United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
EPA-GOO 2-79-035
June 1979
Research and Development
A Demonstrated
Approach for
Improving
Performance and
Reliability of
Biological
Wastewater
Treatment Plants
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-79-035
June 1979
A DEMONSTRATED APPROACH FOR IMPROVING
PERFORMANCE AND RELIABILITY OF
BIOLOGICAL WASTEWATER TREATMENT PLANTS
by
Bob A. Hegg
Kerwin L. Rakness
James R. Schultz
M & I, Inc., Consulting Engineers
Fort Collins, Colorado 80525
Contract No. 68-03-2224
Project Officers
John M. Smith
Benjamin W. Lykins
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or recommendation
for use.
ii
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment, and management
of wastewater and solid and hazardous waste pollutant discharges from municipal
and community sources, for the preservation and treatment of 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 most vital communications link between the researcher and the
user community.
Recent documentation of biological treatment plant performance has shown
that a combination of design, operation, maintenance, and administrative factor
adversely affect plant performance. An approach, called a Composite Correction
Program (CCP), was developed to address all factors limiting performance at
individual facilities. This report documents the CCP that was implemented at
the Havre, Montana Wastewater Treatment Plant and describes the resulting
improvement in performance at that facility.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
111
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ABSTRACT
Recent documentation of the performance of publicly owned wastewater
treatment facilities has indicated that a significant percentage of facilities
are not meeting design and/or permit effluent quality requirements. As a
result, a research activity was implemented to identify, quantify and rank
the factors limiting plant performance. Comprehensive evaluations at thirty
treatment plants were used to determine factors limiting performance in the
areas of administration, maintenance, design and operation. In addition to
the evaluation of performance limiting factors, a method (Composite Correc-
tion Programs) of improving plant effluent quality was developed during the
research effort. This report describes the method which was implemented at
one facility, describes the resulting improvement in performance for that
facility and projects the impact on performance if similar programs were
completed at all thirty facilities evaluated.
A Composite Correction Program (CCP) is designed to address all factors
which limit performance at a particular facility. During this research pro-
ject a CCP was implemented at the Havre, Montana Wastewater Treatment Plant.
The general approach used was to improve the process control decision making
capability of the plant superintendent and to eliminate administrative, minor
design, maintenance and operations factors which were preventing optimum per-
formance. Effluent quality at Havre for 6 months prior to the CCP averaged
31 mg/1 for BOD and 30 mg/1 for TSS. Both BOD and TSS concentrations aver-
aged less than 10 mg/1 for the 8-month period following initiation of the CCP
and development of desired activated sludge characteristics. Between these
two time periods plant BOD- loading increased by 27 percent, yet BOD,- dis-
charged to the receiving stream decreased by 68 percent.
IV
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The major conclusion documented during the Havre CCP was that this
type of program must be implemented over an extended period because of the
inherent long time required to effect biological process response. At Havre
three months were required to achieve good activated sludge characteristics.
Continued involvement for a longer time (over one year) was required to
transfer to the plant superintendent the capability to maintain good process
control. Continued involvement included telephone, written and person to
person on-site consultation.
An analysis of the potential improvement in plant performance that
could be achieved if CCP's were implemented at all thirty facilities evaluated
was developed. Significantly improved performance was projected at twenty-one
of the thirty facilities. If these projections were realized, the mass of
BOD discharged to the receiving streams would be reduced by 490 metric
tons/year (540 tons/year) and the mass of TSS discharged would be reduced by
470 metric tons/year (515 tons/year). In addition, sixteen of twenty-three
facilities that were found to be violating minimum secondary treatment stan-
dards could meet standards without major plant modifications that would re-
quire significant design and construction costs. Implementing CCP's is the
more cost effective approach to achieving desired treatment objectives at
most existing facilities, whether or not major facility design or construc-
tion changes are required.
This report was submitted in partial fulfillment of Contract No. 68-03-
2224 by M & I, Inc., Consulting Engineers, Fort Collins, Colorado, under the
sponsorship of the Environmental Protection Agency. Work described in this
report was accomplished during the period from June, 1975 to December, 1977.
v
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CONTENTS
Disclaimer ±±
Foreword ±±±
Abstract iv
Figures viii
Tables ix
Acknowledgement x
1. Introduction , . . 1
2. Conclusions 4
3. Recommendations 7
4. Havre Composite Correction Program 8
Plant Performance 11
Program Description 15
Phase 1 20
Phase II 22
Phase III 23
Phase IV 26
Discussion , 27
5. Projected Improvement Through Composite Correction Programs . 31
Reduced Pollutants in Plant Effluent 32
Additional Facilities Able to Meet Secondary Standards . . 46
Advantage of a Composite Correction Program 47
References 51
vii
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FIGURES
Number Page
1 Plant flow schematic for Havre, Montana ........ 9
2 Chlorinated effluent BOD and TSS concentrations at
Havre, Montana. . . 14
3 East unit settled sludge concentrations (SSC) at
Havre, Montana. . , 17
4 West unit settled sludge concentrations (SSC) at
Havre, Montana. 18
5 Final clarifier modification at Havre, Montana to
stop short-circuiting ..................... 24
6 Relative time involved for CCP activities 49
viii
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TABLES
Number Page
1 Summary of Performance Data for the Havre, Montana
Wastewater Treatment Plant ... 12
2 Plants for Which an Improvement in Performance Did Occur .... 33
3 Plants for Which an Improvement in Performance Could Occur ... 35
4 Plants for Which an Improvement in Performance Is Doubtful ... 39
5 Summary of Projected Improvement Using CCP's . . ... 43
6 Existing and Potential Performance for Suspended Growth
and Fixed Film Facilities Surveyed 44
7 Performance of Thirty Plants Surveyed Versus Minimum
Secondary Treatment Standards 46
IX
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ACKNOWLEDGEMENT
The project was conducted by M & I, Inc., Consulting Engineers. The
authors were aided by the following personnel:
Wayne C. Irelan, President
Gerald J. Ott, Engineer
Susan R. Martin, Lab Technician
Appreciation is expressed to all managers, operators and other person-
nel of the various wastewater treatment facilities who participated in the re-
search effort. Appreciation is also expressed to all state and EPA regulatory
agency personnel who developed the various lists of facilities as research
candidates, and who actively participated in various phases of the research
program. Appreciation is specifically expressed to Mr. Bruce Carlson, Super-
intendent, City of Havre, Montana Wastewater Treatment Facility for his assist-
ance in completing the Composite Correction Program accomplished as part of
this research effort.
The direction provided and assistance given by Mr. John Smith, Mr. Ben
Lykins and Mr. John Sheehy, of the Environmental Protection Agency, Office of
Research and Development, Cincinnati, Ohio, are greatly appreciated.
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SECTION I
INTRODUCTION
The "Federal Water Pollution Control Act Amendments of 1972" established
goals for the quality of the nation's surface waters and programs to achieve
these goals. A significant aspect of the Act was the expansion of the federal
grant assistance program for the construction of new and the upgrading of
existing wastewater treatment facilities. However, the U.S. Environmental
Protection Agency's annual reports to Congress (1) have indicated that a sig-
nificant number of facilities constructed with federal assistance were not
meeting design standards and/or National Pollutant Discharge Elimination Sys-
tem effluent requirements. Additional reports and articles (2, 3, 4, 5) have
addressed the need for improved operation and maintenance (0 & M) of. municipal
wastewater treatment plants. These documents have pointed to the area of
0 & M as the leading cause of poor plant performance. However, improper or
inadequate 0 & M has become a phrase that has been adopted to describe a broad
range of performance limiting factors. Staffing requirements, operator sal-
aries, design deficiencies, management techniques, industrial wastes, poor
maintenance and inadequate budget are but a few of the items that are commonly
described as 0 & M problems.
In an effort to define the broad area commonly described as poor 0 & M,
a research study was funded by the EPA Office of Research and Development to
identify, quantify and rank the factors causing poor wastewater treatment
plant performance. Two 24-month contracts were awarded simultaneously to
private engineering consultants to conduct the research effort, one in the
Eastern United States and one in the Western United States. This report doc-
uments a portion of the findings of the research effort by the western con-
tractor. A second report titled, "Evaluation of Operation and Maintenance
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Factors Limiting Municipal Wastewater Treatment Plant Performance," describes
the overall findings of the western contractor's research effort. (6)
During the research study a special research approach was developed to
identify the causes of poor performance. This approach was used during thirty
3 to 7-day comprehensive evaluations. One of the major conclusions of the
study was that a number of varied factors limited each plant's performance.
Many of these factors were obvious and were being addressed by various pro-
grams implemented by the cities, state regulatory agencies and EPA. However,
many of the performance limiting factors were not obvious and were not being
addressed by these programs.
Analysis of the complex interrelationship of varied performance limiting
factors and varied programs designed to address these factors led to the de-
velopment of a Unified Concept for Achieving Optimum Plant Performance. The
concept included performance limiting factors in administration, maintenance,
operation and design, and described how each factor could be individually
eliminated, partially eliminated or left un-addressed by existing programs
associated with public wastewater treatment. The concept also related opti-
mum performance to the many performance limiting factors associated with each
plant. The elimination of only a portion of the factors limiting performance
will not result in the desired improved effluent quality at a particular plant.
An approach for improving plant performance was developed in conjunction
with the Unified Concept. This approach was called a Composite Correction
Program (CCP). A CCP is based on optimizing the performance of an existing
- i $,• f
facility by eliminating obstructing factors in administration, design, opera-
tion and maintenance. A major difference between the CCP and many existing
programs is that a CCP concentrates on eliminating all factors contributing to
poor plant performance at an individual plant, whereas existing programs typi-
cally concentrate on specific areas of need representing common problems at a
large number of treatment facilities.
At each of the thirty facilities which were the subject of a comprehen-
sive evaluation in the research study, a varying degree of operational
-------
assistance was provided. The assistance was usually limited to improving pro-
cess control. Assistance in other areas like administration, maintenance,
design and long-term process control was usually not provided due to time and
budget restrictions. However, at the Havre, Montana Wastewater Treatment
Plant extensive follow-up assistance was provided throughout a full year to
demonstrate the conduct of a CCP. This report describes the Havre CCP and
documents the improved performance which resulted. Additionally, the poten-
tial improvement in performance was estimated for the other twenty-nine plants
evaluated assuming similar CCP's were implemented at these facilities.
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SECTION 2
CONCLUSIONS
1. A Composite Correction Program conducted at the Havre, Montana Wastewater
Treatment Facility significantly improved plant effluent quality.
A. Violations of permit standards were eliminated.
B. Plant effluent BOD,, and TSS concentrations were reduced from 31
mg/1 to 10 mg/1 and 30 mg/1 to 9 mg/1, respectively.
2. An increase in plant personnel by one operator and an increase in plant
coverage to 24-hour per day operation successfully reduced the detrimental im-
pact of the following plant features that hindered plant operation and perform-
ance: insufficient digester volume, digester foaming problems, variable air-
lift return pumping rates, return plugging problems and a relatively short
aeration basin detention time..
3. Detailed process evaluation during the Havre Composite Correction Program
enabled a clarifier short-circuiting problem to be identified and corrected.
A. The Havre Composite Correction Program was successful because of a long
time involvement with plant personnel.
A. Twelve weeks were necessary to achieve desired changes in activated
sludge characteristics.
B. One year was required to transfer to the plant superintendent the
ability to make timely and accurate process control adjustments.
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5. Composite Correction Programs without major facility construction com-
pleted at the thirty evaluated facilities would improve plant effluent quality
significantly.
A. Sixteen of twenty-three facilities would meet federally defined sec-
ondary treatment standards now violated. The other seven facilities
would require a major facility modification to meet secondary treat-
ment standards consistently.
B. The masses of BOD,, and TSS discharged would be reduced by an esti-
mated 490 metric tons per year (540 tons/year) and 470 metric tons
per year (515 tons/year), respectively.
C. The masses of BOD,, and TSS discharged would be reduced by an esti-
mated 38 percent and 37 percent, respectively.
6. Significant differences in the performance potential for suspended growth
and fixed film type facilities were noted.
A. Poor performance exhibited at fixed film facilities could not be im-
proved significantly with a Composite Correction Program unless major
facility modifications were also completed. A more conservative de-
sign is necessary for fixed film facilities.
B. Poor performance exhibited at suspended growth facilities could be
improved through Composite Correction Programs without major facili-
ty modifications. Better operation is necessary for suspended growth
facilities.
7. Plant underloading did not promote good plant performance. Hydraulic
loading averaged only 61 percent of design, yet 23 of 30 plants did not meet
\
secondary treatment standards.
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8. Plant expansion through construction is not a satisfactory alternative
to improving plant performance unless it is part of a Composite Correction
Program.
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SECTION 3
RECOMMENDATIONS
1. Implement Composite Correction Programs on a broad scale.
2. Modify existing operations assistance approaches to include the time as-
sociated with stabilizing a biological system.
3. Modify existing training to enable operations personnel to properly apply
concepts of wastewater treatment to process control.
4. Require a more conservative design approach for fixed film wastewater
treatment facilities.
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SECTION 4
HAVRE COMPOSITE CORRECTION PROGRAM
The Havre, Montana Wastewater Treatment Facility, an activated sludge
plant, was designed to treat an average sewage flow of 6800 cu in/day (1.8 mgd).
The plant staff consisted of a superintendent, maintenance manager and two
operators. The plant was operated sixteen hours per day, seven days per week.
Between 1972 and 1975 the original primary treatment plant was expanded to
secondary treatment. Present treatment facilities consist of grit removal,
flow measurement, two aeration basins, two final clarifiers, chlorination,
two aerobic digesters and a sludge lagoon. By design, the Havre facility
is composed of two independent, parallel activated sludge systems. For this
report one is called the "east unit" and the other the "west unit." The plant
flow schematic diagram is shown in Figure 1.
The Havre CCP was completed using a four-man research team of engineers.
Two senior engineers had considerable experience in. plant process control,
administration, maintenance and design. The initial in-plant activities for
the CCP were completed in conjunction with a comprehensive research evaluation
conducted by three team members from July 19, 1976 through July 26, 1976. (6)
At the same time, these team members completed field work for another com-
prehensive evaluation at a smaller facility located in the Havre area. A
follow-up half-day visit to Havre was made by two team members on August 12,
1976. Long-term telephone consultation was provided by one senior engineer,
but reflected the opinions and suggestions of the entire research team.
Prior to the Havre CCP, the approach to process control had been to
maintain the mixed liquor suspended solids (MLSS) concentration at about
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RAW SEWAGE
GRIT
CHAMBER
i
i
WASTE SLUDGE
EAST
UNIT
?
AERATION
BASIN
CHLORINE
CONTACT
BASIN
DISCHARGE TO
MILK RIVER
*
r
AERATION
BASIN
/ FINAL \
r*i A oinir D
WEST j
UNIT 1
f
. 1
A
AEROBIC
DIGESTERS
V
i
SLUDGE
LAGOON
WASTEWATER
SLUDGE
Figure 1. Plant Flow Schematic for Havre, Montana.
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1,000 mg/1 and to maintain the return sludge flow rate at a low, relatively
constant setting (daily average sludge return rate was only 8 percent of the
daily average sewage flow rate). A MLSS concentration analysis was conducted
about three times per week. Based on these results, the volume of sludge
wasted was adjusted.
During the initial in-plant activities, it appeared that effluent quality
could be improved significantly by changing the approach used for process
control. A more comprehensive testing program was initiated, including a
centrifuge test on the mixed liquor, return sludge and waste sludge to deter-
mine concentrations; a settling test on the mixed liquor to determine settling
characteristics; a depth of sludge blanket test to measure the level of the
solids-liquid interface inv the final clarifiers; and a dissolved oxygen test
to determine the aeration basin dissolved oxygen concentrations -(7* 8). Var-
ious daily calculations were initiated to monitor the mass of activated sludge
in the system, mass wasted and mixed liquor settling characteristics. The
values of selected test results were plotted so trends in system response
could be observed. These trends were used to determine when to make process
control adjustments.
Based on test results, dramatic process control adjustments were made
in an effort to improve performance. Initially, process control decisions
were made primarily by the research team. The rationale for these decisions
was always discussed with the plant superintendent. As time progressed
(3 to 4 months) the plant superintendent became more comfortable with test
data interpretation and gradually assumed more and more of the day-to-day pro-
cess control decisions. At that time the role of the research team was di-
rected more toward providing conceptual guidance concerning the development
of stable biological characteristics. Through this training approach the
plant superintendent developed the capability to properly apply concepts of
wastewater treatment to the operation of his facility.
10
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PLANT PERFORMANCE
Performance of the Havre Wastewater Treatment Plant was monitored by
plant personnel twice per week in accordance with the City's NPDES permit re-
quirement. Total suspended solids (TSS) and 5-day Biochemical Oxygen Demand
(BOD,.) analyses were conducted on the raw sewage influent. BOD , TSS and
fecal coliform analyses were conducted on the chlorine contact basin effluent.
All analyses were conducted on 8-hour composited samples except for fecal
coliform, which was conducted on a grab sample. Monthly averages for these
tests from January, 1976 through June, 1977 are shown in Table 1. The data
presented is separated into three time periods. Period 1 is titled "Prior to
Operations Assistance" and represents performance before the CCP was initiated.
Period 2 is titled "Initial Operations Assistance" and represents performance
after the CCP was initiated, but before clarifier inlet baffles were modified.
Period 3 is titled "Final Operations Assistance" and represents performance
after clarifier modifications were completed and better process control was
achieved.
For the 6-month time frame of Period 1 the average plant effluent BOD,.
and TSS concentrations were 31 mg/1 and 30 mg/1, respectively. During three
of the six months, the BOD,, and/or TSS permit standards of 30 mg/1 were vio-
lated. Poor plant performance during Period 1 was attributed to an improper
approach to process control and to sludge handling problems.
During Period 2 process control was being improved, but modifications to
the final clarifiers were not yet made. For the 4-month time frame of Period
2, some improvement in plant effluent BOD!- and TSS concentration was achieved.
The plant effluent average BOD,, concentration was reduced from 31 mg/1 to
24 mg/1. Similarly, the plant effluent average TSS concentration was reduced
from 30 mg/1 to 23 mg/1.
During the 8-month time frame of Period 3, a significant improvement in
plant effluent quality, occurred even though the plant influent wastewater
strength increased. Better plant effluent quality was primarily attributed
to modifications to the final clarifiers and better process control. From
11
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TABLE 1. SUMMARY OF PERFORMANCE DATA FOR THE HAVRE, MONTANA WASTEWATER TREATMENT PLANT.
"D ("\T\ T1 C O
•Dl/JJ _ lOD
PERIOD 1 -
Jan 76
Feb
Mar
Apr
May
Jun
Average
PERIOD 2 -
Jul 76
Aug
Sep
Oct
Average
PERIOD 3 -
Nov 76
Dec
Jan 77
Feb
Mar
Apr
May
Jun
Average
Flow
(MGD)*
Plant Plant
Influent Effluent
(mg/1) (mg/1)
PRIOR TO OPERATIONS ASSISTANCE
1.30
1.26
1.29
1.34
1.29
1.37
1.31
INITIAL OPERATIONS
1.16
1.14
1.11
1.22
332
250
251
259
283
278
276
ASSISTANCE
251
212
292
234
1.16 247
FINAL OPERATIONS ASSISTANCE
1.33
1.33
1.37
1.48
1.34
1.39
1.34
1.27
1.36
225
239
328
357
423
438
387
379
351
17
41
29
37
34
26
31
19
21
28
27
24
11
7.9
12
11
6.8
8.0
12
8.9
9.7
Removal
94.9
83.6
88.4
85.7
88.0
90.6
88.5
92.4
90.1
90.4
88.5
90.4
95.7
96.7
96.3
96.9
98.4
98.2
96.9
97.7
97.1
Plant
Influent
(mg/1)
199
236
204
281
251
266
240
261
220
212
198
223
213
230
215
258
302
307
261
322
264
Plant
Effluent
(mg/1)
27
36
25
42
29
22
30
19
18
33
22
23
14
9.6
8.6
10
8.1
9.4
7.3
5.4
9.1
Removal
86.4
84.7
87.7
85.1
88.4
91.7
87.5
92.7
91.8
84.4
88.9
89.4
93.4
95.8
96.0
96.1
97.3
96.9
97.2
98.3
96.4
Fecal Coliform
Geometric
Mean
(#/100 ml)
630
475
32
112
73
54
127
87
1109
450
120
269
29
35
23
35
12
61
53
50
31
* MGD x 3785 = cu m/day
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Period 1 to Period 3 the raw sewage BOD- concentration increased 27 percent
(i.e., 276 mg/1 to 351 mg/1) , yet plant effluent BOD,, concentration decreased
69 percent (i.e., 31 mg/1 to 9.7 mg/1). The improvement in plant effluent
quality represents a reduction in mass of BOD- discharged to the stream of
104 kg/day (229 Ib/day). Similarly, the mass of TSS discharged was reduced
by 102 kg/day (225^Ib/day).
As a result of the CCP, an improvement in disinfection performance also
occurred. The geometric mean fecal coliform count decreased from 127 per 100
ml during Period 1 to 31 per 100 ml during Period 3. Other benefits were
lower chlorine dosage requirements and less chlorine contact basin mainte^-
nance. The chlorine dosage was reduced to maintain a chlorine residual less
than the maximum allowable concentration of 0.5 mg/1. In fact, a smaller
rotometer had to be installed on the chlorinator to obtain the required lower
dosages. The chlorine cost saving was an estimated 40 percent, or $700 per
year. Less chlorine basin maintenance was required because less basin clean-
ing was necessary. Prior to Period 3 the effluent TSS concentration was de-
creased by 30 percent through settling within the chlorine contact basin.
Solids removal in the contact basin allowed permit violations to be less fla-
grant, but required repeated basin cleaning. During Period 3 these solids
were captured in the final clarifiers, and the time previously spent cleaning
the chlorine contact basin was used for additional process testing, preventive
maintenance and general housekeeping activities.
The improvement in plant performance at Havre is illustrated in Figure 2,
where 7-point moving averages of chlorine contact basin effluent BOD^ and TSS
concentrations are show.. The 7-point moving averages were used to smooth
the variability in individual data points so trends in performance could be
readily observed. As shown in Figure 2, plant effluent BOD,, and TSS concen-
trations decreased over the 18-month period from January, 1976 to June, 1977,
and were at or near 10 mg/1 during the last 7 months. It should be noted that
the graph in Figure 2 is separated into operational phases rather than the
performance periods described earlier. Each of the four phases shown repre-
sents a different operational objective that was established during the CCP.
Each phase is discussed later in this report.
13
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PERMIT STANDARDS
RESEARCH-^!
INITIATED
J F M A M J
J F M
Figure 2. Chlorinated effluent BOD,, and TSS concentrations at Havre, Montana,
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Other benefits of improved effluent quality were operator pride in good
performance and city pride in a good operating facility. These benefits could
not be tangibly measured, but nevertheless existed. In addition, the plant
was a training facility for local college students studying Water and Waste-
water Treatment Technology. Students frequently visited the plant for on-the-
job instruction. Observing a well performing, full-scale plant accentuated
their on-site training.
PROGRAM DESCRIPTION
The first step in implementing the CCP at Havre was to establish a sam-
pling and testing program to monitor process control parameters. Based on
these results, control adjustments were made. Many factors contributed to the
specific operations decisions made. Most important among these .were aeration
basin size, clarifier size, wastewater strength, sludge wasting capability
and return sludge flow controllability. The aeration basin sewage detention
time averaged 6.7 hours. The clarifier surface settling rate averaged 13.6
22p
cu m/day/m (330 gal/day/ft ). The Havre clarifiers had a surface area which
was well developed with overflow weirs and effluent launders. Return acti-
vated sludge was withdrawn from each of the clarifiers through a center hopper.
The return sludge flow rate was adjusted and was measured, but varied with
changes In return sludge density. The wastewater strength, as measured by
TSS and BOD,., was relatively high. Controlled, incremental wasting was
completed every hour of the day by adjusting time clock settings. Waste
activated sludg'e was directed to two aerobic digesters (total capacity 1000
cu m (270,000 gallons)) then to a digested sludge holding lagoon with an
approximate volume of 30,000 cu m (7.9 million gallons). This combination
)
of sludge handling facilities was sufficient so that plant operation was not
limited by inadequate sludge wasting capacity during the CCP. However, it
should be noted that at the required wasting rate the sludge lagoons were
projected to be filled about twice as fast as was projected in the plant de-
sign.
Settled activated sludge in the clarifiers was returned to the aeration
basins with air-lift pumps. A problem existed with return sludge flow control
15
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in that once set, the flow rate did not stay constant. Moderate changes in
the return sludge density caused significant changes in the return sludge
flow rate. A change in density occurred when the clarifier scraper blade
pushed sludge into the center hopper. A variable return sludge flow rate oc-
curred frequently during those portions of the project when rapid sludge set-
tling conditions existed. A slower, yet adequately settling sludge helped
alleviate this problem to a degree.
Separate waste activated sludge pumps for each activated sludge unit
pumped waste sludge from the return activated sludge line to the aerobic
digesters. Each waste sludge pump was operated through a separate time clock.
Activated sludge wasting was automatically completed every hour. The amount
wasted was adjusted by changing the time clock settings. The operators meas-
ured the waste sludge concentration every 4 hours which, combined with the
waste sludge volume information, resulted in good documentation and control
over the mass of sludge wasted.
Sludge was wasted to one of two aerobic digesters. Aerobic digester vol-
ume was not sufficient for complete digestion (hydraulic detention time of 8
days), but during the survey nearly unlimited ultimate sludge disposal capa-
bility allowed the desired quantities of sludge to be wasted from the acti-
vated sludge process. Partially digested sludge (specific oxygen uptake rate
of 6 mg 0 /gm VSS/hr where 1 mg 0 /gm VSS/hr is considered digested) (9) was
pumped to a sludge holding lagoon away from the city. The lagoon had storage
capacity for several years' sludge accummulation. The lagoon location in
relation to prevailing winds was favorable and no odor complaints were re-
ceived concerning the lagoon.
At Havre, the key to good performance was maintaining activated sludge
settling characteristics which were most desirable for the plant design and
loading conditions. It was important to conduct settling tests that appro-
priately depicted the sludge settling characteristics. A one-hour settling
test using a Mallory settleometer was initiated to fulfill this need (7, 8).
The results of this settling test are graphically illustrated in Figures 3 and
4 for the east and west activated sludge units, respectively. These graphs
16
-------
Figure 3. East unit settled sludge concentrations CSSC) at Havre, Montana.
-------
O
03
cr
H-
2
UJ
O
O
O
Figure 4. West unit settled sludge concentrations tSSC) at Havre, Montana.
-------
show trends in settling characteristics in terms of ATC, SSC5 and SSC6()
where:
ATC - Aeration T^ank Concentration in percent by volume using a centri-
fuge. SSC5 and SSC, are the fettled Siludge Concentrations calculated
using the initial measured concentration (ATC) and the volume of sludge
in the settleometer after the indicated time (t) of settling (SSV ).
The equation for this calculation is:
„„_ _ ATC (1000)
t " SSVfc
In Figures 3 and 4, poor activated sludge characteristics of slow set-
tling are indicated by a low value for both SSC.- and SSC,_. Poor characteris-
j bU
tics of too rapid settling are indicated by high SSC and SSC,Q values. De-
sired characteristics of uniform settling are indicated by a low value for
SSCC and a high value for SSC,rt.
J oO
The SSC concentrations were used in lieu of the more conventional sludge
volume index (SVI) because SSC values more completely described the sludge
settling characteristics. The two SSC values depicted the settling pattern
throughout a one-hour time period, rather than at the single 30-minute time
period as with the SVI test. For example, high SSC,- values indicated that
the sludge had the ability to settle and concentrate. The added SSC value
indicated rapid" or slow initial settling. Rapid initial settling was typi-
cally accompanied by a cloudy effluent that had a relatively high BOD con-
centration. A low value of SSC,, in association with a higher SSCftn value was
accompanied by a clear effluent as well as with a concentrated settled sludge.
The settling graphs in Figures 3 and 4 are separated into the four opera-
tional phases also shown in Figure 2, which was discussed earlier. Each of
the four phases represents a different operational objective or event.
19
-------
Phase I
Phase I occurred for nine weeks beginning with the start of the CCP-
Initially, the activated sludge in both the east and west units settled very
fast (high SSC,- and SSC,- values) and left a cloudy supernatant. A relatively
cloudy final clarifier effluent existed, and the plant effluent BOD concen-
tration was higher than the associated TSS concentration, as shown in Figure
2. The ATC values were relatively low at about 2.5 percent by volume, and a
large portion of the total system activated sludge mass was retained in the
clarifiers because of an extremely low return versus wastewater flow percent-
age (8 percent). During Phase I significant changes in plant operation were
made. The first operational objective was to improve the BOD,, and TSS removal
capability of the activated sludge.
After the initial process control test results were obtained, the return
versus wastewater flow percentage was increased from 8 percent to between 40
and 50 percent. However, very poor control over the return sludge flow rate
existed. The return sludge flow rate that was set varied considerably due to
plugging problems, and sometimes the return sludge flow stopped altogether
when left unattended. The need for better return sludge flow control was a
routine topic of discussion between the plant superintendent and the research
team. It appeared that a design modification was required to eliminate the
return sludge plugging problem. However, it was also determined that expanded
operator attention could replace the need for an immediate design modification
to the return sludge facilities. In addition, aerobic digester foaming prob-
lems also required expanded operator attention. Based on these needs, the
superintendent successfully presented a request to the city council for ap-
proval to hire one additional operator and to expand from 16 hour, seven
day-per-week operation to 24 hour-per-day operation for five days and 16 hour-
per-day operation for two days of the week. This administrative decision
eliminated the immediate need for the return sludge design modification and
substantially aided in overall plant operation.
Other process control changes were made at the same time the return
versus wastewater flow percentage was increased. The mass of activated sludge
20
-------
in both the east and west units was increased to improve its BOD,, and TSS
removal capability. An indication of the relative increase in activated
sludge mass is shown in Figures 3 and 4 in terms of the ATC values. The ATC's
were increased and maintained, through wasting, at an initially selected
level of 3.7 percent by volume for the east unit and 4.2 percent by volume for
the west unit. In both units the activated sludge character began to change.
Both the SSC,. and SSC,n values began to decrease, indicating slower overall
settling, and the supernatant in the settleometer began to become less turbid.
The final clarifier effluent clarity improved and the plant effluent BOD_
concentration began to decrease (See Figure 2 at the start of Phase I). How-i-
ever, the activated sludge began to rise in the settleometer prior to the
conclusion of the 60-minute settling tests. At the_ same time, a heavy scum
layer developed on the surface of both final clarifiers and an increase oc-
curred in the amount of activated sludge solids lost in the clarifiers' efflu-
ent. Figure 2 shows increased TSS and BOD,, concentrations in the plant ef-
fluent toward the end of Phase I. It is important to note that nine weeks had
elapsed since the CCP had been initiated and plant effluent quality had not
yet stabilized at an improved level. In fact, plant effluent quality was de-
teriorating. The plant operators were discouraged, but continued to stay
with the project because, according to the plant superintendent, "We believed
in the basic concepts and felt that, logically, it should work."
Process response at the conclusion of Phase I was confusing in that,
based on the control test data, rising sludge should not have occurred and
excessive solids should not have been lost over the clarifier weirs. The
SSC,0 value was only about 7 percent, and based on experience much higher
ou
SSC,_ values had been associated with rising sludge conditions. Also, the
bU
total mass of sludge in each activated sludge unit was too low to expect
rising sludge characteristics. Typically, rising sludge characteristics had
been observed at other facilities when a relatively high and "older" mass of
sludge existed. During a typical CCP a plant visit would have been conducted
to "tie-in" control test data with on-site observations. Budget constraints
prohibited this option.
21
-------
Phase II
Phase II occurred for five weeks and incorporated a short-range opera-
tion's objective to eliminate the rising sludge condition and associated scum
problems. A decision was made to decrease the mass of activated sludge in
both systems through increased wasting, and thereby lower the "age" of the
sludge. This decision was made even though it was known that the existing,
relatively low quantity of activated sludge in the system and slower sludge
settling characteristics did not indicate an "old" sludge condition could be
causing the problems. Subsequently, two events occurred with respect to the
activated sludge character. The sludge settling rate was further decreased
and the sludge rising condition was eliminated. Slower overall settling was
documented through the SSC,n values, which decreased from about 7 percent to
oU
about 5 percent in both the east and west units.
It was anticipated that a reduced system activated sludge inventory would
decrease the SSCL value and would yield a very clear supernatant in the
settleometer (i.e., produce a bulky sludge). It was also felt that a good
quality effluent could be achieved if the sludge blanket could be contained in
the final clarifiers. It was realistically anticipated that a fairly bulky
sludge could be contained in the final clarifiers because of their relatively
2
low overflow rates at about 13.6 cu m/day/sq m (330 gal/day/ft )-
When wasting was increased and total system activated sludge mass was
decreased, the SSC,- values decreased and the supernatant clarity in the set-
tling test jar improved - both as predicted. Activated sludge was contained
in the final clarifiers and their effluent was relatively clear, but for an
unknown reason the clarifiers' effluent contained excessive discreet floe
particles. This situation should not have occurred when the clarifier sludge
blanket was being contained. It was felt that additional influences were pos-
sibly interfering with biological system response. A plant visit would have
been desirable but was not feasible due to budget constraints. The possibili-
ty of some outside influence was discussed with the plant superintendent. The
superintendent reported that since the rising sludge condition had stopped and
22
-------
the scum problem had dissipated, he was able to observe what appeared to be
short-circuiting in the final clarifiers.
During the initial on-site efforts of the Havre CCP, it was observed that
the operators had modified the clarifier inlet baffles. The baffles had been
cut-off about 15 cm (6 in) below the clarifier water surfaces in order to de-
crease the build-up of trapped scum and to eliminate freezing problems that
had occurred during the previous winter. This modification is illustrated in
Figure 5, and proved to be the source of much of the confusion in process
response that was described earlier. When the inlet baffles were modified
some of the mixed liquor that entered the clarifier overflowed the inlet baf-
fle. This condition did not represent a problem when the activated sludge
settling rate was fast, as existed during the initial on-site efforts. How-
ever, when the activated sludge settling rate decreased, solids traveled ac-
ross the clarifier surface toward and over the effluent weirs before they
settled out. This short-circuiting situation became pronounced toward the
end of Phase I and during Phase II when the activated sludge settling rate was
much slower. The short-circuiting problem became more visually apparent at
the end of Phase II when the scum on the clarifier surface had dissipated.
After discussing the effects of the inlet modification with the plant
superintendent, a decision was made to drain down the clarifiers and weld
back on the portions of the inlet baffles that had been removed. This task
was accomplished, and an immediate significant improvement in plant effluent
quality occurred even though the activated sludge settling rate was still
very slow.
Phase III
The elimination of clarifier scum and short-circuiting marked the begin-
ning of another operations objective and the start of Phase III. Effluent
quality had improved significantly, but activated sludge settling characteris-
tics had not yet improved. A decision was made to increase system activated
sludge mass and to again work toward improving the settling rate. The acti-
vated sludge wasting rate was reduced and sludge mass was increased to a pre-
23
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FINAL
CLARIFIER
BEFORE
INLET
BAFFLE
MODIFICATION
\
BAFFLE BELOW
SURFACE
.BAFFLE ABOVE
SURFACE
FINAL
CLARIFIER
AFTER
INLET
BAFFLE
MODIFICATION
Figure 5. Final clarifier modification at Havre, Montana to stop
short-circuiting.
24
-------
selected higher value. The increase in quantity of activated sludge in the
system occurred in both the aeration basins and clarifiers. The quantity
increased in the aeration basin is shown in Figures 3 and 4 in terms of the ATC
value. After holding the ATC at a higher value for about six weeks, the acti-
vated sludge settling rate began to improve. The SSC,~ increased from about
4 percent to about 9 percent in both the east and west activated sludge units.
At that time, problems were encountered with the ultimate sludge disposal
pump. Sludge in the aerobic digesters could not be pumped to the sludge la-
goon, thus activated sludge could not be properly wasted to the digesters from
the activated sludge systems. Due to the relatively long time that was neces-
sary to improve the activated sludge characteristics to the point which had
been achieved, it was decided to protect the east unit sludge characteristics
by continuing to waste from the east unit to the west unit. However, the
method of wasting from the east unit to the west unit was very difficult to
control, and a wide fluctuation occurred in both the east and west unit acti-
vated sludge masses. A stable plant operation did not exist, and the net
effect was a decrease in the activated sludge settling rate for both units
during the one and one-half week period for which the pump was out of service.
These results dramatically pointed out to plant personnel the need for addi-
tional spare parts and better emergency maintenance procedures.
The activated sludge settling rate continued to be relatively slow even
after the pump was repaired and placed into service. The SSC,0 decreased
from about 9 percent before the pump failure to about 5 percent. It should
be noted that during the Phase III bulky sludge conditions, as shown in
Figures 3 and 4, the TSS concentration of the final effluent was greater than
the BOD- concentration, as shown in Figure 2. The BOD,, and TSS concentrations
were relatively low, but not as low as could be achieved. After the ultimate
sludge disposal pump was repaired, the activated sludge system masses in both
units were again held at a controlled, higher level to encourage improved
activated sludge settling characteristics. After four weeks the activated
sludge settling rate began to improve, but continued to increase beyond the
point desired. A drastic increase in the activated sludge settling rate dur-
ing Phase III is shown in the settling data in Figures 3 and 4. During this
very rapid settling condition, the operators reported a more cloudy appearance
25
-------
of the supernatant in the settleometer and in the clarifier effluent. Also,
the BOD- concentration of the final effluent increased and the TSS concentra-
tion decreased. The desired situation of both decreased BOD and TSS and a
stable plant operation did not yet exist.
It is noted that the Havre final effluent quality was always quite good
after the clarifier short-circuiting problem was eliminated. Even during
periods of slow activated sludge settling rates, poor effluent quality was
not experienced. The primary reasons for a relatively good quality effluent
during slow activated sludge settling conditions was the combined benefits of
a wastewater flow rate less than design and a relatively conservative clarifi-
er design size. This reserve capacity is typically not available at most
wastewater treatment plants, yet other installations require the same general
approach in order for an improvement in performance to occur. Correct opera-
tional decisions must be made and adequate time must be allowed to achieve
system response. At Havre, approximately 12 weeks elapsed from the time a
decision was made to increase the ATC's to the time an improvement occurred
in the activated sludge settling rate. A disruption was encountered due to
problems with the ultimate disposal sludge pump, but some type of disruption
was not totally unexpected. During the 12-week time frame no significant
changes in the aeration basin dissolved oxygen (D.O.) concentration or return
sludge flow percentage were made. The aeration basin D.O. concentration
varied from about 4 mg/1 to 7 mg/1. The return sludge flow percentage was
about 40 percent. Also, no chemicals were added to the system to change
sludge character. The most important observation was that three months e-
lapsed before the activated sludge developed more desirable settling charac-
teristics.
Phase IV
The development of a rapid activated sludge settling rate marked the be-
ginning of another operations objective and the start of Phase IV. The active
sludge mass in the system was slightly decreased in an effort to slow down
the activated sludge settling rate and improve its BOD removal capability.
Also, ''fine tuning" of the activated sludge process was initiated to provide
26
-------
the plant operators better control over the activated sludge settling charac-
teristics. The mass of sludge wasted, return sludge flow rates and dissolved
oxygen concentrations were all more carefully controlled. The biological
system was maintained at a point of relative stability through continual oper-
ations adjustments. The superintendent slightly reduced the ATC to slow
down the settling rate and improve its BOD;, removal capability and slightly
increased the ATC to speed up its settling rate and improve its manageability
through better containment within the final clarifiers. Small variations in
activated sludge characteristics and plant effluent quality occurred, but
timely operations adjustments prevented large fluctuations and eliminated ex-
tended periods of poor performance. For an 8-month period the plant effluent
BOD_ and TSS concentrations averaged 10 mg/1 and 9 mg/1,- respectively. The
plant superintendent justifiably believes that this high degree of treatment
can be achieved consistently.
DISCUSSION
The Havre CCP demonstrated that significantly improved performance could
be achieved using existing wastewater treatment facilities. Improved perfor-
mance occurred after several modifications were made to plant operation, de-
sign, administration and maintenance. The plant operator's ability to apply
concepts of process control at his facility was improved. A minor modifica-
tion to the clarifiers was made. An administrative change regarding plant
staffing was implemented. The necessity of a good preventive maintenance
program was reinforced. The CCP also identified the process control parame-
ters that were most critical at the Havre plant with its particular physical
facilities.
The most critical process control parameter at Havre was the sludge set-
tling rate as controlled by the ATC. It was determined that the Havre acti-
vated sludge system performed best when the sludge settling rate was rela-
tively slow (i.e., demonstrated bulky sludge conditions). The reasons for
this were associated with the relatively short aeration time and associated
high BOD,, loading rate, and the relatively large clarifier size which enabled
the slower settling sludge to be contained in the systems. The Havre plant
27
-------
operated well under these conditions, but very close operator attention was
required to maintain the desired sludge characteristics. For example,
wasting was often drastically adjusted each day in order to maintain the de-
sired ATC. The existing Havre facility will always require strict operations
control to achieve a stable operating condition, which will become even more
pronounced when the wastewater flow rate to the facility increases. The
present good effluent quality associated with relatively slow activated sludge
settling rates may not occur as the wastewater flow rate increases. However,
through continued timely adjustments of the critical process control para-
meters, the plant effluent quality should meet the existing NPDES Permit stan-
dards at least until the plant design flow rate is reached.
It is expected that other wastewater treatment facilities will have dif-
ferent critical process control parameters, depending on their specific design
arrangement, wastewater strength and other unique features. For example, in
plants that have a longer aeration basin wastewater detention time, somewhat
less exact control would be expected to maintain a stable operating condition.
In plants that have a proportionately smaller clarifier and a higher clarifier
surface overflow rate, more difficulty would be encountered to operate through
bulky sludge characteristics. It is not expected that all facilities could
get into or out of a bulky sludge condition by following the specific values
for ATC, return rate, D.O. concentration and other control variables which
were discussed in this report.
A major reason for the success of the Havre CCP was the extended length
of time over which the program was conducted. It was noted earlier that
twelve weeks were required to develop a desired activated sludge settling
rate. Additional time was required to transfer the process control decision
making capability to the plant superintendent. The time required to develop
desired activated sludge settling characteristics at other facilities could
easily be equal to or greater than the time required at Havre. This time
requirement in itself supports the conclusion that CCP's must be implemented
over a long time period (i.e., three to six months). However, additional
time (i.e., one to two years) is necessary to adequately transfer to plant
personnel the ability to make timely and accurate in-plant control adjustments.
28
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After a 4-month period, the Havre superintendent satisfactorily made all
short-range control decisions, such as determining wasting requirements to
maintain a desired ATC. After nearly a year the superintendent was also
making long-range decisions, such as selecting the desired ATC value. A
1-year time period was necessary even though the superintendent had two years
of general administration college training, had received formal training for
two years at a water and wastewater technology school and had an excellent
aptitude and personality. It should also be noted that the superintendent
continues to discuss plant operation and performance with the research team
on a periodic basis in order to obtain a second opinion on major control de-
cisions. His not relying on, but using available help to the advantage of
his operation, illustrates the security which he has developed that accompan-
ies the competency which he has achieved. The success of CCP's is equally
dependent upon developing optimum biological conditions and developing opera-
tor competency. Both are time consuming functions.
A major conclusion of the overall research study, for which the Havre CCP
was one segment, was that presently there are not a sufficient number of
persons with adequate background and training to successfully conduct CCP's
on a broad scale. (6) One reason for this occurrence is that a need for
these services has not been developed due to inadequate enforcement and a
general "construction" approach to achieving better plant effluent quality.
Another reason is that process control "authoritative sources»" such as con-
sulting engineers, regulatory personnel, equipment suppliers and others have
not correctly approached operations assistance. Generally, persons who give
technical guidance at biological wastewater treatment plants do not observe
system response for a Ijng period of time. As a result, most do not under-
stand the consequences of their suggestions and seemingly good suggestions
may be incorrect,or correct for the present situation but incorrect at a
later date. Process control suggestions made under these circumstances lead
to improper technical guidance. Furthermore, failure to observe system re-
sponse over the time frame required to see the full impact of recommendations
made does not promote the improvement of technical assistance capability.
Conversely, the approach taken at Havre allowed both plant personnel and re-
29
-------
search team members to use the project as a learning experience. In so doing,
research team members have expanded their assistance capabilities.
Because of the success with the Havre CCP and the obvious need for im-
proved performance at a large number of the facilities studied under the re-
search contract, an analysis of conducting similar CCP's at other facilities
was completed. This analysis and the projected benefits are presented in the
next section of this report.
30
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SECTION 5
PROJECTED IMPROVEMENT THROUGH COMPOSITE CORRECTION PROGRAMS
This section of the report describes the potential improvement in plant
effluent quality which could be achieved if CCP's without major facility up-
grades were conducted at all thirty facilties for which an evaluation was
made during the overall research effort. (6) Also described is the actual im-
provement in performance which occurred at some facilities as a result of
the research evaluations. Some operations assistance was provided to aid in
the collection of research data. The success of this assistance in improving
performance was dependent upon the number and type of performance limiting
factors encountered. Telephone communication similar to that used during the
Havre CCP was maintained with some facilities. Generally, technical assist-
ance provided during the research evaluations included only operations factors
limiting performance, and was specifically limited to improving the operations
capabilities of the process control decision maker. In a few cases, minor
plant modifications were made. The scope of these assistance efforts was
considerably less than the effort expended during the Havre CCP- Improvement
typically was not documented to the same extent. In addition, it could not be
predicted that these plants would continue to perform at the improved level.
Improved performance occurred at seven facilities, including Havre.
During the Havre CCP, activated sludge characteristics went through several
different and typical changes: bulky, scum-producing, rapid settling and
optimum. When combined with extensive operations help, this guided observance
and control of different activated sludge characteristics allowed for the
transfer of process control capability and process understanding to the Havre
superintendent. This time-related training was not completed at the other
six facilities where improved performance occurred.
31
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The research evaluations of various treatment plants were limited to
facilities whose wastewater flow rate was less than 37,850 cu m/day (10 mgd) .
Facilities were evaluated with flows ranging from 26 cu m/day (0.007 mgd) to
30,660 cu m/day (8.1 mgd). The average wastewater flow rate for the thirty
facilities evaluated was 5070 cu m/day (1.34 mgd). Statistically, the size
range of the facilities studied represents the largest number of wastewater
treatment plants in the United States.
Each of the facilities studied must discharge an effluent that does not
violate the federally defined minimum secondary treatment standards. Some
were required to meet more stringent effluent requirements. Twenty-three
of the thirty facilities studied were not achieving desired effluent quality
at the start of the research evaluations. The improvement in performance
which occurred as a result of the research evaluation and the additional im-
provement which could occur if CCP's were implemented at all facilities are
discussed. Improvement in effluent quality is described in terms of reduction
of total mass of pollutants discharged. The reduction of mass of pollutants
discharged is significant relative to the size range of plants evaluated. It
is also significant when described in terms of a percentage improvement from
the former status.
REDUCED POLLUTANTS IN THE PLANT EFFLUENT
For discussion purposes, the thirty facilities evaluated were grouped
into three categories: 1) Plants for which an improvement in performance
did occur, 2) Plants for which an improvement in performance could occur by
implementing a CCP and 3) Plants for which a significant improvement in per-
formance is doubtful without major expansion or modification of the existing
treatment facilities. The associated improvement for each of the thirty
facilities is presented in Tables 2, 3 and 4, which correspond to the above
categories. In the tables, each facility is discussed separately.
Although it cannot be predicted that the plants in Table 2 will maintain
the improved performance achieved as a result of the research evaluation, the
improvement that occurred and the level of treatment indicated could be
32
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TABLE 2. PLANTS FOR WHICH AN IMPROVEMENT IN PERFORMANCE DID OCCUR
Flow
Plant
No.
Actual
mgd*
Before
BOD TSS
mg/1 mg/1
After
Reduction
TSS
mg/1 Ib/day*
BOD
ton/yr*
TSS
Ib/day ton/yr
Plant Type - Comments
022 0.012 0.015 35 60 10 10 2.5 0.5 5.0 0.9 Activated sludge, extended aeration, with polishing
pond. The return sludge flow rate was excessively
high, causing solids loss over the clarifier weir
The R/Q ratio was reduced from about 1000% to about
100%, and excessive solids loss was eliminated.
Presently, all treated sewage flows through a
polishing pond. A pond bypass should be installed
to discharge good final clarifier effluent to the
receiving stream.
029 1-36 1.8 31 30 9.7 9.1 242 44 237 43 Activated sludge, conventional, without primary
ijj clarifier. Changes in return and waste sludge control
to procedure were implemented and a plant deficiency
was corrected. The values shown represent a six-month
average for "Before" data and an eight-month average
for "After" data.
043 0.34 0.38 68 116 10 10 164 30 300 55 Activated sludge, conventional, without primary
clarifier. Insufficient wasting was completed. Only
about half of the sludge grown each day was wasted.
The remainder bulked over the clarifier weir. The
MPDES standards were violated but not reported as
such. Increased wasting controlled sludge bulking.
The plant has an I/I problem. If the I/I problem was
corrected, the facility should continue to perform
we! 1 .
050 0.17 0.18 45 80 10 10 50 9.1 100 18 Activated sludge, extended aeration, without primary
clarifiers. Insufficient sludge wasting was completed.
The approach was to "build solids". The NPDES permit
standards were violated but were not reported as such.
Increased wasting controlled sludge bulking. Opera-
tions testing and process controls were implemented
and good effluent quality maintained.
* mgd x 3785 = cu m/day
** Ib x .453 = kg
*** ton x 0.906 = metric ton (1000 kg)
-------
TABLE 2. PLANTS FOR WHICH AN IMPROVEMENT IN PERFORMANCE DID OCCUR (Continued)
Flow
Before
After
Reduction
Plant
No.
Actual
mgd*
TSS
BOD
TSS
BOD
BOD
mg/1 mg/1 mg/1 mg/1 lb/day** ton/yr*
TSS
lb/day ton/yr
Plant Type - Comments
053 0.11 0.16 32 50 10 10 20 3.7 37 6.7 Activated sludge, extended aeration, without primary
clarifiers. Insufficient sludge wasting.
The approach was to build solids to a specified
level (3000 mg/1). The return rate was too high and
too much "scum" recycle was directed back to the
aeration basin to reach a MLSS of 3000 mg/1 before
solids bulking occurred. Decreased return, controlled
scum withdrawal, and increased wasting, as well as
implementation of operations testing and process
controls were completed, and good effluent quality
was maintained.
060 0.49 1.05 45 37 35 27 41 7.5 41 7.5 Two-stage trickling fi1ter with primary clarifier
(second-stage is an activated bio-filter system). A
valve leaking mixed liquor to the chlorine contact
basin influent was found. Plant effluent still does
not meet NPDES standards because of design limita-
tions in aeration capacity.
061 0.17 0.50 37 42 10 10 38 7.0 45 8.3 Activated sludge, contact-stabilization, without
primary clarifier Inadequate wasting and return con-
trol provided. Sludge wasted to an aerobic digester
and recycled back into activated sludge system.
Return flow rate not controlled. Operations testing
and process control were implemented and good effluent
quality maintained. A plant piping modification
should be completed to operate conventionally rather
than with the contact-stabilization mode to facilitate
operation. In addition, nearly half the operations
cost could be saved by operating only one of the two
plants presently on line (one was recently completed).
TOTAL 2.652
4.085
N/A N/A N/A
N/A
557.5
765
139.4
* mgd x 3785 = cu m/day
** Ib x .453 = kg
*** ton x 0.906 = metric ton (1000 kg)
-------
TABLE 3. PLANTS FOR WHICH AN IMPROVEMENT IN PERFORMANCE COULD OCCUR
Flow
Plant Actual
No. mgd*
Present
TSS
Potential
Reduction
BOD TSS BOD
mg/1 mg/1 mg/1
TSS
mg/1
BOD
Ib/day*
ton/yr*
TSS
Ib/day ton/yr
Plant Type - Comments
002 0.43 0.8 65 117 10 10 197
007 0.041 0.07 54 130 10 10 15
012 8.1 12.0 40 35 30 30 676
013 0.5**** 0.8 22 32 10 10 50
36 384 70 Activated sludge, extended aeration, without primary
clarifiers. Inadequate process understanding and
control, and inadequate clarifier surface development
causes uncontrollable excessive solids loss.
2.8 41 7.5 Activated sludge, oxidation ditch, without primary
clarifier. Inadequate sludge wasting capability at
the plant, as well as inadequate process understand-
ing, testing, and control causes excessive solids
loss.
123 338 62 One-half trickling filter and one-half trickling
filter followed by contact-stabilization with anaero-
bic digestion. Inadequate flexibility in digester
operation, which could be provided with a relatively
small piping change, causes excessive TSS in digester
supernatant recycle and degraded plant performance.
Improved performance would probably not meet stand-
ards consistently.
9.1 92 17 Activated sludge, conventional, without primary
clarifiers and with polishing pond. Insufficient
wasting, inadequate process understanding, testing
and control, and inadequate clarifier surface develop-
ment causes excessive solids loss. In addition,
there was not a pond bypass to discharge good
clarifier effluent when the pond effluent was poor.
* mgd x 3785 = cu m/day
** Ib x .453 = kg
*** ton x 0.906 = metric ton (1000 kg)
**** piow during survey was 0.8 mgd (peak tourist season). Average yearly flow estimated to be 0.5 mgd.
-------
TABLE 3. PLANTS FOR WHICH AN IMPROVEMENT IN PERFORMANCE COULD OCCUR (Continued)
Flow
Plant Actual
No. mgd*
Present
TSS
Potential
Reduction
BOD
TSS
BOD
BOD
mg/1 mg/1 mg/1 mg/1 lb/day** ton/yr*
TSS
lb/day ton/yr
Plant Type - Comments
CO
014 1.0**** 2.0 22 32 10 10 100 18 183 33 Activated sludge, conventional, without primary clar-
ifiers and with polishing pond. Inadequate process
understanding and control caused excessive solids
loss. In addition, there was not a pond bypass to
discharge good clarifier effluent when the pond
effluent was poor
019 0.035 0.065 57 53 10 10 14 2.5 13 2.3 Activated sludge, conventional, without primary clar-
ifier and with polishing pond. Insufficient sludge
wasting and inadequate process understanding, testing,
and control caused incomplete organic removal. In
addition, there was not a pond bypass to discharge
good clarifier effluent when the pond effluent was
poor.
020 .007 .025 47 62 10 10 2.2 0.4 3.0 0.5 Activated sludge, extended aeration, without primary
clarifiers, and with polishing pond. Insufficient
sludge wasting and inadequate process control caused
excess solids loss. In addition, there was not a pond
bypass to discharge good clarifier effluent when the
pond effluent was poor.
027 5.5 10 27 20 10 10 780 142 459 84 Activated sludge, conventional, with anaerobic
digesters. Plant effluent periodically violates mini-
mum permit standards, including 85% removal require-
ment. Inadequate process understanding and control
causes incomplete organic removal.
* mgd x 3785 = cu m/day
** Ib x .453 = kg
*** ton x 0.906 = metric ton (1000 kg)
**** Flow during survey was 1.43 mgd (high tourist season). Average yearly flow estimated to be 1.0 mgd.
-------
TABLE 3.
PLANTS FOR WHICH AN IMPROVEMENT IN PERFORMANCE COULD OCCUR (Continued)
Flow
Present
No.
mgd*
5j_ Design BOD
fc mqd mg/1
Potential
TSS
Reduction
BOD
TSS
BOD
mg/1 mg/1 lb/day** ton/yr*** Ib/day ton/yr
Plant Type - Comments
028 0.15 0.25 29 10 10 10 24
034 5.5
50 48 40 40 459 84
OJ
039
041
0.21
0.13
0.41
.40
44
25
78
25
10
10
20
60
5.4
4.3 0 0 Activated sludge, contact-stabilization, with polish-
ing pond. Inadequate sludge wasting procedure (sludge
wasted to pond) caused excessive sludge accumulation
in pond and anaerobic decomposition to occur in the
pond. The pond was covered with "duckweed" and had no
sunlight penetration. As such, soluble BODc, in pond
effluent was very high and TSS was low. There was not
a pond bypass to discharge good clarifier effluent
when the pond effluent was poor
367 67 Trickling filter with anaerobic digestion. Inadequate
control over flow splitting exercised, which causes
irnbalanced unit loadings. Also, improper anaerobic
digester operation causes excessive solids in super-
natant recycle stream, which, again, is not ade-
quately split and causes imbalanced unit loadings.
11 119 22 Activated sludge, oxidation ditch, with aerated
polishing pond. Insufficient sludge wasting and inade-
quate process control causes excessive solids loss.
There was a pond bypass at this plant.
1.0 5.4 1.0 Two-stage trickling filter, with anaerobic digesters.
Slight plant design modification to change recircula-
tion inlet piping location to a point away from the
final clarifier weirs would improve final clarifier
solids capture capability. It should be noted that
no anaerobic digester supernatant is recycled back
through the plant.
* mgd x 3785 = cu m/day
** Ib x 453 = kg
*** ton x 0.906 = metric ton (1000 kg)
-------
TABLE 3. PLANTS FOR WHICH AN IMPROVEMENT IN PERFORMANCE. COULD OCCUR (Continued)
Flow
Plant
No.
047
Actual
mgd*
0.050
Design
mgd
0.063
Present
BOD
mg/1
36
TSS
mg/1
76
Potential
BOD
mg/1
10
TSS
mg/1
10
Reduction
BOD
lb/day**
11
ton/yr***
2.0
TSS
lb/day
28
ton/yr
5.0
Plant Type - Comments
Activated sludge, extended aeration, with
polishing
055
0.30
0.58
13
23
10
10
7.5
1.4
33
5.9
pond. Insufficient sludge wasting and inadequate
process control causes excessive solids loss. In
addition, there was not a pond bypass to discharge
good clarifier effluent when the pond effluent was
poor.
Activated sludge, extended aeration, with primary
clarifiers and anaerobic digester. Inadequate process
control caused periodic slight solids loss. As a
general rule, standards have been met.
(-0
CO
TOTAL 21.953 35.463
N/A N/A N/A
N/A 2401.1
437.5
2065.4 377.2
* mgd x 3785 = cu m/day
** Ib x .453 = kg
*** ton x 0.906 = metric ton (1000 kg)
-------
.TABLE 4. PLANTS FOR WHICH AN IMPROVEMENT IN PERFORMANCE IS DOUBTFUL
Flow
Plant
Mo.
Actual
mgd*
Potential
Reduction
Design
mgd
Present
BOD TSS
mg/1 mg/1 mg/1 mg/1 lb/day** ton/yr*** Ib/day ton/yr
BOD
TSS
BOD
TSS
Plant Type - Comments
015 1.7 3.6 30 30 Same
021 0.59 0.9
U)
7 Same
024 4.9 6.0 45 31 Same
026 0.15 0.5
Same
Two-stage trickling filter with anaerobic digesters.
Inherent design features in the plant cause good
performance. Plant treats heavy industrial waste and
achieves about 96% to 98% removal. Also, anaerobic
digester supernatant is not recycled back to the
plant, which helps performance significantly. Even
so, standards are not met consistently.
Activated sludge, oxidation ditch, without primary
clarifiers. Some good design features in plant cause
good performance to be possible. At the same time,
good operation overcoming shortcomings in the design
of sludge handling and, in addition, adequate process
control , has caused good performance to be achieved.
Activated bio-filter with chlorine oxidized sludge
handling. Limited aeration capacity causes insuffi-
cient conversion of BOD5 to TSS.
Activated sludge, extended aeration, without primary
clarifiers and with tertiary filters. Plant produces
good effluent nearly all the time. However, periodi-
cally, once to twice per year, for short time periods,
raw sewage is bypassed because bulking sludge clogs
the filters or because of plant mechanical problems.
Individual plant units cannot be bypassed. The flow
must pass through the entire plant or be bypassed.
mgd x 3785 = cu m/day
Ib x .453 = kg
ton x 0.906 = metric ton (1000 kg)
-------
TABLE 4. PLANTS FOR WHICH AN IMPROVEMENT IN PERFORMANCE IS DOUBTFUL (Continued)
Flow
Present Potential
Plant Actual Design BOD TSS BOD__ TS^_
No. mgd* mgd mg/1 mg/1 mg/1 mg/1
BOD
TSS
Ib/day*
ton/yr**
Ib/day ton/yr
Plant Type - Comments
032 0.22 0.5 30 30
Same
•P-
o
035 5.3 5.4 22 20 Same
036 1.6 2.8 22 21 Same
040 0.38 0.63 56 29 Same
063 0.7 1.5 7 10 Same
Trickling filter with anaerobic "cold" digester.
Inherent design features cause plant to perform
satisfactorily with minimum operation. Summer per-
formance was good as measured during survey.
Historical performance questionable because monitor-
ing records were believed inaccurate. Winter perform-
ance believed to be poor because City was going to
enter into a 201 Facilities plan for plant upgrade.
Two-stage trickling filter with anaerobic digester.
Conservative design features and good operation
cause plant to perform as well as expected.
Two-stage trickling filter with anaerobic digester
Conservative design features and good operation cause
plant to perform as well as expected.
Rotating biological surface with anaerobic digesters.
Inadequate aeration capability limits conversion of
BOD5 to TSS.
Activated sludge, extended aeration, without primary
clarifiers. Plant can bypass flow it cannot handle to
a larger facility. Plant saves money when it accepts
more sewage because treated water is used for parks
and golf course watering. At least 1.5 mgd can be
adequately treated by the existing facility. Inade-
quate process control causes limited treatment
capacity. However, because plant can accept less flow,
standards are consistently met.
TOTAL 15.54 21.83 N/A N/A
* mgd x 3785 = cu m/day
** Ib x .453 = kg
*** ton x 0.906 = metric ton (1000 kg)
-------
achieved and likely exceeded if CCP's were implemented at these facilities.
It was recognized that many of the facilities in Table 3 for which improved
performance could be expected would require minor plant modifications as part
of a CCP. These minor modifications were differentiated from major facility
expansions in that they could be completed by plant personnel and/or a local
contractor and would not justify extensive planning ("201" studies), design,
and construction steps normally associated with plant upgrades. An example
minor modification would be adding the piping flexibility to discharge a good
quality mechanical plant effluent when desired, rather than having to dis-
charge a poor quality polishing pond effluent.
Various approaches were used to develop performance data for Tables 2
and 3. Whenever possible, accurate records were used to indicate performance.
However, at some plants the historical data did not reflect known poor per-
formance conditions, especially in plants which had a history of "bulking"
sludge. (Note: "Bulking" as used here does not differentiate between a true
poor settling sludge and an excess solids inventory condition). At plants
which had good sludge wasting records, the amount of solids lost due to bulk-
ing was estimated by determining the amount of activated sludge wasted after
operations assistance was provided and the excessive solids loss condition
was eliminated and comparing this value with the amount of sludge wasted prior
to assistance. In these plants an increase or decrease in the system's sludge
inventory was considered in determining solids loss due to bulking. At plants
with poor sludge wasting records an empirical sludge production value was
calculated based on plant loading and design information. Using these methods,
the amount of TSS lost in the effluent was estimated. Typically, the amount
of BOD,, lost during bulking periods was less than the amount of TSS lost.
During evaluations at five plants, separate samples were collected during
observed bulking periods. These samples were analyzed for BOD- and TSS con-
centration. The average BOD,, to TSS ratio for these samples was 0.5. There-
fore, for plants with a history of sludge bulking, the effluent BOD,, concen-
trations were calculated to be 50 percent of the estimated TSS concentrations,
unless records were available to obtain more specific BOD,, values.
41
-------
In plants with effluent polishing ponds, historical data for BOD- and
TSS removals through the ponds was usually not available. In many of these
facilities the mechanical plant performance was poor and had been poor, as
evidenced by a large sludge accummulation in the ponds. In this respect, the
ponds had been instrumental in removing some of the solids discharged in the
mechanical plant effluent. However, none of these facilities consistently met
standards. Two major points are made with respect to mechanical plants fol-
lowed by polishing ponds. One point is that some pollutant removal occurs
within ponds. The extent of the removal is seasonal in nature and is de-
pendent upon pond detention time, but nevertheless occurs. A second point is
that the addition of polishing ponds did not allow any of the facilities in-
vestigated to consistently meet secondary treatment standards. A polishing
pond was not a satisfactory substitute for good plant operation. Pond by-
passes allowing direct discharge of a high quality mechanical plant effluent
were recommended in conjunction with improved operation at facilities that
had polishing ponds. The addition of pond bypasses was considered a minor
plant modification in establishing the values presented for the potential
performance of plants with effluent polishing ponds.
The actual and estimated potential improvement in plant performance from
Tables 2 and 3 are summarized in Table 5. Overall total improvement is also
shown. This total improvement could be achieved if CCP's, excluding major
facility expansion, were implemented at all twenty-one of the facilities
shown in Tables 2 and 3. The projected total reduction of BOD discharged is
490 metric tons/year (540 tons/yr), and the total reduction of TSS discharged
is 470 metric tons/year (516 tons/yr). This represents a reduction in the
mass of BOD5 and TSS presently discharged of 37.7 percent and 36.9 percent,
respectively.
During the evaluation of improved performance, it was recognized that
significant differences in existing and potential effluent quality existed
between two major facility categories: suspended growth and fixed film. The
suspended growth category was comprised of activated sludge facilities and in-
cluded twenty of the thirty facilities evaluated. The fixed film category
was comprised of trickling filter, rotating biological contractor and acti-
42
-------
vated bio-filter facilities, and included ten of the thirty facilities evalu-
ated. The existing and potential performances from Tables 2, 3 and 4 for each
category are summarized in Table 6.
TABLE 5. PROJECTED IMPROVED PERFORMANCE USING CCP'S WITHOUT MAJOR FACILITY
EXPANSIONS
No. of Plants
Effluent BOD
Total Ib/day*
Total ton/year**
Effluent TSS
Total Ib/day*
Total ton/year**
Improved
Performance
Occurred
7
558
102
765
139
Improved
Performance
Potential
14
2401
438
2065
377
Total
Improved
Performance
21
2959
540
2830
516
* kg/day = Ib/day x 0.453
**Metric tons/year = tons/year x 0.906
The existing performance of the suspended growth and fixed film facili-
ties was nearly the same for BOD . The mean (not weighted average) effluent
concentration was 34 mg/1 for the suspended growth facilities and 37
t-
mg/1 for the fixed film facilities. The mean effluent TSS concentration was
significantly greater for the suspended growth facilities at 52 mg/1, as op-
posed to 31 mg/1 for the fixed film facilities.
Also shown in Table 6 are the high effluent BOD and TSS concentrations
for each facility category. These high concentrations represent the poorest
effluent quality for a given facility within each of the two categories, as
documented in Tables 2, 3 and 4. The poorest effluent quality for a suspended
growth facility was 68 mg/1 for BOD- and 117 mg/1 for TSS, while the poorest
effluent quality for a fixed film system was lower at 56 mg/1 for BOD and
48 mg/1 for TSS. Although some suspended growth facilities are performing
considerably poorer than the fixed film facilities, the potential performance
for suspended growth facilities through CCP's is significantly better than
43
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TABLE 6. EXISTING AND POTENTIAL PERFORMANCE FOR SUSPENDED GROWTH AND FIXED
FILM FACILITIES SURVEYED
Suspended Growth
Fixed Film
No. of Facilities
Total Flow - mgd*
Size Range - mgd*
20
11.8
0.007 - 5.5
10
29.2
0.13 - 8.1
Existing Performance
Effluent BOD - mg/1 (Mean)
(High)
Effluent TSS - mg/1 (Mean)
(High)
34
68
52
117
37
56
31
48
Potential Performance After CCP's
Effluent BOD5 - mg/1 (Mean)
(High)
Effluent TSS - mg/1 (Mean)
(High)
9.2
10
9.6
10
33
56
28
40
Potential Improvement Through CCP's
Additional BOD,. Removed
ton/year (total)**
lb/mg***
Percent Improvement
Additional TSS Removed
ton/year (total)**
lb/mg***
Percent Improvement
324
150
66
378
175
68
215
40
13
137
26
10
* mgd x 3785 = cu m/day
** tons/year x 0.906 = metric tons/year
*** lb/mg x 0.120 = gm/cu m
44
-------
for fixed film facilities. The mean potential effluent BOD,, and TSS concen-
trations for the suspended growth facilities were 9 mg/1 and 10 mg/1, respect-
ively. The mean potential effluent BOD and TSS concentrations for the fixed
film facilities were 33 mg/1 and 28 mg/1, respectively, which is near second-
ary treatment standards.
In both suspended growth and fixed film facilities, an improvement in
effluent quality can be achieved through CCP's without major facility upgrades,
The potential reduction in BOD and TSS for the suspended growth facilities
was 294 metric tons per year (324 tons/year) and 342 metric tons per year
(378 tons/year), respectively. The potential reduction in BOD and TSS for
the fixed film facilities was 195 metric tons per year (215 tons/year) and
124 metric tons per year (137 tons/year), respectively. The total potential
improvement in performance for the suspended growth facilities was slightly
greater than for the fixed film facilities, but was significantly greater per
unit of wastewater flow. The combined wastewater flow rate for the suspended
growth facilities was 44,800 cu m/day (11.8 mgd) compared to 110,600 cu m/day
(29.2 mgd) for the fixed film facilities. The resulting potential reduction
per unit of wastewater flow was significantly greater for the suspended growth
facilities at 18 gm/cu m (150 Ib/mg) for BOD and 21 gm/cu m (175 Ib/mg) for
TSS, compared to 4.8 gm/cu m (40 Ib/mg) for BOD and 3.1 gm/cu m (26 Ib/mg)
for TSS for the fixed film facilities.
The fixed film facilities surveyed exhibited poor performance that can-
not be satisfactorily improved through CCP's which exclude major plant modi-
fications. Major plant modifications are required to expand the unit size
of the secondary treatment process (i.e., implement a more conservative de-
sign) . The potential reductions in pollutant discharge for fixed film facili-
ties with CCP's that exclude major modifications were only about 13 and 10
percent of the existing discharge for BOD and TSS, respectively. The sus-
pended growth facilities exhibited poorer performance than fixed film facili-
ties, but their performance can be improved significantly through CCP's that
exclude major modification. The potential reductions in pollutant discharge
for suspended growth facilities were 65 and 68 percent of the existing dis-
charge for BOD and TSS, respectively. From this evaluation it was concluded
45
-------
that, in general, a more conservative design approach is required for fixed
film facilities and better operation is required for suspended growth facili-
ties.
ADDITIONAL FACILITIES ABLE TO MEET SECONDARY TREATMENT STANDARDS
Most of the thirty facilities surveyed were constructed before the
present secondary treatment standards were promulgated, but all were designed
to provide secondary treatment. A few facilities were required to meet more
stringent standards. For this report, all facilities were analyzed with re-
spect to their ability to meet the minimum monthly secondary treatment stan-
dard of 30 mg/1 for BOD5 and TSS. The results are presented in Table 7. It
should be noted that the division of plants in Table 7 does not correspond to
the division of plants in Tables 2, 3 and 4, since some plants' performance
could be improved with a CCP but would still not meet secondary treatment
standards. Also, at some plants that met secondary standards the performance
could be further improved with a CCP.
TABLE 7. SUMMARY OF PERFORMANCE OF THIRTY PLANTS SURVEYED VERSUS MINIMUM
SECONDARY TREATMENT STANDARDS
Prior to After Preliminary
Preliminary Survey Survey Potential
Number of plants
where standards were
consistently met 7 13 23
Number of plants
where standards were
frequently violated 23 17 7
Prior to the research evaluations only seven facilities were meeting sec-
ondary treatment standards consistently. After the evaluations, which includ-
ed some operations assistance, an additional six facilities, for a total of
thirteen, met standards. Ten more facilities, for a total of twenty-three,
have the potential of meeting standards through implementation of CCP's with-
out major facility modifications. The remaining seven of the thirty facili-
46
-------
ties would require major plant modifications before they would consistently
meet secondary standards.
Three of the seven facilities meeting secondary treatment standards prior
to the research evaluation were considered to have both good design and good
operation. Two of the remaining four facilities were underloaded (50 percent
and 35 percent of design hydraulic loading) and were meeting secondary treat-
ment requirements, but could have performed better. Another was able to con-
sistently meet secondary treatment standards because of the ability to bypass
part of the influent wastewater flow to a larger facility. This facility
would satisfactorily treat a greater wastewater flow by improving plant opera-
tions. The fourth facility performed well when operating, but required total
shut-down and bypassing of raw sewage during periods of bulking sludge and/or
mechanical breakdown. Bypassing did not occur during the evaluation, but the
facility was operating at only 30 percent of its design hydraulic loading. As
loading to the plant increases more bypassing can be expected. Major modifi-
cations will be required to correct the problems at this facility.
ADVANTAGE OF A COMPOSITE CORRECTION PROGRAM
Composite Correction Programs can achieve dramatic improvements in waste-
water treatment facility performance. However, CCP's have typically not been
used to improve performance at existing facilities that violate secondary
treatment standards. The typical approach has been to complete major plant
modifications, usually through the federal construction grant process. This
approach was used at two facilities studied as a part of this research effort
which were violating their permit standards. Just prior to the research
evaluations, major plant modifications were completed which doubled the plant
capacities. During the research evaluations, neither facility was meeting
its permit standard. The original deficiencies that were limiting performance
were not addressed in the plant upgrades. Further, it was judged that if
these deficiencies were corrected before the plants had been expanded, the
expansions would not have been required. The deficiencies that existed prior
to the plant expansions and continued to exist after the expansions still
needed to be corrected before satisfactory performance could be achieved. A
47
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properly conducted CCP at these two plants could have satisfactorily improved
their performance and eliminated the need for expansion. The greatest cost
advantage for CCP's occurs when they eliminate the need for a major facility
modification. For these cases, cost savings through CCP's could reach
several hundred thousand dollars per plant.
Exact costs for a typical CCP are difficult to estimate for a variety of
reasons. A CCP always includes the cost of providing the technical assistance
service and may contain costs necessary for minor plant modifications, staff-
ing additions, spare parts additions, increased sludge handling, etc. The
cost of a CCP is dependent upon facility size and type and the number and
magnitude of factors limiting the plant's performance. Because each facility
is unique in its specific collection of performance limiting factors, the cost
for each CCP would be widely varied. A cost for an 1890 to 18900 cu m/day
(0.5 to 5 mgd) activated sludge plant would typically range from $5,000 to
$50,000. The general approach to conducting every CCP is similar and is des-
cribed in this section of the report. The approach described for conducting
CCP's is relative to the size range of plants evaluated during this research
effort (i.e., less than 37,850 cu m/day (10 mgd).
Implementation of a CCP involves technical assistance time for an ini-
tial on-site visit, telephone consultations and follow-up on-site visits.
The overall time period for which the CCP is conducted is typically-one year.
The relative time involvement for implementing a CCP is illustrated in Figure
6. Time for on-site visits, telephone consultation, and the overall time
period during which the CCP is conducted varies depending upon facility size
and type, plant personnel training, plant personnel attitude and aptitude and
other performance limiting factors that exist at the facility. As such, the
initial on-site visit may require a few days up to several weeks. This ini-
tial visit is followed with "waiting time" and telephone consultation. Tele-
phone consultation with the plant process control coordinator may be main-
tained on a daily, semi-weekly or weekly basis, depending upon the situation.
The waiting time and telephone consultation activities are interspersed with
on-site visits during which problems are investigated further and technical
assistance activities and training are reinforced. The follow-up on-site
48
-------
INITIAL SITE
VISIT
WAITING
TIME
TELEPHONE
CONSULTATION
ON-GOING
SITE VISITS
D
D
OVERALL JIWE FOR CCP (TYPICALLY ONE YEAR)
Figure 6. Relative time involvement for CCP activities.
visits are scheduled at weekly, bi-weekly, monthly or bi-monthly intervals
depending on the need. Each on-site visit typically lasts from one to five
days.
The outlined approach for implementing a CCP has numerous advantages for
achieving and maintaining desired facility performance. The long time in-
volvement greatly increases the chances of identifying and correcting problems
in the administration, maintenance and design areas. Also, the long time
frame is very compatible with optimizing a biological system which has an in-
herently slow responsive nature. Another advantage is that during the time
optimum facility performance is being achieved, process control capability is
transferred to plant personnel so they can maintain performance at the improved
levels. This transfer is accomplished by interspersing on-site, one-on-one
training activities and telephone consultation activities with waiting time.
During the waiting time plant personnel are forced to observe changes in bio-
logical system characteristics and -complete the required process control ad-
justments. Plant personnel must then discuss their observations and adjust-
ments with the technical assistant. This procedure of "guided observance" of
system response is a very effective mechanism to develop the operator's ability
to correctly apply concepts of plant operation to process control. Also the
49
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technical assistant is better prepared to conduct other CCP's due to the ex-
perience gained by accounting for process response over a long period of time.
These advantages are further accentuated.by the fact that plant and adminis-
trative personnel gain long term access to technical guidance at a minimal
cost. Judicious use of waiting time allows the cost for CCP's to be minimized
relative to the long time involvement benefits gained.
Presently, plant upgrading through construction is usually selected as
the alternative for improving the performance at a plant that is violating its
permit standards. Some level of plant modification or upgrade might be con-
sidered adequate to enable facilities to meet standards with a minimum empha-
sis on plant operation. However, twenty-three of the thirty facilities evalu-
ated (6) did not meet secondary treatment standards, yet the average hydraulic
loading of these plants was only 61 percent of design. The average loading
for the seven plants which met standards was not much lower at 55 percent of
design capacity. Plants which met secondary standards were loaded as high as
98 percent of design. It was concluded that plant over design alone did not
significantly promote good performance. However, a CCP conducted in conjunc-
tion with or prior to plant expansion does identify and correct problems at
existing plants and may eliminate the need for a plant expansion at some facil-
ities. In this context, the cost comparison of a CCP versus plant upgrading
through construction is irrelevant. Plant upgrading to achieve better per-
formance cannot be a substitute for a CCP, but rather should only occur as a
part of a CCP.
50
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REFERENCES
1. "Clean Water Report to Congress - 1973, 1974, 1975 Annual Reports", U.S.
Environmental Protection Agency, Washington, B.C., May 1973, June 1974,
June 1975.
2. "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 B.C., (April 11, 1977).
3. Perry, Robert R., "WPCF Role in Improving 0 & M", Journal of Water Pollu-
tion Control Federation, 49, 1635 (1977).
4. Milstone, M.L., "Operations Personnel: They Go Where the Money Is",
Journal of Water Pollution Control Federation, 49, 1949 (1977).
5. Gilbert, Walter G., "Relation of Operation and Maintenance to Treatment
Plant Efficiency", Journal of Water Pollution Control Federation, 48,
1822 (1976).
6. Hegg, B.A., K.L. Rakness, and J.R. Schultz, "Evaluation of Operation and
Maintenance Factors Limiting Municipal Wastewater Treatment Plant Perfor-
mance", report prepared in partial fulfillment of EPA Contract No.
68-03-2224, U.S. Environmental Protection Agency, Cincinnati, Ohio, (1978).
7. Hegg, B.A. , "Procedures Used in Conducting Selected Activated Sludge
Control Tests", M & I, Inc., Consulting Engineers, Fort Collins, Colorado
(October 1973).
8. West, A.W., "Operational Control Procedures for the Activated Sludge Pro-
cess", EPA-330/9-74-001-6, U.S. Environmental Progection Agency,
Cincinnati, Ohio (April, 1973).
9. Ahlberg, N.R., and B.I. Boyko, "Evaluation and Besign of Aerobic Bigest-
ers", Journal of Water Pollution Control Federation, 44, 634 (1972).
51
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4. TITLE AND SUBTITLE
A DEMONSTRATED APPROACH FOR IMPROVING PERFORMANCE AND
RELIABILITY OF BIOLOGICAL WASTEWATER TREATMENT PLANTS
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-79-035
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
June 1979 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Bob A. Hegg, Kerwin L. Rakness, and James R. Schultz
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
M & I, Inc., Consulting Engineers
4710 South College Avenue
Fort Collins, Colorado 80525
10. PROGRAM ELEMENT NO.
1BC821; SOS 2; Task Al
11. CONTRACT/(|pOT U T GOVERNMENT PRINTING OFFICE 1979-657-060/5329
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