OFF-GAS ANALYSIS RESULTS AND FINE PORE
RETROFIT INFORMATION FOR GLASTONBURY, CONNECTICUT
by
R. Gary Gilbert and Russell C. Sullivan
Aeration Technologies, Inc.
N. Andover, Massachusetts 01845
Cooperative Agreement No. CR812167
. Project Officer
Richard C. Brenner
Water and_Hazardous Waste Treatment Research Division
Risk Reduction Engineering Laboratory |
Cincinnati, Ohio 45268 '-
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
Development of the information in this report has been
funded in part by the U.S. Environmental Protection Agency under
Cooperative Agreement No. CR812167 by the American Society of
Civil Engineers. The report has been subjected to Agency peer
and administrative review and approved for publication as an EPA
document. Mention of trade names or commercial products does not
constitute endorsement or recommendation•for use.
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FOREWORD
Today's -rapidly developing and changing technologies and
industrial products and practices frequently carry with,them the
increased generation of materials that, if improperly dealt with,
can threaten both public health and the environment. The U.S.
Environmental Protection Agency (EPA) is charged by Congress with
protecting the Nation's land, air, and water resources. Under a
mandate of national environmental laws, the Agency strives to
formulate and implement actions leading to a compatible balance
between human activities and the ability of natural systems to
support and nurture life. These laws direct EPA to perform
research to define our environmental problems, measure the
impacts, and search for solutions. '
The Risk Reduction Engineering Laboratory is responsible for
planning, implementing, and managing research, development, and
demonstration programs to provide an authoritative, defensible
engineering basis in support of the policies, programs, and
regulations of EPA with respect to drinking water, wastewater,
pesticides, toxic substances, solid and hazardous wastes, and
Superfund-related activities. This publication is one of the
products of that research and provides a vital communication link
between the researcher and the user community. '
As part of these activities, an EPA cooperative agreement
was awarded to the American Society of Civil Engineers (ASCE) in
1985 to evaluate the existing data base on fine pore diffused
aeration systems in both clean and process waters, conduct field
studies at a number of municipal wastewater treatment facilities
employing fine pore aeration, and prepare a comprehensive design
manual on the subject. This manual, entitled "Design Manual -
Fine Pore Aeration Systems," was completed in September 1989 and
is available through EPA's Center for Environmental Research
Information, Cincinnati, Ohio 45268 (EPA Report No. EPA/625-1-
89/023) . The field studies, carried out as contracts under the
ASCE cooperative agreement, were designed to produce reliable
information on the performance and operational requirements of
fine pore devices under process conditions. These studies
resulted in 16 separate contractor reports and provided critical
input to the design manual. This report summarizes the results
of one of the 16 field studies.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
1X1
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PREFACE
In 1985, the U.S. Environmental Protection Agency funded
Cooperative Research Agreement CR812167 with the American Society
of Civil Engineers to evaluate the existing data base ion fine
pore diffused aeration systems in both clean and process waters,
conduct field studies at a number of municipal wastewater
treatment facilities employing fine pore diffused aeration, and
prepare a comprehensive design manual on the subject. This
manual, entitled "Design Manual - Fine Pore Aeration Systems,"
was published in September 1989 (EPA Report No. EPA/725/1-89/023)
and is available from the EPA Center for Environmental Research
Information, Cincinnati, OH 45268.
As part of this project, contracts were awarded under the
cooperative research agreement to conduct 16 field studies to
provide technical input to the Design Manual. Each of: these
field studies resulted in a contractor report. In addition to
quality assurance/quality control (QA/QC) data that may be
included in these reports, comprehensive QA/QC information is
contained in the Design Manual. A listing of these reports is
presented below. All of the reports are available frqm the
National Technical Information Service, 5285 Port Royal Road,
Springfield, VA 22161 (Telephone: 703-487-4650). :
1. "Fine Pore Diffuser System Evaluation for the Green Bay
Metropolitan Sewerage District" (EPA/600/R-94/093) by J.J.
Marx
2. "Oxygen Transfer Efficiency Surveys at the Jones 'Island
Treatment Plants, 1985-1988" (EPA/600/R-94/094) by R.
Warriner
i
3. "Fine Pore Diffuser Fouling: The Los Angeles Studies"
(EPA/600/R-94/095) by M.K. Stenstrom and G. Masutani
4. "Oxygen Transfer Studies at the Madison Metropolitan
Sewerage District Facilities" (EPA/600/R-94/096) by W.C.-
Boyle, A. Craven, W. Danley, and M. Rieth
i
5. "Long Term Performance Characteristics of Fine Pqre Ceramic
Diffusers at Monroe, Wisconsin" (EPA/600/R-94/097) by D.T.
Redmon, L. Ewing, H. Melcer, and G.V. Ellefson
6. "Case History of Fine Pore Diffuser Retrofit at Ridgewood,
New Jersey" (EPA/600/R-94/098) by J.A. Mueller arid P.D.
Saurer
IV
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7. "Oxygen Transfer Efficiency Surveys at the South Shore
Wastewater Treatment Plant, 1985-1987" (EPA/600/R-94/099) by
R. Warriner
8. "Fine Pore Diffuser Case History for Frankenmuth, Michigan"
(EPA/600/R-94/100) by T.A. Allbaugh and S.J. Kang
9. "Off-gas Analysis Results and Fine Pore Retrofit Information
for Glastonbury, Connecticut" (EPA/600/R-94/101) by R.G.
Gilbert and R.C. Sullivan
10. "Off-Gas Analysis Results and Fine Pore Retrofit Case
History for Hartford, Connecticut" (EPA/600/R-94/105) by
R.G. Gilbert and R.C. Sullivan ;
11. "The Measurement and Control of Fouling in Fine Pore
Diffuser Systems" (EPA/600/R-94/102) by E.L. Barnhart and M.
Collins ' '
12. "Fouling of Fine Pore Diffused Aerators: An Interplant
Comparison" (EPA/600/R-94/103) by C.R. Baillod and K.
Hopkins '
13. "Case History Report on Milwaukee Ceramic Plate Aeration
Facilities" (EPA/600/R-94/106) by L.A. Ernest
14. "Survey and Evaluation of Porous Polyethylene Media Fine
Bubble Tube and Disk Aerators" (EPA/600/R-94/104) by D.H.
Houck ;
15. "Investigations into Biofouling Phenomena in Fine Pore
Aeration Devices" (EPA/600/R-94/107) by W. Jansen, J.W.
Costerton, and H. Melcer
16. "Characterization of Clean and Fouled Perforated Membrane
Diffusers" (EPA/600/R-94/108) by Ewing Engineering Co.
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ABSTRACT
In the summer of 1984, the Glastonbury, Connecticut Water
Pollution Control Plant underwent a retrofit from a spiral roll
coarse bubble to a spiral roll fine pore aeration system. Only
diffuser replacement was performed in the aeration tanks. From
November 1985 through September 1988, on-site studies were
performed using off-gas analysis as part of the ASCE/EPA Fine
Pore Aeration Project. This report presents the results of over
160 off-gas tests together with a case history of the retrofit to
upgrade the aeration system. Historical information, retrofit
evolution and implementation, aeration performance after the
retrofit, and comparison of performance with pre-retrofit data
are included in the report. ;
This report was submitted in partial fulfillment of
Cooperative Agreement No. CR812167 by the American Society of
Civil Engineers under subcontract, to the Aeration Technologies,
Inc. under the partial sponsorship of the U.S. Environmental
Protection Agency. The work reported herein was conducted over
the period of 1985-1988.
VI
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TABLE OF CONTENTS
Foreword
Pref eice iv
Abstract vi
Figures ix
Tables ...... xi
Acknowledgements xii
1.0 Introduction 1
2.0 SUMMARY 5
2.1 General 5
2.2 Off-Gas Testing Results ; .... 7
2.3 Operation and Maintenance Observations 8
2.4 Diffuser Cleaning Comments .... 9
2.5 Design Comments 10
2.6 Recommendations ' . . . 12
3.0 HISTORICAL BACKGROUND INFORMATION 15
3.1 The Treatment Facility 15
3.2 The Activated Sludge Process 15
3.3 Original Aeration System 16
3.4 Operational Problems : . ,. , 22
3.5 Retrofit Objectives . 22
3.6 Basis for Changing to Fine Pore Aeration 23
4.0 FINE PORE AERATION RETROFIT DESIGN DESCRIPTION ..... 25
4.1 Basis for Design 25
4.2 Description for Fine Pore Diffuser
Equipment Purchased : . . . 27
5.0 OPERATIONAL PERFORMANCE AND EVALUATION ; . . • . 29
5.1 System Startup 29
5.2 Operating Conditions ...... 30
5.3 Operational Control ...... 30
5.4 Treatment Performance 30
5.5 Aeration Performance Evaluation ., 32
5.5.1 General . . . 32
5.5.2 Oxygen Transfer Efficiency . . . . . . . 59
5.5.3 Clean Water and Mixed Liquor
Performance Criteria ! . . . 61
5.5.4 Measured Apparent Alpha 63
5.5.5 Physical Observations 63
vii
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6.0 ECONOMIC CONSIDERATIONS FOR FINE PORE AERATION .... 65
6.1 Power Use ................ . . . . 65
6.2 Oxygen Transfer Efficiency Comparison ....... 65
6.3 Increase in Actual Efficiency ........ '•'.'.'. 66
6.4 Cost Considerations ............. . . . 67
7.0 RECOMMENDATIONS ...... . ............ 69
7.1 General ................ ".'.'.'"' 69
7.2 Engineering Design ........ ........ 69
7.3 Equipment Design ...... ....... '.'.'.' 70
7.4 Operation .............. ....... 71
7.5 Maintenance ............... '.'.''.'* 72
7.6 Efficiency Considerations ...... '.'. '.'.'•'.'.'. 72
7.7 Clogging Potential ............. . . 73
7.8 Mechanical Reliability ....... '.'.'.'.''.'.'. 74
7.9 Overall Advances and Disadvantages ..... ''.'.'. 74
8.0 REFERENCES
APPENDICES . .
. ................... 77
I-A Summary of Individual Off-Gas Field Tests and "
Computations for Air flow- Weight Averaging . . . 77
I-B Overall Plant Data Sheet Based on Previous Year of"
Record and Supplemental Information ..... . 92
I-C Manufacturer Data and Information for Diffuser"
Retrofit ,
Vlll
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FIGURES
Number
Page
1 Schematic of Secondary Treatment Process ..... ±7
2 Plan Sketch with Tank Dimensions ig
3 Typical Cross Section and Detail 19
4 Typical Diffuser Layout 20
5 Off-Gas Sampling Plan "A" ; 34
6 Off-Gas Sampling Plan "B" '• 36
7 Plant Performance Data
Plan Flow vs. Elapsed Time 37
8 Plant Performance Data :
° Carbonaceous BOD5 vs. Elapsed Time ....... 38
9 Plant Performance Data
MLSS & MLVSS vs. Elapsed Time . . . 39
10 Plant Performance Data
F/M and SVI vs. Elapsed Time 40
11 Overall Tank Performance • •
Apparent Alpha x SOTE vs. Elapsed Time . 47
12 Overall Tank Performance '
Apparent Alpha vs. .Elapsed Time ....... 43
13 ; Aeration Performance - Pass No. 1
•Apparent Alpha x SOTE vs. Elapsed Time ... .. 49
14 Aeration Performance - Pass No. 1
Apparent Alpha vs. Elapsed Time ....... 50
15 Aeration Performance - Pass No. 2 i
Apparent Alpha x SOTE vs. Elapsed Time .'.... 51
16 Aeration Performance - Pass No. 2 i
Apparent Alpha vs. Elapsed Time . 52
ix :
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17 Aeration Performance - Pass No. 3
Apparent Alpha x SOTE vs. Elapsed Time .... 53
18 Aeration Performance - Pass No. 3
Apparent Alpha vs. Elapsed Time 54
19 Aeration Performance - Pass No. 4
Apparent Alpha x SOTE vs. Elapsed Time . . . . 55
20 Aeration Performance - Pass No. 4
Apparent Alpha vs. Elapsed Time ....... 56
21 Overall Aeration Performance by Pass
Apparent Alpha x SOTE vs. Aeration Pass ... 57
22 Overall Aeration Performance by Pass
Apparent Alpha vs. Aeration Pass ....... 58
23 Oxygen Transfer Efficiency Characteristics . . . . 62
x
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TABLES
Number Paae
1 Wastewater Characteristic Information ,
for Off-gas Visits .............. 31
2 Aeration Equipment Retrofit and Off-Gas
Test Chronological Summary . 33
3 Overall Aeration Performance for the Whole Tank . . 41
4 Overall Aeration Performance for Pass No. 1 .... 42
i
5 Overall Aeration Performance for Pass No. 2 .... 43
6 Overall Aeration Performance for Pass No. 3 j 44
7 Overall Aeration Performance for Pass No. 4 .... 45
8 Overall Aeration Performance by Pass ....... 46
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ACKNOWLEDGEMENTS
This investigation and study would not have been possible without
facilities use authorization by the Town of Glastonbury, CT.
Messrs. Ralph Mandeville and Michael Bisi together with the Water
Pollution Control Plant staff provided information and support
which were invaluable to the study. Their cooperation and
assistance are greatly appreciated.
XI1
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1.0 INTRODUCTION
In 1969, the consulting engineering firm of Metcalf & Eddy,
Boston, MA, completed the design of secondary wastewater
treatment facilities for the Town of Glastonbury, Connecticut.
The secondary wastewater treatment facilities included the ac-
tivated sludge process utilizing coarse bubble spiral-roll
aeration. Details of the basic design criteria are contained
in Appendix I-B.
The secondary wastewater treatment facilities were completed
in 1972. The wastewater plant was designed for an "average
1990 hydraulic flow of 3.64 MGD and a peak 1990 hydraulic flow
of 8.13 MGD. The activated sludge aeration system consisted
of two identical four-pass aeration tanks, each 40 feet wide
by 165 feet long with nominal operating liquid depth of 15.0
to 15.5 feet. The original aeration equipment consisted of
Walker Process Jacknife Sparjer - Header Diffuser assemblies
with Delrin coarse bubble sparjers. The Delrin coarse bubble
sparjers contained four 1/4-inch diameter air orifices at 90
degrees to one another. The total airflow capacity per dif-
fuser was 13.1 SCFM at 11 inches of water column headless.
Twenty sparjers were installed on each swing-arm assembly.
Each of four aeration passes per aeration tank contained four
swing-arm assemblies. The total number of sparjers installed
in each aeration tank was 320. The detailed specifications
and drawings for the aeration equipment are contained in Ap-
pendix I-B.
The centerline of the horizontal air manifold of the swing-arm
diffuser assemblies was*approximately 2.5 to 3.0 feet above
the tank floor and 2.5 feet from the tank sidewall. The spar-
jers were submerged with liquid to a depth of about 12.0 feet.
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A spiral-roll aeration and mixing pattern was established by
the aeration equipment placement and tank geometry. The Stan-.
dard Oxygen Transfer Efficiency (SOTE) of the coarse bubble,
sparjer aeration system was estimated to be approximately 6
percent as installed new.
Air for the submerged aeration system was supplied by three
identical 200 HP Hoffman multistage centrifugal ;blowers, each
with a unit airflow capacity of 2,000 to 4,500 SCFM and an
average discharge pressure of 7.0 psig. Operation of only one
blower was required at any given time.
As the cost of electrical energy increased in the mid to late
1970's, population growth in the service area lagged initial
projections, and the popularity of fine pore aeration,equip-
ment increased, strong interest developed on the part of the
Town to retrofit the coarse bubble system with a new, more ef-
ficient fine pore aeration system.
In early 1983, Town public works engineers began to inves-
tigate the feasibility of aeration system retrofit. Bids for!
new fine pore aeration equipment were received by the Town in
October 1983, and a contract for new fine pore tube diffuser
aeration equipment was awarded to FMC Corp. in April 1984.
The new aeration equipment was installed by Town personnel
during the summer of 1984. Start-up of the new fine pore
aeration system began immediately at the completion of instal-
lation. In the spring of 1985, a smaller, more efficient 100
HP centrifugal blower was installed to replace one of the 200
HP units. Detailed information on the new fine pore tube dif-
fuser equipment are contained in Appendix I-C.
This report contains a detailed presentation of the aeration
equipment retrofit project at the Glastonbury Wastewater Treatment
Facility together with the results of over 160 off-gas tests
conducted during six site visits from November 1985 through
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September 1988. Table No. 2, Aeration Equipment Retrofit and Off-
Gas Test Chronological Summary, contains the chronological summary
of the activities which have taken place from the initial design of
secondary wastewater treatment facilities to the completion of off-
gas testing of the fine pore tube diffuser equipment in September
of 19 88-. Appendix I-A contains summary tables for all of f-gas
testing conducted during the field investigation. Table No. 3,
Overall Aeration Performance for the Whole Tank, contains a summary
of all off-gas tests results for the Glastonbury facility aeration
system
This report is divided into the following major topical sections
1.0 Introduction
2.0 Summary
3.0 Historical Background Information
4.0 Fine Pore Aeration Retrofit Design Description
5.0 Operation Performance and Evaluation
6.0 Economic Considerations for Fine Pore Aeration
7.0 Recommendations ;
8.0 References
This Report also contains the following three appendices:
I-A Summary of Individual Off-Gas Field Tests and Computa-
tions for Airflow-Weight Averaging
I-B Overall Plant Data Sheet Based on Previous Year of Record
and Supplemental Information ,. :
I-C Manufacturer Data and Information for Diffuser Retrofit
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The summary section of the report (2.0) SUMMARY) which immediately
follows this section/ contains the significant overview results,
observations, conclusions, and recommendations based on the
detailed findings and evaluations presented in the main body of the
report.
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2.0 SUMMARY
2.1 GENERAL
The replacement of coarse bubble sparjers with fine pore tube
diffusers in the spiral-roll aeration system at the Glaston-
bury wastewater treatment facility has proven to be cost-
effective. Mixed liquor oxygen transfer efficiency (apparent
alpha^xSOTE) increased from an estimated 4.2 percent to over
6.6 percent (57 percent increase in efficiency!) , and blower
power consumption was reduced by approximately 50 KW after the
retrofit with fine pore tube diffusers. The reduced "electri-
cal cost resulted in a savings of about $20,000.00 per year.
The project payback period was less than 18 months.
A chronological summary of the aeration equipment retrofit
project and off-gas testing program is presented in Table No.
2. Plant wastewater characteristic information and opera-
tional parameters for the off-gas site visit tests are con-
tained in Table No. 1. Table Nos. 3 through 8 contain overall
airflow-weighted aeration performance based on the off-gas
test results. These data are presented for the whole tank and
for each aeration pass versus test visit and overall perfor-
mance versus aeration pass.
<1)includes influence of wastewater characteristics, standard
or new diffuser characteristics, and any other effects on
oxygen transfer performance due to biofouling, clogging and/or
changes in diffuser operation such as air leaks or porous
media material changes.
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Figure Nos. 1 through 6 contain sketches and details of the
secondary treatment process schematic, aeration tank dimen-
sions and details, aeration equipment details, and off-gas
sampling plans. Figure Nos. 7 through 10 contain plots of
plant performance data and wastewater characteristics for the
off-gas test visits. Figure No. 11 contains a plot of aera-
tion equipment performance versus airflow per diffuser for
clean water test performance (SOTE) and mixed liquor perfor-
mance (apparent alphaxSOTE) based on the field off-gas testing
and available information on clean water testing. Figure Nos.
12 through 21 contain plots of overall aeration system perfor-
mance for the whole tank and for each aeration pass versus
test visit, and Figure Nos. 22 and 23 contain overall aeration
performance versus aeration pass. Aeration performance data
is based on airflow-weight averaging of individual'off-gas
test results.
Significant detailed technical data are contained; in the three
report appendices. Appendix I-A contains a set of summary
tables of individual off-gas test field measurements including
computations for airflow-weight averaging of the individual
test results. Appendix I-B contains EXHIBIT A.I: Overall
Plant Data Sheet Based on Previous Year of Record plus sup-
plemental information on the basic design criteria for the
secondary treatment process and original aeration equipment
specifications. Appendix l-c contains information and data
concerning the retrofit to fine pore tube diffusers. Diffuser
technical data, and installation, operation, and maintenance
information is included.
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2.2 OFF-GAS TESTING RESULTS
The results of the field off-gas measurements were generally
consistent with the wastewater characteristics and process
operating parameters. There was some variability in all ob-
served and measured values. Off-gas oxygen transfer ef-
ficiency varied somewhat from visit to visit, and variability
increased from test to test and sample point to sample point
measurements. Replicate off-gas results of a single sample
location generally varied by a small amount, with few excep-
tions.
Wastewater flow rate and organic loading varied within a nor-
mal range during the test site visits and from visit to visit.
Process operating parameters such as MLSS concentration, dif-
fuser airflow, and F/M ratio also varied within a normal range
throughout the study.
With the exception of the first site visit in November 1985,
off-gas results from visit to visit did not vary by a great
amount. A possible reason for the rather low results for the
November 1985 testing was that a large amount of coarse bub-
bling was observed during the visit. It was determined that
many of the fine pore tube diffusers were leaking air around
the end gasket connections because of loose retaining nuts.
This problem was corrected before the second off-gas test in
March 1986.
Between March 1986 and September 1987, Aeration Tank No. 2 was
taken out of service for extended periods of time to perform
maintenance work on the buried air supply main and in-tank
maintenance on the concrete work and swing-arm assemblies. In
June 1986, a 100-year flood of the Connecticut River totally
submerged the plant under several feet of water. The plant
was out of operation for several weeks.
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The average whole-tank airflow-weighted oxygen transfer ef-
ficiency (apparent alphaxSOTE) for all tests was 6.6 percent
and ranged from 4.9 to 7.6 percent on a site visit-by-site
visit basis. Excluding the initial test in November 1985, the
average whole-tank efficiency was 7.2 percent. Average
airflow-weighted oxygen transfer efficiencies by aeration pass
varied by a small amount as follows:
Apparent Alpha
Aeration Pass x SOTE, % Aeration Mode
1 * 5.6 Reaeration
2 7.0 influent Pass
3 7.2 Second Pass
4 . 6.9 Third Pass
The average airflow-weighted whole tank apparent alpha for all
tests by site visit was 0.55 and ranged from 0.42 to 0.61.
-~~>*
Excluding the first test, the average apparent alpha was 0.58.
The overall apparent alpha changed very little from test-to-
test and from site visit-to-site visit. Pass No. 1, which
received all of the return activated sludge, experienced an
average apparent alpha of about 0.5, while the remaining three
aeration passes had higher apparent alpha values. Generally,
the inlet of Pass No. 2 (primary effluent feed point) had
lower apparent alpha values than any of the other off-gas
sample locations in Aeration Tank No. 2.
2.3 OPERATION AND MAINTENANCE OBSERVATIONS
Operation and maintenance practices for the new fine pore tube
diffusers differ very little from those practices used for the
coarse bubble sparjer diffusers. Manual measurement of mixed
liquor dissolved oxygen concentration and airflow adjustment
8
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are undertaken on a more frequent basis to maximize the oppor-
tunity to reduce electrical power usage and thereby reduce
costs.
There is no routine, scheduled program for cleaning of the
fine pore tube diffusers. Inspection of the diffusers con-
sists of visual observation of the air pattern at the liquid
surface. Any turbulence and excessive coarse bubbling are
noted. Maintenance is performed on an as-needed basis depend-
ing on the airflow pattern and distribution (back pressure on
individual or multiple dif fusers). Repairs are made by remov-
ing a swing-arm assembly from service, hoisting to the raised
position, and repairing the diffusers as required.
The swing-arm assembly system allows the aeration tank to
remain in service without disruption to the process, while at
the same time, providing for complete access to the diffusers
at any time. Although the mixed liquor transfer efficiency of
this type of system is about 60 to 70 percent of the ef-
ficiency of a full floor coverage fine pore system, the acces-
sibility for maintenance and repair is infinitely better, and
there is no adverse impact on operation and process control
while the equipment is out of service for inspection, clean-
ing, or repair.
2.4 DIFFUSER CLEANING COMMENTS
The fine pore tube diffusers at Glastonbury have been cleaned
once because of internal fouling with mixed liquor solids. No
routine cleaning has been done with a goal of improved oxygen
transfer efficiency. The only cleaning occurred within weeks
after the installation of the new diffusers. At the time of
installation of the new diffusers, the drain holes in the
swing-arm air manifolds (horizontal air header to which the
diffusers are attached) were not plugged. When airflow to the
swing-arm unit was disrupted, mixed liquor flowed back into.
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swing-arm unit was disrupted, mixed liquor flowed back into
the air manifold and swing-arm drop leg. Solids in the mixed
liquor impacted on the inside of the diffusers when air supply
was introduced to the swing-arm assembly. ,
Correction of the fouling problem involved raising of a
swing-arm assembly, removal of the diffusers, disassembly of
the diffusers, detergent cleaning of the tube diffuser media,
reassembly of the diffusers, installation of the diffusers on
the swing-arm assembly, and plugging of the air manifold drain
holes. Because of the time required to disassemble, detergent
clean, and reassemble each diffuser, the unit cost for dif-
fuser cleaning was relatively high ranging from $5.00 to $7.50
per diffuser.
2.5 DESIGN COMMENTS
The retrofit of this small activated sludge secondary
wastewater treatment plant was a project which could be
managed by plant and public works personnel without costly
outside consulting assistance. Initially, Town Public Works
Dept. personnel investigated the various alternate fine pore
systems which could be used at the Glastonbury facility.
Manufacturers were contacted for product information and
equipment recommendations, and visits were made to other
wastewater treatment facilities which had retrofitted from
coarse bubble to fine pore equipment. Valuable information
was gained from these contacts. ,
In the review and selection of fine pore replacement diffusers
on swing-arm assemblies, consideration must be given to the
details of attaching the new diffusers and the condition of
the swing-arm assembly. Swing-arm assembly piping and fit-
tings should be inspected for service condition and possible
modification requirements. Corrosion products must be removed
from the air piping. All drain holes must be plugged, and all
10
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locations for potential air leakage must be inspected and
repaired as necessary. (The drop leg knee joint is a prime
location for air leakage and potential backflow of mixed liq-
uor when air supply to the swing-arm assembly is shut off.)
Lastly, air piping must be capable of draining out all liquid
which enters through the diffusers when air is off. In most
retrofit cases, the new diffusers are mounted on the top of
the air manifold. In some cases, the diffusers are mounted on
the side(s) of the air manifold. In either case, a low-point
drain should be provided on the air manifold. One diffuser
should be attached to the low-point drain to ensure that liq-
uid does not become entrapped in the air manifold during
operation of the equipment.
Each type of diffuser considered for retrofit on swing-arm as-
semblies will have unique SOTE, back pressure, and air" filtra-
tion characteristics. If maximum electrical power savings are
to be realized, the diffuser characteristics must be fully
considered in conjunction with the existing and/or new air
supply equipment. Air filtration requirements will vary from
none to full second stage air filtration depending upon the
specific diffuser to be used. If existing blower equipment is
to be used with the new retrofit equipment, electrical power
savings can only be realized by shutting off blowers or, in
the case of centrifugal blowers, reducing airflow to some
degree. In many cases, existing blowers can be modified to
operate at reduced airflow rates efficiently, thus reducing
electrical power consumption. In other cases, new blower
equipment can be purchased which will match the characteris-
tics of the new diffuser equipment and maximize electrical
power savings at the same time.
11
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2.6 RECOMMENDATIONS
Evaluation of field oxygen transfer performance in spiral-roll
retrofit aeration systems by off-gas testing is viable and
useful. In systems where significant variations in plant
loading and process operating modes occur, a greater number of
off-gas tests, over a longer time base, provide more accurate
average performance information than the results from specific
sample point and/or point-in-time testing.
Fine pore retrofit or new applications' design should be based
on accurate full-scale Standard Oxygen Transfer Efficiency
(SOTE) data and realistic apparent alpha factor values cover-
ing the range of process conditions tank spatial location, and
wastewater characteristic parameters. Where possible, pilot
and/or full scale alpha testing should be undertaken, espe-
cially if unique conditions exist (i.e. industrial waste, spe-
cial process streams, or other factors which could influence
the alpha factor value). Pilot tests should use fouled as
well as clean diffusers.
In the absence of alpha factor values based on specific test-
ing, a design average range of 0.4 and 0.6 should be used for
fine pore tube diffuser spiral-roll aeration systems. The
full range of alpha values could be from less than 0.3 to over
0.7, depending on the many factors which effect alpha under
operating conditions. Therefore, it is very important to con-
sider these factors carefully when designing a new or retrofit
fine pore tube diff user system.
Mixed liquor apparent alphaxSOTE values of 5 to 8 percent (7
percent average) should be considered for fine pore tube dif-
fuser spiral-roll aeration systems operating at 15.0 to 15.5
feet of liquid depth and 12.0 to 12.5 feet of diffuser submer-
gence in the conventional activated sludge process treating
domestic wastewater. The apparent alphaxSOTE values stated
above are based on SOTE values of 11.0 to 13.0 percent in
12
-------
clean tap water, operated under the same conditions of tank
geometry, diffuser density and airflow, and diffuser submer-
gence.
r
In retrofit aeration systems using tube diffusers with retain-
ing nuts, gaskets, and bolts, care must be taken to ensure
that diffuser assembly is proper and that air leakage is
prevented from occurring around gaskets and retaining
hardware. Where existing air piping and swing-arm assemblies
are to be used, cleaning of inside piping surfaces and recon-
ditioning knee joints as necessary must be accomplished prior
to placing the new fine pore tube diffuser equipment in opera-
tion. All drain holes, blow-down legs, and other coarse
bubble system openings in the horizontal air manifold and
swing-arm assembly must be plugged to prevent backflow or
intrusion of mixed liquor into the air piping and diffusers.
Dissolved oxygen monitoring and airflow control instrumenta-
tion should only be as sophisticated as necessary. The
simpler the control system, the better the results. Routine
manual measurement of dissolved oxygen and manual adjustment
of airflow are adequate for small plants such as Glastonbury.
Air supply equipment should match the aeration system. The
airflow range and system pressure requirements of the aeration
equipment must integrate with the blower equipment performance
characteristics if aeration efficiency is to be optimized. In
cases where retrofit of the aeration equipment requires sub-
stantial reduction in air supply, blower turndown
capabilities, shutdown of incremental units, or replacement of
old equipment with new^ smaller equipment must be considered
and evaluated for maximum power reduction potential.
Dissolved oxygen monitoring instrumentation should be checked
and calibrated frequently, if the measurements are to be mean-
ingful .
13
-------
All operating on-line fine pore aeration equipment should be
tested for oxygen transfer efficiency and back pressure on a
routine basis. The results of this testing should be used to
compare equipment performance with expected values of perfor-
mance, and to establish maintenance schedules for cleaning the
equipment. Air leaks should be repaired as soon as possible
to limit intrusion of mixed liquor into the air piping system,
thereby reducing the potential for air-side fouling, to mini-
mize deterioration of the aeration system, and to ensure that
oxygen transfer efficiency is not reduced unnecessarily.
14
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3.0 HISTORICAL BACKGROUND INFORMATION
3.1 THE TREATMENT FACILITY
The Glastonbury wastewater treatment plant serves the Town of
Glastonbury, Connecticut. The secondary activated sludge
treatment facility, designed in 1969 and completed in 1972,
presently processes an average daily flow of about 1.6 MGD and
a maximum daily flow of 2.1 MGD with peaks as high as 2.5 MGD.
The secondary treatment facilities are designed for a 1990
average daily flow of 3.6 MGD and a 1990 peak flow of 8.1 MGD.
Present plant loading is only a fraction of the design loading
values used to size the secondary treatment facilities.
Population growth projections and industrial flow projections
used for the design did not materialize as anticipated.
The wastewater treatment facility contains preliminary,
primary, secondary activated sludge, and waste sludge con-
ditioning unit operations and processes. The conditioned
sludge from this plant is trucked to the Hartford MDC treat-
ment facility for final treatment and disposal.
3.2 THE ACTIVATED SLUDGE PROCESS
The activated sludge process is designed to treat a 3.6 MGD
average daily flow. However, over the past several years, the
average daily flow has been about 1.5 MGD and has not in-
creased due to a lack of growth in the service area as an-
ticipated at the time of design in 1969.
The flow from primary treatment enters the secondary
facilities by gravity. Only one of the two identical aeration
tanks is used for treatment. Each aeration tank is 166 feet
15
-------
long and 40 feet wide with a nominal liquid depth of 15.0 to
15.5 feet. Each aeration tank is divided into four passes of
equal size. Each pass is 82.5 feet long and 20 feet wide.
The normal mode of operation is conventional activated sludge
with provision for step-feed. Return activated sludge (RAS):
is introduced at the head-end of. Pass No. 1, and primary ef-
fluent (PE) is introduced at the head-end of 1 Pass No. 2.
Figure No. 1 contains a schematic of the secondary treatment
process. Schematics of the aeration tank and aeration equip-i
ment are contained on Figure Nos. 2, 3, and 4.
Mixed liquor flows from the aeration tank to two 65-foot
diameter circular final clarifiers. The overflow from the
final clarifiers is chlorinated and discharged to the Connec-
ticut River. Settled sludge from the final clarifiers is
returned to the activated sludge process at an average rate
equal to 34 percent of the plant flow. Waste sludge is
thickened at the plant and then trucked to the Hartford MDC
facility for final treatment and disposal.
3.3 ORIGINAL AERATION SYSTEM
i
The original aeration equipment installed in 1972 consisted of
Walker Process Jacknife Sparjer-Header Diffuser assemblies
with Delrin coarse bubble sparjers installed on the air
manifolds at the end of each jacknife. The Delrin coarse
bubble sparjers contained four 1/4-inch diameter air orifices
at 90 degrees to one another. The total airflow capacity per
diffuser was 13.1 SCFM at 11 inches of water column headless.
Twenty sparjers were installed on each swing-arm assembly.
Each of the four aeration passes per aeration tank contained
four swing-arm assemblies. The total number of sparjers in-
stalled in each aeration tank was 320 units. The sparjers
were uniformly spaced along the air manifolds at 2-foot inter-
vals. No provision for aeration tapering was proyided by this
orientation of the sparjers in the aeration tanks.
16
-------
FIGURE NO. 1
SCHEMATIC OF SECONDARY TREATMENT PROCESS
INF
Aeration Tank No. 2 (in service)
Pass 3
Pass 2
Pass 4
Pass 1
PE
1
Aeration Tank No. 1 (not in service)
_ I
Primary Clarifiers
Waste RAS
Final Clarifiers
Blowers
in
Basement
Control Building
Sludge to
Disposal ""*
Gravity
Thickener
1
NOTE: See following.figures and information in
Appendices I-B and I-C for specific details,
Final Effluent
17
-------
FIGURE NO. 2
PLAN SKETCH WITH TANK DIMENSIONS
NOMINAL LIQUID VOLUME
PER PASS :
25,500 cu. ft.
191,000 gali
NOMINAL TOTAL LIQUID
VOLUME: ;
102,000 cu. ft.
NOMINAL LIQUID SIDE
WATER DEPTH:
15.0 to
15.5 ft.
* Primary effluent inlet
for Contact Stabiliza-
tion Mode. (Site
visitation 1 through
3).
**
Primary effluent inlet
for Conventional Mode.
(Site visitations 4
through 6).
18
-------
FIGURE NO. 3
TYPICAL CROSS SECTION AND DETAIL
w.s.
Swing-Arm
-3'-6'
r-S
H
20 ft.
CROSS SECTION THROUGH AERATION TANK
NTS
Preretrofit Diffuser
Arrangement
Swing-Arm
Retrofit Diffuser
Arrangement
2 Walker
Process Coarse
Bubble Dif-
fusers
3*-0
For details see
Appendix I-B
.4—Swing-Arm
2 FMC PEARL-
COMB Model
SP-35 diffusers
•3f-6'
For details see
Appendix I-C
19
-------
FIGURE NO. 4
TYPICAL DIFFUSER LAYOUT
•4
1
H
•1
|
J
5
I
1
^
x-
S*.
20-ft. lo
tin in ••.
nil in inn
mgmam*
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^
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^
^ FM
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Di
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sw
4
m DS]
4 ,
pe:
*— *
l-« 3-in
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•0^
1
2 ' -(
r
•
See details i
FMC PEARLCOMB
Model SP-35
Diffuser, Typ.
0 diffusers per
swing arm,
4 swing arms
per aeration pass,
4 aeration passes
per tank)
20'-0"
PLAN VIEW SKETCH
NTS
20
-------
Detailed specifications and drawings for the original aeration
equipment are contained in Appendix I-B. Figure Nos. 2, 3,:
and 4 contain dimensions and tank details regarding the aera-
tion equipment placement.
The centerline of the horizontal air manifold of each swing-
arm assembly was positioned 2.5 to 3.0 feet above the aeration
tank floor and 2.5 feet from the tank sidewall. The sparjers
were submerged with liquid to a depth of about 12.0 to 12.5
feet. The sparjers were oriented between the drop-leg of the
swing-arm and the tank sidewall, creating a very narrow band
of aeration.
A spiral-roll aeration and mixing pattern was created by the
aeration equipment placement and tank geometry. The Standard
Oxygen Transfer Efficiency (SOTE) of this coarse bubble spar-
jer aeration system was estimated to be approximately 6 per-
cent as installed new.
Air for the original submerged aeration system was supplied by
three identical 200 HP Hoffman multistage centrifugal blowers,
each with an airflow capacity range of 2,000 to 4,500 SCFM and
an average discharge pressure of 7.0 psig. Operation of only
one blower was required at any given time, and airflow rate
adjustment was accomplished by inlet valve throttling at the
blower suction.
Dissolved oxygen and air supply control were carried out with
manual measurement of dissolved oxygen and manual adjustment
of airflow to Pass Nos'. 1 and 2 and Pass Nos. 3 and 4 with
in-line valves. In addition, each swing-arm assembly con-
tained an isolation valve which could be used to throttle
airflow to the individual swing-arm assembly. ;
21
-------
3.4 OPERATIOKAL PROBLEMS
As the cost of electrical energy increased in the mid-to-late
1970's, and as population growth in the early 1980's lagged
far behind the initial design estimates, the Town of Glaston-
bury developed a strong interest in saving electrical power
costs for aeration. During this same period of time, the
popularity of fine pore aeration equipment was increasing due
to aeration efficiency and power cost considerations. Several
Connecticut communities had retrofitted with fine pore opera-
tion equipment and were experiencing electrical power cost
savings as a result of the retrofits.
Prior to the full retrofit feasibility study, the No. 2 blower
was modified by the manufacturer to provide reduced capacity
and power draw. The blower modification allowed.airflow
turndown from the original surge point of 1,900 SCFM to under
1,600 SCFM, thus providing additional throttling and reduced
power consumption.
Glastonbury's interest in retrofitting to fine pore aeration
equipment was solely based on a desire to reduce electrical
power costs. Both new in-tank equipment and blower modifica-
tions to reduce airflow supply would be investigated.
3.5 RETROFIT OBJECTIVES
With electrical power savings as a primary objective for
retrofitting to fine pore equipment, several important con-
siderations were also made a part of the overall retrofit ob-
jectives. They were:
1. payback of capital cost of the project in as short a
time as possible (24 months desirable).
2. minimize any additional operational and maintenance
costs over the existing aeration equipment.
22
-------
provide the same operational flexibility as the ex-
isting equipment afforded.
keep process results and effluent water quality
standards the same as before the retrofit.
avoid the need the use multiple blower units as much
as possible to keep electrical demand charges as low
as possible.
3.6 BASIS FOR CHANGING TO FINE PORE AERATION
In early 1983, the Town of Glastonbury public works engineers
began to investigate the feasibility of aeration system
retrofit. Initially, various alternate fine pore systems were
investigated. Manufacturers were contacted for product infor-
mation and equipment recommendations, and visits were-made to
other wastewater treatment facilities which had retrofitted
from coarse bubble to fine pore equipment.
It was determined that significant electrical power savings
could be realized by replacing the coarse bubble aeration
equipment with fine pore equipment and perform some modifica-
tions to the air supply equipment to render it compatible with
the new in-tank equipment and, generally, improve aeration
'efficiency.
Since the Town did not want to contract with a consultant to
undertake a costly feasibility study, only proven fine pore
technology was considered. Other types of aeration equipment
with high efficiency claims were not considered. Also, the
continued use of the existing swing-arm assemblies was a
strong consideration, because the equipment was in good
repair, and the operational flexibility afforded was superior
to full-floor coverage equipment which would require that the
aeration tank be taken out of service and dewatered for clean-
ing and maintenance of the diffuser system. For a small plant
23
-------
liXe Glastonbury with only one on-line aeration tank, the
switchover of the entire activated sludge process to a standby
tank was a significant operational consideration.
24
-------
4.0 PINE PORE AERATION RETROFIT DESIGN DESCRIPTION
4.1 BASIS FOR DESIGN
The design basis for retrofitting from the existing swing-arm
coarse bubble diffuser assemblies to fine pore equipment is
contained in the Invitation to Bid documents and attachments
prepared by the Town of Glastonbury. These documents ( BID
IGL-2283) are contained in Appendix I-C. The Invitation to
Bid and supporting documents were sent to several manufac-
turers of both fine pore tube diffuser aeration equipment and
fine pore dome/disc diffuser aeration equipment.
The detailed specification prepared by the Town requested
proposals for "evaluation and equipment recommendations for
modifications to the aeration system at its Water Pollution
Control Facility which is presently operating conventional ac-
tivated sludge with capability of step-feed." The purpose for
the request for proposals was as follows: "The Town is inter-
ested in reducing its energy consumption from generating com-
pressed air for an aeration system as part of its activated
sludge process." The proposal scope for aeration system
modifications which the Town would consider and evaluate in-
cluded the centrifugal blower(s), controls, valving, piping,
and diffuser system(s).
Evaluation parameters used by the Town to compare the various
bids for aeration system modifications were as follows:
1. Energy savings over the current aeration process,
broken down by major components (i.e., blower, con-
trol valve, controls, diffuser).
2. Expected equipment life.
3. Operating energy costs-system life.
25
-------
4. Operating/maintenance system costs-system life.
5. System cost.
6. Equipment flexibility within system life to varying^
flow and biochemical demands.
7. Why vendor recommends the proposed system.
8. Equipment manufacturer resume with the proposed type
of system.
9. Location(s) of proposed equipment/system currently
in use.
The system life was to be taken as 10 years or the actual life
of the proposed equipment if less than 10 years.
Potential bidders were provided with detailed information and
data concerning the existing aeration system. This informa-
tion included:
1. Basic design data (1970 and 1990).
2. Current operating data (1983) .
3. Air compressor performance curves for original and
modified equipment.
4. Aeration tank details.
5. Air header diffuser specifications, sparjer assembly
details, and sparjer back-pressure curves.
Much of the information listed above is contained in Appendix
I-B of this report.
Several bids were received from fine pore tube manufacturers,
both flexible membrane and various rigid media types. At
least one bid was received from the manufacturer of fine pore
dome diffuser equipment.
26
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4.2 DESCRIPTION OF PIKE PORE DIFPUSER EQUIPMENT PURCHASED
Bids were received in October 1983 and an equipment selection
and award was made in April 1984. The successful bidder was
FMC Corp. for the supply of 320 Pearlcomb Diffusers, Model
SP-35.
The Pearlcomb Diffuser is a fine pore tube-type diffuser with
a porous cylindrical tube composed of modified acrylonitrile
styrene copolymer material in the form of uniformly-sized
spheres linked to their points of contact. Each diffuser as-
sembly consists of:
* one tube adapter manufactured from an ABS polymer
provided with a stainless steel insert suitable for
V
connection to a 3/4-inch NPT thread and control
orifice. •' *
* one diffuser tube.
* one end cap manufactured from an ABS polymer.
* one stainless steel rod threaded at both ends with PVC
nut.
* one set of Neoprene gaskets and polyethylene washes.
The diffusers are shipped unassembled and require assembly at
the job site by the installing contractor.
Details of the technical specification for the diffuser; in-
stallation, operation and maintenance instructions; and dif-
fuser detail drawing and diffuser installation drawing are in-
cluded in Appendix I-C of this report.
The existing 3-inch diameter air manifold on each swing-arm
assembly was rotated 90 degrees to orient the air release
holes and pipe clamp assemblies in an upright position. A
1-inch pipe nipple was inserted in each clamp assembly. A
3/4x3/4xl-inch tee was attached to the top of the nipple. A
Pearlcomb Diffuser was attached to each 3/4-inch tee opening.
27
-------
The purchase of air filtration equipment and a new 100 HP Hof-
fman multistage centrifugal blower to replace one of the three
existing 200 HP units was not part of the diffuser and in-tank
work. The existing blowers could not be throttled to a low
enough discharge volume for the new diffuser equipment, and a
smaller capacity unit was needed to accomplish the reduction
in electrical power usage sought as the major objective of the
project.
28
-------
5.0 OPERATIONAL PERFORMANCE AND EVALUATION
5.1 SYSTEM START-UP
Prior to the start-up of Aeration Tank No. 2 with the new fine
pore tube diffusers in the summer of 1984, the average air
supply rate to the activated sludge process was 2,250 SCFM.
After installation of all 320 Pearlcomb Diffusers, the airflow;
was adjusted downward to the surge point on the modified 200
HP blower (about 1,600 SCFM). The purchase of a smaller, more
efficient 100 HP blower in 1985 permitted airflow adjustment
to a range of 1,000 to 1,200 SCFM with airflow rate control
based on manual measurement of the mixed liquor dissolved
oxygen concentration.
Installation of all equipment was performed by Town Public
Works employees. Aeration Tank No. 2 was dewatered and
cleaned prior to the retrofit installation work. ' Modification
of the swing-arm air manifolds and installation of the new
Pearlcomb Diffusers was accomplished from the bottom of the
aeration tank to avoid lifting and lowering of each individual
swing-arm which would be necessary if the installation work
was done topside. -•- -
After a few weeks of operation, it was noted that several dif-
fusers appeared to be clogged or plugged, and airflow patterns
indicated a smaller amount of air was being released from many
diff users. Investigation of the problem revealed that mixed
liquor was backflowing into the blow-down holes in the air
manifolds on each swing-arm assembly and plugging the inside
of the diffusers. Steps were taken to correct this problem
and to thoroughly clean the diffusers.
29
-------
5.2 OPERATING CONDITIONS
Average operating conditions for the period from the retrofit
implementation through the off-gas testing program are con-
tained in Table No. 1 and in Appendix J-B. The average BOD
loading to the plant was 230 mg/1 and approximately 120 mg/1
to the secondary treatment system. Wastewater flow averaged
1.5 MGD with maximum day flows of over 2.0 MGD and peaks to
over 2.5 MGD. MLSS concentration ranged from under 1,500 mg/1
to over 3,000 mg/1. The average detention time in aeration
was 11 hours, and sludge age averaged 12 days.
5.3 OPERATIONAL CONTROL
Operational control for the new aeration equipment Involved
manual measurement of the dissolved oxygen concentration of
the mixed liquor and manual airflow adjustment of the on-line
blower to a flow rate which would achieve a dissolved oxygen
concentration in the mixed liquor of approximately 2.0 mg/1.
Dissolved oxygen measurements were taken two to three times
each day.
5.4 TREATMENT PERFORMANCE
The water quality of the plant effluent remained consistently
high after the implementation of the fine pore aeration system
retrofit. Effluent BOD and suspended solids concentrations
nearly always remained below 10 mg/1.
30
-------
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5.5 AERATION SYSTEM EVALUATION
5.5.1 General
An extensive aeration system performance evaluation has been
undertaken at the Glastonbury treatment facility as part of
the ASCE/EPA Oxygen Transfer Study. From November 1985
[
through September 1988, Aeration Technologies, Inc. conducted
off-gas testing during six separate site visits. Over 160 in-
dividual off-gas tests were performed in Aeration Tank No. 2
to measure and record aeration performance over time. The
results of the field off-gas measurements were compared with
plant water quality data and operating conditions for the
periods in which testing was performed.
Table No. 2 contains a listing of the six site visits together
with test designation identification. Other key event dates
for the Glastonbury retrofit project are contained in the
table. ',
The initial off-gas test visit in November 1985 and the second
off-gas test visit in March 1986 used a sampling plan consist-
ing of two sets of replicate tests at each of the influent and
effluent quarter points of each aeration pass. Each replicate
test set consisted of two individual off-gas tests, one taken
with the hood positioned half way across the aeration pass
width and one taken with the hood placed at the remaining
half-width position. In the first position, the collection
hood airflow was very high compared to the very low airflow
collected at the half-width position furthest from the swing-
arm assembly. (The sampling designation for this sequence of
testing is Sampling Plan "A" and is shown graphically on
Figure No. 5).
For the remaining four off-gas test visits, a sampling plan
using one replicate at each sample point, but with three sets
of tests for each site visit, was adopted. This sampling plan
32
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TIME/DATE
Late 1969
late 1972
Early 1982
Oct. 1982
Oct. 1983
April 1984
June 1984
Fall 1984
Feb. 1985
May 1985
TABLE MO. -> '•
AERATION EQUIPMENT RETROFIT AND
OFF-GAS TEST CHRONOLOGICAL SUMMARY
DESCRIPTTOKT
Final design of Secondary Treatment
Facilities
> i
Completion of Secondary Treatment
Facilities
Investigate feasibility of retrofitting
the coarse bubble aeration equipment
Modification of one 200 HP blower to
reduce capacity
Bids received for fine pore retrofit
equipment
Contract let for new fine pore aeration
equipment
100-year flood shuts plant down for
several weeks
Installation of new fine pore aeration
equipment
Installation of new 100 HP blower
Start-up and operation of new fine pore
aeration system
Nov. 21 & 22, 1985*
Mar. 26 & 28, 1986*
Sept. 17, 1987**
Jan. 11, 1988**
May 17, 1988**
Sept. 7, 1988**
Full Tank Testing - Designated 1A
Full Tank Testing - Designated 2A
Full Tank Testing - Designated 3B
Full Tank Testing - Designated 4B
Full Tank Testing - Designated SB
Full Tank Testing - Designated 6B
through
33
-------
FIGURE NO. 5
OFF-GAS SAMPLING PLAN "A"
o
z
CO
&
pp t
i
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14 16
( i
3
9 11
llO 12
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19
20
23
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31
32
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17 <
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-------
(designated as Sampling Plan «B» and shown graphically on
Figure No. 6) utilized a collection hood which extended across
the full width of the aeration pass. It was believed that the
reduced time necessary to test the total aeration tank on a
once-through basis would be more representative of actual per-
formance conditions in the aeration tank. Also, the use of a
full-width hood eliminated the need to airflow weight-average
the results from two widely differing test conditions (high
airflow and low OTE versus low airflow and high OTE) .
The off-gas test equipment and analysis procedures are in ac-
cordance with the project "Manual of Methods for Fine Bubble
Diffused Aeration Field Studies." The results of all off-gas
testing are summarized in the tables and on the figures. Ap-
pendix I-A contains a summary of the individual test run
results plus the whole-pass and whole-tank airflow weighted
results and the overall airflow weight-averaged results by
aeration pass and for the whole tank for the six test visits.
Plant wastewater and process characteristics for the test site
visits are contained in Table No. 1 . These data are plotted
on Figure Nos. 7 through 10 versus elapsed time, starting with
the site visit in November 1985.
The results of the oxygen transfer performance tests are sum-
marized in Table Nos. 3 through 8. Table No. 3 contains the
overall aeration performance data by site visit for the whole
tank based on airflow weight-averaged results from 24 to 32
individual test runs per site visit. Table Nos.; 4 through 7
contain the overall aeration performance data by site visit
for each aeration pass based on airflow weight-averaged
results from 6 to 8 individual test runs per site visit.
Table No. 8 contains the overall aeration performance data by
aeration pass for all six site visits. Figure Nos. 11 through
22 contain plots of aeration performance in terms of apparent
alphax SOTE and apparent alpha for the whole tank, for each
aeration pass, and by aeration pass based on the airflow
35
-------
FIGURE NO. 6
OFF-GAS SAMPLING PLAN "B"
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