STATE OF THE ART OF
SMALL WATER TREATMENT
SYSTEMS
U.S. Environmental Protection Agency
Office of Water Supply
Washington, D.C.
AUGUST 1977
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This report has been reviewed by Black & Veatch.
EPA, and approved for publication. Approval does
not signify that the contents necessarily reflect
the views and policies of the' Environmental
Protection Agency, nor does mention of trade
names or commercial products constitute endorse-
ment or recommendation for use.
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TABLE OF CONTENTS
Page
I. INTRODUCTION ,1-1
A. PURPOSE .1-1
B. SCOPE .1-2
II. WATER SOURCES Il l
A. SURFACE WATER II-1
B. GROUND WATER II-2
C. COMBINATIONS OF SURFACE AND GROUND WATER . II-2
D. ALTERNATIVES TO TREATMENT II-2
III. WATER QUALITY REQUIREMENTS Ill-1
A. NATIONAL INTERIM PRIMARY DRINKING
WATER REGULATIONS III-l
1. Inorganic Chemicals 111-2
a. Arsenic , 111-2
b. Barium . - III-4
c. Cadmium II1-5
d. Chromium III-6
e. Fluoride , III-8
f. Lead III-9
g. Mercury III-l 1
h. Nitrate ............... III-13
i. Selenium III-l 5
j. Silver Ill-15
2. Organic Chemicals ............ .111-17
a. Chlorinated Hydrocarbon Insecticides Ill-17
b. Chlorophenoxy Herbicides Ill-19
3. Turbidity .111-20
4. Coliform Organisms III-21
5. Radiological 111-23
6. Stabilization II1-2 5
B. SECONDARY DRINKING WATER REGULATIONS ... 111-26
1. Chloride . II1-26.
2. Color 111-27
3. Copper 111-28
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TABLE OF CONTENTS (cont'd)
Page
6
7
8
9
10
11
12
13
Corrosivity
Foaming Agents , . .
Hydrogen Sulfide . , .
Iron
Manganese
Odor
PH ..
Sulfate
Total Dissolved Solids (TDS)
Zinc
IV. WATER TREATMENT FACILITIES
A. UNIT PROCESSES . . . .
1.
Aeration
a. Gravity Aeration ¦
Mechanical Draft Aeration
Diffused Aeration
Applicability and Recommendations
b.
c.
d.
Oxidation
a. Air
b. Chemical
c. Applicability- and Recommendations-
Adsorption . . ... . .
a. Activated Alumina
b. Activated Carbon
c. Applicability and Recommendations
Clarification
a. Coagulation
b. Rapid Mix
, c. Flocculation
d. Sedimentation
e. Softening
f. Applicability arid Recommendations
•TC-2
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TABLE OF CONTENTS (cont'd)
Page
5. Filtration 1V-23
a. Gravity Filters ............ 1V-24
b. Pressure Filters 1V-24
c. Diatomite Filters 1V-25
d. Media . ; . . . . IV-25
1. Single Media IV-25
2. Dual Media IV-27
3. Mixed Media ' . . . . IV-28
e. Backwashing Facilities . . . . . • . . . .' . IV-29
f. Filtration Aids IV-30
g. Applicability and Recommendations IV-30
6. Disinfection .x . . . 1V-31
a. Chlorine IV-32
b. Hypochlorites . IV-37
c. Chlorine Dioxide - . IV-38
d. Ozone IV-38
e. Applicability and Recommendations IV-39
7. Stabilization IV-40
a. Adjustments to pH IV-40
b. Polyphosphate IV-41
c. Silicates 1 • ! IV-41
8. Ion Exchange ! . . . . IV-41
a. Softening by Ion Exchange IV-42
b. Demineralization by Ion Exchange 1V-44
c. Applicability and Recommendations IV-45
9. Membrane Processes 1 IV-46
a. Electrodialysis IV-46
b. Reverse Osmosis . • IV-49
c. Applicability and Recommendations .... . IV-52
10. Fluoridation ,/Defluoridation IV-53
a. Fluoridation . IV-53
b. Defluoridation ' ' . ' IV-56
c. Applicability and Recommendations IV-57
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TABLE OF CONTENTS (cont'd)
Page
B. WATER QUALITY CONTROL IV-57
1, Sampling and Analysis , , . .IV-57
2, Laboratory Facilities IV-59
3, Metering, Instrumentation, and Control IV-60
C. WATER TREATMENT PLANT WASTE DISPOSAL . . . IV-61
1. Sources, Quantities, and Characteristics of Wastes . . .IV-61
a. Sources IV-61
b. Quantities of Wastes Produced . IV-61
c. Characteristics IV-64
2, Waste Disposal Practices . IV-66
a. Direct Disposal . IV-66
b. Vacuum Filtration IV-66
c. Centrifugation IV-66
d. Drying Beds IV-67
e. Lagoons IV-67
f. Discharge to Sanitary Sewers IV-69
g. Spent Brine Solutions IV-70
h. Summary of Waste Disposal Practices ..... IV-70
D. UNIT PROCESS COMBINATIONS IV-71
1. Conventional Facilities . . IV-71
a. Turbidity Removal .IV-71
b. Ion Exchange IV-72
c. Lime Softening IV-72
d. Iron and Manganese Removal IV-74
2. Package Plants IV-76
a. Turbidity Removal IV-78
b. Taste and Odor Control IV-79
c. Softening IV-79
d. Iron and Manganese Removal IV-79
V. UPGRADING EXISTING FACILITIES V-l
A. POLYMER ADDITION V-l
B. FILTER MEDIA REPLACEMENT V-2
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TABLE OF CONTENTS (cont'd)
Page
C. ACTIVATED CARBON REPLACEMENT OF
• FILTER MEDIA V-2
D. RAPID MIX ADDITION ¥-3
E. FLOCCULATION ADDITION . V-3
F. CHEMICAL CHANGE OR ADDITION V-4
G. TUBE SETTLERS V-4
H. IMPROVED HYDRAULIC CONDITIONS . V-5
- I. IMPROVED OPERATION AND MAINTENANCE . ... V-6
1. .Operator Training and Qualifications V-6
2. Improved Monitoring and Surveillance V-7
J. REGIONALIZATION . . . V-8
VI. COST DATA VI-1
. A. CAPITAL COSTS VI-3
1. Unit Processes VI-4
a. Mechanical Draft Aeration ' . . . . •. . VI-S
b.. Diffused Aeration Vl-5
c. Activated Carbon Beds VI-6
d. Activated Alumina Columns VI-6
e. Rapid Mix VI-7
f. Flocculation . . VI-7
' ' g. Sedimentation VI-8
h. Flocculator-Clarifier . ; VI-8
i. Ion Exchange Softening VI-9
j. Pressure Filtration VI-9
k. Gravity Filtration VI-10
1. Demoralization VI-10
m. Electrodialysis • VI-11
n, Reverse Osmosis VI-11
" * o. Chemical Feed VI-11
2. Laboratory Facilities VI-14
3. Waste Disposal Facilities VI-14
' 4. Package Plants ' VI-14
5. Upgrading Existing Facilities VI-15
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TABLE OF CONTENTS (cont'd)
Page
B. OPERATION AND MAINTENANCE COSTS . . . . . . VI-16
1. Unit Processes . Vl-18
a. Mechanical Draft Aeration VI-19
b. Diffused Aeration VI-19
c. Activated Carbon Beds VI-19
d. Activated Alumina Columns ........ VI-19
e. Rapid Mix VI-20
f. Flocculation VI-20
g. Sedimentation . . VI-20
h. Flocculator-Clarifier VI-20
i. Ion Exchange Softening VI-20
j. Pressure Filtration VI-21
k. Gravity Filtration VI-21
I. Demineralization VI-21
m. Electrodialysis VI-21
n. Reverse Osmosis VI-21
o. Chemical Feed VI-22
2. Laboratory Facilities VI-23
3. Waste Disposal Facilities VI-23
4. Package Plants . VI-23
5. Upgrading Existing Facilities VI-23
C. COST DATA EXAMPLES VI-24
1. Example No. 1 . ; .VI-24
a. Capital Cost VI-25
b. Annual Operation and Maintenance Cost .... VI-27
2. Example No. 2 ¦ VI-28
a. Capital Cost VI-28
b. Annual Operation and Maintenance Cost .... VI-29
3. Example No. 3 VI-31
a. Capital Cost VI-31
b. Annual Operation and Maintenance Cost .... VI-32
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LIST OF FIGURES
Following Page
Figure 1 Garnet t, Kansas Water Treatment Plant
Schematic IV-71
Figure 2 Grant Park, Illinois Water Treatment
Plant Schematic IV-72
Figure 3 Troy, Kansas Water Treatment Plant Schematic .... IV-72
Figure 4 Cape Girardeau, Missouri Water Treatment
Plant Schematic IV-76
Figure 5 Mechanical Aeration Capital Cost VI-33
Figure 6 Diffused Aeration Capital Cost VI-33
Figure 7 Activated Carbon Bed Capital Cost VI-33
Figure 8 Activated Alumina Column Capital Cost VI-33
Figure 9 Rapid Mix Capital Cost , VI-33
Figure 10 Flocculation Capital Cost VI-33
Figure 11 Sedimentation Capital Cost .......... VI-33
Figure 12 Flocculator-Clarifier Capital Cost .VI-33
Figure 13 Ion Exchange Softening Capital Cost VI-33
Figure 14 Pressure Filtration Capital Cost VI-33
Figure 15 Gravity Filtration Capital Cost VI-33
Figure 16 Demineralization Capital Cost ¦ VI-33
Figure 17 Electrodialysis Capital Cost . . . • . - VI-33
Figure 18 Electrodialysis Enclosure Capital Cost VI-33
Figure 19 Reverse Osmosis Capital Cost VI-33
Figure 20 Reverse Osmosis Enclosure Capital Cost VI-33
Figure 21 Powdered Activated Carbon Chemical Feed
Capital Cost VI-33
Figure 22 Coagulant Chemical Feed Capital Cost VI-33
Figure 23 Hydrated Lime Chemical Feed Capital Cost VI-33
Figure 24 Polymer Chemical Feed Capital Cost " VI-33
Figure 25 Polyphosphate Chemical Feed Capital Cost VI-33
Figure 26 Chlorine Chemical Feed Capital Cost ' VI-33
Figure 27 Ozone On-Site Generation Capital Cost . VI-33
Figure 28 Calcium Hypochlorite Chemical Feed
Capital Cost VI-33
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4
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LIST OF FIGURES (cont'd)
Following Page
Figure 29 Sodium Hypochlorite Chemical Feed . . ¦ .
Capital Cost VI-33
Figure 30 Sodium Hypochlorite On-Site; Generation
Capital Cost VI-33
Figure 31 Waste Solids Disposal Lagoon Capital Cost VI-33
Figure 32 Package Plant Capital Cost VI-33
Figure 33 Tube Settlers Capital Cost VI-33
Figure 34 Labor—Plant Type 1 & 2
Operation and Maintenance Cost . .VI-33
Figure 35 Labor—Plant Type 3 & 4
Operation and Maintenance Cost VI-33
Figure 36 Mechanical Aeration Operation and Maintenance, Cost . ..VI-33
Figure 37 Diffused Aeration Operation and Maintenance Cost. • . . . VI-33
Figure 38 Activated Carbon Bed Operation and Maintenance Cost . VI-33
Figure 39 Activated Carbon Bed Media Replacement Cost .... VI-33
Figure 40 Activated Alumina Column Operation .and . ...
Maintenance Cost . VI-33
Figure 41 Activated Alumina Column Regenerative Chemical..Cost .. . VI-33
Figure 42 Rapid Mix Operation and-Maintenance. Cost . . . . VI-33
Figure 43 Floeculation Operation and Maintenance Cost ...... . •• . VI-33
.Figure 44 Sedimentation Operation and Maintenance Cost .... . . VI-33
Figure 45 Flocculator-Clarifier.Operation and Maintenance Cost .• . ..VI-33
Figure 46 Ion Exchange Softening O.peration and Maintenance Cost . VI-33
Figure 47 Ion Exchange Softening Regenerative Chemical.Cost . . . .VI-33
Figure 48 Pressure Filtration Unit Process Operation
and Maintenance Cost . VI-33
Figure 49 Pressure Filtration Enclosure Operation
and Maintenance Cost . . . . . ...... . . . VI-33
.Figure 50 Gravity Filtration Unit Process Operation and
Maintenance Cost. . . ... ... . . ... . ¦ . .VI-33
Figure 51 Gravity Filtration Enclosure Operation and
Maintenance.Cost . . , . . . . . .. . . ; .. VI-33
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LIST OF FIGURES (cont'd)
Following Page
Figure 52 Demineralization Power and Enclosure Supplies
Operation and Maintenance Cost VI-33
Figure 53 Demineralization Unit Process Supplies and
Regenerative Chemicals Operation and
Maintenance Cost VI-33
Figure 54 Electrodialysis Unit Process Operation and
Maintenance Cost . * VI-33
Figure 55 Electrodialysis Enclosure Operation and
Maintenance Cost VI-33
Figure 56 Reverse Osmosis Unit Process Operation
and Maintenance Cost VI-33
Figure 57 Reverse Osmosis Enclosure Operation and
Maintenance Cost . ; VI-33
Figure 58 Powdered Activated Carbon Chemical Feed
Operation and Maintenance Cost ¦. . VI-33
«
Figure 59 Coagulant Chemical Feed Operation and
Maintenance Cost VI-33
Figure 60 Hydrated Lime Chemical Feed Supplies
Operation and Maintenance Cost VI-33
Figure 61 Hydrated Lime Chemical Feed Power
Operation and Maintenance Cost VI-33
Figure 62 Polymer Chemical Feed Unit Process
Operation and Maintenance Cost VI-33
Figure 63' Polymer Chemical Feed Power and Enclosure
Operation and Maintenance Cost VI-33
Figure 64 Polyphosphate Chemical Feed Operation and
Maintenance Cost VI-33
Figure 65 Chlorine Chemical Feed Operation and
Maintenance Cost VI-33
Figure 66 Ozone On-Site Generation Unit Process Operation
and Maintenance Cost VI-33
Figure 67 Ozone On-Site Generation Enclosure Operation
and Maintenance Cost VI-33
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LIST OF FIGURES (cont'd)
Following Page
Figure 68 Calcium Hypochlorite Chemical Feed Unit
Process Operation and Maintenance Cost Vk-33
Figure 69 Calcium Hypochlorite Chemical Feed Power
and Enclosure Operation and Maintenance Cost , . .' . . VI-33
Figure 70 Sodium Hypochlorite Chemical Feed Unit
Enclosure Operation and Maintenance Cost ..... VI-33
Figure 71 Sodium Hypochlorite Chemical Feed Power
Operation and Maintenance Cost . ... . . . ... VI-33
. Figure 72 Sodium Hypochlorite On-Site Generation Unit
Process Operation and Maintenance Cost . , .'4 . . . VI-33
Figure 73 Sodium Hypochlorite On-Site Generation Power and
Enclosure Operation and Maintenance Cost . . ... VI-33
Figure 74 Lagoon Waste Solids Removal Cost VI-33
Figure 75 Package Plant Operation and Maintenance Cost .... VI-33
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LIST OF TABLES
Page
Table 1 Processes for Arsenic Removal * 111-3
Table'2 Processes for Barium Removal • , - III-5
Table 3 Processes for Cadmium Removal .......... 111-6
Table 4 Processes for Chromium Removal III-7
Table 5 Processes for Fluoride Removal ¦ . . . . III-9
Table 6 Processes for Lead Removal . . . ... .... . . IIT10
Table 7 Processes for Mercury Removal . . . . . . , . . 111-12
Table 8 Processes for Nitrate Removal 111-14
Table 9 Processes for Selenium Removal . . . ... . . . . 111-16
Table 10 Processes for Silver Removal III-16
Table 11 Processes for Endrin Removal ......... .111-18
Table 12 Processes for Lindane Removal . 111-18
Table 13 Processes for 2, 4, 5^TP (Silvex) Removal . . . . . . 111-20
Table 14 Processes for Turbidity Removal ......... .111-21
Table 15 Processes for Bacteria Reduction . 111-23
Table 16 Maximum Contaminant Levels for Radioactivity 111-24
Table 17 Processes for Radionuclide Removal ....... .111-25
Table 18 Processes for Color Removal : 111-27
Table 19 Processes for Copper Removal 111-29
Table 20 Processes for Iron Removal 111-31
Table 21 Processes for Manganese Removal II1-32
Table 22 Processes for Sulfate Removal II1-34
Table 23 Processes for Total Dissolved Solids Removal 111-35
Table 24 Processes for Zinc Removal 111-36
Table 25 Solids Produced Based on Coagulant Dosage IV-62
Table 26 Solids Produced From Taste and Odor Removal IV-63
Table 27 Analysis of Spent Brine Solution IV-65
Table 28 Garnctt, Kansas Water Treatment Plant
Unit Process Design Data IV-73
Table 29 AT&T — Grant Park, Illinois Water Treatment System
Unit Process Design Data IV-74
Table 30 Troy, Kansas Water Treatment Plant
Unit Process Design Data IV-75
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LIST OF TABLES (cont'd)
Page
Table 31 Cape Girardeau, Mo. Water Treatment Plant
Unit Process Design Data IV-77
Table 32 Comparison of Package Water Supply Treatment Systems . , IV-78
Table 33 Treatment Plant Design Capacity VI-1
Table 34 Water Treatment Chemical Costs ¥1-18
Table 35 Summary of Chemical Feed System
Operation and Maintenance Cost Curves Vl-22
Table 36 Capital Recovery Factors VI-26
Table 37 Example Costs Summary VI-33
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I. INTRODUCTION
When the National Interim Primary Drinking Water Regulations were
promulgated late in 1975, it was estimated that there were about 40,000
community water systems (see Appendix A). Of this total more than 37,000
community systems each served 10,000 or fewer people. Thus, the vast
majority of community water systems would be considered small water systems
(capacities less than about 5700 rn^/day or 1.5 mgd). A previous study [1]
provided technical and economic information for the approximately 3000
community water treatment systems with capacities in excess of 3800 m^/day
(1 mgd).
An economic analysis [2J indicates water systems serving 25-99 persons
will need to spend a total of $6.2 — $9.1 million per year on monitoring,
capital investment, operation, and maintenance to meet the National Interim
Primary Drinking Water Regulations. An equivalent figure of S 109.4 — $151,3
million has been estimated for those systems serving from 100 to 9999 persons.
The economic impact on a specific system will depend on the degree of
treatment required to meet the regulations.
A pyRp0SE
This report is a planning tool which provides information on small water
treatment systems. The content of this report is directed to the governing
bodies responsible for the small water treatment systems so that they can
better understand what is required of them by the National Interim Primary
Drinking Water Regulations regarding treatment of their water and the related
costs. It is directed to the water plant operator or city engin'eer to assist one in
understanding what can be expected of various treatment processes with regard
to meeting the maximum contaminant levels (MCL) specified in the regulations.
"Maximum contaminant level" is defined as the maximum permissible level of a
contaminant in water when measured at the customer's tap. An exception is
turbidity where the maximum permissible level is measured at the water's point
Of entry to the distribution system. Finally the report is directed to consulting
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engineers to assist them in planning for new and/or improved water treatment
systems. The report will provide the engineer with treatment techniques, design
parameters and cost information in regard to meeting the various MCL's.
B. SCOPE
The state of the art of water treatment for small water systems to
meet the drinking water regulations is presented in this report. The plant
capacities considered range from 230 -in^/'day (60,000 gpd) to S700
in ^/day (1.5 mgd), serving a population of 25 and 10,000 respectively.
Discussion of water supply sources compares ground and surface water sources
and covers means of protecting these sources from contamination. The MCL's
included in the regulations are presented along with applicable treatment
techniques and their efficiencies. Unit processes for the treatment of water are
discussed and general, design parameters have been compiled for each process.
These processes include disposal of the treatment plant wastes and laboratory
facilities required to monitor the treatment processes. Examples of conventional
water treatment processes for turbidity removal,, iron removal, chemical
if
softening (heavy metal removal), and ion exchange softening are explained. In
addition commercially available water treatment package plants are described.
Graphs of capital, operation, and maintenance costs show the costs for each
unit process and also for package plants. Examples of how to use the graphs
have also been provided to assist the user.
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REFERENCES
David Volkert and Associates, Monograph of the Effectiveness and Cost of
Water Treatment Processes for the Removal of Specific Contaminants,
68-01-1833, U.S. Environmental Protection Agency, August, 1974.
Energy Resources Company, Inc., Economic Evaluation of the Promul-
gated Interim Primary Drinking Water Regulations, U.S. Environmental
Protection Agency, U.S. Dept. of Commerce NTIS PB, 248 588,
October, 1975.
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II. WATER SOURCES
A variety of sources including surface water, ground water and
combinations of surface and ground water are used as water supply for small
water treatment systems. The selection of a supply source is dependent upon
availability, quality and quantity of water. Considering the small community
water systems, probably the majority use ground water as the source. The
reasons for this will be discussed subsequently.
A. SURFACE WATER
Surface water sources include rivers, streams, lakes and reservoirs. Surface
water is generally available- across the United States except in the Southwest
where surface waters have high total dissolved solids (some are over 1000 mg/1)
[1J. These surface waters are generally unsuitable for potable water supply
without extensive treatment. Surface waters require at least turbidity removal
and disinfection before use as potable water. In some areas of the country,
particularly the Midwest and Western areas, the hardness of the surface waters
is high enough to require softening. The dissolved oxygen in most surface
waters prevents problems associated with iron, manganese, and hydrogen
sulfide. The bottom levels of some lakes and reservoirs may contain soluble
iron or manganese or hydrogen sulfide, but these contaminants can be avoided
by taking water with dissolved oxygen from a higher elevation in the body of
water using multilevel intakes. Other surface waters can exhibit special
problems with tastes, odors, color, inorganic contaminants, or pollution related
contaminants such as pesticides. River water presents additional treatment
complications due to seasonal variations in turbidity, mineral content, industrial
and sanitary waste discharges and other surface water related problems discussed
previously.
Very little protection can be given to some surface water sources. Gross
pollution of rivers and lakes can be prevented by the control of waste
discharges. Multipurpose reservoirs can receive some protection by proper
placement of adequate sanitary facilities. Single purpose water supply reservoirs
can be protected by prohibiting or controlling access to the reservoir watershed.
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B. GROUND WATER
Ground water is generally available from wells throughout the United
States and from springs in some areas. The quality of ground water varies from
water needing only disinfection to water needing extensive treatment for
removal of total dissolved solids. Ground water can also require softening due
to the hardness content. Ground water can contain other substances such as
iron, manganese, hydrogen sulfide, carbon dioxide, radionuclides and inorganic
contaminants, particularly fluoride and nitrate. Treatment must be provided for
each of these if the substances exceed the established limits. Ground water
quality is generally constant and should not contain pesticide contaminants.
Since ground water is generally accessable and usually requires little treatment,
it is usually used as the water supply source for small systems.
Ground water sources can usually be protected by proper well
construction and maintenance. Prior to construction the well should be
properly located and during construction the well should be protected and
properly cased to prevent pollution.
C. COMBINATIONS OF SURFACE AND GROUND WATER
When combinations of surface and ground water are used, the purpose is
usually to provide an adequate quantity of water. However, some combinations
are used to enhance the quality of the water. In very cold weather surface
water may be supplemented with ground water to raise the temperature of the
combined water and speed chemical reactions. In other instances a combination
of surface and ground water might be used in a split treatment softening
process. For most small systems a combination of surface and ground water
would not be economically justifiable.
D. ALTERNATIVES TO TREATMENT
Although most small water systems are in somewhat isolated locations,
some are located near larger systems or close to each other. For these small
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systems a regional water system may be an attractive alternative to extensive
treatment for an individual system. Economies of scale dictate a large regional
system for those waters requiring significant degrees of treatment.
Another possible alternative for some small systems might be switching
water supply sources. A system using a surface water might be able to switch
to a ground water source requiring less treatment. Similarly, a system using
ground water might consider a surface water source or another ground water
aquifer in the area.
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REFERENCES
1. Dennis P. Tihansky, "Damage Assessment of Household Water Quality,"
Journal of the Environmental Engineering Division — ASCE, 905-918
(August, 1974).
BIBLIOGRAPHY
American Water Works Association, Water Quality and Treatment, 3rd edition,
McGraw-Hill, New York, 1971.
Clark, Viessman and Hammer, Water Supply and Pollution Control, 2nd
edition, International Textbook, Scranton, 1971.
Tihansky, Dennis P., "Damage Assessment of Household Water Quality,"
Journal of the Environmental Engineering Division — ASCE, 905-918 (August,
1974).
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III. WATER QUALITY REQUIREMENTS
The primary goal of a water treatment plant is to furnish water safe for
human consumption, A second basic objective is the production of water that
is appealing to the consumer. Quality guidelines are needed in order to evaluate
the suitability of water for public supply purposes. The United States
Environmental Protection Agency (USEPA) has developed primary and
secondary drinking water standards to replace the United States Public Health
Service Standards. Primary standards are based on dangers to health and they
are legally enforceable. If primary regulations are exceeded, either additional
treatment or an alternative water supply source is required to protect the
health of those persons using the water. Secondary regulations are based on
aesthetic considerations and are not enforceable by the USEPA, but may be
enforced by the States, Violation of these aesthetic standards should be
avoided, if possible, to discourage the consumer from turning to some other,
unsafe water.
A. NATIONAL INTERIM PRIMARY DRINKING WATER REGULATIONS
The USEPA has published National Interim Primary Drinking Water
Regulations (Federal Register, Vol. 40, No. 248, December 24, 1975 & Vol. 41,
No. 133, July 9", 1976, see Appendix A) which became effective in June 1977.
These primary standards" xonstitute legal requirements for public supplies,
because they deal 'with substances which are hazardous to health. The fact that
standards are to be periodically reviewed and can be amended and revised by
the USEPA must be considered in determining the need for treatment of a
particular water supply.
The primary regulations include standards for inorganic and , organic
chemicals, turbidity, col if or m bacteria and radionuclides. It is of importance
that the applicable standards are met at the customer's tap except the turbidity
standard which must be met at the point of entry into the distribution system.
Therefore, production of water that does not incur contamination from the
distribution system is necessary.
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The process removal percentages presented for the various contaminants in
the following sections are for a single pass through the process. If a single pass
will not reduce the contaminant to the required MCL, then multiple stages of
the same process or two or. more processes in series might be used.
1. Inorganic Chemicals
A discussion of the significance, possible sources, and processes applicable
to small public water systems for the removal of each inorganic substance for
which limits have been established is included in the following paragraphs.
a. Arsenic. Arsenic is highly toxic and the ingestion of as little as
100 mg can result in severe poisoning.fi] The maximum contaminant level for
arsenic is 0.05 mg/1. The occurrence of arsenic in the environment is due
mainly to natural deposits of the metalloid and to its extensive use in
pesticides. Other sources of contamination include manufacturing processes
such as tanning, dye manufacture and lead shot manufacture and to its use as a
wood preservative. The arsenic concentration of most treated drinking water
supplies in the United States ranges from less than 0.03 to 0.10 mg/1.[2]
High concentrations of arsenic compounds have , been found to occur
naturally in some waters of the Western United States.
Selection of a treatment method for arsenic removal is dependent on
' valence form and initial concentration of the arsenic. The two common valence
forms are arsenite and arsenate. Also called arsenic III (this indicates a valence
of +3), arsenite is a naturally occurring substance and is usually found only in
ground water. Arsenic V (this indicates a valence of +5), or arsenate, can be
found in ground water as a naturally occurring substance and in surface water
as both a natural and industrial pollutant. In water, both valence forms exist in
a relatively insoluble state, except as the sodium or potassium salts.
Various treatment processes will remove arsenic from drinking water.
Table 1 [3. 4] lists unit processes and per cent removals of arsenic for each unit
process.
III-2 •
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Table 1
PROCESSES FOR ARSENIC REMOVAL
Unit Process*
Per Cent Removal
Coagulation, Sedimentation,
and Filtration
Lime Softening
Ion Exchange**
Electrodialysis***
Reverse Osmosis***
Adsorption (Alumina)
90-95
60-90
30-90
55-99
99
80
*Additional process information is discussed in the text follow-
ing this table.
**Anion exchange resin.
•"'Predicted but not experienced.[3]
Laboratory experiments and pilot plant studies have shown that for
coagulation and lime softening, arsenic removals are dependent on the pH of
the water, coagulant dose and initial arsenic concentration-. The following
results [5] were observed during these studies and experiments:
1. Arsenic III removal
Chemical coagulation or lime softening can achieve adequate removals
of arseniclll, if the arsenic concentration is only slightly above the MCL.
Otherwise, oxidation of arsenic III to the arsenic V form is necessary
before treatment. Use of oxidants such as ozone and potassium
permanganate will be effective on arsenic III. The use of chlorine as
an oxidant for arsenic III removal is not advisable as chlorine can
react with certain organic jmaterials to produce chloroform and other
trihalomethanes,
2. Arsenic V removal
a. For initial arsenic concentrations less than 1.0 mg/1, coagulant
dose (alum or ferric sulfate) of 20 to 30 mg/1 and pH between
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5.0 and 7.5, arsenic removals of greater than 90 per cent were
achieved.
b. For initial arsenic concentrations peater than 1.0 mg/1 and other
conditions as above, arsenic removals decreased as initial
concentration. increased. Larger doses of coagulant, however,
achieved higher removals.
c. For initial arsenic concentrations up to 10 mg/1 and pH of 10.8
and above, lime softening can achieve 95 per cent removals.
Below a pH of 10.3. removals decreased to about 30 per cent as
the pH decreased to 8.5.
Ferric chloride and ferrous sulfate have also been used successfully as
coagulants for arsenic removal. [3]
b. Barium. Drinking water should not contain barium in concentrations
exceeding L0 mg/1 because of the toxic effects it has on the heart, blood
vessels and nerves.[l] Barium may be found in some ground waters and in
runoff from areas where barite and witherite are mined. Industrial applications
of barium and its salts include metallurgy, paint manufacture, ceramic and glass
manufacture and other processes. Wastes from these plants may contain
significant levels of barium contamination. Barium concentrations ranging from
0.0 to 1.55 mg/1 have been found in United States treated water supplies.[2]
In addition, several cities and subdivisions have been identified by the State
of Illinois EPA as using well water sources with barium concentrations
greater than the MCL; the highest concentration found was 10 mg/1.[6]
A number of treatment methods can effectively remove barium from
drinking water as shown in Table 2. [3, 5]
Studies have shown that lime softening is capable of achieving 90 per cent
barium removal if the pH is between 10 and 11 and if the initial barium level is
approximately 17 mg/1 or less.[5] Below and above this pH range, removals
decreased. Conventional coagulation is not recommended for barium removal
unless the barium concentration is only slightly above the allowable maximum
of 1.0 mg/1. Removals of only 20 to 30 per cent were achieved even when
coagulant doses of 120 mg/1 were used.
III-4
J
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Table 2
PROCESSES FOR BARIUM REMOVAL
Unit Process*
Per Cent Removal
Excess Lime Softening
Reverse Osmosis**
90
90-97
Ion Exchange
Electrodialysis* *
95
80
* Additional process information is discussed in the text
following this table,
"Predicted but not experienced.[3]
Conventional ion exchange softening treatment can very effectively remove
barium from water. As a result _ of the similarity in behavior of hardness and
barium in ion exchange treatment, the. hardness test can be used to monitor
barium during treatment. When blending is used, caution should be exercised to
prevent excessive barium levels in the finished water.
c. Cadmium. Current evidence indicates that cadmium is biologically a
nonessential, nonbeneficial element of high toxic potential. [1 ] Poisoning from
cadmium-contaminated food and beverages has been documented; ingestion of
cadmium has been associated with hypertension. Cadmium may leach from
galvanized pipes or fixtures used in a water supply system. Only minute traces
of cadmium are found in ground water. However, high concentrations may be
found in surface waters as a result of wastes from the following industries:
electroplating, pesticides, photography, metallurgy and ceramics.
In, water supply systems, cadmium has been found in concentrations
ranging from less than 0.02 me/1 to 3.94 mg/1.[2] The maximum allowable
level of cadmium in drinking water supplies is 0.010 mg/1. Selection of a
treatment method depends on whether the cadmium to be removed is soluble
or insoluble. Table 3 [3,5]lists unit processes for removal of both insoluble
•and soluble forms. The chloride, nitrate and sulfate compounds of cadmium
are highly soluble in water, but the carbonate and hydroxide compounds are
insoluble.
111-5
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Table 3
PROCESSES FOR CADMIUM REMOVAL
Unit Process*
Per Gent Removal
Removal of soluble forms of cadmium:
Reverse Osmosis**
90-98
Ion Exchange**
Electrodialysis**
Stabilization***
100
95
80
Removal of insoluble forms of cadmium:
Coagulation, Sedimentation and Filtration
Lime Softening
20-90
98
~Additional process information is discussed in the text following this table.
**Prcdicted but not experienced.[3J
***Applies only to prevention of corrosion of galvanized piping materials in the
distribution system.
Studies have shown that lime softening is effective if the pH is 8.5-11.3.
Cadmium removals by coagulation are also dependent on pH with the removal
efficiency increasing with increased pH.[5] Based on laboratory studies,
coagulation using ferric sulfate has been more effective than using alum. If the
pH is increased to greater than 1,5, soluble forms of cadmium will form
insoluble compounds and can be removed by coagulation or lime softening as
outlined above.
d. Chromium. Chromium exists in two common valence forms. III and
VI. Chromium is toxic to humans, particularly in the hexavalent state (VI). It
can produce lung tumors when inhaled and is a potent sensitizer of the skin. [ 1 ]
The maximum contaminant level for chromium has been set at 0,05 rng/1-
Sources of chromium contamination in drinking water are largely the
result of industrial pollution. Chromium salts are used in the metal finishing
II1-6
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industry, in the tanning industry and the manufacture of paints, dyes,
explosives, ceramics, paper and many other substances. Chromium compounds
may also be present in the discharge of cooling waters where the water has
been treated with chromium to inhibit corrosion. The chromium concentration
of most treated drinking water supplies ranges from O.Q to 0.079 mg/1. [2]
If treatment for chromium removal is required, the form of chromium,
whether soluble or insoluble, should be identified prior to selection of the
treatment system. Chloride, nitrate and sulfate salts of trivalent chromium are
readily soluble; however, the hydroxide and carbonate compounds are
insoluble. Of the hexavalent salts only sodium, potassium and ammonium
chromates are soluble. The corresponding dichromates are also quite soluble.
Table 4 [3, 5] lists unit processes for the removal of both insoluble and soluble
forms.
Table 4
PROCESSES FOR CHROMIUM REMOVAL
Unit Process*
Per Cent Removal
Removal of soluble forms of chromium;
Reverse Osmosis**
Electrodialysis**
Ion Exchange**
90-97
80
95
Removal of insoluble forms of chromium III:
Coagulation, Sedimentation,
and Filtration
78-98
Lime Softening
Removal of insoluble forms of chromium VI:
70-98
Coagulation, Sedimentation,
and Filtration
Lime Softening
10-98
10
~Additional process information is discussed in the text following this table.
••Predicted but not experienced.[3]
III-7
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Removal of insoluble chromium III can be achieved by alum or iron
coagulation or by lime softening. Studies have shown that pH has only a slight
effect on removals by alum and iron coagulation. Lime softening removals,
however, decrease as the pH drops below 10.6.
Insoluble chromium VI is more difficult to remove by conventional
treatment than insoluble chromium III. Laboratory studies showed that alum
coagulation and lime softening obtained only 10 per cent removal and ferric
sulfate coagulation at best removed 35 per cent of chromium VI. Ferrous
sulfate coagulation, however, achieved removals of 98 per cent.[5]
Chlorination prior to treatment for chromium removal is not recom-
mended because of the possible oxidation of chromium III to chromium VI. If
chlorination before treatment for chromium removal is necessary, ferrous
sulfate is recommended as a coagulant. Prechlorination is also not advisable as
chlorine can react with certain -organic materials to produce trihalomethanes.
e. Fluoride. While fluoride is added to some water supplies to aid in
prevention of dental caries, some communities have the problem of excessive
amount of natural fluoride in their raw water. Excessive fluoride in drinking
water supplies produces dental fluorosis.[1 ] This mottling of the teeth increases
with increasing fluoride concentration.
Only a few regions in the United -States ¦ contain large deposits of
fluoride bearing rock. Fluorides in high concentrations are not common in
surface waters, but may occur in detrimental concentrations in ground water.
Fluorides are used as insecticides, disinfectants, in steel manufacture, for
preserving..wood, and in the manufacture of glass and enamels. Although they
are not normally found in industrial wastes, fluorides may be present as a
result of accidental spillage. Fluoride will be introduced to surface water by
communities which practice fluoridation and then discharge sanitary wastes to
a surface water.
The - amount of water, consequently the amount of fluoride, ingested by
people in a given community is primarily a function of air temperature.
Depending on the annual. average air temperature, the maximum allowable
level of fluoride ranges from 1.4 to 2.4 mg/1, (Refer to Appendix A for
specific allowable levels of fluoride.) Fluoride has been found in water supply
systems in concentrations ranging from less than 0.2 mg/1 to 8.0 mg/1. [2,7]
III-8
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Communities with excessively high natural fluoride levels can utilize any of a
variety of defluoridation processes. Processes for fluoride removal are listed in
Table 5.[31
Table 5
PROCESSES FOR FLUORIDE REMOVAL
Unit Process*
Per Cent Removal
Reverse Osmosis**
EJectrodialysis**
Ion Exchange/Adsorption**
90—97
95
80
Excess Lime Softening
30-70
•Additional process information is discussed in the text
following this table.
**Predicted but not experienced. [3]
The method most commonly used for fluoride removal is the ion
exchange/adsorption process using either bone char or activated alumina as the
exchange resin. Bone char readily removes both fluoride and arsenic; however,
arsenic can interfere with fluoride removal when using bone char. Investigations
showed that bone char which had adsorbed arsenic could not be regenerated. [4]
Activated alumina, however, is readily regenerated when both fluoride and
arsenic are removed. Therefore, activated alumina is the recommended medium to
use for fluoride removal if the raw water contains both fluoride and arsenic.
Where excess lime softening is used for treatment.of high magnesium
water, it has been demonstrated that fluoride is removed by coprecipitation with
magnesium hydroxide.[8] Fluoride removal is directly related to the amount of
magnesium removed. This is indicated by the range of per cent removals in
Table 5. If excess lime softening is to be used for fluoride removal, raw water
quality may require the addition of magnesium to achieve adequate reduction
of fluoride.
f. Lead. Drinking water should not contain lead in concentrations
exceeding 0.05 mg/1. Excess lead is a serious health hazard especially in
III-9
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children. Lead poisoning in children can cause brain damage and kidney damage
sometimes resulting in death. [ 1 ] The most likely sources of lead pollution are
industrial and mining effluents. Natural waters have been known to contain as
much as 0.4 to 0.8 mg/1 of lead, but this situation is rare. Another source of
lead contamination is lead pipe used for water supply systems. If contamination
is due to lead pipes, the best method of control is pipe replacement. Where
replacement of the piping system is not practicable. pH control and
stabilization is the alternative. Concentration of lead in finished drinking water
supplies ranges from 0.0 to 0.64 mg/1.[2]
Lead concentrations in water can be removed by the treatment methods
listed in Table 6.[3, 5] Selection ofa treatment method is dependent on the
form of lead, whether soluble or insoluble. The carbonate and hydroxide
compounds of lead are insoluble; the sulfate and various other lead salts are
soluble.
Table 6
PROCESSES FOR LEAD REMOVAL
Unit Process*
Per Cent Removal
For removal of.soluble forms of lead:
Reverse Osmosis**
90-99
Electrodialysis**
Ion Exchange**
Stabilization***
100
80
95
For removal of insoluble forms of lead:
Coagulation, Sedimentation,
and Filtration
Lime Softening
80-97
98
•Additional process information is discussed in the text following this table.
* "Predicted but not experienced; [3]
""•Applies only to prevention of corrosion of lead piping materials in the
distribution system.
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Insoluble forms of lead are the most common, therefore conventional
treatment methods of coagulation, sedimentation and filtration, or lime
softening will usually be adequate for lead removal. Laboratory studies showed
that ferric sulfate is a more effective coagulant than alum in removing lead. [ S ]
g. Mercury. Exposure to mercury and its compounds poses a serious
threat to man's health. Continued ingestion of small concentrations of mercury
or a one time ingestion of a larger amount can damage the brain and central
nervous system. [ 11 The maximum allowable level of mercury in drinking water
is 0.002 mg/1. Most water supplies in the United States do not contain mercury
or any of its compounds. Studies indicate that mercury in the United States
treated water supplies varies in concentration from 0.0 to 0.033 mg/1.[2]
Industrial and agricultural applications are the most likely source of
mercury contamination. Mercury compounds are used in explosives, antiseptics,
printing, electroplating, herbicides and fungicides. Mercury may occur in either
the inorganic or organic form. The organic form is more important as it is the
more toxic form, the form most likely to be found in water, and the more
difficult form to remove by conventional treatment.!5] In order to. select the
proper treatment method, the form of the mercury contaminant, organic or
inorganic, should be determined. Listed in Table 7 [3.5] are treatment methods
for mercury removal.
Inorganic mercury removals using coagulation, sedimentation and filtra-
tion, or lime softening are dependent on pH of the water. [ 51 It has been
reported that ferric sulfate coagulation achieved 66 per cent removal at pH 7
and 97 per cent removal at pH 8 for a dosage of 18 mg/1 on water containing
0.05 mg/'l of incrrganic mercury. Alum coagulation is less effective; removals of
74 per cent at pH7 and 38 per cent at pH 8 have been shown. Also, as the
turbidity increases, removals by coagulation increase.
Lime softening is moderately effective for inorganic mercury removal,
depending on the pH of the water. Studies have shown that in the 10.7 to
11.4 pH range removals were 60 to 80 per cent, but only 30 per cent was
removed at pH 9.4.
III-l 1
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Table 7
PROCESSES FOR MERCURY REMOVAL
Unit Processes* Per Cent Removal
For removal of inorganic forms of mercury:
Coagulation, Sedimentation.
and Filtration 38—97
Lime Softening 30—80
Granular Activated Carbon less than 80
>..• Ion-Exchange 95-98
Reverse Osmosis** 90-97
Electrodialysis** 80
r I
For removal of organic forms of mercury:
Coagulation, Sedimentation,
and Filtration 30-85
Granular Activated Carbon greater than 80
Ion Exchange 95—98
Reverse Osmosis** 90—97
Electrodialysis** 80
~Additional process information is discussed in the text following this table.
~~Predicted but not experienced.[3]
Activated carbon has been studied for inorganic mercury removal.
Powdered activated carbon will increase removals above that obtained with
coagulation alone. However, doses required to produce significant increases are
much higher than normally used for taste and odor control. Granular activated
carbon was found to be fairly effective although removals are dependent on
contact time and amount of water treated. Inorganic mercury removals of
approximately 80 per cent have been achieved for 15,000 bed volumes of water
(a bed volume is equal to the volume of activated carbon used) with
3.5 minutes contact time on water containing 0.020 to 0.029 mg/1 of mercury.
Ill-12
-------
Several preliminary experiments indicate that the ion exchange process
should be an effective method for inorganic mercury removal. These studies
showed that as much as 90 per cent of inorganic mercury can be removed by
cation and anion exchange resins in series.
Organic mercury is more difficult to remove from drinking water, by
conventional treatment methods, than inorganic mercury. Laboratory experi-
ments and pilot plant studies have shown alum and iron coagulation to achieve
lower organic mercury removals than inorganic mercury under the same test
conditions. Lime softening was also studied and found to be ineffective for
organic mercury removal.
Both powdered and granular activated carbon are effective for organic
mercury removal. Approximately 1 mg/1 of powdered activated carbon is
required for each 0.0001 mg/1 of mercury to be removed from water to reach a
residual level of 0,002 mg/1. Removal of organic mercury using granular
activated carbon was found to be dependent on contact time and amount of
water treated, similar to that found for inorganic mercury. Organic mercury
removals of approximately 80 per cent have been achieved for 25,000 bed
volumes of water with 3.5 minutes contact time on water containing 0.020 to
0.029 mg/1 of mercury.
Preliminary studies carried out on ion exchange for organic mercury
removal indicate results similar to those for inorganic mercury. Removals of
98 per cent were achieved using cation and anion exchange resins.
h. Nitrate. Nitrate in drinking water can cause a temporary blood
disorder in infants called methemoglobinemia (blue baby). Serious and
occasionally fatal poisonings in infants have occurred following ingestion of
waters containing nitrate concentrations greater than 10 mg/1 (as nitrogen).[ 1 ]
Thus the maximum allowable level of nitrate in drinking water is 10 mg/1 (as
nitrogen). This is equivalent to 45 mg/1 of the nitrate ion (NOj). Studies
indicate that nitrate in treated water supply systems varies from 0.02 to
28.2 mg/1 (as nitrogen). [2]
111-13
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Ground waters may acquire nitrates by percolation in areas using nitrate
fertilizers and by cesspool leachings. In addition, nitrates may be added to a
surface or ground water that receives wastes from chemical fertilizer-producing
plants and municipal wastewater treatment plants. Nitrate contamination of
ground water supplies can often be prevented by proper well construction.
Treatment methods for the removal of nitrate from water are listed in
Table 8.C3]
Table 8
PROCESSES FOR NITRATE REMOVAL
Unit Processes* Per Cent Removal
Reverse Osmosis * * 90 - 97
Electrodialysis*? 80
Ion Exchange 98
~Additional process information is discussed in the text
following this table.
**Per cent removal based on manufacturers' recommendations.
Nitrate salts are very soluble; therefore, nitrate removal cannot be achieved
by processes such as lime softening or coagulation. Presently the most practical
method of removing nitrate from drinking water is by ion exchange
treatment.[5] ¦
Anion exchange resins can be used to remove nitrate by replacement with
chloride. However,, pretreatment of water to reduce sulfate, iron or silica
concentrations may be required for efficient operation of the exchanger.
Sulfate decreases the resins' capacity for nitrate removal, thus more frequent
regeneration of the system is required. Iron and silica interfere by clogging the
resin, thus preventing the nitrate from being exchanged.
Use of a cation exchange resin and anion exchange resin (demineralization)
might be necessary if the chloride level in the finished water becomes
undesirably high.
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i. Selenium. Selenium in large amounts is toxic to both humans and
animals. [ 1 ] There is also concern over the possible carcinogenic properties of
the element. More recent findings suggest that small amounts may be beneficial.
The current limit of selenium in drinking water is 0.01 mg/1. Concentrations of
selenium ranging from 0.003' to 0.07 mg/1 have been found in water supply
systems in'the United States.[2]
Some soils, particularly in South Dakota and Wyoming, contain excessive
amounts of selenium. Irrigation return flows from these soils may contain
undesirably high levels of contamination. Selenium pollution may also result
from industrial manufacture of paint, dye, insecticide and rubber.
Prior to selection of a treatment process for removal of selenium, the form
of the contaminant should be identified. The two forms, selenium IV (selenite)
and selenium VI (selenate*), require significantly different treatment methods for
i - :
effective removal. Refer to Table 9 [3, 5] for appropriate processes for removal
of selenium.
Alum and ferric sulfate coagulation, and lime softening* are only
moderately effective on the removal of selenium IV from water. [5] Of these
three methods, tests indicate that ferric sulfate coagulation is the most effective
for removal of selenium IV. The best removal was achieved at the low pH of
5.5 and a trend of decreasing removal with increasing pH was observed.
Tests have shown that alum, ferric sulfate and ferrous sulfate coagulation,
and lime softening are ineffective methods for selenium VI removal from
drinking water. As indicated in Table 9, reverse osmosis and ion exchange are
effective methods for removing both forms of selenium.
j. Silver. A study of the toxic effects of silver added to drinking water
of rats showed pathologic charges in kidneys, liver, and spleen. [1] The
maximum allowable level of silver in drinking water is 0.05 mg/1. Concentra-
tions of silver ranging from 0.0 to 0.03 mg/1 have been found in treated water
supply systems in the United States. 12] Table 10 [3,5] lists unit processes and
their effectiveness for removing silver from water supplies.
111-15
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Table 9
PROCESSES FOR SELENIUM REMOVAL
Unit Process* Per Cent Removal
For selenium IV:
Coagulation, Sedimentation,
., and Filtration 10—85
Softening 20—45
For selenium VI:
Coagulation, Sedimentation,
and Filtration 0-10
Softening 0—10
For either or both selenium forms:
Reverse Osmosis' 90-97
Electrodialysis** 80
Ion Exchange - 95
•Additional process information is discussed in the text preceding this table.
•Predicted but not experienced, [3]
Table 10
PROCESSES FOR SILVER REMOVAL
Unit Process* Per Cent Removal
*-
Coagulation, Sedimentation,
and Filtration 70-90
Lime Softening 70—90
Reverse Osmosis** 90—97
Electrodialysis** 80
Ion Exchange** 95
~Additional process information is discussed in the text
following this table.
~ ~Predicted but not experienced. [3]
IIW6
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Both alum and ferric sulfate coagulation are effective in removing silver
from drinking water.[5] Alum coagulation removals are pH dependent; above a
pH of 8, removals decreased with increasing pH. Both ferric sulfate and lime
softening removals increase as the pH is increased.
2. Organic Chemicals
The organic chemicals included in the National Interim Primary Drinking
Water Regulations can be divided into two classifications; (a) chlorinated
hydrocarbon insecticides and (b) chlorophenoxy herbicides. The insecticides
consist of endrin, lindane, methoxychlor and toxaphene; the two herbicides
included are 2, 4—D and 2, 4, 5—TP (Silvex).
a. Chlorinated Hydrocarbon Insecticides. Manufactured by numerous
companies, these synthetic organic insecticides are widely used, are long-lasting
in the environment and are very toxic to humans. The symptoms of poisoning,
regardless of the compound involved, are similar. When chlorinated hydro-
m
carbons are absorbed into the body, small amounts are stored in the body fat.
Long-range effects of the accumulation of these insecticides in the body are
generally unknown. If any of these complex organic compounds are ingested in
large amounts, death can result from cardiac or respiratory arrest. [ 1 ]
Maximum contaminant levels established for the chlorinated hydrocarbons
(refer to Appendix A) are listed as follows:
The 1969 National Community Water Supply Study indicated pesticide
concentrations in drinking water are generally lower than the allowable
limits.[9] Summarized in Table 11 [5] are unit processes and their effectiveness
for removing endrin from water supplies.
(a) F.ndrin
(b) Lindane
(c) Methoxychlor
(d) Toxaphene
0.0002 mg/1
0.004 mg/1
0.1 mg/1
0.005 mg/1
111-17
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Table 11
PROCESSES FOR ENDRIN REMOVAL
Unit Process
Per Cent Removal
Chlorination, 5 mg/1
Coagulation, Sedimentation,
less than 10
and Filtration
Powdered Activated Carbon*;
35
10 mg/1
20 mg/1
85
92
94
Granular Activated Carbon*,
30 nr/rn^/day (0,5 gpm/ft2) 99
~Preceded by coagulation, sedimentation and filtration.
Unit, processes applicable for lindane removal are listed in Table 12.[5]
Conventional treatment processes are ineffective for reducing lindane levels and
therefore are not included in Table 12. Oxidation is also not included in
Table 12 as experiments have shown only ozone, in uncommonly high
concentrations, to have any appreciable effect in reducing the lindane
concentration.
Table 12
PROCESSES FOR LINDANE REMOVAL
Unit Process
Per Cent Removal
Powdered Activated Carbon*:
5 mg/1
10 mg/1
20 mg/1
30
55
80
Granular Activated Carbon*,
30 m3/m2/day (0.5 gpm/ft2) 99
•Preceded by coagulation, sedimentation and filtration.
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Reverse osmosis has also been studied for lindane removal but it is currently
impractical for that purpose. 15] ¦ ¦
Treatment information is currently not available regarding removal of
methoxyehlor from drinking water. One publication [5], however, predicts that
adsorption with granular activated carbon would effectively remove this
contaminant from a water supply.
In regard to removal of toxaphene from drinking water, coagulation,
sedimentation, filtration and chlorination have proved ineffective. The
recommended treatment method for toxaphene removal is adsorption with
activated carbon. Tests have shown a powdered activated carbon dosage of
5 mg/1 to reduce toxaphene concentrations by 93 per cent.[5]
b. Chlorophenoxy Herbicides. Chemical control of aquatic vegetation is
the principal source of the chlorophenoxy herbicides in drinking water. The
two herbicides included in the drinking water regulations are 2, 4—D and 2, 4,
5—TP (Silvex). Manufactured and sold under various trade names, these
compounds have toxic properties of a generally lower order than chlorinated
hydrocarbons. [ 1 ] Nevertheless, herbicides should be used carefully so as not to
contaminate drinking water.
The maximum allowable levels of 2, 4-D and 2, 4, 5-TP (Silvex) are,
0.1 mg/1 and 0.01 mg/l, respectively. The only effective treatment process at this
time for removal of 2, 4—D is adsorption using activated carbon. Conventional
water treatment processes (coagulation, sedimentation, filtration and oxidation)
have been shown to be ineffective for 2, 4—D removal.[5] Reverse osmosis is a
potential process for removing 2, 4—D from drinking water. However, sufficient
data are not available at this time to recommend it as a practical technique.
Treatment data for the removal of *2, 4, 5—TP (Silvex) are presently not
available. It has been assumed that this herbicide would behave in a manner
similar to 2, 4. 5—T and Table 13 is a summary of expected removals.[5]
111-19
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Table 13
PROCESSES FOR 2, 4, 5-TP (SILVEX) REMOVAL*
Unit Process
Per Cent Removal
Chlorination. 5 mg/1
Coagulation and Filtration
Powdered Activated Carbon:
less than 10
65
5 mg/1
10 mg/1
20 mg/1
80
80
95
Granular Activated Carbon:
99
~Per cent removals listed have been experienced for 2, 4,
5-T and are predicted for 2, 4, 5-TP (Silvex).
3. Turbidity •
Turbidity levels of more than 1 to 5 turbidity units may cause
interference with disinfection processes. This is the major reason for the
maximum contaminant levels of one turbidity unit (monthly average) and five
turbidity units (two-day average) as stated in the National Interim Primary
Drinking Water Regulations. At the discretion of the State, a maximum of five
turbidity units (monthly average) may be allowed if the water supplier can
demonstrate that the higher turbidity does not do any of the following:
(a) Interfere with disinfection.
(b) Prevent maintenance of an effective disinfectant agent throughout the
distribution system.
(c) Interfere with microbiological determinations.
High turbidity can cause consumers to question the safety of drinking the
water.
Turbidity in water may result from suspended and colloidal matter from a
variety of sources. It may be caused by microorganisms: mineral substances;
111-20
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clay or silt and other products of natural erosion; domestic sewage or industrial
wastes; and others.
Treatment methods effective for turbidity reduction include various
combinations of the processes listed in Table 14.13]
Table 14
PROCESSES FOR TURBIDITY REMOVAL
Unit Process Per Cent Removal
Plain Sedimentation 50—95
Coagulation, Sedimentation,
and Filtration 80—99
4. Coliform Organisms
It is of the utmost importance that no pathogenic bacteria be present in
water intended for human consumption. Direct testing for pathogenic bacteria
is difficult and time-consuming, so an indirect test is utilized. A determination
is made of the presence of coliform bacteria. Although coliform bacteria are
usually nonpathogenic, under certain conditions strains of E. coli are capable of
causing disease. Under most circumstances, there are probably several thousand
coliform bacteria present for each pathogenic organism in contaminated water.
Therefore, if coliform bacteria are eliminated from a water, there should be
little concern about the water's safety from a bacteriological standpoint.
Presence in drinking water of any members of the coliform group indicates
deficiencies in treatment of the water.
The National Interim Primary Drinking Water Regulations do not contain
a single number as a limit for coliform bacteria. Maximum contaminant levels
for coliform bacteria have been established based on the frequency of sampling
and the type of test. Refer to Appendix A for coliform bacteria maximum
contaminant levels and monitoring frequency. The minimum number of
coliform test samples per month depends on the population served by the
water system; the larger the population, the greater the number of samples
111-21
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required. The range is from a minimum of one per month for a community
system which serves a population of 25 up to 11 per month for a system which
serves a population of 10,000.
Is '
The membrane filter technique is generally the recommended test method.
However, turbidity may interfere with the membrane filter technique, and the
multiple tube fermentation technique may have to be employed. When the
membrane filter test is used for a facility serving a population of 25 to 10,000,
the maximum number of coliform bacteria shall not exceed any of the
following:
(a) One per 100 ml as the arithmetic mean of all samples examined per
month.
(b) Four per 100 ml in more than one sample per month when less than
20 samples are examined per month. •
(c) Four per 100 ml in more than five per cent of the samples when 20
or more are examined per month.
If the multiple tube fermentation technique is used, two standard portion sizes
may be used in the test. When 10 ml standard portions are used, coliform bac-
teria shall not be found in any of the- following;
(a) More than 10 per cent of the portions in any month.
(b) Three or more portions in more than one sample when less than 20
samples are examined per month.
(c) Three or more portions in more than five per cent of the samples
when 20 or more samples are examined per month.
When 100 ml standard portions are used, coliform bacteria shall not be found
in any of the following:
(a) More than 60 per cent of the portions in any month.
,(b) Five portions in more than one sample when less than five samples
are examined per month.
III-22
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(c) Five portions in more than 20 per cent of the samples when five or
more samples are examined per month. v ;
Bacteria in water. sources are primarily the result of organic waste
pollution. Sources of this waste include decaying vegetative matter, decaying
animal wastes, wastes from food processing plants, untreated sewage and others.
In addition to direct contamination, bacteria may be transported to water by
air dispersion, birds, and other animals including man.
Disinfection is the primary process for the elimination of bacteria from
water. This and other methods of bacterial reduction are listed in Table 15.[3]
Table 15
PROCESSES FOR BACTERIA REDUCTION
Unit Process Per Cent Removal
Chlorination 99
Ozonation 99
Chlorine Dioxide 99
Sedimentation* 0-99
Coagulation* Significant amounts
Filtration* 0-99
*These methods do not, in themselves, provide adequate
bacterial reduction. However, their use prior to disinfec-
tion may significantly lower the costs associated with
disinfection.
5. Radiological
Any dose of ionizing radiation may produce harmful effects to human
health. Both short term and long term damage to human tissue may result from
radioactive contamination. Even if exposure is slight, there may be genetic-
changes or a cancer may develop.
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Radioactivity in public water systems may be generally grouped as
naturally -occurring' or man-made. Radium-226 is the most important of the
naturally occurring radionuclides likely to occur in public water 'systems.
Radium is distributed throughout the United States, particularly in midwestern
and Rocky Mountain states. Usually found only in ground water, radium may
occasionally be found in surface water due to man's activities. In contrast to
radium, man-made radioactivity usually occurs in surface water. Sources of
man-made radioactivity, in addition to fallout from nuclear weapons testings,
are small,, releases from nuclear power plants, hospitals, and scientific and
industrial users of radioactive materials. Maximum contaminant levels for
radioactivity in water supply systems are summarized in Table 16.[3] Refer to
Appendix A for the radionuclide regulations as published in the Federal
Register. ¦
Table 16
MAXIMUM CONTAMINANT LEVELS FOR RADIOACTIVITY
Maximum Allowable
Constituent Level
Combined radium—226 and radium—228 5 pCi/1
Gross alpha particle activity
(including radium—226 but excluding
radon and uranium) 15 pCi/1
Beta particle and photon radioactivity
from man-made radionuclides* 4 mrem/yr
•Based on a 2 liter per day drinking water intake except for tritium and
¦ strontium -90. Average annual concentrations of tritium and strontium -90
assumed to produce a dose of 4 mrem/yr are 20,OCX) and 8 pCi/I, respectively.
Virtually all water sources contain radium, a product of uranium, in trace
amounts. Studies indicate the occurrence of radium-226 in United States
treated water supplies ranges from 0.0 to 135.9 pCi/1. [2 J Also important in
health considerations, strontium -90 concentrations in public water supplies are
about 1.0 pCi/1. based on available data. Remedial measures for excessive
radioactivity in drinking water supplies include dilution of the contaminated
water, change of source, and treatment of the contaminated water. If treatment
111-24
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for removal of radionuclides is necessary, conventional methods are usually
effective'. Listed in Table 17 [5]are various radionuclides and their removal
methods and efficiencies.
Table 17
PROCESSES FOR RADIONUCLIDE REMOVAL
Radionuclide Removal Method Per Cent Removal
Radium Ion Exchange Softening 70-98
Coagulation, Sedimentation,
and Filtration 25
Lime or Lime-Soda Softening 70—90
Reverse Osmosis 95
Beta and Photon Emitters* Lime Softening 87—96
Ion Exchange Softening 75—96
Reverse Osmosis 90—97
"Removal dependent on specific radioisotope present.
6. Stabilization
While stabilization of water is not directly addressed in the Interim
Primary Drinking Water Regulations, it is implied because the maximum
contaminant levels for inorganic chemicals are at the consumer's tap. Thus, if
the water leaves the treatment plant with all contaminants below their
respective maximum contaminant levels, but samples from the distribution
system show values above those maximum contaminant levels, then the water
quality is in violation of, the regulations. Corrosive water can cause
solubilization of certain contaminants listed in the Interim Primary Drinking
Water Regulations.
Cadmium is present in zinc-galvanized iron pipe and may be dissolved by .
corrosion. Corrosive water standing in lead pipes can, under certain conditions,
solubilize enough lead to exceed the MCL.
111-25
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• A noncorrosive water may be maintained throughout the distribution
system -in two ways: (1) by maintaining calcium carbonate saturation
equilibrium with appropriate pH control, and (2) by introducing additives such
as phosphates or silicates. In both cases, a thin protective film is formed on the
interior of the piping, thus protecting it from corrosion,
B. SECONDARY DRINKING WATER REGULATIONS
While primary regulations apply to trace elements, compounds, and
microoganisms affecting the health of consumers, secondary regulations deal
with: the aesthetic qualities of drinking water. The contaminants included in
these secondary regulations do not have a direct impact on the health of
consumers. However, if present in excessive amounts, these contaminants may
affect the palatability of the water and encourage the use of possibly unsafe
water.
In contrast to primary drinking water regulations, the secondary
regulations are not Federally enforceable. As guidelines for suppliers of water,
these regulations are meant to be used to improve the quality of water
delivered. The secondary drinking water regulations contain recommended
maximum contaminant levels for various inorganic chemicals and physical
quality characteristics of drinking water. The USEPA has published Proposed
National Secondary Drinking Water Regulations (Federal Register, Vol. 42,
No. 62, March 31, 1977, see Appendix B). The following substances are
included:
1. Chloride
Chloride in concentrations above 250 mg/1 causes a salty taste in water
which is objectionable to many people.[ 11 ] In addition to adverse taste effects,
significant increases in customer costs due to deterioration of plumbing and
water heaters may be encountered at chloride levels of 500 mg/1. Excessive
chloride levels are most often found in highly mineralized ground water. The
occurrence of chloride in United States drinking water supplies ranges from 1
10-26
-------
to 1.950 rag/1.[2] Chloride is not significantly affected by conventional
treatment processes. Reverse osmosis or electrodialysis can effectively remove
chloride from drinking water. ;
. H
2. Color
Color in drinking water becomes objectionable and unaesthetic to most
people at levels above 15 color units. [ 11 ] The level of this substance does not
directly indicate the safety of a drinking water supply. However, highly colored
water indicates the potential presence of industrial or domestic wastes as well
as mineral or organic materials. Iron and manganese compounds are minerals
which can impart undesirable colors to water. Humus, peat, algae, weeds and
protozoa are examples of organics which contribute color to water. Some
industries whose processes generate color are mining, explosives production,
refining, pulp and paper manufacture, and chemical production.
Selection of a treatment method for removal of color is dependent on the
nature of the substances causing the color. Treatment methods and removal
efficiencies are listed in Table 18.[3]
Table 18
PROCESSES FOR COLOR REMOVAL
Unit Process* Per Cent Removal
Coagulation 95
Filtration 50—95
Reverse Osmosis 99
Ion Exchange 100
Activated Carbon 100
•Additional process information is included in the
following text.
With alum coagulation the best removal is usually achieved with a pH
range of 4 to 6.[2] However, for minimum solubility of the coagulant, the pH
111-27
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should be adjusted to greater than 6 prior to filtration. Color coagulation can
also be achieved with magnesium hydroxide at a pH greater than 11.0. The per
cent removal stated in Table 18 for reverse osmosis applies to all color
producing materials with molecular weights greater than 200. Ion exchange, as
listed in Table 18. applies to the use of special resins for the removal of organic
dye wastes, humates and ligates. The per cent removal listed for activated
carbon in Table 18 is for noncolloidal, soluble, aromatic-structured color
sources.
3. Copper
The proposed maximum contaminant level of 1.0mg/l for copper was
recommended because copper imparts an undesirable taste to drinking water.
Large doses of copper may produce nausea and prolonged ingestion may result
in liver damage.[ 11 ] Small amounts of copper, however, are generally
considered nontoxic. In fact, copper is an essential element in human
metabolism.
In water supplies tested across the United States, copper was found in
concentrations ranging from 0.0 to 8.35 mg/1. [ 21 Copper occurs naturally in
surface waters. Other sources of copper pollution include the corrosive action
of water in copper and brass tubing, industrial effluents and the use of copper
compounds for control of algae. Copper salts are used in fungicides, insecticides
and various industrial processes -such as textile manufacture, tanning,
photography, and electroplating.
Removal of copper from drinking water supplies can be accomplished by
the treatment methods listed in Table 19,[3]
4. Corrosivity
Corrosion causes various problems in the water distribution system,
including tuberculation, leaks, main ruptures, discoloration and loss of chlorine
residual. Corrosion is also responsible for an increase in concentrations of trace
metals, such as lead, cadmium, iron and copper, as the corrosion damages
service lines and household plumbing.
111-28
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Table 19
PROCESSES FOR COPPER REMOVAL
Unit Process Per Cent Removal
Coagulation, Sedimentation,
and Filtration *
Softening *
Reverse Osmosis 90-97
Electrodialysis 80
Ion Exchange 95
Stabilization** 100
*Will reduce copper centration below MCL. [12]
""Applies only to prevention of corrosion of copper piping
materials in the distribution system.
Corrosivity is related to pH, alkalinity, dissolved oxygen, total dissolved
solids and other factors. Therefore a straight-forward maximum contaminant
level has not been proposed.
The adverse effects of corrosion are primarily economic. Therefore, the
cost of corrosion control could be offset by the savings from damage
prevented. Refer to section III A6, Stabilization for a discussion of methods
for controlling corrosion.
5. Foaming Agents
Foaming is an undesirable property of drinking water because it is
aesthetically displeasing and is often associated with contamination. Many
substances in water will cause foam when the water is agitated or air is
entrained. The major class of substances which produce foaming is the anionic
surfactant. Contamination of drinking water supplies by this surfactant results
from household and industrial synthetic detergent pollution.
111-29
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Concentrations of anionic surfactants found in drinking waters have ranged
from 0 to. 2.6 mg/1 in well water supplies and from 0 to 5 mg/1 in surface water
supplies. [ 11] A proposed maximum contaminant level of 0.5 mg/1, as
methylene blue, active substances, was chosen to prevent the occurrence of
visible foam. The treatment method for removal of foaming agents is
adsorption by activated carbon. Removal efficiency ranges from 90 to 100 per
cent [3]
6. Hydrogen Sulfide
Hydrogen sulfide in drinking water often produces very obnoxious odors
characteristic of "rotten eggs". Corrosion of ferrous metals in well pump
assemblies and filters and corrosion of concrete holding and distribution
facilities occurs when hydrogen sulfide levels exceed 0.5 mg/1. [11] Hydrogen
sulfide is often caused by microbial action on organic matter or reduction of
sulfate ions to sulfide by bacteria and can be found in both ground and surface
waters. In addition to its offensive odor and corrosive tendencies, hydrogen
sulfide in association with soluble iron produces black stains on laundered items
and black deposits on piping and fixtures.
Hydrogen sulfide odor is usually identifiable at concentrations of a few
hundredths of a milligram per liter. The proposed maximum level for hydrogen
sulfide is 0.05 mg/1. Treatment methods for removal of hydrogen sulfide from
drinking water include aeration, which is usually not sufficient by itself,
followed by chemical oxidation. For waters with a constant hydrogen sulfide
odor, aeration may produce a fine elemental sulfur precipitate which will
require coagulation, sedimentation and filtration for removal.
7. Iron
Iron is a highly objectionable constituent of water supplies. It may impart
brownish discolorations to laundered goods or a bitter or astringent taste to
water. The proposed maximum level of iron in drinking water is 0.3 mg/1.
Normal diets contain 7 to 35 mg per day and average 16 mg.[ 11 ] Therefore,
the amount of iron permitted in water is small compared to the amount
111-30
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normally consumed and does not have toxicological significance. Sources of
iron pollution include iron-bearing ground water, acid mine drainage,
iron-bearing industrial wastes and corrosion of iron and its alloys. The
concentration of iron in .well-aerated. surface water is usually low. Treatment
methods for iron removal are listed in Table 20.[3]
Table 20
PROCESSES FOR IRON REMOVAL
Unit Process Per Cent Removal
Oxidation
Reverse Osmosis
Electrodialysis
Ion Exchange
Diatomite Filtration
i
Stabilization**
Coagulation, Sedimentation,
and Filtration
'Additional process information is included in the
following text.
**Applies only to prevention of corrosion of iron piping
materials in the distribution system.
***Will reduce iron concentration below MCL. [12]
90-99
80
95
*
100
* **
For a detailed discussion of oxidation methods for. iron removal, refer to
section IV A2, Oxidation. Diatomite filtration can lower iron levels to 0.1 mg/1,
if accompanied by preaeration and alkalinity adjustment. [3]
8. Manganese
As for iron, the principal reason for. limiting this element is to prevent
brownish stains in laundered goods and adverse taste effects in drinking water.
From the health standpoint, there are no data to indicate at what level
III-31
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manganese would be harmful when ingested; the daily intake of manganese
from a normal diet is about 10 mg. [11]
Manganese concentrations in well-aerated surface waters are rarely over
1.0 mg/l.[3] Deep reservoirs can have undesirable concentrations of manganese
in lower portions of the reservoir where reducing conditions prevail. This
manganese can cause problems if the water supply intake is located in the deep
portion of the reservoir or can cause problems for higher intakes during
turnover.* In ground water with reducing conditions, high concentrations of
manganese may be leached from mineral deposits. Manganese frequently
accompanies iron in such ground waters. In addition, manganese is used in the
manufacture of paints, steel, glass, and various other materials. It is also used in
agriculture to enrich manganese deficient soils and may enter water supply
sources through runoff.
The proposed maximum contaminant level for manganese is 0.05 mg/1.
Applicable unit processes for removal of manganese are shown in Table 21.[3]
Table 21
PROCESSES FOR MANGANESE REMOVAL
Unit Process Per Cent Removal
Oxidation
Reverse Osmosis
Electrodialysis
Ion Exchange
Diatomite Filtration
Softening
•Additional process information is included in the follow-
ing text,
"•Will reduce manganese concentration below MCL. [12]
*
90-99
80
95
*
**
111-32
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For a detailed discussion of oxidation methods for manganese removal,
refer to section IV A2, Oxidation. Manganese removal, with preoxidation, to
0.05 mg./l is possible with diatomite filtration.[3] 1
9. Odor
Odor is an important aesthetic quality of water for domestic use. It is
impractical and often impossible to isolate and identify the odor-producing
chemical. Therefore, the senses of smell and taste are used to evaluate odors
and tastes. In most cases, sensations ascribed to the sense of taste are actually
odors.
Undesirable odors in water are caused by vapors from various chemicals
including halogens, sulfides, ammonia, turpentine, phenols, cresols, picrates,
various hydrocarbons and unsaturated organic compounds. Natural waters may
0
be contaminated with odor producing compounds from weeds, bacteria, fungi,
actinomycetes, algae and decaying animal matter. Sewage and industrial wastes
may also contribute odorous compounds to water supplies. In addition, some
inorganic substances, such as metal ions, impart taste and odor to water.
The proposed maximum contaminant level for odor is a Threshold Odor
Number (TON) of 3. For water, the TON is the dilution factor required before
the odor is minimally perceptible. Treatment methods for odor removal include
aeration, activated carbon, ozonation, superehlorination, chlorine dioxide, and
potassium permanganate. Laboratory tests are required to determine the removal
effectiveness of each unit process.
10. pH
The proposed range for pH has been set at 6.5 to 8.5, the lower level to
prevent appreciable corrosion and the higher level to prevent encrustation, taste
and reduced chlorine efficiency. However, the impact of pH in any one water
system will vary with the overall chemistry of the water. Thus, a higher or
lower pH range may be appropriate under specific conditions. Midwest waters,
for example, are usually adjusted during softening to one pH unit above the
Langelier stability pH, usually in the low 9's. Chemical addition of lime, soda
111-33
*
-------
ash or caustic soda is used to increase pH of a water supply; to decrease ,pH,
carbon dioxide, sulfuric acid or hydrochloric acid may be added during the
treatment process.
11. Sulfate
At concentrations above 250 mg/1. sulfates create taste problems; above
600 mg/1, they may have a laxative effect. [11] In addition, high
concentrations of sulfate contribute to the formation of scale in boilers and
heat exchangers.
Sulfates may enter water sources from tanneries, sulfate-pulp mills, textile
mills, and other plants that use sulfate or sulfuric acid. Leachings from gypsum
and other common minerals may contaminate sources of water supply. Also,
oxidation of sulfides, sulfites, and thiosulfates in surface water yield sulfates.
Concentrations of sulfates in United States water supplies range from less
than 0.1 to 770 mg/1.[2] The proposed maximum level of sulfate is 250 mg/1.
Treatment methods for sulfate are listed in Table 22. [3]
Table 22
PROCESSES FOR SULFATE REMOVAL
Unit Process Per Cent Removal
Reverse Osmosis 99
Electrodialysis • 80
Ion Exchange 95
12. Total Dissolved Solids (TDS)
TDS may influence the acceptability of water and a high concentration is
often associated with excessive hardness, taste, mineral deposition or corrosion.
The proposed MCL for TDS is 500 mg/1. Applicable treatment methods for
TDS removal are listed in Table 23 .[13]
III-34
-------
Table 23
PROCESSES FOR TOTAL DISSOLVED SOLIDS REMOVAL
Unit Process*
Per Cent Removal
Chemical Softening
Reverse Osmosis
Electrodialysis
Ion Exchange
80-99
50-90
up to 99
* Additional process information is included in the following texl.
**See text.
The TDS removal by chemical softening is dependent upon the amount of
hardness removed and the relationship between hardness and TDS in the raw
water. A recent publication [ 14] recommended that ion exchange be
considered for TDS removal if the maximum raw water TDS concentration is
less than 2,000 rng/1. Similarly, the application range for electrodialysis and
reverse osmosis is a TDS concentration of 1,000 to 5,000 mg/1 and 1,000 to
10,000 mg/1, respectively. If the maximum TDS level falls within the range of
more than one of these processes. 1,500 mg/1 for example, then an economic
comparison should be used to select a specific treatment method.
Zinc is an essential and beneficial element in human metabolism; the daily
adult human intake averages 10—15 mg.[ 11 ] Zinc in water does not cause
serious adverse health effects but does produce undesirable aesthetic effects. At
concentrations of 5 mg/1, zinc can impart an objectionable taste to water.
Soluble zinc salts, at 30 mg/1, give a milky appearance to water and at 40 mg/1,
they impart a metallic taste.
industrial uses of zinc salts which may contaminate water sources include
the manufacture of dyes, pigments, insecticides and the galvanizing process.
13. Zinc
III-35
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Zinc is rarely found above the trace level in natural waters. Zinc has been
found to occur in United States water supplies in concentrations ranging from
Oto 13 mg/l,[2J The proposed maximum level of zinc is 5 mg/1. Unit processes
applicable for zinc removal are shown in Table 24. [3]
Table 24
PROCESSES FOR ZINC REMOVAL
Unit Process Per Cent Removal
Reverse Osmosis
Electrodialysis
Ion Exchange
Stabilization"'
Softening
•Applies only.to prevention of corrosion of zinc piping
materials in the distribution system.
**Will reduce zinc concentration below MCL. [12]
90-97
80
95
100
111-36
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REFERENCES
1. U.S. Environmental Protection Agency, Statement of Basis and Purpose
for the National Interim Primary Drinking Water Regulations.
2. Floyd B, Taylor, "Trace Elements and Compounds in Waters," Jour
A WW A, 63(1l);728-733 (November, 1971).
3. David Volkert and Associates, Monograph of the Effectiveness and Cost of
Water Treatment Processes for the Removal of Specific Contaminants,
68-01-1833, U.S. Environmental Protection Agency (August, 1974).
4. Ervin Bellack, "Arsenic Removal from Potable Water," Jour AWWA,
63(7):454-458 (July, 1971).
5. U.S. Environmental Protection Agency, Manual of Treatment Techniques
for Meeting the Interim Primary Drinking Water Regulations, May, 1977.
6. G. F. Craun and L. J. McCabe, "Problems Associated with Metals in
Drinking Water," Jour A WWA, 67(11):593-599 (November, 1975).
7. American Water Works Association, Water Quality and Treatment,
3rd edition, McGraw-Hill, New York. 1971.
8. R, D. Scott, et al, "Fluorides in Ohio Water Supplies," Jour AWWA,
29(9):9-25 (September, 1937).
9. L. J. McCabe, et al, "Survey of Community Water Supply Systems," Jour
AWWA, 62(11):670 (November, 1970).
10. Illinois Environmental Protection Agency, Determination of Radium
Removal Efficiencies in Water Treatment Processes for Small and Large
Populations, USEPA (May. 1976).
11. U.S. Environmental Protection Agency, Statement of Basis and Purpose
for the Secondary Drinking Water Regulations.
12. Y. H. Lin and J. R. Lawson, "Treatment of Oily and Metal-Containing
Wastewater ."Pollution Engineering, 5( 11):47 (November, 1973).
111-37
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REFERENCES (Continued)
13. Black & Veatch, Water Management Guidelines for Saudi Arabian Military
Installations, U.S. Army Corps of Engineers (January, 1977).
14. U.S. Department of the Interior, Office of Saline Water and U.S. Bureau
of Reclamation, Desalting Handbook for Planners, 1972.
f
111-38
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BIBLIOGRAPHY
American Water Works Association, Water Quality and Treatment, 3rd edition,
McGraw-Hill, New York, 1971.
Bellack, Ervin, "Arsenic Removal from Potable Water," Jour AWWA,
63(7):454-458 (July, 1971).
Black & Veatch, Water Management Guidelines for Saudi Arabian Military
Installations, U.S. Army Corps of Engineers, January, 1977.
Clark, Viessman and Hammer, Water Supply and Pollution Control, 2nd edition,
International Textbook, Scran ton, 1971.
Craun, G. F. and McCabp, L. J., "Problems Associated with Metals in Drinking
Water," Jour AWWA, 67(11):593-599 (November, 1975).
Culp, Gordon L. and Gulp, Russell L., New Concepts in Water Purification, Van
Nostrand, New York, 1974.
David Volkert and Associates, Monograph of the Effectiveness and Cost of
Water Treatment Processes for the Removal of Specific Contaminants,
68-01-1833, U.S. Environmental Protection Agency, August, 1974.
Lin, Y. H. and Lawson, J. R., "Treatment of Oily and Metal-Containing
Wastewater," Pollution Engineering, 5(11):47 (November, 1973).
McCabe, L. J., Et Al, "Survey of Community Water Supply Systems," Jour
AWWA, 62(11):670 (November, 1970).
Taylor, Floyd B., "Trace Elements and Compounds in Waters," Jour AWWA,
63(11):728-733 (November, 1971).
U.S. Department of the Interior, Office of Saline Water and U.S. Bureau of
Reclamation, Desalting Handbook for Planners, 1972.
Scott, R. D., et al, "Fluorides in Ohio Water Supplies," Jour AWWA,
29(9):9-25 (September, 1937).
111-39
i
-------
BIBLIOGRAPHY (Continued)
U.S. Environmental Protection Agency, Manual of Treatment Techniques for
Meeting the Interim Primary Drinking Water Regulations, May, 1977.
U.S. Environmental Protection Agency, Statement of Basis and Purpose for the
National Interim Primary Drinking Water Regulations.
U.S. Environmental Protection Agency, Statement of Basis and Purpose for the
Secondary Drinking Water Regulations.
Weber, Walter J., Physicochemical Processes for Water Quality Control,
Wiley-Interscience, New York, 1971.
111-40
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IV. WATER TREATMENT FACILITIES
Various types and combinations of treatment units are used to produce
water suitable for human use. The quality of the source and the quality goals
for the finished water form the basis for selecting a method of treatment.
Finished water quality goals are given in the preceding section; the means of
achieving them will be discussed subsequently.
A. UNIT PROCESSES
Selection of water treatment processes is based on the contaminants to be
removed. A variety of unit processes may be required for treatment of the
contaminants listed in Section III. Necessary unit processes are generally the
same for large or small treatment plants, only scaled down for small facilities.
Exceptions to this general rule are discussed where this is not true and a
recommendation is given as to the process most applicable to small water
treatment systems, This section will, therefore, emphasize the unit processes
specifically applicable to water treatment systems serving a population of 25 to
10,000. All design parameters are in terms of plant capacity as opposed to
average daily flow.
1. Aeration
As applied to water treatment, the term aeration refers to processes by
which water and air are brought into contact with each other for the purpose
of transferring volatile substances to or from the water. These volatile
substances include oxygen, carbon dioxide, nitrogen, hydrogen sulfide, methane
and unidentified organic compounds responsible for tastes and odor. Aeration is
not needed at all water treatment plants and a decision as to whether to aerate
or not requires careful assessment of the economic and water quality benefits
achieved by its use.
The water source is an important selection factor. Surface waters usually
exhibit low concentrations of carbon dioxide, no hydrogen sulfide and fairly
IV-1
-------
high dissolved oxygen. Consequently, aeration is not required for the removal
or addition of these gases. However, many surface waters do contain traces of
volatile organic substances that cause taste and odor problems. While the
aeration process is a means of volatile organic matter reduction, conventional
aeration systems are not particularly effective because of the low volatility of
most taste-and-odor producing compounds. Aeration of surface waters usually
cannot be justified on economic grounds.
Ground waters may contain excessive carbon dioxide, methane, hydrogen
sulfide, iron, or manganese concentrations. At lime-soda water softening plants,
any carbon dioxide dissolved in the water at the point of lime application will
consume lime without accompanying softening. For high (>50 mg/1) carbon
dioxide concentrations, as encountered in some ground waters, aeration for its
removal is probably justified. For concentrations on the order of 10 mg/1 or
less, aeration is probably not economically valid. Before a decision to aerate for
carbon dioxide removal, the cost of maintaining and operating the aerator
should be compared to the value of the lime saved and the additional sludge
disposal cost.
Aeration will remove methane, a potentially explosive gas sometimes
encountered in fairly high concentrations in ground water. Methane removed in
appreciable quantities can pose an explosion hazard unless properly disposed.
Aeration is often used for removing hydrogen sulfide from water. It is
effective if the hydrogen sulfide concentration is not more than about 1.0 or
2.0 mg/1. Higher concentrations may require special provisions, such as
prolonged aeration with diffused air or initial aeration in an atmosphere
containing a higher than normal concentration of carbon dioxide followed by a
standard aeration process. Such an atmosphere reduces pH, thus releasing the
H2S form of the sulfide and promotes its removal by aeration.
Ground waters are usually deficient in oxygen and aeration is an effective
means of adding it. Oxygen addition is desirable if iron and manganese removal
is a treatment objective. This is discussed in detail in section IV A2, Oxidation.
The three methods of aeration employed in small water systems
are a) gravity, b) mechanical draft, and c) diffused aeration.
IV-2
-------
a. Gravity Aeration. Various types of gravity aerators have been used in
the water treatment industry. The most practical method of gravity aeration for
small water treatment systems consists of a stack of multiple trays which are
often filled with contact media. Water flows by gravity over the layers of media
and trays. The use of mechanical draft aeration with this method of gravity
aeration is discussed in the following subsection. Information on media and trays
is also included.
b. Mechanical Draft Aeration. This aeration system consists of a tower
through which water droplets fall and air ascends in countercurrent. flow. The
tower usually is made up of a series of trays with wire-mesh, slat or perforated
bottoms over which the water is distributed. In most aerators, coarse media
such as coke, stone or ceramic balls 5 to 15 cm (2 to 6 in) in diameter are
placed in the trays to increase efficiency. Coarse media are especially efficient
when the removal of iron and manganese is of importance. The media becomes
coated with precipitated oxides of iron and manganese, which serve as catalysts
for continuing oxidation reactions. A small basin is often constructed below the
aeration unit to allow entrained air to dissipate. The depth of this basin is
usually 1.8 m (6 ft); the width and length are frequently the same as those of
the aeration unit in question.
Design criteria for mechanical draft aerators are dependent on the type
and concentration of the contaminant involved. In aeration towers, five to
fifteen trays spaced vertically 30 to 76 cm (12 to 30 in) apart are frequently
used. Area requirements for the trays vary from 5.6 to 17.9 cm" per m /day (23
to 73 ft^ per mgd); most require less than 7.3 cm^ per m^/day (30 ft^ per
mgd). Selection of specific design criteria is usually a joint decision by the
manufacturer and engineer. Mechanical draft aeration equipment, of interest for
'S
this report, is available in various capacities ranging from 218 to 5,450 m /day
(40 to 1,000 gpm).
c. Diffused Aeration. Diffused aeration units generally consist of
rectangular basins with d iff user equipment located near the bottom. The
diffusers distribute compressed air into water through orifices or nozzles in air
piping, diffuser plates or tubes. Basins are frequently 2.7 to 4.6 m (9 to 15 ft)
deep and 3.1 to 9.2 m (10 to 30 ft) wide. Ratios of width to depth should not
exceed 2:1 to insure effective mixing. The length of the basin is governed by
the desired retention period, usually 10 to 30 minutes.
0
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The amount of air required depends on the purpose, of aeration, but
generally ranges from 0.075 to 1.12 m^ of air per (0.01 to 0.15 fP of air
per gal) of water treated. . - . ..
Diffused air treatment units conserve the hydraulic head and are not
subject to freezings but require more space than tray aerators. To prevent odor
problems, both types of aeration may require housing if hydrogen sulfide is
being removed. '
d. Applicability and Recommendations. Aeration is recommended as a
treatment process for carbon dioxide, hydrogen sulfide, and odor removal and
as an aid in iron and manganese removal. The decision to use aeration as a
treatment process and selection of the type of aeration to employ must be
based on the quality of the source of water supply and the contaminants to be
removed. An economic analysis should be made to decide between gravity,
mechanical draft, and diffused aeration. Mechanical draft aeration is limited in
applicability to the sizes of aerators manufactured. Diffused* aeration is
generally not economically desirable for small water treatment systems.
However, if diffused aeration can also serve as a chemical mixing unit as well as
an aeration system, then the economics may favor this system.
2. Oxidation
Water treatment utilizes oxidation for various purposes. A number of
oxidants can be used to remove or destroy undesirable tastes and odors, to aid
in the removal of iron and manganese, and to help improve clarification and
color removal. Oxygen, chlorine, and potassium permanganate are the most
frequently used oxidizing agents and each is discussed in following sections.
a. Air. Aeration is used as a method of adding oxygen to water for
oxidation of iron and manganese. For precipitation of 1 mg/1 of iron," 0.14 mg/1
of oxygen is required, and 0.24 mg/1 of oxygen is required for precipitation of
1 mg/1 of manganese. Soluble iron is readily oxidized by the addition of oxygen,
but manganese cannot be oxidized as easily. However,'oxidation of manganese
'is encouraged if the aeration step provides contact between water and previously
precipitated manganese oxide, such as occurs in certain gravity and mechanical
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draft aerators. Media in these units become manganese-coated and catalytic
oxidation of manganese occurs, particularly when the pH has been increased to
greater than 8.5, If the level of manganese to be removed is high, aeration
processes are usually designed to only initiate oxidation of the manganese. More
effective chemical oxidation is then used to achieve acceptable levels of man-
ganese.
Oxidation of organic substances responsible for undesirable tastes and
odors using aeration is usually too slow to be of value. However, if dissolved
gases such as hydrogen sulfide are the cause of taste and odor problems,
aeration will effectively remove them through oxidation and stripping.
b. Chemical. Oxidizing chemicals commonly used in water treatment
include chlorine, chlorine dioxide, ozone and potassium permanganate. Chlorine
and potassium permanganate are the most frequently used chemical oxidants.
Ozone and chlorine dioxide require on-site generation and are relatively
expensive. Compared to air, chemicals are much stronger oxidizers, therefore
more effective. The respective costs for aeration versus chemical oxidation must
be compared with the benefits received before a choice of which process to use
can be made.
Chlorine, chlorine dioxide and potassium permanganate act effectively as
oxidizing agents in destroying taste and odor producing compounds. They also
readily oxidize soluble iron and manganese to insoluble oxides. The oxides of
iron and manganese are then removed by coagulation, sedimentation and
filtration. Difficulties with clarification or color removal which may arise from
dissolved organic compounds often can be reduced by the use of chlorine,
chlorine dioxide and potassium permanganate. They are added to oxidize
interfering organic matter.
Although relatively effective for iron oxidation, chlorine requires longer
contact time than potassium permanganate to effectively oxidize manganese at
levels greater than 0.2 mg/1. Theoretical amounts of chlorine required are
0.64 mg/1 per 1.0 mg/1 of iron and 1.3 mg/1 per 1.0 mg/1 of manganese. In
practice, higher values are used to increase the rate of reaction and provide
chlorine for competing reactions. The rate of manganese oxidation by chlorine
is dependent on pH, chlorine dosage, mixing conditions and other factors. High
pH values favor oxidation of manganese.
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One main advantage of potassium permanganate oxidation is the high rate
of reaction, many times faster than chlorine. Also, potassium permanganate
differs from chlorine in that it does not form additional products that might
intensify odors normally present. Potassium permanganate is not as pH
dependent as chlorine, although the permanganate does react more rapidly as
pH increases. Theoretically, 0.94 mg/1 of potassium permanganate will oxidize
].0mg/l of iron,and 1.92 mg/1 of potassium permanganate will oxidize 1.0 mg/1
of manganese. In actual practice, the amount of permanganate required is
usually less than the theoretical amount. One method of determining the
optimum dose of permanganate is to observe the color of the water after
application of the oxidant. If a slight pink color persists for a minute or two,
the dose is said to be optimum.
As these oxidation processes .are not instantaneous, it is desirable to add
the oxidant, whether chlorine, chlorine dioxide or potassium permanganate, as
early as possible in the treatment process. Early addition of chlorine in the
treatment process is inconsistent with prevention of trihalom ethane formation;
therefore, KMn04 may be the oxidant of choice. The decision whether to use
chlorine or potassium permanganate for oxidation purposes must be based on
the contaminant to be removed, on an economic evaluation of the chemicals,
and tendencies toward trihalom ethane formation.
A method used for removal of iron and manganese is application of
potassium permanganate and filtration through manganese dioxide greensand.
Greensands are naturally occurring silicates of sodium and aluminum.
Manganese dioxide, an oxidizing agent, is affixed to the greensand, and water
containing iron and manganese is passed through this material The manganese
dioxide oxidizes the iron and manganese to insoluble forms which precipitate
onto the greensand filter. After the oxidizing capacity of manganese dioxide
greensand has been depleted, it is regenerated with potassium permanganate. A
modification to this process has been developed wherein the manganese dioxide
is continuously regenerated with potassium permanganate.. Potassium perman-
ganate is continuously fed to the water before entering the filter. The iron and
manganese are oxidized by the potassium permanganate and precipitated on the
filter. If too little potassium permanganate is added, the iron and manganese
are oxidized by the manganese dioxide affixed to the greensand; if too much
potassium permanganate is added, the manganese dioxide greensand is
regenerated. Thus, uniform amounts of potassium permanganate may be added
IV-6
<3
\
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to a water containing varying concentrations of iron and manganese. Where
greensand filtration is preceded by aeration, the amount of precipitated iron
influent to the greensand filter can be large. When this situation exists, a layer
of crushed anthracite coal on top of the exchange medium is sometimes used
to prolong filter runs.
c. Applicability and Recommendations. For small water treatment
systems, it is recommended that chlorine be considered before other oxidants
since chlorine will normally be used for disinfection, too. If the use of chlorine
for oxidation would not be practical, then the use of air or potassium
permanganate should be evaluated on an economic basis. Generally, aeration is
preferred to use of potassium permanganate for oxidation unless high levels of
manganese are to be removed. In that case, the use of potassium permanganate
is necessary. Also, if intermittent tastes and odors are a problem, potassium
permanganate is preferred economically to aeration. Chemical feed equipment
requires a smaller capital expenditure than aeration equipment. In addition, the
chemical oxidant would be used on an intermittent basis so operation and
maintenance costs would be at a minimum.
Oxidation is recommended as a treatment process for hydrogen sulfide
and odor removal, and as an aid in iron and manganese removal,
3. Adsorption
The most important direct applications of adsorption in water treatment
are the removal of arsenic, fluoride and organic pollutants. Basically, adsorptio"
is the attraction and accumulation of one substance on the surface of another.
Two important adsorptive media in the water industry are activated alumina,
often referred to as simply alumina, and activated carbon. Operational
characteristics and regenerative techniques will be discussed for both of these
adsorptive media.
a. Activated Alumina. Activated alumina is a highly porous and
granular form of aluminum oxide. This material is available from several
aluminum manufacturers in various mesh sizes and degrees of purity. Alumina
is used in the water treatment industry for removing arsenic and fluoride. The
treatment process consists of percolating water through a column of the
alumina media. Removal of arsenic and fluoride is accomplished by a
combination of adsorption and ion exchange.
IV-7
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An activated alumina column consists of alumina media in a contact tank.
Either gravity or pressure feed systems can be used. As far as is known, there is
very little difference between removal capabilities of these two systems. For
sizing the surface area of an alumina column, a surface loading rate of 150 to
175 m^/m^/day (2.5 to 3.0 gpm/ft^) is recommended. The volume, and thus
the depth, of media is influenced by the time between regenerations of the
alumina. It is advisable to carry out laboratory and pilot-scale studies on the
water in question to aid in actual design of the activated alumina column.
Use-.-.of the activated alumina process for the removal of arsenic and
fluoride from water is cyclic and regeneration of the alumina media is required
periodically. When the alumina columns become saturated with arsenic and
fluoride, they are regenerated by passing a caustic soda solution through the
media. Excess caustic soda is neutralized by rinsing the activated alumina with
an acid. Prior to the regeneration process, the alumina column is backwashed to
remove accumulated solids that have been strained from the water. Adequate
disposal of the regenerative chemical wash should be provided. One disposal
method which warrants consideration is lagoon evaporation. If permitted by
local conditions, neutralization of the regenerative chemical wash followed by
dilution and discharge to a sanitary sewer should also be considered. Possible
toxic effects of the removed arsenic and/or fluoride should be evaluated prior
to discharge to a sanitary sewer.
If treated water storage facilities are limited or if interruptions of other
treatment plant processes cannot be tolerated, the use of duplicate alumina
contact columns is recommended.
b. Activated Carbon. Adsorption of organic impurities using activated
carbon has been common practice in the waterworks industry for many years.
Activated carbon is especially effective as an adsorbing agent because of its
large surface area to mass ratio. Each activated carbon particle contains a
tremendous number of pores and crevices into which organic molecules enter
and are adsorbed to the activated carbon surface.
Activated carbon has a particularly strong attraction for organic molecules
and thus is well-suited for removal of hydrocarbons, control of taste and odor,
and color removal. At present, activated carbon has been used with only
limited success to remove haioform precursor compounds. Frequent regenera-
IV-8
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tion or replacement of the activated carbon would be required, as its
effectiveness in adsorbing precursor compounds is limited to only a few weeks
after being placed in use.
Excessive fluoride and un-ionized metals such as arsenic and mercury can
be removed from water by adsorption using bone char. However, if used for
arsenic removal, bone char cannot be regenerated and must be used on a
throw-away basis. .
Both the adsorptive and the physical properties of an activated carbon
medium are important. Currently, there is no direct method for determining
the adsorptive capacity of an activated carbon. Adsorptive capacities can be
approximated by the Iodine Number or the Molasses Decolorizing Index. The
Iodine Number indicates the capability of the activated carbon for removing
small molecules. The Molasses Decolorizing Index provides an indication of the
potential of the activated carbon for adsorbing large molecules.
Two types of activated carbon are used in water treatment: powdered and
granular.. Powdered activated carbon is often used for taste and odor control.
Its effectiveness depends on. the source of the undesirable tastes and;odors. This
type of activated carbon is a finely ground, insoluble black powder which can
be fed to water either with dry feed machines or as a carbon slurry. Slurry
methods are usually applicable only in large water treatment plants, therefore
will not be discussed here. The powdered carbon approach offers economic
advantages when a low or infrequent carbon usage is required to solve a specific
problem.
Powdered carbon may be added at any point in the treatment process
ahead of the filters. Actual application points vary depending on local
conditions and contaminants to be removed. Normally, application of carbon is
most effective where pH of the raw water is lowest. Adequate dispersion of the
carbon is necessary; therefore,a settling basin should not be used as a point of
application. Sufficient contact time is also necessary to ensure maximum
adsorption by the carbon. Periods of contact ranging from 15 minutes to one
hour are recommended; Powdered carbon should be applied prior to
chlorination. Compounds that have a chlorine demand will be removed by the
activated carbon; thus,* savings in chlorine will be realized. Also, activated
carbon will efficiently adsorb chlorine thus . wasting both the carbon and
chlorine.
IV-9
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Recent practice recommends the use of carbon for removal of taste and
odor producing organics prior to chlorination. This prevents the formation of
chloro-organics which are very difficult to remove by carbon. High doses of
carbon fed to the filter influent will cause rapid build-up of loss of head and
there is the hazard of carbon "bleed-through". Effluents must be carefully
monitored when carbon is fed to filter influent.
As a rough guide, dosages for taste and odor control vary from 2 to 8 mg/1
for routine continuous application. 5 to 20 mg/1 for intermittent severe
problems and 20 to 100 mg/1 for emergency treatment of chemical spills.
Powdered activated carbon has not been recovered and regenerated in the past.
Powdered activated carbon either settles out in the clarifier or is retained in the
filter. Spent carbon is then disposed of along with other plant waste solids.
Granular activated carbon, used as media in gravity filters, pressure vessels
and specially designed adsorbers, is effective for water treatment purposes.
*
Removal of organics and mercury is the primary use of granular activated
carbon. Activated carbon filters can be used either in place of, or in addition
to, conventional filters.
If activated carbon filters are used in place of conventional filters, special
care must be taken in the design and operation of filter cleansing facilities and
in the selection of activated carbon granule characteristics so that the filters can
be effectively backwashed without the loss of the carbon medium in the
backwash troughs.
The use of activated carbon filters has not been widely practiced in the
past, so optimum configurations and operating rules have not fully evolved.
Many of the guidelines given for conventional filters are also applicable to
activated carbon filters.
Filter depths generally vary from 0.8 to 3.0 m (2.5 to 10 ft), with an
activated carbon layer of 0.3 to *1.5 m (1 to 5 ft) overlying a layer of coarse
gravel above the underdrain system. An intermediate layer of sand, 15 to 46 cm
(6 to 18 in) is sometimes used between the activated carbon and the gravel.
Flow rates through the activated carbon filters are usually 120 to
300 m3/m2/day (2 to 5 gpm/ft2).
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The activated carbon medium must periodically be replaced with new or
regenerated activated carbon. Replacement cycles can vary from 1 to 3 years
for taste and odor removal down to 3 to 6 weeks for removal of haloform
precursors. Regeneration involves (1) removing the spent carbon as a slurry,
(2) dewatering the slurry, (3) feeding the carbon into a special furnace where
the regeneration occurs, (4) water quenching the carbon, and (5) returning it
to use. From 5 to 10 per cent of the carbon is lost during this process. The
choice among the alternatives of ¦ on-site regeneration,' purchase of new
activated carbon, or shipment of spent carbon to a regeneration center will be
governed by economic considerations.
Furnaces for carbon regeneration can be purchased for on-site use, but the
smallest of these has capacity for regenerating 1,360 kg/day (3,000 lb/day) or
the carbon requirements at plants having flows of between 38,000 to
li
76,000 m /day (10 to 20 mgd). Therefore, on-site regeneration is not
economical for small water facilities. Often located near activated carbon
production facilities, regeneration facilities may be too far removed for
economical use by a small water treatment plant. If an existing regeneration
center cannot be used, construction of a regional facility for activated carbon
regeneration should be considered for use by a number of small communities.
If drinking water regulations for halogenated organics are established and
granular activated carbon is used extensively for precursor or haloform removal,
the demand for regeneration facilities will increase.
An alternative to construction, operation and maintenance of an activated'
carbon filter is use of an "adsorption service". The service consists of a
complete modular system furnished to the municipality for a monthly service
fee. Delivery of new carbon and removal of exhausted carbon is then the
responsibility of the leasing company.
c. Applicability and Recommendations. Activated alumina is recom-
mended for removal of arsenic and/or excessive fluoride. Activated carbon can
be used for a variety of purposes. Powdered activated carbon is normally used
only for taste and odor control or for treatment of color. An economic analysis
should be used to determine the applicability of granular activated carbon for
removal of foaming agents, mercury, and organic pesticides. Granular activated
carbon is usually not economical for treatment of color or tastes and odors.
IV-11
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Replacement or regeneration of spent carbon is of concern when using
granular activated carbon. Alternatives available to small water treatment
facilities are purchase of new carbon, regeneration of spent carbon at a
regeneration center, or use of an adsorption service.
4. Clarification
Coagulation, rapid mixing, flocculation, and sedimentation are the
individual processes which make up clarification. Substances producing color
and turbidity can be removed by the clarification process. Clarification can also
be used in the softening of hard water with lime or lime and soda ash.
Clarification followed by filtration is the most widely used process to
remove substances producing turbidity in water. Raw water supplies, especially
surface water supplies, often contain suspended substances causing unacceptable
levels of turbidity. These include mineral and organic substances and
microscopic organisms ranging in size from 0.001 to one micrometer. Particles
in this size range are often referred to as "colloidal" particles. Larger particles,
such as sand and silt, readily settle out of water during plain sedimentation
(without use of chemical coagulation), but settling of colloidal particles using
plain sedimentation is not practical. An important characteristic of particles
suspended in water is the ratio of particle surface area to mass. For large
particles the ratio is relatively low and mass effects, such as sedimentation
under the influence of gravity, dominate. On the other hand, particles in the
colloidal size range have a relatively large surface area-to-mass ratio and these
particles exhibit characteristics dominated by surface phenomena, such as
electric charge. Plain sedimentation, on a practical scale, will not remove
particles of colloidal dimensions. Coagulation and flocculation processes are
required to remove these small particles in sedimentation basins.
a. Coagulation. The terms "coagulation" and "flocculation" are often
used interchangeably to describe the overall process of conditioning suspended
matter in water so that it can be readily removed by subsequent treatment
processes. The coagulation and flocculation processes, though closely related,
are distinct and separable and are defined as follows: the term "coagulation"
means a reduction in the forces which tend to keep suspended particles apart.
The reduction of these repulsive forces allows small particles to join together to
IV-12
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form larger particles which settle readily. The joining together of the small
particles into larger, settleable and filterable particles is called "flocculation".
Thus, coagulation is the precursor of flocculation.
Colloidal particles in suspension in water have electrical charges at their
surface. These charges are usually negative. The charge at the surface of the
particle causes the particle to attract oppositely charged ions present in the
water. The oppositely-charged ions are bound to the outer surface of the
particle and form a "layer" around the particle. Thus, if most of the suspended
particles in a naturally-occurring water have a layer of positively-charged ions
around them, the particles cannot approach each other because of the repulsion
between the positively-charged layers of each. The electrical strength at the
outer surface of the layer of bound ions is frequently referred to as the "zeta
potential". The magnitude of the zeta potential provides an indication of the
repulsive forces between suspended particles.
Negation of the repulsive forces between particles is generally achieved by
adding salts of trivalent aluminum or iron or a synthetic polyelectrolyte
coagulant to the water containing the particles. The aluminum or iron salts
cause a series of reactions to occur in the water; the net result of which is
reduction of the electrical charges on the particle.
Probably the most frequently used coagulant is aluminum sulfate
[approximate formula; AljCSO^)^" H.SHjO]. averaging about 17 per cent
Al2®3; a*so called "alum" or "filter alum". Other aluminum compounds used
as coagulants are potash alum and sodium aluminate, principally the latter.
Salts of iron, such as ferric sulfate, ferrous sulfate, chlorinated copperas
(chlorinated ferrous sulfate), and ferric chloride are also used as coagulants.
Magnesium hydroxide, produced by lime softening of waters high in
magnesium, is another effective coagulant. Organic polyelectrolyte compounds
have also proven effective as primary coagulants. Certain polyelectrolytes, at
low dosage, have been found to significantly enhance the efficiency of turbidity
removal in presedimentation basins, and a number of treatment plants now
utilize polymers for this purpose.
Determination of type and required quantity of coagulant is usually done
through a series of "jar tests". These tests are performed in a laboratory stirrer
by applying varying dosages of different coagulants to representative raw water
IV-13
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samples. The coagulant is rapidly mixed in the water, and the mixture is then
stirred slowly to allow flocculation to take place. Comparison of turbidity
removal efficiencies for each of the various coagulants and dosages yields an
evaluation of the best coagulant and dosage to be utilized. Inasmuch as mixing
times and the quality of the raw water vary, a large number of jar tests are
usually required to determine the optimal treatment process. ,
The pH of the water to be treated often has a significant effect on
coagulation. Aluminum salts are most effective as coagulants at pH values from
6.0 to 7.8. For iron salts, the range of pH values at which coagulation may
occur is somewhat broader. It is very important that coagulation be carried out
within the optimal range of pH values, and, if the pH is not within this range,
it may be necessary to adjust the pH.
There are very few definitive rules to follow .with respect to coagulation,
but the following are useful approximations:
1. Organic turbidity particles are usually more difficult to coagulate
than inorganic particles.
2. The required dosage of coagulant does not increase linearly with an
increase in turbidity. In fact, very high turbidities often coagulate
more easily than low turbidities because of the increased likelihood
of particle collisions.
3. If the suspended particles in water are of a wide range of sizes, they
are usually much easier to coagulate than if all the particles are of
similar size.
Some ions of dissolved salts exert influences on the coagulation processes.
Anions exert a much greater effect than cations, and of the common anions
found in nature, the sulfate and phosphate ions have the greatest effect on
coagulation. Sulfate ions tend to broaden the pH range in which effective
coagulation takes place.
In some cases, coagulation can be improved by the use of coagulant aids
in addition to the usual aluminum or iron coagulants. The most widely used
coagulant aids are activated silica, bentonite clays, and polyelectrolytes.
IV-14
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A partially neutralized sodium silicate solution is known as "activated
silica".-it is often used as an aid to coagulation because it lowers the required
coagulant dose, increases the rate of coagulation, broadens the pH range of
effective coagulation, and causes the floe particles to be tougher, which may
result in longer filter runs. However, preparation of the sodium silicate solution
is difficult, and unless carefully applied, activated silica may actually hinder
coagulation and shorten filter runs.
In water containing high color and low turbidity, the floe produced by the
addition of the aluminum or iron coagulant is often too light to settle rapidly.
Since clays similar to bentonite have a high specific gravity, the addition of
particles of bentonitic clays causes the floe to have a higher specific gravity,
and it settles more readily. Dosages of bentonitic clays generally range from 10
to 50 mg/1. ,
There are a large number of commercial polyelectrolytes currently
available. Polyelectrolytes are long-chain organic compounds which contain
repeating units of small molecular weight. Each of the units has an electrical
charge associated with it, which gives the long-chain molecule a large number of
similar electrical charges. Polyelectrolytes with negative charges are termed
"anionic", while those with positive charges are termed "cationic". Those
having essentially no charge are called "nonionic". Polyelectrolytes act as
bridging mechanisms between particles in water, and cause small floe particles
to agglomerate into large floe particles, with greatly reduced settling times.
Anionic and nonionic polyelectrolytes are often used as coagulant aids in
conjunction with metal coagulants. Cationic and nonionic polyelectrolytes, used
without metal coagulants, have proved effective in reducing turbidity in the
first stage of treatment of waters of high turbidity. Optimum dosages of
polyelectrolytes, which are usually quite low, must be determined by a series of
jar tests..
b. Rapid Mix, In the water treatment plant, coagulation and
flocculation are usually effected in two separate mechanical operations. The
first operation involves rapid mixing of the coagulant and other chemicals, if
needed, including those for pH adjustment and flocculation aid, in a small rapid
mix chamber. The purpose of rapid mixing is to uniformly distribute the
applied chemicals in the water. The interaction between chemical coagulants
IV-15
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and turbidity particles occurs very quickly, so it is essential that the chemical
coagulant be rapidly mixed into the water to insure that the coagulation
process proceeds uniformly. Generally, rapid mixing is accomplished by creating
turbulence with propellers or impellers. As approximate guidelines, the water
flowing into a rapid mix chamber usually requires from 20 seconds to two
minutes to flow through the chamber, and the mixing units usually need 0.3 to
0.6 W per m^/day (1 to 2 hp per fP/second). In small water treatment
facilities, pumps can also be used for mixing.
A useful parameter in the design of rapid mix facilities is the power input
into the water, as measured by the velocity gradient G. Rapid mixing is best
achieved at G values of 500 sec"^ to 1,000 sec"* and detention times of about
* - s
two minutes, although shorter detention times are often used effectively.
Longer detention times for these values of G result in negligible mixing
improvement. If high G values (>10,000 sec"*) are maintained for as long as
two minutes, the subsequent floe formation processes are retarded .significantly.
c. Flocculation. As previously defined, flocculation is the joining
together of small particles into larger, settleable, filterable particles. The
primary force of attraction between colloidal particles present in water is the
van derWaals force, which is a cohesive force in existence between all atoms.
If the repulsive forces between particles, as described under a) Coagulation, can
be sufficiently reduced to allow van der Waals forces to predominate, the
particles will stick together and form larger particles which settle out of the
water more readily.
The likelihood of collisions between particles is often enhanced by slow
mechanical mixing or agitation ("flocculation") of the water. As more and
more particles are joined together, they form flocculent masses which will
subsequently settle out of the water. Any particles which are struck by the
flocculent material as it settles to the bottom are ensnared in the flocculent
mass. '
Flocculation, which follows coagulation, is usually accomplished in large
tanks with some type of mechanical mixing. The mixing in these basins is
intended to promote collisions of the coagulated particles. The motion
imparted to the water in the flocculation basins must be much gentler than the
motion in the rapid mix chambers; otherwise, the shear forces in the turbulent
IV-16
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water would break up agglomerated floe particles. Mixing for flocculation is
often accomplished through the motion of a series of paddles rotating either
parallel or perpendicular to the direction of flow through the basin. Baffles
should be provided, between each set of paddles to minimize short circuiting.
Walking beam flocculators and vertical axial flow flocculators are commonly
used, and can be placed in existing basins.
As in the case of rapid mixing, the value of the velocity gradient G is
useful in estimating the effectiveness of mechanical agitation in flocculation
basins. The optimal range in values of G appears to be between 20 sec"' and
70 sec"'. If the velocity gradient is multiplied by the detention time in seconds,
an additional parameter GT is obtained. This nondimensional parameter can be
used to characterize flocculation basins. Conventional values of GT range from
30,000 to 150,000. Detention times resulting in the best flocculation usually
are between 20 and 60 min.
d. Sedimentation. After the coagulation and flocculation processes have
been completed, the water must pass through a relatively large basin at low
velocity, to allow the floe particles to settle out. This settling-out process is
generally called "sedimentation" or "clarification". The particles removed
during this stage of water purification are usually small and not of high
density; consequently, large tanks are needed to achieve the quiescent
conditions necessary for settling. In the preliminary water treatment process of
"plain sedimentation", only the heavier particles, such as grains of sand, are
removed from the water, as contrasted to the amorphous floe removed in the
post-flocculation sedimentation process.
The most common types of sedimentation basins are the rectangular, ,
horizontal flow and the center-feed, radial flow. In all types of basins, the
design objective is to obtain, as nearly as possible, the condition of ideal flow
through the basin. Ideal flow for a rectangular basin requires that all of the
water entering at one end of the basin should flow in parallel paths of equal
velocity to the effluent end of the basin. Ideal flow exists in a circular basin if
the centrally-fed water moves in radial paths of equal velocity to the outlet
channel of the basin. This ideal flow cannot be attained under actual operating
conditions because of imperfect inlet and outlet arrangements, friction,
turbulence, short circuiting, etc.
IV-17
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A minimum of two sedimentation basins is usually preferred. However, for
many small water treatment plants, two basins are not practical. Use of a single
sedimentation basin is recommended only if adequate storage is available to
meet water demands while the basin is out of service. If more than one basin is
provided, flow division between the basins should be accomplished prior to
application of coagulating chemicals. Thus, the plant would have multiple
parallel-operating, coagulation, flocculation and sedimentation units.
Rectangular basins vary in width from 1.5 to about 7.3 m (5 to about
24 ft). An approximate width to length ration of 1:4 is common. Basin depths
generally range from 2.1 to 4.9 m (7 to 16 ft). Under comparable conditions,
deeper basins usually perform better than shallow ones. In general, the basins
should be sized to provide an average detention time of 2 to 6 hours. Special
conditions may dictate deviation from these general criteria; detention periods
in the range of 8 to 12 hours, or more, may be desirable for the treatment of
highly turbid waters. If the space available for sedimentation basins is severely
limited, the construction of multiple-story basins, in which the water flows
horizontally along one level and then passes upward or downward to flow
horizontally along another level, may be warranted.
An important parameter in the sizing of sedimentation basins is the
"overflow rate", which is defined as the flow rate divided by the surface area
of the basin. The overflow rate is usually expressed in terms of m^/m^/day
(gpd/ft^), In theory, if the settling velocity of a particle is greater than the
overflow rate of the basin and ideal flow exists, the particle will settle out of
the water before the water leaves the basin.
Actual-sedimentation basins are designed to reduce currents which produce
short circuiting and hinder settling. These currents may be the result of inlet or
outlet induced turbulence, wind action, density differences, sludge build-up on
bottom, etc. The settling rates of alum floe in a conventional sedimentation
basin generally range from 0.17 to 0.26 mm/sec, equivalent to overflow rates of
14 to 22 m3/m-,/day (360 to 550 gpd/ft^). If the particles to be removed settle
more rapidly than alum floe, the area of the basin should be reduced
proportionately; and conversely, if the particles settle more slowly, the area of
the basin must be increased.
IV-18
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Estimates of suitable overflow rates for sedimentation treatment of water
of a given quality can be obtained from cylinder settling tests conducted in the
laboratory. The test procedure should approximate full-scale treatment and
settling velocity distribution curves showing fraction of turbidity remaining as a
function of settling velocity should be developed for each test series.! 1]
A large number of carefully conducted tests axe required to assess
adequately the influence of variations in raw water quality on coagulation,
flocculation and settling. For example, water temperature has a significant
effect on particle settling rates. If the settling rate of a particle at 30°C (86°F)
is 2.2 mm/sec, it would be 1.4 mm/sec at 10°C (50° F) and 'only about
1.0 mm/sec at 0°C (32°F). The increase in viscosity of the water at lower
temperatures greatly reduces settling rates. Settling fate determinations should
include tests at the lowest water temperature that will be encountered.
Application of laboratory settling data to actual basin design requires the
exercise of considerable judgment. Experience at existing plants treating the
same or similar raw water may provide valuable guidance and should be
carefully reviewed prior to final decisions on treatment methods, size of basins,
etc.
Flocculation-sedimentation basins, usually circular in plan, can be used to
combine the functions of flocculation and sedimentation. Flocculation is
.accomplished in a circular center well. Sedimentation occurs in the annular
space between the flocculation section and the perimeter effluent weir.
Suspended solids contact claritiers combine mixing, coagulation, floccula-
tion, sedimentation, and sludge removal in a single unit. This type of clarifier
can be very practical for small systems. Coagulation and flocculation take place
in the presence of floe which has been formed previously and cycled back to
the primary mixing and reaction zone. This process maintains a high
concentration of floe particles and enhances the probability of particle
collisions. Settled sludge is removed from the unit continually. The use of these
units usually results in a reduction in the space required for treatment facilities,
and may result in a cost reduction. Solids contact clarifiers are widely used in
connection with lime-soda softening.
A recent development, the "tube" settler, may be used advantageously at
some installations, particularly if the capacity of existing sedimentation basins
IV-19
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must be increased or if little space is available for the construction of new
sedimentation basins. Tube settlers may increase the capacities of sedimentation
basins by 50 per cent or more. For more detailed information on tube settlers,
refer to section V, Upgrading Existing Facilities.
Water containing the suspended particles is often introduced to the
circular basin through a central influent well. The inlet pipe into the influent
well is placed either beneath the basin or suspended from a bridge between the
influent well and outer wall of the basin. The water is discharged from the
influent well into the circular basin, where it flows radially outward toward
outlet troughs along the perimeter of the basin. As in the case of rectangular
basins, the water inlet must be designed so as to minimize turbulence in the
influent flow. A cylindrical baffle at the center of the basin is the most
common type of influent well in use. The outflow from circular basins is
generally collected in an outflow channel which follows all or most of the
periphery of the basin.
Peripheral-feed, circular tanks are also employed. Water is distributed
around the tank perimeter and flows radially toward effluent collection
facilities located in the center.
1. Inlet Arrangements. Inasmuch as the effectiveness of sedimentation
basins is dependent on the degree of attainment of uniform, quiescent flow, it
is essential that the water entering the basin be distributed to minimize
turbulence or intertial currents. Also, the velocities of the water in the pipeline
or flume carrying water to the sedimentation basin must be about 0.15 to
0.6 m/s (0.5 to 2.0 ft/s). Lower velocities will result in deposition of the floe
and sediment in the pipe or flume; higher velocities may cause breakup of the
flocculated particles.
Where inlet pipelines or flumes are used, the conventional methods of
uniformly distributing the water at the influent end of the basin are through
horizontal or vertical slots in a baffle wall, or through a series of orifices in an
inlet chamber. The efficiency of most sedimentation basins is highly dependent
on the design of the inlet arrangement.
2.. Outlet Arrangements. V-notch weir plates are often used for basin
outlets, and these should be installed with provisions for vertical adjustment to
IV-20
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insure uniform flow along the length of the weir. Weir rates commonly vary
from 140 to about 270 m3/day/m (8 to about 15 gpm/ft), with the higher
values for heavier floe, such as that derived from lime softening. Submerged
orifices are also used for basin outlets. Advantages of this type of outlet over
the V-notch weirs include: (1) climatic effects of wind and ice are reduced and
(2) volume above the orifices is available for storage while filter is backwashed.
The recommended maximum velocity through submerged orifices is 0.6m/s
(2 ft/s). Higher velocities may cause currents which inhibit settling or break up
the flocculated particles.
3. Sludge Removal. The solids which settle to the bottom of the
sedimentation basin are called "sludge". This sludge must be removed from the
bottom of the basin before the depth of the sludge becomes great enough to
interfere with effective sedimentation. If the sludge layer becomes too thick,
the effective volume of the basin is decreased resulting in an increase in the
velocity of the water flowing through the basin. The higher velocity of water in
the basin increases the friction between the sludge layer and the water, with
the result that sludge particles are resuspended and enter the outflow from the
basin.
Settled sludge can be removed in either of two ways: (1) by taking the
sedimentation basin out of service periodically for cleaning, usually by flushing,
or (2) by mechanical sludge collectors which consist of slow-moving,
mechanically-driven scrapers. Almost all sedimentation basins are now cleaned
by mechanical devices rather than by taking them out of service. Sludge
scrapers force the sludge into hoppers located at the influent end of the
rectangular sedimentation basins. The sludge is drawn off from the hoppers and
discharged to a point of disposal. These scrapers must move at low velocity so
as to avoid interfering with the settling process. The bottoms of rectangular
sedimentation basins are sloped toward the sludge hoppers to facilitate the
action of the mechanical sludge collectors. The most common slope used is
1:100 (vertical: horizontal),
e. Softening. Water softening is the process of reducing hardness.
Hardness is caused principally by calcium and magnesium ions in water.
Softening of the entire supply is usually justified when total hardness exceeds
300 mg/1 and may prove economically advantageous at hardness levels above
200 mg/1.
IV-21
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Two general types of processes are used for softening. These are the lime-
soda ash process and the cation ion exchange process^often called the zeolite
process. The lime-soda ash process is used principally at water treatment plants
serving a fairly large population. The cation exchange process can be similarly
applied and, in addition, is adaptable to small water treatment facilities.
. Equipment, basins, and filters required for lime softening are generally
similar to the facilities used in conventional coagulation-filtration plants. In
fact, many filtration plants, not originally designed for softening, have been
converted to softening plants by the installation of necessary facilities.
Many lime softening plants, particularly those treating ground water, use
solids contact type basins. These basins provide the functions of mixing, sludge
recirculation, sedimentation and sludge collection in a single unit. Basins of this
type, if properly sized, will provide effective softening and clarification
treatment.
A disadvantage of any lime softening process is the production of a large
volume of sludge of high water content. Provision for sludge disposal in an
environmentally acceptable manner must be considered in designing a lime
softening plant.
Cation exchange or "zeolite" softening is accomplished by exchanging
calcium and magnesium ions for a cation, usually sodium, which does not
contribute to hardness. Basically, this exchange consists of passage of water
through a bed of granular sodium cation media. The calcium and magnesium in
the water react with the media and are replaced with an equivalent amount of
sodium. This reaction is reversible and the exchanger can be regenerated with a
strong solution of sodium chloride (common salt). Disposal of backwash water,
brine waste and rinse water must be carefully considered.. As water with an
increased sodium content, is produced by cation exchange softening, this
process may not be desirable for individuals on low sodium diets. Softening of
hard water using the ion exchange process is discussed in detail in section IV 8.
f. Applicability and Recommendations. Clarification facilities are
readily adaptable to small water treatment systems. Rapid mix, coagulation,
flocculation and sedimentation are recommended for removal of turbidity and
color. Also, laboratory tests have indicated clarification, followed by filtration,
IV-22
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effective in removing the following contaminants: arsenic, cadmium, chromium,
lead, mercury, selenium, silver, radium, endrin and 2,4,5-TP (Silvex). Also an
aid in reducing the bacteria level, clarification should not be used in place of
disinfection. Before the clarification process is selected for treatment of .any
contaminant other than turbidity or color, operational tests with full-size
equipment should be performed.
For design of rapid mix facilities, a detention time of 20 to 30 seconds
and a velocity gradient, G, of 1,000 is recommended. An alternative to the
conventional rapid mix chamber is the use of pumps for mixing. However, a
disadvantage of using pumps is that the mixing cannot be controlled.
The minimum detention time recommended for a floeeulation basin is 20
to 45 minutes, depending on the material to be flocculated. Vertical axial flow
turbines are appropriate for the majority of small water treatment systems.
Paddle reel flocculators parallel to the flow should be compared to vertical
axial flow turbines for use in all but the smallest treatment plants.
Two settling basins are recommended as a minimum for most treatment
facilities. Very small systems such as those using package plants, however, may
use a single sedimentation basin if storage is provided. Flocculation-
sedimentation basins are appropriate for use in small water treatment plants as
are tube settlers. Settling tubes are most commonly used in package water
treatment plants and in modification of existing facilities.
Cation exchange or "zeolite" softening is well-suited for use in small water
treatment systems. In addition to hardness reduction, cation exchange softening
is also an effective method for radionuclide reduction. Lime softening is not
recommended for small water treatment facilities unless an analysis indicates it
to be economically desirable compared to ion exchange softening. Laboratory
tests have indicated lime softening effective in removing arsenic, barium,
cadmium, chromium, fluoride, lead, mercury, selenium, silver, radioactive
contaminants, copper, iron, manganese, zinc and, to a certain degree, TDS.
5. Filtration
Filtration of water is defined as the separation of colloidal and larger
particles from water by passage through a porous medium, usually sand or
IV-23
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granular coal. As water passes through the medium, the suspended particles in
the water are either left in the interstices between the grains of the medium or
left on the medium itself. Sand filtration will remove particles much smaller
than the void spaces between the sand grains. This phenomenon is probably
due principally to the fact that a bed of sand or other similar granular material
possesses a huge surface area, much of which is in contact with the water and
the particles suspended in it. The particles are attracted to the surface of the
granular medium and are held there by relatively strong surface forces. These
surface forces are apparently large enough to attract and bind particles to the
medium surface even though the particles may bear the same electrical charge
as the filter pains. The suspended particles removed during filtration range in
diameter from about 0.001 to 50 micrometers and larger.
Water filters can be classified in various ways. They may be identified
hydraulically as slow or rapid, depending upon the rate of flow per unit of
surface area. Filters are also classed according to the kind or type of filter
media employed, such as sand, anthracite coal, coal-sand, multilayered, mixed
bed, or diatomaceous earth. They may be described according to the direction
of flow through the bed, that is downflow, upflow, biflow, fine-to-coarse, or
coarse-to-fme.
Filters are also commonly distinguished between pressure and gravity (or
free surface) filters.
a. Gravity Filters. Gravity filters are free surface filters and as their
name would imply, are used for filtering water under gravity flow conditions.
Gravity filters are distinguished from pressure filters and are much more
commonly used for municipal applications. The various media types previously
discussed may be used in gravity or pressure filters. Gravity filters are typically
characterized by downflow operation foEowed by an upflow washing of the
filter media to remove the foreign material collected in the bed.
b. Pressure Filters. Pressure filters are very similar in filter bed
construction to a typical gravity filter; however, in a pressure filter the entire
filter apparatus, including media layer, gravel bed, and underdrains, is enclosed
in a steel shell. An advantage of a pressure filter is that any pressure in the
water lines leading to the filter is not lost, as in the case of gravity filters, but
can be used for distribution of the water once it has passed through the
IV-24
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pressure filter. About 0.9 to 3 m (3 to 10 ft) of pressure head is lost in friction
through the filter bed, but any pressure in excess of this can be utilized for
water distribution.
A disadvantage of pressure filters is the potential loss of media during
backwash which cannot be observed,
c. Diatomite Filters. A special type filter which is usually operated
under pressure is the diatomite filter. It consists of a layer of diatomaceous
earth supported by a septum or filter element. This layer of diatomaceous earth
is about 3.2 mm (1/8 in) thick at the beginning of filtration and must be
maintained during filtration by a constant body feed of diatomite filter
medium to the influent unfiltered water. At the conclusion of a filter run, the
layer of diatomaceous earth will have increased in thickness to about 13 mm
<2 •j
'(1/2 inch). Filtration rates generally vary from 30 to 120 rrr/mz/day (0.5 to
2.0gpm/ft). The chief difficulty in using diatomite filters is in maintaining the
diatomaceous earth film of uniform permeability and filtering capability.
Applicable methods for disposal of diatomaceous earth filter sludge include use
of a lagoon or landfill.
d. Media.
1. Single Media. Single media filters are those which employ only one
type of filtering medium as opposed to dual and mixed media filters. Types of
single media filters include rapid sand, slow sand, and anthracite. The vast
majority of present-day water plants use single media filters with the most
common type being rapid sand filters.
Rapid Sand Filters, Rapid sand filters are those filters which commonly
operate at rates. of about 120 to 240 m^/m^/day (2 to 4 gpm/ft^). A
"standard" rate for rapid sand filtration of surface waters is 120 m^/irr/day
(2 gpm/ft ) while ground waters are usually filtered at 180 to 240 m /m /day
¦J
(3 to 4 gpm/ft ). If higher rates are to be used in design, great care must be
taken to insure that all pre filtration treatment processes including coagulation,
flocculation and sedimentation will perform satisfactorily and consistently. High
rate filter operation requires excellence in prefiltration treatment.
The filter medium, which has traditionally been silica sand, is generally
supported on a gravel bed. Beneath the gravel bed lies an underdrain system
which collects the filtered water. The filter sand layer is generally about 64 to
IV-25
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76 cm (25 to 30 in) thick and the supporting gravel bed is usually 30 to 46 cm
(12 to 18 in) thick. Head loss through a clean filter is about 0.3 m (1 ft) and
the filter is cleaned by backwashing when the head loss reaches about 2.4 m
(8 ft).
The filter sand usually has an effective size of 0.35 to 0.50 mm and a
uniformity coefficient of 1.3 to 1.7. The "effective size" of a sample of sand is
a grain diameter such that 10 per cent by weight of the sample has smaller
diameters. The "uniformity coefficient" is the ratio of the grain diameter with
60 per cent of the sample smaller to the grain diameter with 10 per cent of the
sample smaller. A sand to be used as a filter medium is tested by sieve analysis
to determine the gradation of grain sizes in the sand. Sand finer than about
0.3 mm stratifies at, or near, the surface of the filter, thereby shortening the
filter runs. Sand coarser than 1.2 mm is generally too large to effect good
removal of suspended matter. Filter sand should be clean and have a specific
gravity of not less than 2.5. For filtration of low pH water, the sand should
not lose more than 5 per cent by weight when placed in hydrochloric acid.
Filter sands for use in water softening plants are somewhat coarser than those
indicated above. For detailed specifications for filtering material, reference
should be made to "A WW A Standard for Filtering Material", AWWAB100-72,
as published by the American Water Works Association.
The gravel bed beneath the filter sand is designed to keep the sand from
passing into the underdrains and also to distribute the wash water uniformly
during backwashing. Ideally, the gravel bed should be composed of well
rounded gravel, with a uniform variation in diameter from the top of the bed
to the bottom, ranging from about 1.6 mm (1/16 in) at the top to about
25 mm (1 in) at the bottom. It is important for the gravel to have few
irregularly shaped (thin, flat, jagged) stones and to be essentially free of soil,
sand, or organic residue of any kind.
The filter underdrains are placed at the bottom of the gravel bed and serve
a dual purpose: (1) to collect the filtered water, and (2) to distribute
backwash water uniformly beneath the filter sand and gravel bed. Types of
underdrains include perforated pipe-grids and false bottom systems of various
types. Perforated pipe-grid underdrain systems have been used; however, the
false bottom systems are preferred.
IV-2 6
-------
Porous plate or porous block false bottoms are suitable where deposition
within the pores of the plates or blocks is not a problem. If deposition occurs,
the plates or blocks must be cleaned promptly as otherwise there will be a
progressive, undesirable increase in head loss across the plates. Structural failure
may occur during backwashing if clogging is severe. Some false bottom systems
employ vitrified clay blocks containing orifices; others are constructed of
concrete and contain orifices terminating in inverted square pyramids filled
with large and small earthenware spheres. A variety of underdrains of the
false-bottom type have been developed and used successfully.
Slow¦ Sand Filters. Slow sand filters have a similar configuration to rapid'
sand filters with a bed of sand supported by a layer of gravel. The filtration
rate for slow sand filters ranges from 2.9 to 5.9 m jm /day (0.05 to
-------
deep. Some mixing of coal and sand at their interface is desirable to avoid
excessive accumulation of floe at this point. This intermixing also reduces the
void size in the lower coal layer causing it to remove floe which otherwise
might pass through. The coarse to fine media arrangement has an advantage
over a single media filter because the effective depth of the filter bed is
increased as is the length of filter runs.
In a conventional rapid sand filter with a single sand layer that has been
hydraulically classified by backwashing. the smallest sand grains will be near the
top of the bed. Any suspended matter that passes through the top few inches
of sand may pass through the entire filter bed. Thus, the effective depth of a
traditional rapid sand filter is only a few inches. However, when a coarse
medium is placed over a fine medium the filtration ability of the unit is
increased, since the larger particles in the water will be removed in the coarse
medium and the smaller particles will be removed in the fine medium. Flow
rates for dual media filters* can thus be increased to about 240 fri^/m2/day
(4 gpm/ft2). . ..
3, Mixed Media. Mixed media filters are those filters employing more
than" two types of filtering media arranged in a coarse to fine configuration.
Typically, the mixed media: bed consists of three layers: coal with specific
gravity of 1.4 on top, sand with specific gravity of 2.65 in the middle, and
garnet with specific gravity of 4.2 on the bottom. They are normally used in
the proportions of about 60% coal, 30% sand, and 10% garnet by volume.
After backwashing, the three materials become mixed thoroughly'throughout
the depth of the bed. The top of the bed is predominantly coal, the middle is
predominantly sand, and the bottom is mostly garnet, but all three are present
at all depths. In a properly designed mixed media bed, the pore space and the
average grain size decrease uniformly from top to bottom. Just as in single and
dual media filters, the bed is underlain by a layer of supporting gravel.
The vast surface area of the filtering media greatly increases the length of
filter runs. The total surface area of the grains in a mixed media bed is much
greater than for a sand or dual media bed, which makes it much more resistant
to breakthrough and more tolerant to surges in flow rates. One of the primary
benefits of the mixed media bed is an improved finished water quality.
IV-28
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e, Backwashing Facilities. Filter backwashing involves washing the filter
media to remove the material that has been filtered from the water. This
material consists of particles trapped in pore spaces as well as on the surface of
the filter media. Backwash water is applied to the underside of the filter bed
through the underdraws, which should be designed' to provide an even
application of wash water to the filter. The wash water containing the material
removed from the filter medium is carried away in wash water troughs, located
above the surface of the filter medium, Backwashing is necessary whenever the
head loss through the filter exceeds the acceptable value, usually about 2.4 m
(8 ft), or when effluent turbidities are unacceptably high.
The water used for washing the filters should be obtained from protected
storage and can be gravity or pumped flow. As a minimum, sufficient wash
water should be available to allow backwashing of any filter, at , up to
3 9 'J
1200 m /m /day (20 gpm/ftz> for. 10' minutes. Installation , of standby
backwash pumps should be considered to insure reliability. The need for
backwash pumps can be eliminated by construction of an adequately sized
wash water tank at an elevation sufficient to provide the required flow. The
choice between elevated storage tanks and the use of backwash pumps must be
made on a case-to-case basis. Wash water tanks are .usually filled' by small
pumps automatically controlled by the water level.in the wash water tank. The
41
amount of wash water required will generally average about one per cent of the
water filtered and should not exceed five per cent. - • : s
In addition to the backwash facilities, some filters are also installed with
surface wash facilities. Filter agitation would better describe its function as the
surface wash aids in cleaning much more than the filter surface. .
The backwash process does not always wash away all waste material and
mud balls can form from the agglomerated waste within the "filter and on the
surface of the Filter media. These mud balls can eventually become large
enough to clog portions of the filter. An adequate surface wash will prevent
mud ball formation because it aids in agitation of the entire filter bed during
the backwash process, .
Rotary washers are the most common type of surface wash equipment;
however, fixed jets are also used. The surface wash system usually consists "of
horizontal pipes containing a series of nozzles. The horizontal pipes are
IV-29
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connected by vertical pipes to water lines above the filters. The nozzles have
small orifices through which water is forced down onto the filter surface.
Surface washers are usually started in advance of the normal backwash flow and
are turned off just before the end of the backwash period. Surface wash
systems are commonly used with all types of filters,but are especially necessary
for dual and mixed media filters to obtain adequate cleaning deep within the
bed.
f. Filtration Aids, In order to improve the filtrability of the water and
to permit' higher filtration rates, it is often advantageous to add a
polyelectrolyte to the settled water prior to " its passage through the filter:
Polyelectrolytes, also known as polymers, are high molecular. weight, water
soluble compounds which can be used as primary coagulants, settling aids, or
filtration aids. A filtration aid will increase the strength of the chemical floe
and aid in controlling the depth of penetration of floe into the filter.' It. is
usually added directly to the filter influent and the dosage required is normally,
less than 0.1 mg/1.
The use of a filtration aid is usually warranted only for coarse-to-fine
filters which includes dual media and mixed media filters. Conventional
fine-to-coarse rapid sand filters are" rapidly sealed off at the surface when
filtration aids are used. &
g. Applicability and Recommendations, As discussed in section IV4;-
Clarification, filtration after clarification is used in the removal of numerous
contaminants. Rapid sand filters are an acceptable means of water filtration for
most requirements and are quite commonly used today. Dual and mixed media
filters are not as widely used, but are capable of producing an effluent of
higher quality.
Dual-media filters, usually of the coal-sand variety, can be operated at
higher rates-than rapid sand filters with an increase in length of filter runs.
Mixed media filters are an improvement over dual media filters allowing for
operation at even higher rates with longer filter runs. The variations in filter
media only slightly affect the cost of the total filter. A surface wash system
should also be installed in the mixed media filter to aid in backwashing.
IV-30
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Activated carbon filters are to be considered as a method of removing
taste and odor causing organics from water. As discussed in section IV A 3b,
they may be used in place of, or in addition to,conventional filters. The use of
separate activated carbon beds will be more expensive, but is preferred.
In general, gravity .filters are more commonly used than pressure filters in
municipal applications although either is an acceptable means of filtration. The
major disadvantages of pressure filters are that they are completely enclosed
within a steel shell. Thus, access to the filter bed for normal observation and
maintenance is restricted. The steel shells also -require careful periodic
maintenance to prevent internal and external corrosion. However,' for small
systems, the use of pressure filters as opposed to gravity filters is often
advantageous. Initial investment cost savings may'be realized and if the pressure
requirements and conditions in a particular system are such that finished water
pumping can be reduced or eliminated through the use of pressure filters,
additional cost savings may be realized,
6. Disinfection
As; currently practiced in the water treatment industry, disinfection
involves destruction or deactivation of objectionable organisms. These organisms
may be objectionable from the standpoint of either health or aesthetics. They
consist of certain classes of bacteria, viruses, protozoa, and some larger
organisms. Inasmuch as the health of water consumers is of major concern to
those responsible for supplying water, design, of facilities for disinfection must
necessarily be carefully executed.. . •
Chlorination, including the use of chlorine dioxide, and ozonation are the
most frequently used methods of disinfection for potable water treatment.
Other means of disinfection have been attempted with varying degrees of.
success,. These include treatment with reverse osmosis, ultra-violet light, heating
of water, addition of elements similar to chlorine such as bromine or iodine,
and addition of metal ions such as silver.' None has achieved significant
acceptance by the water supply industry. ¦ * *
IV-31
i
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a. Chlorine. The application of various forms of chlorine to water in
order to effect disinfection has come into such common acceptance that
"chlorination" and "disinfection" are almost considered synonymous. Other
modes of disinfection generally lack the persistence of chlorine or are more
costly to use than chlorine.
Terms frequently used in connection with chlorination practice are defined
as follows;
Chlorine Demand, The difference between the concentration of chlorine
added to the water and the concentration of chlorine remaining at the end
of a specified contact period is defined as chlorine demand, Chlorine
demand varies with the water quality, concentration of chlorine applied,
time of contact, and temperature.
Chlorine Residual, The total concentration of chlorine remaining in the
water at the end of a specified contact period is defined as chlorine
residual. Two types of residuals are encountered in chlorination practice.
They are designated: "combined available residual chlorine" and "free
available residual chlorine". They are frequently referred to simply as
"combined residual" and "free residual".
Chlorine is applied to water in one of three forms: as elemental chlorine,
as hypochlorite salts or as chlorine dioxide. The use of hypochlorites and
chlorine dioxide as disinfectants is discussed in subsequent sections.
Elemental chlorine added to water forms hypochlorous acid (HOC1) and
hydrochloric acid (HC1) according to the following reaction:
ci2 + h2o=,hoci + h+ + ci- (6-1)
This equation is usually displaced to the right and very little Cl2 remains in
solution. Immediately after the above reaction takes place, the hypochlorous
acid (HOC1) dissociates into hydrogen and hypochlorite ions, as indicated in
this equation:
HOC1 - H+ + OC1" (6-2)
IV-32
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The degree of ionization is dependent on the pH of the water. At a pH of 6.5,
approximately 90 per cent of the hypochlorous acid is not dissociated. If the pH
is raised to 8,5, about 90 per cent of the hypochlorous acid will have
dissociated to hydrogen and hypochlorite ions, as indicated in equation 6-2.
Between pH 6.5 and 8,5, any chlorine present in the water exists as both
hypochlorous acid and hypochlorite ions. Chlorine existing in water in these
two forms is defined as "free available chlorine".
As shown in equations 6-1 and 6-2, the addition of elemental chlorine to
water results in an increase in the number of hydrogen ions (H+) in solution:
This means that the pH of the water is decreased, and treatment for pH
correction may be required if high concentrations of chlorine are applied.
1." Reactions of Chlorine With Ammonia. If chlorine is added to water
containing ammonia, the ammonia and the hypochlorous acid react to form
compounds known as chloramines. Chlorine will also react with compounds
containing both carbon and nitrogen to form organic chloramines. The relative
amounts of the different chloramines formed are dependent on pH, time,
temperature and the quantities of chlorine and ammonia initially present in the
water. Formation of chloramines greatly reduces the reactivity of the chlorine
and hence longer detention time is required to achieve the same disinfection.
Any chlorine in water which has combined with nitrogen, whether
ammonia nitrogen or organic nitrogen, is known as "combined available
chlorine." It is emphasized that the disinfecting power of combined available
chlorine is of a low order compared with free available chlorine.
2. Reactions of Chlorine with Other Substances. In addition to the
reactions with water and nitrogenous substances, chlorine also enters into
reactions with other materials present in water. Inasmuch as the oxidizing
power of free available chlorine is high, typical inorganic reducing agents such
as hydrogen sulfide, ferrous iron, and divalent manganese are rapidly oxidized
in the presence of chlorine. Chlorine also oxidizes nitrites to nitrates. Organic
materials present in the water will also react with chlorine. The reactions
between chlorine and organic. substances may involve oxidation, substitution
and addition. A multiplicity of chloro-organic compounds is possible. Some,
such as chlorophenol, have been identified and are known to cause
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objectionable tastes when present in trace amounts. The extent and nature of
chlorine's many possible reactions with dissolved organics are not well
defined; but it is known that trihalomethanes are widespread in chlorinated
drinking waters and they result from chlorination. In general, total
trihalomethane concentrations are related to the organic content of the water
and chlorine dosage. At present, a maximum contaminant level for
trihalomethanes has not been established by EPA. However, if a source of low
organic content is not available, special treatment processes that will reduce the
organic concentration prior to chlorination should be investigated. Chlorine
should be applied only after processes which will reduce the organic
concentration and thus decrease the chance of trihalomethane formation.
3. Disinfection Properties of Various Forms of Chlorine, The means by
which chlorine destroys various types of organisms are not known precisely. It
is suspected that the chlorine penetrates cells of microorganisms and disrupts
vital enzyme activities. Various studies have shown that, of the various forms of
chlorine, hypochlorous acid (HOC1) is by far the most powerful disinfectant
The hypochlorite ion (OCT) is far less effective. Also, the disinfecting power of
combined available chlorine -(chloramine) is much less than that of free
available chlorine. In general, about 25 to 100 times as much combined
available chlorine as free available chlorine is required to achieve equal degrees
of disinfection in the same time period. The fact that combined chlorine
persists for a long time in water is often viewed as advantageous from a water
safety standpoint. This persistence is an indication of low reactivity of
chloramine, a distinct disadvantage insofar as the disinfection rate is concerned.
However, chloramine residuals can be used to provide long-lasting residual in
potable water distribution systems.
4. Chlorine Dosages. Chlorination is used to eliminate or inactivate
most water-borne pathogens. Those pathogens that are regarded as the most
significant in water are bacteria, amoebic cysts, and viruses. The efficacy of
chlorination in achieving the desired destruction or deactivation of these three
types of pathogens is strongly dependent on four factors: contact time, pH,
temperature, and the type of chlorination used; i.e., free residual chlorination
or combined residual chlorination. As previously indicated, free residual
chlorination is far more effective than combined residual chlorination. Chlorine
disinfection processes are enhanced by low pH, high temperature, and long
contact time.
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The effectiveness of bacterial disinfection can be checked by bacterio-
logical tests for the presence of organisms of the eoliform group. Pathogens,
such as typhoid bacteria (Salmonella typhosa) are known to be at least as
vulnerable to chlorine as eoliform bacteria. Therefore, coliforms, which are
easily detected by bacteriological methods, serve as indicator organisms for
water safety. On the other hand, eoliform tests may not be indicative of
parasitic protozoa, such as Entamoeba Hystolytica, the causative agent of
amoebic dysentery. The cysts of this organism are far more resistant to chlorine
than eoliform bacteria and chlorination alone cannot be assumed to provide an
ample margin of safety unless relatively high concentrations of free available
chlorine are employed. Free chlorine residuals required to destroy amoebic
cysts (cysticidal residuals) are higher than those usually employed by water
utilities. However, other treatment processes (coagulation, floceulation,
sedimentation, filtration) are effective in removing amoebic cysts and should
always be employed in conjunction with chlorination when treating surface
waters derived from uncontrolled, watersheds.
Disease-producing viruses must be assumed to be present in waters that are
subject to sewage pollution. In general, viruses are more resistant to chlorine
than eoliform organisms and other enteric bacteria. Therefore, negative eoliform
results may not be indicative of virus destruction. The matter of virus removal
or inactivation by water treatment systems needs, and is now receiving,
intensive study. Currently, it is known that, of all the forms of aqueous
chlorine, only un-ionized hypochlorous acid (HOC1) is an effective agent for
virus destruction. A hypochlorous acid concentration of 1.0 mg/1 will
provide viral inactivation within 30 minutes. Therefore, free residual chlorina-
tion at pH values somewhat below about 7.5 is indicated for effective virus
disinfection. At pH values of 7.5, or lower, about 50 per cent or more of the
free available chlorine will be present as hypochlorous acid (HOCi). As in the
case of amoebic cysts, other treatment processes, such as coagulation and
filtration, assist in virus removal.
5, Application of Chlorine, Chlorine may be applied to water in a
variety of locations in the water treatment plant, storage facilities, or
distribution system and in any of several different chemical forms, as discussed
previously. Chlorine should be applied at a point which will generally provide a
contact time of 15 to 30 minutes. A key feature of chlorine application is
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thorough mixing. It is absolutely essential that the chlorine applied to the
water be quickly and thoroughly mixed with the water undergoing treatment.
If required, special chlorine mixing facilities should be provided. In some
systems using raw waters of exceptional bacteriological purity, chlorination is
the only treatment the water receives (all public water supplies should receive
disinfection as a minimum treatment). This is the case with many ground,water
supplies, as chlorine is often added to the pipeline just beyond the
well pumps. In conventional water treatment plants, chlorine may be applied
prior to any other treatment process (prechlorination), following one or more
of the unit treatment processes (postchlorination), or in the more distant points
of the distribution system (rechlorination). Prechlorination is often used
because the water contains a chlorine residual for the entire treatment period,
thus lengthening the contact time. The coagulation, flocculation, and filtration
processes are often improved by prechlorination of the water, and nuisance
algae growths in settling basins are reduced. However, prechlorination is not
universally recommended. Chlorine should be applied after processes which will
remove haloform precursors, such as coagulation and sedimentation or granular
activated carbon adsorption. Haloform precursors are much easier to remove
from water than haloforms. .
6. Chlorination Equipment. Elemental chlorine can be injected into
water with either of two types of chlorine feeders: the direct-feed type and
solution-feed type. Solution feeders are preferable to direct-feed devices because
of increased safety, and ease of control of chlorine feed rates, Chldiination
systems can be controlled either manually or automatically. For small water
treatment facilities, manual control is usually adequate. If automatic controls
are used, provision for manual control during emergency situations should be
included. •
7. Precautions in the Use of Chlorine. The presence of chlorine gas in
the atmosphere of a water treatment plant can pose immediate and serious
health hazards. Adequate ventilation of areas where chlorine gas is to be stored
or handled is a prime safety precaution. Safety equipment such as gas masks or
chlorine detectors must be provided. Chlorine storage and feed facilities should
have outside access only. Safety recommendations are given in the American
Water Works Association's publication "Safety Practice for Water Utilities".
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Valuable data on the properties of chlorine and its safe handling are also
available from the Chlorine-Institute.
b. Hypochlorites. Hypochlorites are classified as either dry or liquid
according to commercial availability. Calcium hypochlorite is the predominant
dry bleach in use today; sodium hypochlorite is the only liquid hypochlorite
disinfectant in general use.
Commercial high-test calcium hypochlorite products (HTH) contain at
least 70 per cent available chlorine. Calcium hypochlorite is an off-white
material and is available in granular or tablet forms. Although a highly active
oxidizer, calcium hypochlorite is relatively stable throughout its production,
distribution and storage. Under normal storage conditions, about 3 to 5 per
cent of the available chlorine content is lost in a year. Calcium hypochlorite
should be kept in shipping containers and stored in clean, dry, cool areas.
Containers should be arranged so that they can be easily moved in event of
leaks.
Readily soluble in water, tablet forms of calcium hypochlorite dissolve
more slowly than granular materials and provide a steady source of available
chlorine over an L8 to 24 hour period. Calcium hypochlorite may be applied
either in dry or solution form. '
Commercial sodium hypochlorite is manufacturered by numerous
companies and is often referred to as liquid bleach. It usually, contains 5 to
15 per cent available chlorine and is available only in liquid form. Sodium
hypochlorite solutions deteriorate more rapidly than calcium hypochlorite.
Storage should be in a cool dark place and a maximum, shelf life of 60 to 90
days is recommended by most manufacturers.
Sodium hypochlorite is less expensive than calcium hypochlorite. This
lower chemical purchase cost may be offset by increased storage and handling
problems. An alternative to purchase of sodium hypochlorite is use of a system
for on-site generation of this disinfectant. Raw materials required are salt,
either in a brine solution or seawater, power and water. Both the salt and water
must be as hardness free as possible to prevent precipitates from fouling the
system. If sodium hypochlorite is to be used for disinfection, an economic
analysis should be used to determine whether it should be purchased or
generated on-site.
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Any hypochlorite solution used in the disinfection process must be
pumped through an injection system into the water to be chlorinated. This
pumping can be accomplished by a diaphragm pump driven by an electric
motor.
c. Chlorine Dioxide. Chlorine dioxide has disinfection properties
approximately equal to those of chlorine. Unstable enough to require on-site
generation, chlorine dioxide is more expensive than chlorine. At this date, there
is no satisfactory test for residual chlorine dioxide. Rarely applied solely for'
the purpose of disinfection, chlorine dioxide is used principally in connection
with taste and odor control.
d. Ozone. Ozone is produced by. the passage of dry air or.oxygen,
between two high-voltage electrodes. Electric discharges through the air or
oxygen between the electrodes result in the formation of ozone. For small
sytems, air feed facilities are the most practical. Like chlorine, ozone is a toxic
substance. Ozone molecules contain three atoms of oxygen and are highly
reactive. Ozone cannot be stored as a compressed gas; it must be generated at
the point of use and used as soon as generated. Advantages of ozone include:
1. Rapid and effective disinfecting action. Ozonation is effective against
amoebic cysts, and bactericidal efficiencies are at least as high as those obtained
with chlorination.
2. Taste, odor, and color problems are largely reduced or eliminated.
3. Temperature and pH variations have little effect on the disinfecting
capability .-.of ozone, except that at high water temperatures it becomes more
difficult to dissolve the ozone in water.
Disadvantages of ozonation include: ' :
1. Large quantities of electric energy are required, about 22 to
26 kWh per kg (10 to 12 kWh per pound) of ozone for air feed systems. Better
efficiency, 4.4 to 8.8 kWh per kg (2 to 4 kWh per pound), is obtained when
oxygen feed systems are employed. : -¦ .
2. Unlike chlorine, ozone provides no residual disinfection capability.
Residual ozone reverts rapidly to oxygen.
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3. Ozone production facilities must be designed to meet the maximum
rate of use because ozone cannot be stored.
4. The equipment required to generate the ozone and inject the large
volume of ozonized air into the water is expensive.
5. Because of the high energy requirements and complexity of ozonation
systems, the probability of system shutdown is higher than with chlorination
systems; consequently chlorination systems are often installed for standby use.
Ozone is being investigated as an alternative disinfectant to" chlorine
because chlorine is implicated in the formation of haloforms. The use of ozone
avoids the formation of compounds such as chloroform, but the reaction
products of ozone have not been identified. Currently, chlorination is to be
preferred over ozonation as a means of disinfection for most water systems.
Ozonation facilities should not be planned at small water treatment plants
unless unusual conditions, which preclude use of chlorination, are encountered.
e. Applicability and Recommendations. Disinfection is used for Bacteria
reduction. For small water treatment facilities, chlorine, calcium hypochlorite
and sodium hypochlorite are the most applicable chemicals for disinfection
purposes. Choice of a specific disinfectant should be based on an economic
analysis. Chlorine is usually the most economical disinfectant for treatment
facilities with a capacity of 2800 m /day (0.75 mgd) and-larger. In general, the
required chlorine dosage will vary from 1 to 10 mg/1 for contact times of from
15 to 30 minutes. Selection of a specific dosage and contact time should be
based on the treatment objective, i.e., disinfection, taste and odor control, etc.
Chlorine solution feeders are recommended for feeding chlorine gas to water.
Hypochlorite will be the most economical disinfectant for the majority of
small water treatment systems. In general, it will be the disinfectant of choice
for treatment facilities with a capacity less than 2800 rn^/day (0.75 mgd). The
decision to use calcium or sodium hypochlorite should be based on an
economic analysis and on other considerations such as storing, feeding and
handling characteristics, Disinfectant dosages mentioned previously must be
increased if hypochlorites are used. Calcium hypochlorite generally has 70 per
cent available chlorine; sodium hypochlorite usually has 5 to 15 per cent
IV-39
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available chlorine. It is usually preferred to use a solution feeder for calcium
hypochlorite. Sodium hypochlorite must be fed through a solution feeder, as it
is only available in liquid form.
An alternative to purchase of sodium hypochlorite is on-site generation.
An economic analysis should be used to evaluate this method or any method of
supplying a disinfecting chemical.,
Use of ozone for disinfection may be desirable in regard to meeting
haloform limits currently being considered by the USEPA. A cost comparison
should be made between the use of ozone and removal of haloform precursor
compounds.
7. Stabilization
Water leaving the treatment plant and entering the distribution system
should be stable. Thus, it should neither be scale-forming nor aggressive for the
temperatures experienced in the distribution system. Two ways of stabilizing
water are (1) adjustments to pH and (2) addition of polyphosphates or silicates,
a. Adjustments to pH. Water is considered to be stable when it is at the
point of calcium carbonate saturation equilibrium. At this point., calcium
carbonate is neither dissolved nor deposited. If the pH is raised from this
equilibrium level, water becomes scale-forming, depositing calcium carbonate.
The water becomes aggressive if the pH is lowered.
An index developed by W. F. Langelier called the Langelier Saturation
Index makes it possible to predict the tendency of a given water to deposit or
dissolve calcium carbonate. The Langelier Saturation Index is equal to the
actual pH of the water minus the pH at saturation. A positive value for the
index signifies the water is oversaturated and has the potential to precipitate
calcium carbonate. A negative number indicates the water is potentially
aggressive. It is desirable to maintain the water at, or slightly above, the
Langelier saturation equilibrium point in order to maintain a thin coating of
calcium carbonate on the pipe interior. This coating protects the metal against
corrosion.
IV-40
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Stabilization of water is most often associated with an upward adjustment
of pH to control corrosion. However, there must be sufficient calcium ions
present in solution for calcium carbonate to form. In low hardness waters,
where there is a calcium ion deficiency, lime (CaO) should be added for raising
the pH. It is economical and will serve as a calcium supply as well as bringing
the pH up. Ln hard waters, there will be sufficient calcium ions present in
solution. Thus, sodium hydroxide or soda ash should be added to raise the pH
without adding to the hardness.
b. Polyphosphate. The addition of polyphosphate can be an effective
method for scale and corrosion control. Maximum temperatures in the
distribution system, retention time, and scaling potential are some of the
factors which have an effect on the performance of the specific polyphosphate
and on the dosage requirement. Generally, a low dosage of polyphosphate, less
than 5 mg/1, can effectively prevent scale even in a severe scaling condition.
When adding polyphosphate for corrosion control, somewhat higher
dosages may be required because it is necessary to form a protective corrosion
inhibiting film throughout the distribution system. Phosphates react with iron
and other minerals in water forming a positive-charged- particle. This particle
migrates to the cathodic area of a corrosion cell and deposits as a thin film
which reduces the corrosion of the metal. After the protective film is
established, dosages can be lowered while maintaining the film. Bimetallic (zinc)
polyphosphate or zinc orthophosphate is usually more effective for corrosion
control than sodium polyphosphate.
c. Silicates. Other additives which are sometimes used as a treatment
for corrosion control include silicates. Sodium silicate in one of the various
proportions of Na?Q and S1O2 has been successfully used. It is a particularly
popular treatment for waters with very low hardness, alkalinity, and pH less
than 8.4.
8. Ion Exchange
Ion exchange is the reversible interchange of ions between a solid ion
exchange medium and a solution. In water treatment applications, ion exchange
IV-41
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is most often used for water softening, but can also be applied to
demineralization by use of cation and anion resins.
a, Softening by Ion Exchange. The ion exchange process which
removes hardness cations from a water supply is termed softening. Hardness is
caused principally by the cations calcium and magnesium; however, cations
such as barium, aluminum, strontium, and others also contribute to the total
hardness of a water supply.
Ion exchange materials for softening .purposes will most generally have ex-
change sites in the sodium form. Hydrogen form resins are also available, but they
are not normally used for softening of drinking water supplies. Sodium cycle
cation resins exchange sodium ions for the hardness cations, thus producing water
with an increased sodium content and a greatly reduced total hardness. Sodium
cycle resins will not appreciably change the total dissolved solids content.
Polystyrene resins are the most popular ion exchange softening materials
in current use. Other substances which have been used as ion exchange media
for softening purposes include natural greensand, processed greensand, synthetic
silicates, sulfonated coal, and phenolic resins, The term "zeolite" has been
applied to any material used as an ion exchange softening medium, but strictly
speaking, it includes only greensands or synthetic silicates.
Softener equipment resembles vertical pressure filtration vessels and
contains internal piping to accomplish backwash, regenerant distribution and
effluent collection; a resin support such as graded gravel or quartz and the
granulated resin are located in the lower half of the vessel. The vessel should be
lined to minimize corrosion.
•5 1
Capacities of 23 to 64 kg per m (10 to 28 kilograins per ftJ) are generally
achieved dependent on regenerant dosage and temperature. Values of
193 m^/m^/day (1 gpm/ft^) minimum flow and 965 m^/m^/day (5 gpm/ft^)
maximum flow are generally used in determining size of the vessel. Resin bed
depth will vary from 0.8 m to 1.8 m (30 inches to 72 inches) to maximize resin
contact time and minimize pressure loss through the exchanger. Continuous
operation, multiple exchanger vessels, and raw water blending can help
accomplish consistent water quality as well as desired flow rates.
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Water supplies, especially surface supplies, often contain materials which
are detrimental to softener operation. Suspended solids must be generally
limited to less than 0.06 mg/1 suspended solids per mg/1 hardness (1.0 mg/1
per gpg) with a maximum acceptable limit of 10 mg/1 total suspended solids.
Hydrogen sulfide and free residual chlorine can be tolerated to 0.5 mg/1 and
1 mg/1 respectively; however, lower residual values are more desirable since
both substances cause resin damage and consequently loss of exchange capacity.
The process for regenerating sodium cycle ion exchange resins generally
involves three steps: (1) backwashing (2) application of a sodium- chloride
solution and (3) rinsing. Since downflow operation is most commonly used in
small ion exchange water softeners, backwashing is required to loosen the
media bed and remove any turbidity particles filtered out of the water during'
softening. Backwashing is performed at rates of 240 to 600 m^/m^/day (4 to
10gpm/ft^), depending on the temperature of the backwash water'and the
density of the medium. Backwash periods usually range from two to five
minutes.
After the unit has been back washed, a sodium chloride solution is applied
to the medium in order to regenerate its softening capabilities. With a
sufficiently high salt concentration, the calcium and magnesium ions in the
medium are replaced by sodium ions. Sodium cycle resins are regenerated with
a
brine solutions providing 96 to 224 kg of sodium chloride per m (6 to
14 lb per ft*1) of resin; regeneration brines are usually 10 to 15 per cent
solutions of salt. The strength of the brine solution and the contact time of the
brine with the softening medium have a direct effect on the exchange capacity
of the regenerated medium. Exchange capacity increases with increasing contact
time. Contact times of 20 to 35 minutes are common. Installations in coastal
areas may use seawater for regeneration, if the seawater is first disinfected and
treated for removal of suspended matter. Sea water- contains only about 3 per
cent salt and the exchange capacity of a softener regenerated with seawater, will
be less than when regenerated with a 10 to 15 per cent salt solution.
Control of regeneration can be automatic, semiautomatic, or manual.
Potable water systems should include automatic regeneration control based, on a
measured quantity of water passing through the exchange material with
provisions for manual override and multiple regeneration based on actual water
quality.
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After regeneration, the excess brine solution must be rinsed from the unit
before softening is resumed. About 2.7 to 12m^ (700 to 3200 gal) of rinse
<2
water is required for each cubic meter (35.3 ft ) of softening material. The
total time needed for backwashing, brining, and rinsing usually varies from.
about 35 to 70 minutes.
Disposal of the waste brine solution from the regeneration cycle is a
problem which requires some attention. Disposal may be accomplished by
evaporation ponds or by discharging into a sanitary sewer system.
b, Demineralization by Ion Exchange. Demineralization is the ion
exchange process which removes the dissolved solids content of a water supply.
Dissolved solids will contain both cations and anions and thus necessitate the
use of two types of ion exchange resins. Demineralization processes have been
devised to handle water with total dissolved solids (TDS) in a range from
500 mg/1 to 2000 mg/1. A method for continuous demineralization utilizing a
moving resin bed is currently being manufactured. Both fixed and moving bed
ion exchange systems are applicable within the same TDS range.
Cation exchange resins for demineralization purposes have exchange sites
in the hydrogen form and are divided into strong acid and weak acid classes.
The anion resins commonly used are divided into strong and weak base classes.
Ion exchange demineralizers can be operated to produce an effluent with a
TDS ranging from less than 10 mg/1 to 200 mg/1. As the proposed MCL for
TDS is 500 mg/1, demineralization costs can be reduced by operation at lower
efficiencies or by blending raw water with treated water having a low TDS.
Dissolved organics, strong ozidizing agents, and suspended solids are
harmful to ion exchange demineralizers. Organics, which may be irreversibly
absorbed in the resin, and chlorine can be removed by carbon adsorption.
Strong oxidizing agents can alter the exchange resin. Suspended solids can
inhibit passage of water through the demineralizer and prevent intimate contact
between the water and exchange resin. Suspended solids can be removed by
filtration. High levels of iron and manganese may resist removal during
regeneration.
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Capacities for cation resins of 23 to 46 kg per (10 to 20
kilograins per ft^) of resin are generally achieved dependent on regenerant type
and dosage.
Cation resins are usually regenerated with sulfuric acid: however,
hydrochloric acid may also be used. Hydrogen cycle resins are regenerated with
sulfuric acid solutions providing 48 to 160 kg of concentrated (66° Baume)
sulfuric acid per m^ (3 to 10 lb per ft^) of resin. Hydrochloric acid solutions
are used which provide 32 to 144 kg of 100 per cent hydrochloric acid pernr
(2 to 9 lb per ft^) of resin in the form of a 10 per cent solution. Anion resins
usually are regenerated with sodium hydroxide (caustic soda) solutions
providing 64 to 160kg of caustic perm (4 to 10 lb per ftJ) of resin applied as
a 3 to 5 per cent solution.
Control of regeneration can .be automatic or semi-automatic, or manual.
The demineralizer equipment will be similar in appearance to softener
equipment; however, there will be two vessels per unit. The internal piping will
be basically the same. Flow loadings .will be similar and waters containing high
turbidity, hydrogen sulfide, and chlorine concentrations will be detrimental to
demineralizer resins in the same manner as softener resins.
Disposal of demineralizer waste solutions from the regeneration cycle can
be accomplished by first mixing the waste from the cation (acidic) and anion
(basic) units in a neutralization basin and then adjusting the pH to comply with
discharge regulations. When properly neutralized, demineralizer wastes may be
discharged to a sanitary sewer system, if permitted by local conditions.
e. Applicability and Recommendations. The ion exchange process
should be considered for any small treatment softening application. It is an
excellent process for softening hard water, producing an effluent with a
nominal hardness of zero under normal operating conditions. However, for
municipal uses, it is neither desirable nor economical to soften an entire water
supply to zero hardness. The softening costs can be reduced considerably by
blending the zero hardness water with unsoftened bypass water. Thus a finished'
water with any desired degree of hardness can be obtained. Use of ion exchange
softening is not recommended for persons on sodium-restricted diets.
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The use of ion exchange systems for demineralization should be
considered for. treatment of water with less than 2000 mg/1 TDS concentra-
tions. Ion exchange demineralizers are capable of producing relatively pure
water, hence blending of treated and untreated water is often desirable because
of lower operation costs. ;
In addition to hardness and TDS reduction, the ion exchange process
should be considered for removal of the following: arsenic, barium, cadmium,
chromium, fluoride, lead, mercury, nitrate, selenium, silver, color, copper, iron,
manganese, sulfate and zinc. .' •
Some general advantages of ion exchange include low capital investment
and mechanical simplicity. The major disadvantages are high regenerant
chemical requirements and disposal of chemical wastes from the regeneration.
process. These factors make, ion exchange more suitable for small systems than
for large ones. •
Disposal of the waste brine solution from the regeneration cycle is, a
problem which requires some attention. For small systems, disposal may be
accomplished by evaporation ponds or by discharge into .a sanitary sewer
system. Regulatory agency requirements in a, particular locality may be. a,
controlling factor in selecting a disposal method. ...
9. Membrane Processes
Brackish waters are widely distributed over the United States and are
found underground as well as in estuaries, rivers,, and .lakes. In some, areas,
brackish water may be the only available water for public supply and
consequently must be treated. Two membrane processes, are commonly used in
desalting applications: electrodialysis and reverse osmosis. Electrodialysis (ED)
uses electric current to transfer salts from feedwater through a.membrane to a
reject stream while reverse osmosis (RO) utilizes hydraulic pressure to force
feedwater. through a membrane to a product .stream. Both, pro cesses use energy
at a rate somewhat dependent upon the amount of salts to be removed.
a. Electrodialysis. Electrodialysis is the. demineralization of water by
the removal . of ions through special membranes under ¦ the influence of a
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direct-current electric field. Until the early 1970's all commercial electrodialysis
installations were of the Fixed polarity type having' an anode and a cathode at
opposite ends, A polarity reversal system has since been developed in which
each electrode intermittently change's electrode polarity to prevent membrane
scaling. Newer membrane stack designs may contain more than one electrode
pair, to permit internal staging. ' '
Operation of an ED system involves the application of a direct-current
potential to' the electrodes. Since the minerals in water dissociate into cations*
and anions, the positively-charged electrode, called the .anode, attracts .anions
present in the water, and the negatively-charged electrode, called the cathode,
attracts the cations.
Two'types of special membranes are'utilized in electrodialysis. The first,
can be permeated by cations but not anions. The second can. be permeated by
anions but not cations. These membranes are arranged in a stack, with
cation-permeable membranes alternating with anion-permeable membranes.
Feedwater enters the spaces. between the membranes and the direct-current
electric field' is applied to the stack, causing the ions to migrate toward the
electrodes. This results in a concentration'of ions in alternate spaces between'
membranes, and the water in the other spaces becomes depleted in ions, or
demineralized. Water is then drawn off from between the membranes in "two
separate streams, one containing most of the ions and the other relatively free
of ions.
Electrodialysis units are generaly limited to a maximum of roughly 50 per
cent TDS removal per stack to avoid excessive ion concentrations near the
membranes. This situation, known .as concentration' polarization; can result in
membrane scaling and degradation! Higher TDS removals are obtained by
operating stacks in series. Product water recoveries usually range from 75 to
95 per cent per stack. Most plants employ 2, 3, or 4 stacks in series (although a
single stack or more than four may be used) and are designed for 60 to 90 per
cent water recovery and 60 to 95 per cent TDS removal. TDS removals over
90 per cent are seldom achieved in practice because' power consumption and
the danger of scaling increase with brine concentration. ' '
One manufacturer of electrodialysis units recommends that flow through
an ED installation not be allowed to drop below about two-thirds of the
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nominal design flow to prevent uneven internal flow and concentration
polarization. This problem can be avoided by intermittent operation, system
storage to equalize flows, or recycling.
Substances such as suspended solids, dissolved organies, hydrogen sulfide,
iron, manganese, and strong oxidizing agents (chlorine, ozone, and perman-
ganate) are deleterious to electrodialysis membranes. In order to remove these
undesirable constituents, the feedwater for an electrodialysis facility should be
pre treated as recommended by the ED supplier. The efficiency of the
membranes may also be greatly reduced by scaling deposits. Hardness, barium,
strontium, iron, manganese, and pH are important factors contributing to
mem brane • seal ing.
Scale prevention for fixed polarity ED unite usually consists of the
following:
® Acidification of the brine recirculation stream to prevent carbonate
and hydroxide scaling.
• Limitation of calcium sulfate concentrations in the brine effluent.
• Reduction of iron to 0.3 mg/1 and manganese to 0.1 mg/1 through
¦ ' pretreatment
¦ • Diversion of a small flow for flushing of electrode compartments to
remove gaseous hydrogen and prevent acidic build-up at the cathode
and remove gaseous chlorine and prevent alkaline build-up at the
.. anode.
. Polarity reversal systems rely upon continuous reversal of compartment
roles to prevent scale formation. Polarity is reversed at roughly 15 minute
intervals so that inadequate time is provided for scale to build up between
membranes, eliminating the need for acid or polyphosphate feed. However,
regular in-place chemical cleaning is essential. Physical disassembly and cleaning
may also be required periodically. Iron and manganese reduction is required
with polarity reversal systems and product water recoveries are lowered by
about 10 per cent by additional flushing requirements. In a large polarity
IV-48
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reversal plant, electrode flushing streams could conceivably be returned to the
feed flow. Membrane life of over five years is possible with proper care and
favorable operating conditions.
The economics of electrodialysis is dependent on a number of factors,
primarily the size of the facility, the characteristics of the feedwater, and the
cost of power.
Process power requirements are roughly 0.8 to 2.6 kWh per m (3 to
lOkWh per, 1000 gal) of product water per 1000 mg/1 reduction-of- total
dissolved .solids concentration. Additional pumping power requirements are-
usually 0.8 to 2.6 kWh per (3 to lOkWh per 1000 gal) of product. Power
inputs are dependent upon plant scale, the fraction of design flow being
treated, and pump and equipment selection."
b. Reverse Osmosis. When two solutions containing different concentra-
tions of minerals are separated by a semipermeable membrane, relatively pure
water will migrate through the membrane from the more dilute solution to the
more concentrated solution. This phenomenon, called osmosis, continues until
the build-up of pressure on the more concentrated solution is sufficient to stop
the flow. If there, were no increase of hydrostatic pressure on the rrfore
concentrated solution, the process would continue until both solutions had
equal concentrations of minerals. The greater the difference in concentration of
solutions separated by a semipermeable membrane, the greater the rate of flow
of. water through the membrane. The amount of pressure which • must be
applied to the more concentrated solution in order to stop this flow is known
as the osmotic pressure. If a pressure in excess of the osmotic pressure is
applied to the more heavily mineralized water, relatively pure water will flow
through the membrane in the opposite direction in a .process called "reverse
osmosis."
More process variations are available in RO than ED. Four RO>
configurations have been developed; hollow fine, fiber, spiral wound, tubular,
and plate and frame. The tubular and plate and frame configurations are
comparatively very bulky and have not found wide acceptance due to space
requirements .and high initial cost. The hollow fine fiber and spiral, wound
configurations are more commonly used.
IV-49
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RO plant layouts generally feature flow schematics to maintain brine flow
rates above a minimum. For example, a plant may have three stages, each
having fewer modules than the previous stage. Above minimum flows are
necessary to. avoid localized build-ups of'ion concentrations near membrane
surfaces (concentration polarization) as in ED. The deleterious effects of this
phenomenon in RO are- higher osmotic pressure requirements, lower salt
rejection, and increased likelihood of scaling and membrane hydrolysis.- To aid
in this respect, manufacturers recommend that feed stream flows not be lower
than three-quarters of the nominal design flow. Uniformity of the feedwater
flow may be maintained in the same manner'as previously-suggested for
electrodialysis.
RO modules have been developed for application to a wide feedwater TDS
range. As TDS contents increase, however, the hydraulic pressure required to
maintain a constant product flow also rises while salt rejection efficiency
declines. Pressures are held constant in normal operation, but power
requirements increase with TDS for a given output because larger feedwater
quantities must be pumped. Standard RO units (suitable for waters up to about
12,000 mg/1 TDS) which are operated at 28 to 35 kg/cm ^ (400' to 500 psi)
achieve 45 to 90 per cent product water recovery and 70 to 99 per'cent salt
rejection.' Rejections of up to 95 per cent are typically achieved. Sea water
desalting modules operate at about 56 kg,'cm- (800 psi), achieve roughly'20 to
40 per cent recovery, and can exceed 99 per cent salt rejection. Power
requirements for the standard modules generally vary from 0.3 to 3 kWh
per nrr (1 to. 11 kWh per 1000 gal) of product water. Power requirements for
•3
sea water desalting are estimated to be 11 to 27 kWh per m- (40 to lOOkWh
per 1000 gal) of product. RO power needs are virtually entirely attributable to
pumping, -but are dependent on a number of factors including plant scale,
pump selection, and membrane age.
The essential element in the reverse osmosis method of demineralization is
the semipermeable membrane. Several types and configurations of membranes
are currently available, with the most widely used being various forms of
cellulose acetate, diacetate, and triacetate, or polyamide membranes. The
characteristics of these membranes vary and constitute an important design
consideration.
IV-50
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RO membranes are subject to flux (water production) decline. This is a
normal process primarily attributable to the high pressures of operation causing
membrane compaction and aggravated by scaling, contamination, bacterial
attack, and high temperatures. For plants operating around 28 kg/cm-
(400 psi), flux declines of 10 to 20 per cent are typically encountered in the
first -2000 hours of operation after which time little further decline" occurs.
Even higher declines are experienced in high pressure (sea water) systems. Flux
reduction must be accounted for in initial system design. Poly amide membranes
are thought to be more resistant to flux decline than are cellulose membranes
of,which the triacetate and diacetate forms are more resistant than the-acetate
form. RO membrane life expectancy is approximately 3 years with proper care
and favorable operating conditions. Salt rejection .does not necessarily decline
with flux and can be maintained with careful operation. "
Application of standard RO modules should be considered for waters up
to about 12,000 mg/1 TDS. Sea water RO. units should be considered as an
alternative to distillation at higher salt contents.
Due to lower water viscosities at higher temperatures, production by RO
units increases with temperature. If the temperature becomes too high,
however, compaction and irreversible flux reduction may result. The effects of
temperature and pressure are closely related. At higher temperatures, hydraulic
pressures must be lowered to prevent damage to the membranes. Cellulose
membranes generally have a maximum normal operating temperature of 29°C
(85°F). Poly amide membranes may be routinely subjected to temperatures as
high as 35°C (95°F). Although both membrane types can withstand even higher
temperatures for short periods without ill effects, optimal operating
temperatures are generally lower than the maximum values recommended.
The performance of an RO installation as in the case of ED, is highly
dependent upon a number of. water quality parameters. Suspended solids and
dissolved organics are both harmful to reverse osmosis membranes and . should
be removed by pretreatment as recommended by RO supplier.
The effect of oxidants upon reverse osmosis units varies. The cellulose
membranes which are very susceptible to bacterial attack are somewhat tolerant
of chlorine. A maximum continuous level of 1 mg/1 free chlorine (or the
IV-51
-------
equivalent oxidizing strength) is recommended. The threat to cellulose
membranes from bacteria is sufficient in nature so that even well waters should
be disinfected. Polyamide membranes are reputed to not be susceptible to
biological attack, but are very sensitive to chlorine. Recommended maximum
continuous exposures are 0.1 mg/1 free chlorine at pH less than 8, and
0.25 mg/1 at pH 8 or higher. While the polyamide membranes are apparently
not subject to biological attack, they may be fouled by biological growths.
Because they are believed to be selectively sensitive to chlorination rather than
oxidation, the use of an alternative disinfectant may be feasible. However, no
information on the effect of ozone on polyamide fibers is available. One
manufacturer of polyamide membranes recommends the use of formaldehyde
on an intermittent basis to control slimes.
Discussed earlier with respect to ED, the scale-related parameters,
hardness, barium, strontium, iron, manganese, and. pH are equally important to
RO operations. Scale prevention measures commonly used include the
following:
• pH adjustment, to between 5,0 to 6.5 to prevent hydroxide and
carbonate scaling.
• Iron and manganese reduction by pretreatment to levels recom-
mended by RO equipment manufacturers.
• Use of a polyphosphate to inhibit calcium sulfate scaling.
' • Limitation of calcium sulfate concentration in brine effluent.
c. Applicability and Recommendations. When confronted with treating
brackish or highly mineralized waters, i.e.. waters with high total dissolved
solids concentrations, membrane processes should be considered.
Both electrodialysis .and reverse osmosis are effective for reducing TDS
concentration and both are . suitable for small applications. Appropriate
.pretreatment is' a major -factor in successful operation of 'both processes.' ;
Electrodialysis and reverse osmosis should also be considered for removing
arsenic, barium, cadmium, chromium, fluoride, lead, mercury, nitrate, selenium,
IV-52
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silver, chloride, copper, iron, manganese, sulfate and zinc. In addition, reverse
osmosis is recommended for reduction of bacteria, radionuclides and.- color.
Advantages of ED as compared to RO include low pressure operation with
no need for high pressure pumps, usefulness over a higher temperature range,
longer membrane life, and a constant rate of production with time.
The primary disadvantage is a proportional increase in power consumption
with increasing salt content which prevents ED from being economically
competitive with RO at TDS levels of roughly 5000 mg/1 and above. Also,
because ED removes only charged particles, nonionics such as bacteria'and
dissolved gases remain in the product water. RO systems on the" other hand,
force product water through the membrane, thus removing' dissolved gases,
bacteria, viruses, and other nonionics as well as ionic species. Standard RO
systems are effective for treating raw waters with TDS concentrations up to
about 12,000 mg/1. Disadvantages of RO include flux reduction with time,
shorter membrane life, and possibly significantly greater pretreatment chemical
requirements.
Each situation should be individually examined to determine which
process should be used for reduction of TDS levels. The economics of the
situation will be the predominant factor in selecting ED or RO.
10. Fluoridation/Defluoridation
Fluoridation is the process of adding fluorides to drinking water in order
to reduce tooth decay. Where necesary, fluorides are removed from water to
prevent dental fluorosis.
a. Fluoridation. Fluorine is the thirteenth most prevalent element in
the earth's crust and is present as fluoride in all natural waters to some extent.
The concentration of fluoride in natural waters is generally less than what-public
health authorities consider to be optimal. Consequently, health departments
often recommend adjustment of the fluoride level by the addition of small
amounts of fluoride compounds to the water.
IV-53
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1. Health Effects of Fluorides in Water. In the 1920's and 1930's, the
incidence of mottling of teeth (dental fluorosis) was definitively linked to the
ingestion of waters that contained high concentrations of fluoride, generally in
excess of 2 mg/1. It was also observed that persons suffering from dental
fluorosis had very few dental caries, and further studies indicated that,
concentrations of fluoride near 1.0 mg/1 greatly reduced the occurrence of
dental caries in children without producing mottling of the teeth.
¦ Inasmuch as fluoridation effects a marked decrease in the number of
dental caries suffered by children, but high concentrations of fluoride cause'
dental fluorosis, the objective of fluoride adjustment in water treatment is to
add enough fluoride to water to reduce dental caries while not adding enough
to cause dental fluorosis.
Maximum concentrations which can be tolerated without the occurrence
of dental fluorosis are given in Appendix ¦ A of this report. These maximum
concentrations- are dependent on the average daily intake of water by children
in any particular location. The average daily intake of water is related to the
average annual maximum daily air temperature, hence maximum fluoride
concentrations are-related lo this temperature parameter. Higher temperatures
dictate a lower maximum allowable level of fluoride.
" 2, Other Effects of Fluoride in Water. The small amount of fluoride
ion added to drinking water does not cause taste or odor nor does it increase
the corrosive properties of the water or cause encrustation in the distribution
system or household plumbing, The use of hydrofluosilicic acid will reduce the
pH and may contribute to corrosion.
tv, ' ' *
3. "-Forms of Fluoride Used in Water Treatment. The most common
compounds used in water fluoridation are sodium fluoride, fluosilicie acid, and
sodium silicofluoride. The choice of which form is best for a water treatment
plant is dependent. largely on the cost of the compound, the availability, and
the mode of fluoride application selected. Other compounds that have been
used successfully by some water utilities include ammonium silicofluoride and
fluorspar. However, these compounds are not recommended for routine
application. The use of ammonium silicofluoride results in an increase in the
ammonia content of the water, which may be objectionable because of the
adverse effect of ammonia on chlorine disinfection, or may be desirable if
IV-54
-------
chloramines are wanted. Fluorspar is not recommended for routine use because
it is difficult to dissolve. Hydrofluoric acid presents such extreme safety and
corrosion hazards that it is not considered suitable for general use as a water
fluoridating agent. . ... "
4. Application of Fluorides. The number. and variety of different
fluoride application devices make it impossible, to describe all of them in this
report. In general, the chemical feeders used can be divided into two
categories;- dry feeders and .solution, feeders. Dry feeders, can be further
divided; intp gravimetric- dry, feeders and volumetric dry, • feeders. The choice
between .gravimetric or volumetric dry feeders must be made on the basis of
feed rates,.accuracy requirements, and overall cost. .
Solution feeders consist of any of several types of positive-displacement
pumps if pressure feed is. used, or a paddle-wheel or bucket apparatus if gravity
feed is used.. Solution feeders are required for application of fluosilicic acid and
may be- used for feeding solutions of . sodium fluoride, etc. Use of zeolite
softened water is recommended for preparing strong solutions of sodium
fluoride; softening reduces scaling problems. The- type of feeder to be used
should be selected on the. basis of capacity,,accuracy, durability, and*corrosion
resistance. - . ¦ ... . . ¦ .
.. 5.- Points of Application of Fluorides. -The most-important, factor in
deciding on a point to inject fluoride is that all of the water must pass this
point. If no such common point exists, more than one, application point
should be used.. If .fluoride is added to .only a portion of the water and
subsequently blended, the blending must include positive mixing of. all water
to insure uniform fluoride concentration. Fluoride is commonly injected into
the. water in the filter effluen t conduit. If ground water is used as a source of
water supply,-the fluoride should be injected beyond the well head to insure
adequate mixing and uniform dosage of fluoride and to prevent precipitation of.
fluoride compounds in the well. Multiple well installations often require a
feeder at each well. It is generally" more desirable to apply fluoride to the water
in a water line leading to a storage,tank, rather than away from a storage tank,
because the flow toward the tank usually, does not vary, as widely or as rapidly
as the flow away from the tank.. The adjustment of the fluoride feed rate is
much easier if the flow does not• change rapidly.
IV-55
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The. application of fluoride in a conventional water treatment plant should
be after filtration, if possible. When fluoride is applied during the alum
coagulation process, some fluoride will be lost. Lime softening will also remove
some fluoride, especially if the concentration of magnesium in the raw water is
high. If calcium hypochlorite and fluoride are both to be used, they should be
applied as far apart as possible. If injected in close proximity, they would form
a precipitate of calcium fluoride.
6, Automatic Control of Fluoridation. In many cases it is desirable to
have the rate of feed of fluoride controlled automatically by a meter measuring
the rate of flow of water to be treated. This is acceptable if the flowmeter to
be installed is proven reliable and if the apparatus for feeding fluoride can
operate at various speeds. If automatic control is used, provisions should always
be made for manual control in the event of failure of the automatic control.
Medical evidence indicates that skin contact with excessive amounts of
fluoride can cause extreme discomfort. Every effort should be expended to
insure that personnel handling fluoride wear protective clothing and that
adequate safety precautions be taken.
b. Defluoridation. Although fluoride in moderate amounts is beneficial
in the prevention of dental-caries, excessive concentrations of fluoride cause
permanent mottling of tooth enamel and, in severe instances, pitting of the
enamel and loss of teeth. The Interim Primary Drinking Water Regulations
developed by the Environmental Protection Agency for maximum allowable
concentration of- fluorides are listed .in Appendix A of this report, Fluoride
MCL's.are approximately two times recommended optimum fluoride levels.
¦ Fluoride- can be removed from water by percolating the water through
granular" beds of. activated alumina, bone meal, bone, char or tii-calcium
phosphate. The fluoride is removed by a combination of ion exchange and
adsorption. When "activated alumina beds become saturated with fluoride, they
are regenerated by treatment with a caustic soda, solution. Excess caustic soda
is removed by rinsing and neutralization with an acid. Mixed-bed demineralizers
' can also, be used to reduce the fluoride concentration. A mixed-bed de-
mineralizer will remove other minerals along with the fluoride. Additional
methods of fluoride removal include sorption on precipitates of aluminum or
IV-56
-------
magnesium hydroxide. Precipitation of substantial concentrations of aluminum
or magnesium is required to effect major reduction in fluoride concentrations.
Saline water conversion methods, such as electrodialysis and reverse
osmosis, have shown promise for achieving reduction of fluoride concentrations.
These methods have been applied to brackish waters and have demonstrated
their ability to remove fluoride, etc.. along with other minerals.
Additional information in regard to defluoridation is included in
section III A of this report, under Inorganic Chemicals.
c. Applicability and Recommendations. Adjusting fluoride concentra-
tions in water supplies to optimum levels should be considered as a method for
reducing tooth decay. Recommended water fluoridation compounds are sodium
fluoride, fluosilicic acid and sodium silicofluoride. Fluoride should be applied
after filtration in a conventional water treatment facility. Recommended,
defluoridation processes for small water treatment systems include reverse
osmosis, electrodialysis, activated alumina, bone char, and, if used for removal
of magnesium, excess lime softening.
Disposal of wastes from defluoridation treatment should be given careful
consideration due to the toxic nature of waste.
B. WATER QUALITY CONTROL
Control of a water treatment facility involves more than valve turning and
button pushing to start and stop equipment. In order to determine which valves
to turn "and which equipment to use the operator must be able to determine
how well the plant is functioning. Not only does the operator need to know
whether the MCL's are being met but also needs to know whether the
treatment processes are under control. To determine all of this the operator
will need laboratory analyses of the water and information provided by plant
instrumentation.
1. Sampling and Analysis
Treated water must be sampled, for contaminants included in the drinking
water regulations, at the proper locations and at the required frequency.
IV-57
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Analyses must be in accordance with the methods prescribed in the regulations.
Since the inorganics, organic pesticides and radionuclides require extensive
equipment and analytical skill these tests must be conducted by a certified
laboratory. Approximate costs per sample for these analyses done by a
commercial laboratory are as follows:
Most state health department laboratories can also perform these analyses.
The rest of the required analyses including turbidity (surface water or
combination ground and surface water), chlorine residual (as a State allowed
substitute for a portion of the coliform analyses), and coliform analyses would
cost from $4 to S10 per sample in a commercial laboratory. To aohieve proper
results, the chlorine residual should be run almost immediately and the
coliform analyses should be run within 24 hours. Use of a commercial
laboratory for chlorine residual analyses is not feasible. Turbidity analyses are
required daily for surface water plants and the cost in a commercial lab would
be very high. The plant operator in all plants should be able to run the
turbidity and chlorine residuals in a plant laboratory facility. Probably only
those facilities of about 3800 m^/day (1 mgd) and larger will want to run
in-plant coliform analyses. For smaller plants either the county or state health
department could probably run the coliform analyses.
In addition to the required tests, each plant should run the following tests
in-plant as a control on the treatment processes:
Temperature of the water is important because it influences the rate of
chemical- reactions, chlorine effectiveness, and the settleability of floe. The
higher the water temperature the faster the chemical reactions and the better the
settleability. The pH and alkalinity of a water are general control parameters
since a number of the chemicals added to tne water raise or lower the values of
Inorganics
Organ ics
Radioactivity
S 90 - $150
$160 - $270
$ 60 - $120
Temperature
pH
Alkalinity
IV-58
-------
these parameters. Effects of pH and alkalinity have been discussed previously
for contaminant removal and treatment techniques.
Other control tests may be required depending on the contaminant
removed or the treatment processes used. For instance, where aeration is used
in a lime softening plant, carbon dioxide could be a control parameter.
2. Laboratory Facilities
Each water treatment facility should have minimum laboratory, facilities to ,
do the following tests: .
Turbidity
Chlorine Residual
pH
Alkalinity
Temperature
The laboratory size required for these tests should be about 11 mr .(120 ft^) .
including space for' laboratory record keeping. A laboratory counter .about 2.4 m
(8 feet) long should be provided with storage space for equipment.
The cost-* for- a minimum laboratory facility would be about $7000. This
can be broken down as follows:
Building
S2200
Furniture
S2300
Equipment
S1850
Supplies
$ 650
TOTAL
S7000
Additional: facilities • and equipment to do coliform tests would cost about
$5500.
* Cost based on engineering estimate.
IV-59
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3. Metering, Instrumentation, and Control
Metering at a small water treatment plant can be kept fairly simple.
Generally all that is needed is a meter on the raw water and one on the
finished water leaving the plant. The raw water rtieter can be a propeller type
meter with flow indication only. The finished wkter meter Should be a venturi
flow tube or propeller meter which at least totalizes flow and possibly records
flow. , ....
Filter instrumentation and control for those supplies which are filtered
should be provided with the :filter package'. The'simplest forifi of control is a
• flow splitter ahead of the filters with; a water level sensor Bn'each" filter which
operates: the filter rate controller;; Another simple method" of contrtil is to
:bperate "the filters with a variable decliiiing ratei'Hbwever sohie'stkte regiilitbry
agencies may not 'approve' this m'ethod. No- indication of the 'filter backwash
rate is required, if - the' flow has been physically limited to1 not exceed the
maximum desirable rate.' However,: indication of head loss through the filter
should be provided. :; . ; - ; .
For surface, water, plants where a;• finished water turbidity sample is
; required daily, it may be advantageous to:put a continuous turbidimeter on the
• filter:effluent. This; turbidimeter will have to. be calibrated and may have' some
maintenance requirements principally related to keeping the -optical, system
clean and aligned. A back up laboratory turbidimeter will still be required for raw
water turbidity and for filtered, water; turbidity when'the: continuous'unit-is out
of semce. ;¦ .* »* <>. :
A control panel should be provided in each water treatment facility. .The
panel should be part of "the plant motor control center. The control panel
should contain all indicators, totalizers, and. recorders for the instrumentation
. discussed above in addition . to remote indication of, the. status of, all,motor
.operated equipment. Actual on-off controls, for. the motors at the treatment
facilities ,should be local to reduce instrumentation and control and. to require
the operator to, go to the piece of equipment,and observe. it. when . starting ;or
stopping it. Remote on-off controls, can be employed for- wells,: distribution
system pumping and other facilities located ,away from ; the . water treatment
plant.
IV-60
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C. WATER TREATMENT PLANT WASTE DISPOSAL
. > Disposal of wastes generated during the various-water treatment .processes
must receive careful consideration. Selection of a disposal method will influence
water treatment,plant location and design, .
1. Sources, Quantities, and Characteristics of Wastes
The wastes generated in a water treatment plant, are composed of .the
natural solids removed from, the raw water, as .well as the chemical precipitates
.resulting from chemical addition. Thei nature .and quantity of the raw. water
, solids will vary from one plant, to .another.. For example, natural; solids removed
.in a surface water plant are idependent upon sediment washed into the, water
supply by rainfall, seasonal algal growths, spring turnover in -lakes, and other
factors. The nature and. quantity of chemical solids are a function of; the
chemicals added and the resulting precipitates.
a.. Sources.! Predominant water treatment plant:wastes are waste solids
in the; sedimentation , basin blowdown: and .the 'filter, backwash water; Other
• wastes include spent brines from regeneration of ion exhange units and spent
granular activated;carbon. : - :• ... ' . .tr - ¦¦
!b; Quantities of; Wastes Produced.- Quantities of wastes can best; be
determined not by measuring the waste stream, but through the use of
chemical mass balance and other available data, such as suspended solids
information. i: r '!
1. Solids Produced by Turbidity Removal Natural solids are normally
removed in sedimentation' basins with the chemically produced solids. If the
suspended solids concentration'(mg/1) in the raw water is'available, then the
amount of waste solids can be calculated directly. If suspended soli'ds data are
not" available then an attempt should be made to con-elate turbidity and
suspended solids. The solids removed can'be calculated as follows, assuming all
natural solids are removed in the treatment process:
IV-61
i
-------
Solids produced (kg/day) = (suspended solids-mg/i) x (0.001) x (flow-m3/day)
Solids produced (lbs/day) = (suspended solids-mg/1) x (8.33) x (flow-mgd)
2. Solids Produced by Chemical Addition. The amount of. waste solids
provided by chemical addition depends on the type of chemical added and the
dose. The following paragraphs describe the chemicals utilized in each process
of water treatment and the amount of solids produced. .. .
Coagulation. A reasonable basis for estimating the * chemical solids
produced, when the coagulant alum is used, is indicated by the following
reactions: -
AljfSO^j ¦ 14 H2O -+ 2A1^+ + SO^" +. MH2O (ionization)!.
2A13+ + 60H"^2A1_(0H)3 " ¦
precipitate
Commercial alum contains about 17 per cent AI7O3 or,9 per cent Al+++.
Inerts are negligible. Essentially all aluminum added to the water is removed.
The sulfate (SO4") component of the alum remains in the water and appears as
a residual mineral in the finished water. , ,
Aluminum hydroxide [Al(OH)g] resulting from alum addition can be
computed from alum use in lbs or kg/day [A 1 c] as follows:
Al(OH)3 = [0.26] IA1 c J (lbs or kg/day) 1 ' "
•" The results of similar calculations made for other coagulants used in water
treatment are shown in Table 25.
Table 25 -
SOLIDS PRODUCED BASED ON COAGULANT DOSAGE
Solids Produced (dry)
lbs or kg/day
[0.26] [Ale] : '
[0.46] [Fee] ; =•'- !
[0.40] [Foe] . ¦ =
[1.0] [Pc]
[0.3] [Na2Si03] " ;
Coagulant
lbs or kg/day
[Ale] Alum
[Fee] Ferric Sulfate
[Foe] Ferrous Sulfate
[Pc] Polymers
[Na2Si03] Activated Silica
IV-62
k
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Taste and Odor Removal The chemicals generally used to oxidize taste
and odor producing compounds are chlorine" and potassium permanganate.
Activated carbon is also used for taste and odor removal but acts as an adsorbent.
The amounts of waste solids produced by the removal of tastes and odors
are developed in a similar manner as those solids produced by the addition
of coagulants. Table 26 presents the chemicals and resulting solids produced
in removing taste and odors.
- " - ' Table 26 ¦
SOLIDS PRODUCED FROM TASTE AND ODOR REMOVAL
Chemicals 1 . Solids Produced (dry)
lbs or kg/day lbs or kg/day
" ' ' • - i - i ' ' .
[AC] Activated Carbon 11.0] [AC]
; [KMn04] Potassium Permanganate [0.55] [KMn04]
[CI] Chlorine None
: '•Lime-Soda Softening. The lime-soda and ion exchange processes are the
softening processes most commonly used to remove hardness from water.
•
-------
Stabilization. Stabilization of lime-softened water may be accomplished
by recarbonation, split treatment, or by the use of polyphosphates.
Polyphosphates contribute nothing to solids production and precipitation
induced by recarbonation or split treatment is accounted for by calcium and
magnesium mass balances. These stabilization processes are not sources of
chemical solids.
Disinfection. Disinfection is usually accomplished by chlorine and/or a
combination ' of ammonia and chlorine (chloramine process). All reaction
products'are soluble;'hence; disinfection produces no chemical solids.
Fluoridation. Some plants'practice fluoride adjustment of the'water. Any
fluoride addition becomes part of the dissolved solids and does not contribute
to'the wastes:'' "
c. Characteristics. Water treatment plant waste products'exhibit various
characteiistics, "depending on their source. Knowledge of these characteristics is
basic to the selection of necessary waste disposal methods.
1.'"Waste Solids from Coagulation with Aluminum Salts. The wastes
produced by coagulation ' with aluminum salts normally have a solids
concentration of 0.5 to 2 per cent when they are removed from a
sedimentation basin. The sludge is usually bulky, and gelatinous in consistency.
It is difficult to dewater and a solids concentration of only 8 to 10 per cent
can .be achieved when it is thickened in a lagoon. Dewatering by mechanical
devices such as the centrifuge has obtained a 15 to 20 per cent solids
concentration. This concentration can only be attained if" the sludge is first
pretreated with a polymer. Without pretreatment, a 5-6 per cent solids
concentration is an upper limit. Vacuum filtration has not "been successful in
dewatering waste solids from water treatment plants.. ,
2. Waste Solids. Produced from Coagulation, with'Iron Salts. The solids
produced from the coagulation of water by iron salts are similar to those
produced by coagulation with aluminum salts. The consistency and difficulty in
dewatering are similar but the iron floes generally are not as fluffy and
gelatinous as alum.
IV-64
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3. Waste Solids from Softening by Chemical Precipitation. The
characteristics of solids from the precipitation of hardness by lime and soda
varies with the composition of the raw water and the dosages of chemicals used
for softening. Waste solids collected in the settling basins of lime and lime-soda
softening plants have been reported to range from 2 to 33 per cent solids
concentration. Softening waste solids have been dewatered in lagoons to a
solids concentration of 50 per cent. Mechanical devices such as centrifuges
can dewater lime softening waste solids, from 40 to 65 per cent solids. The
greater the ratio of magnesium hydroxide (MgCOH^I to calcium carbonate
(CaCOj) the lower the per cent lime softening waste solids concentration.
4.. Filter Wash Water- , Filter backwash water consists of fine natural and
chemically precipitated solids that are not removed in the sedimentation basin.
The solids concentration is low, averaging 0.08 per cent solids (800 mg/1 total
suspended solids). Filter wash water is usually 2 per cent of the water produced.
Filter wash water by itself cannot be dewatered by mechanical means. When
lagoon ed. the solids are allowed to settle and the supernatant is decanted..
J. Spent Brine Solutions. As discussed previously, the characteristics
and amount of waste brines vary widely. The characteristics of a composite
..sample, of spent brine, discharged, from one large zeolite. plant are given in
Table 27. , ' ' ' -'
~ J ¦ ¦ Table. 27 . ' ¦.
ANALYSIS OF SPENT BRINE SOLUTION
Constituent mg/l,.
Sodium and Potassium 3,325
Calcium " ' 1,720
Magnesium " -• 600
Chloride 9,600
• Sulfate . -328
Dissolved Solids 15.654
IV-65
I
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2. Waste Disposal Practices
Various methods of waste disposal .have been used by the water utility
industry. No specific method of waste disposal is most suitable for all wastes,
as the properties of different types of wastes vary considerably.
a. Direct Disposal. The predominant method of disposal of backwash
water and waste solids from"water treatment plants has been'direct discharge to
surface waters; This method is now being abandoned due to regulations for
discharges to water courses set by the Environmental "Protection Agency.
Howevef, the EPA is considering direct discharge to the larger rivers such as the
Missouri, Ohio, and Mississippi Rivers. Other than direct discharge, small water
treatment plants have few reasonable methods of disposal available!
b. Vacuum Filtratibn, Vacuum" filtration equipment is extensively used
for dew ate ring wastewater treatment plant sludges, but its application to water
treatment plant "waste solids is limited. This method utilizes a cylindrical drum
covered with a porous fabric made of metal mesh, steel coils, wool, cotton,
nylon, saran, or one of the new synthetic fiber cloths as filtering media.
Alum waste solids have proven difficult to dewater by vacuum filtration.
The gelatinous nature of the waste solids produced by alum almost precludes
the use of vacuum filtration without precoating the filter with diatomaceous
earth. The cost of precoating is high and the remaining solids-precoat mixture
remains gelatinous in nature and may not be 'suited for ultimate disposal.
Vacuum filtration of lime waste solids Has been more successful but the waste
solids were thickened prior to being vacuum filtered. High costs for equipment,
operation'' and maintenance, and disposal of dewatered waste solids make
vacuum filtration impractical for most small communities.
c. Centrifugation. Centrifuges are becoming more popular for dewater-
ing water treatment wastes since they are able to handle dilute or thickened
waste solids. Alum and softening wastes can be concentrated in a centrifuge to
the per cent concentrations previously discussed.
High capital, operation, and maintenance costs make centrifugation
beyond the financial means of most small communities. There is also the
consideration of the cost of the ultimate disposal of the dewatered waste solids.
IV-66
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d. Drying Beds. Sand beds for drying water treatment waste solids are
basically identical to those employed in sewage treatment. An underdrained
sand bed may include decant at ion, but basically water is removed by drainage
and air drying.' A sufficiently shallow waste solids depth to allow cracking of
the solids down to the sand-solids interface will accelerate drying and yield
drier cakes.
Both the drainage and decantate can be discharged to the sanitary sewer
or discharged to a surface water if the discharge, meets permit requirements.
The dried solids can be removed from the drying beds with a front end loader
but must be disposed of, either in a .sanitary landfill or by direct land
application. A comparison between lagoons and , drying beds shows that drying
beds are more dependent on weather for successful, operation, have more
difficulties in removing sludge, have greater land requirements, incur higher
capital costs, and require more operation and maintenance.
e. Lagoons., The most common treatment method presently utilized at
water treatment plants for handling water, treatment plant wastes is lagooning.
, In areas where ample land is available, which is generally true near small water
treatment plants, lagooning can be quite economical. It takes advantage of
natural temperatures (for evaporation and freezing) to aid in the dewatering of
waste solids. Lagoo'ning is not so much a disposal method as one for
dewatering, thickening, and temporary storage.
.Water is removed by decantation or by evaporation, with some drainage.
Evaporation may provide a hard crust, but the remaining depth can turn into a
viscous liquid upon agitation. In cold climates, freezing aids in dewatering by
separating attached water from the solids. After thawing, the solids are in the
form of small granular particles that settle readily and additional water can be
decanted.
Solids removal is accomplished by a dragline or clamshell. Dumping the
waste solids on the banks can be used to air dry them further prior to later
disposal;
When sufficient land is available, filled lagoons can be abandoned,
eliminating an ultimate disposal problem. In communities where this is not
IV-67
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possible, alternatives include sanitary landfill, land application,and reuse of
products from water treatment plant wastes such as the use of calcium
carbonate as a soil stabilizer. Where waste solids remain in place indefinitely
and the land is not reclaimed, unsightly spoiled land areas "result; ' '
Serious consideration should be given to the disposal of the decantate and
underdrainage. Discharge to a surface water is recommended if. the discharge
meets permit requirements. An alternative method is. discharging to the sanitary
sewer. In water scarce areas, recycling through the water treatment plant has
proven to be economical. In small water treatment plants, however^recycling of
the decantate or underdrainage is economically questionable and can present
operating problems. Recycle of the wash water can be a viable alternative- even
though it may not be operationally desirable.
While operating, costs of lagoons are low, factors such as climate
intermittent or continuous input, solids concentration of the waste, the
availability of one or more lagoons, and the method and place of ultimate
disposal will have a bearing on the land area required.. Generally, at least two
lagoons are needed for waste solids and a third lagoon for backwash water. ¦ .
Current lagoon design practice includes the following: r. , ...
1. Location free from flooding,
2. When necessary, dikes, deflecting gutters, or other means of diverting
surface water. " :"
3. A minimum depth of 4 to 5 feet. ' '¦
4. 3 to 5 years solids storage volume. _ .....
5. Multiple cells. . .. .. e
6. Adjustable decanting devices.
7. Width of lagoon narrow enough to allow removal of waste solids by
dragline, clamshell, scraper, tugger hoist, or any other mechanical
equipment that might be employed. ,
1V-68
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The minimum embankment top width should be 8 feet to permit access of
maintenance vehicles. Lesser top widths can be used for very small installations.
The maximum inner and outer embankment slopes should not be steeper than
3:1, horizontal to vertical, and the minimum inner embankment should not
have a slope less than 4:1, horizontal to vertical. The embankments should be
seeded; Perennial type, low growing, spreading grasses that withstand erosion
and can be kept mowed are most satisfactory' for seeding of embankments. In
general, alfalfa and other-long-rooted crops should not be' used in seeding, since
the roots of-this "type" plant are "apt to impair the "water holding'efficiency of
the dikes. Additional "protection for embankments (riprap) may be necessary
where dikes are subject-to wind action or severe flooding of an adjacent water
course. •:
Problems can exist with insect breeding but can be controlled with
insecticides. Lagoons should be fenced to prevent access by unauthorized
persons.1.--.' ••
f, . Discharge to Sanitary Sewers. An increasingly popular' method' of
disposal of water-treatment plant'-wastes is discharge to the sewage'treatment
facility via sanitary sewers. This would.be particularly true for a -small
community served by sewage lagoons." If the sewage lagoons are of sufficient
size to handle the water treatment wastes, then construction of separate
facilities could not be justified.
Evaluation of the following considerations before the. discharge of water
treatment plant wastes to a municipal wastewater treatment plant is
recommended: ¦. ' ;
1, Possible damage to sewer system due to clogging.
2. Amenability of the waste to existing processes, principally in
mechanical treatment plants. - ' :
3., Hydraulic capacity of sewers, pumping .stations, and sewage treatment
facilities.
4. The effect of waste on the final plant effluent.
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5. A direct connection between the water treatment plant waste disposal
line and the sanitary sewer must be prevented.
6. Waste solids should be discharged over a 24 hour period, not as-a slug
flow. If this is not possible, some other time period, compatible with
' operation of the wastewater treatment plant,- should, be. used. ...
g. Spent Brine Solutions. For a small community, .disposal of spent
brine solutions to the sanitary sewer is the most feasible method of treatment.
The spent brine solution should not be discharged as a slug,but discharged
continuously over a 24 hour period. This will avoid any .damage:' to the
wastewater treatment facility. A small holding basin can be used to equalize the
discharge of the spent brine solution.
h. Summary of Waste Disposal Practices. The current restrictions" on
the discharges to lakes and streams have made water treatment plant designers
look at alternatives to direct disposal. Small communities with: small water
treatment facilities are at a disadvantage since the costs are too high for them
to use mechanical devices to' treat water treatment plant wastes. The
alternatives left to a small community are disposal to a sanitary sewer,
lagooning, and drying beds.
The small community should be made aware of the fact that if their water
treatment plant discharges a waste to a receiving stream or lake, a' discharge
permit called "The National Pollutant Discharge Elimination System-Permit''
(NPDES) 'must be obtained. This permit sets restrictions 'on the - concentration
of parameters, such as suspended solids and pH, that will be discharged to :a
stream or lake. If the water treatment plant does not discharge to a'-waterway,
the permit is not required. This situation would occur if the plant'disposed all
their wastes to the sanitary sewer or they treated waste solids and/or backwash
water with lagoons or drying beds and returned the dec'antate* or drainage to
the water treatment plant or disposed-of it to the sanitary sewer. Therefore, it
is advantageous for the small community to investigate the possibility of-using
their wastewater treatment plant to treat their water treatment plant's "waste.
In many cases, the wastewater treatment facility may -hot be able to
effectively treat wastes due to the increased amount of solids or volume
1V-70
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contributed by the water treatment plant. In this case, the solids must be
treated at the water treatment plant and disposed elsewhere.
For small systems, the most generally used method of dewatering water
treatment plant wastes, except for spent brine solutions, is lagooning. The
drainage and decantate can -be discharged to a surface water or to the sanitary
sewer. The dewatered waste in the lagoons must ultimately be removed and
placed in a sanitary landfill or applied to the land.
D. UNIT PROCESS COMBINATIONS
Generally, more than one unit process will be utilized in a treatment
facility. A possible exception to this might be disinfection which could be the
. single unit process used for treatment of a well supply. Many process
combinations ' could be used for water treatment. Combinations of unit
processes which comprise conventional treatment facilities or package treatment
plants are presented in the following sections.
1. , Conventional Facilities
- ..., Four common types of treatment plants have been selected as examples.of
conventional unit-process combinations constructed at the plant site. Design
.criteria and schematics for existing plants are presented to indicate how unit
-processes can be designed and combined into a treatment plant. The treatment
plants that will-be discussed include (a) turbidity removal, (b) ion exchange,
. (c), .lime softening, and (d) iron and manganese removal.
t. - -a, Turbidity Removal. The turbidity removal plant at Garnett, Kansas
removes- about I00mg/1 suspended, solids from the raw water taken from
-.Lake Garnett and Cedar Creek. Rapid., mix, flocculation, sedimentation, and
filtration are combined to provide a two stage coagulation/filtration plant for
the removal of turbidity. As shown on Figure 1, alum is used as the coagulant
to remove turbidity and lime is fed to provide alkalinity for reaction with the
- alum and to control the pH. Chlorine is added prior to filtration for
IV-71
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EFFLUENT
RAPID SAND
FILTRATION
CHLORINE
SECONDARY
SEDIMENTATION
SECONDARY
FLOCCULATION
ALUM
RAPID MIX
PRIMARY
SEDIMENTATION
PRIMARY
FLOCCULATION
ALUM
LIME
INFLUENT
i
GARNETT, KANSAS
WATER TREATMENT
PLANT SCHEMATIC
£i/"7/-su
FIGURE 1
-------
disinfection of the water. Unit process design data for the Gamett plant is
presented in Table 28.
b. Ion Exchange. A well water serving as the raw water supply for an
AT&T installation in Grant Park, Illinois, contains 375 mg/1 hardness as CaCOj
and 2 mg/1 of iron. To meet requirements for engine cooling water standards the
hardness must be reduced to 100 mg/1. In addition, to meet U.S. Public Health
Service Drinking Water Standards in effect at the time of plant design, the iron
concentration must be reduced.
In order to remove the hardness by a zeolite softener the insoluble iron
must first be removed to prevent fouling of the1 media in the zeolite softener,
thus rendering it ineffective for removing hardness. Figure 2 shows the
placement of a pressure filter; before, the zeolite softener. This removes
turbidity which is a result of insoluble iron formed in the line from the well.
The water is then softened by the zeolite softener. Sodium phosphate is added
after treatment to stabilize the water and sodium hypochlorite is added to
disinfect the water. The , capacity of the , softener is 16,200 grams
(250,000 grains) of hardness. With the.hardness of water equ^l to 375 mg/1,
the Iters'of water softened between regeneration is
16,200 i
„ = 43,200 liters or 43.2 nr (11,413 gallons)
0.375
At a flow rate of 54.5 m^/day (14,400 gpd), two regenerations are needed per
day and the salt tank is refilled every three days. Additional design data are
presented in Table 29.
c. Lime Softening. The City of Troy, Kansas, has constructed wells
along the Missouri River for raw water supply. The raw water is high in
hardness and alkalinity, and contains iron and manganese.
The treatment process illustrated on Figure 3, consists of aeration, excess
lime softening, two-stage recarbonation with intermediate settling, and
filtration. The induced draft aeration serves a dual purpose, oxidizing iron and
manganese so they Van be removed, and removing carbon dioxide which will
reduce the amount of lime needed for softening. Lime is then added in the
solids contact unit, which mixes the lime into the water and allows settling of
IV-72
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INFLUENT
PRESSURE. ,
SAND FILTER
ZEOLITE '
SOFTENER
;EFFLUENT
SODIUM POLYPHOSPHATE
SODIUM HYPOCHLORITE —
GRANT PARK, ILL.
WATER TREATMENT
PLANT SCHEMATIC
FIGURE 2
-------
EFFLUENT
SLUDGE DRYING
BEDS
FILTRATION
CHLORINE
PHOSPHATE
"CARBON' "DIOXIDE
SEDIMENTATION
o
— FERRIC SULFATE
t-t CARBON DIOXIDE
CHLORINE*
_i
CO
SOLIDS CONTACT
AERATION
INFLUENT
TROY, KANSAS
WATER TREATMENT
PLANT SCHEMATIC
FIGURE 3
-------
Table 28
GARNETT, KANSAS WATER TREATMENT PLANT
UNIT PROCESS DESIGN DATA
Design Flow, m^/day (mgd) 378S (1)
Primary Flocculation
Number of units 2 2
Basin dimensions, m (ft) 3.05 x 8.53 (10 x 28)
Sidewater depth (SWD), m (ft) 3.66 (12)
Detention time, hr * 11
Flocculators — hydraulic with baffles
Primary Sedimentation
Number of units , 1 • 1
Basin dimensions, m (ft) , 6.40 x 11.13 (21 x 36.5)
SWD, m (ft) 3.66 . (12)
Detention time, hx ¦ -' 2 ; 2
Overflow rate, nr/m /day (gpd/ft ) 5 ' 45.57 ; (1120)
Rapid Mix
Number of units _ .J 1 = 1
Basin dimensions, m (ft) '1.22 x 1.22 : (4 x 4)
SWD, m (ft) •• : 1.83 (6)
Detention time, sec. 62* 62
'Mixer, watt'(hp) " 2238 (3)
Mixer G factor, .sec"! 700 700
Secondary Flocculation
Number of units ' " ¦ 2 2
Basin dimensions, m (ft) 3.2 x 5.48 (10.5 x 18)
SWD, rn (ft) •' 3.66 (12)
Detention time,-min ' .... 30 30
Mixer, watt (hp) ; '' 1119 (1.5)
Mixer G factor, sec"^ ¦ . (variable — 20 to 100)
Secondary Sedimentation
Number of units 11
Basin dimensions, m (ft) 6.4 x 17.4 (21 x 57)
SWD, m (ft) 3.66 (12)
Detention time, hr 2.3 2.3
Overflow rate, rrr/m /day,- (gpd/ft**) 37.36 (918)
Rapid Sand Filtration , *
Number of units 2 2-
Filter dimensions, m (ft) " 3.66 x 4.57 (12 x 15)
Filter depth, m (ft) 3.05 (10)
Design loading rate, m3/m^/day (gpm/ft^)- 120 (2)
Support gravel depth, cm (in) 26.67 (10.5)
Coarse sand depth, cm (in) 10.16 (4)
Sand depth, cm (in) ; 60.96 (24)
Surface wash units per filter 2 2
Backwash rate, rrr/m /rnin (gpm/ft^) 0.76 (18.7)
IV-73
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Table 29
AT&T - GRANT PARK, ILLINOIS WATER TREATMENT SYSTEM
UNIT PROCESS DESIGN DATA
Design Flow, m^/day (gpd) 54.5 (14,400) ;
Pressure Filtration
Number of units 1.1 ' .. •
Dimensions - inside diameter, cm (in) 76.2, (30). - .
Overall height, m (ft) . 1 1.52 (5)
Design,loading rate, m /m?/day (gpm/ft.) ¦: 120 ,(2).
Operating pressure,"kg/cm^ (psi) •/;<;) S.21, -(75) •, •. ...
Sand media depth, cm (in) 48.26 (19) .
Backwash rate, m^/min (gpm) 0.185, (49),.
Softening • . >u-
Number of units. ; 1 1 ' -V
Overall dimensions,;;L,W,H, m (ft) 1 &0. x- 0=71 x; 1.77/ : (4.92 ,x„2.33 x 5.83)
Capacity; gramsr(grains) -: : 16,200 ir;(25P,00Q) f.
Maximum flow-rate, trP/min (gpm) 0.13 (34) ;. = • . r:
¦ • Backwash rate,-; m3/min (gpm) ,. ¦ v , 0.079,: (21).. 'i
Area of bed. (ft^) 0.4 (4.28)
Ion exchanger, m3 (ft ) 0,27 (9.5)
Salt tank refill, kg (lb) 272 (600)". .
Regenerations per refill • .„6 6 . •
Salt per regeneration, kg (lb) ,f . , 45'. (100)" / _ ••
the resultant precipitates. The water is then recarbonated by the addition of
carbon dioxide which lowers the pH. Recarbonation is accomplished using "a
swimming. pool . type injector chlorinator. Upon recarbonation . additional
precipitates are formed. Ferric sulfate added before the secondary flocculation-
sedimentation unit" will help remove'these fine •precipitates.' •" ' *
After the water is settled the pH receives, finall'adjustment..by, carbon
dioxide addition. The water is then filtered and pumped into the': distribution
system. Disinfection with chlorine can be accomplished at two:"different points.
The design data for this plant are presented in Table 30. " *
d. Iron and Manganese Removal. A i.5-mgd water treatment;plant was
designed to supplement an existing facility for the City of Cape Girardeau,
Missouri. Raw water is taken from a well near the Mississippi River and treated
in a water treatment plant that provides iron and manganese removal. The iron
concentration is as high as 14mg/l which exceeds the proposed secondary
IV-74
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Table 30
TROY, KANSAS WATER TREATMENT PLANT
UNIT PROCESS DESIGN DATA
Design Flow, m^/day (mgd) 2271 (0.6)
Aeration
Number of units 1 1
Type - induced draft - - - ; . .
Tower dimensions; m (ft) . 1.22 'x 1.22-.-' •" (4 x 4)
Sidewater depth (SWD), m (ft) " ¦ 4.26 (14)
Blower capacity, im^'/min (cfm) 28.04 (990)
Solids Contact • J"... . ^
Number of units " 1 1
Basin dimensions, m (ft) 4.57 x 4.57 (15 x 15)
SWD, m (ft) 3.66 '¦ (12) '
- - Up flow-rate-, m^/m?'/rh"in '(gpin/'ft^j •" -'v 0.055- (1 .-35)
Minimum detention time in floe zone, min 30 30 "•••¦
Dimensions flocculation zone, -3.55- (1 1,65)
top DIA, bottom DIA, m (ft) : 1.27,3.28 (4.16, 10.75)
Mixer, watt (hp) ¦ ' 560 (0.75)
Sedimentation
Number of units * 1 1" " '
Retention at design flow, min .74 "74
Overflow rate, m'/m^/min (gpm/ft^) " 0.045 (1.11)
Basin dimensions, m (ft) 4.57 x 4.57 (15 x 15)
..SWD, m (ft), , . . , 3.35 (11) .
Gravity Filtration ,, . ,, r, . . ... , — * - •
Number of units " 2 2
' f Filter dimensions, m (ft) 2,44 x i.83 (8 x 6)
•. • Filter depth, m (ft) . ^ ¦ ' 1.83 ¦ (6)
Design loading rate, m^/'m'/min (gpm/ft ) . ,0.105 . (2.6)
Support gravel depth, cm (in) 25.40 (10)
Sand depth, cm (in) 68.58 (27)
Surfdce wash units"per filter ' 2 2
• ¦ 1 Backwash rate, m /m /min (gpm/ft ) : 0.76 ' (18.7) ¦
Sludge Drying Beds
Number of cells . , 2". 2
Surface area per cell, m (acres) 526 (0.13)
Maximum sludge depth, m (ft) 0.46 - 0.61 (1.5-2.0)
Embankment slope, horzivert 1 1:3 1:3
IV-75
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drinking water regulation for iron of 0,3 mg/1. Although the water is quite
hard, softening is not practiced.
The presence of iron' and manganese in water is objectionable primarily
because the "precipitation of ""the 'metals " alters the appearance of the water,
turning it a turbid yellow-brown to black. The deposition of these precipitates
will cause staining of plumbing fixtures and laundry. The presence of iron and
manganese in water supplies can* also promote growth of microorganisms in
distribution systems. These growths will reduce pipeline carrying capacity and
may clog"'meters and valves. Higher"Concentrations of iron and manganese will
impart a metallic or medicinal taste to the water.
The major treatment ^facilities 'include" one aerator, one flocculator-clarifier
basin, ¦ rapid-mix;-five.,pressure-filters,—and-provisions for chemical addition. A
' schematic of the treatment plant facilities is shown on Figure 4.
Iron and manganese removal will be achieved by oxidation with air,
chlorine, and potassium permanganate. Oxidation transforms the relatively
soluble forms of iron and manganese to insoluble forms. The insoluble forms
can be removed by sedimentation and filtration. Bimetallic polyphosphate is
added after filtration to aid in corrosion control and water stabilization.
Chlorine is added before and after filtration for oxidation and disinfection,
respectively. Design data for the plant are presented in Table 31.
2. Package Plants ' •
A package water treatment plant is a complete treatment system
composed of two or more integral unit processes. for the removal of one or
more contaminants. Package plants are factory assembled and generally skid
mounted so that installation at the site consists of connecting raw and finished
water lines along with the electrical, service. In moderate to cold climates the
package plant should be enclosed in a building with adequate ventilation and
heat. Factory construction of package plants makes them economically
attractive when compared to plants constructed at the site. Even though
package plants are designed for automatic operation they still need periodic
attention .to monitor the process, maintain' chemical solutions, and perform
required maintenance. Too often in the past package plants have been installed
IV-76
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EFFLUENT
CHLORINE
SODIUM S1LICOFLUORIDE
BIMETALLIC POLYPHOSPHATE
FILTRATION
POTASSIUM PERMANGANATE
FLOCCULATOR-CLAR1FIER
CHLORINE
RAPID MIX
POLYMER •
AERATION
INFLUENT
CAPE GIRARDEAU, MO.
WATER TREATMENT
PLANT SCHEMATIC
17" ?(,-*-«
FIGURE 4
-------
-------
Table 31
CAPE GIRARDEAU, MO. WATER TREATMENT PLANT
UNIT PROCESS DESIGN DATA
¦J
Design Capacity, m /day (mgcl) 5677 (1.5)
Aerators
Number of units 1 1
Type-induced draft
Dimensions, m (ft) 2.44 x 2.44 (8. x 8)
Sidewater depth (S\^D), m (ft) 4.26 (14)
Loading rate, m /m^/min (gpm/ft ) 0.65 (16)
Fan motor, watt (hp) '560 (0.75)
Blower capacity, m /min (cfm) 110 (3900)
Flocculation—Sedimentation
Number of units 1 1
Dimensions, dia,. m (ft) 10.97 (36)
SWD, m (ft) 4.26 (14)
Overflow rate, m^/rrr/day (gpm/ft^) 0.04 (1)
Retention time - Sedimentation.min 94 94
Flocculator—Pulsator Type
Pressure Filter
Number of units 5 5
Dimensions, dia, m (ft) 3.05 (10)
SWD (minimum), m (ft) 1.52
C* 'manihf \ Pi £Q
(5)
Capacity, nr/mm (gpm) 0.89 (235)
Loading rate, in /m*"/min (gpm/ft") 0.12 (3)
Support gravel depth, cm (in) 25.4 (10)
Manganese greensand media depth, cm (in) 76.2 (30)
Anthracite media, effective size, mm 0.85-120 0.85-120
Anthracite media depth', cm (in) 20.32 (8)
Maximum backwash capacity, m /m /min
(gpm/ft2) 0.49 (12)
and expected to operate completely unattended resulting in unsatisfactory
performance. Properly selected, operated, and maintained package plants can
perform as well as plants constructed on site.
In addition to complete package plants, various unit processes are available
ready for installation at the site. Ion exchange and membrane processes are
examples of package unit process equipment. These unit processes have been
discussed previously in section IV.
IV-77
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Four common uses of package plants, as discussed in the following
paragraphs, include turbidity removal, taste and odor control, softening, and
iron and manganese removal.
a. Turbidity Removal. Package plants designed for turbidity removal
can treat water with a turbidity up to 200 JTU.
. : , Each plant provides;, chemical feed systems,, mixing, sedimentation,
filtration, and .disinfection. Package: plants of this type; i.e., which provide
¦clarification, and filtration can also remove various inorganic contaminants. A
comparison of the design features of package water supply treatment, systems
from three different manufacturers is presented in Table 32. ' " :
. ¦¦}„.: ¦ ' ¦ ~ i : Table 32 < .. ¦ :¦ . "
'COMPARISON OF PACKAGE WATER SUPPLY TREATMENT"SYSTEMS'
Feature
Manufacturer
B
Unit
Processes ;
Flow Rajige, m^/da*y
(mgd)
Skid Mounted
Mixing-Type. .
• Sedimentation .
Type
Filtration
Type
Media
..-Rate,- m^/mt/day
... ,..(gpm/ft2)
Mixing '
Flocculation .
Sedimentation
Filtration
Disinfection
53-5700
(0.014-1.5)
Yes
Mechanical
Tube Settlers
2-1/2° or 60°
Hexagonal
Pump suction
pulls water
through filter
Mixed
300
(5)
Mixing
Flocculation
Sedimentation
Filtration
Disinfection 1
26-1100
(0.007-0.28) .
Yes
Hydraulic.-; : ¦
Tube Settlers
60° Chevron
Gravity
Standard bed
or dual
120-210 ; -
(2-3.5).
Mixing "
Flocculation .
Sedimentation
Filtration
Disinfection *
1514100'-
(0.04-0.28). ;
Yes
Mechanical
Solids Contact
Gravity
Dual
¦ .',r >.
^10.
(3.5)
IV-78
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b. Taste and Odor Control. Taste and odor , causing substances can be
effectively treated using package plants, which utilize either activated. carbon
for adsorption, potassium permanganate for oxidation, or a combination of.
these two chemicals. Powdered activated carbon can be fed either at the same
point as the coagulation chemicals or directly .to the filter. The point of
application will depend upon the nature, and concentration of substances to be
adsorbed. Some substances are adsorbed quite rapidly, suggesting that the
activated carbon should, .be. applied:- directly' to. the. .filter. However,. only small
dosages of activated carbon .should .be -used to, prevent excessive-.:head: loss' and
potential passage* of: the carbon.-through the filter. .Much, .of the carbon* fed "to
the raw water is not effective in-removing dissolved taste and odor because it as
tied up with alum floe and turbidity. In certain instances,-.greater carbon
contact time is required necessitating carbon application to the incoming raw
water. Potassium permanganate could be fed along with the coagulation
chemicals in the rapid mix unit to oxidize tastes and odors. Potassium
permanganate would be added in place of activated carbon.
c. Softening;* "Package plants designed" for turbidity removal can. be used
for partial softening. Lime is fed to the rapid mix unit and there are no
provisions for recarbonation or a second stage lime addition. The limited .waste
solids handling capabilities restrict the amount of softening that "can be
accomplished. Partial softening presents the potential problem of calcification
of the .filter, media and tubes. Certain maintenance steps must be taken to
prevent calcification from becoming a serious problem. This use of the package
plants would not be generally recommended. ' -
d.. Iron and Manganese Removal. Package treatment plants'"designed for
turbidity removal can also be used for iron and manganese removal; Either
potassium permanganate or a chlorine solution can be fed to the rapid mix to
oxidize the iron and manganese. The precipitated iron and manganese arc then
coagulated and removed in a manner similar to the removal of turbidity with
sedimentation and filtration.
To reduce chemical costs another type of package plant for iron and
manganese removal is available. This plant uses aeration followed by filtration
as the treatment system. Induced draft aeration is followed by gravity filtration
while pressure aerators and filters are used together. This type of iron and
IV-79
-------
manganese removal system should not be used when the concentration of either
contaminant is high. An iron concentration of several mg/1 may cause the filter
to plug up resulting in short filter runs. Concentrations of manganese of about
one mg/1 and above may not be fully oxidized by air alone; additional
treatment would be required.
IV-80
-------
REFERENCE
1. ' LinviI G. Rich, Unit Operations of Sanitary Engineering. Wiley, New. York,
- 1961-;
BIBLIOGRAPHY
ASCE, AWWA, CSSE, Water Treatment Plant Design, A WW A, New York,
1971.
ASTM, Metric Practice Guide, E-380, Philadelphia, 1972.
American Water Works Association. Water Quality and Treatment, 3rd edition,
McGraw-Hill, New York, 1971.
Be Hack, Ervin, Fluoridation Engineering Manual, U.S. Environmental Protection
Agency, 1972.
Clark, Viessman and Hammer, Water Supply and Pollution Control, 2nd edition,
International Textbook, Scranton, 1971. «
Control Options for Organic Chemical Contaminants in Drinking Water, Federal
Register, Vol. 41, No. 136, July, 1976.
Gulp, Gordon L. and Culp, Russel L., New Concepts in Water Purification,
Van Nostrand, New York, 1974.
David Volkert and Associates, Monograph of the Effectiveness and Cost of
Water Treatment Processes for the Removal of Specific Contaminants, 68-01-1833,
U.S. Environmental Protection Agency, August, 1974.
Great Lakes - Upper Mississippi River Board of State Sanitary Engineers,
Recommended Standards for Water Works, Health Education Service, Albany.
New York, 1976.
Haney, Paul D., "Brine Disposal from Cation-Exchange Softeners," Jour A WW A,
41:829, 1949.
IV-81
-------
Steel, E. W., Water Supply and Sewerage, 4th edition. McGraw-Hill, New York,
1960.
U.S. Environmental Protection Agency, Interim Treatment Guide for the
Control of Chloroform and Other Trihalomethanes, 1976.
Weber, Walter J., Physicochemical Processes for Water Quality Control, Wiley-
Interscience, New York, 1971,
e
IV-82
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V. UPGRADING EXISTING FACILITIES
If an existing water treatment plant cannot comply with the maximum
contaminant levels for drinking water, upgrading the facility should be
considered. Various methods of upgrading existing facilities are available.
Uppading techniques suitable for small water treatment facilities are discussed
subsequently. Included are physical, chemical, and operation and maintenance
modifications.
A. POLYMER ADDITION
When upgrading existing facilities is considered, the use of a polymer to
aid the coagulation, sedimentation, or filtration processes should be evaluated.
Polymer addition can improve water quality through increased process
efficiency at relatively low capital cost.
As coagulant aids, polymers increase the size and thus the settling rate of
floe. This is accomplished by adsorption, charge neutralization, and bridging
between particles. For maximum efficiency, the type of polymer, dosage and
point of addition must be determined for each application. Most polymers are
• expensive but only small dosages are required, generally in the range of 0.1 to
1.0mg/l. Proper dosage and the right polymer, as determined by jar or pilot
tests, is. of importance because an excessive or insufficient dose, or the wrong
polymer, can produce a poor floe.
Polymers, used as filtration aids, increase the strength of the floe and
thereby lengthen filter-runs and reduce the incidence of turbidity breakthrough.
Required doses are small, generally less than 0.1 mg/1. Testing must be
performed to. determine the optimum dose of polymer for use as a filtration
aid. The optimum dose exists when the terminal headloss -is reached
simultaneously with the first sign of increasing filter effluent turbidity. When
used, to improve filter efficiency, polymers should be added directly to the
filter influent. Filtration aids should only be used in those filters having-surface
wash equipment or air/water backwash facilities to insure, removal of the deeper
V-l
c
-------
penetrating floe during backwash. The polymer used as a filtration aid will not
normally be the same type which may have been used as a coagulation or
settling aid.
There are a number of commercial polymers currently available. Either
naturally occurring or synthetic polymers can be used. Polymers are available
in both dry and liquid forms. Since the dry polymers are not easily dissolved,
special'mixing and feeding equipment is required. Liquid polymers can be fed
with1 metering pumps and then educted to the point of application. Polymers
are also discussed in section IV A4. Clarification.
B. FILTER MEDIA REPLACEMENT
Existing rapid sand filters may be converted to dual or mixed media filters
by replacement of the existing single media. Some structural modifications may
be required to allow adequate media expansion during backwash.
:> The most common type of dual media filter consists of a coarse to fine
arrangement of anthracite coal and sand. Primary benefits of dual'media filters
'compared to conventional rapid sand filters are longer filter runs and improved
finished water quality. Dual : media filters are discussed in detail in
.section IV A5, Filtration. ; - " '
Typical mixed media filters contain coal,;sand and garnet in a coarse to
fine configuration. . Mixed . media filters have several; advantages over
conventional, rapid sand filters including; higher capacity, capability,;to filter
.poorer quality influent, and longer filter runs. Use of mixed media filters will
provide, optimum, filtration efficiency and will produce lower finished water
turbidities than single or dual media filters. Additional information on mixed
media filters is discussed in section IV A5, Filtration.
C. ACTIVATED CARBON REPLACEMENT OF FILTER MEDIA
-i . i/: .r ?• i •. • - ' -
. Granular .activated,, carbon can be..used in conjunction with conventional
filtration as a method for upgrading an existing treatment facility. A layer of
-------
activated carbon may be used to replace most of the sand in a conventional
filter; most states require some minimum depth of sand under the carbon.
Activated carbon may also be used to replace coal in dual media filters. When
used as a filter media replacement, activated carbon functions as both a
turbidity removal and adsorption unit. Finished water quality can potentially
be enhanced without construction of additional filters or carbon columns.
Detailed information on granular activated carbon is provided in section IV A3,
Adsorption. For most taste and odor removal requirements a contact time of 5
to 7-1/2 minutes is acceptable. Haloform or haloform precursor removal
requires a contact time of 12 to 15 minutes. Replacement of a portion of the
filter media with granular activated carbon could reduce the plant capacity.
Each potential application of media replacement by granular activated carbon
should be evaluated by a knowledgeable engineer.
D. RAPID MIX ADDITION . ,
Effective coagulation, involves intimate mixing of the. coagulant and the
water. Existing water treatment plants with inefficient or overloaded rapid mix
facilities or without any means for coagulant mixing, will not..effectively
remove, turbidity or other contaminants -from, water;'If; chemical mixing by
means of pumps is currently utilized, the chemicals may not-.be adequately
mixed because of failure to achieve uniform distribution. Existing rapid mix
chambers without mechanical mixing should also be evaluated. Baffling alone
may not provide adequate coagulant mixing. Mechanical rapid-mix1 provides a
controlled, efficient unit process for the mixing of chemicals with the water
being treated. Addition of or improvement to rapid mix 'facilities will aid the
clarification process and thus- improve finished water quality. Additional
information on rapid mixing is contained in section IV A4, Clarification.
E. FLOCCULATION ADDITION
Flocculation is a principal mechanism in removing turbidity and various
other contaminants from'water. Inefficient or overloaded fioceulation facilities
-------
should be upgraded. If an existing treatment plant has rapid mix and
sedimentation facilities without flocculation. the addition of flocculation
facilities could enhance finished water quality. Flocculators that use only .
baffles for mixing usually perform well at only one flow rate. Provision of
variable mechanical mixing will enable the flocculation process to be effective,
for,, varying flow rates. The flocculation process is-, discussed in detail in,
section IV A4, Clarification. ;
F. CHEMICAL CHANGE OR ADDITION .
• Upgrading existing - water treatment facilities, may involve.-change of a
chemical currently. used or use of a mew chemical. For . example, if iron and
manganese removal: is.-.-.desired, and only, aeration is-being-used-, addition • of.,
chemical oxidation will improve removal of manganese. Laboratory: and plant
scale tests may be used to select a coagulant better suited ;to the raw water
quality. A coagulant aid or filter aid may also be used as discussed previously.
Another method to be considered when upgrading water treatment facilities is
chemical* Addition for pH adjustment to prevent corrosion in the system.
G. TUBE SETTLERS ••• • •• • • •": ' • • • r-' • - ;
An economic alternative to construction of additional sedimentation basins ,
is installation of tube settlers in existing sedimentation basins. Use of tube
settlers in this manner will produce an effluent of higher quality than is possible
by using the existing basin, only, ... <' : J]
Two basic tube settling systems are currently utilized; (1) parallel 5 cm
(two inch) square: tubes inclined at 60° ; from the horizontal, and (2) parallel
2.54 cm (one inch), hexagonal tubes inclined at 5° from the horizontal. In the
60°.inclined tubes, the" sludge slides down the tubes and is collected beneath
them. The 5° inclined tubes must be cleaned by backwashing with filtered,
water as the basin is drained.
V-4
a
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When tube modules are installed, they should not be located near areas
where turbulence could reduce their effectiveness. In horizontal flow basins, the
inlet end should remain uncovered by the tubes to allow inlet velocity
dissipation. In radial flow basins, the required modules can be placed in a ring
around the basin periphery, leaving an open area to dissipate turbulence. The
top of the tubes should be located 0.6 to 1.2 m (2 to 4 ft) below the water
surface. In general, the 0.6 m (2-ft) minimum should be used in shallow basins.
The 1.2 m (4 ft) submergence is used only in basins with a sidewater depth of
5 to 6 m (16 to 20 ft). These settling modules may utilize radial support beams
in circular basins or support beams spanning the width in rectangular basins. In
basins which have radial launders, it is often possible to suspend the.modules
from the launders.
In some cases there is a tendency for floe build-up to eventually bridge the
tube openings and a blanket of solids on top of the tubes results. Methods of,
removing this accumulation include lowering the water level-of the basin below;
the top of the tubes or occasional use of a water stream or compressed air to
flush out the attached floe. • . • .. ¦
Recommended tube settler, loading rates range , from 120 - to.
'n '¦5 '
240 nr'/m ,/day (2 to 4 gpm/ft^). Selection of a specific overflow rate depends.
on existing clarifier configuration, water temperature, existing clarifier overflow
rate, and desired effluent turbidity. More detailed information relative to the
size, capacity, and configuration of these settlers, and their adaptability to
existing sedimentation basins, may be obtained from manufacturers of such
equipment. The use of tube settlers for a particular application should be
evaluated by an'engineer. ... -. . . •
H. IMPROVED HYDRAULIC CONDITIONS . .
When upgrading water treatment, facilities is necessary,* hydraulic
conditions of existing basins may be improved by use of baffles, by modifying
inlet: and outlet conditions, or by reducing pipe velocities below 0.6:m/'sec.
(2 ft/sec). •
V-5
L
-------
Either horizontal or vertical baffles may be used to prevent short-circuiting
in floceulation basins. Judicious baffling may be added as required or existing
baffles rearranged to enhance flocculating conditions. .
Properly "designed inlets and outlets are also necessary to avoid
short-circuiting through a 'basin. Inlets must be designed to'distribute the water
uniformly over the cross section of each basin. Adequate outlets must be
provided to prevent excessive overflow rates and consequent breakup of floe or
suspension,, of settled solids from floor of basin. Freely discharging ;weirs.have a
tendency to break fragile floe.. Therefore, submerged weirs are recommended to
provide' an 'effective outlet arrangement. Inlet and outlet arrangements are
discussed in more detail in section IV A4, Clarification.
When uppading an existing facility is considered, plant piping should be
reviewed in regard to its, configuration and to the velocity of flow through it.
Velocities in piping following floceulation should , not exceed 0,6 m/sec
(2 ft/sec) to reduce floe breakup because of turbulence. Excessive bends, drops,
etc. also increase turbulence, and thus enhance floe breakup.
I. IMPROVED OPERATION AND MAINTENANCE ,
Regardless of how well.a water treatment plant is designed, if it.is,not
operated and maintained correctly, the treatment.process or processes will-not
perform effectively. Therefore, upgrading various. aspects of plant operation
and maintenance is. a prime consideration.
1. Operator Training and Qualifications
Even in the smallest plants with the simplest types of treatment, only
qualified personnel should be. in charge. Where .experienced operators are not
available locally to control the operation of a. water treatment plant, a qualified
operator should be employed from outside the community or a local person
should receive adequate training to become a properly certified operator.
V-6
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Training courses may be used as a means of upgrading an operator's
qualifications. It is recommended that operators participate in training courses
' on a regular basis, as advancements in the' knowledge and techniques of
treatment processes are constantly being made. Locally 'available in" almost
every state, these courees are sponsored by the state departments of health,
universities, and state and national technical associations.
In addition to training courses, numerous states utilize an operator
certification program as a' means of providing improved plant operation arid to
enhance the professional status of water plant operators. Currently, 39"states
have a mandatory certification program, nine states have a voluntary program arid
two'states have no certification program. '
Another method of improving the operation of a water treatment plant
'"'involves employing ' an' engineer or an operator" from a ia'rger facility as a
consultant. Also; one operator might be employed by several small plants!' The
operator would rotate from plant to plant as required. ' ¦
2. Improved Monitoring and Surveillance
The purpose of making analyses and tests is to control treatment* record
performance, comply with regulations, and indicate means for improved
performance. Control tests should be used to show that the water has been
properly prepared for each major process, that each 'process is' performing
effectively, and that the finished water quality is adequate. Accurate metering
of "¦ both water "and' chemicals is' nedessary"because inaccurate feeding of
chemicals could be economically wasteful and' potentially hazardous to the
health of the community.
As an aid in upgrading plant "performance, the" following control tests can
be used:
¦ •••; ¦" .* Continuous ¦Turbidity-Monitoring-' ; -• *•« -:i;
< .• •; ¦' "Chlorine'Residual .-yz,
r .. ^Alkalinity-= :'>•
Temperature
V-7,
-------
Use of the following equipment can be used to assist the operator in improving
plant performance:
Raw water and plant effluent meters
Filter control
Raw water and,plant effluent turbidimeters'
Residual chlorine recorder
Control tests, metering, instrumentation, and control are discussed in more
detail in section IV B, Water Quality Control.
In addition to water quality monitoring on the plant site, samples taken
regularly from the distribution system should be examined to ensure that
applicable drinking water regulations are met and to ensure that the water is of
high quality when it reaches the consumer.
J. REGIONALIZATION
As discussed • in section IID. Alternatives to Treatment, physical
consolidation of facilities may be desirable for some small water treatment
systems. However, regionalization of treatment or distribution facilities is
neither feasible nor desirable for all small water systems. Other aspects of
regionalization should be considered in an attempt to upgrade existing facilities.
For example, management and administrative functions could be combined;
county, parish or township public service districts could be formed to operate
and maintain several facilities; and a central laboratory could be used by
several small water systems.
V-8
¦
-------
BIBLIOGRAPHY
Water and Resources Management Committee, Survey of State Programs and
Attitudes on Regionalization for Public Water Systems, Environmental
Engineering Division,''American'Society of Civil Engineers, April, 1977.
V-9
-------
-------
VI. COST DATA
Initial investment costs and operation and maintenance costs are presented
herein for conventional water treatment facilities and for package water
treatment plants. The cost curves are intended to assist in evaluating proposed
new facilities and modifications to existing facilities.
Key to the development of these costs is the relationship of population to
water consumption. Provided in Table 33 are the water use projections used in
this report.
Table 33
TREATMENT PLANT DESIGN CAPACITY
Population
Plant Per Capita
Design Rate
(2)
Design Plant
Capacity
(3)=(1)x(2)
m /c/day
(gpcd)
m^/day
(iPd)
¦ 25
9.0
(2400)
227
(60,000)
250
4.6
(1200)
1136
(300,000)
1,000
1.9
(500)
1893
(500,000)
2,500
1.1
(300)
2839
(750,000)
5,000
0.8
(200)
3785
(1,000,000)
10,000
0.6
(150)
5678
(1,500,000)
The plant per capita design rates in Table 33 are based on water usage or
usage rate and on an assumed amount of storage in the system. For the smallest
svstem, no storage was assumed in the system; therefore, the plant design rate
is based on the maximum rate of usage which would be for watering lawns or
gardens. For the largest system,* a normal maximum day per capita usage was
assumed along with adequate storage in the system to supply any water require-
ments which would exceed this rate.
Cost data presented are appropriate for average situations. They should
permit development of preliminary cost estimates for water treatment facilities
VI-1
-------
when used with judgment regarding local conditions. An engineer should be
engaged to review local conditions and to evaluate the manner in which this
report's cost information will be .used.
It is emphasized that the cost data contained in this report cannot be used
as a substitute for detailed cost estimates based on a particular water treatment
situation, Among the many variables, which affect actual construction costs are
the following:
(a) .Characteristics and complexity of specific plant design.
(b) 'Current and projected labor costs.
(c) Contractors' attitudes regarding their need for work.
(d) Availability of materials.
(e) Climate and seasonal factors.
Local factors can also have a significant effect both on construction and on
operation and maintenance costs.
It is essential that the user of the cost estimating methods presented in
this report review all introductory material. In particular, the information
discussed at the beginning of, section VI A, Capital Costs, and section VI B,
Operation and Maintenance Costs, should be understood prior to use of the
cost curves, and tables.
For the most part, each cost curve extends from 227 m^/day (0.06 mgd) to
5680 m^/day (1.5 mgd). Exceptions are the cost curves for diffused aeration,
clarification processes, -filtration, disinfection methods, and package plants. In
general, diffused a re a ti on is not economical for treatment plants with design
flows less than 1890 m^/day (0.5 mgd).
For small water treatment systems, the most applicable range for
clarification, filtration and disinfection unit processes overlaps with the most
applicable range for package plants. This situation is reflected in the cost
curves. The solid portion of each cost'curve indicates the most applicable range
for that unit process or package plant. The dashed portion of these cost curves
indicates the plant design flow range in which conventional unit processes or
package plants might be utilized.
Vl-2
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A. CAPITAL COSTS
Cost curves were -developed for treatment processes judged applicable to
small water treatment systems. These curves relate capital costs to quantities of
water treated and to population served. Estimates of complete water treatment
plants or additions to existing plants'may be developed on the basis of-these
relationships.
Yard piping, fencing (where applicable), and sitework have been-included in
the curve for each unit process. When adding unit process costs together some
of these items may overlap; this may cause the total cost to exceed actual plant
costs by 10 to 25 per cent. - ; • •' •'
Cost data, developed specifically for this report, are based on information
from various manufacturers and on the. experience and judgment of the
investigators. Preliminary designs and engineering cost estimates were developed
for each unit process at various low rates. Estimates of -construction costs are
representative of average price levels as of January, 1977. The Engineering-News
Record Building Cost Index of that date had a value of 1489.
Included in the capital costs are necessary construction costs, a
contingency amount and engineering, legal and administration - fees; A cost for
fencing is provided- for mechanical 'aeration, diffused aeration, rapid mix,
flocculation, sedimentation, ozone contact chamber and waste disposal
(lagoons). For each of the other treatment methods an enclosure is
recommended and separate cost curves are provided. '
• Capital- costs for unit proceses. package plants and enclosures are
developed as follows: • : r- •.
(1) Construction cost — included are necessary costs for equipment,
materials, installation, freight and start-up.. . '
(21 Sitework — estimated as 10 per cent, of the construction cost..,
(3) . Electrical — estimated.as 20 per cent of.the construction cost. •- -
VI-3
-------
(4) Contingency — estimated as 10 per cent of the total of construction
cost, sitework, electrical and fencing (if applicable).
(5) Engineering, legal and administrative — estimated as 15 per cent of
the total of construction cost, sitework, electrical, fencing (if
applicable), and contingency.
Equipment and materials capital costs are based on use of prefabricated,
modular, or factory built/field assembled units to minimize on-site construc-
tion. Design parameters used for sizing unit processes should not be generally
applied to all water treatment situations. Design parameters should be selected
on the basis of raw water characteristics for each application.
Enclosure capital costs include costs for a prefabricated insulated metal
building, foundation, and necessary plumbing and electrical facilities.
Separate cost curves for enclosures and treatment facilities have been
provided to allow the enclosure cost to be deleted where climate would not be
detrimental to treatment process efficiency or equipment integrity. It must be
recognized, however, that the enclosure cost curve includes the foundation.
Therefore, if art enclosure is judged not necessary for'a specific situation, then
a foundation cost must be added to the capital cost for the treatment process
in question. •
Capital costs for laboratory facilities are not provided in "this section of
the report, but are given in section IV B2, Laboratory Facilities. Estimates of
construction costs do not include costs for high service pumping, treated water
storage or extraordinary costs related to large amounts of rock excavation, site
dewatering or piling.
1. Unit Processes
. " Figures 5 through 33 are the capital- cost curves for various water treatment
unit-processes/'Prior-to use of the cost curves," the estimator should carefully
review the following summaries , of equipment, material, and design criteria used
in developing the unit process capital costs. If local conditions require use of
different design criteria or equipment, the capital costs must be revised
accordingly.
VI-4
-------
An example calculation illustrating use of the unit process capital cost
curves is provided in section VI C.
a. Mechanical Draft Aeration, Capital costs for this aeration process
are based on an induced draft aeration unit located above a basin. The
following design criteria are used to develop capital costs for mechanical draft
aeration:
(1) ten trays vertically spaced approximately 0.305 m (12 in) apart.
(2) tray area furnished is 3.9cm^ per m^/day (40 ft^ per mgd).
(3) air supply rate of 0.019 m /min per m /day (2,500 cfm per mgd).
Capital costs for this unit process include costs for the following
equipment and materials: prefabricated aluminum induced draft aeration tower,
blower, motor, basin, foundation, necessary controls., associated valves and
piping, and fencing. Refer to Figure 5 for the mechanical draft aeration capital
cost curve.
b. Diffused Aeration. Diffused aeration capital costs are based on a
system which consists of an aeration tank and the means of supplying
compressed air to this tank. The following design criteria are used:
(1) basin depth of 3 m (10 ft).
(2) basin width from 3 to 6 m (10 to 20 ft).
(3) width to depth ratio less than 2:1. - ...
(4) retention time of 20 minutes.
(5) air supply of 0.67 m^ of air/m^ of water (0.09 ft^/gal).
The following equipment and materials are included in the diffused
aeration capital cost curve: steel aeration tank, foundation, positive displace-
ment air compressor and motor, air piping; air diffusers, inlet filter silencer,
necessary controls, associated valves and-piping, and fencing. Refer to Figure 6
for the diffused, aeration capital cost curve.
VI-5
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c. Activated Carbon Beds. For the activated caibon adsorption process,
capital costs are based on a fixed-bed gravity feed system which uses an 8x30
mesh size granular carbon. Also included is an empty tank for storage and
dewatering of the spent activated carbon. To develop the activated carbon bed
capital cost curve, the following design criteria are used:
(1) media depth of 1.2 m (4 ft),
(2) surface loading rate of 160 m^/m^/day (2.7 gpm/ft^).
(3) contact time of 11.25 minutes.
(4) three cells, each handling one-third of the total flow.
The capital cost curve for activated carbon beds is based on costs for the
following equipment and materials: prefabricated steel three-cell gravity filter
shell including underdrain system and supporting gravel, activated carbon,
surface wash system, backwash system, spent carbon storage tank, necessary
valves, piping and manual controls. Refer to Figure 7 for the activated carbon
bed capital cost curve, along with a capital cost curve for an enclosure.
d. Activated Alumina Columns. Capital costs developed for the
activated alumina adsorption process are, ¦ based on a duplicate-column,
gravity-feed system using grade F-l. 28x48 mesh size alumina. Also, included in
these capita] costs are facilities for i eg en era ting the alumina. Regeneration
involves backwashing with raw water, sodium hydroxide and sulfuric acid. To
prepare the activated alumina column capital cost curve, the following design
criteria are used: -
(1) media depth of 1.07 m (3.5 ft).
(2) surface loading rate of 180 m^/m*/day (3 gpm/ft2).
(3) contact time of 8.7 minutes, .
(4) two cells, each handling one-half of the total flow. -
The following equipment and materials are "included in the activated
alumina capital cost curve: prefabricated steel shell, underdrain system,
activated alumina, supporting gravel, surface wash system, backwash system,
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associated valves and piping, necessary manual controls, chemical feed system
and storage tank for each of the regenerative chemicals, and a mechanical mixer
for the sodium hydroxide storage tank. Refer to Figure 8 for the activated
alumina capital cost curve, and the capital cost curve for an enclosure.
e. Rapid Mix. Capital costs for the rapid mix process are based on a
mixing basin with a flash mixer and a by-pass pipeline with a static mixer. The
static mixer is provided as backup for use when the mixing basin or flash mixer
is out of service. The volume of the mixing basin is specified by the retention
time; the velocity gradient determines the power needed by the mixer. To
prepare the rapid mix capital cost curve, the following design criteria are used:
(1) one basin.
(2) retention time of 45 seconds. ' .
(3) velocity gradient of G = 750 sec" I
The following is a list of equipment and materials included in rapid mix
capital costs: steel basin, foundation, flash" mixer, metal stairs, metal grating,
mixer support, by-pass pipeline with static mixer, necessary controls, associated
piping and valves, and fencing. Chemical feed equipment is not included in the
rapid mix cost estimates. Section VI A1 (o). Chemical Feed, contains'various
chemical feed system costs. Refer to Figure 9 for the rapid mix capital cost
curve. •
f. Flocculation. The flocculation process capital costs are based on
utilizing vertical turbine flocculators in the flocculation basins. The retention
time determines the volume of the basin. The power of the vertical turbine
flocculator is calculated from the velocity gradient (G), The following design
criteria are used: ¦
(1) retention time of 30 minutes. -
(2) velocity gradient of G = 50 sec"'-
(3) two basins, each handling one-half of the total flow.
(4) one vertical turbine flocculator per basin.
VI-7
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Capital costs for flocculation include costs for the following equipment
and materials: steel basin, foundation, vertical turbine floceulator, influent and
effluent devices, metal stairs, floceulator support, metal grating, necessary
controls, associated valves and piping, and fencing. Refer to Figure 10 for the
flocculation capital cost curve.
g. Sedimentation. Capital costs for the sedimentation process are based
on a sedimentation basin sized to allow settling of coagulated particles and
furnished with equipment for removal of the waste solids. The following design
criteria are used to develop the capital cost curve for the sedimentation
process:
. . . (1) retention time of 4 hours.
1 9 "J
(2) surface loading rate of 16 m /m /day (400 gpd/ft ), - .
(3) two basins, each handling one-half of the total flow.
Sedimentation capital costs include costs for the following equipment'and
materials: steel basin, foundation, mechanical waste solids collection equipment
and support, submerged orifice peripheral weir, metal grating, necessary
controls, associated piping and valves, and fencing. Refer to Figure 11 for the
sedimentation capital cost curve. :
h. Flocculator-Clarifier; Flocculation and sedimentation can both be
achieved in a, flocculator-clanfier. Design criteria used to develop the
flocculator-elarifier cost curve are as follows:
(1) .flocculation zone retention time of 30 minutes.
-5
(2) sedimentation zone surface loading rate of 16 m ;'rn-/day
(400 gpd/ft2).
, (3) two basins, each handling one-half of the-total flow.
The flocculator-clanfier capital cost curve includes the following
equipment and materials: steel basin,..foundation, mechanical waste ..solids
collection' equipment and support, vertical turbine floceulator, submerged,
orifice peripheral weir, metal stairs, metal grating, necessary controls, associated
VI-8
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piping and valves, and fencing. Refer to Figure 12 for the flocculator-clarifier
capital cost curve.
i. Ion Exchange Softening, Capital costs for the ion exchange softening
process are based on a complete softening system. This system includes
facilities for blending softened and raw water, and facilities for automatic
backwash and regeneration. Design criteria used to develop the capital cost
curve for ion exchange softening are as follows:
(1) softening 75 per cent of the plant flow and blending with the
remaining raw water.
(2) automatic regeneration and backwash triggered by time?clock control.
Capital costs for ion exchange softening include costs for the following
equipment and materials: complete ' ion exchange softening system with
automatic controls, associated valves and piping, cation exchange resin, brine
tank and necessary regeneration equipment. Refer to Figure 13 for the ion
exchange softening capital.cost curve and an-enclosure capital cost curve. • • ¦
j. Pressure Filtration. Pressure filtration capital cost curves7 are
developed for three surface loading rates. Costs are: based on multiple -unit
filters with automatic control of the backwash cycle. The following design
criteria are used to develop capital costs.for pressure filtration: -
(1) surface loading rates of 120, 240 & 360 m?/m~/day. (2, 4, &
6 gpm/ft2).
(2) three to seven filter cells, each cell handling an equal portion of the
plant flow. . ¦ ••• : :
The capital cost curves for pressure filtration are based on the following
equipment and materials: multiple package"pressure filters',-associated* valves
and piping, automatic controls, surface wash system,. backwash system, and
media. Variance in "media costs is not significant in the cost of the filter. Refer
to Figure 14 for pressure filtration capital cost curves and enclosure capital cost
curves. "
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k. Gravity Filtration. For the gravity filtration process, capital costs
curves are developed for different surface loadings. Variance in media costs is
not significant in the cost of the filter. Provisions are also included for
automatic control of the backwash cycle. To prepare the capital cost curves for
gravity filtration, the following design criteria are used;
(1)-surface loading rates of 120, 240 &. 360 m^/m^/day (2,. 4/ &
"
' 6 gpm/ft^);
(2) three cells, each handling equal flows.
Capital cost curves for gravity filtration include costs for the following
equipment and materials; package triplicate unit, gravity filters, associated
.valves and piping, automatic controls, surface wash pump,.backwash pump, and
media. Refer to Figure 15 for gravity filtration capital cost curves and-enclosure
capital cost curves,
1. Demineralization. For the demineralization process, capital costs are
based on a two-bed system. This system includes facilities for blending
demineralized and raw water, and facilities for .automatic regeneration-
Regeneration involves backwasliing with sulfuric acid and caustic soda.
The following design criteria were used to develop the demineralization
capital cost curve:
(1) de'mineralizing 75 per cent of the plant flow and blending with the
remaining"raw water.
(2). two-bed system.
" (3)' automatic regeneration and backwash triggered by conductivity
control.
¦ (4') .influent TDS of-1000 mg/1 was assumed.
The capital cost curve for demineralization includes costs for the following
equipment and materials: two-bed demineralization system, cation and anion
exchange resins, necessary regeneration equipment, associated valves, piping and
automatic controls. Refer to Figure 16 for the demineralization capital cost
curve and a capital cost curve for an enclosure.
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m. Electrodialysis. The electrodialysis capital cost curve was developed
for a complete multiple-stage electrodialysis system. Costs were obtained for
standard units as rated by the manufacturer for operation with a raw water
TDS concentration of 1500 to 4000 mg/1. For these electrodialysis units,
predicted per cent water, recovery ranges from 65 to 85 and predicted; per cent
TDS removal ranges from 82 to 96. Local water quality may change the rated
capacity of these units.
Electrodialysis capital costs include costs for the following equipment and
materials: skid-mounted reverse polarity electrodialysis unit with'membrane
'¦ stacks, rectifiers, low pressure feed pump, brine recirculation pump, chemical
' • cleaning equipment, cartridge filters, necessary valves, piping and _ automatic
¦ controls.- - Refer to Figure 17 for the electrodialysis capital cost* curve. The
enclosure capital cost curve for electrodialysis is shown on Figure 18.
"n. Reverse Osmosis. The reverse osmosis capital cost curve was
developed for a complete reverse osmosis treatment system. Costs obtained
were for standard units as rated by the manufacturer for operation with a feed
of 1500 mg/1 NaCl at 400 psi; 25°C (77° F), and-75 per cent conversion. Local
water quality may change the rated capacity of these units. .
Capital costs for reverse osmosis include costs for the following equipment
and materials: skid-mounted, membrane-type reverse osmosis unit with hollow
' fine fiber membranes,' high pressure pumps, cartridge filters, acid and
polyphosphate feeding equipment, necessary valves, piping and automatic
controls. Refer to Figure 19 for the reverse osmosis- capital cost, curve.
Presented on Figure 20 is a capital cost curve for an enclosure for this unit
-process.
o. Chemical Feed. Capital costs have been determined for the following
chemical feed systems:
(1) powdered activated carbon. ' . : ¦
(2) coagulants.
(3) hydrated lime. . : . •
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(4) polymer.
(5) polyphosphate.
(6) chlorine.
(7) ozone.
(8) calcium hypochlorite. .. -
(9) .sodium hypochlorite (purchased).
. (10) sodium hypochlorite (on-site generation). , . •
Chemical feed system capital costs include all equipment essential for the
storage, mixing and application of the chemical. Duplication of equipment, i.e.,
a standby system, is not provided,for powdered activated carbon, polyphosphate,
ozone: or sodium hypochlorite (on-site generation) chemical feed systems. Jhe
cost for a standby feeder or metering, pump is included in the chlorine, calcium
hypochlorite and sodium hypochlorite (purchased) chemical feed system capital
costs.. A standby chemical feed system is included, in the coagulant,, hydrated
lime and polymer capital cost curves. For each chemical feed system, separate
capital cost curves have- been developed for selected chemical dosage
concentrations. Figures 21 through 30 show capital cost curves for various
chemical feed systems and their enclosures.
1. . Powdered Activated Carbon. Powdered activated .carbon dosages
used to develop capital ''ost curves for this chemical feed system are 20 mg/1 or
less and 50 mg/1. Refer to Figure 21 for the powdered activated, carbon capital
cost curves and for enclosure capital cost curves. - - • .
2..' .Coagulants, The .coagulant chemical feed capital cost curve is based
on a system dosage capability of up to 50 mg/1.- Refer to Figure 22 for the
coagulant capita] cost curve and for an enclosure capital cost curve. :
3. Hydrated Lime. Hydrated lime capital cost curves are based on
chemical .feed systems capable of feeding 50. mg/1 or. less, 100 mg/1 and 200 mg/1
of .hydrated lime. Refer. to .Figure 23 for these capital, cost curves and for
enclosure capital cost curves. ;
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4. Polymer. Polymer dosages used to develop capital cost curves are
0.5, 1, 3 and 5 mg/1. Refer to Figure 24 for polymer chemical feed capital cost
curves along with enclosure capital cost curves.
5. Polyphosphate. The polyphosphate chemical feed capital cost curves'
are based on a system dosage capability of up to 5 mg/1. Refer to Figure 25
for these capital cost curves and for enclosure capital cost curves. " •
6. Chlorine. The chlorine- chemical feed capital cost curves are based on
selected chlorine dosages of 5 mg/1 and less and 10 mg/1. Shown on Figure 26 are
chlorine capital cost curves and capital cost curves for enclosures.
7/ Ozone", Capital costs for the ozone disinfection process are based"on'
the on-site generation of ozone and its application within-a basin sized to""
provide adequate contact time. Costs included are for air feed ozone generating
equipment. *" " ' ' ' * '*
; The following design criteria are used "for the ozone capital cost 'curves:. .• .• • >
-(1) -contact time of 15 minutes.- 4<;? ._
(2) ozone dosages of 1.5, 5 and 10 mg/1. . " ' "
Capital costs for ozone disinfection include costs for the following
equipment and-materials: ozonator, steel basin, foundation, "metal "stairs, and
fencing for the contact basin. Refer to Figure:27 for the "¦ ozon'e " capital cost:
curves and also for 'enclosure' capital cost "curves. Enclosure capital'costs are
based on enclosures sized only for the ozone" generating equipment.- :
8. Calcium Hypochlorite. - The calcium hypochlorite chemical feed
capital costs are based on calcium hypochlorite dosages of -1.5, 5 and 10 mg/1.
Refer to Figure 28 for calcium hypochlorite feed system capital cost curves and
enclosure capital cost curves.
¦9. Sodium Hypochlorite.' Sodium hypochlorite capital "cost: curves "are
based on chemical feed systems capable of feeding 1.5, -5 and 10 mg/1 sodium-
hypochlorite dosages. These cost curves are applicable kwhen sodium
hypochlorite is purchased. Refer to Figure 29 for these capital cost curves and
for enclosure capital cost curves.
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10. Sodium Hypochlorite (On-Site Generation). The capital costs
developed for sodium hypochlorite on-site generation facilities are based on
using salt in a brine solution as opposed to sea water. Sodium hypochlorite
dosages of 1.5, 5 and 10mg/l are used. Capital costs for this disinfection
process include costs for the following equipment and materials: sodium
hypochlorite generator, brine system, brine tank, and the recycle tank. Refer to
Figure 30 for capital cost curves for sodium hypochlorite on-site generation
facilities and for enclosure capital cost curves.
2. Laboratory Facilities
A capital cost curve for laboratory facilities is not presented in this report.
A cost curve is not necessary as one laboratory size is .applicable for the range
of treatment facility sizes considered. Refer to section IV B2,. Laboratory-.
Facilities, for a laboratory capital cost. -..I
3. Waste Disposal Facilities
Capital costs for a lagoon waste disposal facility are based on disposal of
waste solids from a turbidity removal plant. The following design criteria are used:
(1) turbidity of 50 JTU, ..
(2) aluni dosage of 30 rrig/1. - ¦' ¦'
(3) retention time of 2 years.
(4). influent waste solids consisting of 5 per cent solids.
(5) two-cell lagoon.
Capital costs include costs for excavation, inlet, and outlet appurtenances,
seeding and fencing. Refer to Figure 31 for the lagoon capital cost curve.
4. Package Plants , • .
The capital cost curve for package water treatment plants is based on a
complete treatment facility. Included are costs for the following equipment and
VI-14
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materials; coagulant, polymer, and chlorine chemical feed systems; mechanical
flash mixer; mechanical flocculator; sedimentation; filters; surface wash and
backwash systems; steel basins; and necessary valves, piping and automatic
controls. Refer to Figure 32 for the package plant capital cost curve and for an
enclosure capital cost curve.
5. Upgrading Existing Facilities
Section V of this report discusses various methods available for upgrading
water treatment facilities. Capital cost curves for some of these methods are
provided in section VI Al, Unit Processes. Thus, it is not necessary to discuss
them in this section. The rapid mix capital cost curve is shown on Figure 9 and
the flocculation capital cost curve is shown on' Figure 10. Refer to Figure 24
for the polymer (coagulant or filtration aid) capital" cost curves. Cost
information for use of a new chemical is shown on Figures 21 through 30.
Capital costs are not presented for replacement of filter media,' chemical
change or improvement of hydraulic conditions, operator training, or
monitoring'and control as these'are'best determined for'each water'treatment
situation.
The only upgrading method to be discussed in detail here is use of tube
settlers. Capital costs for this process are based on installation of settling tubes
in an existing sedimentation basin. The following design criteria are used to
develop capital cost curves for the tube settling system:
(1) settling tube surface loading rate of 180 m^/m^/day (3 gpm/ft^).
(2) 5 cm (2 in) square tubes inclined at 60° from the horizontal.
(3) adequate tubes are provided to settle the existing plant {low. "
Capital costs for this method of upgrading water treatment facilities
include costs for PVC settling tubes and the support beams. Refer to Figure 33
for the settling tube capital cost curve.
VI-15
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B. OPERATION AND MAINTENANCE COSTS
Based oil the average cost information presented, total annual operating and
maintenance expenses for various plant components may be developed. Where
It was not possible to base operation and maintenance cost data on manu-
facturers* information, cost elements were estimated.
Actual costs may vary appreciably from the estimated average costs in this
report. However, when used with judgment, the data presented should be of
value for preliminary cost estimates. The user should recognize the inherent
limitations of such estimates and should develop applicable operating cost
estimates based on local conditions.
Cost data were adjusted to indicated cost levels for January 1977. To
update these costs, they may be trended to" the applicable date by using the
"Wholesale Prices and Price Indexes" as published by the Bureau of Labor
Statistics," U.S. Department of Labor. The Wholesale Price Index for
January 1977 is 188.4. If knowledge of a specific local situation indicates a
more appropriate updating method, such information should be utilized.
Major elements of operation and maintenance costs considered include
labor, power* supplies and chemicals. Annual labor cost curves are provided for
the following types of treatment facilities:
Type 1 7-;minimal-treatment such as disinfection only.
Type 2 — package plants.
Type 3 —conventional facility with chemical addition, clarification,
•• " filtration and disinfection.
Type 4 — conventional facility described- above, with one additional special
process such as ion exchange, electrodialysis, reverse osmosis,
•; - activated alumina, etc";
The labor costs indicate the ,total requirements to adequately operate and
maintain the facility. Man-hour requirements- for .-these treatment facilities are
based on desirable levels of operator attention for each type of plant. For the
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Type 1 and Type 2 facilities it is estimated that one part-time operator is
required. For the Type 3 and Type 4 facilities, round-the-clock operation with
one to two operators per shift is recommended. The average hourly earnings
rate (wages plus fringe benefits) used is $7.30. This rate is based on the
National Average Earning Rate published by the U.S. Department of Labor,
Bureau of Labor Statistics, for nonsupervisory employees in the public utility
industry, under "Water, Steam and Sanitary Systems", SIC Code 494-7, as of
January 1977. If local conditions indicate a different earnings rate, such
information should be used. Refer to Figure 34 for annual labor cost curves for
Type 1 and Type 2 facilities. Refer to Figure 35 for annual labor cost curves
for Type 3 and Type 4 facilities. ,
Power cost curves are provided for the applicable unit processes and for
package plants. These power costs are based on equipment power requirements,
and estimate of the operating time .of the equipment, a pov^er, cost of
S0.03 per kWh and a 10 per cent contingency. . .. ..
• !- Cost curves for supplies include costs for normal annual, upkeep and
improvement materials. Unit process supply cost curves include costs for oil,
grease, ' belts, chains, etc. 'Enclosure supply cost curves include, cleaning
materials, paint, etc. The supply costs are based on 5 per cent of the equipment
cost for each unit process and package plant, 2 per cent .of the construction
cost for each enclosure,and a. 10 percent contingency. Supplies cost curves for
electrodialysis and reverse osmosis are exceptions. They-are based on estimated
costs from manufacturers. Electrodialysis supplies range in cost from $0.20 to
$0.30 per 3.8 nr (1000 gal), depending on plant size. Reverse osmosis supplies
range in cost from SO.20 to $0.50 per 3.8 (1000 gallons), depending on
plant size.
< • - ' » ' ¦ i - i . *
Chemical costs are provided in Table. 34 for various chemicals used in water
treatment. These chemical costs are for January 1977 and should be trended as
necessary by using the Wholesale Price Index as discussed previously. "
"» , ' ' ¦ ' ;
Chemicals not listed in Table 34 include: granular activated carbon,
regenerative chemicals for activated alumina, ion exchange softening and
demoralization,- and salt for sodium hypochlorite cin-site generation. Costs for
these chemicals are-provided on cost curves; i ^ '• '
VI-17
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o
Table 34
WATER TREATMENT CHEMICAL COSTS
Chemical
Activated Carbon
(Powdered)
Alum
Packaging
65 lb bags
100 lb bags
Calcium Hypochlorite 100 lb drums
Chlorine 100 lb cylinders
Ferric Chloride
Ferric. Sulfate
175 lb drums
100 .lb bags
Hydrated Lime 50 lb bags
Polyphosphate . 100 lb bags
(Sodium Hexameta) *
Polymer (Dry)
' (Wet)'
Potassium
Permanganate
50 lb & 100 lb bags
55 gallon drums;
i ' ' ¦ ¦
110 lb bap
550 lb bags
Price
1-14 bags, 44.45 cents per lb
15-28 bags, 41,95 cents per lb
29-50 bags, 39.45 cents per lb
1-9 bags, $16 per bag
10-20 bags, $11 per bag
21-100 bags, $9.25 per bag
S81.60 per drum
1-9 cylinders, $30 per cylinder
10-24 cylinders, $26 per cylinder
0-630 lb, 18.65 cents per lb
631-12,000 lb, 17.90 cents per lb
1 bag, $10.15.
2-20 bags, S8.90 per bag
21-100 bags, S7.65 per bag
1-40 bags, S2.85 per bag
41-200 bags, $2.23 per bag
1-9 bags, $36.80 per bag
10-19 bags, S34.80 per bag
varies, use $2.25 per lb
varies, use SO.30 per lb
92.35 cents per lb
73.80 cents per lb
Refer to section VIC for an example of the development of annual
operation and maintenance costs using the labor, power and supplies cost
curves and.the chemical cost table.
1. Unit Processes
Figures 34 through 75 are operation and maintenance cost curves for various
water treatment unit processes. Before using these cost curves, the estimator
VI-18
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should carefully review the following summaries of power requirements arid
chemical dosage rates or regeneration requirements used in developing the unit
process operation and maintenance cost curves. In addition, the preceding
introductory material should be reviewed for general considerations regarding
preparation of labor, power and supplies cost curves and Table 34, Water
Treatment Chemical Costs,
If local conditions dictate use of different design requirements, the
operation and maintenance cost curves must be revised accordingly,
a. Mechanical Draft Aeration.. Operation and maintenance cost curves
developed for mechanical draft aeration include power and supplies, which are
presented on Figure 36. Power requirements are based on the blower motor
horsepower and 24 hour per day operation. • '
b. Diffused. Aeration. Operation and maintenance cost, curves for
diffused aeration include power requirements and supplies, as shown on
Figure 37. Power requirements are based on the compressor motor horsepower
and 24 hour per day use. • •
c. Activated Carbon Beds. Included in the operation and maintenance
cost curves for activated carbon beds are power, equipment supplies, and
enclosure supplies., These three cost curves are presented on Figure 38. An
activated carbon media replacement cost curve is presented on Figure 39. Power
costs are based on . the backwash pump and .surface 'wash pump, motor
horsepower requirements and their use for one hour each day. The media
replacement cost curve is based on shipment of spent carbon to a custom
regeneration facility. Assumed transport distance and regeneration interval are
1610 km (1000 miles), one-way, and 6 months, respectively.. Included in the
media replacement cost curve are freight, regeneration and replacement of
media lost during shipping and/or regeneration. Necessary labor was assumed
provided by the water treatment facility, therefore' no additional cost was
included.
d. Activated Alumina Columns. Operation and maintenance cost curves
for activated alumina include power, equipment supplies and enclosure supplies,
which are presented oh Figure 40. A regenerative chemical cost" curve is also
VI-19
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presented for activated alumina columns on Figure 41, Power requirements are
based on the total motor horsepower for surface wash pump, backwash pump,
chemical feed pumps, and chemical mixer. Use of the backwash and surface
wash pumps is estimated at one hour each day and the chemical feed pumps
and mixer are estimated for use once every six days for 2 hours. The
regenerative chemical cost curve includes cost for sodium hydroxide and
sulfuric acid. Available information indicates that activated alumina. material
must be replaced every 2 to 5 years.
¦ e. Rapid Mix. Rapid mix operation and maintenance cost curves
include power and equipment supplies and are shown on-Figure 42. Power
requirements are based on the flash mixer motor horsepower and 24 hour per
day operation.
f. Flocculation. Operation and maintenance cost curves developed for
flocculation include power and supplies and are shown on .Figure 43. Power
requirements' are based on the turbine flocculator motor ; horsepower and
24 hour per .day use.
g. Sedimentation, Operation and maintenance cost curves developed for
the -sedimentation, process include a cost curve for power and -one for supplies
as shown .on; - Figure 44. The power cost curve is based on the horsepower
requirement,of the sludge collector motor and 24 hour per day. operation.
i ih. Flocculator-CLarifier, Developed for the flocculator-clarifier are :
operation and maintenance cost curves for power and supplies. These two cost
curves.are.shown on,Figure 45. Power costs are based on sludge collector motor
¦horsepower, turbine flocculator motor horsepower, and - 24 hour per .day
operation.
i. Ion Exchange Softening. Ion exchange softening operation .and .
¦maintenance cost: curves include curves for power, equipment supplies and
enclosure: supplies, .which.are shown on Figure 46. A regenerative .chemical cost
curve is provided for ion exchange softening on Figure 47. Power requirements
are -.based on thentotal motor horsepower for backwash, pump and chemical
mixer. Use of this equipment is estimated at one hour per day. The regenerative
chemical cost ¦ curve is based on equipment manufacturer's stated salt require-
ments.
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j. Pressure Filtration. Operation and maintenance cost curves for
pressure filtration include power, equipment supplies, and enclosure supplies
cost curves for surface loading rates of 120, 240 and 360 m^/m?/day (2, 4 and
6 gpm/ft^). Figures 48 and 49 include these nine cost curves. Power costs are
based on backwash pump motor horsepower, surface wash pump motor
horsepower and equipment use one hour each day,
k. Gravity Filtration. Gravity filtration operation and maintenance cost
curves include power, equipment supplies and enclosure supplies cost curves for
O 'J
surface loading rates of 120, 240 and 360 trr/nrr/day (2, 4 and 6'gpm/ft ).
These nine cost curves are presented on Figures 50 and 51'. Power costs are
based on motor horsepower requirements for backwash pump, surface wash
pump, and equipment use for one hour each day.
1. Demineralization. Operation and maintenance cost curves for de-
mineralization include power, equipment supplies, enclosure supplies, and
regenerative chemicals. These curves are shown on Figure 52 and Figure 53.
Power requirements are based on the total motor horsepower for
backwash pump, chemical feed pumps and on use of each of these pumps one
hour each day for systems less than 380m^/day (0.1 mgd) and three hours
each day for systems greater than 380m^/day (0.1 mgd). The regenerative-
chemical cost curve is based on costs for caustic soda and sulfuric acid'.;
m. Electrodialysis. Operation and maintenance cost curves developed
for the electrodialysis unit process include power, equipment supplies and
enclosure- supplies. Power and equipment supplies cost curves- are presented on
Figure-54. Power - costs are based on power requirements for the electrodialysis
process equipment, feed pump motor, brine recirculation pump- motor and
chemical cleaning equipment. Power costs are based on 3 kWh per m (11 kWh
per 1000 gal) and equipment supplies costs include membrane and cartridge
filter replacements plus cleaning chemicals. Figure 55 includes the enclosure
supplies cost curve.
n. Reverse Osmosis. Reverse osmosis operation and maintenance cost
curves include power, equipment supplies and enclosure supplies. Figure 56
¥1-21
-------
includes the power and equipment supplies cost curves. Power costs are based
on 3 kWh perm3 (11 kWh per 1000gal) and equipment supplies costs include
• membrane and cartridge filter replacements along with necessary chemicals. The
enclosure supplies cost curve is presented on Figure 57.
o. Chemical Feed. Operation and maintenance cost curves for chemical
feed systems include power, equipment supplies and enclosure supplies for
various chemical dosages. Summarized in Table 35 are the chemical feed
systems and their appropriate cost curve figure numbers. .
Table 35
• SUMMARY OF CHEMICAL FEED SYSTEM
- OPERATION AND'MAINTENANCE COST CURVES '
Chemical Feed System Dosages (mg/1) Figure Numbers
Powdered Activated Carbon 50 or less 58
Coagulant 50 or less 59
Hydrated Lime 50 or.less, 100 & 200 , 60, 61
Polymer : 0.5, 1, 3 & 5 62, 63
Polyphosphate " 5 or less 64
Chlorine 5 or less & 10 65
Ozone 1.5, 5 & 10 " ' 66, 67
Calcium Hypochlorite 1.5, 5 & 10 68, 69
Sodium Hypochlorite . 1.5, 5 & 10 70, 71
Sodium Hypochlorite : 1.5, .5 & 10 . . . 72, .73
(on-site generation) ,,
Power costs are based on necessary feeders, agitators, mixers, and metering
pumps and 24 hour per day operation. In addition to the chemical feed costs
previously discussed, cost curves for ozone and sodium; hypochlorite (on-site
generation) include the following operation and maintenance costs: power for
chemical generation and supplies- fqr the: generating equipment and enclosure.
vi-22
I k
-------
Ozone power requirements are based on 26 kYVh per kg (12 kWh per lb)
of ozone produced. Power requirements for on-site production of sodium
hypochlorite are based on lQkWh per kg (4.6 kWh per lb) of chlorine
produced. Ozone and sodium hypochlorite production is based on a flow rate
of 70 per cent of plant capacity. The salt requirement for sodium hypochlorite
production is 4.7 kg per kg (4.7 lb per lb) of chlorine produced.
2. Laboratory Facilities
Laboratory costs depend on type and frequency of analyses and type and
condition of testing equipment. Laboratory operation and maintenance costs
should be determined for each local water treatment situation. Therefore, these
costs are not presented in this report,
3. Waste Disposal Facilities
The operation and maintenance cost curve for lagoons is based on waste
solids removal by contract. This cost is related to the total solids produced
using an alum dosage of 30 mg/1 and a turbidity removal of 50 JTU. The
lagoon sludge removal cost curve is shown on Figure 74.
4. Package Plants
Package plant operation and maintenance cost curves include power,
equipment supplies and enclosure supplies as shown on Figure 75, Power
requirements are based on the total'motor horsepower for the flash mixer,
mechanical flocculator, effluent, backwash and chemical feed pumps, and the
chemical mixers. Power costs include equipment use 24 hours per day.
5. Upgrading Existing Facilities
Operation and maintenance cost curves corresponding to the various
upgrading methods described in section V have been discussed previously. Cost
curves are not presented for replacement of filter media, chemical change,
VI-23
-------
improvement of hydraulic conditions, operator training, monitoring, or control.
These are best determined for each water treatment situation. Cost curves for
tube settlers are not included as this upgrading method generally does not
create additional operation or maintenance costs.
C. COST DATA EXAMPLES
Three examples have been prepared which illustrate use of the cost data in
this report. Examples No. 1 and 2 develop capital and operation and maintenance
costs for conventional facilities; Example No. 3 develops similar costs for a
package plant.. As Examples No. 2 and 3 are for facilities with equal capacity,
a comparison of costs for a conventional facility versus costs for a package plant
can be made.
1. Example No. 1
= The. following example is based on treatment of a surface water" for
turbidity: removal in a 3,000 m^/day (0.8 mgd) enclosed conventional plant
with, the following unit processes:
Rapid Mix . ¦ • - ;
Flocculation
Sedimentation
Filtration-gravity with 240 m^/m^/day (4 gpm/ft?) rate
Coagulation Feed-alum-20 mg/1
Polymer Feed-dry 0.5 mg/1 / -
Chlorine Feed—gas—5 mg/1 ...
Lagoons
Laboratory j
VI-24
-------
a. Capital Cost — 3,000 m^/day (0.8 mgd) Conventional Facility.
Rapid Mix (Figure 9)
Flocculation (Figure 10)
Sedimentation (Figure 11)
Filtration—Process (Figure 15)
Filtration—Enclosure (Figure 15)
Coagulant Feed-Process (Figure 22)
Coagulant Feed—Enclosure (Figure 22)
Polymer Feed—Process (Figure 24)
Polymer Feed—Enclosure (Figure 24)
Chlorine'Feed—Process (Figure 26)
Chlorine Feed-Enclosure (Figure 26)
Lagoons (Figure 31)
Laboratory (Section IV, B, 2)
Total
$ 21,000
60,000
275,000
105,000
17,000
15,000
3,700
7,400
3,700
7,000
3,700
9,000
7,00Q
$534,500
An economic evaluation of proposed facilities should include a comparison
of either the present worth or the annual cost of the alternatives; It is common
practice in the water industry to use annual costs for judging alternatives. For
purposes of this report, a plant service life of 30 years and an interest rate of
8 per cent have been assumed. To determine the equivalent annual cost for
repayment of the capital cost, multiply the capital cost by the appropriate
capital recovery factor, as follows:
Annual Capital Cost = < • . . .• -
Capital Recovery Factor (30 yrs @ 8%) .x Total'Capital Cost =
Annual Capital Cost = $47,480
listed in Table 36 are additional capital recovery factors for various interest
rates.
0.0883 x $534,500
VI-25
-------
Table 36 .
CAPITAL RECOVERY FACTORS*
Capital Recovery Factor
Year
i=6%
i=8%
i=10%
i=12%
1 '
1.060 00
1.080 00
1,100 00
1.12000
O
0.545 44
0.560 77
0.576 19
0.591 70
3
0.374 11
0.388 03
0.402 11
0.416 35
4
0.288 59
0.301 92
0.315 47
0.329 23
5
0.237 40
0.250 46
0.263 80
0.277 41
6
0.203 36
0.216 32
0.229 61
0.243 23
7
0.179 14
0.192 07
0.205 41
0.219 12
8
0.161 04
0.174 01 .
0.187 44
0.201 30
9
0.147 02
0.160 08
0.173 64
0.187 68
10
0.135 87
0.149 03
0.162 75
0.176 98
11
. 0.126 79
0.140 08
0.153 96
0.168 42
12
0.119 28
0.132 70
0.146 76
0.161 44
13
0.112 96
0.126 52
0.140 78
0.155 68
14
0.107 58
0.121 30
0.135 75
0.150 87
15
0.102 96
0.116 83
0.131 47
0.146 82
16
0.098 95
0.112 98
0.127 82
0.143 39
17
0.095 44
0.109 63
.0.124 66
0.14046
18
0.092 36
0.106 70
0.121 93
0.137 94
19
0.089 62
0.104 13
0.119 55
0.135 76
20
0.087 18
0.101 85
0.117 46
0.133 88
21
0.085 00
0.099 83
0.115 62
0.132 24
22 •
0.083 05
0.098 03
0.11401
0.13081
23
0.081 28
0.096 42
0.11257
0.129 56
24 ¦
0.079 68
0.094 98
0.111 30
0.128 46
25
0.078 23
0.093 68
0.110 17
0.127 50
26
0.076 90
0.092 51
0.109 16
0.126 65
27
0.075 70
0.091 45
0.108 26
0.125 90
28
0.074 59
0.090 49
0.107 45
0.125 24
29
0.073 58
0.089 62
0.106 73
0.124 66
30
0.072 65
0.088 83
0,106 08
0.124 14
*E. L.
Grant and W, G. Ireson,
"Principles of Engineering
Economy,"
5th edition, Ronald
Press, New York, 1970.
VI-2 6
-------
b. Annual Operation and Maintenance Cost — 3.000 m^/day (0.8 rtigd)
Conventional Facility.
Rapid Mix—Power (Figure 42) $ 690
Rapid Mix-Supplies (Figure 42) 270
Flocculation—Power (Figure 43) 340
Flocculation-Supplies (Figure 43) 500
Sedimentation-Power (Figure 44) 430
¦ Sedimentation—Supplies (Figure 44) 340
Filtration-Power (Figure 50) 95
Filtration-Process Supplies (Figure 50) , 380
Filtration—Enclosure Supplies (Figure 51) 305 <
' Coagulant Feed—Power & Process Supplies (Figure 59) 220 '
Coagulant Feed—Enclosure Supplies (Figure 59) * 70
Polymer Feed—Process Supplies (Figure 62) 120
Polymer Feed—Power (Figure 63) 170
Polymer Feed-Enclosure Supplies (Figure 63) 70
Chlorine Feed—Power (Figure 65) 40
Chlorine Feed—Process Supplies (Figure 65) 75
Chlorine Feed-Enclosure Supplies (Figure 65) 70
Lagoon (Figure 74) 3,700
Chemicals (based on a flow of 70% of capacity)
. (Table 34)
Alum@Sll/bag 3,750.
Chlorine @ S26/cylinder 2,195
Polymer @ $2.25/lb. 1,900
Labor - Plant Type 3 (Figure 35) „ 69,000
(For "Plant Type" description see page VI-16)
Total $84,730
Total Annual Cost =
Annual Capital Cost (pg VI-25) + Annual O&M Cost =
$47,480 + $84,730
Total Annual Cost = $132,210
VI-27
-------
Annual Cost per 1000 m^ (average flow = 70% of capacity)
S132,210 = S172 per 1000 m3
- (3) (365) (0.7)
Annual Cost per 1000 gal (average flow = 70% of capacity)
$132,210 - $0.65 per 1000 gal
(800) (365) (0.7)
2. Example No. 2
The following example is based on treatment of a surface water for
turbidity removal in a 1,100 m /day (0.3 mgd) enclosed conventional plant
with the following unit processes;
Rapid Mix
Flocculation
Sedimentation
Filtration—gravity with 240 rrr/nn /day (4 gpm/ft') rate
Coagulant Feed—alum—20 mg/1
Polymer Feed—dry—0.5 mg/l
Chlorine Feed— gas—5 mg/1
Lagoons
Laboratory
a. Capital Cost - 1,100 m^/day (0.3 mgd) Conventional Facility.
Rapid Mix (Figure 9)
. $ 19,000
Flocculation* (Figure 10)
52,000
Sedimentation (Figure 11)
225,000
Filtration—Process (Figure 15)
92,000
Filtration—Enclosure (Figure 15)
14,000
Coagulant Feed—Process (Figure 22) -
15,000
Coagulant Feed—Enclosure (Figure 22)
3,700
Polymer Feed—Process (Figure 24)
7,400
Polymer Feed-Enclosure (Figure 24)
3,700
VI-28
-------
Chlorine Feed—Process (Figure 26) 7,000
Chlorine Feed—Enclosure (Figure 26) 3,700
Lagoons (Figure 31) 5,000
Laboratory (Section IV, B, 2) 7,000
Total $454,500
Annual Capital Cost =
Capital Recovery Factor (30 yrs 8%) x Total Capital Cost =
O.088S3 x $454,500
Annual Capital Cost = $40,370
Refer to Example No. 1 for discussion of the method used for calculating
annual capital cost.
Refer to Table 36 for additional capital recovery factors.
b. Annual Operation and Maintenance Cost — 1,100 m^/day (0.3 mgd)
Conventional Facility.
Rapid Mix—Power (Figure 42) $' 420
Rapid Mix-Supplies (Figure 42) 240
Flocculation—Power (Figure 43) ' 300
Flocculation—Supplies (Figure 43) - 450
Sedimentation—Power (Figure 44) 370
Sedimentation—Supplies (Figure 44) 300
Filtration—Power (Figure 50) 80
Filtration—Process Supplies (Figure 50) 300
Filtration—Enclosure Supplies (Figure 51) 170
Coagulant Feed—Power & Process Supplies (Figure 59) 220
Coagulant Feed—Enclosure Supplies (Figure 59) 70
Polymer Feed—Process Supplies (Figure 62) 120
Polymer Feed—Power (Figure 63) ' " 170
Polymer Feed—Enclosure Supplies (Figure 63) 70
VI-29
-------
Chlorine Feed—Power (Figure 65)
Chlorine Feed—Process Supplies (Figure 65)
Chlorine Feed—Enclosure Supplies (Figure 65)
Lagoon (Figure 74)
Chemicals based on a flow of 70% of capacity)
(Table 34)
Alum @ $ 11 /bag
Chlorine @ S30/cylinder
Polymer @ $2.25/lb
Labor-Plant Type 3 (Figure 35)
(For "Plant Type" description see page VI-16)
Total
Total Annual Cost =
Annual Capital Cost (pg VI-29) + Annual O&M Cost =
540,370 + 570,355
Total Annual Cost = $110,725
Annual Cost per 1000 m^ (average flow = 70% of capacity)
SI 10,725 = S394 per 1000 m3
(1.1) (365) (0.7)
Annual Cost per 1000 gal (average flow = 70% of capacity)
$110,725 = SI.44.per 1000 gal
(300) (365) (0.7)
40
75
'70
1,800
1,410
960
720
62,000
$70,355
VI-30
-------
3. Example No. 3
The following example is based on treatment of a surface water for
turbidity removal in a 1,100 m^/day (0.3 mgd) enclosed package plant with the
following unit processes:
Rapid Mix
Flocculation
Sedimentation
F iltr at ion—gravity
Coagulant Feed—alum—20 irtg/1
Polymer Feed—dry—0.5 mg/1
Chlorine Feed—gas—5 mg/1
Lagoons
Laboratory
a. Capital Cost - 1,100 m^/day (0.3 mgd) Package Plant. .
Package Plant—Process (Figure 32) $160,000
Package Plant—Enclosure (Figure 32) 37,000
Lagoons (Figure 31) 5.000
Laboratory (Section IV, B, 2) • 7,000
Total $209,000
Annual Capital Cost =
Capital Recovery Factor (30 yrs (§ 8%) x Total Capital Cost =
0.08883 x $209,000
Annual Capital Cost = $18,560
Refer to Example No. 1 for a discussion of the method used for
calculating annual capital cost. Refer to Table 36 for additional capital recovery
factors.
VI-31
-------
b. Annual Operation and Maintenance Cost — 1,100 m /day (0.3 mgd)
Package Plant.
Package Plant—Process (Figure 75) $ 680
Package Plant—Power (Figure 75) ¦ 1,600
- Package Plant-Enclosure (Figure 75) 600
Lagoon (Figure 74) 1,800
Chemicals (based on a flow of 70% of capacity)
(Table 34)
Alum @$11 /bag 1,410
Chlorine @ $30/cylinder 960
Polymer @ $2.25/lb. . 720
Labor—Plant Type 2 (Figure 34) 5,200
(For "Plant Type" description see page VI-16)
Total . . ¦ . $12,970
Total Annual Cost =
Annual Capital Cost (pg VI-31) + Annual O&M Cost =
$18,560 + $12,970
Total Annual Cost = $31,530
Annual Cost per 1000 m^ (average flow = 70% of capacity)
$31,530 =$112 per 1000 m?
(1.1) (365) (0.7)
Annual Cost per 1000 gal (average flow = 70% of capacity)
$31,530 = $0.41 per 1000 gal
(300) (365) (0.7)
VI-32
-------
Table 37
EXAMPLE COSTS SUMMARY
Annual Cost
S per 1,000 n^~~ " $ per 1,000 gal
Example No. 1
3,000 m^/day (0.8 mgd)
Conventional Facility 172 0.65
Example No. 2
1,100 nr*/day (0.3 mgd)
Conventional Facility 394 1.44
Example No. 3
1,100 m^/day (0.3 mgd)
Package Plant 112 0.41
VI-33
-------
100,000
50,000
40,000
-------
100,000
50,000
10,000
1000 2 3 4 56789 10,000
TREATMENT CAPACITY" m5/day
I 1_ ) j 1 1 1 ( 1 1 f—t—)_| 1 1
0.3 05 1,0 1.5 2.0
TREATMENT CAPACITY mfld
" I •' | ¦ 1 1 -—i 1_| —, , 1 1
250 500 1000 • - ,5000 10,000
POPULATION EQUIVALENT
" UNIT PROCESS COST CURVE INCLUDES;
• CONTINGENCIES
• ENGINEERING 8 ADMINISTRATION
• SITEWORK
• ELECTRICAL
• AERATION TANK 8 FOUNDATION
• COMPRESSOR S MOTOR
• AIR PIPING a DIFFUSERS • ...
« INLET FILTER-SILENCER r.
« PIPING, VALVES 8 CONTROLS -
• FENCING
DIFFUSED AERATION
CAPITAL COST
2
FIGURE 6
-------
1,000,000
500,000
100,000
UNIT PROCESS
50,000
10,000
ENCLOSURE
5,000
1,000
100 2 3 456789 1000 2 3 4 5678910,000
TREATMENT CAPACITY m3/d
-------
I ,000,000
500,000
UNIT PROCESS-
¦OT¦
tn
o
o
K
0.
<
O
100,000
50,000
10,000
ENCLOSURE
5,000
1,000
100
4,5 6 7 8 9 1000 2
TREATMENT CAPACITY m3/day
4 5 6 7 8 910,000
H I—I—I-
-I h
0.05 0.1 0.5
TREATMENT CAPACITY mgd
H—t—H—
" 1.0
1.5 2.0
-+-
H h t- | 4 H )¦ I
25
50
100
250 500 1000
POPULATION EQUIVALENT
5000 10,000
UNIT PROCESS COST CURVE INCLUDES:
• CONTINGENCIES
• ENGINEERING 8 ADMINISTRATION
• SITEW0RK
• ELECTRICAL
• ACTIVATED ALUMINA COLUMN,
UNDERDRAIN SYSTEM Q MEDIA ACTIVATED ALUMINA COLUMN
• SURFACE WASH a BACKWASH SYSTEMS
• REGENERATION ' EQUIPMENT CAPITAL COST
• VALVES, PIPING 8 CONTROLS
, 4
FIGURE 8
-------
100,000
50,000
¦40,000
-c*>
!0,000 ' •
1000 2 3 4 5 6 78 9 10,000
TREATMENT CAPACITY m5/day
I ,— 1 -| 1 1 y i—|—h—i—I—t—t 1 '
0.3 0.5 i.O 1.5 2.0
TREATMENT CAPACITY mfld
1 ( 1 ) ( 1 1 |- ( 1 1 1 1 : J
250 500 1000 5000 10,000
POPULATION EQUIVALENT ,
UNIT PROCESS COST CURVE INCLUDES;
• CONTINGENCIES
¦ ENGINEERING a ADMINISTRATION
• SITEWORK
• ELECTRICAL '
"• RAPID MIX BASIN a FOUNDATION _
• FLASH MIXER
• BY-PASS PIPELINE WITH STATIC MIXER
• VALVES, PIPING a CONTROLS
• FENCING
RAPID MIX
CAPITAL COST
5.
FIGURE 9
-------
100,000
50,000
40,000
in
tn
g 30,000
«r
51
<
o
20,000 '
. i.0,000
1000 2 3 4 567 89 10,000
TREATMENT CAPACITY m3/dcy
- • •• ; I - • t • : i-' [- " 1- - • -I 1—t i' t i —\ ¦ 1
0.3 0.5 l.O 1.5 2.0
•TREATMENT CAPACITY mgd
L-1—f—" ' ' 1 ', * —-i I ^—*' " 1 1
250 500 1000 5000 10,000 '
POPULATION EQUIVALENT
UNIT PROCESS COST CURVE INCLUDES":"
• CONTINGENCIES • .
• ENGINEERING B ADMINISTRATION -
. • SITEWORK
' • ELECTRICAL
• FLOCCllLATlON .BASIN 8 FOUNDATION
•VERTICAL TURBINE FLOCCULATOR
•INLET a OUTLET DEVICES ' ' " - •
• VALVES, PIPING 8 CONTROLS '' '
• FENCING ' ¦¦ ¦'
flocculation
CAPITAL COST
FIGURE 10
-------
1,000,000'
500,000
400,000
h~
VI
o 300,000
a.
<
u
200,000
100,000 ¦ • . .
1000 2 3 4 5 6789 10,000
TREATMENT CAPACITY m5/doy
1 1 1 |i —| 1 1 1—|—h-+- —| 1
0.3 0.5 1-0 1.5 2.0
TREATMENT CAPACITY mgd
I ) , 1 , , , 1 | | 4.1 1 : >.
250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVE INCLUDES:
• CONTINGENCIES
• ENGINEERING ft ADMINISTRATION
• SITEWORK
• ELECTRICAL
•SEDIMENTATION BASIN 8 FOUNDATION-.
•WASTE SOLIDS COLLECTION EQUIPMENT
• INLET S OUTLET DEVICES
• VALVES, PIPING a CONTROLS
¦ • FENCING
SEDIMENTATION
CAPITAL COST
?
FIGURE II
-------
1,000,000
500,000
400,000
g 300,000
el-
's:
o
200,000
iOO.OOO
1000 2 3 4 5 6789 10,000
TREATMENT CAPACITY m3/day
I 1 1 . " i 1- \ 1 1 1 1 1—I h-1 ¦ 1 1
0.3 0.5 1.0 1.5 2.0
TREATMENT CAPACITY mgd
1 1_ : 1 1 , 1 1—j—f—,—,—, 1 1
250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVE INCLUDES1
¦; CONTINGENCIES.
* ENGINEERING 8 ADMINISTRATION
* SITEWORK
* ELECTRICAL
•• FL0CCULAT0R-CLAR1FIER BASIN -
8 FOUNDATION
. WASTE SOLIDS COLLECTION EQUIPMENT
* VERTICAL TURBINE FLOCCULATOR
* INLET S OUTLET DEVICES
* VALVES, PIPING a CONTROLS
* FENCING
FLOCCULATOR-CLARIFIER
CAPITAL COST
r. . FIGURE 12
-------
1,000,000
500,000
10,000
5,000
ENCLOSURE-
1,000
100 2 3 4.5 6 7 8 9 1000' 2 3 4 5 6 7 8 910,000
TREATMENT CAPACITY m3/day
I —|— , 1 1 1 ,—,—^^ 1
0.05 0.1 0.5 1.0 ' " 1.5 2.0
TREATMENT CAPACITY mad
I 250 500 1000 ' s'o'oo ' lOJDOO 1
POPULATION EQUIVALENT ...
UNIT PROCESS COST CURVE INCLUDES;
• CONTINGENCIES
• ENGINEERING 8 ADMINISTRATION "
• SJTEWORK
• ELECTRICAL
• ION,EXCHANGE -SOFTENING SYSTEM '
¦CATION EXCHANGE RESIN |0N EXCHANGE SOFTENING
• REGENERATION' EQUIPMENT
• VALVES, PIPI NG a CONTROLS CAPITAL COST
¦•.BACKWASH SYSTEM ~
• ** FIGURE 13
-------
1,000,000
UNIT PROCESS
ENCLOSURE
5,000
1000
1000 2 3 4 5 6789 10,000
TREATMENT CAPACITY m3/day
I 1 1 1 1 1 1_ ( 1 1 , ! j 1 1
0 3 0.5 10 1.5 2.0
TREATMENT CAPACITY mgd
I—i < 1 , , ,—|—i , | i ' i : 1
250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVES INCLUDE;
• CONTINGENCIES
•.ENGINEERING 8 ADMINISTRATION
• SITEWORK
• ELECTRICAL
• PACKAGE PRESSURE FILTERS 8 MEDIA
• SURFACE WASH 8 BACKWASH SYSTEMS
• VALVES, PIPING 8 CONTROLS
PRESSURE FILTRATION
CAPITAL COST
10
FIGURE 14
-------
1,000,000
500,000
-U> 100,000
t—
m
o
o
0.
o
50,000
360 m
10,000
1000
2 3 4 5
TREATMENT CAPACITY m3/day
UNIT"PROCESS
ENCLOSURE
8 9 10,000
-t (• H
10
-I H
0.3
L_
0.5
1.5
TREATMENT CAPACITY mgd
—I 1
500 1000
-I i 1—I—"—¦ 1
5000 10,000
EQUIVALENT
2.0
250
POPULATION
UNIT PROCESS COST CURVES INCLUDE =
• CONTINGENCIES
¦ ENGINEERING 8 ADMINISTRATION
• SITE WORK
• ELECTRICAL
• PACKAGE GRAVITY FILTERS S. MEDIA
• SURFACE WASH S BACKWASH SYSTEMS
« valves, piping a controls
GRAVITY FILTRATION
CAPITAL COST
U
FIGURE 15
-------
1,000,000
500,000
-UNIT PROCESS
100,000
50,000
ENCLOSURE-
10,000
5,000
1,000
100 2 3 4 5 6 7 8 9 1000 2 3 4 5 6 7 8 910,000
TREATMENT CAPACITY m3/
-------
10,000,000
5,000,000
cn
a
u
! ,000,000'
o_
<
u
500,000
100,000*
100
0.05
25
4 5 6 7 8 9 1000 2 3 4 5678910,000
TREATMENT CAPACITY m3/bay
-H-
-+-
o.i 0:5
TREATMENT CAPACITY mgd
-f 1—
1,0
1.5 2.0
-H 1 1 —I 1 1 ! I I HI l-l
50 100 250 500 1000 . 5000 10,'
POPULATION EQUIVALENT
,000
UNIT PROCESS COST CURVE INCLUDES:
• CONTINGENCIES
• ENGINEERING S ADMINISTRATION
• SITEWORK
• ELECTRICAL
• REVERSE POLARITY
ELECTRODIALYSIS SYSTEM
13
ELECTRODIALYSIS
CAPITAL COST
FIGURE I?
-------
1,000,000
500,000
- I
¦»
w
o
o
<
K
(L
<
O
100,000
50,000'
10,000
5,000
1,000
100
3- 4 5 6 7 8 91000 2 3 4 5 6 7 8 910000
TREATMENT CAPACITY m'/doy
4——I 1 . 1 |
0.05
0.1 0.5
TREATMENT CAPACITY mid
_l— 1—(—i-H"
1.0
IS 2.0
1
-t~
-f-
H—I I I- < t I I-
25
50
100 250 500 ©00
5000 10,000
POPULATION EQUIVALENT
ELECTRO DIALYSIS ENCLOSURE
CAPITAL COST
FIGURE 18
-------
100,000'
100
4 5 6 7 8 9 1000 2
TREATMENT CAPACITY m3/day
-4 1 1- f ( |
0.05
-+-
-h
4 5 6 7 6 910,000
0.1 0.5 "
TREATMENT CAPACITY mgd
^4-
i.o
—i —
1,5 2.0
4-
—f j 1-
50 100 250 500 1000
POPULATION EQUIVALENT
50^00 IO'POO
-H-
25
UNIT PROCESS COSJ CURVE INCLUDES:-..
'• CONTINGENCIES
•ENGINEERING &- ADMINISTRATION: *• -J.
• SITEWORK
• ELECTRICAL
• MEMBRANE TYPE REVERSE
OSMOSIS SYSTEM
REVERSE OSMOSIS
CAPITAL COST
FIGURE 19
-------
I,000|0b 2 5 6 "78'9 1000 ~~Z~ " 3 "~4 5 6 7 8 910,000
TREATMENT CAPACITY m3/doy
H—I I t I ; 1 1 1 1—=—I 1—t-f-
0.05 0.1 0.5 1.0 1.5 2.0
TREATMENT CAPACITY mgd
H i 1 1 1 1— 'MM
- oc
25 50 100 250 500 1000 5000 10,000
POPULATION EQUIVALENT
REVERSE OSMOSIS ENCLOSURE
CAPITAL COST
FIGURE 20
16
-------
10,000
5,000
4,000
fe
o
o
3,000
<
H
a.
<
o
2,000
< 20mg/l
UNIT PROCESS
&0 m
•ENCLOSURE
C 20mg/l
1000
1000 2 3 4 5 6 7 8, .9 10,000
TREATMENT CAPACITY m'/day
-» 1 i 1 1—I—I-
0.3 0,5 - 1.0 1.5 • 2,0
TREATMENT. CAPACITY mg
• CONTINGENCIES
• ENGINEERING a ADMINISTRATION
• SITEWORK
• ELECTRICAL
• CHEMICAL FEED EQUIPMENT
POWDERED ACTIVATED CARBON
CHEMICAL FEED
CAPITAL COST
FIGURE 21
X?
-------
100,000
50,000
- UNIT PROCESS
<50
b-
o 10,000
u.
_i
Cl.
<
o
5,000
<50mg/t
ENCLOSURE
1000 •
1000 2 3 4 -56789 10,000
TREATMENT CAPACITY m3/ day
' 1 1 1 1 1 1 1—) 1—i—i—i—| H 1
0,3 0.5 t.O "1.5 2.0 '
TREATMENT CAPACITY mgd
I 1 1 1 1 1 1 1 1—|—i—i 1 1
250 500 1000 5000 10,000
POPULATION" EQUIVALENT
UNIT PROCESS COST CURVE INCLUDES =
• CONTINGENCIES
• ENGINEERING S ADMINISTRATION
• SITEWORK
• ELECTRICAL
• CHEMICAL FEED EQUIPMENT
COAGULANT
CHEMICAL FEED
CAPITAL COST
FIGURE 22
18
-------
100,000
50,000
-------
100,000
50,000
UNIT PROCESS
10,000
0,5mg/I
ENCLOSURE
5,000
3 mg/l
I mg/l
1000
iOOO 2 3 4 56789 10,000
TREATMENT CAPACITY m5/doy
, , 1 j ,—,—,—H
-i 1 1—i—t—i—t-
250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVES INCLUDE
• CONTINGENCIES
• ENGINEERING 8 ADMINISTRATION
• SITEWORK
• ELECTRICAL
• CHEMICAL FEEO EQUIPMENT
0.3 0,5 1.0 1.5 2.0
TREATMENT CAPACITY mgd
POLYMER
CHEMICAL FEED
CAPITAL COST
FIGURE 24
20
-------
10,000
5,000
4,000
-ENCLOSURE
<5 mg/l
to
g 3,000
< 5mg/l
-UNIT PROCESS
a
o
2,000
1000
1000 2 5 4 56789 10,000
TREATMENT CAPACITY m3/day
i , 1 1 , ) 1 ,—| 1—,—,—,—1 1 1
0.3 0.5 1.0 1.5 2.0
TREATMENT CAPACITY mgd
I 1 : 1 ) 1 1 1 ) 1—I 1 1 1 1
250 5 00 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVE INCLUDES:
• CONTINGENCIES
• ENGINEERING & ADMINISTRATION
• SITEWORK
• ELECTRICAL
• CHEMICAL FEED EQUIPMENT
POLYPHOSPHATE
CHEMICAL FEED
CAPITAL COST
FIGURE 25
-------
100,000
50,000
cn
Q
o
10,000
£L
<
u
5,000
UNIT PROCESS
< 5mg/l
¦ENCLOSURE
1000
1000 2 3 4 56789 lOpOO
TREATMENT CAPACITY mJ/doy
I 1 1 1 1 1 1 t f t 1—i—i—| 1 1
0.3 0.5 i.O 1.5 2,0
TREATMENT CAPACITY mgd
l_
1 1 , , ,—|—,—i—(—i—
250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVES INCLUDE ;
• CONTINGENCIES
• ENGINEERING & ADMINISTRATION
• SITEWORK
• ELECTRICAL
• CHEMICAL FEED EQUIPMENT
CHLORINE
CHEMICAL FEED
CAPITAL COST
FIGURE 26
-------
1,000,000
500,000
S 00,000
UNIT PROCESS
50,000
4/V
H
as
O
o
Gl
u
10,000
5,000
ENCLOSURE
1000
1000
2 3 4 5
TREATMENT CAPACITY ms/doy
0.3
H h
0.5 1.0
TREATMENT CAPACITY mgd
1.5
L.
250
500 1000
H 1 1 »
5000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVES INCLUDE:
• CONTINGENCIES
• ENGINEERING 6 ADMINISTRATION
• SITEWORK
• ELECTRICAL
• AIR-FEED OZONE GENERATING SYSTEM
• CHEMICAL FEED EQUIPMENT
10,000
£ 3 He>T£
9 10,000
2.0
OZONE
ON-SITE GENERATION
CAPITAL COST
23
FIGURE 27
-------
to 0,000
50,000
¦»
b-
in
g 10,000
a.
< i
o
5.000
Smg/I
I 5mg/l
iQmg/l
l.5mg/l
UNIT PROCESS
5 mg/>
ENCLOSURE
1000
1000 2 3 4 56789 10,000
TREATMENT CAPACITY m3/day
I 1 1 1 1 1 ( 1 1 1 1—i—i—| 1 1
0.3 0.5 1.0 1.5 2-0
TREATMENT -CAPACITY mgd
-t- 1 1 1 1 1 1 H
250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVES INCLUDE
• CONTINGENCIES
• ENGINEERING & ADMINISTRATION
• SITE WORK
• ELECTRICAL
• CHEMICAL FEED EQUIPMENT
CALCIUM HYPOCHLORITE
CHEMICAL FEED
CAPITAL COST
FIGURE 28
i
-------
10,000
5,000
4,000<
UNIT PROCESS
1.5 mg/i
3,000
2,000
1000
1000 2 3 4 56789 10,000
TREATMENT CAPACITY m3/ day
I ) 1 1 1 ( 1 , j 1 ,—,—,_| 1 1
0.3 0.5 1.0 1.5 2.0
TREATMENT CAPACITY mgd
J j__ 1 1 1 1 1 1 f—|—i 1 1
250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVES INCLUDE>
» CONTINGENCIES
• ENGINEERING S ADMINISTRATION
• SITEWORK
• ELECTRICAL
• CHEMICAL FEED EQUIPMENT
NOTE:
ENCLOSURE CAPITAL COST FOR ALL
SIZES IS $3700.
SODIUM HYPOCHLORITE
CHEMICAL FSED
CAPITAL COST
FIGURE 29
-------
100,000
50,000
V)
o
o
a.
<
o
10,000
UNIT PROCESS
ENCLOSURE
5mg/l
1.5 mg/l
UNIT PROCESS
ENCLOSURE
5,000
1000
1000 2 3 4 5 6 7 8 9 10,000
TREATMENT CAPACITY m3/day
!¦— t —>¦ - —I 1 1 1 } f I—I 1—| 1 ¦ ¦ - J
0.3 0.5 10 1.5 2 0
TREATMENT CAPACITY mgd
I , 1 1 1 , 1 ,—|—|—| 1 1
250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVES INCLUDE =
• CONTINGENCIES
• ENGINEERING 8 ADMINISTRATION
• SITEWORK
• ELECTRICAL
• SALT FEED SODIUM HYPOCHLORITE
GENERATING SYSTEM
« CHEMICAL FEED EQUIPMENT
SODIUM HYPOCHLORITE
ON-SITE GENERATION
CAPITAL COST
FIGURE 30
aS
i
-------
100,000,
50,000-
1
CO
O
a
_i
<
CL
<
O
10,000'
5,000:- - -
1,000-. - . - - ¦ - -- -J
100 2 3456789 1000 2 3 4 5 6 7 8 910,000
TREATMENT CAPACITY rr.3/day
J 1 1 )- f j- | 1 1 i i 1 1—t-t-| 1 1 I
0.05 0.1 0.5 1.0 1.5 2.0
TREATMENT CAPACITY, mgd
-1 1 1 1 1 1—f-
{44-M- [¦¦¦¦
300 IOC
25 50 100 250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVE INCLUDES
• CONTINGENCIES
• ENGINEERING 8 ADMINISTRATION
• EXCAVATION
• FENCING
WASTE SOLIDS DISPOSAL
LAGOON
CAPITAL COST
FIGURE 31
27
-------
1,000,000
500,000
UNIT PROCESS
«
o
o
100,000
ENCLOSURE
50,000
i
10,000
100
TREATMENT CAPACITY m3/day
J 1 i—|—1—S—| i 1 \ 1—-t H -» I-)—¦ —t- |—
0.05 0 1 0.5 1.0 1,5 2.0
TREATMENT CAPACITY mfld
I 1 1 1 1 1 1 1—i h|h h I
25 50 100 250 500 1000 5000 10,000
POPULATION EQUIVALENT
UNIT PROCESS COST CURVE INCLUDES:
* CONTINGENCIES
* ENGINEERING 8 ADMINISTRATION
" INSTALLED PACKAGE TREATMENT SYSTEM
PACKAGE PLANT
CAPITAL COST
28
FIGURE 32
-------
fOOjOOOr
50.000-
|