WATER POLLUTION CONTROL RESEARCH SERIES • 17O9ODOY12/7O
FEASIBILITY OF COMPUTER CONTROL
OF
WASTEWATER TREATMENT
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes
the results and progress in the control and abatement
of pollution in our Nation's waters. They provide a
central source of information on the research, develop-
ment, and demonstration activities in the Water Quality
Office, Environmental Protection Agency, through inhouse
research and grants and contracts with Federal, State,
and local agencies, research institutions, and industrial
organizations.
Inquiries pertaining to WateJr Pollution Control Research
Reports should be directed to the Head, Project Reports
System, Office of Research and Development, Water Quality
Office, Environmental Protection Agency, Room 1108,
Washington, B.C. 20242.
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FEASIBILITY OF COMPUTER CONTROL
OF WASTEWATER TREATMENT
by
American Public Works Association
Chicago, Illinois 60637
for the
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE
Project #17090 DOY
Contract #14-12-580
December, 1970
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price $1.00
Stock Number 5501-0145
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SUPPORTING AGENCIES
City of Tempe, Arizona
City of Kelowna, British Columbia
City of San Jose, California
City of Los Angeles, California
City of Marietta, Georgia
City and County of Honolulu
City of Peoria, Illinois
City of Wichita, Kansas
City of Bloomington, Minnesota
City of New York, New York
City of Toronto, Ontario
City of Philadelphia, Pennsylvania
City of Pittsburgh, Pennsylvania
City of Oak Ridge, Tennessee
City of Fort Worth, Texas
City of Richmond, Virginia
Municipality of Metropolitan
Seattle, Washington
City of Seattle, Washington
City of Madison, Wisconsin
EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents
necessarily reflect the views and policies of the
Environmental Protection Agency.
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STEERING COMMITTEE
Joseph V. Radziul (Chairman), Chief of Research and Development, Philadelphia Water Department
Waddy M. Allnut, Chief of Bureau of Business Management, Department of Public Works, Richmond, Virginia
Ben Cramer, Director, Organization and Methods Division, Fiance Department, City of Toronto
Harry Fite, Chief of Information Systems Division, U. S. Department of Transportation
Charles V. Gibbs, Executive Director, Municipality of Metropolitan Seattle
Sam Hobbs, Director of Public Works, Bloomington, Minnesota
E. Steve Savas, Deputy City Administrator, Office of the Mayor, City of New York
Project Director
Richard H. Sullivan
Principal Investigator
Harold D. Oilman
ADVISORY COMMITTEE
Waddy M. Allnut, Chief of Bureau of Business Management, Department of Public Works, Richmond, Virginia
Peter G. BardezBanian, City Finance Director, Peoria, Illinois
R. R. Blackburn, Assistant Director of Public Works, San Jose, California
Walter J. Brown, City Manager, Marietta, Georgia
Ben Cramer, Director, Organization and Methods Division, Finance Department, City of Toronto
C. W. Dotts, Administrative Supervisor, Department of Public Works, Wichita, Kansas
Charles V. Gibbs, Executive Director, Municipality of Metropolitan Seattle
Jack M. Graham, Public Works Director, Fort Worth, Texas
Herbert J. Hellen, Civil Engineer IV, City Engineering Division, Madison, Wisconsin
Sam Hobbs, Director of Public Works, Bloomington, Minnesota
Douglas L. Jonas, Management Engineer, Seattle, Washington
Yoshio Kunimoto, Chief Engineer, Honolulu, Hawaii
Otto V. Kendzior, Administrative Assistant, Department of Public Works, Pittsburgh, Pennsylvania
E. P. Lawrence, City Engineer, Kelowna, British Columbia
Joseph V. Radziul, Chief of Research and Development, Philadelphia Water Department
O. K. Rickman, Public Works Director, Oak Ridge, Tennessee
E. Steve Savas, Deputy City Administrator, Office of the Mayor, City of New York
Robert J. Snyder, Director of Public Works, Tempe, Arizona
Donald C. Tillman, Chief Deputy City Engineer, Los Angeles, California
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AMERICAN PUBLIC WORKS ASSOCIATION
Board of Directors
Myron D. Calkins, President
William W. Pagan, Vice President
Ross L. Clark, Past President
Ray W. Burgess Erwin F. Hensch
Lt. Gen. Frederick J. Clarke Leo L. Johnson
Harmer E. Davis Timothy J. O'Leary
Donald S. Frady Lyall A. Pardee
Wesley E. Gilbertson Frederick R. Rundle
Herbert Goetsch Gilbert M. Schuster
Robert D. Bugher, Executive Director
APWA RESEARCH FOUNDATION
Board of Trustees
Samuel S. Baxter, Chairman
W. D. Hurst, Vice Chairman
Fred J. Benson William S. Foster
John F. Collins D. Grant Mickle
James V. Fitzpatrick Milton Offner
Milton Pikarsky
Robert D. Bugher, Secretary-Treasurer
Richard H. Sullivan, General Manager
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ABSTRACT
This report contains the results of an investigation into the use of digital
computers for management and control of wastewater treatment facilities. The
objectives of the study included the generation of guidelines for implementation of
digital computers for these purposes and recommendations for further relevant
research.
For the purpose of gathering information, visits were made to plants and the
literature was searched. A survey was conducted of current practices and problems in
the operation of wastewater treatment plants. Emphasis was placed on the processes of
secondary treatment with regard to management and control of unit processes,
continuous monitoring needs, the influences of regulatory agencies, and certain local
conditions. A set of guidelines and steps for computer control implementation and
peripheral applications were evolved.
It was concluded that both off-line computer applications and on-line computer
control in wastewater treatment are feasible and should be implemented.
This Report was submitted in fulfillment of Contract 14-12-580 between the
Environmental Protection Agency, the American Public Works Association and
nineteen cost sharing local governmental agencies.
KEY WORDS: Computers, Wastewater Treatment, Monitoring, Control
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CONTENTS
Page
SECTION 1
SUMMARY AND RECOMMENDATIONS
Objectives 1
Conclusions 1
Recommendations 2
SECTION 2
WASTEWATER TREATMENT PROCESSES AND CONTROL APPLICATIONS
Wastewater Treatment System 3
Process Control Computer System 3
Common Treatment Processes, Variables and Instrumentation 4
Continuous Monitoring and Control 13
SECTION 3
SOME ASPECTS OF HIGHER ORDER TREATMENT
Introduction 23
Microstraining 23
Chemical Coagulation 23
Filtration 24
Activated Carbon 25
Ammonia Removal by Air Stripping 26
Ion Exchange 26
SECTION 4
SURVEY OF WASTEWATER TREATMENT PLANTS 29
SECTION 5
DATA NEEDS OF REGULATORY AGENCIES
Introduction 31
Regulatory Agency Data Requirements 31
Automatic Control and Regulatory Agency Data 32
SECTION 6
GUIDELINES FOR COMPUTER IMPLEMENTATION
Introduction 35
Technical Justification for Computer Control 35
Sources of Economic Justification for Computer Control 40
Preliminary Information Needs for Computer Control 42
Mathematical Modeling Applications 43
SECTION 7
MEASURED STEPS TOWARD PLANT AUTOMATION
Introduction 47
Design of Plant Management Information Reporting System 47
Vll
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CONTENTS (Continued)
Design of Computerized Equipment Maintenance File 49
Computer Programs for Reporting, PM Files, and Other Off-line Uses 49
Plant Instrumentation Review and Upgrading 50
Preliminary Automation Study and Computer System Specification 50
Implementing Plant Automation 51
SECTION 8
LOCAL INFLUENCES ON PLANT AUTOMATION
Public Concern 53
Water Quality as a Resource 53
Regional Water Pollution Control Systems 53
Controlled Plant Influent 54
SECTION 9
ADVANCED RESEARCH ON CONTROL SYSTEMS 57
SECTION 10
RECOMMENDED RESEARCH
Development of a Suspended Solids Probe 59
Development of Instrument for Rapid Determination of Biological Oxygen Demand . . 59
Development of Instrument for Rapid Fecal Coliform Counting 59
User's Experience Instrumentation Study for Wastewater Treatment Processes 60
Analyses and Procedures for Computer Control of Wastewater Treatment Processes ... 60
Augmented Instrument Study 61
Computer Implementation for Monitoring and Control of a Wastewater Treatment Plant 62
feasibility Study for Rapid Mercury Analysis 62
Development of an On-line Phenol Sensor Probe 63
Development of an On-line Trace Oil Monitor Instrument 63
SECTION 11
ACKNOWLEDGEMENTS 65
SECTION 12
GLOSSARY 67
SECTION 13
REFERENCES 69
SECTION 14 - APPENDIX
CONTINUOUS MONITORING INSTRUMENTATION SURVEY
Method 71
Results and Uses 71
Vlll
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ILLUSTRATIONS
Figure
1 Northeast Water Pollution Control Plant,
Philadelphia, Pa 3
2 Process Computer, Peripheral Equipment and
Industrial Tie-ins 4
3 Common Processes in Secondary Wastewater Treatment °. . . 5
4 Monitoring and Control of Common Wastewater
Treatment Processes 14
5 Map of Metro Seattle Wastewater Collection System 16
6 Filter Backwash Monitor 25
7 Example of a Data Logger 33
8 Excerpt from the Computer Generated NELOG Summary
Report 37
9 Off-Line vs. On-Line Computer Control 44
10 Computer Assisted Straight-Line Regression Analyses 45
11 Automatic Plot of Two Variables vs. Time 46
12 Off-Line Computer Generated Excerpts from Wastewater
Treatment Plant Reports 48
13 Using the Time-Sharing System 50
14 Whittier Narrows Water Reclamation Plant 55
TABLES
Table
1 Common Wastewater Treatment Processes 6
2 Loose Treatment Control of BOD 4Q
3 Improved Treatment Control (With Computer) of BOD 40
4 Measurements for Wastewater Treatment Processes 72
5 Automatic Monitoring Instrumentation for Wastewater
Treatment Processes 73
6 Symbols and Abbreviations 75
7 Manufacturers of Automatic Samplers • 76
8 Manufacturers' Addresses 77
IX
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FOREWORD
The completion of this report, Feasibility of Computer Control of Wastewater Treatment,
marks the completion of the second phase of APWA Research Foundation Project 66-6 which
was designed to investigate the feasibility of computer control of public works processes. The
first report, Public Works Computer Applications, was published as APWA Special Report No.
38. The Special Report provides a plan of action for public works officials to computerize
information and control systems — or to extend the use of computer systems now in use. The
report called attention to the expanding role of the computer for traffic and transportation
systems, water supply and distribution, environmental management, and waste collection and
disposal. The report offered guidelines on feasibility studies, selecting equipment, preparing staff
and space, and beginning operations.
This report is a detailed examination of the use of process computers in wastewater
management. The need for this detailed investigation was apparent upon investigation of the uses
which have been reported have been primarily for data logging.
In contrast, considerable use of computer process control was found in industrial treatment
facilities. Thus, this project was initiated to determine the feasibility of computer process
control. The initial report was prepared by the General Electric Re-entry and Environmental
Systems Division. General Electric worked closely with the Steering Committee to prepare the
final report. Additional input data were provided by the APWA staff. Throughout the study it
was pointed out by treatment plant personnel that sensors are not generally available for
wastewater treatment plant processes. Sensors that are available have not been designed or
constructed for use in this field. Devices which have been installed, generally have been
extensively modified.
Manufacturers should work towards the development of requisite sensors suitable for the
adverse environment in which they must be used as a design consideration. It is readily apparent
that the use of process computers for the control of wastewater treatment plants would
materially improve efficiency of plants and plant management and perhaps reduce treatment
costs.
Joseph V. Radziul, Chairman
Steering Committee
XI
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SECTION 1
SUMMARY AND RECOMMENDATIONS
The summary of this study is reported in
the following paragraphs under the headings of
Objectives and Conclusions. Considerations for
further action are included in the
Recommendations part of this section.
OBJECTIVES
The threefold objectives of this wastewater
treatment study were as follows:
1. To .analyze the advantages and
limitations associated with the use of computers
in the management and control of wastewater
treatment facilities,
2. To document potential applications
and utilization procedures, and
3. To recommend further research to
achieve full computer implementation for
wa&tewater treatment operations and associated
management functions.
The following tasks were completed in
support of the above objectives:
1. A survey of wastewater plants was
made to determine the critical problems in
treatment and whether continuous monitoring
and computer control could help solve these
problems.
2. Visits were made to wastewater plants
utilizing computer applications and automation
at Seattle, Washington; Hyperion (Los Angeles),
California; Whittier-Narrows, California and
Philadelphia, Pennsylvania to assess these
applications.
3. Documentation of treatment
processes and operational reports were received
from the surveyed plants and studied to
determine their feasibility for automation.
4. Information on continuous
monitoring instrumentation for wastewater
treatment was acquired from manufacturers for
use in the instrumentation survey.
5. Numerous documents covering
automation and treatment were investigated in a
literature survey.
6. Meetings and discussions were held
with plant management, consultants,
government regulatory agencies and the Project
Steering Committee.
CONCLUSIONS
Resulting from the above tasks are the
following conclusions:
1. While conventional treatment systems
do have serious disadvantages and limitations,
they will continue to be the most broadly
applied for the next 20 years.
2. While no new large scale innovation
threatens to replace conventional treatment,
modifications to the processes and
supplementary processes are being implemented.
Examples are chemical coagulation and
oxygenation.
3. Personnel pose a real problem in the
operation of plants. Difficulties arise in
obtaining qualified personnel, in training
operators and maintenance men and in reliable
follow-through of operational instructions.
4. Interest in computer applications and
automatic control is widespread among plant
management.
5. A recognition of the advantages of
off-line computer uses was unanimous with
general appreciation of automated management
reporting, maintenance scheduling, inventory
control, payroll and accounting.
6. Skepticism was apparent among plant
management regarding on-line computer control
of plant processes.
7. Computer hardware and
communication equipment are available and
reliable for use in industrial process control and
are suitable for application to wastewater
treatment as well.
8. Off-line computer implementation for
plant data handling and management
information reporting is being successfully
practiced; it can serve a wide range of beneficial
applications and is fully feasible today.
9. On-line instruments to sense some of
the variables considered essential to .continuous
monitoring and control of wastewater treatment
(such as BOD, bacteria and volatile acids) are
not on the market.
10. Computer control of the more critical
treatment processes, activated sludge and
anaerobic digestion is possible in a limited sense
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based upon experienced operator control, and
will require further study before optimization
via computer control is achieved.
RECOMMENDATIONS
The actions indicated from the above
conclusions are as follows:
1. Plant management should consider
using off-line computer data processing for all
areas of plant data handling: reports,
maintenance files and scheduling, inventory
control, and business areas. Computer
availability for off-line applications may exist via
a municipal facility, a nearby service bureau,
time-sharing or the plant's computer.
2. Studies are recommended to develop
the mathematical-logical relationships of the
plant physical processes, notably the activated
sludge and anaerobic digestion processes. The
studies should result in the development of
control strategies for supervisory or closed-loop
control.
3. Further work must be done in the
development of reliable, maintenance-free,
on-line sensors. An in-depth survey of users'
experience with analytical instrumentation and
sensors in wastewater treatment plants should be
conducted. The survey would provide guidelines
for improvement and innovative approaches to
solving the problems of continuous monitoring
of wastewater treatment processes.
4. Plant management should give serious
consideration to computer control of plant
processes, despite the lack of both knowledge
and sensors in some areas of wastewater
treatment. Today's impetus in plant controls is
toward increased application of local closed
loops with advanced instrumentation. Some
examples are return sludge on the basis of
blanket level, aeration rate to maintain a
dissolved oxygen level and variable speed
pumping for uniform plant flow. These local
processes can be integrated to achieve greater
operational and economic benefits via computer
control of centralized plant monitoring,
automatic analyses, timely reporting and
improved plant controls. Only by application of
computer control can the wastewater treatment
process be optimized as a total integrated
system.
5. Design of new plants or modification of
medium size (15 to 50 mgd) existing plants
should incorporate automatic controls of the
highest degree available. This should yield
economies of scale, operation and management
and prepare the plant for future conversion to
full computer control.
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SECTION 2
WASTEWATER TREATMENT PROCESSES AND CONTROL APPLICATIONS
WASTEWATER TREATMENT SYSTEM
The w-astewater treatment system
comprises wastewater collection, treatment and
disposal. All three aspects must be considered in
the application of computer monitoring and
control. The main emphasis of the study is on
the conventional wastewater plant, such as
typically shown in Figure 1, through secondary
treatment and sludge disposal, and on the role of
the computer to upgrade the system. The
processes, operational variables and
instrumentation for sensing and control are
examined from phase to phase with a view
toward the feasibility of automatic monitoring
and control.
The tertiary and advanced waste treatment
(AWT) processes are still relatively new and in
the demonstration stage. Although not included
in the processes listed in Table 1, some of the
techniques are covered briefly in Section 3.
PROCESS CONTROL COMPUTER SYSTEM
The process control computer is the key to
automatic monitoring and control of wastewater
treatment. This digital computer control system
includes:
1. Central processor to perform
computations and logic,
2. Core storage to retain both data and
instructions for immediate access to central
processor,
3. Auxiliary storage, such as disk, drum
and tape to retain data and instructions, and
4. Peripheral equipment such as card
reader and card punch, input-output keyboard,
printer and cathode ray tube for communication
with a user.
The process computer has all the
capabilities of a purely digital machine. In
addition, it has an added set of peripheral
components to accommodate the direct
monitoring and control of industrial processes,
as illustrated in Figure 2. .Such computer
applications are commonplace in the chemical,
petroleum and steel industries among many
others.
Figure 1. Northeast Water Pollution Control Plant, Philadelphia, Pa.
(This plant uses activated sludge and anaerobic digestion.)
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PROCESS ACTUATORS &MNTROLURS
PROCESS SENSORS & TRANSDUCERS
INPUT / OUTPUT & CENTRAL PROCESSOR
Figure 2. Process Computer, Peripheral Equipment and Industrial Tie-ins
The following is a summary of computer
capabilities that suggest a more efficient
operation than by manual control. The
computer can:
1. Monitor operations and provide
accurate, useful information — periodically or
on demand,
2. Generate alarms for off-normal
conditions,
3. Perform conventional controller
functions with greater ease and flexibility,
4. Duplicate consistently the best-known
control strategies on a continuous basis,
5. Make programmed decisions on more
variables and data than a human — more rapidly,
more usefully, and
6. Maintain operating levels among
diverse processes within limiting constraints.
COMMON TREATMENT PROCESSES,
VARIABLES AND INSTRUMENTATION
Identified in Table 1 are the physical
processes prevalent in a large number of
treatment plants. Automation of most existing
wastewater treatment plants requires an
examination of these phases of treatment.
Briefly delineated in Table 1 are each function,
the role of management, and effectiveness
measures for operation. Consideration is also
accorded to the existing status of pertinent
analytical instrumentation. In Figure 3 is
depicted a schematic flow diagram of the
common wastewater treatment processes that
appear in Table 1.
Computer implementation for control in a
wastewater treatment plant necessitates the
availability of process monitoring signals on a
continuous or sampled data basis. There are two
types of instrumentation for acquiring process
information:
1. In-stream probe or sensor which
generates an analog signal of the variable
measured, and
2. Automated analytical procedure (or
automated wet chemistry) which samples a
quantity from the flow and subjects the sample
to an automatic laboratory procedure, requiring
reagents. Although the procedure may be rapid,
a certain amount of time must elapse before a
variable is measured.
Certain wastewater characteristics must be
measured to achieve efficient treatment.
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COLLECTION SYSTEM
REGULATOR
(COMBINED
SEWER)
PLANT INFLUENT
GATES
MECHANICAL
SCREENS
GRIT
REMOVAL
RAW
WASTE WATER
PUMPS
EFFLUENT RECIRCULATION
SLUDGE
DISPOSAL
SLUDGE
DEWATERING
T
ANAEROBIC
DIGESTION
SLUDGE
PRIMARY
SEDIMENTATION
SLUDGE
THICKENING
LIQUID RETURNS
WASTE WATER
SLUDGE
Figure 3. Common Processes in Secondary Wastewater Treatment
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TABLE 1. COMMON WASTEWATER TREATMENT PROCESSES (1 of 6)
Function
Operational management
Effectiveness measures
Monitored variables and use
Available
on-line
instruments
On-line
instrument needs
Divert excess wet weather
flow to receiving waters (in
combined sewer systems or
systems subjected to exces-
sive infiltration and inflow).
Prevent dry weather
overflow.
Investigate pollution
overflows.
Repair malfunctions.
Regulator monitoring and control
No dry weather overflows.
Reduced stream pollution.
Reduced surveillance costs.
Depth to detect outfall sewer
overflows.
Flow to outfall sewer (in dry
weather).
Depth Flow measurement Im-
provement, since Venturl
meters and Parshall flumes
are. difficult to Install and
expensive. Given sewer
cross-section, slope and
roughness, the depth
measurement could yield
a more accurate, com-
puted flow (via computer).
Regulate raw sewage flow
into plant.
Allow plant maintenance.
Capture and prevent coarse
material from entering
plant, thereby protecting
piping and equipment.
Screened material shredded
and returned to wastewater
or trucked away for disposal.
Regulate influent flow to help
maintain steady state flow
through treatment processes.
Optimize screen-cleaning
activity.
Too little causes excessive
back-up; too much leads to
high maintenance costs and
operational costs.
Plant influent gates
Prevention of plant influent
surges.
Preservation of steady plant
flow.
Mechanical screens
Minimized influent back-up.
Reduced screen cleaning
costs.
Minimal coarse solids to
plant.
Depth to prevent flood levels Depth
in adjacent residential areas. Flow
Influent flow to approach
steady state design range.
Liquid level to detect high Depth
head-loss across screen and to Flow
initiate cleaning cycle.
Adequate (see section 13,
Instrument survey).
Adequate (see section 13,
Instrument survey).
Raise the level of influent
wastewater for continu-
ation through plant
Maintain steady-state design
range flows through plant.
Wet well level maintained
above minimum level for
suction, and below maximum
level to prevent flooding.
Best control of steady-state
design flow through plant.
Raw wastewater pumping
Control pumping for maxi-
mum efficiency and life.
Steady plant flow.
Depth of wet well kept Depth
within normal limits. Flow
Flow to approach steady- Power
state. Current
Electrical power for opera- Voltage
tion and determination of Bearing
pump efficiency. temperature
Bearing temperature to
protect pump.
Elapsed time meter to
monitor pump life and
maintenance requirements.
Adequate (see section 13,
Instrument survey).
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TABLE 1. COMMON WASTE WATER TREATMENT PROCESSES (2 of 6)
Function
Operational management
Effectiveness measures
Monitored variables and use
Available
on-line
instruments
On-line
instrument needs
To remove abrasive, chiefly
inorganic materials, thereby
minimizing pump wear, pre-
venting clogging, and simpli-
fying sludge handling and
disposal.
Removed grit is disposed of
by incinerator, burial, dump,
or landfill.
Maintain optimal, steady
channel velocity to settle
high density grit and to pass
low density organics.
Analyze grit for organic
matter to determine grit
channel efficiency.
Maintain mechanical grit
removal equipment.
Grit channel
Minimal appearance of grit in
primary settling and sub-
sequent plant equipment,
especially in digesters.
Minimal organic settling in
grit channel.
Channel flow and depth to
determine velocity.
Grit channel entry as moni-
toring point for wastewater
characteristics (pH, temper-
ature, BOD, COD, DO, TOC,
SS, percent volatile matter,
phosphates, nitrogen, ORP,
toxic metals, and toxic
compounds).
Depth BOD
Flow Phenol
pH Toxic material detector.
Temper- On-line instrumentation
ature for phosphates and nitro-
COD gens, COD and TOC com-
TOC prises automated analytical
Phosphates procedures (automated
Nitrogens wet chemistry). Detec-
ORP tion by probe or sensor
Chromium in the stream flow would
Copper be more direct and would
DO yield a real-time measure-
ment.
Although a suspended
solids on-line instrument
is available for the high
ranges, none exists that is
suitable for less than 500 mg/1,
the level of suspended solids
for influent wastewater.
Remove settlable and
floatable solids (and as-
sociated BOD).
Ascertain removal of sludge,
scum, grease and oil.
Minimize downtime of skim-
ming, sludge collecting, and
pumping equipment.
Maintain proper sludge density
for pumping.
Determine pollutant removal
efficiencies.
Primary sedimentation
Maximum removal of
suspended solids in the
primary effluent and
floatable material.
Removals include scum,
grease and oil.
Influent and effluent COD
measurements of BOD (or TOC
COD or TOC), SS, percent pH
volatile matter to evaluate DO
efficiency of removals. Sludge
pH and DO in effluent are density
important to further treat- Flow
ment.
Flow over weir controlled
and steady to promote sedi-
mentation.
Sludge density to control
pumping for sludge removal.
BOD to measure removal
efficiency.
SS to measure removal
efficiency.
No on-line device has yet
proved reliable for primary
tank use to measure sus-
pended solids or BOD.
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TABLE 1. COMMON WASTEWATER TREATMENT PROCESSES (3 of 6)
oo
Function
Operational management
Effectiveness measures
Monitored variables and use
Available-
on-line
instruments
On-line
instrument needs
Remove BOD and SS by means
of biological activity and
subsequent settling.
Maintain healthy, active
organisms through the bal-
ance of influent, effluent,
and sludge-return flows.
Maintain proper loading rates,
satisfactory DO level and
good mixing throughout tank.
Provide sufficient sampling
of variables.
Control applied air to
maintain aerobic conditions
Activated sludge (aeration tank)
Maximized BOD removals and
sludge density index.
Minimized need for applied
air with resultant power
savings.
BOD (influent and effluent)
to determine removal ef-
ficiencies.
DO to maintain optimum
level in aeration tank for ap-
plied air flow.
Mixed liquor suspended solids
(MLSS) to determine return
sludge needs.
ORP to indicate the state of
oxidation and oxygen utili-
zation.
Flow to approach steady-state
design range.
Return sludge flow to verify
required rate.
pH as alarm indicator if too far
from normal.
Temperature for record pur-
poses and correlation studies.
DO
MLSS
ORP
Flow
PH
Temperature
BOD to oplinn/c return
sludge mix.
Remove solids settling
in effluent from secondary
treatment units (aeration
tanks or trickling filters).
Provide activated sludge
return to the aeration tank.
Maintain timely removal of
properly concentrated set-
tled solids for fresh return
activated sludge.
Maintain proper level of
sludge blanket.
Maintain design value of
surface application rate.
1 Activated Sludge Process Automated. Water and Sewage Works.
May 1970.
2Stack, V.T. Continuous Monitoring Devices - Treatment
Plants. Proceedings Ninth Engineering Conference,
Instrumentation, Control and Automation For Water Supply
and Wastewater Treatment Systems. University of Illinois,
College of Fngmccrmp 1967.
Secondary clarification
High removals in effluent of
BOD, COD, SS.
Rate of liquid overflow from
clarifier to indicate effluent
flow.
Sludge blanket level in tank
to determine start of sludge
removal.
ORP to indicate condition of
sludge.
BOD (or COD or TOC) and SS
in effluent to indicate removal
efficiency.
Nitrogens and phosphates to
indicate removals of respective
nutrients.
Temperature for record pur-
poses and correlation studies.
DO in effluent to indicate
effect on receiving waters.
pH as alarm indicator when
outside normal range.
PH
DO
SS
Sludge
blanket
Flow
ORP
COD
Nitrogens
Phosphates
BOD
No on-line instrumentation is
available to directly indicate
biological characteristics,
such as the status of the
bacterial culture in the return
sludge.
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TABLE 1. COMMON WASTEWATER TREATMENT PROCESSES (4 of 6)
Function
Operational management
Effectiveness measures
Monitored variables and use
Available
on-line
instruments
On-line
instrument needs
Remove BOD and SS by
means of biological activity
in stone or plastic media
followed by settling.
Destroy bacteria prior to
discharge of effluent
into receiving waters.
Concentrate a dilute
sludge, maintaining a
pumpable viscosity.
Maintain well distributed,
unclogged flow, proper
loading rates, effluent re-
cycling, and adequate air
circulation.
Check influent and effluent
for removal efficiencies.
Prevent toxic or high pH
materials from entering.
Trickling filter
Steady, continuous flow.
High percent BOD and SS
removals.
Maintain satisfactory
operational chlorination
equipment.
Observe safety regula-
tions.
Maintain satisfactory
chlorine residual.
Control rate of feed.
Maintain satisfactory
pumping operations.
Check sludge blanket
density.
Monitor flow rates.
Extract samples for
testing.
Control flow of dilution
water (when required).
Flow of influent and re-
cycling to retain steady-state
design range.
BOD to determine removal
efficiency.
pH as alarm indicator when
outside normal range.
Temperature for record
purposes.
Chlorination (disinfection of effluent)
Overall bacterial kill or
bacterial concentration with
minimum chlorine application.
Flow to pace chlorine
application.
Chlorine residual to determine
Sludge thickening
Maximized increase of total
solids.
BOD (or COD or TOC), SS,
turbidity to determine re-
moval efficiencies and load to
receiving waters.
Nitrogens and phosphates to
indicate nutrient load to re-
ceiving waters.
Bacterial content to determine
effectiveness of disinfection
and load to receiving waters.
Total solids of influent vs
underflow to evaluate thicken-
ing efficiency.
Percent of volatile matter in
influent and underflow to
indicate organic loading.
Flow and SS content of
dilution water to balance
influent, effluent
measurements.
Flow rate of influent, under-
flow, and overflow to measure
loading.
BOD (or COD or TOC) and SS
of overflow to indicate loading
of return to primary sedimenta-
tion tank.
Flow
pH
Temperature
BOD
Flow
Turbidity
COD
TOC
Chlorine
residual
Nitrogens
Phosphates
BOD
SSbelow500mg/l
Bacteria sensor
Chlorine demand would generate
direct determination of required
dosage.
Flow
SS (high)
COD
TOC
Sludge-
density
BOD
SS (below 500 mg/1)
Total solids
Percent volatile matter
-------
TABLE 1. COMMON WASTEWATER TREATMENT PROCESSES (5 of 6)
Function
Operational management
Effectiveness measures
Monitored variables and use
Available
on-line
instruments
On-line
instrument need1.
Decompose organic
matter in a controlled
environment devoid of
free oxygen.
Good digestion yields:
1) An innocuous
sludge that de-waters with
mechanical filtration.
2) A gas, approximately
65 percent methane, useable
for general heating purposes,
to heat sludge, or in engines
• to generate power. Excess
is burned.
3) A supernatant liquid
of low solids concentration.
Maintain:
1) Safety code
2) Temperature control
3) Continuous feed rate.
4) High solids in feed
5) Complete digester
mixing
6) Monitoring of volatile
solids loadings
7) Monitoring of digester
detention time
8) Minimal pH variation
9) Alkalinity to assure
proper buffering capacity
10) Monitoring of volatile
acids as digestion indicator
I 1) Lime feed for pH
adjustment
12) Gas burner
Sludge digestion (anaerobic)
Rate and composition of gas
formation are reliable in-
dicators of the speed and
success of digestion.
Volatile solids reduction
indicates effective digestion.
1) Raw sludge feed:
Total solids
(above minimum percent
volatile matter) to indicate
organic load.
pH for preferred range is
6.8 to 7.4.
2) Digester contents:
pH for optimal operation
range.
ORP to indicate oxidation
activity.
Alkalinity for buffering.
Volatile acids to prevent high
concentrations.
Temperature for optimal value.
Total solids to indicate loading.
Percent volatile matter to in-
dicate digestible solids.
Level indication to keep below
maximum, especially with
floating covers.
3) Gas produced:
Percent CO2 indicates
digester activity.
Rising percent CO2 indicates
process unbalance.
High methane percent in-
dicates good digester activity.
Volume indicates total gas
production.
4) Digested sludge:
pHof 6.8 to 7.4 is pre-
ferred range for digestion.
Total solids to indicate good
digestion.
Alkalinity to check proper
buffering.
Temperature for optimal
digester range.
Flow to indicate withdrawal
rate.
PH
ORP
Alkalinity
Temperature
Level
Carbon
dioxide
Methane
How
Total solids
Percent volatile mallei
Volatile acids
-------
TABLE 1. COMMON WASTEWATER TREATMENT PROCESSES (6 of 6)
Function
Operational management
Effectiveness measures
Monitored variables and use
Available
on-line
instruments
On-line
instrument needs
Reduce the moisture content
of sludge to a cake form suit-
able for disposal by inciner-
ation or landfill.
Continuous process coats
liquid sludge on a porous
medium drum through which
liquid is drawn by vacuum,
leaving the solid to form a
cake which is removed.
The drum is coated by sludge
while rotating partially sub-
merged in a vat.
During rotation the coating
is vacuum dried, then re-
moved just before that
portion submerges again
in the sludge.
Dispose of sludge at sea by
barge or pipeline.
Digested sludge is preferred
because it should be innocuous,
of low volatile content, less
likely to create nusiance con-
ditions, and more conducive
to mixing and dispersion.
Maintain:
1) Equipment
2) Proper sludge
condition
3) Operating vacuum
4) Drum submergence,
speed, and feed rate.
5) Maximum solids
concentration in feed.
6) Functioning filter
(change if necessary).
7) Sampling for per-
formance evaluation.
Maximize solids con-
centration in a pumpable
sludge:
Prevent nusiances from
odors, floating material,
bottom deposits, and
toxic matter.
Locate discharge point to
prevent beach pollution.
Control transport in pipe-
lines to utilize tides for
carrying solids away.
aiudge dewatering vacuum filtration)
Minimal moisture content of
removed filter cake.
Maximum rate of dry solids
cake produced (Ibs/sq ft/hr).
Sludge disposal (at sea)
Minimal local beach pollution
and nusiance at discharge
point.
1) Sludge feed: Flow
Total solids above Weight
minimum value.
Percent volatile matter
indicates organic load.
Flow to determine feed
rate.
Chemical demand to in-
dicate conditioning needs.
2) Cake:
Total solids should be of
high concentration.
Percent volatile solids to in-
dicate organic content.
Total weight for total cake
production rate.
3) Filtrate:
Total solids should be of
low concentration.
Percent volatile matter to in-
dicate organic content.
Flow to indicate rate of
liquid separation.
Flow (pipeline) to record Flow
disposal rate. Density
Bacterial sampling (pipe- (solids)
line) to monitor area
surrounding outfall.
Solids content for concen-
tration efficiency.
Volume loading (barge) for
records.
Solids loading (barge) for
concentration efficiency.
Total solids
Percent volatile matter
Bacteria detection
-------
Measurements are taken at a plant influent
point, at certain locations in the treatment
processes and at the plant effluent. Those
recommended for monitoring at the entrance to
the grit channel (as a plant influent point) are
shoun in Table 1 They include pH,
temperature, biochemical oxygen demand
(BOD) or chemical oxygen demand (COD) or
total organic carbon (TOQ, suspended solids
(SS), dissolved oxygen (DO), percent volatile
matter, phosphates, nitrogen.
oxidation-reduction potential (ORP) and toxic
metals and compounds. While not necessarily
involved in direct control of the grit channel,
these measurements indicate the chemical,
physical and biological nature of the flow
entering the plant. Plant efficiency is determined
by the removals of pollutants, such as BOD, SS,
phosphates, nitrogen and the toxic matter. Some
items such as pH, temperature, and ORP must
be within specified normal ranges to allow
satisfactory treatment in other plant operations
(sedimentation, digestion and the activated
sludge process). The variables are discussed in
the following paragraphs.
pH
pH indicates the acid-base condition of
sewage flow. Fresh sewage is slightly alkaline;
stale sewage is acid. pH is important for
anaerobic digestion and can be detected
automatically with a probe. '
Temperature
Temperature is important to certain
treatment processes, especially digestion, and is
automatically measured with a sensor.
BOD
BOD indicates the oxygen requirements of
the organic and chemical matter. BOD removal
is a prime function of treatment. No fully
acceptable direct BOD measuring device or
methodology exists.
COD and TOC
COD and TOC are frequently suggested as
substitutes for BOD. Data correlations are being
tested at some plants (Philadelphia, Pa.3 and
'Guarino, OF. and G.W. Carpentar. Philadelphia's Plans Toward
Instrumentation and Automation of the Wastewater Treatment
Process. 5th International Water Pollution Research
Conference San 1 ranciseo, California. July 29, 1970.
Seattle, Washington) with varying degrees ot
success. The following methods of predicting
BOD from TC and COD resulted from studies at
the Philadelphia Northeast Water Pollution
Control Plant, and any correlation, however, is
generally characteristic of the plant and its own
data and is not usually applicable to other
plants.
Method I
Method II
Simultaneous equations I Linear Regression
BOD = 0.82 COD - 0.98 TC | BOD = 43 + 0.66 COD
, -0.88TC
Deviation breakdown
Deviation breakdown
Deviation of
estimate
from actual
(percent)
Percent of
time
0-10 50
0-20 67
0-30 83
Deviation of
estimate
from actual
(percent)
Percent of
time
0-10 33
0-20 92
0-30 100
COD
COD measures the total oxygen consuming
capacity of the wastewater and can indicate the
chemical loading on a plant. While COD can be
measured quickly by automated wet chemistry4,
there is no continuous monitoring sensor.
TOC
TOC yields an indication of the organic
carbon in the wastewater. Through an automated
analytical procedure, TOC has demonstrated its
applicability in wastewater monitoring2. A TOC
determination specifically represents oxidation
of only carbonaceous materials. While inorganic
carbon may cause interference, it is removed by
acid treatment of the sample or by a separate
determination and subtraction of the inorganic
carbon from the total sample reading (TC).
SS
SS solids floating or in suspension,
determined according to "Standard Methods",
indicate the suspended solids concentration in
4Milbury, W.F., V. Stack, N.S. Zaleiko, F.L. Doll. A
Comprehensive Instrumentation System for Simultaneous
Monitoring for Multiple Chemical Parameters in a Municipal
Activated Sludge Plant. Preprints 16tn Annual Analysis
Instrumentation Symposium, ISA. Pittsburgh, Pa. May 25-27,
1970.
-------
the wastewater. A continuous monitoring sensor
is on the market (Keene) for the 500 to 5000
mg/1 range. Higher ranges can be measured via
dilution, but no continuous monitoring
instrument is available for direct measurement
of suspended solids concentrations of less than
500 mg/1.
DO
DO indicates the oxygen dissolved in the
liqwid and is essential for bacterial activity. DO
is measurable by on-line probe.
Percent Volatile Matter
This is a measure of the organic content in
suspended solids in a sampling of sewage. The
volatile content is determined by ignition of the
suspended solids with a weight loss due to
burning of the volatile matter. The inorganic
solids remain.
Phosphates
These constitute a nutrient in wastewater.
Orthophosphates and total phosphorous can be
detected by automated wet chemistry2
Nitrogen
Nitrogen indicates the nitrogenous nutrient
presence in the wastewater. Automated wet
chemistry systems can be used for total
Kjekdahl nitrogen, ammonia nitrogen, nitrites
and nitrates2. The relative quantities of
ammonia nitrogen, nitrite and nitrate
compounds indicate the degree to which the
nitrogen compounds are oxidized (nitrification).
ORP
ORP is the potential required to transfer
electrons from the oxidant to the reductant and
presents a qualitative measure of the state of
oxidation in the treatment processes. Sensors
permit continuous monitoring.
Toxic Compounds and Metals
These may be present in sewage, especially
industrial wastes. These include phenols and
aldehydes as well as hexavalent chromium,
copper, cadmium, zinc and nickel. Above certain
thresholds, they are toxic to bacteria, especially
in the digestion process and can cause a
significant reduction in treatment efficiency.
2Ibid.
CONTINUOUS MONITORING AND
CONTROL
For years analyses in wastewater treatment
have depended upon elaborate, time-consuming
chemical procedures which yield results too late
to exert direct control. While many tests
continue to be made on samples in the
laboratory, notably BOC, the tests for solids
content, bacterial analyses and others are being
replaced with the on-line sensors or automated
analytical procedures. These new continuous
monitoring devices yield rapid intelligence of
plant operations and enable- the application of
timely, corrective measures as off-normal trends
appear. The applications of the measured
variables in control loops are described chiefly to
introduce some broad approaches to the logic
and computations suitable for process computer
control. Monitoring and control of the common
wastewater treatment processes are illustrated in
Figure 4.
While many loops can be currently closed
via local analog controls, the central computer
can simplify the local equipment, accommodate
all plant closed loop controls and generate
integrated logging and reporting. The general
control sequence can be divided into the
elements of 1) Monitoring, 2) Data gathering, 3)
Status determination, 4) Data processing, 5)
Decision making, 6) Control execution, 7)
Verification, and 8) Evaluation.
ENVIRONMENTAL FACTORS
The measurement and recording of rainfall
and other meteorological data can add to the
total information delivered to the central
computer. Such information can be used to
relate environmental factors to the treatment
plant influent. A specific case is the prediction of
flow patterns in the collection system to control
routing and storage of such flows in order to
prevent hydraulic overloading of a collection
system or the treatment plant.
REGULATOR MONITORING AND CONTROL
Centralized monitoring and control of
regulators can result in significant reduction of
13
-------
o
a
o
a.
9
a
a
2
o
a
f
1
(5
I
a
••»
?
CA
CPR
CR
D
DO
OS
F
G
MLSS
Nit
OD
ORP
Phoi
SB
SO
Sit Sol
ss
T
TD
To»
Turb
V
VA
{%> VM
O
- Alkalinity
- Chlorine application
— Cake production rate
- Chlorine residual
- Depth
- Dliiolvtd
— Drum ipeed
- Flow
- Gate
- Mixed liquir cuipended solids
- Nitrogens
- Oxygen demand IBOD or TOC or
COD I
- Oxidation reduction potential
- Photphatet
- Sludge blanket
- Sludge density
- Settletble tolidt
— Suipended solids
- Temperature
- Tub depth
- Toxic mated or compoundi
- Turbidity
- Vacuum
- Volatile ac»di
- Percent volatile matter
Sampling point* and computer logging
Waitewater
Sludge
(J Monitor and computer logging
t^
ff^ Computer control
O
-------
Variable
Sampling
point
SS
OD
Phos
Nit
PH
ORP
T
Set
Sol
Do
%VM
Turb
V.A.
Alk
Tox.
Grit channel,
M1 XXXXXXXXX X
Primary
sedimentation,
M2
Aeration, M3
Trickling
filter, M4
Secondary
clarification,
M5
Plant effluent,
M6
Digester, M7
X X
X
X
X
X X X X
XXX
X X
X
PLANT EFFICIENCY MONITORING
Besides the variables monitored (see
diagram) others may be applied at key points in
the plant for determining plant efficiencies,
logging, historical records, and correlation studies.
They are not all automatic, and not all need be
measured.
X X X X X
XXX
X X
DIAGRAM NOTATIONS
Aeration: DO monitored to determine
aeration rate. MLSS monitored to
determine return sludge flow. M3
monitoring.
Chlorination: Chlorine residual monitored to
determine chlorine application.
M6 monitoring.
Clarification: Flow monitored for optimal set-
tling. Sludge blanket level
monitored to determine sludge re-
moval flow. M5 monitoring.
Digester: Temperature determines sludge
circulation for heating. Gas analy-
sis and other variables determine
sludge loading as well as liquor
and sludge withdrawals. M7 moni-
toring.
Grit channel: Flow and depth monitored to
achieve optimal grit settling. Peri-
odic (time- controlled) grit
removal. M1 monitoring.
Mechanical Cleaner mechanism actuated by
screens: differential level across screen.
Plant influent Gate position determined by flow
gate: and sewer backup depth.
Primary Compute total flow for optimal
sedimentation: settling. Sludge density dictates
sludge pumpage rate. M2 monitor-
ing.
Pumping: Approach steady state plant flow.
Regulator: Overflow determined by flow and
depth of collection system.
Thickener: Sludge density determines sludge
pumping rate. Liquid overflow re-
turn monitored.
Trickling Flow and wastewater variables
filter: monitored to determine recircula-
tion rate. M4 monitoring.
Vacuum Operation monitored by tub level,
filtration: drum speed, vacuum, incoming
sludge density and rate of cake
production.
-------
5. Map of Metro Seattle Wastewater Collection System
combined sewer overflow to receiving waters. To
achieve the objective of using available storage
within the existing combined sewers for
regulating stormwater flows, the Municipality of
Metropolitan Seattle, as indicated by the map in
Figure 5, is installing a "Computer Augmented
Treatment . and Disposal System (CATAD)".
Reduction of both the frequency and magnitude
of wastewater overflow is part of Seattle's
objective. It is further anticipated that flow to
the treatment plant will be kept under control
within specified limits. When overflows cannot
be avoided, the system will control discharges at
selected stations to minimize harmful effects on
marine life or public beaches. Monitoring within
the system includes:
1. Level of trunk lines, interceptors and,
in some cases, tide,
2. Regulator and outfall gate positions,
3. Influent level and pump speeds at
pump stations, and
4. As many as 23 separate alarm and
control contact status points.
Implementation of the system over the area
indicated in Figure 5 is based upon centralized
computer control operating in conjunction with
automatic local station controls to utilize
storage in the trunk sewers. Within the
permissible limits for back-up of wastewater, the
computer will control5:
I. The position of the regulator gate
which diverts flow from the trunk sewer into the
interceptor sewer,
2. The position of the outfall gate which
allows flow to the receiving waters, and
3. The number of operating pumps and
the pump speed to build up storage of
wastewater in the interceptor and trunk sewers
upstream of pumping stations.
5Metropolitan Engineers. Municipality of Metropolitan Seattle
Sewage Disposal Project Contract No. 68-1 for Computer
Augmented Treatment and Ditpoal System. March 1968.
16
-------
Within the collection system aside from
the hydraulic variables, such variables as DO, pH,
toxic compounds and metals, gaseous hydrogen
sulfide and combustible gas detectors can be
monitored from various points to provide useful
information for operation of the collection
system and the treatment plant, the data can
provide early warnings of future maintenance
problems and hazardous conditions within the
collection system. The data may also help in
locating sources of undesirable industrial waste
dumps or spills.
GATES
Gate control is utilized to prevent flow
surges into the plant while simultaneously
avoiding nearby residential flooding due to
excessive back-up.
Under computer control, internally stored
reference flows and depths for the sewer system
can be compared with measured flows and
depths to determine the desired gate setting and
to deliver the adjustment signal as necessary.
On-line monitoring is especially applicable
to a multiple influent gate system where two or
more gates are regulating raw sewage flow to the
plant, and the problem of simultaneous control
is more complex. With computer stored
intelligence of system capacity, programmed
schemes can control emergencies in combined
sewer collection systems (such as local storms).
The high flow from one part of the system may
be permitted to enter the plant while a low flow
component is further reduced via gate control,
utilizing the permissible back-up in the sewer.
Where the situation approaches the allowable
system capacity constraints, an alarm can signal
off-normal conditions.
MECHANICAL SCREENS
Removal of coarse material from the plant
influent causes an accumulation of debris on the
upstream side of the screen. This creates a
sufficiently large difference in water level across
the screen for automatic control to initiate the
scaper activity thereby removing the coarse
material' for disposal. The time interval between
checks should not exceed 1/2 hour.
Should the scraper malfunction, an alarm
can be triggered on the basis of no scraper
activity, excessive influent main depth, excessive
head-loss across screens, and excessive flow
reduction.
To prevent scraper breakdown, a counter
for the number of cleaning operations or an
elapsed time meter could signal the optimal
period to apply preventive maintenance to the
equipment.
GRIT CHANNEL
The effectiveness of grit channel operation
is based upon differential sedimentation. The
flow velocity through the channel is slow
enough to allow the high density grit to settle,
while the lower density organic solids remain in
the effluent. Flow and depth in the grit channel
should be monitored so that the velocity can be
kept constant despite wastewater flow
variations.
Through use of multiple, parallel channels,
continuous monitoring and control can regulate
the division of total flow among the channels.
The number in use as well as the optimal
velocity of the channels can be determined
according to total plant influent flow.
Grit removal by mechanical devices such as
scrapers, conveyors and screws should be
monitored for operation every half hour to
prevent possibility of miring under too heavy
grit deposits.
RAW WASTEWATER PUMPING
Monitoring of pump operation can
accommodate the following functions:
1. Maintaining steady state plant flow,
2. Prevention of flooding condition,
3. Pump cycling and speed changes to
accommodate flow changes and to increase
pump life,
4. Pump operation at peak efficiency,
5. Prevention of excessive power
demand factor,
6. Alarms for off-normal flow and level
conditions,
7. Alarms for pump malfunction, and
8. Alarms for bearing temperature.
With the above conditions under
continuous monitoring, a computerized
mathematical model can be developed from the
pump requirements for control of raw
wastewater pumping. Control of flow into the
17
-------
plant via variable speed pumping can minimize
hydraulic transients. Complex multiple influent
channels and pumping requirements are feasible
for computer control.
PRIMARY SEDIMENTATION
The requirements of primary settling
include a steady, optimal surface application
rate and overflow weir rate to promote solids
settling, and sludge density monitoring for
control of solids removal. Floating debris is
removed by a skimming device for discharge into
a scum sump and subsequent disp&sal.
Monitoring of the surface application or
overflow weir rate can exert control on the rate
of flow to the primary tank to maintain design
flow rates.
Sludge removal can be based upon sludge
density. Under density monitoring, a thick
sludge is preferred for efficiency of removal and
for subsequent treatment. The upper limit on
sludge density is based upon the pump
capability. Control of the mechanical collectors
also contributes to sludge density. Time intervals
between sludge removal cycles should be
adjusted to maintain aerobic conditions
throughout the sedimentation tanks.
ACTIVATED SLUDGE (AERATION TANK)
Aeration tank control involves:
1. Flow rate of influent (from primary),
2. Flow rate of return sludge,
3. Flow rate of effluent,
4. Flow of air to maintain dissolved
oxygeri (DO) levels, and
5. Sampling and measurement of
wastewater and mixed liquor characteristics to
determine operating levels.
A real time BOD reading could optimize
our mix on a minute-to-minute basis6 a quote
from one plant operator. Since there is no
acceptable continuous BOD monitoring
instrument, other properties of wastewater must
be used for control of the aeration tank mix.
One alternative is to measure the
concentration of mixed liquor suspended solids
(MLSS)7 which can be used to determine the
return sludge flow. However, the concentration
of solids in the aeration tank liquor is strongly
dependent upon the nature of the wastewater8.
This would require therefore a local adjustment
of the MLSS — return sludge relationship based
upon the operator's experience.
Aeration may be applied by diffused air
generated by blowers or mechanical agitation.
Control is expedited via the quantity of diffused
air or power to the mechanical aerators. The
loop is closed by signals from strategically
located DO probes in the tank to maintain an
optimal DO level consistent with the needs of
bacterial activity and economy (prevention of
excessive power usage). Monitoring can be
continuous with DO probes, but an outage
should not exceed a half hour.
Biological systems are sensitive to step
changes9 in the wastewater characteristics.
Sudden temperature changes can increase
effluent turbidity of the clarifier, and sudden
changes in BOD or pH can cause the sludge
blanket to deflocculate. Maintaining constant
conditions tends to stabilize the process,
however, plant influent characteristics are
subject to sudden changes in chemical nature.
Continuous monitoring and computer data
logging can alert operators to indications of
changing characteristics.
Optimal control of aeration tank activity
must be integrated with clarifier control, since
they are sequential processes with controlled
feedback.
The direct use of oxygen for aeration from
on-site oxygen generators or sale of the gas is
currently being tested and proving economically
feasible. The supply of oxygen can be
automatically controlled in direct proportion to
the BOD of the influent wastewater1 °
^Crises in the Megalopolis Demand New Electronics. Electronic
Design 1 January 4, 1968.
1 Mixed Liquor Suspended Solids Analyzer/Controller, Bulletin
No. 8200. Keene Corporation Water Pollution Control Division,
Aurora, Illinois.
8Cosens, K.W., The Operation of Sewage Treatment Plants.
Public Work Publication.
9Knowles, C.L., Improving Biological Processes. Chemical
Engineering/Desk Book Issue. April 27, 1970.
10Oxygen Can Replace Aeration. The American City June
1970.
18
-------
TRICKLING FILTER
Control of trickling filter operation is again
a matter of maintaining a steady state influent in
both flow and wastewater characteristics with
no material in the flow toxic to bacteria. Forced
air draft may be added to improve aeration in
the filter.
With little to control, good continuous
monitoring and logging of the variables which
can affect operation such as pH, temperature,
influent flow return (where used), flow and
toxicity, can help improve operations.
SECONDARY CLARIFICATION
Control in secondary clarification
comprises:
1. The maintaining of the proper sludge
blanket level,
2. The removal of as concentrated a
sludge as possible within the constraint of
pumpability,
3. The removal of settled sludge as
quickly as possible to prevent septicity, and
4. The setting of the proper fraction of
sludge removal for return to the aeration tanks
as seeding.
Since the purpose of the return sludge is to
provide thriving bacteria to meet the aeration
tank influent, the wastewater characteristics of
that influent are also important. Optimal control
of return sludge flow should be based upon
flow, temperature, pH and DO, as well as on
BOD. Of further importance is the population
and health of the bacteria. No sensor exists to
identify either the species or condition of the
bacteria.
In one article a successful application of
sludge removal on the basis of blanket level
control is described.1 A sensing head probe is
located at a preset level in the settling tank and
detects the sludge blanket level via the gap
between an infrared source and a photocell.
When the blanket reaches the specified level, the
light source is cut off, initiating the sludge
draw-off mechanism from the tank.- As the
sludge blanket drops below the desired level, the
sensing head probe halts sludge draw-off. While
sensing can be continuous, the interval between
checks should not exceed five minutes.
Nevertheless, to accommodate the factors
relating to the return sludge flow would require
a comprehensive study to determine the nature
of the relationships among the variables from
which the control model could evolve.
CHLORINATION
The chief function to control is chlorine
dosage which can be done automatically as a
combination of pacing with flow and adjusting
the rate by the chlorine residual measurement.
The residual recorders measure the free chlorine
remaining in the flow after a specified contact
period and yield a dosage verification which is
converted to a dosage adjustment for subsequent
flow. Close control is important since
insufficient feed rate will not fully destroy
bacteria, and too much is wasteful. The interval
between checks should not exceed five minutes.
A chlorine demand instrument would determine
the dosage directly.11
MONITORING OF RECEIVING WATER
Monitoring of receiving water is certainly a
part of the total wastewater treatment system.
Besides chlorine residual of the plant effluent,
such variables as DO, pH, turbidity and
conductivity are monitored in the receiving
water. Other variables are cited for measurement
in Table 4, Measurements for Wastewater
Treatment Processes. Aside from plant effluent
area, water quality stations may be located both
upstream and downstream of the plant.
In most areas, regulatory agencies collect
this information. Hence this topic is further
covered under Section 5, "Data Needs of
Regulatory Agencies."
SLUDGE THICKENING (GRAVITY)
Sludge thickening by gravity is similar to
Water and Sewage Works, op. cit.
s, A., and H.F. Hanson. Water, Water Everywhere, But-
Control Engineering. May, 1970.
19
-------
primary sedimentation where solids are
concentrated to form a sludge blanket. The chief
control operation is proper removal of the
thickened sludge. Through utilization of a
nuclear radiation or sonic device, the density of
the thickened sludge can be continuously
monitored to initiate intervals of removal by
pumping.
SLUDGE DIGESTION (ANAEROBIC)
Anaerobic digestion is a critical operation
easily subject to instability. In the process
bacteria groups work simultaneously to consume
organic matter. One group breaks down the
material to the acid stage, while another
continues the conversion to methane and carbon
dioxide. In a favorable environment, a balance is
maintained among the different groups; the
acids are consumed as they are formed, and the
pH remains in a suitable range for the methane
bacteria.
Instability is a problem because of the
generally greater prevalence of acid producing
bacteria over methane bacteria. Thus, unless a
digester has been sufficiently seeded and
properly fed, the smaller population of methane
bacteria may be unable to keep pace with the
acid forming bacteria. As the production of acid
lowers the pH, the methane bacteria become
seriously inhibited.
The variables involved in digester operation
include temperature, pH, alkalinity, carbon
dioxide, methane, volatile acids, percent volatile
matter, rate of raw solids feed, rate of digested
sludge removal and rate of supernatant liquor
removal.
Volatile acid determinations provide
valuable information concerning the anaerobic
degradation of raw organic solids as well as the
environmental conditions for methane
production.12While the value of the volatile acid
test is recognized, it is a laboratory procedure.
Gas analysis is another indicator of digester
activity and can be performed on-line. The
proportion of methane and carbon dioxide
remains fairly constant during normal operation.
However, at the onset of disestion troubles, the
carbon dioxide content of the gas increases.
Continuous gas analysis can indicate satisfactory
or off-normal operation and is useful to control
digester activity (with volatile acid testing to
confirm conditions).
Temperature is essential to satisfactory
digester activity "and should be kept around 95
deg F. Heat application can be controlled by the
digester temperature.
pH can indicate the presence of excess
volatile acids. Below a pH of 6.5, methane
producing activity becomes inhibited. An acid
neutralizing agent, such as lime, will raise the
alkalinity and bring back more favorable
conditions of pH (around 7.2) for methane
production. Thus pH or alkalinity monitoring
can control lime feed.
The addition of raw solids and sludge
removals must not disturb the desired delicate
volatile acids — methane balance.
Sludge density or solids content of the feed
should also be monitored to assure proper
loading to the digester tanks. Pumping a thin
sludge may wash out the alkalinity and upset
digester balance.
There are many factors involved in
monitoring and controlling digester activity, and
they can be synthesized into a mathematical
model. In its simplest sense, (using continuous
monitoring variables) pH can determine lime
feed; gas analysis and sludge density can
determine raw solids feed and sludge removal.
A mathematical model was developed to
study anaerobic digestion, 13 and its problems
of failure and start-up. The quantities cited as
effective in decreasing start-up time and
preventing digester failure were seed sludge, pH
and digester loading. To study the problems of
digester start-up and failure, which are transients
rather than steady state operation, necessitated
use of a dynamic (time-varying) model. In this
case a steady state model would be ineffective.
12Sawyer, C.N. and P.L. McCarty. Chemistry for Sanitary
Engineers. McGraw-Hill Book Company. 1967.
^Andrews, John F., Dynamic Model of the Anaerobic Digestion
Process. Proc. Paper 6418. Journal of the Sanitary Engineering
Division, ASCE, pp 95-116. Feb., 1969.
20
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SLUDGE DEWATERING (VACUUM
FILTRATION)
Although sludge is most frequently
dewatered in open or covered drying beds,
controls are minimal. The vacuum filtration
technique was selected for discussion because it
can save labor, is rapid and is suitable for
automated control.
In this process a thickened and conditioned
sludge coats a filter on a rotating drum through
which a vacuum extracts the liquid. Continuous
monitoring should include flow, density and
chemical conditioning of influent sludge, level of
drum submergence, effectiveness of the vacuum,
effectiveness of the filter, drum rotation and
rate of sludge cake produced. Information
brought to the computer can be logged and
checked for values outside normal ranges to
trigger alarms.
Equipment control is chiefly maintenance
of the proper level of drum submergence in the
sludge tub to keep up with removal by coating
of the rotating drum. Closed loop control
operates the sludge flow to the tub to retain the
set point level.
21
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SECTION 3
SOME ASPECTS OF HIGHER ORDER TREATMENT
INTRODUCTION
Continued refinement and higher removals
beyond secondary standards are becoming a
necessity in the search for quality effluent from
wastewater treatment plants. Thus, secondary
effluents are being subjected to further
processing involving chemical application,
settling, filtration and mechanical separation.
Those briefly considered here are described
with respect to the process, its removal
capability and requirements for monitoring and
control. They include microstraining, chemical
coagulation and settling, filtration, carbon
columns, ammonia stripping, and ion exchange.
The examples of higher order treatment
cover tertiary for increased removals of BOD
and suspended solids and advanced waste
treatment (AWT) for special removals such as
phosphorus, nitrogen or minerals. Refined
removals of suspended solids, organics,
inorganics and nutrients are covered.
MICROSTRAINING
Microstraining removes suspended solids
and the associated BOD. The microstrainer14
equipment consists of a rotating drum covered
with a very fine stainless steel woven fabric
through which wastewater is strained. As the
drum revolves, wastewater enters through one
end under gravity and strains out through the
drum wall, leaving suspended material trapped
on the inner surface. Meanwhile above and
outside the drum, jets of water strike through
the mesh and force the trapped material into a
trough just inside the drum to be carried away as
waste washings to the primary settling tank.
The microstrainer performs mechanical
separation of solids. Therefore any BOD
removals are associated with the suspended
solids. Results from different operational studies
showed varying degrees of removals:
SS: 50-89 percent of influent
BOD: 30-81 percent of influent
Supervision is minimal with an intelligent
operator checking equipment once a shift.
Continuous automatic monitoring could
detect local electric power, water level, drum
rotation, raw water influent flow, strained water
effluent flow, washwater flow, and wastewater
flow. The information could be logged
periodically with allowance for an alarm upon
detection of an off-normal value.
Continuous turbidity measurement could
monitor the improvement of clarity. Samplings
would be required for laboratory tests of BOD
and suspended solids. It is also important to
continuously monitor head loss across the
microstrainer to indicate blockage.
CHEMICAL COAGULATION
The addition of chemical coagulants such
as alum and lime to secondary effluent in a rapid
mixing basin initiates the chemical coagulation
process.15 This flash mixing is followed by
gentle agitation by rotating paddles to form
large size floe which traps solid particles
including organic matter and bacteria. The solids
are then settled in a basin and removed by
sludge scrapers, while the effluent flows over
weirs into collecting troughs. Coagulant aids
such as activated silica, clay and polyelectrolytes
are also used to enhance floe formation and
improve settling.
In a feasibility study at Dayton, Ohio,
where chemical coagulation and settling were
applied to secondary effluent,16 the following
conclusions were drawn:
1. Overall phosphate removal was 89
percent with alum, 89 percent with lime at pH
of 9.5 and up to 97 percent with lime at pH of
11+.
2. At a pH of 11 the chemical treatment
phase was capable of reducing the phosphate
14Dixon, R.M. and G.R. Evans. Experiences with Microstraining
on Trickling Filter Effluents in Texas. 48th Texas Water and
Sewage Works Associations Short School. March, 1966.
15Marks, R. H. Wastewater Treatment. A Special Report, Power.
June, 1967.
16Tossey, D.F., P.J. Fleming, and R.F. Scott. Tertiary
Treatment by Flocculation and Filtration. Journal of the
Sanitary Engineering Division, Proceedings of the American
Society of Civil Engineers, 7106 SA1. Feb., 1970.
23
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content from 28 mg/1 to 1.5 mg/1, a greater than
94 percent removal.
3. Chemical settling significantly
improved effluent quality over plain settling.
4. Overall BOD removal up to 97 percent
was achieved.
5. With alum and silica the chemical
treatment phase was capable of reducing the
BOD content from 26 mg/1 to 4 mg/1, an 84
percent removal.
6. Overall suspended solids removals
were 89 percent with indications, however, that
a portion of the suspended matter may have
been chemical coagulant.
7. With alum and silica the chemical
treatment phase was capable of reducing the
suspended solids content from 127 mg/1 to 21
mg/1, an 83 percent removal.
Clarification efficiency can be continuously
monitored via turbidity measurements, while
BOD and suspended solids tests are performed in
the laboratory. Continuous monitoring should
include analyses of the wastewater
characteristics, such as pH, temperature, and
DO.
Choice of coagulant and coagulant aid will
depend upon the results of experimentation at
the plant. With a choice selected, the dosage
must also depend upon experimentation such as
the jar test.
It is possible to relate coagulant dosages to
plant variables suitable for continuous
monitoring such as pH, temperature, turbidity
and wastewater characteristics of influent and
effluent flow. Other variables relating to
coagulation are zeta potential and streaming
current, which have possibilities for
development into continuous, on-line
instruments. Where these measurements are
feasible, an empirical relationship can be
developed suitable for implementation in a
process computer to control dosage application.
FILTRATION
Filtration is generally used on the effluent
from chemical coagulation and settling. The
filter media is usually sand and other media such
as anthracite. As the wastewater flows through
the filter bed, suspended particles are captured,
thereby effecting a reduction in turbidity.
However, through continued use of the filter,
the trapped particles build up head loss,
necessitating removal of the material by filter
washing.
In the City of Dayton study16 referred to
under Chemical Coagulation, rapid sand
filtration was used to polish the effluent of the
wastewater treatment plant. Some of the results
of filtration usage were:
1. With no prior chemical treatment,
filtration of settled trickling filter effluent
produced overall removals of 91 percent
suspended solids and 80 percent BOD during
poor trickling filter performance. When trickling
filter operation improved, the corresponding
figures for sand filtration resulted in an overall
removal rise for BOD to 95 percent.
2. Following chemical treatment it was
also stated, "It was possible to polish effluents
to a higher degree than plain settling alone".
3. When preceded by chemical
coagulation, the filtration phase of treatment
removed 30 percent to 70 percent of the applied
phosphate load.
Steady flow and gradual flow changes are
essentials for filtration control since transients
cause increases in effluent turbidity or
breakthrough. Flow and limitations on the rate
of change of flow can be monitored and
controlled via computer. In open tank filters,
continuous monitoring is also important for
tank level to prevent flooding, head-loss to
initiate backwash and level of water storage (for
backwashing). Pumps for feed and backwash
should also be monitored.
To measure filter efficiency, turbidity can
be monitored automatically, but suspended
solids (low levels) and BOD analyses must be
performed on samples in the laboratory. All
continuously monitored data can be computer
stored for logging, off-normal checking to alarm
and management reporting.
The initiation of backwash as well as the
backwash cycle can be controlled by computer.
A simple routine can examine information
acquired from the filter, and on the basis of
response to a few questions, determine whether
16Tossey. D.F., et. al., op.cit.
24
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Figure 6. Filter Backwash Monitor
to start the cycle. Information is examined on
v/hether the filter is in operation, the head loss is
too high, the washwater tank is sufficiently full,
and another filter is operating. If the proper
responses are received the filter is submitted to
the backwash cycle. The monitoring scheme is
flow-charted in Figure 6.
ACTIVATED CARBON
Filtering wastewater through granular
activated carbon results in adsorption and
absorption of biodegradable and
non-biodegradable organic matter. Turbidity and
color are also significantly reduced. Batch mixing
of carbon is commonly used in municipal water
treatment to remove tastes and odors. However
in wastewater treatment, columns of granular
activated carbon are considered more practical to
use because separation and regeneration of spent
carbon for reuse present less difficulty than the
batch process.17 The carbon is periodically
rejuvenated by draining to concentrate the slurry
and by high temperature furnace heating to
remove the adsorbed organic matter. The cycle
of use and reactivation results in a 5 percent loss
of granular carbon.15
In operations at the South Tahoe Public
Utility District "over 80 percent of all organic
material found in the secondary effluent was
removed by carbon treatment".18
At a Pomona pilot treatment plant19 ' a
carbon adsorption system was operated for over
a year with achievement of over 90 percent
17Burleson, N.K., W.W. Eckenfelder, and J.F. Malina. Tertiary
Treatment of Secondary Industrial Effluents by Activated
Carbon, 23rd Industrial Waste Conference, Purdue University.
Lafayette, Indiana.
15Marks, R.H.,op. cit.
18Slechta, A.F. and G.L. Culp. Water Reclamation Studies at the
South Tahoe Public Utility District. Journal Water Pollution
Control Federation. May, 1967.
19FWPCA U.S. Dept. of Interior. Summary Report Advanced
Waste Treatment. Publication WP-20-AWTR-19.
25
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suspended solids and 80 percent total COD
removals (77 percent dissolved COD removal).
At the same time regeneration losses averaged 10
percent.
Some absolute figures on carbon column
removals in the Pomona study included:
SS (mg/1): from 10 to less than 1,
COD (mg/1): from 47 to 9.5,
TOC(mg/l): from 13 to 2.5,
Nitrate, as N (mg/1): from 6.7 to 3.7,
Turbidity (JTU): from 10.3 to 1.6.
The sizeable nitrate reduction was
attributed to biological activity within the
carbon column.
In the Pomona operation continuous
carbon column monitoring for efficiency
included COD, TOC, ammonia and ultraviolet
absorbance (2537 Angstrom). It was found that
ultraviolet absorbance correlated well enough
with TOC to be considered as a possible control
variable for operation.
One of the most important functions of
monitoring is to determine when the carbon
adsorptive capability is spent. At the South
Tahoe installation where COD and TOC are
continuously monitored, carbon is withdrawn
for reactivation when COD reaches 20 mg/1 or
TOC reaches 7.5 mg/1.
AMMONIA REMOVAL BY AIR STRIPPING
Ammonia stripping is a technique for
removing volatile NH3- Ammonia may exist in
water as volatile NH3 or ionized ammonium,
NH4+. When the pH is raised to 10 or above in
the wastewater, the predominant form of
ammonia is the NH3- Being volatile it can be
driven off as a gas by air-contact. This is
accomplished in towers where the liquid flows
steadily downward as air is blown across.19
Experimentation to seek economically high
removals continues with variation in tower size,
configuration, internal structure, pH and flow
rate of wastewater, flow rate and direction of air,
and recycling. Removals of ammonia from 85 to
95 percent were achieved under different
conditions. Greater air circulation can boost
removal to 98 percent.18
Some advantages of nitrogen removal by
ammonia stripping include:
1. Gaseous form removal, requiring no
extra handling,
2. No requirement for nitrogen
conversion to nitrate, and
3. Increase of the pH to a range suitable
for ammonia stripping by previous lime
coagulation for phosphate and turbidity
removal.
Some of the problems which arise with
ammonia stripping include: 1) poor efficiency in
winter due to freezing of water and high
solubility of ammonia, and 2) formation of
calcium carbonate scale in the tower from the
lime application of earlier treatment phases.20
Continuous monitoring must include
wastewater flow, pH, and air flow to assure
proper conditions for the design removals.
Ammonia NH3 influent, effluent monitoring is
required to determine removal efficiency.
ION EXCHANGE
Ion exchange presents a method for
wastewater demineralization by the removal of
undesirable cations and anions. Certain resins
have the ability to exchange ions from a
solution. Under proper conditions the polluting
cations are exchanged for hydrogen and the
polluting anions for hydroxyl ions.
During treatment,21 wastewater flows
through the resin until it begins to reach its
exchange capacity. This is evidenced by
breakthrough or reappearance of the undesirable
ions in the effluent. Once the exchange bed loses
its ion removal effectiveness, treatment is halted
while the bed is backwashed to remove dirt, and
regenerated. The operational cycle then resumes.
Since ion exchange materials may be
contaminated by solids and organics in the
wastewater, some prior tertiary removals are
recommended.
19,
'ibid.
18
Slcchta, A.F. op. cit.
20FWQA., U.S. Dept. of Interior. Current Status of Advanced
Waste Treatment Processes. Advanced Waste Treatment
Research Laboratory, Division of Process Research and
Development. July, 1970.
21Eckenfelder, W.W. Industrial Water Pollution Control.
McGraw-Hill Book Company. 1966.
26
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Studies on the removal of ammonia at the
South Tahoe Public Utility District18 were very
encouraging. With an influent of 18 to 28 mg/1,
the ion exchange resin showed the capability of
treating an average of 400 bed volumes before
breakthrough reached 1 mg/1 of ammonia
nitrogen. With successive regeneration and
operation the resin lost little exchange capacity
and exhibited no significant organic fouling.
It has been suggested that demineralization
is so effective that only a portion of the total
wastewater flow need be treated.19
18Slechta, A.F.,op. cit.
19FWPCA U.S. Dept. of Interior, op. cit.
Continuous monitoring is important to
both the operational and the regeneration
cycles. Monitoring influent and effluent
presence of the undesirable ion during operation
yields both the efficiency of removal and the
onset of breakthrough. Through repeated
cycling, sufficient data may be accumulated to
prepare a curve of ion removal efficiency vs.
cumulative volume of flow as treatment
progresses toward breakthrough. The curve can
be used to determine optimum operational cycle
time.
The regeneration cycle requires clean
rinsing water and chemicals which may be
costly. Monitoring the application of
regenerative materials and duration of the cycle
can lead to optimal economic operation.
27
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SECTION 4
SURVEY OF WASTEWATER TREATMENT PLANTS
Survey forms were sent to the larger
wastewater treatment plants across the country.
Information was requested on plant processes,
the problems of plant operational management
and process control, and experience and
opinions regarding computer applications. Of
the 40 forms sent, 22 returns were received.
The survey attempted to determine:
1. Where are the most critical problems
in wastewater treatment?
2. Could continuous monitoring of the
problem processes help? and
3. Consequently, could digital computer
control solve the problem!
Among the survey forms received, nineteen
contained information on the type of
wastewater treatment distributed as follows:
No.
7
1
9
2
1 Type
primary
intermediate
secondary
tertiary
Plant-flow capacity was reported in million
gallon per day (mgd) on 21 forms, as follows:
Number
3
4
4
7
1
1
1
| Capacity (mgd)
< 10
11-50
51 - 100
101 - 200
300
343
750
In response to the question, What plant
processes require close control and could be
improved by continuous monitoring? one-half of
the returns stated All. While this answer has
merit, it does not convey any sense of priority.
Those processes selected are listed in descending
order of frequency of appearance on the returns,
as follows:
Process |
sludge digestion
activated sludge
chlorination
vacuum filtration
incineration
sludge pumping
Percent cited
26
19
18
14
13
10
The question, What is the most critical
problem in plant operational management?
received almost unanimous response on
problems with plant personnel. The complaints
in descending order were as follows:
Complaint
Percent cited
Unreliability of follow-through 44
Obtaining qualified men 19
Communications 13
Training 12
Lack of process feel; sensing changes 12
The question, What is the most critical
problem in plant process control? received
answers attributing the problems to the
following:
Causes
| Percent cited
External 17
Excess and peak flows
Industrial spills
Harmful material entering system
Variations in influent sewage
strength
Operations 60
Monitoring, but no control
Lack of timely recognition
of malfunctions
Lack of process flexibility
Lack of timely data to maintain
balance in:
digesters
aeration tanks
Handling and disposal of sludge
Safe disposal in oceans
Equipment 23
Pumping
Density meter calibrations
Incinerator operation and
maintenance
The question, Do you use a computer to
assist plant operations and management? was
positively answered by ten returns, which is
about 40 percent of those received. Only one
respondent was applying the computer to an
on-line, plant-control operation, influent
pumping. The device, used at the headworks of
the Deer Island Treatment Plant, Boston, is not a
digital computer but a pneumatic controller that
continuously monitors flow and elevations at
three he ad works: Pumping is adjusted to
maintain predetermined levels in the shafts of
the headworks in accordance with the signals
29
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received. The remaining applications "/ere
related to plant operations and business services,
as follows:
Event
No. of
Applications
Operations
Plant periodic reporting
Maintenance planning and
reporting
Chemical results
Engineering research
Services
Payroll and personnel
accounting
Cost accounting and billing
Requisitioning
8
4
2
1
1
8
5
2
1
The question, Are you contemplating use
of the computer? was answered positively by
twelve respondents, of which four are currently
using some computational facility.
No. and contemplated uses (with
overlap):
5 automation
1 accounting
10 undesignated
The question, What are the benefits and
disadvantages of computer applications in
sewage treatment? received answers which
indicated recognition of the benefits from the
following:
Benefit
• Data logging
Long term data storage
Process monitoring and alarms
Operational maintenance scheduling
Summary and exception reporting
Inventory control
Quality control analyses
Reduced labor costs
Studies and operational evaluations
Suggested disadvantages included the
following:
Disadvantages
Cost
Additional justification
Loss of personalized process fee!
Too great reliance on sensors (distrust
of instruments)
Manual inputs from laboratory testing
are too late for control
(instrumentation disadvantage)
Need for measurement standards of
input variables
A question was posed requesting comment
on any special local conditions which would
influence computer applications in wastewater
treatment. Although the responses varied, some
significant opinions appeared in more than one
of the returns, as follows:
1. Local regulatory agencies stipulate
specific and consistent plant effluent quality. To
minimize plant process fluctuations and produce
consistent effluent load, process computer
control may be necessary.
2. To upgrade the waterway system into
which the plant discharges, it is felt that
computer control offers an opportunity for
closer control of treatment processes by timely
adjustments to influent flow rates and sewage
composition. This should aid in producing a
more satisfactory overall discharge.
3. Lower hardware costs, packaged
software at reasonable prices, higher labor costs,
and regulatory agency demands for more
information all will contribute to a greater use
of computers.
4. Increasing costs of operation may lead
to automation (forcing function).
5. Cost may be prohibitive to the local
administration which sanctions expenditures.
There is no question that computer
applications for wastewater treatment processes
are receiving a great deal of attention. Among
some larger plants, off-line applications are
already commonplace, and management is giving
strong consideration to computer
implementation for continuous monitoring and
control. The survey has indicated the pressures
on plant management to upgrade effluents and
to reduce costs. The returns cited that 60
percent of the most critical problems in plant
process control were attributable to internal
plant operations involving manpower.
Improvements can be realized through higher
quality labor, training programs, and better
tools, such as continuous monitoring
instrumentation and computer controls.
30
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SECTION 5
DATA NEEDS OF REGULATORY AGENCIES
INTRODUCTION
Throughout the country state agencies
acquire data on the operation of wastewater
treatment plants, chiefly to document effluent
characteristics and to tabulate statistics. Most
regulatory agencies investigate the pollution of
streams and its causes. They foster the
promulgation of regulations to establish water
quality standards. Whenever a pollution problem
is evident, new treatment facilities or
improvement of older plants are often
prescribed by the regulatory agency. Lack of
compliance with regulatory orders may result in
rejection of local building permits, suspension of
treatment permits, adverse publicity, fines or
imprisonment. The Federal Water Quality Acts
have engendered the recent adoption of more
stringent standards by the states. They have
effectively required the upgrading of practically
all wastewater treatment plants. Inherent in the
new regulations are construction time tables,
stream and effluent standards, monitoring and a
rigorous program of enforcement.
Industrial waste discharges are subjected to
similar abatement regulations. The FWQA
estimated that over half the load on public waste
treatment facilities originates from industry.
Pending Federal guidelines for construction
grants stipulate pre-treatment of industrial
wastes before acceptance into a municipal
sewerage system and the establishment of
industrial waste surcharges.
The Federal construction grants program
further encourages the development of
comprehensive river basin-wide programs for
pollution abatement22. The percentage of
awards for grants are determined to some extent
on the degree that new treatment works as well
as Metropolitan and regional plans fit into a
basin-wide approach.
The requirements of both the Federal and
State regulatory agencies can be summarized as:
1. High water quality standards for
receiving waters, necessitating greater pollutant
removals than currently practiced.
^•Federal Register. Volume 35, Number 128. July 2,1970.
2. Strong encouragement of
regionalization approaches to implement the
new removal standards.
3. Rig i d enforcement of discharge
regulations.
4. Pre-treatment of industrial wastes
financed by the industry itself.
5. Increased surveillance with more
sophisticated instrumentation and analyses to
assure compliance.
REGULATORY AGENCY DATA
REQUIREMENTS
The prime concern of the regulatory
agencies is the effect of wastewater effluent on
the local receiving waters. Stream surveillance is
usually accomplished indirectly through the
medium of operational reports from the
regulated facilities. Report requirements may be
comprehensive or minimal in nature. A
comprehensive report may include operational
data and removal efficiencies from all phases of
plant processing as well as information on
bypasses and conditions of receiving waters. A
minimal report may address itself directly to
effluent characteristics. Information is reported
on total daily flow, raw influent and final
effluent values of pH, settlable solids, suspended
solids, BOD, and effluent data on bacterial
analysis and chlorine residual.
In many cases the criticism is that very
little is done with these reports beyond storage
for historical record purposes, especially where
state-wide reporting brings in huge quantities of
information. The data should be used to observe
trends and present information for local plant
construction.
Each state has its own reporting system,
although data requirements are somewhat
similar. It would also appear that standard
reporting formats for all plants have not been
established for any state.
Samples of reports and forms examined
include the following:
1. New York State Department of
Health Report on Operation of Sewage
Treatment Plant (Form San. 46 10M 2-10-68
31
AWBLRC LIBRARY U.S.
-------
(7D232)). The form is rigidly defined, very
comprehensive and states: "These reports
should present a representative picture of
operating conditions at the plant so that this
Department may be informed and be able to
advise and assist the operator in correcting
difficulties and maintaining the maximum
efficiency of the treatment plant at all times."
2. New Jersey State Department of
Health Monthly Operating Report of Sewage
Treatment Plant (Form WP-5 Jan 68). This is a
basic flexible form with allowance for specifying
variables to be measured and laboratory tests.
3. Renton Treatment Plant, State of
Washington, report for the state agency is
essentially the plant's own monthly report.
4. Hyperion Treatment Plant, Los
Angeles, California, report on analyses of plant
effluent and digested sludge is tailored to the
plant and is comprehensive with emphasis on
monitoring of ocean waters and beach
conditions.
5. The Pennsylvania State Department of
Health has adopted minimum information
requirements to evaluate state-wide plant
efficiencies. With few exceptions the report
requires raw and final effluent values of settlable
solids, suspended solids, BOD, and pH, as well as
daily flow, population served, relative stability,
and chlorine residual.
The new regulations of the Department of
Interior published March 31,1970 require data
for evaluating new treatment works construction
applications. The FWQA may demand detailed
data on the sources of pollution for the entire
river basin, the volume of discharge from each
source, the character of effluent, the present
treatment, the water quality effect, and so on.
These requirements may include not only
measurement of variables, but extensive analyses
as well. It appears that the geographic and
physical situation may be the determinant of
some of the requirements.
AUTOMATIC CONTROL AND
REGULATORY AGENCY DATA
Automatic control and monitoring of
wastewater treatment and water quality are fully
compatible with the data needs of regulatory
agencies. The goals of automated control include
both improved data and an improved and more
timely reporting process.
A second aspect is that the regulatory
agency report can be a direct fall-out of the
plant management information system. It can be
assumed that any data requested by the state is
already a segment of plant reporting or will have
to be incorporated into it. Under computer
implementation an internal data bank of plant
operational information is stored as the basis of
automatic control and information processing.
Where a computer program system is written to
process plant data into a management hierarchy
of periodically generated reports, the regulatory
agency report is just a part of the system.
Another consideration is the action taken
by the regulatory agency upon receipt of the
report. The assumption that a great store of
state-wide environmental control data is arriving
at a central location presents an opportunity for
statistical studies and analyses on a large scale
basis. The data can be processed into an
overview of the status of water pollution control
throughout an entire region. Plant effluent
variables can be processed into long term trend
plots for observation as well as indications for
action.
The total approach presented here for a
regulatory agency could not readily be
accomplished on a purely manual basis because
of the volume of information qcquired, and the
sophistipated statistical nature of the processing.
The increased scope of regulatory agency data
processing can be directly compatible with
computer implementation in wastewater
treatment.
The Municipality of Metropolitan Seattle
uses a basic data logger device (See Figure 7) to
monitor the Green and Duwanish Rivers. The
system automatically samples measurements
from five water quality analyzers on the rivers in
a cycled sequence, usually hourly, and prints
them on the typewriter. Some of the variables
measured are dissolved oxygen, conductivity,
pH, and turbidity. The logger concurrently
punches data onto a paper tape which is later fed
to offline computers for statistical analysis and
reporting purposes.
32
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Figure 7. Example of a Data Logger
(Water Quality Monitoring at Metropolitan
Seattle, Washington)
Another water resource management
approach being given serious consideration is the
establishment of basin-wide water quality
monitoring systems. 'The use of electronic data
processing techniques as a management tool
becomes necessary for the control of water
pollution because the magnitude of the problem
is too great to be controlled manually".23 Such
a monitoring system should be designed to
provide immediate, accurate information on the
extent, nature and movement of pollutants at
remote stations. Its objectives should include
provisions for:
1. Constant surveillance of water
pollution and its sources
2. Warning networks
3. Information on fishkills
4. Assistance in further development of
water quality standards and regulations
5. Exploitation of the water resource
6. Means for analyzing special problems
7. Aid in evaluating local water pollution
control problems
The physical system includes a network of
remote stations containing automatic sampling
and continuous water quality monitoring
equipment. Data are transmitted to a central
station which will receive and process the
signals, and may then calculate and display the
results. The fundamental premise of the system
is continuous monitoring with direct connection
to an electronic computer.24 In this manner the
system may track the hydraulic flow of a
pollutant as well as its identity. Pollution
sources can result from continuous flow, diurnal
patterns, seasonal variations and instantaneous
releases such as storm overflows or industrial
spills. Continuous monitoring may identify the
temporal nature of the flow. An alarm system
associated with continuous monitoring can
signal an operator's attention at the central site
or at some watchdog headquarters, should the
presence of a toxic substance or abnormally high
pollutant appear.
23Ellis, Eddie E. The Application of Electronic Data Processing
Techniques to Water Pollution Control. Florida Ail and Water
Pollution Control Commission.
24Schieber, John R. Continuous Monitoring. Chemical
Engineering. Deskbook Issue. April 27,1970.
33
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SECTION 6
GUIDELINES FOR COMPUTER IMPLEMENTATION
INTRODUCTION
Implementing a digital computer into an
operational plant presents a challenge to all
disciplines involved in plant management and
operation. The decision to investigate the
possibilities of automation is to embark on long
range, dedicated planning by management. What
are the considerations? First, you must know
your plant and its system, where administration
and communication begin and end, the physical
boundary, the technology operations and
control. These form the basis for the technical
justification of computerized process control.
Equally important are the economics relevant to
computer implementation. Can sufficient
sources and amounts of cost improvement be
found to pay for the automation system for
either existing plants or those in the design
stage? Can economies of design, scale and
operation be effectuated? What are the tradeoffs
of computer costs versus savings in manpower,
materials and plant space?
Improvement of product quality cannot be
discounted. Greater percentage removals
through better process control via computer can
be translated into capital costs for newly
designed or existing plants. A small guaranteed
increase in percent removal accomplished
through automation will more than justify the
expenditures for the control system.
TECHNICAL JUSTIFICATION FOR
COMPUTER CONTROL
Recent technical literature proliferates in
discussions of computer control of industrial
processes. Some criteria2 5 have been suggested
as comprising a basis for technical feasibility of
computer control. While they are considered in
context to industrial, profit-making operations,
these criteria are applicable to waste water
treatment. The -status of the process and its
suitability with regard to automated operation
are examined. Questions are asked whether it is
worth the expense, time and manpower to
•^Scrimgeour, J.H. How to Assess the Economic Justification
for Process Computer Control Canadian Controls and
Instrumentation. Canadian General Electric. April, 1968.
implement a computer. In essence, automation
should not be considered where production is
smooth, steady-state, free of disturbances,
relatively simple and operating at high
efficiency. This is not the case in wastewater
treatment. Influents are variable in flow and
quality. Process stages are not optimized, so that
greater percentage removals are possible with
proper control. Effluent improvement and
overall efficiency can be enhanced. Process
disturbances do occur and can have dire effects.
With population and industrial growth,
regulatory agency requirements are becoming
more stringent to' preserve the quality of our
environment. These increasing removals are
taxing the capability of present day plants both
in capacity and controllability. New
sophisticated controls and treatment procedures
must be implemented to accommodate the
demands of an affluent society with a high
standard of living. Computer control can offer
an upgrading of operations.
Once the basic premise of automated
process control is accepted, then the feasibility
of computer implementation can be considered.
Can the process be automated? Can the
computer communicate with the process? Are
models or systems for this process control
application available, or can they be developed?
What is the cost? What is the degree of
improvement?
Process Improvement
One benefit to be expected from computer
control is some improvement in the quality of
the throughput and management of the process.
The survey of plant management in Section 4
disclosed the need for improvement in the
following general areas:
1. Balance in the critical treatment
phases of:
a) Activated sludge,
b) Anaerobic digestion, and
c) Sludge conditioning,
2. Accurate plant data and its timely
implementation, and
35
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3. Plant operational and maintenance
personnel.
As an example of improvement in plant
management, the City of Philadelphia can be
cited for an effective, well maintained computer
program for information reduction. Implementa-
tion of the NELOG2 6 program, a management
information system for the Northeast Water
Pollution Control Plant, has:
1. Reduced the tune required for record
keeping,
2. Minimized human errors,
3. Eliminated long, cumbersome data
sheets,
4. Eliminated tedious hand calculations,
5. Permitted detection of out-of-spec
input data,
6. Permitted standard deviation
computations for all data on a daily basis,
7. Added more calculated parameters
than the manual version of the original report,
8. Reduced manual processing needs by
almost a half man-year per year for original
report,
9. Standardized procedures for data
acquisition,
10. Initiated a data bank for model
building,
11. Initiated simulation and engineering
studies, and
12. Established a basis for and major step
toward closed loop control.
The computerized version of NELOG, of
which an excerpt is shown in Figure 8, has
permitted more calculations and data checks
which were not possible with the original
manual version. The additional features are
valued at approximately three man years.
Another example of process improvement
via computer implementation is the electronic
data logger monitoring system at the Los
Angeles Hyperion Wastewater Treatment Plant.
This system monitors operation of ten electric
power generators which supply the plant and air
blowers. The engines are fueled almost entirely
(94 percent) by gas from the digester system.
The logger generates operational parameters on
26Guarino, C.F and J.V. Radziul. Data Processing in
Philadelphia. Journal Water Pollution Control Federation.
August, 1968.
two typewriters periodically with out-of-spec
values printed in red to alert the operator. There
are output and data controls such as frequency
of printing, arbitrary selection, and output
hold except for the alarm condition. Currently
there is no feedback control to engine
operation. The logger has eliminated manual
monitoring, thereby yielding a manpower
saving of three men, their overhead and backup
and "does a better job".
Disturbances in Processing
If all processes are steady-state and
function smoothly over long periods of time,
then computer control may be unnecessary. If
computer assistance is desired, off-line computer
calculations may be generally sufficient to
define the control requirements. However, in a
secondary sewage treatment plant, operations
are generally vulnerable to disturbances with
regard to:
1. The unpredictable nature of the plant
influent in both quality and quantity, and
2. The critical problem of maintaining
healthy hordes of hungry organisms for
biological treatment.
Some specific plant disturbances are cited:
1. Storms can raise the influent flow well
beyond plant capacity
2. A toxic spill entering the plant can kill
the bacteria and upset the biological activity
3. A power failure will cease pumping,
aeration, clarification, etc.
4. Digesters are frequently reported as
going sour, or failing, and it can take weeks for
the unit to return to normal.
With continuous monitoring of the influent
flow and critical plant processes, imminent
changes can be recognized, and corrective action
taken before the disturbances cause critical
conditions.
Process Complexity
Secondary treatment is complex. A
well-monitored plant requires' continuous
measurement of variables during each stage of
the treatment process. The Northeast Water
Pollution Control Plant at Philadelphia with a
design capacity of 175 mgd, lop approximately
400 measurements per day, which aid in the
operation and maintenance of this plant.
36
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3/19/70
PHILADELPHIA WATER DEPARTMENT
NORTHEAST WATER POLLUTION CONTROL PLANT
JANUARY-OECEMBEFU 1969
***OVERALL PLANT SUMMARY***
PAGE
01
02
03
. _ -
._
SEWAGE FLOW
FHL
DLL "~
TOTAL - ,
PRIMARY BY-PASS
PRIMARY TREATMENT
SECONDARY BY-PASS -
SECONDARY TREATMENT
KG
1775.91
3154.74
4930.65
0.04
4929.38
0.40
4928.98
SEWAGE ANALYSIS COM3 — RAW-- -SETTLED-
RAW FHL
PH 6.7 7.3
SETTLEABLE SOLIDS
(MG/L) 6.6 4.2
SUSPENDED SOLIDS
(MG/L) 317.5 191.6
PCT. VOLATILE 71.7 80.8
5 DAY BOD(MG/L) 231.8 146.1
PLANT EFFICIENCIES
. .... . _ -
PRIMARY TANKS (LOAD TO PLANT)
(SEPARATE INFLUENT SAMPLES)
MA (PRIMARIES IE 2)
CS (PRIMARIES 3£4)
COMB " "
PRIMARY TANKS (LOAD
TO PRIMARY TANKS)
(fQMRIMFD INFLUENT SAMPLES! -
IVrUflty-livLL/ A IT| I l_ Vs I— 1 « • -«Jr*liri«l_OJ-
MA (PRIMARIES l£2)
CS (PRIMARIES 3£4)
COMB - - - - -
SECONDARY PROCESS "
MA - - -
CS
COMB
PLANT LOAD TO FINAL EFFLUENT
MA
-- CS - .- - — -
COMB
PRIMARY TANK LOAD TO
FINAL EFFLUENT
"MA
re ..
oo - - -
COMB
. DLL MA CS
7.2 7.3 7.3
8.1 0.2 0.0
379.9 185.0 131.0
77.9 79.9 79.6
275.6 191.6 126.5
MGD
58.34
103.69
162.03
1.27
161.99
0.01
161.98
PCT
36.02
63.98
_. ..
" ~
.. - .. - _.. __
-FINAL- COMB
MA
7.3
0.0
82.9
84.8
95.9
SUS.SOL. BOD
PCT. REMOVAL PCT
28.31
52,22
44.59
-
43.46
49.61
46.68
51.43
49.14
51.25
65.99
77.49
74.18
, . , _ __ . . .....
73.74
75.35
74.76
.REMOVAL
4.64
39.50
27.20
22.02
34.43
27.92
47.51
56.35
50.44
49.85
74.48
64.24
. ._.. ..
59.96
72.08
64.54
CS FINAL
7.4 7.3
0.0 0.0
60.8 77.3
85.7 83.1
54.1 79.3
DELTA PSI
(1000 LBS
REM/KG)
0.37
0.66
0.53
0.51
0.60
0.57
0.78
0.60
0.71
0.74
1.50
1.23
1.29
1.20
1.27
Figure 8. Excerpt From the Computer Generated NELOG Summary
Report (Northeast Water Pollution Control Plant, Phila., Pa.)
37
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The degree of complexity in both
monitoring and control is too great for one
operator to respond to all plant conditions. As a
tool to tie into monitoring and control, the
computer can process data, make decisions and
generate commands well within the sensitivity of
the wastewater treatment process. Complex
systems with multiple stations for sampling and
feedback of data are well within the
state-of-the-art of process computer
applications. The lack of automated wastewater
treatment plants must be attributed to other
reasons. The control capability of computers has
been demonstrated in other bulk processing
industries such as petroleum refineries, steel
refineries and chemical plants.
Automatic Operation
The questions of process improvement,
disturbances and complexity have been
discussed. The system now must be examined
for suitability to computerized operation. One
important conversion to computer operations is
data logging and management reporting, the
improvement of data collection and recording
for better operator control.
Many analog loops exist in sewage
treatment27. Some are:
1. Air flow regulated by dissolved
oxygen measurements,
2. Return sludge proportioned back to
the aeration tanks to maintain a desired
mass-to-food ratio,
3. Pos t-chl orin a t ion regulated
automatically on the basis of flow and residual
chlorine control,
4. Variable speed wastewater pumping to
maintain more Uniform flow to the treatment
process,
5. Bar screen clearing on the basis of
increased head loss
6. Level sensor to determine rate of
pumping into primary tank,
7. Sludge density to determine when to
pump from primary tank, and
8. Pumping station control of number of
pumps stepped on or off according to flow
requirements.
The existence of local analog loops
indicates that local hardware can be made
compatible with digital computer closed loop
control.
Despite the potential of closed loop
control, the human factor is still very strongly
present in the wastewater treatment plant, and
the operator is still the most important monitor
and decisionmaker.
Computer-Process Communication
Computer control requires considerable
communication equipment to tie the computer
to the process for both monitoring and feedback
control. Internally the computer central
processor looks to core memory for its stored
data. If a routine is called to operate on
information sampled from the plant process,
then that information will have been sampled,
brought to the computer, converted to input
data, read in and stored for digital processing.
Communication equipment is reliable and
converters, remote scanners, recorders, telemetry
and telephone lines. Any variable that can be
measured can be incorporated into a centralized
control system. But, not every pertinent variable
can be automatically and continuously sensed as
cited in Section 1.
continuously sensed as cited in Section 1.
Sensors as probes or electrodes used in
wastewater treatment are subjected to a hostile
environment. They get coated and attacked by
the materials in the stream flow. Satisfactory
operation of sensors, however, can be
maintained by adequate preventive maintenance
measures2 8.
Process Models
Closing control loops or replacing analog
with digital loops requires a computer stored
process model to interpret the sampled variable
and to generate a control signal response.
27
Ryder, Robert S. Automatic Control for Smaller Water and
Wastewater Facilities. Proceedings, Ninth Sanitary Engineering
Conference. University of Illinois College of Engineering.
February 7-8. 1967.
28Puzniak, T.J., W.F. Benusa, and J.A. Condron. Mobile Water
Conservation Laboratory. Preprints, 16th Annual Analysis
Instrumentation Symposium. May 25-27, 1970
38
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The relationships among the variables in
each treatment process must be defined and
implemented into the computer software as
control algorithms. They may result from
mathematical models based upon scientific
theory of treatment, from empirical
relationships based upon regression analysis of
plant data, or from both.
The Federal Water Quality Administration
is sponsoring a study of mathematical modeling
of wastewater treatment processes29. Virtually
all phases of conventional secondary treatment
are being modeled with further work continuing
into advanced and tertiary treatment.
At some treatment plants correlation
studies are being performed to statistically
uncover relationships among variables of
sufficient significance to be suitable as control
algorithms. However, the predictive capability of
a statistical relationship for one plant may be of
little value to another plant treating different
waste. Each plant should make its own study
based upon its own data to evolve its specific
empirical relationship for a particular control.
LABOR ALLOCATION AND MAINTENANCE
One of the most critical problem areas in
wastewater treatment is the cost and quality of
labor. Competent personnel are difficult to find,
and labor costs keep rising. In a sewage plant
labor is stigmatized, and few care to work there.
Some proponents say that those that do should
be paid premium wages. The reduction of
manual labor requirements in a wastewater
treatment plant via automation can yield
economic significance and add prestige to this
industry.
Those areas which are designated as under
computer responsibility will become tied into
the system for automatic monitoring, reporting
and control. The respective changes will be
reflected throughout the system as reductions in
operational.labor requirements in such functions
as equipment adjustments, monitoring, data
logging and report preparation.
29Srnith, R., R.G. Eilers, and E.P. Hall. Executive Digital
Computer Program for Preliminary Design of Wastewater
Treatment Systems. Water Pollution Control Research Series
Publication No. WP-20-14. Cincinnati, Ohio. August, 1968.
Under automated operations, the emphasis
of labor applications will shift from equipment
operation to equipment maintenance, thus
requiring a higher quality worker.
The response from the APWA survey
(Section 4) includes direct references to the
labor and maintenance areas as sorely in need of
improvement. Specific recommendations were
noted with regard to standardized, well
documented maintenance procedures assisted by
computer stored records.
An available computer presents the
opportunity for automatic storage and
processing of the files for equipment
maintenance. Such computer stored files can
aptly supplement a plant-wide comprehensive
program of preventive maintenance.
Management can establish a new program of
maintenance records on all major equipment
with designated functions to be performed at
specified intervals for optimum operational
performance and life. Some of the operations of
computer stored preventive maintenance files
may include:
1. Daily listing of required maintenance
work,
2. Daily file updating of work
performed,
3. Reminders for work falling behind,
and
4. Special studies on maintenance cost
and equipment depreciation.
In short, computer control offers a
potential three part economic advantage in:
1. The elimination of some labor
operations,
2. The improvement of equipment
maintenance via better labor utilization, and
3. Centralized, computer processed
preventive maintenance files.
The presence of a sophisticated computer
complex and its associated controls will demand
higher calibre plant personnel to operate and
maintain the equipment. Labor standards and
grading will correspondingly have to be modified
upwards. It will be necessary to train plant
operators and maintenance personnel to work
with the computer controlled system. This
training period is usually of short duration,
relatively inexpensive and provided by the
equipment manufacturer.
39
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As the system evolves, some
reprogramming may also be necessary to
optimize computer operations. This should be
performed in-house or by the original
programmers and should be economically
feasible, yielding improved operation at reduced
costs.
SOURCES OF ECONOMIC JUSTIFICATION
FOR COMPUTER CONTROL
Implementation of computer control can
be a costly, time-consuming and critical
undertaking. Economic justification must be
sought to determine how automation costs can
be self-liquidating, if they are to be borne by the
general public. Under commercial production,
the improvement of a few percent in product
output and a more efficient use of raw materials
and power are expected to pay for the computer
complex and the systems engineering costs. In
wastewater treatment the product is not an item
to be marketed, unless direct reuse is
contemplated. The pay-off can be a social
investment in effluent quality improvement and
the associated abatement in pollution of the
receiving waters. Internal factors should be
examined for an economic return, such as labor
savings, improved maintenance, reductions in
power and material usage, and less costly control
equipment.
Many areas of plant processing can be cited
as capable of yielding economic return under
computer control. A true economic evaluation
can only be resolved by plant management and
supervisory personnel because they are familiar
with and responsible for the day-to-day
operation, the changes to be put into effect
under computer implementation and the
associated influences on operational costs.
In general, for existing plants automation
can defer expansion and the consequent capital
costs. For new plants, automation offers
increased processing capability for the same size
or allows smaller plant construction, thereby
permitting savings in land needs and capital
costs.
Higher Quality Product
The ultimate goal of any wastewater
treatment plant is to produce the highest quality
effluent achievable, consistent with its design
and good operating procedure. Where plant
removals have been significantly upgraded, the
surrounding area can realize some economic
returns from the correspondingly upgraded
quality of the local receiving waters. These may
be in the form of renewed recreational activity
such as fishing and boating, improved influent
for a water treatment plant downstream and
new lands for development. The state and local
governments could realize a sizeable income
from increased taxables of the land around the
streams.
Operational Efficiency
Computer assisted plant control should
permit plant operation at higher removal
efficiencies with less variations. Consider a
hypothetical case of a plant operating in the
percent BOD removal range of 75 to 90 with an
average of 85. If the percent BOD removals
could be raised to a range of 90 to 95 with an
average of 92.5, the BOD loading to the
receiving water would be halved3 °. Consider the
BOD reduction and stream loading per 1000
pounds BOD influent in Tables 2 and 3.
TABLE 2. LOOSE TREATMENT CONTROL
OF BOD
BOD
Percent
removal
Pounds
removed
Pounds
to stream
min. 75 750 250
max. 95 950 50
ave. 85 850 150
TABLE 3. IMPROVED TREATMENT CONTROL
(WITH COMPUTER) OF BOD
BOD
Percent
removal
Pounds
removed
Pounds
to stream
min. 90 900 100
max. 95 950 50
ave. 92.5 925 75
Although a plant may be deliberately
designed for a higher capacity than normal
design to accommodate wide variations of
influent quality and quantity, the capability of
closer automated control may deem the added
capital costs unnecessary. As cited above, it
should be possible to operate the plant closer to
its designed maximum efficiency with a lesser
degree of variation.
^Andrews, John F. Dynamic Modeling and Simulation of
Biological Processes Used for Waste Treatment. Environmental
Systems Engineering Dept., Clemson University. June 30,
1969.
40
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More efficient plant control should lead
to reduced usage of input materials such as
compressed air, chemicals and fuels and
consequent reduced in-process inventory and
warehouse space.
Improved plant control should result in
more efficient usage of electrical energy. For
instance, automatic monitoring of total power
usage can cause an alarm whenever power
consumption is approaching that peak demand
which raises the power rate for the month. At
the warning alarm, steps can be taken, if
possible, to prevent the peak from occurring
by shutting down some less essential
equipment. On the other hand, should the
peak have occurred, then during the ensuing
period of high rate charges, the computer can
generate control rules to make the best use of
the extra power charge.
Digital Versus Analog Loops
Closing control loops via the digital
computer can yield a saving through elimination
of the hardware associated with analog devices,
such as the analog-controller, its panel set-up
and alarm equipment. It has been
suggested: "the economic crossover point
between conventional analog instrumentation
(both electronic and pneumatic) and direct
digital control lies somewhere around 100
loops".3 1 Yet, cost alone is an insufficient basis
for comparison. Consideration must be allotted
to some of the benefits of digital over analog
control to which it is difficult to assign an
economic value, such as:
1. Operational improvement,
2. More easily implemented changes in
control conditions,
3. Sampling, storage and computational
operations with the control data, and
4. Remote availability of data.
It is possible with a digital, closed loop to
make subtle custom changes to the system via
changes in the program. The control strategy can
be arbitrarily modified almost at will without
requiring equipment additions or changes. The
control engineer is not constrained to working
^Forecast, Evolutionary and Revolutionary Trends in Process
Control. Chemical Engineering. January 13, 1969.
out the best trade-off with the available analog
products.
By-Products
As stated previously plant effluent is
usually not a product for sale. High quality is
sought to prevent pollution of the receiving
waters. With sufficiently high removals, it also
has been possible to find some economically
useful applications of the water other than
merely losing it to the local streams. Some
examples of such water reclamation32 from
wastewater treatment plants are cited:
1. Washing tanks and watering the plant
lawns and shrubbery,
2. Ground water recharging or control of
salt water intrusion,
3. Industrial use notably for cooling,
4. Agricultural use in irrigation and
watering of golf courses, and
5. Recreational use through a series of
treatment ponds.
Water reclamation is a growing economic
consideration in water resources management.
With increased water needs in the future the
importance of water reclaimed from municipal
return flows must begin to look more like a
resource rather than a waste.
Other by-product yields from wastewater
treatment which may b epossible sources of
ieconomic return are:
1. Digester gas to heat the plant, to heat
sludge entering the digesters and to fuel the
power generator engines,
2. Dried sludge for sale as fertilizer, and
3. Composting of sludge for use as a soil
conditioner.33
Intangible Benefits
The availability of the computer offers a
tool for engineering studies and research.
Monitoring and control data retained in
computer storage can be periodically processed
to generate new parameters for the on-line
32McGaughey, P.H. Engineering Management of Water Quality.
McGraw Hill Book Company. 1968.
33Clark, J.W. and W. Viessman. Water Supply and Pollution
Control, p. 453. International Textbook Company. Scranton,
Pa. 1965.
41
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control functions. New approaches to system
operation can be tested in simulation studies
with the computer. The day-to-day operation is
its own evaluation of effectiveness. The
computer simultaneously yields information and
avails itself for modifications of its programmed
routines where the functions show a need for
improvement.
In these days of great concern over
pollution abatement, a plant that does its job
well becomes an acclaimed asset to the
community.
Via improved, more efficient operation,
monitoring and maintenance under computer
control, equipment can be expected to last
longer, thereby allaying capital expenditures.
The revived importance and recognition of
the critical nature of pollution control has served
to attract additional capable engineers into plant
operation. These progressive engineers are
already applying experimental approaches to
treatment and are eager to investigate computer
control. This next dimension in treatment
practices will increase the challenge of a new,
sophisticated technology and further enhance
the attraction of highly capable engineers.
PRELIMINARY INFORMATION NEEDS FOR
COMPUTER CONTROL
Some assessment of the operational load on
the computer occasioned by process control as
well as desired off-line operations should be
sought.
The Plant System and Computer Responsibility
An evaluation requires a thorough
knowledge of the total plant, identified as a
system. Management must define the boundary
of the treatment system, which may go beyond
the physical plant to include the sewer network
lines or portions of them and the receiving
waters, to whatever vicinity they are affected by
the effluent. Where gaseous effluents and odors
are a possibility, the surrounding air should
come within the system boundary.
Once the treatment system and its
boundaries are defined, the overall area of
computer implementation and responsibility
within that system can then be determined.
Management must judge the extent of functional
responsibility and area of control to be
encompassed by the computer, or left to
supervisory control by humans.
System Inputs and Outputs
The boundary of computer responsibility is
delineated for inputs and outputs of material,
energy and manpower. These variables relate
directly to the objective of highest quality
effluent at minimum consumption of energy,
material and manpower within the constraints of
the wide variations in quality and quantity of
influent.
In the wastewater treatment plant, inputs
have the following influent identification: flow
(mgd), temperature, suspended solids
concentration, biochemical oxygen demand and
concentrations of other contaminants. As the
major stream flow, the influent identifies the
sewage strength to be processed, and therefore
determines the requirements on other inputs
which are utilized in the treatment process.
These minor stream flow inputs may include
power, chemicals, water, air flow and gas.
Outputs from the plant can include the effluent
to the receiving waters characterized by the
same stream flow parameters as well as chlorine
residual. Other outputs include sludge and gas
generated.
A clearly delineated definition of system
inputs and outputs under jurisdiction of the
computer helps to determine the goals necessary
to optimize operations and the functions to be
performed.
Operation Review
The approach to plant process automation
must be accompanied by an investigation of all
facets of operational management and
processing functions; All too often reporting
forms become obsolete; the report hierarchy
changes; new hand-made forms are invented, and
standardization collapses. A modernized,
up-to-date standardization and streamlining of
information processing must be established.
Each process should be investigated to
develop a logical control procedure based upon
experience and quality engineering practices.
Measurements, 'decisions, computations,
whenever involved should be entered as steps in
42
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an operational control procedure. Such activities
when documented become an empirical basis for
a standardized approach to computer control.
A complete review of maintenance
procedures should be performed to establish a
schedule of preventive maintenance functions
and a standardized log for the work.
A preliminary order must be achieved and
documented, guided by economy and efficiency
before steps can be taken toward computer
implementation. This approach leads to a
studied awareness of plant functions by
management and allows a better communication
with the automation engineers.
MATHEMATICAL MODELING
APPLICATIONS
Mathematical Modeling and Simulation
In the application of computers to control
of a physical process, the loop is eventually
closed through use of a mathematical model of
the process. The mathematical model can be
defined as a logical-mathematical representation
of a concept, system or operation. The model
operates on the measured variables and
calculates the proper values of adjustable
variables to actuate the required control. As an
abstraction from a real world situation, the
mathematical model is an attempt to simplify
the existing complexities for each of the
control computations, while simultaneously
generating data of sufficient accuracy to
represent the real system in required
applications.
The word simulation occurs in association
with mathematical modeling. There is a
distinction in definitions although the two terms
complement each other. The mathematical
model is the tool, the actual
mathematical-logical system, the program built
for a digital computer. The applications to
which the model is subjected comprise
simulation. This is particularly true in digital
computer programmed models where the test
cases operate the mathematical model under
varying simulation conditions.
Mathematical models can be used off-line
in a strictly digital simulation atmosphere to
study a physical system. The constants can be
changed to represent different versions of the
system, and the variables can be incremented to
modify the operating conditions. For example,
in a wastewater collection system some of the
constants are shape of conduit, length of
conduit, slope of conduit and friction factor. If
any of these factors are changed, the represented
physical system, i.e., the mathematical model, is
changed. On the other hand, flow supplies,
branch inputs and pump operations, are
variables. When these values are changed, and in
a real hydraulic system they change continually,
the original system remains the same, but it has
been subjected to different operating conditions.
So, in a programmed hydraulic collection
system, a given model is entered once into the
computer, while test cases or simulation
conditions on the model may be run ad
infinitum.
The value of digital simulation lies in the
flexibility of operation. A simulated system can
be put through its paces and operated under all
variations of normal and extreme conditions.
The system can be checked out and evaluated,
and never leave the computer. Many questions
can be asked during simulation. The validity of
the answers is a function of how well the model
represents the true system or prototype.
Information that can be acquired during
operation of the mathematical model includes:
1. Sensitivity and range of adjustable
variables,
2. Variables most suitable for control,
3. Interactions among variables,
beneficial or detrimental,
4. Variable combinations applicable to
control,
5. Sources of disturbances and their
corrective action,
6. Operational effectiveness and
improvement,
7. Required variables and accuracy,
8. Superfluous variables,
9. Potential for model improvement, and
10. Response to simulated emergencies.
The information acquired during the
simulation runs may be used to design new
systems or to develop models for automatic
control.
43
-------
With plant operations simulated, the
computer will allow an engineer to experiment
beyond anything that would be tolerated by
management in the real plant. Each subsystem
can be exercised through the widest variations of
its parameters to determine the best operational
range. Furthermore, the opportunity exists
through modeling to apply optimization
techniques to an objective function, such as cost
minimization, and its constraints.
Once a fully off-line digital simulation
model has been checked out, it is adaptable for
use in a process control, on-line loop. Figure 9
illustrates the relationship of the computer to a
control process on an off-line and an on-line
basis. Note that the loop can be closed without
the man when the computer is on-line.
Delay
t
Off -Line
Computer
1
a. Process Operation
Assisted by Off-Line Computer
L_»
i
Records
On-Line
Computer
\
,- •
Process
b. Process Operation
Assisted by On-Line Computer
Figure 9. Off-Line vs. On-Line Computer Control
Mathematical Modeling for Wastewater
Treatment Processes
One of the areas cited as needing further
development in computer control of wastewater
treatment is mathematical modeling. Interest is
strong, and much work is being done from at
least two directions, the empirical (often
referred to as practical) and the theoretical
approach.
The empirical approach is being taken by
many researchers in wastewater treatment
plants. In a well-monitored plant, data are
available for a great variety of variables, many of
which are directly related to process control.
With statistical analysis and the digital
computer, these can be subjected to correlation
studies. Where indications of high correlation
appear, the data can be processed by a regression
analysis, such as least squares, to generate a
functional relationship. This new function can
serve as the approximate or empirical law
governing the variations of a dependent variable
with one or more independent variables and can
therefore be considered a mathematical model
for the particular plant process. Where empirical
relations are used, they are properly referenced
as backed by experimental verification.
In this method it is also very useful to plot,
if possible on an automatic plotter tied into a
digital computer, all the original data points as
well as the generated curve. The picture
enhances the feel for the new function. In
Figure 10 are shown cases of data points plotted
along with the computer generated straight line
function. In Figure 11 two variables are plotted
versus time to demonstrate their
interdependence.
While the above empirical approach seeks a
relationship among data purely for data's sake
with no guidance except what is extracted by
the statistics, the alternate approach to
mathematical modeling seeks a theoretical
foundation to the relationship. All parameters
involved are identified and assigned dimensions.
Physical and chemical laws are cited as the basis
for formulas among the variables.
The Federal Water Quality Administration
has been sponsoring the development of
mathematical models for wastewater
treatment28 U» fit a system approach
framework. The models are for specific
treatment processes, such as a primary settler,
digester, trickling filter, etc. The models operate
on a stream vector of wastewater flow
28Smith, R., et. al. op. cit.
44
-------
M
§
i
o
CD
00
100
50
COR.COEF.
NUM. SAMP.
X AVERAGE
YAVERAGE
STD. ERR.
"T"VALUE
16
165.
56.47
0.57
51.28
2.054
0.1 0.3 0.5 0.7 0.9
PERCENT ONA
2000
i
a
u
COR.COEF
NUM. SAMP.
X AVERAGE
YAVERAGE
STD. ERR.
" VALUE
= 19
= 293.
= 399.58
= 40.60
= 140.38
= 3.310
LB BOD/CU. FT.
100.
Figure 10. Computer-Assisted Straight-Line
Regression Analyses at Metropolitan Seattle,
Washington, Basis for Development of
Empirical Laws Relating Plant Variables.
descriptive parameters, such as volume flow,
solid BOD, dissolved BOD, total suspended
solids, volatile suspended solids, etc. For a given
process a stream vector is numerically defined,
enters the treatment component, is processed
through the model equations and is converted
for exit from the treatment component
according to the calculated removals. By
associating a sequence of treatment component
models, with travel and conversion of the stream
vector tying the processes together, the unit
process models can be assembled into simulated
plants. The computer program system operated
under control of an executive routine also
computes the cost of operation and an
evaluation of performance.
Thus, an arbitrary assemblage of
wastewater treatment unit processes can be
fabricated into a plant model. The model can
then be subjected to a series of simulated
wastewater conditions with variations in flow,
contaminants and relative strength of
contaminants. Each case will generate an
evaluation with respect to cost and contaminant
removal effectiveness of the individual processes
and the system as a whole. Costing refers to
computation of capital costs, debt amortization,
plant operation and maintenance ". . . with a
fair degree of reliability".34 While the emphasis
is on design analysis in these FWQA studies,
further investigation could reveal their
applicability to plant control as well.
34Smith, Robert. Preliminary Design and Simulation of
Conventional Wastewater Renovation Systems Using the
Digital Computer. U.S. Department of Interior, FWPCA No.
WP-20-9.
45
-------
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-OCT.-10-69
-OCT.-11-69
till
••••••«•*•*«»«»•««•••***•*••*•••*•
-OCT.-12-69
-OCT.-1J-69
PLOt DESCRIPTION OF SMALLEST LARGEST SCALE
CHAR VARIABLE VALUE VALUE 1 INCH -
I LOS dOO REMOVtD/LBS SOLIDS UNDER AER. OCT. 0.00 0.06 O.OO
i_ L*S BOD APPLIED/IBS SOLIDS UNDER AER. OCT. 0.01 0.10 0.00
CS — ABBREVIATION FOR CONTACT STABILIZATION
Figure 11. Automatic Plot of Two Variables vs. Time. (Generated From a Computer Stored Data Bank
Indicates Correlation of BOD Removal vs. BOD Input of Contact Stabilization System
at Philadelphia.)
46
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SECTION 7
MEASURED STEPS TOWARD PLANT AUTOMATION
INTRODUCTION
The approach to wastewater treatment
plant automation is seen as a coordinated effort
to establish computer control of plant
processing and management information.
Careful planning and study are required to
incorporate into a functioning plant as powerful
and critical a tool as the digital computer. The
technologies required necessitate a team of plant
management associated with expertise in
wastewater treatment processes,
instrumentation, plant hardware,
communications and process computer
application.
Computer implementation can be designed
into new plants, existing plants or expanding
plants (such as primary to secondary). A
preliminary automation study can develop the
required automation steps for compatibility
with the particular situation.
Despite the lack of both treatment
knowledge and adequate instrumentation in
some areas, there are sufficient workable
applications to encourage automation. The
challenge can be met and solved once the effort
is made. A series of measured steps are presented
toward the goal of automated plant control.
Each is designed to yield new confidence in the
system while setting the stage for the next step.
These steps are briefly introduced in the
following four paragraphs.
Systemize Plant Data Handling
Allow a digital computer to process all the
manual work for plant reporting and the
retention of records for equipment maintanance.
Other areas of off-line computer application
include engineering design and analysis,
inventory control, payroll and accounting.
Improve Instrumentation and Supervisory
Control
Where possible, implement improved,
automatic monitoring instrumentation
compatible with computer inputs. Centralize
plant communications, reporting and
supervisory control at a conveniently located
supervisory panel and associated computer
console.
Convert to Automated Operation
Allow the computer to assist in
decision-making by implementing some of the
basic operator logic of supervisory control into
the computer. Initiate a study (based upon the
improved data collection) to develop
mathematical relationships among the
measurements involved in closed loop control.
Test the control methods off-line (modeled in a
computer) to prove them out.
Closed Loop Control
Program the checked-out off-line control
models into the on-line (tied into equipment)
system and retain those that continue to prove
feasible. At this stage the digital computer is
implemented into the dynamics of the plant
operational system for both closed loop control
and the processing of management information.
The following procedure is designed to
gradually evolve a beneficial computer presence
in the plant. While instrumentation is improved
and supervisory control is centralized, the
computer operations initially are non-critical,
non-control applications. They are relatively
simple, based upon current plant procedures and
involve no real time closed loops. Computerizing
plant information and maintenance records can
serve a useful purpose for plant management,
while personnel gain experience working in a
computer environment. By the time
programming is initiated for real time plant
control, the computer presence and its operation
will have become a familiar and dependable ally
of plant processing.
DESIGN OF PLANT MANAGEMENT
INFORMATION REPORTING SYSTEM
An initial approach to the wastewater
treatment plant reporting system is to review
thoroughly and update current procedures for
direct compatibility with the needs of
operational management and the requirements
of computer implementation. The revisions
47
-------
should be implemented manually as soon as
possible so that operational personnel' can gain
experience with the new requirements prior to
computer implementation. This will facilitate
verification of the automated version. Three
excerpts from automated municipal wastewater
plant reports are shown in Figure 12.
Consider, for example, a plant preparing to
expand from primary to secondary treatment.
Minimal primary reporting will be expanded to
secondary where the amount of information to
report as well as the justification for the
computer will increase considerably. An early
adjustment to computer reporting on the smaller
DAY (PLANT EFFICIENCY ><
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PITTSBURGH S EH AGE TREATMENT PLANT
ALLEGHENY COUNTY SANITARY AUTHORITY
PITTSBURGH, PA
SUMMARY OF PURIFICATION ACCOMPLISHED
SCREENINGS GRIT TANKS IN USE
REMOVED REMOVED
PRE- SEDI-
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MONTH OF MARCH 1970
SUSPENDED SOLIDS SETTLEABLE SOLIDS
RAH FINAL REMOVED RAH FINAL RE-
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TOTALS.
AVERAGES.
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SUSPENDED SOLIDS NO AVG., LBS REMOVED IS UE1GHTED.
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Figure 12. Off-line Computer Generated Excerpts from Wastewater Treatment Plant Reports
48
-------
scale of primary treatment information can serve
to familiarize personnel with computer
applications and ease the expansion into
secondary treatment reporting.
Furthermore, where plant automation is
the eventual goal, the reporting system is the
basis of operational information for studies of
control by process computer. The reports
become a comprehensive source of the entire
scope of plant operational data. With both a
store of conveniently tabulated data and the
digital computer (as the tool) available, control
guideline studies can be made without disturbing
plant operation. An essential point previously
mentioned is the necessity for each plant to base
its approach to control on information gathered
from its own operations.
DESIGN OF COMPUTERIZED EQUIPMENT
MAINTENANCE FILE
A major computer application in a
wastewater treatment plant is the design of a file
for equipment maintenance records.
To continue with the example of a plant
augmenting to secondary treatment, the
preventive maintenance (PM) file is designed at
an early stage for the primary treatment plant
with its lower equipment complement. In this
manner the small scale system can be more
easily implemented and operated before the
plant grows into secondary treatment. Once the
file is in operation, new equipment data can be
incorporated at any time.
The file itself should retain information on
equipment identification, PM schedules, PM
work monitor, and breakdown repairs. Some of
the applications can be:
1. Scheduling and monitoring PM work,
2. Reporting on PM status,
3. Reminder of backlogged maintenance,
and
4. Special studies on maintenance.
The basis for a PM file system should be
implemented manually as soon as possible to
accustom plant personnel to the concept,
thereby facilitating eventual computer operation
of the system.
COMPUTER PROGRAMS FOR REPORTING,
PM FILES, AND OTHER OFF-LINE USES
The preparation of the computer programs
is based upon the revised manual systems for
plant reporting, preventive maintenance records,
and other applications such as inventory control,
payroll and accounting. The key to a successful
computer program is a clear, well-delineated
program design document which can serve
simultaneously as:
1. The description of an operational
system procedure understood by the user and
meeting his needs and
2. A guide to the programmer as he
writes instructions for the computer.
The transition toward computerized
reporting extends through manual
implementation of the reporting revisions and
adoption of preventive maintenance
record-keeping. Operating manually with the
system will allow it to check itself out as a viable
plant information exchange and communication
procedure.
An inexpensive approach to gain
experience and know-how in these early stages is
to write the programs for a time-sharing,
desk-side computer installation, such as is shown
in Figure 13. The time-sharing approach ties the
user into a modern, large-scale digital computer
at modest rentals. Other facilities may be
available, such as a municipal finance
department or service bureau. They may be
suitable and economic, but do not give the user
immediate access to the computer.
The programs are written to implement the
revised manual reporting procedures.
Automating a functioning manual system should
allow very little change in the basic information
interfaces for users even as reports come to be
generated by the computer.
Automated information systems are a
reality and can be achieved. The success of the
system requires a coordinated team effort,
dedicated and committed to a completed
product and backed by management.35
35Sullivan, J.L. What to do Until the Computer Comes (Part I
and II). Willing Water, AWWA. Dec. 15, 1969 and Dec. 31,
1969.
49
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Figure 13. Using the Time-Sharing System
PLANT INSTRUMENTATION REVIEW AND
UPGRADING
Simultaneous with the information and
maintenance studies, a survey of all plant sensors
and instrumentation should be performed. The
emphasis should be on the replacement of
laboratory procedures with on-line probes, solid
state instrumentation and automated analytical
procedures, suitable for continuous or sampled
data monitoring and compatible with digital
computer input. It should be noted that
automation depends upon a sampled signal
available from the controlled process. Upgrading
the sensors improves plant process surveillance
and the quality of plant reporting, and puts the
plant into a more suitable status for
implementation of closed loop control.
PRELIMINARY AUTOMATION STUDY AND
COMPUTER SYSTEM SPECIFICATION
The initial phases of this plant automation
approach introduce and make use of off-line
computer work through a time-sharing system or
other off-line computer arrangements. For plant
control the process computer, which has the
capability of tying directly into the plant system
and doing on-line work, must be considered. The
process computer is the tool to improve plant
operations immediately, and more so in the
future, as familiarity with its capabilities grows,
and management acquires confidence in its
application.
Because process computer hardware must
be assembled and software programmed for its
own special use, namely, the tie-in with the
wastewater treatment plant, a study should be
made prior to implementation to define its role.
Unlike the time-sharing or other off-line digital
computer into which any problem can be fed,
the process computer is a dedicated, special
purpose tool, programmed, in this case, to serve
the improvement of wastewater treatment in its
many complex facets of plant operation. To
determine the computer functions, it is essential
to study the plant by a team of plant
management, wastewater treatment experts and
computer application consultants. The
preliminary automation study should review all
plant operations and controls, both present and
planned, to determine where the computer can
be used to enhance the work of management
and to improve treatment. The study should
define the changes in operational procedure, the
hardware and computer software requirements,
the plant monitoring and control equipment, a
schedule for implementation and budgetary
costs.
The study results in a document to assist
plant management in arriving at agreed upon
procedures for continuation into the
development of the system and specifications
for the process computer.
The computer system specifications should
establish the operational requirements of the
process computer, its equipment complement.
such as quantity of immediate access memory
(core), auxiliary memory (disks, drum or
magnetic tape), input-output and peripheral
devices. The requirements for control displays.
coordinated with plant management, can also be
established. Consideration j^hould be given to
requirements for the plant controller console.
displays and alarms.
50
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IMPLEMENTING PLANT AUTOMATION
The previous steps in the progress toward
automation are planned to include a sufficient
elapse of time for smooth operation to develop
between the off-line digital computer and daily
plant procedures. Upgraded instrumentation
should also be operating reliably. The goals to
accomplish include:
1. Development of a reliable, digital
computer presence at the plant,
2. Management recognition of the
advantages of digital computer applications in
wastewater treatment,
3. Management desire to increase
implementation of the computer beyond off-line
informauon processing into plant monitoring
and operational control, and
4. Implementation of continuous
monitoring instrumentation to allow the
broadest range of computer monitoring and
control.
A satisfactory experience with a rented
computer will help ease phasing of the process
computer into plant operations.
Implementation of plant automation will
put the computer into the heart of plant control
and operation, on-line a 24-hour day. The
approach is to initiate automated plant
operation primarily with data logging,
monitoring for alarms and information
reporting. System hardware can be checked out
in conjunction with less critical plant functions,
and prior to the initiation of closed loop
control.
As the system is checked out and
confidence grows, the more readily defined
loops for operation control which may be direct
conversions of manual control can be closed
through the computer. The more complex
control functions will continue to be studied via
statistical and correlation analyses of the
relevant collected and processed data until
satisfactory control algorithms are evolved.
The initially implemented computer system
is finally promoted to satisfactory operation of
feasible closed loops, but not without
overcoming great and frequently discouraging
obstacles which should be anticipated. At this
stage, study continues toward closing other
loops as well as seeking improvement of those
already operational. Further investigation should
be directed toward developing optimization
techniques to minimize cost, maximize
contaminant removals, stabilize plant
throughput, etc.
Seeking improvement is a never-ending
cycle.
51
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SECTION 8
LOCAL INFLUENCES ON PLANT AUTOMATION
During preparation of this report certain
situations were observed which related directly
to automation of wastewater treatment plants
and yet could not be categorized in the
preceding sections. They do relate to local
conditions however. The subjects considered are
public concern over local water pollution, water
quality as a resource and regionalization, all
affecting operation of the local wastewater
treatment plants. A discussion is also included
on the unique Whittier Narrows Water
Reclamation Plant at Los Angeles, California.
PUBLIC CONCERN
Where the local populace has become
aroused over the problems of pollution, or
where the receiving waters are heavily used for
recreation, the wastewater plants are sensitive to
criticism. If occurrences of polluted outfalls are
aired via the news media, plant management will
attempt to upgrade the effluent and prevent
overflows. Seeking approaches to improve
operations and to tighten controls, management
will consider automation.
On the other hand, where there appears to
be no problem and no local complaint about the
effluent, there is a reluctance to change
anything.
However, the state regulatory agencies and
the Federal government are exerting pressure to
upgrade effluents regardless of any apparent
local indifference. As the pollution control
agencies enforce their requirements through
both funding assistance and fines, the plants will
have to respond.
WATER QUALITY AS A RESOURCE
Concern is growing for the preservation of
local bodies of water as resources to be
protected from deterioration. Whether it is a
stream, river, estuary, lake or ocean, the
regulatory agencies are seeking to determine the
quality status of the waters. There is widespread
interest in monitoring, prediction of future
conditions and pollution control measures.
Automation techniques suitable for
continuous monitoring are available. When
associated with a careful maintenance program,
a network of water quality analyzers located at
key points can yield reliable in-stream data. The
information can be transmitted to a central
computer to be logged, analyzed and reported
with alarms for off-normal or emergency
conditions.
Once the monitoring intelligence is
converted to a set of properties of the body of
water, quality status can be determined relative
to what is desired. Where the status falls short,
management of the water resource must be
established to improve quality. As a
consequence regulatory agencies impose
restrictions upon the outfalls of municipal and
industrial water pollution control plants.
Automation and digital computers can play
an even larger role as further steps in
sophistication are implemented. These include
mathematical models of the diffusion and decay
of pollutants and the variations in water quality
variables through the body Of water.
As a direct result of comprehensive water
resources management, regulatory agencies have
begun to stipulate specific upper limit quantities
on effluent loadings to receiving waters.
Constant BOD and suspended solids loadings in
plant effluents are more difficult to maintain
than percentage removals. Hence the use of a
process control computer may be necessary to
minimize plant process fluctuations and produce
a more consistent effluent load.
REGIONAL WATER POLLUTION CONTROL
SYSTEMS
One approach to improvement of local
water resources is through a regional authority
to manage water pollution control. Because of
their geographic association in a natural drainage
area, several communities, crossing political
boundaries, can join to build a comprehensive
treatment facility and a common collection
system. The regional facility offers economic as
well as practical benefits over separate, smaller
53
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plants.36 Some of these are:
1. Scale of economy for capital and
operating budgets,
2. Reduced cost per community,
3. More available revenue to attract
higher calibre personnel,
4. Improved operation and control
through greater available skills,
5. More efficient inventory,
6. More efficient overall regional
planning for improvement and expansion, and
7. More effective compliance with
regulatory agencies.
Furthermore, although the bypassing of
raw sewage to the local receiving waters is far
more detrimental from a large centralized plant,
such a likelihood is greatly reduced. With proper
contingency provisions, the large plant can
divert flow among its units when one is out of
service. On the other hand, a small plant
generally has only one unit.
A large scale regional water pollution
control plant with quality personnel is better
equipped technically and economically to move
into higher degrees of treatment and computer
control. A large secondary treatment plant
already has the skills, while small, local plants
generally cannot afford them. Another incentive
for the adoption of basin-wide pollution control
systems is the Federal Government's promotion
of such approaches to plant improvements in its
grants program.22
Despite the advantages and Federal
encouragement of the basin-wide approach to
water pollution control, some words of caution
are suggested. The central location of a
treatment facility requires a comprehensive
collection system of very long sewer lines.
Effluents which would normally flow into local
tributaries and augment the stream flow are
carried away to be treated and disposed of at the
central plant. Thus an area-wide depletion of
stream flow is possible.
Simultaneously all the wastewater is
focused to the regional plant and creates an
Oluv*.-n. N.W.. B.C. Scalf, and J.B. Copcland Jr. Economics of
Regional Sewerage Systems. Public Works. April 1970.
—Federal Register, op. cil.
inordinately large outfall at one location. The
long lines transporting raw sewage to the central
plant could be subject to septicity and odor
problems.
It is generally felt that the advantages of
regionalization outweigh the disadvantages.
Nevertheless, each such plan should be carefully
reviewed. With so much emphasis on centralized
treatment systems, some studies should be
undertaken to assess the real value of these plans
on a geographic basis to arrive at either
modifications to the plan or recommendations
for the preferred geographic regions.
CONTROLLED PLANT INFLUENT
One of the requirements for optimum
wastewater treatment is the attainment of a
steady flow. Since raw wastewater flow is
characteristically not steady, some influent
control to allow constant flow would aid the
cause of improved treatment and automation. A
basin for raw wastewater storage prior to plant
entry could prove useful for equalizing flow,
especially during storms.
The Whittier Narrows Water Reclamation
Plant, shown in Figure 14, uses another
approach. The plant itself is superimposed on
the existing sewerage system. A steady rate of
15 mgd is pumped from a large trunk sewer
passing through the plant site. The large sewer
carries 50 mgd of principally domestic sewage.
Inlet pumps from Whittier Narrows are set for a
constant rate and "maintain a steady hydraulic
loading 24 hours a day".3 7
All sewage solids upon separation are
returned to the trunk sewer for transport
downstream to another plant. Water reclamation
is executed by channeling effluent to spreading
basins for percolation into the ground and
subsequent use in water supply. Hence the
favorable flows situation extends to steady plant
effluents as well as influent.
Primarily an activated sludge treatment
plant with well controlled steady flows, the
Whittier Narrows plant is ideally amenable to
closed loop control and makes use of a high
degree of instrumentation. Variable speed
37Parkhurst. J.D. and W.E. Garrison. Wliitlier Narrows Water
Reclamation Plant Two Years of Operation. Civil
Lnginecring. Sept.. 1964.
54
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Figure 14. Whittier Narrows Water Reclamation Plant
wastewater pumps automatically maintain flow
to the primary tank. In the final clarifier, the
sludge blanket level is continuously sensed by a
Hach falling-stream turbidity meter which
determines the rate of sludge withdrawal for
return to aeration. The blowers supplying air
operate virtually unattended. Chlorine residual is
continuously monitored, and chlorine
automatically fed to the effluent. These controls
permit minimal use of manpower, two operators
and one laboratory technician on a six day,
48-hour week.
The Whittier Narrows plant is a unique and
advantageous system of operating a wastewater
treatment plant where flow can be regulated to
meet plant requirements. Its success has resulted
in future planning in Los Angeles County for
other such plants to be superimposed on
existing sewerage networks, and can serve as a
model for other communities.
55
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SECTION 9
ADVANCED RESEARCH ON CONTROL SYSTEMS
The need for sensing for mounting
operations which are primarily organic rather
than chemical in nature was recognized
throughout the project. Information concerning
rapid BOD determination artd control of the
activated sludge process was obtained and is
presented here to give an indication of how
control may be achieved.
RAPID BOD DETERMINATION
The BOD test, which defines the
pollutional strength of wastewater, is one of the
most important variables in plant monitoring and
control. However, the industry standard for BOD
is based upon a five-day incubation period to
generate a value. This eliminates the possibility
of using BOD for real-time operational control.
There have been studies, notably by R.A. Arthur
•of Rose Polytechnic Institute and R.S. Ingols of
Georgia Institute of Technology to determine
BOD in much shorter time.
r Professor Arthur makes use of an
automatic respirometer to determine the oxygen
uptake of bacteria cultures.38 The instrument
manometically senses the reduction in partial
pressure of the oxygen as it is consumed by the
wastewater sample, converts it to an electrical
signal and continuously records the value. The
result is a graph of oxygen consumption versus
time. The immediate advantages are an
elimination of tedious data taking and curve
plotting.
A series of oxygen uptake curves generated
by the system were investigated to determine
whether they could serve to predict the five-day
BOD from a much shorter period of plotted
data.3 9 The comparison with a standard five-day
BOD dilution test of a- series of oxygen uptakes
through a four-hour period yielded an average
error of 21.3 percent. A similar seven-hour
38Arthur, R.M., An Automated BOD Respirometer, Proceed-
ing of the Nineteenth Industrial Waste Conference, May
5, 6, 7, 1964, Purdue University
39Arthur, R.M. and Hursta, W.N., Short Term BOD Using the
Automatic Respirometer, Proceedings of the 23rd Industrial
Waste Conference, May 7, 8, 9, 1968, Purdue University
period test yielded an average error of 1'5.8
percent. These errors are not considered large
when it is recalled that the five-day BOD is
reported to have an accuracy of plus'or minus 20
percent.
Further study involved the fitting of
quadratic functions to the uptake data of 48
plots. For each run the standard deviation of the
computed curve from the actual uptake curve
was computed yielding the following table of
results:
Hours of
Demand Curve
7
4
3
Percent Deviation
From Quadratic Fit
2.1
5.0
7.5
The reference concludes that the five-day
BOD can be predicted with reasonable accuracy
using four hours of uptake data from the
automatic respirometer.
Through continued research Professor
Arthur has evolved an automatic respirometer
capable of yielding an oxygen demand
measurement within fifteen to thirty minutes.
Although the reading is not the standard
BOD5 Professor Arthur claims it is suitable for
monitoring and control.
Professor Ingols performs a repetitive short
term BOD Test40 utilizing a dissolved oxygen
electrode unit. A measured sample is aerated for
a nine minute period in a chamber while the DO
reduction is recorded. The device can generate
information every ten minutes on the rate of
oxygen depletion at the selected sampling point.
The author states that the dissolved oxygen
during each period is recorded, and the records
"compared to indicate what BOD load exists."
Analytical relationships are not discussed.
The purpose of the "repetitive, short term
BOD test" is to generate information for
40Ingols, R.S., Short Term BOD, Water & Sewage Works, April
1968
57
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optimum monitoring and control of an activated
sludge plant. Automatic sampling, recording and
analysis is clearly stated as necessary to provide
the operator with frequent and sufficient current
information to promote better decisions and to
reduce periods of uneconomic or inefficient
operations.
Recent improvements in the short term
BOD detector permit a one minute detection
time, allowing for a permissable minimum period
of five minutes between readings. The oxygen
uptake is computed by an automatic subtraction
of initial DO from final DO.
CONTROL OF THE ACTIVATED SLUDGE
PROCESS
P. Brouzes of Omnium d'assainissement,
France, has installed control systems for the
activated sludge process which can control
aeration and excess sludge removal continuously
according to the pollution load.41 At least
twenty of these systems are currently
operational in France at a cost of about $20,000
to install. Practically automatic operation of the
Brouzes, P., Automated Activated Sludge Plants with
Respiratory Metabolism Control, Advances in Water Pollu-
tion Research, Proceedings of the 4th International Confer-
ence, Prague, 1969
plant is assured with controls varying in
complexity from the simple regulator to the
analog computer. The instantaneous pollution
load and specified operating conditions define
the automatic removal of excess sludge.
Maintaining a constant dissolved oxygen
concentration determines the air input.
The method avoids "empirical" control
practices of constant air input and periodic
sludge removals based on volume, or weight. The
empirical approaches lead to uneconomical
safety margins and uncontrolled variations hi the
growth rate of microorganism cultures.
Inherent in the Brouzes process is
intelligence of the growth rate of an activated
sludge culture. The author demonstrates through
a mathematical derivation (in the
aforementioned reference) that the growth rate
can be defined, instantaneously detected,
controlled and regulated.
The derivations relate the energy required
for oxygenation to the pollution load. Since the
excess sludge removal is also related to the
pollution load, the power consumed by the
blowers can be used to control the removal of
waste activated sludge.
The simplicity and advantages of economy
in the Brouzes method offer more promise than
other methods dependent upon online
measurement of organics.
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SECTION 10
RECOMMENDED RESEARCH
As a consequence of the work performed on
the study Feasibility of Computer Control of
Waste-water Treatment, recommendations for con-
tinued research have evolved. These are listed
and described. For each project, the need, ob-
jective, and time required are stated.
DEVELOPMENT OF A SUSPENDED SOLIDS
PROBE
Introduction
A probe-type instrument could be
developed to measure the concentrations and
densities of various size particles in water, using
an electrolytic (Coulter-type) counter. These
counters are commercially available,
batch-measuring instruments which size and
count particles in an aqueous medium, with a
sensitivity of one micron or less.
By developing: l)a continuous-flow
sampling probe and 2) automatic data processing
of the output pulses, the counter could be used
to give a continuous measurement of the
number of particles in any desired size range.
Furthermore the size range could be adjusted
electronically without modifying the probe.
Objectives
The objectives of the proposed program
are: 1) to evaluate several flow-through
sampling concepts which have been developed,
2) to develop the electronic logic circuitry to
pulse-height analyze the resulting pulses and
3) to categorize and enumerate them according
to particle size.
Time Estimate
The time will require a fifteen-month effort.
DEVELOPMENT OF AN INSTRUMENT FOR
RAPID DETERMINATION OF
BIOCHEMICAL OXYGEN DEMAND
Introduction
It may be possible to develop a near
real-time instrument to measure oxygen demand
which would correlate with the 5 day BOD test.
Because the rate of oxidation of a
substrate is a function of its concentration in
most enzyme reactions, controlled constant
addition of oxygen should result in maintaining
the oxygen tension of an oxidizing wastewater
sample at a level which is dependent on "the
rate of oxidation and therefore on the
concentration of oxidizable materials. The
resulting QI tension should therefore be a
measure of short term BOD.
Objectives
The objectives of the research include the
design and verification of a device employing a
controlled oxygen addition method of BOD
analysis. Design parameters must be established
for O2 diffusion rate, 02 demand rate, and ©2
tension which will determine pumping rate and
coil dimensions. A laboratory breadboard must
be designed, constructed, and tested and the
results compared to Standard Methods for BOD
analysis, using a variety of sample sources.
The correlation between the proposed
short term BOD and the standard 5 day BOD
must be evaluated to determine quantitative
relationships. These relationships will depend on
supplementary characterization of the sample by
other rapid chemical analysis means.
Time Estimate
It is anticipated that this program will
require a two-year schedule.
DEVELOPMENT OF AN INSTRUMENT FOR-
RAPID FECAL COLIFORM COUNTING
Introduction
A technique is under development at
General Electric by which the 24-48 hour
coliform test can be performed in approximately
4 hours. This is based upon metabolizing a
labeled nutrient to produce radioactively labeled
metabolic products. These products can be
conclusively identified and measured long before
measurable colonies have formed. The heart of
this method is the GE silicon avalanche diode
which can detect very low concentrations of the
radioactive metabolic effluents.
Objectives
In the proposed study, this technique is to
be extended to very short culture periods,
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providing near real-time analysis of coliform
counts. Microorganisms in a water sample are to
be concentrated on the membrane filter and
exposed to Endo broth MF enriched with
14C-lactosc. ' 4CO2evolved by lactose fermenters
will be captured by a getter and the radiation
monitored by a GE avalanche detector.
Read-out is contemplated on a digital printer or
strip clnirt recorder.
The feasibility study will correlate the level
of radiation monitored with the actual number
of viable fecal coliforms in the original sample.
Time Estimate
The feasibility study for near real-time
fecal coliform counting will require a fifteen-
month program.
An instrument to perform this analysis
might be developed by adapting the liquid-
liquid extractor of the General Electric phenol
analyzer to separate the mercury ions from
interfering cations.
ANALYSES AND PROCEDURES FOR
COMPUTER CONTROL OF WASTEWATER
TREATMENT PROCESSES
Introduction
With nationwide concern for upgrading
secondary treatment and seeking .higher quality
effluents via tertiary treatment, computer
control can help. There is a need for analyses of
wastewater treatment processes with regard to
computer control, since most current studies
and computer simulations examine optimization
of process design.
Before consideration can be given to the
computer, management must thoroughly
analyze plant operational control, process by
process. This can be done in a general way
among different plants to accommodate the
most common treatment phases as well as the
new advanced types.
One of the major considerations in
computer control of wastewater treatment is the
list of tasks to be assigned to the process control
computer. For each treatment facility to be
associated with automatic monitoring and
control, the information entering the computer,
the logic and computations relevant to reporting
and control, and the information leaving the
computer must be defined. The logic and
computation procedures are written in flow
chart form to serve two documentation
purposes:
1. A record of the process requirements
for monitoring and control identifiable to plant
management, and
2. Guidelines for computer
programming.
The document will also serve to determine
hardware and software requirements for plant
automation.
Objectives
The objectives of the proposed project are
to develop and document the computer-stored
procedures for continuous monitoring and
control of wastewater treatment. The steps are
to be prepared for existing wastewater treatment
plants encompassing processes through tertiary
and advanced treatment, and will reflect the
most advanced thinking and good practices of
engineering management.
Time Estimate
To perform an analysis and to develop flow
charts for monitoring and control of wastewater
treatment processes will require a fifteen-month
schedule.
USERS' EXPERIENCE INSTRUMENTATION
STUDY FOR WASTEWATER TREATMENT
PROCESSES
Introduction
Among the major impediments to the
achievement of full computer control of
wastewater treatment is the lack of satisfactory
sensors for continuous process monitoring.
Some sensors do not coyer a wide enough
range; others are unreliable; and for some
wastewater treatment processes, no continuous
monitoring instrumentation is available. Thus,
there is a need for a comprehensive field study
of users' experiences with installed and
operating on-line instrumentation to learn their
recommendations for improvements and to
define bases for new instrumentation. Such a
study would provide a base-line and direction
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from which manufacturers could proceed to
fulfill this need.
Background
As a result of the survey relating to
Computer Control of Wastewater Treatment
(SECTION 4) and recent contacts with managers
of treatment facilities, it has become apparent
that there are fundamental gaps in continuous
monitoring technology for wastewater
treatment. It is still impossible to react quickly
enough to variations in plant influent, and in
certain treatment processes, to minimize
undesirable effluent characteristics. It is,
therefore, equally impossible to implement
continuous computer control on those variables.
Inefficiencies and attendant uneconomical plant
operations still occur, and the quality of the
effluent may not always meet or exceed
established criteria.
While industry is continuing to improve
monitoring devices with better packaging and
solid state circuitry, plant management still finds
them requiring too much attention for
satisfactory operation.
Objectives
The objectives of this study will be to
determine, on a nationwide basis, for each
process within primary, secondary, and tertiary
wastewater treatment plants:
1. The effectiveness of installed and
operating on-line sensors,
2. The effectiveness of installed and
operating automated analysis instrumentation,
3. Present needs for improvement in
existing instrumentation, and
4. Present needs for new
instrumentation.
The effectiveness of installed and operating
instrumentation will be gauged by considering
such characteristics as its performance (e.g.,
range, accuracy, response time, etc.) with
relation to the variable being measured; costs
(•procurement, installation, operation and
maintenance), and simplicity of connection to
the process. Present and future needs must not
only be expressed in general terms, but must be
quantified into specifications which can be used
to develop the needed instrumentation.
Time Estimate
To perform the survey of users' experience
in wastewater treatment instrumentation will
require a fifteen-month schedule.
AUGMENTED INSTRUMENT SURVEY
Proposed Future Work on the Instrument
Survey
The usefulnes and value of the instrument
survey included in this document (Section 13)
can be increased by: l)expanding the
information content, 2) enlisting the aid of
equipment manufacturers, 3)building a
computerized data bank, and 4)making the
information readily available.
Expand Information Content
The introductory nature of the information
contained in the present survey necessarily limits
the amount of useful data which can be
presented. To • help a user more effectively
narrow down his search for candidate
instruments, it is recommended that the survey
be expanded. This would provide room for such
potentially useful information as: cost, power
requirements, maintenance requirements
(recalibration, duration for unattended
operation — some analyzers require reagents to
be replenished and/or their sensors to be
cleaned); optimal equipment for readout,
recording, transmission and telemetry; more
detail on ranges of measurement; information on
specific applications and limitations; and so on.
Enlist Aid of Equipment Manufacturers
To facilitate the gathering of information
and to ensure that all applicable equipment
offered by a manufacturer is included in the
survey, it is proposed that the manufacturers
themselves generate the information. This would
eliminate the need to glean information from
catalogs, and would ensure that all information
is current. By going directly to the
manufacturers, information could also be
requested which might not normally be included
in their catalogs (e.g., price, maintenance
requirements, specific applications or
limitations).
Because information of this type is subject
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to frequent changes, especially pricing, a
procedure for periodic updating would be
provided. The ultimate situation would be one
in which the manufacturers would keep the
survey alive, once it gained acceptance, by
deeming it essential to their product's visibility.
Build a Computerized Data Bank
As the survey grows in size, it would
eventually become more efficient to build a
computerized data bank to eliminate the
handling of unwieldly card decks. This would
also provide a degree of flexibility that would be
difficult to achieve with the present system.
When generating the software for the data
bank, special attention would be given to
facilitating its use by personnel without
programming skills. The software can be
designed to lead the user through all of the
operating steps in response to his initial typing
in of key request words. Provisions can be made
for detecting input errors and allowing the user
to see changes before they are finalized
(especially important when deleting data).
Make the Information Readily Available
The success of the survey will ultimately
depend upon its acceptance as a useful source of
accurate data for wastewater instrumentation
and equipment. In order to promote and
encourage its use, the survey should be
published in technical journals and trade
magazines as well as a separate technical paper.
Publishers should be informed of the potential
value that a survey of this type could have, that
is, its periodic publication as a special feature of
a journal.would not only add to the value of the
sponsoring publication, but could also boost its
circulation.
Time Estimate
To build the data bank and its associated
computer program for information on available
continuous monitoring instrumentation would
require a fifteen-month schedule to completion
COMPUTER IMPLEMENTATION FOR
MONITORING AND CONTROL OF A
WASTEWATER TREATMENT PLANT
Introduction
The study. Computer Control of
Wastewater Treatment, has evolved a
documented Guidelines for Computer
Implementation. It is recommended that they be
put to practice. There are sufficient workable
applications to encourage an approach toward
automation, despite the lack of both treatment
knowledge and adequate instrumentation in
some areas. To achieve a computer controlled
wastewater treatment plant is the ultimate goal
of this study.
The requirements of a project of this
magnitude can only be briefly outlined in this
document. The text contains two sections
suitable as a guide to computer applications.
These are:
• SECTION 6 Guidelines for
Computer Implementation
• SECTION 7 Measured Steps
Toward Plant Automation
Objective
To automate a medium sized (10 to 50
mgd) secondary wastewater treatment plant by
process computer implementation.
FEASIBILITY STUDY FOR RAPID MERCURY
ANALYSIS
Introduction
The recent public concern with mercury
pollution indicates that analysis for mercury
content, however inconvenient, will increasingly
be required. Neutron activation analysis is
beyond the resources of most laboratories. In
order to achieve the sensitivity required, atomic
absorption spectroscopy requires sample
concentration and liquid-liquid extraction.
Neither of these methods are readily adaptable
to field laboratory operations. There is a definite
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need for a low-cost method for simplifying
and/or automating the assay technique.
An instrument to perform this analysis
could be developed by adapting the liquid-liquid
extractor of the General Electric phenol
analyzer to separate the mercury ions from
interfering cations.
Objectives
The objective of this program is to
ascertain and optimize the technical details
involved in adapting the semi-automatic
liquid-liquid extraction capabilities of the
GE-developed phenol analyzer to colorimetric
mercury determination. Work could be
performed to determine the nature of the
necessary modifications, and then to obtain'the
optimal conditions, reagent concentrations,
reaction duration and procedure.
Time Estimate
This feasibility study will require a
fifteen-month effort.
DEVELOPMENT OF
SENSOR PROBE
AN ON-LINE PHENOL
Introduction
A probe-type sensor for phenol and
phenolic derivates could be developed, based on
the General Electric phenol analyzer. This
batch-type analyzer uses liquid-liquid extraction
to separate phenolics from a wide variety of
interfering substances. The extracted phenolics
are reacted by standard methods to produce a
characteristic absorption line at 457 m/z, and
their concentration is measured
spectrophotometrically. The current General
Electric analyzer will detect phenolics in water
with a sensitivity of 0.1 to 1.0 part per billion.
A probe-type sensor could be developed by
1) partitioning the phenolics with a selective
membrane rather than a liquid-liquid extractor
and 2) measuring their concentration directly by
fluorescent spectroscopy, thereby eliminating
the colorimetric reactions and
spectrophotometry.
Objectives
The objectives of the proposed research
are: 1) to evaluate the partition coefficients for
various membrane materials, some of which have
been developed for specific-ion probes, 2) to
measure the fluorescent efficiency of the
partitioned phenolics, and 3) to design a
prototype sensor for continuously measuring
phenolics in water.
Time Estimate
The feasibility evaluation and prototype
fabrication of a continuous probe-type phenol
analyzer will require an eighteen-month schedule.
DEVELOPMENT OF AN ON-LINE
OIL MONITOR INSTRUMENT
TRACE
Introduction
There is an urgent need for an instrument
to make real-time in-situ measurements of trace
oil in water, including thin films and dispersed
and/or emulsified oil. The present method is to
take a sample to a laboratory, concentrate the
oils and then measure them by solubility tests,
by chemical reactions, or by IR absorption or
spectroscopy.
A concept has been evolved for an
instrument which would continuously draw a
sample of the oil/water, extract and concentrate
the oils, and measure them by IR absorption at a
critical wavelength.
A continuously sampling, real-time
technique capable of making quantitative
measurements in the low ppm. range must
perform two functions: It must first concentrate
the oil, and second, it must 'analyze the
concentrated sample. The proposed method is
to:
1. Concentrate the oils by
countercurrent solvent extraction and
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2. Measure them by IR transmission
spectroscopy.
This lends itself to a continuous monitor which
draws a sample through an extractor into the
flow-through absorption cell. The key to this
technique is the countercurrent liquid-liquid
extractor developed at the General Electric
Company and which can partition and
concentrate the oils in real-time.
Objectives
The objectives are to investigate the
extraction efficiencies and IR transmission
windows of various solvents, provide a
laboratory feasibility demonstration of the
concept, and establish an engineering prototype
design. Test results can be presented in terms of
IR spectrometer absorption curves,
nephelometric scattering, and photographs of
the state of emulsification of the oil used in each
test.
Time Estimate
The task will require a fifteen-month effort
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SECTION 11
ACKNOWLEDGEMENTS
The American Public Works Association is deeply indebted to the following persons and their
organizations for the services they rendered to the APWA Research Foundation in carrying out this study
for the 25 local governmental jurisdictions and the Federal Water Quality Administration who
co-sponsored the study. Without their cooperation and assistance the study would not have been
possible.
Steering Committee
Joseph V. Radziul (Chairman), Chief of Research and
Development, Philadelphia Water Department
Waddy Allnut, Chief of Bureau of Business Management,
Department of Public Works, Richmond, Va.
Ben Cramer, Director, Organization and Methods Division,
Finance Department of the City of Toronto
Charles V. Gibbs, Executive Director, Municipality of
Metropolitan Seattle
Sam Hobbs, Director of Public Works, Bloomington, Minn.
E. Steve Savas, Deputy City Administrator, Office of the Mayor
of the City of New York
Harry File, Chief of Information Systems Division, U.S.
Department of Transportation
Consultants
Carmen Guarino, Deputy Commissioner, Water Pollution
Control, Philadelphia Water Department
Morris H. Klegerman, Alexander Potter Associates, Consulting
Engineers
Anton Sparr, Alexander Potter Associates, Consulting Engineers
Wastewater Treatment Plant Management
Robert Bargman, Director, City of Los Angeles, Bureau of
Sanitation
Jack Betz, Assistant Director, City of Los Angeles Bureau of
Sanitation
Walter E. Garrison, Assistant Chief Engineer, County Sanitary
District of Los Angeles County
Gabriel Lapidus, PhD, Chief, Lab Branch, Water Pollution
Control Division, Washington, D.C.
Charles V. Gibbs, Executive Director, Municipality of
Metropolitan Seattle
Carmen Guarino, Deputy Commissioner, Water Pollution
Control, Philadelphia Water Department
Regulatory Agencies
Larry Miller , Assistant Director, Division of Sanitary
Engineering, Pennsylvania Department of Health
Christian Beechwood, Regional Sanitary Engineer, Bureau of
Sanitary Engineering, State of Pennsylvania.
General Electric Staff
M.Y. Goodman, Computer Applications Engineer, Re-entry and
Environmental Systems Division
F.W. Morris, Water Resources Analyst, Re-entry and
Environmental Systems Division
E.O. Potthoff, Applications Engineer, Industrial Sales Division
W.E. Sauer, PhD, Environmental Sciences Laboratory, Re-entry
and Environmental Systems Division
65
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SECTION 12
GLOSSARY
ACTIVATED CARBON. Carbon particles usually
obtained by carbonization of cellulosic material in
the absence of air and possesing a high absorptive
capacity.
ABSORPTION. The taking up or into a solid, gas,
liquid or dissolved material.
ADSORPTION. The adherence of a gas, liquid, or
dissolved material on the surface of a solid.
AEROBIC. Requiring the presence of free elemental
oxygen.
ALGORITHM. A fixed step-by-step procedure for
accomplishing a given result.
ANAEROBIC. Requiring the absence of air or free
elemental oxygen.
AN I ON. A negatively charged ion in an electrolyte
solution, attracted to the anode under the influence
of electric potential.
BREAKTHROUGH. The point where an ion
exchange column begins to lose its ion removal
capability.
BUFFERING. The use of certain combinations of
chemicals to stabilize the pH values of solutions.
CATION. The ion in an electrolyte which carries the
positive charge and which migrates toward the
cathode under the influence of a potential difference.
CHLORINE DEMAND. The difference between the
amount of chlorine added to water or wastewater and
the amount of residual chlorine remaining at the end
of a specified contact period. The demand for any
given water varies with the amount of chlorine
applied, time of contact, and temperature.
CLARIFICATION. Any process or combination of
processes the primary purpose of which is to reduce
the concentration of suspended matter in a liquid.
CLARIFIER. A unit the primary purpose of which is
to secure clarification. Usually applied to
sedimentation tanks or basins.
COMPUTER MEMORY. A device for storing
information and instructions in a digital computer.
Examples of memory include magnetic core, disks,
drums, and tape.
DIGESTERS. Tanks in which sludge is placed to
permit digestion to occur. Also called sludge digestion
tank.
EMPIRICAL FORMULA. A formula developed to
describe a relationship on the basis of experience and
data gathered from actual operations.
FEEDBACK (CONTROL). An automatic furnishing
of data concerning the output of a machine to an
automatic control device so that errors may be
corrected.
FILTRATE. The liquid which has passed through a
filter.
FLOW CHART. An orderly representation of a
process. A graphic illustration in which activities are
defined and their interrelationships are illustrated.
INFILTRATION. The discharge of groundwater into
sewers, through defects in pipelines, joints, manholes
or other sewer structures.
INFLOW. The discharge of any kind of water into
sewer lines from such sources as roof leaders, cellar
and yard area drains, foundation drains, commercial
and industrial so-called clean water discharges, drain
from springs and swampy areas, etc.
INPUT-OUTPUT DEVICES. Devices for entering and
extracting information from-computers: card readers,
card punch, typers, printers, cathode ray tubes, etc.
INTERMEDIATE TREATMENT. The removal of a
high percentage of suspended solids and a substantial
percentage of coloidal matter, but little dissolved
matter.
KJELDAHL. The Kjeldahl method employs sulfuric
acid as the oxidizing agent to free nitrogen as
ammonia .from organic compounds in the standard
nitrogen testing procedure.
MATHEMATICAL MODEL. The mathematical
representation of a process or operation for which
solutions can be obtained for a set of input variables.
MIXED LIQUOR. A mixture of activated sludge and
organic matter undergoing activated sludge treatment
in the aeration tank.
MODELING. A simulation technique for the analysis
of operations and systems.
NITRIFACATION. The conversion of nitrogenous
matter into nitrates by bacteria.
OFF-LINE COMPUTER. A free standing digital
computer not tied into an industrial process.
ON-LINE. Tied into a process and operating
continuously.
ON-LINE COMPUTER. A computer which is
integrated into the dynamics of a process; a process
control computer.
OUTFALL. 1) The point, location, or structure
where wastewater or drainage discharges from a
sewer, drain, or other conduit. 2) The conduit leading
to the ultimate disposal area.
PARSHALL FLUME. A calibrated device developed
by Parshall for measuring the flow of liquid in an
open circuit.
PATHOGENIC. A description of organisms which
may cause disease in the host organism by their
parasitic growth.
PERCOLATION. The movement or flow of water
through the interstices or the pores of a soil or other
porous medium.
67
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PERIPHERAL DEVICES. Input/output equipment
used to make hard copies or to read in data from hard
copies (typer, punch, tape reader, Line printer,
cathode ray tube, plotter).
PRIMARY SETTLER. The first settling tank for the
removal of settleable solids through which wastewater
is passed in a treatment works.
PROCESS COMPUTER. A digital computer having
direct communication capability with an industrial
process for data sampling and equipment control.
REGENERATION. The process of restoring an-ion
exchange material to the state employed for
adsorption (in ion exchange).
REGRESSION ANALYSIS. The analysis of the
association among several variables.
SCANNER, REMOTE. A device which will, upon
command, connect a specified sensor to measuring
equipment and cause the generation of a signal
suitable for input to a computer.
SIMULATION. Operating a logical-mathematical
representation of a concept, system or operation.
SLUDGE. 1) The accumulated solids separated from
liquids, such as water or wastewater, during
processing, or deposits on bottoms of streams or
other bodies of water. 2) The precipitate resulting
from chemical treatment, coagulation, or
sedimentation of water or wastewater.
SLUDGE BLANKET. Accumulation of sludge
hydrodynamically suspended within an enclosed
body of water or wastewater.
STEADY-STATE PROCESS. A process which has
reached a relatively stable operation, no longer
changing with time.
STREAM VECTOR. An identification of the
variables comprising wastewater characteristics which
are changed by treatment processes.
STREAMING POTENTIAL - The difference of elec-
trical potential between a porous diaphram, or other
permeable solid, and a liquid which is passing through
it. This arises from an imposed movement of solvent
through capilaries.
SUBSTRATE. 1) The substances used by organisms
in liquid suspension. 2) The liquor in which activated
sludge or other matter is kept in suspension.
SUPERNATANT. The liquid standing above a
sediment or precipitate.
SUSPENDED SOLIDS. 1) Solids that either float on
the surface of, or are in suspension in, water,
wastewater, or other liquids, and which are largely
removable by laboratory filtering. 2) The quantity of
material removed from wastewater in a laboratory
test, as prescribed in Standard Methods for the
Examination of Water and Wastewater and referred to
as nonfilterable residue.
TELEMETRY. The system of measuring, transmitting
and receiving apparatus for indicating, recording or
integrating at a distance, by electrical translating
means, the value of a quantity.
TIME-SHARING. The simultaneous use of a
computer system from multiple terminals; provides
economics through cost-sharing.
TOTAL SOLIDS. The sum of dissolved and
undissolved constituents in water, or wastewater,
usually stated in milligrams per liter.
TOXIC. Usually referred to in this document as fatal
to the aerobic and anaerobic organisms.
TRICKLING FILTER. A filter consisting of an
artificial bed of coarse material, such as broken stone,
clinkers, slate, slats, brush, or plastic materials, over
which wastewater is distributed or applied in drops,
films, or spray from troughs, drippers, moving
distributors, or fixed nozzles, and through which it-
trickles to the underdrains, giving opportunity for the
formation of zoogleal slimes which clarify and
oxidize the wastewater.
VARIABLE. A quantity to which an unlimited
number of values can be assigned in an investigation.
ZETA POTENTIAL. An electrical charge at the
boundary between particles and the suspending
medium that is related to repelling forces between
floccules.
68
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SECTION 13
REFERENCES
1. Guarino, C.F. and G.W. Carpentar. Philadelphia's Plans
Toward Instrumentation and Automation of the
Waste-water Treatment Process. 5th International Water
Pollution Research Conference. San Francisco, California.
July 29,1970.
2. Milbury, W.F., V. Stack, N.S. Zaleiko, F.L. Doll. A
Comprehensive Instrumentation System for Simultaneous
Monitoring for Multiple Chemical Parameters in a Municipal
Activated Sludge Plant. Preprints 16th Annual Analysis
Instrumentation Symposium, ISA. Pittsburgh, Pa. May
25-27,1970.
3. Activated Sludge Process Automated. Water and Sewage
Works. May, 1970.
4. Stack, V.T., Continuous Monitoring Devices - Treatment
Plants. Proceedings Ninth Engineering Conference,
Instrumentation, Control and Automation for Water
Supply and Wastewater Treatment Systems. University of
Illinois, College of Engineering. 1967.
5. Metropolitan EngineeisMunicipality of Metropolitan
Seattle Sewage Disposal Project Contract No. 68-1 for
Computer Augmented Treatment and Disposal System.
March 1968.
6. Crises in the Megalopolis Demand New Electronics.
Electronic Design 1. January 4, 1968.
7. Mixed Liquor Suspended Solids Analyzer/Controller,
Bulletin No. 8200. Keene Corporation Water Pollution
Control Division, Aurora, Illinois.
8. Cosens, K.W., The Operation of Sewage Treatment Plants.
Public Works Publication.
9. Knowles, C.L., Improving Biological Processes. Chemical
Engineering/Desk Book Issue. April 27, 1970.
10. Oxygen Can Replace Aeration. The American City. June
1970.
11- Hess, A., and H.F. Hanson."Watcr.Water Everywhere, But" -
Control KnginceringMny 1970.
12. Sawyer, C.N. and P.L. MeCarty. Chemistry for Sanitary
Engineers. McGraw-Hill Book Company. 1967.
13. Andrews, John !•"., Dynamic Model "f the Anaerobic
Digestion Process. Proc. Paper 6418 Journal of the
Sanitary Engineering Division, ASCE, pp 95-116. Feb.,
1969.
14. Di\on, R.M. and G.R. Evans. Experiences with
Micros!raining on Trickling Filter Effluents in Texas. 48th
Texas Water and Sewage Works Associations Short School.
March, 1966.
15. Marks, R.H., Wastewater Treatment. A special Report,
Power. June, 1967.
16. Tossey, D.F., P.J. Fleming, and R.F. Scott. Tertiary
Treatment by Flocculation and Filtration. Journal of the
Sanitary Engineering Division, Proceedings of the American
Society of Civil Engineers, 7106 SAL Feb. 1970.
17. Burleson, N.K., W.W. Eckenfelder, and J.F. Malina. Tertiary
Treatment of Secondary Industrial Effluents by Activated
Carbon. 23rd Industrial Waste Conference, Purdue
University. Lafayette, Indiana.
18. Slechta, A.F. and G.L. Culp. Water Reclamation Studies at
the South Tahoe Public Utility District. Journal Water
Pollution Control Federation. May, 1967.
19. FWPCA U.S. Dept. of Interior. Summary Report Advanced
Waste Treatment. Publication WP-20-AWTR-19.
20. FWQA., U.S. Dept. of Interior. Current Status of Advanced
Waste Treatment Processes. Advanced Waste Treatment
Research Laboratory, Division of Process Research and
Development. July, 1970.
21. Eckenfelder, W.W. Industrial Water Pollution Control.
McGraw-Hill Book Company. 1966.
22. Federal Register. Volume 35, Number 128. July 2, 1970.
23. Ellis, Eddie E. The Application of Electronic Data
Processing Techniques to Water Pollution Control. Florida
Air and Water Pollution Control Commission.
24. Schieber, John R. Continuous Monitoring, Chemical
Engineering. Deskbook Issue. April 27, 1970.
25. Scrimgeour, J.H. How to Assess the Economic Justification
for Process Computer Control. Canadian Controls and
Instrumentation. Canadian General Electric. April, 1968.
26. Guarino, C.F. and J.V. Radziul. Data Processing in
Philadelphia. Journal Water Pollution Control Federation.
August, 1968.
27. Ryder, Robert S. Automatic Control for Smaller Water and
Wastewater Facilities. Proceedings, Ninth Sanitary
Engineering Conference. University of Illinois College of
Engineering. F'ebruary 7-8, 1967.
28. Puzniak, T.J., W.F. Benusa, and J.A. Condron. Mobile
Water Conservation Laboratory. Preprints, 16th Annual
Analysis Instrumentation Symposium. May 25-27, 1970.
29. Smith, R., R.G. Eilcrs, and E.P. Hall. Executive Digital
Computer Program for Preliminary Design of Wastewater
Treatment Systems. Water Pollution Control Research
Scries Publication No. WP-20-14. Cincinnati, Ohio. August,
1968.
30. Andrews, John F. Dynamic Modeling and Simulation of
Biological Processes Used for Waste Treatment.
Environmental Systems Engineering Dept., Clemson
University. June 30, 1969.
69
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31. Forecast, Evolutionary and Revolutionary Trends in
Process Control. Chemical Engineering. January 13, 1969.
32. McGaughey, P.H. Engineering Management of Water
Quality. McGraw Hill Book Company. 1968.
33. Clark, J.W. and W. Viessman. Water Supply and Pollution
Control, p. 453. International Textbook Company.
Scranton.Pa. 1965.
34. Smith, Robert. Preliminary Design and Simulation of
Conventional Wastewater Renovation Systems Using the
Digital Computer. U.S. Department of Interior, FWPCA
No. WP-20-9.
35. Sullivan, J.L. What to do Until the Computer Comes (Part I
and U). Willing Water, AWWA. Dec. 15, 1969 and Dec. 31,
1969.
36. Classen, N.W., B.C. Scalf, and J.B. Copeland, Jr. Economics
of Regional Sewerage Systems. Public Works. April 1970.
37 Parkhurst, J.D. and W.E. Garrison. Whit tier Narrows Water
Reclamation Plant - Two Years of Operation. Civil
Engineering. Sept., 1964.
38.
39.
40.
41.
Arthur, R.M., An Automated BOD Respirometer, Proceed-
ing of the Nineteenth Industrial Waste Conference, Mav
5, 6S 7, 1964, Purdue University
Arthur, R.M. and Hursta, W.N.,.Short Term BOD Using the
Automatic Respirometer, Proceedings of the 23rd Industrial
Waste Conference, May 7, 8, 9, 1968, Purdue University
Ingols, R.S., Short Term BOD, Water & Sewage Works, April
1968
Brouzes, P., Automated Activated Sludge Plants with Res-
piratory Metabolism Control, Advances in Water Pollution
Research, Proceedings of the 4th INternational Conference,
Prague, 1969
70-
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SECTION 14 - APPENDIX
CONTINUOUS MONITORING INSTRUMENTATION SURVEY
METHOD
The survey has compiled a list of automatic
monitoring instrumentation on the market for
continuous monitoring of wastewater treatment
processes and receiving waters.
The survey 'tabulated: an instrument
listing, manufacturers names and addresses,
abbreviations, symbols and a list of those
variables which are usually measured for
monitoring a specific treatment process. (Table
4). Excluded from this survey are portable and
laboratory instruments, and those requiring
manual samples.
The instrument listing has been subdivided
according to classification, i.e., water quality,
flow, level, etc. This listing and the one of
measurements vs. wastewater treatment
processes can guide the user in instrument
selections.
Data were obtained from manufacturers'
catalogs and from those who advertise in trade
journals, such as: Public Works magazine,Water
and Wastes Digest, Water and Sewage Works,
Pollution Equipment News, and the American
City.
DESCRIPTION OF SURVEY DATA AMONG
THE LISTINGS
A format was selected which utilizes two
standard 80-column computer cards for each
instrument description. The first card contains
information about the instrument itself. The
second card contains the manufacturer and some
additional information. A description of each
field heading follows (Table 5):
1. Variable. This describes what the
instrument measures. Where H2O QUAL
indicates that there are many possible
measurements, the COMMENTS field should be
referred to for the specific variables measured.
2. Instrument. Manufacturer's name for
his instrument. In many instances, a range of
model numbers is indicated, while in other cases,
only the name of the instrument line has been
given (e.g., MAGNETIC FLOWMETERS and
TURBINE FLOWMETERS have numerous
models which depend upon pipe size).
3. Ranges. Where an integer or M (for
multiple) appears within the specified range
limits, or that the number of ranges can be
achieved by virtue of the numerous models
available, each of which may have one or more
ranges.
4. Range Limits. This indicates the
extreme ranges of measurement.
5. Method. The method or basic
principle used to achieve the measurement is
cited. For water quality monitor packages, this
may be blank because of the numerous methods
used to measure multiple parameters.
6. Outputs. Standard and optional
output signals are listed.
7. Manufacturer. The name may be
shortened due to lack of field space. However,
the complete name is given under the list of
MANUFACTURERS NATVIES and
ADDRESSES.
8. Comments, Other Outputs, Water
Quality Variables. This field is used to provide
other useful information. For water quality
instruments, this field will contain specific mea-
surements available.
The symbols and abbreviations for Table 5
are given in Table 6, and the manufacturers'
addresses are listed in Table 8. Table 7 contains
a list of thirteen manufacturers of automatic
sampling equipment for one or more variables.
RESULTS AND USES
A user of the compilation will have at his
fingertips, virtually all potentially useful
continuous monitoring instruments and their
manufacturers. Inquiries to a manufacturer will
be more direct and the time shortened, since a
caller will already have basic details about
specific instruments.
71
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TABLE 4. MEASUREMENTS FOR WASTEWATER TREATMENT PROCESSES
Measurements
-J
10
Process
pH
Temp
ORP
DO
BOD
COD
TOD
P04
. Toxic
metals
NO
CL
Alkal-
inity
Susp.
NHS
KJEL-
DAHL
N
Liquid
How
Level
Gas
volume
%
co2
%
Methane
Air
flow
Influent flow (at plant)
Bar screen
Raw wastewater pump
Grit channel
Primary sedimentation
Trickling filter
Aeration tanks
Secondary clarificrs
Oxidation pond
Chlorine contact chamber
Return sludge
Primary sludge
Waste activated sludge
Stodge thickening (gravity)
Sludge thickening (floatation)
Sludge digestion
Sludge dewatering
Ehitriation
Pipeline to sea
Incineration
Receiving water
X X
X X
X X
X X
X
X
X X
X X
X
X
X
X X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Sludge
level
Sludge
level
Sludge
level
X
X
-------
TABLE 5
AUTOMATIC MONITORING INSTRUMENTATION FOR WASTEWATER TREATMENT PROCESSES (1 of 2)
Variable Instrument
Flow Series 600 magnetic mtrs
Flow Flumes, weirs, nozzles
Flow Magnetic resonance meter
Flow Universal'venturi
Flow Brooks-mag flowmeter
Flow Fullview, armet rotameters
Flow Magnetic flowmeters
Row Turbine flowmeters
Flow Flumes and weirs
Flow All-metal meters
Flow Orifices, nozzles, Venturis
Flow Swirlmeter
Flow Turbine flow transmitters
Flow Primary device flow mtrs
Row Magnetic flow transmitter
Flow Propeller type meters
Flow Stevens flow metrs (4 mdls)
Flow Mark V flow meter
Flow Varea-meter
Flow Le flowmeter
Range Limits
Method
Manufacturer
FLOW MEASURING INSTRUMENTS
M
1
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
.l-30Mgd
5-50 Gpm
To 16K Gpm
100K Gpm
1-2. 5K Gpm
To 100K Gpm
To 36K Gpm
To 90 mgd
To 320 gpm
To 20K gpm
-30K scfm
.2-30Kgpm
To 60K gpm
To SDK gpm
1.5-2K gpm
Unlimited
Primary
Mag res
Primary
Emf
Rotameter
Emf
Turbine
Primary
Rotameter
Primary
Vortex
Turbine
Primary
Emf
Turbine
Primary
Fluid Drag
Rotameter
Ultrasonic
V
V, A, dig
Press
V, A, Tm, R, rcdr
V, press, rly
A, press, tm
Vac, A, rcdr
Press, A, rcdr
A, press, rly
A, press, rcdr
Vac A, rcdr
Vac
Press, A, rly, tm
A, rcdr, rly, tm
Vac, tm, rly
Rcdr, dig, im
V, rcdr
American Meter
Badger Meter Mfg
Badger Meter Mfg
Bif
Brooks Instrument
Brooks Instrument
Fischer and Portei
Fischer and Porter
Fischer and Porter
Fischer and Porter
Fischer and Porter
Fischer and Porter
Foxboro
Foxboro
Foxboro
Hersey-Sparling
Leopold and Stevens
Ramapo
Wallace and Tiernan
Westinghouse
Comments, other Outputs, Water Quality Variables
Brochure not received
Uses Badger ML-MN trmtr to sense level (Flow)
Totalizer avail. Special fluid properties required
Pressure transmitter required. Available from Bif
Totalizer avail. Pneumatic output available
Totalizer avail. Also for metering gases
Rc'dr output also
Totalizer available
Uses Fischer and Porter float actuated transmitters
Rcdr output also. Also for metering gases
Uses DP transmitters
Gas flow only. Totalizer available
Brochure not received
Press and float types. Brochure not received
Rcdr output. Total flow output also
For weirs, flumes. Uses float or bblr. Total flow
Uses strain gage. Higher pipe flows available
Brochure not received. Also for metering gases
Single range per instrument. Pipe and open channels
OJ
LEVEL MEASURING INSTRUMENTS
Level Model LM10A
Level Float-operated transducer 1 3.5-30 ft
Level Press-operated transducer 1 231 ft adj
Level ML-MN transmitter 1 32 inches
Level Series 200 liquilite 1 Fixed Ivl
Level Sonargage (3 mdls) 3 .5-150 ft
Level Super-sensor 2 Fixed Ivls
Level Float-actuated trmtrs M 0-37 ft
Level Dp transmitters M 0-2K inch
Level Liquid level instruments
Level Uni-sonic mdls 100, 200 1 0-200 ft
Level Stevens liquid Ivl instr M
Level Level controls 1 Fixed Ivl
Level Metritape level sensor M 2-500 ft
Level Interface/solids Ivl Ctrl 1 Fixed Ivl
Level Liquid level controller 2 Fixed Ivls
Level LSI27-1C Liqui Ivl det 1 Fixed Ivl
Level P5200 series Ivl indie 1 2-150 ft
Level Zyrotron liq Ivl Ctrl sys 2 Fixed Ivls
Sldglvl Mdl 8100 sldg Ivl Ctrl 1 Fixed Ivl
Sonic
Float
Press
Float
Electronic
Sonar
Float
Press
Float, bblr
Sonic
Float, bblr
Float
R tape
Lite refl
Liq end
Thermal R
Press
Resistance
Photoel
R,V,A, rly, tm
V, Avrly, tm
V
Rly, tm
A, bed, rly, rcdr
Rly
Press, A, rcdr
A, nress, rcdr
Rcdr, dig, tm
Rly
V,A,R, rly, dig
Rly
Rly
Rly
V, rly
Rly
Rly
West Marine Elec
Autocon
Autocon
Badger Meter Mfg
Controlotron
C. W. Stevens
Farris Chemical
Fischer and Porter
Fischer and Porter
Foxboro
Inventron
Leopold and Stevens
Liq Lvl Lectronics
Metritape
Met-Pro Water Treatmt
Photronic
Trans-sonics
Trans-sonics
Zyrotron Industries
Keene
Rcdr output
Rcdr output, adjustable range
Use with primary devices—flumes, weirs, open nozzles
Models 3000, 3100, 3200
High and low level control applications
Used with Fischer and Porter flumes and weirs, also
Range suppression provided
Brochure not received
Also for sludge Ivl
4 models avail (3 with floats, 1 with bblr)
Rcdr output. Upper limit based on tape length
Mon and Ctrl liquid or solid particles level
High and low level control applications
V output assumed (To meter)
High and low level control applications
Part size Mdl 2150 cont part mon
PARTICLE SIZE MEASURING INSTRUMENTS
2 2-100 mic Lite scatr Rcdr, rly Particle Technology Digital printer available
-------
TABLE 5
AUTOMATIC MONITORING INSTRUMENTATION FOR WASTEWATER TREATMENT PROCESSES (2 of 2)
Variable
H20 qual
H20 qual
H20 quit
H20 qual
H20 qual
H20 qual
H20 qual
H20 qual
H20 qual
H20 qual
Instrument
Range Range Limits
CL
CL
CL
CL
CND
CND
CND
DO
DO
DO
F
F
ORP
ORP
ORP
Mdl 880 resid anlzr-ctrlr
CL resid anlzr and mon
Resid CL anlzr mdl A-792
Electrolytic CND cell
CND monitor MDL 560B
Mdls 101-11 5 CND sensors
DO analyzer mdl 1101
Dissolved oxygen anlzr
Mdl 3000 DO analyzer
Mdl 900F Fluoride anlzr
Method
Outputs
Manufacturer
Comments, other outputs, water quality variables
Mdls 1200,1250,1400,1500
Mdl 9500 Water Qual Mon
Series 8000 anlzrs/ctrlrs
(Variable name) meas sys
Series CR 2 & CR anlzrs
H20 qual sys (4 mdls)
Mdl 1-1000 Water qual mon
Mdl 900
CSM 6 Monitor
Series 1600 H20 qual mon
WATER QUALITY MEASURING INSTRUMENTS (MULTI-VARIABLE INSTRUMENTS)
Mdls 330-331 ORP sensors
Potential cell
02 Demand Oxymand
PH Mdls RC, 1C, R4, 30
PH
PH PH Electrode assembly
PH Mdl 20 and cont rcdg mtr
PH Mdls 320-323 PH sensors
Sludge Den Mdl 400
Susp slds Mdl ISO fluid anlzr
Susp slds Mdl 8200 anlzr/ctrlr
Susp slds W.P.R.L. Susp slds mon
TB CR Turbidimeters (4 mdls)
TB Turbidiphot
TC Mdl 1610 TC analy zer
TC TC analyzer Mdl 1212
TEMP
TEMP Thermocouple and thermohm
TEMP Temperature probe
TOC Mdl 1600 TOC analyzer
TOD Mdl 225 TOD analyzer
M
M
M
M
M
M
M
M
M
0-100 PPM
WATER QUALITY
6
5
5
M
M
2
2
3
M
1
1
1
M
3
1
3
M
1
1
2
1
0-20 PPM
0-10 PPM
0-20 PPM
0-1 OK PPM
0-25 PPM
0-1 S PPM
.1-100 PPM
0-100ML02
2-12 PH
0-14 PH
0-1
10-1 SOK PPM
500-SK PPM
0-SK MG/L
0-10KJTU
10 PPM Adj
0-50 C
0-4K MG/L
0-200 PPM
Color, othr
Color.othr
Color
Color
MEASURING
Amper
Amper
Amper
Electrode
Electrode
Electrode
Polar
Electrode
Electrode
Respir
Electrode
Electrode
Electrode
Electrode
Sonics
Back scatr
Electronic
Photoel
Nephel
Photoel
Liq tube
Thrmoc, R
Thermlster
Infrared
Combustion
V,AMdig, rly, tm
A, rcdr, tm
V, dig, tm, rly
A, rcdr, rly, tm
V, rly, rcdr
V, rly, rcdr, tm
V, rcdr, tm
V, rly, dig, tm
V, rcdr, dig, tm
INSTRUMENTS
V, rly, tm, press
A, rly, rcdr
A, V, rly, tm
V, rly
V
V, rcdr, rly
V,A
V
V
V, rly, rcdr
V, rly, rcdr, dig
V, rcdr
V
V, A, rly, rcdr
V, rcdr, rly
A, rcdr, rly
V, rly, rcdr
Rly, rcdr
V,
V,A, dig rly, tm
V, rcdr
AES
Beckman
Delta Scientific
Foxboro
Hach Chemical
Honeywell
KDI Poly-Technic
Robertshaw
Technicon
Union Carbide
(SINGLE VARIABLE
BIF
Capital Controls
Fischer and Porter
Wallace and Tiernan
Leeds and Northrup
Myron L
Universal Interloc
Union Carbide
Wallace and Tiernan
Weston and Stack
Beckman
Fischer and Porter
Fischer and Porter
Universal Interloc
Wallace and Tiernan
R.M.A. Development
Analytical Measuremts
Fischer and Porter
Leeds and Northrup
Limnetics
Universal Interloc
National Sonics Corp.
Gam Rad
Keene
Partech
Hach Chemical
Photronic
AES
Union Carbide
Fischer and Porter
Leeds and Northrup
Limnetics
AES
Ionics
Basic, NH3> BR, CA, CR, CU, F, HD, HY, I, FE, NO, PO4, SO, &
Basic &
Basic, NH3, BR, HD, CL, CM, CR, CU, CY, F, HY, FE, I, PO4, flow, &.
PH, CL, TB, ORP, CND
F, SI, PO^, CM, SO, HD, FE, CL, HY, CU, PE, PH, &.. Mon & Ctrl
Basic, &. Lvl and low velocity outputs also
Basic, CA, NO, F, DC, CU, PB, AG, SO, BR, CY, HD, I.PER. THI, &.
Brochure not received
NH,, NO, PO4, PH, HD, PN, SI, CU, F, FE, CR, DC, &,. Rcdr output
Basic (except SRI) &
INSTRUMENTS)
Brochure not received
Rcdr output avail
Brochure not received
5 CND cells avail depending on application
Flow, immersion types, Mdl 700 MA trmtr-anlzr avail
Brochure not received
Brochure not received
Uses mdl A-40 DO probe. For gas meas also
Brochure not received
Brochure 'not received
Flow, immersion types. Mdl 1021 trmtr-anlzr avail
Brochure not received
Automatic periodic sampling for monitoring and Ctrl
Brochure not received
Brochure not received
Range is adjustable
Flow, immersion, in-line types. Trmtr-anlzr avail
For meas susp slds and control of turbidity
Models 1031, 1720, 1861, 1889
Brochure not received. Mdl 1620 measures TOC and TC
Brochure not received
Brochure not received
Brochure not received
Range is adjustable
Mdl 1620 measures TOC and TC
Notes:
(2)
Symbols and abbreviations are given in Table 6
Refer to Table 8 for addresses of manufacturers
-------
TABLE 6
SYMBOLS AND ABBREVIATIONS
A CURRENT (AMPERAGE)
ACJ AOJUSTABLEIRANGE OR SPREAD IS ADJ)
AG SILVER
AMPER AMPEROMETRIC
ANLZRIS) ANALYZER(S)
AVAIL AVAILABLE
BASIC BASIC WATER QUALITY VARIABLES (TOTAL OF 8)
BBLR BUBBLER
BCD BINARY COOED DECIMAL
BOO BIOCHEMICAL OXYGEN DEMAND
BR BROMIDE
C CENTIGRADE
CA CALCIUM
CC CADMIUM
CL CHLORINE
CM CHROMATE
CND CONDUCTIVITY (BASIC VARIABLE)
COD CHEMICAL OXYGEN DEMAND
CDLOR COLORIMETRIC
CONT CONTINUOUS
CR CHROMIUM
CTRL CONTROL
CTRLR(S) CONTROLLER(S)
CU COPPER
CY CYANIDE
OC DISOLVED CHLORIDES (BASIC VARIABLE)
DET DETECTOR
DIG DIGITAL
DO DISOLVED OXYGEN (BASIC VARIABLE)
EMF ELECTROMOTIVE FORCE
FE IRON
F FLUORIDE
FT FEET
GPM GALLONS PER MINUTE
HO HARDNESS
HY HYDKAZINE
H20 HATtR
I K1DIDF
INDIC INDICATOR
JTU JACKSON TURBIC.ITY UNITS
K 1000 (FOR EXAMPLE, 4K - 4Cm
LIO LIUUID
LITE LIGHT
LVL(S) L6VELIS)
M MULTIPLE RANGES WITHIN MIM/MAX LIMITS
PRCDUCED UY SINGLfc/MULTIPLE MDOEL
MAG MAGNETIC
MCL(S) MODEL(S)
MFAS "tASURINC
MGO MILLION GALLONS PFR DAY
MG/L MILLIGRAMS/LITER
MIC MICRONS
ML WILLILITERS
MON MONITOR, MONITORING
MTR(S) METER(S)
NEPHEL NEPHELOMETRIC
NH3 AMMONIA
NO NITRATE, NITRITE
ORP OXIDATION REDUCTION POTENTIAL (BASIC VARIABLE)
OTHR OTHER
02 OXYGfcN
PART PARTICLE
PB LEAD
PF PERMANGANATE
PER PERCHLORATE
PH PH (BASIC VARIABLE)
PHOTOEL PHOTOELECTRIC
PNL PHENOLS
PO-4 PHOSPHATE
POLAR POLAROGRAPHIC
PPM PARTS PER MILLION
PRESS PRESSURE
PRIMARY PRIMARY FLOW MEASURING DEV ICE(HEIR,VENTURI,£TC.I
OUAL (JUALITY
R RESISTANCE
RCDG RECORDING
RCDR RECORDER
REFL REFLECTION
RES RESONANCE
RESID RESIDUAL
RESPIR RESPIROMETRIC
RLY RELAY
SCATR SCATTER
SCFM STANDARD CUBIC FEEI PER MINUTE
SI SILICA
SLOG SLUDGE
SLDS SOLIDS
SO SULFIOE, SULFATE
SRI SOLAK RADIATION INTENSITY (BASIC VARIABLE)
SUSP SUSPENDER
SYS SYSTEM
TP TURBIDITY (BASIC VARIABLE)
TC TOTAL CARBON
TFMP TEMPERATURE (BASIC VARIABLE)
THI THIOCYANATE
THRMOC THERMOCOUPLE
TM TELEMETRY
TCC TOTAL ORGANIC CARHON
TOD TOTAL OXYGEN DEMAND
TREATMT TREATMENT
TRMTR(S) TRANSMITTERS)
V VOLTAGE
VAC A-C VOLTAGE
VARIOUS VARIOUS MODELS AVAILABLE
C OTHFK VARIABLES AVAILABLE
75
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TABLE 7
MANUFACTURERS OF
AUTOMATIC SAMPLERS
Brailsford & Company, Inc.
Milton Point
Rye, New York 10580
Instrument Specialties Company
4700 Superior
Lincoln, Nebraska 68504
Sirco Controls, Ltd.
8815 Silkirk Street
Vancouver 14, British Columbia
Sanitary Engineering Research Company
4205 31st Avenue South
Minneapolis, Minnesota 55455
N-Con Systems, Inc.
410 Boston Post Road
Larchmont, New York 10538
Chicago Pump
622 Diversey Parkway
Chicago, Illinois 60614
Infilco Compnay
P.O. Box 5033
Tucson, Arizona 85703
Megator Corporation
136 Gamma Drive
Pittsburg, Pennsylvania 15238
Penberthy
P.O.Box 112
Prophetstown, Illinois 61277
Sigma Motor, Inc.
3 North Main Street
Middleport, New York 14105
Testing Machines, Inc.
6078 Sherbrooke Street
W. Montreal 28, Quebec
Calhoun & Sons Instruments
8227 Hampton
Gross He, Michigan 48138
Pro-Tech, Inc. •
Lester Industrial Center
Lester, Pennsylvania 19113
76
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TABLE 8
MANUFACTURERS ADDRESSES
AES Automated Environmental Systems
135 Crossways Park Drive
Woodbury, New York 11797
American Meter Controls, Inc.
13500 Philmont Avenue
Philadelphia, Pennsylvania 19116
Analytical Measurements, Inc.
31 Willow Street
Chatham, New Jersey 07928
Autocon Industries, Inc.
995 University Avenue
St. Paul, Minnesota 55104
Badger Meter Manufacturing Co.
4545 West Brown Deer Road
Milwaukee, Wisconsin 53223
Beckman Instruments, Inc.
2500 Harbor Boulevard
Fullerton, California 92634
BIF
345 Harris Avenue
Providence, Rhode Island 02901
Brooks Instrument Div.
Emerson Electric Company
Hatfield, Pennsylvania 19440
Capital Controls Co., Inc.
Advance Lane
Colmar, Pennsylvania 18925
Controlotron Corporation
35 Central Avenue
Farmingdale, L. I. New York 11735
C. W. Stevens, Inc.
P.O. Box 619
Kennett Square, Pennsylvania 19348
Delta Scientific Corporation
120 East Hoffman Avenue
Lindenhurst, New York 11757
Farris Chemical Compnay, Inc.
P.O. Box 10126
Knoxville, Tennessee 37919
Fischer and Porter Company
Warminster, Pennsylvania
Foxboro Company
Neponset Avenue
Foxboro, Massachusetts 02035
Gam Rad, Inc.
16825 Wyoming Avenue
Detroit, Michigan 48221
Hach Chemical Company
Box 907
Ames, Iowa 50010
Hersey-Sparling Meter Company
4097 North Temple City Boulevard
El Monte, California 91730
Honeywell Industrial Div.
1100 Virginia Drive
Fort Washington, Pennsylvania 19034
Inventron Industries, Inc.
6508 South Arizona Avenue
Los Angeles, California 90045
Ionics, Inc.
65 Grove Street
Watertown, Massachusetts 02172
KDI Poly-Technic, Inc.
10540 Chester Road
Cincinnati, Ohio 45215
Keene Corporation
Water Pollution Control Div.
1740 Molitor Road
Aurora, Illinois 60507
Leeds and Northrup Company
Sumneytown Pike
North Wales, Pennsylvania 19454
Leopold and Stevens, Inc.
P.O. Box 25347
Portland, Oregon 97225
Limnetics, Inc.
6132 West Fond Du Lac Avenue
Milwaukee, Wisconsin 53218
Liquid Level Lectronics, Inc.
P.O. Box 1002
Richardson, Texas 75080
Met-Pro Water Treatment Corporation
5th Street and Mitchell Avenue
Lansdale, Pennsylvania 19446
Metritape Controls, Inc.
50 Commonwealth Avenue
West Concord, Massachusetts 01781
Myron L. Company
656 First Street
Encinitas, California 92024
National Sonics Corporation
43 Milbar Boulevard
Farmingdale, New York 11735
Partech, Ltd.
7 Broadwater Road, Welwyn Garden City
Hertfordshire, Great Britain
Particle Technology, Inc.
734 North Pastoria Avenue
Sunnyvale, California 94086
Photronic, Inc.
411 Cheltena Avenue
Jenkintown, Pennsylvania 19046
Ramapo Instrument Company, Inc.
Bloomingdale, New Jersey 07403
R.M.A. Development, Inc., Products Division
P.O. Box 1222
Fond Du Lac, Wisconsin 54935
Robertshaw Controls
P.O. Box 400
Knoxville, Tennessee 37901
Technicon Corporation
Tarrytown, New York 10591
Trans-Sonics, Inc.
P.O. Box 326
Lexington, Massachusetts 02173
Union Carbide Corporation
Instrument Department
5 New Street
White Plains, New York 10601
Universal Interloc, Inc.
17401 Armstrong Avenue
Santa Ana, California 92705
Wallace and Tiernan Div.
25 Main Street
Belleville, New Jersey 07109
Western Marine Electronics
509 Fairview Avenue North
Seattle, Washington 98109
Westinghouse Electric Corporation
P.O. Box 1488
Annapolis, Maryland 21401
Weston and Stack, Inc.
1426 Lewis Lane
West Chester, Pennsylvania 19380
Zyrotron Industries, Inc.
600 Huyler Street
South Hackensack, New Jersey 07606
77
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1
Accession Number
w
5
2
Subject Field & Group
05D
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
The American Public Works Association, Chicago, Illinois 60637
Title
FEASIBILITY OF COMPUTER CONTROL OF WASTEWATER TREATMENT
1 Q Authors)
American Public Works Association
16
21
Project Designation
EPA Contract
14-12-580; APWA 66-68
Note
22
Citation
23
Descriptors (Starred First)
*Computers, *Wastetfater Treatment, *Monitoring, *Control
25
Identifiers (Starred First)
27
Abstract
ABSTRACT: This report contains the results of an
investigation into the use of digital computers for
management and control of wastewater treatment
facilities. The objectives of the study included the
generation of guidelines for implementation of digital
computers for these purposes and recommendations for
further relevant research.
For the purpose of gathering information, visits were
made to plants and the literature was searched. A survey
was conducted of current practices and problems in the
operation of wastewater treatment plants. Emphasis was
placed on the processes of secondary treatment with
regard to management and control of unit processes,
continuous monitoring needs, the influences of regulatory
agencies, and certain local conditions. A set of guidelines
and steps for computer control implementation and
peripheral applications were evolved.
It was concluded that both off-line computer applications
and on-line computer control in wastewater treatment are
feasible and should be implemented.
This Report was submitted in fulfillment of_ Contract
14-12-580 between the Environmental Protection Agency,
the American Public Works Association and nineteen cost
sharing local governmental agencies.
Abstractor
R.
H
WR.-102 (REV.
WRSIC
. Sul
JULY
.1
ivan
Institution
)969) SEND, WITH COPY
APWA
OF DOC
Research
UMENT. TO:
Foundation
WATER RESOURCE
U.S. DEPARTMENT
WASHINGTON. D. C
QF THE
. 20240
INTERIOR
* CPO: 1970 — 389-930
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