EPA-600/2-81-  155
                                         August 1-981
       PARALLEL EVALUATION OF AIR-AND
           OXYGEN-ACTIVATED SLUDGE
                     by

                Scott Austin
                  Fred Yunt
              Donald Wuerdeman
   Los Angeles County Sanitation Districts
         Whittier, California  90607
           Contract No. 14-12-150
               Project Officer

              Irwin J. Kugelman
        Wastewater Research Division
Municipal Environmental Research Laboratory
          Cincinnati, Ohio  45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
    OFFICE OF RESEARCH AND DEVELOPMENT
   U.S. ENVIRONMENTAL PROTECTION AGENCY
         CINCINNATI, OHIO  45268

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                                   TECHNICAL REPORT DATA
                            (Please read Instntcnons on the reverie bef
1  RE>~O"HTNO".~~      "
  EPA-6QQ/2-81- 155
                                    ORP-Beport
4 TITLE AND SUBTITLE

 PARALLEL EVALUATION OF AIR-AND OXYGEN-ACTIVATED SLUDGE
                                                          5>REPOHT DATE

                                                             August 1981
                                                           6 PERFORMING ORGANIZATION CODE
Scott  Austin,  Fred Yunt, Donald Uerdeman  and Walter
E. .'Harrison
                                                           8 PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND AD3RESS
 County Sanitation Districts of Los Angeles  County
 1955  Workman nil] Road
 Whi,ttier,  California 90607
                                                           10 PROGRAM ELEMENT NO
                                                           AZB1B, D.U. B-113.Task D-1/3D
                                                          11 CONTRACT/GRANT NO.

                                                          Contract No.  14-12-150
12 SPONSORING AGFNCY NAME AND ADDRESS
riuniciparEnvironnental Research Laboratory - Cin., OH
Office  of Research  and Development
U.S.  Environmental  Protection Aaency
Cincinnati,  Ohio  45268
                                                          13. TYPE OF REPORT AND PERIOD COVERED
                                                          Final, Feb. 1975  -  Dec.  1976
                                                          14. SPONSORING AGENCY CODE
                                                          EPA/600/14
15 SUPPLEMENTARY NOTES
Pro.ject. Of f icer:   Irwi n Kugelman   (513)  684-7633
16 ABSTRACT
                                        ABSTRACT
 To
     provide data on the relative merits  of  air and oxygen in the activated  sludge  pro-
  cess,  two 1900-m3/day (0.5-mgd) activated  sludge pilot plants, one air and one oxygen
  system,  were operated side-by-side at the  Joint Water Pollution Control  Plant, Carson,
  California.   Both of the pilot plants met  the applicable discharge limitations for
  everything but three trace metals, but  the oxygen system provided a more stable
  operation.

  Primary  differences in performance concerned ammonia nitrogen removals and energy
  consumption.   Differences in sludge  production were not significant.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b IDENTIFIERS/OPEN ENDED TERMS
                                              *Air-activated sludge,
                                              *0xygen-activated  sludge,
                                               Sludge production,
                                               Sludge settleability,
                                               Power consumption
                                                                        c. COSATI Field/Group
* Sewage treatment,
* Activated sludge process,
  Sludge,
  Clarification,
  Energy
 13B
18 DISTRIBUTION STATEMENT

  Release  to  Public
                                             19 SECURITY CLASS (This Report)
                                              Unclassified
                                                                         21. NO OF PAGES
52
                                              20. SECURITY CLASS (This page]
                                              Unclassified
                                                                         22 PRICE
EPA Form 2220-1 (Rev. 4-77)

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 HEAJ,
                                            DISCLAIMER
          This report has been reviewed by  the  Municipal  Environmental Research
          Laboratory, U.S. Environmental  Protection  Agency, and approved for
          publication.   Approval does not signify that the contents necessarily  reflect
          the views and policies of the U.S.  Environmental Protection Agency, nor does
          mention of trade names or commercial  products  constitute endorsement or
          recommendation for use.
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                                  .EQREWORD.
         The  U.S.  Environmental Protection Agency  was  created because of Increasing
         public  and government concern about  the dangers  of pollution to the health
         and  welfare of the American people.   Noxious  air,  foul  water and spoiled
         land are  tragic(testimonies to the deterioration of our natural environment.
         The  complexity of that environment andjthe  interplay of its components
         require a concentrated and integrated  attack  on  the problem.

         Research  and development is that necessary  first step in problem solution;
         it  involves defining the problem, measuring its  impact, and searching
         |£|r_s_oJut_Lons.._|.The ^r)'|oip^ljnjncojnmentaj .Research. Labo,r.alory_de.velop.s new^
        "~~^'  improved technology and systems  tojprevent,  treat,  and manage wastewatef
and



















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and solid and hazardous waste pollutant discharges from municipal and com-
munity sources, |to preserve and treat public drinking water supplies, and to
minimize the adverse
pollution. Tbji-s/gpubl
provides a most
community.

vital


This report presents
and performance (data
economic, social,
i cat ion is one of
health, and aesthetic effects of



the products of that research and j
communications link between the researcher and the user
I


1
design details, operating experiences, and operating
for a parallel operation of an air-activated and an
oxygen-activated sludge pilot plant. Consideration of the operational re-
sults presented {herei
and potential mi









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n is recommended for design engineers, facility planners,
nicipal users of an oxj










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Francis T.
Director
/gen-activated sludge system.
Mayo

Municipal Environmental Research
Laboratory
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                                          -ABSIRACL
                         i
         To provide data on the relative  merits of air and oxygen in the activated
         sludge process,(two 1900-m3/day  (0.5-mgd) activated sludge pilot plants, one
         air and one oxygen system, were  operated side-by-side at the Joint Water
         Pollution Control Plant,  Carson,  California.   Both of the pilot plants met
         the applicable discharge  limitations  fir everything but three trace metals,
         but the oxygen system provided a more stable  operation.
                         p                       I
         Primary differences in performance  concerned  ammonia nitrogen removals
         jlDjdjBnergy_ cc^n_sump_tion./2.,Di_fferences_ itn_sl_udge EIodu.ctjon_
         cant.            ,     "
         This report was (submitted  in fulfillment  of  Contract No. 14-12-150 by the_
              3/8'
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                                                                                   m
 Foreword,
''Abstract	!		. L.		...........    iv
 Figures...	I	!	                 vi
 Tables.
                                                                                   v
         Abbreviations and  Symbols	....!...	  viii

         -—?. Ll _Jn^_rod_uC^ i 2H« • -172— JLI-JL: -_u —• • L. -_i-- -_^ -j_t • j_^« J_L • J^.*+A • j_t -.u •_!	L

            2.  Conclusions.	!	     2
                Selection  and  Description of the Pilot  Plants,
                   Ai r gsp^ajged turbine system. J		,
                   High purity oxygen system...!,..	,,
                   Final clarifiers.	i	
                Operation of the  Pilot Plants.
                   'Startup	J.
                   Pilot Iplant  operational phases
                Discussion of Results
                   Effluent quality...
                   Sludge production,
                   Sludge settleability,
                   Power
                   Depenc
                 consumption.
                 ability and maintenance
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                             FIGURES
                 Aeration basin  and  deep-tank submerged turbine  aerator
                 Oxygen system reactor	(	,	,
                 UNOX reactor with surface aerators	,
                 Soluble[COD versus  aeration time	
          10

          11
                                                                   Page

                                                                     4
                                                                     6
                                                                    11
                                                                    23
  Effluent  soluble COD versus MCI^T	    24
  Nonfilterable  COD and BOD5 ver|us VSS	    27
  Hexane  extractables versus effluent suspended  solids	    29
	SJudge  growth ^petkj^._._.._._.._]_.._._. •^•^.•^_-±i.*±i.-^..±±-^_i •	31_-
  Analysis  of  net sludge production using MCRT
 _as the  independent variable...!	    35
 'Analysis  of  net sludge production using the food-to-
    microorganism ratio as the independent variable	    36
  Initial-fettling  rates.
38
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                                             TABLES
         Number
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 3
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 8

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10
11
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                 Design criteria for pilot  plants	
                 Summaryiof operational  parameters--air-sparged turbine
                   system	1	,
                 Summaryjof operational  parameters—oxygen system	
                 Summary.of effluent quality—air  system	
                 Summary'of effluent quality—oxygen system	
                 Effluent clarity	>		
                 Trace constituent removal  by means of air-ac"t"iv,ated
                   s TTJdcje .77 . ^Y, ?. .77 77. 77". 77. 77", 77. 77. 77*. ."77.77 .77 ."77 ."
                 Trace constituent removal  by means of
                   oxygen-activated sludge	i.	
                 Assumed oxygen transfer  rates.!	
                                                                                    8

                                                                                   13
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                                                                                   21
                                                                                   22
                                                                                   26
                                                                                   32
                                                                                   40
                 Oxygen Astern operating  characteristics	     41
                 Power consumption
                                                                                  42
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EL
-AB8RE.V.I A J.I.ON SUND-SYMBOLS
         ABBREVIATIONS
            BOD
            BODR
            BOD5
            COD
            CODR
            DO R
            DTST
              --tbiochemical  oxygen  demand
              --ibiochemical  oxygen  demand removed
              --.5-day biochemical  oxygen  demand
              --(chemical  oxygen  demand!
              —(chemical  oxygen  demand;removed
              --dissolved  oxygen
              --"deep  tank  submerged turbine
             SR
            JWPCP
            MCRT
            MLSS
            MLVSS
            NTP
            RWQCB
            SOTR
            SVI
            SWD
            TPVSS
            VSS
        SYMBOLS
                                      _
              --.initial  settling  rate  J
              --'Joint  Water  Pollution  Control  Plant
              --|mean cell  residence  time
              --jmixed  liquor suspended!sol ids
              3-n/ni'xed  liquor volatile  suspended  solids
              --jnormal temperature  andlpressure
              --iRegional Water  QualityfControl Board
              --standard oxygen transfer  rate
              --jsludge volume index    1
              --jside water depth       J
              --'total  plant  volatile suspended solids
              --[volatile suspended  sol'ds
           a,  B

            C
            c*

         dC/dT
                variables to correlate
              clean water results
                ,   to mixed  liquor conditions
             — I system dissolved oxyge|i concentration
             --(equilibrium  dissolved  oxygen concentration  at
                '   zero uptake
             --joxygen transfer rate
             —.mean cell residence time
             --'microorganism decay coefficient
             -- ivolumetric mass transfer coeficient



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V/Q --aeration period
Y --[growth yield coefficiei



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                                  SECTION 1

                                INTRODUCTION
Since the introduction of high-purity, oxygen-activated sludge, a contro-
versy has existed concerning the relative merits of air and oxygen in the
activated sludge process, but very few data are available on side-by-side
operation of relatively large-scale systems with comparable engineering.

As part of the research effort involved with Federally-mandated secondary
treatment at the Joint Water Pollution Control Plant (JWPCP) in Carson,
California, the County Sanitation Districts of Los Angeles County constructed
two 1900-m-Vday (0.5-mgd) activated sludge demonstration plants.  One incor-
porated the UNOX high purity oxygen process, and one used an air-sparged
mechanical aerator.  The primary purpose of the study was to obtain data
pertinent to the selection and design of an activated sludge system at the
JWPCP, but the nature of the research facilities allowed a direct comparison
of the two activated sludge processes.  The pilot plants were operated on
identical feed.  Equal engineering care was taken in the design of the
aeration systems, and identical clarifiers were used.  Unfortunately, the
research motivations in establishing the operating parameters for the two
plants were different.  The oxygen system was operated to refine specified
design parameters, while the air system was operated to determine its
capabilities and limitations.

The JWPCP is a 15-m-Vsec (350-mgd) primary treatment plant treating a mixture
of domestic and industrial wastes.  These facilties allowed a good comparison
of the two activated sludge alternatives for treating relatively concentrated
municipal wastewater.

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                                 SECTION 2

                                CONCLUSIONS
Both activated sludge systems are capable of producing effluents meeting the
JWPCP discharge limitations for everything but certain trace metals, which
will require source control.  But the oxygen system is somewhat more stable
and flexible in its operation.

The two systems obtained good removals of soluble organics, and factors
affecting solids separation in the final clarifier are most significant in
terms of their effects on effluent quality.  The most notable detrimental
factors encountered in the study were excessive aerator power inputs, which
sheared the floes in both systems, and nitrification-denitrification, which
caused the settled sludge from the air system to resuspend.

The major difference between the two systems in terms of pollutant removals
concerns ammonia nitrogen.  The oxygen system did not nitrify.  At the JWPCP,
where the ammonia discharge limitation is high enough to impose no con-
straint, this characteristic is an advantage in that it eliminates rising
sludge resulting from nitrification-denitrification.

Claims have been made that oxygen-activated sludge processes produce less
sludge than air-activated sludge processes.  In this study, a comparison was
made based on total plant solids and the difference was found to be insigni-
ficant at the 90-percent confidence level.  The trend, however, was for the
oxygen system to produce more sludge.

Because of modifications to the pilot plant's aeration equipment that were
made to prevent floe shear, an energy consumption comparison was considered
inappropriate. A paper study indicates that substantial energy savings may be
expected with the oxygen system.

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                                  SECTION 3

                  SELECTION AND DESCRIPTION OF THE PILOT PLANTS
AIR-SPARGED TURBINE SYSTEM

The location of the Districts' JWPCP in an urban area placed a definite land
constraint on the proposed secondary treatment system for that plant.  When
preliminary site layouts were made for a conventional activated sludge system
with the standard 4.6-m-deep (15-ft-deep) aeration tanks and an optimistic
6-hr aeration period, no excess land was available for waste activated
sludge processing.  Because of this land constraint, the Sanitation Districts
proceeded to evaluate activated sludge systems that  could reduce the land
area required for secondary treatment.  One of those alternatives was the
deep tank submerged turbine (DTST) system.  The DTST system was selected not
only because of the land savings from the deeper tank (7.6 m or 26 ft) but
also because the submerged turbine is a more efficient oxygen transfer device
than the conventional coarse bubble air diffusers.  The land savings from the
deeper tank and the possibility of reducing the aeration period made the DTST
system a realistic candidate system for secondary treatment at the JWPCP.

The aeration basin for the DTST system (Figure 1) was designed for a 3.5-hr
detention time (V/Q) at a design flow of 1900 m^/day (0.5 mgd).  The aeration
basin was 6.1  x 6.1 m (20 x 20- ft) with a 7.6-m (25-ft) side water depth
(SWD) and 1.5-m (5-ft) freeboard.  To insure a complete mix system, 0.51-m
(1.7-ft) baffles were provided on each wall running the full tank depth.

The design of the submerged turbine aerator itself was based on an ability to
supply sufficient oxygen transfer capability to treat the JWPCP primary
effluent in a 2-hr aeration period (V/Q).  The turbine aerator had a 45-kW
(60-hp) drive unit with a 7.6-m (25-ft) long, 0.25-m (10-in) diameter steel
shaft and a 1.5-m (5-ft) diameter impeller.  The shaft was supplied in two
sections of 6.1  -m (20-ft) and 1.5 m (5 ft) to provide the flexibility
of evaluating both a 6.1-m (20-ft) and 7.6-m (25-ft) water depth.

Air was introduced into the aeration tank at the perimeter of the mixer/
impeller through a sparged ring apparatus.  Two 0.28-m^/sec (10-cfs) air
compressors were provided, with one acting as a standby.

HIGH-PURITY OXYGEN SYSTEM

One of the major advantages offered by the pure oxygen biological treatment
process is the ability to reduce the period of time required for treatment
of a wastewater by increasing the rate at which oxygen can be dissolved into

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the mixed liquor within the biological reactor. The results of preliminary
studies using Union Carbide's 0.6-1/sec (10-gpm) mobile pilot plant verified
this claim, as acceptable effluent quality was achieved at aeration periods
as short as 1.5 hr (V/Q).

Based on this preliminary testing, the oxygen pilot plant was designed for an
aeration period of 2.5 hr (V/Q) at the design flow of 1900 m^/day (O.S^mgd).
The biological reactor is 7.3 x 7.3 m (24 x 24 ft) with a 3.7-m (12-ft) SWD.
The total height of the basin is 4.6"m (15-ft) (Figure 2).  As is typical with
the sealed reactor type of pure oxygen system, the reactor was subdivided into
four equal-volume, completely mixed chambers with inside dimensions approxi-
mating a 3.7-m (12-ft) cube.  To insure complete mixing in each of the four
reactor stages, there are four anti-swirl baffles per stage located along the
diagonals a distance of 1.2-m (4*ft) from the center of the section.  These
baffles are 0.36-m (1.2-ft) wide and extend the entire depth of the tank.  An
extension is provided along the bottom 1.8-m (6 ft) of each baffle, which
runs toward the tank section center for a total of 0.61-m (2 ft).  This
modification was included to insure good baffling during operation using
surface aerators, if so desired.

As a result of competitive bidding, Union Carbide Corporation was awarded a
contract for the construction of the pure oxygen biological reactor, which
was to be built into the existing pilot plant influent pumping station and
final clarifier system. The reactor was designed to incorporate a submerged
turbine/gas recirculation compressor arrangement for oxygen dissolution in
each reactor stage.  The mixers in stages 1 and 2 were driven by 3.7-kW
(5-hp) motors, while those in stages 3 and 4 were driven by 2.2-kW (3-hp)
motors (Figure 2).

Having been introduced into the gas space above the liquid level  in stage 1
of the reactor, the oxygen was withdrawn from the gas space above the stage 1
mixed liquor level by a compressor and pumped through the center  of the
0.15-m (6-in.) diameter turbine shaft.  The gas exited the shaft  through a
rotating sparger located approximately 0.3 m (1-ft) from the bottom of the
reactor at the base of the shaft.  Four rectangular turbine blades were
located about 0.3 m (1-ft) above the rotating sparger, which, when operated
at their normal speeds (130 rpm in stages 1 and 2, 82 rpm in stages 3 and 4),
maintained a completely mixed regime while dissolving sufficient  amounts of
oxygen to meet the biological demand.  Oxygen which did not go into solution
and carbon dioxide coming out of solution as a by-product of the  biological
reaction in the first stage passed through an opening in the gas  space into
the second stage where it was introduced into the mixed liquor by the same
compressor/turbine arrangement as the first stage.  In like manner, the gas
proceeds through the third and fourth stages of the reactor, with the unused
oxygen and other gases being ultimately passed through a vent in  the fourth
stage to the atmosphere.

The dissolved oxygen concentration in each stage was controlled by varying
the recirculated gas flow from the compressor to the sparger at the base of
the turbine shaft.   This  was accomplished by means of a 50-mm (2-in.)  bypass
valve located between the compressor discharge and a rotary joint gas inlet

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                                     -RECIRCULATION-
                                      COMPRESSORS
 SECTIONS!
                                      NOTE: I m = 3.28 ft.
                              Figure 2.  Oxygen' system reactor.
        at the top of the turbine.   By  opening this  valve,  a  portion  of  the  recircu-
        lation gas can Be bypassed back  into the  gas  space, thus  reducing  the  volume
        of gas which is  introduced ;into  the  Liquid through  the  turbine for dissolu-
        tion.

        The oxygen supply system  is  controlled through  a  pressure transmitter-set
        point controller] arrangement  in  which the flow  of oxygen  from the  storage
        facility to itsjpoint of  introduction at  the  first  stage  is automatically
        controlled in order to maintain  a constant pressure in  the gas space above
        the first stage.'  When the pressure controller  indicates  a pressure  that is
        below the pressure set point, an increased signal is  sent to  a control  valve,
        which increases Ithe pure  oxygen  gas flow  into the reactor and, hence,  the
        pressure in the igas space over  the first  stage.   Likewise, if the  gas  space
        pressure exceeds the set  point  value, Ihe gas flow  is reduced until  the
        pressure approaches the desired  value."
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        The flow of gas 'through the reactor  is
                                       monitored at all times so that the
amount of oxygen utilized during the treatment process can be determined.
Since the reactor is sealed, the monitoring of oxygen utilization is accom-
 '•Hshed by simply measuring the mass flow rate of pure oxygen into the
        i
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SECTIONS
HERE   S
        \
        th'e  vent  stack  rn  the  fourth stage.   In the latter case, it is necesary to
        measure  and  record the oxygen composition of the vented gas continuously,
        [since  a  significant portion  is composed of gaseous byproducts of the chemical
        and  biological  ireactions  that take place while the wastewater is under
        aeration.
                        b;                       I
          ree final  sedimentation  tanks were designed for the project using the
        jDistricts' basic  criteria  for rectangular final sedimentation tanks.  Two of
        the tanks were  of the  same size to allow evaluation of both the submerged
        turbine  system  and the high purity oxygen system at the same overflow rate of
        |28.5-m3/m2/day  (i70r>gpd/ft2)  at the design flow 1 900 ^m3/ day (0.5-mgd).  The
        third tank was  designed for an overflovl  rate of 18.3 m3/m2/day (450 gpd/ft2)
        at the 1900-m^/d'ay (0.5-mgd)  flow.  It (was used to evaluate lower overflow
        rates in either (system and to provide the flexibility required to evaluate
        flower  aeration  times  and,  hence,  flows
                                                of greater than I900~m3day (0.5-mgd)
        ijin either pilot'plant.
        Uj.	^ _  6-1/2"	1
        The two final  sedimentation  tanks designed for 28.5-m3/mZ/day (700 gpd/ft?)
        ijwere 3-m  (10-ft)j  deep,  3-m (10-ft)  wide,  and 22-m (72-ft) long.  These tanks
        have a 2-hr  hydr.aulic detention  time and  a flowthrough velocity of 3.2 mm/sec
        |(0.6 ft/min) at |the  1900-m3/day  (0.5-mgd)  flow and 30-percent recycle.  The
        jthird final  s£dnme"ntation  tank had  the (same width and depth as the two 22-m   j
        !j(71-ft) tanks, b'ut  it was  34-m (111-ft):  long.   The hydraulic detention at 1900-
        im-Vday (0.5-mgd)j  flow and  30-percent recycle was 3 hr, and because it had the*
        Jsame cross sectional area  as  the shorter  sedimentation tank, the flowthrough
        ('velocity was the  same.   The  same weir length was provided on all three
        jjsedimentation  ta'nks, so that  at  the design flow, the weir loading was 62.1-
        irn3/m/day  (5000«g'pd/ft2).

        The design criteria  used  for  the biological reactors and the associated
        final sedimentation  tanks  have been summarized in Table 1.
BEGIN
LAST LINEl	
OF TEXT £>>
        I
              3/81
                                                                                        BOTTOM OF
                                                                                        IMAGE ARE^
                                                                                        OUTSIDE
                                                                                        DIMENSION
                                                                                        FOR TABLES
                                                                                       >AND SLLUS-
                                                                                        TRATSONS
           EPA-2S7 (Cin.)
           (0761
                                          PAGE NUMBER

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                TABLE  1.   DESIGN CRITERIA FOR PILOT  PLANTS
Item
_ r1
Biological Reactors:
Average flow, m3/day (mgd)
Length, m (ft)
Width, m (ft)
Average water depth, m (ft)
No. of stages
Detention time (V/Q), hr
Oxygen Storage Tank:
Number
Volume, m3 (ft3) NTP

Capacity, m3/hr (ft'/hr)


Final Clarifiers:
Number
Length, m (ft)
Width, m (ft)
Average water depth, m (ft)
Overflow rate, m3/m2/day (gpd/ft2)
Detention time
(Q + 1/3 return), hr
Weir loading rate, m3/m/day (gpd/ft)
Flowth rough velocity
(Q + 1/3 return), mm/sec (ft/min)
Air
System

1900 (0.5)
6.1 (20)
6.1 (20)
7.6 (25)
1
3.5

--
--

--

Standard

2
22 (72)
3.0(10)
3.0(10)
28.5(700)

2.0
62.1 (5000)

3.2 (0.6)
Oxygen
System

1900 (0.5)
7.3 (24)
7.3 (24)
3.7 (12)
4
2.5

1
9900
(350,000)
' 140
(4940)
Large

1
34 (111)
3.0 (10)
3.0 (10)
18.3 (450)

3.0
62.1 (5000)

3.2 (0.6)
].
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                                 PAGE NUMBER

-------
                                  SECTION 4

                        OPERATION OF THE PILOT PLANTS
STARTUP

Air Sparged Turbine Pilot Plant

Upon completion of the clear water testing of the DTST aerator in December
1974, the DTST system was started up in January 1975.  The pilot plant was
seeded with waste activated sludge from the Pomona Water Reclamation Plant.
From the middle of January until mid-February, the flow to the unit was
gradually increased from 380-to llOQ-m^/day (0.1-to 0.3-mgd).  However, during
this period, the effluent was characterized by cloudiness and the biology was
marked by an apparent dispersed floe.  A meeting with the mixer manufac-
turer's representatives was called in mid-February. The discussions indicated
that the probable cause for high effluent turbidity and dispersed floe was
shearing of the floe.  To alleviate this problem the manufacturer agreed to
decrease the energy input to the basin by reducing the aerator speed from 54
to 46-rpm.  The mixer horsepower was thereby reduced 37-percent.  Once the
mixer speed was reduced, the improvement in effluent quality was almost
immediate.  Within a few days, the cloudiness in the effluent disappeared and
a good biological floe appeared.

UNQX Pilot Plant

The oxygen biological treatment pilot plant was started up on June 27, 1975,
by drawing air into the reactor through the recirculation gas compressors
with no seed being added.  The system responded very quickly, and by July 15,
1975, what appeared to be a good, stable sludge had been achieved.  A series
of mechanical difficulties was encountered at this time that hindered the
normal progression of operation toward a steady-state condition.  However,
after almost 45 days of operation, during which the unit had been seeded, it
became apparent that continued poor effluent quality (high turbidity and
suspended solids) was the result of causes other than these mechanical
startup difficulties.

During this period, the system was operated over various hydraulic and
organic loading rates and investigations were made as to possible toxic
compounds in the primary effluent.  However, toxicity was soon dismissed as a
possible cause of poor effluent quality, not only by an examination of
primary effluent trace constituent concentrations, but also by the fact that
the DTST system was being operated concurrently without showing any signs of
toxic effects.

-------
Through further  investigation, other possible causes  (such as  low pH and floe
shear through excessive turbine blade tip speeds) were eliminated.  The major
factor was finally traced to an energy  intensity problem related to oversized
gas recirculation compressors and resulting floe shear due to  the flooding of
the spargers by  excessive pumping rates.  An expedient solution was achieved
in early September 1975 by drastically  reducing the flow of recirculated gas,
the result of which was significant improvement in effluent quality in
general and a decrease in turbidity in  particular.  The improvement was still
not to the level that had been achieved  in 1973 during the operation of Union
Carbide's 0.6-1/sec (10-gpm) mobile pilot plant, but  the effluent being
produced was within the State and Federal discharge requirements.

As outlined earlier, the pure oxygen pilot plant was  originally designed
with provisions  made for conversion from submerged turbines to surface
aerators at a later date, if so desired.  However, with the accelerated State
construction grants program and the ensuing decision  to design a full-scale
oxygen surface aeration system at the JWPCP, immediate steps were taken to
convert the pilot plant to a surface aeration system.

On September 25, 1975, the pilot pl-ant  was taken out  of service following a
short period of  good operation under diurnal flow conditions.  On October 3,
1975, the installation of the surface aeration equipment was completed and
the system was restarted.  The influent flow was gradually increased to 1500-
tn^/day (0.4-mgd), and beginning on October 23, 1975,  the first period of good
steady-state operation was obtained and was subsequently sustained for a
3-wk period.  Following this period, it was intended  that the  influent
feed flow be changed to simulate the JWPCP diurnal flow pattern but diffi-
culties relating to the operation of the system using surface  aerators
prevented this progression.

Soon after the system was restarted with the surface  aerators  installed, a
great deal  of gas was observed escaping above the clarifier inlet diffusers.
In addition, the oxygen utilization data gathered during the surface aerator
operation was not at all in agreement with similar data gathered both during
the earlier operation using submerged turbines and during the  1973 operation
of the 0.6-1/sec (10-gpm) mobile pilot plant.  It was assumed, therefore,
that gas from trte fourth stage of the reactor was somehow being trapped
within the mixed liquor and was subsequently being purged as the liquid
entered the final clarifier.  It was theorized that the only way in which
such large volumes of gas could be conveyed out of the reactor and into the
mixed liquor piping would be the result of the aerator umbrella creating
excessive turbulence in the trough downstream of the  overflow weir in the
fourth stage of  the reactor as illustrated in Figure  3.  With such unmeasured
quantities of gas escaping, it was impossible to accurately measure the
critical parameter of oxygen utilization.

In mid-December  1975, a baffle was installed in front of the overflow weir in
the fourth stage of the pilot reactor by representatives of Union Carbide.
The purpose of the baffle was to prevent the aerator  umbrella from extending
into the trough  downstream of the weir.  This baffle, however, was not
sufficient as the gas leakage was reduced but not eliminated entirely.   It
became clear that in order to completely correct the  problem,  the pilot plant

                                     10.

-------
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                           NOTE: | m = 3.28 ft
           Figure 3.   UNOX reactor with surface aerators
         would  have  to  be  taken  out of service and a much larger baffle installed.
         Since  a  short  timetable was available for completion of the first phase of
         the  full-scale oxygen secondary treatment design, it was necessary that the
         research  studies  of design criteria and the actual  design of the secondary
         system be conducted simultaneously.  Because of this, it was decided that
         operation of the  pilot  plant be continued despite the difficulty in assessing
         oxygen utilization.

         The  next  2-mo  were  spent developing methods of improving sludge settleability
         so that  critical  design parameters  related to the secondary clarifiers could
         be evaluated.   By mid-March 1976,  goodi steady operation had been established
         and  a  5-mo  studj[  of clarifier performance was begun.  By mid-April, however,
         it became apparent  that even though steady-state operation was being main-
         tained,  the effluent turbidity was  stijjl  not equal  to that which has been
         obtained  earlier  during the mobile  pilot  plant studies.  Microscopic studies
         of the secondary  effluent led to the conclusion that the floe was being
         sheared  by  the aerators to a certain extent, which  was the cause of the
BEGIN     cloudiness  in  trie effluent.  On April 29, 1976, the mixer speed in the fourth
LAST LINE si-age  of  the reactor was reduced from 68  rpm to 45  rpm, which represents a _
OF TEXT wredyction in power  of about 33 percent.!	
             _           j                    _  ,
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                                                                             BOTTOM OF
                                                                             IMAGE ARE/
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                                                                             AND ILLUS-
                                                                             TRATIONS
EPA-287 {Cm.)
                               PAGE NUMBER

-------
The effect of the power reduction in the fourth stage of the reactor was two-
fold.  First, the effluent turbidity was improved as expected following the
change.  Second, the gas leakage into the clarifier was further reduced but
not eliminated.  Following the extended steady-state operating period and
clarifier evaluation, the pilot plant was taken out of service and a larger,
more permanent baffle was installed in place of the one installed earlier.
On September 13, 1976, the pilot plant was re-seeded and since that time the
system has performed very well.  There is no longer any gas leakage into the
clarifiers, and useful oxygen utilization data have become available.

PILOT PLANT OPERATIONAL PHASES

Air Sparged Turbine Pilot Plant

As previously mentioned in the startup subsection, initial startup opera-
tional problems were encountered from the high energy input to the aeration
basin, which were manifested in shearing of the floe.  After these startup
problems were resolved in mid-February through slowing down of the aerator's
speed, the pilot plant started its first steady-state phase in February 1975.
The time period of February 1975 through March 1976 has been divided into
nine steady-state operational phases.  The basic criteria used in defining
steady-state operational phase were the mean cell residence time (MCRT or Oc)
and aeration period (V/Q).  These two major operational parameters or in-
dependent variables were held constant for a given mode of operation.  The
resulting operational data for the nine phases are summarized in Table 2.

The pilot plant operational phases can be further divided into two areas.
Phases I through VI were conducted to determine the operational limitations
of the DTST system and to verify the organic and trace constituent removals
that the diffused air activated sludge pilot plant achieved during a previous
study.  Although Phases VII through IX do not show much variation between the
basic operational parameters of MCRT and aeration period, extensive testing
of the final clarifiers was conducted during these phases.  During Phases VII
through IX, a secondary operational parameter, recycle rate, was varied to
determine its,effect on the solids inventory, clarifier hydraulics, and
loading rates.  Also, the DTST operation for Phases VIII and IX was conducted
to provide parallel operation data for comparison with the oxygen pilot
plant.  Although Phases VIII and IX do not correspond to a specific phase
of operation for the oxygen system, they do represent parallel operational
periods and, for the most part, all of the pilot plant data can be used to
compare the two types of systems based on similar operational  conditions.

Phase I represents the first steady-state operational period of the DTST
pilot plant.  During this phase, the pilot plant was operated at a 5.6-hr
aeration period and a 6.8-day MCRT was maintained.  The 7-day MCRT was
maintained to keep a high level of solids within the system.  These solids
were maintained to ease the transition to the shorter aeration periods and
higher loadings for which the system was designed.  Under these operational
conditions, partial nitrification was achieved.   The partial nitrification
and the long detention time in the final  clarifier resulted in denitrification
and, hence, rising sludge in the final clarifier.  To alleviate the rising


                                     12

-------
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TABLE 2. SUMMARY OF OPERATIONAL PARAMETERS -- AIR-SPARGED TURBINE SYSTEI^





































PARAMETER

DATES
Start
End
Duration, days
Flow Pattern
REACTOR
Influent Flow, m3/day (mgd)

Recycle, %
Hydraulic Detention Time
V/Q, hr
V/(Q+R), hr
MLSS, mg/1
Volatility, %
Mean Cell Residence Time
Reactor Solids, days
Total System Solids, days
Organic Loading Rate
BODR/MLVSS, kg/kg/day
BODR/TPVSS, kg/kg/day
CODR/MLVSS, kg/kg/day
CODR/TPVSS, kg/kg/day
BODA, kg/rrvVday (Ib/ft3/day)

Sludge Production
VSS/BODR, kg/kg
VSS/CODR, kg/kg
CLARIFIER
Overflow Rate, m3/m2/day (gpd/ft2)

Detention Time
V/Q, hr
V/(Q+R), hr
Solids Loading Rate, kg/m3/day (lb/ftj/day)
Return Sludge Concentration, %
SVI, ml/g
m
m

TL
^




co oo 3; O
;H — Q -0 m
O " m m
2 a «
rn
r


i
i
i

PHASE
I

2/9/75
3/1/75
21
Steady

1200
(0 32)
90

5 6
2 9
3100
72

5 1
6 8

0 34
0 26
0 80
0 60
0 75
(12 0)

0 51
0 22

18 3
(450)

4 0
2 1
107
(1714)
0 7
252
II

3/9/75
3/29/75
21
Steady

1700
(0 45)
65

4 0
2 4
3400
73

3 7
5 4

0 38
0 27
1 07
0 74
1 00
(16 0)

0 64
0 27

21 3
(523)

2 8
1.7
117
(1874)
0 9
183
III

4/6/75
5/3/75
29
Steady

1700
(0 45)
45

4 0
2 8
2600
74

2 2
3 3

0 49
0 33
1 30
0 87
1 03
(16 5)

0 79
0 34

16 9
(415)

4 3
3 0
63
(1009)
0 9
163
IV

5/11/75
6/21/75
42
Steady

1900
(0 50)
40

3 5
2.5
4000
73

3 7
5 5

0 30
0 23
0 90
0 60
1 15
(18 4)

0 73
0 30

18 3
(450)

4 1
2 9
103
(1650)
0 9
165
V

7/20/75
8/30/75
42
Steady

1700
(0 45)
44

4 0
2 8
2300
73

1 8
2 8

0 70
0 47
1 61
1 06
1 34
(21 5)

0 70
0 35

16 1
(395)

4 5
3 1
54
(865)
0 9
227
VI

9/28/75
10/25/75
28
Steady

1500
(0 40)
29

4 5
3 5
3300
70

3 0
4.3

0 49
0 33
1 16
0 82
1 24
(19 9)

0 56
0 26

14 7
(361)

5 0
3 9
63
(1009)
1 2
200
VII

10/26/75
11/20/75
26
Steady

1500
(0 40)
38

4 5
3 3
3300
71

3 2
4 3

0 44
0 30
1 00
0 75
1 12
(17 9)

0 63
0 31

14 7
(361)

5 0
3 6
68
(1089)
1 1
160
VIII



11/27/75
12/25/75
29

Steady



1500
(0
40)

50

4
3

5
0



3600
70

3
4

0
0

4
5

44
30






1.00
0
1
(19

0
0

14
75
20
2)

63
30

7







(361)

5

n


3 3
83
(1329)
1 1
173

y


IX

3/4/76
3/25/76
22
Steady

1300
(0 34)
47

5 3
3 6
2900
70

3 6
5 9

0 45
0 29
1 10
0 68
0 97
(15 5)

0 60
0 27

19 4
(476)

3 6
2 5
83
(1329)
0 9
146





































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-------
sludge problem, the sludge was removed as rapidly as possible from the final
clarifier as indicated by the 90-percent recycle rate.

As the system showed signs of stabilizing, the aeration time was decreased to
4.0-hr and the MCRT was reduced to 5.4 days.  At these conditions, the DTST
system was able to maintain good organic removals and effluent clarity, but
rising sludge was still a problem, which again resulted in an inordinate
amount of solids being carried over the weir into the effluent.

During Phase III operation, the aeration period was maintained at 4.0 hr, but
the MCRT was lowered from 5.4 to 4.0 days.  Under these conditions the or-
ganic removals remained good.  The problem of solids carry over in the final
effluent was alleviated by switching to the longer final clarifier as indi-
cated by the lower over flow rate of 16.8- m3/m2/day (412 gpd/ft2)

The aeration period was lowered to 3.5- hr in Phase IV, and to maintain rea-
sonable loading rates on the system at this short aeration period, the plant
solids were increased by increasing the MCRT to 5.6 days.  Good treatability
was observed under these operational conditions.

Phase V operation constituted the highest sustained loading period of the
study for the DTST pilot plant.  Although the aeration time was increased
slightly to 4.0 hr, the MCRT was reduced to 2.8' days.  Even though the DTST
was able to treat the wastewater under these conditions, the pilot plant was
extremely sensitive to operate.  This was reflected by a 2-wk period within
this phase when the effluent suspended solids averaged 30 mg/1.  The pilot
plant, however, soon reached an overloaded condition after this short period
of good operation, and the effluent quality started to decline.

The aeration period was increased to 4.5-hr, and the MCRT was increased to a
more manageable 4.3-days in Phase VI.  The DTST system responded to these
operational changes, and stable operation of the pilot plant resumed.

Phases VII and VIII were a continuation of Phase VI with the aeration period
and MCRT remaining the same for all three phases.  However, the 30-percent
recycle rate in Phase VI was increased to 40 percent in Phase VII and 50-
percent in Phase VIII.  During these phases, the effect of the sedimentation
tank hydraulics, overflow rate, and solids loading rate on the thickening of
the return sludge was studied.  Also, the effect of the recycle rate on the
mass flow back to the reactor was studied.

The aeration period was further increased to 5.3 hr in Phase IV while the
MCRT was increased to 5.9 days.  This operational mode was run to see if the
DTST system could operate under conventional conditions and not have the
nitrification-denitrification problems that were associated with Phase I.

UNQX Pilot Plant

Simply stated, the major objectives of the high purity oxygen pilot plant
studies were twofold: first, to gather information that would be pertinent to
the full-scale treatment plant design effort that was being conducted con-
currently and, second, to develop operational techniques which could simplify

                                      14

-------
the startup and operation of this full-scale system.  The 0.6-1/sec (10-gpm)
mobile pilot plant had provided treatability information and data to allow
some equipment sizing, but certian key design questions were left unanswered
at the completion of the mobile pilot plant testing.  First, the clarifier
used during the preliminary studies was an unconventional circular model that
provided low overflow rates and a great deal of sludge storage capacity.
Since the full-scale system would be operated using rectangular clarifiers
that were smaller in relation to the biological reactor than had been the
case during the preliminary studies, it was imperative that the performance
of rectangular clarifiers be evaluated.  This evaluation is critical since
the operation of a high purity oxygen system is generally limited by the
ability of the secondary clarifier to store and convey sludge solids.

The second key question to be addressed by the 1900-m3/day (0.5-mgd) plant
operation concerned the system oxygen requirements, particularly the daily
fluctuation in oxygen demand, which is a result of the diurnal  variation in
flow and organic loading at the JWPCP.  Information in this regard would have
a direct bearing on the selection of equipment for the cryogenic oxygen
generating system that is being provided to supply oxygen to the biological
treatment system.

The priorities of the 1900-mVday (0.5-mgd) pilot project following the July
1975 startup were to stabilize the system at design conditions as quickly as
possible and to collect data relative to the required design information.
Beyond this, information regarding system limitations and overall operation
would be documented.  This phase of operation would require the more rigorous
approach to pilot operation of biological treatment systems wherein the
system performance would be evaluated over an entire range of organic loading
rates and aeration periods.

As a result of the startup difficulties outlined earlier in this report,
acceptable operation of the pilot plant could not be achieved before late
September 1975.  Only 4 days of good operation (Phase I) were recorded before
the pilot plant was taken out of service on September 25, 1975, for,  the
installation of surface aerators.  From this point until mid-October 1976,
the operation of the pilot plant has been divided into eight periods, which
are representative of good steady operating periods and/or periods during
which specific objectives were being met.  Operational parameters are sum-
marized in Table 3.

Phase I, though it includes only 4 days of testing, is significant in that
it represents the first successful pilot operation in which the system was
operated under a simulated diurnal plant flow condition.

Phase II represents the first period of good operation following the instal-
lation of surface aerators in the biological reactor.  During this period,
attempts were made to stabilize the operation at the 7-day design MCRT
in order to begin the evaluation of the rectangular clarifier as well as to
further establish the organic removal  and oxygen demand relationships.  It
was during this period, however, that the gas "boiling" problem outlined
earlier was first discovered.  By late October 1975, the difficulty became


                                     15

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TABLE 3. SUMMARY OF OPERATIONAL PARAMETERS -- OXYGEN SYSTEM
-^ . , • . 1













































\











































PARAMETER

DATES
Start
End
Duration, days
Flow Pattern
REACTOR
Influent Flow, m3/day (mgd)

Recycle, %
Hydraulic Detention Time
V/Q, hr
V/(Q+R), hr
MLSS, mg/1
Volatility, %
Mean Cell Residence Time
Reactor Solids, days
Total System Solids, days
Organic Loading Rate
BODR/MLVSS, kg/kg/day
BODR/TPVSS, kg/kg/day
CODR/MLVSS, kg/kg/day
CODR/TPVSS, kg/ kg/day
BODA, kg/mJ/day (Ib/ft3/day)

Oxygen Utilization
02/BODR, kg/kg
09/CODR, kg/kg
Sludge Production
VSS/BODR, kg/kg
VSS/CODB, kg/ kg
CLARIFIER
Overflow Rate, m3/m2/ day (gpd/ft2)

Detention Time
V/Q, hr
V/(Q+R), hr
Weir Loading Rate, m3/m/day
(ft3/ft/dav)
Solids Loading Rate, kq/m^/day
(Ib/ft3/day)
Return Sludge Concentration, %
SVI, ml/g
r
?i

'



PHASE
I

9/22/75
9/25/75
4
Diurnal

1900
(0 51)
40

2 5
1 8
3800
75

1 8
3 4

0 70
0 31
1 67
0 89
2 15
(34 4)

1 36
0 71

0 97
0 48

18 7
(159)

3 7
2 8
79 1
(852)
98
(1568)
1 05
78
II

10/27/75
11/10/75
15
Steady

1500
(0 40)
40

3 1
2 2
2800
73

2 5
5 9

0 74
0 31
1 52
0 64
1 73
(27 7)

—
—

0 60
0 29

23 2
(570)

3 0
2 2
62 6
(674)
90
(1440)
1 06
153
III

12/1/75
12/30/75
30
Steady

1400
(0 37)
44

3 4
2 3
4200
74

3 4
6 8

0 52
0 26
1 11
0 56
1 62
(25 9)

—
—

0 64
0 28

21 2
(521)

3 3
2 3
52 2
(562)
127
(2032)
1 40
99
IV

2/1/76
2/17/76
17
Steady

1700
(0 45)
41

2 8
1 9
4600
72

1 9
5 6

0 60
0 20
1 31
0 45
2 03
(32 5)

—
—

0 63
0 29

25 4
(625)

2 8
1 9
68 9
(741)
168
(2688)
1 54
65
V

2/18/76
2/29/76
12
Steady

1900
(0 51)
42

2 5
1 6
3300
75

1 7
3 4

0 83
0 42
1 61
0 81
2 05
(32 8)

—
--

0 78
0 40

28 4
(698)

2 4
1 7
77 0
(829)
134
(2114)
1 18
83
VI

3/31/76
5/20/76
51
Steady

1900
(0 51)
40

2 5
1 8
3900
74

1 9
4 4

0 69
0 29
1 54
0 64
2 00
(32 0)

--
—

0 80
0 36

27 9
(686)

2 5
1 8
101 2
(1089)
152
(2432)
1 36
77
VII

6/21/76
9/14/76
85
Steady

1800
(0 48)
38

2 6
1 9
4100
77

2 7
4 8

0 57
0 33
1 15
0 66
1 76
(28 2)

—
—

0 69
0 33

27 5
(676)

2 5
1 8
99 4
(1070)
141
(2256)
1 22
83
VIII

9/30/76
10/13/76
14
Steady

1900
(0 51)
40

2 5
1 8
4420
75

2 1
3 8

0 48
0 27
0 95
0 54
1 63
(26.1)

1 52
0 81

0 84
0 42

18 1
(445)

3 8
2 7
101 5
(1092)
113
(1808)
1 34
113
IX

10/28/76
11/7/76
11
Diurnal

1900
(0 51)
39

2 5
1 8
3700
70

2 0
4 2

0 67
0 32
1 46
0 69
1 94
(31 0)

1 24
0 69

0 98
0 38

28 4
(698)

2 5
1 8
102 3
(1101)
147
(2352)
0 88
124
X


11/9/75
11/24/76
16

Diurnal

1600
(0 43)
47

3 1
2 1
3990
70

3 0
6 6

0 55
0 24
1 07
0 47
1 54
(24 6)

1 48
0 71

0 74
0 38

23 3
(573)

2 9
2 0
84 2
(906)
141

































(2256)
0 99
114


XI

12/10/76
12/23/76
14
Diurnal

1600
(0 43)
39

3.0
2 2
3840
77

2 8
5.4

0 51
0 27
1 05
0 55
1 44
(23 0)

1 49
0 70

0 66
0.37

23 2
(570)

2 9
2 1
85 8
(923)
126
(2016)
0 94
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clearly defined and a decision was made to forego the oxygen utilization
investigations until a later date so that the evaluation of the final clari-
fier could proceed.

The turbulence created at the clarifier inlet by the escaping gas resulted in
an unusual amount of solids being lost through the clarifier skimming system.
Because of the difficulty in both measuring and controlling this solids loss,
the actual phase average cell MCRT was less than the desired 7-day level.
Attempts at controlling this solids loss to sustain good operation at the
desired MCRT ultimately resulted in the loss of steady-state conditions and
an end to this phase of the pilot operation.

Because of the construction at the JWPCP, it became necessary to relocate the
pump suction lines of the pilot plant influent pump station.  As a result of
this change, it was not possible to operate the pilot plant at the design
flow rate (1900 m^/day or 0.5-mgd) during most of December 1975.  Though,
by strict definition, a steady-state condition was never achieved during this
period, Phase III of the pilot plant study represents a period of good stable
operation under adverse conditions.  During this period, attempts were made
to improve sludge settleability.  Moreover, the first attempt was made toward
correcting the gas leaking problem outlined earlier through the addition of a
baffle by representatives of Union Carbide^

During January and the early part of February 1976, several attempts were
made to stabilize the operation at both the design flow (1900
-------
finally terminated on May 20, 1976, when repeated power outages, created by
construction at the JWPCP, resulted in a pilot plant upset.

Continuing construction interruptions prevented a rapid return to steady oper-
ation.  However, by June 21, 1976, the pilot plant was once again at steady-
state conditions and a second sustained period of good operation (Phase VII)
under design loading and conditions was begun.  During this phase of opera-
tion, additional data were compiled relating both to organic and hydraulic
parameters.  Specifically, a series of radioactive tracer studies were begun
during Phase VII which were designed to determine the movement of sludge
solids through the final clarifier.

At the conclusion of the first series of clarifier tracer studies, the pilot
plant was taken out of service and corrections were made to the baffle in the
fourth stage of the reactor.  This revision was outlined earlier in this re-
port.  After completing the baffle, operation was resumed in the longer of
the two pilot clarifiers in order to accommodate further testing of sludge
solids movement by the radioactive tracer method.  Phase VIII summarizes the
nearly 4 wk% of operation in the long pilot clarifier, which represents the
only change from operation during Phase VII.

Following the tracer studies, the flow was diverted back to the shorter
clarifier and the diurnal flow pattern was again instituted.  Some difficul-
ties were encountered with the operation of the flow controller, but the
pilot plant was stabilized in "the diurnal flow pattern by October 28, 1976.
Phase IX extended from October 28 to November 7, 1976, and was characterized
by a 1900-m3/day (0.5-mgd) average diurnally varied feed rate and a constant
return sludge flow rate.

The clarifier operation during Phase IX was generally unsatisfactory.  During
the peak flow periods, the sludge blanket would rise to within 0.6 m (2-ft) of
the surface, which resulted in an increase in effluent suspended solids.  The
peak flow in the diurnal cycle resulted in a clarifier overflow rate in
excess of the design peak loading of 37-m3/ m2/day (900 gpd/ft2), so on
November 8, a 1900-m3/day (0.5-mgd) peak flow diurnal flow pattern was intro-
duced.  Phase X extended from November 9 to November 24, 1976, and includes
the data from the reduced diurnal flow pattern.  During this period, the
operation of the pilot plant improved, but the clarifier sludge blanket
remained high during peak flow and the effluent suspended solids remained
above the Federally-mandated 30 mg/1.

Further investigation indicated that the variation in the recycle ratio re-
sulting from the constant return sludge flow and the diurnal influent flow
was responsible for the poor clarifier performance.  During low flow, the
return ratio was high and the mixed liquor became more concentrated.  When
peak flow was reached, this concentrated mixed liquor was pushed into the
clarifier and the clarifier loading was extremely high.  This high solids
loading was responsible for the high blanket and poor effluent.

To overcome this difficulty,  it was necessary to operate the return sludge
in a diurnal flow pattern.  During Phase XI, December 10 to December 23,
                                     18

-------
1976, the same diurnal influent flow pattern employed in Phase X was used,
but the return sludge flow was varied to maintain a constant recycle ratio.
The return sludge had to be manually adjusted; therefore,  because of manpower
limitations, the pilot plant was operated at a constant flow of 1500 m^/day
(0.4-mgd) during the weekends.  The frequent changes in operation modes
caused minor upsets, but the pilot plant did produce satisfactory effluent
quality.
                                     19

-------
                                 SECTION 5

                           DISCUSSION OF RESULTS
EFFLUENT QUALITY

Activated sludge systems consist of two component units—the aerator/reactor
and the final clarifier.  The quality of the final effluent is related to the
interaction of the component parts, and poor effluent may be caused by an
inadequacy of only one part.  The effluent quality of the air and oxygen
systems is described in Tables 4 and 5.

Soluble COD and BOD

A primary indicator of the adequacy of the reactor in terms of oxygen trans-
fer and treating the wastewater is the removal of soluble organics.  In all
phases, for both pilot plants, the soluble BODc removals equalled or exceeded
95 percent.  Phase average effluent soluble BOD5 concentrations were 6 mg/1
or less.  These BOD measurements are low enough that differences between the
two systems are not considered significant.

A small but definite difference between the systems is, however, apparent in
the soluble COD data.  The oxygen system produced effluent with consistently
higher soluble COD.  The data plotted in Figure 4 indicate that the principle
cause of this is the lower aeration time maintained in the oxygen reactor.
The oxygen data fit an eyed-in linear extrapolation to the air data reason-
ably well.  The actual function should turn upward at the lower aeration
times, reaching the influent concentration of 250+ mg/1 at zero aeration
time.  Such a curve might be drawn to represent a better fit to the data in
Figure 4.

When the soluble COD data are grouped according to aeration time and plotted
against MCRT (Figure 5), it is apparent that, except at low values of less
than 3™days, the MCRT has very little effect on soluble COD removal.

Suspended Solids

Secondary effluent solids concentrations depend on the effectiveness of the
final clarifier.  High effluent suspended solids, however, may be an indica-
tion of poor clarifier design, poor aerator design, or poor plant operation.
During startup, both 190Q-m3/day (0.5-mgd) pilots plant experienced periods
of high effluent suspended solids and turbidity, which were alleviated by
reducing the power input to the final stages of the reactors.
                                      20

-------
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TABLE 4. SUMMARY OF EFFLUENT QUALITY, — AIR SYSTEM
-































































,
PARAMETERS

Aeration Period (V/Q), hr
MCRT (Total System), days
Flow Pattern
Suspended Sol ids
Influent, mg/1
Effluent, mg/1
Removal , %
Total BOD
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Soluble BOD .
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Total COD:
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Soluble COD
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Grease (By Hexane Extraction)
Influent, mg/1
Effluent, mg/1
Removal , %
Ammonia
Influent, mg/1 N
Effluent, mg/1 N
Removal , %
n
in H
VI | v~


PHASE

I
5 6
6 8
Steady

167
89
46.7

178
15
91 6
118
2
98 3

458
118
74 2

262
49
81.3

51 2
8.2
84 0

35.1
14.2
59.5

II
4.0
5 4
Steady

179
80
55 3

167
17
89 8
102
3
97 1

447
152
66 0

247
56
77 3

40 6
6 1
85 0

32 4
20.3
37.3

III
4 0
3.3
Steady

167
67
59.9

172
15
91 3
98
3
96 9

453
130
71.3

234
59
74 8

36 5
4 8
86.8

34.7
27.8
19 9

IV
3 5
5.6
Steady

170
22
87 1

171
8
95 3
101
4
96 0

460
77
83.3

241
56
76 8

37 8
1.0
97.4

34 7
31 6
8.9

V
4 0
2.8
Steady

204
110
46 1

224
16
92 9
126
5
96 0

513
191
62 8

265
72
72 8

-
_
_

31 4
27.8
11.5

VI
4.5
4.3
Steady

204
36
82.4

234
12
94 9
132
4
97 0

556
91
83 6

257
57
77 8

-
-
_

36.3
32.1
11 6

VII
4 5
4.3
Steady

165
37
77.6

212
12
94 3
129
2
98.4

483
92
81 0

270
55
79.6

-
_
_

33.3
27 5
17 4



VIII
4
4
5
5


Steady

216
54
75

226
13
94
109
2
98.

515
111
78

256
48
81

_
_
_

34
32
6

I



0



2


2



4



3





1
1
1






























IX
5 3
5 9
Steady

177
29
83 6

211
18
91 5
119
2
98 3

517
84
83 8

282
54
80 9

_
_
_

37 7
30.7
18 6


































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TABLE 5. SUMMARY OF..E^L-UENT; QUALITY |— OXYGEN SYSTEM \
^ 1











—





















3

































PARAMETERS

Aeration Period (V/Q) , hr
MCRT (Total System) , days
Flow Pattern
Suspended Sol ids
Influent, mg/1
Effluent, mg/1
Removal , 7,
Total BOD,,
Influent, nig/1 0
Effluent, mg/1 0
Removal , 7
Soluble BODS
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Total COD
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Soluble COD
Influent, mg/1 0
Effluent, mg/1 0
Removal , %
Grease (By Hexane Extraction)
Influent, mg/1
Effluent, mg/1
Removal , 7,
Ammonia
Influent, mg/1 N
Effluent, mg/1 N
Removal , %
PHASE
I
2 5
3 4
Diurnal
189
17
91 0

219
11
95 0

131
4
96 9

467
81
82 7

249
62
75 1

42 6
1 0
97 7

31 8
26 3
17 3
11
3 1
5 9
Steady
165
18
89 1

221
7
96 8

132
3
97 7

523
87
83 4

213
68
68 1

38 4
0 9
97 7

34 2
31 4
8 2
111
3 4
6 8
Steady
242
28
88 4

231
12
94 8

105
3
97 1

554
94
83 0

258
58
77 5

47 1
3 0
93 6

33 2
30 5
8 1
IV
2 8
5 6
Steady
201
54
73 1

238
20
91 6

122
5
95 9

561
122
78 3

279
59
78 9

55 8
4 4
92 1

31 6
31 3
0 9
V
2 5
3 4
Steady
172
28
83 7

219
21
90 4

121
6
95 0

486
100
79 4

283
67
76 3

41 6
2 5
94 0

36 4
31 0
14 8
VI
2 5
4 4
Steady
202
21
89 6

212
12
94 3

115
3
97 4

536
88
83 6

279
66
76 3

62 4
1 7
97 3

36 9
31 5
14 6
VII
2 6
4 8
Steady
142
17
88 0

187
8
95 7

93
2
97 8

438
82
81 3

255
64
74 9

63 8
1 6
97 5

31 6
29 5
6 6
VIII
2 5
3 8
Steady
140
14
90 0

176
5
97 2

90
1
98 9

400
71
82 2

260
58
77 7

45 8
1 3
97 2

33 8
28 9
14 5
IX
2 5
4 2
Diurnal
150
48
68 0

204
13
93 6

134
1
99 3

415
116
72 0

272
64
76 5

46 0
6 2
86 5

27 8
28 0
-0 7
X
3 1
6 6
Diurnal
130
34
73 8

173
12
93 1

100
2
98 0

431
97
77 5

280
63
77 5

39 2
2 8
92 9

34 3
28 7
16 3
XI
3 0
5 4
Diurnal
120
20
83 3

185
6
96 8

124
2
98 4

446
83
81 4

305
65
78 7

40 6
2 3
94 3

37 2
33 8
9 1

































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0 <, 1 2 3 4 5 6
' ' / AERATION TIME, hr*
i
Figure 4. Soluble COD versus aeration time.
startup, the oxygen system met the Federal discharge standard of not
more than 30 mg/jl for a 30-consecutive-day. average in all phases except IV




and IX
traced
solids
During
. In both of these cases, the high effluent suspended solids can be
to high clarifier solids loadingi. In Phase IV, the highest clarifier
loading of the study, 168 kg/m2/|day (34- lb/ft?7day) , was experienced.

'






Phase IX, the average solids loading was lower, but during the peak of
jthe diurnal flow pattern, the solids leading exceeded those in Phase IV. A
major cause of the periodic high loadinigs in Phase IX rested in the return
[sludge





operation'. During Phase IX, the feed flow was varied in a diurnal
Flow pattern, but the return sludge flow was held constant. During low flows,
the relatively high return sludge ratio] would result in a concentrated mixed
liquor
trated
in the reactor. When the influent flow was increased, the concen-
mixed liquor was forced into the clarifier at a hiqh flow rate and
;orresponding high solids loading rate. Two steps were taken to correct this
BEGIN condition. The return sludge flow was varied in proportion to the influent
LAST LINE £l2_w to mainta"in| a more nearly constanti mixed liquor concentration, and the
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                                             3         4
                                             MCRT, days*
                        Figure  5.   Effluent soluble COD versus MCRT.
                                               I
                        i                       1
         low to the unit was decreased from  a  1,900-m^/day  (0.5-mgd)  average  flow to a
        1900-m3/day (O.ff-mgd) peak flow.       1

        The deep tank submerged turbine system [met the  30-mg/l effluent  suspended
        solids standard lonly in Phases IV  and  IX.  Phases  VI  and  VII  were  charac-
        terized by generally low effluent  suspended solids with a few unusually  high
        days.  Without those days, the 30-mg/l [standard would  have been  met  in those
        phases as well, j The poorer performance of the  air system is  due in  part to
        characteristics ,of air activated sludge and in  part to the way the system was
        operated.       j                       I

        Three basic causes of high effluent  suspended solids  were observed during the
        DTST study.  Durjing startup and Phases {ill and  V,  the  sludge  did not floc-
        culate and settle well.  These conditions were  attributed to  excessive shear
        in the reactor d'uring startup and  the  low MCRT's of 3.3 and  2.8-days main-
BEGIN
LAST LINE
OF TEXT r
i. a j lieu uui iny riia^co ill aim », p capci. i; I vc i jr . i
' 1 | BOTTOM Or
1 1 ( IMAGE AREX
Those low MCRT'sjwere used to control the nitrification-denitrif ication that | OUTS1DE
had occurred during Phases I and II. during the early part of the study, the 1 DIMENSION
D-TST plant was operated in a manner conducive to partial nitrification. WhenJ Ff)n TAH, FS
A ip i 	 ] 	
'J V „_ t^^Kiiii^^iica
^AND SLLUS-
J TRATIONS
          EPA-287 (Gin.)
                                          PAGE NUMBER

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the sludge was stored in the clarifier, nitrate and nitrite nitrogen were
reduced to nitrogen gas.  Bubbles formed which attached to sludge particles
and resuspended them.  Nitrifying bacteria grew more slowly than other
activated sludge organisms, and the nitrification-denitrification conditions
were eliminated by reducing the aeration time and/or the MCRT.  In Phases III
and V, however, the rising sludge was replaced by bulking sludge, and no
improvement in effluent quality was achieved.

During Phases VI, VII, and VIII, the system was operated at the same aeration
time and MCRT, but the recycle rate was varied from 30-percent to 40 percent
and 50-percent.  At the 30- and 40-percent recycle rates (Phases VI and VII,
respectively) the pilot plant produced a generally good effluent, but at the
50-percent recycle rate (Phase VII), the clarifier was overloaded and the
pilot plant produced poor effluent.

Although the oxygen pilot plant produced low suspended solids effluent more
frequently than the air system, it is unfair to conclude from that infor-
mation alone that oxygen activated sludge produces a lower suspended solids
effluent.  The oxygen system in these studies was operated much more con-
servatively than the air system.  The oxygen system was operated within the
known capability of such a system with an emphasis on refining certain design
parameters, but the air system was operated to define the limitations of the
deep tank turbine aeration system.

Both plants did demonstrate an ability to produce a good quality effluent.
The air system, however, did prove to be more sensitive to operate.  The main
causes of this sensitivity is the tendency of the system to achieve partial
nitrification, which resulted in rising sludge, and the measures that were
necessary to control that condition.

Effluent Clarity

Clarity of an effluent is an aesthetic quality which is difficult to quantify.
Since suspended solids greatly affect this quality, only periods with compar-
able effluent suspended solids concentrations can be used for comparisons.
Those phases which averaged between 20 and 30 mg/1 suspended solids were
selected, and the data are presented in Table 6.

The turbidity in these effluent samples exhibited a correlation with sus-
pended solids for each system, but the air system had slightly lower turbidi-
ties for given suspended solids concentrations.  However, the Secchi disc
transparencies, which were measured in the secondary clarifiers, indicate
that the air system should have produced a much clearer effluent.   Visibility
in the final clarifiers was 20 to 40--percent greater in the air system.  This
confirms a general observation that whenever both systems were operating
well,  or rising sludge was present in the air system, the liquid fraction in
the clarifier was much clearer in the air system than in the oxygen system.
Similarly, the supernatant in the laboratory settling tests was visually much
clearer for the air system than the oxygen system.  No explanation for this
is available at this time.
                                     25

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DROPPED
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WPQW6 GUIDE SHEET
                            CENTER
                            OF PAGE
                                                                       TOP OF
•I "
'1
TABLE 6. "EFFLUENT CLARITY
i • , !


_.. 	 _, 6-V2" 	 -'- 	 	 	 	
SYSTEM '
Air
}
Oxygen •
PHASE
IV
IX
III
V
VI
SUSPENDED
SOLIDS,
mg/1
22
29
28
28
21
TURBIDITY,
NTU
12
16
17
21
14
SECCHI DISC
TRANSPARENCY,
m (ft)
0.68 (2.2)
0.63 (2.1)
0.49 (1.6)
0.44 (1.4)
0.55 (1.8)
_-
I
t
1
        Total COD and9B00;'
                        I
        Since the secondary effluent  suspended
                               solids are primarily escaped biologi-
        cal floe, a direct correlation should exist between  the  effluent  volatile
        suspended solids (VSS) and the effluent  BODs  and COD.  Cell material
        (C5H7N02) requires 1.42 times its massjin oxygen for complete  oxidation.1
        If the effluent iVSS are considered to be cell material,  the nonfiltrable
        (soluble) COD and the nonfiltrable ultimate BOD will be  1.42 times  the VSS.
        Figure 6 compares the nonfiltrable
        the effluent VSS concentrations.
                           COD
and ultimate BOD concentrations to
        A least squares pinear regression analysis was conducted on the oxygen  COD
        data. The resulting line failed to pass through the origin, but the dis-
        crepancy was not! statistically significant (40-percent confidence).   The
        slope of the regression line was, therefore,  adjusted to pass  through the
        origin.  A similar analysis was conducted on  the air COD data, and the  same
        line was established.  For both systems:
                        I
                        I      Total COD - Soluble COD = 1.49 VSS
        The COD to VSS riatio of 1.49 is
        the theoretical |1.42 value.
                        a reasonable experimental  approximation of
        1.  Metcalf & Eddy,  Inc., Mastewater  Eng ineering, McGraw-Hill  Book  Company,'
            New York, New York,  1972, p. 490.
          E7A-287 (Cin.)
          (4-76)
                                         PAGE NUMBER
                                                                                       TRAT10NS

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                                                                          	TCP 0?
DROPPED
HEAD,
BEGIN
SECTIONS,    ,
HERE   t>   (
                     u
                     I
                                	_1L.
BEGIN
LAST LINE
OF TEXT E>_
       I
120
  0
             -  100
             o»
             E
             UJ
             Q
             UJ
             o
                90
                80
                70
                60
             y  50
             CD
             a:  40
             .j
             fe  30
             o
                20

                 10
                  0
i     i      I
  LEGEND
    COD
 A  OXYGEN
 •  AIR
    BOD5    .
 •  OXYGEN
 •  AIR
   0    10   20   30   40   50  60   70   80
                       VSS, mg/i
                                                                    90
                   Figure 6.   Nonfiltrable  COD and BODs versus VSS.
            3/8"
                                                                         •c=4
                                                             BOTTOM OF
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         (4-76)
                                    PAGE NUMBER

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  HERE
DROPPED
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BEGIN
SECTIONS
HERE
TCP! RUG GUIDE SHEE"
                              CENTER
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>, IMAGE
BEGIN
LAST LINE
OF TEXT
*-— v
>
JS
F
fj
$_yisual inspection of Figure 6 indica
Tlinear correlation with VSS. The hi
for either system was 21 mg/1.
Hexane Extractab'les (Grease)
;T.h~e phase-average effluent hexane extr
;mgd) pilot plants and the two smaller
effluent suspended solids in Figure 7.
two parameters is evidenced in Figure
0 and a slope of! 0.086 is the linear n
large-scale systems. A linear regress
yields a hexane 'extractable to suspend)
hexane extractable concentration backgi
1
While a theoretical relationship betwei
been established to substantiate the e.
final clarification for grease removal
the grease removal efficiencies of the
elfcept-the- var ratton6cVus'ed~b;y h rgh-ef 1
I
Ammonia-Nitrogen
$
Four oxidation s,ta,tes of nitrogen are
vated sludge system. Nitrogen in wast<
(-3). Reduced nitrogen is found free
acids. In the presence of dissolved o;
nitrogen may beioxidized to nitrite ni
gen (+5) through a process called nitr-
with the appropriate bacteria present,
elemental nitrogen (N? gas) by denitri
!
Ammonia nitrogen may be removed by niti
No indications of nitrificaton in the <
nitrate and nitrjite nitrogen were near
the associated solids handling study 11
moval was due to cell synthesis. 3
Low ammonia nitrogen removals are char<
systems since nitrification generally <
process. There iare usually two reason:
2. Stahl, J. F.;, Hayashi, S. T. Austii
Operation of Small Scale Activated
Water Pollution Control Plant, Los
Whittier, California, April 1974.
3. Austin, S. R., Memorandum - Reduce<
Secondary Treatment System, Los Am
Whittier, California, January 1978!
ies that the BODg data do not represent |
ghest-phase average total 8005 recorded
ictable data from both 1900-m3/day (OT?
scale-pilot plants'1 are plotted against
| A direct relationship between these
[. The line drawn with an intercept at
egression of the data from the two
ion of all data shown in Figure 7
id solids ratio of 0.067 and a soluble
•ound level of 0.9-mg/l.
in grease and suspended solids has not
cperimental data, the importance of
has been emphasized. No difference in
air and oxygen systems was found
•"luent— suspen"ded~so"Vi'ds. 	 *>
'mportant in the operation of an acti-
>water is normally in the reduced state
is ammonia or as a component of ami no [
cygen and specific bacteria, ammonia
:rogen (+3) and then to nitrate nitro- '
fication. In a reducing environment,
these oxidized forms may be reduced to
:i cat ion.
•ification or by conversion to cells.
»xygen system were observed. Effluent
zero, and a mass balance performed for
idicated that all reduced nitrogen re-
icteristic of most high purity oxygen
Joes not occur during the reaction
, given for this phenomenon: first,
i, S. R., Shamat, N., Summary Report -
Sludge Pilot Plants at the Joint
Angeles County Sanitation Districts,
i Nitrogen Mass Transfer in the JWPCP
jeles County Sanitation Districts,
I
                                                                            AREA
                                                                            BOTTOM OF
                                                                            IMAGE ARE;
                                                                            OUTSIDE
                                                                            DiWiENSION
                                                                            FOR TABLES
                                                                                ILLUS-
                                                                            TRATIONS
           EPA-287 ICin.l
                                             PAGE NUMBER

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  FIRS"
  LiME OF
  *-—vy
    ^  r*
  HERE r-~
                         : SHEE
                     CENTER
                     OF PAGE
                  TOP OF
                 xSiMAGE
                 =1 AREA

              10
           o> 8
           E
           UJ  7
           CO  '
           <
           LU
           o:
           2  6
           UJ
           DO  5
              4
           UJ

           1  2
           UJ
  II      1111
             LEGEND
A LARGE  SCALE OXYGEN SYSTEM
• SMALL SCALE  OXYGEN SYSTEM
• LARGE  SCALE  AIR SYSTEM
* SMALL SCALE  AIR SYSTEM
                                     JL
                                    I
                                                            I    T

                                                                 *
J_
I
                          20    30   40    50   60    70   80
                          EFFLUENT SUSPENDED SOLIDS, mg/i
                                              90   100
              Figure 7>.  Hexane extractables iyersus effluent suspended solids.
                                                                            r-
LAST LINE'
OF TEXT d;
             3/8
         EPA-287 (Cin.f
         (4-7G)
                                     PAGE NUMBER
                                                          1 OUTSIDE
                                                         -* DIMENSION
                                                         J FOR TABLES
                                                         VAND ILLUS-
                                                          , TRATSONS

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WP1KG GUIDE SHEET
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                            OF PAGE
  HERE  c^juj-e  oxygen  systems  are high-rate systems,  which usually means that the   	
        [process  is operated  at a low MCRT, thus reducing the possibility that
DROPPED  nitHfying organisms  will  establish themselves within the biomass;  second,
HEAD   post  pure oxygen  systems are sealed reactors to maximize oxygen utilization.
BEGIN   rs  a  result,  there  is a reduction in tlie pH of the mixed liquor through the
SECTIONS '[dissolution  of  carbon dioxide which further inhibits the growth of  nitrifying
HERE   cjpcteria.       |	|	
         Ammonia nitrogen  removals  up to 60 percent were observed in the air system.
         In  fact,  controlling  nitrification  was
         of  the  air  pilo^  plant.   Nitrification
         rising  sludge  and  high  effluent  suspended  solids.
         In  order  to control  nitrification,  the
                               a major consideration in the operation
                               followed by denitrification caused
                               aeration time and MCRT were reduced.
         The  ammonia nitrogen  removals  after Phase II  may be attributed to cell
         synthesis.

         Trace  Metals,  Cyanide,  and  Phenols
                                                                               TOP OF
                                                                                MAGE
                                                                               AREA
         €ert-ai-n-trace  consti Wt'eh'ts-were-morritored- during the-act-rvated-s-Tudtje—
         studies  at  the JWPCP.   The  data from the  1900-m3/day (0.5-mgd)  pilot  plants
         confirmed the  data from the small-scale  systems,  so a reduced  sampling
         schedule was employed  on the larger  systems.   The data from all  four  systems
         are  presentedqln/flT.ables 7 and  8.   The Discharge  limitations imposed  by the
         California  Regional  Water Quality Control  Board  (RWQCB)  on  the JWPCP  are also
         included.       !

         Chromium, nickel, and  zinc  are the three  trace constituents that are  in vio-
         lation of the  RI^QCB  standards  and will {require source control  in the  Joint
         Outfall  System. SRemovals of these metajjs  were  similar in the four activated
         sludge systems with  67 to 74-percent of  the chromium, 23 to 50-percent of the
         nickel,  and 55 to 68 percent of the  zinc  being removed.

                        i                       i
         The  influent arsenic concentrations  were  near  the detection limit,  so the re-
         moval data  are of minimal  value.   Removals  of  the other  metals ranged from
        |l40 to 83 percent, with neither the air nor  the oxygen systems  having  a clear
         advantage.      '

         Cyanide  and phenols  are organic complexes  that are subject  to  oxidation.
         Cyanide  removals ranged from 64 to 86 percent  with the oxygen  system  obtain-
        jling  the  higher Removals.   Removal  of phenols was  98 percent or  higher, with
         the  air  system producing effluents at or  below the detection limit.
BEGIN
LAST LINE
OF TEXT
(SLUDGE  PRODUCTION

One  of  the most(important  claims  made  on  behalf  of  pure  oxygen  is  that  the
net  growth of  solids  in  these  systems  will  be  less  than  a  similar  air system
when operated  all the  same  MCRT.   Since!a  large portion of  the cost of waste-
water treatment iis  usually associated  with  solids processing and sludge
handling, this claim  would represent ajsignificant  savings in both capital
•and  operating  costs.   The  claim  is  based  on  a  comparison between the two   —•
     $ 3/8"      M
     /	I	
           EPA-287 (Cm.)
           (4-76)
                                         iiiill
                                         PAGE NUMBER
                                                                      BOTTOM OF
                                                                      IMAGE ARE/
                                                                      OUTSIDE
                                                                      DIMENSION
                                                                     „ FOR TABLES
                                                                    \>AND ILLUS-
                                                                     , TRATIONS

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I 5>
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               ca
               m
               tr>
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33 O (,)
                                                                                                                                 : o

                                                                                                                           - x u ro
                                                                                                                           "-   -   m
                                                                                                                                  U
                                                                                                                                           - I r  TI to
  > •   .
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  |L-^


  ir1'
- f . - , -
^ J_
TABLE 7. TRACE CONSTITUENT REMOVAL cBY MEANS OF AIR-ACTIVATED SLUDGE















" ^ ^ _~\
**




Constituent

Arsenic
Cadmium
Total Chromium
Copper
Lead
Mercury
Nickel
Si Iver
Zinc
Cyanide
Phenol s
RWQCB Standard

Average,
mg/1
01
02
005
20
10
001
10
02
.30
10
50
10% of
Time,
mg/1
02
03
--
30
20
002
.20
.04
50
.20
1.00
1900-m3/day (0 5-mgd) Pilot Plant

Influent,
mg/1
01
017
28
22
15
--
.26
010
1.36
0.14
2 88

Effluent,
mg/1
01
008
08
06
06
--
18
006
0 58
0 05
0 01

Removal ,
%
0
53
71
73
60
__
31
40
57
64
99+
1 6-1/sec (25-gpm) Pilot Plant

Influent,
mg/1
02
020
47
33
15
0007
30
012
1 43
38
1 41

Effluent,
mg/1
01
008
14
11
06
0003
23
005
46
08
01

Removal ,
%
50
60
70
67
60
57
23
58
68
79
99+
% Samples
Over
W% Standard
0
0
100
2
0
0
63
0
35
3
0

\
\















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                  m >
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                     m
) S»

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-c ft
SSK
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a
1 
2 P



U
o T -H c D w
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hi m T "' 5
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. ^ __ - - _ . ._ , ^. ^ ^ . _, . . _ . -j . . . , , _,
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i
TABLE 8. TRACE CONSTITUENT REMOVAL BY MEANS 0^ OXYGEN-ACTIVATED SLUDGE






















Constituent

Arsenic
Cadmium
Total Chromium
Copper
Lead
Mercury
Nickel
Silver
Zinc
Cyanide
Phenols
RWQCB Standard

Average,
mg/1
01
02
005
20
10
001
.10
02
30
.10
50
10% of
Time,
mg/1
02
03
—
30
20
002
20
04
50
20
1 00
1900-m3/day (0 5-mgd) Pilot Plant

Influent,
mg/1
..
* 024
27
22
* 14
--
23
* 015
1 01
--
--

Effluent,
mg/1
	
* 007
07
06
* 03
--
15
* 004
40
--
--

Removal ,
%
	
*71
74
73
*79
--
35
*73
60
--
--
0 6-1/sec (10-gpm) UNOX Mobile Pilot Plant

Influent,
mg/1
02
024
46
35
15
0007
.30
.013
1 27
35
1 62

Effluent,
mg/1
01
004
.15
06
08
0002
23
.003
57
.05
03

Removal ,
%
50
83
67
83
47
72
23
77
55
86
98
% Sampl es
Over
10% Standard
0
0
100
0
0
0
80
0
55
0
0















*Results of only one analysis


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                                                                                                                                                                                        m > -o

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  BEGIN
  FIRST
  LINE OF
  TEXT
               GUIDE SHEET
                                    CENTER
                                    OF PAGE
  HERE E^fsyjtems  that  shows the net sludge production (VSS produced/CODo) of air    	|
         systems  to be greater for any given organic loading rate (CODR/MLVSS) than a
                                        TOP OF
                                        IMAGE
                                        'AREA
DROPPED
HEAD,
BEGIN
SECTIONS
similarly operated oxygen system.

From an analysis of the data collected
both from the small- and large-scale
units the Districts have concluded there is little difference between  the
HERE

        ^"1"*"
        oxygen systems in terms of sludge production.  When  an  analysis  of
                    iTTfll^TraTetrw^—
         biological  reactor  (which is the method used by proponents of pure oxygen),
         the  data  does  indeed indicate that theloxygen system produces less sludge.
         It  is  the belief of the authors, however, that the mass of solids within the
         entire biological  system must be considered in order to obtain a true indica-
         tion of the level  of sludge production!  This means that the solids that are
         present in  the final clarifiers must be included when the total system solids
         are  calculated.] When the data is re-eyamined in this way, the oxygen system
         will no longer demonstrate an advantage over air systems in terms of sludge
         production. This  reversal is due to the fact that a greater portion of the
         total  system solids will  be contained within the clarifiers of an oxygen
         system than is typically encountered iri air-activated sludge systems.  As was
         o'StTrned -e-ar-l-ieF,HmprVve'd--shjdge- sett-Ting- and -oxygen—transfer—cap"ab~rl ity  E^
         allows the  oxygen  system to be operated as a high-rate system.  As a result,
         as much as  50  percent of the total  system solids will be carried in the final
         clarifiers. If'the air and oxygen  systems are compared based on reactor
         solids only, then4ia significant portio^i of the oxygen solids will be elimin-
         ated form the9a1nahysis, thus falsely indicating a higher organic loading rate'
         than that imposed  on the air system.

                        '
         A sludge  growth [kinetics analysis based on total system solids is presented
         in Figure 8.  Linear regression lines (developed by treating the MCRT as the
         independent variable)  are shown for the air and oxygen data along with the 90-
         percent confidence  limits for the location of the oxygen line.  It is not
         possible  to reject, with 90-percent confidence, any line falling within
         these  limits asithe true line from whi£h the oxygen data were generated.
         Since  the air  system regression line falls within these confidence limits,
         the  oxygen  growth  kinetics are not  distinct from the air kinetics at the 90-
         percent confidence  level.             I
                        I                      I
         The  observed net! sludge production  data (which includes the VSS in the waste
         sludge plus the'effluent) are plotted as points in Figures 9 and 10.  Iden-
         tical  data  are presented  in both figures.  The graphic display of the data
         points shows that  it is difficult to determine which system has a higher net
         sludge production.
BEGIN
LAST LINE
OF TEXT J
        The curves  superimposed  on  the data in
        the growth  kinetics  shown on Figure 8.
                                       Figures 9 and 10 were developed from
                                        The two linear regression lines for
        the  air  and  oxygen  system  shown  on  Figure 8 (developed using the MCRT as the
        independent  variable)  are:             I
                 1/8C  = 0.58 (F/M) - 0.21

                 1/9C  = 0.81 (F/M) - 0.32
         Air System

         Oxygen System
        i
              3/8'
           EPA-287 (Csn.
           14-76)
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 BOTTOM OF
 IMAGE ARE>
[ OUTSIDE
I DIMENSION
 FOR TABLES
fAND ILLUS-
 TRATIONS

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  BEGIN
  FIRST
  LINE OF
  TEXT
  HERE
    TWWG GUCDE SHEET
                            CENTER
                            OF PAGE
DROPPEC
HEAD,
BEGIN
SECTI
HERE
0,4
           0.3
        o
        T3
         o
        CD
        LJ
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        UJ
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         I     T     I     1     I
                 LEGEND
     A LARGE  SCALE OXYGEN SYSTEM
     • SMALL SCALE OXYGEN SYSTEM
     • LARGE  SCALE AIR SYSTEM
    '• SMALL SCALE AIR SYSTEM
                         •OXYGEN SYSTEM DATA
                         •AIR SYSTEM  DATA
                                    90% CONFIDENCE  LIMITS
                                    OF OXYGEN DATA.
             0   O.I   0.2   0.3  0.4  0.5   0.6   0.7   0.8   0.9   1.0   I.I
               FOOD-TO-MICROORGANISM RATIO  (CODR/VSS), kg/day/kg
BEGIN
LAST LINE
OF TEXT
                        Figure 8.  Sludge growth kinetics
            3/8
         EPA-287 (Cm.)
         (<9-7S)
                                    PAGE NUMBER
TOP OF
IMAGE
AREA
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0.5
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SLUDGE PRODUCl
9 9
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/— \ 	 	 — -

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•
LEGEND
1 I 1 1 1
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A LARGE SCALE OXYGEN SYSTEM
• SMALL SCALE OXYGEN SYSTEM
" • LARGE SCALE AIR SYSTEM
• SMALL SCALE AIR SYSTEM
I i i i
) ! 2 3 4
1 1 1 1 1





5 6 7 8 9 10
^




MCRT (TPVSS), days
i !
Figure 9. Analysis of net sludge production using MCRT as the independent
variable. j
These equations are in the form of
i
1/9C = Y (F/M)-kd
where : '
1
ec = MCRT
, -r
F/M = food-to-microorganism ratio
Y = growth yield coefficient










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                                LEGEND
                   A  LARGE SCALE OXYGEN SYSTEM
                   •  SMALL SCALE OXYGEN SYSTEM
                   •  LARGE SCALE AIR SYSTEM
                   •  SMALL SCALE AIR SYSTEM
                      	OXYGEN
                                 'AIR
       TOP OF
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       'AREA
                 0
34567
  MCRT (TPVSS), days
                                                               8
10
        Figure 10.
                  Analysis of net sludge production  using the food-to-microorganism
                  ratio  as the independent variable.
      k(j = microorganism  decay coefficient

      The net sludge  production (VSS/CODp  in  kg/kg) is defined as follows:

                     iNet sludge Production =  Y/(l + kd6c)

                     1                      i
      The air and oxygen  curves shown in Figure  9 were derived using  the above     I
      formula for netisludge production withjY and kj being supplied  from the
      linear regression analysis in Figure 81  Though the linear regression lines ijj8011™
      Figure 8 were sh|own to be statistically  insignificant at the 90-percent
      confidence limits,  it is interesting to  note that the curves in Figure 9
OF TEXT cfindicate  that the oxygen system  has  a higher net sludge  production
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        TWWG GUIDE SHEET
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;A__linear regression analysis  was  also  conducted  on  the data in Figure 8 usijigj
F/M as the independent variable,  rather  than  the MCRT.  The linear regression*
analysis assumes that the  independent  variable  is exact and adjusts the line
to best fit theidata.  Therefore,  using  F/M  as  the  independent variable
rather than thejMCRT produces siightlyjdifferent lines than those shown on
                                                                               AREA
BEGIN
    c
OF TEXT
Figure 8.  The linear regression  lines
variable are:   !
                                        produced  using F/M as the independent
                          1/9C   =  0.50 (F/M)  - 0.15

                          1/9C   =  0.32 (F/M)  - 0.02
        The  air  and  oxygen  curves  presented in
        viously  given  formula for  net sludge pi
        from the  linear Degression lines given
                                                 Air  System

                                                 Oxygen  system
                                        Figure  10  were  derived  using the pre-
                                        oduction with Y and kj  being supplied
                                        above.  This analysis  shows that at
        MCRT's of  above i5  days,  the  oxygen system again has a higher net sludge pro-
        duction than  the air  system.
        Be£ause_qf_                     __
        pitas es of  the  oxygensystem operation
                                                      data_form_the_ l_a_st_fouc,
                ..,-,-.. _.,	 _r_. ......  ,,ave  not  been  used.   On  both  Figures 9"
and 10, those data would have tended to move  the  oxygen  system sludge pro-
duction curve upward at the lower MCRT s.
SLUDGE SETTLEABjLlpITY
              •^ ~ I / \j

Two parameters are commonly used  to  indicate  sludge  settleability.   The
sludge volume index (SVI)  is the  inverse  of the  settled  sludge concentration
expressed in ml/(g, and the initial settling rate (ISR)  is  the maximum rate at
which the sludge interface drops  during the test.
                I                       U
The 30-min SVI data were presented previously in Tables  2  and 3.   The
phase-average oxygen system SVI varied[from 65 to  153 ml/g,  with  an average
of 99 ml/g, and Ithe air system produced SVI's of 146 to  252  ml/g,  with an
average of 167 ml/g.                   I

The ISR data resulted from one series of  tests which was conducted  during a
period when the !performance of both  pilot  plants was charcterized  as "good."
In this series of tests, the oxygen  sliidge settled about three times as fast
as the air sludge (Figure  11).  These are  the results of only one  test, but
they are in qualitative agreement withIthe general experience at the JWPCP.

The oxygen sludge definitely settles better and  gravity  thickens better than
the air sludge. I However,  it is not  possible  at  this time  to determine the
extent to which |this is an innate property of oxygen-activated sludge or a
function of the reactor design.        1
                I                       I
One factor which affected the sludge settleability in both of these systems
was the power input.  During the  starttip  of each pilot plant it was necessary
to reduce the mijxer power in order to pVoduce an acceptable  effluent.  Ex-
cessive power input shears the floe, wJjich can cause poor  settleability of
    sludge and a1 turbid effluent.
              3/8"
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           (4-7S)

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             20


             10


              5
          E

          UJ
          UJ
          en
          <
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              0.5


              0,2


              O.I


              0.05
                                 I        T      r    i   i   1  I   i
                                   NOTE: Im/hr  =  3.28 ft./hr.
                                                   OXYGEN
                                    AIR
                 1,000
                              2,000            5,000        10,000
                                    SUSPENDED SOLIDS, mg/I
20,000
                       |   'Figure 11.   Initial; settling rates.

        POWER CONSUMPTION

        In the present economic climate, one  of  the most  important factors involved
        in the comparison of air- and oxygen-activated  sludge  processes concerns
        energy consumption.   Since power intensity problems  in both pilot plants
        required the aeration equipment to be operated  at  speeds  lower than design, a
        comparison based  on  the pilot plant data  is inappropriate.  Additionally, the
        effects of scale would be difficult  to
        aerator efficiencies will produce more
                                               predict,  so estimates  based  on typical
                                               applicable results.
        The standard oxygen transfer rates  (SOTR's)  presented  in Table 9 are represen j (MAGE
        tative of present mechanical aeration  technology,  although specific equipment  OUTSIDE
        may differ fromjthose values.   In the  ease of  the  submerged turbine, a 50:5D_J DIMENSION
BEGIN
LAST LINE
OF TEXT empower split between the mixer and compressor was  assumed.   As  indicated  in
                                                                                     BOTTOM OF
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          (4-73)
                                         PAGE NUMBER
        _J FOR TABLES
         \>AND ILLUS-
          TRATIONS

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WONG GUIDE SHEET
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OF PAGE ^
9, different mechanical
efficiencies were assigned to the mixer and __
^compressor to obtain wire power consumf
The oxygen trans


SECTIONS * 	
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fer equation

dC = ct K a
^^^r i
dT L
is:

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* '

itions .

(1)

	

                                                                                       TOP OF
                                                                                        AREA
         where:
        kd-
	J.
                           jj£  =  oxygen transfer rate, mg/l/hr
                           dt

                           KI a  =  volumetric  mass transfer coefficient, hr"1
                             L                 ]

                           C*  =  equilibrium dissolved oxygen concentration
                                  at  zero uptake, mg/1

                           C   =  system dissolved oxygen concentration, mg/1
                        fa,  3    =  variables  to  correlate clean water results
                        ,          to  mixed  liquor  conditions.
         By  adding  a  power  intensity term (V/P)J  it  is  possible to obtain an equation
         in  which the IteW'side  has  the  same  units  as the SOTR.
                          SOTR   -!£(»)   .
                                          V
(8C*-C)
        where:
             V   = tank volume  (]03-m3)

             P   = power (kW)
         It  is now possible  to  apply  the  standard
         constant K|_aV/P land then  determine  the
         dition.         '
                                   conditions  in Table 9 to obtain  the
                                 oxygen transfer rate under field con-
        The air system was a completely mixed  ifeactor  with  dissolved  oxygen  (DO)
        maintained  at  Kmg/1.   Using  an equivalent  depth  (the depth  associated with
        a saturation DO jof C*)  at 0.4  of  the air  introduction depth,  and  the con-
        ditions listed i,n Table  9, the calculations are straightforward.
        Since the oxygen system  is muilti-staged,  the  model  is  slightly more -com-    I
        plicated.  Based on the  conditions  observed  in pilot  studies  (DO,  gas  purity, i
        and oxygen uptak'e rate,  see Table 10)  and  communications  with manufacturers,  a
        model was developed which allowed the  calculation  of  required K|_a's  in each   I
        stage.  Since KLa is proportional to power,  the data  allow  the power  fraction!
BEGIN    ln eac'1 sta9e to! be calculated.  The transfer  efficiency  at field  conditions  !
LAST LINEi[Ln__each stage was calculated,  and an average based on the power distribution  §
OF TEXT jJfJFmndes the ove'rall efficiency.  The  power  required  to extract the  pure      I
              3/8"
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                                          PAGE NUMBER

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                                                                                                                                CO DO ^ O
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                                                                                           T
                                                                               CO
                                                    TABLE 9.    ASSUMED OXY'GEN  TRANSFER  RATES
                a Standard Conditions   Gas  Purity = 21% 02,  Water Temperature = 20°C,   Dissolved Oxygen = 0 mg/1.


                  a =  1 00, B = 1  00




                  Efficiencies   Gear Box =  0 96, Coupling = 0 95, Motor = 0  92




                c Efficiencies   Blower = Q  70,   Coupling = 0 95, Motor = 0  92
                                                                                                                              n co
                                                                                       V
    > Tl O O ^ C"3

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    pj 30 S q > -I
^






System
Surface Aerator

Submerged Turbine
Total System

Mixer

Compressor

Standard Oxygen
Transfer Rate3
(Delivered Power)



kg/kWh (Ib/hp-hr)
2 13 (3 50)


1 70 (2 80)





Power
Consumption
(Delivered)


kWh/kg
(hp-hr/lb)
0 469
(0 285)

0 588
(0 348)
0 294
(0 179)
0 294
(0 179)


Power
Transfer
Efficiency



0 839b



0 839b

0 612C

Power
Consumption
(Wire)


kWh/kg
(hp-hr/lb)
0 559
(0 340)

0 830
(0 505)
0 350
(0 213)
0 480
(0 292)
Oxygen
Transfer
Rate3
(Wire Power)

kg/kWh
(Ib/hp-hr)
1 79
(2 94)

1 20
(1 98)




                                                                                                                                                       m

                                                                                                                                                       (ft


                                                                                                                                                       m
                                                                                                                                                       m
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                                                                                                                                           £1°
                                                                                                                                           m > TJ

                                                                                                                                           > O 0
                                                                                                                                              m y
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               TABLE  10.  OXYGEN  SYSTEM  OPERATING  CHARACTERISTICS

Stage
1
2
3
4
Gas
Purity
% 02
80
70
65
50
Dissolved
• Oxygen,
mg/1
9 1/3
7
5
2
Power
Fraction
0.46
0.27
0.15
0.12
oxygen from the atmosphere must be added to the aerator power  in order to
provide a fair comparison.

The results of these calculations are presented in Table  11.   The oxygen
systems use substantially less energy in this analysis.   The surface
aerator oxygen system, in fact, is estimated to require only 52-percent of
the energy used by the air system, and the submerged turbine oxygen system
is projected to need 62-percent of the energy used by the air  system.  Be-
cause of land constraints at the JWPCP, depths greater than 5-m (15-ft)
were required for the air system, so surface aeration was not  evaluated
for the air system
DEPENDABILITY AND MAINTENANCE

In the JWPCP studies, the oxygen-activated sludge process has proven to be
very stable and has generally recovered from upsets very quickly.  The major
operational problems have been associated with the appurtenant equipment,
which is much more complex than is encountered in most air systems.  Because
of the potential for explosions in the enriched atmosphere, oxygen-activated
sludge systems must be equipped with an explosive vapor detector.  This
equipment has proven subject to frequent failures, which have automatically
shut down the total aeration system.

One maintenance item that has not been quantified, and had not been expected,
concerns life of the clarifier flight chains.  The oxygen effluent has proven
to be much more aggressive to the cast links than the air effluent.  This is
probably a result of the higher dissolved oxygen content and the lower pH of
the oxygen effluent.
    t 3/8"
  EPA-237 (C,n.)
  (4-76)
    ILLUS-
TR AT IONS
                                 PAGE NUMBER

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                                         TABLE 11.'   POWER CONSUMPTION
CD "• •
m

•Z. i -&':
C  rv>

£  ' " -.

ffi I'----
33 [,.
System
Air
Oxygen
Oxygen
Aerator
'Type
Submerged
Submerged
Surface
Water
Depth',
m (ft)
7.6 (25)
4.6 (15)
4.6 (15)
Power Consumption (Wire Power),
kWh/kg 02 transferred, (hp-hr/lb 02 transferred)
Aeration
Equipment3
1.28 (0.78)
0.44 (0.27)
0.31 (0.19)
Oxygen
Generation"

0.35 (0.21)
0.35 (0.21)
Total
1.28 (0.78)
0.79 (0.48)
0.66 (0.40)
          Turbine  plus compressor:   Water Temperature =  23 C,  a  = 0.80,    3 = 0.95,



        b Based on JWPCP design, 90% oxygen utilization.
   fJ^O^gf S

   ph'j^i^i
   l-,i. i,|fjm|o
     i C/)    >s ~^
                                                                                         _JJ.
                CD


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     gjrAs_ a biological/process,  the air system seemed  to  be more sensitive than the
       oxygen system.  Due  to  the air system's!tendency to nitrify and the associated
       rising sludge,  it was  necessary to operate the  air system at low aeration
       times and low MGRT's.   Operating in this marginal  region has contributed to
       the sensitivitylof  the air system.
                       i                        I                                     _J
      ^Mechanically, the air  system was much  simpler and  less  subject to malfunctions
        :'h-arr-t h e~oxyg e rrfsy s t em":	1	
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           EPA-287 (On.)
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