United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
EPA-600/2-80-016
June 1980
Research and Development
Evaluation of
Pollution Control
Processes
Upper Thompson
Sanitation District
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Develbpment, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research ;
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7, interagency Energy-Environment Research and Development
8. "Special" Reports i
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-80-016
June 1980
EVALUATION OF POLLUTION CONTROL PROCESSES
Upper Thompson. Sanitation District
by
Bob A. Hegg
Kerwin L. Rakness
Larry D. DeMers
M & I, Inc., Consulting Engineers
Fort Collins, Colorado 80525
and
Robert H. Cheney
Upper Thompson Sanitation District
Estes Park, Colorado 80517
Grant No. R-803831-01
Project Officer
Edwin Earth
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does men-
tion of trade names or commercial products constitute endorsement or recommen-
dation for use.
ii
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health and
welfare of the American people. The complexity of that environment and the
interplay between its components require a concentrated and integrated attack
on the problem.
Research :and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment and management
of wastewater and solid and hazardous waste pollutant discharges from munici-
pal and community sources, for the preservation and treatment of public drink-
ing water supplies, and to minimize the adverse economic, social, health and
aesthetic effects of pollution. This publication is one of the products of
that research; a most vital communications link between the researcher and the
user community.
This report describes one of the first municipal wastewater treatment
facilities specifically designed for two-stage nitrification and effluent dis-
infection with ozone.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
iii
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ABSTRACT
The Upper Thompson Sanitation District (UTSD) .advanced wastewater treat-
ment facility, located in Estes Park, Colorado, incorporated several unique
unit processes. Among these were flow equalization,, attached growth nitrifi-
cation, mixed media filtration and ozone disinfection. Plant design flow was
5,680 cu m/day (1.5 mgd). Average weekly operating flows ranged from 1,140 cu
ra/day to 3,790 cu m/day .(0.3 mgd to 1.0 mgd). The activated sludge, nitrifi-
cation and filtration processes have two parallel trains. By selectively using
one half of the available units design flow conditions were achieved at one-
half the plant design flow rate. Therefore the weekly average flow rates
during the research project ranged from 40 percent to 134 percent of design
and the BOD5 loading ranged from 14 to 228 percent of design.
Overall plant performance in terms of 6005 and TSS removal was consis-
tent, averaging 95 percent and 96 percent, respectively. Ammonia oxidation
was not as consistent, due to loading extremes and cold weather operating con-
ditions. Performance characteristics of two nitrification tower media types
(plastic dumped and redwood slats) were different. The redwood media per-
formed better during cold weather operation, but the recirculation (R/Q) ratio
was about 3 times higher than used for the plastic media. The plastic media
performed better during warm weather operation (R/Q ratios similar). Both
media types experienced periods of solids sloughing. Neither media type per-
formed at a desired optimum performance level although design requirements
were achieved.
The mixed media filters worked well for polishing the nitrification tower
effluent under normal conditions, but plugged immediately when extensive
solids sloughing from the tower occurred. The filters were also used as part
of a denitrification study to demonstrate the effectiveness of dual purpose
nitrogen removal and effluent polishing capability. The results showed that
denitrification capability existed when methanol was added to the filter in-
fluent. Filter plugging after relatively short filter runs (2-3 hours) halted
the studies.
The air-fed ozone disinfection system was, operated intermittently because
of required modifications. Special studies were conducted to determine per-
formance information. When operating, good disinfection performance was
achieved, but high ambient ozone concentrations in the working environment
plus failure of materials exposed to ozone (piping and diffusers) caused peri-
odic system shutdown. Modifications are indicated for new ozone systems (not
completed at the UTSD plant due to cost) so that more cost effective and
trouble free operating systems might be possible.
IV
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The pressure filter sludge dewatering unit worked well in its application
at the UTSD plant, but required a relatively high polymer usage and cost due
to the type of sludge dewatered.
This report was submitted in fulfillment of Grant No. R-803831 by the
UTSD under the partial sponsorship of the U.S. Environmental Protection
Agency. This report covers a period from July 1975 to March 1979, and was
completed as of May 1979.
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CONTENTS
Disclaimer « ii
Foreword ................ iii
Abstract ....... ...... iv
Figures ° viii
Tables ° ix
Acknowledgment x
1. Introduction . . -^
2. Purpose and Scope 3
3. Conclusions . 4
4. Recommendations ............ .... 17
5. Description of Facilities ....... 19
General 19
Raw Sewage Pumping - Lift Stations ....... 21
Flow Equalization ., 22
Grit Removal . . 24
Activated Sludge 25
Aeration System 25
Clarification System 26
Sludge Pumping System 27
Nitrification 28
Mixed Media Filtration 30
Ozone Disinfection 32
Sludge Handling . 37
Sludge Treatment 37
Sludge Dewatering and Disposal 38
Miscellaneous Facilities 41
Stand-by Power 41
Plant Laboratory 41
Potable and Non-Potable Water Supply . 42
6. Data Collection and Analytical Procedures ...... 43
Analytical Procedures and Quality Control ..... 43
Analytical Schedule and Sample Type and Collection Frequency. . 46
7. Results and Discussion 50
General 50
Flow Equalization 51
Grit Removal 55
Activated Sludge 55
Nitrification 65
Plastic - Start-Up 70
Plastic - Cold Weather 72
vii
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CONTENTS (Continued)
Plastic - Warm Weather 74
Redwood - Start-Up ...... 78
Redwood - Cold Weather 79
Redwood - Warm Weather 82
Redwood Update - Warm Weather 86
Redwood Update - Cold Weather ..... 87
Overall Nitrification Evaluation ..... 90
Denitrification 91
Start-Up Interval » . . . . 92
Methanol Full-Feed Interval .... ..... 95
Filter Performance (Physical Parameters) ......... 99
Mixed Media Filtration ..... 102
Ozone Disinfection ..... 109
General 109
Data Collection ..... 109
Ozone in Air - Concentration and Mass Measurements . 109
Ozone in Water - Concentration Measurements ..... m
Electrical Power Consumption Measurements ...... 112
Miscellaneous Measurements ..... 112
Data Evaluation and Discussion 113
Ozone Air Pretreatment 113
Ozone Generator Production ............. ng
Ozone System Power Requirements 122
March 1979 Update 130
Generator Flooding ..... 131
Dew Point Monitoring ..... 133
Generator Production Verses Dew Point ..... 133
Generator Power Requirements Verses Dew Point. . 134
Ozone Contacting System ..... 134
Disinfection Performance ..... 141
Sludge Dewatering and Disposal 145
Overall Treatment Plant Performance ..... 151
Operation and Capital Cost 154
Lift Stations ..... 154
Flow Equalization and Grit Chamber ..... 155
Activated Sludge . ..... 155
Nitrification ..... 156
Filtration ..... 157
Ozone Disinfection ,,.... 153
Sludge Handling . . ..... 159
Miscellaneous 160
Summary of Cost Information ..... 161
8. References 163
Appendices 164
viii
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FIGURES
Number
Page
1 Plant flow schematic diagram of the Upper Thompson .;...
Sanitation District Wastewater Treatment Plant ...;=. . . . 20
2 Equalization basin flow schematic diagram . . i. .;. . . . .' . 22
3 Ozone generation schematic diagram . . . . ........ 33
4 Ozone contact basin schematic diagram . . ,; . . . . . . . '35
5 Mainstream sampling stations during the research project . . . 46
6 Flow equalization basin influent and effluent dissolved :. -, :
oxygen concentration : '- 52
7 Plant influent wastewater flow rate during the research
project .;->.« .', 57
8 Activated sludge influent BOD5 loading and effluent
BODg residual 57
9 Activated sludge influent NIfy-N loading and effluent
NIfy-N residual 58
10 Nitrification tower ammonia loading and ammonia oxidized
during the research project . 69
11 Nitrification tower ammonia loading and ammonia oxidized
during the plastic start-up operating period ... 70
12 Nitrification tower ammonia loading and ammonia oxidized
during the plastic cold weather operating period 72
13 Nitrification tower ammonia loading and ammonia oxidized
during the plastic warm weather operating period 75
14 Nitrification tower ammonia loading and ammonia oxidized
during the redwood start-up weather operating period 78
15 Nitrification tower ammonia loading and ammonia oxidized
during the redwood cold weather operating period 80
16 Nitrification tower ammonia loading and ammonia oxidized
during the redwood warm weather operating period ....... 82
17 Nitrification tower ammonia loading and ammonia oxidized
during the redwood update warm weather and redwood update
cold weather operating periods 88
18 Percent N02/N03~N removal versus methanol to nitrate
feed ratio for Period A and Period B denitrification study . . 97
19 Filter head loss rate during Period A and Period B methanol
full-feed operating interval 100
20 Mixed media filter influent and effluent BOD5 concentration . . 106
21 Mixed media filter influent and effluent TSS concentration . . 106
22 Comparison of Dasibi meter and wet chemistry ozone/air
concentration measurements
IX
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FIGURES (Continued)
Number Page
23 Change in air pretreatment dew point with drying tower
operating time 117
24 Change in ozone production with dew point at two generator
power settings .. 118
25 Ozone generator production at various generator power
utilization 121
26 Refrigerant drier operating time at various in-let air
temperatures and an air flow rate of 79 cu m/hr (47 scfm) ... 124
27 Measured power utilization for the existing UTSD ozone
generation system 126
28 Comparison of theoretical and actual UTSD ozone generation
system power utilization .... 129
29 Schematic design of dew point cup and dew point measuring
device 131
30 Activated Sludge and overall plant ZOV$ removal efficiency
during the entire research project ... 153
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TABLES
Number
1 Fish Creek and Thompson River Lift Station Characteristics . . 21
2 Flow Equalization Basin Characteristics 23
3 Grit Removal System Characteristics 24
4 Aeration Basin Characteristics 26
5 Clarifier Characteristics .... 27
6 Activated Sludge Pumping Characteristics ..... 28
7 Nitrification Tower Characteristics 28
8 Mixed Media Filter Characteristics . . . 30
9 Ozone Disinfection System Characteristics 32
10 Aerobic Digester Characteristics 38
11 Pressure Roller Filter and Sludge Hauling Truck
Characteristics 39
12 Description of Analytical Procedure Implemented During the
UTSD Research Project 44
13 Analytical Schedule for the Mainstream Samples 48
14 Summary of Flow Equalization Basin Influent and Effluent
Chemical and Microbiological Quality ...... 53
15 Summary of Activated Sludge Performance for Operational
Period I and Period IV . ' 59
16 Summary of Activated Sludge Performance for Operational
Period II and Period V .............. 62
17 Summary of Activated Sludge Performance for Operational
Period III and Period VI 63
18 Summary of Nitrification System Results 67
19 Significant Events During the Plastic Start-Up Period .... 71
20 Significant Events During Plastic Cold Weather Period .... 74
21 Significant Events During Plastic Warm Weather Period .... 77
22 Significant Events During Redwood Cold Weather Period .... 81
23 Summary of Results During Redwood Warm Weather Period .... 34
24 Significant Events During Redwood Warm Weather Period .... 85
25 Significant Events During Redwood Update Cold Weather Period . 89
26 Summary of Data Collected During Period A and Period B
of the Denitrification Special Study . 94
27 Summary of Performance of Mixed Media Filtration System . . . 103
28 Summary of Comparison of Continuous Measurement Dasibi
Ozone Meter Results with Wet Chemistry Results 110
29 Effect of Dew Point and Power Setting on Ozone Production . . us
30 Potential Decrease in Ozone Dosage for Observed Changes
in Air Dew Point . 119
xi
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TABLES (Continued)
Number
31 Summary of Power Consumption for the Air Pretreatment and
Cooling Water Units 125
32 Ozone Generator Power Requirements 127
33 Total Ozone System Power Requirement at an Air Flow
of 79 cu m/hr (47 scfm) 128
34 Total Ozone System Power Requirement at an Air
Flow of 118 cu m/hr (70 scfm) 128
35 Comparative Dew Point Readings of Dew Point Cup
versus Shaw Mini Hygrometer, March 15,1979 132
36 Summary of Ozone Disinfection Performance Data for
Selected Time Periods 144
37 Sludge Concentrator Performance During Start-Up 147
38 Summary of Operation and Performance Data for 60-
Day Period 148
39 Summary of Cost Data for Sludge Dewatering 150
40 Summary of UTSD Plant Performance 152
41 Capitol CostUpper Thompson Wastewater Treatment
Plant 161
42 Annual Operating Costs - Upper Thompson Wastewater
Treatment Plant 162
xii
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ACKNOWLEDGEMENT
The grantee for this project was the Upper Thompson Sanitation District.
Mr. Giles Gere, Chairman of the Board, was the Principal Investigator for the
research effort. M & I, Inc. served as a subcontractor for the District and
acted as the technical advisor for the research efort.
Appreciation is expressed to all of the UTSD and M & I, Inc. personnel
who worked on the research effort.
UTSD Staff:
Plant Superintendent
Lab Chemist
Plant Operators
M & I, Inc. Staff:
Project Manager
Project Engineer
Project Technician
Lab Chemist:
Mr. Robert Cheney
Ms. Barbara Baldwin
Mr. Rawle Alloway
Mr. Larry Boehme
Mr. Roger Hess
Mr. Tim Hunter
Mr. Bob Tardy
- Mr. Bob Hegg
- Mr. Kerwin Rakness
-Mr. Larry DeMers
-Mr. Larry Stanton
Mr. Jan Cranor
- Mrs. Sue Martin
Appreciation is also expressed to Mr. Edwin Barth, Project Officer; Mr.
Al Venosa and Mr. Ed Opatken, EPA MERL - Cincinnati, Ohio, for their direction
and assistance regarding the research effort, and to Dr. Sumner M. Morrison,
Colorado State University, Fort Collins, Colorado, for technical advice re-
garding microbiological testing.
xiii
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SECTION 1
INTRODUCTION
The Upper Thompson Sanitation District (UTSD) Wastewater Treatment Plant
is located near the mountain community of Estes Park, Colorado. Estes Park is
the gateway city to the east entrance of the Rocky Mountain National Park and
as such is highly tourist oriented. The rivers in the area are scenic and are
used for many recreational purposes, including trout fishing. In an effort to
protect the uses of the Big Thompson River and also to protect the tourist
industry of the area, the Upper Thompson Sanitation District was formed to
provide wastewater treatment services to the area surrounding the Town of
Estes Park. To provide these services a new wastewater treatment plant and
new collection sewers and interceptors were constructed. The new plant incor-
porated: flow equalization, activated sludge, fixed film nitrification, mixed
media filtration and ozone disinfection. The inclusion of this variety of
processes at one plant prompted the United States Environmental Protection
Agency (U.S. EPA) to fund a research grant to evaluate the performance, cost
and design features of the facility. Data collection for the research project
was conducted over a two year period. This report discusses the findings of
the research effort.
The UTSD plant design flow rate was 5,680 cu m/day (1.5 mgd). However,
the activated sludge, nitrification and filtration processes were designed
with multiple components, and therefore, through separate use of these compo-
nents, design loading rates could be achieved at flow rates less than the
total plant design. Initially, the wastewater flow rate from the newly con-
structed UTSD collection system was not expected to achieve desired flows for
the research effort, even if only half of the process components were used.
Therefore, as part of the research project, a tie-line between the UTSD
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collection system and the collection system from another District serving the
Town of Estes Park was installed. Supplemental flow from the Estes Park Sani-
tation District was used to achieve desired flow rates during the research
evaluation period.
Two different types of media were evaluated for the fixed film nitrifica-
tion process, namely redwood media and plastic "dumped" media. These media
were evaluated during winter months to determine the effect of temperature on
the nitrification process. Ozone was used at the UTSD for disinfection. The
ozone system was one of the first full-scale wastewater ozone disinfection
systems in the United States. Several "state of the art" problems were en-
countered and continuous operation was not achieved during the data collection
phase of the research project. Some system modifictaions were necessary to
achieve continuous operation and others were indicated to achieve a more cost-
effective operation. The difficulties encountered during system operation are
presented in this report and conclusions are made concerning various aspects
of an ozone system1s operation, maintenance and design.
The UTSD plant, interceptor, and collection systems were new and were
started-up only 3 months before the research project was initiated. Plant
start-up problems were encountered which were compounded by a major flood (Big
Thompson Flood Disaster - July 1976 [1]) that washed-out a major interceptor
line that served the plant (Thompson River Interceptor). Considerable time
and effort were expended to recover from the effects of the flood and from a
variety of plant start-up problems. As an example, lower than desired plant
flow rates occurred during the first summer of data collection due to a
reduced tourist trade in the community after the flood.
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SECTION 2
PURPOSE AND SCOPE
There were several objectives of the UTSD research project. A major
objective was to evaluate the overall performance, cost and design aspects of
the UTSD advanced waste treatment facility. Additionally, operating costs,
maintenance considerations and costs, and design related considerations were
documented and evaluated for each unit process. Evaluation of individual unit
processes included several special aspects. Two different media materials
were utilized in the nitrification tower: redwood slat and plastic "dumped"
media. Each media type was operated for approximately one year during the
data collection phase of the research effort. The project also involved a
special study to evaluate denitrification performance using the mixed media
filters (not an original design capability). Methanol was added as the carbon
source for the denitrification process, and performance, maintenance and
design aspects regarding denitrification operation using the mixed media
filters was evaluated.
The time period for the evaluation of the various processes ranged from
two months to two years, with the evaluation of some processes overlapping
that of others. The wastewater flow that was treated was all the flow from
the UTSD collection system as normally received, plus some of the flow from
the Estes Park Sanitation District collection system. The intent was to
achieve a wastewater flow rate that would allow most of the processes to be
evaluated at design flow conditions (i.e., accomplished by taking some of the
multiple components out of service).
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SECTION 3
CONCLUSIONS
The flow equalization basin provided very satisfactory hydraulic
dampening of the flow received at the UTSD wastewater treatment
facility.
A. Daily average flows ranged from 15 percent to 67 percent of the
5,680 cum/day (1.5 mgd) plant design value, and no problems were
encountered with sufficient basin storage capacity for flow
equalization.
B. The basin effluent pinch valve flow controller assembly control-
led the flow rate +2% from the set rate, when functioning.
1) At very low flow rates the pinch valve was severely re-
stricted and maintenance problems developed with the flow
control assembly.
2) An isolation plug valve located on the basin effluent line
was used to control flow when the pinch valve was not work-
ing, and the flow rate was controlled to a variation of +15
percent of the set rate.
2. Aeration and mixing were not provided in the original design of the
UTSD flow equalization basin, but no major operational or performance
problems were associated with this mode of operation.
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A. Fall, winter and spring basin effluent D.O. concentrations were
above 1 mg/1. Summer D.O. concentrations were below 1 mg/1, but
no odor problems were evident.
B. Relatively low wastewater temperatures and/ or immediate removal
of settleable solids from the flow equalization basin were felt
to be contributing factors to the absence of odor problems from
the flow equalization system.
C. Other than D.O. concentrations, no significant chemical or bio-
logical changes in wastewater characteristics occurred within the
flow equalization basin.
D. A J.2 cm to 2.5 cm (1/2 in. to 1 in.) grease build-up occurred on
the basin walls. Periodic cleaning prevented further build-up
and also prevented odor problems from developing.
3. The aerated grit, removal proces consistently performed in a satis-
factory manner.
4. The activated sludge process experienced extreme variations in
hydraulic and organic loading, and variable effluent BOD5, TSS, and
~N concentrations occurred.
A. The wastewater flow rate and 6005 load during the project aver-
aged less than design (i.e. design was 2840 cum/day (0.75 mgd))
with one half of the activated sludge units in service , but
reached a level much greater than design during the summer
tourist season.
1) Flow averaged 65 percent of design, but reached levels of
134% of design values. The 6005 loading averaged 60 per-
cent and reached levels of 228 percent of design values.
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2) High flow and BOD5 loadings during the summer tourist sea-
son of the year (3 months), degraded activated sludge ef-
fluent quality.
B. Low flow and BOD5 loadings occurred during the fall, winter and
spring seasons of the year (9-months), and nitrification occurred
in the activated sludge process during a portion of that time.
1) During this period, BOD5 loading averaged 50 percent of
design.
2) Extensive ammonia oxidation occurred during the fall until
the Christmas holiday tourist season.
3) Ammonia oxidation abruptly stopped when the BOD5 load in
creased by 140 percent during the one-week Christmas holiday
season of 1976 and 1977.
4) Ammonia oxidation did not re-occur after the Christmas holi-
day flows subsided, probably due to the low temperature of
the wastewater (4-5°C).
5) Very low aeration basin biomass concentration was implemented
during the fall of 1976 to discourage nitrification. No con-
trol over aeration basin dissolved oxygen concentration was
exercised.
a) MLVSS concentration was 920 mg/1.
b) Extensive nitrification was not eliminated.
c) BOD5 removal efficiency was 76 percent.
6) Higher aeration basin biomass concentration was implemented
during the fall of 1977 to improve BOD5 removal. No con-
trol over aeration basin dissolved oxygen concentration was
exercised.
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a) MLVSS concentration was 2830 mg/1.
b) Extensive nitrification occurred.
c) BODg removal efficiency improved to 88%.
5. The fixed-film nitrification process experienced extreme fluctuations
in ammonia loading and wastewater temperature, and variable ammonia
oxidation occurred. Each media type (redwood and plastic dumped) was
operated under a start-up, cold weather and warm weather period.
A. For both media types the volume (one side of tower) was identi-
cal at 386 cu m (13S780 cu ft). Specific surface area for the
plastic dumped media was 89 sq m/cu m (27 sq ft/cu ft) and for
the redwood 46 sq m/cu m (14 sq ft/cu ft).
B. Acclimation of nitrifying organisms during the start-up periods
for both media types was severely limited because of low ammonia
loading to the tower (activated sludge system was nitrifying).
C. Cold weather operation for both media types included an abrupt
increase in the ammonia loading to the tower following the
Christmas holidays. Different oxidation capabilities were noted
for each media type, but different operating procedures also
occurred.
1) Overall oxidation performance during cold weather operation
for both media types averaged 25 percent for the redwood
media and 30 percent for the plastic media, but good pre-
winter start-up conditions did not exist.
2) Plastic media NH^N oxidation averaged 3.6 kg/day
(8 Ib/day) and reached a maximum oxidation of 6.8 kg/day
(15 Ib/day). The tower recirculation ratio (R/Q) was rela-
tively low at 0.74.
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3) Redwood media NH^-N oxidation averaged 5.9 kg/day (13
Ib/day) and reached a maximum oxidation of 9.5 kg/day (21
Ib/day). The tower R/Q ratio was 2.2.
D. Warm weather operation for both media types included very high
ammonia loadings (166 percent design), and different oxidation
capabilities were noted for each media type. Also, different
operating characteristics were observed.
1) Plastic media oxidation capability initially increased rapid-
ly during warm weather, and reached a maximum oxidation rate
of 36 kg/day (80 Ib/day) or about 40 percent of the total
~N loading. The R/Q ratio was 0.74.
2) Redwood media oxidation capability responded more slowly, and
reached a maximum oxidation rate of 23 kg/day (50 Ib/day)
which was also about 40 percent of the total NH^-N loading.
The R/Q ratio was 0.77.
3) Both media types appear to achieve a maximum oxidation rate
which would indicate that nitrification system design should
be based on peak daily or peak weekly values.
4) Specific area (dry media) oxidation rates corresponding to
the apparent maximum oxidation capability were:
Plastic =1.03 gm/day/sq m (0.21 Ib/day/ 1000 ft2 media
surface
Redwood =1.27 gm/day/sq m (0.26 Ib/day/ 1000 ft2 media
surface
Plastic specific area oxidation rate was 20% less than red-
wood, but the plastic media had 52% more total media surface
area [i.e. 89 sq m/cu m (27 ft2/ft3) versus 46 sq m/cu m
(14 ft2/ft3)].
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5) Excessive solids sloughing from the nitrification tower im-
mediately plugged the mixed media filters and occurred with
both media types.
a) The plastic media experienced relatively frequent
(weekly) excessive solids sloughing conditions.
b) The redwood media experienced limited (monthly) excessive
solids sloughing, and not to the extreme that was experi-
enced with the plastic media.
E. Important, updated information concerning redwood cold weather
tower performance was developed after the data collection phase
of the research project was over, and when better pre-cold
weather tower start-up conditions were experienced.
1) Dissolved oxygen control in the activated sludge aeration
basin was used to inhibit nitrification which allowed higher
ammonia loadings to the nitrification tower.
2) An average 94 percent ammonia oxidation occurred in the fall
of 1978 when the tower loading was 26 gm/day/cu m (1.6
lb/day/1000 ft3) or 24 percent of design load.
3) Some increase in ammonia oxidation occurred when the 1-week
Christmas holiday ammonia load reached an average 39 kg/day
(85 Ib/day) or 91 percent of design.
a) Higher levels of ammonia oxidation were achieved during
this higher loading period, but the percent of incoming
ammonia oxidized decreased to a low of 42 percent.
b) Acclimation of the tower to an expected higher loading
may be necessary through artificially feeding ammonia by
chemical addition methods prior to receipt of the load.
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4) Subsequent to the Christmas holiday season and during cold
weather operation, ammonia load dropped to pre-holiday
levels. Ammonia oxidation decreased from 13.6 kg/day to 7.3
kg/day (30 Ib/day to 16 Ib/day), while tower effluent waste-
water temperature varied from 1°C to 4°C. The tower R/Q
ratio was similar to te previous winter at 2.0, and the indi-
cation was that a significant cold weather effect on nitrifi-
cation performance occurred.
F. Bench tests indicated that lower temperature and low pH signifi-
cantly reduced the rate of ammonia oxidation, but given suffi-
cient time complete nitrification always occurred.
1) Lower nitrification rates are probably experienced at the
UTSD Plant because of low winter time wastewater temperature
(1°C to 4°C) and overall lower wastewater pH and alkalinity
(typically less than 6.5 and 100 mg/1, respectively).
2) Additional time (i.e. more tower media by simultaneouly
placing into service both towers) and/or higher pH (i.e.
alkalinity addition) may be necessary to consistently achieve
high levels of ammonia removal under present loading condi-
tions at the UTSD facility.
G. Better ammonia oxidation capability for both media types was
associated with a higher R/Q ratio (i.e. greater than 2 rather
than less than 1), although an optimum R/Q ratio was not deter-
mined.
6. Denitrification capability was the subject of a special study and
commenced when methanol was added to the influent to the mixed media
filters. Extensive filter plugging due to biological growth forced
the study to be halted.
10
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A. An acclimation time of 7 days was required for the system to
reach full NC^/NOg-N removal potentional.
1) Wastewater temperature was about 10°C..
2) Acclimation time excludes the time when the amount of metha-
nol added was less than the D.O. requirement of the waste-
water.
B. To achieve 90 percent NC^/NOg-N removal, the methanol to
nitrate (M/N) ratio was about 4.4.
C. Extensive filter plugging (i.e. backwashing required every 2-3
hours) occurred within 2-3 weeks and caused the study to be
halted.
7. The mixed media filter process worked well to polish the nitrifica-
tion tower effluent, but had to be bypassed when extensive sloughing
of solids from the tower occurred.
A. An average 65 percent to 75 percent reduction in the BOD^, TSS,
and turbidity values occurred. Respective effluent concentrations
were 10 mg/1, 6 mg/1 and 2.1 NTU, excluding the times when the
filter was bypassed because of plugging problems due to tower
sloughing.
B. The tower's excessive solids sloughing caused the filter to plug
within 10 minutes, and forced the filters to be bypassed until
sloughing ceased.
8. The ozone disinfection process was the subject of a special study.
Several state of the art problems occurred which hindered continuous
operation, but important information was developed regarding system
operation, maintenance and design as follows:
11
-------
A. The "Dasibi Meter" continuous measurement ozone concentration
meter readings correlated well with wet chemistry results, after
the meter was properly set up and calibrated.
1) Ozone and purge air flow to the meter was controlled at
2 1/min.
2) The meter span setting was adjusted based on wet-chemistry
results.
B. The ozone generator periodically "flooded" and was damaged due to
malfunctions within the air pretreatment system.
1) A cobaltous chloride color changing indicator that was pro-
vided to show an increase in air dew point was not sensitive
to gradual changes, and potential problems associated with
dew point could not be detected until far along.
2) A dew point meter was more sensitive to gradual changes in
dew point, but "flooding" still occurred when the meter was
monitored only once per day.
3) A dew point meter with associated high dew point level alarm
and/or automatic system shutdown would substantially reduce
generator "flooding" potential.
4) The dew point meter should be checked against a dew point cup
measuring instrument to verify meter accuracy and/or properly
set the high dew point level alarm.
C. The air pretreatment refrigerant drier required special main-
tenance considerations.
12'
-------
1) The drier voltage of 440 volts was compatible with the volt-
age of the ozone generator, but required special order parts
because 220 volt refrigeration units were more common in the
community,)
2) Repairs to the refrigerant drier were quite technical and had
to be completed by an experienced repair man who had special
equipment..
D. , More information should be developed by ozone equipment manufac-
turers on ozone production versus dew point levels over the en-
tire ozone generator operation range, to provide design engineers
and plant operators with a better basis for ozone system design
and operation*
E. Ozone production of the UTSD ozone generators was not signifi-
cantly lower at air flow rates of 79 cu m/hr (47 scfm) as opposed
to air flow rates of 118 cu m/hr (70 scfm).
F. Ozone generation system power utilization at the UTSD plant Was
greater at lower ozone production levels due to the relatively
constant power requirements of the air pretreatment unit, and
caused inefficient power usage under current operating condi-
tions.
1) Total power utilization varied from about 55 kWh/kg
(25 kWh/lb) at production levels of 0.32 kg/hr (17 Ib/day) to
33 kWh/kg (15 kWh/lb) at production levels of 1.08 kg/hr
(57 Ib/day).
2) Lower ozone production levels of 0.32 kg/hr (17 Ib/day) are
usually sufficient at the UTSD plant for current wastewater
flow rates and ozone dosage requirements, thus the least ef-
ficient power utilization values presently exist.
13
-------
3) More efficient power utilization values over the entire range
of ozone generation system operation would improve system
power consumption and cost at lower than design wastewater
flow rates and ozone dosage requirements, and should be con-
sidered for all ozone system designs*
G. Contact basin off-gas, ozone discharge and other sources of ozone
leakage have caused excessively high ambient ozone concentrations
in and around the plant area, and, has required that several sys-
tem design modifications be made.
1) The contact basin had to be totally covered and sealed.
2) The off-gas exhaust system was redesigned.
3) The basin baffles and scum skimmers were modified.
4) The unplastized polyvinyl chloride (UPVC) ozone piping was
replaced with stainless steel piping.
5) The ozone off-gas must be destroyed. A heat/catalyst ozone
destruct unit was designed and constructed.
H. An epoxy joint on the original ozone diffusers was not ozone
resistant and failed. As a result, new diffusers with a mechan-
ical joint had to be installed.
I. The UTSD ozone contact basin was designed for 90 percent transfer
efficiency and was based on incomplete information.
1) Ozone transfer efficiency was variable and was affected by
wastewater quality.
a) Typically, the transfer efficiency was between 50 and 60
percent.
14
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b) The transfer efficiency increased when the wastewater
quality was poor.
c) With good wastewater quality, measured ozone transfer ef-
ficiencies correlated well with ozone/liquid gas transfer
theory.
2) To ensure achieving a desired, minimum transfer efficiency,
ozone contact basin design should be based on ozone/liquid
gas transfer theory.
J. Good disinfection performance has occurred at the UTSD plant when
the ozone diffusers were in good condition and the system was
operated consecutively for several days.
1) Effluent fecal coliform concentrations averaged less than the
design requirement of 200 per 100 ml at applied ozone dosaes
of about 7 mg/1.
2) When the ozone system was operated for only a short period of
time, poor disinfection was experienced and increased ef-
fluent TSS concentrations occurred due to biological slime
growth sloughing off of the contact basin walls and piping.
9. The sludge dewatering unit functioned very satisfactorily in its
application at the UTSD plant.
A. The sludge dewatered during the research period had been con-
tained in the aerobic digester for a long period of time, and was
quite inert and difficult to dewater.
1) The VS/TS ratio was 58 percent.
2) The specific oxygen uptake rate was less than 0.5 mg/hr/gm
VSS.
15
-------
B. A 60-day dewatering test was conducted with the following
results:
1) The total amount of sludge dewatered during the 60-day period
was 18.9 metric dry tons (20.8 dry tons).
2) The dry weight percentage of solids in the dewatered sludge
was 11 percent.
3) An average production rate of 99 kg/hr (217 Ib/hr) of dry
solids occurred.
4) The polymer dosage required was 25 kg/metric ton (50 Ib/ton)
of dry sludge.
5) The polymer cost was ($62.22/ton) of dry sludge.
10. The total capital cost for the 5,680 cum/day (1.5 mgd) UTSD waste-
water treatment plant was approximately 3 million dollars. The
average operating cost at existing wastewater flow rates which were
32 percent of design and excluding research-associated costs, was
$123,064 per year or 18.6<£/cum (70.3^/1000 gal) treated.
16
-------
SECTION 4
RECOMMENDATIONS
1. Prior to the peak flow, summer tourist season, acclimation of the
activated sludge system for the increased loading should be initi-
ated.
2. Modify operation of nitrification tower as indicated by results of
the research project.
A. Place into service both sides of the tower to provide additional
contact time to overcome the nitrification rate reducing effects
of the wastewater's low temperature, and relatively low alkalin-
ity and pH values.
B. In general, maintain increased tower recirculation (R/Q) ratios
and maintain constant tower wetting rates. Continue to evaluate
performance to determine the optimum R/Q ratio.
C. Discourage ammonia oxidation in the activated sludge system, by
decreasing the D.O. concentration in the aeration basins.
3. Substantially decreased filter hydraulic loading rates should be in-
vestigated with respect to using mixed media filters for the dual
purpose of denitrification and effluent polishing.
4. Special considerations should be incorporated into ozone disinfection
system designs.
17
-------
A. Incorporate a dew point meter with a high dew point level alarm
and/or automatic system shut-down in all air pretreatment unit
designs, in order to reduce generator "flooding" potential.
B. Require ozone generator manufacturers to provide ozone production
information for various dew point levels and for the entire ozone
generator operating range, in order to provide design engineers
and plant operators with a better basis for ozone system design
and operation.
C. Provide for more efficient power utilization over the entire
range of ozone system production, in order to improve system
power consumption and operating cost at lower than design waste-
water flow rates and/or ozone dosage requirements.
D. Base the design minimum transfer efficiences for ozone disinfect-
ion system contact basins on ozone/liquid gas transfer theory, in
order to be assured of consistently good disinfection performance
as well as consistently achieve expected ozone transfer efficien-
cies.
E. Provide ozone destruction capability for the contact basin off-
gases.
F. Provide suitable grade stainless steel piping for ozone gas dis-
tribution.
18
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SECTION 5
DESCRIPTION OF FACILITIES
The Upper Thompson Sanitation District (UTSD) Wastewater Treatment Plant
was one of two plants serving the Town of Estes Park and the surrounding com-
munity. The UTSD was formed in 1971 to primarily serve the area surrounding
the Town. The Estes Park Sanitation District served the Town of Estes Park.
The wastewater treated at both facilities was mostly domestic.
The UTSD treatment plant, collection lines, and a portion of the
interceptor sewers were constructed co-currently and were placed in operation
in March, 1976. Line construction in the Estes Park area was expensive and
difficult because of the rugged mountain terrain. Delayed construction of
some of the UTSD collection system was an area of concern with respect to the
volume of flow that would initially be treated at the UTSD plant during the
research project. It was desired to treat a level of flow approaching the
design loading rate of the plant. About 1,140 cu m/day (0.3 mgd) was expected
from the initial UTSD lines- Additional flow was obtained from the Estes Park
Sanitation District through a tie-line that was constructed as part of the
research project.
Wastewater flow in the Estes Park and UTSD service areas varied signifi-
cantly from summer to winter because of a high influx of tourists during the
summer months. The average winter flow at the UTSD facility during the
research project was about 1,510 cu m/day (0.40 mgd), while the average summer
flow was about 3220 cu m/day (0.85 mgd). These averages included the flow
from the Estes Park tie-line. The overall average plant flow during the
19
-------
project was 1,930 cu in/day (0.51 mgd), and therefore about 70 percent of the
design loading was achieved by operating one-half of the plant units.
A flow schematic for the UTSD facility is shown in Figure 1. All waste-
water was pumped to the plant from lift stations serving two river basins and
was directed to a flow equalization basin. Equalized flow was directed to the
grit chamber then to the activated sludge process. Secondary clarifier
effluent was pumped over the nitrification tower and was then directed to the
flow equalization basin. Equalized flow was directed to the grit chamber then
to the activated sludge process. Secondary clarifier effluent was pumped over
the nitrification tower and was then directed to the mixed media pressure fil-
ters. Filter effluent was disinfected in the ozone contact basin, directed
through a filter backwash water storage tank and discharged to the Big
Thompson River. All sludge produced in the plant was eventually settled in
the secondary clarifier. Waste sludge and scum was pumped to an aerobic
digester for stabilization and mass reduction* Digested sludge was dewatered
by a pressure roller filter and was hauled to a sanitary landfill. All
FISH CREEK
Plant ^1
Influent 1
1
Plant j_
Influent
XTO Saniti
Landfill
Affluent To
Big Thompson
River
Wastewater Flow
Return Sludge
U/<*»tA eiurln*
LJU How Equalization
Station *"" f~fM\k
\ Aeration ^
. - - Grit
RIVER \ Chamber ,
Lift ^Rate Controller |?|
Station
1 1 Secondary
Aerobic T L Cfarifiers J
Sludqe ^ \ /
Concentrator j x. f
Digester | | 1 | | T
iry '^' = ! ' * '
Nitrification ^E ' VJ( -^w
^. A Tower *^*"^ zrz: waste Sludge j
. . ..OyrtfV* ^nnta^t iww^i «S^,,IYI ^
Tdiik i
Pressure Filters
Figure 1. Plant flow schematic diagram of the Upper Thompson
Sanitation District Wastewater Treatment Plant.
20
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internal side stream flows were directed back to the Thompson River Lift
Station. A well equipped laboratory was provided for process evaluations.
Due to the elevation of the UTSD facility (2,290m (7,500 ft) above sea level),
all treatment units except the nitrification tower were covered for protection
from the weather as well as for aesthetic purposes. The nitrification tower
was open to the atmosphere to allow for oxygen transfer. About 0.91 m (3 ft)
of freeboard above the tower media provided for some weather protection.
RAW WASTEWATER PUMPING - LIFT STATIONS
The UTSD collection system served two drainage basins in the Estes Park
area, Fish Creek and Big Thompson. The collection system in the Big Thompson
basin is the bigger of the two, and during the research project about 90 per-
cent of the total plant flow was received from this basin. All wastewater
that was collected from both systems was pumped to the treatment plant. The
Thompson River lift station was located at the plant site and the Fish Creek
lift station about one-half mile from the plant.
The lift stations consisted of a wet-well, dry-well, pumps and a comminu-
tor with bar screen by-pass. The characteristics of each lift station is
shown in Table 1.
TABLE 1. FISH CREEK AND THOMPSON RIVER LIFT STATION CHARACTERISTICS
Item
Description
Fish Creek Lift Station
Wet-Well Capacity
Pumps
Number
Capacity (each)
Communitor
Number
Capacity
8,250 gal
3 - 40 hp each
900 gpm
1
4.0 mgd
(continued)
21
-------
TABLE 1. (Continued)
Item
Description
Thompson River Lift Station
Wet-Well Capacity
Pumps
Number
Capacity (each)
Comminutor
Number
Capacity
9,430 gal
3 25 hp each
1,350 gpm
1
7.4 mgd
gal x 3.785 = 1; gpm x 0.0631 = I/sec; mgd x 3785 = cu m/day; hp x 0.746 = kw
FLOW EQUALIZATION
Flow from both lift stations was directed to the flow equalization basin.
Effluent flow rates from the basin were then controlled to provide a consis-
tent flow rate to the downstream unit processes. The flow equalization system
was constructed to dampen the highly variable daily flow rate conditions
expected and to facilitate optimum performance of the downstream processes in
order to produce a consistently high quality effluent.
1
TO
CHAMBER
BASIN OVERFLOW
TO
GRIT CHAMBER
TO
KAMBER
t ,f
FLOW EQUALIZATION
BASIN WITH BOTTOM
SCRAPER
<\
\
ISOLATION VALVES^
y M r^ i_i r^
/ PINCH ^-MAGNETIC
/ VALVE FLOWMETER
^
INFLUENT VALVES
^
1
^DRAIN LINE
/ VALVE
k i
r
)
BYPASS VALVE^j
'; BYPASS VALVE
. 1
^THOMPSON LIFT ^
STATION INFLUENT
,FISH CREEK
LIFT STATION
INFLUENT
EQUALIZATION BASIN
EFFLUENT
Figure 2. Equalization basin flow schematic diagram.
22
-------
The major components of the flow equalization system include the equali-
zation basin, which was equipped with a scraper' mechanism and a water level
indicator-recorder; a magnetic flow meter with inputs to a flow indicator-
recorder-totalizer and to the flow control system; and a modulating pinch
valve complete with actuator and automatic control system. A flow diagram
showing the piping location and valves is shown in Figure 2. The basin char-
acteristics are shown in Table 2.
TABLE 2. FLOW EQUALIZATION BASIN CHARACTERISTICS
Characteristic
Description
Shape
Sidewater depth
Capacity of sloped area
Capacity of rectangular area
Total storage capacity
Scraper Mechanism - corner sweep
Rectangular with sloped bottom
12 ft
520 gal
324,900 gal
325,400 gal
0.5 hp
ft x 0.305 = m; gal x 3.785 = 1; hp x 0.746 = kW
Equalized flow was obtained by means of a pinch valve assembly, located
on the effluent line, which was operated and controlled by a combined elec-
tronic/pneumatic system that utilized a flow signal from a magnetic flow
meter. Once a desired flow rate was obtained, the pinch valve opened and
closed as necessary to compensate for an increase or decrease in the level of
the basin. As the level increased due to a higher basin influent flow rate,
the pinch valve closed to compensate for the increased head which would tend
to increase flow above the desired rate. Conversely, as the basin level de-
creased due to a lower basin influent flow rate, the pinch valve opened to
compensate for the decreased head which would tend to decrease flow below the
desired rate. The operation was completely automatic, and once a flow rate is
set it is maintained unless the basin emptied. The .set flow rate could be
exceeded if the rate was set to low and the basin filled and overflowed.
No aeration or mixing of the contents of the basin was provided. It was
expected that septicity conditions in the basin would not occur. However,
23
-------
provisions were made to add a jet aeration mixing system if septicity became a
problem. Without mixing, settleable organic material which entered the basin
was scraped to the hopper discharge and immediately removed. As such the flow
equalization basin did not provide for equalization of the plant loading in
the form of settleable solids.
The flow equalization system included the plant influent flow monitoring
system. A magnetic flowmeter was used to provide flow information as well as
control of the pinch valve. However, this meter was bypassed if the flow to
the equalization basin was bypassed to the aerated grit chamber. Under this
condition plant flow could be measured using the mixed media filter effluent
flow measuring instruments.
GRIT REMOVAL
The major components of the grit chamber include the grit basin, the air
diffusion system and the classification equipment. The grit system character-
istics are shown in Table 3.
TABLE 3. GRIT REMOVAL SYSTEM CHARACTERISTICS
Characteristic
Description
Shape
Volume
Settling Velocity
Grit Quality
Compressor
Rectangular with hoppered bottom
18,750 gal
1 ft/sec.
80 to 100 mesh
15 hp
gal x 3.785 - 1; ft/sec x 0.3048 = m/sec; hp x 0.746 = kW
Flow from the equalization basin, flow bypassed around the equalization
basin, or flow that overflowed the equalization basin was direcetd to an
aerated grit chamber where grit material was settled out and collected in the
chamber's hoppered bottom. The settled material was then pumped to a centri-
fugal classification unit where organic material that had settled in the cham-
ber was separated from the grit. The dewatered grit material was then stored
24
-------
in containers for disposal at a sanitary landfill. Air was supplied to the
grit basin to provide a method of controlling the settling velocity of the
material within the basin and to enhance grease flotation. Grease retained in
the aerated grit chamber was manually removed.
ACTIVATED SLUDGE
The major components of the activated sludge process include the aeration
system, clarification system and sludge pumping systems. A description of
each system and a discussion of the operational aspects of each system is
presented below.
Aeration System
The aeration system was comprised of the aeration basins, and oxygen
transfer and basin mixing equipment. Aeration basin mixing and oxygen trans-
fer was accomplished by a combination of mechanical mixers (fixed pier sub-
merged turbine) and a supply of compressed air. Compressed air from blowers
was discharged into the aeration basins directly beneath the submerged tur-
bines. The compressed air formed large bubbles upon release into the liquid
which were sheared into smaller bubbles and dispersed by the mixer. The
required mixing of the basin contents was supplied by the submerged turbines.
Two identical basins with a common center wall were provided. Both
basins were provided with separate influent flow control, return sludge lines,
and air supply lines. A dividing gate was located on the common wall sepa-
rating the two basins. This gate provided for flexible use of the basins.
The basins could be operated independent of one another or could be used
together in a variety of flow patterns. During the research project the gate
was closed which allowed only one basin to be used. The basin characteristics
are summarized in Table 4.
25
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TABLE 4. AERATION BASIN CHARACTERISTICS
Characteristics
Description
Aeration Basins
Number
Surface Dimensions (each)
Sidewater Depth (each)
Capacity (each)
Detention Time (No recirculation
included)
One Basin @ 0.75 mgd
Two Basins @ 1.5 mgd
Turbine Mixers
Number (per basin)
Size
Air Blowers*
Number
Capacity (each)
Size (each)
63 ft x 31 ft
17 ft
248,000 gal
7.9 hr
7.9 hr
2
25 hp
1200 scfm
75 hp
*Blowers also used for aerobic digester air supply.
ft x 0.305 « m; gal x 3.785 = 1; hp x 0.746 = kW; cfm x 0.028 = cu m/min
Clarification System
The clarification system consisted of two clarifier basins each with a
sludge collection mechanism. The clarifiers were center feed and peripheral
withdrawal units and were equipped with both a surface and bottom scraper
mechanism for removing scum and sludge, respectively. Scum was moved to a
scum hopper and pumped to the aerobic digester. Sludge was returned back to
the aeration basin or was wasted. Return sludge was withdrawn from the clari-
fier using a rapid withdrawal mechanism. Sludge to be wasted was scraped to a
sludge hopper located at the center of each clarifier and was pumped to the
aerobic digesters. The clarifier characteristics are summarized in Table 5.
26
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TABLE 5. CLARIFIER CHARACTERISTICS
Characteristic
Description
Clarifiers
Number
Diameter (each)
Surface area (each)
Sidewater depth (each)
Weir Length (each)
Capacity (each)
Overflow rate* 0.75 mgd
Weir Overflow Rate*
Hydraulic D.T.*
Waste sludge hopper
Location
Capacity
Sludge Mechanism
Type
Drive Motor
2
40 ft
1,256 sq ft
10 ft
126 ft -
98,500 gal
600 gal/day/sq ft
5,970 gpd/ft
3.2 hr.
bottom of clarifeir
100 gal ,
Combined rapid withdrawal with
bottom scrapers
0,33 hp
ft x 0.305 = m; sq ft x 0.093 = sq m; gal x 3.785 = cu m gal/day/sq ft x 0.041
= cu m/day/sq m; hp x 0.746 = kW; gal/day/ft x 0.0124 - cu m/day/m
* One basin in service @ 0.75 mgd
Sludge Pumping Systems
The activated sludge pumping system consisted of two return sludge pumps
and one waste sludge pump. The return sludge pumps were variable non-clog
centrifugal pumps and could be operated independently or together. The pump
discharge was directed to the aeration basin, but could be directed to the
aerobic digester, if desired. The return sludge flow rate was measured using
a venturi tube. Flow rates were indicated adjacent to the pumps and on the
main control panel. The waste sludge pump was a constant speed vortex pump.
The waste sludge flow rate was measured using a magnetic type flow meter and
was indicated and totalized. A summary of the characteristics of the acti-
vated sludge pumping system is shown in Table 6.
27
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TABLE 6. ACTIVATED SLUDGE PUMPING CHARACTERISTICS
Characteristics
Description
Return Sludge Pumps
Number
Type
Capacity
Return Sludge Flow Meter
Number
Type
Waste Sludge Pump
Number
Type
Capacity
Waste Sludge Metering
Number
Type
2 - 5 hp each
Variable speed non-clog centrifugal
250 - 1200 gpm
Venturi Tube
1 - 1.5 hp
Constant Speed Vortex
100 gpm
Magnetic Meter
gpm x 0.0631 <- I/sec; hp x 0.746 = kW
NITRIFICATION
Effluent from the activated sludge system was directed to a wet-well and
pumped to an attached growth nitrification tower. The tower media was origi-
nally designed to be redwood slats. However, in conjunction with the research
project the tower was divided into two equal sections and two types of media
(redwood and dumped plastic) were installed. Flow could be directed to one
side of the tower only, or to both sides depending on flow conditions. During
the research project only one side of the tower was operated at a time. A
summary of the nitrification system characteristics is shown in Table 7.
TABLE 7. NITRIFICATION TOWER CHARACTERISTICS
Characteristic
Description
Wet-Well Capacity
By-Pass
Pumps
Number
59,500 gal
Overflow to ozone contact basin
2 - 30 hp each
(continued)
28
-------
TABLE 7. (Continued)
Characteristic
Description
Type
Capacity (each)
Nitrification Tower
Media Depth
Surface Area (one side)
Volume (one side)
Hydraulic loading rate (each side)
@ 0.75 mgd and no recycle
Ammonia loading rate (each side)
@ 0.75 mgd and 15 mg/1 NH4~N
Recycle Rate (maximum)
@ 0.75 mgd and one pump
Media (Specific Surface Area)
Redwood Media
Plastic Dumped Media
Distribution System
Type
Nozzles
Variable speed non-clog
centrifugal pumps
0 - 2250 gpm
14 ft
984 sq ft
13,780 cu ft
0.53 gpm/sq ft
6.8 Ib NH/t-N/day/1000 ft3
4:1
14 sq ft/cu ft
27 sq ft/cu ft
Fixed
Vari-flow
ft x 0.305 = m; sq ft x 0.093 = sq m; cu ft x 0.028 = cu m; sq ft/cu ft x 3.28
= sq m/cu m; gal x 3.785 = 1; gpm x 0.0631 = I/sec; gpm/sq ft x 40.7 =
1/min/sq m; lb/day/1000 ft3 x 16 = sq m/cu m; hp x 0.746 = kW.
Two variable speed nonclog centrifugal pumps were used to pump activated
sludge effluent to the nitrification tower. Secondary effluent was distri-
buted over the tower surface through a fixed nozzle distribution system. The
nozzles that were originally installed had a fixed splash plate design and
poor flow distribution over the media surface occurred especially at lower
flow conditions. These splash plates were later replaced with spring loaded
splash plates (Neptune Microfloc Vari-flow nozzles) and good distribution was
obtained even with variable flow rates to the tower.
Flow through the tower was directed to a wet-well located beneath the
tower. Gravity flow from the wet well was directed to the mixed media filters
(the level of flow in the wet well served to pressurize the filters). Addi-
tionally, a controlled and measured portion of the tower flow could be
recycled back to the towers.
29
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MIXED MEDIA FILTRATION
The filtration system consisted of a chemical addition and rapid mixing
system, four pressure filter vessels, a backwash water storage basin and a
backwash wastewater storage basin. A summary of the mixed media filtration
system characteristics is shown in Table 8.
TABLE 8. MIXED MEDIA FILTER CHARACTERISTICS
Characteristic
Description
Mixed Media Filters
Number
Shape
Media Surface Area (each)
Media
Underdrains
Surface Wash (each)
Vessel Relief Valves
Loading Rate
Recommended
Actual @ .75 mgd with 2 filters
Backwash System
Backwash Pumps
Number
Type
Capacity (each)
Backwash Supply Storage Volume
Surface Wash Pump
Number
Type
Capacity
Backwash Wastewater Basin
Storage Volume
Discharge
Chemical Feed Systems
Feed Pumps (Alum)
Number
Type
Capacity
Alum Storage Volume
Cylinderical (8 ft diameter x
18 ft long)
144 sq ft (8 ft dia x 18 ft long)
Anthracite coal, sand and gravel
Perforated PVC pipe lateral
placed in support gravel
Three - six foot diameter water-
jet rotary sweep.
Air and pressure relief valves
5 gpra/sq ft
3.. 6 gpm/sq ft
2 - 40 hp each
Constant speed centrifugal
2,500 gpm
42,000 gal
1 - 15 hp
Constant speed centrigual
200 gpm
40,000 gal
Thompson River Lift Station
Diaphragm
2 to 50 gph
4,000 gal
(Continued)
30
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TABLE 8. (Continued)
Characteristic
Description
Polymer Feed Pumps
Number
Type
Capacity
Polymer Preparation
In-Line Mixer
Diaphragm
1-22 gph
Dry Polymer Mix System
1 - Walker Process Instro-Mix
sq ft x 0.093 = sq m; ft x 0.305 = mj gpm/sq ft x 40.7 = 1/min/sq m;
gpm x 5.45 = cu m/day; gal x 3.785 = 1; gph x 0.091 = cu m/day; hp x 0.746=kW.'
A coagulant aid could be added to the influent to the filters through an
in-line flash mixer. Liquid chemical storage and feed pumps and dry chemical
preparation and feed pumps were provided as part of the coagulant aid system.
Chemicals could also be added at the effluent weir of the activated sludge
aeration basins and at the nitrification tower wet well. This flexibility
allowed the chemical feed system to be used to add chemicals for phosphorus
removal and/or chemicals for alkalinity adjustment. As part of the research
project a methanol feed system was installed whereby methanol could be added
to the mixed media filter influent at the in-line mixer. The purpose of the
methanol addition was to evaluate denitrification capability using the media
of the filters to support the denitrifying organisms.
The filter backwash sjrstem was provided to release and return all parti-
cles that had been trapped in the filter media to the head of the plant. An
automatic system for initiating and controlling the backwash sequence was
provided. When the head loss through a filter reached a predetermined level,
the filter was ,taken off line, backwashed and returned to service. The back-
wash cycle could also be initiated manually by the plant operators and this
procedure was used during the pro'ject. Components of the backwash system
included the backwash water storage basin, backwash and surface wash pumps,
and the instrumentation and control equipment to operate the system.
The backwash water storage basin was located directly beneath the admin-
istrative offices, and contained ozonated plant effluent. A morning glory
31
-------
overflow weir in the basin directed plant effluent from the basin to the plant
outfall line.
Backwash wastewater from the filters was stored in a concrete storage
basin located beneath the laboratory. The discharge from the basin was
directed to the Thompson River Lift Station at a controlled rate, pumped to
the flow equalization basin and directed back through the plant.
OZONE DISINFECTION
The UTSD ozone disinfection process was one of the first full-scale ozone
wastewater disinfection processes in the United States. Several "state of the
art" problems were encountered and modifications to the original ozone system
design were necessary. In this section of the report the ozone system is des-
cribed as it was modified. The reason for and the extent of the modifications
are discussed later in the report. Ozone disinfection was an area of special
study; consequently, the following section contains a detailed description of
the disinfection system.
The ozone disinfection process consisted of two air-fed ozone generator
units and one ozone contact basin. Each generator unit was designed to pro-
vide adequate disinfection at the plant design flow rate. The second genera-
tor unit was provided for stand-by. The two units were identically con-
structed and were labeled No. 1 and No. 2. A summary of the ozone system
characteristics is presented in Table 9.
TABLE 9. OZONE DISINFECTION SYSTEM CHARACTERISTICS
Characteristic
Description
Generation System
Number
Air Pretreatment (2 units)
Components
Capacity
Compresser(15 hp each), cooler,
drying tower
78 scfm (drying tower limitation)
(Continued)
32
-------
TABLE 9. (Continued)
Characteristic
Description
Dew Point (maximum)
Generator (2 units)
Manufacturer
Type
Capacity @ 1% by weight
Dosage @ 1.5 mgd
Cooling System (1 unit)
Media
Capacity
Contact Basin
Ozone Transfer
Shape
Volume
Detention Time @ 1.5 mgd
-51°C
We Isbach
"Iron Lung"
76 Ib/day
6 mg/1
Well Water
20 gpm
Fine Bubble Tube Diffusers
Rectangular, with vertical ser-
pentine flow pattern
14,500 gal
14 min
cfm x 0.028 = cu m/min; Ib/day x 0.454 = kg/day; gpm x 0.063 = I/sec; gal x
3.785 = 1; mgd x 3785 = cu m/day; hp x 0.746 = kW.
Ozone was generated by two Welsbach air-fed units, Model CLP-68F20L. A
schematic diagram of the ozone generation equipment is shown in Figure 3.
AIR
BLEED OFF
COMPRESSOR 1
TO AIR
PRETREATMENT
r N
;
\ /
^_
REFRIGERANT
DRYER
"SEPARATOR
^
I
1
POWER
WATT-HOUR
METER
TO CONTACT
BASIN
LEFT
RIGHT
CONTROLLER"
c
GENERATOR *
E
^
-y
^^^^^
DRYING TOWERS
Figure 3. Ozone generation schematic diagram.
33
-------
Three components made up each system: generator, power supply and air pre-
^
treatment. Each generator was designed to produce 1.43 kg/hr (76 Ib/day) of
ozone at a minimum concentration of 1 percent by weight, which provided for a
maximum ozone/liquid dosage of 6 mg/1 at the plant design flow of 5,680 cu
m/day (1.5 mgd). The generators were "iron lung" tube type units each con-
taining 68 tubes. The generators were water cooled using potable well water
flowing at a rate of approximately 1.26 I/sec (20 gpm). Power was supplied to
the generator through variable voltage transformers. A controller assembly
was used to adjust the voltage from the transformer to the generator, which
controls the ozone generator output. The controller was designed for manual
or automatic adjustment. During the research project manual adjustments based
on generator amperage readings were used.
The air pretreatment components of the ozone generation system were an
air compressor, refrigerant drier and air drying towers. Air pretreatment was
designed to provide particle-free dry air with a dew point of -51°C at a pres-
sure between 41.3 k N/sq m and 103 k N/sq m (6 and 15 psig). During the
research project, the air pretreatment pressure was maintained at 51.6 k
N/sq m (7.5 psig).
Ambient air was compressed to 51.6 k N/sq m (7.5 psig) by a Nash Model L3
water ring compressor. The compressor operates at a constant speed and had an
output of about 160 cu m/hr (94 scfm). The standard conditions used through-
out this report are one atmosphere pressure and 25°C temperature. A baffle
separator was provided to separate the water and air. A bleed-off air valve
was provided downstream of the baffle separator. The bleed-off valve at this
point was determined to be necessary during the research project to enable the
air flow rate to the drying towers to be controlled to prevent overloading of
these units.
Compressed air was cooled to between 3.3°C and 5.6°C in a Zeks, Model 9J
refrigerant drier, in order to remove excess moisture in the air. The unit
was designed so that the air dew point leaving this unit did not exceed 8.9°C.
Refrigerant dried air was further dewatered to a dew point less than -51°C in
34
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a Kemp Model 100 UEA-1 absorptive drier. The drier used molecular sieves and
activated alumina as absorptive material. Dual towers were provided for con-
tinuous operation. Tower operation was cycled at 8-hour intervals to provide
regeneration of one tower while the other was in use. Each tower was rated by
the manufacturer at 131 cu m/hr (78 scfm) air flow.
The ozone contact basin was located adjacent to the mixed media filters
in the main control building. The ozone generation units were located on a
mezzanine above the contact basin. The ozone contact basin was 1.30 m (4.25
ft) wide, 11.6 m (38.0 ft) long and 3.66 m (12 ft) deep, which would give an
ozone contact time of 14 min at 5,680 cu m/day (1.5 mgd) design flow. The
first 8.22 m (27 ft) of the ozone basin was divided into nine equal sized com-
partments with U.P.V.C. baffles. The baffles were placed to allow vertical,
serpentine flow of effluent through the basin. A schematic of the contact
basin is shown in Figure 4.
BACKWASH
EiASIN
OVERFLOW
WEIR^
" COVER
PLATES)
-Q
DRAIN
6666
OZONE
DESTRUCT UNIT
CONTACT BASIN
VENT
INFLUENT
UPVC BAFFLE
OZONE DIFFUSER
Figure 4. Ozone contact basin schematic diagram.
35
-------
Treated water from the ozone basin passed over a weir and into the back-
wash water storage basin where it is used for backwashing the mixed media
filters. The ozone contact basin and the backwash water storage basin share a
common air space above their respective water surfaces due to the described
overflow weir arrangement.
The contact basin was covered with aluminum plates which were bolted in
place. Hypalon gasket material was placed beneath all joints. Additionally,
silicone sealant was used to cover all exposed joints. Ozone laden off-gas
from both the contact and backwash water storage basins was discharged through
a rpof mounted exhaust fan. The fan provided a negative pressure (about 0.64
cm of water) in each basin so as to prevent ozone leakage into the main con-
trol building and/or offices. A water spray nozzle was located in the vent
duct above the ozone basin tank cover to prevent foam from blocking the
exhaust air flow.
Ozone was injected into the effluent in the contact basin through porous
stone diffusers. The diffusers were Kullendite, Model FAO 50 as manufac-
tured by Ferro Corporation. The diffusers were located in each of the nine
baffled areas. Each diffuser was 6.4 cm (2-1/2 in) in diameter and 61 cm (24
in) long, and had an air permeability between 1.42 and 1.78 cu m/min/sq m/cm
(12 and 15 scfm/ft^/in) and a maximum pore diameter of 140 microns. Distri-
bution piping consisted of Type 304 Schedule 40 stainless steel piping with
welded and threaded joints. Distribution of ozone to each compartment was
controlled by nine individual valves. Both the diffusers and distribution
piping represented modifications of the original equipment.
Four adjustable height weir scum skimmers were located along the length
of the ozone contact basin to facilitate removal of any scum that may be
generated as a byproduct of ozonation. Scum removed by the skimmers can be
pumped to the head of the plant for recycle, or pumped to the secondary clari-
fiers.
36
-------
An ozone off-gas destruct unit is shown in Figure 4. The unit was a
heat/catalyst ozone destruct system which was installed after the data collec-
tion phase of the project was completed. The ozone destruct unit represented
a major design modification, which will be further discussed. The ozone
destruct system was designed by Emery Industries and consisted of an off-gas
heating unit, a proprietary catalyst, and an exhaust fan. The system design
inlet flow rate was 5.6 cu m/min (200 scfm) and the inlet temperature was 5°C.
The heating system was capable of elevating the temperature of this volume of
the off-gas to a maximum value of 149°C (300°F). At this maximum temperature
the heat-catalyst system was designed to discharge a very low maximum residual
ozone concentration of 0.1 ppm (vol) when the heat/catalyst inlet ozone con-
centration was 3,000 ppm (wt) or lower. At this heating requirement, the
system was designed with a variable heating system and normal system operation
called for an operating temperature of 71°C (160°F). At this temperature the
system, was designed to discharge a maximum residual ozone concentration of
1.0 ppm (vol) when the inlet ozone concentration was 3,000 ppm (wt) or lower.
At this normal operation heating requirement, the power consumption for the
system would be 7.5 kW for heating plus 0.5 kW for the exhaust fan.
SLUDGE HANDLING
t
The sludge handling system consisted of two aerobic digesters, one pres-
sure roller filter, and one sludge hauling vehicle. The digesters were used
for sludge holding, digestion and partial thickening. The pressure roller
filter was used for further sludge dewatering prior to ultimate disposal. The
sludge hauling truck was used to transport the thickened sludge to the ulti-
mate disposal site.
Sludge Treatment
Sludge treatment was provided by aerobic digesters, which included the
digester basins, oxygen transfer and basin mixing, supernatant removal and
sludge removal systems. A summary of the characteristics of the aerobic
digestion system is presented in Table 10.
37
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TABLE 10. AEROBIC DIGESTER CHARACTERISTICS
Characteristic
Description
Aerobic Digester Basins
Number
Surface Dimensions (each)
Sidewater Depth (each)
Capacity (each)
Turbine Mixers
Number (per basin)
Size
Air Blowers*
Number
Capacity (each)
Size
63 ft x 31 ft
17 ft
246,000 gal
2
25 hp
1200 scfm
75 hp
ft x 0.035 « m; gal x 3.785 =1; hp x 0.746 = kW; cfm x 0.028 = cu m/min
*Blowers also used for aeration basin oxygen supply.
The aerobic digesters received waste sludge and scum from the secondary
clarifiers. Two digester basins were provided, and could be operated in
series or in parallel. Oxygen supply and basin mixing were provided by a sub-
merged turbine aeration system, which were identical to the system provided in
the activated sludge aeration basins.
Each basin had supernatant and sludge removal capability. Supernatant
removal was used to partially thicken the digested sludge and to improve the
performance of the digestion process and the sludge dewatering pressure roller
filter. Supernatant flow was directed to the Thompson River Lift Station
where it was pumped to the flow equalization basin and recycled back through
the plant. The sludge removal piping was located beneath the floor of the
basins and was used to transport sludge to the pressure roller filter. These
lines could also be used to drain the basin contents back to the Thompson
River Lift Station.
Sludge Dewatering and Disposal
Digested sludge was dewatered prior to ultimate disposal with a Smith and
Loveless Model 40-1 pressure roller filter. The pressure roller filter system
38
-------
consisted of a sludge conditioning unit (sludge feed pump, polymer mix tank
and metering pump, flash mixer and flocculator), and a sludge dewatering unit
(primary and secondary screens, spray cleaning jets, transition chutes, and
three double pressure rollers), and a sludge transportation unit (conveyer
belt from dewatering unit to sludge hauling vehicle). Dewatered sludge was
hauled to the disposal site with a covered dump truck, which had a modified
dump body so that it was watertight. A summary of the characteristics of the
pressure roller filter and sludge hauling truck is given in Table 11.
TABLE 11. PRESSURE ROLLER FILTER AND SLUDGE HAULING TRUCK CHARACTERISTICS
Characteristic
Description
Sludge Conditioning Equipment
Sludge Feed Pump
Type
Capacity
Polymer Mix Tank
Type
Volume
Polymer Feed Pump
Type
Capacity
Flash Mix
Tank Size
Mixer Drive
Flocculator
Tank Size
Flow Pattern
Paddle Drive
Sludge Dewatering
Primary Stage
Screen Type
Screen Size
Secondary Stage
Screen Type
Screen Size
Pressure Rollers
Transportation Stage
Conveyer Belt Size
Sludge Hauling
Vehicle Type
Capacity
Variable speed, diaphragm pump
0 - 40 gpm
Fiberglass
250 gal
Variable speed gear pump
0-1.5 gpm
12 in Dia. x 42 in long (21 gal)
0.5 hp (variable speed)
48 in x 24 in x 46 in (230 gal)
Horizontal Serpentine Flow
0.5 hp (variable speed)
Endless, monofilament open mesh
40 in wide x 46 in long
Endless, monofilament open mesh
40 in wide x 48 in long
3 sets with variable pressure
adjustment
16 in wide' x 24 ft long
Covered watertight dump truck
7 cu yd
gpm x 0.063 = I/sec; gal x 3.785
0.305 = m; cu yd x 0.765 = cu m.
1; in x 2.54 = cm; hp x 0.746 = kW; ft x
39
-------
Sludge from the digester was pumped at a controlled rate to the sludge
conditioning system. Polymer addition involved the injection of a stream of
polymer solution into the sludge feed line. The mixture of polymer and sludge
then entered a flash mixer where rapid mixing dispersed the polymer throughout
the sludge particles. A flocculator followed the flash mixer, and the mechan-
ism provided a plug flow condition together with gentle agitation. The condi-
tioned sludge then entered the primary stage of the sludge dewatering segment
of the system.
The primary stage of the dewatering unit consisted of an endless, hori-
zontal, open-mesh screen which traveled around two rollers. A third roller
was located midway between the two end rollers and resulted in a slightly ele-
vated portion of the screen. As the conditioned sludge moved onto the primary
screen, the free water drained away and the flocculated sludge particles were
trapped on the screen. Further release of water was obtained by passing the
sludge over the elevated roller. At the end of the primary stage the sludge
was transferred to the secondary stage of the dewatering unit. A jet spray
bar located above the returning portion of the primary screen cleaned
entrapped sludge particles from the screen mesh. The filtrate from the pri-
mary stage, which consisted of the released water, non-captured sludge, and
spray water, collected in a drain located below the primary screen.
Sludge from the primary stage was transferred to the secondary stage
where it was deposited onto a screen identical to the primary screen. Three
sets of pressure rollers were located along the secondary screen, each set
having one roller above and one roller below the upper portion of the screen.
As the sludge moved from one set of rollers to the next, progressively higher
pressure was applied to the sludge. With this arrangement water was squeezed
from the sludge three times before leaving the dewatering unit. The resulting
sludge cake dropped to a conveyor system where it was transported to a truck.
Similar to the primary screen, the secondary screen had a jet spray bar to
clean, the sludge particles trapped in the screen mesh. Released water, non-
captured sludge, and spray water from the secondary stage were collected in a
40
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drain and together with the primary filtrate flowed back to the Thompson River
Lift Station then back through the plant.
The conveyer system that transported dewatered sludge to the sludge
hauling truck was equipped with a scraper that cleaned the conveyer belt prior
to its return cycle. The sludge hauling truck was a covered dump truck that
was modified so that the tailgate was watertight. Also, special gate latch
hooks were provided to prevent the gate from accidently opening during trans-
port to the disposl site. Two sludge disposal sites were utilized, the com-
munity sanitary landfill and community park areas that were being reclaimed.
MISCELLANEOUS FACILITIES
Stand-by Power
The plant and lift stations were provided three different power sources:
Big Thompson loop power and South loop via the Estes Park substation, and two
stand-by generators (one at the plant and one at the Fish Creek Lift Station).
The power supply automatically switched to the other power loop when one of
the two power loops failed. Each power loop could supply the plant with its
full operating power requirement.. If both power loops fail, the stand-by
generators automatically start. The plant standby generator was a 625 kva
diesel fuel powered unit and provided the plant with only part of its full
power requirement. It had the capability of operating the Thompson River Lift
Station, one aeration blower, the return sludge pumps, the ozone generation
system, and other supporting equipment to provide a minimum of secondary
treatment and disinfection. The Fish Creek Lift Station stand-by generator
was a 125 kva diesel fuel powered unit and could operate all the pumps in the
lift station.
Plant Laboratory
The laboratory at the UTSD plant was expanded and equipped to conduct all
standard microbiological and wet chemistry analyses conducted during the
41
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research effort. The analyses that were conducted are summarized in Appen-
dices A through F. The laboratory was located in the main plant building in a
9.9 m (32.5 ft) by 4.1 m (13.5 ft) room with total counter length of 13.7 m
(45 ft).
Potable and Non-Potable Water Supply
The plant was designed with its own potable water supply system. The
system included a shallow well located near the plant site, a chlorination
unit, a pressurized storage tank, and a pumping system. The well was located
near the Thompson River Lift Station and the chlorination unit and pumping
system was located in the lift station dry-well. Potable water was supplied
to the plant laboratory, restrooms, ozone generation system, filter control
system, and raw sewage pumps. The system was capable of supplying 2.5 I/sec
(40 gpm) of potable water at 413 k N/sq m (60 psig) pressure.
The plant non-potable water supply system was ozone contact basin ef-
fluent, and was used for plant washdown and outside irrigation. The system
consisted of a pressurized storage tank and a pumping system. The system is
capable of supplying 6.3 I/sec (100 gpm) of non-potable at 461 k N/sq m (67
psig) pressure.
42
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SECTION 6
DATA COLLECTION PROCEDURES
To evaluate the individual unit processes at the UTSD facility an exten-
sive sample collection and analysis schedule was implemented. However, the
laboratory was only partially functional from plant start-up in March 1976
until October, 1976, due to equipment delivery delays and other start-up
problems. A limited analytical schedule was followed using the M & 1, Inc.
laboratory located in Fort Collins, Colorado until the full analytical sched-
ule was implemented at the UTSD laboratory. As closely as possible a similar
sample collection and analysis schedule was maintained throughout the project.
However, some modifications were necessary in order to allow for special test-
ing to be completed on various unit processes and to conduct quality control
checks.
Analytical Procedures and Quality Control
The procedures used for data analysis during the research project were
Standard Methods and/or EPA procedures with minor modifications. A listing
of the specific procedures for each analysis and description of the modifica-
tions used is presented in Table 12.
43
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TABLE 12. DESCRIPTION OF ANALYTICAL PROCEDURES IMPLEMENTED DURING
RESEARCH PROJECT
Analysis
Procedure
Comment
BOD5
COD
TSS
TKN
NH4-N
Std. Methods, p. 543*
Std. Methods, P.550-554,
Std. Methods, p.94.
EPA Manual, p.159-163**
EPA Manual, p.175-181
N02&N03-N EPA Manual, p.201-206
Total P EPA Manual, p.251-255
Alkalinity Std.Methods, p.278-282
PH
Samples not seeded; in-bottle dilu-
tions made, 2 dilutions per sample run;
same bottle initial and final D.O.'s
made using an electronic D.O. meter.
20 ml aliquots used; standards of
potassium hydrogen phthalate run with
each set.
Gooch crucibles and glass fiber filters
used.
Micro procedure used; titrimetric or
Nessler finish used as necessary; Stan-
dard solutions of glutamic acid run
with each set.
Micro procedure used; titrimetric or
Nessler finish used as necessary; Stan-
dard solutions of ammonium chloride run
with each set.
10.0 mg/1 of N03~N used instead
of 1.0 mg/1 to achieve complete activa-
tion of cadmium-copper column. This
alteration assured constant color de-
velopment. Standard solutions run with
each set.
Persulfate digestion used; digested
samples neutralized with sodium hydrox-
ide to phenophthalien pink color (not
to metered pH 7) then 5N sulfuric acid
added until pink color dissipated;
standard solutions run with each set.
Potentiometric titration to pH 4.5;
Tris (Hydroxymethyl) aminomethane used
to standardize sulfuric acid titrant.
Orion 701 digital pH meter, calibrated
at pH 4 and pH 7 before each set of
measurements.
(continued)
44
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TABLE 12. (Continued)
Analysis
Procedure
Comment
D.O.
Coliform
Std.Methods, p.922-925;
928-935 and 937-939
YSI Model 54RC electronic oxygen meter
with field and BOD probe air calibrated
prior to each set of measurements.
MPN analysis used on ozonated samples;
membrane filter technique used on other
samples; two or more dilutions run on
each sample.
*Standard Methods 14th ed., 1975, APHA, AWWA, WPCF.
**Methods for Chemical Analysis, 1972, Environmental Protection Agency.
The routine analytical schedule incorporated several quality control as-
pects. Routine maintenance, cleaning and calibration of all instruments was
conducted. Also, modifications were made to some equipment to reach the re-
quired performance level (i.e«, special high altitude operating pressure gauge
for the autoclave and special pretreatment of influent to the distilled water
system). Class A, borosilicate glassware was used for volumetric measurements
and was washed with lab detergent, rinsed with tap water, rinsed with dis-
tilled water and air dried; or acid cleaned, rinsed with distilled water, and
air dried. ACS reagent grade chemicals and high quality distilled water
(specific conductance less than 5 micromhos/cm) were used to make all rea-
gents, except for Nesslers reagent which was purchased commercially. Routine
duplicate analyses and standard samples, where applicable, were conducted on
at least 10% of all analyses. Special microbiological samples were analyzed
by three laboratories: the UTSD lab, the M & I lab and the Water Quality lab
at Colorado State University. The quality control checks conducted on all
duplicate, standard, and split samples indicated that satisfactory techniques
were implemented and maintained at the UTSD lab.
All raw data were developed using bench cards and calculations were double
checked before recording the results on the weekly data sheets. Weekly aver-
ages of the data were then computed and were recorded on data summary sheets.
The weekly average results for each unit process are presented in process
45
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sequence from Appendix A through Appendix F and serve as the basis for the
data evaluations made in this report.
Analytical Schedule and Sample Type and Collection Frequency
To aid in sample identification and analysis, the mainstream sampling
stations were numbered as shown in Figure 5.
FISH CREEK
LIFT STATION
CD ©
!
\
THOMPSON RIVER
LIFT STATION
FLOW EQUALIZATION
J!
ACTIVATED SLUDGE
[NITRIFICATION TOWER |
©I©
MIXED MEDIA FILTRATION
OZONE CONTACT BASIN |
BIG THOMPSON RIVER
*Note 5 - Sample when Redwood Media was used.
6 = Sample when Dumped Plastic Media was used.
7 = Sample during denitrification special study.
8 = Sample during normal operation.
Figure 5. Mainstream sampling stations during the research project.
46
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During the course of the research project some sample points were deleted
and others were activated during the different evaluation periods. Sample
station No. 2 (Fish Creek Lift Station) was not sampled because of its remote
location and because the flow from this lift station represented less than 10%
of the flow to the plant. Sample station No. 5 (Nitrification tower effluent
- Redwood media) and sample station No. 6 (Nitrification tower effluent -
Dumped media) were used correspondingly when each of the different media types
were evaluated. Sample station No. 7 (Mixed-media Filter - Denitrification
effluent) was activated only during the methanol addition/denitrification
phase of the research effort. During all other times of the project sample
station No. 8 (Mixed media filter effluent) was used. Sample station No. 3
(Flow equalization basin effluent), station No. 4 (Activated sludge effluent)
and station No. 9 (Ozone contact basin effluent) were used throughout the
research project. Sample station No. 10 was not used for the routine research
project results.
Different types of samples were collected depending on the nature of the
parameter analyzed. Grab samples and/or in-situ measurements were used for
dissolved oxygen, pH, fecal coliform, total coliform and temperature measure-
ments. Composite samples were collected for the BOD^, COD, TSS, TKN-N,
NIfy-N, N02&N03-N, Total P and alkalinity measurements. The composite
samples were collected both automatically and manually. Two refrigerated
automatic samples (Isco Model 1580R) were used to collect the samples at
sample station No. 1 (Thompson River Lift Station Influent) and station No. 3
(Flow Equalization Basin Effluent). The automatic sampler at station No. 1
collected the samples proportional to flow through operation according to the
number of lift station pump cycles. The sampler at station No. 3 collected
equal volume samples every 2 hours, and since the flow rate from the equaliza-
tion basin was controlled at a constant rate throughout the day the sample was
collected proportional to flow. The daily composite samples were collected
manually at all other sample stations. During the first four months of the
research project (June 1976-September 1976) composite samples were collected
for a period of 8 hours to 16 hours each day. During the remaining twenty-two
month data collection phase of the project, equal volume samples were
47
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collected at 2-hour intervals for a 24-hour period. Because the flow rate
through the plant was controlled at a constant rate, the composited equal
volume samples were proportional to flow.
Composite samples were collected on Sunday through Thursday and were ana-
lyzed Monday through Friday. Grab samples were collected Monday through
Friday. The analytical schedule that was followed is shown in Table 13.
TABLE 13. ANALYTICAL SCHEDULE FOR THE MAINSTREAM SAMPLES
Analysis
TSS
COD
TKN-N
NH N
N02&N03-N
Total P
Alk
Alk
BOD5
Coliform
(Tot. & Fecal)
Coliform
(Tot. & Fecal)
D.O.
PH
Temp
Frequency
5/wk
t*
"
it
ti
ii
2/wk
2/wk
2/wk
5/wk
5/wk
5/wk
5/wk
Sample Type
Composite
ti
ti
tt
tf
"
ii
It
tt
Grab
Grab
in-situ
Grab
in-situ
Sample
1
5
1
1
1
7
1
1
1
, 3
or
, 3
, 3
, 3
or
, 3
, 3
, 3
, 4
6,
, 4
, 4
, 4
8,
, 4
, 4
, 4
, 5
9
, 7
, 5
, 5
9
, 5
, 5
, 5
or
or
or
or
or
or
or
Station*
6,
tt
ti
it
11
8
6,
6,
6,
6,
6,
7 or 8,
7 or 8,
7 or 8,
7 or 8,
7 or 8,
7 or 8,
9
9
9
9
9
*1. Thompson River Lift Station Influent.
3. Flow Equalization Basin Effluent.
4. Activated Sludge Clarifier Effluent.
5 or 6. Nitrification Tower Effluent - Redwood or Dumped Plastic Media.
7 or 8. Mixed Media Filter Effluent - Denitrification Phase or Normal Phase.
9. Ozone Contact Basin Effluent.
In October 1977, the analytical frequency for Total P and for COD was re-
duced to 2 and 3 times per week, respectively, based on an analysis of the
5-times per week results. The analysis was made for one week of each month
for a 10-month period from December 1976 to September 1977. The analysis of
the COD results compared the data for 5 days to data for 3 days within the
same week. On the average these values were within 1.5 percent of each other.
48
-------
Similarily, comparing the weekly results of Total P for the 5 days of analysis
to 2 days of results showed that oil the average these values were within 2.0
percent of each other. Reducing the analytical schedule enabled the staff to
devote laboratory time to special testing, yet it did not adversely affect the
results of the data collected.
In addition to analyses of the wastewater, various analyses of the in-
plant sidestreams were conducted periodically. The analyses were conducted on
grab samples of waste sludge, aerobic digester supernatant, aerobic digester
sludge, dewatered sludge, activated sludge mixed liquor, backwash wastewater,
sludge dewatering recycle, and river samples. The various analyses conducted
included BOD5, TSS. D.O., PH, TKN, N02&N03-N, NH4~N, Total P, COD,
ALK, Total Coliform, Fecal Coliform, SVI, and VSS.
49
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SECTION 7
RESULTS AND DISCUSSION
GENERAL
Data required for the evaluation of the overall performance, cost and
design aspects of the UTSD treatment system and for each of the individual
unit processes was collected for a 105-week period. The effluent from the
individual unit processes was not sampled during the initial and final por-
tions of this 105-week data collection period. Initial laboratory start-up
problems postponed some individual unit process analyses for three months
until 10/3/76. During the final portion (i.e., last two months) of the data
collection effort, special testing for the ozone and denitrification systems
was accomplished in place of sampling and analyzing all of the unit processes.
Thus, of the 105 weeks during which overall performance information was col-
lected, data was collected on a routine basis for the individual unit process-
es for an 88-week period. During June 1977, the activated sludge process was
removed from service to provide modifications to the gates between the two
aeration basins and the two aerobic digesters. No data was collected during
this period.
In this section of the report the evaluation of individual unit processes
is presented as they occur in the plant flow schematic, beginning with the
flow equalization process. Also presented are the results of separate special
studies conducted on the denitrification, ozonation and sludge dewatering sys-
tems. Finally, an overall evaluation of all processes is presented.
50
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FLOW EQUALIZATION
The flow equalization process was used to control the wastewater flow rate
and the recycle flow rates through the UTSD plant. Wastewater was pumped to
the basin from both lift stations, and a controlled rate of flow was dis-
charged from the basin. (All in-plant recycle streams were returned to the
Thompson River Lift Station). The liquid volume in the basin would typically
increase during the day and decrease during the night, corresponding to waste-
water flow variations. The equalization basin was not equipped with an aera-
tion or mixing system to keep solids in suspension, although structural
provisions were made if operating conditions warranted oxygen addition and/or
mixing. As designed, however, settleable solids entering the basin would
settle to the bottom of the basin and were then scraped to the center of the
basin where the discharge pipe was located. Provisions to handle the organic
variations in loading associated with this arrangement were provided in down-
stream systems.
These aspects of the flow equalization process that were evaluated in-
cluded:
a) Affects of minimal mixing and no oxygen addition.
b) Characteristics of influent and effluent.
c) System operations and maintenance requirements.
d) Performance with respect to hydraulic dampening capability.
Since minimal mixing and no oxygen addition were provided the possibility
of low D.O. conditions and odor problems existed. The basin influent and
effluent D.O. concentrations were measured daily for a one-year time period.
Figure 6 shows the 4-week average D.O. results throughout the period of inves-
tigation. As shown, the fall, winter and spring influent and effluent D.O.
concentrations were above 1 mg/1. The summer effluent D.O. concentrations
were minimal (0.1 mg/1), but no odor problems were experienced. The relative-
ly high D.O. concentrations during the colder periods of the year were attri-
buted to the relatively cold wastewater temperature (5°C to 6°C in the winter)
and resulting reduced biological activity in the equalization basin. The
51
-------
!
s
>
J'A'S'O'N'D'J'F-M'A'M-J'J'A'S'O-N'P'J'F.M'A'M.J.J
1976 1977 1978
Figure 6. Flow equalization basin influent and effluent
dissolved oxygen concentration.
lower D.O. concentration in the summer was attributed to a higher wastewater
temperature of about 18°C., which affected both the soluability of oxygen as
well as increasing the biological activity. The absence of odors during the
summer was partially due to shorter basin detention times associated with
higher summertime flow rates. The basin detention time at. one-half plant
design flow of 2,840 cu m/day (0.75 mgd) and at a basin level of 1.8 m (6 ft)
is 5.2 hr. During the summer a flow of 2,840 cu m/day (0.75 mgd) was reached
and often exceeded. Another major reason for minimal odors during the summer
was attributed to the fact that the settleable organic material in the
wastewater was removed from the basin shortly after it entered, much more
rapidly than the average hydraulic detention time indicates. Thus, these
solids were not available to contribute to the biological activity which could
produce odors.
Other than a change in the D.O. concentration, no significant chemical or
biological changes in wastewater characteristics occurred within the flow
52
-------
equalization basin. A summary of results of various parameters analyzed in
the basin influent and effluent is shown in Table 14.
TABLE 14. SUMMARY OF -FLOW EQUALIZATION BASIN INFLUENT AND EFFLUENT
_ CHEMICAL AND MICROBIOLOGICAL QUALITY* _
Percent
Difference
Basin
Basin
Xi -
Parameter
BOD5 (mg/1)
TSS (mg/1)
COD (mg/1)
TKN (mg/1)
NH4-N (mg/1)
Alk as CaC03
Total P (mg/1)
Dissolved Oxygen
Total Coliform**
Fecal Coliform**
Influent (Xx)
218
200
351
20.6
12.6
109
5.5
(mg/1) 4.1
4.0 x 106/100 ml
1.1 x 106/100 ml
Effluent (X2)
213
180
330
22.4
12.9
108
5.8
2.6
4.6 x 106/100 ml
1.1 x 106/100 ml
\ *2 1
2.3
11.1
6.4
-8.0
-2.3
0.8
-5.2
57.6
-13.0
0
*Summary of data from 11/28/76 to 12/24/77.
**Geometric Mean.
For all parameters analyzed except dissolved oxygen and total coliform,
the percent difference between influent and effluent ranged from -8.0 percent
to 11.1 percent. These differences are felt to be within accepted sampling
and/or testing accuracy. The total coliform difference was -13 percent, but
the fecal coliform difference was negligible. The difference in D.O. concen-
tration was 58 percent. This change was attributed to biological activity
within the basin, but as mentioned earlier did not result in any odor pro-
blems. The flow equalization process was evaluated for one full year of the
two-year data collection phase of the research project. Data collection was
then stopped because chemical and microbiological changes through the basin
did not appear to be significant, and it was felt that more time could be
devoted to data collection for special studies and other process evaluations.
The equalization basin was rectangular in shape and had an overflow side-
water depth of 3.66 m (12 ft). The total basin volume was 1,230 cu m (325,440
53
-------
gal). Typically, the basin operated between fill depths of 0.91 m and 2.7 m
(3 ft and 9 ft). At the flow rates experienced during the research project no
problems were encountered with basin capacity respective to sufficient stor-
age volume for flow equalization. However, daily average flows ranged from 15
to 67 percent of design plant flows. The flow rate from the equalization
basin was measured by a magnetic flow measuring instrument (mag meter). The
signal from the mag meter was used to indicate and totalize the flow rate and
also was used to activate the flow control equipment. The mag meter signal
was sent to a controller assembly where it was compared to a set rate value
that was "dialed" in by the operators. The controller would then open or
close a "pinch valve" to increase or decrease the basin effluent flow rate as
called for. This system, when functioning, controlled the flow rate from the
basin to +2 percent from the set rate which resulted in excellent dampening of
the hydraulic flow.
Some problems were experienced with the flow equalization process, mainly
in the area of flow measurement and control which prevented the system's use
on a continuous basis. Problems included calibration difficulties with the
mag meter and problems with the mechanism that opened or closed the pinch
valve. The mag-meter was difficult to calibrate due to the lower than design
flows that were received at the plant. The meter was especially difficult to
calibrate when flow rates were only about 20 to 30 percent of design values.
The pneumatically driven arm that opened and closed the pinch valve had to be
pinched down quite substantially. This situation was believed to have con-
tributed to occasions of improper valve functioning. Unlike the downstream
processes, the mag meter and flow control valve were not provided as parallel
trains and therefore were sized based on total plant design flow. During the
time the pinch valve assembly and mag meter were non-functional an alternative
method of flow control was implemented. This alternative method consisted of
making routine adjustments to a plug valve located on the basin effluent line.
The plant flow variation using this method of control was approximately +15
percent of the desired flow rate. It is anticipated that these operational
54
-------
problems should occur less frequently as flow increases, and that future
difficulties will be easier to correct and/or prevent since the operators have
gained more experience with the system.
During the flow equalization evaluation period a grease build-up of about
13 mm to 25 mm (0.5 in to 1 in) occurred on the basin walls. This build- up
did not result in any odor problems and did not present an aesthetic problem
since the basin was covered. Periodic basin cleaning at 3-month intervals
prevented excessive grease build-up. An operational problem was encountered
when the scraper mechanism motor burned out. With the scraper not operating,
slug loads of settleable solids were directed to the activated sludge basins
when the basin was drained, down. Flow equalization had to be halted until the
motor was repaired.
GRIT REMOVAL
The grit removal system for the UTSD system was designed with a great
deal of flexibility to facilitate grit and grease removal. Because the col-
lection system was new, very little grit was received at the plant site. Air
was supplied to the grit basin to aid in grease floatation. However, very
little grease accumulated in the grit basin. As mentioned, most of the grease
accumulated within the flow equalization basin. Within the grit removal
building slight odors could at times be detected, but no serious odor problems
ever developed. In general, the grit removal process performed in a very
satisfactory manner.
ACTIVATED SLUDGE
The activated sludge treatment process directly followed the flow equali-
zation and grit removal systems. With this arrangement all flow to the acti-
vated sludge process was equalized prior to entry to the process. However,
the organic solids loading was not equalized because of the design character-
istics of the flow equalization system. Because of the flow equalization
55
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design and the fact that no primary clarifiers were provided, all settleable
solids that were received at the plant were received in the activated sludge
aeration basins and eventually were wasted from the secondary clarifier. This
arrangement caused the organic loading to the system to be quite variable
within a day.
Seasonal variations in hydraulic and organic load occurred because the
plant served a summertime tourist oriented community. The flow to the plant
during the research project is graphically illustrated in Figure 7. The plant
organic load as represented by BOD5 is depicted in Figure 8. Flow to the
plant during the summer of 1976 was lower than the following tourist seasons
because of the Big Thompson flood disaster on July 31, 1976, which signifi-
cantly reduced the community's tourist trade. The peak tourist season lasts
about 3 months: June, July and August. During that time the flow to the
plant was about 134 percent greater than the design flow. (Note: half plant
design values are used for design flow because only half of the activated
sludge units were in service). The BOD5 loading during these peak flow
periods was as much as 228 percent of design values. However, during the rest
of the year the wastewater flow and 8005 loading averaged about 50 percent
of design values.
The lower BOD^ loadings during the winter, non-tourist season were
caused by lower wastewater flows coupled with relatively low BOD^ concentra-
tion of about 100 mg/1 to 150 mg/1. (See weekly data values presented in
Appendix B) . These lower BOD^ concentrations were attributed to "bleeder"
water. Bleeder water refers to tap water that is run continuously to keep
water lines from freezing. This approach is used frequently at high altitudes
where deep ground frost is common and where dwellings are not occupied full
time. The significantly higher BOD5 loadings during the summer tourist sea-
son were caused by higher wastewater flows coupled with much higher BOD^
concentrations of 250 mg/1 to 400 mg/1. The higher BOD5 concentrations
during the summer were partially attributed to a small volume, high strength
waste discharged into the UTSD collection system through a septic tank and
56
-------
O)
E
o
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.6
0.5
0.4
0.3
0.2
0.1
o.o
t
N
S^
A
-
.
"
_..
._.
r
i
._.
_ DESIGli
\ ! ,
K.
/
"*"
FL
^
*
ow-
^/
-^
\
/
x
....
I
UJ
z
LU
INSTALLATION OF Qt
..
j X
\
y
i
^
-
^
^ '
L/
"~i
'
/
l^
K
/
^
~H
1976
1977
1978
Figure 7. Plant influent wastewater flow rate during the research project,
(mgd x 3785 = cum/day)
* Design flow for 1/2 of the activated sludge process in service.
3200
3000
2800
2600
2400
DESIGN LOAD -x
1976
1977
1978
Figure 8. Activated sludge influent BOD5 loading and effluent BOC5 residual
(Ib/day x 0.454 = Kg/day) "
*Design loading for 1/2 of the activated sludge process in service.
57
-------
chemical vault dump station. As such, the flow variation throughout the
project (See Figure 7) was not as pronounced as the BODc; loading. (See
Figure 8).
The treatment objective of the activated sludge process was to reduce the
plant effluent 8005 concentration and to facilitate ammonia oxidation in the
nitrification tower. However, the variable organic content of the influent
played an important part in the system being able to meet this objective. To
evaluate the effect of the variable system loadings, the research results were
divided into six different operational time periods (I to VI) as shown in
Figure 8. In Period 1 and IV, low BOD^ loadings encouraged nitrification in
the activated sludge system. The influent ammonia loading and ammonia in the
activated sludge effluent is shown in Figure 9. This data is also subdivided
into the six operational time periods. In Period III and VI, extremely high
BODc loadings for relatively short periods of time caused excessive amounts
JA'S-O
1976
N'D-J'F-M'A'M
1977
J.J.A-S
D
J F. M-AM- J J
1978
Figure 9. Activated sludge influent ammonia loading and ammonia residual
(Ib/day x 0.454 - Kg/day).
*Design load for 1/2 of the activated sludge process in service.
58
-------
of 8005 in the activated sludge effluent. In Period II and V, relatively
low BOD5 loadings occurred, but a sudden change in plant BOD 5 loading
coupled with extremely cold wastewater temperatures discouraged nitrification
in the activated sludge system.
Period I and IV are characterized by relatively low BOD^ loadings and a
high degree of nitrification occurring in the activated sludge process. A
portion of the results for Period I were omitted from discussion because of
the Big Thompson flood disaster on 7/31/76. After the flood the plant was
seeded with sludge from the Estes Park Sanitation District. The Estes Park
plant was nitrifying, and the nitrifying seed sludge continued to convert
ammonia at the UTSD plant. Nitrification during Period I continued for 20
weeks due to the relatively low BODj loading to the activated sludge pro-
cess. Nitrification occurred for 16 weeks during Period IV even though BOD 5
loading was higher, because of the long mean cell residence time that was
maintained in the system. A summary of activated sludge performance for
Period I and IV is shown in Table 15.
TABLE 15. SUMMARY OF ACTIVATED SLUDGE PERFORMANCE FOR
OPERATIONAL PERIOD I AND PERIOD IV
Parameter
Flow (mgd)
BOD5
Influent (mg/1)
Effluent (mg/1)
Removal (%)
TSS
Influent (mg/1)
Effluent (mg/1) .
Removal (%)
TKN
Influent (mg/1)
Effluent (mg/1)
Period I
8/8/76 to 12/26/76
0.32
146
35
76
135
26
81
21
6.3
Period IV
9/4/77 to 12/25/77
0.39
260
31
88
224
30
87
26
5.3
59
(Continued)
-------
TABLE 15. (Continued)
Parameter
Nlty-N
Influent (mg/1)
Effluent (mg/1)
N02&N03-N
Influent (mg/1)
Effluent (mg/1)
Alkalinity (as CaC03)
Influent (mg/1)
Effluent (mg/1)
pH (median)
Influent (units)
Effluent (units)
MLSS (mg/1)
MLVSS (mg/1)
MCRT (days)
F/M BOD5/MLVSS (kg/kg/day)
Organic Load (Ib BOD5/day/
1000 ft3)
Clarifier OFR (gpd/ft2)
Period I
8/8/76 to 12/26/76
(20 weeks)
14
2.5
0.8
12
84
33
6.8
6.0
1670
920
9
0.21
12
255
Period IV
9/4/77 to 12/25/77
(16 weeks)
15
1.7
0.3
15
113
23
7.0
6.0
3730
2830
38
0.11
27
310
mgd x 3785 = cu m/day; Ib BOD5/day/1000 ft3 x 16
gpd/ft2 x 0.0408 - cu m/day/sq m
gm/cu m/day
The average effluent ammonia concentration during Period I was 2.5 mg/1.
This resulted in a very low ammonia loading to the nitrification tower.
Operational controls were implemented to discourage ammonia oxidation in the
activated sludge system. Increased sludge wasting was implemented to reduce
the system mean cell residence time. The result was not effective in dis-
couraging ammonia oxidation and had a negative effect on BOD5 removal,
which was only 76.0 percent. Therefore, in Period IV (one year later) no
attempt was made to discourage ammonia oxidation with operational changes.
60
-------
Extensive ammonia oxidation occurred (effluent ammonia concentration was 1.7
mg/1), but BOD5 removal improved averaging 88.1 percent. The organic remo-
val during these two operational periods was satisfactory, but high levels of
ammonia oxidation affected the performance of the nitrification tower dis-
cussed in a later section.
Organic loadings to the activated sludge process were relatively low in
Periods II and V; however, these periods were characterized by limited nitri-
fication in the activated sludge process. Two factors were felt to be respon-
sible for the limited ammonia oxidation that occurred. At the onset of each
of these periods a rapid and substantial increase in both hydraulic and
organic loading to the plant occurred due to a large influx of tourists during
the Christmas holiday season. Wastewater temperatures typically decrease to
winter time lows during this same period, also. Due to the influx of people,
the BOD5 loading increased during the start of Period II by 140 percent over
the 4-week period prior to the holiday period. At the start of Period V, the
BOD5 loading similarly increased by 141 percent. This increase in BOD5
loading and the associated increase in sludge wasting appeared to be directly
associated with the decreased ammonia conversion that occurred in the acti-
vated sludge process. After the holiday periods loading returned to the
pre-holiday levels but nitrification capability did not reoccur. It was felt
that the low wastewater temperature of only 4°C to 5°C during most of both
Period II and Period V discouraged the return of the nitrifying organisms. A
summary of activated sludge performance for the entire Period II and Period V
interval is shown in Table 16. The rapid changes in the hydraulic and organic
loading that characterized the beginning of each of these periods, is shown in
the average weekly values presented in Appendix B.
61
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TABLE 16. SUMMARY OF ACTIVATED SLUDGE PERFORMANCE FOR
OPERATIONAL PERIOD II AND PERIOD V
Period II
Parameter 12/27/76 to 6/12/77
Flow (mgd)
BOD5
Influent (mg/1)
Effluent (mg/1)
Removal (%)
TSS
Influent (mg/1)
Effluent (mg/1)
Removal (%)
TKN
Influent (mg/1)
Effluent (mg/1)
NH4-N
Influent (mg/1)
Effluent (mg/1)
N02&N03-N
Influent (mg/1)
Effluent (mg/1)
Alkalinity (as CaC03)
Influent (mg/1)
Effluent (mg/1)
pH (median)
Influent (unit)
Effluent (unit)
MLSS (mg/1)
MLVSS (mg/1)
MCRT (days)
F/M, BOD5/MLVSS (Ib/lb/day)
Organic Load (Ib BOD5/day/1000 ft3)
Clarifier OFR (gpd/ft2)
0.50
157
27
83
130
19
85
16.0
10.5
9
8
1.1
1.8
84
78
7.2
6.8
1495
1170
7
0.28
21
398
Period V
12/25/77 to 5/14/78
0.46
169
14
92
168
17
90
23.5
16.8
15
14
1.4
1.5
109
104
7.2
6.8
3720
2865
18
0.09
20
366
mgd x 3785 - cu m/day; Ib BOD5/day/1000 ft3 x 16 = gm/cu m/day; gpd/ft2
x 0408 = cu m/day/sq m
62
-------
The fact that nitrification ceased is common to both Period II and V.
The abrupt halting of nitrification in the activated sludge resulted in a sud-
den increase in ammonia loading to the nitrification tower, which impacted
tower performance as described in a late section.
Although many similarities existed between Period II and V, the activated
sludge system was operated in a dramatically different fashion. Since control
of MCRT had not produced desired results during 1976, it was decided to try
and improve organic removal capability during the winter of 1977. As a result
the MLVSS concentration was maintained 2.5 times greater during Period V than
during Period II. The effect was better BOD5 removal during Period V,
averaging 92 percent versus 83 percent BOD5 removal during Period II.
Periods III and VI were characterized by dramatic increases in hydraulic
and organic loadings associated with the influx of tourists during the summer.
A summary of the activated sludge loading and performance during these periods
is presented in Table 17. As noted the first 4 weeks of Period III are
TABLE 17. SUMMARY OF ACTIVATED SLUDGE PERFORMANCE FOR
OPERATIONAL PERIOD III AND PERIOD VI
Parameter
Period III
6/12/77 to 9/4/77
Period VI
5/14/78 to 7/30/78
Flow (mgd)
BOD5
Influent (mg/1)
Effluent (mg/1)
Removal (%)
TSS
Influent (mg/1)
Effluent (mg/1)
Removal (%)
0.91
397
89
78
271
123
55
0.80
310
43
86
250
20
92
(continued)
63
-------
TABLE 17. (Continued)
Parameter
TKN
Influent (mg/1)
Effluent (mg/1)
Nlfy-N
Influent (mg/1)
Effluent (mg/1)
N02&N03-N
Influent (mg/1)
Effluent (mg/1)
Alkalinity (as CaC03)
Influent (mg/1)
Effluent (mg/1)
Period III
6/12/77 to 9/4/77
44
28
25
24
0.6
2.0
172
144
Period VI
5/14/78 to 7/30/78
26
22
17
0.9
4.5
151
116
pH (median)
Influent (unit) 7.2
Effluent (unit) 7.0
MLSS (mg/1) 3125
MLVSS (mg/1) 2270
MCRT (days) 5
F/M (Ib BOD5/lb MLVSS) 0.67
Organic Load (Ib BOD5/day/1000 ft2) 95
Clarifier OFR (gpd/ft2) 724
7.2
6.8
4103
3086
8
0.31
65.0
636
mgd x 3785 = cu m/day; Ib BOD5/day/1000 ft3 x 16 * gm/cu m; gpd/ft2 x
0.0408 = cu m/day/sq m
omitted because the plant was involved in a scheduled shut- down during which
time modifications were made to the gates separating the aeration basins.
This shut-down required reseeding and start-up during Period III, which
further hindered performance.
64
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The BOD5 load during Period III was 4.6 times greater than during
Period II. Similarly, the BOD5 load was 3.2 times greater during Period VI
than during Period V. (Note: Period VI loading was lower because the Estes
Park Sanitation District flow was stopped on June 1, 1978). These increased
loadings occurred over a three-month period, and no changes in the activated
sludge process configuration were made. (i.e., one-half of the activated
sludge process units were in service). The rapid increase in loading resulted
in reduced process efficiency. It should be noted that the loading itself
and/or process operating parameters like organic loading, F/M, clarifier over-
flow rate; etc., were not significantly high in themselves. The main aspect
that led to disrupted performance was the occurrence of the higher loading
over a relatively short period of time and associated inability of the acti-
vated sludge system to quickly react. This aspect of a long time for biologi-
cal system response has been further supported by other research.(2) To
achieve satisfactory performance during the high summer loading period it is
necessary that the UTSD plant staff allow sufficient time prior to the peak
summer loadings to acclimate- the activated sludge process to handle the peak
loading conditions.
Insignificant ammonia oxidation occurred during Period III and Period VI.
This was felt to be due to the relatively high organic loadings. At the same
time a significant increase in ammonia load to the nitrification tower
occurred.
NITRIFICATION
The wastewater directed over the nitrification tower consisted of flow
received from the activated sludge process plus flow that was recirculated
around the tower. The maximum pumping volume to the tower was 22,710 cu m/day
(6 mgd), which provided a maximum recirculation capability of 4:1 at the plant
design flow rate. The tower was divided into two equal volumes, each contain-
ing a different type of media. The east side of the tower contained plastic
dumped media which had a specific surface area of 89 sq m/cu m (27 sq ft/cu
ft). The west side contained redwood media which had a specific surface area
65
-------
of 46 sq m/cu m (14 sq ft/cu ft). In order to approach design loadings on the
media, only one half of the tower was operated at' any one time; a side by side
comparison of the two types of media was not possible. During the project the
plastic media was operated first and continued through September, 1977. The
redwood media was then operated for the duration of the project.
Each media type was operated during three different phases called: start-
up, cold weather and warm weather periods. The separation point between the
cold weather and warm weather periods was arbitrarily selected as the poinj:
when the tower effluent wastewater temperature dropped below 8°C. Using this
division point resulted in a split of approximately 5 months of cold weather
operation and 7 months of warm weather operation during a one-year time frame.
The start-up period for each media type occurred during a warm weather period.
Therefore, during the two-year data collection phase of the research effort
each media type was operated during a warm weather start-up period, a cold
weather operating period and a warm weather operating period. These operating
periods are labeled plastic start-up; plastic cold weather; plastic warm
weather; redwood start-up; redwood cold weather and redwood warm weather oper-
ation.
After the data collection phase of the research project was completed,
additional and important data was obtained relative to the performance of the
nitrification tower. Operation using the redwood media was continued, and
some warm-weather and some cold-weather results were documented. (Note:
These results were obtained on 1 to 2-day per week composite samples as op-
posed to 5-day per week composite samples collected during the research pro-
ject. Additionally, only a portion of the -analyses conducted during the
project were completed. This additional evaluation was separated into two
operational periods called redwood update - warm weather and redwood update -
cold weather.)
Table 18 presents the average data for the selected operational phases
that were evaluated. An evaluation of this data is presented in the discus-
sions of the various operational phases. It is important to note that the
66
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67
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UTSD nitrification system was designed to meet an ammonia discharge limit of
54.8 kg/day (120 Ib/day) which is the level that was projected to protect
against ammonia toxicity in the Big Thompson River under 7 day, 10 year low
flow conditions. This discharge limit would allow an effluent ammonia concen-
tration of 10 mg/1 at the design flow rate of 5678 cu m/day (1.5 mgd). This
design requirement was met throughout the research project. However, the
evaluation of nitrification capability presented in this report is based on
the ability of the nitrification process to perform at more constraining
levels of effluent ammonia concentration (i.e. > 2 mg/1 NH^-N) and/or at
greater than 90 percent ammonia oxidation across the tower.
An overall summary of the nitrification results for the entire research
project showing mass of ammonia applied to the tower and mass of ammonia con-
verted to nitrate nitrogen by the tower is graphically illustrated in Figure
10. Also shown are the dates associated with the various operational periods.
The bottom line in the graph depicts mass converted and not mass remaining in
the tower effluent. As shown, the mass of ammonia applied was extremely vari-
able throughout the project, ranging from less than 2.3 kg/day (5 Ib/day) to
more than 114 kg/day (250 Ib/day). The low ammonia loadings were usually
associated with periods where nitrification was occurring in the activated
sludge process. The high ammonia loadings occurred during the summer tourist
season.
The mass of ammonia oxidized also varied substantially throughout the
research project. Many operational and environmental factors contributed to
this variability. Low ammonia loading to the tower resulted because nitrifi-
cation occurred in the activated sludge process; a rapid increase in ammonia
loading occurred during the Christmas holiday season and extremely high
ammonia loadings occurred during the summer tourist season. In addition, dif-
ferent operational procedures were implemented as the project progressed, the
major change being in the amount and method of maintaining recirculation
around the tower. Environmental factors such as wastewater pH, alkalinity and
temperature also contributed to the variability of tower performance. These
aspects are discussed for each of the operational phases evaluated.
68
-------
8838 g-8883888838
cvicMeMeMWcM'^'T-T-i-T-
( Aep/sqi ] N39OH1IN VINOWWV
0^*01
-3 T-
M
H
69
-------
Plastic Start-Up (July 11, 1976 to November 27, 1976 - 20 wks)
Data collection for the nitrification tower plastic start-up period began
on July 11, 1976, but was interrupted on July 31, 1976, when the Big Thompson
flood disaster occurred. Because of this interruption the data presented in
Table 18 for this period includes only those results after the effects of the
flood were minimized (i.e., 8/22/76 to 11/27/76). The period ends on 11/27/76
when the tower effluent temperature dropped below 8°C. During the plastic
start-up period the ammonia loading to the tower was minimal because nitrifi-
cation occurred in the activated sludge process. The average ammonia loading
to the tower was only 6.9 gm/day/cum (0.43 Ib day/1000 ft3), or 6 percent of
the design loading of 109 gm/day/cum (6.8. Ib day/1000 ft3). This low
loading limited the development of nitrifying organisms on the plastic media.
The variations in ammonia loading and ammonia oxidation for the plastic start-
up phase are graphically depicted in Figure 11.
g
6O
SO
40
30
< 20
10
NH4<-N t »PLII
A
14 21 28 4 11 18 25
PL: STIC
STAI
T-l '
8 15 22 29 6 13 2O 27 3 1O 17 24
SON
1976
Figure 11. , Nitrification tower ammonia loading and ammonia oxidized
during the plastic start-up operating period.
70
-------
The tower operational procedure during the plastic start-up period was to
maintain a fairly high tower recirculation (R/Q)ratio (average was 4.9). The
corresponding tower wetting rate averaged 52 1/min/sq m (1.28 gpm/ft2) and
varied from 39 to 56 1/min/sq m (0.97 to 1.38 gpm/ft2). During the other
operational periods the R/Q ratio and associated tower wetting rates were
generally decreased. Initially, the tower wetting rate was quite variable,
but finally was controlled at a more constant rate. The reasons for the
changes in. R/Q and tower wetting rate are presented in the operational phases
where the changes occurred.
The R/Q ratio and wetting rate was maintained at higher levels during the
plastic start-up period because the original tower distribution system could
not evenly distribute a low flow rate over the media surface. At low flow
rates it was felt that poor, distribution resulted in loss of utilization of
part of the dumped media in the upper portion of the tower. Therefore, the
system's original fixed splash-plate nozzles were replaced with a variable
flow splash-plate nozzle, which automatically adjusted themselves to provide
good distribution at low flow rates. The new nozzles functioned very satis-
factorily and provided an even distribution of flow over the media surface at
low, as well as higher flow rates. A summary of the significant events that
occurred during the plastic start-up period is presented in Table 19.
TABLE 19. SIGNIFICANT EVENTS DURING THE PLASTIC MEDIA START-UP PERIOD
Date - ' Event
July 11, 1976
July 31, 1976
August 22, 1976
October, 1976
Plastic dumped media section of tower placed into
operation.
Big Thompson Flood Disaster occurred.
Data collection subsequent to the flood initiated.
Replaced fixed splash-plate nozzles with variable
flow nozzles.
(Continued)
71
-------
Date
TABLE 19. (Continued)
Event
August thru November,
1976
August thru November,
1976
Tower influent ammonia concentration quite low due
to nitrification in the activated sludge process.
Tower recycle (R/Q) ratio and wetting rate were
high at 4.9 and 52 1/min/sq m (1.28 gpm/sq ft),
respectively.
Plastic - Cold Weather (November 28, 1976 to April 23, 1977 - 21 wks)
The plastic cold weather operating time period began when the tower efflu-
ent wastewater temperature dropped below 8°C. Initially, a low ammonia
loading existed and lasted for about 4 weeks, as shown in Figure 12. Then,
ammonia oxidation ceased in the activated sludge process and a higher ammonia
loading was applied to the tower for the remaining 17 weeks of the plastic
£ 40 _
z
ui
30
< 20
< 10
PLASTIC
GOLD WEA
1 8 15 22 29 5 12 19 "26 2 8 16 23 2 8 16 23 30 6 13 2O
Figure 12. Nitrification tower ammonia loading and ammonia oxidized
during the plastic cold weather operating period.
72
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cold weather operating period. A summary of the results for the 17-week
period of cold weather operation with a higher ammonia loading is shown in
Table 18. The ammonia loading during this time period averaged 32 gm/day/cum
(2.0 lb/day/1000 ft^) or 465 percent greater than during the start-up
period. However, this loading was still only about 30 percent of the design
loading rate.
Initially the operational approach during the plastic cold weather period
was to maintain a fairly high tower recycle ratio (R/Q) of about 2.8. How-
ever, ammonia oxidation began to gradually decrease from about 80 percent to
30 percent. It was felt that higher recycle rates were contributing to tem-
perature losses in the tower, which in turn were contributing to the decreased
tower performance. Therefore, the tower R/Q ratio was reduced gradually from
a peak of 2.8 to 0. This gradual reduction occurred over an 8-week period,
and no recirculation was provided for another 8-week period. When
recirculation was reduced and eventually stopped, nitrification performance
did not improve; in fact, ammonia removal further decreased to only about 20
percent. This gradual reduction in ammonia removal is illustrated in Figure
12; which depicts the mass of ammonia applied and mass oxidized during the
plastic - cold weather period. Tower recirculation was stopped on 1/23/77,
and was not started until the week of 3/13/77. During that time the amount of
ammonia oxidized in the tower dropped from 3.6 kg/day (8 Ib/day) to 2.3 kg/day
(5 Ib/day), while ammonia loading to the tower remained fairly constant at
about 12.7 kg/day (28 Ib/day). It was concluded that minimal recirculation
did not improve nitrification performance.
During the week of March 13, 1977, recirculation was again implemented at
an R/Q ratio of about 1*5. Subsequent to this change, ammonia oxidation in-
creased from about 20 percent to 50 percent over a 5-week period, although the
tower effluent temperature also gradually increased from 4°C to 8°C. It
appeared that by providing some recirculation ammonia oxidation capability im-
proved, but the benefits of recirculation alone could not be confirmed because
wastewater temperature also increased. A summary of the events that occurred
during the plastic - cold weather operating period is shown in Table 20.
73
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TABLE 20. SIGNIFICANT EVENTS DURING THE PLASTIC - COLD WEATHER PERIOD
Event
Date
11/28/76 to 12/26/76
(4 weeks)
12/26/76 to 1/1/77
(1 week)
11/28/76 to 1/22/77
(8 weeks)
1/23/77 to 3/19/77
(8 weeks)
3/20/77 to 4/23/77
Low ammonia loading to tower due to nitrification in
activated sludge process.
Ammonia oxidation in activated sludge process
ceased.
Ammonia oxidation performance decreased from about
80 percent to 30 percent, over which time tower
recirculation rate was gradually decreased from
about 2.8 to 0.
No recirculation provided, and ammonia oxidation
decreased from about 30 percent to 20 percent.
Recirculation provided at R/Q ratio of about 1.5;
tower effluent temperatures gradually increased from
about 4°C to 8°C; and ammonia oxidation gradually
increased from about 20 percent to about 50 percent.
Plastic - Warm Weather (April 24, 1977 to September 24, 1977 - 22 weeks)
On April 24, 1977, the tower effluent temperature above 8°C and the
plastic - warm weather operational period began. This operating period con-
tinued until the redwood media was placed on line on September 25, 1977. In
total, this period continued for 22 weeks but was interrupted for 2 weeks in
order to complete a scheduled repair to the activated sludge aeration basin
gates. A summary of results during the plastic warm weather period is shown
in Table 18.
The ammonia oxidation performance of the tower during the plastic - warm
weather operational period is illustrated in Figure 13. As shown, the amount
of ammonia loading and oxidation increased dramatically from 4/24/77 to
6/18/77. Two important points are depicted in Figure 13; the rapid increase
in the amount of ammonia oxidized and the overall maximum amount of ammonia
oxidized. The amount of ammonia oxidized increased from about 17 kg/day to 36
kg/day (37 Ib/day to 80 Ib/day) within a 4-week period, which relates to a
0.73 kg/day/day (1.6 Ib/day/day) increase. This rate of increase in ammonia
74
-------
"Figure 13. Nitrification tower ammonia loading and ammonia oxidized
during the plastic warm weather operating period.
oxidation capability is compared to the response of the redwood media.later in
the report. A maximum ammonia oxidation capability of about 36 kg/day (80
Ib/day) was achieved. A similar maximum ammonia oxidation also occurred later
in this phase after a scheduled interruption occurred. Ammonia loading during
this period was much greater than the maximum oxidation rate that was
achieved. As such, relatively poor ammonia removal percentages were achieved
(i.e. 48 percent). It is noted that an oxidation of 36 kg/day (80 Ib/day)
represents an oxidation per unit volume in the tower of 93 gm/day/cu m (5.8 Ib
/1000 ft^/day). The corresponding oxidation per unit of media surface area
in the tower was 1.03 gm/day/sq m (0.21 lb/day/1000 ft2) of media surface.
These values will be compared to the removal performance of the redwood media
later in the report.
75
-------
During the plastic warm weather operational period problems were encoun-
tered due to periodic extensive sloughing of solids from the tower. Sloughed
solids plugged the mixed media filters which resultd in shut-down of both the
filters and the nitrification tower. The tower had to be shut down since it
was an integral part of the mixed media pressure filter system. These period-
ic shut-downs dramatically pointed out the limitations of the mixed media fil-
ters to handle periods of high solids loss from the nitrification system, as
described later.
It was originally felt that a portion of the sloughing problem was due to
the diversion of raw wastewater over the tower during the two week period in
June 1977 when the gate structure between the activated sludge aeration basins
was modified. This diversion was felt to have contributed to the development
of a greater mass of carbonaceous organisms that sloughed off the tower when
the raw wastewater flow to the tower ceased. However, sloughing was occurring
prior to this time and continued after the gate modification for the remaining
11 weeks of the plastic warm weather evaluation period. Flow variations that
occurred in tower wetting rates was felt to be another possible cause of the
tower sloughing problem. However, no direct correlation between wetting rates
and sloughing could be established from the data.
For the 4-week period from 7/17/77 to 8/13/77 while sloughing occurred
periodically and while loading exceeded oxidation, the amount of ammonia oxi-
dized varied from 34 to 39 kg/day (75 to 87 Ib/day). This relatively small
fluctuation could lead to the conclusion that the system had reached a consis-
tent and maximum ammonia oxidation level. However, the tower sloughing and
periodic shut-down (maximum 1-day duration at minimum 1-week intervals) may
have hindered the nitrification system's ability to attain a higher level of
ammonia oxidation. Despite the interference of tower sloughing, it was felt
that the data indicated that the tower was capable of oxidizing a maximum
fixed amount of ammonia. This conclusion is significant in that it requires
j
that design loading be based on the maximum expected ammonia load that would
occur for an average daily or weekly period, and not be based on yearly
76
-------
average loading conditions. A summary of the significant events that occurred
during the plastic * warm weather operating period is shown in Table 21.
TABLE 21. SIGNIFICANT EVENTS DURING PLASTIC WARM WEATHER PERIOD
Date
4/24/77 to 5/21/77
(4 weeks)
5/22/77 to 6/18/77
(4 weeks)
6/19/77 to 7/2/77
(2 weeks)
7/3/77 to 9/3/77
Event
- Ammonia oxidation increased from 50 to 60 percent.
- Mass of ammonia oxidized increased from 25.7 lb/
day to 34.3 Ib/day, while ammonia loading remained
fairly constant at about 2.7 lb/1000 ft3/day.
- Tower recirculation ratio ranged from 1.0 to 1.6.*
- Tower wetting rate averaged 0.83 gpm/ft2 and
ranged from 0.76 to 0.92 gpm/ft2.
- Tower ammonia loading increased four fold from 2.7
to 11.3 lb NH3/1000 ft3/day. (Note: 11.3 lb
NH3/1000 ft3/day is 166% of design load).
- Ammonia oxidation decreased from 86 to 46 percent,
but mass of ammonia removed increased from 34
Ib/day to 80 Ib/day (i.e., rate of increase was
1.6 Ib/day/day).
- Extensive sloughing of solids from tower occurred,
which required shut-down of mixed media filters
due to plugging.
- Tower effluent temperature increased from 10°C to
15°C.
- Tower recirculation rate varied from 0 to 1.2 de-
pending on flow rate.
Activated sludge aeration basin gates modified and
all flow from the grit removal basin
was diverted directly to the nitrification tower.
- Extremely high ammonia loading to tower occurred,
ranging from 7.4 to 18.3 lb/1000 ft3/day, or
109 percent to 269 percent of design.
- After a 2-week period to overcome the effects of
raw wastewater being directed over the tower, the
maximum amount of ammonia oxidized was about 80
Ib/day while loadings were almost 3 times that
value.. (Note: 80 Ib/day relates to 5.8 lb/
day/1000 ft3 and 0.21 Ib/day/1000 ft2 media
surface).
(continued)
77
-------
TABLE 21. (Continued)
Date
Event
7/3/77 to 9/3/77
(Continued)
9/4/77 to 9/24/77
- Extensive sloughing of solids continued.
Procedures were implemented to reduce the
sloughing, including maintaining a nearly
constant hydraulic load on the towers, and were
met with only moderate success.
Ammonia oxidation in activated sludge process reoc-
cur red.
Ib/day x 0.454 = kg/day; lb/day/1000 ft3 x 16.0 = gm/day/cum; gpm/ft2 x
40.7 - I/day/sq m
lb/day/1000 ft2 x 4.88 = gm/day/sq m
Redwood - Start-Up (September 25, 1977 to November 19, 1977 - 8 weeks)
On September 25, 1977 the redwood media was put into operation and the
plastic media was removed from service. This change involved adjusting the
proper valves to divert the influent to the other half of the tower. The red-
wood start-up period lasted for 8 weeks
until 11/19/77, when the tower effluent
temperature dropped below 8°C. During this
time a negligible amount of ammonia was
directed to the tower due to nearly com-
plete nitrification that was occurring
in the activated sludge process. The
ammonia loading during the first week of
start-up was 59 gm/day/cum (3.67 Ib/day/
1000 ft3). But, the ammonia loading to
the tower for the entire phase averaged
6.4 gm/day/cum (0.4 lb/day/1000 ft3)
because less than 1.6 gm/day/cum (0.1 lb/
day/1000 ft3) occurred for 7 weeks of
the 8-week start-up period. These low
loadings limited the development of a
nitrifying population. A summary of the
results during the redwood start-up period
>>
o
111
O
O
tc
o
X
20
10
1977
Figure 14. Nitrification tower
ammonia loading and ammonia ox-
idized during the redwood start-
up weather operating period.
78
-------
is shown in Table 18, and a graphical illustration of NH^-N load and Nlfy-N
oxidized is shown in Figure 14.
Redwood - Cold Weather (November 20, 1977 to April 22, 1978 - 22 weeks)
The cold weather period using the redwood media began on 11/20/77, when
the tower effluent temperature dropped below 8°C« The lowest weekly average
wastewater temperature during the 22-week time period was 3°C, and occurred
for 2 separate one-week periods. During the first 5 weeks of the cold weather
operational period, minimal tower ammonia loading existed because extensive
nitrification occurred in the activated sludge process. High organic loading
and low temperatures which occurred over the Christmas holidays caused nitri-
fication in the activated sludge process to cease, and for the next 17 weeks
the redwood tower was loaded at an average level of 59 gm/day/cum (3.7
lb/day/1000 ft^) which was 54 percent of the design loading rate. The fol-
lowing discussion about redwood - cold weather operation includes data col-
lected during the 17-week time period only. A summary of the results for the
17-week period is shown in Table 18.
The increase in tower ammonia loading began on 12/25/77, and continued
throughout the remaining 17 weeks of the cold weather operational time period.
A graphical illustration of the amount of ammonia applied to the tower and
amount oxidized in the tower for the redwood cold weather period is shown in
Figure 15. As shown, negligible ammonia oxidation occurred for the first 2
weeks. Subsequently, a gradual increase in ammonia oxidation occurred to a
maximum level of 9.1 kg/day (20 Ib/day), which was about 45% of the tower
loading. The increase in ammonia removal to 20 Ib/day occurred over a 15-week
period, for an average increase of 0.077 kg/day/day (0.17 Ib/day/day).
The maximum oxidation level of 9.1 kg/day (20 Ib/day) was better than was
obtained during the previous year when the plastic media was operated. Dif-
ferent operational procedures may have contributed to this occurrence. The
most important operational change was in the tower recirculation ratio. The
R/Q ratio during the plastic cold weather operation was always quite low, and
79
-------
80
70
60
REPWOOD
COLD WEA.THER
i * :" ! ' -M r-
83 30 7 14 21 28 4 11 18 25 1 8 15 22 1 8
Figure 15. Nitrification tower ammonia loading and ammonia oxidized
during the redwood cold weather operating period.
was eventually reduced to zero during most of the period. Conversely, the R/Q
ratio during the redwood cold weather operation was substantially higher at
2.5. It appeared that a higher recirculation ratio improved ammonia oxidation
performance during the cold weather operation. During the first winter
(Plastic Cold Weather Period) it was felt that recirculation would possibly
reduce the wastewater temperature and adversely affect ammonia oxidation capa-
bility. However, during the redwood cold weather period with recirculation,
the temperature drop through the tower averaged 1°C. A similar temperature
drop occurred during the plastic cold weather period when negligible recircu-
lation was provided, thus a significant effect of high recirculation on waste-
water temperature was not observed.
80
-------
The better cold weather tower performance using the redwood media may be
attributed to the type of media itself. Possibly, the rough surface texture
of the redwood as compared to the plastic material enhanced growth attachment.
However, because of the differences in the recirculation ratio during each
period and because of the indication that a higher recirculation ratio im-
proved ammonia oxidation capability, no definite conclusions can be drawn as
to which media type performed better during cold weather operation. Also, no
definite conclusion can be drawn about overall cold weather tower performance
because a limited population of nitrifying organisms was established during
start-up. Additional information regarding cold weather operation for the
redwood media was collected after the data collection phase of the research
project was concluded. In this case, good pre-cold weather start-up condi-
tions existed. A summary of the significant events for the redwood cold
weather period is shown in Table 22.
TABLE 22. SIGNIFICANT EVENTS DURING REDWOOD - COLD WEATHER PERIOD
Date
11/20/77 to 12/24/77
(5 weeks)
12/25/77 to 12/31/77
(1 week)
12/25/77 to 4/22/78
(17 weeks)
Event
Negligible ammonia loading to tower due to exten-
sive nitrification in activated sludge process.
Nitrification in activated sludge process ceased.
- Tower ammonia loading averaged 3.7 lb/
day/1000 ft3 or 54 percent of design loading.
- Ammonia oxidation increased from 4 to 47 percent.
- Negligible ammonia oxidation occurred during first
2 weeks (i.e., about 2 Ib/day).
- Gradual increase in ammonia oxidation occurred
over next 15 weeks to a maximum level of 20 Ib/day
(i.e., average 0.17 Ib/day/day increase).
- Tower recirculation ratio averaged 2.5 and tower
wetting rate averaged 0.98 gpm/ft2.
lb/day/1000 ft3 x 16 = gm/day/cum; Ib/day x 0.454 = kg/day; gpm/ft2 x 40.7
= 1/min/sq m
81
-------
Redwood - Warm Weather (April 22, 1978 to July 29, 1978 - 14 weeks)
On April 23, 1977, the tower effluent wastewater temperature increased
above 8°C, which marked the beginning of the redwood warm weather operating
period. A summary of the results for the redwood warm weather operating
period is shown in Table 18 and Table 23. The results shown in Table 23 are
separated into two 7-week periods, one representing the time period when the
loading was below the design level and the second when the load was above the
design level.
A graphical illustration of the ammonia loading and ammonia oxidized in
the redwood warm weather period is shown in Figure 16. As shown, ammonia
oxidized through the tower gradually increased from about 10.4 to 19.5 kg/day
(23 to 43 Ib/day) from 4/23/78 to 6/10/78 (7 weeks), for an average rate of
increase of 0.18 kg/day/day 0.08 kg/day/day (0.40 Ib/day/day). This rate was
2.4 times greater than the rate of increase that occurred during the cold
180
160
- 140
120
100
80
O
a
60
40
20
REDNIOOD
WAFM WEATh
-Nf
OXI 3IZE
ER
APPI IED
\
26 3 10 17 24 31 7 14 21 28 5 12 19 26
AM J J
1978
Figure 16. Nitrification tower ammonia loading and ammonia oxidized
during the redwood warm weather operating period.
82
-------
weather period (i.e., 0.81 versus 0.08 kg/day/day (0.41 versus 0.17
lb/day/day)), but was not as good as occurred for the plastic media. The
plastic media increased its ammonia oxidation rate during a similar time
period for the previous year an average 0.73 kg/day/day (1.6 lb/day/day). It
appeared that the plastic media provided a more rapid response to increased
ammonia loading during warm weather. Also, the maximum level of ammonia
oxidized by the plastic media at about 36 kg/day (80 Ib/day) was greater than
the maximum level oxidized by the redwood media. The average mass of ammonia
oxidized by the redwood media for the 7-week period from 6/11/78 to 7/29/78
was about '23 kg/day (50 Ib/day). Thus, the plastic media responded more
rapidly to a higher tower loading and performed at a greater ammonia oxidation
level than the redwood media. A possible reason for this occurrence may be
due to the increased surface area of the plastic media at 88 sq m/cum (27
ft2/ft3) as opposed to 46 sq m/cum (14 ft2/ft3) for the redwood media.
These dry specific surface area values exclude the surface area attributed to
growth on the media which would increase both values by an unknown amount. A
comparison of the maximum unit oxidation rates for each media shows that the
plastic material oxidized a maximum 1.03 gm/day/sq m (0.21 Ib/day/1000 ft2)
of media surface and the redwood material removed a maximum 1.27 gm/day/sq m
(0.26 Ib/day/1000 ft2) media surface. According to these values the redwood
media oxidized about 20 percent more ammonia per unit of surface area, but
overall the plastic media oxidized more ammonia because it had 52 percent more
total media surface area.
The indication from the comparisons of media performance is that the plas-
tic media had better overall ammonia oxidation capability than the redwood
media. However, the plastic media was being loaded at a much higher level
when its maximum ammonia oxidation occurred (i.e. , at an average 218 gm/day/-
cum (13.6 lb/1000 ft3/day) versus 147 gm/day/cum (9.2 Ib/day/1000 ft3).
This higher loading may have caused the plastic media to remove more ammonia.
However, ammonia oxidation capability may not be the only factor that in-
fluenced media performance,, During the redwood warm weather operational
period minimal sloughing of solids occurred, unlike the problem with routine
solids sloughing during the plastic warm weather operating period. During
83
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TABLE 23. SUMMARY OF RESULTS DURING REDWOOD WARM WEATHER PERIOD
(APRIL 23, 1978 TO JULY 29, 1978)
4/23/78 to
Parameter 6/10/78
Number of Weeks
Flow (Q) (mgd)
Recirculation Flow (R) (mgd)
Recirculation Ratio (R/Q)
Tower Wetting Rate (gpm/f t2)(min)
(Av.g)
(max)
Ammonia Nitrogen Loading
(lb/ day/1000 ft3)
BOD Loading (lb/day/1000 ft3)
Temperature Influent (°C)
Effluent (°C)
Ammonia Nitrogen Influent (mg/1)
Effluent (mg/1)
Removal (%)
Total Kjeldohl Nitrogen
Influent (mg/1)
Effluent (mg/1)
Nitrite plus Nitrate Nitrogen
Influent (mg/1)
Effluent (mg/1)
pH (median) Influent (units)
Effluent (units)
Alkalinity Influent (mg/1)
(as CaC03) Effluent (mg/1)
7
0.74
0.62
0.84
0.78
0.96
1.15
4.8
9.0
10
10
11
5.9
45
14
8.0
2.0
6.9
6.6
7.1
105
62
6/11/78 to
7/29/78
7
0.76
0.53
0.70
0.80
0.91
1.12
9.2
22
15
15
20
12
39
23
19
5.3
11.0
6.7
7.1
123
69
4/23/78 to
7/29/78
14
0.75
0.58
0.77
0.78
0.94
1.15
7.0
16
13
13
15
9.1
41
18
14
3.7
9.0
6.6
7.1
114
65
mgd x 3785 - cum/day; gpm/ft2 x 40.7 = 1/min/sq m; lb/day/1000 ft2 x
16.0 - gm/day/cum
84
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each media type's warm weather operation condition, similar hydraulic wetting
rates were experienced (i.e., redwood - 38 1/min/sq m average and 32 to 47
1/min/sq m variation (0.94 gpm/ft2 average and 0.78 to 1.15 gpm/ft2
variation) versus plastic - 3.9 1/min/sq m average and 27 to 48 1/min/sq m
variation (0.95 gpm/ft2 average and 0.66 to 1.18 gpm/ft2 variation). The
reason for sloughing from the plastic media and negligible sloughing from the
redwood media was not known. The problem with the periodic solids sloughing
by the plastic media was not that it significantly reduced ammonia oxidation
performance, but rather that it plugged the mixed media filters and required
system shut-down and bypass. This condition could have been avoided by using
a different solids capturing unit, like a clarifier.
An important conclusion for both types of media was that an apparent maxi-
mum ammonia oxidation rate was achieved. The removal rates achieved possibly
could have been improved by further optimizing operational adjustments, but
the data indicates that some maximum oxidation level would be achieved. As
such, nitrification towers should be sized on the anticipated peak daily or
peak weekly ammonia loading, and not on an average yearly value. A summary of
the events that occurred during the redwood warm weather operating period is
shown in Table 24.
TABLE 24. SIGNIFICANT EVENTS DURING REDWOOD WARM WEATHER PERIOD
Date
Event
4/23/78 to 6/10/78
(7 weeks)
- Tower ammonia loading was gradually increasing,
but was less than the design loading (i.e., varied
from 3.4 to 6.5 lb/1000 ft^/day or from 50 to
96 percent of design load).
- Ammonia oxidation percentage remained constant at
about 45%.
Ammonia oxidation level increased as ammonia
loading increased and ranged from 20 Ib/day to 43
Ib/day. (Rate of increase was 0.47 lb/day/day).
- Tower hydraulic loading averaged 0.97 gpm/ft2
and varied from 0.78 to 1.12 gpm/ft2.
(Continued)
85
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TABLE 24. (Continued)
Date
Event
6/11/78 to 7/29/78
(7 weeks)
Minimal sloughing problems were encountered.
Tower recirculation ratio varied from 0 to 1.9 as
flow rate varied.
Tower effluent temperature increased from 8°C to
12°C.
Tower loading averaged 9.1 lb/1000 ft3/day and
varied from 7.7 to 10.8 lb/1000 ft?/day, which
was an average 134 percent above design load and
varied from 113 to 159 percent above design
loading.
Average ammonia oxidation rate was about 40%.
Maximum ammonia oxidation reached 69 Ib/day for a
one-week period, but was variable and averaged
about 50 Ib/day for the 7-week period.
Tower wetting rate averaged 0.92 gpm/ft2 and
varied from 0.80 to 1.12 gpm/ft2.
Tower recirculation ratio averaged 0.71 and ranged
from 0.54 to 1.08.
Minimal solids sloughing problems were, encount-
ered.
lb/day/1000 ft3 x 16.0 = gm/day/cum; Ib/day x 0.454 = kg/day; gpm/ft2 x
40.7 - 1/min/sq m
Redwood Update - Warm Weather (October 22, 1978 to November 18, 1978 - 4
weeks)
Subsequent to the data collection phase of the research project, limited
but important information was developed regarding nitrification tower perform-
ance as shown in Figure 17. The most important fact was that the tower was
loaded at a higher ammonia level prior to cold weather conditions than was
achieved during the previous 2 years. The average tower loading was 26
gm/day/cum (1.6 lb/day/1000 ft3), whereas loadings of only 1.6 and 6.4
gm/day/cum (0.1 and 0.4 lb/day/1000 ft3) were achieved in 1977 and 1976,
respectively. The loading of 26 gm/day/cum (1.6 lb/day/1000 ft3) was about
24 percent of design. At that loading during warm weather operation the tower
was achieving nearly complete ammonia oxidation. A complete summary of
86
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results for this time period is shown in Table 18. As shown, the average am-
monia oxidation percentage was 94 percent. Therefore, unlike the previous two
years the tower was receiving ammonia and was nitrifying prior to cold weather
operation. The ammonia loading to the nitrification tower was increased by
preventing nitrification in the activated sludge process. This was accom-
plished by substantially reducing and maintaining a low D.O. level. D.O.
levels less than 0.5 mg/1 were maintained in the aeration basin whereas levels
of 2-4 mg/1 were maintained during the previous two years. This operational
change increased the ammonia loading to the tower, but more importantly
allowed the tower to become acclimated for nitrification prior to cold weather
operation.
Redwood Update - Cold Weather (November 20, 1978 to February 24, 1979 - 14
weeks)
On 11/20/78, the tower effluent temperature dropped below 8°C. As shown
in Figure 17, from 11/20/78 until 12/24/78, ammonia oxidation rate was excel-
lent. The oxidation rate varied from 90 to 95 percent. Between 9.1 and .13.6
kg/day (20 and 30 Ib/day) of ammonia were removed and the tower loading was
about 24 to 35 gm/day/cum (1.5 to 2.2 lb/day/1000 ft3) or 22 to 32 percent
of design. For two weeks from 12/26/78 and until 1/3/79, the.ammonia loading
more than doubled to 36 kg/day (80 Ib/day) due to the Christmas tourist
season. During that time the amount of ammonia oxidized increased from 13.6
to 18.2 kg/day (30 to 40 Ib/day), but was only 50 percent of the influent
loading. The tower was not able to quickly respond to the rapid increase in
ammonia loading over the 8-day Christmas holiday period. It was concluded
that the tower must be previously acclimated to these peak loading conditions
in order to be able to oxidize the increased amount of ammonia at the expectd
higher loading conditions.
After the Christmas holiday season the tower loading again dropped to
about 13.6 to 18.2 kg/day (30 to 40 Ib/day). At these loadings the tower am-
monia oxidation was about 10.9 to 14.5 kg/day (24 to 32 Ib/day), which repre-
sented an 80 percent removal. This level of ammonia oxidation was better than
87
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100
REDWOOD UP 3ATE
WARM WEATHER
18 25 1 8 15 22 29 6 13 20 27 3 10 17 24 31 1 14 21 2«
Figure 17. Nitrification tower ammonia loading and ammonia .oxidized during
the redwood update warm weather and redwood update cold weather
operating periods.
the two previous cold weather seasons, but was reduced from the 90 percent
that occurred prior to the Christmas holiday season. The 80 percent ammonia
oxidation rate continued for 3 weeks from 1/7/79 to 1/27/79. Then, extremely
cold weather occurred and the tower effluent temperature dropped to 1°C.
Subsequently, tower ammonia oxidation gradually decreased from 80 percent to
50 percent, and only about 6.8 to 9.1 kg/day (15 to 20 Ib/day of ammonia was
oxidized. It is interesting to note that this level of ammonia removal was
similar to that obtained during the redwood cold weather operational period of
the previous winter. A summary of the results for the redwood cold weather
period is shown in Table 18.
88
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The updated information for cold weather tower operation indicated that
initially, better ammonia oxidation existed when the tower was properly
acclimated prior to the cold weather season. However, tower performance was
affected by the cold weather and the tower oxidation rate decreased from 90
percent to 50 percent of the influent load. During this time, similar tower
recirculation ratios and wetting rates existed at about 2.0 and 35 1/min/sq m
(0.86 gpm/ft2), respectively, as existed during the previous cold-weather
period (i.e., 2.2 and 40 1/min/sq m (0.98 gpm/ft2)). The tower effluent
temperature ranged from 8°C to as low as 1°C to 2°C. These lower temperatures
were 1°C to 2°C colder than previous winters due to a much colder than normal
winter. It was concluded that even if the tower was acclimated, a significant
cold weather effect does exist at the relatively cold wastewater temperatures
experienced at the UTSD plant. A summary of the events that occurred during
the redwood update cold weather period is shown in Table 25.
TABLE 25. SIGNIFICANT EVENTS DURING REDWOOD UPDATE - COLD WEATHER PERIOD
Date
Event
11/20/78 to 12/24/78
(5 weeks)
12/24/78 to 1/6/79
(2 weeks)
1/7/79 to 1/27/79
1/28/79 to 2/24/79
(4 weeks)
Ammonia oxidation varied from 90 to 95 percent.
About 30 Ib/day of ammonia was removed.
Tower loading was about 2.2 lb/day/1000 ft3 or
32 percent design.
Tower loading rapidly doubled to 80 Ib/day
(i.e., 5.8 lb/day/1000 ft3 or 85 percent
design).
Tower loading decreased to 30 to 40 Ib/day
(i.e., 2.2. to 2.9 lb/day/1000 ft3, or 32
to 43 percent of design).
Ammonia oxidation was about 80 percent.
Tower loading remained at 30 to 40 Ib/day.
Tower effluent temperature varied from 1°C
to 3-°C (colder than previous two winters).
Ammonia oxidation decreased from 80 to 50
percent.
Ib/day x 0.454 = kg/day; lb/day/1000 ft3 x 16.0 = gm/day/cum
89
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Overall Nitrification Evaluation
Nitrification tower performance as compared to a > 90 percent oxidation
capability was marginal throughout the research project, except during the
fall and early winter of 1978, when 90 to 95 percent ammonia oxidation existed
and the tower loading was about 32 percent of its design value. Several
events occurred during various times of the research project that contributed
to the tower's low overall ammonia oxidation efficiency. Among these were:
negligible tower loading during start-up, rapid increases in tower loading
during cold weather operation, summer loadings on one half of the tower that
were significantly greater than design, periodic sloughing of solids from the
tower which necessitated periods of shutdown, varying tower recirculation
ratios, and low wastewater temperatures during cold weather operating periods.
In addition to these items several other factors were felt to be potentially
detrimental to ammonia oxidation capability of the tower; low pH and alkalin-
ity. Controlled bench studies were conducted to test the potential impact of
these items on the ammonia oxidation capacity of the UTSD plant.
The results of the bench test special studies showed that given sufficient
time, complete nitrification always occurred. When alkalinity was added and
the pH was increased, the rate of ammonia oxidation increased substantially
and complete nitrification eventually occurred in all batch tests. It should
be noted that the optimum pH for nitrification is above neutral (approximately
pH 8.6). The pH of the tower influent was always on the acid side of neutral,
and ranged from pH 5.8 to pH 6.8.
From these bench scale studies it was concluded that the full scale nitri-
fication results during the research project could have been dramatically in-
fluenced by low wastewater pH. It was hypothesized that the lower overall pH
values hindered the rate of ammonia oxidation capability through the towers,
and sufficient time and/or exposure to the nitrifying microorganisms was not
available to achieve good nitrification at the loading rates experienced.
This hypothesis could not be confirmed during the research project.
90
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Under present loading conditions it may be necessary to place the entire
tower (both the redwood and plastic media) into service to achieve better
ammonia oxidation capability. In so doing increased contact time with nitri-
fying microorganisms would be attained which would overcome the documented
nitrification rate reducing effect of the low wastewater temperature and the
hypothesized nitrification rate reducing effect of the relatively low waste-
water pH. Also, increased ammonia oxidation capability would be provided for
the peak ammonia loading time of the year (i.e., summer, tourist season).
Better and possibly near complete nitrification may occur under existing
loading conditions using all of the tower, except when shock loading condi-
tions occur. To adequately handle the shock loads, tower acclimation using
chemical ammonia addition may be required. Then, as plant flow rates and
tower ammonia loadings increase, pH adjustment may be necessary to increase
the rate of ammonia oxidation to consistent conversions of greater than 90
percent. It is noted that the existing nitrification facilities are not
required to perform at high levels (i.e. > .90 percent ammonia oxidation effi-
ciencies to meet the original projected design requirements.
DENITRIFICATION
The UTSD plant was designed to oxidize ammonia through the nitrification
tower. Solids that were generated and sloughed from the tower were to be
removed in the mixed media filters. This combination of unit processes was
thought to have a potential for nitrogen removal by denitrification within the
mixed media filters. If this was feasible, less expense would be encountered
because the filter could serve a dual purpose as a polishing filter and as a
support media for the denitrifying micro-organisms. The evaluation of the
suitability of the mixed media filters for full scale denitrification was com-
pleted during two time periods. Period A lasted for 34 days (4/3/78 to
5/9/78) and Period B for 24 days (5/21/78 to 6/14/78). Twelve days time
separated the two periods. The two time periods were differentiated by the
number of filters on line and by a slightly different wastewater temperature.
During Period A, one filter was on line and the average wastewater temperature
91
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was 9.4°C. During Period B, two filters were operated and the average waste-
water temperature was 13.1°C. Two filters were placed into operation during
Period B because of an increase in the plant flow rate, and because the filter
used in Period A had a tendency to plug when methanol was added.
Filter influent and effluent flow proportioned samples were collected
every two hours for a 24-hour period from Sunday through Thursday. Analyses
conducted on most of the composited samples include N02/N03-N, NH3-N,
TKN, ALK, COD, BOD5, and TSS. Temperature, D.O. and pH tests were conducted
on grab samples. The performance of the filter with respect to run time and
backwash requirements was also of special interest. Therefore, filtration
rate, run time, head loss, backwash rate and backwash duration information was
collected prior to, during, and after the denitrification study.
Start-Up Interval
Methanol was added to the filter influent to encourage the denitrification
process. The methanol storage and feed system to provide this capability was
designed and installed as part of the research project. Methanol was added to
the filter influent at a point preceeding the existing in-line mixer. The
amount of methanol added to accomplish denitrification was carefully con-
trolled, since it was assumed that excessive methanol addition would lead to
"break-through" and an increased BOD5 and COD concentration in the filter
effluent. The theoretical formula for determining the amount of methanol
required has been developed by McCarty, et. al. as follows (3):
Cm - (2.47) (N03-N) + 1.53 (N02-N) + 0.87 (D.O)
where: Cm - mg/1 of methanol required.
N03-N = mg/1 of nitrate nitrogen in influent.
N02~N = mg/1 of nitrite nitrogen in influent.
D.O. = mg/1 of dissolved oxygen in influent.
Assuming that typical (4) influent concentrations to a denitrification
process would be 25 mg/1 nitrate, 0.5 mg/1 nitrite, and 3 mg/1 D.O., the
92
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theoretical amount of methanol indicated by this equation to achieve complete
nitrogen removal would be 2.5 times the amount of nitrate in the feed system.
Using the above assumed concentrations, the methanol requirement to satisfy
the D.O. demand would be 4 percent of the total feed requirement. The percen-
tage of methanol to satisfy the D.O. demand for the UTSD system was much
greater than 4 percent. This increased demand of methanol to satisfy the D.O.
requirement greatly influenced the start-up procedures.
The combined average of the results for both Period A and Period B are
shown in Table 26. Also shown is information collected prior to the denitri-
fication study. The start-up interval was separated into two time frames.
One was labeled "Methanol Less than D.O. Requirements" (i.e. less than 0.87 x
D.O. concentration) and the other "Methanol Greater than D.O. Requirements".
As shown in Table 26, N02/N03~N removal prior to the denitrification study
did not exist, in fact an increase occurred in the N02/N03~N concentration
of the filter effluent. Correspondingly, there was an expected reduction in
the NH^-N and alkalinity concentrations of the filter effluent. Apparently,
sufficient D.O. existed in the filter influent to allow nitrification to occur
within the filter.
During start-up of the denitrification study, methanol was initially added
in small quantities which were gradually increased. It was felt that exces-
sive methanol additions would lead to breakthrough and an increase in the
BOD5 concentration of the final effluent. Therefore, during the initial
start-up period the amount of methanol that was added was not sufficient to
reduce the D.O. concentration to a point where denitrification would become
predominant. An average 9.6 Kg/day (21.1 Ib/day) of methanol was added where-
as the methanol requirement to satisfy the D.O. requirement was 16.8 kg/day
(37.1 Ib/day) (i.e., 0.87 x mass of D.O. in filter influent). The result was
that sufficient D.O. still existed to allow nitrification to dominate the
reaction within the filter, and the effluent N02/N03-N concentration at
6.5 mg/1 was greater than the influent concentration at 5.5 mg/1. However, at
the same time, the effluent BOD5 concentration increased by about 100 per-
cent to 16 mg/1, indicating that some methanol breakthrough occurred. It
93
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TABLE 26. SUMMARY OF DATA COLLECTED DURING PERIOD A AND
PERIOD B OF THE DENITRIFICATION SPECIAL STUDY
Start-Up (Acclimation)
Prior To Methanol Methanol
Evaluation Less Than Greater Than
Parameter Periods D.O. Required D.O. Required
Number of Days
(Combined Periods)
Wastewater Flow (mgd)
Methanol Added (Ib/day)
M/N Ratio (Ib/lb)
Methanol Demand for
Oxygen Req'd (Ib/day)*
D.O. Inf (mg/1)
N02N03-N Inf (mg/1)
Eff (mg/1)
Removal (%)
Filter Head Loss Rate
H/L (ft/hr)
Filter Rate (gpm/ft2)
BOD5 Inf (mg/1)
Eff (mg/1)
Removal (%)
TSS Inf (mg/1)
Eff (mg/1)
Removal (%)
COD Inf (mg/1)
Eff (mg/1)
Removal (%)
TKN-N Inf (mg/1)
Eff (mg/1)
Removal (%)
NH4-N Inf (mg/1)
Eff (mg/1)
Removal (%)
Alkalinity Inf (mg/1)
Eff (mg/1)
Removal (%)
Organic Nitrogen
Inf (mg/1)
Eff (mg/1)
Removal (%)
35
0.46
0
0
25.1
7.5
5.3
6.5
-23
0.26
2.22
24
8.1
66
12
4
64
45
34
24
13.7
11.4
17
10.6
9.2
13
74
63
12
3.1
2.2
29
11
0.69
21.1
0.67
37.1
7.4
5.5
6.5
-18
0.50
3.03
27
16
41
11
2
75
43
34
21
8.3
6.7
19
6.5
5.6
14
64
57
11
1.8
1.1
39
14
0.72
72.1
1.97
35.5
6.8
6.1
5.3
13
0.61
2.31
36
17
53
18
3
83
47
39
17
9.5
7.8
18
7.2
6.3
13
68
72
-6
2.3
1.5
35
Methanol
Full Feed
Interval
34
0.60
111
2.64
27.8
6.4
8.4
3.8
55
0.85
2.26
30
19
37
19
4
78
49
40
18
8.3
6.4
23
6.3
5.7
10
57
64
-12
2.0
0.7
65
mgd x 3785 = cum/day; Ib/day x .454 = kg/day; gpm/ft2 x 40.7 = 1/min/ sq
*Calculated assuming 0.87 Ib methanol per 1.0 Ib D. 0.
m
94
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should be noted that the methanol concentration in the filter effluent was not
measured, thus it was not known if the increased BOD5 concentration was due
to methanol or due to a byproduct of the reaction. The term methanol break-
through was used to describe increased organics in the efluent whch contri-
buted to a higher BOD 5 concentration.
Despite the methanol breakthrough it was decided to add methanol at a rate
that exceeded the D.O. requirement. When this was done, denitrification began
to dominate the reaction and the study was considered to change from a pre-
start-up to a start-up condition. Period A had pre-start-up interval of 9
days and Period B only 2 days. For each start-up interval, 7-days time was
required before the denitrification rate reached its full potential. The con-
clusion was that the true start-up condition was reached only after the
methanol feed rate exceeded the D.O. requirement, and was not heavily in-
fluenced by the pre-start-up time period when the methanol feed rate was less
than the D.O. requirement.
An average N02/N03-N removal of 13 percent occurred during the start-
up period when the methanol feed rate was greater than the D.O. requirement.
Correspondingly, the filter effluent BOD 5 concentration was greater at 17
mg/1 than during the period prior to the study at 8.1 mg/1. However, con-
clusive evidence of methanol breakthrough did not exist because the influent
BOD5 concentration during start-up at 36 mg/1 was also greater than prior to
the study at 24 mg/1. But, a trend for a slight increase in effluent BOD5
due to methanol breakthrough is evident.
The influent TSS concentration was"also slightly greater during start-up
at 18 mg/1 than prior to the study at 12 mg/1, but the effluent TSS concen-
tration was better during start-up at 3.0 mg/1 than prior to the study at 4.3
mg/1. Better TSS'removal occurred indicating that biological growth within
the media enhanced the filtering action. However, this biological growth also
reduced the filter run time and increased the filter head loss rate which
eventually caused the study to be halted.
95
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Methanol Full-Feed Interval
Methanol was initially added to the filters in small amounts to encourage
the growth of the denitrifying microorganisms and to minimize breakthrough.
The dosage was then gradually increased as denitrification proceeded. This
period of evaluation was called the methanol full-feed interval. The full-
feed operating interval of Period A was 19 days and for Period B 15 days
(total of 34 days). During each of these full feed operating intervals the
amount of methanol added varied which provided different methanol to nitrate
(M/N) feed ratios. The ratios encountered includes the requirements for
nitrite and oxygen. Typically, methanol requirements for these parameters are
small relative to the nitrate requirement (4). In this report the M/N ratios
presented were calculated using mg of methanol fed per m g of N02/N03-N in
the influent as a basis. It is noted, however, that the methanol requirement
to satisfy the oxygen demand was higher than typical. Actual M/N ratios to
achieve complete denitrification reportedly have ranged from 2.5 to 3.5 (4).
Similar ratios were tested during the UTSD denitrification study. The percen-
tage removal of N02/N03~N compared to the corresponding M/N feed ratio is
shown in Figure 18. Data to make this analysis was available for twenty-one of
the thirty-four full feed days.
The average N02/N03-N removal during methanol full-feed was 55 per-
cent, and ranged from 29 percent to 99 percent. This range of removal
appeared to be directly related to variable M/N ratios as shown in Figure 18.
A linear relationship was developed between the N02/N03-N removal percen-
tage and the M/N feed ratio. The number of data points for this analysis was
limited due to the relatively short duration of each of the study periods
caused by filter plugging problems. As shown in Figure 18, a M/N feed ratio
of about 4.4 is indicated to achieve 90 percent removal of N02/N03-N,
which is higher than the reported values mentioned earlier. Several reasons
may have contributed to the higher M/N ratio, including relatively low
operating temperature, too short a reactor detention time, and a relatively
high influent D.O. concentration.
96
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PERIOD A, TEMP = 9.4°C
DT=20MIN
APERIOD B, TEMP = 13.1 C
DT = 26 MIN
M/N RATIO
Figure 18. Percent N02/N03-N removal versus methanol to nitrate feed
ratio for Period A and Period B denitrification study.
The average wastewater temperature for Period A was 9.4° C and for Period
B 13.1° C. A slight trend for higher removal at a given M/N ratio when the
wastewater is of a higher temperature is qualitatively illustrated in Figure
18. More af the data points for NC^/NOg-N removal for the higher tempera-
ture Period B are above the line of best fit. However, significant and con-
clusive data does not exist with these data points.
The reactor detention time varied from Period A to Period B, because one
filter was used during Period A and two filters were used during Period B.
The average wastewater flow rate during Period A was 1820 cum/day (0.48 mgd)
and during Period B, 2840 cum/day (0.75 mgd). The corresponding reactor
detention times with the appropriate number of filters on line was 20 min for
Period A- and 26 min for Period B. Reactor detention time was determined by
using the entire volume of the mixed media pressure vessels. Media only
occuppied approximately one half of the reactor volume, and therefore only
about one half the detention time calculated was under packed bed conditions.
97
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These detention times were apparently sufficient to allow denitrification to
proceed, but may have been too short to allow complete denitrification in
accordance with available methanol.
During the periods of study the average influent D.O. concentration was
relatively high at 6.4 mg/1 and the N02/N03~N concentration relatively low
at 8.4 mg/1. The calculated M/N ratio includes the oxygen requirement because
it is typically small (4 percent) relative to the nitrate requirements (4).
For the full methanol feed period shown in Table 26 the average oxygen
requirement was 25 percent of the M/N ratio. If the M/N ratio of 4.4 to
achieve 90 percent N02/N03~N removal, as indicted in Figure 18, was ad-
justed for the oxygen requirement, then the M/N ratio would be 3.3 and move in
line with reported values. The large amount of methanol required to satisfy
the oxygen requirement at the UTSD was felt to be the major contributing
factor to the higher than expected M/N ratios per unit NC^/NOg-N removal
shown in Figure 18.
During full methanol feed some methanol breakthrough apparently existed
because both the BOD 5 and COD concentration of the filter effluent were
greater than prior to the study and their respective removal efficiencies were
lower. The effluent BODj concentration increased from 8.1 mg/1 to 19 mg/1,
and the 8005 removal efficiency decreased from 66 to 37 percent. The ef-
fluent COD concentration increased from 34 mg/1 to 40 mg/1, and the COD
removal efficiency decreased from 24 to 18 percent. It should also be noted
that most of this data was collected when the N02/N03~N removal was less
than 90 percent, and methanol addition was apparently less than the N02/~
~N requirement.
The only other major chemical change in the filter effluent that was mea-
sured during the denitrification study was in the alkalinity. During methanol
addition the alkalinity of the filter effluent was greater than the filter in-
fluent. The TKN removal was slightly higher and NH3~N removal was slightly
lower. The overall results of the denitrification study to this point indi-
cates that methanol addition to the mixed media filters does allow
98
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denitrification to proceed, and 90 percent N02/N03~N removal can occur if
sufficient methanol is added to achieve the necessary M/N ratio. Some
methanol breakthrough occurs., but does not increase the BODc concentration
to unacceptably high values. However, as shown in Table 26, the filter's rate
of headless (H/L) increased significantly when methanol was added. This
increase in the rate of headless eventually caused the study to be halted and
will be further discussed.
Filter Performance (Physical Parameters)
The increase in the filter headless rate could be attributed to an in-
crease in solids production from denitrification and/or to the type of solids
that were generated. The theoretical formula for solids production is as
follows:
Cb = 0.53 N03-N + 0.32 N02~N + 0.19 D.O.
where Cb = biomass production - mg/1
N03~N = Nitrate concentrations influent - mg/1
N02~N = Nitrate concentrations influent - mg/1
D.O. = D.O. concentrations influent - mg/1
Using the full-feed average N02/N03~N and D.O. concentrations at 8.4
mg/1 and 6.4 mg/1, respectively, the theoretical biomass production was cal-
culated at 5.7 mg/1. This value was 30 percent of the average influent TSS
concentration of 19 mg/1. This increase in the solids removal requirement may
have caused the filter headless rate to increase somewhat, but not to the
extent that occurred.
The rate of filter headless was obtained by dividing the change in the
filter loss of head between backwashes (H in Hg or ft of H20) by the length
of time between backwashes (L in hours). Typically, the change in filter loss
of head between backwashes was about 3.7 m (12 ft). The parameter that
changed the H/L ratio was the length of time between backwashes. A low H/L
ratio was desirable because it indicated that there were a minimum number of
filter backwashes required.
99
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The daily average H/L ratios for both Period A and Period B are shown in
Figure 19. The H/L ratio during the methanol full-feed interval is shown.
The average filtration rate during these periods was 92.0 1/min/sq m (2.26
gpm/ft2).
6
cc
X
x 4
i
ui
a 3
I 2
o
PERIOD A
PERIOD B
; i i i i i .I. iiiii i_iiiiiii\iiiiiiL_
19 21 23 25 27 29 1 3 5 7 9 31 2 4 6 8 10 12 14
APRIL
MAY
1978
JUNE
6 -
cc
X
4 x
ui
3 I
V)
2 O
111
Figure 19.
Filter head loss rate during Period A and Period B methanol
full-feed operating interval, (ft/hr x 0.305 = m/hr).
As shown for Period A, the H/L ratio increased during the end of April and
then decreased again. The reason for this increase was attributed to an in-
creased wastewater flow rate. In Period B, the H/L ratio increased on 6/1/78
and again on 6/10/78, and decreased on subsequent days. In both of these
cases the filters were taken off line for a period of up to 24 hours, which
enabled them to recover somewhat. However, as shown, the H/L ratio increased
significantly on the last operating day of both periods. Filter run times
were reduced from about 24 hours to only 2 to 3 hours in both periods, and the
system had to be shut down in both cases. This substantial reduction in fil-
tration capability was the single most detrimental aspect concerning denitri-
fication using the mixed media filters.
100
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It was concluded from these results that substantially lower surface
loading rates would be required if denitrification using a mixed media filter
is to be feasible. However, several significant aspects concerning the UTSD
study temper this conclusion. The filter influent D.O. concentration was
higher than typically expected and probably contributed to excess biological
growth on the filter media. The type of biological growth and/or the amount
of growth associated with these higher D.O. values may have enhanced the fil-
ter plugging problem. JFull documentation as to the validity of co-currently
utilizing mixed media filters for filtration and denitrification cannot be
made based on these results. What can be concluded is that the dramatic
impact of filter plugging on this dual usage of mixed media filters certainly
makes the denitrification aspect certain and worthy of special attention
during similar future studies. Furthermore, a full-scale system design should
not be completed without further study.
The filter backwash rate and duration during the dentrification study was
maintained at 509 1/min/sq m (12.5 gpm/ft2) and 15 min, respectively.
Because of the relatively short periods of study, no attempt was made to
change the backwash rate or duration during each evaluation period. After the
evaluation had been completed, the backwash rate and duration were changed to
determine any effects associated with the type of backwashing. In total,
three different types of backwashing were investigated. The first type was a
continuation of the backwash rate of 12.5 gpm/ft2 and duration of 15 min.
This was implemented after Period A on the one filter that was used for deni-
trification during that period. The H/L ratio initially was about 6.0, and
the backwashing frequency had been reduced to two hour intervals. After 6
days and 12 backwashes, the H/L ratio decreaed to 0.5 and the backwashing
frequency had increased to 24 hours intervals.
After the Period B evaluation, two different types of backwashing were im-
plemented, one on each of the two filters that were used for denitrification
during that period. On one filter a program of backwashing at a lower rate
for a longer period of time was implemented. A rate of 8.7 gpm/ft2 for 23
101
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min. was used to try to achieve longer scrubbing action within the media.
The H/L ratio initially was about 4.5 and the backwash frequency was about
every 2 1/2 hours. After seven days and 14 backwashes, the H/L ratio
decreased to 0.5 and frequency of backwashing had increased to 24 hour
intervals. On the other filter that was used for denitrification during
Period B, a rate of 13.2 gpm/ft2 for 15 min. was used to achieve a more
violent backwashing action. In this case the H/L ratio was again 4.5 and the
backwash frequency was about every 2 1/2 hours. After only 4 days and 8
backwashes, the H/L ratio was reduced to 0.5 and the frequency of backwashing
had increased to 24 hour intervals. The higher backwashing rate improved the
recovery rate of the filter and represented a better backwashing program.
MIXED-MEDIA FILTRATION
Effluent from the nitrification tower was directed to the mixed-media
filters where suspended material was captured and removed. The filtration
system consisted of four pressure vessels, each containing a mixture of three
different types of media and a gravel support system. The flow rate through
the filters was matched to the nitrification tower flow rate by the use of a
bubbler-tube system and rate-of-flow controllers. Filter backwashing was
accomplished manually, but could also be initiated automatically. Ozonated
plant effluent served as the backwash water supply. Backwash wastewater
flowed to a separate storage basin and was eventually discharged at a control-
led rate to the Thompson River Lift Station.
Data on filter performance was collected for the period of October, 1976
through April, 1978. Beginning in April, 1978, a study to determine the suit-
ability of the filters for denitrification was initiated. Data during this
period was included in the denitrification section of this report. A summary
of the filter's performance showing the mean values of the data collected and
excluding periods of excessive sloughing from the nitrification tower is pre-
sented in Table 27. The effects of' sloughing and other significant events
that occurred during the evaluation period are discussed separately. For the
periods presented in Table 27, the overall average wastewater flow rate was
102
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TABLE 27. SUMMARY OF PERFORMANCE OF MIXED-MEDIA FILTRATION SYSTEM
Parameter
Mean Value
Removal %
BOD5-mg/l
Influent
Effluent
COD-mg/1
Influent
Effluent
TSS-mg/1
Influent
Effluent
Turbidity-NTU
Influent
Effluent
Ammoniamg/1
Influent
Effluent
Total Phosphorus-mg/1
35
10
56
36
22
6
6.1
2.1
5.9
5.3
71
36
73
66
10
Influent
Effluent
Fecal Coliform-#/100 ml*
Influent
Effluent
Flow mgd
Range (1 Filter)
Range (2 Filters)
Hydraulic Loading-gpm/f t2
Range (1 Filter)
Range (2 Filters)
Head Loss Rate-ft/hr
Range (1 Filter)
Range (2 Filters)
Backwash Frequency-#/week
Range (1 Filter)
Range (2 Filters) .. ,;:
Backwash Rate-gpm/ft2
Backwash Time min
Backwash Volume-gal
4.7
4.4
4.75 x 104
4.28 x 104
0.47
0.18 - 1.12
0.45 - 1.12
2.02
0.87 - 5.40
1.09 - 2.70
0.56
0.009 - 1.31
0.51 - 4.63
9.7
2-31
. 9 -; 46
13.0
14.4
26,096
6
10
*Expressed As Geometric Mean
mgd x 3785 = cu m/day; gpm/ft2 x 40.7 = 1/min/sq m; ft/hr x 0.3048 =
m/hr; gal x 3.785 = 1
103
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1780 cu m/day (0.47 mgd). The lowest flows received at the plant typically
occurred during the fall, winter and spring. The highest flows occurred
during the summer when peak daily flows of 3785 cum/day (1.0 mgd) were
received. During the low flow periods, only one of the four filters was in
service. For approximately three months during the summer, when the influent
flow was typically greater than 2840 cu m/day (0.75 mgd), two filters were
utilized. This approach to filter usage resulted in an average hydraulic
loading of 82 1/min/sq m (2.02 gpm/ft2).
The filter backwashing and operating sequence utilized the following pro-
cedure: a predetermined maximum filter head-loss (i.e. 3.7 m (12 ft) of
HoO) was set on the filter control panel, and as the head loss reached this
level an alarm was sounded. The operator then took that filter off-line for
backwashing, and the next filter in the series was placed in service. In this
manner all four filters were maintained in an operable condition and were not
allowed to be idle along enough to become septic. The filter plugging rate
was quantitatively measured in terms of the head-loss rate. The head-loss
rate (H/L) was determined by dividing the head-loss (H) by the length of time
between backwashes (L). The average head-loss rate was 0.17 m/hr (0.56 ft/hr
and varied between 0.06 and 0.21 m/hr (0.2 and 0.7 ft/hr). The frequency of
filter backwashing averaged about ten times per week. This evaluation ex-
cludes periods where excessive sloughing of solids from the nitrification
tower occurred. When the towers were not sloughing, the influent wastewater
was typically of high quality which explains the relatively low head-loss
rates and long filter runs.
An average backwash rate of 530 1/min/sq m (13 gpm/ft2) for about 14.5
minutes resulted in the utilization of 100 cu m (26,100 gallons) per backwash.
Backwash rates were varied throughout the evaluation period, but no evaluation
to optimize rates and minimize backwash volume was completed.
In general, the filters worked well in polishing the effluent from the
nitrification towers (influent to the filter). An average 71 percent reduc-
tion occurred in BOD5, while the average reduction in COD averaged 37
104
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percent. A mean reduction of 73 percent for TSS and 66 percent for turbidity
was also achieved. Minimal reductions occurred in ammonia, total phosphorus
and fecal coliform concentrations.
The trends in filter performance are depicted graphically by the weekly
average values for influent and effluent BOD5 and TSS concentrations shown
in Figures 20 and 21, respectively. For the first five months of the evalua-
tion (i.e. through March, 1977) consistent BOD5 and TSS removals were
achieved through the filters with concentrations in the filter effluent aver-
aging 5 mg/1 and 4 mg/1, respectively. During this period one filter was in
service and the hydraulic loading was approximately 70 1/min/sq m
(1.7 gpm/ft^). For the next two months until a portion of the plant was
bypassed for modification in June, some deterioration in effluent quality
occurred. The mean TSS concentration in the effluent increased to 7 mg/1, and
the BODc; level increased to 11 mg/1. During this time only one filter was
in service, yet plant flow had increased significantly. The hydraulic
loading to the mixed media filter was increased by about 60 percent, to 110
1/min/sq m (2.7 gpm/ft2). This higher hydraulic loading was felt to be the
major factor that contributed to the slightly deteriorated effluent quality.
The activated sludge aeration basins were bypassed for two weeks in June
1977, to modify the gate separating the activated sludge basins. When the
plant was placed back in operation in July, two filters were put on line to
handle the high summer flows. With the two filters in service, the hydraulic
loading still averaged 102 1/min/sq m (2.5 gpm/ft2) for the months of July
and August, 1977. However, the filter influent TSS and BOD5 concentrations
increased to 38 mg/1 and 118 mg/1, respectively, which were the highest levels
reached during the total evaluation period. Much of the BOD5 was in soluble
form which was a result of trying, to "start-up" the activated sludge process
during the high summer flow period. It should also be noted that during this
time a higher than normal strength sewage was being received at the plant due
to contributions of waste from the dump station, including septic tank and
chemical toilet waste. The filters performed well in removing the suspended
solids; however, the backwash frequency increased to a high of 46 times per
105
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O»N»D»J«F»M«A»M«J«J«A»S»O«N»D«J»F«M«A
Figure 20. Mixed media filter influent and effluent BOD^ concentration
during the research project.
O)
(O
w
I-
Figure 21. Mixed media filter influent and effluent TSS concentration.
106
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week which was considerably greater than the average frequency of 10. The
BOD5 removal was not nearly as good as the TSS removal.
Also during the summer of 1977, sloughing of the biological mass from the
nitrification tower media (plastic media was in service) occurred in quanti-
ties that resulted in almost immediate plugging of the filters. Typically
when a period of sloughing occurred the biological mass from the tower would
plug a filter within 10 minutes and another filter would have to be put on
line. These extremely low filter run times required frequent backwashing
which depleted the volume of backwash water. When all of the filters were
plugged or when the volume of backwash water was depleted, the nitrification
and filtration systems were bypassed. A change in tower operation to provide
for a more constant hydraulic loading allowed the sloughing problem to become
less severe, but the problem was not eliminated. It was concluded that with
the occurrence of tower sloughing, the filters could not be depended on for
solids removal. This conclusion is significant when considering a design for
a solids capturing process following an attached growth nitrification system.
It is noted that a similar plugging problem occurred with the filters when
activated sludge solids were lost from the final clarifier. An overall con-
clusion was that the mixed media filters worked very well to polish the normal
effluent of the upstream processes, but was not suitable during periods of
process upset or tower sloughing. A sedimentation basin may be more effective
during periods of upset such as sludge bulking or solids sloughing. To this
end, a possible design consideration for the UTSD facility would be to combine
the function of the tower wet-well with that of an overflow clarifier. With
this option available the heavy solids could be removed by a sludge collector
mechanism, thus eliminating the filter's rapid plugging problem.
From September 1977, until the end of November 1977, the TSS and BOD5
concentration of the influent to the filters averaged 33 mg/1 and 32 mg/1,
respectively, which were lower than the summer loadings. Respective concen-
trations in the effluent were to 9 mg/1 and 12 mg/1. The mean hydraulic
loading also decreased to 65 1/min/sq m (1.6 gpm/ft2). The decreased
loading allowed the frequency of backwashing to return to more reasonable
values, averaging once per day.
107
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From December, 1977, until April, 1978, consistent TSS removal was
achieved across the filter. The mean TSS concentration in the effluent during
this period was 4 mg/1. BOD5 values in the effluent were more sporadic, but
the mean concentration was still only 6 mg/1. At the same time the lowest
average head loss rate was achieved during the project at 0.07 m/hr (0.22
ft/hr). This value is approximately half of the rate that existed during the
previous winter of 1977. As noted by the TSS graph in Figure 21, the influent
solids concentrations and effluent quality were almost identical for these two
winter periods. The major difference between the 1978 and 1977 winter filter
head-loss rate was associated with the operation of the activated sludge sys-
tem. As previously discussed, a higher mass was held in the activated sludge
system during the 1978 winter, which resulted in improved BOD5 removal. The
sludge characteristics associated with the two levels of activated sludge sys-
tem mass apparently were responsible for different forms of effluent suspended
solids, and consequently different head-loss rates through the filters.
In conclusion, the mixed media filters normally worked well to polish the
UTSD plant effluent. However, during periods of heavy sloughing from the
nitrification tower or periods of solids loss from the activated sludge clari-
fier bypassing of the filters was required.
108
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OZONE DISINFECTION
General
The ozone disinfection system was not run continuously during the two-
year data collection phase of the research project, because several system
modifications were necessary before safe, continuous operation could occur.
The system was operational on a periodic basis, and during portions of the
two-year data collection phase of the research project separate special
studies were completed to evaluate the performance, design and cost aspects of
the system's operation. This section, of the report describes the results of
the special studies.
Data collection for the ozone system special studies included chemical
and microbiological analyses, ozone in air concentrations and mass measure-
ments, ozone in water-concentration measurements, electrical power consumption
measurements and other miscellaneous measurements. Since the use of ozone in
wastewater treatment is a relatively new application, the equipment and proce-
dures used to collect the ozone data are described.
Data Collection
Ozone in Air - Concentration and Mass Measurements
The ozone concentration in the ozone/air flow from the generators was
measured by a wet chemistry procedure and by a high concentration continuous
reading ozone meter (Dasibi High Concentration Ozone Meter, Model 1003-AH).
The wet chemistry method involved a sodium thiosulfate titration of a prepared
solution of potassium iodide which had been exposed to a known volume of the
ozone/air flow stream. A detailed description of the testing and data record-
ing procedures is included in Appendix G.
An alternate acceptable method of monitoring ozone concentration in air
was available after the Dasibi continuous reading ozone meter was properly
set-up and calibrated. Originally, meter readings did not correlate with wet
109
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chemistry results. The problem was isolated to the ozone/air and purge air
flow rate to the meter. Lowering and controlling the ozone/air and purge air
flow rates to about 2 1/min resulted in consistant meter readings that corre-
lated well with wet chemistry results. A comparison of meter results with wet
chemistry results is shown in Table 28 and Figure 22. Due to the good
correlation between wet chemistry and Dasibi meter results, it was concluded
that the Dasibi meter could be used to determine the ozone in air
concentrations so that additional data points could be less tediously
obtained. However, the Dasibi meter was used to obtain only about 25 percent
of the ozone/air concentration measurements used in this report, because the
problem with the meter was not corrected until the later part of the research
evaluation.
TABLE 28. SUMMARY OF COMPARISON OF CONTINUOUS MEASUREMENT DASIBI OZONE
METER RESULTS WITH WET CHEMISTRY RESULTS
Date
7/19/78
7/21/78
7/25/78
Dasibi Meter
Span Setting
Number of Tests
Average Wet Chemistry*
Result (ppm(vol))
Average Actual Dasibi*
Reading (ppm(vol))
Average Difference (%)**
Range of Difference (%)
80570
4
5598
5532
0.1
-0.2 to 2.0
80570
9
5372
5351
0.4
-0.7 to 2.6
80570
5
3222
3204
0.6
-0.7 to 1.7
*Corrected to standard conditions of 1 atmosphere pressure and 25°C temp.
(Wet Chemistry - Actual Dasibi) (100)
(Wet Chemistry)
**Percent Difference
110
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The ozone/air concentration was
combined with the generator air flow to
obtain the mass of ozone produced. The
generator air flow was measured with a
Fischer and Porter Series 10A3500
"Flowrator" meter. The recorded flow
was corrected to standard pressure and
temperature conditions of one atmosphere
and 25°C.
S 600O
o.
a.
^5000
z
5
< 4000
111
1C
OC 300O
111
1-
UJ
S 2000
m
Q
/
DIRECT COR
o ACTUAL
/
/
/
RELAT
X
>
ON
X
X
0 1000 20OO 30OO 40OO 50OO 6000 7000
WET CHEMISTRY RESULT- PPM IVOL)
Figure 22. Comparison of Dasibi
meter and wet chemistry ozone/
air concentration measurements.
The ozone/air concentration of the
contact basin offgas was measured using
a wet chemistry procedure. A detailed
description of the testing and data
recording procedures 'is included in
Appendix H. The flow rate of off-gas
through the vent duct was measured using a pitot tube. The pitot tube was not
ozone resistant so the off-gas flow rate determinations were made with the
ozone generator shut down and only the air pretreatment system running. Off-
gas flow measurements were taken at different air flow rates from the air
pretreatment unit. The data points were very reproducible and a curve was
developed relating off-gas flow rate to air flow rate from the ozone
generation system. The curve was used to determine off-gas flow rate during
testing of the ozone disinfection system. (See Table H-2 of Appendix H). The
off-gas flow rate, corrected to standard conditions, was coupled with the
off-gas concentration and was used to obtain the mass of ozone contained in
the contact basin off-gas.
Ozone In Water - Concentration Measurements
Ozone residual concentrations in the effluent from the ozone contact
basin were initially made using a volumetric titration procedure. Using this
procedure it became apparent that the color change at the end of the titration
was nearly impossible to detect. It was decided that an amperometric titra-
tion method would be employed. An amperometric titrator was purchased and was
used to obtain ozone/water concentrations. During the research evaluation
111
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period, good disinfection results were often obtained with no detectable or
negligible ozone residuals.
Electrical Power Consumption Measurements
Ozone generator and air pretreatment power consumption measurements were
made with a Sangamo type S3DS watt-hour meter, which was tied into the elec-
trical feed lines to both the ozone generator and air pretreatment units. The
meter provided the capability to determine totalized kilowatt-hour readings,
maximum kilowatt demand readings and instantaneous kilowatt demand readings.
A sample of the data sheet used to record test information and calculate power
requirement values is included in Table G-2 of Appendix G.
Miscellaneous Measurements
Other measurements and gauge readings were taken in conjunction with gen-
erator production determinations as shown in Table G-2. of Appendix G. The air
pretreatment dew point was measured with a Shaw Model "S" Mini Hygrometer
which had a Red Spot probe. Using the meter, the changes in air dew point
from the air pretreatment system were recorded throughout the day. The air
dew point as measured by this procedure typically ranged from -70°C to -54°C.
(Note: new information developed in March, 1979 indicated that these results
were inaccurate. The magnitude and impact of the inaccurate readings on the
results are presented at the end of this section.
The air compressor seal water pressure reading was recorded daily and
also every time ozone generator production testing was conducted. The seal
water pressure was the line pressure of the water that entered the water, ring
seal. The pressure gauge was located before a filter screen in the water
supply line. When the in-line filter screen became plugged, varying seal
water pressure indicated the varying water flowrate to the seal. A variable
flowrate affected the compressed air temperature, which in turn affected power
consumption of the refrigerant drier.
112
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Data Evaluation and Discussion
The discussion of results from the research evaluation of the UTSD ozone
disinfection system is separated into four general categories: ozone genera-
tion, ozone system power requirements, ozone contacting system and disinfec-
tion performance.
During the UTSD research evaluation the ozone disinfection system was
intermittently operated. Intermittent operation resulted from numerous prob-
lems requiring design or operations changes. Several of the problems
encountered were associated with the "state of the art" design of one of the
first full-scale ozone wastewater disinfection systems in the United States.
Much conflicting and confusing information was provided by various "ozone
experts" in regard to the UTSD ozone disinfection system. The conflicting
information provided often delayed the correction of the design and Operation-
al problems encountered. The major disadvantage of the intermittent operation
of the ozone disinfection system was that a thorough evaluation of disinfec-
tion performance was not achieved.
Ozone Air Pretreatment
The three components of the ozone generation system were air pretreat-
ment, ozone generator and power supply. These three areas were evaluated both
separately and in combination during the course of the research effort. The
ozone generation system performance was dependent upon good quality dry air.
As such, the operation and performance of the air pretreatment system was just
as important as the operation and performance of the generator itself.
Several problems were encountered with the air pretreatment system and
the potential for some problems to reoccur exists. Steps are being taken to
eliminate this potential.
The air compressor for each air pretreatment system was a constant speed
unit and continuously discharged an air flow of 160 cu m/hr (94 scfm). By
bleeding-off excess air, the air pretreatment system could operate at variable
113
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air flow rates. Originally, excess air from the compressor was bled-off after
passing through the air drying tower. Each drying tower was rated at a
maximum air flow of only 130 cu m/hr (78 scfm), thus was constantly
overloaded. This caused an excessive high dew point of the "dried" air.
Subsequently, a minor modification was made by installing a bleed-off valve
after the air compressor and before the air drying tower so that excess air
was bled-off before the air drying tower. Varible air flow not to exceed the
air pretreatment system's ability to provide dry air is highly desirable, but
a more economical means of providing variable air flow is required.
Compressed air was directed through a refrigerant drier that had an input
voltage of 440 volts. This voltage was compatible with the voltage to the
ozone generator, but when operational problems were encountered with the
refrigerant drier it was quickly learned that all parts locally available were
for 220 volt refrigeration units. These parts were not suitable for the in-
stalled 440 volt refrigerant drier, and parts had to be special ordered which
delayed the unit's repair. The time delay for repair of the refrigerant drier
was the main reason Generation System No. 1 was not operable during most of
the time the production data used for this report was developed. To maintain
both ozone generation systems fully operational, the UTSD will have to pur-
chase additional spare parts for the refrigerant driers. Also, the UTSD staff
was not trained nor had the necessary equipment to repair the refrigerant
unit. The corrective maintenance and spare parts problems encountered with
the UTSD 440 volt refrigeration system should be considered during the design
of air pretreatment capability for other ozone systems.
Each of the two air drying towers contained activated alumina, molecular
sieves and alumina balls desiccant material to absorb the water in the air and
lower the dew point to less than -51°C. One tower "dried" air from the com-
pressor while the other tower was regenerated by a combination of heating the
desiccant material to release the bound water and purging the tower contents
with dry air to remove the excess moisture. The towers were cycled for drying
and regeneration at 8-hour intervals.
114
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Generally, the air drying towers worked well after the air bleed-off
valve was moved to a location in the air flow scheme which was prior to air
entering the towers. However, "sticking" occurred in the linkage of the pneu-
matically operated switching mechanisms used to alternate the towers from the
drying to regeneration cycles. The linkage was lubricated, but the potential
for this problem to reoccur still exists. The signal for cycling the drying
towers is electrical while the tower switching mechanism is pneumatic. If
problems are encountered with the pneumatic switching mechanism, the electri-
cal system will still indicate that the towers are functioning normally even
though "wet" air could be passing through the tower that is regenerating. If
this occurrs, excessive moisture could be directed to the ozone generator.
Under this condition the ozone generator could be "flooded". The term flooded
is used to describe moisture buildup in the ozone generator which causes
short-circuiting and can cause electrode tube and/or fuse failure.
On several occasions flooding of the ozone generator did occur. Once
flooding occurred due to a problem with the refrigerant drier. The refrig-
erant drier motor overheated and burned out, for an as yet unknown reason. A
new refrigerant drier was ordered. When received, careful electrical checks
were made during its installation to try to isolate the problem.
Flooding of the ozone generator on three other occasions has been tenta-
tively associated with problems of variable seal water pressure to the water
ring air compressor. These generator floodings were expensive because several
electrode tubes and fuses blew out. The greater the seal water pressure the
greater the water flow rate through the compressor and the lower the tempera-
ture of compressor air. The temperature of the compressed air was important
because if the temperature was too high the refrigerant drier could not cool
the air to reduce the dew point and the air drying tower was overloaded. The
flooding problems were believed to have occurred due to plugging of an in-line
filter screen which was used to remove any particulate matter from the water
that was directed to the compressor. Plugging caused the flow of water to the
compressor to decrease and the temperature of the compressed air to increase
and eventually led to overloading of the drying tower. The entire seal water
115
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supply system is being re-evaluated to determine what design modification or
preventive maintenance checks can be instituted to reduce the frequency and/or
effects of the screen plugging problem.
Although sources of ozone generator flooding problems have been isolated,
the potential of flooding still exists. It appears that a high dew point
alarm and an associated automatic generator shut^off is necessary to prevent
the expense and loss of production associated with generator flooding. Origi-
nally, the relative air dew point was monitored with cobaltous chloride color
changing indicator. This indicator was inadequate as an alarm or protection
device for the ozone generator for two reasons: 1) Someone had to see the
color change and shut down the system before flooding occurred and 2) the
color change was not sensitive to gradual changes in dew point so potential
problems could not be detected until they were quite far along.
A dew point indicator was purchased as part of the research project to
obtain more exact information on air dew point versus generator production.
This indicator has greatly aided in the detection of changes in dew point and
correction of problems before flooding of the generator occurred. However,
the potential for generator flooding still exists since operator observations
of the indicator on a continuous basis is still required to detect any prob-
lems. As a better solution, a high level dew point alarm and associated auto-
matic generator shut-down is being considered. To date, this would have saved
the UTSD at least $1,600 in electrode tubes and fuses during the past two
years of operation.
Ozone Generator Production
Many parameters can influence the rate of ozone production including:
power supply, air dew point, ozonated air temperature which is influenced by
the volume of air directed through the generator and the ozonated air heat re-
moval capability of the cooling water jacket. These items are not all inclu-
sive, but were selected for analysis because they represented those items
within the realm of operational control for the UTSD system.
116
-------
The UTSD ozone generators were designed to supply ozone at a rate of 34.3
kg/day (76 Ib/day) at an air flow of 118 cu m/hr (70 scfm). The ozone produc-
tion for Generation System No. 2 only is discussed, because Unit No. 1 was not
operational. The production rate for different air dew point levels will be
presented because the ozone production rate decreased as the dew point of the
air increased. This change in production may be a significant operational
consideration with respect to continuous, satisfactory effluent disinfection.
The production rate will also be compared to the relative power setting of the
generator for two different air flow rates, namely the design air flow rate of
118 cu m/hr (70 scfm) and a lower air flow rate of 79 cu m/hr (47 scfm).
The air dew point readings increased proportionately to the drying tower
operating time. Typically, soon after a regenerated tower came on-line and
began drying, the air dew point reached its lowest level. As the tower dried
more air, the dew point increased. Apparently, as the desiccant absorbed and
contained more and more moisture, less moisture was absorbed as indicated by
the dew point readings. The rate of increase of the dew point was greater at
the design air flow rate of 118 cu m/hr (70 scfm) than at the lower air flow
rate of 79 cu m/hr (47 scfm). The changes in air dew point for the two air
flow rates versus drying tower operating time is shown in Figure 23.
The drying time per operating cycle
for each tower was eight (8) hours. The
lowest dew point reading shown in Figure
23 is -72°C., although readings as low as
-74°C were achieved. The highest dew
point recorded was -54°C. All dew point
levels recorded, except when obvious air
pretreatment problems were noted to cause
generator floodings, were better than the
manufacturer's rated minimum dew point
level of -51°C. The UTSD ozone air pre-
treatment system functioned very satis-
factorily.
0:47 SCFM AIR FLOW
A =70 SCFM AIB FLOW
01 2345678
DRYING TOWER OPERATING TIME-MRS.
Figure 23. Change in air pre-
treatment dew point with drying
tower operating time (scfm x
1.70 = cu m/hr.)
117
-------
The change in ozone production per
degree of change in dew point was evalu-
ated at different generator power set-
tings. Two power settings were evaluated
and results are shown in Figure 24 and in
Table 29. In general, the ozone produc-
tion level decreased as the air dew point
increased, even though the manufacturer's
rated dew point level of -51°C as measured
by the dew point indicator was achieved
throughout the drying cycle.
As shown in Table 29, the mass
decrease in ozone production per degree Figure 24. Change in ozone pro-
change in dew point was about three times duction with dew point at two
generator power settings (Ib/day
greater for the 130 amp power setting than x Q.454 = kg/day).
for the 40 amp setting. However, the
percentage change was slightly less for the 130 amp setting at 1.70%/°C. than
for the 40 amp setting of 1.93%/°C. From the data presented it was shown that
OZONE PRODUCTION - LB/DAY
_i 10 W * Ul 01
o o o o o o c
^,
"^
'°OQ000W
. © 130
^^
© 40
°oo»
AMPERE
\
AMPERE
0-0
X,
-7O -66 -62 -58
AIR DEW POINT -°C
TABLE 29. EFFECT OF DEW POINT AND POWER SETTING ON OZONE PRODUCTION
Dew Point
130 Ampere
40 Ampere
Maximum Production - 72°C.
- 70°C.
Minimum Production - 56.5°C.
- 59.5°C.
Total Dew Point Increase
Ozone Production Decrease
Specific Ozone Production Decrease
Mass Decrease
Percent Decrease
57 Ib/day
42 Ib/day
15.5°C.
15 Ib/day
0.97 lb/day/°C.
17.1 Ib/day
13.6 Ib/day
10.5°C.
3.5 Ib/day
0.33 Ib/day/°C.
Ib/day x 0.454 = kg/day
118
-------
ozone production decreased considerably with a decrease in dew point, which is
important with respect to ozone dosage to the wastewater. The implications of
these findings on design and operation are significant.
At the UTSD plant the wastewater flow rate was controlled through a flow
equalization basin and a negligible variation in daily plant flow occurred.
The ozone dosage to the effluent was manually controlled by adjusting the
generator power setting. However, at a given power setting the ozone dosage
decreased as the dew point increased. The potential magnitude of the decrease
in ozone dosage for observed changes in air dew point is summarized in
Table 30.
TABLE 30. POTENTIAL DECREASE IN OZONE DOSAGE FOR OBSERVED CHANGES IN
AIR DEW POINT (CONSTANT GENERATOR POWER SETTING AT 130 AMPS)
Air Dew Point*
-72°C.
Air Dew Point
-56.5°C.
Wastewater Flow (mgd)
Ozone Dosage
(mg/1)
(Ib/day)
1.37
5.0
57**
1.37
3.7
42**
mgd x 3785 = cu m/day; Ib/day x 0.0189 = kg/hr.
*The manufacturer's minimum rated dew point level was -51°C.
As shown in Table 30, the ozone dosage could vary from 5.0 to 3.7 mg/1 if
the air dew point changed from -72 to -56.5°C (a. change that was observed
during a typical drying cycle). A change in dosage because of dew point is
important from a design and operation basis because disinfection performance
is influenced by ozone dosage. Therefore, ozone production information at
different power settings and at variable dew point levels are required in
order to properly design and operate ozone disinfection systems. In the final
analysis it may be required that ozone systems be designed with multiple units
which have the air pretreatment drying towers changed sequentially so as to
reduce the overall effect of a rise in dew point on ozone production.
119
-------
It should be noted that the sensitivity of the system disinfection capa-
bility to ozone dosage was not evaluated due to the intermittent operation of
the UTSD ozone system. It may be that an ozone dosage between 3.7 and 5.0
mg/1 yields the same general disinfection level, especially when other system
variables like effluent COD, TSS and fecal coliform concentrations are con-
sidered. If the disinfection capability is not overly sensitive to this range
of dosages the dosage variation because of dew point would not be as critical.
This aspect should be further evaluated. However, it is still concluded that
more information should be developed by ozone manufacturers on ozone
production versus dew point levels and ozone production versus generator power
settings in order to provide design engineers and plant operators with a
better basis for ozone system design and operation.
The major factors affecting ozone production are generator power setting,
air dew point and ozonated air temperature, which is influenced by the air
flow rate to the ozone generator and the heat removal capability of the cool-
ing water jacket. The cooler the temperature of the ozonated air, the less
rapid ozone will be decomposed after it is generated. The UTSD ozone genera-
tor begins producing ozone at a consistant, reproducible level at a power set-
ting of 40 amps. The maximum power setting tested was 150 amps, when the
generator voltage was 450 volts. For the production evaluation the mass of
ozone produced was determined for power settings at 10 amp intervals between
40 and 150. The ozone production values shown in this report were taken when
the air dew point was between -70°C. and -74°C as indicated on the Shaw meter.
This dew point level represented the best condition for ozone production with-
in the limits of the air pretreatment unit.
To insure that the cooling water system was performing at optimum condi-
tions, the cooling water jacket was inspected for possible scaling which could
have reduced its heat removal effectiveness. No scaling was noted at cooling
water jacket sites that were inspected. This was as expected because no scal-
ing problems were encountered on other equipment in the plant that used the
same water supply. The temperature of the cooling water ranged between 10°C
and 12°C, which was within the ozone manufacturer's specifications.
120
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The actual temperature of the ozonated air was not recorded. However,
the relative temperature of the ozonated air was investigated within the
limits of the UTSD system by adjusting the air flow rate to the generator.
The design air flow rate of 118. cu m/hr (70 scfm) was expected to develop the
lowest ozonated air temperature, and in turn produce the highest mass of ozone
at a given power setting. The lower air flow rate of 79 cu m/hr (47 scfm) was
expected to produce a lower mass of ozone, especially at the higher power
settings. The ozone production levels for the two air flow rates is shown in
Figure 25. As shown, ozone production is nearly the same for both air flow
rates at all generator power settings, although the higher flow rate generally
had a slightly higher ozone production level. Apparently, the ozone air temp-
erature change and hence ozone production was not significantly affected with-
in the range of air flow rates capable for the UTSD system. The fact that
little production difference was shown for the lower air flow rate is signifi-
cant, because a smaller and/or slower speed air compressor could have been
used which would have resulted in an electrical power savings.
SCFM AIR FLOW
o=47 SCFM AIR FLOW
40 50 60 7O 80 90 100 110 120 130 140 15O
GENERATOR SETTING - AMPS
Figure 25. Ozone generator production at various generator power settings
(Ib/day x 0.0189 = kg/hr); (scfm x 1.70 - cu m/hr).
121
-------
The ozone production levels shown in Figure 25 ranged from 7.7 kg/day (17
Ib/day) to 26 kg/day (57 Ib/day), and a fairly uniform increase in production
occurred for each 10 amp increase of the power setting. The maximum ozone
production level was 26 kg/day (57 Ib/day). This occurred at the air flow
rate of 79 cu m/hr (47 scfm). The maximum amp setting was not tested at the
design air flow rate of 118 cu m/hr (70 scfm), because the ambient ozone
concentration within the building became too high on that test day and the
ozone generator was shut down.
The maximum ozone production level of 26 kg/day (57 Ib/day) at 79 cu m/hr
(47scfm) air flow was 25 percent less than the manufacturer's rated value of
34 kg/day (76 Ib/day). Based on comparable results for other amp settings, it
is not expected that the ozone production level at the design air flow of 118
cu ra/hr (70 scfm) would be significantly higher. The reason for the lower
than design ozone production level was not known and is still being investi-
gated. All known influences on ozone production were optimized during the
ozone production tests, including lowest achievable air dew point as measured
by the Shaw meter and clean (no scaling) water jacket. Also, prior to produc-
tion testing the generator was thoroughly cleaned, all electrode tubes were
removed and checked for damage, and all tubes were replaced according to the
manufac turer's recommendat ions.
Ozone System Power Requirements
One of the advantages considered in the selection of ozone for the UTSD
plant was on-site production. On-site production capabilities were felt to be
desireable when compared to chlorine and dechlorination chemical costs and
chemical hauling in the canyon roads which led to the plant. The initial cost
of the ozone generation equipment and the anticipated power costs associated
with the continuous generation of ozone were considered in this selection.
During the research, an evaluation of the ozone generation power requirement
was made to determine if the initial cost assumptions were adequate.
The UTSD ozone system has been intermittently operated, and the typical
operating procedure was to dose at a rate to insure disinfection. No attempt
122
-------
was made to optimize ozone dosage. As such, realistic values for power
required to generate adequate ozone to achieve disinfection were not obtained.
However, power consumption over the operating range of the ozone generating
system were determined (i.e.,. ozone generation "mapping"). Each major unit of
the ozone system were separately evaluated. Presently, power is consumed by
the air pretreatment system, by the cooling and seal water system, and by the
ozone generation process. In the future, an ozone destruct unit for the con-
tact basin off-gas will add to the power consumption.
Power consumption for the air pretreatment system included power for the
air compressor, refrigerant drier, air drying tower heater, pneumatic control
system air compressor, and electrical control circuit. The power requirements
for the air compressor, refrigerant drier and air drying tower heater were
most significant. The power requirement for the pneumatic control system air
compressor and electrical control circuit were insignificant in terms of total
power usage, and were not included in the power consumption evaluation.
The air compressor operated continuously and used 8.35 kW of electrical
energy. The air compressor was designed to provide a nominal 118 cu m/hr (70
scfm) air flow to the ozone generator. As described, the unit discharged 160
cu m/hr (94 scfm) of air, and the excess air had to be bled-off to avoid over-
loading the air drying tower. It was also determined that generator produc-
tion did not significantly change from an air flow rate of 118 cu m/hr (70
scfm) to a lower rate of 79 cu m/hr (47 scfm).
The instantaneous power consumption of the refrigerant drier was 2.0 kW.
However, a lower average daily power consumption was determined because the
drier operating time varied with the inlet air temperature and air flow rate
to the drier. As described, inlet air temperature increased as the air com-
pressor seal water pressure decreased. Generally, the average inlet air temp-
erature was about 33°C. The relationship between the refrigerant drier oper-
ating time and inlet air temperature for an air flow rate of 79 cu m/hr (47
scfm) is shown in Figure 26. At an inlet air temperature of 33°C., the
average refrigerant drier operating time was 11.1 hrs/day. A similar
123
-------
DRYER OPERATING TIME - HRS /DAY
M * O> OJ O N *
fS
>
X
-<
>
s***
s
,!
X*
'
x
J*
26 28 30 32 34 36
INLET AIR TEMPERATURE -t
Figure 26. Refrigerant drier
operating time at various in-
let air temperatures and an air
flow rate of 79 cu m/hr (47
scfm).
evaluation for the higher flow rate of
118 cu m/hr (70 scfm) indicated an aver-
age operating time of 14.4 hr/day. These
operating times were coupled with the 2.0
kW instantaneous power consumption to
determine the average daily power re-
quirements of the refrigerant drier.
The air drying tower used electrical
energy in the tower regeneration cycle.
During regeneration the tower was heated
by an electrical heater that had an in-
stantaneous power requirement of 3.65 kW.
The 8-hour regeneration cycle consisted
of tower "heating" for 4 hours and
"cooling" for 4 hours. During the 4-hour
heating cycle, heater operation was
controlled by a high temperature cut-off and a lower temperature start-up
system. Therefore, actual heater operating time was less than the total 4
hours. The average heater operating time per heating cycle was determined to
be 3.25 hours, resulting in a daily average electrical usage of 1.48 kW.
One other use of power for the ozone system was supply water for ozone
generator cooling and for air compressor operation. This water was provided
by the plant potable water pumping system. A special power consumption
measurement taken to determine the power usage of the potable water system
indicated that the average daily power consumption was 2.2 kW. The potable
water demand for the ozone generation operation was about 95 percent of the
total plant potable water usage. Therefore, the power required to supply
water to the ozone generation system was 2.10 kW.
Air pretreatment power consumption data is shown in Table 31. The daily
average power consumption for the air compressor and air drying tower heater
was not affected by air flow rate. Power consumption of the refrigerant drier
124
-------
was affected by air flow rate. However, the net effect was that the daily
average power consumption was not significantly different for the two air flow
rates.
TABLE 31. SUMMARY OF POWER CONSUMPTION FOR THE AIR PRETREATMENT
AND COOLING WATER UNITS
Unit
Ins tantaneous
Power Consumption
Daily Average
Power Consumption
Air Compressor
Refrigerant Drier
Air Drying Tower
Cooling and Seal Water
TOTAL
(kW)
8.35
2.00
3.65
5.00
@47 scfm
(kW)
8.35
0.93*
1.48**
2.10***
12.86
USE 12.9
@ 70 scfm
(kW)
8.35
1.20*
1.48**
2.10***
13.13
USE 13.1
scfm x 1.70 = cu m/hr.
*Refrigerant Drier on-time at an average inlet air temperature of 33°C.
**Average drying tower heater on-time of 3.25 hours per 8-hours cycle.
***Average potable water pump on-time of 10.5 hours. (95% of potable water
used for cooling and seal water).
The power requirement of the ozone generator increased as the level of
ozone production increased. The most important consideration was the power
required to produce a given mass of ozone (i.e., power utilization in terms of
kWh/lb). Two different air flow rates were used in determining generator
power utilization, and power consumption measurements were taken at 10 amp
intervals starting where reliable and reproducible ozone production began (40
amps) and were continued to the generator's maximum setting (150 amps).
Power consumption for the ozone generator had to be carefully determined
because power consumption measurements for the air pretreatment and the gener-
ator were combined in the readings obtained from the single ozone system watt-
hour meter. In order to attain the power consumption for the ozone generator
the power consumed by the air pretreatment units that were operating at that
time was subtracted from the total measured ozone system power that was indi-
cated by the watt-hour meter. Using this procedure, reproducible ozone gener-
ator power consumption values were obtained.
125
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The ozone generator production,
power consumption and power utilization
values for the two evaluated air flow
rates are shown in Table 32. Generator
power consumption varied from a low of
4.4 kW to a high of 25.1 kW as the gen-
erator amperage setting increased.
Ozone production also increased as the
amperage increased, but at a lesser rate
than power consumption as evidenced by
the increase in power utilization.
Power utilization increased from a low
of 13.7 kWh/kg (6.2 kWh/lb) to a high of
23.6 kWh/kg (10.7 kWh/lb), which is
graphically illustrated in Figure 27.
The power utilization values shown
in Table 32 for Ozone Generator No. 2
were obtained under conditions that
would yield maximum ozone production.
These conditions include: air dew point
equal to or less than -70°C as measured
by the Shaw meter, all electrode tubes
24
22
CD 20
'8
i 16
Z
o
- 14
io
DC
111
5
o
GENERATOR PLUS
|AIR PRETREATMENT
AND COOLING
GENERATOR ONLY
0 = 47 SCFM AIR FLOW
A=70 SCFM AIR FLOW
0 10 20 30 40 50 60
OZONE PRODUCTION - LB/DAY
Figure 27. Measured power utili-
zation for the existing UTSD ozone
generation system (scfm x 1.70 =
cu m/hr; Ib/day x 0.454 = kg/day,
kWh/lb x 2.21 = kWh/kg).
operational, negligible scaling of the cooling water jacket and a recently
cleaned ozone generator. It should be noted that a series of power utiliza-
tion measurements were taken before Generator No. 2 was cleaned. The un-
cleaned generator power utilization was an average 15 percent greater than
values that are presented for the cleaned generator.
A summary of the total ozone system power requirements for each air flow
rate evaluated is shown in Table 33 and 34. The power utilization values for
the two air flow rates were compared graphically in Figure 27. As shown,
power utilization for the two air flow rates was not significantly different.
Apparently, the difference in air flow rates which represented a fairly broad
126
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TABLE 32. OZONE GENERATOR POWER REQUIREMENTS
Ozone Generator
Ozone Production
Amperage
(ampere)
40
50
60
70
80
90
100
110
120
130
140
150
@
47 scfm
(Ib/day)
16.8
22.8
27.4
31.5
35.1
43.1
45.9
50.0
51.8
55.4
56.3
-------
r
TABLE 33. TOTAL OZONE SYSTEM POWER REQUIREMENT AT AN AIR FLOW OF
79 CU M/HR (47 SCFM)
Generator
Power
Setting
(ampere)
40
50
60
70
80
90
100
110
120
130
140
150
Ozone
Production
(Ib/day)
16.8
22.8
27.4
31.5
35.1
43.1
45.9
50.0
51.8
55.4
56.3
Power Consumption
Generator Support Systems Total
(kW)
4.4
6.2
7.8
9.7
11.4
15.1
17.0
19.7
21.4
23.5
25.9
(kW)
12.9
12.9
12.9
12.9
12.9
12.9
12.9
12.9
12.9
12.9
S2.9
(kW)
17.3
19.1
20.7
22.6
24.3
28.0
29.9
32.6
34.3
36.4
38.8
Power
Utilization
(kWh/lb)
24.7
20.1
18.1
17.2
16.6
15.6
15.6
15.6
15.9
15.8
16.5
*Air Compressor - 8.35 kW, Refrigerant Drier
Heater - 1.48 kW and Cooling Water Pumping =
= 0.93 kW, Air Drying Tower
2.10 kW.
TABLE 34. TOTAL OZONE SYSTEM POWER REQUIREMENT AT AN AIR FLOW OF
118 CU M/HR (70 SCFM)
Generator
Power
Setting
(ampere)
40
50
60
70
80
90
100
110
120
130
140
150
Ozone
Production
(Ib/day)
17.1
22.9
32.5
36.2
40.0
43.9
47.2
50.3
53.9
56.8
____
Generator
(kW)
4.6
6.4
9.9
11.4
13.1
15.1
17.2
18.8
20.8
22.6
Power Consumption
Support Systems
(kW)
13.1
13.1
13.1
13.1
13.1
13.1
13.1
13.1
13.1
13.1
Total
(kW)
17.7
19.5
i
23.0
24.5
26.2
28.2
30.3
31.9
33.9
35.7
Power
Utilization
(kWh/lb)
24.8
20.4
17.0
16.2
15.7
15.4
15.4
15.2
15.1
15.1
Ib day x 0.454 - kg/day; kWh/lb x 2.21 = kWh/kg
*Air Compressor =8.35 kW, Refrigerant Drier = 1.20 kW, Air Drying Tower
Heater = 1.48 kW and Generator Cooling Water = 2.10 kW.
128
-------
24
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.*
NERATOR PL
Fi PRETREATH
MD COOLING
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ON
^
Sw>.
X
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70 SCFM AIR 1
ACTUAL _j
EQUIPMENT
SPEC
Wtai
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'"'
less efficient electrical energy usage
occurs at lower ozone production require-
ments. The fact that the power utiliza-
tion increases dramatically at low
production requirements has significant
impact when applied to wastewater treat-
ment plant operation.
At the UTSD plant, variations in
wastewater volume and effluent quality
occur. Although flow equalization is
available, plant flows have ranged from
1140 cu m day (0.3 mgd) to 3,780 cu m/day
(1.0 mgd). To optimize ozone dosages in
line with these flow variations, an
adjustable ozone generation system is
required. The present system at the UTSD
facility is adjustable by varying the
amperage setting but at low ozone produc-
tion operating requirements, the system
operates in the least efficient electri-
cal energy usage range.
Similarly, municipal wastewater treatment plants are typically designed
for future and larger flow rates. Also, most of these facilities are designed
without flow equalization capabilities. As such, lower ozone production
requirements will most likely occur during the design life and even during
diurnal periods. At a lower ozone production requirement, the power utiliza-
tion value could be much greater than at design production levels which would
result in operation of a proportionately less economical ozone disinfection
system than would occur at design flows. The need for economical ozone pro-
duction over an adjustable range exists. In order to have this flexibility a
more uniform power usage efficiency must be developed. Multiple ozone genera-
tion and/or multiple air pretreatment units should be considered in order to
O 10 20 30 4O SO 60 70 SO
OZONE PRODUCTION - LB /DAY
Figure 28. Comparison of equip-
ment specifications and actual
UTSD ozone generation system power
utilization (scfm x 1»70 = cu m/hr) ;
Ib/day x 0.0189 = cu m/hr; kWh/lb
x 2.21 = kWh/kg.
129
-------
achieve more uniform power utilization values for a broad range of ozone pro-
duction requirements that can be expected to occur with municipal wastewater
treatment facilities.
The UTSD ozone system was intermittently operated because of periodic
high ambient ozone concentrations in the plant working environment. Several
modifications to the ozone piping and contact basin were made to reduce the
ambient ozone concentration when the generators were operated. One remaining
modification is an ozone destruct unit for the off-gases from the ozone con-
tact basin. This unit has been designed and is being constructed, and repre-
sents another source of power consumption associated with the ozone system.
The expected power consumption is between 8 and 17 kW.
March 1979 Update
During the data collection phase of the research project the dew point of
the air from the USTD ozone generator air pretreatment system was measured
with a Shaw Model "S" Mini Hygrometer which had a red spot probe. This data
indicated that the air pretreatment system worked well in that the dew point
of the air varied from -74°C to -54°C, where -51°C was the dew point recom-
mended by the manufacturer. However, subsequent to the data collection phase
of the research effort, new information was recieved that indicated that the
Shaw dew point meter may be giving inaccurate readings(6). Subsequently, the
ozone manufacturer was contacted regarding this item and consented to sending
a dew point cup measuring device to the UTSD plant for purposes of measuring
the dew point of the air from the air pretreatment system. The dew point cup
was received and comparative dew point readings were taken in March, 1979.
A diagram of the dew point cup measurement device is illustrated in
Figure 29. As shown, the air stream is directed onto the side of a polished
stainless steel cup that is attached to an outer container. About 2.5 to 5 cm
(1 to 2 inches) of acetone is placed into the cup and ice is slowly added to
the acetone until water in the "dry air" stream condences on the polished
stainless steel. A thermometer that had been placed into the acetone/dry icer
130
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mixture is then read, and the tempera-
ture reading at that instance is the
dew point reading of the air stream.
Using this procedure reproducible
results were obtained and were consid-
ered to be quite accurate measurements
of the air dew point. (Note: A mini-
mum amount of tygon tubing is used to
pipe the air flow to the dew point cup
to avoid possible moisture uptake in
the tygon tubing.)
THERMOMETER
OUTLET
POLISHED
STAINLESS
STEEL CUP
OBSERVATION
WINDOW
INLET
OUTER
'CONTAINER
Figure 29. Schematic Diagram
of dew point cup air dew point
measuring device.
The dew point results using the
dew point cup were found to be signi-
ficantly higher than the results using
the Shaw Mini Hygrometer, as shown in
Table 35. The dew point cup results
ranged 42°C, from -53°C to -11°C, while the Shaw meter readings ranged only
-6°C, from -74°C to -68°C. The Shaw meter-definitely was not as sensitive as
the dew point cup. More importantly however, the Shaw meter results indicated
that dew point levels for the air pretreatment system were better than minimum
acceptable levels of 51°C specified by the ozone manufacturer. Conversely,
the dew point cup results indicated that the dew point was usually higher than
the desired minimum value of -51°C.
Based on this new information of the actual dew point of the air being
greater than specified by the ozone manufacturer, different conclusions are
indicated for some of the information presented in the text of this report.
Some conclusions remain essentially unchanged and still other new conclusions
are dictated. The remaining discussion is presented with respect to the new
and more accurate dew point information.
Generator Flooding As discussed, several occasions of generator flooding
occurred. In order for this condition to occur, the air drying towers must be
131
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saturated condition, the desiccant material in the towers loses effectiveness
as a drying agent. It is suspected that the desiccant in the UTSD drying
tower is ineffective. New desiccant material has been ordered.
TABLE 35. COMPARATIVE DEW POINT READINGS OF DEW POINT CUP
VERSUS SHAW MINI HYGROMETER, MARCH 15. 1979
Drying Tower
Operating Time
(hr)
Air Dew Point
Dew Point Cup Shaw Mini Hygrometer
Ozone*
Concentration
(ppm/vol)
0
1
2
3
4
5
6
7
8
-42
-53
-41
-34
-26
-19
-15
-12
-11
-72
-74
-74
-72
-72
-70
-69
-68
-68
«
2683
2756
2648
2621
2502
2368
2314
2195
2170
*0zone concentration using Dasihi Meter. Generator air flow was 118 cu ml
hr (70 scfm).
The generator flooding problem was associated with four major items; 1)
continuous overloading of the air drying towers, 2) sticking of the linkage in
the tower switching mechanism, 3) refrigerant drier failure and, 4) low water
flow to the water ring compressor due to plugging of an in-line filter that
could not be detected due to improper placement of an in-line pressure gauge.
The cause of the refrigerant drier failure was unknown. It is now suspected
that the failure was due to an extreme high temperature oveloading problem
caused by item number 4 above. Of all the above mentioned items, item number
2 was most directly related to operational considerations. The other items
were related to the design arrangement of the ozone system purchased as a
&
package unit from the manufacturer. These items have now been corrected by
installing an air flow valve after the air compressor and before the refriger-
ant drier and air drying towers, and by placing the pressure gauge used to
indicate the pressure of the water to the water ring compressor at a point
after the inline filter screen.
132
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Dew Point Monitoring A conclusion was reached that a method of monitoring
the dew point and sounding an alarm for a high dew point level was necessary.
This conclusion is now more valid than ever. In addition to preventing
generator flooding, it would also have reduced the rate of desiccant failure
that apparently has occurred at the UTSD plant. However, in view of the poor
accuracy of the Shaw dew point meter, an expanded aspect of the conclusion
that a dew point meter and alarm should be provided, is that a dew point cup
measuring device should also be provided in -order to properly calibrate the
dew point meter and/or properly set the dew point high level alarm.
Generator Production Verses Dew Point'The Shaw dew point meter indicated that
the air dew point was always better than the manufacturer's minimum acceptable
level of -51°C. The later obtained dew point cup results indicated that the
opposite was true, and thus the air pretreatment system was not functioning
satisfactorily. The ozone production results did change when the Shaw meter
indicated a change in dew point, but the actual dew point values were probably
higher than the minimum acceptable levels. A quantitative figure of the
actual dew point values was not obtained, but values of 30 to 40°C higher than
minimum acceptable levels may have occurred. The conclusion that ozone pro-
duction changes as dew point chnages is still valid, but for a different range
of dew point values than indicated previously. It should be noted that,
according to the ozone equipment manufacturer, ozone production does not
change appreciably when the actual dew point is lower that -51°C. This could
not be verified at the UTSD plant, but hopefully will be when the new desic-
cant material is installed.
The conclusion that ozone dosage will vary during a drying tower cycle
along with the recommendation that accompanied it, was extremely critical for
the actual air dew point levels experienced. They are less critical if gener-
ator production does indeed change only slightly during a typical drying tower
cycle, when the actual dew point level is always lower than 051°C. However,
the concept of the conclusion and associated recommendation still is valid,
and it is still felt tha much benefit would be derived if ozone generator
133
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manufacturers would provide specific, or at least a range of generator produc-
tion values for various power settings and dew point levels for their particu-
lar systems. This information would greatly aid design engineers in system
design, and also would be extremely beneficial to plant operators since they
would be able to periodically check their system's performance with expected
values. In so doing, minor problems may be corrected if the system perform-
ance was noted to be poorer than expected, and corrective action initiated
which may prevent major and more costly problems from occurring.
The maximum ozone production level of the UTSD generator was 1.26 kg/day (57
Ib/day); which was 25% less than rated by the manufacturer. The major reason
for the lower ozone production level is now attributed to a low actual dew
point of the air fed to the generator. It is not known if the generator will
meet or exceed production specifications when the drying tower desiccant is
replaced and the dew point is lowered, but certainly much better performance
is expected.
Generator Power Requirements Verses Dew PointThe actual power utilization
values obtained during the research project were greater than expected design
values, because the ozone production rate was lower than expected. It is now
felt that the major reason for the low producton levels was due to a higher
than minimum acceptable dew point of the air feed stream. When the dew point
decreases, the level of ozone production is expected to increase and the rela-
tive power utilization values decrease. However, this aspect was considered
in the discussion of ozone system power requirements. Therefore, no changes
in the overall conclusion regarding ozone power requirements as discussed are
necessary.
Ozone Contacting System
Ozone produced in the generators was directed to the ozone contact basin.
Several design modifications were made to the ozone contact basin and ozone
piping arrangement. Some of the modifications represent "state of the art"
design changes that evolved over the 2-year operation period of the UTSD ozone
134
-------
system. The modifications made include: contact basin covering, basin ex-
haust changes, baffle and scum skimmer changes, and ozone piping and diffuser
replacement and an ozone destruct system.
An initial obstacle in operating the ozone disinfection system was the
presence of high ambient ozone concentrations in the operator working environ-
ment. Present minimum acceptable standards for human exposure to ozone are
0.1 ppm by volume for a period not to exceed 8 hours. During initial start-
up, ambient ozone concentrations of 3-5 ppm by volume for 2-hour periods, with
peaks of 15-30 ppm by volume were encountered.
It was determined that a portion of these high ambient ozone concentra-
tions were the result of a partially covered contact basin. Additionally, the
part of the tank which was covered was not sealed. The contact basin was
modified by covering the entire basin with aluminum plates and sealing the
joints with hypolon gasket material. It was anticipated that a covered and
sealed basin would prevent off-gas leaks.
When the revisions were completed, ozonation was again attempted but high
ambient ozone concentrations still occurred. This problem was isolated to
ineffective sealing of the basin cover. A silicone caulk was applied in a
continuous bead to obtain a positive seal. High ambient ozone concentrations
above the contact basin were reduced, but were then detected in the main plant
offices. Off-gas that could no longer escape through the basin cover was
being forced to the air space above the backwash water storage basin. This
basin was adjacent to the ozone contact basin and below the main plant
offices. Additionally, contact basin off-gases were not being properly vented
to the roof discharge because foam produced by the addition of air and ozone
to the contact basin was blocking the exhaust air flow to the vent duct.
To correct the problem of off-gas leakage from the backwash storage
basin, a duct connecting the existing ozone contact basin with the air space
above the backwash storage tank was installed. The addition of the duct elim-
inated high ambient ozone concentrations in the plant offices, because when
135
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foam blocked the movement of air above the water surface of the ozone contact
basin the ozone laden off-gases would transfer to the backwash water storage
basin where they would be pulled back into the main exhaust duct and dis-
charged. This duct provided an alternate means for ozone laden air to be
removed when foaming occurred. In addition to the duct modification, a water
spray nozzle was installed in the ozone contact basin duct to depress the foam
as it developed. It should be noted that the excessive foaming problem
occurred during ozone system start-up and typically lasted for only 2-3 hours.
During initial operation of the ozone contact system it was determined
that short-circuiting of flow was occurring across the top of the compartment
baffles. This short-circuiting resulted when air/ozone from the diffusers
"air-lifted" the water level in the basin. The baffles were raised slightly,
but not to the extent that air movement to the exhaust vent was blocked.
The air-lift action caused by the diffuser system also caused flooding of
the scum skimmer mechanisms which were initially set too low. The adjustment
range of the skimmer units was expanded and adjustment handles were extended
through the basin cover. To facilitate adjustment of the overflow weir
plates, plexiglass sight windows were installed into the basin cover above
each skimming unit. To date, the continuous use of the scum skimmers has been
unnecessary as little foam or the predicted gelatinous type froth has been
produced. The lack of appreciable foam or froth is believed to be due to the
high quality water entering the ozone contact basin. This water has very lit-
tle material (i.e., total suspended solids) available to be coagulated into
froth.
The combination of modifications allowed operation of the ozone system
whenever the wind was blowing sufficiently to remove the ozone laden off-gases
from the area surrounding the discharge stack. The system bad to be shut down
when the wind was not blowing because high ambient ozone concentrations would
develop in and around the plant area. The UTSD was instructed by State
Department of Health officials to operate the ozone system to achieve disin-
fection, but the District was allowed to shut down the system when necessary
136
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to prevent human exposure to high ambient concentrations of ozone. Under this.
arrangement, it is estimated that the ozone disinfection system was operated
only about 50 percent of the time.
The UTSD ozone system was operated under these conditions for about one
year when problems were encountered with the ozone diffusers and with leaks in
the ozone piping. The original ozone piping from the generator to the ozone
diffusers was Schedule 80, U.P.V.C. pipe with both solvent weld and threaded
joints. The problems with leakage occurred around the joints and along
straight pipe sections near pipe hangers. This leakage problem may have been
caused by inadequate care during installation; however, good plumbing prac-
tices by the contractor were felt to exist because very few problems occurred
with other plant piping systems. Although no definite conclusions could be
developed, the leakage in the ozone piping may have occurred as a result of
ozone exposure over a one-year time period and not due to poor workmanship.
Because of the excessive ozone leakage of the D.P.V.C. pipe, all piping
was replaced with Schedule 40, Type 304 stainless steel. Some of the stain-
less steel pipe connections were threaded and some were welded. Some of the
threaded stainless steel connections were noted to leak and were tightened,
but some could not be sealed and were eventually welded. It was concluded
that welded connections provided the best assurance for sealing.
When U.P.V.C. piping was replaced new ozone diffusers were also in-
stalled. The diffusers were connected to the stainless steel pipe outside
the basin, and the pipe with diffusers was lowered into the basin aided by the
structural integrity of the stainless steel pipe. During installation of the
diffusers an additional reason for replacing the U.P.V.C. piping with stain-
less steel pipe was noted. Upon removal of the U.P.V.C. pipe that had been
submerged in the contact basin it was noted that the pipe was extremely brit-
tle and shattered easily when dropped. The U.P.V.C. pipe's condition was not
felt to be acceptable for long-term operation, and replacement with stainless
steel pipe was considered appropriate. These results indicate that strong
137
-------
consideration should be given to using suitable grade stainless steel pipe and
welded connections for all ozone/air piping.
The UTSD Ozone contact basin achieved ozone transfer efficiencies ranging
from 35 to 70 percent. Transfer efficiency (TE) as used in this context was
calculated as follows:
TE
(Mass of Ozone Produced - Mass of Ozone in Off-Gas) (100)
Mass of Ozone Produced
Typically, the transfer efficiencies were between 50 and 60 percent,
which were considerably less than the design TE of 90 percent. One reason for
the lower than expected TE was breakdown of the ozone diffusers.. The original
ozone diffusers were tubuler in shape and were attached to a piping connection
nipple with a "2-part epoxy bond". The epoxy served in a structural as well
as a gas sealing capacity. Because the measured transfer efficiencies were
lower than expected, the contact basin was drawn down and the diffusers were
inspected. It was noted that the epoxy had become extremely soft. The dif-
fuser manufacturer claimed that the epoxy would probably become "a little
soft" when exposed to water. A new diffuser was exposed to water for 3 months
in the laboratory. No softening effect was noted. During this time the TE
had reduced from 50 to 60 percent to only about 35 percent. The contact basin
was again drained and this time some diffusers were noted to have completely
separated from the connection nipple and had fallen to the bottom of the con-
tact basin.
The original ozone diffusers were replaced. The new ozone diffusers were
porous stone and were also tubular in shape, but a bolted stainless steel con-
nection and hypolon gasket material were incorporated in the diffuser con-
struction. This construction eliminates the need for the two part epoxy bond
which was not ozone resistant. Operation with the new diffusers has been
limited and final conclusions concerning the suitability of the diffusers has
not been reached.
138
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After installation of the. new ozone diffusers and stainless steel piping,
TE tests were conducted and were found to be similar to efficiencies that were
attained when the ozone system was first started up, namely 50 to 60 percent.
These values were better than the 35 percent efficiency attained when some of
the original diffusers were known to have failed, but were still less than the
design efficiency of 90 percent. A re-evaluation of the ozone contact basin
design was made.
The UTSD ozone contact basin design was similar to a basin that was de-
signed and tested in 1971 at the Louisville, Kentucky Wastewater Treatment
Plant. The ozone basin at Louisville was reported to have consistantly
achieved 90% or greater TE. At about that same time at the University of
Louisville, research work was conducted to measure the TE of a contact basin
similar to the basin that was tested at the Louisville plant, and a paper was
published concerning the results. The author reported that the 90% to 95% TE
that was achieved at the Louisville plant could not be duplicated at the Uni-
versity laboratory. Laboratory results indicated a TE of about 50%. The dif-
ference in transfer efficiency was attributed to a "with reaction" consumptive
use of the applied ozone at the Louisville plant, which was ozonating secon-
dary effluent. The phrase "with reaction" implies that the effluent being
treated had a high ozone demand and that available ozone was consumed by this
demand. Thus TE appeared much higher because of this ozone demand. The tests
completed at the University of Louisville, which did not correlate with Louis-
ville plant results, were labeled "without reaction" test results. These
"without reaction" tests also correlated well with ozone/liquid gas transfer
theories.
Transfer efficiencies achieved at the UTSD facility have also correlated
well with ozone/liquid gas transfer theories, and are believed to be more in
line with the "without reaction" tests conducted at the University of Louis-
ville. The wastewater ozonated at the UTSD plant is tertiary effluent and of
considerably better quality than typically associated with secondary treat-
ment .
139
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The belief that the DTSD ozone contact basin was performing similarly to
the "without reaction" tests as established at the University of Louisville
was further supported. Periodically, the ozone transfer efficiency has
reached a level of about 70 percent. When this occurred, poor disinfection
results were often achieved even if disinfection previously occurred at
similar ozone dosages. At the same time, the TSS concentration through the
basin increased. This condition existed when the ozone generator was started
after being shut down for a day or two. The air pretreatment system was
always operated, thus air was continuously diffused into the wastewater. When
the ozone generator was shut off or was operated at a very low ozone dosage
level, biological growth developed in the basin in the form of a slime on the
basin walls, the U.P.V.C. baffles, and other surface media in the basin. When
the ozone generator was started and operated at a higher ozone dosage, a "with
reaction" ozone consumption probably occurred and increased the ozone transfer
efficiency to near 70%. At the same time, the biological slime would slough-
off and increase the contact basin effluent TSS concentration which interfered
with the disinfection capability of the system. However, when the UTSD ozone
contact basin is operated on a continuous basis it is expected that it will
operate according to gas/liquid transfer theories. It was concluded that the
basin is achieving expected ozone transfer efficiency for the quality of
effluent treated. Based on these developments, design considerations for
desired ozone contact basin transfer efficiencies should be based on
ozone/liquid gas transfer theories.
Biological slime build-up occurs in the' UTSD ozone contact basin when the
ozone generator is shut down and/or operated at a very low ozone dosage level.
Because of this problem with intermittent ozone operation, a good disinfection
versus ozone dosage relationship was not obtained. When continuous ozonation
and continuous good disinfection is achieved, the ozone dosage will be adjust-
ed to determine the minimum level necessary to achieve disinfection. Transfer
efficiency tests will be made to determine the effective ozone dosage as
opposed to applied ozone dosages (i.e., dosage excluding the ozone lost in the
off-gas) so that a common basis of comparison can be made with other ozone
disinfection systems.
140
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To achieve continuous ozonation, several options were considered to
control the off-gas ozone discharge. Among these were: heat destruct, heat/
catalyst destruct, activated carbon, recycle to sludge, and discharge through
a tall stack. The option selected was heat/catalyst destruct. Heat destruct
was rejected because of an excessively high power consumption. Activated
carbon was rejected because of its explosive potential when combined with
ozone. Recycle to sludge and discharge through a tall stack were rejected
because they were felt to likely result in transferring the problem to another
area within the plant. The heat/catalyst ozone destruct system for the,
contact basin off-gases has been designed and is being constructed. The
system is manufactured by Emery Industries. An off-gas ozone destruct unit
should be strongly considered for all newly designed ozone systems.
In March, 1979, the off-gas destruct unit was installed and operated for
only a short period of time, because a 0.39 kW (1/2 hp) fan motor.used to draw
the off-gas through the destruct unit burned out. The smaller motor is being
replaced with a 0.75 kW (1 hp) motor. Preliminary indications are that the
off-gas ozone destruct unit satisfactorily reduced the ozone concentration in
the off-gas to satisfactoy levels to allow continuous operation of the ozone
system. Quantitative information was not obtained, but from a qualitative
stand-point the system was acceptable.
Disinfection Performance
Operation of the ozone disinfection system at the UTSD plant was sporatic
due to a variety of problems that resulted in high ambient ozone concentra-
tions representing a hazard to operating personnel. Shown below is a synopsis
of the problems encountered.
141
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Time Period
June - December, 1976
Comment
High ambient ozone concentrations due to
partial cover over contact basin.
December, 1976 - February, 1977 Good disinfection achieved, but equipment
to measure ozone dosages and transfer ef-
ficiencies not available.
March - April, 1977
May - June, 1977
Good disinfection achieved.
Poor disinfection achieved because of ozone
diffuser problem.
July - October, 1977
System shut down for inspection and repair
of original ozone diffusers.
October - December, 1977
Relatively good disinfection, but only with
extremely high ozone dosages because of
further problems with ozone diffusers.
January - April, 1978
Design, construction and installation of
new ozone diffusers completed.
May - September, 1978
Sporatic operation due to excessively high
ambient ozone levels in and around the
plant area due to high ozone concentrations
in contact basin exhaust. Plans and speci-
fications for off-gas ozone destruct system
developed.
Routine collection of analytical data for the ozone system was initiated
during the week of December 12, 1976. Results from these analyses for the en-
tire research period are shown in Appendix F. The majority of the results
142
-------
shown are weekly arithmetic averages of data collected based on the analytical
schedule that was presented in Table 13. Coliform results shown in Appendix F
are weekly geometric means of the individual coliform determinations.
Coliform data was developed using the membrane filter (Gelman Filter)
technique through the week of April 10, 1977. Results after April 10, 1977
were developed using the Most Probable Number (MPN) technique.
In general, good disinfection performance could be achieved when the
ozone diffusers were in good condition and the system was operated for an ex-
tended period of time (several days). Disinfection performance was poor when
problems were occurring with diffusers and when the ozone system was operated
on an intermittent basis. A summary of performance data for selected time
periods is shown in Table 36. Periods 1, 2 and 3 represent data collected
when the original ozone diffuses were in operation. Period 4 represents data
collected after the new diffusers were installed.
During the 8-week time period for Period 1, the original ozone diffusers
were new and were operating satisfactorily. Very good disinfection occurred
at an average applied ozone dosage of about 11 mg/1. The effluent- fecal coli-
form concentration was reduced to 30 per 100 ml, much better than the design
standard of 200 per 100 ml. The COD reduction during Period 1 was 12 percent
and the TSS reduction was 36 percent. Both the influent COD and TSS concen-
trations were relatively low at 30 mg/1 and 5 mg/1, respectively.
During Period 2 the average applied ozone dosage was about 9 mg/1, but
disinfection performance deteriorated significantly. The effluent fecal coli-
form concentration was 2,080 per 100 ml. The reason for the poor performance
was primarily attributed to problems with the ozone diffusers. During Period
3 disinfection improved, but only after the applied dosage was more than
doubled to about 1'9 mg/1.
The performance data for Period 4 represents information collected after
the new ozone diffusers were installed. The data was collected for two dif-
ferent time periods because of problems with intermittent ozone generation and
143
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biological slime build-up. Effluent disinfection was achieved during Period
4. The effluent fecal coliform concentration was only 9 per 100 ml at an
applied ozone dosage of about 7 mg/1.
These performance data are limited, but indicate that good disinfection
can be achieved with the UTSD ozone system. More definitive conclusions are
expected when the ozone destruct unit for the contact basin off-gas is opera-
tional and continuous ozonation can be implemented.
SLUDGE DEWATERING AND DISPOSAL
Sludge dewatering facilities are provided at the Upper Thompson Plant to
condition the sludge from the aerobic digesters for land disposal. Process
operation is discussed in this section. Areas investigated included the
digested sludge characteristics, design features, and initial performance
data. Results were collected during an initial start-up period and then
through a 60-day testing period.
Start up of the Upper Thompson Plant began in April, 1976; however, oper-
ation of the sludge concentrator did not begin until nearly two years later in
February, 1978. This delayed operation was caused by delays in finalizing the
design and construction of portions of the sludge handling system. Throughout
this two year period the waste sludge from the activated sludge system was ac-
cumulated in the two aerobic digesters. This long detention time resulted in
a very well digested sludge, as indicated by a specific oxygen uptake rate of
less than 0.5 mg/hr/gm VSS and the volatile solids to total solids ratio of
less than 60 percent. An additional factor that affected the digester sludge
occurred during the Big Thompson flood disaster (July 31, 1976). A 76 cm
(30-inch) main interceptor river crossing was washed out and resulted in a
large amount of silt-laden water entering the activated sludge system. Conse-
quently, the contents of the activated sludge process were wasted to the aero-
bic digesters. The silt material coupled with the long sludge detention time
resulted in a large mass of inert material contained in the aerobic digesters.
145
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Because of the unusual characteristics of the sludge to be dewatered,
several tests were required to select the most suitable polymer. A six place
paddle mixer was used to perform standard jar tests on the digested sludge.
Several types of polymer were investigated, and once a specific polymer was
chosen several dosages were investigated to determine the optimum
concentration. The polymer used through most of the study was Nalco 627.
During start-up of the sludge concentrator, a major limitation with the
sludge feed system to the concentrator was detected. Because of head condi-
tions, the sludge feed pump could not maintain the flow rate. to the concen-
trator at a constant level. With a varying sludge flow rate the desired poly-
mer dosage was difficult to maintain. As a result the characteristics of the
conditioned sludge varied which directly affected concentrator performance.
With the original arrangement, a .diaphragm pump was located in-line between
the aerobic digesters and the sludge concentrator. However, the liquid level
in the digester was higher than the concentrator which created a positive head
on the sludge pump. Sludge would flow by gravity through the diaphragm pump,
limiting the pumps capability to control the sludge flow rate. As a result, a
modification was necessary. As a temporary solution, a 1140 1 (300-gal) tank
was placed inside the sludge handling building and sludge from the digesters
was allowed to flow by gravity to the tank where it was then g.umped to the
concentrator. This method of operation required the attention of an operator
to direct sludge into the 1,140 ml(300-gal) tank, but it did insure a constant
sludge flow to the concentrator. As a more permanent solution, a progressive
cavity pump was installed in place of the diaphragm pump (March 1979).
The results of initial testing on the sludge concentrator are shown in
Table 37. The testing was conducted in May, 1978, after the sludge feed sys-
tem had been modified to provide a constant feed rate. Although no quality
tests on the digested sludge were performed for trial 2, the characteristics
should have been similar to those shown in trial 1 since the digester contents
had been maintained for such a long time period. During the two testing
periods the solids concentration of the sludge cake was 9.1 and 9.6 percent by
weight. Solids capture varied from 78 to 82 percent, whereas captures greater
146
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than 90 percent were expected.. The reason for the low solids capture was par-
tially attributed to the extremely digested condition of the sludge being
dewatered. It is noted that the digester contents had a very low pH (4.2
units). Sodium bicarbonate was added on several occasions to attempt to in-
crease the pH but bench scale tests indicated that much more biocarbonate
would be required to effect the pH. It was decided to dewater the sludge
already contained in the digester and to attempt to control the characteris-
tics of any future sludge through operational controls.
The average of the results for the two trials shown in Table 37 indicate that
approximately 110 Kg (245 Ib) of sludge (dry wt) were fed to the concentrator
TABLE 37. SLUDGE CONCENTRATOR PERFORMANCE DURING START UP
Trial 1
Trial 2
Date
Duration hours
Sludge Characteristics
Total Solids - mg/1
Total Voltile Solids - mg/1
VS/TS Ratio - %
Temperature - °C
Specific Oxygen Uptake Rate mg 02/hr/gm VS
pH - units
March 3, 1978 March 4, 1978
4.9 3.8
32,560
17,760
55
29
0.13
4.2
Performance
Influent Flow Rate - gpm
Total Solids, Cake - %
Suspended Solids, Filtrate - mg/1
Sludge Feed Rate - Ib/hr (dry wt.)
Sludge Cake Produced - Ib/hr (dry wt.)
Sludge Lost in Filtrate - Ib/hr (dry wt.)
Solids Capture - %
Polyer Dosage - Ib/ton sludge (dry wt.)
15
9.1
4,480
245
190
55
78
39
15
9.6
2,770
245
200
45
82
41
gpm x 0.0631 = I/sec; Ib/hr x 0.454 = kg/hr; Ib/ton x 0.50 = kg/metric ton
147
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per hour, and with a solids capture of 80 percent, 90 Kg/hr (200 Ib) of sludge
cake (dry wt) was produced at a polymer dosage of 20 Kg/metric ton (40 Ib/ton)
of sludge.' It is noted that the speed of the primary and secondary screens
had to be carefully controlled to avoid solids loss over the screen edge
during these trials.
Subsequent to these initial tests, operation and performance data on the
sludge concentrator was collected over a 60-day testing period from August 1
to October 1, 1978. A summary of this data is shown in Table 38. Overall
performance during this period was better than that obtained during the ini-
tial testing period in May. Additional operations experience was felt to have
contributed to the improved performance. During the 60-day period, sludge
with an 11 percent solids content was produced which yielded 18,900 kg (41,700
Ib) of dry sludge solids. To condition the sludge, 25 kg (50 Ib) of polymer
per ton of dry solids was required. On the average it required 8.3 hours to
produce one metric ton of dry sludge solids.
TABLE 38. SUMMARY OF OPERATION AND PERFORMANCE DATA
Date
Duration - hr
Sludge Characteristics
Total Solids - mg/1
Total Volatile Soilds - mg/1
VS/TS Ratio - %
Temperature - °C
Specific Oxygen Uptake Rate - mg 02/hr/gm VS
pH - units
August 1, 1978 to October 1, 1978
192
25,400
14,660
58
No Data
No Data
5.5
Performance
Influent Flow Rate
Total Solids, Cake - %
Suspended Solids, Filtrate - mg/1
Sludge Feed Rate - Ib/hr (dry wt.)
Sludge Cake Produced - Ib/hr (dry wt.)
Sludge Lost in Filtrate - Ib/hr (dry wt.)
Solids Capture - %
Polymer Dosage - Ib/ton sludge (dry wt.)
20
11
2,070
254
217
37
85
50
gpm x 0.0631 = I/sec; Ib/hr x 0.454 = kg/hr; Ib/ton x 0.50 = kg/metric/ton
148
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During the 60-day testing period, an operation problem was encountered
with the inlet and outlet flapper valves on the sludge feed pump. These
valves collected pieces of rags and bits of plastic from the sludge. The
valves would then not seat properly and the flow would slowly decrease. To
minimize this problem, the output of the pump was checked once or twice per
hour, and adjusted to maintain a 75 1/min (20 gpm) flow. During the 60-day
test period the pump was taken apart five times to remove the rag and plastic
build-up on the valve seats. Approximately 30 min of cleaning time was "re-
quired each time the pump was taken apart.
Additional operational problems had to do with maintaining a good sludge
floe. It was 'determined that when sodium bicarbonate was added and the
digester sludge. pH increased to greater than 7, the cationic polymer that had
been used had little effect on flocculating the sludge. Flocculation problems
also occurred when attempts to dewater sludge from one of the digesters that
had not had any waste activated sludge added to it for 3 weeks were made.
This sludge produced such a poor floe that the primary screen of the concen-
trator could not trap the floe particles. When sludge was processed from the
other digester that had waste activated sludge fed to it daily, a good floe
was again achieved.
The spray jets used to clean the primary and secondary screens also pro-
vided some operational difficulties. Plant effluent was used to supply water
to the 1.2-mm (3/64 inch) jets, and small particles clogged the jets. The
semi-plugged spray jets would not adequately clean the screens. To minimize
the plugging problems, the jets were cleaned before each 6 hour filter run.
An inline strainer is being investigated to aid in trapping these small parti-
cles before they entered the spray jet. The strainer should not have to be
cleaned as often, and more importantly the effectiveness of the spray jets
would be maintained.
During operation of the sludge concentrator, water and solids (filtrate)
were returned to the plant headworks. The added water is from the water
released from the sludge, the water added by the inline polymer diluter, and
149
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water added by the jet cleaning sprays. The water released from the sludge
was about 57 1/min (15 gpm), the water added by the inline polymer diluter
about 30 1/min (8 gpm) and the water required to operate the spray jets about
57 1/min (15 gpm) for a total volume of about 144 1/min (38 gpm). Solids in
the filtrate result from the sludge lost through or over the edge of the
travelling screens. The filtrate total suspended solids concentration during
the test period averaged 2,070 mg/1. The amount of solids in the filtrate
varied directly to the dryness of the sludge. The highest solids content of
the filtrate, 4,740 mg/1, occurred with a poorer sludge cake of 9.4 percent
while the lowest solids of 344 mg/1 occurred with a good sludge cake
of 12.1 percent.
A cost breakdown for the 60-day testing period is shown in Table 39. A
total of 114 man hours was required for operation of the sludge concentrator.
This labor included time for start up, operation, maintenance and clean up.
Electrical power to operate the sludge dewatering system was estimated to be
176 kW/metric ton (88 kW/ton) of dry sludge solids. The cost was obtained by
multiplying the total kilowatt consumption by the UTSD power cost factor of
$0.035/kW. Sludge cake transportation included allowances for gasoline and
the drivers' time, but insurance and depreciation on the truck were not
included.
TABLE 39. SUMMARY OF COST DATA FOR SLUDGE DEWATERING
Labor
114 man hrs.
x $5.00/hr -
$570
Polymer
1060 Ibs x
$1.221/lb =
$1,294
Power Costs
1830 kW x
$0.035/kW =
$64
Hauling
$60.00 labor (@ .58 hrs/ton)
15.92 gas (@ $0.65/gal)
$75.92 Total
Cost Per Ton Dry Sludge Removed
Labor: $570 t 20.8 tons
Polymer: $1,294 ^20.8 tons
Power - $64.06 - 20.8 tons
Hauling & Labor: $60.00 t 20.8 tons
Hauling & Gasoline: $15.92 * 20.8 tons
TOTAL
$27.40
62.22
3.08
2.88
.76
$96.34/Ton Dry Sludge
Ib x 0.454 = kg; hr/ton x 0.907
- metric ton
hr/metric ton; gal x 3.785 = 1; ton x 0.907
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The total cost of sludge dewatering as shown in Table 39 was about
$87/metric ton ($96/ton) dry sludge solids. The labor and polymer costs com-
prised 93 percent of the total cost.
The sludge concentrator was relatively easy to operate once the proper
polymer dosage was determined. The full attention of an operator was not
required and periodic checks were all that was necessary. Overall, the unit
performed well despite the quite difficult-to-dewater aerobically digested
sludge. It is expected that even better performance in terms of lower cost
and a thicker sludge cake can occur, when a less inert sludge is processed.
OVERALL TREATMENT PLANT PERFORMANCE
The UTSD advanced wastewater treatment facility functioned under a vari-
ety of operating conditions throughout the data collection phase of the
research project. Plant flows ranged from. 30 percent to 134 percent of the
design flow (Note: half plant design flow values were used because only half
of the plants major units were in service). The BOD^ load ranged from 50
percent to 228 percent of design. Despite these wide variations 'in loading,
overall plant performance was quite good. A summary of the performance and
the effluent quality for each unit process for the period of the research pro-
ject is shown in Table 40. It should be noted that the effluent for each pro-
cess was not sampled all the time during the data collection phase of the
research effort. Initial plant lab start-up problems postponed individual
unit process analyses for three months until October 3, 1976. Also, special
testing for the ozone and denitrification systems was completed during the
last two months of the data collection effort in place of sampling and ana-
lyzing every unit process. Thus, of 105 weeks of overall performance informa-
tion, 88 weeks of data were collected on all individual unit processes. Data
presented in Table '40 is for this 88-week period.
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TABLE 40. SUMMARY OF UTSD PLANT PERFORMANCE*
Parameter
Flow (mgd)
BOD5 (mg/1)
Removal (%)
TSS (mg/1)
Removal (%)
COD (mg/1)
Removal (%)
TKN (mg/1)
Removal
NH4-N (mg/1)
Removal
Alkalinity
as CaCOs (mg/1)
Removal
Influent
0.49
201
169
358
22.5
13.1
106
Activated
Sludge
Effluent
0.49
31
85
22
87
58
84
11.6
48
9.1
N/A
76
28
Nitrification
System
Effluent
0.49
34
83
21
88
55
85
8.6
62
5.5
N/A
49
54
Mixed Media
Filter
Effluent
0.49
11
95
6
96
35
90
6.8
70
4.9
N/A
45
58
Ozone
Contact
Effluent
0.49
11
95
6
96
35
90
6.4
72
4.8
N/A
45
58
mgd x 3785 - cu m/day
*Summary of data for 88 weeks from 10-3-76 to 6-10-78, excluding the 4-week
period from 6-12-77 to 7-9-77 when modifications to the plant were
completed.
Although each parameter could be discussed, it is felt that BOD5 can be
used to indicate the variations in organic loading and performance that occur-
red throughout the project period. The average influent BOD5 concentrations
shown in Table 40 was 201 mg/1, indicating a typical domestic waste. However,
further data evaluation indicated that an extreme variation in waste strength
occurred. The winter season wastewater BOD^ concentration was only about
100 to 150 mg/1, and the summer BOD5 concentration ranged from 250 to 400
mg/1. The BOD5 removal efficiency ranged from 85 percent to 98 percent
during the course of the study. A graphical illustration of BOD5 removal
efficiency is shown in Figure 30. The lower removal efficiency of 85 percent
was attributed to system start-up conditions after plant modifications were
made in June 1977.
152
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Also shown in Figure 30 is the BODg removal efficiency across the acti-
vated sludge system. As shown, activated sludge removal efficiencies were
generally lower and more variable during the beginning portion of the project
and more consistent and higher toward the end. More experienced process oper-
ation by plant personnel coupled with changes in system operation that were
earlier discussed were contributing factors to this occurrence. It should be
noted that lower overall plant 6005 removal occurred near the very end of
the project even though activated sludge removal was quite good. The reason
for this is due to higher BODg in the mixed media filter effluent due to
methanol addition during the denitrification special study.
Many minor and some major modifications have been implemented at the UTSD
facility. These modifications coupled with the understanding of the loading
conditions that are associated with the UTSD facility should allow continued
good and even improved process performance. As such, the UTSD should be able
to maintain a high quality effluent.
DENITRIFICATION SPECIAL STUDY
1-22
1977
1978
Figure 30. Activated sludge and overall plant BODr removal efficiency
during the entire research project.
153
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OPERATION AND CAPITAL COST
The plant was constructed in 1975 and 1976, and the capital costs
presented are associated with this period. Total capital cost for the UTSD
treatment facility was approximately $3 million, or about $2 million per 3,785
cu m/day (1 mgd) of treatment capacity. This cost includes all subsequent
modifications made in the plant design. Data on the operational cost of the
plant were collected during the research project. The average annual opera-
ting cost during the research project was $152,210. Since the research pro-
ject required additional manpower effort, this cost is not reflective of nor-
mal operation. The projected annual operating cost, excluding research
project costs, was $123,000. In the following subsections the overall capital
and operating costs are broken down for each of the specific unit processes.
A summary of individual process costs, as well as total costs, is also pre-
sented.
Lift Stations
Two lift stations, Fish Creek and Big Thompson, were used to pump the
collected wastewater to the treatment plant. The lift stations consisted of a
wetwell, dry-well, pumps and a comminutor with bar screen by-pass. The total
capital cost for both lift stations was $189,720. The cost for the pumps and
comminutors comprised about $37,000 of this total. Construction materials and
labor for the lift stations cost an additional $80,000. Piping, electrical
systems, equipment controls, and site preparation at $72,720 accounted for the
remainder of the total lift station cost. The capital cost of the lift
stations was approximately 6.4 percent of the total plant cost.
Operational cost for the various treatment processes were divided into
three categories: supplies, labor and power. Supplies for the lift stations
consisted mostly of lubricants for the equipment. Since this cost was minor
compared to the total cost, it has been included in the miscellaneous section
of this analysis. Labor used for the inspection and maintenance of the lift
154
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stations was estimated to be 2.5 hours per day. The annual labor requirement
was then computed as 912 man-hours, which was 10.2% of the total annual staff-
ing cost and amounted to $5,016. The power requirement for the lift station
was based on the horsepower of the operating pumps with respect to the total
plant horsepower. This percentage, when used in conjunction with the average
power cost for the plant of $3,766 per month, provided an estimate of the
monthly power cost. The monthly power cost for the lift stations was $107, or
$1,284 per year. When the labor and power costs were combined, the annual
operation cost of the lift station was $6,300.
Flow Equalization and Grit Chamber
The capital cost of the flow equalization basin and grit removal units
was $270,540, or approximately 9.1 percent of the total plant cost. Of this
amount, $55,440 was the cost of the grit basin and related equipment, and the
flow equalization basin and clarifier equipment. Materials and labor utilized
in the construction of these facilities accounted for $116,730, and the
remainder of the capital cost at $98,370 was the result of the associated
piping, electrical systems, equipment controls and site preparation. It
should be noted that site preparation for the UTSD was a significant cost,
since much excavation work was done by blasting.
The cost of routine supplies for these units was negligible and was in-
cluded in the miscellaneous section of this analysis. The labor cost associ-
ated with these units was based on 1.55 hours per day for inspection, grit
handling and scheduled maintenance for a total labor requirement of 565 man-
hours per year. The resulting labor cost was $3,108 per year. Based on the
horsepower requirements, the preliminary treatment's share of the power cost
was $211 per month, or $2,532 per year. When the power and labor costs are
combined, the annual operation cost for preliminary treatment totaled $5,640.
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Activated Sludge
The activated sludge system consisted of two aeration basins, two clari-
fiers, and the associated mechanical equipment. The estimated capital cost
for the activated sludge system was $569,400, which accounted for about 19.2
percent of the total plant cost. Equipment cost including aerators, clarifier
mechanisms, return and waste pumps and blowers was $119,680. Construction
materials and labor accounted for an additional $243,055. Other capital costs
at a total of $206,665 were for piping, electrical systems, equipment controls
and site preparation.
The cost for supplies was considered negligible for this process and was
included in the miscellaneous section. During the research project the man-
power requirement for process control and sampling of this process was esti-
mated to be 3,107 man- hours per year. The resulting cost for this effort was
$17,090. A series of control tests were performed by the plant operators, and
the frequency of this testing varied from four to six times per day. From 1
to 1-1/2 hours were necessary to complete a set of control tests. Additional
time was required to develop and analyze the data and to implement the indi-
cated process adjustments. Following the research project the frequency of
performing the control tests and collecting samples for this process was
reduced to twice per day, thus decreasing the manpower involvement to 1,969
man-hours per year and the annual labor cost to $10,830. The power cost for
the activated sludge process system was based on the horsepower requirement of
the blowers, turbines and pumps. The percentage of the power cost attribut-
able to the activated sludge process was $1,126 per month. Total operational
cost during the research project was $30,512 per year; however, following the
project the annual cost decreased to $24,342 due to the decreased labor
requirement.
Nitrification
Components of the nitrification system included the tower with two types
of media - redwood and plastic, the recirculation pumps, and a wet-well.
156
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The capital cost associated with the nitrification system was $366,760, or
12.4 percent of the total plant cost. Of this total, the tower structure,
media and pumps accounted for $188,130. Materials and labor for construction
of the system cost an additional $17,200. Other capital costs at $161,430
were allocated to the piping, electrical systems, equipment controls and site
preparation.
The major operational costs for the nitrification system were based on
labor and power .requirements. An average of 0.34 man-hours per day were
necessary for operation of the tower resulting in an annual labor cost of
$682. Most of this time went to maintenance and inspection of the recircula-
tion pumps. Only limited maintenance was required on the tower or distribu-
tion nozzles. The power cost, based on the horsepower of the recirculation
pumps with respect to total plant horsepower, was estimated to be $552 per
month, or $6,624 annually. The subtotal for operation cost of the nitrifica-
tion tower was an estimated $7,306 per year.
Filtration
Major items within the filtration system include the mixed-media filters,
backwash storage basin, backwash wastewater storage basin, pumps and the chem-
ical feed system.
Approximately 12.8 percent of the total capital cost, or $378,510, was
allocated to the filtration system. Cost of the filter units, backwash pumps
and the chemical feed system accounted for $152,390. Materials and labor
included in the construction of basins and the filter room were estimated to
cost $74,200. The remainder of the capital cost at $154,880 went to the as-
sociated piping, electrical systems, equipment controls and site preparation.
Although a chemical feed system was included in the filter design, chemi-
cal addition was not practiced during the research project. The major opera-
tional costs were the result of manpower and power needs. The manpower re-
quired was mainly for filter backwashing. When the head loss through a filter
157.
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reached a preselected level, an alarm was sounded. The operator then trans-
ferred the nitrification tower effluent to a clean filter, and initiated the
approximately 15-minute backwash cycle on the dirty filter. The frequency of
filter backwashing varied considerably during the research project, but the
average backwash frequency was ten times per week. Manpower requirements of
1.25 man-hours per day were allocated for these activities. This resulted in
an annual manpower cost of $2,508. The only power cost associated with the
filtration system was the demand by the backwash pumps. This amounted to only
$108 per year. Total operational cost, including labor and power, was $2,616
annually.
Ozone Disinfection
Components of the ozone system include the air pretreatment equipment,
generators, contact basin and diffusers, and the off gas destruct unit. The
capital cost of this system was $341,460, or 11.5 percent of the total plant
cost. As discussed previously in the ozone evaluation section, several modi-
fications were necessary in the system design, the most important being the
piping and diffusers changes ($14,380) and the off gas destruct unit ($21,330)
addition. The costs associated with these changes have been included within
the capital cost. Approximately $160,300 of the capital cost was for equip-
ment including: air pretreatment equipment, ozone generators, diffusers and
piping, ozone monitoring equipment, and the off-gas destruct unit. Materials
and labor utilized for construction amounted to $48,740. The cost for associ-
ated piping, electrical systems, equipment controls and site preparation was
$132,420.
Operation of the ozone disinfection system required about $1,000 per year
for materials. Most of this cost went to the purchase of electrode tubes and
fuses. Manpower was required for daily inspection of the air pretreatment and
ozone generation equipment. An additional 180 man-hours per year were neces-
sary for inspection and cleaning the ozone generator units. These activities
required an average of 1.2 man-hours per day, which resulted in an annual cost
158
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of $2,354. Determination of the power cost for ozone generation was diffi-
cult, since the unit was not continuously operated. Values obtained during
intermittent operation were used to extrapolate the power costs shown. Costs
shown are based on continuous operation. Since the off-gas destruct unit has
been recently added to the system, the plant power records do not reflect this
additional cost. Based on an 8 kW demand for the destruct unit, a power cost
was estimated for off-gas destruction. The power cost for the entire ozone
system was estimated to be $8,916 annually. When the cost of the materials,
labor and power were combined, the annual operational cost totaled $12,270.
Sludge Handling
Sludge digestion, dewatering and disposal are included in this category.
The following items make up the sludge handling process: digester basins,
aerators, blowers, sludge pump, dewatering equipment and the sludge truck.
The capital cost for this system totaled $453,850, or 15.3 percent of the
total cost. Of this amount, approximately $120,970 went to the associated
equipment, and $169,350 was directed to materials and labor for construction
of the structures. Other capital costs of $163,530 were associated with pip-
ing, electrical systems, equipment controls and site preparation.
Supplies for the sludge handling system were, for the most part, related
to sludge dewatering and disposal. The annual cost for chemical polymer was
$3,318, based on dewatering 90 tons of sludge (dry wt. basis) per year. Also,
about $184/year went to transportation of the sludge cake to ultimate dis-
posal. Total cost for supplies were then $3,502 per year. The manpower
requirement for sludge handling was 2.8 man-hours/day or 1,018 man-hours per
year, for an annual cost of $5,599. Most of the manpower requirement went to
drawing supernatant from the aerobic digesters and to operation and mainte-
nance of the sludge dewatering system. The power demand of the sludge
handling system was mostly due to the operation of the aerators and the
blowers. An annual cost of $8,616 was allocated for the power requirements of
sludge handling. The total operation cost, including supplies, labor and
power, was $17,717 per year.
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Miscellaneous
The remainder of the total capital cost of the plant, $391,470, was in-
cluded in a miscellaneous category. The plant laboratory and associated
equipment accounted for $59,630, and $331,840 went to material and labor costs
for the plant administration and control building. Major equipment included
in the main plant building included the standby generator, non-potable water
supply system, and the heating and ventilation systems.
The majority of the plant expenditures for supplies could not be specifi-
cally divided among the previously discussed processes; consequently, they
were presented in this subsection. Items included within this category were
the following: operation supplies, repairs and maintenance, insurance, natur-
al gas, lab chemicals, telephone, transportation, equipment rental and office
supplies. The combined cost for these supplies was $22,311 per year.
Other manpower needs that were not discussed in the previous processes
included management, vacations and the laboratory effort. A total of 7,950
man-hours per year were expended in these areas; however, reductions were made
subsequent to the research project. The laboratory manpower decreased from
4,780 man-hours to 2,156 man-hours by reducing the various sampling and
testing frequencies. Management manpower decreased from 2,000 man-hours to
600 man-hours. Because of these reductions and the reductions in activated
sludge man-power, the vacation time also decreased from 1,170 man-hours to 717
man-hours. The scale down of the plant staff did not affect the plant opera-
tion, since the additional manpower was being directed toward the research
effort. The miscellaneous manpower requirement following the research project
decreased from the original 7,950 man-hours to 3,473 man-hours for an annual
cost of $19,102 as opposed tok $42,052 per year.
The miscellaneous power cost for the plant was $5,460 annually. Power
for the laboratory, plant building and small equipment systems are included.
The total operational cost for the miscellaneous category, excluding research
associated costs, was $46,873 per year.
160
-------
Summary of Cost Information
The UTSD plant was built for a design life of 20 years. A summary of the
total capital cost for the plant is shown in Table 41. Also shown is the
yearly capital cost for 20 years at a 6-1/4 percent interest rate, which is
the bond interest rate for the UTSD plant. Using the design flow for the
plant of 5,680 cu m/day (1.5 mgd) and the yearly capital cost of $263,330, the
capital cost for wastewater treatment then became 12.7^/cu m (48
-------
operation's unit cost of 18.6
-------
SECTION 8
REFERENCES
1. Interim Report for Research Project, "An Evaluation of Pollution Control
Process, Upper Thompson Sanitation District," prepared by M & I, Inc.,
Consulting Engineers, Fort Collins, Colorado, for EPA MERL Cincinnati,
Ohio (January 1977).
2. Hegg, B.A., K.L. Rakness, and J.R. Schultz, "A Demonstrated Approach for
Improving Performance and Reliability of Biological Wastewater Treatment
Plants," report prepared in partial fulfillment of EPA Contract
No. 68-03-2224, by M & I, Inc., Fort Collins, Colorado, for U.S. EPA,
Cincinnati, Ohio (1973).
3. McCarty, P.L., L. Beck, and P. St. Amant, "Biological Denitrification of
Wastewater by Addition of Organic Materials. Proceedings of the 24th
Industrial Waste Conference, May 6, 7, and 8, 1969, Lafayette, Indiana,
Purdue University (1969).
4. Process Manual for Nitrogen Control, U.S. Environmental Protection Agency,
Technology Transfer Publication (October 1975).
5. Hill, A.G. and H.T. Spencer, "Mass Transfer in Gas Sparged Ozone Reactor",
Proceedings of the First International Symposium on Ozone for Water and
Wastewater Treatment sponsored by the International Ozone Institute
(1975).
6. Personal communication with Mr. Ed Opatken, MERL, Cincinnati, Ohio,
September, 1978.
163
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APPENDIX G
TABLE G-l. PROCEDURE FOR OZONE AIR CONCENTRATION TESTING
AT THE. UPPER THOMPSON SANITATION DISTRICT
1. Set ozonator at desired amperage setting. Record generator information
on data sheet (See Table A-2).
2. Check Dasibi Meter zero, span and control and sample frequency readings
and adjust if necessary.
3. Prepare wet test chemistry equipment (See Figure A-l).
a. Add 400 ml of 2% KI Solution to each of two 500 ml gas washing
bottles (Note: Fritted glass diffuser was not used on ozone-air
inlet tube).
b. Connect gas washing bottles in series and connect ozone supply line
and wet test meter.
c. Level wet test meter and adjust water level in the meter.
4. Open vent valve and vent test line for two (2) minutes.
5. Read and record three consecutive Dasibi Meter readings,
6. Set two-way valve to direct ozone-air gas flow to the gas washing
bottles and open flow control valve to full open (metering valve set for
2 liters/minute).
7. Run approximately 4.5 liters of gas flow through the bottles and record
field data information on data sheet (See Table A-2).
8. Take gas washing bottles to laboratory immediately and have another
person read and record three more Dasibi Meter readings.
9. Quantitatively transfer liquid from gas washing bottles to two separate
1 liter erlynmeyer flasks. Rinse tubes and bottles at least three
times.
10. Immediately add 10 ml of 2N Sulfuric Acid (H^SO^.
11. Read initial buret volume which contains 0.1N sodium thiosulfate
solution (^28203). Note: Standardize N32S203 using the
dichromate method. (Standard Methods Ed. 14, pp. 316).
12. Quickly titrate the darker of the 2 flasks to a pale yellow color with
the Na2S203).
13. Add 5 ml starch indicator (See Standard Methods Ed. 14, pp. 317 for
starch preparation) and carefully titrate by drop until clear.
14. Add 5 ml starch indicator to second flask and again carefully titrate
dropwise until clear.
15. Record final volume buret reading and determine total volume of titrant
used. Record on data sheet.
16. Complete calculations on data sheet (See Table A-2).
212
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OC
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213
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TABLE G-l. OZONE PRODUCTION DATA RECORDING SHEET
OZONE SYSTEM PERFORMANCE DATA
OZOHE UTILIZATION AND TRANSFER CALCULATIONS
Date , Time of Analysis
IKFORMATIOM
Vrnr Caa; Plw _ scf» (25°C) (see graph)
Wet Tf«t Hctert Voluae _ L Temperature
Water Vapor Pressure _ in. H20 (see graph)
LAB IKFORMATIOK
Ve ! e, .JTtjj C jte tjEC.l Titratioa _ rals N of Ha2S203 _ mole eq/L
Titratlon . _ mis N of Na2S203 _ mole eq/L
Manometer in. H20 (suction is negative)
Concentration In Off Gas:
Calculate weight of ozone trapped in KX solution.
- ("L-is-si, (Iltcotlon
eq/l)
ml) (2* IF R3)
' vmole eq '
L ' \**..*.»...MMI ««., ,, mole eq ' ^ gm-ml ' "
Calculate volume of gas that paaed through wet test meter.
Where: ' V, Actual volume L
?2 " Standard Pressure - 406.8 in H20
P, » Adjusted Pressure "(Plant Atmospheric Pressure (7460) of, 314 in. H20)
- (water vapor pressure) + (wet test manometer pressure - Note:
negative). PI - - + in. H20
T2 - Standard Temperature (absolute) - 77°F + 459.6 - 536.6°R
Tj - Actual Temperature (absolute) °F - 459.6 = °R
Calculate ozone concentration in off gas.
C-
T>
pp«/vol - ( _ vg/L air) (1,000,000)
Qzoil^ Cengfflntration;
ppm/vol (25°C)
Calculate weight of ozone trapped in KI solution.
Calculate Residual Ozone Concentration.
IS) <-
mg/L H20 - (__
PapqjLJ^at in VffiQCi
Calculate ozone lost in vent.
lb»/d«y - ( ft3/min
R«*idual OEQBC!
g/L air) (28.32 L/ft3)
(1440 min/d.y)
Calculate aaount of residual ozone in the water.
ib.rtay - C «S/L H20) ( mgd) (8.34 lbs/8al) - .
tt Transfer:
_lbs/day
Percent Clone Transfer - Cozone supply rate (Ibs/day) - ozone lost in vent (lbs/dav» (100)
ozone supply rate (Ibs/day)
_(lbs/day) (100)
_(Ibs/day)
Effceetvg Ozoqe Dosage;
_mg/L H20
Ibs/day
Concentration of Effective Ozone Dosage - (Percent Transfer efficiency) (applied ozone dosage) - ( %) ( mg/L H 0)
(Continued)
214
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TABLE G-2 (CONT). OZONE PRODUCTION DATA RECORDING SHEET
OZONE SYSTEM PERFORMANCE DATA
GENERATOR OUTPUT, APPLIED OZONE DOSAGE,'' DISINFECTION RESULTS, POWER REQUIREMENTS (Continued)
Calculate Ozone supply rate.
Ibs/day - (
Applied Ozone Dosage;
mg/L H20 - (_
ftVmin) ( _ mg/L alt) (28.32 l/ft') t^^o Tjf' <144° -^/^^
Its/day) (
DISINFECTION RESULTS
Values expressed in number of coliforms/100 ol
OTN
Total
Fecal
1ft V
0, Basin
Effluent
_lbs/day
Calculate Power Utilization
p
(^2.) (4.8 watts/sec)
-------
APPENDIX H
TABLE H-l. PROCEDURE FOR CONTACT BASIN OFF GAS TESTING
AT THE UPPER THOMPSON SANITATION DISTRICT
1. Prepare wet test chemistry equipment (See Figure B-l).
a. Add 400 ml of 2% KI solution to one gas washing bottle.
b. Connect wash bottle to test line and wet test meter.
c. Connect vacuum line to wet test meter vent.
d. Level wet test meter and adjust water level in the meter.
e. Open vacuum valve until moderate gas flow rate is established.
2. Run approximately 12 liters of gas through the botle and record field
information on data sheet (See Table B-2).
3. Take gas washing bottle to laboratory immediately.
4. Quantitatively transfer liquid from gas washing bottle to a 1 liter
Erlenmyer flask. Rinse tube and bottle at least 3 times.
5. Immediately add 10 ml of 2N Sulfuric Acid (H2S04).
6. Read initial volume of buret which has been filled with 0.1N sodium
thosulfate solution (^28203). Note: Standardize Na2S203
using the dichromate method. (Standard Methods Ed. 14, pp. 316).
7. Quickly titrate to pale yellow with ^28203.
8. Add 5 ml starch indicator (See Standard Methods - Edition 14, pp. 317
for starch preparation) and slowly titrate by drop to a clear end
point.
9. Record final volume of buret and determine total volume titrant used.
Record information on data sheets (See Table B-2).
10. Complete calculations on data sheet (See Table B-2).
216
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60
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217
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TABLE H-2. OZONE OFF-GAS DATA RECORDING SHEET
OZONE SYSTEM PERFORMANCE DATA
GENERATOR OUTPUT, APPLIED OZONE DOSAGE, DISINFECTION RESULTS, POWER REQUIREMENTS
Date Time of Analysis
rtna TKTCP.KATIOT
Ceaeratort No.
Voltage
_volts Amperage _
Catjrgolert Exchanger Temperature
Separator Pressure
Air Co»prapjor; Seal Water Pressure
A_lr Pratcgataentt Voluae cfa
Pattbj HaCert Reading
W«t Teat Hetcrt Volume
Inlet Temperature _
_amps Controller Setting
isig Temperature _
ipm/vol Corrected Reading ppm/vol
_L Temperature F Man
Water Vapor Pressure In. H20 (see graph)
Heating Toueri On Off Refrigeration; On
Off
Main Pressure pslg
°F Dewpolnt ( °c)
_in. H20 (suction Is negative)
Left
System Amperage
Watt-Hour Hater - Revolutions
Wat Test Kagar; Titration
sis N of
Na2S2°3 -
Leg 1 Amperage _
Leg 2 Amperage _
Leg 3 Amperage _
Time sec.
_ mole eq/L
QOTPUT AM LAPPLIED 020KE DOSAGE CALCULATIONS
Calculate Height of ozone trapped in KI Solution.
(Tltratlm
DASIBI INFORMATION
Span
Inlet Temp. °F
Meter Readings:
Wt- (-
L ' ^ *"' vmole eq' * gm-ml
Calculate voluae of gas that passed through wet test meter.
in. H20J
Where t Vj - Actual voluae in L
P2 - Standard Pressure - 406.8 in. H20
P! - Adjusted Pressure - (Plant Atmospheric Pressure (7460) of 3X4 in. H20)
Right f
- (water vapor pressure) + (wet test manometer pressure - Note: suction is
negative).
T2 - Standard temperature (absolute) - 77°F + 459.6 - 536.6°R
Tj Actual Temperature (absolute) - °F + 459.6 -
Calculate ozone concentration.
S/L air - ( ag) ( j-) - mg/L air
pp«/vol - ( r-rrr*8) (1,000,000) (-J-) - ppn/vol (25°C)
Calculate ozonated air flow rate.
Where: V^ - Actual Volume in Ft3
_scfm (25°C)
P2 Standard Pressure (absolute) - Gauge Pressure-*- Atmospheric Pressure = 6 psig + 14.7 psi - 20.7 psla
P! - Actual Pressure (absolute) ~ Gauge Reading (pslg) 4- Plant Atmospheric pressure (7460) of 11.34 psi o
) x 0.036 psi/in.
T2 " Standard Teaperature for Rotameter (absolute) - 70°F + 459.6 - 529. 6°R
°F + 459.6 - _
Actual Tetaperature for Rotaneter (absolute) - _
- Standard Temperature of 25°C (absolute) » 77°F + 459.6 » 536. 6°R
(Continued)
218
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TABLE H-2 (CONT) .. OZONE OFF-GAS DATA RECORDING . SHEET
OZOHE SYSTEM PERFORMANCE DATA
14
MATER VAPOR PRESSURE
VK
TEMPERATURE
|,
10
55 60 65 70
WET TEST METER TEMP. (°F)
75
80
OFF GAS FLOW BATE
OZONE ROOM EXHAUST COVERED, SCUM CAPS ON, OUTFALL SUBMERGED
195
190
185
180
175
170
165
160
1 1 1
-
-
- .
1 1 1
1 1 1
o/
1 1 1
o/
^
1 ( 1
1 1 1
^
1 1 1
1 I 1
J
s
-
1 1 1
~~r~i .1
/
/**
i i i
J* ''
i i i
' ' -
-
-
-
-
-
t i
20 30 40 50 60 70 80 90
GENERATOR FLOW-scfm (25°C)
© ACTUAL TESTS
219
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1, REPORT NO,
EPA-600/2-80-016
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
EVALUATION OF POLLUTION CONTROL PROCESSES
Upper Thompson Sanitation District
5. REPORT DATE
June 1980 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHORtS) ~~ ~~
Bob A. Hegg, Kervin L. Rakness, Larry D. DeMers,
and Bobert H. Cheney
8. PERFORMING ORGANIZATION REPORT NO.
JRFORMING ORGANIZATION NAME AND ADDRESS
Upper Thompson Sanitation District
P.O. Box 568
Estes Park, Colorado 80517
10. PROGRAM ELEMENT NO.
A35B1C SOS #3 Task C/09
11. CONTRACT/GRANT NO.
Grant R-803831
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research LaboratoryGin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
5/76-9/79 Final
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Edwin F. Earth - Project Officer
(513) 684-7641
P 4,4,. Upper ThomPson Sanitation District (UTSD) advanced wastewater treatment
facility, located in Estes Park, Colorado, incorporated several unique unit processes.
Among these were flow equalization, attached growth nitrification, mixed media filtra-
tion and ozone disinfection. Plant design flow was 5,680 cu m/day (1.5 mgd to 1.0 ragd
The activated sludge, nitrification and filtration processes have two parallel trains
By selectively using one half of the available units design flow conditions were
achieved at one-half the plant design flow rate.
Overall plant performance in terms of BOD5 and TSS removal was consistent,
averaging 95 percent and 96 percent, respectively. Ammonia oxidation was not as con-
sistent, due to loading extremes and cold weather operating conditions. Performance
characteristics of two nitrification tower media types (plastic dumped and redwood
slats) were different.
The air-fed ozone disinfection system was operated intermittently because of
required modifications. Special studies were conducted to determine performance
information. When operating, good disinfection performance was achieved.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Wastewater*
Nitrogen cycle*
Activated sludge process
Electric power demand
Disinfection
Attached growth
Ozone disinfection*
Nitrification
Denitrification
13B
IISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)'
None
21. NO. OF PAGES
234
20. SECURITY CLASS (Thispage)
None
22. PRICE
EPA Farm 2220*1 (9-731
220
ft U.S. GOVERNMENT PBINTINQ OFFICE: 1980 -657-146/5698
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