United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/022 May 1988
x°/EPA Project Summary
Aeration Equipment Evaluation:
Phase I - Clean Water Test
Results
Fred W. Yunt and Tim 0. Hancuff
An oxygen transfer performance
evaluation was conducted on
submerged air aeration systems at
the Joint Water Pollution Control
Plant of Los Angeles County
Sanitation Districts (LACSO). The
non-steady state clean water test
procedure was used. Systems
chosen for evaluation represented
various submerged generic aeration
devices including several types of
both fine and coarse bubble
dfffusers. Jet aerators and static
aerators were also tested.
Seven manufacturers, repre-
senting seven different aeration
systems, participated in the study.
An eighth system utilized historically
in many LACSD treatment plants and
throughout the country was tested to
provide a reference point All testing
was conducted in the same outdoor
tank using identical procedures in
order to standardize test conditions.
The results of this study
indicated that, of the systems tested,
fine bubble diffusion equipment
transferred oxygen most efficiently in
clean water. Jet aerators transferred
oxygen more efficiently than static
aerators and other coarse bubble
systems but not as efficiently as fine
bubble diffusers. Because the values
of wastewater correction factors
(alpha and beta) are dependent on
the type of aeration device tested,
the relative performance of one
aerator to another in wastewater may
be different than observed in these
clean water tests.
This Project Summary was
developed by EPA's Water Engineering
Research Laboratory, Cincinnati, 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
Analysis of clean water test data for
various submerged aeration devices is
the first step toward defining the oxygen
transfer performance of such equipment.
While clean water test results indicate
general trends in an aeration system's
oxygen transfer performance, they do not
necessarily reflect that system's
performance under process conditions.
The logical second step, therefore, is an
oxygen transfer evaluation of selected
submerged aeration equipment in mixed
liquor under field operating conditions.
A comparison of the data generated
by the above two types of tests provides
an estimation of the wastewater alpha
correction factor. The alpha factor
typically is less than unity and results in
lower oxygen transfer rates in process
waters than in clean (tap) waters. The
value of alpha varies with wastewater
characteristics, process operating
conditions such as SRT and the F/M
loading rate, type of aeration equipment
(bubble size), aeration system layout,
aeration tank geometry, the degree of
prior treatment received (e.g., the alpha
factor has a higher value at the effluent
end than the influent end of a plug flow
aeration tank), and the relative state of
aerator cleanliness. The last factor refers
primarily to fine bubble (fine pore)
diffusers, which tend to clog or foul with
time in mixed liquor operation. Because
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partially fouled diffusers generally
transfer less oxygen than clean diffusers,
the term apparent alpha factor rather
than alpha factor is used when
comparing the mixed liquor and clean
water oxygen transfer performance of
diffusers that are operating with an
indeterminate degree of fouling.
Since clean and process water
oxygen transfer performance can vary
widely, it was considered essential to
undertake a two-phase test program.
The first phase, which is the subject of
this report, included only clean water
testing. Several fine and coarse bubble
submerged aeration systems were tested
in the same tank under the same
operating conditions. Based on the
results of these tests, the three systems
with the highest oxygen transfer rates
were selected for further oxygen transfer
testing under process water conditions.
The clean water tests were
conducted in the Districts' Joint Water
Pollution Control Plant in Carson, CA.
The subsequent process water (mixed
liquor) tests were carried out in parallel
trains at LACSD's Whittier Narrows
Water Reclamation Plant in El Monte,
CA. The results of the process water
testing will be presented in a follow-on
report.
The three major objectives of this
project were to:
• evaluate the clean water oxygen
transfer performance of various
generic types of submerged aeration
equipment under identical testing
conditions and using identical testing
methods,
• demonstrate the effects of changing
water depth and operating power
levels on aeration equipment
performance, and
• evaluate the two most highly
regarded oxygen transfer data
analysis methods currently in use.
Project Outline
This study was devised as an
evaluation of distinct generic types of
submerged aeration equipment; it was
not intended to be an evaluation of
various manufacturers' equipment of the
same generic type. Due to the large
variety of fixed orifice coarse bubble
diffusers on the market, however, more
than one example of this generic type
was tested. The aeration equipment
tested is summarized in Table 1.
System H, FMC Corporation's
coarse bubble Deflectofuser* (sparger),
was not included in the initial scope. It
was added at a later date and tested only
at the 4.6-m (15-ft) water depth
because of its widespread use at that
depth both nationwide and in the
Districts' treatment plants.
The tests were conducted at water
depths of 3.0 m (10 ft), 4.6 m (15 ft), 6.1
m (20 ft), and 7.6 m (25 ft). A range of
nominal power densities was evaluated
at each depth. The manufacturers, with
the exception of FMC Corporation for
their Deflectofuser system, were given
the choice to test at one of the following
two ranges of power options:
Option 1: 13.2, 26.3, and 39.5 nominal
W/m3 (0.5, 1.0, and 1.5
nominal hp/1,000 ft3),
Option 2: 7.9, 13.2, and 26.3 nominal
W/m3 (0.3, 0.5, and 1.0
nominal hp/1,000 ft3).
It was hoped that each manufacturer
would select the range that was most
typical of its equipment's application in
mixed liquor. All manufacturers tested
chose Option 1 with the exception of the
Norton Company, which selected Option
2. The 3 to 1 range in power for both
options was intended to demonstrate the
aeration equipment's ability to handle
diurnal variations representative of typical
process loading patterns.
The manufacturers were responsible
for designing the layout of their
equipment subject to the constraints of
this study. Each manufacturer was
allowed, if desired, to change its
equipment configuration at each depth
tested. It was required, however, that the
same configuration be used for all tests
at a given depth.
Test Facility
An outdoor, all-steel, rectangular
aeration tank located at the LACSD Joint
•"Mention of trade names or commercial products
does not constitute endorsement or
recommendation for use.
Water Pollution Control Plant with
dimensions of 6.1 m x 6.1 m x 7.6 m
sidewater depth (SWD) (20 ft x 20 ft x 25
ft) was used for all tests. Prior to the start
of this project, the tank was steam
cleaned and all exposed metal surfaces
were coated with coal tar epoxy. Potable
water was used in all clean water tests
conducted in this study. Average
characteristics of the supplied water
were: total dissolved solids = 500 mg/L,
pH = 8.25, hardness = 225 mg/L as
CaCOs, and turbidity <0.1 turbidity units.
The air delivery system used for this
project consisted of a Roots Model
RAS-60 rotary positive blower driven by
a 56-kW (75-hp) electric motor.
System air was filtered by an Air Maze
DA dry-type filter. A 1-m3 (35-ft3)
pulsation dampening tank was also
included in the system between the
blower and the airflow measurement
elements. System air rate was adjusted
by bleeding off excess air at the blower.
Test Procedures
The basic clean water test procedure
employed was the non-steady state
method. This method uses sodium sulfite
to deoxygenate the clean water and
cobalt chloride to catalyze the reaction
Samples were withdrawn from the tank
and collected in BOD bottles and
chemically fixed for later dissolved
oxygen (DO) measurement by the
lodometric (Winkler) method.
Airflow Measurements
Airflow measurements were made with
two different primary flow elements: an
orifice plate and an Annubar. Dual flow
measurements were taken to ensure
greater accuracy. Furthermore, to provide
acceptable accuracy over the wide range
of flow rates encountered, two different
Table 1.
System
Description of Aeration Systems Subjected to Clean Water Testing
Description
Manufacturer
A Fine bubble ceramic dome diffusers applied
in a total floor coverage configuration
B Fine bubble plastic tube diffusers applied in
a dual aeration configuration (Pearlcomb)
C Jet aerators
D Static tube aerators
£ Variable orifice coarse bubble diffusers
F Fixed orifice coarse bubble diffusers
G Fixed orifice coarse bubble diffusers
H Fixed orifice coarse bubble diffusers
(Deflectofuser) [tests conducted at a 4.6-m
(15-ft) depth only]
Norton Company
FMC Corporation
Pentech-Houdaille Industries, Inc.
Kenics Corporation
C-E Bauer of Combustion
Engineering, Inc.
Sanitaire - Water Pollution Control
Corporation
Envirex, Inc.
FMC Corporation
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sized air lines were used, both with
appropriately sized orifice plates and
Annubar equipment.
DO Sample Collection
Sample Locations
Water samples to be analyzed by the
Winkler method were collected from four
locations in the aeration tank. Two
vertical sampling "stacks" were
employed, each with two sampling
locations. Submersible sample pumps
were installed in the first stack at mid-
depth and at 0.6 m (2.0 ft) off the bottom
of the tank; the second stack had
submersible pumps installed at mid-
depth and 0.6 m (2.0 ft) below the
surface of the tank. The heights of the
pumps were adjustable for proper
placement at the various water depths
evaluated.
Sample Collection Procedure
Samples for DO analysis were
pumped through plastic tubing by
submersible pumps from the aeration
tank to the sampling station where
samples were collected in BOD bottles.
Copper discharge nozzles for the four
pumped samples were mounted on a
plywood board to enable one operator to
control the four samples simultaneously.
An attempt was made to collect
approximately eight samples for the
Winkler analysis between 20% and 80%
saturation, although additional samples
were taken below 20% and above 80%
saturation. Sample water was pumped
continuously to purge the BOD bottles
until the desired time, "t," after which the
sampling device was withdrawn and the
BOD bottles stoppered. If necessary, 1
or 2 sec were allowed before stoppering
the BOD bottles to allow any small air
bubbles to rise to the surface and
escape. The overflow water from the
BOD bottles was caught in a 208-L
(55-gal) tank and continuously pumped
back to the aeration tank.
Sampling Rates
The submersible pumps for the
Winkler samples were sized so a BOD
bottle could be filled three to five times in
15 sec (0.06 to 0.10 L/sec = 1.0 tq 1.6
gpm). This was done to ensure adequate
displacement of the water in the BOD
bottle and to minimize the detention time
in the sample lines (approximately 10
sec). All pump rates and sample line
lengths were maintained equal so that
the samples from the various locations
would represent the same time "t."
DO Measurements
The official DO measurements were
made by the Winkler method on
captured samples. The azide
modification of the Winkler titration
method was used with alkali-iodide-
azide reagent #2 as stated in Standard
Methods. This reagent was selected
because it reportedly reduced the
volatility of iodine and thus provided a
more accurate DO measurement.
Samples were set up immediately after
capture and titrated within 1.5 hr. The
thiosulfate used for the titrations was
standardized once each day.
Deoxygenation Procedure
Cobalt chloride was used as a catalyst
in the deoxygenation reactions. It was
added once at a dosage of 0.1 mg/L as
cobalt ion to each batch of test water.
The chemical crystals were added to the
mix tank and allowed to dissolve for at
least 30 min prior to discharging the
solution into the aeration tank. After
cobalt addition to the aeration tank, at
least another 30 min was allowed prior to
the start of the first test.
Anhydrous sodium sulfite was used to
deoxygenate the water prior to the start
of each test. The amount of sodium
sulfite added was approximately 1.5
times the stoichiometric requirement for
oxygen removal. The salt was dissolved
in approximately 379 L (100 gal) of water
prior to the start of each run. The brine
addition to the tank was accomplished
within a 2-min period. The solution was
pumped equally into the four tank
quadrants through a 4-hose addition
system. Distribution was, therefore, as
even and rapid as possible. The
chemical mix tank and delivery hoses
were immediately flushed with tap water
to wash all residual sodium sulfite into
the aeration tank.
A decision was made to discard each
water batch after the accumulated
sodium sulfite concentration had reached
1,000 mg/L. At that time, samples were
taken for laboratory analyses to
determine the chemical properties of the
"post-test" water. Analyses were also
conducted prior to using a water batch to
determine the "pre-test" condition.
These measurements included pH,
alkalinity, hardness, sulfate, total
dissolved solids, cobalt, iron, and
manganese.
Aerator Power Determinations
In addition to power for an air supply,
aeration equipment may also require
power for a mixer or a pump. Of the
eight systems evaluated in this study,
only the jet aeration system required
pump power in addition to the power for
the air supply. Power determination is
discussed in detail in the full Project
Report, and equations are given for
calculating air nominal power, air
delivered power, air brake power, air wire
power, pump delivered power, pump
brake power, and pump wire power. All
power requirements used in this report to
calculate aeration efficiencies (kg or Ib QZ
transferred per kWh or hp-hr of
electricity consumed, respectively) were
based on wire power.
Analysis Methods
The transfer of gas into a liquid can be
described by the two-film theory
proposed by Lewis and Whitman
(Principles of Gas Adsorption, Ind. Eng.
Chem., 16:1215, 1924), expressed as
follows:
dC/dt = KLat(C*-C) (1)
where:
dC/dt = oxygen transfer rate per unit
volume, mg/Uhr
K|_at = overall volumetric mass
transfer coefficient for test
conditions, hr1
C* = DO saturation value, mg/L
C = DO concentration, mg/L
This is the differential form of the
basic equation and states that the oxygen
transfer rate per unit volume is directly
proportional to the DO deficit (C* - C).
The oxygen transfer rate, dC/dt, is a
function of many variables, including the
type of aerator, the aeration tank
geometry, the nature of the liquid, and
the liquid temperature. Equation 1 was
originally developed to describe oxygen
transfer in small, shallow containers. It
has been generalized to the case of
large, deep aeration basins that are
completely mixed. If complete mixing is
not achieved, the use of Equation 1 to
define the oxygen transfer capabilities of
an aeration system may lead to
significant errors.
All data analysis methods share one
common trait; they define an analytical
procedure to calculate oxygen transfer
rate. This always includes the
fundamental determination of both the
volumetric mass transfer coefficient, K|_at,
and the DO saturation value, C*.
Eight data analysis methods were
originally planned to be incorporated in
the Project Report. A computer program
was developed to analyze data using all
eight methods. It was later decided,
however, to include only the analysis
results in the Project Report of the two
-------
most highly regarded methods. The two
methods the Districts considered to be
the most highly regarded were 1) the
log-deficit model with a measured
equilibrium, hereinafter referred to as the
equilibrium method, and 2) the
transformed integrated form of the basic
equation, hereinafter referred to as the
exponential method.
The equilibrium method is described
by the following equation:
ln(C*-C) = KLat(t/3600)
+ In(C'-Cj) (2)
where:
Cj = initial DO concentration, mg/L
t = time in sec
The conversion factor of 3600 is utilized
to make compatible the units of K|_at in
hr1and t in sec.
The equation for the exponential
method is given below:
C = C* • (C*-C-^
exp [-KLat (t/3600)] (3)
The two methods of analysis are
different in the ways the error structure of
the data is handled and the saturation
value is obtained. The exponential
method provides estimates of three
parameters, K|_at, C*, and Cj. It uses the
entire data set to estimate C*. The
equilibrium method involves a log
transformation of the data, such that the
latter measurements of C in a test run
are weighted more heavily than the early
measurements. This method utilizes a
measured saturation value obtained from
a few data points at equilibrium
conditions and, thus, provides an
estimation of only a single parameter,
K|_at- Both methods assume the same
model (Equation 1), and if all the data fit
this model exactly, no differences would
exist between the respective estimates of
the parameters. In general, however, the
exponential method is the preferred
procedure because it does not require
long aeration times to obtain an accurate
estimate of C* and it provides more
accurate estimates of K|_at if the test data
do not precisely fit the basic model. The
exponential method is the basis of the
recommended ASCE Standard for
Measurement of Oxygen Transfer in
Clean Water (ASCE, ISBN 0-87262-
430-7, New York, NY, July 1984).
Test Results
Overview
To utilize clean water test data
intelligently, it is essential that the
limitations of the test be realized. Clean
water data alone cannot be used to
predict oxygen transfer performance in
mixed liquor. To relate clean water
oxygen transfer results to anticipated
aerator performance in mixed liquor, two
correction factors are required. The first
factor, alpha (a), is the oxygen transfer
coefficient correction factor. The second
factor, beta (P), is the oxygen saturation
correction factor. These correction
factors are applied to the basic aeration
equation as follows:
dC/dt = a KLat(pC* - C) (4)
Only with accurate alpha and beta
factors, used in conjunction with clean
water data, can successful prediction of
oxygen transfer performance in activated
sludge be achieved. As previously
mentioned, the alpha factor, the ratio of
wastewater K[_a to clean water K|_a, can
vary widely as a function of several
site-specific considerations. For the
type of equipment tested during this
study, alpha factors from 0.35 to 0.95
have been reported. Beta factors of 0.96
to 0.99 are common for municipal
waste waters.
Since aeration equipment oxygen
transfer efficiency is usually highly
dependent on test medium char-
acteristics, it is common to specify
equipment compliance requirements on
the basis of clean water tests. Because a
clean water test is repeatable, it may be
used to demonstrate general trends in
aeration performance with regard to
airflow rates, diffuser location, tank
geometry, and other parameters. When
the aerator's alpha and beta factors are
known for a particular wastewater, clean
water tests also provide meaningful data
for activated sludge aeration system
design. Even then, the process flow
regime used can have a significant effect
on alpha. For example, alpha will tend to
approach a constant value throughout a
completely mixed aeration tank, whereas
it will increase from inlet to outlet of a
plug flow tank as the influent wastewater
becomes progressively more treated.
Tabular Data
The Project Report contains 16 tabular
summaries of the test data, two each for
the eight aeration systems tested. One
table for each system contains the
results of the exponential method of data
analysis, the other the results of the
equilibrium method of analysis. Only one
table (Table 2) is presented in this
Summary, a comparison of the
exponential method and equilibrium
method analysis results for the Norton
fine bubble dome diffuser system.
Information provided in the first four
columns of Table 2 identifies and
characterizes the tests. Results of the
exponential method of analysis are
summarized in columns 5 through 9. The
last five columns summarize the results
of the equilibrium method of analysis.
The K|_a2o values shown are the overall
volumetric mass transfer coefficients at a
standard water temperature of 20°C,
while the C*0 numbers are the DO
saturation values at 20 °C and a standard
barometric pressure of 1.00 atmosphere.
Standard oxygen transfer efficiency
(SOTE), standard delivered aeration
efficiency (SDAE), and standard wire
aeration efficiency (SWAE) data
represent actual field determined clean
water values corrected to standard
conditions of 20°C, 1 atmosphere, 0
mg/L DO, and 36% relative humidity.
The data in Table 2 indicate close
agreement in test results between the
two data analysis methods for the Norton
system. Similar agreement was observed
for the other seven aeration systems. The
average ratios of Ktaarj (exp.
method)/K|_a2O (equil. method) and
SWAE (exp. method)/SWAE (equil.
method) were 0.990 and 0.995,
respectively, for all eight systems
encompassing 100 test runs. For the
K|_a2o rat'°. the maximum value for any
one run was 1.10, while the minimum
ratio was 0.88. For the SWAE ratio, the
maximum and minimum run values were
1.06 and 0.93 respectively. The close
agreement in these results indicates that
the test data fit the basic model (Equation
1) extremely well for all eight systems.
Graphical Data
A total of 15 graphs are presented in
the Project Report comparing the oxygen
transfer performance of the various
aeration systems. Four of these 15
graphs are presented in this Project
Summary to illustrate key representative
results of the entire test program. SOTE
and SWAE are shown as functions of
water depth for the middle nominal power
density in Figures 1 and 2, respectively.
In Figures 3 and 4, SOTE and SWAE are
graphed, respectively, against delivered
power density for the 4.6-m (15-ft)
water depth. This water depth was
selected because many municipal
treatment plants around the country use
aeration tanks with a similar depth.
The middle nominal power density
data plotted in Figures 1 and 2 represent
a power level of 26.3 W/m3 (1.0 hp/1,000
ft3) for all aeration equipment except
Norton. Norton selected a middle power
density of 13.2 W/m3 (0.5 hp/1,000 ft3)
The data points at the four water
depths tested are connected by straight
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-------
lines in Figures 1 and 2 for five of the
seven systems represented. For the
Kenics and Sanitaire Systems, however,
discontinuous lines are shown. It was felt
that equipment configuration changes at
the different depths strongly influenced
the results of these two systems;
consequently, only points for the same
configuration layout are connected for
Kenics and Sanitaire.
It is apparent in Figure 1 that
increases in water depth produced
increases in SOTE for each manufacturer
configuration tested. The three highest
3?
fc
o
50
40
30
20
10
0
• Norton
• Kenics
* Pentech
* FMC (Pearlcomb)
o Sanitaire
o Bauer
& Envirex
NOTE:
7 ft = 0.305 m
20
0 5 10 15
Water Depth (ft)
Figure 1. Comparative plot of SOTE vs. water depth at middle power density tested.
25
10
• Norton
• Kenics
* Pentech
* FMC (Pearlcomb)
o Sanitaire
o Bauer
A Envirex
t
NOTES:
7 n = 0.305 m
7 Ib/wire hp-hr = 0.608 kg/kWh
I 1
10 15
Water Depth Iff)
20
25
Figure 2. Comparative plot of SWAE vs. water depth at middle power density tested.
curves represent the ceramic dome and
plastic tube fine bubble diffusers and the
jet aerators. The coarse bubble aeration
equipment tested is represented by the
lower curves. The variable orifice coarse
bubble diffuser SOTE curve is at the
bottom of the coarse bubble diffuser
band.
The data in Figure 2 indicate that the
effects of increasing water depth on
SWAE depend on the generic type of
aeration equipment tested. While the fine
bubble diffusers appear to have been
relatively unaffected by changes in water
depth, SWAE improved with increasing
water depth for the coarse bubble
diffusers, static aerators, and jet aerators.
The two highest curves represent the two
fine bubble diffuser systems, while the jet
aerators, static tube aerators, and coarse
bubble diffusers generally grouped
together in the lower band of curves. The
variable orifice diffuser results again were
the lowest.
The jet aeration system's SWAE
values are lower in relation to the
SWAE's of the coarse bubble aeration
systems than would be expected based
on the comparative iSOTE values of the
two types of equipment. This is most
likely due to the need for two prime
movers (blower and pump) to operate the
jet aerators versus only one (blower) to
operate any of the other systems
evaluated.
As seen in Figure 3, the aeration
equipment producing fine bubbles -
Norton, FMC Pearlcomb, and Pentech -
exhibited peak oxygen transfer
efficiencies at the lowest delivered power
density for the 4.6-m (15-ft) water
depth. Equipment that produces coarse
bubbles generally showed the opposite
trend, with peak valves occurring at the
greatest delivered power density. The
curves for most of the equipment are
relatively straight with the exception of
the jet aeration system. The order in
SOTE values, from highest to lowest, is
as follows: Norton, Pentech, FMC
Pearlcomb, and Kenics, followed by the
other coarse bubble systems clustered
closely together. Similar trends and
orders were observed at the other water
depths studied, with the exception that
the Kenics static tube aerator SOTE fell
within rather than above the coarse
bubble curve band.
Five of the systems demonstrated little
variation in SWAE for the 4.6-m (15-ft)
water depth over the range of delivered
power densities evaluated (Figure 4). The
systems that did exhibit significant
variation over this range - Norton, FMC
Pearlcomb, and Pentech - all generate
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/iall bubbles. Both Norton and FMC
produced their peak SWAE values at the
lowest delivered power density, while for
40 r
30
SS
s
20
10
Pentech, the peak SWAE occurred at the
middle delivered power density. From
highest to lowest, the order in SWAE
• Norton
• Kenics
A Pentech
+ FMC (Pearlcomb)
O Sanitaire
0 Bauer
A Envirex
0 FMC (Deflectofuser)
NOTE:
/ hp/1.000 ft3 - 0.026 kW/m3
0 0.5 1.0 1.5 2.0
Delivered Power Density (hp/1000 ft3)
figure 3. Comparative plot of SOT£ vs. delivered power density at J5-ft water depth.
ki
10
9
8
7
6
5
3
2
1
• Norton
• Kenics
A Pentech
+ FMC (Pearlcomb)
O Sanitaire
O Bauer
A Envirex
0 FMC (Deflectofuser)
O—
NOTES:
1 hp/1.000 ft3 = 0.026 kW/m3
1 Ib/wire hp-hr = 0.068 kg/kWh
0.5 1.0 1.5
Delivered Power Density (hp/'WOO ft3)
2.0
Figure 4. Comparative plot of SWAE vs. delivered power density at 15-ft water depth.
values is Norton; FMC Pearlcomb;
Kenics; Pentech; FMC Deflectorfuser,
Envirex, and Sanitaire grouped together;
and Bauer. The impact of two prime
movers on the energy consumption of
the jet aeration system in relation to its
relative high SOTE values is again clearly
evident. The Norton and FMC Pearlcomb
systems also generated the highest
SWAE values at the other depths tested.
Conclusions
This clean water study provided
considerable insight into oxygen transfer
performance characteristics of various
submerged aeration devices. The
following conclusions were reached:
• For a given water depth and delivered
power density, the SWAE's of the fine
bubble dome diffusers (Norton) in a
total floor coverage mode were
substantially better than those of any
other system tested.
• For a given water depth and delivered
power density, the SWAE's of the fine
bubble tube diffusers (FMC
Pearlcomb) in a dual aeration mode
were substantially better than those of
either the jet aerators (Pentech) or the
various coarse bubble devices
(Kenics, Sanitaire, Envirex, FMC
Deflectofuser, and Bauer).
• For a given water depth and delivered
power density, the SWAE's of the jet
aerators were usually better than those
of the various coarse bubble diffusers
(with the exception of the Sanitaire
fixed orifice coarse bubble diffusers in
a total floor coverage mode).
• For a given water depth, delivered
power density, and with similar
configurations, the SWAE's of the
various coarse bubble diffusers were
similar.
• For a given configuration and water
depth, SWAE decreased significantly
with increasing delivered power
density for the fine bubble tube
diffusers, reached a mid-point
maximum value for the jet aerators,
and exhibited very little change for the
coarse bubble diffusers.
• For a given configuration and
delivered power density, the SWAE
values of the fine bubble diffusers
were relatively unaffected by
increases in water depth and usually
increased significantly for the other
aeration devices with the exception of
the static tube aerators at the upper
water depths.
• For a given water depth and delivered
power density, the SOTE's of the fine
bubble dome diffusers in a total floor
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coverage mode were substantially
better than those of any other system
tested.
For a given water depth and delivered
power density, the SOTE's of the fine
bubble tube diffusers in a dual
aeration mode and the jet aerators
were similar and significantly better
than those of the various coarse
bubble diffusers.
For a given water depth and delivered
power density, the SOTE's of the
various coarse bubble diffusers were
very similar when installed in similar
configurations.
For a given configuration "and water
depth, SOTE decreased significantly
for the fine bubble diffusers and jet
aerators with increasing delivered
power density and usually increased
slightly for the various coarse bubble
diffusers (with the exception of the
static tube aerators, where SOTE was
not significantly affected by changes
in delivered power density).
For a given configuration and
delivered power density, SOTE
increased substantially with increasing
water depth for all systems tested.
The use of a total floor coverage
configuration with the Sanitaire fixed
orifice coarse bubble diffusers
appeared to improve the performance
of this system significantly.
With the exception of the Sanitaire
system, the changes in aerator
configuration selected by the
manufacturers at different water
Fred W. Yunt and Tim O. Hancuff are with the County Sanitation Districts of Los
Angeles County, Los Angeles, CA 90607.
Richard C. Brenner is the EPA Project Officer (see below).
The complete report, entitled "Aeration Equipment Evaluation: Phase I - Clean
Water Test Results," (Order No. PB 88-180 351/AS; Cost: $25.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
depths did not appear to result in
significant changes in oxygen transfer
performance.
• The exponential and equilibrium
methods of clean water data analysis
provided nearly identical results under
the conditions of this study. Based on
100 test analyses, the average ratio of
the SWAE obtained with the
exponential method to the SWAE
obtained with the equilibrium method
was 0.995, with a standard deviation in
the ratio of 0.0169.
The full report was submitted in
fulfillment of Contract No. 14-12-150
by the County Sanitation Districts of Los
Angeles County under the partial
sponsorship of the U.S. Environmental
Protection Agency.
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-88/022
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