United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-102 Feb. 1984
&EPA Project Summary
Development of Standard
Procedures for Evaluating
Oxygen Transfer Devices
William C. Boyle
In an effort to obtain consensus
standards for the evaluation of aeration
devices in both clean and dirty water,
the American Society of Civil Engineers
(ASCE) established a Subcommittee on
Oxygen Transfer Standards. The objec-
tives of the subcommittee were to
1. review and critically evaluate the
state-of-the-art of oxygen trans-
fer testing,
2. evaluate and critically review
existing standards and identify
critical areas of disagreement and
uncertainty,
3. develop documentation for recom-
mendations for interim standards
and recommended verification
methodology, and
4. prepare these standards and sub-
mit them for ASCE consensus
evaluation.
The full report presents the outcome
of this review process and provides
recommended procedures for testing of
oxygen transfer devices in both clean
and dirty water.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory, Cincinnati. OH,
to announce key findings of the research
project that are more fully documented
in a separate report of the same title (see
Project Report ordering information at
back).
Introduction
Although considerable effort has been
devoted to oxygen transfer technology
over the years, unanimity of opinion has
not been achieved in developing standard
procedures to evaluate oxygen transfer
devices. Presently, manufacturers rely on
clean water shop tests for describing the
oxygen transfer capability of aeration
equipment. These capabilities are nor-
mally expressed as standardized oxygen
transfer rates (SOTR) in clean water at
zero dissolved oxygen (DO) at 20°C.
Subtle differences in the method of data
analysis can produce differences of 10
percent in the clean-water SOTR. More-
over, this uncertainty is further magnified
when translating clean-water, test-tank
transfer rates to actual plant conditions.
Because of differences in wastewater
characteristics, tank geometry, waste-
water temperature, mixing, and other
system characteristics, uncertainties of
up to 50 percent may be introduced.
There is little question that a consensus
standard is needed for oxygen transfer
devices. Although there are several
standard procedures, they are concerned
primarily with the methodology of experi-
mental measurement and do not deal
adequately with the interpretation and
application of data to engineering design.
Moreover, there is no general agreement
among engineers and manufacturers as
to which standard procedure or set of
procedures to use. Because of this, the
wide variety of techniques employed
result in substantial variations in test
results for the same device in clean-
water tests. Even larger variations will be
evident in translating these results to
full-scale design. Only when standard
procedures are developed through consen-
sus agreement among experts in the field
will a better degree of uniformity,
accuracy, and economy result. Even
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then, continued updating of the standard
will be required.
In January 1977, ASCE established a
volunteer Subcommittee on Oxygen
Transfer Standards, under the Committee
on Environmental Standards (Technical
Council on Codes and Standards). The
Subcommittee was divided into subgroups
with responsibilities for addressing five
important areas: (1) oxygen transfer
modelling and data interpretation, (2)
unsteady-state, clean-water transfer
testing, (3) oxygen transfer measurements
m respiring systems, i.e., field testing of
oxygen transfer devices, (4) corrections
for wastewater characteristics and
temperature (alpha, beta, and temperature
corrections), i.e., translation of clean
water data to dirty water performance,
and (5) geometry and mixing considera-
tions. Several Subcommittee members
were later assigned the tasks for also
evaluating methods for power and air
flow measurements. The results of the
deliberations of this Subcommittee are
included within the text of the full report.
The proposed interim standard procedures
described therein are the outgrowth of
several years of study, discussion, and
compromise. They represent a group
effort based on the experience of experts
in the field from industry, government,
consulting firms, and universities.
The Subcommittee is satisfied that the
interim standard procedures proposed in
the full report represent the state-of-the-
art today. Such procedures will be of little
value to the profession unless they are
used and continuously critiqued. Only
when standard procedures are developed
through consensus agreement will a
better degree of uniformity, accuracy,
and economy result. Even then, continued
updating o the standard will be required.
This Subcommittee will continue to
function as a standards development and
review group under the ASCE Technical
Council on Codes and Standards.
The recommended procedures are
delineated under the appropriate sections
of the report. A brief synopsis of the
topics addressed in each section is
provided below.
Modelling and Data
Interpretation
The basic model used to analyze clean-
water unsteady-state test data is expressed
as:
dC/dt = KLa(C« - C) (1)
where:
C = effective average DO concentra-
tion in the liquid phase, m/L3
C£ = average DO saturation concen-
tration attained at infinite time,
m/L3
t = time, t
Ki_a= apparent volumetric mass trans-
fer coefficient, t"1
Detailed discussion on the theoretical
model for oxygen transfer is described in
this section for both completely mixed
and compartmentalized systems. The
impact of gas side corrections to these
models for submerged aeration is dis-
cussed, and equations for this system are
presented.
Methods to estimate the parameters
KLa, C», and C0 for unsteady-state,
clean-water tests, where C0 is the DO
concentration at t= O estimated from the
model, are discussed. The full report
recommends that the data from these
tests be analyzed by nonlinear regression.
The model of this analysis is in the
exponential form of Equation 1:
C = C« - (Ci -C0)exp(-KLa t) (2)
A secondary method of analysis, where
programmable calculators or computers
are not available, is a linear regression
applied to the logarithmic form of
Equation 1:
In
-c
-Co
= -KLa t
(3)
This equation would be used to estimate
both the parameters Ki_a and Ci.
Examples of application of the model to
unsteady-state, clean-water test data are
presented. Methods of data presentation
n a standard format are provided.
Translation of test data to field conditions
is outlined by way of calculations.
Computer programs for the nonlinear
least squares method are described and
presented m the report appendices in
both FORTRAN and BASIC languages.
Unsteady-State. Clean-Water
Testing
A recommended unsteady-state, clean-
water test procedure for aeration equip-
ment is described. Details are given on
advance preparation, geometry and
aerator placement, air flow rate and
power measurements, water quality and
water quality monitoring, deoxygenation
chemicals and their addition, system
stability, sampling, DO analysis and
recording, data analysis, data interpreta-
tion, data reporting, and detergent
testing. Following these outlined proce-
dures, an in-depth and referenced
discussion follows on each procedural
item including a brief literature review
and a discussion of controversial issues.
This section has served as the basis for
a clean water test procedure currently
being prepared by the ASCE Subcommit-
tee on Oxygen Transfer Standards as an
ASCE Standard.
Field Testing of Oxygen
Transfer Devices
A thoretical development is presented
to assist in properly selecting and
evaluating field test methods for aeration
devices. A general model is developed for
the analysis of a variety of test procedures.
Important field measurements including
DO, oxygen uptake rate, temperature,
and alpha and beta corrections are
discussed.
Field test procedures are each discussed
in detail with respect to the description of
the test, the method of data evaluation,
example calculations, and test limitations.
The tests described include
• steady state continuous tests,
• steady state batch tests,
• unsteady state continuous tests
(including the use of H2O2>,
• unsteady state batch tests (includ-
ing the use of HzOz), and
• mass balance tests for aerated
lagoons.
Brief descriptions of tracer techniques,
off-gas analysis, and a dual, unsteady-
state method are also presented.
Translation of Clean Water
Data to Dirty Water
Performance
The literature dealing with several
factors that influence the translation of
clean-water, oxygen transfer test data to
field conditions is reviewed. Alpha, beta,
and temperature corrections are also
discussed together with recommenda-
tions on estimating these parameters for
wastewater, including possible analytical
test procedures.
Geometry, Scale-up, and
Mixing Considerations
The influence of basin geometry and
mixing on the translation of oxygen
transfer data from one system to another,
including information on current experi-
ence with these physical factors, is briefly
described. Rule-of-thumb recommended
values related to scale-up are provided.
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Gas Flow Measurement
A detailed analysis of the methods used
to measure and calculate air flow is
presented and includes discussions on
primary flow devices, secondary flow
devices, selection of proper devices,
details on the setup of primary and
secondary devices in a test situation,
troubleshooting, dealing with pulsation
problems, additional measurements for
air flow calculations, standard conditions,
conversion of volumetric flow rates from
standard to actual conditions, and
recommended standardization of airflow
measurement.
Power Measurement
Standard techniques are recommended
for power measurement and measure-
ment and calculations of gas power,
turbine pump power, and mechanical
aerator power.
The full report was submitted in
fulfillment of Cooperative Agreement No.
CR805868 by the American Society of
Civil Engineers under the partial sponsor-
ship of the U.S. Environmental Protection
Agency.
William C, Boyle is with the University of Wisconsin, Madison, Wl 53706.
Richard C. Brenner is the EPA Project Officer (see below).
The complete report, entitled "Development of Standard Procedures for Evalu-
ating Oxygen Transfer Devices," (Order No. PB 84-147 438; Cost: $25.00,
subject to change} will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, MA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
t>US GOVERNMENT PRINTING OFFICE 1984-759-015/7309
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