xvEPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
EPA-600/9-83-021
December 1983 ^
Research and Development
Operation and
Maintenance of
Publicly-Owned
Treatment Works
(POTW's):
Proceedings of the
EPA National
Conference
-------
EPA-600/9-83-021
December 1983
OPERATION AND MAINTENANCE OF
PUBLICLY-OWNED TREATMENT WORKS (POTW's)
PROCEEDINGS OF THE
EPA NATIONAL CONFERENCE
Chicago, Illinois
January 12-14, 1982
Sponsored by the
Municipal Environmental Research Laboratory
and
Center for Environmental Research Information
U.S. Environmental Protection Agency
Administered by
Roy F. Weston, Inc.
West Chester, Pennsylvania 19380
Contract No. 68-03-3055
Project Officer
Gary R. Lubin
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
-------
DISCLAIMER
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use by the U.S. Environmental Protection
Agency.
ii
-------
FOREWORD
The Environmental Protection Agency was created because of increasing
public and governmental concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of the environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is the first necessary step in problem solution;
it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
Improved technology and systems to prevent, treat, and manage wastewater and
the solid and hazardous waste pollutant discharges from municipal and com-
munity sources; to preserve and treat public drinking 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 vital communications
link between the researcher and the user community.
These Proceedings present information on improved POTW operation, main-
tenance, design, performance and energy effectiveness.
Francis T. Mayo
Director
Municipal Environmental
Research Laboratory
iii
-------
PREFACE
This proceedings is a compilation of the papers presented at EPA's
National Conference on the Operation and Maintenance of POTW's held in
Chicago, Illinois on January 12-14, 1982. The purpose of the conference
was to present information on improved POTW operation, maintenance, design,
performance and energy effectiveness. Most of the information presented
at this conference was based upon results from research funded through
the Plant Operation and Design Program of EPA's Municipal Environmental
Research Laboratory, Wastewater Research Division in Cincinnati, Ohio.
This proceedings is intended to provide a permanent record of the
information presented at this conference and to make those involved in
POTW operation, maintenance, and design aware of the type of research
funded through EPA's Plant Operation and Design Program. The conference
was organized into five different sessions corresponding to major areas
of program interest.
All of the papers and final reports resulting from the research
funded by the Plant Operation and Design Program are listed in a separate
reference section of this proceedings. Copies of the material listed in
the reference section are not generally available through the Environmental
Protection Agency. Most of these references are only available through
the National Technical Information Service (NTIS), 5285 Port Royal Road,
Springfield, VA 22161 unless they are part of a published periodical.
IV
-------
TABLE OF CONTENTS
TITLE
Foreword
Preface
Session No. 1
Paper No. 1
Paper No. 2
Paper No. 3
Session No. 2
Paper No. 4
Paper No. 5
Paper No. 6
Paper No. 7
O&M of Wastewater Treatment
Processes
"Results of National O&M Cause
and Effect Survey,"
Bob A. Hegg
"A Model Protocol for the
Comprehensive Evaluation
of POTW's,"
Albert C. Gray and Hugh D. Roberts
"Operation and Maintenance
Considerations of Land
Treatment Facilities,"
Kimm Perlin
Improving the Performance of
Conventional Wastewater
Treatment Processes
"Making-Do with Clarifier
Hydraulic Overload,"
Robert M. Crosby
"Minimizing Impact of Side Streams
on Total Plant Performance,"
Roy 0. Ball
"Composite Correction Program -
Concepts and Demonstration,"
Bob A. Hegg
"Application of Intrachannel
Clarifiers in the Oxidation
Ditch Process,"
Harold J. Beard
PAGE
iii
iv
14
42
63
63
78
95
105
-------
TABLE OF CONTENTS
(Continued)
Paper No. 8
Session No. 3
Paper No. 9
Paper No. 10
Paper No. 11
Session No. 4
Paper No. 12
Paper No. 13
Paper No. 14
Session No. 5
Paper No. 15
Paper No. 16
TITLE PAGE
"Biological Fouling of Fine 119
Bubble Diffusers,"
William C. Boyle and David T. Redmon
Improving Process Reliability 136
"Stability and Reliability of 136
Biological Processes,"
Edward D. Schroeder and Salar Niku
"Evaluation and Documentation of 159
Mechanical Reliability of
Conventional Wastewater Treatment
Plant Components,"
David W. Shultz and Van B. Parr
"Fail Safe Design Concepts," 171
Roy 0. Ball
Improving POTW Design 176
"Design Deficiencies in POTW's," 176
Roy 0. Ball
"Performance Capabilities and 182
Design of Oxidation Ditch
Processes,"
William F. Ettlich
"Performance and Design of 195
RBC Processes,"
Warren H. Chesner
Energy Conservation in Municipal 201
Wastewater Treatment
"Energy Conservation in Unit 201
Processes and Sludge Management,"
Daniel Cortinovis
"A Composite Approach to Energy 210
Conservation Through Process
Optimization - Some Case Studies,"
Ashok K. Singhal, Phillip N. Loud
and Donald W. Lystra
vi
-------
TABLE OF CONTENTS
(Continued)
TITLE PAGE
Paper No. 17 "Alternative Energy Sources in 232
Municipal Wastewater Treatment:
the Wilton, Maine Experience,"
David R. Fuller
Reference Section: Plant Operation and Design Program - 255
Related Publications and Papers
vii
-------
SESSION NO. 1
O&M of Wastewater Treatment Processes
PAPER NO. 1
RESULTS OF NATIONAL O&M
CAUSE AND EFFECT SURVEY
by
Bob A. Hegg
Vice President Plant Operations Division
M & I, Inc., Consulting Engineers
4710 South College Avenue
Fort Collins, Colorado 80525
-------
RESULTS OF NATIONAL 0 & M CAUSE AND EFFECT SURVEY
Bob A. Hegg , Vice President Plant Operations Division
M & I, Inc., Consulting Engineers
INTRODUCTION
The Federal Water Pollution Control Act with Amendments established
goals for the quality of the nation's public waters. A major aspect of the
act was an expanded construction grants activity through which new waste-
water treatment facilities were constructed and existing facilities up-
graded. However, the U.S. Environmental Protection Agency's (EPA) annual
reports to Congress (1) have indicated that a significant number of the
facilities constructed with Federal grant assistance have not provided the
desired effluent quality. Other reports and articles have supported these
conclusions (2, 3, 4).
In response to these findings, EPA1s Office of Research and Develop-
ment initiated a three and one-half year research program to identify,
quantify and rank the factors causing poor wastewater treatment plant per-
formance. M & I, Inc., Consulting Engineers was selected to complete the
two-phase project in the Western United States. To accomplish the research
objectives, comprehensive plant evaluations were conducted in facilities in
nine Western states. Initially, 271 facilities were considered for study.
Ninety-eight were visited and fifty were selected for comprehensive studies
(5, 6, 7).
RESEARCH APPROACH
The major objective of the project was to identify and rank the fac-
tors causing poor wastewater treatment plant performance. Because a limit-
ed number of facilities were studied,a specialized plant selection proce-
dure was established. The major target of facility selection was plants
that were supposedly developed to meet specific treatment requirements. As
such, "operable plants" which were loaded within currently used design cri-
teria, which were operated using reasonable staffing levels and were not
having major equipment problems with critical process units were selected.
Additional selection criteria limited the facilities to biological waste-
water treatment plants with flows less than 37,850 cum/day (10 mgd) and to
plants not involved in enforcement action.
EPA Regions VII and VIII and nine state regulatory agencies were
informed of the plant selection criteria. These agencies suggested a total
of 271 facilities for research. Of the facilities suggested, half-day site
visits were conducted at 98 facilities. Fifty of these facilities were
selected for the more comprehensive studies. Both plants that were meeting
treatment requirements and plants that did not meet requirements were
selected.
The comprehensive plant evaluations were typically conducted with one
and one-half to two man-weeks of effort over a four to ten-day period.
-------
Persons conducting the surveys were sanitary engineers with experience in
plant operations and in identifying and evaluating performance-limiting
problems. During each evaluation the research team worked with plant per-
sonnel to eliminate any obvious and controllable performance-limiting prob-
lems. This action-oriented, assistance approach to data gathering necessi-
tated open communication between plant personnel and research personnel.
As such, a service to the plant owner was provided while more accurate and
less apparent research information was collected.
Each in-plant evaluation was followed by a written report which docu-
mented the problems identified. Recommendations to the city or sanitation
district were offered, but implementation of these was voluntary.
Problems limiting plant performance were evaluated using a list of 71
pre-defined factors. Each factor was assigned from zero to three points in
proportion to the adverse effects that factor had on an individual plant's
performance. The results from all individual surveys were combined to
obtain an overall ranking of these factors.
PRESENTATION OF DATA
Only 13 of 50 facilities surveyed consistently met minimum secondary
treatment standards as defined in CFR 38-159. The mean hydraulic loading
on all plants surveyed was 66 percent of design flow. The mean hydraulic
loading for the 37 facilities that violated standards was also 66 percent
of design flow. These loadings were in line with plant selection criteria,
in that the plants studied were within design limits and supposedly were
capable of meeting required effluent standards.
Table 1 shows the ranking of all 71 factors for the 50 facilities
evaluated. The number of times each factor occurred is also shown. An
average of 13 and a range of 4 to 30 performance-limiting factors were
documented at individual facilities. Many different performance-limiting
factors were noted, and no two facilities had an identical combination of
factors.
The two highest ranking factors were inadequate operator application
of concepts and testing to process control and inadequate sewage treatment
understanding. These findings indicate that many operators were not ade-
quately trained. It could be concluded that expanded training programs are
necessary, but it was observed that "trained" operators did not properly
apply concepts of operation to process control. Therefore, expanded train-
ing appears necessary, but modifications to existing programs are needed.
Any attempt to modify and improve training must include a full awareness of
the number three ranked factor, improper technical guidance concerning
plant operations. Improper technical guidance was documented from authori-
tative sources including design engineers, state and federal regulatory
personnel, operator training program staff, other plant operators and
equipment suppliers.
These findings indicate that other sources have limited the capability
of operators: first to attain adequate sewage treatment understanding and
-------
TABLE 1. RANKING OF FACTORS LIMITING PERFORMANCE
£
8
i
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
M «
1
2
3
4
5
5
7
8
8
10
11
12
13
14
15
15
15
18
19
19
21
22
22
22
25
25
27
27
27
27
31
31
33
33
33
33
Factor
Limiting
Performance
Operator Application of Concepts
and Testing to Process Control
Sevage Treatment Understanding
Technical Guidance
Sludge Vasting Capability
Process Control Testing
Process Controllability
Process Flexibility
Aerator
Infilt ration/Inflow
Clarifier (Secondary)
Ultimate Sludge Disposal
Sludge Treatment
Familiarity with Plant Needs
(Adminstrators)
Performance Monitoring
Policies (Administrators)
Laboratory Space and Equipment
Disinfection
Plant Coverage
Unit Process Layout
Preliminary (Design)
forking Conditions
Equipment Malfunction
Alternate Power Source
Alarms Systems
Motivation (Operators)
Number (Staff)
Scheduling and Recording
(Maintenance)
Adequacy (0 & M Manual)
Productivity (Operators)
Aptitude (Operators)
Return Process Streams
Training Operators
Industrial (Loading)
Insufficient Funding
Housekeeping
Pay (Operators)
,. :s
O • O V*
O-«« « V
KHK.C5
48
28
25
26
32
32
24
17
24
16
19
19
11
16
10
16
11
15
7
15
12
8
13
13
12
11
11
10
9
8
7
9
6
9
8
7
A.
3
96
55
54
51
47
47
45
35
35
28
27
24
20
18
17
17
17
16
15
15
14
13
13
13
12
12
11
11
11
11
10
10
9
9
9
9
8
4J
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
50
60
61
62
63
64
65
66
67
68
69
70
71
m
MB.
e
37
38
38
38
41
41
41
41
41
46
46
46
49
49
51
52
52
52
52
52
52
58
58
58
58
58
63
63
63
63
63
63
63
63
63
Factor o
Limiting ^
Performance *
Plant Inoperability Due to Weather
Lack of Unit Bypass
Flow Proportioning to Units
Supervision
Equipment Age
Insufficient Time on Job
Lack of Program (Maintenance)
Manpower (Maintenance)
Unnecessary Expenditures
Flow Backup
Plant Management
Plant Location
Hydraulic (Loading)
Toxic (Loading)
8
Lack of Standby Units for Key
Equipment
Process Automation Control
0 & M Manual, Use by Operators
Quality of Equipment
Level of Education
Organic (Loading)
Submerged Heirs
Bond Indebtedness
References Available
Staff Expertise (Emergency
Maintenance)
Critical Parts Procurement
Technical Guidance (Emergency
Maintenance)
Unit Design Adequacy, Primary
Process Automation, Monitoring
Equipment Accessibility for
Maintenance)
Shift Staffing Adequacy
Times
Factors
Occurred II
6
7
6
5
6
5
5
5
5
5
3
2
3
3
2
2
2
2
2
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
£
g
8
7
7
7
£
6
6
6
6
5
5
5
4
4
3
2
2
2
2
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
-------
second to apply this understanding to process control. Just as important,
the improper technical guidance and associated lack of understanding by
authoritative personnel has carried over into plant design. Five of the
top ten factors limiting performance were process design oriented. These
areas of inadequate design in order of severity were: sludge wasting cap-
ability, process controllability, process flexibility, aerator and secon-
dary clarifier. The inability of persons involved with plant design to
properly apply the technology necessary to develop adequate treatment
facilities, coupled with the improper operations technical guidance from
these and other sources, indicates that the plant performance problem is
widespread and not limited to strictly plant personnel.
This analysis of the top ten performance-limiting factors indicates
that problems limiting facility performance are interrelated, and a
straight forward approach to improved performance by addressing these fac-
tors is not readily apparent. Other evaluations of selected individual
factors support this conclusion. The approach used to evaluate other fac-
tors was to relate the potential problem area to plant performance. Sever-
al prominently discussed factors were evaluated using this approach: plant
staffing, operator salaries, aerator size and operator certification.
Figure 1 shows staff size plotted versus plant flow rate. As shown by
the least squares line of best fit, staff size increased with plant flow.
The thirteen fully shaded dots represent the plants where secondary treat-
ment standards were met. If a larger number of operations personnel was
100
tL
tu
ta
2
u.
u.
<
CO
l-
o
10
1.0
0.1
• STANDARDS MET
O STANDARDS NOT MET
M3/DAY ' MGD » 3785
O -
.01 0.1 1.0 10
PLANT FLOW RATE -MGD
Figure 1. Staff Size versus Plant Flow Rate
-------
the key to the solution of the plant performance problem, shaded dots
representing plant where standards were met would tend to be located above
the line of best fit. Six of thirteen points are below the line, and a
correlation between plant staffing and performance could not be made.
A similar analysis was performed for staff salaries. As shown in
Figure 2, higher salaries did not appear to correlate directly with better
treatment.
O
O
oc
V)
u.
ML
CO
20
18
16
14
12
10
• STANDARDS MET
O STANDARDS NOT MET
M3/DAV - MOD x 3T8S
O
O O
.01
0.1 1.0
PLANT FLOW RATE- M6D
10
Figure 2. Staff Salary versus Plant Flow Rate
Aerator loadines in oounds of ^005 per day per 1000 cubic feet are
presented in Figure 3. As used here, "aerator" refers to the facility
utilized for the conversion of soluble organic matter into settleable
organic matter. Examples of aerators are trickling filters, activated
sludge aeration basins and activated bio-filters. The extreme scatter of
data did not lend itself to a line of best fit; however, aerator loading
appears to increase gradually as plant flow rate increases. Nine of the
thirteen plants that met standards had low aerator loadings, less than 15
Ib BOD5/day/1000 cu ft. A premature conclusion could be that low aerator
loadings are a key to improved performance, and therefore more conservative
design criteria are needed. However, just as many facilities with low
aerator loadings violated secondary effluent standards. A conservative
design approach may help, but it is not reliable in achieving desired
performance. It is also suggested that improved performance through very
conservative design is not the most cost effective alternative.
-------
"• 80
0
O
2 70
^.
< 60
O
o
r
.01 0.1 1.0 1<
PLANT FLOW RATE - MGD
Figure 3. Aerator Loading versus Plant Flow Rate
The relationship between operator certification and plant performance
is summarized in Table 2. Only 40 percent of the facilities which had "A"
and "B" certified operators were found to be meeting effluent standards.
This was a higher percentage than for the lower and noncertified
operator's facilities. Certification of treatment plant operators seems to
be a step in the right direction, but it too does not appear to be the
total answer.
TABLE 2. EVALUATION OF OPERATOR CERTIFICATION VERSUS PLANT PERFORMANCE
Certification Class
Of
Number of
Secondary Treatment Standards
Chief Operator*
"A"
"B"
"C"
"D"
None
Facilities Surveyed
15
10
9
9
7
Met
6
4
1
1
1
Violated
9
6
8
8
6
%Met
40
40
11
11
14
-------
Evaluation of the data collected indicated that each facility was
typically limited from achieving good performance by a combination of
factors unique to that facility. Evaluations of high ranking factors did
not lead to any positive conclusions regarding methods to improve indivi-
dual plant performance on a broad scale.
UNIFIED CONCEPT FOR ACHEIVING OPTIMUM PLANT PERFORMANCE
Many programs and activities are available that deal with correcting
the performance limiting factors at wastewater treatment facilities.
Examples are operator training schools, operator certification programs,
the NPDES permit program, Federal and State construction grant programs,
design seminars, 0 & M manuals, and regulatory agency inspections. All of
the facilities evaluated had participated in one or more of these activi-
ties; however, in most cases the implementation of these programs did not
result in a particular plant achieving a desired level of performance.
Apparently, the combinations of factors unique to each facility were not
compatible with or were not adequately addressed by the programs that had
been implemented, and several performance-limiting factors continued to
degrade plant effluent quality.
The interrelationship between factors limiting performance and pos-
sible solutions was further defined for the research project in a "Unified
Concept for Achieving Optimum Plant Performance." The Concept is illus-
trated in Figure 4. The goal is tc obtain an optimum performance level for
GOAL
OPTIMUM PERFORMANCE
PLANT
POSITION 2
/
T
\P
PLANT
POSITION i
FACTORS LIMITING PERFORMANCE
• ADMINISTRATION
•MAINTENANCE
• OPERATION
•DESIGN
Figure 4. Unified Concept
-------
a given treatment plant. The horizontal line represents the position of a
treatment facility with respect to optimum performance. The length of the
horizontal line represents the combined magnitude of all factors limiting
performance at that plant. Administrative, maintenance, operation and/or
design factors that limit performance tend to increase the length of the
horizontal line and move a plant away from the goal (Plant Position 1).
These factors are indicated by the number and length of arrows pointing
downward.
Performance limiting factors are typically addressed through implemen-
tation of programs such as enforcement, a construction grant, an operator
training program, etc. Correction of a factor or group fo factors moves a
plant's position closer toward the goal of optimum performance. However,
if all the performance-limiting factors are not addressed, the plant will
only move to Position 2. At Position 2 the length of the horizontal line
is shorter indicating fewer or less severe performance-limiting factors
remain, but optimum performance has not been achieved and effluent quality
may or may not meet requirements.
The Concept can be illustrated with an example. Assume that a plant's
performance was severely limited (Position 1) by two factors: a hydraulic
overload and poor process control. If the plant's overload problem was
corrected through a plant modification supported by a construction grant
but poor process control continued, the plant's position would improve
(Position 2) but the plant would not achieve optimum performance. This
example illustrates why many programs have not been able to achieve desired
performance at a particular facility: all the factors significantly limit-
ing performance at that facility were not corrected.
COMPOSITE CORRECTION PROGRAM
Ideally, optimum performance can be achieved only if all of the fac-
tors limiting performance are corrected. This objective can be more
directly and positively addressed by implementing a single comprehensive
program at each facility. In such a manner, the comprehensive program can
address the factors limiting performance unique to that facility. This
approach has been termed a Composite Correction Program (CCP) and is con-
ceptually illustrated in Figure 5.
As illustrated, a CCP addresses all the performance-limiting factors
at a particular facility (Plant Position 1), and can thus ideally achieve
optimum plant performance. To demonstrate this approach, a CCP was imple-
mented at Havre, Montana, as a part of the research project. A separate
report was prepared describing the implementation and results (6). Plant
effluent BOD^ and TSS concentrations are shown in Figure 6, and are indi-
cative of the capability of the CCP approach to improve performance of an
individual facility plagued by various unique combinations of factors.
A CCP could not be implemented at all of the facilities surveyed
because the combination of factors limiting performance was not usually
amenable to correction within the budget constraints of the research
project. However, sufficient data was collected at each research facility
-------
GOAL
OPTIMUM PERFORMANCE
PLANT
POSITION 2
COMPREHENSIVE
APPROACH
T
T
PLANT
yosmoN 1
FACTORS LIMITING PERFORMANCE
•ADMINISTRATION
•MAINTENANCE
• OPERATION
•DESIGN
Figure 5. Unified Concept - Composite Correction Program
1980
Figure 6. Results of CCP approach - Havre, Montana
10
-------
to project the probable results of implementing a CCP. A dramatic improve-
ment in overall performance would occur. Table 3 presents a summary of the
performance of the fifty facilities evaluated in relation to secondary
treatment standards. CCP's without major facility upgrades could allow 27
additional plants to meet secondary treatment. Ten plants would require a
major upgrade as part of the CCP in order to meet secondary standards.
TABLE 3. PERFORMANCE OF FIFTY PLANTS EVALUATED
VERSUS SECONDARY TREATMENT STANDARDS
Prior to Research Potential After CCP*
Standards Violated 37 10
Standards Met 13 40
*In this evaluation the option of a major facility upgrade was excluded as
a portion of the CCP.
An evaluation of all facilities surveyed showed that the performance
of 38 facilities could be improved using the CCP approach (excluding major
facility modifications). The projected average improvement in effluent
quality was 25 mg/1 for BOD^ (59 percent decrease) and 46 mg/1 for TSS
(63 percent decrease).
The CCP approach provides a viable method for improving plant perform-
ance at individual treatment facilities and should be implemented on a
broad scale. However, incentives are needed to encourage the use of CCP's,
and qualified personnel are required to implement CCP's (5, 6). Personnel
who implement CCP's must be able to recognize and prioritize actual
performance-limiting factors in the broad areas of design, operation,
maintenance and administration. These persons must then be in a position
to implement recommendations over a long enough time period to insure that
desired performance is achieved and maintained. A properly implemented CCP
utilizes all available resources to economically correct the unique combin-
ation of factors limiting performance at a particular facility.
CONCLUSIONS AND RECOMMENDATIONS
Conclusions of the research effort were separated into two categories:
conclusions on all facilities and conclusions concerning individual treat-
ment plants. For all facilities, it was determined that individual facili-
ties are hindered from achieving desired performance by multiple factors
unique to each facility. As such, specific programs implemented to address
selected factors at all facilties will have a limited correlation between
program implementation and improved performance at individual plants. This
conclusion is significant in that large scale programs normally are
assessed on their most obvious intended impact. It is thus conceivable
that programs could be excluded from development or eliminated because of
their inability to show a direct correlation between program implementation
and improved plant performance. Yet these programs may be very necessary
11
-------
to address the high ranking and frequently occurring performance limiting
factors identified.
For individual plants it was concluded that multiple and unique
factors limit a facility's performance. The scope of these factors is
often beyond the plant operator's control (i.e., improper technical gui-
dance and design deficiencies). To achieve a direct correlation between
an individual plant's performance and program implementation, a comprehen-
sive site-specific effort is required.
Based on the above conclusion, the following recommendations were
developed.
-All Facilities - Implement programs to address identified high
priority factors. Implementation must be achieved with a full
awareness of the difficulty in directly assessing impact.
- Individual Facilities - Implement programs to support initiation of
comprehensive site-specific efforts (CCP's) at individual facili-
ties. For example, enforcement for noncomplying facilities could be
used to encourage CCP activities.
ACKNOWLEDGEMENTS
The data upon which this publication is based was compiled pursuant to
Contract Nos. 68-03-2224 and 68-03-2572 with the Office of Research and
Development, U.S. Environmental Protection Agency, Cincinnati, Ohio. The
guidance and assistance from Mr. John M. Smith, who served as project
officer for the Environmental Protection Agency, is gratefully acknow-
ledged. The cooperation and assistance provided by federal, state and
local water pollution control agencies is also gratefully acknowledged.
REFERENCES
1. "Clean Water Report to Congress - 1973, 1974, 1975 Annual Reports",
U.S. Environmental Protection Agency, Washington, D.C., May 1973, June
1974, June 1975.
2. Gilbert, Walter G.,"Relation of Operation and Maintenance to Treatment
Plant Efficiency", Journal of Water Pollution Control Federation, 48,
1822 (1976).
3. "Continuing Need for Improved Operation and Maintenance of Municipal
Waste Treatment Plants", Report to the Congress by the Comptroller
General of the United States, Washington, D.C., (April 11, 1977).
4. "Costly Wastewater Treatment Plants Fail to Perform As Expected",
Report to the Congress by the Comptroller General of the United States,
Washington, D.C., (November 14, 1980).
5. Hegg, B.A., K.L. Rakness and J.R. Schultz, "Evaluation of Operation and
Maintenance Factors Limiting Municipal Wastewater Treatment Plant
12
-------
Performance", EPA-600/2-79-034, NTIS No. PB-300331, U.S. Environmental
Protection Agency, Cincinnati, Ohio (1979).
6. Hegg, B.A., K.L. Rakness and J.R. Schultz, "A Demonstrated Approach for
Improving Performance and Relaibility of Biological Wastewater Treat-
ment Plants", EPA-600/2-79-035, NTIS No. PB-300476, U.S. Environmental
Protection Agency, Cincinnati, Ohio (1979).
7. Hegg, B.A., K.L. Rakness and J.R. Schultz, "Evaluation of Operation and
Maintenance Factors Limiting Municipal Wastewater Treatment Plant
Performance - Phase II", EPA-600/2-80-129, NTIS No. PB-81-112864, U.S.
Environmental Protection Agency, Cincinnati, Ohio (1980).
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
13
-------
PAPER NO. 2
A MODEL PROTOCOL FOR
THE COMPREHENSIVE EVALUATION
OF PUBLICLY OWNED TREATMENT WORKS
by
A. C. GRAY
Project Manager
and
H. D. ROBERTS
Project Engineer
Gannett, Fleming, Corddry & Carpenter, Inc.
P.O. Box 1963
Harrisburg, Pennsylvania 17105
14
-------
A MODEL PROTOCOL FOR COMPREHENSIVE EVALUATION OF PUBLICLY OWNED TREATMENT
WORKS
Albert C. Gray and Hugh D. Roberts , Project Manager and Project Engineer
Gannett, Fleming, Corddry & Carpenter, Inc.
INTRODUCTION
Findings of EPA sponsored studies conducted during the 1970's indicate
that: a) at least 50 percent of the publicly owned treatment works (POTW's)
constructed under the federal construction grants program (PL 92-500) are
not achieving permit compliance (1); b) poor plant performance is usually
due to a combination of inhibitory factors (2, 3); c) implementation of a
composite correction plan (CCP) could bring the great majority of these
plants into compliance without requiring major plant expansion or upgrading.
The key to developing an effective CCP is the performance of a comprehensive
plant evaluation which results in the identification of performance limiting
factors and an analysis of the degree to which each factor impacts treatment
efficiency. An effective plant evaluation will provide the basis for prior-
itization of requisite corrective measures which then can be implemented to
bring about treatment performance improvements in a timely, cost effective
manner. Conversely an improperly conducted evaluation can result in wasted
time and effort in implementing inappropriate corrective procedures.
In the course of conducting research to determine factors limiting
performance of biological treatment plants in the eastern U.S., 53 detailed
plant evaluations were performed over a three year period. Of necessity, to
promote efficiency and uniformity, an evaluation protocol to be followed by
the field research teams was developed. This methodology and related exper-
ience have been incorporated in a model plant evaluation protocol manual
which is the subject of this paper. The manual presents a systematic ap-
proach to conducting a comprehensive performance evaluation of a municipal
wastewater treatment plant. The ultimate objective of the evaluation is to
identify and rank causes of poor plant performance. In the context of this
evaluation procedure plant performance is measured by the consistency with
which effluent quality meets the provisions of the NPDES permit.
The manual breaks down the evaluation into five major problem areas;
design, performance monitoring, operation, maintenance and administration.
In addition, the manual reviews the preparatory steps to be completed before
the actual plant visit. Such preevaluation activities can be instrumental
in assuring that data collection will be productive, efficient, and complete.
A section on the preparation of the evaluation report is also included.
The protocol manual has been designed for use by an evaluation team
that includes at least one individual with wastewater treatment engineering
expertise and one individual with plant operation training and experience.
In the case where a plant is small enough to be evaluated by one person,
that individual should be a professional engineer who also holds operations
certification. As noted above, this manual reviews the evaluation of treat-
ment plant performance only insofar as effluent quality is concerned. Other
aspects of performance, most notably energy utilization efficiency have not
15
-------
been addressed. Other references (4,5,6,7) have been, or are being, devel-
oped for that purpose. Furthermore, the manual does not provide guidance
for in depth analysis of management issues or alternatives. Rather, we are
concerned here with the "First Level" evaluation in which factors that di-
rectly impact effluent quality are investigated. The findings of the EPA
biological plant performance surveys indicate that tangible performance im-
provements can be realized through implementation of programs on an oper-
ational level without necessarily making major management changes. This is
not to minimize the significance of effective management to treatment plant
performance. Over the long term good management practices will facilitate
continuous optimization of plant performance and certainly improve the cost
effectiveness of treatment. At least one reference currently addresses
wastewater utility management in some detail (4). Finally, while the eval-
uation protocol manual reviewed in the following pages sets forth guidelines
for structuring and conducting an evaluation, it is not to be considered all
inclusive. Each treatment plant will present the evaluator with certain
unique features and no single manual could cover all such contingencies.
Other available references can and should be used to supplement the protocol
manual. These include EPA published guidelines on NPDES compliance sampling,
(8), facility staffing (9), methods for chemical analysis (10), and detailed
evaluation of plant unit processes (11).
PRELIMINARY ACTIVITIES
In order to minimize time in the field and to maximize the quality of
information gained, the necessary preliminary procedures should include:
1) Contacting cognizant regulatory officials to
obtain all existing relative data.
2) Contacting responsible treatment authority or municipal
officials to inform them of the proposed evaluation.
5) Contacting the treatment plant superintendent to inform him of
the proposed evaluation, and to discuss the purpose and scope.
4) Estimation of time, manpower requirements, and
materials needed to conduct the evaluation.
5) Formulation of field sampling and analytical program.
Some comments regarding these preevaluation tasks are presented in the
following paragraphs.
REGULATORY AGENCY CONTACTS
The leader of the evaluation team should obtain all existing information
on subject plant that may be on file with the EPA or state environmental con-
trol agency. Data to be acquired from the regional EPA office includes at
least the STORET records for the subject facility and the EPA Form 7500-5
survey form, If one has been completed. The State Regulatory Agency should
be assessed to obtain copies of the NPDES permit, monitoring records and any
16
-------
design related information that may be on file. These data are to be care-
fully reviewed to identify performance limiting problems that have been
previously noted, and to observe past trends in effluent quality.
NOTIFICATION OF POTW AUTHORITY AND MUNICIPAL OFFICIALS
The chairman of the POTW owning authority and the head of the municipal
department responsible for plant operation must be notified of the planned
evaluation. The responsible official is usually the head of the department
of public works or the municipal sanitation department. The NPDES permit can
be checked to determine the responsible official. These officials should be
notified in writing two weeks prior to the scheduled evaluation. Written
notification should be followed with a telephone contact one week prior to
the evaluation.
The written notification should indicate the reason for the evaluation;
for example, to determine what factors are responsible for the failure of the
treatment plant to meet its discharge permit. The scope of the evaluation
should be briefly summarized, and the dates on which field work will be per-
formed indicated. The responsible official should be asked to have his plant
superintendent available throughout the field study period to respond to
questions raised by the evaluation team and to provide copies of operating
records. Furthermore, the responsible official is to be notified that the
budgetary information for the most recent fiscal year is desired for review
by the evaluation team, and that an individual should be designated as a con-
tact for the evaluation team regarding budgetary and other administrative
information. Names of the evaluation team personnel and the designated team
leader should be included in the notification.
The administrative officials should be made aware of the positive aspect
and tangible benefit that can result from the undertaking such as the identi-
fication of areas where 0 & M programs can be improved. Such improvements
may involve minimal investment when compared to structural upgrading, but
significant performance improvement may be achieved. The concept that should
be communicated is that the evaluation is the first step in maximizing the
return on the investment represented by the pollution control plant. If
these idea's are clearly communicated, negative attitudes will be reduced and
cooperation from the plant staff and administrators will facilitate the
evaluation process.
NOTIFICATION OF THE POTW SUPERINTENDENT
Contact with the plant superintendent should not be made until the re-
sponsible authority or municipal official has discussed the scope and pur-
pose of the evaluation with the plant superintendent. Then the team leader
should call the superintendent to explain the nature of the evaluation to
the superintendent, inform him of how much of his or his staff's time may be
required, and answer his questions concerning the type and extent of infor-
mation he will be asked to provide. The team leader should indicate the
specific operating records and technical references he will inspect during
the field investigation. The intent of contacting the plant superintendent
is both to solicit his cooperation and to allow him some time to prepare so
17
-------
that information retrieval is expedited. No written contact need be made.
Again, the concept that the evaluation team's findings may benefit his
plant's performance is to be communicated to the superintendent.
CONTACTING CONSULTING ENGINEER OF RECORD
When the plant administration is notified, the name and address of the
design engineering firm should be obtained. The administrator may refer the
evaluation team leader to his consultant engineer to answer plant specific
questions. In any case, the administrative official should be asked to give
clearance to his engineer to release information regarding plant design to
the evaluation team. The team leader should then directly contact the con-
sultant and request to be given a copy of the basis of design, which may be
returned to the consultant at the conclusion of the evaluation. Also, at
this time, the scope and purpose of the evaluation should be discussed with
the consultant. He should be asked for his suggestions concerning areas or
facets of plant operation that should be specifically observed during the
evaluation.
ESTIMATION OF EVALUATION TIME
Field time required for a comprehensive evaluation is a function of
size of plant, complexity of treatment process, and the amount of cooperation
provided by the plant operating staff. A minimum of three days in the field
should be allowed for plants with design capacities of 11,355 cu m/d (3.0
mgd) or less and a minimum of five days field evaluation time should be al-
lowed for larger plants. The cutoff point between three and five day field
studies is somewhat arbitrary and based on average conditions. Judgment
must be exercised in making adjustment in time allotments for plants where
unusual or extenuating circumstances exist. It is better to overestimate
the time required to conduct a comprehensive evaluation than plan for too
tight a schedule. The slower pace will allow the evaluation team to better
observe plant operations and to converse at some length with the operators.
Such conversations can provide additional insight into problems which would
otherwise be missed in the rush of a tight schedule. Also, the slower eval-
uation pace can result in an atmosphere in which the operating staff feels
the evaluation team is providing some technical assistance to them. Under
such circumstances, a good attitude and the cooperation of the plant staff
increases the quality of the evaluation.
ESTIMATION OF REQUIRED MANPOWER
The provision of proper staffing involves two considerations. The
number of individuals required to accomplish all tasks within the three to
five day time frame must be determined. Just as important, however, is that
the evaluation team include individuals with appropriate training and ex-
perience to gather all performance, design, operational, maintenance and
administrative information, and to perform necessary sampling and field
analysis. The number of individuals required to perform these tasks is a
function of the size and complexity of the treatment plant. Since com-
plexity of the treatment facility normally increases with design flow, man-
power requirement can be related to plant size. Table 1 shows the recom-
18
-------
mended number of staff for an evaluation team as a function of plant design
flow. This staffing guide should be viewed as a minimal allocation of
manpower.
TABLE 1
GUIDE TO STAFFING REQUIREMENTS FOR COMPREHENSIVE EVALUATIONS
Plant Design Flow No. of Investigators
cu m/d mgd
11,355 3 1
11,355-94,625 3-25 2
94,625-227,100 25-60 3
227,100 60 3 or more
Every evaluation team must include two categories of technical expertise;
plant design and process operations. In the case of small plant evaluations
where only one individual is involved, that individual must be an engineer
who has had experience in treatment plant design or review of such designs,
and has been involved in facets of plant operations. He should also be a
registered professional engineer and hold state certification as an operator,
in states where certification programs exist. Although an individual with
this dual certification is not always available, experience and a working
knowledge in both areas is absolutely necessary. In the case where an
evaluation team is comprised of two or more individuals, at least one sani-
tary engineer and one certified operator should be included. Other indi-
viduals on the team may be technicians familiar with sampling, analysis, and
field measurement techniques. These personnel would perform field data col-
lection tasks under the supervision of one of the senior team members.
One of the senior team members should be designated as the evaluation
team leader. The duties of the team leader include: (1) making all pre-
liminary contacts, (2) collecting and coordinating review of previously
available data, (3) overseeing scheduling, transportation, and lodging ar-
rangements, (4) reviewing and approving of field sampling program, (5) co-
ordinating field work, and (6) preparation of the evaluation report.
DETERMINATION OF REQUIRED EQUIPMENT AND MATERIALS
To enhance efficiency and organization of the field data collection
effort, several forms have been developed for the protocol manual. As part
of the preliminary activities, copies of these forms should be reviewed so
that the evaluation team understands the data requirements and format before
proceeding into the field. All available preevaluation information should
be entered on the forms prior to the field study and confirmed during the
field investigation.
19
-------
The Field Analysis Requirement Form is a guide to be used to design the
sampling and analysis program portion of the evaluation. It should be com-
pleted prior to the on-site work so that proper sample containers, reagents,
and instruments can be obtained. However, a process flowsheet and some
plant design information is needed to complete the form. If this information
is not available, then sampling program decisions will necessarily be made in
the field, in which case the team must be sure to bring sufficient sample
containers and reagents to cover any contingency.
The following items are to be obtained, cleaned and calibrated prior to
conducting the field study:
1. Sample Bottles - Approximately 1/2 liter capacity, sufficient
number to sample plant influent, effluent, and interprocess
streams at least daily during the 3-5 day survey. One hundred
sample bottles will normally be sufficient.
2. Automatic Composite Samplers - To be used for sampling all
wastewater flows including influent, primary effluent,
secondary clarifier effluent, and final discharge.
3. Reagents for Sample Preservation - Sulfuric acid, nitric
acid, mercuric chloride.
4. 50 Liter Cooler - For sample storage and transport.
5. Field pH Meter
6. Field D.O. Meter
7. Tape Measure - 30.5 m (100 ft.)
8. Bucket and Rope
9. Stop Watch
10. Dye Tablets
11. Protective clothing including boots and wet weather gear
12. Calculator
13. Clipboards
LABORATORY ANALYSES
The extent of laboratory analysis to be performed on collected samples
depends on several factors. Of primary importance are the analyses for
parameters required to quantify the process control indicators, which will
vary with the treatment process flowsheet. Also, analyses for all discharge
permit parameters should be performed on influent, effluent, and unit pro-
cess flows so that removal of these pollutants may be profiled through the
20
-------
TABLE 2. SUGGESTED SAMPLING AND ANALYSIS PROGRAM
Analyses
BOD,- (total
BOD, (soluble)
Settleable sot ids
Suspended solids (total)
Suspended solids (volatile)
Dissolved oxygen
Phosphate"
Ammon i a nit rogen-'-
A\ka1in i ty
PH
Chlor i ne res i dua1
Feca1 coliform
Me ta Is ••
Where app1i cable
-------
facility. Table 2 presents a general guideline indicating analyses to be
performed on samples obtained from various points in the treatment process.
Daily samples should be obtained at each indicated sampling point. Where
possible, composite samples should be collected. Whether these should be
time proportioned or flow proportioned, depends on the flow characteristics
at the particular sampling point. Use of automatic samplers, wherever pos-
sible, is strongly recommended. This will reduce manpower requirements
while improving sample integrity. Samples for solids analysis must be col-
lected manually, but several samples per day should be combined into one
composite. For all samples collected, careful judgment must be used in
determining the actual point where a unit process will be sampled to assure
that a timely representative sample is obtained.
Table 3 shows recommended sampling locations for the various plant unit
processes. In the case of multiple parallel units, each unit should be
individually sampled in order to isolate problems. There are many unusual
or specialty processes that are not specifically covered in Table 3. In
deciding where to sample such processes, the evaluator must exercise careful
judgment. Every effort must be made to obtain the most representative sample
in light of the purpose ofr sampling at the point in question. Additional
references (8,11) will be useful in establishing sampling details.
Since no person is more familiar with access to the various plant units
than the operator, Table 3 should be reviewed with him at the start of the
field survey. The operator will be able to indicate where sampling ports,
free discharges, or other appropriate sampling points can be found. If
there is a serious problem with accessing a particular flow, and it is
critical to the evaluation, alterations such as inserting a valve or tap in
a line must be discussed with the supervisory operator. The long-term
advantages of having complete sampling access for purposes of process con-
trol should be explained at that time. It may be necessary to postpone the
evaluation for several days to allow any necessary modifications to be made.
TABLE 3
RECOMMENDED SAMPLING POINTS
Plant Influent Wet well, after bar screen,
comminutor and raw sewage pumps
Grit Removal Near effluent weirs, approximately
2 feet beneath surface
Primary Clarifier Free discharge into effluent
launder (over weir)
Trickling Filter Effluent junction box, beneath
surface (or manhole if no junction
box exists)
22
-------
TABLE 3
(Continued)
Aeration Tank
Sludge Return
Secondary Clarifier
Disinfection Unit
Plant Effluent
Raw Sludge
Primary Digester
Secondary Digester
Thickener
Polishing Pond
Polishing Filters
ESTIMATING THE COST OF AN EVALUATION
Near center of tank, 2 feet beneath
surface (D.O. should be run at
several depths)
Free discharge into aeration tank,
return sludge distribution box,
sampling valve on return pump
Free discharge at weir into
effluent launder
Near effluent weir (if chlorine
residual is to be run, sample
should be fixed)
At outfall discharge
Sampling port on sludge transfer
line (or lines), free discharge
into aerobic digester
Tap on line between primary and
secondary digester
Supernatant - at collection sump
or port on recycle line, free fall
discharge at plant headworks
Sludge - free discharge to drying
beds, influent line to thickener,
influent line to holding tank for
dewatering equipment
Dewatering holding tank, influent
line to holding tank
Near effluent weir or other
discharge device
Tap on filter effluent line,
discharge to chlorine contact tank
A budget for the comprehensive evaluation must be prepared during the
planning stage. The variables that impact the cost of an evaluation include:
duration of the survey, number of team members, extent of sampling and
analysis program, and transportation, lodging and subsistence costs. A guide
for estimating the funds to be budgeted for an evaluation is given in Table
4. Experience indicates the costs of comprehensive evaluations typically
23
-------
N)
Cost Center
TABLE 4
A Cut tie To Estimating The Cost Of A Comprehensive Evaluation
Variable No. 1 Variable No. 2 Variable No. 3
Constant
A. Pro-1C valuation Act I vl l li'.s No. roan-hours x Average payroll
1. Make contacts ;m
-------
TABLK 4 (Cont'd)
Cost C(nn t c t
c.
_
1 . Diita Kcilucl. Ion iiiul
analys Is
Variable No. I
Variable No. 2 Variable No. 3 Constant
No. man-hours x Average payroll
rate (S/hr)
Subtotal
N3
Ul
2. Writ Inf, and edit I nf.
Typing and assi-mb 1 I nj;
'i. I'r lilt I nj; and
dncLI on
Subtotal
No. man-lionrs x Average payroll
rate ($/hr)
No. man-hours x Average payroll
rate ($/hr)
No. of paf.oij
KeproductIon
rate ($/pagi?)
Total Evaluation Com
-------
fall in the range of $3,000 to $8,000, including all field work and the
preparation of an evaluation report.
MONITORING DATA COLLECTION
Three potential sources of monitoring data exist by which the perform-
ance of a treatment plant and its individual unit processes should be evalu-
ated. First, there are the plant operating reports that document all anal-
yses performed at the facility. The results of analyses performed on samples
collected as part of the evaluation are the second source of monitoring data.
The third source is the sampling and analysis information maintained by the
regulatory agency in certain states.
PLANT MONITORING DATA
A member of the survey team should obtain copies of all monitoring data
and reports maintained by the plant staff during the previous 12 months.
Such information would include overall plant performance data such as flow
records, influent and effluent 6005, suspended solids, phosphorus, nitrogen,
and pH analyses. As a minimum, Such information should include results of
all tests performed in accordance with the NPDES monitoring requirements,
set forth in the plant's permit. Other available monitoring data maintained
at the plant may include: primary effluent BOD^ and suspended solids, MLSS
MLVSS, and aeration basin dissolved oxygen (D.O.) and pH, and digester per-
formance indicators, including alkalinity, volatile acids, temperature, and
pH. Results of analyses on side streams such as return sludge, digester
supernatant, thickener overflow, and dewatering filtrate should also be
requested.
EVALUATION MONITORING DATA
One of the tasks performed by the evaluation team during a survey is the
collection of samples for the purpose of monitoring process performance.
Table 2 discussed earlier in this paper, indicates the inter-unit streams
and process contents which should be sampled during the evaluation. The
typical analyses to be performed on these samples have also been indicated.
Sample volume requirements and preservation methods should be predetermined
before arrival in the field.
REGULATORY AGENCY DATA
Certain state water pollution control agencies periodically conduct
sampling and analysis studies at treatment plants within their jurisdiction
as a check on performance. By contacting the respective state agencies,
such data may be available for evaluation purposes or for confirming
evaluation monitoring data.
Some general guidelines should be followed relative to samples col-
lected in the field. Samples should be split and labeled aliquots pre-
served in accordance with intended analyses. Samples should be delivered
as expeditiously as possible to the designated laboratory. Complete
written instructions should be left with the laboratory supervisor speci-
26
-------
fying analytical parameters, suspected concentration ranges, reporting re-
quirements for results, and deadlines for reported results. If the evalua-
tion team does not have prior knowledge of a lab oratory, a visit to review
items such as sample chain of custody, quality assurance, and record
keeping procedures is suggested.
DESIGN ANALYSIS
An important part of the comprehensive evaluation is to evaluate the
basis of design and to compare the plant facilities in place with the basis
of design. The objectives of this portion of the comprehensive evaluation
are to (1) discern any design factors which may limit the ability of the
plant to meet its permit conditions, (2) determine the limitations on oper-
ations imposed by design, and (3) identify minor design deficiencies that
may be easily and inexpensively corrected. This analysis will include exam-
ination of process design parameters, such as detention times, hydraulic
and organic loadings, recirculation rates, and sludge age. Also, a visual
comparison of plans and specifications to existing equipment and layout must
be made to determine if changes have been made either at the time of con-
struction or thereafter. The adverse impact of some design errors or omis-
sions, such as undersized unit processes, is easily perceived. However,
the evaluation team must also establish the extent to which more subtle de-
sign problems adversely impact the performance of the treatment plant.
Examples of such problems could be inadequate sludge return or wasting
capacity, or poor control over recycle flows. Inadequate process flexibility
is another potential design problem that may not be readily apparent on
initial review of the basis of design.
General design information can be obtained from several sources. These
include: the preliminary engineering report or 201 Facilities Plan prepared
for the plant, the plant basis of design, the O&M manual, as-built drawings
retained by owner, design drawings retained by the consultant engineer, and
permit applications on file with the state regulatory agency. In addition
to all unit process design information, Design wastewater characteristics
and flows must also be determined. As a minimum the general background
information that must be obtained to evaluate the treatment plant design
includes:
Average design flow
Peak design flow (rate)
Design BOD5 and suspended solids loadings
Design service population
Design year
— Age of existing facility
— Present average flow
— Present peak flow (rate)
Present BOD5 and suspended solids loadings
— Present service population
— Volume of industrial wastewater
— Character of industrial wastewater (6005,
suspended solids, heavy metals, toxics, etc.)
Volume of infiltration/inflow
27
-------
In addition, review of recent operating records, or regulatory agency
inspection records, must be conducted to obtain information on current waste-
water flows and characteristics. Records of any infiltration/inflow analyses
that have been performed are available from the plant owner or the consulting
engineer.
The major portion of the design evaluation phase is devoted to the
analysis of individual unit process designs. This analysis consists of de-
termination of process design parameters and loadings, comparison of these
parameters with good engineering practice, and comparison of design para-
meters with values realized in the process under actual operating conditions.
Thorough evaluation of unit process design will provide the necessary infor-
mation to establish the existence and degree of the following potential
plant performance limiting conditions:
1. Poor process design which subverts the ability of a process
to meet design intent. For example: .excessive solids loading
on a secondary clarifier, inadequate detention time in an
aeration tank, etc.
2. Construction or installation which does not conform to design.
An example would be clarifier weirs installed out of level,
causing short circuiting in the unit.
3. Inadequate process flexibility. This situation interferes with
the operator's ability to adjust the process to variations in
wastewater conditions. An example of this would be an activated
sludge return line for which flow cannot be adjusted.
4. Poor process selection. An example would be the use of the con-
tact stabilization mode of the activated sludge process to treat
wastewater which is highly variable in organic strength.
5. Incompatibility of unit process with the constituent removal re-
quirements. An example of this would be the use of a secondary
clarifier to achieve effluent suspended solids concentrations of
less than 20 mg/1.
All unit process design evaluations must be conducted with the above
five potential problem areas being carefully considered.
It can be expected that some of the following unit processes must be
evaluated at any biological treatment facility:
Raw sewage pumping
Screening
Shredding
Grit removal
Flow measurement
Primary sedimentation
Trickling filters
Aeration (Activated Sludge)
28
-------
Rotating biological contactors (RBC)
Secondary sedimentation
Disinfection
Filtration
Microscreening
Carbon adsorption
Land application (wastewater)
Thermal sludge conditioning
Sludge thickening
Anaerobic digestion
Aerobic digestion
Sludge dewatering
Land application (sludges)
Design and current loading parameters must be obtained for each of these unit
processes. A form is provided in the protocol manual to facilitate collec-
ting this data. Though the collection of design data is a somewhat routine
undertaking, the evaluation team must be continually aware that the data
must be complete to definitely determine whether unit process design is in
any way placing limitations on the plant's performance.
The protocol manual sets forth guidelines for the collection and manip-
ulation of data for each of the above listed unit processes, although
brevity precludes such detail in this paper. Design parameters to be in-
vestigated and raw data needed to calculate them are specified for each unit
process. Various references such as "UPCF Manual of Practice No. 8" (12),
the EPA Technology Transfer Series, and tests such as that edited by Metcalf
and Eddy (13), can be used to establish ranges for design parameters
considered representative of good engineering practice.
In conducting the design analysis the evaluation team must be aware
that all potential design problems are not necessarily evident upon an
analysis of unit process loadings. Factors such as process flexibility,
accessibility of sampling points for process control, capability to divert
and balance flows, and calibration requirements for process control
instruments should be evaluated.
OPERATIONAL INVESTIGATIONS
The evaluation of operational capabilities and limitations comprises
an extremely important segment of a comprehensive evaluation of a treatment
facility. This area historically has not been given adequate consideration
in plant evaluations. Operational factors affecting plant performance range
from qualitative factors such as the personal characteristics and traits of
operators (e.g., process knowledge and general aptitude), to more quantita-
tive physical constraints placed on the staff, such as deficiencies in lab-
oratory equipment or a lack of reference materials. The evaluation team
must be objective but diplomatic during all of its fact-finding activities,
out this is especially true in relation to operations. The operators may be
very sensitive to question in this area, because they may interpret the
evaluator's questions as an attempt to assess their job performance. To
29
-------
some degree, operator job performance must be assessed in this section of the
comprehensive evaluation.
In the evaluation protocol, plant operational practices are divided into
four major categories: operating personnel, plant monitoring, process con-
trol, and operations references. The information to be obtained for each
category is discussed. Also, for comparison purposes, acceptable baseline
capabilities are given wherever possible which will assist the evaluator in
determining the adequacy or acceptability of plant operational procedures and
resources. A form for the purpose of summarizing operational data is
included in the protocol manual.
The best engineered plant would not perform to its potential without the
management provided by a capable operator. Conversely, many poorly designed
plants can and do perform satisfactorily with respect to effluent criteria
due to conscientious and capable operators. Through discussions with the
plant superintendent the evaluation team must establish the abilities and
limitations of the operating staff. At small plants this may involve in-
depth discussions with only one operator. At larger facilities, the in-
vestigations should be directed toward the chief operator for each shift or
the individuals in charge of overall operations, those in charge of specific
process operations (i.e., digester control operator), and those responsible
for laboratory functions.
The evaluator should determine the level of education of each of the
responsible operating personnel. For individuals in supervisory positions
and in situations where there is only one operator the equivalent of a high
school graduate would be considered baseline. The evaluation team must
assess the level of knowledge that the plant operators have regarding waste-
water treatment. The aptitude of the operating personnel in this regard
must be assessed through question-and-answer sessions in which treatment
theory and process control techniques are discussed. Careful analysis of
the operators responses is the best way to determine his ability to compre-
hend and apply the concepts of wastewater treatment. Specific questions to
be asked depend on the type and complexity of treatment process involved.
For example, in the case of an activated sludge plant the operator might be
asked if he has ever encountered a bulking problem and, if so, what action
he took in response. He might further be asked if he feels his process can
be controlled by F/M or mean cell residence time techniques and how this
might be accomplished. The operator of a trickling filter plant might be
asked about his plant's recirculation control capabilities. Questions con-
cerning sludge handling and disposal, and laboratory techniques should also
be posed.
Operator attitude has an important bearing on the overall performance
of a plant. A good attitude toward operating the plant is an indication
that the personnel are at least expending the effort to produce a high
quality effluent. Evaluation of operator attitude is necessarily subjective.
Often a poor attitude is evidenced by excessive complaining about working
conditions; an antagonistic reaction to the evaluation; placing all culpa-
bility for performance problems on the engineer, plant administration, or
regulatory entities; an inability to get along with others; high rate of
30
-------
absenteeism; or (of most importance) indifference toward the problems at the
plant. This last manifestation of poor attitude is usually accompanied by
poor records keeping, poor condition of equipment, and inadequate laboratory
testing. It is recognized that in many instances operators complaints are
justified by the circumstances. The evaluator must judge the degree to which
the operator is offering constructive criticism, and conversely, the degree
to which negativism and attitude problems prevail.
Monitoring activities conducted at a treatment facility by the opera-
ting personnel are a good indication of the emphasis placed on operations,
and the operator's understanding of process control. The evaluation team is
responsible for making value judgment relative to several types of monitoring
activities. Firstly, the sampling program followed at a treatment plant must
be compared with recommended or required procedures. Performance sampling
should conform with permit requirements. Such requirements may include com-
posite sampling. The frequency of sampling may also be specified. If sam-
ples are going to be held for any period longer than a few hours before be-
ginning the laboratory analyses, preservation techniques should be routinely
employed. Laboratory procedure should be evaluated by direct observation of
technicians, or at least by means of detailed interview of technicians re-
garding their analytical methods and laboratory procedures. A form has been
provided in the protocol manual for performing the laboratory evaluation.
Process testing should be evaluated in a manner similar to performance
testing. Although these tests are not required by permit, effective process
control of certain unit processes, such as the activated sludge system or the
anaerobic digester, requires such tests be conducted in order that appropri-
ate control adjustments may be made. Unlike the performance testing case,
process testing scope and frequency will not be set forth in regulatory per-
mits. Therefore, the evaluator must use judgment and references in setting
a framework of acceptable process testing at a given plant. Table 5 pre-
sents a guide for evaluating the acceptability of process control testing
for various processes and interprocess streams, for plants in the small,
medium, and large design categories. The table may be used as a general
guide, but specific conditions at each plant should be taken into
consideration when applying the table in the field.
Maintaining adequate records of plant monitoring is an important aspect
of operations. Records should include copies of NPDES monitoring reports
dating back at least two years and complete records of all process monitoring
for the current and previous year. As a minimum, annual summary sheets of
all performance and process monitoring should be filed at the plant for all
previous years. Neatness and organization of monitoring records should be
assessed.
An effective process control program is essential if a biological
treatment plant's performance is to be optimized. This is especially true
in the case of activated sludge systems. However, process control is not
something that will be easily quantified by the evaluation team. In most
cases, the evaluators will have to rely on discussions with the plant
superintendent and/or operators to supplement available records and
observations.
31
-------
Table 5
Guide for Evaluationg Process Testing
PRIMARY EFFLUENT
Less than 1 mgd
1 to 5 mgd
Greater than 5 mgd
TRICKLING FILTER EFFLUENT
Less than 1 mgd
1 to 5 mgd
Greater than 5 mgd
MIXED LIQUOR
Less than 1 mgd
1 to 5 mgd
Greater than 5 mgd
RETURN SLUDGE
Lesi than 1 mgd
1 to 5 mgd
Greater than 5 mgd
THICKENED SLUDGE
Less than 1 mgd
1 to 5 mgd
Greater than 5 mgd
PRIMARY DIGESTER
Less than 1 mgd
1 to 5 mgd
Greater than 5 mgd
DIGESTED SLUDGE
(Aerobic and Anaerobic)
Less than 1 mgd
1 to 5 mgd
Greater than 5 mgd
Suspended
BOO, Solids
1 /wk 1 /wk
2/wk 2/wk
2/wk 2/wk
1 /wk 1 /wk
2/wk 2/wk
2/wk 2/wk
2/wk
Vwk
Daily
1/wk
2/wk
4/wk
1/wk
2/wk
2/wk
-
I/mo
1/wk
2/wk
Volatile
Suspended
Solids 0.0. pH
Da i } y
Daily
Daily
Daily
Daily
Daily
1/wk Daily Daily
2/wk 3/daY Daily
lt/wk 3/day Daily
1/wk
1/wk
2/wk
1/wk
2/wk
2/wk
1/wk - 2/wk
2/wk - Daily
2/wk - Daily
1/mo
1/wk
2/wk
Volatile
Alkalinity Acids
-
-
-
-
-
1/wk 1/wk
2/wk 2/wk
2/wk 2/wk
-
DEwrtTERED SLUDGE
Less than 1 mgd " l/m°
1 10 5 mgd " '/wk
Greater than 5 mgd " 2/wk
RETURN STREAMS (Thickener
overflow, secondary digester
supernatant, filtrate)
Less than 1 mgd 1/mo I/mo
I to 5 mgd >/wk 1/wk
Greater than 5 mgd 2/wk 2/wk
1/mo
1/wk
2/wk
I /mo
1/wk
2/wk
32
-------
The evaluation team must determine how knowledgeable the operator is
with respect to process control methods. Are the typical process control
parameters, such as food to microorganism ratio (F/M) and mean-cell resi-
dence time (MCRT), familiar to the operator? Does the operator understand
how to calculate these parameters and does he know what reasonable values
are? Is he aware of the process control monitoring (i.e., influent 8005,
MLSS, volume of sludge wasted, etc.) which must be performed to determine
such control parameters? The evaluation team must determine if a rational
process control stategy exists and how thoroughly that strategy is
implemented.
Previous plant performance surveys have shown that at some plants, the
operator performs the recommended process tests, but makes no effective use
of the information. For example, MLSS levels may be monitored daily, al-
though no attempt is ever made to adjust sludge wasting routines in order
to maintain an optimum MLSS concentration. Through discussions with the
operator and review of plant records the evaluation team must determine
whether the process monitoring data is being used to control the
facility's performance or simply being compiled.
Good technical references are a significant asset to the operator with
respect to efficient plant operation. The operations manual prepared
specifically for the plant is the most important reference. Other reference
materials relating to operations include manufacturer's literature, publica-
tions by professional organizations such as the Water Pollution Control
Federation, and EPA documents.
The evaluation team should judge the adequacy of the operations manual
at each plant. A comprehensive operations manual will address all aspects
of the plant including laboratory functions, testing, process control, and
safety. Start-up and shutdown procedures for all equipment should be pre-
sented in a stepwise fashion. The control center or panel should be des-
cribed in detail with particular emphasis on the features of automatic con-
trol systems. The manual should include detailed schematics of the plant
piping that show all pumps, valves, and similar control devices. Trouble-
shooting procedures should be described in detail. The manual should con-
tain a detailed process control procedure. This procedure should include
all process testing requirements as well as centerlines and ranges for key
process control parameters. The evaluation team should discuss the adequacy
and use of the manual with the operator.
Operational literature is frequently supplied to the treatment plant by
equipment manufacturers. These references provide operators with specific
information on equipment and unit processes that is intended to supplement
the comprehensive operations manual. The evaluation team should first as-
sess the availability and extent of such information at the plant itself.
The evaluators should also determine whether the manufacturer's information
fills any voids in the comprehensive manual.
Operations publications from professional organizations include Manuals
of Practice (MOP) prepared by the WPCF and various state association hand-
books. Such publications provide the operator with additional insight
33
-------
regarding items such as process control techniques and troubleshooting.
Those reference materials are particularly important if the plant lacks a
detailed comprehensive manual. The evaluation team should note the pre-
sence or absence of such publications. Do the operators find these refer-
ences helpful? Are these publications frequently consulted? The contents
and scope of these references should be discussed with the operator. An-
other reference source for treatment plant operations is made available by
EPA under the Technology Transfer Series. The evaluation team should note
the availability of these references at the plant site, and should inquire
as to their value to the plant staff. Do plant operators find these pub-
lications understandable? Have the manuals been used or merely stored on
site.
In summary, thorough evaluation of operational factors is critical to
the comprehensive evaluation. Successful investigation of this area re-
quires in-depth conversations with the operating staff as well as careful
analysis of operating records and observed process control and testing
techniques. The evaluation team should be prepared to devote at least 50
percent of its field time to this effort.
MAINTENANCE INVESTIGATIONS
Maintenance of the treatment plant is a primary responsibility of the
staff. Maintenance duties typically range from performing routine main-
tenance functions, such as lubrication, to on-site major repair of equipment.
The plant maintenance program and its degree of success are a function of
design and construction methods, as well as staff capabilities. Various
aspects of plant maintenance must be examined by the evaluation team and are
discussed in the protocol manual.
The evaluators are directed to note all process units or equipment which
are inoperable at the time of the evaluation. Through discussions with the
operator, the team should determine the length of downtime for each unit,
the performance and maintenance history of the unit, and estimate the level
of effort that would be required to put the unit back in operation. The
evaluation team must assess the impact of out of service units on plant
reliability and performance. The evaluation team should also document which
major plant processes are provided with multiple units to provide backup
capabilities or partial treatment during maintenance periods. The evaluators
must question, in depth, the plant operators and maintenance staff with re-
spect to which processes or equipment are the major problems from the main-
tenance viewpoint and where they feel additional preventive procedures or
spare parts inventory are warranted.
Any units in operation but in need of repair should be noted. Symptoms
of such needed repairs are noisy bearings in motors, seal and gland water
leaking from pumps, oil leaking from mechanical parts (other than minor drip-
page), and excessive digester fuel consumption for heating purposes. The
evaluation team should reveiw with the plant maintenance personnel each of
the units determined to be in need of repair or servicing; noting their com-
ments regarding the reasons for such conditions, any proposed repair schedules,
and any long-range programs for eliminating such conditions in the future.
34
-------
Scheduling of routine or preventive maintenance is to be assessed.
Examples of such maintenance include: lubrication, periodic draining and
cleaning of tanks, repairing sludge scraping and skimming mechanisms, re-
packing pumps, replacing bearings, cleaning diffusers on air headers and
nozzles on trickling filter distributors, and cleaning flow measuring devices
and monitoring equipment. Is such maintenance performed on schedule or only
when time permits? Records for each piece of equipment requiring maintenance
should include the date and cost of repairs, time to repair, manpower expen-
ditures, materials, and outside contractor costs. Generally, the evaluation
team should determine whether the emphasis at the plant is placed on pre-
ventive or corrective maintenance. The existing spare parts inventory and
procurement procedures should be carefully assessed.
To effectively deal with emergency situations the plant must maintain
certain baseline capabilities or provisions. An alternate power source
(i.e., gasoline- or diesel-powered generators, or a second power service
line from a separate substation) should be provided. Audible alarms should
alert failures of major equipment items, such as pumps, chemical feeders,
mixers, or aerators. Also, portable pumps should be readily available in
case of flooding. The manpower resources available to the plant in times of
emergency must be assessed. Such manpower includes permanent staff and
personnel from other departments or private contractors that may be brought
in on short notice. Contingency plants and provisions for emergency
communications should be reviewed.
In short, the evaluation of plant maintenance practices involves visual
observations to assess housekeeping practices and equipment upkeep, careful
review of maintenance schedules and records, review of spare parts availa-
bility, and an evaluation of the maintenance references available to the
operator. The protocol manual includes a maintenance checklist to be
completed by the evaluation team.
ADMINISTRATION
A wastewater treatement facility must obviously be operated within the
constraints of administrative policy and provisions. In some cases blatant
administrative shortcomings such as severe understaffing or under budgeting
may directly inhibit treatment plant performance. In other cases, however,
administrative shortcomings of a more subtle nature may indirectly impact
effluent quality. The latter condition may be difficult to discern by an
evaluation team. Indeed a thorough management-administrative evaluation
could constitute a separate study of greater scope than the entire evalua-
tion covered by the manual discussed in this paper. As indicated earlier,
in depth analysis of wastewater utility management is the subject of other
references. However, the protocol manual does present guidelines for a very
general assessment of administration which is designed to expose major plant
performance limiting problems. Four key aspects of plant administration are
reviewed: plant staffing, budeting, staff training, and use of outside
technical experts.
It is unrealistic to expect any treatment facility to produce an efflu-
ent which consistently meets permit requirements and design performance
35
-------
standards if the plant does not have a sufficient number of employees to pro-
vide needed operation and maintenance. In an evaluation, plant staff respon-
sibilities are grouped according to the following classifications: manage-
ment, operations, maintenance, laboratory, and clerical. Unfortunately,
labor breakdown at treatment facilities is not always in accordance with
these classifications. For example, at small plants, a single employee may
be responsible for all five labor categories. Even at large plants, an in-
dividual may be called an operator, although his duties include laboratory
or clerical work. If an employee's time is divided between two or more
labor categories, an estimate of the fraction of total time devoted to each
category should be made. This should be accomplished by discussing the re-
sponsibilities and duties of each plant employee with the superintendent,
and with his help, establishing the percentage of working time which each
employee devotes to each of the five categories. The evaluation team should
also note the number and specific days of the week that the plant is atten-
ded, the number of shifts staffed and the duty hours, and the types of per-
sonnel staffing and the categories of activities undertaken during the
various shifts.
After the staffing information is gathered, the evaluation team must
assess the adequacy of: 1) the number of plant employees, 2) the distribu-
tion of manpower among the five labor categories, and 3) shift coverage.
Where deficiencies are noted, the team should discuss with the superintendent
the extent to which these deficiencies have affected the performance of the
plant. Also, the evaluation team must determine how successfully the present
plant staff could respond to any noted deficiencies, and assess the need for
additional personnel. For example, if a deficiency is evident in the area
of process control, the evaluator must determine (in this example) whether
the currently employed personnel can handle the additional responsibilities
to correct the deficiency.
One reference for estimating baseline staffing requirements is the EPA
technical report entitled, "Estimating Staffing for Municipal Wastewater
Treatment Facilities". (9) Because all plant specific contingencies could
not possibly be covered, the staffing estimates prepared according to guide-
lines given in this document are not to be considered absolute requirements.
However, this reference provides the mechanics for making a first order
estimate of staffing heads for a given size and type of facility and should
be used as such.
Budgeted funds for operation and maintenance are often cited as being
responsible for deficiencies in performance. However, many facilities are
operated effectively on tight budgets and are able to meet performance stan-
dards. The evaluator must discern when funding is used as an excuse for
poor performance when it is not the true cause. Also, the team must deter-
mine not only the adequacy of the operating budget, but the impact that bud-
6et has on performance. The evaluation team must renew and analyze plant
budget data. The protocol manual includes a form for organizing such data.
For reference purposes, the publication, "Analysis of Operation & Main-
tenance Costs for Municipal Wastewater Treatment Systems", (14) can be used.
36
-------
It presents the results of comprehensive cost surveys for plants of various
types, sizes, and geographical locations and can be used to compare operating
costs at a particular facility with the costs at similar facilities within the
same geographic area. The drawback to using the document to develop stan-
dards of comparison is that it is not known how many plants included in the
data base may have been inadequately funded.
If the adequacy of budgeting is suspect or the inadequacy is documented,
the evaluation team should identify the needed improvements in budget amounts
and categoreies. Areas where budget shortfalls are perceived should be
scrutinized to determine how plant performance is being specifically impacted,
for example, low salaries may be responsible for operation being left to
incapable or poorly trained individuals.
Level of staff training is considered to be an administrative matter,
because entry level requirements as well as the opportunity to participate in
training courses are determined by those individuals with administrative re-
sponsibility for the plant. Discussions should be held with the plant oper-
ators to determine the extent of training received. Completion of formal
courses should be noted. Attendance at conferences and seminars should be
assessed. The team should determine the number and level of certified
operators on the plant staff. State certification is an indication of basic
background knowledge of waste treatment fundamentals.
In some instances, plants have instituted relatively sophisticated on-
the-job training programs, in which the more experienced, better trained,
senior operators convey their knowledge to new or inexperienced employees
through formal hands-on training seminars or programs. Also, in many cases,
consultants are retained to provide training during start-up of new or up-
graded facilities. Whenever programs such as these are encountered, the
evaluators should determine their relative effectiveness.
The extent to which consultants or outside technical experts are em-
ployed is also an administrative decision. The evaluation team should dis-
cuss with the plant superintendent or appropriate administrative official the
extent of their use of consultants or other technical experts. Is there an
on-going service agreement with a consultant or is technical assistance only
called upon when problems develop? The evaluation team must also assess the
effectiveness of technical assistance that has been employed.
Finally, evaluation of plant administration involves some subjective
judgment regarding attitudes and policies. In some cases municipal officials
have considered treatment plant needs a low priority item relative to other
municipal services. Such attitudes will be reflected in plant condition and
performance. The evaluation team can only discover problem attitudes and/or
policies through careful interview of officials and plant staff.
REPORT PREPARTAION
The plant evaluation report must summarize data and present conclusions
resulting from the on-site observations and analyses and related computations.
In addition, the report should make specific recommendations for improving the
37
-------
plants performance within the limitations of operational, maintenance, ad-
ministrative or minor structural changes. The effectiveness of the evalua-
tion as a foundation for preparation of the CCP will be a function of the
quality of the report.
Although rigid report guidelines cannot be followed in all situations,
certain components are essential to the evaluation report. For this reason
the protocol manual presents a standardized report format indicating the
areas that should be covered in the report. The suggested report structure
is as follows:
Section 1. Summary - This section of the report briefly summarizes
the performance of the facility and identifies the major
problems or deficiencies noted during the survey.
Section 2. Description of Plant - This section describes the plant's
location and presents a general description of the plant.
A process flow schematic should be included. Permit
criteria should be recorded. Additional information to
be presented includes: age of facility, date of most
recent upgrading, and point of discharge.
Section 3. Design Evaluation - This section presents a unit-by-unit
analysis of the treatment facility, addressing all major
unit processes. The process design evaluation should
include the completed "Design Evaluation Summary" form.
A discussion of design errors, deficiencies, and over-
loads should be included, along with their impact on
plant and process performance.
Section 4. Performance Evaluation - This section summarizes the
plant's actual performance as it relates to both design
intent and optimum capabilities. Performance should also
be described statistically in terms of its compliance with
NPDES limitations over the 12-month period. Annual average
flows, influent and effluent pollutant concentrations,
pollutant loadings, and percent removals should be documented.
Section 5. Operations Evaluation - This section summarizes the findings
based on investigations of plant operational practices. The
completed forms, "Laboratory Testing Capability and Per-
formance" and "Summary of Operations Performance Indicators"
should be included in this section. All observations with
respect to operating practices and procedures should be
reported. This section should identify, in detail, poten-
tial operationally oriented causes of performance problems.
Where program improvements are necessary, such needs should
be treated.
Section 6. Maintenance Evaluation - This section summarizes the results
of maintenance investigations. The completed form,
"Summary of Maintenance Performance Indicators" should be
38
-------
included. The section should include observations made
concerning maintenance programs. Areas of plant mainten-
ance that can be cited as potential causes of performance
problems should be identified. Additional maintenance
needs should be noted.
Section 7. Administration Evaluation - The completed forms, "Wastewater
Treatment Facility Annual Operating Budget" and "Summary of
Administrative Practices and Policies" should be included
in this section. Administrative shortcomings should be
reported, as well as their apparent impact on other plant
areas. Needed improvements in plant administrative
procedures are to be noted.
Section 8. Plant Evaluation Summary - The "Plant Evaluation Summary"
should be presented, including a brief discussion on how to
interpret the information contained in the summary.
Instructions for completing this document are included in
the protocol manual.
Section 9. Conclusions and Recommendations - This section presents all
relevant conclusions regarding plant design, performance,
operation, maintenance, and administrative factors adversely
affecting plant performance. Causes of performance problems
should be summarized. Actions to correct shortcomings should
be classified as either:
1. Improvements needed to correct deficiencies that
have been directly correlated with performance
problems (first priority), or
2. Improvements needed to correct deficiencies,
although performance problems cannot be directly
correlated with such deficiencies (second priority).
Each corrective action should also be classified with
respect to being either:
1. A non-capital expenditure improvement, which is any
action not involving the construction or modification
of major physical facilities (first priority), or
2. a capital expenditure improvement, which is any action
involving the construction or extensive modification
of major physical facilities (second priority).
Wherever possible, the costs of implementing the corrective
actions should be estimated. Specific recommendations
should be presented. With few exceptions, recommendations
must be limited to those corrective actions classified as
"first priority" in both of the categories above.
39
-------
Exceptions would Include any improvement that would require no (or minimal)
cost. This section should also include a statement of the best effluent
quality believed by the evaluator to be achievable if all non-capital
intensive recommendations were to be implemented.
REFERENCES
1. Gilbert, W.G., Relation of Operation and Maintenance to Treatment
Plant Efficiency, Journal Water Pollution Control Federation,
48(7): 1822-1833, 1976.
2. Gray, A.C., Roberts, H.D., and Paul, P.E., "Evaluation and
Documentation of the Effects of Operation and Maintenance Practices
on the Performance of Selected Biological Treatment Plants", Final
Report, Municipal Environmental Research Laboratory, U.S.
Environmental Protection Agency, Cincinnati, Ohio.
3. Hegg, B.A., Rakness, K.L., and Schultz, J.R., "Evaluation of
Operation and Maintenance Factors Limiting Municipal Wastewater
Treatment Plant Performance", EPA-600/2-79-034, NTIS No. PB-
300331, U.S. Environmental Protection Agency, Cincinnati, Ohio
(1979).
4. Wastewater Utility Management Manual, prepared by Government
Finance Research Center, July, 1981.
5. Energy Conservation in the Design and Operation of Wastewater
Treatment Facilities, Water Pollution Control Federation, 1981.
6. Energy Conservation in Municipal Wastewater Treatment, EPA-430/9-
77-011, U.S. Environmental Protection Agency, Washington, D.C.,
March 1978.
7. Energy Conservation at Wastewater Treatment Plants, Special
Publication, Technical Practice Committee, WPCF.
8. NPDES Compliance Sampling Inspection Manual, NTIS No. PB-81-153211,
U.S. Environmental Protection Agency, Washington, O.C.
9. Estimating Staffing for Municipal Wastewater Treatment Facilities,
MO-1, U.S. Environmental Protection Agency, Washington, D.C., 1973.
10. Methods for the Chemical Analysis of Water and Wastes, EPA-600/4-
79-020, U.S. Environmental Protection Agency, Cincinnati, Ohio 1979.
40
-------
11. Hinrichs, D.J., "Inspectors Guide for Evaluation of Municipal
Wastewater Treatment Plants", U.S. Environmental Protection Agency,
Contract No. 68-014727, 1979.
12. Miorin, A.F., ed., Wastewater Treatment Plant Design, WPCF Manual
of Practice No. 8, 1977, 560 pp.
13. Metcalf and Eddy, Inc., Wastewater Engineering, McGraw Hill Book
Company, New York, N.Y., 1972, 734 pp.
14. Analysis of Operations and Maintenance Costs for Municipal Waste-
water Treatment Systems, EPA-430/9-77-015, NTIS No. PB-283471,
U.S. Environmental Protection Agency, Washington, D.C., February
1978.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agnecy's peer and administrative review policies and approved
for presentation and publication."
41
-------
PAPER NO. 3
OPERATION AND MAINTENANCE CONSIDERATIONS
OF LAND TREATMENT FACILITIES
by
Kimm Perlin
Project Engineer
Roy F. Weston, Inc., Designers-Consultants
West Chester, Pennsylvania 19380
42
-------
OPERATION AND MAINTENANCE CONSIDERATIONS OF LAND TREATMENT
FACILITIES
Kimm Perlin, Project Engineer
WESTON, Designers-Consultants, West Chester, PA
INTRODUCTION
Land treatment of municipal wastewater has been practiced
since 1840. The use of land to treat domestic wastewater has
received major impetus recently with the passage of the 1972
Amendments (PL 92-500) and the 1977 Amendments (PL 95-217) to
the Federal Water Pollution Control Act. The 1977 Amendments,
the Clean Water Act, provide certain incentives for funding land
treatment systems through the U.S. Environmental Protection
Agency (EPA) Construction Grants Program.
Previous EPA research has focused on two aspects of the land
treatment of wastewater: The long-term environmental effects of
land treatment, and the design considerations for land treatment
systems. None of this research adequately addresses the issues
of operation and maintenance of land treatment systems. The
purpose of the study described in this report was to provide in-
formation on operation and maintenance, staffing, and costs.
Also, the study was intended to describe problems currently
being experienced at land treatment sites due to operator and/or
design limitations. The study was divided into two phases.
In the first phase, a project team visited various sites
using land treatment systems to collect information on practices
currently in use. The information was collected on several gen-
eral areas. One area was facility staffing. The data collected
included numbers and functions of the people engaged in operat-
ing and maintaining the land treatment system and other treat-
ment systems at the site.
Other types of data collected during the site visits were in
the areas of process control and operational information. In-
formation collected included the operational strategy used by
the operator to decide where, when, and how much wastewater
should be applied. A third area in which data were gathered
during the site visits was operation and maintenance costs. Da-
ta on operation and maintenance costs of the land treatment sys-
tem were collected, and if possible, divided into salaries, en-
ergy, chemicals, materials, and other well-defined categories.
43
-------
During the site visits, data were also collected on factors
that hinder the operation and maintenance of a land treatment
facility. The adequacy of the groundwater monitoring practices
was also assessed during the site visits. Neighbors whose prop-
erty was adjacent to or in the vicinity of the land treatment
system were interviewed to determine the impact of the land
treatment system on private individuals.
The second phase of the study was the development of defini-
tive recommendations for procedures to improve the operation and
maintenance of land treatment systems.
The recommendations were developed from two different view-
points. The first viewpoint involved the type of land treatment
system. Therefore, all three major types of land treatment sys-
tems were visited: slow-rate (irrigation), rapid infiltration
(infiltration-percolation), and overland flow systems. The sec-
ond viewpoint involved the degree of preapplication treatment
associated with the facility. Therefore, facilities where pri-
mary-, secondary-, and tertiary-treated wastewater is applied
were visited. In addition, facilities with different types of
treatment, e.g., trickling filter versus activated sludge secon-
dary treatment, were visited. The potential effects of climatic
conditions were also included.
The overall goal of the research project was to make specif-
ic recommendations to improve and optimize the operation and
maintenance of land treatment systems.
BACKGROUND
The evaluation of a land treatment system is different from
the evaluation of typical wastewatfr treatment process in that
there is little in the way of direct evidence as to the effec-
tiveness of the land treatment system. Therefore, determination
of the adequacy of a land treatment system must rely on circum-
stantial evidence.
The following data are needed to assess the adequacy of a
land treatment system:
• Design loadings as compared to typical design
limitations.
• Compliance/noncompliance with applicable state
and Federal regulations/guidelines.
• Visual observations (aesthetics, plant health,
soil condition, etc.).
44
-------
• Maintenance practices.
• Operational practices.
It is only through consideration of such parameters that the
performance of a land treatment system can be adequately as-
sessed. In other words, a direct standard, such as effluent
quality, by which the system can be gauged is not available.
Therefore, adherence to reliable design, operation, and mainte-
nance practices are used to determine the presumptive adequacy
of a system.
The sites visited were selected based on a variety of fac-
tors, including degree and type of preapplication treatment,
climatic conditions, and type of land application system. Using
these guidelines, the selected sites have been plotted geograph-
ically, as shown in Figure 1. The sites are clustered around
California, Michigan, and Texas since this is representative of
the geographical distribution of land treatment systems in the
United States. Figure 1 also presents the five different cli-
matic zones in the United States, as presented by Sullivan, et
al (1973) (1). At least one site was visited in each of the
climatic zones.
During the site visits, a trip questionnaire/checklist was
completed for each location. The types of data collected are
summarized in Table 1. The majority of information learned dur-
ing the site visits is believed to be factual. Certain ques-
tions, however, required estimation on the part of the treatment
plant personnel in order to supply the required information. In
cases where the personnel were unable to provide the information
requested, the data were estimated, if possible, by the inter-
viewers.
Of the questions posed, the budgetary questions proved to be
the most difficult to answer. One question involved the budget
information for the operation and maintenance of the facility.
For the majority of the facilities visited (26 out of 28), the
budget information obtained applied to the entire treatment fa-
cility as the funds spent on land application were not separated
from those for preapplication treatment. This necessitated es-
timation to ascertain how much money was spent in each area.
Furthermore, at some of the smaller facilities, collection and
treatment costs were lumped together and had to be separated.
The budgetary problem is further complicated by the fact
that it is sometimes difficult to decide if equipment is part of
the preapplication treatment or the land application treatment
45
-------
A - Mediterranean Climate -
Dry Summer, Mild, Wet Winter
B - And Climate ~ Hot, Dry
C - Humid Subtropical - Mild Winter,
Hot, Wet Summer (Washington. Oregon
Area Mild, Moist Summer)
D - Humid Continental - Short
Winter, Hot Summer
E - Humid Continental - Long
Winter, Warm Summer
(Adapted from Sullivan, et al, 1973)
FIGURE 1. GEOGRAPHICAL AND CLIMATIC LOCATIONS
OF LAND TREATMENT SITES VISITED.
46
-------
TABLE 1. SUMMARY OF DATA COLLECTED DURING SITE VISITS
Background Information
- Contributory population, flows, loadings
- Final disposition of wastewater
- Budget
- Instrumentation, electrical consumption
- Analytical data
Staffing
- Certification
- Background data
- Preapplication and land application staffing
Maintenance
- Preventative maintenance program
- Operation and maintenance manual
Wastewater Preapplication Treatment System
- Physical facilities (type and number)
- Process flow diagram
Land Treatment System
- Wastewater storage
- Wastewater distribution
- Buffer zones, site access
- Application rates
- Soils information
- Groundwater monitoring
Facility Layout
- Preapplication treatment
- Land application system
Land Application - Agricultural Viewpoint
- Operational strategies (wastewater applications,
time and amount)
- Operational problems
- Crop management
Land Application - A Neighbor's Viewpoint
- Problems
- Changes
47
-------
system. For example, a holding pond following secondary treat-
ment may actually function as an oxidation pond, thereby appear-
ing to be part of the preapplication treatment system. One could
also consider the holding pond as nothing more than an effluent
holding pond, however, and therefore, part of the land applica-
tion system.
The second problem question, closely related to the budgeta-
ry dilemma, involved staffing requirements for the preapplica-
tion treatment and the land treatment systems. The problem in-
volves dividing the hours which are spent daily into preapplica-
tion and land application treatment.
A further complication to both the budgetary and staffing
information is afforded by the different operational practices
at the treatment plants. For example, at one location the pre-
application treatment and land treatment systems may be operated
and maintained by the same staff, whereas at another facility,
the duties at the land treatment facility may be shared by the
wastewater treatment facility personnel and/or farmer. At a
third facility, however, the operation and maintenance of the
land application system may be performed entirely by a farmer.
Therefore, only costs incurred by the municipality during the
land treatment portion were included, and no attempt was made
to calculate costs incurred by the farmer in the operation of
the land application facility, as the majority of these costs
would be incurred during irrigation of a normal farm.
An additional problem question concerned determining the
land treatment operating strategy. The problem, however, was
not how the facility was operated, but rather why the facility
was operated in the mode that it was. Typically, it appeared
that operational practices were gained through experience, and
once practices were successful, no attempt was made to change
the operation of the facility. Therefore, when questioned about
the operation of the facility, the operators could typically re-
spond about how something was done, but not necessarily why it
was done.
EVALUATION OF CURRENT OPERATION AND MAINTENANCE PRACTICES
This section presents a summary of the information which was
collected during the site visits. The 28 site visits included
18 slow rate, seven rapid infiltration, and four overland flow
systems (one system was both slow rate and rapid infiltration).
Table 2 presents background information on the land treatment
systems. Similarly, Table 3 gives a description of the physical
facilities at each land treatment site. Information relative to
the operation and maintenance of the land treatment systems is
contained in Table 4, with Table 5 presenting land treatment
system loading rates. Data on groundwater monitoring are pre-
sented in Table 6 along with monitoring parameters and frequen-
cy.
48
-------
TABLE 2. LAND TREATMENT SYSTEMS, BACKGROUND INFORMATION
Weather Data"
Fac H Uy Name
Villaup of Lake (ieorqe. WWTP
North Hr anrh Fire District No.
City of Hart WWTF
Ci ty of Fremont WWTI'
Village of Ravenna STP
City of Wayland WWI'P
Font ana Reg ional Plant No. '1
Pomona Wat*>r Reclamation Plant.
Whitt ier Nar rows Water Heel amat
Palmdale Water Reclamation Plan
Irvine Ranch Water District
City of Tulare WPCF
City of Kerman WWTP
City of Manteca WWQCF
F,l Dort-ido Hills WWTP
U.S. Army COK, WES Overland Flo
Fa Ikner WWTF
F,a s 1 ey Comb i nfd Utilities Sys ttM
Flow Project
Town of Wareham WPCF
Chatham WPCF
Town of Barnstable WPCF
Kendal/Crosslands l.aqoon System
Land i s Sewaqf An t hority
C'amphe 1 1 Soup (Texa s) , Inc .
City of Coleman WWTP
City of Santa Anna WWTP
City of Winters WWTP
City of Sweetwater WPCP
Site
Number
001
002
00!
004
005
006
007
008
009
01 0
Oil
012
013
014
015
016
01 7
018
019
020
021
022
02 )
024
025
026
027
02 H
Type of Years in Adjacent
System Operation 1-and Use8
HI
SH
SR
SR
SH
SR
RI.SH
SR
HI
SR
SR
SR
SR
SR
SH
OF
OF
OF
HI
HI
HI
SH
RI
OF
SH
SH
SR
SR
41
5
6
5
1 1
9
27
50
18
23
11
35*
4
17
5
4
3
2
8
9
45
7
iO
16
50
1 4
56
22
R
R , C , A
A
A
R,A
A
I ,A,O
H , C , I , A , 0
H,C
A
R ,C,A,O
A
A, I
A
A,O
A
A,H
A, H
H
R
C, R
R
I
C , I , A
A
A
A
A
Preapplicat ion Water
Effluent to Source in
Land Treatment Vicinity
100
100
100
100
100
100
100
Winter 33
Summer 66
100
100
100
100
100
100
40
33
100
100
100
100
100
100
100
100
70
100
100
100
Public
Well
Well
Well
Well
Well
Public
Public
Publ ic
Publ ic
Public
Well
Well
Well
Public
Publ ic
Public
Pu b 1 i c
Pu h 1 i c
Well I Public
Public
Public
Public
Public
Publ ic
Public
Public
Publ ic
Average
Annual
Temperature
°C
6.2
7.8
8.3
8.9
6.5
8.8
1 7.6
16.7
1 6.7
16.4
16.6
17.4
16.8
15.9
13.1
18.8
15.9
15.4
11.1
9.7
11.1
11.9
12.2
1 7.3
18.6
18.6
18.2
17.4
Estimated
Average Mean Annual
Annual Class A
Precipitation Pan Evaporation
m
0.95
1.09
0.84
0.64
0.80
0.82
0.32
0.42
0.42
0. 20
0. 31
0.24
0.26
0.30
1.01
1.31
1.38
1.32
1.01
1.10
1.01
1.10
1. 02
1. 15
0.68
0.68
0.55
0.56
m
0 .84
0.89
0.94
1 . 02
0 . 99
1 . 02
1.75
1.65
1.65
1.78
1.52
2.29
2 . 29
2.03
1.65
1. 52
1 .40
1.30
0.86
0 . 81
0.86
1.19
1. 14
1.91
2.41
2.41
2.49
2: 54
R = Residential
C = Commercial
I = Industr i a)
A = Agricultural
O = Other
From nearpst weather station.
WWTP - Wastewat f r t reat merit plant
WPCF - Water pollution control facility
WWTF - Wastewater treatment facility
STP - Sewage treatment plant
WWQCF - Wastewater quality control facility
WPCP - Water pollution control plant
-------
TABLE 3. LAND TREATMENT SYSTEMS, PHYSICAL FACILITIES
Facility Nam*
Village of take George WWTP
North Branch Fire District
No. 1 WPCF
City of Hart WWTF
City of Fremont WWTP
Village of Ravenna STP
City of Wayland WWTP
Fontana Regional Plant No. 3
Pomona Water Reclamation Plant
whittier Narrows water
Reclamation Plant
Palmdale water Reclamation Plant
Irvine Ranch Water
District
City of Tulare WPCF
City of Herman WWTP
City of Manteca WWQCF
El Dorado Hills WWTP
U.S. Army COE, WES
Overland Flow Site
Falkner WWTF
Easley Combined Utilities Sys-
tem Overland Flow Project
Town of Wareham WPCF
Chatham WPCF
Town of Barnstable WPCF
Kendal/Crosslands Lagoon System
Land is Sewage Authority
Campbell Soup (Texas), Inc.
City of Coleman WWTP
City of Santa Anna WWTP
City of Winters WWTP
City of Sweetwater WPCP
alncludea potential storage, such
Type Instru-
of menta-
Site Sys- tlon
No. tern System
001
002
003
004
005
006
007
oo a
009
010
Oil
012
013
014
015
016
017
018
019
020
021
022
023
024
025
026
027
028
as
RI
SR
SR
SR
SR
SH
RI.SR
SR
RI
SR
SR
SR
SR
SR
SR
OF
OF
OF
RI
RI
RI
SR
RI
OF
SR
SR
SR
SR
var i able
No
Yes
No
No
No
NO
No
Yes
No
No
Yes
No
No
No
No
Yes
No
Yes
No
No
No
Yes
No
Yes
No
No
NO
No
levels
Waste-
Water Land
Stor- Area.
age* U»edb
days
0
162
102
472
297
258
0
nd
0
42
98
28
3
4
7
N/A
118
44
0
0
0
51
0
0
0
369
9
15
ha
2.
13.
34.
24.
8.
31.
20.
29.
405»
279
2
8
a
1
1
6
3
1
607-809
(Seaso
205
87.
106
8.
0.
1 .
1.
1.
0.
3.
3.
26.
na 1
8
1
50
06
9
6
38
2
2
3
235
23.1
10.9
10.5
115
in oxidation
Sand
Silt,
Sand,
Sand,
Sand,
Sand,
Sand,
Widely
Sand
Silt,
Silt,
)
Sand,
Sand,
Sand,
Silt,
Silt,
Silt,
[.oam,
Sand
Sand,
Sand,
Silt,
Sand
Clay
Clay,
Clay,
Silt,
Silt,
Soil 1
sand,
loam
loam
clay
loam,
loam
Vpe
loam
clay
vary i nq
sand,
sand ,
loam
Inam
loam
loam
1 oam
loam,
clay ,
loam
loam*"
loam
1 oam,
loam ,
sand,
loam,
loam
clay.
clay
sand
silt
silt
clay,
clay
ponds using 0.61 m (t
Slope
of
Land i
Flat
Steep
Moderate
Flat
Flat
Moder ate
Flat
Flat-steep
Flat
Flat
Number
of
Ground-
water
Monitor-
ng Wells
24
6
6
32
0
rj
(J
0
16<
4
Flat-moderate 0
Flat
Flat
Flat
Moderate
0
0
1
0
Fl at-moder at *• 0
Flat-moderate 0
Moderate
Flat
Flat
Flat
Mod e r a t e
Flat
Moderate
Flat
Flat
Flat
Flat
,,
0
0
0
11
3
0
0
0
0
0
waste-
water
Distri-
bution
System
G,P
p
p
G, P
G
P
G,P
G,P
G
P
P
G
G,P
G,P
P
P
P
p
G
G
G
P
G,P
P
G
P
G,P
G,P
n Wg s t ewa t e r AjjpHca t i on System
Inf i Itrat ion beds
Fixed nozzles
Gated pipe, ridge and furrow
Border str i p
Border st r ip
Center p i vot, big qun spiay
Inf iltration beds, ridge fc fur row
Spr ay r ridqe and furruw
InliItration beds
Side-wheel rol1 spray
Spray, ridge and furrow, drip
Border strip, ridge and furrow
Ridqe and furrow
Border str ip
Spray
Trouqh distr i but Jon
Spray
Fixed nozzle, trough, op«;n pipe
InfiJ tration beds
Inli Itrat ion beds
Inf iItrat ion beds
Spray
Inf iItrat ion beds
Spray
Border str ip
Side-wheel roll spray
Border str ip
Border strip
operated this way. Based on current flow rate, not including precipitation or evaporation effects.
blncludes only land area in use, not land available for use.
Cflat 0-3«i moderate 3-81; steep over 8».
dAn 11,356-m3 storage basin is currently under construction.
^Imported sand has been used for replacement.
WV1TP - waatewater treatment plant
WPCF - Water pollution control facility
WWTF - Wastewater treatment facility
STP - Sewage treatment plant
WWQCF - Wastewater quality control facility
WPCP - Water pollution control plant
-------
TABLE 4. LAND TREATMENT SYSTEMS INFORMATION
Type
of
Facility Name
Village of Lake George WWTP
North Branch Fire District
No. 1 WPCF
City of Hart WWTF
City of Fremont WWTP
Village of Ravenna STP
City of Wayland WWTP
Fontana Reqional Plant No. 3
Pomona Water Reclamation Plant
Whittier Narrows Water
Palmdale Water Reclamation Plant
Irvine Ranch Water District
City of Tulare WPCF
City of Herman WWTP
City of Manteca WWQCF
El Dorado Hills WWTP
U.S. Army COE, WES
Overland Flow Site
Falkner WWTF
Easley Combined Utilities System
Overland Flow Project
Town of Wareham WPCF
Chatham WPCF
Town of Barnstahle WPCF
Kendal/Crosslands Lagoon System
Landis Sewage Authority
Campbell Soup (Texas), Inc.
City of Coleman WWTP
City of Santa Anna WWTP
City of Winters WWTP
aDoes not include electrical usa<
nOP - Operating permit
PTQ - Preappl icat ion treatment
Site Sys-
No. tern
001
002
003
004
005
006
007 RI
008
009
010
Oil
012
01 3
014
015
016
017
018
019
020
021
022
023
024
025
026
027
028
RI
SR
SR
SR
SR
SR
,SR
SH
RI
SR
SR
SR
SR
SR
SR
OF
OF
OF
RI
RI
HI
SR
RI
OF
SR
SR
SR
RH
0
0
0
0
0
0
0
Gravity-$12. 16/1 ,000 m3
Pressure-$48. 93/1 ,000 m3
$16.21/1 ,000 m3
$4.05/1 ,000 m3
S32.43-$64.86/l ,000 m3
City receives 25% of crop
$l,000/yr for water
$181/ha/yr for land
$10.71/ha/yr for land
$100/month*$31/l ,000 m3
0
0
0
0
0
0
0
Average
Elec-
OtM Manual
Type Which System
of Addresses Oper-
Regu- Land ated
trical latory. Application as Buffer
Usage Permit On Hand? Designed? Zone Size
kwh/mo
1,365
4,700
16,228
3,505
0
14,000
11,250
16,933
0
0
Not known
0
194
10,000
Not known
Not known
360
2,326
0
Q
Q
3,630
0 3,460
0 Not known
$129.87/ha/yr for land 0
Farmer pays pumping cost 727
$8.09/ha/yr for entire site 3,000
0 2,700
PTQ
OP
GWQ
GWQ
SWDQ
GWQ
PTU
PTQ
PTQ
PTQ, GWQ
PTQ
PTQ
PTQ
PTQ, GWQ
PTQ, SWDQ
None
SWDQ
None
SWDQ
OP
OP
PTQ
OP
SWDQ
SWDQ
OP
OP
OP
No
Yes
Yes
Yes
No
Yes
No
N/A
N/A
N/A
N/A
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Ye s
Yes
No
No
Yes
Being written
No
N/A
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
No
No
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
m
76
61
15
15
15
0
91 RI basins
6 Citrus grove
0
0
0
0
0
0
0
0
400
0
15
30
305
30
46
0
30 +
6
305
30
15
Public Access Controls
Woods
Fence
Fence
Fence
Fence
Fence
Fence
Signs-
None
Fence
Signs
None
Signs
None
None
None
Signs
Fence
Fence
Fence
None
Fence
and signs
and signs
and signs
and signs
ana signs
and signs--RI basins
-citrus grove
and signs
and signs
and signs
One field--fence and signs
Other field—none
None
Fence
Fence
Fence
Fence
Fence
and signs
and signs
;e by end users unless paid by authority.
gual ity
quality
GWQ - Groundwater quality ,
cCity of Pomort* Water Department purchases water for $9.26/1,000 m->.
WWTP - Wastewater treatment plant
WPCF - Water pollution control facility
WWTF - Wastewater treatment facility
STP - sewage treatment plant
WWQCF - Waatewater quality control facility
WPCP - Water pollution control plant
-------
TABLE 4. LAND TREATMENT SYSTEMS INFORMATION
Ul
rO
Facility Name
Vlllaqe of Uke George WWTI'
North Branch Flte District
No. 1 WPCF
City of Hart WWTF
City o( Fremont WWTP
Village of Ravenna STP
City of Way land wwn>
Fontana Regional Plant No. '»
Pomona Water Reclamation Plant
Whittler Narrows Water
Heclamat ion Plant
Palmdale Water Reclamation Plant
Irvine Ranch Water District
City ol Tulare WPCK
City of Kertnon WWTP
City of Manteca WWOCF
Kl Dorado Mil Is WWTP
U.S. Army COF. , WKS
Overland Flow Site
Falkner WWTF
Eaaley Combined Utilities sys-
Town of Wareham WPCF
Chatham WPCF
Town of Barnstable WPCF
Kendal/Crosslands Laqonn System
Landis Sewage Authority
Campbell Soup (Texas), Inc.
City of Coleman WWTP
City of Santa Anna WWTP
City of winters WWTP
City of Sweetwater WPCP
Site
_No.
001
002
003
004
005
006
007
008
009
010
01 1
012
01 i
01 4
01S
016
01 7
nin
019
020
021
022
023
024
02S
026
027
028
Kjy
WWTP - Waatewater treatment plant
STP - Sewage treatment plant
:ility
Typ
ol
Sys
tern
HI
SH
SH
SH
SH
S.H
HI
SH
SR
HI
SH
SH
SH
SH
SH
OK
tit
OK
HI
HI
HI
SH
HI
OF
SH
SH
SH
ty
Su
e La nd H
Treatment
Syitem le
Management Dl
Wastewater agency
waslewater aqency
Wastewater aqency
Wastewater aqency
Wastewater agency'1
Wantewater aqency
and farmer
City of Pomona and
enrt users
t.Al'FCU
Fa rmpr
owners ar,r.oc.
Farmer
Fa rmpr
Farmer
(iolf course
ICOF-)
Wastpwater agency
and ClPlflBOn Univ.
Wastewater agency
wautpwater agency
Wastewater agency
Camphel 1 Soup
and farmer
and farmer
Fa rmpr
Fa rmpr
Vi*ui
rr ace
unoff Months
Col- System
cted/ in
verteo t'se_
Ye -i 1-12
Yea 1-12
Yes 4-11
Yen 4-11
Yer. 4-11
Yes ',-»
YP-! HI 1-1?
S H 4-10
No 1-12
Yer. 1-12
No 2-10
No
Nn
Yes
No
Yen
Yer,
Yer,
No
Ypj;
Yes
Yes
Yes
1-12
1-12
1-12
1-12
1-1 i'
1-12
1 12
1 -1 2
1 -1 2
1-1 2
1-12
1-12
1-1 1
1-12
iu J.UUCTU;
TyjpgB o f_ _rr ops
Not appl icabl p
Maple:;, beech PS, h i rch«*s ,
white pine, spruce, f it
Pi HP, hardwood , uncu 1 1 i vated
Alfalfa, o»t s . r ye
Uncul t i vat pd
Allaltrt, timothy, qisRp, clover
Sft-qraf>pf mils, oranqor.
Not app) it-dbl f
AH a 1 f a, oatr.
t.roccol i , can I i flowr r , 1 jnd-
scapp
cor n
oat R, cot t on. a 1 dionds
Har 1 py , oat F , cor n
ryp , tier mud a
Her mud a, reed canary, 1 f?.ru*>
Fescue , ryp
Not appl icabl *•
Not appl icahl *>
Not appl icahl «•
Heechcr., maples, popl ut , o.tk-
Not appl 1 r-flt.l '•
rye
Alfalfa, Johnson qi ass
Coastal Bermuda, Sudan qrar.s
Coaata 1 Bermuda, Sudan,
Johnpon, and Mer.rue qrasses.
An-
Farm-
ing
Pr ac-
Who ticeB
Harvests Di f-
N/A
Not appl icabl e - N/A
Not appl icable - N/A
Not appl icable - N/A
Human con sump- Fa rmer Ves
t l on
m
-------
TABLE 5. LAND TREATMENT SYSTEM LOADING RATES
Faci1i ty Name
North Branch Fire District No. 1 WPCF
City of Hart WWTF
City of Fremont WWTP
Villaqe of Ravenna STP
City of Wayland WWTP
Fontana Regional Plant No. 3
Pomona Water Reel amat i on Plant
PaImdale Water Reclamat ion PI ant
Irvine Ranch Water District
City of Tulare WPCF
City of Kerman WWTP
City of Manteca WWQCF
El Dorado Hills WWTP
Kendal/Crosslands Lagoon System
City of Coleman WWTP
City of Santa Anna WWTP
City of Winters WWTP
City of Swpetwater WPCP
Villaqe of Lake Georqe WWTP
Fontana Req ional PI ant No. 3
Whittier Nar rows Water Reclamation Plant
Town of Wareham WPCF
Chatham WPCF
Town of Barnstahle WPCF
Land i s Sewage Au thor i ty
U.S. Army COF,, WES Overland Flow Site
Falkner WWTF
Easley Combined Ut i 1 i t ier, System
Overland Flow Project
Campbell Soup (Texas), Inc.
Site
Number
002
003
004
005
006
007
008
010
Oil
012
013
014
015
022
025
026
027
028
001
007
009
019
020
021
023
016
017
018
024
Type
of
Suspended
Hydr aul ic
System mm/wk
ER
SR
SR
SR
SR
SR
SR
SR
SR
SR
SR
SN
SR
SR
SR
SR
SR
SH
RI
RI
RI
RI
RI
RI
RI
OF
OF
OF
OF
21.
69.
76.
42.
54.
33.
43.
1 7.
58.
40.
32.
18.
76.
45.
1,130
330
2,110
m/yr
8 1.1
5 2.4
2 2.6
1.2
2 1.1
6 1.6
0 1 .4
2 2.3
0 0.89
4 3.0
6 2.1
3 1.7
3 0.95
2 4.0
7 1.2
40.5
17.3
49. 7t>
27.1
Winter 380 28.8
Summer 72
400
6 i. 5-254
17.
Raw 1 19
Ponci 103-19
40.
0
12.0
21 .0
3.3-13.2
8C
3
6 2.1
Organic
kg BOD5/ha/yr
40.7
1,208
316
287
1,623
637
2,253
89
1 ,471
320
67.2
266
1,775
21 5
23,862
17,162
4,103
5,616
87.6-349
11,810
1 ,446-2,740
12,790
Nutrients
Solids
kg SS/ha/yr
2,
1,
1,
4,
1,
2,
8,
12,
5,
4,
1 J9-
10,
3, 098
5,
45.2
101
817
247
699
070
53
382
428
16.8
578
365
132
897
771
471
405
555
--
982
-5,871
595
kg NH3-N/ha/yr kg NOj-N/ha/yr
5.4 63.7
- _
__
472 5.9
99.1
" u 1 a t e d
454
445 16.9
219
-_
_ _
_ _
4,995 43.1
_ _
_ _
_ _
55.0-222
-_
944 79.9
42.8-80.7 28.0-52.8
370d
kg T-P/ha/yr
15.6a
49. 3a
87
-_
410
15?a
__
--
149a
_-
4, 335
__
39. 3-158
172
64.0-121
160
^Phosphorus measured as PO^.
bBased on total water infiltrati
cDesiqn application rate.
dTotal - N.
n, not only recla imed water.
Key
WWTP - Wastewater treatment plant
WPCF - Water pollution control facility
WWTF - Wastewater treatment facility
STP - Sewaqe treatment plant
WWQCF - Wastewater quality control facility
WPCP - Water pollution control plant
-------
TABLE 6. GROUNDWATER MONITORING DATA
age of L»k* Georqr
HWTP
North Branch Fir*
Distrlet No. 1 WPCK
City of Bart WWTK
City of Fremont WWTP
Type Number
F«c i1i ty of of
Number System Welln
001 HI 24
City of Wayland WWTP
Heel a mat ion Plant
Palrodale Water
Reclamat ion Plant
City of Mantec* WWQCF
Easley Combined Utilities
System Overland Flow Project
Kenda I/ Cross lands Lagoon
OO1)
009
010
014
018
022
SH
RI
SH
SH
OF
SR
5
1 6
2
9
S
7
System
Groundwater
Monitor i nq
Wells installed by Rensselaer
Polytechnic Institute for
research purposes only
pK, alkalinity, hardness,
sulfate, chlori de, ammonia -N,
nitrate-N, phosphate
Static water elevation,
chlor ide, specilie conductance, pM
Hardness, alkalinity, ammonia-N,
nitrate-N, phosphorus, MBAS, COD
Static water elevation, chloride,
specific conductance
pH, hardness, alkalinity, ammonia-N,
nitrate-N, nitrite-N, phosphorjs, su 1 fate
No samples are taken due to problems
with wells. New wells are to be installed.
Major minerals, nitrogen compound E, cot),
BOD, TDS, electrical conductance, pH, odor
Trace metals, chlorinated hydrocarbons
Va r lous wastewater pa rameter s measured in
farmer ' s t wo i rr i gat ion wel]B
Static water elevation, ammonia-N, nitrite-N,
nitrate-N
Groundwater moni tor ing lor research
purposes only
Static water elevation, pH, ammonia-N,
nitrite-N, nitrate-N, phosphate, fecal
col iforms
Sam^l e
Freguency
I/month when not
frozen
1/month
J/year
•I/year
1/year
4/year
I/year
2/year
4/year
4/year
Land i s Sewaq e Authority
Water table el vat ion
L'ont i nuous
Pour local domestic wells aleo monitored.
-------
Of the 28 sites visited, facility 002 (North Branch Fire
District No. 1, Dover, Vermont) was located in the coldest area,
with a mean annual temperature of 7.8°C (46.0°F). The Uti-
ca, Mississippi overland flow site was located in the warmest
area, with a yearly average temperature of 18.8°C (65.8°F).
Precipitation ranged from a high of 1.38 m/yr (4.53 ft/yr) at
the Falkner, Mississippi facility to a low of 0.20 m/yr (0.66
ft/yr) at the Palmdale, California Water Reclamation Plant.
Yearly annual estimated Class A pan evaporation ranged from a
high of 2.54 m (8.3 ft) in Sweetwater, Texas, to a low of 0.81 m
(2.7 ft) in Chatham, Massachusetts.
Wastewater storage at the facilities ranged from 0 to a high
of 472 days at facility 004 (City of Fremont, Michigan). Stor-
age included any potential storage due to a variable level in an
oxidation pond, plus storage in holding basins. Of interest, is
the fact that none of the seven rapid infiltration systems visi-
ted had on-site storage. The overland flow site at facility 024
(Campbell Soup, Paris, Texas) had no storage, whereas the other
overland flow sites had storage based on a variable level in the
preapplication treatment oxidation ponds. There were only two
slow-rate systems which had no provisions for wastewater stor-
age; these were facilities 008 and 025 (Pomona, California Water
Reclamation Plant, and the Coleman, Texas Wastewater Treatment
Plant). In both of these plants, however, provisions existed
for surface discharge.
The land area receiving wastewater varied from a low of 0.38
ha (0.94 acres) at the Chatham, Massachusetts facility, to a
high of 809 ha (2,000 acres) associated with the Irvine Ranch
Water District, California. The land area usage has been plot-
ted as a function of flow rate in Figure 2. As would be expect-
ed for the three different types of systems, three distinct
areas on the graph are prevalent. The lowest land requirement
is for the rapid infiltration systems. The highest land re-
quirement is for the slow-rate systems. In the middle area are
the four overland flow plants. Facility 024 (Campbell Soup,
Paris, Texas) appears slightly higher on the curve than some of
the other overland flow systems. This can be accounted for by a
recent expansion, and the fact that the facilities receive in-
dustrial wastewater with a high organic loading. Also plotted
in Figure 2 are the application land area requirements for mod-
erately-favorable conditions, as taken from "Water Reuse and Re-
cycling," Volume 2, OWRT/RU-79-2, U.S. Department of Interior,
1979 (2) . Since the smallest flow contained in this report is
0.044 m^/s (1.0 mgd), the plots are extrapolated for lower
values. The field data compare favorably with the OWRT data.
55
-------
EC
OWRT/RU-79/2 Data
Extrapolated
A-SR
• -RI
• -OF
0.1
0.0004
(0.01)
Land Treatment Row, m3/s (mgd)
FIGURE 2. LAND AREA USED AS A FUNCTION OF FLOW RATE
'
-------
A wide variety of wastewater distribution equipment and ap-
plication system types were seen during the survey. In addi-
tion, at nine of the 28 sites, wastewater was distributed by
both gravity and pumping. At three of these sites, i.e., facil-
ities 001,007, and 023, the older portions of the systems re-
ceived gravity flow, while pumping was required for the newer
portions.
A variety of contractual agreements exist, and typically
these agreements are for the slow-rate system, with the excep-
tion of facility 009 (Whittier Narrows Water Reclamation Plant,
California) where wastewater is purchased for groundwater re-
charge. In the remaining facilities, the agreements typically
are for the purchase of wastewater or for rental of a portion of
the city-owned land, with the stipulation that the wastewater
will be utilized. At facility 012 (Tulare, California), the
stipulation is that the city will receive 25 percent of the
crop-generated revenues.
Of the sites visited, all of the rapid infiltration and ov-
erland flow systems were operated 12 months out of the year. It
should be remembered, however, that the overland flow systems
were all located in mild climates. Of the 18 slow-rate systems,
only six are operated less than 12 months of the year. Of
these, the citrus crop irrigation at facility 007 (Fontana, Cal-
ifornia Regional Plant) is included. In this case, however, as
there is a rapid infiltration system also available, the slow-
rate system is not operated during the colder months.
The types of crops grown and the ultimate use of the crops
are presented in Table 4 for the slow-rate and overland flow
sites. Of the seven rapid infiltration sites visited, only the
Chatham, Massachusetts facility had any major plant growth in
the basins. This was just weed growth which had not been re-
moved.
At the remaining sites (with the exception of Ravenna, Mich-
igan) , a wide range of crops are grown. At three sites, trees
are irrigated but not harvested. At the Utica, Mississippi
overland flow site, the vegetation was tested and discarded. In
Falkner, Mississippi the vegetation was cut and left in the
field. At the Easley, South Carolina overland flow site, the
grass was baled; it is currently used only for erosion control,
as permission has not yet been granted for it to be used as ani-
mal feed. At the remaining sites, crops are grown and used for
either human or animal consumption.
57
-------
At the 13 facilities where the major objective of the land
treatment system was crop production, the superintendent or
foreman involved was queried as to whether or not the farming
practices were different than at neighboring farms of equal soil
type growing the same crop. At only three facilities were the
farming practices the same as practices at neighboring farms.
LAND TREATMENT SYSTEM STAFFING AND OPERATION AND MAINTENANCE
The staffing requirements for both the preapplication and
land treatment systems were analyzed and then compared to num-
bers presented in the literature. In addition, data pertaining
to the number of shifts per day and days per week that the sys-
tems are staffed were collected. Utilizing these data, the in-
formation in Figure 3 was calculated, which presents the staff-
ing for the three land treatment systems (independent of preap-
plication treatment) as a function of facility size. Staffing
requirements were also compared to OWRT data for the land treat-
ment portion of the facility.
The slow rate staffing requirements were typically less than
reported in the OWRT report, whereas the rapid infiltration and
overland flow staffing requirements are in general agreement.
Based on the limitations of the data collected and the
amount of data collected, the following conclusions can be
reached: 1) For the slow-rate land treatment system, the staff-
ing requirement is independent of the degree of preapplication
treatment; 2) For the rapid infiltration system, the labor re-
quired decreases as the degree of preapplication treatment in-
creases; 3) No conclusions should be reached for the overland
flow systems due to the insufficiency of data; 4) For the same
degree of preapplication treatment, slow-rate land treatment
systems were less labor intensive than rapid infiltration sys-
tems.
As was done with staffing, the operations and maintenance
costs were compared to the OWRT data, and the results are pre-
sented in Figure 4. As was seen with the staffing requirements
(and also because of) the slow-rate systems were typically less
expensive than OWRT data, whereas the rapid infiltration and
overland flow systems were in general agreement. A major cause
of this apparent disparity for slow-rate staffing and operation
and maintenance costs being typically lower than OWRT data is
caused by the system being operated in conjunction with a local
farmer. The farmer incurs a portion of the costs and therefore
the municipality need not incur the cost. Furthermore, based on
the visits, operations are improved by joint operation.
58
-------
0.01
0.0004
(0.01)
0.0044
(0.1)
0.044
(1.0)
Flow, m3/s (mgd)
0.438
(10)
4.38
(100)
FIGURE 3- LAND TREATMENT STAFFING
-------
Updated
OWRT/RU-79/2
Data
All Costs Second Quarter 1980
1,000
0.0004
(0.01)
0.0044
(0.1)
0.044
(1.0)
Flow, m3/s (mgd)
FIGURE k. LAND TREATMENT OPERATIONS AND MAINTENANCE COSTS
60
-------
Given the wide range of facilities which were visited, it is
not surprising that both preapplication and land application
treatment operation and maintenance unit costs vary greatly.
The least expensive preapplication treatment cost was $0.011/
m3 ($0.04/1,000 gal), whereas the most expensive preapplica-
tion treatment facility cost was $0.725/m3 ($2.74/1,000 gal).
The land treatment operation and maintenance costs also varied
widely, with the least expensive facility costing $0.0005/m3
($0.002/1,000 gal), whereas the most expensive facility cost
$0.207/m3 ($0.78/1,000 gal). The total treatment operation
and maintenance cost, which is more than likely the most acc-
urate cost, varied from a low of $0. 014/m3 ($0.05/1,000 gal)
to $0.744/m3 ($2.82/1,000 gal).
Based on the small sample size and the various limitations
of the cost data collected, the following conclusions can be
made utilizing the cost data collected: 1) The slow-rate land
treatment operation and maintenance costs are unaffected by de-
gree of preapplication treatment; 2) The rapid infiltration sys-
tem operation and maintenance costs decrease as the degree of
preapplication treatment increases.
EVALUATION OF OPERATION AND MAINTENANCE PRACTICES
The equipment for any land treatment system consists basi-
cally of piping, pumps, controllers, and application equipment.
With the exception of the wastewater application equipment,
wastewater treatment plant maintenance personnel should be fa-
miliar with all of the equipment, and its operation should not
be a problem. With minimal personnel training, the maintenance
of wastewater application equipment should pose no major prob-
lem.
Although the performance of a land treatment system must be
based on circumstantial evidence (with the exception of the
overland flow system), it would appear that the majority of fa-
cilities are well run, and their performance is in line with
typical performance specifications.
Based on operation of the land treatment system (without re-
gard to regulatory restraints), it is believed that a slow-rate
land treatment system can operate without major problems with a
minimum of primary preapplication treatment. Similarly, a rapid
infiltration system can operate with a minimum of primary preap-
plication treatment if the required bed maintenance is prac-
ticed. It appears that the overland flow system can operate
successfully with a minimum of preliminary (screening and grit
removal) treatment.
61
-------
DESIGN DEFICIENCIES
The most common preapplication treatment design deficiency
involved preapplication ponds which were unprotected from the
effects of erosion caused by wind-induced waves.
A wide variety of design deficiencies were noted with
regard to the land treatment systems. Only at one location were
the design deficiencies severe enough to substantially hamper
facility operations. The design deficiencies included:
unnecessary pumping; insufficient storage volume; improper nozzle
selection; lack of consideration of the effect of soil type and
texture during selection of irrigation equipment; application
areas subject to public access; and improper grading causing
ponding.
REFERENCES
1. Sullivan, R.H., et al. "Survey of Facilities Using Land
Application of Wastewater". EPA 430/9-73-006,
NTIS No. PB-227351, U.S. Environmental Protection
Agency, Washington, D.C., July 1973.
2. U.S. Department of the Interior, Office of Water
Research and Technology. "Water Reuse and Recycling",
Volume 2, Evaluation of Treatment Technology.
OWRT/RU-79/2, April 1979.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
62
-------
SESSION NO. 2
Improving the Performance of Conventional Wastewater
Treatment Processes
PAPER NO. 4
MAKING-DO WITH CLARIFIER HYDRAULIC OVERLOAD
by
Robert M. Crosby
President
Crosby, Young and Associates, Inc.
1201 E. 15th Street, Suite 108
Piano, Texas 75074
63
-------
MAKING-DO WITH CLARIFIER HYDRAULIC OVERLOAD
Robert M. Crosby, President
Crosby, Young and Associates, Inc.
INTRODUCTION
In 1977, the engineering services firm: Crosby, Young and
Associates, was organized with the specific purpose of finding
ways of improving the hydraulic characteristics and solids sepa-
ration effectiveness of settling tanks. The idea was born during
a brief hydraulic study of the secondary clarifiers at the
Trinity River Authority's 60 mgd Central Wastewater Treatment
Plant in Grand Prairie, Texas. Naively, the writer had applied
open-water dye tracer techniques to a tank to define the through-
flow route of the bulk fluid, in the expectation that the fluid
path would also show the most likely route of solids transport.
It should be no surprise to anyone that the guess was a good one.
The general procedure was developed by physical oceano-
graphers to trace the route and ultimate fate of pollutants dis-
charged to natural waters. Usually, a boat was steered over a
defined course while towing sensors or taking frequent samples to
define the three-dimensional distribution of indicative parame-
ters such as temperature, dissolved oxygen, or the concentration
of an injected tracer dye. For the first clarifier flow pattern
study, we chose one of these oceanographer's tools, continuously
injected Rhodamine WT, a stable fluorescent dye. The test clari-
fier is shown in cutaway, Figure 1. We were interested in flow
phenomena in a vertical longitudinal section, between the inlet
and weir region, from top to bottom. Our "boat" was the travel-
ing bridge. The resulting contours of equal dye concentration
for one sampling run are shown in Figure 2. From this, we were
able to estimate an excessively fast transport of fluid directly
from the bottom inlet ports to the overflow weirs, with a dead
region at the upper right.
Weirs
Inlets
Figure 1. Cutaway view of a rectangular secondary clarifier.
64
-------
NLET
END
100 90
80 70 60 50 40 30 20
LONGITUDINAL DISTANCE FROM ("LET ENO (PERCENT)
Figure 2. Isolines of dye concentration in a rectangular
secondary clarifier.
To interrupt the high velocity jets and provide better
vertical distribution of the incoming mixed liquor, the design
engineer simply placed half-cylinders of pipe on the clarifier
floor, 6 inches from the inlet wall, Figure 3. Monthly average
effluent total suspended solids and associated BOD immediately
dropped dramatically, Table 1. Using longer-term data, TSS
dropped from 84 to 17 mg/1, a reduction of 79%. Material and
labor cost for modifications to the four secondary clarifiers
was $20,000.
Table 1.
Month
BOD
TSS
Figure 3. Baffling for bottom inlet ports.
Effluent Quality Before and After Baffling, TRA Central
Jun Jul Aug Sep Oct Nov Dec
64
60
80
43
75
56
56
37
A
17
14
33
17
31
20
Baffle installed
65
-------
WHAT IS HYDRAULIC OVERLOAD?
The "Ten State Standards"(1) place limits on overflow rate:
for a conventional activated sludge secondary, 1200 gpd/sq ft for
peak hourly effluent rate. Most readers will recall that surface
area overflow rate is derived from Camp's(2) ideal geometric
derivation, Figure 4. If fluid moves uniformly, horizontally in
any cross-section, vo is the minimum vertical velocity for all
particles which will settle out completely. In this ideal case,
v0 is exactly equal to effluent rate divided by surface area.
Thus, surface area overflow rate. Not everyone recognizes that
the same geometric model can be used to derive vo which does not
include surface area at all.
However:
V0 = m
where T = time
Figure 4.
VH
L
Camp's geometric settling zone model
alternate derivations.
with
But, by definition of nationally or locally accepted design
standards, a clarifier is hydraulically overloaded if the surface
area is too small for a given effluent rate.
REALITY
Unfortunately, most real clarifiers don't behave much like
the ideal model. Figure 5 contrasts an ideal flow pattern assumed
by Camp's model with the kind of pattern more commonly observed.
Note that the upflow occurs over a relatively small fraction of
the surface area. Henceforward in this presentation, real flow
patterns will be described, with emphasis on simple modifications
which were successful in making the clarifiers behave more
ideally.
I
Figure 5. Ideal versus real flow patterns.
66
-------
MAKING REAL CLARIFIERS WORK BETTER
To date, we have conducted analyses of 13 full-scale operat-
ing clarifiers. Of the 13, 12 were found to have either internal
or upstream problems which degraded their effectiveness in captur-
ing solids. One of the most common problems, the subject of
considerable honest controversy, is the sludge blanket.
Importance of Blanket Control
What is a sludge blanket? Various optical and sonic sensors
are marketed which provide an indication of a change in some fuz-
zily defined property of the water column at a certain depth. One
very simple device, called a Sludge Judge, lets the operator see
a sample of the fluid column and judge the depth of mostly-
compacted solids. In the scientific literature one often finds a
fixed concentration, such as 2000 mg/1, defined as a blanket. In
fact, we felt compelled to make up a new term: Virtual Blanket,
to describe the depth above which horizontal flow occurs, usually
in a zone of fluidized solids.
To illustrate this, Figure 6(a,b,c) is a series of snapshots
of dye concentrations in a radial section of a peripheral feed,
peripheral overflow secondary after 35, 70, and 105 min.
Figure 6. Peripheral feed clarifier flow pattern time-series
35, 70, and 105 min, 65% of design hydraulic load.
67
-------
In all of these, it can be clearly seen that the most prominent
horizontal flow is occurring approximately 4 ft from the tank's
bottom, indicated by the lower portion of the 140 parts per
billion (ppb) dye contour in Figure 6c. When we look at the
distribution of the square-root of solids concentrations in the
same radial section, Figure 7, we see that the still-fluid
Figure 7.
Peripheral feed clarifier square-root of TSS distri-
bution, 65% of design hydraulic load.
part of the blanket falls between the 20 and 40 contours, which by
squaring, are translated to a range of 400-1600 mg/1. All the
snapshots of this flow pattern test series were made at a con-
trolled overflow rate of 65% of the clarifier's design overflow
rate.
At 100% of design hydraulic loading, the same clarifier pro-
duced a similar time series with a modest virtual blanket of 4 ft
thickness. Figure 8a is the flow picture at 105 min. The 160 ppb
contour is most representative of the horizontal flow depth, again
4 ft from the bottom. Figure 8b shows the square-root of TSS dis-
tribution during this test series. The 20 contour, representing
400 mg/1 of solids was somewhat deformed by the flow.
-100-.
-no...
_ 40
I
Figure 8. Peripheral feed clarifier flow pattern after 105 min
(a) and the square-root of TSS distribution (b), 100%
design hydraulic load, 4 ft blanket.
68
-------
At the same flow rate with a virtual blanket 7 ft from the
bottom, Figure 9a, the pattern of flow is disturbed; Figure 9b is
suggestive of turbulent eddies at the left-hand side. From subse-
quent flow pattern tests elsewhere, these eddies seem to be char-
acteristic of flows in cases where the blanket is in close
proximity to the inlet baffle, resulting in a relatively small
cross-sectional area for initiation of horizontal flow.
Figure 9. Peripheral feed clarifier square-root of TSS distri-
bution (a) and disturbed flow pattern (b), 100%
design hydraulic load, 7 ft blanket.
In an extreme case, the blanket may rise to a depth at which
the lower extremity of the inlet baffle is actually covered by a
high blanket. In the case shown in Figure lOa a bulking sludge
was the cause. The upward curving contours just outside the feed-
well are suggestive of a partial solids blowout at this location,
but Figure lOb shows that horizontal flows, Lest defined by the
80 ppb contour, were occurring in a fluidized solids zone of
between 1600 and 2500 mg/1 concentration. Effluent quality based
on TSS was excellent at the time.
Figure 10.
Centerfeed clarifier, bulking sludge distribution (a)
and resultant flow pattern in 19 min (b).
One plant we studied briefly, maintains consistently low
effluent TSS by means of a high return sludge rate which essen-
tially strips the blanket, Figure lla. There is some tendency
for the throughflow to climb up the peripheral wall, Figure lib,
but the zero-blanket practice works for this plant.
69
-------
Figure 11.
Center feed clarifier with high underflow rate,
square-root of TSS distribution (a) and flow pattern
in 16 min (b).
Holly Hill, Florida's small rectangular secondaries initial-
ly had a high velocity, sludge trough scouring throughflow, shown
in Figure 12a. We balanced the inlet ports hydraulically with
concrete blocks in the mixed liquor channel and replaced the
side-to-side baffle structure with close-in reaction baffles,
with the apparent result of a more benign throughflow pattern,
Figure 12b. It can be seen here that the blanket was fairly low.
However, when the solids rose to somewhere near mid-depth, Figure
13, the cross-sectional area available for horizontal throughflow
was reduced, and effluent TSS quality deteriorated seriously.
Figure 12.
Flow pattern after 15 min in a small rectangular
secondary before modification (a), and after (b).
Blanket was low in both cases.
Figure 13.
Flow pattern after 15 min in a small rectangular
secondary after modification, but with flow con-
stricted by a high blanket.
70
-------
In general, what seems to happen with a virtual blanket too
near the feedwell is a turbulent, high velocity horizontal flow,
illustrated in Figure 14. Figure 14 is a composite of numerous
samplings of suspended solids in a radial section of a blast
furnace scrubber thickener. One such contour plot is shown in
Figure 15.
Figure 14. "Average" solids behavior in a center feed blast
furnace thickener, high blanket.
Figure 15.
Solids distribution in a blast furnace thickener,
high blanket.
These examples were given to illustrate the writer's belief
in the importance of controlling blanket depth with respect to
inlet baffling. In rare cases of very small flow variability, a
blanket which resides above the feedwell depth can result in very
low effluent suspended solids, probably through the simple physi-
cal means of filtration. In the majority of cases studied, there
seems to be a decided advantage in maintaining a blanket as far
from the lower extremity of baffling as practicable. (It is
recognized that a low blanket may also result in low solids con-
centrations for wasting.) The worst cases of effluent quality
seem to be associated with a medium blanket height, especially
when there is little clearance between the compacted sludge and
the bottom of a feedwell.
71
-------
Upgrading Modifications
In every case we have studied so far, the design standard
requiring inlets which distribute the flow equally, vertically,
has been ignored. The common practice is to encourage immediate
downflow of the solids by inlet baffling. There is a widely held
belief that the downflow feature of most inlets enhances solids
contact and flocculation. Although this may be true, forced
downflow also abets development of a density flow which is, in
many cases, detrimental to effluent quality. Earlier, it was
shown that a bottom-inlet clarifier was improved significantly by
encouraging inlet region upflow and breaking up inlet jets. In
at least one case, the same effect was achieved by accident.
The Bubble-Curtain Phenomenon—
In a large rectangular secondary in Central Florida, the
traveling bridge sludge removal mechanism scraped and lifted
sludge only on movement from the effluent end toward the inlet.
The result was a resident deposit up to 4% solids concentration
on the tank floor near the inlet end. The sludge was septic and
producing fine bubbles. The flow pattern which resulted is shown
in Figure 16. The shape of the 20 and 25 ppb dye contours at
_ i r _
f JF
Figure 16. Large rectangular secondary's flow pattern with a
methane "bubble curtain" causing vertical mixing
near the inlet.
upper left clearly shows the upward movement of fluid at the
quarter point, just where bubbling could be seen at the surface.
The 5 and 10 ppb contours at the right are strongly suggestive of
a near-ideal plug flow condition. The solids distribution near
the overflow weirs is shown in Figure 17. With the 10 mg/1 TSS
contour below the weir, effluent suspended solids were less than
10 mg/1, despite a hydraulic load 33% above design. This is very
close to the ideal solids distribution one would expect from
Camp's geometric flow model presented earlier. Obviously, no
modifications were recommended for these clarifiers.
72
-------
Figure 17.
Near-ideal solids distribution in a large rectangu-
lar secondary in which vertical mixing occurs near
the inlet.
The Stamford Baffle—
Center feedwell, peripheral overflow clarifiers are the most
common secondaries in the United States today. The initial flow
pattern tests at Stamford, CT, Figure 18a showed a relatively
rapid fluid transport in a zone about 12 feet deep, with a sharp
upturn at the periphery. Not surprising was the tendency of the
solids to follow the flow, Figure 18b. At this time, we felt
Figure 18.
Center feed clarifier flow pattern (a) and solids
distribution (b) before baffling, Stamford, CT.
(Note: Solids are not square-roots.)
that the expedient modification would be a peripheral baffle to
interrupt the upflow. Figure 19a is the initial flow pattern
snapshot after baffle installation. The baffle can be seen at
the right, roughly to scale. The flow was turned back toward the
center as hoped. The solids were also more favorably distrib-
uted, Figure 19b. Later, we recognized the probable cause of
upflow in the flow pattern radial section. The test radial sec-
tion was directly in line with one of four inlet ports, inside
the feedwell. A plot of the time variation of solids near the
second dot from the top in the right-hand line of sample points
in Figure 19 before baffle installation is shown in Figure 20a.
The time between peaks was exactly the period of sludge riser
pipe passage. After baffle installation, we measured the weir-
wall solids plot shown in Figure 20b. The variable solids
73
-------
Figure 19.
Center feed clarifier flow pattern (a) and square-
root of TSS distribution (b) after peripheral baffle
installation.
to
Tint t
Figure 20.
Time-variation of TSS near the weirs at Stamford
before baffling (a) and after baffling (b).
phenomenon was almost certainly caused by persistent jets from
the inlet ports, periodically interrupted by the rotating sludge
header riser pipes. This was confirmed by a solids tracer study,
Figure 21. Figure 21a shows the position of the sampling cross-
section, at mid-radius (shaded) near the blanket. Figure 21b
shows the concentration of sludge dye near the blanket interface,
20 min after dye release in the mixed liquor feed pipe.
The result of the peripheral baffle at Stamford was a 38%
reduction in effluent TSS. Material and labor cost was about
$3000 for the marine plywood prototype.
Figure 21.
Location of the mid-radius sampling section (a) for
the sludge jet test. Sludge dye concentrations are
contoured at the right (b).
74
-------
The Morganton Baffle—
The pre-modification flow pattern in a radial section of
Morganton's center feed circular secondary clarifiers is most
clearly illustrated in Figure 22. The Morganton pure oxygen
Figure 22.
I
Intense density-flow pattern before baffling,
Morganton, NC.
sludge apparently developed a strong density flow which essen-
tially ignored the feedwell. Near the periphery, horizontal
flow was less than 1 ft thick. Flow rebounded, or splashed on
the peripheral wall. At this plant, we also believed we saw a
periodic disturbance in weir-wall solids resulting from sludge
header rotation. As an easy first modification, we therefore
slowed the header rotation to 56% of the design speed at a cost
of $75. The result was an effluent TSS reduction of 10.4%. The
second modification at Morganton was a ring baffle/flocculation
chamber at mid-radius, extending from the bottom of the tank
upward to mid-depth. The baffle was intended to interrupt the
forceful density flow which was shown in Figure 22. The flow
pattern after baffle installation is shown in Figure 23a. As
expected, the throughflow regime was radically altered. Fortu-
nately the solids distribution was also benign, Figure 23b.
Figure 23.
Post-modification flow pattern (a) and square-
root of TSS distribution (b), Morganton, NC.
Material cost for this modification, installed by plant opera-
tors, was about $3000. An additional 37.5% reduction in effluent
TSS was realized. Thus, an overall effluent TSS reduction of
nearly 48% was accomplished at Morganton for a material cost of
only $3100 per clarifier. At last report, the plant now meets
its permit requirements consistently by sending 60% of its flow
to the modified clarifier and 40% to a second, parallel unit
which has had only the header speed reduction modification.
75
-------
PITFALLS OF GENERALIZATION
In the 13 clarifiers we've looked at to date, we have yet to
meet the same set of effluent degrading circumstances twice. In
deciding on clarifier upgrading measures, there is no substitute
for careful observation, measurements, and the application of
common-sense. The writer is frequently asked to analyze problems
by long-distance or on observation of surface phenomena alone.
The conclusions reached by this short cut method are almost
always wrong. For example, surface observations in a chemical
plant's secondaries clearly showed a line of bubbles which fol-
lowed the single tube sludge header around the tank. The first
guess was that the nominal 4 inch clearance of the header above
the tank floor was allowing septic sludge to accumulate below,
with the header disturbing this layer just enough to skim the
methane bubbles. The clarifier had a very low overflow rate, but
about 200% underflow rate. The flow pattern, Figure 24, gave an
entirely unexpected picture. Instead of diving toward the suc-
tion header, the tracer dye avoided the header entirely. The
header was completely inactive; all sludge was being returned by
way of a missing seal at the center of the tank. The problem was
repaired within hours, with a new seal fabricated on-site.
Figure 24.
Flow pattern in a center feed circular secondary
with an inactive sludge header.
Generalizations must be possible, but this writer does not
know how to make them, with the possible exception of those
comments already made regarding blanket control. There is no
known substitute for the application of a sense of how fluid
behaves, backed by the kind of graphic data which has been pre-
sented in this paper. Dispersion tests, long used as a measure
of hydraulic efficiency, are seen only as back up data; they do
not define the reasons for fluid problems. On the other hand,
flow pattern tests, although considerably more complicated and
costly to perform, can clearly define hydraulic problems in such
a way that solutions become obvious.
76
-------
This nation now has tens of thousands of municipal and
industrial clarifiers whose hydraulic characteristics will be
found to closely resemble the examples given here. It seems a
reasonable goal to upgrade the "bad actors" to achieve more
nearly ideal performance before we proceed with major capital
expenditures to provide additional hydraulic capacity in the
traditional, or design standard dictated sense. If such design
standards are to be applied, the design engineer and the regula-
tory agencies should recognize their shortcomings in light of the
real clarifier hydraulic behavior which has been illustrated
REFERENCES
1. Great Lakes - Upper Mississippi Board of State Sanitary
Engineers. Recommended Standards for Sewage Works.
Health Education Service, Inc., Albany, New York, 1978
PP 60-1 to 60-3.
2. Camp, T.R. Sedimentation and the Design of Settling
Tanks. Transactions Am. Soc. C.E., No. 2285, 1946,
pp 895-936.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
77
-------
PAPER NO. 5
MINIMIZING IMPACT OF SIDE STREAMS
ON TOTAL PLANT PERFORMANCE
by
Roy 0. Ball, Ph.D., P.E.
Principal
ERM - North Central, Inc.
200 South Prospect Avenue
Park Ridge, Illinois 60068
78
-------
MINIMIZING IMPACT OF SIDE STREAMS ON TOTAL PLANT PERFORMANCE
Roy O. Ball, Ph.D., P.E.
Principal
ERM-North Central, Inc.
The objective of this conference is to provide technical
input to operators and designers of publicly owned treatment
plants with the overall goal of improving POTW reliability and
performance. The objective of this paper is to provide
information on an EPA technical report (soon to be available)
with regard to the impact of side streams on main stream
performance.^
What are side streams? Side streams are those hydraulic
flows which result from sludge or waste stream treatment and
disposal activities. For example, the supernatant flow from a
gravity thickener; the filtrate from a vacuum filter; the
supernatant from a secondary digester; and, the liquor from heat
treatment operation are all examples of side streams. If these
side streams are returned into the main stream treatment
process, then they may represent an added load on the
facilities. This added load may be purely hydraulic or it may
contain significant amounts of pollutants, such as BOD or TSS,
or it may contain acidity and alkalinity which might
significantly vary the pH in the main stream.
Bob Hegg described many of the conditions that can effect
POTW reliability and performance. Although not specifically
included in his catalog, side streams are one of the factors
that can degrade POTW performance, both in theory and in fact.
Must the side streams degrade POTW performance? Based on the
analysis described in the Side Streams Report, side streams do
not have to degrade POTW performance. The fact that they do, or
appear to, is related to the duration of the return event. If
the side stream is returned evenly, then it would appear to be a
rare situation at which the side streams could degrade main
stream performance, even if those side streams had not been
included in the original design basis for the facilities.
How do we determine if side streams are a problem? That is
one of the major objectives of the side stream's report. The
side stream's report is composed of three major sections. The
first section has to do with the investigation and evaluation of
the plant to answer the question "If there are operational
problems, can they be attributed to side streams?" The
procedures outlined in this section will enable a definitive
answer to that questions. The second section of the report
deals with mitigation of the impact of the side streams. The
remaining sections of the report deal with handling the effect
of the side streams, or mitigating them. The side stream effect
79
-------
can be mitigated in two ways: by changing the source of the
side stream, that is the fludge treatment or disposal facility
that is generating the flow; and by altering the operation of
the main stream process.
In addition to these three major sections, appendices are
included which provide information as to the average quality
characteristics of side streams as reported in the literature,
and also the indexing procedure which was followed to prioritize
the side stream matrix; that is which side streams from which
facilities being returned to which main stream processes are the
most important and worthy of discussion.
The manual provides a user guide with information needed to
use the monitoring program, evaluation algorithm, control
algorithm, design modification matrix, and design information.
Also included in the side stream manual is a detailed example.
Three checklists are provided to help the user work through the
algorithm. In this paper, it is not possible to display the
full scope of the report, but only to indicate the types of
material that can be found.
2
Figure 1 shows the process matrix evaluated. The selection
of side stream generator/treatment process pairs was based on an
indexing procedure. The procedure included factors for the
population served by POTW's with that side stream, the side
stream average quality and the cost of treating the side stream
pollutants.
Table 1 shows literature references describing side stream
quality. It can be seen that little agreement is evident
between references. For many of the side streams, the refer-
enced quality differs by three or more orders of magnitude.
Figure 2 shows a summary of the evaluation algorithm
process, while Figure 3 indicates where sampling would be
required in order to complete the evaluation algorithm.
Figure 3 shows an example of one of the algorithms; in this
case, for primary clarification. It can be seen that even this
"simple" process requires 33 steps and may refer the analyst to
one or more of three design methods for mitigation and one
method for operational control.
Figure 4 shows a similar process for activated sludge.
Here, 77 steps are required, up to 13 design mitigation methods
may be recommended, and up to 25 operation methods may be
recommended.
Figure 5 shows an example of an operational methods algo-
rithm for primary clarifiers, and Figure 6 shows a correspon-
ding algorighm for activated sludge. In each case,
80
-------
once all the main stream changes that can be made have been
made, the user is referred to side stream operational control
algorithms; an example of which (in this case for gravity
thickeners) is shown in Figure 7.
After all operational methods have been implemented, some
design modifications are described in the manual. Most of the
modifications deal with increasing the time span over which the
side stream is returned.
In summary, the side streams manual represents a flexible
and powerful tool to diagnose and mitigate the impact of side
streams at POTWs.
Presentation based on a study and report by Roy F. Weston, Inc
for EPA MERL.
2
The Figures and Tables used in this paper duplicate those
used in the Side Streams Report.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
81
-------
Sidestream Generator
Gravity Thickener (GT)
Dissolved Air Flotation (DAF)
Anaerobic Digestion (AnD)
Aerobic Digestion (AeD)
Vacuum Filter (VF)
Centrifuge (C)
Belt Filter Press (BF)
Sand Drying Bed (SB)
Lagoon (LA)
Heat Treatment (HT)
Wet Air Oxidation (WAO)
Pressure Filter (Filter Press, FP)
Purifax(PX)
Treatment Process
Primary
(P)
o
o
•
0
•
•
•
•
o
•
•
6
•
Activated
Sludge
(AS)
Trickling
Filter
(TF)
Rotating
Biological
Contactor
(RBC)
•
•
e
•
No evaluation required
Evaluation required
FIGURE 1. PROCESS MATRIX
82
-------
Table 1
Summary of Literature Review
00
Sldestream Abbreviation
Generator
Gravity GT
Thickening
Dissolved Air DAF
Flotation
Anaerobic AnD
Digestion
Aerobic Digestion AeD
Vacuum Filtration VF
Numbers
In Use
940
3l"t
6.796
4,750
1,912
Solids Retention BOD.
% References mg/C
80-95 3, "12,49,59, 75 100-400
70-99.1 4,39,40,42,48,55, 50-3,950
59,60,64,75,121
2-11,014
5-6,350
80-99.5 33,65,70,75,94, 10-10,000
96,120
References
35,49,72,75
72,75
13.14,29,49,55,
56,57,72,75,76,
87,995,100,108,
121
1,21,52,55.75.121
14,55,75,108,122
ss
mg/L
98-2,500
20-2,440
100-32,400
10-41 ,800
160-20,000
References
3.7,25.35,42,49,
59,61.64,72,74,75,
77,81.10«-,118(120,
121
"t.25,39,40,42,49,
55,59,60,64,67,72,
75,76,87,94,95,100,
104,108,114,121
12,13,14,21,49,55,
56,57.62,72,75,76.
87,94,95.100,104,
108,114,121
1,4,52.55.64,75,
121
4,14,25,26,33,36,
42,47,55,65,70,72,
75,80,87,94,96,108,
114,120,121
CentrifugalI on
368
30-98
3,4,6,21,33,40, 173-10,000 49,75,87,122
42,43,55,72,75,
83,87,94,96,98,
104,108,115,121
122
100-20,000
2,3,4,20,21,25,33,
40.42,49,55.72,75,
83,87,94,96,98,108,
114,115,120,211,122
Belt Fl 1 ter Press
Sand Drying Beds
Lagoons
Heat Treatment
Wet Air Oxidation
Pressure Filter
Purl fax
BF
SB
LA
HT
WAD
FP
PX
132
10,939
797
170
13
157
69
22-99.8
85-100
90-99+
90-99+
96-100
"1,33.36,94,117,
122
33,108
49
49
18,33,75,96
46-146
6-6,000
150
1 ,600-15,000
3,000-10,000
1 ,000-6,500
100-350
122
14,
49
47,
42,
72,
14,
55,
25
14.
29
14
48
75
29
49
16
,55,
.29,
."•9.
,108
.32,
,72,
,108
72
,108
30,32,
50,55,
.121
37
75
.42,
,108
37.
56,
51,
,121
30-3,400 4,9,16,33.36.55.94,
96,117.122
20-800 14,33,54,72,104,112
71 49
50-11,400 14,25,32,42,48,49,50,
55,72,75.87,103,108,
112
20-500 14,32,42,49,55,75,99
100-1,926 4,25,26,33.42,55,75,
96.121
50-150 14,16,112,121
-------
Chlorination
Influent f
\
\
i
•
i
oo
•e-
u.
i
Activated
Sludge
Forward Flow--Wastewater
Forward Flow-Sludge
Sidestream Flow
Sample Point
FIGURE 2 PROCESS
MONITORING PROGRAM
12
Effluent
To
Discharge
To Ultimate
Disposal
-------
No
Mainstream Treatment Process
Evaluation Algorithms
Primary Treatment
Evaluation
Secondary Treatment
Evaluation
Evaluation Algorithm
Checklist
Anything New Added?
Yes
Operational
Mitigation Algorithms
Design Modification
Matrix
Operational Mitigation I Design Modification
Algorithm Checklist I Matrix Checklist
I
-I Has Everything Been Implemented? I
Yes
Ranking
J
-I Implementation I
End of Evaluation
FIGURE 3. SUMMARY OF EVALUATION PROCESS
85
-------
©
FIGURE k. EVALUATION OF SIDESTREAM IMPACT ON PRIMARY CLARIFICATION
86
-------
Were Any
Implementation
Steps. Either
Operational Or
Design. Required
That Had Not
Previously Been
Implemented?
Possibilities Are
No
FIGURE A (CONTINUED).
EVALUATION OF SIDESTREAM IMPACT ON
87
PRIMARY
CLARIFICATION
-------
Is Secondary
Effluent S S
and/or BODs
Concentration(s)
^ 35 mg/f
No
No Impact
Yes
Measure/Calculate
Forward Flow (W.'O
Sidestream) To
Secondary Treatment.
i.e Influent Q -
(Primary Sludge Q
- Sidestream Q) =
Forward Flow
Is Fofward Flow
To Secondary-
Treatment Less
Than Design Forward
Flow'
No
Collection System
Enforcement Problems
and'or Secondary
Treatment Design
Deficiencies Exist
No Further Evaluation
of This Parameter is
Possible Go To,
51
Yes
Measure'Calculate
Forward Flow (With
Sidestream) To
Secondary Treatment.
i.e.. Influent Q -
Sidestream Q -
Primary Sludge Q
Forward Flow
Is Forward Flow To
Secondary
Treatment Less
Than Design
Forward Fiovv9
Mo
Have Operational
Methods To Reduce
Impact Been
Implemented7
Yes
Implement
Design Methods [l(
and L-
Continue
Algorithm
Evaluation
Go To
Implement Operational
Methods To Reduce
Sidestream
Hydraulics
Continue
Algorithm
Evaluation Go To
FIGURE
EVALUATION OF SIDESTREAM IMPACT ON ACTIVATED SLUDGE
88
-------
Measure pH of
Forward Flow (W/O
Sidestream) To
Secondary Treatment
Is pH Between
6.5 and 8.5?
No
Provide Collection
System
Enforcement
Yes
Measure pH of
Forward Flow (With
Sidestream) To
Secondary
Trealment
Is pH Between
65 and 8 5?
No
Have Operational
Methods To Reduce
Impact Been
Implemented9
Yes
No
Yes
No Further Evaluation
of This Parameter
Is Possible Go To
Implement
Design
Methods
and
Continue Algorithm
Evaluation S ,
GoTo (60
Implement
Operational
Methods TO
Reduce
Sidestream pH
Possibilities Are:
Belt Filter
Press
Continue
Algorithm
GoTc
FIGURE S (CONTINUED). EVALUATION OF SIDESTREAM IMPACT ON ACTIVATED SLUDGE
89
-------
Measure Reactor
D O Level (W O
Sioesttearm Nnie
Maintain D O
Is the Secondary
Influent Suspended
Solids Concentration
Less Than 100 mo/L?
trnpleftient Operational
Collection System
Enforcement
Prootems and-or
Secondary
Treatment Design
Deficiencies Exist
Note Oo Not Change
Implement •Opec ationai
During Measurement
Evaluation. Go Tot 75
Were Any Implementation
Steps. Either Operational
Or Design. Required
That Had Not Previously
Been Implemented-'
Possibilities Are
FIGURE 5 (CONTINUED).
EVALUATION OF SIDESTREAM IMPACT ON
ACTIVATED SLUDGE
90
-------
Schedule Adjust
Sludge Removal
To Maintain A
Sludqi1 RlanHt-t ot
1 j leet iCircuiai
Fo' Hec'.anguia'
Oanhers Maintai
;ne S'uage
inven!or> in the
5unp Beiow the
C:anfie' F oor
WAO
For Plants
Equipped With
Constant Rate
Sludge Removal.
Adjust Primary
Sludge Removal
To Occur More
Frequently, But
For A Shorter
Period of Time.
Allow Only 1 -2 foot
Change In the
Sludge Blanket
Depth
FIGURE 6. OPERATIONAL METHODS TO REDUCE THE
91
IMPACT OF SIDESTREAMS ON
PRIMARY CLARIFIERS
-------
Dampen Flo*
Surges To the
Basmis) By
Limiting A Feed
Valve or Gale
Position Allow
Level Changes To
Occur In Feed
Cnannefs or
Piping Observe
Each Shift to
Prevent Overflow
Su'ges To me
Seconfla'y
Ciantiertst by
Limiting A Basin
Discharge Valve or
Gate Position
AIIOW Level
Changes To Occui
In ine Basin
Effluent Channels
Or Piping ODserve
Each Shift To
FIGURE 7. OPERATIONAL METHODS TO REDUCE SIDESTREAM IMPACTS ON A.S.
92
-------
&_t
O2>
X/ 1
Reduce the
Variability In the
Waste Sludge
Removal By
Wasting Sludge on
A More
Continuous Basis
1
y\
<34> '
For Plants
Equipped With
Variable Rate
Sludge Removal
/£\
X7 ,
V
'
For Plants
Equipped With
Constant
Rate
Sludge Removal
/£~
N/^ i
Adjust Waste
Sludge Rate To Be
Continuous The
Desired Waste
Rate Should Be
Based on
Controlling the
Activated Sludge
Process
Through
F M. MCRT Etc
1
Adjust Waste
Sludge Removal
To Occur More
Frequently. But
For Shorter
Periods of Time
The Desired
Waste Volume
Should Be Based
on Controlling the
Activated Sludge
Process
Through
P.M. MCRT. Etc
-
r
^36^
\/ i
Go To
GT
DAF
AND
AED
VF
C
BF
SB
LA
HT
<110>
X
<130>
<<40>
x.
<160>
X
<180>
x
<200>
X
<210>
x
<220-
WAO \S
FIGURE 7 (CONTINUED).
OPERATIONAL METHODS TO REDUCE
SIDESTREAM IMPACTS ON A.S.
93
-------
<8>
Th'c^el
<8> ,
\\ -lie'
'^
M'li'T'.'e - se o*
NX 1
Wasie Actuated
Siudges
Separate
<«> ,
*es
i
Measure me
Suspended SaMs
Concentrations Jn
me Thtcke^^1
Overflows
.
SS
^\s '
t
No
ves
F
Cons.de- 3'end.ng
Siudges To
increase Qv&an
Tnickenet
Performance
Perform Jar Tests
To Evaluate
Tmckener
Blended Sludges
\y^ 1
W-i- S;udye
Resu': tr A
Decrease tn ;ne
Overflow SOMQS
Bssi1-.: or jar
\/ l
>
Ope'^ie
ThtCKeners With
Btenaed Sfudges.
Chemica;
Facilities'1
\/
Yes
Evaluate
Thickener
Ftoccui^nt Aids By
Performing jar
Tests ana UM
No
— »
r
A'here Possible
Reduce ifie Solids
Retention Time in
the Tfucken«ns,y
To Minimize Septic
Cond'tions Take
Unneeded Units
Ouf ot Service jf
Required
r
<8> „
is The Piani
Equrppea Wdh An
Aeraied GM
Yfes
Where Possible.
Redirect the
Thickener
Overflow
Upstream of ;ne
Grrt ChaTiDef TO
Elevate the DO
Belore Entering
the Clanfier
i r
i
No
<93>
Minimize ir>e
Sludge Retention
Time In the
Primary C'anfiers
<8> .
Reduce me
Variability In the
Thickener
Overflow Rate By
Scheduling the
Pumping of
Primary and
Secondary
Sludges on A More
Conlmuous Basts
Likewise.
Schedule Sludge
Pumping From" the
Tntckener(s) on A
More Continuous
Basis
'
\^/ 1 '
For Plants
Equ pped With
Variable Rate
Sludge Pumping
*S ' '
Adjust Sludge
Pumping From Ifte
Thickener{s) To
Be Continuous
,.
<$>
'
For Plants
Equipped With
Constant Rate
Sludge Pumping:
Adjust Studge
Pumping From the
Thicneoerts) To
Occur More
Frequency But For
Shorter Periods of
Time.
'
r
Return To
Appropriate
Evaluation of
SKJestream Impact
Algorithm
Primary ( 1 )
Activated (*n\
Sludge \3/
Trtckling (gj)N
FIGURE 8. OPERATIONAL METHODS TO REDUCE THE IMPACT OF
GRAVITY THICKENERS
94
-------
PAPER NO. 6
COMPOSITE CORRECTION PROGRAM-
CONCEPTS AND DEMONSTRATION
by
Bob A. Hegg
Vice President Plant Operations Division
M & I, Inc., Consulting Engineers
4710 South College Avenue
Fort Collins, Colorado 80525
95
-------
COMPOSITE CORRECTION PROGRAM - CONCEPTS AND DEMONSTRATION
Bob A. Hegg, Vice President Plant Operations Division
M & I, Inc., Consulting Engineers
INTRODUCTION
Non-compliance of wastewater treatment facilities has been the focus of
numerous studies, seminars, and published articles for a number of years.
Several of these studies were funded by EPA1s Office of Research and Devel-
opment and have been collectively referred to as the "National 0 & M Cause
and Effect Survey" (1,2,3,4).
Conclusions of these research efforts can be broadly summarized in two
categories: conclusions on all facilities and conclusions concerning
inidividual treatment plants. For all facilities it was determined that
individual facilities are hindered from achieving desired performance by
multiple factors unique to each facility. As such, specific programs imple-
mented to address selected factors at all facilities will have a limited
correlation between program implementation and improved performance at indi-
vidual plants. This conclusion is significant in that broad scale programs
normally are assessed on their most obvious intended impact. It is thus
conceivable that programs could be excluded from development or eliminated
because of their inability to show a direct correlation between program
implementation and improved plant performance. Yet these programs may be
very necessary to address the high ranking and frequently occurring perform-
ance limiting factors indentified.
For individual plants it was concluded that multiple and unique factors
limit a facility's performance. The scope of these factors is often beyond
the plant operator's control (i.e., improper technical guidance and design
deficiencies). To achieve a direct correlation between an individual
plant's performance and program implementation, a comprehensive site speci-
fic effort is required. The comprehensive site specific program was
described in concept as a Composite Correction Program (CCP). The purpose
of such a program is to address the multiple and unique factors that limit a
facility's performance.
An evaluation that was completed for the 50 plants studied in the ori-
ginal EPA research is shown in Table 1. At the start of the research pro-
ject, 13 out of 50 facilities were consistently meeting secondary treatment
standards. In other words, 37 facilities were frequently violating secon-
dary treatment standards which was defined as 30 mg/1 8005 and TSS. By
looking at the factors limiting performance, an assessment was made that 40
of the 50 facilities could consistently meet secondary treatment standards
without a major facility upgrade and only ten would require some kind of
upgrade. Nine of those ten that would require an upgrade were trickling
filter facilities. Most of the evaluations were done at plants in northern
climates so there was a direct relation with climate and the affect on pro-
jected trickling filter performance. The potential for broad scale improve-
ment without major upgrades represented an appealing aspect of the research
results.
96
-------
TABLE 1. PERFORMANCE OF 50 PLANTS VS. SECONDARY TREATMENT STANDARDS (4)
Prior to Evaluation
Potential Without Upgrade
Standards
Frequently
Violated
37
10
Standards
Consistently
Met
13
40
CASE HISTORIES
Case histories demonstrating the Composite Correction Program (CCP)
approach for two facilities will be presented.
CASE HISTORY - PLANT A
A. Description
Plant A is a 1700 cum/day (0.45) mgd contact-stabilization activated
sludge plant. Wastewater treatment processes include flow measurement, con-
tact-stabilization activated sludge, secondary clarification, and chlorine
disinfection. About 25 percent of the influent wastewater can be diverted
to sewage lagoons for land application purposes. Sludge handling includes
treatment in aerobic digesters and land application of liquid sludge.
B. Current Process Loading
TABLE 2. SUMMARY OF PROCESS LAODINGS FOR PLANT A
Parameter
Raw Sewage
Flow
BOD5
TSS
Units
cum/d (mgd)
mg/1
mg/1
Value
1070 (0.28)
210
209
Contact Stabilization
Contact Basin Wastewater
Dent ion Time
*Reaeration Detention Time
**0rganic Loading
Secondary Clarifier
Surface Loading
hrs 2.1
hrs 13
gm/day/cum (Ib 336 (21)
BOD5/day/1000 cu ft)
cum/day/sq m (gpd/sq ft) 23.7 (580)
*Based on 100% return flow percentage
**Based on contact plus reaeration volume
97
-------
D.
Factors Addressed During CCP
Administration:
1. Modified permit to allow discharge from contact-stabilization
plant and not "polishing pond".
2. Emphasized priority for sludge disposal and obtained commitment
for sufficient manpower and equipment to accomplish the task.
Operation:
1. Implemented improved and expanded process control and sludge
wasting program.
2. Developed operator skills in making process control adjustments
based on proper interpretation of test results.
Design:
1. Modified piping to direct raw sewage to ponds and/or to plant.
2. Obtained sludge hauling truck and "installed sludge measuring
devices.
Maintenance:
1. Repaired leak in walls between aerobic digester, reaeration basin
and contact basin.
2. Repaired raw sewage flow meter and chlorine feed system.
Performance
100
FIGURE 1. Plant A Effluent Quality
98
-------
E. Discussion
At the start of the CCP Plant A was rated as a 1140 cum/day (300,000
gpd) facility and had received a Cease and Desist Order from the state regu-
latory agency for frequent violations of its effluent BOD5 and TSS limita-
tions. When the plant consistently achieved effluent compliance at flows
greater than 1140 cum/day (300,000 gpd), its capacity was officially up-
graded to 1700 cum/day (450,000 gpd). As such, a threatened tap moratorium
by the State was avoided. Over twelve months were required to obtain opti-
mum, stable performance. The impact of improved process control was demon-
strated by the ability to avoid wide fluctuations in final effluent quality.
Improved performance plus a dramatic increase in plant capacity were the
major aspects of this CCP.
CASE HISTORY - PLANT E
A. Description
Plant E is a 5680 cum/day (1.5 mgd) activated sludge facility. Waste-
water treatment processes include a flow diversion structure, flow measure-
ment, screening, grit removal, lift station, activated sludge aeration,
secondary clarification, disinfection, and a holding pond. Effluent from
the ponds is discharged to the river and/or to multi-media filtration and
land application for reuse. Sludge is wasted to a regional facility for
processing.
B. Current Process Loading
TABLE 3. SUMMARY OF PROCESS LOADINGS FOR PLANT E
Parameter Units Value
Raw Sewage
Flow cum/day (mgd) 5675 (1.50)
BOD5 mg/1 195
TSS mg/1 160
Effluent
BOD5 mg/1 8
TSS mg/1 14
Activated Sludge
Wastewater Dentention Time hrs 11
Organic Loading gm/day/cum (Ib BOD^/day/
1000 cu ft) 424 (26.5)
Secondary Clarifier
Surface Loading cum/day/sq m (gpd/sq ft) 24.4 (597)
99
-------
D.
Factors Addressed During CCP
Administration:
1. Improved communication between laboratory personnel and plant
staff.
2. Modified shift coverage to improve process control capability.
Operation:
1. Implemented improved and expanded process control program.
2. Changed the mode of operation from complete mix to plug flow.
3. Adjusted return sludge, waste sludge and dissolved oxygen levels.
4. Developed operator skills in making process control adjustments.
Design:
1. Modified aeration basin discharge overflow weirs.
2. Installed valve to control flow splitting to final clarifiers.
3. Modified flow splitter to aeration basins.
4. Changed the drive on aerators to increase speed.
Maintenance:
1. No changes.
Performance
i.e
t.*
01.(
i O.fr
u
H..
o
u!o.2-
• »
/ \ /AY - FLOW SOLO
/ V \
/\
' 1 S—*
/
K
a
9
U
1
IU
o
1978
J
1970
1080
FIGURE 2. Plant E Wastewater Flow
100
-------
E. Discussion
Plant E was located adjacent to a large interceptor and was capable of
treating selected amounts of sewage. Remaining flow was treated by a down-
stream facility. Increased treatment capacity meant decreased charges from
the downstream plant. In addition, increased capacity made more water
available for reuse to irrigate a golf course. A severe sludge bulking
problem had limited this facility's ability to treat increased flows. Using
the CCP approach the plant flow capacity for 1979 was increased 90 percent
over 1978 values. Flows for 1980 were increased by 350 percent. Effluent
standards have consistently been met throughout these flow increases. A
$55,000 annual cost savings for 1980 was projected, due to decreased charges
from the downstream facility. An additional benefit was that water avail-
ability for reuse was no longer limited by plant capacity. During this CCP
the benefits of optimizing process control to obtain maximum capacity from
existing facilities was clearly demonstrated.
COLORADO PROJECT
The Environmental Protection Agency (EPA) gave a grant to the State of
Colorado to try and demonstrate the effectiveness of the CCP and how it
might be utilized to improve facility performance on an areawide basis. The
project was enforcement related in that all of the activities in this pro-
ject were carried out under the Enforcement Division of the Colorado Depart-
ment of Health, and each plant evaluated was aware of the potential enforce-
ment action. Three steps were involved in the project:
1. The State and EPA jointly identified poor performing facilities.
2. M & I, Inc. was to conduct comprehensive evaluations (3,4) at the
identified plants.
3. M & I, Inc. was to implement CCP programs and achieve the desired
performance.
Some of the initial results will be summarized. Many of the owners did
not realize their responsibility for achieving compliance at a wastewater
treatment facility. In initial interviews with the facility owners, which
was part of the evaluation effort, many felt that the regulatory agency, the
design engineer, the operator, the equipment supplier and others were
responsible for the performance of their plant. They were confused in sum-
marizing their particular responsibility in achieving compliance at their
facility.
Another result was that much confusion was found to exist among plant
owners and personnel if the State or EPA focused on specifics like the need
for grounds maintenance or plant fencing during an evaluation. It was
observed that recommendations made by a regulatory agency resulted in tre-
mendous effort and enthusiasm to address these suggestions often at the
expense of efforts to improve plant performance. Plant owners place a pri-
ority on regulatory agency recommendations, often at the expense of focusing
efforts on plant performance as a goal. In addition, many owners had imple-
mented specific recommendations from regulatory agencies only to find that
desired performance had not been achieved and the regulatory agency had
101
-------
returned. In one case, a facility owner made the comment that if the regu-
latory agency came back one more time, they would turn the keys for the
plant over to them. Another confusing aspect for owners was their under-
standing of the regulatory role. Do they enforce or do they assist? On
numerous occasions regulators had taken an active role in directing specific
aspects of a facility's operations. By doing so, they assumed a portion of
the responsibility for plant performance in the eyes of the owner. This
also has served to confuse the owner as to what his true responsibility is
in achieving compliance. The important aspect of these results is that it
indicates that the regulatory agency may be better off to let the owner
develop their own specific actions while emphasizing owner responsibility to
achieve plant performance.
A couple of other results can be placed into the broad categories of
political and training limitations.
Political Limitations - We found in a very real sense that the con-
struction grants program is rewarding poor performance. In our original
research study we always initiated efforts by holding discussions with the
owners and explained the possibility of improving performance. At an un-
named plant in Wyoming one owner said, "We don't want your help. We just
got high enough on the priority list to get funding for a new facility, and
if we improve performance, we could lose our priority ranking." As such, a
negative incentive has resulted to a degree from the grants program.
Another key limitation in our original research and in the State of
Colorado study was identifying a poor performing plant. Much discussion has
centered on the definitions of poor performance, i.e., how many months does
it take to be out of compliance, how may bad samples, and what constitutes a
good sampling program to document poor performance. In the Colorado study
we attempted to use the NPDES discharge monitoring reports. This approach
allowed identification of a few facilities but does not appear adequate as a
true indicator of a plant's performance. Presently, the job of identifying
a poor performer often falls upon regulatory agency field personnel. Prob-
lems that these regulatory people face in assuming this responsibility will
be discussed later.
Training Limitations - The third ranking factor limiting wastewater
treatment plant performance identified in our original research (4) was
improper technical guidance. This factor still exists. For example, almost
each month you can pick up a technical publication and find conflicting
reports. Particular topics especially subject to conflicting reports are
causes and cures for bulking sludge or the impact of side streams on process
performance. Often, magnitudes of difference may exist in the descriptions
of an approach to take to correct these problems. Other claims that have
remained flagrant are those describing activated sludge processes that never
require wasting of sludge and that need little or no attention to operate.
Another training limitation that also still exists is operator application
of concepts. Many operators have had a great deal of classroom training but
cannot apply this training to their particular facility. What has worked to
overcome this limitation is on-site training specific to a particular
facility.
102
-------
A lack of authoritative understanding of process capability also repre-
sents a training limitation. Authoritative understanding and specifics of
process capability for biological systems is admittedly a tough area to
quantify. However, the continuing disagreement of "experts" has done little
to make the field more easily understood. For example, if you put activated
sludge "experts" in one room, it would be difficult to conclude what consti-
tutes good settling sludge, what constitutes poor settling sludge, what
constitutes good return rates, etc. As such, a lot of confusion exists as
to the exact capability that can be expected from the activated sludge pro-
cess. Process understanding and capability are important to everyone that
is involved in evaluating wastewater treatment facilities. It has been
documented that many factors limit a facility's performance (3,4). These
factors can be administrative, design, operation or maintenance related.
They can all appear to have equal weight and importance especially if a
facility is out of compliance. How then do you set priorities on what
should be addressed first?
The necessary first step is process understanding. With good process
understanding you can put priorities on maintenance, design or administra-
tion limitations to support the process needs. Without process understand-
ing as a basis, priority setting becomes a maze of trial and error efforts.
Several unresolved issues remain in trying to develop an areawide com-
pliance strategy for the Colorado CCP project. A focus on performance can
be acnieved through enforcement. Indeed many of the plants that we have
been able to go into and improve and directly address performance problems
have been because the owner's focus was brought to bear by an enforcement
activity. However, there has been some reluctance to use enforcement as a
very strong tool to bring this focus about. Should enforcement be stronger
to accelerate the understanding of the plant performance/owner responsibil-
ity relationship?
A second step is identifying poor performance. A regulatory agency is
in a tough role in making an initial assessment. Ideally, they should not
make specific recommendations at a particular facility nor should they make
interim recommendations. Yet they have to get the facility owner to focus
on performance. To accomplish these objectives, the evaluator must have an
idea of the steps that are probably logical to get a plant from its present
state to compliance without dictating the steps to the owner. Otherwise, he
will confuse and cloud the focus on performance. Another unresolved issue
is who should conduct comprehensive evaluations or conduct CCP's. Should
that De a role of the EPA or state agencies or should it be done privately?
Trie tools are available to improve performance. The mechanisms to provide
impetus to using these tools are apparently lacking.
103
-------
REFERENCES
1. Gannett, Fleming, Cordry and Carpenter, Consulting Engineers, Harris-
burg, Pennsylvania. Evaluation of Operation and Maintenance Factors
Limiting Biological Wastewater Treatment Plant Performance. Report No.
EPA-600/2-79-087 (July 1979).
2. Hegg, B. A., K. L. Rakness and J. R. Schultz. A Demonstrated Approach
for Improving Performance and Reliability of Biological Wastewater
Treatment Plants. M & I, Inc., Consulting Engineers, Fort Collins,
Colorado, Report No. EPA-6-00/2-79-035 (June 1979).
3. Hegg, B. A., K. L. Rakness and J. R. Schultz. Evaluation of Opera-
tion and Maintenance Factors Limiting Municipal Wastewater Treatment
Plant Performance. M & I, Inc., Consulting Engineers, Fort Collins,
Colorado, Report No. EPA-600/2-79-034 (June 1979).
4. Hegg, B. A., K. L. Rakness and J. R. Schultz. Evaluation of Operation
and Maintenance Factors Limiting Municipal Wastewater Treatment Plant
Performance - Phase II, M & I, Inc., Consulting Engineers, Fort Collins,
Colorado, Report No. EPA-600/2-80-129 (August 1980).
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
104
-------
PAPER NO. 7
APPLICATION OF INTRACHANNEL CLARIFIERS
IN THE OXIDATION DITCH PROCESS
by
Harold J. Beard
President
Beard Engineering, Inc.
P.O. Box 3838
Baton Rouge, Louisiana 70821 3838
105
-------
.APPLICATION OF INTRACHANNEL CLARIFIERS IN THE OXIDATION DITCH PROCESS
Harold J. Beard, President
Beard Engineering, Inc.
INTRODUCTION
Conventional solutions to the wastewater enigma faced by many communi-
ties today, often results in high capital expenditure, as well as increas-
ing operation and maintenance costs over the life of the project. The
increasing awareness of the need for energy conservation has led many
EPA construction grant applicants to the EPA Innovative/Alternative Program
which Congress incorporated into the Clean Water Act of 1977. The purpose
of the I/A program is to develop new technologies that will meet required
effluent limits with a minimum amount of resources. Since its introduction,
communities have had the incentive to utilize this program because of
the associated cost savings. That is, the federal government would pay
for 85% of design and construction of all or part of a treatment process
determined to meet the requirements of the I/A program. Even though
communities and their consultants have been required to look at alternatives
for treatment since the enactment of the Federal Water Pollution Control
Act Amendment of 1972, it was not until the introduction of promised
cost and energy savings that the program was vigorously embraced. As
a result, consulting engineers have gone beyond the alternative technologies
of land treatment and sludge composting to advance the state-of-the-art
by the introduction of innovative technology to conventional treatment
schemes.
One of the most common conventional treatment schemes utilized to
meet effluent standards imposed as a result of individual discharge stream
requirements is that of activated sludge treatment for biological oxidation
of organic material present in influent wastewater. The purpose of this
paper is to describe the innovative technologies applied to the activated
sludge treatment process found to be most suitable for the city of
Winnfield, Louisiana.
The existing Winnfield, La. wastewater treatment facility consisted
of a 1.2 - mgd single stage high rate trickling filter system with an
anaerobic single stage sludge digester and drying beds. The alternatives
evaluated were subject to a detailed analysis to determine the one that
would be most cost-effective, implementable, environmentally sound and
energy efficient, and yet would be simple to operate and maintain. A
multi-screening process eliminated those treatment schemes that would
not satisfy a majority of the present guidelines such as unavailability
of land, resource conservation and use of existing structures. The
alternative system that adequately satisfied the selection criteria and
was subsequently selected through a detailed analysis of effluent
requirements, wastewater characteristics, capital cost, operating cost,
energy consumption and sludge handling and environmental consideration
was an extended aeration process utilizing an oxidation ditch with
intrachannel clarifiers.
106
-------
IMMEDIATE ADVANTAGES OF THE INTRACHANNEL CLARIFIER
Design criteria for an oxidation ditch is based on the theoretical
destruction of all organic matter applied by using an extended aeration
period and increased aeration. The raw wastewater flow is fed directly
to the ditch where the contents are aerated and kept in continual motion.
The aerated sewage is then passed to a final settling tank which utilizes
mechanical scraping devices to move settled active solids to a collection
point in the tank. A portion of the collected sludge is then picked up
by return sludge pumping system and returned to the oxidation ditch in
order to maintain a desired mixed liquor suspended solids concentration. (1)
A most obvious advantage to the "intrachannel clarifier" system of
mixed liquor clarification is the significant savings associated with both
energy consumption and construction. In contrast with the conventional
external clarifier which requires feed and/or return sludge pumping, once
the influent has been fed to the oxidation ditch, except for aeration
purposes, no further energy consumption is required for clarification
purposes. Since no external basin is required, there is also a definite
savings in construction costs. Any treatment system selected should be
relatively simple and easily operable by an operator of medium skill and
training. The process equipment and controls should not be highly
sophisticated. An additional advantage to be realized of the "intrachannel
clarifier" is the possible reduction in plant operational expertise required
with respect to sludge waste and return pumping associated with maintaining
optimum MLSS concentration.
In June of 1981, a proposal was submitted by the city of Winnfield,
Louisiana to the EPA Municipal Environmental Research Laboratory for
the purpose of requesting a Research Cooperative Agreement for bench and
pilot scale testing of an intrachannel clarifier design. Evaluation of
various clarifier designs would be in conjunction with an anticipated EPA
Step 2 Construction Grant for proposed wastewater treatment facilities.
Previous testing of an intrachannel final clarifier in the oxidation
ditch at the wastewater treatment facility located in Campbel1svi1le,
Kentucky led to the first generation development of a unique final
sedimentation process. This intrachannel clarifier system was shown to
provide significant construction and energy cost savings as compared
to conventional final clarifiers. However, the results of this testing has
led the staff of Beard Engineering, Inc. to the identification of several
variables which when optimized, may significantly enhance the clarifier
performance, and result in additional cost savings. Since the intrachannel
clarifier was shown to provide satisfactory clarification and sludge return
characteristics for a secondary treatment level, consideration has been
given to the possibility of improving the concept by eliminating the need
for sludge scraping mechanisms. The first generation intrachannel system
utilized scraper mechanisms for both sludge and scum removal.
It is the intent of the research program to utilize developed math-
ematical models and calculations to successfully design and subsequently
construct an intrachannel clarifier which can substantially reduce the
107
-------
capita] and OSM costs required for sewage treatment.
INTRACHANNEL CLARIFIER CONCEPT
The boat shaped clarifier operates within the channel of an oxidation
ditch, thereby immediately returning sludge to the mixed liquor stream.
With placement of the unit in the direct flow of the mixed liquor, the
stream flow is restricted to that channel area between the clarifier and
the bottom of the ditch and between the walls of the ditch and the unit.
In the area of the channel beneath the "boat clarifier" the velocity of
the stream is therefore increased and a net head difference is produced.
Because the bottom of the unit is open at various locations with variable
sludge ports, this head differential is sufficient to actually pull a
quantity of flow and therefore the settled sludge from the inside of the
clarifier and back into the mixed liquor stream. It is for this reason
that no sludge pumping or scraping is required.
The head differential created by the restriction of the stream flow
will also result in a lowering of the channel depth along the sides of
the boat clarifier.(2,3) This difference of water levels between the
inside and the outside of the clarifier will allow for the removal of
floating debris in the clarifier. Surface baffles within the boat will
direct floatables towards several adjustable scum ports on both sides
of the unit. The debris will be returned to the ditch through these scum
ports and will be continuously removed from the ditch surface with
additional baffling.
RESTRICTION OF FLOW
As previously mentioned, the boat clarifier concept operates on
the principal that as flow is restricted in a channel, this transition
produces a net head difference less than that of the flow prior to this
transition. So that a minimum of loss occurs in the available head
difference produced, the cross sectional surface area of the boat and
its front end design are critical to tranquil flow around and beneath
the clarifier. A mathematical analysis of eleven (11) different cross
sectional shapes was performed to determine which would achieve the maximum
velocity increase beneath the clarifier in a rectangular channel and yet
expose the smallest amount of surface area to the stream flow in order
to minimize frictional losses of energy. In a rectangular open channel,
we know that flow is equal to the velocity times the cross sectional area
of the channel. With the flow remaining constant in the channel and
through the restricted area beneath the boat, the velocity in the
restricted area would then be a function of the cross sectional areas
as fol lows:
V2 * Vl
A2
Where A., and V. are associated with the channel upstream of the
clarifier and A«, and V_ are associated with the mixed liquor stream
beneath and around the clarifier.
108
-------
CHANNEL WATER LEVEL AND CRITICAL DEPTH
Having determined the ideal clarifier cross section for a rectangular
channel, the proper operating depth of the clarifier can be established
considering the water level and velocity in the channel. Clarifier depth
in the channel must produce a sufficiently large head differential to
provide proper skimming and sludge return flows. Therefore, there is
a minimum clarifier depth required for proper operation.
The maximum clarifier depth is that depth at which a hydraulic jump
will occur. If this "critical depth" is exceeded, high velocity in the
restricted area beneath the clarifier will result in a hydraulic jump
where the channel flow exits the restricted area. A hydraulic jump must
be avoided since its turbulence results in a large loss of energy. (Figure 1)
Therefore, for a given velocity and water level in the channel there
is a certain minimum and maximum clarifier depth. Calculations were
performed using five different water levels, three clarifier depths, the
selected channel cross section, and a channel velocity of 1 ft/sec.
Similar calculations were performed using a velocity of 1.5 ft/sec to
evaluate the clarifier depths required for the normal velocity range of
oxidation ditches.
These calculations were used to plot curves of velocity beneath the
clarifier vs. water level in the channel at the three clarifier depths
and two channel velocities. A critical depth curve was plotted using
the velocity at critical depth for each water level and each channel
velocity. The resulting plot (Figure 2) can be used to find the maximum
clarifier depth for a given water level at a velocity in the channel of
1 fps. Similar curves can be developed for other stream velocities in
the channel .
The calculations were also used to plot curves of head differential
vs. water level in the channel at the three clarifier depths and two
channel velocities. Therefore, for a certain clarifier depth, channel
water level, and channel velocity the curves can be used to find the head
differential. If head differential is known then the skimming and sludge
return flows can be calculated. (Figure 3)
In summary, this clarifier design involves developing a set of curves
of velocity beneath the clarifier vs. channel water level. These curves
are used to determine the maximum allowable clarifier depth for a certain
water level and velocity in the channel. A second set of curves of head
differential vs. channel water level can be used to calculate skimming
and sludge return flows for a certain clarifier depth, channel water
level, and channel velocity.
SLUDGE CHARACTERISTICS
An evaluation of sludge settling characteristics must be included
in order to properly design the clarifier internals. For evaluation
109
-------
purposes an artificial sludge was produced utilizing ferric chloride.
This sludge was prepared to have a Sludge Volume Index of 73 at a solids
concentration of 3000 mg/1. Thus, the settling characteristics of this
iron sludge were very similar to typical activated sludge in a domestic
wastewater treatment plant.
Settling column tests were performed by recording the interface
height at regular time intervals as the sludge blanket settled in a one
liter graduated cylinder. This data was then used to develop the settling
curve shown in Figure b. Analysis of this curve reveals that a compressive
settling zone is formed in approximately nine minutes when the sludge
blanket occupies A6% of the volume of the cylinder.
As shown in the lower portion of this curve, settling of the sludge
blanket is considerably slower once the compressive zone is formed. This
type of settling occurs in the bottom portion of a conventional clarifier
where the sludge is collected and pumped from the clarifier basin. Since
settling sludge is rapidly returned to the mixed liquor stream via ports
distributed over the entire floor of the boat clarifier, there will be
no formation of a compressive zone. For this reason the boat clarifier
operates more as a phase separator continuously drawing off sludge, rather
than a conventional and somewhat quiescent settling basin which requires
bottom scraping.
To dramatize the effects of continuous sludge draw off, a more
realistic settling test was developed utilizing a graduated cylinder from
which the artificial sludge was withdrawn from the bottom at various rates
of millimeters/minute.
This test data was used to develop the settling curves shown in
Figure 5- These curves are a graphical presentation of a column of
influent water as it moves through the length of the boat towards the
bow. It is anticipated that these curves will represent the actual shape
of the sludge blanket which will form subsequent to various adjustments
of the sludge ports.
From the previous settling column tests, it was determined that
ultimate settling would result in a sludge blanket which would occupy
13% of the volume of the cylinder. To represent the effects of sludge
draw off on the volume of sludge per unit volume of the clarifier, the
initial settling curve in Figure 4 was converted to the percentage curve
shown in Figure 6. Analysis of this curve reveals that as the total
volume of the cylinder decreases, a direct result of draw off, the
percentage of sludge in the remaining volume increases. For example,
in 18 minutes the sludge occupies k$% of the remaining volume and at 28
minutes it occupies 5&% of the volume.
In combining the results of the settling tests, it was concluded
that the sludge blanket which will form in the boat clarifier will be
affected by the percentage of boat volume removed through the sludge ports
and the amount of time required for the flow to move the length of the
clarifier.
110
-------
ANALYSIS OF CLARIFIER FLOWS
In order to determine the optimum amount of clarifier volume which
should be removed through the sludge ports, it was necessary to perform
an analysis of all flows in the clarifier.
Initially it must be recognized that the flow into the rear of the
clarifier is determined entirely by what is removed from the effluent
launderers (0.), the surface skimmer (Q ), and the sludge return ports
(Q.) on the bottom.
The value of Q, is determined by plant capacity and is therefore
a constant. The value of 0__ is such that movement of the surface water
is sufficient to remove floating debris through the skimming ports. For
the purpose of developing a mathematical model, it is assumed that Q, = Q_
and therefore Q, can be varied to determine its effect on the sludge blanket
formation. In the analysis it was assumed that the bottom of the clarifier
was evenly spaced with the (10) sludge ports. With the ultimate sludge
settling volume of 13% in mind, the percentage of sludge per unit volume
of the clarifier was determined for 10 cummulative time intervals. These
determinations were made for various Q_ values and resulting total volumes
(0_) =0, + 0. + Q,• The resulting percentages were then used to determine
approximately how much flow (Q,) was being removed in excess to that which
would be required to remove the average volume of sludge. These excess
amounts, or "safety factors" were then plotted against their respective
Q- to 0_ ratios.
To dramatize the effect of flow time in the clarifier, a similar
curve was developed with effluent launders placed in the rear of the boat
where the influent comes in.
Mathematical models were also done on uneven flows on the ten port
openings with the greatest flow being from the rear of the boat clarifier
where the initial wastewater flows into the clarifier and the smallest
flow from the bow where the launders were located. These results showed
an improvement in removal over the equal flows. In these calculations
the same ratios of 0- to QT were utilized as with the ten even flows so
that relative data and effects could be established.
The resulting Figure 7 reveals that the maximum efficiency of sludge
removal occurs when approximately 64% to 65% of 0- is removed through
the sludge ports and the effluent launders are located in the bow of the
boat.
SLUDGE FLOW FROM CLARIFIER BOTTOM
The two determining factors which effect the flow from the sludge
ports on the bottom of the clarifier are the head differential produced
by the restriction of flow and the size of the ports themselves.
For the purpose of this explanation, the following assumptions were
made:
111
-------
A) The velocity in the channel is 1 ft/sec.
B) The cross sectional area of the channel is 11.52 ft^/linear foot.
C) The skimmer port is set at .5" below the water level when the
channel is not flowing.
D) The head loss under the clarifier is 1 inch.
Assuming the bottom of the clarifier is -750 ft. from the bottom of
the channel and the water level is at 2.4 ft., the total head differential
is then 1.91 inches (head differential created by difference in velocity
based on Bernoulli).
Therefore, the available head for sludge flow Q3 is:
1.91" - 1.0" - .5" = .41"
The velocity exiting the bottom (less opening losses is determined
by the equation V =—» /2gh. Therefore, the exit velocity is:
x 32.2 x
V3 = 1.48 ft./sec.
This velocity then allows the calculation of the total opened area in
the bottom required to achieve a 0.3 of 64% to 65% of 0_j.
Recognizing that there are numerous variables that effect the amount
of open area, it is advisable to have the bottom of the clarifier designed
so that the sludge port opening can be varied.
The proposed bench scale model will be built identical to the full
scale system with all influent ports, effluent weirs, and scum and sludge
removal ports being operational and variable.
Initial testing will involve determination of the most efficient
clarifier orientation with respect to the channel bottom and water depth.
In our mathematical development of the boat clarifier, headless beneath
the unit was determined for a wood structure. However, since the bench
scale model is to be fabricated from fiberglass, it is believed that the
actual velocities and head differentials produced by restriction of the
channel flow will approach and perhaps surpass those calculated in the
mathematical analysis. Velocities and head differentials will be recorded
for what is hydraulicaly the most efficient boat configuration utilizing
various clarifier and channel depths. The approach channel velocity will
also be varied to collect similar data for the normal velocity range
common to oxidation ditch wastewater treatment systems.
The next portion of the testing procedure will involve the use of dye
or fine bubbles to video record the actual flows produced beneath, around
and within the clarifier. This data will allow for actual refine-
112
-------
merit of the clarifier shape both internally and externally. Again, this
will include a variance in the channel and clarifier depths as well as
approach velocities.
Finally, once the most efficient boat configuration and orientation
have been determined, the same artificial sludge used in the mathematical
development will be introduced into the oxidation ditch. Also, sludge
and skimmer ports will be adjusted so that optimum flows are achieved
for both sludge blanket and floatable solids removal from the clarifier.
At this time it is most important to note the conservative assumptions
made during development of this concept. The calculations for determining
the optimum Q_ to QT ratio and subsequently the length of the boat clarifier,
were based on the assumption that there is a specific amount of time required
for the sludge to attain the ultimate compressibility of 13% of total
volume. However, since this concept involves continuous removal of sludge
it is anticipated that actual testing will result in a much shorter sludge
blanket. Also, settling curves where developed for sludge which occupied
the entire depth of the settling columns. When the artificial sludge
enters the rear of the clarifier, a baffle will direct the flow down
towards the sludge removal ports. Therefore, the solids particles will
actually start their descent to the bottom of the clarifier at or below
the mid-depth point. Again it is anticipated that this will result in
a shorter sludge blanket and subsequently quicker removal of all solids.
Upon conclusion of the testing procedure, all pertinent data will
be utilized to modify the original mathematical model. It is this resulting
configuration and channel requirements upon which design of a pilot model
will be based.
REFERENCES
1. John W. Clark et al., Water Supply and Pollution Control,
International Textbook Co., New York, 1971.
2. Victor L. Streeter and E. Benjamin Wylie, Fluid Mechanics, 6th
ed., McGraw-Hill Book Co., New York, 1975.
3. Calvin Victor Davis and Kenneth E. Sorensen, Handbook of Applied
Hydraulics, 3rd ed., McGraw-Hill Book Co., New York, 1970.
4. Metcalf & Eddy, Inc., Wastewater Engineering, McGraw-Hill Book
Co., New York, 1972.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
113
-------
-------
4.5-,
4.0.
Clarifier .400 Ft.
From Bottom
.525 Ft. From
Bottom
.650 Ft. From
Bottom
.710?
Critical Depth
Curve
Channel Velocity 1.0 Fps
Note: Critical Depths
Are Plotted
Re 1 a t i ve To Clarifier
Depths
1.4
—T—
1.9
2.4
Depth (Feet)
2.9
3.4
Figure 2. Velocity Beneath Clarifier vs. Channel Depth
115
-------
Clarifier .^00 Ft.
From Bottom
525 Ft. From
Bottom
650 Ft. From
Bottom
Channel Velocity 1.0 Fps
2.1* 2.9
Channel Depth (Feet)
Figure 3. Head Differential vs. Channel Depth
116
-------
4-1
-C
Ol
QJ
:r
(0
j-j
o
0)
3:
0)
o
(0
100 ,
90.
80.
.70.
60.
50.
40-
30.
20 _
10.
0
i
T
T
T
T
T
.22
T 1 1 T^T 1 1 1 r
0 2 k 6 8 10 12 14 16 18 20 22 2k 26 28 30 32
Time (Min.)
Figure 4. Settling Curve For Artificial Sludge
D i splacement
Volume
SIudge
Blanket
Zone
Very Clear
Zone
i—T—i—r—T—i—i—i—i—r—r—i—i
8 10 12 14 16 18 20 22 24 26 28 30 32
Time (Minutes)
Figure 5- Test No. 5 Bottom Removal Settling Curves
117
-------
100%
removal of blanket
Figure 6.
T—i 1 r
12 ]k 16 18
Time (Min.)
% Of Maximum Settlement
Launder in Front
Maximum Efficiency
Occurs at 6k to 65%
Launder in Back
50 6T
% Of Total Flow
Figure 7. Safety Factor vs. Flow From Bottom Clarifier
118
-------
PAPER NO. 8
BIOLOGICAL FOULING OF FINE BUBBLE DIFFUSERS
by
William C. Boyle
Professor of Civil & Environmental Engineering
University of Wisconsin
Madison, Wisconsin
and
David T. Redmon
Engineer
Ewing Engineering Company
Milwaukee, Wisconsin
119
-------
BIOLOGICAL FOULING OF FINE BUBBLE DIFFUSERS
William C. Boyle, Professor of Civil & Environmental Engineering, University
of Wisconsin, Madison, WI
David T. Redmon, Engineer, Ewing Engineering Co., Milwaukee, WI
Aerobic biological processes continue to be the most popular methods for
the treatment of municipal and industrial wastewaters. The supply of oxygen
to the biomass in activated sludge and aerated lagoons represents the single
largest energy consumer in the treatment plant. Recent studies indicate that
from 50 to 90 percent of the net power demand for a treatment plant lies
within the aeration system (1). It is not surprising, therefore, that engi-
neers continue to seek the most efficient aeration systems for new and
existing wastewater treatment facilities in order to provide energy-
conserving operation.
Although there is considerable controversy over which aeration system
provides the most favorable oxygen transfer efficiency, the fine bubble
diffusion of air has recently gained renewed popularity as a very competitive
high efficiency system. Yet, considerable concern has been registered re-
garding the maintenance of fine bubble systems owing to their susceptibility
to clogging. Diffuser clogging, if severe, may lead to deterioration of
aeration efficiency resulting in an escalation of power costs. Furthermore,
troublesome maintenance of diffusers may consume a substantial amount of
operator time.
Originally, oxygen was diffused into wastewater through perforated pipes
located at the bottom of the aeration tank. The development of the porous
plate for aeration was considered an important advance in the diffused air
process because of the high transfer efficiency of this fine pore diffuser
(2). Porous diffuser plates were used in activated sludge processes as early
as 1916 and they became the most popular method of aeration by the 1930's (3,
4). Shortly after their installation, however, it became clear that clogging
could be a problem. Early work by Bushee and Zack (5) at the Sanitary
District of Chicago from 1922 to 1924 prompted the use of coarser media to
avoid severe clogging problems. Similar studies confirmed this at Milwaukee
in the early 1930's. In a comprehensive review of fine bubble diffuser ser-
vicing, Roe (2) outlined a number of causes of diffuser clogging. This list
has been expanded over the years and is presented in Table I.
It was clear even in the early years of fine bubble diffusion that
clogging was highly site specific and quite often difficult to forecast (4,
6). Diffuser clogging was chronic at some plants after only a few months of
operation, yet, at others, virtually no difficulties with clogging arose.
Substantial effort was applied in the early years to reducing internal clog-
ging by means of efficient air cleaning (7,8,9), a practice still performed
today. External clogging was not as easy to analyze or control, however, and
operations research concentrated primarily on treating the symptom rather
than the cause.
120
-------
TABLE I. CAUSES OF DIFFUSER CLOGGING
Air Side
• Dust and dirt from unfiltered air
• Oil from compressors or viscous air filters
• Rust and scale from air pipe corrosion
• Construction debris due to poor clean up
• Wastewater solids entering through diffuser or pipe leaks
Liquor Side
• Fibrous material attached to sharp edges
• Inorganic fines entering media at low or zero air pressure
• Organic solids entering media at low or zero air pressure
• Oils or greases in wastewater
• Precipitated deposits, including iron and carbonates
• Biological growths on diffuser media
TESTS FOR CLOGGING
In 1934, Roe (2) indicated that clogging of air diffusers could best be
monitored by measuring air main pressure changes with time for each aeration
tank. Further, he indicated that visual observation of the aeration tank
surface could often provide evidence of severe diffuser fouling. Over the
years, little change has been made in this technique. As indicated by Roe,
sequential readings of air main pressure, air flow and temperature are made
(Figure 1). A plot of air pressure at a given standard air flow rate versus
time is subsequently used to detect fouling. One of the major factors that
severely limits the precision of this method is that the differential pres-
sure across the diffusion element itself, which is the parameter of principal
interest, is very small relative to the pressure in the main. Other factors
and variables that further limit the precision of the method include the
water surface elevation in the aeration tanks, water temperature, air flow
variation, and variable line losses.
A method that measures the drop across selected diffusion elements at
measured flow rates is considered to be of far greater accuracy and preci-
sion. An example of such a system is shown in the detail sketch on Fig. 1.
Flow may be determined by observation of manometer A which measures the dif-
ferential across the previously calibrated control orifice C. Manometer B
measures the pressure drop across the diffusion element itself, or the
dynamic wet pressure (DWP).
Dynamic Wet Pressure
The dynamic wet pressure, DWP, is the pressure differential across the
diffusion element alone when operating in a submerged condition and is ex-
pressed in terms of inches of water, at some specified flow rate. It
differs substantially from the permeability test, where the specific air flow
rates are typically much higher and where surface tension of the submerging
liquid is not a factor.
121
-------
Valve
PLAN VIEW SCHEMATIC
DETAIL
'See Detail
Air Source
Air Flow Control
Orifice
Header^7
Figure 1. Measurement of Air Line and Diffuser Pressure
In the dynamic wet pressure test, most of the pressure differential is
due to the force or pressure required to form bubbles against the force of
surface tension and only a small fraction of the total pressure gradient is
required to overcome frictional resistance.
The DWP is normally relatively insensitive to airflow rate. This
results since the surface tension effect is not greatly influenced by flow
rate in flow ranges normally applied and the contribution of frictional re-
sistance is a small part of the total pressure gradient.
That the frictional resistance is small with respect to the total, can
be shown as follows:
Assume the typical airflow rate at average design conditions is
about 2 SCFM per square foot of diffuser surface area. Since the
frictional resistance is only 2.0 in. wg. at 25 SCFM Cspecific
122
-------
permeability of 25) and this unit is typically operated at 2 SCFM
under average design conditions, its theoretical frictional
resistance at this rate is roughly 2.0/25.0 of 2 in. wg. or
about 0.2 in. wg. The total DWP at 2.0 SCFM is about 6.9 in. wg.
So the frictional resistance at this airflow rate is roughly 3%
of the total resistance.
The DWP test is of value in analyzing diffuser fouling in at least two
ways. It is a much more sensitive indicator of fouling than air main pres-
sure readings and the analysis of the DWP vs. flow relationship gives some
indication of the nature and type of fouling.
Bubble Release Pressure
The bubble release pressure (BRP) test provides a means of comparing the
relative effective pore diameter at any point on the surface of a ceramic
element to other point(s) on its surface. Ewing Engineering Company develop-
ed this test procedure as a tool to assess the uniformity of pores on the
surfaces of ceramic diffusers.
The bubble release pressure test, as indicated by the name, measures the
pressure in inches of water gauge required to emit bubbles from a localized
point on the surface of a submerged and thoroughly wetted porous diffuser
element. This is accomplished by forcing air at a very low rate of flow into
the diffuser and measuring the pressure of the air when bubbles are released
from the diffuser at the point in question.
The test procedure was developed from a similar test found in ASTM,
Part 41, under Standard Test Method E128-61. This standard describes a
technique for measuring the maximum pore on a porous structure and uses the
force to make bubbles in a known fluid to calculate a capillary diameter
corresponding to this force or pressure.
Ewing Engineering Company modified the hardware to suit their needs and
used BRP observations of a statistically significant number of points on the
element to ascertain the degree of uniformity. After determining the air
flow distribution on several elements on which BRP data was available, it
became apparent that the BRP test data was a sensitive indicator of flow
distribution.
This test has been applied to a variety of fine pore diffuser elements.
It has been found to be a sensitive indicator of the degree of fouling of
porous diffusers and provides a quantitative means of assessing the rate and
location of plugging.
Furthermore, analysis of partially fouled diffusers have given indica-
tion that the BRP test is even more sensitive than the DWP test. Conse-
quently, in diffuser fouling investigations, the use of these test methods
permits significant shortening of the test period required to obtain defini-
tive conclusions about diffuser clogging.
123
-------
Air Profile Test
The airflow profile test uses quantitative techniques to evaluate the
uniformity of air release across the surface of ceramic diffusers while
operating rather than appraising uniformity by visual means. This is accom-
plished by testing the element at an air rate which is approximately equal
to 2 SCFM/sq. ft., or at the recommended design rate, with anywhere from
2-8 inches of water over it.
The rate of air release from small areas is measured by displacing water
from an inverted graduated cylinder and recording the rate of displacement
of water with a stopwatch. The same sites monitored in the BRP test are
tested in this procedure. By combining the cylinder area and the rate of air
discharge, a flux rate, expressed as SCFM/sq. ft. or other convenient units,
can be calculated. By comparing the individual readings with one another,
a quantitative measure or graphical representation of the profile can be
generated.
The combination of DWP, BRP, and flow profile tests applied to new
diffusers and at various stages in their operating history, provides a very
useful diagnostic tool in evaluating the rate, the nature and the effect of
fouling, be it organic or inorganic, on fine bubble porous diffusion ele-
ments. It is also effective in appraising the effectiveness of various
cleaning procedures.
BIOFOULING OF DIFFUSERS
The occurrence of biological growths or slimes on fine pore diffusers
was recognized early after their application in activated sludge. Roe (2)
indicated that biological growths were found on the liquor side of most
diffusers in operation. He attributed this growth primarily to the non-
uniformity of the diffuser medium. There were very few published reports of
serious diffuser clogging problems attributed to biological growths,
however. Anderson (9) indicated that fungal growths were commonly found on
diffusers at the Sanitary District of Chicago Southwest Plant with heaviest
growths occurring in the summer near the influent end of the aeration tanks.
These growths produced little measurable effect on air line pressure loss
except during the summer of 1944 when an exceptionally heavy growth of
Saprolegnia s£ developed. No reason for the unusual growth that year was
cited. Beck (3) reported a severe clogging of diffuser plates after 69 days
at the Chicago North Side Works where return sludge was aerated. The plate
surfaces, clogged with approximately 1/8 inch of biological slime, were
refurbished by aeration over a 45 day period without addition of wastewater.
Lamb (10) referred to one or two cases where biological slimes caused in-
creased head loss of fine bubble tube diffusers but no details were given.
In 1980, Houck and Boon (11) carried out an extensive survey of 19
wastewater treatment plants in the United Kingdom, the Netherlands, and the
U.S. that employed fine bubble dome diffuser aeration devices. The major
objective of this work was to assess long term oxygen transfer performance
and operation and maintenance history of dome diffuser aerators. As a part
of this study, the authors reported that the major operational problem
124
-------
associated with dome diffusers was the formation of biological slimes on
diffusers operating in zones of high volumetric loading and/or low dissolved
oxygen. In only two cases, however, were domes observed to contain excessive
amounts of biological slime (Beddington, U.K., and Madison, WI). All other
plants apparently exhibited signs of "coarse bubbling" which the authors
attributed to the development of biological slimes. The authors further
cited pilot plant work at the Water Research Centre at Stevenage, U.K. which
verified the causes of diffuser sliming as the result of very high loading
rates (12). No data was presented, however.
Madison, Wisconsin observed a severe biological sliming problem in the
early part of 1980, about two years after installation (13). Heavy infesta-
tions of stalked ciliates (predominantly Epistylis) were observed on the dome
surfaces and the plastic air piping. Slime cover on the domes was not uni-
form, completely covering some domes while being almost absent on other
adjacent domes. It appeared that slightly more growth occurred on domes in
the first pass and less in the third pass of this step aeration system. This
plant experienced high BOD loading throughout the first half of 1980, the
predominant source being several dairies in the community. Prior to this
heavy loading period no apparent heavy slime growth was noted on the dif-
fusers when the tanks were dewatered. Following the high loading period in
early 1980, the domes were steam cleaned in-place and returned to service.
Since that time, the domes have been periodically checked. Some slime growth
has reappeared but it contained few stalked ciliates and was more diverse in
biological population. The slime was easily removed with high pressure water
hoses. Since the high load incidence, in 1980, there has not been a recur-
rence of the heavy biological slime formation at the plant.
Biofouling Agents
Over the years, several investigators have analyzed the biological
slime that developed on fine bubble diffusers. A synopsis of these findings
appears in Table II. In most cases when biological slimes were found, no
specific identification was provided but descriptions of color or consistency
were given.
TABLE II. BIOFOULING AGENTS
Worms - Tubifex, Aulophorus
Iron bacteria - Crenothrix
Stalked ciliates - Epistylis
Filamentous bacteria
Fungii - Saprolegnia
"Biological slime"
Source
[Setter (7),
[Setter (7)]
[Setter (7),
[Setter (7)]
[Anderson (9)]
[Roe (2), Wisley
Cont.(5), Lamb
& Boon (11)]
Madison (13)]
Madison (13)]
(6), Op &
(10), Houck
The occurrence of Epistylis (species undetermined) as a predominant
organism in the biological slime on the domes at Madison, Wisconsin was
125
-------
interesting. Further investigation of the heavy plant loads during the
severe bioslime incidence, indicated that an unusually high amount of dairy
wastewater including whey was discharged during that period (13). Metabolic
studies with Epistylis have indicated that this attached ciliate, unlike many
others, may feed on inert wastewater nutrients as well as bacteria (14).
Whether the presence of specific nutrients in the dairy waste promoted the
unusual bloom of Epistylis and subsequent formation of heavy slime growths
on the ceramic diffusers or whether the presence of this organism was inci-
dental to the real causative agent in the bioslime at Madison is uncertain.
The almost complete absence of Epistylis in subsequent biological slimes at
Madison suggests that the waste characteristic itself (rather than organic
load or low dissolved oxygen) may have played a predominant role in the
development of serious bioslimes on the diffusers at that plant.
Causes of Biofouling
The published literature does not contain any report of a controlled
study on the causes of bioslime development in activated sludge diffused air
systems. Most hypothesis have been based on observations at operating
plants. The major causes of biofouling that have been proposed based on
field experience are presented in Table III. Roe (2, 15) indicated that
quite often a film of biological growth appeared on the diffuser surface
and even grew into the pore structure of ceramic diffuser plates. He indi-
cated that poor air distribution within the plate resulted in biological
growths along and within the quiescent pore spaces. Lamb (10) speculated
that these slimes appeared after the pores of the diffuser had become clogged
by dirt from the inside or incrustation from the outside. Setter (.7) pro-
posed that biological clogging became more severe as the BOD loading increas-
ed and as the permeability of the plates decreased. He also suggested that
sufficient air flow rate per diffuser should be maintained in order to avoid
excessive biofouling. Both Setter (7) and Anderson (9) suggested that bio-
logical clogging appeared to be seasonal. Heaviest fungal growths were
found to occur during the summer months (9).
TABLE III. CAUSES OF BIOFOULING
Uneven air distribution in diffuser (2, 7, 10)
Low air flow rate per diffuser (7)
High organic loading (7, 11)
High temperatures (7, 9)
Low dissolved oxygen concentration (11)
Low permeability of diffusers (6, 7)
Waste characteristics
The field study of 19 diffused air plants conducted by Houck & Boon
(11) provided additional data on bioslime formation. These investigators
claimed that the formation of biological growths on dome diffusers was the
result of high organic load and/or low dissolved oxygen. They speculated
that the growth was exacerbated by extreme plug flow aeration tank design.
Boon and Burgess (12) also reported heavy slime growth development on dome
126
-------
diffusers in pilot plant studies using organic loads to a first stage aera-
tion tank of up to 420 Ib BODc/1000 ft.3/day.
Similar excessive slime growth problems reported for the activated
sludge plant at Madison occurred during high organic load conditions. A
synopsis of the data collected at Madison prior to and following this bio-
fouling incident is presented in Table IV. Several interesting points should
be emphasized regarding this and other studies. The organic loads (expressed
as Ib BOD5/1000 cu ft/d) to the Madison plant prior to heavy biofouling
averaged about 20. During the heavy load period, the average rose to about
35 and subsequently dropped after the first six months of 1980 to about 29
where it has remained. Only during the heavy load period in the first six
months of 1980 did a severe slime development occur. This was coincident
with heavy dairy waste loadings including whey which were discontinued by
mid year. At the time of this heavy slime infestation, the plant was being
operated in a step aeration mode.
TABLE IV. DIFFUSER STUDIES - MADISON NINE SPRINGS PLANT
Aeration Tank Information:
Tanks 1-6 each 31' x 135' x 15.5' deep (2-3 pass tanks)
Diffusers: Ceramic Domes - Tapered Aeration
In Service: October, 1977
DATE
10/27-12/77
1/78-6/78
7/78-12/78
1/79-6/79
7/79-12/79
1/80-6/80
7/80-12/80
Mode of
Operation
CS
CS
CS
CS
S/CS
S
S
F/M
(LB/DLB)
0.27
0.29
0.25
0.23
0.37
0.34
0.34
BOD LOAD
(LB/1000 FT^/D)
20.3
22.3
17.2
19.2
25.5
34.6
29.2
OTE
_
14
18
-
-
7.5-8
8-10
NOTES
Dewater tanks -
diffusers OK
Dewater tanks -
heavy slime
Steam cleaned
diffusers
Dewatered - mod-
erate slime
Steam cleaned
diffusers
1/81-6/81
7/81-11/81
S
S
0.33
0.39
30.1
30.4
-
16
Dewatered - mod-
erate slime
OTE by off gas
CS - Sludge Reaeration in First Pass
S - Step Aeration
In contrast to this, the slime infested aeration tanks at the Beddington,
U.K. works were only loaded at 11 Ib BOD5/1000 cu ft/day but the plant did
127
-------
receive heavy industrial waste loadings. Other plants surveyed by Houck &
Boon (11) experienced loadings ranging from about 10 to over 110 Ib BOD5/1000
cu ft/d. Some of these plants experienced coarse bubbling, but no severe
sliming problem was reported (all diffusers likely were coated with some
biological material but the authors did not present quantitave evidence of
severe fouling). A review of operating records at the Milwaukee Jones
Island West Plant during the years 1952-66 (16) indicated BOD loadings ave-
raging 60 Ib BOD5/1000 cu ft/d. This plant received substantial amounts of
industrial waste. No severe biofouling incidences have been reported for the
ceramic plates at this plant during that time although incrustations and rust
contributed to clogging problems.
The point to be made from this scant information is that biofouling is
apparently highly plant and waste specific. No generalizations may yet be
made in reference to specific causes of severe biofouling. The Madison
experience strongly suggests that their problem was waste specific and inter-
mittent (not unlike the problem of sludge bulking in many plants); the prob-
lem at Beddington, on the other hand, is endemic, but, again, is likely due
to plant and waste specific characteristics.
The Effects of Biofouling
The development of a biological growth on diffuser media could have
several effects on diffuser performance. One might develop the following
sequence of events that would occur as the biofilm developed.
As air passes through the media, biological growths begin
to develop along the media where little air passes (e.g., over
the finer pores). This mat continues to develop and begins to
overlap regions where air is escaping. The presence of the
bioslime leads to bubble coalescence along the media. The effect
of this progressive clogging might produce little noticeable
change in DWP unless the biological slime envelopes the entire
media surface. Under these conditions, the uniformity of the
air released from the diffuser may be detrimentally affected
and poor distribution may result. The OTE may decrease as
bubble coalescence occurs and there could be visible changes
in bubble patterns and the appearance of "coarse bubbling" at
the surface. This type of diffuser clogging may not be evident
as routinely measured by air line pressure losses or demand for
more air (as a result of some loss in transfer efficiency).
The biological slime may fluctuate in thickness and extent with
season. Its net effect may not be serious depending upon the
extent of slime development.
Other mechanisms of biological clogging may also occur as well as the
one outlined above. Several investigators have speculated that biofouling
occurs after or simultaneously with internal clogging or external encrusta-
tion. For such a situation, the following scenario might take place.
Since porous media represents a distribution of pore sizes,
air will initially flow through the coarser pores first where
128
-------
resistance to flow is the lowest. Particulates in the air or
chemical encrustations could begin to lodge within the larger
pores forcing air to the next smaller pore size. This would
result in the progressive utilization of the finer pores producing,
perhaps, more uniform distribution and finer air bubbles.
Increases in DWP could be small at this point. As time progresses,
the next size pores could begin to fill, eventually resulting in
the utilization of the finest pore openings. As the effective
cross-section through which air passes is restricted, finer
bubbles may form and dynamic wet pressures would increase to a
point where significant air line losses would be detected.
Heavier biological growth would begin to develop in the quiescent
regions at the diffuser. Eventually the biological mat may
result in bubble entrapment and coalescence. The net effect of
this progressive clogging might be an increase in OTE up to a
point (as air distribution improves and bubble size decreases)
followed by a drop in OTE as coarser bubbles begin to form.
Dynamic wet pressures would slowly rise to a point where only
the finer pores are carrying air; after this, pressures would
rapidly rise. At this stage, depending upon diffuser shape and
general design considerations, coarse bubbles may form or major
short circuiting of air past gaskets or around bolts may occur.
At these high air flow rates per unit area, a continuous stream
of bubbles may be discharged from these locations and the diffuser
would no longer behave as a fine pore device. Surface tension
would no longer be measureable and the area would act like a
very large pore. DWP would not change at this point and the major
effect would be a substantial loss in OTE as the behavior of the
device approached that of a coarse bubble diffuser. In another
case, where no outlet for air flow is available within the
diffuser element, the extent of fouling could be such as to
severely restrict flow to a point where DWP (and BRP) rapidly
increased to a point where significant air line pressures would
require diffuser cleaning.
Presently, there is not a great deal of evidence to support either of
these hypotheses of progression of biological clogging. Historically, the
literature indicated that biofouling normally produced little change in DWP.
Isolated incidences at Madison and Beddington, U.K. suggested that severe
biological slime development produced dramatic changes in DWP and BRP. An
example of the effects of heavy biofouling of a ceramic dome at Madison is
presented in Figures 2-5. In this example, it is seen that the DWP at 0.75
SCFM increased from about 6 inches to about 18 inches after severe clogging
(Figure 2). BRP values on the top side of the dome increased from about 6
inches of water to a range of 14 to 10 inches after bioslime development
(Figure 3). There was a slight increase in BRP on the bottom side of the
dome increasing from about 6 inches to 7.5 inches (Figure 4). It was clear
that in this case, the bioslime produced the major resistance to air flow.
Note in the air flow profiles of Figure 5, the majority of the air passed
out along the periphery of the center bolt washer and the edges of the dome
once a clogging mat had developed within the main body of the dome. Even
when new, the air flow profile suggested that air distribution was not ideal
129
-------
,* 60
g 50
. 40
- 30
u 20
13
V)
LU
a:
Q.
i-
UJ
o
8
6
5
4
3
2
I 1
FOULED
CLEAN
I
I
0.5 1.0 1.5 2.0
AIR RATE - SCFM
2.5 3.0
Figure 2. Dynamic wet pressure for clean and clogged dome - Madison,WI.
but once clogging was initiated, the biological slime exacerbated the air
flow distribution producing excessively high rates in very localized regions.
It is likely that this condition Ipd to severe reductions in OTE, but no data
is currently available to substantiate this under properly controlled condi-
tions.
Of significant interest in diffuser fouling phenomenon is the impact of
the slime on OTE. Results from Madison (Table IV) suggest that the severe
biofouling of the domes produced dramatic reductions in OTE. Once cleansed,
these diffusers appeared to essentially return to their original high level
of efficiency. It should be carefully noted, however, that the field OTE
measurements made at Madison were crude, at best. Early measurements were
made during the sludge reaeration process whereas later measurements were
made in the aeration tanks when operated as a step aeration process. Dif-
ferences in alpha could have strongly influenced the comparison of these
data.
The phenomenon referred to as "coarse bubbling" has been used as a
visual indicator of diffuser biofouling (11). In some instances, this de-
duction has been shown to be correct. There are other cases, however, where
the incidence of "coarse bubbling" may be due to other factors. These
authors have had the opportunity to visit several plants where "coarse
bubbling" occurred intermittently. The coarse bubbles were most noticeable
at the influent end of the aeration tanks and would appear and disappear
130
-------
CD
LU
o:
co
CO
LU
cc.
CL
LU
CO
<
LJ
_l
UJ
cc
u
_1
CD
00
r>
m
18-
16
12
10
8
Figure 3. Bubble release pressures for the top of a clean and
clogged dome - Madison, WI.
throughout the day. No diffuser sliming was noted at these plants. Cur-
rently, it is believed that coarse bubbles may occur as the result of the
presence of high surfactant concentrations. Poorly mixed influent with
mixed liquor may produce zones of high surfactant concentration with concomi-
tant low surface tension. These zones may fluctuate as waste flow and
characteristic change, but would be most noticeable at points of waste
influent flow.
The response of different types of diffuser materials and shapes to
biofouling is not well documented. At Madison, those aeration tanks equipped
with ceramic and plastic tube diffusers did not experience the severe bio-
fouling problem that was prevalent in the ceramic dome aeration tanks. The
waste load to all the tanks was similar and tank geometry was approximately
the same. Presently no explanation is available for these observed differ-
ences.
Design for Biofouling Control
Until better information is available on the causes of biofouling of
fine bubble diffusers, it is difficult to delineate specific design criteria
to control the process of biological fouling.
131
-------
I
UJ
cc
g 8
CO
UJ
tr ,
UJ
CO
< 4
UJ
_J
LU
BOTTOM
FOULED
BOTTOM
CLEAN
UJ
_j
GQ
m
Z>
GQ
Figure 4. Bubble release pressures for the bottom of a clean and
clogged dome - Madison, WI.
There is a certain amount of field evidence that suggests that the
design of the diffuser element itself is important in preventing extreme
fouling problems. Uniform distribution of air throughout the media would
seem to be of paramount importance. Furthermore, it is quite likely that
there is a minimum air flow rate per diffuser that is required to prevent
encroachment of bioslimes on the diffuser surface. Herein lies one dilemma
with diffuser design since low air flow rates normally produce higher OTE
and there is a temptation to size aeration facilities to favor better trans-
fer efficiencies. Unfortunately, the placement of high diffuser densities
(and concomitant reduced air flow rates per diffuser) in an aeration tank to
take advantage of the more favorable transfer efficiencies may eventually
lead to maintenance problems and eventual loss of efficiency due to bio-
fouling. More data needs to be collected to corroborate this reasoning,
however.
The clean water testing of fine bubble diffusers is most often used by
engineers to size aeration systems for dirty water testing. Although engi-
neers attempt to account for this translation through the use of an alpha
correction, little thought has been given to changes that may occur in dif-
fuser properties once placed in the dirty water over a period of time. BRP
measurements made on selected diffusers removed from operating plants suggest
that air flow distributions may be significantly changed. This may produce
substantial changes in OTE, not accounted for in the clean to dirty water
132
-------
u_
o
CO
o
CO
I
LJ
!5
cc.
X
:D
_J
u_
cr
6-
5-
2
I
FOULED
CLEAN
Figure 5.
translation.
Air flux rate for a clean and clogged dome - Madison, WI.
(Average flux rates for concentric circles.)
Houck and Boon (11) recommended that aeration tanks be designed to
avoid excessively high localized organic loading which might lead to fine
bubble diffuser clogging. They recommended the use of low length to width
ratios, step feeding and tapered aeration as means to reduce potential clog-
ging problems. Another approach would be to employ a coarse bubble or
mechanical aeration system at the influent end of plug flow systems. The
loss in efficiency may be well worth the decrease in diffuser maintenance.
There has been considerable interest generated recently in the in situ
cleaning of fine bubble diffusers including internal gas cleaning as well as
mechanical jetting, steaming or brushing. In any event, aeration tanks
employing full floor coverage units should employ some type of rapid tank
draining facility.
If biological fouling is considered to be primarily the result of the
wastewater characteristics, pretesting of selected diffusers in that waste-
water may be highly desirable. The installation of a test fixture employing
two or more diffusers within an existing aeration tank has provided very
useful information on diffuser clogging potential of selected wastewaters
(17). A test fixture instrumented in a fashion similar to that in Figure 1
was used. DWP measurements made over a two to three month period provided
133
-------
useful data on clogging potential. Laboratory follow up analyses on indivi-
dual diffusers provided additional data on air flow distribution and BRP
thereby providing a sensitive indicator of the relative degree and progres-
sion of clogging.
B10FOULING - FUTURE RESEARCH
The impact of long-term fine bubble diffuser operation in wastewater
with respect to maintenance requirements and OTE is still poorly documented.
It is clear that some biological growth will develop on diffuser surfaces but
the impact of that growth on performance is unclear. Research should be
directed under controlled experimental conditions toward measuring the pro-
gression of biological fouling employing sensitive BRP and air flow distribu-
tion techniques. These studies should include a variety of diffuser mat-
erials and geometry. The selection of diffuser systems is often predicated
on the performance of clean diffusers in clean water. The long term changes
in OTE during diffuser operation in wastewater should be more clearly deli-
neated in order to provide the engineer with a clearer picture of what
happens to OTE over the design life of the diffuser.
As energy costs continue to escalate, engineers will seek more effective
energy conserving systems for the transfer of oxygen to wastewater. Until a
better understanding of the behavior of fine bubble diffusers under long-
term field conditions can be delineated, doubts will continue to be raised
regarding the effectiveness of the fine bubble system. Furthermore, mis-
application of these systems in certain situations may result in a greater
expenditure of manpower and energy than would be estimated.
ACKNOWLEDGEMENTS
The authors wish to acknowledge the cooperation and assistance of
Mr. Paul Nehm and Mr. Tim Weir of the Madison Metropolitan Sewerage Commis-
sion. Their contributions to a better understanding of biofouling are
greatly appreciated. We also acknowledge the assistance and counsel of
Mr. Jerry Wren, of Sanitaire-Water Pollution Control Corp, Milwaukee.
REFERENCES
1. Wesner, G. M., et al. Energy Conservation in Municipal Wastewater
Treatment. EPA 430/9-77-011; Office of Water Program Operations; U.S.
EPA; March, 1978.
2. Roe, F. C. The Installation and Servicing of Air Diffuser Mediums,
Water and Sew. Wks, 81:115, 1934.
3. Beck, A. J. Diffuser Plate Studies, Sew. Wks. Jour., 8:22, 1936.
4. Committee on Sewage Disposal. The Operation and Control of Activated
Sludge Sewage Treatment Works, Sew. Wks. Jour., 14:3, 1942.
5. Bushee, R. J. and Zack, S. 1. Test on Pressure Loss in Activated Sludge
Plants, Eng. News Record, 93:21, 1924.
6. Wisley, W. H. Summary of Experience in Diffused Air Activated Sludge
Plant Operation, Sew. Wks. Jour., 15:909, 1945.
7. Setter, L. R. Air Diffusion Problems at Activated Sludge Plants, Water
& Sew. Wks., 95:450, 1948.
134
-------
8. Setter, L. R. and Edwards, G. P. Experimental Laundering of Air
Diffuser Plates, Sew. Wks. Jour., 17:867, 1945.
9. Anderson, N. E. Tests and Studies on Air Diffusers for Activated
Sludge, Sew. and Ind. Wastes, 22:461, 1950.
10. Lamb, M. Designing and Maintaining Porous Tube Diffusers Wastes
Engineering, 25:405, 1954.
11. Houck, D. H. and Boon, A. G. Survey and Evaluation of Fine Bubble Dome
Diffuser Aeration Equipment. EPA 600/S2-81-222; Municipal Environ.
Research Lab; U.S. EPA; Oct. 1981.
12. Boon, A. G. and Burgess, D. R. Treatment of Crude Sewage in Two High
Rate Activated Sludge Plants Operated in Series, Water Poll. Control
73:382, 1974.
13. Nehm, P. History of Norton Dome Fine Bubble Diffused Aeration at MMSD.
An Internal Report to MMSD, July 1981.
14. Pillai, S. C. and Subrahmangan, V. The Role of Protozoa in Aerobic
Purification of Sewage, Nature (London), 154:179, 1944.
15' 1933 F' C' SeWage Aeration by Diffused Air, Sew. Wks. Jour., 5:813,
16. Leary, R. D., Ernest, L. A. and Katz, W. J. Effect of Oxygen Transfer
Capabilities on Wastewater Treatment Plant Performance, Jour. Water
Poll. Cont. Fed., 40:1298, 1968.
17. Wren, Jerome; Personal Communication; Sanitaire-Water Pollution Control
Corp., Milwaukee, WI, 1981.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
135
-------
SESSION NO. 3
Improving Process Reliability
PAPER NO. 9
STABILITY AND RELIABILITY OF BIOLOGICAL PROCESSES
by
E. D. Schroeder
and
Salar Niku
Department of Civil Engineering
University of California, Davis
Davis, California 95616
136
-------
STABILITY AND RELIABILITY OF BIOLOGICAL PROCESSES
E.D. Schroeder and Salar Niku
Department of Civil Engineering
University of California, Davis
Davis, CA 95616
Biological wastewater treatment processes are treated by designers, operators
and regulators as steady state processes that do not fail. The same designers,
operators and regulators fully recognize that these systems experience wide ranges
of loading, and environmental parameters, and that the systems often do fail. Despite
this knowledge process design is based on steady state assumptions, whether a kinetic
or a loading factor approach is used, and operation is based on the same approach.
It is an accepted fact that biological treatment processes are not completely stable
or reliable but present deterministic and conceptual models so not come close to
providing adequate descriptions of process behavior. The principle factors that are
missing are satisfactory dynamic models that incorporate hydrodynamic coupling and
knowledge of actual stochastic variation in process performance. The purpose of
this paper is to discuss results of a study in which daily data from 43 activated
sludge and 11 trickling filter plants was analyzed. Previous reports based upon this
study will be summarized and the work will be extended to applications in design,
operation and regulation (1, 2, 3, 4, 5).
Probabilistic Approaches To Process Analysis
Statistical methods have been used to correlate process variables for a very
long time. An early example is the NRC report (6). In this study mean effluent
BOD_ and suspended solids values from trickling filter plants at 34 military
installations were used to develop removal efficiency relationships (the NRC formulas).
The mean values used were based on monthly values and for periods varying up to
20 months. The relationships developed were statistically weak, even assuming that
comparison of the data populations was appropriate (7). Other studies of one or a
few plants have resulted in expressions for predicting process performance (8,9) but
the expressions have not been widely accepted.
More recently work has been directed at determining the variation in effluent
quality and process performance (10,11,12,13,14,15). With the exception of Hovey
et al. work (15) the previous studies were based upon a large amount of data from
one or a few plants within a limited geographical region. Hovey et al. considered
annual data for a one year period from 28 plants some of which are included in this
study. Most of Hovey et al's plants were in California, but a few were from the
Midwest. A general conclusion of these workers was that a log-normal distribution
provided the best fit to the data. Hovey et al. did not find a generally satisfactory
probability density function but did find excellent correlation between the effluent
characteristics percentile (i.e. the percentile value of a given concentration value)
and the annual mean for individual plants. A similar result had previously been
reported by Townshend (16).
Considering the number of physical and environmental variables affecting
wastewater treatment plant performance it is unlikely that a particular model,
deterministic or stochastic, will fit every situation. Variation in effluent quality
would be expected to have a log-normal component because the effects of many
137
-------
variables are linked together multiplicatively. Thus it is not surprising that previous
workers have found good log-normal fits to their data and that in this study the
log-normal distribution could be rejected in only 13 of the 43 cases.
Use of Distributions
When a distribution has been established a number of useful relationships can
be developed. These include determination of the probability that a given plant can
meet a particular discharge standard (reliability), the relative range of product quality
with respect to discharge standards and/or the mean value from the process (stability)
and the effect of selected variables (eg. temperature) and process parameters (eg.
overflow rate/design overflow rate) on process performance. These determinations
were done for the plants studied and the results are summarized below:
Process Reliability
In considering the reliability relationships developed it should be remembered
that the plants used in this study were chosen because they were believed to be
well operated and sources of good data. Thus the reliability relations should be
appropriate for use in design and as measures of expectation. As stated above
reliability is the probability that a chosen standard (eg. 30 d average BOD- _< 30
g/m ) will be met.
Construction of reliability model requires that a distribution function be chosen.
Because it provided the best overall fit the log-normal distribution was chosen. It
is also desirable to have a model stated in arithmetic rather than log terms. For
this reason the effects of the log-normal distribution were incorporated into a single
parameter, the coefficient of reliability (COR) that relates the chosen standard, X ,
to the mean effluent value, m , required to meet the standard a given fraction of
the time.
m =(COR)X (1)
A O
That is if the standard X is to be met a given fraction of the time the
actual process mean effluent value must be m . The theoretical COR value is
derived from the log-normal distribution probability density function.
I]54} (2)
In
138
-------
where V = coefficient of variation = a /m
X XX
Z, = standard normal variate
a = arthmetic standard deviation
A.
Values of the COR are given in Table 1 for selected values of V and percent
reliability, and the relationship is presented in graphical form in Figure 1.
Use of equation (1) for design, operation or regulation requires some knowledge
of "reasonable expectations." The first step is to verify that the COR values
developed from the log-normal distribution can be used to predict actual process
performance. Verification requires comparison of the predicted reliability based on
measured values and Table 1 or Figure 1 with calculated reliability from data.
Results are given in Tables 2 and 3 for activated sludge and trickling filter plants
respectively.
Process Stability
Stability is often used in a qualitative sense or with respect to a particular
situation. A quantitative definition of stability must reflect the commonly understood
definition to be accepted and useful. Two general approaches might be used. First
the occurrence of upsets might be cataloged and stability defined in terms of number
of upsets per year or the ratio of upset days to non-upset days. This approach is
only quasi-quantitative because the definition of "upset" is qualitative. Additional
problems result from the facts that activated sludge plants are generally termed
upset only when effluent suspended solids are high, a visually observable situation
and attached growth process behavior is quite different than suspended growth
systems. A second approach is to define a parameter as a measure of stability.
Suggested parameters include the standard deviation, S , coefficient of variation, V
(ratio of standard deviation to mean) and coefficient of stability, COS (ratio 01
variance to mean). Both ratios suffer from the fact that processes with a low mean
value can have the same coefficient as ones with high mean values. For example
a plant with mean effluent mean and standard deviation values of 6 and 3 g/m
respectively, will have the same coefficient of variation as a plant with mean and
standard deviations of 50 and 25 g/m .
Standard deviation was chosen as the basic stability parameter in this study
because a definite, unnormalized measure of dispersion is provided and because it
is a widely understood term. Further support for the choice was provided when
strong correlations between the standard deviation and the mean annual maximum
value and the COS were found (Table 4). By itself stability is only a relative
parameter, that is the larger S the less stable the plant. A reference value or
cut off point is needed that divides plants into unstable and stable groups. This
was done arbitrarily after plotting mean and range vs standard deviation (Figures
2-5). Both range and mean lend to have higher values for plants with standard
deviations greater than 10 g/m as either BOD5 or SS. The effect is quite pronounced
with activated sludge plants (Figure 2 and 3) and less so with trickling filters (Figures
ft and 5).
Outliers: Inclusion of range (or maximum value) as a factor in defining stability
forces consideration of outliers: single points that greatly deviate from the general
139
-------
TABLE 1. COEFFICIENT OF RELIABILITY3 AS A FUNCTION
OF Vx AND RELIABILITY FROM POOLED PLANT DATA
Row 1 for BOD, Row 2 for SS
Reliability
VX
0.3
0.*
0.5
0.6
0.7
0.8
0.9
1.0
50%
1.08
1.08
1.11
1.11
1.1*
1.15
1.17
1.18
1.20
1.22
1.2*
1.26
1.28
1.30
1.32
1.35
80%
0.85
0.87
0.80
0.8*
0.77
0.80
0.73
0.77
0.70
0.7*
0.67
0.72
0.65
0.69
0.62
0.67
90%
0.7*
0.75
0.68
0.70
0.63
0.65
0.58
0.61
0.55
0.57
0.51
0.5*
0.*8
0.51
0.*6
0.*8
95%
0.6*
0.66
0.57
0.59
0.51
0.53
0.*6
0.*9
0.*3
0.*5
0.39
0.*2
0.37
0.39
0.3*
0.36
99%
0.50
0.*9
0.*3
0.*2
0.38
0.36
0.3*
0.32
0.30
0.29
0.28
0.26
0.25
0.2*
0.23
0.22
100%
0.39
0.3*
0.32
0.27
0.27
0.23
0.2*
0.20
0.21
0.17
0.19
0.15
0.17
0.1*
0.16
0.13
140
-------
0.1 02 0.3 0.4 0.5 0.6 0.7 0.3 0.9 1.0 U 12 U 1.4 1.5
NORMALIZED MEAN , mx/Xs
Figure 1. Reliability versus normalized mean for different
coefficients of variations.
141
-------
TABLE 2. COMPARISON OF PREDICTED AND MEASURED PERFORMANCE
OF ACTIVATED SLUDGE PLANTS ACROSS THE UNITED STATES
to
Plant
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
VX
0.75
0.52
0.67
0.62
0.57
0.56
0.54
0.99
0.91
0.38
0.90
0.43
0.87
0.95
0.86
0.51
0.72
0.34
0.42
0.49
0.56
0.48
0.58
1.11
0.70
X/30a
0.33
0.28
0.33
0.61
0.54
0.55
0.71
0.55
0.83
1.01
0.62
0.55
0.55
0.77
0.89
0.16
0.06
0.08
0.16
0.26
0.14
0.14
0.10
0.81
0.43
BOD
%time <
Predicted
97.10
99.80
98.30
87.50
92.30
92.60
82.40
87.20
73.50
56.30
84.30
95.10
88.00
76.60
70.20
99.99
99.99
99.99
99.99
99.90
99.99
99.99
99.99
75.30
95.10
30 R/m3
Measured
99.1
100.0
97.8
87.9
91.2
91.4
86.5
91.5
70.3
60.1
90.4
95.0
88.6
77.9
68.8
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
73.7
95.2
vx
1.17
0.43
0.32
0.83
0.74
0.73
1.27
1.26
0.98
0.32
1.70
0.79
1.13
1.37
1.21
0.55
1.13
0.47
0.48
0.64
0.58
0.53
0.56
1.33
1.07
X/30
0.37
0.21
0.48
0.87
0.71
0.73
0.56
0.70
1.48
1.96
0.34
0.49
0.49
1.16
0.94
0.18
0.09
0.15
0.27
0.23
0.21
0.19
0.12
0.63
0.40
ss
%time <
Predicted
93.80
> 99.99
99.40
71.10
80.20
78.10
86.00
80.40
52.70
2.30
93.40
91.50
89.20
64.40
70.50
> 99.99
> 99.99
> 99.99
> 99.99
99.70
99.90
> 99.99
> 99.99
83.20
93.10
30 R/m3
Measured
96.2
100.0
100.0
75.5
85.5
83.3
89.9
86.1
58.0
3.1
94.2
94.3
89.0
67.9
70.6
100.0
100.0
100.0
100.0
99.5
99.5
100.0
100.0
81.9
97.0
a_
X is the actual arithmetic mean value of the data (BOD or SS) in the plants.
-------
TABLE 2 (continued)
Plant
Number
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
VX
0.48
0.51
0.48
0.89
0.95
0.78
0.41
0.90
0.60
0.86
0.70
0.61
1.20
0.68
0.37
0.43
0.68
1.27
X/30
0.30
0.42
0.46
0.14
0.20
0.36
0.80
0.60
0.29
1.05
0.22
0.70
0.55
2.85
0.48
0.30
0.69
0.71
BOD
%time <
Predicted
99.80
97.90
97.30
99.80
99.20
96.60
77.80
85.20
99.40
62.00
99.70
82.00
86.50
8.20
98.70
99.90
81.90
79.90
30 R/m3
Measured
100.0
98.3
99.2
100.0
100.0
95.3
72.5
84.2
99.7
64.8
100.0
84.3
86.5
12.1
98.8
100.0
85.8
84.2
VX
0.66
0.62
0.80
0.58
0.70
0.44
0.38
0.75
0.52
1.07
0.53
0.76
1.37
0.93
0.60
0.69
1.30
1.68
X/30
0.32
0.30
0.30
0.33
0.34
0.36
0.80
0.73
0.49
1.18
0.24
0.64
2.17
2.67
0.29
0.33
0.95
1.41
SS
%time <
Predicted
98.60
99.20
98.10
99.00
97.90
99.60
78.60
73.10
95.60
59.80
99.90
84.10
40.50
19.80
99.40
98.20
70.80
61.10
30 R/m3
Measured
98.9
100.0
98.1
99.5
98.9
98.9
80.0
80.9
97.3
64.9
100.0
76.0
51.1
21.9
99.6
97.7
77.8
71.6
-------
TABLE 3
COMPARISON OF PREDICTED AND MEASURED
PERFORMANCE OF TRICKLING FILTER PROCESSES
Plant
Number
1
2
3
4
5
6
7
8
9
10
11
VX
0.46
0.67
0.75
0.36
0.38
0.25
0.73
0.15
0.39
0.30
0.65
X/30
1.11
0.36
0.34
1.94
0.94
0.90
0.77
1.44
1.70
0.70
0.61
BOD
%time <
Predicted
49.3
97.6
97.4
4.3
63.8
70.9
76.6
2.1
11.1
91.4
87.1
30 g/m3
Measured
49.6
97.5
98.3
8.0
57.9
72.6
75.5
1.1
17.8
97.6
88.2
VX
0.59
0.62
0.79
0.27
0.48
0.40
0.63
0.40
0.43
0.61
0.55
X/30
1.75
0.72
0.70
1.83
0.61
0.50
0.80
1.13
1.37
0.79
0.54
55
%time <
Predicted
22.6
80.6
80.5
1.6
90.5
97.7
75.0
45.0
28.8
75.8
92.7
30 g/m3
Measured
19.4
78.1
76.2
5.6
93.1
98.1
70.7
45.8
28.5
72.8
93.4
Predicted percentages represent areas under the normal probability curve F(Zi_^), where
j.-, is
In
equal to:
1)'
See Reference 5 for details,
-------
TABLE 4. PEARSON CORRELATION COEFFICIENTS3, r, OF ANNUAL
DATA FOR H3 ACTIVATED SLUDGE TREATMENT PLANTS0
x sx vx
X 1.00 0.92 0.19
S 1.00 0.53
V 1.00
Max
COS
X
S
V
Max
COS
BOD
Max COS
0.80 0.74
0.9* 0.94
0.61 0.74
1.00 0.93
1.00
Antilog
(LnSx)
0.17
0.43
0.78
0.36
0.58
X
0.81
0.82
0.38
0.80
0.75
1.00
SX
0.67
0.82
0.64
0.87
0.87
0.88
1.00
VX
0.30
0.54
0.71
0.64
0.68
0.34
0.65
1.00
ss
Max
0.56
0.74
0.66
0.82
0.83
0.81
0.97
0.71
1.00
COS
0.50
0.72
0.71
0.81
0.84
0.75
0.97
0.74
0.98
1.00
Antilog
(Ln5x)
0.34
0.60
0.72
0.63
0.72
0.34
0.58
0.80
0.57
0.61
a The Pearson correlation coefficient, r, for variables X and Y is defined as:
1
g
n X. - X Y. - Y
Y = — 7 — - _ — - __ j giving the cross correlation between any two
n i=l x y chosen plant variables, such as X = BOD and
Y = SS
All measurements are at 0.001 significance level
-------
iUU
ISO
160
-
—
-
-
140 h
120
IOC
SO
60
40
20
-
-
i i
• Wean
1 |
i i i
1 1
i
ei "2
ij
i
STABLE
UNSTABLE
t
-
_
— S'andaid deviation
— Ranje
-
-
-
-
*i
0
Plant
-r
1
"i
"". 'i
*7 o"',^ !
Ill
4
Numbers x
£
^.
v
1
'!
•i
i
« i
, !
"
'
i
1
i * 1 i
= «
z i |
I
X
i •
i
i"
! -''
^i i -
III
i ;!-
: ' "•
t | i
: -
i ; —
i — "^^j
^ •
„-"
•
I
>
i
J
li
i
jj "
|
i *
i
1"
I
i 1
i
t
j
i
i
1
»
'
1 )
i
1 !
I
j-
-
•>
4>
1 1
12 16 20 24 28
Standaid deviation (t/m )
Figwe 2. Mean, standard deviation, and range of effluent BOD
concentration in different treatment plants.
146
-------
2CC
180
160
- 120
ICO
8G
SO
40
20
STABLE UNSTABLE
Vejn
SSanaard deviation
Plan! Nu.T.im
12 ' 16
Standard deviition d
20
J J
I
2<
2S
Figure 3. Mean, standard deviation, and range of effluent suspended solids
concentration in different treatment plants.
147
-------
CD
CXO
cz
-o
ro
cr
o
ra
TJ
cr
CO
ro
O)
160
140
120
100
80
60
40
20
0
STABLE
-^-
UNSTABLE
^-
—— Standard Deviation ^
Range
• Mean
Plant Number
7
1 1
1 1
0 4 8 12 16 20 24
T
Standard Deviation (g/tn )
Figure 4. Variability of effluent BOD as a
function of standard deviation.
148
-------
cu
00
-a
c:
o
—
O)
Q
•o
ra
c:
ra
cu
200
180
160
140
120
100
80
50
40
20
0
/I
iii 11111 iiiyii
STABLE UNSTABLE ~
*•
••
M
- St.
D-
• We
-
.
o
indard Deviation
nge
an
Plant Number.
-
-
-
. u
-
1 1
f\ •
\
?
(
~^
t
r\
•
t i
O
*»•
CD
t
m
»
1
CD
OO
X
i . lA . .
-
-
-
-
-
-
-
-
i
-
-
V
•* r\ tf f^ A "<^i"\ *^
12 16 20 28 32
Standard Deviation (g/m )
Figure 5. Variability of effluent suspended solids concentration
as a function of standard deviation.
149
-------
trend. These points often greatly effect or even dominate the standard deviation.
For example a number of extreme values occur in the effluent BOD,- data for both
of the plants of Figure 6. Possible causes of the extreme values include mechanical
failure, measurement error, introduction of toxicants, unusual weather and natural
stochastic variation. If the cause is other than stochastic variation the points are
true outliers and may be disregarded in determining the process characteristics.
Removing the upper one-percent of data resulted in decreasing the standard deviations
of the BOD- and suspended solids concentrations by an average of 1.6 and 3.6 g/m
respectively, but the relative stability ranking of the 43 activated sludge plants did
not change.
Cyclic Patterns: It is well known that flow rates to municipal wastewater treatment
plants tend to have weekly and seasonal cycles. Thoman (8), Adams and Gemmel
(9) and Lin and Heinke (17) used spectral and harmonic analysis to remove non-random
components from effluent data. They found significant weekly, seasonal and annual
cycles. Similar cycles can be seen in Figure 6 for plant 10. In the 43 plants used
in this study seven (10,14,15,24,29,30, and 35) were found to have significant cyclic
patterns. Five of the eleven trickling filter plants exhibited significant weekly cycles
and overall the BOD- and suspended solids concentrations tended to be below average
on Sundays. Seasonal patterns were evident at all 11 trickling filter plants with
improved performance in the summer.
Plant Configuration and Size: Seven types of activated sludge process were included
in the study although most were either conventional or stepfeed systems. Results
of considering annual statistics of each process type as a data population are given
in Table 5. The results are interesting because for the four configurations with
more than one representative there is a clear order of performance.
Plant size is also of interest because of trends toward construction of large
regional facilities. The results of this study, which included plants with average
flows ranging from less than 3000 to more than 750,000 m /d (0.8 to 200 mgd) are
similar to those of Hovey et al. (12). No correlation between plant size and
performance could be found. Thus improved performance does not appear to be a
valid reason for regionalization.
Process Parameters and Variables
A number of parameters and variables were correlated with process
performance using multiple regression analysis. These included wastewater
temperature, time lag, flow, sludge volume index (SVI), mean cell residence time
(MCRT), food to microorganisms ratio (F/M) mixed liquor suspended solids (MLSS),
recycle solids concentration (X ), recycle rate (Q ), influent BOD and influent
suspended solids. Twenty one of the 43 activated plants and all 11 trickling filter
plants had sufficient data to allow evaluation of these parameters. Lag time refers
to lagging input and output values in time to determine if processing time is a
factor. Variation in a number of the variables and parameter correlated significantly
with variation in effluent BOD5 and suspended solids concentration but the pattern
was not consistent. That is in some plants wastewater temperature was most
important, in others influent BOD and in others flow rate was the principle factor.
In general less than half the variation in effluent quality could be explained by the
conbined effects of the process parameters and variables.
150
-------
(29 164 ZOI Z37 2T* 311 547
"I 1 1 1 1 1 1 1 1 1 1 1 1 1
- T
n I
i > i i i i i | | 'i | | 1 1 1 | 1 1 1 1
36 7 5 tO9 >46 195 2'9 2*6 29? 529 366
Time (days)
Plant No 10
IB S4 Bl 128 1«« 201 J37 27< 311 347
T 1 1 T
J
E
_ B3 -
O
o
3d -
27 *
Bh ! . i i i . ' . i i.i i 1
C 3fl 73 109 146 133 2
Time (day*)
Figure 6. Typical time-series plots of effluent BOD
and SS concentrations.
151
-------
TABLE 5. STATISTICS OF THE ANNUAL EFFLUENT BOD AND
SS CONCENTRATION DATA FOR DIFFERENT PROCESS TYPES
Ui
N5
Process type
No. of
plants
Mean Standard
deviation
* Sx * Sx
Coef. of
variation
V^ Q
A 3x
Conventional
Complete-mix
Step-Feed/Aeration
Contact Stabilization
Extended Aeration
Kraus
Aerated Lagoon
All Plants
18
5
13
4
1
1
1
43
12.80
16.82
10.84
38.38
14.41
24.02
30.35
15.76
BOD
6.85
6.67
7.68
32.08
13.43
9.54
13.24
8.28
28.17
5.31
9.85
11.61
11.28
7.99
6.51
7.56
20.92
10.49
0.69
0.77
0.68
0.76
0.37
0.41
0.38
0.70
0.25
0.13
0.25
0.14
0.23
SS
Conventional
Complete-Mix
Step-Feed/Aeration
Contact-Stabilization
Extended-Aeration
Kraus
Aerated Lagoon
All Plants
18
5
13
4
1
1
1
43
14.92
19.88
16.23
40.88
8.82
24.12
58.79
19.40
10.53
14.19
16.65
26.75
17.03
16.02
19.65
16.83
37.66
5.28
9.26
18.71
18.35
18.61
16.92
23.89
26.18
20.60
0.86
1.00
0.83
0.90
0.60
0.38
0.32
0.84
0.38
0.51
0.34
0.14
0.37
Average values from all plants, not calculated from parameter averages
-------
Design and Operation Applications
The results of this study provide useful tools for both design and operation
of biological wastewater treatment plants. The key relationships are Equation (1),
Table 1 and Figure 1. It is important to recognize that a desired reliability must
be chosen and that 100 percent reliability is impossible. Thus choosing a reliability
value is the first step in application. The second step is consideration of the
coefficient of variation (Vx). In general the higher the mean va^ue the lower the
estimated V . Because ensuring stability requires QX = <_ 10 g/m the value of V
is partially constrained. For example if a standard of 30 g/m (BOD or suspended
solids) is to be met 99% of the time and a is to be maintained below 10 g/m or
x
less, the mean design (or operating) value is determined from a modified form of
Table 1. As can be seen in Table 6 setting a reliability constraint of 99% results
in required m and a values that will be extremely difficult to meet.
X X
Discharge standards now in general use are considerably less stringent than
those of the above example because they are based on weekly and monthly averages.
For a log-normally distributed population if the distribution of the means (weekly
or monthly) has the same arithmetic mean and variance as the total population the
geometric distribution of the means is also log-normal with a mean (m]nQM^ equal
to the log of the population mean (m. y) and a variance, Oi^r-i^ equal to the
population variance, o. x, divided by the averaging period, n (1). Although discharge
standards would be better stated in geometric terms (3) they are in fact stated as
arithmetic averages. These can be related to the geometric values through Equation
(«) and (5)
"inx - ln -2 + '
mlnx - in "\ - °lnx
A population having an arithmetic mean and standard deviation of 30 and 10
g/m3 respectively will have a log mean of 3.35 and a log standard deviation of 0.32.
The 30 day log goemetric mean value and log geometric standard deviation values
are then 3.35 and 0.058. These values can be used with Equations (6) and (7) to
obtain the geometric mean and standard deviation.
Thus the population will have, a geometric mean of 28.6 g/m and a geometric
standard deviation of 1.65 g/m . To have a 99 percent probability that the 30 day
153
-------
TABLE 6: DESIGN WL and a FOR X = 30 g/m3
X A »>
Vx
0.3
0.*
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.5
99th
Percentile
COR
0.53
0.44
0.37
0.32
0.28
0.25
0.22
0.20
0.17
0.14
mx
15.9
13.2
1.1
9.6
8.4
7.5
6.6
6.0
5.1
4.2
ax
4.8
5.28
5.6
5.8
5.9
6.0
6.0
6.0
6.1
6.3
154
-------
arithmetic mean value of 30 g/m will not be exceeded the combination of design
geometric means and standard deviation shown in Table 6 is necessary.
The rn_., values of Table 7 are reasonable and attainable in activated sludge
processes. Aftnough apparently quite small the standard deviations are also reasonable
and attainable. The key factor is that 30 day a values are related to single day
value, by lA^O~. A second problem results from the fact that a method of designing
for a standard deviation does not exist. In practice it must be assumed that standard
deviations attainable in other plants are possible in the one being designed.
Recommended Design Values
In conventional process design procedures average and peak loadings are
incorporated into steady state models. In essence the 7 and 30 day averages used
by regulating agencies is ignored and an attempt is made to design a system that
will meet the requirements everyday. The general procedure of applying the
log-normal distribution to design value selection was given above. Comparison of
process by process configuration and setting a stability criteria of a =10 g/m
resulted in the values given in Table 8. The recommended effluent 5b values are
difficult if not impossible to incorporate directly into a design. Obtaining these low
values will require conservative overflow rates, however.
Operation
Application of statistical procedures to process operation provides a method
of assessment and trend for a particular plant. Plants incorporating computer control
can be provided with programs for the necessary calculations. Most plants do not
have this capacity but the calculations are quite simple and once set up do not
require more than a few minutes a week to update. Correlation with these results
requires a years data and there is an advantage in having a complete seasonal cycle.
If desired a longer period at a given plant would be useful, also. At a particular
installation monthly values could be used and compared to the same periods on an
annual basis.
When the time period has been chosen it would be advisable to determine the
most appropriate statistical distribution to use. In most cases this will be the
log-normal distribution but there is no reason to assume it to be the best in all
cases. For the first period the log mean and log standard deviation values are
calculated in the normal manner. The process of subtracting out the initial value
and adding a new one is very straight forward and can be taught to operating staff
without a background in statistics as a series of steps on a pocket calculator. One
approximation must be made in determining the standard deviation because the mean
value changes on a daily basis. It would be unusual for the mean to change enough
in one or two days to effect the standard deviation significantly however. An
alternative is to maintain a running years data on a cassette for a desk top
minicomputer. The actual mean value could then be used in determining the standard
deviation.
Knowledge of the statistical parameters associated with performance is useful
in comparing a given plant to others and in assessing performance trends. For
example it is useful to know if an apparently increasing mean value is within expected
normal variation or if performance is actually decreasing. Detecting what plant
155
-------
TABLE 7: GEOMETRIC MEAN AND STANDARD
DEVIATION FOR 99th PERCENTILE AND 30 g/ni - 30 DAY
ARITHMETIC AVERAGE
VGM MGM °GM
Step
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
TABLE 8:
PROCESS
Process Type
feed/aeration
Conventional
Complete Mix
Contact Stabilization
g/m3
27.9
27.2
26.6
26.0
25.4
24.8
24.3
23.7
23.2
22.7
RECOMMENDED
CONFIGURATION
Number
Plants
13
18
5
4
g/m3
0.3
0.5
0.8
1.0
1.3
1.5
1.7
2.0
2.1
2.3
DESIGN VALUES BY
(Niku et al, 1981b)
of BOD _< SS _<
g/m3 g/m3
15 12
15 12
13 10
13 11
156
-------
component is failing is beyond the scope of the simple statistical methods used here,
but in large plants more sophisticated analysis may be useful. An example would
be estimating the effects of industrial spills.
As noted above weekly and seasonal cycles exist at many plants. Knowledge
of these cycles can be used in operation. In many plants maintenance is scheduled
for low flow seasons, already, but operational response could include temporary unit
shut down over weekends, modifying aeration rates during periods of known low or
high organic loading rates and changing process parameters in advance of influent
characteristics changes.
Regulation Applications
Regulatory agencies typically evaluate performance on the basis of violations.
While this is a reasonable method considerable knowledge is added if it is known
that violations should be considered characteristic of a given plant because the
average and standard deviations are high. Response to violations will undoubtably
be different for plants having a high probability of repeatedly violating standards
than for those with good reliability and stability.
Simple, standardized programs can be used with minicomputers in making
statistical evaluations. In evaluating single plants manipulation of a years data is
not time consuming and the information provided is far more useful than reports of
particular violations.
REFERENCES
1. Niku, S., E.D. Schroeder and FJ. Samaniego (1979). "Performance of Activated
Sludge Processes and Reliability Based Design" Journal of Water Pollution Control
Federation, 5J., 2841.
2. Niku, S. and E.D. Schroeder (198la). "Stability of Activated Sludge Processes
Based on Statistical Measures" Journal Water Pollution Control Federation, 53,
457.
3. Niku, S., F.J., Samaniego and E.D. Schroeder (1981b). "Discharge Standards
Based on Geometric Mean" Journal Water Pollution Control Federation 53, 471.
4. Niku, S. and E.D. Schroeder (1981c) "Factors Affecting Effluent Variability From
Activated Sludge Processes, Journal Water Pollution Control Federation, 53, 546.
5. Niku, S., R.S. Haugh and E.D. Schroeder (198Id). "Performance of Trickling
Filter Plants" in press Journal Water Pollution Control Federation.
6. National Research Council (1946). "Sewage Treatment at Military Installations"
Sewage Works Journal, _18, 789.
7. Schroeder, E.D. and G. T. Tchobanoglous (1975). "Another Look at The NRC
Formula: Water and Sewage Works, 122, No. 7, 58.
157
-------
8. Fair, G.M. and H.A. Thomas (1950). "The Concept of Interface and Loading in
Submerged, Aerobic, Biological Sewage - Treatment Systems," Journal and
Proceedings, Institute of Sewage Purification, pt. 3, 235.
9. Caller, W.S. and H.B. Gotaas (1964). "Analysis of Biological Filter Variables"
Journal Sanitary Engineering Division, ASCE 90, SAG, 59.
10. Adams B.3. and R.S. Gemmel (1973). "Performance of Regionally Related
Wastewater Treatment Plants," Journal Water Pollution Control Federation, 45,
2088.
11. Thoman R.V. (1970). "Variability of Waste Treatment Plant Performance" Journal
Sanitary Engineering Division, ASCE, 96, 819.
12. Hann, R.W. et al. (1972). "Evaluation of Factors Affecting Discharge Quality
Variation" Texas Water Quality Board, Environmental Engineering Division, Austin,
TX.
13. Bertheoux P.M. (1974). "Some Historical Statistics Related to Future Standards
Journal Environmental Engineering Division, ASCE, 100, 443.
14. Popel, H.J. (1976). "A Concept for Realistic Effluent Standards" Progress in
Water Technology, 8, 1, 69.
15. Hovey, W.H., E.D. Schroeder and G. Tchobanoglous (1979). "Activated Sludge
Effluent Quality Distribution" Journal Environmental Engineering Division, ASCE,
105, 819.
16. Townshend, A.R. (1968). "Statistical Analysis of the Effluent Quality of Biological
Sewage Treatment Processes," Proceedings, Third Canadian Symposium on Water
Pollution Research, Toronto, 272.
17. Lin, K.C. and G.W. Heinke (1977). "Variability of Temperature and Other Process
Parameters, A Time Series Analysis of Activated Sludge Data" Progress in Water
Technology, 9, 2, 347.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
158
-------
PAPER NO. 10
EVALUATION AND DOCUMENTATION OF MECHANICAL RELIABILITY
OF CONVENTIONAL WASTEWATER TREATMENT PLANT COMPONENTS
by
David W. Shultz
Senior Research Engineer
and
Van B. Parr
Staff Scientist
Southwest Research Institute
San Antonio, Texas 78284
159
-------
EVALUATION AND DOCUMENTATION OF MECHANICAL RELIABILITY OF CONVENTIONAL
WASTEWATER TREATMENT PLANT COMPONENTS
David W. Shultz, Senior Research Engineer
Van B. Parr, Staff Scientist
Southwest Research Institute
INTRODUCTION
There are approximately 21,000 publicly owned municipal treatment
plants (POTWs) operating in the U.S. at the present time, with 1000-1200
new plants being constructed each year (1)(2). Since 1957, Federal grants
exceeding $20 billion have been awarded to help state and local governments
construct these treatment plants. Once constructed, local governments become
responsible for plant operation in accordance with effluent discharge permit
requirements established by the National Pollutant Discharge Elimination
System (NPDES).
Many POTWs are apparently not meeting NPDES permit requirements. The
General Accounting Office (GAO) concluded in 1970 that operation and
maintenance problems with POTWs had been widespread for many years and
had resulted in inefficient plant operations (3). A 1975 EPA analysis of
954 POTW inspections showed 386 plants had sufficient design and operational
performance data to determine whether the plant was meeting design criteria
for biochemical oxygen demand (BOD) removal. 40 percent of 305 plants were
operating below design criteria for suspended solids removal. Other studies
have indicated significant problems of non-compliance by POTWs with NPDES
permits (4)(5)(6).
In recognition of these operational and maintenance problems, the
U.S. EPA initiated a national research program dealing with performance
and reliability of POTWs. A significant part of the effort involves
determining the reliability of various mechanical components used at POTWs.
This study was conducted by Southwest Research Institute (SwRI) to
quantify the In-service reliability of critical mechanical components found
in four types of secondary wastewater treatment plants. The four types of
plants Included in this study were air activated sludge, oxygen activated
sludge, trickling filter, and rotating biological contactor. The reliability
statistics determined included mean time between failure (MTBF), mean time
to repair (MTTR), and availability as a percent of scheduled operating
time.
The technical approach, results, and conclusions are discussed in
the following sections.
TECHNICAL APPROACH
Criticality Analysis
To determine the In-service reliability of critical mechanical
components, the first step was to identify the critical components. The
160
-------
following components were identified as critical (i.e., failure would have
an immediate impact on effluent quality); pumps, power transmissions, motors,
compressors, diffusers, valves, controls, and conveyors.
A criticality analysis was then conducted to determine the component-
application combinations to be included in the study.
A failure mode, effects, and criticality analysis was then performed
for each of the four types of plants. In performing the analysis, it was
assumed that there was no equipment duplication and that the plant was
operating at the design condition. The resulting criticality rating for
each component-application combination reflected the degree of impact on
the effluent quality (significant, minimal, or no impact) as a function
of time after failure (0-4 hours, 4-12 hours, or 24 hours).
From this analysis, the components selected for inclusion in the data
collection effort were:
(1) Raw and intermediate wastewater pumps, power transmission and
motors for all plant types,
(2) Return activated sludge pumps, power transmission and motors
for air and oxygen activated sludge,
(3) Recirculation pump, power transmission and motors for trickling
filter and rotating biological contactors,
(4) Motors and power transmission for final clarifiers for all plant
types,
(5) Motors, power transmission, compressors, valves, controls and
diffusers used in dissolved air production application and
mechanical aerators in air activated sludge plants,
(6) Motors, power transmission, recirculation pumps, controls,
diffusers and valves used in oxygen generation, application and
recirculation in oxygen activated sludge plants,
(7) Liquid application systems for trickling filter plants,
(8) Compressors, motors, power transmission and controls used in
primary clarifiers and primary sludge pumping in trickling filter
and RBC plants,
(9) Recirculation pump controls used in secondary treatment in RBC
plants,
(10) Raw and intermediate wastewater pump controls used in all plant
types and valves used in raw and intermediate pumps in trickling
filter plants,
161
-------
(11) Controls used in dosing siphon in secondary treatment in trickling
filter plants,
(12) Controls used in final clarifiers for all plant types, and
(13) Pumps, motors, power transmission and pressure vessels used in
disinfection for all plant types.
Having defined the data collection requirements, the next step involved
the selection of treatment plants having adequate records from which these
data could be collected.
Data Source Selection
The data source selection process involved the following tasks: develop
a list of candidate plants, select plants for one-day screening visits,
conduct the one-day visits, and select study plants.
A candidate list of approximately 200 treatment plants was developed
utilizing information from the U.S. EPA staff, equipment manufacturers
and sales representatives, SwRI and subcontractor contacts, treatment plant
operators and the literature. The criteria used to develop this list were
primarily (1) that the plants satisfied the plant type requirements (i.e.,
air or oxygen activated sludge, RBC, or trickling filter); (2) there was
an indication these plants would be willing to participate in the study;
and (3) maintenance records were available.
Using information about these plants, forty-two plants were selected
for direct contact by telephone. As a result, seventeen plants were
identified for further consideration. One-day screening visits were then
scheduled for each plant. The one-day visits were made to discuss the project
with plant personnel and verify the suitability of plant records for the
study.
Following the one-day visits, the treatment plants to be included in
the data acquisition effort were selected. Criteria used to make the
selection were as follows:
(1) Existence of adequate and complete preventative and corrective
maintenance records for all major equipment components at each
plant,
(2) Existence of plant equipment typical of the generic equipment
found in the four types of treatment plants under consideration,
and
(3) An indication that plant operations and maintenance personnel
were willing to cooperate in the data collection effort.
Data Acquisition
A schedule was developed for visiting the various plants.
162
-------
Upon arrival at each plant, the data collection team (engineer/operator
and engineering technician) met with the plant staff involved. This meeting
provided an opportunity for the data collection team to further explain
the project and discuss possible uses of the project results.
At this point, data collection was started. Maintenance records for
each critical component were reviewed. Data collection forms were used to
code all data. An example is shown in Figure 1. Required data elements
are shown at the top of this form. All data collected in the field were
encoded using a numbering system which was developed to allow analysis of
the data using a computer program. These codes are shown in the appropriate
columns in Figure 1. For example, column one contains the code number 04-
8731. The first two digits, 04, identify the plant location. The second
four digit number represents a record number used to identify that specific
piece of equipment. Column two, plant type, shows the number 05, which
identifies this plant as a combination air/oxygen activated sludge plant.
Codes for each of the remaining 23 columns are shown, with a description
of what each code means shown below the code. Column 23 was for recording
actual down time of sludge processing systems. Data for the sludge processing
systems at each facility visited were recorded as shown at the bottom of
Figure 1. These data allowed calculation of the mean time between failure
and availability of the system.
The data collection from plant records often required a degree of
judgment and interpretation. This was especially true when deciding when
equipment had actually failed. A failure was defined as when the mechanical
component no longer performed its intended function due to a failure of
that component's subcomponent(s). In contrast, an equipment malfunction
was defined as situations where the equipment could be placed back into
service by minor cleaning and/or adjustments. Only data for down time
considered to be caused by failure were recorded. Malfunctions including
pump blockages, reduction in blower capacities due to dirty air filters,
and plugging of air diffusers were not recorded. If interpretation of
maintenance records was questionable, the data collection team conferred
with plant maintenance staff to decide whether a failure had occurred.
Data Analysis
A computer program entitled "Wastewater Reliability Analysis
Program—WRAP" was written to handle the sorting and analysis of the data
base. Reliability, maintainability, maintenance and availability statistics
were calculated from the data base across all plants for:
(1) Components,
(2) Components by application,
(3) Components by size,
(4) Components by generic group,
(5) Components by generic group by application, and
163
-------
PLANT
LOCATION
4
J
^
;
£
5
"*
ll
b
S
;
|
7
ui
in
B
;
f
SB
a
£
j
5
u
IU
s
_J
Ul *
M •"
0 *
II
(J
£
a
Si
O- (_
u
Ul
5
4
13
w
:> UJ
i*
14
°£
-I r1
4 4
U U
IS
Ir
16
o
»• a:
17
f
t«
0 O
18
5
t
IB
19
s
fi
J
it
20
z
X
85
21
1
1!
22
U.
O
fl
2i
o
* -
£. a -
Its
24
g
O
Ul ...
_J .
d 5
>J 0
25
o
UJ
?
*~ IT
sl
O tt
WASTEWATER
04 - 8731
cc
" ED
O 2
Z 0
z
t-
5 t
a 3
05
w
Y.
u
4
Z Z,
93
1°
§1
03
Z
UJ
2
<
cc
4
SECOND
01
PUMPS
0114
cc
a.
cc
a
D X
a 4
03
a
|
a
. cc
5 4
[ INTERM
WASTE*
04
2
O
O
o
o"
o
023
-J £
« ?
CO
|| BEARIN
|| DOUBLE
01
4 K
2°
2 X
H *
1 EFFLUE
1 WITHIN
TREATMENT
0777
(*•
o>
D
99
o
o
01
cc
3
4
U.
00
*
z
0
z
EQUIPMENT
08
J
NORMA
04
V)
cc
o
i
CO
CM
03
cc
I
CM
in
K
X
1C
04
z
2
UJ
4
CC
0
02
o
UJ
o
REPLA
000
O
z
^-
o
z
006
en
CC
2
4
I
U
ALLIS
00
t
o
z
h-
o
z
02
Ul
o
4
Z
t-
z
4
2
Ul
p
u
CORRE
0879
01
t-
snonv |;
0008
V)
O
X
CO
SLUDGE PROCESSING EQUIPMENT
04 - 4321
* £
6 5
I
2
S t
J Z
a ^
05
w
u
p 0
COMBIN
AIR/ OX
10
cc
0
4
INCINER
0776
10
en
5
99
O
o
1 1
ILURES
4
u.
1584
TIME
HOURS
it
0879
o>
01
AUGUS
FIGURE 1. SAMPLE OF A FIELD DATA COLLECTION FORM
-------
(6) Components by generic group by size.
In addition, failure distribution information by subcomponent type
for the first four categories listed above were also calculated. Also,
reliability and availability statistics were calculated for sludge processes,
The statistics calculated from the data serve as the best summary of
the data base in terms of the reliability, maintainability, maintenance,
availability and subcomponent failure distribution parameters for the nine
wastewater treatment plants. This information should be useful to other
plant owners and operators, equipment manufacturers, and plant designers.
RESULTS
Component Performance Statistics
The performance statistics on critical components and sludge processes
which were calculated from the data gathered at nine wastewater treatment
plants are as follows:
Reliability Statistics—
Overall mean time between failures (Overall MTBF)
Maximum mean time between failures (Max MTBF)
Minimum mean time between failures (Min MTBF)
Lower limit 90% confidence level for the mean time between failure
point estimate (overall 90% CL)
Maintainability and Maintenanct Statistics—
Mean time to repair (MTXR)
Preventative maintenance man hours per unit per year (PM-HRS/
Unit/YR)
Corrective maintenance man hours per unit per year (CM-HRS/
Unit/YR)
Availability Statistics—
Inherent availability (AVI)
Operating availability (AVO)
Where AVI = MTBF . Total Hrs (TH) - TH Down Time (THU)=
MTBF + MTTR ' Total Hrs (TH)
These statistics have been grouped as follows:
(1) By component,
(2) By component by generic group,
(3) By component by application,
(4) By component by size/capacity,
(5) By component by generic group by application, and
(6) By component by generic group by size/capacity.
165
-------
TABLE 1. RELIABILITY AND MAINTENANCE DATA FOR PUMPS—OPEN
IMPELLER CENTRIFUGAL BY APPLICATION
Operating Overall Min. Max. Overall
Hrs MTBFl MTBF MTBF 90% CL PM-Hrs 2 CM-Hrs/3
No. of No. of (x 106 (x 106 (x 106 (x 106 (x 106 Unit/ Unit/ MTTR4 _
Application Units Failures Hra) Hrs) Hrs) Hrs) Hrs) Year Year (Hrs) AVI AV
o6
Raw Waste-
water Pumping 34 60
Intermediate
Wastewater
Pumping 9 9
Return Acti-
vated Sludge
Handling 27 28
TOTAL 70 97
.9277 .01530
.1669
1.0230
2.1176
.01727
.01303 .009442 .317900 8.483 .99400 .98450
.01175 .107900 .787100 6.667 .99960 .95480
.03569 - - .02835 .001745 .102800 6.786 .99980 .99980
.02166 .01530 .03569 .01911 .003428 .094773 7.825 .99962 .98955
3CM
4MTTR
5AVI
6AVO
«" Mean Time Between Failures
= Preventive Maintenance
= Corrective Maintenance
= Mean Time to Repair
= Inherent Availability
= Operating Availability
-------
An example of the type of reliability, maintainability, maintenance,
and availability statistics which were calculated from the data is shown
in Table 1, data for pumps by application.
Table 2 is an example of data on subcomponent failures by component
type.
Table 3 is an example of the "by component" grouping showing reli-
ability statistics for the eight components included in the data base,
across all plants.
TABLE 2. PUMPS—OPEN IMPELLER CENTRIFUGAL
Rank
1
2
3
4
5
No. of
Subcomponent Type Failures
Impeller Wear Ring or Plate
Seal, Packed, Water, Oil, Grease
Lubricated
Solenoid Valve
Bearing, Ball, Double Row
Bearing, Cast, Pillow
15
14
14
6
5
Relative
Frequency
.197
.184
.184
.079
.066
TABLE 3. MEAN TIME BETWEEN FAILURE (MTBF) FOR COMPONENTS
Component
Pumps
Power Transmissions
Motors
Compressors
Diffusers, air /water
Valves
Controls
Conveyor (unconfined
materials handling)
Overall
MTBF
(x 106 Hrs)
.032066
.035620
.066700
.007140
.018130
.014440
.083580
.148480
Min.
MTBF
(x 106 Hrs)
.021662
.017850
.010880
.005620
.012630
.008930
.003930
.061750
Max.
MTBF
(x 106 Hrs)
.074191
.710910
.114820
.083920
1.834000
.032590
.100640
.358560
Overall
90% CL
(x 106 Hrs)
.028630
.033170
.061220
.006310
.016670
.010400
.075690
.116900
Table 4 presents the maintainability, maintenance, and availability
statistics for eight components across all plants.
167
-------
TABLE 4. MAINTENANCE STATISTICS FOR COMPONENTS
Components
Pumps
Power Transmissions
Motors
Compressors
Diff users, air/water
Valves
Controls
Conveyor (unconfined
materials handling)
PM-Hrs/
Unit/Yr
.00227
.00032
.00098
.03399
.00065
.00684
.00025
.00055
CM-Hrs/
Unit/Yr
.05177
.00469
.00660
.17843
.04664
.73845
.00261
. 10086
MTTR
(Hrs)
9.541
2.273
6.854
0.960
8.305
11.615
3.696
4.768
AVI
.99968
.99994
.99989
.99987
.99951
.99879
.99996
.99996
AVO
.99116
.99898
.99816
.99306
.99875
.96446
.99870
.99980
Sludge Process Performance Statistics
As previously indicated, failure data for sludge processes were
collected at the nine treatment plants. Table 5 presents the results of
the data analysis for five processes.
TABLE 5. WWTP REPORT-RELIABILITY OF SLUDGE PROCESSES
Operating No. of
Hours Failures
Process (x 106 Hrs)
Sludge Process External
to WW Treat, Process
Anaerobic Digestion
Incineration
Sludge Thickening DAF
Vacuum Filter
.780 400
.678 40
.374 454
.406 702
.697 1150
MTBF
(x 106 Hrs)
.195
.167
.824
.577
.606
90% CL AVO
(x 106 Hrs)
.183
.137
.776
.550
.583
.997
.100
.723
.994
.931
CONCLUSIONS
Based upon the results of the performance data collection and analysis
effort conducted during this project, the following general conclusions
are made:
(1) Three types of performance statistics (reliability,
maintainability, and availability) have been determined for
selected critical mechanical components of wastewater treatment
plants.
168
-------
(2) These statistics were not available elsewhere in the literature,
from manufacturers or owners of equipment.
(3) These performance statistics can be used by design engineers as
a tool to (a) compare and predict performance of generic equipment
in various applications, and (b) design reliability into new
treatment plants.
(4) These data can be used by operators of wastewater treatment plants
to develop spare parts inventories for new equipment and establish
preventative maintenance programs.
(5) In spite of the significant number of operating hours included
in this study, this data base does not cover all the size ranges
or types of equipment found in the 20,000 treatment plants
operating in the U.S. Lacking are data for many small size range
components. It was found that these records are not routinely
kept by the smaller plants surveyed during this study.
(6) The quality of data obtained from the nine treatment plants was
good. The form of record keeping sometimes required judgments
as to appropriateness with respect to project data requirements.
(7) Effluent quality from wastewater treatment plants can be expected
to improve (to the extent that equipment failure causes decreases
in quality) over the long term by use of performance statistics
by design engineers and operators. Training will be required to
help these people know how to utilize such data. For example,
design engineers can utilize these data as an additional tool
to be used for the selection of equipment, determination of the
reliability and availability of unit operations as well as entire
treatment systems, and the prediction of operational performance
of equipment in various applications. Plant owners/operators
can utilize preventative and corrective maintenance data to help
refine overall future maintenance budget and staffing projections.
Knowledge of equipment failure rates and subcomponent failures
can provide input into determining spare parts inventories.
REFERENCES
1. Smith, J. M., F. L. Evans, and J. H. Bender. Improved Operation
and Maintenance Opportunities at Municipal Treatment Facilities.
Wastewater Research Division, MERL, EPA, Cincinnati, Ohio, 1980.
45 pp.
2. U.S. EPA, Clean Water Report to Congress, Washington, B.C., 1975-
1976.
3. Comptroller General of the United States. Continuing Need for
Operation and Maintenance of Municipal Waste Treatment Plants.
Report to Congress, Washington, D.C., CED-77-46, April 1977.
169
-------
4. Hegg, G.A., K.L. Rakness, and J.R. Schultz. Evaluation of
Operation and Maintenance Factors Limiting Municipal Wastewater
Treatment Plant Performance. EPA 600/2-79-034, NTIS No.
PB-300331/AS, June 1979.
5. Gray, A.C., P.E. Paul, and H.D. Roberts. Evaluation of Operation
and Maintenance Factors Limiting Biological Wastewater Treatment
Plant Performance. EPA 600/2-79-078, NTIS No. PB-80-108947,
July 1979.
6. Weston, R.F., Inc. Manual for Identification and Correction of
Typical Design Deficiencies at Municipal Wastewater Treatment
Facilities. Draft Report, Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, Cincinnati,
Ohio, October 1981.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
170
-------
PAPER NO. 11
FAIL SAFE DESIGN CONCEPTS
by
Roy 0. Ball, Ph.D., P.E.
Principal
ERM - North Central, Inc.
200 South Prospect Avenue
Park Ridge, Illinois 60068
171
-------
FAIL SAFE DESIGN CONCEPTS
Roy 0. Ball, Ph.D., P.E.
Principal
ERM-North Central, Inc.
The objective of this investigation on "fail safe" was to
evaluate the potential application of fail safe concepts to the
design and/or operation of POTW's.l If application of the
concept appears promising, then EPA would consider an expanded
R&D investigation of fail safe POTW design and operation.
The first question we had to answer in this investigation
is, "what is fail safe?" It is easier to say what fail safe is
not then what it is. The objective of investigating fail safe
operations is to improve POTW reliability without reliance on
sophisticated operation, mechanical redundancy, or elaborate
instrumentation. As you can see, the term fail safe is
different from that used in other fields. Based on the
exclusionary criteria above, there appear to be three major
concepts that can be considered fail safe: mechanical
interlock, mechanical simplicity, and latent energy.
Mechanical interlock are those processes in which
performing action A insures that action B is also performed,
generally through direct mechanical linkage. An example
(unrelated to POTW operation) is providing that the only key
that can lock a car is the ignition key. In POTW's, a simple
example is a center pivoted chute to divide waste sludge flow to
one of two tanks. If the chute is pivoted to one tank, it
necessarily excludes the other.
The second concept is mechanical simplicity, the ultimate
of which is no moving parts. Other speakers of this conference
are addressing the subject of mechanical reliability; that is,
extending the mean time between failures, failure being defined
as an operation that reduces the effluent quality from the
facility. Mechanical simplicity, for the purposes of fail safe,
is defined as being fewer failure modes of equal probability;
that is to say if the facilities in any two plants are compared
one to one, and one plant contains fewer items having equally
probable failure modes, then one plant is said to be more
mechanically simple compared to the other. A common example
would be a plant in which there is an influent lift station and
also a lift station between primary and secondary treatment.
Elimination of one of the lift stations provides a more
mechanically simple plant.
The third concept is that of latent energy. Four separate
categories of latent forces have been identified.
172
-------
The first is gravity, which would include hydraulic head
and density related phenomena.
The second latent energy source is electromagnetic
radiation which would include incident solar radiation.
Wherever there is a naturally generated source of
electromagnetic radiation, then there is an opportunity to
capture that radiation as a free energy source or, more
realistically, a reliable energy source.
The third type can be generally referred to as the
teleonomic behavior of bacteria and plants. By teleonomic, we
mean that for reasons of their own, bacteria and plants exist
and grow wherever it is possible to do so. By virture of their
existence and growth, they necessarily create gradients, and
thereby the opportunity for transport of materials and their
subsequent oxidation or alteration. Although we may provide
conditions where such bacteria or plants can flourish, we in
fact are not tampering with their intent or desire to grow,
reproduce, and multiply.
The fourth type of latent energy includes molecular forces
which would include such things as forces described by Hamaker
constants and viscosity.
Why are these fail safe operations attractive? In general,
they replace operation skills with maintenance skills and in
many conditions, it is more practical to provide consistent,
reliable maintenance than it is consistent, reliable operation.
The next step in this evaluation was to provide a list of
examples of fail safe operations that achieve certain
objectives. For example, if the objective is liquid/solid
separation, such devices as gravity sedimentation, swirl
concentrators (which trade inertia for separation energy), and
hydros ieves are processes which seem to embody one or more fail
safe principals. A fourth example is the enhancement of
coagulation and flocculation by ion addition.
Examples of fail safe operations which accomplish flow
regulation are side leaping weirs (frequently used in stormwater
management ) , proportional weirs (often used to control
velocities in grit chambers), siphons, and other hydraulic
structures.
In addition to defining fail safe devices, it was necessary
to determine the objectives of main stream treatment.
Approximately 35 objectives within five major categories; flow
control, pretreatment, primary treatment, secondary treatment,
and post-treatment were defined. As an example, secondary
treatment frequently consists of two parts: a bioreactor and a
clarifier. The objectives of the clarifier are fivefold:
173
-------
1. to remove particulate BOD;
2. to return biosolids to the reactor (with the objective
of reducing its size);
3. concentrate waste activated sludge;
4. store the concentrated waste activated sludge; and
5. remove suspended solids from the effluent stream.
Therefore, when we consider the application of fail safe
operations, we do not need to replace all five objectives
(conventionally achieved with some degree of success) of a
secondary clarifier with a single device. We can, rather,
improve or satisfy some of the objectives by fail safe means.
For example, two of the fail safe devices which were discussed
in this evaluation were in-channel clarification and porous wall
reactors. For in-channel aeration, the objective of returning
biosolids to the raactor is now achieved in a fail safe way, as
the solids are never removed in the first place. In the porous
wall reactors, several of the objectives are achieved. The
biosolids return is achieved because, again, they are never
removed from the reactor. In addition, because very high mixed
liquors can be maintained, the removal of particulate BOD and
the concentration and storage of waste activated sludge are also
accomplished using fail safe concepts. Due to the build-up of
microbial growth in the pores of the walls, the removal of TSS
from the effluent stream is also achieved with very high
efficiency. In fact, the reactors must be cycled to allow
digestion of this film or the head difference between the inside
of the reactor and the exterior will become too great.
In this investigation, therefore, we ended up with a matrix
which compared treatment objectives such as those described
above, with fail safe operations. In each block of the matrix,
the type of fail safe concept was identified; that is,
mechanical interlock, mechanical simplicity, or latent energy.
It was also indicated whether or not that operation was fully
applicable to that objective, inapplicable to that objective, or
partially applicable. Where it was partially applicable, it
could be either based on climate, topography (for example,
available hydraulic head) or other factors. It was also
indicated whether or not the fail safe operation could be
applied on both a new and a retrofitted basis or only new or
only retrofitted.
In summary, the major benefit of fail safe operations is
that they require maintenance and not operation. The major
problem with fail safe operations is that they require
maintenance and not operation. Once the fail safe devices are
installed, there is little active control, in many cases, that
174
-------
can be exerted. For these reasons, a fail safe installation
generally needs steady flow and good administration.
Where can fail safe be applied? Small plants without
fulltime operators would appear to be a natural application.
Also, remote sites where several plants are supervised by one
person would seem to be candidates. The Department of Defense
installations, which frequently have excellent maintenance but
transient operation, would appear to be another place where
these concepts can be applied. Because of the problems of
steady flows, it is possible that some of these concepts are
applicable at very large facilities as well.
In summary, as stated before, the objective of this study
was to. determine the potential for application of fail safe
principals to POTW's. Based on the review described above, we
believe that the potential is significant.
Presentation based on a study by Roy F. Weston, Inc. for
EPA MERL.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
175
-------
SESSION NO. 4
Improving POTW Design
PAPER NO. 12
DESIGN DEFICIENCIES IN POTWs
by
Roy 0. Ball, Ph.D., P.E.
Principal
ERM - North Central, Inc.
200 South Prospect Avenue
Park Ridge, Illinois 60068
176
-------
DESIGN DEFICIENCIES IN POTWs
Roy 0. Ball, Ph.D., P.E.
Principal
ERM-North Central, Inc.
So far in this symposium, you have heard a number of pre-
sentations describing EPA funded reports, all of which have the
objective of describing factors which can prevent POTWs from
proper operation and attaining their design effluent quality.
Bob Hegg has discussed his survey of facilities and identifi-
cation of any such factors. Kimm Perlin described factors
involved in the operation and maintenance of land treatment
facilities which can impact performance. Bob Crosby has
described his measurements of the flow and secondary clarifiers.
I presented a description of the report on side streams which
can, in some cases, have very serious effects on plant per-
formance. Professor Boyle has described biofouling of aerators.
Dave Schultz has discussed the mechanical reliability of
facilities and how to prevent treatment plant failures due to
mechanical problems. Ed Schroeder has provided statistical
information on the overall performance and reliability of
plants. With regard to new concepts for facilities or rather
the reapplications of old concepts, this morning I described
the fail safe feasibility investigation and Jon Bender discussed,
as part of the design information series, the effect of hydrau-
lic variation on treatment performance.
The design deficiencies report I wish to now describe is
a catalog of factors or actions that either did or did not
occur during the design process that could impact the perfor-
mance or operability of the POTW. The report is in 14 major
sections by process area. For each section, the deficiencies
are grouped as being either general, hydraulic, structural,
electrical, mechanical, or instrument related. The deficien-
cies each carry a number, and on the matrices at the front of
the report, it is possible to rapidly locate any particular
deficiency by using the matrix numbers as indicated in this
example. Alternatively, the operator designer can turn to the
section on a particular process and rapidly leaf through all of
the identified deficiencies of the mechanical type to insure
that his design has included and dealt with any such potential
problems.
I will now describe the organization and format of the
design deficiencies report in more detail. The report was
designed to facilitate the location of information concerning
typical design deficiencies found in various wastewater
treatment systems and, more specifically, individual unit
operations, and to reference the deficiencies noted with re-
lated solutions. The report is divided into two main sections:
177
-------
• Design Deficiencies Matrix
• Design Consideration and Correction Modules for POTWs.
Design deficiencies commonly found in the POTWs are cate-
gorized in a matrix format. The 15 categories utilized are
listed below:
Number Category
1.0 General Plant Design
2.0 Preliminary Treatment
3.0 Primary Treatment
4.0 Air Activated Sludge
5.0 Oxygen Activated Sludge
6.0 Trickling Filter
7.0 Disinfection
8.0 Anaerobic Digestion
9.0 Aerobic Digestion
10.0 Sludge Dewatering
11.0 Lagoons
12.0 Land Application
13.0 Sludge Disposal
14.0 Sludge Reduction
15.0 Rotating Biological Contactors
The deficiencies within each category are further grouped
according to type and then numerically referenced to unit opera-
tions and components specific to the category. The deficiency
groups used include:
• Layout, Arrangement, and Placement of Components in
Design of Plant.
• Hydraulic Design Considerations.
• Mechanical Design Considerations.
• Electrical/Instrumentation Design Considerations.
• Safety Considerations.
• Environmental Considerations.
The design deficiencies listed in the matrix are discussed
in "Design Consideration Modules" in terms of items that should
be reviewed by the engineer furing design of a new or expansion
of an existing wastewater treatment plant. Features of the
module format are as follows:
• The report section, design consideration category, and
applicable unit operation or component are indicated in
178
-------
the upper left-hand corner.
• A treatment plant block flow diagram is presented
in the upper right-hand corner. The deficiency cate-
gory represented by the module is shaded to allow the
reader to visually identify the portion of the plant
discussed.
• The design deficiencies, including reference number
and description, are presented in a column on the left
side of the page and the associated design considera-
tion discussed in a column opposite the deficiency.
• The reference numbers for the deficiencies discussed
in each module are summarized at the bottom of the
page. This facilitates locating specific deficien-
cies when referring to the modules.
• The modules are sequentially numbered for cross-refer-
encing with the module table of contents.
Suggested methods to correct the design deficiencies,
when already present at an existing wastewater treatment
facility, are presented in the document. The correction pro-
cedure, where applicable, includes the following items:
• Method.
• Materials.
• Cost.
• Sketch.
The format of the document allows the reader the flexi-
bility to obtain information either through the deficiency
matrix or the design consideration/correction modules. A POTW
operator experiencing a specific problem at his plant should
first refer to the deficiency matrix in order to identify the
appropriate module(s) that describes methods that can be used
to correct the problem. On the other hand, an engineer may
wish to proceed directly to the design consideration modules
in order to identify those items he should review during de-
sign of a specific unit operation or component.
The correct procedure for using the design deficiency
matrix is as follows (see Figure I for illustration):
1. Select the appropriate matrix category (i.e., pre-
liminary, primary, activated sludge, etc.) and
refer to that section of the matrix.
2. Determine which deficiency group (i.e., mechanical,
hydraulic, safety, etc.) the problem falls under
and turn to that portion of the matrix.
179
-------
3. Identify the applicable unit operation or component
and move down that column until the desired defi-
ciency is located. (NOTE: If the deficiency is not
listed, refer to the deficiency list and determine
if it is listed under another unit operation.)
4. Use the three digit deficiency reference number to
identify the related deficiency/correction module as
follows:
1st Digit — Category Number
2nd Digit — Unit Operation/Component
number (i.e., column number)
3rd Digit -- Deficiency Number
5. Turn to the deficiency/correction module that has
has the same category and unit operation/component
number.
6. Read down the left-hand column to the applicable
deficiency reference number.
7. The suggested correction method is described in the
opposite right-hand column.
8. Related considerations aimed toward preventing the
deficiencies during design are also discussed in
the opposite right-hand column.
In many examples, the deficiency correction at existing
POTWs was a reiteration of the design consideration. To
avoid repetition, only the design consideration is presented.
All the deficiencies described in this report seem to
persist in the design field. Perhaps the reason is that the
person who performs the conceptual design of the plant, al-
though he may have in mind many of these difficulties, does
not fully communicate his concerns to the people preparing
the plans and specifications. Frequently, too, the plans
and specifications are not reviewed by someone knowledgeable
and experienced in the operation and maintenance of treatment
plant facilities. Also, if there are such deficiencies, many
times they are of a positional nature and may not be readily
corrected without redoing much of the final design. Whatever
the reason, it appears that few, if any, firms have attempted
to make such a comprehensive catalog of problems that can
occur. The intent of this catalog is not to substitute our
judgment or discretion for the designers, but rather to pro-
vide an indication of problems that have arisen at other treat-
ment facilities and have been considered serious enough to
180
-------
impact the performance or operability of the facility.
At this point, I would like to ask members of the audience
to provide us with examples of design deficiencies that they
have noted. For my part, I will point out whether or not
these are included in the catalog or what other allied defi-
ciencies are also included, if any.
Based on the degree of participation here, it is evident
that this subject is of some general interest to members of
our profession. It is EPA's hope, and mine, that this docu-
ment will serve as a valuable starting point for the contin-
ued cataloging of such deficiencies, with the ultimate objec-
tive of improving the operability and reliability of POTWs.
DEFICIENCY
Lack of hoists over larger pieces of equip-
ment -
Lack of spare pumps.
Lack of walkways around tanks, limiting
operator access.
Tal 1 above-ground tanks frequently require
operator to climb long stairways.
No prov Islons for moving equi pment and
suppl les from one bul Idlng floor to another.
Ol 2
i
_, \5
2 1 V:
UJ I LJ
z 1 dj
UJ A
1
2
3
Ox
*
\
1
\
3
^
a:
3;
ac
Q.
\
\
\
\
\
\
k
o:
0
o
o
LU
LO
1
1 ,
y
(
5
CJ
Ul —
O 0
:D z
in 3:
I
b
O
UJ t~
O UJ
w a
y
/
/
7
<4
UJ Ul
J*a
I
2
8/
/I
t-
s
UJ Ul
O —
^ O
—I Z
,/, -
7a - GENERAL PLANT DESIGN
9
-j
UJ tn
0 Q-
(/> O
10
z
o
K-
O
UJ
u.
o
1 1
en
Z
o
o
<
_J
12
z
o
h-
O
Q -J
Z O-
I) <
13
UJ
3
O
Q-
— 1 Z
;£ I
W> tt.
1
2
3
ft
Z
O
<
> QC
CC VI
UJ Z
z o
UJ O
15
o:
o
i—
3
O
CO
Deficiency Reference Number is:
FIGURE 1
Presentation based on an investigation and report
by Roy F. Weston, Inc. for EPA MERL
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
181
-------
PAPER NO. 13
PERFORMANCE CAPABILITIES AND DESIGN
OF OXIDATION DITCH PROCESSES
by
William F. Ettlich
Vice President
Culp/Wesner/Culp
El Dorado Hill, California 95630
182
-------
PERFORMANCE CAPABILITIES AND DESIGN OF OXIDATION DITCH PROCESSES
William F. Ettlich, Vice President
Gulp/Wesner/Gulp
DESIGN FEATURES OF OXIDATION DITCH PLANTS
An oxidation ditch plant is typically an extended aeration type of
activated sludge process that uses a continuously recirculating closed loop
channel or channels as an aeration basin. The aeration basin is normally
sized for a 24-hour hydraulic retention time, but may be designed for any
other detention time. Mechanical aerators are commonly used for mixing,
oxygen supply, and for circulation of mixed liquor. Generally, these are
horizontal brush, cage, or disc-type aerators designed specifically for
oxidation ditch plants. Secondary clarifiers similar to those used in
other activated sludge processes are normally provided. Primary clarifica-
tion is not usually included in oxidation ditch plant design.
The typical oxidation ditch aeration basin is a single channel or
multiple interconnected concentric channels. An oxidation ditch plant
normally consists of one or more basins of either type operated in parallel
depending on the flow and operation mode required. Channel geometry can
vary to include many possible configurations, however, the single oval
configuration is the most common. The multiple concentric channel basin
can have any number of interconnected channels with three to five being
typical and provides some process flexibility since it can be changed to
other activated sludge modes with minor modification. Typically, the outer
channel is used for aerobic digestion of the waste activated sludge. Shallow
channels are typically four to six feet deep with 45 degree sloping side
walls. Deep channels have vertical side walls and are normally 10-12 feet
deep. The channels are usually lined to prevent erosion and leakage. Ditch
lining can be reinforced concrete, gunite, asphalt, or thin membranes.
Typically, shallow channels with sloped side walls are constructed of con-
crete poured against earth backing with welded wire mesh reinforcing. Deep
vertical wall channels require reinforced concrete walls.
Several manufacturers supply oxidation ditch brush or disc type
mechanical aerators. These units may be either fixed or floating. The
aerators normally span the channel width and may be installed in one or
more locations around the channel. The aerators must supply the required
oxygen to the channel and impart a sufficient velocity in the channel
(>1.0 FPS) to keep the channel contents in suspension. Oxygen transfer
capabilities of an aerator will vary depending on the particular design,
rotational speed and submergence. Most units operate in the range of 60 RPM
to 110 RPM with a submergence of 2 to 12 inches and produce oxygen transfer
rates of from 3 to 5 Ibs of oxygen per hour. The number of aerators pro-
vided depends on the size, configuration and oxygen requirements of the
plant. A minimum of two aerators should be installed so that at least
partial aeration can be maintained with one unit out of service.
183
-------
There are many available configurations of plants and aerators and it
is recommended that care be taken to select the most energy efficient con-
figuration because aerator energy is a major operating expense for oxidation
ditch plants. There should be little actual difference between manufacturers
aerator power requirements for given size plants.
The real problems (and differences) in rotor configurations are mechani-
cal; the drive unit, line bearings, seals, aerator torque tube, materials of
construction and similar considerations. These are the features that will
have the greatest impact on long term operation and maintenance of the plant.
The mechanical features should receive careful consideration in design
and preparation of specifications. Most of the bearings associated with
aerators are of the ball or roller type; grease lubricated with seals.
Therefore, bearings and drive units should be protected from splashing water
both to keep the water off and to provide convenient access for maintenance
personnel. Extension of bearing grease fittings up to convenient locations
on catwalks or easily accessible locations will certainly contribute to more
satisfactory maintenance. Means for field alignment of bearings should be
provided and bearings should be carefully aligned prior to operation. The
bearing supports for horizontal aerators may be up to 30 feet apart and
differential settling with eventual loss of alignment may occur if this is
not considered in the structural design of the aerator support foundation.
Generally, bearings with some self alignment capability will provide more
satisfactory long term service, but this feature does not reduce the need
for proper structural design and initial alignment.
Some means must be provided for removal of the aerator; either a per-
manently installed lifting mechanism, a portable lifting mechanism, or
access for mobile lifting equipment.
Many problems were caused by the aerator "slinging" mixed liquor onto
adjacent structures and onto aerator bearings, couplings, seals, and drive
units. Most aerators have "slingers" at each end, but they only compound
the problem when the wind is blowing as liquid flying off the "slinger" is
blown by the wind. Mixed liquor which lands on adjacent walkways causes
ice formation when it is cold and algal growths cause slippery conditions
at other times. Bearings and drive units should be adequately shielded from
the inevitable liquid spray.
The long narrow aeration channel of the oxidation ditch plant provides
a complete mix activated sludge process. Even though a plug flow mode would
seem to be applicable, the minimum velocity of 1.0 fps results in a cycle
time of less than 15 minutes in the longest channels used. Compared to the
typical 8 to 24 hour detention time design, the channel circuit time becomes
insignificant. Therefore, the oxidation ditch may be considered a completely
mixed activated sludge process (CMAS) with respect to organic load. It is
not completely mixed with respect to dissolved oxygen profile because this
profile can vary significantly around the channel and vertically within the
channel. The mixed liquor can pass through varying oxygen rich or deficient
zones as it passes around the channel.
184
-------
The procedure for design of an oxidation ditch plant is basically the
same as used for an extended aeration process with emphasis given to the
hydraulic considerations imposed by the basin geometry. The manufacturers
can provide assistance in design for specific applications.
Some low alkalinity wastewaters may require pH adjustment when subjected
to extended aeration because of nitrification.
Oxidation ditch plants are designed for long sludge retention times
and nitrification will occur if sufficient oxygen is provided. Usually, suf-
ficient oxygen should be provided for complete nitrification in addition to
satisfying the carbonaceous BOD requirements. Complete mix activated sludge
plant design procedures have been described by McKinney(l), Eckenfelder^),
and Monod'-^, and presented in a unified model by Goodman(^,5) . j{- ^_s
frivolous and time consuming to compare the nuances of these various models;
proper use of any of these models results in sufficiently accurate results
for design purposes.
Screening seems to be the single most important pretreatment step. If
rags, boards, and other similar objects are not removed prior to the ditch
they will cause trouble with the aerators and will, in most cases, plug
sludge control valves (telescoping valves), sludge lines, sludge pumps, and
weirs. Few problems have been observed or reported directly related to
inadequate grit removal although it is certain that this grit accumulates in
the ditch and will have to be removed at some time.
Generally, final clarifier design is consistent with other activated
sludge processes. A surface overflow rate of 400 to 500 gpd/sq ft is recom-
mended for average daily flows and 1,000 to 1,200 gpd/sq ft at peak flows.
Many plants are constructed with 8 foot deep clarifiers, but depths of 10
to 14 feet provide greater process reliability.
Any biological plant design must consider the quantity of sludge pro-
duced, the nature and stability of the sludge, and suitable disposal pro-
cedures. An oxidation ditch plant, operated in the extended aeration mode,
has certain inherent advantages relative to sludge handling and disposal.
Oxidation ditch plants can be operated at a 20 to 30 day SRT resulting in a
sludge having characteristics similar to a well stabilized aerobically
digested sludge. A conventional activated sludge plant operated at a 4 to
10 day SRT will produce a sludge with high residual biodegradable organic
content. If placed on drying beds or on the land, it will become odorous
and objectionable. Aerobic digestion of this sludge for 7 to 15 days is
normally required to produce a stable product suitable for disposal on
drying beds or the land. For a properly operated conventional activated
sludge plant plus aerobic digestion the total SRT prior to disposal will be
15 to 20 days. In effect, the oxidation ditch extended aeration process
provides sludge stabilization equivalent to conventional activated sludge
plus aerobic digestion.
In most oxidation ditch plants where the extended aeration process is
used (16 to 24 hours aeration detention) sludge is wasted directly to open
185
-------
drying beds. In a few cases sludge is wasted directly to tank trucks which
spread the liquid sludge on the plant grounds or on adjacent land. Field
inspections of oxidation ditch plants revealed no odor problems at plants
using either method. The field inspections consistently confirmed the lack
of odor problems with sludge from the extended aeration oxidation ditch
plants. Several plants complained of insufficient drying bed capacity
because of poor dewaterability especially during periods of cold or wet
weather. Adequate drying bed capacity must be considered carefully in design.
Some design engineers and regulatory authorities may require additional
sludge stabilization for oxidation ditch plants operated in the extended
aeration mode. Part of the consideration may be the possibility of periodic
poor operation of the process. Also, future flow increases may force opera-
tion of the plant at shorter SRT's to the point where additional sludge
stabilization is required.
The quantity of sludge produced is related to the characteristics of
the incoming wastewater solids. Normally, wastewater solids contain frac-
tions that are inert, volatile and nonbiodegradable, and volatile and bio-
degradable. The inert (nonvolatile) and volatile/nonbiodegradable fractions
will accumulate in the system solids inventory in proportion to the SRT.
Normally 20 to 25 percent of the raw waste suspended solids are inert. The
remaining 75 to 80 percent are volatile solids with, typically, 30 to 40 per-
cent nonbiodegradable. Therefore, about half of the incoming suspended
solids are not subject to biological action and will accumulate in the mixed
liquor in proportion to the SRT. Proper sludge wasting is absolutely neces-
sary in extended aeration plants as with conventional activated sludge plants
or the excess solids will be automatically wasted periodically in the
secondary clarifier effluent.
COMPARATIVE PERFORMANCE & RELIABILITY
Performance and reliability data for oxidation ditch plants were
developed from actual plant operating records, obtained from published
literature, telephone and letter contact with operating plants, visits to
operating plants, EPA records, special studies, and engineer's files. There
were very few plants where complete data could be obtained for all desired
parameters. In addition, reliance had to be placed on the sampling and
analysis methods used by various plant personnel. It is recognized that these
procedures are not consistent from plant to plant and therefore, not always
directly comparable. Nevertheless, the results represent the data as obtained
without modification. Inordinately high or low readings were not removed
from the data during compilation because most plants experience these varia-
tions at one time or another. It is felt that these variations do occur in
oxidation ditch plants as in most other activated sludge plants.
Oxidation ditch plant performance was developed primarily from monthly
average data. Generally, the data from a plant were not used unless several
data points were available. Plant daily performance data, when available,
were converted to monthly averages, which were then analyzed for each plant.
186
-------
Where possible, the performance is calculated for both summer and
winter. Winter is arbitrarily determined to be the months of November
through March. The "average" performance was determined by averaging the
performance of all of the individual plants. The high and low individual
plant performance is shown to establish the range limits of individual plants.
Based on an analysis of available data it was found that both BOD5 and
suspended solids removal appear to be relatively independent of plant
capacity.
Performance data from 29 oxidation ditch plants from various United
States and Canadian locations are summarized as follows:
SUMMARY PERFORMANCE OF 29 OXIDATION DITCH PLANTS
Effluent, mg/L
Removal
BOD
High plant
Average
Low plant
Suspended solids
High plant
Average
Low plant
Winter
55
15.2
1.9
26.6
13.6
3.1
Summer
34
11.2
1.0
19.4
9.3
1.9
Average
annual
41
.12.3
1.5
22.4
10.5
2.4
Winter Summer
37
92
99
81
93
98
86
94
99
82
94
98
Average
annual
87
93
99
82
94
98
The performance of competing biological treatment processes was also
evaluated and the data are summarized as follows:
PERFORMANCE - COMPETING BIOLOGICAL PROCESSES
Activated sludge
(1.0 mgd)
Activated sludge
(Package Plants)
Trickling filters
Rotating biological
contactor
Effluent, mg/L
TSS
31
28
26
23
26
18
42
25
Removal, %
TSS BOD5
81
82
79
84
79
78
Analysis of data from 12 operating oxidation ditch plants showed the
reliability for meeting various BOD5 and TSS effluent standards as follows:
187
-------
RELIABILITY - OXIDATION DITCH PLANTS
% of time effluent concentration (mg/L) less than
10 mg/L 20 mg/L 30 mg/L
TSS 8005 TSS 6005 TSS 6005
Best plant 99 99 99 99 99 99
Average all
plants 65 65 85 90 94 96
Worst plant 25 20 55 55 80 72
Of the plants analyzed, the effluent BOD^ and TSS seldom exceeded a
maximum of 60 mg/L.
The reliability of competing biological treatment processes was
evaluated on the same basis and is summarized as follows:
AVERAGE RELIABILITY - COMPETING BIOLOGICAL PROCESSES
% of time effluent concentration (mg/L) less than
10 mg/L 20 mg/L 30 mg/L
TSS BOD5 TSS BOD5 TSS BOD5
Activated sludge
(1.0 mgd) 40 25 75 70 90 85
Activated sludge
(Package Plants) 15 39 35 65 50 80
Trickling filters - 2 - 3-15
Rotating biological
contactor 22 30 45 60 70 90
An oxidation ditch plant is capable of 95% to 99% nitrification without
design modifications. This high degree of nitrification even at wastewater
temperatures approaching 0°C is possible due to the 24-hour hydraulic reten-
tion time in the channel(s) and the capability of operating at a high solids
retention time (SRT) of 10 to greater than 50 days.
Nitrogen removal by single-stage biological nitrification-denitrifica-
tion has also been achieved at properly designed and well operated oxida-
tion ditch plants. Nitrogen removal is achieved by producing both aerobic
and anoxic zones within the same channel. These zones are created by
controlling the aerator oxygen transfer rate so that mixed liquor dissolved
oxygen is depleted within a portion of the aeration channel.
The carbon source for the anoxic zone (denitrification) is provided by
feeding the raw sewage into the channel upstream of the anoxic zone. With
careful operation, 80% nitrogen removal has been achieved in a single
channel oxidation ditch plant.
188
-------
OXIDATION DITCH PLANT OPERATION
As a group, oxidation ditch plants appear to perform consistently well
in spite of limited operation and maintenance in a number of cases. All
plants visited appeared to have adequate aeration capacity, adequate
velocity in the ditch, an acceptable mixed liquor and a lack of odor or
other nuisance. In general, the operators were able to obtain good treat-
ment results in almost all cases. Sludge handling and disposal was
relatively simple and trouble free, however, in some cases operators re-
ported difficulties in dewatering the sludges on open drying beds due to
lack of proper bed area or due to slow dewatering of the sludge. The plants
were easy to keep in service and would operate for long periods of time
with very little operation and maintenance. Many plants operated for periods
of time unattended (evenings and weekends) without significant problems.
No particular type of oxidation ditch plant seemed to stand out as superior
or substandard; the relative performance depended on many more factors such
as original design criteria (clarifier surface overflow rate for instance)
and operational procedures. There are some exceptions to these comments
and a few oxidation ditch plants have been removed from service because of
operational problems. These cases are the exception.
The most serious process operation difficulties resulted from equip-
ment related problems.
Many of the plants visited were manned only during a single shift and,
in many cases, for only a portion of a single shift. A number of plants
received little or no attention during weekends. Assuming no mechanical
malfunctions, the plants perform well for long periods (days to weeks at
a time) with little or no operator attention. Most plants practiced regular
or periodic sludge wasting. In some cases sludge wasting was not practiced,
but this caused eventual or regular carryover of excess solids in the
effluent.
Almost without exception, operators and administrative personnel were
well satisfied with the plants. In most cases the plants were meeting state
discharge requirements.
A study of EPA Region VII of winter performance of secondary waste-
water treatment facilities concluded "...in general, the facilities were
not meeting the secondary treatment effluent definition on the average
except for the oxidation ditch subset".
All plants visited exhibited good mixed liquor characteristics (by
visual observations). Some plants reported more than desired carryover of
solids in the effluent and it is believed that the cause was either ex-
cessive oxygenation of poor management of sludge return wasting.
Many plants could reduce the level of oxygenation in the aeration basin
without detrimental effect and reduce energy cost. There were no signs of
lack of oxygen. One plant was cycling the aerator one hour on and one hour
off and reported excellent results for over a year. Several other plants
189
-------
were considering this scheme to lower operating costs and reduce oxygen
levels.
When screening or comminution is not regularly and properly carried
out, rags and debris tend to cause problems in the plant expecially in the
return sludge system.
One deep type (10 feet) single channel plant reported poor mixing in
the ditch.
A number of plants lacked sufficient drying bed capacity which may
have led to erratic sludge wasting practices. This problem was also re-
ported by EPA Region VIII personnel.
A number of plants lacked proper laboratory facilities and equipment.
Some even lacked a building. These facilities are necessary for proper
operation and maintenance of a wastewater treatment plant.
As with any plant containing mechanical equipment, oxidation ditch
plant equipment was subject to problems, malfunctions, and failures. As
a general observation, oxidation ditch plants are capable of long periods
of operation without mechanical problems and appear to operate with a very
high mean time between equipment failures, particularly with proper pre-
ventative maintenance and inspection programs.
The following is a general summary of mechanical problems as related
by plant personnel.
1. Some plant personnel reported that drives trip out on momentary
electrical failures and do not restart upon restoration of power.
This causes problems with unattended operation and consideration
should be given to maintained-contact type electrical control
for drives such as lift pumps, aerators, sludge return pumps,
and other items in cases where plants operate unattended. Time
delays can be provided so all drives do not restart at the same
time.
2. Some troubles were reported with return sludge pumping. In
general, centrifugal, non-clog pumps seemed to give good service
especially when a separate potable grade seal water source was
used. Air lift pumps were not common as would be expected at
plants with mechanical aeration. A number of plants returned
sludge by gravity to the raw sewage lift station and pumped it
to the ditch with the raw sewage. This increased the size of
the lift pumps, but eliminated one set of pumping.
3. Comminutors were a continuing maintenance problem. They required
regular cleaning and care. Some operators had so many problems
they stopped using the comminutor and allowed unscreened sewage
to flow into the ditch. Almost without exception this caused
problems in the return sludge system by clogging the sludge
return rate adjustment valve (generally a telescoping valve)
190
-------
or pumps. This altered the sludge return rate and caused process
problems if not detected early. Oscillating type comminutors
appear to give best service, but still require regular maintenance.
4. Access walks should be designed to avoid receiving spray from
aerators even under various wind conditions. This spray creates
hazardous conditions because of algal growths and freezing.
This oversight created continuing maintenance problems and
should be considered in all designs.
5. Sludge reportedly settled in channels at some plants where flow
control walls were not installed as recommended by manufacturers.
6. There are some reported corrosion in final clarifiers which re-
sulted in materials failures (bolts in particular). These units
should be drained and inspected annually. Any corrosion should
be removed and the area recoated.
7. Weirs are a maintenance problem and must be cleaned frequently;
in some cases as often as daily.
8. Aerators and aerator drives account for a major portion of the
mechanical problems. Most plants experienced the following
aerator related problems every two to five years per aerator unit.
a. Loss of some "teeth" from brush type aerators due to cor-
rosion of bolts or damage sustained while handling the
aerators is a common occurance. This generally is not a
serious problem and can be repaired during periodic shut-
downs. Some manufacturers have redesigned their aerators to
minimize this problem.
b. Bearing problems were reported in gear drives, line shafts,
and aerator shafts. Experience whould seem to indicate a
bearing problem every 2 to 5 years per aerator. These
problems result from poor selection of bearings, constant
splashing of water onto the bearing, improper initial align-
ment, differential settlement of bearing support structures
and similar problems. Some manufacturers have taken steps
to reduce bearing problems by using self aligning bearings,
double seals, and by providing water shields, but bearing
problems can still be expected. The magnitude of the bear-
ing problem is not excessive and normal plant maintenance
programs can handle this problem.
c. Flexible couplings between line shafts caused problems on
multiple concentric ring type plants.
d. At one plant some of the disc aerators loosened from the
shaft and had to be shimmed and reclamped.
191
-------
e. Gear reducer output shaft seals need replacing about once a
year at some plants.
f. There are a number of plants where gear reducer failure was
experienced within a year of plant startup. This was
probably due to improper initial alignment or differential
settling of the aerator support structure.
g. A couple of plants have experienced aerator torque tube
failure or excessive deflection with very long aerators. At
one plant the tube failed, collapsing in the middle. One
consultant not requires solid shafts on all aerators rather
than hollow torque tubes. It may be well to avoid the use
of very long aerators. If a wide ditch is necessary, the
, width can be spanned using two shorter aerators driven by
a common drive.
h. Protective covers around bearings, couplings and drive units
are not provided at most installations. Spray from the
aerators keeps these components wet and possibly contributes
to short life. The "slingers" at each end of the aerator
are ineffective because wind blows this "tail" of water
sideways onto adjacent components such as bearing and drive
units. Corrosion and grit on shafts probably contributes
to short seal life. For maximum service life and minimum
maintenance these components should be shielded from water
spray. Some manufacturers are taking steps to modify their
standard designs to provide spray baffles and shields.
i. Some drive configurations require the aerator to be lifted
out of position to remove the gear drive. This is a diffi-
cult operation requiring a crane. Access for a mobile crane
should be provided to all aerators or other lifting pro-
visions designed into the plant.
Cold weather problems related to oxidation ditch plants appear to be
minimal except in severe climates. Those which have been identified are
listed. These comments are based on visits and literature.
1. Final clarifiers should be covered where this is typical practice
for other types of plants.
2. In moderately cold areas the spray from aerators will freeze on
adjacent structures, bearings, gear reducers, and like equipment
making maintenance difficult. Drive components should be covered
to provide shielding from spray or these drives mounted in
isolated compartments.
3. In moderately cold areas some problems were reported from ice
build-up on clarifier scum collection boxes and eventual jamming
of skimmer mechanisms.
192
-------
4. Problems were reported with freezing of spray around aerators.
The problem is solved by covering aerators in moderately cold
areas, providing heated covers in very cold areas, and providing
heated buildings over the aerators or over the whole ditch in
extremely cold areas. When installed inside buildings, a shield
should be provided over aerators to control spray.
5. In areas with periods of very cold weather all equipment requir-
ing regular maintenance or service should be housed.
6. Poor mixed liquor settling was experienced during winter months
at several plants in cold weather locations. This was probably
due to filamentous growths resulting from the low winter loadings.
Waste activated sludge handling requirements depend on the plant de-
sign and operation. Plants operated with a 24-hour channel hydraulic
retention time at 20 to 30 day SRT produce a biologically stable waste
sludge that can be handled without causing significant odor problems.
Plants operated with 6 to 8 hour channel hydraulic retention time and less
than 10 day SRT require additional sludge treatment, typically aerobic
digestion. Some problems have been noted in dewatering activated sludge
directly on sand beds from plants operated at a 24-hour hydraulic retention
time. These sludges tend to dewater very slowly requiring significantly
increased sludge drying bed area. In areas where wet and cold weather are
common, sludge drying bed area should be even larger. Some plants are
operated indefinitely without formal sludge wasting allowing solids to build
up in the aeration channel. This type of operation is considered marginal
because the plant is prone to periodic clarifier upsets resulting in high
final effluent solids.
CONCLUSIONS
Oxidation ditch plants are capable of consistently achieving high
levels of BOD,- and TSS removals with minimum operation. High levels of
nitrification (95%-99%) are possible with proper operation. Nitrogen
removals as high as 80% can be achieved in a single channel plant with
careful operation of the aeration equipment to produce aerobic and anoxic
zones within the channel. Increased operator attention is required to
produce the high levels of nitrogen removal.
193
-------
REFERENCES
1. McKinney, R.E. Mathematics of Complete Mixing Activated Sludge.
Trans. Amer. Soc. Civil Eng. , 128, Part III, Paper No. 3516 (1963).
2. Eckenfelder, W.W., Jr.; O'Connor, D.J. Biological Waste Treatment.
Pergamon Press, Oxford, England (1961).
3. Monod, J. Research on Growth of Bacertia Cultures. Herman et Cie
Paris (1942).
4. Goodman, B.L.; Englande, A.J. A Unified Model of the Activated
Sludge Process. Journal Water Pollution Control Federation, 46, 2,
p. 312, February, 1974.
5. Goodman, B.L. Monod Type Relationships Applied to Complete Mixing
Activated Sludge. Unpublished, January 25, 1973.
6. Draft Report. Winter Performance of Secondary Wastewater Treatment
Facilities. EPA Region VII.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
194
-------
PAPER NO. 14
PERFORMANCE AND DESIGN OF RBC PROCESSES
by
Warren H. Chesner
Partner
Engineering Consultants & Associates
Fort Lee, New Jersey 07024
195
-------
PERFORMANCE AND DESIGN OF RBC PROCESSES1
Warren H. Chesner, Partner
Engineering Consultants & Associates
Fort Lee, New Jersey
INTRODUCTION
Rotating Biological Contactor (RBC) Systems have been in operation in
this country treating municipal wastewaters for more than ten years. Over
260 municipal wastewater installations were in operation as of 1979 with
design flowrates ranging from 0.01 mgd to 5^* mgd.
RBC performance in terms of treatment efficiency, power requirements
and equipment have been almost exclusively defined by equipment vendors.
Vendors have provided design curves for both carbonaceous and nitrogenous
removal, recommendations for stagina and flow distribution, projected power
consumption and media, shaft and drive requirements.
During the operating history of RBC's in this country, additional in-
formation has become available through the literature and through the
collection of plant data from which to evaluate RBC performance and design.
This historical record has revealed relevant information which should as-
sist the designer, operator and vendor in evaluating, designing and opera-
ting RBC systems.
CARBONACEOUS BOD PROCESS PERFORMANCE AND DESIGN
A comparison of cumulative performance versus vendor design guidelines
for sixteen RBC facilities approaching design flow revealed that RBC per-
formance was less than that predicted by vendor design recommendation for
average influent municipal wastewater concentrations ranging from 97 to
21^ mg/1 BOD, with hydraulic loadings in the range of approximately 0.5 to
3.0 gpd/sf (1).
1. The absolute value of the vendor curves are based
upon field data accumulated at specific locations
which may not reflect RBC performance elsewhere.
2. Plant performance is the result of a series of
unit processes. Poor secondary clarifier per-
formance would adversely effect recorded RBC
performance.
3. Operation and maintenance practices at specific
plants influence overall plant performance
which would reflect upon RBC performance.
1 Presentation based on a study by Roy F. Weston, Inc. for EPA MERL.
196
-------
Some of the specific process problems the facilities encountered were
the result of one or more of the following:
1. Unanticipated sidestream loadings
2. Low influent concentrations
3. High organic loadings
Unanticipated sidestream loadings such as return supernatant from
sludge treatment processes or septage disposal can result in organic over-
loads to the RBC system. These can be corrected by planning for the addi-
tional load by either increasing the RBC treatment capacity or better
equalizing the sidestream flow to the system.
Low influent concentrations (less than 100 mg/1 raw BOD) are common in
sewerage systems with inflow/infiltration problems. Lower organic concen-
trations with altered wastewater characteristics and treatability result
in reduced performance. The solution to these problems again rests with
proper facility planning with respect to anticipated wastewater conditions.
High organic overloads is a problem resulting from oxygen deficiency
within the biofilm. This condition can result in the competitive growth
of nuisance organisms and reduced organic removal rates. The condition
which results in an organic overload is dependent upon many factors. For
a given media, these include rotational speed, influent flow distribution,
organic concentration, and flowrate.
Rotational speed influences the film thickness, the aeration of the
reactor liquid as well as the residence time per rotational cycle that the
biofilm is exposed to thp atmosphere and the reactor liquid. Too slow a
speed can result in excessive residence time in the liquid, with little
oxygen ava i1able.
Proper influent flow distribution is necessary to evenly distribute
the influent flow and loading to all parts of the media, and to avoid over-
loading individual shafts or portions or shafts.
Organic concentration and flowrate jointly determine the organic load.
Individually organic concentration determines the mass transfer driving
force, and flowrate the reactor or treatment retention time. The greater
the organic concentration, the greater the demand for oxygen. The greater
the flowrate, the shorter the retention and the higher the reactor organic
concentration adjacent to the biofilm.
Organic overloads typically occur in the initial stages of RBC systems,
One vendor (2) presently recommends a maximum first stage organic loading
of k.O pounds of soluble BOD per day per 1000 sf of media to avoid over-
loading in mechanically driven systems. A review of twenty-three facili-
ties around the country with and without the reported presence of organic
overloads for 12-foot diameter discs operating at rotational speeds of
approximately 1.6 rpm revealed a first stage loading of 6.4 pounds of BOD
197
-------
(total) per day per 1000 sf as the first stage loading beyond which organic
overloads were reported (1).
EQUIPMENT AND MAINTENANCE
RBC equipment can be subdivided into various components: media, shaft,
bearings, drive and media supports (radial arms).
Each vendor offers media with their own unique configuration. In
general, there are two types of media: standard and high density. Stan-
dard density contains approximately 100,000 sf per 25-foot shafe, and high
density which is packed more tightly contains 150,000 sf per 25-foot shaft.
Disc media is constructed by extruding high density polyethylene into in-
dividual sheets which are subsequently formed into the desired surface con-
figuration. These individual sheets are cut into pre-shaped segments each
representing one-eighth of the total circular disc. Some manufacturers
group the pre-shaped slices together to form a wedge of media held in place
by penetrating rods or straps. The wedges are supported by steel arms
radiating from the shaft. As the shaft rotates, the steel arms in turn
rotate the media. A second method of construction is a unitized self
fupporting plastic disc, mounted on and driven by a square shaft. In this
case, the pre-shaped pieces are connected to form circular plates that are
welded together and mounted in the shaft. A reinforced hub provides the
transfer of drive from the shaft to the media. A third type recently in-
troduced consists of strips of high density polyethylene which are vacuum
formed, spirally wound and heat welded in a continuous wrapping process on
a ci rcular shaft.
The RBC shaft and media can be driven directly by motor (most commonly
rated at 7-5 hp) or by recently introduced air drive systems which make use
of the buoyant force of compressed air released into the reactor to drive
the disc.
A survey of equipment history in RBC facilities (1) revealed signifi-
cant problems with respect to the reliability of certain components of the
system. A summary of the results of this survey are presented in Table 1.
The results indicate an unusually high percentage of shaft failures
(8.5%), with almost all occurring in the first stage where higher loadings
and heavier growth occur. Bearing problems were not significant, but re-
ported radial arm problems (30%) were high. Reported medial problems were
most commonly reported in radial arm facilities (80%), the result of a
shifting of the media, relative to the radial arm. Drive problems were not
major. The average years of operation prior to reported problems were low
in all cases, which is indicative of design deficiencies as opposed to
normal equipment wear.
Solutions to equipment problems rests with both the vendor and the
engineer to insure that the equipment is specified properly and utilized
within its design limitations.
198
-------
A survey of maintenance requirements, presented in Table 2, revealed
little manpower requirements directly attributable to RBC maintenance or
process control.
Equipment
Shaft
TABLE 1. RBC EQUIPMENT SURVEY
No. of Percent
Facilities Reported Reporting
Surveyed Fa!lures Failure
17
No. of
Shafts
Percent
Shaft Shaft
Failures Failures
12*
8.5
Percent
No. of Bearing Bearing
Bearings Failures Failures
Average Years
Of Operation
At Failure
1.9
Bearing
Radial Arm
17
18
50
282
No. of
Shafts
23
3.3
Radial
Arm
Fa i1ures
Percent
Radial Arm
Failures
30
Media
Drive
17
17
5-**
29
18
Percent
No. of Chain Chain
Shafts Failures Failures
1M 8 6
2.3
* Of the 12 reported shaft failures, 11 occurred in the first stage.
** Of 5 facilities with media problems, k were radial arm type.
TABLE 2, MAINTENANCE REVIEW
No
. of Plants
Surveyed
20
k
No. of
Shafts
2-8
10-*<8
Equipment Maintenance
Man-Hours Per Week
0.25-7
3-13
POWER PERFORMANCE
Energy utilization is rapidly becoming the major O&M item in many
wastewater treatment facilities. Selection of processes with low energy
requirements is a major priority. A power survey of seven mechanically
driven systems revealed an average power requirement of approximately 3-^
for a 25-foot shaft with standard density media and 3-8 kw for a 25-foot
shaft with high density media. Table 3 presents the results relative to
reported vendor values.
kw
199
-------
TABLE 3. MANUFACTURER POWER ESTIMATES AND FIELD OBSERVATIONS
Manufacturer
Autotrol
Clow
Hormel
Walker
Average Field
Power Requi
Standard Media
2
2.k
2.3
2.5
3.*»
rements (kw)
Hi -Den si ty Med i a
3
2.6
2.6
3.1
3.8
Observat ions
Energy utilization will vary from stage to stage in RBC facilities
with the initial stages utilizing more energy than the latter stages. This
was judged to be due to the greater friction resulting from heavier growth
on the media. Power requirements were also found to be proportional to
the third power of the rotational velocity, which limits the cost effec-
tiveness of increased rotational speed to enhance treatment performance.
CONCLUSIONS
The operating history of RBC facilities has revealed design limitations
with respect to organic overload, a suspect record with respect to equip-
ment problems and higher than anticipated power requirements. Additional
care is warranted in the selection and the design of the RBC process for
municipal wastewater treatment. Sufficient facility information is avail-
able for designers to assess the loading requirements, equipment history,
and power requirements of the process. Vendors must address equipment
deficiencies which should not be limiting to RBC performance.
REFERENCES
1. Review of Current RBC Performance and Design Procedures;
EPA-MERL; to be published in 1982
2. Autotrol Design Manual; 1979
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
200
-------
SESSION NO. 5
Energy Conservation in Municipal Wastewater Treatment
PAPER NO. 15
ENERGY CONSERVATION IN UNIT PROCESSES
AND SLUDGE MANAGEMENT
by
Daniel Cortinovis
Operating Services Department
Brown and Caldwell
Walnut Creek, California 94596
201
-------
ENERGY CONSERVATION IN UNIT PROCESSES AND SLUDGE MANAGEMENT
DANIEL CORTINOVIS, OPERATING SERVICES DEPARTMENT
BROWN AND CALDWELL
INTRODUCTION
The key link between a valid design concept for energy-efficient
wastewater treatment and the realization of that goal is the treatment plant
operator. His understanding of the processes and equipment systems and his
ingenuity in dealing with changing conditions make energy conservation and
recovery possible. He needs a grasp of the interrelations between unit
processes and their costs in dollars and energy so he can fine-tune the plant
to optimize the use of our resources.
All of the wastewater treatment plants in the United States consume only
about 0.25 percent of the nation's electricity, but that amounts to several
hundred million dollars worth of energy. As this figure increases and energy
supplies continue to dwindle, more emphasis is being directed toward energy
conservation in plant design and operation.
Since most treatment facilities depend largely on electricity as their
source of energy, this paper will begin by defining in general how power rate
schedules are set up. Treatment plant operators need to understand the
methods used to compute the plant's power bill so that they can direct their
energy-saving efforts toward cost-saving as well.
Examples of energy-conservation techniques used in various plants are
described using generalized case examples. The operator's role in optimizing
the use of energy is the focus of these discussions, with emphasis on areas
such as biological treatment, solids handling, and energy recovery. The
intent of this presentation is that operators will relate these examples to
situations in their own plants to aid them in devising programs for
conserving energy.
POWER RATE SCHEDULES
In past years, before there was commonly thought to be an energy crisis,
large users of electrical power received discounts as their consumption
increased. This encouraged industrial growth and increased power generation
by the utilities. Because of regulatory pressure and the increased emphasis
on conservation, rate schedule structures have not been drastically revised.
A. Energy and Demand
Energy is defined as the quantity of power used per unit time, measured
as kilowatt-hours (kWh). Demand is an instantaneous measurement of the power
being used at any particular time. It is measured in kilowatts (kW), which
can be related to the effective horsepower of the equipment in operation at
the time.
202
-------
An energy charge is made for each kWh used to pay the utility's
operating costs for generating the power. A demand surcharge may also
be assessed each billing period, based on the maximum demand sustained
throughout a specified time interval such as 30 minutes. This surcharge pays
the capital costs for having generating capacity available to meet the
demand.
B. Time-of-Day Demand
In areas where the demand threatens to exceed power production capacity
at certain times, a sliding scale is being used to adjust the demand
surcharge to the time of day and the season. This is intended to discourage
large customers from creating a high demand during peak times, such as summer
afternoons when a large number of air conditioners are running.
Some manufacturing operations are probably able to adjust their
production schedules to avoid peak demand periods, but doing this in a
wastewater treatment plant requires a lot of ingenuity because of the lack of
control over incoming flow and loadings. However, some possibilities are:
1. Flow storage prior to treatment.
2. Shutting down solids processing during demand peaks and catching
up later.
3. Storing digester gas or other fuel and generating power during peak
demand periods.
An example of a peak-period demand surcharge schedule for a plant with a
monthly demand greater than 4,000 kW is shown below.
Demand charge per kW Summer
On peak (early summer and late
winter afternoons) $4.20
Partial peak (mornings and evenings) 0.35
Off peak (nights, Sundays, holidays) None
C. Other Charges
Winter
$2.80
0.35
None
Several other factors which affect the dollar amount of the monthly
power bill are:
Customer charge—A flat rate service charge for each metered
connection as assessed.
Voltage adjustment—Customers taking delivery at voltage higher
than 2 kV may get a demand charge discount.
Power factor—The ratio of lagging kilovolt ampere hours to
kilowatt hours consumed increases or decreases the total bill,
depending on how much it deviates from a specified ratio (usually
about 0.85).
203
-------
Facility charge—If the utility spends more constructing service
facilities for a customer than they receive in revenue, an
additional charge may be made as a percent of the excess.
Energy cost adjustment—A variable charge per kWh is made to cover
changes in the cost of fuel used to generate power.
ENERGY-SAVING TECHNIQUES
Specific methods for trimming energy costs are outlined below, using
generalized case examples based on actual operating plants. With some
techniques, the cost savings result from reduction in demand peaks. In most
cases, an overall reduction in energy consumption is the primary method of
saving money. The most important aspect of an energy conservation program is
a total system approach. For each operational change initiated to save
energy, the whole facility must be considered to ensure that a corresponding
increase does not occur in another area.
A. Power Monitoring
Relatively inexpensive instrumentation is now available for constant
monitoring of both energy use and demand. Installation of monitoring
equipment at the plant's incoming substation and at individual motor control
centers supplies on-line information to the operations staff, telling
them how much power is being used in which areas. This information is
essential, especially if time-of-day demand peaks are being shaved through
operational modifications. Where digital computer systems (or even small
microprocessors) are available, the data can be trended and totalized to aid
in interpretation and record keeping.
B. Unit Capacity Optimization
Plant managers should carefully evaluate process operations to determine
when treatment units should go in and out of service, especially in plants
where the load changes seasonally. Although short-term fluctuations in
loading may not dictate changes, anticipation of and response to seasonal
variations can save significant amounts of energy while still maintaining
effluent quality. Accurate judgments are required—for instance, cutting
back on anaerobic sludge digester mixing may save only minimal amounts of
energy while causing a disastrous upset. In contrast, secondary treatment
units such as activated sludge aeration tanks and high-head oxidation
towers are very energy intensive and should not be operated far below design
capacity. Clarifiers, on the other hand, require a very small amount of
power and may enhance treatment efficiency when multiple units are operated
at low overflow rates.
A municipal secondary treatment plant using high purity oxygen activated
sludge was designed for 120 million gallons per day (mgd). The flow
configuration uses 8 biological reactor trains and 12 clarifiers. Although
the nominal design flow for each reactor train is 15 mgd, the oxygen
204
-------
dissolution capacity is adequate for at least twice that to handle seasonal
load increases and a possible future requirement for nitrification. Since
each of the eight trains uses 400 horsepower (hp) of mixers, a significant
energy savings is realized by operating only three or four trains for the
actual average dry-weather flow of 80 mgd. All available clarifiers are
used, since they have only 1-hp drive motors. During low loading periods,
mixers on some stages can be shut down, saving up to $5.00 per hour each.
C. Aeration Blower Control
In most conventional activated sludge plants, the largest consumers of
energy are the blowers or mechanical devices used to supply air to the
aeration tanks. Many plants in past years were designed with strictly manual
control of the aeration system, due to the following factors:
1. Reliable on-line instruments for measuring the dissolved oxygen
(DO) level of the mixed liquor in the aeration tanks were not yet
available.
2. The cost of energy was much lower than now, as compared to the
relative cost of instrumentation systems.
3. The state of the art of activated sludge process control was less
advanced.
Now that energy costs are high and DO control systems fairly reliable,
the majority of new plants are being designed with these control systems and
many agencies are adding them to their existing plants. Although there have
been some attempts to control mechanical aerators by DO level, most of the
current systems use diffused aeration with suction-throttled centrifugal
blowers. An electrical signal from the DO probes in the tanks is usually
converted to a pneumatic signal which controls automatic air distribution
valves on the headers to each aeration tank pass. A pressure sensor on the
blower discharge manifold upstream of the distribution valves controls
the inlet guide vanes on the blowers to maintain a constant pressure in the
manifold. Analog or digital control loops can be used.
The energy consumption is reduced with DO control because centrifugal
blowers use less power when the suction is throttled. The turndown limit
(surge point) is usually about 50 percent of design capacity, so several
blowers of different sizes may be used to provide a better coverage of
operating ranges. The activated sludge process is subject to upset at low DO
levels, so controlling the DO at higher levels for higher loadings protects
effluent quality.
Many oil refineries have activated sludge systems for treatment of their
process wastewater. For two systems which originally used single-speed
mechanical aerators with no control systems, studies showed that installation
of completely new aeration systems using DO control with diffused air and
centrifugal blowers could save enough in power costs to pay for the new
equipment in several years. Some particular considerations which contributed
to this analysis were:
205
-------
1. Due to the cyclic nature of refinery processes, the incoming
waste load varies widely over periods of short duration.
2. The temperature of the wastewater is unusually high which cuts into
aeration efficiency and makes a more efficient system more cost-
effective.
D. On-Site Power Generation
The current emphasis on the environment and energy has focused attention
on the production of "bio-gas" from digesting organic matter. Municipal
waste treatment plants have used the anaerobic digestion process for over
50 years to stabilize sludge before utilization or disposal. The gas
produced, containing about 65 percent methane, has been used in boilers to
produce heat for the digesters and plant site buildings. In some larger
plants, the excess gas is used to generate power.
One problem with using digester gas for power generation is the high
initial capital cost and high maintenance costs for large reciprocating
engines. Another problem, particularly with primary plants, has been that
the greatest excess of gas is available in the summer, when heat requirements
are less and power requirements lower due to decreased flows. Experience
with engine-generator design and the development of gas turbines have helped
to minimize maintenance costs. Some plants expanded to secondary treatment
have found a drastic shift in their seasonal energy requirements, with summer
peaks occurring for biological treatment of food processing wastes. The
advent of cogeneration, where induction generators are operated in parallel
with utility power, will also contribute to the cost effectiveness of
installing on-site power generation systems.
A 55-mgd primary and secondary plant located in a largely agricultural
area treats a mixture of domestic sewage and seasonal cannery wastes.
Methane gas from anaerobic digesters is used to fuel three piston engines
driving variable-frequency generators. Two generators power the effluent and
effluent pumps using the variable-frequency feature to control pump motor
speed. The third unit powers other plant equipment when extra gas is
available. In 1980, 36 percent of the power used in the entire plant was
generated on-site at a savings of over $150,000. Hot water from the engines'
cooling system is circulated through a reservoir loop to heat the digesters
and plant buildings.
E. Heat Reclamation Systems
Heat is produced in some treatment plant processes while being required
in others. Waste heat can be recovered in large quantities from incinerators
boilers, and engines. It is transferred in water to heat sludge digesters
and plant buildings or in steam to power turbines driving mechanical
equipment. Operational control is critical because the systems are often
complex, with the balance between heat requirements and availability
constantly changing as changes occur in plant load, flow, and ambient air
temperature.
206
-------
One type of system uses a hot water reservoir loop to circulate waste
heat from digester gas-powered engines to digester and building heating
systems. Thermostatically controlled valves and pumps regulate the flow
of water to the various units. A balance in the system is maintained by
disposing of excess heat in exchangers located in the wastewater flow stream.
In emergencies, heat from auxiliary boilers or resistance-type electrical
heaters is added. Because no automatic system can anticipate changes in
variables such as digester gas availability and ambient temperatures, the
experience of the operators is relied upon for judgments as to when engines
should be started or control set points changed.
F. Solids Handling Trade-Offs
The push for secondary treatment expansions mandated by the 1972 Water
Pollution Control Act often resulted in a decrease in emphasis on solids
handling and disposal. Now that many new secondary plants are on line, the
full impact of increased sludge production and changes in its characteristics
are being realized. Processing and disposal or utilization of solids is
rapidly becoming the most cost- and energy-intensive aspect of wastewater
treatment, especially as urban sprawl increases the distance between
treatment plants and land areas available for disposal.
The operator's success in reducing the overall amount of energy consumed
in solids handling processes will depend on his recognition of the
relationships between trade-offs in which he can make choices. Some examples
of these follow:
1. Vacuum or belt filters are very energy-efficient devices for
dewatering some types of sludges. Correct chemical conditioning of
the sludge is critical and relates to energy use because higher
production and lower moisture content mean shorter running time for
equipment and lower offhaul costs.
2. The use of centrifuges for dewatering digested primary and secondary
sludges is becoming more common because of the difficulty in
thickening these sludges. When centrifuges are operated at a low
capture, the operator may have the illusion that he is producing a
lot of cake at a low chemical dosage. He should realize that the
cost and energy penalty is high for this because solids recycled
through the plant have to be retreated and reheated in the digesters
before he gets another chance to remove them. In-plant solids
recycle is also a major cause of effluent quality degradation.
3. When sludge is to be incinerated, dryness is usually of paramount
importance because large amounts of supplemental fuel are required
when excess water is fed to the furnaces. Most dewatering equipment
will produce a drier cake at lower throughput, so it becomes the
responsibility of the operations staff to operate more dewatering
units on a longer schedule if the trade-off is favorable.
4. The difference between being able to use a low-energy land disposal
or composting operation or a higher technology, more energy-
intensive alternative often depends on the operator. He can ensure
207
-------
adequate sludge stabilization through efficient process operation
and develop favorable public relations by taking prompt action on
odor and nuisance problems.
G. Pumping and Hydraulics
Operators cannot be expected to redesign the hydraulic profile of a
treatment plant, but they can often save energy by making some simple
adjustments. The approach of the design engineer is usually to conserve as
much pumping head as possible in equipment and structure design, since it is
estimated that each foot of head will cost about $500 per year per mgd in
energy. However, the design must allow operational flexibility and leave
room for possible future expansion, so pumps are sometimes oversized and head
losses designed in.
Treatment units such as synthetic media oxidation towers (modern
version of the "trickling filter") depend on recirculat ion pumping for
aeration and contact between waste and microorganisms. Using frequent
loading rate calculations, the operator can adjust the recycle rate to the
minimum necessary to maintain process efficiency. Excess recirculation only
wastes energy and will not increase removals. This also applies to return
activated sludge pumping. It may be easier to crank the pumps up to high
speed and forget about them, but careful sludge blanket monitoring will
result in an increase in solids concentration, which will allow lower pumping
rates.
SUMMARY
1. Wastewater treatment plants in the United States depend primarily
on electrical power as a source of energy, consuming about
0.25 percent of the nation's total.
2. The size of the monthly power bill depends on the amount of energy
used and the magnitude of the demand, as well as several other
factors.
3. Plant operators need to understand the energy interrelationships
and individual impact of variables under their control so that they
can fine-tune the treatment processes to reduce energy consumption.
4. Some energy saving programs and techniques currently in use are:
A. Shaving demand peaks by careful operations scheduling.
B. Optimizing process units to reduce the amount of equipment in
service.
C. Aeration equipment control automation by dissolved oxygen level.
D. Power generation using gas from sludge digesters.
208
-------
E. Reclaiming excess heat from mechanical systems, such as
engines and incinerators.
F. Evaluation of solids handling energy trade-offs.
G. Conservation of hydraulic head.
views of the
209
-------
PAPER NO. 16
A COMPOSITE APPROACH TO ENERGY CONSERVATION
THROUGH PROCESS OPTIMIZATION
SOME CASE STUDIES
by
Ashok K. Singhal, P.E.
Vice President/Treasurer
and
Phillip N. Loud
Engineer
and
Donald W. Lystra, P.E.
Vice President
Ayres, Lewis, Norris & May, Inc.
Ann Arbor, Michigan 49481
210
-------
A COMPOSITE APPROACH TO ENERGY CONSERVATION
THROUGH PROCESS OPTIMIZATION
Some Case Studies
Ashok K. Singhal, P.E., Vice President/Treasurer; Phillip N. Loud, engineer;
and Donald W. Lystra, P.E., Vice President
Ayres, Lewis, Norris & May, Inc., Ann Arbor, MI
INTRODUCTION
Municipal wastewater systems are heavy users of energy, not only directly
through the use of electricity, natural gas, and other fuels but indirectly
through the use of large quantities of chemicals produced by energy-intensive
manufacturing processes. Table 1 summarizes energy consumption for the
manufacturing of the various chemicals used for wastewater treatment. A recent
study by the U.S. Office of Water Research and Technology showed water and
wastewater systems to be the largest single component of energy consumption by
local units of government, averaging about 25 percent of the total municipal
energy use (1). Moreover, recent utility rate studies have shown that the
direct energy costs of wastewater systems account for fully 20 percent of their
total operating budgets (2).
During the past three years, Ayres, Lewis, Norris & May, Inc., (ALNM) has
performed energy audits for eight wastewater treatment facilities in Michigan.
This paper summarizes the findings of the energy audits. The main objectives
of these audits have been threefold:
— to establish energy consumption profiles of the buildings and the
treatment processes;
— to identify, analyze, and rank cost-effective retrofit measures and
operational and maintenance strategies which will conserve energy;
— to develop an on-going energy management program.
ENERGY AUDIT METHODOLOGY
An energy audit is defined as a critical examination of an energy-consuming
facility for the purpose of identifying energy conservation opportunities.
Because of the overall complexity of wastewater facilities and the various
technical specialties represented by their processes and equipment, the audits
were broken down into smaller components. This made it possible to create
specialized audit packages that could be addressed by team members from
appropriate technical fields. The following subsystems were identified.
Treatment System: all processes and equipment used to treat wastewater
and render it suitable for discharge into the receiving stream.
Capacity Control System: equipment used for pumping wastewater at
various points in a treatment process.
Heating, Ventilating, and Air Conditioning System (HVAC): equipment
that provides the control for the internal environment of buildings,
including the building envelope itself.
211
-------
Electrical Systems: equipment that distributes electricity to plant
loads and provides artificial illumination for the interior and exterior of
the facility.
An auditing team of technical specialists in civil, sanitary, mechanical,
and electrical engineering, as well as architecture, was created to perform the
energy audits at each of the study sites. The auditing procedures involved a
review of existing documents and records, site visits, operator interviews,
identification of energy conservation opportunities (ECOs), analysis of ECOs,
and reporting.
Audit team members were instructed to look for ECOs in the following
general areas: changes to operational and maintenance strategies; equipment
changes (i.e., same function, different device); design changes (i.e., dif-
ferent function, different device); and relaxation or modification of design
standards.
DESCRIPTION OF STODI SITES
Table 2 summarizes design capacity, service area population and the type of
treatment for the eight sites studied. All facilities rely primarily on
electricity and natural gas for their energy requirements except Ann Arbor
which also uses fuel oil. Electricity is typically used as the energy source
for motor drives and illumination, whereas natural gas is used as the energy
source for building heat, water heating, digester heating, sludge incinera-
tion, and chemical pretreatment.
The breakdown by energy source of total energy consumption at each study
site is given in Table 3. The breakdown of energy consumption for each site
within the four functional subsystems is shown in Table 4. In general, more
than half of the energy used by the wastewater facilities is for treatment
equipment and relatively little for pumping. The total energy consumption and
energy cost per cubic meter of water treated at each of the facilities is given
in Table 5. As shown in the table, these costs vary from $57 per million gallon
at Wyoming, Michigan, to $133 per million gallon at E. Lansing, Michigan.
PROCESS OPTIMIZATION
In the process of identifying energy conservation opportunities at the
wastewater treatment plant sites, it was recognized that the treatment systems
account for 50 percent or more of the total energy consumed at a wastewater
plant. As shown in Table 4, at the eight sites studied, treatment systems
accounted for 44 percent of the total energy consumed at Wyoming, Michigan, to
75 percent at Ann Arbor, Michigan. In addition, treatment systems also utilize
considerable amount of chemicals which have an indirect impact on energy
consumption through manufacturing and transportation. Therefore, it was recog-
nized that process optimization should be a very integral part of an energy
audit plan at a wastewater treatment plant. Process optimization would serve a
dual purpose of conserving energy, as well as chemicals.
A six-step model for treatment process optimization used during the energy
audits is summarized in Table 6. The first step is to review historical
212
-------
records from a treatment plant to establish the present plant performance in
terms of influent water quality parameters, chemicals used, and process
performance parameters for each of the unit processes. This information is
generally obtained from the monthly operational summary sheets submitted to the
State regulatory agencies. The data is summarized both graphically and in
tabular form to establish trends and history. Figure 1 provides a summary of
operational records for the Cadillac, Michigan, Wastewater Plant as an example.
The second step is to compare the plant performance parameters with the
expected design performance for each unit process. In this process, a
comparison of the actual plant efficiencies is made with the expected design
efficiencies. In addition, during this stage, marginal utilities of adding
various chemicals in the processes are also established. Marginal utility is
defined by the following equation in reference to Figure 2:
Ay
Marginal Utility =
A
where £> y = increm ental removal of a pollutant
^x = incremental cost of the chemical to
remove a pollutant
In general, the idea is to add a chemical to a point where the marginal
utility is one, or more than one. If from reviewing the historical records, it
is found that the marginal utility for some of the chemicals is considerably
less than one in actual plant performance, it would be an indication of gross
process inefficiencies and deficiencies. Thus, Step 2, would generally pro-
vide a fairly good idea regarding the processes that are performing less than
optimally.
The third step in the process optimization is to review the physical and
chemical parameters effecting each unit process. The purpose of this step is
to identify and pinpoint the reasons for poor performance of the unit processes
identified in Step 2. As an example, at one of the treatment sites studied,
ferric chloride was being added in the aeration system for phosphorus removal.
Considerable amount of chemical was being used without achieving the desired 80
percent phosphorus removals. After reviewing the physical and chemical
parameters associated with mixing and flocculation of the chemical, it was
discovered that the aeration system was resulting, in excessive shear velocities
(G) resulting in G values of 130 to 150 sec— , thus breaking up the floe
particles. As a result of the investigations, the chemical feed point was
moved toward the tail-end of the aeration system and the amount of air was
reduced to provide a shear velocity (G) of 60 to 65. This change resulted in a
considerable improvement in phosphorus removals as well as the amount of
chemicals used for phosphorus removal. Prior to initiating this change, 80 mg/1
of ferric chloride was being used along with 0.5 mg/1 polymer. Subsequently,
ferric chloride dosage was reduced to 50 mg/1 and the polymer was eliminated
completely. In another instance, the chemical percipitation process was
resulting in a poor floe formation during the winter months of operation. It
was noted that fine pinpoint floe was being formed which was not coagulating
properly. Investigations of the parameters effecting the flocculation process
indicated that the plant had a fixed speed floe mixer providing adequate
213
-------
flocculation energy during the warmer months but was not capable of providing
the necessary energy for flocculation during the colder months. It was noted
that with the falling water temperatures, the viscosity of the wastewater went
up by approximately 50 percent resulting in a similar increase in the power
requirements for flocculation as shown by the following formula. A change in
the flocculation process improved the results considerably.
G =~yP/u.V where G=mean velocity gradient (sec^) ,
P=power required (ft-lb/sec)
jaat 20 C (58 F) = 1.009 >i=absolute fluid viscosity
juat 5°C (1M°F) = 1.519
V=f locculator volume (cu ft)
The fourth step in the process optimization is to review alternate ap-
proaches for achieving process results in order to conserve energy as well as
chemicals. The purpose of this step is to see if a particular process can be
changed or altered to achieve the desired results at a lower overall cost. An
example of this would be changing a chemical feed point in the process or using
alternate chemicals. At one of the treatment sites, lime was being used for
phosphorus removal. Because of the high hardness of the wastewater, a
considerable amount of lime was being added to achieve desired 80 percent re-
movals. Lime also produced large quantities of sludges. Replacement of lime
with ferric chloride resulted in considerable energy and cost savings.
Once an alternate approach has been identified for a process, the fifth
step is to conduct lab scale studies using alternate chemicals or process
parameters for achieving the desired results. The purpose of the lab tests is
to provide adequate data for evaluating cost effectiveness of a particular
change being contemplated. It should be noted that the lab tests should
reflect the actual operating conditions as closely as possible. For example,
if a given treatment process is operating under low temperature conditions, the
lab tests should also be performed under similar temperature conditions.
Following the lab scale studies and a cost effectiveness analysis of alternate
approaches being considered, a decision should be made regarding conducting
full plant scale studies which is the sixth and final step. In conducting full
plant scale studies, it is very important that process parameters be monitored
very closely and be evaluated in terms of the changes that are being made. As a
result of the full plant scale studies, if the proposed changes are found to be
cost effective, they should be implemented.
IDENTIFICATION OP ENERGY CONSERVATION OPPORTUNITIES
In order to identify the energy conservation opportunities at the study
sites, the following conceptual model of energy consumption was utilized:
Energy Source In Conversion System Function Out
(e.g., electricity, gas) (e.g., light bulb, (e.g., light, motion,
motor, boiler, etc.) heat)
Energy Consumption Model
214
-------
As the model illustrates, energy enters a conversion system and is trans-
formed into a useful function. Therefore, there are three basic ways to
conserve energy and/or cost which correspond to each phase of the model.
1. Use a Less Expensive Source:
— change fuel
— use off-peak electricity
— use waste energy
— use renewable source (solar, wind, etc.)
2. Increase System Efficiency:
— improve performance
— improve maintenance
— change equipment
3. Modify Functions:
— eliminate unnecessary functions
— retain function but use less
— substitute less expensive function
Based on the above conceptual model as a guide, energy conservation
opportunities were identified at each of the study sites. These can be divided
into low cost or no cost energy conservation measures and those requiring
capital investment for implementation. Low cost measures are typically
operational measures which cost less than $500 to implement and have a payback
period of less than one month. The most commonly encountered low cost measures
in each of the four functional areas are discussed below:
Architectural
Low cost architectural measures typically involve insulating, weather-
stripping, caulking, and repointing. These measures generally serve to reduce
infiltration or slow the rate of heat transfer through a structural membrane.
These measures can be implemented by plant staff and result in savings in the
annual heating load. Implementation costs for most facilities are generally
$100 or less.
Heating, Ventnating and Air Conditioning
Three major low cost energy conservation measures in the HVAC subsystem are
identified in almost every wastewater treatment facility. These measures
include dialing down temperature settings, reducing outside air flow, and fine
tuning boiler burners.
Dialing down plant thermostat settings plantwide from 72° to 68° will
effectively reduce the plant heating load by approximately 9-10 percent. In
many cases, certain areas can be heated to even lower temperatures providing
even greater savings without any implementation cost.
Reductions in outside air quantities of 10-50 percent are typically
proposed in wastewater plants equipped with heating systems utilizing mixing
air boxes. These changes have resulted in heating load reductions of up to 20
percent.
215
-------
Fossil fueled boilers are typically operated with too much excess air and
potentially dirty heat exchangers. Inexpensive flue gas testing kits costing
around $200 have been utilized to fine tune boiler operations to improve burner
efficiencies by 2-4 percent. A plant with a $10,000/yr boiler fuel cost would
pay for the test kit in one year with a 2 percent increase in efficiency.
Treatnent Process Systems
Low cost operational changes to the treatment process systems which result
in energy savings typically involve the operation of more efficient pumps, the
reduction in chemicals fed through process optimization as discussed earlier,
or a reduction in total aeration requirements.
Variances in operating efficiency of redundant pumps, identified during an
energy audit, often result in a low cost measure recommending increased
operation of the most efficient pump. Similar pump efficiencies may often
differ by 3-7 percent depending on age and utilization. A three percent
difference in efficiency for a 50 hp pump running continuously represents a
potential savings of $960 annually ($0.05/kwh).
Reductions in quantities of chemical fed does not typically result in large
direct energy savings. However, the secondary impacts on sludge production and
process efficiency can potentially result in large energy savings.
Aeration systems in wastewater plants typically represent 30-60 percent of
total plant electrical energy consumption. An analysis of the air requirements
for several activated sludge plants has resulted in an identification of
potential reductions in aeration levels of 12-27 percent at cost savings of
approximately $3,000-$3i*,000 annually. Figure 3 shows an example of potential
for reducing air at a wastewater treatment plant.
Elfictrical/niunlnatlon Systems
The most common low cost energy conservation measures applicable to
electrical/ illumination systems fall into the categories of lamp replacement,
delamping, and fixture cleaning.
Many wastewater plants utilize standard fluorescent lamps for operating
areas, as well as pipe galleries. Reduced wattage fluorescents typically
consume 20 percent less power and cost approximately 33 percent more than
standard bulbs. A program of replacing standard fluorescents when they burn
out with reduced wattage bulbs provides energy savings capable of 6-month
paybacks for each bulb.
Regular cleaning of fixture housings, reflectors, and diffusers can im-
prove lamp efficiencies by as much as 35 percent. Clean fixtures operate at a
lower temperature which can typically lengthen the life of a lamp by 25-30
percent.
Another potentially significant area of electrical cost savings is in
electric billing structures. Communities who are currently on "flat rate"
electric structures may qualify for "variable" rate electric contracts with
216
-------
their utility. Wastewater facilities often benefit from variable rate struc-
tures due to their inherent diurnally and seasonally varying electric demands.
Cost savings ranging from 15-25 percent have been seen in our studies from
simple contractual changes to variable rate structures incorporating on-peak,
off-peak, and kw demand components into the billing.
Tables 7 through 10 summarize capital cost energy conservation measures for
four of the treatment plant sites studied. In general, capital cost measures
dealing with HVAC and illumination systems have the fastest payback period
while the architectural items have the slowest payback. Treatment systems
offering the greatest potential for conservation are related to sludge handling
and disposal and aeration system modifications.
Based on the energy audit studies, the following is a checklist of
potential energy conservation opportunities (ECOs) at a wastewater treatment
plant.
Ventilation and Cooling System ECOs
— Close off unoccupied areas by blocking supply register
— Shut off system and open windows
— Raise cooling temperatures to 78 (non-reheat)
— Install ventilating equipment timeclocks
— Install ceiling fans in high bays
— Install local switches for exhaust fans
— Install economizer/enthalpy control
— Close air dampers during morning warm-up
— Install attic ventilation
— Use window fans
— Redirect air diffuser in non-cooling seasons
— Maintain filters monthly
— Check damper operations monthly
— Check belt tension monthly
— Post and use operational and schedule sheet
Heating System ECOs
— Reduce outside air
— Waste heat utilization
— Tune-up boilers
— Repair and/or replace steam traps
— Repair hot water and steam leaks
— Reduce boiler pressure in response to load
— Fire one boiler at full load rather than two at part load
— Maintain boiler instruments
— Reduce space temperatures to 65
— Reset space temperature during off hours
Hot Water System ECOs
— Repair leaks
- Reduce water temp. - 105 F (handwashing only), 120 F (showers)
— Install water flow restrictors/flush dams
217
-------
— Install timers on hot water heaters and circulating pumps
— Insulate hot water tank
— Turn off hot water in summer
— Flush system annually
Illumination System ECOS
— Use higher efficiency fixtures and lamps
— Clean fixture lenses and reflectors
— Remove lights (and disconnect ballasts) where not needed
— Install time-out switches
— Use photocells/timeclocks on exterior lights
— Install multi-level brightness controls
— Use high reflectance paint on interior surfaces
— Install night-lighting system
Electrical System ECOs
— Install electric metering and sub-metering
— Clean or replace contact surfaces on motor starters
— Increase conductor size on large motors
— Use high efficiency motors and transformers for replacement
— Correct low power factor
— Install load warning or load shedding devices
— Keep electric motors in good condition
(lubricate, replace worn bearings, check alignment, clean,
tighten belts and pulleys)
Aeration System ECOs
— Change fuel source (utilize digester gas-driven engine)
— Improve oxygen transfer efficiency
(change header placement geometry, optimize mixing pattern,
retrofit coarse bubble with fine bubble diffusers, increase
operating depth)
— Modify blower function
(variable speed drives, throttling blower suction for hp sav-
ings, automatic control based on D.O., adjusting volume based
in diurnal/seasonal variations, meet mixing requirements at
low loadings)
Sludge Handling System ECOs
— Digester gas utilization
(electric generation with heat recovery, blower drive, pump
drive, boiler fuel)
— Waste heat recovery from incineration
218
-------
CONCLUSIONS
Based on the information acquired from the study of the energy conservation
opportunities available at the various treatment sites, the following conclu-
sions have been identified:
(1) Municipal wastewater systems in Michigan rely almost entirely on
electricity and natural gas for their energy requirements. The
reliance on each of these two energy sources is roughly equal.
(2) The major components of energy consumption in wastewater systems are
electricity for aeration blower drives and natural gas for sludge
heating and incineration. Therefore, these areas offer the greatest
opportunity for conservation.
(3) The six-step process optimization model presented in this paper can be
quite successfully used in identifying energy and chemical conserva-
tion opportunities related to treatment processes.
(H) No obvious relationship exists between the size of a wastewater
facility and the efficiency with which it consumes energy.
(5) It is projected that municipal wastewater systems in Michigan could
reduce their electricity consumption by about 15 percent and their
natural gas consumption by about 20 to 25 percent through the implemen-
tation of cost-effective energy conservation measures.
(6) Approximately 15 to 20 percent of the total identified energy-saving
potential in a wastewater system can be achieved through operational
and maintenance changes costing less than $500 and having an average
simple payback period of less than one month.
(7) Significant energy conservation opportunities relating to HVAC and
illumination systems exist in municipal wastewater facilities because
of the unusual occupancy pattern in many areas of the facility.
(8) Municipal wastewater facilities have significant indirect energy im-
pacts as a result of their consumption of large quantities of chemicals
produced by energy-intensive manufacturing processes.
REFERENCES
1. An Explanatory Study of Possible Energy Savings as a Result of Water
Conservation Practices. NTIS No. PB-260 490. Prepared for the Ofce. Water
Res. and Technol., Washington, D.C. (Jul. 1976).
2. In-house rate studies: Ayres, Lewis, Norris & May, Inc., Engineers -
Architects -Planners, Ann Arbor, Michigan.
"The work described in this paper was not funded by the U.S. Environ-
mental Protection Agency. The contents do not necessarily reflect the
views of the Agency and no official endorsement should be inferred."
219
-------
TABLE 1
ENERGY REQUIREMENTS FOR CHEMICAL PRODUCTION
Chemical
Activated Carbon
Alum
Ammonium Hydroxide
Carbon Dioxide
Chlorine
Ferric Chloride
Lime (Calcium Oxide)
Methanol
Oxygen
Polymer
Salt (Sodium chloride)
Evaporated
Rock and Solar
Sodium Hydroxide
Sulfur Dioxide
Sulfuric Acid
Fuel ,
(Btu/ton) x 10
102. Oa
2.0a
41. Oa
2.0
42.0
10.0
5.5a
36. Oa
5.3
3-0
4.0a
0.5
37.0
0.5
1.5
Power
(kwh/lb)
4.9
0.1
2.0
0.1a
2.0a
0.5a
0.3
1.7
0.25a
0.1
0.2
a
0.024a
1.8a
0.0243
0.1
Source: "Energy Conservation in Municipal Wastewater Treatment,"
U.S. EPA., March, 1978.
alndicates principal type of energy used in production. Does not
include energy for transportation.
220
-------
TABLE 2
SITES STUDIED
Study Site
E. Lansing, MI
Big Rapids, MI
Alma, MI
Wyoming, MI
Cadillac, MI
Ann Arbor, MI
Saline, MI
Greenville, MI
Design
ML/d
68
9
9
72
8
30
7
5
Capacity
mgd
18.0
2.4
2.5
19.0
2.0
8.0
1-9
1.3
Service
Area
Population
105,000
16,500
9,700
59,600
10,200
104,000
6,500
8,000
Type of
Treatment3
T/AS/POjj/NH
S/AS/PO,
S/AS/POjj/NH
S/TF/AS/POjj
T/AS/RBC/PCL/NH
S/AS/PO^/NH
T/TF/PO^
S/TF/PO,
Sludge
Handling
Facilities
SD/SI
AN
CSS
CSS
AN/SD
AN/SD/SI
AN/SD
AN/SD
Primary - P
Secondary - S
Tertiary - T
Activated Sludge
- AS
Trickling Filter - TF
Rotating Biological Contactor - RBC
Phosphorus Removal - PCv
Ammonia Removal - NH_
Anaerobic Digestion - AN
Aerobic Digestion - AE
Sludge Dewatering - SD
Sludge Incineration - SI
Chemical Sludge Stabilization - CSS
221
-------
TABLE 3
ENERGY CONSUMPTION BY FUEL TYPE AT EACH STUDY SITE
(in percent)
Study Site
East Lansing, MI
Big Rapids, MI
Alma, MI
Wyoming, MI
Cadillac, MI
Ann Arbor, MI
Saline, MI
Greenville, MI
Electricity
47
46
82
60
52
25
44
81
Natural Gas
53
54
18
40
48
60
56
19
Fuel Oil
0
0
0
0
0
15
0
0
TABLE 4
BREAKDOWN OF ENERGY CONSUMPTION BY FUNCTIONAL SUB-SYSTEMS
(in percent)
Study Site
East Lansing, MI
Big Rapids, MI
Alma, MI
Wyoming, MI
Cadillac, MI
Ann Arbor, MI
Saline, MI
Greenville, MI
Capacity
Control
System
10
5
9
11
11
4
26
26
Treatment
System
72
58
70
44
49
74
57
54
HVAC
System
14
31
18
41
36
14
15
18
Illumination
System
4
6
3
4
4
8
2
2
222
-------
TABLE 5
ENERGY CONSUMPTION AND ENERGY COST
OF WASTEWATER TREATED AT EACH FACILITY
Energy C onsu m ption
per m
Energy C ost
Study Site
East Lansing, MI
Big Rapids, MI
Alma, MI
Wyoming, MI
Cadillac, MI
Ann Arbor, MI
Saline, MI
Greenville, MI
kj/m3x103
6.1
3.9
1.8
2.6
4.2
4.7
2.2
5.8
Btu/milgalxlO6
21.9
14.0
6.6
9.2
14.9
16.9
7-8
20.9
per m
$0.035
0.026
0.017
0.015
0.034
0.023
0.016
0.028
per mil gal
$133
98
63
57
131
89
59
105
223
-------
TABLE 6
A MODEL FOR TREATMENT PROCESS OPTIMIZATION
(1) REVIEW OF HISTORICAL RECORDS (H) REVIEW ALTERNATE APPROACHES FOR
- chemicals used/mg ACHIEVING PROCESS RESULTS
- influent water quality ~ changing chemical feed point
- effluent water quality (NPDES Permit) ~ ^circulation of solids
- process performance parameters ~ alternate chemicals
(2) PLANT PERFORMANCE VS. EXPECTED ~ varying treatment needs
DESIGN PERFORMANCE (winter VS" SUmmer)
- theoretical vs. actual performance <5> CONDUCT LAB SCALE STUDIES
£ from (1) above - run jar tests with different chemicals
- establish efficiencies of various unit and chemical do3aees
processes - evaluate results
- establish marginal utility of adding (6) CONDUCT PLANT SCALE STUDIES
chemicals , .
— change one parameter at a time
REVIEW PARAMETERS AFFECTING THE , .. ,
UNIT PROCESSES ~ evaluate results
grit removal " ^P^ent plant changes
rapid mixing
flocculation
settling
aeration
-------
TABLET
LIST OF ENERGY CONSERVATION OPPORTUNITIES
ANN ARBOR WASTEWATER TREATMENT PLANT
Description
Reduce Heat Recovery
Unit Capacities
Power Factor Correction
Digester Gas Utilization
(Blower Engine)
(Heating)
Activated Sludge Aeration
Lab Exhaust Hood Makeup
Insulate Digester Covers
Install (1) Boiler Economizer
Insulate Blank Walls
Roof Insulation
Install (2) Boiler Economizers
Replace Overhead Doors
Annual Energy
Savings
76,800 kwh
2,500 ccf
248,330 kwh
44,896 ccf
486,850 kwh
2,845 ccf
2,290 kwh
110,500 kwh
5,000 ccf
4,550 ccf
2,156 kwh
941 ccf
6,100 ccf
747 ccf
Annual
Cost
Savings
$ 3,455
1,000
2,592
11,170
17,958
21,910
1,138
103
4,972
2,000
1,820
97
376
2,440
299
Implementation
Cost
$ 3,000
4,880
25,935
62,000
4,500
26,180
20,000
24,600
6,505
25,000
4,465
Payback
Period
(yrs)
0.7
1-9
2.2
2.8
3.6
5.3
10.0
13-5
13-7
14.3
14.9
Base Costs:
Electricity = $.045/kwh;
Natural Gas = $.40/ccf , where ccf=100 cubic feet
No direct energy savings associated with this ECO.
^Digester heating equipment purchased separately.
-------
TABLE 8
LIST OF ENERGY CONSERVATION OPPORTUNITIES
EAST LANSING WASTEWATER TREATMENT PLANT
Energy Conservation Opportunities
Projected Annual Energy & Cost Saving
Electricity Natural Gat Total
Amount Cost Amount Cast Amount Cost
(kwhr) (S) (cuft) ($) tatuxlO') ($)
Impiemen- Simple
t of ion PoyoocK
Cost Period
($) (years)
Installation of More Efficient
Variable-Speed Drives
Preferential Operation of Most
Efficient Row Sewage Pumps
Monitoring of Pump Efficiency1
Reduction of Fuel Requirements
Far Sludge Incineration
Recovery of Incinerator
Exhaust Heat'
Bypassing of Tertiary Filters '
Modification of Aeration System
Lowering of Water Level in
Equalization Basin
Cleaning of Boiler
Reduction of MV-2 Use
Reduction of Outside Air
Recovery of Waste Heat
from Aeration Blowers
Installation of Water Source
Heat Pumps*
Installation of Insulated Glass
Recovery of Waste Meal from
Transformers
Increase in Conductor Size'
Correction of Motor Circuit
Power Factor1
Reptocement af Standard
Fluorescent Fixtures with
low-Wattage Fluorescent
Fixtures
Replacement of Incandescent
Lamps with Self-Sal las ted Metal
Halide Fixtures
Replacement of Mercury Vapor
Fixtures with High-Pressure
Sodium Fixtures
Replacement of Manual Switches
with Time-Out Switches
TOTALS
SS.SOO 1,780 -- -- 189.4 1,780 27,000 15.2
4,000 200 » » 20.5 200 -0- -0-
- 29,200,000 87,400 29,200 87,400 1,200,000 13.7
3K.OOO 12,700
Ml,iOO 20,500
25,200
114,000
1,351.5 12,700
2,189.8 20,500
1,450,000 4,350 1,450 4,350
910 473,000 1,420 559 2,230
4,527,000 13,580 4,527 13,580
148,000 440
148
91,200
2,971.4
273 91.2
4*0
300
273
3.713
395.9 3.713
70,800 5.4
-0- -0-
800 0.18
-0- -0-
7,700 0.57
-0- .0-
75,000 250
11,195 41
37,000 10
40,200 1,290
97,900 3,130
48.500 1,550
108.500 3.470
137.2 1,290 3,240 2.5
334.1 3,130 3,370 I.I
iSS.S 1,550 2,520 1.4
370.3 3,470 l,7«0 0.5
1,535.400 49,143 35,889,200 107.443 44,101 157,I0( 1,440,385
1This ECO is unquontif ioble within the scope of this study so no values are given far costs or savingx.
>Th*_*"*fQ>' savings associated with mis ECO are estimated in Section 2.2.4. It was beyond the scape of mis study to
estimate the implementation costs, therefore, all values for mis ECO were omitted rather man inflate the totol energy
savings far all ECOs relative to implementation costs.
•Annual totals cannot be estimated for this ECO because it applies to only certain periods of the year. Weekly savings
estimates are given in Section 2-2.4.
i mis ECO involves changing from one heating source to another, only the total savings in Stu was given.
'The energy which could be saved through mis ECO and me cost to implement the ECO are both dependent on the extent
of implementation, therefore these estimates ware not included.
226
-------
TABLE 9
LIST OF ENERGY CONSERVATION OPPORTUNITIES
BIG RAPIDS WASTEWATER TREATMENT PLANT
Energy Conservation Opportunities
Reduction of Lift Pump Speed
Reduction of Blower Operation
Use of Fine Bubble Aeration
Oiffusers
Increased Uxe of Digester Gas
Solar Heating of Digester]
Reduction of Sludge Trucking '
Modification of Final Effluent
Supply Pumping
Cleaning of Boiler
Installation of Nighttime
Setback Controls
Reduction of Temperature in
Storage Room
Modification of Gravity Turbines
Reduction of Outside Air
Us* of Waste Digester Gas
Weatherstripping of Double-
Door Astragals
Enclosure of Existing Main
Entrance
Recovery of Waste Heat
from Transformers
Projected Annual Energy & Cost Savings
Electricity Natural Gas Total
Amount Cost Amount Cost Amount
(kwhr) ($) (cuft) ($) (BtuxlO1)
4,000 160 » — 13.6
30,700 1,228 -- -- 104.8
111,300 4,500 -- — 379.8
£00,000 1,800 £00
1,845,000 5,535 1,845
130.5
154,000 6,160 -- -- 525.6
42,000 126 42
370,000 1,110 370
136,000 410 136
93,500 280 93.5
704,000 2,120 704
270,000 810 270
18,500 55 18.5
6,600 20 6.6
12,300 492 -- -- 41.9
Cost
($)
160
1,228
4,500
1,300
5,535
1,175
6,160
126
1,110
410
280
2,120
810
55
20
492
nplemen- Simple
tation Payback
Cost Period
($) (years)
100
-0-
10,000
-0-
150,000
-0-
2,670
600
5,000
200
320
4,600
9,000
70
1,020
4,920
0.625
-0-
2.22
-0-
27.1
-0-
0.43
4.3
4.5
0.49
1.14
2.2
II. 1
1.3
51
10
Increase in Conductor Size :
Replacement of Incandescent
Fixtures with Low-Wattage
Fluorescent Fixtures
Replacement of Incandescent
Lamps with Self-Ballasted
Metal Halide Fixture)
Replacement of Mercury Vapor
Fixtures with High-Pressure
Sodium Fixtures
Replacement of Manual Switches
with Time-Out"Switches
TOTALS
40,200 1,610
48,127 1,930
6,131 245
20,150 300
137.2 1,610
164.3 1,930
2,940 1.8
490 0.25
20.9 245 770 3.1
68.8 300 230 0.35
426,908 17,075 4,085,600 12,266 5,673 26,066 192,980
The energy saving associated with thii ECO is 1022 gallons of gasoline, worth
The energy which could be saved through rhis ECO and the cost to implement
of implementation, therefore these estimates were not included.
$1,175 assuming a cost of $1.15/gal.
the ECO are both dependent on the extent
227
-------
TABLE 10
LIST OF ENERGY CONSERVATION OPPORTUNITIES
SALINE HASTEtfATER TREATMENT PLANT
Description
Destratifier Fans
Digester Gas Utilization
Replace Electric Unit
Heaters
Timer Light Switches
Outside Lighting Lamps
Incandescent Replacement
Lower Wattage Lamps
Insulate Digester Roof
Insulate Bldg Roofs
Storm Windows
Variable Frequency Drive
Annual
Energy
Savings
195 ccf
12,180 ccf
706 kwh
795 kwh
1,446 kwh
6,495 kwh
844 kwh
4,060 ccf
590 ccf
78 ccf
70,000 kwh
Annual
Cost
Savings
$ 22
4,139
240
40
72
325
42
1,421
206
27
3,500
Implemen-
tation
Costa
$ 240
7,300
600
120
339
2,030
194
1,800
3,050
250
12,800
Payback
Period
(yrs)
10.9
1.7
2.5
3.0
4.7
6.2
3.5
1.3
14.8
9.3
3.7
Based on $.05/kwh and $.35/ccf
ccf = 100 cu ft natural gas
kwh = kilowatt hours electricity
228
-------
FIGURE 1
SUMMARY OF OPERATING DATA
WASTE WATER TREATMENT PLANT, CACHLLAC, MICHIGAN (MARCH 76-SEPT. 78!
229
-------
FIGURE 2.
MARGINAL UTlL\T>f OF C*EM\GAL ADDITION
1
REMOVALS
COST OF CHEMICAL USAGE
MARGINAL UTILITY = INCREMENT*!
INCREMENTAL COST OF
CHEMICAL
230
-------
3! -
JO-
Zl
zt*
9
*
J 2Z,
f
Ift
17
16
14.
IZ
FIGURE 3
EXCESS AIR USED FOR
ANN /\RBOR WWTP
LE.VBL
7 \O
O
ill
417
"4-OO
JUU AUCs
OCT NOV P6£. JAN FE& MAR AfR MAY JUKI
ASRAT\ON
231
-------
PAPER NO. 17
ALTERNATIVE ENERGY SOURCES IN MUNICIPAL WASTEWATER
TREATMENT: THE WILTON, MAINE EXPERIENCE
by
David R. Fuller
Director of Technical Services
Wright - Pierce Architects and Engineers
Topsham, Maine 04086
232
-------
ALTERNATIVE ENERGY SOURCES IN MUNICIPAL WASTEWATER TREATMENT:
THE WILTON, MAINE EXPERIENCE
David R. Fuller , Director of Technical Services
Wright-Pierce Architects and Engineers
INTRODUCTION
The Municipal Wastewater Treatment Plant at Wilton, Maine was designed
to incorporate energy conservation and alternative energy features such as
active and passive solar space and process heating, effluent heat recovery,
digester gas generation and utilization, ventilation air heat recovery, and
electricity generation using digester gas. Designed in 1975 by Wright-
Pierce Architects and Engineers of Topsham, Maine and Douglas A. Wilke,
Architect and Solar Consultant of Glen Head, New York, the plant became
operational in September, 1978. Wright-Pierce received a grant from the
U.S. Environmental Protection Agency to monitor the plant's energy systems
from May, 1979 to March, 1981. This paper discusses the design of the
Wilton facility; the results of the monitoring program; and recommendations
for design improvement, with emphasis on the solar heating systems.
233
-------
DESCRIPTION OF TKEATMENT PLANT
The Wilton Wastewater Treatment Plant was designed to provide second-
ary treatment of the wastewater generated by the Town's population of
4,200, with the added requirement that there be zero discharge to the
receiving stream at streamflows less than 0.12 m /d the seven-day, ten-year
draught flow (7/Q/10).
Figure 1 is a process flow diagram. Wastewater is lifted into the
plant by screw pumps. Preliminary treatment consists of grit removal,
comminution, flow measuring, sampling, and screening. Secondary biological
treatment consists of rotating biological contactors (RBC). Final clarifi-
cation takes place in two peripheral feed clarifiers. The effluent is then
disinfected and discharged.
To meet the 7/Q/10 streamflow limitations, a 4.5 ha spray irrigation
plot directly north of the treatment facility is utilized. This system is
designed for 10 continuous days' operation during drought conditions.
Sludge, consisting of screenings from the preliminary screens and
sludge from the final clarifiers, is combined and mixed in a raw sludge
holding tank, then pumped to anaerobic sludge digesters for stabilization.
High-rate two-stage mesophilic digestion is used. Following digestion the
sludge is pumped to the dewatering area, then conveyed to the disposal
vehicle and trucked to a local farm for spreading on fields.
Architecture is a key element in any project where energy conservation
and the use of alternative energy sources are prime objectives.
Due to Wilton's cold climate, the entire plant is enclosed in two
structures with all the processes placed close together to keep the struc-
tures as small as practicable and reduce hydraulic runs, while providing
for future expansion. Gravity is used to avoid unnecessary pumping.
The building is shaped to hold snow on the roof and collect drifts of
snow against walls for increased natural insulation during the colder
months. Projections past the wall lines adjacent to glazed surfaces reduce
surface wind velocity and cut heat loss, as do recessed windows and doors.
Basic concrete materials were chosen for walls and roofs, because of
heat retention potential and low maintenance factors. Insulated glass is
used in all windows.
The building interior spaces are partitioned to separate areas re-
quiring different temperatures and different air changes for maximum con-
trol of heat loss. Partitions and doors between spaces with a temperature
differential of more than 6°C are insulated. Wherever possible, trans-
lucent fiberglass partitions are used so lighting from adjacent spaces can
be shared . Natural ventilation and air flow is controlled by louvers and
windows.
The building is built into a hillside, with little exposure to the
north, to minimize the exterior surface. Shrubs and trees provide wind
234
-------
FIGURE 1
TREATMENT PROCESS DIAGRAM
1 SCREW PUMPS
2 GRIT CHAMBER
3 COMMINUTOR
4 BAR SCREEN BY-PASS
5 FLOW MEASURING & SAMPLING
6 PRIMARY SCREENS
7 ROTATING BIO-CONTACTORS
8 SECONDARY CLARIFIERS
9 FLOW MEASURING & SAMPLING
10 CHLORINE CONTACT CHAMBER
11 PLANT EFFLUENT
12 SPRAY IRRIGATION
13 PRIMARY SLUDGE
14 SECONDARY SLUDGE
15 SECONDARY SKIMMINGS
16 SLUDGE HOLDING
17 SLUDGE TRANSFER
18 SLUDGE HEATER
19 SLUDGE RECYCLE PUMPS
20 ANAEROBIC SLUDGE DIGESTERS
21 SLUDGE HOLDING
22 SLUDGE DEWATERING PUMP
23 DEWATERING UNIT
24 DEWATERED SLUDGE
25 HYPOCHLORITE GENERATION
26 HYPOCHLORITE STORAGE
27 METERING PUMPS
DESIGN CRITERIA
Quantity of sewage
0.02 m3/s
Influent BOD
200mg/i (340 kg/d)
Influent suspended solids
200mg/1 (340 kg/d)
Effluent BOD
20 mg /1 (34 kg / d) •• 90% removal
Effluent suspended solids
20mg/l (34 kg/d): 90% removal
Sludge quantity to digesters
9.5 mVd at 3.5% solids
Methane yield
HO to I25 m3/d
Methane heat value
22,400 kJ/m3or 2.4 to 2.7 GJ/d
RAW SEWAGE
3CZ
13
235
-------
breaks. Reflection off snow in front of the building and on an earth mound
to the west supplements solar energy collection. The enclosing structures
are oriented southward to achieve maximum value from the sun's direct
energy through both passive and hydronic solar energy collection devices.
Insulated translucent fiberglass panels are oriented to the south at a
60 d£gree tilt for passive collection of solar energy. The panels cover
89 m , have a light transmission factor of 45% and a 0.29 "U" factor.
2
Flat plate hydronic solar collector panels covering 130 m set at a 60
degree slope form the south roof of the treatment plant. The collector
consists of an extruded aluminum plate and frame, copper tubing to trans-
port the collector fluid, and two panes of low iron content tempered glass.
The backs of the collectors are insulated with 114 mm of rigid polyiso-
cyanurate foam board insulation. An ethylene glycol solution is pumped
through these panels and heated to 50°- 60°C by the sun.
Although solar energy is used for space heating and domestic hot
water, its primary purpose is to provide heat for the anaerobic digesters.
The methane gas produced in the digestion process can be stored and used
not only in the methane boiler for heating purposes, but to run the plant's
emergency generator. This application of solar energy attempts to overcome
two of the main constraints on its widespread acceptability, namely its
traditional seasonal use and the difficulty of storing solar energy. By
using solar to heat the digesters, the solar equipment is used year round,
significantly decreasing the pay-back period. By producing methane as part
of the anaerobic sludge digestion process, solar energy is effectively
stored in the form of a compressible, combustible gas, a much more ef-
ficient storage medium than the usual hot air or water.
A sophisticated heating and ventilating design had to be achieved in
order to accomplish the energy goals. Because the main component is solar
energy using flat plate collectors in a cold climate, a basic constraint on
the heating system design was the use of relatively low temperature hot
water (50°C.) instead of the conventional 90°C water. Energy conservation
practices become extremely important when dealing with such low tempera-
tures. The thermal zoning of rooms to allow for individual room tempera-
ture control is very important. The office, locker room and laboratory
which are clustered at the northeast end of the building can be maintained
at 20°C for the operator's comfort. The rest of the areas in the plant
will experience seasonal and diurnal temperature fluctuations, dropping to
as cold as 7°C in winter and perhaps approaching 30°C on warm, sunny days
in the summer. The operators are normally not in these areas for any
extended period of time. It also should be kept in mind that most of these
areas contain processes which normally are not housed. The operator is
very important to the success of the energy conservation effort, in that he
must see to it that temperature controls are properly set, the doors are
kept closed and that temperatures are set back at night.
The heating system is designed for cascading the heating loads. The
digesters can be heated with 49°C water, building space heating can be
236
-------
accomplished with 38°C water and ventilation units use 32°C water. The
water which heats the digesters can, in turn, be used to supply heat to the
building's heating system and ventilation units without requiring supple-
mental heat between steps. The system maintains the flexibility of supply-
ing heat directly to one specific load as required.
Ventilation is a major problem in energy efficient heating design for
wastewater treatment plants, in that many of the process areas require many
air changes. In order to avoid throwing heat away, the plant makeup air is
conditioned with the exhaust air before it is vented.
Solar energy is the prime source of heat, both for the sludge diges-
tion process and the building. A secondary source of heat is the methane
gas produced in the anaerobic digesters, and its availability is intimately
dependent upon the success of solar heating. Another source of heat is an
electric heat pump which utilizes the heat energy available in the plant's
effluent. This heat pump is approximately three times as efficient as
electric resistance heat, and its use in wastewater treatment facilities
can be very cost-effective.
Figure 2 represents the inter-relationships among the heating sources
and heating loads. Heat from the solar collectors can either be trans-
mitted directly to the heat distribution system or can be sent to the solar
energy storage tank, which is a 7.5 m water tank. Which route it takes
depends on the relative temperatures of the solar collector loop and the
solar storage tank and on the needs of the system for heat.
Fueled by digester gas produced in the anaerobic digesters, the meth-
ane boiler comes on only when there is a call for heat that cannot be
satisified either by direct input of solar energy or by hot water stored in
the solar storage tank. The heat pump operates only when solar is un-
available either directly or indirectly and methane is unavailable.
Backing up the three primary heat sources are some secondary sources
which can be significant. Methane is used as the prime fuel for the
plant's 55 KW electric generator in addition to fueling the methane boiler.
Propane is stored on site in case of prolonged power outages when the
supply of methane is exhausted, but is not normally used as a fuel for the
generator. When the generator is operating it gives off a great deal of
heat. It is cooled by water from the solar storage tank, thus becoming a
usable source of heat.
The solar storage tank can be considered a heat source. It is used
for short-term storage of excess energy which is not directly usable. By
utilizing the storage capacity, the operator does not waste potentially
usable energy from the solar collectors or the electric generator. Heat
from the solar storage tank can either be put into the heat distribution
system or go directly to heating domestic hot water. The hot water heater
can be heated electrically, but it is unlikely that this will often be
required.
237
-------
FIGURE 2
ENERGY SYSTEMS CONCEPTUAL DIAGRAM
U>
oo
1 PROPANE
| (STANDBYf
PLANT
EFFLUENT
HYDRO NIC
SOLAR
COLLECTORS
METHANE
BOILER
SOLAR
STORAGE
HEAT
EXCHANGER
ELECTRIC
GENERATOR
L-ELECTRIC
POWER
ELECTRICJ
POWER ^
HEAT
DISTRIBUTION
SYSTEM
ELECTRC POWER
(SUPPLEMENTARY)
HEAT RECOVERY
PASSIVE
SOLAR
-------
Passive solar energy is provided by translucent fiberglass panels for
direct heating and lighting. Finally, building ventilation air is con-
ditioned by exhaust air through the use of a heat exchanger.
To accomplish the objectives of the digester gas system, two levels of
storage are used. J5hort duration storage is accomplished by compressing
the gas to 138 KN/m . This is a conditioning storage mode used to insure
steady flow of methane for digester mixing and to prevent too rapid cycling
of the high pressure methane storage compressor. Longer duration storage
is accomplished through the high pressure methane storage system, in which
methane is compressed to 1,380 KN/m . It is from the high pressure gas
storage tank that the boiler and generator are supplied.
ENERGY MONITORING OBJECTIVES AND DESCRIPTION
The objectives of the energy systems monitoring program were to pre-
dict, verify, and summarize the performance of the building thermal systems
on a totally integrated basis that is not available through predictive
analysis of individual components.
These objectives are tied very closely to the basic energy conserving
design of the plant. Each subsystem is not especially unique in design by
itself; however, the integrated subsystems pose complex problems in the
interaction of process variables. This is especially prevalent in inter-
action between energy sources, i.e. solar input, methane boiler, heat pump;
and energy users, i.e. digesters, building heating and ventilation.
The integration of these subsystems is unique; and the design was
based, in part, on data provided by solar, emergency generator, boiler and
digester manufacturers who have detailed knowledge of their equipment but
limited knowledge of the total system. It is in these areas that the
system was monitored to determine how the components interface.
Active Solar
In the active solar subsystem an ethylene glycol water solution is
circulated through collector plates which are heated from the sun's rays.
This energy is then exchanged to the plant circulating water system. An
underlying design premise is to use solar energy whenever it is available,
with the use as a function of exchanged temperature. The total performance
of this subsystem needed to be determined.
Solar insolation was measured (for (1) direct, diffuse and reflected
and (2) direct and diffuse only) and continuously recorded on a strip chart
with an integrated digital output as well. Solar plate temperature and
glycol flows and temperatures were also recorded. A hydronic BTU computer
monitored the total heat from the solar heat exchanger for both analog and
digital recording. Electrical input to solar pumps was also monitored.
239
-------
Digester
The digester subsystem again is not especially unique in its function
and design; however, the integration with the total system and its part in
the energy conserving nature of the plant is unique. The digester gas
released becomes an important part of the total operation, as it was de-
signed to be used in the gas boiler "in normal operation and the emergency
generator when excess gas is available.
A determination was made to the quality and quantity of gas produced
and where it is used. The properties and quantities of the sludge flow in
and out of the digester, the sludge and digester temperatures and the
heating and electrical requirements were monitored.
Effluent Heat Pump
The heat pump extracts heat from the effluent for use in the heated
water system.
Electrical input and heating output were monitored continuously with
digital outputs. Additionally, temperature and pressure drops across the
evaporator and condenser and the auxiliary pump electrical usage were
monitored. The unit coefficient of performance was determined for various
conditions.
Passive Solar
Light/heat transmitting panels are employed in this plant. Their
contribution to the total plant energy provides useful design data for
scaled-up plants.
Solar insolation and solar transmissivity were measured and con-
tinuously recorded. Space temperature and heating requirements were also
monitored to give an indication of the heat storage effect of the struc-
tural mass of the building.
Weather Data
All design calculations for this plant were based on weather data
provided by the National Weather Bureau. Environmental conditions were
monitored using a small weather station located at the Wilton treatment
plant. The data can be used as a correlation for actual plant performance
especially in solar input as a function of ambient temperature, wind
velocity, season, etc.
Electrical/Fuel Consumption
This plant's equipment was designed for high efficiency, high power
factor and low energy consumption. High pressure sodium lighting was
employed where possible with selective switching and task lighting. Equip-
ment was arranged for selective running from the emergency generator de-
pending on gas production.
240
-------
All significant electrical usage was monitored and audited by function
so the total energy requirements for systems such as solar can be determin-
ed.
Digester gas production and propane usage were recorded.
Ventilation Air Heat Recovery
An air-to-air heat exchanger is used to recover heat from plant ex-
hausts. The efficiencies for varying conditions were determined and the
increased fan power pressure drops were recorded.
Domestic Hot Water System (DHW)
The DHW system is designed to recover heat from either the storage
tank or the system return water whenever possible. A hydronic BTU computer
monitored its output along with the electrical input. System losses and
the recovery pump requirements were determined.
Process Flow
Temperatures were recorded at various points to determine the heat
transfer between the process flow and the plant.
RESULTS
The monitoring system was designed and installed based on anticipated
results. Generally, the equipment was of sufficient sensitivity and range
to provide valid results. With the available data, each major component of
the heating system was analyzed and evaluated for its energy and cost-
effectiveness .
From Table 1 it can be seen that each of the energy subsystems, except
for Digester Gas Production, was a net energy producer and net cost saver.
However, the pay-back periods generally were greater than are economically
justifiable.
241
-------
TABLE 1
ENERGY AND COST-EFFECTIVENESS SUMMARY
Component
Active Solar
Passive Solar
Heat Pump
Generator Heat
Recovery
Air-to-Air Heat
Exchanger
Digester Gas
Production
Energy Output/
Input Ratio
(1)
Value Output/,-,
Input Ratio ('
113
9.0
0.59
86
6.1
0.72
Cost-Effective
11.5
32%(3)
2.9
3.5
N/A
1.5
No
No
Yes
No
(4)
Yes
No
1
The Energy ratio is the total energy produced divided by the energy input
required.
2
The Value Ratio is the dollar value of the energy produced divided by
input energy cost.
Actual average monthly solar radiation transmitted through panels from
June 1, 1979 to April 1, 1980.
\
Due to low usage; if used more, it could be cost-effective.
242
-------
Active Solar
Table 2 summarizes the active solar system data between June, 1979 and
April, 1980, as follows:
1. Recorded clear day insolation levels were consistently above
ASHRAE estimates with an average difference of 13.8% (Item 9).
2. The recorded percent of possible sunshine was 60% versus an
average of 52% predicted (Item 5). This is consistent with the
unusually low precipitation levels experienced.
3. The average incident solar radiation was 37.3% above that esti-
mated (Item 11).
4. The total solar energy collected was 122 GJ (Item 16) which was
64% of that estimated.
5. The overall solar system efficiency, being the net energy
collected divided by the total incident available, was 23% (Item
15).
An overall efficiency of 23% is significantly lower than that an-
ticipated. A great deal of effort was spent in investigating the reasons
which were presumed to be one or more of the following:
1. Data/Instrumentation error.
2. Collector Heat Loss Factor
a. Inadequate thermal isolation.
b. Possible convective losses between the absorber plate and
the rigid insulation.
3. Collector Heat Transfer Losses
a. Air within the fluid loop.
b. Effect of the glycol solution.
4. Control sequencing and response.
5. Collector response sensivity.
6. Collector efficiency losses due to dirt accumulated during con-
struction.
While all of these factors (excluding the first) certainly contribute
to the solar system performance, the overriding cause appears to be the
combination of all of them coupled with and the lack of an accurate cal-
culation procedure to simulate this interaction.
There is obviously a significant difference between instantaneous
collector efficiency and day-long or, more importantly, year-long collector
efficiency. Instantaneous efficiencies are useful in comparing various
243
-------
Table Z
N)
HOHTII1.T SUMMARY UiO SOLAR UTILIZATION
I Month
2 Hays in Month
3 A5HRAE Clear Day Insolation (W/m») (A)
It r.riimmaii Clear Day Insolation (W/m«) (Bl
5 (Iran Percent of Possible Sunshine (Cl
6 Probable Available (4 x 5)
7 Recorded Averaxe. Insolation (W/m1 Day)
8 Recorded Cleat Day Insolation (W/m* Day) (D)
9 Recorded l/ASIIRAE I (g / 3) (E>
10 Recorded Clearness (7 / 8) (N)
11 Recorded I/Probable I (7 / 6)
IB Percent Solar (16 / 17 x 100) (Ml
19 Average Daily Temperature (°C)
A Solar insolation for the 21sl of each month, 44° latitude., 59" tilt from the horizontal, fscing due south.
B. Solar insolation for the 15th of each month, 44" latitude, 60" tilt from the horizontal facing 2° west of south.
O.ita used in original projections.
C. Tabulation derived from "Normals, Means, and Extremes" table in U.S. Weather Bureau publication, Local ClImatological
Data. 53 percent average using Albany, New York.
D. Actual clear day data recorded for each month.
E. 13.8 percent over ASIIRAE clear day data.
F. 37.3 percent over probable available insolation.
G. Probable net collected 6x collector efficiency factors.
H. Net collected (water side of solar heat exchanger).
I. 64.2 percent of that estimated.
J. 23 percent of recorded incident solar collected.
K. For 119.5 m collector surface, 122.9GJ/10 months.
L. Healing load includes process, transmission and ventilation loads.
M. 23 percent overall being supplied by solar.
N. Actual average percent of possible sunshine - 60 percent.
Jan
31
229
217
43
93
149
277
1.21
0.54
1.60
41
23
0.56
IS. 5
7.45
101.63
7
-7
Feh
29
276
263
51
134
198
300
1.09
0.66
1.48
63
44
0.71
22.4
13.25
92.16
14
-8
Mar
31
266
273
53
145
172
338
1.18
0.51
1.19
71
44
0.62
25.4
14.06
91.54
15
-1
Apr
30
267
Z57
53
136
..
..
..
..
65
..
__
_.
—
..
9
May
31
248
234
57
133
..
—
--
..
..
61
..
..
—
..
..
--
II
Jun
30
238
220
62
136
191
?64
1.11
0.72
1.40
62
33
0.54
17.4
10.31
16.96
61
ir
Jui
31
243
722
63
140
198
237
0.9;
0.84
1.42
69
28
O.'il
14.1
8.93
9.99
89
22
Aug
31
259
239
61
146
172
309
1.19
0.56
1.18
78
402
0.54
24.5
12.90
17.16
75
17
Sep
30
272
257
58
149
228
304
1.12
0.75
1.53
83
79
0.95
34.5
13 16
29.33
88
12
Oct
31
260
260
54
140
123
301
1.16
0.41
0.88
77
3.3
0.43
27.2
10.67
46.58
23
8
Nov
30
221
2J2
39
9O
112
262
1.16
0.43
1.24
46
27
0.58
21.6
8.22
47.24
17
4
Dec
31
205
199
38
76
137
245
1.19
0.56
1.81
33
35
I.OB
25.9
11 33
8.7.44
13
— 4
See N(
A
B
C
D
E
N
r'
G
II
I
J
K
\.
H
-------
types of collectors under similar steady state conditions, but tend to
create a misleading picture of the efficiency of water heating systems
operating over long periods.
In the month of March, for example, approximately 1/3 of the incident
radiation was of too low an intensity to collect. In many cases the col-
lector plate temperature never reached a usable or threshold level although
considerable insolation was available. An illustration of these losses in
long term efficiency is shown in Figure 3 for a clear day. The corres-
ponding losses for a cloudy day are obviously greater, particularly if the
solar radiation intensity equals the critical, or threshold intensity.
- '/COLLECTED. V
•;.-( USABLE)-'.'.
•SOLAR ENERGY;'
TOTAL SOLAR
RADIATION
-PERIOD OF COLLECTOR OPERATION'>\'.'.'X
CRITICAL OR THRESHOLD' INTENSITY^t^i',_
LOSSES DURING
COLLECTOR OPERATION
( IF TEMPERATURE
DIFFERENCE 6 CONSTANT)
SUNRISE | NOON I SUNSET
SOLAR ENERGY TOO LOW IN INTENSITY TO COLLECT, TYPICAL FOR SUNRISE a SUNSET CONDITIONS
FIGURE 3 COLLECTION OF SOLAR RADIATION THROUGHOUT THE DAY
The dominant factor in establishing the threshold intensity level is
the temperature difference between the absorber plate and the ambient air.
If this difference is minimized by either a warmer climate or a cooler col-
lector fluid, as in the case of a heat pump assisted system, or both; then
this threshold level would be reduced and the long term system efficiency
improved. For example, in the case of a heat pump/solar system with an
average collector fluid temperature of 10°C and an ambient temperature of
24°C, the threshold intensity level would actually be negative, enabling
the system to collect heat without solar radiation.
As indicated, the causes were investigated for the lower overall
efficiency based on the assumption that the estimating procedures were
accurate. Numerous alternative procedures were studied with similar in-
flated results. In the course of the investigation several publications
were discovered which included test data for actual solar systems monitored
for a one year period. The results of these studies are similar to the
findings to date at the Wilton plant. Each of the systems monitored con-
245
-------
sisLeu of flat plate collectors, non-selective coating, with two glass
covers. The tirst involved a 50 m2 solar system located in Morton Grove,
Illinois (1). This system was monitored in 1975 by the Fluid Handling
Division of ITT and had an overall efficiency of 21%. The second system
was located in Fort Collins, Colorado (2). It was monitored for one year
by the Solar Energy Applications Laboratory at Colorado State University
and had an overall efficiency of 19%.
Passive Solar
The passive solar array is built into the wall at two levels. Solar
radiation passes through the array providing both heating and lighting in
the Clarifier Room. Each bank of panels has an overhang which tends to
shade them during the summer months when heating is not required. Operable
windows cool the space when the temperatures become excessive. The energy
collected during these times is lost and, therefore, not considered useful.
Increasing the transmissivity and/or decreasing the "U" factor would
increase the net quantity of collected solar radiation. More would be pro-
vided as useful during the winter but more would have to be dumped during
the summer. For the panels, varying the ratio of transmissivity/"U" factor
and estimating the net energy collected would provide an indication of what
a change in that ratio would do to the system. Other factors such as
overhangs, the blocking effect of the internal panel spacers, and vari-
ations in trar.saiissivity with incident angle also need be considered.
For this installation, the variation in overall performance appears
adequate, transmissivity increasing during the winter, decreasing during
the summer. The overhang is responsible for a decrease in transmissivity
during the summer up to a daily average of 14 percent.
Heat Pump
The heat pump operating time was greater than anticipated during this
period. The Coefficient of Performance (COP) was a quite acceptable 2.9
during the heading season. The generation of the heating energy gave a net
cost savings and the payback period was reasonable (11.4 years). Had the
heat pump operating time equaled the projected operating time, the payback
period would have been closer to i'.5 years, which is still reasonable.
The actual and projected hours of operation are based on present
operating conditions. As the plant flow increases and digester gas pro-
duction increases, the heat pump may be used less with an increasing pay-
back period due to less operating time.
To date, the operation and maintenance problems encountered have been
relatively small. A good deal of time, however, has been spent in cleaning
the effluent strainers. Records should be kept for several years to deter-
mine realistic O&M costs for the system.
246
-------
Generator Heat Recovery
The generator heat recovery loop operated approximately one half hour
per week during the generator exercise period. During part of that time,
the recovery loop was not used because the storage tank temperature was
warmer than the maximum generator cooling heat exchanger allowed. Town
water was then used to cool the generator. This condition will arise
regularly during the summer when there is a limited heating demand and the
active solar system is able to provide most of the heating required.
The generator could be exercised for longer periods of time during the
heating season when digester gas is available.
The generator heat recovery loop has the highest energy output/input
ratio, but the payback period is the worst. This is due to the low periods
of use being experienced. Increased usage would increase cost-
effectiveness .
Digester Gas Generation
The digester gas generation system is, from Table 1, an energy and
value loser. However, process requirements must also be considered when
evaluating this system.
Reflected Solar Radiation
The attempt to measure the magnitude of the ground reflected solar
radiation component met with limited success. The reflected component for
peak nonclear days was within the experimental accuracy of the equipment
being used. The average daily reflected component consists of both re-
flected and some diffuse solar insolation. Thus no meaningful data on the
magnitude of the reflected componenet were gathered. Part of the reason
for this was the minimal snow cover experienced during the winter of
1979-80.
Electrical Usage
Even with the heat pump operating more and the generator operating
less than anticipated, the total electrical usage has been 12.5 percent
less than projected.
247
-------
ENGINEERING EVALUATION
Several areas have been recognized where design modifications might
significantly improve the performance of the energy system.
Hydronic Solar System
The solar heating system should be designed to supply thermal energy
to heat the digester only, not be part of an integrated space/process
heating system. While theoretically more efficient, the operating dif-
ficulties associated with a highly integrated system result in significant
system losses. The following guidelines apply:
a. The solar system should be designed to service the digester
directly with a glycol loop through the sludge heat exchanger.
b. The solar system should be designed to "dump" excess heat into
the secondary digester and/or a storage tank. A heat exchanger
should be provided to recover heat from sludge transferred from
the primary digester to the secondary digester and/or from sludge
wasted from the secondary digester.
c. The solar/sludge heat exchange system should be designed to
operate with service fluid temperature of 43° to 46°C. The
effectiveness of solar thermal energy collection improves sig-
nificantly with lower operating temperatures.
d. The ratio of solar collector surface area in m2 to sludge flow in
m3/d should be approximately 25:1 (i.e., 10 m3/d of sludge re-
quires 250 m2 of solar collector surface), assuming climatic
conditions similar to Wilson and digester insulation of R-20.
e. A conservative evaluation of expected sludge flow should be used
in sizing the solar collector array. Generally, sizing should be
based on average flow over the design life, or less.
f. Solar heating system design details:
1. The collector should be a flat plate design.
2. The collector tilt angle should be optimized for maximum
yield approximately 4:S days prior to and following winter
solstice.
3. Systems capable of digester heating with fluid temperature
of 43° to 46°C should use single glazing.
4. Systems requiring digester heating fluid temperatures
greater than 48°C should use double glazed collectors.
5. The solar collector must be a low mass, quick response
collector with a selective surface of a/e = 0.95/0.10,
where a/e is the ratio of absorptivity to emissivity.
248
-------
6. The associated hydronic system instrumentation and controls
must be designed to respond more quickly to the availability
of useable solar energy. Generally this requires a simpler
system design.
7. The solar collector array should be designed for thirty year
operation without significant maintenance and no replace-
ment.
g. The solar collector may form a roof under the following guide-
lines :
1. The collector absorber plate must be thoroughly thermally
isolated from the building support structure.
2. All seals must be high temperature silicone or equivalent.
3. All metals must be compatible or dielectrically isolated.
4. The collector glazing elements must be capable of simple
replacement.
5. The rear of the collector array should be within a heated
space and be accessible from the interior.
6. The rear of the collector should have R-20 insulation.
1. The tilt angle should be a minimum of 45 degrees.
h. Domestic hot water required for plant personnel should be sup-
plied through a takeoff heat exchanger on the main system.
As discussed below, it is doubtful that solar heating of anaerobic
digester can be shown to be cost-effective under current accepted economic
projections, or under any conceivable circumstances except for a small
range of treatment plant sizes, perhaps 0.04 m3/s to 0.10 m3/s. However,
if other factors (socio-political, regulatory, etc.) dictate, the above
guidelines will assure the most cost-effective use of solar thermal energy
for digester heating. It should be noted that advances in solar collector
technology since 1975 have incorporated many of the above guidelines.
Passive Solar Heating
1. Passive heating should be applied to "occupied" areas such as the
office and laboratory. It is less effective in areas exposed to water
surface such as Wilton's clarifier room, but may be desirable for
natural lighting purposes. Such areas should be heated minimally,
with thermostats set at 5°C. The movement of wastewater in these
areas will largely maintain temperatures greater than 5°C.
2. In areas to be heated to 20°C±, passive solar collectors should be
fitted with manually operated insulated shutters.
249
-------
Heat Pump
The effluent pick up tank should be sized to minimize drawdown pro-
blems associated with plant flow variations and designed to facilitate
maintenance of intake screens.
Instrumentation
Keep instrumentation as simple as possible. The instrumentation tends
to become complicated when integrating solar and other alternative energy
systems with the heating, ventilating and processes of the treatment plant.
Digester Gas System Design
The Wilton wastewater treatment plant's energy systems design has
received a great deal of attention. Since the inception of the energy
systems monitoring project, reports have been written concerning the eco-
nomic feasibility of solar-assisted anaerobic sludge digestion (3,4). It
is the author's opinion that some of these reports are overly optimistic
and that the operating results at Wilton do not justify this optimism.
The basis for the Wilton design is that the use of flat plate hydronic
solar collectors in concert with anaerobic sludge digestion is symbiotic,
that the low temperature thermal energy produced by the solar collectors
can be used to heat the digesters, replacing a portion of the digester gas
produced which would have to be burned to heat a similar nonsolar-assisted
digester. The gas thus replaced can be stored for use as a fuel for the
production of direct thermal energy (boiler), electrical energy (engine-
generator) , or mechanical energy (engine-drive). The cost-effectiveness of
active solar energy production is strengthened when so combined with an-
aerobic digestion. Its payback is quicker because the thermal energy is
needed year-round to heat the sludge. Storage of solar energy is much more
efficient in the form of the compressible, combustible, gas produced as a
byproduct of digestion than as hot water or air. This is the rationale
advanced to support the Wilton design and used to substantiate claims of
widescale cost-effective applicability in other reports.
The problem with the solar digester scenario is in its cost-
effectiveness; Wilton successfully demonstrates its technological feasi-
bility. The evidence from Wilton and elsewhere indicates, however, that
the payback on active solar systems is longer than anticipated due to
actual operating efficiencies being significantly lower than projected from
instantaneous design data efficiencies.
The other major flaw in the solar digester scheme is that heat can be
recovered, directly or indirectly, from the digester gas more cost-
effectively than by using solar. A study done by Wright-Pierce (5) to
determine possible innovative and alternative technologies for use at a
wastewater treatment plant being designed for Caribou, Maine indicates that
if there is sufficient sludge to justify anaerobic digestion as a stabili-
zation process, then it is more cost-effective to 1) burn the gas to heat
the digesters; 2) use the gas to fuel an engine-generator set to produce
250
-------
electricity and recover the heat given off by the engine to provide
digester heating; or 3) fuel an engine-drive set to operate equipment
(replacing electricity), with engine tieat recovery. If sludge digestion is
justified, then the heat recovered from any of the above systems will be
much more significant than any feasible solar contribution. If there is
not sufficient sludge to make anaerobic digestion cost-effective, then
adding solar will not make it so (this is Wilton's situation).
Wright-Pierce's report to EPA on the Wilton Energy Monitoring project
evaluated the cost-effectiveness of solar heated anaerobic digestion for a
range of treatment plant sizes (6). The conclusions from this analysis of
anaerobic digestion, with and without solar heating, compared with lime
stabilization for sludge processing were:
1. For wastewater treatment plants the size of Wilton's (1730 m3/d),
anaerobic digestion is not cost-effective and adding solar heat
make:; it even less so.
2. For a 3785 m3/d wastewater treatment plant, anaerobic digestion
is marginally cost-effective, but adding solar heat does not
improve its cost-effectiveness and in fact makes lime stabiliza-
tion more cost-effective.
3. For larger plants (37,850 m3/d), anaerobic digestion is clearly
cost-effective; and there is no use for solar heating, because
all heating requirements caa be met with waste heat recovery from
the use of digester gas.
It appears that there is no role for solar heating in association with
anaerobic digestion. Based on work done by others (4), if solar heating is
not cost-effec-cive when applied to anaerobic digestion, it is doubtful that
it is cost-effective with any wastewater treatment process. It should be
noted that no attempt has been made here to consider climatic conditions
other than those encountered in Wilton, Maine, or other treatment proces-
ses. However, it is doubtful that solar heating of anaerobic digestion can
be shown to be cost-effective in any climate, regardless of primary and
secondary treatment processes used.
The analysis indicates that the price of conventional energy (oil,
electricity) will have to increase substantially more than projected and
the cost of solar heating substantially decrease before solar heating of
anaerobic digestion can become cost-effective, and then only for a
relatively insignificant number of small wastewater treatment plants; those
large enough for anaerobic digestion to be cost-effective compared to other
sludge stabilization methods, but too small for the gas produced to be
sufficient to render the plant thermally self-sufficient.
Non-economic (socio-political, regulatory) factors may mandate a
greater use of solar thermal energy, in which case solar heating of
anaerobic digesters may be justifiable for small facilities. The argument
has been made that solar should be incorporated into wastewater treatment
251
-------
plants, because it is an environmentally compatible "soft" energy source
and is independent of factors which might interrupt the supply of con-
ventional fuels. The reasoning is that if there is a sudden curtailment of
conventional energy supplies, public facilities such as wastewater treat-
ment plants probably would be among the first to be cut off. Therefore,
incorporation of solar energy and other alternative energy sources safe-
guards the operation of the treatment facility and the resultant environ-
mental protection.
By far the most energy used in wastewater treatment is electrical
energy to run equipment. Even if solar heating could be shown to be cost-
effective, the impact on total energy use in treatment plants would be
relatively insignificant.
CONCLUSIONS
The results of the monitoring data analysis and engineering evaluation
of the energy systems at the Wilton, Maine wastewater treatment plant have
led to the following conclusions:
1. Wastewater treatment plant effluent heat recovery, through the use of
a water-to-water heat pump is cost-effective under relatively severe
temperature conditions.
2. Ventilation air heat recovery is cost-effective.
3. Generator cooling loop heat recovery may be cost-effective if in-
creased use of the generator is warranted.
4. Passive solar heating, although not cost-effective as analyzed for the
Wilton plant, can be made cost-effective with design modifications.
5- Solar system instantaneous efficiencies, when applied to clear day
insolation levels and the mean expected percent sunshine, may lead to
an overly optimistic evaluation of the actual long-term performance.
These losses are related to the system threshold insolation intensity
and the random weather patterns. It would, therefore, appear that
computer simulation, using averaged hourly weather data and system
performance criteria, is required to accurately estimate the long-term
efficiencies. Moreover, since the threshold intensity level is pre-
dominantly affected by the difference in the average collector fluid
and ambient temperatures, the long-term efficiency may be signifi-
cantly reduced in northern climates.
6. Solar thermal energy collection for the purpose of producing supple-
mental heat for anaerobic sludge digesters is probably not cost-
effective under currently accepted economic projections, regardless of
size or location of the facility.
252
-------
RECOMMENDATIONS
Based on the work done on the Wilton Treatment Plant monitoring pro-
ject, the following are recommended:
1. A more realistic procedure must be developed for accurately
estimating active solar heating system performance for the pur-
pose of designing solar installations for space or process heat-
ing. Computer simulation models, taking into account site-
specific hourly weather data, solar collector system response
time, and inherent system losses should be developed to ac-
curately evaluate alternative solar designs for cost-
effectiveness during the preliminary design of a project. On-
site weather data should be collected prior to the design phase
to take into account site-specific microclimatology.
2. Although the it was concluded that solar heating of anaerobic
digesters is probably not cost-effective, guidelines have been
developed (see ENGINEERING EVALUATION) which should, if followed,
significantly increase the efficiency of solar heating of
digesters.
3. Passive solar heating of treatment plant structures can be cost-
effective if applied to "occupied" areas such as the office and
laboratory if good energy conservation principles are followed in
the design of such areas. It is less cost-effective when applied
to process areas exposed to water surfaces. In the latter case,
it is important that room thermostats be set at 5°C, a temper-
ature which can largely be maintained by the water passing
through these areas. Combined with task heating (if necessary)
and proper energy conservation design, passive solar heating and
lighting can be cost-effective in process areas.
4. Effluent heat recovery through the use of a heat pump is cost-
effective. Operational problems can be minimized by properly de-
signing the effluent sump from which the heat pump draws to pro-
vide sufficient capacity at minimum plant effluent flows.
5. Instrumentation and controls should be simplified as much as
possible. The theoretical advantages of integrated energy sys-
tems can be offset by complicated trouble-prone instrumentation.
6. The available evidence indicates that solar heating of anaerobic
digesters is probably not cost-effective in accordance with the
EPA guidelines, regardless of size of the treatment facility.
There has been significant interest expressed throughout the
United States in pursuing this concept under widely varying
conditions of climate, process, size, etc. It is recommended,
therefore, that EPA undertake modeling of the application of
solar heating of anaerobic digesters to determine its cost-
effectiveness under different conditions to determine if the
conclusions drawn from the Wilton project can be generalized.
253
-------
In the meantime, it is recommended that EPA not promote solar
heating of anaerobic digesters and require detailed supporting
documentation for any grantee requesting EPA Construction Grant
Program funds for the design and construction of such facilities,
REFERENCES
1. Solar Heating Systems Design Manual. Training and Education
Department, Fluids Handling Division, ITT Bulletin TESE-576.
2. Solar Heating and Cooling of Residential Buildings - Sizing,
Installation and Operation of Systems. U.S. Department of
Commerce, Economic Development Administration, Stock No.
003-011-00085-2.
3. Use of Solar Energy to Heat Anaerobic Digesters.
EPA 600/2-78-114, NTIS No. PB 286940, U.S. Environmental
Protection Agency, Cincinnati, Ohio, 1978.
4. Overly, P., and C. Franklin (Acurex Corp.) Solar Energy for
Pollution Control. EPA Contract No. 68-03-2567, 1978.
5. Wright-Pierce. Conceptual Design Report, Grimes Mill Waste-water
Treatment Plant, Caribou, Maine. 1979.
6. Fuller, D.R., D.A. Wilke, P.L. Thomas and A.J. Lisa (Wright-
Pierce) . Integrated Energy Systems Monitoring of Municipal
Wastewater Treatment Plant in Wilton, Maine. EPA Contract No.
68-03-2587, 1981.
"This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved
for presentation and publication."
254
-------
PLANT OPERATION AND DESIGN PROGRAM
Related Publications and Papers
December 1981
Areawide Assessment Procedures Manual. July 1976. EPA-600/9-76-014,
U.S.EnvironmentalProtectionAgency, Cincinnati, OH. Order No.
PB-271863/AS* (Set--3 Volumes)
Bender, J. H, March 1978. Parallel Evaluation of Constant and Diurnal
Flow Treatment Systems. EPA-600/Z-78-034, U.S. Environmental Protection
Agency, Cincinnati, OH. Order No. PB-281401/AS*
Bender, J. H. January 1979. "The Oxidation Ditch Process: Superior
Performance and Reliability at Low Cost," Environmental Research Brief.
U.S. Environmental Protection Agency, Cincinnati, OH.
Benjes, H. J. December 1976. Cost Estimating Manual - Combined Sewer
Overflow Storage and Treatment.EPA-600/Z-76-286, U.S.Environmental
Protection Agency, Cincinnati, OH. Order No. PB-266359/AS*
Benjes, H. H., J. A. Faisst, and T. S. Lineck. Capital and O&M Cost
Estimates for Biological VJastewater Treatment Processes.August 1979.
DraftReport,MunicipalEnvironmentalResearchLaboratory, U. S.
Environmental Protection Agency, Cincinnati, OH.
Chesner, W. H., and J. J. lannone. February 1980. "Current Status of
Municipal Wastewater Treatment with RBC Technology in the U.S.," In:
Proceedings: First National Symposium/Workshop on Rotating Biological
Contactor Techno!ogyTVolume I, EPA-600/9-80-046a, U.S. Environmental
Protection Agency, Cincinnati, OH. Order No. PB-81-124539*
Collins, M. A., and R. M. Crosby. October 1980. "Impact of Flow
Variation on Secondary Clarifier Performance," Presented at 53rd Annual
Conference WPCF, Las Vegas, NV.
Construction Costs and Operation and Maintenance Requirements for
Vlastewater Fi1tration. Draft Report, Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH.
Costs of Chemical Clarification of Wastewater. Draft Report, Municipal
Environmental Research Laboratory, U.S. Environmental Protection Agency,
Cincinnati, OH.
Crosby, R. M. Evaluation of the Hydraulic Characteristics of Activated
Sludge Secondary ClarifieTs"^ November 1981. Draft Report, Municipal
Environmental ResearchCaBoratory, U. S. Environmental Protection
Agency, Cincinnati, OH.
255
-------
Crosby, R. M., and J. H. Bender. March 1980. "Hydraulic Considerations
That Affect Secondary Clarlfler Performance," Technology Transfer. U.S.
Environmental Protection Agency, Cincinnati, QW. ~~
Efficient Treatment of Small Municipal Flows at Dawson, Minnesota.
October1977.EPA-625/Z-77-015,075^EnvironmentalProtection
Agency, Cincinnati, OH.
Ettllch, W. F. December 1977. Transport of Sewage Sludge.
EPA-600/2-77-216, U.S. Environmental Protection Agency, Cincinnati, OH.
Order No. PB-278195/AS*
Ettllch, W. F. March 1978. A Comparison of Oxidation Ditch Plants to
Competing Processes for Secondary and Advanced Treatment of Municipal
Wastes. EPA-600/2-78-051,CmEnvironmental Protection Agency,
Cincinnati, OH. Order No. PB-281380/AS*
Ettlich, W. F., and A. E. Lewis. August 1977. User Acceptance of
Wastewater Sludge Compost. EPA-600/2-77-096, ti7*T. Environmental
Protection Agency, Cincinnati, OH. Order No. PB-272095/AS*
Ettlich, W. F., and A. E. Lewis. June 1978. A Study of Forced Aeration
Composting of Wastewater Sludges. EPA-600/2-78-057, U.S. Environmental
Protection Agency, Cincinnati, OH. Order No. PB-285232/5BE*
Evaluation and Control of Sidestreams in Publicly Owned Treatment
Works.July1981.DraftReport,MunicipalEnvironmentalResearch
Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH.
Evaluation and Documentation of Mechanical Reliability of Conventional
Plant Components.December 1980.Draft Report, Municipal Environmental
Research Laboratory, U.S. Environmental Protection Agency, Cincinnati,
OH.
Evans, F. L. July 1979. "Summary of National Operational and
Maintenance Cause and Effect Survey," Technology Transfer. U.S.
Environmental Protection Agency, Cincinnati, OH.
Ewing, L. J., Jr., H. H. Almgren, and R. L. Culp. June 1978. Effects
of Thermal Treatment of Sludge on Municipal Wastewater Treatment~Costs.
EPA-600/2-78-073, U.S. Environmental Protection Agency, Cincinnati, OH.
Order No. PB-285707/AS*
Foess, G. W., J. G. Meenahan, and D. Blough. August 1977. Effects of
Flow Equalization °_" the Operation *"d Performance of an Activated
Sludge Plant.EPA-600/Z-77-138, U.S. Environmental Protection Agency,
Cincinnati, OH. Order No. PB-272656/AS*
256
-------
Foess, G. VI., J. G. Meenahan, and J. M. Harju. December 1976.
Evaluation of Flow Equalization at a Small Wastewater Treatment Plant.
EPA-600/2-76-181, U.S. Environmental Protection Agency, Cincinnati, OH.
Order No. PB-260375/AS*
Gray, A. C., P. E. Paul, and H. D. Roberts. October 1980. "Operational
Factors Affecting Biological Treatment Plant Performance," JWPCF, 52:7,
pp 1880-1892.
Gray, A. C., P. E. Paul, and H. D. Roberts. July 1979. Evaluation of
Operation and Maintenance Factors Limiting BiologicalWastewater
Treatment Plant Performance. EPA-600/2-79-078, OT Environmental
Protection Agency, Cinclnatl, OH. Order No. PB-80-108947*
Gray, A. C., P. E. Paul, and H. D. Roberts. Evaluation and Documentation
of Operation and Maintenance Factors Limiting Biological Treatment and
Plant Performance, Phase IT.FinalReport,MunicipalEnvironmental
Research Laboratory, U.S. Environmental Protection Agency, Cincinnati,
OH.
Grover, K. October 1979. "Don't Blame the Operator," American City
and County.
Handbook for Identification and Correction of Typical Design
Deficiencies of Municipal Wastewater Treatment Facilities.October
1981.Draft Final Report, Municipal Environmental Research Laboratory,
U.S. Environmental Protection Agency, Cincinnati, OH.
Harber, A. F., and R. C. Bain. July 1979. Novel Methods and Materials
of Construction. EPA-600/2-79-079, U.S. Environmental Protection Agency,
Cincinnati, OH. Order No. PB-80-113681*
Hegg, B. A., K. L. Rakness, and J. R. Schultz. October 1977.
"Evaluation of Operation and Maintenance Factors Limiting Municipal
Wastewater Treatment Plant Performance," Presented at Rocky Mountain
Water Pollution Control Association, Albuquerque, NM.
Hegg, B. A., K. L. Rakness, and J. R. Schultz. March 1978. "Evaluation
of Operation and Maintenance Factors Limiting Municipal Wastewater
Treatment Plant Performance," JWPCF. 50:3 pp. 419-426.
Hegg, B. A., K. L. Rakness, and J. R. Schultz. March 1978. "Summary -
O&M Factors Limiting Wastewater Treatment Plant Performance," Presented
at O&M Workshop - Steering Committee for the Joint U.S./Canada Great
Lakes Commission.
Hegg, B. A., K. L. Rakness, and J. R. Schultz. October 1978.
"Evaluation of Operation and Maintenance Factors Limiting Municipal
Wastewater Plant Performance - Phase II," Presented at 51st Annual
Conference WPCF, Anaheim, CA.
257
-------
Hegg, B. A., K. L. Rakness, and J. R. Schultz. June 1979. A
Demonstrated Approach for Improving Performance and Reliability oT
Biological Uastewater Treatment Plants. LPA-600/2-79-035, - ITST
Environmental Protection Agency, Cincinnati, OH. Order No.
PB-300476/AS*
Hegg, B. A., K. L. Rakness, and J. R. Schultz. June 1979. Evaluation
of Operation and Maintenance Factors Limiting Municipal Wastewater
Treatment Plant Performance. EPA -600/2- 79-034, — tiTST. — Environmental
Protection Agency, Cincinnati, OH. Order No. PB-300331/AS*
Hegg, B. A., K. L. Rakness, and J. R. Schultz. March 1980. "Evaluation
of O&M Factors Limiting Wastewater Plant Performance," Pollution
Engineering.
Hegg, B. A., K. L. Rakness, and J. R. Schultz. October 1980. "Case
Histories - Improving Wastewater Treatment Plant Performance," Presented
at 53rd Annual Conference WPCF, Las Vegas, NV.
Hegg, B. A., K. L. Rakness, J. R. Schultz, and L. D. DeMers. August
1980. Evaluation of Operation and Maintenance Factors Limiting
^u^-lP8! __Wa!5ewa.ter Treatment Plant Performance, Phase II.'
EPA-600/2-80-129, UTs"! Environmental Protection Agency, Cincinnati,
OH. Order No. PB-81-112864*
Hourly Diurnal Variations in P"blic1y Owned Wastewater Treatment
Facilities" September H58T7 EPA-bOO/2-81-218, [TTST Envi ronmental
Protection Agency, Cincinnati, OH. Order No. PB-107954/AS*
Lykins, B. W., Jr., and J. M. Smith. January 1976. Interim Report on
the Impact of PL 92-500 on Municipal Pollution Control Technology.'
EPA-60U/Z-76-018, U.S. Environmental Protection Agency, Cincinnati, OH.
Order No. PB-248212/AS*
McMahon, R. F. Socioeconomic Impacts of Water Quality Strategies.
Final Report, Municipal Environmental Research Laboratory, 01 5".
Environmental Protection Agency, Cincinnati, OH.
Niehus, D. C. Incentives for Improved Operation and Maintenance of
Municipal Treatment Plant. Unpublished Report, Municipal Environmental
Research Laboratory, ll.S. Environmental Protection Agency, Cincinnati,
OH.
Niehus, D. C., G. A. Brown, and J. M. Houthoofd. August 1981. "Survey
of Private Sector Provision of Operation and Maintenance Services to
Publicly Owned Treatment Works," Newsbrief. U. S. Environmental
Protection Agency, Cincinnati, OH.
N1ku, S. , E. 0. Schroeder, and F. J. Samaniego. December 1979.
"Performance of Activated Sludge Processes and Reliability Based
Design," JWPCF, 51:12, pp 2841-2857.
258
-------
N1ku, S. and E. D. Schroeder. April 1981. "Stability of Activated
Sludge Processes Based on Statistical Measures," JWPCF, 53:4, pp
457-470. - H
Niku, S. and E. 0. Schroeder. May 1981. "Factors Affecting Effluent
Variability from Activated Sludge Processes," JWPCF, 53:5, pp 546-559.
Nitrogen Removal In a Flow Modulated, Single State Oxidation Ditch.
Draft Report, Municipal Environmental Research Laboratory, UTS".
Environmental Protection Agency, Cincinnati, OH.
Ongerth, J. E. May 1979. Evaluation of Flow Equalization 1n Municipal
Wastewater Treatment. EPA-6UU/2-/9-096, U.S. Environmental Protection
Agency, Cincinnati, OH. Order No. PB-80-139835*
Operation and Maintenance Considerations of Land Treatment Systems.
July 1981. Draft Final Report, Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH.
Performance of Activated Sludge Processes: Reliability, Stability, and
September 1981. EPA-600/2-81-227, U.S. Environmental
Protection Agency, Cincinnati, OH. Order No. PB-109604/AS*
Performance of Biological Wastewater Treatment Plants: Effects of Toxic
Pollutants. September 1980. Draft Report, Municipal Environmental
Research Laboratory, U.S. Environmental Protection Agency, Cincinnati,
OH.
Performance of Trickling Filter PJants: Reliability, Stability, and
Variability! September 1981. EPA-600/2-81-228, U7T. Environmental
Protection Agency, Cincinnati, OH. Order No. PB-108143/AS*
Review of RBC Design Procedures, and Process, O&M, Equipment and Power
Performance. September 1980. Draft Report, Municipal Environmental
Research Laboratory, U.S. Environmental Protection Agency, Cincinnati,
OH.
Roberts, H. D., A. C. Gray, and P. E. Paul. Model Protocol for the
Comprehensive Evaluation of Publicly Owned Treatment Works Performance
and Operation. May 1982, EPA 600/2-82-015, NTIS No. PB 82-180 480, U.S.
Environmental Protection Agency, Cincinnati, Ohio.
Schultz, J. R., B. A. Hegg, and K. L. Rakness. October 1980. "Realistic
Sludge Production for Activated Sludge Plants Without Primary
Clarifiers," Presented at 53rd Annual Conference WPCF, Las Vegas, NV.
Smith, J. M., F. L. Evans III, and J. H. Bender. May 1980. "Improved
Operation and Maintenance Opportunities at Municipal Treatment
Facilities," Presented at 7th U.S. /Japan Conference on Sewage Treatment
Technology.
259
-------
Vlesner, G. M. November 1977. Energy Requirements for Municipal
Pollution Control Facilities. EPA-600/Z-77-Z14,OuEnvironmental
Protection Agency, Cincinnati, OH. Order No. PB-276989/AS*
Wesner, G. M., G. L. Gulp, T. S. Uneck, and D. J. Hlnrlchs. June 1978.
Energy Conservation In Municipal Wastewater Treatment. EPA-430/9-77-011
(MCD-32), U.S. Environmental Protection Agency, Washington, DC. Order
No. PB-81-165391*
*Ava11able from: National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
260
OUSGPO: 1983— 759-102/0788
------- |