WATER POLLUTION CONTROL RESEARCH SERIES
17050 DAM 11/71
       APPLICATION OF ROTATING
     DISC PROCESS TO MUNICIPAL
       WASTEWATER TREATMENT
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, develop-
ment, and demonstration activities in the Water Quality
Office, Environmental Protection Agency, through inhouse
research and grants and contracts with Federal, State,
and local agencies, research institutions, and industrial
organizations.

Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Chief, Publications
Branch (Water) Research Information Division, R&M,
Environmental Protection Agency, Washington, D. C. 20460.

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  APPLICATION OF ROTATING DISC PROCESS

                    TO

     MUNICIPAL WASTEWATER TREATMENT
                    by

           Autotrol Corporation
           Bio-Systems Division
         5855 North Glen Park Road
        Milwaukee, Wisconsin  53209
                  for the

     OFFICE OF RESEARCH AND MONITORING

      ENVIRONMENTAL  PROTECTION AGENCY
          Project  No.  17050 DAM
         Contract  No.  lU-12-810
             November, 1971
For sale by flic Superintendent of Documents, U.S. Government Printing Office
           Washington, D.C. 20402 - Price 75 cents

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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 recommen-
dation for use.
                       ii

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                                ABSTRACT
 A prototype  package plant incorporating the  rotating  disc wastewater
 treatment process was  tested on municipal wastewater  at  the Village of
 Pewaukee, Wisconsin, to evaluate its  treatment  capabilities and estab-
 lish guidelines  for operation and testing of a  full-scale rotating disc
 demonstration plant soon to be put into operation  at  Pewaukee.  The
 package plant included a rotating bucket feed mechanism, ninety-one 1.75-
 meter diameter discs divided into two stages, and  a secondary  clarifier
 with a sludge-removal  mechanism.  Variables  tested included hydraulic
 loading, rotational disc speed, sludge recycle,  and wastewater tempera-
 ture as it varied with climatic conditions.

 At a hydraulic loading of 1.5 gpd/ft   of disc surface, the package plant
 achieved 87$ removal of BOD and 80$ removal  of  suspended solids to yield
' an effluent  of 20 mg/1 BOD and suspended solids  when  treating  effluent
 from the existing primary clarifier.   At the same  hydraulic loading, B$%
 removal of ammonia nitrogen was obtained to  yield  an  effluent  of  3.5 rog/1.

 Low maintenance requirements and low  power consumption were demonstrated
 by the rotating disc process during the test program.

 This report  was submitted in fulfillment of  Project 17050 DAM, Contract
 lit-12-810, under the sponsorship of the Environmental Protection  Agency.
                                    iii

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iv

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                       CONTENTS
Section                                          Page



   I     Conclusions                              1



  II     Recommendations                          3



 III     Introduction                             5



  IV     Process Description                      7



   V     Description of Test Unit                 9



  VI     Test Program                            19



 VII     Test Results                            23



VIII     Comparison to Previous Experience       55



  IX     Comparison to Other Processes           59



   X     Acknowledgments                         6l



  XI     References                              63



 XII     Glossary                                65



XIII     Patents and Publications                67



 XIV     Appendix                                69

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                          FIGURES


Number                                                 page

  1     Prototype Rotating Disc Package Plant           10

  2     Rotating Bucket Feed Mechanism                  11

  3     Molded Polystyrene Discs                        12

  It     Two-Stage Disc Assembly with Drive Motor        13

  5     Secondary Clarifier and Sludge Scoop            15

  6     Rotating Disc Package Plant Dtestails             17

  7     Pewaukee, Wisconsin,: fest Site                  20

  8     BOD Removal vs. Hydraulic: Loading               21*

  9     Effluent BOD Concentratdion vs.
        Hydraulic Loading                               2$

 10     BOD Removal Kinetics                            26

 11     Suspended Solids Removal vs.
        Hydraulic Loading                               29

 12     Effluent Suspended Solids Concentration
        vs. Hydraulic Loading                           30

 13     COD Removal vs. Hydraulic Loading               32

 ll;     Effluent COD1 Concentration vs.
        Hydraulic Loading                               33

 1^     Ammonia Nitrogen Removal vs.
        Hydraulic Loading                               3U

 16     Effluent Ammonia Nitrogen Concentration
        vs. Hydraulic Loading                           35
                            vi

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                    FIGURES (cont'd)


Number

  17    Ammonia Nitrogen Removal vs.
        Effluent BOD Concentration                       37

  18    Ammonia Nitrogen Removal Kinetics                38

  19    Ammonia Nitrogen Conversion Ratio
        vs. Hydraulic Loading                            39

  20    Ammonia Nitrogen Conversion Ratio vs.
        Degree of Ammonia Nitrogen Removal               1|0

  21    Kjeldahl Nitrogen Removal vs.
        Hydraulic Loading                                U2

  22    Effluent Kjeldahl Nitrogen Concentration
        vs. Hydraulic Loading                            1^3

  23    Total Nitrogen Removal vs. Hydraulic Loading     UU

  2k    Effluent Total Nitrogen Concentration vs.
        Hydraulic Loading                                1*5

  25    Power Requirement vs. Disc Speed                 U7

  26    Power Consumption vs. Degree of Treatment        1*8

  27    Sludge Production vs. Degree of Treatment        5>0

  28    BOD Removal Compared to Previous Testing
        in the U.S.                                      $6

  29    BOD Removal Compared to European Experience      8
                          VI1

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                      TABLES




Number                                         Page

  1     Rotating Disc Unit Specifications         16

  2     Average Wastewater Characteristics       19

  3     Sampling and Analysis Program            22

  k     Determination of Carbonaceous and
        Nitrogenous BOD                          2?

  5     Mixed Liquor Characteristics             5l

  6     Effect of Sludge Recycle on
        Treatment Efficiency                     53

  7     Comparison with Previous Test Unit       55
                       viii

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                                 SECTION I

                                CONCLUSIONS
 1.  The rotating disc method of wastewater treatment provides a. compact,
     highly efficient means of obtaining BOD, suspended solids, and
     ammonia nitrogen removal from domestic wastewater.

 2.  The simplicity of the process and its mechanical equipment result
     in a very low requirement for maintenance.

 3.  Low maintenance requirements and low power consumption make the
     rotating disc process well suited to package plant applications and
     for fulfilling wastewater treatment needs in remote areas.

 U.  The rotating disc method of wastewater treatment can achieve in
     excess of 90$ BOD and suspended solids removal and produce effluents
     of less than 15 mg/L BOD and suspended solids when operated at the
     proper hydraulic loading.

 5.  Carbonaceous BOD removal by the rotating disc system is first order
     with respect to BOD concentration up to approximately 90$ reduction.

 6.  At treatment levels above. 80$ BOD removal and effluents below
     35 rog/1 BOD, approximately 50$ of the remaining BOD is carbonaceous
     and 50$ nitrogenous.

 7.  Ammonia nitrogen removal by the disc system is first order with
     respect to ammonia nitrogen concentration.  Removals in excess of
     95$ are achieved, and effluents of less than 0.5 nig/1 ammonia nitro-
     gen are produced at the proper hydraulic loading.

 8.  Because carbonaceous BOD removal and ammonia oxidation are first
     order, the primary design criterion for rotating disc systems is
     hydraulic loading as gpd/ft2 of surface covered with biomass.
     Peripheral velocity of the rotating discs, and the number of stages
     of discs are also important design criteria.

 9,  The optimum rotational disc speed for BOD, suspended solids, and
     ammonia nitrogen removal is approximately 58 ft/min peripheral
     velocity (3.2 RPM on the test unit).

10.  BOD and suspended solids removal are unaffected by wastewater
     temperatures above 50F.  Ammonia nitrogen removal is unaffected by
     wastewater temperatures above 5UF.  Below these temperatures, lower
     hydraulic loadings are required for a given degree of treatment.

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11.  Power consumption at the optimum disc speed is 0.2 Hp-Hr/lb. BOD
     removed when providing 87$ BOD removal and an effluent of
     20 mg/1 BOD.

12.  BOD removal by the rotating disc system during this investigation
     compares well to that obtained during a previous investigation and
     demonstrates first order behavior over the range of lU? to 1*26 mg/1
     BOD domestic wastewater.

13.  BOD removal, during this investigation does not compare well to
     European experience.  The reason for this is thought to be the wider
     disc spacing used on European disc systems, which yields a longer
     retention time at a given hydraulic loading and therefore a higher
     degree of treatment.

lU.  Disc units which are operated in tanks closely contoured to the
     shape of the discs should have disc spacing greater than 0.5 inch,
     surface to surface, to obtain full utilization of the surface area.

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                               SECTION II

                            RECOMMENDATIONS
This investigation has allowed the evaluation of the rotating disc method
of wastewater treatment.  During the course of the testing, several
aspects of rotating disc process operation were revealed which warrant,
further investigation.  Most of these were beyond the scope of the pres-
ent investigation or could not be tested with the available test
equipment.  This testing was conducted oil a two-stage disc unit.
European experience indicates that three and four-stage, operation allows
significantly higher hydraulic loading for equal treatment.  Additional
testing on a four-stage disc system at various hydraulic loadings should
be conducted to verify the improved performance.

The disc spacing of the test unit in this investigation yielded^a;liquid
holding capacity less than that of European disc systems.  The, lower
retention time occurring at a given hydraulic loading resulted in a lower
degree of treatment than in European systems.  Additional testing at
various disc spacings will be required to determine the optimum disc
spacing which will maximize the effectiveness of the disc surface area.

All testing in this investigation was under constant flow conditions.
Diurnal flow variations and flow patterns encountered in other domestic
wastewater applications should be tested to determine their effect on
treatment efficiency by the disc process.

Because both stages of discs in this investigation were mounted on the
same shaft and driven by a single drive mechanism, the optimum rotational
velocity determined applies only when all discs in the system are rotated
at the same velocity.  In a multi-stage disc plant, there is probably an
optimum rotational velocity for each successive stage of discs as the
wastewater undergoes a progressively increasing degree of treatment.
Additional studies to optimize the rotational speed of each stage in a
multi-stage disc system would improve the already low power consumption
of the disc process.

Sludge production measurements from this investigation were erratic.
Additional sludge production measurements should be made on a multi-stage
disc system to more accurately determine its sludge production at various
degrees of treatment.

Sludge recycle rates tested in this investigation were too low to affect
any operating or performance parameters of the system.  Additional studies
at higher recycle rates should be conducted to determine the effect of
this process variable.

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Biological solids generated by the rotating disc appear to have char-
acteristics which would make them conducive to mechanical separation,
such as sand filtration or microscreening.  Tests should be conducted
on both secondary clarifier effluent and rotating disc mixed liquor to
establish the technical feasibility of mechanically clarifying rotating
disc process effluents.

It has been demonstrated in this investigation that any desired degree
of ammonia nitrogen oxidation can be achieved in the disc system by
operating at the proper hydraulic loading without adjustment of normal
municipal wastewater pH.  It would be of value to determine whether
ammonia nitrogen oxidation rates could be increased in the disc system
by chemically adjusting the pH of the mixed liquor of disc stages where
nitrification was occurring.
                j-                    .
Many of the above recommendations on further testing of rotating disc
systems can be incorporated into the testing and evaluation program for
the rotating disc demonstration plant at Pewaukee, Wisconsin.  This
will be done to the extent possible within the scope of the evaluation.

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                              SECTION III

                             INTRODUCTION
The rotating disc process is a secondary biological wastewater treat-
ment system.  It has been used for wastewater treatment in Europe for
12 years.  At present, there are over 600 commercial installations,
primarily in West Germany, France, and Switzerland, ranging in size
from 12 people to 100,000 population equivalent and treating a variety
of domestic and industrial wastes.  Research and development work has
been conducted on this process in the United States since 196?, and
several commercial installations are now in operation and under con-
struction in this country.

The object of this investigation was to test a rotating-disc unit
under field conditions with municipal wastewater and evaluate treat-
ment levels at various rates of hydraulic loading.

The results of the tests were to be compared to previous testing and
used to establish guidelines for the testing and evaluation of a
UOO,000-GPD rotating disc treatment plant constructed with Environ-
mental Protection Agency demonstration grant funds at the Village of
Pewaukee, Wisconsin.

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                              SECTION IV

                          PROCESS DESCRIPTION
The system consists of a number of large-diameter, lightweight plastic
discs, which are mounted on a horizontal shaft and placed in a semi-
circular shaped tank.  The discs are rotated while approximately
one-half of their surface area is submerged in the wastewater.  Imme-
diately after startup, organisms present naturally in the wastewater
begin to adhere to the rotating surfaces and multiply until, in about
one week, the entire surface area of the discs is covered with an
approximately 1/16 to 1/8 inch thick layer of biomass.

In rotation, the discs carry a film of wastewater into the air where
it trickles down the surface of the discs and absorbs oxygen.
Organisms in the biomass then remove both dissolved oxygen and
organic materials from this film of wastewater.  As the discs con-
tinue rotation through the bulk of the wastewater in the tank,
further absorption of dissolved oxygen and organic materials is
performed by the biomass.  Operating in this manner, the rotating
discs serve several functions:  provide a medium for the development
of a fixed biological growth, contact of the growth with the waste-
water, and aeration of the wastewater.  Shearing forces exerted on
the biomass as it is passed through the wastewater cause excess
biomass to slough from the discs into the mixed liquor.  This prevents
clogging of the disc media and maintains a constant microorganism
population on the discs.  The mixing action of the rotating discs
keeps the sloughed solids in suspension until the treated wastewater
carries them out of the disc sections for separation and disposal.

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                               SECTION V

                        DESCRIPTION OF TEST UNIT
Figure 1 shows the prototype rotating disc package plant used for the
investigation.  It consists of a wet well and rotating bucket feed
system, a two-stage rotating disc treatment system, and a secondary
clarifier with a rotating sludge scoop, all incorporated into a single,
semi-circular shaped tank.  This package system is intended to operate
in conjunction with primary treatment and sludge disposal facilities.

In operation, primary treated wastewater flows into the wet well,
where a series of buckets, attached to the same shaft that rotates
the discs, deposit it via a trough into the first stage of discs (see
Figure 2).  An overflow connection maintains a constant level in the
wet well and, therefore, a constant feed rate.  At a given disc speed
the feed rate is varied by changing the number of feed buckets.

The disc section contains ninety-one 1.75-meter diameter discs, which
are divided into two approximately equal-size stages.  The stages are
divided by a bulkhead and connected by a trough, so that they operate
in series.  The discs, which are molded from expanded polystyrene beads,
are 0.5 inch thick and spaced on 1.0-inch centers.  Figure 3 shows
construction features of the type of discs used in the package plant.
There are eleven intrinsically molded bosses on the surface of each
disc, which act as spacers.  Eight of the bosses are located near the
perimeter of each disc, two are near the center, and one forms the hub
of the disc.  Rods pass through holes in the bosses and are attached
to spider-like arms located at each end of a stage of discs.  The arms
are attached to the main shaft, which passes through all the discs in
the package plant.  The system of main shaft, spider-arms, connecting
rods, and bosses uniformly distributes the driving torque applied to
the discs and provides support to the discs as they are rotated through
the wastewater.  The type of disc and support structure described here
has been used in Europe for 12 years without any reported mechanical
failure of the discs.

Power is supplied to the discs by a 1/6-hp motor, which is mounted on a
structure between the disc section and the secondary clarifier.  Power
is transmitted to the main shaft by the friction of a chain passing
over a circular metal strip, the same diameter as the discs and mounted
on the last set of spider arms.  See Figure U.

Mixed liquor passes from the last stage of discs into the clarifier
through an opening in the bulkhead separating them.  To minimize the
effects of turbulence, the opening is located in the corner of the
clarifierj and a pipe directs the flow against the bulkhead beneath the
water level.

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              Figure 1
Prototype Rotating Disc Package Plant
                  10

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           Figure 2
Rotating Bucket Feed Mechanism
              ! 1

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                             SIZES AVAILABLE
                             6 FT. AND 10FT. DIA.
     Figure

Molded Polystyrene Discs
 MOLDED
 POLYSTYRENE
 DISCS
                                             DISC-NOMINAL
                                         THICKNESS OF V2 IN.
                              RIGIDITY MAINTAINED
                              BY MOLDED SPACERS

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                Figure 4
Two-Stage Disc Assembly with Drive Motor
                    i

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Settled sludge is removed by the rotating scoop and reservoir system
shown in Figure 5.  The scoop system is driven independently at 2 to
6 rph to allow adjustment for sludge removal requirements.  As the
empty reservoir passes into the water, it draws sludge up through the
scoop and hollow connecting arms until it is full.  Then, as the
reservoir leaves the water, it empties the sludge through hollow
support arms into the hollow drive shaft.  From there it flows out
of the system for treatment and disposal.  Clarifier overflow passes
over a weir to an outlet located in the opposite corner from the inlet.

The clarifier has an operating volume of U55 gallons and an overflow
area of 32 square feet.  The overall size of the package unit is ap-
proximately 15 feet long, 6.5 feet wide, and 6.5 feet high.  It has a
design capacity of 8,000 gpd.

Additional details on the test unit are listed in Table I and shown in
Figure 6.
                                    1U

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              Figure 5
Secondary Clarifier and Sludge Scoop
                  L5

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                        TABLE 1



           Rotating Disc Unit Specifications






 1.  Disc Velocity                  2  - 5 RPM



 2.  Disc Diameter                  5.7U ft.  (1.75 m)



 3.  Number of Stages               2



 U.  Number of Discs - Stage 1,  U5



                     - Stage 2,  U6
                       Total:        91



 5.  Total Effective Disc Area      U,600 ft2  (1*28 m2)



 6.  Disc-Tank Volume,  Gross         700 gal.  (2.65 m )



                       Net          280 gal.  (1.06 m3)



 7.  Submerged Volume of Discs      U20 gal.  (1.59



 8.  Clarifier, Surface Area         32 ft2 (2.98  m2)



 9.  Clarifier, Volume               U55 gal. .(1.73



10.  Clarifier, Weir Length         5 ft. (1.52m)








 * Based upon a bio-mass thickness of 0.1 inches  (2.5 mm)
                          16

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                                    Figure 6
                         Rotating Disc Package Plant Details
                               1st Staae
Feed Mechanism,
  6'-2"
                                                         Disc Drive Motor

                                                            Effluent

                                                                    Effluent
                                                                    Discharge

                                                                    Sludge
                          Scoop Drive
                          Secondary Clarifier
                                                                            Sludge
                                                                           Discharge

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18

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                               SECTION VI

                              TEST PROGRAM
The package plant was installed in a garage-like structure to protect it
from wind, heavy precipitation, and freezing temperatures and was located
within the grounds of the treatment plant of the Village of Pewaukee,
Wisconsin.  Figure 7 shows the location of the test unit within the
treatment plant grounds.

The present Pewaukee treatment plant is rated at 0.3 MGD and includes an
uncovered trickling filter, primary and secondary clarifiers, an
anaerobic digester, and sludge drying beds.  Secondary sludge is drained
into the wet well, usually during night hours when low flows are ex-
perienced.  Sludge from the primary clarifier is normally pumped to the
digester twice daily.  Digester supernatant is returned to the wet well
during these pumping periods.  The primary clarifier effluent employed
in this investigation, therefore, contained unknown amounts of anaerobic
digester supernatant and trickling filter sludge.

Tests were begun in November, 1969, and conducted for 6 months under
the contract.  At its own expense, Autotrol Corporation extended the
test period to October, 1970, to provide a full year of operating data
and allow a more complete study of the process.  During the year of
operation, the primary effluent had the characteristics shown in Table 2.
                                 TABLE 2


                   Average Wastewater Characteristics


                                           mg/1
                   BOD

                   Suspended Solids        128

                   COD                     323

                   Ammonia Nitrogen         18.2

                   Kjeldahl Nitrogen        28.9

                   Phosphorus               11.7

                   Temperature, F          
                                    19

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ro
                Primary
                Clarifier
Bldg. for
Rotating
Disc Unit
      Secondary
      [Clarifier
                                   Chlorine
                                   Contact
                                    Tank
                                                                  Figure 7
                                                         Pewaukee, Wisconsin, Test Site
                                          To Pewaukee  River

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The test unit was connected to the overflow of the existing primary
clarifier.  An overflow piping arrangement was used in the wet well
of the test unit to obtain a constant depth of wastewater which
maintained constant feed rates.  Variables investigated included
hydraulic loading of 5>0 to 920 gph, rotational disc speed of 2 to $ rpm,
sludge recycle of 1 and 2% of wastewater flow, and wastewater tempera-
ture as it changed with the climate.

A relatively wide range of mixed liquor temperatures was encountered in
this investigation.  Lower temperatures are believed to be related to
the amount of infiltration in the Pewaukee sewerage system during spring
periods of thawing and rainfall.

Since the experimental flow rates were relatively low compared with the
total Pewaukee plant flow, all discharge lines from the test facility
were directed to the existing trickling filter.  These included wet well
overflow, effluent, and secondary clarifier sludge.  Sludge was dis-
charged by gravity from the clarifier into a 0-gallon drum.  A sump
pump transferred the sludge to the effluent discharge line connecting
the test unit with the trickling filter.

When tested, recycling of sludge was accomplished by a peristaltic pump
connected to the base of the $0-gallon sludge drum.  This pump was
actuated about 10 minutes per hour by an automatic timer and delivered
the recycled waste sludge to the inlet of the first stage of discs.

Four (li) NAPPE-PORTA-POSITER samplers were installed to take twenty-
four hour composite samples at the following four sampling points: the
wet well, the first stage mixed liquor, the second stage mixed liquor,
and the effluent from the secondary clarifier.  When it was not possible
to obtain a twenty-four hour composite sample, a grab sample was taken
for analysis.  In June, 1970, of the test period, these samplers were
replaced with samplers which were equipped with refrigeration.

Samples were taken, and laboratory analyses were performed as indicated
in Table 3.  Procedures employed in these analyses were in accordance
with the "Standard Methods for The Examination of Water and Wastewater,"
Twelfth Edition, 1965, APHA.AWWA. WPCF.
                                   21

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                           TABLE  3

                Sampling and Analysis  Program


Analysis                            Sampling Points    *

Temperature                            B

pH                                     A,  D

Dissolved Oxygen                       A,  B, C,  D

Chemical Oxygen Demand                 A,  D

Sludge Solids                          D

Settleable Solids                      A,  B, C,  D

Total Suspended Solids                 A-,  B, C,  D

Volatile Suspended Solids              A,  B, C,  D

Biochemical Oxygen Demand              A,  D

Total Phosphorus                       A,  B, C,  D

Dissolved Phosphorus                   A,  D

Ortho-Phosphorus                      .A,  B, C,  D

Kjeldahl Nitrogen                      A,  B, C,  D   .

Ammonia Nitrogen                       A,  B, C,  D

Nitrate Nitrogen                       A,  B, C,  D

Nitrite Nitrogen                       A,  B, C,  D
* A  Wet Well, B  First Stage Mixed Liquor, C  Second Stage
  Mixed Liquor, D  Effluent from Secondary Clarifier.
                            22

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                              SECTION VII

                              TEST RESULTS
The test unit was operated for a period of several weeks under each set
of operating conditions.  Data collected each day is presented in the
Appendix.  Arithmetic averages of the data collected under each set of
operating conditions are also presented in the Appendix.  The averages
were used for all data correlations.  The majority of the.following
correlations are presented as a function of hydraulic loading, which has
been found to be the primary design criterion for the rotating disc
process.  Hydraulic loading is measured as the amount of wastewater flow
per unit of time per unit of surface area covered by biological growth.

BOD Removal

Figures 8 and 9 show percent removal and effluent concentrations for
BOD as a function of hydraulic loading.  Retention time in the disc
sections is also shown for purposes of reference.

Separate loading curves are drawn for the disc speed range of 3.2 to
5 RPM and for 2 RPM for wastewater above 50F, and 5 RPM for wastewater
below 50F.  The data points at 3.2 RPM and U.3 to 5 RPM appear to
follow the same correlation, so a single curve was drawn to include
this entire range of disc speed.  This was done for all data correla-
tions at wastewater temperatures above $0F.

At a hydraulic loading of 1.0 GPD per ft2, 90$ BOD removal was
Obtained with this two-stage system.  An effluent BOD concentration of
20 mg/1 was obtained at a loading of 1.5 GPD/ft2, which represents 90$
overall removal when including primary treatment on an average municipal
wastewater.  When treatment requirements call for just roughing treat-
ment, the disc system can obtain 70$ removal at a loading of U.8 gpd/ft .

Rotational disc speed had a significant effect on treatment efficiency.
While 3.2 and U.3-5 RPM gave very similar performance, 2.0 RPM gave
significantly lower perfornace over the entire range of hydraulic loads
tested.  The reasons for this are the increased efficiency of mixing
within a stage, more effective contact between the biomass and the
wastewater, and increased aeration rate at the higher speeds.

Wastewater temperature does not appear to affect BOD removal above 50F.
Below 50F, BOD removal rates decrease significantly; however, equal
treatment can be obtained at reduced hydraulic loading.

Figure 10 reveals some aspects of the kinetics of BOD removal in the
disc system.  Five-day BOD removal (solid line) is close to first order
up to 70 to 80$ reduction.  At higher degrees of treatment, the reaction
rate decreases considerably.  This can be explained by the data in
Table U.
                                   23

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(0
>
O
Q
O
    100-j
     80-
     60-
40-
               SYMBOL
          O-0-O
                                            Figure 8


                                 BOD Removal vs.  Hydraulic Loading
DISC RPM


4.3 - 5

3.2

2.0

5.0
ML TEMP, F


50 - 67


58 - 68

63 - 67

39 - 49
     20-
             Retention Time, Minutes
            o  o      o    in
            CO  
-------
fO
vn
     Q
     O
     -P
     c
     
-------
tn
C
-H.
0)
Q
O
ffl
     4 -
                                      Figure  10
                                 BOD Removal  Kinetics
                                 Operating Conditions


                                 3.,2-5 RPM
                                 Temp.> 50*P

                                  ~  Total BOD

                                  *~  Carfooraaceouis  BOD
                 20
       40        60

Retention Time, Minutes
       26
80
100

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                           TABLE k


      Determination of Carbonaceous and Nitrogenous BOD

Date
9-1
9-8
9-9
9-9 (6-day)
10-1
Flow
GPH
300
300
300
300
503

RPM
2
2
2
2
2
Inlet
APHA*
168
169
I61i
182
137
BOD
ATU**
157
165
173
176
._.
Outlet
APHA
32
28
33
k3
3k
BOD
ATU
16
16
16
17
26
 ^American Public Health Association Method ("Standard Methods")
**As above with 0.5 rog/1 allylthiourea in dilution water to
  suppress nitrification.    Reference (l).
                             27

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Several tests were conducted to determine the proportions of carbonaceous
and nitrogenous BOD in the disc system effluent.  Addition of allyl-
thiourea to the BOD^dilution water to suppress nitrification had no
significant effect, on the BOD of primary effluent.  However, use of
allylthiourea in BOD tests of disc system effluent indicates that efflu-
ents of less than 35 mgA BOD consist of about 50$ nitrogenous BOD.
Carbonaceous BOD removals then corresponding to 80 and 90$ "Standard
Methods" BOD removal would be 90$ and 95$, respectively.  A reason for
the extent of-nitrification occurring in the 5-day BOD test is the
presence of nitrifying organisms in the effluent from the final stage of
discs.

If all effluents of 80$ or better BOD removal are assumed to be 50$
nitrogenous (this has been verified in subsequent"tests up to 95$ BOD
removal), the kinetics of carbonaceous BOD removal can also be shown in
Figure 10 (dotted line).  Carbonaceous BOD removal appears to be first
order up to 90$ reduction.  Above this degree of treatment, carbon-
aceous BOD removal remains first order, but at a reduced rate because
of the predominance of a nitrifying culture on the discs.

Figure 10 is based on test data for wastewater above 50F.  A similar
relationship can be developed for wastewater below 50F, however, only
limited data is available.

Suspended Solids Removal

Figures 11 and 12 show suspended solids removal and effluent concentra-
tions as functions of hydraulic loading on the disc sections and
clarifier;  For a disc section loading of 1.5 to 2.5 gpd/ft2 and a
clarifier overflow rate of 200 to 380 gpd/ft2, 80$ suspended solids re-
duction was obtained.  This yielded an effluent concentration of about
20 mg/1.

A 380-gpd/ft2 overflow rate in the secondary clarifier corresponds to a
retention time of about 70 minutes.  This relatively low retention time
for a 380 gpd/ft2 overflow rate is due to the semi-circular shape and
29-inch maximum sidewater depth of the clarifier.  A suspended solids
removal of 90$ and an effluent of 11 mg/1 were produced at a disc
surface loading of 1.0 gpd/ft2.

Disc speed did not have as significant an effect on suspended solids
removal.  While higher percentage removals were obtained at 3.2 and
U.7 RPM than at 2 RPM, lower effluent solids concentrations were pro-
duced at 2 RPM.  The reason for this is that lower influent solids
concentrations existed during the 2 RPM tests.
                                  28

-------
(Si
    O
    e
    m
    'O
    H
    rH
    O
    W5

    d
    0)
    T3
    C
    0)
    a
    CO
                          Clarifier Overflow Rate, GPD/Ft'
        100'
                  100
                 200
300
400
500
600
700
800
         80-
         60-
40-
         20-
                                                                  Figure 11
                                                            Suspended Solids Removal
                                                            vs.  Hydraulic Loading
                                2         3         4          5
                           Hydraulic Loading on Disc Surface,

-------
   100-

    90-

    80-
hJ

2   70-
en
-j   60-
r^
o
CO
CD
cu
en
d
to
M-l
W
40J
C   30-
0)
20-

10-
     0
                                     Figure 12
               Effluent Suspended Solids Concentration  vs.  Hydraulic Loading
                                         SYMBOL
                                               DISC RPM  ML TEMP.,  F
                                                               54
                                                               58
                                                               63
                                                               39
                                                                67
                                                                68
                                                                67
                                                                50
       0
                                                4
                                                      I
                                                      5
                   Hydraulic Loading on Disc Surface, GPD/Ft"

-------
Wastewater temperature affects suspended solids removal in the same
manner as BOD removal j i.e., below 50F, lower hydraulic loadings are
necessary to attain the same removal.  The mixing action of the discs
appears to flocculate suspended solids very well at all speeds tested
and indicates potential for simultaneous biological treatment and
flocculation of nutrients with chemical precipitants.  The suspended
matter remaining in the clarifier effluent is filamentous and
flocculent and would appear to filter well in either a sand filter
or a micros creen.

COD Removal

COD reduction in Figures 13 and lU shows relationships of hydraulic
loading and disc speed similar to those for BOD and suspended solids
removal.  One difference is that at wastewater temperatures below
50F some chemically oxidizable materials are extremely resistant to
biochemical oxidation.  COD reduction at 2 gpd/ft2 was not signif-
icantly different from that at 0.25 gpd/ft2.

Ammonia Nitrogen Removal

Figures 15 and 16 show ammonia nitrogen reduction and effluent concen-
tration as a function of hydraulic loading.  Separate loading curves
are again shown for the different disc speeds and wastewater tempera-
tures.  At a hydraulic loading of 1.5 gpd/ft2, where a 20 mg/1 effluent
BOD was produced, about 85$ removal of ammonia nitrogen was also
achieved.  An effluent concentration of less than 1.5 mg/1 was produced
at a loading of 1.0 gpd/ft2.  At still lower loadings during tests on
wastewater below 50F, effluents of less than 0.5 mg/1 ammonia nitrogen
were produced.  Ammonia nitrogen analyses during the low temperature
tests were reported to the nearest mg/lj therefore, the reported values
of 0.0 mg/1 actually represent the range 0.0 to 0.5
The rotating disc method of wastewater treatment is capable of achieving
high degrees of ammonia removal in short retention times for two reasons.
One is that the system operates as a fixed film biological reactor in
which a "captive" population of microorganisms is able to acclimate it-
self to the particular wastewater it is treating.  The other is that by
arranging discs in a series of stages, the fixed cultures in successive
stages each adapt to the wastewater as it undergoes a progressively
increasing degree of treatment.  In the case of the two-stage unit
tested in this investigation, the first stage developed a culture
adapted to metabolizing carbonaceous BOD.  With the majority of the
carbonaceous matter removed from the wastewater, the second stage then
developed a nitrifying culture which metabolized the nitrogenous matter.
                                    31

-------
      100"
       80-
       60-
                                                    Figure 13
                                          COD Removal vs. Hydraulic Loading
       40-
ro
SYMBOL
o-e-O
EMD-H
DISC RPM
4.3 - 5
3.2
2.0
5.0
                                  ML TEMP.
54 - 67
58 - 68
63 - 67
39 - 50
       20-
                             T
                             2
                                     I
                                     4
                                              i
                                              6
                        Hydraulic Loading/ GPD/Ft'

-------
  125-,
                                      Figure  14
                     Effluent COD Concentration vs. Hydraulic  Loading
  100-
O-
Q
O
U
   75-
   50-
   25-
                                        tjL  TEMP. , F

                                        54 - 67

                                        58 - 68

                                        63 - 67

                                        39 - 50
W
                I
                1
n          i          l          i
 23          4      2    5
 Hydraulic Loading,  GPD/Ft
I
6
l
1

-------
   100-



    90-



    80-



    70-
>   60H
C
O
    50-
    40-
    30-
    20-
    10-
                                            Figure 15
                          Ammonia Nitrogen  Removal vs.  Hydraulic Loading
DISC RPM   ML TEMPy F
           54 - 67

           58 - 68

           63 - 67

           39 - 50
                              Hydraulic Loading,  GPD/Ft'

-------
0)
tn
O
M
-P
-rH
c
O
-P
0)
iH
4-1
w
    20 -i
    15 -
    10 -
     5 -
     0 -
                                                          Figure  16
                                             Effluent Ammonia Nitrogen Concentration
                                                   vs. Hydraulic Loading
                                                               ML TEMP, F
           54
           58
           63
           39
67
68
67
50
                            Hydraulic Loading
                           "I	1	
GPD/Ft'
       T
       5
           1
           7
T
 1

-------
This is shown graphically in Figure 17.  Ammonia nitrogen removal did
not begin in this two-stage system until the BOD concentration had been
reduced to about 60 mg/1.  At this point, ammonia removal began and
increased rapidly until, at a remaining BOD concentration of about
12 mg/1, ammonia nitrogen removal was virtually complete.  This rela-
tionship was true for all disc speeds and wastewater temperatures.

The data on ammonia removal at the higher disc speeds and temperature
range is plotted as a function of retention time in Figure 18.  The
straight-line relationship shows that ammonia removal in the disc system
is first order with respect to ammonia concentration at least up to 9h%
removal and down to 1.3 mg/1 effluent ammonia nitrogen.  The same type of
relationship can be shown for low wastewater temperature, however, only
limited data is available.

Because both carbonaceous BOD and ammonia nitrogen removal are approx-
imately first order with respect to carbonaceous BOD and ammonia nitrogen
concentration, hydraulic loading is the primary design criterion for the
rotating disc process.

Most of the ammonia nitrogen removal consists of oxidation to nitrate
and nitrite nitrogen.  Figure 19 shows the ration of nitrate and nitrite
nitrogen produced per unit ammonia nitrogen removed for the various
disc speeds and wastewater temperatures tested.  At the higher hydrau-
lic loadings, a greater proportion of the ammonia removal is attributable
to cell synthesis.  At the lower loadings, where nitrifying organisms
predominate, a greater proportion of ammonia removal is conversion to
nitrate and nitrite.  This data is generalized for all disc speeds and
temperatures in Figure 20 as a function of degree of ammonia removal.
It shows that a maximum of about 80/S conversion to nitrate and nitrite
is obtained at the point of virtually complete nitrification.  The
other 20$ is accounted for by cell synthesis, ammonia stripping by the
discs, and possibly some denitrification.

All tests in this investigation were conducted at normal municipal
wastewater pH.  The pH of wastewater is reported to have a significant
effect on the rate of biological nitrification.^)   it would be a
worthwhile investigation to attempt to accelerate nitrification rate
by chemical addition for. pH adjustment in later stages of a.multi-stage
disc system.  This would be especially important for reducing surface
area requirements when wastewater temperatures were below $0F.
                                    36

-------
VjJ
-0
   m
   >
   o
   E
tr>
O
M
-P
-H
2-

(0
H
G
O
       lOO-i
        80-1
     60-
        40-
        20-
                                                        Figure 17
                                                 Ammonia Nitrogen Removal vs.
                                                 Effluent BOD Concentration
                                                 SYMBOL    DISC RPM  ML TEMP,  F
                                                        4.3 - 5

                                                        3.2

                                                        2.0

                                                        5.0
54 - 67

58 - 68

63-.- 67

39 - 50
                                25                  50
                                     Effluent BOD Concentration,  mg/1
                                                                       75

-------
Cn
fi
H
c
H
OJ
g
c
0)
tn
O
M
-P
H
3

n)
H
C
O
  100

   90

   80

   70


   60


   50



   40-




   30-
   20 J
    9-


    8

    7
    5



    4-1
         Figure  18


Ammonia Nitrogen Removal Kinetics






     Operating Conditions
     3.2 - 5  ^.PM

     Temp. >  54F
                T          I          I           I

                20         40        60         80

                     Retention Time, Minutes
                                 100
                             38

-------
VjJ
    0)

    O
    E
    0)
    -P
    H
    m
    -H
    -p
    H
    c
O
d
T3
O
H
CM
    (1)
    tn
    O
   -H
   a
    (N
   O
   S
    I
         1.0
          .8 -
      .6 -
          .4-
      .2 -
                        Figure 19
Ammonia Nitrogen Conversion Ratio  vs.  Hydraulic Loading


                             SYMBOL  DISC RPM  ML TEMP, F
      l*J
                                      4.6 - 5.0 54 - 67

                                                58 - 68

                                                63 - 67

                                                39 - 50
                                                    H GMZI  3.2
                                                         2.0
                       I
                       1
                              I
                              2
                     r
                     3
                                                             5.0
I
5
I
6
I
7
                                    Hydraulic Loading, GPD/Ft"

-------
      1.0'
P
H

3  O
3  g
O  

-------
Kjeldahl Nitrogen Removal

Kjeldahl nitrogen removal and effluent concentrations shown in Figures 21
and 22 follow patterns very similar to ammonia nitrogen removal.  At a
given hydraulic loading, removal percentages are somewhat lower and
effluent concentrations somewhat higher than for ammonia nitrogen.  The
difference is attributable to residual soluble and colloidal organic
nitrogen and organic nitrogen in the suspended matter remaining in the
clarifier effluent.

Total Nitrogen Removal

Total nitrogen removal did not exceed 60$, and effluent concentrations
did not go below 10 mg/L under any of the test conditions.

Total nitrogen removal was accomplished primarily through cell synthesis
and settling, although ammonia stripping and possibly some denitrification
are likely to have occurred.  The removal limits of 66%and 10 mgA in
the effluent are imposed by formation of nitrate and nitrite nitrogen
from ammonia by nitrifying organisms.

Some correlation exists among hydraulic loading, disc speed, and waste-
water temperature as they affect nitrogen removal and effluent nitrogen
concentrations in Figures 23 and 2k.  The greater removal of nitrogen at
the higher disc speeds and wastewater temperatures reflects greater bi-
ological activity and incorporation of nitrogen into cell synthesis
under these conditions.  Ammonia stripping would also be more signifi-
cant at the higher temperatures and disc speeds.

Phosphorus Removal

Total phosphorus removals in the data summary in the Appendix vary gen-
erally from 10 to 30$ with an overall average of about 20$.  No apparent
correlation could be found between phosphorus removal and any of the
primary operating parameters of the system.  On the average, 0.02 units
of phosphorus were removed'per unit BOD removal.  This is higher than
the normal phosphorus requirement in biological wastewater treatment of
0.01 unit per unit of BOD present.  The difference is likely due to
flocculation and settling of organically bound phosphorus, because
orthophosphorus concentration generally increased rather than decreased
through the disc unit.

-------
f>O
   O
   e
   0)
   c
   a)
  -P

  -H
   0)
  o\o
100




 90





 80





 70-





 6CL





 50-





 40.





 30_





 20-
                                  Figure 21

                 Kjeldahl Nitrogen  Removal vs. Hydraulic  Loading
                                                         DISC  RPM  ML TEMP, F
54^ -67


58 - 68



63 - 67


39 - 50
                                 Hydraulic Loading, GPD/Ft'

-------
     25-1
o
s
c
0
H
4J

-------
  rH
  (0
  >

  i
S
  -p
  -H
  o
  H
  <#>
100 -

 90 -

 80 -

 70 -

 60 -

 50 -

 40 -

 30 -

 20 -

 10 -
         0
                           SYMBOL   DISC RPM   ML TEMP, F
                           o-o-o
                           EMD-Q
4.3 - 5
3.2
2.0
5.0
50 - 67
58 - 68
63 - 67
39 - 49
                       Figure  23
                  Total Nitrogen  Removal
                  vs.  Hydraulic Loading
                               1                              I
                               2         3         4.5
                                 Hydraulic Loading, GPD/Ft2

-------
    50 -|
                                     Figure 24
             Effluent  Total Nitrogen Concentration vs.  Hydraulic Loading
 O
 H
 -P
 td
 M
 -p
 fi
. 0)
 O
 c
 O
 O
 rH
 rfl
 4J
 O
 EH
 
-------
Power Consumption

The expanded polystyrene used for disc fabrication is very buoyant.
In operation, the buoyancy of the discs offsets the weight of the
biomass and the disc support structure, so that power to overcome
friction between the biomass and the wastewater is the only power
required for rotation.  Figure 25 shows power measurements made on
the package plant as a function of disc speed.

Power requirements were determined by mounting a hydraulic motor in a
cradle and measuring reaction torque at various speeds.  (See Figure 5.)
Very little power is required to operate the package plantj however,
power requirements do increase rapidly with disc speed.  Previous cor-
relations have shown package plant performance at 3.2 and U.3-5 rpm to
be superior to that at 2.0 rpm.  In spite of this, Figure 26 shows that
a speed of 2.0 rpm makes more efficient use of power for all the treat-
ment levels obtained.  However, considering that much less surface area
is required for a given degree of treatment, the increased power con-
sumption at higher disc speeds seems justified.

At the disc speed of 3.2 rpm, 5.2 lb. BOD are removed per hphr for
87$ BOD reduction through the discs and an effluent of 18 mg/1 BOD.
This power consumption converts to 8 HP per MGD plant capacity or 0.2
hp-hr per 1,000 gal. of wastewater treated.  This power requirement
applies to consumption by the discs and bearings only and does not
include motor or drive inefficiencies.

Power consumption by the rotating disc process would be optimized
further than what was accomplished during this investigation.  In
determining the optimum disc velocity, it was necessary by nature of
the construction of the test unit to operate both stages of 'discs at
the same rotational velocity.  In a multi-stage disc system, it seems
likely that each successive stage of discs would have an optimum
velocity which would decrease as the degree of treatment increased.

Sludge Production

Sludge production by the test unit was calculated by subtracting the
suspended solids concentration in the clarifier effluent from the
suspended solids concentration in the second stage of discs.  This
difference represents the amount of sludge solids which settled in the
clarifier.  Dividing this by the decrease in BOD concentration through
the test unit yields sludge production as sludge produced per unit BOD
removed.

-------
   0.30-1
   0.25 -
         Figure 25

Power Requirement vs.  Disc Speed
   0.20 -
   0.15 -
O
a
   0.10 -
   0.05 -
                  I
                  1
                    Disc Speed,  RPM
                            I          T
                            4          5
I
6

-------
                                     Figure 26
                     Power  Consumption vs. Degree  of Treatment
o
0)

o

0)
   Q
   O
   m
t-  xi
CXI  rH
  M
  X
  I

  ex
  K
o

-p


to

o
u

0)

o
        20 1
        18 -
        16 -
        14 -
        12 -
        10 -
         8 -
         6 _
         4  _
         2 -
                                                                                   ML TEMP

                                                                          DISC RPM  F
                                                                  OO-0  4.3-5.0
                                            75
                                    % BOD Removal

-------
Sludge production as a function of degree of treatment is presented in
Figure 27.  The data is scattered, which may indicate difficulty in
obtaining accurate mixed liquor samples.  Sludge production appears to
be much higher when treating wastewater below 5>0F.  NO consistent
effect of disc speed can be noted.  Sludge production does appear to
decrease as the degree of treatment increases as would be expected.
At a BOD removal of 86%, which would correspond to an effluent of
20 mgA BOD> 05 to 0.6 lb. sludge were produced per Ib. BOD removed.
Sludge solids were 80$ volatile under all test conditions.

Sludge production will be examined more closely during testing of the
demonstration plant at Pewaukee.

Mixed Liquor Characteristics

The parameters of pH, dissolved oxygen concentration, and suspended
solids for the mixed liquor of the two stages of discs are summarized
in Table 5.

For wastewater above $0F, suspended matter decreased from Stage 1 to
Stage 2 to a concentration generally under 100 mg/1.  Mixed liquor
solids are filamentous and very dense and appear to settle and thicken
well.  They also would appear to be readily removed by mechanical
means, such as sand filtration or microscreening.  In treatment
applications where an alternative to a settling tank for secondary
clarification is desirable, mechanical separation may be possible when
using the rotating disc system for secondary treatment.  This is an
area which warrants investigation.

For wastewater temperatures below 0F, suspended matter generally
increased from Stage 1 to Stage 2 to concentrations ranging from 130
to 2^0 mg/l  This accounts for the higher calculated sludge produc-
tion rate at lower wastewater temperatures.

Effluent pH varied from 7.2 to 8.0 at wastewater temperatures above 0F,
Below 50F, pH varied from 7.6 to 8.5  Higher pH values at the colder
temperatures may have contributed to the high degrees of nitrification
obtained in spite of the low temperatures.  A pH of 8.5 is near the
optimum reported for biological nitrification. (2)

Disc speed may also have had an effect on pH.  At 2 RPM, pH ranged from
7.2 to 7.6.  At 3.2 to h.7 RPM, pH ranged from 7.6 to 8.0.  More effec-
tive stripping of dissolved C02 may be the reason for the higher pH
values.  The higher pH values could have contributed to better nitri-
fication at the higher disc speeds.
                                          AWBhlKC LIBRARY U.S. EPA
                                  1*9

-------
   1.50
0)
>
O
e
0)
  1.25
H
c
Q)
13
0)
U
  0.75-
tn
'Ci
d
   0.50-
   0.25-
                           Figure 27
                Sludge Production vs. Degree of Treatment
                 SYMBOL

                 Q-O-O.
 DISC RPM  ML TEMP.
                 70
 4.3  -  5.0

 3.2

 2.0

 5.0
50 - 67

58 - 68

63 - 67

39 - 49
 T         I

75        80
    % BOD Removal
          85
 I

90
 I

95

-------
           TABLE 5




MIXED LIQUOR CHARACTERISTICS




    TEST PERIOD AVERAGES
Test Period
Dates

11/13-12/19

12/23-1/19

1/20-2/9

2/10-2/13

2/25-3/2

3/3-3/9

U/l-5/15

5/20-6/5

6/10-6/19

6/22-7/17

7/22-8/7

8/12-8/17

8/18-8/21

8/2U-8/29

8/31-9/11

9/1U-9/25

9/28-10/3

10/7-10/23

Disc
Stage

1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
Susp.
Solids
(mg/1)
275
99
228
122
1U6
200
202
256
250
131
15U
167
138
97
268
123
238
126
132
91
171
U9
128
72
196
89
167
96
170
50
139
8U
IQU
60
88
121

RPM

5
5
5
5
5
5
5
5
5
5
5
5
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
3.2
U.3
U.3
U.6
U.6
U.7
U.7
2.0
2.0
2.0
2.0
2.0
2.0
U.7
U.7

P.O.























1.7
3.6
3.3
3.7
3.8
5.1
1.0
2.6
2.0
3.8
2.6
U.O
3.1
U.O
Temp.
F.

5U

50

U9

U2
_
39

U5



58
_
61
_
66
_
68
_
67

66
_
67
_
66
_
6U
_
63
w
63
-

pH

_
7.3

7.6

8.0

7.6

8.5

8.5

_
_
8.2
_
8.0
-
7.8

7.9

8.0
_
7.7
_
7.6

7.6

7.2

_
-
-
              51

-------
Samples of mixed liquor taken for laboratory analyses were 2ii-hour com-
posites.  Because the mixed liquor solids and supernatant were of
necessity kept in the same container for the 2U-hour sampling period,
the laboratory analyses for solids, nitrogen, and phosphorus may not be
truly indicative of conditions which existed in the mixed liquors.

Dissolved oxygen concentration in Stage 1 varied from 1.0 to 3.8 mg/1,
depending upon hydraulic loading and disc speed.  Stage 2 dissolved
oxygen concentrations were 1 to 2 mg/1 higher than Stage 1.  Less than
1.0 mg/1 of dissolved oxygen was consumed in the secondary clarifier, so
that effluent dissolved oxygen concentrations were always several milli-
grams per liter.  At wastewater temperatures below 0F, dissolved
oxygen concentrations in the effluent ranged between 7 and 10 mg/1, which
indicates that mixed liquor concentrations were also quite high.

Sludge Recycle

Several brief tests were conducted to determine if recycling settled
secondary sludge to the first stage of discs would enhance treatment of
the wastewater.  Sludge removed from the clarifier by the scoop system
was collected in a drum and pumped into the first stage of discs at
rates of 1% and 2% of the wastewater flow.

Table 6 is a summary of operating data during sludge recycle and during
comparable periods without sludge recycle.  The amounts of sludge re-
cycled apparently had little effect on the concentration of mixed
liquor solids.  As a consequence, there was no distinct effect on
treatment efficiency.  At the 1% recycle rate, BOD and COD removals
were lower than without sludge recycle.  Suspended solids removal
increased in one case and remained the same in the other.  Ammonia
nitrogen removal increased in one case and decreased in the other.  At
the 2% recycle rate, BOD and COD removals increased; however, mixed
liquor solids concentrations were actually lower with sludge recycle
than without.

The proportion of volatile to fixed solids in the mixed liquor was
unchanged by recycling sludge.  The sludge recycle rates tested had no
apparent effect on any system parameters.  To determine the effect of
sludge recycle, further tests at much higher recycle rates will be
necessary.  This is being planned during testing of the demonstration
plant at Pewaukee.

-------
                                TABLE 6

            Effect of Sludge Recycle on Treatment Efficiency
Sludge
Recycle
Rate
Te
-------

-------
                              SECTION VIII

         COMPARISON TO PREVIOUS ROTATING DISC  PROCESS EXPERIENCE
Previous testing of a rotating disc system on municipal wastewater in
the U.S. was conducted at the Jones Island Sewage Treatment Plant of
the Milwaukee Metropolitan Sewerage Commission.  These tests were , 
conducted under Environmental Protection Agency Contract 1U-12-2U.
Table 7 is a comparison of the Jones Island test unit and operating
conditions with those for this investigation.  Figure 28 compares the
design hydraulic loading curve determined from Figure 8 at higher
temperatures and disc speeds with the results of the Jones Island
tests.  The Jones Island test unit yielded equal or .better percentage
BOD removals at all hydraulic loadings tested, even though the organic
loading was considerably higher.  This demonstrates that the rotating
disc process is first order with respect to BOD concentration from
1U7 mg/1 at least up to U26/mg/l for municipal wastewater.

A factor contributing to the better performance by the Jones Island test
unit was the larger number of stages of discs.  Residence time distribu-
tion tests on the 10-shaft unit revealed that U-6 equivalent, completely
mixed stages in series were obtained at the wastewater flows tested.
A separate stage of treatment for each shaft was not obtained because of
the high degree of backmixing between adjacent shafts.  Similar tests on
the Pewaukee test unit indicated that each stage was thoroughly mixed,
and it therefore operated as a two-stage reactor.
                                TABLE  7
                   Comparison with Previous  Test Unit

                                      Jones Island  Pewaukee
       a.   Disc Diameter,  Ft.              1             5.7U
       b.   Disc Velocity,  RPM             15-30        2-5

       c.   Disc Shafts or  Stages,  No.      10           2
       d.   Effective Disc  Area,  Ft2       500          U,600

       e.   Disc Spacing Surface  to        O.kk         0.5
           Surface, In.
       f.   Net Tank Volume, Gal.          UO           280
       g.   Ratio f, gal,,                  0.08         0.06
                 d, ft/
       h.   Temperature, F                50-68        39-67
       i.   Average Influent BOD            U26          Ihl
           Concentration,  mg/1

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  100
(0
o
   90 -
   80 -
  70  -
  60  -
  50  -
                                                 Figure  28
                                         BOD  Removal  Compared  to  Previous
                                           Testing  in The United  States
                                         0
                     Jones  Island-Test  Data
           From
           Figure  8
                                Hydraulic Loading,  GPP/Ft"
                I
                2
I
4
I
6
I
8
10
 I
12

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Another factor contributing to better performance by the Jones Island
unit is a greater liquid-holding capacity per unit surface area.  This
means that at a given hydraulic loading in gpd/ft^, the Jones Island
unit had a longer retention time.  The importance of liquid holding
capacity per unit surface area is shown in Figure 29, where the per-
formance curve from Figure 8 is compared to European experience with
the rotating disc process.(*)  European disc systems have 0.85 inch
spaces, surface to surface, between discs, which, in contoured-bottora
tankage, yields a liquid holding capacity of 0.085 gal/ft^ of-disc
surface.  The European experience on multistage disc systems also
indicates that a U-stage disc plant can be loaded at a 30$ greater
rate than a 2-stage plant and achieve the same degree of treatment.
The reason for this is that the more favorable residence time distri-
bution of a U-stage system and the approximately first order BOD
removal kinetics of the disc process increase the overall BOD removal
rate.

The U00,000-gpd demonstration plant at Pewaukee, Wisconsin, is con-
structed in four stages and with 0.085 gal. liquid capacity per sq. ft.
of disc surface, which will verify the treatment capacity experienced
in Europe.

The correlation of disc speed with various treatment parameters has
been done on the basis of revolutions per minute in this report.  To
utilize disc speed as a design criterion requires that a measure of
disc speed common to all disc diameters be used.  The peripheral or
circumferential velocity is such a measure and, because it is also
directly proportional to the average velocity of the disc surface area,
strongly suggests that it be utilized as a design criterion.  The Jones
Island tests with 1.0-ft. diameter discs at 15-30 RPM, the tests re-
ported here on 5.7 ft. diameter discs at 2-5 RPM and European experience
with 10-ft. diameter discs at 1-2 RPM indicate peripheral speed to be
a common design criterion.  Tests at various disc speeds during the
evaluation of the demonstration plant at Pewaukee will help verify
peripheral velocity as a basic design criterion.
                                     57

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 lOOr
  90
  80
(0
o
a)
 70
ffl
<*>
  60
  50
  40
                                                          Figure 29
                                                     BOD Removal Compared to
                                                     European Experience
                                    Hydraulic Loading, GPD/Ft
                                  i	i	I	

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                               SECTION IX

                      COMPARISON TO OTHER PROCESSES
A complete comparison of the rotating disc process to other processes
should include capital cost comparisonsj but since this is beyond the
scope of this investigation, the discussion will be limited to oper-
ating characteristics of the processes.

The rotating disc process is similar to the trickling filter process
in that'they are both fixed film biological reactors.  There are some
key differences, however, which give the disc process some important
benefits*  In the disc system, the biomass is passed through the
wastewater rather than the wastewater over the biomass.  This provides
intimate contact of all of the organisms with the wastewater and pre-
vents problems with clogging of the media by excess biomass.  Shearing
forces created! by rotation at peripheral disc velocities of 30 to
60 ft/rain continuously and uniformly strip excess biomass from the
discs.  Continuous wetting of the entire biomass also prevents develop-
ment of the flies often associated with trickling filter operation.

Aeration with rotating discs is a very positive means of supplying
sufficient dissolved oxygen to the attached bioraass and prevents
development af anaerobic conditions.  Both the intensity of contact
between the biomass and the wastewater and the aeration rate can be
controlled simply by adjusting the rotational speed of the discs.
This can be done to suit a particular wastewater and its treatment
requirements..

Wastewater retention time can also be controlled by selecting an ap-
propriate: disc spacing and tank size.  This allows much higher degrees
of treatment to be obtained than in the trickling filter process where
relatively short retention times are unavoidable.  It is unnecessary
to recycle effluent to achieve minimum wetting rates or aid in
sloughing as in the trickling filter.  This allows the disc process to
take advantage of the benefits of staged operation, which would other-
wise be destroyed by effluent recycle.

The rotating disc process is somewhat similar to the activated sludge
process in that it has a suspended culture in its mixed liquor..  How-
ever, the suspended culture is estimated to represent less than $ of
the total amount of biological solids on the discs and would therefore
contribute only marginally to the treatment.  Because of this, the
disc process is not upset by variations in hydraulic or organic loading
(5,67) as is the activated sludge process.  Like the activated sludge
process, the disc process does produce a sparkling clear effluent when
operated at appropriate hydraulic loadings.

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Two problems encountered in the operation of activated sludge treatment
plants are start-up at flows much lower than design flow and operation
during periods of very low flow.  Operating a rotating disc plant at
low initial flows or during periods of very low flow will yield efflu-
ents of higher quality than at design flow. 'During periods of no flow,
effluent can be recycled at a nominal rate to maintain biological
activity.(5)

Minimal operator attention and low power consumption are attractive fea-
tures of the rotating disc process when compared to the activated sludge
process, especially for package plant applications and for wastewater
treatment needs in remote locations.  Unlike the activated sludge process,
the rotating disc process can be designed for any degree of treatment and
the secondary sludge will settle well.

The rotating disc process lends itself well to upgrading existing treat-
ment facilities.  Because of its modular construction, low head loss and
shallow excavation, ,it can be installed to follow existing primary treat-
ment plants, including Imhoff tanks and septic tanks.

Many state regulatory agencies are requiring treatment plants to be
designed to achieve various degrees of nitrification as well as BOD and
suspended solids removal.  To achieve this with the activated sludge
process requires that the plant be constructed in at least two stages of
aeration, settling and sludge recycle.  The rotating disc process has
demonstrated in this investigation that it can achieve any desired degree
of nitrification with one settling tank and no sludge recycle.

A disadvantage to the disc process is the need for covering the discs to
protect the biological growth from freezing temperatures and precipitation
and protect the: discs from wind damage and vandalism.  For installations
as large as 100,000 population equivalent in Europe, heating and forced
ventilation of the enclosure have not been found necessary.  European
winters are not as severe as in the northern United States j so the demon-
stration plant at Pewaukee, Wisconsin, should demonstrate any need for
heating or forced ventilation.         '

Although an enclosure is an additional expense^for the disc process,
aesthetic requirements for wastewater treatment facilities may dictate
providing enclosures for all treatment processes in the near future.

In winter, a covered treatment plant will experience fog and condensation
from water evaporating from the relatively warm wastewater.  This will
accelerate corrosion and create slippery footing within the enclosure.
To avoid this problem with rotating disc plants, a semicircular shaped,
insulated cover has been developed to be supplied, as an integral part of
a disc assembly.  It covers only the discs and drive components.  Fog and
condensation are restricted to the atmosphere surrounding the discs, and
less treatment plant area needs to be covered.
                                  60

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                                SECTION X

                             ACKNOWLEDGMENTS
The support of David Kluge, Village Engineer for Pewaukee,  Wisconsin is
gratefully acknowledged.

The construction and operation of the test facility analytical work and
report preparation were performed by a team from Autotrol Corporation,
consisting of Ronald L. Antonie, Franklin J. Koehler,, Robert J. Hynek,
Henry H. Horns, and Robert T. Baugh.

Appreciation is expressed for the support of the project by the Water
Quality Office, Environmental Protection Agency, and the help provided
by Dr. Robert L. Bunch, Project Officer.
                                  61

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62

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                             SECTION XI

                             REFERENCES
 1.   Wood, L.  B.,  Monis,  H.,  "Modifications  to  The BOD Test," J. Proc.
     Inst. Sew.  Purif., pp 350-356 (1966).

 2.   Wild, H.  E.,  Jr.,  Sawyer,  L.  N., McMahon,  T. C., "Factors Affec-
     ting Nitrification Kinetics," Water Pollution Control Federation
     Journal,  pp 18U5-185U (Sept., 1971)

 3.   "Municipal  Sewage  Treatment with A ROTATING BIOLOGICAL CONTACTOR,"
     Federal Water Pollution  Control Administration, Department of
     The Interior, by Allis-Chalmers Research Division, Milwaukee,
     Wisconsin,  Contract  No.  1U-12-2U,  Modification No. 2 (May, 1969).

 U.   Hartmann, H., "Der Tauchtropfkorper," Oesterreichische
     Wasserwirtschaft.  Volume 17,  N. 11/12,  pp  26U-269  (196?).

 5.   Antonie,  Ronald L.,  "Response of The BIO-DISC Process to
     Fluctuating Wastewater Flows," presented at the 25th Purdue
     Industrial  Waste Conference,  May 5-7, 1970.

 6.   Popel, F.,  "Construction,  Degradation Capacity and Dimensioning
     of Rotating Biological Filters," Eidg.  Technische Hochschule,
     Zurich-Fortbildungskurs  der EWAG  (196U).

 7.   Marki, E.,  "Results  of Experiments by EWAG with The Rotating
     Biological  Filter,"  Eidg.  Technische Hochschule, Zurich-
     Fortbildungskurs der EWAG (196U).

 8.   Antonie,  R. L., "The BIO-DISC Process:   New Technology for The
     Treatment of  Biodegradable Industrial Wastewater," Chemical
     Engineering Progress Symposium Series,  Water-1970, Volume 67,
     Number 107, 1971,  pp 585-588.

 9.   Antonie,  R. L., Welch, F.  M., "Preliminary Results of A Novel
     Biological  Process for Treating Dairy Wastes," 2Uth Purdue
     Industrial  Waste Conference (1969).

10.   Antonie,  R. L., Van Aacken, Karen, "Rotating Discs Fulfill Dual
     Wastewater Role,"  Water & Wastes Engineering, pp 37-38
     (Jan., 1971).
                                    63

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                             REFERENCES (cont'd)
11.  "Rotating Biological Contactor," Allis-Chalmers Research Center for
     FWQA Contract 1U-12-2U, Phase I Report (1968).

12.  Welch, F. M., "Preliminary Results of A New Approach in The Aerobic
     Biological Treatment of Highly Concentrated Wastes," 23rd' Purdue
     Industrial Waste Conference (1968).

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                  SECTION XII



                   GLOSSARY










D.O.       Dissolved Oxygen



Effl.      Effluent



QPD        Gallons per Day



Infl.      Influent



mg/1       Milligrams per Liter



ML         Mixed Liquor



NH^-N      Ammonia Nitrogen



Nk         Kjeldahl Nitrogen



N03-N      Nitrate Nitrogen



N02-N      Nitrite Nitrogen



Rem'd      Removed



RPM        Revolutions per Minute



Susp.      Suspended



Vol.       Volatile



SS         Suspended Solids

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66

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                              SECTION XIII

                        PATENTS AND PUBLICATIONS


No patents have been applied for as a result of work done during this
project.

An oral presentation of the results of this project was made at the  U3rd
Annual Conference of the Water Pollution Control Federation, Boston,
Massachusetts, October h-9t 1970.  Limited distribution of copies of the
presentation has been made to individuals who specifically requested them.
                              67

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68

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SECTION XIV
 APPENDIX
69

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NOTES: fl) % SETTLED  SLUDGE!  BV VOLUME OF INFLUENT  C2) SETTLED  15 MINUTES  (3) INCLUDES  NITRITES

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                                               PEWAUKEE TEST DATA SUMMARX
                                               10 Ml I'DC! 17] 17 | 19 I 19
                                              9i8;9i8.swum;.  . .'gisi .
                                                 '   '    !   '"'   -,C3)
                        u.u: lA I i	i	'

                      i  ftflO.OL.__ I _7I.
                           1.5!  . ^_	1.0
                                 	Q.o.oee

                 40 5t\.M...6.0. 10.8,....,43!^
                 3.3..3.1.32'4.R7.8	3.5: f*
                 37. 4.6:.4.2U.2: 9.7-...  : 2.9. &
                 "M 4-Z Aa'TgM .. ?J. &
SETTLED SLUDGE  BV VOLUME Of INfLUENT (2) INCLUDES  NITRITES  (3) REFRIGERATED  SAMPLE   (4) SUSP. MATTER

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                                                     PEWAUKEE  TEST DATA  .SUMMARY
NCfTES: (% SETTLED SLUDGE BV VOLUME OF INFLUENT <2) INCLUDES  NITRITES (3) RE1FRIGERATCD SAMPLE

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                                                        PEWAUKEZ TE5T  DATA  SUMMARX
NOTES: fDXSETTLED SLUDGE BX VOLUME OF WUIENT C2)INCLUDES NITRITES O) REFRIGERATED SAMPLE  (4)ALLyLTHIOUREA_ADOED3 CONCENTRATION .JM6/L IN BOD TESTS

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  SELECTED WATER
  RESOURCES ABSTRACTS
  INPUT TRANSACTION FORM
                  1. Report No.
                    3. Accession No.
                                    W
  4. Title
         Application of Rotating Disc Process
         to Municipal Wastewater Treatment
  7. Author(s)
         Ronald  L.  Antonie, Franklin J. Koehler
                                    5. Report Date

                                    6.

                                    8. Performing Organization
                                      Report No,
  9. Organization
         Autotrol  Corporation,  Milwaukee, Wisconsin
         Bio-Systems Division
                                   10. Project No.

                                       17050 PAM
                                   11. Contract I Grant No.

                                       14-12-810
                                   13. Type of Report and
                                      Period Covered
 12. Sponsoring Organization
 IS. Supplementary Notes
 16. Abstract

         A prototype package plant incorporating the rotating  disc
    wastewater treatment process  was tested on  municipal wastewater at
    the Village of  Pewaukee, Wisconsin, to evaluate its treatment cap-
    abilities and establish guidelines for operation and testing of a
    full-scale rotating disc demonstration plant soon to be put  into
    operation at Pewaukee.  The package plant included a rotating bucket
    feed mechanism,  ninety-one 1.75-meter diameter discs divided into
    two stages, and a secondary clarifier with  a sludge -removal  mechanism.
    Variables tested included hydraulic loading, rotational disc speed,
    sludge recycle,  and wastewater temperature  as it varied with climatic
    conditions.
         At a hydraulic loading of 1.5 gpd/ft2  of disc surf ace, the package
    plant achieved  87% removal of BOD and 805 removal of suspended solids
    to yield an effluent of 20 mg/1 BOD and suspended solids when treating
    effluent from the existing primary clarifier.  At the same loading,
    85% removal of  ammonia nitrogen was obtained to yield an effluent of
    3 . 5 mg/1 .
         Low maintenance requirements and low power consumption  were dem-
    (bbstrated by fchf> !-<">> a t:i rig e\i ar; pTT>r!p>gg H 111*1 rig
 17a. Descriptors
 11'b. Identifiers
             Wastewater Treatment
             BOD Removal
             Nitrification
             BIO-DISC Process, Rotating Disc Process,  Rotating
             Biological  Contactor, Tauchtropkorper
  17c. COWRR Field & Group
  18. Availability
19. Security Class.
   (Report)

20. Security Class.
   (Page)
21. No. of
   Pages

22. Price
Send To:
                                               WATER RESOURCES SCIENTIFIC INFORMATION CENTER
                                               U.S. DEPARTMENT OF THE INTERIOR
                                               WASHINGTON, D. C. 20240
  Abstractor    Ronald L.  Antonie   I institution   Autotrol Corporation
WRSIC 102 (REV. JUNE 1971)
                                                6PO 913.2*1

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