DRAFT
DEVELOPMENT DOCUMENT
EFFLUENT LIMITA??ONS GUIDELINES
STANDARDS 0PERFORMANCE
WATER SUPPLY INDUSTRY
ENVIRONMENTAL PROTECTION AGENCY
MARCH 1975
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NOTICE
The attached document is a DRAFT CONTRACTOR’S REPORT. It
includes technical information and recorendations submitted
by the Contractor to the United States Environmental Protection
Agency (“EPA”) regarding the subject industry. It is being
distributed for review and co nt only. The report is not
an official EPA publication and it has not been reviewed by
the Agency.
The report, including the recowendations, will be undergoing
extensive review by EPA Federal and States agencies, public
interest organizations, and other interested groups and per-
sons during the coming weeks. The report and in particular
the contractor’s recoumiended effluent limitations guidelines
and standards of performance is subject to change in any and
all respects.
The regulations to be published by EPA wider Section 304 (b)
and 306 of the Federal Water Pollution Control Act, as amended,
will be based to a large extent on the report and the corents
received on it. However, pursuant to Sections 304 (b) and 306
of the Act, EPA will also consider additional pertinent tech-
nical and economic information which is developed in the course
of review of this report by the public and within EPA. EPA
is currently performing an economic impact analysis regarding
the subject industry, which will be taken into account as
part of the review of the report. Upon completion of the
review process, and prior to final promulgation of regulations,
an EPA report will be issued setting forth EPA’ a conclusions
concerning the subject industry, effluent limitation guide-
lines and standards of performance applicable to such industry.
Judgments necessary to promulgation of regulations under Sec-
tions 304 (b) and 306 of the Act, of course, remain the responsi-
bility of EPA. Subject to these limitations, EPA is making
this draft contractor’s report available in order to encpur-
age the widest possible participation of interested persons
in the decision making process at the earliest possible time.
The report shall have standing in any EPA proceeding or court
proceeding only to the extent that it represents the views of
the Contractor who studied the subject industry and prepared the
information and ricoandations. It cannot be cited, referenced,
or represented in any respect in any sszch proceedings as a
statement of EPA’s views regarding the subject industry.
U, S. Environmental Protection Agency
Office of Water and Hazardous Materials
Effl qent Guidelines Division
Washington, D.C. 20460
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SORI-EAS-75-103
DEVELOPMENT DOCUMENT FOR
EFFLUENT LIMITATIONS GUIDELINES
AND STANDARDS OF PERFORMANCE
Draft Final Report to
ENVIRONMENTAL PROTECTION AGENCY
On a Study of the
Water-supply Industry
Project 3324f Report 6
Southern Research Institute
2000 Ninth Avenue South
Birmingham, Alabama 35205
March 1975
Project 3324-VI
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DRAFT
ABSTRACT
This report presents the findings of a study of the Water
Supply Industry for the purposes of developing effluent
limitation guidelines, and standards of performance for the
industry to implement Sections 304, 306, and 307 of the Federal
Water Pollution Control Act of 1972 (PL92-500). Guidelines and
standards were developed for the entire water supply industry,
which was divided into three subcategories. The effluent
limitations guidelines given in this report set forth the
degree of reduction of pollutants in effluents from existing
point sources that is attainable through the application of
best practicable control technology currently available
(BPCTCA), and the degree of reduction attainable through the
application of the best available technology economically
achievable (BATEA). The BPCTCA is to be achieved by July 1,
1977, and BATEA by July 1, 1983. Standards of performance
for new sources are based on the best available demonstrated
technology (BADT).
None of the plants in subcategory I use lime or lime—soda
softening processes, and the recommended pH range is 6.0 to
9.0. Plants in subcategories II and III do use lime or lime-
soda softening processes, and the recommended pH range is 6.0
to 10.5. For all three subcategories the total suspended
solids loadings recommended for BPCTCA (1977) are computed by
methods based on statistical analysis of the data.
The recommended procedures for BATEA (1983) involve recycle of
filter backwash water and the liquids separated from solids in
solids—separations units (e.a., lagoon overflows).
The rationale for the development of the recommendations are
presented herein.
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DRAFT
CONTENTS
Section Page
I. CONCLUSIONS i
II. RECOMMENDATIONS 4
III. INTRODUCTION 7
A. Purpose and Authority 7
B. Basis for Guidelines Development 8
C. Description of the Water-Supply Industry 11
D. Description of Water—Treatment Processes 14
1. Presedimentation 17
2. Coagulation 17
3. Softening 21
4. Iron and Manganese Removal 25
5. Filtration 26
6. Dissolved-Solids Removal 27
IV. CATEGORIZATION OF THE INDUSTRY 34
A. Rationale for categorization and sub-
categorization 34
V. WASTE CHARACTERIZATION 42
A. Characteristics of Waste Waters 42
1. Sludges from processes that use
coagulation 42
2. Sludges from plants that use lime or 43
lime-soda softening 43
3. Sludges from iron and manganese
removal processes 43
4. Filter backwash water 43
B. Basis for Characterizing Wastes 43
VI. SELECTION OF POLLUTANT PARAMETERS 45
A. Definition of Pollutants 45
B. Basis for Selection of Pollutant Parameters 45
iii
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DRAFT
CONTENTS (Continued)
Section Page
C. Rationale for Selection of Pollutants 46
1. suspended solids 46
2. pH 47
3. Iron and manganese 47
4. Total dissolved solids 49
5. Fluoride 49
D. Rationale for Rejection of Constituents as
Pollutant Parameters 50
1. Oxygen demand parameters (BOD and COD) 50
2. Toxic heavy metals 5].
3. Sulfate and chloride 53
VIII CONTROL AND TREATMENT TECHNOLOGY 54
A. In-Plant Technology 54
1. Plant operation 55
2. Plant design 55
3. Organic polymers 55
4. Filter backwash recycling 55
5. Chemical recovery 56
a. Alum recovery 57
b . Lime recovery 58
i. Fluid bed calcining 59
ii. Rotary-kiln process 61
iii. Multiple-hearth furnace 63
c. Magnesium bicarbonate recovery 65
d. Brine recovery 68
B. End-of-pipe Waste Treatment Technology 69
1. Preliminary treatment systems 69
a. Sludge flow equalization and
storage tanks 69
b. Thickening of sludges 71
c. pH neutralization 72
2. Dewatering systems 72
a. Lagoons 72
i. Operational and design factors
for lagoons 74
iv
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DRAFT
CONTENTS (Continued)
Section Page
ii. Application to subcategory 75
(a) Category I 75
(b) Category II & III 76
iii. Plant visits 77
iv. Summary 77
b. Vacuum filtration 78
i. Operational and design features 78
ii. Application to subcategory 80
(a) Category I 80
(b) Category II & III 81
c. Filter press 82
i. Design and operational features 83
ii. Operating personnel 85
iii. Building requirements 85
iv. Chemical/physical conditions 85
v. Precoat materials 88
vi. Application to subcategories 88
(a) Category I 88
(b) Category II 89
Cc) Category III 89
vii. Summary 89
viii.Effluent quality 90
d. Sand drying beds 90
1. Operational and design features 90
ii. Sludge characteristics 91
iii. Climatic conditions 91
iv. Depth of application 91
v. Application of technology
to subcategory 92
(a) Category I 92
(b) Category II 93
(c) Category III 93
vi. Summary 93
(a) Advantages of drying beds 93
(b) Disadvantages of drying
beds 93
(C) Effluent quality 94
e. Disposal to sanitary sewer 94
i. Application to subcategories 94
(a) Category I 94
(b) Category II & III 95
ii. Ion-exchange softening 96
iii. Summary 96
V
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DRAFT
CONTENTS (Continued)
Section Page
f. Centrifuge 97
i . Type of centrifuges 97
(a) Horizontal shaft units 98
(b) Vertical shaft units 101
ii. Treatment technology applied
to subcategories 101
(a) Category I 101
(b) Category II 102
(c) Category III 102
iii. Summary 104
iv. Effluent quality 104
g. Miscellaneous treatment
technologies 104
is Freezing 104
ii. Land application 105
iii. Spray irrigation 105
iv. Land reclamation 106
v . Sludge plowing 106
vi. Heat drying 106
vii. Specialty recovery 106
C. Case Studies 107
1. Case I 107
2. Case II 109
3. Case III 111
4. Case IV 113
5. Case V 115
6. Case VI 117
7. Case VII 119
8. Case VIII 121
VIII. COST, ENERGY, AND NON-WATER QUALITY ASPECTS 123
A. Costs of Alternative Control and
Treatment Technologies 123
1. Existing treatment costs 123
a. Lime recovery 123
b. Disposal to sanitary sewer 125
c . Vacuum filtration 125
2. Model Cost Systems 125
vi
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DRAFT
CONTENTS (Continued)
Section Page
a. Costs of pH control 129
b. Ultimate disposal costs 131
c. Operation 131
d. Economics 133
e. Coagulation plants 133
i. Lagoon - 3,785 Cu rn/day
(1 MGD) plant 135
ii. Disposal to the sanitary
sewer - 3,785 cu rn/day (1 MGD) 137
iii. Sand drying beds, 75,700
Cu rn/day (20 MGD) 138
iv. Filter press — 189,250 Cu
rn/day (50 MGD) 140
f. Coagulation-softening plants 141
i. Lagoon — 3,785 Cu rn/day
(1 MGD) and 75,700 Cu rn/day
(20 MGD) 142
ii. Lagoon — 75,700 Cu rn/day
(20 MGD) 144
iii. Filter press — 189,250 Cu
rn/day (50 MGD) 145
g. Softening plants 147
i. Lagoon — 3,785 Cu rn/day (1 MGD)
and 75,700 Cu tn/day (20 MGD)
plant 147
ii. Lagoon - 75,700 Cu rn/day
(20 MGD) plant 149
iii. Centrifuge - 189,250 cu rn/day
(50 MGD) 150
iv. Lime recovery - 189,250 Cu
rn/day (50 MGD) 152
B. Reduction Benefits of Alternative Control
and Treatment Technoloties 153
C. Non-water Quality Aspects 158
1. Land use 158
2. Energy use 159
3. By—product generation and recovery 160
4. Air pollution aspects 160
5. Noise 160
6. Odors 160
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DRAFT
CONTENTS (Continued)
Section Page
IX. BEST PRACTICABLE CONTROL TECHNOLOGY
CURRENTLY AVAILABLE - EFFLUENT LIMITATIONS 161
A. Procedure for Determining Effluent
Limitations 162
B. Zeolite Brines 166
X. BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE - EFFLUENT LIMITATIONS 167
XI. NEW SOURCE PERFORMANCE STANDARDS AND
PRETREATMENT STANDARDS 169
A. New Source Performance Standards 169
B. Pretreatment Standards 169
XII. ACKNOWLEDGMENT 170
XIII. GLOSSARY 171
viii
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DRAFT
TABLES
Page
Table 11-1 Allowance to Adjust the Annual
Average Waste Load for Plant Size
and Raw Water Hardness 6
Table 111-1 Production of Water for Domestic Use
From Waste—Producing Water—Treatment
Plants 12
Table 111-2 Production of Water for Industrial
Use From Waste—Producing Water—
Treatment Plants 13
Table 111-3 Main Processes Used in Water
Treatment 18
Table IV-l Sample Data Form 35
Table IV-2 Comparisons Between Verified Samples
and Total Number of Municipal Water-
Treatment Plants Listed in USPHS
1963 Survey 38
Table V-i Mean Raw-Waste Loads for the
Subcategories 44
Table VI-l Toxic Heavy Metals Concentrations
Reported 52
Table Vu-i Suiiunary of Identified and Visited
Sludge Treatment Processes 103
Table VIII—l Summary of Water Cost Data (1970) 124
Table VIII-2 Lime Recalcination Plants Visited
(1974 Data Except Where Noted) 126
Table VIII-3 Disposal to Sanitary Sewer 127
Table VIII-4 Vacuum Filtration of Water Plant
Sludge 128
Table VIII-4(a) Hauling and Disposal Cost 132
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DRAFT
TABLES (Continued)
Page
Table VIII-5(a) Reduction Benefits Derived from
Model Treatment of Wastes Water
Treatment Process-Coagulation 154
Table VIII-5(b) Reduction Benefits Derived from
Model Treatment of Wastes Water
Treatment Process—Coagulation—
Softening 155
Table VIII-5(c) Reduction Benefits Derived from
Model Treatment Wastes Water
Treatment Process-Softening 156
Table VIII-6 Calculations of Total Sludge
Production 157
Table IX-l Allowances to Adjust the Annual
Average Waste Load Size and Raw
Water Hardness 165
Table XIV Conversion Factors 194
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DRAFT
F IGURES
Page
Figure 111-i Sample data sheet from data-
processing program 10
Figure 111-2 Cumulative production volumes as
a percentage of total U. S.
production by the major-waste—
producing water—treatment plants 15
Figure 111-3 Cumulative production volume as
a percentage of total U. S.
production by waste-producing
water-treatment plants 16
Figure 111-4 Processing steps for zeolite
softening plant 29
Figure 111-5 Processing steps for sedimentation
basin-centrifuge plant 30
Figure 111-6 Processing steps for complex
recalcination water-treatment plant 31
Figure VI-l Distribution of product water for
215 water supplies 48
Figure Vu-i Recovery of lime for reuse—fluid
bed processes 60
Figure VII-2 Recovery of lime for reuse—rotary
kiln processes 62
Figure VII-3 Cross section of a typical multiple
hearth incinerator 64
Figure VII—4 Lime recovery magnesium process
flow diagram 67
Figure Vu-S Cross—sectional view of Permutt
Spiractor showing flow 70
Figure VII-6 Elements of pH control system 73
Figure VII-7 Rotary vacuum filter system 79
Figure vu-B Side view of a filter press 86
xi
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DRAFT
FIGURES (Continued)
P age
Figure VII-9 Cutaway view of a filter press 87
Figure Vil-lO Cross section of concurrent flow
solid-bowl centrifuge 98
Figure VII-li Schematic diagram of a basket
centrifuge 99
xii
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DR1 .FT
SECTION I
CONCLUSIONS
In this study of the water-supply industry (SIC 4941), the
nature and the amounts of the raw wastewater loadings were
found to depend on the types of processes and the combinations
of processes in the treatment of the raw water used as feed.
The size of water-treatment plants and the hardness of the
raw water had significant effects on raw wastewater loads.
Therefore the types of processes and the combinations of
processes were used as the basis of subcategorization, and
an equation was developed from multiple linear regressions
of the collected data to provide allowances for the effects
of plant size and raw—water hardness. The subcategories
developed for the water-supply industry are:
Subcategory I - Plants that use one of the following
processes: coagulation, oxidative iron—and—man-
ganese removal, direct filtration, or diatomaceous
earth filtration. In plants grouped in Category I
only one of the above solids-removal processes is
used. Combinations of two or more solids removal
processes are included in other categories.
Subcategory II - Plants that use only the chemical*
(i.e., lime or lime—soda) softening processes. No
combinations of solids-removal processes are included.
Subcategory III - Plants that use combinations of coagu-
lation and chemical softening, or oxidative-iron-
manganese removal and chemical softening.
Plants in these categories generate wastewaters with sludges
of buspended solids, but differ in treatability of sludges,
the amounts of wastewater, the pH of the wastewater, and the
concentrations and loadings of suspended solids in the waste—
waters. The concentration or loading of suspended colids in
*Chemical softening is used in this report as a collective term
to cover either lime or lime-soda softening so th&z re et..cions
of the two terms (lime and lime—soda) can be avoided.
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DRAFT
wastewaters before any waste treatment is termed the “raw
waste load.”
There are plants in the three subcategories that use zeolite
iron removal or zeolite softening processes in combination
with the solids-removal processes identified in the subcate-
gories. These plants were not treated as a subcategory; but
separate provisions, described below, were made for the
wastewaters from the zeolite processes.
Pollutants are defined to be constituents in wastewaters in
concentrations posing potential detriment to the environment.
For the three subcategories of plants that generate waste—
waters, pollutants were found to be pH and total suspended
solids (TSS).
If a zeolite process is used in combination with any of the
subcategorized solids_±:emoval processes, the following consti-
tuents are pollutants: total dissolved solids (TDS), dis-
solved iron, dissolved manganese, and the fluoride ion.
However, none of these pollutants found in waste zeolite
brines was the subject of the effluent limitations guidelines
to be met by 1977 because there is no adequately demonstrated
control and treatment technology. For the effluent limita-
tions guidelines to be met by July 1, 1983, the pollutants
in waste zeolite brines will not be subject to limitations
because the brines will be segregated from other wastes,
reclaimed, and reused, and only a solid waste will be
generated.
Water-treatment plants that use the processes of dissolved—
solids removal or defluoridation generate wastewaters that may
contain potentially detrimental concentrations of TDS or
fluoride. However, for these wastes, no adequate control or
treatment technology has been demonstrated. Therefore, the
means for disposal of the wastewaters from these processes
will be judged individually with the following possibilities
for disposal in mind: discharge to a sewer, controlled dilu-
tion prior to discharge to a water—course, discharge to the
ocean, or deep—well injection.
A few water—treatment plants use presedimentation basins. In
these much of the suspended solids in the raw water settles,
and the sludge generated is discharged continuously into the
source from which the raw water came. Studies of the costs
and energy requirements needed to dewater such sludges and
transport the dewatered sludges to landfill sites indicate
unfavorable cost—benefit ratios for this treatment in a
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DRAFT
number of cases. Since the total number of plants with pre-
sedimentation basins is small compared with the total number
of waste-producing plants, no across-the—board limitations
are recommended for the wastes from presedirnentation basins.
Instead, each case should be judged individually.
Few of the verified data sheets used as a data base for this
study were from plants that treat water for use by industry
(24 out of 782 total). From statistical analysis of these
24 plants, there appears to be no significant differences
between the wastes from industrial water-treatment plants
and the wastes from other plants. Therefore, the industrial
plants we included with the total number of plants for the
statistical studies to develop effluent limitation guidelines.
However, additional data from industrial water—treatment plants
may be desirable.
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DRAFT
SECTION II
RECOMMENDAT IONS
The effluent limitations commensurate with the best practic-
able control technology currrently available (BPCTCA) recoin-
mended for each of the three subcategories identified in
Section I were established by applying the “statistical var-
iability factor,” which describes the day-to-day variations
in wasteloads, to the annual average waste loads.
The annual average loadings of TSS are given in terms of kilo-
grams of TSS per 1000 cubic meters of product water (kg/bOO Cu
r n) , and in English units of pounds per million gallons (lb/MG),
and are defined by the following equation.
Eq. Il-i L0.6+S+H
where: L = annual average loading of TSS, kg/bOO Cu m
S = allowance for plant size taken from Table 11—1,
kg/l000 cu m
H = allowance for hardness of raw water taken
from Table 11-1, kg/l000 Cu m
For all categories an annual average waste load of 0.6
kg/bOO cu m (5 lb/MG) of product is recommended for what is
termed the “base-load” plant. The basis for this 0.6 kg/bOO
cu m (5 lb/MG) waste load stems from multiple-regression
analyses of the data. The base-load plant is a large plant
[ >1,893,000 cu rn/day (>500 MGD)] that does not use chemical or
softening processes. For smaller plants an additional allow-
ance for plant size, S , is recommended. The magnitude of the
allowance depends on the plant size as shown in Table 11—1.
For plants in Category I, chemical softening is not performed.
Therefore, no allowance is given for the hardness of the raw
water, and only the size allowance, S , in Table 11-1 is applic-
able. For plants in Categories II and III, in which chemical
softening is performed, the hardness allowance, H, in Table
11—1 is used.
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DRAFT
The allowable waste load of TSS calculated by equation 11-1
will be the annual average waste load , whereas the daily
maximum waste load should be used to express the effluent
limitations. As explained in Section IX daily maximum values
of waste loads, which are short-term limitations that must
not be exceeded, can be obtained by the use of the statisti-
cal “variability factor”. The statistical variability factor
for TSS loadings was found to 6.6, when the available data
on TSS loadings in effluents from solids—separation devices
in the water supply industry was analyzed statistically.
The daily maximum loading limitation will be 6.6 x L, when
L is calculated from equation 11-1 and Table 11—1.
At present, this limitation should be viewed as tentative
because few data were available to establish the statistical
variability factor, V. More data are being sought and a more
definitive value of V may be established, when additional
data are obtained.
The pH ranges recommended as limitations for three categories
are the following:
Subcategory I - pH from 6.0 to 9.0
Subcategory II - pH from 6.0 to 10.5
Subcategory III - pH from 6.0 to 10.5
Effluent limitations are recommended that are based on the
best available technology economically achievable (BATEA).
For all three categories it is recommended that the super—
natants from solids—separation devices be recycled for use as
feed water to the plant. It is also recommended that in any
plants that use either the zeolite softening or zeolite-iron-
and-manganese—removal processes the waste brines will be
segregated from other wastewaters, reclaimed, and reused for
regeneration.
The recommended technology and effluent limitations for new
sources are the same as those described above as BPCTCA, except
that for new sources filter backwash water will be recycled to
the feed end of the plant. It is recommended that the tech-
nology and effluent limitations identified above as BATEA be
reconsidered after the necessary developmental work is per-
formed to demonstrate the reliability and acceptability of
recycling the water-borne discharges from solids—separations
systems used to treat sludges, and of segregating spent
zeolite brines, reclaiming and reusing them for regeneration.
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Table 11-I
Allowances to Adjust the Annual Average Waste
Load for Plant Size and Raw Water Hardness
Plant size,a 1000 <3.8 3.8—11.4 11.4—38 38—114 114—379 379—1136 1136—1893 >1893
cu rn/day
MGD (<1) (1—3) (3—10) (10—30) (30—100) (100—300) (300—500) (>500)
S (allowance),
kg/bOO Cu in 0.70 0.50 0.40 0.30 0.20 0.10 0.05 (0)
lb/MG (5.8) (4.2) (3.3) (2.5) (1.7) (0.8) (0.4) (0)
Hardness,a mg/i 0—100 100—200 200—300 300—400 400—500 500—600 600—700
H(aliowance),
kg/1000 cu in 0.13 0.24 0.35 0.46 0.56 0.67 0.78
lb/MG (1.1) (2.0) (2.9) (3.8) (4.7) (5.6) (6.5)
a) Annual average total hardness expressed as mg/i of CaCO3
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DRAFT
SECTION III
INTRODUCTION
A. Purpose and Authority
Section 301(b) of the Act requires the achievement by not
later than July 1, 1977, of effluent limitations for point
sources, other than publicly owned treatment works, which are
based on the application of the best practicable control tech-
nology currently available as defined by the Administrator
pursuant to Section 304(b) of the Act. Section 301(b) also
requires the achievement by not later than July 1, 1983, of
effluent limitations for point sources, other than publicly
owned treatment works, which are based on the application of
the best available technology economically achievable which will
result in reasonable further progress toward the national goal
of eliminating the discharge of all pollutants, as determined
in accordance with regulations issued by the Administrator
pursuant to Section 304(b) of the Act. Section 307 of the
Act requires the achievement by new sources of a Federal stan-
dard of performance providing for the control of the discharge
of pollutants which reflects the greatest degree of effluent
reduction which the Administrator determines to be achievable
through the application of the best available demonstrated
control technology, processes, operating methods, or other
alternatives, including, where practicable, a standard
permitting no discharge of pollutants.
Section 304(b) of the Act requires the Administrator to pub-
lish, within one year of enactment, regulations providing
guidelines for effluent limitations setting forth the degree
of effluent reduction attainable through the application of
the best practicable control technology currently available
and the degree of effluent reduction attainable through the
application of the best control measures and practices achiev-
able including treatment techniques, process and procedure
innovations, operation methods and other alternatives. The
regulations proposed herein set forth effluent limitations
guidelines pursuant to Section 304(b) of the Act for the water
supply source category.
Section 306 of the Act requires the Administrator, within one
year after a category of sources is included in a list pub—
lished pursuant to Section 306(b) (1) (A) of the Act, to
propose regulations establishing Federal standards of perfor-
mances for new sources within such categories.
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DRAFT
B. Basis for Guidelines Development
The effluent limitations guidelines and performance standards
recommended in this report were developed from analysis of
information in the literature, reports from the American
Water Works Association and from individual companies, Refuse
Act Permit Program (RAPP) applications, state-agency files,
and information gathered by personal visits to water-treat-
ment plants to identify potential subcategories and exemplary
plants and to obtain information on water use and wastewater
characteristics. On—site studies of potential exemplary
plants were subsequently conducted to verify this information
and observe the control and treatment technology employed to
achieve exemplary performance. Discussions were also held
with consultants and others with knowledge of the manufactur-
ing and waste—treatment practices in the industry.
Some information was obtained about more than 2500 waste—pro-
ducing water-treatment plants, and detailed information was
collected for 1467 of the more than 9000 waste—producing
water-treatment plants identified as currently in operation.
The sources and types of information consisted of
- 656 applications to the Corps of Engineers for
Permits to Discharge under the Refuse Act Permit
Program (RAPP). However, less than 50 of the
RAPP applications contained enough information
to characterize such factors as wastewaters, con-
trol and waste treatment practices employed,
amounts of chemicals used, and the processes
used in treating raw water.
- Many reports from the files of state agencies with
responsibility for environmental protection. These
reports contained valuable information about the
compositions of raw water and product water, the
treatment processes, and the amounts of chemicals
used.
- On—site inspections of water—treatment plants that
provided flow diagrams and detailed information on
the practices used in water—treatment and waste
management, and on the control and treatment
methods, equipment, and costs.
- Other sources of information including EPA techni-
cal reports, trade literature, personal and tele-
phone interviews and meetings with regional EPA
8
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DRAFT
personnel, industry personnel, and consultants, and
information from the American Water Works Assoc-
iation.
The reliability of the data was verified by sending data
sheets with the information obtained from the above sources
to each of 2500 water treatment plants for correction of any
incorrect or out—of-date data and for addition of any missing
data. Of the 2500 data sheets sent to the water—treatment
plants, 782 were verified (or corrected and verified) and
returned. In addition, personal visits were made to 151
plants, and samples were taken and analyzed at 128 of these.
The data base used in development of charts, tables, and
figures includes only the 782 plants for which data have
been verified. The 782 plants represent approximately 8% of
the total waste-producing plants, including both municipal and
industrial plants.
The information obtained in this way was compiled by data
processing techniques and used to prepare data sheets, such
as that illustrated for a hypothetical plant in Figure 111-1,
and analyzed for the following:
- Identification of distinguishing features that could
potentially provide a basis for subcategorization of
the industry. These features included composition
of raw water, in—plant processes used for treatment
of wastes, plant size and age, and other features
which are discussed in detail in Section IV.
- Determination of the waste characteristics for each
subcategory as discussed in Section V including
the volume of water used, the sources of the waste
streams in the plant, and the type and quantity of
constituents in the wastewaters.
- Identification of those constituents, discussed in
Section VI, which are characteristic of the indus-
try and present in measurable quantities, thus being
pollutants subject to effluent limitations guide-
lines and standards.
The control and treatment technologies employed at exemplary
plants were identified during the on—site studies, and are
discussed in Section VII.
9
-------
SUnnAMT OF DATA I -OR PLAi’fl P.IJPIbFR y999
CATELiUN I 21 EPA RFLJI(Ji’U I I
SLUOGESAWIC WATER MUIRO
LO ’(K ‘4U00Y FILTER PLANT SLUDGEBANIc
S T
AVERAGE DAILY FLOWS (MGD) INTAKF
30,0000
TREATP’ENTS PENFURME!) QN RA WAlER
PRODUCT CKNASH CSR*
2V,00oO 0,6500 0.3350
ISR** TOT WASTE
0,0120 0,9970
PRE$Eu
AERAT ION
COAGULATION
SF0 BASIN
ZEOL SOFT
jR..QX 0N
FRS
ACT CARBON
PLANT USES SURFACE WATER SOURCE
Li l IE
CHLOR D’E
ALUM
ACT CARBON
NACL
20,000
1,200
25,000
&000
400, 000
CU FE NA
MG H G CAL 105
‘ I
Z N MN
.—CONT 1NUOUS SLI1On R t.i0VAt
fl—INTERMITTANT SLUDGE REMOVAl
$—ZEhD INDICATES NO DAEA, —t 15 USE” TO REPkESENT AN ACTUAL MrAsutFo ZERO
a.CALCULATFr) WA5Tt rflNCENTkfLTIOIa 1 )EI IVEJ FP’JM PARA’IFTER RFMUVFD AND TOTAL
W*5T 1 FLOr.
a
P h
‘-3
CHEMICALS ADDED (PPM)
I - I
0
0 .00
0,00
0,00
0,00
0,00
0,00
0,00
0,00
0,00
0,00
0,00
0,00
0,00
0,00
0.00
0,00
0,00
0,00
0,00
0,00
4 100 ,00
380 ,00
166,90
41840, 10
I 127,7
TURI4 CHEM ADM I IIARD
50,00
0,50
4113,08
11979,25
1851 , 13
60,00
—1,00
500, 70
141520,30
22 43 ,19
0 ,00
0,00
29,6B
R bO, SR
1079. F7
300 ,00
160,00
1168,30
338a0,70
5 594,10
14,00
16,00
0 ,00
0.00
1 (5,00
RAW AND PRODUCT CONCENTRATIONS
SOURCE 600 COD
T Sot
705 755
TYS
AMMONIA
1CM
t03
P HOS
COLOR
RAW CONCS
804 AL. CL
0 .00
0,00
o,oo
—1,00
0,00
18,00
PROD CP4C$
0,00
0 .00
0,00
0,02
0,00
—1.00
LB/MGwPRD
0.00
0,00
0.00
0.00
0,00
150,2 1
TOIL LBID
0,00
0,00
0,00
0,00
0,00
‘1356,09
w5T CONC,
0,00
0,00
0,00
0,00
0,00
b72, b
CA
F
502
CD
ON
CO
RAW CONCI
145,00
0,30
0,00
—1,00
—1,00
0,00
PROD CNCS
80,00
0,50
0,00
—1,00
•1,00
0,00
LB,MGPRD
5 2.a3
0,0 0
0,00
0,00
0,00
0.00
TOIL LB/D
15fl 0,33
0.00
0,00
0 .00
0,00
0,00
wST CONC .
2510.12
0,30
0,00
0,00
0,00
0,00
NI
SE
PAW CONC$
0,60
1,20
20,00
t8, 00
—1,00 550,00
—1,00
2,00
0,00
—1,00
0,0 1
0 ,90
PROD C’ C
0,03
,o7
0,oD
ti 00
—1,00 500.00
—1.00
1,70
0,00
—1,00
—1,00
0,00
LB/MG PRD
41 ,76
9 ,03
0,00
116,53
0,00 017.25
0.00
2,50
0,00
0,00
0,08
7,18
TOIL IB/D
137,94
27S. 7
0,00
3 88,o7
0,00 22100,25
0.00
72.60
0,00
0,00
2,42
20 5 ,12
WST C{JNC
21,34
a2,3?
20,00
527.05
0,04 2369,32
0,00
12,92
0,00
0,00
0,37
32,19
—1.00
—1,00
0,00
0,00
0 • 00
35,00
90,00
0,tiO
0.00
35.00
Figure 1 1 1—i. Sample data sheet from data-processing program
-------
D1 A.FT
The information, as outlined above, was then evaluated in
order to determine what levels of technology constituted the
“best practicable control technology currently available,”
and the “best available demonstrated control technology.”
In identification of such technologies, various factors were
considered. These included the feasibility of using tech-
nology employed by other industries, the total cost of appli-
cation of control technology in relation to the effluent
reduction benefits to be achieved, non—water quality environ-
mental impact (including energy requirements), and other
factors as discussed in Section VIII.
C. Description of the Water-Supply Industry
The water-supply industry is classified by the Department of
Commerce as SIC group 4941. This classification includes
plants that treat water primarily for domestic, commercial,
and industrial use, but excludes facilities that distribute
water for irrigation.
The 1963 Inventory of Municipal Water Facilities* listed more
than 40,000 water-supply plants that distribute water for
domestic or commercial use. However, of these plants, only
4590 plants used treatment processes that can produce water-
borne wastes. These plants distribute about 14 billion gal ’-
ions of water per day.
There are 9402 plants listed in “Water rJse in Manufacturing,
1967 Census of Manufacturers” that distribute water primar-
ily for industrial use. However, only 5159 of these plants
use processes that can produce water—borne wastes. These
5159 plants distribute approximately 9.6 billion gallons
of water per day.
Table 111-1 shows the total numbers of municipal water-treat-
ment plants that utilize each type or combination of types
of waste-producing process. The average daily productions of
treated water in millions of gallons per day (MGD) from each
type or combination and the total production from all plants
are also shown.
*The results of the 1972 Inventory of Municipal Water Facili-
ties have not been completely processed, and were therefore
not used.
:1.1
-------
DRAFT
Treatment processa
Coagulation
Softening
Iron removal
Coagulation-soft-
ening
Coagulation - iron
removal
Softening - iron
removal
Coagulation - soft-
ening — iron
removal
Other
Total
Number
of
plants
2358
353
1117
265
Total
production,
1000 cu in/day
38082.0
1132. 5
2869.0
8502.2
349.7
(MGD)
(10061.3)
(299.2)
(758 .0)
(2246.3)
(92.4)
(348.2)
a) As listed in the 1963 Inventory of Municipal Water Facilities,
U. S. Department of Health, Education, and Welfare, Public
Health Service, Washington, D.C.
b) Average per plant.
Table-IIL—l
Production of Water for Domestic Use From
Waste-Producing Water-Treatment Plantsa
Average
daily
produc t 0 b
1000 cu rn/day CMGD )
16.2 (4.30)
3.22 (0.85)
2.57 (0.68)
32.10 (8.48)
5.07 (1.34)
3.60 (0.95)
69
366
45
17
4590
13.63
6.36
11.54
1317.9
612 . 4
107.9
52973.7
(3.60)
( 1.68 )
(3.05)
(161.8)
(28.5)
(13995. 7)
12
-------
DRAFT
Table 111-2
Production of Water for Industrial Use From
Waste-Producing Water-Treatment Plantsa
Tr ca tine n t
processa
Coagulation
Filtration
Softening
Ion—Exchange
Settling
Number of
p lantsa
889
1559
3159
1402
480
Average total
daily production
per plant
1000 cu rn/day (MGD )
5,825.1 (1539)
3,652.5 (965)
662.2 (176)
(151)
(2115)
571.5
8,005.3
Daily production
of all plants,
1000 cu rn/day (MGD )
14,183.9 (3,747.4)
15,609.7 (4,124.1)
5,771.7 (1,524.9)
2,192.3 (579.2)
10,529.5 (2,781.9)
a) As listed in Water Use in Manufacturing, 1967 Census of
Manufacturers, U.S. Department of Commerce, Bureau of the
Census, from U. S. Government Printing Office, Washington, D.C.
13
-------
DRAFT
Similar data are shown in Table 111—2 for waste-producing
water-treatment plants that primarily distribute water for
industrial use. The source of the data in Table tfl-2 did
not indicate the number of plants that used combinations of
the 5 processes given in Table 111—1. Obviously many plants
used combinations of processes because of the total number
of plants that treated water is 5159, and the su m of the
plants shown in Table 111-1 to use individual processes is
7489. More than 94% of the water treated for use in indus-
try is used by industries in only 6 major SIC categories:
pulp and paper products (SIC 26), primary metals (SIC 33),
chemicals and allied products (SIC 28) , petroleum and coal
products (SIC 29), food and kindred products (SIC 200, and
textile mill products (SIC 22).
Figure 111-2 shows the percentages of the production of the
total of the 4590 waste-producing plants that are produced
by all plants in each process-type category that are smaller
than or equal to the sizes given on the abscissa. Figure
111-3 displays the same information, except that the scales
on the ordinate and abscissa are greatly expanded so that the
initial portions of the curves can be seen more clearly. Water-
treatment plants that use the coagulation process either singly
(C) or in combination with softening (Cs) obviously produce by
far the roost water (and also the most wastes). Figure 111—3
shows that if only plants producing 378.5 Cu rn/day (0.1 MGD)
or more, are the smallest plants to be affected by the effluent
guidelines limitations, all but 0.6% of the total wastes would
be covered.
D. Description of Water—Treatment Processes
The purpose of a water-treatment plant is to remove or inac-
tivate constituents in the water that are undesirable for the
intended use. Constituents that might be removed in water-
treatment plants include suspended solids, colloids, iron and
manganese, ions that cause hardness, and materials that
impart color, odor, or taste. Some water—treatment plants
are relatively simple because only one of the constituents
14
-------
DRAFT
100
c i SOFTENING
90 — ®SOFTENING AND IRON AND MANGANESE REMOVAL
®IRON AND MANGANESE REMOVAL
Z 80—
2 ®COAGULATION AND SOFTENING
70 ®COAGULATION
60-
U-
0 50— —
w
2 40- —
I —
O 200 400 600 800
PRODUCTION (MGD)
Figure 111—2 Cumulative production volume as a percentage
of total U.S. production by the major—waste-
producing water-treatment plants
15
-------
DRAFT
PLANT SIZE (1000 gd/day)
Figure 111-3 Cumulative production volume as a percentage of
total U.S. production by waste-producing
water-treatment plants.
250
0
COAGULATION AND IRON AND MANGANESE REMOVAL
COAGULATION ,SOFTENING AND IRON AND MANGANESE REMOVAL
COAGULATION AND SOFTENING
SOFTEN ING
SOFTENING AND IRON AND MANGANESE REMOVAL
IRON AND MANGANESE REMOVAL
COAGULATION
z
0
I —
C-)
oO.
0
-J
0
LLO..
0
U i
>
I.-
4
-J
:,0.
U
0.1
00
50 100 150 200
16
-------
DRAFT
mentioned above must be removed. The processes and sequence
of processes used in water-treatment plants depend primarily
on the impurities present in the raw water and the intended
use of the product water. For example, a plant that has
access to raw water with acceptable turbidity, color, odor,
taste, and hardness but with undesirably high concentrations
of iron needs only to remove the iron and inactivate the
bacteria to make the water acceptable for municipal use.
Another plant might have access to raw water that contains
several of the undesirable constituents listed above. Such
a plant would have to use a combination of many processes.
Table 111-3 shows the individual processes used in water-
treatment plants, the purpose of each process, the type of
water-borne waste produced, and typical devices used for
each process. Only the last 6 processes in Table 111-3
produce water—borne wastes. These processes are discussed
briefly, below.
1. Presedimentation
Presedimentation is often used with raw waters that contain
relatively high concentrations of easily settled suspended
solids, such as sand and silt. Presedimentation is per-
formed in basins designed to provide adequate detention time
to allow coarser particles to settle. Normally, only organic
polymers are added to the raw water to aid settling, if any
additives are used. The designs of presedimentation basins
vary, but all design features have the common objective of
providing the most quiescent flow possible, since turbulence
re-entrains solids that have already settled. Most presedi—
mentation basins are designed for continuous sludge re-
moval or have provisions for frequent sludge removal, so
that accumulated sludge will not decrease the effective vol—
ume of the basin and thus decrease the detention time. The
solids content of the sludges produced in these basins varies
widely, and may range up to 20% solids, depending on the
method and frequency of sludge removal.
2. Coagulation
Coagulation and flocculation followed by sedimentation and
filtration are used to separate fine particles and colloidal
17
-------
DP.-.FT
Table 111—3
Main ?rc esses Csed ri Water Treat ent
Type of water-
borr.e wastes
pro ced
Alteration of
the ccncart:a-
tions of vola-
tile zaterials,
oxidation of
dissoived itetals
Contact beds Cr
trays, s ra:..
aerators, s:lash
aerators
Disinfection
Inactivation of
of bacteria
None
Chlorirazcrs, oz:r-
ators, feeders for
hypochiorites or
chlorine dioxide
Corrosion
Control
Taste ar.d
odor controi
Stabilization
of the water
to r ini ize
corrosion in
. : ......:
u...S .. .LOfl
sys te
Rer oval or
inact1vat on of
— .4.,_._1._
CO i.St
that cause ob-
j ectionable
tastes or odors
Feeders for chcs-
phates, r.ypoc icr-
ites, silicatc-s,
alkalais
Feeders for
acti ’ateci car on
To ad ust
fluoride
content to
des . r able
1 eve is
Pre-sedi-
Reroval of
easJv settled
solids
Slurry of
easily settled
solids
Basins, la cons,
?rc ce S S
P r ose
Aeration
Typical de : ces
None
None
None
Fluoride
None Feeders for
fluoride-containing
che .icals
is
-------
DRAFT
Table 111-3 (continued)
Main Processes Used in Water Treatment
Type of water-
borne wastes Typical devices
Process Purpose produced used
Coagulation Removal of Sludges Chemical feeders,
small-sized rapid mixers,
suspended thickeners, floc-
solids, col— culators, sediment
bids and color basins, filters
Softening Removal of Sludges or Chemical feeders,
ions that brines rapid mixers,
cause hard- zeolite (ion-
ness exchange) columns,
thickeners, sedi-
meritation basins,
centrifuges, filters,
calciners, and
chemical recovery
units
Iron and Removal of Sludges Chemical feeders,
Manganese iron and filters of various
removal manganese types
ions
Filtration Removal of Sludges Various types of
solids not filters (e.g., multi-
removed by media, anthrafilt,
settling slow or rapid gravity,
pressure, sand)
Dissolved- Reduction in Brines Reverse osmosis,
solids dissolved electrodialysis,
removal solids content flash evaporation
units
19
-------
DRAFT
materials from water. Colloids or fine particles in suspen-
sions either have or acquire electrical charges on their sur-
faces, Ions that have charges opposite in sign to the surface
charges collect in the shell of water inirnediately adjacent to
the surface of the particles. These double layers of electri-
cal charge cause the particles to repel each other because of
the electrostatic repulsion of like charges. Thus, the electri-
cal double layers inhibit or prevent interparticle collisions
so that the fine particles do not collide and agglomerate into
larger particles that will settle.
The process of coagulation is used to destabilize suspensions
of fine particles. Materials termed coagulants are used to
minimize or neutralize the electrical double layers at the
surfaces of fine particles. Once the electrical double layers
are minimized or neutralized, interparticle collisions can and
do occur as a result of Brownian motion. The frequency of col-
lisions is increased by gentle agitation, and flocculation of
particles occurs. The agitation, or mixing, used in floccula-
tion must be great enough to enhance particle collisions, but
not so great as to break up existing flocculated particles.
Within the range of agitation, flocculation of particles occurs
and the size of the floc increases until the agglomerated par-
ticles are large enough to settle rapidly. The suspension is
then fed into sedimentation basins in which quiescent condi-
tions are maintained and settling occurs. The supernatant
fluid from the sedimentation basins is then filtered to remove
any remaining particulate matter.
Materials used as coagulants include polyelectrolytes and metal
salts, such as aluminum sulfate and ferrous sulfate. Sodium
aluminate and lime are used in some instances to adjust the
pH to optimum ranges, and ozone, chlorine, and other oxidants
are used for some waters to oxidize metal salts. Although
some polyelectrolytes are used by themselves, polyelectrolytes
are more often used in conjunction with metal salts to aid
flocculation.
The steps in the coagulation—flocculation process are:
(a) pre-oxidation, if needed to overcome difficulties with
clarification or color removal; (b) mixing of the coagulant
with the water; and (c) gentle agitation to promote the inter-
particle collision needed for flocculation. The mixers
used for mixing coagulant and water are usually termed
rapid mixers or flash mixers. The mixing is performed under
conditions of high turbulence to ensure adequate dispersion of
chemicals in the water. The gentle agitation that promotes
20
-------
DRAFT
flocculation is performed by horizontally and vertically
baffled mixing basins, by a variety of mechanical mixing
devices, or by aeration in a few plants.
Sedimentation is carried out in basins. A variety of designs
for both inlet and outlet devices for settling basins is used
in various plants to provide conditions for settling. They
all have the goals of elimination of short-circuiting, and the
minimization of eddy currents or other agitating actions that
would disturb and re-entrain solids already deposited. Sedi-
mentation basins differ in the means provided for removal of
sludge. In some plants the sludge is removed continuously by
means of rakes or blades that push the sediment to outlets in
the bottom of the basins. In other plants sludge is allowed
to accumulate in the sedimentation basins until the effective
volume of the basins is reduced and the basins need cleaning.
The periods between cleanings may vary from a few weeks to more
than a year, depending on the basin volume and the turbidity
of the raw water. Basins that are equipped for mechanical
removal of sludge usually have sloping bottoms, so that most
of the sediment flows out with the water when the basins are
drained for cleaning. Sediment that does not flow out with the
water is usually flushed out with hoses.
The sludges from coagulation plants are low in solids concen-
tration (<2%) and are difficult to dewater. These sludges and
methods of treating and disposing of them are discussed in
detail in Section VII.
3. Softening
Softening processes are used to reduce the concentration of
substances that cause hardness in water. Calcium and magne-
sium compounds are most common although salts of other biva—
lent metals contribute to hardness in some waters. “Carbonate
hardness” is the term used to designate the hardness that
stems from the bicarbonates of calcium and magnesium; “non-
carbonate hardness” refers to the hardness caused by sulfates,
chlorides, or nitrates of calcium and magnesium.
The two general types of processes used for softening are
chemical softening, and zeolite softening. In chemical
softening either lime is used alone to remove carbonate
hardness, or both lime and soda ash are used to remove both
carbonate and non—carbonate hardness.
21
-------
DRAFT
When lime alone is mixed with the raw water, the calcium and
magnesium bicarbonates are converted to calcium carbonate
and magnesium hydroxide, which have very low solubilities in
water and therefore precipitate. When both lime and soda ash
are added, calcium and magnesium sulfate are converted to cal-
cium carbonate and magnesium hydroxide and the calcium and
magnesium bicarbonates are converted to the carbonate and
hydroxide forms, which precipitate*. Thus, the addition of
both lime and soda ash removes both carbonate and non-car-
bonate hardness while the addition of lime alone removes only
carbonate hardness.
Because more lime and higher values of pH are needed to cause
precipitation of both calcium and magnesium, and because still
more lime is needed if the raw water contains free C02 and
sodium carbonate, the lime softening process has several var-
iations. If the raw water contains more than about 40 mg/l
of magnesium (expressed as CaCO3), the usual practice is to
reduce the magnesium content below this value by the addition
of lime in excess of that needed to precipitate calcium. The
pH of the resulting water is usually too high for distribution.
The treated water can be recarbonated with carbon dioxide to
convert excess calcium hydroxide to solid calcium carbonate,
which can be settled out. Alternatively, only part of the
raw water is treated to remove both calcium and magnesium,
and the treated water is mixed with raw water to reduce the pH
and convert excess calcium hydroxide to calcium carbonate.
The process of choice depends largely on the composition of
the raw water, as measured by alkalinity, free carbon dioxide,
calcium content, magnesium content, and non—carbonate hardness.
Recarbonation is often practiced to stabilize the water for
distribution even in plants that only remove carbonate
hardness.
Regardless of the variation of the lime—softening process used,
the steps in processing include mixing the chemicals with the
water, flocculation, and settling. Mechanical rapid—mixers
are preferred for mixing the chemicals with water to ensure
dissolution and thorough mixing of the lime with water. For
*A detailed discussion of the chemical reactions involved is
given in Water Quality and Treatment , compiled and edited by
the American Water Works Association and published by the
McGraw-Hill Book Co., New York (1971).
22
-------
DRAFT
the flocculation and sedimentation steps, flocculation and
sedimentation basins similar to those used in coagulation
plants may be used. However, since calcium carbonate and mag-
nesiuin hydroxide precipitate more readily on the surface of
previously formed particles, recirculation of sludge to the
rapid-mix device is usually practiced.
In some water—treatment installations the three functions of
mixing, flocculation, and settling are carried out in solids-
contact softeners. In these devices a rapid-mixing zone, a
zone to allow time for the chemical reactions and floculation
and particle growth to occur, and a zone for settling are
provided within a single unit.
In plants that recarbonate the water with carbon dioxide gas,
a recarbonation basin is required. The carbon dioxide may be
provided by combustion of a carbonaceous fuel. If the fuel is
used to heat a boiler, the use of stack—gas scrubbers, blowers,
control valves, and pipe is required. In some plants fuels
such as natural gas are burned in submerged combustion units
mounted in the recarbonation basin so that the gases enter the
water directly. Some small plants purchase and store carbon
dioxide as a liquid.
The water overflowing the sedimentation basin (or settling
zone in solids—contact softeners) is filtered with conven-
tional filters (described later) to remove the small amounts
of solids in the water from sedimentation basins.
The process known as zeolite softening is an ion—exchange pro-
cess. Certain solid natural and synthetic materials have the
property of exchanging ions in their matrix with ions in
water in contact with the solids. These materials have nega-
tively charged ions that are fixed by chemical bonds to the
solid matrix, and positively charged ions that are free to
move within the interstices of the solid matrix. When gran-
ules or particles of these solids are in contact with water
that contains ions, the mobile positive ions within the zeo-
lite solid particles can exchange with positive ions in the
water. In zeolite softening, a bed of the solid zeolite par-
ticles is equilibrated with a strong sodium chloride solution
prior to use for softening so that the mobile positive ions
within the solid will be sodium ions. The water to be
softened is then allowed to flow through the bed of zeolite
particles, and the sodium ions within the particles exchange
for calcium and magnesium ions in the water. The hardness-
23
-------
DR .FT
causing calcium and magnesium ions are removed from the water
and replaced by sodium ions, which will not cause hardness.
In this way the water is softened.
A given amount of ion—exchange material will not soften
water indefinitely. Calcium and magnesium will continue to
enter the solid until most of the fixed negative ions on the
solids matrix are associated with calcium and magnesium
instead of sodium. The zeolite then loses its capacity to
sorb more calcium and magnesium, and the ion exchange capacity
must be regenerated.
Regeneration is accomplished by contacting the bed of zeolite
with a concentrated solution of sodium chloride (i.e., a
brine). During regeneration, sodium ions are driven into the
zeolite because of their high concentration in the brine, and
calcium and magnesium ions transfer from the zeolite into the
brine. After the strong brine is rinsed from the interstices
of the zeolite bed with water, water to be softened is
admitted to the bed, and sodium ions in the solid are again
exchanged for hardness-causing ions in the water.
Zeolite softeners may be operated with either pressure or
gravity flow. Gravity flow is almost always used for large
plants. The flow may be either upf low or downf low, and the
vessel may be made of concrete, steel, or wood. Steel pres-
sure vessels are used with pressurized flows, and the flow is
virtually always downf low.
On completion of the softening part of the cycle, the beds are
backwashed (upf low) to loosen and expand the zeolite bed and
to flush out any particulate matter that may have collected on
top of the bed. (With gravity upf low, the backwash part of the
cycle is not required.) The zeolite bed is then regenerated by
the introduction of sodium chloride brine through distributors
arranged above the top of the bed. If good regeneration is to
be achieved, the brine must pass uniformly through the bed of
particles without channeling or by-passing any portion of the
bed. The distributor systems are designed to achieve such
uniform distribution.
At the end of the regeneration part of the cycle, the brine
must be removed from the bed. Rinse water pumped through
the distributor system pushes the brine ahead of it in
“piston” flow. During the last part of the rinse cycle, the
rinse water is pumped very rapidly through the bed to remove
24
-------
DRAFT
the last traces of brine. Upon completion of the rinse cycle,
the bed is returned to softening duty.
In addition to the vessels that contain the zeolite granules,
there must be brine tanks, pumps, and timed-control valves to
maintain the proper sequence of events.
4. Iron and Manganese Removal
Iron and manganese are objectionable in water for municipal use
for several reasons. Precipitates of these elements, which
occur upon oxidation of the soluble forms of iron and manga-
nese, result in highly-colored turbid water, which leads to
discoloration in the laundry, and on bathroom and kitchen f ix-
tures. In addition, these elements in concentrations greater
than a few mgi ]. impart an undesirable taste to the water.
Moreover, the presence of these elements in water can promote
the growth of certain bacteria. Iron and manganese are
removed from the water as an incidental feature of the lime
and lime-soda softening processes. However, certain water
plants need to remove iron and manganese but do not need to
soften the water.
The main processes used specifically for iron and manganese
removal includes precipitation by oxidation, and filtration.
Aeration is most often used as the oxidizing step, but other
oxidants such as chlorine and potassium pernianganate are also
used. Chlorine is often added following aeration to provide
additional oxidation. If the pH of the water is too low for
efficient removal of iron, lime is added to adjust the pH.
Powerful oxidants, such as chlorine, chlorine dioxide, or
potassium permangante, are used mainly to treat waters that
contain manganese, since oxidation of soluble manganese
compounds by air is too slow.
The oxidation of iron and manganese is not rapid. Therefore,
time is provided in retention tanks for the reaction to occur
and for agglomeration of the precipitates to filterable size.
The water with agglomerated precipitates is then filtered.
The filter backwash water in iron removal plants contains the
precipitated iron and manganese, and is usually highly colored.
The filters are usually pressurized rapid-sand filters which
will be described in the sub-section on filtration.
25
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DRAFT
5. Filtration
Filtration is usually the final step in removing solids
regardless of which processes precede the filtration steps.
The filters most often used in water—treatment consist of a
thin layer of filter aid deposited by flow on a bed of granu-
lar material, such as sand, held in place by gravity or the
direction and velocity of flow. The objective of filtration
is to reduce the turbidity of the feed water by removal of
suspended matter.
The size of the suspended matter removed by filters ranges
from a few millimicrons (colloids and viruses) to about
50,000 xnillimicrons (silt and sands). Types of matter removed
include colloids, viruses, algae, bacteria, clay particles,
and silt.
Attempts have been made, and are continuing to be made, to
develop the theory of filtration to allow prediction of per-
formance. Factors that have been considered in filtration
theory include sand size, velocity of the water toward and
past the sand, temperature, density of suspended particles,
and size of the particles which affect the probability of a
suspended particle intercepting a particle in the combination
of filter aid and granular matter of the supporting bed, and
other factors, such as pH, type of coagulant, and size and
strength of floc, which affect the adherence of an intercepted
particle to the particles in the filter. At the present, how-
ever, the theory of filtration is not adequately predictive,
and pilot plant tests are almost always used prior to instal-
lation of new filtration facilities.
Several types of filters are used in water—treatment plants.
Most widely used is the rapid—sand filter, which usually con-
sists of a support medium of several layers of different sized
gravel and a layer of carefully sized sand on top of the
gravel. The layers of gravel are graded in size. The bottom
layer is coarse gravel, laid in a container, usually concrete,
that is provided with an underdrain system for collection of
the water into a pipe for transferral to a filtered—water
chamber. subsequent layers are each several inches of sized
sand (from 0.4 to 1 mm in diameter). As filtration proceeds,
the sand layer collects suspended matter and the resistance of
the filter to water flow increases. Eventually the head re-
quired to force water through the filter becomes excessive and
the filter must then be backwashed. Filters are backwashed by
forcing filtered water into the bottom of the container and
upward through the layers of gravel and sand. The upward flow
26
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D1 AFT
of water expands the bed of sand and flushed the collected
sediment from the sand.
Of other filters in use in water-treatment plants, the main
types are multi-media filters and pressurized filters. Multi-
media filters are composed of several layers of sized mate-
rials. At the bottom, for example, graded sizes of garnet
gravel (density = 3.1) might be overlaid with successive layers
of silica gravel (density = 2.6), and alluvial anthracite
(density = 1.5). Multi-media filters are designed to permit
penetration of the suspended matter through the top-most layer
and into the underlying layer of sand. This deep penetration
makes possible longer filter runs between washings than are
possible with single medium filters in which penetration is
only a few inches. The long filter runs are desirable to
conserve water used for backwashing and to reduce labor costs.
Pressure filters are similar to gravity-type, rapid-sand f ii-
ters in construction and operation, but the under4rains,
gravel, and sand are housed in a cylindrical tank, and the
water is passed through the filter under pressure. The tank
axis may be either vertical or horizontal. Pressure filters
are used mainly when raw water is furnished under pressure,
and filtered water is to be delivered without further pumping.
The waste from the filtration step is the backwash water with
its load of sediment that was flushed from the filter. The
treatment and disposal of filter backwash water are discussed
in Section VII.
6. Dissolved—Solids Removal
Processes for removal of dissolved solids include e].ectrodi-
alysis, reverse osmosis, and distillation processes. Detailed
descriptions of these processes are available from The Office
of Saline Water, U. S. Department of the Interior. Therefore,
only brief descriptions are given here.
Electrodialysis is a process in which many ion-exchange membranes
are arranged parallel to each other to form solution compart-
ments held between a pair of electrodes. The feed water flows
through every other solution compartment. When a voltage is
applied to the electrodes, electrolytic solids in the feed
water are removed; transported across the ion—exchange membranes
into a waste—brine stream flowing through the solution compart-
ments between the ones that contain feed solution. Electro-
dialysis units from the various suppliers differ in design but
they all produce a waste brine.
27
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DRAFT
Reverse osmosis is a pressure-operated process in which pun-
f Led water transfers through special membranes that pass water
but block impurities. Reverse osmosis equipment is made in a
variety of designs. However, in all designs a concentrated
brine is left on the high—pressure side of the reverse osmosis
membranes after purified water is transferred through the mem-
branes. This concentrated brine is sent to waste.
There are a variety of distillation processes used for dissolved—
solids removal. In all of them purified water is removed from
feed water as a vapor and condensed to give the product water.
The solution left unvaporized contains the impurities originally
present in the feed water, but the impurities have been con-
centrated into a small volume of water. This concentrated brine
is sent to waste.
At present, there are no waste—treatment processes or practices
that are usable to adequately treat waste brines from dissolved—
solids removal processes. These brines are usually disposed of
by discharge to a watercourse, or to deep wells.
Schematic diagrams of several types of treatment plants are
presented in Figures 111-4, 111-5, and 111—6 to illustrate the
sequence of processing steps and the different types of chem-
ical additives used for various purposes.
Figure 111-4 illustrates a simple water-treatment plant, which
obtains water from wells. The water is relatively hard, but
extremely low in turbidity. About 80% of the influent water
is softened in six zeolite softeners, and about 20% of it
bypasses the softeners. The combined product water (about
6400 cu rn/day (1.7 MGD) is disinfected with chlorine, and
distributed. The zeolite softeners are regenerated twice a
day with a saturated NaC1 solution. The waste brine from
regenerations is discharged to the sewer, and eventually enters
a municipal sewage treatment plant.
Figure 111-5 illustrates the steps in a fairly simple process-
ing plan that utilizes sedimentation basins and centrifuges.
28
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DRAFT
Distribution
Figure 111-4.
Processing Steps for Zeolite
Softeninq Plant
Washbrine to Sewer
Wells
Zeolite
Softener
Chlorine
Washbrinc
29
-------
Re servo ii’
Figure 111-5.
Processina Steps for
Sedimentation Basin -
Centrifuqe plant
(I )
0
Sludge
Distribution
Centrate
To Landfill
p j
-------
Chlorine
D1 AFT
Woshwoter Storage
Figure 111—6.
Processing Steps for Complex Recalcination
Water-Treatment Plant
Ash
Fuel Oil
31
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DRAFT
The influent water, which is obtained from a reservoir, is of
medium hardness but of high turbidity. The influent water
plus a recycled stream of sludge from the second sedimentation
basin is mixed with lime and iron sulfate in a rapid mixer,
and then allowed to flocculate. The water then goes through
two sedimentation basins in series. The sludge from the
first basin, about 5% solids, is concentrated to 50—60% solids
in a centrifuge. The paste from the centrifuge is pumped with
a Moyno pump into a storage hopper. It is eventually hauled
to a land-fill site about 20 km (12 miles) distant. The rela-
tively clear centrate (about 0.5% solids) is sent back to the
reservoir. The sludge from the second sedimentation basin is
recycled to the rapid mixer. The overflow from the second
basin is distributed.
Figure 111-6 is an example of a relatively complex combination
of processing steps for water-treatment. This plant obtains
its water from wells. The influent water is hard and also
has a relatively high concentration of suspended solids.
Most of this influent water is mixed with lime in a rapid mixer,
and then flocculation is allowed to occur. The effluent from
the flocculator is transferred to a first stage of sedimenta-
tion. The effluent from the first sedimentation basin plus
part of the influent water is mixed with soda ash and chlorine
and sent to two more sedimentation basins operating in series.
The effluent from the third sedimentation basin is filtered with
sand filters, sent to the clearwell, and then distributed.
Sludge in the first sedimentation basin is removed continuously
by scrapers. The solids concentration varies between 12% and
18%. The solids are primarily CaCO3. This sludge is sent to
a gas scrubber and then to a thickener in which the solids con-
centration is raised to 20%. The sludge from the thickener is
centrifuged to a sticky cake of about 60% solids. Enough dry
CaCO3 is added in a cagemill to reduce the stickiness and form
lumps of CaCO3. These lumps are dried with waste gas from the
calcination step. The dried sludge travels with the waste gases
to a cyclone where separation of solids occurs. Part of the
dried sludge is recycled to a cagemill to control stickiness;
and the rest is stored in a hopper for feed to the calciner.
In the calciner, CaCO3 is converted to lime by driving off
C02. Fuel oil is used for heat. Agglomerated pellets of
lime are removed at the bottom of the calciner and trans-
ferred by bucket elevator to a lime—storage hopper. This
lime is ready for recycle to the rapid mixer at the start of
the process.
32
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DRAFT
Sludge from the second sedimentation basin and backwash water
from the sand filters are recycled to the rapid mixer. Sludge
from the third sedimentation basin plus the thickener over-
flow and the centrate from the centrifuge are sent to a 16—
acre lagoon, where the solids settle.
These three figures illustrate the range of complexity of
processes employed for water treatment. However, the treat-
ment plants may also differ significantly in the nature of
the chemicals and additives employed. These include: lime
and soda ash for softening or pH control; iron sulfate, alum-
inum sulfate, and organic polyelectrolytes for coagulation and
flocculation; activated carbon for taste and odor control and
f or removal of organic matter; sodium chloride for regenera-
tion of ion-exchange materials; chlorine and ozone for disin-
fection; and potassium permanganate or other oxidants for
removal of iron and manganese.
33
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DRAFT
SECTION IV
CATEGORIZATION OF THE INDUSTRY
Rationale for Categorization and Sub—categorization
The goal of this study is the development of effluent limi-
tations that are equitable to all plants but that meet the
aim of the Act, which is the elimination of pollutant dis-
charges from all point sources. To achieve this goal a judg-
ment must be made as to whether separate effluent limitations
are appropriate for different segments (i.e., subcategories)
of the industry.
The quality of raw waters used in the water supply industry
varies widely, and the sizes of water treatment plants also
vary widely within the industry. Other factors, such as types
of processes used, vary also. With such differences in raw
water quality, size, and other factors, it is logical to con-
sider the establishment of separate effluent limitations for
different subcategories of the industry.
Within the allotted time, adequate categorization of the water-
supply industry with such a large number of waste-producing
plants required detailed information about a statistically
meaningful number of plants, and analysis of the data by sta-
tistical techniques. The data for categorizing the industry,
and for characterizing the wastes as described in Section V,
were obtained from applications for permits to discharge
wastes under the Refuse Act Permit Program (RAPP), from the
literature, from the files of regional EPA offices and state
agencies with responsibility for environmental control, and
from discussions during personal visits to water—treatment
plants. From these sources, some information was obtained
about more than 2500 water-treatment plants, and detailed
information about 1467 waste—producing water-treatment plants.
Plant visits were made to 151 of the 1467 plants.
Some of the information needed for this study was not avail-
able from the raw sources, and some of it, especially that
obtained from RAPP applications, was known to be out-of-date.
Therefore, the data from raw sources were transcribed onto
data forms that had blanks for all items needed for this study.
A sample data form is included here as Table IV-1. These
34
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Table IV-l
DRAFT
Sample Data Form
I. Name of Facility
Locat on __________________________________City Zip Code___________________
I L. Treatment Processes
(chuck blocks of
processes used)
Indicate Type
LI Pretreatment ______________ ____________—
D Coagulation Alum Iron Other
LI Chemical Softening Lime____ Lime Soda______
LI Zeolite Softening
Iron-Manganese Removal
Dissolved Solids Removal
fl Filtration
Other Treatment
III. intake Source (Cjrcle Type)
1. Surface
2. Ground
3. Surface & Ground
Avg. Raw Water Volume __________MGD Avg. Raw Water Temperature °F
Avg. Distributed Water Volume MCD for Jan. ______ for July -
Is the uroduct water primarily for industrial use or public use (circle one).
If industrial, give primary usage. (i.e. cooling, cleaning, etc.) _______________
IV. Chemicals Added -
(Prior to Filter) (After Filter)
Annual Average for 1973
ppm or lb/day ppm or lb/day
1. Lime (as CaO) _______ _______ 1. Lime _______
2. Alum (specify type) ______ ______ 2. Sodium chloride ______
3. iron coagulant _______ _______ 3. Other _______
(specify type)
4. Poiy ter _______
5. Activated carbon _______
6. Potassium permanganate _______
7. Soda Ash _______
3. 1I xanetaphosphates ________
9. Sodium chloride _______
lO SodLum hydroxide _______
11. Other (list all) ________
V. Are flocculation or filter aids used? __________If so, (type) ___________; lb/cay_________
1 ) Average daily backwash volume MCD , or
Average no. of backwashes per week ___________
Average amount of water per backwash __________MGD
(B Average volume basin blowdown for continuous sludge removal MCD
C. Aver ige discharge for periodic cleaning of basins ____________MG
Number f cleanings per year _____________
If above is unknown, please indicate your best estimate of amount of sludge produced par
year tn the followina soaces as million gallons. Aluo, estinate tons of dry solids per
yeer. _________________________________________________________________
35
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Table IV—l (continued)
Sample Data Form
(D) Amount regeneration brine for zeolite softening gal/regener ion (if applicable)
Concentration of regeneration brine, weight% ___________
Total anount of rinse water __________gal.
How much backwash water used? _____________gal.
CE) What is the ultimate fate of the filter backwash; recycled, direct discharge to sewer, direct
dLscharge to stream, or treated in any way before discharge? (circle one).
If treated, describe treatment and ultimate point of discharge. ______________________________
(F) What is the ultimate fate of the sludge; direct discharge to sewer, direct discharge to stream.
or treated in any way before discharge? (circle one)
If treated, describe treatment_________________________________________________________ - _ _ _ _ _ _ _
(G) What is the ultimate fate of the brine! recycled, direct discharge to sewer, direct discharge
to stream, or treated in any way before discharge? (circle one if applicable).
If treated, describe treatment
(II) If lagoons are used indicate the ultimate fate of water overflow and ultimate fate of Lagoon
sludge
VI. ParamcLer (units in ppm annual average)
Waste Discharges
Raw Distributed Filter Lagoon Other (Identify)
Water Water Backwash Sludge Overflow
Total suspended solids
(most important) - _ _ _ _ _ _ _ _ _ _ _ _ _
‘lotal solids . — _ _ _ _ _ _ _ _ _ _ _ _ _ _
Total dissolved solids ____________
Total aLkalinity (as CaCO 3 ) __________ ________ ______ ________ _______________
p 1 1 _____________ __________ _______ _________
Total hardness (as CaCO 3 ) _________ ______ ________ — _ _ _ _ _ _ _ _ _ _ _ _ _
Aluminum _________ _______ _________ — _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Chloride ____________ ________
Conductivity (p mho/cm) ___________ ________ _____ ________
Calctum
iron
Magnesium ___________ ________
Manganese ____________ ________
Turbidity (jtu) — -
Are any more complete analyses or studies of wastes available?__________
If you have a turbidity to suspended solids conversion factor, please indicate average factor used
and the maximum and minimum factors.
Over what range of turbidity is the factor usable? to______________ units
Your Name Telephone No.________________
Position Area Code
36
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DRAFT
forms were mailed to each. of the plants for which most of the
necessary data was available along with instructions for
updating and completing the forms (e.g., the use of annual
values for flows and concentrations of wastewater constitu-
ents). Each company was asked to verify, or correct and ver-
ify, data. From this mailing we received verified data for
782 waste-producing water-treatment plants, or about 7% to 8%
of the total number of waste-producing water-treatment plants.*
These verified data were used as the basis for categorizing
the industry and for characterizing the wastes. Table IV-2
shows the ranges of plant sizes and the number of plants using
each of the three main water—treatment processes for the
plants for which verified data were obtained and for the mun-
icipal facilities listed in the USPHS 1963 Survey.
In establishing categories and subcategories, the first step
was to prepare a list of factors that could affect the qual-
ity and quantity of discharge wastes, and for which data could
be obtained from statistically meaningful nwnbers of water-
treatment plants. These factors included the age of the
plant, the size of the plant, the continuous or intermittent
nature of waste discharges, the use of the water, the raw
water quality, the treatment processes used, and the waste—
treatment processes used. As data were acquired about indi-
vidual water—treatment plants, the age of a water—treatment
plant was found not to be truly identifiable in most instances,
because of frequent expansions or modifications.
Few of the verified data sheets used as a data base for this
study were from plants that treat water for use by industry
(24 out of 782 total). From statistical analysis of these 24
plants, there appears to be no significant differenc be-
tween the wastes from industrial water-treatment plants
and the wastes from other plants. Therefore, the industrial
plants were included with the total number of plants for the
statistical studies to develop effluent limitation guidelines.
However, additional data from industrial water—treatment plants
may be desirable.
*Information from the U. S. Public Health Service survey of
municipal facilities made in 1973 is not yet fully available,
and the 1967 Census of Manufacturers was the most recent source
of data for industrial facilities. Therefore, an up-to-date
total of the waste-producing plants is not available.
37
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Table IV-2
Comparisons Between Verified Samples and Total Number
of Municipal Water—Treatment Plants Listed in USPHS
1963 Survey
Sample Total in 1963 Survey
Number of Size Range (Average Size Range (Average
Process p lantsa Production), 1000 Number of Production), 1000
Used cu rn/day (MGD) plants Cu rn/day (MGD)
Coagulation 420 <0.4 — 1408 2737 <0.4 — 1378
(<0.1 — 372) (<0.1 — 364)
Softeningb 321 <0.4 — 715 1029 <0.4 — 613
(<0.1 — 189) (<0.1 — 162)
Iron and Manganese 225 <0.4 — 257 1597 <0.4 — 231
(<0.1 — 68) (<0.1 — 61)
a) Number of plants using the process listed; some plants use more
than one of the processes.
b) Includes all types of softening processes .
C) Includes all types of iron-removal processes.
-------
DRAFT
The verified data were analyzed first by assuming that the
water—treatment processes or combination of processes used
within a plant would significantly affect the quality, quan-
tity, and treatability of the wastewaters discharged from the
plant, and then by grouping together all plants employing
a given process or combination of processes. Thirty-six
tentative subcategories were established based on the use of
processes or combinations of processes, and all plants using
each process or combination were grouped together. The mean
raw and treated waste loads and the standard deviations of the
wasteloads for plants grouped in each tentative subcategory
were first determined. At this stage of the analysis the
standard deviations indicated such a broad distribution of
wasteloads within each tentative subcategory that significant
differences between waste loads in the subcategories could be
discerned in very few cases.
Further statistical analyses were performed to explore the
effects on wasteloads of factors such as plant size, raw
water quality (primarily hardness, pH, and turbidity), and
the amounts and type of chemicals or other additives used to
treat the water. In these analyses two statistical techniques
were used: the determination of the “best—fit” lines for the
data, which turned out to be a log-normal distribution, fol-
lowed by the application of statistical “F” and “T” tests,
modified appropriately for log-normally distributed data; and
the application of multiple-linear regression analyses. With
these statistical tools and with consideration of differences
in treatability and quality of wastes from different pro-
cesses, the 36 tentative subcategories were reduced to three
subcategories. The multiple linear regressions showed that
plant size and raw-water hardness had significant effects on
the waste loads from plants within each of the three subcate-
gories. An equation which was developed from the regressions
provided for differences in allowances in waste loads, plant
size, and raw water hardness. This equation and the waste—
load allowances which are reached are presented in Section Ix.
The three subcategories are:
Category I - Plants that use only coagulation, oxidative
iron and manganese removal, direct filtration, or dia-
tomaceous—earth filtration. Only one of the above
solids-removal processes is used. Plants with combina-
tions of two or more solids—removal processes are
included in other categories.
39
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DRAFT
Category II — Plants that use the lime or lime-soda
softening processes.
Category III - Plants that use combinations of coagu-
lation and chemical softening, or oxidative iron-and-
manganese removal and chemical softening.
The wastes from the zeolite softening process or from zeolite
iron-removal processes were not included in this categoriza-
tion plan because there is no adequately demonstrated control
and treatment process that could be used in 1977. There is a
reclamation process that has been demonstrated on a small
plant scale and that will be useable by 1983. The wastes from
zeo].ite processes will be considered individually. Similarly,
because of the lack of adequately demonstrated control and
treatment, the wastes from dissolved—solids removal processes,
and from defluoridation processes, were not placed into
categories, but will be judged individually.
40
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DRAFT
SECTION V
WASTE CHARACTERIZATION
The processes used in the water—supply industry are designed
to remove materials that are undesirable for the intended use
of the product water. The undesirable materials include sus-
pended solids, colloids, ions that cause hardness, substances
that cause color or odor or both, iron compounds, managanese
compounds, ions, such as fluoride or heavy metals that can
have detrimental effects on many of the biota, and toxic
chemicals present in the source water. Normally the inacti-
vation or removal of bacteria and other disease producing
organisms is common to all plants.
A. Characteristics of Waste Waters
The undesirable materials present in wastes from water—treat-
ment plants depend on the type of process used. Most waste-
producing water—treatment plants use one or more of the fol-
lowing processes: softening, iron and manganese removal, and
coagulation followed by flocculation and sedimentation. Vir-
tually all plants use some type of filtration. The wastes
from each of these processes differ and are described below.
1. Sludges from Processes that Use Coagulation
Coagulant sludges may contain sand or silt, dissolved or col-
loidal organic material, microscopic organisms, and materials
such as aluminum hydroxides or polyelectrolytes that stem from
the chemicals used. The sludge has a very low solids content
ranging downward from 2%, and is gelatinous in nature and
light tan to black in color depending on the constituents in
the source water and the type of coagulants used. Because
they are gelatinous, coagulant sludges are difficult to dewa—
ter. With conventional lagoons, typical solids contents of
dewatered coagulant sludges range from 10% to 15% which are
not high enough to handle conveniently as a solid when clean-
ing lagoons. Solids contents of at least 20% are desired for
convenience in handling. Lagoons in which freeze—thaw cycles
occur produce dewatered sludges of slightly higher solids
contents (about 17% to 18%), but these sludges are still dif-
ficult to handle. Vacuum filters operating in a precoat mode
have produced cakes with solids contents in the range of 20%
to 30%, when treating coagulant sludges. However, the weight
41
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DRAFT
of the precoat material often equals the weight of dry solids
in the sludge. Sand drying beds have also produced dewatered
sludges with solids contents greater than 20% from coagulant
sludges. The volume of sludge produced by a coagulation—
flocculation plant is usually in the range of 1% to 5% of the
water treated.
2. Sludges from Plants that Use Chemical Softening
Calcium carbonate is the main constituent in the sludges from
chemical softening operations. Generally, 80% to 95% of the
weight of solids in the softening sludges is calcium carbonate.
Other materials that may be present include hydrated oxides of
magnesium, iron, and aluminum, silt, and organic matter.
Softening sludges are usually easier to dewater than coagulant
sludges, but the ease of dewatering varies widely from plant
to plant. Factors that affect the treatability of the sludge
include the ratio of calcium to magnesium, and the amount of
gelatinous solids present. Gelatinous solids may stem from
colloids, iron and manganese, or other materials. The solids
content of settled softening sludges can vary from 2% to 30%.
The volume of softening sludges is usually in the range of
0.3% to about 5% of the volume of water treated.
3. Sludges from Iron and Manganese Removal Processes
The sludges from iron and manganese removal processes are
highly colored and often gelatinous. These sludges are
retained by the filters, and constitute a part of filter back-
wash water in plants that remove iron and manganese. The
nature of filter backwash waters is discussed in the next
section.
If the ratio of iron and manganese to silt or other easily
filtered matter is high (as it is in some groundwaters), the
sludges from iron—and—manganese—removal processes are usually
gelatinous. Such gelatinous sludges may be almost as diffi-
cult to dewater as sludges from coagulation plants.
4. Filter Backwash Water
Filter backwash water may contain particles of silt and clay,
hydrated oxides of iron, manganese and aluminum, activated
carbon, and suspended organic materials. Typical solids con-
tents range up to 1500 mg/i. The volume of washwater ranges
42
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DRAFT
from 1.5% to 5% of the water treated, but this can be deceptive
unless the washwater is equalized. If filter backwash is not
equalized, the instantaneous flows may be high enough to scour
solids from the bottoms of lagoons, or cause serious upsets in
the operation of other solids-separation devices. The solids in
filter washwater normally can be easily settled unless gela-
tirious iron and manganese precipitates predominate, as men-
tioned above. Lagoons are sometimes used to allow settling
of filter backwash water. The lagoon supernatant is often
recycled to the plant intake or discharged to a sanitary
sewer.
Other waste—producing processes used in the water supply
industry include zeolite softening, which produces brines con-
taining the chlorides of sodium, calcium, and magnesium, and
fluoridation processes, which produce brines containing
sodium and calcium fluorides.
B. Basis for Characterizing Wastes
With the analyses normally used for wastewaters, the consti-
tuents in wastewaters from the water—supply industry are
reported as pH, total solids, total dissolved solids, color,
turbidity (as an indicator of suspended solids) , hardness,
and alkalinity. Other constituents reported in wastewaters
from some water—treatment plants include iron, manganese, cal-
cium, magnesium, sulphate, chlorides, phosphate, and silica.
For the wastewaters from the water—supply industry to be ade-
quately characterized, certain information must be available
from a statistically meaningful number of individual water-
treatment plants in each of the categories and subcategories.
The types of information needed and the number of verified
data sheets obtained were discussed in Section IV in the
discussion of categorization.
It is desirable to characterize both the raw wastes and
treated wastes. Information about raw wastes is desirable be-
cause even in solids—separation units where sludge is continu-
ously discharged (e. ., settling basins with continuous discharge)
some of the solids may accumulate. In solids-separation units
with intermittent sludge discharge, most of the solids settle
and are only discharged periodically during basin cleaning.
Data on the volumes and compositions of treated wastes were
reported on the data sheets from some of the plants for which
we obtained verified data, but acceptable data on the annual
or monthly averages of pollutant loads in raw wastes were
43
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DRAFT
almost non-existent. Therefore, raw-waste loads were com-
puted by a mass-balance method, since all materials that enter
the plant in either the raw water or as additives must leave
in the product water and the effluents from solids—separation
units or they must be accumulated in the solids-separation
units. In the mass—balance procedure, any changes resulting
from chemical reactions (e.a., hydrolysis of alum to aluminum
hydroxide) were accountedf or.
The mean raw waste loads of TSS for each of the three subcate-
gories are given in Table V-l.
Table V-i
Mean Raw Waste Loads for the Subcategories
Mean Raw Waste Load
kq/l000 cu m
Subcategory
(lb/MG)
I
32.
2
(268)
II
21.
7
(181)
III
54.
1
(451)
Wasteloads were expressed as kilograms of pollutant per thousand
cubic meters of product water (pounds per million gallons). The
use of concentrations of pollutants to express waste loads was
avoided for two reasons: (a) low concentrations of pollutants
can be achieved even with large quantities of pollutants being
discharged by using large quantities of waste water, and
(b) some mechanical dewatering devices now in service generate
wastewaters with relatively high concentrations of TSS in the
wastewaters (50 to 100 mg/l), but the volume of wastewater is
so low that the kilograms of pollutant per cubic meter is con-
siderably less than that achieved with lagoons, which can be
considered the standard solids—separation device in the water
Supply industry.
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SECTION VI
SELECTION OF POLLUTANT PARAMETERS
A. Definition of Pollutants
Section 502 of the Federal Pollution Control Act Amendments of
1972 defines the term ollution as “. . . the man-induced
alteration of the chemical, physical, biological, and radio-
logical integrity of the water.” The term pollutant is
defined as “industrial, municipal, and agricultural waste
discharged into water.”
For purposes of this report ollutants are defined as chemical,
physical, biological, or radiological constituents of dis-
charged water that are present in measurable concentrations
by routine analytical procedures acceptable to the EPA, and
that have the potential for being detrimental to the
environment.
B. Basis for Selection of Pollutant Parameters
The selection of pollutant parameters was based on cons ider-
ation of Environmental Protection Agency permits for discharge
of wastewaters from a number of water—treatment plants, on
discussions with personnel of state agencies with responsi-
bility for environmental control, on discussions with person-
nel of regional EPA offices, on consideration of information
published by the AWWA, on discussions of the discharge of
wastewaters by members of the AWWA, and on information about
wastewaters found in our survey of the literature.
Suspended solids, pH, iron, manganese, fluoride, and total
dissolved solids are considered pollutants for various sub-
categories according to the definition used for this report.
The rationales for selection or rejection of constituents
in wastewaters are discussed below.
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C. Rationale for Selection of Pollutants
1. Suspended Solids
In the water-supply industry suspended solids in wastewaters
stein from the separation of insoluble matter from product
water, one of the main functions of a water—treatment plant.
The insoluble matter is suspended in the liquid phase of
wastewaters as sludge. The total suspended solids (TSS) in
sludges from water-treatment plants may include both inorganic
and organic matter. The former may include sand and silt,
clay, and insoluble hydrated metal oxides, and the latter may
include flocculated colloids and compounds that contribute to
color, as well as algae and other microorganisms.
Solids in suspension are esthetically displeasing. Because
suspended solids increase the turbidity of the water, the
penetration of light into the water is reduced, and the photo-
synthetic activity of aquatic vegetation can be impaired.
Suspended solids can settle out of a stream to form deposits
that can be detrimental. These deposits can destroy fauna
that breed and grow in or near the bottoms of streams and
serve as food for fish and other aquatic life. The deposits
can also blanket and destroy spawning grounds for fish.
As pointed out later in Section VII, sludges can be treated
by several devices to separate solids from the liquid phase
to produce a supernatant with low concentrations of TSS that
is suitable for discharge. In addition, it has been shown
that recycling of the supernatants from such solids—separation
devices to mix with the raw-water feed can be accomplished at
low cost without adverse effects. In this way a closed-cycle
with no discharge of water—borne wastes can be attained.
For all of the above reasons TSS is selected as a pollutant
parameter for all subcategories. However, extensive studies
made at plants along one highly turbid river have shown that re-
turning the raw waste sludge to the highly turbid source in-
creases the turbidity of the stream by an insignificant incre-
ment. In some instances the incremental increase in turbidity
is less than the precision of many turbidimeters used for rou-
tine monitoring. These studies have also shown that the benef it-
cost ratio for dewatering the sludge and hauling it to landfills
is very low, and that the amount of energy used in treating and
hauling is high. Because of these factors the disposal of sludge
from plants that must use highly turbid water as feeds (>200 JTU
on an annual average basis) should be judged on an individual
basis.
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The hydrogen-ion concentration in an aqueous solution is
represented by pH, which is defined as the negative logarithm
of the hydrogen—ion concentration in a solution. On the pH
scale ranging from zero to fourteen, a value of seven represents
neutral conditions in which the concentrations of hydrogen
and hydroxyl ions are equal. Values of pH less than seven
represent acidic conditions; values greater than seven repre-
sent basic condition.
In the water-supply industry, pH is easily measured and is a
direct indicator of potential detriment to the environment.
Wastewaters with pH values markedly different from the pH
values of the receiving stream are potentially detrimental to
the environment because, at outfalls and prior to complete
mixing of wastewaters with receiving waters, there can be a
zone in which there is a sudden change of pH, and a sudden
change of pH can damage or kill the biota that is engulfed in
the change. Therefore, pH is selected as a pollutant parameter.
From the study of the constituents in wastewaters from the 782
plants for which we have verified data, only the categories
that utilize chemical-softening processes discharge waste-
waters with values of pH that might be detrimental. Because
of the nature of chemical-softening processes, the product
water and the liquid phase of the wastewaters have essentially
the sante pH. Figure VI-l shows the distribution of maximum
reported pH values of product water from 215 water treatment
plants that reported pH values.
If the pH range recommended by EPA for other industries (i.e.,
6.0 to 9.0) were recommended for the categories that use chem-
ical-softening proceses, even the product water from many plants
would have values of pH outside that range. Therefore, for
categories that use chemical softening, a slightly expanded
range of pH is recommended in Sections IX, X, and XI. For
other categories, the usual pH range of 6.0 to 9.0 is
recommended.
3. Iron and Manganese
Iron and manganese are removed from raw feed water by many
plants because of the objectionable tastes they impart to
water, and the discolorations and other difficulties that the
presence of iron and manganese causes from many uses of water.
Iron and manganese are removed by chemical softening and zeo—
lite processes, and by a process that employs oxidation of the
soluble lower—valence forms of iron and manganese to the
47
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2
5
0.I6% 0.31 %
20.53%
DRAFT
0
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5
pH
Figure VI-l.
Distribution of Product Water for 215
Water Supplies
0.
z
I-
0
a.
I J
C l )
I-
z
4
0.
-J
-j
4
U-
0
I-
z
LU
U
LU
a.
11.0
48
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DRAFT
insoluble higher-valence forms. In this oxidative process,
precipitates containing the two elements are filtered from the
water, and the filter backwash contains the precipitated iron
and manganese compounds.
For all categories except those that utilize zeolite pro-
cesses, the iron and manganese that are removed from the raw
water exist in the waters as insoluble hydrated oxides; but
in categories utilizing zeolite processes, iron and manganese
can exist in soluble forms. Therefore, for categories using
zeolite processes, iron and manganese are selected as
pollutants.
4. Total Dissolved Solids
The USPHS 1962 Drinking Water Standards set forth a recom-
mended limit of 50 mg/i of TDS. However, many communities
use water containing much higher concentrations of TDS (up to
4,000 mg/i). Such waters are not desirable for several rea-
sons, but often they are used as the least objectionable
alternatives.
For most categories of water—treatment plants, local water
quality requirements and available water supplies will dictate
whether TDS will be considered a pollutant. However, mass
balances based on data from our survey show that the dissolved
solids concentrations are so high in regeneration brines from
zeolite—softening or zeolite—iron—removal processes (up to
35,000 mg/i) that TDS should be considered a pollutant
parameter for this category.
For the effluent guidelines limitations to be promulgated in
1977, TDS will not be considered a pollutant because an accept-
able control and treatment technology has not been demon-
strated. However, for the 1983 limitations, TDS is designated
a pollutant parameter, since processes for reclaiming zeoiite
brines have been developed on a pilot-plant scale.
5. Fluoride
In our survey of 782 water—treatment plants, 246 plants
reported data on fluoride. For soluble consituents, such as
fluoride, the composition of the liquid phase of wastes will
be essentially the same as the composition of the product
water. The mean concentration of fluoride in the product
water from the 246 plants that reported data on fluoride was
49
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0.66 mg/i. The maximum concentration reported was 3 mg/i;
the minimum concentration was <0.01 mg/i. Depending on the
temperature of the water, fluoride in concentrations higher
than 1.4 to 2.4 mg/i tends to cause mottled tooth enamel,
especially in children, but a number of communities use water
that contains 3 mg/i, or more, because the alternative sup-
plies are even less desirable. Fluoride in concentrations
higher than 10 mg/i are potentially detrimental because they
can cause nausea, vomiting, and even death if enough of the
water is ingested. Since the liquid phase of wastewater is
essentially the same composition as product water, for all
subcategories of plants except those that use zeolite pro-
cesses the data indicate the maximum concentration of fluo-
ride in the wastewaters from those categories will not exceed
3 mg/i. Therefore, fluoride is not considered a pollutant
parameter for those subcategories. For the subcategories
that do use zeolite processes, the fluoride concentrations in
the regenerant brines can reach detrimental levels, and it is
therefore considered a pollutant parameter for those categories.
D. Rationale for Rejection of Constituents
as Pollutant Parameters
Other constituents in wastewaters from water—treatment plants
that were considered during the selection of pollutant para-
meters include: Biochemical oxygen demand (BOD), chemical
oxygen demand (COD), sulfate, chloride, and toxic heavy
metals. The parameters of temperature and Freon extractibles
(oil and grease) were rejected because none of the processes
used in the treatment of water results in temperature changes,
or is a source a oil and grease.
1. Oxygen Demand Parameters (BOD and COD )
Biochemical oxygen demand (BOD) refers to the amount of oxygen
needed to stabilize biodegradable matter under aerobic condi-
tions. BOD is measured by a test in which a seed culture of
microorganisms is added to the sample of water to be evalu-
ated, and allowed to metabolize the biodegradable material in
the sample over a period of five days. The seeded sample is
held under specified standard conditions during the 5-day
test. The result of the 5-day test is referred to as BOD5.
Chemical oxygen demand (COD) provides a measure of the equi-
valent oxygen required to oxidize the materials in a waste—
water sample under specified stringent conditions that include
50
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the use of a strong oxidant and a catalyst under acid condi—
tions. The test procedure requires about three hours and is
therefore more rapid than the BOD5 test. However, the results
of the test give no direct evidence of the potentially detri-
mental effects to a watercourse because both refractory (re-
sistant to biological action) and non—refractory materials
are oxidized in the test for COD. In contrast, the BOD5 test
does give direct evidence of potentially detrimental effects
despite the disadvantages sometimes mentioned in connection
with the BOD5 (e.a., the time required, the sensitivity to
toxic materials, and the need for acclimatization of the seed
culture in some instances).
The main source of BOD and COD in wastewaters from water—treat-
ment plants is algae that grows in filters, sedimentation
ponds, and lagoons. Wastewaters from water-treatment plants
almost always have low values of BOD5 (30 to 300 mg/i), but
the COD can range higher (30 to 5,000 mg/i). Activated car-
bon and cell bodies of microorganisms are relatively refrac-
tive to the BOD5 test, but are oxidized in the COD test.
Even at the higher levels of SOD that are measured by the
BOD5 test in wastes from water-treatment plants, the potential
for detrimental effects will be small if reasonable limita-
tions are established for suspended solids as given in Sections
IX, X and XI. High levels of COD in wastes have not proved
to be detrimental in themselves. Therefore, neither BOD nor
COD was selected as a pollutant parameter.
2. Toxic Heavy Metals
Many heavy metals can be detrimental or toxic to aquatic biota,
if they are present as dissolved species in concentrations
exceeding certain limits, which differ for each metal. The
1962 U. S. Public Health Service Drinking Water Standards list
the following mandatory limits for the concentrations of cer-
tain metals in drinking water: arsenic, 0.05 mg/i; cadmium,
0.01 mg/i; hexavalent chromium, 0.05 mg/i; lead, 0.05 mg/i;
mercury, 0.002 mg/i; and silver, 0.05 mg/i. The same Standards
list these recommended limits: copper, 1.0 mg/i; iron (dis-
solved), 0.03 mg/i; manganese (dissolved), 0.05 mg/i; and
zinc, 5.0 mg/i.
In the publication of the U. S. Geological Survey (U. S.
Department of the Interior) entitled “Public Water Supplies
of the 100 Largest Cities in the United States, 1962” only
the concentrations of dissolved iron and manganese exceed
51
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the above limits, and then only for a few cities that have no
better alternative sources of water. The survey of the drink-
ing water in 702 localities published by the EPA entitled
“Chemical Analysis of Interstate Carrier Water Supply Systems,
October 1973” showed 2 of the 702 waters analyzed exceeded the
mandatory limits of chromium, 1 out of the 702 exceeded the
limit on lead, and 6 of 702 exceeded the limit on mercury.
In our survey of 782 plants only 112 plants reported on the
concentrations of one or more heavy metals in their product
water. The reported maximum, minimum, and mean concentrations
of cadmium, copper, nickel, lead, zinc, and mercury are given
in Table VI-l below.
TABLE VI-1
Toxic Heavy Metals Concentrations Reported
Metal
Cadmium
0.01
0.01
—0—
<0.01
21
Copper
1 • 0 b
0.23
—0—
0.03
90
Nickel
—
0.1
—0—
0.01
21
Lead
0.05
0.05
—0—
0.02
43
Zinc
50 b
0.67
—0—
0.03
44
Mercury
0.002
not
reported
0.001
1
a) USPHS mandatory maximum
b) USPHS recommended maximum
For the categories that do not use zeolite processes, the con-
centrations of heavy metals in the liquid phase of the wastes
are essentially the same as the concentrations of the product
water. Therefore, based on the data obtained in our survey,
none of the plants that reported on heavy metals had concen-
trations of the metals that exceeded the USPHS Drinking
Water Standards.
The combined data from the three surveys indicate that the
concentrations of dissolved heavy metals in the product water
do not exceed the USPHS mandatory limits except in a few
instances. Since the liquid wastes from water—treatment plants
have essentially the same composition as the product waters,
the concentrations of heavy metals are low enough in most
wastes that across-the-board limitations are not warranted.
Restrictions on heavy metals may be needed in some instances to
meet water quality requirements, but these cases can be judged
locally.
DWS
standardsa
mg/i
Concentration, mg/i
max. mm . mean
Number of plants
reporting the
constituent
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3. Sulfate and Chloride
Sulfate and chloride anions are found in almost all wastes
from water—treatment plants. For all subcategories except
those that utilize zeolite processes or dissolved-solids
removal processes, these two anions will be present in the
liquid phase of wastes at the same concentrations as those in
the product water. The USPHS Drinking Water Standards do not
list mandatory limits on these two anions, but do list recom-
mended limits (250 mg/i for each). The reason for the recom-
mended limits is that both in excess impart an unpleasant
taste to water, and sulfate is a laxative. However, some
communities use water supplies with high concentrations of
sulfate, or chloride, or both (up to 990 mg/i) because there
are no better alternatives.
For categories that utilize zeolite processes, the concen-
trations of sulfate and chloride can reach very high levels
in the brines. However, both sulfate and chloride are consti-
tuents in total dissolved solids, and monitoring TDS is more
convenient than monitoring sulfate and chloride. Since TDS is
an indirect indicator of sulfate and chloride, sulfate and
chloride were not selected as pollutant parameters.
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SECTION VII
CONTROL AND TREATMENT TECHNOLOGY
Current technology for the control and treatment of water
plant waste consists primarily of solids separation and dis-
posal. These have been accomplished in a number of ways,
including: lagooning, thickening, mechanical dewatering,
discharging to the sanitary sewer, drying in beds, and dis-
posing on land. Treatment of wastes from dissolved-solids
removal processes consists typically of deep well injection,
ocean disposal, disposal to sanitary sewer, or dilution of
the brine wastes. Recovery of water—treatment chemicals is
practiced at a number of water plants. Lime recovery is
practiced at eight water-treatment plants at present. Alum
recovery is planned for a large water plant now under con-
struction and is currently practiced at water plants in Japan,
Scotland, and France. The recovery and recycle of magnesium
compounds have been studied in full scale at two water—treat-
ment plants, one of which is under design to include these
processes. Brine recovery from ion exchange softening has
been practiced on a demonstration scale. The production of
magnesium compounds is planned at a large softening plant in
the near future.
The large volumes of filter backwash wastes, amounting to 2
to 5% of plant production, generally necessitate separation
of these wastes for treatment. Forty—six plants have been
identified that recycle the backwash wastewater to the plant
influent. While most plants recycle directly, some plants
clarify this waste prior to recycling and pump the sludge
to the waste treatment system.
Except for filter backwash recycling, most of the currently
used technology is of the end-of-plant category, relying on
lagoons. For those plants choosing landfills to dispose of
lagoon sludge, the landfill operations are generally poor.
In many cases, private hauling contractors are responsible for
selection of the disposal site, where, in many cases, no means
of compacting or covering the sludge are provided.
A. In-Plant Technology
The wastes from water—treatment plants consist primarily of
undesired suspended and dissolved constituents found in the
raw water. Little can therefore be done to reduce these
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wastes by source control. Good water conservation results in
an increase in waste concentrations, particularly in the f ii—
ter backwash recycle. The methods discussed below reduce or
change chemical additive requirements and subsequently affect
wastes produced.
1. Plant operation
The proficiency of water plant operators is often measured by
the quality of the finished product and the quantity of chem-
icals applied for treatment. Well trained operators who are
guided by the results of adequate laboratory tests can often
reduce chemical requirements without degrading finished water
quality. Since larger plants are usually more adequately
staffed and equipped they tend to use fewer pounds of chemical
additives per million gallons of water treated, when compared
with smaller plants having similar raw water.
2. Plant design
Coagulant requirements can be affected by the plant design and
greatly reduced, for example, by minor plant alterations, such
as properly baffled mixing chambers and settling basins, or by
the use of high-energy flocculation.
3. Organic polymers
In many cases, organic polymers have been used to replace
part or all of the inorganic coagulants. Their use not only
substantially reduces the amounts of waste solids generated,
but also produces a sludge that is more readily dewaterable.
When raw waters have very low turbidity clays are occasionally
added with the polymers, and their addition offsets the advan-
tages otherwise attainable. Polymers are generally effective
at low concentrations, they are biodegradable, and they are
relatively insensitive to coagulation pH. The use of polymers
has been restricted to applications where cost savings can be
demonstrated when compared to inorganic coagulants. The deter-
mination of cost effectiveness does not generally include
Waste—treatment alternatives.
4. Filter backwash recycling
As discussed in Section V, filter backwash wastes are extremely
voluminous but low in solids concentration. Visits have been
55
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made to twenty—nine plants practicing filter—backwash recycle.
These plants treated raw waters of widely varying quality
with a variety of treatment processes and no technical prob—
lems were experienced when the filter backwash was recycled.
In most cases, the costs of filter backwash recycling cannot
be justified from water savings alone; however, in arid
regions net savings may be possible.
Backwash recycle facilities usually include an equalization
basin to maintain the recycle feed rates below 5% of the
plant raw water flow. In some instances, filter backwash
water is clarified and only the supernatant is recycled, while
the sludge underf low is pumped to the sludge-treatment system.
Where recycle is accomplished without clarification, facilities
for the mechanical removal of sludge are not required. The
equalization basin is designed to achieve natural scouring
of the solids to prevent accumulation.
Recycle of filter backwash water has little effect on the net
waste—solids production from a water treatment plant. Some
plants treating very low turbidity raw water report some bene-
ficial effects, which might lower coagulant requirements
slightly. Other plants report slight increases in coagulant
requirements due to recycle.
Some concern has been expressed about possible probl ins of
taste and odor in the finished water when filter backwash is
recycled. With the notable exception of one new plant on the
West Coast, no problems with taste and odor have been reported
at the plants visited. Some plants that were visited do have
taste and odor problems in the raw water at times. Water
rights may decrease the acceptability of recycle of filter
backwash water in certain geographical areas.
These in-plant modifications or suggestions are qualitative
in nature. As mentioned earlier, most of the wastes result
from raw water contaminants; thus in—plant modifications have
only limited effects. The effects appear to be greatest when
relatively clear, raw water is treated with inorganic coagulants.
5. Chemical, recovery
There has been increased emphasis in recent years on chc mical
recovery as a means of reducing waste production and ch mi cal
costs. The nature of ch mjcal recovery and the processes
utilized are discussed below.
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a. Alum recovery
Although no alum recovery plants now operate in this country,
a large water—treatment plant incorporating alum recovery is
presently under construction. Water plants in Scotland,
France, and Japan are successfully utilizing alum recovery.
The technology involved in alum recovery is comprised of the
following steps:
1) The alum sludge is thickened to greater than 2%
solids.
2) Sulfuric acid is utilized to recover aluminum values
at a pH of approximately 2.0. A contact time of 20 to
30 minutes is usually required.
3) Acidification improves dewatering properties of
the sludge and the separation of dissolved aluminum
sulfate is accomplished by thickening, pressure fil-
tration, or both.
4) Alum is recycled to the raw water at a controlled
rate, and the dewatered sludge is neutralized with
lime and disposed of as landfill.
The primary problem area in alum recovery appears to be the
dissolution of heavy metals, color—causing materials, and
other components of sludge at the low pH. The pilot and lab-
oratory studies in this country have been conducted primarily
with good quality raw water, although full scale pilot studies
were conducted for one year at Tampa, Florida, where a highly
colored water was treated. Problems were experienced with
color build up in the recovered alum at this plant.
A recently developed alum recovery process utilizes inciner-
ation to destroy organics prior to the acidification step.
In this process the alum sludge is thickened, dewatered,
incinerated, acidified for alum recovery, separated from the
sludge, and reused. This process has been used at a pulp and
paper mill recovering alum used for color removal.
Alum recovery reduces waste solids, particularly in the treat—
ment of waters of relatively low turbidity, also increases
the fi].trability of the residual sludge.
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b. Lime recovery
For many years, softening plants have been faced with sludge
disposal problems due to the large quantities of sludge gen-
erated. Theoretically, 3.57 kg (7.86 ib) of calcium carbo-
nate is produced for each kilogram (2.2 ib) of lime fed in
removal of calcium alkalinity hardness. If all of the cal-
cium carbonate were calcined to calcium oxide as:
CaCO3 CaO + C02
two kilograms (4.4 ib) of lime would be available for each
kilogram (2.2 lb) fed. Conunercial quicklime usually contains
only 85% to 95% calcium oxide, and as lime also reacts with
some of the magnesium, C02, etc. present in the raw water,
the amount of sludge prodi ced is generally assumed to be
about 2.5 kg (5.5 lb) dry basis, for each kilogram (2.2 ib)
added. This amount would allow recovery of about 1.3 times
the amount of lime fed. Thus, lime recovery would not only
allow for a great reduction in waste solids, but also pro-
vide some recovery of costs from the sale of excess lime. In
addition, the carbon dioxide released on calcination would be
available for use in finished water stabilization.
Eight water plants in the United States are now recovering
lime. Three primary recovery processes are used: the rotary
kiln, the multiple hearth furnace, and the fluidized bed cal-
ciner. Typically 2.0 to 2.8 million kg cal (8 to 11 million
Btu) are required for calcination. The exact heat requirement
depends on the moisture content of the sludge and on the
efficiency of operation. All lime—recovery plants now in
operation treat waters of low turbidity. The primary contam-
inant is magnesium hydroxide.
In the calcination processes it is desirable to remove magne-
sium hydroxide before calcination. Magnesium hydroxide, in
sludges not separated prior to calcination, will be converted
to a hard—burned magnesium oxide, which does not slake readily
and tends to build up as an impurity in the lime. Carbona-
tion, i.e., dissolving magnesium hydroxide by treatment of
the sludge with the carbon dioxide-containing exhaust gases,
converts the insoluble magnesium hydroxide to soluble
magnesium bicarbonate as:
Mg(OH)2 + 2 C02 - Mg(HCO3)2 (soluble)
The solubility of magnesium ions increases with an
increase in the partial pressure of carbon dioxide. Approx—
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imately sixty minutes contact time is required for 90% con-
version to magnesium carbonate depending on mixing conditions
and gas flow rate. Two plants employ the carbonation process
and one of these was visited during this study. A more
sophisticated system to improve separation efficiency at the
plant visited has been designed.
Following carbonation, thickening is provided for separation
of the clear magnesium bicarbonate solution and concentration
of the calcium carbonate. Dewatering of the thickened sludge
can be accomplished by either vacuum filtration or centrifu-
gation. Washing of the filter or centrifuge cake increases
the removal of magnesium carbonate by rinsing away the satur-
ated interstitial solution.
Another means of separating the magnesium values is by thick-
ening without carbonation and use of centrifugation to sepa-
rate the denser calcium carbonate from the magnesium hydroxide.
Typically 30% of the total sludge solids must be wasted in
the centrate in order to separate 50% of the total magnesium
values from the sludge. Lagoons are often provided for the
centrate solids. Thus, the centrifugation is only moderately
efficient in the separation of magnesium values and produces
a sizeable waste in the centrate. Centrifugation will be
discussed specifically in a later section.
Separation of the silt fraction from the calcium carbonate
has been attempted, prior to calcination, with a hydrocyclone
and a centrifuge and after calcination with air classifica-
tion; but these techniques have been only moderately success-
ful. Froth flotation for separation of silt has been inves-
tigated on laboratory scale and has shown promising results.
A pilot scale study is now underway for further evaluation of
this process for calcium carbonate beneficiation.
Many of the large softening plants in this country utilize
surface water containing considerable amounts of suspended
solids. An acceptable separation technique for contaminants
would allow lime recovery at many of these plants.
1. Fluid bed calcining
Figure Vu-i is a simplified flow diagram of a fluid bed cal-
ciner. The dewatered cake from centrifugation is discharged
to a pug mill (a mixing device) which combines the moist cake
with previously dried calcium carbonate dust. The resulting
material, about 80% solids, is delivered to a cage mill where
59
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Vent Fan
FtGURE Vu-I Recovery of Lime for Reuse—Fluid Bed Process.
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DRAFT
the particles are dried by the hot calciner exhaust gases,
beaten into a fine powdery dust, and transported by the gas
stream to a cyclone. In the cyclone the solids are separated
from the hot gases which continue on to the vent fan. The
dried particles are either conveyed to a storage bin or
added to the raw water thus beginning the cycle again.
The calciner reactor is constructed in two sections. The
upper section is the furnace area in which the solids are
heated while suspended in a vertical air stream called the
“fluidizing air”. The lower portion holds the newly formed
lime, and permits it to cool prior to removal from the
reactor. The lower section serves to preheat the fluidizing
air.
The particle size of the lime produced is controlled primar-
ily by the feed of soda ash and the amount of dried sludge
recycled. The combination of extremely fine particle sizes
and the fluid bed allows calcination temperatures generally
in the range of 760-870°C (1400-1600°F) which is considerably
below the ranges of the two other calcination processes
discussed.
The lime produced is spherical in shape, typically 0.32 cm
(1/8 in) in diameter, and practically dust free. A new fluid
bed calciner is being planned at one city. Preliminary plans
indicate that a 90.7 metric ton/day (100 ton/day) calciner,
including sludge thickener, holding tanks, and centrifuge,
will be constructed on a 27.4 m x 42e7 m (90 ft x 140 ft)
plot of ground.
This process allows considerable flexibility in operating,
and it can be easily placed in an attractive, compact build-
ing. At one installation only three men are needed to oper-
ate the calciner for a 16-hour day, including all routine
maintenance.
ii. Rotary-kiln process
A flow diagram of a typical rotary-kiln calcining plant is
shown in Figure VII-2. The lime sludge is first dewatered
by centrifugation, and the sludge is then fed to the kiln as
a slurry of toothpaste consistency consisting of 65% solids.
A chain section in the kiln transfers heat from the kiln gas
to the cake. The kiln shell has a refractory lining, rotates
at approximately 1 rpm, and is inclined to a slope of 4.2
cm/rn (1/2 in/ft) to facilitate the travel of the sludge
toward the firing end. Retention time in the kiln is usually
61
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Secondary
Scrubber
Water
Bucket
Elevator
Air
Pnmary Air
Fan
FIGURE VIl-2 Recovery of Lime for Reuse—Rotary Kiln Processes.
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DRAFT
1-1/2 hours. The sludge is nodulized and converted into
quicklime in the calcining zone then discharges into an
integral tube cooler. The cooler tubes are mounted in the
periphery of the kiln shell and contain flights to move the
product uphill and discharge it into a screw conveyor. The
lime is then transferred to storage by bucket elevator.
Air is supplied to the gas or oil burner for flame control.
cooling air enters the tube coolers through the product dis-
charge ports. The temperature within the kiln at the calcin-
ing zone is maintained at approximately 1100°C (about 2000°F),
and the temperature of the kiln exhuast gas at the feed end
housing is about 200°C (about 400°F). A scrubber removes
traces of dust before releasing the exhaust gas to the
atmosphere.
iii. Multiple-hearth furnace
The multiple-hearth furnace is composed of a series of verti-
cally stacked hearths as shown in Figure VII—3. Dewatered
calcium carbonate is added to the top hearth where it begins
to dry completely. Variable speed rabble arms move the
material in a circular motion until it falls to the next
hearth. Usually, the top two or three hearths are not fired
but are provided to dry the material before it reaches the
calcining hearths. The discharge between hearths is alter-
nately on the periphery and in the center and provides a
spiralling effect. The angle of the rabble teeth determines
the direction of the product movement.
Each hearth can be temperature programmed. Typically, the
calcining zone is maintained at 980—1010°C (1800-1850°F) with
the bottom two to three hearths not fired but provided for
product cooling and pre-heating of the draft air.
Operational variables include feed rates, rabble rate, tem-
perature, air volume, and dust recycle. A dry cyclone is
normally provided with recycle of the collected material to
lower hearths.
Primary advantages and disadvantages
Rotary kiln
Advantages - Operationally simple. Can be coal fired, rela-
tively low power requirements, present water
63
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FIGURE VIl-3 Cross section of a typical multiple hearth incinerator.
FLUE GASES
RABBLE ARM
AT EACH HEARTH
COOLING AIR FAN
64
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DRAFT
plant applications are successful, small
down time reported, pelletized produced
Disadvantages — Large land area required, large tonnages
are required for economics, 24-hour oper-
ation required, generally unattractive
aesthetically.
Fluid bed
Advantages — Small land requirements, intermittent oper-
ation feasible, lower fuel requirements due
to lower calcining temperatures, product
almost dust free, no moving parts in
calciner, can be attractively housed.
Disadvantages — High power costs, more operationally soph-
isticated, can have high soda ash require-
ments, presently requires fuel oil or
natural gas. Extremely noisy due to fans,
compressors, etc.
Multiple hearth furnace
Advantages — Small land requirements, intermittent oper-
ation feasible, operationlly simple, accu-
rate temperature profile possible.
Disadvantages — Product powdered, maximum temperature avail-
able is 1010°C (1850°F), presently requires
fuel oil or natural gas.
c. Magnesium bicarbonate recovery
A water-treatment process which has been recently developed
uses magnesium bicarbonate as the primary recyclable coagu-
lant. This coagulation process is a combination of water
softening and conventional coagulation. Sufficient lime
slurry is added to a water containing magnesium carbonate or
to which magensiuni carbonate has been added to precipitate
both calcium carbonate and magnesium hydroxide, which have
properties similar to aluminum hydroxide. Carbonation of the
sludge selectively dissolves the magnesium hydroxide as mag-
nesiurn bicarbonate, which can be recovered by thickening and
vacuum filtration for recycle and reuse. The filter cake,
composed primarily of calcium carbonate and clay, may be dis—
65
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DRAFT
posed of as landfill or the calcium fractions recovered for
calcination. A froth flotation process has been shown in
laboratory studies to be effective for separating calcium
carbonate from clay with greater than 90% purity obtainable.
A demonstration scale project is underway at present to
study this separation technique. In the application, the
filter cake composed of calcium carbonate and clay is reslur-
ned and the calcium carbonate floated off for recalcination.
The carbon dioxide produced in the recalcination is used for
both sludge carbonation and finished water stabilization.
The clay in the flotation underf low can be dewatered and
disposed of as landfill.
There are three general applications of the processes
involved:
1) The use of magnesium bicarbonate as a coagulant with
the recycle of magnesium bicarbonate and sludge dewater—
ing as an integral part of the process. This is appli-
cable to those waters relatively low in magnesium con-
tent with insufficient lime usage to consider lime
recovery.
2) Magnesium bicarbonate recycle using flotation for
calcium carbonate beneficiation prior to lime recovery.
The carbon dioxide produced in lime recovery is used for
sludge carbonation and finished water stabilization.
The impurities separated by flotation are dewatered and
disposed of as landfill. This process is applicable for
waters moderately high in hardness with sufficient lime
usage to make recalcination economically feasible.
3) Precipitation of the magnesium ions present in the
hard raw water, use of lime recovery with flotation ben—
eficiation, and recovery of magnesium bicarbonate. The
separated magnesium bicarbonate is not recycled to the
raw water, but processed to recover valuable magnesium
compounds. The saturated magnesium bicarbonate solution
is warmed to 45°C (113°F), air is used to strip out car-
bon dioxide, and magnesium carbonate is precipitated.
Pilot studies at one city have shown that extremely pure
magnesium carbonate can be economically produced. This
process, of course, would be applicable to waters high
in magnesium content with sufficient lime usage to con-
sider lime recovery. The units required are shown in
Figure VII-4.
66
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F I kiTkkkl
STABILIZAT 0N
RAW WATER
Mg(I1C0 3 ) 3 STORAGE
RECYCLE
THICKENER
REPULP
TU H BID l1 V
FIGUREVIL-4 Lime recovery magnesium process flow diagram.
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DR.AFT
The primary emphasis of this water-treatment process is the
reduction of sludge by the recovery and reuse of the three
water—treatment chemicals used: lime, carbon dioxide, and
magnesium oxide.
A full scale lime and magnesium bicarbonate recovery system
is under design at one water-treatment plant treating a
highly colored water of low turbidity. For the application
under design there will be no waste discharge. The colored
material removed from the water will be converted to carbon
dioxide when the sludge is calcined.
Two plant scale studies have been conducted with success on
the first of the three applications discussed above. Although
separation of clay and calcium carbonate on a continuous
basis has not been demonstrated, a demonstration scale study
is now underway for the third category.
d. Brine recovery
Ion—exchange softening is used as a water—treatment process
for a number of municipal supplies. Industrial water-treat-
ment plants use this process more extensively for water
softening than municipalities.
The backwash brine wastes can be recovered by conventional
lime—soda ash softening, which precipitates the dissolved
magnesium and calcium values as an insoluble sludge. The
brine is then filtered and recycled for reuse.
Typical ion-exchange regeneration cycles allow separation of
the brine wastes into fractions to improve the economy of
this recovery process. The fractions are:
1) Rinse water low enough in salt to be discharged in
the most convenient manner without risk of damage to
the environment.
2) Brines high enough in concentration to produce risk
of damage to the environment if discharged without treat-
ment. These brines are usually mixed chlorides of cal-
cium, magnesium and sodium.
3) Final rinse water, low in hardness, but containing
sodium chloride. These may be reconstituted and reused.
68
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DRAFT
Fraction two represents the wastes that are to be treated
for recovery.
While the brine waste represents only 2% to 5% of the water
treated, chemical requirements for treatment can be more
expensive than if the raw water were treated by lime or lime-
soda softening initially. In waste regeneration brines, all
of the hardness has been converted to non-carbonate hardness,
which requires soda ash treatment. Since soda ash is consid-
erably more expensive than lime and is sometimes difficult to
obtain zeolite softening with recovery of brine wastes by pre-
cipitation may not be financially justified.
Brine recovery would appear to be technically feasible and
should be considered for existing zeolite installations. New
installations should give careful consideration to the eco-
nomics of the total treatment. Brine recovery and recycle
produce less sludge on a dry-solids basis than conventional
lime-soda softening. However, considerable quantities of
sludge must be dewatered and disposed of. Another process
change which merits attention for new installations is the
moving—bed zeolite softener or continuous—regeneration zeo—
lite softener. In this process, the exhausted zeolite is
continually replaced with regenerated zeolite to allow an
equalization of the waste—brine regeneration stream. Some
savings have been reported for continuous regeneration because
of more efficient utilization of. the exchange media.
The spiractor process has also been found to be a satisfac-
tory device for brine recovery, producing a dense, non—gela-
tinous sludge which readily dewaters. The spiractor process
is shown schematically in Figure VII—5.
B. End-of-pipe Waste Treatment Technology
The following is a discussion of various end-of—pipe techno-
logies presently used in the water supply industry.
1. eliminary Treatment Systems
a. Sludge flow equalization and storage tanks
Flow equalization and storage facilities may be required to
reduce the volume fluctuation of waste effluent streams. A
69
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SOFTENED
WATER OUTLET
FIGURE VlI-5 Cross-Sectional View of Permutt Spiractor Showing Flow.
CHEMICAL
INLETS
RAW WATER
INLET
DRAW-OFF
VALVE FOR
ENLARGED
CATALYST
70
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DRAFT
number of factors must be considered in determining whether
such facilities are needed: the waste—treatment process used,
plant physical facilities, variation in water production,
raw water quality, and operational characteristics of the
waste treatment process. Generally, water plants without
continuous sludge collection will require some means of
sludge flow equalization and storage, particularly if waste-
waters are to be discharged to the sanitary sewer system.
b. Thickening of sludges
Thickening of clarifier sludges prior to dewatering performs
two functions. It reduces the sludge volume to be treated,
and it provides a more concentrated slurry for dewatering.
An increase in solids concentration of from 1% to 3% reduces
the sludge volume to one-third, and thus reduces the size of
the system components because of the smaller volume to be
handled. Increasing the slurry solids in the feed to a
mechanical. dewatering device can greatly increase the loading
rate.
Various conditioning agents are used to increase supernatant
clarity and sludge solids concentration. Typically, organic
polymers are used in concentrations normally in the range of
0.5 to 2.0 kg per metric ton (1-4 lbs/ton) of dry solids.
The overflow is generally recycled to the plant influent;
however, in at least one case it is sold to a nearby industry
for cooling water.
Alum or iron hydroxide sludges generally can be thickened to
2 to 6% solids while lime sludges can be readily thickened
to greater than 35% solids. Typical solids loading rates
for alum sludges range from 20 to 60 sq in per dry kkg per
day (200 to 600 sq ft per dry ton per day) while softening
sludge thickeners are designed with loading rates 3 to 5
sq m/kkg/day (30 to 50 sq ft/ton/day).
For discharge to sanitary sewers thickening may not be desir-
able because of plugging of the collection system. This will
be discussed in more detail in a later section.
Gravity thickening is a low energy process that requires
little operation attention if properly designed. Attention
given to polymer feed, if applicable, and underfiow pumping
rates. Equalization is often provided by a thickener designed
for this purpose; thus in many instances a thickener will
serve both functions.
71
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DRAFT
c. pH neutralization
Some water—treatment processes may produce wastes with high
or low values of pH not within normal acceptable limits for
discharge. Coagulation of organic color can take place at a
pH as low as 5.0 while excess-lime softening often exceeds
a pH of 11.3. In excess—lime softening, a recycle of the
liquid fraction of the sludge discharge will eliminate the
need for pH adjustment as well as reduce lime dosage slightly.
This should be both technically and economically feasible at
most plants. In addition to the sludge flow, the entire
contents of the settling basin would represent a waste with
an unacceptable pH, if emptied on a periodic basis.
Special sludge treatment processes such as filter pressing
and alum recovery may produce wastes that must be neutralized
prior to discharge to a receiving water or a sanitary sewage
system. Recycle of filter press filtrate has been reported
to cause process upsets at one plant treating a low alkalinity
raw water.
A waste stream that requires neutralization may be remote
from the water-treatment plant. An automatically pH—con-
trolled acid or alkali feed system including an alarm and a
failsafe recycle system will ensure proper pH control of
waste effluent. If the pH has not been adjusted within the
acceptable range, the waste will be recirculated back to its
origin (e.g., lagoon). Retention times of 10 minutes should
provide adequate contact time for neutralization of wastes
before discharging them. Figure VII-6 illustrates a simple
system of neutralization.
2. Dewatering Systems
a. Lagoons
Lagoons are one of the oldest methods used to treat water
plant wastes. Because of their relatively low cost, lagoons
continue to be one of the most popular methods of disposal
used today.
Often, lagooning is not so much a method of disposal as it is
a method of dewatering, thickening, and temporarily storing
the wastes. However, the use of lagoons is somewhat limited
by the availability of cheap land relatively close to the
plant.
72
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Chemical
Control
Element
Analyzer
Pump
Sensrng
Electrodes
Mix Tank
Effluent
FIGURE VI1-6
Elements of pH Control System.
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DRAFT
There are basically two types of lagooning operations used in
the water industry. There is the continuous—fill or storage
type of lagoon, which is used primarily for lime softening
sludges where large areas of cheap land are available. When
completely filled, the lagoon is abandoned for a new site
with eventual reclamation of the old lagoon area.
The other type of lagoon is the fill—and-dry or decanting-
type operation, which is used for both lime softening and
metal hydroxide water-plant sludges.
Usually, two or three lagoons are necessary for alternate
filling, decanting, and drying with subsequent removal of the
“dried” sludge.
I. Operational and design factors for lagoons
Although lagoons are being used throughout the water indus—
try, very little specific design criteria are available.
Some factors which should be considered in lagoon insta].la—
tions include:
1) The location should be free from flooding with the
bottom of the lagoon above the maximum groundwater table.
2) Surrounding areas must be graded to divert surface
water from the lagoon.
3) The lagoon should have a minimum depth of 1.2 - 1.5
m (4 — 5 ft).
4) There should be at least two units to allow indepen-
dent decanting, drying, and cleaning.
5) Adjustable decanting devices should be used - sub-
merged orifice, flash boards, floating outlet, etc.
6) Cleaning should be convenient.
7) The storage capacity should provide for at least one
year’s production of sludge.
8) Easy-access roads and loading ramps. Dikes should
be of a shape and size to permit maintenance and mowing,
and for trucks, cranes or front—end loaders to work in
or around the lagoons for sludge removal. If clam shell
74
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DRAFT
or drag line is to be used for cleaning, consideration
should be given to boom length and lagoon dimensions to
allow accessability of all areas of lagoon for cleaning
using this method.
9) There should be at least eight hours retention
time.
10) Baffles or other devices should be used to prevent
short circuiting.
Lagoons are generally built solely by enclosure of a land
surface by dikes or by excavation. Drainage is usually not
maximized by underdrains, or by surfacing with sand. Sludge
is added continuously or intermittently until the lagoon is
filled; then the lagoon is abandoned or cleaned. If the
lagoon is to be cleaned, a standby lagoon is normally
required. This will allow maximum concentration of the
lagooned sludge, if excess water is removed by decanting.
The sludge is allowed to dry naturally for 6 to 12 months.
The design configuration of lagoons is extremely important
to proper operation. Lagoon dimensions and berm width should
be designed to allow access to all areas of the lagoon for
cleaning. One of the most important factors in lagoon design
is the inlet and outlet structures. The inlet should be
above the maximum sludge level with baffling to minimize
scouring and short circuiting. In addition, the outlet should
be designed to accomodate surges of backwash water and to
provide a gradual discharge, and thereby maximize the deten-
tion time and solids removal. The outlets can be a floating
type discharge, overflow weir, pumps, removable flash boards,
or submerged orifices. Of these, the multiple submerged
orifice or floating overflow types probably have the greatest
overall utility and flexibility, if retention time or sludge
storage capacity needs to be adjusted.
Some lagoons have naturally permeable bottoms and others
have been designed with underdrain systems to aid in dewater-
ing. Depending upon the character of lagoon underflow, it
may be recycled or discharged directly.
ii. Application to subcategory
(a) Category :r
Alum sludge is difficult to dewater by lagooning. However,
it will gradually consolidate sufficiently to provide a 10%
75
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DRAFT
to 15% solids content. Water removal is normally by decanta-
tion or by evaporation with some drainage. Evaporation may
provide a hard crust on the surface but the sludge below the
crust is thixotropic, capable of turning into a viscous
liquid upon agitation with near zero shear resistance under
static load. Therefore, lagooned alum sludge cannot be
easily handled nor does it make good landfill material. An
alternative method of lagooning, which works well with alum
sludge, combines freezing as part of the process in cold cli-
mates. To be successful, the sludge depth should be shallow.
Thin layers of sludge, when frozen in winter and later thawed,
will dramatically increase in drainage and settling rates,
and produce fine granules of material. It has been reported
that freeze-thaw can result in a decrease to one—sixth of the
original sludge volume, and an increase to 17.5% solids. It
should be emphasized that natural freeze—thaw is effective
only with shallow sludge because of the insulating effect of
the overlying ice and sludge.
(b) Category II & III
Compared with alum sludges, sludges from water softening
plants are more easily dewatered in lagoons. The higher
specific gravity of the particles aids consolidation. In
instances where the sludge must settle through ponded water,
a maximum consolidation of 40% by weight of dry solids can be
expected; 20% to 30% is more typical. In lagoons in which
the supernatant is allowed to flow off, an upper limit of 50%
dry solids can be obtained with lime sludge. The lagoon cap-
acity required for disposal of the sludge is dependent upon
the physical characteristics of the material and the extent
to which it is dewatered during impoundment. Where the lime
sludge has been dewatered to about 50% moisture content, the
lagoon capacity requirement has been reported as about 160
cu m/yr/l000 cu m/day/lOO mg/i (0.5 acre—ft/yr/MGD/l00 mg/i)
hardness removed.
Lagoons have been used for brine wastes from the regeneration
of ion—exchange softeners. Normally lagoons are used for
storage or as evaporation ponds. If used for evaporation,
the problem of disposing of the residual salts remains. If
the soil is porous, brine seepage from the lagoon may result
in mineralization of nearby surface streams or ground water.
The use of a lagoon for temporary storage and the subsequent
release to a water course has been carried out. However,
this method requires an adequate water course for discharging
and careful control of discharges to avoid environmental
damage to the receiving stream.
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DRAFT
iii. Plant visits
From existing reports, our literature survey, and actual
plant visits, at least 109 plants that use lagoons to treat
water plant sludge have been identified. Plant visits were
conducted at 66 of these plants, and samples were taken at
15 of these locations. Lagooned alum sludges range from 2.4%
to 30% solids with an average of 4.5% solids. Lagooned lime
softening sludges range from 20% to 60% with an average of
50% solids.
Loading rates for lagoons ranged from 0.54 to 289.3 kg/year/sq
m (0.11 to 59.2 lbs/year/sq ft). In the effluent from those
lagoons that have good design and operating features, TSS
ranged from 3 to 34 mg/i with an average of 11.0 mg/i for 11
lagoon effluents that were sampled. The data on TSS in the
lagoon effluents may not reflect extreme accuracy since many
of the samples were grab samples or short—term composite
samples.
There are very few data available from the continuous inoni—
toring of lagoon effluents. For this reason, a composite
sampler was placed at one lagoon installation, and 24—hour
composite samples were taken over one month. The lagoon
selected was treating an alum sludge. The TSS in the lagoon
effluent ranged from 5 mg/i to 23 mg/i. With a time-averaged
value of 10.3 mg/i. The average total aluminum concentration
was 0.97 mg/i with a range of from 0.33 to 1.5 mg/i as Al.
iv. Summary
The data accumulated to date on lagoon operations must be
appraised in light of the limited amount of monitoring data
available. In addition, many lagoons presently in operation
are grossly overloaded with very little, if any, attention
given to their operation. It has been demonstrated, however,
that a well designed, properly operated lagoon can produce an
effluent of good quality. This effluent is recycled to the
plant influent in a number of the plants visited with no
technical problems reported.
The major problem in many lagoons used to treat water plant
sludge is that the sludge is not sufficiently concentrated so
that it can be removed from the lagoon directly to a landfill.
Therefore, further drying is recommended for ease of handling
and disposal. This can be accomplished by transferring the
77
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DRAFT
wet sludge to a drying area where the sludge can be spread
over a larger area to improve drying. Alternatively, sand
drying beds or some type of mechanical dewatering device can
be used to further dewater the lagooned sludge. However,
when used in this manner, the lagoon serves only as a tank
for clarifying, thickening, and storing sludge, and the
economics of sludge handling in such a system should be
closely evaluated.
Advantages and Disadvantages
Advantages — Low capital costs, little maintenance
required, simple in design, low energy
requirement.
Disadvantages - Poor dewatering efficiency for alum sludge,
large land requirements, dependent upon
climatic conditions for drying, little
operational flexibility.
b. Vacuum Filtration
Vacuum filtration has been used for many years for dewater—
ing sewage sludges. Recently, vacuum filtration has
found successful application for dewatering calcium carbonate
sludges produced in water softening. Precoat vacuum filters
have been used to dewater alum and iron hydroxide sludges.
While most of the vacuum filter installations have been of
the drum or rotary type in at least one installation a hor-
izontal-belt type vacuum filter is being used.
i. Operational and design features
Figure VII-7 illustrates the basic components of a rotary
vacuum filter. The units are a vacuum pump, a filtrate pump,
a filtrate receiver, a filter drum, and a filter drive. A
number of materials have been used as filter media. Washing
of the filter cake can be included along with a number of
types of discharge devices, dependant upon filter cake char-
acteristics. A power requirement of 3.07 kw/sq m (0.382
hp/sq ft) of filter area has been reported. Operational
variables include vacuum level, drum speed (which controls
cake forming and drying time), chemical conditioning, and
depth of drum submergence.
78
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FIGURE Vu-i.
Rotary vacuum filter system.
0
SUJOGI PUMP.
TANS
VA,
PUMP
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DRAFT
The rotary vacuum precoat filter is a modification of a con-
tinuous rotary vacuum filter particularly applicable to dewa-
tering metal hydroxide sludges. This type of filter utilizes
long filtration cycles (6 to 40 hrs) while eliminating the
problem of filter cloth blinding common to continuous rotary
vacuum filters. A precoat of filter aid 5 to 10 cm (2 to 4
in) in thickness is applied to the filter by introducing a
slurry of filter aid into the filter bowl and applying vacuum
to the rotating filter drum. After the precoat is in place
and the remaining slurry displaced from the filter bowl, the
sludge is introduced into the bowl and the filter cycle is
started. The precoated drum is submerged in the sludge from
30% to 50% and is continuously rotated at speeds of one revo-
lutiori per minute or slower with continuous vacuum applied to
the cake. The liquid from the sludge is drawn through the
permeable precoat, through the septum and vacuum lines, and
into the filtrate receiver. Due to the nature of the filter
aid, the sludge solids are entrapped on the surface and in
the cake. As filtration proceeds, a precision—mounted sharp-
ened knife is advanced against the cake to shave of f the
deposited solids (and a very thin layer of precoat) to expose
a clean, permeable surface of filter aid to the sludge to be
filtered during the next submergence. The knife is continu—
ous].y advanced at a fixed (but adjustable) rate of a fraction
of a millimeter per drum revolution to within about 1 cm
(3/8 in) of the filter septum. Thus, in a single revolution
of the drum, sludge solids, are deposited, dewatered and
removed.
Sludge thickening is usually provided in both a precoat and
rotary vacuum filter application. The thickener is usually
designed to provide a thickened feed material, equalize
sludge flow, and provide sludge storage to allow flexibility
in filter operation. A precoat filter is generally operated
continuously. However, a non-precoat filter is often designed
to operate only eight hours per day, five days a week.
ii. Application to subcategory
(a) Category I
Precoat vacuum filtration has been studied on a demonstration
scale for the treatment of an alum sludge. Filtration rates
are generally reported in terms of liters per square meter
per minute (gallons per square foot per minute). Typical
rates for an alum or iron sludge are 122 - 245 1/sq rn/mm
(3 - 6 gal/sq ft/mm) which would correspond to a solids
80
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DRAFT
loading rate of 1.27 to 2.54 kg/sq rn/hr (0.26 to 0.52
lb/sq ft/hr). Excellent filtrate quality has been reported,
generally less than 10 mg/i of suspended solids. Precoat
material weight can equal or exceed the total kilograms of
dry sludge dewatered, and add to disposal cost. Filter cake
solids range from 20% to 30%, which also increases ultimate
disposal costs because of the quantity of sludge to be
disposed of.
In one study a vacuum filter was used without precoat to
dewater an alum sludge. Very low cake solids (less than 15%)
were reported. In most instances the sticky metal hydroxide
sludges have been found to “blind” the filter cloth when the
precoat mode was not used.
Precoat vacuum filters are often used in industry to dewater
metal hydroxide sludges.
Advantages and Disadvantages
Advantages — Low land requirement, low operational
requirement, particularly for precoat
filter, very high quality filtrate.
Disadvantages - High capital cost, requires 24—hour oper-
ation for precoat, precoat increases ulti-
mate disposal costs, low cake solids, high
power costs, in excess of 82 kw per metric
ton (100 hp per ton) dewatered reported.
(b) Category II & III
Vacuum filtration has found greatest application in dewater-
ing softening sludges as indicated by the fact that all but
one of the operating vacuum filters identified are for this
category. When vacuum filtration is used to dewater CaCO3
sludge, filtration rates of 196 to 293 kg/sq rn/hr (40 to 60
lbs/sq ft/hr) have been achieved with the filter cakes con-
taining as much as 80% solids. As the magnesium hydroxide
fraction of the sludge increases, the filtrate rate and solids
Content of the cake decrease. Filter feeds typically contain
25% to 35% solids.
When vacuum filtration is used to dewater a softening—coagu-
lation sludge, filtration rates in the range of 24 — 98
kg/sq rn/hr (5 - 20 lbs/sq ft/hr) have been achieved with
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the lower rates occurring with sludges containing low propor-
tions of calcium carbonate and high portions of coagulation
sludge. Cake solids in excess of 60% have been reported.
Vacuum filter installations typically operate less than 8
hours per day with no dewatered sludge storage provided. The
filters are usually designed to discharge directly into a
truck.
Filtrate quality for the above applications is in the range
of 100 to 1000 mg/i suspended solids. This is largely depen-
dent upon belt material and sludge characteristics.
iii. Summary
Advantages — Minimal land requirements, excellent cake
characteristics, minimal operator attention,
low power requirements, less than 0.82 kw/
metric ton (1 hp/ton) solids CaCO3 sludge.
Disadvantages - High capital cost, filtrate quality requires
recycle or treatment
c. Filter press
The filter press, having been first introduced iii the early
part of the century, is not a new device, but it received
relatively little attention in the water—supply industry in
this country until the 1960s. A filter press is a semi-con-
tinuous batch device for mechanically dewatering sludges. It
is made up of the following basic components, or sub—systems:
1) A frame
2) A limited number of filter plates
3) A sludge feed system
4) A pressure system
5) A power source, and
6) A control system
The frame is usually an overhead or a side—bar frame. It is
a rigid structure to insure proper alignment of filter plates
for pressing.
The filter plates are usually constructed of forged steel or
cast iron with an epoxy-resin coating, or a molded rubber
coating, however, some wooden filter plates are used. End
plates are permanently affixed to the frame, one end of which
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is stationary. The frames are circular or rectangular with
a raised outer ring. When two adjacent plates are brought
together they form chambers of fixed capacity. The surfaces
of the plates have means of holding the filter media from the
plate surface to allow formation of hydraulic flow channels
through which the filtrate may pass. The filter medium is a
fabric material and either has a caulked attachment to the
plates or is draped over the plates. The filter medium is
designed to retain solids and may or may not be pre-coated
with a hydraulically applied porous medium. The filtrate
passes into and out of the flow channels through ports located
at diagonal corners on the rectangular plates and at the tops
and bottoms of the circular plates.
The sludge is usually fed into the filter press by a pump
although air injectors have been utilized. The capacity
and control of the feed system are critical to good operation
and under some conditions may require an equalization system.
An equalization system usually is an injector type which aids
the pump in feeding the sludge to the press at the beginning
of the cycle when high feed rates are required. As the fil-
ter cycle continues, the need for the high rates of feed is
no longer required and the primary means of sludge feeding is
utilized by itself.
The primary difference between the two main filter press sys-
tems centers around their internal operating pressure. One
system operates at about 16.3 atm abs (225 lbs/sq in) and the
other system operates at a pressure of 7.8 atm abs (100
lbs/sq in).
A power source is required to produce air for the filtering
operations and also to provide power for the ancillary pieces
of equipment involved in filter pressing operations. This
power requirement varies considerably, but a minimum figure
of 33 to 66 kwh/metric ton (30 to 60 kwh/ton) of dry solids
produced is often quoted.
The filter press is operated from an electrical panel. The
degree of sophistication of control varies with different
applications. Manual, remote, semi-automatic or automatic
control of filter presses can be obtained.
i. Design and operational features
The sludge to be dewatered is usually a settled precipitate
or floc slurry. Such slurries vary in composition, ranging
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from less than 1% solids by weight to 15%. Very dilute
sludges require thickening. The thickeners most commonly
used are gravity thickeners although mechanical devices have
been used. Thickened sludge then passes to the conditioning
tanks. Sludge is conditioned primarily by chemical means,
although some physical agents have been used. The purpose of
conditioning is to alter the properties of the sludge so
water can be removed more readily.
Conditioned sludge is fed to the press at a very high rate
initially. The sludge enters the cha mbers through a central
feed system and is driven to the circumferential zone of the
chamber by the applied pressure. As the cake builds, the
feed rate slows and the pressure builds. Once a predetermined
pressure is reached, the cycle is complete and the sludge
remaining in the central feed zone is returned to the
conditioning tank.
Once the press is opened, the plates are separated one at a
tine, by mechanical means, to allow the cake to fall free.
The cake usually drops out quickly as the plates are sepa-
rated. Cakes range in weight from 14 kg (30 lbs) to more
than 91 kg (200 lb) depending upon the size of the press.
The cake may be dropped directly into a truck or to a con-
veyor system which transports it to a truck or to an incin-
erator. in one proprosed system, the fly ash from the incin-
erator is re—circulated within the system and is used as a
physical conditioning agent for the sludge.
System variations most commonly encountered are:
1) Application of a pre—coat material to the filter
media prior to feeding the conditioned sludge to the
press.
2) Baclcwashing the filter media with an acid solution
after completion of the filter cycle.
3) Internal operational pressure of 16.3 atm abs (225
lbs/sq in) (high pressure) as opposed to internal oper-
ating pressures of 7.8 atm abs (100 lbs/sq in) (low
pressure). Both pressures refer to end-of—cycle
pressures.
Generally, it can be stated that systems operating at the
higher internal pressures precoat prior to filtering to pre-
vent cloth blinding, whereas systems operating at lower
pressures do not precoat but backwash with an acid solution
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after each cycle. Figures Vu—S and VII-9 illustrate
operating features of a filter press.
ii. Operating personnel
At least one operator per shift is required per press regard-
less of size. Many of the equipment manufacturers advocate
a much smaller manning requirement. However, of the instal-
lations reviewed to date, the number of personnel per filter
is approximately five per shift. Actual requirements are
dictated by the level of skill of the personnel, the local
union regulations, the degree of automation, and the method
of handling chemicals.
Major contributors to manpower requirements are:
1) Maintenance
2) Chemical handling equipment
3) Size of operation.
iii. Building requirements
The total weight of a filter press ranges from 9 to 63.5
metric tons (10 to 70 tons), which necessitates adequate
building and structural engineering.
The minimum space requirements are approximately 7.6 m x 12.2
m x 9.1 m high (25 ft x 40 ft x 30 ft high), for a single
press with storage tanks on the outside of the buildings.
The addition of a second press would increase the minimum
building dimensions 1.5 m to 4.6 (5 to 15 ft) in the desired
direction.
iv. Chemical/physical conditioners
Chemical conditioning agents:
Metallic salts — Alum, or iron salts
Polyelectrolytes - High—molecular-weight
organic polymers
pH - Lime
Physical conditioning agents are primarily filter aids, but
physical conditioning may also include ultrasonic vibration,
heat, freezing, solvent extraction, or electrodialysis.
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FIXED END
ELECTRIC
CLOSING GEAR
TRAVELLING END
c I
OPERATING
FIGURE VII-8. Side view of a filter press.
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FILTER CLOTHS
FIGURE V 11-9. Cutaway view of a filter press.
SLUDGE
FILTRATE DRAIN HOLES
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v. Precoat materials
Some of the materials used and tested as precoat materia3.s
are:
Fly ash
Diatomaceous earth
Marble dust
Solka Floc
Peat
Ground slag
Coal dust
Clay
Cement kiln dust
Coke breeze
Talc
Perlite
vi. Application to subcategories
Presently there are only two operational systems in the coun-
try dewatering water-treatment wastes by filter pressing.
Both of these are dewatering an alum sludge. However, there
are approximately twelve additional systems under construc-
tion or in the design phase. Therefore, remarks directed
toward this technology are for a large part necessarily drawn
from:
1) pilot plant studies,
2) information drawn from application of this technology
to other industrial wastes,
3) engineering.
(a) Category I
Alum coagulation sludges are presently being successfully
dewatered by filter pressing operations at two solids handling
facilities in the southeast. One installation has no thick-
ening facilities, while the other does. Comparing the oper-
ations of the two installations over similar operating
periods shows no immediately obvious advantages of thickening.
The installation without thickeners requires a relatively
small increase in conditioning chemicals, primarily attribu-
table to the lower feed solids, operates at the same cycle
time as the other installation, and yet produces a drier cake.
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There are no iron-removal plants in this subcategory employ-
ing this technology and none is currently under design. Gen-
erally, iron-removal plants that produce a solid waste use
groundwater as a raw water source and the waste would be a
metal hydroxide sludge without silt or other large particu-
lates. Such sludges exhibit poor dewatering characteristics.
The technology has been successfully applied to a similar
waste (Fe(OH)3) in the steel industry. These wastes generally
require slightly higher lime dosages and precoat of the
filter medium.
(b) Category II
There are no installations utilizing a filter press to dewater
lime softening sludge, but a plant presently under construc-
tion should be operational in early 1975. A marked difference
between the technology as applied to this subcategory compared
to other subcategories is that there appears to be no need for
conditioning the lime sludge. When filter presses were used
in tests to dewater lime sludge without conditioning the
sludge solids in the filter cake were in the 40% to 50% range.
Limited data also indicated that the filtrate had a high sus-
pended—solids concentration.
Studies done on water-treatment plant sludges, not specifically
related to filter pressing operations, have shown that a high
magnesium content in the sludge adversely affects the settl—
ability of the solids.
(c) Category III
There are no plants in this subcategory applying this tech-
nology and currently none under design. Some preliminary
work that has been done on water—treatment plant sludges in
general suggests that filter performance will be better as
the ratio of softening sludge to coagulant sludge increases.
vii. Summary
Advantages — Long, useful life, low cake moisture, high
overload capacity, good filtrate quality,
low land requirement.
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Disadvantages — High capital cost, restrictive structural
and building requirements, moderate main-
tenance requirements, moderate energy
requirements, relatively high labor require-
ments.
viii. Effluent quality
Cake solids % (by weight) 40 —60
Filtrate suspended solids (mg/i) <100
Filtrate pH >10.5
d. Sand Drying Beds
The proven treatment of waste sludges from municipal waste-
water treatment plants by sand drying beds suggests utiliza-
tion of similar techniques in the dewatering of water—treat-
ment plant sludges. With a few notable exceptions, this tech-
nology is predominately applied in the southern and western
sectors of the United States and generally to small, rural
water—treatment plants.
i. Operational and design features
Sand drying beds are constructed similar to a sand filter but
with less sand depth. Working down from the top one would
encounter from a few centimeters to about 60 centimeters of
sand over a layer of gravel that is usually 8 cm to 30 cm
(3 in to 12 in) deep. Gradation in the size of the gravel
varies according to the designer. If size gradation is not
used, the sand and gravel layers are usually separated with a
cloth fabric, such as burlap. The beds may or may not be pro-
vided with an underdrain system. If underdrains are not pro-
vided, the bed is constructed over a permeable soil. A var-
iation not in use in this country, but reported in operation
in England, is the wedgewire bottom. This drying bed floods
the under chamber during the early days after application to
retard draining. This slow draining period is reported to
increase the ultimate cake solids concentration.
The mechanisms involved in this dewatering process are:
1) Draining
2) Decanting
3) Drying.
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Most of the moisture is removed from the sludge by draining,
however, this mechanism alone is not sufficient to produce a
handleable cake. Drying is essentially accomplished through
evaporation.
The use of drying beds is affected by many factors, which can
be broadly grouped into the following:
1) Sludge characteristics
2) Climatic conditions
3) Depth of application of the sludge
4) Composition of the drying beds
ii. Sludge characteristics
Initial moisture content and nature of the sludge are the
most important determining factors for design of drying beds.
Initial moisture content is the percent solids by weight in
the sludge at time of application. The nature of the sludge
is characterized by its amorphous quality, compressibility,
and resistance to filtration (specific resistance).
iii. Climatic conditions
The effectiveness of air drying is most closely associated
with evaporation rate, but is also determined by precipita-
tion, sunshine, air temperature, relative humidity, and wind.
iv. Depth of application
The depth of application is the depth of sludge at the end of
the period of the initial rapid dewatering (decanting or
draining or both). Generally, less than two hours is required
for this initial dewatering.
The principal problems encountered in sand drying operations
have been:
1) penetration of the sludge into the sand, thus plug-
ging the bed, and
2) insufficient drying to produce a handleable cake.
Both conditions can be alleviated somewhat by conditioning
the sludge.
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v. Application of technology to subcategory
(a) Category I
Sludge drying beds similar to those described in preced-
ing paragraphs have been used successfully to dewater alum
sludges. At present there are several drying beds being
designed, and constructed. The design criteria used and the
surface area required vary, dependent on the previously men-
tioned conditions, and especially tIAe depth of application.
One investigation has shown that the drying time increases at
applications greater than about 0.3 m (1 ft) by a factor of
three, when the depth is doubled and factors of six and nine
when the depths are trebled and quadrupled. In some success-
ful drying operations the sludge has been applied at depths
up to 0.6 m (2 ft). For one proposed drying operation, it
is suggested that the sludge be applied from sprayers to
depths of less than 2.5 cm (1 in). The pitfalls of using
loadings expressed in kg/sq m (lb/sq ft) without consider-
ing drying cycle time are recorded in the history of suc-
cessful operations.
The use of conditioning agents has been shown to enhance dewa—
tering. The use of polymers at a large plant in the northeast
is claimed to be “the prime factor” in successfully dewater-
ing their sludge. In plants where Large amounts of powdered
activated carbon are used, the need for conditioning is
reduced or eliminated because the carbon acts as a physical
conditioning agent.
Air drying is often utilized in conjunction with bed drying.
In these instances, the sludge cake is removed from the beds
just as soon as it is handleable (at about 20% solids and
spread on soil for further drying)
The range of loadings at successful drying bed installations
are from 0.5 to 12.2 kg/day/sq m (0.1 to 2.5 lbs/day/sq ft).
Little is reported in the literature concerning disposal of
iron hydroxide sludges on drying beds. There are two cases
where this technology is utilized for a sludge that is pre-
dominantly iron hydroxide. A similar waste is generated by
metal plating operations and these sludges have been suc-
cessfully dewatered on drying beds.
One water—treatment plant under construction has been designed
to provide a two-cell slow—sand filter for dewatering sludge.
The proposed loading rate is 400 1/day/sq in (10 gal/day/sq ft).
Based on existing installations and information gained from
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other industrial designs, considerations for iron sludges
should closely parallel those for alum sludges.
(b). Category II
Sand bed drying of sludge has not seen extensive application
in subcategory II. Calcium carbonate sludges are so much
easier to dewater than metal hydroxide sludges that drying
beds are usually not needed. The importance of application
depth is lessened and for lime sludges the depth of applica-
tion is not as important as for wastes from plants in Cate-
gory I. Lime softening plants, therefore, decrease their
surface area requirements by increasing the depth of appli-
cation. Thus, a drying bed becomes a lagoon in essence.
There is only one known installation using drying beds for a
lime softening sludge.
(c) Category III
The comments made for Category II apply also to Category III.
As tI e CaCO3 percentage in the mixed sludge increases, the
sludge becomes easier to dewater.
vi. Summary
(a) Advantages of drying beds
Low labor requirements (routine)
Low maintenance requirements (routine)
Low power requirements
Low capital expenditure
Unlimited useful life
Mechanically independent
No skilled operators needed
(b) Disadvantages of drying beds
High land—area requirements
High labor requirements periodically
Subject to climatic perturbations
Low overload capacities
May require extensive and costly pretreatment (condi-
tioning, thickening, etc)
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(c) Effluent quality
Cake solids % (by weight) 20 to 60
Filtrate suspended solids (mg/i) 200 - 600
e. Disposal to sanitary sewer
The disposal of water-treatment plant wastes into sanitary
sewer systems has been practiced at a number of cities for
some time. The effect of this discharge on the performance
of the waste treatment plant is largely a function of the
type of sludge, the method of discharge, the waste treatment
process, the waste treatment physical facilities (particularly
sludge digestion and dewatering), as well as the adequacy
of the collection system. In the past, water plant wastes
have generally been discharged to the sanitary sewer at little
or no cost to the water utility. However, recent Environmental
Protection Agency regulations require that waste treatment
utilities which receive grants adopt equitable “user” charges
for all industrial discharges. These charges are generally
based on hydraulic flow, pounds of BOD, and pounds of sus-
pended solids. The user charge is developed so that the total
annual cost for treatment is prorated for each of these con-
stituents in order that an industrial discharger pays an
equitable share of the treatment cost. In a number of cities
contract negotiations are in progress to reflect these new
costs for accepting water plant wastes.
i. Application to subcategories
(a) Category I
Alum sludges have been shown to have some beneficial effects
on sewage treatment. Increased removal of solids, BOD, COD,
and phosphorous have been found in primary sedimentation after
alum sludges have been admitted to the control waste—treatment
system. Alum sludges amounting to as much as 50% of the total
solids inflow to a waste-treatment plant have reportedly
caused no severe difficulty, but some increase in fuel require-
ments for sludge incineration has been reported due to an
increase in the inert fraction and water content. An
Environmental Protection Agency—sponsored demonstration pro-
ject is now underway in California to monitor the effects of
alum sludges on an activated sludge treatment plant.
The results of a recently completed study made in Tampa,
Florida, indicated that the maximum dosage of water plant
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sludge in the inflow to the activated sludge plant should not
exceed 40 mg/i. Greater dosages caused problems attributable
to reduced sludge densities.
At one plant that was visited alum sludge was discharged at a
rate of 90.7 metric tons (100 tons) in a 24—hour period to a
946,250 cu rn/day (250 MGD) sewage treatment plant. Continu-
ous sludge collection at the water plant was not provided,
thus the basins were cleaned at six month intervals. It was
reported that no severe problems were experienced at the sew-
age treatment plant as a result of this practice.
A number of iron-removal water plants discharge their waste to
a sanitary system. The effects are similar to the discharge
of alum sludges. As these sludges are essentially metal
hydroxides with less inert material than most alum sludges,
they might be expected to have a more detrimental effect on
dewatering than alum sludges, but .no detrimental effects were
noted.
At one city, a sewer ordinance limited the acceptable iron
concentration thus requiring the water-treatment plant to
change from ferric sulfate to alum as a primary coagulant.
It is possible that some ordinances limit the amount of alum-
inum acceptable for discharge to sanitary sewers.
Discharge to a sanitary system provides a means for region—
alization of sludge treatment and, possibly, a means of lower-
ing the cost of dewatering because of the economies associated
with larger sized plants. This is particularly important for
small water—treatment plants at which costs of waste treatment
could be excessive. It could also have the effect of diminish-
ing monitoring and reporting requirements by the water utility.
(b) Category II & III
Sludges from softening plants have caused problems in plugging
of the sewer system, overloading of digestors, and damaging
primary sludge collection mechanisms because of excessive
torque needed to collect sludge. These problems have been
encountered primarily because of the rapid settling character-
istics and the large quantities of sludge to be disposed of.
Calcium carbonate sludges thicken and dewater well, and it
would appear that discharge to the sanitary sewer would be
practical only where on-site treatment is restricted by land
requirements. The addition of calcium carbonate sludge, which
has excellent dewatering characteristics does not materially
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affect the dewatering properties of the sewage sludge. For
this reason it may be considerably more expensive to dewa-
ter the combined sludge. An exception may be when chemical-
physical waste treatment plants are utilized and the primary
clarifier may have been designed for dense sludges. Where
lime recovery is practiced, the water plant sludges will pro-
vide additional calcium values.
ii. Ion—exchange softening
The disposal of brine wastes into the sanitary sewer systems
would generally add only additional hydraulic load to the
plant. Normally, the brine wastes are discharged using an
equalization system to insure dilution and prevent “slug”
loading of the waste treatment plant. The sewage plant serves
primarily as a means of further di lution and discharge to the
receiving water. There were no systems identified that had
set a limit on dissolved solids for discharge to the sanitary
sewer. However, increased ionic strength could adversely
affect the operation of sewage treatment plants.
iii. Summary
In a number of cases the water and sewer departments are man-
aged under one authority and accurate cost accounting is not
undertaken. It would appear that a reasonable cost for solids
dewatering at a sewage treatment plant is in excess of $55/dry
metric ton solids ($50/dry ton solids).
Advantages - No land area requirements, limited capital
expenditure required, no Federal or State
permit requirements, dewatering costs could
be lower due to economy of scale, ability to
handle wider fluctuation in water plant
solids, hauling costs for ultimate disposal
can be reduced because of economies of scale,
Federal and State monitoring requirements
would be eliminated.
Disadvantages - Waste sludge may not be compatible with the
sewage—treatment—plant process, particu-
larly where primary treatment is not
required, wastewater plants will require
additional handling facilities, and possi-..
bly additional digestor capacity, additional
fuel requirements for sludge incineration
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due to increased water content and inerts,
existing ordinances may prohibit discharge.
f . Centrifuge
Centrifuges are continuous, mechanical dewatering devices.
Centrifugal force is used to increase the sedimentation rate
of the solid materials in the sludge. The basic components
of the centrifuge dewatering operation are:
1) Housing and frame
2) Rotating bowl
3) Conveyor
4) Sludge feed system
5) Power source
The housing provides the structural integrity of the unit
and shields the high-speed moving parts. The frame provides
rigidity needed for the high speed moving parts, and a means
to firmly secure the centrifuge to an appropriate base.
The rotating bowl is spun at high revolutions to impart high
forces on the solids and speed settling. The bowl also
contains the sludge during dewatering.
The conveyor moves the settled solids along the bottom of the
bowl to the discharge point.
The sludge feed system must be able to deliver sludge solids
ranging from 3% to 30% at feed rates anywhere from 1.3 to
15.8 1/sec (20 to 250 gpm).
The power source is required to drive the motor providing
rotational motion to the bowl and the ancillary equipment.
i. Types of centrifuges
Basically the types of centrifuges can be broadly broken down
into two groupings: horizontal and vertical shaft units as
shown in Figure Vil-lO and Vu-li.
(a) Horizontal shaft units
Waste sludges are delivered to the centrifuge by a stationary
supply pipe, which passes through the conveyor hub discharg-
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ERLOAD SHEAR
DEVICE
TORQUE OVERLOAD
SWITCH
SOLIDS DISCHARGE
PORTS AND PLOWS
/
CONVEYOR
GEAR DRIVE
FIGURE vn-io Cross section of concurrent flow solid-bowl centrifuge.
-------
FEED
FIGURE VU-li Schematic diagram of a basket centrifuge.
SKIMMINGS
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ing the sludge into the bowl. The rotating bowl imparts a
centrifugal force greater than 1000 times the force of gravity,
which drives those consitutents with the greatest densities
to the circumferential zone of the centrifuge. From this zone
the solids are picked up by the conveyor, which is usually a
helical screw (scroll), and continuously moved to the discharge.
The bowl has a conical shape at the end where the solids are
discharged. This reduced diameter section enables the con-
veyor to move the solids out of the liquid pool for discharge.
The bowl is also provided with effluent weirs, which are
usually opposite the solids discharge, which pool the sludge.
Both the conveyor and the bowl rotate, but the rotation of the
conveyor is slightly slower than that of the bowl. The pool
depth (pond) is determined by the weirs. The continuous feed
forces the clarified liquid (centrate) over the weirs to the
discharge. Because centrifugation classifies particles pri-
marily by specific gravity, the separation is generally not
clear cut and the resulting centrate is usually high is sus-
pended solids.
Horizontal centrifuges were the earlier units used and are by
far the most popular. They are quite often identified as
scroll centrifuges receiving their name from the helical
screw conveyor. There are two variations among the horizontal
units, they are:
1) Countercurrent flow
2) Concurrent flow
Countercurrent flow
These units are of the type initially described where the cake
is discharged at the opposite end of the bowl (conical end)
from the centrate. This type of centrifuge has the obvious
problem of disturbing the settled solids by the opposing dir-
ection of movement between the liquid and solids.
Concurrent flow
These units are fed through the conveyor hub in a manner sim-
ilar to that just described for the countercurrent units with
the feed entering the bowl at the cylindrical end. The solids
are forced to the outside to form an annular ring, with the
solids on the periphery and the liquids near the center. The
ring is advanced towards the conical end hydraulically and by
the conveyor. The liquid moves with the solids until it
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reaches the beginning of the conical section where it encoun-
ters the effluent weirs. It passes over the weirs and is
discharged. The conveyor moves the solids up the conical
section to the discharge port.
(b) Vertical shaft units
These units are a relatively new development. They are quite
often identified as basket centrifuges. Basket centrifuges
are semi—continuous, batch devices. However, for units pro-
ducing a pwnpable cake, an option does exist to introduce a
skimmer for continuous operation. Two types of baskets exist:
1) Solid (irnperforate)
2) Porous filter (perforate)
In the operation of basket centrifuges, the sludge enters
from a stationary, directional feed pipe, which directs the
influent sludge towards the walls of the basket. The sludge
is discharged from the feed pipe at the bottom of the rotating
basket. Centrifugal force concentrates the solids on the bas-
ket wall. The top of the basket has a lip (weir) over which
the liquid is decanted. When the solids reach a specified
level, the feed sludge is stopped, and a knife rotating coun-
ter to the basket’s direction scrapes the solids from the wall
and pushes them through the open bottom of the basket.
The two types of basket centrifuges work identically except
for the passage of centrate through the basket wall in the
perforate type.
ii. Treatment technology applied tb subcategories
(a) Category I
A review of sludge disposal practices in the mid—].960’s indi-
cated there were no installations successfully dewatering alum
sludges by centrifugation. Several installations have been
built for centrifugation of alum sludges but none have proven
successful. Several recent pilot-plant studies indicate suc-
cessful operations are possible. These recent successes are
believed attributable primarily to conditioning of the sludges
With polyelectrolytes, usually introduced to the sludge within
the centrifuge.
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A large water—treatment plant on the west coast has designed
and constructed a centrifugation installation which should go
on line in early 1975. A cake containing 16% solids is anti-
cipated from the centrifuges. It will be trucked to a sani-
tary landfill for disposal. The centrate will be used to
augment low stream flows in the vicinity, when of sufficient
quality, or returned to the reclamation clarifier. Another
plant in the northeast has a similar installation under design.
(b) Category II
The application of centrifuges in this subcategory is wide-
spread. Centrifuges are used exclusively in all dewatering
of calcium carbonate sludges in municipal water—treatment
plants prior to recalcining. These applications, shown in
Table VII-l, are all solid bowl units. One installation
utilizes a basket centrifuge that is in series with a solid
bowl unit. When the solid bowl unit is overload, the over-
load is treated by the basket centrifuge.
(C) Category III
One installation in this subcategory now uses centrifugation
for dewatering sludges. This plant has four centrifuges,
which were installed primarily for the purposes of dewatering
a calcium carbonate sludge. However, the alum sedimentation
basins at the filtration plant are cleaned semi—annually and
the sludge is dewatered in the centrifuges. It should be
noted that there is an appreciable carryover of suspended
solids from the softening plant. It is believed this carry-
over assists in the dewatering. Normally, dewatering is a
two-step operation with the first pass being a very coarse cut
and yielding a low quality centrate. This initial centrate
is stored and the following day rerun with the addition of
polymers. The cake is sent to a landfill and the centrate is
either discharged to the sewage system or recycled within the
plant. The cake solids from the second cut range from 45 to
50%. At this point the centrifuge cake resembles a paste.
Watertight bulk storage and trucks are required to handle this
material. It appears that the consistency of the cake deter-
iorates somewhat as the result of the use of a ribbon screw
to convey the cake from the centrifuge discharge to the stor-
age hopper.
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Table V1I-l
Suxrunary of Identif led and Visited
Sludge Treatment Processes
No. of existing plants No. of existing plants No. of plants that
Method of Sludge use this method that use this method & have this method
Handling were visited under construction
Discharge to a 37 15 1
sanitary sewer
Recycle of filter 46 29 6
backwash water
Drying beds 21 6 1
Lagoons 109 66 9
Filter presses 2 2 4
Centrifuges 13 1 4
Vacuum filters 7 3
Belt presses 1
Chemical recovery 9*
Spray Irrigation 3
& Dust Control
Reuse
*Al1 of these are recalcining plants
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iii. Summary
Advantages - High degree of flexibility, low area require-
ments, low routine maintenance, no skilled
operators needed, low building requirements,
low initial costs for a mechanical device.
Disadvantages - Low to moderate equipment life, high power
requirements, may require extensive and
costly pre-treatment (conditioning, thick-
ening, etc.), high labor requirements
periodically, does not produce a solid cake,
low centrate quality.
iv. Effluent quality
Cake solids % (by weight) 15 - 65
Centrate suspended solids (mg/i) 500 — 300,000+
g. Miscellaneous treatment technologies
This section includes some treatment technologies that have
shown promise or have been proposed for use in the treatment
of water plant wastes. Also included are several methods
that are not treatments per se, but are disposal techniques.
i. Freezing
Freezing has often been proposed as a method for treating
coagulation sludges. It is not, in fact, a treatment but is
actually a conditioning process. Freezing can occur by nat-
ural or mechanical means. Several freezing operations of each
type are reportedly operating successfully in Europe. All of
the work done to date in this country has been pilot scale.
Several investigators have reported the effect of natural
freezing on lagooning of alum sludges. These lagoons were not
designed specifically to take advantage of natural freezing as
discussed briefly under lagoon treatment. However, a dewater-
ing installation being designed will incorporate natural freez-
ing to assist sand drying operations. Results show that the
solid fraction will naturally settle to 15 to 20% solids by
weight after freezing, and the clarified supernatant will have
less than 100 mg/i of total suspended solids.
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The principal reasons for not using mechanical freezing
have been:
1) High capital costs
2) High initial operating costs*
3) Low mechanical reliability**
ii. Land application
Land application is not a treatment technique, but rather a
disposal means. Applications discussed below will be limited
to the methods of disposal in which the sludge receives no
prior treatment.
iii. Spray irrigation
Early studies showed that the application of alum coagulation
sludges to the soil plugged the surface, prevented further
passage of water, and killed vegetation. In several cases
sludge has been sprayed from a tank—truck on vegetation beside
the road for up to one year, and no detrimental effects to the
infiltration properties of the soil or to the vegetation were
encountered. Rates of application are riot known in this case.
Alum sludge spray applications are known to be in use. One
is solely for wetting dirt roads within the water shed as a
dust—control measure. The second utilizes sprinkler heads,
which rotate delivering a rain—type mist over approximately a
0.10 hectare (0.25 acre) area. Application areas are alter-
nated and the quantity of sludge applied varies with the sea-
sons. Generally, the rate of application is 3028 liters per
sprinkler head per hour (820 gallons per sprinkler head per
hour) limited to no more than six hours during the hotter
summer months.
t A considerable energy input is required for initial cooling
cycle.
**Because of stresses attributable to the expansion of the
sludge when frozen.
1.0 s
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iv. Land reclamation
This method considers the use of the dilute sludges (usually
thickened) to improve existing land values, either for aes-
thetic or for economic reasons. Such methods include disposal
to abandoned quarries and mines. In one case, the thickened
alum sludge is being used to raise the elevation of the land.
Here low dikes are pushed up by earth—moving equipment and the
slurry is discharged behind them. The area appears to be
dusty, but the local residents do not consider it a nuisance.
In one section where it was reported that the sludge has been
dumped earlier, sufficient vegetation has sprung up to support
the grazing of livestock.
V. Sludge plowing
This method has been tested several places, but apparently
has not been carried out routinely. The sludge plow has a
large pressurized tank which is mounted over a tractor drawn
plow. The sludge is discharged directly into the furrow
turned by each plow blade. After several days there is no
visible evidence of the sludge, but erosion of the barren
soil can be a problem.
vi. Heat drying
Several investigators have suggested heating as a method of
destroying the amorphous properties of the coagulation sludges,
but they have concluded that the process is uneconomical due
to the low fuel value of the sludge. However, a system which
utilizes broad-band sonic energy combined with forced draft
heat to dry the sludge is proposed for an alum sludge pilot
study in early 1975.
vii. Specialty recovery
There have been several studies of the use of water—plant
waste in other industrial or agricultural processes. The
most widespread use to date has been to use softening sludges
for soil conditioners and stabilizers. Coagulation sludges
have been used intermittently in building bricks. They have
also been used as fillers in fertilizers. Softening wastes
have been used as paint pigments. The waste from a spiractor
unit has been used for well points to drain foundations dur-
ing construction and as beach sand. Softening sludges have
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also been used on occasions to neutralize acidic industrial
wastes. One plant in south Florida sells their softening
sludges for $1.65/metric ton ($1.50/ton) for use as a pH-sta-
bilizer for soil. Calcium carbonate sludges have also been
used as stabilizers for ponds and roads.
The establishment of a regional reclamation facility to serve
several water—treatment plants has been proposed and offers
some promise for recycling and recovery possible regardless
of plant size, especially in the case of lime softening plants.
C. Case Studies
1. Case I
Case I is a study of the use of a filter press for a coagula-
tion waste. This plant has a nominal capacity of 132,500
cu rn/day (35 MGD). Alum is used to treat a moderately turbid
river water.
Waste characteristics
The plant produces two wastes: filter backwash water and sed-
imentation basin sludge. The approximate composition of the
wastes based on information obtained from plant personnel and
laboratory analysis of samples collected on August 26 and 27,
1974 are:
Filter backwash water 100 — 600 mg/i TSS
Sedimentation basin sludge 62,000 mg/i TSS
The major contributing elements are:
clays, silts and insoluble organics 94%,
aluminum hydroxide 4%,
activated carbon and inerts in
the chemical feed 2%.
Based on the 1973 Annual Report, the plant produces 2755 metric
tons (3,037 tons) of dry solids annually.
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Waste treatment facilities
The waste treatment facilities include three holding basins
with pumping capabilities and two 1.63 m (64 in) high-pres-
sure filter presses with auxiliary equipment.
The filter backwash water is sent to a 1325 Cu m (0.35 MG)
capacity holding basin from which it is pumped back to the
head of the plant.
The sedimentation basin sludge is blowndown “on call” by the
filter press operation to a 283 cu m (0.075 MG) holding basin
which is provided with a rotating arm and air agitation.
The filter press is precoated with diatomacous earth at approx-
imately 36.5 kg/cycle (80 lbs/cycle) . The sludge is condi-
tioned with 6% to 10% by weight hydrated lime before being
fed to the press. Cycle times vary from 40 mm to about 80
mm depending on the solids concentration in the feed sludge.
The filtrate is used to wash the filter press prior to pre-
coating, and as a carrier for the precoat material. The excess
filtrate is periodically discharged to a sanitary sewer oper-
ated by the municipality. The filtrate usually has a pH range
from 11 to 12.5 with less than 100 mg/i suspended solids. The
filter cake is approximately 45 % solids and is regularly
hauled to an approved landfill. Some demand has been generated
for the cake as a yard and garden material. The cake has been
used on occasions around the plant for fill material and sup-
ports a healthy ground cover.
Cost
The entire facility cost $2,807,560 in 1969. The estimated
annual operating costs are projected below. The method of
retiring the debt is not known, therefore, a reasonable inter-
est rate and expected service life for the equipment were used.
Labor, maintenance and chemical costs were taken from the 1973
Annual Report. Power requirements were calculated as follows:
The connected horsepower for three months in 1974 were
averaged and then projected for an annual usage.
A unit cost of $0.02/kwh was then used to determine
this cost, based on the assumption that the power
requirements during 1973 were the same as those for the
three-month period that was monitored.
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Annual Cost
Debt Service (est) ($2,807,560 @ 6% for 30 yrs) $204,000
Labor and Maintenance 162,457
Power (est) CConnected hp/month x 0.745 x $0.02
x 12) 26,457
Chemicals 17,717
TOtal annual cost $r4 10,210
Unit Cost
$/1000 cu in of water produced ($/MG) $/dry metric ton ($/dry ton )
$8.48 ($32.10) $148.95 ($135.10)
Summary
This installation may be considered somewhat atypical as it
does not provide a thickener and uses air ejectors rather
than pumps to transfer the sludge from the conditioning tank
to the press. The capability of this dewatering device has
been successfully demonstrated for an alum sludge. Some of
the success may be largely attributable to the nature of the
sludge, e.a., the high solids to aluminum hydroxide ratio.
2. Case II
Case II, is a 6,056,000 cu rn/day (1600 MGD) coagulation plant
treating a very low turbidity raw water. This extremely large
water-treatment plant was constructed on fill material forming
a peninsula in Lake Michigan. Additional land for waste treat-
ment facilities would be extremely expensive (approximately
$500,000/hectare ($200,000/acre)], if not impossible to
acquire. Therefore, the sludge from the sedimentation basins
is sewered.
Waste characteristics
Three primary sources of waste are generated at this plant:
filter backwash water, clarifier sludge blowdown, and solids
from the raw water mechanical screens.
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Filter backwash
Filters are backwashed at this plant utilizing computer con-
trol. Filters operate in sets of twelve each. When one fil-
ter is indicated to need backwashing, all filters are washed
in succession automatically. This backwash cycle requires
forty minutes and produces 272,500 Cu in (72 MG) of washwater.
At present the filter backwash water is disposed of into
Lake Michigan.
Clarifier sludge blowdown
Clarifier blowdown consists of a combination of aluminum
hydroxide and suspended solids removed from the raw water.
This plant represents an unusual case in that the suspended
solids during much of the year are primarily due to algae and,
therefore, organic in nature. A suspended solids concentra-
tion of 0.7% solids is typical with a BOD and COD of 182 and
2,015 respectively. An ammonia concentration of 6 mg/i was
reported. The sludge is stored and pumped approximately every
five days to the sanitary sewer system. An average of 7570
cu m (2 MG) of waste containing 54.4 metric tons (60 tons) of
dry solids are pumped to the sanitary system each time.
Mechanical screen discharge
This material is primarily algae, sticks, small fish, etc.
and is returned to Lake Michigan with the filter backwash
water. It was reported that as much as 13.61 metric tons
(15 tons) per hour of fish have been collected from the screens.
It is impossible to characterize or quantify this waste due to
its heterogenous nature. This plant reported that future plans
may include cornmjnutors with discharge to the sanitary system.
Treatment of waste waters
Plans have been completed and bids taken, for recycling of
filter backwash water; however, the project was delayed to
secure additional Federal funding, which was not supplied.
It is estimated that it will now cost $12 million to construct
the recycle system. No firm plans exist for completion of
this project.
Local ordinances prohibit the discharge of any waste water to
Lake Michigan. For this reason six water—treatment plants,
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in addition to the plant under discussion, discharge wastes
to the regional sanitary system. All industrial dischargers
are charged pro rata waste treatment costs. These costs based
on the operation of a 3,785,000 cu rn/day (1000 MGD) secondary
sewage treatment plant are:
$57.33/dry metric ton of solids ($52.00/dry ton of solids)
$48.51/metric ton BOD5 ($44.00/ton BOD5)
$6.61/bOO cu m of flow ($25.00/MG of flow)
The capital cost of the pumping and force system to the
collection systems was $600,000. Detailed sludge analysis
reports are maintained.
Summary
Discharge to the sanitary system has proved to be an accept-
able disposal method for this large treatment plant. No
problems were reported at the sewage treatment plant although
the water plant sludge represents about 15% of the total solids
entering the sewage treatment plant.
While discharge of sludge to the sanitary sewage system has
greatly reduced the waste discharge from this plant, consid-
erable waste in the form of filter—backwash water is still
being discharged untreated.
3. Case III
Case III illustrates sand—drying operations for a coagulation
plant. This plant has a nominal capacity of 208,200 cu rn/day
(55 MGD) and uses alum and polymers to treat a moderately tur-
bid river water.
Waste characteristics
The plant produces two wastes: filter backwash water and
sedimentation basin sludge. The approximate composition of
the waste based on information obtained from plant personnel
and laboratory analyses of samples collected August 29 and
October 3, 1974 indicates that major contributing elements
are:
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clays, silts, and insoluble organics 85%,
aluminum hydroxide 12.5%,
ferric hydroxide 1.4%,
polymer 1.1%
Based on the nominal capacity of the plant and average raw
water conditions the plant produces about 1789 metric tons
(1966 tons) of dry solids annually.
Waste treatment facilities
All wastes are sent to a 30.5 meter (100 ft) diameter thick-
ener-clarifier. The overflow from the thickener—clarifier is
discharged to the raw water source. The quality of the over-
flow varies considerably depending on the waste being received.
Filter washwater quite often causes short circuiting and agi-
tation of the settled sludge thus reducing the quality of the
discharge. It was estimated by plant personnel that with nor-
mal operations there is approximately 25 to 50 ppm of suspended
solids in the discharge. Underf low from the thickener is
applied to one of three sand drying beds, providing a total
surface area of 734 sq m (7900 sq ft). The sludge applied to
the bed during observation was 12 - 13% solids and the average
depth of application was 50 cm (20 in). The cycle time
reported was twenty-one days giving an average loading of
approximately 4.4 kg/sq rn/day (0.9 lbs/sq ft/day). The f ii-
trate from the underdrain is discharged back to the raw water
source. The dried sludge is taken from the beds at 20% to
40% solids (32% for the cycle ending 10/3/74). Removal of
the dried sludge requires a backhoe and operator, a dump truck
and driver, and a laborer. Removal under normal operation
requires the use of the above personnel and equipment for
eight hours, one day a week. However, drying during the win-
ter months is less complete and an additional truck and
laborer are required. The sludge is stockpiled on site.
Cost of operation
Capital expenditures for the dewatering facilities were not
available. The costs given reflect only operating and clean-
ing costs. The costs developed are based on the following
assumptions:
• Extra labor and equipment will be required four
months per year.
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• Annual sludge production is predicted by average
chemical dosages and raw water quality.
• The cost of the cleaning in October 3, 1974 is
assumed as an average cleaning cost.
Annual Cost
Operation and Maintenance $15,000/year
Unit Costs
Cost per dry metric ton dewatered $8.38
(Cost per dry ton dewatered) ($7.60)
Cost per 1000 Cu m of water treated $0.20
(Cost per MG of water treated) ($0.75)
Summary
Presently the plant is investigating the feasibility of put-
ting a surge tank ahead of the thickener and adding more dry-
ing beds to nearly double the present capacity. This plant
is located in the southeastern United States, where the 1973
annual average temperature was 15.4°C (50.7°F), relative
humidity was 71.8%, precipitation was 181.9 cm (71.6 in), wind
velocity was 10.5 kin/hour (6.5 mph), and the sun shines 52%
of the time. A lesser application depth would probably result
in a drier cake, however, limitations on the area available
for sand-drying beds would not allow this.
4. Case IV
Case IV is a 75,700 cu rn/day (20 MGD) softening plant treat-
ing a moderately hard well water. Two primary waste streams
are produced at the plant, filter backwash and clarifier blow-
down. The plant recycles filter backwash water and utilizes
a vacuum—filter system to dewater the clarifier sludge.
Waste characteristics
Filter backwash
Approximately 87 cu rn/mm (23,000 gpm) of backwash wastes
are piped to a lagoon for settling. The supernatant is
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pumped back to the plant influent. The sludge, which is
almost pure calcium carbonate, is pumped to the sludge thick-
ener. The filter backwash waste is relatively low in sus-
pended solids, has a pH ranging from 8.0 to 9.5, and is vol-
uzninous with intermittent flow.
Clarifier underf low
Approximately 63.5 metric tons/day (70 tons/day) of dry solids
are produced consisting primarily of calcium carbonate with a
small amount of magnesium hydroxide and lime inerts. The
total solids in the blowdown ranges from 3% to 7%. The total
solids in the thickened sludge exceeds 30%. Approximately
62.5 cu rn/day (16,500 gal/day) of clarifier underflow are
produced.
Description of waste handling facilities
Two 14.9 kw, 1.5 Cu rn/mm (20 hp, 400 gpm) pumps are utilized
to pump the clarifier blowdown sludge to a 10.7 m (35 ft) dia-
meter thickener. A 3.7 kw, 0.75 cu rn/mm (5 hp, 200 gpm)
pump is used to pump the backwash-lagoon sludge to this same
thickener.
The thickened sludge, which is about 30% solids, is pumped to
two vacuum filters with a total filter area of 40.9 sq m
(440 sq ft) having 66 kw (88.5 hp) connected horsepower. The
filter cake, about 65% solids, is discharged directly to a
truck where it is disposed of to various civic groups and
Construction companies
The filter backwash water is discharged to a lagoon; the sup-
ernatnat is recycled back to the plant inlet; and the sludge
is pumped to the vacuum filter.
Cost of treatment
System Capital Cost Power Cost 0 & M*
( 1971) ( $/yr) ( $/yr )
Vacuum filter 246,000 2,163 650
Sludge thickener 210,900 1,625 6,900
Washwater recovery 169,700 1,711 500
*operating and maintenance
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Sludge disposal costs are estimated at $13,000 per year. The
total cost for dewatering and disposal of the clarifier sludge
as well as the filter backwash recycle, amounts to approxi-
mately $29.59 per metric ton ($26.84/ton) based on a thirty
year service life at 7% interest.
It should be noted that the sludge handling facilities at
this water—treatment plant were designed to handle six times
the present solids production rate.
Treatment efficiency
Filtration rates in excess of 290 kg/sq rn/hr (60 lbs/sq ft/hr)
have been achieved, while producing a filter cake of 65% to
70% solids. Presently, 3400 metric tons per year (3,750
tons/year) of dry solids are dewatered. The filtrate is pumped
to the municipal waste treatment plant, only a few hundred
feet from the filter operation.
S uinina y
Case IV is a zero discharge plant with the exception of the
filtrate from the vacuum filter, which is not recycled only as
a matter of convenience. The filter cake produced is given
to contractors as a soil stabilizer. The total annual cost
for achieving this system of near zero discharge was approx-
imately $8.19/bOO Cu m ($31/MG) of water produced.
5. Case V
The water-treatment plant for Case V is a large, 643,000 Cu
rn/day (170 MGD) nominal capacity coagulation—softening plant.
However, attention will be focused on the softening process
only. Softening is accomplished using zeolite cation-exchange
units to remove an average of 325 mg/i of hardness from approx-
imately two-thirds of the plant’s throughput. There are two
waste streams generated from the softening process, one is
discharged to the sanitary sewer and the other is routed to an
evaporation pond and the dry cake is landfilled.
Waste characteristics
The wastes from the softening plant come from two sources:
1) Brine filtration
2) Cation-exchange regeneration
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This plant produces its own brine solution. The salt is
received by railcar and dumped into a large mixing tank. From
the mixing tank, the brine is filtered through a sand filter.
The brine sand filter must be backwashed periodically. This
backwash water is the source of the first waste stream and is
sent to an evaporation pond. After evaporation of the water
fraction, the remaining cake, which consists primarily of
impurities in the salt, is removed and landfilled.
Softening is accomplished by zeolite cation-exchange units.
Regeneration of the zeolite is accomplished by passing a solu-
tion of sodium chloride (regeneration brine) through the bed
of exhausted resin. The average composition of regeneration
brine is 0.24 kg of salt per liter of water (2 lbs/gal). Sev-
eral washings with fresh water following the regeneration with
brine are required. The total. volume of wastes for regenera-
tion, washwater, and brine solution varies widely. Approxi-
mately 136.3 cu m (36,000 gallons) are required for the older
zeolite units being used and approximately 276.3 cu m (73,000
gal) are required for the new units. The softening units pro-
duce slightly more than 3.785 million cu m (1 billion gal-
lons) of liquid waste annually. The analysis of a composited
sample taken on July 31, 1974 is believed to represent the
average composition of these wastes. There were slightly
greater than 150,000 mg/i of total solids, approximately
500 mg/l of suspended solids, 62,000 mg/i of chlorides and the
solution had a conductivity of 96,000 mhos/cm.
Waste treatment facilities
The brine filters are backwashed periodically. The backwash
water is pumped to an evaporation pond. The dried cake from
the pond is transported to a landfill. The regeneration brine
and wasliwater are discharged to a sanitary sewer which leads
to a 1,324,750 cu rn/day (350 MGD) primary waste treatment
plant. The regeneration wastes represent less than 1% of the
flow into the waste treatment plant the total effluent is
piped to an ocean discharge.
Operating costs
Through a long term contract with the sanitary authority this
plant is permitted to discharge its regeneration wastes,
within a specified upper limit, to the sanitary sewer. The
contract had no provisions for renegotiation and the existing
arrangement greatly favors the water authority. The water
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authority further agreed to pay $16,000 annually plus an addi-
tional $1 for each 3,875 cu m (1 MG) of waste discharged to
the sewer system.
Annual Cost
Debt Service ($100,000 @ 2.4%)
Annual service charge
Surcharge (@ $1/3,785 cu m (MG)]
Annual cost
Unit Cost
$4,000
$16,000
$1,000
$21,030
Cost per 1000 cu m
(Cost per MG)
Cost per 1000 Cu m of water treated
(Cost per MG of water treated)
Summary
$5.40
($20.42)
$0.87.
($0.24)
The sanitary authority feels that the contract is costing them
approximately $100,000 annually. Discharge to the sanitary
system primarily provides dilution and a means of waste
carriage to the ocean.
6. Case VI
The water-treatment plant for Case VI produces 245,000 Cu
rn/day (65 MGD) of finished water. The feed to the plant is
a surface water with high turbidity and high hardness. Coag-
ulation and softening are carried out simultaneously using
lime, soda ash, polymers and alum.
Waste characteristics
The main wastes from this plant stem from presedimentation,
from the clarifier, and from backwashing the filters.
Presedimentation
Presedimentation is provided at the raw water intake, which is
3 to 5 km (2 to 3 miles) from the treatment plant. The raw
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water is mechanically screened, chemically treated and clari-
fied. The screenings are returned with the blowdown from the
presedimentation clarifier to the raw water source. The
chemical treatment consists of chlorination, feed of potassium
permanganate when required, and low dosages of alum or polymer
during high raw water turbidity. Raw water turbidities in
excess of 3,000 mg/i, are typically reduced to 400 mg/l by
presedinientation. Under these conditions, some 635 metric
tons (700 tons) of dry solids are discharged each day back to
the river at a solids concentration of approximately 1%.
Storage is provided in the presedimentation clarifier to
equalize pumping of the partially clarified water.
Clarifier blowdown
Sludge blowdown is to one of two fill—and-dry lagoons. Super-
natant is recycled to the plant influent. The suspended solids
in the supernatant are generally less than 30 mg/i.
The characteristics of the clarifier blowdown are largely a
function of presettled water quality. The proportion of cal-
cium carbonate in the sludge ranges from 50% when the raw
water is highly turbid, to more than 80% when the raw water is
low in turbidity. The clay fraction generally ranges from
18% to 48 % with the remaining 2% consisting of aluminum
hydroxide, polymers, and carbon.
Filter backwash water
The flow of a filter backwash water is equalized in a 379 cu m
(100,000 gal) equalization basin and is then recycled to the
plant influent. These facilities were constructed at a cost
of $198,000 in 1956. Both the lagoon overflow and filter back-
wash are returned to plant influent with a common pumping sys-
tem. A 2.3 Cu rn/mm (600 gprn) pump and a 5.3 Cu rn/mm (1400
gpm) pump are provided for this purpose. With connected power
of 7.5 kw (10 hp) and 14.9 kw (20 hp) respectively.
Lagoon cleaning
The sludge, which is predominantly calcium carbonate, dewaters
readily in a lagoon to approximately 60% solids. Six-month
cycles are typical. A private contractor cleans the lagoons
and hauls the sludge to the nearest landfill approximately
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1.6 km (1 mile) away at a cost of $60,000 per year. Based on
a solids production of 40.8 metric tons/day (45 tons/day) at
a water-treatment rate of 94,625 cu rn/day (25 MGD) this would
amount to a cost of $4.02/dry metric ton ($3.65/dry ton)
ultimate disposal costs. Much longer haul distances are
anticipated in the near future.
Capital cost of the two lagoons, one constructed in 1956 and
the other in 1963 was $34,000. Little operational costs other
than cleaning are experienced. Approximately 2 hectares
(5 acres) of land are utilized for the lagoons. Additional
lagoon capacity will be required as water production increases.
Summary
With the exception of the presedimentation clarifier blowdown,
the plant for Case VI is a zero discharge plant. All filter
backwash and clarifier—sludge supernatant is recycled to the
plant inlet with no difficulty.
The sludge, which is primarily calcium carbonate, dewaters
readily in the lagoon with a modest cost for ultimate disposal.
The presedimentation system is not manned full time. A dewa—
tering system at this location would cost many times more in
both capital and operating costs than the system now in
existence.
7. Case VII
The plant for Case VII is a 151,400 cu rn/day (40 NGD) coagu-
lation-softening plant that used centrifugation to dewater
their wastes. The plant uses ferrous sulfate and lime to
treat hard water with low turbidity from an impounded source.
The finished water has moderate hardness.
Waste characteristics
There are two sources of waste coming from the plant: filter
backwash water and sedimentation—basin sludge. The composi-
tion of the waste based on information obtained from plant
personnel and lab analyses of samples collected on August 20,
1974 is:
119
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DRAFT
CaCO3 95%,
clayl, silts, and insoluble organics 4%,
Fe(OH)2, Mg(OH)2 and activated carbon (when added) 1%.
Based on a nominal production of 151,400 cu m/day (40 MGD) of
water the plant generates approximately 37.9 metric tons (41.7
tons) of solid waste. Part of the settled sludge is recycled
to the head of the plant. Some of the solids produced in the
sedimentation basin are carried over onto the filters and dis-
charged from the plant with the filter backwash water. On a
typical day, approximately 3,400 cu m (0.9 MG) are used in
washing filters, carrying with it about 1067 kg (2,350 lb) of
solids. The washwater is discharged to the raw water source.
Waste treatment facilities
The sludge is collected in the sedimentation basins and deliv-
ered continuously by several 1.12 kw (1.5 hp) pumps to a
sludge holding tank. The holding tank is agitated with air to
keep solids in suspension. Air for agitation is provided by
an air compressor driven by 18.6 kw (25 hp) motor. The sludge
is transferred from the holding tank to each of the two cen-
trifuges at rates varying from 0.3 to 0.6 cu m/min (75 to 150
gpm) at solids concentrations from 5% to 15%. The centrate is
discharged to the sanitary sewer. The solids concentration in
the centrate range from less than 1% to nearly 5%. The cake
(of paste consistency) ranges in solids from 50% to 60% and it
is delivered by a 3.7 kw (5 hp) motor driven pump to a hopper
building for temporary storage prior to trucking.
The cake (paste) is trucked approximately 19 km (12 miles) to
a privately owned landfill for ultimate disposal where no
charge for dumping is levied.
The centrifuges were not purchased at the same time, therefore,
two capital costs and different interest rates were used in
the calculations of costs. One centrifuge was purchased in
1973. The centrifuges are not housed in a building, therefore,
no expenses of this type are included. Some assumptions were
made in the economic analysis. They were: (a) the salvage
value for the equipment at the end of its useful life is zero,
(b) the land required for the installation is valued at $20,000
(No true figure could be obtained as the land was already
owned by the water company), and (c) the costs for ultimate
disposal are not included.
120
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DRAFT
Annual Cost
Capital recovery ($60,000 @ 6%)
Capital recovery ($80,000 @ 8%)
Operation
Maintenance
Annual cost
Unit Cost
$4,700
7,500
17, 310
4,000
$33, 510
Cost per 1000 cu m of water produced
(Cost per MG of water produced)
Cost per metric dry ton dewatered
(Cost per dry ton dewatered)
8. Case VIII
$0.61
($2. 30)
$2.42
($2.20)
Case Viii illustrates the operation of a direct filtration
plant that treats 227,100 Cu rn/day (60 MGD). The raw water
is from an impounded source, and is of high quality. This
plant utilizes sand drying beds to dewater its wastes after
reclaiming a large percentage of the liquid fraction. The
water—treatment plant feeds alum, polymers, and when needed,
activated carbon.
Waste characteristics
A mass balance was used to determine the waste produced.
Average chemical additions and an average raw water quality
was assujned for the mass balance. Information concerning
backwash volumes and frequency of backwashing was used to
determine the theoretical solids concentration in the waste.
This calculated figure checked closely with the analysis of a
composite sample collected at the plant on August 2,1974.
Therefore, it was estimated that a representative composition
of the wastes would be;
Al (OH) 3
organic polymer
activated carbon
turbidity in the raw water
50% to 75%,
7% to 12%,
35%,
4% to 12%.
Approximately 600 metric tons (660 tons) of dry solids are
separated by the filters each year, all of which must be
removed in backwashing. An additional 13.6 metric tons (15
121
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DRAFT
tons) of solids are added annually to the backwash water by
chemicals used in washwater reclamation. It is estimated that
there is a total of 2,537,000 cu m (675 MG) of waste produced
annually.
Waste treatment facilities
The backwash water flows to a 3,785 cu m (1 MG) basin from
which it is pumped to a 45,420 cu rn/day (12 MGD) upf low clar-
ifier where alum and polymers are added as coagulants. The
clarified water flows by gravity back to the head of the
plant. The excess sludge is pumped to one of five 18.3 in x
30.5 in (60 ft x 100 ft) sand drying beds. The filtrate from
the drying bed underdrains flows to the head of the water-
treatment plant. The sludge is pumped to the beds and
repeatedly applied as it is drawn from the clarifier. The
switching from one bed to another is determined primarily by
visual observations. When the cake is removed, the dried
depth of the sludge is approximately 30 cm (1 ft). All beds
are cleaned annually.
122
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DRAFT
SECTION VIII
COST, ENERGY, AND NON-WATER QUALITY ASPECTS
A. Costs of Alternative Control and Treatment
TechnoI gies
Three types of financial data are included in this document.
The first, in Section VII, reports specific costs in case
studies so that the sludge-treatment and disposal costs for
the selected study systems could be evaluated. Capital costs
and interest rates reported reflect the actual year of instal-
lation and are not corrected to present costs. Ainortization
of capital costs is calculated by a sinking-fund method.
The second type of financial information presented compares
sludge—treatment costs for various cities using selected treat-
ment alternatives. This data is intended to present informa-
tion of a more general nature. The capital costs are for the
year of installation. However, operations costs reflect the
most recent information available.
The third type of financial information is based on model sys-
tems. The costs for these models are intended to reflect
conditions slightly above average in construction complexity.
Cost information reported in Section VIII is divided into two
segments: treatment costs presently experienced by the water
industry, and costs predicted by treatment of mode]. systems.
The data for the former were collected from plant visits, the
literature, or personal telephone contact. The latter costs
were estimated using various assumptions, which are indicated
for each model. In this Section the costs for the implementa-
tion of the various model treatment alternatives are compared
with 1970 water cost and revenue data compiled from Operating
Data for Water Utilities 1970, AWWA. A summary of this data
is shown in Table VIII-l.
1. Existing Treatment Costs
a. Lime recoveri
As discussed in Section VII, lime recovery is practiced at
eight water plants in this country. Cost data that were col-
123
-------
¶ ab1e VIII—1
Sunmary of Water Cost Data (1970)*
Type Plant Nominal Size Average Production Cost RevenL’e
1000 cu in (M CD) 1000 cu in (MGD) $11000 ($/MGD S/1000 (S/MGD
per day per day cu am of of cu am of of
product product) product product)
coagulation 3.8 (1) 54 (1.4) 81.6 (309) 155.6 (589)
I— Coagulation 75.7 (20) 76.8 (20.3) 59.2 (224) 126.0 (477)
bJ
‘ Coagulation 189.3 (50) 196.2 (51.8) 41.7 (158) 79.2 (300)
Softening 3.8 (1) 4.7 (1.2) 140.8 (533) 214.0 (810)
Softening 75.7 (20) 75.7 (19.9) 84.0 (3181 131.6 (498)
Softening 189.3 (5Q)** 75.7 (19.9) 65.0 (246) 101.5 (384)
Coagulation & Softening 3.8 (1) 5.4 (1.4) 136.6 (517) 198.4 (751)
Coagulation & Softening 75.7 (20) 71.5 (18.9) 66.6 (252) 155.1 (587)
Coagulation & softening 189.3 (50) 184.7 (48.8) 61.6 (233) 117.3 (444)
* - Updated to December 1974 using Consumer Price Index
** — No plants of this size reporting
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DRAFT
lected during plant visits are shown in Table VIII-2. The
data on the multiple-hearth installation at the Lake Tahoe
sewage treatment plant were added for comparison purposes.
These data allow some general economic comparison between lime
recovery devices. Specific comparison is impossible due to
variations in the sizes of the facilities, dates of construc-
tion, and unit costs. While the economics of lime recovery
are not always competitive with purchased lime, consideration
of the cost of sludge disposal makes recalcination very
attractive in many cases.
b. Disposal to sanitary sewer
Fifteen plants were visited that discharge wastes to sanitary
sewer systems. In most cases no charge was made to the water
treatment plant. However, this policy is changing as a result
of increased waste treatment costs and increased regulation.
In most cases where there is a charge and where filter back-
wash water is recycled, the primary charge is based on sus-
pended solids. The cost for disposal to a sanitary sewer,
not including capital costs or operating costs, ranged from
$22.05 to $239.25 per dry metric ton ($20.00 to $217.00 per
dry ton) of solids. Table VIII-3 contains a summary of cost
information obtained from plants visited that currently dis-
charge wastes to sanitary sewers. Total disposal costs of
$82.69 to $110.25 per metric ton ($75.00 to $100.00 per ton)
may be considered normal.
c. Vacuum filtration
Five plants were visited that use vacuum filters to dewater
sludges which are predominantly calcium carbonate. A number
of reports were available from the literature or pilot or
demonstration studies of the use of pre—coat vacuum filters
for dewatering iron—hydroxide or alum sludges. As indicated
in Table VIII-4 the operating costs are considerably higher
for dewatering these sludges than for dewatering calcium car-
bonate sludges. Ultimate disposal costs can also be expected
to be higher for these sludges because of the higher moisture
contents and the additional loading of pre—coat materials.
2. Model Cost Systems
Three plant sizes were chosen for each category; 3,785 cu
rn/day (1 MGD), 75,700 Cu rn/day (20 MGD), and 189,250 Cu rn/day
125
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a) 1973 data
h) Included in operation costs
c) Included in fuel cost
d) Soda ash cost of $13.34/metric ton ($12.10/ton) of lime
e) Sewage sludge, 1969 costs
City
Miami
Dayton 8
I -I
Ann Arbor
Lansing
st.
Lake Tahoce
Table VIII—2
Lime Recalcination Plants Visited
(1974 Data Except where Noted)
Production Type Costs S/r etric ton (S/Ton !
Metric tons (Tons/day) Date cal- el Power Opera-
per day Lnsta lied cinor tion
81.63 (90) 1948 Rotary 10.47 0.97 6.14
(9.50) (0.88) (5.57)
83.44 (92) 1960 Rotary 8.57 (c) 11.08
(7.77) (10.05)
6.98 (7.7) 1968 Fluid— 8.37 5.49 15.52
Solids (7.59) (4.98) (14.08)
14.51 (16) 1954 Flui.— 2.5.95 4.47 13.21
Solids (14.47) (4.05) (11.90)
22.68 (25) 1968 Fluid— 9.37 6.80 22.57
Solids (8.50) (6.17) (20.47)
9.98 (11) 1968 Multiple 14.55 1.43 8.03
Hearth (13.20) (1.30) (7.28)
ain
tenanco
2.00
(1.81)
(b)
2.35
(2. 13)
3.90
(3.54)
6.54
(5.93)
4.98
(4.52)
Capital
Costs $
856.000
1.500.000
1,200,000
440, 000
1,750,000
Total
19.58
(17.76)
19.65
(17.82)
31.73
(28.78)
37.54
(34.05)
45.28
(41.07)
28.70
(26.03)
-------
Table VIII—3
Disposal To Sanitary Sewer
Water Plant
Plant Size & Type Cost Basis Annual Sewage Plant Dewater Remarks
ID Cu n/day S/metric ton S/lOaD cu m S/kg BOD Cost Size & Type Device
No (MGD) of solids of waste (S/lb BOD) S Cu rn/day
(S/ton) (S/MG) (MGD)
85 113,550 68.05 52.47 150,000 30,280 Vacuum 50 of total solids
(30) (61.72) (198.00) (8) Filter due to WTP — no
Alum Seconcary problems reported
86 189.250 153.24 12,460
(50) (580.00)
Alum
87 473,125 4.49 16,794 1,324,750 Charge based on vol—
(125) (17.00) (350) ume, plant operating
Zeo li.te Pririary cost affected by
salinity
1436 1,994,695 57.33 6.61 96.92 400,000 946,250 Lagoons 15.3% of solids
(527) (52.00) (25.00) (44.00) (250) handled at STP. Advise
Alum keeping below 20%
1437 3,785,000 57.33 6.61 96.92 660.000 3,785,000 Vacuum 4.9% of dry solids
(1000) (52.00) (25.00) (44.00) (1000) filter, at STP
Alum drying
beds
M.W.D. 757,000 22.05 27,000
of S.C., (200) (20.00)
3 en son
WTP
Detroit l93, 35 34.18 24,000 946,250 Incinerator roble s
(51) (31.00) (250) wore reported at t res.
Alum A.S. The value of sludac
dropped. Co ustio was
not self-supporting.
Basin cleanco each 6 riorths.
100 ton in 24-hour period.
-------
Table VIII-4
VacLum Filtratioi of Water Plant Sludge
Opera tir g
Size costa Opera’.ing Cake
City I D Date Type Capital sq in $/metric ton time sulic.s
No Status installed sludge cost($) (sq ft) (SJdry on) (hr/wk) per c t Rei ar .s
91 Plant 1972 CaCO 3 501000 b 13.9 6.2 15 65—20
visit (150) (5.6)
92 Plant 1974 265,242 29.3 —— —— 65—80
visit (315) Under construction
1442 Plant 1969 56 , 000 b 27.9 40 65—80
visit (300)
1444 Plant 1968 491454 b 13.9 20 65—60
visit (150)
93 Plant 1971 “ 246,700 40.9 3.2 20 65—80
visit (440) (2.9)
94 Reøort 1972 Alum 76,000 38.6 18.5 40 15 Pilot study
(416) (16.8)
95 Report 1971 Alum 61,000 13.9 189.4 168 18—22 Pilot study
(150) (172)
96 Report 1974 Iron 200,000 32.5 133.3 168 25—30 Laboratory study
hydroxide (350) (121)
97 Report 1969 Alum 331,000 111.5 123.3 168 25 Model se idy
(1200) (112)
98 Report 1969 D.E. 60,000 5.0 33.0
(54) (30)
a) Excludes capital cost
b) Equipment cost only
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DRAFT
(50 MGD). The model sludge-dewatering systems chosen were
based on engineering judgment for the plant size and cate-
gory under consideration. In some instances more than one
model was chosen for illustrative purposes.
As discussed in Section VII the selection of alternative
treatment systems is complex and, in many cases, governed by
specific plant conditions. Thus, while it would appear that
one alternative should be used exclusively from a cost stand-
point, local conditions may make this impossible. Consider-
able study is required in selecting a sludge dewatering and
disposal system for a specific plant.
In the case of industrial water treatment plants, costs pre-
sented would be applicable in only isolated cases. Solids-
removal facilities are often already present, with the solids
production from water treatment only a small percentage of
the total industrial waste solids production. Thus, in many
cases, industry may be capable of treating their water plant
sludges at lower costs than the municipal utilities can.
The alternative sludge-treatment systems generally are com-
posed of two separate operations: dewatering, and ultimate
disposal. The costs are calculated independently and suinmar—
ized for the various models.
a. Costs of pH control
A detailed cost estimate for the pH-control system described
in Section VII is given below. The costs estimates are based
on lagoon overflows for the different sized model plants. For
purposes of computing annual chemical costs, concentrated sul-
furic acid is used to reduce a hypothetical hydroxide alkalin-
ity of 70 mg/i as CaCO3.
Costs
1) pH sensor, signal converter, multi—position
controller, alarm contact and recorder $3,200
2) Neutralization (mixing) tank
(a) 3,785 cu rn/day (1 MGD) plant 1,800
(b) 75,700 cu rn/day (20 MGD) and 189,300
cu rn/day (50 MGD) plants 6,000
129
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DRAFT
Costs
3) Valves — Emergency shut—off auto control
(a) 3,785 Cu rn/day (1 MGD) plant $3,000
(b) 75,700 cu rn/day (20 MGD) and 189,300
Cu tn/day (50 MGD) plant 4,400
4) Mixing device (all applications) 1,000
5) Chemical storage
(a) 3,785 cu rn/day (1 MGD) None
(b) 75,700 cu rn/day (20 MGD) and 189,300
(50 MGD) plant 10,000
6) Chemical feed pump (all applications) 1,000
7) Emergency recycle pump
(a) 3,785 cu rn/day (1 MGD) 1,000
(b) 75,700 cu rn/day (20 MGD) 2,000
Cc) 189,300 Cu rn/day (50 MGD) 3,000
8) Piping (10% of sub—total)
9) Electrical & instrumentation (20% of sub—total)
Capital Cost
( Sub—total )
3,785 Cu rn/day 75.7 x 1000 Cu rn/day 189.3 x 1000 cu rn/day
( 1 MGD) ( 20 MGD) ( 50 MGD )
$11,100 $27,600 $26,600*
Annual Chemical Cost
$50 $2,920 $7,l60*
*For an alum recovery system it is assumed that the plant size
would be 189,300 cu rn/day (50 MGD) and lime is used for neu-
tralization, the capital cost of this system is estimated at
$24,000 and the annual lime costs would be determined by the
amount of wasting required.
130
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DRAFT
b. Ultimate disposal costs
The cost analysis for ultimate disposal is based on the haul-
ing of wet cake. Alum and iron hydroxide sludges are assumed
to have a bulk density of 1200 kg/cu m (75 lbs/cu ft). Sof t-
ening-coagulation sludges are assumed to have a density of
1800 kg/cu m (ill lb/cu ft). Two truck sizes, 3.82 Cu m
(5 cu yd) and 9.17 cu m (12 cu yd), were considered in calcu-
lating hauling costs. Models requiring hauling more than
11.74 Cu m (15 Cu yd) of waste sludge each haul period are
assumed to use the 9.17 cu m (12 cu yd) truck. In practice
this is dictated by the availability of trucks, access roads,
haul distances, etc. The following assumptions were made in
this cost analysis.
Labor (including fringes) $5.50/hour
Diesel fuel, oil & maintenance:
9.17 cu m (12 cu yd) truck $0.12/km ($0.19/mile)
3.82 cu m (5 Cu yd) truck $0.10/km ($0.16/mile)
Truck cost:
9.17 cu m (12 cu yd) truck $38,000
3.82 cu m (5 Cu yd) truck $25,000
Capital recovery:
[ 8% for 5 years assuming 643,600 km (400,000 miles)]
9.17 cu m (12 cu yd) truck $0.07/km ($0.11/mile)
3.83 cu m (5 cu yd) truck $0.04/km ($0.07/mile)
Landfill disposal charge: $1.96/cu m ($1.50/cu yd)
Costs for hauling and disposal are illustrated in Table
VIII—4a.
c. Operation
Water plants are considered to operate twenty—four hours a
day and 365 days a year. Sludge—treatment devices have been
designed with a reasonable overload factor to handle reason-
able variations in sludge production because of changes in raw
water quality and water production. Forty-eight hour filter
runs are assumed with a backwash rate of 10.2 1/sec/sq m (15
gpm/sq ft) for twelve minutes duration. Filtration rates of
1.4 1/sec/sq m (2 gpm/Sq ft) are used for sizing the filters;
131
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Table VIII—4 (a)
Hauling and Disposal Cost
$/wet Cu m ($/wet Cu yd)
Truck Size
— 3.82 Cu m
9.17 Cu m
(LZ Cu yd)
(5 Cu y )
16.09
(10)
3.61
(2.76)
5.55
(4.24)
32.18
(20)
5.26
(4.02)
9.14
(6.99)
48.27
(30)
6.84
(5.23)
12.74
(9.74)
The following is an illustration for the use of these tables. Assume:
Alum sludge:
907 metric tons (1,000 tons)/year of dry solids
30% solids content in cake to be landfilled at
a haul distance of 16.09 km (10 miles) using a
3.82 cu xn (5 cu yd) truck.
Total sludge weight
= 907
0.3
= 3023 metric tons (3333 tons)/year
Volume
Cost
= 3023 x 1000 kg/metric ton
1199 kg/cu in
= 2522 Cu in (3336 Cu yd)
= $5.55 x 2522
Annual cost
$14,000
Haul Distance
kilometers (miles)
I -I
S/dry metric ton
= $15.44 ($14.14/dry ton)
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DRAFT
two filters are used in the 1 MCD plant, eight filters in the
20 MGD plant, and twenty filters in the 50 MGD plants.
To prevent surging problems at the plant influent when filter
backwash is recycled flow—equalization tanks are provided in
all cases. The size is dependent upon several factors rela-
ted to providing the ability to wash filters during off-peak
water demand periods.
d. Economics
In developing the economics for these models a number of
assumptions are made:
Land purchase @ $24,700 per hectare ($10,000 per acre)
8% interest for capital recovery
Capital recovery period is proportional to the
expected life of the facility
Piping is calculated as 10% of the unit-price sub-
total, except for filter backwash piping,which was
estimated separately since it constitutes a large
percentage of the recovery system
Construction interest @ 8%
Power @ $0.02/kwh
Taxes & insurance @ 2% of capital cost
Labor @ $5.50/hour
e. Coagulation plants
Three plant sizes are considered for each subcategory. The
three sizes, 3,785 cu rn/day (1 MGD), 75,700 Cu rn/day (20 MGD),
and 189,250 cu rn/day (50 MGD), are presented to represent
plants in the range of 378.5 to 37,850 cu rn/day (.1 to 10
MGD), 37,850 to 113,500 cu rn/day (10 to 30 MGD), and in excess
of 113,500 Cu rn/day (30 MGD). Based on the 1963 USPHS survey,
in terms of numbers of coagulation plants, the percentage
falling into each size group were 92%, 5%, and 3%, respec-
tively. In terms of total water production the percentages
were 28%, 19%, and 53%, respectively.
133
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DRAFT
In each of these models a number of assumptions are made for
raw water quality and chemical feeds. For this subcategory
these assumptions are:
Raw Water Quality 30 mg/i turbidity
slight taste or odor
Chemical Feed 20 mg/i alum
15 mg/i hydrated lime
5 mg/i activated carbon
A constant relationship between turbidity in JTU and suspended
solids in mg/i is assumed to be 1:1.
Ten per cent of the feed lime is insoluble and inert and will
be removed with the other solid wastes.
The activated carbon (AC) is assumed to be non—reactive and
does not alter the reactions in any way. Thus, each ppm of
activated carbon fed appears in the waste.
Two wastes are assumed to be produced by the water treatment
plants in this subcategory. They are:
Filter backwash water, and
Sedimentation—basin sludge
These wastes are assumed to be produced in the following
manner and in the quantities indicated for each MG of water
treated.
Raw Water Contribution kg/bOO Cu in (lb/MG)
(Dry_Weight_Basis) ____________
Turbidity — 30 mg/i 30 (250)
Feed-Chemical Contribution
(Dry Weight Basis)
Alum — 30 mg/i 7.9 (66)
Lime — 15 mg/i (10% insoluble) 1.5 (12.5)
Activated carbon - 5 mg/i 5.0 ( 42 )
Total Wastes Produced 44.4 (370.5)
134
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DRAFT
The average backwash volume is assumed to be three percent
(3%) of the filtered water. For the small plants, 3,785 Cu
rn/day (1 NGD), it is assumed that no sludge-collection mechan-
isms are installed and sedimentation-basin sludge is removed
semi—annually. In plants in which collection devices are
provided, 75,700 cu ni/day (20 NGD) and 189,250 cu rn/day (50
MGD), 1.5% of the daily throughput of water is used for trans-
port of the solids (clarifier blow—down).
For the 3,785 cu rn/day (1 MGD) plant in which basins are
cleaned semi-annually, all of the clarified water is assumed
to be used in washing down the basin. An additional 113.6
Cu m (30,000 gal) of water are assumed to be used in washing
the basin with fire hoses. Two (2) sedimentation basins are
assumed. They provide four (4) hours retention time. Each
basin holds 317.9 Cu m (84,000 gal); thus, 836 cu m (228,000
gal) [ 2(113.6 + 317.9)] of liquid wastes are produced semi-
annually. In the larger water treatment plants, hourly blow—
down is assumed.
i. Lagoon - 3,785 cu rn/day (1MGD) plant
This model represents the most coiwnonly used method of treat-
ing wastes for small plants with reasonable land area avail-
able. As discussed in Section VII lagoonirig of alum sludge
often does not produce a material suitable for landfill and
additional air drying may be required. This model assumes
that the sludge Cleaned from the lagoon can be landfilled
directly.
Two lagoons are utilized in the model providing five years of
sludge storage in each. Filter backwash is recycled directly
to the plant influent and the costs for this system are shown
in the first column. The costs shown in the second column are
without recycle.
135
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DRAFT
Capital Cost
Land purchase
Washwater holding basin
Washwater piping
Valves & fittings
Recirculation pumping
Lagoon construction
Inlet and outlet construction
Yard piping & electrical
(20%)
Engineering & contingencies
(20%)
Construction interest
Total Capital Cost
With
Filter Backwash
Recycle
9,000
19,000
18,000
2,700
5,000
6,600
2,000
12,460
14,952
1,200
$90,912
Without
Filter Backwash
Recycle
11,000
32,000
4,800
8,500
2,000
11,660
13,992
1,100
$85,052
Annual Cost
Debt service (8% for 30 years)
Labor & maintenance (Lagoon
operations, contractural
removal)
Labor (Monitoring requirements)
2 hr/wk
Power (17 hr/day)
Taxes & insurance (2% of
Capital Cost)
Annual Dewatering Cost
Ultimate disposal cost
8,075’ 7,555
1,075 1,880
858 858
150
— 1,818 1,701
$11,976 $11,994
61.5 metric tons/year (67.6 tons/year) of sludge at 15%
solids to be hauled 16 km (10 miles) using a 9.17 cu m
(12 cu yd) truck
136
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DRAFT
Total cost
$/metric ton
$/1000 cu m of water treated ($/MG) of solids — $/ton
With filter back-
wash recycle $9.57 ($36.24) $214.43 ($194.50)
Without filter
backwash recycle $9.58 ($36.28) $214.72 ($194.76)
ii. Disposal to the sanitary sewer —
3,785 cu rn/day (1 MCD )
In some cases land availability may be a problem for even the
small water treatment plants. The best alternative for these
plants may be in disposing to the sanitary sewer. The model
assumes a one mile force main to the sanitary system.
As stated, the 3,785 cu rn/day (1 MGD) plant was assumed not
to have a continuous sludge removal in the settling basin.
The filter backwash basin was oversized to equalize the flow
from basin cleaning to the sanitary sewer.
Capital Cost
Washwater and sludge holding basin 70,000
Washwater piping 18,000
Valves & fittings (15%) 2,700
Recirculation pumping 5,000
Construction of 1.6 km (1 mile) of 10 cm
(4 in) force main and pumps to connect
with existing sewage system 38,000
Rights of way and easements 10,000
Engineering & contingencies (20%) 28,740
Construction interest 6,897
Total Capital Cost $179,337
137
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DRAFT
Annual Cost
Debt service (179,337 @8% for 30 years)
Labor & maintenance
Power
User charge for disposal to sewer*
Taxes & insurance
Total Annual Cost
Annual sludge production
Sludge transport water
Total annual wastes produced (dry
weight)
Total Cost
15,932
825
175
8,687
3,586
$28,205
60,291 kg (132,800 lb)
1741 Cu in (460,000 gal)
61.5 metric tons
(67.6 tons)
$/1000 cu m of water produced ($/MG )
$21.14
($80.01)
$/metric ton
of solids
$473.49
( $/dry ton )
($429. 49)
iii. Sand drying beds — 75,700 cu rn/day (20 MGD )
In this model 1,233.5 metric tons (1,369 tons) of solids will
be dewatered annually by the sand drying operations. It is
assumed that the water plant has sludge—collection equipment
installed. The sludge will be periodically “blowndown” to a
*] is assumed that no cost recovery charge will be levied
against the water authority since their waste flows are
seldom expected to exceed 10% of the waste—water-treatment
plant’s average flow, therefore, no charge is required.
There is a user charge based on solids and flow dnly. A
charge of $15.85/bOO cu in ($60/MG) for flow and a fixed
charge of suspended solids in excess of “normal domestic”
sewage (taken as 200 mg/i) of $O.055/kg ($0.025/lb) is
assumed. No credit is given for waste characteristics below
“normal domestic” sewage.
138
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DRAFT
thickener. A thickener is provided for sludge storage as
well as for increasing the solids concentration and reducing
the volume of sludge applied to the beds. The overflow is
assumed to be of sufficient quality to be recycled to the
plant influent.
A 20% safety and inclement weather factor has been added in
sizing the beds, which are sized for 3.9 kg/sq in /10 day dry-
ing cycle (0.8 lb/sq ft/b day drying cycle).
Capital Cost
Land
Washwater holding basin
Washwater recovery piping
Valves & fittings @ 15%
Recirculation pumping
Thickening facilities
Drying bed construction
Yard piping & electrical (20%)
Engineering & contingencies (20%)
Construction interest
45,000
70,000
90,000
13,500
15,000
220,000
556,667
202,033
202,033
73,000
Total Capital Cost
$1,487,233
Annual Cost
Debt service ($1,487,233 @8% for 30 years)
Labor & maintenance
Power
Taxes & insurance
Total Dewatering Cost
Ultimate disposal cost
132,157
16,000
1,510
38,040
$187,707
1,229 metric tons/year (1,352 tons/year) of sludge at
30% solids to be hauled 16 km (10 miles) using a 9.17
cu m (12 cu yd) truck.
Total cost
/1000 cu m of water produced ($/MG )
$7.48
($28.33)
$/metric ton
of solids
$167.76
( $/dry ton )
($152. 16)
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DRAFT
iv. Filter press — 189,250 cu rn/day (50 MGD )
Large plants are generally located in areas with limited avail-
able land. Mechanical dewatering devices will find greatest
application for these plants. For alum sludges filter press-
ing is the most widely accepted of the mechanical dewatering
systems.
For the filter press operation 15% (by weight) lime is used
for conditioning, 34.2 kg (75.2 lb) of diatomaceous earth per
100 sq in (1076 sq ft) of filter area is used for precoating.
Cyle time for the filter press is assumed to be 2.5 hours.
Thickeners are provided f or partial dewatering of the sludge.
The filtrate will be returned to the thickener and the thick-
ener overflow is assumed to be of sufficient quality to be
recycled to the plant influent. The filter presses will be
operated 8 hours a day initially and will be of sufficient
size to allow for the addition of enough plates to increase
the initial capacity by 30% without an increase in operating
time. This provides a 300% overload capacity for expansion,
water production peaks and fluctuations in raw water quality
when 24-hour operation is used. The building will provide
sufficient space to allow for installation of a second filter
press should the need arise. The climatic and aesthetic con-
ditions permit bin storage of chemicals outside the building.
Capital Cost
Land
Washwater holding basin
Washwater recovery piping
Valves & fittings (15%)
Recirculatjon pumping
Thickening facilities
Chemical storage bins
Building
Filter press & ancillary equipment
Piping (10%)
Electrical
Engineering & contingencies (20%)
Construction interest
Total Capital Cost
7,500
70,000
90,000
13,500
25,000
556,000
100,000
250,000
2,000,000
311,200
622,400
809,120
223,000
$5,077,720
140
-------
DRAFT
Annual Cost
Debt service ($5,088,820 @8% for 30 years) 491,710
Labor 62,500
Power 10,090
Chemicals 59,250
Taxes & insurance 101,554
Annual Dewatering Cost $725,104
Ultimate disposal costs
Solids production, metric
tons/year (tons/year) — 3,084 (3,400) sludge
91 (100) lime inerts
176 (194) diatornaceous earth
3,350 metric tons/year (3,684 tons/year) of sludge at
40% solids to be hauled 32 km (20 mi) using a 9.17 cu
m (12 cu yd) truck.
Annual ultimate disposal cost = $37,161
Total cost
$/metric tons
$ 11000 cu m of water produced (s/MG) of solids ( $/d y ton )
$13.00 ($49.22) $247.41 ($224.40)
f. Coagulation-softening plants
The three plant sizes evaluated, 3,785 cu rn/day (1 MGD),
75,700 cu rn/day (20 MGD), and 189,250 cu rn/day (50 MGD), rep-
resent water plants in the size range of 378.5 to 37,850 Cu
rn/day (.1 to 10 Z4GD), 37,850 to 113,550 cu rn/day (10 to 30
MGD), and greater than 113,550 cu rn/day (greater than 30 MGD).
The percentage of plants in each of the above size groups was
86%, 6.5% and 7.5% according to the 1963 USPHS Survey. The
percentages of the total water produced in each size group
were 19.5%, 14.1% and 66.4%.
The dewaterability of sludges in this subcategory depends on
the ratio of coagulant sludge to softening sludge, as was dis-
cussed in Section v i i. Hard, turbid, river water is assumed
141
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DRAFT
to be the feed to these plants. The average composition of
the raw water is assumed to be:
Turbidity (JTU) 600
Hardness removed (mg/l as CaCO3) 115
The following chemical dosages are assumed:
Lime (CaO) for the 75,700 Cu rn/day
(20 MGD) and 189,250 Cu rn/day (50 MGD) 200 mg/i
Hydrated lime (Ca(OH)2) for the 3,785
cu rn/day (1 MGD) plan 264 mg/i
Alum 7 mg/i
Ferric sulfate 3 mg/i
Activated carbon 1 mg/i
Potassium permanganate 1 mg/i
Hydrated lime (Ca(OH)2) is used for the 3,785 Cu rn/day Cl MGD)
plant. It is assumed that 1.7 parts of waste are produced for
each part of hydrated lime fed. For the 75,700 Cu rn/day (20
MGD) and 189,250 cu rn/day (50 MGD) plants, it is assumed that
quick lime (CaO) is used, and 2.25 parts of solid waste is
produced for each part of lime fed. Thus, 3,271 kg (7,205
lb) of solid waste are produced for each 3,785 cu m (1 MG) of
water treated regardless of the form of lime used. Automatic
sludge-collection devices are assumed to be used in all plants.
kg of waste/
Contribution 1000 cu rn ( lb/MG )
Turbidity — 425 mg/i 425 (3539)
Lime — 200 x 0.9 x 2.25) mg/i 405 (3372)
Lime inerts — (20 x 0.1) mg/i 20 (167)
Alum — (7 x 0.26) mg/i 1.8 (15)
Ferric sulfate 1.4 (12)
Potassium permanganate -
(1 x 0.55) mg/i 0.6 (5)
Activated carbon - 1 mg/i 1.0 ( 8 )
Total Wastes Produced 854.8 (7118)
i. Lagoon - 3,785 Cu rn/day (1 MGD)
& 75,700 cu rn/day (20 MGD )
Lagooning was assumed to be the method of dewatering the
sludges from the 3,785 Cu rn/day (1 MGD) and the 75,700 cu
142
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DRAFT
rn/day (20 MGD) plants in this subcategory. Two lagoons are
assumed to be used for each size of plant. For the 3,785 cu
rn/day (1 MGD) plant it is assumed that each lagoon can store
the wastes accumulated over 3 years. For the 75,700 cu rn/day
(20 MGD) plant, the storage capacity of each lagoon is assumed
to be sufficient for 6 months. Decanting devices will be pro-
vided to allow for drawing of f the clarified supernatant from
different levels. The quality of the supernatant is assumed
to be satisfactory for discharge to receiving waters after pH
correction. Thickening is not deemed necessary for either
lagooning operation.
Lagoon - 3,785 cu rn/day (1 MGD)
Capital Cost
Land purchase
Washwater holding basin
Washwater piping
Valves & fittings (15%)
Recirculation pumping
Inlet & outlet pumping
Lagoon construction
pH control system
Yard piping & electrical (20%)
Engineering & contingencies (20%)
Construction interest
With
Filter Back-
wash Recycle
18,500
19,000
18,000
2,700
5,000
2,000
15,565
14,300
16,153
19,384
1,700
Without
Filter Back-
wash Recycle
20,000
0
32,000
4,800
0
2,000
16,005
14,300
17,821
21,385
2,000
Total Capital Cost
$118,002
$130,311
Annual Cost
Debt Service (@8% for 30 years)
Labor & maintenance (lagoon
operations)
Labor (monitoring requirements)
3 hr/wk
Power
Chemicals
Taxes & insurance
Annual Dewatering Costs
10,482 11,575
12,280 13,290
858
130
72
_______ 2,606
$26,300 $28,531
858
280
40
2,360
143
-------
Ultimate disposal costs
1181 metric tons/year (1299 tons/year) of sludge at
50% solids has to be hauled 16 km (10 miles) using a
9.17 cu m (12 cu yd) truck.
Annual ultimate disposal cost $4,828
Total cost
$/metric ton
of solids ( $/dry ton )
Lagoon - 75,700 cu rn/day (20 MGD) plant
Capital Cost
Land purchase
Washwater holding basin
Washwater piping
Valves & fittings (15%)
Recirculation pumping
Lagoon construction
Inlet & outlet structures
pH control system
Yard piping & electrical (20%)
Engineering & contingencies (20%)
Construction interest
51,000
70,000
90,000
13,500
5,000
39,000
4,000
35,900
61,680
74,016
12,000
Total Capital Cost
$456,096
$602,360
$/1000 cu m of water produced ($/MG )
With filter backwash $22.53
Without filter backwash $24.15
($85.28)
($91.39)
$26.36
$28.25
($23.96)
($25.68)
With
Filter Backwash
- Recycle
Without
Filter Backwash
Recycle
56,000
234,000
35,100
41,500
4,000
35,900
81,300
97,560
17,000
144
-------
DRAFT
Annual Cost
Debt service (@8% for 30 years)
Labor & maintenance (lagoon
operations - contracted
removal)
Labor (monitoring require-
ments) 3 hrs/wk
Power
Chemicals
Taxes & insurance
Annual Dewatering Cost $187,719 $206,830
Ultimate disposal cost
23,620 metric tons/year (25,982 tons/year) of sludge
at 50% solids has to be hauled 16 km (10 miles) using
a 9.17 cu m (12 cu yd) truck.
Annual ultimate disposal cost = $96,579
Total cost
$/metric ton
_________________________________ of solids ( $/dry ton )
iii. Filter press — 189,250 cu rn/day (50 MGD )
As discussed previously, filter pressing is considered only
where land limitations require the use of a mechanical de-
watering device. For filter press operations of this combina-
tion sludge, a model is developed to handle 59,050 metric tons
(64,950 tons) of solid waste annually. The presses are sized
to operate 20 hours a day. A cycle time of one hour is
assumed for normal operations. The presses will be capable
of a 30% expansion by simply adding plates, thus, with addi-
tional plates a 50% overload capacity is provided. For the
purposes of this model, conditioning of the sludge and pre-
coat of the filter are assumed to be unnecessary. A holding
tank with air agitation is used to provide storage and uni-
forinity of the feed sludge. Sedimentation basins are assumed
40,539 53,539
134,000 135,000
858
280
2,920
9,122
858
130
5,256
12,047
$11000 cu m of water treated ($/MG )
With filter backwash
Without filter backwash
$10.29 ($38.94)
$10.98 ($41.56)
$12.04
$12 .90
($10.94)
($11.67)
145
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DRAFT
to have collection mechanisms installed and afford sufficient
control to provide uniform sludge density to the press.
Capital Cost
Land
Washwater holding basin
Washwater recovery piping
Valves & fittings (15%)
Recirculation pumping
Sludge holding basin
Filter press & auxiliary equipment
Building
Piping (10%)
Electrical (20%)
Engineering contingencies (20%)
Construction interest
5,000
70,000
90,000
13,500
25,000
155,000
1,900,000
250,000
250,850
501,700
652,210
156,530
Total Capital Cost
$4,069,790
Annual Cost
Debt service ($4,069,790 @ 8% for 30 years)
Labor (21 x $10,000)
Power (@ $0. 02/KWH)
Taxes & insurance
Annual Dewatering Cost
Ultimate disposal costs
401,292
210,000
44,900
79,000
$735,192
59,050 metric tons/year (64,950 tons/year) of sludge
at 40% solids has to be hauled 32 km (20 miles) using
a 9.17 cu m (12 Cu yd) truck.
Annual ultimate disposal cost =
Total cost
$439,559
$/1000 Cu in of water produced ($/MG )
$17.01
($64. 37)
$/metric ton
of solids
$19.89
( $/dry ton )
($18.09)
146
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DRAFT
g. Softening plants
In the softening category there are no plants greater than
113,550 Cu rn/day (30 MGD) indicated in the 1963 USPHS Survey.
However, several large softening plants are known to exist
now. Therefore, 3,785 cu rn/day (1 MGD), 75,700 Cu rn/day (20
MGD), and 189,250 Cu rn/day (50 MGD) size plants will be
evaluated.
Based on data in the 1963 USPHS Survey, the size range of
378.5 to 37,850 cu rn/day (0.1 to 10 MGD) represents 98.4%
of the total number of plants and 66.5% of the total water
produced. The remainder are in the 37,850 to 75,700 CU rn/day
(10 to 20 MGD) category.
A hard, clear ground water of the following average composition
is assumed:
Thrbidity (JTU) 2
Hardness removed (mg/i)
(as CaCO3) 100
The following chemical dosages are assumed:
Lime (CaO) for the 75,700 cu rn/day
(20 MGD) and 189,250 cu rn/day
(50 MGD) plants 139 mg/i
Hydrated lime (Ca(OH)2) for the
3,785 cu rn/day (1 MGDT plant 184 mg/i
Hydrated lime (Ca(OH)2) is used for the 3,785 cu rn/day (1 MGD)
plant. It is assumed that 1.9 parts of waste are produced for
each part of hydrated iime fed. For the 75,700 Cu rn/day
(20 MGD) and 189,250 cu rn/day (50 MGD) plants, quick lime (CaO)
is used, and 2.5 parts of solid waste are produced for each
part of lime fed. Thus, 1314 kg (2,894 ib) of calcium
carbonate are produced for each 3,785 Cu rn (1 MG) of water
treated regardless of the form of lime used. Automatic sludge
collection devices are assumed to be used in all plants.
i. Lagoon - 3,785 Cu rn/day (1 MGD) & 75,700 cu rn/day
( 20 MGD) plants
Lagooning has been the selected method of dewatering the sludges
from the 3,785 cu rn/day (1 MGD) and the 75,700 cu rn/day (20 MGD)
plants in the softening subcategory. Two lagoons will be con—
structed for each plant size. It is assumed that each lagoon
147
-------
DRAFT
has sufficient capacity to store the wastes produced in three
years by the 3,785 cu rn/day (1 MGD) plant recycling filter
backwash water, and the waste produced in 2 years by the
plant not recycling backwash water. For the 75,700 cu m
(20 MGD) plant each lagoon is assumed to be large enough to
store the wastes produced in 6 months regardless of washwater
disposition.
pita1 Cost
Land purchase
Washwater holding basin
Washwater piping
Valves & fittings (15%)
Recirculation pumping
Lagoon construction
Inlet & outlet structures
pH control system
Yard piping & electrical (20%)
Engineering & contingencies (20%)
Construction interest
12,200
19,000
18,000
2,700
5,000
11,030
2,000
14,300
16,846
20,215
1,700
Total Capital Cost
$122,191
$114,415
Annual Cost
Debt service (@ 8% for 30 years)
Labor & maintenance (lagoon
operations - contractual
removal)
Labor (monitoring require-
ments) 3 hr/wk
Chemicals
Power
Taxes & insurance
Annual Dewatering Cost
With Without
Filter Backwash Filter Backwash
Recycle Recycle
10,932 9,903
5,000 6,300
858
75
130
________ 2,288
$19,632 $19,554
With Without
Filter Backwash Filter Backwash
Recycle Recycle
12,200
32,000
4,800
11,030
2,000
14,300
15,266
18,319
1,500
858
40
280
2,459
148
-------
DRAFT
Ultimate disposal cost
479 metric tons/year (528 tons/year) of sludge at
50% solids is to be hauled 16 km (10 miles) using
a 9.17 Cu m (12 cu yd) truck.
Annual ultimate disposal cost = $3,015/year
Total cost
$/1000 cu m of water treated ($/MG )
$/metric ton
of solids
( $/dry ton )
ii. Lagoon -75,700 Cu
rn/day (20 MGD) plant
Capital Cost
With
Filter Backwash
Recycle
Without
Filter Backwash
Recycle
Land purchase
Washwater holding
Washwater piping
Valves & fittings (15%)
Recirculation pumping
Lagoon construction
Inlet & outlet structures
pH control system
Yard piping & electrical (20%)
Engineering & contingencies (20%)
Construction interest
35,000
70,000
90,000
13,500
5,000
26,900
4,000
35,900
56,060
67,272
10,000
Total Capital Cost
$413,632
$567,520
With filter
backwash $16.39 ($62.05) $47.29 ($42.89)
Without filter backwash $16.34 ($61.83) $47.13 ($42.74)
40,000
234,000
35,100
34,000
4,000
35,900
76,600
91,920
]..6,000
149
-------
DRAFT
Annual Cost
Debt service (@ 8% for 30 years) 36,742 50,097
Labor & maintenance (lagoon opera-
tions - contractual removal) 74,000 75,000
Labor (monitoring requirements)
3 hr/wk 858 858
Chemicals 2,920 5,256
Power 1,030 130
Taxes & insurance 8,273 11,350
Annual Dewatering Cost $123,823 $142,691
Ultimate disposal cost
9,578 metric tons/year (10,560 tons/year) of sludge at
15% solids has to be hauled 16 k in (10 miles) using a
9.17 Cu in (12 Cu yd) truck.
Annual ultimate disposal cost = $38,772
Total cost
$/metric ton
$/l000 cu in of water treated ($]MG) of solids ( $/dry ton )
With filter backwash $5.88 ($22.27) $16.98 ($15.40)
Without filter backwash $6.57 ($24.86) $18.95 ($17.18)
iii. Centrifuge - 189,250 cu rn/day (50 MGD )
Centrifugation is the method of choice assumed for illustrating
the costs for dewatering the sludge from the 189,250 cu rn/day
(50 MGD) softening plant. The system is assumed to handle
23,945 metric tons (26,400 tons) of sludge annually. It is
assumed that a thickener-clarifier will be provided to reduce
the flow to the centrifuge, to allow storage, and to provide
flexibility for the system. The thickener overflow is recycled
to the washwater holding basin and from there to the intake of
the plant. The centrifuge building provides the necessary plumb-
ing, wiring and space for installation of a second centrifuge
at a later date. The centrifuge is assumed to be capable of
providing 60% overload capability without appreciable decrease
in performance.
150
-------
DRAFT
The purpose of this model is to present costs for a centrifuge
operation. As previously mentioned in Section VII, centrifuga-
tion produces a liquid waste stream (centrate) of lesser
quality than that from the other mechanical devices, and the
centrate may not meet proposed standards. Further treatment
or recycling may be required.
Capital Cost
Land
Washwater holding basin
Filter backwash recovery piping
Valves & fittings (15%)
Recirculation pumping
Thickener-clarifier
Centrifuge
Building with storage hopper for
centrifuge cake
Piping (10%)
Electrical (20%)
Engineering & contingencies (20%)
Construction interest
10,000
70,000
90,000
13,500
25,000
300,000
53,000
240,000
80,150
176,330
211,596
43,000
Total Capital Cost
$1,312,576
Annual Cost
Debt service ($1,312,576 @ 8% for 20 years)
Labor & maintenance (1,725 man—hours)
Power
Taxes & insurance
Annual Dewatering Cost
Ultimate disposal cost
133,758
9,500
19,000
26,251
$162,258
23,945 metric tons/year (26,400 tons/year) of sludge
at 50% solids has to be hauled 32 km (20 miles) using
a 9.17 cu m (12 Cu yd) truck.
Annual ultimate disposal cost = $142,931
151
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DRAFT
Total cost
$/1000 cu in of water treated (s/MG )
$4.42
($16. 72)
$/metric ton
of solids
$12.75
( $/dry ton )
($11.56)
iv. Lime recovery - 189,250 cu rn/day (50 MGD )
For comparative purposes the costs for lime recovery are com-
pared to the 189,250 cu rn/day (50 MGD) model for dewatering
and disposal of lime sludge. The lime kiln is assumed to be
a rotary kiln rated at 54.4 metric tons/day (60 tons/day) of
CaO, which will provide 50% excess capacity for future require-
ments. Operating and power costs are based on those shown ear-
her in this section. A credit of $30.93/metric ton CaO ($28/
ton) is assumed for the lime recovered. The credit for car-
bon dioxide (for use in settled water stabilization) is assumed
to be $16.52/metric ton ($15/ton) based on a plant usage of
2,512 metric tons (2,281 tons) each year.
Capital Cost
Land
Washwater holding basin
Filter backwash recovery piping
Valves & misc. fittings (15%)
Recirculation pumping
Thickener-clarifier
Centrifuge
Building with transfer conveyors, bins, etc.
lime kiln
Piping (10%)
Electrical (20%)
Engineering & contingencies (20%)
Construction interest
20,000
70,000
90,000
13,500
25,000
300,000
53,000
275,000
800,000
164,650
329,300
428,090
102,742
Total Capital Cost
$2,671,282
152
-------
DRAFT
Annual Cost
Debt service ($2,671,282 @ 8% for 20 years) 272,226
Labor & maintenance 228,916
Power & fuel 153,457
Taxes & insurance 53,426
Annual Lime Recovery Cost $608,025
Total annual cost for lime recalcination
$/Metric ton of sludge ($/ton) $/Metric ton of CaO ($/ton )
$25.36 ($23.03) $44.29 ($41.12)
Value of lime @ $30.87/metric ton CaO = $413,952/year
($28/ton)
Value of carbon dioxide @ $16.50/metric $ 34,216/year
ton ($15/ton)
Total chemical recovery credit = $448,168/year
$ 11000 cu m of water treated ($/MG )
$2.31 ($8.76)
B. Reduction Benefits of Alternative Control and
Treatment Technologies
The costs estimated in this section indicate that except for
centrifugation of softening sludge the use of the technologies
described in Section VII will result in a solids loading of
less than 0.6 kg/bOO cu m (5 lb/MG) product, when recycle
of the filter backwash is practiced. If recycle of filter
backwash is not practiced, the load on the receiving water
is nearly doubled, again excluding centrifugation of softening
wastes. Table VIII-5 (a) through (c) presents the reduction
benefits achieved by the treatment systems assumed for the
models.
In Table VIII-6 the amount of total suspended solids now pro-
duced in this county by water treatment processes has been
estimated. The solids produced per million gallons of water
treated was determined from the data obtained for the 782
plants covered by our survey. The municipal water production
153
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Table VIII-5 (a)
Reduction Benefits* Derived From Model Treat vent of wastes
Water Treatment Process-Coagulation
Model
(size—waste
treatment!
Metric
Waste
tons
Produced
(Tons)
(Year)
Waste Discharged to
Metric tons (Tons)
year (year)
Receiving Waters
kg (].bs)
1000 cu in (MG)
Reduction
in loading
year
disposal)
%
3785 Cu m - lagoon
(1 MGD)
Filter backwash recycled 62 (68) 0.03 (0.03) 0.02 (0.17) 99.96
Filter backwash not recycled 62 (68) 0.85 (0.94) 0.94 (7.85) 98.62
3785 cu rn/day - sanitary sewer 62 (68) 0 0 100
(1 MGD)
75,700 Cu rn/day — drying b€ds
(20 MCD)
Thickener recycle 1234 (1360) 2.04 (2.25) 0.08 (0.64) 99.83
Without thickener recycle 1234 (1360) 3.98 (4.39) 0.15 (1.25) 99.68
189,250 cu rn/day — filter press
(50 MGD)
Thickener recycle 3084 (3400) 0 0 100
Without thickener recycle 3084 (3400) 6.35 (7.00) 0.10 (0.80) 99.79
*Benef its computed based on reduced solids loading to the receiving waters
-------
Table ‘ 1 1 11-5 (b)
Reduction Benefits Derived From Model Treatment Of Wastes
Water Treatment Process-Coagulation-Softening
Model
Waste Discharged
To
(s ize—waste
Waste Produced
Receiving
Waters
Reduction
Treatrnent/
Disposal
Metric tons (Tons)
year (year)
Metric tons (Tons)
year (year)
1000
kg
cu rn
(lb)
(MG)
in
Loadsng
%
3785 cu n/day - lagoon
(1 MGD)
Filter backwash recycled 1193 (1315) 0.66 (0.73) 0.51 (4.21) 99.94
Filter backwash not recycled 1193 (1315) 1.38 (1.52) 1.05 (8.17) 99.88
Ut
U ,
75, 100 cu n/day — lagoon
(20 MGD)
Filter backwash recycled 23,854 (26,300) 13.20 (14.60) 0.51 (4.21) 99.94
Filter baflwash not recycled 23,854 (2 ,300) 27.57 (30.40) 1.05 (8.77) 99.88
189,250 cu rn/day — filter press
(50 MGD)
Filter backwash recycled and
thickener recycled 59,635 (55,600) 8.86 (9.77) 0.13 (1.07) 99.99
Filter backwash and thickener
not recycled 59,635 (65,600) 14.73 (16.24) 0.21 (1.78) 99.98
*Senefits computed based on reduced solids loading to the receiving waters
-------
Model
(size-waste
trea tr ent/
disposal)
3785 cu rn/day - lagoon
(1 MGD)
Filter backwash recycled
Filter backwash not recycled
75,700 cu rn/day — lagoon
(20 ;IGD)
Filter backwash recycled
Filter backwash not recycled
V i
0 i
189,250 cu rn/day - centrifuge
(50 I4GD)
Filter backwash recycled
Th ckener and filter backwash
recycled
189,250 cu rn/day
(50 MGD)
Centrifuge & recalcination
Filter backwash recycled
Tnickener recycled
Centrate recycled
Table VIII—5 (c)
Reduction Beneflts* Derived From Model Treatment Wastes
Water Treatment Process—Softening
Waste Discharged to
Receiving Waters
____________ ______ Metric tons ( Tons) kg
year (year) 1000 cu n
Waste Produced
Reduction
Metric tons (Tons)
(lb
in
loading
year
(year)
(MG)
%
479
(528)
0.66
(0.73)
0.51
(4.21)
99.94
479
(528)
1.38
(1.52)
1.05
(8.77)
99.88
9,578
(10,560)
13.20
(14.60)
0.51
(4.21)
99.94
9,578
(10,560)
27.57
(30.40)
1.05
(8.77)
99.88
23,945
(26,400)
245.43
(270.59)
3.74
(31.21)
23,945
(26,400)
239
(264)
3.65
(30.46)
99.00
23,945
(26,400)
0 0 100
P::j
*Benef its computed based on reduced solid loading to the receiving waters
-------
Table VIII—6
Calculations of Total Sludge Production
Municipaib IndustrialC Total
1000’ Cu rn 1 . etric tons 1000 cu x t ietric tons 1000 Cu m Xec.ric tons
kg/bOO Cu per day per day per day per day per day per day
Category (lb/MG) (MGD) (tons/day) (?IGD) (tons/day) (NGD) (tons/day)
Coagulation 43.90 38,080.9 1,669.8 5,174.1 226.8 43,255.0 1,896.5
(366) (10,061) (1,841) (1,367) (250) (11,428) (2,091)
Softening 382.75 1,131.8 432.6 2,108.2 806.3 3,240.0 1,239.0
(3,191) (299) (477) (557) (889) (856) (1,366)
U,
Iron
removal 29.39 2,869.0 84.4 2,869.0 84.4
(245) (758) (93) (758) (93)
Coagulation 236.54 8,501.1 2,009.0 8,501.1 2,009.0
Softening (1,972) (2,246) (2,215) (2,246) (2,215)
All Categories 50,582.7 4,195.8 7,282.3 1,033.1 57,865.1 5,228.9
(13,364) (4,624) •(1,924) (1,139) (15,288) (5,765)
a) From data base developed in our survey
b) 1963 USPHS Survey PT
C) 1967 Census of Manufacturers, Water Use in Manufacturing
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DRAFT
figures were estimated from data in the 1963 USPHS Survey. In-
dustrial water production in the various treatment categories
was estimated from data in the 1967 Census of Manufacturers,
“Water Use in Industry.”
The estimated total amount of suspended solids in the wastes
from the water-supply industry is given in the last column of
Table VIII-6. The data used in Table VIII-6 were the most
recent data available. Thus the current total amount of
suspended solids is undoubtedly greater. Rather than
arbitrarily estimate the current total suspended solids, the
value of 1,908,000 metric tons/year (2,104,000 tons/year) will
be used.
The use of BPCTCA, as identified in Section IX, would reduce
the amount of TSS discharged to 423 metric tons/year (465
tons/year).
There are nwnerous process configurations of the proposed
treatment systems and with judicious water management zero
discharge of water may be accomplished. The benefits gained
by closing the cycle are not great as would be indicated by
the last column of Table vIII—6. However, in some instances
the additional costs are also relatively small. There are a
number of water—treatment plants presently discharging no
liquid wastes, which demonstrates the applicability of the
discussed alternatives.
C. Non-water quality aspects
There are several non-water—quality aspects of the treatment
and disposal of water plant wastes, and there are both bene-
fits and liabilities as well as uncertainties involved. The
areas in which the non-water—quality aspects will have their
greatest impact are: land use, energy use, by-product genera-
tion and recovery, air pollution, noise, and odors. Each of
these will be discussed in the following paragraphs.
1. Land Use
One of the more obvious impacts is the additional land required
for installation of treatment systems. In some cases, the
land requirements are minimal; but in others, such as drying
beds and lagoons, the land requirements can be quite substan-
tial, depending on the size of the plant, and the unit
processes employed. Rather large land areas may be required
for ultimate disposal of the dewatered sludge. These land
requirements may prevent maximum beneficial land utilization
and present an esthetically unpleasant site. The use of land
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in this way could also serve to reduce the tax base for the
affected governmental unit, which in turn would reduce its
gross revenues. However, use of the land for lagoons or land-
fills is not always a liability. Short-term liabilities such
as ultimate disposal sites, abandoned quarries and strip mines,
can and have been turned into long—term assets by proper
planning and reclamation projects. Additionally, use of deep
shaft mines and deep well injection of wastes have helped to
alleviate subsidence problems in several areas. The effects
of leachates from land application of these wastes is believed
to be negligible, but this belief has not been confirmed.
2. Energy Use
The energy required to treat and dispose of the wastes from
water treatment plants was estimated with the use of two models.
The first model was an energy—intensive system with a mechanical
dewatering device and recycle of filter backwash, filtrate, and
centrate. The second model was an energy—conserving system in
which there was no recycle, and lagoons were used to treat the
waste. For both models wast&s were generated by a hypothetical
75,7000 cu rn/day (20 MGD) water-treatment plant. For the
energy-intensive systems it was assumed that 64 km (40 mile)
roundtrip was required for ultimate disposal, and for the con-
servative system it was assumed that a 32 km (20 mile) round
trip was needed.
If it is assumed that there are 1.91 million metric tons (2.1
million tons) of dry waste generated annually, then the energy—
intensive system would add approximately 373 million kwh to our
existing energy budget. This figure represents less than 0.002%
of the Nation’s 1970 total energy consumption. Approximately
55% of this expenditure is utilized in ultimate disposal of the
dewatered waste.
In the second system the energy expenditure for dewatering the
waste in lagoons, cleaning the lagoons and ultimate disposal
represents less than 0.0006% of the 1970 energy consumption.
Almost all of the energy is utilized for removing and hauling
the dewatered waste.
Based on the above estimates, the impact of the additional
energy needed to properly treat and dispose of wastes from
water-supply plants appears to be negligibly small.
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3. By-Product Generation and Recovery
The use of these wastes to produce a saleable product outside
the water industry has been proven feasible in a few isolated
cases. More attention to this area is anticipated and recom-
mended for the future. From an ecological and conservational
standpoint, processes such as alum recovery, lime recovery,
and magnesium carbonate recovery should be thoroughly evaluated.
4. Air Pollution Aspects
If all of the sludge to be disposed of were trucked 64 km (40
miles) roundtrip as specified in the energy intensive system
then approximately 34.9 million km (21.7 x 106 miles) would be
logged in disposing of the dewatered sludge. This would result
in a total emission from gasoline—powered vehicles of 2,195
metric tons (2,421 tons) annually and would represent roughly
0.003% of the total 1965 automotive emissions. If all of the
sludge were to be carried by diesel powered trucks the total
annual emission would be reduced by approximately 40%.
Noise
Most water-treatment plants generate a fairly high level of
noise (85-95 dB(A)) within battery limits because of such
equipment as pumps, compressors, etc. Equipment associated
with in—process, or end—of—pipe systems could produce similar
levels, depending upon the device selected. If noise levels
become too great they can be attenuated somewhat by protective
devices (earplugs), walls, acoustical shields, and physical
separation (sound levels decrease with the square of the dis-
tance from the source). Another source of noise pollution is
from trucks hauling wastes. These levels can exceed those
given above if uncontrolled, and could be a source of irrita-
tion to the people in the immediate vicinity.
Depending upon the frequency, 85 dB can be considered a critical
level for ear damage. In California a noise limit has been set
at 82 dB for highway traffic.
5. Odors
Some odor problems have been reported with lagooning operations,
but this is not considered a serious problem as such operations
are customarily in sparsely populated areas.
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SECTION IX
BEST PRACTICABLE CONTROL TECHNOLOGY
CURRENTLY AVAILABLE--EFFLUENT LIMITATIONS
Effluent limitations commensurate with the best practicable
control technology currently available (BPCTCA) have been
established for each subcategory within the water-supply
industry. These effluent limitations are based on the infor-
mation presented in Sections III through VIII. Factors that
were specifically considered include:
a. The total cost of application of technology in
relation to the effluent reduction benefits to be
achieved from such application.
b. The processes employed in water—treatment plants.
c. The processes employed for treatment of wastes.
d. The treatability of the wastes.
e. The engineering aspects of the application of
various types of control techniques.
f. Changes in the processes, or sequence of processes
used to treat water.
g. Non-water-quality environmental impact of the appli-
cation of technology to reduce waste loadings with special
emphasis on the requirements for energy.
The BPCTCA is based on both in-plant and end-of—pipe technology.
BPCTCA in-plant technology is based on control practices widely
known and used within the water-supply industry, and includes
the following:
a. Equalization of filter backwash water to minimize
periodic excursions of the volumetric flowrate to solids—
separation devices.
b. Utilization of continuous effluent discharge instead
of intermittent discharge.
c Reclamation of lime where practicable.
l61
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DRAFT
d. Modification of existing lagoons to minimize
scouring and short-circuiting.
The end-of-pipe treatment technology for BPCTCA is based on
waste—treatment processes now in use in the water—supply
industry, and includes lagooning, thickening, mechanical
dewatering, disposal to sanitary sewers, drying beds, and land
disposal. Because of differences in the treatability among
sludges, pilot plant tests are almost always necessary before
a specific treatment system can be selected for application
in a given water treatment plant.
In a water-supply plant, the waste—treatment systems should
be used to treat only polluted water. Unpolluted storm run-
of f water should be diverted from lagoons, since an increased
flowrate into lagoons can increase the pounds of solids being
discharged.
A. Procedure for Determining Effluent Limitations
The annual average wasteloads that are the basis for the efflu-
ent limitations guidelines to be used by plants that discharge
wastes to a watercourse instead of discharging to a sanitary
sewer were determined by the “flow—and-concentration” method.
In this method the annual average concentration of a pollutant
that can be attained reliably in the discharge from a properly
designed and well operated waste-treatment system is determined.
Then, the mean annual average wastewater flow from plants in
each subcategory (expressed as a percentage of the product—
water flow) is determined. The attainable annual average con-
centrations and the mean annual average wastewater flows
expressed as a percentage of product water flow are used to
calculate the effluent limtations for each pollutant and each
subcategory. The effluent limitations are expressed in terms
of kilograms of pollutant per thousand cubic meters of product
water and in English units (lb/MG). Since the concentrations
and waste flows are annual averages, the effluent limitations
will be in terms of annual averages at this stage of the
determination.
A long—term parameter, such as the annual average waste load,
is not adequate in itself to establish short-term limits that
should not be exceeded. However, the effluent limitations,
which are short—term limits, can be established from annual
averages by statistical analysis of the variations in waste
loads, if the variations from day—to-day are known or measured
over a sufficient period.
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The methods used in this study to determine the attainable
annual average concentrations of TSS in wastewaters, to find
the mean annual average waste flows, and to statistically
analyze the day—to—day variations in waste loads are described
below.
The attainable annual average concentrations of TSS in waste—
waters were established from studies of TSS concentrations in
the effluents from lagoons. Since lagoons are used more often
within the industry than other methods of solids-separation
because of their low cost and low energy requirements, and
since other means of solids separation result in lower load-
ings of TSS in the effluent than is attainable with lagoons,
lagoons were considered the standard solids—separation
method in the water-supply industry. Data on the loadings
of TSS in effluents from lagoons were used for establish-
ing effluent limitations. From existing reports and plant
visits, 109 plants that use lagoons to treat sludges from
water—treatment processes were identified. Interviews with
personnel and studies of existing plant data were made during
66 visits to plants with lagoons, and a sampling program was
conducted at 15 of these plants. Eleven of these 15 lagoons
were judged to be well designed and operating properly. The
concentration of TSS in the effluents from these 11 lagoons
ranged from 3 mg/l to 34 mg/i. The average concentration of
TSS in the effluents from these 11 lagoons was 11 mg/i. The
data obtained during the sampling programs must be viewed with
caution because the sampling was carried out, of necessity, only
over a short period (a day or less). However, studies con-
ducted by others over extended periods ranging to more than
a year show that with well designed and properly operated
lagoons an annual average TSS concentration of 20 mg/i can be
maintained, which is in line with the data obtained in our
short-term sampling programs.
The mean annual average waste flows expressed as a percentage
of the flow of product water were determined for each sub—
category by statistical analysis of the data on annual aver-
ages of the backwash flowrates, blowdowns from sedimentation
basins and production rates of finished water. A combination
of statistical techniques was used including determination of
means and standard deviations, and the application of statis-
tical “F” and “T” tests and multiple regression analyses to
determine the factors that significantly affect the annual
average waste flows.
For each subcategory, linear regression equations were
developed that expressed the waste flow as a function of plant
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DRAFT
size (i.e., annual average production rate) and of raw water
hardness, which were the only two factors found to have sta-
tistically significant effects on the waste flow. From these
equations and the attainable concentration of TSS in waste—
waters (20 mg/i) the following equation was developed.
Eq. IX-la L = 0.6 + S + H
in which L is in
kg/bOO Cu m
Eq. IX-lb or L=5+S+H
in which L is
in lb/MG
where: L = annual average waste load of TSS, kg/bOO cu m
(lb/MG)
S = allowance for plant size, taken from Table IX—l
kg/bOO Cu m (lb/MG)
H = allowance for hardness of raw water, taken from
Table IX-l, kg/l000 Cu m (lb/MG)
For all categories an annual average waste load of 0.6
kg/bOO cu m (5 lb/MG) of product is recommended for what is
termed the “base—load” plant. The basis for the 0.6 kg/bOO
cu m (5 lb/MG) waste load stems from the multiple regression
analysis of the data. The base-load plant is a large plant
[ >1.89 million cu rn/day (>500 MGD)] that does not use lime or
lime—soda softening processes. For smaller plants an additional
allowance for plant size, S , is recommended. The magnitude of
the allowance depends on the plant size as shown in Table TX-i.
For plants in Category I lime or lime-soda softening is not
performed. Therefore, no allowance is given for the hardness
of the raw water, and only the size allowance, S , in Table
IX-l is applicable. For plants in Category II and III, in
which lime or lime-soda softening is performed, the hardness
allowance, H, in Table IX-l is also used.
A long-term parameter, such as annual average TSS loading, is
not adequate in itself to establish effluent guideline limits,
which are short—term maxima that must not be exceeded. The
quantity and quality of the effluent from a properly designed
and well operated waste—treatment system changes continually
for several reasons.
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Table IX-1
Allowances to Adjust the Annual Average Waste
Load for Plant Size and Raw Water Hardness
Plant size,a 1000 <3.8 3.8—11.4 11.4—38 38—114 114—379 379—1136 1136—1893 ‘1893
cu rn/day
MGD (<1) (1—3) (3—10) (10—30) (30—100) (100—300) (300—500) (>500)
S (allowance),
kg/bOO cu m 0.70 0.50 0.40 0.30 0.20 0.10 0.05 (0)
lb/MG (5.8) (4.2) (3.3) (2.5) (1.7) (0.8) (0.4) (0)
Hardness,a mg/i 0—100 100—200 200—300 300—400 400—500 500—600 600—700
H (allowance),
kg,’lOOO cu in 0.13 0.24 0.35 0.46 0.56 0.67 0.78
lb/MG (1.1) (2.0) (2.9) (3.8) (4.7) (5.6) (6.5)
a) Annual average total hardness expressed as mgi ]. of CaCO3
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DRAFT
It should be emphasized that the variability factor that was
developed from the available data on TSS loadings in the
effluents from lagoons (i.e., V = 6.6) is presented here for
tentative use because the maximum period of time for which
there were data to establish the variability factor was
three months. Additional data are being sought and a more
definitive value of V may be designated when the additional
data become available.
The pH ranges recommended as limitations for the three cate-
gories are:
Subcategory I - pH from 6.0 to 9 .0
Subcategories II and III - pH from 6.0 to 10.5
Zeolite brines
If any water-treatment plant that uses the unit processes
ltsted in Categories I, II, or III also uses either zeolite
softening or zeolite iron and manganese removal, the spent
brines may contain the following pollutants: total dissolved
solids, dissolved iron, dissolved manganese, and fluoride.
For the BPCTCA effluent guidelines, no across-the-board limi-
tations are recommended for these pollutants because there is
no adequately demonstrated control or treatment technology.
However, it is recommended that segregation and equalization
of the brines be practiced and that the following disposal
technologies be considered for each plant on an individual
basis: discharge to sewer, controlled dilution prior to dis-
charge to a watercourse, deep—well injection, and discharge
into the ocean.
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SECTION X
BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE--EFFLUENT LIMITATIONS
The best available technology economically achievable (BATEA)
was determined by identifying the very best control and treat-
ment technology employed by a specific point source within
the industrial category or subcategory.
The following factors were considered in determining BATEA
technology:
a. The processes employed.
b. The engineering aspects of the application of various
types of control techniques.
c. Process changes.
d. The cost of achieving the effluent/reduction result-
ing from application of BATEA technology.
e. The non—water—quality environmental impacts (includ-
ing energy requirements).
With the best available technology economically achievable
by 1983, the waste effluents from solids—separation systems
are recycled for use as feed water, and spent brines from
zeolite regeneration are segregated from other wastewaters,
reclaimed, and reused for regeneration.
A number of water treatment plants recycle filter backwash
water at present, and when the BPCTCA is promulgated, the dis-
charges from solids—separation systems will have 20 mg/i of
TSS on an annual average basis. The concentration of TSS in
many raw waters used by water treatment plants often exceeds
20 mg/l so that the discharges from solids-separation systems
will be an acceptable feed. Discussions have been given in
the literature about the possibility of tastes and odors in
product water resulting from recycling filter backwash water
and lagoon effluents. However, in our survey and personal
visits to plants, out of the 782 plants surveyed, 46 recycled
backwash water, and none had difficulties with odors and
tastes.
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Spent zeolite brines have been reclaimed in a concentration
and composition suitable for reuse as regeneration brines on
a demonstration scale. Tile basic technology, which is lime-
soda softening, has been in use to remove calcium and magne—
siwn from waters for many years.
In 1983 the BATEA will be to recycle zeolite brines and efflu-
ents from solids—separation systems. The only discharges
from these processes will be the rinse waters from the regen-
eration part of the cycle used in zeolite processes; dissolved
solids concentrations in these rinse waters are not to exceed
4000 mg/i. The rinse waters will be equalized prior to
discharge.
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SECTION XI
NEW SOURCE PERFORMANCE STANDARDS
AND PRETREATNENT STANDARDS
A. New Source Performance Standards
A new source is defined as ‘ t any source, the construction of
which is commenced after the publication of the proposed regu-
lations prescribing a standard of performance.
The technology and effluent limitations utilized for new
sources should be that defined in Section IX as the Best
Practicable Control Technology Currently Available. After
the necessary developmental work is performed to demonstrate
the reliability and acceptability of recycling the water-
borne discharges from solids—separation systems and of
reclaiming and reusing spent zeolite brines, the technology
defined as best available technology economically achievable
may eventually provide a more effective treatment system; the
performance standards should then be revised accordingly.
B. Pretreatment Standards
The wastewater characteristics that could be incompatible with
a well designed and operated publicly owned wastewater treat-
ment plant are the suspended solids content and the pH of wastes
from solids-separation units, and the TDS content and possible
detrimental concentrations of heavy metals and fluoride in
waste zeolite brines. To avoid malfunctions of the publicly
owned wastewater treatment plants, a judgment should be made
individually as to the levels of suspended solids, pH, TDS,
heavy metals, and fluoride that should be allowed to enter a
particular treatment system along with the normal municipal
waste load. Consideration should be given to the concentra-
tions of the above pollutants, the present municipal waste
load, and the capacity of the treatment systems to insure
that a proper degree of dilution is maintained.
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SECTION XII
ACKNOWLEDGMENT
The program was carried out under the direction of Robert E.
Lacey, Senior Chemical Engineer, assisted by Don B. Hooks,
Assistant Chemist, George F. Brockman, Adjunct Research
Advisor, Thomas A. Davis, Senior Chemical Engineer, Walt R.
Dickson, Research Chemist, M. David Bishop, Field Engineer,
Larry D. Willians, Field Engineer, H. Bernard Stewart, Field
Technician, and R. Eugene Godwin, Field Technician.
Acknowledgment is made of the sizeable contributions of the
sub-contractor firm of Black, Crow, and Eidsness, Inc., of
Gainesville, Florida and especially Dr. Cliff Thompson,
Dr. A. P. Black, and Mr. William Durkin.
Appreciation is expressed to Chet Rhines, Charles Cook and
other individuals in the EPA Effluent Guidelines Division
and other EPA offices who assisted in performing this study.
Special acknowledgment is made of the assistance of Martin
Halper, Project Officer, whose efforts are greatly appreciated.
Sincere appreciation is expressed for the assistance provided
by the AWWA and especially to Mr. Eric F. Johnson, Executive
Director, Mr. David Preston, Assistant Executive Director, and
Mrs. Charles A. Buescher, Head of the Ad Hoc Committee on
Environmental Control
We would also like to acknowledge the aid of personnel of many
state environmental agencies for their cooperation in the
study, especially Shel Darity of the Ohio EPA, and Michael
Kovach and Gordon Olivier of the Michigan Department of Health.
Lastly, appreciation is expressed to personnel of each of the
water-treatment plants that were visited, and of those that
responded to our many questions asked of them by telephone or
in letters.
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SECTION XIII
GLOSSARY
Definitions and Terminology
Absorption : The taking up of one substance into the body of
another.
Acre—foot : A volume of water 1 ft deep and 1 acre in area,
or 43,560 Cu. ft.
Activated carbon : Carbon particles usually obtained by car-
bonization of cellulosic material in the absence of air and
possessing a high adsorptive capacity.
Adsor tion : The adherence of a gas, liquid, or dissolved
material to the surface of a solid.
Aeration : (1) The bringing about of more intimate contact
between air and a liquid by one or more of the following
methods: (a) spraying the liquid in the air, (b) bubbling
air through the liquid, or (c) agitating the liquid to promote
surface absorption of air. (2) The supplying of air to con-
fined spaces under nappes, downstream from gates in conduits,
etc., to relieve low pressures and to replenish air entrained
and removed from such confined spaces by flowing water. (3)
the relieving of the effects of cavitation by admitting air
to the section affected.
Aerator : A device that promotes aeration.
Agglomeration : The coalescence of dispersed suspended matter
into large flocs or particles which settle rapidly.
Algae : Primitive plants, one— or many—celled, usually aquatic,
and capable of photosynthesis.
Alkali : Any of certain soluble salts, principally sodium,
potassium, magnesium, and calcium, that have the property of
combining with acids to form neutral salts and may be used in
chemical processes such as water and wastewater treatment.
Alkaline water : (1) Water have a pH greater than 7.0.
(2) Water high in percent sodium (approaching and exceeding
6.0), but relatively low in total dissolved solids.
Alkalinity : The capacity of water to neutralize acids, a
property imparted by the water’s content of carbonates, bicar-
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bonates, hydroxides, and occasionally borates, silicates, and
phosphates. It is expressed in milligrams per liter of
equivalent calcium carbonate.
Alum : A common name, in the water and wastewater treatment
field, for commercial-grade aluminum sulfate (Al2(S04)3•14H20).
Amortization : (1) Gradual reduction, redemption, or liquida-
tion of the balance of an account according to a specified
schedule of times and amounts. (2) Provision for the extin-
guishment of a debt by means of a sinking fund.
Analysis : (1) The record of an examination of water or waste—
water. (2) The resolution of complex problems, bodies, or
liquids into their elements.
Anion : A negatively charged ion in an electrolyte solution,
attracted to the anode under the influence of electric potential.
Annual flood : The maximum 24-hr average rate of flow occur-
ring in a stream during any period of 12 consecutive months.
It is the usual practice to consider the 12-month period as
extending from October 1 of one year to September 30 of the
following year.
Annual variation : The general pattern of a particular element
throughout the year, obtained by plotting the normal values of
the element for each month and connecting the points by a
smooth curve.
Anode : Positive pole of an electrolytic system.
Arid : (1) A term applied to regions where precipitation is
so deficient in quantity, or occurs at such times, that agri-
culture is impracticable without irrigation. (2) In clima-
tology, a term applied to climates which have rainfall insufficient
to support vegetation.
Artificial recharge : Replenishment of the groundwater
supply by means of spreading basins, recharge wells, irrigation,
or induced infiltration of surface water.
Assimilative capacity : The capacity of a natural body
of water to receive: (a) wastewaters, without deleterious
effects; (b) toxic materials, without damage to aquatic life
or humans who consume the water; (c) BOD, within prescribed
dissolved oxygen limits.
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Back wash : The reversal of flow through a filter to wash clog-
ging material out of the filtering medium and reduce conditions
causing loss of head. Also called filter wash.
Backwashing : The operation of cleaning a filter by reversing
the flow of liquid through it and washing out matter previously
captured in it. Filters would include true filters such as sand
and diatomaceous-earth types but not other treatment units such
as trickling filters.
Basin : (1) A natural or artificially created space or struc-
ture, surface or underground, which has a shape and character
of confining material that enable it to hold water. The term
is sometimes used for a receptacle midway in size between a
reservoir and a tank. (2) The surface area within a given
drainage system. (3) A shallow tank or depression through which
liquids may be passed or in which they are detained for treatment
or storage.
Biochemical oxygen demand (BOD) : (1) The quantity of oxygen
used in the biochemical oxidation of organic matter in a specified
time, at a specified temperature, and under specified conditions.
(2) A standard test used in assessing wastewater strength.
Blowdown : (1) The removal of a portion of any process flow to
maintain the constituents of the flow within desired levels.
Process may be intermittent or continuous. (2) The water dis-
charged from a boiler or cooling tower to dispose of accumulated
salts.
Brine : Concentrated salt solution remaining after removal of
distilled product; also, concentrated brackish, saline or sea
waters containing more than 36,000 mg/l of total dissolved solids.
Broad-crested weir : A weir having a substantial width of
crest in the direction parallel to the direction of flow of
water over it. This type of weir supports the nappe for an
appreciable length and produces no bottom contraction of the
nappe. Also called wide-crested weir.
Buffer : Any of certain combinations of chemicals used to
stabilize the pH values or alkalinities of solutions.
Carbonation : The diffusion of carbon dioxide gas through a
liquid to render the liquid stable with respect to precipitation
or dissolution of alkaline constituents.
Cathode : The pole of an electrolytic cell which attracts
positively charged particles or ions (cation).
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Cation : The ion in an electrolyte which carries the positive
charge and which migrates toward the cathode under the influence
of a potential difference.
Centrifugal dewatering of sludge : The partial removal of water
fLom wastewater sludge by centrifugal action.
Centrifuge : A mechanical device in which centrifugal force is
used to separate solids from liquids and/or to separate liquids
of different densities.
Chemical coagulation : The destabilization and initial
aggregation of colloidal and finely divided suspended matter by
the addition of a floc-forming chemical.
Chemical gas feeder : A feeder for dispensing a chemical in
the gaseous state. The rate is usually graduated in gravimetric
terms. Such devices may have proprietary names.
Chemical oxygen demand (COD) : A measure of the oxygen—consuming
capacity of inorganic and organic matter present in water or
wastewater. It is expressed in the amount of oxygen consumed
from a chemical oxidant in a specific test. It does not dif-
ferentiate between stable and unstable organic matter and thus
does not necessarily correlate with biochemical oxygen demand.
Also known as OC and DOC, oxygen consumed and dichromate oxygen
consumed, respectively.
Chemical sludge : Sludge obtained by treatment of wastewater
with chemicals.
Chlorine : An element ordinarily existing as a greenish—yellow
gas about 2.5 times as heavy as air. At atmospheric pressure
and a temperature of -30.1°F, the gas becomes an amber liquid
about 1.5 times as heavy as water. The chemical symbol of
chlorine is Cl, its atomic weight is 35.457, and its molecular
weight is 70.914.
Cipolletti weir : A contracted weir of trapezoidal shape, in
which the sides of the notch are given a slope of one horizontal
to four vertical to compensate as much as possible for the effect
of end contractions.
Clarification : Any process or combination of processes the pri-
mary purpose of which is to reduce the concentration of suspended
matter in a liquid.
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Clarifier : A unit of which the primary purpose is to secure
clarification. Usually applied to sedimentation tanks or basins.
Clal : (1) Soil consisting of inorganic material the grains of
hich have diameters smaller than 0.002 mm. (2) A mixture of
earthy matter formed by the decay of certain minerals. The corn—
position of clays varies widely and dictates its use. It is some-
times used in water to aid coagulation and to remove tastes and
odors.
Clear well : A reservoir for storage of filtered water of suf-
ficient capacity to prevent the necessity of frequent variations
in the rate of filtration with variations in demands.
Coagulant : A compound responsible for coagulation; a floc—form—
ing agent.
Coagulant aid : Any chemical or substance used to assist or mod-
if y coagulation.
Coagulation : In water and wastewater treatment, the destabil-
ization and initial aggregation of colloidal and finely divided
suspended matter by the addition of a floc-forming chemical or
by biological processes.
Coagulation basin : A basin used for the coagulation of sus-
pended or colloidal matter, with or without the addition of a
coagulant, in which the liquid is mixed gently to induce agglom-
eration with a consequent increase in settling velocity of
particulates.
Coefficient of fineness : The ratio of suspended solids to tur-
bidity; a measure of the size or particles causing turbidity, the
particle size increasing with coefficient of fineness.
Colloids ; (1) Finely divided solids which will not settle but
may be removed by coagulation of biochemical action or membrane
filtration; they are intermediate between true solutions and sus-
pensions.
Combined water : Water held in chemical combination and remaining
after hygroscopic water evaporates; it will not evaporate and is
driven of f only by heating.
Composite wastewater sample : A combination of individual samples
of water or wastewater taken at selected intervals, generally
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hourly for some specified period, to minimize the effect of the
variability of the individual sample. Individual samples may
have equal volume or may be roughly proportional to the flow at
time of sampling.
Conductance : A measure of the conducting power of a solution
is expressed in mhos.
Conductivity bridge : A means of measuring conductivity
whereby a conductivity cell forms one arm of a Wheatstone bridge,
a standard fixed resistance forms another arm, and a calibrated
slide wire resistance with end coils provides the remaining two
arms. A high-frequency alternating current is supplied to the
bridge.
Continuous sludge-removal tank : A sedimentation tank equipped
to permit the continuous removal of sludge.
Contracted weir : A rectangular notched weir with a crest width
narrower than the channel across which it is installed and with
vertical sides, extending above the upstream water level, which
produce a contraction in the stream of water as it leaves the
notch.
Co per sulfate : A chemical prepared from copper and sulfuric
acid and having the formula CuSO4•5H20. Usually used to control
algal growths. Also called blue vitriol, blue copperas, blue-
stone, cupric sulfate.
Data : Records of observations and measurements of physical facts,
occurrences, and conditions, reduced to written, graphical, or
tabular form.
Decantation : Separation of a liquid from so lids, or from a
liquid of higher density, by drawing off the upper layer after
the heavier material has settled.
Degree of treatment : A measure of the removal effected by
treatment process with reference to solids, organic matter,
BOD, bacteria, or other specified matter.
Demineralization : Reduction of the mineral content of water by
a physical, chemical, or biological process; removal of salts.
Detention time : The theoretical time required to displace the
contents of a tank or unit at a given rate of discharge (volume
divided by rate of discharge).
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Detergent : (1) Any of a group of synthetic, organic, liquid
or water-soluble cleaning agents that are inactivated by hard
water and have wetting—agent and emulsifying-agent properties
but, unlike soap, are not prepared from fats and oils. (2) A
similar substance that is soluble in oil and capable of holding
insoluble foreign matter in suspension. (3) Any cleansing
agent, including soap.
Dewater : (1) To extract a portion of the water present in a
sludge or slurry. (2) To drain or remove water from an enclosure.
Dialysate : Stream being depleted of salt in electrodialysis.
Dialysis : The separation of a colloid from a substance in true
solution by allowing the solution to diffuse through a semiper-
meable membrane.
Diatomaceous—earth filter : A filter used in water treatment, in
which a built—up layer of diatomaceous earth serves as the
filtering medium.
Diatomjte : A type of earth composed of diatomic skeletons, used
for filtering water and other liquids; diatomaceous earth.
Dilution : Disposal of wastewater or treated effluent by discharg-
ing it into a stream or body of water.
Discharge : (1) As applied to a stream or conduit, the rate of
flow, or volume of water flowing in the stream or conduit at a
given place and within a given period of time. (2) The passing
of water or liquid through an opening or along a conduit or
channel. (3) The rate of flow of water, silt, or other mobile
substance which emerges from an opening, pump, or turbine, or
passes along a conduit or channel, usually expressed as cubic
feet per second, gallons per minute, or million gallons per day.
Disinfection : The art of killing the larger portion of micro-
organisms in or on a substance with the probability that all
pathogenic bacteria are killed by the agent used.
Dissolved oxygen : The oxygen dissolved in water, wastewater,
or other liquid, usually expressed in milligrams per liter, parts
per million, or percent of saturation. Abbreviated DO.
Dissolved solids : Theoretically, the anhydrous residues of the
dissolved constituents in water. Actually, the term is defined
by the method used in determination. In water and wastewater
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trt atment the Standard Methods tests are used.
Distillation : A process of evaporation and recondensation used
for separating liquids into various fractions according to their
boiling points or boiling ranges.
Distribution system : (1) A system of conduits and their
appurtenances by which a water supply is distributed to consumers.
The term applies particularly to the network or pipelines in the
streets in a domestic water system.
Domestic consumption : The quantity, or quantity per cap-
ita, of water supplied in a municipality or district for domestic
uses or purposes during a given period, usually one day. It is
usually taken to include all uses included within the term munici-
pal use of water and quantity wasted, lost, or otherwise unaccounted
for.
Dose : (1) The quantity of substance applied to a unit quantity
of liquid for treatment purposes. It can be expressed in terms of
either volume or weight, e.g ., pounds per million gallons, parts
per million, grains per gallon, milligrams per liter, or grams
per cubic meter. (2) Generally, a quantity of material applied
to obtain a specific effect.
Drifting-sand filter : In the United States, an obsolete
type of rapid sand filter in which the sand drifts from the point
where it enters to the point where it is drawn off to be washed.
This type of operation causes the sand to be removed continuously
and returned clean with the raw water as the filter operates,
there being no interruption in the operation of the filter for
sand washing.
Drinking-water standards : (1) Standards prescribed by the
U. S. Public Health Service for the quality of drinking water
supplied to interstate carriers. (2) Standards prescribed by
state or local jurisdictions for the quality of drinking water
supplied from surface—water, groundwater, or bottled—water sources.
D y feeder : A feeder for dispensing a chemical or other fine
material 1n the solid state to water or wastewater at a rate
controlled manually or automatically by the rate of flow. The
constant rate may be either volumetric or gravimetric.
Dry suspended solids : The weight of the suspended matter
in wastewater or other liquid after drying 1 hr. at 103°C.
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Effluent : (1) A liquid which flows out of a containing space.
f2) Wastewater or other liquid, partially or completely treated,
or in its natural state, flowing out of a reservoir, basin, treat-
ment plant, industrial treatment plant, or part thereof.
Electrodialysis : Process for removing ionized salts from water
Uirough the use of ion—selective ion—exchange membranes and an
applied electrical potential.
Electrometric titration : A titration in which the end point is
aitermined by observing the change of potential of an electrode
immersed in the solution titrated.
Egualizing basin : A holding basin in which variations in flow
and composition of a liquid are averaged. Such basins are used
to provide a flow of reasonably uniform volume and composition
to a treatment unit. Also called balancing reservoir.
Evaporation rate : The quantity of water, expressed in terms of
depth of liquid water, evaporated from a given water surface per
unit of time. It is usually expressed in inches depth per day,
month, or year.
Ferric sulfate : A soluble iron salt, Fe2(S04)3 formed by
reaction of ferric hydroxide and sulfuric acid or by reaction
of iron and hot concentrated sulfuric acid. Also obtainable
in solution by reaction of chlorine and ferrous sulfate.
Ferrous sulfate : A soluble iron salt, FeSO4•7H20, contain-
ing seven molecules of water. Sometimes called copperas, sugar
of iron, green vitriol, iron vitriol.
Filter : A device or structure for removing solid or colloidal
material, usually of a type that cannot be removed by sedimen-
tation, from water, wastewater, or other liquid. The liquid is
passed through a filtering medium, usually a granular material
but sometimes finely woven cloth, unglazed porcelain, or specially
treated paper. There are many types of filters used in water or
was tewater treatment.
Filtering medium : (1) Any material through which water, waste-
water, or other liquid is passed f or the purpose of purification,
treatment or conditioning. (2) A cloth or metal material of
some appropriate design used to intercept sludge solids in sludge
filtration.
Filter plant : In water treatment works, the processes, devices,
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and structures used for filtration of water.
Filter press : A press operated mechanically for partially
separating water from solid materials.
Filter rate : The rate of application of material to some process
involving filtration, for example, application of wastewater
sludge to a vacuum filter, wastewater flow to a trickling filter,
water flow to a rapid sand filter.
Filter run : (1) The interval between the cleaning and washing
operations of a rapid sand filter. (2) The interval between
the changes of the filter medium on a sludge—dewatering filter.
Filter wash : The reversal of flow through a rapid sand filter to
wash clogging material out of the filtering medium and reduce
conditions causing loss of head.
Filtrate : The liquid which has passed through a filter.
Filtration : The process of passing a liquid through a filtering
medium (which may consist of granular material, such as sand,
magnetite, or diatomaceous earth, finely woven cloth, unglazed
porcelain, or specially prepared paper) for the removal of sus-
pended or colloidal matter.
Filtration rate : The rate of application of wastewater to a
filter, usually expressed in million gallons per acre per day
or gallons per minute per square foot.
Flash mixer : A device for quickly dispersing chemicals uni-
formly throughout a liquid.
Floc : Small gelatinous masses formed in a liquid by the reaction
of a coagulant added thereto, through biochemical process, or
by agglomeration.
Flocculation : In water and wastewater treatment, the agglomer-
ation of colloidal and finely divided suspended matter after
coagulation by gentle stirring by either mechanical or hydraulic
means.
Flocculation agent : A coagulating substance which, when added
to water, forms a flocculent precipitate which will entrain
suspended matter and expedite sedimentation; examples are alum,
ferrous sulfate, and lime.
Flocculator : (1) A mechanical device to enhance the formation
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of floc in a liquid. (2) An apparatus for the formation of
floc in water and wastewater.
Flow : (1) The movement of a stream of water or other mobile
substance from place to place; a stream of water; movement of
silt, water, sand, or other material. (2) The fluid which is
in motion. (3) The quantity or rate of movement of a fluid;
discharge; total quantity carried by a stream. (4) To issue
forth or discharge.
Grab sample : A single sample of wastewater taken at neither
set f.ime nor flow.
Grain per gallon : A measure of the concentration of solutions,
equal to 17.1 mg/i.
Gravity filter : A rapid sand filter of the open type, the oper-
ating level of which is placed near the hydraulic grade line of
the influent and through which the water flows by gravity.
Greensand : Sand consisting entirely or in large part of particles
of the mineral glauconite, a hydrous potassium iron silicate. At
one time used extensively in water-softening processes.
Groundwater : (1) Subsurface water occupying the saturation zone,
from which wells and springs are fed. In a strict sense the term
applies only to water below the water table. Also called phreatic
water, plerotic water.
Hardness : A characteristic of water, imparted by salts of calcium,
magnesium, and iron such as bicarbonates, carbonates, sulfates,
chlorides and nitrates, that cause curdling of soap and increased
consumption of soap, deposition of scale in boilers, damage in
some industrial processes, and sometimes objectionable taste. It
may be determined by a standard laboratory procedure or computed
from the amounts of calcium and magnesium as well as iron, alum-
inum, manganese, barium, strontium, and zinc, and is expressed as
equivalent calcium carbonate.
Head : (1) The height of the free surface of liquid above any
point in a hydraulic system; a measure of the pressure or force
exerted by the fluid. (2) The energy, either kinetic or poten-
tial, possessed by each unit weight of a liquid, expressed as the
vertical height through which a unit weight would have to fall
to release the average energy possessed. It is used in various
compound terms such as pressure head, velocity head, and loss of
head.
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Heavy metals : Metals that can be precipitated by hydrogen sulfide
in acid solution, for example, lead, silver, gold, mercury, bismuth,
copper.
Hydrologic cycle : The circuit of water movement from the atxnos—
phere to the earth and return to the atmosphere through various
stages or processes such as precipitation, interception, runoff,
infiltration, percolation, storage, evaporation, and transpiration.
Also called water cycle.
Imhoff cone : A cone—shaped graduated glass vessel used to measure
the appproximate volume of settleable solids in various liquids of
wastewater origin during various settling times.
Impoundment : A pond, lake, tank, basin, or other space, either
natural or created in whole or in part by the building of engineer—
ing structures, which is used for storage, regulation, and control
of water.
Ion : A charged atom, molecule, or radical, the migration of which
affects the transport of electricity through an electrolyte or,
to a certain extent, through a gas. An atom or molecule that has
lost or gained one or more electrons. By such ionization it becomes
electrically charged. An example is the alpha particle.
Ion exchan : (1) A chemical process involving reversible inter-
change of ions between a liquid and a solid but no radical change
in structure of the solid. (2) A chemical process in which ions
from two different molecules are exchanged.
Ion-exchange treatment : The use of ion—exchange materials such
as resin or zeolites to remove undesirable ions from a liquid
and substitute acceptable ions.
Ionization : The process of adding electrons to, or removing
electrons from, atoms or molecules, thereby creating ions. High
temperatures, electrical discharges, and nuclear radiation may
cause ionization.
Lagoon : (1) A shallow body of water, as a pond or lake, con
taming raw or partially treated wastewater.
Lagooning : The placement of solid or liquid material in a basin,
reservoir, or artificial impoundment for purposes of storage,
treatment, or disposal.
Land disposal : Disposal of wastewater onto land.
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Lime : Any of a family of chemicals consisting essentially of
calcium hydroxide made from limestone (calcite) which is composed
almost wholly of calcium carbonate or a mixture of calcium and
magnesium carbonate.
Lime and soda—ash process : A process for softening water by the
addition of lime and soda ash to form the insoluble compounds of
calcium carbonate and magnesium hydroxide.
Lime-soda softeniny : A process whereby calcium and magne-
sium ions are precipitated from water by reaction with lime and
soda ash.
Liquor : Water, wastewater, or any combination; commonly used
to designate liquid phase when other phases are present.
Loss of head : (1) The decrease in energy head between two
points resulting from friction, bends, obstructions, expansions,
or any other cause. It does not include changes in the elevation
of the hydraulic grade line unless the hydraulic and energy grade
lines parallel each other. (2) The difference between the total
heads at two points in a hydraulic system.
Loss-of-head gage : A gage, on a rapid sand filter, that indi-
cates the loss of head involved in the filtering operation,
whereby the operator is able to ascertain the need for filter
washing. Some gages are of the indicating-recording type.
Median : In a statistical array, the value having as many cases
larger in value as cases smaller in value.
Membrane filter : A filter made of plastic with a known pore dia-
meter. It is used in bacteriological examination of water.
Membrane selectivity : Ability of a membrane to allow passage of
only cations or anions. Usually expressed as a fraction, with
1.0 being the ideal value.
Methyl-orange alkalinity : A measure of total alkalinity of an
aqueous suspension or solution. It is measured by the quantity
of sulfuric acid required to bring the water pH to a value of
4.3, as indicated by the change in color of methyl orange. It
is expressed in milligrams CaCO3 per liter.
Milligrams per liter : A unit of concentration of water in
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wastewater constituent. It is 0.001 g of the constituent in
1,000 ml. of water. It has replaced the unit formerly used
commonly, parts per million, to which it is approximately equi-
valent, in reporting the results in water and wastewater analysis.
Navigable water : Any stream, lake, arm of the sea, or other
naturalThody of water that is actually navigable and that, by
itself or by its connections with other waters, is of sufficient
capacity to float watercraft for the purposes of commerce, trade,
transportation, or even pleasure for a period long enough to be
of commercial value; or any waters that have been declared navigable
by the Congress of the United States.
Neutralization : Reaction of acid or alkali with the opposite
reagent until the concentrations of hydrogen and hydroxyl ions
in the solution are approximately equal.
Nonionic surfactant : A general family of surfactants so
called because in solution the entire molecule remains associated.
Nonionic molecules orient themselves at surfaces not by an
electrical charge, but through separate grease-solubilizing and
water-soluble groups within the molecule.
Optimum point of coagulation : The hydrogen-ion concentration
(pH value) at which the best floc occurs in the shortest time
in the coagulation process.
Osmosis : The process of diffusion of a solvent through a semi-
permeable membrane from a solution of lower to one of higher
concentration.
Oxidation : The addition of oxygen to a compound. More generally,
any reaction which involves the loss of electrons from an atom.
Oxidizable salt : A salt occurring in solution in groundwater,
such as ferrous sulfate or carbonate or the corresponding salts
of iron and manganese, that may be oxidized to other forms and
that is deposited from solution upon exposure to air or to dis-
solved oxygen in surface water.
Parshall flume : A calibrated device developed by Parshall for
measuring the flow of liquid in an open conduit. It consists
essentially of a contracting length, a throat, and an expanding
length. At the throat is a sill over which the flow passes at
Belanger’s critical depth. The upper and lower heads are each
measured at a definite distance from the sill. The lower head
need not be measured unless the sill is submerged more than about
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67 percent.
Parts per million : The number of weight or volume units of a
minor constituent present with each one million units of the
major constituent of a solution or mixture. Formerly used to
express the results of most water and wastewater analyses, but
more recently replaced by the ratio milligrams per liter.
Percolation : (1) The flow or trickling of a liquid downward
through a contact or filtering medium. The liquid may or may
not fill the pores of the medium. Also called filtration.
(2) The movement or flow of water through the interstices or
the pores of a soil or other porous medium. (3) The movement
of groundwater in streamline flow in any direction through small
interconnected and saturated interstices of rock or earth,
principally of capillary size. (4) The water lost from an
unlined conduit through its sides and bed.
Permeability : The property of a material that permits appre-
ciable movement of water through it when it is saturated and the
movement is actuated by hydrostatic pressure of the magnitude
normally encountered in natural subsurface water. Perviousness
is sometimes used in the same sense as permeability.
p : The reciprocal of the logarithm of the hydrogen-ion concen-
tration. The concentration is the weight of hydrogen ions, in
grams, per liter of solution. Neutral water, for example, has
a pH value of 7 and a hydrogen—ion concentration of lO— .
Phenolphthalein alkalinity : A measure of the hydroxides plus
one half of the normal carbonates in aqueous suspension. Mea-
sured by the amount of sulfuric acid required to bring the water
to a pH value of 8.3, as indicated by a change in color of
phenolphthalein. It is expressed in parts per million of calcium
carbonate.
Postchlorination : The application of chlorine to water or
wastewater subsequent to any treatment, including prechiorination.
Potable water : Water that does not contain objectional pollution,
contamination, minerals, or infective agents and is considered
satisfactory for domestic consumption.
Potassium permanganate : A purple crystalline salt of potassium
and manganese used as an oxidizing agent for tastes and odors
or for iron or manganese removal (KMnO4).
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Prechlorination : The application of chlorine to water or
wastewater prior to any treatment.
Precipitate : (1) To condense and cause to fall as precipitation
as water vapor condenses and falls as rain. (2) The separation
from solution as a precipitate. (3) The substance precipitated.
Precipitation : (1) The total measurable supply of water received
directly from clouds as rain, snow, hail, or sleet, usually
expressed as depth in a day, month, or year, and designated as
daily, monthly, or annual precipitation. (2) The process by
which atmospheric moisture is discharged onto a land or water
surface. (3) The phenomenon that occurs when a substance held
in solution in a liquid passes out of solution into solid form.
Presettling : The process of sedimentation applied to a liquid
before subsequent treatment.
Pressure filter : A rapid sand filter of the closed type, having
a vertical or horizontal cylinder of iron, steel, wood, or other
material inserted in a pressure line,
Private water supply : A water supply not available to the
general public because it is located on or has outlets on pri-
vate property to which the public does not have access or legal
right of entry.
Rapid sand filter : A filter for the purification of water, in
which water that has been previously treated, usually by coag-
ulation and sedimentation, is passed downward through a filter-
ing medium. The medium consists of a layer of sand, prepared
anthracite coal, or other suitable material, usually 24-30 in.
thick, resting on a supporting bed of gravel or a porous medium
such as carborundum. The filtrate is removed by an underdrain—
age system which also distributes the wash water. The filter is
cleaned periodically by reversing the flow of the water upward
through the filtering medium, sometimes supplementing by mechan-
ical or air agitation during washing, to remove mud and other
impurities which have lodged in the sand. It is characterized
by a rapid rate of filtration, commonly from two to three gallons
per minute per square foot of filter area.
Raw wastewater : Wastewater before it receives any treatment.
Raw water : (1) Untreated water; usually water entering the first
treatment unit of a water treatment plant. (2) Water used as a
source of water supply taken from a natural or impounded body of
water, such as a stream, lake, pond, or underground aquifer.
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RecarbOflation : (1) The process of introducing carbon dioxide
as a final stage in the lime—soda ash softening process in order
to convert carbonates to bicarbonates and thereby stabilize the
solution against precipitation of carbonates. (2) The diffusion
of carbon dioxide gas through liquid to replace the carbon dioxide
removed by the addition of lime. (3) The diffusion of carbon
dioxide gas through a liquid to render the liquid stable with
respect to precipitation of dissolution of alkaline constituents.
Receiving body of water : A natural watercourse, lake, or ocean
into which treated or untreated wastewater is discharged.
Recharye : Addition of water to the zone of saturation from
precipitation, infiltration from surface streams, and other
sources.
Recharge well : A well constructed to conduct surface water or
other surplus water into an aquifer to increase the groundwater
supply. Sometimes called diffusion well.
Recycling : An operation in which a substance is passed through
the same series of processes, pipes, or vessels more than once.
Regeneration : (1) In ion exchange, the process of restoring
an ion-exchange material to the state employed for adsorption.
(2) The periodic restoration of exchange capacity of ion-exchange
media used in water treatment.
Regeneration efficiency : In ion exchange, regeneration level
divided by breakthrough capacity.
Reservoir : A pond, lake, tank, basin, or other space, either
natural or created in whole or in part by the building of engineer-
ing structures, which is used for storage, regulation, and control
of water. Sometimes called impoundment.
Revolving screen : A screen or rack in the form of a cylinder
or continuous belt, which is revolved mechanically. The
screenings are removed by water jets or automatic scrapers, or
manually.
Saline water : Water containing dissolved salts——usually from
10,000 to 33,000 mg/i.
Sanitary sewer : A sewer that carries liquid and water—carried
wastes from residences, commercial buildings, industrial plants,
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and institutions, together with minor quantities of ground-,
storm, and surface waters that are not admitted intentionally.
Schmutzdecke : A “dirty skin” or layer of flocculent material
that forms on the surface of a sand filter.
Screen : A device with openings, generally of uniform size, used
to retain or remove suspended or floating solids in flowing water
or wastewater and to prevent them from entering an intake or
passing a given point in a conduit. The screening element may
consist of parallel bars, rods, wires, grating wire mesh, or
perforated plate, and the openings may be of any shape, although
they are usually circular or rectangular.
Sedimentation : The process of subsidence and deposition of
suspended matter carried by water, wastewater, or other liquids,
by gravity. It is usually accomplished by reducing the velocity
of the liquid below the point at which it can transport the
suspended material. Also called settling.
Sedimentation basin : A basin or tank in which water or
wastewater containing settleable solids is retained to remove
by gravity a part of the suspended matter. Also called sedimen—
tation tank, settling basin, settling tank.
Sediment concentration : The ratio of the weight of the sediment
in a water sediment mixture to the total weight of the mixture.
Sometimes expressed as the ratio of the volume of sediment to the
volume of mixture. It is dimensionless and is usually expressed
in percentage, for high values of concentration in parts per
million for low values.
Sequestering agent : A chemical that causes the coordination
complex of certain phosphates with metallic ions in solution so
that they may no longer be precipitated. Hexametaphosphates are
an example: calcium soap precipitates are not produced from
hard water treated with them. Also, any agent that prevents an
ion from exhibiting its usual properties because of close com-
bination with an added material.
Settleable solids : (1) That matter in wastewater which will
not stay in suspension during a preselected settling period, such
as one hour, but either settles to the bottom or floats to the
top. (2) In the Imhoff cone test, the volume of matter that
settles to the bottom of the cone in one hour.
Settling tank : A basin or tank in which water or wastewater
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containing settleable solids is retained to remove by gravity a
part of the suspended matter. Also called sedimentation basin,
sedimentation tank, settling basin.
Slow sand filter : A filter for the purification of water in
which water without previous treatment is passed downward through
a filtering medium consisting of a layer of sand or other suit-
able material, usually finer than for a rapid sand filter and
from 24 to 40 in. thick. The filtrate is removed by an underdrain-
age system and the filter is cleaned by scraping off and replacing
the clogged layer. It is characterized by a slow rate of filtra-
tion, commonly 3—6 mgd/acre of filter area.
Sludge : (1) The accumulated solids separated from liquids, such
as water or wastewater, during processing, or deposits on bottoms
of streams or other bodies of water. (2) The precipitate result-
ing from chemical treatment, coagulation, or sedimentation of
water or wastewater.
Sludge cake : The sludge that has been dewatered by a treatment
process, the moisture content depending on type of sludge and
manner of treatment.
Sludge collector : A mechanical device for scraping the sludge
on the bottom of a settling tank to a sump from which it can be
drawn.
Sludge dewatering : The process of removing a part of the water
in sludge by any method such as draining, evaporation, pressing,
vacuum filtration, or centrifuging. It involves reducing from a
liquid to a solid condition rather than merely changing the
density of the liquid (concentration) on the one hand or drying
(as in a kiln) on the other.
Sludge dryer : A device for removal of a large percentage of
moisture from sludge or screenings by heat.
Sludge filter : A device in which wet sludge is partly dewatered
by means of vacuum or pressure.
Sludge solids : Dissolved or suspended solids in sludge.
Sodium carbonate : A salt used in water treatment to increase
the alkalinity or pH value of water or to neutralize acidity.
Chemical symbol is Na2CO3. Also called soda ash.
Sodium hexametaphosphate : Graham’s salt; sodium 1:1 phosphate
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glass; sodium polyphosphate; glassy sodium phosphate. The mole-
cu].e is currently considered to be an amorphous linear polymer of
more than six units; in the past (NaPO3)6 has been given as the
formula. It is soluble in water and insoluble in organic solvents.
In general, it is used as a sequestering, dispersing, and defloc-
culating agent.
Sodium hydroxide : A strong caustic chemical used in treatment
processes to neutralize acidity, increase alkalinity, or to raise
the pH value. Also known as caustic soda, sodium hydrate, lye,
and white caustic. Chemical symbol is NaOH.
Soft water : Water having a low concentration of calcium and
magnesium ions. According to U.S. Geological Survey criteria,
soft water is water having a hardness of 60 mg/i or less.
Soil orosity : The percentage of the soil (or rock) volume
that is not occupied by solid particles, including all pore
space filled with air and water. The total porosity may be cal-
culated from the formula:
Percent pore space = (1 - volume weight/specific gravity) x 100
Split treatment : The treatment of as large a part of water as
possible by water softening and the subsequent neutralization
of excess calcium hydroxide with untreated water or with water
treated in a different manner.
Sump : (1) A tank or pit that receives drainage and stores it
temporarily, and from which the drainage is pumped or ejected.
(2) A tank or pit that receives liquids.
Sump_pum : A mechanism used for removing water or wastewater
from a suinp or wet well; it may be energized by air, water,
steam, or electric motor. Ejectors and submerged centrifugal
pumps, either float— or manually controlled, are often used for
the purpose.
Su rnatant: The liquid standing above a sediment or precipitate.
Surface wash : A supplementary method of washing the filtering
mediizm of a rapid sand filter by applying water under pressure at
or near the surface of the sand by means of a system of stationary
or rotating jets.
Suspended solids : (1) Solids that either float on the surface
of, or areijn suspension in, water, wastewater, or other liquids,
and which are largely removable by laboratory filtering. (2) The
quantity of material removed from wastewater in a laboratory test,
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as prescribed in “Standard Methods for Examination of Water
and Wastewater” and referred to as nonfilterable residue.
Titration : The determination of constituent in a known volume
of solution by the measured addition of a solution of known
strength to completion of the reaction as signalled by observation
of an end point.
Total solids : The sum of dissolved and undisso].ved constituents
in water or wastewater, usually stated in milligrams per liter.
Turbidixueter : An instrument for measurement of turbidity, in
which a standard suspension usually is used for reference.
Turbidity : (1) A condition in water or wastewater caused by
the presence of suspended matter, resulting in the scattering and
absorption of light rays. (2) A measure of fine suspended matter
in liquids. (3) An analytical quantity usually reported in
arbitrary turbidity units determined by measurements of light
diffraction.
Unaccounted—for water : Water taken from a source into a
distribution system that is not delivered to the consumers or
otherwise accounted for.
Volatile solids : The quantity of solids in water, wastewater,
or other liquids, lost on ignition of the dry solids at 600°C.
Wash water : Water used to wash filter beds in a rapid sand
filter.
Wash—water gutter : A trough or gutter used to carry away the
water that has washed the sand in a rapid sand filter. Also
called wash—water trough.
Wash—water rate : The rate at which wash water is applied to a
rapid sand filter during the washing process. Usually expressed
as the rise of water in the filter in inches per minute or gallons
per minute per square foot.
Wash-water tank : An elevated tank at a rapid sand filtration
plant, into which water is pumped at a rate such that the tank
swill be filled between washings and set at a height such that
the wash water will have a pressure of about 15 psi at the
strainers.
Waste : Something that is superfluous or rejected; something
that can no longer be used for its originally intended purpose.
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Wastewater disposal : The act of disposing of wastewater by
any method. Not synonymous with wastewater treatment.
Wastewater outfall : The outlet or structure through which
wastewater is finally discharged.
Wastewater reclamation : Processing of wastewater for
reuse.
Wastewater treatment : Any process to which wastewater is
subjected in order to remove or alter its objectional constituents
and thus render it less offensive or dangerous.
Watercourse : (1) A natural or artificial channel for passage
of water. (2) A running stream of water. (3) A natural stream
fed from permanent or natural sources, including rivers, creeks,
runs, and rivulets. There must be a stream, usually flowing in
a particular direction (though it need not flow continuously) in
a definite channel, having a bed or banks and usually discharging
into some other stream or body of water.
Water quality : The chemical, physical, and biological character-
istics of water with respect to its suitability for a particular
purpose. The same water may be of good quality for one purpose
or use, and bad for another, depending on its characteristics and
the requirements for the particular use.
Water softening : The process of removing from water, in whole or
in part, those cations which produce hardness.
Water supply : (1) In general, the sources of water for public
or private uses. When U.S. Public Health Service and state stan-
dards have been met, the supply is termed “an approved water
supply.” (2) The furnishing of a good potable water under sat-
isfactory pressure for domestic, commercial, industrial, and public
service, and an adequate quantity of water under reasonable pres-
sure for fire fighting.
Water supply facilities : The works, structures, equipment, and
processes required to supply and treat water for domestic,
industrial, and fire use.
Water supp ly source : A stream, lake, spring, or aquifer
from which a supply of water is or can be obtained.
Water supply system : (1) Collectively, all property
involved in a water utility, including land, water source, col—
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lection systems, dams and hydraulic structures, water lines
and appurtenances, pumping system, treatment works, and general
properties. (2) In plumbing, the water distribution system in
a building or complex of buildings, including appurtenances.
Water system : Collectively, all of the property involved in
the operat ion of a water utility, including land, water lines
and appurtenances, pumping stations, treatment plants, and
general property.
Water treatment : The filtration or conditioning of water to
render it acceptable for a specific use.
Waterway : (1) Any body of water, other than the open sea,
that is or can be used by boats as a means of travel. (2)
Any natural or artificial channel or depression in the surface
of the earth that provides a course for water flowing either
continuously or intermittently.
Weir : A device that has a crest and some side containment of
known geometric shape, such as a V 1 trapezoid, or rectangle, and
is used to measure flow of liquid. The liquid surface is exposed
to the atmosphere. Flow is related to upstream height of water
above the crest, to position of crest with respect to downstream
water surface, and to geometry of the weir opening.
Well : (1) An artificial excavation that derives water from the
interstices of the rocks or soil which it penetrates. (2) A
shaft or hole into which water may be conducted by ditches to
drain other portions of a piece of work.
Well field : A tract of land containing a number of wells.
Zeolite : A group of hydrated aluminum complex silicates, either
natural or synthetic, with cation—exchange properties.
Zeolite filter : In water softening, a filter designed to remove
certain chemical constituents from water by base exchange, where
the zeolite takes the place of the filtering medium.
Zeolite process : The process of softening water by passing it
through a substance known in general as a zeolite, which exchanges
sodium ions for hardness constituents in the water.
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TABLE 14
CONVERSION FACTORS
Multiply (English Units) by To Obtain (Metric Units)
English Unit Abbreviation Conversion Abbreviation Metric Unit
acre ac 0.405 ha hectares
acre — feet ac ft 1233.5 Cu m cubic meters
barrel (376 ib) bbl 0.207 kkg metric tons
British Thermal Unit BTU 0.252 kg cal kilogram — calories
British Thermal Unit/pound BTU/lb 0.555 kg cal/kg kilogram calories/kilogram
cubic feet/minute cfm 0.028 cu rn/mm cubic meters/minute
cubic feet/second cfs 1.7 cu rn/mm cubic meters/minute
cubic feet cu ft 0.028 cu rn cubic meters
cubic feet cu ft 28.32 1 liters
cubic inches cu in 16.39 cu cm cubic centimeters
degree Fahrenheit O f 0.555(°F—32) 1 °C degree Centigrade
feet ft 0.3048 in meters
gallon gal 3.785 1 liters
gallon/minute gpm 0.0631 I/sec liters/second
horsepower hp 0.7457 kw kilowatts
inches 2.54 cm centimeters
inches of mercury in Hg 0.03342 atm atmospheres
pounds lb 0.454 kg kilograms
million gallons/day MGD 3,785 cu rn/day cubic meters/day
mile mi 1.609 km kilometer
pound/square inch (gauge) psig (0.06805 psig +1)’ atm atmospheres (absolute)
square feet sq ft 0.0929 sq in square meters
square inches sq in 6 452 sq cm square centimeters
tons (short) t 0.907 kkg metric tons (1000 kilograms)
yard y 0.9144 in meters
______________________
‘ . 3
1. Actual conversion, not a multiplier.
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