y>EPA
                                  United States
                                  Environmental Protection
                                  Agency
                                  Municipal Environmental Research
                                  Laboratory
                                  Cincinnati OH 45268
                                  Research and Development
                                  EPA-600/S2-81-155  Sept. 1981
Project  Summary
                                  Parallel   Evaluation  of  Air-  and
                                  Oxygen-Activated  Sludge

                                  Scott Austin, Fred Yunt, and Donald Wuerdeman
                                    To provide  data on the relative
                                  merits of air and of oxygen in the
                                  activated sludge process, two 1,900-
                                  mVday (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. Although
                                  both pilot plants met the applicable
                                  discharge limitations for  everything
                                  but three trace metals, the oxygen
                                  system provided a more stable opera-
                                  tion.
                                    Primary differences in performance
                                  concerned ammonia nitrogen removals.
                                  Calculated  differences  in energy
                                  consumption indicate a savings might
                                  be expected with the oxygen system.
                                  Differences in sludge production were
                                  not significant.
                                    This Project  Summary was devel-
                                  oped by EPA's Municipal Environ-
                                  mental Research Laboratory. Cincin-
                                  nati, OH, to announce key findings of
                                  the research project that is fully
                                  documented in a separate report of the
                                  same title (see Project Report ordering
                                  information at back).

                                  Introduction
                                    Since the introduction of high-purity,
                                  oxygen-activated sludge, a controversy
                                  has existed  concerning the relative
                                  merits of  air and of oxygen in the
                                  activated sludge process. Very little
                                  data, however, were available on side-
                                  by-side operation  of relatively large-
                                  scale systems with comparable engi-
                                  neering.
                                    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 Dis-
                                  tricts of Los Angeles County constructed
                                  two 1,900-m3/day (0.5-mgd) activated
                                  sludge demonstration  plants.  One
                                  incorporated 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 system, and
                                  identical clarifiers were used. The
                                  research motivations in establishing the
                                  operating parameters for the two plants
                                  were different: the oxygen system was
                                  operated to refine specified design
                                  parameters, whereas the air system
                                  was operated to determine its capabili-
                                  ties and limitations.
                                   The  JWPCP is a 15-mVsec (350-
                                  mgd) primary treatment plant treating a
                                  mixture of  domestic and industrial
                                  wastes. This facility allowed a good'
                                  comparison of the two activated sludge
                                  alternatives for  treating relatively
                                  concentrated municipal wastewater.


                                  Selection and Description of
                                  the Pilot Plants

                                  Air-Sparged Turbine System
                                   Locating the Districts' JWPCP in an
                                  urban  area  placed a definite land
                                  constraint on the proposed secondary

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treatment system for that plant. When
preliminary site layouts were made for a
conventional  activated sludge  system
with the standard 4.6-m (15-ft)  deep
aeratiorrtanks and an optimistic 6-hr
aeration  period,  no excess land was
available for waste activated  sludge
processing. Because  of this land con-
straint, 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  sub-
merged 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.

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
wastewater by increasing the rate at
which oxygen can be dissolved  into the
mixed liquor within the biological
reactor. The results of preliminary
studies using  Union  Carbide's 0.6-
L/sec (10-gpm) mobile  pilot plant
verified this claim  since  acceptable
effluent quality was achieved at aeration
periods as short as 1.5 hr (V/Q).
  As a  result of competitive bidding.
Union Carbide Corporation* constructed
the pure oxygen biological  reactor,
which was to utilize 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.
  Table  1 compares the design criteria
for the air-sparged system and the high-
purity oxygen system as well  as the
associated final clarifiers. Tables 2 and
3 summarize the operational parameters
for  the air and oxygen  systems,  respec-
tively.
Table 1.    Design Criteria for Pilot Plants

               Item
      Air
    System
Oxygen
System
 Biological Reactors:
  Average flow, m3/day (mgd)                1900 (0.5)         1900 (0.5)
  Length, m (ft)                              6.1 (20)            7.3 (24)
  Width, m (ft)                               6.1 (20)            7.3 (24)
  A verage water depth, m (ft)                  7.6 (25)            3.7 (12)
  No. of stages                              1                  4
  Detention time (V/Q), hr                    3.5                2.5
 Oxygen Storage Tank:
  Number                                      —              1
  Volume, m3 (ft3) NTP                          —              3900
                                                               (350.000)
  Capacity,  m3/hr (ft3/hr)                        —               740
                                                               (4940)
                                            Standard            Large

 Final Clarifiers:
  Number                                   2                  1
  Length, m (ft)                              22 (72)            34 (111)
  Width, m (ft)                               3.0 (10)            3.0 (10)
  Average water depth, m (ft)                  3.0(10)            3.0(10)
  Overflow rate. m3/m2/day (gpd/.f?)         28.5 (700)         18.3 (450)
  Detention time
   (Q x 1/3 return), hr                       2.0                3.0
  Weir loading rate. m3/m/day (gpd/ft)       62.1 (5000)        62.1 (5000)
  Flowthrough velocity
   (Q x 1/3 return), mm/sec (ft/min)          3.2 (0.6)           3.2 (0.6)
'Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use by the U.S. Environmental Protection
Agency.
Discussion of Results

Effluent Quality
  Activated sludge systems consist of
two component units—the reactor and
the final clarifier. The quality of the final
effluent is related to the interaction of
the component parts, and poor effluent
quality 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 BOD
  A primary indicator of the adequacy of
the reactor in terms of oxygen transfer
and treating the wastewater  is the
removal  of soluble organics.  In  all
phases, for both pilot plants, the soluble
BOD5 concentrations were 6  mg/L or
less. These BOD measurements are low
enough that 'differences  between the
two systems are not considered signifi-
cant.

Suspended Solids
  Secondary effluent solids concentra-
tions depend on the effectiveness of the
final clarifier. High effluent suspended
solids, however, may be an indication of
poor  clarifier design, poor aerator
design, or poor plant operation. During
startup,  both 1,900-m /day <0.5-mgd)
pilot plants experienced periods of high
effluent suspended solids and turbidity,
which were alleviated by reducing the
power input to the final stages of the
reactors.


Sludge Production
  One of the most important claims
 made on behalf  of pure oxygen is thai
the net growth of solids in these
systems will be  less than  a similar air
system  when operated at the  same
 mean cell residence time (MCRT). Since
a large portion of the cost of wastewater
treatment  is  usually  associated with
solids processing and sludge handling,
this claim would represent a significant
savings in both  capital  and operating
costs. The claim is based on a comparison
between the two systems that shows
the net sludge production of air systems
to  be  greater for any  given  organic
loading  rate than a similarly  operated
oxygen system.
  From an analysis of the data collected
both from this and an earlier, smaller-
scale study, the Districts have concluded
there is little difference between the an

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Table. 2.    Summary of Operational Parameters—Air-Sparged Turbine System
      Parameter                                                   .      Phase

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

Recycle. %
Hydraulic Detention Time:
V/Q, hr
V/(QxR). hr
MLSS, mg/L
Volatility. %
Mean Cell Residence Time:
Reactor So/ids, days
Total System Solids, days
Organic Loading Rate:
BODR/MLVSS. kg/ kg/ day
BODn/TPVSS. kg/kg/day
CODR/MLVSS, kg/kg/day
CODn/TPVSS, kg/kg/day
flODA. kg/ m3/ day fib/ ft3 /day)

Sludge Production:
VSS/BOD*. kg/ kg
VSS/CODn, kg/ kg
CLARIFIER:
Overflow Rate, m3/m2/day (gpd/ff)

Dentention Time:
V/Q, hr
V/(Q+R), hr
Solids Loading Rate, kg/ m3/ day
(Ib/ft3/day)
Return Sludge Concentration, %
SVI. ml/g
1

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
1450)

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
J450)

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
121.5)

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
1361)

5.0
3.6
68
(1089)
1.1
160
VIII

11/27/75
12/25/75
29
Steady

1500
(0.40)
50

4.5
3.0
3600
70

3.4
4.5

0.44
0.30
1.00
0.75
1.20
(19.2)

0.63
0.30

14.7
(361)

5.0
3.3
83
(1329)
1.1
173
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
and oxygen systems in terms of sludge
production. When an analysis of  the
system  is made based on the  mass of
micrporganisms contained within  the
biological reactor (which is the method
used by proponents of pure oxygen), the
data do indeed indicate that the oxygen
systems produces less sludge. The
authors believe, however, that the mass
of solids within the entire biological
system  must  be considered to obtain a
true  indication  of  the level of sludge
production. This means that the solids
present in the final clarifiers must be
included when  the total system solids
are calculated. When  the data are
reexamined  in  this way,  the  oxygen
system  will no  longer demonstrate an
advantage over  air systems in terms of
sludge  production. This  reversal  is
because a greater portion of the total
system  solids will be contained within
 le clarifiers of  an oxygen system than
 is typically encountered in air-activated
 sludge systems. Improved sludge settling
 and oxygen transfer  capability allows
 the oxygen system to be operated as a
 high-rate system. As a result, as much
 as 50% of the total system solids will be
 carried in the final  clarifiers.  If  the
 comparison of air and oxygen systems is
 based on  reactor solids only, then a
 significant portion of  the oxygen solid
 will  be eliminated from the  analysis,
 thus falsely indicating a higher organic
 loading rate than that imposed on the air
 system.


Sludge Settleability
   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.
  ISR data are reported from one series
of tests conducted during a period when
the performance of both pilot plants was
characterized as "good." In this series
of tests, the oxygen sludge settled about
three times as fast as the air sludge.
Although these results are the product
of limited testing, they are in qualitative
agreement with the general operating
experience of the JWPCP pilot plants.
  The oxygen  sludge definitely settled
and gravity thickened better than the air
sludge during this project. At this time,
however, it's impossible to determine
the extent to which this  is an innate
property of oxygen-activated sludge or a
function of the reactor design.
  One  factor that affected the sludge
settleability  in both of these systems
was power input.  To  produce an
acceptable eff I uent during the startup of

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Table 3.     Summary of Operational Parameters—Oxygen System
          Parameter
                                                                        Phase
                               I
                                       II
                                                III
                                                         IV
                                                                         VI
                                                                                 VII
                                                                                         VIII
                                                                                                   IX
                                                                                                                     XI
 DATES'
  Start
  End
 Duration, days
 Flow Pattern

REACTOR:
  Influent Flow, rrf/day fmgd)

  Recycle. %
  Hydraulic Detention Time-
  V/Q, hr
  V/(Q+R), hr
  MLSS. mg/L
  Volatility. %
  Mean Cell Residence Time:
  Reactor Solids, days
  Total System Solids, days
  Organic Loading Rate:
  BODH/MLVSS. kg/kg/day
  BODn/TPVSS. kg/kg/day
  CODR/MLVSS. kg/kg/day
  CODR/TPVSS, kg/kg/day
  BODA, kg/m3/day (Ib/ft3/day)

  Oxygen Utilization.
  02/BODK, kg/kg
  Oi/CODn, kg/kg
  Sludge Production:
  VSS/BODR, kg/kg
  VSS/COD*. kg/kg

 CLARIFIER:
9/22/75 10/27/75 12/1/75  2/1/76  2/18/76 3/31/76  6/21/76  9/30/76  10/28/76  11/9/75   12/10/71
9/25/75 11/10/75 12/30/75 2/17/76 2/29/76 5/20/76  9/14/76  10/13/76  11/7/76   11/24/76  12/23/71
   4       15       30       17       12       51      85       14        11        16        14
 Diurnal   Steady    Steady   Steady   Steady   Steady    Steady   Steady    Dirunal    Dirunal    Diurnal
  1900
 (0.511
  40

  2.5
  1.8
 3800
  75

  1.8
  3.4

  0.70
  0.31
  1.67
  0.89
  2.15
 134.4)

  1.36
  0.71

  0.97
  0.48
 1500
 (0.40)
  40

 31
 2.2
 2800
  73

 2.5
 5.9

 074
 0.31
 1.52
 0.64
 1.73
127.7)
 0.60
 0.29
1400
fO 37)
 44

3.4
2.3
4200
 74

3.4
6.8
1700
(0.45)
 44

2.8
1.9
4600
 72

1.9
5.6
1900
(0.51)
 42

2.5
1.6
3300
 75

1.7
34
1900
(0.51)
 40

2.5
1.8
3900
 74

1.9
4.4
1800
(0.48)
 38

2.6
1.9
4100
 77

2.7
4.8
1900
(0.51)
 40

2.5
1.8
4420
 75

2.1
3.8
0.52
0.26
1.14
0.56
1.62
(25.9)
0.60
0.20
1.31
045
2.03
(32.5)
0.83
042
1.61
0.81
2.05
132.8)
0.69
0.29
1.54
0.64
2.00
(32.0)
0.57 '
0.33
1.15
0.66
1.76
(282)
0.48
0.27
0.95
0.54
1.63
(26.1)
0.64
0.28
0.63
0.29
0.78
0.40
0.80
0.36
0.69
0.33
 1.52
 0.81

 0.84
 0.42
 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
 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
 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
 070

 0.66
 0.37
Overflow Rate, m3/ rrf/day (gpd/ff)

Detention Time:
V/Q, hr
V/IQ+R). hr
Weir Loading Rate, m3/m/day
(ff/ft/day)
Solids Loading Rate, kg/ m3/ day
(Ib/ff/day)
Return Sludge Concentration, %
SVI, ml/g
18.7
(459)

3.7
2.8
79.1
(852)
98
(1568)
1.05
78
23.2
(570)

3.0
2.2
62.6
(674)
90
(1440)
1.06
153
21.2
(521)

3.3
2.3
52.2
(562)
127
(2032)
1.40
99
25.4
(625)
.
2.8
1.9
68.9
(741)
168
(2688)
1 54
65
28.4
(698)

, 2.4
1.7
77.0
(829)
134
(2144)
1.18
83
27.9
(686)

2.5
1.8
101.2
(1089)
152
(2432)
1.36
77
27.5
(676)

2.5
1.8
99.4
(1070)
141
(2256)
1.22
83
18.1
(445)

3.8
2.7
101.5
(1092)
113
(1808)
1.34
113
28.4
(698)

25
1.8
102.3
(1101)
147
(2352)
0.88
124
23.3
(573)

2.9
2.0
84.2
(906)
141
(2256)
0.99
114
23.2
(570)

2.9
2.1
85.8
(923)
126
(2016)
094
101
each pilot plant, the mixer power had to
be  reduced.  Excessive  power input
shears the floe, which can cause poor
settleability of the  sludge and a turbid
effluent.

Power Consumption
  In the present  economic climate,
energy consumption is one of the most
important factors involved in comparing
the  air  and  oxygen activated sludge
processes. Since power intensity prob-
lems 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 inappro-
priate. Additionally, because the effects
of scale would be difficult to predict,
estimates based  on typical aerator
efficiencies produce more applicable
results.
  The  results of  power  consumption
estimates made usi ng the above ground
               rules indicate that the oxygen systems
               use substantially less energy.  The
               surface aerator oxygen system, in fact,
               is estimated to require only 52% of the
               energy used by the air system, and the
               submerged turbine  oxygen system,
               62%. Because of land constraints at the
               JWPCP, aeration tank depths greater
               than 5 m (15 ft) would be required with
               an air system, so  surface  air aeration
               was not evaluated.

               Conclusions
                 Both air- and oxygen-activated sludge
               systems can produce effluents meeting
               the JWPCP discharge  limitations for
               everything but certain trace metals,
               which  require  source  control.  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 ii
                                               terms of their effects on effluent quality
                                               The most notable detrimental factor
                                               encountered in the study were excessiv
                                               input of aerator power, which sheare
                                               the floes in both systems, and nitrifica
                                               tion-denitrification,  which caused  trv
                                               settled  sludge from the  air system t
                                               resuspend.
                                                  The major difference between the tw
                                               systems in terms of pollutant removal
                                               concerns ammonia nitrogen. The oxyge
                                               system did  not nitrify. At the JWPCF
                                               where the ammonia discharge limitatio
                                               is high  enough to impose no constrain'
                                               this characteristic is  an  advantage  i
                                               that it eliminates rising sludge resultin
                                               from nitrification-denitrification.
                                                  Claims have been made that oxygen
                                               activated sludge processes produce les
                                               sludge than air-activated  sludg
                                               processes. In this study, the total plar
                                               solids were compared and the different^

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Table 4. Summary of Effluent Quality— Air Stream
Parameters

Aeration Period (V/Qj. hr
MCRT (Total System), days
Flow Pattern
Suspended Solids:
Influent, mg/L
Effluent, mg/L
Removal, %
Total BODS:
Influent, mg/L
Effluent. mg/L
Removal. %
Soluble BODS:
Influent, mg/L
Effluent. mg/L
Removal, %
Total COD:
Influent, mg/L
Effluent, mg/L
Removal, %
Soluble COD:
Influent, mg/L
Effluent, mg/L
Removal. %
Grease (By Hexane Extraction}:
Influent, mg/L
Effluent, mg/L
Removal, %
Ammonia Nitrogen:
Influent, mg/L
Effluent, mg/L
Removal, %
1
5.6
6.8
Steady

167
89
47

178
75
92

118
2
98

458
118
74

262
49
81

51
8
84

35
14
6O
II
4.0
5.4
Steady

179
80
55

167
17
90

102
3
97

447
152
66

247
56
77

41
6
85

32
20
38
III
4.0
3.3
Steady

167
67
60

172
15
91

98
3
97

453
130
71

234
59
75

37
5
86

35
28
20
IV
3.5
5.6
Steady

170
22
87

171
8
95

101
4
96

460
77
83

241
56
7*7

38
1
97

35
32
9
Phase
V
4.0
2.8
Steady

204
110
46

224
16
93

126
5
96

513
191
63

265
72
73

—
—
—

31
28
10

VI
4.5
4.3
Steady

204
36
82

234
12
95

132
4
97

556
91
84

257
57
78

—
—
—

36
32
11

VII
4.5
4.3
Steady

165
37
78

212
12
94

129
2
98

483
92
81

270
55
80

—
—
—

33
28
15

VIII
4.5
4.5
Steady

216
54
75

226
13
94

109
2
98

515
111
78

256
48
81

—
—
—

34
32
6

IX
5.3
5.9
Steady

177
29
84

211
18
92

119
2
98

517
84
84

282
54
81

—
—
—

38
31
18
was found to be insignificant at the 90%
confidence  level. The trend, however,
was for the oxygen system to produce
more sludge.
  Because of modifications made to the
pilot plant's aeration equipment to
prevent floe shear, an energy consump-
tion comparison was considered inap-
propriate. A paper study indicates that
substantial  energy savings  may  be
expected with the oxygen system.
  The  full  report  was  submitted  in
partial  fulfillment of Contract No.  14-
12-150 by Los Angeles County Sanita-
tion Districts under the sponsorship of
the U.S. Environmental Protection
Agency.

-------
Table 5.    Summary of Effluent Quality—Oxygen System
Parameters
Aeration Period IV/Q). hr
MCRT (Total System), days
Flow Pattern
Suspended Solids:
Influent, mg/L
Effluent, mg/L
Removal, %
Total BOD:
Influent, mg/L
Effluent, mg/L
Removal, %
Soluble S005:
Influent, mg/L
Effluent, mg/L
Removal, %
Total COD:
Influent, mg/L
Effluent, mg/L
Removal, %
Soluble COD:
Influent, mg/L
Effluent, mg/L
Removal, %
Grease (By Hexane Extraction):
Influent, mg/L
Effluent, mg/L
Removal, %
Ammonia Nitrogen:
Influent, mg/L
Effluent, mg/L
Removal, %

1
2.5
3.4
• Diurnal

189
17
91

219
11
95

131
4
97

467
81
83

249
62
75

43
1
98

32
26
19

II
3 1
5.9
Steady

165
18
89

221
7
97

132
3
98

523
87
83

213
68
68

38
1
97

34
31
9

III
3.4
6.8
Steady

242
28
88

231
12
95

105
3
97

554
94
83

258
58
78

47
3
94

33
31
6

IV
2.8
5.6
Steady

201
54
73

238
20
92

122
5
96

561
122
78

279
59
79

56
4
93

32
31
3

V
2.5
34
Steady

172
28
84

219
21
90

121
6
95

486
100
79

283
67
76

42
3
93

36
31
14
Phase
VI
2.5
4.4
Steady

202
21
90

212
12
94

115
3
97

536
88
84

279
66
76

62
2
97

37
32
14

VII
26
4.8
Steady

142
17
88

187
8
96

93
2
98

438
82
81

255
64
75

64
2
97

32
30
6

VIII
2.5
38
Steady

140
14
90

176
5
97

90
1
99

400
71
82

260
58
78

46
1
98

34
29
15

IX
2.5
4.2
Diurnal

150
48
68

204
13
94

134
1
99

415
116
72

272
64
77

46
6
87

28
28
0

X
3.1
6.6
Diurnal

130
34
74

173
12
93

100
2
98

431
97
78

280
63
78

39
3
92

34
29
15

XI
3.0
5.4
Diurnal

120
20
83

185
6
97

124
2
98

446
83
81

305
65
79

41
2
95

37
34
8
                                          Scott Austin and Fred Yunt are with, and Donald Wuerdeman was with, Los
                                            Angeles County Sanitation Districts, Whittier, CA 90607.
                                          Irwin J. Huge/man was the EPA Project Officer (see below).
                                          The complete report, entitled "Parallel Evaluation of Air- and Oxygen-Activated
                                            Sludge," fOrder No. PB 81-246 712; Cost: $8.00, subject to change) will be
                                            available only from:
                                                  National Technical Information Service
                                                  5285 Port Royal Road
                                                  Springfield, VA  22161
                                                  Telephone: 703-487-4650
                                          Richard C. Brenner, the present contact, can be reached at:
                                                  Municipal Environmental Research Laboratory
                                                  U.S. Environmental Protection Agency
                                                  Cincinnati, OH 45268
                                                                           ft US GOVERNMENT PRINTING OFFICE, 1981 — 757-012/7355

-------
United States                      Center for Environmental Research                                pees pajd
Environmental Protection         v     Information                                                 Environmental
Agency                           Cincinnati OH 45268                                          Protection
                                                                                         Agency
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