V-/EPA
                                  United States
                                  Environmental Protection
                                  Agency
                                  Municipal Environmental Research
                                  Laboratory
                                  Cincinnati OH 45268
                                  Research and Development
                                  EPA-600/S2-81-196 Dec. 1981
Project Summary
                                  Evaluation  of  a  Treatment
                                  Lagoon for  Combined
                                  Sewer  Overflow

                                  Daniel J. Connick, William C. Pisano, and Gerald L. Aronson
                                   Results are summarized of a 2-year
                                 study to assess the effectiveness of
                                 the world's largest facultative lagoon
                                 for treating combined sewer overflow
                                 and  the polishing effluent from a
                                 secondary wastewater treatment
                                 plant. The project was divided into five
                                 different activities, each of which
                                 evaluated a different  aspect  of the
                                 overall treatment scheme.
                                   The first activity was to determine
                                 the physical characteristics  of the
                                 lagoon (size, aerator  locations, and
                                 influent and effluent discharge levels).
                                 Second, lagoon performance was
                                 evaluated for changes in the degree of
                                 aeration, which has the dual function
                                 of mixing the lagoon  and increasing
                                 the oxygen levels above those provided
                                 by natural reaeration. Third, the
                                 pollutant removal performance of the
                                 lagoon was evaluated for different
                                 discharge levels and detention periods.
                                 Removal efficiencies were determined
                                 by daily sampling of the influent and
                                 effluent and of water at several
                                 locations within the lagoon. Fourth,
                                 the effects of the stormwater loadings
                                 on lagoon performance were assessed
                                 to determine the buffering capacity of
                                 the lagoon for treating volumes of
                                 highly polluted,  intermittent  flow.
                                 Fifth, full-scale application of sequen-
                                 tial chlorine and chlorine dioxide
                                 disinfection was evaluated.
                                   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
                                   The  East Chicago Sanitary  District
                                  (ECSD) operates a wastewater treatment
                                  plant that handles about 19 mgd* of dry
                                  weather municipal wastewater from
                                  the city of East Chicago, Indiana.  This
                                  wastewater includes industrial  dis-
                                  charges. Secondary treatment consists
                                  of a conventional activated  sludge
                                  process. The East  Chicago  sewerage
                                  system has  combined sewers with
                                  overflows containing both direct indus-
                                  trial discharges and runoff from indus-
                                  trial areas. Bacterial contamination of
                                  the Grand Calumet River has occurred
                                  in the past as a  result of  combined
                                  sewer overflows (CSO).
                                   In the late 1960's, the ECSD received
                                  a demonstration grant to construct and
                                  evaluate the world's largest facultative
                                  lagoon.  The facility was  intended to
                                  polish the secondary effluent from the
                                  wastewater treatment plant (WWTP)
                                  and to  provide preliminary treatment
                                  with disinfection to the combined sewer
                                  overflows. The project was to demon-
                                  strate the feasibility of this technique for
                                  dual CSO treatment and secondary
                                  effluent polishing at an industrial urban
                                  area.
                                   The city's objective was to meet the
                                  state,  regional, and federal water
                                 *To convert mgd to mVs, multiply by 0.044.

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quality  requirements for the Grand
Calumet River by improving the quality
of effluent from  the East Chicago
wastewater treatment plant and over-
flows from the Magoun Avenue pump-
ing station. Interception of the combined
sewer overflows prevents discharge of
raw wastewater into the Grand Calumet
River, thus eliminating excessive bac-
terial levels after storms and providing
improvement in other respects. The
improved quality of the Grand Calumet
River Basin and of the lower reaches of
Lake  Michigan  will  enable increased
industrial and recreational use of these
waters. The value of  the project to the
federal  water program was to demon-
strate a proven wastewater treatment
approach for handling combined sewer
overflows.
Physical Characteristics of the
Lagoon and Related
Appurtenances

  Construction of the East Chicago
treatment  lagoon  began in 1969 and
was completed in  1971. During con-
struction, several actions were under-
taken  that  resulted in substantial
changes from the original design. The
original lagoon design specified a 700-
by 900-ft basin with levee sides and a
maximum  water depth of  40 ft. Field
surveys indicated  that the post-con-
struction lagoon surface area remained
unchanged,  but that the water depth
was considerably less than that originally
planned. Depth readings were measured
throughout the lagoon. Readings within
15  m (50 ft) of the shore on any side
reflected the 2 to 1 slope of the levee
sides. Depths throughout the remainder
of the basin ranged from 7.62 to 9.75 m
(25 to 32 ft), with an overall average of
9.1  m (30.1 ft).  Volume of the post-
construction lagoon is estimated to be
142.2 million gal.
  Final construction  of the  influent
system included a 9-ft-wide by 8-ft-high
concrete channel along the north side,
with final  discharge  through  a 48-in.
conduit. Original intentions were that
the influent be controlled by means of
four outlets from the influent channel,
with a combined capability of handling
the entire Magoun Avenue Pumping
Station flow of 178 mgd. The capacity of
the single 48-in. conduit is insufficient
to handle the combined sewer overflow
(CSO)  and overflow  of the  influent
spillway during major storms.
  The lagoon effluent mechanism was
to have incorporated four controlled
outlets  feeding  a concrete channel
within the south  levee. A  concrete
apron corner with a dry weather flow
channel was substituted for the original
system.  Currently, no  means exist for
directly  controlling lagoon inflow and
outflow. Influent enters the lagoon at a
single  point  source and is  directly
related to pump rates. Effluent rates are
directly related to lagoon water surface
levels and  discharges from  a single
point.
Aerators
  Depth  of  the  detention basin was
designed to allow partial oxygen deple-
tion, yielding aerobic surface treatment
with anaerobic  bottom waters. The
depth of the aerobic layer is controlled
by eight surface aerators. The aerators
are  single speed, 50-hp, electically
driven units with  waterproof cables
connecting the units to onshore power
transformers. No guards are provided to
protect the upper section from induced
spray, nor is there any mechanism to
manipulate the area of inflow to limit
deep water draw.
Pumping Stations
  During rainly periods, CSO from 20
percent of East Chicago reaches the
Magoun Avenue Pumping Station and
is pumped  into the  lagoon.  Before
lagoon construction,  CSO from this
station was pumped  directly  to the
Grand Calumet River.
  A dry-weather flow lift station was
incorporated into the  original  facility
design to pump all the wastewater
treated at the  East Chicago secondary
plant to the lagoon. Three fixed-speed
pumps were installed  within the lift
station. Two were capable of pumping 8
mgd each to the lagoon, and the third
unit had the capacity to pump 3 mgd.
Dry-Weather Lagoon
Performance
  The lagoon evaluation period of 56
weeks was divided into several phases
based on prevalent influent rates to the
lagoon.  Six weeks were without any
inflow. The influent rate was 3 mgd for
33 weeks. Fifteen weeks of evaluation
were conducted at an influent rate of
18.8 mgd, which isthe maximum inflow
rate provided by all three pumps. The
final 2 weeks of the evaluation program
were conducted at a reduced flow rate
of 11.3 mgd. Flows were reduced during
this period to help evaluate the effects of
detention time on lagoon performance.
  Pollutant  loadings into the  lagoon
were a function  of the East Chicago
WWTP flow rate and the concentrations
of  individual constituents within the
treatment plant effluent. Influent to the
lagoon was controlled on a volume basis
by  the  operation of the  lift pumps.
Concentrations of wastewater constit-
uents were  mainly a  function of the
degree  of treatment provided by the
secondary plant. Because of the com-
bined effects of erratic influent pollu-
tional  loads and variable treatment
efficiency, the treatment plant effluent
concentrations varied widely.
  Statistical  reduction  of the  lagoon
performance data are shown in Tables
1, 2, and 3 for  the three  evaluation
periods. Except for organic pollutants,
the influent  concentrations were rea-
sonably consistent over the  three
evaluation periods.  The organic con-
taminant increases during the low-flow
period could have  been due to seasonal
changes, since the cold weather may
have  reduced treatment plant  effec-
tiveness.
  The average pollutant removals for
the three flow rates are summarized in
Table 4. Effluent concentrations are
listed as averages of the flow period.
Percentage removals for each flow rate
were determined using  the average
influent and effluent concentrations.
Also listed  are  the overall removal
efficiencies considered bypasses when
the secondary effluent  exceeds the
pumpage rate of 11.3 mgd. No flows are
bypassed at a pumpage rate of  18.8
mgd.
  The  results  listed in Table 4  were
expected,  considering  the nature of
difficulties encountered with the lagoon's
operation. Little aeration was provided
during most of the 3-mgd flow period.
Although long detention periods were
theoretically possible during this period,
severe short-circuiting of influent flow
effectively minimized the actual treat-
ment time. Lagoon removal efficiencies
for  the 11.3  mgd flow rate were higher
than those computed at the higher rate
of 18.8  mgd.) This result was expected,
since a theoretical detention time of 12
days is possible at 11.3 mgd, but only 7
days of detention are provided at 18.8
mgd. Aeration/dye tracer studies

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Table 1.

Para-
meter
BODe
BODs
COD
TOC
TSS
VSS
TS
NOs
TP
Turbidity]
Summary of lagoon

Mean
cone.
(mg/l)
36
44
155
47
168
75
1585
...
1.30
80
performance
Influent
No. of
samples
1
28
60
81
71
68
52
...
52
78
* Test period covered August 1978 to April
t Turbidity values in JTU.
>
Table 2.

Para-
meter
BODe
BODs
COD
TOC
TSS
VSS
TS
NOs
TP
Turbidity]
Summary of lagoon

Mean
cone.
(mg/l)
21.
23.
117.
39.
230.
68.
1639.
6.3
1.13
113.
performance
Influent
No. of
Samples
12
12
14
12
15
15
15
15
14
13
at an influent

Std.
dev.
--
33.4
49.5
45.
267.
110.
757.
...
1.49
51
1979.
at an influent

Std.
dev.
11.
17.3
112
10.7
407.
79.
370.
3.7
.67
61.
rate of 0.13

Coeff.
var.
(%>
--
76
32
96
159
147
48
...
115
64

rate of 0.49

Coeff.
var.
(%)
92
75
96
27
177
116
23
59
59
54
m3/s 13 mgd)*

Mean
cone.
(mg/l)
17
30
83
28
35
24
1365
...
.57
40

m3/s (11.3 mgd)

Mean
cone.
(mg/l)
22.
13.
57.
26
16.
9.
1323.
6.1
.23
21.

Effluent
No. of
samples
69
28
60
81
71
68
62
...
62
78

*
Effluent
No. of
Samples
12
12
14
12
15
15
15
15
14
13


Std.
dev.
13.9
29.5
30.1
10.9
23.
20
579
—
.80
10.



Std.
dev.
8.5
8.3
19.
5.7
6.6
5.3
201.0
4.7
.12
10.7


Coeff.
var.
(%)
82
105
36
39
66
83
50
...
140
25



Coeff.
var.
(%)
37
64
33
22
41
59
15
77
52
51
 Test period covered August to September 1979.
\Turbidity values in JTU.

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Table 3. Summary of lagoon performance at an influent
Influent
Mean
Para- cone. No. of Std.
meter (mg/l) samples dev.
50De 18. 17 8.8
BODs 22. 17 10.3
COD 120. 1
TOC 40. 23 17.0
TSS 144. 25 147.
VSS 60. 25 51.
TS 1626. 25 333.
NOs 5.5 1
TP 1.24 23 .72
Turbidity^ 83. 22 54.
* Test period covered May to August 1979.
t Turbidity values in JTU.
rate of 0.82 m3/s (18.8 mgd)*
Effluent
Coeff.
var.
(%)
49
47
-
42
102
85
20
-
58
65

Mean
cone. No. of Std.
(mg/l) samples dev.
26. 19 18.5
21. 19 18.5
79. 23 34.7
28. 23 9.6
32. 25 11.4
21. 25 9.0
1571. 1
5.5 1
.34 23 .22
21. 23 9.6

Coeff.
var.
(%)
71
88
44
34
36
43
-
-
65
42

Table 4. Summary of average pollutant removal efficiencies for three influent flow rates
0. 13 m3/s (3 mgd) 0.49
Influent* Effluent* Removal Influent*
Parameter (mg/l) (mg/l) (%) (mg/l)
fiODe 36. 17. 53 21.
BODs 44. 30. 32 23.
COD 155. 83. 46 117.
TOC 47. 28. 42 38.6
TSS 168. 35. 79 230.
VSS 75. 24. 68 68.
TS 1585. 1365. 14 1639.
NOs - - - 6.3
TP 1.3 .57 56 1.13
Turbidity 80. 40. 49 113.
m3/s(11.3
Effluent*
(mg/l)
22.
12.7
57.
25.9
16.
9.
1323.
6.1
.23
21.
mgd) 0. 82 m3/s (18.8 mgd)
Removal Influent Effluent* Removal
(%) (mg/l) (mg/l) (%)
18. 26.
45 22. 21. 4
51 120. 79. 34
33 40. 28. 31
93 144. 32. 78
86 60. 21. 65
19 1626. 1571. 3
3 5.5 5.5 0
80 1.24 .34 73
91 83. 21. 75

Overall
Removal^
(%)
--
27
31
20
56
52
11
2
48
55
* Mean concentrations.
t Overall removal at 0.49 m3/s (11.3 mgd) rate, considering untreated bypassed flows.
                                  4

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shown  that  even with  the limited
aeration provided during evaluation at
these flow rates,  nearly complete
lagoon mixing occurred. Influent pol-
lutant concentrations were quite similar
and temperature variations were min-
imal, thereby eliminating  the possible
effects of these variables.
  Based on the  overall removal rate
(including bypasses), the higher inflow
rate of 18.8 mgd is considered optimum.
At the 11.3 mgd pumping rate, excess
secondary treatment plant effluent is
discharged to the river without further
treatment. The removal rates at the
11,3-mgd flow rate are less than those
at the 18.8-mgd rate, with the exceptions
of  BOD, total solids (TS), and N03. The
NO3 removals are low in both situations.
TheTS and BOD removals were impaired
by four storm events during the higher
flow period. These occurrences caused
pollutant washout from the WWTP that
resulted in high residual loadings to the
lagoon.
  Limited removal  of TS  during both
flow periods  resulted from  the  poor
settling of fine particles. Although
suspended  solids (SS) removals were
high, these loadings represent only a
small fraction of the TS load. The results
suggest that the settling velocities of the
fine solid participates are insufficient to
overcome lagoon currents and scouring
near aerators. This problem was further
complicated by the high occurrence of
aerator failures. Quiescent settling
zones near nonoperational  units devel-
oped, and upon restart, bottom scouring
occurred often, and to the extent that
the surrounding surface waters became
visually black.
Wet-Weather Lagoon
Performance
  Assessment of lagoon  performance
for storm events is extremely difficult.
First,  the  pumped effluent  from  the
wastewater treatment plant  varied so
much that any estimate of dry-weather
loadings would have been subject to
considerable error. Second, the auto-
matic samplers  monitoring  both  the
influent and  effluent were  prone to
mechanical malfunctions, resulting in
incomplete representations  of storm
events. Third, the wet-weather events
were never totally monitored,  since the
washout period was always substantially
longer than the period during which the
samplers were in operation. The average
removals for  the three storm  events
approximated the removal rates during
dry-weather flow.


Aeration Studies

Lagoon Mixing and Flow
Characteristics for Various
Aeration Schemes
  Lagoon flow patterns are determined
by the rate of inflow into the lagoon and
by the number and locations of aerators
in operation. The lagoon was originally
designed to contain nine equally spaced
aerators.  The current  configuration
includes eight irregularly spaced units.
Random down time of the units resulted
in numerous combinations of aerators
in operation during the lagoon evaluation
period. Lagoon flow and mixing patterns
could not  be directly  assessed for  all
such  combinations. Several studies
were performed to ascertain the effects
of aeration  on  lagoon flow patterns.
Documentation  of short-circuiting and
limited detention times was needed for
data reduction and analysis.
  Dye studies performed under several
of these conditions demonstrated the
general trend of induced low patterns.
Influent discharge from the 48-in. feed
line tended to flow directly across the
lagoon. The extent of the immediate
flow across the lagoon was a function of
initial  influent  momentum and thus
flow rate. As expected, higherf low rates
extended the flows further across the
lagoon. Without aeration, lagoon flow
patterns allowed limited mixing  of the
interlagoon waters, with most of the
inflow rising to the surface and flowing
to the effluent  spillway with minimal
detention time and limited treatment.
  Evaluation  of the mixing character-
istics of a single aerator indicated that
each unit was  capable of influencing
lagoon water flow patterns to a distance
of more than 100 ft.  Aerators create
flow patterns that extend to the lagoon
bottom  near  the units.  Flow patterns
generally moved toward the aerators at
depths below 10 ft and away from the
aerators  above this depth. Water
velocity generally decreased with
distance from the aerator and with
depth.
  With  the aerators in operation, the
lagoon waters were adequately  mixed
with the influent. Operation of all eight
aerators mixed the lagoon completely,
producing high removal rates at optimum
detention times. Analysis later indicated
that only four aerators were required to
mix the lagoon completely. Each 50-hp
surface aerator effectively mixed 35 mil
gal indicating a  requirement of 1.3
hp/mil gal in a water body approximately
30 ft deep.
Lagoon Performance With and
Without Aeration
  Several  days after the startup of the
rehabilitated lift pumps, oxygen levels
stabilized at low levels. A period with
high flow and no aeration began at this
time and was characterized by oxygen
levels below 0.5 mg/l and temperatures
near 20°C. Removal efficiencies for this
period are listed  in Table 5. Average
influent concentrations of most constit-
uents were similar during periods of
aeration and no aeration. Analyses of
aeration  effects  were  made after
suficient aeration occurred to replenish
Table 5.  Mean pollutant removal rates
         under different aeration
         schemes at a flow rate of
         0.82 m3/s (18.8 mgd)
Parameter
No aeration:}
BODel
BODs
COD
TOC
TSS
VSS
TS
NOs
TP
Turbidity§
Influent Effluent
mean* mean* Removal
(mg/l) (mg/l) (%)

21
25
139
40
192
76
1782
2.21
1.42
97

34
23
91
27
32
23
1607
.94
.26
17

.-
6
35
32
83
69
10
57
82
83
Aeration:*
BODs
COD
TOC
TSS
VSS
TS
NOs
TP
Turbidity§
  16
  20
  93
  41
  89
  42

3.40
0.92
  17
  18
  58
  31
  34
  19

3.54
0.33
11
37
24
62
54
63
* Mean concentrations.
t 5/26/79 to 6/25/79.
j BOD analysis using elecrolytic BOD
  respirometer.
§ Values in JTU.
**7/7/79 to 8/7/79.

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the dissolved oxygen levels  in  the
lagoon. Removal efficiencies for  the
period with high oxygen and complete
mixing  are also listed  in  Table 5.
Comparison of the  removal  rates
indicates that each treatment scheme
provided superior removal for certain
parameters.
  As shown throughout the study, the
electrolytic  method of BOD analysis
using a respirometer (BODe) failed to
indicate any reduction of BODe  in the
lagoon.  BOD and COD showed slightly
better removal rates with aeration, but
removal efficiencies for all  other
parameters tended to be better when
aerators were not operating. Without
aeration, improved nitrate removal
results from denitrification within zones
of depleted oxygen.  With  aeration,
induced currents limit the settling of
solids, as reflected in the  decreased
removals.
  The disadvantage of reduced deten-
tion time appears  to  be more than
compensated by the lower degree of
flow turbulence. Parameters that re-
quire  lengthy reaction times and rea-
sonable oxygen levels (such as BOD and
COD)  receive  a greater degree of
treatment under conditions conducive
to complete mixing and reoxygenation.
Suspended solids and the large mass of
fine solids require quiescent conditions
for optimal removal, as provided in the
lagoon without aeration. Those param-
eters  that are typically tied  up  in the
solid  particulates—total particulates
(TP),  for example—indicate similar
removal rates and are therefore primarily
removed by settling.  Reductions in
parameters  such as BOD  and COD,
which are impeded by decreased oxygen
levels, are also  related to  the solids
fraction and thus undergo some removal
by this  mechanism. The data indicate
that this mechanism is less effective.
Optimum  treatment  conditions, then,
would consist of a water body high in
oxygen  content and sufficiently quies-
cent to promote particulate settling. In
the case of a treatment lagoon, these
conditions could be achieved by using
initial aeration to levels beyond the
depletion capability  of the wastewater
and following it with a zone of quiescent
flow toward the effluent to  maximize
settling conditions.


Removal  of Heavy Metals
  The inflow of heavy metals and their
presence throughout the lagoon was
monitored.  Approximately 75 samples
were evaluated for iron,  cadmium,
chromium,  copper, lead,  zinc, and
mercury (Table 6). Influent lead and zinc
concentrations appear to have been
reduced as a result of treatment in the
lagoon.
Disinfection Studies

Review of Disinfection at
ECSD Facility
  The  original  disinfection design
specified chlorine as the disinfecting
agent and the construction of a chlorine
contact chamber at the lagoon effluent.
The  latter was omitted,  however, and
limited contact time was developed by
installation of a steel weir in the effluent
chamber. A high-rate chlorine/chlorine
dioxide system was installed to disinfect
lagoon  effluent waters.
  In a previously published bench-scale
study,* high-rate disinfection of com-
bined sewer  overflows  with chlorine
and chlorine dioxide was evaluated to
aid in the design and operation of full-
scale treatment facilities. The report
concluded that a four-logarithm reduc-
tion in  indicator bacteria was obtained
with dosages of 25 mg chlorine/I or 12
mg chlorine dioxide/I and a 2-minute
contact time. Disinfection was enhanced
beyond the expected additive effect by
using sequential addition of chlorine
followed by chlorine dioxide in 15 to 30
seconds. Addition of 8  mg  chlorine/I
followed  by 2 mg chlorine dioxide/I
provided reductions similar to the single
dosages noted above. The ECSD disin-
fection system was designed on this
basis.
Disinfection Program Results
  The disinfection evaluation program
was divided into three phases. The first
phase dealt with routine bacterial
monitoring of  the lagoon disinfection
system for dosage rates established and
maintained by ECSD  to meet permit
requirements for the National Pollutant
Discharge Elimination System (NPDES).
The data collected during  this period
have limited practical value because of
continuous malfunction  of  the  disin-
fection system. The second phase
consisted of a controlled set of varied
*Moffa, P.E., et al.  Bench-Scale High-Rate
Disinfection of Combined Sewer Overflows with
Chlorine and Chlorine Dioxide, EPA-670/2-75-
021, April 1975.
chlorine/chlorine dioxide  dosage ex-
periments. This program was aimed at
developing  various equivalent  dosage
combinations for comparable fecal
coliform kill  effectiveness. The final
phase  of work  was a  special  bench-
scale study using chlorine and chlorine
dioxide to augment the data deficiencies
of the second phase.
  Bacterial analyses  of  the  lagoon
effluent were conducted every other day
during the evaluation period. Bacterial
types monitored included total coliforms,
fecal coliforms, and fecal streptococci. A
statistical  evaluation of the  colony
counts for  each bacteria type  and
relationships among  types was  per-
formed. Residual bacteria counts fol-
lowing secondary and lagoon treatment
were roughly 1  percent of typical raw
wastewater values, as indicated by the
arithmetic and  geometric  means. The
linear correlations  among bacteria
types  were poor. Analysis of the t-
statistic implied no correlation among
the three types.
Chlorine/Chlorine Dioxide
Kill Studies
  The  dosage  experiment  program
began with chlorine only. Doses of 2.5
to 6.5 mg chlorine dioxide/I were added
to yield background data to determine
the actual  chlorine dioxide  efficiency
during detailed evaluation of the
disinfection system.
  Effluent coliform levels varied widely
throughout the study period, with fecal
coliform  colony  counts ranging from
600 to 200,000  per 100  ml. This
variance created difficulty in the overall
evaluation, since equivalent kills, as
determined on  a  percentage or log
removal basis, would actually yield a
wide range of effluent levels.
  Little difference in disinfection  ef-
f icieny  occurred with sequential chlorine
dioxide addition.
Bench-Scale Chlorine/
Chlorine Dioxide Experiments
  The  referenced bench-scale study
indicated optimum  sequential  dose
delays of 15 to 30 seconds. The full-
scale disinfection operation at East
Chicago  could not be analyzed under
these conditions  because of the fixed
locations of the diffusers and limited
lagoon effluent. After  much data
analysis, little advantage was seen with
sequential chlorine dioxide  addition

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after delays of 45  to  90 seconds. A
small-scale bench study was performed
for  this project  allowing  the  desired
sequential delay times of 15 to 30
seconds.
  Chlorine was added in dosages of 1,2,
3, and  4 mg/l,  with  no  sequential
chlorine dioxide addition. Next, sequen-
tial additions  of chlorine dioxide  in
doses of 0.5 to 3.0 mg/l  were added
after  30-second delays  to samples
prechlorinated with 1 and 2 mg chlorine
dioxide/I.  Selected  sequential dosage
combinations were also applied using a
15-second delay period. Disinfection
was greater with increased  chlorine
dosage. The bench study data indicate
increased  disinfection with sequential
chlorine dioxide  addition and benefits
from reducing the delay period between
doses from 30 to  15 seconds.
Table 6.   Heavy metal concentrations in the lagoon

                             Influent
Effluent
Metal
Fe
Cd
Cu
Pb
Zn
Cl
Hg
Mean
(W/n
38.3
5.9
186.5
200.2
603.5
107.7
2.52
Std.
dev.
198.0
6.3
220.
234.
1763.
191.
2.18
Mean
(ug/l)
5.3
6.9
53.5
79.4
120.3
90.6
2.45
Std.
deav.
12.2
22.0
81.0
123.0
261.0
160.5
5.0
Conclusions
  Results of the East Chicago lagoon
evaluation clearly indicate that relatively
good treatment can  be  provided by a
deep  stabilization pond.  During dry
weather  flow periods, the  lagoon
provided removal capabilities of 30 to 70
percent for the secondary effluent,
depending on the parameter.
  The  reoxygenation function of the
aerators  was  found  to  be necessary.
Under most circumstances, four aerators
were  adequate, but  at  times of high
organic loading, the use  of  all  eight
appeared to be more advantageous.  In
this study, surface aeration of 0.015 hp
per pound BOD applied to the lagoon per
day proved to be adequate.
  Disinfection results indicated that
chlorination should be used until more
reliable chlorine dioxide equipment  is
provided. The  chlorine dioxide system
should  be reconstructed  to  provide
extensive mixing upon initial disinfection
addition,  and it should provide a 15-  to
30-second delay time between doses.
  This work was  submitted in partial
fulfillment of Grant No.  11023FAV by
East Chicago Sanitary District under the
sponsorship of the U.S. Environemental
Protection Agency.
   Daniel J. Connick, William C. Pisano, and Gerald L. Aronson are with Environ-
     mental Design & Planning, Inc., Allston (Boston), MA 02134.
   Richard P. Traver was the EPA Project Officer (for contact, see below).
   The complete report, entitled "Evaluation of a Treatment Lagoon for Combined
     Sewer Overflow," (Order No. PB 82-105 214; Cost: $11.00, subject to change}
     will be available only from:
           National Technical Information Service
           5285 Port Royal Road
           Springfield, VA 22161
           Telephone: 703-487-4650
   For information, contact Richard Field at:
           Storm and Combined Sewer Section
           Municipal Environmental Research Laboratory—Cincinnati
           U.S. Environmental Protection Agency
           Edison, NJ 08837
                                                                             U.S. GOVERNMENT PRINTING OFFICE :1 981—559-09Z/3349

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