CASE HISTORY OF FINE PORE DIFFUSER
RETROFIT AT RIDGEWOOD, NEW JERSEY
by
James A. Mueller and Paul D. Saurer
Manhattan College
Bronx, New York 10471
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.
11
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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
SS6n u P? u 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 ot 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.
f ~As.,P*rt of thฃse 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 facdmes employing fine pore aeration, and prepare a comprehensive-design manual on
the subject This manual, entitled "Design Manual - Fine Pore Aeration Systems," was completed
m 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 m 16 separate contractor reports and provided critical input to the design manual
Ihis report summarizes the results of one of the 16 field studies.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
111
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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 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 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 from
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 JJ. Marx
2. "Oxygen Transfer Efficiency Surveys at the Jones Island Treatment Plants, 1985-1988"
(EPA/600/R-94/094) by R. Warriner
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
5. "Long Term Performance Characteristics of Fine Pore 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 and P.D. Saurer
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
iv
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11. "The Measurement and Control of Fouling in Fine Pore Diffuser Systems"
(EPA/600/R-94/102) by E.L. Barnhart and M. Collins
1-2. "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 April 1983, the Ridgewood, New Jersey Wastewater Treatment Plant underwent a retrofit
from a coarse bubble to a fine pore aeration system. Also, process modification from contact
stabilization to tapered aeration occurred. This report presents a case history of plant and aeration
performance of each system form 1981 through 1986. Extensive aeration studies were conducted on
the fine pore aeration system in 1985 and 1986 to highlight the changing oxygen transfer efficiency
with time and evaluate cleaning frequency requirements to maintain the efficiency at a viable level.
An economic evaluation including bid prices, maintenance costs, and payoff period based on power
savings is included.
This report was submitted in partial fulfillment of Cooperative Agreement No. CR812167
by the American Society of Civil Engineers under subcontract to Manhattan College under the
partial sponsorship of the U.S. Environmental Protection Agency. The work reported herein was
conducted over the period of 1985-1986.
VI
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CONTENTS
Foreword
111
Preface
iv
Abstract
vi
Figures ;
ฐ ix
Tables
xii
Acknowledgments
I. Introduction ,
II. Plant Description ,
A. Original Activated Sludge Plant . . '. 3
B. Basis for Plant Upgrade ,-
C. Fine Pore Diffuser Retrofit o
IE. Field Study Description
IV. Clean Water Performance 20
A. Coarse Bubble System 20
B. Fine Pore System'. ." ..'... 20
V.
Case History Summary (Oct. 1981-Sept. 1986) ... 25
VI. ASCE Study Qune 1985-Sept. 1986) 31
A. Summary -, *
B. 24 Hour Study 0une 16-17, 1986) 53
1. Description of Study 53
2. Plant Conditions 53
a. Plant Characteristics 53
b. Influent Load Variability 57
3. Results 57
a. Offgas 57
1. Diurnal OTE20 and Alpha VariabHity '.'.'.'.'. 57
2. Longitudinal OTE20 and Alpha Variability 63
3. Gas Flow and Dissolved Oxygen Variability 63
4. Comparison of Offgas to Manometer Measured
Gas Flow 7Q
Vll
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CONTENTS (continued)
b. Steady State 7Q
1. OTE20 Comparison 70
2. Oxygen Uptake Rates 75
4. Parameter Correlations 76
C. Effect of Cleaning on Aeration Equipment 83
D. Problems Encountered and Solutions 88
1. Nocardia Foam 88
2. Four Lunger and In Situ Dome DWP Taps 91
VII. Plant Performance - Coarse Bubble and Fine Pore Systems ............... ...... 95
A. Operating Conditions and Controls ..................... 95
B. Treatment Performance .................................... 99
1. Influent and Effluent Characteristics ........................ 99
2. Sludge Production Comparison .............................. 107
3. Recycle Stream Impact on Fine Pore Aeration System ................. 107
C. Air Utilization Comparison ........... .................. H2
VIII. Economic Analysis .......................................
IX. Conclusions ....................................... '
X. References .................................. _ ..... ^s
Appendices
A. Nocardia Foam Effect Analysis ...................................... 129
B. Offgas Summary Data Sheets: Equilibrium Conditions
(available as a separate document)
vm
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LIST OF FIGURES
No.
1. Ridgewood Plant Layout and Flow Diagram for the Coarse
Bubble Aeration System
Page
2. Ridgewood Plant Layout and Flow Diagram for the Fine
Pore Aeration System 10
3. Influent Baffle Design (Fine Pore System).; 11
4. Effluent Baffle Design (Fine Pore System) 12
5. Aeration Grid Design (Fine Pore System) 13
6. Offgas and Nonsteady State Test Setups.. 18
7. SOTE versus Gas Flow (Coarse Bubble) 21
8. SOTE Versus Gas Flow (Fine Pore) 21
9. Original and Modified Fine Pore Dome Distribution 22
10. Effect of Diffuser Density on SOTE 24
11. OTE20 Summary - Coarse and Fine 27
12. Alpha Summary - Coarse and Fine 28
13. Effect of One Tank in Service on OTE20 43
14. Effect of One Tank in Service on Alpha 44
15. Effect of Gas Flow on OTE20 47
16. Diurnal Raw Plant Flow. 56
17. Diurnal TSS Concentration 59
18. Diurnal Soluble TOG Concentration.. 59
19. Diurnal TSS Load 60
20. Diurnal Soluble TOG Load 60
21. Diurnal OTE20 64
22. Diurnal Alpha 64
23. Avg. Grid OTE20 vs. Distance. '... 66
IX
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LIST OF FIGURES (cont'd)
Mi. / Page
24. Avg. Grid Alpha vs. Distance 66
25. Diurnal Gas Flow. 68
26. Diurnal Grid D.0 68
27. Grid Gas Flow vs. Distance... 69
28. Grid D.O. vs. Distance 69
29. Grid A Diurnal Dissolved Oxygen 71
30. Test #60 D.O. Variability 71
31. Gas Flow Comparison 73
32. Off gas and Steady State OTE Comparison 77
33. Diurnal Oxygen Uptake Rate... 78
34. Grid 0^ Uptake vs. Time...... 78
35. Effect of 02 Uptake on OTE20. 81
36. Effect of 0 Uptake on Alpha. 81
37. Effect of Soluble TOC Load on Alpha 82
38. Cleaning Effect on OTE20 (Tank #3) 86
39. Cleaning Effect on OTE20 (Tank #4) 87
40. Total Mass (TSS) in System - Coarse and Fine 96
41. F/M Ratio - Coarse and Fine , 97
42. Sludge Age - Coarse and Fine 98
43. Plant Raw Influent Flow - Coarse and Fine 101
44. TSS Influent and Effluent - Coarse and Fine... 102
45. BOD5 Influent and Effluent - Coarse and Fine 103
46. N-NEL, NO, Influent and Effluent - Coarse and Fine 104
47. Plant Removal Efficiencies - Coarse and Fine 106
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LIST OF FIGURES (cont'd)
Nฐ^L Page
48. Air Utilized - Coarse and Fine 113
%
49. Air Utilized Per Gallon Influent - Coarse and Fine 114
50.. Air Utilized Per BOD Removed - Coarse and Fine. 115
51. Savings in Power Consumption 121
52. Fine Pore Power Costs and Savings 122
XI
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LIST OF TABLES
Page
1. Ridgewood Tank Sizes 5
2. Original Coarse Bubble Aeration System in Ridgewood Tanks 1&2.. 7
3. Projected Energy Savings for the Fine Pore Retrofit 9
4. Fine Pore Aeration Retrofit in Ridgewood Aeration Tanks 3&4 15
5. Description of Aeration Studies 17
6. Summary of Aeration Results 26
7. Estimated Yearly Average OTE20 and Alpha Values for Both
Aeration Systems . 29
8. Summary of Aeration Tests, 1985 & 1986 32
9. Process Conditions for all Tests, 1985 & 1986 37
10. Nonsteady State and Offgas Aeration Results for Ridgewood
Tank #3, 1985 & 1986 40
11. Nonsteady State and Offgas Aeration Results for Ridgewood
Tank #4, 1985 & 1986 42
12. Effect of One Tank in Service on OTE20 and Alpha 45
13. Parameter Correlation Results, 1985 & 1986 46
14. Steady State Test Conditions, 1985 & 1986 49
15. Steady State Results, 1985 & 1986 51
16. Description of 24 Hour Study 54
17. Plant Characteristics During June 1986 55
18. Diurnal Load to Aeration Tank (24 Hour Study) 58
19. Offgas Aeration Results for 24 Hour Study 61
20. Daily Average OTE20 and Alpha (Total Mass Method, 24 Hour
Study) 62
21. Grid OTE20 and Alpha for 24 Hour Study 65
22. Grid Gas Flow and Dissolved Oxygen Values for 24 Hour Study.... 67
23. OTE20 Correction for DO Variation During Test 60 72
xii
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LIST OF TABLES (cont'd)
Plant
24. Steady State Test Conditions, 24 Hour Study 74
25. Steady State Results, 24 Hour Study 75
26. Parameter Correlations, 24 Hour Study ." 79
27. Cleaning Frequency at Ridgewood for Tank 3 84
28. Cleaning Frequency at Ridgewood for Tank 4 85
29. Nocardia Foam Oxygen Uptake Rates 90
30. Foam Corrected Oxygen Transfer Efficiencies 92
31. Average Operating Conditions for Both Aeration Systems at
Ridgewood 95
32. Plant Performance Results for Fine and Coarse Bubble
Aeration Systems 100
33. Sludge Wastage Results for Fine and Coarse Bubble Systems 108
34. Influent and Recycle Loads to Aeration Tank ;... 109
35. TSS Recycle Stream Impact on Aeration Tank Load 110
36. Average Blower Power Reduction for Fine Pore System 117
37. Yearly Dome Cleaning and Repair Costs .....118
38. Nocardia Foam Chlorination and Cleanup Costs V........ 119
39. Summary of Dome System Maintenance Yearly Costs 120
40. Dome System Economic Summary at Ridgewood 123
Xlll
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ACKNOWLEDGEMENTS
The authors of this paper would like to acknowledge the support of
John Lagrosa and the entire staff at the Ridgewood Wastewater Treatment
Plant. The work of numerous Manhattan College students is acknowledged,
especially: Peter Gerbasi for conducting the initial work on the pro-
ject and refining measurement techniques in foam; Laurie Davanzo for
computer programming, Dennis Scannell, Elizabeth da Rocha Lima, Laura
Gavin and Peter Elliott for testing and analysis support; and the
various project engineers on the student field laboratories. Finally,
thanks to Eileen Lutotnski for her patience in preparing the report.
xiv
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I. INTRODUCTION
The Ridgewood Water Pollution Control Facility is a 3 MGD
activated sludge plant located in northwest Bergen County, New Jersey.
The plant, treating 100% municipal wastewater, has undergone both pro-
cess modification and diffuser retrofit. Completed in April 1983, the
modification and retrofit changed the plant from a contact stabilization
process using coarse bubble spargers to a conventional activated sludge
process using fine pore domes. The purpose of the plant retrofit was to
reduce energy consumption and minimize power costs. The capital costs
of the project are being paid off on a monthly basis using the actual
energy cost savings realized from reduced blower power consumption.
Prior to and immediately following the plant upgrade, field
aeration studies were conducted by Manhattan College to provide a sig-
nificant data base on oxygen transfer efficiency of the coarse bubble
system and newly installed fine pore system. Both clean and dirty water
data were obtained using nonsteady state testing techniques for the
majority of the studies. Within a year of installation, a significant
deterioration in fine pore diffuser performance occurred resulting in
lower energy cost savings than originally projected. No diffuser main-
tenance or dome cleaning was practiced during this period. After \%.
years of operation, the domes were hosed clean and additional diffusers
added.
This present study was begun in June 1985, a little over two
years after initial dome installation. The objectives of the study were
to (1) provide an in-depth case history of a municipal treatment plant
retrofit from coarse bubble to fine pore diffusers, and (2) evaluate the
impact of dome cleaning on diffuser performance. To accomplish these
objectives, additional field studies were conducted for the next 1%
years during which diffusers were periodically cleaned with either water
hosing or acid brushing. Three measurement techniques were used to
evaluate oxygen transfer efficiency; steady state, nonsteady state, and
offgas.
This report presents the results of the present data collec-
tion and combines them with the historical data base to obtain an in-
depth case history of the retrofit. The impact of plant operation and
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cleaning frequency is evaluated. Comparisons of the three measurement
techniques are provided along with problems encountered and corrections
required when measuring transfer efficiencies in tanks with high levels
of "Nocardia" foam. Results of a 24 hour study to provide estimates of
the diurnal fluctuations in diffuser performance are included. Finally,
an economic evaluation including bid prices, maintenance costs, and
actual power costs savings is conducted. Changes in sludge production
and disposal costs are also included.
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II. PLANT DESCRIPTION
A. Original Activated Sludge Plant
The original activated sludge plant was constructed in 1959
with a design capacity of 5 MGD but an actual operational flow of 3 MGD.
The wastewater is substantially 100% municipal sewage with insignificant
industrial inputs. The effluent from the plant discharges to the
Ho-Ho-Kus Brook approximately three-quarters of a mile above its junc-
ture with the Saddle River which discharges to the Passaic River thence
to Upper New York Bay.
The plant flow diagram is given in Figure 1 with unit sizes
given in Table 1. Influent flow to the primary treatment portion of the
plant is by gravity with the screens, grit chambers, and primary clari-
fiers constructed below grade. Only primary clarifier #1 is used for
the raw wastewater flow with the #2 clarifier used for sludge super-
natant settling. The primary clarifier #1 effluent discharges to a wet
well from which it is lifted by four centrifugal pumps to the inlet
channel of the aeration tanks. Return sludge is combined with the pri-
mary effluent in the influent channel. The mixed liquor flowed to aera-
tion tank #1, used as the contact tank in the original contact stabili-
zation process. From the contact tank, flow was discharged to both
secondary clarifiers which are center feed and peripheral effluent draw-
off. Four contact chambers are used for chlorination prior to discharge
to the Ho-Ho-Kus Brook.
Return sludge was drawn off the center hopper in each secon-
dary clarifier and returned to aeration tank #2 for stabilization prior
to combining with the primary effluent. Sludge is wasted from the
secondary portion of the system to the primary clarifier. The combined
primary-secondary sludge is pumped to the primary digester, which is
mixed and. heated, and thence to the secondary digester for supernatant
separation. Sludge is then hauled by truck offsite for incineration at
another plant. Vacuum filtration was originally used for sludge de-
watering prior to disposal on a sod farm or onsite land application. It
was abandoned in August 1982 due to high chemical and energy costs.
Land application was also no longer viable due to more stringent regula-
tions.
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TABLE 1
Ridgewood Tank Sizes
Unit
Grit Chamber
Primary Clarifier
Aeration Tanks
Tanks 1 & 2
Tanks 3 & 4
Secondary Clarifier
Chlorine Contact
Anaerobic Digesters
Number
2
2
2
2
2
4
2
Dimensions,
Width or
Length Diameter
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113 24
116 24
75
42.5 11
60
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Approximate
Depth
6.5
9.6
14.8
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10.6
6.5
24.7
Tank
Volume,
Gallons
12,000
204,000
300,000
308,000
350,000
23,000
522,000
Average value at 10:00 a.m. on 1/12/87 for tanks 3 and 4 at a raw flow of 4 MGD
with both secondary clarifiers operational.
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Sludge supernatant was settled in primary clarifier #2 and
aerated in aeration tank #3 until the oxygen demand was satisfied and
nitrification occurred as determined by a marked decrease in alkalinity.
After the supernatant oxygen demand was satisfied, the contents of tank
#3 were pumped into the primary effluent flow causing insignificant
impact on the secondary system. An unknown quantity of sludge was also
discharged from primary clarifier #2 to on-site lagoons which have been
abandoned since August 1982 and subsequently filled in.
An additional sludge recycle stream to the aeration tank
influent is solids settling in the chlorine contact chamber. Once per
month the supernatant from the contact chambers is drained and the sep-
tic sludge layer on the bottom of the tanks is pumped back to the aera-
tion tank influent. Aeration tank #4 was not utilized in the original
plant due to the lower raw wastewater flow than designed.
In the original plant the aeration system consisted of coarse
bubble Walker sparjers. Two manifolds were located adjacent to the side
wall of each aeration compartment providing spiral roll wide band aera-
tion. The number of diffusers is given in Table 2. Water level varies
since the two tanks are hydraulically connected with no free overfall
existing in the aeration tank. At high flows tank depth is greater than
at low flows, thus a range of tank depths is given with a typical depth
taken as 14.8 ft. providing a tank volume of 300,000 gallons. Air lift
pumps using approximately 15% (300 scfm) of the total plant gas flow
were located in compartment 2-4 and used to return the aeration influent.
As indicated in Table 2, two blowers were continually used to
supply the air requirements for the total plant. Temperature, pressure
and gas flow measurements were available on the blower discharge. For
tanks #1 and #2 both flow tube and orifice plate data was available as
shown in Mueller et al., 1982. During summer months, blower capacity
was often unable to maintain measurable D.O. in the aeration tanks
resulting in periodic odors.
B. Basis for Plant Upgrade
Plant retrofit from coarse bubble to fine pore diffusers was
undertaken to reduce energy costs of the blowers. Specific design
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TABLE 2
Original Coarse Bubble Aeration System
in Ridgewood Tanks 1 and 2
AERATION TANKS
Type Diffuser
# Compartments
2
Surface Area/Compartment, ft
# Sparjers/Compartment
# Sparjers/Tank
2
Diffuser Density, ft /Diffuser
Height of Diffusers off Tank
Bottom, ft
Tank Water Depth
Tank #1
Contact
Walker Sparjers
4
, 678
40
160
17.0
2
^14.5-15.5 ft
Tank #2
Stabilization
Walker Sparjers
4
678
28
112
24.2
2
M4.5-15.5
BLOWERS
Name
Type
Nominal Rating
Total Number
Number in use at any one time
Typical Efficiency
Spencer Turbine - Turbo-Compressor Model 362
Centrifugal
75 hp
5
2
43%
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criteria used for the retrofit is not available. However, field studies
were undertaken by Manhattan College (Mueller, et al., 1982) to charac-
terize the coarse bubble system. Based on these results a projection of
fine pore system advantages was made. The average transfer efficiency
for the coarse bubble diffusers in batch and flowing systems in the con-
tact and stabilization tanks was 4.8% at zero D.O. Using an alpha of
0.4 from laboratory data and a cleahwater efficiency of 28% for dome
diffusers, an oxygen transfer efficiency of 11.1% at zero D.O. was pro-
jected. This would allow one blower to be used instead of two at the
same oxygen utilization rate of the coarse bubble system.
Table 3 summarizes the economic advantages anticipated from
the upgrade. Based on energy savings, a payoff period of 6.2 years was
estimated for the retrofit. During summer months, odors from the aera-
tion tanks would be eliminated due to ability to maintain measurable
D.O. at all times with the fine pore system. Based on a COD balance,
less secondary sludge production was anticipated due to the ability to
supply more oxygen with the fine pore system. This would eliminate
oxygen limitation thus providing greater sludge endogenous respiration.
C. Fine Pore Diffuser Retrofit
In the Fall and Winter of 1982, a fine pore diffuser (Gray
"Fine Air") system was installed in tanks #3 and #4 at Ridgewood. To
minimize total plant gas flow, air lift pumps were abandoned with return
sludge pumped from the secondary clarifiers directly to the aeration
tank influent channel. The contact stabilization process was also aban-
doned with mixed liquor flow to both aeration tanks in parallel operated
in the conventional plug flow mode as shown in Figure 2.
At the influent and effluent ends of both tanks, wooden baf-
fles were installed to distribute and collect the flow across the total
aeration tank width to minimize short circuiting as shown in Figures 3
and 4. Figure 5 indicates the full floor cover system used in the ret-
rofit (Burde, 1983). Four grids were used in each tank with a greater
number of domes from inlet to effluent end providing tapered aeration to
balance oxygen supply with demand. All domes are 7 inch diameter
Carborundum (Aloxite) diffusers which were initially connected to the
-------
TABLE 3
Projected Energy Savings for the Fine Pore Retrofit, Mueller et al., 1982
Aeration System
SOTE, %
T, ฐC
a
f,
scfm
CL, tng/1
OTE
G
# Compressors
Power Drawn, kwhr/day
Power Cost, $/yr @ 6.5c/kwhr
Bid Price for Retrofit
Pay-off period
Coarse Bubble
8.6
20
. 0.55
0.99
0
4.8
2100
2
3000
71200
-
-
Fine Pore
28.0
20
0.40
0.99
0
11.1
1100
1
1500
35600
$218,000
6. 1 yrs
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saddles approximately 10" off the bottom using plastic (acetal) bolts.
After 1-1/2 years of operation all bolts were replaced with brass due to
bolt failures, and diffuser density increased at the inlet of the plant to
reduce gas flow per dome as summarized in Table 4.
On 12 April 1983, the fine pore system was started and
continues in operation to the present. The waste sludge handling system
differed somewhat from the coarse bubble operation since the sludge
lagoons were no longer available for excess sludge removal. Initially
overflow from primary clarifier #2 containing digester supernatant was
discharged directly to the influent without prior aeration. In mid 1985
aeration compartment #2-4, still containing the original sparjers, was
placed in operation to reduce digester supernatant load. A separate
small blower was used to aerate this tank.
Often during summer months, sludge accumulation in the plant
was significant due to abandonment of the sludge lagoons with aeration
tanks #1 and #2 periodically used for waste sludge storage. Digester
sludge supernatant quality during this time was generally poor with a
significant quantity of digested solids probably recycling through the
aeration system. A significant amount of "Nocardia" growth appeared in
the late Spring or early Summer months and remained until the Winter.
This resulted in a thick surface foam layer periodically overflowing from
the tanks. The poor quality digester supernatant return was felt to
contribute markedly to "Nocardia" growth.
14
-------
TABLE 4
Fine Pore Aeration Retrofit in Ridgewood Aeration Tanks 3 and 4
Grid
Each Tank
Type Diffuser
Surface Area, ft2
Number of Grids
Tank Water Depth, ft
Height of Diffusers off Tank
Bottom, inches
7" Gray/Fine Air Domes
2784
. 4
14.5-15.5
10
B
D
696 696 696 696
Initial Operation 4/83-9/84
# Diffusers
Dome Density, ft2/dome
540
5.15
180 160 100 100
3.87 4.35 6.96 6.96
Final Operation 9/84-present
# Diffusers
Dome Density, ft2/dome
650
4.28
234 208 104 104
2.97 3.35 -6.69 6.69
15
-------
III. FIELD STUDY DESCRIPTION
Since October, 1981, eight field aeration studies have been
conducted at the Ridgewood WWTB. Extensive testing was conducted in
Study 8 with 67 aeration tests performed over a 1% year period. Pre-
vious studies were not as extensive, but provide a reasonable data base
to highlight the changing oxygen transfer efficiency of the fine pore
system with time. A summary of the studies can be found in Table 5.
The oxygen transfer efficiency was measured using three dif-
ferent techniques; 1) offgas, 2) nonsteady state, and 3) steady state.
Initial studies utilized the nonsteady state technique for clean and
wastewater tests, while the final study used offgas, nonsteady and
steady state techniques. The offgas method is considered the most accu-
rate, simply because it is a direct measure of oxygen transfer. The
OTE20 calculated for each technique is at standard temperature using
zero dissolved oxygen concentrations and g(0.99) corrected clean water
oxygen saturation values.
The offgas testing procedure utilized at Ridgewood from August
1985 to September 1986 was based on the protocol given in both 1) Manual
of Methods for FBDA Field Studies, Appendix A, and 2) the Operations
Manual supplied by Ewing Engineering. The Mark V Aerator-Rator offgas
analyzer, manufactured by Ewing Engineers, was used in the field stud-
ies. Prior to a test, hoods were positioned at the center of each grid
as shown in Figure 6. Typically, a test would begin in the morning with
calibration of all DO probes in a bucket of clean water which had been
saturated and DO measured in duplicate by Winkler technique. A leak
test would then be conducted as indicated on pg 41, FBDA. A small
nitrogen cylinder was purchased for this purpose. A significant leak
was obtained only once when the dessicant was replaced and fittings not
properly tightened. Prior to and after testing each day, the local
weather bureau would then be called for barometric pressure, air temper-
ature, and relative humidity. Testing of the hood connection was con-
ducted prior to startup in August by forcing a rubber stopper into the
underside of the hood opening in the wood. A leak was found requiring
additional sealant around the flange. Similar testing was conducted
when the hoods were removed in December with no leaks being found.
16
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After the leak testing and calibration, the 50 ft. length of vacuum
hose was connected to the first hood. Offgas readings were taken alter-
nately using reference then offgas measurements, typically 3 to 5 read-
ings were taken at each station. The average OTE20 value from each sta-
tion was weighted according to gas flow or dome distribution and then
summed to obtain a tank average value. If foam was not present, gas
flow would be increased to attain an equilibrium condition. This was
judged to be reached when hood pressure was about 0.6-0.8 inches of
water and the hood was stable in the water with no noticeable gas escap-
ing from the sides of the hood. Two samples of offgas would typically
be taken for Orsat analysis for carbon dioxide. DO was measured at each
hood location generally using two probes, one on each side of the hood.
Upon completion of a test at a station, the vacuum hose would be con-
nected to the next hood location and the test repeated. Typically a
test would require one hour to complete after measurement began. In the
case of severe foaming, when accurate gas flow measurement could not be
attained, a complete test could be conducted in less than one hour since
equilibrium gas flow conditions were not attempted.
Nonsteady state data was collected using D.O. probes located at
mid-depth in four equal volume grids in the aeration tanks. Two probes
were used in each grid to obtain replicate data. Nonsteady state test-
ing was normally conducted for a time period of 4/K_a as recommended by
ASCE for clean water tests. At each location, the K-,af values were
obtained using the ASCE three parameter estimation model and the average
value used to represent the total tank. Gas flow measurements were
obtained using pressure drop readings across a flow tube with header
temperature and pressure measurements to correct to standard conditions.
The nonsteady state equations required to obtain the oxygen transfer
rate are developed in "Nonsteady State Field Testing of Surface and
Diffused Aeration Equipment," (Mueller, 1983).
Steady state testing, the simplest technique, was conducted to
evaluate its adequacy compared to offgas and nonsteady state techniques.
The measured oxygen uptake rates were used to indicate constant test
conditions and to serve as a basis for data correlation. The steady
state equations required to obtain the oxygen transfer rate are given in
Mueller, 1983.
19
-------
IV. CLEAN WATER PERFORMANCE
A. Coarse Bubble System
In order to evaluate standard oxygen transfer efficiency
(SOTE) and the oxygen saturation value (C*20) clean water studies
were conducted on both the coarse bubble sparger and fine pore dome
systems. The SOTE values are used to determine alpha, the ratio of
the OTE20 under process conditions to that in clean water. The
saturation value is used to provide the driving force required to
correct the measured OTE values under process DO conditions to the
maximum OTE20 under zero DO conditions.
The clean water study on the sparger system was conducted
in November, 1981. Three individual tests were conducted and resulted
in a |3Cl,2o of 9.54 mg/1 with beta equal to 0.99 (Mueller, 1982).
Figure 7 illustrates the relationship between gas flow and SOTE.
At gas flows of 6 and 12 scfm/diffuser, SOTE is a constant at 8.6%.
B. Fine Pore System
In March 1983, four clean water studies were conducted on
the newly installed fine pore system. These tests resulted in an
[3CLZO equal to 10.26 mg/1 with beta equal to 0.99 as previously
(Mueller, 1983). Figure 8 presents the effect of gas flow on SOTE
for the fine pore system under the original and the modified dome
density. Unlike the sparger system, increased gas flows significantly
decrease SOTE. Aeration tanks 3 and 4 were modified by increasing
the average dome density from 5.15 ft^/dome to 4.28 ft2/dome in late
fall of 1984. The dome configuration for each density is shown in
Figure 9. No clean water studies were conducted after the modifi-
cation, therefore, the following model was employed to evaluate the
effect of increased dome density (Huibregtse, 1986).
Q
S = submergence, ft
D = density, diff/ft2
Q = air flow per diffuser, scfm
20
-------
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30 -
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20 -
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35
30 -
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15 -
10 -
5 -
SOTE VERSUS GAS FLOW
11/21/81. COARSE BUBBLE SYSTEM
-a
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10
2 4
GAS FLOW PER DIFFUSER(Gsd). scfm/diff.
SOTE VERSUS GAS FLOW
3/25/83. FINE PORE SYSTEM
1
12
SOTE = 32.1 - 5.47 * Gsd
DENSITY ป 4.28 sf/diff,
SOTE = 31.6 5.38 * Gad
DENSITY => 5.16 af/diff
14
1 - 1 - 1
0.2 0.4
1 - 1 - 1 - 1 - 1 - 1
0.6 O.8 1
1 - 1 - 1 - 1 - 1 i i i r
1.2 1.4 1.6 1.8
GAS FLOTT PER DEFFUSER(GBd), acfm/dlff.
21
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By maintaining submergence and air flow as constants in the model the
effect of different dome densities on SOTE can be evaluated. Figure 10
illustrates this effect, as dome density increases the SOTE also
increases. SOTE, increased by 1.6% at constant submergence and airflow
rates resulting in a scaleup factor of 1.016. The equation used to
calculate SOTE as a function of gas flow for Ridgewood is:
SOTE = 31.6 - 5.38(GOT.) (original)
DlJ
SOTE = 32.1 - 5.47(GCT.) (modified)
oL)
23
-------
Figure 10. EFFECT OF DIFFUSER DENSITY ON SOTE
(Huibregtse.Rooney.Rasmxissen 1983)
1.200
O
I
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W
1.180 -
1.180 -
1.140 -
1.120 -
1.100 -
1.080 -
1.060 -
1.040 -
1.020 -
1.000
0.980 -
0.960 -
0.940 -
0.920 -
0.900
1.016 (SUF)
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DIFFUSER DENSITY, square ft/diffuser
24
-------
V. CASE HISTORY SUMMARY (Oct. 1981-Sept. 1986)
Table 6 summarizes the 8 field studies conducted at the
Ridgewood WWTP. Two studies were conducted on the coarse bubble system
while the remaining 6 studies were performed on the fine pore aeration
system. Figures 11 and 12 illustrate the variability in OTE20 and
alpha values measured from October 1981 through September 1986. The
coarse bubble OTE20 results are values measured in each bay, while the
fine pore values represent average tank values. Batch test conditions
and low and high gas flows are shown by different symbols. Estimated
yearly averages are indicated for the two systems under both low and
high gas flows. These values are summarized in Table 7.
The nonsteady state technique was employed to evaluate the
coarse bubble system. Testing was initiated on October 21, 1981 with 5
batch wastewater, 2 flowing wastewater, and 3 clean water tests con-
ducted. In July of 1982, 18 nonsteady state flowing wastewater tests
were conducted. For each of the flowing wastewater tests the primary
clarifier effluent and return sludge flows were reduced using a tempo-
rary sluice gate. This provided reduced load conditions and positive
dissolved oxygen concentrations for testing. The OTE20 results on the
coarse bubble system were from 3.6 to 6.4% under wastewater conditions,
while the clean SOTE was 8.6%. The coarse bubble system had an esti-
mated yearly OTE20 average of 4.8% and an alpha of 0.55.
Testing of the fine pore aeration system began in March of
1983, using the nonsteady state technique for both clean and waste-
water. The results of the clean water transfer efficiencies were from
21.3 to 30.2%, while the batch wastewater values ranged from 15.9 to
20.3% all on tank 3 at high and low gas flows respectively. The batch
test results are conducted with highly treated effluent and mixed
liquor in the endogenous phase, not representative of plant operation
under actual wastewater conditions. A total of 14 tests were performed
from June 1983 to March 1985 (studies 4 through 7), again, using the
nonsteady state technique. The OTE20's measured during this period
showed a significant decline in the beginning of 1984. The first aera-
tion test of tank 4 in March 1984 resulted in an OTE20 of only 5.7% and
in July of the same year it decreased to 4.8%. The transfer efficiency
25
-------
TABLE 6
Summary of Aeration Results
Range of OTE Results
SOTE, % OTE20, %
Type of
Study Pates of Study System Ei& GS . Low Gs H18h Gs Low Gs.
10/1-11/21 Coarse 8.5-8.7* 8.5* 4.2-5.0 4.9-5.3
1981
7/9-7/21 Coarse 3.6-6.4 4.3-6.4
1982
3/25-3/31 Fine 21.3-22.5* 27.6-30.2* 15.9-17.6* 17.4-20.3*
1983
6/28 Fine 12.0 17.0
1983
3/14 Fine 5.7 6.4-7.0
1984
7/10-7/11 Fine 4.8-9.1 11.8
1984
3/05 Fine 7.7
1985
6/13/85- Fine 5.2-11.9 7.0-15.2
9/03/86
*
Batch Tests
26
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TABLE 7
Estimated Yearly Average OTE20 and Alpha Values
For Both Aeration Systems
System
Coarse
Fine
Fine
Number
of
Time Period Tests
1981-3/83 25
1985-1986 21
7
1986-1987 20
4
Gas
Flow
High
& Low
High
Low
High
Low
OTE20,
%
4.8
1
7.5
8.9
9.6
12.6
Alpha
0.55
0.36
0.36
0.41
0.48
29
-------
of tank 3 went from 17% to 6.4% (Study 5) and 11.8% (Study 6) all under
low gas flows. The reason for the difference in transfer efficiency
between the tanks may be due to the fact that tank 3 was hosed clean
before it went into service for the clean water testing. Tank 4 did
not receive any cleaning and had significant algae growth on the domes.
The reason for the overall decline in transfer efficiency was discov-
ered in the Fall of 1984 when aeration tanks 3 & 4 were drained and
hosed. Approximately 15 and 40 domes were missing from tanks 3 and 4
respectively with many of the plastic bolts loose. All the plastic
bolts were replaced by brass bolts and the dome density was increased.
Thus, the low OTE20's measured before the cleaning (Studies 5 & 6) are
a result of the poor condition of the aeration grids and coarsing due
to missing domes. The one test of Study 7 in March 1985 at high gas
flow yielded an OTE20 of 7.7%.
From June 1985 to September 1986, 66 flowing wastewater tests
and 1 batch wastewater test were conducted (Study 8). The off gas and
nonsteady state technique was employed during the final stage of the
case study, with steady state analysis also performed. The measured
OTEZO's showed a large degree of variability during the study with
results ranging from 5.2 to 15.2%. In 1985 the fine pore system had an
OTE20 average of 7.5% and an alpha of 0.36 under high gas flows. Under
low gas flows, the average values were 8.9% and 0.36. Average alpha
values did not change due to the fact that low and high gas flow test-
ing was conducted at approximately the same time of the day. Thus the
wastewater effect on OTE20 remained constant. For 1986 the estimated
OTE20 average was 9.6% with an average alpha of 0.41 under high gas
flows. Under low gas flows conducted in the morning hours during low
load, the average values were 12.6% and 0.48. Since no significant
correlation existed between alpha and gas flow per dome as discussed
later, the lower alpha value at high gas flow is due to the greater
wastewater load in the afternoon compared to morning hours. Nocardia
foam was a problem during these studies and tended to affect the OTE
results. This effect is further defined in the "Problems encountered
and solutions" section of this report.
30
-------
VI. ASCE STUDY 0UNE 1985-SEPT. 1986)
A. Summary
Table 8 presents a summary of the individual tests conducted
in 1985 and 1986 for Study 8. As mentioned, Nocardia foam present on
the aeration tank was a major obstacle in performing the aeration tests
and in some cases terminated a test. Often, Nocardia foam interfered
with gas flow measurements and for a few tests provided unrealistically
high OTE due to the oxygen uptake of the foam. A 24 hour study (tests
51-60) was conducted in June 1986 and a detailed analysis of the data
can be found in a separate section.
Table 9 gives the process conditions for each test in Study
8. Weekly or monthly average BOD,, and MLVSS values were used if the
laboratory staff at Ridgewood did not perform the particular analysis
on the test day. Tables 10 and 11 present the nonsteady state and off-
gas aeration results for each aeration tank. Two gas flows are given,
one measured using a differential manometer in the blower building and
the other measured using the offgas analyzer. When good testing condi-
tions are present (no foam) the two values agree within 10% or better.
All.aeration calculations using gas flow are performed with the mano-
meter measured values. Figures 13 and 14 illustrate the effect of one
aeration tank in service on the performance of the system. Low and
high gas flow tests are indicated by the different symbols. The high
gas flow average OTE20 and alpha for one tank.in service is approxi-
mately 7.1% and 0.36, respectively. Two aeration tanks in operation
yielded a high gas flow average OTE20 of 8.9% and 9.9% with alpha
values of 0.39 to 0.42. The average OTE20 for low gas flows with two
aeration tanks in service was 9.5 with an alpha value of 0.39. Thus,
having one aeration tank in service with a detention time less than 2
hours results in reduced performance of the aeration equipment, these
results are summarized in Table 12.
Table 13 and Figure 15 indicate that as gas flow to the aera-
tion tank increases OTE20 decreases with an r2 value of 42%. Gas flow
per dome varied from 0.4 to 2.8 scfm/dome. Using the hypothesis test-
ing procedure for the correlation coefficient (Blank, p. 521), it was
31
-------
TABLE 8
Summary of Aeration Tests, 1985 & 1986
Test
1
2~
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Date
1985
6/13
6/18
6/20
6/25
6/25
7/11
7/18
7/18
7/25
7/25
8/7
8/9
8/13
8/15
8/15
9/3
9/11
Tank
3
3
3
4
3
4
4
3
4
3
3
4
4
4
-
4
4
4
Test
Type
NSS
NSS,SS
NSS.SS
NSS,SS
NSS,SS
NSS,SS
NSS.SS
NSS,SS
NSS
NSS
OG
OG.SS
OG
OG,SS
NSS,SS
OG
OG
Comments
0_ limited, septic conditions
Heavy foaming Tank 3
Heavy foaming Tank 3
Light foam Tank 4
Light foam Tank 3
Tank 4 cleaned and refilled
Light foam due to chlorination
Tank 3 cleaned and refilled
Light foam due to
chlorination
Light foam due to
chlorination
Batch Test-limited gas flow
Medium foam Tank 4 -
insufficient gas flow
measurement. OTE20 cor-
rected for Nocardia foam
uptake.
Only 1 grid tested due to
foam pulled into analyzer
Medium foam Tank 4 -
gas flows could not be
determined. OTE20 cor-
rected for Nocardia foam
uptake.
Medium foam - Tank 4
Heavy foam Tank 4 - gas
flows could not he measured
OTE for grid C estimated.
OTE20 corrected for
Nocardia foam uptake.
Heavy foam Tank 4 - OTE20
corrected for Nocardia
foam uptake.
(continued....)
32
-------
TABLE 8 (cont'd)
Test
Date
1985.86
Tank
Test
Type
Comments
18
9/11
19
20
21
22
23
24
25
26
27
10/21/85
10/24
10/30
11/1
11/1
11/8 '
11/8
11/15
11/15
4
4
3
3
3
3
3
3
OG
OG
OG,SS
OG.SS
OG,SS
OG,SS
OG,SS
OG,SS
OG,SS
28
29
30
31
11/22
12/11
12/11
12/18
OG Heavy foam Tank 4 - gas flows >1500
scfm could not be measured. OTE20
corrected for Nocardia foam uptake
Heavy foam tank 4-gas flow could not
be determined.
Heavy foam tank 4-gas flows could
not be determined.
Medium foam-gas flows could not be
determined. Tank 3 acid cleaned
and refilled.
No foam-gas flow accurately measured
No foam-gas flow accurately measured
No foam-low gas flow test. Accurate
measurement not obtained.
No foam-high gas flow test. Accurate
measurement not obtained.
.No foam-gas flow accurately measured
No foam-high gas flow. Gas flow
accurately measured.
SS No foam-OG tests 28-31 invalid due
to leak in analyzer. SS results
used in analysis.
OG,SS No foatn-gas flow not determined
accurately. Tank 4 acid cleaned
and refilled.
OG,SS No foam-accurate gas flow measure-
ment obtained.
OG,SS No foam-low gas flow. Gas flow not
determined accurately.
(continued...)
33
-------
TABLE 8 (cont'd)
Test
Date
1986
Tank #
Test
Type
Comments
32 4/21/86
33
34
35
4/21
4/22
4/22
3
3
3
NSS,SS
OG.SS
OG, NSS,
SS
36
37
38
39
40
41
42
4/23
5/29
6/2
6/4
OG
5/6
5/15
5/22
3
3
3
OG
OG,SS
OG,SS
OG,SS Domes cleaned beginning of April by
hosing. Low gas flow and dilute
waste water due to heavy rain.
One final clarifier out of ser-
vice. (1 compressor on.)
2 compressors on
1 compressor on
2 compressors on
Linearity slightly off, moisture
may have gotten into micro fuel
cell. Final clarifier back in
service. (1 compressor on.)
Hoods caulked. (2 compressors on.)
Tank 4 down. All flow through
Tank 3 (2 compressors on.)
Tank 4 down. Two compressors left
on overnight. Nearly septic con-
ditions and foam starting to
develop. (2 compressors on.)
OG,SS Tank 4 down. Primary clarifier
overflowing and digester super-
natant overloading aeration tank.
Nearly septic conditions, foam
developing, and high uptake. (2
compressors on.)
OG,SS Tank 4 put back in operation in
morning. Lower uptakes and foam
disappearing. (2 compressors on.)
OG,SS Reaction time for micro fuel cell
slowing down. Primary clarifier
not overflowing and digestor
supernatant not overloading aera-
tion tank. (2 compressors on.)
(continued...)
34
-------
TABLE 8 (cont'd)
Test
43
44
45
46
47
48
Date
1986 Tank #3
6/4
6/5
6/5
6/10
6/10
6/12
3
3
3
3
3
. 3
Test
Type
OG.SS
OG.SS
OG.SS
OG.SS
OG.SS
OG
Comments
Second compressor must be turned
between 8:00-9:00 AM.
2 compressors on
2 compressors on
2 compressors on
2 compressors on
1 compressor shut off 8:00 P.M.
on
last
night due to humidity. Usually
shut off at 3:00 A.M. Possibly
septic conditions through the
night. Test started at 8:00 A.M.
49 6/12 3 OG Second compressor turned on at 9:00
A.M. with testing immediately fol-
lowing.
50 6/12 3 OG Two compressors on, OTE dropping
with increasing influent load.
Test started at 10:00 A.M.
51-60 6/16-6/17 3 OG Total of 10 runs throughout a 24-
hour period.
61 6/30 3 OG Nocardia foam covering entire tank
(3"-6" thick). High uptake in
foam. 2 compressors on. OTE20
corrected for Nocardia foam uptake
62 6/30 3 OG 2 compressors on. OTE20 corrected
for Nocardia foam uptake.
63 7/08 3 OG Foam covering entire tank (2'-3'
thick). Poor testing conditions.
2 compressors on. Results not
presented in report.
(continued...)
35
-------
TABLE 8 (cont'd)
Date Tank Test
Test 1986 # Type Comments
64 7/31 3 OG Foam covering entire tank (1/2 to I1
thick). Chlorine surface spray
being employed to kill foam.
Spray concentration is about 0.3
mg/& of chlorine. 2 compressors
on. Results not presented in
report.
65 8/06 3 OG No foam covering tank. Surface
spray appears to be wiping out the
foam. 2 compressors on.
66 8/21 3 OG Tank 3 acid cleaned on 8/20. Back
in operation that night with sig-
nificant foam levels developing
immediately. 2 compressors on.
Results not presented in report.
67 9/03 3 OG Foam level very low. 2 compressors
on.
OG - offgas
NSS - nonsteady state
SS - steady state
36
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-------
TABLE 12
Effect of One Aeration Tank in Service on OTE20 and Alpha
Tests
1-10
Year
1985
One Aeration Tank
in Service
OTE20
Alpha
Two Aeration Tanks
in Service
OTE20
8.9%
9.5%*
Alpha
0.39
0.39*
11-27
1985
7.1%
0.36
38-40
1986
7.3%
0.36
41-67
1986
9.9%
0.42
Low gas flow averages
45
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47
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determined that r2 was large enough to be statistically significant.
Table 13 also shows the effect of unit 0? uptake on average tank OTE20.
Higher unit uptake rates cause the OTE20 to decrease. This effect is
further defined with grid unit uptake values impacting grid OTE20. The
higher unit uptakes in grid A result in lower OTEZO's, while grids C &
D have the lowest unit uptakes and the highest OTE20's. A significant
correlation exists for the grid values, but not for the tank averages.
This is due to tank average values removing the variability within the
tank. Therefore, the impact of unit 0. uptake on OTE20 is more signif-
icant with respect to location in the tank than with average values
over a period of time.
Tables 14 and 15 present the steady state test conditions and
results. Typically, the steady state OTE20 values differed from the
offgas OTE20's by ฑ 20% with higher differences not uncommon. The
steady state technique relies on an accurate measurement of the oxygen
uptake rate in the tank. Often, the aeration tanks at Ridgewood were
oxygen limited with the steady state OTE20 on the average greater by
approximately 11-12% than the offgas or nonsteady state values.
48
-------
TABLE 14
Steady State Test Conditions, 1985 & 1986
Test
2 .
3
4
5
6
7
8
12
14
15
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
38
39
40
Average
Flow
(vv
MGD
3.7
4.0
4.0
4.1
3.8
3.6
3.6
3.9
3.8
3.9
5.1
4.0
3.8
5.1
4.2
4.4
3.9
5.1
4.8
4.0
4.4
5.6
4.8
5.6
3.8
4.4
4.8
5.1
Detention
Time,
to
hrs
3.9
3.6
3.6
3.5
3.8
4.0
4.0
1.8
1.9
1.8
1.4
1.8
1.9
1.4
1.7
1.6
1.8
1.4
3.0
3.6
3.3
2.6
3.0
2.6
3.8
1.6
1.5
1.4
Field
Oxygen
Saturation
*
Value, C ,.
oof
rag/ S.
9.96
9.88
9.68.
9.77
9.87
9.78
9.74
9.72
9.49
9.49
10.79
10.73
10.73
10.95
10.86
11.06
11.05
11.07
11.45
11.45
11.66
11.26
11.26
11.31
11.30
10.83
10.28
10.27
Average
Tank
Dissolved
Oxygen, Cr
3.9
1.0
2.4
1.2
2.4
2.7
1.6
0.7
0.7
0.6
3.4
0.9
0.4
0.5
0.8
2.9
3.1
3.2
3.3
3.5
2.1
1.4
2.8
1.3
5.4
1.2
1.5
0.1
Average
Tank
Oxygen
Uptake, R
mg/ฃ/hr
23.3
30.8
39.9
33.4 .
44.9
40.5
46.2
61.8
66,2
63.3
23.1
36.4
38.0
23.9
29.7
24.3
28.3
24.3
17.1
33.8
20.3
12.7
18.3
13.4 ,
13.1
26.5
35.8
71.9
Average
Unit Tank
Oxygen
Uptake
Rate,
mg/gVSS/hr
10.8
14.2
18.4
15.4
20.8
18.7
21.4
28.6
30.6
29.3
10.7
16.8
17.6
11.0
13.7
11.2
13.1
16.6
7.9
15.6
9.4
5.9
8.5
6.2
6.1
12.3
16.6
33.2
49
-------
TABLE 14 (cont'd)
Test
41
42
43
44
45
46
47
48
49
50
61
62
65
Average
Flow
(Qi+QR)
MGD
4.6
5.0
3.9
4.6
4.4
5.0
4.6
5.6
6.7
5.6
4.9
4.5
5.5
Detention
Time,
to
hrs
3.2
2.9
3.7
3.1
3.3
2.9
3.1
2.6
2.1
2.6
2.9
3.2
2.6
Field
Oxygen
Saturation
Value, C ,
oof
nig/*
10.23
10.37
10.33
10.20
10.19
10.24
10.23
10.09
10.13
10.13
9.94
9.95
9.48
Average
Tank
Dissolved
Oxygen, CT.
mg/1
1.6
3.7
2.3
2.9
1.8
3.2
2.4
0.5
0.6
0.9
0.6
0.4
2.7
Average
Tank
Oxygen
Uptake, R
mg/ฃ/hr
30.2
25.1
28.6
34.4
39.3
32.0
35.8
29.7
36.6
31.1
64.7
58.9
27.1
Average
Unit Tank
Oxygen
Uptake
Rate,
mg/gVSS/hr
14.0
11.6
13.2
15.9
18.2
14.8
16.6
13.7
16.9
14.4
29.9
27.2
12.5
50
-------
TABLE 15
Steady State Results, 1985 & 1986
Test
2
3
4
5
6
7
8
12
14
15
21
l
22
23
24
25
26
27
28
29
30
31
32
33
34
35
38
39
Oxygen
Transfer
Coeff .
Vf
1/hr
4.0
3.5
5.6
4.0
6.1
5.8
5.7
6.9
7.6
7.1
3.4
3.8
3.7
2.3
3.0
3.2
3.8
3.4
2.2
4.4
2.2
1.3
2.3
1.4
2.5
2.8
4.2
Standard
Oxygen
Transfer
Coeff.
Vf20'
1/hr
3.9
3.3
5.2
3.7
5.8
5.4
5.3
6.4
6.9
6.5
3.6
3.9
3.9
2.5
3.2
3.4
4.0
3.7
2.5
4.9
2.5
1.5
2.6
1.6
2.8
2.9
4.2
ss1
OTE20,
%
9.1
9.3
10.2
10.7
12.1
10.8
15.2
8.5
11.7
11.0
6.2
6.7
6.6
8.7
5.5
8.1
6.4
8.5
5.2
10.2
8.6
12.7
10.3
12.8
8.9
6.0
7.7
NSS OG
OTE20, OTE20,
% %
8.6
7.4
7.4
9.1
9.7
8.1
9.9
6.8
8.5
6.2
6.1
5.7
9.2
6.2
8.7
7.0
5.2
7.2
8.1
12.9
8.4
15.2
7.2 11.6
6.5
8.6
Steady .State
Difference from
Offgas or NSS OTE20
% Diff.
+ 5.8
+25.7
+37.9
+ 17.6
+24.7
+33.3
+53.5
+25.0
+37.6
0.0
+10.2
+ 14.9
-5.6
-12.2
-6.6
-8.3
-0.7
+42.4
+6.1
-1.03
+22.6
-15.8
+19.1, -23.3
-7.2
-10.6
(continued...)
51
-------
TABLE 15 (cont'd)
Test
40
41
42
43
44
45
46
47
48
49
50
61
62
65
Oxygen
Transfer
Coeff .
Vf
1/hr
7.1
3.5
3.9
3.6
4.8
4.8
4.7
4.7
3.1
3.9
3.4
7.0
6.2
4.1
Standard
Oxygen
Transfer
Coeff.
Vf20*
1/hr
7.1
3.5
3.9
3.6
4.7
4.7
4.7
4.6
3.1
3.8
3.4
6.7
6.0
3.7
ss1
OTE20,
%
10.8
8.8
9.3
8.6
11.2
11.0
11.2
11.4
13.9
9.4
9.3
17.0
15.4
10.3
NSS OG
OTE20, OTE20,
% %
6.8
8.5
10.6
8.2
10.6
9.0
11.7
10.7
12.4
11.4
10.6
8.7
8.4
10.0
Steady State
Difference from
Offgas or NSS OTE20
% Diff.
+58.4
+ 4.1
-12.3
+ 4.6
+ 5.3
+22.7
- 4.1
+ 7.0
+ 12.4
-18.1
-12.9
+95.4
+83.3
+ 2.4
SS = Steady State, NSS ~ Nonsteady State, OG = Offgas
Diff. =
SS OTE20 - OG or NSS OTE20
OG or NSS OTE20
52
-------
B. ASCE 24 Hour Study (June 16-17, 1986)
1. Description of Study
On June 16-17, 1986 a 24 hour study was performed at the
Ridgewood Wastewater Treatment Plant. The purpose of this study was to
examine the variability in OTE20 during a day and attempt to correlate
OTE20 with changing process conditions. The study consisted of both
offgas and steady state analyses conducted on Aeration Tank #3 through-
out the day. The aeration tank was analyzed at the center point of each
grid for a total of 4 stations. The first test, Test 51, started at
8:50 a.m. on June 16th and the last test, Test 60, ended at 8:00 a.m. on
June 17th for a total of 10 tests. Eight of the tests were performed
with 2 compressors on, while the remaining two tests had only 1 compres-
sor on.. The one compressor runs were performed at 3:30 and 6:30 a.m. on
June 17th. A summary of the study can be found in Table 16.
During each offgas test, a wastewater sample was taken at each
station to measure the oxygen uptake rate. Also, dissolved oxygen con-
centrations were measured at each station. The oxygen uptake rate and
dissolved oxygen concentration were both measured using YSI Model 57
probes with the oxygen uptake rate being recorded on a Cole Farmer
recorder.
ป
The primary clarifier effluent was sampled hourly using an
ISCO sequential automatic sampler to determine changing influent condi-
tions. The samples were kept on ice until soluble TOG and total sus-
pended solids analyses were conducted the following day. To assist in
monitoring the changing influent conditions, the dissolved oxygen con-
centration was continuously recorded in Grid A (influent) throughout the
study.
2. Plant Conditions
a) Plant Characteristics
Table 17 presents the plant characteristics for the 24
hour study and for the month of June. The daily average influent flow
during the 24 hour study, 2.8 mgd, was 9.7% lower than the monthly
average of 3.1 mgd. Figure 16 illustrates the influent flow variability
53
-------
13
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COCMu">OOOCOCMCOvฃ>l
Or-Hr-Ir-ICMCMOOOO
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CU
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il r-l iI r-l
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rH r** r^ป r^ r^
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-------
TABLE 17
Plant Characteristics During June 1986
Average Values
Month of June
During
24 Hour .Study,
16-17 June
Difference
from Monthly Value
Flow; (MGD)
RAW
RAS
WAS
BOD ; (mg/ฃ)
Plant Influent
Primary Clarifier Effluent
Plant 'Effluent
% Removal .
Suspended Solids; (mg/t)
Plant Influent
Primary Clarifier Effluent
Plant Effluent
% Removal
MLVSS (mg/JO
Waste Sludge Concentration,
mg/ฃ VSS
NH*-N; (ing/1)
Primary Clarifier Effluent
Plant Effluent
N03-N; (mg/ฃ) - Plant Effluent
F/M (lb BOD /lb MLVSS-day)
Sludge Age, days
3.1
1.3
0.108
229
198
19
91.7
195
182
9
95.4
1654
7710
63.1
27.7
12.1
0.29
2.4
2.8
1.3
0.124
! 198
174
18
90.9
223
155
6
97.3
1972
64.8
49.3
7.4
0.19
2.6
-9.7
0
+ 14.8
-13.5
-12.1
-5.3
-0.9 '
+ 14.4
-14.8
-33.3
+2.0
+ 19.2
+0.3
+43.8
-38.8
-34.5
+8.3
55
-------
o
1-
Q-
. iH
Of g
o
I MM
< N
z
a:
2
a
n
n
n
n
OQ
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n
n
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w
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56
-------
during the study with peak flow occurring at 10:00 a.m. and low flow
conditions at 6:00 a.m. The BOD and suspended solids removals for both
the aeration study and the month of June were excellent - from 90 to
97%. Partial nitrification was occurring. The food to mass ratio (F/M)
was significantly lower during the aeration study, 0.19 Ib BOD /lb
MLVSS, due to the combination of reduced influent BOD and increased
MLSS concentration. Overall plant characteristics for the 24 hour study
were considered typical and provided a good opportunity to evaluate the
performance of the aeration system.
b) Influent Load Variability
The diurnal total suspended solid (TSS) and soluble TOG loads
to the aeration tank are presented in Table 18. The daily average TSS
load is 6625 Ib/day, while the soluble TOG load is 557 Ib/day. Figures
17 through 20 illustrate the primary clarifier effluent TSS and BOD
concentrations and loads. At 9:00 a.m. the TSS concentration was 1025
mg/A while the load is 30,000 Ib/day. This is due to secondary sludge
wasted during the night to the primary clarifier being flushed out as
the plant influent flow increased from 1.4 to 3.3 mgd between 6:00 and
8:00 a.m., resulting in peak solid loadings to the aeration tank. The
WAS for the previous night was 133,000 gal/day, 19% higher than the
monthly average. Soluble TOG load starts increasing at 6:00 a.m. and
remains above average from noon to midnight, with peak conditions occur-
ring between 8:00 and 10:00 p.m.
3. Results
a) Offgas
1. Diurnal OTE20 and Alpha Variability
Table 19 gives the aeration results for each test
conducted in the 24 hour study. Table 20 presents the average OTE20 and
alpha values for the day using a total mass method. This method sums
the mass of oxygen transferred over a day and divides it by the sum of
mass of oxygen supplied over a day;
ฃ Mass 0? Transferred
OTE = -=-
Mass 0ซ Supplied
57
-------
TABLE 18 ;
Diurnal Load to Aeration Tapk (24 hour study)
Date
1986
6/16
6/17
6/17
6/17
6/17
6/17
6/17
6/17
6/17
6/16
6/16
6/16
6/16
6/16
6/16
6/16
6/16
6/16
6/16
6/16
6/16
6/16
6/16
6/16
. Time C
from ' C
Midnight
hours
0100
0200
0300
0400
0500
0600
0700
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
Midnight
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
Noon
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0
21.0
22.0
23.0
Average
Primary :
larifier Effluent
oncentration, mg/1
TSS
213
136
113
72
94
61
73
228
218
1025
285
255
420
430
283
310
183
215
193
201
318
270
320
235
260
Soluble
TOG
24.Q
20.9
17.7
16.5
14.4
14.7
12.8
16.8,
17.?
23.2
.19.0
17.9
22.6
21.5
26.0
32.2
30.3
34.9
22.9
29.4
33.8
35.5
)
34.3
31.2
23.7
Plant
Raw
Flow,
MGD
2.9
2.5
2.0
1.7
1.5
1.5
1.4
2..?.
3.4
3.5
3.6
3.5
3.4
3.3
3.2
3.1
3.0
2.9
2.9
3.0
3.1
3.3
3.2
3.1
2,8
Primary
Clarifier Effluent
Load, Ib/day
Soluble
TSS
5152
2836
1885
1021
1176
738
852
4183
6182
29920
8557
7443
11910
11834
7553
8015
4579
5200
4668
5029
8222
7431
8540
6076
6625
TOG
580
436
295
234
180
178
149
308
488
677
570
523
641
592
694
832
758
844
554
736.
874
977
915
807
557
58
-------
DIURNAL TSS CONCENTRATION
i
if
Q* ป
11
o^
o
10
B
Figure 18.
SOLUBLE TOO, mg/
J..X -
1 -
0.9 -
0.8 -
0.7 -
0.6 -
0.5 -
0.4 -
0.3 -
0.2 J
0.1 -
0 -
(
D
D D
n D D ฐ D
i n D n n
n D n
ฐ ฐ o ' '
a n Q
i i i i i , , 1 , , ,
> 4 8 12 16 20 ZA
TIME FROM MIDNIGHT, hours
n WAITWT.V aA'unDT'C'C! ittfi Tn^-r-, -n.ป
-" **ป ** ปปjtai * ******** *i T r~'Tr." n itibTVT* JC\fX\ L* fl ฅ
DIURNAL SOLUBLE TOC CONCENTRATION
40 -i
35 -
30 -
25 -
20 -
15 -
10 -
5 -
0 -
0
24 HOUR STUDY, 6/16-17/86
n a
a p
n
a
n
p
i
a D a
n D
n
a -. a
a n n
an
I I I | i | , , , , ,
-* 8 12 16 20 24
TIME FROM MIDNIGHT, hours
D HOURLY SAMPM3S Avn vno Tkปv
59
-------
figure 19
32
DIURNAL TSS LOAD
24 HOUR STUDY, 6/16-17/86
. 3
30 -
28 -
26
24 -
22 -
20 -
18 -
16 -
14 -
12 -
10 -
8 -
6 -
[
4 -
p
0
n n
n n a
n
D
T-
D n
r
~T~
8
12
16
20
24
TIME FROM MIDNIGHT, hours
HOURLY SAMPLES AVG. FOR DAY
Figure 20. DIURNAL SOLUBLE TOC LOAD
24 HOUR STUDY, 6/16-17/86
13
O ง
ง
SOLUBI
A
0.9 -
0.8 -
0.7 -
0.6 -
0.5 -
0.4 -
0.3 -
0.2 -
0.1 -
0 -
C
n
n
n
D a
n
D
a
D
a
i a
1 u a
n
D
n
n n
n
n n
D
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4 8 12 16 20 2-<
TIME FROM MIDNIGHT, hours
n HOURLY SA'VTPT.ias Avn trnn TปA-V
60
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resulting in an OTE20 of 10.7%. The average gas flow was 1088 scfm
resulting in a BSOTE of 23.0%. Thus the average alpha for the.day was
0.46. Time weighted averages resulted in an OTE20 of 10.8% and an alpha
of 0.47, approximately the same as the previous mass weighted values.
Figures 21 and 22 illustrate the variability in OTE20 and
alpha throughout the day with the high values measured at 7:00-8:00 a.m.
while the low values occurred around noon. This tends to correlate with
the soluble TOG load data illustrated in Figure 20. As the soluble TOC
load starts increasing around 6:00 a.m., the OTE20 starts decreasing
around 8:00 a.m. Thus, there is a lag time of approximately 2 hours
before the increasing load fully impacts the aeration tank. This is
explained by aeration tank detention times of approximately 3 hours.
The soluble TOC load remains above average from noontime on, while the
OTE20 is below average for the remainder of the day. The drop in alpha
at 3:30 and 6:30 a.m. is explained by oxygen limitation caused by
reduced gas flows with only one compressor on.
2. Longitudinal OTE20 and Alpha Variability
Table 21 presents the OTE20 and alpha values for
each grid and Figures 23 and 24 illustrate longitudinal effect on OTE20
and alpha, respectively. OTE20 increases from 9.4% at the influent end
to 12.5% at the effluent end. Alpha reacts the same, increasing from
0.39 to 0.54. This is explained by reduced substrate concentrations
near the effluent end of the aeration tank.
3. Gas Flow and Dissolved Oxygen Variability
Table 22 and Figures 25 and 26 present the diurnal
gas flow and grid dissolved oxygen concentrations for the 24 hour study.
Only one blower was in operation between 3:00 and 7:00 a.m. with gas
flows of approximately 500-700 scfm. Figures 27 and 28 illustrate the
tapered air effect on station average gas flow and dissolved oxygen
concentrations. Grid A receives almost twice the gas flow of grids C
and D. The highest average dissolved oxygen occurs in grid B, 2.3 mg/&,
with the tapered air decreasing it to 1.9 and 1.5 mg/& in grids C and D,
respectively.
63
-------
Figure 21,
DIURNAL OTE2O
24 HOUR STUDY, 6/16-17/86
***
14 -
13 -
12 -
! -
a ป -
m
* D
q ซป -
, * 7-
1 -
0)
o 5 -
3 -
2 -
1 -
0 -
(
n OTE
Figure 22.
1 -,
0.9 -
0.8 -
0.7-
0.6 -
8 0.5 -
0.4-
0.3 -
0.2 -
0.1 -
0 -
D a
n n
a
a
3
*
A / \
S \ 1 ^~ ~_ _^__*_
\ / ~~~*
'
I 1 | ~I 1 | | | ] ] 1
) 4 8 12 16 20 &
TIME FROM MIDNIGHT, hours
Ort lif A ff^f HTfl'f f* I flMHIt li ITlP1 n T1 I T>TT~ T^ rt
ปU MASfiS nJSlvrtllJSU AVur* A TANS DซO*
DIURNAL ALPHA
24 HOUR STUDY, 6/16-17/86
D
n a
P D n
"' 1 -i "" i ... ..,-,.,.... ,., ,. , .,.,...,._ ....,- ,
8
12
16
20
24
TIME FROM MIDNIGHT, hours
a TEST VALUES MASS WEIGHTED AVG.
64
-------
TABLE 21
Grid OTE20 and Alpha for 24 Hour Study
Test
51
52
53
54
55
56
57
58
59
60
Time Weighted Avg.=
Std. Deviation =
A
11.1
7.7
8.2
8.9
7.7
8.2
10.1
11.3
12.3
11.1
9.4
1.6
OTE20 %
Grid
B
11.2
9.6
9.8
10.2
9.1
9.7
10.1
11.3
13.0
12.1
10.4
1.2
ALPHA
C
12.6
11.4
12.2
12.8
12.0
12.2
13.4
13.7
13.4
15.9
12.7
1.2
D
13.0
12.1
11.8
12.0
11.2
11.5
12.2
13.5
14.4
14.8
12.5
1.2
Grid
Test
51
52
53
54
55
56
57
58
59
60
Time Weighted Avg. =
Std. Deviation =
A
0.47
0.33
0.34
0.38
0.32
0.34
0.43
0.43
0.45
0.47
0.39
0.06
B
0.47
0.41
0.42
0.43
0.39
0.41
0.44
0.43
0.48
0.51
0.43
0.04
C
0.56
0.52
0.53
0.54
0.52
0.54
0.60
0.52
0.52
0.77
0.55
0.07
D
0.58
0.55
0.51
0.51
0.49
0.51
0.54
0.51
0.55
0.71
0.54
0.06
65
-------
23.AVG. GRID OTE2O VS. DISTANCE
15
24 HOUR STUDY, 6/16-17/86
o
N
14 -
13 -
12 -
11 -
10 -
9 -
8 -
7 -
6 -
5 -
4 -
3 -
2 -
1 -
20
40
T~
60
I
100
120
AVG. GRID VALUE
DISTANCE FROM INFLUENT, ft
STD. DEVIATION
Figure 24. AVG. GRID ALPHA VS. DISTANCE
24 HOUR STUDY, 6/16-17/86
0.9 -
0.8 -
0.7 -
0.6 -
0.5 -
0.4 -
0.3 -
0.2 -
0.1 -
I
20
1
40
T~
60
80
100
120
AVG. GRID VALUE
DISTANCE FROM INFLUENT, ft
STD. DEVIATION
66
-------
TABLE 22
Grid Gas Flow and Dissolved Oxygen Values for 24 Hour Study
Offgas Measured Gas Flow, scfm
Test
51
52
53
54
55
56
57
58
59
60
Time Weighted Avg.=
Std. Deviation =
Test
51
52
53
54
55
56
57
58
59
60
Time Weighted Avg.=
Std. Deviation =
A
372
390
346
367
341
351
373
244
206
364
339
57
"A
1.6
1.3
1.4
1.8
1.2
1.2
3.0
1.2
1.0
4.6
1.8
1.1
B
312
331
326
327
331
331
355
224
192
315
308
50
Dissolved
B
2.4
2.1
2.2
2.3
1.8
2.0
3.6
0.8
1.2
5.0
2.3
1.1
Grid
C
182
192
171
162
173
179
184
111
116
215
169
31
Oxygen, mg/A
Grid
C
2.2
1.4
1.3
1.5
1.6
1.6
3.6
0.4
0.2
5.4
1.9
1.5
D
182
192
171
162
173
179
184
111
116
215
169
31
D
2.0
1.2
1.1
1.3
1.0
1.1
2.5
0.2
0.2
4.5
1.5
1.2
Total
Tank
1048
1105
1014
1018
1018
1040
1096
690
630
1109
985
163
Avg.
Tank
2.1
1.5
1.5
1.7
1.4
1.5
3.2
0.7
0.7
4.9
1.9
1.2
67
-------
Figure 25
ajjH-
o^
1.5 -r
1.4 -
1.3 -
1.2 -
1.1 -
1 -
O.O -
0.8 -
0.7 -
0.6 -
0.5 -
0.4 -
0.3 -
0.2 -
0.1 -
0 -
DIURNAL GAS FLOW
24 HOUR STUDY, 6/16-17/86
T~
8
T~
12
I
16
]
20
24
TIME FROM MIDNIGHT, hours
Figure 26.
I
I
DIURNAL GRID DO
24 HOUR STUDY,8/16~ 17/86
D GRID A
TIME FROM MIDNIGHT, hours
GRID B o GRID C
GRID D
68
-------
Figure 27. GRID GAS FLOW VS. DISTANCE
500
I
400 -
300 -
200 -
100 -
Figure 28
I
m
I
3.5 -
3 -
2.5 -
2 -
1.5
1
0.5 -
24 HOUR STUDY, 6/16-17/86
20
40
1
60
1 r
80
100
DISTANCE FROM INFLUENT, ft
AVG. GRID VALUE J^ STD. DEVIATION
GRID DO VS. DISTANCE
24 HOUR STUDY,6/16-17/86
I
20
40
60
I
80
I
100
DISTANCE FROM INFLUENT
AVG. GRID VALUES X - STD. DEVIATIONS
120
120
69
-------
Near septic conditions exist in Grids C and D at 3:30 and 6:30
a.m. with one compressor on. When the second compressor is turned on at
7:00 a.m. the dissolved oxygen concentration approaches 5 mg/ฃ resulting
in a marked increase in alpha from 0.52-0.55 to 0.71-0.77 in Grids C and
D as shown in Table 21.
Figure 29 shows dissolved oxygen concentrations monitored con-
tinuously in grid A with specific point values representing the average
concentration used for grid A in the offgas analysis. Figure 30 illus-
trates the changing dissolved oxygen concentrations from 7:00 to 8:00
a.m. with an average concentration of 4.6 mg/ฃ used in the offgas analy-
sis in Test 60. Table 23 presents the OTE20 corrections for changing
dissolved oxygen concentrations. Instead of using an average D.O., the
D.O. at the specific sampling time is used in the calculation. The ori-
ginal OTE20 for grid A was 11.6% while the corrected value is 11.1%.
The tank OTE20 was corrected from 13.2 to 13.1%. .Although not signifi-
cant in this case for overall tank values, this adjustment should be
utilized when DO changes occur during an offgas test.
4. Comparison of Offgas to Manometer Measured Gas Flow
Figure 31 presents the offgas and manometer measured
gas "flow with respect to each test. The values agree reasonably well
with an average percent difference from the manometer measured gas flow
of approximately 10%.
b) Steady State
1. OTE20 Comparison
The test conditions and results from the steady
state analysis can be found in Tables 24 and 25, respectively. The
steady state OTE20's are used for comparative purposes against the more
accurate offgas OTE20's. Two steady state OTE20's are calculated, one
using manometer measured gas flow and the other using offgas measured
gas flow. The OTE20's calculated with manometer measured gas flows
ranged from 8.0 to 12.1%. The OTE20's calculated using offgas measured
gas flows ranged from 9.2 to 13.1%. The % difference between steady
state OTE20, using manometer measured gas flow, and offgas OTE20 was
70
-------
29. GRID A DIURNAL DISSOLVED OXYGEN
24 HOUR STUDY, 6/16-17/86
6
I
o
CO
m
5 -
4 -
3
2 -
1
Figure 30.
I
i
01
i
r~
4
T"
8
I
12
I
16
20
TIME FROM MIDNIGHT, hours
24 HOUR DATA <> TEST DATA
TEST #60 DO VARIABILITY
24 HOUR STUDY. GRID A, 7:10-7:20 AM
TIME FROM MIDNIGHT, hours
24 HOUR DATA o TEST DATA
24
71
-------
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73
-------
TABLE 24
Steady State Test Conditions, 24 Hour Study
Test
51
52
53
54
55
56
57
58
59
60
Average
Flow To
Aeration
Tank
"i R
(mgd)
4.9
4.6
4.3
4.2
4.6
4.2
3.1
2.8
2.7
4.6
Average
Detention
Time
t .
o'
(hr)
3.0
3.2
3.3
3.4
3.1
3.4 .
4.7
5.2
5.3
3.1
Field
Oxygen
Saturat .
Value
*
c
ซf
mg/ฃ
10.09
10.07
9.98
9.96
9.93
9.90
9.89
9.89
9.96
9.96
Average
Tank
Uptake
R,
mg/ฃ/hr
39.3
45.8
47.4
46.3
35.9
33.5
30.9
29.3
24.5
27.5
Average
Tank
Dissolved
Oxygen
Cr,
mg/ฃ
2.1
1.5
1.5
.1.7
1.4
1.5
3.2
0.7 .
0.7
4.9
Wastewater Temp. = 21.0 - 21.5ฐC
Volume Aeration Tank = 0.3 MG
Influent Dissolved Oxygen, C. =0.1 mg/H,
*
Standard Oxygen Saturation Value 3C = 10.26 mg/ฃ
& &
Note: Both C and C include beta effect of 0.99
74
-------
CO
CO
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33
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from -19.3% to +13.6%. Figure 32 illustrates this comparison with
respect to time. The steady state OTEZO's were significantly lower than
the offgas values from 6:00 a.m. to 10:00 a.m. This is a result of food
limited conditions. The food in a sample taken during the above tests
is completely oxidized as the sample is oxygenated. Thus the measured
oxygen uptake in the food limited sample is lower than the actual oxygen
uptake in the aeration tank resulting in lower OTEZO's. From about 4:00
p.m. to midnight some oxygen limitation apparently existed in the aera-
tion tank providing higher measured uptake rates than in situ and higher
steady state OTE's.
2. Oxygen Uptake Rates
Figures 33 and 34 illustrate the oxygen uptake rates
with respect to time of-day. The average tank oxygen uptake rates are
low at 6:00 a.m. (24.5 rog/ฃ/hr) and high at 4:00 p.m. (47.4 mg/A/hr).
Figure 34 shows values for each station throughout the day. Grid A
typically had significantly higher oxygen uptake rates than did grid D
due to the reduced substrate concentrations in the effluent end of the
aeration tank. During the high load periods in the afternoon, oxygen
uptake rate in grid A is as high as 54 mg/ฃ/hr. An increase in the
oxygen uptake rate is observed around 7:00 a.m. This correlates well
with OTE20, as Figure 21 shows OTE20 starting to decrease shortly after.
However, at 9:00 p.m. the oxygen uptake rate drops below the average
while the OTE20 also, decreases. This could be attributed to an increase
in flow from 2.9 to 3.3 MGD causing the oxygen uptake rate and MLSS
concentration to decrease, with the unit oxygen uptake remaining
relatively constant. Unfortunately, only daily average MLSS
concentrations are available.
4. Parameter Correlations
The regression analyses output can be found in Table 26. Both
the best fit equation relating the parameters and its coefficient of
determination (r2) are presented. The coefficient of determination rep-
resents the portion of the sum of squares of deviations of the Y values
76
-------
O
ฃ
o
o
o
Q
on
*H
3
o
I-H
3-i
fa
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n
'NaOAXO Q3AT[OSSI(I (INV
77
-------
Figure 33.
Figure 34.
01
O
DIURNAL OXYGEN UPTAKE RATE
60
50 -
40 -
30 -
20 -
10 -
24 HOUR STUDY, 6/16-17/86
50 -
ft
A 40 -
1
2J 30~
3
e 20-
N
O
10 -
0 -
c
-
D
D
n
a
n
a
a
D
|
i.i i i i i i i i i i 1
> 46 12 16 20 2'
TIME FROM MIDNIGHT, hours
n AVG. TANK AVG. FOB DAY
GRID O2 UPTAKE VS. TIME
24 HOUR STUDY, 6/16-17/86
<ฃ
8
12
1
16
D GRID A
TIME FROM MIDNIGHT, hours
+ GRID B O GRID C
1 1
20
A GRID D
24
78
-------
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about their mean that can be attributed to a linear relationship between
Y and X. Simply stated, r2 tells what percent of the Y variable is
explained by the X variable.
It should be noted that another variable, gas flow, is a
factor involved in the correlations. Gas flow is relatively constant
during the two blower tests, but is reduced by half for the one blower
runs. Therefore, values measured during one blower operation are not
included in the correlations.
Figure 35 shows the effect of grid oxygen uptake rates on grid
OTE20's. As oxygen uptake rate increases, OTE20 decreases. As with
OTE20, Figure 36 shows that alpha decreases as oxygen uptake rate in-
creases. The effect of primary clarifier effluent soluble TOC load on
grid A alpha is shown in Figure 37. Using the t statistic in the hypo-
thesis testing procedure evaluated whether or not the correlations were
significant (Blank, pg. 521). The regression output for each correla-
tion performed is summarized in.Table 26. Again, no significant cor-
relation exists for the tank average or grid average values similar to
the results in Table 13.
80
-------
Figure 35.
o
3
Figure 36.
EFFECT OF O2 UPTAKE ON OTE2O
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
24 HOUR STUDY. GRID VALUES
95% CONFIDENCE
LIMITS
i
20
r~
40
60
GRID 02 UPTAKE, mg/l/hr
n f SQUARED=28* Y=16.1 - 0.130(X)
EFFECT OF O2 UPTAKE ON ALPHA
24 HOUR STUDY, GRID VALUES
0.9 -
0.8 -
0.7 -
0.6 -
0.5 -
0.4 -
0.3 -
0.2 -
0.1 -
95% CONFIDENCE
LIMITS
i
20
I
40
60
GRID O2 UPTAKE, mg/l/br
f SQUARED=28* Y=0.743-0.00675(X)
81
-------
Figure 37. EFFECT OF SOLUBLE TOO LOAD ON ALPHA
0.9 -
0.8 -
0.7
0.6
0.5
0.4
0.3
0.2 -
0.1 -
GRID A VALUES. NO LAG TIME
95% CONFIDENCE
LIMITS
0.2
r SQUARED=53X
0.4 0.6 0.8
(Thousands)
SOLUBLE TOC, Ib/day
Y=0.485-0.00016(X)
82
-------
C. Effect of Cleaning on Aeration Equipment
Tables 27 and 28 present the cleaning frequencies for aeration
tanks 3 and 4 at Ridgewobd. Two methods of cleaning were utilized on
the dome diffusers, acid brushing and water hosing. To acid clean the
domes a % carboy of 20% HC1 diluted 1:1 was used to brush each dome.
The water hose cleaning used a high pressure stream of water from a fire
hose sprayed directly onto the domes from the top of the aeration tank.
Typically an aeration tank was out of service for less than 15 days
during a cleaning.. The first cleanings were conducted in September 1984
on aeration tank 4 and October 1984 for aeration tank 3. As mentioned
previously, approximately 40 and 15 domes, respectively, were missing
from the aeration tanks with a large number of domes loose. The plastic
bolts were replaced by brass bolts and the dome density increased by
adding 110 new domes. The future cleanings showed the brass bolts to be
effective and did not require tightening until 1 year later. In gen-
eral, slime deposits did build up on the domes on the liquid side, with
hosing effectively removing it.
Figures 38 and 39 illustrate the OTE20 and alpha values for
1984 through 1986 with cleaning times indicated. It is difficult to
evaluate an immediate cleaning effect on OTE20' because of changing
wastewater characteristics and availability of data before and after a
cleaning. For example, an immediate increase in OTE20 can be seen after
the July 17th and July 28th 1985 cleaning on aeration tank 3. The low
gas flow OTE20 measured before the cleanings was 9.1% and increased to
9.9% after the first hose cleaning. After a second cleaning by acid
brushing the low gas flow OTE20 increased to 11.5%. However, primary
clarifier effluent BOD for the above tests (5,8,10) decreased from 159
mg/& to 141 and 97 mg/Jl. Thus, it is not clear what immediate impact,
if any, cleaning had on OTE20. An overall cleaning effect can be seen
from Figures 38 and 39. The OTE20s measured in 1984 gradually increase
with the successive cleanings and suggest that a scheduled frequency of
cleaning is desirable to maintain the efficiency of the aeration system.
83
-------
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87
-------
D. Problems Encountered and Solutions
1. Nocardia Foam
The major problem in collecting OTE data at the Ridgewood WWTP
was Nocardia foam present on the surface of aeration tanks 3 and 4.
Foam developed in late May of 1985 and was present through the Fall of
the same year. It redeveloped at the end of June, 1986 and again was
present through late Fall. The offgas technique for measuring OTE is
directly affected by the presence of foam. Relatively high offgas flow
rates are unattainable without pulling foam into the offgas hoses, thus
terminating the test. Also, the high oxygen uptake rate of the foam
provided unrealistically high OTE. This was especially true with low
offgas flow rates providing longer detention times through the foam
under the hoods during offgas testing. The foam also affected the non-
steady state technique using hydrogen peroxide due to the extremely high
oxygen demand of the foam reducing the incremental change in tank DO
from 10 mg/ฃ down to about 3 mg/Jl.
Three strategies were employed to combat this problem; 1)
reduce the foam in the aeration tanks, 2) modify the offgas hoods to
allow measurement, and 3) measure the foam oxygen uptake rate and
correct the offgas OTE values.
To reduce the foam in the tank, a chlorine surface spray was
tried initially. A drum of 15% sodium hypochlorite was diluted 4:1 and
sprayed across the tank surface with a garden hose over about 1 hour.
After use of three 55 gallon drums supplied by Ridgewood at a cost of
about $200 the foam disappeared. However it again reappeared within a
week and a second application was made at ASCE costs. It again reap-
peared indicating the chlorine spray was not a long term solution.
Injection of gaseous chlorine at the inlet of the aeration tank also
proved fruitless due to the high demand. Finally a foam suction system
discharging back to the primary clarifier with chlprination at the
clarifier inlet had some measure of success in controlling foam at 1 to
2 ft. levels in the tank. Low sludge ages were also attempted with only
1 aeration tank held in service, however this had no significant impact
on the foam. To date it appears that foaming at Ridgewood will continue
88
-------
to be a significant problem through the summer months into the early
fall.
Hood modification was then employed in an attempt to measure
offgas flow rates in 1 to 3 feet of foam. The 1.5" diameter, offgas pipe
was extended vertically 18" followed by a 90 degree elbow and another
length of pipe to act as a foam break and return. At low tank foam
levels, a few inches, this worked satisfactorily. However at high foam
levels it did not. A 5 gallon plastic jug was finally modified and used
as a foam collector to provide reasonable gas flow measurements. Data
collection for OTE measurement was conducted at relatively low gas flows
in the presence of foam. Higher gas flows, were attempted until the jug
was close to full. If the results of the gas flow summation were not
within 10% of the tank measured value, the weighted average OTE was
calculated based on prior gas flow distributions or on dome distribu-
tion.
To evaluate the effect of foam oxygen uptake on OTE measure-
ments using the offgas technique, a mass balance as shown in the
Appendix was performed about the aeration system including the offgas
hoods. The resulting equation takes into account initial oxygen concen-
tration, foam detention time and foam uptake rate.
Rft
OTE20, = OTE20 -
SL m C
go
where :
t _
ฐf GH
r - 16 PM
go T~
OTE = oxygen transfer efficiency in liquid
OTE = Measured oxygen transfer efficiency
Rf = Foam oxygen uptake rate (mg/H min)
t ,. = Foam detentiobn time (minutes)
89
-------
V = Foam volume (ft3)
H
= Hood gas flow (scfm)
P = Oxygen Partial Pressure (mm Hg)
M =32 g02/mole
T = Ambient air temperature (ฐK)
C = Ambient gas phase 0 concentration, mg/ฃ
Table 29 presents the foam oxygen uptake rate measured at the Ridgewood
plant. The average tank foam oxygen uptake rate was 340 mg/Jl/hr while
the suspended solids concentration in the foam was about 18,000 mg/ฃ.
The average uptakes were relatively constant in the first two grids at
400 to 430 mg/ฃ/hr but showed a significant reduction in the last two
grids, down to 300 and 250 mg/ฃ/hr at the effluent. It appears that the
uptakes in the foam parallel the uptakes in the aeration tank, which are
higher in the first two grids and significantly lower in the latter two.
Thus, there must be significant correlation between the activity in the
foam and the activity in the tank.
Test
Lima's Thesis
51 and 52
57
TABLE 29
Nocardia Foam Oxygen Uptake Rate
Date
1985
6/30/86
7/14/86
9/03/86
Level
(ft)
2
0.25-0.5
2
0.25
Grid
A
347
390
551
B
380
438
380
408
C
387
180
334
D
262
120
367
02 Uptake
Rate of
Collapsed
Foam,
(mg/ฃ-hr)
344
268
415
Average 430 400 300 250
340
Note: Foam uptake measured in collapsed state
volume collapsed _ 1
volume foam 4
90
-------
Nocardia foam was present in 14 of the 52 offgas tests per-
formed. Table 30 shows the measured OTE20's and the foam corrected
OTE20's evaluated in these tests. The foam correction for OTE is con-
sidered a best estimate. Its accuracy is limited by lack of foam uptake
data on actual test dates "and lack of actual offgas hood foam volumes.
The OTE measured in each grid was corrected by using the average foam
uptake and gas flow measured in that grid. The degree of correction is
a function of the gas flow rates through the, offgas hood. Relatively
high gas flow rates, causing short detention times in the foam, resulted
in small correction factors. Conversely, relatively low gas flow rates,
causing long detention times in the foam, resulted in large correction
factors. This is observed in test 66 where the OTE20 measured is 11.8%
while the foam corrected value is 4.7% with foam detention times greater
than 10 minutes. However, due to the magnitude of the correction, the
validity of the test is in question. Foam oxygen uptake rates were not
measured on the test day and simultaneous steady state data is not
available. This was also the case in tests 63 and 64. Therefore, the
results from these tests are not presented in the case history study.
The steady state OTE20 calculated in test 21 indicates the uncorrected
offgas OTE20 to be a better estimate than the foam corrected value.
Therefore, the uncorrected value is presented in the Case History study.
2. Four Lunger and In Situ Dome DWP Taps
A second problem area has been with the 4 lunger. Initially
difficulty was encountered due to the wet gas supply provided by Ridge-
wood from the grid blowoff piping. Plant personnel.subsequently changed
the supply line by tapping the header piping instead of using the blow-
off from the manifolds which solved the moisture problem. Difficulties
also occurred with maintaining the single dome at 1.5" head loss. Dur-
ing the study it was generally set higher to insure gas flow did not
reduce to zero. During winter months operation was poor, with periodic
clogging and freezing of the lines occurring. Similar problems existed
for the dome pressure taps with clogging and freezing of the lines.
Moisture buildup continuously was a problem and often terminated the DWP
measurements. Due to lack of available plant personnel and equipment
problems, proper 4 lunger and in situ DWP monitoring could not be con-
ducted.
91
-------
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94
-------
VII. PLANT PERFORMANCE - COARSE BUBBLE AND FINE PORE SYSTEMS
A. Operating Conditions and Controls
In reviewing the operating conditions and controls of the
coarse bubble and fine pore aeration systems not only diffuser type but
method of aeration was changed. The coarse bubble system operated under
a contact-stabilization method, while the fine pore system utilizes a
conventional tapered air method. Within these two systems operating
parameters and plant performance vary considerably.
The contact-stabilization (coarse) system operated at a lower
food to mass(F/M) and higher solids retention time(SRT) than the tapered
air (fine) system as shown in Table 31.
TABLE 31
Average Operating Conditions for Both Aeration Systems
at Ridgewood
System
Coarse
Fine
Dates
1/80-03/83
4/83-12/86
Average
TSS in
System
Ibs.
35,900
21,500
Average
F/M
Ib BOD5/d-lb MLVSS
0.13
0.25
Average
SRT
days
17.7
7.2
The F/M is based on the pounds of BOD,, per day in the primary
clarifier effluent divided by the pounds of MLVSS in the aeration tanks
and secondary clarifiers. The SRT is based on the pounds of MLVSS in
the aeration tanks and secondary clarifiers divided by the pounds per
day leaving the system as waste activated sludge and effluent solids.
Figures 40 through 42 illustrate the variability and average values of
sludge mass, F/M and SRT for each aeration system. The mass in the
system was fairly constant during the operation of the coarse bubble
system. For approximately the first year after the startup of the fine
pore system plant solids were almost twice the average. This correlates
with low F/M and high SRT values for the same time period. Also, the
air supplied to the fine pore system during this period was well above
average as shown later in this report.
'95
-------
Figure 40. Total Mass (TSS) in System - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
TOTAL MASS (TSS) IN SYSTEM(1/81 - 3/83)
n
,0
CO
B
i
m
50
i I -i ' ' I I I I I I I I I i I I i i i i j i i
6 9 12
6 9 12 3 6 9 12
n MONTHLY AVERAGE
MONTHS
SYSTEM AVERAGE
FINE PORE DOME SYSTEM
TOTAL MASS (TSS) IN SYSTEM(5/83-13/86)
' ' ' I I I I I I I I I I I I I I I I I I I I I I I I
6 9 12 3 6 9 12 3 6 9 12 3 6
n MONTHLY AVERAGE
SYSTEM AVERAGE
-------
H
I
2
o
0.6
Figure 41. F/M Ratio - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
F/M RATIO (1/81 - 3/83)
0.5 -
0.4 -
0.3 -
0.2
0.1 -I
I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I | | | | |
3 6 9 12 3 6 9 12 3 69 12 3
n MONTHLY AVERAGE
MONTHS
SYSTEM AVERAGE
FINE PORE DOME SYSTEM
F/M RATIO (5/83 - 12/86)
i i ' ' i I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I I I I I I I I
69 12 36 9 12 3 69 12 3 69 12
n MONTHLY AVERAGE
MONTHS
SYSTEM AVERAGE
97
-------
af
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3"
tt
to
f
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&
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Figure 42. Sludge Age - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
SLUDGE AGE (1/81 - 3/83)
' ' I I I I I I I I I I I I I I I I I I I I I I I
9
12
D MONTHLY AVERAGE
MONTHS
SYSTEM AVERAGE
FINE PORE DOME SYSTEM
SLUDGE AGE (5/83 - 12/86)
' I ' ' I I I I I I I I I I I I I I I I I I I I I I I I I I I. I I
6 9
n MONTHLY AVERAGE
MONTHS
SYSTEM AVERAGE
98
-------
The coarse bubble system required continuous 2 blower opera-
tion and all valves to the tank wide open. The increased efficiency of
the fine pore system provided flexibility with respect to air supply.
Dissolved oxygen concentrations are monitored in grid B in both aeration
tanks. During low load periods, one blower is utilized. Regulating the
amount of air supplied during aeration is a function of the amount of
dissolved oxygen present in the tanks. When the dissolved oxygen con-
centration drops to 0.6 mg/ฃ, a second blower is turned on. Butterfly
valves can adjust the gas flow to each grid, but typically are wide open
during operation.
B. Treatment Performance
1. Influent and Effluent Characteristics
Table 32 lists the average monthly . influent and effluent
values for the coarse bubble and fine pore aeration system. The coarse
bubble results represent the period from January 1980 to March 1983,
while fine pore values cover the period of May 1983 to December 1986.
Average influent concentrations have decreased since the fine pore aera-
tion startup in April, 1983, due to an increase in average flow, from
2.9 to 3.3 MGD as shown in Figure 43. Periodic high monthly flows are
due to infiltration and inflow during wet weather with high groundwater
tables.
Figures 44 through 46 show the monthly influent and effluent
concentrations for both aeration systems. Significant variability
occurred especially for the fine bubble system due in part to the sig-
nificant flow variability. High effluent BOD and suspended solids
losses occurred from the fine pore system in the winter of 1983-84. The
solids recycle load from the chlorination tank sludge were roughly five
times greater than normal during this period due to the high effluent
solids from the secondary clarifier. A marked decrease in the total
mass of solids in the aeration tank and clarifier also occurred during
this time as solids were rapidly wasted from the system to reduce 0
demand.
Figure 46 indicates a marked increase in nitrification during
the summer months for the fine pore system due to the higher D.O. levels
99
-------
TABLE 32
Plant Performance Results for Fine and Coarse Bubble Aeration Systems
Average Values and Standard Deviations ( ) for Each System
Parameter
Raw Flow
TSS
BOD
NH.+-N
4
NO~-N
Units
MGD
rag/a
Ib/d
mg/ฃ
Ib/d
mg/ฃ
Ib/d
mg/ฃ
Ib/d
Coarse (1/80-3/83) Fine (4/83-12/86)
Influent
2.89
(0.55)
148
(25)
3530
(661)
207
(23)
4940
(738)
Effluent
6.1
(1.8)
147
(53)
13.1
(1.3)
316
(69)
28.7
(3.5)
692
(84)
% Removal Influent
3.27
(0.74)
96 152
(2) (48)
4150
(1010)
94 195
(1) (43)
5320
(962)
37
(10.2)
1009
(279)
Effluent
13
8
355
(267)
15
(5)
410
(129)
28
(13)
'764
(376)
6.8
(5)
185
(192)
% Removal
91
(8)
92
(4)
25
(27)
100
-------
1
Figure 43. Plant Raw Influent Flow - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
RAW INFLUENT PLOW (1/81 - 3/83)
' i i < i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i
D MONTHLY AVERAGE
MONTHS
SYSTEM AVERAGE
FINE PORE DOME SYSTEM
RAW INFLUENT FLOW (5/83 - 12/86)
i i l l i I I I I I I I I I I I I I i I I I I I I l I l
69 12 36 9 12 3 6 9 12 3 6 9 12
n MONTHLY AVERAGE
SYSTEM AVERAGE
-------
W
W
IH
Figure 44. TSS Influent and Effluent - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
260
TSS INFLUENT & EFFLUENT (1/80 - 3/83)
n
i i i i i i l i i l i i
i i i i i i i i i l i i i i
9
12
MONTHS
EFF. TSS
SYSTEM AVERAGES
260
FINE PORE DOME SYSTEM
TSS INFLUENT & EFFLUENT (5/83 - 12/86)
I I I I I I I I I I I I I I I I I I I I I 1 I l I I
n
6 9 12 3
INF. TSS
MONTHS
EFF. TSS
SYSTEM AVERAGES
102
-------
to
ง
n
Figure 45. BODc Influent and Effluent - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
1
to
Q
O
n
n
280 -
260 -
240 -
220 -
200 -
180 -
160 -
140 -
120 -
100 -
80 -
60 -
40 -
20 -
0 -
A
H A
V ^\ /sA / ^
\ -H^V*" ^ V 'l*Vl
ฐ t
~i i ' i ' i i i i i i i i i r~i i i i 1 i i i r~i 1111 i i i | i i r~i
36 9 12 3 6 9 12 3 6 9 12 3
MONTHS
INF. BODS + EFF. BOD5 SYSTEM AVERAGES
FINE PORE DOME SYSTEM
BOD5 INFLUENT & EFFLUENT (5/83 - 12/86)
I I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I
n
INF.
6 9
BODS
12
MONTHS
EFF. BODS
SYSTEM AVERAGES
103
-------
Figure 46. N-NH3, N03 Influent and Effluent - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
N-NH3 EFFLUENT (1/80 - 3/83)
55
w
70
60 -
50 -
40 -
30 -
20 -
10 -
10 -
i i i i i r i i i i i i i
69 12 38
9
n EFF. N-NH3
MONTHS
SYSTEM AVERAGE
FINE PORE DOME SYSTEM
N-NH3.N-NO3 INFL.& EFF.(5/83 - 12/86)
12
.IMF.N-NH3
EFF. N-NO3
I I I I I I I I, TTT T TT 1 I I I .1 I I I I I I I I I I I I I I I
6 9 12 3 8 9 12 3 6 9 12 3 6 9 12
n INF. N-NH3
MONTHS
A EFF. N-NO3
X EFF. N-NH3
104
-------
maintained in the aeration tanks. Thus the oxygen demand on the fine
pore system was significantly greater than on the coarse bubble system
due to the oxidation of the nitrogeneous load. Figure 47 summarizes the
% removals obtained by both systems showing the coarse bubble consis-
tently outperformed the fine pore system on BOD,, and TSS removals while
nitrogen removal occurred in the fine pore system, but not in the coarse
system. Periodic low suspended solids and BOD removal efficiencies in
the fine pore system was due to the inability of Ridgewood's sludge hand-
ling system to adequately waste sludge without the availability of the
sludge lagoons.
105
-------
Figure 47. Plant Removal Efficiencies - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
PLANT REMOVAL EPFICIENCIES(1/80 - 3/83)
100
^ + i + i- i t i -K
1
00 -
80 -
70 -
60 -
50 -
40 -
30 -
20 -
10 -
100
' ' I I ' I I i I I I I I I 1 I I 1 I I I I I I I I I I I I I I I I I I I
3 6 9 12 3 6 9 12 3 8 9 12 3
MONTHS
n BODS REMOVAL + TSS REMOVAL
FINE PORE DOME SYSTEM
PLANT REMOVAL EFFICIENCIES(5/83-12/86)
1
6 9
BODS REMOVAL
12
l i I i i I I i i I I i I I I I i I I I i i i
12 3 6 9 12 3 6 9 12
MONTHS
+ TSS REMOVAL
+N-NH3 REMOVAL
106
-------
2. Sludge Production Comparison
The startup of the fine pore diffuser system was expected to
reduce aeration costs and sludge production. An 18% reduction in secon-
dary sludge production was predicted (Phase I, 1982). Analysis of
actual field data, shown in Tahle 33, shows an increase in secondary
sludge production of 980 Ib/day and an average increase of 585 Ib/day
being hauled off site. This is due to the high F/M of the fine pore
system and sludge discharged to onsite lagoons during the operation of
the coarse bubble system thus reducing the amount of sludge hauled off-
site. The lagoons were phased out in August of 1982 and data is not
available as to the amount of sludge handled by them. On the average
20.5% of the influent TSS was hauled offsite during the operation of the
coarse bubble system, while 31.6% of the influent TSS was hauled offsite
for the fine pore system (Holmes, 1986).
The thickening characteristics of the contact stabilization
sludge from the coarse bubble system were better than those from the
conventional fine bubble system as indicated by the greater WAS and pri-
mary clarifier under flow (digester influent) concentrations.
3. Recycle Stream Impact on Fine Pore Aeration System
The majority of flow to the aeration tanks is comprised of the
primary clarifier effluent and return activated sludge (RAS). However,
the recycle streams from the chlorination tank and the anaerobic diges-
tor supernatant significantly contribute to the aeration tank load.
Tables 34 and 35 present the recycle stream loads based on average
monthly values and during their period of return.
Chlorination is the final process stage at Ridgewood prior to
discharging secondary effluent into the Ho-Ho-Kus Brook. The tanks are
drained and cleaned of sediment on an average of once each month. The
tank is divided into 4 sections, with 2 of 4 sections generally cleaned
at one time to allow uninterrupted plant operation during the cleaning
process. Field tests (Holmes, 1986) indicate that there is a 15% sus-
pended solids removal rate across the chlorination tank. Based on that
removal, and a cleaning rate of once per month, the chlorination tank
recycle stream solids concentration averaged approximately 2200 mg/Jl.
107
-------
TABLE 33
Sludge Wastage Results for Fine and Coarse Bubble Systems
Parameter
LOADS. Ib/d
Secondary Waste Solids
Effluent
WAS
TOTAL
Average TSS Values for each System
Coarse Fine
(1/80-3/83) (4/83-12/86)
147
2000
2147
355
2770
3125
Digester Influent
Sludge Haulage
Lagoon Storage
4350
725
>0
4430
1310
0
CONCENTRATIONS. mg/Jt
WAS
Digester Influent
Sludge Haulage
6700
42000
50200
5850
31800
45100
108
-------
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PS PL, O Q
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-------
TABLE 35
TSS Recycle Stream Impact on Aeration Tank Load
Average Return Time
per day
% of Return to Aera-
tion Tank
Average Return Cycle
Average TSS Concen-
tration
Flow
Recycle TSS Load
% of Aeration
Influent Load
% of Primary
Effluent Load
(2)
Units
(hrs)
Chlorination
Tank
97.6
Settled
Digester
Supernatant
4
lOO(assumed)
(mg/ฃ)
(MG/hr)
(lb/hr)
(%)
1. 1 /month
2200
0.05
900
27
Daily
4570
0.0023
90
3
900
63
(1)
(2)
Average Aeration Influent Load = 3400 lb/hr
Average Primary Effluent Load = 103 lb/hr
110
-------
Thus, the recycle stream results in a 27% increase in suspended solids
load to the aeration tank during the cleaning process which typically
takes 2 hours. The chlorination tank load is approximately 9 times
greater than the primary clarifier effluent load and 6 times that of the
average daily raw influent load during the recycle period.
Combined primary and secondary sludges for the primary clari-
fier underflow are pumped to digester No. 1 which is mixed and heated.
Settled sludge is removed from digester No. 2 and hauled offsite, while
supernatant is discharged to primary clarifier No. 2 for further set-
tling. From there, settled sludge is disposed of and supernatant is
returned to the system where it is mixed with primary influent or aer-
ated prior to return. Presently, it is aerated in aeration tanks No.
2-4 to satisfy the oxygen demand before discharging into the aeration
tank influent stream. The digester supernatant load was based on an
assumed average concentration of 9400 mg/ฃ and was derived from field
sampling. The settled supernatant load was based on an average concen-
tration of 4570 mg/ฃ. This results in a 3% increase of the load enter-
ing the aeration-tanks during its period of return. It is a 63% in-
crease over the average raw influent load and a 86% increase over the
average primary effluent load.. The field sampling was conducted in
November and December of 1985 and may not represent typical loadings
from the digester recycle. In fact, summer loadings from digester
recycle are suspected to be significantly higher for the fine pore
system due to the solids wasting difficulties mentioned previously.
Ill
-------
C) Air Utilization Comparison
It was anticipated that the fine pore diffuser retrofit would
enable Ridgewood to reduce energy costs by operating one blower rather
than two, because of the increased efficiency of the new system. Plant
records indicate an average blower usage of 2950 kwh/day for the coarse
bubble system. The average blower usage predicted for the fine pore
system was 1475 kwh/day; actual records show an average value of approx-
imately 2090 kwh/day. This translates to a 28% reduction of blower
usage. This is a substantial savings of blower time, but is below the
anticipated 50% reduction. Typical plant operation utilizes two blowers
during high flow and load periods, while one blower is used during low
load periods.
Figure 48 illustrates the air flow rates for the coarse bubble
and fine pore aeration systems. The average air required for the coarse
bubble system is 2.75 MCF/day, while 1.63 MCF/day is the average value
for the fine pore system. From the startup of the new system to the
beginning of 1984, the average air supplied was approximately 2.5
MCF/day with the second blower utilized a large percentage of the time.
Plant conditions were poor during this time with high solid levels in
the system (Figure 40) and coarsing in the aeration tank due to loose
and missing domes. Second blower on time has increased from 24% of the
time in 1984 to 65% in 1986. The increased on time for the second
blower is a result of a greater oxygen demand of the system due to
nitrification. A seasonal nitrification permit will go into effect for
Ridgewood starting in April, 1987. Thus, the blower on time in 1986 may
be typical in order for Ridgewood to meet the new standard.
Figure 49 shows the amount of air necessary to treat 1 'gallon
of influent wastewater. Roughly, 1 CF of air was necessary for 1 gallon
of influent wastewater during the operation of the coarse bubble system.
Due to the fine pore diffuser retrofit approximately 0.5 CF is necessary
to treat 1 gallon of influent wastewater. As shown in Figure 50, the
coarse bubble system required 610 cubic feet of air per pound BOD,, re-
moval compared to 370 for the fine pore system.
112
-------
1
a
p
IS
3.5
Figure 48. Air Utilized - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
AIR UTILIZED (1/81 - 3/83)
3 -
1.5 -
1 -
0.5 -
.
69 12
1 ' ' ' I 1 I I I I I I I I I I I
6 9 12 3 6 9
MONTHS
12
D MONTHLY AVERAGE --- SYSTEM AVERAGE
FINE PORE DOME SYSTEM
AIR UTILIZED (5/83 - 12/86)
I ' ' ' I I I I I I I I I I I I I I I i i i i
6 9 12 3 6 9 12 3 6 9 12
6 9 12
0.5 -
n MONTHLY AVERAGE
MONTHS
113
SYSTEM AVERAGE
-------
Figure 49.
1
o
i
S
o
Air Utilized Per Gallon Influent - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
2
1.9
1.8
1.6
1.5
1.4
1.3
1.2
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
AIR UTILIZED (1/81 - 3/83)
43
i l i l I i l l l l l
3 6 9 12
n MONTHLY AVERAGE
i l i i l i l l l l l i l l l i l i i i
3 6 9 12 3 6 9
MONTHS
l l l
12
2
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
SYSTEM AVERAGE
FINE PORE DOME SYSTEM
AIR UTILIZED (5/83 - 12/86)
6 9 12 3
a MONTHLY AVERAGE
l I ' ' I l l I I l I t I I I l l l i i i i i i i
6 9 12 36 9 12 3 6
12
MONTHS
114
SYSTEM AVERAGE
-------
Figure 50. Air Utilized Per BODj- Removed - Coarse and Fine
COARSE BUBBLE SPARGER SYSTEM
AIB UTILIZED (l/8i - 3/83)
I ' ' I ' I I I I I I I I I i I I I I I I I I I I I I I I I I 1
MONTHLY AVERAGE
MONTHS
SYSTEM AVERAGE
FINE PORE DOME SYSTEM
AIR UTILIZED (5/83 - 12/86)
II I I I I I I I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I
n MONTHLY AVERAGE
SYSTEM AVERAGE
-------
VIII. ECONOMIC ANALYSIS
. Preliminary assessment indicates that fine pore aeration retrofit
would enable Ridgewood to reduce their blower power consumption by 50%
(Burde, Phase I, 1982). Actual power reduction is approximately 28%, as
shown in Table 36.. The values presented in Table 36 are averages from 1984
through 1986. Table 37 presents a breakdown of the yearly dome cleaning
and repair costs incurred with fine pore diffuser retrofit. The yearly
labor costs are based on 1 man day = $175, derived from an average salary
of $20,000 per year divided by 230 workdays per year multiplied by 2 for
overhead. The lack of cleaning initially was balanced by the extensive
cleaning performed in 1985 to attempt to evaluate the cleaning effect on
oxygen transfer efficiency and therefore, 1985 values do not represent
typical cleaning costs. No additional manpower requirements were needed
for foam cleanup. Table 39 summarizes the maintenance costs incurred with
the fine pore system. Total maintenance costs per year since April 1983
have been $2780/year for the fine pore system, while essentially no
maintenance was required for the coarse bubble system.
Figure 51 illustrates the savings in power consumption obtained
by the fine pore aeration system. Two blower operation requires 89700
kwhr/month, while average actual power consumption is about 63400
kwhr/month. Figure 52 shows the cumulative power consumption costs and
savings. The projected cost for the coarse bubble system is based on
continuous two blower operation. Approximately 40% of the bid price has
been paid off from April 19.83 to December 1986. The bid price for
retrofitting the plant with fine pore diffusers was $218,000 to be paid off
monthly from the power savings incurred with the new aeration system. The
bid price is a present worth value including capital costs and anticipated
interest charges over a payoff period of 7 years at 9%. Based on a 50%
power consumption reduction and 1982 power costs, the payoff period was
projected at 6.1 years. Based on actual payments the predicted payoff
period is approximately 9.7 years. If the increased dome maintenance cost
is included, the projected payoff period is 11.1 years as shown in Table
40.
116
-------
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-------
TABLE 37
Yearly Dome Cleaning and Repair Costs
Year
A/83-12/83
1984
1985
1986
Year
Type of # of
Cleaning Cleanings $/cleaning3
Hose1 0 0
Acid2 , 0 0
Hose
Acid
Hose
Acid
Hose
Acid
4/83-12/83
1984
2
0
8
3
3
1
Dome System Repairs
Description
No repairs performed
Adjust and replace domes
175
0
175
375
175
375
Total
Average
Yearly
Cost
0
$700
Yearly
Cost
0
0
350
0
1400
1125
525
375
$3775
$1005/year
1985
1986
and bolts, increase dome
density, ^ 4 man days
Tighten bolts and seal
cracks with hot glue gun,
**ป 2 man days
No repairs performed
Total
Average
$350
0
$1050
$280/year
1 man/day for 1 tank = 1 man day
2 2 men/day for 1 tank = 2 roan days
Based on $175/man*day
Based on 3-3/4 years
118
-------
TABLE 38
Nocardia Foam Chlorination and Cleanup Costs
Foam Chlorination
Year
4/83-12/83
1984
1985
1986
"
Year
4/83-12/83
1984
1985
1986
Description
Not required
Not required
6 drums (^ $67/drum) of 15% NaOCฃ
^ 3 man days
Automatic Surface Spray ^ $900
- pump setup
- hoses with lawn sprinklers
- pump replacement motor
- 'v 4 man days
Construct Permanent Spray System
- nozzles
- piping
- ^ 5 man days
Total
Average1
Foam Cleanup
Cleanup
Frequency
Weeks of Foam #/week
^ 0 0
10 0
26 1
18 0.4
Total
Average1
Yearly
Cost
0
0
$1825
$875
$2700
$720/year
Yearly
Cost2
0
0
2275
630
$2905
$775/year
Based on 3-3/4 years
2
Based on % man day/cleanup
119
-------
TABLE 39
Summary of Dome System Maintenance Yearly Costs
Yearly Cost for
Year
4/83-12/83
1984
1985
1986
Average
Cleaning
0
350
2525
900
1005
Repairs
0
700
350
0
280
Foam
Chlorination
0
0
1825
875
720
Foam
Cleanup
0
0
2275
630
775
Total
0
1050
6975
2405
2780
Based on 3-3/4 years
120
-------
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(spuDsnoqx)
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122
-------
TABLE 40
Dome System Economic Summary at Ridgewood (1983-1986)
$/year
Power Savings from Retrofit 22400
Increased Maintenance 2780
Net Savings from Retrofit 19620
Fine Pore System Bid Price* 218000
Projected Payoff Period 11.i years
(Based on Average Power Savings & Maintenance
Costs
Actual Payoff Period 9.7 years
(Based on Actual Payments 4/83-12/86)
Capital cost + interest expenses (7 years, 9%).
123
-------
Installation of the fine pore done system has produced a
significant improvement in effluent quality with respect to nitrogen
oxidation. Although BOD and suspended solids quality has deteriorated
slightly, the high degree of nitrification obtained in the summer months
significantly reduced the overall oxygen demand on the HoHo-Kus brook.
This increased effluent quality is not taken into account in the eco-
nomic analysis. Starting in May 1987, Ridgewood will require seasonal
nitrification and thus the oxygen demand will be consistently higher on
the fine pore system during the summer months than it was on the coarse
bubble system. Due to the improved effluent quality obtained by the
fine pore system, the Village of Ridgewood is paying off the remainder
of the capital cost in a lump sum payment.
124 .
-------
IX. CONCLUSIONS
1. In the Ridgewood retrofit from coarse bubble to a fine pore
aeration system the process was also modified from a contact stabiliza-
tion system to a conventional activated sludge system. The coarse
system had an average F/M of 0.13 Ib BOD5/day-lb MLVSS and an SRT of
17.7 days while the fine pore system operated at an F/M of 0.25 Ib
BOD /day-lb MLVSS and an SRT of 7.2 days. The sludge handling system
was also modified during the retrofit in that on-site lagoons were no
longer available for sludge disposal. This resulted in a net secondary
sludge increase of approximately 8% and about a 70% increase in sludge
haulage.
2. A significant improvement in effluent quality with respect to
nitrification occurred in the fine pore system where during summer
months 85 to 95% nitrification could be obtained compared to none for
the coarse bubble system. Thus fine pore system installation provided
the capability to obtain improved effluent quality and reduce the oxygen
demand on the receiving stream at Ridgewood. Since this will become a
permanent requirement in 1987 for Ridgewood, no additional retrofit
should be required. Greater BOD5 and suspended solids removal was
obtained with the coarse bubble system, 96 and 94% respectively, com-
pared to the 91 and 92% obtained for the fine pore system. To a large
extent it is felt that this decrease in effluent quality is due to the
inability of the sludge handling system at Ridgewood to remove sludge
effectively from the system without usage of the onsite lagoons.
3. Over the six years of study at Ridgewood the coarse bubble
system, being in operation for 25 years, exhibited an average OTE20 of
4.8% with an average alpha value of 0.55 requiring the usage of two
blowers for plant operation. In operation for 3-3/4 years the fine pore
system, during normal operation with two tanks in service, provided an
average OTE20 of approximately 9.5% during daytime high load periods
with an alpha value of 0.40.
4. The Ridgewood retrofit to the fine pore system provided a 28%
reduction in aeration power consumption. Based on an average power cost
of 0.0746 $/kwhr, the resulting power savings is $22,400/yr. Increased
maintenance cost of $2780/year were also incurred for the fine pore
125
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system. Using the net savings of $19,620/year with a capital cost of
$218,000 provided a projected payoff period of 11.1 years. Based only
on sayings in blower power, the actual payoff period was projected at
9.7 years. Both estimates are significantly greater than the 6.1 years
projected in the original design. However, the Village of Ridgewood is
paying off the remainder of the capital costs after approximately 4
years of operation, due to the ability of the fine pore system to
nitrify and meet new permit requirements.
5. After two years of operation with the fine pore system, a
significant Nocardia foam problem resulted. Its onset occurred in the
early summer months and lasted through the fall. At times foam over-
flowing the aeration tank caused operational problems with respect to
foam cleanup on the site. It is suspected that foam developed when
significant organic loads from the sludge recycle streams were dis-
charged to the aeration tank resulting in periods of septic conditions.
Minimization of plant overload in 1986 delayed the onset of foaming back
from May to the end of June.
6. During periods of dome cleaning, one tank was taken out of
service for anywhere from a few days to a two-week period, resulting in
a higher organic loading rate and oxygen demand on the aeration tank in
operation. Also, during summer months in 1983 through 1985, nitrifica-
tion control was attempted by taking one aeration tank out of service
thus increasing the F/M of the system. Both of these situations caused
significant overload on the tank, probably aiding in Nocardia growth,
and definitely yielded lower oxygen transfer efficiencies and alpha
values for the dome system. This caused a reduction in tank OTE20 from
the 1986 average value at high gas flows of 9.9% with an alpha of 0.42
to 7.1% with an alpha value of 0.36.
7. A 24-hour sampling study at Ridgewood in June 1986 showed
OTE20 to range from 9.5% to 13.1%s resulting in alphas of 0.43 to 0.59.
The latter value occurred during low load early morning hours. The
daily value occurred during low load early morning hours. The daily
average OTE20 for this study was 10.7% with an alpha of 0.46. This was
a period of good plant operation with no Nocardia foam present on the
tanks.
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8. Both OTE20 and alpha showed statistically significant
correlations with oxygen uptake rate and influent TOC load. The greater
the uptake rate, the lower the OTE20 and alpha value. For both clean and
dirty water, OTE20 correlated well with gas flows. The higher the gas
flow, the lower the OTE20 value.
9. Alpha values are based on manufacturer's OTE data using new
diffusers and the measured field values where most diffusers are in
service for a considerable amount of time. Thus the alpha values
incorporate the effects of both wastewater characteristics and any
diffuser deterioration. True alpha values can only be determined by
clean water testing of the existing plant diffusers.
10. The impact of acid cleaning and simple diffuser hosing at
Ridgewood was difficult to evaluate. Changing wastewater characteristics
and process conditions at the plant masked any significant improvements
due to cleaning. It appears that inspection and maintenance on the
aeration system should be accomplished at least once a year at which time
hosing would be employed. The best time is in the spring, prior to the
onset of the summer high temperature conditions when both aeration tanks
should be maintained in service to minimize overload.
11. Both offgas and nonsteady state testing appear reliable at
Ridgewood, the offgas testing providing oxygen transfer efficiencies at
specific locations in the tank while nonsteady state testing provides
only an overall average tank value. The steady state testing, technique
markedly overestimates oxygen transfer efficiency during oxygen limiting
conditions when portions of the aeration tank are septic. From the
24-hour study results, the steady state technique underestimates the
oxygen transfer efficiency during food limiting periods. However, oxygen
uptake rates, obtained for the steady state technique, are useful in
correlating results. Also, the steady state results provided an
indication of the accuracy of the off gas tests during high foam
conditions when significant oxygen uptake rates occurred in the foam
layer above the aeration tank.
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X. REFERENCES
1. Belitto, A. "Field Lab Aeration Study," Manhattan College
Environmental Engineering and Science Program, March 1985.
2. Burde Associates, Ridgewood, New Jersey WPCP, "Operation and
Maintenance Manual," June 1983. ,
3. Blank, L. "Statistical Procedures for Engineering, Management
and Science," McGraw-Hill Series, 1980.
4. Elliott, P.; Chung, I.; Kharkar, S. "Nonsteady State Field
Testing of Ridgewood Aeration System," Manhattan College
Environmental Engineering and Science Program, Field Lab, April
1984.
5. Huibregtse, G. - personal communication 9/25/86 (- data from an
internal report and results published in: Huibregtse, G. ; Rooney,
T.; & Rasmussen, D. "Factors Affecting Fine Bubble Diffused
Aeration," JWPCF, p. 1057, August 1983), 1986.
6. Hildreth, S. "Effects of Hydraulics on Nonsteady State Field
Testing in Tapered Aeration Tanks," Manhattan College Envi-
ronmental Engineering and Science Program, Graduate Thesis,
December 1983.
7. Holmes, T., Ridgewood Wastewater Treatment Facility - "Plant
Performance Comparison," Manhattan College Environmental
Engineering and Science Program, Graduate Thesis, May 1986.
8. Mueller, J. "Ridgewood Aeration System Analysis, Phase I, Coarse
Bubble Sparger System," Manhattan College Environmental Engi-
neering and Science Program Report to Burde Associates, May 1982.
9. Mueller, J. "Nonsteady State Field Testing of Surface and
Diffused Aeration Equipment," Manhattan College Environmental
Engineering and Science Program, July 1983.
10. Mueller, J. "Ridgewood Aeration System Analysis, Phase II. Fine
Bubble Dome System," Manhattan College Environmental Engineering
and Science Program, May 1983.
11. Mueller, J.; Elliott, P.; Chung, I. "Nonsteady State Analysis
of Ridgewood Tanks 3 & 4," Manhattan College Environmental
Engineering and Science Program, August 1984.
12. Saurer, P.; Heaney, J.; Rogers, J.; Srinvasan, S. "Field Lab
Aeration Study," Manhattan College Environmental Engineering and
Scienc Program, May 1986.
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APPENDIX A
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NOCARDIA FOAM EFFECT ANALYSIS
A. Hood Foam Volume 4 '
J^"'
by 3'
Hood Volume = 1/2 x 4 x 8 = 16 ft"
iK1^)2
Pipe Volume = ^' =
4 3' = 0.037 ft (neglect pipe volume)
B. Mass Balance
(1) Free Body Diagram
G, C
Rf vf
T
R , V
T
, C
go
Foam
Liquid
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(2) OTE Definition
OTE
G(CgQ - Cgl)
cci;
(Cgo - cง2)
m ci;
Cg, = (1 - OTE )Cg^ - Eqn 2
OTE = oxygen transfer efficiency in liquid
OTE = oxygen transfer efficiency measured
in liquid and foam
(3) Foam Mass Balance
- GCg2 = RfVf
= RfVf + GCg2
R V
-g + Cg2 - Eqn 3
Substitute Equation 2 into Equation 3
RfV
Cg1 = -pr^- + (1 - OTE )Cg - Eqn 4
i Lr ID O
Substitute Equation 4 into Equation 1
R,V_
Cg '
R V
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R V
OTEn = OTE -
SL m Cg G
R to
= ฐTEn, - -CT~ " Eqn 5
Vf
to,. = -p detention time (minutes)
, = Foam oxygen uptake rate (mg/Jl/min)
C = initial oxygen concentration (mg/Jl)
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