EPA 440/1-77/084
Supplement For
PRETREATMENT
to the
Development Document
for the
STEAM ELECTRIC
POWER GENERATING
Point Source Category
.^osr^
U.S. ENVIRONMENTAL PROTECTION AGENCY
APRIL 1977
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SUPPLEMENT FOR PRETREATMENT
TO THE DEVELOPMENT DOCUMENT
for the
STEAM ELECTRIC POWER GENERATING
POINT SOURCE CATEGORY
Douglas M. Costle
Admini strator
Andrew W. Breidenbach, Ph.D.
Assistant Administrator
for Water and Hazardous Materials
Eckardt C. Beck
Deputy Assistant Administrator for
Water Planning and Standards
ri
Robert B. Schaffer
Director, Effluent Guidelines Division
John Lum
Project Officer
April 1977
Effluent Guidelines Division
Office of Water and Hazardous Materials
U.S. Environmental Protection Agency
Washington, D.C. 20460
SB
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ABSTRACT
This document presents the findings of an extensive study of
that section of the Steam Electric Power Generating Industry
which discharges industrial wastes to publicly owned
treatment works (POTW). Its purpose is to develop
pretreatment standards to implement section 307 (b) of the
Federal Water Pollution Control Act Amendment of 1972 for
the Existing Power Plants.
Pretreatment standards, recommended in Section II of this
report set forth the degree of effluent reduction achievable
through the application of control technology currently
available for those pollutants which are determined not to
be susceptible to treatment by a POTW or which would
interfere with the operation of such works. These
pretreatment standards set forth the degree of effluent
reduction achievable through application of the available
demonstrated control technology, processes, operating
methods, or other alternatives. These standards must be
achieved no later than three (3) years from the date of
promulgation.
Supporting data and rationale for development of pretreat-
ment standards are contained in this report.
iii
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LIST OF CONTENTS
Page
ABSTRACT iii
TABLE OF CONTENTS V
LIST OF FIGURES ix
LIST OF TABLES xi
I. CONCLUSIONS 1
II. RECOMMENDATIONS 3
III. INTRODUCTION 9
General Background 9
Purpose and Authority 10
Scope of Work and Technical Approach 10
General Description of the Industry 13
Process Description 13
Publicly-Owned Treatment Works (POTW) 22
IV. INDUSTRY CATEGORIZATION 25
Introduction 25
Industry Categorization 25
Factors Considered 25
Age 25
Size 26
Fuel 26
Geography 26
Mode of Operation 28
Raw Water Quality 28
Volume of Water Used 28
Pretreatment Technology 28
V. WATER USE AND WASTE CHARACTERIZATION 29
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Introduction 29
Principles of Operation of steam Electric
Power Plant 29
Water Use and Waste characterization by
Category 32
Condenser Cooling Water 34
Water Treatment 42
Demineralizer Regenerant Wastes 47
Boiler Slowdown 49
Maintenance Cleaning 53
Ash Handling Systems 58
Air Pollution Control Equipment 65
The POTW Process 70
Flows of POTW Receiving Steam Electric
Wastewaters 77
VI. CONSIDERATION OF POLLUTANT PARAMETERS 85
Introduction 85
The Consideration of Pollutant
Parameters 85
Properties of Pollutant Parameters
Considered 86
VII. TREATMENT AND CONTROL TECHNOLOGY 105
Introduction 105
End-of-Pipe Treatment Technology 105
Treatment of Major Pollutants 106
End-of-Pipe Technology for Major
Waste Streams 114
Water Management 120
In-Plant Control Techniques 121
vi
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Material Substitution 121
Water Conservation and Wastewater Reuse 125
VIII. COST, ENERGY AND OTHER NON WATER QUALITY
ASPECTS 129
Introduction 129
Cost Reference and Rationale 130
Costs for Pretreatment 133
Levels of Pretreatment 131
Cost Estimates 1UU
Ultimate Disposal 151
Energy Considerations 155
IX. BEST PRACTICABLE PRETREATMENT TECHNOLOGY 157
X. ACKNOWLEDGEMENTS 163
XI. REFERENCES 165
XII. GLOSSARY 168
APPENDIX A - STATISTICAL ANALYSIS OF HISTORICAL
DATA 179
APPENDIX B - WATER GLOSSARY 221
APPENDIX C - METRIC UNITS CONVERSION TABLE 253
VII
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LIST OF FIGURES
Page
III-l Principal Fuel Use by Number 16
III- 2 Principal Fuel Use by Megawatts 17
III-3 Year of Construction by Number 18
H Year of Construction by Megawatt 19
III- 5 Process Flow Diagram Steam Electric
Power Industry 21
III- 6 Wastewater Treatment Sequence 23
V-l Typical Boiler for Coal-Fired Furnace 31
V-2 Single-pass Condenser 33
V-3 Fossil-Fueled Steam Electric Power
Plant - Typical Flow Diagram 35
V-U Once-Through and Recirculating
Cooling Systems 38
V-5 Diagram of Wet Induced - Air Cooling
Tower 3 9
V-6 Natural Draft Wet Cooling Tower
(Counter Flow) 40
V-7 Commonly Used Makeup Water
Treatment Methods U5
V-8 Flow Diagram for Recirculating
Bottom Ash System 59
V-9 Flow Diagram for Air Pollution Control
Scrubbing System 68
V-10 Flow Diagram of Secondary Treatment
Methods 7 H
V-11 Wastewater Treatment Flow Diagram 75
V-12 Flow Diagram for Sludge Treatment 76
V-13 Flow Diagram of Nitrification -
Denitrification Process 79
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VIII-1 Model Waste Pretreatment Plant - 25 MW
Generating Facility 143
VIII-2 Model Waste Pretreatment Plant - 500 MW
Generating Facility 146
VIII-3 Cooling Water System Slowdown Treatment
for Level D Pretreatment 153
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LIST OF TABLES
Page
III-l Total Steam Electric Plants
in the Contiguous United States 14
III- 2 Steam Electric Plants Discharging
to Municipal Sewers in the Contiguous
United States 15
IV- 1 Power Plant Waste Types 27
V-1 Raw Waste Flows and Loadings -
Condenser Cooling Systems U3
V-2 Raw Waste Flows and Loadings -
Water Treatment 50
V-3 Effluent Flows and Loadings -
Water Treatment 52
V-4 Raw Waste Flows and Loadings -
Boiler Slowdown 54
V-5 Raw Waste Flows and Loadings -
Maintenance Cleaning 57
V-6 Ash Disposal Methods 60
V-7 Raw Waste Flows and Loadings -
Ash Handling 63
V-8 Effluent Flows and Loadings -
Ash Handling 6U
V-9 Power Plant and POTW Flows 80
V-10 Raw Waste Flows and Loadings -
Combined Discharge to POTW 81
V-11 Comparison of Parameter Values
Plant Raw Wastes 83
VII-1 End-of -pipe Treatment Methods 107
VII-2 Solid/Liquid Separation Systems 110
Vll-3 Treatment of Major Pollutants 112
U Typical Composition of Boiler Chemical
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Cleaning Wastes 119
VII-5 Typical Composition of Boiler Fireside
Wash Wastes 119
VII-6 Recovery Processes for Flue Gas
Desulfurization Systems 126
VIII-1 Wastewater Treatment Costs and Resulting
Waste-load Characterization for Typical
Plant 135
VIII-2 Wastewater Treatment Costs and Resulting
Waste-load Characteristics for Typical 136
Plant
VIII-3 Summary of Capital Costs Oil and Gas
Fired Plants - 25 MW Plant 137
VIII-4 Wastewater Treatment Cost and Resulting
Waste-load Characteristics for Typical
Plant 141
VIII-5 Wastewater Treatment Costs and Resulting
Waste-load Characteristics for Typical
Plant 142
VIII-6 Summary of Capital Costs Coal Fired
Plant 145
VIII-7 Assumed Unit Costs 147
VIII-8 Operating Costs - Pretreatment of Low
Volume and Metal Cleaning Wastes 149
VIII-9 Estimated Capital Costs - Chemical
Works Pretreatment Plant Level C 152
VIII-10 Estimated Capital Cost - Cooling Water
System Slowdown Treatment 154
VIII-11 Estimated Capital Costs - Cooling Water
System Slowdown Treatment 154
Xll
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SECTION I
CONCLUSION
An engineering evaluation of steam electric power generating
plants that discharge all or a portion of their aqueous
wastes to publicly-owned treatment works (POTW) was
conducted to establish the basis for pretreatment standards.
For the purpose of establishing such standards it was deemed
practical to divide the wastes from power plants into the
following waste-types:
o Condenser Cooling System
o Boiler Water Treatment
o Boiler Slowdown
o Maintenance Cleaning
o Ash Handling
o Drainage
o Air Pollution Control Devices
o Miscellaneous Waste Streams
This division is identical to that presented in the
development document for direct dischargers (14) in this
industry with the deletion of Construction Activity. This
division was found to be valid as examination of process
characteristics and raw wastes were not found to be
significantly different from those of direct dischargers.
Conduct of the work involved contact with 49 steam electric
power generating stations, representing 50 percent of the
estimated 98 stations discharging chemicals wastes to a
POTW. Engineering visits and data collection were made to
23 stations. Sampling of raw and pretreated wastes was
obtained from eight (8) stations. Additionally, prior work
conducted by the EPA, data collected in response to NPDES
and local discharge permit monitoring, industrial effluent
data, and relevant literature prepared by the EPA and
electrical trade journals were evaluated.
Based on the above evaluation, the following conclusions
were reached:
o Pollutants discharged by the population of plants
discharging to the POTW are similar to those of
direct dischargers.
o The division of waste types developed above is
valid for the purpose of characterizing the waste
sources.
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o Treatment technologies described in the development
document for the effluent limitations guidelines
for this industry are also applicable to plants
discharging to the POTW.
A survey of current industry practices has indicated that
most plants provide little pretreatment of chemical type
wastes at the present time. Based upon information provided
in this document regarding pollutant properties and raw
waste characteristics, it is determined that some of the
pollutants discharged by the Steam Electric Power Generating
Point Source Category will interfere with or be treated
inadequately by Publicly Owned Treatment Works (POTW).
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SECTION II
RECOMMENDATIONS
As a result of the findings and conclusions contained in
this report, the pretreatment standards for existing power
plants in compliance with the mandates of the Federal Water
Pollution Control Act Amendment of 1972 are summarized
below:
General Unit Subcategory*
For the purpose of establishing pretreatment standards
under Section 307 (b) of the Act for a source within the
General Unit subcategory, the provisions of 40 CFR 128 shall
not apply. The pretreatment standards for an existing
source within the general unit subcategory are set forth
below.
(a) No pollutant (or pollutant property) introduced
into a publicly owned treatment works shall interfere with
the operation or performance of the works. Specifically,
the following wastes shall not be introduced into the
publicly owned treatment works:
(1) Pollutants which create a fire or explosion hazard
in the publicly owned treatment works.
(2) Pollutants which will cause corrosive structural
damage to treatment works, but in no case pollutants with a
pH lower than 5.0, unless the works is designed to
accommodate such pollutants.
(3) Solid or viscous pollutants in amounts which would
cause obstruction to the flow in sewers, or other
interference with the proper operation of the publicly owned
treatment works.
(4) Pollutants at either a hydraulic flow rate or
pollutant flow rate which is excessive over relatively short
time periods so that there is a treatment process upset and
subsequent loss of treatment efficiency.
(b) In addition to the general prohibitions set forth
in paragraph (a) above, the following pretreatment standard
establishes the quality or quantity of pollutants or
pollutant properties controlled by this section which may be
introduced into a publicly owned treatment works by a source
subject to the provisions of this subpart.
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(1) There shall be no discharge to publicly owned
treatment works of polychlorinated biphenol compounds such
as those used for tranformer fluid.
(2) The quantity of copper discharged in metal cleaning
wastes to publicly owned treatment works shall not exceed
the quantity determined by mulitplying the flow of metal
cleaning wastes times 1 mg/1.
(3) The quantity of oil and grease in the plant*s
combined discharge to the publicly owned treatment works
shall not exceed the quantity determined by multiplying the
flow of the combined discharge times 100 mg/1.
(c) Any owner or operator of any source to which the
pretreatment standards required by paragraph (a) above are
applicable, shall be in compliance with such standards upon
the effective date of such standards. The time for
compliance with standards required by paragraph (b) above
shall be within the shortest time but not later than three
years from the effective date of such standards.
Small Unit Subcategory*
For the purpose of establishing pretreatment standards
under Section 307 (b) of the Act for a source within the
Small Unit subcategory, the provisions of UO CFR 128 shall
not apply. The pretreatment standards for an existing
source within the small unit subcategory are set forth
below.
(a) No pollutant (or pollutant property) introduced
into a publicly owned treatment works shall interfere with
the operation or performance of the works. Specifically,
the following wastes shall not be introduced into the
publicly owned treatment works:
(1) Pollutants which create a fire or explosion hazard
in the publicly owned treatment works.
(2) Pollutants which will cause corrosive structural
damage to treatment works, but in no case pollutants with a
pH lower than 5.0, unless the works is designed to
accommodate such pollutants.
(3) Solid or viscous pollutants in amounts which would
cause obstruction to the flow in sewers, or other
interference with the proper operation of the publicly owned
treatment works.
(4) Pollutants at either a hydraulic flow rate or
pollutant flow rate which is excessive over relatively short
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time periods so that there is a treatment process upset and
subsequent loss of treatment efficiency.
(b) In addition to the general prohibitions set forth
in paragraph (a) above, the following pretreatment standard
establishes the quality or quantity of pollutants or
pollutant properties controlled by this section which may be
introduced into a publicly owned treatment works by a source
subject to the provisions of this subpart.
(1) There shall be no discharge to publicly owned
treatment works of polychlorinated biphenol compounds such
as those used for tranformer fluid.
(2) The quantity of copper discharged in metal cleaning
wastes to publicly owned treatment works shall not exceed
the quantity determined by mulitplying the flow of metal
cleaning wastes times 1 mg/1.
(3) The quantity of oil and grease in the plant's
combined discharge to the publicly owned treatment works
shall not exceed the quantity determined by multiplying the
flow of the combined discharge times 100 mg/1.
(c) Any owner or operator of any source to which the
pretreatment standards required by paragraph (a) above are
applicable, shall be in compliance with such standards upon
the effective date of such standards. The time for
compliance with standards required by paragraph (b) above
shall be within the shortest time but not later than three
years from the effective date of such standards,
Old Unit Subcategory*
For the purpose of establishing pretreatment standards
under Section 307 (b) of the Act for a source within the Old
Unit subcategory, the provisions of 40 CFR 128 shall not
apply. The pretreatment standards for an existing source
within the old unit subcategory are set forth below.
(a) No pollutant (or pollutant property) introduced
into a publicly owned treatment works shall interfere with
the operation or performance of the works. Specifically,
the following wastes shall not be introduced into the
publicly owned treatment works:
(1) Pollutants which create a fire or explosion hazard
in the publicly owned treatment works.
(2) Pollutants which will cause corrosive structural
damage to treatment works, but in no case pollutants with a
pH lower than 5»0, unless the works is designed to
accommodate such pollutants.
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(3) Solid or viscous pollutants in amounts which would
cause obstruction to the flow in sewers, or other
interference with the proper operation of the publicly owned
treatment works.
Pollutants at either a hydraulic flow rate or
pollutant flow rate which is excessive over relatively short
time periods so that there is a treatment process upset and
subsequent loss of treatment efficiency.
(b) In addition to the general prohibitions set forth
in paragraph (a) above, the following pretreatment standard
establishes the quality or quantity of pollutants or
pollutant properties controlled by this section which may be
introduced into a publicly owned treatment works by a source
subject to the provisions of this subpart.
(1) There shall be no discharge to publicly owned
treatment works of polychlorinated bi phenol compounds such
as those used for tranformer fluid.
(2) The quantity of copper discharged in metal cleaning
wastes to publicly owned treatment works shall not exceed
the quantity determined by mulitplying the flow of metal
cleaning wastes times 1 mg/1.
(3) The quantity of oil and grease in the plant's
combined discharge to the publicly owned treatment works
shall not exceed the quantity determined by multiplying the
flow of the combined discharge times 100 mg/1.
(c) Any owner or operator of any source to which the
pretreatment standards required by paragraph (a) above are
applicable, shall be in compliance with such standards upon
the effective date of such standards. The time for
compliance with standards required by paragraph (b) above
shall be within the shortest time but not later than three
years from the effective date of such standards.
Area Runoff Subcategory*
For the purpose of establishing pretreatment standards
under Section 307 (b) of the Act for a source within the Area
Runoff subcategory, the provisions of 40 CFR 128 shall not
apply. The pretreatment standards for an existing source
within the area runoff subcategory are set forth below.
(a) No pollutant (or pollutant property) introduced
into a publicly owned treatment works shall interfere with
the operation or performance of the works. Specifically,
the following wastes shall not be introduced into the
publicly owned treatment works:
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(1) Pollutants which create a fire or explosion hazard
in the publicly owned treatment works.
(2) Pollutants which will cause corrosive structural
damage to treatment works, but in no case pollutants with a
pH lower than 5.0, unless the works is designed to
accommodate such pollutants.
(3) Solid or viscous pollutants in amounts which would
cause obstruction to the flow in sewers, or other
interference with the proper operation of the publicly owned
treatment works.
(U) Pollutants at either a hydraulic flow rate or
pollutant flow rate which is excessive over relatively short
time periods so that there is a treatment process upset and
subsequent loss of treatment efficiency.
(b) Any owner or operator of any source to which the
pretreatment standards required by paragraph (a) above are
applicable, shall be in compliance with such standards upon
the effective date of such standards.
*The definitions of these subcategories are the same as
those used for the effluent limitations guidelines
regulations.
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SECTION III
INTRODUCTION
General Background
The involvement of the Federal Government in water pollution
control dates back to 1948 when Congress enacted the first
comprehensive measure aimed specifically at this problem.
At that time the Surgeon General, through the U.S. Public
Health Service, was authorized to assist states in various
ways to address the problem. The emergence of a national
water pollution control program came about with the
enactment of the Water Pollution Control Act of 1956 (Public
Law 84-660). To date this law remains the basic law
governing water pollution. It establishes the basic system
of technical and financial assistance to states and
municipalities, as well as enforcement procedures by which
legal steps can be initiated against polluters.
The present program dates back to the Water Quality Act of
1965 and the Clean Water Restoration Act of 1966. Under the
1965 Act, states were required to adopt water quality
standards for interstate waters, and to submit to the
Federal Government, for approval, plans to implement and
enforce these standards. The 1966 Act authorized Federal
participation in construction of sewage treatment plants.
On amendment, the Water Quality Act of 1970, extended
Federal activities into such areas as pollution by oil,
hazardous substances, sewage from vessels, and mine
drainage.
Originally, pollution control activities were the
responsibility of the U.S. Public Health Service. In 1961,
the Federal Water Pollution Control Administration (FWPCA)
was created in the Department of Health, Education and
Welfare, and in 1966, the FWPCA was transferred to the
Department of the Interior. The name was changed in early
1970 to the Federal Water Quality Administration and in
December 1970, the Environmental Protection Agency (EPA) was
created by Executive Order as an independent agency outside
the Department of the Interior. Executive Order 11574 on
December 23, 1970, established the Permit Program, requiring
all industries to obtain permits for discharge of wastes
into navigable waters or their tributaries under the
provisions of the 1899 River and Harbor Act (Refuse Act).
The permit program immediately became involved in legal
problems resulting in a court ruling that effectively
stopped issuance of a significant number of permits. It did
result in the filing with EPA, through the U.S. Army Corps
of Engineers, of applications for permits which, represent a
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complete inventory of industrial waste discharges. The
granting of a permit under the Refuse Act was dependent on
the discharge being able? to meet applicable water quality
standards. Although EPA could not specify methods of
treatment, they could require minimum effluent levels
necessary to meet water quality standards.
The Federal Water Pollution Control Act Amendments of 1972
(the "Act") made a number of fundamental changes in the
approach to achieving clean water. One of the most
significant changes was from a reliance on water quality
related effluent limitations to a direct control of
effluents through the establishment of technology-based
effluent guidelines to form an additional basis, as a
minimum, for issuance of discharge permits. The permit
program under the 1899 Refuse Act was plciced under full
control of EPA, with much of the responsibility to be
delegated to the States.
PURPOSE AND AUTHORITY
Under the Act, the Environmental Protection Agency is
charged with establishing pretreatment standards to protect
the operation of publicly-owned treatment works and to
prevent discharge of pollutants which pass through such
works inadequately treated.
As part of this Act, Section 307(b) states that the
Administrator shall "publish proposed regulations
establishing pretreatment standards for introduction of
pollutants into treatment works (as defined in Section 212
of this Act) which are publicly owned for those pollutants
which are determined not to be susceptible to treatment by
such treatment works or which would interfere with the
operation of such treatment works. Pretreatment standards
under this section shall specify a time for compliance not
to exceed three years from the date of promulgation."
This report is prepared for the purpose of developing
pretreatment standards for existing sources. Pretreatment
standards for new sources have been promulgated October of
1974, (together with the effluent limitations guidelines for
the Steam Electric Power Generating Point Source Category).
SCOPE OF WORK AND TECHNICAL APPROACH
The pretreatment standards proposed herein were developed in
the following manner. A comprehensive survey was conducted
of over 1200 steam electric generating stations in the
United States. The stations were screened in two stages:
(1) the entire population was screened and cross-matched
using available references and (2) 230 stations were
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contacted by telephone. The list of plants that discharge
to a POTW was first studied for the purpose of determining
whether separate standards would be required for different
divisions within the list. The analysis was based upon
fuels used, size production process employed, wastewater
pretreatment at plant sites, and other factors. The raw
waste characteristics for each subcategory were then
identified. This included an analyses of (1) the source and
volume of water used in the process employed (2) the
constituents (including thermal) of all wastewaters
including constituents which result in taste, odor, and
color in water, (3) the effect of the constituent on the
operation of the POTW and (4) the adequacy of the POTW in
treatment of such constituents. Wastewaters which should be
subject to pretreatment standards were identified.
The full range of control and pretreatment technologies
existing within each subcategory was identified. This
included identification of each distinct control and
pretreatment technology, including both in-plant and end-of-
process technologies, which are existent or capable of being
designed for each division. It also included an
identification of the amount of constituents and the
chemical, physical, and biological characteristics of
pollutants. Effluent levels resulting from the application
of each of the pretreatment and control technologies were
also identified. The problems, limitations, and reliability
of each pretreatment and control technology were also
identified. In addition, the nonwater quality environmental
impact, such as the effects of the application of such
technologies upon other pollution problems, including air,
and solid waste, were also identified. The energy
requirements of each of the control and treatment
technologies were identified as well as the cost of the
application of such technologies.
The information, as outlined above, was then evaluated in
order to determine what levels of technology are available
for effluent reduction. In identifying such technologies,
various factors were then considered. These included the
total cost of application of technology, the age of
equipment and facilities involved, the process employed, the
engineering aspects of the application of various types of
control techniques, process changes, nonwater quality
environmental impact (including energy requirements), and
other factors.
Data for identification and analyses were obtained from a
number of sources. These sources included EPA research
information; EPA, state, and local environmental personnel;
trade associations; published literature; qualified
technical consultation; historical information on effluent
11
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quality and quantity; and on-site visits including
analytical programs and interviews at steam electric plants
throughout the United States which were known to have above
average waste pretreatment facilities. All references used
in developing the pretreatm€:nt standards reported herein are
listed in Section XI of this; document.
Twenty-three operating plants were visited and eight were
sampled. Composite samples over a sixteen hour period were
obtained from these eight plants and were analyzed for
parameters mentioned in Section V. Information was obtained
from as many as fifteen (15) plants for each waste-type
division. Both in-process and end-of-pipe data were
obtained as a basis for determining "citer use rates
capabilities and effluent loads. Permit application data
was of value for the purposes of this study when such data
covered outfalls serving only steam electric power
operations.
Cost information was obtained directly from industry during
plant visits, from engineering firms, equipment suppliers,
and from the literature. These costs have been used to
develop general capital, operating, and total costs for each
pretreatment and control method. This generalized cost data
and specific information obtained from plant visits was used
to estimate cost effectiveness in Section VIII and elsewhere
in this report.
Certain plants were selected for in-depth analysis from the
total population of those visited. These plants were plants
discharging representative waste types or employing above
average treatment technology or having substantial
quantities of historic effluent data.
The following selection criteria were developed and used for
selection of plants visited and sampled.
1. Representative plant with respect to fuel type,
size, geographical location and other factors.
2. Plants that discharge types or quantities of waste
representative of those delineated in Section IV.
Plants that have treatment,
GENERAL DESCRIPTION OF THE INDUSTRY
The Steam Electric Power Industry is made up of 1273 plants
throughout the contiguous United States. Of these plants an
estimated 7.7 percent or 98 plants discharge wastewaters to
publicly-owned treatment works and are thus covered by the
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scope of this document. In this study 49 plants discharging
to POTW were contacted.
Statistics for this section were estimated based on a truly
random sampling of steam electric power plants contained in
the "Environmental Assessment of Alternative Thermal Control
Strategies for the Electric Power Industry" by Michelle M.
Zarubica of the Office of Planning and Evaluation of the
Environmental Protection Agency (18).
Steam Electric plants discharging to the POTW tended to be
smaller on the average than plants discharging to surface
water. These plants averaged about 150 MW for a total
capacity of 14,500 MW which compares with an average
capacity and total generating capacity of about 400 MW and
506,700 MW for the entire Steam Electric Industry. (See
Tables III-l and III-2). Of these plants, an estimated 72
percent are publicly-owned and 28 percent are investor
owned.
Most of the Steam Electric plants that discharge to POTW (68
percent) use gas as their principal fuel compared to 31
percent for the entire industry (Figures III-l and III-2).
Conversion of some plants from gas to oil is expected due to
shortage of natural gas.
Plants which discharge wastewaters to POTW tend to have
units older than plants which discharge to surface waters.
Tables III-l and III-2 show that 29 percent of the plants
which discharge to POTW were built since 1960 as compared to
38 percent for the entire population. Also, plants built
since 1960 represent 48 percent of the generating capacity
of plants discharging to POTW compared to 78 percent for the
entire Steam Electric Industry. (See Figures III-3 and III-
4).
Approximately 24 percent of all electrical generation is
nuclear powered but no plants of this type were observed to
discharge to the POTW. Nonetheless, nuclear plants are
included in this document, since their chemical waste
discharges are similar in nature to those discharged by non-
nuclear facilities (14) .
Steam Electric plants discharging to POTW are located in all
regions of the country with somewhat higher than average
concentrations in the Midwest and in California.
Process Description
The "production" of electrical energy involves utiliation
and conversion of chemical or nuclear energy. Present day
methods of utilizing energy of fossil fuels are based on a
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Table III-l. TOTAL. STEAM ELECTRIC PLANTS IN THE
CONTIGUOUS UNITED STATES
Total Number of Plants = 1273
Total Number of Units = 3011
Total Number of Megawatts^ 506,654
Average Station Size = 398
Percentage of Plants Confirmed as Discharging
to Municipal Sewers - by Number = 7.7%
by Megawatts = 2.9%
Principal Percentage by Percentage by
Unit Fuel Number Megawatts
Gas 31.0
Oil 14.6
Coal 49.3
Nuclear 5.1
100.0
Percentage by Percentage by
Unit Built In Number Megawatts
1970's 17.6 57.6
1960's 20.3 20.1
1950's 36.1 17.6
1940's 16.0 3.7
1930's 6.5 0.8
1920's 2.7 0.1
1910's 0.8 0.1
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Table II1-2. STEAM ELECTRIC PLANTS DISCHARGING TO
MUNICIPAL SEWERS IN THE CONTIGUOUS UNITED STATES
Total Number of Plants = 98
Total Number of Units = 277
Total Number of Megawatts - 14504
Average Station Size = 148
Principal
Unit Fuel
Gas
Oil
Coal
Nuclear
Percentage by
Number
67.7
17.7
14.7
0.0
Percentage by
Megawatts
44.1
54.0
1.9
0.0
100.0
100.0
Unit Built In
1970's
1960's
1950's
1940's
1930's
1920's
1910's
Percentage by
Number
5.
23.
35.3
23.5
5.9
5.9
0.0
100.0
Percentage by
Megawatts
4.3
43.2
47.0
5.2
0.2
0.1
0.0
100.0
15
-------
TOO
90
80
70
OVERALL PLANTS
POPULATION DISCHARGING
TO POTW'S
OO
o
UJ
CJ
o:
60
50
40 J
30
20
10
GAS
FIGURE III-l
OIL
PRINCIPAL FUEL
COAL
NUCLEAR
Principal Fuel Use by Number
16
-------
100
90
80
•=C
CS
o
LlJ
cs
Cd
UJ
a.
70
60
50
40
30
20
10 . .
OVERALL PLANTS
POPULATION DISCHARGING
TO POTW'S
GAS
OIL
PRINCIPAL FUEL
COAL
NUCLEAR
FIGURE III-2. Principal Fuel Use by Megawatts
-------
100 .
90
80
70
OVERALL DISCHARGING
POPULATION TO POTW'S
CO
C_3
o:
60
50
40
30
20
10
1910
1920 1930 1940, 1950 1960
YEAR PLANT BUILT
1970
FIGURE III-3. Year of Construction by Number
18
-------
100 .
90
80
5 70
3
-------
combustion process, followed by steam generation to convert
the heat first into mechanical energy and then to convert
the mechanical energy into electrical energy. The maximum
theoretical efficiency that can be obtained in converting
heat to work is limited by the temperatures at which the
heat can be absorbed by the steam and discarded to the
environment. The upper temperature is limited by the
temperature of the fuel bed and the structural strength and
other aspects of the boiler. The lower temperature is
ideally the ambient temperature of the environment, although
for practical purposes the reject temperature must be set by
design significantly above the highest anticipated ambient
temperature. Within these temperatures, efficiencies are
limited to about t»0 percent regardless of any improvement to
the machines employed. For any steam electric power
generation scheme, therefore, a minimum of 60 percent of the
energy contained in the fuel must be rejected to the
environment as waste heat
Fossil- fueled steam electric power plants produce electric
energy in a four-stage process, shown in Figure III-5. The
first operation consists of the burning of the fuel in a
boiler and the conversion of water into steam by the heat of
combustion. The second operation consists of the conversion
of the high- temperature, high-pressure steam into mechanical
energy in a steam turbine. The steam leaving the turbine is
condensed to water, transferring heat to the cooling medium,
which is normally water. The turbine output is conveyed
mechanically to a generator, which converts the mechanical
energy into electrical energy. The condensed steam is
reintroduced into the boiler to complete the cycle.
The theoretical water-steam cycle employed in steam electric
power plants is known as the Rankine cycle. Actual cycles
in power plants only approach the performance of the Rankine
cycle because of practical considerations. Thus, the heat
absorption does not occur at a constant temperature, but
consists of heating of the liquid to the; boiling point,
converting the liquid to vapor and superheating (heating
above the saturation equilibrium temperature) the steam.
Superheating is necessary to prevent excess condensation in
the turbines and results in an increase in cycyle
efficienty. Reheating, the raising of the; t€>mperature above
saturation of the partially expanded steam, is used to
obtain improvements in efficiency and again to prevent
excess condensation. Preheating of coriderisate to near
temperatures with waste heat, is also used for this purpose.
Condensers cannot be designed to operate ait theoretically
optimum values because it would require infinitely larger
equipment. All of these divergences from the optimum
theoretical conditions cause a decrease in efficiency and an
increase in the amount of heat rejected per unit of
20
-------
STEAM
TV)
FUEL INLET
BOILER
ASH OUTLET
TURBINE
BOILER FEED WATER
CONDENSER
GENERATOR
J
ELECTRIC
POWER
COOLING WATER IN
COOLING WATER OUT
FIGURE III-5
Process hlow Diagram
Steam Electric Power Industry
-------
production. As a result, only a few of the larger and newer
plants approach even the efficiencies possible under the
ideal Rankine cycle. Also, as a result of second law
limitations, modifications of the steam cycle of an existing
plant are not likely to result in significant reductions in
heat rejection.
Publicly-Owned Treatment Works (POTW)
The POTW process is broken down into three basic treatment
methods; primary, secondary, and tertiary. Primary
treatment consists of the removal of coarse materials,
settleable solids, oil and grease, floating material, and
the reduction of biological oxygen demand. Most POTW employ
secondary treatment which converts soluble and colloidal
organic material into settleable flocculant material that
can be removed by sedimentation. Secondary treatment which
consists of biological treatment, is often enhanced by the
addition of chemicals such as iron, aluminum salts, and
polymeric flocculants. The use of tertiary treatment
processes are still uncommon and include the removal of
chemical constituents not affected by primary and secondary
treatment. Tertiary treatment is intended to remove
chemicals which promote algae growth and unwanted aquatic
vegetation. A more detailed description of the POTW process
can be found in Section V.
The POTW receiving wastewaters from steam electric plants
vary in size and treatment process employed. Plant size is
determined by human population and industrial waste load of
the area served. Those contacted in this study ranged from
200,000 gpd to 350,000,000 gpd in size. Treatment methods
are determined by flow, waste load pollutant constituents,
economics, energy and removal requirements, and plant age.
There are a large number of wastewater treatment processes
in use whose application is related both to the
characteristics of the waste and the degree of treatment
required. These processes are shown in Figure III-6.
22
-------
ro
00
PRIMARY
TREATMENT
SECONDARY
TREATMENT-
TERTIARY
TREATMENT
SCREENING AND
6»n REMOVAL
i
EOUALIZATIOH MD
STOSACL
OR SEPARATION L
CHEMICAL 1
A001UON A«0 I
COAGULATION f
FlOTATIOd
SEDIMENTATION
-,
H
-
-
ACTUATED
SLUDGE
LAGOONS
FILTER
AERATED
LAGOON
j
-
H
~
^ COAGULATION
AND
SEDIMENTATION
1
FILTRATION
|
H CARBON
ADSORPTION
i
i ION
-
L
_
STA8LIZATIDN
BASIN
SEDIMENTATION
RECEIVING
WATERS
' CONTROLLED OR
' TRAXSPOPTtO
• DISCHARGE
FIGURE III-6. Uastewater Treatment Sequence
-------
SECTION IV
INDUSTRY CATEGORIZATION
INTRODUCTION
An evaluation of steam electric power industry stations
discharging chemical wastes to publicly-owned treatment
works (POTW) was necessary to determine whether
categorization and subcategorization would be helpful in the
preparation of effluent pretreatment standards for this
industry. Subcategorization was based on distinguishing
factors within groups of plants.
This method of subcategorization was also used and is
discussed in detail in the "Development Document for
Effluent Limitation Guidelines and New Source Performance
Standards for the Steam Electric Power Generating Category"
October 1974 (18) .
Standards will be established for each waste source and can
then be applied and utilized in the manner of a building
block concept. In the case of combined waste streams the
appropriate standards will be combined and weighted
proportional to stream flow. The eight waste types are
presented in Table IV-1.
The following were considered for industry categorization:
ager size, fuel, geography, mode of operation, raw water
quality, volume of water used, and pretreatment technology.
INDUSTRY CATEGORIZATION
The wastes of this industry have been divided according to
the individual waste source. Marked differences in type and
level of pollutants were observed in facilities with
different fuel type, boiler and pretreatment practice.
These differences were considered together with age, size,
geography, mode of operation, and feed water hardness in the
development of possible subcategorization.
FACTORS CONSIDERED
Age
Power plants discharging to the POTW tend to be older than
surface water discharging plants. In steam electric power
plants, individual generation units are often installed at
different times over a number of years. Newer units tend to
be thermally more efficient then older units and use less
fuel per killowatt hour of electricity produced. Because of
25
-------
fuel economics newer units generally tend to be used for
base load production while other units are employed as
peaking and cyclic units. Increased fuel efficiency may
reduce wastewater loads such as ash transport water, wet
scrubber water, etc.
Size
Although the size of steam electric power plants discharging
to POTW varies significantly, the basic process is common to
all facilities. Plant size was found to have little affect
on quantity of treated effluent. Plants discharging to
sanitary sewers tend to be smaller than power plants
discharging to surface water.
Fuel
Plants discharging to POTW were identified as burning all
three major fossil fuels, coal, oil, and gas. In contrast to
the entire population of steam electric plants in the U.S.
the majority of plants contacted in this study use gas as
fuel. Fuel-related wastes such as ash control transport
water and coal pile drainage, can contribute to wastewater
discharge. The presence of sulfur in the fuel may require
scrubbers. Therefore, the affect of different fuels on
certain processes and effluents is useful for
subcategorization.
Geography
Usually, steam power plants that discharge to the POTW are
located near or within municipal boundaries. Most of the
plants contacted were, in fact, situated in downtown areas.
Plants discharging to the sewers were located in nearly all
geographical regions of the United States. It is noted that
recent trends toward larger power generating stations, and
the institution of mine-mouth coal fed plants, have resulted
in increased rural plant construction and a reduced number
of municipally-located plants.
26
-------
TABLE IV-1
I. Condenser Cooling System
A. Once-Through
B. Recirculating
II. Boiler Water Pretreatment
A. Clarification
B. Softening
C. Ion Exchange
D. Evaporator
E. Filtration
F, Other Treatment
III. Boiler or PWR Steam Generator
A. Slowdown
IV. Maintenance Cleaning
A. Boiler or PWR Steam Generator Tubes
B. Boiler Fireside
C. Air Preheater
D. Misc. Small Equipment
E. Stack
F. Cooling Tower Basin
V. Ash Handling
A. Oil-Fired Plants
1. fly ash
2. bottom ash
B. Coal-Fired Plants
1. fly ash
2. bottom ash
VI. Drainage
A. Coal Pile
B. Contaminated Floor and Yard Drains
VII. Air Pollution Control Devices
A. SO2 Removal
VIII. Miscellaneous Waste Streams
A. Sanitary Wastes
B. Plant Laboratory and Sampling Systems
C. Intake Screen Backwash
D. Closed Cooling Water Systems
27
-------
Mode of Operation
Many of the plants discharging into POTW are peaking and
cyclic stations. The type of pollutants generated from base
load, peaking, and cycling facilities are similar. The
quantity of effluent per unit of energy generated is
expected to be greated for peaking facilitites. Some of the
plants generate steam for sell and for electrical
production.
Raw Water Quality
Hardness would indeed affect operation by increasing the
frequency of regeneration of the deioriizer or recharging the
softener. The harder the raw water the more frequently the
deionizer anion and cation must be regenerated and the hot
lime and zeolite units have to be recharged. For cooling
tower intake, poor water quality would reduce the
concentration factor and thereby increase discharge flow and
pollutant loading.
Volume of Water Used
Water use varies greatly even among plants of approximately
the same size. For cooling water, flow is primarily
effected by the efficiency of the boiler system and
temperature across the condenser. For chemical wastewater,
factors such as a good maintenance procedure and raw water
quality are sometimes more important than the capacity of
the plant. For water short areas, the cost of the water
supply encourages water conservation. Volume of certain
water streams, such as boiler blowdown, can be greatly
affected by the amount of steam produced for seridout.
Pretreatment Technology
Of the plants discharging into POTW, many plants discharge
all of their wastewater effluent to municipal sewer systems;
others discharge only a portion. The extent of pretreatment
varies widely from no pretreatment to integrated plants
using systems such as equalization, neutralization, etc.
None of the facilities visited or contacted have
pretreatment facility equivalent to that required to achieve
BPCTCA.
28
-------
SECTION V
WATER USE AND WASTE CHARACTERIZATION
INTRODUCTION
Specific water uses and the waterborne wastes involved in
steam electric plants discharging into publicly-owned
treatment works (POTW) are described in this section, along
with other process waste materials. Process waters are
characterized as raw waste loads from specific processes
associated with the production of electricity. These are
generallly expressed as grams per megawatt hour (MWH) of
electricity generated. Water uses are given in terms of
liters per MWH, or as liters per day and waterborne waste
loads in mg/liter or grains per MWH. Based on available
data, it does not appear that the quantity of pollutants
discharged is directly proportional to electrical
generation. Factors such as raw water quality, maintenance
procedures, etc., can be just as influential in determining
chemical loadings as electrical generation. The waste
treatments used by both power plants and POTWs are
described, and amounts and types of waterborne waste
effluents after treatment are characterized.
PRINCIPLES OF OPERATION OF STEAM ELECTRIC POWER PLANT
In a steam electric power plant, thermal energy, produced by
rapid chemical combustjon or nuclear fission reaction, is
first tranformed into hi--,h pressure, high temperature steam,
and then to mechanical energy through expansion of the steam
in a turbine. The process can be divided into four stages.
The first operation consists of fuel combustion in the
boiler furnace to produce high pressure, superheated steam.
The steam is conveyed to a turbine where it is allowed to
gradually expand and cool in the various turbine stages to
convert the thermal energy into electrical energy via
mechanical energy. In the third operation the steam exiting
from the final stage of the turbine is condensed to water,
transferring the heat to a cooling medium, which is normally
water. Finally the condensed steam is reintroduced into a
boiler by a pump to complete the cycle.
The power cycle components can be divided into three
principal units:
o steam boiler
o steam turbine
o condenser
29
-------
Each of the cycle components provides an energy transfer and
transformation function necessary to convert the heat energy
into useful work. The following are descriptions of these
three units. A more extensive discussion on the principles
of design and operation of steam electric power plants can
be found elsewhere (14,16).
Boilers
All boilers use the same basic design, that is, they are
large multi-tube heat exchangers surrounded by a furnace.
The feedwater circulates within the tubes where it is
heated, vaporized, and superheated producing steam to drive
the steam turbine generators. Many different boiler
arrangements are used. Oil and gas-fired boilers somewhat
are simpler than coal-fired boilers because in most cases
liquid and gaseous fuels do not require the conveyers,
pulverizers, and ash collection equipment necessary in coal-
fired boilers. The boiler structure may be either exposed
or enclosed depending on local weather conditions, and is
usually very large to accommodate the large tube surface
areas required. Air heat€;rs, economizers, and other
sections of the boiler are us:ed to extract the maximum
amount of heat from the combustion gases before they are
discharged to the environment. This serves to increase the
boilers efficiency: the ratio of heat converted to steam to
the heat input value of the burning fuels. Modern power
boilers are able to achieve 85 to 90 percent efficiencies;
the remaining 10 to 15 percent of the input heat value is
discharged to the environment with the exhaust gases. This
loss is referred to as the "stack loss." Figure V-l shows a
typical boiler for a coal fired furnace.
Steam Turbine
The steam turbine consists of alternate rows of nozzles and
blades on wheels. Each row of nozzles and its associated
row of blades is called a turbine stage. As the steam
expands through the nozzles, the pressure decreases and the
velocity and specific volume increase. When the steam comes
in contact with the blades a part of the momentum (kinetic
energy) is transferred to the blades. The turbine shaft and
generator are caused to rotate and electricity is produced.
There are many different types of turbines and turbine
arrangements in use. Most of the turbines are of the
condensing type, discharging the steam from the last stage
at below atmospheric pressure. The efficiency of a turbine
is highly sensitive to the exhaust pressure (back pressure).
Turbines designed for once-through cooling systems are
generally operated at lower back pressures than that
designed for closed cooling systems.
30
-------
Oust
collector
Primary
superheater
Economizer
-\ -\ Air heater
Cinder
reinjsction
forced
aroftfon
(in back)
Induced
. draft fan
Figure V-]. Typical Boiler for Coal-Fired Furnaces
31
-------
In most turbine arrangements a portion of the steam leaves
the casing before the final stage. This type of turbine is
referred to as extraction turbine. The extracted steam is
used for feedwater heating purposes. In some turbines, a
portion of the steam is extracted from intermediate stages,
reheated in the boiler, and returned to the turbine or
another turbine as a means of improving overall efficiency.
Steam Condensation
Steam leaving the final stage of the turbine is condensed
into water in the condenser. This is essentially a very
large shell and tube heat exchanger designed to withstand
the high vacuums associated with modern steam turbine power
cycles. Heat is transferred from the exhaust steam to an
external cooling water system which may draw water from a
surface or underground source, or from the cooling tower.
There are two types of condensers; the single-pass and the
two-pass condensers. If all the water flows through the
condenser tubes in one direction, it is call a single-pass
condenser. If the water passes through one half of the
tubes in one direction and the other half in the opposite
direction, it is referred to as a two-pass condenser. A
single-pass condenser usually requires a larger water supply
than a two-pass condenser and generally results in a lower
temperature rise in the cooling water. Many condensers have
divided water boxes so that half the condenser can be taken
out of service for cleaning while the unit is kept running
under reduced loads. Condensers are periodically cleaned
mechanically as part of regular scheduled maintenance
procedures. Some plants employ continuous on-line
mechanical cleaning. Figure V-2 shows a typical single-pass
condenser.
WATER USE AND WASTE CHARACTERIZATION BY CATEGORY
The results obtained on power plant wastes from visiting
twenty-three plants and sampling eight do not differ
substantially from those reported in the "Development
Document for Effluent Limitations Guidelines and New Source
Performance Standards for the Steam Electric Power
Generating Point Source Category" (14).
The majority of the water used in steam electric generating
plants is for condenser cooling water. Lesser amounts are
used for boiler makeup water, bearing cooling water,
equipment cleaning, and other miscellaneous purposes.
Figure V-3 shows a typical Steam Electric process diagram
with wastewater sources.
Waste discharges can be classified under two categories:
continuous discharges, and intermittent discharges. Wastes
32
-------
co
co
1
/I
OUT
(HEATED)
STEAM FROM TURBINE EXHAUST
0
CONDENSATE
TO PUMP
\
0 (
) 6
ft
0
COOLING WATER IN
(COLD)
FIGURE V-2. Single-pass Condenser
-------
are produced on a continuous basis from the following (if
applicable): cooling water systems, ash handling systems,
wet-scrubber air pollution control systems, and boiler
blowdowns (some of the streams can be intermittant). Waste
discharges are produced intermittently by boiler water
treatment operations such as ion exchange, filtration,
clarification, and evaporation. Intermittent discharges are
also produced during miscellaneous equipment cleaning
operations and from sanitary and laboratory wastes.
The following discussion is a categorization and description
of water uses and waste discharges within typical generating
plants. Some of the following has been summarized from
Reference 11, which contains a more detailed discussion of
water use and waste characterization. Data obtained from
the site visits and sampling program are discussed below.
CONDENSER COOLING WATER
The condenser cooling systems can be classified as (1) once-
through, or (2) recirculating. Of the twenty-three plants
surveyed, seven use once-through, thirteen use
recirculating, one plant is a hybrid, and two plants operate
only at peak periods and are therefore not included in this
section.
Once-Through Systems
In areas where large amounts of water are available from
natural sources, the simplest method of condensing steam is
to withdraw water from the source, pass it through a
condenser, and discharge it back into the same source at a
higher temperature. Biocides such as chlorine or
hypochlorites are usually added to systems of this type to
minimize biological growth within the condenser. Of the
plants surveyed in this study, none were observed to
discharge once-through cooling systems to POTW.
Recirculating Systems
Condenser cooling water can be recirculated within the
plant. This is accomplished by providing some sort of
artificial cooling device, such as a pond or a cooling
tower, to cool the cooling water by evaporating a portion of
it before recirculating it back to the condenser. Ponds are
used only where large areas of inexpensive land are
available, since a large plant may require over 1,000 acres
of pond surface. Cooling towers may be either of the wet or
dry types, and are used where sufficient land for ponds is
unavailable or too expensive. Since all cooling devices
(except dry cooling towers, which are rare) transfer the
process waste heat to the atmosphere by evaporation.
-------
CO
en
RAW
i
i
,
i
i
- WASTE- •
W WATER
CHEMICALS
1
WATER
'• TREATMENT
i
WASTE- *
WATER
CHEMICALS
— i *
BOILER TUBE
CLEANING, FIRE-
SIDE & AIR'
PREHEATER
WASHINGS
FUEL—*
COMB'N AIR--«
BOTTOf
ASH
'
1
HATER FOR '" ""f ™
PERIODIC CLEANING !
t
1
. FLY ASH •VWNkXXXX CHEMICALS
COLLECTION
_ __^ AND/OR S02
STEAM f SCRUBBING-
iitfln DEVICE
f l^^l
L FLUE 1 [URBINE 1 .U'A-TU'ATCr •
I WES . I GENERATOR ! J ,
f — --^^^__^^ i
STEAM -1 ; CHEMICALS
GENERATING * CK
BOILER S" X * +'. • ONCE THROUGH
/ \ " COOLING WATFR
1 ^ 1- f rrvmr-,-rc V. '• RECIRCULAT ING COOLING WATER
SLOWDOWN ]• I CONDE.NSER * -' ' ' ' "" " ' "
\ /*1 * i ^
\. j/ , , \ COOLING TOWER /
DISCHARGE TO ^ \
WATER BODY * \ U^CHEMICALS
CONDENSATE WATER, \ f,*
* MAKEUP WATER ^V 'f
1* ' ••
+
BLOWDOWN
«NS\V\\\CHEHICALS
WATER
SANITARY WASTES
LABORATORY & SAMPLING
WASTES, INTAKE SCREEN
BACKWASH, CLOSED COOLING
WATER SYSTEMS, CONSTRUC-
TION ACTIVITY
LEGEND:
LIQUID FLOW
GAS & STEAM FLOW
\\XOl\\.
\\s\\v\
CHEMICALS
OPTIONAL FLOW
WASTEWATER
FIGURE V-3 - Fossil-Fueled Steam-Electric Power Plant - Typical Flow Diagram
-------
Additional water must be added to the system to make up for
these losses due to evaporation, drift and blowdown.
Various chemicals are added to recirculating cooling systems
to prevent biological growth in cooling towers and to
control scale accumulation and corrosion in condensers.
These include biocides such as chlorine, hypochlorites, and
organic chromates; corrosion inhibitors such as organic
phosphates, sodium phosphate, chromates, and zinc salts; and
fungicides.
Wastes that may be discharged to a POTW from recirculating
cooling systems originate from cooling tower blowdown.
Blowdown is the discharge from the cooling tower of a
portion of water either constantly or intermittently to
prevent the concentration buildup of salts that may form
scale deposits within the condenser. This blowdown will
contain calcium, magnesium, and sodium cations in
combination with carbonate, bicarbonate, sulfate, and
chloride anions. Additionally, various amounts of the
conditioning chemicals will be present. Sulfuric acid is
also used in closed cycle cooling systems.
The rate of blowdown can be estimated by the use of the
following equation: (Ref. 1)
B = Ev - D(01)
C-l
where: B is the blowdown rate; Ev is evaporation
rate; D is drift losses; and C is the
cycles of concentration defined as the
ratio of the concentration of a critical
chemical species in the blowdown to that
in the makeup water.
The evaporation rate (Ev) from cooling towers averages about
1.5 percent of the cooling water flow for every 10°C rise in
cooling water temperature as the water passes through the
condensers. The drift rate (D) for new cooling towers is
about 0.005 percent of the cooling water flow for mechanical
draft towers, and about 0.002 percent for natural draft
towers (Reference 1). Cycles of concentration (C) is an
expression of the buildup of any constitutent in the cooling
water system from its original value in the makeup water.
In practice, C is usually between 4 and 6. For very high
quality makeup water, C may be as high as 15, and for very
saline water, C may be as low as 1.2-1.5.
Figure V-4 shows typical once-through, and recirculating
cooling system flow diagrams. Figures V-5 and V-6 show two
types of wet cooling towers.
36
-------
Water Use
Once-Through Systems. Seven of the twenty-three plants
surveyed use a once-through cooling system to remove the
waste heat from the process. The water usage in liters per
MWH at the plant studied is given below:
Plant No.
9369
7420
9163
6387
8356
6421
6294
Water Usage Liter/MWH
9.33x104
3.3x104.
1.18x105
3.68x105
2.57x105
2.24x105
8.28x104
A similar range of water use for once-through condenser
cooling of Ixl05_ to 3.5xl05_ liters per MWH was reported
elsewhere (14).
The water use data were plotted against power generation
rate to determine the effect of that function on the
quantity of water used. (See Appendix A) . The results of
the statistical analysis suggest that, based on the
available data, there is at best a poor correlation between
water use for once-through cooling system and generation
rate for plants in this study. Although the overall trend
suggests that the water use may decrease slightly with
increasing generation rate, this is not substantiated by the
statistical analysis of available data. One explanation for
such phenomena is that cooling water pumps are in on-or-off
modes. For a facility with two cooling water pumps,
production would have to be less than half of the design
capacity before the cooling water flow would decrease. For
some facilities, the pumps are always kept in operation to
lessen pump maintenance. Another explanation is the change
in temperature across the condenser between stations.
Recirculating Systems. Thirteen of the 23 plants surveyed
use a recirculating condenser cooling system to remove waste
heat from the process. Waste heat is removed from the
cooling water by means of evaporation and blowdown. Water
usage in liters per MWH at the plants studied is given
below:
37
-------
EXHAUST STEAM
FROM TURBINE
SURFACE
WATER •
CONDENSER
DISCHARGE TO
-^SURFACE WATER
CONDENSATE
EXHAUST STEAM
FROM TURBINE
EVAPORATION
CONDENSER
COOLING
TOWER
MAKEUP
WATER
CONDENSATE
COOLING WATER
FIGURE V-4 . Once-Through (top) and
Reelrculating (bottom) Cooling
38 Systems
-------
WATER IN. fr
SPRAY ELIMINATOR
PUMP
=[
6
AIR IN
FILL
AIR IN
FIGURE V-5 . Diagram of Wet Induced-Air Cooling Tower
39
-------
HOT WATER
DISTRIBUTION
DRIFT
ELIMINATOR
FILL l^-^-c-— —
AIR
INLET
COLD WATER
BASIN
FIGURE V-6
Natural-Draft Wet Cooling Tower
(Counter-Flow)
40
-------
Plant No. Water Usage Liters/MWH
9600 1.64x101*
9650 3.21x103
9369 1.80x101
9371 3.44x103
8816 2.14x102
9585 8.39x102
8696 5.6x10^
8135 1.41x104.
8392 1.76x104
6293 4.1x103
7308 1.8x103
8875 2.36x103
8231 2.53x103
The water usage data was plotted on log-log paper versus the
production rate to determine the effect of the plant size on
the quantity of water used. (See Appendix A). The results
of the statistical analysis suggest that, based on the
available data, there is no correlation at all between water
use for recirculating condenser cooling and production rate.
Although the overall trend suggests that the water use may
increase slightly with production rate, this is not
substantiated by the statistical analysis. An explanation
for such phenomena is that the blowdown from a recirculating
cooling system is not only a function of electrical
generation capacity, intake water quality, geographical
location, and governmental regulations, but also of other
factors.
Raw Waste Load
The raw wastes from the recirculating condenser cooling
process include:
o Chemical additives to control growth organisms such
as algae, fungi, and slimes;
o Chemical additives to inhibit corrosion; and
o Concentrations of solids, metallic salts, and
acidic and alkaline ions due to evaporative loss.
Initially, all of these wastes are waterborne, but some,
such as suspended solids and metallic salts settle and must
be removed from cooling tower basins periodically. Also,
the settling of metallic salts cause scale formation on
condenser tubes and may be removed occasionally usually with
an acid solution. The remainder of the raw wastes are
either removed from the wastewater by treatment
technologies, or are discharged to the sewer systems.
41
-------
Waterborne wastes are shown in Table V-1 for plants 8392,
8231, 9650, 8135, 8696, and 7308 from which data was
obtained. The waterborne raw waste values indicate that the
major components by weight in recirculating condenser
cooling streams are dissolved and total solids, and chemical
oxygen demand.
Wastewater Treatment
None of the plants using once-through condenser cooling
systems discharge to POTW. Thirteen plants using
recirculating condenser cooling systems discharge cooling
tower blowdown to the POTW. None of the thirteen plants
discharging recirculating condenser cooling wastewaters to
POTW employed any treatment technologies. Wastes were
discharged directly to the POTW without treatment.
Effluent Waste Loads
Information was not obtained on the composition of
recirculating condenser cooling wastes after treatment since
no plants performed any treatment before discharge to the
POTW. Waterborne wastes present in the recirculating
condenser cooling discharge to the POTW can be found in
Table V-1.
WATER TREATMENT
To compensate for steam losses through leakage and boiler
blowdown, additional water must be added to the boiler.
Particularly in high-pressure boilers, this water must be of
extremely high quality, and must undergo extensive
treatment. If the water is taken from a municipal supply,
treatment may consist of dual media filtration, reverse
osmosis filtration, and demineralization. Older, low-
pressure steam plants may treat boiler makeup water solely
with evaporators. Some steam electric plants treat water by
clarification and softening followed by demineralization. A
more detailed description of those treatment schemes and
their associated wastes follows.
Clarification is a process for removing suspended solids.
After water is lime treated, clarification can be used to
remove dissolved solids. Chemical coagulants such as alum,
ferrous sulfate, ferric sulfate, sodium aluminate, and
polyelectrolytes are added to the water to aid the
agglomeration of dissolved impurities by adsorption,
absorption, and sedimentation. The particles are allowed to
settle, and the clarified water is drawn off and filtered.
Softening is used in conjunction with clarification to
precipitate calcium and magnesium. Clarification and
softening wastes consist of sludges and filter washes.
-------
Table V-l . RAW WASTE FLOWS AND LOADINGS CONDENSER-COOLING SYSTEMS
Pl-'NT NO.
UAOTfWAUR SOURCE
FL04
PAR/SOFTER
LC1 j r
?ro-iide (Bromate)
COO
Ch rori un
r h ro- i jri*6
Copper
C/-jn»<)« (Total)
I rcn
Nic>el
Cii arc Grease
Prosphate 'Total)
Total Dissolved Solids
Total Sjspended Solids
Total Solids
Surfactants
Zinc
8392
Cooling Tower
RlDJtdO*IL_
L/Oay
238455.0
mg/1
1.4Z
9.8
4.9
3.3
0.02
0.02
0.48
0.03
1.0
3.25
886.0
2.9
889.0
1.5
L/I1WH
745.81
g/MWH
10.4
7.3
3.65
2.46
0.01
0.01
0.35
2.43
660.78
2.16
660.8
1.11
8135
Cooling Tower
Slowdown
L/Day
53959.0
7.09
102.91
0.02
0.004
0.014
7.43
943.45
3.89
946.73
0.48
L/HWH
321 .51
g/HHH"
2.28
33.14
0.001
0.005
2.39
303.74
1 .25
304.85
0.15
8696
Cool-ing Tower
Slowdown
L/Day L/MwII
217788.9 18.03
rng/l
2.2
25.2
<0.02
0.012
0.35
<0.005
0.32
<0.03
2.4
0.06
2860
33
2893
0.09
g/MWH
0.39
0.45
0.0002
0.002
0.005
0.043
0.001
51.5
0.59
52.19
0.001
7308
Cooling Tower
Slowdown
L/Day
(1)
mg/1
5.7
64
1.39
0.76
0.7
0.025
1.63
0.04
1.9
0.95
5111
59
5170
0.7
L/KUH
(1)
g/MWH
(1)
8231
Cool 1 ng Tower
L/Day
58Q.365.4
mg/1
0.009
O.l0
0.15.
0.03
1.0
8.3
0.02
L/MHH
555.37
g/MWH
0.004
0.06
0.08
4.0
0.01
9650
Cooling Tower
Blowdown
—T/TTTn L/M^'M
1067370.0 1292.2
ng-/T •
0.07
0.044
0.05
0 29
0.03
4.0
0.08
16.0
2.04
g/H»H
0.09
0.05
0.06
0.37
5.16
0.1
20.67
2.63
co
(1) Flow could npt be measured.
-------
Clarifier sludge consists of either alum or iron, hydroxides
plus suspended and dissolved impurities, softening sludge
consist of calcium carbonate and suspended and dissolved
impurities, and some softening sludges may also contain
magnesium hydroxides. Filter washes contain suspended
solids either carried over from the clarifier or contained
naturally in the unclarified water.
Demineralization (ion exchange) is a process that removes
mineral salts by adsorption on a resin. Two types of resins
exist: cationic (for the removal of cations) , and anionic
(for the removal of anions) . These resins may be used
separately, (one following the other) , or they may be
combined in a mixed-bed (demineralizer) , After a period of
use, ion exchange resins become saturated with ions, and
must be regenerated. Anionic resins are regenerated with
sodium hydroxide solution followed by water rinse to remove
excess sodium hydroxide. The regeneration waste will have a
high pH and will contain the exchanged anions, which are:
sulfate, chloride, nitrate, and phosphate. Cationic resins
are regenerated with sulfuric acid, and the regeneration
waste from those units will have a low pH and will contain
calcium, magnesium, potassium, and sodium ions.
Evaporation is simply a distillation process for the removal
of impurities. Evaporators usually consist of a horizontal
vessel heated by a waste heat source, which is usually
exhaust steam from the turbines. Steam from the evaporation
of water in the vessel is drawn off and condensed in an
external condenser. To prevent a concentration buildup of
salts which contribute to scaling problems within the
vessel, a portion of the water is drawn off as blowdown.
This blowdown has a high pH, and contains the same chemicals
present in the raw water feed, which have been concentrated
by a factor of three to five. Calcium carbonate and calcium
sulfate precipitates may also be present in the blowdown if
present in the water feed in sufficiently high
concentrations. Phosphate is sometimes added to the raw
water feed to lessen the precipitation of calcium salts
Reverse osmosis is a process used by some plants to remove
dissolved salts. The technique consists of forcing water
through a semipermeable membrane under a pressure greater
than the osmotic pressure of the dissolved salts. The salts
are concentrated on one side of the membrane and the
purified water is collected on the other. The concentrated
salt solution (brine) is discharged as a waste.
Chemical Additions. After treatment, various chemicals are
added to the boiler makeup water. These include hydrazine
or sodium sulfite (to remove dissolved oxygen) , sodium
-------
RAW WAHR
l\C 1 D
CAT1M
^-r-^
,,
DhGASI-
FILR
!
CAUSTIC
AN I OK
WASTl
DEIONIZfD WATER
WAS IF
Two-Bed Ion Fxchanqe Oerrnneral i?er !/'ith Deoasifier
* MIXEi)
RLSIK
ACID
WASTf
DEIONIZED WATER
Mixed-Bed Ion Exchange Demineratizer
PRCiSURF
VC5SEL
FEED
WATER
HIGH PRESSURE
PUMP
SEMI
PtRMEABLE
MEMBRANE
•PERMEAT
(PRODUCT
WATER)
REGULATINCi
VALVt
CONCENTRATE (WASTEWATER)
Reverse Osmosis Membrane Filter
Finure V-7. Commonly Used Make-Up Water Treatment Methods
45
-------
RAW WATER
SLOWDOWN
WASH
i
•
FILTER
1
WASTEWATER
FILTERED
WATER
S^>CL
J
DEIONIZED
WATER
WASTEWATER
Lime Softening, Filtration & Sodium Zeolite Water Treatment Process
PRE-
TREATMENT
FEED
WATER
CONDENSER
JTWiT"
COND.
EVAPORATOR
I
TREATMENT
CHEMICALS
Evaporation Process
U
CLARIFIER
RAW WATER
CLEAR _
WATFR
CONDENSED
BOILER FEED
EVAPORATOR
SLOWDOWN
SLUDGE
Clarification Process
FIGURE V-7. Commonly Used Water Treatment Methods
(Continued)
46
-------
phosphate (to prevent scale formation by precipitating
calcium and magnesium salts), and sodium hydroxide, ammonia,
morpholine, or cyclohexylamine (to control pH).
Figure V-7 shows six (6) commonly used water treatment
methods.
Water Use
Boiler Makeup Water. Sixteen of the twenty-three plants
surveyed provided information on their boiler makeup water
usage. The water use in liters per MWH at the plants
studied is given below.
Plant No. Water Usage Liters/MWH
9650 36.76
9369 79.56
9371 36.73
8816 29.93
9585 1.59x102
8696 4.15
8135 4.03x10.1
9163 1.32x102.
6387 1.08x10.3
8356 1.78x102^
8392 1.19x10.3
6293 6.81
7968 3.116x102
6421 4.58x101
6294 1.06x102.
8231 5.43x101
The water usage data was plotted on log-log paper versus the
production rate to determine the effect of the plant size on
the quantity of water used. The results of the statistical
analyses suggest that, based on the available data, there is
a fair correlation between water use for boiler makeup and
production rate. The overall trend appears to be a decrease
in water usage with increasing production rate.
Demineralizer Reqenerant Wastes. Thirteen of the twenty-
three plarits surveyed presented information on their
demineralizer system regenerant water usage. The water
usage in liters per MWH at the plants studied is given
below:
Plant No. Water Usage, Liters/MWH
Regenerant
9650 65.75
9369 17.51
47
-------
9371 27.55
9585 3. 24x102^
8696 U.56
9163 18.38
6387 13.46
8356 4.22x102
8392 7.1
6293 9.01
8875 11.35
6421 39.23
6294 5.69
The water usage data was plotted on log-log paper versus the
production rate to determine the effect of plant size on the
quantity of water used. The results of the statistical
analysis suggest that, based on the available data, there is
no correlation at all between water use for the regeneration
of demineralizer system and the production rate. This
result is not unexpected,, since the regenerant water is a
function of intake water quality, frequency of regneration,
size of individual demineralizer plants, etc,
Raw Waste Load
The raw wastes from the water treatment process include:
o Mineral salts, suspended solids and other
constituents removed from the raw water supply.
o Chemicals used by the water treatment units.
Of the twenty-three plants visited, three use hot lime-soda
ash softening and zeolite ion exchange, two use hot lime-
soda ash softening, filtration, and zeolite ion exchange,
two use reverse osmosis and deionization, twelve use cation-
anion ion exchange, one uses deionization and evaporation,
one uses hot lime-soda ash softening, zeolite ion exchange
and evaporation, and one us€»s deionization and evaporation.
Solid wastes are not generated in large quantitites during
the regeneration process. The major source of solid wastes
are calcium carbonate and magnesium hydroxide from the lime-
soda ash softening processes. Waterborne wastes for plants
in terms of grams per MWH are given in Table V-2.
Wastewater Treatment
Fifteen plants discharge water treatment waste streams to
POTW. Five of these plants practice some type of
pretreatment before discharge. Plant 6293 uses lime
settling; plant 9369 uses equalization and neutralization;
plant 7308 uses equalization, neutralization, and oil
48
-------
skimming; plant 8696 uses equalization, settling, and oil
skimming and plant 7116 uses equalization, neutralization,
and settling.
Effluent Waste Loads
Table V-3 shows the composition of pretreated wastewater
discharge to the POTW in terms of concentration and waste
loads for plant 6293.
BOILER SLOWDOWN
To prevent the accumulation of calcium and magnesium salts
on the internal boiler surfaces, phosphates are usually
added to precipitate the salts. The precipitate is removed
continuously or intermittently by withdrawing a portion of
the boiler water as blowdown. Blowdown wastes have a high
pH, may, depending on boiler pressure contain high dissolved
solids concentration. Blowdown from boilers treated with
phosphate may contain hydroxide alkalinity and will contain
phosphate, and blowdown from boilers treated with hydrazine
will contain ammonia and depending on boiler pressure, may
also contain sulfite.
Raw Waste Load
The raw wastes from boiler blowdown contain:
o Products of chemical additives to remove oxygen;
o Chemical additives to prevent scale or inhibit
corros ion; and
o Concentrations of dissolved solids and other
constitutents present in the boiler feedwater.
Boiler blowdown does not generate large quantities of solid
waste. Sludge, consists principally of precipitated iron,
calcium and magnesium salts, where phsophate treatment is
used and is maintained in a fluid form and removed by the
blowdown. Blowdown may contain ammonia when treated with
hydrazine.
Waterborne wastes for two plants in terms of grams per MWH
are given in Table V-U.
The waterborne raw waste values indicate that the major
components by weight in boiler blowdown streams are
dissolved solids, chemical oxygen demand, and total
phosphates.
Wastewater Treatment
-------
Table V-2 RAW WASTE FLOWS AND LOADINGS - WATER TREATMENT
PlAKl NO.
VASTEVATCR 10UHCE
tLO»
PARAMETER
COOj
BroMlde (Bronatt)
COO
CfcromiiiM
Chronlue'6
Copper
Cja.ilde (Tot a
0.02
0 005
0.02
0.005
0 07
O.OJ
1.0
0.05
174
1.0
174
0.011
0.02
I/HUH
(1)
9/Ngt,
(387
Blo«do.n _.
WCdr
17166.7
*9/l
1.8
.---
?OQ
0.11
0.004
0.15
0.014
10.4
0.09
1.0
1004
9440
10444
0.32
47.69
9/MWH
0.08
9 53
0.005
0.007
0.0006
0.49
0.004
47.88
450.2
98.08
o.ots
6387
— , LLoiiUJiiL __„
L/Day
7570
•9/1
10.4
cr I
0.1
0.007
0.12
0.005
0.44
0.25
1.0
22980
44
23024
0.09
252 33
9/HWII
2.62
Ml. 55
0.0?
0.001
0.03
0.0011
0.11
0.06
5798.6
11.1
5809.7
0.02
6387
I/Day
408'S
•9/1
15.2
•
7Ł.C
0.02
0.005
0.02
0.006
0.33
0.03
1.0
6.20
2228
93
2321
0.11
L/
113.
55
9/H.rt
1 .
72
:
O.OJO'.
0 002
o.ocot
0.
043
0.
252.
105.
263.
7
9
6
t
0.
01
82)1
Denlncrallzer
Rpgpncr tlon
1/04X
227IU
m9/l
0.07
0.006
0.02
1.26
0.14
13.2
31
0.06
L/niH
21.73
g/MUH
C.001
0.0001
0.02
0 003
0 28
0.63
0.001
8231
'\-P'J
dn.e
IW/I
0.02
0.005
0.02
0.03
0 03
8 2
6.8
0.38
0.01
U'.'M
2,46
Q/ttlH
0.02
O.OU
0.0009
9650
Soqpfif rat Ion
il'J>/
1105 T.
*'.l\
0.2
0 01
0.59
9.46
0.2
1 U
U.7
0.21
I /'•-••
ti e
ured.
-------
Table V-2. RAW WASTE FLOWS AND LOADINGS - WATER TREATMENT
(CONTINUED)
PLANT NO.
WASTEWATER SOURCE
FLOU
PARAMETER
BOD5
Bromide (Bromate)
COO
Chromium (Total )
Chromi um+6
Copper
Cyanide (Total)
Nickel
Oil and Grease
Phosphate (Total)
Total Dissolved
Soli,ds
Total Suspended
Solids
Total Solids
Surfactants
Zinc
8696
Cation Demin-
e r a 1 i z e r
X. R e q e n e ra t i o n
L/Day L/MWH
\J1355{21 0.94
mg/1 q/MWH
6.0 0.005
0.03 0.00002
13.6 0.012
0.07 0.00006
0.008 Neg.
1.3 0.001
v-0.005
i fi 9 n n n Q
I . u c u . uuy
<0.03
<1 .0
14.0 0.013
3960 3.72
30 0.03
3990 3.75
<0.01
0.03 0.00002
7308
Evaporator
Bl owdown
L/Day L/MWH
(!) (1)
mg/1 g/MWH
5.16 (1)
20.8
0.08
0.036
2.61
0.028
09 9
. C-L.
<0.03
1 .9
12.6
2532.66
14.5
2547.16
0.44
7308
Zeol i te
Softener Back-
Wash
L/Day L/MWH
4920.5(2) 0.29
ing /I g/MWH
27 0.008
0.07 Neg
384 0.11
<0.02
0.016 Neg
0.13 Neg
<0.005
^*nc7 - _ - - -
0.20 0.00005
1.4 0.0004
0.5 O.O'OOl
28066 8.21
18.4 0;005
28084.4 8.22
0.021 Neg
0.08 0.00002
(1) Flow could
(2) Discharges
not be measured
1 hour per day
51
-------
Table V-3. EFFLUENT FLOWS AND LOADINGS - WATER TREATMENT
PLAHT MO.
WASTEWATER SOURCE
FLOW
PARAMETER
B005
Bromide (Bromate)
COD
Chromium
r h r Q m i nm + 6
Copper
Cyanide (Total)
Iron
Nickel
Oil and Grease
Phosphate (Total)
Total Olssolved Solids
Total Suspended Solids
Total Solids
Surfactants
21nc
6293
Lime Softener Effluent
L/Day L/MWH
1.6351.2 68.13
mg/1
1.5
5.9
0.02
0.026
0.02
0.005
1.23
0.03
1.0
152.0
245.0
397.0
0.011
0.2
g/MWH
0.1
0.4
0.001
0.001
0.001
0.08
10.35
16.69
27.04
0.0001 ,
0.0001
8696
Diluted Demineral izer
L/Day L/MWH
54504 4.57
mg/1
34.0
- - - -
81 .0
0.05
.02
0.85
0.09
9.36
25.02
0.04
g/MWH
0.0007
0.0001
0.020
0.001
0.13
0.35
0.0005
-------
Thirteen plants discharge boiler blowdown to POTW, of which,
three practice some type of pretreatment. Plant 9369 uses
equalization and neutralization, plant 7116 uses
equalization, neutralization and settling and plant 7308
uses equalization, neutralization and oil skimming.
Effluent Waste Loads
Although recovery of the blowdown is not practiced in most
cases, this option should be considered since the blowdown
water is almost always of better quality than the make-up
water.
Information was not available on treated waste streams from
boiler blowdown.
MAINTENANCE CLEANING
Boiler Tubes. Boiler tubes must be cleaned occasionally to
remove accumulations of scale. A multitude of cleaning
mixtures are used to accomplish this purpose. These
include: alkaline cleaning mixtures with oxidizing agents
for copper removal, acid cleaning mixtures, alkaline
chelating rinses, organic solvents, and proprietary
solvents. Wastes from these cleaning operations will
contain iron, copper, zinc, nickel, chromium, hardness, and
phosphates. In addition to these constituents, wastes from
alkaline cleaning mixtures will contain ammonium ions,
oxidizing agents, and high alkalinity; wastes from acid
cleaning mixtures will contain fluorides, high acidity, and
organic compounds; wastes from alkaline chelating rinses
will contain high alkalinity and organic compounds; and
wastes from most proprietary processes will be alkaline and
will contain organic and ammonium compounds.
Boiler Fireside Cleaning. The fireside surface of boiler
tubes collects airborne dust, fuel ash, and corrosion
products. These materials are removed from time to time
with high-pressure hoses. Alkaline chemicals may be used
for safety and neutralization.
Wastes from this operation will be more or less acidic
depending on the sulfur content of the fuel, and will
contain hardness, suspended solids, iron, nickel, zinc, and
other metals.
Air Preheater Cleaning. Air preheaters are used to heat
ambient air that is used for combustion, and collect soot
and fly ash. High-pressure hoses are used to remove these
materials. The wastes from this operation will be more or
less acidic, depending on the sulfur content of the fuel,
and will contain suspended solids, magnesium salts, iron.
53
-------
Table V-4.
RAW WASTE FLOWS AND LOADINGS - BOILER SLOWDOWN
PLANT NO.
WASTEWATER SOURCE
FLOW
PARAMETER
BODg
Bromide (Bromate)
COD
Chromi urn (Total )
Ch romi um+6
Copper
Cyanide ( lotal )
I ron
Nickel
Oil and Grease
Phosphate (Total)
Total Dissolved Solids
Total Suspended Solids
Total Solids
Surfactants
Zinc
6293
Boiler Slowdown
L/DAY
17030.4
mg/1
11.7
157.0
0.02
0.007
0.19
0.005
1.4
0.03
2.2
18.7
1405.0
2.7
1407.7
0.05
L/MWH
70.96
g/MWH
0.83
11.1
0.0001
0.01
0.1
0.15
1 .32
99.7
0.19
99.9
0.003
8392
Boiler Slowdown
L/DAY
1665.4
mg/1
10.8
2.0
0.02
0.009
0.06
0.014
0.08
0.03
1 .0
19.8
118.0
6.9
125.0
0.02
L/MWH
5.20
g/MWH
0.06
0.000]
Neg.
0.0003
Neg.
0.0004
0.1
0.61
0.036
0.65
0.0001
8231
Boiler Slowdown
L/DAY
5715
mg/1
0.02
0.005
0.02
0.03
0.03
14.8
0.05
31
0.01
L/MWH
5.47
g/MWH
0.08
0.17
9650
Boiler Slowdown
L/DAY
(1 -
mg/
0.02
0.005
0.0?
0.03
0.03
5.3
0.05
8.3
0.02
L/MWH
(1)
gJHWH
Neg.
en
(1) Flow could not be measured.
(2) pH values for plants: #6293=12.0, #8392-10.6, #8231=9.0, #9650=9.5
-------
copper, nickel, and chromium. Vanadium may also be present
if the plant is oil-fired.
Stack Cleaning. High pressure water is used to clean fly
ash and soot from stacks. The frequency that this cleaning
is required is dictated by the fossil fuel used. Wastes
from this operation may contain suspended solids, metals,
oil, and high or low pH values.
Cooling Tower Basin Cleaning. Deposits of carbonates on the
bottoms of cooling towers and growth of algae on cooling
towers are removed occasionally with water. The wastes
contain suspended solids as a primary pollutant.
Miscellaneous Small Equipment. Occasional cleaning of plant
equipment such as condensate coolers, hydrogen coolers, air
compressor coolers, and stator oil coolers is performed.
Detergents, wetting agents, and hydrochloric acid are often
used during cleaning. Wastes from these operations will
contain suspended solids, metals, oil, and low or high pH.
Raw Waste Load
The raw wastes from maintenance cleaning consist of the
cleaning solution and the material removed from the
equipment. Boiler fireside, air preheater, and boiler tube
cleaning account for most of the wastewater generated in
maintenance cleaning. No plants were performing maintenance
cleaning during the time of our visitation and sampling.
Typical waterborne wastes are shown in Table V-5 for
wastewaters from air prehater, boiler fireside, and tube
cleaning. This information was obtained from Reference 14.
Information was not available on cooling tower basin and
stack cleaning wastewaters.
The major components by weight in the three cleaning waste
streams are dissolved solids, hardness, metals, chlorides
and sulfates.
Water Use
At infrequent intervals, certain power plants components
such as condensate coolers, oil coolers, compressors,
boilers, etc., are chemically cleaned with a solution of
hydrochloric acid, or a detergent. Typical flow rates are
summarized below.
Waste Waste Typical Flow
Stream Flow or Volume Frequency or Volume
Maintenance Cleaning
55
-------
Boiler Tubes 3-5 Boiler Once/7 Months- 1 boiler per
Volumes once/100 mos. 1-2 hours
Boiler Fire- 24-720xl03gal 2-8/yr 300,000 Gal
side
Air Preheater U3-600xlQ3gal 4-12/yr 200,000 Gal
Misc. Small No Date
Equipment
Stack No Data
Cooling Tower No Data
Basin
Wastewater Treatment
Plant 7308 discharges maintenance cleaning wastewater to a
POTW through an industrial wastewater collection system and
this was the only plant surveyed which disposed of cleaning
wastewaters in this way.
Effluent Waste Loads
Information was not obtained on the composition of
maintenance cleaning wastes after treatment.
ASH-HANDLING SYSTEMS
One of the products of the combustion of coal and oil in
electric utilities is ash. Ash which falls to the bottom of
the furnace is called bottom ash; ash which leaves the
furnace with the flue gas is called fly ash. Fly ash is
usually collected from coal-fired units with electrostatic
precipitators and from large oil-fired units with cyclones.
The function of ash-handling systems is to remove
accumulated bottom ash and fly ash.
Two types of ash-handling systems exist: dry systems and wet
systems. Dry systems use a mechanical conveyance devices
for the transport of ash and are not a source of liquid
wastes. Wet systems use water for the transport of ash, and
in many cases, discharging it into a settling pond or basin.
Wet systems are either of the open type or the closed type.
Open systems discharge supernatant from the settling basin
into either a receiving water or a POTW. Closed streams
recycle the supernatent back to the ash-transporting sluice
for reuse. Figure V-8 shows a flow diagram for
recirculating bottom ash system. Periods of extended
56
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Table V-5. RAW WASTE FLOWS AND LOADINGS - MAINTENANCE CLEANING
No. of Plants
Wastewater Source
Cleaning Frequency
(#/yr)
Flow (1000 liter)
Parameter (Kg)
BODc
b
Bromide (Bromate)
COD
Chromi urn (Total )
.. . +6
Cnronn urn
Copper
Cyani de (Total )
I ron
Nickel
Oil and Grease
Phosphate (Total)
Total Dissolved
Solids
Total Suspended
Solids
Total Solids
Surfactants
Zi nc
7 plants
Air Preheater
4-12
163-2,271
Kg
0-6.82
2.6-15.9
0.21-26.88
0-2.02
0.97-3862
8.14-170.38
0.02-2.66
1 ,448-20,096
217-4,898
1 ,188-29,744
0.13-11 .36
2 plants
Boiler Fireside
2-8
91-2,725
Kg
0
8.63-515.00
0.01-0.45
0-0.11
13.63-408.90
0-13.63
0.12-5.04
1 ,363-15,948
54.07-1 ,736
1 ,817-18,551
0.91-13.04
7 olants
Boiler Tubes
0-2
568-18,622
Kg
0.45-19,387
0.21-10,524
0.06-931 ,185
0.51-595.96
42,592-133,826
0.02-3.48-
111 .11-43,598
0-1 ,590
111 .11-48,868
0.35-391 ,098
57
-------
rainfall may cause problems with closed systems, since some
water may have to be withdrawn from the settling basin and
discharged. Similarly, extended periods of dryness may
evaporate excessive amounts of water from the settling
basin, requiring the addition of supplementary water to the
system.
Ash pond effluents from coal- fired plants contain a wide
variety of constitents whose concentrations can vary widely
depending on the particular coal used. Generally, the
overflows contain high levels of dissolved solids, suspended
solids, hardness, sulfate, sodium, magnesium, chloride, and
alkalinity. Metals originally present in the coal may also
be present.
Ash is produced in oil-fired plants in very small
quanitities. It has been found that oil ash does not settle
as well as coal ash. In some utilities, the oil fly ash is
recycled into the furnace, increasing efficiency and
reducing the disposal problem.. Ash pond overflows from oil-
fired plants have some of the same characteristics as those
from coalfired plants, and may additionally contain high
concentrations of vanadium.
Table V-6 contains an itemization of the types of ash
handling systems used by the plants that were visited.
Water Use
Of the twenty- three plants visited in this study, only four
used water to convey fly and bottom ash to ash ponds; the
remaining plants use dry ash transport systems. Of the four
plants utilizing wet systems, all were coal-fired. Plant
9163 uses 2.65x102^ liters per MWH, the only plant using
water for fly ash transport. The other three plants 6387,
8356, and 6294, respectively use 43.09, 3. 61x10! and 11.39
liters per MWH for bottom ash transport.
Raw Waste Load
Oil-Fired Plants. Fuel oils contain only about one percent
of the amount of ash commonly found in coal, consequently,
ash disposal problems from oil-fired plants are
significantly less.
Fly Ash. Many of the oil-fired plants visited used
mechanical cyclones to remove fly ash from the flue gases.
A dry system is usually used to remove the collected ash.
In other plants, no fly ash collection system is necessary
because of the low ash content of the oil used. In these
plants, most of the ash in the flue gases collects on the
interior surfaces of the boiler and is removed by high
58
-------
EVAPORATION LOSS
ASH HANDLING
SYSTEM
EVAPORATION
LOSS
; i
RECYCLE
MAKE-UP
RAINFALL
1
SETTLING POND
OVERFLOW
ASH SLUDGE FOR
DISPOSAL
FIGURE V-8.
Flow Diagram for Recirculatlng Bottom
Ash System
59
-------
Table V-6. ASK DISPOSAL METHODS
PLANT NO.
9600
9650
9369
9371
7435
3816
9585
7116
<3596
3135
9163
6387
8392
6293
7308
8875
7968
6421
6214
6294
TYPE OF PLANT
Oil and Gas
Oil and Gas
Oil and Gas
Oil and Gas
Coal , Oi 1 , end Gas
0 i 1 a n d G a s j
Gas
Oil and Gas
Oil and Gas
Oil and Gas
Coal
Coal
Gas
Coal
Oil
Oil and Gas
Coal and Gas
Oil and Gas
Coal
Coal and Gas
ASH
FLY ASH
1
3
3
3
1
3
9
'
3,5
3
3
1
3
4
3
DISPOSAL
None Requ
None Requ
None Requ
None Requ
None Requ
None Requ
SYSTEM
BOTTOM ASH
i red
i red
i red
i red
i red
i red
2
4
2
4
2
4
2
4
6
7
2
7
4
8
CM
O
Key: (1) Soot blowing steam
(2) Fireside washing
(3) Dry collection system from electrostatic and/or mech-
anical precipitators, ash then hauled to landfill.
(4) Dry collection sy'stem-ash landfilled.
(5) Air wash in stack to control fly ash-discharges to
POTW
(6) Wet collection system with settling sump-(overf1ow
from sump' goes to POTW)
(7) Vacuum system using steam, ash landfilled, condensate
from steam goes to POTW.
(8) Wet system discharging to surface water.
(9) Wet system, does hot discharge to POTW
-------
pressure steam (soot blowing steam),. and passes through the
stack to the atmosphere.
Bottom Ash. Some of the oil-fired plants visited needed
fireside washing to remove bottom ashr other plants had dry
collection systems that removed ash for land disposal.
Coal-Fired Plants. The amount of ash produced by coal-fired
plants is much greater than that produced by oil-fired
plants, requiring the use of more complex ash-handling
systems.
Fly Ash. Electrostatic precipitators or mechanical cyclones
are used in most of the coal-fired plants to collect fly
ash. The collection systems from these units are usually
dry, and the final ash disposal is on land. One plant. No.
9163, used an additional system for fly ash control,
consisting of a wash in the stack that discharged excess fly
ash to a POTW.
Bottom Ash. Methods for disposing of bottom ash varied
widely among the coal-fired plants that were visited.
Plants 7485 and 9163 used dry collection systems for the
land disposal of bottom ash. Plant 6387 was the only plant
visited that used a wet transport system in combination with
a settling sump. Two plants No. 6293 and 7628 used a vacuum
collection system with steam. One plant. No. 6294, has an
ash settling basin which overflows to surface water. Plant
No. 6214 has a totally dry ash system.
Table V-7 shows raw waste loadi.ig for two plants, 6293 and
6387.
Wastewater Treatment
Oil-Fired Plants. Because of the small quantities of ash
produced by oil-fired plants, none of the visited plants had
ash treatment systems.
Coal-Fired Plants. Only one plant, No. 6387, used a
settling basin in conjunction with a wet ash transport
system. Most of the other coal-fired plants had no need for
an ash treatment system, since these plants used dry
collection systems, followed by land disposal,
Effluent Waste Loads
Oil-Fired Plants. Effluents from ash cleaning of oilfired
plants are present for those plants which used fireside
cleaning for ash removal.
61
-------
Coal-Fired Plants. Plant No. 6387 is the only visited plant
that discharged a significant amount of waste from an ash
handling system to a POTW. The discharge consists of the
overflow from the ash settling sump. Treated effluent is
shown in Table V-8.
DRAINAGE
Floor and Yard Drains. Floor and yard drains collect wastes
from leakage and numerous cleaning operations, and may
discharge to a POTW. The waste will contain dust, fly ash,
coal dust from coal-fired plants, oils, and detergents.
Coal Pile. The storage of large quantities of coal is
necessary for coal-fired plants to insure continuous
operation and to simplify delivery by the supplier. A 90-
day supply is normally maintained. Coal storage piles are
of two types: active and storage. Active piles are used
continuously and are subject to infiltration by rainwater.
Storage piles are used for the long-term storage of coal,
and are usually protected from rainfall with some sort of
seal, which can be either a layer of asphalt or a layer of
fine coal dust covered with lump coal.
Waste discharges from coal storage piles are the product of
drainage from rainfall. This drainage can be either acidic
or alkaline. Acid drainage is the result of the reaction of
pyrite (FeSŁ) with water and oxygen, which produces iron
sulfate and sulfuric acid. This type of drainage is highly
acidic, has a low pH, and contains a large amount of ferrous
iron and some aluminum. Alkaline drainage occurs when acid
drainage is neutralized by alkaline material present in the
coal, or when the coal has a low pyrite content. Alkaline
drainage is characterized by a pH of 6.5 to 7.5 or greater,
little acidity, and significant concentrations of ferrous
iron. If the ferrous iron concentration is high enough, the
iron may precipitate upon oxidation and hydrolysis.
Drainage from coal piles may contain in addition to the
aforementioned constituents, high concentrations of
dissolved solids and significant amounts of copper, zinc,
and manganese. Other materials may also be present that are
the result of the reaction of sulfuric acid with minerals
and organic compounds present in the coal.
Raw Waste Load
Coal Pile. Almost all of the plants that were visited
allowed coal pile drainage to drain to either the surface
water, storm sewers, or nearby land. An exception was plant
No. 9163, which stored all of its coal under roof, thus
eliminating any drainage problems.
62
-------
Table V-7.
RAW WASTE FLOWS AND LOADINGS - ASH HANDLING
PLANT NO.
WASTEWATER SOURCE
FLOW
PARAMETER
BODC
b
Bromide (Bromate)
COD
Chromium
Chromi um+6
Copper
Cyani de (Total )
I ron
Nickel
Oil and Grease
Phosphate (Total)
Total Dissolved
Solids
Total Suspended
Solids
Total Solids
Surfactants
Zinc
6293
Ash Transport
Bl owdown
L/Day
2725?
mg/1
3.0
1235.0
0.37
0.030
0.16
0.005
76.0
0.24
1 .0
3.4
388.0
1144.0
1532~0
0.55
L/MWH
1 1 3. 55
g/MWH
0.34
140.23
0.04
0.003
0.018
0.0005
8.62
0.03
0.38
44.05
129.90
173.95
0.06
6387
Ash Transport
Bl owdown
L/Day
45420:0
mg/1
1.2
---
290.0
0.12
0.009
0.20
0.112
6.2
0.03
1.0
0.02
1894.0
1651 .0
3545.0
0.08
L/MWH
126.16
g/MWH
0.15
36.58
0.015
0.001
0.025
0.014
0.78
0.003
238.95
208.30
447.26
0.01
63
-------
Table V-8. EFFLUENT FLOWS AND LOADINGS - ASH HANDLING
PLANT NO.
WASTEWATER SOURCE
FLOW
PARAMETER
BODC
b
Bromide (Bromate)
COD
Chromi urn
Chromi um+6
C o p p e r
Cyanide (Total )
I ron
Nickel
Oil arid Grease
Phosphate (Total)
Total Dissolved Solids
.Total Suspended Solids
Total Solids
Surfactants
Zinc
6387
Settled ash transport
effluent
L/Dsy
45420.0
mg/1
1 .0
43.1
0.02
0.011
0.2
0.012
0.33
0.03
T .0
0.02
2980.0
70.0
3050.0
0.02
L/MWH
126.16
g/MKH
5.43
0.001
0.002
0.001
0.04
375.97
8.83
384.80
0.002
64
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General chemical characteristics of coal pile drainage were
discussed under the previous heading. Reference 16 lists
ranges for some of the elements present in coal pile
drainage, which are shown below:
Element Concentration Range, mg/1
Copper 1-4
Iron 0.1-5
Zinc 1-15
Floor and Yard Drains. Drainage from floor and yard drains
in most cases can be assumed to be a negligible waste
source. Many plants exercise meticulous care to prevent oil
leaks and spills from reaching floor drains by using drip
pans and oil absorbing materials. Some plants particularly
those in open areas or in dry regions, have no need for yard
drains and have no drains installed.
Reference 16 list characteristics of wastes from yard and
floor drains, which are summarized below:
Parameter Concentration Range (mg/1)
BOD 2-1
TSS 0-5
pH Low-Neutral
Surfactants Present
Chromium 0-20
Lead Present
Phosphorous 0-10
Oil and Grease Present
Wastewater Treatment
None of the plants that were visited used any type of coal
pile drainage treatment system.
One plant No. 7116 discharged floor drainage (along with
other wastes) to a settling tank before discharge to a POTW.
Other plants discharged floor and yard drainage without
treatment either directly to surface water or to a POTW.
Effluent Waste Loads
Information was not available on treated wastewater before
discharge to the POTW,
AIR POLLUTION CONTROL EQUIPMENT
Liquid waste disposal problems associated with air pollution
control equipment are mainly limited to systems for the
65
-------
control of SO2. Control, systems for SO2 can be further
divided into "throwaway" and "recovery" processes. Throwaway
processes produce a sludge or cake that must be disposed of.
Recovery processes produce either elemental sulfur, sulfuric
acid, or gypsum, which are marketable to some degree and
have limited disposal problems. The following discussion
will be limited to a throwaway process.
The greatest number of existing flue gas desulfurization
systems (including recovery and throwaway) use tail-end
scrubbing with lime and/or limestone. Those scrubbing
systems, installed after the boiler, remove particulates as
well as sulfur dioxide by reacting the flue gas with
slurries of lime or limestone forming calcium sulfates and
sulfites. The calcium sulfate/sulfite sludge is usually
piped to large settling ponds.
A small number of existing throwaway systems are of the
double-alkali type. In these systems, sodium or ammonium
salts are used as a scrubbing solution. After contacting
the flue gas, the scrubbing solution is reacted with
limestone or lime to precipitate calcium sulfite and sulfate
and regenerate the solution for recirculation to the
scrubber. Scrubber wastes consist of a dry filter cake.
Figure V-9 shows a flow diagram for an air pollution control
scrubbing system.
Wat er Use
None of the twenty-three plants visited in the study used
water to control SOx emissions. This can be accounted for
by the fact that the majority of the plants burned low
sulfur (1 percent) coal or oil thereby eliminating the need
for air pollution control devices.
Raw Waste load
None of the utilities visited had flue gas desulfurization
equipment. Wastes from these systems are mostly in the form
of sludges, which are disposed of on land.
Wastewater Treatment
None of the plants discharged SOx removal wastewaters to the
POTW.
Effluent Waste Load
Information was not available on treated wastewater.
MISCELLANEOUS WASTE STREAMS
66
-------
Sanitary Wastes, Sanitary wastes from steam-electric plants
are similar to municipal domestic wastes with the absence of
laundry or kitchen wastes. The volume of waste flow is
dependent upon the number of employees.
Plant Laboratory Wastes. Many steam-electric plants have
laboratories for the chemical analysis of various process
streams within the plant. Depending on the analyses
performed, the waste from this source will contain a large
variety of chemicals, albeit in small amounts.
Intake Screen Backwash. Power plants that withdraw cooling
water from a natural body, such as a lake or river, use
traveling screens to prevent debris from entering the intake
system. The debris from these screens are usually
collected.
Supplementing Cooling Water Systems. These cooling systems
are generally maintained for such uses as bearing and gland
cooling for pumps and fans. The systems may be oncethrough
or recirculating. Chemicals are not used in oncethrough
systems, except for occasional shock chlorination.
Recirculating systems use water of high purity, supplemented
by pretreated makeup water. Chromates, borates, and
nitrates are used in recirculating systems to prevent
corrosion.
Construction Activity. The construction of buildings and
equipment adjacent to power plants can cause the presence of
additional amounts of suspended solids and turbidity in the
storm-water runoff due to the erosion of soil disturbed by
the construction activity.
Water Use
Hqu s eke e pi nq. Housekeeping water usage, which includes
floor washing and sanitary water (bathrooms, sinks, etc.),
amounts to less than one percent of the total. Only one
plants of the twenty-three in the study had any substantial
floor wash water usage these being plant No. 6294 with 0.29
liters per MWH. The following table lists the water for
sanitary purposes.
Plant No. water Usage, Liters/MWH
9600 1.05
9369 7.96
8816 2.74
9585 6.23
9163 4.29
6387 6.73
8356 26.12
67
-------
STACK GASES
STEAM TO TURBINES
BOILER
. FLUE GASES I
INI? T
SCRUBIIEH IIQIJOF]
FIGURE V-9. Flow Diagram For Air Pollution Control
Scrubbing System (Ref. 14)
68
-------
6293 4.73
8392 5.03
8875 t).4
7968 11.55
6421 6.00
6294 1.74
Miscellaneous Cooling. Miscellaneous cooling needs include
bearing cooling water, cooling of compressors, and other
extraneous equipment* cooling needs. Water usage varied for
six plants from a low of 1.59 liters per MWH for plant No.
9396 to a high of 1.45x10.4 for plant No. 8356. Using the
least squares analysis method for the normalized data, a
coefficient of determination of 0.945 was calculated
indicating that approximately 94 percent of the data
variance could be accounted for by the least squares
straight line.
Raw Waste Load
Sanitary Wastes. Reference 14 states that the per capita
sanitary waste load is generally 25-35 gal/day (94.5-132
liters/day) from steam-electric power plant. The reference
also lists the number of employees per MW that may be
expected to be found at typical power plants:
operational personnel: 1 per 20-40 MW
maintenance personnel: 1 per 10-15 MW
administrative personnel: 1 per 15-25 MW
The flow, BODJS, and suspended solids per capita load can be
estimated by the following (14):
Flow BODS TSS
Office-Administrative 0.95 cu 30cj 70g[
(per capita) m/day (0.071b) (0.15 Ib)
(25 gpd)
Plant (per capital) 0.133 cu 40g 85g[
m/day (0.09 Ib) (0.19 Ib)
(35 gpd)
Plant Laboratory Wastes. The volume of wastes from in-plant
laboratory can be assumed to be negligible. Reference 14
suggests that if a toxic materials problem is found to
originate from a laboratory drain, it may be appropriate to
either: (1) change the test procedure, (2) contain the waste
for seperate treatment, or (3) remove the waste from the
site.
69
-------
Supplementary Cooling Water Systems. Wastes are discharged
from recirculating cooling systems during blowdown, which
may typically be twenty liters per day with a settleable
solids content of 1-2 ppm (14) . Additional wastes are
discharged during drainage and cleaning operations, which
are infrequent.
Plants which use once-through systems may discharge the
effluent from the entire system to a POTW. This waste
stream will probably contain chlorine, and the stream is
usually of significant volume.
Construction Activity and Intake Screen Backwash. The
nature and duration of these wastes do not contribute
significantly to the total waste load.
Wastewater Treatment
Sanitary Wastes. Sanitary wastes are generally discharged
directly to POTW or septic tanks without treatment. An
exception is plant 7116, which pretreats sanitary wastes
(along with other wastes) in a settling tank before
discharge to a POTW.
Plant Laboratory Wastes. Most plants combine laboratory
drains with other sanitary plant plumbing, and discharge the
waste without pretreatment.
Supplementary Cooling Water Systems. Supplementary cooling
system wastes are usually discharged directly, although one
plant 7116, discharged the waste to a settling tank before
discharge to a POTW.
Construction Activity and Intake Screen Backwash. Most
plants do not treat these wastewaters. Intake screens are
generally backwashed into the water source.
Effluent Waste Loads.
Information is not available on treated effluent from
miscellaneous waste streams.
THE POTW PROCESS
Preliminary Physical Treatment
Most POTW employ initial physical treatment of wastewater
for the removal of course materials, settleable solids,
grease, and floating material.
Bar Racks and Comminutors. These devices are used as the
first step in wastewater treatment to remove large solid
70
-------
materials. Bar racks consist of large, parallel steel bars
placed perpendicular to the flow of wastewater. The bars
trap and retain large solidsr which are removed mechanically
by a series of vertically-moving rakes connected to a motor-
driven, endless chain belt. The solids are scraped off the
racks with large mechanical arms, and may then either be
collected for land disposal or ground in disintegrators and
returned to the flow. Smaller POTW may use comminutors,
which are motor-driven cutting devices partially submerged
in a narrow channel, to grind up large materials as they
pass through.
Grit Chambers. Grit chambers are usually found in larger
POTW. They are generally located after bar racks, and are
designed to remove sand, cinders, or other heavy particles
that have high settling velocities. Grit chambers may be of
two types: horizontal-flow, and aerated. Horizontal-flow
grit chambers consist simply of a channel designed to
maintain a constant flow velocity regardless of the volume
of water passing through the channel. The flow velocity is
lowered sufficiently over that of the influent wastewater to
allow grit to settle to the bottom. Removal of the grit may
be done either mechanically or by hand.
Aerated grit chambers consist of a spiral-flow aeration
tank. The velocity of flow in aerated chambers is
determined by the volume of the tank and the quantity of air
that is supplied. Aerated grit chambers are always cleaned
mechanically.
Primary Sedimentation. Primary sedimentation is used after
preliminary removal of solids in racks and grit chambers and
prior to biological treatment. The purpose of primary
sedimentation, when used prior to biological treatment, is
to reduce the suspended solids and BOD load on the
biological treatment units. This is accomplished in large,
rectangular (or circular) sedimentation tanks that provide a
sufficient detention time for the removal of settleable
solids and floating material. Grease and other floating
materials are skimmed off from the surface with skimmers.
Solids that settle to the bottom of the tank (known as
primary sludge) are mechanically pushed into a hopper, where
they are collected for further treatment. Primary
sedimentation tanks, if designed properly and operated
correctly, will remove 50 to 65 percent of the suspended
solids in the influent wastewater and from 25 to 40 percent
of the BOD. If primary sedimentation is used as the only
means of treatment, the effluent is usually chlorinated to
remove pathogens.
Secondary Biological Treatment
71
-------
Secondary biological treatment is used to convert soluble
and colloidal organic material into settleable flocculant
material that can be removed in sedimentation tanks. Two
types of biological treatment processes are most often
employed: (1) the activated-sludge process, and (2)
trickling filters.
Activated-Sludge Process. The activated-sludge process
consists of an aerated basin containing a large mass of
microorganisms and flocculated solids, known as the mixed
liquor, followed by a sedimentation tank in which the solids
are removed. The sedimentation tank may either be part of
the same structure as the aeration basin, or it may be
completely separate. Part of the solids that settle in the
sedimentation tank (the secondary sludge) is removed for
further treatment, and part is recycled to the aeration
basin. The effluent from the sedimentation tanks is usually
chlorinated.
Bacteria make up the largest portion of the microorganisms
present in the activated sludge, and are responsible for the
majority of the waste steibilization that occurs. The
mechanisms by which bacteria stabilize a waste is twofold,
consisting of: (1) consumption of organic matter, which is
partially oxidized to lower energy compounds and partially
converted to new cellular material, and (2) the production
of polymers and slime that bind bacterial cells and other
suspended material into flocculant particles that can be
removed by sedimentation. Other microorganisms may also be
present, such as protoza, which consume bacteria that have
not flocculated, and rotifers, which consume small floe
particles that have not settled. Activated sludge systems
are usually from 55-95 percent efficient in removing BOD,
and from 55-95 percent efficient in removing suspended
solids (Figure V-10).
Trickling Filters. Trickling filters consist of a bed of
rocks or plastic material that support a growth of microbial
material (slime layer). Wastewater is sprayed over the top
of the bed, which is circular, with a rotating distributor.
As the waste percolates through the bed, organic material is
adsorbed onto the slime layer. At periodic intervals,
partly because of the increase in thickness of the slime
layer, the microorganisms in the layer lose their ability to
cling to the surface of the filter media and the slime layer
is washed off by the waistewater (a process called
"sloughing") . (Figure V-10) .
Trickling filters are divided into two categories: low-rate
and high-rate, based on organic loading rates. Both types
of filters achieve equivalent BOD removal efficiencies, but
high-rate filters are advantageous since they have a higher
72
-------
rate of BOD removal (and thus can accept higher influent
flow rates) than low-rate filters. This is achieved by
recycling a portion of the influent to return viable
organisms back to the filters. Low-rate filters have no
recycle. Both types of filters are followed by a settling
tank (clarifier) to remove suspended solids produced during
sloughing. The effluent from the settling tank is generally
chlorinated. Trickling filters are from 50-95 percent
efficient in the removal of BOD, and 30-92 percent efficient
in the removal of suspended solids.
Figure V-11 shows a wastewater treatment process diagram
utilizing activated sludge or trickling filters.
Treatment and Disposal of Sludge.
The problem of disposing of sludges produced during primary
and secondary treatment is one of the most complex tasks
faced by the engineer. Techniques for dealing with sludges
are varied, but most involve: (1) digestion, followed by (2)
conditioning, and (3) dewatering and drying (Figure V-11).
Digestion is a biological process for reducing the volume of
sludge. Two types of digesters are in use: anaerobic, and
aerobic. Anaerobic digesters are closed, heated tanks in
which various microorganisms decompose organic and/or
inorganic matter without the presence of oxygen, forming
methane, carbon dioxide, and sludge solids. The methane
that is involved during the process can be used as a fuel,
and its rate of production is one of the best measures of
the satisfactory operation of the digester. Chemical
conditioning, followed by centrifugation or vacuum
filtration, is usually used to treat sludge solids during
anaerobic digestion. Chemical conditioning involves the use
of ferric chloride, lime, alum, or organic polymers to
coagulate the solids and release absorbed water.
Centrifugation and vacuum filtration are physical operations
that are used to remove water from the sludge solids prior
to final disposal.
Aerobic digestion is much like the activated sludge process,
involving consumption of organic compounds in sewage by an
aerated mass of microorganisms. As the supply of organic
material run out, the microorganisms begin to consume their
own protoplasm. Sludge solids from aerobic digesters are
stable and are more easily dewatered by vacuum filtration or
drying on sand beds.
Advanced Waste Treatment
Many chemical constituents present in wastewater, especially
nitrogen and phosphorus, are slightly affected by
73
-------
INFLUENT
WASTE SLUDGE
SLUDGE
RETURN
FINAL
SEDIMENTATIO!\
ACTIVATED SLUDGE PROCESS
I
EFFLUENT
INFLUENT
TRICKLING
FILTER
SLUDGE
WET
WELL
SLUDGE RETURN LINE
EFFLUENT
TRICKLING FILTER PROCESS
FIGURE V-10. Flow Diagram of Secondary Treatment Methods
74
-------
en
SCREENINGS
INFLUENT
GRIT
SLUDGE
WASTE SLUDGE
PRIMARY
BAR RACKS GRIT CHAMBERS SEDIMENTATION
DERATION TANK SETTLING TANK
ACTIVATED SLUDGE
'TREATMENT SCHEME
C1
.
L
|
!
>i
RETURN SLUDGE |
!
Y
EFFLUENT
CHLORINE
CONTACT CHAMBER
SCREENINGS
INFLUENT [_
GRIT
SLUDGE
,,ASTE SLUDGE
RETURN EFFLUENT I
1
1
BAR RACKS
GR
|
— *
1
>
PRIMARY
IT CHAMBERS SEDIMENTATION
TRICKLING
FTITFRS
SE
\
*~
EFFLUENT
TTLING TANK CHLORINE
CONTACT CHAMBER
TRICKLING FILTER
TREATMENT SCHEME
FIGURE V-ll. Wastewater Treatment Flow Diagram
-------
ANAEROBIC SLUDGE
DIGESTION
CHEMICAL CONDITIONING
CENTRIFUGE
SLUDGE FROM SEDIMEN-
TATION TANKS
DIGESTED
SLUDGE
CENTRATE
SUPERNATANT
SLUDGE DISPOSAL SCHEME
DEWATERED SLUDGE JO
ULTIMATE DISPOSAL
FIGURE V-12. Flow Diagram for Sludge Treatment
-------
conventional primary and secondary treatment. Since these
chemicals can have adverse effects on the receiving water by
promoting the growth of algae and other unwanted aquatic
vegetation, their removal is desirable in some cases.
Although tertiary treatment processes are still uncommon,
their use is receiving considerable attention. Two
processes, nitrification for the removal of nitrogen, and
precipitation for the removal of phosphorus, will be
discussed.
Nitrification-Denitrification. This process appears to be
the most promising for the removal of nitrogen. The
technique involves aerobic conversion of ammonia to the
nitrate form (nitrification), followed by anaerobic
conversion of the nitrates to nitrogen gas
(denitrification). Both steps involve the production of
specialized groups of bacteria, and require detailed
attention to operating and environmental conditions.
Denitrification requires the addition of a supplemental
carbon source for successful operation; methanol is usually
used. Nitrification-denitrification is from 60-65 percent
efficient in removing nitrates. Figure V-13 shows a flow
diagram of the nitrification-denitrification process.
Chemical Precipitation. Precipitation of phosphorus can be
achieved by the addition of chemicals such as lime, alum,
and ferric chloride, or sulfate. These chemicals are
usually added to the raw wastewater and the phosphorus is
precipitated during primary sedimentation, however, these
chemicals can also be added in the activated-sludge aeration
tank or to the secondary clarifier. Removal of phosphates
by precipitation in primary sedimentation tanks is from 90—
95 percent efficient.
Flows of PQTW Receiving Steam-Electric Wastewaters
The wastewaters discharged by steam-electric plants vary
greatly in flow and waste loadings. For the twenty-three
plants visited during this study, the steam-electric
wastewaters represented less than five percent of the total
POTW influent. Table V-9 lists the combined discharge rate
for each steam-electric plant along with the associated POTW
influent flow and treatment scheme.
Raw Waste Load
Waste loads in the total combined waste streams discharge
from power plants are affected by any occurrence in the
steam-electric which use and discharge water. The
waterborne waste loads in the combined discharge for six (6)
plants are shown in Table V-10. The major pollutants are
chemical oxygen demand and dissolved and total solids, with
77
-------
lesser values of iron, nickel, phosphates and total and
hexavalent chromium.
WASTE COMPARISON
Effluent data gathered from the eight (8) plants sampled
during this study were compared with similar data gathered
in support of the "Development Document for Effluent
Limitations Guidelines and standards of Performance for the
Steam Electric Power Generating Point Source Category" (14).
Comparison was made to identify similarities and differences
in the quality and quantity of aqueous plant effluents.
Waste streams for which data was available for comparison
include:
o Recirculating Condenser Cooling Water
o Water Treatment Wastes
o Boiler Slowdown
o Ash Handling Wastes
These data may be found in Table V-11.
Recirculating Condenser Cooling Water
Flow data in this study tended to coincide with lower flows
reported in the development document (14) and were similar.
Concentrations of BOD, phosphate, dissolved solids,
suspended solids, total solids, and zinc observed in this
study were within the range of those reported in the
Development Document. Concentrations of chromium, copper,
iron and nickel observed in this study tended to be lower
than those reported in the development document. This
difference is probably due to a number of factors, includin
g lower influent loadings of these heavy metal components,
and less corrosive nature of the intake waters.
Water Treatment Wastes
Flows and parameter concentrations of wastes observed in
this study were within the range of those reported in the
development document (14) . Pollutants observed were
identical to those reported in Reference 14.
Boiler Slowdown
Flow data for boiler blowdown observed in this study was
within the range of those reported in the development
document. Pollutants observed were identical to those of
Reference 14. Concentrations of all parameters observed in
78
-------
VD
WASTE SLUDGE WASTE SLUDGE
pH ADJUSTMENT k ORGANIC PH ADJUSTMENT
CARBON I CHEMICAL
! SOURCE ,' ADDITION
SECONDARY
EFFLUENT
i
' \
S ^\ ' 1
r^ W A TT-J
f v y '
PLUG FLOW REACTOR
SI IIOGF RFT1IRN - -
1
<
' /
X
PLUG FLOW REACTOR
. .._,,, Si !ID(5F RFTI1RN ... -..
^\ FINAL EFFLUENT
1 , „. '*»
J
SETTLING TANK
SETTLING TANK
NITRIFICATION
DENITRIFICATION
NITROGEN REMOVAL
SCHEME
FIGURE V-13. Flow Diagram of Nitrification-Dentrification Process
-------
Table V-9.
POWER PLANT AND POTW F'LOWS
Plant
No
9600
9650
9369
9371
7485
8816
9585
7116
8696
8135
9163
6387
8392
6293
7308
8875
7968
6421
6214
6294
Combi ned Flow
to POTU, gpd
U/d)
No data (plant has been
using POTW for only one
year)
100,00
(378,000)
8,350
(8,880)
15,000
(56,700)
1 ,580
(5,970)
2,000
(7,560)
600
(2,270)
Data incomplete
72,000
(272,293)
150,400
46,900
(177,000)
9,500
(35,900)
126,000
(476,000)
9,100
(34,400)
902,000
(3.41 x 106)
423,000
(1 .60 x 10°)
Data Incomplete
24,050
(93, 308)
No data - operates only
50 hours/yr
4, 2'jQ
(16, 088)
5OTW Average
Flow, gpd
(1/d)
97.5 x 106
(369 x 106)
2.4 x 106
(9.1 x 1Q6)
10.0 x 106
(22.7 x 106)
300,000
'. 1 .1 x 106)
350 x 106
(1 ,320 x 106)
4.5 x 106
(17.0 x 106)
3.5 x !06
(13.2 x 106)
350 x 106
(1 ,320 x 106)
% of POTW
f 1 ow
0.10
0.098
0.15
0.50
0.01
0.01
...
0.02
POTW
Treatment Scheme
Activated sludge,
anaerobic digestion
Rotati ng biological
surfaces; anaerobic
digestion
Activated sludge,
aerobic digestion
Activated sludge,
aerobic digestion
Activated sludge,
anaerobic digestion
Oxidation pond
Activated sludge
Activated sludge,
anaerobic digestion
No >OTV< at present - to be hooked up
to West Palm Beach POTW in 1978 - Sewers
presently run to ocean
10 x 106
C8 x 106i
220,000
(832,000)
1.5 x 106
(5.7 x 106)
Z x 106
(7.6 x 106)
315 x 106
(1 , 190 x 106)
31.1 x 106
(IZ'O x 106)
---
1 .4 x 106
(5.3 x 106)
1.4 x 10r
(5.3 x 10b)
1.1 x 106
(5..1 x 106)
0.47
4.3
8.4
0.46
0.29
1 .4
1.76
---
0.30
Trickling filters;
anaerobic digestion
Trickling filters;
no digestion
Activated sludge,
aerobic digestion
Activated sludge
trickling filters
anaerobic digesters
Primary treatment only
secondary treatment
facilities being built
Activated sludge,
trickling filters,
anaerobic digestion
Activated sludge
Activated sludge
Activated sludge
80
-------
Table V-10. RAW WASTE FLOWS AND LOADINGS - COMBINED DISCHARGE TO POTW
PLANT NO
V.'ASTEWATER SOURCE
FLOW
PARf-X.ETER
30D5
COD
Chromi ufn
ChroiM un
Copper
Cyanide (Total)
Iron
Nickel
Oil and Grease
Phosphate (Total)
Total Dissolved
Solids
Total Suspended
Sol Ids
Total Solids
Surfactants
Zinc
6387
Combined Discharge
L/Qdy L/K'.-.'H
518,000 1870
mg/ 1 g/I'M
8.4 16
49.0 9!.6
-------
this study were similar to those reported in the development
document with the exception of BOD, and zinc. BOD values
observed in this study tended to be higher than those
reported in the development document. Observed zinc values
tended to be lower. Zinc concentrations are understandably
lower for all discharges observed in this study due to use
of municipal water as influent water.
Ash Handling Wastes
Wastewater flows of ash handling wastes observed in this
study were within the range of those reported in the
development document (14) ., Pollutants observed were
identical to those reporte in Reference 14. Concentrations
of parameters observed in this study were within the range
of those reported in the development document, with the
exception of phosphate. Phosphate concentrations observed
in this study were higher than those reported in the
development document. Higher maximum phosphate
concentrations are probably due to the variable nature of
coal impurities.
Summary
Overall, values, of effluent flows and parameter
concentrations observed in this study were similar to those
reported in data referenced in the development document
(14). Pollutants observed were identical to those reported
in Reference 14. The few parameters in this study that lay
outside the range of development document data tended to be
lower, reflecting the higher quality of the municipal water
used as influent water for the stations contacted in this
study. Therefore, it may be concluded that the stations
reported in by the results of this study discharge
pollutants similar to those (direct dischargers) affected by
the development document (14) .
82
-------
Table V-11.
COMPARISON OF PARAMETER VALUES
PLANT RA'J WASTES
i""""*-*^ WASTE
^---^STREAM
PARAMETER^-v^^
Fl OW (\ /DAY^
PARAMETER. NG/L
BOD L0
BUU Hj
COD L0
LJU H,
CHROMIUM
TOPPFR
hi
IRON -^
1KUN HT1
NICTFI
punCDUATC LO
RECIRCULATING
CONDENSER
COOLING WATER
THIS
STUDY
53,600
238,400
1.4
22
10
102
0.02
5
0.02
0.7
0.5
1.6
0.03
0.04
0.1
rMJi. MM It -gj— - -3 —
TDS L0
iui HI
TSS L0
lbb HI
TS ^°
15 HI
7TMP LO
Z.lNv. Hf
886
5,111
3
59
889
5,170
0.1
1.5
REF.14
109,000
27,258,000
2
18
36
436
10-
120
63 !
1 ,740
50
1,150
80
150
0.1
18
150
32,700
2
220
750
32,700
0.3
3,000
WATER TREATMENT
WASTES
THIS
STUDY
4,277
40,900
1.0
REF.14
150
135,000,000
0
40 344
2.0
0
76 | 44Q
0.02
0.1
O.C2
2.6
0.02
10.4
0.03
0.25
0.05
0.05
2.168
0.006
3.09
0.015
37.5
0.007
0.56
0.1
I 14.0 87.2
0.16
23,000
1.0
j 1,780
0.1G
1 ,958
0.02
2
35,235
0
300
15
36,237
0
0.44 j 4.5
BOILER SLOWDOWN
THIS
STUDY
5,715
17,030
10.8
11.7
2.0
157
.02
.02
.02
.19
.03
1.4
.03
.03
.05
19.8
118
1 ,405
2.7
31
125
1407.7
.01
.05
REF.14
4,530
4,233,000
0
6
0
784
0.001
1.5
0
0.3
0.03
0.3
0
0.13
0.01
29
5
26,006
0
300
5
26,077
0.1
1.2
ASH HANDLING
WASTES
THIS
STUDY
27,252
45,420
1.2
3.0
"240
1,235
0.12
0.37
0.16
0.2
6.2
76.0
0.03
0.24
0.02
3.4
388
1,894
1,144
1,651
1,532
3,545
0.03
0.55
REF.14
18,170
98,436,000
0
30
2
306
0.045
40
.009
100
0.001
2,100
0.01
10
0
0.24
83
32,423
4
236
35
32,412
0
0.52
00
U)
-------
SECTION VI
CONSIDERATION OF POLLUTANT PARAMETERS
INTRODUCTION
Aqueous pollutants* originating from steam electric power
generating facilities are considered in this section to
determine if they interfere with the operation of publicly-
owned treatment works (POTW) and if they are susceptible to
treatment by such treatment works.
THE CONSIDERATION OF POLLUTANT PARAMETERS
Pollutants were considered on the basis of their potential
for interference with the operation of treatment works and
on the basis of their treatability by such worksr as
follows:
° Potential interference with POTW
The pollutant may impair the activity of biological
treatment systems by either causing the death of
some or all of the microorganisms that are
essential to the operation of the POTW, or
impairing the activity of these microorganisms so
that their waste-consuming efficiency is lowered.
Examples of treatment units that may be adversely
affected by pollutants are: trickling filters,
activated sludge units, anaerobic digesters, and
nitrification units. Additionally, consideration
is given to other characteristics of power plant
discharges which would interfere with other parts
of the POTW such as transport piping.
o Susceptibility to treatment
Pollutants were considered that are not removed or
that are removed inadequately by treatment works.
For those pollutants which are partially removed,
the problem of disposing the sludge that contains
such pollutants is also considered.
The remainder of this section is devoted to a discussion of
the properties of the pollutants considered, the effect of
these pollutants on treatment works, and their treatability
in treatment works.
85
-------
PROPERTIES OF POLLUTANT PARAMETERS CONSIDERED
Acidity and Alkalinity -
Although not a specific: pollutant, pH is related to the
acidity or alkalinity of a. wastewater stream. It is not a
linear or direct measure of either, however, it may be
properly used as a surrogate to control both excess acidity
and excess alkalinity in water. The term pH is used to
describe the hydrogen ion - hydroxyl ion balance in water.
Technically, pH is related to the hydrogen ion concentration
or activity present in a given solution. pH numbers are the
negative logarithm of the hydrogen ion concentration. A pH
of 7 indicates neutrality or a balance between free hydrogen
and free hydroxyl ions. Solutions with a pH above 7
indicate that the solution is alkaline, while a pH below 7
indicates that the solution is acidic. Knowledge of the pH
of water or wastewater is useful in determining necessary
measures for corrosion control, pollution control, and
disinfection. Waters with a pH below 6.0 are corrosive to
water works structures, distribution lines,, and household
plumbing fixtures such as iron, copper, zinc, cadmium, and
lead. Low pH waters not only tend to dissolve metals from
structures and fixtures but also tend to redissolve or leach
metals from sludges and bottom sediments. The hydrogen ion
concentration can affect the "taste" of the water and at a
low pH, water tastes "sour."
Extremes of pH or rapid pH changes can exert stress
conditions or kill aquatic life outright. Even moderate
changes from "acceptable" criteria limits of pH are
deleterious to some species. The relative toxicity to
aquatic life of many materials is increased by changes in
the water pH. For example, metalocyanide complexes can
increase a thousand-fold in toxicity with a drop of 1.5 pH
units. Similarly, the toxicity of ammonia is a function of
pH. The bactericidal effect of chlorine in most cases is
less as the pH increases, and it is economically
advantageous to keep the pH close to 7.
Most bacteria (and other protists) that are essential to the
operation of a biological treatment system cannot bear pH
levels above 9.5 or below 5.0. The pH range for optimum
growth generally lies between 6.5 to 7.5. Depending on the
volume of a particular waste and the acidity or alkalinity
of the waste in the treatment unit, an incoming waste of
extreme pH could have a substantially adverse effect on a
treatment unit.
Acidity. Acidity is defined as the quantitative ability of
a water to neutralize hydroxyl ions. It is usually
expressed as the calcium carbonate equivalent of the
36
-------
hydroxyl ions neutralized. Acidity should not be confused
with pH value. Acidity is the quantity of hydrogen ions
which may be released to react with or neutralize hydroxyl
ions while pH is a measure of the free hydrogen ions in a
solution at the instant the pH measurement is made. A
property of many chemicals, called buffering, may hold
hydrogen ions in solution from being in the free state and
being measured as pH, The bond of most buffers is rather
weak and hydrogen ions tend to be released from the buffer
as needed to maintain a fixed pH value.
Highly acid waters are corrosive to metals, concrete, and
living organisms, exhibiting the pollutional characteristics
outlined above for low pH waters. Depending on buffering
capacity, water may have a higher total acidity at pH values
of 6.0 than other waters with a pH value of 4.0.
Highly acid wastes can exhibit the same detrimental effects
on microorganisms as wastes of low pH. The acidity of an
incoming waste is particularly important in the operation of
anaerobic digesters, where the pH for optimum operation is
6.6 to 7.6 An incoming waste of high acidity that causes
the pH of an anaerobic system to drop below 6.2 will
severely upset the operation of the unit. Wastes of high
acidity are also corrosive to the metals and concrete that
make up the structure of any treatment unit.
Alkalinity. Alkalinity is defined as the ability of a water
to neutralize hydrogen ions. It is usually expressed as the
calcium carbonate equivalent of the hydrogen ions
neutralized.
Alkalinity is commonly caused by the presence of carbonates,
bicarbonates, hydroxides, and to a lesser extent borates,
silicates, phophates, and organic substances. Because of
the nature of the chemicals causing alkalinity, and the
buffering capacity of carbon dioxide in water, very high pH
values are seldom found in natural waters.
Excess alkalinity, as exhibited in a high pH value, may make
water corrosive to certain metals, detrimental to most
natural organic materials, and toxic to living organisms.
Ammonia is more irritating at higher pH. The lacrimal fluid
of the human eye has a pH of approximately 7.0 and a
deviation of 0.1 pH unit from the norm may result in eye
irritation for the swimmer. Appreciable irritation will
cause severe pain.
A waste of high alkalinity can interfere with the operation
of a treatment unit, causing the death of microorganisms and
the corrosion of structural materials.
87
-------
Oil and Grease
Because of widespread use, oil and grease occurs often in
wastewater streams. These oily wastes may be classified as
follows:
° Light Hydrocarbons. These include light fuels such
as gasoline, kerosene, and jet fuel, and
miscellaneous solvents used for industrial
processing, degreasing, or cleaning purposes. The
presence of these hydrocarbons may make the removal
of other heavier oily wastes more difficult.
° Heavy Hydrocarbons, Fuels, and Tars. These include
the crude oils, diesel oils, #6 fuel oil, residual
oils, shop oils, and in some cases, asphalt and
road tar.
o Lubricants and Cutting Fluids. These generally
fall into two classes: non-emulsifiable oils such
as lubricating oils and greases, and emulsifiable
oils such as water soluble oils, rolling oils,
cutting oils, and drawing compounds. Emulsifiable
oils may contain fat, soap or various other
additives.
These compounds can settle or float and may exist as solids
or liquids depending upon factors such as method of use,
production process, and temperature of wastewater.
Oil and grease even in small quantities causes troublesome
taste and odor problems. Scum lines from these agents are
formed on water treatment basin walls and other containers.
Fish and waterfowl are adversely affected by oils in their
habitat. Oil emulsions may adhere to the gills of fish
causing suffocation, and the flesh of fish is tainted when
microorganisms that were exposed to waste oil are eaten.
Deposition of oil in the bottom sediments of water can serve
to inhibit normal benthic growth. Oil and grease exhibit an
oxygen demand.
Levels of oil and grease which are toxic to aquatic
organisms vary greatly, depending on the type and the
species susceptibility. However, it has been reported that
crude oil in concentrations as low as 0.3 mg/1 is extremely
toxic to freshwater fish. It has been recommended that
public water supply sources be essentially free from oil and
grease.
Oil and grease in quantities of 100 1/sq km (10 gallons/sq
mile) show up as a sheen on the surface of a body of water.
The presence of oil slicks prevent the full aesthetic
88
-------
enjoyment of water. The presence of oil in water can also
increase the toxicity of other substances being discharged
into the receiving bodies of water.
Oil and grease can cause problems with scum formation in wet
wells and clarifiers. Mineral oils in particular can coat
solid particles that are present in wastes. The particles
hinder biological^ activity and increase maintenance
problems. Free oil (as measured by CC14 extraction) has
reportedly interfered with aerobic biological treatment at
concentrations of 50 to 100 mg/1 (15).
Oxygen Demand (BOD and COD)
Organic and some inorganic compounds can cause an oxygen
demand to be exerted in a receiving body of water.
Indigenous microorganisms utilize the organic wastes as an
energy source and oxidize the organic matter. In doing so
their natural respiratory activity will utilize the
dissolved oxygen.
Biochemical oxygen demand (BOD). BOD is the quantity of
oxygen required for the biological and chemical oxidation of
waterborne substances under ambient or test conditions.
Materials which may contribute to the BOD include:
carbonaceous organic materials usable as a food source by
aerobic organisms; oxidizable nitrogen derived from
nitrites, ammonia and organic nitrogen compounds which serve
as food for specific bacteria, and certain chemically
oxidizable materials such as ferrous iron, sulfides,
sulfite, etc. which will react with dissolved oxygen or are
metabolized by bacteria. In most industrial and municipal
wastewaters, the BOD derives principally from organic
materials and from ammonia (which is itself derived from
animal or vegetable matter).
The BOD of a waste exerts an adverse effect upon the
dissolved oxygen resources of a body of water by reducing
the oxygen available to fish, plant life, and other aquatic
species. Conditions can be reached where all of the
dissolved oxygen in the water is utilized, resulting in
anaerobic conditions and the production of undesirable gases
such as hydrogen sulfide and methane. The reduction of
dissolved oxygen can be detrimental to fish populations,
fish growth rate, and organisms used as fish food. A total
lack of oxygen due to the exertion of an excessive BOD can
result in the death of all aerobic aquatic inhabitants in
the affected area.
Water with a high BOD indicates the presence of decomposing
organic matter and an associated increase in bacterial
concentrations that degrade its quality and potential uses.
89
-------
A by-product of high BOD concentrations can be increased
algal concentrations and blooms which result from
decomposition of the organic matter and which form the basis
of algal populations.
The BOD5_ (5-day BOD) test is used widely to estimate the
pollutional strength of domestic and industrial wastes in
terms of the oxygen that they will require if discharged
into receiving streams. The test is an important one in
water pollution control activities,, to evaluate the design
and efficiencies of wastewater treatment works, and to
indicate the state of purification or pollution of receiving
bodies of water.
Complete biochemical oxidation of a given waste may require
a period of incubation too long for practical analytical
test purposes. For this reaison, the five day period has
been accepted as standard, and the test results have been
designated as BODJ5. Specific chemical test methods are not
readily available for measuring the quantity of many
degradable substances and their reaction products. Reliance
in such cases is placed on the collective parameter, BODj>
which measures the weight of dissolved oxygen utilized by
microorganisms as they oxidize or transform the gross
mixture of chemical compounds in the wastewater. The
biochemical reactions involved in the oxidation of carbon
compounds are related to the period of incubation. The
five-day BOD normally measures only 60 to 80 percent of the
carbonaceous biochemical oxygen demand of the sample, and
for many purposes this is a reasonable parameter.
Additionally, it can be used to estimate the gross quantity
of oxidizable organic matter.
The BODS^ test is essentia.lly a bioassay procedure which
provides an estimate of the oxygen consumed by
microorganisms utilizing the degradable matter present in a
waste under conditions that are representative of those that
are likely to occur in nature. Standard conditions of time,
temperature, suggested microbial seed, and dilution water
for the wastes have been defined and are incorporated in the
standard analytical procedure. Through the use of this
procedure, the oxygen demand of diverse wastes can be
compared and evaluated for pollution potential and to some
extent for treatability by biological treatment processes.
Because the BOD test is a bioassay procedure, it is
important that the environmental conditions of the test be
suitable for the microorganisms to function in an
uninhibited manner at all times. This means that toxic
substances must be absent and that the necessary nutrients,
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such as nitrogen, phosphorous, and trace elements, must be
present.
Chemical Oxygen Demand (COD). COD is a purely chemical
oxidation test devised as an alternate method of estimating
the total oxygen demand of a wastewater. Since the method
relies on the oxidation-reduction system of chemical
analyses rather than on biological factors, it is more
precise, accurate, and rapid than the BOD test. The COD
test is widely used to estimate the total oxygen demand
(ultimate rather than 5-day BOD) to oxidize the compounds in
wastewater. It is based on the fact that organic compounds,
with a few exceptions, can be oxidized by strong chemical
oxidizing agents under acid conditions with the assistance
of certain inorganic catalysts.
The COD test measures the oxygen demand of compounds that
are biologically degradable and of many that are not.
Pollutants which are measured by the BOD5_ test will be
measured by the COD test. In addition, pollutants which are
more resistant to biological oxidation will also be measured
as COD. COD is a more inclusive measure of oxygen demand
than is BODJ3 and will result in higher oxygen demand values
than will the BOD5> test.
The compounds which are more resistant to biological
oxidation are becoming of greater and greater concern not
only because of their slow but continuing oxygen demand on
the resources of the receiving water, but also because of
their potential health effects on aquatic life and humans.
Many of these compounds result from industrial discharges
and some have now been found to have carcinogenic, mutagenic
and similar adverse effects, either singly or in
combination. Concern about these compounds has increased as
a result of demonstrations that their long life in receiving
waters - the result of a slow biochemical oxidation rate
allows them to contaminate downstream water intakes. The
commonly used systems of water purification are not
effective in removing these types of materials and
disinfection such as chlorination may convert them into even
more hazardous materials.
Thus, the COD test measures organic matter which exerts an
oxygen demand and which may affect the health of people. It
is a useful analytical tool for pollution control
activities. It provides a more rapid measurement of the
oxygen demand and an estimate of organic compounds which are
not measured in the BODS test.
Total Suspended Solids (TSS)
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Suspended solids include both organic and inorganic
materials. The inorganic compounds include sand, silt, and
clay. The organic fraction includes such materials as
grease, oil, tar, and animal and vegetable waste products.
These solids may settle out rapidly and bottom deposits are
often a mixture of both organic and inorganic solids.
Solids may be suspended in water for a time, and then settle
to the bed of the stream or lake. These solids discharged
with man's waste may be inert, slowly biodegradable
materials, or rapidly decomposable substances. While in
suspension, they increase the turbidity of the water, reduce
light penetration and impair the photosynesthic activity of
aquatic plants.
Chromium (Cr
Chromium is an elemental metal usually found as a chromite
(FeCr20jJ). The metal is normally processed by reducing the
oxide with aluminum.
Chromium and its compounds are used extensively throughout
industry. It is used to harden steel and as an ingredient
in other useful alloys. Chromium is also used in the
electroplating industry as an ornamental and corrosion
resistant plating on steel and can be used in pigments and
as a pickling acid (chromic acid) ,
The two most prevalent chromium forms found in industry
wastewaters are hexavalent and trivalent chromium. Chromic
acid used in industry is a hexavalent chromium compound
which is partially reduced to the trivalent form during use.
Chromium can exist as either trivalent or hexavalent
compounds in raw waste streams, but hexavalent chromium
predominates at the conditions found in most wastes.
Hexavalent chromium treatment involves reduction to the
trivalent form prior to removal of chromium from the waste
stream as a hydroxide precipitate.
Chromium, in its various valence states, is hazardous to
man. It can produce lung tumors when inhaled and induces
skin sensitizations. Large doses of chromates have
corrosive effects on the intestinal tract and can cause
inflammation of the kidneys. Levels of chromate ions that
have no effect on man appear to be so low as to prohibit
determination to date. The recommendation for public water
supplies is that such supplies contain no more than 0.05
mg/1 total chromium.
The toxicity of chromium salts to fish and other aquatic
life varies widely with the species, temperature, pH,
valence of the chromium, and synergistic or antagonistic
effects, especially that of hard water. Studies have shown
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that trivalent chromium is more toxic to fish of some types
than hexavalent chromium. other studies have shown opposite
effects. Fish food organisms and other lower forms of
aquatic life are extremely sensitive to chromium and it also
inhibits the growth of algae. Therefore, both hexavalent
and trivalent chromium must be considered harmful to
particular fish or organisms.
Hexavalent chromium has been shown to interfere with the
operation of activated sludge systems and anaerobic
digesters (22) and nitrification units (15). Slug doses of
hexavalent chromium of 500 mg/1 to activated sludge systems
have been shown to reduce BOD removal efficiency by 11
percent and COD removal efficiency by 13 percent, for
periods as long as 32 hours. Slug doses of 300 mg/1 to
anaerobic digesters have caused gas production to cease for
seven days, and doses of 500 mg/1 have ceased gas production
permanently. The nitrification process is severely affected
at Cr+6 concentrations in raw sewage on the order of 2 mg/1
to 5 mg/1. The effects on these systems can be multiplied
by the presence of iron, copper, and high acidity, since
these constituents exert synergistic effects with chromium
(16).
Depending on the influent concentration, significant amounts
of Cr+6 can pass through activated sludge systems; the
removal efficiency has been reported to be as low as 17
percent at influent Cr+6 concentrations of 50.0 mg/1, but as
high as 78 percent at concentrations of 0.5 mg/1 (22).
Copper (Cu)
Copper is an elemental metal that is sometimes found free in
nature and is found in many minerals such as cuprite,
malachite, azurite, chalcopyrite, and bornite. Copper is
obtained from these ores by smelting, leaching, and
electrolysis. Significant industrial uses are in the
plating, electrical, plumbing, and heating equipment
industries. Copper is also commonly used with other
minerals as an insecticide and fungicide.
Traces of copper are found in all forms of plant and animal
life, and it is an essential trace element for nutrition.
Copper is not considered to be a cumulative systemic poison
for humans as it is readily excreted by the body, but it can
cause symptoms of gastroenteritis, with nausea and
intestinal irritations, at relatively low dosages. The
limiting factor in domestic water supplies is taste.
Threshold concentrations for taste have been generally
reported in the range of 1.0 to 2.0 mg/1 of copper while
concentrations of 5 to 7.5 mg/1 have made water completely
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undrinkable. It has been recommended that the copper in
public water supply sources not exceed 1 mg/1.
Copper salts cause undersirable color reactions in the food
industry and cause pitting when deposited on some other
metals such as aluminum and galvanized steel. The textile
industry is affected when copper salts are present in water
used for processing of fabrics. Irrigation waters
containing more than minute quantities of copper can be
detrimental to certain crops. The toxicity of copper to
aquatic organisms varies significantly, not only with the
species, but also with the physical and chemical
'characteristics of the water, including temperature,
hardness, turbidity, and carbon dioxide content. In hard
water, the toxicity of copper salts may be reduced by the
precipitation of copper carbonate or other insoluble
compounds. The sulfates of copper and zinc and of copper
and cadmium are synergistic in their toxic effect on fish.
Copper concentrations less than 1 mg/1 have been reported to
be toxic, particularly in soft water, to many kinds of fish,
crustaceans, mollusks, insects, phytoplankon and
zooplankton. Concentrations of copper, for example, are
detrimental to some oysters; above 0.1 mg/1. Oysters,
cultured in seawater containing 0.13 to 0.5 mg/1 of copper,
deposit the metal in their bodies and become unfit as a food
substance.
The toxic effects of copper are compounded when certain
other metals are present. Copper and zinc have been
reported to be five times as toxic when combined than would
be expected considering the toxicity of each metal
separately. Increased toxicological effects of a similar
magnitude have been noted between copper and cadmium, and
other synergistic toxic effects of copper have been observed
when mercury or phosphates are present. conversely,
sulfide, high pH, and certciin chelating agents (such as
EDTA) have been reported to be antagonistic with copper
(16).
Copper, as well as most metals, is generally not susceptable
to treatment by biological treatment processes at POTW.
Research has shown that up to half of the input metal will
pass through the treatment plant, with about 30 to 50
percent of the copper which passes through the plant
appearing in the soluble state. Digestion has been impaired
by copper continuously fed at 10 mg/1, and slug doses of
copper at 50 mg/1 for four hours in an unacclimated system
have resulted in greatly decreased efficiencies of treatment
plants for up to 100 hours.
-------
The copper that is removed from the influent stream by the
POTW is absorbed on the sludge, or it appears in the sludge
as the hydroxide of the metal. Experimental data shows that
when dried sludge is spread over tillable land, the copper
tends to remain in place down to the depth of tillage,
except for that copper that is taken up by plants grown in
the soil. Copper tends to concentrate in the roots of
plants, and has shown little tendency to migrate to other
parts of the plant. In most cases, the concentration of
copper in plants will kill the plant before it has reached a
high enough concentration to evidence harm in animals that
may eat the plants, although it is reported that copper
concentrated in plants has resulted in fatalities among
sheep.
Cyanide (CM)
Cyanide is a compound that is widely used in industry
primarily as sodium cyanide (NaCN) or hydrocyanic acid
(HCN). The major use of cyanides is in the electroplating
industry where cyanide baths are used to hold ions such as
zinc and cadmium in solution. Cyanides in various compounds
are also used in steel plants, chemical plants, photographic
processing, textile dying, and ore processing.
Of all the cyanides, hydrogen cyanide (HCN) is probably the
most acutely lethal compound. HCN dissociates in water to
hydrogen ions and cyanide ions in a pH dependent reaction.
The cyanide ion is less acutely lethal than HCN. The
relationship of pH to HCN shows that as the pH is lowered to
below seven there is less than one percent of the cyanide
molecules in the form of the CN ion and the rest is present
as HCN. When the pH is increased to 8, 9, and 10, the
percentage of cyanide present as CN ion is 6.7, 42, and 87
percent, respectively. The toxicity of cyanides is also
increased by increases in temperature. A. rise of 10°C
produced a two-to threefold increase in the rate of the
lethal action of cyanide.
In the body, the CN ion, except for a small portion exhaled,
is rapidly changed into a relatively non-toxic complex
(thiocyanate) in the liver and eliminated in the urine.
There is no evidence that the CN ion is stored in the body.
The safe ingested limit of cyanide has been estimated to be
something less than 18 mg/day, part of which comes from
normal environment and industrial exposure. The average
fatal dose of HCN by ingestion by man is 50 to 60 mg. It
has been recommended that a limit of 0. 2 mg/1 cyanide not be
exceeded in public water supply sources.
The harmful effects of the cyanides on aquatic life is
affected by the pH, temperature, dissolved oxygen content.
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and the concentration of minerals in the water. The
biochemical degradation of cyanide is not affected by
temperature in the range of 10°C to 35° C while the toxicity
of HCN is increased at higher temperatures.
On lower forms of life and organisms, cyanide does not seem
to be as toxic as it is toward fish. The organisms that
digest BOD were found to be inhibited at 60 mg/1 although
the effect is more one of delay in exertion of BOD than
total reduction.
Certain metals such as nickel may form complexes with
cyanide to reduce lethality, especially at higher pH values.
On the other hand, zinc and cadmium cyanide complexes may be
exceedingly toxic.
Research has shown that concentrations of 1.0 to 2.0 mg/1 of
cyanide (as HCN) in influent, sewage adversely affect the
performance of activated sludge units and anaerobic
digesters, and 2.0 mg/1 of cyanide inhibits the
nitrification process. The quality of trickling filter
effluent has been reported to be severely affected at
influent cyanide concentrations of 30 mg/1 (15).
Iron (Fe)
Iron is an abundant metal found in the earth's crust. The
most common iron ore is hematite from which iron is obtained
by reduction with carbon. Other forms of commercial ores
are magnetite and taconite. Pure iron is not often found in
commercial use, but it is usually alloyed with other metals
and minerals, the most common being carbon.
Iron is the basic element in the production of steel and
steel alloys. Iron with carbon is used for casting of major
parts of machines and it can be machined, cast, formed, and
welded. Ferrous iron is used in paints, while powdered iron
can be sintered and used in powder metallurgy. Iron
compounds are also used to precipitate other metals and
undesirable minerals from industrial wastewater streams.
Iron is chemically reactive and corrodes rapidly in the
presence of moist air and at elevated temperatures. In
water and in the presence of oxygen, the resulting products
of iron corrosion may be pollutants in water. Natural
pollution occurs from the leaching of soluble iron salts
from soil and rocks and is increased by industrial
wastewater from pickling baths and other solutions
containing iron salts.
Corrosion products of iron in water cause staining of
porcelain fixtures, and ferric iron combines with tannin to
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produce a dark violet color. The presence of excessive iron
in water discourages cows from drinking and, thus reduces
milk production. High concentrations of ferric and ferrous
irons in water kill most fish introduced to the solution
within a few hours. The killing action is attributed to
coatings of iron hydroxide precipitates on the gills. Iron-
oxidizing bacteria are dependent on iron in water for
growth. These bacteria form slimes that can affect the
aesthetic values of bodies of water and cause stoppage of
flows in pipes.
Iron is an essential nutrient and micronutrient for all
forms of growth. Drinking water standards in the U.S. have
set a recommended limit of 0.3 mg/1 of iron in domestic
water supplies based not on physiological considerations,
but rather on aesthetic and taste considerations.
Iron has no effect on the activated sludge process except at
very high concentrations (on the order of 1000 mg/1). The
effect of iron on the sludge digestion process has been
reported to be much greater - iron levels above 5 mg/1 in
digesters have caused interference with the process, due to
the release of acidity when the iron is hydrolyzed. These
effects may be magnified by the synergistic effect of
chromium on iron, or decreased by the antagonistic effects
of sulfide, cyanide, and high pH on irons (16).
Nickel (Ni)
Elemental nickel is seldom found in nature in the pure
state. Nickel is obtained commercially from pentlendite and
pyrrhotite. It is a relatively plentiful element and is
widely distributed throughout the earth's crust. It occurs
in marine organisms and is found in the oceans. Depending
on the dose, the organism involved, and the type of compound
involved, nickel may be beneficial or toxic. Pure nickel is
not soluble in water but many of its salts are very soluble.
The toxicity of nickel to man is believed to be very low and
systemic poisoning of human beings by nickel or nickel salts
is almost unknown. Nickel salts have caused the inhibition
of the biochemical oxidation of sewage. They also caused a
50 percent reduction in the oxygen utilization from
synthetic sewage in concentrations of 3.6 to 27 mg/1 of
various nickel salts.
Nickel is extremely toxic to citrus plants. It is found in
many soils in California, generally in insoluble form, but
excessive acidification of such soil may render it soluble,
causing severe injury to or the death of plants. Many
experiments with plants in solution cultures have shown that
nickel at 0.5 to 1.0 mg/1 is inhibitory to growth.
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Nickel salts can kill fish at very low concentrations.
However, it has been found to be less toxic to some fish
than copper, zinc, and iron,. Data for the fathead minnow
show death occurring in the range of 5 to 13 mg/1 depending
on the alkalinity of the water.
Nickel is present in coastal and open ocean with
concentrations in the range of 0.1 to 6.0 mg/1, although the
most common values are 2 to 3 mg/1. Marine animals contain
up to 400 mg/1, and marine plants contain up to 3,000 mg/1.
The lethal limit of nickel to some marine fish has been
reported as low as 0.8 ppm. Concentrations of 13.1 mg/1
have been reported to cause a 50 percent reduction of the
photosynthetic activity in the giant kelp (Macrocystic
pyrifera) in 96 hours, and a low concentration was found to
kill oyster eggs.
Nickel can inhibit the operation of activated sludge units
and nitrification units. Up to a five percent decrease in
the BOD removal efficiency of. activated sludge units has
been reported at nickel influent concentrations of 2.5 to
10.0 mg/1. Slug doses of nickel of 200 mg/1 to activated
sludge units have been reported to seriously reduce
treatment efficiency (22). Severe inhibition of the
nitrification process has been reported at nickel influent
concentrations of 0.5 mg/1 (15).
Significant amounts of nickel can pass through treatment
units - the activated sludge process has been reported to be
only approximately 30 percent efficient in the removal of
nickel.
Phosphorus (P)
Phosphorus occurs in natural waters and in wastewaters in
the form of various types of phosphates. These forms are
commonly classified into orthophosphates, condensed
phosphates (pyro-, meta-, and polyphosphorus), and
originally bound phosphates. These may occur in the soluble
form, in particles of detritus, or in the bodies of aquatic
organisms.
The various forms of phosphates find their way into
wastewaters from a variety of industrial, residential, and
commercial sources. Small amounts of certain condensed
phosphates are added to some water supplies in the course of
potable water treatment. Large quantities of the same
compounds may be added when the water is used for laundering
or other cleaning since these materials are major
constituents of many commercial cleaning preparations.
Phosphate coating of metals is another major source of
phosphates in certain industrial effluents.
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The increasing problem of the growth of algae in streams and
lakes appears to be associated with the increasing presence
of certain dissolved nutrients, chief among which is
phosphorus. Phosphorus is an element which is essential to
the growth of organisms and it can often be the nutrient
that limits the aquatic growth that a body of water can
support. In instances where phosphorus is a growth limiting
nutrient, the discharge of sewage, agricultural drainage, or
certain industrial wastes to a receiving water may stimulate
the growth, in nuisance quantities, of photosynthetic
aquatic microorganisms and macroorganisms.
The increase in organic matter production by algae and
plants in a lake undergoing eutrophication has ramifications
throughout the aquatic ecosystem. Greater demand is placed
on the dissolved oxygen in the water as the organic matter
decomposes at the termination of the life cycles. Because
of this process, the deeper waters of the lake may become
entirely depleted of oxygen, thereby destroying fish
habitats and leading to the elimination of desirable
species. The settling of particulate matter from the
productive upper layers changes the character of the bottom
mud, also leading to the replacement of certain species by
less desirable organisms. Of great importance is the fact
that nutrients inadvertently introduced to a lake are, for
the most part, trapped there and recycled in accelerated
biological processes. Consequently, the damage done to a
lake in a relatively short time requires a many fold
increase in time for recovery of the lake.
When a plant population is stimulated in production and
attains a nuisance status, a large number of associated
liabilities are immediately apparent. Dense populations of
pond weeds make swimming dangerous. Boating and water
skiing and sometimes fishing may be eliminated because of
the mass of vegetation that serves as a physical impediment
to such activities. Plant populations have been associated
with stunted fish populations and with poor fishing. Plant
nuisances emit vile stenches, impart tastes and odors to
water supplies, reduce the efficiency of industrial and
municipal water treatment, impair aesthetic beauty, reduce
or restrict resort trade, lower waterfront property values,
cause skin rashes to man during water contact, and serve as
a desired substrate and breeding ground for flies.
Phosphorus in the elemental form is particularly toxic, and
subject to bioaccumulation in much the same way as mercury.
Colloidal elemental phosphorus will poison marine fish
(causing skin tissue breakdown and discoloration). Also,
phosphorus is capable of being concentrated and will
accumulate in organs and soft tissues. Experiments have
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shown that marine fish will concentrate phosphorus from
water containing as little as 1 ug/1.
Zinc (Zn)
Occurring abundantly in rocks and ores, zinc is readily
refined into a stable pure metal and is used extensively for
galvanizing, in alloys, for electrical purposes, in printing
plates, for dye manufacture and for dyeing processes, and
for many other industrial purposes. Zinc salts are used in
paint pigments, cosmetics, Pharmaceuticals, dyes,
insecticides, and other products too numerous to list
herein. Many of these salts (e.g., zinc chloride and zinc
sulfate) are highly soluble in water; hence it is to be
expected that zinc might occur in many industrial wastes.
On the other hand, some zinc salts (zinc carbonate, zinc
oxide, zinc sulfide) are insoluble in water and consequently
it is to be expected that some zinc will precipitate and be
removed readily in most natural waters.
In zinc mining areas, zinc has been found in waters in
concentrations as high as 50 mg/1 and, in effluents from
metal-plating works and small-arms ammunition plants, it may
occur in significant concentrations. In most surface and
ground waters, it is present only in trace amounts. There
is some evidence that zinc irons are adsorbed strongly and
permanently on silt, resulting in inactivation of the zinc.
Concentrations of zinc in excess of 5 mg/1 in raw water used
for drinking water supplies cause an undesirable taste which
persists through conventional treatment. Zinc can have an
adverse effect on man and animals at high concentrations.
In soft water, concentrations of zinc ranging from 0.1 to
1.0 mg/1 have been reported to be lethal to fish. Zinc is
thought to exert its toxic action by forming insoluble
compounds with the mucous thai: covers the gillss, by damage
to the gill epithelium, or possibly by acting as an internal
poison. The sensitivity of fish to zinc varies with
species, age and condition, as well as with the physical and
chemical characteristics of the water. Some acclimatization
to the presence of zinc is possible. It has also been
observed that the effects of zinc poisoning may not become
apparent immediately, so that fish removed from zinc-
contaminated to zinc-free water (after 4 to 6 hours of
exposure to zinc) may die 48 hours later. The presence of
copper in water may increase the toxicity of zinc to aquatic
organisms, but the presence of calcium or hardness may
decrease the relative toxicity.
Observed values for the distribution of zinc in ocean waters
vary widely. The major concevrn with zinc compounds in
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marine waters is not one of acute toxicity, but rather of
the long-term sublethal effects of the metallic compounds
and complexes. From an acute toxicity point of view,
invertebrate marine animals seem to be the most sensitive
organisms tested. The growth of the sea urchin, for
example, has been retarded by as little as 30 ug/1 of zinc.
Zinc is readily taken up and translocated within plants.
The activity of zinc is most profound in acid soils and
decreases in the presence of large amounts of phosphates, as
would be found in sludges from POTW. For each unit increase
in the pH, there is a hundredfold decrease in the toxicity
of zinc. In plants the poisoning mechanism is iron
deficiency, and to avoid this, lime must be added to the
soil to maintain soil pH above 6.0. Generally, zinc will
kill the plants before reaching concentrations harmful to
animals in the plants.
Dissolved zinc is generally not susceptible to treatment by
biological treatment processes at POTW. In slug doses, and
particularly in the presence of copper, dissolved zinc can
interfere with or seriously disrupt the operation of POTW
using biological processes by reducing overall removal
efficiencies, largely as a result of the toxicity of the
metal to biological organisms. However, zinc solids (in the
form of hydroxides or sulfides) do not appear to interfere
with biological treatment processes on the basis of
available data. Such solids accumulate in the sludge, where
subsequent effects depend on the sludge disposal method.
Polychlorinated Biphenyls (PCBs)
Polychlorinated biphenyls (PCBs) are a family of partially
or wholly chlorinated isomers of biphenyl. The commercial
mixtures generally contain UO to 60 percent chlorine with as
many as 50 different detectable isomers present. The PCB
mixture is a colorless and viscous fluid, relatively
insoluble in water, that can withstand very high
temperatures without degradation. PCB's do not conduct
electricity, and the more highly chlorinated isomers are not
readily degraded in the environment.
PCBs are used in paints, inks, and plastics. They are also
found in hydraulic systems, in transformers and capacitors,
and in the wastes from the reprocessing of certain papers.
The major uses of PCBs can be grouped into three major
categories: open uses, partially closed system uses, and
closed system uses. Open uses include paints, inks,
plastics, and paper coatings. The PCBs in all of these
products contact with the environment and can be leached out
by water. The so-called carbonless carbon paper contains
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PCBs in the encapsulated ink and is claimed to be
responsible for the PCBs found extensively in recycled
paper. PCBs have been used as plasticizers in polyvinyl
chloride (PVC) and chlorinated rubbers.
Uses of PCBs in partially closed systems include the working
fluid in heat exchangers and hydraulic systems. These
systems have a potential for leakage of the PCB fluid either
during use or after being discarded.
The electric industry is the single major consumer of PCBs
mainly in a closed loop system in transformers and
capacitors. PCBs are ideal for use in large transformers
and power capcitors, since they are non-flammable and do not
conduct electricity, but still transfer heat well. The
fluid is generally sealed into the unit to prevent loss, but
leakage may occur from some transformers through gaskets or
broken oil level viewing glasses. Release of PCBs into the
environment may also occur during the drainage and
replacement of oil in defective transformers, or if old or
defective capacitors are disposed of in landfills and
broken while being buried. Transformers and capacitors
account for about 63 percent of all PCB use.
Agreement is not universal on exactly how PCBs are released
into the environment or in what quantities. Analyses of
water samples from 30 major tributaries to the Great Lakes
indicate widespread contamination, with 71 percent of all
samples having detectable concentrations (greater than 10
parts per trillion). PCBs have been found in all organisms
analyzed from the north and south Atlantic, even in animals
living under 11,000 feet of water. It is reported that one-
third of the human tissue sampled in the United States
contains more than one part ptvr million (ppm) of PCBs.
Once in the environment, PCBs appear to persist for a long
time. Evidence for this can be seen in the fact that in
most areas of the continent and through out the Atlantic
Ocean more PCB than DDT is found in the animals, even though
three times more DDT is produced each year and all of it is
discharged directly into the environment. Based on present
available data, it seems safe to assume the PCBs are present
in varying concentrations in every species of wildlife on
earth.
Liver damage is a common effect of PCBs on all species,
while the occurrence of edema, skin lesions, and
reproductive failure is species-specific. Hatchability of
eggs is noticeably decreased by exposure to PCBs. PCBs have
been shown to produce lethal and sublethal effects on fish
and animals, including reduced reproduction of the species
and abnormal young.
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PCBs may be removed by up to 70 percent or more from
domestic wastewaters during biological treatment (22).
However, PCBs appear to simply accumulate unchanged in
treatment tank sludges, and are not biodegraded or converted
to other more readily degradable substances during treatment
(23). Disposal of treatment sludges in landfills could then
release PCBs into the environment once again. There is some
evidence, however, that PCBs are destroyed during
incineration of sewage sludge (24).
Ethylenediamine Tetracetic Acid (EDTA)
No definitive information on the toxicity or treatability of
EDTA in biological treatment systems is available to EPA at
the present time.
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SECTION VII
TREATMENT AND CONTROL TECHNOLOGY
Introduction
Treatment and control technologies for potential pollutants
discharged from steam electric power generating plants
discharging to publicly-owned treatment works (POTW) are
outlined in this section. In-process controls discussed
include those techniques which are normally used by the
industry or by industries employing similar processes. Such
controls include process modifications, materials
substitution, raw materials and products recovery, water
conservation and wastewater reuse, and general good
housekeeping practices.
Wastewater effluents discharged to publicly-owned treatment
facilities are sometimes treated by end-of-process physical
or chemical systems to remove pollutants which can upset
operation of the POTW or which may be treated inadequately.
Such treatment methods are numerous, but they generally fall
into one of three broad categories in accordance with their
process objectives. These include pH control, removal of
dissolved materials, and separation of phases.
Of the twenty-three plants surveyed only eight provide end-
of-pipe treatment to their waste, before discharging it to
POTW. The extent of treatment applied varies in accordance
with the local requirements for discharge limitations. Most
of the plants use retention ponds to equalize the flow to
POTWs. These ponds also serve as sedimentation basins for
partial removal of suspended solids by gravity settling and
are sometimes equipped with skimming devices to remove
floating oil. A detailed description of end-of-pipe
treatment techniques used is presented in Section V of this
report.
END-OF-PIPE TREATMENT TECHNOLOGY
Treatment Technologies Available
If a pollutant in a waste stream is not acceptable for
discharge to the publicly-owned treatment plant, end-of-pipe
treatment must be provided to remove the pollutant or reduce
it to allowable limits. Only a few existing plants
discharging into POTW provide end-of-pipe treatment. Yet,
basic technology is available to reduce nearly all of the
pollutants produced by steam electric generating plants.
For certain pollutants, in-plant controls are probably the
preferred control strategy. This technology is shown in
105
-------
Tables VII-1 and VII-2. Table VII-1 lists potential
dissolved matter removal methods and Table VII-2 provides a
similar list of solid liquid separation processes. Most of
the processes listed are in use for treatment of steam
electric or other industrial or municipal water and
wastewaters.
TREATMENT OF MAJOR POLLUTANTS
Available technology and efficiency of their removal for
major pollutants are shown in Table VII-3. These are based
on data obtained from several different industries who
discharge pollutants similar to those observed in this
industry. The following is a brief discussion of the
technologies associated with removal of pollutants from the
power plant.
Total Dissolved Solids. Removal of total dissolved solids
(TDS) from wastewaters is one of the more difficult and more
expensive waste treatment procedures. Where TDS result from
heavy metal or hardness ions, reduction can be achieved by
chemical precipitation methods; however, where dissolved
solids are present as sodium, calcium, or potassium
compounds, then TDS reduction requires more specialized
treatment, such as reverse osmosis, electrodialysis,
distillation, and ion exchange.
Total Suspended Solids. Suspended solids removal can be
achieved by sedimentation and filtratiom operations.
Sedimentation lagoons are commonly used at steam electric
power plants. Some plants employed configured tanks. Tanks
can be used where space limitations are important. Tanks
constructed for solids removal usually have built-in
facilities for continuous or intermittent sludge removal.
Designs based on maximum flow anticipated can provide the
best performance. Equalization can be provided to regulate
flow. The retention time required is related to the
particle characteristics.
Oil and Grease. Certain preventative measures can be
applied to prevent spillage of oil and the entrance of oil
into the plant drainage system. Flotation is efficient in
removing emulsified oil and requires minimum space. It can
be used without chemical addition, but demulsifiers and
coagulants can improve performance in some cases. Whenever
possible, primary separation facilities should be employed
to remove free oil and solids before the water enters the
flotation unit. Multistage units are more effective than
single-stage units. Partial recycle units are more
effective than full-pressure units. Oil removal facilities
including single-cell flotation can achieve effluent oil and
106
-------
Table VII-1 .
END-OF-PIPE TREATMENT METHODS
Method
Neutra 1 i zati on
Chemi cal reduction
Preci pi tatlon
Ion exchange
Liquid/liquid
extract! on
object! ves
usua 1 ly to wi thin
reducti on of
hexaval ent
chromium to
trlvalent
chromi urn
removal of ions
by formi ng s 1 i ght-
ly soluble salts
removal of i ons by
sorpti on on surface
nf a SO" » d n-a t>-i x
removal of soluble
organics or chemi-
cal ly charged pol -
lutants
Chpmicals or Process
lime
sulfur dioxide, pH range of
sodi un bisulfite, 2-3
sodium' metabi sulfi te,
ferrous sal ts
lime, hydrogen optimum pH
soda ash moved
synthetic cation may require pH
ant on exchange adjus tment
resins
immiscible solvents may require
that may contain pH adjustment
chelating agents
E f f i c i ency of
99. 7%
copper-96 . 6s
z1nc-99.7S
phosphate-93.6X
cyamde-99°.
copper-95*
1ron-lOOX
cadmi um-92X
nickel-lOOS
z1nc-75S
phospha te-90i
sul fate-97-
alum1num-98S
phenol -991
chromi um-99t
n1ckel-99S
z1nc-99%
Muoride-68S
iron-991
•olybdenum-90*
Advantages
1 -opera tes at
amb i en t en v i ron -
men t
2-we 11 sui ted for
3-hi gh ra te of re-
actions
ambient en-
v i ronmen t
2-wel 1 s ui ted
to automati c
control
1 -operates at
ambient en-
automa ti c control
1 -operates at am-
2-well sui ted to
3-can be used to
1 -can be used to
able cons ti tuents
scaling in sludge
tanks and
condui ts
1 arge
qudnti ti es
of sludge
3-may generate
toxic by-
products
careful pH s 1 udge
control
2-presence of
oxidants
{oxygen,
feme ion)
qu i red dose
of the reduc-
ing agent
3-Sulfur di-
oxide is
toxic and
corrosive
1-requires periodic removal o'f
careful pH s 1 udge
control
more than a
single step
to remove a
mixture of
Ions
3-presence of
chel ati ng
agents ( i .e . ,
cyani de) i n-
creases the
solubi 1 i ty of
many metals
effluent
jected to
attack by
oxi di 21 ng
agents (i.e.
ni tri c acid)
3-subjected to
cloggi ng and
foul i ng
4-costly to
operate
1-effluent re- periodic regenera-
qui red addi- tlou of sol vent
tlonal
2-subjected to
chemical in*
tcrference
3-sol vent sys-
ttH may
deteriorate
Mi th repeate
ust
Demons trati on
by industry
by industry
by industry
status
nsively
used primarily in water
treatment operation for
production of boiler fee
water
process 1s not highly
developed for industrial
-------
Table VII-1. END-OF-PIPE TREATMENT METHODS (CONTINUED)
Method
Disinfection
objectives
destructl on of
ml croorgam sms
Chfmi ca 1 s or
chlorine, hypo-
chlorite salts ,
phenol .phenol
salts of heavy
meta 1 s , chlori ne
dioxide
Process
Efficiency of
may requi re pH
adjustment
Advantages
1 -operates at
ambient en-
vi ronmen t
2-well suited to
automati c control
Limitations
1-may cause
taste and
color pro-
blems
2-di si nfectant
are toxic
compounds
Requi red maintenance
period i c 1 oadi rtg
of chemicals
Demonstration
disinfection
by industry
s tatus
by chlorine
Adsorption
Chemical oxidation
O
Co
Dis ti11ati on
removal of sorbable activated carbon, may require pH
contaminants synthetic sorbents adjustment
destruction of cya- chlorine, hypochlo- pH=9 5-10
mdes rite salts, ozone (first step)
pH=8 (second
step)
separa ti on of dis-
solved ma t te r by
evaporafi on of the
water
1-multistage flash may require pH
distillation adjustment
2-multiple-effect
long-tube verti-
cal evaporation
3-submerged tube
evaporation
4-vapor compres-
s ion
depend on
was te
99 6 *
1005
the !-high removal ef -
qui remen t
bient tenperature
2-we 11 su i ted to
au to ma t i c
control
1 -produces hi gh
qua 1 1 ty water
2-can be used to
recover va 1 u-
ab 1 e cons ti t-
uents
1 -waste re- periodic reg«*nera-
t reatment
regenerati on
during re-
9
ful pH con- sludge and loading
trot of chemi ca 1 s
2-may nrnrfi_'C*
poi sonous
gas
3-second re-
action is
slow
4-subjected to
chemi ca 1
i nterference
1-high energy periodic cleaning to
requirement remove scale
2-may requi re
pretrea tment
of waste
3-cause sea 1 -
i ng of
boi 1 ers and
heat ex-
changers
a. may requ i re
post treat-
ment of
water
practiced extensively
by industry
practiced extensively
by industry
practiced only to a moderate
extent by industry, pnmarjl
the submerged tube type unit
Reverse osmosi s
Electrodi a lysis
separation of di s-
solved matter by
f11tration through
a semi permeable
membrane
removal of
dissolved
polar compounds
1-tubular membrane
2-hoHow-ft Her
modules
3-Spiral-wound flat
sheet membrane
solute is exchanged
between two liquids
through a selectlve
semi permeable mem-
brane in response to
differences in chemi-
cal potential between
two liquids
TDS-62-965
1-produces high
quality water
2-can be used to
recover valuable
const!tuents
3-operates at am-
bi er-1 tempera-
ture
1-can be used to
recover and re-
use va1uable
chemicals
2-produces hi gh
qua 11ty water
1 - 11mi ted range periodic replacement of
of operating membrane
tempera tures
and concen-
trati ons
2-membrane i s
susceptible
to fouli ng by
suspended
solids or
attack by
many chemi-
cals
1-membrane 1s
subjected to
foul ing by
suspended
solids
2-membrane and
electrode are
subjected to
periodic replacement of
membranes and electrodes
very 11 r-,1 ted use in
industrial wastewater
treatment
not practiced by
i ndustry
-------
Table VII-1. END-OF-PIPE TREATMENT METHODS (CONTINUED)
Method
objectives
equi pment
used
Efficiency
of
Advantages
Limitations
Required maintenance
Freezing
separation of so-
1ute from 11qyid
by crystallizing
the solvent
1-direct refriger-
ati on
2-indirect refrig-
eration
1-produces high
quality water
2-low operating
tempera lure
mhibi t s
corrosion
1 -ht gh energy
requ j rement
?-refrigerant
pay be con-
tatni na ted in
the direct
refri geration
method
periodic cleaning and re-
placement of filters and
sc reeris
unproven method
waste treatment
application
o
VO
-------
Table VII-2
Unit
operation
Process
objectives
Methods or
units csed
Re tentl on
tine
Chemicals
used
Efficiency
of removal
Advantages
Skimming
Clarification
Flotation
Micros training
Filtration
Screening
TMckenlng
Pressure
filtration
Heat drying
Ultraflltratlon
removal of floating
solids or liquid
wastes from the water
removal of suspended
solids by settling
separation of sus-
pended solids by
flotation fo!lowed by
s k I mm 1 n g
removal of suspended
solids by passing the
wastewater through a
mlcroscreen
removal of suspended
solids by filtration
through a bed of sand
and gravel
removal of large solid
matter by passing
through screens
concentration of
sludge by removing
water
1-settUng ponds
2-clarfflers
1-15 mln
45 mln
70-901 1-slmple to operate
2-reduces down stream
treatment
3-hlgh efficiency of
removal
l-froth flotation
2-dlspersed air
flotation
3-dlssolved air
flotation
4-gravlty flotation
5-vacuum flotation
1-muttlmedla bed
2-mlxed media bed
20-30
mln
N/A
H/A
1-coarse screens
2-bar screens
3-commur1cat1ng
devices
1-grav1ty thUk-
enl ng
2-alr flotation
thickening
separation of solid from
liquid by passing
through a semlpermeable
membrane under pressure
reduce the water content 1-flash drying
of sludge 2-spray drying
3-rotary kiln
drying
4-multfple hearth
drying
separation of macro-
molecules of sus-
pended matter from the
waste by filtration
through a semlpermeable
membrane under pressure
N/A
N/A
1-3 hrs
N/A
N/A
coagulan ts ,
coagulant al ds
pH adjustment
aluml urn and
ferrl salts.
actlv ted sl-
1 1 ca rganf c
polym ri.
none
none
none
none
none
none
none
to
15 mg/1
90-991
70-80%
(23*)
50-60*
50-99%
50-99X
depends on
the nature
of sludge
to 50-75%
moisture
content
to 81
mol sture
content
Total solid
removal of
951 and
above
1-hfgh efficiency of
removal 1 n short
l-eff1dent process
1-no chemicals require
ment
2-1ow cost of opera-
3-h1gh efficiency of
removal of large
particles
1-low Initial and
operating costs
2-small land re-
qul rement
3-no chemicals re-
quf rement
4-partial removal of
dissolved matter
1 -protect down stream
treatment equipment
1-facllitates further
s ! udge process 1 ng
at ml nf mum cos t
2- flotation thickeners
are more ef f 1 ci ent
than gravl ty thlck-
1-htgh separation
ef f 1 ci ency for
difficult to re-
move solids
2-Hlter cake has a
low water content
3-suspended solids
content of f 1 1 -
trate is low
4-minlmum maintenance
1-produces dl s-
posabl e product
1-low capital Instal-
lation and operating
costs
2-unsensl tfvl ty to
the chemical nature
of waste
3-no waste pre-
treatnent 1s re-
qu1red
Sandbed drying
Vacuum
filtration
removal of moisture
from sludge by evapor-
ation and drainage
through sand.
solid liquid
separation by vacuum
1-covered beds
2-uncovered beds
filtration
1-2 day
as filter
15-20%
produces
301 solid
in filter
cake
1-low costs of
cons truetlon.
operation and
malntenance
l-h1gh1y efficient
process
Centrlfugatfon
liquid/sol Id separ-
ation by centrifugal
force
1-dl.sc centrifuge
2-basket centrifuge
3-conveyor type
centrifuge
N/A
moisture 1s
reduced to
65-70*
1-small space
requi rement
{-simplicity 1n
operati on
Emulsion
breaking
separation between
emulsified oil and
water
2-8 hour
110
alumlnum
salts. Iron
salts, pH
adjustment
(3-4)
>99l
l-h1ghly efficient
process
-------
Table VII-2. SOLID/LIQUID SEPARATION SYSTEMS (CONTINUED)
Unit operation Limitation
Skimming
conta i ni ng
mat ter
tnergy
requl rement
floating
Main tenance
periodic 1 ubr 1 -
cat i en
Demons tratt on
s ta tus
practt ced
1 ndus try
extensively by
Clarification 1-h fgh operating cost nominal
Flotation
1-efMciency depends on nominal
the nature of the par-
ticles surface
periodic loading practiced extensively by
of chemicals and industry
removal of siudge
routine maintenance practiced extensively by
of pumps and motors industry
Mlcrostraln1ng
1-may result 1n high
head loss
2-1ow e ffici ency of
remova I of sira 11
particles
routing cleaning
of screens
practiced only to a moderate
extent, primarily 1n municipal
wastewater treatment plants
Filtration 1-wastewater with high
suspended solids con-
ten t require pre-
treatment
2-n T gh 1osses of head
3-produces wastewater
4-opera t ion is com-
11cated and re -
quf res traim ng
sma 11
routlne ma1n-
tenance of pumps
practiced extensively primarily
In water treatment plant
Screen\ng
ThIcken i ng
1-minor effect on
overa11 treatment
2-may result in high
h««d loss
1-sens itive to fIow
rate of both
effluent and sludge
remova1
sma) ]
periodic cleaning
perlodi c cleanlng
1 ubri cation
practiced extensively
by Industry
practiced extensively
by industry
Pressure 1 -short life of filter
fl 1 tration cloth
2-raquires operating
personne1
small
periodic cleaning
and replacement
of filter
not practiced by
Industry
Heat drying
1 -costly process
high
periodic cleaning
rotary kilns are used
by industry to small
extent
Ul trafi1tration
1 - 1imlted range of
operat1ng tempera-
tu re
2-membrane 1s sus-
ceptible to attack
by many chemi ca1s
3 - 11 m 11 e d range of
app1i ca 11ons
4-membrane can be
fouled by suspended
sol ids
nomlna1
routine maintenance used by Industry
of pumps primarily to treat
o11y was te
Sandbed drying
1 -requi res a 1arge
area of land
small
perlodic removal
of sludge
practiced extensively
by Industry
Vacuum
fi 1 tration
Centri fugatlon
1 -n»o^ operating r.ominal
cos t
2-fiItrate may re-
qui re further
t rea tment
1-high operating nominal
cos t
2-may produce nolse
periodic cleaning practiced extensively
and replacement by Industry
of filter media
periodic lubrfca- equipment for 1n-
ti on and cleaning dustrial wastewater
treatment is under
deve1 opment
Emu)sion
break i ng
1 -t equir es segre-
gation of oily
waste from non
o 1 ly was te
small
111
routine maintenance practiced extensively
of pumps and motors by industry
and periodic re -
moval of sludge
-------
Table VII-3. TREATMENT OF MAJOR POLLUTANTS
Pollutant
Common
pH
Total suspended solids
Specific
0i1and Grease
Hexavalent chromium
Chromium (total)
Iron
Copper
Zinc
Chlorine
Treatment method
1 - Neutralization
1 - Clarification
2 - Flotation
3 - Filtration
1 - Skimming
2 - Gravity flotation
3 - Dissolved air flotation
1 - Chemical reduction
1 - Precipitation
2 - Ion exchange
1 - Precipitation
1 - Precipitation
2 - Ion exchange
1 - Precipitation
2 - Ion exchange
1 - Dissipation
2 - Aeration
3 - Chemical reduction
Residual concentration
achievable (mg/1)(17)
to pH of 5.5 to 9
5-30
5-15
2-10
10-30
20
15
0-1
0.006
0.01
0.3
< 1.
0.03
0.5-2.5
20
Below detection limits
Below detection limits
Below detection limits
112
-------
grease levels as low as 10-20 mg/1, while multistage units
can achieve 2-10 mg/1.
Chromium. The most common method of chromium removal is
chemical reduction of hexavalent chromium to the trivalent
ion and subsequent chemical precipitation. The standard
reduction technique is to lower the waste stream pH to 3 or
below by addition of sulfuric acid, and to add sulfur
dioxide, sodium bisulfite (or metabisulfite or
hydrosulfite) , or ferrous sulfate as a reducing agent.
Trivalent chromium is then removed by precipitation with
lime at pH 8. 5-9.5.
The residual of hexavalent chromium after the reduction step
depends on the pH, retention time, and the concentration and
type of reducing agent.
A process for chromate removal from cooling water has been
recently developed. This is an electrochemical process
whereby an electrical current is applied to a consumable
iron electrode. The resulting ferrous ions react with the
wastewater chromate in accordance with the following
equation:
3 Fe2+ + CrOft =+ 4 H^O = 3 Fe3+ + Cr3+ + 80H^ (1)
Because of the alkaline pH both the iron and chromium
precipitate as metal hydroxides and are subsequently removed
in a clarifier. The produced ferric ion further enhances
the coagulation and settling of suspended solids.
Chromate residuals from this process have been reported to
be less than 0.05 ppm. Costs of treatment are claimed to be
fairly low and the operation is automaticall controlled.
The process is also applicable for removal of other metals
ions such as zinc, copper, nickel, tin, iron, etc. (16) .
Copper. Effluent concentrations of less than 1 mg/1 can be
consistently achieved by precipitation with lime employing
proper pH control and proper settler design and operation.
The minimum solubility of the metal hydroxide is in the
range of pH 8.5-9.5. In a power plant, copper can appear in
the wastewater effluent as a result of corrosion of copper-
containing components of the necessary plant hydraulic
systems. Normally, every practicable effort is made, as a
part of standard design and operating practice to reduce
corrosion of plant components. Copper is not usually used in
construction of once-through boilers and consequently, is
rarely found in corresponding spent cleaning solutions (12).
Iron. In general, acidic and/or anaerobic conditions are
necessary for appreciable concentrations of soluble iron to
113
-------
exist. "Complete" iron removal with lime addition,
aeration, and settling followed by sand filtration has been
reported. Existing technology is capable of soluble iron
removals to levels well below 0.3 mg/1. Failure to achieve
these levels would be the result of improper pH control.
The minimum solubility of ferric hydroxide is between 7 and
8 (12). In some cases, apparently soluble iron may actually
be present as finely divided solids due to inefficient
settling of ferric hydroxide. Polishing treatment such as
rapid sand filters will remove these solids. In a power
plant, iron, as with copper, can appear in the wastewater
effluent as a result of corrosion to iron-containing
components of the necessary plant hydraulic systems.
Normally, every practicable effort is made, as a part of
standard design and operating procedure, to reduce corrosion
of plant components. Excessively stringent effluent
limitations on iron, as with copper, may necessitate
complete design and alter
-------
Continuous Waste Strgams. Continuous wastewater streams
consist primarily of cooling system wastes, either of the
once-through or the recirculating system blowdown type.
None of the plants contacted in this study were found to
discharge once-through cooling water to publicly-owned
treatment facilities. Where such discharge occurs,
consideration should be given to removing this discharge
from the sanitary sewer system, since the large hydraulic
loading will decrease the effectiveness of the POTW
treatment process.
Residual chlorine contained in once-through cooling water
discharges can be removed by so-called "dechlorination"
processes. Methods of dechlorination include addition of
reducing chemicals, passage through fixed beds of activated
carbon and aeration. Reducing chemicals include sulfur
dioxide (SO2) , sodium bisulfite (NaHSO_3) , and sodium sulfite
(Na.2SO_3) . ~~ Of these agents, sodium bisulfite is most
commonly used (19). Granular activated carbon as adsorb
chlorine compounds and is oxidized by it to carbon dioxide.
Oxidizing chlorine compounds such as chlorine (C12),
hypochlorous acid (HOCl) , chlorine dioxide (C10_2) and
nitrogen trichloride (NC1_3) are sufficiently volative to be
removed by aeration (19). Other active chlorine species are
not as volatile and may not be removed. Data available to
date do not indicate that heat discharged in this waste is a
problem to a POTW.
Closed cycle or recirculating cooling water system blowdown
is discharged into POTWs by a number of plants. The
discharge may be continuous or intermittent. Significant
parameters of pollutants that may be found in cooling water
blowdown may include chlorine, hypochlorous acid, sodium
hypochlorite, phosphates, chromates, zinc compounds, organic
biocides, dispersing agents, and depending on the
constituents in the makeup water supply, various inorganic
salts resulting from the concentration of those constituents
and the necessity of maintaining the pH within certain
limits. Pretreatment may be necessary if certain types of
inhibitors and biocides are used as internal treatment in
the cooling water system. These are likely to inhibit
biological activity at the publicly-owned treatment
facilities and will therefore have an adverse effect on the
treatment operation. The extent of this effect will depend
on the relative volumes of cooling tower blowdown and
domestic wastewater. Organic compounds used as inhibitors,
biocides, or dispersing agents are not likely to be degraded
by secondary biological treatment and will therefore pass
through the publicly-owned treatment facilities and be
discharged to the receiving waters. Toxicity studies are
being conducted with individual proprietary compounds in
order to establish permissible levels of discharge.
115
-------
End-of-pipe technology is available to remove most inorganic
pollutants. Many inorganic pollutants have low solubilites
at alkaline pH, and can be removed by adding lime or another
form of alkali. The degree of removal is a function of the
solubility of the pollutant at high pH. Some specific
pollutants such as chromium can be removed by ion exchange,
but the ultimate disposal of the spent regenerants presents
problems.
Periodic Wastes. Periodic wastes include waste resulting
from boiler and service water treatment, boiler blowdown
(can be continuous) , ion exchange water treatment, water
treatment evaporative blowdown, boiler and air heater
cleaning, other equipment cleaning, laboratory and sampling
streams, floor drainage, cooling tower basin cleaning,
blowdown from recirculating wet-scrubber air pollution
control systems, and other relatively low volume streams.
These include all the wastes that are classified as "ash
transport" and "metal cleaning" wastes. For plants
discharging wastes to publicly-owned treatment facilities,
boiler blowdown is generally not a significant source of
pollution. Water treatment wastes may or may not be
significant depending on the source of the water and method
of treatment. Since most plants discharging wastes to
publicly-owned treatment facilities also obtain their water
from the municipal water supply system, the wastes will
consist of normal constituents of the water supply, plus any
chemicals used in the treatment process. If the treatment
process is ion exchange, the wastes will contain inorganic
acids and alkalis. Combination of wastes from anion and
cation exchanges will generally result in combined waste
stream that is acceptable to the treatment plant. If the pH
of the combined waste stream is outside the range of 6.0 to
9.0 normally acceptable to biologically based treatment
process, neutralization may be required.
Evaporation blowdown is usually high in dissolved solids,
but otherwise acceptable for discharge to the publicly-owned
treatment facilities. The dissolved solids consist
primarily of concentrated constituents of the public water
supply and do not have any adverse effect on the treatment
plant, receiving water.
Floor drains may be a significant source of pollution, with
oil and grease as the most significant parameter. The
regulations for direct discharge limit oil and grease for
all low volume wastes taken collectively to 20 mg/1 on any
one day, and 15 mg/1 average for 30 consecutive days, but
local authorities may impose more severe limits. Most
municipal pretreatment ordinances also limit oil and grease
so that pretreatment may be required for removal of this
pollutant.
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End-of-pipe technology is available and is used by some
plants. The technology consists of gravity separators,
either unassisted or assisted by flocculants and/or
dissolved air flotation, followed if necessary by
filtration. The technology is able to meet the desired
standards at a minimal cost. However, to meet desired
standards efficiently only those waste streams containing
excessive oil and grease should be passed through the
treatment unit.
Metal Cleaning Wastes. The most significant of the periodic
wastes in terms of their potential impact on the publicly-
owned treatment facilities are metal cleaning wastes. Metal
cleaning wastes are produced intermittently while units are
shut down. The efficiency of electric power production
depends largely on the efficiency of heat transfer between
the combustion products and the boiler water. All metallic
heat transfer surfaces have a tendency to either corrode or
collect deposits. Both corrosion products and deposits
reduce the efficiency of heat transfer and must therefore be
removed periodically.
There are two main types of cleaning operations: waterside
and fireside. Waterside cleaning consists of cleaning the
inside of tubes, and other boiler water passages. Due to
the inaccessibility of these surfaces, the only practical
and generally accepted method of cleaning is by chemical
means. The cleaning typically proceeds in three stages: a
bromate soak, an acid cleaning (usually inhibited
hydrochloric acid), and finally a passivation stage. The
total operation takes about two days and produces about five
boiler volumes of wastes, with each stage consisting of a
fill, drain, fill and rinse operation lasting about one and
one-half to two hours. For multi-unit plants, only one
boiler is cleaned at any one time, so that the majority of
the plant is operating during the cleaning cycle.
Fireside cleaning is more mechanical, consisting of high
pressure nozzles directed against the surfaces to be
cleaned. The cleaning solution often contains alkalis to
dissolve oil, and grease and detergents to keep the removed
material in colloidal suspension. Fireside cleaning is done
on both the fireside of the boiler. Similar cleaning
procedures are employed on the air preheater.
Pollutants contained in the cleaning solutions consist of
both the chemicals used in the cleaning solution and the
material removed from the heat transfer surfaces. Tables
VII-4 and VII-5 give ranges of composition for chemical
cleaning and fireside cleaning wastes, respectively. These
pollutants are generally not removed by biological secondary
treatment and may have an adverse effect on the treatment
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process, depending on the ratio of metal cleaning wastes to
total flow at the publicly-owned treatment plant.
Options for process modifications for metal cleaning wastes
are small. End-of-pipe technology is available for the
removal of most of the pollutants resulting from metal
cleaning operations.
Basic technology for removing pollutants from the waste
stream consists of retention, storage and combination of
waste streams, raising the pH to precipitate metallic salts,
removal of precipitated solids and pH readjustment of final
effluent for discharge to public sewers. Operating data
from many power plants shows that copper from the metal
cleaning wastes can be reduced to less than 1 mg/1 by lime
or caustic soda addition. Two of these plants use chelating
agents in their cleaning process while all of the remaining
facilities do not. The power plants which discharge into
POTW can achieve the 1 mg'/l copper limitation more readily
since they do not have to reduce iron at the same time to 1
mg/1.
Since metal cleanings are infrequent operations, (some
plants clean their boiler only once every five years) many
plants prefer to have them hauled off and treated by private
contractors. Most of the expertise for treating cleaning
wastes has been developed by the cleaning contractors who
are generally being asked to include waste treatment and
disposal as part of the cleaning contract.
Ash Transport Water. Hydraulic systems for handling bottom
ash are used primarily by coal-fired plants. The
preliminary listing of plants discharging to publicly-owned
treatment plants contain coal-fired plants. Hydraulic
systems are used for fly ash removal, usually in conjunction
with scrubbers for sulfur dioxide removal. Where scrubbers
are part of the air pollution control system, provision has
to be made for handling of the sludges resulting from the
operation. This sludge is not suitable for disposal to the
public sewer system.
Air Pollution Control Wastes. There is normally little
liquid effluent from sulfur dioxide scrubbers. The water
within the system is usually recycled as much as possible by
dewatering the sludge to a filter cake. Some water leaves
the system as steam with the gaseous emissions and some
water becomes entrained in the sludge cake, but the
objective of good operation is to minimize the amount of
water in the sludge cake. The water retained in the sludge
cake is sufficient to meet the requirements for system
blowdown.
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Table VI1-4.TYPICAL COMPOSITION OF
BOILER CHEMICAL CLEANING WASTES
Component Amount, T_b_.
Hydrochloric Acid 46,500
Iron 3,800
Copper 500
Sodium Bromate 930
Ammonium Carbonate 1,675
Ammonium Hydroxide 14,600
Chromate Inhibitors 1,600
Thiourea 7,750
Ammonium Bifluoride 3,775
Sodium Carbonate 7,750
plus small amounts of silica, phosphates, nickel,
zinc, aluminum, titanium, manganese and magnesium
Size of unit 500 MW
Volume of wastes 95,000 gal
Table VII-5. TYPICAL COMPOSITION Of
BOILER FIRESIDE HASH HASTES
Component Concentration, mg/1
Suspended Solids 1,000 - 3,000
Iron 500 - 1,000
Copper 10 - 20
Nickel 50 - 300
7inc 15 - 25
Oil and Grease 150 - 300
Volume, gal/KW IGC 200 - 1,000
(once/year for each boiler)
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Occassional Wastes. Occassional wastes are those that are
caused by contamination of stormwater runoff by materials
stored on the plant site. The principal type of contaminated
stormwater is coal pile runoff, and this is restricted to
coal fired plants. A significant number of urban plants
have been converted from coal to oil fired, but still retain
the coal capability and may keep a coal reserve stored on
the site. The coal reserve may become a significant source
of pollution due to the interaction of water and air with
some of the impurities in the coal, notably iron and sulfur.
No plants discharging coal pile runoff to publicly-owned
treatment facilities were uncovered during the industry
survey.
A type of process modification would be to cover the
inactive coal pile with plastic sheeting the way a baseball
infield is covered in the rain. This would eliminate the
formation of pollutant containing waste stream.
Alternately, the waste stream, once produced, can be
neutralized with lime as an end-of-pipe treatment, and any
suspended solids allowed to settle. This practice is common
in related industries.
WATER MANAGEMENT
The varied uses that are metde of water in a power plant and
the wide range of water quality required for those uses
present this industry with an unusual opportunity for water
management and wastewater reuse. Indeed, many plants
developed water management programs that make use of all the
wastewater streams produced by recycling them into unit
processes which tolerate lower water quality (e.g. ash
handling). However, to develop and implement a water
management program of no discharge, it is necessary to
evaluate the water requirement of each segment of the
process as well as the specific factors which affect
individual plant water needs. Such factors include the
nature of the raw water source, the location of the plant
and its climatic environment, water availability and water
cost, and the local requirement for effluent limitations.
The chemical composition of the raw water source affects the
magnitude of the discharge from almost every segment of the
process. To deionize water with high dissolved solids
content to produce boiler feedwater, the ion exchange system
produces more regenerant. Further, highly dissolved solids
contents would also lower the concentration cycle of closed-
loop recirculations cooling system, and therefore would
increase the blowdown from these systems. In areas of
excessive rainfall closed-loop recirculating systems would
have to be bled more often to prevent the systems from
overflowing and may indeed be difficult to operate. In areas
where the rate of evaporation is greater than the rate of
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precipitation, such systems would require makeup water to
maintain the flow. Water availability and cost would have
an impact on the plant incentive to conserve water. The
extent of wastewater treatment provided by the plant would
depend on how stringent the local requirement for effluent
limitations are.
IN-PLANT CONTROL TECHNIQUES
Control of wastewater effluents produced by the industry can
be best achieved by incorporating in-process changes capable
of reducing the volume of wastewater discharged, or reducing
the amount of pollutants in the discharge.
Such changes can be classified under one of the following
categories:
o Process modifications;
o Materials substitution;
o Water conservation and wastewater reuse;
o Raw materials and product recovery; and
o Good housekeeping practices.
Application of such techniques can result in multiple
benefits, including savings in construction and operation
costs of on-site wastewater treatment plants and in sewer
surcharge and other charges associated with the use of
publicly-owned treatment facilities.
In power generating plants there are theoretical
opportunities for a number of such control measures.
Practically, the opportunities are limited by the cost of
any major process change under "retrofit" conditions, that
is, conditions which require substantial mechanical and
structural changes to an existing plant.
Process Modifications
A great number of process modifications are available to
reduce the quantities of wastewater from a power generating
plant, or to eliminate it altogether. In order to present
these potential modifications in an orderly manner, this
section has been further divided into subsections, each
dealing with an individual wastewater stream.
Once Through Cooling Water. Switching from a once-through
to a closed or open recirculating cooling system would
greatly reduce the amount of wastewater discharged. This
can be shown by balancing the quantity of heat rejected by
each of the systems. For a once-through cooling system this
quantity is equal to the product of the water flow times the
condenser temperature rise. For a recirculating system it
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can be assumed that all the heat is rejected by evaporation.
Neglecting drift and windage losses the following equation
can be written:
B = T (2)
F q(C-l)
where B/F is the ratio of the blowdown from a recirculating
system to the discharge from once-through cooling system, T
is the condenser temperature rise, q is the amount of heat
required to evaporate a unit weight of water, and C is the
concentration cycle. The concentration cycle is defined as
the ratio of the concentration of a limiting parameter in
the makeup water to that in blowdown. For a typical
condenser temperature rise of 10°C and for q equal to 555
kcal/liter of water, even at a concentration cycle of 2,
approximately 98 percent reduction in the volume of
wastewater produced would be achieved. This reduction in
cooling water consumption can also be classified under water
conservation and wastewater reuse category.
Switching from once-through to a recirculating cooling
syste, however, is costly and not always feasible. Power
plants contacted in this study that utilize once-through
systems discharge the effluent directly to surface water.
Such discharges are subjected to EPA regulations which limit
the temperature and the chlorine concentration of waste
effluents to be discharged to surface water.
Excess total residual chlorine concentration in effluents
from once-through cooling system can be minimized by
monitoring and controlling free available chlorine
concentrations in the discharge stream. A further technique
to reduce total residual chlorine discharged is to
chlorinate during periods of low condenser flow.
Alternatively, the chlorine input to once-through cooling
water can be reduced to a level below the concentration
required for complete fouling control. Any biological
growth which may result would be removed by mechanical means
(12) . This approach however, is limited by the
configuration of the process piping and structures involved
at any plant.
Closed Condenser Cooling System Slowdowns. Although the
volume of recirculating cooling system blowdown is
considerably smaller than the amount of wastewater
discharged from a once-through system, it is also
significantly more polluted. The effluent contains a higher
dissolved solids concentration due to the evaporation of a
large portion of the cooling water. In addition, chemicals
added to inhibit scale formation, corrosion, and fouling
would also be present in the blowdown water.
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Slowdown from a recirculating cooling system can be disposed
of by evaporation. In warm, dry climates, and where land
costs are relatively low, such as in the southwest, blowdown
streams can be collected in ponds and allowed to evaporate.
Such ponds are usually lined with impervious material such
as clay or plastic to prevent water infiltration and
subsequent pollution of the groundwater aquifer (12) .
The residual chlorine concentration in blowdown streams
discharged to POTW can be controlled. This can be achieved
by one of the following methods:
o Regulation through feedback instrumentation;
o Splitting the condenser influent into two streams
and chlorinating one at a time;
o Reducing the length of the chlorination period.
Chlorination is now being questioned by health authorities
who must meet increasingly stringent bacteriological and
waste discharge requirements. An increased chlorine dosage
which may provide satisfactory disinfection requirements may
also be responsible for release of an excessive amount of
polluting material to the aquatic environment. Current
reports show that even trace amounts of chlorine are harmful
to aquatic life (12) .
Water Treatment Wastes. Substitution of reverse osmosis or
electrodialysis for ion exchange to produce boiler feed
water will greatly reduce the discharge from this section of
the process. However, the technical feasibility of the
reverse osmosis process is limited by the chemical
characteristics of the raw water source and by economics,
and for some plants polishing the product water by ion
exchange will still be necessary, depending on the boiler
operating pressure.
Ash Handling Wastes. Ash handling is the conveyance of the
accumulated bottom and fly ash combustion solid waste
product to a disposal system. This is accomplished by dry
or wet processes. In the dry process the ash is transported
to the disposal area by pressurized air, vacuum, or
mechanical means. Dry ash handling systems do not generate
wastewater and may allow a credit for the sale of the ash
for its metal content. Bottom ash from oil fired furnace,
for example, can be sold for its vanadium content.
The wet process can be either open or closed-loop systems.
In the closed-loop system the ash is slurried in water and
conveyed to a pond or clarifier where settling occurs. The
clarified overflow from the settling pond is recycled to the
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boiler. The closed-loop ash handling system does not
generate wastewater except in areas of excessive rainfall
where the system must be periodically bled. In such cases
the blowdown may be treated in a separate system to remove
metal ion by precipitation and suspended solids by
clarification. In areas where the rate of evaporation is
higher than the rate of precipitation, evaporation losses
from closed-loop ash handling systems can be supplemented
with wastewater from other unit processes such as cooling
tower blowdown. Open-loop ash handling systems are a source
for wastewater since the transporting water is used but once
to convey the ash to the settling ponds. This wastewater
source can be eliminated by switching to dry or closed-loop
type systems. Open-loop ash handling systems should be
avoided when possible as the effluent from the ash pond may
require additional treatment before it can be discharged.
Coal Pile Runoff. The extent of contamination of coal pile
runoff can be reduced by properly constructing the coal
storage area. Inactive coal piles can be sprayed with tar
or covered with plastic sheeting to seal the surface to
water infiltration. A drainage system should be constructed
to collect the most polluted portion of the storm. In areas
where the rate of evaporation is higher than the rate of
precipitation runoff can be disposed of by evaporation in
ponds. Alternatively, cocil pile drainage can be used in
processes which tolerate low quality waters such as ash
handling systems. If the plant is located near a mine such
water can be used in the coal washers to remove mineral
matter. Diversion of this waste to ash ponds was also
considered. However, because of the low pH of such wastes,
coal ash can be leached by the water resulting in the
formation of additional waterborne pollutants.
Air Pollution Control Scrubbing Devices. The non-recovery
scrubbing process for SO^ removal from flue gas may also be
a source of wastewater if the system is bled to remove spent
solvent. This is a closed-loop type system employing
recycled lime scrubbing liquor. The process requires makeup
water for saturating the boiler gases. Changing to SOŁ
recovery systems would reduce the discharge from this part
of the process as well as allow a credit for the sale of
recovered sulfur dioxide or other sulfur products. Table
VII-6 lists some of the 3OŁ recovery processes currently
available. It should be emphasized, however, that some of
the listed processes have reached only the pilot plant stage
of their development and cost estimates for their
installation and operation are somewhat higher than those
for the non-recovery processes.
Material Substitution
-------
The blowdown from a recirculating cooling system can be
reduced by increasing the concentration cycle. This can be
achieved by substituting scale-forming ions with more
soluble ions, or by using sequestering agents such as
polyolesters and phosphonates to prevent deposition of
precipitated solid phases. These dispersing agents,
however, can become pollutants in the blowdown water.
Lime softening of cooling water makeup prior to its
introduction into the system would also increase the
concentration cycle, though it may be costly because of
large volumes of water requiring treatment.
Installation of plastic or plastic-coated system components
would reduce the extent of treatment of cooling water
makeup. Plastic exhibits considerable resistance to
corrosion and erosion. Many new installations using cooling
towers employ plastic.
Where publicly-owned treatment plants containing a tertiary
step are used, phosphate and nitrate based corrosion
inhibitors could be substituted for chromates as these
pollutants are removed by a tertiary treatment step.
Chrornate-based compounds can also be substituted by a
recently developed synthetic organic corrosion formulation
which is not as toxic as chromate to microorganisms. This
formulation contains a blend of organic sequestrants and
antifoulants for control of mineral and organic fouling
together with corrosion inhibitors which provide protection
to all system metals (1U). Film-form-^g sulfophosphated
organic corrosion inhibitor has also been developed. The
substance is effective in both fresh and salty water, and
may be considerably less toxic than chromate (11*).
To reduce the amount of metals in wastewater from cooling
system blowdown and from chemical cleaning operations,
boilers and condenser cooling systems could be constructed
of non-polluting materials. Tubes and piping could be made
of special alloy metals or coated so as to reduce corrosion
and scaling, but this can be prohibitively costly. Cooling
towers can be constructed out of concrete and ceramic
materials and thus reduce the need for additives to the
cooling water system. Switching to low sulfur fuels can
also eliminate the need for air pollution control devices.
Water Conservation and Wastewater Reuse
Different water uses in the plant require water of widely
varying quality. These range from the almost zero solids
requirements for boiler feedwater makeup to the almost
unlimited solids allowed for ash transport water or scrubber
water supply. Consequently, the wastewater produced in the
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Table VI1-6. RECOVERY PROCESSES FOR FLUE GAS DESULFURIZATION SYSTEMS
Process
Double alkali
system
Chemilbau
system
Hydrogen sulfite
system
Wellman-Lord
system
Cat-Ox^ system
Shell flue gas
system
Sorbent System
Mode of S02_
Removal
Aqueous solution of Chemical
Sodium hydroxide , absorption
Sodium sulfate, & oxides with
sodium bisulfite CA(OH)2
Sulfur Recovery
Precipitation of
dissolved sulfur
Fluidized bed. of
activated carbon
solution of sodium
citrate, citric
acid and sodium
thiosulfate
Aqueous solution
of sodium sulfate
and sodium
bisulfite
A bed of cupric
oxide supported
activated
alumina
Product
Calcium sulfate
Calcium sulfite
Catalytic oxidation
to H2S04
and physical
absorption
Chemical
absorption
Chemical
absorption
Catalytic
oxidation of
S02. to SQ3 with
02. at 850°F
(vanadium oxide)
Oxidation to
cupric sulfate
Thermal stripping
with hydrogen at
1000°F and
catalytic reduction
with H2S
Precipitation of
dissolved sulfur
with H2S
Sulfur,
S02
Sulfur
1iquid
Thermal
regeneration by
vacuum and
catalytic reduction
with natural gas
Sulfur
78% sulfuric acid
Concentrated
S02
-------
plant also vary widely in quality. This opens many
opportunities for wastewater reuse.
Cooling system blowdown can be reused for ash transport or
as scrubber water supply. Boiler blowdown water is usually
better than the feed water supply and can be reused in the
plant for other purposes.
Boiler blowdown can be reduced by installing a heat recovery
system. In such a system the blowdown is discharged into a
flash tank operating at a lower pressure than the boiler
pressure. Because of the reduced pressure a portion of the
blowdown water evaporates to form low pressure steam which
can be condensed and reused as boiler feedwater. The
reduction in blowdown that can be achieved by this method
depends on the pressure difference between the boiler and
the flush tank. The use of a heat recovery system for
boiler blowdown will also increase the thermal efficiency of
the plant.
Spent regenerants and rinses from the ion exchange system
are also of a quality suitable for many purposes, where
dissolved solids are not a limiting factor.
Some of the periodic waste streams could be recycled or
reused if sufficient storage is available to hold these
streams until needed. Metal cleaning wastes after pre-
treatment or treatment could be used for low quality water
uses such as ash transport or scrubber supply. However, the
cost of storage may make such reuse prohibited.
Materials Recovery
Nearly all chromates, used as corrosion inhibitors, can be
recovered using properly designed ion-exchange beds.
Regenerant streams from the beds, which contain a relatively
high concentration of chromate, can be returned to the
cooling system as a usable corrosion inhibitor. Plants
which soften boiler feedwater with lime can reuse lime
sludge in their air pollution control system for 302^
removal. Recoverying heat from boiler blowdown would reduce
thermal discharges from this segment of the process, as well
as increase the thermal efficienty of the process. Recycling
of fly ash back to the furnace can be employed to increase
thermal efficiency by burning products of incomplete
combustion. It is also possible to recover vanadium from
oil ash with high vanadium content. Spent regenerants from
ion exchange system can be used where the quality of the
acid and alkaline solutions is not critical. For example,
the acid solutions can be used in recirculating cooling
system to maintain the pH of the water below saturation.
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Air pollution control devices, on the other hand, may
require an alkaline source of water.
Good Housekeeping Practices
There are numerous alternative methods ranging from taking
precautionary measures against spills of chemical solutions
or oil to pump sealing to prevent leaks. Facilities should
be constructed so that oil and grease contaminated water
will not drain directly into other water systems or be
diluted by rainfall runoff. Cleaning up oil spills,
maintaining equipment to minimize leaks, and supporting an
effective surveillance program will also minimize
contamination of wastewater effluents. Controlling
additions of chemicals to waters used in the various units
of the process would reduce their concentrations in the
effluents streams. Flow of water into the plant should be
regulated in accordance with production rate.
SUMMARY
A variety of wastewater control and treatment technologies
are available for the steam electric power industry. Since
the water needs, and the requirements for wastewater
discharge are specific to each individual plant, each
control and treatment system must be developed in accordance
with the individual plant requirement and should be
integrated in a comprehensive water management program.
Special consideration should be given to in-process control
techniques. Often, such technique can be found easy and
inexpensive to implement and yet, they can result in
substantial reduction in water consumption and wastewater
discharge.
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SECTION VIII
COST, ENERGY, AND OTHER NONWATER
QUALITY ASPECTS
INTRODUCTION
This section discusses cost estimates for control and
treatment technologies described in previous sections,
energy requirements for these technologies, and nonwater
quality related aspects such as reuse of water within the
plant. Ultimate disposal of brines and sludges, effect of
land availability, user charges and pollutants limitations
imposed by POTWs and other factors relating to the steam
electric power generating point source category are also
discussed in this Section.
Costs are developed in greater detail for those waste
sources which potentially are discharged to POTWs and are
potentially subject to pretreatment requirements. These
include the following:
o Low Volume Wastes
o Metal Cleaning Wastes
o Cooling Tower Slowdown
o Area Runoff and Ash Pond Discharges
Other waste streams such as ash transport water, boiler
blowdown, and once-through cooling water are provided in the
latter part of this section.
The pollutants in discharges to POTWs are similar to those
for direct discharge to surface water, as covered in the
Development Document for this industrial category.
Discharges of wastewater needing pretreatment and the extent
of pretreatment vary greatly from plant to plant depending
on the fuel used, chemical additives employed, and a host of
other variables. These variations influence the pretreatment
costs so significantly that general industry costs presented
in this section should be considered order of magnitude
numbers.
For most power plant wastes, the pretreatment for discharge
to POTW can involve control of three parameters of
pollution, pH, suspended solids, and oil and grease.
Control of pH neutralizes any undesirable acidity or
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alkalinity. Treatment for suspended solids then removes
suspended metals as well as other suspended material. Oil
and grease is separated from the water phase of the low
volume wastes and skimmed off.
COST REFERENCES AND RATIONALE
Cost information contained in this report was obtained from
the following sources:
o Engineering estimates based on published cost data
for equipment, construction, and installation;
o Estimates and guidelines for estimating contained
in the Development Document for steam electric
industry discharges to surface water and the other
EPA documents;
o Quotations for materials and supplies published in
current trade journals.
o Cost data obtained as a result of direct inquiry to
industry for data on actual installations.
Interest Rates and Equity Finance Charges
Capital investment cost estimates for this study have been
based on 10 percent capital cost which represents a
composite value for either interest rate paid or the
required return on investment.
Time Basis for Cost Adjustment
All estimated costs are taken from July, 1976 prices or
where necessary adjusted to this time basis using the ENR
construction cost index of 2413 (July 1, 1976).
Useful Service Life
The useful service life of all wastewater treatment and
disposal facilities is a function of the process involved,
the quality of the equipment and design, its use patterns,
the quality of maintenance and several other factors.
Whereas individual companies often use service lives based
on actual local experience, for the purpose of internal
authorization, the Internal Revenue Service provides
uidelines for tax computational purposes which are intended
to reflect approximate average life experience.
The following useful service life values were chosen for use
in this report from the literature, discussions with
representatives of industry, and IRS guidelines data:
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o General process equipment 10 years
o Buildings, sewers, ponds, etc. 20 years
o Material handling equipment and
vehicles 5 years
Depreciation
The allocation of the cost of capital assets such as
treatment and disposal equipment less salvage (if any) over
the estimated useful service life of the unit or facility in
a systematic and rational manner as a non-cash expense is
termed depreciation. For IRS tax purposes and to make
suitable financial allowance for equipment replacement
several types of depreciation are used. Simple straightline
depreciation was used as the basis of calculations in this
report.
Capital Costs
Capital costs have been defined for this study as all
initial out-of-pocket cash expenditures for provision of
wastewater treatment and disposal facilities. These costs
will include research, development, and feasibility studies
necessary to characterize and design the facilities land and
site preparation costs when applicable, equipment,
construction, installation, and start-up costs, costs of
buildings, services and engineering (allocated where
necessary) , contractor profits and contingency costs if such
exist.
Annual Capital Costs
Most capital costs are accrued during the year or two prior
to actual use of the facility. This present worth sum can
be converted to equivalent uniform annual disbursements over
the life of the facility by utilizing the Capital Recovery
Factor Method:
Uniform Annual Disbursement = (P) (i) (1+i) n
where P = present value (capital expenditure) ,
i = interest rate, %/100
n = useful life in years
Operating Expenses
Annual costs of operating pretreatment facilities include
labor, supervision, materials, maintenance, taxes,
insurance, and power and energy. Operating costs combined
with annual ized capital costs give total costs for
pretreatment operations.
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Rationale for Model Plants
Plant costs are estimated for model plants rather than for
any actual plant. Model plants are defined to have sizes of
25 MW and 500 MW capacity, which are representative of large
and small-sized operation.
Definition of Levels of Treatment and Control
Costs are developed for various types and levels of
technology:
Minimum (A or basic level). That level of technology which
is equalled or exceeded by most or all of the involved
plants.
Usually, money for this treatment level has already been
spent (in the case of capital investment) or is being spent
(in the case of operating and overall costs).
B,Cfp--LeveIs. Successively greater degrees of treatment
with respect to critical pollutant parameters. Two or more
alternative treatments are developed when applicable.
Basis for Pretreatment Costs
In development of cost estimates found in Tables VIII-1,
VIII-2, VIII-4, and VIII-5, it is assumed that only the
following wastewater effluents are discharged to POTWs and
may, therefore, require pretreatment.
o Low Volume Wastes
o Metal Cleaning Wastes
o Cooling Tower Slowdown
o Area Runoff and Ash Bond Discharges
o Boiler Slowdown
Low volume wastes include ion-exchange regenerants, spills,
leaks, air pollution control system bleed offs, area
washdowns, and other miscellaneous wastewater streams.
Metal cleaning wastes include tube and fireside boiler
cleaning products, as well as air cleaner wastes.
Area runoff includes rainwater runoff from coal piles. Ash
pond overflows and blowdowns are designated as discharges.
Costs have been addressed iseparately for the following
wastes:
o Ash Transport Water
o Boiler Blowdown
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Reasons for addressing these sources of wastes separately
are discussed in detail in Section VII, but are also
discussed briefly below.
Ash transport water from coal-fired plants is generally
recirculated after sedimentation, and the purpose of
sedimentation is process rather than pollution control.
Overflows from ash ponds are included in the wastewater for
pretreatment.
Boiler blowdown can be, and sometimes is, discharged to POTW
without pretreatment. In can be handled at the combined
plant without incremental costs. However, based on data
contained in Section V the quality of boiler blowdown is
better than that required for almost any in plant use, and
it is recommended that boiler blowdown not be mixed with
other waste streams for discharge to the POTW.
No plant contacted in this study was found to discharge
once-through cooling water to a POTW. Therefore, costs are
not generated for pretreatment requirements.
Cost Variances
The effects of age, location, and size on costs for
treatment and control have been considered and are in the
body of this section.
COSTS FOR PRETREATMENT
Waste types covered in this subsection include low volume
wastes, metal cleaning wastes, cooling tower blowdown, area
runoff and ash pond discharge. Since the wasteload differs
depending on the fuel source used, cost estimates for
pretreatment of wastewater effluents from steam electric
plants have been divided into those plants burning gas or
oil and those using coal.
Oil and Gas Fired Plants
Oil and gas-fired plants probably will have no ash pond
discharge, no air pollution control wastewater, or coal pile
runoff. Therefore, these plants have essentially ion-
exchange regenerants, miscellaneous low volume wastes,
cooling tower blowdown and metal cleaning wastes.
Estimated wastewater volumes in liters/day (GPD) for the
plant sizes given are:
25 MW Plant 500 MW Plant
133
-------
o Low Volume Wastes
Ion-exchange re
generants 11,400(3000) 454,000(120,000)
Miscellaneous 3,800(1000) 151,400 40,000)
o Metal Cleaning
Wastes 380(100) 10,200( 2,700)
o Cooling Tower
Slowdown 94,600(25,000) 1,892,000(500,000)
The low volume wastes contain primarily acids and/or bases
and perhaps some oil. The metal cleaning wastes contain
acids, bases, metals, oil and grease, and suspended solids.
Cooling tower blowdown may contain chromates, chlorine,
chlorinated phenols, mercury, phosphate, zinc and many other
additives commonly used in cooling tower systems. For
purposes of cost analysis, however, cooling tower blowdown
is assumed to contain only free chlorine (chlorine is the
most commonly reported biocide used).
Defined Pretreatment Levels
The raw wastes requiring pretreatment prior to POTW disposal
are similar to those described in the Development Document
for direct dischargers, and use has been made of the data on
wastewater volumes, waste loads and other information
contained therein. The minimum pretreatment level, defined
as Level A, consists of that level of technology which is
equalled or exceeded by most or all of the existing plants.
This level involves some flow equalization and combining of
wastes to get the benefit of some neutralizing and diluting
effects. Expenditures, both capital and operating are small.
Level B pretreatment involves equalization of low volume
wastes, neutralization to a pH 6-9 and skimming of surface
oil. Metal cleaning wastes are stored in a large tank or
small pond and fed slowly to the neutralization tank for
small volume wastes and boiler blowdown. There is no
pretreatment of cooling tower blowdown.
Level C pretreatment is the same as Level B except that the
metal cleaning wastes are neutralized, clarified and
discharged. Provision is made for sludge removal.
Level D pretreatment is essentially that for BPCTCA for
direct discharge to surface water. For this level all waste
streams with exception of the cooling tower blowdown are fed
into a tank for pH adjustment (optimum in the 9-11 pH
range), oil is skimmed from the liquid surface, and
suspended solids are removed in a clarifier. Acid is then
added to reduce pH to 6-9 prior to discharge. Cooling tower
134
-------
DRAFT
TABLE VIII-1
WASTEWATER TREATMENT COSTS AND RESULTING
WASTE-LOAD CHARACTERISTICS FOR TYPICAL PLANT
SUBCATEGORY ^ Ojl _o.r Gas F1 red PI ant
PLANT SIZE __H-'jW
PLANT AGE
PLANT LOCATION
COSTS OF TREATMENT TO ATTAIN SPECIFIED LEVELS
COST CATE80RY
TOTAL INVESTED CAPITAL
ANNUAL CAPITAL RECOVERY
ANNUAL OPERATIVE AND MA'STEMANCS
COSTS (EXCLUDING CKERJYAND POWER!
ANNUAL INS P.tt AKO PO*E* COSTS
TOTAL ANNUAL COSTS
COSTS($) TO ATTAIN LEVEL
A
10,000
$1,600
Small
Small
1,600
B
50,000
8,150
10,000
Small
18,150
c
60,000
9,760
13,000
500
23,260
0
120,000
19,500
15,000
500
35,000
E
KCSULTIHt VASTE-LOAO CKAnACTCRISTICS
(a) TSS
Fe
Cu
pH
Oil & Grease
(t\\ cvno n
^Dj rres LLp
RAW
(UN-
TRF.ATED)
300
i ?nn
200
A
300
1 9on
200
_
CONCENTRATIOf
AFTER
8
300
i onn
200
6-9
t««/l)(p»m)
TREATMENT TO 1
c
100
< 1.0
6-9
< 100
-EVEL
D
• 100
-------
TABLE V I I I - 2
WASTEWATER TREATMENT COSTS AND RESULTING
WASTE-LOAD CHARACTERISTICS FOR TYPICAL PLANT
SUBCATEGORY Oil or Gas Fired Plant
PLANT SIZE
PLANT AGE
500 MW
.YEARS
PLANT LOCATION
COSTS OF TREATMENT TO ATTAIN SPECIFIED LEVELS
COST CATE90RY
TOTAL INVESTED CAPITAL
ANNUAL CAPITAL RECOVERY
ANNUAL OPERATING AMD MAINTENANCE
COSTS (EXCLUDIN9 ENER8YAND POWER)
ANNUAL CNER4Y AND POWER COSTS
TOTAL ANNUAL COSTS
COSTStfc) TOATTAIN LEVEL
A
80,000
13,000
Small
Small
13,000
B
300,000
48,800
60,000
1,000
109,800
c
300,000
48,800
80,000
2,000
130,800
0
-700,000
114,000
130,000
3,000
247,000
E
RESULTIN* WASTE-LOAD CHARACTERISTICS
(a) TSS
Fe
Cu
nM
P"
fin 1 ? Cloaca
ui j c* urt?ubc
(b) Free CL?
RAW
(UN-
TREATED)
300
1200
200
A
300
- 1200
200
CONCENTRATION
AFTER
B
300
1200
200
6-9
(m«/U(»m)
TREATMENT TO t
C
100
<1.0 ,
6-9
if
< inn
.EVEL
D
100
<1.0
<1.0
fi-Q
< ?n
0.5
E
(a) Low volume and metal cleaning wastes combined
(b) Cooling Tower Slowdown
NOTE: TSS, Fe, and Cu, raw wastes concentrations estimated from Table A-V-20
of Development Document EPA 440/1-74029 a (12)
Level A - Flow Equalization
Level B - Equalization of low volume wastes, followed by neutralisation
to pH 6-9, skimming of surface oil. Metal cleaning wastes combined
with low volume wastes and neutralized without sludge removal.
Level C - Same as Level B except meta! cleaning wastes neutralized, clarified
with sludge removal and discharged.
Level D - Equalization, pK adjustment, oil skimming, clarification, reacidi-
fication. Cooling tower blowa'own treated with sulfite.
136
-------
blowdown is treated separately with sulfite to remove free
chlorine.
Costs and estimated effluent concentrations achieved for oil
and gas-fired plants are given in Table VIII-1 and VIII-2.
Detailed model description for Level D is given in the
following subsection.
Costs for Levels A, B, and C are roughly estimated from cost
experience with similar wastewater volumes and compositions
in other industries as well as from steam electric power
plants.
Capital cost data for wastewater pretreatment facilities for
oil and gas-fired steam electric power plants discharging to
public sewerage systems are summarized in Table VIII-3.
Table VII1-3. SUMMARY OF CAPITAL COSTS OIL AND GAS-
FIRED PLANTS 25 MW PLANT
$ Per KW IGC
Pretreatment Technology Level
Category A B <
Low Volume Wastes 0.38 1.20 1.20 1.60
Metal Cleaning Wastes 0.02 0.80 1.20 1.0
Cooling Tower Blowdown NT NT NT 1.66
Boiler Blowdown NT NT NT 0.54
TOTAL COST O.UO 2.00 2.HO U.8
500 MW Plant
$ Per KW IGC
Pretreatment Technology Level
Category A B C D
Low Volume Wastes 0.15 0.50 0.50 0.79
Metal Cleaning Wastes 0.01 0.10 0.10 0.20
Cooling Tower Blowdown NT NT NT 0.31
Boiler Blowdown NT NT NT 0.10
TOTAL COST 0.16 0.6 0.6 l.UO
Note: NA not applicable to discharge to POTW
NT Not treated
137
-------
A - Flow equalization.
B - Equalization and neutralization of low
volume wastes to pH 6-9, skimming of
surface oil. Metal cleaning wastes
and neutralized.
C - Same as Level B except metal cleaning
wastes neutralized, clarified and
discharged. Provision is made for sludge
removal.
D - Equalization, pH adjustment, oil skimming,
reacidification, clarification. Cooling
tower blowdown treated with sulfite.
Coal-Fired Plants
Coal-fired plants have ash pond discharges, air pollution
control wastewater, coal pile runoff, ion-exchange
regenerants, miscellaneous low volume wastes, cooling tower
blowdown and metal cleaning wastes.
Estimated wastewater volumes in liters/day (GPD) for the
plants sizes given are:
25 MW 500 MW
o Low Volume Wastes
- Air Pollution Wastes 3800 (1000) 151,100 (10,000)
- Ion Exchange Regenerants liaOO (3000) 154,000 (120,000)
- Miscellaneous 3800 (1000) 15,100 (10,000)
o Metal Cleaning Wastes 380 ( 100) 10,200 ( 2,000)
o Cooling Tower 91,600(25000) 1,892,000(500,000)
Blowdown
o Area Runoff 3,800( 1000) 91,600 ( 25,000)
o Ash Pond Discharge 3,800( 1000) 75,700( 20,000)
o Boiler Blowdown
The low volume wastes contain primarily acids bases and
suspended solids. The metal cleaning wastes contain acids,
bases, metals, and suspended solids. Cooling tower blowdown
as discussed for oil and gas-fired plants may contain a
variety of additives but for purposes of this cost
development is assumed to contain only free chlorine. Area
runoff contains acid, suspended solids and possibly some
metals. Ash pond discharges contain suspended and dissolved
solids.
138
-------
The minimum level for pretreatments, defined as Level A,
consists of that level of technology which is equalled or
exceeded by most or all of the existing plants. This level
involves some flow equalization and neutralization resulting
from the combination of waste streams of differing pH.
There is no control or treatment of runoff. Expenditures,
both capital and operating are small.
Level B pretreatment involves equalization of low volume
waste streams, neutralization to pH of 6-9. Metal cleaning
wastes are stored in a large tank or small pond and fed
slowly to the treatment system for low volume wastes. There
is no control of area runoff.
Level C pretreatment is the same as Level B except that the
metal cleaning wastes are neutralized, clarified and
discharged. Provisions is made for the sludge removal.
Level D pretreatment involves technology that will in
general meet the requirements of BPCTCA for direct discharge
to surface water. For this level area runoff from coal
piles and ash transport water overflow are retained in a
pond and fed continuously to a central pretreatment system.
Metal cleaning wastes are similarly retained and fed
continuously to the system. The pretreatment system itself
is described in a following subsection. It consists
primarily of a tank for pH control and oil skimming and a
clarifier for suspended solids removal.
Costs and effluent quantities for the four treatment levels
for coal-fired plants are summarized in Tables VIII-4 and
VIII-5.
Capital cost data for wastewater pretreatment facilities for
coal-fired steam electric power plants discharging to public
sewerage systems are summarized in Table VIII-6.
Model Pretreatment Plants - Level C Technology
The interim final pretreatment standards required the
reduction of copper in the metal cleaning wastes to 1 mg/1
and of oil and grease to 100 mg/1 in the plant's combined
discharge to the POTW. The equipment required to achieve
these standards are compatible to that required to achieve
Level C. Although most, if not all, of the power plants can
comply with the 100 mg/1 of oil and grease requirement by
employing good housekeeping techniques, cost data for oil
skimmer are included.
Model pretreatment plant costs have been developed for power
plants of 25 MW and 500 MW capacity of combined pretreatment
facilities for low volume and metal cleaning wastes.
139
-------
Estimates are for national average costs and do not consider
regional differences in construction costs. All estimates
are based on the following technology: pretreatment for pH
adjustment to not less than 5, flow equalization so that the
instantaneous peak discharge does not exceed five times the
monthly average flow rate, removal of oil and grease from
the plant's combined discharge to less than 100 mg/1, and
reduction of copper to 1 mg/1 from the metal cleaning
wastes.
Estimated operating costs are presented for centralized
pretreatment facilities for each model plant size. Operating
costs include labor, fuel and power, chemiceils, maintenance,
residue removal and management. Actual operating costs may
vary widely for those shown herein because of variations in
processes, degree of automation, and allocation of joint
labor costs.
Power plants sizes selected for model treatment plants are
25 MW and 500 MW. The 25 MW is typical of the smaller
plants discharging to POTWs and listed in the ERGO survey
sample (18). Eighty-seven and one half percent of all
plants listed and discharging to POTWs have less than 100 MW
IGC, with 37.5 percent having less than 25 IGC. Seventy-six
percent of the generating capacity discharging to POTWs is
in the size range between 2!>0 and 1000 MW, and the 500 MW
plant is considered representative of this large size group.
For the 25 MW model plant it was assumed that pretreatment
would be a batch operation with low volume and metal
cleaning wastes combined. Treatment would consist of
gravity separation (skimming) of oils, followed by lime
precipitation of metals, sedimentation, withdrawal of
sludge, adjustment of pH to a neutral range, and controlled
discharge. Figure VIII-1 is a flow diagram for a small
batch plant. For the 500 MW it was assumed that pretreatment
would be on a semicontinuous basis. Metal cleaning wastes
would be stored in an equalization tank, and bled into the
treatment operation at a controlled rate. The treatment
process would consist of oil and grease skimming in the
equalization tank, lime addition in the reactor,
sedimentation and clarification, and final adjustment of pH
before discharge to the public sewer. Sludge from the
clarifier would be dewatered on vacuum filters, with the
filtrate returned to the treatment plant influent. Figure
VIII-2 is a flow diagram of this process.
Cost Variances
Age affects the cost of pretreatment in terms of cost per
unit of power produced primarily because age affects
-------
TABLE VI11-4
WASTEWATER TREATMENT COSTS AND RESULTING
WASTE-LOAD CHARACTERISTICS FOR TYPICAL PLANT
SUBCATEGORY Coal Fired Plant
PLANT SIZE ?5 MW
PLANT AGE JLLUL. YEARS PLANT LOCATION
COSTS OF TREATMENT TO ATTAIN SPECIFIED LEVELS
COST CATE90RY
TOTAL INVESTED CAPITAL
ANNUAL CAPITAL RECOVERY
ANNUAL OPERATING AND MAINTENANCE
COST* (EXCLUDING ENER8Y AND POWER)
ANNUAL EMEf.SY AND POWER COSTS
TOTAL AKNUAL COSTS
COSTS (}) TO ATTAIN LEVEL
A
20,000
3,250
Small
Small
3,250
B
75,000
12,200
15,000
Small
27,200
c
90,000
14,600
18,000
500
33,100
D
143,000
23,300
20,000
500
46,300
E
RESULTING WASTE-LOAD CHARACTERISTICS
PARAMETER
(a) TSS
Fe
Cu
oH
rn
nil X, Rvpflcp
/h^ Eroa fl o
\ D ) r ree ° ' 2
MAY;
TREATED)
300
1200
200
A
300
1200
200
CONCENTRATION
AFTER
B
300
1200
200
6-9
(mg/U (KM)
TREATMENT TO
C
100
<1.0
6-9
-------
TABLE VI11-5
WASTEWATER TREATMENT COSTS AND RESULTING
WASTE-LOAD CHARACTERISTICS FOR TYPICAL PLANT
SUBCATEGORY
PLANT SIZE
PLANT AGE J|
Coal Fired Plant
500 MW
.YEARS
PLANT LOCATION
COSTS Of TREATMENT TO ATTAIN SPECIFIED LEVELS
F
COST CATE90RY
TOTAL INVESTED CAPITAL
ANNUAL CAPITAL RECOVERY
ANNUAL OPERATING AND MAINTENANCE
COSTS (EXCLUDING EMER9YANO POWEK)
AWHUAL tMERCY AKO POWER COSTS
TOTAL ANNUAL COSTS
COSTS ($3 TO ATTAIN LEVEL
A
100,000
16,300
Small
Small
16,300
B
350,000
57,000
70,000
2,000
129,000
c
350,000
57,000
93,100
2,500
152,600'
0
790,000
128,500
163,800
3,000
295,300
E
RESULTING WASTE-LOAD CHARACTERISTICS
(a) TSS
Fe
Cu
nU
pH
Ui I & brease
/u\ c ».«i ^ ••* n /^
(o) rree 112
RAW
(UN'
TRFA7EO!
300
1200
."'200
—
A
300
1200
200
1
CONCENTRATION
AFTER
B
300
1200
200
6-9
— — —
(m«/l) (pp«)
TREATMENT TO t
C
100
< 1.0
6-9
< 100
-EVEL
D
100
< 1.0
< 1.0
6-9
*• 20
Or
. 0
E
(a) Low volume and metal cleaning wastes combined
(b) Cooling Tower Slowdown
NOTE: TSS, Fe, and Cu, raw wastes concentrations estimated from Table A-V-20
of Development Document EPA 440/1-74029 a (12)
Level A - Flow Equalization
Level B - Equalization of low volume wastes, followed by neutralization
to pH 6-9, skimming of surface oil. Metal cleaning wastes combined
with low volume wastes and neutralized without sludge removal.
Level C - Same as Level B except metal cleaning wastes neutralized, clarified
with sludge removal and discharged.
Level D - Equalization, pH adjustment, oil skimming, clarification, reacidi-
fication. Cooling tower blowdown treated with sulfite.
142
-------
Table VI11-6. SUMMARY OF CAPITAL COSTS COAL FIRED PLANTS
25 MW Plant
$ Per KW IGC
Pretreatment Technology Level
Category A B
- *J ij
Low Volume Wastes
Metal Cleaning Wastes
Cooling Tower Slowdown
Area Runoff
Ash Handling Wastes
Boiler Slowdown
TOTAL COST
Category
Low Volume Wastes
Metal Cleaning Wastes
Cooling Tower Slowdown
Area Runoffs
Ash Pond Discharges
Boiler Slowdown
TOTAL COST
NOTE: NA - Not applicabl
NT - Not treated
LEVELS OF PRETREATMENT
A - Flow Equalization
B - Equalization and neutral
0.78
0.02
NT
NT
NT
NT
0.80
500 MW Plant
A
0.19
0.01
NT
NT
NT
NT
0.20
e to discharge
ization of low
2.00
1.00
NT
NT
NT
NT
3.00
B
0.60
0.1
NT
NT
NT
NT
0.70
to POTW
volume
2.40
1.20
NT
NT
NT
NT
3.60
C
0.60
0.10
NT
NT
NT
NT
0.70
wastes to
2.58
1.2
1.66
0.19
0.19
0.10
5.92
D
0.92
0.2
0.31
0.05
0.05
0.10
1.63
pH 6-9 skimming of surface oil. Metal cleaning wastes
combined with low volume wastes and neutralized without
sludge removal.
C - Same as Level B except metal cleaning wastes neutralized,
clarified and discharged. Provision is made for sludge
removal.
D - Equalization, pH adjustment, oil skimming, clarification,
reacidification. Cooling tower blowdown treated with
sulfite.
143
-------
efficiency and plants with lower effficiency will produce
more wastes per unit of power produced. Plants with lower
efficiency will also have lower utilization and therefore
produce fewer units of power in relation to their installed
capacity.
Size
Size is related to age in that the older plants are more
likely to be smaller than the newer plants. This relation
likely to be smaller than the newer plants. This relation
is shown in detail in the Development Document (14). Size
affects the cost of pretreatment as shown by the two plant
sizes, 25 MW and 500 MW.
Location
Location affects costs of pretreatment because of
differences in construction costs and labor rates in various
parts of the U.S. and because the choice of the treatment
technology and the cost of providing that technology are
related to the availability of land. For plants discharging
to public sewers, it may be assumed that they are located in
urbanized areas, where land availability is somewhat
limited. The extent of that limitation will vary widely
depending on the size of the urban area, the location of the
plant in that area, and the location of the area within the
U.S. Cost estimates are presented for two cases, (1) where
tankage can be constructed at ground level, and (2) where
tankage must be supported on a steel framework over existing
facilities because no other land is available.
COST ESTIMATES
Low Volume and Metal Cleanirig Wastes
Low volume wastes include all wastewaters other than those
for which specific effluent limitations have been
established. Waste sources include wet air pollution
control systems, water treatment systems, laboratory and
sampling streams, floor drainage, cooling tower basin
cleaning, and blowdown from service water systems. For the
purpose of cost estimating, metal cleaning wastes have been
combined with low volume wastes as the most cost effective
method of handling these two waste sources. Pretreatment
cost allottment to each type of waste has been estimated and
the capital costs are given in Table VII1-9 and operating
costs are given in Table VIII-8. This cost is conservative
since most of the plants only need to treat for metal
cleaning wastes.
Capital Costs
144
-------
LIME
ACID
01
LOW VOLUME WASTES
200 gpd/MW
METAL CLEANING WASTES
4 gpd/MW
BOILER SLOWDOWN
v
244 gpd/MW
OIL & GREASE
TO SEWER & POTW
SLUDGE
(CaS04)
FIGURE VIII-1. Model Waste Pretreatment Plant 25 MW Generating Facility
-------
CLEANING WASTES (5.4 gpd/MW)
BOILER TUBE -,
BOILER FIRESIDE -
AIR PREHEATER -
5.4 gpd/MW
EQUALIZATION
TANK
OIL & GREASE
LOW VOLUME WASTES
WATER TREATMENT -i
AIR POLLUTION CONTROL-
FLOOR DRAINS-
LABORATORY & SAMPLING-
LIME
CLARIFIER
330 gpd/MW
VACUUM
FILTER
SEWER TO
POTW
FIGURE VIII-2. Model Waste Pretreatment Plant 500 MW
Generating Facility
146
-------
Table VIII-9 provides estimated capital cost of pretreatment
plants for control of low volume and metal cleaning wastes,
where sufficient land is available to construct all
facilities at ground level.
If land availability is limited, treatment plant components
may have to be stacked vertically and tankage supported on
steel framework. This would double the cost of the
installation of the equipment.
Operating Costs
Operating costs include labor; fuel, power and other
utilities; supplies (principally chemicals); maintenance;
removal and disposal of residues; and management.
Assumed unit costs for basic parameters of operating costs
are shown in the following table.
Table VII1-7. ASSUMED UNIT COSTS
labor, per hour,
including fringe benefits $8.50
Electricity, per kwh 0.04
No, 2 Fuel oil, per MM Btu 2.50
Chemicals
Lime, per ton 30.00
Sulfuric Acid, per ton 50.00
Cost Data for Other Streams
Ash Transport Water
Ash transport water is the water used in the hydraulic
transport of bottom or fly ash. Since the water serves only
as a carrier of the ash, water quality is not a significant
consideration. As a matter of fact, a high level of
suspended solids is desirable since it facilitates the
subsequent settling out and removal of the ash.
Settling basins are a normal component of ash transport
systems. They may be either of the mechanical clarifier or
natural lagoon (ash pond) type. Wet ash is removed from the
clarifiers and disposed off site. The supernatent water is
recycled to the process. The only routine blowdown from the
system is the water removed with the wet ash. Waste streams
result from overflows during periods of precipitation and
for intermittant blowdown purposes.
At one of the plants visited, blowdown from a recirculating
water system used to transport fly ash from oil fueled
147
-------
boilers was discharged to the POTW. This waste can be
combined with area runoff and could be treated together.
Costs for pretreatment of discharges from ash transport
systems are estimated from the volume of the portion coming
to the retention pond.
Boiler Slowdown
The quality of boiler blowdown is generally higher than the
quality of the raw water source, which for most plants
discharging to POTWs is the municipal water supply. If
boiler blowdown is discharged to the waste stream, it will
tend to dilute the wastes and make any treatment less
efficient. Boiler blowdown should therefore be returned to
the plant service water system, and in most plants this is
done. Therefore, no costs have been developed for
pretreatment of this waste source.
Cooling System Wastes
Cooling system wastes are discharges of water that have been
used to cool the main condenser surfaces. Cooling systems
are either of the once-through or recalculating type. There
are no known plants which discharge once-through cooling
water to a POTW. Recirculating systems require blowdown
which becomes a waste source.
Levels of Treatment
Levels A thru C treatment for cooling system blowdown
consists of discharge to the POTW without pretreatment. If
the only biocide or other cooling water treatment chemical
used is chlorine and the POTW does not impose restrictions
on chlorine in discharges to the sewer, cooling water
blowdown may be discharged without pretreatment. In that
case the only costs will consist of the sewer service
charges. Level D treatment for residual chlorine consists
of dechlorination and possible pH adjustment and meets the
requirements of effluent limitation guidelines for BPT for
direct discharge. Level D treatment for cooling water
system blowdown is shown in Figure VIII-3.
Capital Costs
Table VIII-10 presents estimates for capital costs of
pretreatment for cooling water system blowdown. These costs
assume that chlorine is used as a biocide, that the POTW
requires removal of residual chlorine, and that no other
biocides or inhibitors unacceptable to the POTW are added to
the cooling water system.
-------
TABLE VIII-8
OPERATING COSTS-PRETREATMENT OF
LOW VOLUME AND METAL CLEANING WASTES
Installed Generating Capaci
Items
Operating Labor
Maintenance
Utilities
Water
Electric Power
Sewer Charge
Chemicals and
Supplies
Total
Anriual production, KWH
(1)
(2)
(3)
(4)
(5)
(6)
25 MW(7)
$1,700
3,000
200
40
500
15.000
$20,440
2.0xl08
500 MW(8)
$17,000
18,000
2,000
2,400
20,000
101,000
$160,400
4.0xl09
Notes to Table VIII- 8
(1) 25 MW Plant - 4 hrs/wk 200 hrs/yr
500 MW Plant - 40 hrs/wk 2000 hrs/yr
(2) 3% of capital cost
(3) City water @ .60/100 gall
(4) 25 MW Plant - 5 kwh x 200 hrs
500 MW Plant - 30 kwh x 2000 hrs
(5) Sewer service charge @ .30/1000 gal
(6) Lime 500 mg/1
Sulfuric Acid 100 mg/1
(7) Design flow: Low volume wastes: 5,000 gpd (from DD)
Metal cleaning wastes: 25,000 gallons batch
(8) Design flow: Low volume wastes 200,000 gpd (from DD)
Metal cleaning wastes: 500 , 000 gal Ions batch
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Operating Costs
Operating costs for pretreatment of cooling system blowdown
pretreatment consists of operating labor, maintenance, and
chemicals for dechlorination. They are summarized in Table
VIII-9.
Area Runoff
The area runoff subcategory includes runoff from material
storage.
Coal is stored in open piles and oil is stored in covered
tanks. Materials storage therefore represents a significant
source of waste only for coal-fired plants. And since the
burning of oil produces only about two percent of the amount
of ash produced by the burning of coal, ash ponds are a
feature of coal burning plants primarily. Material storage
wastes from coal piles and ash ponds are therefore
applicable to coal burning plants only.
No plants discharging area runoff to POTWs were found in the
industry survey.
Level D treatment for coal pile runoff and ash pond
overflows consists of neutralization and sedimentation. Its
cost is a function of the size of the catchment area covered
by the coal pile and the ash pond and the design
meteorological conditions at the particular site. The
regulation (40 CFR 423.40) require that treatment facilities
be sized to treat the runoff from a 10-year, 24-hour
rainfall event to produce an effluent having suspended
solids of less than 50 mg/1 and a pH between 6.0 and 9.0.
The applicable technology consists of lined ponds capable of
holding various volumes of runoff.
Capital Costs
For a 500 MW plant, a coal pile representing 90 days storage
will occupy 10 - 40 acres. A retention basin designed to
provide one hour detention at the maximum 10 minute rate
associated with a 10-year, 24 hour storm will generally meet
the effluent requirement. Depending on location, such a
retention basin could cost $27,000, $96,000, exclusive of
land, or $0.05-$0.19 per KW IGC.
Operating Costs
Operating costs for pretreatment facilities for runoff from
coal piles and ash ponds are limited to chemicals for
neutralizing. It is estimated that chemicals for this
purpose would cost $360 per year for a 25 MW plant and
150
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$7,200 per year for a 500 MW plant. This corresponds to a
unit cost of .0018 mils per KWH generated for a 90 percent
capacity factor.
The following table (VIII-11) presents estimates for capital
costs of pretreatment plants for Level C treatment of low
volume and metal cleaning wastes for a coal-fired plant
where sufficient land is not available.
ULTIMATE DISPOSAL
Costs For Land Destined Solid Wastes
Waste treatment processes discussed in this report are
separation techniques which produce a liquid fraction
suitable for discharge to the public sewer or reuse within
the plant and a liquid or solid residue which requires
ultimate disposal. Many of the processes produce sludges
containing between 0.5 and 5.0 percent solids. These
sludges are generally further dewatered at the site to 15 to
30 percent solids and then disposed off site. The following
paragraphs discuss techniques and costs of dewatering and
ultimate disposal applicable to steam electric power plants.
User Charges For Sewer Service Of the twenty-three plants
visited in this study only 15 percent reported separate
charges for sewer service, while 35 percent reported
surcharges on their water bills for sewer service.
Approximately fifty percent did not report charge for sewer
service as they were municipal utilities whose internal
billing systems did not allow for tracking of such charges.
The average charge for sewer service in this industry is
$0.06/1000 1 ($0.23/1000 gal).
Evaporation Ponds
Evaporation ponds are used by the industry as a method of
ultimate disposal, particularly in the arid areas of the
southwestern United States. The extensive land requirements
make it unsuited for use in urban areas where plants
discharging to POTWs are generally located.
Conveyance Off Site
The cost of this method of disposal is entirely related to
the distance between plant and disposal site. Alterte
methods of conveyance are trucks, railroads and pipelines.
Trucking is most economical for distances under 50 miles.
Costs are of the order of ($.01-$0.13 per 1000 liter)
($0.05-$0.50 per 1,000 gallon) miles exclusive of final
disposal charges.
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Table VIII-9 ESTIMATED CAPITAL COSTS CHEMICAL
WASTES PRETREATMENT PLANT LEVEL C
Installed Generating Capacity
Description 25 MW 500 MW
Equalization Tank $ 28,000 $ 115,000
Reactor 2,000
Clarifier 2,000 5,000
Pumps 1,000 4,000
Piping 2,000 5,000
Subtotal, major equipment J 33,000 | 131,000"
Installation & Foundations 17,000 65,000
Instrumentation 4,000 14,000
Subtotal, construction
costs $ 54,000 $ 210,000
Enginnering & Contin-
gencies 16,000 60,000
Total, land not limited' $ 70,000 $ 270,000
Premium for limited land
construction 20,000 80,000
Cost per KW IGC $ 2.80 $ 0.54
Limited Land Premium 0.80 0.16
Estimated cost allottment, unlimited land
Low volume wastes 2.40 0.60
Metal cleaning wastes 1.20 0.10
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CONDENSER
1
COOLING
TOWER
MAKE-UP
SLOWDOWN (1000
. gpd/MW)
r
SULFITE
LIME
ACID
MONITOR
RESIDUAL
CHLORINE
PH
1
i
CONTACT TANK
SEWER
FIGURE VIII-3. Cooling Water System Slowdown Treatment
For Level D Pretreatment
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Table VIII-io ESTIMATED CAPITAL COST
COOLING WATER SYSTEM BLOWDOWN TREATMENT
Description
Contact Tank
Chemical Feed System
Piping
Subtotal, major equipment
Installation & foundations
Instrumentation
Subtotal, construction costs
Engineering 6 contingencies
Total Cost
Cost per KW IGC
Installed Generating Capacity
25 MW 500 MW
$10,000
4,000
6,000
$20,000
10,000
2,000
$32,000
9,600
$41,600
$ 1.66
$40,000
10,000
25,000
$75,000
37,000r
5,000
$117,000
35,000
$153,000
$ 0.31
Table VIII-11 ESTIMATED OPERATING COSTS
COOLING WATER SYSTEM BLOWDOWN TREATMENT
Description
Operating Labor
Maintenance
Chemicals
Total
Insta]led^ Generating Capacity
25~MW 500 MW
$1,000
1,200
500
$2,700
$4,000
6,000
10,000
$20,000
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Landfills
Landfills are the most common method of disposal of solid
wastes. Costs of disposal at landfills range from $1 to $9
per metric ton ($2-10 per ton). Recent federal regulations
require landfills to provide leachate control, so that
soluble components of the wastes cannot cause groundwater
pollution.
ENERGY CONSIDERATIONS
In contrast to the effluent guidelines for thermal
discharges, the promulgation of standards for pretreatment
is not expected to involve significant energy requirements
or to have a measurable impact on the energy production of
the power plant. None of the treatment technologies
described herein affect the power generating cycle and
therefore do not require "retrofitting" to the extent that
the performance of the plant is impaired. None of the
processes involve a change of state and the only
requirements for energy are for possible pumping needs.
Even these needs are site dependent and many power plants
may find it feasible to install the equipment in such a
manner that repumping is not required.
For estimating purposes it has been assumed that a
pretreatment plant handling low volume and metal cleaning
wastes from a 25 MW generating plant would have a connected
load of 5HP and that a similar plant for the 500 MW
generating facility would have a connected load of 30 HP.
Each plant would operate the equivalent of 800 hours per
year, at full connected load. Under these conditions, the
energy consumption by the waste treatment facilities would
constitute about 0.02 percent of the generating capacity of
the 25 MW generating plant and less than 0.01 percent of the
generating capacity of the 500 MW plant.
Land Requirement
Many of the stations potentially affected by this study tend
to be located in urbanized areas. Land requirements are
important to such stations, as additional land may be
difficult to purchase. Estimated land requirements to
install Level C technology are given in the table below:
Station Estimated
Size Land
MW, IGC Requirement, Acres
10 0.2
25 0.3
37 O.H
155
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345 1.1
500 1.6
Land estimates are based on usage of tanks for equalization,
mixing, settling, etc., and do not include credits for
stacked construction. They contain space allowances for
equipment, pumps, piping, foundation and electrical
equipment and include treatment equipment for low-volume,
metal cleaning and cooling tower wastes. If basins are used
for equalization, etc., then land usage is expected to
double. If stacked construction is employed, then land
usage is expected to decrease by 67 percent. Land
requirements need not be a problem, as treatment modules can
be erected above existing generating equipment using
stacking procedures.
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SECTION IX
BEST PRACTICABLE PRETREATMENT TECHNOLOGY
After careful consideration of the information in this
document and the draft financial impact study, pretreatment
standards were developed. The best practicable pretreatment
technology required to comply with these standards includes
(1) oil skimming to reduce oil and grease in the plant's
combined discharge to the POTW to less than 100 mg/1, and
(2) lime precipitation to reduce copper in the metal
cleaning wastes to less than 1 mg/1.
The methodology employed in the development of the
pretreatment standards and the selection of the best
practicable pretreatment technology is delineated below:
A detail survey was conducted to determine the number of
plants affected by the pretreatment standards. Some of the
plants from this population were visited and sampled.
Plants were visited to determine whether significant
differences exist between these power plants and power
plants which discharge directly into navigable waters.
Further, various waste streams were sampled from
representative power plants to determine the type and level
of pollutants. In defining the characteristics of various
waste streams, data from the site visits and sampling
program were used in conjunction with information in the
development document for effluent limitations guidelines for
this industry dated October 1974 and other sources. The
compatibility of each raw waste characteristic with
municipal treatment works was then considered. The
constituents of the wastewaters which should be subject to
limitations were identified.
The control and treatment technologies were identified.
This included an identification of each distinct control and
treatment technology, including both in-plant and end-of-
process technologies, which is existent or capable of being
designed. It also included an identification of the
effluent level resulting from the application of each of the
technologies. In addition, the non-water quality
environmental impact, such as the effects of the application
of such technologies upon other pollution problems, were
identified. The energy requirements of the control and
treatment technology were determined as well as the cost of
the application of such technologies.
The information, as outlined above, was then evaluated in
order to determine what levels of technology reflected the
application of the recommended pretreatment technologies.
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In identifying such technologies, various factors were
considered. These included the total cost of application of
technology, the age and size of facilities involved, the
fuel used, the mode of operations, the engineering aspects
of the application of various types of control techniques,
non-water quality environmental factors (including energy
requirements) and other factors.
The data upon which the above analysis was performed
included EPA sampling and inspections, consultant and EPA
reports, industry submissions, and other sources.
(2) Summary of conclusions with respect to the general unit
subcategory (Subpart A), small unit subcategory (Subpart B),
old unit subcategory (Subpart C) and area runoff
subcategorization (Subpart D) of the steam electric power
generating point source category.
(i) Categorization
It is determined that all the facilities discharging into
POTW should be subject to the same pretreatment standards.
The standards for the general unit subcategory, small unit
subcategory and old unit s;ubcategory are the same and the
pretreatment standards for the area runoff subcategory is
different because of the nature of its discharge. Many
factors were considered in this determination, but the
largest contributing factors are (1) the production process,
(2) the type and level of pollutants, (3) the treatability
of wastewaters, and (4) the cost of the application of such
technologies.
(ii) Waste characteristics
There are two different types of waste produced by steam
electric power plants. The first type consists of the
chemical wastes which originate from different processes and
operations within a plant. These wastes are highly variable
from plant to plant, depending on fuel, raw water quality,
processes used in the plant and other factors. The known
significant pollutants and pollutant properties from these
wastes include pH, total suspended solids, iron, copper,
nickel, zinc, chromium, oil arid grease, and chlorine.
The second type of waste consists of the waste heat produced
by the plant and disposed to the environment through the
cooling water system.
(iii) Origins of wastewater pollutants
Wastewater streams from power plants can be classified into
(1) metal cleaning wastes, (2) cooling system wastes, (3)
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boiler blowdown, (4) ash transport water, and (5) low volume
waste.
Metal cleaning wastes are those wastes which are derived
from cleaning of metal process equipment. These equipment
include, but are not limited to, boiler tube, boiler
fireside, and air preheater. Pollutants and pollutant
properties in these wastes include oil and grease, iron,
copper, nickel, zinc, total suspended solids, chromium and
pH.
All condenser cooling systems can be classified as (1) once-
through or (2) recirculating. Biocides such as chlorine or
hypochlorites are usually added to once-through cooling
water to minimize biological growth within the condenser and
may, therefore, be discharged. The wastes from the
recirculating cooling system include chemical additives to
control growth of organisms (such as chlorine hypochlorites
and organic chromates) , chemical additives to inhibit
corrosion (such as organic phosphates, chromates and zinc
salts), and material present in the intake waters (but at a
much higher concentration due to evaporative loss).
Boiler blowdown wastes normally have a high pH and high
dissolved solids (except high pressure boiler) . Phosphates
which are used to precipitate the calcium and magnesium
salts are also found in boiler blowdown.
One of the products of the combustion of coal and oil is
ash. These ashes are sometimes transported by water to a
settling pond or basin. Some or all of the water from the
settling pond or basin may be discharged. The chemical
characteristic of ash handling wastewater is basically a
function of the fuel burned. The pollutants and pollutant
properties in the ash handling wastes from coal fired plants
include TSS, pH, iron, aluminum, mercury and oil and grease.
TSS, pH, oil and grease, and sometimes vanadium are found in
the ash handling wastes from oil fired plants.
Area runoff are the product of drainage from rainfall. This
waste stream may contain TSS and oil and grease. Runoff
from coal pile may also contain iron, high or low pH
(depending upon the type of coal), copper, zinc and
manganese.
Low volume wastes include ion exchange water treatment,
water treatment evaporative blowdown, laboratory and
sampling streams, floor drainage, cooling tower basin
cleaning, ash pollution device effluent and any aqueous
power plant wastes which have not been mentioned. These
wastes contain primraily TSS and oil and grease.
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(iv) Treatment and control technologies
Wastewater treatment and control technologies have been
studied for this industry to determine what is the best
pretreatment technology.
The following discussions of treatment technologies provide
the bases for the pretreatment standard. These discussions
do not preclude the selection of other wastewater treatment
alternatives which provide equivalent or better levels of
treatment.
(a) Oil and Grease. Oil skimmers have been demonstrated to
reduce oil and grease concentration to less than 20 mg/1,
far less than the limitation established here. Most, if not
all, of the power plants can comply with this requirement if
they employ good housekeeping techniques.
(b) Copper. The treatment of metal cleaning wastes would
consist of oil and grease skimming in the equalization tank,
lime addition in the reactor (to attain a pH level of
approximately 9) and sedimentation and clarification (to
achieve a total suspended solids of 30 mg/1). Effluent
concentrations of 1 mg/1 total copper are achievable by the
application of this technology. Numerous chemicals are also
removed by this treatment. Pollutants significantly removed
by this treatment include nickel, zinc and chromates.
It is emphasized that in-piant measures to recycle and reuse
wastewater to minimize discharge to municipal treatment
works are included as part of the recommended pretreatment
technology.
The pretreatment technology described above for the removal
of copper requires disposal of the pollutants removed from
wastewaters in the form of sludge. In order to insure long-
term protection of the environment, special consideration of
disposal sites must be made. All landfill sites where such
hazardous wastes are disposed should be selected so as to
prevent horizontal and vertical migration of these
contaminants to ground or surface waters. In cases where
geologic conditions may not reasonably ensure this, adequate
legal and mechanical precautions (e.g., impervious liners)
should be taken to ensure long term protection to the
environment from hazardous materials. Where appropriate,
the location of solid hazardous materials disposal sites
should be permanently recorded in the appropriate office of
legal jurisdiction.
(v) Determination of incompatibility
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Characteristics of waste streams described above were
analyzed for incompatibility with POTW. Factors considered
in determining incompatibility include (1) susceptibility of
the pollutant to treatment by a secondary treatment system,
and (2) interference of the pollutant with the operation of
the POTW.
Copper, nickel and zinc from the metal cleaning wastes were
found to be incompatible because (1) they can interfere with
the operation of the POTW, (2) they may not be adequately
treated, and (3) they pose a threat to the receiving waters
beyond and to plants grown on soil treated with sludge from
the POTW. Pretreatment standard for copper from the metal
cleaning wastes of 1 mg/1 is imposed. Limitations are not
imposed for nickel and zinc because they are indirectly
controlled through the regulation of copper. In certain
cases, copper may not be present in significant quantity,
but nickel and zinc will still be present in high
concentrations. In such cases, it will be necessary for
individual POTW operators to regulate nickel and zinc to
levels which are achievable via lime precipitation.
Oil and grease from power plants is primarily petroleum
based. This type of oil and grease is less biodegradable in
secondary plants than oil and grease of vegetable and animal
origin. Pretreatment standard of 100 mg/1 of oil and grease
is imposed to ensure (1) the proper operation of the
biological treatment system, (2) adequate treatment by the
POTW, and (3) proper transport of wastes to the treatment
system.
Pretreatment standards other than those described above and
the general standards carried over from 40 CFR 128 is
determined not to be necessary at the present time.
(vi) Cost estimates for control of wastewater pollutants
Cost information was obtained from engineering firms,
available literature, development documents for effluent
limitation guidelines (October, 1974) for this industry, and
from plants contacted. User charge data were obtained from
power plants and POTW.
The utilities affected by the regulation should have little
or no trouble in obtaining the capital necessary for the
construction of the pretreatment facilities. The annual
revenue requirements are projected to increase the cost of
electricity by .11 mills/kwh at the affected plants.
(vii) Energy requirements and non-water quality
environmental impacts.
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The major non-water quality consideration which may be
associated with the recommended pretreatment technologies is
the generation of metals-bearing solid wastes. In most
cases, these wastes will be landfilled.
Other non-water quality aspects, including energy, noise and
air pollution, will not be perceptibly affected.
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SECTION X
ACKNOWL EDGMENTS
The preparation of this report was accomplished through the
efforts of the staff of the Environmental Engineering
Department, Hittman Associates, Inc., Columbia, Maryland
under the overall direction of Mr. Burton C. Becker, Vice
President, operations. Mr. Dwight B. Emerson and Mr. J.
Carl Uhrmacher shared direction of the day-to-day work on
the program.
Mr. John Lum, Project Officer, Effluent Guidelines Division,
through his assistance, leadership, and advice has made an
invaluable contribution to the preparation of this report.
Mr. Lum provided a careful review of the draft report and
suggested organizational, technical and editorial changes.
He also was most helpful in making arrangements for the
drafting, presenting, and distribution of this report.
Mr. Ernest P. Hall, Jr., Assistant Director, Effluent
Guidelines Division and Mr. Harold B. Coughlin, Branch
Chief, Effluent Guidelines Division, Mr. Devereaux Barnes,
and Mr. Elwood Forsht, Project Officers, Effluent Guidelines
Division offered many helpful suggestions during the
program.
Appreciation is extended to the Federal Power Commission,
Washington D.C., and to Mr. Vick Saulys, Region V Office of
the Environmental Protection Agency, Chicago, Illinois,
acknowledgment to James Ferry-EPA/Office of Planning and
Evaluation Garry F. Otakie-EPA/Office of Water programs,
Theordore Landry-EPA Region I, Fred Roberts EPA Corvallis,
Oregon Environmental Research Laboratory, Harvey Lunenfeld-
EPA Region II, Mr. Robert Burm-EPA Region VII, Gary
Liberson-EPA Office of Analysis and Evaluation for
assistance and cooperation rendered to us in this program.
Additionally, we wish to thank Mr. John Rose of Daniel P.
Frankfurt, PC, for his invaluable aid.
Also our appreciation is extended to the staff of the
Environmental Engineering Department of Hittman Associates,
Inc. for their assistance during this program. Specifically,
our thanks to:
Dr. Leon C. Parker, Senior Chemical Engineer
Dr. T. Goldshmid, Environmental Engineer
Mr. J. Carl Uhrmacher, Senior Chemical Engineer
Mr. Roger S. Wetzel, Environmental Engineer
Mr. Craig S. Koralek, Environmental Engineer
Mr. Kenneth G. Budden, Environmental Engineer
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Mr. Robert G. Matysek, Junior Chemical Engineer
Mr. Carroll E. Stewart, Chemical Engineer
Mr. Robert T. Brennan, Environmental Engineer
Mr. Efim M. Livshits, Environmental Engineer
Mr. Anthony T. Shemonski, Environmental Engineer
Mr. Werner H. Zieger, Environmental Engineer
Mr. Don s. Kondoleon, Environmental Engineer
The physical preparation of this document was accomplished
through the efforts of the secretarial and other non-
technical staff members at Bittman Associates, Inc., and the
Effluent Guidelines Division. Significant contributions
were made by the following individuals:
Kaye Starr, Effluent Guidelines Division
Nancy Zrubek, Effluent Guidelines Division
Barbara A. White, Hittman Associates, Inc.
164
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SECTION XI
REFERENCES
1. Barker, P.A., "Water Treatment for Steam Generating
Systems", Industrial Water Engineering, March/April
1975.
2. City Council of Roswell, New Mexico, Ordinance No. 933,
Industrial Waste Ordinance of The City of Roswell,
New Mexico.
3. Dean, John G., Bosqui, Frank L., and Lanouette,
Kenneth H., "Removing Heavy Metals from Wastewater,"
Environmental Science and Technology, Volume 6,
No. 6, June 1972.
4. Duffey, J,G. Gale, S.B., and Bruckenstein S.,
"Electrochemical Removal of Chromates and Other
Metals," Cooling Towers, Volume 2, pp. 44-50, 1975.
5. Goldstein, Paul, "Control of CHemical Discharges for
the Steam Electric Power Industry, NUS Corporation,
Pittsburg, PA., Presented at Conference on Water
Quality - Considerations for Steam Electric Power
Plants, Atomic Industrial Forum, Inc., Phoenix, AZ,
January 1975.
6. Nail, Douglas E., "The Influence of EPA Guidelines
on Treatment of Power Plant Wastes," Industrial
Water Engineering, Volume 12, No. 6, December 1975 -
January 1976.
7. Office of Science and Technology, Electric Power
and the Environment, August 1970.
8. Patterson, J.W., et al, Wastewater Treatment Technology,
Illinois Institute for Environmental Quality, Chicago,
Illinois, August, 1971.
9. Scott, David L., Pollution in the Power Industry,
D.C. Heath and Co., Lexington, MA, 1973.
10. Stratton, Charles L., and Lee, G. Fred, "Cooling
Towers and Water Quality," Journal of the Water
Pollution Control Federation, Volume 47, No. 7,
July 1975.
11. Teknekron, Inc., Water Pollution Control of the
Steam Electric Power Industry - Assessment of the
Costs and Capabilities of Water Pollution Control
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Technology for the Steam Electric Power Industry,
Volume 1, Berkley, CA, December 1975.
12. Teknekron, Inc., Water Pollution control of the
Steam Electric Power Industry - Economic Impact of
Water Pollution Control in the Steam Electric
Power Industry, Volume 2, Berkeley, CA, December,
1975.
13. Teknekron, Inc., Water Pollution Control for the
Steam Electric Power Industry - Appendix, Volume 3,
Berkeley, CAr December 1975.
1U. U.S. ENvironmental Protection Agency, Development
Document for Proposed Effluent Limitations Guidelines
and New Source Performance Standards for the Steam
Electric Power Generating Industry, October, 197U.
15. U.S. Environmental Protection Agency, Office of
Water Program Operations, Pretreatment of Pollution
Introduced into Publicaliy Owned Treatment Works
October 1973.
16. U.S. Environmental Protection Agency, Office of
Water Program Operations, State and Local Pretreatment
Programs (Draft Federal Guidelines) Volume 1, August,
1975.
17. U.S. Federal Power Commission, Statistics of
Publicly Owned Electric Utilities in the United
States 1970, Washington, D.C., February 1972.
18. U.S. Environmental Protection Agency, Office of
Planning and Evaluation, Environmental Assessment
of Alternative Thermal Control Strategies for the
Electric Power Industry, December 197U.
19. Fair, G.M., Geyer, C.G., and Okum, D.A., Water
and Wastewater Engineering, New York, NY, 1968.
20. U.S. Environmental Protection Agency, Development Document
for Proposed Effluent Limitations Guidelines and Standards
of Performance for the Machinery and Mechanical Products
Manufacturing Category, June 1975.
21. Private communication with EPA Region II.
22. U.S. Department of Health, Education, and Welfare,
Interaction of Heavy Metals and Biological
Sewage Treatment Processes, Public Health Service,
Division of Water Supply and Pollution Control,
Cincinnati, Ohio (May, 1975).
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23. D.J. Dube, Oilman D. Veith, and G.F. Lee, "Polychlorinated
Biphenyls in Treatment Plant Effluent," Journal of the
Water Pollution Control Federation, Volume 46, No. 5,
May, 197U, pp. 966-72.
24. Pollution Abstracts, 5, (September, 1974) Abstract
No. 74-0444-J.
25. F.D. Sebastian, T.D. Allen, and W.C. Laughlin, Jr.,
"When Disposing of Sludge You May Want to Think Thermal,"
Water and Wastes Engineering, Volume 11, No. 9,
September, 197U, pp. 47-9.
167
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SECTION XII
GLOSSARY
Absolute Pressure. The total force per unit area measured
above absolute vacuum as a reference. Standard atmospheric
pressure is 101,326 N/I12 (14.696 psi) above absolute vacuum
(zero pressure absolute).
Absolute Temperature. The temperature measured from a zero
at which all molecular activity ceases. The volume of an
ideal gas is directly proportional to its absolute
temperature. It is measured in °K (°R) corresponding to °C
+ 273 (°F + 459).
Anion. The charged particle in a solution of an electrolyte
which carries negative charge.
A-thracite. A hard natural coal of high luster which
contains little volatile latter.
Approach Temperature. The difference between the exit
temperature of water from a cooling tower, and the wet bulb
temperature of the air.
Ash. The solid residue following combustion of a fuel.
Ash Sluice. The transport of solid residue ash by water
flow in a conduit.
Backwash. Operation of a granular fixed bed in reverse flow
to wash out sediment and reclassify the granular media.
Bag Filters. A fabric type filter in which dust laden gas
is made to pass through woven fabric to remove the
particulate matter.
Base. A compund which dissolves in water to yield hydroxyl
ions (OH-).
Base-Load Unit. An electric generating facility operating
continously at a constant output with little hourly or daily
fluctuation.
Biocide. An agent used to control biological growth.
Bituminous. A coal of intermediate hardness containing
between 50 and 92 percent carbon.
Slowdown. A portion of water in a closed system which is
wasted in order to prevent a built-up of dissolved solids.
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Boiler. A device in which a liquid is converted into its
vapor state by the action of heat. In the steam electric
generating industry, the equipment which converts water into
steam.
Boiler Feedwater. The water supplied to a boiler to be
converted into steam.
Boiler Fireside. The surface of boiler heat exchange
elements exposed to the hot combustion products.
Boiler Scale. An incrustation of salts deposited on the
waterside of a boiler as a result of the evaporation of
water.
Boiler Tubes. Tubes contained in a boiler through which
water passes during its conversion into steam.
Bottom Ash. The solid residue left from the combustion of a
fuel, which falls to the bottom of the combustion chamber.
Brackish Water. Water having a dissolved solids content
between that of fresh water and that of sea water, generally
from 1000 to 10,000 mg per liter.
Brine. Water saturated with a salt.
Bus Bar. A conductor forming a common junction between two
or more electric circuits. A term commonly used in the
electric utility industry refer to electric power leaving a
station boundary. Bus bar costs would refer to the cost per
unit of electrical energy leaving the station.
Capacity Factor. The ratio of energy actually produced to
that which would have been produced in the same period had
the unit been operated continously rated capacity.
Cation. The charged particles in solution of an electrolyte
which are positively charged.
Carbonate Hardness. Hardness of water caused by the
presence of carbonates and bicarbonates of calcium and
magnesium.
Circulating Water Pumps. Pumps which deliver cooling water
to the condensers of a power plant.
Circulating Water system. A system which conveys cooling
water from its source to the main condensers and then to the
point of discharge. SYnonymous with cooling water system.
169
-------
Clarification. A process? for the removal of suspended
matter from a water solution.
Clarifier. A basin in which water flows at a low velocity
to allow settling suspended matter.
Closed Circulating Water System. A system which passes
water through the condensers, then through an articial
cooling device, and keeps recycling it.
Coal Pile Drainage. Runoff from the coal pile as a result
of rainfall.
Condensate Polisher. An ion exchanger used to adsorb minute
quantities of cations and anions present in condensate as a
result of corrosion and erosion of metallic surfaces.
Condenser. A device for converting a vapor into its liquid
phase.
Construction. Any placement, assembly, or installation of
facilities or equipment (including contractural obligations
to purchase such facilities or equipment) at the premises
where the equipment will be used, including preparation work
at the premises.
Convection. The heat transfer mechanism arising from the
motion of a fluid.
Cooling Canal. A canal in which warm water enters at one
end, is cooled by contact with air, and is discharged at te
other end.
Cooling Lake. See Cooling Pond.
Cooling Pond. A body of water in which warm water is cooled
by contact with air, and is either discharged or returned
for reuse.
Cooling Tower. A configured heat exchange device which
transfers reject heat from circulating water to the
atmosphere.
Cooling Tower Basin. A basin located at the bottom of a
cooling tower for collecting the falling water.
Cooling Water System. See Circulating Water System.
Corrosion Ihibitor. A chemi.cal agent which slows down or
prohibits a corrosion reaction.
170
-------
Counterflow. A process in which two media flow through a
system in opposite directions.
Critical Point. The temperature and pressure conditions at
which the saturated-liquid and saturated-vapor states of a
fluid are identical. For water-steam these conditions are
3208.2 psia and 705.U7°F.
Cycling Plant. A generating facility which operates between
peak load and base load conditions. In this report, a
facility operating between 2000 and 6000 hours per year.
Cyclone Furnace. A water-cooled horizontal cylinder in
which fuel is fired, heat is released at extremely high
rates, and combustion is completed. The hot gases are then
ejected into the main furnace. The fuel and combustion air
enter tangentially, imparting a whirling motion to the
burning fuel, hence the name Cyclone Furnace. Molten slag
forms on the cyclinder walls, and flows off for removal.
Deaeration. A process by which dissolved air and oxygen are
stripped from water either by physical or chemical methods.
Deaerator. A device for the removal of oxygen, carbon
dioxide and other gases from water.
Degasification. The removal of a gas from a liquid.
Dejonizer. A process for treating water by removal of
cations and anions.
Demineralizer. See Deionizer.
Demister. A device for trapping liquid entrainment from gas
or vapor streams.
Dewater. To remove a portion of the water from a sludge or
a slurry.
Dew Point. The temperature of a gas-vapor mixture at which
the vapor condenses when it is cooled at constant humidity.
Diesel. An internal combustion engine in which the
temperature at the end of the compression is such that
combustion is initiated without external ignition.
Discharge. To release or vent.
Discharge Pjpe or Conduit. A section of pipe or conduit
from the condenser discharge to the point of discharge into
receiving waters or cooling device.
171
-------
Drift. Entrained water carried from a cooling device by the
exhaust air.
Dry Bottom Furnace. Refers to a furnace in which the ash is
collected as a dry solid in hoppers at the bottom of the
furnace, and removed from the furnace in this state.
Dry Tower. A cooling tower in which the fluid to be cooled
flows within a closed system. This type of tower usually
uses finned or extended surfaces.
Dry Well. A dry compartment of a pump structure at or below
pumping level, where pumps are located.
Economizer. A heat exchanger which uses the heat of
combustion gases to raise the boiler feedwater temperature
before the feedwater enters the boiler.
Electrostatic Precipitator. A device for removing particles
from a stream of gas based on the principle that these
particles carry electrostatic charges and can therefore be
attracted to an electrode by imposing a potential across the
stream of gas.
Evaporation. The process by which a liquid becomes a vapor.
Evaporator. A device which converts a liquid into a vapor
by the addition of heat.
Feedwater Heater. Heat exchangers in which boiler feedwater
is preheated by steam extracted from the turbine.
Filter Bed. A device for removing suspened solids from
water, consisting of granular material placed in horizontal
layers and capable of being cleaned hyclraulically by
reversing the direction of the flow.
Filtration. The process of passing a liquid through a
filtering medium for the removal of suspned or colloidal
matter.
Fireside Cleaning. Cleaning of the outside surface of
boiler tubes and combustion chamber refractories to remove
deposits formed during the combustion.
Flue Gas. The gaseous products resulting from the
combustion process after passage through the boiler.
Fly Ash. A portion of the non-combustible residue from a
fuel which is carried out of the boiler by the flue gas.
172
-------
Fossil Fuel. A natural solid, liquid or gaseous fuel such
as coal, petroleum or natural gas.
Generation. The conversion of chemical or mechanical energy
into electrical energy.
Heat Rate. The fuel heat input (in Joules or BTU) required
to generate a KWH.
Heating Value. The heat available from the combustion of a
given quantity of fuel as determined by a standard
calorimetric process.
Humidity. Pounds of water vapor carried by 1 Ib of dry air.
Ion. A charged atom, molecule or radical, the migration of
which affects the transport of electricity through an
electrolyte.
Ion Exchange. A chemical process involving reversible
interchange of ions between a liquid and a solid but no
radical change in the structure of the solid.
Lignite. A carbonaceous fuel ranked between peat and coal.
Makeup Water Pumps. Pumps which provide water to replace
that lost by evaporation, seepage, and blowdown.
Mechanical Draft Tower. A cooling tower in which the air
flow through the tower is maintained by fans. In forced
draft towers the air is forced through the tower by fans
located at its base, whereas in induced draft towers the air
is pulled through the tower by fans mounted on top of the
tower.
Mill. One thousandth of a dollar.
Mine-mouth, Plant. A steam electric powerplant located
within a short distance of a coal mine and to which the coal
is transported from the mine by a conveyor system, slorry
pipeline or truck.
Mole. The molecular weight of substance expressed in grams
(or pounds).
Name Plate. See Nominal capacity.
Natural Draft Cooling Tower. A cooling tower through which
air is circulated by natural or chimney effect. A
hyperbolic tower is a natural draft tower that is hyperbolic
in shape.
173
-------
Neutralization. Reaction of acid or alkaline solutions with
the opposite reagent until the concentrations of hydrogen
and hydroxyl ions are about equal.
New Source. Any source, the construction of which is
commenced after the publicated of proposed section 306
regulations.
Nominal Capacity. Name plate - design rating of a plant, or
specific piece of equipment.
Nuclear Energy. The energy derived from the fission of
nuclei of heavy elements such as uranium or thorium or from
the fusion of the nuclei of light elements such as deuterium
or tritium.
Once-through Circulating Water System. A circulating water
system which draws water from a natural source, passes it
through the main condensers and returns it to a natural body
of water.
Overflow. (1) Excess water over the normal operating limits
disposed of by letting it flow out through a device provided
for that purpose; (2) The device itself that allows excess
water to flow out.
Osmosis. The process of diffusion of a solvent thru a semi-
permeable membrane from a solution of lower to one of higher
concentration.
Osmotic Pressure. The equilibrium pressure differential
across a semi-permeable membrane which separates a solution
of lower from one or higher concentration.
Oxidation. The addition of oxygen to a chemical compund,
generally, any reaction which involves the loss of electrons
from an atom.
Packing (Cooling Towers) . A media providing large surface
area for the purpose of enhancing mass transfer, usually
between a gas or vapor, and a liquid.
Precipitation. A pheonomenon that occurs when a substance
held in solution in a liquid phase passes out of solution
into a solid phase.
Preheater (Air). A unit used to heat the air needed for
combustion by absorbing heat from the products of
combustion.
174
-------
Peak-load Plant. A generating facility operated only during
periods of maximum demand, in this report is is a facility
operating less than 2000 hours per year.
Penalty. A sum to be forfeited, or a loss due to some
action.
Plant Code Number. A four-digit number assigned to all
powerplants in the industry inventory for the purpose of
this study.
Plume (Gas). A conspicuous trail of gas or vapor emitted
from a cooling tower or chimney.
Powerplant. Equipment that produces electrical energy,
generally by conversion from heat energy produced by
chemical or nuclear reaction.
Psychrometric. Refers to air-water vapor mixtures and their
properties. A psychrometric charg graphically displays the
relationship between these properties.
Pulverized Coal. Coal that has been ground to a powder,
usually of a size where 80 percent passes through a #200
U.S.S. sieve.
Pump Runout. The tendency of a centrifugal pump to deliver
more than its design flow when the system resistance falls
below the design head.
Pyrites. Combinations of iron and sulfur found in coal as
FeS2.
Radwaste. Radioactive waste streams from nuclear power-
plants.
Range. Difference between entrance and exit temperature of
water in a cooling tower.
Rankine Cycle. THe thermodynamic cycle which is the basis
of the steam-electric generating process.
Rank of Coal. A classification of coal based upon the fixed
carbon on a dry weight basis and the heat value.
Recirculation System. Facilities which are specifically
designed to divert the major portion of the cooling water
discharge back to the cooling water intake.
Recirculation. Return of cooling water discharge back to
the cooling water intake.
175
-------
Regeneration. Displacement from ion exchange resins of the
ions removed from the process solution.
Reheater. A heat exchange device for adding superheat to
steam which has been partially expanded in the turbine.
Relative Humidity. Ratio of the partial pressure of the
water vapor to the vapor pressure of water at air
temperature.
Reinlection. To return a flow or portion of flow, into a
process.
Reverse Osmosis. The process of diffusion of a solvent thru
a semi-perable membrane from a solution of higher to one or
lower concentration, affected by raising the pressure of a
more concentrated solution to above the osmotic pressure.
Reduction. A chemical reaction which involes the addition
of electrons to an ion to decrease its positive valence.
Saline Water. Water containing salts.
Sampling Stations. Locations where several flow samples are
tapped for analysis.
Sanitary Wastewater. Wastewater discharged from sanitary
conveniences of dwellings and industrial facilities.
Saturated Air. Air in which the water vapor is in
equilibrium with the liquid water at air temperature.
Saturated Steam. Steam at the temperature and pressure at
which the liquid and vapor phase can exist in equilibrium.
Scale. Generally insoluble deposits on heat transfer
surfaces which inhibit the passage of heat through these
surfaces.
Scrubber. A device for removing particles and/or objection-
able gases from a stream of gas.
Secondary Treatment. The treatment of sanitary wastes water
by biological means after primary treatment by
sedimentation.
Sedimentation. The process of subsidence and deposition of
suspended matter carried by a liquid.
Sequestering Agents. Chemical compunds which are added to
water systems to prevent the formation of scale by holding
the insoluble compunds in suspension.
176
-------
Service Water Pumps. Pumps providing water for auxiliary
plant heat exchangers and other uses.
Slag Tap Furnace. Furnace in which temperature is high
enough to maintain ash (slag) in a molten state until it
leaves the furnace through a tap at the bottom. The slag
falls into the sluicing water whwere it cools,
disintegrates, and is carried away.
Slimicide. An agent used to destroy or control slimes.
Sludge. Accumulated solids separated from a liquid during
processing.
Softener. Any device used to remove hardness from water.
Hardness in water is due mainly to calcium and magnesium
salts. Natural zeolites, ion exchange resins, and
precipitation processes are used to remove the calcium and
magnesium.
Spinning Reserve. The power generating reserve connected to
the bus bar and ready to take load. Normally consists of
units operating at less than full load. Gas turbines, even
though not running, are considered spinning reserve due to
their quick start up time.
Spray Module (Powered Spray Module). A water cooling device
consisting of a pump and spary nozzle or nozzles mounted on
floats and moored in the body of water to be cooled. Heat
is transfered principally by evaporation from the water
drops as they fall through the air.
Station. A plant comprising one or several units for the
generation of power.
Steam Drum. Vessel in which the saturated steam is
separated from the steam-water mixture and into which the
feedwater is introduced.
Supercritical. Refers to boilers designed to operate at or
above the critical point of water 22,100 kn/m2 and 374.0°C
(3206.2 psia and 705.4°F).
Superheated Steam. Steam which has been heated to a
temperature above that corresponding to saturation at a
specific pressure.
Thermal Efficiency. The efficiency of the thermodynamic
cycle producing work from heat. The ration of usable energy
to heat input expressed as percent.
177
-------
Thickening. Process of increasing the solids content of
sludge.
Total Dynamic Heat (TDH). Total energy provided by a pump
consisting of the difference in elevation between the
suction and dischage levels, plus losses due to unrecovered
velocity heads and friction.
Turbidity. Presence of suspended matter such as organic or
inorganic material plantkton or other microscopic organisms
which reduce the clarity of the water.
Turbine. A device used to convert the energy of steam or
gas into rotation mechanical energy and used as prime mover
to drive electric generation.
Unit. In steam electric generation, the basic system for
power generation consiting of a boiler and its associated
turbine and generator with the required auxiliary equipmet.
Utility. Public utility. A company, either investorowned
or publicly owned which provides service to the public in
general. The electric utilities generate and distribute
electric power.
Volatile Combustion Matter. The relatively light components
in a fuel which readily vaporize at a relatively low
temperature and which when combined or reacted with oxygen,
give out light and heat.
Wet Bottom Furnace. See slag-tap furnace.
Wet Bulb Temperature. The steady-state, nonequilibrium
temperature reached by a small mass of water immersed under
adiabatic conditions in a continous stream of air.
Wet Scrubber. A device for the collection of particulate
matter from a gas stream and/or absorption of noxious gases
from the stream.
Zeolite. Complex sodium aluminum silicate materials, which
have ion exchange properties and were the original ion
exchange materials before synthetic resins were processed.
178
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APPENDIX A
STATISTICAL ANALYSIS OF HISTORICAL DATA
Effluent pretreatment standards achievable by steam electric
power plants discharging their wastewater effluents into
publicly-owned treatment facilities were determined from
statistical analysis of historical data describing the
pollutants concentration over extended periods of time. Of
the three plants analyzed only one provides partial
pretreatment which includes flow equalization, oil removal,
and settling. The remaining two plants discharge untreated
waste. This appendix describes the statistical approach
used and presents results of that analysis.
The statistical analysis was based on the assumption that
the data are normally distributed, that is, their frequency
of occurrence is fully defined by two statistical
parameters: The mean X and the standard deviation s. Each
set of data representing the variation of concentration of a
particular pollutant in treated effluent was statistically
examined to determine the mode of normal distribution that
best describes its frequency of occurrence. Both arithmetic
and logarithmic modes of normal distribution were
considered. The degree of fit of the data to any particular
mode was determined by calculating the coefficients of
skewness and of kurtosis. The former measures the symmetry
of the distribution diagram and the latter measures the
height of the peak of the diagram relative to that of a
normal curve. A perfect fit to normal distribution is
indicated by a zero coefficient of skewness and a
coefficient of kurtosis of three.
If neither the arithmetic nor the logarithmic modes of
normal distribution describe the frequency of occurrence of
a data set, a modified logarithmic mode was employed to
"force" the data into normal distribution. This mode is
referred to as the three-parameters logarithmic type of
normal distribution. It is assumed that deviation from
normal distribution occurs in the tails of the frequency
curve where the probability of occurrence is very low.
Thus, it is assumed that deviation of data from the perfect
logarithmic mode of normal distribution is due to small
sample size. The overall effect of this deviation is to
increase the variance of the data set. The three-parameters
approach is designed to remove this deviation in the tails
by adding or subtracting a constant number, smaller than the
first element of the data set, to each member of the sample.
The exact value of the constant is determined by iterating a
series of mathematical expressions designed to generate a
179
-------
zero coefficient of skewriess and a value of approximately
three for the coefficient of kurtosis.
The mathematical treatment of data was carried out by a
computer program. Each set of data was initially read by
the computer which sorted elements in ascending order. The
computer then calculated the first four moments and the
coefficients of skewness and kurtosis for each of the three
modes of normal distribution. The statistical coefficients
of the three-parameters logarithmic mode of normal
distribution were determined by initially assigning an
arbitrary constant to be added to each element of the data
set. The computer calculated the coefficient of skewness
and determined from its value whether the deviation from
normal distribution occurred at the lower or upper tail of
the diagram. A deviation in the lower tail was indicated by
a negative value and the computer proceeded to correct it by
adding to each of the elements half of the arbitary
constant. A positive coefficient of skewness was corrected
by subtracting half of the constant. This was repeated
until a zero coefficient of skewness was obtained. The
computer then calculated the percent cumulative of each
element in the series and converted it to standard deviation
expressed as probit (standard deviation plus five).
Based on the values of the coefficients of skewness and
kurtosis the mode of normal distribution that best described
the distribution of the data set was selected and the data
were subjected to a least squares analysis as a function of
the corresponding probits to determine the coefficients of
regression (slope, intercept, and coefficient of
determination). The regression line was used to determine
the 99 percent confidence upper limits.
Table A-1 lists the mathematical expressions used to
calculate the various statistical parameters. These are
shown in Tables A-2 to A-6 for various pollutants discharged
from three pants. Each of these tables shows the calculated
values of the first four moments, and the coefficients of
skewness and kurtosis, for each of the modes of normal
distribution. Also shown in these tables are the constants
used to normalize the distribution of the data, the
coefficients of regression (slope, intercept, and
coefficient of determination), and the 99 percent confidence
limits. Plots of the best fit data and their regression
lines are shown in Figures A-1 to A-19. The statistical
parameters of the best fit data are summarized in Table A-7.
The historical data analyzed are listed in Table A-8.
Water usage data listed in Section V of this report have
also been statistically analyzed by the three modes of
normal distribution. The results are listed in Table A-9
180
-------
and plotted in Figures A-20 to A-23. In all of the water
usage categories examined, the distribution of the data
could be normalized by the three parameter approach. This
is indicated by the numerical values calculated by the
coefficients of determination which measure the "goodness of
fit" of the regression line. The values were always greater
than 90 percent.
The water usage data were also plotted on log-log paper
against production rate to determine the effect of plant
size on the quantity of water used. These plots are shown
in Figures A-2U to A-27 and the coefficients of the
statistical regression analysis expressed in logarithms are
shown in Table A-10. The results indicate that based on the
available data, there is no correlation between water usage
in each of the categories and production rate, as indicated
by the low values calculated for the coefficients of
determination.
181
-------
Table A-l. MATHEMATICAL EXPRESSIONS FOR DETERMINATION
OF STATISTICAL PARAMETERS
First moment m = - / „ X^ (mean)
1 n 2 -2
~*
-
Second moment m = - J~* X^ - X (variance)
* 3
Third moment m = - \~*' K - ^ * > X, + 2X
3 n / , i n /_, i
1=1 i=l
n n n
1 V- V4 4 77" V* Y3 x 6 V"2 V Y2 TV"4
Fourth moment m^= - ) j X^ - — X / _, X^ + — X / . X^ - 3X
1=1 1=1 i=l
Coefficient of skewness 7i = m
Coefficient of kurtosis Y± - m4
~7T
m2
Probit Q = / e dt
x*
/OO i2
el
o
277
X = t - Co + C»t + C2f ^
1 + djt + d2t^ + d3t
P = X + 5
182
-------
Slope
DRAFT
n n
Ev*
y. 2-»
i- x=
EX*
1
n
Intercept
a2 = P -
P = i=l
Coefficient of determination
Li=l
i=l
1=1-
X1
n
C
- the value of element i of a data set. X-f=Xj for arithmetic mode,
Xj=log X-j for logarithmic mode, and X^log (X-j + a) for three-
parameters mode of normal distribution, where a is the added or
subtracted constant.
- number of elements in a data set
- 2.515517 d} - 1.432788
- 0.802853 d2 - 0.189269
- 0.010328 d3 - 0.001308
e(Q)< 4.5 x ICT"
183
-------
Table A-2; STATISTICAL ANALYSIS OF HISTORICAL DATA (MG/L)
Plant No. 7308 Wastewater Source: Retention Pond
Pollutant
Mode of Normal
Distribution
Statistical
Parameter
Mean •
Variance
Third Moment
Fourth Moment
Coeff. of Skewness
Coeff. of Kurtosls
Correction Constant
Slope
Intercept
Coeff. of Determination
992 Confidence Limit
Iron
Arithmetic
4.75
0.68
0.28
0.77
0.49
1.63
1.88
-4.67
0.91
6.67
Logarithmic
4.86
0.005
0.00
0.00
0.4
1.51
Nickel
Arithmetic
2.40
51214.64^
—
—
1.45^
3.18(1)
Logarithmic
1.73
0.09^
0.035(l)
0.026^'
1.21(1)
2.87{1)
Three
Parameters
Logarithmic
1.3
0.60(1>
0.00
0.780)
o.oo '0)
2.160)
-0.92
1.150)
-4.170)
0.970)
3.1
Silver
Arithmetic
0.04
1.680)
-2.530)
6.640)
-1.15<1>
2.330)
1.58(D
-3.52(1)
0.33 0)
0.07
Logarithmic
0.04
0.020)
-o.oosO)
0.0020)
-1.750)
2.330)
CO
.Ł»
(1) calculated with data x 100
-------
Table A-3. STATISTICAL ANALYSIS OF HISTORICAL DATA (MG/L)
00
en
Plant No. 7308 Vtestewater Source: Cooling Tower Basin
Pollutant
>^^ Mode of Normal
^~>^D1str1bution
Stat1sticaV""s\>^
Parameter ' ^""^-^^^^
Mean
Variance
Third Moment
Fourth Moment
Coeff. of Skewness
Coeff. of Kurtosls
Correction Constant
Slope
Intercept
Coeff. of Determination
99J Confidence Limit
Iron
Arith-
metic
5.27
10.55
12.70
255.14
0.37
2.29
4.26
-16.0
0.96
12.83
Loga-
rithmic
3.92
0.12
-0.02
0.03
-0.63
2.05
Copper
AH th-
metlc
0.34
2535.43
190480.68
...
1.49
3.23
Loga-
rithmic
0.64
0.24
0.14
0.17
1.22
2.96
Three
Para-
meters
Loqa-
•Mthmic
0.58
0.72
0.00
1.31
0.00
2.48
-0.04
1.19
-5.21
0.87
0.8
Chromium
Arith-
metic
2.90
605.02(1)
20240. 16
--_
1.36(1)
3.760)
Loga- ,
Mthmlc
2.08
0.12(1)
(U
0.000
0.03(1)
0.14<"
2.23^
Three
Para-
meters
Loga-
rithmic
2.03
0.15«>
U)
0.00
0.05C)
0.00(l)
2.29(')
-0.14
0.507("
-1.25
0.96^
2.93
(1) calculated with data x 100
-------
Table A-3. STATISTICAL ANALYSIS OF HISTORICAL DATA (MG/L) 1C.ON!JNUED!
Mode of Normal
^^Distribution
StatisticaT^1^^^
Parameter ^"-'v^^
Mean
Variance
Third Moment
Fourth Moment
Coeff. of Skewness
Coeff. of Kurtosis
Correction Constant
Slope
Intercept
Coeff. of Determination
99* Confidence Limit
Lead
Arith-
metic
0.29
543.1
11025.36
712419.5
0.87
2.41
Loga-
rithmic
0.2
0.15
-0.02
0.04
-0.29
2.02
Three
Para-
meters
Loga-
rithmic
0.33
0.08
0.00
0.01
0.00
2.00
0.05
0.37
-0.41
0.93
0.45
Zinc
Arith-
metic
3.9
36S961.o(*)
--.-
--.
,.H(2)
4.5,(a)
Loga-
rithmic
1.38
(2)
0.33
o.,a'21
o.K121
10.94U
(2)
2.34
Three
Para-
meters
Loga-
rithmic
0.8
1.09<«
(2)
0.0
(2)
2.51
o.o-('}
2.1 <2)
-0.4
1.39^)
-5.31^)
0.98(2)
3.51
pH(D
Arith-
metic
6.4
20.5<3)
t-i)
-129.5
1640.0^)
-,.3,(3)
3.89l3>
Loga-
rithmic
6.3
0.001 .
(3)
0.00
O.OG<3)
-,.5(3)
-3.43<3)
Three
Para-
meters
Loga-
rithmic
6.4
o.oO)
0.0(3)
0.0^)
0.0(3)
-4.03^3)
8.02
0.01.(3)
2.07(3)
0.78(3)
6.4
CO
cr>
(1) pH units
(2) calculated with data x 100
(3) calculated with data x 10
-------
Table A-4. STATISTICAL ANALYSIS OF HISTORICAL DATA (MG/L)
Plant No. 8696 Wastewater Source: Derolnerallzer
Pollutant
Mode of Normal
*""**»>[) i s trlbu 1 1 on
Statlstical^^^
Parameter ^^^^^
Kean
Variance
Third Moment
Fourth Moment '
Coeff. of Skewness
Coeff. of Kurtosls
Correction Constant
Slope
Intercept
Cceff. of Determination -
991 Confidence Limit
PH(1)
Arith-
metic
5.5?
14.13
26.64
319.44
0.50
1.60
Loga-
rithmic
4.161
0.10
-0.001
0.02
-0.05
1.78
Three
Para-
meters
Loga-
rithmic
4.26
0.09
0.00
0.015
0.00
1.71
0.204
0.35
-1.09
0.93
9.26
Suspended Sol Ids
Arith-
metic
32.67
4053.73
737828.37
2.86
10.35
Loga-
rithmic
12.02
0.26
0.19
0.27
1.42
3.86
Three
Para-
meters
Loga-
rithmic
'8.55
0.70
0.00
1.68
0.00
3.40
-3.54
0.96
-4.09
0.92
97.56
BOOS
Arith-
metic
2.53
3.21
3.1
23.98
0.54
2.32
2.07
-7.82
0.94
6.89
Loga-
rithmic
0.25*
0.18
-0.05
0.08
-0.75
2.60
COO
Arith-
metic
28.83
424.58
12699.82
718259.0
1.45
3.98
Loga-
rithmic
23. 441
0.07
0.007
0.015
0.39
2.69
Three
Para-
meters
Loga-
rithmic
22.27
0.11
0.03
0.00
2.95
-3.65
0.38
• -0.64
0.94
28.20
00
(1) prt units
-------
Table A-5. STATISTICAL A:;.".YSIS OF HISTORICAL DATA (MG/L)
oo
00
Plant No. 8696
Pollutant
^^ Mode of Normal
^\^t)istribution
Statistical^>^^
Parameter ^^"-^
Mean
Variance
Third Moment
Fourth Moment
Coeff. of Skewness
Coeff. of Kurtosis
Correction Constant
Slope
Intercept
Coeff. of Determination
99J Confidence Limit
Wastewater Source: Cooling tower blowdown
PH
-------
Table A-C. STATISTICAL ANALYSIS OF HISTORICAL DATA (MG/L)
00
10
Plant No. 8392 Nastewater Source: Cooling tower Boiler
Pollutant
Mode of Normal
— -s^Distrlbution
Statistical ^^^
Parameter ^"^^^^
Mean
Variance
Third Moment
Fourth Moment
Coeff. of Skewness
Coeff. of Kurtosis
Correction Constant
Slope
Intercept '
Coeff. of Determination
991 Confidence Limit
Chroma te
Arithmetic
14.94
7.31
32.69
394.28
1.65
7.37
Logarithmic
14.46
0.05
0.0002
0.0001
0.66
5.63
Three
Parameters
Logarithmic
14.53.
0.01
0.00
0.001
0.00
5.37
-5.62
0.12
0.34
0.77
16.24
Phosphate
Arithmetic
17.1
13.98
10.86
569.44
0.20
2.90
Logarithmic
16.59
0.009
-0.0003
0.0002
-0.36
2.82
Three
Parameters
Logarithmic
16.51
0.002
0.00
0.00
0.00
-3.10
19.99
0.05
1.31
0.97
17.18
-------
Table A-7. STATISTICAL PARAMETERS SUMMARY FOR BEST FIT DATA (MG/LJ
Cooling Tower Slowdown
Source (Plant 8596)
Parameter
PH
Suspended Solids
BOOS
COO
Source
Parameter
Chromate
Phosphate
Statistical
Mode
Arithmetic
3-Farameter
Logarithmic
3-Paraneter
Concentration
Mean
7.46
13.59
2.36
26.40
991
Confidence
Limit
8.11
15.39
3.85
27.55
Cooling Tower Slowdown
(Plant 8392)
3-parameter
14.53
16.24
Source Cooling Tower Basin
(Plant 7308)
Parameter
Fe
Cu
Cr
Pb
Zn
PH
Statistical
Mode
AH thmetlc
3-pararceter
3-parameter
3-parameter
3-parameter
3-parameter
Concentration
Mean
5.27
0.58
2.03
0.33
0.8
6.4
99t
Confidence
Limit
12.83
0.80
2.93
0.45
3.23
6.4
Source Retention Pond
Parameter
Fe
N1
A9
AM thmt-tlc
3-parameter
Arithmetic
4.75
1.3
.0.04
6.67
3.1
0.03
Demlneral 1 zer •
(Plant 8696)
Statistical
Mode
3-parameter
3-parameter
Arithmetic
3-parameter
99!
Concentration Concentration
Mean Limit
4.26 9.26
8.55 97.56
2.53 6.89
22.27 28.20
Boiler
(Plant 8392)
3-parameter
16.51 17.78
vo
o
-------
ljbJe_A-8. HISTORICAL DATA (MG/L)
Plant No. 8696
Cooling Tower Slowdown
pH 7.27. 7.94, 7.08, 7.4, 7.26, 7.72, 7.14, 7.5, 7.33.
7.72, 7.4, 7.97, 7.14, 7.25. 7.35, 7.23. 7.65, 7.39,
7.98. 7.35
SS 11.0, 23.0, 23.0, 14.0, 15.6, 12.0, 7.2, 13. 11.6,
16.0, 19.6, 13.5, 17.6, 11.0, 12.0, 8.4
BOD- 2.7, 3.0, 1.0, 2.1, 3.7, 3.7, 3.3, 3.8, 3.9. 2.9,
5 3.2,2.5,2.2,1.9,1.6,1.3,1.4,1.6
COD 24.0, 29.0, 27.0, 12.0, 33.0. 30.0, 30.0, 31.0.
2.2, 24.0, 23.0, 21 .0, 20.0
. Oemineralizer Backwash
pH 1.0, 5.77, 1.95, 3.23, 2.86, 3.26, 9.52, 2.16, 6.42,
2.72, 10.10, 9.87, 11.65, 9.8, 1.72, 12.0, 2.7, 2.78
SS 96.0, 8.4, 11.0, 9.6, 5.6, 6.4, 4.0, 5.2, 19.0,
10.8, 3.6, 8.6, 84.0, 8.0, 264.0, 6.4, 4.8
BOD, 4.7, 0.3, 0.2. 0.7, 0.9, 1.0, 2.7, 5.8, 6.2, 3.2,
5 3.0,2.8,3.3,2.1,3.8,1.6,0.8;
22.0, 19.0, 21,0. 7.0, 13.0. 22.0, 22.0, 24.0.,
•~ ~ 39.0, 13.0, 71.0, 57.0, 18.0, 20.0, 83.0,
Chromate 16,0, 24,0, 18.0, 14.0, 16.0, 14.0, 14.0, 14.0, 14.0,
12.0, 10.0, 14.0, 14.0, 16.0, 14.0, 14.0. 16.0, 16.0,
14.0
Bojler
Phosphate 15.0, 18.0, 16.0, 26.0, 19.0. 15.0, 18.0, 13.0, 20.0,
17.0, 14.0, 12.0, 10.0, 20.0, 13.0, 21.0, 19.0, 18.0
Plant No. 7308
Retention Pond
Fe 4.0, 179.0, 4.0, 6.0, 5.0
N1 1.35, 6.9, 1.1, 1.72, 0.95
Ag 0.05, 0.05, 0.05. 0.02
Cooling Tower Basin_
Fe 11.4, 7.25. 5.75. 1.0. 7.5, 3.5, 4.5. 1.3
Cu 0.05,1.35.0.12,0.1,0.1
Cr 2.0, 4.0, 4.0, 8.6, 1.1, 0.55, 1.5, 1.5
Pb 0.25, 0.75, 0.05, 0.6, 0.25, 0.25, O'.IS, 0.06
Zn 7.85, 18.75, 0.8, 0.7, 0.45, 1.75, 0.54, 0.41
191
-------
500
100
50
Ł
-------
co
^ 100
Ł
<
I—
Q
Q
c;
O
50
10
3.0
4.0
I
5.0
PROBITS
6.0
7.0
FIGURE A-2. Normal Distribution Diagram for Phosphates Concentration
In Boiler Slowdown (Plant 8696)
-------
50
10
to
-pi
o
Q
LU
I—I
_l
-------
100
cr.
Q
UJ
M
OL
O
3.0
6.0
PROBITS
FIGURE A-4.Normal Distribution Diagram for COD Concentration
In Wastewater From Demineralizer(Plant 8696)
195
-------
50
CT)
•=1
Q
Q
UJ
ex.
O
10
3.0
4.0
5.0
PROBITS
6.0
7.0
FIGURE A-5, Normal Distribution Diagram for Supser.ded Solids Concentration
In Cooling Tower Slowdown (Plant 8696)
-------
IO
<
t—
Q
o:
o
3.0
4.0
5.0
PROBITS
6.0
7.0
FIGURE A-6. Normal Distribution Diagram for COD Concentration In
Cooling Tower Slowdown (Plant 8696)
-------
50
10
vo
00
Q
Q
LU
M
a:
o
©
3.0
4.0
5.0
PROBITS
6.0
7.0
FIGURE A-7. Normal Distribution Diagram for Chromates Concentration In
Cooling Tower Slowdown (Plant 8392)
-------
10
10
<Ł>
E
-------
ro
8
~ 9.0
-------
07
2 3
M
s:
K
O
2 2
3.0
4.0
5.0
PROBITS
6.0
7.0
FIGURE A-10. Normal Distribution Diagram for BODs
Concentration in Demineralizer Backwash
(Plant 8696)
201
-------
io'
<
m
o
10
3.0
4.0
5.0
PROBITS
6.7
7.0
FIGURE A-ll, Normal Distribution Diagram for Normalized Nickel
Concentration in Retention Pond (Plant No. 7308)
202
-------
10'
Q
LJ
10
3.0
4.0
5.0 ',
PROBITS
6.0
7.0
FIGURE .A-12.Normal Distribution Diagram for Normalized
Chromium Concentration in Cooling Tower Basin
(Plant No. 7308)
203
-------
•10'
<
h-
<
c:
o
10
o
3.0
4.0
J
5.0
PROBITS
6.0
7.0
FIGURE A-13. Normal Distribution Diagram for Normalized
Lead Concentration in Cooling Tower Basin (Plant No. 7308)
204
-------
10'
< 10'
Q
UJ
M
an
o
10
3.0
4.0
5.0
PROBITS
6.0
7.0
FIGURE A-14. Normal Distribution Diagram for Normalized
Zinc Concentration In Cooling Tower Basin (Plant No. 7308)
205
-------
8.0
crt
7.0
6.0
Q
Ul
2 5-0
_j
<
«r-
o
z
4.0
3.0
4.0
5.0
PROBITS
6.0
7.0
FIGURE A-15. Normal Distribution Diagram for Iron
Concentration in Retention Pond (Plant No. 7308)
206
-------
O)
S
12.0
10.0
8.0
ro
o
o
o
6.0
Di
o
4.0
2.0
3.0
4.0
5.0
PROBITS
6.0
7.0
FIGLFRE A-16. Normal Distribution Diagram for Iron Concentration
In Cooling Tower Basin (Plant No. 7308)
-------
ro
8
200
o
o
150
ef.
O
O
UJ
-------
8.0
6.0
Q
UJ
OL
O
2.0
©
4.0
I
5.0
PROBITS
6.0
FIGURE ' A-18. Normal Distribution Diagram for Silver
Concentration Retention Pond (Plant No. 7308)
209
-------
Q
Q
LU
t—i
_l
=C
O
10
3.0
4.0
5.0
6.0
7.0
PROBITS
FIGURE A-19. Normal Distribution Diagram for Normalized
topper Concentration Cooling Tower Basin (Plant No. 7308)
210
-------
Table A-9.
STATISTICAL ANALYSIS OF WAT.ER USAGE
DATA BY CATEGORY
Mater Usage
Category
Mod* of W-*!
\. Oistribct'3-i
Statistical ^\^
Parameter \^
Mean
Variance
Third Moment
Fourth Moment
Coefficient of Skemss
Coefficient of Kurtosis
Correction Constant
Slope
Intercept
Cofff. of Deterafnaefon
941 Confidence Unit
Once-through
Cooling Hater
,10'
Arithmetic
29.43
228.14 '
3681.88
(U
l.OS
3.08
Logarithmic
(2)
1.42
0.10
0.00
0.00
0.33
2.12
Three
Parapeters
Logaritrvric
(?)
1.23
0.10
0.00
0.00
0.00
2.01
-7.86
2.66
0.13
0.99
2.37
^ecirc-'ating
Coolin9 Water
Arithwt'C
6.2
37.50
231.39
3060 0
1.01
2.18
Logan thmic
(?)
O.S9
0.17
0.03
0.06
0.41
2.06
Three
Paraveters
logarithmic
(?)
0.49
0.25
0.00
0.16
0.00
2.43
-0.51
4.07
0.00
0.92
0.86
Boiler Nake-^p
Hater
Arithmetic
370
(1)
(1)
(1)
2.2
6.98
Looaritnr.ic
(2)
1.99
0.55
0.05
0.74
0.12
2.49
Three
Parameter
Logarithmic
(2!
1.99
0.59
0.00
O.89
0.00
2.S8
-1.20
8.04
0.00
0.96
4.23
Oerii'era'lzer
Hater
Arithmetic
74.28
(1)
(1)
(1)
1.95
5. OS
Looarithntc
(?)
1.38
0.36
0.20
0.36
0.94
2.81
Three
Paraaieter
(.Maritime
1.12
0.73
0.00
1.45
0.00
2.70
-4.31
10.97
0.00
0.97
1.31
(1) Greater than 10*
(2) Expressed as logarithms
-------
Table A-10. STATISTICAL PARAMETERS OF REGRESSION ANALYSIS
OF WATER USAGE AGAINST PRODUCTION RATE
^"^^^ Water Usage
^\Category
Statisti cal^"^^
Parameter ^\.
Slope
Intercept
Coefficient of
Determination
Standard Error of
Estimated Water
Use on Production
Rate
Standard Error
of Intercept
Standard Error
of Slope
Once-through
Cool ing Water
-0.13
6.14
0.11
0.23
0.17
0.94
Recirculating
Cooling Water
0.06
3.08
0.00
0.77
2.09
0.37
Boiler Makeup
Water
-0.92
7.1
0.47
0.57
1 .45
0.26
Demineralizer
Water
0.03
1.52
0.00
0.65
1.76
0.31
ro
-------
10'
10
cs
10
3.0
4.0
i
5.0
PROBITS
6.0
7.0
FIGURE A-23. Normal Distribution Diagram for Normalized
Ion Exchange Water Usage Data
213
-------
10'
Ul
03
«=c
ct:
ui
H-
«t
IOJ
3.0
4.0
I
5.0
PROBITS
6.0
7.0
FIGURE A-20 . Normal Distribution Diagram for ;Normalized
Once-Through Usage Data
214
-------
10"
cr
*r:
oo
10'
10
4.0
5.0 6.0
PROBITS
7.0
FIGURE A-22. Normal Distribution Diagram for Normalized
Boiler Makeup Water Usage Data
215
-------
10'
100
cu
cc:
LU
10'
10'
102
3.0
e
4.0
5.0
PROBITS
6.0
7.0
FIGURE A-21. Normal Distribution Diagram for Normalized
Cooling Water Usage Data
216
-------
10'
10'
to
10
I I
90 Percent Confidence Limit
Regression Li
90
i i
i i
10'
10° 10b
PRODUCTION RATE (MWH)
10
FIGURE A-27. Demineralizer Water Usage vs. Annual Production
Rate
217
-------
I I
I I
x 10'
3
nt c
*-
o
•^ L7'n" ©
10-
10"
FIGURE A-24
I I
I J
I
io5 io6 io7
PRODUCTION RATEX
(MWH)
Once-Through Cooling Water Use vs. Annual
Production Rate
218
-------
10'
10
00
5 10-
10'
10
rcent ConfldenceJ-lmlt _
95 Percentj.
95 Percent_ Confidence ^U ^
I
I
10
10a 10°
PRODUCTION RATE (MWH)
10'
FIGURE A-25
Recirculating Cooling Water Use vs. Annual
Production Rate
219
-------
10'
10'
LU
cr
«=c
10'
10
10
10
,7
FIGURE A-26
PRODUCTION RATE (MWH)
Boiler Makeup Water Use vs. Annual Production
Rate
220
-------
APPENDIX B
WATER GLOSSARY
Acid-washed activated carbon - Carbon which has been con-
tacted with an acid solution with the purpose of
dissolving ash in the activated carbon.
Acidity - The quantitative capacity of aqueous solutions to
react with hydroxyl ions. It is measured by titration
with a standard solution of a base to a specified end
point. Usually expressed as miligrams per liter of
calcium carbonate.
Acre-foot - (1) A term used in measuring the volume of water
that is equal to the quantity of water required to cover
1 acre 1 ft deep, or 43,560 cu ft. (2) A term used in
sewage treatment in measuring the volume of material in
a trickling filter. One acre-foot contains 43,cu ft of
water.
Activated Carbon - Carbon which is treated by high-tempera-
ture heating with steam or carbon dioxide producing an
internal porous particle structure. The internal
surface area of granular activated carbon is estimated
to be about 3,600 sq ft gr.
Activiated Sludge Treatment Process - (See Sludge,
Activated).
Adsorption - The adhesion of an extremely thin layer of
molecules (of gas, liquid) to the surfaces of solids
(granular activiated carbons for instance) or liquids
with which they are in contact.
Adsorption isotherms (activated carbon) - A measurement of
adsorption determined at a constant temperature by
varying the amount of carbon used or the concentration
impurity in contact with the carbon.
Advanced Waste Treatment - Any treatment method or process
employed following biological treatment (1) to increase
the removal of pollution load. (2) to remove substances
that may be deleterious to receiving waters or the
environment. (3) to produce a high-quality effluent
suitable for reuse in any specific manner or for dis-
charge under critical conditions. The term tertiary
treatment is commonly used to denote advanced waste
treatment methods.
221
-------
Aerated Pond - A natural or artificial wastewater treatment
pond in which mechanical or diffused air aeration is
used to supplement the oxygen supply.
Aeration - The bringing about of intimate contact between
air and liquid by one of the following methods spraying
the liquid in the air, bubbling air through the liquid
(diffused aeration) agitation of the liquid to promote
surface absorption of air (mechanical aeration).
Aerobic - Living or active only in the presence of oxygen.
Aerobic Biological Oxidation - Any waste treatment or pro-
cess utilizing aerobic organisms in the presence of air
or oxygen, as the agent for reducing pollution load or
oxygen demand or organic substances in waste. The term
is used in reference to secondary treatment of wastes.
Algicide - Chemicals used in the control of phytoplankton
(algae) in bodies of water.
Alkalinity - The capacity of water to neutralize acids, a
property imparted by the water's content of carbonates,
bicarbonates, hydroxides, and occassionally borates,
silicates, and phosphates. It is expressed in miligrams
per liter of equivalent calcium carbonate.
Anaerobic - Living or active only in the absence of free
oxygen.
Anaerobic Biological Treatment - Any treatment method or
process utilizing anaerobic or facultative organisms in
the absence of air for the purpose of reducing the
organic matter in wastes or organic solids settled out
of wastes commonly referred to as anaerobic digestion or
sludge digestion when applied to the treatment of sludge
solids.
Anaerobic Waste Treatment - Waste stabilization brought
about through the action of microorganisms in the
absence of air or elemental oxygen. Usually refers to
waste treatment by methane fermentation.
Anion Exchange Process - The reversible exchange of negative
ions between functional groups of the ion exchange
medium and the solution in which the solid is immersed.
Used as a wastewater treatment process for removal of
anions, e.g., carbonate.
Anionic Surfactant - An ionic type of surface-active sub-
stances that has been widely used in cleaning products.
222
-------
The hydrophilic group of these surfactants carries a
negative charge in washing solution.
Apparent Density (Activated Carbon) - The weight per unit
volume of activated carbon.
Appurtenances, Sewer - Structures, devices and appliances,
other than pipe or conduit, which are integral parts of
a sewerage system: such as manholes flush tanks, surface
inlets.
Aquifer - A subsurface geological structure that contains
water.
Assimilative Capacity - The capacity of a natural body of
water to receive: (a) wastewaters without deleterious
effects: (b) toxic materials, without damage to aquatic
life or humans who consume the water; (c) BOD within
prescribed dissolved oxygen limits.
Autooxidation - A chemical system which will oxidize auto-
matically when some set of conditions are met such as
temperature, oxygen supply, moisture content, etc.
Backflow Prevention - A system designed to protect potable
water from wastewater contamination which could occur if
wastewater pressure exceeds potable water pressure over
a cross-connection where one or more check valves fail.
Backsiphonage - The flowing back of contaminated or polluted
water from a plumbing fixture or cross connection into a
water supply line, due to a lowering of the pressure in
such line.
Backwashing - The process of cleaning a rapid sand or mech-
anical filter by reversing the flow of water.
Bacterial Examination - The examination of water and waste-
water to determine the presence, number, and identifi-
cation of bacteria. Also called bacterial analysis.
Baffles - Deflector vanes, guides, grids, gratings, or
similar devices constructed or placed in flowing water
or sewage to (1) check or effect a more uniform dis-
tribution of velocities; (2) absorb energy; (3) divert
guide, or agitate the liquids; and (1) check eddy
currents.
Banks, Sludge - Accumulations on the bed of a waterway of
deposits of solids of sewage or industrial waste origin.
223
-------
Bed Depth (Activated Carbon) - The amount of carbon
expressed in length units which is parallel to the flow
of the stream and through which the stream must pass.
Bioassay - (1) An assay method using a change in biological
activity as a qualitative or quantitative means of
analyzing a materials reponse to industrial wastes and
other wastewaters by using viable organisms or live fish
as test organisms.
Biochemical Oxygen Demand (BOD) - (1) The quantity of oxygen
used in the biochemical oxidation of organic matter in a
specified time, at a specified temperature, and under
specified conditions (2) standard test used in assessing
wastewater strength.
Biocides - Chemical agents with the capacity to kill bio-
logical life forms. Bactericides, insecticides, pesti-
cides, etc. are examples.
Biodegradable - This part of organic matter which can be
oxidized by bioprocesses, e.g., biodegradable deter-
gents, food wastes, animal manure, etc.
Biological Wastewater Treatment - Forms of wastewater treat-
ment in which bacterial or biochemical action is inten-
sified to stablize, oxidize, and nitrify the unstable
organic matter present. Intermittent sand filters, con-
tact beds, trickling filters, and activated sludge
process are examples.
Blowoff - A controlled outlet on a pipeline, tank, or
conduit which is used to discharge water or accumu-
lations of material carried by the water.
Branch - (1) A special form of vitrified sewer tile and cast
iron pipe used for making connections to a sewer or
water main. They are called T, Y, T-Y, double Y, and V
branches according to their respective shapes. (2) Any
part of a piping system other than a main.
Broad-Crested Weir - A weir having a substantial width of
crest in the direction parallel to the direction of flow
of water over it. This type of weir supports the nappe
for an appreciable length and produces no bottom
contraction of the nappe. Also called widecrested weir.
Buffer - Any of certain combinations of chemicals used to
stablize the pH values or alkalinities of solutions.
224
-------
Bulking Agent - A fine solid material which is sometimes
added to a wastewater stream to produce clarification or
coagulation by adding bulk to the solids.
Bulking, Sludge - A phenomenon that occurs in activated
sludge plants whereby the sludge occupies excessive
volumes and will not concentrate readily.
Cake, Sludge - The material resulting from air drying or
dewatering sludge (usually forkable or spadable).
Calibration - The determination, checking, or rectifying of
the graduation of any instrument giving quantitative
mea surements.
Carbon Column A - A column filled with granular activated
carbon whose primary function is the preferential ad-
sorption of a particular type or types of molecules.
Carbon Tetrachloride Activity - The maximum percentage
increase in weight of a bed of activated carbon after
air saturated with carbon tetrachloride is passed
through it at a given temperature.
Catalyst - A substance which accelerates or retards a
chemical reaction without undergoing any permanent
changes.
Cation Exchange Process - The reversible exchange of
positive ions between functional groups of the ion
exchange medium and the solution in which the solid is
immersed. Used as a wastewater treatment process for
removal of cations, e.g. calcium.
Cationic Surfactant - A surfactant in which the hydrophilic
group is positively charged; usually a quaternary
ammonium salt such as cetyl trimethyl ammonium bromide
(CeTAB) , C1j>H3_3N + (CH_3) 3^ Br Cationic surfactant as a
class are poor cleaners, but exhibit remarkable
disinfectant properties.
Cesspool - An underground pit into which raw household
sewage or other untreated liquid waste is discharged and
from which the liquid seeps into the surrounding soil or
is otherwise removed. sometimes called leaching
cesspool.
Chamber Detritus - A detention chamber larger than a grit
chamber usually with provision for moving sediment
without interrupting the flow of liquid. A settling
tank of short detention period designed, primarily to
remove heavy settleable solids.
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Chamber/ Flowing-Through - The upper compartment of a two-
story sedimentation tank.
Chamber, Grit - A small detention chamber or an enlargement
of a sewer designed to reduce the velocity of flow of
the liquid, to permit the separation of mineral from
organic solids by differential sedimentation.
Chelating Agents - A chelating agent can attach itself to
central metallic atom so as to form a heterocyclic ring.
Used to make ion-exchange more selective for specific
metal ions such as nickel, copper, and cobalt.
Chemical Analysis - The use of a standard chemical analyti-
cal procedures to determine the concentration of a
specific pollutant in a wastewater sample.
Chemical Coagulation - The destabilization and initial
aggregation of colloidal and finely divided suspended
matter by the addition of a floe-forming chemical.
Chemical Oxygen Demand (COD) - (1) A test based on the fact
that all organic compounds, with few exceptions can be
oxidized to carbon dioxide and water by the action of
strong oxidizing agents under acid conditions. Organic
matter is converted to carbon dioxide and water regard-
less of the biological assimilability of the substances.
One of the chief limitations is its ability to dif-
ferentiate between biologically oxidizable and biolo-
gically inert organic matter. The major advantage of
this test is the short time required for evaluation (2
hr). (2) The amount of oxygen required for the chemical
oxidation of organics in a liquid.
Chemical Precipitation - (1) Precipitation induced by addi-
tion of chemicals, (2) the process of softening water by
the addition of lime and soda ash as the precipitants.
Chemisorption - Adsorption where the forces holding the
adsorbate to the adsorbent are chemical (valance)
instead of physical (van der Waals).
Chlorination - The application of chlorine to water or
wastewater, generally for the purpose of disinfection,
but frequently for accomplishing other biological or
chemical results.
Chlorination break point - The application of chlorine to
water, sewage, or industrial waste containing free
ammonia to the point where free residual chlorine is
available.
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Chlorination, Free Residual - The application of chlorine to
water, sewage or industrial wastes to produce directly
or through the destruction of ammonia, or of certain
organic nitrogenous compounds a free available chlorine
residual.
Chlorine, Available - A term used in rating chlorinated lime
and hypochlorites as to their total oxidizing power.
Also a term formerly applied to residual chlorine; now
obsolete.
Chlorine, Combined Available Residual - That portion of the
total residual chlorine remaining in water, sewage or
industrial wastes at the end of specified contact
period, which will react chemically and biologically as
chloramines or organic chloramines.
Chlorine Demand - The quantity of chlorine absorbed by
wastewater (or water) in a given length of time.
Chlorine, Total Residual - Free residual plus combined
residual.
Chlorite, High-test Hypo - A combination of lime and
chlorine consisting largely of calcium hypochloride.
Chlorite, Sodium Hypo - A water solution of sodium hydroxide
and chlorine, in which sodium hypochlorite is the
essential ingredient.
Cipolletti Weir - A contract weir of trapezoidal shape, in
which the sides of the notch are given a slope of one
horizontal to four vertical to compensate as much as
possible for the effect of end contractions.
Clarifier - A sedimentation tank.
Clear Well - A reservoir containing water which has been
previously filtered or purified before goining into the
standpipes or distribution system.
Coils, digester - A system of pipes for hot water or steam
installed in a sludge digestion tank for the purpose of
heating the sludge being treated.
Collection Systems - Piping and/or channel systems for
gathering storm, domestic or industrial wastewaters.
Can be combined or separate.
Collector, Grit - A device placed in a grit chamber to
convey deposited grit to one end of the chamber for
removal.
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Collector, Sludge - A mechanical device for scraping the
sludge on the bottom of a settling tank to a sump pump,
from which it can be drawn by hydrostatic or mechanical
action.
Colloids - A finely divided dispersion of one material
called the "dispersed phase" (solid) in another material
which is called the "dispersion medium" (liquid).
Normally negatively charged.
Color - A measure of water quality, made by eye or with
proper instrumentation.
Color Bodies - Those complex molecules which impart color
(usually undesirable) to a solution.
Comminution - The process of cutting and screening solids
contained in wastewater flow before it enters the flow
pumps or other units in the treatment plant.
Compatable Pollutant - A specific substance in a waste
stream which alone can create a potential pollution
problem, yet is used to the advantage of a certain
treatment process when combined with other waste
streams.
Complexing - The use of chelating or sequestering agents to
form relatively loose chemical bonding as a means of
treating certain pollutant such as nickel, copper, and
cobalt.
Composite Wastewater Sample - A combination of individual
samples of water or wastewater taken at selected
intervals, generally hourly for some specified period,
to minimize the effect of the variability of the
individual sample. Individual samples may have equal
volume or may be roughly proportioned to the flow at
time of sampling.
Concentration, Hydrogen Ion - The weight of hydrogen ions in
grams per liter of solution. Commonly expressed as the
pH value that represents the logarithms of the
receiprocal of the hydrogen ion concentration.
Conductance - A measure of the conducting power of a
solution equal to the reciprical of the resistance. The
resistance is expressed in ohms.
Contact Coagulation - A water clarification process which
involves the addition of a coagulant with appropriate
mixing for the purpose of floe formation within a filter
media, which will be periodically back-flushed to permit
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the separation of the resulting solids from the main
wastewater stream.
Contamination - A general term signifying the introduction
into water of microorganisms, chemicals, wastes or
sewage which renders the water unfit for its intended
use.
Contracted Weir - A V-notch or other shaped cross-section
weir for the purpose of flow measurement, as opposed to
a broad width weir for the purpose of level control.
Contraction - (1) The extent to which the cross-sectional
area of a jet, nappe, or stream is decreased after
passing an orifice, weir, or notch. (2) The reduction in
cross-sectional area of a conduit along its longitudinal
axis.
Control Section - The cross-section in a waterway which is
the bottleneck for a given flow and which determines the
energy head required to produce the flow.
Corporation Cock -A valve for joining a service pipe to a
street water main; it is generally owned and operated by
the water utility or department. It cannot be operated
from the surface.
Countercurrent Efficiency (Activated Carbon) - The unique
advantage of a carbon column that permits spent anti-
vated carbon to adsorb impurities before the semi-
processed stream comes in contact with fresh carbon.
This allows the maximum capacity of the activated carbon
to be utilized.
Crest - The top of a dam, spillway, or weir, to which water
must rise before passing over the structure.
Critical Bed Depth (Activated Carbon) - In a carbon column
the critical bed depth is the depth of granular carbon
which is partially spent. It lies between the fresh
carbon and the spent carbon and is the zone where
adsorption takes place. In a single-column system this
is the amount of carbon that is not completely utilized.
Cross Connection - A water supply network and/or wastewater
collection system which as been designed so as to pre-
vent "cross-connections" which could result in func-
tional damage to the system. The simpliest system is to
have two separate systems, but this would not be
justified if intersystems usage occurs only
occasionally, hence back-flow preventers and other means
are often used.
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Cross-Sectional Bed Area (Activated Carbon) - The area of
activated carbon through which the stream flow is
perpendicular.
Curb Cock - A shutoff valve attached to the water service
pipe from the water basin to the building installed near
the curb, which may be operated by means of a dye key to
start or stop flow in the water supply lines of a
building.
Current Meter - A device for determining the velocity of
moving water.
Curve, Oxygen, Sag - A curve that represents the profile of
dissolved oxygen connect along the course of a stream,
resulting from deoxygenation associated with biochemical
oxidation of organic matter and reoxygenation through
the absorption of atmospheric oxygen and through
biological photosynthesis.
Data - Records of observations and measurements of physical
facts, occurrences, and conditions, reduced to written,
graphical, or tabular form.
Data Correlation - The process of the conversion of reduced
data into a functional relationship and the development
of the significance of both the data and the
relationships for the purpose of process evaluation.
Data Reduction - The process for the conversion of raw field
data into a systematic flow which assists in recognizing
errors, omissions and the overall data quality.
Data Significance - The result of the statistical analysis
of a data group or bank wherein the value or signi-
ficance of the data receives a thorough appraisal.
Dechlorination Process - A process by which excess chlorine
is removed from water to a desired level, eg. 0.1 mg/1
maximum limit. Usually accomplishment by chemical
reduction, by passage through carbons beds or by
aeration at a suitable pH.
Degreasing - The process of removing greasejs and oils from
sewage, waste, and sludge.
Demand, Biochemical Oxygen (BOD) - The quantity of oxygen
utilized in the biochemical oxidation of organic matter
in a specified time period and at a specified
temperature. It is not related to the oxygen require-
ments in chemical combustion being determined entirely
by the availability of the material as a biological food
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and the amount of oxygen by the microorganisms during
the oxidation.
Desorption - The opposite of adsorption. A phenomenon where
an adsorbed molecule leaves the surface of the
adsorbent.
Detention Time - The time allowed for solids to collect in a
settling tank. Theoretically detention time is equal to
the volume of the tank divided by the flow rate. The
actual detention time is determined by the purpose of
the tank. Also, the design resident time in a tank or
reaction vessel which allows a chemical reaction to go
to completion, such as the reduction of chromium +6 or
the destruction of cyanide.
Dialysis - The separation of a colloid from a substance in
true solution by allowing the solution to diffuse
through a semi-permeable membrane.
Diatomaceous Earth - A filter medium used for filtration of
effluents from secondary and tertiary treatments,
particularly when a very high grade of water for reuse
in certain industrial purposes is required also used as
an adsorbent for oils and oily emulsions in some
wastewater treatment designs.
Differential Gauge - A pressure gauge used to measure the
difference in pressure between two points in a pipe or
receptacle containing a liquid.
Diffuser - A porous plate or tube through which air is
forced and divided into minute bubbles for diffusion in
liquids. Commonly made of carborundum, alundum and
silica sand.
Diffusion, Ridge and Furrow Air - A method of diffusing in
an aeration tank of the activated sludge process, where
porous tile diffusers are placed in depressions treated
by the sawtooth construction of the tank bottom, in rows
across the tank at right angles to the direction of
flow.
Diffusion, Spiral Flow Air - A method of diffusing air in a
aeration tank of the activated sludge process, where by
means of properly designed baffles and the proper
location of diffusers, a spiral helieal movement is
given to both the air and the liquor in the tank.
Digestion - The biochemical decomposition of organic matter
which results in the formation of mineral and simpler
organic compounds.
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Disinfection - (1) The killing of the larger portion (but
not necessarily all) of harmful and objectionable
microorganisms in or on a medium by means of chemicals,
heat, ultraviolet light, etc. (2) The use of a chemical
additive or other treatment to reduce the number of
bacteria particularly the pathogenic organisms.
Dissolved Oxygen (DO) - The oxygen dissolved in sewage,
water, or other liquid, usually expressed in miligrams
per liter or percent of saturation. It is the test used
in BOD determination.
Dissolved Solids - Theoretically the anhydrous residues of
the dissolved constituents in water. Actually the term
is defined by the method used in determination. In
water and wastewater treatment the Standard Methods
tests are used.
Diurnal Flow Curve - A curve which depicts flow distribution
over the 24 hour day.
Drinking Water Standards - Standards defined by law and
applied to the quality of drinking water.
Educator (Activated Carbon) - A device with no moving parts
used to force an activated carbon water slurry through
pipes to the desired location.
Effluent - (1) A liquid which flows out of a containing
space (2) sewage, water or other liquid, partially or
case may be, flowing out of a reservoir basin, or the
use may be flowing out of a reservoir basin, or
treatment plant or part thereof.
Electrical Conductivity - The reciprocal of the resistance
in ohms measured between opposite faces of centimeter
cube of an aqueous solution at a specified temperature.
It is expressed as microohms per centimer at temperature
degrees Celsius.
Elutriation - A process of sludge conditioning in which
certain constituents are moved by successive flushing
with fresh water or plant effluent thereby reducing the
need for using conditioning chemicals.
Emergency Procedures - These various special procedures
necessary to protect the environment from wastewater
treatment plant failures due to power outages, chemical
spills, equipment failures, major storms and floods,
etc.
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Emulsion Breaking - The method of preventing the carryover
of oils from one process to another by eliminating free
oil by flotation, and emulsions by the addition of
aluminum or ferrous sulfate.
End Contraction - (1) The extent of the reduction in the
width of the nappe due to a constriction caused by the
ends of the weir notch. (2) The walls of a weir notch
which does not extend across the entire width of the
channel of approach.
Energy Head - The height of the hydraulic grade line above
the center line of a conduit plus the
Equalization Tank - A capacity used to equalize wastewater
flows or pollutant concentrations in effluents thus
distributing it more evenly by hours or days.
Euetrophic Conditions - Lake water quality degradation by
enrichment of nutrients resulting in characteristics
undersirable for means use of water. Plant growth in
forms of microscopic algae and rooted aquatic weeds
become prevelent in such situations.
Fats (Wastes) - Triglyceride esters of fatty acids.
Erroneously used as synonomous with grease.
Faculative - Having the power to live under different
conditions either with or without oxygen.
Feeder, Chemical Dry - A mechanical device for applying dry
chemicals to water sewage at a rate controlled manually
or automatically by the rate of flow.
Feeder Chemical Solution - A mechanical device for applying
chemicals in liquid to water and sewage at a rate
controlled manually or automatically by the rate of
flow.
Filter, High-Rate - A trickling filter operated at a high
average daily dosing rate. All between 10 and 30 mgd
acre, sometimes including recirculation of effluent.
Filter, Intermittent - A natural or artifical bed of sand or
other fine-grained material to the surface of which
sewage is intermittently added in flooding doses and
through which it passes, opportunity being given for
filtration and the maintenance of aerotic conditions.
Filter, Low-Rate - A trickling filter designed to receive a
small load of BOD per unit volume of filtering material
and to have a low dosage rate per unit of surface area
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(usually 1 to H mgd/acre). Also called standard rate
filter.
Filter, Rapid Sand - A filter for the purification of water
where water which has been previously treated, usually
by coagulation and sedimentation is passed downward
through a filtering medium consisting of a layer of sand
or prepared anthracite coal or other suitable material,
usually from 2H to 30 in thick and resting on a
supporting bed of gravel or a porous medium such as
carborundum. The filrate is removed by an underdrain
system. The filter is cleaned periodically by reversing
the flow of the water upward through the filtering
medium: sometimes supplemented by mechanical or air
agitition during backwashing to remove mud and other
impurities that are lodged in the sand.
Filter, Roughing - A sewage filter of relatively coarse
material operated at a high rate as a preliminary
treatment.
Filter, Trickling - A filter consisting of an artifical bed
of coarse material, such as broken stone, clinkers,
slats, or brush over which sewage is distributed and
applied in drops, films, or spray, from troughs,
drippers moving distributors or fixed nozzles and
through which it trickles to the underdrain giving
opportunity for the formation of zoogleal slimes which
clarify and oxidize the sewage.
Filter, Vacuum - A filter consisting of a cylindrical drum
mounted on a horizontal axis, covered with a filter
cloth revolving with apartial sumergence in liquid. A
vacuum is maintained under the cloth for the larger part
of a revolution to extract moisture and the cake is
scraped off continously.
Filtration, Biological - The process of passing a liquid
through a biological filter containing media on the
surfaces of which zoogleal films develop which absorb
and adsorb fine suspended colloridal and dissolved
solids and which release various biochemical end
products.
Float Gauge - A device for measuring the elevation of the
surface of a liquid, the actuating element of which is a
buoyant float that rests on the surface of the liquid
and rises or falls with it. The elevation of the
surface is measured by a chain or tape attached to the
float.
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Floe - A very fine, fluffy mass formed by the aggregation of
fine suspended particles.
Flocculator - An apparatus designed for the formation of
floe in water or sewage.
Flocculation - In water and wastewater treatment, the
agglomeration of colloidal and finely divided suspended
matter after coagulation by gentle stirring by either
mechanical or hydraulic means. In biological wastewater
treatment where coagulation is not used, agglomeration
may be accomplished biologically.
Floatation - The rising of suspended matter to the surface
of the liquid in a tank as scum by aeration, the
evolution of gas, chemicals, electrolysis, heat, or
bacterial decomposition and the subsequent removal of
the scum by skimming.
Flowrate - Usually expressed as liters/minute (gallons/
minute) or liters/day (million gallons/day). Design
flowrate is that used to size the wastewater treatment
process. Peak flowrate is 1.5 to 2.5 times design and
relates to the hydraulic flow limit and is specified for
each plant. Flowrates can be mixed as batch and
continuous where these two treatment modes are used on
the same plant.
Flow-Nozzle Meter - A water meter of the differential medium
type in which the flow through the primary element or
nozzle produces a pressure difference or differential
head, which the secondary element, or float tube than
uses as an indication of the rate of flow.
Flow-Proportioned Sample - A sampled stream whose pollutants
are attributed to contributing streams in proportion to
the flow rates of the contributing streams.
Frequency Distribution - An arrangement or distribution of
quantities pertaining to a single element in order of
their magnitude.
Gauging Station - A location on a stream or conduit where
measurements of discharge are customarily made. The
location includes a stretch of channel through which the
flow is uniform and a control downstream from this
stretch. The station usually has a recording or other
gauge for measuring the elevation of the water surface
in the channel or conduit.
Grab Sample - A single sample of wastewater taken at neither
set time nor flow.
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Grease - In wastewater, a group of substances including
fats, waxes, free fatty acids, calcium and magnesium
soaps, mineral oils, and certain other nonfatty
materials. The type of solvent and method used for
extraction should be stated for quantification.
Grease Skimmer - A device for removing floating grease or
scum from the surface of wastewater in a tank.
Grit - The heavy matter in water or sewage such as sand,
gravel and cinders.
Grit Chamber - A detention chamber or an enlargement of a
sewer designed to reduce the velocity of flow of the
liquid to permit the separation of mineral from organic
solids by differential sedimentation.
Hardness - A characteristic of water, imparted by salts of
calcium, magnesium, and iron such as bicarbonates,
carbonates, sulfates, chlorides, and nitrates that cause
curdling of soap, deposition of scale in boilers, damage
in some industrial process, and sometimes objectionable
taste. It may be determined by a standard laboratory
procedure or computed from the amounts of calcium and
magnesium as well as iron, aluminum, manganese, barium,
strontium, and zinc, and is expressed as equivalent
calcium carbonate.
Heat of Adsorption - The heat given off when molecules are
adsorbed.
Heavy Metals - A general name given to the ions of metallic
elements such as copper, zinc, chromium, and aluminum.
They are normally removed from a wastewater forming an
insoluble precipitate (usually a metallic hydroxide).
Hook Gauge - A pointed, U-shaped hoot attached to a gradu-
ated staff or vernier scale, used in the accurate
measurement of the elevation of a water surface. The
hook is submerged, and then raised, usually by means of
a screw, until the point just makes a pimple on the
water surface.
Hydraulic Surge - A pressure increase in a pipeline which
accompanies a sudden decrease in the flow velocity. In
some cases this increased pressure may cause rupture of
the pipe.
Industrial Wastes - The liquid wastes from industrial pro-
cesses as distinct from domestic or sanitary wastes.
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Incineration - The combustion (by burning) of organic matter
in wastewater sludge solids after water evaporation from
the solids.
Index, Sludge - The volume of mililiters occupied by aerated
mixed liquor containing 1 gram of dry solids after
settling 80 min. commonly referred to as the Mohlman
index. The Donaldson index which is also commonly used
is obtained by dividing 100 by the Mohlman index.
Influent - Sewage, water or other liquid, either raw or
partly treated, flowing into a reservoir basin, or
treatment plant or any part thereof.
Invert - The floor, bottom or lowest portion of the internal
cross section of a closed conduit.
Iodine Number (Activated Carbon) - The iodine number is the
miligrams of iodine adsorbed 1 gram of carbon at a
filtrate concentration of 0.02N iodine.
lonization - The process of the formation of ions by the
splitting of molecules of electrolytes in solution.
Irrigation Spray - Irrigation by means of nozzles along a
pipe on the ground or from perforated overhead pipes.
Lagoon - (1) A shallow body of water as a pond or lake,
which usually has a shallow, restricted inlet from the
sea. (2) A pond containing raw or partially treated
wastewater in which aerobic or anaerobic stabilization
occurs.
Lime - Any of a family of chemicals consisting essentially
of calcium hydroxide made from limestone (calcite) which
is composed almost wholly of calcium carbonate or a
mixture of calcium and magnesium carbonates.
Liquor, Mixed - A mixture of activated sludge and sewage in
the aeration tank undergoining activated sludge
treatment.
Liquor, Supernatant - (1) The liquor overlying deposited
solids. (2) the liquid in a sludge digestion tank which
lies between the sludge at the bottom and the floating
scum at the top.
Loss of Head Gage - A gage on a rapid sand filter which
indicates the loss of head involved in the filtering
operation whereby the operator is able to ascertain the
need for filter backwashing.
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Macropore - The pores in activated carbon which are larger
(diameter) than l.OOOA.
Makeup Carbon - Fresh granular activated carbon which must
be added to a column system after a regeneration cycle
or when deemed necessary to bring the total amount of
carbon to specification.
Manometer - An instrument for measuring pressure. It
usually consists of a U-shaped tube containing a liquid
the surface of which is one end of the tube moves
proportionally with changes in pressure on the liquid in
the other end. Also, a tube type of differential
pressure gauge.
Mean Velocity - The average velocity of a stream flowing in
a channel or conduit at a given cross section or in a
given reach. It is equal to the discharge divided by
the cross sectional area of the reach. Also called
average velocity.
Mesh Size (Activated Carbon).- The particle size of granular
activated carbon as determined by the U.S. Sieve series.
Particle size distribution within a mesh series is given
in the specification of the particular carbon.
Methylene Blue Number (Activated Carbon) - The methylene
blue number is the milligrams of methylene blue adsorbed
by 1 gram of carbon in equilibrium with a solution of
methylene blue having a concentration of 1.0 img/1.
Methylpranqe Alkalinity - A measure of the total alkalinity
of an aqueous suspension or solution. It is measured by
the quantity of sulfuric acid required to bring the
water pH to a value of 1.3 as indicated by the change in
color of methyl orange. It is expressed in miligrams
CACO3_ per liter.
Micropore - The pores in activated carbon which range in
size (diameter) from 10 to lrOOO A.
Mjligrams Per Liter (mq/1) - This is a weight per volume
designation used in water and wastewater analysis.
Mixed Media Filtration - A filter which uses 2 or more
filter materials of differing specific gravities
selected so as to produce a filter uniformly graded from
coarse 1.. fine.
Monitoring - (1) The procedure or operation of locating and
measuring radioactive contamination by means of survey
instruments that can detect and measure, as dose rate.
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ionizing radiations (2) the measurements sometimes
continous, of water quality.
Most Probable Number (MPN) - That number of organisms per
unit volume that, in accordance with statistical theory,
would be more likely than any other number to yield the
obserbed test result with the greatest frequency.
Expressed as desnity of organisms per 100 ml. Results
are computed from the number of positive findings of
coliform-group organisms resulting from multiple-portion
decimal-dilution plantings.
Nappe - The sheet or curtain of water overflowing a weir or
dam. When freely overflowing any given structure, it
has a well-defined upper and lower surface.
Neutralization - Reaction of acid or alkali with the
opposite reagent until the concentrations of hydrogen
and hydroxyl ions in solution are approximately equal.
Nitrification - The conversion of nitrogenous matter into
nitrates by bacteria.
Nonjonic Surfactant - A general family of surfactants so
called because in solution the entire molecule remains
associated. Nonionic molecules orient themselves at
surfaces not by an electrical charge, but through
separate grease-solubilizing and water-soluble groups
within the molecule.
Nonsettleable Matter - The suspended matter which does not
settle nor float to the surface of water in a period of
one hour.
Nonsettleable Solids - Wastewater matter that will stay in
suspension for an extended period of time. Such period
may be arbitrarily taken for testing purposes as one
hour.
Notch - An opening in a dam, spillway, or measuring weir for
the passage of water.
Nozzle - (1) A short, cone-shaped tube used as an outlet for
a hose or pipe. The velocity of the merging stream of
water is increased by the reduction in cross sectional
area of the nozzle (2) a short piece of pipe with a
flange on one end and a saddle flange on the other end.
Nutrients - Materials which are considered to be essential
to support biological life.
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Odor Control - The elimination of odor-causing valatile
substances associated with organic matter, living
organisms, and cases. The most common, control
measurement in use are the application of activated
carbon residual chlorination, chlorine dioxide, ozone
and aeration.
Odor Threshold - The point at which after successive dilu-
tions with odorless water, the odor of a water sample
can just be detected. The threshold odor is expressed
quantitatively by the number of times the sample is
diluted with odorless water.
Oil and Grease - Those materials which are exgractable from
wastewater with hexane, chloroform if other content of
these specific solvents pollutants in water or waste-
water (in mg/1 of ppm) which can significantly influence
the environment.
Open-Channel Flow - Flow of a fluid with its surface exposed
to the atmosphere. The conduit may be an open channel
or a closed conduit flowing partly full.
Operation Qualifications, Treatment Plant - Usually defined
by a licence issued by local authorities.
Organic Matter - Chemical substances of animal or vegetable
origin, or more correctly of basically carbon structure,
comprising compounds consisting of hydrocarbons and
their deviations.
Organic Nitrogen - Nitrogen combined in organic molecules
such as protein, amines, and amino acids.
Orifice - (1) An opening with closed perimeter, usually of
regular form, in a plate, wall, or partition, through
which water may flow generally used for the purpose of
measurement of control of such water. The edge may be
sharp or of another configuration (2) the end of a small
tube such as a Pitot tube.
Orifice Plate - A plate containing an orifice. In pipes,
the plate is usually inserted between a pair of flanges,
and the orifice is smaller in area than the cross
section of the pipe.
Orthophosphate - An acid or salt containing phosphorus as
PO4..
Outfall - The point or location where sewage or drainage
discharges from a sewer, drain, or conduit.
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Overflow Storm - A weir, orifice, or other device for
permitting the discharge from a combined sewer of that
part of the flow in escess of that which the sewer is
designed to carry.
Oxidation - The addition of oxygen to a compound. More
generally, any reaction which involves the loss of
electrons from an atom.
Oxidation Pond - A basin used for retention of wastewater
before final disposal, in which biological oxidation of
organic material is effected by natural or artifically
accelerated transfer of oxygen to the water from air.
Oxidation Reduction Potential (ORP) - The potential required
to transfer electrons from the oxidant to the reductant
and used as a qualitative measure of the state of
oxidation in wastewater treatment systems.
Oxygen Consumed - The quantity of oxygen taken up from
potassium permananganate in solution by a liquid
containing organic matter. Commonly regarded as an
index of the carbonaceous matter present. Time and
temperature must be specified.
Oxygen Dissolved - Usually designated as DO. The oxygen
dissolved in sewage water, or othe rliquid usually
expressed in parts per million or percent of statura-
tion.
Ozone - Oxygen in molecular form with three atoms of oxygen
forming each molecule. Atmospheric oxygen is in
molecular form but each molecule contains two atoms of
oxygen. Ozone is formed by passing high voltage
electric charges through dry air. The third atom of
oxygen in each molecule of ozones is loosely bound to it
and is easily released.
Parshall Flume - A calibrated device developed by Parshall
for measuring the flow of liquid in an open conduit. It
consists essentially of a contracting length, a throat,
and an expanding length. At the throat is a sill over
which the flow passes as critical depth. The upper and
lower heads are each measured at a definite distance
from the sill. The lower head not be measured unless
the sill is submerged more than about 67 percent.
Pathogenic Bacteria - Bacteria which may cause disease in
the organisms by their parasitic growth.
pH - The reciprocal of the logarithm of the hydrogen ion
concentration. The concentration is the weight of
241
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hydrogen ions, in grams per liter of solution. Neutral
water, for example, has a pH value of 7 and hydrogen ion
concentration of 10.7.
pH Adjustment - A means of maintaining the optimum pH
through the use of chemical additives. Can be manual or
automatic, or automatic with flow corrections pH
adjustment is not a linear function.
Phenolein Alkalinity - A measure of the hydroxides plus
one half of the normal carbonates in aqueous suspension.
Measured by the amount of sulfuric acid required to
bring the water to a pH value of 8.3, as indicated by a
change in color of phenolphthaiein. It is expressed in
parts per million of calcium carbonate.
Pitot Tube - A device for measuring the velocity of flowing
fluid by using the velocity head of the stream as an
index velocity. It consists essentially of an orifice
held to point upstream and connected with a tube in
which the impact pressure due to velocity head may be
observed and measured. It also may be constructed with
an upstream and downstream orifice, or with an orifice
pointing upstream to measure the velocity head or
pressure and piezometer holes in a coaxial tube to
measure the static head or pressure, in which case the
difference in pressure is the index of velocity.
Pollution Load - A measure of the strength of a wastewater
in terms of its solids or oxygen-demanding characteris-
tics, or in terms of harm to receiving waters.
Pollution Water - The introduction into a body of water of
substances of such character and of such quantity that
its natural quality is so altered as to impair its
usefulness or render it offensive to the senses of
sight, taste, or smell.
Polyelectrolytes - Used as a coagulant or a coagulant aid in
water and wastewater treatment (activated carbon is
another coagulant aid). They are synthetic polymers
having a high molecular weight. Anionic negatively
charged. Nonionic carry both negative and positive
charges (Cationic postively charged most popular).
Pond, Sewage Oxidation - A pond either natural or artifical
into which partly treated sewage of discharged and in
which natural purification processes take place under
the influence of sunlight and air.
Poolingf Filter - The formation of pools of sewage on the
surface of filters, caused by surface cloggings.
2H2
-------
Pore Volume (activated carbon) - The pore volume is the
difference in the volumetric displacement by granular
activated carbon in mercury and in helium at standard
conditions.
Preaeration - A preparatory treatment of sewage consisting
of aeration to remove gases, add oxygen, or promote
flotation of grease and aid coagulation.
Prechlorination - (1) Chlorination of water prior to filtra-
tion. (2) Chlorination of sewage prior to treatment.
Precipitation, chemical - (1) Precipitation induced by
addition of chemicals (2) The process of softening water
by the addition of lime and soda ash as the
precipitants.
Pretreatment - Any wastewater treatment process used to
reduce pollution load partially before the wastewater is
introduced into a main sewer system or delivered to a
treatment plant for substantial reduction of the
pollution load.
Primary Treatment - A process to remove substantially all
floating and setteable solids in wastewater and
partially to reduce the concentration of suspended
solids.
Probability Curve - A curve that expresses the cumulative
frequency of occurrence of a given event, based on an
extended record of past occurrences. The curve is
usually plotted on specially prepared coordinate paper,
with ordinates representing magnitude equal to, or less
than, the event, and abscissas representing the
probability, time, or other units of incidence.
Process Activated Sludge - A biological sewage treatment
process in which a mixture of sewage and activated
sludge is agitated and aerated. The activated sludge is
subsequently separted from the treated sewage (mixed
liquor) by sedimentation, and wasted or returned to the
process as needed. The treated sewage overflows the
weir of the settling tank in which separation from the
sludge takes place.
Process, Biological - The process by which the life
activities of bacteria, and other microorganisms in the
seach for food break down complex organic materials into
simple, more stable substances. Self-purification of
sewage polluted streams, sludge digestion, and all so-
called secondary sewage treatments result from this
process. Also called biochemical process.
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Process, Oxidation - Any method of sewage treatment for the
oxidation of the putrescible organic matter the usual
methods are biological filtration, and the activated
sludge process.
Purification Degree - (1) A measure of the completness of
destruction or removal of objectionable impurities.
such as bacteria and hardness from water by natural
means (self-puriciation) or by treatment (2) A measure
of the removal, oxidation, or destruction of solids
organic matter, bacteria, or other specified substance
effected by sewage treatment processes.
Putrefaction - Biological decomposition of organic matter
accompanied by the production of foul-smelling as-
sociated with anaerobic conditions.
Rate Oxidation - The rate at which the organic matter in
sewage is stablized.
Ratio Dosing - The maximum rate of application of sewage to
a filter on any unit of area, divided by the average
rate of application on that area.
Reactivation (activated carbon) - The removal of adsorbates
from spent granular activated carbon which will allow
the carbon to be reused. This is also called regen-
eration and revivfication.
Reaeration Sludge - The continous aeration of sludge after
its intial aeration in the activated sludge process.
Recirculation - The refiltration of all or a portion of the
effluent in a high rate trickling filter for the purpose
of incoming flow to reduce its strength.
Reduction overall - The percentage reduction in the final
effluent as compared with the raw sewage.
Reoxygenation - The replenishment of oxygen in a stream from
(1) dilution water entering the stream (2) biological
oxygenation through the activities of certain oxygen
producting plants and (3) atmospheric reaeration.
Reservoir - A pond, lake, tank, basin, or other space either
natural in origin or created in whole or in part by
building of engineering structures. It is used for
storage, regulation, and control of water.
Recorder - A device that makes a graph or other automatic
record of the stage, pressure, depth, velocity, or the
244
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movement or position of water controlling devices,
usually as a function of time.
Recovery Products - Substances regarded as wastewater
pollutants which are recovered for their potential value
through sale or reuse; recovery often is used to lower
or partially offset treatment (or recovery) costs.
Rectangular Weir - A weir having a notch that is rectangular
in shape.
Reduction Practices - (1) Wastewater reduction practices can
mean the reduction of water usage to lower the volume of
wastewater requiring treatment and (2) the use of
chemical reductant materials to lower the valance state
of a specific wastewater pollutant.
Reduction Treatment - The opposite of oxidation treatment
where in a reductant (chemical) is used to lower the
valence state of a pollutant to a less toxic form e.g.
the use of SO2 to "reduce" chromium +6 to chromium +3 in
an acidic solution.
Refractory Orqanics - Organic pollutants which are
chemically oxidation, e.g. DDT pesticide.
Residual Chlorine - Chlorine remaining in water or waste-
water at the end of specified contact period as combined
or free chlorine.
Salinity - (1) The relative concentration of salts, usually
sodium chloride, in a given water. It is usually
expressed in terms of the number of parts per million of
chloride (Cl). (2) A measure of the concentration of
dissolved mineral substances in water.
Sampler - A device used with or without flow measurement to
obtain an aliquot portion of water or waste for
analytical purposes. May be designed for taking a single
sample (grab) , composite sample, continous sample,
periodic sample.
Sanitary Sewer - A sewer that carries liquid and water-
carried wastes from residences, commercial buildings,
industrial plants, and institutions together with minor
quantities of ground-storm, and surface waters that are
not admitted intentionally.
Screen - (1) A device with openings, generally of uniform
size, used to retain or remove suspended or floating
solids in flowing water or wastewater and to prevent
them from entering an intake or passing a given point in
245
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a conduit. The screening element may consist of
parallel bars, rods, wires, grating, wire mesh, or
perforated plate, and the openings may be of any shape,
although they are usually circular or rectangular. (2)
A device used to segregate granular material such as
sand, crushed rock, and soil into various sizes.
Secondary Settling Tank - A tank through which effluent from
some prior treatment process flows for the purpose of
removing settleable solids.
Secondary Wastewater Treatment - The treatment of wastewater
by biological methods after primary treatment by sedi-
mentation.
Second Stage Biological Oxygen Demand - That part of the
oxygen demand associated with the biochemical oxidation
of nitrogenous material. As the term implies, the
oxidation of the nitrogenous materials usually does not
start until a portion of the carbonaceous material has
been oxidized during the first stage.
Sed JMesTtation - The process of subsidence and deposition of
suspended matter carried by water, wastewater, or other
liquids, by gravity. It is usally accomplished by
reducing the velocity of the liquid below the point at
which it can transport the suspended material. Also
called settling.
Seeding Sludge - The inoculation of undigested sewage solids
with sludge that has undergone decomposition for the
purpose of introducing favorable organisms, thereby
accelerating the intial stages of digestion.
Sewage Combined - A sewage containing both sanitary sewage
and surface or storm water with or without industrial
wastes.
Sewage Dilute - Sewage containing less than 150 ppm of
suspended solids and BOD (weak sewage)„
Sewage Industrial - Sewage in which industrial wastes pre-
dominate .
Sewage Raw - Sewage prior to receiving any treatment.
Sewage Settled - Sewage from which most of the settleable
solids have been removed by sedimentation.
Sewage Storm - Liquid flowing in sewers during or following
a period of heavy rainfall and resulting therefrom.
246
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Sewer - A pipe or conduit, generally closed, but normally
not flowing full for carrying sewage and other waste
liquids.
Sewer Intercepting - A sewer which receives dry-weather flow
from a number of transverse sewers or outlets, and
fequently additional, predetermined quantities of storm
water (if from a combined system) and which conducts
such waters to a point for treatment or disposal-
Semipermeable Membrane - A barrier, usually thin, that per-
mits passage of particles up to a certain size or of
special nature. Often used to separate colloids from
their suspending liquid, as in dialysis.
Settleable Solids - (1) That matter in wastewater which will
not stay in suspension during a preselected settling
period, such as one hour, but either settles to the
bottom or floats to the top. (2) In the Imhoff cone
test, the volume of matter that settles to the bottom of
the cone in one hour,
Skimming Tank - A tank so designed that floating matter will
rise and remain on the surface of the wastewater until
removed, while the liquid discharges continously under
certain walls or scum boards.
Sludge - The solids (and accompanying water and organic
matter) which are separated from sewage or industrial
wastewater in treatment plant facilities. Sludge
separation and disposal is one of the major expenses in
wastewater treatment.
Sludge Conditioning - A process employed to prepare sludge
for final disposal can be thickening, digesting,, heat
treatment etc.
Sludge Digestion - The process by which organic or volatile
matter in sludge is gasified, liquidfied, mineralized,
or converted into more stable organic matter through the
activities of either anaerobic or aerobic organisms.
Sludge Disposal - The final disposal of solid wastes includ-
ing the use of sewage sludges as fertilizers and soil
builders; dumping sludge at sea; and filling lowlying
lands.
Sludge thickening - The increase in solids concentration of
sludge in a sedimentation of digestion tank.
Spills - A chemical or material spill is an unintentional
discharge of more than 10 percent of the sewage daily
247
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usage of a regularly used substance. In the case of a
rarely used (one per year or less) chemical or
substance, a spill is that amount that would result in
10% added loading to the normal air, water or solid
waste loadings measured as the closest equivalent
pollutant.
Stabilization Lagoon - A shallow pond for storage of waste-
water before discharge. Such lagoons may serve only to
detain and equalize wastewater composition before
regulated discharge to a stream, but often they are used
for biological oxidation.
Stabilization Pond - A type of oxidation pond in which
biological oxidation of organic matter is effected by
natural or artifically accelerated transfer of oxygen to
the water from air.
Staff Gauge - A graduated scale, vertical unless otherwise
specified, on a plank, metal plate, pier, wall etc.,
used to indicate the height of a fluid surface above a
specified point or datum plane,
Stage Discharge Relation - The relation between gauge height
and discharge of a stream or conduit at a gaugint
station. This relation is shown by the rating curve or
rating table for such stations.
Static Head - (1) The total head without reduction for
velocity head or losses; for example, the difference in
the elevation of headwater and tail water of a power
plant. (2) The vertical distance between the free level
of the source of supply and the point of free discharge
or the level of the free surface.
Steady Flow - (1) A flow in which the rate or quantity of
water passing a given point per unit of time remains
consrant. (2) Flow in which the velocity vector does
not change in either magnitude or direction with respect
to time at any point or section.
Steady Uniform Flow - A flow in which the velocity and the
quantity of water flowing per unit remains constant.
Stilling Well - A pipe, chamber, or compartment with com-
partively small inlet or inlets communicating with a
main body of water. Its purpose is to dampen waves or
surges, while permitting the water level within the well
to rise and fall with the major fluctations of the main
body of water. It is used with waterrneasuring devices
to improve accuracy of measurement.
248
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Submerged Weir - A weir that when in use, has the water
level on the downstream side at an elevation equal to or
higher than, the weir crest. The rate of discharge is
affected by the tail water. Also called drowned weir.
Suppressed Weir - A weir with one or both sides flush with
the channel of approach. This prevents contraction of
the nappe adjacent to the flush side. The suppression
may occur on one end or both ends.
Surveys - The gathering of numerical and other forms of data
from the field, or plant site for the subsequent purpose
of data reduction, correlation and analysis leading to
improve water supply, treatment, use and wastewater
treatment, described in total as a Water Management
Program.
Suspended Matter - (1) Solids in suspension in water,
wastewater or effluent. (2) Solids in suspension that
can be removed readily by standard filtering procedures
in a laboratory. 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.
Tertiary Treatment - A process to remove practically all
solids and organic matter from wastewater. Granular
activated carbon filtration is a tertiary treatment
process. Phosphate removal by chemical coagulation is
also regarded as a step in tertiary treatment.
Threshold Odor - The minimum odor of the water sample that
can just be detected after successive dilutions with
odorless water. Also called odor threshold.
Titration - The determination of a constituent in a known
volume of solution by the measured addition of a solu-
tion of known strength to completion of the reaction as
signaled by observation of an end point.
Total Organic Carbon (TOC) - TOC is a measure of the amount
of carbon in a sample originating from organic matter
only. The test is run by burning the sample and
measuring the CO produced.
Tracer - (1) A foreign substance mixed with or attached to a
given substance for the determination of the location or
distribution of the substance. (2) An element or
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compound that has been made radioactive so that it can
be easily followed (traced) in biological and industrial
processes. Radiation emitted by the radioisotope
pinpoints its location.
Treatment Efficiency - Usually refers to the percentage
reduction of a specific or group of pollutants by a
specific wastewater treatment step or treatment plant.
Turbidmeter - An instrument for measurement of turbidity, in
which a standard suspension usually is used for
reference.
Turbidity - (1) A condition in water or wastewater caused by
the presence of suspended matter, resulting in the
scattering and absorption of light rays. (2) A measure
of fine suspended matter in liquids. (3) An analytical
quantity usually reported in arbitrary turbidity units
determined by measurements of light diffraction.
Turbulent Flow - (1) The flow of a liquid past an object
such that the velocity at any fixed point in the fluid
varies irregularly. (2) A type of liquid flow in which
there is an unsteady motion of the particles and the
motion at a fixed point varies in no definite manner.
Sometimes called eddy flow, sinuous flow.
Ultimate Biochemical Oxygen Demand - (1) Commonly, the total
quantity of oxygen required to satisfy completely the
first-stage biochemical oxygen demand. (2) More
strickly, the quantity of oxygen required to statisfy
completly both the first-stage and the second-stage
biochemical oxygen demands.
Velocity Area Method - A method used to determine the dis-
charge of a stream or any open channel by measuring the
velocity of the flowing water at several points within
the cross section of the stream and summing up the
products of these velocities and their respective
fraction of the total area.
Velocity Meter - A water meter that operates on the prin-
ciple that the vanes of the wheel move at approximately
the same velocity as the flowing water.
Velocity of Approach - The mean velocity in a conduit im-
mediately upstream from a weir, dam, venturi tube, or
other structure.
Vena Contracta - The most contacted sectional area of a
stream jet, or nappe issuing through or over an orifice
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or weir notch. It occurs downstream from the plane of
such notch or orifice.
Venturi Flume - A open flume with a contracted throat that
causes a drop in the hydraulic grade line. It is used
for measuring flow.
Venturi Meter - A differential meter for measuring flow of
water or other fluid through closed conduits of pipes,
consisting of a venturi tube and one of several pro-
prietary forms of flow-registering devices. The dif-
ference in velocity heads between the entrance and the
contracted throat is an indication of the rate of flow.
Venturi Tube - A closed conduit or pipe, used to measure the
rate of fluids, containing a gradual contraction to a
throat, which causes a pressure-head reduction by which
the velocity may be determined. The contraction is
usually, but not necessarily, followed by an enlargement
to the original size.
Volatile Solids - The quantity of solids in water, waste-
water or other liquids, lost on ignition of the dry
solids at 600°C.
Wastewater Survey - An investigation of the quality and
characteristics of each waste stream, as in an
industrial plant or municipality.
Water Level Recorder - A device for producing, graphically
or otherwise, a record of the rise and fall of a water
surface with respect to time.
Water Meter - A device installed in a pipe under pressure
for measuring and registering the quantity of water
passing through it.
Water Renovation - Wastewater treatment of sufficient degree
to allow the reuse of water for one or more purposes in
a given water supply/treatment system.
Weir - (1) A diversion dam. (2) A device that has a crest
and some side containment of known geometric shape, such
as a V, trapezoid, or rectangle and is used to measure
flow of liquid. The liquid surface is exposed to the
atmosphere. Flow is related to upstream height of water
above the crest, to position of crest with respect to
downstream water surface, and to geometry of the weir
opening.
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APPENDIX
METRIC UNITS
CONVERSION TABLE
MULTIPLY (ENGLISH UNITS)
EKGLISH UNIT ABBREVIATION
acre
acre - feet
British Thermal
Unit
British Thermal
Unit/pound
cubic feet/minute
cubic feet/second
cubic feet
cubic feet
cubic inches
degree. Fahrenheit
feet
gallon
galIon/minute
horsepower
inches
inches of mercury
pounds
million gallons/day
mile
pound/square
inch (gauge)
square feet
square inches
tons (ehort)
yard
* Actual conversion, not a multiplier
OU.S.GOVERNMENTPRINTINGOFFICE 1977- 234-846:6285
by TO OBTAIN (METRIC UNITS)
CONVERSION ABBREVIATION METRIC UNIT
hectares
cubic meters
kilogram - calories
kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
killowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric tons (1000 kilograms)
meters
ac
ac ft
BTU
BTU/lb
cfm
cfs
cu ft
cu ft
cu In
F"
ft
gal
gpm
hp
in
in Hg
Ib
mgd
mi
psig
sq ft
sq in
t
y
0.405
1233.5
0.252
0.555
0.028
1.7
0.028
28.32
16.39
0.555(°F-32)*
0.3048
3.785
0.063]
0.7457
2.54
0.03342
0.454
3,785
1.609
(0.06805 psig +1)*
0.0929
6.452
0.907
0.9144
ha
cu ra
kg cal
kg ca] /kg
cu m/niin
cu m/rflin
cu m
1
cu cm
°C
m
1
I/sec
kw
cm
atm
kg
cu m/day
km
atm
sq m
eq cm
kkg
m
253
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