FLUORIDATION
 ENGINEERING
   Do not WEED. This document
   should be retained in the EPA
   Region 5 Library Collection.
           ENVIRONMENTAL PROTECTION AGENCY
                OFFICE qp WATER
                HAZARDOUS MATERIALS
               WATER SUPPLY DIVISION

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Fluoridation  Engineering  Manual
                        by

                    Ervin Bellack
        ENVIRONMENTAL PROTECTION AGENCY

          Office of Water and Hazardous Materials

                 Water Supply Division

                      1972

                   Reraint 1974
                   U.S. Invironmentai Protection Agency
                   He^ion 5, Library (PL-12J)
                   77 West Jackson Boufevard, 12th Ftooi
                        ,  !L  60604-3590

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                              Preface
   The fluoridation of water supplies has been termed one of the most signifi-
cant health  advances  in recent years. This manual  is intended to assist local
and  state engineers in  designing fluoridation installations, and water  plant
personnel in operating them, so that the fullest advantage of the  benefits of
fluoridation can be achieved.
   No matter how  well a fluoridation installation is designed, it is ultimately
the "man at the water plant" who insures its successful operation by his aware-
ness of  the  importance  of his task and by his conscientious adherence to the
principles of good water plant practice. This manual is particularly dedicated
to his assistance.
   The addition of fluorides to water supplies involves, more than the addition
of other chemicals, particular emphasis on accurate feed rates. The philosophy,
"if a little is good,  more will be better," or the false economy in feeding less
than the optimum amount, have no place in the practice of fluoridation. The
optimum concentrations have been arrived  at by countless studies involving
millions of people, and these  same studies have shown that failure to  conform
to the  optimum  concentration defeats  the whole  purpose of  "controlled"
fluoridation. It is hoped  that  this manual will not only  place  the desired
stress on this aspect, but will provide assistance to the operator in maintaining
that optimum concentration.
   The  planner of a  fluoridation installation should carefully  consider  the
options  open to him,  among them the choice of chemical and thus the choice
of equipment. The quantity of water pumped may affect these choices, as will
considerations of  economy, convenience, and location. While it is the intention
of this manual to  provide information on the criteria governing  the selection of
an optimal system,  there is no intent to take the place of expert advice where
such is needed.

                                          Ervin Bellack
                                          Chemist
                                          Office of Water and Hazardous Materials
                                          Water Supply Division
                                          Environmental ftotection Agency

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                        Contents
  I    INTRODUCTION	    1
           Natural Fluoridation	    1
           Blending	    2
           Controlled Fluoridation	    3
 II    COMPOUNDS USED IN CONTROLLED FLUORIDATION ...    4
           Sodium Fluoride	    4
           Fluosilicic Acid  	    5
           Sodium Silicofluoride  	    6
           Other Fluoride Chemicals	    7
III    FEEDERS USED FOR ADDING FLUORIDES  	    9
           Solution Feeders  	    9
           Dry Feeders  	   12
           Testing Procedures for Dry Feeders  	   18
           Checking Particle Size  	   19
           Auxiliary Equipment  	   19
           Meters  	   20
           Scales	   20
           Softeners	   21
           Mixers	   21
           Dissolving Tanks	   22
           Flow Meters	   24
           Day Tanks	   24
           Bag Loaders	   25
           Dust Collectors and Wet Scrubbers	   25
           Alarms	   25
           Vacuum Breakers  	   25
           Hoppers 	-	   26
           Weight Recorders	   26
           Controllers   	   27
           Eductors	   27
           Pumps  	   27
           Timers  	   28
           Hopper Agitators  	   28
           Flow-Splitters	   28
IV    PREPARATION OF FLUORIDE SOLUTIONS  	   31
           Manual Technique	   31

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             Automatic Devices	   33
             Calculations Involving Solutions	   42
  V     SELECTING THE OPTIMAL FLUORIDATION SYSTEM  	   47
             Location of Feeder 	   47
             Fluoride Injection Point	   50
             Type of Feeder and Chemical  	   51
             Chemical Availability	   54
             Chemical Storage and Handling 	   56
             Cross-Connection Considerations	   57
             Automatic Proportioning (Pacing)  	   57
             Installation	   59
             Solution Feeder Installations	   59
             Dry Feeder Installations	   59
             Valves and Meters	   60
             Installation Plans	   60
 VI     CONTROL AND SURVEILLANCE	   63
             Analytical Procedures	   63
             The Standard Methods	   63
             Alizarin Visual Method	   64
             SPADNS Method	   64
             Electrode Method	   65
             Test Kits	   66
             Sampling	   66
             Calculations and Record-Keeping	   66
             Monitors	   68
             Trouble-Shooting  	   72
             Low Fluoride Readings	   73
             High Fluoride Readings	   73
             Varying Fluoride Readings	   74
             Other Problems	   75
 VII     MAINTENANCE	   77
             Cleaning and Lubrication  	   77
             Spare Parts	   77
             Inspection and Re-Calibration	   77
             Leaks 	   78
             Precipitates 	   78
             Storage Area	   79
             Laboratory	   79
VIII     SAFETY AND HAZARDS IN HANDLING FLUORIDE
        CHEMICALS	   81
             Safety Equipment and Chemical Handling	   81
             Ingestion	   81
             Inhalation  	   81
             Safety Precautions	   82
             Acid Handling	   82
                                  VI

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                 First Aid	  82
                 Fluoride Exposure Symptoms	  82
                 Treatment	  83
       IX    TECHNICAL PROBLEMS ATTRIBUTED TO
             FLUORIDATION	  85
                 Corrosion	•. . .  85
                 Encrustations	  85
                 Fluoride Losses	  86
                 Compatibility	  86
                 Tastes and Odors	  87
                 Industrial Processes	  87
                 Environmental Effects	  87
        X    REFERENCES AND SUGGESTED READING	  89
APPENDIX    ABBREVIATIONS  	  93
                                   vn

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                          Illustrations
Figure                                                           page
   1       Positive-displacement Solution Feeders	   10
   2       Screw-Type Volumetric Dry Feeder  	   13
   3       Roll-Type Volumetric Dry Feeder  	   14
   4       Belt-Type Gravimetric Dry Feeder  	16
   5       Gravimetric Dry Feeder - "Loss-in-Weight" Type	   17
   6       Typical Arrangements of Fluoride Feeders and
             Auxiliary Components	   29
   7       Typical Arrangement of Dry Feed Hoppers and
             Dust Collectors   	   30
   8       BIF Downflow Saturator  	   35
   9       W & T Downflow Saturator	   36
  10       Precision Upflow Saturator	   37
  11       Checking Delivery Rate of a Solution Feeder  	   44
  12       Fluoridation Check-List	   48
  13       Acid Feed Installation 	   51
  14       Solution Feed Installation	   52
  15       Diluted Acid Feed System	   53
  16       Dry Feed Installation with Volumetric Feeder  	   54
  17       Dry Feed Installation with Gravimetric Feeder	   55
  18       Fluoridation Nomograph  	   70
  19       Fluoridation Alignment Chart   	   71
Table
   1       Characteristics of Fluoride Compounds	    8
   2       Detention Time of Sodium Silicofluoride in Dissolving Tanks   23
   3       Preparation of Solutions of Sodium Fluoride  	   34
   4       Recommended Maximum Feed Rates for Downflow Sodium
             Fluoride Saturator	   38
   5       Specific Gravity of Fluosilicic Acid Solutions at 17.5°C  ...   45
   6       Fluoride Calculation Factors   	   69
                                 Vlll

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                           Chapter  I
INTRODUCTION
   Although the  dental profession  can claim the credit for first  ascribing
dental  mottling to  some unknown  constituent of drinking  water, it  was a
water plant chemist who first implicated the element fluorine. Initially, it was
thought that if fluorine was indeed the element responsible in some way for
tooth discoloration, it was  a  deficiency  rather than an excess which brought
about the mottling. As analytical techniques were refined and data began to
accumulate, the true role of fluoride in water was revealed. Now we know that
a deficiency of fluoride can lead to extensive tooth decay, and that  an excess
is the cause of mottling, or as it is now known, dental fluorosis.
   The element, fluorine, ranks  thirteenth in  abundance in the earth's crust,
and  twelfth  in the  oceans. It is also thirteenth in abundance in the human
body,  and although the concentrations  vary widely,  it is  found in  every
water supply used by man for drinking purposes.  Because of the wide  distri-
bution of the element, the  difficulty in attempting to grow plants or animals
without it and its role in the formation of human bones and teeth, fluorine (as
the fluoride ion)  is now considered  to be essential to the normal growth and
development of man.
   Fluorine, like chlorine a gaseous halogen, is never found in the free state but
always occurs  in  combination with other elements as fluoride compounds.
In water solution, these compounds dissociate into ions, and it is these fluoride
ions which are analytically determined and are the-form in which fluorine is
assimilated by man. The fluoride compounds most commonly found in the
earth's crust are fluorspar and apatite, calcium fluoride and a complex calcium
fluoride-phosphate,  respectively. However, in water only the fluoride ion (F~)
can be detected without more than an educated guess as to the nature of the
compound from  which the ion  was derived. Thus, since there is no way one
fluoride ion can be distinguished from another, there is no difference between
fluoride ions dissolved from the earth's  crust and fluoride ions occurring in
water  due to  the deliberate  addition  of fluoride  compounds  by  man.

NATURAL  FLUORIDATION
   After the cause of dental  fluorosis was ascertained,  and  the  concomitant
observation was made that dental caries was relatively absent in the presence of
fluorosis,  it followed  logically that  these observations should be verified by
examining the teeth of children in many areas and analyzing  the drinking
water supplies  in those areas. The examination of the teeth of many thousands
of children, and the fluoride analysis of hundreds of water supplies  showed a

                                    1

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remarkable relationship between the concentration of waterborne fluoride and
the incidence of dental caries. The relationship, or actually three  distinct
relationships, are as follows:

   1. When the fluoride level  exceeds about  1.5 ppm, any further  increase
      does not  significantly decrease the incidence of decayed, missing or filled
      teeth,  but does  increase  the occurrence  and  severity of mottling.
   2. At a fluoride level of approximately  1.0 ppm, the optimum occurs —
      maximum reduction  in caries with no aesthetically significant mottling.
   3. At  fluoride levels  below  1.0 ppm  some  benefits occur, but  caries
      reduction  is not so great and gradually decreases as the fluoride levels
      decrease until, as zero fluoride is approached, no observable improvement
      occurs.
   Since,  as  noted above,  all water supplies contain measurable amounts of
fluoride, it can  be said that all water supplies are fluoridated. However, since
only  those water supplies  containing fluoride concentrations in excess  of 0.7
ppm  (in the  continental United  States)  have appreciable dental significance,
ordinarily these are the ones we refer to as being naturally fluoridated.
   Thus, fluoridation is not  something new, as many people suppose,  but is
actually  a process  performed  by nature for many centuries. What  we now
refer to as "controlled fluoridation" is only man's attempt to overcome the
vagaries of nature in her random and sometimes inefficient process of putting
fluoride ions  in our drinking water.

BLENDING
   It was actually  many years after the role of fluoride in water was first
determined that the idea of imitating the natural process was first suggested,
and  the onset  of World War  II resulted  in another delay before  the first
demonstration  project could begin. During the interval, hundreds of studies
were undertaken for  the purpose of verifying the fluoride-caries relationships
and  for determining the validity of proposed  experimental controlled  fluori-
dation of municipal water  supplies.
   Although  it  is  generally accepted that  the  first controlled fluoridation
projects  began  in 1945 in the cities of Grand Rapids, Michigan, Newburgh,
New York, and Brantford, Ontario,  it was several years earlier that at least one
city, without attendant fanfare, began efforts to adjust the fluoride content of
its water supply in order to bring the level to the optimum for dental  benefits.
The  feat  was accomplished  by blending the water from two sources  —  one
providing water with  a natural fluoride content above the optimum, the other
providing water deficient in natural fluoride content. Since  then, other cities
have adopted the blending process, either for  raising the fluoride level  in the
major source of water by  adding water  from  a high-fluoride well,  or for
reducing the overall fluoride level by adding water from a low-fluoride  source
to an existing  high-fluoride well supply. Unfortunately, the achievement of
controlled fluoridation by the blending of water from two sources is limited
to those areas where high-fluoride waters occur. When blending is possible, the

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water consumers gain more  than  dental benefits and economic advantages —
they also conserve  the supply of drinking water by making use of quantities of
water which otherwise would not be considered acceptable.

CONTROLLED  FLUORIDATION
   The third type  of fluoridation, in  addition  to  natural and that achieved
by blending, is the one in which the  fluoride  content of a water supply is
adjusted by the deliberate addition of a chemical  compound which provides
fluoride ions in water solution. This type  of fluoridation, beginning with the
three cities mentioned above,  is  now practiced in  approximately 5,000
communities serving over 80 million persons. With the residents of almost 3,000
additional communities consuming water containing at least 0.7 ppm  fluoride
from natural sources, this means that 56% of the nation's population on public
water supplies (90 million persons) had access to water with a dentally signi-
ficant concentration of fluoride as of 1970.
   The graduation  of controlled fluoridation from an experimental procedure
into  an established water plant practice has not  been without problems. Few,
if  any, of these problems were of an  engineering  nature,  for  the controlled
addition of a chemical to a water supply can hardly be considered something
new. For  the  most part,  adding  fluoride is just like adding  any of several
different chemicals commonly  added  as part of  the  usual water  plant
practices. The feeding equipment is  in general  the same equipment used for
feeding alum, soda ash, lime, or other chemicals. Only the nature of the chemi-
cal and  the  purpose for which it is  added are  different,  and therein lies the
problem.
   For some reason, fluoridation has  aroused a controversy out of all propor-
tion  to  the simple premise  of adjusting  the concentration of a mineral in
which a particular  water is deficient. Even the  premise  is not new - waters
which are deficient in alkalinity  or hardness are  often  supplemented  with
appropriate  compounds  at  the water  plant and  no  one  seems to mind.
Apparently, it is just the word, "fluoride," which has stirred the imagination
of so many concerned citizens. The  confusion  with the word, "fluorine," is
understandable  for fluoridation was originally termed, "fluorination," and
fluorine, of course, is a toxic and  highly reactive gas. But the controversy goes
beyond  this, to such areas as mass medication, legal  rights, and a host of others
too numerous to mention. It  may be of interest to point out that chlorination
received a similar reception, and that  resistance to this type of water treatment
still exists today.
   As far  as the water  plant operator or engineer need  be concerned, the
addition of fluoride to a water supply is well within his province,  and it is his
duty to  follow the directives of the health officials and governing  body of his
community  in  not  just  adding  fluorides, but  in doing  the  job right

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                          Chapter  II
                   Compounds   Used   In
                 Controlled  Fluoridation
SODIUM  FLUORIDE
   Theoretically, any compound  which forms fluoride ions in water solution
can be used  for adjusting upward the fluoride content of a water supply.
However, there are  several practical considerations involved in selecting com-
pounds. First, the compound must have sufficient solubility to permit  its use
in routine water plant practice. Second, the cation to which the fluoride ion is
attached  must  not  have  any undesirable characteristics. Third,  the material
should be relatively inexpensive, and readily available in grades of size and
purity which are suitable for the intended use.
   The first fluoride compound  used in controlled fluoridation was sodium
fluoride, selected not only on the basis of the above criteria, but also because
its  toxicity  and physiological effects  had been so  thoroughly studied.  In
addition, sodium fluoride is the reference standard used in measuring fluoride
concentration. Once fluoridation became an  established practice, other com-
pounds came into use, but  sodium fluoride, because of its unique physical
characteristics in addition to its  other  advantages in  some situations, is still
one of the  most widely used chemicals.
   Sodium fluoride is a white, odorless material available either as a powder or
in the form of crystals of various sizes. Its formula weight is  42.00, specific
gravity 2.79, and  its solubility  practically constant  at  4.0  grams per 100
milliliters of water at temperatures generally encountered in water-treatment
practice. The pH (hydrogen-ion concentration) of solution varies with the type
and amount  of impurities, but  solutions prepared from the usual grades of
sodium fluoride exhibit pH's near neutrality.  It is available in purities ranging
from 90 to over 98 percent,  the impurities consisting of water, free acid or
alkali, sodium silicofluoride, sulfites and iron, plus traces of other substances.
   Powdered  sodium  fluoride is produced in different densities,  the  light
grade  weighing  less than 65 pounds  per cubic foot and the heavy  grade
weighing about  90 pounds per cubic foot. A typical sieve analysis of powdered
sodium fluoride shows 99 percent through  200 mesh and 97 percent through
325 mesh.  Crystalline sodium fluoride is produced  in various size ranges,
usually designated  as coarse, fine and extra-fine, but  some manufacturers can
furnish lots in specific mesh sizes. The crystalline type is preferred when manual
handling is involved, since the absence of fine powder  results in a minimum of
dust.

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   Sodium fluoride is manufactured by Allied Chemical Corporation, Industrial
Chemicals Division; J.T. Baker Chemical  Company; Chemtech Corporation;
and Olin Chemicals, but is usually sold through distributors who are located in
most cities. In 1970, sodium fluoride sold for 18 to 25 cents per pound, F.O.B.
point of manufacture, the price depending largely on the quantity purchased.
Normal packing is in 100 Ib. multi-ply paper bags or fiber drums holding up to
400 pounds.
   Sodium fluoride has a number of  other  industrial uses,  one of which
requires that the material be tinted a blue color. Some state regulations specify
that  only  tinted sodium fluoride be used in order to distinguish it from other
water-treatment chemicals.

FLUOSILICIC ACID
   Fluosilicic Acid, also known as hydrofluosilicic, hexafluosilicic, silicofluoric,
or even "silly" acid, is a 20 to 35% aqueous solution of H2SiF6 with a formula
weight of 144.08. It is a colorless (when pure), transparent, fuming, corrosive
liquid  having  a  pungent  odor and an  irritating action on the skin.  Upon
vaporizing, the acid decomposes to form hydrofluoric acid and silicon tetra-
fluoride, and under conditions where an equilibrium between the fluosilicic
acid  and  its decomposition products  exist, such as at the  surface of strong
solutions, etching of glass will  occur. All solutions of fluosilicic acid exhibit a
low  pH,  and  even at  a  concentration low  enough  to produce 1  ppm  of
fluoride ion there can be a significant  depression of the pH of poorly buffered
waters.  (Example:  Water containing 30 ppm IDS, pH 6.5. After H2SiF6 was
added to produce 1 ppm F, pH dropped to 6.2.)
   Fluosilicic acid is manufactured by  two different  processes, resulting in
products having differing characteristics. The largest proportion of the acid is a
by-product of phosphate  fertilizer manufacture, and this  type  is  relatively
impure  and seldom exceeds 30% strength. A smaller amount of acid is pre-
pared from hydrofluoric acid and silica,  resulting  in  a purer product at a
slightly higher strength.  Acid prepared from phosphate rock contains colloidal
silica in varying amounts, and  while this is of little consequence when the acid
is used as received, dilution results in the formation of a visible precipitate of
the silica. Some  suppliers of fluosilicic acid sell a "fortified" acid, which has
had a small amount of hydrofluoric acid added to it to prevent the formation
of the  precipitate. Acid prepared from  hydrofluoric acid and silica does not
normally form a precipitate when it is diluted.
   Fluosilicic acid  is  produced by many fertilizer manufacturers, but only a
limited  number of these recover the acid  for  sale  as such. Among the latter
group  are  Stauffer Chemical  Company, Fertilizer Division; U.S. Industrial
Chemicals Company, Division of National Distillers and Chemical Corporation
(through Conservation Chemical Company of  Illinois); USS Agri-Chemicals
Division of U.S. Steel  Corporation; Agrico Chemical Company, Division  of
Continental Oil Company; W.R. Grace,  Agricultural Products Division; Sobin
Chemicals, Inc.;  and Kerr-McGee Chemical  Corporation. Harshaw Chemical
Company,  Division of Kewanee Oil Company, produces  acid made by the
hydrofluoric acid-silica process.

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   Since  fluosilicic acid contains a high proportion of water, shipping large
quantities can be quite expensive. Larger users can purchase the acid directly
from the manufacturers in bulk (tank car or tank truck) lots, but smaller users
must  obtain the  acid  from  distributors who  usually pack it in drums or
polyethylene carboys. In 1970,  fluosilicic  acid in bulk sold for $51.00 to
$58.00 per  ton, 23% basis, F.O.B. point of manufacture. Smaller quantities
sold for  8 to 15 cents per  pound, 30% basis. This method of pricing comes
about due to the variable characteristics of the acid as it comes from fertilizer
plants. Rather than  attempt to adjust the acid strength  to some  uniform
figure, producers sell the acid as it comes, and the price is adjusted to com-
pensate for acid strength above or below  the  quoted figure. Note  that the
"23% basis" type of pricing  applies only  to bulk quantities. It is the usual
practice  for the supplier to furnish assay reports of the  acid strength of each
lot.
   Like other fluoride compounds, fluosilicic acid has a number of industrial
uses, one of which is in the manufacture of hydrofluoric acid, and thus in an
indirect way, other fluoride compounds.
SODIUM SILICOFLUORIDE
   Fluosilicic  acid can readily be  converted into various  salts, and one of
these,  sodium  silicofluoride,  is  the most  widely  used chemical for  water
fluoridation. Undoubtedly,  the principal reason for the popularity is  one of
economics,  for  sodium silicofluoride   is  the  cheapest of  the  compounds
currently in use. The conversion of fluosilicic  acid, essentially  a  low-cost
by-product which contains too much water to permit economical shipping, to a
dry material containing a high percentage of available fluoride, results in a com-
pound having most of the advantages of the acid with few of its disadvantages.
Once it was shown that silicofluorides form  fluoride ions in water  solution as
readily as do simple  fluoride compounds,  and  that there  is  no difference in
physiological  effects,  the  silicofluorides (and  fluosilicic  acid) were rapidly
accepted  for water fluoridation, and in some cases displaced the use of sodium
fluoride.
   Sodium silicofluoride is a white, odorless crystalline powder. Its molecular
weight is 1 S8.06 and its specific gravity is 2.679. Its solubility varies from 0.44
grams per 100 milliliters of water at 0° Centigrade to 2.45 grams per 100 mini-
liters at  100°C. The pH's of solutions are definitely on the acid side, saturated
solutions usually exhibiting a  pH between 3.0  and 4.0.  Sodium silicofluoride
is available  in purities of 98% or better, the principal irnpuiities being water,
chlorides and silica.
   Sodium silicofluoride is sold in two commercial forms — regular and fluffy.
The former has a density of about 85 pounds per cubic foot while the latter
has a density of about 65 pounds pei cubic foot. A typical sieve analysis of the
regular grade  shows more than 99% through a 200-mesh sieve and more than
10% through a  325-mesh  sieve. For  best  feeding characteristics, other size
specifications may be selected, experience having shown that a low  moisture
content plus a relatively narrow si/e distribution results  in a material which is
handled better by dry feeders.

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   Sodium silicofluoride  is  manufactured  by  Agrico Chemical  Company,
Division of Continental Oil Company; Kerr-McGee Chemical Corporation; Olin
Chemicals; Tennessee  Corporation,  (Cities Service),  Industrial  Marketing
Division, and  possibly other manufacturers of  fluosilicic acid.  Considerable
quantities of the material are imported, and numerous distributors handle it. In
1970, prices ranged from 8 to 10 cents per pound F.O.B. point of manufacture.
Sodium silicofluoride is normally packed  in bags and drums similar to  those
used for sodium fluoride. Blue-tinted material is sometimes available.

OTHER FLUORIDE COMPOUNDS
   Ammonium silicofluoride, magnesium silicofluoride, potassium fluoride and
calcium fluoride  (fluorspar) either are being or have  been used for water
fluoridation,  and at one time  hydrofluoric acid  was also used. Each has
particular properties which make the material desirable in a specific application,
but none of these have wide-spread application.
   Ammonium silicofluoride has the peculiar advantage of supplying all or
part of the ammonium ion necessary for the production of chloramines when
this  form of  disinfectant is  preferred to chlorine  in  a particular situation.
   Magnesium silicofluoride  and potassium fluoride have  the advantage of
extremely high solubility,  of particular importance in such applications as
school fluoridation  when  infrequent  refills of the solution container are
desired. In addition, potassium fluoride is quite compatible with potassium
hypochlorite, so a mixture of the two solutions can be used for  simultaneous
fluoridation and chlorination.
   Calcium fluoride (fluorspar) is the  cheapest of the  compounds ever used
for fluoridation but it is  also the least soluble. It has been successfully fed by
first dissolving it in alum solution, and then utilizing the resultant  solution to
supply both  the  alum needed for  coagulation  and the fluoride  ion. Some
attempts have been made to feed fluorspar directly in the form of ultra-fine
powder, on the premise that  the powder would eventually dissolve or at least
remain in suspension until consumed.
   Hydrofluoric acid, although low  in cost, presents too much of a safety and
corrosion hazard to be acceptable for water  fluoridation, although  it has been
used in a specially designed installation.
   A number of other fluoride compounds have been suggested for use in watei
fluoridation,  among them ammonium and sodium bifluoride.  These  latter
materials have advantages of solubility  and cost,  but their potential corrosive-
ness has hindered acceptance.
   The  chemical  and physical characteristics, costs,  shipping  containers,
storage requirements, etc., of the three commonly-used  fluoride compounds
are summarized  in  Table 1. The selection  of  a compound for a particular
application can be based at least in  part on the information in this table, but
such intangible factors  as  personal  preference  often  influence  the  ultimate
decision.

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   The manufacturers of the various fluoride compounds can provide technical
data and  specification sheets which  will assist the  prospective purchaser in
selecting the appropriate grade  of  chemical  for the type  of feeder used.
Another helpful adjunct is a sieve shaker and a set of testing sieves, so the user
of a dry chemical can identify a product which feeds to his satisfaction and so
he can then specify that product in future purchases. Sieve shakers sell for less
than $100 (for the hand-powered models) up to over $500 (for motor-driven
models equipped with timers). Sieves  are variable in  price, depending on such
factors as  material of construction and size of openings. A sieve shaker and set
of sieves will find many other applications in a water plant,  ranging from
grading  filter sand to testing many of the treatment chemicals.
           Table 1. CHARACTERISTICS OF FLUORIDE COMPOUNDS
Hem
Form
Molecular Weight
Commercial Purity, %
Fluoride Ion, %
(100% pure material)
Lb. required per MG for 1.0
ppm F at indicated purity
pH of Saturated Solution
Sodium Ion contributed at
1.0 ppm F, ppm
Storage Space, cu. ft. per
1000 Ib. F ion
Solubility g per 100 g Water,
at 25°C
Weight Ib pei cu ft
Cost:
Cents per Ib
Cents per Ib available F
Shipping containers
Sodium Fluoride
NaF
Powder or Crystal
42.00
90-98
45.25
18.8 (98%)
7.6
1.17
22-34
4.05
65-90
18-25
41-57
100-lb bags
125-400-lb
fiber drums, bulk
Sodium Silicofluoride
Na2SiF6
Powder or
Very Fine Crystal
188.05
98-99
60.7
14.0 (98.5%)
3.5
0.40
23-30
0.762
55-72
8-10
13-17
100-lb bags
125-400-lb
fiber drums, bulk
Fluosilicic Acid
H2SiF6
Liquid
144.08
22-30
79.2
35.2 (30%)
1.2 (1% solution)
0.00
54-73
Infinite
10.5 Ib/gal (30%)
2'/2 - 15
14-63
13-gal carboys
55-gal drums, bulk

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                         Chapter  III

       Feeders  Used   For  Adding Fluorides

   A  chemical  feeder,  such as the  type used for adding  fluorides or other
substances  to a water supply, is a mechanical device which  measures out
quantities of the  chemical and administers them to the water  at the pre-set
rate.  Feeders are designated as either solution or dry types,  depending on
whether  the  chemical  is measured as volumes of solution or as volumes or
weights of dry chemical. In either case,  the chemical is in the form of a solution
when it is introduced into the  water. Dry feeders are further sub-divided into
two categories, volumetric and gravimetric, depending on whether the chemical
is measured by volume or weight. It should be again noted that fluoride feeders
are not something new, but are the same as feeders which have been used for
many  years  for measuring and administering chemicals not  only in water
plants, but also in many industrial applications.
SOLUTION FEEDERS
   In  general, a solution feeder is nothing more than a small pump, of which
there  are almost  unlimited varieties.  For feeding fluoride solutions, almost
every  type which has ever been  used  for feeding other water treatment
chemicals has fJund application, with at most only minor modification in
construction details.
   If  there is indeed any requirement for a fluoride  solution feeder which
distinguishes it  from feeders for other purposes, it is accuracy  and constancy
of delivery, for the optimum fluoride  level has been prescribed between very
narrow limits  and thus requires that the fluoride be added in precise proportion
to the quantity of water being treated. This requirement favors the so-called
positive-displacement pump or  feeder, defined as a feeder which delivers a
specific volume of liquid for each stroke of a piston or rotation of an impeller.
Of course, very few feeders deliver replicate volumes under all conditions, for
such factors as  pressure and viscosity  can affect the volume displaced by the
driving member of the pump.  However, by using  fluoride  solutions of fixed
strength  and  by feeding  against a fixed pressure, the positive displacement
feeder has shown sufficient reliability  for this purpose.
   For delivery against pressure, there are two  general types of solution
feeders — the piston feeder and the diaphragm feeder. In the former type, a
reciprocating  piston  alternately forces solution out  of a chamber and then,
on its return stroke, refills the chamber by pulling solution from  a reservoir. In
the latter type, a flexible diaphragm driven either directly  or indirectly  by a

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                                              STROKE-POSITION
                                              CONNECTING ROD

                                                  ECCENTRIC
OUTLET
                                                                                   INLET
                                                                            DIAPHRAGM
                                                       POSITIVE-DISPLACEMENT
                                                         DIAPHRAGM PUMP
POSITIVE-DISPLACEMENT PLUNGER PUMP
                   CAM AND PISTON
                                                       GEAR
      VANE SLIDING
                                                           VANE SWINGING
                   Figure 1. Positive Displacement Solution Feeders
                                            10

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mechanical linkage performs a similar function. When the mechanical drive for
the feeder is  an electric motor,  a  gear  box or system  of belts and pulleys
determines  the  number of strokes in a given  time  interval.  Pneumatic  or
hydraulic drives are  also available, and these permit the use of a meter con-
tactor to provide stroking which is in direct  proportion to water flow instead
of being at a fixed rate.
   For gravity feed, there  are several types of solution feeders which operate
on the paddle-wheel principle. A rotating wheel  equipped with small buckets
dips  solution from a constant-head  tank and discharges the solution into the
water to be treated. Rate  of feed can be varied by changing the size of the
buckets or their number, by changing  the rate of rotation of the wheel, or by
varying the proportion of the bucket contents which is emptied.
   Ordinarily,  such solution feeding devices as centrifugal pumps, pot feeders,
or head tank and orifice are not used for fluoridation because of their relative
inaccuracy.  However,  in  addition  to  the  piston and  diaphragm  feeders
mentioned above, there are several types of rotary pumps which qualify as
positive-displacement feeders. These include gear, swinging-vane,  sliding-vane,
oscillating  screw,  eccentric  and cam pumps  and  various  modifications  of
these. Figure  1  illustrates various types of solution  feeders.
   The criteria used  in  selecting  a feeder are capacity,  corrosion resistance,
pressure capability, and of course  accuracy and durability. A point to consider
is that most feeders perform most accurately  near mid-range of both stroke
length  and  stroking frequency  and should  be selected  accordingly. At the
extremely low feed rates required by small installations, the diaphragm feeders
are superior to  the  piston types.  Most  feeders come equipped  with  plastic
heads and resilient check-valves, both of which are satisfactory  for fluoride
solutions  unless  the pressure  is  over   100#/sq. in.  For  higher  pressures,
corrosion-resistant alloys, such as 316  stainless steel or Carpenter 20 alloy, are
required for feeder head construction.
   Since  most  solution feeders are  adjustable both for stroke  length, which
determines the volume  of liquid delivered per stroke, and stroke frequency,
usually expressed in strokes-per-minute (SPM), both factors should be consid-
ered in selecting the size of feeder for a particular  application.
An example of feeder selection follows:
Problem:  Select a solution feeder for the following application:
   Water flow - 200 gpm @ 75 psi
   Fluoride source — saturator (produces a 4% sodium fluoride solution,
                    18,000 ppm as F-)
   Desiied fluoride level —  1.0 ppm
Calculated solution feed rate:  Rj XCj = R2  X C2
   where R!   =  water rate, in gal/min
        Ci    =  fluoride level, in ppm
        R2    =  solution feed rate, in gal/min (the unknown quantity, in this
                 case)
        C2    =  solution strength, in ppm

                                     11

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   then: 200 gal/min X 1.0 ppm = (x) X 18,000 ppm
           _  200 gal/min X 1.0 ppm = 0.011 gal/min
        W=          18,000 ppm

        0.011j£X60min = 0.67 gal
             mm      ~EF         nr
Feeders available:
Manufacturer A, Model  1203,  three-step pulley drive.
   Delivery rate: @ 13 SPM (Strokes per Minute), 0.02 - 0.3 gph @ 100 psi
                @ 26 SPM, 0.04 - 0.6 gph
                @ 46 SPM, 0.06-1.06 gph
Manufacturer B, Model 5701-111, single speed (37.5 SPM)
   Delivery rate: 0.5 - 5 gph maximum
Manufacturer C, Model  12000, electronic stroking control (3 - 72 SPM)
   Delivery rate: 0.01 -1.6 gph
Selection: The required delivery rate falls within the range of all three feeders,
so all are possibly acceptable. However, the delivery rate would require the
highest stroke  frequency of  the  feeder  from Manufacturer  A, a situation
which, while not unacceptable, is not preferred. Similarly, the  delivery rate is
too close to the minimum of the feeder from Manufacturer B to be completely
satisfactory. The feeder from  Manufacturer C appears  to be the best choice,
since  the delivery  rate  is approximately in the middle of its range. A further
investigation into the feeder characteristics should be made in order to ascertain
the combination of output per  stroke and stroke frequency which would be
required, and to verify  that neither of these is near the extremes of the feeder
capability.
   In  addition  to  the  feeder  specifications and operating data contained in
manufacturers' bulletins, assistance in feeder selection can be obtained directly
from  most manufacturers, some of whom supply a questionnaire which, when
completed  by  the  prospective purchaser, provides  detailed information for
more  thorough evaluation of requirements.

DRY FEEDERS
   A dry  feeder is a device for metering a dry, powdered chemical at a predeter-
mined rate. It can be based on volume or weight measurements, the former type
being known as a volumetric while the latter is known as a gravimetric feeder.
Generally, volumetric dry feeders  are simpler, less expensive, deliver slightly
smaller quantities  and  are slightly less accurate. Gravimetric dry feeders are
capable of delivering extremely large quantities in a given time period, are
extremely accurate, more expensive, and are readily adapted to recording and
automatic control. By  attaching a weighing and controlling mechanism to a
volumetric feeder, it  is possible  to convert  one  to  a gravimetric type.
                                    12

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           MOTOR


    GEAR REDUCER

     FEED  RATE
REGISTER AND  FEED
 ADJUSTING KNOB
         SOLUTION
         CHAMBER
                                                                  HOPPER
 ROTATING AND
 RECIPROCATING
 FEED  SCREW
VACUUM  BREAKER
 WATER INLET
                                                                  JET  MIXER
                          Figure 2. Screw-Type Volumetric Dry Feeder

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MOTOR-DRIVEN
  AGITATOR
                                       FLOAT
                                      HOPPER
                                   GUIDE VANES
                                        FEED  SLIDE
                                     FEED ROLLS
                             TO DISSOLVING CHAMBER '
                Figure 3. Roll-Type Volumetric Dry Feeder
                                  14

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   Volumetric dry feeders  are available in several types, distinguished by the
means used for measuring  and delivering the dry chemical. Among the types
are the rotating roller, rotating disc, rotating and/or reciprocating screw, star
wheel, moving  belt, vibratory  pan,  oscillating hopper and combinations of
these principles. See Figures 2 & 3  for illustrations of some  of the types of
volumetric dry feeders.
   There are two general types of gravimetric  dry feeders —  those based on
loss-in-weight of the feeder hopper and those which are based on the weight of
material  on  a  section  of  moving  belt.  Many gravimetric dry feeders  also
incorporate some of the features of volumetric feeders, in that they have a
rotary feed mechanism between the hopper and the weighing section  or use a
mechanical vibrator to move chemicals out of the hopper. Since ultimately it is
the weight of material per unit of time that is measured and regulated, such
variables as material density  or consistency have no effect on feed rate. This
accounts for the  extreme accuracy of which these  feeders are capable. Gravi-
metric dry feeders are illustrated in Figures 4 and 5.
   The stream or ribbon of dry material which is discharged from a dry feeder
falls into a dissolving chamber where it is dissolved in water (see the section on
Auxiliary Equipment). The solution thus prepared either falls by gravity into an
open flume or clear well, or is transferred by a continuously-running pump or
eductor into a pressure main.
   The choice between  a volumetric or gravimetric feeder is largely governed
by  size and economics. The gravimetrics are more expensive but have greater
capacity,  and are also basically more accurate. The  selection of  one of the
types of volumetric feeders  involves several factors,  among  them size,  cost,
accuracy,  and personal  preference.
   Dry  feeders are  designed  to handle  powdered  materials, but not  all such
materials are handled with  equal ease. For example, material which is too fine
will  flow  like a liquid right through  the  measuring mechanism ("flooding").
Some materials will form an arch in the hopper and when the arch collapses,
emit a cloud of dust and then flood  the feeder. Other powders, either hydro-
scopic by  nature (water-attracters)  or  produced with a  significant  moisture
content, tend to form lumps which will affect the feed rate or not be fed at all.
For  most  consistent feeding, a narrow size distribution  and  a  low  moisture
content is the best. A study of feeding problems  with sodium silicofluoride
resulted in the development of a "feedability index" (F):
F =  100-(A+B+ IOC),   where A is the percentage  retained on  a 100-mesh
                        sieve, B is the percentage  passing  through a 325-
                        mesh sieve, and  C  is  the  percentage of moisture.
In almost every case, a feedability index below  80 proved to be unsatisfactory,
80 - 90 good, 90-100 excellent.
Examples: A  shipment  of sodium silicofluoride was sampled and subjected
to  particle-size  analysis (see  the  section on  particle size testing)  with the
following  results: 3%  retained  on  100-mesh  sieve,  9%  passed through the

                                    15

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3
I'
•u
re3
I
ro
re
fr
            FEED
          SECTION
            GATE
        POSITIONER
           GATE
                                        YOKE
                                                MAGNET
                                                           POISE
                                                         WEIGHT
                                                                     SCALE BEAM

                                                                             MERCURY
                                                                             SWITCHES
                                                                            WEIGH BELT
                                           WEIGH DECK
                                            FLEXURES

                                        STATIONARY  DECKS

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 TRANSITION
 HOPPER
HELIX TYPE
-FEEDER MECH.
VARIABLE RATE-
SPEED SET FROM
PHOTOCELL
                                                          CONTROL PANEL
                                                           RATE SETTER
                                                          -SCALE BEAM
                                                            VARIABLE SPEED
                                                            FEEDER MOTOR
           Figure 5. Gravimetric Dry Feeder - "Loss-in-Weight" Type



 325-mesh sieve. The moisture content was 0.05%.  Applying the feedability
 formula:

   F  = 100 - [3 + 9 + (10 X .05)]  = 87.5

   (Although all figures are percentages, the feedability index is an  abstract
   number.)

 This material showed good feeding characteristics.
   A second  shipment  of  sodium  silicofluoride, when sampled  and tested
 similarly, gave  the  following results:  1%  retained  on 100-mesh  sieve,  20%
 passed  through the  325-mesh sieve. The moisture content  again was 0.05%.

 From the feedability formula:

   F  = 100 - (1 + 20 + 0.5) = 78.5

 As could be expected, this material was troublesome, the excess of ultra-fine
 powder (the  portion  passing through  the  325-mesh  sieve) causing  arching,
 flooding, and  dust  problems.
                                    17

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   The AWWA Standards for Sodium Silicofluoride (and Sodium  Fluoride)
limit the moisture content of these materials, and although the particle sizes
are not precisely defined, the statement is made that the materials "shall be
suitable for feeding  with a conventional dry-feed machine  as used in water
treatment." In many cases, individual  water plants have devised size specifica-
tions  which assist them in purchasing chemicals handled adequately by the
feeders on hand. Ordinarily, chemicals specified as meeting AWWA Standards
produce minimal feeding problems, but such is  not the case with some non-
standard or imported chemicals.
   Other problems related  to the operation of a dry feeder  are mentioned in
the sections on auxiliary equipment and maintenance. As with solution feeders,
manufacturers'  bulletins and  direct technical  assistance can be utilized in the
selection of appropriate equipment for a particular application. The criterion
used in selecting the size of a dry feeder is similar to that used in selecting a
solution feeder — they both operate most reliably  when the delivery rate is near
mid-range. All too often, dry feeders  are used on water supplies which are so
small  that the feeder is operating at dead minimum or even below this rate, this
latter feat being accomplished by  equipping the  feeder with a cycle timer.
Obviously, accurate and uniform fluoride feed rates cannot be expected under
these  conditions.

TESTING PROCEDURES FOR DRY FEEDERS
   To  determine the accuracy and reliability  of  a dry feeder, a small balance
or scales and a stop-watch, or a watch with a sweep-second hand, are required.
Insert  a shallow pan or sheet of  cardboard between the measuring mechanism
and dissolving chamber of the feeder while the feeder is operating,  making sure
that all the chemical which feeds through will be collected. Collect the chemical
which is fed in several short periods, for example,  five periods of  five minutes
each.  Weigh each of the amounts collected and the total. Provided the weigh-
ings and timings are accurate, the individual samples will indicate the uniformity
of feed, and the  total will indicate the  accuracy of feed rate.
   Example:   Weights of sodium silicofluoride collected  in 5-minute periods:
              35 grams
              35
              34
              36
              35
Total:       175 grams      Average:  35 grams/minute
Uniformity:  35 i 1 gram in 5 minutes (about 3% variation).
^  .          35 grams  X  60 min  = 420 grams/hr or 0.925 Ibs/hr
Feed rate:      g&  .        —r—
                5 mm          hr
   The uniformity of feed in this case would be acceptable. If fluoride levels
are to be  maintained within  10%, the feeder  delivery rate should  certainly be
maintained at the highest  accuracy possible. Repeating a test, as above, but
with  longer  sampling periods,  would  tend  to show smaller percentage  of
variation,  provided,  of course,  the feeder is in good order.

                                     18

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CHECKING PARTICLE SIZE
   Dry chemicals are  often furnished in specified particle sizes, and to insure
freedom from handling or feeding problems, it can be helpful to determine the
degree of adherence to specifications. For example, crystalline sodium fluoride
for use in a down-flow saturator should be in the  20-60 mesh range, and sodium
silicofluoride should be relatively free from extremely coarse or extremely fine
particles for best feeding characteristics.
   The size  of particles is usually determined  with  a set  of standard sieves,
the size  designation  then referring  to the range of sieve sizes which best
describes those particles. For example, a 20-60  specification means that most
particles pass  through a size  20 sieve but are retained by a size  60 sieve (the
larger the sieve number, the smaller the openings).
   The testing procedure is determined somewhat by the apparatus used, but
generally a set of standard testing sieves is stacked, coarsest on top and progres-
sively finer toward the bottom, above a collecting pan. A weighed amount of
material is placed in the uppermost sieve, the set  of sieves shaken gently
(mechanically) for about five minutes, and then the portion collected  by each
sieve and the pan weighed separately.
   Example:   100 grams of sodium silicofluoride,  sieves:
              100, 140, 200, 325, and pan.
   Results:    On 100 mesh    10 grams
              on 140          25
              on 200          30
              on 325          30
              in pan            5
   Assuming the moisture content of this particular material was 0.05% or less,
applying the feedability formula would give the following results:
   F= 100-(10 + 5 + 0.5) = 87.5
This result would indicate that the material should feed satisfactorily through a
dry feeder.

AUXILIARY EQUIPMENT
   For the simplest system, one involving a manually prepared  fluoride solution
and a proportioning pump feeding the solution into a  water supply flowing at a
fixed rate, the requirements for auxiliary equipment  are minimal. A dissolving
tank, either a paddle or electric  mixer for  stirring,  a platform  scale  and the
feeder itself are all the equipment needed. A vacuum breaker, to prevent pulling
un-metered quantities of fluoride solution into the  system in the event of a low-
pressure situation, can be incorporated into the  design of the feeder. Extras
could include an alarm system for detecting and reporting low solution levels,
a softener for removing hardness  constituents from the solution water, a small
meter for measuring the amount of water used  in solution preparation, etc. As
the size  and  complexity  of  the  fluoridation system grows,  the number and
complexity  of  these pieces  of  auxiliary  equipment  increases, and their
desirability  becomes  transformed to  necessity.

                                    19

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METERS
   The water meter, often absent in  the  smallest water plants, is one of the
primary requisites for accurate fluoride feeding.  If the supply is un-metered,
calculation of fluoride feed rate  will  have to be by guesswork, and even the
selection of an  appropriate feeder will have to be somewhat chancy. The type
of meter used for water flow depends largely on  the flow rate; disc or piston
meters are used for  low flows, and compound, propeller or magnetic meters
used for the higher flow rates. Unfortunately, meters are usually sold by pipe
size, not  flow rate, so all too often the water meter is grossly oversized for the
flow rate  through it. Since  most meters are least accurate at the  low end of
their  measurement range,  the result is  that  water flow is not  accurately
measured. The  remedy is to select a meter no larger  than necessary to handle
the maximum  flow  rates expected,  even if the pipe and meter  sizes don't
match. In some cases this may involve the use of pipe reducers to adapt the
water main to the meter, a practice which is acceptable provided pressure loss
as a result of this arrangement is not excessive.
   Other applications for water meters, besides the  main supply  meters dis-
cussed above, are  on supply lines for solution make-up water. In the case  of
the sodium fluoride saturator, a meter is a necessity, for without one it would
be impossible to  calculate the  fluoride feed  rate. Since water usage rate in a
saturator  installation is minimal, the meter must be the smallest available
(usually %").

SCALES
   In any  fluoridation  installation, except one  based on  a sodium fluoride
saturator, scales are a necessity for either weighing the quantity of dry  material
to be used in solution preparation, weighing the quantity of solution fed, or for
weighing the quantity of dry fluoride compound or fluosilicic acid delivered
by the appropriate feeder.
   The type of scales can vary from a small household-type  used for weighing
a pound or two of sodium  fluoride to be used in solution preparation to the
complex built-in  mechanism of a gravimetric dry feeder. The most generally
applicable type is the platform scale,  on which can be  placed a solution tank,
carboy of acid, or an entire  volumetric dry feeder. Although the scales may be
specifically designed for the application, as are those supplied by manufacturers
with volumetric dry  feeders, in many cases an ordinary hardware store type of
scales  will  be  perfectly  satisfactory.  Some minor modifications,  such as
removing  the wheels or rotating  the  beam, may be necessary, but as long as
the scales have  sufficient capacity and sensitivity there is no  reason why they
cannot be  used. Capacity and  sensitivity  are  the only serious considerations,
and  the points to remember are  that the scale must be capable of weighing
the tank and its  contents when full  or the volumetric feeder and its hopper
when full, with measurements to  the  nearest pound  or better. For small scales
used for measuring sodium fluoride to be  used in manual solution preparation,
sensitivity to the nearest ounce should be sufficient.

                                    20

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   No particular  problems should be encountered when mounting equipment
 on platform scales, except when there  is connection to a water line,  or the
 discharge line from the dissolving chamber of a volumetric dry feeder is fixed
 in place. It should be remembered that this dissolving chamber, or solution pot,
 is also mounted  on the scale platform and thus all connections to it must be
 flexible enough to permit the scale to operate.

 SOFTENERS
   When a fluoridation system involving the use of sodium fluoride solutions
 is being  considered, it should be remembered  that, while sodium fluoride is
 quite soluble, the  fluorides of calcium and magnesium  are not. Thus, the
 fluoride ions in solution will combine with calcium and magnesium ions in the
 make-up water and form a precipitate which can clog the feeder, the injection
 port, the feeder suction line, the saturator bed, etc. For this reason, water used
 for sodium fluoride dissolution should  be  softened  whenever  the hardness
 exceeds 75 ppm,  or even if the hardness is less than this figure but the amount
 of labor involved in  clearing  stoppages or  removing scale  is objectionable.
 Remember, the entire water supply need not be softened — only the water used
 for solution preparation.
   Two types of  softening treatment are available - ion exchange and the use
 of polyphosphates (calgon, micromet, etc.). Since the volume of water  to be
 softened is  usually  quite small, a household type of zeolite water softener is
 usually adequate. This type of softener operates on the ion-exchange principle,
 and  can be  installed directly in the pipeline used for solution make-up. When
 softening capacity is exhausted, the zeolite (or synthetic resin) can be regener-
 ated with brine made from common salt.
   Polyphosphates can be used for sequestering (keeping in solution) calcium
 and magnesium, the amount required usually amounting to 7 to 15 mg/1. The
 polyphosphate may be added directly into the solution tank, but if an eductor
 is used  both  the eductor water and the dissolving  water should be treated.
 (See the section  on eductors.)  In the latter case, some type of feeder will be
 required for adding the polyphosphate.

MIXERS
   Whenever solutions  are prepared, whether it be  manual preparation  of
 sodium fluoride solutions, dilution of fluosilicic acid, or the dissolution of the
 output of dry feeder,  it is particularly important that the solution be homo-
geneous.  Slurries must not be tolerated in  the  feeding of fluorides,  since
undissolved  fluoride compound can go  into solution  subsequently, causing a
higher-than-optimum situation, or if  the fluoride compound  remains undis-
solved, a lower-than-optimum  situation  will result. Undissolved  material can
also  result in the  clogging of feeders and other devices having small openings,
and if allowed to accumulate, results in  considerable waste.
   In the manual preparation of solutions, thorough  mixing is a must.  Even
when a  solution  is being  diluted, as in  the  preparation of fluosilicic acid

                                   21

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dilutions, the two liquids must be thoroughly mixed, since liquids of differing
specific gravities tend to stratify, and such stratification could result in feeding
a solution  too concentrated, or at the other extreme, plain water. Sodium
fluoride is quite soluble, but even the preparation of the most dilute solutions
requires sufficient agitation. Undissolved material will remain in the bottom of
the dissolving tank  while  a too-dilute solution is  being  fed, and even if it
gradually dissolves, the strong solution formed at the bottom of the tank will
tend to remain in its  own stratum.
   While a paddle, accompanied by sufficient "elbow grease," (manual mixing)
will suffice  for the preparation of the dilute solution, a mechanical mixer is
preferred. Mixers come  in various sizes,  with shafts and  propellers made  of
various materials. A fractional horse-power mixer  with a  stainless-steel shaft
and propeller will be satisfactory for sodium fluoride solutions,  and a  similar
mixer with a corrosion-resistant alloy or plastic-coated shaft and  propeller will
handle fluosilicic  acid.
   The dissolution  of sodium silicofluoride m the solution pot of a dry feeder
can be accomplished by  a jet mixer, but again a mechanical mixer is preferred.
Because of  the low solubility  of  sodium silicofluoride, particularly in cold
water, and the limited retention time available for dissolution, violent agitation
is  a  must to prevent  the  discharge  of a slurry.  Preferred materials of con-
struction are 316 stainless steel or plastic-coated steel.

DISSOLVING  TANKS
   The  dry  material discharged from a  volumetric or gravimetric feeder is
continuously dissolved  in  a chamber beneath  the feeder, from whence the
clear  solution falls or is pumped into the water to be  treated. This chamber,
variously referred to as the solution pot, dissolver tank, solution tank,  or
dissolving chamber,  may be a  part of the feeder or a separate  entity. While
some chemicals  can be  fed directly into flumes  or  basins  without using a
dissolving tank, the  fluorides are not among them. The necessity for accurate
feed rates will not permit the possibility of slurry feed or  the  formation of
build-ups of undissolved dry material.
   Dissolving tanks come in sizes from 5  gallons up, the size often determined
by  the size  of  the feeder under which they are  mounted.  If there is a choice,
the largest  size available  should be  used for fluoride compounds.  Mixing of the
chemical with water is accomplished by a system  of baffles, and agitation can
be provided by a paddle driven by jets  of water, or,  as  mentioned above, a
mechanical  mixer. Experience  has shown that  the  jet  mixer  is  not nearly so
dependable   as   a  good mechanical mixer,  even under  ideal  conditions.
   The failure  to produce a clear, homogeneous  solution discharge fiom the
dissolving tank of a  dry  feeder indicates that (1) the dissolving chamber is too
small, (2) the detention  time is too shoit, (3) too little solution  water is being
provided, (4) agitation is insufficient, or (5) diy chemical is short-circuiting and
is not Deing adequately mixed wiin (lie water.

-------
   Detention time, the length of time the fluoride compound remains in the
dissolving tank, has been determined experimentally to be a minimum of five
minutes to provide a concentration which is one-fourth the  maximum solu-
bility,  provided  the  water temperature is above 60°F and the chemical is  in
the form  of  a fine powder. If the chemical is in  the form of crystals or the
water temperature is below 60°F, the dissolving time should be  doubled; if
both, the  time should be tripled  (i.e. 15 minutes). Table 2 gives some relation-
ships between detention  time, dissolving-chamber  capacity,  and  water flow
rate  for sodium silicofluoride dry  feed rates.

       Table  2. DETENTION TIME OF SODIUM SILICOFLUORIDE
                       IN DISSOLVING TANKS

Feed Rate
#/hr
1
2
3
4
5
6
7
8
9
10
20

Min. Water Flow Rate
Required for Solution
1 gpm
2
3
4
5
6
7
8
9
10
20

5
5 min










Dissolving Tank Size (Gal.)
10
10 min
5









25
25 min
12.5
^.3
6.2
5






50
50 mm
25
16.7
12.5
10
8.3
7.1
6.2
5.5
5

100
100 min
50
33.3
25
20
16.7
14.3
12.5
11.1
10
5
   In order to use the table, read across (horizontally) from the feed rate which comes
   closest to your specific application. The figure in the next column will be the
   minimum water flow rate required for dissolving the chemical. The next figure, or
   figures, will be the detention time for each given dissolving  tank  size. Where no
   figure is given, the detention time for the particular tank size would have been less
   than five minutes and would therefore be inadequate. Remember, if the water flow
   rate is increased above  the specified minimum, the detention time is decreased
   proportionately, and a larger tank may be required.
   Short-cii cutting  is essentially a function of the dissolving tank design, and
is more likely to occur in the smaller size tanks. The remedy, if short-circuiting
does occur, is to add baffles to the tank so that the path of the chemical to the
outlet  of  the  chambei  is  sufficiently  circuitous  to  provide the  necessary
detention  time  for solution.
   Since the  usual atrangement for a dissolving tank is to have the water inlet
below  the  outlet, a cross-connection requiring adequate safety measures exists.
If the dissolving tank is not already equipped with a coirectly-placed vacuum-
breaker, one should be installed on the water inlet as ncai  as possible to the
point of entry. If there is a solenoid or manually operated valve on  the water
inlet line, the vacuum breaker must be installed between the valve and the tank
for adequate cross-connection protection.

-------
FLOW METERS
   A  flow  meter,  in  contrast to an ordinary water meter, measures rate of
flow rather than volume of flow. While those used for measuring flow rates in
large  pipelines operate on various differential-pressure principles, the flow
meters applicable to small flows are usually based on the lifting of a spherical
or cylindrical  "float" by the hydraulic  action of a flowing fluid in a vertical
tube.
   In  a water plant where the water output is variable,  as in cases where more
than one pump is used, a flow-meter on the main serves two purposes: it will
indicate the flow rates on which the fluoride feeder or feeders must operate,
and if so designed, will provide an electrical, pneumatic  or hydraulic signal
which can  be  used to adjust the feeder output to correspond to  changes in
water flow rate. This  type of flow meter is discussed further in the section on
system selection.
   The flow meter  used in small pipelines, often known as a rotameter, finds
application on the water  supply to the dissolving chamber of a dry feeder.
Since, as mentioned above, detention time is a function  of water  flow rate.
among other things, the  flow must be regulated and maintained at the  pre-
scribed figure.
   The flow meter  must be selected on  the basis of pipe size,  nature of fluid
(water)  and particularly, the  range of flows expected.  For greatest accuracy,
the range of the flow meter should coincide with the range of flows which will
be encountered in the particular installation.

DAY TANKS
   A day tank is just what the name implies — a tank which holds a day's supply
of a particular water treatment chemical. It is a convenient, and often necessary,
means for isolating the supply of fluoride solution which will be fed during one
day or shift at the water plant.
   The day tank is a necessity when feeding fluosilicic acid, particularly if the
acid is received and stored in a large tank. In order to provide a record of the
weight of acid fed,  a small quantity of the acid is pumped or siphoned into a
small  tank  mounted on a platform scale, and it is from this day tank that the
fluosilicic acid is fed into the water system. A similar arrangement can be used
for sodium fluoride solutions or fluosilicic acid dilutions. A large batch of the
solution or dilution can be prepared, and a smaller amount transferred to the
day tank mounted  on the platform scale.  This system reduces the  amount of
labor  for preparing solutions  or  dilutions,  and  is an additional  safeguard
against over-feeding.
   Materials of construction  for day tanks are determined by the chemical
being used, but plastics such as polyethylene are generally applicable. The tank
can be provided with graduations or some sort of gauge so that  approximate
volume measurements can be used. Commercial mixing tanks are available with
the day tank mounted on the cover, a convenient means for  preparing fluosilicic
acid dilutions, but this arrangement  does not permit weighing the acid, so
volume  measurements must be relied upon.

                                    24

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BAG LOADERS
   When the hopper of a dry feeder is directly above the feeder, that is, when
the operator has to lift the chemical to a considerable height in order to fill the
hopper, a  bag loader  is  more a necessity  than a convenience. A bag loader is
essentially a hopper extension large enough to hold a single 100-pound bag of
chemical. The front of the loader is hinged so that it will swing down to a more
accessible  height.  The operator places a bag in the hinged section,  opens the
bag and then swings the section back into position. This device not only lessens
the labor required to empty a bag, but also eliminates  a good part of the dust
resulting from bag emptying.

DUST COLLECTORS AND WET SCRUBBERS
   The handling of powdered dry chemicals invariably results in the generation
of various quantities of dust. When the quantities of fluoride compounds being
handled are small, ordinary care  will minimize  the dust  problem,  and good
housekeeping plus an exhaust fan will  keep  the storage and loading area
relatively dust-free.  However, when  larger quantities (i.e., more  than one bag
at a time) are  handled,  dust  prevention and collection  facilities  should be
provided.
   A dust canopy, completely enclosing the hopper-filling area,  and provided
with an exhaust fan,  will prevent the dissemination of dust throughout the
loading area. To prevent the escape of dust into the atmosphere and thence into
the area surrounding the water plant, dust filters can be incorporated into the
exhaust system.
   Dust collectors and  exhaust fans are sometimes  incorporated into the
hoppers of  the larger dry  feeders.
   Wet scrubbers  are  a means  for removing dust from exhausted air. The air
flows through a chamber in which there is a continuous water spray. The air is
thus "scrubbed" clean and  the erstwhile dust particles  are dissolved or carried
down the drain  by water.

ALARMS
   To prevent underfeeding or even loss of feed, alarm systems can be included
in either solution or dry feed systems. The alarm will serve to alert the operator
to the fact that the level of solution in the day tank is low, or that it is time to
add another bag of dry chemical to a hopper.  An alarm can also  notify the
operator that the  water supply to a  saturator or to a dissolving tank has either
stopped or diminished.
   The alarms are based on level switches, flow switches, pressure switches, etc.

VACUUM BREAKERS
   Any  time there is  a water connection to a  chemical  solution there is the
possibility of a  cross-connection. This can be in  the supply line to a saturator
or dissolving tank, or in the  discharge from either of these  or any solution
feeder.

                                   25

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   The  simplest method for  preventing a potential siphonage situation is to
provide an  air-gap in  the  line.  When pressure  is high enough to make an
air-gap  impractical, (as in  the supply line  to a  dissolving chamber) a  device
known  as a vacuum-breaker  must be used. A vacuum-breaker is essentially a
valve which is kept closed by  water pressure, but  when the water pressure fails,
the valve opens to atmosphere allowing air  to be drawn into the system rather
than potentially hazardous solutions.
   For  utmost safety,  the  vacuum breaker  should be installed as close  to the
chemical solution as possible, and especially must be elevated above the lip of
the tank and on the discharge  side of the last control valve.
   In those States where  mechanical vacuum  breakers are not  permitted,
potential siphonage hazards can be eliminated by other means. See the section
on cross-connections.

HOPPERS
   Most dry feeders come equipped with  a  hopper, but for  larger installations
additional hopper capacity is often desired. Quite often this entails extension of
the existing hopper up to the floor above, not only increasing hopper capacity
but making  it  easier to fill.  If at  all feasible, the chemical storage should be on
the floor  above the feeder.  If the extension hopper  reaches  to about  12"
above the floor of the storage room the edge of the hopper can  serve as a
fulcrum point as an aid to upending drums or barrels.
   In small plants, it is desirable  to have the chemical hopper large enough to
hold slightly more  than  the entire shipping container of chemical. Thus the
hopper  will not be completely empty before there is enough room in it for
the contents of a'fresh bag or drum. By loading an entire container in this
manner, there  will be less handling of chemical and a saving of time. There will
be less dusting, with improved working conditions. There will be less chance of
spillage, with  consequent saving  of chemical. By not allowing the hopper to
become completely empty, there will be  less chance of arching and flooding,
and also less chance for an  interruption in feed.
   Hoppers, whether those  supplied  with the feeder or those constructed at
the plant, may require  vibrators to insure uniform feed. A rotary valve can be
installed between the hopper and the feeder  to prevent flooding, and a gate can
be installed  in  the  extension hopper to limit the  amount of material falling to
the feeder hopper at any given time.

WEIGHT RECORDERS
   Whenever a platform scale is used to measure the amount  of dry chemical
or solution  fed during a given period, a  recorder can  be attached  so that a
record of the  weight of chemical  fed can  be obtained. Many volumetric dry
feeders  have such recorders available  as an accessory (along  with the scales) so
that the loss-of-weight  feature makes the  feeder somewhat equivalent to a
gravimetric dry feeder.

                                   26

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CONTROLLERS
   The  feed  rate of a dry  feeder or metering pump can be automatically
adjusted to be proportional to water flow, a feature which is almost indis-
pensable when the water flow rate is extremely variable. When there is only one
service pump, operating at a fixed  rate, the feeders can be tied electrically to
the pump operation and the fluoride feed will remain in the predetermined
proportion. When two pumps are used, two separate feeders can be used, or one
feeder can be adjusted manually each time  the second pump cuts in or out.
For more than two pumps, or where there is no fixed delivery rate, manual
adjustment becomes impractical.
   Controllers are based on  the use of some type of primary flow measuring
device, such as an orifice  plate, venturi meter, or magnetic meter. The con-
troller adapts the indication of flow rate to an electrical, pneumatic or hydraulic
impulse which  in  turn  activates  an adjusting mechanism  on the feeder.
   To go one  step further, an automatic continuous analyzer can be used to
monitor the treated water, and the analysis information used in place of flow
information. The signal from the analyzer recorder is used to adjust the feeder
to produce a pre-determined fluoride concentration in a closed-loop arrange-
ment. This system, although admittedly expensive and not entirely foolproof,
has the advantages of compensating  not  only for changes  in water flow rate,
but also  for  changes in raw-water fluoride  levels, chemical  purity,  etc.

EDUCTORS
   An eductor is a device which uses water pressure  and flow for transporting
other  fluids. In fluoridation, it finds application in transporting the solution
from the dissolving chamber of a dry feeder and injecting that solution into a
pressure main. Water at a pressure substantially higher than  that of the dis-
charge head is required to operate an eductor.
   While the solution from the dissolving chamber is diluted by the action of
the eductor, there  will be  no effect on the  fluoride concentration  in the
treated water since  the water to operate the eductor is taken from the flow
which is being treated.
   To prevent the introduction of air into the main, the eductor should draw
fluoride solution from a  solution  well which is supplied continuously with
water through a float-controlled valve.

PUMPS
   Pumps  find application in situations similar  to those where  an eductor is
used,  and are also used for transferring  fluosilicic acid from storage to  day
tank and for transferring other fluoride solutions. Centrifugal pumps are most
commonly  used, since  they can  be throttled without  harm  and can  run
continuously.
   The choice of materials of construction  of pumps is as critical  as it is for
solution  feeders. Pump heads and impellers, and  also pipe lines, must be
resistant to the material being handled or there will be leaks and pump failures

                                    27

-------
to contend  with. The avoidance of slurry  transfer is important, also, since
slurries tend to be abrasive and can damage pump heads, impellers and packing.

TIMERS
   An interval timer is basically a clock mechanism, usually electric, which
closes or opens an electric switch upon receipt of a signal, holds the switch in
position  for the pre-set  time  interval  and then reverses the switch position.
Timers are  frequently used in  conjunction  with  water meter contactors to
operate solution feeders. When  the contact is made in the water meter, the
timer is  energized  and  the  feeder  will  run  for  the  period  selected.  The
momentary  contact made by the meter contactor, while sufficient to produce
a stroke  of a solenoid-operated feeder, is  too short to operate an electric-
motor operated feeder. Thus,  the timer serves to extend the impulse received
from the contactor.
   Another  application of a timer is for those installations where the minimum
reliable feeder setting is  still too high for the water flow. In these cases, the
timer can be set to provide a proportion of the full-time feed rate. For example,
by setting the timer  to operate the feeder at 75% of each 1-minute period, the
feed  rate  will only  be 75% of that obtained  without  the  use of the timer.
   A  word  of caution: Using a proportional  timer at  low percentages, and
particularly  for long interval  settings, can result in cyclic  fluoride levels. If
there is insufficient  detention time in clear  wells or pipelines before water
reaches  the  consumers, the on-off action of the  feeder will be  apparent in
alternately too-high  and  too-low fluoride readings. The  remedy is, other  than
using a smaller feeder, to make the  proportioned time interval as short as
possible.
HOPPER AGITATORS
   To promote the smooth and even flow of dry  material in a hopper, some
sort  of agitation is helpful. The hopper agitator may take the form of a device
which imparts vibration  magnetically  or mechanically  to the outside  of the
hopper, or may be a rotating member inside the  hopper.
   Many  dry  feeders incorporate  a  hopper  agitator into their construction.
FLOW-SPLITTERS
   When  the effluent  from the dissolving chamber of  a dry feeder is to  be
used  for more than one point of fluoride  application, the effluent can  be
divided  with  a  flow-splitter.  This device is  nothing more than a movable
baffle in  the dissolving chamber which can be adjusted to vary the proportion
of solution flowing out of two  outlets.
   An example of an application involving a flow-splitter would be  when two
water sources, with no  common  point for  fluoride  injection, are  to  be
fluoridated with a single  dry feeder. By adjusting the splitter so that the  right
proportion of fluoride is  fed to each source, the cost of an additional feeder is
saved.
   It  should be noted that a flow-splitter is grossly  inaccurate and should not
be used except when no other alternative is available.

                                    28

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                                 (5)  VARIABLE SPEED

                                    CONTROL UNIT
                 „    110 VOLT

             FLOW (8)    POWER "

             METER       SUPPLY

             MODEL 304
      o
HYDROFLUOSILICIC ACID

STORAGE TANK
                                                            SIGHT GAGE
                                         (ft) FOOT VALVE
(?) BAG LOADING HOPPER — ft_
(5) LOSS OF WEIGHT if—.
RECORDING SCALE ~-«|
J-l
POWER SUPPLY -~"^n
\\
	

CHEMICAL BAG
I
/ QHELIX FEEDER MOD
•^ POWER SUPPLY
^; PACIN
®~M! C"H"A N"I C~A i~ M~I X"E R~
. ... (IF REQUIRED)
iiiiMi® °ISSOLVE" NO
J' T
-------
         DUST COLLECTOR
          HOPPER COVER
      HOPPER SCREEN

       FLOOR FLANGE
     HOPPER  RETAINER
       VIBRATOR (OPTIONAL)

        HELIX  FEEDER MODEL 25-04


        WEIGH SCALE —
          FEEDER  BASE
                                                      APPROX. 10 FT
                            53
                                                     DRAIN
   Figure 7. Typical Arrangement of Dry Feed Hoppers and Dust Collectors
   Figures 6 and 7, and Figures 13 through 17 illustrate the use and arrange-
ment  of various  pieces of auxiliary  equipment in fluoridation installations.
                                    30

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                           Chapter  IV
         Preparation  Of  Fluoride  Solutions
MANUAL TECHNIQUE
   The most basic fluoridation  system, involving the least expenditure for
equipment, is one involving the proportional feeding of a fluoride solution into
a water flow in  a pipeline. The only requirements are the preparation of a
fluoride solution  of known concentration, and then pumping that solution into
the water  so that the desired fluoride concentration in the water is achieved.
Of the most commonly used fluoride compounds, sodium fluoride and fluosil-
icic acid are  of  sufficient  solubility for preparation of solutions of fixed
strength which then  can be fed with a metering pump.
   Fluosilicic acid, already a solution as  purchased, can be fed directly  from
the shipping container, from an intermediate storage  tank (day tank), or can
be diluted and fed as a solution considerably weaker than the 22 - 30% acid
solution originally purchased. Dilution is necessary in small  water  plants,
where the water  flow to be treated is so low that the smallest proportioning
pump cannot be  adjusted to a low enough feed-rate setting for undiluted acid,
or where the feeder cannot be expected to operate reliably at the extremely low
setting required.  As pointed out in the section on Feeders, extremes in  feed-
rate range should be  avoided, and even the  smallest feeder will not deliver a
fraction of a drop per stroke with any degree of reliability.
Example:
   Data known:
   Water flow rate - 100 gpm
   Cone, of fluosilicic acid - 25%
   Concentration of F wanted - 1.0 ppm
   Specific gravity of acid - 1.22
   Problem:
   Find volume of acid  to be fed per minute, and the volume of acid to  be
   delivered per stroke  of a feeder which operates at 46 strokes per minute.
   Calculations:
   R! X Cl = R2 X C2, where:  R, = water flow rate in gal/min
                             Cj = desired F level in ppm
                             R2 = feed rate
                             C2 = solution strength as F

                                  31

-------
   then: 100 gal/min X 3785 ml/gal X 1.0 ppm = (x) X 25% X 79%

      , ,   100 gal/min X 3785 ml/gal X 1.0 ppm
      W   25% X 79% X 1.22 (specific gravity)
   By  expressing  percentages  as  decimals,  and ppm  as the  fraction
   1/1,000,000, units will cancel to give:
      , ..    , ,   ,;  .      ,    1.6 ml/min     _ „,.,.   .,    ,
      (x) =  1.6 ml/mm,  and —	r~n—:— = 0.035 ml/stroke
      v '                   46 strokes/mm
   Obviously,  the  above  volume per stroke is  too small  (a  drop is usually
considered to be  0.05 ml)  to be handled by even  the  smallest  feeder, so
dilution of the acid is mandatory for reliable feed. If the acid were diluted at
the ratio  of one gallon  to  nine gallons of water (resulting in acid of 2.5%
strength),  the  volume of acid to be fed per minute would be:

   1001 gal/min X 3785 ml/gal   Y1/inannmn      ^
   0.025 X 0.79  X  1.02 (sp.  gr.) X i/1'000'000 0  P?m>
                                 = 19 ml/min
   19 ml/min         n  .,  .,   .
   ., c  '—.  .    =0.41 ml/stroke
   46 Strokes/mm
   The above volume is  well within the capability of a small solution feeder,
for example, one which has a delivery range of 0.1  to 1.0 ml/stroke. Note that,
while decreasing  the stroke  frequency would permit  larger  volumes  to be
handled per stroke, such practice  also has its limitations, since  infrequent
stroking results in cyclic variations in fluoride levels in the water.
   The dilution  of fluosilicic  acid should  be  made by carefully pouring the
measured  volume (or weight) of acid into a measured volume of water. (While
adding water to acid would not be particularly hazardous in this case, because
of the low strength of commercial acid, it  is always good practice to add  acid
to water rather than the  reverse.) All containers used for handling even dilute
acid  must be made of a  material resistant  to the corrosive effects of the  acid
(plastic  or hard rubber  are suitable) and  the solution  should be thoroughly
mixed with a plastic or wooden paddle. Avoid splashing or spilling, wear  pro-
tective gloves and  clothing, and mop up all spills with a solution of soda ash or
other alkaline material followed by several clear water rinses. The solution tank
should  be kept on a  platform scales, and records kept  of the weights or
volumes of acid and water used in each batch of solution prepared, and particu-
larly of the weight of solution  fed.
   Precaution:  Dilution  of  fluosilicic acid can result in the formation  of  a
precipitate (silica) when  the dilution is in the  range of ten to  twenty parts of
water to one of acid. Such precipitation, which can result in clogged feeders,
valves and orifices, can be avoided by using fortified acid (acid to which a small
amount of hydrofluoric  acid has been added by the supplier) or by using acid
manufactured from hydrofluoric acid rather than from phosphate rock.
   Sodium Fluoride, being soluble up to 4% (4 pounds in 100 pounds of water)
can be fed as a solution by dissolving a weighed amount of the dry material in a

                                    32

-------
measured volume of water. By usual means, a 4% solution is difficult to attain,
so for practical purposes,  solution strength should be limited to  about 2%.
Example:
   Data known:
   Water flow rate  - 100 gpm
   Sodium  fluoride solution -  8 Ibs  of 99% pure NaF dissolved in 50 gal. of
                              water
   Problem:
   Find volume of solution to be fed per  minute to produce a concentration
   of 1.0 ppm F in the water.
   Calculations:
   RI X Ci = R2 XC2;  R2 = RI XCt   where   R! = water flow rate in
                              C2                   gal/min
                                              Ci  = desired F level in ppm
                                              R2 = feed rate
                                              C2  = solution strength as F
   100 gal/min X 1.0 ppm   _nmo   ,/   .
   8300 ppm (from Table 3) ~ °'012 gal/mm
   0.012 gal/min X 3785 ml/gal = 46 ml/min
   At the relatively low concentrations used in sodium fluoride solutions,  the
specific gravity is so close to 1.0 that volume measurements  instead of weight
may be  used in calculations of feed rate.
   Although sodium fluoride solutions are not particularly corrosive, a plastic
container is preferred for preparation  of solutions. The mixture may be stirred
with a  paddle  until the  sodium fluoride  is completely dissolved,  or a  small
mechanical mixer  may be.used. Table 3  gives quantities of sodium fluoride
and  water to be used for various solution strengths.

AUTOMATIC DEVICES
   Because  sodium  fluoride has a maximum solubility of around 4% (18,000
ppm as F), regardless of substantial variations in water temperature,  devices for
automatically preparing saturated solutions can be used.  The  use of these
devices  eliminates  the need for weighing sodium fluoride, measuring solution
water volume, and for stirring to insure dissolution.
   The  principle of a saturator, as these devices are called,  is that a saturated
solution will result if water is allowed to trickle through a bed containing a large
excess of sodium fluoride.  There are two  general types of saturators - upflow
and  downflow. In the  latter type, the solid sodium fluoride is isolated from
the prepared solution by a plastic cone or a pipe manifold. A filtration barrier
is  provided by  layers of sand and gravel  to prevent  particles of undissolved
sodium fluoride from infiltrating the solution area under the cone or within the
pipe manifold (Figs. 8, 9, & 10). In the upflow type, no  barrier is  used, since
the  water comes up through the bed of sodium  fluoride and the  specific

                                   33

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  Table 3. PREPARATION OF SOLUTIONS OF SODIUM FLUORIDE
Pounds of
NaF
(98% pure)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
GALLONS OF WATER
10
1.2
5200
2.3
10300















20
0.6
2600
1.2
5200
1.75
7750
2.3
10300













30
0.4
1750
0.8
3500
1.2
5200
1.55
7000
2.0
8600












40
0.3
1300
0.6
2600
0.9
3900
1.2
5200
1.5
6500
1.8
7800
2.0
9000










50

0.5
2100
0.7
3100
1.0
4200
1.2
5200
1.4
6200
1.65
7300
1.9.
8300
2.1
9300








60

0.4
1750
0.6
2600
0.8
3500
1.0
4350
1.2
5200
1.4
6000
1.6
6900
1.75
7800
1.95
8600
2.15
9450






70

0.3
1500
0.5
2250
0.7
3000
0.85
3700
1.0
4300
1.2
5200
1.35
6000
1.5
6700
1.7
7400
1.85
8200
2.0
8900





80


0.45
1950
0.6
2000
0.75
3300
0.9
3900
1.0
4600
1.15
5100
1.3
5850
1.5
6500
1.6
7200
1.8
7800
1.9
8400
2.1
9100



90


0.4
1750
0.5
2300
0.7
2900
0.8
3500
0.9
4000
1.05
4650
1.2
5200
1.3
5800
1.45
6400
1.6
6900
1.7
7500
1.8
8100
1.95
8600
2.0
9000

100


0.4
1600
0.5
2100
0.6
2600
'0.7
3150
0.8
3650
0.95
4200
1.1
4700
1.2
5200
1.3
5750
1.4
6250
1.5
6750
1.65
7300
1.8
7800
1.9
8300
2.0
8800
The above table gives strengths of solutions prepared by dissolving the given weights of
sodium fluoride in various volumes of water. The upper figures represent  approximate
solution strength in percent sodium  fluoride, while the lower figures represent approxi-
mate solution concentration in ppm F.  Example: If 2 Ibs of NaF  are dissolved in 50
gallons of water, what is the solution strength? Reading across (horizontally) from 2 Ibs
to the 50 gal. column gives 0.5% NaF and 2100 ppm F.
The  absence  of  figures  in  a column  indicates that  the preparation  of the particular
solution would be impractical or impossible.
                                      34

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LINE BEING TREATED
       SATURATED
       SOLUTION -
   CHEM-0 FEEDER
                                     W ATER METER
                                                    /
   WALL MTD  SHELF

      OVERFLOW

   GRANULAR NoF
   MIN  OF 10  FOR
   47.  SOLUTION

   4   TO 6   OF 1/8
      TO 1/4  SAND
   {TORPEDO SAND)

    2   COARSE
 GRAVEL (1   TO  2
                                     LEVEL CONTROL
                                     •*-"FLOAT VALVE
                                        SPRAY
                                     /NOZZLE
                                           FOOT  VALVE
                   DRAIN
                            SATURATED
                            SOLUTION  NoF
                                                                      MULTIPORT
                                                                       VALVE

DL
VE

L
L


ZEOLITE
SOFTENER


n. n

-E



— i
                                                                                      WATER SUPPLY
                                                                                      BRINE TUBING
                                                                              BRINE
                                                                              TANK
 DRAIN
[/
                               Figure 8. BIF Downflow Saturator

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                                                ANTI-SIPHON
                                                VAl
                                                            DIAPHRAGM
                                                            PUMP
 WATER  .
 SOFTENER
                                                                SATURATED
                                                                FLUORIDE
                                                                TO POINT OF
                                                                APPLICATION
                                    DRAIN-'
                                    PLUG
                   Figure 9. W & T Downflow Saturator

gravity of the solid material keeps it from rising into the area of clear solution
above. In the downflow type, the feeder takes suction from within the cone or
manifold, while in the  upflow type, the feeder suction intake floats  on the
solution  in  order to  avoid  withdrawal  of undissolved sodium  fluoride.
   When a downflow-type saturator is in  operation, water is admitted at the
top of the  saturator tank (there is an air gap to avoid the possibility of a cross-
connection)  and the  level is  regulated with  a float-operated controller. The
water then trickles down through the bed of sodium fluoride, the solution is
clarified  in  the sand  and gravel  filter bed and ends up as a clear,  saturated
solution  at the bottom of the tank where it is withdrawn by the feeder. The
feeder adds the prepared solution, at the desired rate, to the water system. The
only operator attention required  is to  see that an adequate quantity of sodium
fluoride is  kept in the saturator and that the saturator is kept in a reasonably
clean condition (See Table 4).
                                    36

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           HOW  CONTROL-

          SVPHON BREAKER.

           SOLENOID VALVE.
                             WALL
                             OUTLET
                             US VAC.
   ANTI-SIPHON VALVE
PCPC 5000 SERIES
 FLUORIDE
                                                    !•.--'-
     50 GAL. POLY -
     ETHYLENE TANK

WATER  "V**™0 SOLUTION
SOFTENER
               -*f*
         •iff-
          PCPC LIQUID"*
            LEVEL SWITCH

                  3/4" NPT
                  OVERFLOW
                                                   &:::.

                                                    -V3/4'-AitTVoAirSOPTIONAl'
          Figure 10. Precision Up-Flow Saturator

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  Table 4. RECOMMENDED MAXIMUM FEED RATES FOR DOWNFLOW
                  SODIUM FLUORIDE SATURATOR
Bed Depth
6"
6%"
7"
7&"
8"
8*4"
9"
9&"
10"
60°F
950 gpm
200 ml/min
1065 gpm
225 ml/min
11 90 gpm
250 ml/min
1300 gpm
275 ml/min
1425 gpm
300 ml/min
1550 gpm
325 ml/min
1660 gpm
350 ml/min
1780 gpm
375 ml/min
1900 gpm
400 ml/min
Water Temperature
50°F
830 gpm
175 ml/min
950 gpm
200 ml/min
1065 gpm
225 ml/min
11 90 gpm
250 ml/min
1300 gpm
275 ml/min
1425 gpm
300 ml/min
1550 gpm
325 ml/min
1 660 gpm
350 ml/min
1780 gpm
375 ml/min
40°F
710 gpm
150 ml/min
830 gpm
175 ml/min
950 gpm
200 ml/min
1065 gpm
225 ml/min
11 90 gpm
250 ml/min
1300 gpm
275 ml/min
1425 gpm
300 ml/min
1550 gpm
325 ml/min
1 660 gpm
350 ml/min
In the above table, the lower figures represent the maximum feed rate (or
withdrawal rate) of saturated  sodium fluoride solution  for each given bed
depth of sodium fluoride at each of three saturator water supply temperatures.
The upper figures represent the water flow rate which can be fluoridated to
a level of 1.0 ppm F for each respective solution feed rate, assuming there is
less than 0.1 ppm natural fluoride  content in the water. Higher flow rates
can be fluoridated if there is a higher natural fluoride content or if the desired
level is less than 1.0 ppm F.
To prepare a downflow saturator for use:
 1.   With the manifold (W & T) or cone (BIF) in place, carefully place by
     hand a  2-3" layer of coarse, clean gravel (1-2" size) in the saturator
     tank, around the  manifold or cone and over the manifold or over the
     lower edge of the cone. Then place another 2 - 3" layer  of finer gravel
     (ft - 1" size) over the coarse gravel.
                                  38

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 2.  Place a 4-6" layer of clean, sharp filter sand over the gravel. (Do not use
     beach sand, clayey sand or ordinary soil.) Level the sand surface. (A 12"
     bed of 1/8" to 1/4" filter gravel can be substituted  for the sand and
     coarse gravel layers.)
 3.  Add 200 Ibs of coarse crystalline sodium fluoride (Olin 20 - 60 mesh,
     Allied coarse crystal,  or similar. Do not  use powdered NaF or fine
     crystal.) Add water to keep down the dust and to assist in leveling the
     fluoride surface.
 4.  Check to see if the float has  room to  operate. If necessary make a
     depression in the fluoride surface to provide clearance for the float and
     float-rod.
 5.  If you have not already done so, connect a cold-water supply line to the
     water  intake  of  the saturator.  The line  should contain a small water
     meter (1/2") for use in calculating feed rate, and there should be a  shut-
     off valve between the meter and  the saturator.
 6.  Turn on the water supply and adjust the float position if necessary. The
     low-water-level should be no less than 2" above the fluoride surface, and
     the high-water level should be just below the overflow outlet.
 7.  Insert the feeder suction line  into the pipe leading to the inner cone or
     manifold as the case may be. Adjust the length of suction line so that the
     foot-valve and strainer are  2 - 3" above the bottom of the saturator
     tank. The saturator is now ready for use.
 8.  By looking  through the translucent wall of the saturator tank you should
     be  able to distinguish the layers of fluoride, sand and gravel. When the
     thickness of  the  fluoride  layer decreases  to 6",  add  another  100#
     quantity of fluoride. It would be wise to add  the fluoride when the
     water level  is at  its lowest level, or if necessary, to shut off the water
     temporarily until there  is enough room  for the fluoride without causing
     water to come out of the overflow opening.
 9.  If the saturator is  being used at a high rate, that is, if more than  1000
     gpm  of water are  being  treated, fluoride  should be  added daily in
     sufficient amounts to  keep the  fluoride layer at a thickness of at  least
     10". The same daily additions of fluoride should be made if the make-up
     water temperature is below 60°F, even if less than 1000 gpm of water are
     being treated.
10.  Before more fluoride is added to the saturator, the surface of the fluoride
     layer in the  saturator should  be scraped free of  accumulated  dirt,
     insoluble material  or the slimy film of  fine  particles that sometimes
     forms. Such routine maintenance  permits  better percolation  of water
     through the fluoride  layer  and extends the length  of time between
     clean-outs.
11.  At  regular intervals, depending on severity of use, the saturator will have
     to be cleaned out. A typical schedule calls for a clean-out every  three
     months when the quantity of water being treated is in the 100 gpm area

                                    39

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     and the accumulation of dirt in the saturator is moderate. The clean-out
     procedure is as follows:
     a.  Continue using the saturator until the level of sodium fluoride is as low
        as practicable. Shut off the water supply  to permit the level of water
        to  drop down to the fluoride layer. This step minimizes the wastage
        of chemical and  decreases the amount of material which will have to
        be removed.
     b.  Scoop out the remaining  sodium fluoride, the sand and gravel. If the
        sand and gravel  are to be re-used, place them in separate buckets. If
        fresh sand and gravel are available, bury the dirty material.  The old
        sodium fluoride can be flushed down a drain or buried.
     c.  Remove the  inner cone or manifold assembly and clean the  inside of
        the saturator tank. Replace the cleaned cone or manifold.
     d.  If the old sand and gravel are to be re-used, wash them repeatedly
        with water until all traces of fluoride and dirt are removed. Then
        reconstruct the filter bed of sand and gravel as before with either the
        cleaned or fresh material.
     e.  Add sodium  fluoride as  before  and return the saturator to normal
        operation. (Don't forget  to turn  on the  water  supply again.)
12.  If the  water supplied to the saturator is hard (more  than 75 ppm hard-
     ness), a household-type water softener in  the line will minimize the
     amount of  insoluble  material accumulating in the  saturator and thus
     increase the interval between clean-outs.
13.  Use the  readings of the water  meter on  the saturator supply line to
     calculate the amount of fluoride  fed. A 4% solution of sodium fluoride is
     equivalent to 18,000 ppm F. Thus:
     Gallons of water supplied to  saturator -, , _ ,_.       „
     Tr-n	T—;	——j	X 18,000 = ppm F
     Gallons of water pumped                        rr
   (See Page 43 for example problem.)
   In an upflow  saturator,  undissolved sodium fluoride forms its own bed,
below which water is forced upward under pressure. A spider  type  water
distributor located at  the bottom  of the tank contains hundreds of very small
slits. Water,  forced under pressure through these slits, flows upwards through
the sodium fluoride bed at  a controlled rate to assure the desired 4% solution.
The water pressure requirements  are 20  psi minimum  to 125 psi maximum,
and the flow is regulated at 4 gpm. Since introduction of water to the bottom
of the saturator constitutes a definite  cross-connection, a mechanical syphon-
breaker  is  incorporated  into the water  line.  Where  such  devices  are not
permitted, the saturator  can be factory-modified to include  an air-gap and a
water feed-pump.
To prepare an upflow saturator for use:
  1.  With  the distributor  tubes  in  place, and  the floating suction device
     removed, add 200 to 300 pounds of sodium fluoride directly to the  tank.
     (Any type of sodium  fluoride can be used, from coarse crystal to fine

                                  40

-------
     powder, but fine crystal will  produce less dust than powder and will
     dissolve better than coarse  material.)
 2.  Connect the solenoid water valve to an electric outlet and turn on the
     water supply. The water level should be slightly below the overflow; if it
     is not, the liquid level switch should be adjusted.
 3.  Replace the  intake float and  connect it to the feeder intake line. The
     saturator is now ready for use.
 4.  By looking through the translucent wall of the saturator tank you should
     be  able to see the level of undissolved sodium fluoride. Whenever the
     level is low enough, add another 100# quantity of fluoride.
 5.  The water distributor slits are supposed to be essentially self-cleaning, and
     the accumulation  of insolubles and precipitates does not  constitute as
     serious a problem as it does in a downflow saturator. However, periodic
     cleaning is  still required. Frequency of cleaning is dictated by the severity
     of use and  the rate of accumulation of debris.
 6.  Because of the thicker bed of sodium fluoride attainable in an upflow
     saturator,  higher withdrawal  rates are possible. With 300# of sodium
     fluoride  in the  saturator tank, more than 1000 ml/min of saturated
     solution can be fed, a rate  sufficient to treat about 5000 gpm of water
     to a fluoride level of 1.0 ppm.
 7.  Precautions  regarding hard water  apply  similarly  to  both types  of
     saturators.
 8.  Method for calculating  the  amount of fluoride fed is the same for both
     types of saturators. The fixed water inlet rate  of 4 gpm should register
     satisfactorily ori a  1A" meter.
   The preparation of solutions  of  fluoride compounds, whether performed
manually or automatically, requires a certain amount of care. The sources of
possible error in the dilution  of fluosilicic acid are:
 1.  Incorrect volume or weight of acid.
 2.  Incorrect volume or weight of water.
 3.  Incomplete mixing.
 4.  Miscalculation of acid strength as received.
 5.  Miscalculation of fluoride concentration in dilution.
   In the manual  preparation of sodium fluoride  solutions, the sources of
possible error  are:
 1.  Incorrect weight of sodium fluoride.
 2.  Incorrect weight or volume of water.
 3.  Incomplete dissolution.
 4.  Incomplete mixing.
 5.  Attempting concentration  above 2%.
 6.  Miscalculation of  fluoride  concentration in the sodium fluoride.

                                    41

-------
 7.  Miscalculation of fluoride concentration of the solution.
   The  proper  function of a  device  for  automatically preparing  solutions
(saturator) can be adversely affected  by the  following:
 1.  Insufficient quantity of sodium fluoride.
 2.  Water too cold for feed rate used.
 3.  Withdrawal rate too high.
 4.  Sifting of sodium fluoride through sand and gravel (downflow type).
 5.  Lifting of sodium fluoride (upflow type).
 6.  Wrong crystal size (downflow type).
 7.  Failure to scrape surface (downflow type).
 8.  Short-circuiting (downflow type).
 9.  Insufficient water supply (stoppage or valve closing).

CALCULATIONS INVOLVING SOLUTIONS

   As in the examples above, the  equation, RI  X Ct = R2  X C2 (water flow
rate  times  fluoride level desired equals solution feed rate times fluoride con-
centration  of the solution), should be used to calculate the theoretical mean
fluoride  concentration for a given time  interval.  Obviously, accurate figures
for weights or volumes of materials used are necessary for accurate calculations.
The  use of appropriate units  (which can be  cancelled arithmetically)  will
produce  a calculated  result in the desired units and will  verify the proper
insertion of figures into the equation. For instance,  with R! in gallons, Ct in
ppm, and C2 in pr^m, R2  will be in gallons. A calculated result  in any other
units would indicate an error.
Some examples of typical calculations are given below.
Example 1: A water plant pumps 300,000 gallons of water in one  day. Sodium
   fluoride solution, prepared by  dissolving 8# of 98% NaF in 50 gallons of
   water, is the  fluoride source. The solution tank is mounted on scales, and
   the  scales indicate  that 250# of solution was  fed. What is the calculated
   fluoride level  in the treated water?
                   RV" I"1   	 O V f~*  • f   	  D  Y" f
                  1 A V^i  — K2 A L-2 ,l-i   —  t\2 A ^-2
   calculations:                              —	=
    R! in Ibs, R2 in Ibs, C2 in ppm)
    ,    250 Ibs X 8300 ppm (from Table 3)   . 0_
    Di =	°-—v           ' = 0.83 ppm
           300,000 gal X 8.34 Ib/gal
Example 2: If 250,000 gallons of water are pumped, and 150 Ibs of a fluosilicic
   acid solution containing 25% acid diluted at the rate of 1 gallon to 9 gallons
   of water are  fed, what is the theoretical fluoride level?
                     R2 XC2
   Calculations: Ct =—5	
                       *M
   (R! in Ibs, R2 in Ibs, C2 in %)

                                    42

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      _ 150 Ibs X 0.025 (acid strength) X 0.79 (available F)
    1 ~         250,000 gal X 8.34 Ib/gal
                = 0.000142 % or 1.42 ppm

Example 3:  In a saturator installation, the saturator supply meter shows that
   12 gallons of water were admitted, while the master meter indicated that
   200,000  gallons of water were pumped. What is the  calculated  fluoride
   concentration?
                     R2 X C2
   Calculations:  C i = - 5 -
   (R2 in gallons, R! in gallons, C2 in ppm)
      _ 12 gal X 18,000 ppm (F cone, of saturated solution of NaF)
    1 ~                     200,000 gal.
                            = 1 .08 ppm

   If there is an appreciable natural fluoride level in the untreated water, that
amount should be added  to the  calculated level  based  on  fluoride added.
Similarly, when calculating feed rates, the natural fluoride concentration should
be subtracted from the desired level  in order to determine the quantity to be
added.
   In  order to verify the delivery rate of a solution feeder, for example when
starting up a solution  feed fluoride  installation or when  making adjustments
to a feed rate that is too high or too low, some simple procedures are available.
Simply measuring  the output from the discharge outlet of  the feeder is unsatis-
factory, since even the output of so-called positive-displacement feeders varies
with pressure. One acceptable way is to measure a volume of the liquid being
pumped, preferably in a graduated cylinder. Then carefully insert the suction
tube  of the  feeder into the  cylinder (without losing prime or spilling  any
solution).  Feed for a timed interval, withdraw the suction tube and note the
volume  of solution remaining. The  difference  will represent the volume fed
during the measured interval. Another way is to equip the  solution tank with a
calibrated sight glass. By closing  the valve between the  sight glass and tank,
while the  feeder is operating normally, solution will be withdrawn from the
sight glass  only, and the volume fed over a timed interval can be  calculated.
This system  has  the  advantage  of freedom  from interruption  of  fluoride
addition. After the measurement, opening the valve will be all that is necessary
to do to resume normal feed (Fig. 1 1).
   Solution strength can also be verified, either by chemical analysis  or by
specific gravity  measurement. The  extreme dilution required  for chemical
analysis introduces possibility for  considerable error, and specific gravity
measurements are at best only an approximation, but either of these procedures
will suffice to detect gross  errors  in solution preparation.  The care with which
the dilutions and measurements are  made will determine  the degree to which
the results can be  relied upon.

                                    43

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                                                    PROPORTIONING
                                                           PUMP
I
SIPHON^^"^
ALVE i
SUCTION
i
GAGE
:

J
a )



y y
li-i^,fel>j^r:vr^*-V\V.i»;:l^^
           Figure 11. Checking Delivery Rate of a Solution Feeder
   When analytical methods are used, the electrode procedure is most suitable,
since its range far exceeds that of colorimetric methods. By  standardizing the
electrode in the area in which it is to be used, concentrations up to 1,000 ppm
F  can  be  determined with  acceptable  accuracy.  Obviously,  preparation of
standards must  be  done with painstaking  care.
   Specific gravity of technical fluosilicic acid seldom agrees closely with the
published figures, which are  based on relatively pure acid, but in the greater
dilutions the figures are at least acceptable.  (Assay  procedures are  available
for the acid as purchased. See the AWWA  specifications.) Specific gravity
measurements must be made  at the temperature specified in the tables (Table
5), and glassware  used should be exposed as briefly as possible and rinsed
thoroughly after use to preclude etching. (See the AWWA Standards for com-
plete instructions.)
                                    44

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    Table 5. SPECIFIC GRAVITY OF FLUOSILICIC ACID SOLUTIONS
                             AT 17.5°C.
Specific
Gravity
1.0040
1.0080
1.0120
1.0161
1.0201
1.0242
1.0283
1.0324
1.0366
1.0407
1.0449
1.0491
1.0533
1.0576
1.0618
1.0661
1.0704
1.0747
1.0791
1.0834
Weight of H2SiF6 in Solution Expressed in:
Pounds per gallon
0.042
0.084
0.127
0.170
0.213
0.256
0.300
0.345
0.389
0.434
0.480
0.525
0.571
0.618
0.665
0.712
0.759
0.807
0.856
0.904
Percent H2SiF6
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
Degrees Baume1
0.6
1.2
1.7
2.3
2.9
3.4
4.0
4.6
5.1
5.7
6.2
6.8
7.3
7.9
8.4
9.0
9.5
10.1
10.6
11.2
Note:
These figures apply only to pure H2SiF6 in distilled water, but they
may be used to obtain approximate values for solution strengths.
                                45

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                           Chapter  V
 Selecting  The  Optimal  Fluoridation  System
   Among the considerations in choosing the right fluoridation system for a
particular  situation are:  population  served (or water usage rate), chemical
availability, cost, type of operating personnel available, and just plain personal
preference on the  part of the person or persons making  the decision. While
there is no one specific type of fluoridation system which is solely applicable.
to a specific situation, there are some general limitations imposed by the size
and type  of  water facility. For example, a large metropolitan water plant
would  hardly be  likely to consider  a fluoridation installation involving the
manual preparation of batches of solution, any  more than would a small
facility consisting of a number of unattended  wells consider the appropriate
number of gravimetric dry feeder installations.
   Figure  12  is a  check-list, based essentially on water pumping rates, which
can be used as a  rough guide in differentiating between the various types of
fluoridation  installation.  Obviously,  the population divisions  are  flexible,  at
least within  limits, so considerable overlap   can be expected.  Other  consid-
erations,  such  as  the  water plant lay-out and personal preference  can be
expected to  influence  a  choice which does not  necessarily fall within the
selected limits.
   For the smallest water plant, some type of solution feed is  almost always
selected. There is  almost no lower limit to the ranges of the  smallest metering
pumps, and  even  if the feed rate for  solution were impractically low,  a more
dilute solution would solve the problem. Conversely,  there is almost no upper
limit to the capacity of gravimetric dry feeders, or to pumps, for that matter,
so the largest water plants can select either dry feed with sodium silicofluoride
or direct feed of  fluosilicic acid. For all those water plants in between, there
will be a choice, modified only by individual circumstances.  Assistance  can be
obtained from SHD Engineers, manufacturer's representatives, or consultants.

LOCATION  OF FEEDER
   Before  a type  of feeder can be selected,  sufficient and appropriate space
for its  installation must be provided.  If there is an existing water plant, where
other water treatment chemicals are being fed,  usually space for an additional
feeder  is no  problem. If there is no treatment plant, as is  often the case with
well supplies, then there  may be a well house, or  perhaps even some type of

                                   47

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Figure 12. Fluoridation Check-List
Chemical And System
Water Flow Rate
Population Served By
System Or Each Well Of
Multiple-Well System
Chemical Cost, FOB
Manufacturer
Chemical Cost/lb
Fluoride Ion
Equipment Cost/Unit
Equipment Required
Feed Accuracy
Chemical Specifications
And Availability
Handling Requirements
Feeding Point
Other Requirements
Hazards
Sodium Fluoride
Manual Solution
Preparation
Less Than 500 gpm
Less Than 5000
22 - 25 i /lb
50 -Sit
$100 -$500
Solution Feeder,
Mixing Tank, Scales,
Mixer
Depends On Solution
Preparation And
Feeder
Crystalline NaF,
Dust-Free, In Bags
Or Drums. Generally
Available.
Weighing, Mixing,
Measuring
Injection Into
Filter Effluent Line
Or Main
Solution Water May
Require Softening
Dust, Spillage,
Solution Preparation
Error
Sodium Fluoride
Automatic Solution
Preparation
Less Than 2000 gpm
Less Than 10,000
20 - 22t/lb
46 - 50
-------
Fluosilicic Acid
23 - 30%
More Than 500 gpm
More Than 10,000
$51-$58/ton
(23% Basis)
14 - 16tf
$500 And Up
Solution Feeder, Day
Tank, Scales, Transfer
Pump
Depends On Feeder
Sodium Silicofluoride Or Sodium Fluoride
Dry Feed
More Than 100 gpm More Than 2 MGD
More Than 10,000 More Than 50,000
Sodium
Silicon.
9 - \0il Ib
Sodium
Fluoride
18 - 20t lib
4l-46i
$1,000 And Up
Volumetric Dry Feeder,
Scales, Hopper,
Dissolving Chamber
Usually Within 3%
Sodium Sodium
Silicon. Fluoride
8-9tf/lb 18-20^/lb
$3000 And Up
Gravimetric Dry Feeder,
Hopper, Dissolving Chamber
Usually Within 1%
Bulk Acid In Tank Cars
Or Trucks. Available
On Contract
Powder In Bags, Drums Or Bulk. Generally Available.
All Handling By Pump
Injection Into Filter
Effluent Line Or Main
Acid-Proof Storage
Tank, Piping, Etc.
Corrosion, Fumes,
Leakage
Bag Loaders Or Bulk Handling Equipment Required
Gravity Feed From Dissolving Chamber Into Open Flume
Or Clear-Well, Pressure Feed Into Filter Effluent Line
Or Main
Dry Storage Area, Dust Collectors, Dissolving-Chamber
Mixers, Hopper Agitators, Eductors, Etc.
Dust, Spillage, Arching And Flooding In Feeder And Hopper
                                    49

-------
shelter near an elevated storage  tank. The feeder must be placed in a dry,
sheltered area,  near to the point of fluoride injection, and preferably in  a
place  which has storage space for chemicals. There  must be electrical power
available,  in  most  cases,  and  a  water line  for  solution preparation unless
undiluted fluosilicic acid  will be  used. The location must be accessible for
chemical replenishment and maintenance. Other than these basic requirements,
consideration should  be given  to the desirability for isolation of chemical
storage  from other materials, for adequate ventilation and for general con-
venience.

FLUORIDE INJECTION POINT
   The first and most important consideration in selecting the fluoride injection
point  is  that it must  be a point through which all the water to be treated
passes. In a water plant, this can be in a channel where  the other water treat-
ment  chemicals are added, it can be in a main coming from the filters, or it can
be in  the clear well. In a well-pump system, it can be in the discharge line of a
pump, if there is only one, or if there is more than one pump it can be in the
line leading to  the elevated tank  or other storage facility. If there is a com-
bination of facilities, say a treatment plant for surface water plus supplemental
wells, it must be a point where all water from all sources passes. If there is no
such common point,  it means that separate fluoride feeding installations  will
have to be made for each water facility. If at all possible, a point through which
all the water passes at a fixed rate  or rates should be selected. For example, the
water from one or more well pumps is being discharged into a main leading to
an elevated storage tank. Water from the storage tank passes through a point
which might seem to  be acceptable. In the latter case, flow can vary from that
of maximum demand on the system to that of minimum demand, making the
adjustment of the  fluoride  feed rate more difficult than it would be if it were
based on the fixed delivery rate of the pump or pumps. Thus, a better choice
would be to inject fluoride into  the main leading to the storage tank, where
the flow rates are  those of the pump deliveries.
   Another consideration in selecting a fluoride injection point is the question
of fluoride losses in filters. Whenever possible, fluoride should be  added after
filtration  to  avoid the substantial losses which can occur, particularly with
heavy alum doses or when magnesium is present and the lime-soda-ash softening
process is  being used. On rare occasions it may be  more  practical to  add
fluoride before filtering, such as in the case where the clear well is  inaccessible
or so far away  from the plant that moving chemicals would be uneconomical.
   When other  chemicals are being fed, the question  of chemical compatibility
must  be considered.  If  any of these other chemicals contain calcium, the
fluoride injection point should  be as far away as possible in order to minimize
loss of fluoride by precipitation. For example, if lime (for pH control) is being
added to the main leading from the filters, fluoride  can be added  to the same
main  but at another point, or it can be added to the clear well. If the lime is

                                   50

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 being added to the clear well, the fluoride should be added to the opposite
 side. Another factor in selection  of injection point is the desirability of having
 the feeder as close to this point as possible.

 TYPE OF FEEDER AND CHEMICAL
    For the smaller water plants,  the amount of chemical used is small enough
 so that the cost per pound is not a major factor. Thus, sodium fluoride or
 fluosilicic acid, even though relatively expensive in small lots, can both be used.
 The decision of whether to use a manually prepared sodium fluoride solution,
 a saturator, diluted or undiluted fluosilicic acid depends on the quantities to be
 fed, the skill of the  operator,  the availability and desirability  of acid,  and
 personal preference.
CHEMICAL PUMP WIRED IN
CONJUNCTION WITH WEU PUMP
                   FOOT VALVE ASSEMBLY
                                 '/i/nimrm/.'n/
                      Figure 13. Acid Feed Installation

                                     51

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   Perhaps the simplest  fluoridation installation is one based on the use of
fluosilicic acid, provided  the acid can be fed undiluted. The acid is supplied in
carboys or drums, which need  only be mounted on a platform scale to serve
as the feeding source. A  solution feeder, mounted on a shelf above the carboy,
draws acid and injects it  into a main in proportion to the water flow. An anti-
siphon valve  is usually part of the feeder, and such extras as a loss-of-weight
recorder can  be added (Fig. 13).
   If the  supply is too  small  to  be able  to utilize undiluted fluosilicic acid,
a sodium fluoride  solution or  diluted acid feeding system is almost as simple.
The equipment would be essentially the same as the acid feeding system plus
that needed for dilution  or solution preparation.
   A sodium fluoride solution-feed installation may be  arranged as in Fig.  14,
or the mixing  tank and  transfer pump eliminated by using the day tank  for
                                                       ALARM
             WATER SUPPLY

                     TRANSFER PUMP
 MIXER
                                                     --PLACE ON PLATFORM  SCALE
                    Figure 14. Solution Feed Installation

                                     52

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  solution preparation. Similarly, the diluted acid feed system illustrated in Fig.
  15 can be simplified by manual addition of the acid to the day tank, particu-
  larly if  the  acid  is purchased in small carboys which  permit easy handling.
     Except for the fact that the solution strength may be relatively  high (4%),
  the use of a sodium fluoride saturator provides  the  basis for  an  extremely
  simple  and virtually fool-proof solution-feed installation. Once the solution
  feeder has been adjusted, the only operator attention required is the occasional
  replenishing  of chemical (without  weighing) and  cleaning of  the saturator
  (Figures 8, 9, and 10).
     Sodium silicofluoride  dry feed is limited to  water plants  large  enough to
  accommodate a volumetric  or gravimetric feeder. Volumetric dry feeders are
  capable  of feeding at very low rates, and some of the smallest disc types, such
  as those used for  pilot plant installations, are able to handle water rates as low
  as 25 gpm. If an open channel for feeding by gravity (from the  dissolving tank)
  is not available, an eductor or centrifugal  feed pump can be used for injecting
  fluoride solution into a main (Fig. 16).
                                   WATER SUPPLY
        TRANSFER P

— 	 	

307. ACID
J
II
'{"
!:
1
                                   ('       II  [AIR GAP
                                  .45^    „  --r	
                                   _ _    |l
:.:  ft
                                              ^
            OVERFLOW

               MIXER
                                                DAY TANK
                                             (PLACE ON PIATFORM SCAIEI
E-^. •
                   Figure 15. Diluted Acid  Feed System

                                      53

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                                      VOLUMETRIC FEEDER
                                           f»
                                                       LOSS-OF-WEIGHT RECORDER
           Figure 16. Dry Feed Installation with Volumetric Feeder
   The roll-type and screw-type volumetric dry feeders are capable of handling
flow rates from less than 100 gpm to several MGD. Gravimetric dry feeders are
applicable to flows from about 2 MGD up to the largest water usage encount-
ered (Fig.  17). Of course, any  of the dry feeders can  be used for sodium
fluoride as well as sodium silicofluoride.

CHEMICAL AVAILABILITY
   Fluoride chemicals are plentiful, but having the right one in the right place
at the  right time may not be as simple as it might seem. The availability of
compounds  derived from phosphate  fertilizer production, fluosilicic acid and
sodium silicofluoride, is tied  in with fertilizer sales, so if there is a decline in
                                   54

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    BEL! TYPE 	
GRAVIMETRIC FEEDER
   SOLUTION TANK
          Figure  17. Dry Feed Installation with Gravimetric Feeder
such  sales there is  a  decline in recovery  of the  fluoride compounds. Such
occurrences are rare, and can be circumvented in large measure by purchasing
these chemicals on a contract basis. Most suppliers will preferentially deliver to
contract customers when there  is a shortage.  Sodium fluoride is derived from
fluorspar, so it not tied in with fertilizer production.
   In any  case, it would be wise to investigate  the  availability  of fluoride
chemicals through a local supplier before making a choice. Ordinarily, stocks
of chemicals on hand at local distributors' warehouses are sufficient for the
smaller water plants even if there is a temporary shortage. It is the large user
of fluosilicic acid  who must be  assured of an  ample supply before committing
himself to  an installation designed around the use of the acid for fluoridation.
                                    55

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   Planned usage of a saturator installation hinges on the availability of coarse
crystalline sodium  fluoride, at least for the down-flow types. There are only a
limited number of manufacturers  who produce  this grade, so not all distrib-
utors will routinely carry it in stock. Planning for two different chemicals will
allow continued   operation  in  the  event of a  shortage  of  one of them.

CHEMICAL STORAGE AND HANDLING
   There are a number of criteria governing the selection of a storage site for
fluoridation chemicals. The  dry chemicals must be kept dry,  they  must be
convenient to the  hopper in which they will be loaded, they should preferably
be  isolated from  other  water treatment  chemicals  to preclude accidental
intermixing; the storage area  must  be clean and well ventilated, and should be
equipped with running water and  a  floor drain for ease in cleaning up spills.
Fluosilicic  acid presents particular problems  in storage,  for the  vapors are
corrosive and will  even etch  glass. Containers must be kept tightly closed, or
vented to the outdoors when the container is being fed from. Large quantities
of acid can be stored in underground or enclosed tanks equipped with outside
vents.
   Sufficient area  for storage of bagged chemicals  should be provided, since
piling bags too high can cause compacting and "massing" of crystals,  resulting
in lumps and irregular feeding characteristics. Similar conditions can result from
long periods of storage, so  an over-supply of chemicals should  be  avoided.
   For dry-feed chemicals, particularly if considerable quantities are to be
handled, it is preferable to have a  storage  area on the floor above the feeding
equipment.  This  arrangement  allows dumping bags  or drums directly into
extension hoppers without extensive lifting.
   Bags, fiber drums and steel drums should be stored on pallets so that air can
circulate beneath them. Dry  chemicals will cake if allowed to get damp, and
steel drums will rust.
   The disposal of empty fluoride  containers  has always been a problem. The
temptation to re-use fiber drums is difficult to overcome, since the drums are
convenient and sturdy. Paper bags  are dusty and could cause a hazard if they
are burned, and empty acid  drums could contain enough acid to cause con-
tamination or even injury. The best approach is to rinse all empty containers
with  plenty of water - even  the paper bags  are strong enough to withstand
repeated rinses. After all traces of fluoride are removed, the bags can be buried
or burned  (if an incinerator  is available). Even supposedly well-rinsed drums
should never be used for purposes where  traces of fluoride could present a
hazard.
   If possible, the storage area should be kept locked  and not used for any
other purpose. Particularly,  workers should  be  warned  against  eating in a
fluoride  storage area.
   A smooth, impervious  floor will be easier to keep clean. A  concrete floor
laid directly on the  ground tends to be  damp  and should be avoided. An
exhaust fan, dust collector and/or  wet scrubber should be used to keep the air

                                    56

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 relatively dust-free. Respirators, goggles,  gloves,  aprons  and other protective
 clothing should be available for workers.
   The quantity of chemical  to  be kept in storage  depends on individual
 circumstances. Unless a  delay or shortage is anticipated, no more than  is
 necessary should be kept on hand. Dry chemicals tend to cake and get lumpy
 on long storage, and large quantities of acid present a hazard. The exception to
 the  latter  is when  it is economical to purchase acid in tank-truck lots, in
 which case an enclosed or underground  storage  tank with adequate venting
 and precautions against  accidents must be provided. (Note: The storage tank
 may be located outdoors if no other space is available. Fluosilicic acid, being
 mostly water,  is subject to freezing. The freezing point of a 22% solution  is
 about 4°F.)
   For relative space requirements  for  storage  of chemicals, see Table  1.

 CROSS-CONNECTION CONSIDERATIONS
   As  mentioned in the  section  on feeders, water inlets to solution tanks,
 dissolving chambers, etc., often constitute a cross-connection when the inlet
 is below the level of solution. Whenever possible, the inlet line should have an
 air gap as  a positive safety precaution.  In cases where pressure is  too high to
 make  an air gap practical, a vacuum breaker must be installed at  an elevated
 location between all other restrictive devices (such as valves) and the point of
 entry into the solution container.
   Checks  for possible cross-connections  should  be made  not only when the
 fluoridation installation is in the design stage, but also when later modifications
 occur.

 AUTOMATIC PROPORTIONING (PACING)
   When water flows at  a fixed rate, the  fluoridation installation  is relatively
 simple since the fluoride feed rate, once adjusted to the proper ratio need not
 be  changed unless  there is  a  change in pump  delivery,  feeder  delivery or
 chemical purity. However, when  the flow is variable, such as when there are
 multiple pumps or when pump delivery  varies with demand, a variable fluoride
 feed rate also becomes necessary. In some cases, such as when there are two or
 three pumps,  each   with a fixed  delivery rate, it is possible to use separate
 fluoride feeders, each tied electrically to the individual pump operation, and
 each adjusted to feed fluoride in the correct ratio to the water delivered by that
 pump. In other cases, such as when  the changes in water flow are  predictable
 and  infrequent, it  may  be possible to  manually adjust  the feeder to a pre-
 determined setting which corresponds to the new  water flow rate. If neither of
 the above  apply, or are  impractical or inconvenient, some means for  auto-
matically adjusting  the fluoride feed rate to the water flow rate must be pro-
vided.  This automatic adjustment is  called "pacing."
   For smaller  water plants,  particularly those using a solution feed system,
a water meter contactor,  with or without an interval timer, can be used to pace
the feeder. Essentially, a  water  meter contactor is a switch which is geared to

                                    57

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the water meter movement so that it will make contact at specified gallonage
intervals. Thus,  the impulse from the water meter contactor, when related to
the feeder  motor, will  energize the feeder in proportion to the  meter's
response to  flow. In cases where the  duration of impulse is too short (momen-
tary switch  contact) to activate the feeder motor, an interval timer, connected
between the contactor and motor, can be set for appropriate time durations.
To preclude extensive cycling and resultant wide variations in fluoride  con-
centration, the contacts should be as close together  as possible, and if a timer
is used, the  durations of timed feeder operation should be as long as possible,
just short of possible overlap at the maximum flow  rate. (Some small solution
feeders, usually  solenoid operated, are particularly adapted to meter-contactor
operation.)
   Larger water plants, already equipped with flow meters- and/or recorders,
can utilize the signal from these devices to adjust feeder delivery electrically,
pneumatically, or hydraulically. If this type of pacing is contemplated, feeders
which have  adjusting  mechanisms compatible with the  type of flow-meter
signal available must be  specified.
   If the plant does not have flow meters which are readily adaptable to pacing
the fluoride feeders, or no flow meters at all, various types of meters can be
installed specifically for the purpose. For example, an orifice plate assembly
with a D/P cell transmitter will furnish an electrical signal which can be  used
for control  of feeders.
   Another  device providing an electrical  signal  is  a magnetic flowmeter.
A signal converter will adapt the signal from one of these to a form which can
be used for adjusting some types of feeders. Other types of flowmeters require
the use of recorder-controllers which  modify a pneumatic or hydraulic  pressure
line flow so that  the  pressure thus modified will adjust the delivery rate of
either a dry or solution feeder equipped for the purpose. On solution feeders,
the adjustment is made to the stroke length; on dry feeders, the adjustment can
be made through a variable-speed drive, a poise-positioner, etc. The pneumatic
or hydraulic signals adjust variable-speed drives mechanically, while  electrical
signals accomplish the same purpose through a silicon-controlled rectifier (SCR).
   Another  type of paced fluoride feed can be  accomplished without the use
of remote  flow-meter signals. In this case,  a solution feeder is  operated
directly  (hydraulically) by a special water meter which  diverts water under
pressure to  the  feeder's driving piston in  proportion to the rate of water flow
in the main. (See also controllers)
   As stated earlier, while there is no one specific type of fluoridation instal-
lation which  is  solely applicable to  a specific situation, there is usually one
which is preferable. The best installation  is one that has the best combination
of the following factors:
  1.   Minimum cost of equipment, consistent with good performance.
  2.   Simple mechanical feeding device, either liquid or dry.
  3.   A simple piping and injection system.
  4.   Minimum handling of chemicals.

                                     58

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 5.   Minimum labor operations.
 6.   Minimum maintenance.
 7.   Means for maintaining reliable and permanent records.
 8.   Minimum chemical cost, consistent with water plant size.

INSTALLATION
   The illustrations (Figs 13 to 17) show the  general arrangement  of equip-
ment in  typical fluoridation installations. Some factors to consider are prox-
imity to fluoride application point, proximity to chemical storage, availability
of solution water and accessibility for operation and maintenance.

SOLUTION FEEDER INSTALLATIONS
   A  solution feeder should be placed  above  the  solution container if at all
possible  to  lessen the chances for siphoning.  The suction line should be as
short and straight as possible,  and there should be a foot-valve and strainer at
its terminus.  If the suction line tends to curl or float in the solution, it may be
necessary to weight it. Weights usually furnished with solution feeders are made
of porcelain, but any heavy material which  is resistant to the solution may be
used.
   The discharge line from the feeder should also be as short and straight as
possible, but circumstances may  sometimes require that a long discharge  line
be used.  If such is the case, try to avoid sharp curves or loops in the line which
could provide sites for precipitation buildup and subsequent blockage. If the
solution is being injected into a pipeline,  the injection fitting should be installed
preferably at the bottom or underside of the pipe. Injecting  solution into the
top of a pipe should be  avoided since air  collects there and  can work its way
into the injection check valve  or the discharge line and cause air-binding. There
should be  a check  valve  and  an anti-siphon valve at the injection point.
   Most solution feeders come  equipped  with, or have available as an accessory,
an anti-siphon discharge  valve. This may  be mounted directly on the feeder
head, or  at the injection  point as above. In addition, particularly if solution is
to be fed into an open channel or a low-pressure pipeline, a "loaded" discharge
valve  should  be used. This is  a spring-loaded check or diaphragm valve which
will not open until the feeder  discharge pressure exceeds a certain fixed value.
A common setting is  about  15  psi.
   When mounting a solution  feeder on a shelf or platform above the solution
container, it is  advisable  to  off-set it  sufficiently  to permit access to  the
container (or saturator)  for filling and cleaning.

DRY FEEDER INSTALLATIONS
   When installing a  dry  feeder, placement should  be such that solution from
the dissolving chamber can fall  directly  into  the  chemical feed channel if
possible. If other considerations dictate that the feeder be placed some distance
from  the point of application, the drain  line  should be as direct as possible,

                                    59

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with adequate slope and of sufficient size to preclude precipitation build-ups
and subsequent stoppages.
   Obviously, the dry feeder installation must be on a firm, level foundation if
the scales are expected to perform satisfactorily. If there is a small hopper on
the feeder, it must be readily accessible for filling, and if an extension hopper
is used, it should extend vertically upward to  the filling area without angles
which could trap material. For the water supply line to a  volumetric feeder,
there must be a section  of flexible hose between  the dissolving chamber and
the water pipe to  permit  free movement of the  feeder and scale platform.
   The water supply line to a dry  feeder must be equipped with an air-gap
or mechanical vacuum-breaker, or some other type of anti-siphon device. The
air gap is the simplest and  most  positive protection  against the dangers of a
cross-connection. If water pressure is too high to permit the use of an air gap,
one of the other devices may be used, but  in any case the vacuum-breaker
must be  placed between the point of entry to the feeder dissolving chamber
and any restrictive device in the pipeline, and must be installed in an elevated
location.


VALVES AND METERS

   Shut-off valves are sometimes installed where solution is fed under pressure.
Their use permits  repairs to the feeder or discharge  line, but they also are a
hazard.  Attempting to  feed solution  when  the valve is closed can result  in
ruptured diaphragms or  discharge  lines, or even severely  damaged feeders. If
there is to be a shut-off valve at the injection point, always make sure it is kept
in the fully-open position.
   The use  of  a  sodium fluoride saturator  requires that a water meter be
placed in the water supply line. A shut-off valve in this line is a necessity  to
permit dismantling  and cleaning  the saturator.  The valve must be  placed
between  the water meter and the saturator inlet so  that the meter chamber will
remain filled with water and thus will register properly.
   No water supply can be properly fluoridated unless the water flow rate in the
main is known, and calculated fluoride levels cannot be made unless a record
of total  flow is available. Thus, a master water meter on the main is a pre-
requisite for fluoridation.  While  flow requirements  may  dictate the type  of
water meter to install where none now exists, some thought should be given to
utilizing a meter signal for pacing a fluoride feeder.

INSTALLATION PLANS
   Planning a fluoridation  installation usually must be done with the con-
currence or approval of State Health Departments. However, before deciding
on a specific design, the sections on chemicals, feeders and auxiliary equip-
ment should be scanned for possible alternatives or inclusions.  The  installation
design can then be submitted for approval. Some examples  of preliminary
planning of a fluoridation installation follow.

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   Example 1. A small water supply consists of an unattended well pump, pump-
ing into an elevated storage tank. The  pump operation is controlled by an
altitude switch on the elevated tank. There  is no other water treatment, and
the only building is a small shed at the well site. Water pumping rate is about
250 gpm.
   Plan:  Provided  the shed at  the well site is large enough and  of reasonably
sound construction,  a saturator and solution  feeder can be placed inside. The
solution  feeder can be tied electrically to  the operation of the  well pump so
that feeding cycles will coincide with the on-off operation of the well pump.
The fluoride injection will be directly into the pump discharge line. If there is
enough room in the  shed, and  the building is weather-tight and can be locked,
a few bags of sodium fluoride can also be stored inside (off the floor). A water
meter ought to be installed in the main, if there is none at present, and a hypo-
chlorinator added as soon as possible.
   Example 2.  A  water  treatment  plant is presently feeding chlorine, alum,
soda ash and carbon to a surface supply. There is an open channel in the plant
where  post-filtration  chemicals are  added.  The service pumping rate is 3000
gpm, and water is pumped directly from the clear well to the mains.
   Plan:  Since bulk fluosilicic acid is currently available nearby, the economics
of acid use appear favorable.  The acid storage tank can be  placed outdoors,
with a day tank and feed pump located at the site of post-filtration chemical
feed. An alternative system, for feeding sodium silicofluoride, will be provided.
This will consist of  a gravimetric dry  feeder with the dissolving chamber dis-
charge falling into the post-filtration feed channel. Chemical storage will be on
the floor above the feeder, where there is a separate area provided for fluoride
chemicals. An extension  hopper from the feeder to the storage floor facilitates
loading.  Either feed  system  will be  controlled  by electrical signals from a
rate-of-flow transmitter on the main.
   Example 3. A city's water supply consists of eight wells, all of which pump
directly into the  mains.  There  is an elevated storage tank, but it rides on the
water system and  there  is no point in the system where all the water can be
treated. Pumping rates vary from 200 to 500 gpm, with the operation of each
well pump controlled by pressure switches on  the mains.
   Plan: Since there is no central point where all the water can be fluoridated
with a single feed system, each well  pump will  have to be  considered as an
individual water supply. The  most economical  approach would be to use a
solution feeder  and fluosilicic acid at each pump location. The  acid would be
purchased in carboys and  platform scales will be provided at each  location.
Operation of feeders  will be  controlled by well  pump operation. Meters and
hypochlorinators will also be  installed at each location.
                                    61

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                           Chapter  VI
                 Control  And  Surveillance
ANALYTICAL PROCEDURES
   The ability to detect and measure accurately trace amounts of fluoride ion
was the key to the discovery of both the benefits and hazards of fluoride in
water. Now that fluoride  is being deliberately added to water, it is perhaps
even more essential that the quantities present be measured accurately. Not
only must the fluoride concentration of the untreated water be determined, so
that  one will know how much to add, but also the fluoride concentration of
the treated water must be determined as confirmation that the correct amount
of chemical is being added.
   Because the quantity of fluoride ion being measured is so  small (usually
about 1 part fluoride  ion to 1 million  parts water, or 1 milligram in a liter of
water), the analytical method must be adapted to the measurement of these
quantities and  the accuracy of measurement must be  well within the limits
established as the  maximum permissible variation from the optimum concen-
tration.  Thus, if a concentration of 0.9  to  1.1 (l.ChtO.l)  ppm is considered
optimal for a certain area, the analysis must be accurate to 0.1  ppm or better
in order  that one  is assured the actual concentration succeeds  or fails to fall
within these limits.
   It should be remembered that all  fluoride analysis concerns the determin-
ation of the quantity  of fluoride ion in solution, irrespective of the source of
that  ion. It may come from fluoride compounds occurring naturally  in the
water,  or from fluoride  or silicofluoride compounds added  to  the  water.
There is  no method for distinguishing one fluoride ion from another, nor is
there any method for determining to which metallic ion the fluoride ion was
originally attached.

THE STANDARD METHODS
   The generally-accepted analytical methods are outlined in detail in the latest
edition of "Standard Methods for the Examination of Water and Wastewater."
The Thirteenth Edition (1971) lists three methods: the Alizarin Visual (Scott-
Sanchis), the Photometric  (SPADNS)  and the Electrode Methods. There are
additional methods available, mostly based on colorimetric principles similar to
those used in the first two methods above, and there are modifications of the
Standard Methods which adapt them  to the use of simplified equipment and
                                 63

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procedures,  that  is,  the  co-called "test kits."  "Standard  Methods"  also
describes a preliminary distillation procedure, a step necessary when substances
present in the water interfere with the accurate  determination of the fluoride
ion. As with  the analytical methods themselves, other preliminary procedures
are available, but, just as with the unlisted analytical methods, these procedures
are regarded as inferior to the one listed in "Standard Methods."

ALIZARIN VISUAL METHOD
   The basis  for the alizarin visual method is the zirconium-alizarin reaction,
in which a red lake (a deep color) is produced by the combination of alizarin
and zirconium. Any fluoride present in the water sample or standard solution
removes zirconium from the reaction, thus decreasing  the intensity of color
present. In water samples which are high in fluoride, the only color apparent is
the yellow color of the unreacted dye. (Alizarin is sensitive to pH and its color
will vary from purple in alkaline solutions to yellow in acid.) Conversely, in
low fluoride  samples, the color approaches  the  deep  red of the  zirconium
alizarin  lake.  Intermediate  fluoride  concentrations give colors which  are
intermediate  between these  two. The reaction is  not an  immediate one,  but
progresses with time. After one hour, the reaction rate  is extremely slow,  and
for this reason,  the  time interval between  adding reagent  and making  the
measurement has  been selected as 60 minutes.
   The color  comparisons are made in 100-ml Nessler  tubes - tall glass cylindri-
cal tubes with flat bottoms. Usually, these are held in a rack with a reflector
below the tubes so that light is reflected  up  through the longitudinal axis of
the tubes to the eye of the observer. In practice, a number of tubes containing
standard fluoride solutions  at fixed concentration intervals are prepared in
addition  to  the  tubes containing the unknown samples. Fluoride reagent is
added to both standards and samples, and after the one-hour color development
time,  the  unknown samples  are  compared visually with the standards and a
determination made  by matching the colors. Sometimes,  this involves inter-
polation. For example, if the color of the  unknown sample appears to be mid-
way between that of an 0.8 ppm  standard and a 1.0 ppm  standard,  the
unknown  sample  is determined to have a  fluoride concentration of 0.9 ppm.
Obviously, the smaller the interval between standards, the greater the likelihood
of attaining a close match between color of sample  and that of one of the
standards.

SPADNS METHOD

   The photometric method is based on a  reaction similar  to the one used for
the alizarin visual  determination - a  dye lake is formed with  zirconium  and
SPADNS dye, and any  fluoride present has the effect of decreasing the intensity
of color. However, the colors produced by different concentrations of fluoride
are all shades of  red, making it almost impossible to detect these differences
by eye and making the use of a photometer imperative.

                                   64

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   A photometer is  an instrument for detecting differences in color,  and
 consists of a light source, a means for producing monochromatic light, and a
 photocell for measuring the intensity  of  the  light transmitted  through the
 sample. There  are  two general types of photometer;  the  filter photometer
 which produces monochromatic light by the use of a colored glass filter,  and
 the  spectrophotometer which achieves the  same end by the use of a prism or
 diffraction grating.
   The operating procedure  for  the use of the photometer in the SPADNS
 method for fluoride analysis depends  on the particular instrument used, but
 in general the determination consists of adding a measured volume of reagent
 to a measured volume of sample, placing a portion of the mixture in a cell or
 cuvette, placing the cell in the  instrument  and  taking the  absorbance reading.
 The absorbance reading is then  converted to fluoride concentration by consult-
 ing a curve prepared by plotting  the absorbance of known standard .solutions
 against their concentrations. Unlike the visual method, the photometric method
 involves a reaction which is instantaneous, permitting completion of the analysis
 within seconds after the reagent is added.


 ELECTRODE METHOD

   The electrode method  is based on  the  use of a specific-ion  electrode,
 resembling somewhat the electrodes used for pH determinations.  In the case
 of the fluoride electrode, the key element is a laser-type doped single  crystal
 through which only fluoride ions can move. When the  electrode  is immersed
 in a solution  containing fluoride ions, an electrical potential is set up between
 the  solution  and  a standard  fluoride solution  within the electrode.  This
 potential, expressed in millivolts,  can be either  positive or negative depending
 on  whether the fluoride concentrations of the  sample is lower or higher than
 that of the internal solution.
   Since  only fluoride ions can  move through the crystal, the  electrode is
 essentially specific for fluoride. A buffer is added to the sample to eliminate
 potential  interferences  and  to  insure uniform electrode  response despite
variations in  total  ionic  concentrations in  the sample.
   In  addition to  the  fluoride electrode  itself, the equipment  needed  for
 fluoride determinations includes a reference electrode and a meter for reading
the millivolt potential. As with the photometric method, the fluoride electrode
method requires that a standard  curve be prepared using  solutions of known
fluoride concentration.
   Except for the electrode method, none of the  fluoride analytical methods are
entirely specific for fluoride, and can be subject to  error caused by  other
substances in the water. To avoid the effect of these interferring substances,
the water sample can be distilled  from a solution  of sulfuric acid. The acid
converts  the  fluoride to a volatile compound  which  is distilled over by  the
application of  heat, leavir" u"hind most  other  mineral constituents  of  the
water.

                                   65

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TEST KITS
   Test kits based on the standard methods include color comparators, portable
colorimeters, and portable ion-meters. The color comparators, based on the
alizarin visual method, use a set of permanently colored standards with which
the reagent-treated  sample is  compared.  These  standards take  the  form of
colored glass or colored liquids in glass vials, and eliminate the necessity of
preparing  standards each time  a water sample is to be analyzed. The portable
colorimeters, based  on the SPADNS method,  are small photometers which are
pre-calibrated so that the  fluoride concentration  in a reagent-treated sample
can be read directly from a scale or chart without the necessity of preparing
standards  or a standard curve.  The portable electrode meter is  similar, in that
the scale of the meter is essentially pre-calibrated so that fluoride  concentra-
tions  are  read  directly  instead of  being  converted  from millivolt readings.

SAMPLING
   Surveillance  of fluoridation, based on these analytical methods, is absolutely
necessary for control of the process. While state health departments may require
only occasional tests, a minimum sampling of once per day is recommended.
Sampling should include both  the plant tap and some point in the distribution
system, and if the water source is a surface supply, a raw water sample as well.
   When fluoridation is just starting,  sampling should be more frequent, and
should include  a representative number of points in the distribution  system.
The fluoride ion, being a stable and persistent substance, provides an excellent
indicator  of flow patterns, and distribution system analyses  will  show how
long it takes for fluoridated water to reach the ends of mains  and whether or
not untreated  water is  entering the  system. One  possibility of the  latter
occurring  is when a reservoir  or standpipe is merely "riding"  on the  system,
contributing unfluoridated  water  during periods of low or no  pumping.
Eventually,  the water in  such storage facilities  is replaced with fluoridated
water, but  in  some instances, the  exchange is  so slight  that a considerable
amount of time elapses after fluoridation begins before the full fluoride level
is reached. Other possibilities include infiltration and cross-connections.

CALCULATIONS AND  RECORD-KEEPING

   Besides analytical  determinations  of fluoride  concentration in the water,
daily  records  of weight of chemical  fed and volume  of water treated will
provide a record of the theoretical fluoride concentration for that day and will
furnish an additional check on the adequacy of the treatment process. Most
states  require  that records be  kept  for both  analytically determined and
calculated fluoride concentrations.
   The calculations are simple, using the same  formula previously used for
dosage calculations, etc.:

                                    66

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   RI X Cl  = R2  X C2, where R!  is the rate or quantity of water being
treated in gpm or gallons,

        C i is the fluoride concentration in the water
           in ppm,
        R2 is the rate or quantity of fluoride compound
           added in Ibs/min or Ibs,
        C2 is the fluoride concentration in the
           compound used, in percent or Ibs/100 Ibs.
So, the  calculated  fluoride concentration (not including any fluoride already
present in the water) is:
           R2 XC2
     Cl=~~R7~
By converting gallons to pounds, and  cancelling units, the results will be in
pounds per million pounds, or ppm.
Examples:
 1.  A plant  is using sodium fluoride solution, 2% strength (7 Ibs dissolved
in  40 gal. of water. See  Table 3), and fed  100 gallons in one day. During that
day, 1  million gallons of water were pumped. What is the calculated fluoride
concentration (disregarding any natural fluoride content)?
         _ R2 X C2 _ 100 gal. X 7 lbs/40 gallons X 0.45 X 0.98
       1 ~    R!         8.331bs/galX 1,000,000 gal
              (0.45 is the fraction of sodium fluoride which
              is fluoride ion, 0.98 is the commercial purity)
   d = 0.92 Ibs/million Ibs, or 0.92 ppm
 2.  When 50 Ibs of 23% fluosilicic acid  are added to 1 million gallons of
water how much fluoride has been added (in ppm)?
      _ SO Ibs X 0.23 X 0.79
     1 ~ 1,000,000 gal X8.33 Ibs/gal
   (0.23 is the acid  strength,  0.79  is  the fraction of H2SiF6  which  is
   fluoride ion.)
                =  1.09 Ibs/million Ibs, or  1.09 ppm
 3.  A dry feeder record indicated a loss  in weight of 26 pounds of sodium
silicofluoride in one day. During that time, 1.8 million gallons of water were
treated. The commercial purity of the sodium silicofluoride was 98%. Calculate
the concentration of fluoride added.
      =    26 Ibs X 0.607 X 0.98
     1 ~ 1,800,000 gal X 8.33 Ibs/gal
   (0.607 is the fraction of Na2SiF6 which is fluoride ion, 0.98 is the commer-
   cial purity.)
                =  1.03 ppm

                                   67

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   In  calculating  the pounds  of fluoride ion added, both  the  fraction of
fluoride ion in  the pure compound and the purity  of the chemical must be
taken into account,  as in the above examples. Note  that these  calculations
give the  amount  of  fluoride added. If there  is a measurable concentration
of fluoride in the water before this addition, it must be taken into account in
order  to find the total theoretical fluoride concentration. For example, if the
raw water in (1.) above had 0.5 ppm F before treatment, and 0.2 ppm after
flocculation and filtering, the  total  F concentration would  be 0.2 plus 0.92
or 1.12 ppm. Note again that raw water fluoride  can be reduced by filtration,
and only  that  natural  fluoride present at the point  of fluoride compound
addition may be included in the  calculations.
   Calculations  can be simplified by  using  charts or tables, such as Tables
3 and  6.
Examples:
  1.  Given the same conditions as in No. 1. above, calculate  the fluoride
concentration using Table 3.
        100 gal. X 9000 ppm  no
   c'=	1,000,000     =0-9PPm
   (Note that using tables will give approximations only.)
  2.  Using information from  Table 6, calculate Example (2.) above. If 45.7
Ibs of 23% acid will add 1.0 ppm F  to 1 million gallons of water, 50 Ibs. would
add: 50/45.7 or 1.09  ppm.
  3.   Using information from Table 6, calculate Example (3.) above.
   Calculation:  The table gives pounds of chemical for 1 million  gallons. For
1.8 million gallons, the quantity  to produce  1.0 ppm would be: 1.8 X 14 Ibs.
Since  26  pounds were actually  used,  the fluoride  concentration would be:

   1.8  X  14Slbs.  X L°PPm= !-03 ppm
   Another device often  used to simplify calculations is the nomograph, or
alignment chart (Figs. 18 & 19). Nomographs are available for specific com-
pounds, or for  several different materials as in the illustrations. They may take
into account the purity of the chemical, or may not. In any case,  they are not
likely to be very accurate, but are useful for  at least getting rough estimates of
chemical requirements or, by working backwards, for  estimating the theoretical
fluoride concentration achieved.
MONITORS
   A monitor is a device for automatically providing a continuous record of
analyses: in this case, for providing a continuous record of fluoride concentra-
tion. The advantage of a continuous record over a spot-check, such as a daily
fluoride analysis, is that  the continuous record will show the fluoride concen-
tration at any given  time  rather than only at the  one time the daily sample
was taken. This type of record could prove helpful  in answering complaints
regarding under- or over-feeding, as well as in detecting variations in fluoride

                                    68

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             Table 6. FLUORIDE CALCULATION FACTORS
Compound
Sodium
Fluoride
Sodium
Silicofluo-
ride
Fluosilicic
Acid
Available F
(Pounds F per Pound of
Compound at 100% purity)
0.4525
0.607
0.792
Commercial
Purity
95%
96%
97%
98%
99%
95%
96%
97%
98%
98.5%
99%
20%
21%
22%
23%
24%
25%
26%
27%
28%
29%
30%
Pounds Compound
per Million Gallons
of Water to Add
1 .0 ppm F
19.4
19.2
19.0
18.8
18.6
14.5
14.3
14.1
14.0
13.9
13.8
52.5
50.0
47.8
45.7
43.8
42.0
40.5
38.9
37.4
36.3
35.2
The figures in the column at the extreme right can be used for calculating the
amount of fluoride compound to add for quantities of water other than one
million gallons. For example, the amount of 97% sodium fluoride needed for
100,000 gallons  would  be 100,000/1,000,000 or 0.1  the amount indicated.
For two million  gallons, the amount of fluoride compound needed would be
twice as much, etc.
Similarly, if other than 1.0 ppm F is to be added, because of the presence of
natural fluoride or because of an optimum concentration other than 1.0 ppm,
multiplying the figures in the right-hand column by the appropriate factor will
give the number of  pounds to use.  For example, if there  is 0.3  ppm  F
occurring naturally, and the optimum level is 0.8 ppm, only 0.5 ppm would
have to be added, or 0.5 as much as indicated.
(Level desired, 0.8 ppm, minus natural fluoride, 0.3 ppm, eqvals 0.5 ppm, the
amount to be added.)
                                 69

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                                      INSTRUCTIONS
1.  Substract the natural level from the desired
   level to get the fluoride treatment figure
   (ppm fluoride ion added).

2.  Draw a line from the flow figure straight
   through the fluoride treatment figure to
   the fluoride ion line.  The intersection will
   show the pounds  of fluoride ion per day
   required.

3.  This weight of fluoride ion may be obtained
   from any of the chemicals listed.  Starting
   at the pounds of  fluoride  ion per day required.
                                                    draw a horizontal line to the right and read
                                                    the weight of dry chemical or  volume of
                                                    liquid chemical required.

                                                  4. Thus in the example, a flow of 600 gpm
                                                    requiring 0. 9 ppm fluoride ion added
                                                    requires 6. 45 pounds of fluoride  ion per
                                                    day.  This can be obtained from 14. 8 Ib
                                                    per day of sodium fluoride,  11. 0 per day
                                                    of sodium silicofluoride,  2. 55 gal per day
                                                    of 30% fluosilicic acid,  or 44. 2 gal per day
                                                    of saturated sodium fluoride solution.
                            Figure 18. Fluoridation Nomograph

                                               70

-------
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-------
concentration for unexplained reasons. If the monitor is equipped with an alarm
system, it  can  alert the operator to feeder malfunctions or other problems
affecting fluoride level.
   Most  monitors  are  actually  continuous or  semi-continuous  analyzers,
performing colorimetric or electrical  analyses on  a  flowing  sample  stream
or on discrete water samples taken at close time intervals. Some monitors use
the SPADNS procedure, metering out reagent in  proportion to  sample flow
and then passing the treated sample through a photometer. A recorder converts
absorbance readings of the photometer to concentration figures which then
appear on  a recorder  chart.  Other monitors  use  the  electrode procedure,
either  with or  without the addition of buffer. When no buffer is used, the
fluoride and reference electrodes are immersed in the water sample stream and
an appropriate recorder converts millivolts of potential to parts per million of
fluoride.  Obviously, the absence of buffer may render this  type of monitor
unreliable when there is a  change in water quality. When buffer is used, the
monitor record is definitely more reliable. A monitor using buffer is necessarily
more complicated, since metering pumps must be  used for both water sample
and buffer  to insure maintenance of the correct ratio of volumes of each. Still
another monitor uses a different type of electrode and buffer, and is based on
an  analytical  procedure adapted  specifically  to  flowing  sample  streams.
   There  are  other  types of monitors which are not analyzers, for example,
the one based on conductivity measurements. The differences in conductivity
between  untreated  water and water after fluoride has been  added  can be
interpreted to give  the  amount of fluoride  added, but here again we have a
system which may be unreliable  when  a  change  in water quality  occurs,
especially if that change involves a change in the  raw water  fluoride content.
   Some  water plants employ monitors on both the raw water and the  treated
water,  the  former being used to alert the plant operator to changes  in raw
water fluoride level. If  the treated-water monitor is equipped as  a controller,
it can  be used  to automatically adjust the fluoride feeder to deliver fluoride
compound  so that  the final fluoride concentration is maintained within pre-set
limits.
   It should be pointed out that a monitor, even one used as a controller, does
not relieve  water plant personnel from the necessity for making the prescribed
fluoride analyses at the  prescribed intervals. If for no other reason, the regular
spot-checks will serve  to verify  the proper functioning and accuracy of the
monitor.

TROUBLE-SHOOTING
   The ideal situation  occurs when  the  fluoride feed rate is accurately
calculated,  the water  flow rate  does not vary,  and  once  set,  the fluoride
feeder  operates merrily day after day, providing  exactly the desired concen-
tration of  fluoride  in the water without  the slightest variation and with no
attention from the  operator  other  than  the occasional refilling of a hopper.
There may be such  situations, but even if they exist, the water plant personnel
ought  to know about the  potential difficulties and how to overcome them.

                                    72

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LOW FLUORIDE READINGS

   When the  fluoride  concentration  determined by analysis  is consistently
lower than  that determined by calculation, there are a number of possible
explanations. Presuming that  the calculations are correct, and are based on
accurate weight and flow figures, the first logical suspect is the analysis. If alum
is used for flocculation, traces of aluminum  in the finished water can interfere
markedly with colorimetric analysis, always influencing the readings negatively.
A high iron  content can do the same thing if the SPADNS method is used. In
rare cases, chloride  and alkalinity can  interfere also, but the concentrations of
these would have to be extremely high. The analysis of a distilled sample, or
conversion to the electrode analytical method can confirm or rule out this
potential error.
   If the  analysis  can be verified as accurate, the'next suspect would be
chemical purity. Fluosilicic acid  has  the most  variable purity, and can be
anywhere  from over 30  down  to 20% pure.  Ordinarily,  the manufacturer
specifies the purity of a given batch,  but  if there is some doubt, the  acid
should be analyzed according to  directions given in AWWA  Specifications.
Sodium fluoride and sodium  silicofluoride  usually exhibit less variation in
purity, but  occasionally  a  relatively impure lot is found. The AWWA specifi-
cations  give procedures  for  determining  purity of  these  materials  also.
   If sodium fluosilicate is being used,  the possibility of incomplete solution
should be  explored  next. An examination of the feeder dissolving chamber and
the area near  where  the  solution is being fed  should reveal  deposits of
undissolved  chemical if detention time is insufficient, solution water flow rate
wrong, or baffling of the dissolving chamber ineffective.
   In the case where manually prepared solutions are used, incomplete mixing
can be  at fault, as can be the measurement of both  chemical and water.
   If none of the above possibilities prove to be the source of error, and all
measurements and calculations have been checked out,  it may  be advisable to
check out the water system to find  out if unfluoridated water is entering at
some  point  and is  thus diluting the water being fluoridated at  the  plant.

HIGH  FLUORIDE  READINGS

   When fluoride concentration determined  by analysis is consistently higher
than that determined by calculation, analysis, and chemical purity can also be
the sources  of error. The presence of Calgon  or other  polyphosphate  is the
usual cause  of analytical error in the positive direction. Failure to eliminate
chlorine from the water sample can  also  lead to high  results  in colorimetric
analysis.
   Failure to take into account the  fluoride content of the raw water may
result in adding more  fluoride than  is needed, and surface supplies, which
can. show  considerable variability, should be analyzed daily in order that the
correct  dose can be calculated. If the water supply comes from wells, the

                                   73

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variability is much less, but in the case  of a higher-than-calculated fluoride
concentration the possibility of  a contribution  from  a high-fluoride well
should be investigated.


VARYING FLUORIDE  READINGS

   The most difficult  type of problem to solve  is  the  situation when the
fluoride  concentration  is  variable even  though calculations show that the
fluoride  feed rate  is  in  the desired  proportion to  water flow  rate. One
possibility which can be readily eliminated is the fluoride feeder. A check on
the delivery rate, with weight  measurements  at  short intervals, will  reveal
whether  or  not the feeder delivery rate is constant.
   Almost all of the factors which can produce consistently low or consistently
high  fluoride analyses can  also  produce variable  errors,  if  the analytical
interference, the chemical purity, the raw-water fluoride or the completeness
of chemical  solution are  variable conditions. In the latter case, undissolved
sodium silicofluoride  can eventually  go into solution after  a quantity of
undissolved material accumulates at some point, and a solution feeder can begin
drawing from a concentrated stratum after feeding from a dilute stratum in an
improperly mixed solution tank.
   One of the  causes  of  varying fluoride content in a treated  water system
is  the intrusion, on an  intermittent basis, of un-fluoridated water into the
system. This can be from an outside water source, such as a well or a connection
to another  system,  or can be from a storage  reservoir which is part  of the
system. The lattej situation occurs usually when fluoridation is just beginning,
and no attempt  has been made to fluoridate  the reservoir separately. What
happens  then is that during  periods when no water  is being pumped,  or the
pumping rate is less than  the demand, water flows into the system from the
reservoir, and  since this   water  has not yet been  fluoridated, low-fluoride
readings  will result,  particularly at the sampling points nearest the reservoir.
Eventually,  what with flow  pattern  reversals  as the  pumps operate inter-
mittently, the reservoir contents will become displaced by fluoridated  water,
but there have been cases, involving a large reservoir at the end of the water
system, when it has  taken years before  there was a complete turn-over  of the
reservoir contents. The obvious solution to this type of problem is, of course,
to fluoridate the reservoir separately at the time  fluoridation of the system
begins, if such is possible.
   A  similar situation  occurs  when an  elevated tank or other storage facility
merely "rides" on the system, and  its contents rarely enter the system or at
best there is only slight intermixing. Sampling points near the tank will have
varying fluoride  concentrations - normal when there  is pumping, and low
when water is  being drawn from  the tank. The solution here is to allow the
tank contents to drain into the system before fluoridation begins and then not
refill  the tank until the  entire system is up  to the  optimum fluoride level.

                                    74

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   Cyclic fluoride levels can result when the feeder is operated intermittently,
such as when capacity  is reduced by the use of a cycle  timer, and there is
insufficient storage capacity between the feeder and the consumers. Detention
time in mains or storage facility between feed point and first consumer is an
important factor in providing homogeneous fluoridated water.

OTHER PROBLEMS
   There are undoubtedly  many  other possible  causes  for fluoride levels
which  aren't  exactly what they are supposed to be, but one thing is certain -
fluoride doesn't "disappear" in the pipelines, nor is it likely that fluoride will
concentrate  at  points or become  leached out of incrustations in the mains.
Unlike chlorine,  fluoride does not  have the ability to dissipate,  and even
though trace  amounts are incorporated into tubercles in pipelines, the extreme
insolubility of these formations precludes subsequent dissolution. When there
is  an unexplained difference  between the calculated  and observed fluoride
concentration, more often  than not, the calculations are at fault. If they are
not, and none of  the  above  possibilities apply or they can otherwise be
eliminated, common sense  and a knowledge  of the  individual system should
enable the operator to locate and correct the cause of trouble.
   It should be noted that over- or under-feeding for short periods, for example
a variation of 0.2 or 0.3 ppm for two or three  days, actually is of no serious
consequence, but such  variations should be investigated since they may be
indications of potential  problems  of a more  serious nature.
   Erratic feed  rates or  failure to feed are usually due to problems which are
discussed in  the  chapter entitled, "Maintenance."  Saturator  problems are
discussed in the chapter on solution preparation, and other potential troubles
are mentioned in the chapter on "Selecting the Optimal Fluoridation System."
                                   75

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                          Chapter  VII
                          Maintenance
   To insure uninterrupted and unvarying fluoride feed, proper maintenance of
equipment is required. This includes maintaining not only the fluoride feeder,
but also all the appurtenances, feed lines and the laboratory testing equipment
as well.

CLEANING  AND LUBRICATION
   Like any  other mechanical  device, fluoride feeders must be kept clean and
lubricated if they are expected to  perform their  function efficiently.  A
regular program of maintenance will also minimize costly break-downs and
insure long life for the equipment. Electric  motors usually come with a pre-
scribed schedule for  lubrication - the right  type, amount and frequency  of
lubrication are all important. Gear boxes must be kept filled to the prescribed
level with the proper lubricant,  and all moving parts and unpainted metal
surfaces should be kept clean and rust-free. If there are grease fittings, the
proper grade,   quantity  and  frequency of greasing should be observed.

SPARE  PARTS
   Fluoride  feeders and  related equipment, when  purchased,  usually are
accompanied by  an instruction booklet and/or parts list.  The instruction
book will contain information on maintenance  and repairs, and the parts list
will enable the operator to select replacement parts when needed.
   If these papers have been lost, a  call or letter to the manufacturer of the
equipment or his representative  will  suffice  for replacement. The equipment
man will  also be happy to suggest a list of  spare parts to be kept on hand.
Having parts available  can greatly minimize  the length of shut-downs due  to
equipment failure. In  the larger water plants, having an  entire  spare feeder
available may prove to be prudent.

INSPECTION AND RE-CALIBRATION
   The best fluoride feeders  will feed as  intended only if the measuring
mechanism  is  kept clean  and  operative. Thus, the  diaphragms or pistons  of
solution feeders, the rolls, belts,  discs or screws  of dry feeders and associated
mechanisms  of both types should be regularly inspected for signs of wear  or
damage and  repairs or replacements made before the machine actually breaks

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down. Even with all parts in the best mechanical condition, fluoride delivery
can be affected by  leaks, spillages, build-ups of precipitates from solutions or
accumulations  of  dry  chemicals  on  or  around  measuring mechanisms.
Occasional re-calibration of the feeder will reveal  evidence of potential mal-
function, and is generally a good idea for insuring accurate feed rates.

LEAKS
   Leaks in and around the discharge line of a solution  feeder are  more than
an annoyance — they can materially  affect  the quantity of solution delivered
and thus result in low  fluoride levels. Leaks are always somewhat corrosive,
ranging from the salt effect of  sodium fluoride solutions to the acid corrosion
of fluosilicic acid. Even the smallest leak can result in damage to the feeder,
appurtenances  or surroundings is left unattended. Leaks of strong solutions
result in  the formation of crystalline deposits which, if allowed to build up,
make subsequent cleaning difficult.  A leak in  the suction line  of a  solution
feeder, while not immediately apparent,  will adversely affect delivery and can
eventually  lead to  air-binding and   cessation  of feed.  Air-binding can  also
be caused by injecting  fluoride solution at the top of a main, where air can
collect.
   Leaks in a dry  feeder installation cause a dust problem, and if there is a
leak in the feeding mechanisms, for example around the rollers of a volumetric
feeder, there will be an error in feed  rate. The  dust represents, in  addition to
an economic loss, a hazard to equipment and personnel.
   Leaks in equipment not related to fluoride feed can present problems none-
theless. For example,  a water leak  can  result in dampness and  subsequent
caking of dry chemicals. A leak  in a chlorine gas system can result in damage to
feeders and associated equipment, etc. Leaks in other dry feed equipment can
result in dust contamination of the fluoridation installation.

PRECIPITATES
   Anytime strong solutions are used, the possibility of precipitation build-up
is  present. In  a  solution  feed system, precipitates in  the feeder pumping
chamber  or on the check-valves will affect delivery rate or  even stop the
feeder entirely.  Deposits in suction or feed  lines can build up until flow stops,
and a coating of insoluble matter on a saturator bed can prevent water from
percolating through. If the deposits are the  result of water hardness, softening
the make-up water will eliminate the pioblem. If softening  is impractical,
frequent  inspection and removal of th
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   Tanks in which solutions  are prepared invariably show precipitates of the
insoluble impurities from the chemical used or of insoluble compounds formed
by the reaction of the chemical with mineral constituents of the water. If a
separate tank is used for solution preparation, and the clear supernatant layer
transferred to  a day  tank, problems will be minimized,  but not necessarily
completely eliminated.
   A regular schedule for cleaning out  a saturator should be established, the
time interval between cleanings depending on the amount  of usage and the
accumulation of impurities in the saturator. The cleaning operation is described
in the chapter on solution preparation.

STORAGE AREA

   Storage  areas, while not necessarily a major factor in maintaining accurate
feed of fluoride, need also to be kept in an orderly and clean condition. Bags
of dry chemicals should be piled neatly on pallets, with empty bags rinsed out
and disposed of promptly. Whenever possible, whole bags should be emptied
into  hoppers, since partially  empty bags present a spillage  hazard and are a
nuisance to store.  Metal drums should be kept off the floor and kept tightly
closed. The storage area for  fluoride chemicals should be well isolated from
areas used  to store other  chemicals  to  preclude mix-ups, and all  extraneous
material, such as lubricating oil and cleaning equipment, should be kept out of
the area. Both  the stored chemicals and the  general  area  should be kept free
of dust,  not only from the chemicals used in fluoridation but from other
chemicals stored or used nearby. In general, a neat and clean storage area is an
indicator of good water plant  practice and maintenance.

LABORATORY

   The  laboratory or  fluoride testing  area  calls  for special  precautions in
cleanliness. The merest  hint  of fluoride dust on glassware can result in gross
analytical errors. Dirty pipets or other measuring glassware can produce errors
in volume measurements,  and proper drainage is hindered, resulting in carry-
over  of solutions from one sample to the next. In  colorimetric analysis, dirty
glassware prevents accurate color determination whether the method is visual
or photometric. Permanent standards for colorimetric test kits, since they are
difficult to clean,  should  be  kept covered  when not in use. Reagent bottles,
buffers and standard solutions should all be kept tightly closed when not in
use. Evaporation ruins not only the reagents, but acid fumes from them can
damage objects nearby. Analytical  instruments  should  always be  covered
when not in use,  since fumes and  dust can corrode electrical connections,
cloud mirrors,  and result  in  expensive repairs or replacement.
   The use of  phosphate-based detergents for cleaning glassware presents a
hazard because  of potential interference of phosphates in colorimetric analysis.
Since tap  water contains fluoride,  it is  imperative that  all  glassware  be
thoroughly rinsed in distilled water of good  quality.

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   The  quality of distilled water is  best  verified  by conductivity measure-
ments, but when equipment for this procedure is  lacking, help can often be
obtained from State Health Departments. This help can  take the form of
checking a water  plant's distilled water or of furnishing  a  sample of good
quality  distilled water  for  comparison. Comparing fluoride  analyses of the
plant's distilled water vs. that furnished by the State will reveal contamination,
if  any.  (Many State Health Department laboratories  will furnish  a standard
fluoride solution for check purposes,  also.)
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                        Chapter  VIII

                     Safety  And Hazards

           In  Handling  Fluoride  Chemicals

SAFETY EQUIPMENT AND  CHEMICAL HANDLING

   Admittedly, fluoride chemicals, in the large quantities likely to be present
in a water plant, present a health  hazard to plant personnel. While fluorides in
water, at the recommended concentration  of about 1.0 ppm, have been
exhaustively studied and have been firmly established as safe beyond question,
the fluoride levels to which a water plant operator can be exposed are at least
potentially much higher. Since the operator  is presumably already drinking
water containing the optimum level of fluoride, any  additional contact with
fluorides constitutes overexposure. Obviously, the best safety measure is the
prevention of unnecessary hazards, and  this  implies  the proper handling of
fluoride chemicals and the use of adequate safety  equipment.

 INGESTION

   Overexposure to fluoride chemicals can be the result  of ingestion, inhalation,
or bodily contact with spills. The most likely source  of oral exposure would
be  the contamination of food or drink, either by accident  (such as if the
fluoride chemical were mistaken for sugar  or salt) or through carelessness (such
as if  meals  were eaten in areas where  fluorides were  stored  or applied).

INHALATION

   Perhaps the greatest chance for overexposure to fluoride chemicals comes
from  the  accidental inhalation of dust.  While the use of masks and other
protective devices is commendable, everything possible  should  be  done to
minimize the production of dust. Logically, if fluoride sacks are  moved care-
lessly  or if the bags are emptied  too quickly, the concentration of fluoride
dust in the air will rise. Cautious handling will help a great deal in keeping the
concentration of fluoride dust at a safe  level. As examples: bags should not be
dropped; bags should be opened with an  even slit  at the top to avoid tearing
down  the side; and the contents of bags should be poured gently into hoppers.
The use  of crystalline chemicals  and installation of bag-loading  hoppers are
other  ways for reducing the production of dust in  the air. Good ventilation is
absolutely necessary in work areas,  even if there is no visible dust and masks are
worn.

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SAFETY PRECAUTIONS
   The recommended safety equipment for handling fluoride chemicals includes
goggles, gloves,  aprons,  boots,  dust  masks, respirators,  exhaust  fans, dust
collectors, etc. While  the use of this equipment will minimize an individual's
contact with the chemicals,  additional safeguards  should be applied. First,
meals and snacks should be eaten in non-work areas in order to avoid contact
with fluoride powders and dust. If there are no cafeterias or spare rooms, then
going outdoors should be considered  whenever possible. If it is necessary to
eat in a work  area,  then person should be  additionally cautious in avoiding
contamination of food. (Blue-tinted sodium fluoride and sodium silicofluoride
will  prevent mistaking fluoride  for food,  and will also give clues  as to the
dispersion of fluorides in the work area.)
   Second, the  use  of properly labeled fluoride  containers will  minimize
the danger of mistaken identity, or the inherent danger of a container Which
has no label at all. It is best to keep  fluoride chemicals in their original con-
tainers, but  if this is  not always practical, these chemicals should be kept in
labeled containers restricted to fluoride chemicals only. A  further precaution,
required in some States, is to keep fluoride  chemicals in a separate, locked,
storage area.

ACID HANDLING
   Fluosilicic acid requires special precautions in handling. Spilling on the skin,
splashing in  the eyes and inhaling vapors are all serious hazards. The absorption
of fluoride through the skin is negligible, but the acid is corrosive and it is this
characteristic which constitutes  a hazard  in skin contact. Careful handling,
quick rinsing of spills or splashes, the  use of respirators, and especially ventila-
tion are the best safety measures.

FIRST AID
   There is no record of any water plant operator ever being seriously injured
in the handling of fluoride chemicals,  but knowledge of first-aid measures for
treatment of accidental fluoride over-exposure is a good thing to have.

FLUORIDE EXPOSURE SYMPTOMS
   It is important to be able to detect if someone is   suffering from over-
exposure  to fluorides, so  that  treatment can be initiated  early, thereby
increasing the patient's chances  for  complete  recovery.  In acute poisoning,
generally  the  first  symptoms to appear are vomiting, stomach cramps and
diarrhea. If the poisoning is due  to the igestion of large amounts of fluorides,
the  vomitus  may be white or colored, depending  on whether the fluoride
contains dye. The appearance of the vomitus may be important in determining
whether fluoride is indeed the toxic agent. Illness could be due to something
else.  Usually the patient becomes  very weak, has  difficulty in speaking, is
thirsty, and has disturbed color vision.

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   The signs  of acute poisoning by inhalation consist of sharp biting pains in
the nose followed by a nasal discharge or nosebleed. The most likely response
to an acid spill or splash is a tingling or burning sensation, or if the eyes are
involved, severe eye irritation.

TREATMENT
   The importance of rapid  treatment cannot be over-emphasized. Once acute
poisoning by  fluoride is apparent, treatment should be initiated while awaiting
proper medical  assistance. The treatment is as follows:
 1.  Remove the patient from exposure and keep him warm.
 2.  Administer  3  teaspoonsful of  table  salt in a glass  of warm  water.
 3.  Induce  vomiting by irritating the back of the throat with a  spoon.
 4.  Administer  a  glass of milk.
 5.  Repeat  the salt and vomiting procedure  several  times.
   Treatment for the individual suffering from nosebleed after inhalation of a
high concentration of fluoride consists of the following:
 1.  Remove the patient from exposure.
 2.  Place the patient's head  back while  placing absorbent material inside
     the  nasal  passages. Change the material often.
 3.  Take the  individual to a  physician.
   Treatment for an individual  suffering from acid exposure consists of rapid
and thorough rinsing of the affected area with copious quantities of water.
Further  treatment,  if   necessary,  should  be  performed  by  a  physician.
   In summary, the first goal in  fluoride handling safety is to prevent poisoning
resulting from  overexposure; this  means,  use  safety equipment  and avoid
unnecessary contact. Next,  be alert  to  the early  signs of fluoride-related
illness  in  yourself and your co-workers. Should illness from fluoride occur,
react quickly with the proper treatment for the patient.
   Remember,  no water  plant personnel have ever been seriously injured by
fluorides. Do you want to be the first?
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                            Chapter  IX

                    Technical  Problems

              Attributed  To  Fluoridation

   As stated earlier,  feeding fluorides is  essentially the same as feeding other
water treatment chemicals, and problems can be expected just as they can be
with  other  chemicals.  However, due  to  the  controversial nature  of the
fiuoridation process,  many of the problems attributed to fluoridation are more
imagined than real.

CORROSION
   One  of the first objections  to  the  feeding  of  fluorides  was  that the
chemicals were thought to be extremely corrosive and would cause disinte-
gration of the pipelines. Part of this erroneous conception can be traced to the
confusion over  fluoride versus fluorine, and  the association of fluoride with
hydrofluoric acid. It  is  well known that fluorine is a violently reactive gas, and
especially that hydrofluoric acid is strong enough to eat glass.  What is added
to the water is an essentially neutral salt of hydrofluoric acid, or fluosilicic
acid or one of its salts, not fluorine or hydrofluoric acid. Fluorine could not be
used,  since it is too  hazardous and too expensive, and hydrofluoric acid has
been used in only one fluoridation installation. But even if they  were used, the
important thing to remember is that the amount being put in the water  is
usually around  one  part per million as  the fluoride ion,  and one part per
million of the  most  corrosive substance would have little or no effect at this
dilution.  Fluosilicic  acid and its salts exhibit  a low pH  in solution, the
depression of pH being most apparent in poorly buffered waters, but there is
no indication that such waters have their corrosivity increased by the addition
of fluoride. There has been no reported instance of pipeline corrosion traceable
to the fluoride content of the water.

ENCRUSTATIONS

   The analysis of tubercles  and other  pipeline encrustations has in some
cases revealed an extremely high fluoride concentration, even in places where
fluoridation was not practiced! This revelation has  given  rise to  fears that
fluoride will be absorbed in the pipeline, then released at  dangerously high
concentrations  at  some future time.  Again,  these fears are groundless. The
deposition of fluoride in pipeline  precipitates is so gradual  that the quantity
lost from the water  cannot be detected by the best analytical  means, and

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studies  have  shown that feed-back from such  postulated  sources as pipe
coatings, tuberculation, treatment sludges and storage-reservoir sediments does
not occur. On the contrary, these studies show  that to achieve undesirable
fluoride ion concentrations from such additions would require suspensions of
the coating, sludge, or rust in quantities so great  as to render the water non-
potable and unfit for use. Even hydrant flushings  with water clearly unaccept-
able for normal use have not produced concentrations of fluoride above the
optimum  recommended  in  the  U.S.P.H.S.  Drinking Water Standards.  In
another study, the  use of a cold-chisel was required to dislodge the fluoride-
containing tubercles and even this extreme means failed to produce an  appre-
ciable increase in the fluoride concentration.
   A  related fear is  that  it is impossible to  maintain  a  constant  fluoride
"residual" in a long pipeline. Part of this fear is based on the deposition of
fluoride in tubercles or other encrustations, as mentioned above, and  part is
based on experience with chlorine. But fluoride is an ion, not a gas or unstable
entity  as are chlorine  or  the hypochlorite radical,  and the term, "residual,"
does not  apply here. Fluoride is  not dissipated by  organic materials, as is
chlorine, and there is no "demand" to  be satisfied before the amount added
can be detected in the water. In other words, the fluoride added to the water
can be  fully accounted  for by analysis immediately  or at  any subsequent
time.  A study has proved that neither the length of line, period of flow, age
of pipe, nor materials to which the water is exposed affect  significantly the
average fluoride ion content in  distribution systems.

FLUORIDE LOSSES
   There is one situation which does result in the loss of fluoride, and  that is
when  the  fluoride is added  before  coagulation  and  filtering,  or  before
softening by the lime-soda ash process. In  either of these processes fluoride is
lost by precipitation  or  absorption on floe, and the amount of loss  is pre-
dictable. (At a dosage rate of 100 ppm alum, fluoride loss will be about 30%.
Loss of fluoride in the  softening process  is directly proportional to the con-
centration of magnesium in the water or the lime.) In most cases such losses
can be avoided by  merely changing the fluoride  addition point to a pipeline
leading from the filters or to the clearwell itself.

COMPATIBILITY

   The  question  of compatibility of fluoridation with  chlorination  or  any
other water treatment process  has been raised, but  aside from the processes
mentioned above, there  does not appear to be any significant conflict. One
possible exception  to this occurs when calcium-containing compounds, such
as lime or calcium hypochlorite, are used. If the  calcium-containing chemical
and fluoride  are  injected in  close proximity,  a precipitate  of calcium
fluoride will form, the amount of precipitate depending on the concentrations
of  the respective  solutions. The obvious  preventive measure is to space  the
respective injection points as far apart  as possible.

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TASTES AND ODORS
   Objectionable tastes or odors of the water have been attributed to fluoride,
but  one can  surmise  that  this imaginary response  can be attributed  to  a
mental association of fluoride with chlorine. Taste panels have verified that
the fluoride ion is both  tasteless  and odorless, even  at much higher concen-
trations than those employed in water treatment.

INDUSTRIAL PROCESSES
   When fluoridation first  began, there were fears  that fluoridated water
would adversely affect many industrial processes  which use  the water. Some
of the processes  investigated included baking, brewing, ice-making,  and the
manufacture  of chemicals, porcelain enamel and  frit,  drugs, soap, porcelain
insulators, food, beverages,  etc. The  effects of fluoridated water on steam
generation and sewage treatment have  also been  investigated. In only two
cases has there been any problem, and one of these is still not fully understood.
The  first case  involved the manufacture  of baby food, in which  the  long
cooking process could possibly result in  the concentration of fluoride as the
water evaporated. The Food and Drug Administration has ruled that the  facts
in each particular case will be controlling, or in other words, there will be an
objection only if there is a significant concentration of fluoride in a particular
case.  In  such a case, defluoridated water  will have to be  used. The other
problem involved the manufacture of ice, in which  an increased number of
cracked ice blocks was found after fluoridation began. While this phenomenon
has never been explained, the cracking of ice blocks  can be corrected by the
use of a commercial additive commonly used by ice manufacturers long before
fluoridation began.

ENVIRONMENTAL EFFECTS
   Recently,  as part  of the  increased  interest  in the  environment, there  have
been fears that the waste  water from municipalities which practice fluoridation
will be a detriment to the body of water which receives it, and that the fluoride
concentration in such bodies of water will  continually build up as a result.
Experts agree that fluoride, in the concentrations  usually found in municipal
wastewater, is not in any way harmful to fish or other aquatic life. Actually,
since  all  bodies of water naturally contain some quantities of fluoride, there
is very little  change in the fluoride concentration of the water in these bodies,
due  to  the diluting  effect of rain and run-off. As for the oceans and  seas,
these naturally contain about 1.4 ppm fluoride, so the addition of municipal
waste water  results  in a localized  lessening of the  fluoride concentration.
Fluoride will  not concentrate in a river any more than it will in a pipeline, and
the blending  of fluoridated  wastewater with the normal flow again results in
dilution.
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                           Chapter X
       References  And Suggested  Reading
   The following list of books, articles, and manufacturers' bulletins contains
much helpful information on fluoridation  practice in general and on specific
installations and pieces of equipment. The books are usually available  in the
larger libraries,  and engineering reference  libraries  will probably have the
technical journals in which the articles appeared. Manufacturers' bulletins can
be obtained from company representatives  or from the company itself. (Com-
pany addresses are given the first time the company name appears in the list.)

 1.  Manual  of Water Fluoridation  Practice, by  F.J. Maier. McGraw-Hill
Book Company,  Inc.,  New  York ($8.50)
 2.  Fluoridation of Water Supplies, Ref. 2-SIC 49-2, B.I.F., a unit of General
Signal Corporation, Providence, Rhode Island 02901. (Free copies on request)
 3.  Fluoridation  Systems,  Wallace  & Tiernan  Division,  Belleville,  New
Jersey  07109. (Free  copies on  request)
 4.  Fluoridation  Systems  Designed  for  Hydrofluosilicic  Acid,  Precision
Control Products Corporation, Waltham, Massachusetts 02154. (Free  copies
on request)
 5.  Fluorides (Water Fluoridation with Sodium Fluoride), Allied Chemical
Corporation,  Morristown,  New Jersey 07960.  (Free  copies on  request)
 6.  AWWA  Standards  for Sodium  Fluoride, Sodium Silicofluoride  and
Fluosilicic Acid. AWWA, January  1971 and  June 1971. ($1.00 each for
Members,  $2.00  each  for Non-Members)
 7.  Standard Methods for the Examination of Water and Wastewater, (13th
Edition) APHA, New York. ($22.50 for Non-members, $16.50 for Members of
APHA, AWWA, or APCF)
 8.  Fluoridation Chemicals - The Supply  Picture, by E. Bellack and R.J.
Baker, JAWWA, April  1970. (Free copies  from the authors)
 9.  Fluoridation in Major  Cities of the United States, by W.T. Ingram and
G.W. Moore, JAWWA, September 1959.
10.  Upflow Saturator, Precision Control Products Corporation, Information
Letter No. 49.
11.  B.I.F. Sodium Fluoride Saturator, BIF Specification Data Sheet 1210.
201-2.

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12.  W & T Fluoride Saturator, W & T Brochure 60.510.
13.  Water Meter Operated Feeder, W  & T Brochure 80.110.
14.  W & T Loss-of-Weight Recorder, W & T Brochure 370.120.
15.  W & T Volumetric Dry Feeders, W & T Brochures 320.100 & 320.120.
16.  W & T Gravimetric Dry Feeder, Brochure 310.100.
17.  W & T Solution Feeders, W & T Brochures 80.120 and 80.135.
18.  Precision Solution Feeders, Precision Control Bulletin 132.
19.  The Art of Feeding Fluoride, BIF  2.20-3.
20.  Water Fluoridation  with  Fluosilicic Acid, Technical Bulletin F-l-670,
Grace Agricultural Products Division, Baltimore, Maryland 21203.
21.  Guidelines  to Automatic  Proportional  Chemical  Feeding,  Precision
Bulletin  960-357.
22.  Continuous Analysis and  Control of Fluoride, by R.J. Walker and R.R.
Smith,  JAWWA, April 1971.
23.  Anafluor Continuous Fluoride Analyzer, Fischer & Porter Specification
17S4000 & 17S4400, Fischer & Porter  Co., Warminster, Pa.  18974.
24.  Chemonitor  pF   Fluoride  Analyzer,  Calgon   Bulletin  No.  B-5-054.
Calgon  Corp., Pittsburgh, Pa.  15230.
25.  Practical Automation of Water  Treatment  Monitoring and Control
Systems, by  H.M. Rivers & G.W.  Sweitzer, Calgon Corporation.
26.  Fluoride Automatic, Continuous Analyzer/Controller, Delta  Scientific
Specification  Sheet  8030, Delta  Scientific Corp., Lindenhurst, N.Y.  11757.
27.  Foxboro Model  32FMS  -  A  Fluoride Measuring System for Potable
Water,  General Specification Sheet GS  6-1A2 A, The Foxboro Co., Foxboro,
Mass. 02035.
28.  A  Selective  Ion  Electrode System  for  Fluoride  Analysis, by R.H.
Babcock & K.A.  Johnson, The Foxboro Company.
29.  Automatic Fluoride Monitor, Advance Information Bulletin,  E.I.L.
(Electronic  Instruments Limited) England. (Cambridge Instrument Company,
Ossining, New York 10562).
30.  Technicon CSM-6 Water  Monitor, Technicon Instruments Corporation,
Tarrytown,  New York 10591.
31.  Beckman  Fluoride  Ion  Analyzer,  Beckman  Bulletin 4102,  Beckman
Instruments, Inc., Fullerton, Calif.  92634.
32.  Water  Analysis  Instrumentation,  Hach Series CR-2 Bulletin, Hach
Chemical Co.,  Ames,  Iowa 50010.
33.  AES Series 1400 Process  Analyzers, Automated Environmental Systems,
Inc., Woodbury, L.I., New York 11797.
34.  Safe Handling of Water Works Chemicals, by R.W. Ockershausen, JAWWA
Vol. 63, June  1971.
35.  W & T Fluoride Analyzer, W & T Cat. File 810.030.
36.  Automatic Control  for Precision Chemical Metering  Pumps, Precision
Bulletin 240.

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37.   Omega Gravimetric Dry Feeder, BIF Ref. No. 31-12.201-1.
38.   Omega Volumetric Dry Feeder, BIF Ref.  No. 25-04.201-1.
39.   BIF Diaphragm Pumps. BIF Ref. 1210-201-1.
40.   BIF Rotodip Feeder. BIF Ref. No. 65.201-1.
41.   Manual  or  Automatic Fluoridator,  Fischer &  Porter  Specification
70D1100.
42.   Cabinet-Mounted  Fluo-chlorinator.    Fischer &  Porter  Specification
70F3400.
43.   Chemical  Feed Pump. W  &  T Cat.  File  940.100.
44.   Water Fluoridation. Olin  Chemicals, Stamford, Conn. 06904, Product
Application Bulletin CD-169-1070.
45.   Sodium Fluoride;  Chemtech, St. Louis, Mo. 63143, Product Data Sheet,
July 1970.
46.   Polyethylene Tanks for Precision Chemical Metering Pumps, Precision
Bulletin 960386.
47.   Fiberglas Tanks. Owens-Corning Fiberglas Corp., Toledo, Ohio 43601,
Pub. No. 1-PE-3578-F.
48.   mRoy Controlled Volume Pumps. Milton Roy Co., St. Petersburg, Fla.
33733, Bulletin No. 15.001.
49.   mRoy Packaged  Chemical  Feed Systems, Milton Roy  Co., Bulletin
15.002.
50.   Corrosive  Chemical Feeding,  BIF  Ref.  1200.20-1.
51.   Metering Pumps  Series  1700, BIF  Ref.  1700.20-1.
52.   Dry  Material Feeders,  BIF Ref. 25.20-1.
53.   Fluoridation  Equipment  for  Potable  Water Supplies, BIF Ref. No.
2-SIC 494.2.
54.   Chemicals Used in Treatment of Water and Wastewater, BIF Ref. No.
1.21-15.
55.   Application  of Fluorides  to Water,  by W.T. Ingram,  Water & Sewage
Works, May 1961.
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                            Appendix
The following symbols and abbreviations are employed throughout this manual.
Abbreviation
   APHA
   AWWA
   °C
   cm
   cone
   cuft
   °F
   ft
   g
   gal
   gph
   gpm
   hr
   in
   JAWWA
   1
   Ib
   m
   mg
   MGD
   mg/1

   min
   ml
   mm
             Referent

American Public Health Association
American Water Works Association
degree (s) Centigrade
centimeter(s)
concentrated
cubic foot (feet)
degree (s) Fahrenheit
foot (feet)
gram(s)
gallon (s)
gallons per hour
gallons per minute
hour(s)
inch(es)
Journal of the American Water Works Association
liter(s)
pound (s)
meter(s)
milligram (s)
million (s) of gallons per day
milligrams per liter (sometimes used interchange-
   ably with ppm)
minute (s)
milliliter(s)
millimeter(s)
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Abbreviations
              Referent
   mV
   m/u
   PH
   ppm

   psi
   rpm
   sec
   spgr
   SPM
   sqcm
   sqft
   sq in
   sqmm
   IDS
   WPCF
millivolt (s)
millimicron (s)
Hydrogen ion potential (a measure of the acidity
   or alkalinity of a solution. A pH of 7.0 indi-
   cates neutrality; below  7.0  indicates acidity
   and  above 7.0 indicates alkalinity)
parts per  million  (pounds of  fluoride ion per
   million  pounds of water,  etc.)
pounds per square inch (water pressure)
revolutions per minute
second (s)
specific gravity
strokes per minute (of a solution feed pump)
square centimeter(s)
square foot (feet)
square inch(es)
square millimeter(s)
total dissolved solids (in water)
Water Pollution Control Federation
                            US GOVERNMENT PRINTING OFFICE 1973- 759-907/1129
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