• TABLE OF CONTENTS
HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Introduction
 Theoretical considerations
 Experimental materials and...
 Results and discussion
 Summary and conclusions
 Recommendations for further...
 Appendix
 Reference
 Bibliographical sketch
 Copyright






Title: Magnesium carbonate, a recycled coagulant for water treatment
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Title: Magnesium carbonate, a recycled coagulant for water treatment
Physical Description: Book
Language: English
Creator: Thompson, Cliff Green, 1941-
Publisher: s.n.
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Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
        Page iv
    List of Tables
        Page v
        Page vi
        Page vii
    List of Figures
        Page viii
        Page ix
        Page x
        Page xiii
        Page xi
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Theoretical considerations
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
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        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
    Experimental materials and methods
        Page 34
        Page 35
        Page 36
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        Page 53
        Page 54
        Page 55
    Results and discussion
        Page 56
        Page 57
        Page 58
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        Page 130
        Page 131
    Summary and conclusions
        Page 132
        Page 133
        Page 134
    Recommendations for further study
        Page 135
        Page 136
        Page 137
        Page 138
    Appendix
        Page 139
        Page 140
        Page 141
        Page 142
    Reference
        Page 143
        Page 144
        Page 145
        Page 146
        Page 147
        Page 148
        Page 149
    Bibliographical sketch
        Page 150
        Page 151
        Page 152
    Copyright
        Page 153
Full Text












Magnesium Carbonate, A Recycled
Coagulant for Water Treatment













By

CLIFF GREEN THOMPSON


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY










UNIVERSITY OF FLORIDA
1971












ACKNOWLEDGMENTS


The author wishes to express his appreciation to his

committee chairman, Dr. J.E. Singley, for his assistance

and guidance throughout the course of this graduate research

work. The author is most deeply grateful for the learning

experience derived from the association with Dr. A. P. Black.

His inspirational enthusiasm and tireless assistance to a

large degree made this dissertation possible. Appreciation

is extended to Dr. P. L. Brezonik and Dr. G. M. Schmid for

giving freely of their time and assistance.

Gratitude is extended to Mrs. Jeanne Dorsey for her

typing of this dissertation. To my fellow students, Mr.

Roger Yorton and Mr. Roy Burke,for their assistance in analyti-

cal and statistical techniques the author extends his

appreciation.

To my wife and two children, a special appreciation

is extended for their forebearance and understanding during

these past three years.









CONTENTS


Page

ACKNOWLEDGMENTS ...................... ................. ii

LIST OF TABLES ........................................... v

LIST OF FIGURES ...................................... viii

ABSTRACT ......... ................ .................... x

CHAPTER

1 INTRODUCTION ...... ........................... 1

2 THEORETICAL CONSIDERATIONS.................... 12

Magnesium Chemistry ...... .... ...... .... 12
Colloidal Destabilization ................. 26
Chemical and Physical Properties of
Organic Color ............................. 28
Chemical and Physical Structure of
Montmorillonite and Emathlite Clays.... 30
Chemistry of Iron Corrosion and Control
by Calcium Carbonate Deposition......... 31

3 EXPERIMENTAL MATERIALS AND METHODS ........... 34

Methods ............... .................... 34
Materials ................................ 36
Preparation of Materials .................. 38
Analytical Techniques ...................... 45
Jar Test Procedures ...................... 50
Recovery Studies .......................... 52
Coagulation Using Recovered Magnesium
Bicarbonate ................ .......... 55

4 RESULTS AND DISCUSSION............ ... ........ 56

Coagulant Studies of Synthetic Waters...... 56
Study of Natural Waters .. ............ 62
Solubility of Magnesium Hydroxide.......... 84
Determination of Conditions for Lowest
Treatment Cost ......................... 85


iii











Electrophoretic Mobility as a Measure
of Treatment Efficiency ............... 97
Prediction of the Required Coagulant
Dose ................................ .. 103
Coagulant Recovery.......................... 106
Coagulation with Recovered Magnesium....... 114
Comparison of Values for Residual
Magnesium Determined by EDTA With
Those Determined by Atomic Absorption.... 116
Application of the Process................ 120
Photographic Comparison of the Formation
of Flocs Produced With Magnesium
Carbonate and with Alum................. 124

5 SUMMARY AND CONCLUSIONS...................... 132

6 RECOMMENDATION FOR FURTHER STUDY............... 135

APPENDIX ........................ ...... .... .. .... 139

REFERENCES ...................................... .... 143

BIOGRAPHICAL SKETCH ....................... ......... 150


1


CHAPTER


Page









LIST OF TABLES


Table Page

1 Chemical Analysis of Organic Color ........... 42

2 Magnesium Carbonate Required for Coagulation
of Organic Color and Emathlite Turbidity ...... 56

3 Lime and MgCO Coagulation of a Fuller's
Earth Turbidity, Synthetic Water ................. 58

4 MgCO Coagulation of a Highly Colored,
Fuller's Earth Turbidity, Synthetic Water ..... 59

5 Magnesium Carbonate Dosage Required to
Coagulate Organic Color and Montmorillonite
Turbidity ....................................... 60

6 Coagulation of a Highly Colored Synthetic
Water with MgCO ............ ...... .......... .. 61

7 MgCO3 and Alum Coagulation of Montgomery,
Alabama Water .......... ... ... ............. ..... 63

8 MgCO3 and Alum Coagulation of Mobile River
Water, Mobile, Alabama ....... ...... ..... ....... 64

9 Effect of Alum as a Flocculant Aid in
Color and Turbidity Coagulation with
Magnesium Carbonate ........ ............... 65

10 Coagulation of Atlanta, Georgia Water with
MgCO3 and Alum ................ ................ 67

11 MgCO and Alum Coagulation of Baltimore,
Maryland Water *................. .............. 68

12 Lime and Alum Coagulation of Birmingham,
Alabama Water ................................. 69

13 MgCO3, Lime, and Alum Coagulation of
Chattanooga, Tennessee Water .................. 70

14 Coagulation of Cleveland, Ohio Water with
Lime and Alum ............. .................... 71








Table Page

15 Coagulation of Detroit, Michigan Water
by Precipitation of Magnesium Present by
Lime Addition ........................... ..... 72

16 Coagulation of Huntsville, Alabama Water
With MgCO3 and with Alum ....... .... .......... .. 73

17 MgCO3 and Alum Coagulation of Jackson,
Mississippi Water ............................. 74

18 MgCO3 and Alum Coagulation of Lanett, Alabama
Water ....................................... 75

19 Lime and Alum Coagulation of Louisville,
Kentucky Water ....... ........................ 76-

20 MgCO3, Lime, and Alum Coagulation of
Nashville, Tennessee Water ................... 77

21 MgCO3 and Alum Coagulation of Opelika,.
Alabama Water ..................... ............ 78

22 Lime, MgCO3,and Alum Coagulation of
Philadelphia, Pennsylvania Water .............. 79

23 Coagulation of Richmond, Virginia Water
With MgCO3 and Alum .,,.. ......... ....... ... 80

24 MgCO3 and Alum Coagulation of Tuscaloosa,
Alabama Water ............... ..... .............. 81

25 MgCO3, Lime, and Alum Coagulation of
Washington, D.C. Water ........................ 82

26 Comparison of Raw and Treated Chemical
Characteristics for 17 Natural Waters ........ 83

27 Economic Comparison of Treatment Methods
for 17 Natural Waters ......................... 98

28 Relationship Between Electrophoretic
Mobilities and Settled Color or Turbidity
for 12 Natural Waters .................. ......... 99

29 Required Magnesium Dose as Related to
Physical and Chemical Characteristics for
17 Natural Waters ....................... ... ..104








Table Page
30 Carbonation of Sludge Produced from the
Coagulation of 36 Liters of Synthetic Water
Containing 200 mg/1 of Organic Color and
50 mg/1 Turbidity .............................. 107

31 Carbonation of Sludge Produced from the
Coagulation of 36 Liters of Synthetic
Water Containing 200 mg/l Organic Color
and 15 mg/l Turbidity ........................... 108

32 Carbonation of Sludge Produced from the
Coagulation of 36 Liters of Synthetic Water
Containing 50 mg/l Organic Color and 15
mg/l Turbidity ................................. 109

33 Carbonation of Sludge Produced from the
Coagulation of 36 Liters of Synthetic Water
Containing 15 mg/l Organic Color and 15
mg/l Turbidity ................................ 110

34 Carbonation of Sludge Produced from the
Coagulation of 36 Liters of Natural Water
Containing 200 mg/l of Organic Color and
50 mg/l Added Montmorillonite Clay-
Turbidity........................................ 110

35 Coagulant Recovery Studies .................... 112

36 Magnesium Solubility as a Function of pH
for Coagulant Recovery Studies .................. 113

37 Evaluation of Twice Recycled Magnesium
in Coagulation of Synthetic Water .............. 115

38 Comparison of Atomic Absorption and EDTA
as Methods for Magnesium Analysis .............. 118

39 Calculated Potential Production of
MgCO3.3H20 by 20 American Cities, 1968.......... 140

40. Calculations for Potential Consumption of
MgCO-.3H20 by Water Treatment Plants
in tne United States ............................ 142


vii









LIST OF FIGURES


Figure Page
1 Effect of High pH on Poliovirus 1 (LSc) in
Flocculated (500 mg/l Ca(OH)2), Sand-
Filtered Secondary Effluents at 250C ......... 9

2 Solubility Diagram for Magnesium in Water
at Atmospheric Conditions ................... 16

3 Temperature Influence on Magnesium
Solubility .................................... 17

4 Effect of pH on Mobility for the Indicated
Coagulant Dosages ............................. 21

5 Solubility of MgCO3.XH 0 as a Function of
Time for the Indicate hydrate Forms ........ 25

6 Multiple Stirrer for Jar Tests................. 35

7 Flash Evaporator Used to Concentrate
Organic Color ................................. 40

8 Zeta-Meter Used to Determine Particle
Mobility ..................................... .... 48

9 Solubility of Mg(OH) (As MgCO. 3H20) as a
Function of pH for 21 Natural waters ............ 86

10 Treatment Cost in $/M.G. for CaO and CO2
to Raise the Raw Water pH to 10.5 and
Reduce the pH Back to pH 9.0 for Stabilization .. 88

11 Partial Treatment Costs in $/M.G. for CaO,
CO2 and MgCO3 as a Function of Coagulation pH ... 89
12 Treatment Cost in $/M.G. as a Function of the
Raw Water Total Alkalinity ..................... 91

13 Treatment Cost in $/M.G. as a Function of
Coagulation pH .................................. 92

14 Treatment Cost in $/M.G. as a Function of the
Amount of MgCO3 Precipitated .................... 93


viii










15 Settled Color as a Function of Particle
Mobility During Coagulation, Jackson,
Mississippi Water .......... ............. ... .. 101

16 Settled Turbidity as a Function of
Coagulation Mobility Lanett Water ........... 102

17 Magnesium Recovery by Carbonation ............. 111

18 Comparison of Atomic Absorption and EDTA
as Analytical Methods of Determining
Magnesium in Natural Waters .................. 117

19 Flow Diagram for Turbidity Removal Plant
Using MgCO3 and Lime Recalcining ............... 121

20 Photographic Comparison of MgCO and Alum
Floc During Rapid Mixing in the Removal of
Organic Color ................................. 125

21 Photographic Comparison of MgCO3 and Alum
Floc During Flocculation in the Removal of
Organic Color ................................. 126

22 Photographic Comparison of the Rate of
Settling for MgCO3 and Alum Flocs Formed
in the Removal of Organic Color .................. 128

23 Photo-Micrographs of Alum and MgCO3 Floc
Formed in the Removal of Organic Color,
Magnified 100 Times ................... ........... 129

24 Photo-Micrographs of Alum and MgCO3 Floc
Formed in the Removal of Organic Color,
Magnified 200 Times ............................ 130

25 Magnesium Carbonate Floc Magnified 200
Times with Calcium Carbonate Crystals Present-.. 131


Figure


Page









Abstract of Dissertation Presented to the Graduate
Council of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of Doctor of Philosophy

MAGNESIUM CARBONATE, A RECYCLED
COAGULANT FOR WATER TREATMENT

By

Cliff Green Thompson

June, 1971

Chairman: J. E. Singley
Major Department: Environmental Engineering

An entirely new system for water coagulation has

been developed which allows reuse of the coagulant, lime,

and carbon dioxide produced in lime recovery. The use of

magnesium carbonate in place of alum has many advantages,

the most important being the elimination of sludge disposal.

problems which today is the most difficult problem facing

the water works industry. Magnesium carbonate hydrolyzes

with lime to form magnesium hydroxide, which has properties

quite similar to the hydrolysis products of aluminum. The

magnesium is almost completely precipitated at the high pH

range of coagulation 11.0 11.3, and can be recovered from

the sludge by carbonation and reused. Carbonation converts

the insoluble Mg(OH)2 to the soluble forms of magnesium,

MgCO3 and Mg(HCO3)2,. which can be separated from the calcium

carbonate and turbidity by vacuum filtration. The filtrate

containing the magnesium values can then be recycled and

reused while the filter cake is readily disposed of as land

fill, eliminating sludge disposal problems. The magnesium

carbonate used in this study was produced from the water


L









softening sludge at Dayton, Ohio. The new technology of

recovering magnesium carbonate from the sludges of water

plants softening high magnesium waters will make available

up to 150,000 tons per year of low cost magnesium carbonate.

This study was divided into three research areas:

the use of MgCO3 as a coagulant for both synthetic and

natural waters; the recovery of magnesium values by carbon-

ation from the sludge; and the reuse of the recovered magne-

sium for coagulation.

The results of the coagulation studies show that mag-

nesium carbonate hydrolyzed with lime is as effective as

alum for the removal of both turbidity and organic color in

both synthetic and natural waters. An equation was developed

for prediction of the required coagulant dose based on the

physical and chemical characteristics of the raw water.

Organic color had the greatest effect on the coagulant

requirements, with the type or level of turbidity exhibiting

only minimal effects. A study of various flocculants

revealed that for each water a specific flocculant was usu-

ally found superior to all others tested. In general, how-

ever, soft waters responded best to 0.5 ppm dosages of alum,

whereas either activated silica or potato starch produced

better flocs in hard waters. For most waters, measurement

of particle mobility was found to be an effective tool for

evaluating the coagulation of turbidity and organic color.

A series of curves has been prepared so that a graph-

ical solution can be made for the optimum coagulation pH









and for the cost of the lime, carbon dioxide, and magnesium

carbonate based on jar test results. The cost estimates are

based on magnesium solubility relationships found in the

coagulation studies which are considerably higher than would

be predicted by theory. The conditions of full-scale appli-

cation will probably be more favorable for more complete

precipitation of the magnesium hydroxide due to the longer

reaction time and mass action effect during coagulation.

The cost analysis, even based on conservative estimates,

indicates significant savings in treatment costs for most

waters with no consideration given for the many benefits of

this process. All of the magnesium hydroxide precipitated

can be recovered by carbonation with no problems of color

release or sludge dewatering for most waters.

The chemical characteristics of waters coagulated

with magnesium carbonate are in most cases superior to waters

coagulated with alum. When magnesium carbonate is used, the

treated waters have alkalinities ranging from 30 to 50 mg/l,

giving soft waters sufficient alkalinity for stabilization

by p1H adjustment. For water high is carbonate, hardness,

softer waters are produced by treatment with magnesium car-

bonate than with alum.


xii


I














CHAPTER 1. INTRODUCTION


Iron and particularly aluminum salts have served well

in the coagulation and clarification of water since their

common usage in the early 1900's. Many investigators con-

sider the highly hydrated and gelatinous property of the

hydrolysis products to be a main attribute for their effec-

tiveness. This property however. makes dewatering and dis-

posal of the sludge produced from the treatment process

extremely difficult and costly. Water plant wastes are

recognized today as an industry-wide pollution problem that

must be solved. It is estimated that over 1,000,000 tons of

alum sludge are produced each year with less than eight percent

receiving treatment of any kind before disposal.

The characteristics of the waste products from water

plants are highly variable both within and among plants. A

considerable effort has been made to characterize these

wastes with the following ranges in characteristics being

reported:2,3,4

Total Solids 1,000 17,000 mg/1

Suspended Solids 75% 90% of Total Solids

Volatile Solids 20% 35% of Total Solids

BOD 5$ (Ultimate BOD
coInsderably higher) 30 150 mg/1

COD (Higher value where
activated carbon present) 500 15,000 mg/1









The reduction of volume and moisture content is of

primary concern in alum sludge disposal. In a study of two

water plants, Neubauer2 found the volume of alum sludge pro-

duced to range from .12 to .26% of the total plant flow.

Methods, which have been employed with varying degrees of

success, to concentrate and dewater alum sludge include:

1) Gravity thickening, stirred thickeners, and

lamella sedimentation2,67
2,3,5
2) Lagoons23

3) Drying beds8

4) Wedge wire filtration9

5) Vacuum filtration6

6) Pressure filtration6

7) Centrifugation6
6
8) Freezing-

As a means of offsetting some of the costs for treating the

sludge, alum recovery has been attempted at several water

plants. Jewell0 in 1903 patented sulfuric acid regenera-
11
tion of alum and in 1923 Mathis obtained a similar patent.
12
In 1951 Black Laboratories2 suggested utilizing sulfur

dioxide gas from boiler stacks as a source of sulfuric acid

for alum recovery at Orlando, Florida. Roberts and Roddyl3

reported on investigations for alum recovery at Tampa,

Florida which later was practiced for a short while but was

discontinued due to operational problems. Tampa's source

of raw water varied widely in hardness and organic color

content. Aluminum sulfate was used only during times of









high organic color making recovery an intermittent opera-

tion. Higher dosages of recovered alum had to be used due

to the release from the sludge of organic color,reducing the

effectiveness of the coagulant. The Asaka Purification

Plant in Tokyo reports recovery of as much as 80% of the
14
aluminum using the sulfuric acid process. Iron or manga-

nese, which might be present in the sludge, is also solu-

bilized. This causes an increase in the concentration of

these elements, making it necessary to waste a portion of
15
the recovered alum from time to time. Alum recovery is

also practiced at the Daer Works in Scotland and is being

investigated for use at Minneapolis, Minnesota.16

Lime recovery in softening plants is practiced in

several American cities with profitable operations being

reported for two cities.1617 The excess lime produced is

sold to neighboring cities for a profit. Lime recovery is

presently economically attractive only for softening plants

using 20 to 25 tons of lime a day.

While there are many methods of treating an alum

sludge, only in unusual cases has the treatment been found

to be satisfactory or economically attractive. The AWWA

conference report on plant needs states

In summation, the principal needs are to
find effective and economical means, through
research, to dispose of water treatment plant
wastes by direct treatment of sludge, or by
eliminating undesirable chemicals, such as alum,
through changes in water treatment methods.









In answer to these needs, an entirely new system of

water treatment chemistry has been developed utilizing mag-

nesium carbonate as the coagulant. The addition of suffi-

cient lime slurry to a water containing magnesium bicarbon-

nate and/or to which magnesium carbonate has been added,

precipitates both magnesium hydroxide and calcium carbonate.

Carbonation of the sludge solubilizes the magnesium, as mag-

nesium bicarbonate, which can be recovered by vacuum filtra-

tion and the filtrate recycled and reused. The filter cake

of CaC03 and clay is easily handled and disposed of as land

fill. Lime recovery would further reduce the volume of

sludge to be disposed of.

The flocculant properties of magnesium hydroxide have

long been evident. It is these properties, however, which

have troubled conventional water softening plants. The

gelatinous nature of magnesium hydroxide, in many ways

similar to the hydrolysis products of aluminum, makes the

dewatering of the sludge difficult. Also, where recovery

of lime is practiced, the magnesium hydroxide must be sepa-

rated before calcination because of build-up of insoluble

magnesium oxide in the recovered lime. Various techniques

have been developed to separate the magnesium hydroxide from

the calcium carbonate. The use of a centrifuge to selec-

tively classify it into the centrate does not provide the

degree of separation needed. Three-phase selective soft-

ening has been used at Lansing, Michigan for some years
18
during the winter months of low water demand. In this









process, the dosage of lime added in the first phase is just

sufficient to precipitate the calcium bicarbonate and con-

vert the magnesium bicarbonate to the soluble carbonate. In

the second phase, excess lime is added to precipitate all

magnesium hardness as Mg(OH)2. This requires a lime dosage

well above stoichiometry. This second phase effluent with

a pH of about 11.3 passes to the third phase where it is

mixed with just enough raw water to utilize the excess lime

in removing calcium hardness. Phases and 3 sludges are

mainly CaCO3 phase 2 sludge mainly Mg(OH)2. Since this

process cannot be used to soften waters containing either

color or turbidity and requires extremely careful control,

it is seldom used.

Bureau of Mines Technical Paper No. 68419 describes

an industrial process for separating MgO from its ores,

brucite or dolomite, in which the calcined and finely ground

ore is slurried and chilled. The MgO present is then dis-

solved by pure CO2 with continuous cooling to neutralize

the high heat of hydration of the MgO.

Black & Eidsness20 were able to selectively dissolve

the Mg(OHI)2 from the CaCO3 in the lime-soda softening sludge

at Dayton, Ohio, thus making it possible to recalcine the

CaCO3 and produce high quality quicklime. This sludge car-

bonation basin, the only one of its kind in the world, has

been operating successfully since 1958.

While magnesium hydroxide is generally regarded as a

liability it has been recognized as an effective coagulant.








21
Flentje, in 1927, found increasing clarification efficiency

in the water treatment plant at Oklahoma City as excess lime

was added. He reasoned this to be due to precipitation of

magnesium as the hydroxide. Several jar tests were per-

formed which indicated that magnesium, in the form of mag-

nesium chloride, is an effective coagulant. The excess lime

treatment was practiced in conjunction with ferric sulfate

on a full plant scale, to treat the hard, turbid river water.

The objective was to employ the magnesium bicarbonate natu-

rally present in the water. Flentje noted no decrease in

filter runs, less algae in the settling basins, and greater

bacteria removal. No attempt at coagulant recycle was made

and the excess lime fed was not sufficient to quantitatively

precipitate the magnesium present in the water.
22
In 1966, Lecompte reported the use of magnesium

carbonate as a coagulant for the reclamation of water within

a paper mill. Lime was reacted with magnesium carbonate,

produced by the reaction of finely ground magnesium oxide

and bicarbonate alkalinity present in the water, to precipi-

tate magnesium hydroxide. No attempt was made at magnesium

recovery. The water to be treated contained 0.5 to 1.0

pounds of suspended solids per one thousand gallons with

fluctuations in organic color. The chemical cost of the

water produced was estimated at sixty-five dollars per mil-

lion gallons with additional disinfection benefits noted due

to the excess causticity.










Although water chemists have long recognized the

effectiveness of magnesium hydroxide as a coagulant, the use

of magnesium salts has not received acceptance for economic

reasons. Both the chloride and the sulfate cost more per

pound than alum and their use, in conjunction with lime,

would increase the non-carbonate hardness of the water being

treated in direct ratio to the make-up dosage required. The

cost of magnesium carbonate currently quoted at 16 per

pound, has always been prohibitive. However, three factors

now indicate, even demand, that the widespread use of magne-

sium carbonate receive most careful consideration:

1) As stated previously, treatment of water plant

wastes is becoming mandatory. The dewatering

of this sludge is an integral part of the mag-

nesium recovery process.

2) Recovery and recycle of a coagulant hav not proven

practical in the past. An economical, easily

controlled process is now available for the

recovery of magnesium carbonate for coagulant

recycle.

3) A new low-cost source of magnesium carbonate will
23
soon be available. It will be recovered at

low cost from the sludges produced by major

plants softening high magnesium waters. Such

plants will be able to substantially reduce

their chemical treatment costs by (a) elimi-

natine the use of alum, (b) sale of recovered









magnesium carbonate and (c) recalination,

recycling and reuse of lime. Of perhaps equal

importance is the fact that in so doing, they

will have eliminated their individual sludge

pollution problems.

For many waters this new treatment method will re-

sult in considerable economic savings, and for all waters,

it will solve the problem of sludge dewatering and disposal.

As coagulation will take place generally in the pH range of

11.0 to 11.4, the need for prechlorination should be mini-
24 25
mized and in many cases eliminated. Houston2 and Hoover25

were among the first investigators to report the effect of

high pH on disinfection in water treatment. In 1952, Riehl

et al.26 reported that at a pH level of 11.0 to 11.5 and a

contact time of four hours, the removal of bacterial organ-

isms is on the order of 100%.

Alum and ferric sulfate have been shown to be effec-
27
tive in the coagulation of viruses. However, these inves-

tigators found that viruses removed in the floc fraction

were not destroyed and active virus can be recovered from

the floc. Berg et al.28 have found that disinfection of

polio virus can be accomplished by high pH. Figure 1, from

this publication, shows the effect of pH on the survival of

polio virus as a function of time. It can be concluded that

bacteria and virus not only can be removed by the new treat-

ment process but disinfection of the organisms will also

take place.

















100 _










I ^<
O m







-- -











1 pH 10.1 --------
-- ~ ~ ~ ~ ~ -- 0--- n108--*--- -- ---- ---





o----o pH 10.8
S .----- pH 11.1 -


0 20 40 60 80 100 120 140
Time-min
Fig. 1. Effect of High pH on Poliovirus 1 (LSc) in Flocculated (500 mg/1 Ca(OH)2),
Sand-Filtered Secondary Effluents at 250C

(from Berg et al.28)









In this high pH range of coagulation, complete pre-

cipitation of iron and manganese should occur, possibly elim-

inating the need for more costly treatment methods. This pH

environment would be unfavorable for aquatic growths in set-

tling basins. The overall effect would be reduction in thd

use of chlorine and subsequent cost savings at the same time

increasing the treatment efficiency.

In initial studies of new technology, important areas

of research must be left for future investigations because

of time limitations. The use and recycle of magnesium car-

bonate is an entirely new concept in water treatment chemis-

try. Initial research efforts have been planned to deter-

mine if this process is technically and economically feasi-

ble. The scope and objectives of this research were there-

fore as follows:

1) Evaluation of the parameters involved in the use

and recycle of magnesium carbonate as a coagu-

lant for both organic color and turbidity in

soft waters. Studies of both synthetic and

natural waters are included in this phase of

the research.

2) Development of a predictive equation to determine

the magnesium requirements based on the physi-

cal and chemical characteristics of a water.







11

3) Demonstration of the effectiveness of this new

process on a broad spectrum of natural waters.

Waters from the largest cities in the country

were chosen to provide a wide spectrum of range

in chemical and physical characteristics.

4) Estimation of the chemical cost of treatment using

this new technology and comparison with the

chemical costs using alum treatment.

5) Comparison of the chemical characteristics of the

treated waters using magnesium carbonate and

alum treatment.













CHAPTER 2. THEORETICAL CONSIDERATION


Magnesium Chemistry

Magnesium Equilibrium in Water

Magnesium is present to some extent in almost all

natural waters. As a rule, magnesium content increases with

increasing water hardness. The ratio of Mg /Ca++ is quite

variable but almost always less than 1.

In Peason's, system of classifying metals,29 magnesium

is classed in group A, the same as aluminum. The elements

of this group are visualized as having spherical symmetry

with the electron sheaths not readily deformed by adjacent

charged ions. Metals in this classification tend to form
-2 -3
insoluble precipitates with OH CO and PO4 with simple

electrostatic binding of cation and ligand used to explain

complex stability.

In natural water systems, magnesium can be found in

many solid phases. Considering only a system composed of

carbon dioxide, magnesium, and water, one can calculate

which solid phase controls magnesium solubility. The solid

phases of magnesium present are:








AG30 -log Ko0
(KCal mol )

1) Brucite Mg(OH)2
Mg(OH)2(s) t Mg+ + 20H- -15.8 11.6

log ,, E~g++] =
log [-g- = -pKso + 2pK 2pH
[Mg(OH )2]

log [Mg++] = 16.4 2pH

2) Magnesite MgCO3
MgCO3(s) Mg"' + CO3 6.7 4.9

log Mg++] = -pKso logCT log

log [Mg ] = -4.9 logCT log a2

3) Nesquehonite MgCO3.3H20
MgCO 33H20(s) Mg++ + CO3 + 3H20 +7.4 5.4

log [Mg+ = -pKso logCT log a

log [Mg++] = -5.4 logC log a2
^T








A G30
AGl mo
(KCal mol 1)


S 30
-log K
so


4) Hydromagnesite Mg4(C03)3(OH)-23H20

Mg4(C03)3(OH)2-3H20 t 4Mg+2 + 3C03-2 + 20H- + 3H20

log [Mg++]


= -1/4pKs + 1/2pK2 3/4 logC
logT


- 3/4 log a2 1/2pH


= -.4 3/4 logCT 3/4 log a2 1/2 pH
T


+40.2


29.5







15

As Nesquehonite is less soluble than magnesite at all pH

values, magnesite will not be considered. In Figure 2, a'

pH-stability diagram is shown for a total carbonate concen-
_3
tration of 103M. Brucite is by far the least soluble at

pH values above 9 with hydromagnesite controlling solubility

from pH 9 to approximately 7.5. Nesquehonite is the least

soluble at pH values below 7.5. Dolomite, CaMg(CO3)2, is a

very common stable phase found in nature but attempts to

precipitate a dolomite phase from supersaturated solutions
31
under atmospheric conditions have been unsuccessful.

Considerable effort has been expended in determining

the solubility product-constant for Mg(OH)2. The following

table lists some of the values reported in the literature.

Investigator toC pkp

Gallaher32 25-30 11.28
Ryzner et al. 80 11.28
Krige and Arnold34 20 10.85
Travers and Nouvel35 18 10.60
Kline36 25 11.00
37
Britton37 Room 10.64
Bube38 25 10.92
Gjaldbach39 18 10.92
Dupre and Bialas40 18 10.92
Herz and Muhs41 29 10.31
Kohlrausch and Rose42 18 10.87
Loven3 10 10.76

Magnesium hydroxide becomes less soluble at increased

temperature. Figure 3 taken from Larson, Lane, and Neff4


shows this effect.



























-I-




-2- I- MgCO33H20
2-Mg4(CO3)3(OH)2 3H20
3-Mg(OH)2

-3



-4.




-5




5 7



FIG. 2 SOLUBILITY DIAGRAM
CONDITIONS. TOTAL


/ -.
/ -
/
/
A


FOR MAGNESIUM IN WATER AT ATMOSPHERIC
CARBONATE 10' M









































0 50 70 90 110 130 150 170 190 210
Temperature F
Fig. 3 Temperature Influence on Magnesium Solubility (from Larso, Lane,
and Neff )
The dashed curves represent magnesium solubility (as
parts per million CaCO ); the solid curves, pH
variation. The solubility curves are based on the
35solubility product constants of Travers and Nouvel
solubility product constants of Travers and Nouvel.


.12.0


j 10.0









The solubility products reported were for pure dis-

tilled water systems, extrapolated to zero ionic strength.

Many factors tend to increase the solubility of magnesium

in natural waters. Solubility increases with increase in

ionic strength as expressed by the Debye-Huckel relationship:

pK = p K (nZM2 + mZN2)(1
so so +

where:

MnNM(s) Z nM + mN

Kso [M]ntN]m A n Am
so M N

u = ionic strength

An illustration of this effect on the Ksp for Mg(OH)2 using

a pK = 11.0
u = 0 u = .01 u = .1 u = .3
pKsp 11.00 10.73 10.20 9.95

Complexation of the magnesium with both organic and inorganic

ligands increases the solubility. The formation of ion pairs

also tends to increase the solubility. Ion pairs differ from

complexes in that the metal ion and the base are separated by

one or more water molecules while for a complex the ligand is

immediately adjacent to the metal cation.45 It is reported

that while complex former present in solution may often have

little or no effect on the solubility of solids, they may

however affect the kinetics of nucleation and of growth and

dissolution of crystals.4

Lime is commonly used to precipitate magnesium from

water as magnesium hydroxide. The hydroxide concentration








of the water can be increased to the necessary level only
after converting all of the CO2 and HCO3 to CO3 These
well-known softening reactions are:
1) CO2 + Ca(OH)2 : CaCO3 + H20
2) Ca(HC03)2 + Ca(OH)2 t 2CaCO3 + 2H20
Magnesium bicarbonate is converted to magnesium car-
bonate and magnesium hydroxide on further addition of lime
as:

3) Mg(HC03)2 + Ca(OH)2 t MgCO3 + CaCO3 + 2H20
4) MgCO3 + Ca(OH)2 < Mg(OH)2 + CaCO3
If the magnesium in the water is non-carbonate hardness,
there would be no net change in total hardness, only an
exchange of calcium for magnesium as:
5) Mg++ SO4 + Ca(OH)2 Mg(OH)2 + Ca + SO4
Magnesium carbonate used as a coagulant does not add
to the total dissolved solids as shown in equation (4).- The
lime dosages necessary for coagulation and softening can be
calculated as:

Reaction Lime required, mg/l of Ca(OH)2

CO2 + Ca(OH)2 CO2 x Ca(O2 =74


Ca(OH) 74
2(HC03) + Ca(OH)2 Alk (as CaCO3) x CaCO 2 0=

Ca(OH)2 74
MgCO3.3H20 + Ca(OH)2 MgC03 3H20 x MgCO3.3H20 138=


Mg ++ (Ca(OH2 74
Mg + Ca(OH)2 Mg (CaCo3) x CaCO3 100









In practice 90% pure lime CaO would be slaked and used.

Thus, the total lime dosage found above should be multiplied
100 56 CaO
by 90 74 Ca(OH)2 or 0.82 times the Ca(OH)2 value determined.

CaCO3 suspended in water has been found to be nega-

tively charged while magnesium hydroxide is positively
46
charged.46 While the particles have been found to coexist,

absorption usually takes place and one predominates, giving

the floc either a net positive or negative charge. For a

water containing both calcium and magnesium, the mobility

tends to become less negative as the pH increases. Figure 4

demonstrates this effect found in the coagulation study of

water used by Montgomery, Alabama. This is due to formation

of Mg(OH)2 which can cause charge reversal if sufficient mag-

nesium is present. Flocculation-of calcium carbonate sus-

pensions using coagulant aids is not necessarily accompanied

by a decrease in negative mobility. 4 These investigators

reported that mobility in itself is not a reliable indicator

of the degree of flocculation.

Salts other than magnesium carbonate could be used as

the source of magnesium. Once the magnesium is recycled,

it would be in the carbonate or bicarbonate form. However

any make-up magnesium salt, such as MgSO4 or MgCI2, would

increase the non-carbonate hardness as shown in reaction 5.

Magnesium Recovery

As discussed in the introduction, the solubilization

of magnesium by carbonation has been practiced by industry






























10.9 -



10.8



10.


::. 1. .12 .: .

Mobility(-) u/lec/v/cm


FIG. 4 EFFECT OF pH ON MOBILITY FOR THE
INDICATED COAGULANT DOSAGES









for many years. However, such processes have generally been

carried out with supersaturated magnesium solutions and pure

CO2. While these processes must be carefully controlled,

magnesium recovery from water plant sludges is quite simple,

with little control required. The reactions which take place

are:

Mg(OH)2(s) + CO2 MgCO3 + H20

MgCO3 + CO2 + H20 + Mg(HCO3)2

Whether the reaction occurs in one or two steps is not

known.

Black and Eidsness,20 carbonating a sludge containing

Mg(OH)2 and 36 g/l of CaCO3 with 11% C02,found that only 80
mg/l of CaCO3 was dissolved after 30 minutes'carbonation at

a gas flow five times that required to dissolve all of the
47
Mg(OH)2 present. According to Johnston, who studied the
solubility of calcium and magnesium carbonates in natural

waters, the equilibrium ratio at 160C is [Mg++]/[Ca++ =

14,000 when the partial pressure of CO2 in the atmosphere

is great enough to prevent precipitation of Mg(OH)2.

Another explanation for teise phenomena is that a saturated

solution of Ca(HCO3)2 has a lower pH than a saturated solu-

tion of Mg(HCO3)2. As carbonation proceeds, the pH is

buffered at a pH of approximately 7.5, due to the Mg(HCO3)2,

allowing little of the calcium to dissolve.

Magnesium hydroxide may also react with the bicarbon-

ate to produce magnesium carbonate as:









Mg(OH)2 + Mg(HC03)2 + 2H20 o 2MgCO3 3H20

If complete solution of Mg(OH)2 is desired, obviously pre-

cipitation of MgCO33H20 should be avoided. In practice,

this is avoided by incremental addition of fresh sludge to.

the carbonation basin and maintaining a sludge-water ratio

such that a super-saturated solution of Mg(HCO3)2 is not

produced.

Production of Magnesium Carbonate

At present magnesium, carbonate is produced from four

major sources.48

1) From sea water without evaporation, using sea

water and lime as the principal raw materials.

2) From bitterns or mother liquors from the solar

evaporation of sea water for salt.

3) From deep-well brines.

4) From dolomite.

Investigators are not in agreement regarding the

formulae for the several forms of magnesium carbonate. For

this dissertation it will be assumed that at least three

salts may be prepared by aerating an aqueous solution of

magnesium bicarbonate: the penta-hydrate MgCO3.5H20 pre-

cipitated below 13.5C; the tri-hydrate MgCO3-3H20 precip-

itated between 13.5 C; and a "basic carbonate" whole com-

position is most commonly given as 4MgCO3.Mg(OH)2"x H20

precipitated above 50 C, most rapidly and completely by

boiling. Both the penta-hydrate and the tri-hydrate slowly









revert to the basic carbonate, 5 Mg*04C02.xH20, upon exposure

to the atmosphere. This reversion is accelerated when mois-

ture is present and at elevated temperatures. When heated

to 1000C, dry MgCO3'3H20 is quite stable.49 MgCO3.3H20

exhibits an interesting change in solubility on heating to

1000C. Figure 5 demonstrates this increased solubility

effect. The data for this figure were collected from ana-

lytical studies of the MgCO 33H20 sludge produced in Dayton,

Ohio. It is .assumed that the conversion to the basic car-

bonate involves recrystallization of the aqueous solution.

At 2000C, dry material loses water and CO2 without the addi-

tion of water. Possibly partial decomposition furnishes some
49
water which can then assist further conversion.

Magnesium carbonate, which is used primarily in the

paint, printing, rubber and pharmaceutical industries,sells

from $.16/lb for the technical grade to $.22/lb for the USP

grade.50 Most of the product produced today is the basic

carbonate, 4MgCO3 Mg(OH)2'xH20.

As discussed in the introduction, a new source of

magnesium carbonate will be soon available at a greatly re-

duced cost. A process has been developed by A. P. Black and

the city of Dayton, Ohio to recover it from water softening

plant sludges.23 preliminary calculations, included in the

appendix, indicate that as much as 150,000 tons of magnesium

carbonate (MgCO3'3H20) can be produced each year by the

twenty cities shown. Substitution of MgCO3'3H20 for alum in

the more than 4,000 water treatment planes now using it


























0A16


o0



SE o Heated to 103*C for I hr. as MgC03-3HZ0
I- 200*C for 2 hrs. as MgC03-3H20
o 200*C tor 2 hrs. as MgCO3"ZH20
S- Air dried as MgCO 3H20

4-




2 4 6 8 10 12 14 16 18
TIME (Min.)


FIG. 5 SOLUBILITY OF MgCO-sXH20 AS A FUNCTION OF
TIME FOR THE INDICATED HYDRATE FORMS









would require approximately 100,000 tons per year, assuming

85% recovery and re-cycling of the magnesium and 15% make-

up. These calculations are also included in the appendix.

The cost to produce MgCO3'3H120 with this new techno-

logy has been estimated to be less than $.02/lb.51


Colloidal Destablization


Colloidal destablization is believed to occur in two

steps. The first, which is assumed to occur very rapidly,

has been referred to as perikinetic coagulation52 or coagu-
53
lation.53 In this step, chemical and physical interaction

between the colloid to be removed and the coagulant takes

place. Two broad theories have been advanced to explain

the mechanism. The older, chemical theory, assumes stabi-

lization to be due to chemical interactions, such as com-

plex formation and proton transfer. The physical theory

emphasizes the concept of the electrical double layer.

Counter-ion adsorption and compaction of the diffuse portion

of the double layer are assumed to neutralize the colloidal

charge and bring about coagulation.
52
After coagulation, orthokinetic coagulation or

flocculation50 takes place, normally requiring a longer time

period with gentle mixing conditions. During this step,

interparticle bridging of the coagulated colloids forms

larger floc particles.

The first coagulants, alum and iron salts, were

chosen for their highly gelatinous properties. Later









54,55
investigators attributed the Shultz-Hardy 55 effect as
56
the main attribute of these coagulants. However, more

recent investigators found that the hydrolysis products were
52 57 58
much more effective than the trivalent metal cations.525758

Many investigators have reported the effect of anions on the
56,57,59 The
broadening of the optimum pH for coagulation. 5759 The

displacement of hydroxide ions by highly coordinating anions

has been proposed as the mechanism for these phenomena.60

In 1928, Mattson61 demonstrated the relationship

between microelectrophoretic mobility of colloidal particles

and the aluminum salt dosages. However, this technique re-

mained almost forgotten until 1959 when Pilopovich et al.5

studied the effects of pH, alum dosage, zeta potential, and

base exchange capacity of clay particles on coagulation.

Several investigators reported that base exchange capacity
n 52,58
was an important factor in coagulation.5258 It was also

found that, while good coagulation often occurred near zero

mobility, no absolute relationship existed.58

In a series of papers, Packham proposed that coagu-

lation was due almost entirely to a physical enmeshing or

sweeping down of particles by the highly gelatinous property

of the aluminum hydrolysis products. H!e found that the

type of dispersed phase had relatively little effect on

coagulation conditions. Packham's work and other recent

investigators seem to support the early contentions that the

sticky, gelatinous, property of a coagulant is possibly most









important. The mechanism of coagulation seems to be depen-

dent upon the properties of the dispersed phase and the

conditions which are present during coagulation.


Chemical and Physical Properties of Organic Color


While the origin of organic acids found in natural

waters is still a subject of controversy, most investigators

report that it is due to aqueous extraction from soil or

decaying vegetation. Some investigators propose that color

in water is an intermediate step in the transformation of

organic matter from living or decaying woody tissue to the
62
soil organic complex.62

The structure of the organic acids has been proposed

to be aromatic with hydroxy, carboxy, methoxy, and carbox-

ylic acid groups.6 Black and Christman, using an electro-

dialysis cell with membranes of varying pore sizes, found

that 78% of the organic acid molecules were between 3.5 and

10 m.63 However, light scatter data for this same organic
64
color suggested a larger size. An elemental analysis of

organic color extracted from ten highly colored natural

waters gave the following results.63

Carbon 44.99 54.10%

Hydrogen 1.46 4.23%

Oxygen 38.76 47.93%

Some investigators have found nitrogen present, but the

carbon/nitrogen ratio is reported to be higher for more

highly colored lakes indicating nitrogen as an impurity.64









The molecular weight of the colored acids is generally

believed to range from 450to 10,000. However Gjessing, using

Dioflo ultra-filtration membranes reported approximately 85

percent of the organic acids present had a molecular weight

higher than 20,000.65

Kitano observed that organic acids influenced inor-

ganic solubility equilibrium and subsequent precipitation

products.66 Shapiro has found considerably more iron in

solution in natural waters than would be predicted by

theoretical solubility equilibria.67 He proposed peptiza-

tion of the iron by humic acids with some chelation as the
68
possible mechanism. Olcham and Gloyna propose the mecha-

nism for increased iron solubility to be the ability of the
+3 +2
humic acids to reduce Fe to its more soluble form Fe

and the subsequent complexation of the iron by the humic

acids.

Color has been found to vary in intensity as a func-
69
tion of pH. Singley et al.69 have developed a nomograph

which will correct the color intensity at any pH to that at

pH 8.3, an arbitrary standard.

Black et al.70 have found a stoichiometric relation-

ship between the ferric sulfate dosage required for satis-

factory color removal and the raw water color in a study of

colored waters from different regions of the United States.









Physical and Chemical Structure of Montmorillonite and
Emathlite Clays


Montmorillonite

The structure of this group of clays is derived from

isomorphous substitution of the prototype pyrophyllite.7

Pyrophyllite is a three-layered clay composed of two tetra-

hedral and one octahedral sheets made up of oxygen, silica,

hydroxide, and aluminum. The substitution of a lower

positive valence element for one of higher valence results

in an excess of negative charge as would be the case for the

substitution of magnesium for aluminum. This excess charge

is compensated by the adsorption, on the layer surfaces, of

cations; which are too large to be accommodated in the

interior of the lattice. These compensating cations can be

easily exchanged in the presence of water, thus they are

termed exchangeable cations. The amount that can be ex-

changed, expressed in milliequivalents for 100 grams of dry

clay, is called the cation exchange capacity (CEC) or the

base exchange capacity (BEC) of the clay.

Montmorillonite, when placed in water, undergoes

interlayer swelling which leads to an increase in clay

volume. This swelling allows exchange of interlayer cations

thus montmorillonite clay has a high base exchange capacity.

Emathlite

Emathlite or fullers earth is considered an illite

clay. It is also a three-layered clay but does not undergo









interlayer swelling. Lattice substitutions occur predomi-

nately in the tetrahedral sheet with potassium ions acting

as the principal compensating cations. Since only the

external cations are exchangeable, the cation exchange

capacity is considerably lower than for montmorillonite

clays.

Chemistry of Iron Corrosion and Control by
Calcium Carbonate Deposition

In the corrosion reaction, iron replaces the hydro-

gen ions of water at the anode while at the cathode hydro-

gen ions are removed. Under aerobic conditions the hydro-

gen ion can be removed as:

02 + 4H+ + 4e 2 2H20

02 + 2H20 + 4e 4011

2H + 2e H H2

Thus oxygen's role in corrosion is the removal of hydrogen

ions from the metal surface. This will cause an increase

in pH of the solution near the cathodic region of the cor-

roding surface. At the same time, iron passes into solution

in a ferrous condition at the anodic area such as

Fe + CO3 FeCO3 + 2e

Fe + HC03 FeCO3 + H + 2e

Feo + OH- Fe(OH)+ + 2e








Under anaerobic conditions, the rate of corrosion is a func-

tion of pH with the corrosion products normally carried away

as:

Feo + 2H+ tFe2+ + H2

The basic objective of corrosion control with calcium

carbonate is the deposition of a thin, impervious layer of

the material on the metal surface. The development and

maintenance of this layer is dependent upon many variables,

including pH and total alkalinity. The "Baylis Curve"72

developed by Baylis in 1935 describes the pH necessary to

maintain the calcium carbonate coating as a function of the

total alkalinity. Langelier subsequently developed an

equation for calcium carbonate which can be used to define

this same required pH in a more sophisticated manner. Larson

and Buswell7 4 and Ryznor7 5 developed indices which simpli-

fied the determination of the optimum pH for calcium carbon-

ate protection of the distribution system. The pH for calcium

carbonate equilibrium can be calculated but the many factors

involved makes it difficult to apply in practice. pH, temper-

ature, total carbonate concentration, total dissolved solids,

calcium, velocity of the water in the main, and the presence

of preformed crystals all affect this equilibrium. Many

investigators indicate a lower limit for alkalinity and hard-

ness of 35 to 40 mg/1 where calcium carbonate precipitation

is employed for corrosion control. It has been established

that the calcium carbonate deposits formed in low alkalinity

waters are large and irregular while in high alkalinity









waters dense, uniform coatings with small anodic and cathodic

regions are found, offering better protection against corro-

sion.76 There is evidence that the rate of corrosion can

increase in low alkalinity and hardness waters where an

attempt is made to employ calcium carbonate precipitation.7

This has been related to a high pH differential between the

anode and cathode because of reduced buffer capacity of the

water at the elevated pH.















CHAPTER 3. EXPERIMENTAL 4MTERIALS AND METHODS


Research efforts should of necessity begin with con-

trolled basic systems and advance in complexity as informa-

tion is obtained. This study begins with synthetic water,

where system variables can be established so it is possible

to study a single variable at a time. Many methods have been

employed to evaluate coagulation processes78 but the jar test

has been the most widely used and was the primary method

chosen for this study. An improved version of the jar test

apparatus was used as shown in Figure 6. The jar test con-

sists of a series of jars, containing the adjusted para-

meters under study, with mixing provided to simulate actual

plant conditions. Normally a settling period follows mixing,

where settling can be evaluated. Modifications have been

made in order to increase the information obtained. The

parameters measured during this study included:

1) Coagulation pH

2) Forms of alkalinity and hardness

3) Settled color and turbidity

4) Electrophoretic mobility



"'Manufactured by Taulman Equipment Company, Atlanta,
Georgia.












































FIG. 6 MULTIPLE STIRRER FOR JAR TESTS









5) Residual magnesium

6) Hardness, alkalinity and color of stabilized

water

7) Visual observation of floe properties and settling

rates.

Coagulant recovery was. studied in detail for both

synthetic and natural waters. A volume of water was coagu-

lated to produce from one to two liters of sludge which was

then carbonated, monitoring calcium, magnesium and organic

color released. The recovered magnesium was reused in order

to evaluate any change in coagulation effectiveness. Some

filtrability studies of the carbonated sludge were performed.


Materials


Montmorillonite and Emathlite Clay Suspensions

The montmorillonite was montmorillonite #23 (Bentonite)

obtained from Ward's Natural Science Establishment, Inc.,

Rochester, New York. The emathlite was obtained from Mid-

Florida Mining Company, Lowell, Florida.

Organic Color

Approximately 160 liters of highly colored water was

collected from runoff in the Austin Carey Forest, near

Gainesville, Florida. The water was very low in turbidity

and ionic strength.









Magnesium Carbonate

The magnesium carbonate was prepared from water

softening plant sludge at Dayton, Ohio. The wet magnesium

carbonate was shipped to Gainesville where it was air dried.

The analysis for alkalinity and magnesium of a solution

containing .5g of the material allowed calculation of the

hypothetical formula, which was found to be the tri-hydrate

of magnesium carbonate, MgCO3 3H20. A chemical analysis

performed by the Research and Analytical Laboratory of the

Monsanto Chemical Company, Dayton, Ohio, of a similar batch

of magnesium carbonate produced in-April of 1970 indicated

the following composition:


Constituent
Magnesium Oxide, MgO
Calcium Oxide, CaO
Carbon Dioxide, CO2
Silicon Dioxide, SiO2
Aluminum Oxide, Al203
Ferric Oxide, Fe203
Sulfur Trioxide, SO3
Chloride, C1
Total Insolubles
Loss on Ignition


Percent by Weight
29.44
0.07
32.50
<0.01
0.005
<0.01
<0.01
<0.001
<0.01
70.67









Flocculant Aids

The flocculant aids studied included an anionic
,. -,- I,..,- ,
potato starch, Hamaco 196, Alum, AP30, and activated

silica.

Synthetic Water Constituents

Reagent grade CaCl2, NaHCO3, and K2S04 were used to

prepare stock solutions for adjusting the calcium, alkalin-

ity, and sulfate concentrations of the synthetic water.


Preparation of Materials


Clay Suspensions

Both clays were pulverized by jar milling for twenty-

four hours. Approximately 20 grams of the pulverized clay

and 10 grams of reagent grade sodium chloride were added to

four liters of water. The slurry was mixed for twenty-four

hours and then dewatered using No. 40 Whatman filter paper

in a Buchner funnel. The clay was washed with distilled

water and resuspended in four liters of distilled water.

After several hours of mixing, the slurry was allowed to

settle to remove the larger clay particles. The supernatant

was withdrawn for use as a stock turbidity solution.



"A product of Staley Manufacturing Division, Decatur,
Illinois.
""Certified Aluminum Sulfate Crystals, Al2(SO4)3.18H20.
***A product of Dow Chemical Company, Midland, Michigan.

A product of Philadelphia Quartz, Philadelphia,
Pennsylvania.









This process was similar to that used by Black and
79
Hannah to give a more uniform suspension, allow greater

precision of measurement, and to promote exchange reactions

due to the high zeta potential associated with the sodium

form of the clay. These authors, using the same clays,

found the base exchange capacity of fullers earth to be 26.5

milliequivalents per liter and that of the montmorillonite

to be 115 milliequivalents per liter. The base exchange

capacities of these clays were determined by the ammonium

acetate method used in soil analysis.80

Organic Color Concentrate

A highly concentrated, pure form of naturally occur-

ring organic color was needed. Various methods have been

employed to concentrate organic cclor such as vacuum distil-

lation, carbon adsorption, freezing, and ion exchange.

Vacuum distillation was chosen because of its simplicity,

availability of a large vacuum still, and reportedly minor

effects on the chemical nature of organic color.

The water collected was first filtered through Whatman

41 ashless filter paper. The color was then concentrated
3-
using a Precision Scientific Flash evaporator as shown in

Figure 7 The operating vacuum was maintained by a vacuum
'-'--'-
pump at 4-6 cm of mercury and a temperature of less than



"Product of Precision Scientific Company, Chicago,
Illinois.
^"Product of Welsh Scientific Company, Skokie, Illinois.




























































FIG. 7 FLASH EVAPORATOR USED TO CONCENTRATE
ORGANIC COLOR









400C. The capacity of the vacuum pump limited the evapora-

tion rate to about 2.5 1/hr.

The evaporation procedure was semi-continuous. The

feed rate was adjusted to match the evaporation rate. When

the color in the evaporator reached the desired concentra-

tion, the evaporator was emptied and the procedure repeated.

The color concentrate was filtered through a series

of Whatman 40 + 41 paper then through Millipore""* .8p and

.45i filters. The concentrated color was then placed in

dialysis tubing and dialized against distilled water for

twenty-four hours. Chemical analyses of the untreated, con-

centrated, and treated concentrate are shown in Table 1.

All chemical analyses were run in accordance with the pro-

cedures outlined in Standard Methods with metal ion deter-

mined by atomic absorption analysis. The two batches of

raw water were collected to obtain the desired volume of

color concentrate. The color concentrate was stored at 40C

in tightly stoppered liter bottles.

Synthetic Waters

A synthetic water whose composition was designed to

represent, as nearly as possible, a typical soft surface

water of low alkalinity and total hardness was prepared from

the stock solutions listed elsewhere.



"'Product of Millipore Filter Corporation, Bedford,
Massachusetts.









TABLE 1


CHEMICAL ANALYSIS OF ORGANIC COLOR


pH
Conductivity (pmho/cm)
Color (pH 8.3)
Acidity (mg/l CaCO3)
COD (mg/l)
TS (mg/1)
VSS (mg/1)
NH3N (mg/1)
Organic N (mg/1)
TOC (mg/1)
C/N Ratio
ZN (mg/1)
Cu (mg/1)
MN (mg/l)
Fe (mg/1)
Mg (mg/1)
Na (mg/1)
Ca (mg/1)


Raw #1
4.70
48.5
700
20.1
117'
0.190
0.103
0.41
3.14
39.5
12.6
< .1
0.04
0.03
8.2
1.3
5.1
1.9


Raw #2
4.45
57.5
690
25.0
108
0.182
0.983



<.1
0.04
0.04
6/4
1.0
4.3
1.2


Concentrate
4.00
520
15,150
320
2,660
2.76
2.08



1.20
0.40
0.70
106
18
8.2
8.0


Filtered and
Dialized Concentrate
4.40
230
13,250
200
2,010
2.00
1.66



1.20
0.20
0.45
98
1 0
2.3
5.0


Color
COD
Acidity.
Conductivity
Volume


Concentration Factor
21.8
22.8
15.9
10.3
26.7









The synthetic stock solutions were prepared using

deionized distilled water so that 1 ml = 50 mg of Ca(as

CaCO3), alkalinity (as CaC03) and SO4 Working solutions

were prepared by diluting these stock solutions 10 to 1 with

deionized distilled water so that 1 ml = 5 mg of the desired

constituents.

The synthetic water had the following composition:

Milliequivalents ppm Milliequivalents ppm

Ca ------- 0.500 10.0 HCO3 ------- 0.500 30.5
Na ------- 0.500 11.5 SO2 ------- 0.500 24.0
------- 0.500 19.5 Cl- ------- 0.500 17.7
1.500 1.500

Total alkalinity as CaCO3 --------- 25 ppm

Total hardness as CaCO3 ---------25 ppm

Total dissolved solids --------- 114 ppm

Coagulants

Alum

The alum stock solution was prepared by adding rea-

gent grade aluminum sulfate to deionized distilled water so

that 1 ml was equal to 10 mg of aluminum sulfate. This

solution was stored at 4 C and used daily to prepare working

solutions by dilution with distilled water so that 1 ml =

1 mg of aluminum sulfate.

MgC03 3H2O

For dosages of less than 15 mg/l of MgCO3-3H20, it

was added as a solution containing exactly 0.5000 g of the









material in 1 liter of demineralized water. Fresh solutions

were prepared weekly.

When dosages greater than 15 mg/l were to be used,

they were accurately weighed into 15 ml beakers and quantita-

tively transferred to the stirred water sample as a slurry.

In the case of synthetic waters, deionized water was used to

prepare the slurry; for natural waters, the water itself was

used.

Flocculants

Alum

A fresh solution containing 0.1 mg/ml of A12(S04)3"

18H20 was prepared daily from a stock solution stored at

40C.

Starch

The starch solution was prepared daily by slowly

sifting 1.0 gram of starch into 1 liter of deionized dis-

tilled water and rapidly mixed with a magnetic stirrer. A

working solution was prepared by diluting 10 to 1 with

deionized distilled water so that 1 ml = 0.1 mg of starch.

Activated Silica

The activated silica solution was prepared and

activated in the following manner:

1) 10 nil of distilled water was added to a 100 ml

graduated cylinder.

2) 5 ml of 348 gram/! solution of "N" brand sodium

silicate added.









3) 5 ml of 1 N NH.C1 was added with constant stir-

ring to the graduated cylinder.

4) After 5 minutes'aging, the solution was made up

to 100 ml volume with distilled water and mixed

thoroughly.


Analytical Techniques


Determination of Turbidity and Color

A Lumetron Model 450 Filter Photometer" was used for

both color and turbidity determinations. Sufficient accuracy

was obtained using the red 650 mp filter and 75 mm cell

light path for turbidity determinations. A calibration curve

was prepared plotting optical density obtained for a sample

against the turbidity values previously obtained for the

sample using a Jackson Candle Turbidimeter as described in
81
Standard Methods. The turbidity solutions used for this

calibration procedure were prepared using the emathalite

clay stock solution.

Organic color was measured using a 560 mp filter and

the 75 mm cell light path. The calibration curve for color

was obtained by plotting optical density as a function of

various dilutions of Platinum-Cobalt Color Standard."



"Product of Photovolt Corporation, New York, New York.
-' '-
""Purchased from Fisher Scientific Company, Fair Lawn,
New Jersey.









When color and turbidity were both present in a sample,

a procedure outlined in the Lumetron Operating Manual82 was

followed. This procedure takes advantage of the fact that

organic color absorbs light more strongly at shorter wave

lengths. Color would therefore have little interference in

the measurement of turbidity. The following procedure was

used to determine color in the presence of turbidity:

1) For various levels of turbidity the optical densi-

ties were measured at 650 mp. An average value

was determined for the ratios between the

optical density at 560 mu and 650 mp. This

average value represents a constant for any

level of turbidity and will be denoted as R.

2) The optical density of the sample was determined

at 560 mp and 650 my.

3) R multiplied by the optical density at 650 mi

represents the interference due to turbidity.

Substracting this product from the optical

density found at 560 my gives a value which can

be used to determine the color from the calibra-

tion curve previously prepared.

Atomic Absorption

Iron, sodium, magnesium, and calcium were determined

by use of a Model 1301 Beckman Atomic Absorption Unit"in

combination with a Beckman DBG Grating Spectrophotometer and



"product of Beckman Instrument, Inc., Fullerton,
California.









Beckman Potentiometric Recorder with scale expander. The

procedures outlined in Methods for Analyses of Selected Metals

in Water by Atomic Absorption3 were followed. The standards

were prepared as described with the exception of iron, for

which reagent grade ferrous ammonium sulfate was used to pre-

pare the standard solution. A calibration curve was obtained

each time the samples were run, plotting absorbance versus

concentration.

Electrophoretic Mobility

The electrophoretic mobility determinations were made

using a Zeta-Meter, shown in Figure 8. The samples were

analyzed immediately after collection using the 8 power

microscope objective and a two-hundred volt potential. The

procedure outlined in the Zeta-Meter Manual was followed

for all determinations. Normally 10 particles were tracked

for each sample.

Stabilization of Treated Waters

In order to make possible a comparison of both physi-

cal and chemical parameters of waters coagulated with magne-

sium and with alum, all samples were stabilized to pH 9.0.

Waters coagulated with MgCO3 were stabilized with CO2. Those

coagulated with alum were stabilized with freshly filtered,

saturated lime water.


p..Product of Zeta-Meter, Inc., New York, New York.

























* I-


w-wg


III111


FIG. 8 ZETA-METER USED TO DETERMINE PARTICLE MOBILITY


Si\


#I-


ii"`









Stabilization of Water Coagulated With Alum

Approximately 300 ml of settled water, filtered if

necessary, was transferred to a 500 ml beaker, placed on a

magnetic stirrer and titrated with clear saturated lime water

to pH 9.0, measured by a glass electrode. The sample was

then filtered through Whatman No. 40 paper and color, total

alkalinity, total hardness, calcium and magnesium determined.

Stabilization of Water Coagulated With Magnesium Carbonate

Approximately 300 ml of settled water was transferred

to a 500 ml beaker, placed on a magnetic stirrer, approxi-

mately 1 g of reagent grade powdered CaCO3 added and the

suspension carbonated by blowing through a pipette with rapid

mixing. Three to five minuteswere required to reduce the pH

to 9.0, measured by a glass electrode, as above. The suspen-

sion was then filtered thru Whatman No. 40 paper and color,

total alkalinity, total hardness, calcium and magnesium

determined.

Alkalinity

The alkalinity titrations were performed using 0.02 N

H2SO4 with phenolphthalein and methyl purple indicators as

described in Standard Methods. The sulfuric acid was

standardized using standard 0.02 N sodium carbonate, also

as described in Standard Methods.

Hardness

Total and calcium hardness were determined by titra-

ting with carefully standardized EDTA, following exactly the









procedures as described in Standard Methods. Many determi-

nations were checked by atomic absorption.

pH Measurement

All pH measurements were made using a Corning Model.7

pH Meter with a Corning Combination glass and Ag/AgCl,

electrode. The pH meter was calibrated daily using solutions

prepared from concentrated standard buffer solutions pur-

chased from W. H. Curtin and Company.


Jar Test Procedures


The jar test procedures were very similar for the

natural and synthetic waters and the discussion will be ap-

plicable to both series. The procedure outlined will follow

chronological order with the differences between the series

discussed in the order in which they occur. In every in-

stance where magnesium is used, it is added in the tri-

hydrate form, MgCO3'3H20. In this text and tables it has

been referred to as magnesium carbonate or MgCO3.

Preliminary Determinations

Chemical and physical analyses were performed on each

natural water prior to jar testing. These tests included

pH, color, turbidity, alkalinity, hardness, and magnesium.

A sample of each natural water was filtered through No. 40



"Corning Glass Works, Philadelphia, Pennsylvania.









Whatman filter, acidified to approximately pH 2 with concen-

trated HC1, and stored in a glass bottle for analysis by

atomic absorption for magnesium and iron.

The coagulant dosages were chosen to give undertreat-

ment of the water at the lower dosages and overtreatment at

the higher dosages. Based on previous experience, this range

in chemical dosages could usually be determined from the

results of the chemical and physical analyses. For synthe-

tic waters, these parameters were, of course, chosen for

each jar test.

For both, the quantity of water to total 1 liter after

the addition of all dosages was calculated and added to each

jar.

Details of Jar Test Procedure

For studies where the magnesium carbonate was added

as a slurry, at least two minutes of mixing at 100 RPM was

provided after the slurry addition. The lime slurries were

then added to the jars. The initial addition required

approximately one minute with two additional minutes needed

to rinse the six beakers in order to complete the quantita-

tive transfer of the lime slurry. When flocculant aids were

used, they were added approximately three minutes after the

lime addition. Incremental addition of starch was evaluated

using six dosages, one minute apart. Three were added dur-

ing rapid mix and three during the flocculation period.









Samples for electrophoretic mobility determinations

were taken during rapid mixing, approximately one minute

after flocculant aid addition or approximately three minutes

after lime addition when no flocculant aid was used. The

mixing speed was then slowed to 10 to 12 RPM and maintained

for 15 minutes. After visual observations of the floe

characteristics, 100 ml samples were collected and filtered

through Whatman No. 40 filter paper for immediate determina-

tions of alkalinity.

After the flocculation period, mixing was stopped and

the jars allowed to settle for twenty minutes. At that time

samples of the supernatant were taken for color and turbi-

dity analysis. pH determinations were then made on all jars

and the water in selected jars was stabilized, filtered and

analyzed.

The studies using alum were performed in a similar

manner. For several very low alkalinity waters pre-lime was

added first, using a saturated calcium hydroxide solution to

increase the total alkalinity of the water. Electrophoretic

mobilities were not determined on these waters.


Recovery Studies


The recovery of magnesium from the sludges produced

in coagulating both synthetic and natural waters was eval-

uated. The synthetic waters were prepared to give a range

in organic color of from 15 to 200 and a montmorillonite

turbidity range of from 15 to 50. Coagulation was carried









out in a forty-liter Pyrex jar usirg a small Lightning mixer

with a -rheostat to control the mixing. The quantity of

water to total 36 liters after the addition of all dosages

was added to the jar. The salt solutions were then added

using the concentrated stock solutions to reduce the volumes

added.

As before, coagulant dosages were estimated from pre-

vious jar tests. The magnesium carbonate was vigorously

slurried and quantitatively added to the rapidly mixed water.

After approximately three minutes, the lime slurry was added.

Five minutes after the lime addition, the alum was added and

the rapid mixing continued for two additional minutes. The

mixing was then slowed and maintained for twenty minutes at

a speed which would keep the floc in suspension.

The floc was allowed to settle for a period between

several hours and overnight in some cases. The clear super-

natant was carefully syphoned from the sludge layer and a

composite sample collected for analyses.

The sludge was then poured into a 2 liter graduated

cylinder and measured. In all but the first two experiments

the volume was then made up to 2 liters with distilled water

before carbonation.



*Mixing Equipment Company, Rocheote', New York.









Sludge Carbonation

Carbonation of the sludge was performed using a

cylinder of specially prepared gas containing 15% CO2 and

85% air. A 2 liter graduated cylinder was placed on a large

magnetic stirrer for continuous mixing during carbonation.

The flow of CO2 was regulated using a gas pressure regulator,

so that fine, well dispersed bubbles were produced. A car-

borundum stone diffuser was used to disperse the CO2 into

the sludge with no attempt made to measure the gas flow rate.

Fifty-milliliter samples were taken at predetermined

time intervals and filtered through Whatman No. 40 filter

paper. pH determinations were made on the filtrate; 10 ml

samples were titrated for alkalinity, and a dilution of the

remainder prepared for color analysis. After organic color

had been determined, the samples were acidified and stored

for future analysis for magnesium and calcium by atomic'

absorption. The sludge was carbonated in most cases until a

pH in the range of 7.5 to 7.0 was reached.

The remaining sludge was filtered through No. 40

Whatman paper using a vacuum flask and Buchner funnel.

Several filterability studies were made using polymers and

calcium carbonate as filter aids. Two general methods of

evaluation were employed determination of the time to

dewater 100 ml of the sludge and determination of the total

volume that could be filtered before clogging occurred.









Separan AP30" was used in the polymer evaluation.

Incremental addition of 1 mg/l of the polymer, followed by

determination of the time for filtration of 100 ml of the

sludge provided data used to determine the effect of the

polymer on sludge filterability.

The filtrates from several of the recovery studies

were stored to be used as recycled coagulant.


Coagulation Using Recovered Magnesium Bicarbonate


Coagulation, using both the standard jar test appa-

ratus and the 40 liter Pyrex jar with the variable speed

Lightning mixer, was evaluated using recovered magnesium.

The required volume of recovered magnesium bicarbonate to

give the desired coagulant dosage was added and the coagu-

lation tests performed as discussed previously.

The coagulation of selected synthetic and natural

waters was repeated, using the solutions of magnesium bicar-

bonate recovered as described above, and results `identical

with those obtained with the original magnesium carbonate

were obtained. This was done with jar tests and with

"recovered" coagulant in the 40 liter vessel.


*A product of Dow Chemical Company, Midland, Michigan.










CHAPTER 4. RESULTS AND DISCUSSION


Coagulant Studies of Synthetic Waters

Emathlite clay turbidity was used in the first

studies of synthetic waters. An experiment was designed

to determine the relationship between the level of turbi-

dity and/or organic color present and the dosage of magne-

sium carbonate required for satisfactory treatment of the

water. The alkalinity and hardness were held constant at

25 mg/l as CaCO3. An acceptable treatment would give a

settled turbidity less than 3.5 mg/l and color less than 15

mg/l. A minimum of six jars were required to determine the

lowest dosage of magnesium carbonate for each combination

of color and turbidity. Table 2 summarizes the data used

in the development of this relationship for emathlite tur-

bidity.

TABLE 2

MAGNESIUM CARBONATE REQUIRED FOR COAGULATION OF
ORGANIC COLOR AND EMATHLITE
TURBIDITY

MgCO3 Color Turbidity
4 15 60
20 50 60
90 200 60
20 50 20
90 200 20
90 200 100
10 50 100
50 100 100









A stepwise, linear regression equation was calculated
85
using a BMDO2R Computer Library program.8 The general form

of the regression equation was:

Y = A + blX1 + b2X2

where:

Y = magnesium carbonate dose

A = constant

X1 = the variable, either color or turbidity, which

is most significant in reducing the total

sums of squares

X2 = the variable remaining

b = regression coefficient for X1

b2 = regression coefficient for X2

The equation resulting is:

Y = -3.95 + .48 color + .02 turbidity

For the data shown, color and turbidity account for 98.67%

of the variations in the required magnesium dosage with a

highly significant F value of 44086 and standard error of

the estimate of 5.22.

Lime along with a flocculant, starch, was found to

satisfactorily flocculate the emathlite turbidity as shown

in Table 3. Possibly the fine particles of turbidity served

as a nucleii for calcium carbonate precipitation which was

in turn agglomerated by the starch to a size which would

settle.

Magnesium carbonate's effectiveness in color removal

is demonstrated in Table 4. The color present seemed to improve










LIME AND


TABLE 3
MgCO3 COAGULATION OF A FULLER'S EARTH TURBIDITY,


SYNTHETIC WATER


Characteristics of raw water
Alkalinity as CaCO3 25
Total Hardness as CaCO3 25
pH. ......... ...8.30
Organic Color 0
Turbidity ...... 100
Type Clay . Emathlit- r.Ly


:0 o
Dosage in ppm 1 j Alkalinity H Alkalinity Hardness oj
r- 0 --
o C 0 rl r-i ) ro
Jar bO o r-i .o .0 0 C' M M o C0
Jo w oa o A o o o o 4o 0 o o to
No. uo f,-4 pH u : U U m c C NC T Cm

1 0 95 0.4 10.80 3.3 46 56 0

2 2 97 0.4 10.90 2.1 -.95 50 48 0

3 4 100 0.4 10.95 2.0 -.42 58 44 0

4 6 102 0.4 10.95 1.6 -.54 52 44 0

5 10 105 0.4 10.95 1.5 -.36 58 44 0

6 15 110 0.4 10.95 1.0 -.40 62 40 0


Comments







TABLE 4

MgCOo COAGULATION OF A HIGHLY COLORED,
FULLER'S EARTH TURBIDITY, SYNTHETIC WATER

Dosage in ppn 4 Alkalinity Alkalinity Hardness : o
S4 o 0 ( U
Jar O 0 0 0 0 i 0 0 to
NJar o n o o o o u o a 0 pc
No. uo = pH u a U A C NC T d mE

1 75 130 0.4 11.10 >50 10.0 60 118 0

2 100 144 0.4 11.10 >25 2.0 69 78 0

3 120 155 0.4 11.05 14 1.5 59 52 0

4 140 166 0.4 11.05 10 1.2 62 40 0 9.0 9 0 52 52 1 53

5 160 177 0.4 11.10 12 1.9 50 44 0

6 180 188 0.4 11.10 16 3.8 43 48 0


Characteristics of raw water
Alkalinity as CaCO3 25
Total Hardness as CaCO3 25
pH. . . 8.30
Organic Color .... 200
Turbidity ...... 20
Type Clay . .. Fuller!s Earth


Comments









the size of the floc as well as its settleability. No

attempt was made to measure the magnesium in solution after

coagulation in these early experiments. It was found how-

ever, that good floc formation took place at a pH above

11.0; therefore the pH of coagulation was maintained from

11.0 to 11.25.

The experiments with montmorillonite clay turbidity

were designed in a similar manner to determine the effect

of color and turbidity on the coagulant dosage. The data

used to develop this relationship are shown in Table 5

below:

TABLE 5

MAGNESIUM CARBONATE DOSAGE REQUIRED TO COAGULATE
ORGANIC COLOR AND MONTMORILLONITE TURBIDITY

MgCO3 Color Turbidity
85 200 20
90 200 100
80 200 60
15 50 20
15 50 100
15 50 60
40 100 100


The equation determined is:

Y = -10.24 + .47 color + .03 turbidity

Color and turbidity account for 99.41% of the variation in

required magnesium dosage with a highly significant F value

of 710 and standard error of the estimate of 3.24. As with

the emathlite turbidity, lime, aided by a flocculant, was

satisfactory in removing montmorillonite clay turbidity.

In Table 6, the effectiveness of MgC03 in color and mont-

morillonite clay turbidity removal is shown.








TABLE 6

COAGULATION OF A HIGHLY COLORED SYNTHETIC WATER WITH


Characteristics of raw water
Alkalinity as CaCO3 25'
Total Hardness as CaCO3 25
pH. ......... 8.30
Organic Color .... 200
Turbidity ...... 60
Type Clay . .. Montmorillonite


Comments


MgCO3


Dosage in ppm Alkalilkalinity Alkalinity Hardness o
H rl : -r4 0I
a o r-i 0 (U (ti
Jar to 0a a ,-i .In I cn cw P o C u
o r uo -0 -o o o o o wH
No. < pHl u 1 u j C NC T 0 M

1 40 117 .5 11.05 56 3.7-.81 68 96 0

2 45 120 .5 11.05 46 6.-.88 60 96 0

3 50 122 .5 11.05 45 12.C-.91 68 80 0

4 60 128 .5 11.05 34 12.7-.80 54 72 0

5 70 134 .5 11.05 31 2. -.91 60 72 0

6 80 140 .5 11.15 23 1.1-.80 64 72 0 9.0 14 4 46 41 0 41 9
~ ~ -- -









The use of starch as a flocculant for lime coagula-

tion was studied for both clays. Fifteen experiments were

conducted where all system parameters but starch were kept

constant. Starch dosages of .2 to 1.6 mg/l were found to

reduce the final turbidity in 6 experiments, to have no

effect in 6, and to increase the final turbidity in 3.

Three experiments were performed with all parameters but

the method of starch addition kept constant. The starch

was added as a single dose to one jar and in six increments

to the second jar as discussed in a previous chapter. The

incremental addition increased the efficiency in one test,

had no effect in another, and decreased the efficiency in

the third. Drew Floc 21, a cationic starch, was used un-

successfully in one experiment.


Study of Natural Waters

The first natural waters studied were obtained from

the Talapoosa River, a source of water for Montgomery,

Alabama. Seven sets of jar tests were performed on this water

with the results from selected jar tests shown in Table 7.

Color and turbidity removal was comparable to alum treatment.

The hardness and alkalinity of the magnesium carbonate treated

water, 44 mg/l as CaCO3, would allow p1H adjustment for

corrosion control. This would not be the case for the alum

treatment as the alkalinity and hardness were 13 and 22 mg/I

respectively. This has led to serious corrosion problems.

Water was also obtained from the Mobile River near

Mobile, Alabama and evaluated in a similar manner with the








TABLE 7

MgC03 AND ALUM COAGULATION OF MONTGOMERY, ALABAMA WATER


0 5
Dosage in ppm 4 4 Alkalinity 4 Alkalinity Hardness o
SH "H "HO

Jar E -- .n .oi ffi r' cn n & o ed Pn 0 M ,.u
o 0 o a o o o o 0 0 o 0 o
No. 0 uo U pH u a U V o u C NC T w M

1 30 125 .5 11.10 15 3.2 -.83 78 52 0

2 35 130 .5 11.20 10 1.6 -.69 76 56 0


3 45 125 .5 11.20 12 2.6 -.44 88 56 0

4 50 115 .5 11.15 9 1.6 -.40 80 60 0 9.0 6 4 40 44 0 44


5 50 125 .5 11.20 7 1.4 -.35 86- 60 0 9.0 5 3 41 44 0 44

6 2 6.3 6 0.6 -.19 0 0 6 9.0 6 4 9 13 9 22


Characteristics of raw water
Alkalinity as CaCO3 16 *
Total Hardness as CaCO3 13
pH. ......... .7.00
Organic Color .... 50
Turbidity ...... 165
Type Clay ...... .. Natural


Comments









TABLE 8


MgCO3 AND ALUM COAGULATION OF MOBILE RIVER WATER, MOBILE, ALABAMA

Dosage in ppm 4 Alkalinity Alkalinity Hardness j C

Jar W o ,-1 w a o 0 n cl n u
u 0 0 o o U 0 0 0
No. uo pH u a 0 o o o C NC T

1 30 130 .5 11.15 10 2.0 -.78 86 48 0

2 35 130 .5 11.15 10 1.6 -.69 76 56 0

3 45 115 .5 11.20 13 2.5 -.45 84 56 0 11

4 45 125 .5 11.25 12 2.6 -.44 88 56 0 10

5 40 115 .5 11.10 10 2.6 70 50 0 9.0 9 8 44 52 1 53

6 0 023 7.2 6 2.0 .55 0 0 33 9.0 8 8 30 38 14 52


Characteristics of raw water
Alkalinity as CaCO3 42
Total Hardness as CaCO3 42
pH. ......... 6.95
Organic Color .... 33
Turbidity ...... 39
Type Clay ..... ..Natural


Comments









selected results for both treatment methods shown in Table

8. It was found that very small dosages of alum were very

effective as a flocculant aid. In seven sets of jar tests

with alum addition the only variable, a 0.5 mg/1 dosage of

alum, gave an average of 17% settled color reduction and

50% turbidity reduction as shown in the Table 9.


Table 9

EFFECT OF ALUM AS A FLOCCULANT AID IN COLOR AND
TURBIDITY COAGULATION WITH MAGNESIUM CARBONATE


Montgomery







Mobile


MgCO3
50
50
50
45
45
50
50

40
40
40
40
40
40
40
40
40
40
40


LH
11 0
11.30
11.30
11.25
11.25
11.00
11.00

11.00
11.00
11.00
11.00
11.00
10.95
10.95
11.05
11..05
11.15
11.15


Alum
0
0.5
0.75
0
0.5
0
0.5

0
0.25
0.50
1.00
1.5
0
0.5
0
0.5
0
0.5


Settled
Color
10.8
8.7
9.0
13
12.5
15
12

14.5
13.0
13.2
10.0
11.2
18
16
16.5
12.5
13.0
10.0


Settled
Turbidity
1.0
0.4
0.5
1.6
1.3
1.0
0.2

0.6
0.4
0.3
0
0
1.4
0.6
1.5
0.6
1.0
0.6


Alum addition increased the size and rate of floc growth and

made the electrophoretic mobility less negative. A signifi-

cant linear relationship between mobility and the color or

turbidity reduction has been found for most of the waters

as will be discussed later.









In the study of waters from cities throughout the

country, it was found that many of the waters contained a

considerable amount of magnesium. For these waters, lime

addition precipitated the magnesium present, requiring no

additional magnesium carbonate. In Tables 10 through 25,

selected data from these studies are presented. In every

case magnesium carbonate gives color and turbidity reduc-

tions comparable to alum treatment. The floc formation

with magnesium carbonate occurs at a faster rate, the floc

formed is larger in size, and settling is more rapid due

to the greater floc density. For the waters of high alka-

linity and hardness, activated silica was found to be the

most effective flocculant aid.

Magnesium present in the natural waters was in most

cases in the noncarbonate form. Removal of magnesium as

Mg(OH)2 by lime addition will not decrease the total hard-

ness of the stabilized water, merely substitutes calcium

hardness for magnesium hardness. This can be advantageous

in the case of high magnesium waters where the formation of

magnesium silicate scales in hot water heaters is a prob-

lem.

The raw water analyses, together with the chemical

characteristics of the waters following both alum and mag-

nesium carbonate treatment are given for the waters studied

in Table 26. For the 17 waters studied, treatment with

magnesium carbonate gave a stabilized water with alkalini-

ties ranging from 29 to 55 mg/l as compared with those









TABLE 10


COAGULATION OF ATLANTA, GEORGIA WATER WITH MgCO3 AND ALUM

0 0
Dosage in ppm W 4 Alkalinity 4 Alkalinity Hardness 3

Jar 100 a o 0 o o
No. aU U O pH U vi PH C NC T

1 20 91 .5 11.15 24 23.0-.45 64 60 0

2 30 97 .5 11.15 20 14.0-.34 76 64 0

3 40 103 .5 11.15 15 4.6 0 68 76 0 9.0 11 0 45 45 0 45 16

4 40 118 .5 11.25 2 1. C.41 92 60 0 9.0 0 38 38 0 38 10

5 10 7.50 9 6.C 0 0 10

6 13 7.4 8 3. 0 0 8 9.0 0 16 16 2 18


Characteristics of raw water
Alkalinity as CaCO3 11
Total Hardness as CaCO3 13
pH. ... ... 7.65
Organic Color .... 38
Turbidity ...... 104
Type Clay ...... Natural
Magnesium as CaCO3 4


Comments


Raw water mobility -1.24









TABLE 11


MgCO3 AND ALUM COAGULATION OF BALTIMORE, MARYLAND WATER

Dosage in ppm Alkalinity 0 Alkalinity Hardness C Y
J _s rg*i i 0p __*_
SCfO CG -H -H =f r-l <1) (a
Jar Wo ( -1 e r-i c m n) C. o 0 Cr u
3 co= a0 o o 0 o o o oo
No. uo r-i pH u U U a a u C NC T

1 -- 95 2 11.15 2.1 -.57 74 48 0 9.0 0 54 54 32 86 10

2 15 105 1.5 11.15 3.5 -.47 70 60 0

3 20 105 .5 11.15 2.5 -.33 64 56 0

4 25 107 .5 11.15 2.1 0 56 60 0 9.0 0 40 40 29 69 16

5 8 6.00 1.3 0 0 10 9.0 24 24 30 54

6 10 6.00 0.6


Characteristics of raw water
Alkalinity as CaCO3 12
Total Hardness as CaCO3 40
pH. . . 6.00
Organic Color .... 4
Turbidity ...... 2
Type Clay ....... Natural
Magnesium as CaCO3 13


Comments








TABLE 12

LIME AND ALUM COAGULATION OF BIRMINGHAM, ALABAMA WATER


Dosage in ppm 4 4 Alkalinity W Alkalinity Hardness j
*4 10 r-4 0 WC)
0 H4 .fl, .-4 (0
Jar ca r-i o ( m P 0 n o C U u
0o r o M o 0 o o 0 0 0 C0
No. pH 0 a C NC T (W

1 90 .5 10.70 8 15 -.55 45 70 0

2 130 .5 11.15 7 4.5 -.58 72 48 0 9.0 3 2 37 39 5 44 14

3 140 11.18 8 5.5 -.58 80 48 0


4 150 .5 11.25 8 4.6 0 81 62 0 9.0 3 0 52 52 9 61 18

5 15 7.50 8 1.0 0 0 62

6 20 7.45 6 0 0 0 60 8.8 7 8 63 71 16 87 25


Characteristics of raw water
Alkalinity as CaCO3 74
Total Hardness as CaCO3 83
pH .. . . .7.60
Organic Color .... 12
Turbidity ...... 10
Type Clay ...... Natural
Magnesium as CaCO3 25


Comments


Raw water mobility -.77







TABLE 13

MgCO3, LIME, AND ALUM COAGULATION OF CHATTANOOGA, TENNESSEE WATER

o
Dosage in ppm Alkalinity 4 Alkalinity Hardness | o
SC 0 H '- Q c
Jar a a Mn co CL 0 C r. oU
S0 o 0 0 4J U 0 0o
No. Go o pH U o z 8 C NC T c
CO) ___ liii _I
1 120 .5 11.15 19 15 -.81 86 56 0 9.0 6 0 42 42 20 62 11

2 15 116 .5 11.10 15 10 -.42 64 60 0 9.0 6 0 38 38 18 56 13

3 20 125 .5 11.15 15 10 0 86 68 0

4 25 128 .5 11.15 11 7 1.38 82 72 0 9.0 4 0 44 44 22 66 16

5 15 7.30 11 3.0 0 0 40

6 20 7.25 8 1.8 0 0 3R 9.0 7.0 0 51 51 31 82 15


Characteristics of raw water
Alkalinity as CaCO3 48
Total Hardness as CaCO3 71
pH. .. . .. 7.85
Organic Color .. 24
Turbidity ...... 15
Type Clay . .. Natural
Magnesium as CaCO3 15


Comments


Mobility of raw water -1.07








TABLE 14


COAGULATION OF CLEVELAND, OHIO WATER


Characteristics of raw water
Alkalinity as CaCO3 92'
Total Hardness as CaCO3 127
pH. .......... 8.10
Organic Color .. 5
Turbidity ...... 6
Type Clay ...... Natural
Magnesium as CaCO3 34


WITH LIME AND ALUM


Comments


Dosage in ppm 4 Alkalinity 0 Alkalinity Hardness

S0 0 0 4o o o
No. 0 .o pH U = 0 U V o U C NC T


1 90 2.0 10.35 2 4.8 -1.0 14 44 0 9.0 1 0 39 39 31 70 27

2 90 4.0 10.35 2 3.3 -1.0; 14 50 0 9.0 1 0 47 47 32 79 27

3 160 11.2 2 6.0 0 76 28 0 9.0 0 38 38 32 70 13

4 180 .5 11.35 2 2.7 +.57 88 28 0 9.0 0 36 36 32 70 9

5 8 7.9C 2 4.0 0 0 88

6 10 7.80 2 2.6 0 0 86 9.0 0 98 98 38 136







TABLE 15

COAGULATION OF DETROIT, MICHIGAN WATER BY
PRECIPITATION OF MAGNESIUM PRESENT BY LIME ADDITION


Characteristics of raw water


Alkalinity as CaCO3
Total Hardness as CaCO3
pH . .


Comments


80
100
7.90


Organic Color 0


Turbidity . .
Type Clay . .
Magnesium as CaCO3


2.5
Natural
30


Dosage in ppm 4 Alkalinity a Alkalinity Hardness on
Dosage -- in pp r -i -- -- Alaint o ----------- 0
IIrl 3 r r 0
Jar a ,-i r e cn n o ( r u
0o 1c4 0 0 0 n U 0 0
No. v 4 pH 8 o o C NC T |c

1 75 4.0 10.70 3.5 14 38 0


2 40 1.0 10.50 5.5 2 56 0 9.0 0 42 42 31 73

3 120 3.0 11.10 9.0 -.34 50 28 0

4 120 11.10 6.0 -.53 9.0 0 37 37 20 57 20

5 150 .5 11.20 5.0 -.46 74- 24 0 9.0 0 35 35 17 52 9

6 15 7.60 2.0 0 0 74. 9.0 0 86 86 26 112 30









TABLE 16


COAGULATION OF HUNTSVILLE, ALABAMA WATER WITH MgCO3 AND WITH ALUM

Dosage in ppr Alkalinity a Alkalinity Hardness | c
r4 (r y t4 -H 0 r-i 0u n) T
Jar too .0 0 1 f c. ( o en m U U U
S0 o o o o 0 4 o 0 o H"
No. uo pH u z U u U C NC T m Le

1 0 0 7 7.5 5.0 3.0 -.48 0 0 50 9.0 6 52 58 33 91 20 71

2 15 120 .5 11.15 3.0 3.8 -.37 88 48 0

3 20 125 .5 11.15 1.0 2.5 0 92 60 0 9.0 2 28 30 24 54 14 40


*4 20 125 .5 11.15 3.0 6.4 -.56 86 64 0

5 20 110 .5 10.95 1.0 0.0 -.48 54 44 0 31

6 30 115 .5 11.05 1.0 0.0 0 62 44 0 24
I -


Characteristics of raw water
Alkalinity as CaCO3 54
Total Hardness as CaCO3 84
pH. ........ .7.5
Organic Color .... 4
Turbidity ...... 13
Type Clay . Natural


Comments


*Hal95 at .5 mg/1








TABLE 17


MgCO3 AND ALUM COAGULATION OF JACKSON, MISSISSIPPI WATER

Dosage in pp-m 4 Alkalinity 1 Alkalinity Hardness m
0, H rl o -u
Jar 0O M- a o c- 0 Cl C r
J o o 0 o 0' 0 0
No. Uo pH u : 0 u C NC T w~

1 20 90 .5 11.10 30 9.3 -.84 74 52 0

2 30 95 .5 11.10 27 7.7 -.69 66 64 0

3 40 113 .5 11.20 18 1.6 -.51 78 68 0

4 50 119 .5 11.15 5 2.4 -.24 74 56 0 9.0 5 2 38 39 0 39 11

5 20 6.80 12 0 0 0 9

6 5 6.607 0 0 0 8 9.0 8 0 16 16 7 23
6.60 -- __I


Characteristics of raw water
Alkalinity as CaCO3 10
Total Hardness as CaCO3 12
pH. . . 7.55
Organic Color ... 27
Turbidity ...... 7.4
Type Clay . Natural
Magnesium as CaCO3 2


Comments








TABLE 18

MgCO3 AND ALUM COAGULATION OF LANETT, ALABAMA WATER


Characteristics of raw water
Alkalinity as CaCO3 17
Total Hardness as CaCO3 17
pH. ......... 7.55
Organic Color . 30


Turbidity . .
Type Clay . .


Comments


105
Natural


Dosage in ppm 4 4 Alkalinity Alkalinity Hardness i o
S1 l 0 -U
H H l (d )
Jar CY o -i CO c 0 o U
So 0 0 0 o 0 4j 0 0 w
No. O r- pH U z ( U U c N o C NC T w

1 30 105 .5 11.15 30 5.0 -.32

2 35 108 .5 11.15 13 3.0 +.37

3 40 110 .5 11.15 11 2.0 +.47 94 60 0 14

4 35 125 .5 11.25 13 2.4 +.34 87 54 0 9.0 4 0 53 53 8 61 13


5 10 7.10 13 3.6 0 0 7 9.0 5.0 2 16 18 5 23

6 5 7.0C 11 3.6 0 0 5 9.0 5.0 2 12 14 9 25









TABLE 19


LIME AND ALUM COAGULATION OF LOUISVILLE, KENTUCKY WATER

Dosage in ppr v Alkalinity S Alkalinity Hardness ; n
S-- 0 u
0 o *H *-1 .f l a- En
Jar = I ao o a d o C1 0 C u
;a Io o o o 0 0 U 0 O
No. o o H L : -F U U 0 0 C NC T C ~

1 60 2.0 10.75 3 14.5 34 60 0

2 120 2.0 11.20 3 8.0 92 60 0

3 100 .5 10.90 10 7.81.38 42 60 0 9.0 5 0 32 32 61 83 17


4 140 .5 11.25 4 4.5~.73 80 56 0 9.0 4 0 28 28 55 81 12

5 10 7.35 6 1i. 0 0 50 9.0 5 0 59 59 62 121

6 15 7.30 4 1.4 0 0 48
1.


Characteristics of raw water
Alkalinity as CaC03 51
Total Hardness as CaCO3 110
pH. .. . .. 7.50
Organic Color .... 11
Turbidity ...... 106
Type Clay ...... Natural
Magnesium as CaCO3 33


Comments


Mobility of raw water -.98








TABLE 20


MgCO3, LIME, AND ALUM COAGULATION OF NASHVILLE, TENNESSEE WATER

Dosage in ppm Alkalinity 2 Alkalinity Hardness C N
S'0 r 0 *- H U(
Jar to o .-i o 1 a a 0 o C o co r U
No ooo o 0 0 0 0 0 o o 0 0
No. pH 0 0 8 U 0 o C NC T CU w s
1 110 .5 10.95 8 5.4 .63 43 54 0 9.0 8 2 40 42 16 58 15 .0.3

2 150 11.20 7 2.8 -.60 98 58 0 9.0 4 0 38 38 20 58 12

3 10 116 11.00 8 6.0 -.67 48 44 0

4 15 120 .5 11.00 8 4.6 -.57 56 44 0 9.0 6 4 33 37 15 52 19 0

5 LO 7.55 8 2.6 0 0 66

6 .2 7.50 7 1.6 0 0 65 9.0 8 12 61 73 24 97
|7


Characteristics of raw water
Alkalinity as CaC03 71
Total Haraness as CaCO3 86
pH. . .. . 7.60
Organic Color .... 8
Turbidity ...... 7.5
Type Clay ...... Natural
Magnesium as CaCO3 17


Comments








TABLE 21

MgC03 AND ALUM COAGULATION OF OPELIKA, ALABAMA WATER

Dosage in ppm 1 j Alkalinity w Alkalinity Hardness o
*H 0
C- -i -- 0 U) U
Jar c o o o o o o w M o o0 M
No. z pH 0 04 C NC T U 0
pH C NC T ar

1 5 90 .5 10.95 7 13 -.81

2 10 92 .5 11.10 1 16 -.68 66 32 0 10

3 20 106 0 11.10 2 12.5-.49

4 25 109 .5 11.15 3 3.4 .43 72 32 0 9.0

5 7 6.90 7 1.C

6 O 6.80 4 0 0 0 14 9.0 3 18 21 9 30


Characteristics of raw water
Alkalinity as CaCO3 17
Total Hardness as CaCO3 17
pH. ......... 6.95
Organic Color . 10


Turbidity . .
Type Clay . .


Comments


14
Natural








TABLE 22

LIME, MgCO3, AND ALUM COAGULATION OF PHILADELPHIA, PENNSYLVANIA WATER


Dosage in ppnm r Alkalinity o Alkalinity Hardness >
0 r O ) U
Jar o .0 .0 n n i o o C 0
o 0 U 0 0o o 0 0 U o 00
No. UO r- pH U tn u C NC T M

1 120 .5 11.15 10 2.6 0 86 76 0 9.0 7 0 34 34 34 68 10

2 135 .5 11.25 10 1.4 0 106 68 0 9.0 5 0 35 35 31 66 7

3 10 133 .5 11.13 6 2.6 +.36 94 80 0 9.0 5 0 34 34 32 66 13

*4 60 10.75 6 0.4 36 62 0 9.0 0 48 48 39 87 18

5 L5 7.10 9 1.8 0 0 30

6 20 7.05 7 1.0 0 0 28 9.0 5 0 56 56 39 95 24


Characteristics of raw water
Alkalinity as CaCO3 34
Total Haraness as CaC03 69
pH. ......... 7.40
Organic Color .... 14
Turbidity ...... 41
Type Clay ...... Natural
Magnesium as CaCO3 24


Comments


*2.0 mg/1 "Si02









TABLE 23


COAGULATION OF RICHMOND, VIRGINIA WATER WITH MgCO3 AND ALUM

Dosage in ppm 4 4 Alkalinity w Alkalinity Hardness
--- -- ---t4 T -< --- -- ---- 0 ---- 1 -------- --- I -- 1)0
0 H 4 fl .lH 0-
Jar m 0 o 0 o o o n o U
Jar Cl) fl Mf c, W C1. 0
WO &0 n= 0 ,- 0 0 0 0 4- U 0 0 bO
No. Uo U pH o a U 0 0 C NC T Ca M

1 20 110 .5 11.25 23 14.0 0 78 52 0

2 25 112 .5 11.25 16 5.81.34 80 54 0

3 30 125 .5 11.30 12 2.6 .43 98 50 0 9.0 5 0 40 40 15 55 15

4 40 120 .5 11.25 9 2.8.62 86 56 0 9.0 5 0 38 38 15 53 17

5 3 20 7.80 19 6 0 0 24 9.0 12 0 29 29 24 53

6 3 3 7.70 12 2. 0 0 22 9.0 8 0 31 31 24 55


Characteristics of raw water


Alkalinity as CaCO3


Comments


27


Total Hardness as CaCO3 43
pH. . ... . .7.90
Organic Color . 30


Turbidity . .
Type Clay . .


24
Natural


Magnesium as CaC03 7









MgCO3 AND


TABLE 24

ALUM COAGULATION OF TUSCALOOSA, ALABAMA WATER


Characteristics of raw water
Alkalinity as CaCO3 4.0
Total Hardness as CaCO3 5.0
pH. .. . .. 6.3
Organic Color .... 26
Turbidity ...... 4
Type Clay ...... Natural


Dosage in ppm 1 j Alkalinity 0 Alkalinity Hardness o
*d *l .' i rj 0
o a0 r- 0 -- o
n aH 0 fi U- w0
Jar Mo -s -i i c o n
,,0 u nO 0 0 0 0 4- 0 0
No. uo pH 0u o i U E C NC T M
o I pH C NC T-

1 15 83 .5 11.05 19 2.6 -.87

2 20 86 .5 11.10 16 2.0 -.7.6

3 20 97 .5 11.20 12 0.6 -.37

4 25 100 .5 11.25 8 0.5 -.39 95 32 0 9.0 2 38 40 2 42 12

5 -- 1 7 6.70 7 .1 -.43 0 0 3 9.0 3 6 9 6 15

6 -- 2 7.00 9 .1 0


Comments







TABLE 25

MgCO3, LIME, AND ALUM COAGULATION OF WASHINGTON, D.C. WATER

0 S
Dosage in ppm 4 4 Alkalinity Alkalinity Hardness H o

U 0 0 0 4J o 0 a0 0
Jar Mo | ^ 3 m o^ 0 5 5 _
No. pH o a u o u C NC T m

*1 120 11.10 12 3.0 0 76 48 0

*2 10 127 11.10 8 2.2 -.49 78 48 0

3 15 130 .5 11.10 7 2.0 -.41 72 54 0

4 20 117 .5 10.95 11 2.6 -.72 56 64 0 9.0 5 4 44 48 27 75 18

5 L5 7.45 10 3.0 0 0 37

6 20 7.40 6 1.5 0 0 33 8.4 7 0 40 40 36 76 17


Characteristics of raw water
Alkalinity as CaC03 41
Total Hardness as CaCO3 71
pH. ......... 7.50
Organic Color . 15


Turbidity . .
Type Clay . .
Magnesium as CaCO3


Comments


Mobility of raw water -.96

*.5 mg/l Hal96


50
Natural
17


















TABLE 26

COMPARISON OF RAW AND TREATED CHEMICAL CHARACTERISTICS FOR 17 NATURAL WATERS



RAW WATER CHARACTERISTICS MgCO3 TREATMENT ALUM TREATMENT
CITY _
Total Total Magnes- Total Total Total Total
Turbidity Color ikalindL ardness ium as Alkalinity Hardness Alkalinity Hardness
CaCO-
Atlanta, Ga. 104 38 11 13 -4 38 38 16 1
Baltimore, Md. 2 4 12 40 13 29 53 24 54
Birmingham, Ala. 10 12 74 83 25 40 47 71 87
(a) 15 24 48 71 15 38 56 51 82
Cleveland, Ohio 6 5 92 127 34 36 68 98 136
Detroit, Mich. 3 0 80 100 30 37 57 86 112
Huntsville, Ala(b) 13 4 54 84 13 30 54 52 91
Jackson, Miss. 8 27 10 12 2 39 39 16 23
Lanett, Ala. (c) 105 30 17 17 6 55 55 18 23
Louisville, Ky. 106 11 51 110 33 32 83 59 121
Montgomery, Ala. 165 50 13 16 3 44 44 13 22
Nashville, Tenn. 8 8 71 86 16 32 50 73 97
Opelika, Ala. 14 10 17 17 4 33 33 21 30
Philadelphia, Pa. 41 14 34 69 24 34 66 56 95
Richmond, Va. 24 30 27 43 7 38 53 29 55
Tuscaloosa, Ala. 4 26 4 5 1 40 42 9 15
Washington. D. C. 50 15 41 71 17 40 68 40 76

(a) Requested to be deleted from publication
(b) Tennessee River used for source of raw water
(c) Chattahoochee River used for source of raw water







84
resulting from alum treatment, which ranged from 9 to 98

mg/1. Values for stabilized hardness ranged from 33 to 83

mg/1 as compared with 15 to 136 mg/1 for alum treatment.

Six of the waters coagulated with alum are too low in hard-

ness and alkalinity to use pH adjustment effectively for

corrosion control. In addition, eight waters would benefit

by the reduction in total hardness resulting from using

magnesium carbonate rather than alum.


Solubility of Magnesium Hydroxide

The solubility of magnesium hydroxide has been deter-

mined by many investigators. In this study is was increas-

ingly evident that the magnesium remaining in solution after

coagulation was many times more than would be predicted by

theory. There are several reasons for this apparent in-

crease in solubility, as discussed previously. In the jar

tests the time allowed for equilibrium was usually only one

hour. In plant use, four to six hours are normally allowed

for precipitation which should decrease the magnesium solu-

bility. It is the magnesium hydroxide which is precipitated

that causes colloidal destabilization and only this portion

of the magnesium dosage can be recovered and reused.

The solubility of magnesium hydroxide under jar test

conditions varied for each of the natural waters studied.

It would have been desirable to determine this solubility

relationship for each water, but because of a lack of suf-

ficient data, a composite of 70 observations of magnesium









concentrations at varying pH values for all of the waters

studied was used. A simple linear regression analysis

between log magnesium and pH was used to determine the

experimental Ksp. This value was found to be 1.66 x 10-10

with a standard error of the estimate equal to 1.27.

The solubility relationship found is shown in Figure

9, where the magnesium is plotted as magnesium carbonate

tri-hydrate. This composite solubility relationship is used

in determining recovery efficiencies and cost estimates for

the natural waters studied.


Determination of Conditions for Lowest Treatment Cost

Each water requires a specific amount of magnesium

hydroxide for satisfactory treatment. The solubility re-

lationship developed allows calculation of the amount of

magnesium carbonate which must be fed to precipitate this

amount at various coagulation pH values. For the economic

evaluations, three chemical costs will be considered:

1) Dosage of 90% quicklime required to provide the

optimum pH

2) Amount of CO2 required to:

a) solubilize the Mg(OH)2 in the sludge and

b) reduce the high pH of the treated water to

the pH of stabilization

3) Amount of "make-up" MgCO3.3H20 to be added.

In addition three alternative conditions are considered:

Case I. Lime recovery is practiced, providing CO2

at no cost and 90% lime at $.006/lb,


























Temp. 25 C
Experimental K,, 1.66 X 10-10
100- Theoretical K,, 2.5 X 10-"
Experimental Determination






\'* 4 I


10.20


10.60


11.00


11.40


FIG. 9 SOLUBILITY OF Mg(OH)2 (AS MgCO3 3HgO) AS

FUNCTION OF pH FOR 23 NATURAL WATERS


I-----~-~--~--p-.










Case II. Lime is purchased at $.01/lb but CO2 is

available at no cost from a source within or

near the water plant.

Case III. Lime is purchased at $.01/lb and CO2

generated at a cost of $.0l/lb,

A cost of $.05/lb was assumed for the MgCO3.3H20.

A series of curves have been developed that will

allow a graphical determination of the pH for coagulation

at the least cost. The lime required to increase the pH

from 10.5 to some desired value is independent of the total

carbonate present in the water. In Figure 10, the cost to

raise the pH from 10.5 to the desired pH is shown for the

three cases considered. Figure 10 also includes the cost

of CO2 to stabilize the water back to pH 10.5. The MgCO3.

3H20 cost curve was developed from the solubility relation-

ship curve. It was assumed that MgCO3.3H20 left in solu-

tion represented a cost, i.e. make-up coagulant. Summing

the magnesium carbonate cost and the lime and CO2 costs for

the three cases, a total cost curve is shown in Figure 11.

The optimum pH values and costs can then be determined as:

Cast I pH = 11.35

Cost = $ 9.57

Case II pH = 11.15

Cost = $10.85

Case III pH = 11.00

Cost = $12,45














































20 40 60 80 100 120 140 160 180 200
ALKALINITY (Mg/I as CaCO,)


FIG. 10 TREATMENT COST IN $/M.G. FOR CoO AND CO2 TO
RAISE THE RAW WATER pH TO 10.5 AND REDUCE
THE pH BACK TO pH 9.0 FOR STABILIZATION


12.00-


10.00-



0oo-



S 6.00-
o




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