart (38) felt aerated lagoons
left a lot to be desired when applied to animal manures.  The
effluent from aerated lagoons treating animal manure cannot
be discharged directly to streams as they contain too much
salt and suspended solids.  Improper applications have pro-
duced poor systems that failed to work properly.  Yet, it
should be recognized that many systems are working properly.

The treatment of slaughter house wastes from Farmbest in
Iowa Falls, Iowa, utilizes anaerobic-aerated lagoons in
series.  The aerated lagoons consist of two cells in series
after the anaerobic lagoons with 40 days detention.  Aeration
was supplied by a diffused aeration system employing 52,000
ft. of plastic tubing.  Three 595 cfm compressors at 9 psi
are available for aeration.  The first lagoon gave 92% BOD
removal and 79% suspended solids reduction.  The second
lagoon gave 45% BOD removal and 50% suspended solids reduct-
ion.  The turbulence created by the diffused aeration system
was adequate to mix the wastes but were not adequate to keep
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the suspended solids in suspension.  The final effluent con-
tained 30 mg/1 BOD and 48 mg/1 suspended solids for 99%
treatment.

The Sterling Processing Company in Oakland, Maryland, employs
two aerated lagoons in series to handle poultry processing
wastes (40).  The first pond is 590 ft. long, 140 ft wide,
and 6 ft. deep while the second pond is 230 ft. long, 140 ft.
wide and 6 ft. deep.  Diffused aeration is supplied through
104 Link Belt Aero Circulators at the rate of 2800 cfm. The
raw wastes range from 800 to 1000 mg/1 BOD.  The effluent
from the first aerated lagoon has 70-100 mg/1 BOD while the
final effluent has 30 mg/1 BOD.  The total aeration time is
14 days.

It can be seen that aerated lagoons have had extensive use
in treating industrial wastes.  Much has been learned from
these industrial applications because they have covered
a wide range of loading conditions and have employed several
different design concepts.  One of the important parts of
aerated lagoons is the aeration equipment.  Both mechanical
aerators and diffused aeration have been employed in aerated
lagoons.

                   AERATION EQUIPMENT

MECHANICAL AERATION:

Mechanical aeration has been used in activated sludge systems
since 1920 but little scientific progress was made on mech-
anical aeration in the United States prior to their use in
the Glatfelder aerated lagoon.  Weston and Stack (41)
studied the surface, turbine type aerator using sodium sulfite
in tap water.  The sodium sulfite removed the oxygen from the
water and permitted determination of the rate of reaeration.
They found that the mechanical aerator could transfer from
3 to 4 pounds of oxygen per HP-hour.

Examination of mechanical aerators by Eckenfelder (42) in-
dicated that 10 to 20% of the oxygen transfer was due to sur-
face aeration and the rest was caused by the mechanical device
proper.  Mechanical aerators were found to transfer 4.0 to
4.5 Ibs 02/HP-hr at 0 mg/1 D.O. and 20C.  Eckenfelder de-
signed a basic equation to permit translation of data from
one set of conditions to another set.
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       N  =  N  Csw"CL   .1.02(t~20>.-
            o g-	

where N   =  Ibs  Op transferred/HP-hr  in water  at  20 C
            and  0 mg/1 D.O.

       N  =  Ibs  02 transferred/HP-hr  in lagoon under operating
                  conditions

     Csw  =  2 saturation  in lagoon,  mg/1

      CL  =  02 in lagoon,  mg/1

      Cg  =  02 saturation  in water at  20C, mg/1

       t  =  lagoon temperature,  C

       "i  =  02 transfer ratio of waste to water

One important observation was that tank geometry was signi-
ficant in selecting the number of aerators.   Unfortunately,
no insight  was  given  on the effect tank geometry had on
aeration  selection.

Weston (43)(44) made  a careful evaluation of  the Infilco
Vortair aerator.  He  found that the  turbine type aerator
created a hydraulic jump  with air being pulled in behind the
blades.   The turbine  then shears the air into tiny bubbles.
As the turbine  speeds  up, the blades overlapped and reduced
oxygen transfer.  Power requirements for turbine type aera-
tors were related to  power number and submergence, permit-
ting proper design of  turbine size,  speed and power.  It
was found that  this type  of aerator  transferred 3.7 Ibs
02/HP-hr. at low speeds and 3.1 Ibs  02/HP-hr  at high speeds.


Evaluation  of surface  aerators by McWhirter (45) indicated
good mixing was not easily achieved.  This resulted in vari-
ations in K-^a at different points in the aeration tank.
Lightnin  mixer  produced uniform mixing and oxygen transfer.

Paddle wheel mechanical aerators were almost  as old as acti-
vated sludge.   The Haworth paddles at Sheffield, England,
were the  first  mechanical aerators; but it was the Kessener
brush in  Holland in 1926  that was the first,  high velocity
brush type  aerator.  Eventually, the cage rotor replaced
the brush aerator.  One of the first studies  in the United
States on cage  rotors was at Iowa State University  (46).
The cage  rotor  was 27  1/2" diameter, 3 ft. long, and driven
with a 10 HP motor.  The  data collected by Knight indicated
5.65 Ibs  02 transfer/ft,  of rotor length at 12 inches sub-
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mergence and 100 RPM.  He, too, felt that oxygen transfer
was affected by water volume and geometry of tank.  Studies
of one tank could not be applied to another tank.

Baumann and Cleasby followed up with Knights data in a re-
latively small test tank  (47).  They found that the cage
rotor transferred different rates of oxygen at different
submergences and different speeds of rotation.  One of the
problems in evaluating mechanical aerators was in the relat-
ionships between water power requirements and wire power
requirements.  The waterpower requirements measure the theore-
tical power required while the wire power measures the paid-
for-power.  Frankly, only the latter really counts.  It was
found that motor and gear reducer losses accounted for a 25%
loss in power through the system.

Few consulting engineers were concerned about mechanical
aeration in 1965, much less the cage rotor.  Kalinske (48)
recognized that  oxygen transfer with mechanical aerators
was related primarily to the water pumped through the aerator.

            Qo = Qw(C2-Cl>
  where     Q  = Ibs 02/time

            Q  = Ibs water flow/time

            C- = 0- cone, at outflow, mg/1

            Cl ~ 2 conc< at inflow, mg/1

There was also a factor related to oxygen transfer per pass
through the aerator.  Kalinske rated K a to pumped flow, the
transfer factor, and tank volume.
                  Q K
            K _ _  w
            x\. a  	
             L     w


  where       K = the oxygen transfer efficiency per pass

              w = tank water mass, Ibs.

He felt complete mixing was important to oxygen transfer;
but the water pump concept was his most important contribu-
tion.

Theoretical concepts were of little value outside of techni-
cal meetings.  Yet, a few people began to recognize that
mechanical aerators would have more widespread use if methods
were developed for proper field testing.  Union Carbide was
faced with the use of aerated lagoons and developed the tech-
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niques needed to evaluate the aerators  (49).  The Institute
Plant of Union Carbide consisted of 3-5 MG earthen basins 17
ft. deep with 4-6 75 HP mechanical aerators.  The KLa at 20C
was determined to be 1.45/hour.  Studies at Rockford, Illinois,
with a 450,000 gallon tank, 70 ft. diameter and 17 ft. deep
with one 75 HP mechanical aerator gave a KLa of 6.6/hour.  It
was obvious that many factors affected oxygen transfer but
techniques were available to evaluate mechanical aerators.

Eckenfelder and Ford (50)(51) presented an old concept to
translate basic oxygen transfer data from one unit to another
unit.  They felt that 60% of the oxygen was transferrred
in the spray and 40% in the turbulence and entrainment.  A
bottom velocity of 0.4 to 0.5 fps was needed to prevent
bottom deposition of solids.  It was found that 0.3 HP/1000
cf of aeration volume was required for minimum mixing.

The cage rotor came into its own with its application to con-
fined hog manure treatment.  The University of Illinois (52)
studied three different types of cage rotors at 100 RPM.  The
angle iron cage rotor had 1.6 Ibs 02/ft. of rotor.  The rec-
tangular  plate had 1.7 Ibs 02/ft.  The expanded metal rotor
had 1.0 Ibs 02/ft. at 2 inches immersion and 1.5 Ibs 02/ft.
at 4 inches immersion.  It appeared that the rectangular
plate rotor was the most efficient aerator of those studied.
With increased application of caged rotors to confined animal
buildings, it was apparent that more data would be forth
coming in the future.  One thing for certain, mechanical aera-
tion came into its own with development of the aerated lagoon.

DIFFUSED AERATION:

Oxidation ponds worked well for domestic sewage as long as
they were not loaded excessively.  Diffused aeration equip-
ment was added to oxidation ponds in an effort to increase
the oxygen transfer.  In order to distribute the oxygen over
the entire oxidation pond, plastic tubing with tiny slits
was sunk to the bottom of the pond.  Diffused air was blown
through the complex distribution system to give broad aera-
tion.  One of the first installations was in Tinley Heights
near Chicago (53).  A 0.9 acre pond, 4.5 ft. deep was design-
ed for a BOD load of 30 Ibs/acre/day but was soon overloaded.
In 1961 2500 ft. of plastic tubing was added to the pond;
and air was supplied by a 5 HP, 54 cfm air compressor opera-
ting at 10 psi.  One and one-half years data indicated a load
of 130 Ibs BOD/acre/day.  The raw wastes had a BOD of 174
mg/1 while the effluent had a BOD of 29 mg/1.  The suspended
solids changed from 134 mg/1 to 54 mg/1.  These data show
that the BOD in the sewage was converted to suspended solids,
not all of which settled in the pond.
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The Raytown, Missouri,  Southwood oxidation pond (54) was
overloaded and expanded by adding mechanical aeration.  Con-
tinued increases in organic loading resulted in the need
for additional oxygen.   Approximately 24,000 ft. of plastic
tubing was added to a 4.8 acre oxidation pond together with
a 30 HP air compressor, 590 cfm at 9 psi.  The estimated
organic load was 1,000  Ibs BOD per day.

Lee's Summit, Missouri, also found itself with an overloaded
oxidation pond (55).   The Little Cedar Creek oxidation pond
was designed for 60,000 ft. of plastic tubing.  Initially,
42,000 ft. was installed with two 25 HP air compressors,
1,000 cfm at 9 psi.  The oxidation pond covered 25 acres with
a depth of 5 feet.

The success of diffused aeration to increase the organic
load on oxidation ponds soon led to the design of aerated
lagoons employing plastic tubing.  Norway, Maine (56) con-
structed a 10 acre aerated lagoon employing 23,500 ft. of
plastic tubing with a 25 HP air compressor, 500 cfm.  The
BOD load was designed for 600 Ibs/day with 90-95% reduction.
Sludge accumulation was expected to be only 6 inches in 50
years.

Tertiary treatment began to be a problem in the 1960's.  Ponds
were placed after primary and secondary treatment plants to
produce a higher quality effluent.  Mound, Minnesota, and
Spring Park, Minnesota  employed an aerated lagoon following
an activated sludge system (57).  The aerated lagoon had a
retention peirod of 7.5 days at 1.25 MGD design flow.  The
BOD load at design flow was only 20 Ibs/acre/day but it was
the most difficult part of the BOD to remove.  A 15 HP air
compressor, 215 cfm air, supplied the required air to the
plastic tubing.  The BOD reduction was 96 to 98%.

Two cell aerated lagoons were designed to produce maximum
BOD reduction.  The Harvey, North Dakota, STP (58)  had two
1 1/2 acre diffused aeration aerated lagoons, with 20 days
retention.  Air was supplied by two 15 HP air compressors,
270 cfm at 9 psi, through 15,000 ft. of plastic tubing.  Only
one compressor was used at any one time.  The primary cell
was loaded at 400 pounds BOD/acre/day while the secondary
cell was loaded at 100  pounds BOD/acre/day.  The final efflu-
ent had a BOD of 22 mg/1.

The largest diffused aeration aerated lagoons were construct-
ed at Regina, Saskatchewan (59).  Two 105 acre lagoons were
designed to take the overload from a trickling filter plant.
The ponds had a 40 day  retention with 845,000 ft. of plastic
tubing and 30-30 HP air compressors, 595 cfm at 9 psi.  The
air flow was 0.582 cfm/lb BOD applied.  The final effluent


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BOD was 20 mg/1, 90% reduction.

McKinney  (60) reported on the first detailed study of diffused
aeration aerated lagoons. Examination of the aerated lagoons
at Lee's Summit, Missouri, and Raytown, Missouri, gave suffic-
ient data to evaluate this treatment system.  The Lee's Summit
oxidation pond was converted to an aerated lagoon with 30 days
retention time.  The average BOD of the raw wastes was 125 mg/1
while the effulent averaged 26 mg/1.  The COD of the influent
averaged 360 mg/1 and the effluent averaged 156 mg/1.  A major
fraction of the effluent COD was in suspended solids, which
averaged 70 mg/1.  The effluent suspended solids were largely
algae cells.  The low effluent BOD indicated that most of
the algae were dead.  The primary operating problem was clogg-
ing of the plastic tubing aerators with calcium carbonate.
Periodic application of hydrochloric acid to the air distri-
bution system was needed to keep the aerators clean.  The
Raytown, Missouri system employed a mechanical aerated lagoon
ahead of 4.8 acre oxidation pond.  The oxidation pond was con-
verted to a diffused aeration aerated lagoon by adding 24,000
ft. of plastic tubing and a 30 HP air compressor.  The mech-
anical aerated lagoon employed two 15 HP surface aerators in
a 24 hour retention basin.  The BOD of the raw sewage was
180 mg/1.  The mechanical aerated lagoon reduced the BOD to
80 mg/1 while the diffused aeration aerated lagoon reduced
the BOD to 30 mg/1.  The change in COD was from 460 mg/1 to
300 mg/1 to 200 mg/1.  The final effluent suspended solids
averaged 70 mg/1.  Both treatment systems were loaded at
10,000 PE and produced essentially the same effluent quality
in spite of the fact that the Raytown plant had one-fifth
the size of the Lee's Summit plant.  These results helped to
confirm the fact that the effluent quality from long retention
period treatment plants is controlled by the growth and dis-
charge of algae rather than by incomplete treatment of the
wastewaters.

The multiple cell diffused aeration aerated lagoon has con-
tinued to gain popularity  (61-63).  The success of the plastic
tubing led to the development of other forms of diffused
aeration.  The air gun was developed to give mixing and
aeration in a deep lagoon.   Basically, the air gun consists
of an air chamber and a long open tube.  Air is supplied to
the air chamber until a given discharge pressure is reached.
The air then discharges to the open tube which becomes an air
lift pump.  Material is drawn in at the bottom of the tube
and discharges at the top like a gun.  Fisher  (64)(65) report-
ed on the use of an air gun aerated lagoon for treating potato
processing wastewaters.  The aerated lagoon was 850 ft. long,
280 ft. wide and 9 ft. deep with 127 air guns.  Air was sup-
plied by two axial flow air blowers, 40 HP, 780 cfm at 9 psi.
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With 16 days aeration time the BOD was reduced from 855 mg/1
to 72 mg/1.  Two ponds in series after the aerated lagoon re-
duced the BOD to 29 mg/1.

Another air tube has been developed by Polcon Corporation
(66).  This air tube employs an internal helix to mix the
air with the fluid being aerated.  Each helixor aerator uses
22-28 scfm air.  At 23 scfm the aerator will transfer 2.7
Ibs oxygen/hour to the wastes being treated, according to the
manufacturer.

The different forms of aeration equipment for aerated lagoons
has led to numerous claims and counter claims.  In an effort
to determine the best equipment for aerated lagoons, a com-
parative study was made on three types of aerators at
Winnipeg, Canada (67).  Three parallel aerated lagoons were
constructed to treat 0.5 Imp. MGD.  The plastic tubing aerat-
ed lagoon had a 30 day retention period using two cells in
series with a depth of 10 feet.  A 30 HP compressor supplied
the air to the plastic tubing.  The air gun aerated lagoon had
a 20 day retention period with a 17 ft. depth.  Air was sup-
plied by 54 air guns with a 40 HP air compressor.  The mech-
anical aeration aerated lagoon used 8-20 HP units in series
with 20 days retention and a 11 ft. depth.  A study over a
21 month period indicated a raw waste with 175 mg/1 BOD and
188 mg/1 suspended solids.  The plastic tubing unit had an
effluent with 37 mg/1 BOD, 34 mg/1 SS, 12.6% nitrogen reduc-
tion, and 23.3% phosphorus removal.  The effluent from the
mechanical aeration unit had 38 mg/1 BOD, 39 mg/1 SS, 14.6%
nitrogen reduction, and 19.5% phosphorus removal.  The data
indicated no significant differences in treatment efficiency
for these three systems.  The major problem in all three units
was accumulation of solids in the aerated lagoons.  Solids
assumulated at the rate of one ton per Imp. MG of wastes
treated.   Accumulation of this amount of solids was unexpect-
ed and no provisions were made for its removal.  Other opera-
tional problems included clogging of both the plastic tubing
and the air gun and ice accumulation on the surface aerator.
Cost data for the three systems were as follows:
                               Capital Cost   Operating Cost
Plastic tubing                  $336,800$46/Imp MGD
Air gun                          301,000        49/Imp MGD
Surface aerator                  347,800       100/Imp MGD

It can be seen that diffused aeration was the most economical
form of aeration in these systems.  Unfortunately, the three
aerated lagoons were designed as long term aerated lagoons
and werenot necessarily optimum for waste treatment.  The
net result is that these data can be misleading if care is
not taken to properly apply them.
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LOW TEMPERATURE

One of the major operational problems with aerated lagoons
has been low temperature.  Low temperature affects surface
aerator by building up ice on the aerator, throwing it out
of balance.  Low temperature also slows the rate of metabol-
ism.  When mixing is not sufficient, solids will settle out
and build up in the aeration tank.  When the temperature
increases, the settled solids will undergo more rapid metabol-
ism and increase the load on the aerators.

Studies in Alaska (68) with a diffused aeration system at
the Eielson Air Force Base for domestic sewage showed 66%
BOD removal with a 40-50 mg/1 effluent.  The temperature of
the aeration tank contents was 1C.  It appeared that opti-
mum results occurred with a 20 day retention period.  This
study was later expanded to cover two additional systems (69).
BOD reductions up to 87% were achieved in the field.  Better
treatment results required longer aeration periods.

Canadian research on mechanical surface aerators (70)  indicat-
ed that icing conditions required mounting the aerators on
permanent structures rather than on floats.  There was some
concern on the value of aerated lagoons at low temperatures.
The low rate of metabolism raised the question as to the
validity of aeration during cold periods.

Sludge settling tests in Alaska (71) demonstrated that the
settled solids did not undergo significant decomposition in
the winter but did in the summer.  Biological decomposition
was found to follow the Van't Hoff-Arrhenius relationship
between 0.5 and 20C.  The oxygen demand was 1.49 times the
BOD removed.  Measurement of settled sludge from the Eielson
Air Force Base aerated lagoon indicated that solids would
concentrate to 9.1% with 87% volatile solids.  It was felt
that onehalf inch accumulation of sludge could be expected
yearly.

Design of aerated lagoons under low temperature conditions
has been examined recently  (72-74) .  Deep lagoons are prefer-
red to shallow lagoons because of heat loss characteristics.
Experience has shown that the perforated plastic tubing clogs
easily.  Hydrochloric acid for cleaning the plastic tubing
has been used but is short lived and poses a definite problem.
Large bubble air diffusers create less operational problems.
Two cells in series give better effluent quality than single
cells.  From the experience to date diffused aeration is
preferrable to mechanical surface aeration.  BOD reduction  is
related to aeration time and temperature.  To maintain a high
degree of treatment, 80-90% BOD reduction, the aeration time
must be increased as the temperature decreases.  The BOD
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reduction in the summer is controlled by the production of
algae in the effluent.  With proper design, aerated lagoons
can perform satisfactorily at low temperatures.  Currently,
there are 17 aerated lagoons in operation in Alaska and many
more are in operation in Canada.  The key is proper design.

DESIGN CONCEPTS

At the present time no state has any published criteria for
the design of aerated lagoons.  By and large aerated lagoons
have either evolved by trial and error or have been designed
from the concepts of Eckenfelder and 0'Conner  (3) or
McKinney (5).  Over 100 aerated lagoons have been construct-
ed in the United States during the past decade; but few
studies have been made to develop sound design criteria.  Cor-
relation of published data with fundamental concepts of bio-
logical treatment offers a sound approach to develop basic
design criteria for aerated lagoons.

Part of the problem with aerated lagoons has been the failure
to apply the fundamental concepts of biological waste treat-
ment together with sound hydraulic concepts. Actually, there
are three variations of aerated lagoons: completely mixed,
facultative and aerated oxidation ponds.  This classifica-
tion by Benjes (11) is very important in developing sound
design criteria.   The failure to recognize these modifica-
tions has been a serious source of confusion in evaluating
design criteria.

WASTE CHARACTERISTICS

The first step in designing any waste treatment system is to
determine the waste characteristics.  Too often generalized
waste characteristics are so vague that the actual wastes
have no real relationship to the plant design.  The net re-
sult is poor operations.  Of primary concern are the BOD and
the suspended solids.  Secondarily, nitrogen and phosphorus
are assuming greater importance.  It should be recognized
that wastes can be essentially soluble or a combination of
soluble and suspended solids.  These two types of wastes
have significantly different characteristics as far as aera-
ted lagoons are concerned even if their total BOD is the same.

Domestic sewage generally has a 5 day BOD between 200 and
400 mg/1 with from 200 to 500 mg/1 suspended solids.  Where-
ever possible, analysis of domestic sewage should be made
prior to developing design criteria.  Where direct analyses
of wastes are not possible, reasonable estimates must be
made of the basic criteria.  For small communities a BOD
value of 200 mg/1 and a suspended solids value of 240 mg/1
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is reasonable.  For new subdivisions the BOD value of 240 mg/1
and a suspended solids value of 300 mg/1 is adequate.  The
relationship between soluble and suspended BOD generally
changes with the length of time in the sewer system.  Very
fresh sewage may have 75% of the BOD in suspended form; while
septic sewage can have less than 50% of the BOD as suspended
solids.  Normal domestic sewage can be assumed to average
60% suspended BOD unless more definite data are available.
The suspended solids in domestic sewage are generally 80 to
85% volatile.  Approximately 40% of the volatile suspended
solids are non-biodegradable.  This non-biodegradable frac-
tion of suspended solids has been a primary source of error
in biological treatment plant design in the past.  The non-
biodegradable suspended solids and the inorganic suspended
solids must either be removed by the treatment system or
pass out with the effluent.  These inert solids are not a
problem with soluble industrial wastes.

EFFLUENT QUALITY

The effluent quality from any waste treatment plant is
determined by the water quality requirements of the receiving
stream.  The current trend today is for a high degree of
treatment, BOD and suspended solids less than 30 mg/1.  For
normal domestic sewage this means 85% BOD removal and an
equivalent suspended solids reduction.  Operational data
indicate that aerated lagoons can meet these effluent require-
ments provided the metabolic reactions are complete and the
suspended solids are removed.

The metabolic reactions are controlled by microorganisms,
mixing, oxygen, and other environmental factors such as pH,
temperature, and time.  Turbulence required for rapid meta-
bolism runs counter to good suspended solids separation.  An
independent solids separation system appears to be a necess-
ity for high quality effluent from aerated lagoons.

Operational data have shown that aerated lagoons are not
very efficient in removing nitrogen and phosphorus.  Basic-
ally, nitrogen and phosphorus are removed by metabolism in
biological systems with some adsorption into microbial sur-
faces a possibility.  Removal of the microbial cells is need-
ed for any significant nutrient reduction.  Yet, minimum
solids handling is one of the positive features of aerated
lagoons.  The failure to remove solids from aerated lagoons
explains why aerated lagoons are not useful for nutrient re-
moval .

COMPLETELY MIXED AERATED LAGOON

Design of the completely mixed aerated lagoon requires that


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adequate mixing is supplied so that the entire contents of
the aeration tank are maintained in suspension.  A minimum
velocity of 0.5 fps must be maintained if microbial solids
are to be kept in suspension.   Mixing is normally generated
by the aeration device, requiring a balance between the mix-
ing function and the aeration function.  To date completely
mixed aerated lagoons have utilized mechanical surface aera
tors which aerate the mixed liquor by punping it into the
air.  The surface aerator favors a deep lagoon over a shallow
lagoon.  The deep lagoon, 10-15 ft., has a smaller surface
area and better mixing characteristics than the shallow la-
goon.

The aeration time is controlled by the rate of initial meta-
bolism and the extent of endogenous respiration desired. The
rate of initial metabolism is a function of the structure of
the organic matter in the wastes as well as temperature.  A
simple organic waste is easier to treat than a complex waste.
Soluble organics are metabolised more rapidly than insoluble
organics.  Aerated lagoons are easily affected by temperature
with a change in rate of metabolism by a factor of two for
each 10C temperature change.   Minimum temperature controls
the rate of metabolism in the final design.  At 20C (68F)
the maximum rate of metabolism is approximately 240 mg/1 BOD
/hour.  Since oxygen transfer and microbial separation are not
practical at such high ratio of metabolism it is necessary
to compromise on the aeration period.  Considering normal
variations in waste characteristics of domestic sewage, a 24
hour aeration period makes a convenient design period.   The
balance between power requirements for oxygen transfer and
for mixing indicates that complete mixing aerated lagoons are
optimum around 24 hours aeration capacity  (11).  Below 24
hours aeration oxygen transfer controls; while power for mix-
ing controls above 24 hours.

With a 24 hour aerated lagoon, the lagoon acts as a surge
tank to level out the oxygen demand peaks.  Yet, it must be
recognized that the peak oxygen demand must be met when it is
added to the aerated lagoon.  The peak hourly BOD load for
domestic sewage is generally less than 200 percent of the
average hourly BOD load.  Considering a domestic sewage of
200 mg/1,  the peak BOD load will be 16.7 mg/1/hour.  The
oxygen demand rate will be created by the metabolism of the
incoming wastes and the endogenous respiration of the micro-
bial cells in the mixed liquor.  The oxygen demand rate re-
lated to the metabolism of the peak BOD load can be estimated
as being equal to 0.5 the BOD load rate, 8.4 mg/1 hr in this
example.  The endogenous rate can be determined from the act-
ive cells in the aeration tank.  With completely mixed system,
the average concentration of active microbial cells can be
calculated from the following equation:
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              Ma =
                   K Fi
                    s
        where Ma

              Fi

               t

              Km

              Ks

              Ke
KmKet + Km + Ke + !_
                  t

average active mass of microbes,  mg/lVSS

average influent BOD, mg/1

aeration time, hours

metabolism factor, 15/hr @ 20C

synthesis factor, 10/4/hr @ 20C

endogenous respiration factor,  0.02/hr
 @ 20C
Si nceKe and ^ are small compared to Km and Ks,  this equation
can be simplified as follows:
              Ma =
0.7 Fi
(Ket+1)
The various factors, Km, Ks, and Ke, are dependent on temper-
ature and change by a factor of two for each 10 C tempearture
change from 20 C.  With 24 hours aeration at 20 C, Ma = 0.47
Fi.  At 30C, Ma = 0.36 Fi; and at 10C, Ma = 0.56 Fi.  For
the domestic sewage example, Ma would be 112 mg/1 VSS at
10C, 94 mg/1 VSS @ 20C,and 72 mg/1 @ 30C.

The endogenous oxygen demand rate can be calculated from the
following equation.

                      1.14 KeMa
               Qug

In the domestic sewage example the endogenous oxygen demand
rate would be 1.3 mg/l/hr at 10 C, 2.1 mg/l/hr at 20 C, and
3.3 mg/l/hr at 30 C.  The peak oxygen demand rate can be
calculated as the sum of the metabolism demand plus the en-
dogenous demand; 9.7 mg/l/hr at 10 C, 10.5 mg/l/hr at 20 C,
and 11.7 mg/l/hr at 30 C.  It can easily be seen that the
peak oxygen demand will have to be met at the maximum temper-
ature of the aeration system.

The oxygen transfer characteristics of any aeration system
can be determined from the following equation.

                         
-------
       where -^  = oxygen demand rate, mg/l/hr
              0  = oxygen concentration in water at
               s   saturation, mg/1
               0 = oxygen concentration in the aeration
                   tank, mg/1
               *^ = oxygen transfer coefficient in mixed
                   liquor
               B = oxygen saturation coefficient in mixed
                   liquor

             K a = oxygen saturation transfer rate co-
                   efficient, 1/hr.


With raw sewage <* and B are less than 0.5 normally.  As the
microbes purify the wastes, the values of -f and B approach
unity.  In properly operated aerated lagoons treating normal
domestic sewage, ^ of 0.9 and B of 0.95 are reasonable.  At
20C KLa should be 1.34/hr at sea level.  It is important
that the aerator meets the desired K^a and the minimum vel-
ocity of 0.5 fps at the fartherest point from the aerator.
Proper pumping of the fluid into the air can both move the
fluid and transfer the oxygen.  It appears that a pumpage
of 415 cfm/HP is close to the maximum pumpage that can be
expected from a mechamical aerator at the present time.  As
the horsepower of the aerator increases, the pumpage per
unit of power expended decreases.  Thus, it is normally more
economical to use several small units than one large unit.
The use of multiple units has value in operations as the im-
pact of a mechanical failure will be proportionately reduced,
Each separate design must be evaluated on its own merits as
there is no simple guide for aerator selection.

The effluent BOD is determined by the unmetabolised wastes
passing through the aeration unit and endogenous respiration
of the active microbial mass.  The unmetabolised waste BOD
for a 24 hour aeration or longer aerated lagoon will be less
than 1.0 mg/1 carbonaceous BOD.  In effect, the microbial
solids form the BOD in the effluent.  The carbonaceous BOD
for the effluent suspended solids can be determined from the
following equation.

             Eff. BOD = 0.8 Ma (C only)

Nitrification related only to the nitrogen released during
endogenous respiration could increase the BOD in the efflu-
ent.
             Eff. BOD = 1.12 Ma  (C+N)
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Evaluating the system for 24 hours aeration at 20C, the BOD
values can be expressed in terms of the influent BOD.

      Eff. BOD = 0.38 Fi  (C only)
      Eff. BOD = 0.52 Fi  (C+N)

Thus, one should expect from 48 to 62% BOD reduction in a
properly designed, completely mixed aerated lagoon with 24
hours aeration at 20C.  Greater BOD reduction could be ex-
pected with separation of the microbial solids.

Unfortunately, the dispersed characteristics of the micro-
bial solids precludes rapid flocculation and sedimentation.
The unmetabolised microbial solids pose a problem of further
stabilization.  Originally, it was recommended that an oxi-
dation pond be placed after the aerated lagoon to permit the
microbial solids to settle and be stabilized.  The inorganic
elements remaining will stimulate the algae to grow up in
the oxidation pond.  The BOD and suspended solids in the
final effluent will be determined by the algafe and not by
the microbial solids discharged from the aerated lagoon.
Maximum removal of algae requires at least a two cell oxida-
tion pond with series operation.  A rock filter at the efflu-
ent end of the oxidation pond will assist in removing excess
algae and will produce the highest quality effluent with a
minimum of effort.

If land is limiting, it is possible to place several
aerated lagoon cells in series to produce maximum degradation
prior to discharge to sedimentation pond.  The sedimentation
ponds can be quite small when compared with the conventional
oxidation pond utilized directly after the aerated lagoon.
The sedimentation ponds can be quite deep, 8 to 10 ft.,
when compared to the depth of oxidation ponds, 3 to 4 feet.
This increased depth permits sludge storage until the sludge
can be removed and placed on the land.

Normal oxidation ponds have a loading rate of 40 pounds BOD
/acre/day-  The 24 hour aerated lagoon-oxidation pond com-
bination has an area approximately 40% the area of an oxi-
dation pond for treating the same volume of wastes.

Addition of a second aerated lagoon in series with the first
aerated lagoon would reduce the active microbial mass by 2/3.
A third aerated lagoon would probably reduce Ma approximately
2/3 of that in the second aerated lagoon.  Thus, the three
celled aerated lagoon system would result in an effluent with
around 10 mg/1 BOD.  The final solids separation cell can be
of 1 to 5 day capacity depending upon the desired frequency
of cleaning of the sedimentation pond.  This system would
greatly reduce the land area required but would require more
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carefully constructed tanks and aeration equipment.  The aera-
tor design would be based on mixing and not on oxygen transfer
The oxygen demand in the second and third aerated lagoons
would be low compared with the first aerated lagoon.

The effluent suspended solids from the first aerated lagoon
will be composed of the active microbial mass  (Ma), the en-
dogenous mass of dead cells (Me),  the inert, inorganic mass
(Mii),  and the inert organic Mass (Mi).  As indicated
previously, the active microbial mass (Ma) is a function of
the food added to the system.   The endogenous mass is a
function of the active mass (Ma)  and the aeration time.  Ap-
proximately 20% of the organic matter synthesized during meta-
bolism cannot be biodegraded in the aeration tank and remains
as inert volatile matter in the form of dead microbial cells
(Me) .

          | Me = 0.2 KeMat

With a 24 hour aeration unit at 20C the endogenous mass (Me)
will equal 0.1 Ma.  It is possible to express both Ma and
Me in terms of the incoming BOD (Fi).

           Ma + Me = 0.52 Fi

The inert inorganic solids (Mii)  in the mixed liquor and in
the effluent will be the sum of the inert inorganics in the
raw wastes plus 0.1 (Ma+Me) which was formed from soluble ions
during microbial synthesis.

           Mii = Mii in raw waste + 0.1 (Ma+Me)

Normally, Mii in raw wastes will be approximately 20% of the
total suspended solids.

           Mii = 0.2 M in raw wastes + 0.05 Fi

With domestic sewage Mii will be approximately 60 mg/1 in a
24 hour aerated lagoon at 20C.

The inert organic solids (mi)  normally average 40% of the
raw waste volatile suspended solids.   In terms of total
suspended solids in the raw waste Mi will be approximately
32%.  For domestic sewage Mi will be from 75 to 80 mg/1.
Thus, the inert solids in domestic sewage can be expected
to be around 140 mg/1, 58% of the suspended solids in the
raw wastes.  When Ma and Me are added to Mii and Mi to form
the total suspended solids (MT) in the system, MT will aver-
age essentially the same as the influent.  It is little
wonder that some engineers have felt that this fact demon-
strated  that suspended solids in domestic sewage were not


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biologically degraded,  Actually, the microbes metabolised
the biodegradable organic suspended solids but metabolism
of soluble organics produced additional suspended solids.
The net effect is no apparent change in suspended solids while
there is actually a change in type of solids.

The actual reduction in mass in the second aerated lagoon
will be only 0.8 the change in Ma since Me produced will equal
0.2 the change in Ma.  With normal domestic sewage the de-
crease in the total suspended solids will be 50 mg/1.  The
decrease in the third aerated lagoon would be less than 20
mg/1 suspended solids.  The total solids reduction with three
24^hour aerated lagoons would be approximately 30%.  The re-
maining sludge could be concentrated to 1.5 to 2.0% in the
sedimentation cells.  Storage should be sufficient to hold
solids during winter period.

A recent study  (75) in Canada attempted to evaluate the CMAS
equations presented in this section as well as the equations
developed by Eckenfelder.  The Canadian study examined data
from two aerated lagoons which had been in operation for
several months.  The aerated lagoon at Windsor was construct-
ed in 1965 with 4 days retention at an average flow of 60,000
gallons per day.  The loading rate was 20 Ibs BOD/100 cf/day
and a 20 HP fixed surface aerator was used.  The town of
Durham had a 4.2 day retention at an average flow of 290,000
gallons per day.  The BOD loading was only 3 Ibs BOD/1000 cf/
day with four-5 HP fixed surface aerators.  It was concluded
that the CMAS equations presented in this design section
were reasonable provided introgenous metabolism was consider-
ed.  On the other hand, Eckenfelder's equatons were very
specific for each type of waste and required individual eval-
uation.  They cautioned that the general application of either
method should not be considered unless the design engineer
is well aware of the design limitation of biotreatment.  There
is no doubt that design equations must be evaluated against
field results to determine their usefulness, but it is impor-
tant that they are properly evaluated.  As pointed out pre-
viously, CMAS units should be designed on the basis of short
term aeration, 24 hours, if they are to be truly completely
mixed.  Although, designed as CMAS units, these two plants
studied were not completely mixed and could not be expected
to check the CMAS equation exactly.   The data presented
showed that the system was not completely mixed or that the
data was not representative of the wastes entering the plant.
It was apparent that adequate power was not available for
complete mixing with the aerator employed.  In effect, these
two aerated lagoons were actually facultative aerated lagoons
rather than being completely mixed aerated lagoons.  Engine-
ers are to be cautioned to use proper design criteria and
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proper evaluation of operational data.  Improper evaluation
of operational data such as occurred in this Canadian study
can create misimpressions as to the validity of sound design
concepts.  Since the article cannot be removed from print or
corrected, it will continue to cause misunderstanding for
years to come.

The completely mixed aerated lagoon can produce the desired
effluent, 85% BOD and suspended solids reduction, with a 24
hour aeration period aerated lagoon combined with a normal
stabilization pond and terminal rock filter or two addition-
al 24 hour aerated lagoons with a one to five day retention,
deep sedimentation pond.

FACULTATIVE AERATED LAGOON

Most aerated lagoons constructed to date would have to be
classified as facultative aerated lagoons.   Basically, facul-
tative lagoons are designed with long aeration periods, 7 to
20 days.  The aeration equipment is designed to transfer
the theoretical oxygen demand but is too small to keep the
solids in suspension.  The net effect is for all heavy solids
to settle out in the aeration cell.  Only the dispersed
microbes are maintained in suspension with the soluble organ-
ics.  The microbial reaction is dependent upon the contact
time within the aeration zone.  The organic matter which
settles to the bottom of the aerated lagoon undergoes anaer-
obic metabolism and slowly releases organics into solution.
The solids sedimentation and anaerobic decomposition makes
scientific evaluation of facultative aerated lagoons all but
impossible.  Soluble wastes will react differently than
wastes with high concentrations of suspended solids.  Thus
each waste must be evaluated separately.

Experience has generally favored 70 to 80% BOD reduction with
facultative aerated lagoons having 4 to 8 days retention.
Normally, aeration equipment has been sized on 1.5 to 2.0
Ibs 02/HP-hr without regard to mixing.  The oxygen require-
ments have been determined from the total oxidation of the
wastes at 1.5 pounds of oxygen per pound of BOD added.  The
results of the facultative aerated lagoon are highly variable
and subject to considerable temperature effects.  The rate
of reaction changes by a factor of two for each 10C temper-
ature change.

The advantage of the facultative aerated lagoon lies in the
fact that both biological stabilization and solids separa-
tion occur in the same pond.  Adequate volume must be pro-
vided for sludge storage so that sludge removal can be ac-
complished at infrequent intervals.  It must be recognized
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that sludge removal is an essential part of the facultative
lagoon design.

The disadvantages of the facultative aerated lagoon is the
lack of control over the biological process.  The microbial
growth is slow because the microbial population is low.  In
effect, the microbes move from a favorable growth environment
to an unfavorable environment as they move from the aerobic
mixing zone to the quiescent zone.  There is a continuous in-
termix between the volume of fluid around the aeration unit
and the adjacent fluid.  Maximiim microbial growth efficiency
can be achieved only with complete mixing of the aeration
tank contents.  As the organic solids accumulate in the aera-
ted lagoon, the unmetabolised load accumulates and creates
periodic overloads and resulting odor nuisances.  Unfortunate-
ly, facultative lagoon performance cannot be predicted ac-
curately, making scientific design impossible.  The operation-
al characteristics of each facultative aerated lagoon are
a surprise to the design engineer, the owner, and the regula-
tory authorities.  Experience gives a few rough guidelines
but no specific design criteria.

AERATED OXIDATION PONDS

The overloading of oxidation ponds resulted in the develop-
ment of aerated oxidation ponds; i.e., oxidation ponds to
which diffused air was added over a large portion of the pond
area.  More often than not, municipalities employing oxida-
tion ponds continue to load until odor nuisances create suf-
ficient complaints to require action.  Needless to say, these
municipalities demand instant solutions and  are quick to
blame the engineers for not producing instant answers.  The
problem was a simple one to define but a difficult one to
solve.  Overloading the oxidation pond could be alleviated
by the addition of oxygen; but the problem was one of dis-
tributing the oxygen over the very large area of the oxidation
pond.  In.recent years, the popularity of diffused aeration
systems for overloaded oxidation pond systems has increased
tremendously and is being extensively employed.

Oxidation ponds stabilize the organic matter in the waste-
waters through the action of bacteria which metabolise aero-
bically if the system is to be relatively odor free.  The in-
organic componants of the wastewaters stimulate the growth of
algae at the surface of the ponds.  The algae release oxygen
which the bacteria can use; but in producing oxygen, the
algae also produce organic matter that must be stabilized.
In most oxidation ponds the oxygen demand by the algae in the
dark far exceeds the oxygen detfiand by the bacteria in stabil-
izing the wastewaters.  As the load on a given oxidation pond
exceeds the oxygen capacity of the algae under relatively
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quiescent conditions,  improvement can be made by the addition
of additional oxygen or by mixing to permit more efficient
growth of the algae.  Mixing permits the algae to be carried
from the surface down into the lower portion of the pond.
Some of the algae settle out on the pond bottom and are
removed from the reaction system.  Fresh nutrients are
carried to the surface where additional algae growth and
oxygen production results.  Without removal of the algae,
the effluent quality of the higher loaded oxidation pond
will be increased; but there will be no odors.  Two cell
ponds and tapered mixing helps distribute the algae over
the system so that some settling occurs near the end of the
pond system.

The vague characteristics of the algae phase of the oxida-
tion pond makes it difficult to design the aerated oxidation
pond with assuracne of the results to be obtained.  General-
ly, the aerated oxidation ponds are designed to accept the
full organic load by the aeration equipment without concern
for the activities of the algae.  The important aspect of
the aerated oxidation pond is the fluid pumpage.  Each type
of diffused aeration equipment must be evaluated on its own
merits since each system has its own specific characterist-
ics.  Experience has indicated that a fluid turnover time
of 5 minutes in the waste influent area and 20 minutes near
the waste effluent area is more than adequate.  The control-
ling factor in the design is the oxygen demand rate in the
dark.  Adequate oxygen must be available to meet the oxygen
demand from both the bacteria and the algae.

Experience has indicated that deep aerated oxidation ponds
are more efficient than shallow aerated oxidation ponds.
Where possible, aerated oxidation pond depths are increased
to 10 ft. to give improved mixing and oxygen transfer char-
acteristics.  Plastic tubing is spaced at 5 ft. centers at
the influent end and 20 ft. centers at the effluent end.
Air is supplied with a positive displacement air compressor
operating at 9 psi pressure.  Normally, air is supplied
at the rate of 700 cubic feet per day per pound of BOD.
Since calcium carbonate type deposits form around the small
orifices in the plastic tubing, it is necessary to clean out
the plastic tubing at periodic intervals, normally at 3
month intervals.  Gaseous hydrochloric acid is used for
cleaning the orifices.  Approximately 2 Ibs of HC1 gas is
required for each 1000 ft. of tubing.  The dilution of HC1
in the pond is adequate to prevent any adverse conditions
from developing.

A second type of diffused aeration system employs air dis-
charge below a round tube with the tube acting as an air
life pump to create circulation and aeration at the same time.
                            102

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The spacing of the tubes is dictated by the magnitude of the
organic load and the degree of mixing desired.  The air tubes
utilize approximately 10 scfm air per tube which are spaced
at 10 ft. centers.  Liquid depths with the air tubes normally
are 15 feet to insure maximum mixing for minimum air.  Data
has indicated an oxygen transfer capability of 1.5 Ibs/hr/gun.
Because of the specific nature of the equipment required for
aerated oxidation ponds, each manufacter  must be contacted
for specific design criteria.  Engineers should be cautioned
that equipment manufacturers have a tendency to be overly
optimistic about the operational characteristics of their
equipment.

Where aerated oxidation ponds have been designed as such in-
itially, the retention period will normally be at least 30
days at full design load.  The fact that aerated oxidation
ponds are 2.5 to 3 times deeper than conventional oxidation
ponds; the surface area loading appears higher than normal.
Since surface area has little significance in aerated oxi-
dation ponds, engineers should not be concerned with surface
area loading design factors.  The overall BOD reduction is
related to removal of suspended solids as indicated previous-
ly.  There is no specific BOD reduction that can be predicted
for aerated oxidation ponds at the present time.  Current
research into suspended solids reductions would indicate
that a high degree of BOD reduction is possible, at least
90% where the effluent suspended solids are reduced below 20
mg/1.
RESEARCH NEEDS

Research on aerated lagoons is needed to examine the various
types of aeration equipment.  Field studies are needed to
determine the actual quantities of oxygen transferred and
the mixing produced both in the primary zone, immediately
around the aerator, and in the secondary zone beyond the
primary zone.  Little information is available on pond design
and aeration equipment design.  The net result is that aera-
ted lagoon design lacks scientific design aside from the
completely mixed aerated lagoons.

The removal of suspended solids from aerated lagoon effluents
deserve further study the same as with oxidation ponds.  Short
retention period sedimentation ponds designed to minimize
wind mixing should be evaluated as a method for producing
satisafctory effluents.  Multicell ponds should also be evalu-
ated as final polishing units for aerated lagoon effluents.

Methods for solids removal from aerated lagoons needs investi-
gating.  Since solids settle in the aerated lagoon and
                             103

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accumulate at a faster rate than in oxidation ponds, provi-
sion must be made for periodic solids removal.  To date no
research has been carried out on removal and disposal of
solids in aerated lagoons.

Further research is needed on the temperature effects on
aerated lagoons.  The lack of solids separation and sludge
return to the aerated lagoon makes it more vulnerable to temp-
erature variations.  The temperature  effects would be more
significant in completely mixed aerated lagoon since the
retention period is very short compared with the facultative
aerated lagoon.

Operational evaluation is needed on existing aerated lagoons
to permit the building up of a data base from which to evalu-
ate aerated lagoon design and operation.  The lack of ade-
quate data is a major deficiency in aerated lagoon design
development.

Aerated lagoons represent an intermediate treatment system
between oxidation ponds and activated sludge.  There is a
real need for good aerated lagoons but further research is
needed before we develop aerated lagoon technology to the
level required to meet future water quality criteria.

CONCLUSIONS

The current state of the art for aerated lagoons indicates
that engineers have not utilized the fundamental concepts
of biotreatment systems to arrive at sound design criteria.
Several hundred aerated lagoons have been constructed in the
United States during the past decade with little scientific
basis for design.  These aerated lagoons have performed
reasonably well considering how they were designed, construct-
ed, and operated.  Yet, with proper application of sound bio-
treatment design fundamentals most of these plants could have
been better designed so that they would have produced a sup-
erior effluent quality to that being produced.

Proper design of aerated lagoons requires a balance between
the waste load, the microbes, mixing, oxygen and retention
time.  The complete mixing aerated lagoon with a 24 hour
aeration period represents the optimum system for domestic
sewage.  With 24 hours retention the aeration system balances
the most efficient utilzation of energy for mixing and oxygen
transfer.  The system has sufficient capacity to absorb
shock load variations and still permit complete metabolism
without nitrification becoming a major factor in effluent
quality.  The fundamental problem with the 24 hour aerated
lagoon is proper separation and disposal of suspended solids.


                           104

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short term, deep sedimentation ponds, rock filters, or sand
filters are needed to produce BOD reductions in excess of
50%.  it is possible to obtain 90% BOD reduction from aerated
lagoons provided the suspended solids are removed.  Oxidation
ponds following 24 hour aerated lagoons are not desirable
because of the large algae production that will result.

Facultative aerated lagoons have been the primary type of
aerated lagoons constructed to date.  Surface aeration equip-
ment ^ have been placed in large ponds having several days re-
tention to produce localized aeration.  The mixing is not
adequate for maintaining solids in suspension.  The net re-
sult is that solids settling occurs in the quiescent sections
of the facultative aerated lagoons.  Algae growth also occurs
in facultative aerated lagoons.  Although most facultative
aerated lagoons are designed on the basis of total oxygen
demand, there is no way to predict the effluent quality.  Ex-
perience has yielded from 60 to 90 percent BOD reduction de-
pending upon the individual design.  Review of operational
results did not produce any valid design concepts that can
be applied to facultative aerated lagoons.

The third form of aerated lagoons is the aerated oxidation
pond.   Aerated oxidation ponds have resulted from the need to
add oxygen to overloaded oxidation ponds in as simple a
fashion as possible.  Diffused aeration through plastic
tubing or round, vertical tubes produces slow mixing which
permits more efficient growth of algae and better distribu-
tion of the oxygen resources throughout the pond.  Two cells
are usually required to produce some separation of the algae
produced during the rapid metabolism of the waste matter.
Normally, 30 days retention are required for aerated oxida-
tion ponds designed from scratch.  Longer periods are avail-
able in overloaded oxidation ponds.  With separation of algae
90 percent BOD reduction is possible.  The effluent quality
from aerated oxidation pond will be a function of the sus-
pended solids in the effluent.  Essentially, the diffused
aeration eliminates the odor nuisances from overloading and
serves as a temporary treatment process until a more perman-
ent system can be designed and constructed.

With increased emphasis on maximum effluent quality, aerated
lagoons as they have been used in the past will have to be
modified to produce the effluent quality desired for the
future.  It should be recognized that with minor modifications
all three types of aerated lagoons can produce better than
90% BOD reduction.  Because of their simplicity of design
and operation aerated lagoons are going to play a definite
role in the treatment of liquid wastes from small municipal-
ities and small industries.  The key to success is the proper
application of basic fundamentals.
                             105

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    VanEs, D.W., "A Comparative Study of Aerated Lagoon
    Treatment of Municipal Wastewaters",  Presented at 2nd
    International Symposium on Waste Treatment Lagoons,
    Kansas City, Mo.,  June 23-25,  1970.

68. Reid, L.C., "The Aerated Sewage Lagoon in  Artie Alaska"
    Paper presented at 17th Annual  Convention  of Western
    Canada Water & Sewage Conference, September 1965.

69. Reid, L.C. and Benson, B.E.,  "Observations on Aerated
    Sewage Lagoons in Artie, Alaska" 18th Annual Convention
    of the Western Canada Water &  Sewage Conf., September
    15, 1966.

70. Black, S.A., "Icing on Mechanical Aerators on Lagoons
    Under Cold Climate Operating Conditons", Research Paper
    #2018, Ontario Water Resources  Commission, October, 1968.

71. Reid, L.C., "Design and Operation Considerations for
    Aerated Lagoons in the Arctic  & Subartic"  Report #102,
    Arctic Health Research Center,  PHS, College,  Alaska,
    Nov., 1968.

72. Pohl, E.F., "Design Parameters  for Cold Climate Aerated
    Sewage Lagoons", Presented at  the 2nd International
    Symposium on Waste Treatment Lagoons", Kansas City, Mo.,
    June 23-25, 1970.

73. Clark, S.E., Coutts, H.J. and  Jackson, R., "Alsaka
    Sewage Lagoons", presented at  2nd International Symposium
    for Waste Treatment Lagoons,  Kansas City,  Mo., June 23-25,
    1970.

74. Pearson, B.F.,  "Aerated Lagoons at High Elevations",
                           112

-------
Presented at 2nd International Symposium on Waste Treat-
ment Lagoons, Kansas City, Mo., June 23-25, 1970.
                         113

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                      SECTION  VI

                    ANAEROBIC LAGOONS

Anaerobic lagoons were the inevitable result of the wide-
spread use of stabilization ponds.  Increased organic dis-
charges and the need for greater economy pushed lagoon load-
ing rates higher and higher, eventually exceeding the natural
stabilization capacity of the ponds.  Failures resulted. Fail-
ures were not recognized, however, by the usual criteria of
poor effluent quality although this too occurred.  Odors pro-
claimed the failures to everyone, expert and layman alike,
and nuisance qompXain'ts were the result.

Anaerobic lagoons, however, are more than overloaded stabili-
zation ponds.  They are units intentionally designed to
create anaerobic conditions for the purpose of accomplishing
the desired destruction of organic matter and the stabiliza-
tion of wastewaters.  Experience has shown that anaerobic
lagoon designs which create the basic conditions favorable
to complete digestion will accomplish stabilization of waste-
waters without nuisance odors.

High-temperature high-strength wastewaters are particularly
amenable to treatment by anaerobic lagoons.  As a result,
they have been used extensively for certain industrial waste
such as those from the meat packing industry.  However, ana-
erobic lagoons have also been used from Australia to Canada
to successfully treat municipal wastewaters, generally as
pretreatment units followed by oxidation ponds.  The process
has also been widely applied to the treatment of slurries
of animal manure originating from confined livestock feeding
operations.  Lagoons treating animal manures, although
accomplishing anaerobic stabilization of organic matter, sel-
dom, however,  receive sufficient flow to result in a waste-
water effluent.

The treatment efficiency of anaerobic lagoons may range from
25 to 90% although units operating satisfactorily will gener-
ally accomplish a 60 to 80% BOD reduction.  High concentra-
tions of BOD, suspended solids, and sometimes hydrogen sul-
fide occur in the effluents depending upon the initial char-
acteristics of the incoming wastewaters.  BOD concentrations
of 100-500 mg/1 in the effluents of anaerobic lagoons are
common; and, as a result effluents must receive further treat-
ment prior to discharge to a receiving body of water.  Usual-
ly the additional treatment is provided by oxidation ponds.

All lagoons designed to function anaerobically have not,
however, performed in an acceptable odor-free manner.  In
some cases the reasons for the failures are clear while in
other cases the cause of failure is not apparent.  Design


                            115

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criteria that have proved satisfactory for some areas with
certain wastewaters have resulted in miserable failures
when inappropriately applied to other wastewaters and climat-
ic conditions.

Designs which failed to create a wastewater environment
favorable to anaerobic digestion with gasification were de-
stined to failure.  Inappropriate attention to basic factors
including temperature, pH, the nature of the organic material,
and the dispersion and mixing of these organics with pro-
perly acclimated organisms probably were the cause of many
failures.  Other failures remain unexplained.

The following section reviews the existing design criteria
and operating experiences for anaerobic lagoons.  Modifica-
tions in designs reported in the literature are noted.  The
underlying fundamental principles that govern the success
or failure of anaerobic lagoons are summarized and areas
of needed additional information that will result in effic-
ient trouble-free and nuisance-free wastewater systems to
provide the best treatment at the lowest cost.

Development of Design Criteria

The design criteria that exist for anaerobic lagoons are
impirical in nature.  The successes and failures of earlier
lagoons in a particular region have served to provide the
guidance for future designs.

Parker e_t al. (1) were among the first to advocate the ad-
vantages of~~a pond system designed specifically to operate
as an anaerobic unit.  Studies conducted in Melbourne,
Australia on anaerobic lagoons 3 ft deep with a 2-5 day de-
tention revealed that BOD removals up to 600 Ib per day/
acre occurred at summer temperatures  (64F).  Removals of
450 Ib BOD per day/acre occurred in the winter  (52F).  The
treatment in the anaerobic lagoons was attributed to both
sedimentation and digestion; however, the comparably high
BOD removal efficiency was considered to be dependent upon
the development of a digesting sludge layer.

Continued experience with anaerobic lagoons in Australia
resulted in design criteria for that region.  Considering
normal strength sewage, it was reported  (2) that anaerobic
lagoons would provide about 60 to 70% BOD removal with
design BOD loadings of 900-1200 Ib per day/acre and 675 Ib
per day/acre in winter.  Lagoon depths of 3 to  5 feet were
standard at that time.  Occasional extreme odor nuisances
occurred at these loadings particularly at the  commencement
of operation of new units, although a certain amount of odor
                           116

-------
was normally present.  Removal of solids accumulations were
required only at 6 to 10 years intervals.

In the U.S.A. satisfactory experiences with a pilot plant
in the early 1950*s led to the design by Sollo  (3) of an
anaerobic pond ,to treat meat packing wastes at Moultrie,
Georgia.  Loading of the unit was computed on a volume basis
in recognition of its similarity to a sludge digester. Aver-
age data reported for the pilot unit revealed that a BOD
reduction of 65% occurred with a 4.6 day detention period
and a BOD loading of 11.2 lb/1000 cu ft/day.  The full scale
anaerobic pond had a water depth of 14 ft and a surface
area of 1.4 acres and recirculation of lagoon contents was
provided.  During the first four years, BOD concentrations
were reduced from an average of about 1100 mg/1 to 160 mg/1
through the anaerobic lagoon, a removal efficiency of about
85%.  Heating facilities for the lagoon were not provided
and it was noted that as pond temperatures dropped below
75F a reduction in removal efficiency could be expected.

Following these early studies by Sollo,  wide spread appli-
cation of anaerobic lagooning was found in the meat industry.
These anaerobic lagoons were generally designed on an organ-
ic loading basis of 15 to 20 Ib BOD/1000 cu ft/day, usually
with 15 ft depths.  In most cases these lagoons were designed
to function in areas with more severe climatic conditions
than those of Georgia.  Pretreatment, such as grease removal
was frequently provided.  BOD removal efficiencies of 60 to
80% were expected and in most cases the effluents were dis-
charged to aerobic stabilization ponds for additional treat-
ment.  Design criteria as reported for several systems treat-
ing meat wastes are given in Table 5.

Coerver  (4)(5) reported that design criteria for anaerobic
lagoons serving small abattoirs and packinghouses  in
Louisiana had been developed with a somewhat different ap-
proach.  Three small ponds in series were layed out to  re-
ceive the wastewaters from the abattoirs.  The first pond
was anaerobic and received all the wastes from the slaughter-
ing including blood and paunch manure.  This pond was design-
ed on the arbitrary basis of one acre foot for each 500 hog
units of slaughtering per week.  Pond depths were usually
limited to 2 to 3 feet to accommodate high ground water con-
ditipns.

In the 1960's, lagoons were coming into vogue in the animal
production industry.  Water carried manure handling systems
were being designed to serve confined feeding operations for
poultry, swine, and cattle.  These early lagoons were often
designed and constructed to receive the manure slurries with-
out consideration being given to the characteristics of the
                             117

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00
                                          Table 5

              Criteria Used for the Design of Anaerobic Lagoons Treating Meat Wastes
Reference

(6)
(7)
(8)
(9)
(10)
BOD
Loading
lbs/1000
20*
15
15
15
--
Cells

2-series
1
2-parallel
2-parallel
3-parallel
Depth
ft
15

15
15
18-20
Detention
days
5.12
	
4.5
	
3-5
Recirculation

Yes
Yes
No
No
Yes
                                   or series
        *Minimum temperature of 75F. specified.
       **Extensive pilot studies preceeded design.

-------
animal waste or the principles involved in its destruction.
Suggested design criteria was mistakenly patterned after
that of early aerobic la,goons.

Following field studies of operating lagoons, Dornbush and
Andersen  (11) discussed certain environmental factors and
suggested an arbitrary design limit of 5 to 10 Ibs of vola-
tile solids per 1000 cu ft of lagoon for South Dakota con-
ditions.  The temperature considerations were considered
critical and water depths of 5-8 feet were suggested.

The results of extensive investigations of animal manure
characteristics and treatment of manure slurries in anaero-
bic lagoons have been published by Hart (12)(13) and Loehr
(14)(15)(16)(17).  Hart (12) reported design criteria for
lagooning of animal wastes in terms of cubic feet per animal
recalculated from results of several investigators in differ-
ent climatic locations.  These data are presented in Table 6.
Performance of animal waste lagoons was judged largely in
terms of freedom from odors.

Animal waste lagoons are designed for the special purpose
of destruction and stabilization of organic manures.  Solids
accumulate until they require removal but there is seldom
an overflow of liquid to create a water pollution problem.

Anaerobic lagoons have been widely accepted in regions of
Canada for the treatment of municipal wastewaters.  By 1966
there were 69 communities in Alberta, Canada using anaerobic
ponds (10).  In Canada the anaerobic ponds are termed "short
detention" ponds and have detention periods ranging from 2 to
4 days with liquid depths maintained at 8 to 10 ft.  Maximum
organic loadings that are permitted are 4000 Ibs BOD/acre/
day when the liquid depth is 10 feet  (21).  This may be
compared with the design organic loading rate of from 30 to
50 Ib/acre/day for the secondary ponds to which the short
detention pond effluent is discharged.  Other studies (22)
have suggested that depths to 15 ft would be desirable in
Canada where conditions permitted, and that the outlet be
located about 5 ft below the liquid surface.  Depths 18 to
20 ft were used by Stanley  (10) to conserve heat at Edmonton,
Canada.

Following extensive studies of lagoons in California, Oswald
(23) has maintained that methane fermentation within anaerob-
ic lagoons may be regarded as the sine qua non  of nuisance
free anaerobic pond performance.  As a result,  he contended
that to design an anaerobic lagoon that will be odor-free,
the design must result in environmental control with conditions
favorable to methane fermentation.  An important factor would
include an adequate population of methane forming bacteria
                              119

-------
                                     Table 6
Researcher(s),
  Location
Manure Stabilization Pond Loading Rates (18',
                         Recalculated
   Recorded              Loading Rate
 Loading Rate            cu ft/animal
                      Evaluation of
                      Performance
Clark, Illinois  (18)
Dornbush & Andersen
South Dakota (11)

Kart & Turner,
California (13)
Dornbush & Andersen
South Dakota (11)
                                      SWINE
    4-20 ft2/hog
    3-10 ft deep
40-60 cu ft/hog
                      550 hogs/acre-year,   475 cu ft/hog
                      5-7 ft deep
    130-170 cu ft/hog
130-170 cu ft/hog
    45 & 67 cu ft/100-lb  45 & 67 cu ft/100 Ib
    pig                   animal


    124 cu ft/100-lb pig  124 cu ft/100-lb
                          animal
                                     POULTRY
    3.64 ft2/chicken
    less than 2 ft deep

    3.64 ft2/chicken
    4 ft deep
5.5 cu ft/hen
                                            14.6 cu ft/hen
Malodorous,
unsatisfactory

Satisfactory
Satisfactory
                      Somewhat, but
                      not excessively,
                      odorous
                      Satisfactory
"Vile odors"

Much better

-------
Researcher (s),
  Location
        (Continued) Table 6
                    Recalculated
  Recorded          Loading Rate
Loading Rate	cu ft/animal
                       Evaluation of
                       Performance
Cooper,
California(19)
Hart & Turner
California(13)
Witzell et al.,
WisconsinT20T
Hart & Turner
California(12)
575 Ib BOD/acre-day;6 cu ft/hen
1.09 ft2/hen
5-6 ft deep
8.35 cu ft/hen
13.6 cu ft/hen
49.8 cu ft/hen
8.35 cu ft/hen
13.6 cu ft/hen
49.8 cu ft/hen
               CATTLE

60 ft top diameter  1,547 cu ft/bull
40 ft bottom diameter
5 ft deep-6 bulls
795, 1,000, &
   1,830 cu ft
1,000-lb animal
795, 1,000,  &
  1,830 cu ft
1,000-lb animal
                       "No odor"
Very malodorous
Satisfactory
Algal-laden pond,
satisfactory
but overdesigned
                       Satisfactory
Satisfactory

-------
to break down the organic acids resulting from the initial
putrefaction of sludge solids accumulating on the bottom
of the anaerobic lagoon.   Other necessary environmental
factors would include a temperature in excess of 15C and
preferably in the range of 32C, a pH from 6.8 to 7.2, an
alkalinity of about 2,000 mg/1 and the complete absence of
dissolved oxygen.

Oswald (23)  reported that in California,  the BOD loading
necessary to create conditions in which anaerobic reactions
predominate may be as little as 100 Ibs/acre/day in the
winter or as much as 400  Ibs per acre/day in the summer.
Greater depths and specific pond shapes have been suggested
by Oswald.  Increasing the depth of ponds to 12-14 feet
will allow organic loadings up to 1,000 Ibs/acre/day in the
California climate.

These reports reveal the  versatility of anaerobic lagoons.
Municipal and industrial  wastewaters and animal manure
slurries have all been treated successfully.  However,
design criteria that have evolved appear to have a regional
conotation and a wide variety of units have been used to
express design loading rates.

The economic advantage of higher loading rates for anaerobic
lagoons has been widely recognized and the expected BOD
removal efficiency for anaerobic lagoons ranged from 60%
upward in most cases.  There, however, is one prime consid-
eration that influences the design and acceptability of ana-
erobic lagoons more than  any other single factor.  This
factor is the risk of ending up with a treatment unit that
produces nuisance odors.

Operating Experience with Anaerobic Lagoons

A major advantage of ponds or lagoons for wastewater treat-
ment is the minimal attention to maintenance and laboratory
control that has been necessary for operation of these treat-
ment facilities.  This advantage has, however, been detri-
mental in evaluating the  criteria used in design and the
resulting performance of  anaerobic lagoons.  Reports of
operating experience and  resulting removal efficiencies have
sometimes been based on short-term observations which may
not have extended through the most critical climatic con-
ditions.  Valuable information has, however, been reported
for a number of operating anaerobic lagoons treating munici-
pal and industrial wastewaters.

Municipal Wastewaters - Evaluation of the long term results
of operation of large anaerobic and aerobic lagoons to treat
                           122

-------
normal strength sewage were reported in 1959 by Parker e_t al.
(2).  Maximum summertime BOD removals by an anaerobic lagoon
ranged from 578 to 1806 Ib per day, acre which was in excess
of the removal of 600 Ib per day/acre reported earlier for
experimental lagoons.  BOD removal in the anaerobic units
was generally 60-70% although it dropped to about 50% in
winter.  Winter BOD removals ranged from 420 to 540 Ib per
day/acre which approximated the experimental values of 450 Ib
per day/acre.  Detention times were less than 5 days.  Extreme
odors occurred at the commencement of the operation of the
anaerobic lagoons; however, the aerobic lagoons remained odor-
free after receiving the effluent from the anaerobic units.

Parker and Skerry (24) have reported the Ipading and perform-
ance of three anaerobic lagoons treating municipal wastewaters
in Australia during summer and winter conditions.  Selected
data are shown in Table 7.  Samples of sludge solids collected
at various points in the lagoons were characterized and re-
lated to lagoon performance and sludge depth.  Sludge depths
were observed to increase during the winters when biological
activity and BOD removals were low.  Higher effluent sulfide
concentrations appear to have been associated with greater
sludge depths.  The lagoons were all constructed 3 to 3 1/2
ft deep.  From the BOD data expressed as Ib/day/acre, removals
would appear to increase with an increase in loading.

An extensive summary of operating experiences including
climatic conditions, design criteria, and operational pro-
blems and practices for waste stabilization ponds located
in Canada has been reported by Fisher e_t al. (21) . Intense
odors from lagoons were generally associated with the spring
ice break-up and anaerobic short-detention ponds tended to
exhibit less intensive spring odors even though low intensity
odors were emitted throughout the year.  Excessive odor
nuisance was associated with organic overloading of the pond,
high sulfate water, and exposed sludge mounds.

Brisban et al. (22)  have reported the results of detailed
studies of anaerobic ponds treating municipal wastewater at
two locations in Canada.  At Moose Jaw, Canada, two ponds
of 3.4 acres, each 10 ft deep, were operated as primary
units with about 7 days detention and loading rates of 1080
Ib BOD/acre/day.   Anaerobic lagoon temperatures rarely
exceeded 15C in summer and dropped to near freezing in
winter.  Severe odors developed soon after start-up and per-
sisted.  Attempts to control odors by draining and flushing
with secondary pond effluent revealed that a sludge mound
                              123

-------
                                    Table 7

                  Summary of Loading and Performance Data for
       Anaerobic Lagoons Treating Municipal Wastewater in Australia (24)
 Item
Season

BOD-mg/1
 Influent
 Effluent
 % Removed

Influent
 SS mg/1

Effluent
 Sulfide-mg/1
 Dissolved
  02-mg/l
 pH

Water Temp.
  C

Sludge Depth-in,
 Near inlet
 Near outlet

BOD-lb/day/acre
 Loading
 Removed
Werribee
Summer
448
157
65
436
14
nil
6.7
20
17
14
482
313
145W
Winter
407
291
28
436
8
nil
6.1
15
24
27
438
125

Wangaratta
Winter Summer
358
118
67
394
1.0
nil
7.0
15
10
7
910
630
270
137
49
	
___
3.8
7.0
24
10
9
710
350

Winter
222
149
33
	
0.3
nil
6.7
12
14
14
584
192
Kerang
Spring
190
101
47
323
140
nil
7.1
21
30
30
2800
1280

-------
8 ft deep had accumulated after .two years.  The ponds were
finally taken out of service during the summer because of
odors.  During intense odor periods removal efficiencies
remained high: 70% for suspended solids, 55% for BOD,60%
for COD, 75% for grease and 90% for coliforms.

At the Sutherland lagoon site at Saskatoon, Canada  (22), four
anaerobic lagoons each 0.27 acres and 17 ft deep were opera-
ted at loadings that increased over a 3 year period from 1300
to 2600 Ib BOD/ac/day or 3.7 to 7.0 Ib BOD/1000 cu ft of
initial volume.  Although lagoon temperatures were comparable
to those of the Moose Jaw lagoons odors were never a serious
problem.  Sludge accumulated to depths of 12.5 ft after 4
years at a rate of 0.014 cu ft/cap/day.  Gas samples collect-
ed at the lagoon contained 58 to 64% methane.

Typical removal efficiencies for the two Sutherland anaerobic
lagoons when operated in series were reported  (22) as:

                                   Percent Removal
                                 Winter       Summer

           5 day BOD               35           50
           Suspended Solids        70           70
           COD                     40           55
           Grease                  65           70
           Coliforms/ml            80           90

After a four-year operating period, the reported percent
removals were 10 to 20 percentage points lower.  Possible
explanations for the fewer odor problems at the Sutherland
lagoon compared to those at Moose Jaw included the increased
depth, the lower sulfate content of the sewage, the shorter
lagoon detention time and the much smaller lagoon surface
(22) .

Industrial Wastes -  Organic concentrations both solid and
dissolved,of industrial wastewaters are frequently several
orders of magnitude greater than those of municipal waste-
waters.  During recent years, certain industries, such as the
meat processing, have recognized the inherant advantages
of anaerobic lagooning and applied this process for the stab-
ilization of high-strength organic wastewaters.

The present extent of application of anaerobic lagoons for
the treatment of industrial wastes is not known.  A survey
by Porges  (25) in 1962 revealed that 197 anaerobic lagoons
were in service at that time with the leading users being
the canning industry with 79, meat and poultry 29, paper 18,
textile 17, and sugar 16.  The information presented would
                             125

-------
indicate that many of these anaerobic lagoons were overloaded
aerobic ponds.  Unfortunately, the literature provides only
a limited number of accounts of the operations of anaerobic
lagoons or the effectiveness of the treatment provided.

A summary of operating data for representative anaerobic
lagoons treating industrial wastewaters is presented in
Table 8.  Variation has existed in the lagoon designs serving
particular industries to compensate for a wide variety of
waste characteristics and local climatic factors.  Not all
of the anaerobic lagoons have operated nuisance free.

The effectiveness of anaerobic lagooning of meat processing
wastes has been well established.  BOD removal efficiencies
of 60-90% (Table 8) have been consistently demonstrated at
organic loadings of 10-30 Ibs of BOD/1000 cu ft of lagoon.
Nuisance odors have generally not been a problem with meat
wastes.

Meat processing wastes contain high concentrations of organic
matter with BOD and suspended solids concentrations frequent-
ly in excess of 1000 mg/1.   Pretreatment of meat processing
wastes before discharge to anaerobic lagoons has been report-
ed.  These processes include primary sedimentation and grease
recovery (3) or only grease removal (6)(9).  Anaerobic la-
goons have,  however, effectively treated meat waste without
pretreatment.  Removals in excess of 90% have been reported
for anaerobic lagoons receiving the unsegregated wastes from
small slaughterhouses including blood and paunch manure(4).

The extent of accumulation of solids in anaerobic lagoons
will vary considerably depending primarily upon the quantity
and characteristics of the wastewater, the degree of destruc-
tion of the organic material by digestion and the concentra-
tion of solids carried with the effluent.  Loehr  (17) has
provided tables to estimate the approximate time required
for anaerobic lagoons to fill with nonbiodegradable solids.
Solids have been found to accumulate at various rates in
anaerobic lagoons treating meat wastes.   The shallow ponds
receiving paunch manure have required solids removal after
a couple of years.  With preliminary treatment, the solids
buildup on the lagoon bottom is reported to be extremely
slow  (8) (31); however, in one case, a grease scum layer
1.6 ft deep reduced the lagoon volume and detention time by
17.5% (31).

Enders et al. (8) have studied the solids concentrations at
various depths in a 15 ft deep anaerobic lagoon receiving
slaughterhouse waste through an inlet near the bottom.  The
bottom 5-6 feet of the lagoon was found to contain a relative-
ly concentrated sludge of 3 to 4% volatile solids.  Above a
                           126

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                                            Table  8
to
      Investigator/s
        Reference
        Operating Data for Anaerobic Lagoons
           Treating Industrial Wastewaters
Type of     BOD Concentration-mg/1     BOD
 Waste      Influent      Effluent   Removal
Bod Loading,. Temper-
lbs/1000 ft  ture C
Sollo (3)
Rollag &
Dornbush (6)
Enders et al.
(8)
Wymore & White
(9)
Hester &
McClurg (26)
Dietz et al.
(7)
Coerver (14)
Parker (27)
Meat
Meat
Meat
Meat
Meat
Meat
Meat
Fruit
Tomato
Citrus
1096
940
1880
	
1703
3000
2070
3380
728
939
159
458
350
670
122
300
158
445
163
241
85
58
87
64
92
90
92
86
77
74
.5
.2

.9
.8

.4
.8
.6
.4

16.1
31.4
12.7
9.0
	
	
630*
628*
662*

25
22-27
	
24
25-26
	


-------
                                      (continued)   Table 8
00
Investigator/s
Reference
Canham (32) (28)
Howe et al .
(291
Cooper et al.
(19)
Mclntosh &
McGeorge (30)
Loehr (16)
Type of
Waste
Tomato
Peas
Corn
Chemical &
Fermentation
Rendering
Corn
Products
Milking
Parlor
BOD Concentration-mg/1
Influent Effluent
982
1444
2164
10,000
1870
<4000
1030
1030
599
2000-
	
	
160
830
BOD
Removal
39.8
37
47.5
60-80
88
58
92
85
20
BOD Loading
lbs/1000 ft3
33.9
23.2
15.9
228*
	
9
9
Temper-
ature C
14-24

5,10,15
19-36
21
38
29
2
       *lb BOD/acre/day

-------
well-defined sludge blanket, volatile solids concentrations
were less than 0.1%.  Placement of the lagoon outlet 2 ft
from the surface resulted in the raw wastewater passing up
through the concentrated sludge blanket.  Average removals
for the surveys during the summer were 87% for BOD, 76% for
volatile solids and 78% for COD.  Removal efficiencies de-
creased substantially when higher than average influent
flows occurred.

Recirculation of sludge solids was provided at an anaerobic
lagoon treating packing house wastes in order to simulate
an anaerobic contact process (26).  Sludge with 2% solids
was returned from the center of the bottom of the anaerobic
lagoons and recycled with inflow at a ratio of 1:1 to a man-
hole preceeding a corner inlet near the surface of the lagoon.
Lagoon temperatures ranged from 66-90F and BOD removal
efficiencies for a four-year period averaged 79.6%.  A heavy
sludge bank accumulated near the inlet of the lagoon.

Anaerobic lagoons treating slaughterhouse wastes have been
reported to operate without nuisance odors.  Grease and
solids form a scum crust on the lagoon surface providing
insulation and excluding oxygen from the lagoon contents.
Coerver (4) reported that the shallow anaerobic ponds in
Louisiana were odor free only after the crust was formed on
the shallow ponds and suggested that paunch manure was
advantageous to the formation of an adequate crust.

The high temperatures of meat slaughtering wastes are pro-
bably a major factor contributing to the success of anaerobic
lagoon treatment in the more severe climates.   With detention
periods of 3 to 5 days 80% removals were reported for a
lagoon system in Canada (10).  After a thick scum crust had
developed on a lagoon in Minnesota effluent temperatures
averaged 87F for a weekly period even though average air
temperatures were -2F (31).

Cannery waste treatment with anaerobic lagoons has been
reported to be successful in several instances.  Canham  (28)
reported,  however, that cannery waste lagoon systems have
generally been designed to serve as storage areas for a
seasons wastes.  Odor remains a problem with cannery lagoons.

Canham (32) reported the successful use of anaerobic digest-
ion of mixed tomato and lima bean wastes in a lagoon located
in Indiana.  An abundance of sludge from a previous canning
season was available for seed and a single raft-mounted mixer
was used to create movement of the lagoon contents and mixing
with the raw wastes.  Lagoon temperatures ranged from 64 to
84F and lagoon pH from 5.4-7.2.  BOD reduction was 39.8%
with an average loading of 33.9 Ib BOD/1000 cu ft and an
average detention time of 2.54 days.  The system operated odor

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free throughout the season.

Subsequent studies that were made in 1950-53 of anaerobic
lagoons treating wastewaters from canning of peas and corn
were reported by Canham (28).   The anaerobic lagoon was
double the size reported for the tomato wastes and four
mixers were employed.  Digested sludge (175,000 gal) was
added to seed the lagoon.   BOD loadings ranged from 12.5 to
27.8 lb/1000 cu ft and removals from 22 to 69%.  A severe
odor problem in the digester led to the addition of sodium
nitrate for odor control.  The blades of one mixer were ad-
justed so that it agitated the lagoon surface creating a
"Semianaerobic and semiaerobic digester," ajcondition con-
sidered advantageous at the time for odor control.  Based
on the necessity of methane formation for odor-free anaerobic
lagoon performance as stated by Oswald (23) , the increased
mixing to induce oxygen into the system may have been detri-
mental .

Parker (27), following pilot studies, utilized anaerobic
lagoons for the successful treatment of cannery wastes in
Australia.  Fruit canning wastes (apricots, peaches and
pears) were mixed with sewage treatment plant effluent that
supplied nitrogen and phosphorus and with digester sludge
to supply methane organisms before discharge to the lagoons.
In another case, lime was added to tomato and citrus wastes
to maintain a pH above 7.0 before lagooning in a similar
manner.  Oxidation ditches were used to treat the anaerobic
lagoon effluent.  The anaerobic lagoons were found to operate
odor-free when BOD loadings were 600 Ibs/acre/day for fruit
wastes, 400 Ibs/acre/day for tomato processing wastes and
200 Ibs/acre/day for citrus wastes.  BOD removals were 75
to 80%.  Sludge accumulations have not been a problem with
a maximum depth of 9 inches measured adjacent to the inlet
after 5 years.  A considerable cost advantage was shown for
the anaerobic lagoon - oxidation ditch system in comparison
with aerobic lagoon or spray irrigation systems.

Gilde (33) reported that a 15 ft deep anaerobic lagoon with
a four day detention and a design loading of 12 Ibs BOD/
1000 cu ft/day accomplished a 65% BOD reduction on a cannery
waste.  The lagoons were installed to alleviate solids de-
position problems and associated odors in the aerobic lagoons
that had previously received the cannery wastes.

Cooper et al. (19) reported results indicating that anaerobic
lagooning has been successfully applied to wastewaters from
a rendering plant, a hide washing plant and a poultry (manure)
unit.  The presence of purple sulfur bacteria were noted to
contribute to the odor free operation of these lagoons.
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An 88% BOD removal was reported for the anaerobic lagoon,
(7 ft deep with 160 days detention) treating the rendering
wastes at a BOD loading of 228 Ib/acre/day.  Gas production
was measured to range as high as 2400 cu ft/acre/day with
70.3% methane.  Pilot plant studies were strongly suggested
prior to the design of anaerobic ponds because of the lack
of fundamental knowledge of the design parameters involved.

Anaerobic lagooning has also been applied to wastewaters
from the industrial chemical and fermentation processes  (29).
Pilot studies revealed that BOD removals of 60 to 80% could
be achieved at temperatures ranging from 22C to 5C.  Vola-
tile acids, alkalinity and BOD concentrations were all ob-
served to increase with each successive drop in temperature.

Starch refining wastes that had temperatures ranging from
91-114F have been found particularly amenable to treatment
with anaerobic lagoons.  Mclntosh and McGeorge  (30) reported
that an anaerobic cell accomplished BOD reductions from  58%
in winter to 92% in summer at lagoon temperatures of 60F
and 90F respectively.  The pH of the raw starch wastes was
adjusted from 4.5 to 9-11 with caustic soda and a recircula-
tion system provided continuous seeding of the influent.
Three-inch plastic foam rafts were used to insulate a pprtio
of the anaerobic cell and to maintain higher lagoon tempera-
tures.  Solids accumulations near the inlet were removed with
a dragline.  Odor problems encountered during the early
stages of operation were combatted with ammonia nitrate
feed.

Milking parlor waste treatment in anaerobic lagoons has
been reported to be satisfactory by Loehr and Ruf  (16).  At
a loading of 9 Ib BOD/day/1000 cu ft, reductions were 85%
for the summer, with liquid temperatures at 85F, and 20%
for the winter with liquid temperatures of 35F.  Solids
were settled out during the winter period but digestion was
not active until spring.  When solids that had accumulated
in the lagoon were removed in the early winter, the perform-
ance was affected.  Decreased alkalinity and increased volatile
acids concentrations occurred in the bottom sludges; however,
the lagoon recovered in the summer.  A general decrease  in
efficiency was noted as the winter progressed.

Swine manure lagoons were studied in South Dakota to deter-
mine their ability to dispose of solids in an odor free
manner  (34).  Active digestion in lagoons to the extent  that
ebullition of gases created a mixing action resulted in
odor-free lagoons.  Supernatant of an odor-free lagoon was
found to have a volatile acids concentration equal to about
15-30% of the alkalinity whereas volatile acids concentra-
tions always exceeded the alkalinity for highly odorous

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lagoons.  The lagoons did not have an effluent.  Lagoons
which had developed active decomposition during the previous
summer maintained sufficient "seed" material through the
winter to avoid offensive odors the following spring.  Sim-
ilar observations have been made for a poultry manure lagoon.
(11) .

Effluent Quality and Quality Criteria

Anaerobic lagoons have not been considered adequate as a
complete wastewater treatment unit except when the volume
of flow is so small that evaporation and seepage eliminates
the necessity of an effluent.  For example, effluents from
anaerobic lagoons treating feedlot wastes could pollute a
receiving body of water (35).  The effluents are high in
oxygen demanding materials and solids.  As a result, design-
ers have found it necessary for the effluent to be discharg-
ed to secondary biological treatment units usually oxidation
or stabilization lagoons.   Secondary treatment has also been
satisfactorily provided with activated sludge units (7)  and
an oxidation ditch. (27).

The quality of effluent from an anaerobic lagoon is dependent
to a considerable extent on the wastewater being treated.
High strength wastes might be expected to yield potent efflu-
ents.   BOD concentrations of 100 to 300 mg/1 occur in anaer-
obic lagoon effluents treating municipal wastewaters (Table
 8 ) with somewhat higher concentrations resulting with in-
dustrial wastewaters  (Table 8 ).  Experience has shown that
effluent BOD concentrations will probably range from 40 to
70% of inflow BOD for municipal wastewaters and 10 to 40% for
industrial wastewaters.

Digestion of solids in anaerobic lagoons accomplishes con-
siderable stabilization of the organic matter; however, the
nutrient elements of nitrogen and phosphorus are released
to the lagoon liquid.  For example, with a slaughterhouse
waste, a 30 mg/1 organic nitrogen reduction through the ana-
erobic lagoon was accompanied by an increase of 30 mg/1 in
ammonia  (6).  Thus, the effluent for anaerobic lagoons usual-
ly contains high concentration of nutrient chemicals such as
nitrogen and phosphorus which are readily available to sup-
port biological growth in subsequent secondary treatment
units.

Theory

The anaerobic lagoon might be considered as analogous to the
septic tank.  During the two to ten day detention, the solids
entering the lagoon with the wastewater either settle to the
bottom as sludge or rise to the top as scum.  This solids

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 separation would, account for a removal efficiency of 25 to
40% on a purely physical basis.  Early investigators, how-
ever, recognized that anaerobic lagoons provided removals in
excess of that accounted for by simple sedimentation.

Parker et al.  (1) in 1950 reported the results of early
studies with anaerobic lagoons explaining:

        The high efficiency of the anaerobic lagoon in
        removing BOD is dependent on the development 
        of digestion in the sludge layer.  Organic
        matter is converted to methane and carbon
        dioxide under anaerobic conditions and the
        gassing of the sludge layer seeds the sewage
        flowing over it.

In this manner, the organics remaining in the supernatant
were subjected to treatment.

The underlying treatment mechanism of the anaerobic lagoon
is anaerobic digestion, a process which has been subjected
to intensive investigation to unravel the complex reactions
and to understand the limitations involved.  Review of
several sources  (36)(37) would provide extensive coverage
of the theory and fundamental factors that may be related
to the anaerobic lagoon.

Digestion of complex organic material in the anaerobic
environment can be simplified and summarily described as
occurring in two sequential stages.  In the initial -state,
the complex materials such as carbohydrates, proteins, and
fats are biologically converted and fragmented by processes
of hydrolysis and fermentation to the simpler organic end
products including aldehydes and alcohols but principally
fatty organic acids.  For this reason, the mixed groups of
facultative and anaerobic organisms that accomplish this
initial conversion, are commonly termed "acid formers."
The organisms derive small amounts of energy from the re-
actions which in turn is converted to bacterial cell growth.
Relatively little stabilization of organic matter as would
be measured by BOD or COD reduction occurs in this initial
stage of the conversion.  The organic matter simply undergoes
an antecedent breakdown in preparation for the second stage
reaction.

The methane formation stage of digestion proceeds, with a
favorable environment, where the first stage ends.  Organic
acids produced during the initial breakdown are converted
by the methane-forming organisms to gaseous end products,
principally methane and carbon dioxide.  It is with this
second conversion that the waste stabilization occurs, being
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directly proportional to the methane produced (38).  The
gaseous end products released in the final stage of organic
digestion may escape from the liquid as in the case of hydro-
gen sulfide, carbon dioxide and methane, or remain in the
liquid to serve as a buffering system as with ammonia and
carbon dioxide.  The maintenance of conditions to accomplish
a proper balance between the two groups of organisms is
essential to prevent the development of low pH conditions by
the acid formers and to accomplish relatively nuisance free
treatment in the anaerobic lagoon.

The application of the simplified theory to the design of
an anaerobic biological wastewater treatment system, such as
an anaerobic lagoon, must depend upon the proper relationships
between the organic matter in the wastes, the microorganisms
which can metabolize the organic matter, the generation time
of the microorganism, the temperature of the treatment system,
the wastewater retention period, the pH, the alkalinity, the
nutrient elements, and proper mixing (39).

It is generally recognized that the organisms involved in
methane formation are more vulnerable to adverse environmen-
tal factors such as low temperature or low pH and particular-
ly the presence of dissolved oxygen.  Table 9  contains the
range of values as listed by Oswald (23) for environmental
factors at which the organic acid formation and methane fer-
mentation reactions may be useful for waste treatment in ponds.
As has been noted previously, design of anaerobic lagoons to
obtain the conditions conducive to continuous methane formation
would, in theory, be most desirable.

Design and Operation Modifications

Several variations in the design and operation of anaerobic
lagoons appear to have merit in that they probably have im-
proved removal efficiency or solved operation problems.
The development of an environment which will result in ade-
quate methane formation should apparently be the major ob-
jective in order that odor nuisances will be avoided.

Lagoon temperature, to a large extent a climatic factor,
plays an important part in the success of anaerobic lagoons.
Nearly all anaerobic ponds have been observed to function
better during the summer.  In Australia and California ade-
quate temperatures in excess of 15C can be maintained with
the asssstance of solar radiation throughout most of the
year with lagoon depths of about 3 feet.  In Canada, where
the major source of heat would probably be the incoming
wastes, deep ponds with short detention are found to be more
satisfactory.  In Israel (40) extra-deep ponds  (5 meters)
were found to develop thermal gradients which would
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       Required Conditions or Levels for Indicated
          Biological Reaction i.n Ponds  (23)
  Environmental
     Factors
  Organic Acid
    Formation
                   Mln.   Opt.  Max.
                       Methane
                    Fermentation
                           Mln.  Opt.  Max.
Population

(No. per ml.)
Nutrients

Oxygen  (mg/1)
Time (days)
Initial/Active
Temperature, C
PH
Alkalinity  (mg/1)
Antecedent reac-
tions
Competitive reac-
tions
Predators
Toxic sub-
stances

Energy  source
Redox potential
E mv
 n
Heterotrophs facul-
tative
10
  8
10
  10
10
  12
Carbohydrates,
Protein, fat
0

1/6
4
4.3

0
5-10
1/12
25
6.5
Unknown
1

1
40
7.5

0 0

10
15
6.8
500
Organic synthesis

Oxidation
     Unknown
Salts, heavy metals
Nutrients
-0.1
      + 0.2
Mesophilic bac-
teria
    Unknown
Organic acids,
Alcohols
                                 0    0
                               40-120
                                 40  100+
                                 32   40
                                 7.0  7.2
                                 2000  -
              Organic acid
              formation
              Oxidation
                  Unknown
              Oxygen, copper,
              salt,  chromium
              heavy  metals
              Nutrients
              -0.10  -0.5  -
                            135

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in effect result in a facultative pond layer floating over
an anaerobic layer; however, temperatures remained above
15C in all layers throughout the year.

Oswald (23) has suggested that the development of thermal
layers makes possible recirculation from the final aerobic
pond to the primary anaerobic lagoon for the purpose of elim-
inating odors.  If the water temperature of the aerobic pond
is warmer than the water on the bottom of an anaerobic pond,
a layer with dissolved oxygen will reportedly overlay the ana-
erobic pond eliminating sulfide odors.  The possible instru-
sion of oxygen into the anaerobic zone where it would be
detrimental to methane formation is avoided solely by the
thermal density layers.

Oswald has suggested that special designs of the anaerobic
lagoon near the inlet to create a special sludge digestion
chamber have proved advantageous.  A conical-shaped enlarge-
ment with increased depth surrounding the inlet was one of
the designs suggested.  Another design would employ a sub-
merged baffle to surround the digestion zone into which the
influent was discharged.  These designs had been used to
prevent intrustion of oxygen into the digesting sludge when
recirculation from the aerobic ponds for odor control was
included in the design.

Obtaining intimate contact between the raw influent and
active methane forming organisms in the lagoon may be expect-
ed to result in increased BOD removals and possible less odor
problems.  Parker and Skerry (24) have suggested that shallow
lagoons bring the deposited sludge closer to the supernatent
where gas evolution  would achieve mixing.  Dornbush and
Andersen  (11) stressed the importance of the mixing that oc-
curred in animal manure lagoons with gas bubbling action and
used a pump to artificially mix sludge banks deposited on
the bottom of a poultry lagoon for the purpose of eliminat-
ing odors.

The designs suggested by Oswald to create a digestion chamber
near the lagoon inlet would be expected to accomplish mixing.
Enders e_t al.  (8) reported that for a lagoon receiving slaugh-
terhouse wastes a sludge blanket developed to a depth of
about 5 ft.  As a result the placement of the inlet near the
bottom would be expected to accomplish the desired mixing.
At other lagoons recirculation of sludge to the inlet accom-
plished the mixing  (3) (26).  Canham  (28) has reported improved
results with a single raft-mounted mixer placed near the in-
let of a cannery waste lagoon; however, a later installation
with four mixers experienced odor problems.
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Recirculation of supernatent has also been used to seed
incoming wastes.  Over 200,000 gallons of effluent were
returned daily to innoculate the incoming wastewater at a
corn starch plant (30).  Recirculation of supernatent from a
second anaerobic lagoon in series at a rate of 1.3 to 1 for
the raw wastes resulted in a 5-6% increase in BOD removal
efficiency in two anaerobic lagoons treating slaughterhouse
wastes (31).

In northern climates where for prolonged periods the major
source of heat may be the incoming wastes, floating covers
have been used for anaerobic lagoons.  A plastic foam raft,
3 inches thick, was installed to cover 30,000 sq ft of an
anaerobic lagoon treating corn products wastes (30).  The
insulating value of the plastic foam was sufficient to cause
snow to remain on top of the cover during the winter with
liquid temperatures of 85F underneath (41).  A similar
plastic foam cover has been used to prevent heat loss from
a packinghouse waste lagoon  (7).

With meat packing wastes a natural scum cover forms on anaer-
obic lagoons as a result of grease and paunch manure in the
waste.  This natural cover proved to be adequate insulation
to prevent the lagoon temperatures from dropping below 75F
in Minnesota,  (6) although preliminary design had indicated
that external heat would be required and a support column
had been constructed in the lagoon for an underwater gas-fired
heater.  The heater was never installed.  Subsequent studies
on this anaerobic lagoon  (31) determined that the grease
scum layer had a thermal conductivity of 0.38 BTU/hour-F-ft.
Snow would accumulate on the surface of the scum crust.

Covers on anaerobic lagoons may be beneficial for the preven-
tion of odors.  Coerver  (4)(5) reported that anaerobic lagoons
treating slaughterhouse wastes became nuisance free only after
a crust had formed over the lagoon surface.  It would appear
that the scum covers or crusts would be beneficial in prevent-
ing a condition more favorable for methane forming bacteria.
This would appear to be particularly important for the shallow
anaerobic ponds described by Coerver.

The scum crusts and sludge in an anaerobic lagoon may be ex-
pected to eventually accumulate to considerable depths and
require removal.  In order to accomodate the use of a dragline
for solids removal, Coerver  (4) suggested that anaerobic
lagoons be designed to be long and narrow with the length at
least three times the width.  The use of pumps also proved
satisfactory for removal of sludge accumulations  (3)(30).
Sludge removed from the lagoons dried without the creation
of a nuisance.
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When the grease and paunch cover of an anaerobic lagoon
serving packing plants in Edmonton, Canada became 5 to 6 ft
in thickness, removal was accomplished by burning resulting
in a saving of several thousand dollars  (42).  The scum was
sprayed with fuel oil and kerosene and ignited with a gaso-
line flame.  The resulting smoke pall was reported to be
light in density and to have dissipated within 1/2 mile
from the lagoons; as a result there were no complaints.  The
burning action continued for a considerable time surviving
two high intensity rain storms and several snowfalls.

The literature contains accounts of start-up procedures that
have avoided a prolonged period of nuisance odors when an
anaerobic lagoon is  put into service  (6) (17).  These pro-
cedures approach those used for starting a sewage sludge di-
gester including provisions for an adequate population of
microorganisms (methane formers) suitable to complete the
digestion and consideration for the major environmental fac-
tors of temperature and pH.

Summer would be the preferable start-up time for an anaerobic
lagoon when the contents can be maintained at temperatures
well in excess of the suggested 15C minimum.  Temperatures
approaching 35C would be preferable.  A high initial popu-
lation of methane formers must be provided with an initial
seeding of sludge from a municipal sludge digester or simi-
lar source undergoing active anaerobic digestion.  Lime feed
may be used to control the pH in the lagoons to the desired
range of 6.8 to 7.2.

Research Needs

Temperature - Thermal considerations should receive greater
attention in the design of anaerobic lagoons particularly
in the colder climates.  Primary sources of incoming heat
to the lagoon include solar energy and heat transmitted with
the incoming waste.  If heat sources are insufficient to
compensate for the heat losses that may occur via the efflu-
ent and through conduction, convection, evaporation and
radiation, measures to limit these losses would be in order.
These measures might include shortening the detention time
of the lagoon,  limiting recirculation, or utilizing insula-
ting lagoon covers either natural or artificial.  The measures
would be successful only if the total heat input of the in-
coming waste is expected to maintain an adequate lagoon tem-
perature.

Limitations in the activity of the methane formers at 15C
would appear to establish the lower temperature limit that
must be maintained throughout the lagoon, particularly in
the sludge deposits on the bottom.  When heat input from
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wastes appears insufficient to maintain this 15C tempera-
ture, it may be possible to separate waste streams on a
basis of temperature and divert cold waste streams to second-
ary units after sedimentation.  Heat input by artificial
means could also be used.

Lagoons located in Australia and California rely primarily
on solor heat to maintain adequate temperatures, consequently,
shallow ponds with large surface areas have proved successful
even with relatively dilute municipal wastes.  In Canada
deeper ponds with less surface area exposed to the atmosphere
have proven more satisfactory for treatment of  municipal
wastewater although odor problems have been encountered.

These lagoon adaptations signal the need for measuring the
total heat input in future studies which evaluate loading and
treatment efficiencies of anaerobic lagoons.  Temperature
measurements in bottom sludge accumulations as well as in
the overlying supernatent would determine if minimum accept-
able temperatures were being maintained throughout the entire
system.  There appears to be a serious lack of information on
tht total temperature environment at field installations.

Loading and Detention Time -  The organic loading parameter
is widely used asa basis for the design of anaerobic lagoons.
Naturally this term may be confusing because it has been ex-
pressed in terms of area as Ibs BOD/acre/day or in terms of
volume as Ibs BOD/1000 cu ft/day or Ibs volatile solids/1000
cu ft/day etc.  Describing the organic loading term as a
function of area would not appear to be adequate because the
digestion process and hence the stabilization of the wastes
may take place throughout the entire depth of the wastes
lagoon.  However, the loading rates can be compared when the
lagoon depth is known.  For example, an anaerobic lagoon 3
feet deep with a BOD loading of 600 Ibs/acre/day would have
a BOD loading of 4.6 lbs/1000 cu ft/day.  Nevertheless, or-
ganic loading is not an enitrely satisfactory expression be-
cause it does not consider detention time.

The computation of organic loading considers both wastewater
flow and wastewater concentration and an increase in either
flow or concentration of the influent would increase the or-
ganic loading of the anaerobic lagoon.  However, the lagoon
detention time will be influenced only by changes in flow.
The approximate variation of treatment efficiency of the
digestion process with detention time is known - treatment
efficiency increases with detention time but at a decreasing
rate.  Consequently, for a given organic loading, a higher
influent concentration would be expected to result in greater
removal efficiency because of the increased detention time.
This is borne out by the high removals attained by anaerobic


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lagoons with high strength industrial wastes even at higher
organic loadings.

The nature of the organics either soluble or settleable
that would make up the organic loading would, however, be of
particular significance with respect to the efficiency of
anaerobic lagoons.  The settleable portion would be easily
retained for long periods in the lagoon even though conditions
for complete stabilization may not exist.  This would explain
substantial BOD removals in the winter when methane production
would be retarded.  The solids would merely be stored as
sludge until conditions more favorable to digestion occur
and the stabilization takes place.  The soluble organics,
however, would be in transit continually and as a result the
detention time of the anaerobic unit would determine the ex-
tent of stabilization.

At the present time, there is little information available
concerning the nature of the BOD that remains in the efflu-
ent of anaerobic lagoons.  With anaerobic contact and sludge
digestion systems, the major portion of the BOD in the efflu-
ent is attributed to the solids which are carried from the
systems.  This, however, has not been demonstrated with ana-
erobic lagoons.  If, for instance, a large portion of the
effluent BOD is of a soluble nature, measures including re-
circulation or mixing as well as increasing the detention
time may be required to improve the efficiency.  These
measures would naturally be in addition  to maintaining an
overall satisfactory environment for methane formation.
Sludge Accumulations and Odors - Numerous accounts of com-
plaints of odors from anaerobic lagoons of all types would
seem to deter their adoption by all but the most adventurous.
Equally frequent reports of successful operation with high
removal efficiencies at low costs and without odor complaints
create a dilemma for those who must make the final decisions.
A ray of hope seems to be emerging from the multitude of ob-
servations and reports.  Meager information seems to point
the accusing finger at sludge deposits accumulated on the
bottom of lagoons as being a major source of noisome odors.

It is reasonable to assume that solids settling from waste-
waters in lagoons will begin to undergo decomposition depend-
ing on the total environment.  With low water temperatures
or an inadequate population of methane formers the first
stage of digestion, that of acid formation, will proceed with-
in the sludge accumulations because of the ability of the
"acid formers" to function in the less favorable environment.
The resulting organic acids would quickly exceed the limited
buffering within the sludge accumulations and the pH would
begin to drop to further limit the performance of the methane
formers.
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Organic acids would be expected to accumulate and an acid
sludge bank or "pocket" would develop.  It is hypothesized
that these acid sludge accumulations are a major source of
odors in lagoons.  Odors will be produced in the acid sludge
until this localized "pickling" environment is altered, either
through dispersion by mixing, pH adjustment, or development
of an adequate population of methane formers to break down
the acids.

The numerous reports of malodors after anaerobic lagoons had
been initially put into service, and the success usually en-
countered in avoiding odors when recently constructed lagoons
were seeded with an active sludge would tend to support this
hypothesis.  Success reported in eliminating vile odors by
artificially mixing and accumulated solids in a poultry lagoon
with a pump provides additional substantiation.

Odors in the spring of the year have come to be expected in
northern climates.  During long severe winters, after lagoon
temperatures have dropped and digestion has ceased, solids
from raw incoming wastewaters settle to form a blanket of
raw sludge over the "seed" sludge remaining on the lagoon
bottom from the previous year.  Odors are probably produced
in this overlaying blanket when the initial organic breakdown
results in an acid sludge.  Malodors will continue to occur
until favorable temperatures reach the active sludge from the
previous year and "gassing" begins.  When sufficient gas
is produced in the lower layer to result in a bubbling action,
the self induced mixing will break up the acid sludge layer
resulting in an adjustment of pH and a rapid correction of
the odor problem.

More information on the actual conditions that exist in sludge
layers of lagoons that are experiencing extreme odor problems
is needed.  In situ measurement of sludge temperature, pH, and
ORP combined with the results of analyses of sludge samples
for volatile acids, alkalinity and hydrogen sulfide, would
greatly assist in determining the significance of solids as
the major source of odors.  Once the major source is estab-
lished, corrective measures may be devised.

In summary, research activities with anaerobic lagoons should
be directed at more clearly defining:

      (1) the thermal environment throughout lagoons,
      (2) the natural of the organics in both the lagoon in-
          fluent and effluent,
      (3) the actual detention time of organics within the
          lagoon, and
      (4) the relative importance of sludge accumulations as
          a major source of nuisance odors.


                             141

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With this information, design criteria that would result in
a satisfactory waste-stabilizing environment within lagoons
can be established.
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                     LITERATURE  CITED

 1.  Parker,  C.D.,  Jones,  H.L.  and  Taylor, W.S.,  "Purification
    of Sewage in Lagoons,"  Sewage  and  Industrial Wastes,  22,
    760-775,  (1950).

 2.  Parker,  C.D.,  Jones,  H.L.  and  Green, N.C.,  "Performance
    of Large Sewage Lagoons at Melbourne, Australia,"  Sewage
    and Industrial Waste,  31,  133-152,  (1959).

 3.  Sollo, F.W., "Pond Treatment of Meat Packing Plant Wastes",
    Proceedings  of Symposium on  Waste  Stabilization  Lagoons,
    USPHS, Region VI, Kansas City, August 1-5,  1960.

 4.  Coerver,  James F., "Anaerobic  and  Aerobic Ponds  for
    Packinghouse Wastes Treatment  in Louisiana," Proc. 19th
    Ind.  Waste Conf., Purdue Univ., Ext. Ser. 117,  200, (1964).

 5.  Coerver,  J.R., "Lousiana Practice  and Experience with
    Anaerobic-Aerobic Pond  System  for  Treating Packinghouse
    Wastes",  JWPCF, 3j6, 931, (1964).

 6.  Rollag,  D.A. and Dornbush, J.N., "Anaerobic Stabilization
    Pond Treatment of Meat  Packing Wastes,"  Proc.  21st Ind.
    Waste Conf., Purdue Univ., Ext. Ser.  121, 768,  (1966).

 7.  Dietz, J.C., Clinebell, P.W. and Strub,  A.L.,  "Design Con-
    siderations  for Anaerobic Contact  Systems,  " JWPCF,  38,
    (1966) .

 8.  Enders,  K.E.,  Hammer, Mark J. , Weber, Clint L.,  "Field
    Studies  on an Anaerobic Lagoon Treating  Slaughter  House
    Waste,"  Proc.  22nd Ind. Waste  Conf.,  Purdue Univ., Ext.
    Ser. 129, 126, (1967).

 9.  Wymore,  A.H., and White, J.E., "Treatment of a  Slaughter-
    house Waste Using Anaerobic  and Aerobic  Lagoons,"  Proc.
    23rd Ind. Waste Conf.,  Purdue  Univ.,  Ext. Ser.  132,  601,
    (1968) .

10.  Stanley, D.R., "Anaerobic and  Aerobic Lagoons  Treatment  of
    Packing  Plant Wastes,"  Proc. 21st  Ind. Waste Conf.,  Purdue
    Univ.,  Ext.  Ser. 121, 275,  (1966).

11.  Dornbush, James N. and Andersen, John R.f "Lagooning of
    Livestock Wastes in South Dakota", Proc. 19th  Ind. Waste
    Conf.,  Purdue Univ., Ext. Ser. 117, 317,(1964).
                              143

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12.  Hart,  Samuel A. and Turner, Marvin E., "Lagoons for Live-
    stock Manure," JWPCF, 37, 1578, (1965).

13.  Hart,  S.A.  and Turner,  M.E., "Waste Stabilization Ponds
    for Agricultural Wastes," In Advances in Water Quality
    Improvement, University of Texas Press, Austin, Texas,
    457, (1968).

14.  Loehr,  R.C.  and Agnew,  R.W., "Cattle Wastes - Pollution
    and Potential Treatment," Journ. San. Engr. Div., ASCE,
    93, SA4, 66, (August 1967).

15.  Loehr,  R.C., "Effluent Quality from Anaerobic Lagoons
    Treating Feedlot Wastes," JWPCF, 39_, 384, (1967).

16.  Loehr,  R.C.  and Ruf, J.A., "Anaerobic Lagoon Treatment
    of Milking Parlor Wastes, " JWPCF,  40, 84, (1968).

17.  Loehr,  R.C., "Anaerobic Lagoons-Considerations in Design
    and Applicaton," American Soc.  Agric. Engrs,  Trans. 11,
    3, 320, (May-June, 1968).

18.  Clark,  C.E., "Hog Wastes Disposal by Lagooning," Jour.
    San. Engr.  Div., ASCE,  91, SA6, 27,  (December 1965) .

19.  Cooper, Robert C., Oswald, William J. and Bronson,
    Joseph C.,  "Treatment of Organic Industrial Wastes by
    Lagooning,"  Proc. 20th Ind. Waste Conf.,  Purdue Univ.,
    Ext. Ser.  118,  357,(1965).

20.  Witzall, S.A.,  McCoy, E. and Lehner, R.,  "What Are the
    Chemical and Biological Reactions When Lagoons are Used
    for Cattle?" Paper 64-417, American Society of Agricul-
    ture Engineers, St. Joseph, Michigan, (1964).

21.  Fisher, Charles P., Dryman, W.R. and Van Fleet, G.L.,
    "Waste Stabilization Pond Practices in Canada" In Ad-
    vances in Water Quality Improvement, Univ. of Texas Press,
    Austin ,Texas,435,(1968).

22.  Brisban, K.J.,  Forsberg,. C.R.,  McDonald,  R.A. and McGrath,
    N.W.,  "Anaerobic Waste Stabilization Ponds,"  Water and
    Pollution Control  (Canada), 105, 31,  (1967).

23.  Oswald, W.J., "Advanced in Anaerobic Pond Systems Design"
    Advances in Water Quality Improvement, University of
    Texas Press, Austin, Texas, 409, (1968).
                           144

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24. Parker, C.D. and Skerry, G.P., "Function of Solids on
    Anaerobic Lagoon Treatment of Wastewater," JWPCF,  40,
    192, (1968).

25. Forges, Ralph>  "Industrial, Waste Stabilization Ponds in
    the United States", JWPCF, 35, 456, (1963).

26. Hester, B.L. and McClurg, P.T., "Operation of a Packing
    Plant Wastes Treatment Plant", presented at 25th Purdue
    Ind. Waste Co'nf. ,  (May 5-7, 1970).

27. Parker, C.C., "Food Cannery Waste Treatment by Lagoons
    and Ditches at Shepparton, Victoria, Australia," Proc.
    21st Ind. Waste Conf., Purdue Univ., Ext. Ser. 121,
    21T4";(1966) .

28. Canham, R.A., "Stabilization Ponds in the Canning In-
    dustry", In Advanced in Water Quality Improvement, Univ.
    of Texas Press, Austin, Texas, 464,(1968).

29. Howe, David 0., Miller, A.P. and Etzell, J.E., "Anaerobic
    Lagooning  A New Approach to Treatment of Industrial
    Wastes", Proc.  18th Ind. Waste Conf.,  Purdue Univ., Ext.
    Ser., 115, 233, (1963).

30. Mclntosh, G.H.  and McGeorge, G..G. , "Year Round Lagoon
    Operation", Food Processing,  (Jan. 1964).
                                                      i
31.  Tofflemire, Tracy James, "Factors Influencing Anaerobic
    Pond Treatment of Meat Packing Wastes," Unpublished M.S.
    Thesis, South Dakota State University,  (1966).

32. Canham, R.A. "Anaerobic Treatment of Food Canning Wastes",
    Proc. 5th Ind.  Waste Conf., Purdue Univ., Ext. Ser. 72,
    145, (1950).

33. Gilde,, L.C., "Experiences of Canning and Poultry Waste
    Treatment Operations", Proc. 22nd Ind. Waste Conf., Pur-
    due Univ.,  Ext. Ser. 129, 675,  (1967).

34. Curtis, David R.,  "Evaluation of and Tentative Design
    Criteria for Anaerobic Lagoons as a Method of Swine Man-
    ure Disposal in South Dakota", Unpublished M.S. Thesis,
    South Dakota University,  (1965).

35. Loehr, R.C., "Effluent Quality from Anaerobic Lagoons
    Treating Feedlot Wastes", JWPCF,  39, 384,(1967).
                             145

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36.  McKinney, Ross E.,  Microbiology for Sanitary Engineers,
    McGraw-Hill Book Co., Inc., (1962).

37.  McCarty,  P.L., "Anaerobic Waste Treatment Fundamentals",
    Public Works, 93,  No. 9,  10,  11,  12,  (Sept.-Dec. 1964).

38.  McCarty,  Perry L.,  "Anaerobic Treatment of Soluble
    Wastes",  In Advances in Water Quality Improvement, Univ.
    of Texas  Press,  Austin, 336,  (1968) .

39.  Dague, Richard R.,  McKinney,  Ross E.  and Pfeffer, John T,
    "Anaerobic Activated Sludge," JWPCF,  38, 220,  (1966).

40.   Wachs, A.M. and Berend,  A.,  "Extra Deep Ponds," In
    Advances  in Water  Quality Improvement,  Univ.  of Texas
    Press, Austin, Texas, 450,  (1968).

41.  Etzel, James E., "Industry's  Idea Clinic", JWPCF, 36,
    931,  (Aug. 1964).

42.  Duncan, G.P., "Grease Removal from a  Sewage Lagoon,"
    Western Canadian Water and Sewage Conference  Bulletin,
    18,  (Aug. 1967).
                           146

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                      SECTION VII

                   ACKNOWLEDGEMENTS

This State of the Art Review of Wastewater Lagoons was the
joint effort of three people:

       Dr. James N. Dornbush
       Professor of Civil Engineering
       South Dakota State University
       Brookings, South Dakota

       Dr. John W. Vennes
       Professor of Microbiology
       University of North Dakota
       Grand Forks, North Dakota

       and

       Dr. Ross E. McKinney
       Parker Professor of Civil Engineering
       University of Kansas
       Lawrence, Kansas

Responsibility for the primary material was as follows:

  1. Oxidation Ponds: Drs. John W. Vennes and
                      Ross E. McKinney
  2. Aerated Lagoons: Dr. Ross E. McKinney
  3. Anaerobic Lagoons: Dr. James N. Dornbush

The support of the Missouri Basin Engineering Health Coun-
cil under the Chairmanship of Mr. A. E. Williamson, Director,
Wyoming Division of Sanitary Engineering is gratefully ac-
knowledged.

The assistance for this project by the Water Quality Office,
Environmental Protection Agency, and the patient encourage-
ment provided by Mr. Otmar Olsen, the Grant Project Officer,
is acknowledged with sincere thanks.
                            147

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                       SECTION VIII

                        GLOSSARY

Acid Formers - Bacteria which metabolise organic matter in
the absence of dissolved oxygen with the formation of organ-
ic acids.

Active Microbial Mass - The living fraction of biological
sludges.

Aerated Lagoons - Large ponds that use mechanical aeration
for oxygen transfer.

Aerated Oxidation Pond - A large wastewater treatment pond
employing diffused aeration systems for mixing as well as
supplemental aeration.

Aerobic Bacteria - Single cellular, non-photosynthetic plant
cells which grow in the presence of dissolved oxygen.

Air Gun - A tube type aeration system employing a special
air chamber which discharges a slug of air periodically
like a gun.

Algae - Microscopic plants which carry out photosynthesis
in the presence of sunlight.

Alpha Coefficient - An oxygen transfer factor determined
by the chemical composition of the wastewaters and affecting
the rate of transfer of oxygen from the gas phase to the
liquid phase.

Anaerobic Lagoons - A deep pond designed to operate as a
combined sedimentation unit and an anaerobic digester.

Anionic Polyelectrolyte - Large complex organic molecules
which form insolublecompounds in water with a negative
electrical charge.

Beta Coefficient - An oxygen transfer factor determined
by the soluble chemical composition of the wastewaters and
affecting the saturation of oxygen in the liquid phase.

BOD  (Biochemical Oxygen Demand) - The quantity of oxygen
utilized by microorganisms in the stabilization of organic
matter at 20C over a period of time.
                           148

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Cage Rotor - A mechanical aerator employing a number of
rlat metal plates spaced at regular intervals along hori-
zontal rods suspended between two circular end plates and
rotated along a horizontal axis at a speed of less than
100 RPM.

Carbon Filter - A filter of activated carbon used to adsorb
organic matter from water.

Cationic Polyelectrolytes - Large complex organic molecules
which form insoluble compounds in water with a positive
electrical charge.

Chemical Precipitation - The destabilization and aggregation
of colloidal and finely divided suspended matter by the
addition of a floe forming chemical.

Chlorinated Hydrocarbons - Organic compounds of carbon,
hydrogen and chlorine.

Chlorination - The process of adding chlorine to water or
wastewaters.

Ciliated Protozoa - Single cell microscopic animals with
cilia for motility.

COD (Chemical Oxygen Demand)- A measure of the oxygen con-
suming capacity of wastewaters obtained by a 2 hr sulfuric
acid-dichromate refluxing.

Coliform Bacteria - Gram negative, non-sporing forming
bacilli that ferment lactose with the production of acid
and gas and are found primarily in the intestines of man
and animals.

Complete Mixing - A high degree of turbulent mixing in
which the fluid turnover is approximately one to two minutes.

Crustaceans - Aquatic anthropods having a body covered with
a hard shell or crust.

Denitrification - The process of microbial nitrate reduction
with the production of nitrogen gas.

Diffused Aeration - Aeration produced in a liquid by passing
compressed air through a diffuser.

Endogenous Mass - The mass of microbes remaining after
endogenous respiration had metabolised all of the biodegrad-
able cellular material.
                           149

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Endogenous Respiration - The microbial metabolism of intra-
cellular tissue.

Enteric Pathogens - Disease producing microorganisms that
normally grow in the intestines of warm blooded animals.

Facultative Aerated Lagoon - A large wastewater treatment
pond employing mechanical surface aerators which produces
aerobic zones around the aerators and allow solids to
settle out in quiescent areas.

Fecal Coliforms -  Coliform bacteria that are derived from
the intestinal tract of man and warm blooded animals.

Fungi - Non-photosynthetic, multicellular microscopic
plants that grow in water.

Inert Inorganic Mass - Inorganic suspended solids in waste-
waters,which remain insoluble.

Inert Organic Mass - Organic suspended solids in wastewaters
which are resistent to biological degradation in conventional
biotreatment systems.

Microorganisms - Tiny plant and animal organisms which can
be observed only by use of a microscope.

Microstraining - Process of removing suspended particles from
water by filtering through a woven metal cloth of a fine
mesh.

MPN (Most Probably Number) - The number of organisms per
unit volume based on statistical analysis normally used
for coliform bacteria.

Natural Purification - The stabilization of organic or in-
organic compounds by the microorganisms normally found in
nature.

Nitrification - Aerobic microbial oxidation of ammonia to
nitrites and then to nitrates.

Non-Biodegradable Suspended Solids - Organic suspended
solidsthat are not readily metabolised by microorganisms.

Oxidation Ditch - A modification of activated sludge which
utilizesa mechanical aerator to move the mixed liquor
around a circular ditch.
                            150

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Oxidation Ponds - Large ponds of shallow depth with long
fluid retention times which utilize symbiosis between
bacteria and algae.

Percolation - The flow of liquid downward through a filter-
ing medium.

Photosynthes is - The process of converting carbon dioxide,
water and inorganic salts into organic matter with energy
from light with chlorophyll as a catalyst.

Primary Sedimentation - The first stage of wastewater treat-
ment consisting of gravity separation of suspended solids.

Protoplasm - Cellular tissue within the microbial cell wall.

Raw Sewage - Untreated wastewaters.

Rock Filter - A submerged filter utilizing rocks as a media
for removing algae from oxidation ponds.

Rotifers - Multicellular, microscopic animals with cilia
that resemble rotating wheels when in motion.

Sand Filtration - A filter composed of graded sand designed
to remove small suspended solids.

Spray Irrigation - The spreading of wastewaters on agricul-
tural land by spraying.

Supernatant - The liquid standing above a sediment or pre-
cipitate.

Surface Aerators - Mechanical aerators which dissolve oxygen
in water by pumping the water into the air.

Suspended Solids - Solids in suspension in water which can
be removed by standard laboratory filtration techniques.

Symbiosis - Two organisms living together with the production
of a greater reaction than the organisms alone.

Turbidity - Finely dispersed suspended solids in water.

Virus -  Tiny microscopic mucleo protein particles which
multiply within specific hosts, creating a disease within
the host.

Waste Treatment Lagoons - Large ponds used for wastewater
treatment7
                            151

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Zooplankton - Microscopic animals in water.
                           152

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1
Access/on Number

w
5
2
Subject Field & Group



SELECTED WATER RESOURCES

ABSTRACTS
INPUT TRANSACTION FORM
Organization
   Title
       Waste  Treatment Lagoons - State of  the  Art
1 Q Authors)
James N
John W.
McKinney
. Dornbush
Vennes
1 z Project Designation
Project # 17090EHX
21 Note

29 Citation
23
    Descriptors (Starred First)

    Wastewater Treatment*, Water Pollution Control*, Aerated  Lagoons*,
    Anaerobic Lagoons*, Oxidation Ponds*, Sewage Treatment, Industrial
    Wastnwater Treatment.
25
   Identifiers (Starred First)
   Operation of Wastewater Treatment Lagoons*,  Design of Wastewater
   Treatment Lagoons*, Concepts of Wastewater Treatment Lagoons, Field
   Data from Wastewater Treatment Lagoons.
27
    Abstract
    This report  compiles  the State of the Art for wastewater treatment
    lagoons as existing in 1970 based upon the published literature and
    field evaluations.

    Wastewater treatment  lagoons comprise oxidation ponds,  aerated lagoons,
    and anaerobic  lagoons.  Oxidation ponds are large,  shallow ponds designed
    to treat  domestic  sewage from small communities or  subdivisions.  Aerat-
    ed lagoons use mechanical aeration devices to supply oxygen for the
    microbes  for treating domestic sewage and industrial wastes.   Anaerobic
    lagoons are  designed to treat primarily strong industrail wastes from
    meat processing industries.

    The evaluation of  current state of the art with biological theory
    offers new approaches for improving wastewater treatment lagoons.
Abstractor
  Ross E. McKinney
                         Institution
                              University  of
 WR:'02 (REV. JULY 1969)
 WRSI C
                        SEND, WITH COPY OF DOCUMENT. TO: WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                                             U.S. DEPARTMENT OF THE INTERIOR
                                             WASHINGTON, D. C. 20240
                                                  *U.S. GOVERNMENT PRINTING OFFICE: 1972-484-484/138 1-3

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