WATER POLLUTION CONTROL RESEARCH SERIES 12120 ESW 06/71
i/71
Magnesium Carbonate,
A Recycled Coagulant
for Water Treatment
U.S. ENVIRONMENAL PROTECTION AGENCY
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WATER POLLUTION COITROL RESEARCH SERIES
The Water Pollution Control Research Series describes the
results and progress in the control and abatement of pollution
in our Nation's waters. They provide a central source of
information on the research, development and demonstration
activities in the Environmental Protection Agency? through
inhouse research and grants and contracts with Federal, State,
and local agencies, research institutions, and industrial
organizations.
Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Chief, Publications Branch
(Water), Research Information Division, R&M, Environmental
Protection Agency, Washington, B.C. 20^60.
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MAGNESIUM CARBONATE, A RECYCLED COAGULANT
FOR WATER TREATMENT
by
Department of Public Utilities
City of Gainesville
P. 0. Box 490, Gainesville, Florida
for the
ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Monitoring
Project # 12120 ESW
June, 1971
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EPA Review Notice
This report has been reviewed by the Environmental Protection
Agency and approved for publication. Approval does not
signify that the contents necessarily reflect the views and
policies of the Environmental Protection Agency nor does
mention of trade names or commercial products constitute
endorsement or recommendation for use,
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.00
ii
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ABSTRACT
An entirely new system of water treatment has been developed. It is a
unique combination of softening and conventional coagulation, and may
be used for all types of waters, surface or ground, hard or soft.
Magnesium carbonate is used as the coagulant and lime is added to pre-
cipitate gelatinous Mg(OH)2, which is as effective as alum for the
removal of both turbidity and organic color. The floes formed are
larger and heavier than alum floe, since they are "loaded" with CaCO^.
The sludge, composed of a slurry of CaC03, Mg(OH)2 and clay is carbonated
with C02 and the Mg(HO)2 selectively and completely dissolved as the
bicarbonate. The carbonated slurry is filtered and the filtrate re-
cycled to the point of addition of chemicals to the raw water and re-
precipitated with lime thus recovering both the coagulant and the sludge
water. In small plants, the filter cake of CaC03 can be used as land
fill. In larger plants, it is slurried in a flotation cell and the
clay separated and used as land fill. The purified CaCOo is filtered
and the cake passes to a multiple hearth furnace or Kiln and calcined
to high quality lime. Chemical treatment costs are substantially reduced
for most waters and the quality of the treated water is superior to that
treated with alum.
This report was submitted in fulfillment of Water Quality Research
Grant Project 12120 ESW with the Environmental Protection Agency.
Key Words: Water Purification, Coagulation, Chemical Precipitation,
Sludge Treatment, Industrial Wastes.
ill
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CONTENTS
Section
I Conclusions
II Recommendations
III Introduction
IV Theoretical Considerations
V, Experimental Materials and Methods
VI, Results and Discussion
VII Acknowledgements
VIII References
IX Appendix
1
3
5
11
23
33
77
79
87
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FIGURES
1 EFFECT OF HIGH pH ON PQLIOVIRUS 1 (LSc) IN
FLOCCULATED (500 mg/1 CaCOH)2), SANDr-
FILTERED SECONDARY EFFLUENTS AT 25°C 10
2 SOLUBILITY DIAGRAM FOR MAGNESIUM IN WATER AT
ATMOSPHERIC CONDITIONS, TOTAL CARBONATE » 10~% 13
3 TEMPERATURE INFLUENCE ON MAGNESIUM SOLUBILITY 15
4 EFFECT OF pH ON MOBILITY FOR THE INDICATED
COAGULANT DOSAGES ' 17
5 SOLUBILITY OF MgC03»XH20 AS A FUNCTION OF TIME
FOR THE INDICATED HYDRATE FORMS 20
6 SOLUBILITY OF Mg(OH)2 (AS MgC03'3H20) AS A
FUNCTION OF pH FOR 23 NATURAL WATERS 44
7 PARTIAL TREATMENT COSTS IN $/MG FOR CaO, C02
AND MgC03 AS A FUNCTION OF COAGULATION pH 46
8 TREATMENT COST IN $/MG AS A FUNCTION OF
COAGULATION pH 47
9 TREATMENT COST IN $/MG FOR CaO AND C02 TO RAISE
THE RAW WATER pH TO 10.5 AND REDUCE THE pH BACK
TO pH 9.0 FOR STABILIZATION 48
10 TREATMENT COST IN $/MG AS A FUNCTION OF THE RAW
WATER TOTAL ALKALINITY 49
11 TREATMENT COST IN $/MG AS A FUNCTION OF THE
AMOUNT OF MgC03 PRECIPITATED 50
12 SETTLED COLOR AS A FUNCTION OF PARTICLE MOBILITY
DURING COAGULATION, JACKSON, MISSISSIPPI WATER 56
13 SETTLED TURBIDITY AS A FUNCTION OF COAGULATION
MOBILITY - LANETT WATER 57
14 MAGNESIUM RECOVERY BY CARBONATION 65
15 FLOW DIAGRAM FOR TURBIDITY REMOVAL PLANT USING
MgC03 AND LIME RECALCINING 69
vi
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Page
» • ^^< •
16 PHOTOGRAPHIC COMPARISON OF Mgco3 AND ALUM FLOC
DURING RAPID MIXING IN THE REMOVAL 0? ORGANIC COLOR 72
17 PHOTOGRAPHIC COMPARISON OF MgCOo AND ALUM FLOC
DURING FLOCCULATION IN THE REMOVAL OF ORGANIC COLOR 73
18 PHOTOGRAPHIC COMPARISON OF THE BATE OF SETTLING
FOR MgCO- AND ALUM FLOGS FORMED IN THE REMOVAL
OF ORGANIC COLOR 74
19 MAGNESIUM CARBON FLOC (MAGNESIUM HYDROXIDE DARK
WITH ABSORBED COLOR AND CALCIUM CARBONATE CRYSTALS)
MAGNIFIED 200 TIMES 75
20 PHOTOMICROGRAPH OF ALUM FLOC MAGNIFIED 100 TIMES 75
21 PHOTO-MICROGRAPH OF ALUM FLOC MAGNIFIED 200 TIMES 76
vii
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TABLES
NOj Page
1 Chemical Analysts pf Organic Color 26
2 Magnesium Carbonate Required for Coagulation of
Organic Color and Emathlite Turbidity 33
3 Coagulation of Puller's Earth Turbidity With
MgC03 and- With Lime 35
4 Coagulation of a Synthetic-Water Containing
Both Organic Color and Fuller*s Earth Turbidity
with MgC03 36
5 Dosage of MgC03 Required to Coagulate Organic
Color and Montinorillonite Turbidity 34
6 Coagulation of a Highly Colored Synthetic Water
with MgC03 37
7 Effect of Alum as a Flocculant Aid in Color and
Turbidity Coagulation With Magnesium Carbonate 38
8 MgCOo and Alum Coagulation of Montgomery, Alabama
Water 39
9 MgCO., and Alum Coagulation of Mobile River Water,
Mobile, -Alabama 40
10 Comparison of the Chemical Characteristics of 17
Raw and Treated Natural Waters 42
11 Economic Comparison of Treatment Methods for 17'
Natural Waters 54
12 Relationship Between Electrophoretic Mobilities'
and Settled Color or Turbidity for 12 Natural Waters 55
13 Amount of Magnesium Precipitated as Related to
Physical and Chemical Characteristics for 17
Natural Waters 59
14 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 61
15 Carbonation-of Sludge Produced from the Coagulation
of 36 Liters of Synthetic Water Containing 200 mg/1
Organic Color and 15 mg/1 Turbidity 62
viii
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No;
16 Carbonatton of Sludge Produced from the Coagulation
of 36 Liters of Synthetic Water Containing 50 mg/1
Organic Color and 15 mg/1 Turbidity 63
17 Carbonation of Sludge Produced from the Coagulation
of 36 Liters of Synthetic Water Containing 15 mg/1
Organic Color and 15 mg/1 Turbidity 64
18 Carbonation of Sludge Produced from the Coagulation
of 36 Liters of Natural Water Containing 200 mg/1
of Organic Color and 50 mg/1 Added Montmorillonite
Clay Turbidity 64
19 Coagulant Recovery Studies 66
20 Magnesium Solubility as a Function of pH for
Coagulant Recovery Studies 60
21 Evaluation of Twice Recycled Magnesium in
Coagulation of Synthetic Water 68
22 Coagulation of Atlanta, Georgia Water with MgCO-
and Alum 88
23 MgCO.j and Alum Coagulation of Baltimore, Maryland
Water 89
24 Lime and Alum Coagulation of Birmingham, Alabama Water 90
25 MgCOo, Lime, and Alum Coagulation of Chattanooga,
Tennessee Water 91
26 Coagulation of Cleveland, Ohio Water with Lime and Alum 92
27 Coagulation of Detroit, Michigan Water by Precipitation
of Magnesium Present by Lime Addition 93
28 Coagulation of Huntsville, Alabama Water With MgCO
and With Alum 94
29 MgCO^ and Alum Coagulation of Jackson, Mississippi Water 95
30 MgC03 and Alum Coagulation of Lanett, Alabama Water 96
31 Lime and Alum Coagulation of Louisville, Kentucky Water 97
32 MgC03, Lime, and Alum Coagulation of Nashville,
Tennessee Water 98
ix
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No. Page
33 MgCOo and Alum Coagulation of Opelika, Alabama Water 99
34 Lime, MgCOn, and Alum Coagulation of Philadelphia,
Pennsylvania Water 100
35 Coagulation of Richmond, Virginia Water With
MgC03 and Alum 101
36 MgCOo and Alum Coagulation of Tuscaloosa, Alabama Water 102
37 MgCOo, Lime, and Alum Coagulation of Washington, D. C.
Water 103
38 Calculated Potential Production of MgCOo'SHLO by
20 American Cities, 1968 104
39 Calculations of Potential Consumption of
by Water Treatment Plants in the United States 106
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SECTION I. CONCLUSIONS
1) Magnesium carbonate,hydrolyzed with lime, is as effective as alum
for the removal of both turbidity and organic color from surface
waters. The floes formed are larger and heavier than alum floes
and settle better.
2) An optimum dosage of magnesium hydroxide is required for acceptable
treatment of each water. This requirement is related to the
physical and chemical characteristics of the water, with organic
color having the greatest effect. This relationship, determined
for 17 natural waters, is:
Optimum MgC03'3H20 dosage (mg/1)
= 8.33 + .03 (turbidity)
+ .46 (organic color) - .03 (total alkalinity)
+ .14 (total hardness).
The coefficients for color and turbidity in the several natural waters
used were in excellent agreement with the coefficient in the equations
developed for synthetic waters.
3) Neither the base exchange capacity of the clay nor the level of
turbidity present had a significant effect on the optimum coagulant
dosage.
4) For each water studied, one specific flocculant was usually found
superior to all others tested. In general, however, soft waters
responded best to 0,5 ppm dosages of alum, whereas either activated
silica or potato starch produced better floes in hard waters.
5) The measurement of electrophoretic mobility is an effective analytical
tool for evaluating coagulation efficiency, particularly in the
coagulation of organic color. Charge reversal does not result in
restabilization of the colloidal particles.
6) In the study with natural waters, considerably more magnesium was
found in solution after coagulation than would have been predicted
from theoretical magnesium hydroxide solubility data. This may
have been due to the fact that true equilibrium was not reached
in the relatively short settling periods allowed. A significant
difference was found between values for residual magnesium determined
by EDTA and those determined by atomic absorption spectrophotometry.
7) A series of graphs make.s possible the determination of the optimum
coagulation pH and the chemical treatment cost for lime, CO,,, and
MgCOo based on jar test results. While the cost data are based on
conservative estimates, significant savings in treatment costs are
indicated for most waters without considering the many other benefits
resulting from the use of this new treatment process.
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8) Carbonation recovered nearly 100% of the magnesium hydroxide from
the sludge with an insignificant amount of calcium solubilization.
Release of coagulated color is not a problem where the average color
in the water is less than 100. Filterability of the carbonated
sludge will not be a problem for most waters. However, in the case
of very soft waters the sludge will be low in CaCO- and it may be
necessary to add a synthetic organic polyelectrolyte or an inert
filter aid to provide satisfactory filterability.
9) The use of magnesium carbonate in most cases produces a treated water
with superior chemical characteristics compared to water treated with
alum. When magnesium is used, the treated waters have alkalinities
ranging from 30 to 50 mg/1, giving soft waters sufficient alkalinity
for calcium carbonate stabilization or softening waters high in
carbonate hardness.
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SECTION II. RECOMMENDATIONS
The problem of neglecting important research areas in new technological
studies is discussed in the Introduction. While many new and exciting
findings are reported as a result of this work, many more challenging
areas of research have been exposed. For discussion purposes, these
studies are divided into "applied" and "basic" research studies.
A two year research project should be initiated to implement this new
process, first on pilot plant scale and later in a suitable municipal
water plant. This study is required before this new process can be
utilized in water plants throughout the country. The objectives of such
a project would be to study or evaluate the following:
1) Operational procedures and problems in the use of this new process
to treat a soft, colored, highly turbid river water subject to
wide variations in chemical and physical characteristics.
2) Economic considerations of all cost involved in the use of this
new process including projected capital expenditures for plant
modifications.
3) Instrumentation and control of the carbonation and coagulant
recycle processes.
4) Sludge filterability and the methods available for improvement.
The effect of increasing hardness on sludge filterability will
be studied by adjusting the raw water characteristics over a
fairly wide range.
5) The effect of this new process on the future design of floccula-
tion and settling basins. Laboratory observations indicate that
less mixing and settling time is required as compared with alum
treatment.
6) The benefits resulting from the increase in alkalinity and
hardness resulting from the treatment of very soft water using
magnesium carbonate. Comparison will be made of the corrosion
or deposition potential of waters treated with magnesium
carbonate and with alum.
7) Bacteriological removals in each unit to determine if pre-
chlorination is required.
8) Iron and manganese removal to determine if the high pH is
sufficient to precipitate the two metals completely.
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Magnesium carbonate offers considerable promise in the treatment of
municipal and industrial wastes. Magnesium forms a very insoluble
complex, magnesium ammonium phosphate, which, when precipitated with
MgCO-j and lime, could provide tertiary sewage treatment at an acceptable
cost. Simultaneously color, turbidity, and biological and chemical
oxygen demand would be reduced to low and hopefully to satisfactory
levels. Lime and magnesium values can be recovered and recycled as in
water treatment, thus reducing the chemical costs. A research project
to investigate this application has been begun at Gainesville, Fla.
Magnesium carbonate treatment of industrial wastes high in color such as
the pulp and paper wastes, tannery wastes, textile dye wastes, etc.
appears very attractive. More industrial plants have an unlimited supply
of carbon dioxide in the stack gases and many already recover lime. A
method of coagulant recycling for these highly, colored wastes should be
developed. This might be accomplished by the addition of a strong oxidant
to the recycle stream after which the magnesium could be recovered by
precipitation as magnesium carbonate tri-hydrate. The precipitated
magnesium could be lightly calcined, 500-600°C, to burn off the organics
and then reused.
The release of absorbed undesirable constituents by carbonation for
coagulant recovery is in need of further study. For an industrial waste
this might include heavy metals while the release of iron and manganese
would be of concern in water treatment.
Basic research on the chemical interactions between magnesium and com-
plexing ligands should be undertaken. Complexation, chelation, and ion
pair formation should be studied. These mechanisms could possibly ex-
plain the lower magnesium values reported by EDTA titration as well as pro-
vide information as to how this problem can be eliminated. It is possible
that the stability constants for some of these magnesium-ligand complexes
are greater than that for the EDTA-magnesium complex under certain con-
ditions. Possibly a strong oxidant will destroy these complexes,
allowing an accurate titration of the magnesium by EDTA.
The identification of various magnesium species formed at high pH is an
area for further research. Possibly polynuclear, strongly hydrated
hydrolysis products form, as has been proposed for aluminum. Additional
study of the effect of both anions and cations on the mobility of
magnesium hydroxide floes should be conducted.
The removal of tastes and odors is a serious problem faced by practically
all municipal water treatment plants treating soft surface waters. The
effect of the very high pH values used in coagulation with magnesium
carbonate and lime on the removal of these tastes and odors by activated
carbon and by other methods should be carefully studied.
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SECTION III, 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 consider the highly hydrated and gelatinous property
of the hydrolysis products to be a main attribute for their effectiveness.
This property however makes dewatering and disposal 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 character-
istics being reported:2>3,4
Total Solids
Suspended Solids
Volatile Solids
BOD,5x (Ultimate BOD
considerably higher)
COD (Higher value where
activated carbon present)
1,000 - 17,000 mg/1
75% - 90% of Total Solids
20% - 35% of Total Solids
30 - 150 mg/1
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, Neubauer found
the volume of alum sludge produced 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
sedimentation >"»'
2) Lagoons2'3'5
3) Drying beds8
Q
4) Wedge wire filtration
5) Vacuum filtration6
6) Pressure filtration
7) Centrifugation6
8) Freezing6
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As a means of offsetting some of the costs for treating the sludge, alum
recovery has been attempted at several water plants, Jewell10 in 1903
patented sulfuric acid regeneration of alum and in 1923 Mathis11 obtained
a similar patent. In 1951 Black Laboratories12 suggested utilizing sulfur
dioxide gas from boiler stacks as a source of sulfuric acid for alum
recovery at Orlando, Florida. Roberts and Roddy13 reported on investiga-
tions 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 operation. 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 aluminum using
the sulfuric acid process.1^ Iron or manganese, which might be present
in the sludge, is also solubilized. This causes an increase in the con-
centration of these elements, making it necessary to waste a portion of
the recovered alum from time to time.1^ Alum recovery is also practiced
at the Daer Works in Scotland** and is being investigated for use at
Minneapolis, Minnesota.^
Lime recovery in softening plants is practiced in several American cities
with profitable operations being reported for two cities.1"'1^ 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 needs1" 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 magnesium carbonate as the coagu-
lant. The addition of sufficient lime slurry to a water containing
magnesium bicarbonate and/or to which magnesium carbonate has been
added, precipitates both magnesium hydroxide and calcium carbonate.
Carbonation of the sludge solubilizes the magnesium, as magnesium bi-
carbonate, which can be recovered by vacuum filtration and the filtrate
recycled and reused. The filter cake of CaCO^ 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
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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 separated before calcination
because of build-up of insoluble magnesium oxide in the recovered lime.
Various techniques have been developed to separate the magnesium hy-
droxide 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 softening has been used at
Lansing, Michigan for some years during the winter months of low water
demand.1^ In the research activities herein described, the dosage of
lime added in the first phase is just sufficient to precipitate the
calcium bicarbonate and convert 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
the stoichiometric amount. 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 1 and 3 sludges are mainly CaCO-, - phase 2 sludge mainly Mg(OH)».
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. 684 * 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 dissolved by pure C0« with continuous cooling to neutralize the
high, heat of hydration of the MgO.
9 n
Black and Eidsness were able to selectively dissolve the Mg(OH)2 from
the CaCOo in the lime-soda softening sludge at Dayton, Ohio, thus making
it possible to recalcine the CaCO., and produce high quality quicklime.
This sludge carbonation basin, the only one of its kind in the world,
has been operating successfully since 1958.
While magnesium hydroxide was formerly regarded as a liability it has
been recognized as an effective coagulant. 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
performed which indicated that magnesium, in the form of magnesium
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 naturally 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.
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In 19667 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 precipitate
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
million 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 that the widespread use of magnesium
carbonate should receive the most careful consideration:
1) As stated previously, treatment of water plant wastes is becoming
mandatory. The dewatering of this sludge is aninherant benefit
of the magnesium recovery process.
2) Recovery and recycle of a coagulant have not proven practical in
the past. An economical, easily controlled process is not
available for the recovery of magnesium carbonate for coagulant
recycle.
3) A new low-cost source of magnesium carbonate will soon be avail-
able. 3 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) eliminating the use of alum, (b) sale
of recovered magnesium carbonate and (c) recalcination, 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 result 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 minimized
and in many cases eliminated, Houston^ and Hoover" were among the
first investigators to report the effect of high pH on disinfection in
water treatment. In 1952, Riehl e_t al_. reported that at a pH level of
11.0 to 11.5 and a contact time of four hours, the removal of bacterial
organisms is on the order of 100%.
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Alum and ferric sulfate have been shown to be effective in the coagulation
of viruses,^? However, these investigators found that viruses removed
in the floe fraction were not destroyed and active virus can be recovered
from the floe. Berg e£ al_« 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 to some extent bacteria and virus can be re-
moved by the new treatment process.
In this high pH range of coagulation, complete precipitation of iron and
manganese should occur, possibly eliminating the need for more costly
treatment methods. This pH environment would be unfavorable for aquatic
growths in settling basins. The overall effect would be reduction in the
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 carbonate is an entirely new concept in water
treatment chemistry. Initial research efforts have been planned to
determine if this process is technically and economically feasible.
The scope and objectives of this research were therefore as follows:
1) Evaluation of the parameters involved in the use and recycle
of magnesium carbonate as a coagulant 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 physical and chemical characteristics
of a water,
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.
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100
10
pH 10.1
pH 10.8
pH 11.1
20
40
60 80
Time-min
100
120
140
Fig. 1. Effect of High pH on Poliovirus 1 (LSc) in Flocculated (500 rag/1 Ca(OH)t),
Sand-Filtered Secondary Effluents at 25° C
(from Berg e_t al. ^°)
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SECTION IV, THEORETICAL CONSIDERATIONS
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"l~t"/Ca"H" is quite variable but almost always less than 1.
In Pearson's system of classifying metals, 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 de-
formed by adjacent charged ions. Metals in this classification tend to
form insoluble precipitates with OH", CO- , and P07 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 carbln dioxide, magnesium, and
water, one can calculate which solid phase controls magnesium solubility.
The solid phases of magnesium present are:^-*
A °30 ™
A -log Kso30
-
(KCal
1) Brucite - Mg(OH)2
Mg(OH)2(s) * Mg++ + 20H" -15.8 11.6
108 • -*» + 2pK» - 2pH
log [Mg] = 16.4 - 2pH
2) Magnesite - MgCO,,
3
MgC03(s) * Mg"^ + C03= 6.7 4.9
log [Mg^] - -pKSQ - log^ - log a2
log iMg**] = -4.9 - logc - log a2
11
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-log
(KCal mol"1)
3) Nesquehonite - MgC03'3H20
MgC03'3H20(s) * Mg44 + C03 + 3H20 +7.4 5.4
log [Mg*] = -PKSO - log^ - log «2
log [Kg"*"1"] = -5.4 - logc - log a2
4) Hydromagnesite - Mg4(C03)3(OH)2' 3H20
Mgi(C03)3(OH)2'3H20 * 4Mg+2 + 3C03~2
+ 20H- + 3H20 +40.2 29.5
log [Mg^] = -l/4pKsQ + 1/2PK2
- 3/4 logr - 3/4 log «„ - 1/2PH
U'p /
= -.4 - 3/4 log,, - 3/4 log a9 - l/2pH
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 concentration of 10"%. 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(C03)2, is a very common
stable phase found in nature but attempts to precipitate a dolomite phase
from supersaturated solutions under atmospheric conditions have been
unsuccessful.
Considerable effort has been expended in determining the solubility
product-constant for Mg(OH)p. The following table lists some of the
values reported in the literature.
Investigator t C pk,
SP
Gallaher32 25-30 11.28
Ryzner et_ al.33 80 11.28
Krige and Arnold34 20 10.85
Travers and Nouvel35 18 10.60
Kline36 25 11.00
Britton37 Room 10.64
Bube38 25 10.92
Gjaldbach39 18 10.92
Dupre and Bialas40 18 10.92
12
-------
I-'
-3
-4
-S
9
pH
13
FIG. 2
SOLUBILITY DIAGRAM FOR MAGNESIUM IN WATER AT ATMOSPHERIC
CONDITIONS. TOTAL CARBONATE » I0's M
(Stumm, W. and James J. Morgan. Aquatic Chemistry, Fig. 5-10)
-------
Investigator t°C p_kgp
Herz and Muhs41 29 10.31
Kohlrausch and Rose 18 10.87
Loven43 10 10.76
Magnesium hydroxide becomes less soluble at increased temperature.
Figure 3 taken from Larson, Lane, and Neff44 shows this effect.
The solubility products reported were for pure distilled 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 relation
ship:
pK = pCKon - (nZM2 + mZN2)("5
r o
so " so ' 'I +
where:
M N (s) * nM + mN
n m
Kso - [M]"[N]'» Aj A*
u = ionic strength
An illustration of this effect on the K for Mg(OH) using a p°K =11.0
u = 0 u = .01 u = .1 u = .3 S°
pK 11.00 10.73 10.20 9.95
sp
Cotnplexation 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
matal 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. It is reported that while complex formers 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 C02 and
to C03=. These well known softening reactions are:
1) C02 + Ca(OH)2 * CaCO_3 + H20
2) Ca(HC03)2 + Ca(OH)2 * 2CaCO_3 + 2H20
14
-------
.12.0
no
10.0
9.0
30
50
Fig. 3
70
150
170
110 130
Temoerature - *F
Temperature Influence on Magnesium Solubility
190
210
(from Larson, Lane,
and Neff44)
The. dashed curves represent magnesium solubility (as parts per
million CaC03); the solid curves, pH variation. The solubility
curves are based on the solubility product constants of Travers
and Nouvel.35
-------
Magnesium bicarbonate is converted to magnesium carbonate and magnesium
hydroxide on further addition of lime as;
3) Mg(HC03)2 + Ca(OH)2 2 MgC03 4- CaC03 + 2H20
4) MgC03 + Ca(OH)2 * Mg (OH) 2 + CaCO,
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 magnesi-
as:
5) Kg"1"* + S04= + Ca(OH)2 * Mg(OH)2 + Ca^ + S04=
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/1 of Ca(OH)2
CO, + Ca(OH)9 C00 x Ca(OH)2 2i =
22 C02 44
2(HCOo~) + Ca(OH)2 Alk (as CaCO,) x Ca(OH)2 74 =
J CaC03 100
MgCO '3H,0 + Ca(OH), MgCO,,-3H00 x Ca(OH)2 74 =
3 l z J 2 MgC03-3H20 100
Mg^ + Ca(OH), Mg4^ (CaCO,) x Ca(°H)2 _Zi =
z J CaC03 100
In practice 90% pure lime CaO would be slaked and used. Thus, the total
lime dosage found above should be multiplied by 100 56 CaO Or 0.82
times the Ca(OH) value determined. 90 74 Ca(OH)2
CaC03 suspended in water has been found to be negatively charged while
magnesium hydroxide is positively charged. While the particles have
been found to coexist, absorption usually takes place and one pre-
dominates, giving the floe 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). which can cause charge
reversal if sufficient magnesium is present. Flocculation of calcium
carbonate suspensions using coagulant aids is not necessarily accompanii
by a decrease in negative mobility, ° These investigators reported thai
mobility in itself is not a reliable indicator of the degree of floccul,
tion.
Salts other than magnesium carbonate could be used as the source of
magnesium. Once the magnesium is recycled, it would be in the carbonat'
16
-------
10.7
pH VS. HOBIUTt
O - 50 «s/l KgCOj
Q - 45 »g/l MgCO
.2 .3
Hoblllty(-) U/««/V/CB
FIG, 4 EFFECT OF pH ON MOBILITY FOR THE
INDICATED COAGULANT DOSAGES
-------
or bicarbonate form, However any make-up magnesium salt, such as MgSO.
or MgCl2, 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 for many years. However,
such processes have generally been carried out with supersaturated
magnesium solutions and pure CC^. While these processes must be care-
fully controlled, magnesium recovery from water plant sludges is quite
simple, with little control required. The reactions which take place are:
Mg(OH)2(s) + C02 * MgC03 + H20
MgC03 + C02 + H20 2 Mg(HC03)2
Whether the reaction occurs in one or two steps is not known.
on
Black and Eidsness, carbonating a sludge containing Mg(OH)2 and 36 g/1
of CaCO., with 11% C02, found that only 80 mg/1 of CaCOo was dissolved
after 30 minutes' carbonation at a gas flow five times that required to
dissolve all of the Mg(OH) present. According to Johnston, who studied
the solubility of calcium and magnesium carbonates in natural waters, the
equilibrium ratio at 16°C is [Mg*f ]/ [Ca"14"] = 14,000 when the partial
pressure of C02 in the atmosphere is great enough to prevent precipitation
of Mg(OH)2> Another explanation for these phenomena is that a saturated
solution of Ca(HCC>3)2 has a lower pH than a saturated solution of Mg(HC03)2
As carbonation proceeds, the pH is buffered at a pH of approximately 7.5,
due to the Mg(HC03) , allowing little of the calcium to dissolve.
Magnesium hydroxide may also react with the bicarbonate to produce
magnesium carbonate as:
Mg(OH)2 + Mg(HC03)2 4- 2H20 * 2MgC03'3H20
If complete solution of Mg(OH)2 is desired, obviously precipitation of
MgCO-i'SH^O 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(HC03)2 is
not produced.
Production of Magnesium Carbonate
At present magnesium carbonate is produced from four major sources.
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.
18
-------
3) From denp^well brines.
A) 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 MgCO~'5H,,0 precipitated be-
low 13.5°C; the tri hydrate MgCC^-SJ^O precipitated between 13.5°C and
50°C and a "basic carbonate" whose composition is most commonly given
as AMgCOyMgCOH^'x FLO precipitated above 50°C, most rapid.ly and coir-
pletely by boiling. Both the penta-hydrate and the tri-hydrate slowly
revert to the basic carbonate, SMgO'ACC^'xH^O, upon exposure to the
atmosphere. This reversion is accelerated when moisture is present and
at elevated temperatures. When heated to 100°C, dry MgC03'3H20 is quite
stable. MgCC^'Sl^O exhibits an interesting change in solubility or.
heating to 100°C. Figure 5 demonstrates this increased solubility
effect. The data for this figure were collected from analytical studies
of the MgCOo'S^O sludge produced in Dayton, Ohio. It is assumed that
the conversion to the basic carbonate involves recrystallization of the
aqueous solution. At 200°C, dry material loses water and COp without
the addition of water. Possibly partial decomposition furnishes some
wa.er 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 tech-
nical grade tc $.22/lb for the USP grade. 50 Most of the product produced
today is the basic carbonate,
As discussed in the introduction, a new source of magnesium carbonate
will be soon available at a greatly reduced cost. A process has been
developed by A. P. Black and the city of Dayton, Ohio to recover it from
water softening plant sludges. •* Preliminary calculations, included in
the appendix, indicate that as much as 150,000 tons of magnesium carbon-
ate (MgCO^'S^O) can be produced each year by the twenty cities shown.
Substitution of recycled MgCOo'StUO for alum in the more than 4,000
wf.ter treatment plants now using it 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 MgCOs'Sl^O with this new technology has been estimated
to be less than $.02/lb.5l
Colloidal Destabilization
Colloidal destabilization is believed to occur in two steps. The first,
which is assumed to occur very rapidly, has been referred to as
perikinetic coagulation-5 or coagulation. 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 stabilization to be due
19
-------
H@ofe4 1o I05°C for I hr. «e
200*C for 2 hre. as
2OO°C tor 2 tir». oe
Air drM os HgCOs • 5H20
S 10
TIHE (Uln.)
12
14
FIG. 5 SOLUBILITY OF f¥fgCOs-XHtO AS A FUNCTION OF
TIME FOR THE INDICATED HYDRATE FORMS
-------
to chemical interactions, such, as complex formation and proton transfer.
The physical theory emphasizes the concept of the electrical double
layer. CounterT-ion adsorption and compaction of the diffuse portion of
the double layer are assumed to neutralize the colloidal charge and
bring about coagulation.
After coagulation, orthokinetic coagulation5 or flocculation50 takes
place, normally requiring a longer time period with gentle mixing con-
ditions. During this step, interparticle bridging of the coagulated
colloids forms larger floe particles.
The first coagulants, alum and iron salts, were chosen for their highly
gelatinous properties. Later investigators attributed the Shultz-
Hardy-^j" effect as the main attribute of these coagulants.56 However,
more recent investigators found that the hydrolysis products were much
more effective than the trivalent metal cations.52,57,58 Many investigators
have reported the effect of anions on the broadening of the optimum pH
for coagulation.-*" >57,59 ^he displacement of hydroxide ions by highly
coordinating anions has been proposed as the mechanism for these
phenomena.
In 1928, Mattson° demonstrated the relationship between microelectro-
phoretic mobility of colloidal particles and the aluminum salt dosages.
However, this technique remained almost forgotten until 1959 when
Pilopovich et^ al. 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 was an
important factor in coagulation.52,58 jt was aiso found that, while
good coagulation often occurred near zero mobility, no absolute relation-
ship existed.5°
In a series of papers, Packham proposed that coagulation was due almost
entirely to a physical enmeshing or sweeping down of particles by the
highly gelatinous property of the aluminum hydrolysis products.5' He
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 dependent 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 soil
organic complex."2
21
-------
The structure of the organic acids has been proposed to be aromatic with
hydroxy, carboxy, methoxy, and carboxylic acid groups. Black and
Christman, using an electrodialysis cell with membranes of varying
pore sizes, found that 78% of the organic acid molecules were between
3.5 and 10 my. However, li-Bljt scatter data for this same organic
color suggested a larger size, ^ An elemental analysis of organic color
extracted from ten highly colored natural waters gave the following
range of results,"-^
Carbon - 44.99 - 54,10%
Hydrogen - 3.86 - 5.05%
Nitrogen - 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. The molecular weight of the colored acids
is generally believed to range from 450 to 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. ^
Kitano observed that organic acids influenced inorganic solubility
equilibrium and subsequent precipitation products. "^ Shapiro has found
considerably more iron in solution in natural waters than would be pre-
dicted by theoretical solubility equilibria. He proposed peptization
of the iron by humic acids with some chelation as the possible mechanism.
Oldham and Gloyna^ propose the mechanism for increased iron solubility
to be the ability of the humic acids to reduce Fe+^ to its more soluble
form Fe+2 and the subsequent complexation of the iron by the humic acids.
Color has been found to vary in intensity as a function of pH. Singley
e_t_ aJL have developed a nomograph which will correct the color intensity
at any pH to that at pH 8.3, an arbitrary standard.
Black e_t _§!_• have found a stoichiometric relationship between the ferric
sulfate dosage required for satisfactory color removal and the raw water
color in a study of colored waters from different regions of the United
States.
22
-------
SECTION V, EXPERIMENTAL MATERIALS AND METHODS
Research efforts should of necessity begin with controlled basic systems
and advance in complexity as information 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 processes'" 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. The
jar test consists of a series of jars, containing the adjusted para-
meters under study, with mixing provided to simulate actual plant con-
ditions. 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
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 coagulated 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.
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.
23
-------
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, MgCO^'SH^O. 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 Percent by Weight
Magnesium Oxide, MgO 29.44
Calcium Oxide, CaO 0.07
Carbon Dioxide, CO, 32.50
Silicon Dioxide, S102 <0.01
Aluminum Oxide, A1203 0.005
Ferric Oxide, Fe203 <0.01
Sulfur Trioxide, 803 <0,01
Chloride, Cl" <0.001
Total Insolubles <0.01
Loss on Ignition 70.67
Flocculant Aids
The flocculant aids studied included an anionic potato starch, Hamaco 196,
Alum, AP^O, and activated silica.
Synthetic Water Constituents
Reagent grade CaCl^, NaHCO^, and ILjSO, were used to prepare stock solution
for adjusting the calcium, alkalinity, and sulfate concentrations of the
synthetic water.
Preparation of Clay Suspensions
Both clays were pulverized by jar milling for twenty-four hours. Approxi-
mately 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.
70
This process was similar to that used by Black and Hannah ? to give a
more uniform suspension, allow greater precision of measurement, and
to promote exchange reactions due to the high zeta potential associated
24
-------
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 milli-
equivalents per liter and that of the montraorillonite to be 115 milli-
equivalents per liter. The base exchange capacities of these clays
were determined by the ammonium acetate method used in soil analysis.
Preparation of Organic Color Concentrate
A highly concentrated, pure form of naturally occurring organic color
was needed. Various methods have been employed to concentrate organic
color such as vacuum distillation, 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 using a Precision Scientific
Flash evaporator. The operating vacuum was maintained by a vacuum pump
at 4-6 cm of mercury and a temperature of less than 40°C. The capacity
of the vacuum pump limited the evaporation rate to about 2.51/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 concentration, the evaporator was emptied and the procedure
repeated.
The color concentrate was filtered through a series of Whatman 40 + 41
paper then through Millipore . 8y and . 45)j 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 procedures outlined in Standard
Methods with metal ion determined 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 4°C in tightly
stoppered liter bottles.
Preparation of 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.
The synthetic stock solutions were prepared using deionized distilled
water so that 1 ml = 50 mg of Ca(as CaCO.,) , alkalinity (as CaCO-j) and
SO/~. 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:
25
-------
TABLE 1
CHEMICAL AN'ALYSIS OF ORGANIC COLOR
pH
Conductivity (
Color (pH 8'. 3)
Acidity" (mg/1 CaCOo)
COD (mg/1)
TS (mg/1)
VSS (mg/1)
NH3N (mg/1)
Organic N (mg/1)
TOC (mg/1)
C/N Ratio
Cu
MN
Fe
Mg
Na
Ca
0*8/1)
(mg/1)
(mg/1)
(mg/1)
Raw #1
Raw #2
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
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
,150
320
,660
2,
76
2.08
Filtered and
Dlalized Concentrate
4.40
230
13,250
200
2,010
2.00
1.66
1.20
0.40
0.70
106
18
8.2
8.0
1.20
0.20
0.45
98
1 0
2.3
5.0
Color
COD
Acidity
Conductivity
Volume
Concentration Factor
21.
22
8
8
15.9
10.3
26.7
-------
Milliequiyalents ppm Mllliequivalents ppm
10.0 HCOo --^—0.500 30.5
11,5 SOjZ -^ ---- 0,500 24.0
19.5 Cl~ - --- —0.500 17.7
1,500
Total alkalinity as CaCO-j -r --- <-— r- ---- . 25 ppm
Total hardness as CaCOo — <-«- — .^-w --- 25 ppm
Total dissolved solids r^_^,r,r,^_ ,_, -, ^^
Alum
The alum stock solution was prepared by adding reagent 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.
MgCQ3;3H20
For dosages of less than 15 mg/1 of MgCOo'SI^O, 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/1 were to be used, they were accurately
weighed into 15 ml beakers and quantitatively 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 Al« (SO, ) ,. 'ISl^O was prepared
daily from a stock solution stored at 4°C.
Starch:
The starch solution was prepared daily by slowly sifting 1.0 gram of
starch into 1 liter of deionized distilled 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 ml of distilled water was added to a 100 ml graduated cylinder.
27
-------
2) 5 ml of 348 gram/1 solution of "N" brand sodium silicate added.
3) 5 ml of 1 N NH.C1 was added with constant stirring to the
graduated cylinder,
4) After 5 minutes1 aging, the solution was made up to 100 ml
volume with distilled water and mixed thoroughly.
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 my 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 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 my 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.
When color and turbidity were both present in a sample, a procedure
outlined in the Lumetron Operating Manual"^ 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 densities were
measured at 650 my. An average value was determined for the
ratios between the optical density at 560 my and 650 my. 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 my and
650 my.
3) R multiplied by the optical density at 650 mp represents the
interference due to turbidity. Subtracting this product from
the optical density found at 560 my gives a value which can be
used to determine the color from the calibration curve pre-
viously 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 Beckman Potentiometric Recorder with scale
28
-------
expander, The procedures outlined In Methods for Analyses of Selected
Metals in Watery by Atomic Absorption"^ were' followed. The standards
were prepared as described with, the exception of iron, for which
reagent grade ferrous ammonium sulfate was used to prepare 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.
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 physical and chemical
parameters of waters coagulated with magnesium and with alum, all samples
were stabilized to pH 9.0. Waters coagulated with MgCOo were stabilized
with CC>2. Those coagulated with alum were stabilized with freshly
filtered, saturated lime water.
Stabilization of Water Coagulated with Alum:
Approximately 300 ml of settled water, filtered if necessary, was trans-
ferred 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, approximately 1 g of reagent grade powdered
CaCOo added and the suspension carbonated by blowing through a pipette
with rapid mixing. Three to five minutes were required to reduce the
pH to 9.0, measured by a glass electrode, as above. The suspension
was then filtered through Whatman No. 40 paper and color, total alkalinity,
total hardness, calcium and magnesium determined.
Alkalinity
The alkalinity titrations were performed using 0.02 N ^SO, with phenol-
phthalein 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 titrating with carefully
29
-------
standardized EDTA? following exactly the procedures as described in
Standard Methods, Many determinations were checked by atomic absorption,
pH. Measurement
All pR 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 purchased 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 applicable 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 instance where magnesium is used, it is added in the tri~hydrate
form, MgCOySt^O. In this text and tables it has been referred to as
magnesium carbonate or
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 Whatman filter, acidified to approximately pH 2 with
concentrated HC1, and stored in a glass bottle for analysis by atomic
absorption for magnesium and iron.
The coagulant dosages were chosen to give undertreatment 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
synthetic 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 quantitative 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 during rapid mix and three during the flocculation period,
30
-------
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 paper
for immediate determinations of alkalinity.
After the flocculation periods, mixing was stopped and the jars allowed
to settle for twenty minutes. At that time samples of the supernatant
were taken for color and turbidity 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 evaluated. The synthetic waters were
prepared to give a range in organic color of from 15 to 200 and a mont-
morillonite turbidity range of from 15 to 50. Coagulation was carried
out in a forty-liter Pyrex jar using 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 previous 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 deep the floe in suspension.
The floe was allowed to settle for a period between several hours and
overnight in some cases. The clear supernatant 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.
Sludge Carbonation
Carbonation of the sludge was performed using a cylinder of specially
prepared gas containing 15% C02 and 85% air. A 2 liter graduated cylinder
31
-------
was placed on a large magnetic stirrer for continuous mixing during
carbonation, The flow of CC^ was regulated using a gas pressure regulator,
so that fine, well dispersed bubbles were produced, A carborundum stone
diffuser was used to disperse the CCU into the sludge with no attempt
made to measure the gas flow rate,
Fif tyr-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 f ilterability 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 AP was used in the polymer evaluation. Incremental addition
of 1 mg/1 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 f ilterability.
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 apparatus and the 40 liter
Pyrex jar with the variable speed Lightning mixer, was evaluated using
recovered magnesium. The required volume of recovered magnesium bi-
carbonate 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 bicarbonate 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.
32
-------
SECTION VI. RESULTS AND DISCUSSION
Coagulant Studies of Synthetic Waters
Emathlite clay turbidity was used in the first studies of synthetic
waters, since clays of this type have been employed by others for
coagulation studies. An experiment was designed to determine the rela~
tionship between the level of turbidity and/or organic color present
and the dosage of magnesium carbonate required for satisfactory treatment
of the water. The alkalinity and hardness were held constant at 25 mg/1
as CaCO-. An acceptable treatment would give a settled turbidity less
than 3.5 mg/1 and color less than 15 mg/1. 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 turbidity.
TABLE 2
MAGNESIUM CARBONATE REQUIRED FOR COAGULATION OF
ORGANIC COLOR AND EMATHLITE
TURBIDITY
Color Turbidity
J
4
20
90
20
90
90
10
50
15
50
200
50
200
200
50
100
60
60
60
20
20
100
100
100
A stepwise, linear regression equation was calculated using a BMD02R
Computer Library program.85 xhe general form of the regression equation
was:
Y = A + b^ + b2X2
where:
Y = magnesium carbonate dose
A = constant
X]_ = 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 X,
b2 = regression coefficient for X2
33
-------
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 440°° 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 the size of the floe as
well as its settleability. No attempt was made to measure the magnesiun
in solution after coagulation in these early experiments. It was found
however, that good floe formation took place at a pH above 11.0; there-
fore 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
DOSAGE OF MgCO., REQUIRED TO COAGULATE ORGANIC
COLOR AND MONTMORILLONITE TURBIDITY
MgCO,,
,3
85
90
80
15
15
15
40
Color
200
200
200
50
50
50
100
Turbidity
20
100
60
20
100
60
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 MgCOo in color and
34
-------
TABLE 3
COAGULATION OF FULLER'S EARTH TURBIDITY WITH MgC03 AND WITH LIME
Jar
No.
1
2
3
4
5
6
Dosage in ppip
CO
w> o
r
0
?.
4
6
1C
15
CM
s-^.
n3 ZZ
U 0
95
97
100
102
105
110
v£>
n) o\
53 -H
0.4
0.4
0.4
0.4
0.4
"
0.4
PH
10.80
10.90
10.95
10.95
10.95
10.95
u
o
fM
C
O
x
JO
•M
Turbid
3.3
2.1
2.0
1.6
1.5
1.0
Mobility
-.95
~.A2
-.54
-.36
-.40
Alkalinity
w
o
46
50
58
52
58
62
<*>
O
o
56
48
44
44
44
40
r<1
O
C_>
32
0
0
0
0
.0
0
o
j->
,0 rn
^ ex
4.J
C/3
M
0
rH
O
CJ
Alkalinity
O
0
U
ro
O
O
Hardness
C
NC
T
Magnesium
as CaC03
_
00
Oi
Characteristics of raw water
Alkalinity as CaC03
Total Hardness as CaC0
Comments
25
Organic Color ..
Turbidity
Type Clay
8.30
100
Eraathli t-Q Cla
-------
TABLE 4
COAGULATION OF A SYNTHETIC WATER CONTAINING BOTH ORGANIC COLOR
AND FULLER'S EARTH TURBIDITY WITH MgCO-j
Jar
No.
1
2
3
4
i
5
6
Dosage in ppm
00 O
2 0
75
100
120
140
160
180
o o
130
144
155
166
177
188
u; •-<
0.4
0.4
0.4
0.4
0.4
0.4
-
11.10
11.10
11.05
11.05
11.10
11.10
0
i-H
O
o
>50
>25
14
10
12
16
Turbidity
10.0
2.0
1.5
1.2
1.9
3.8
Mobility
Alkalinity
a
0
60
69
59
62
50
43
0
c_>
118
78
52
40
44
48
CO
o
O
0
0
0
0
JO
0
0
AJ
C3 "H.
c/>
9.0
o
o
o
9
Alkalinity
o
0
0")
0
o:
52
Hardness
C
52
NC
1
T
53
Magnesium
as CaCO-j
o\
Characteristics of raw water
Alkalinity as CaC03 25
Total Hardness as CaC03 25
pH 8.30
Organic Color .... 200
Turbidity 20
Comments
Type Clay Fullers Earth
-------
TABLE 6
COAGULATION OF A HIGHLY COLORED SYNTHETIC WATER WITH MgCO,
Jar
No.
1
2
3
4
5
6
Dosage in ppiv
co
60 O
S 0
40
45
50
60
70
80
CN
<0 &
0 0
V— • '
117
120
122
128
134
140
3
i— 1
<
.5
.5
.5
.5
.5
.5
PH
11.05
11.05
11.05
11.05
11.05
11.15
p
o
.H
0
o
56
46
45
34
31
23
Turbidity
3.7
6.0
12. C
12.8
2.£
M
Mobility
-.81
-.88
-.91
-.80
-.91
-.80
Alkalinity
o
68
60
68
54
60
64
ro
O
O
96
96
80
72
72
72
CO
o
o
ac
0
0
0
0
^0
0
o
j_i
_/~» *^r*I
« G.
JJ
CO
9.0
VJ
o
•H
O
u
14
Alkalinity
f>
o
0
4
o
o
o
sc
46
Hardness
C
41
NC
0
T
41
Magnesium
as CaC03
9
U)
Characteristics of raw water
Alkalinity as CaCO-j 25
Total Hardness as CaC03 25
pH 8.30
Organic Color .... 200
Turbidity . 60
Comments
Type Clay Montmorillonite
-------
montmorillonite clay turbidity removal is shown.
The use of starch as a flocculant for lime coagulation 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/1 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 experi-
ments 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 Floe 21, a cationic starch, was used unsuccessfully 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 8. Color and turbidity removal was comparable to alum treatment.
The hardness and alkalinity of the magnesium carbonate treated water,
44 mg/1 as CaCO^, would allow pH adjustment for corrosion control. This
would not be the case for the alum treatment as the alkalinity and
hardness were 13 and 22 mg/1 respectively. This has led to serious
corrosion problems because of the lower buffer capacity.
Water was also obtained from the Mobile River near Mobile, Alabama and
evaluated in a similar manner with the selected results for both treat-
ment methods shown in Table 9. 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 7.
TABLE 7
EFFECT OF ALUM AS A FLOCCULANT AID IN COLOR AND
TURBIDITY COAGULATION WITH MAGNESIUM CARBONATE
Settled Settled
Montgomery MgC03 £H Alum Color Turbidity
50 11.30 0 10.8 1,0
50 11,30 0.5 8.7 0.4
50 11.30 0.75 9.0 0.5
45 11.25 0 13 1.6
45 11.25 0.5 12.5 1.3
50 11.00 0 15 1.0
50 11.00 0.5 12 0.2
38
-------
TABLE
MgC03 AND ALUM COAGULATION OF MONTGOMERY, ALABAMA WATER
Jar
No.
1
2
Dosage in ppm
60 O
S o
30
35
3 | 45
4
5
6
50
50
CM
C_J O
125
130
125
115
125
s
3
.5
.5
.5
.5
.5
2)
PH
11 . 10
11.20
11.20
11.15
11.20
6.3
o
rH
O
15
10
12
9
7
6
Turbidity
3.2
1.6
2.6
1.6
1.4
0.6
jj
r->
,JD
S
-.83
-.69
I-.44
-.40
-.35
f.19
Alkalinity
0
78
76
88
80
86
0
o
52
56
56
60
60
0
0
o
cc
0
0
0
0
•o
6
o
ji X
TO ft,
to
9.0
9.0
9.0
0
o
U
6
5
6
Alkalinity
ro
O
O
4
3
4
o
y
40
41
9
Hardness
C
44
44
13
NC
0
0
9
T
44
44
22
Magnesium
as CaC03
1
;
OJ
Characteristics of raw water
Alkalinity as CaCO-j 16
Total Hardness as CaC03 13
pH 7.00
Organic Color .... 50
Turbidity 165
Type Clay Natural
Comments
-------
TABLE 9
MgC03 AND ALUM COAGULATION OF MOBILE RIVER WATER, MOBILE, ALABAMA
Jar
No.
1
2
3
i
4
Dosage in ppn1
r- es
COO
%z o
30
35
45
45
i
5
6
40
0
.-^
"3 33
O O
130
130
115
125
115
0
£5
i— }
.5
'5
.5
.5
.5
23
PH
11.15
11.15
11.20
11.25
11.10
7.2
i-i
o
r-l
O
0
10
10
13
12
10
6
>.
u
•l-f
T)
•M
^>
M
3
H
2.0
1.6
2.5
2.6
2.6
X
u
•H
r— |
•H
,0
,O
^
-.78
-.69
-.45
-.44
2.0 [-.55
Alkalinity
P"!
O
86
76
84
88
70
0
f"i
0
o
48
56
56
56
50
0
ro
0
y
0
0
0
0
.0
33
o
o p*"!
a o-
to
9.0
9.0
M
o
c-l
0
u
9 •
8
Alkalinity
rO
o
u
8
8
r**>
o
o
44
30
Hardness
C
52
38
NC
1
14
T
53
52
s
3 «0
••-< O
-------
Mobile MgCO-}
40
40
40
40
40
40
40
40
40
40
40
pH.
11,00
11.00
11.00
11,00
11,00
10.95
10.95
11.05
11,05
11.15
11,15
Alum
0
0,25
0.50
1.00
1.5
0
0.5
0
0.5
0
0,5
Settled
Color
14.5
13,0
13,2
10.0
11.2
18
16
16.5
12.5
13.0
10.0
Settled
Turbidity
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 floe growth and made the
electrophoretic mobility less negative, thereby increasing the Van der
Waals attractive forces. A significant 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, re-
quiring no additional magnesium carbonate. In Tables 22 through 37,
selected data from these studies are presented. In every case magnesium
carbonate gives color and turbidity reductions comparable to alum treat-
ment. The floe formation with magnesium carbonate occurs at a faster
rate, the floe formed is larger in size, and settling is more rapid due
to the greater floe density. For the waters of high alkalinity 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 non-
carbonate form. Removal of magnesium as Mg(OH)2 by lime addition will
not decrease the total hardness of the stabilized water, merely substitute
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 problem.
The raw water analyses, together with the chemical characteristics of
the waters following both alum and magnesium carbonate treatment are
given for the waters studied in Table 10. For the 17 waters studied,
treatment with magnesium carbonate gave a stabilized water with alkalini-
ties ranging from 29 to 55 mg/1 as compared with those 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
hardness 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.
41
-------
TABLE 1Q
COMPARISON OF THE CHEMICAL CHARACTERISTICS OF 17 RAW AND TREATED NATURAL WATERS
| CITY
1
|
Atlanta, Sa.
^Baltimore, Md.
SBirrainghaiE, Ala.
1 (a)
^Cleveland, Ohio
betroit, Mich.
'Huntsvllle, Ala^b)
L'ackson, Miss.
jLanett, Ala. (c)
SLouisville, Ky. .
tMontgoittery, Ala.
ijNashvilic, Term.
•Opelika, Ala.
^Philadelphia, Pa.
jXichr.«nd, Va.
UTuscaloosa, Ala.
Iwa.ihinr.toiu. U. C.
RAW V/ATER CHARACTERISTICS
Turbidity
104
2
10
15
6
3
13
8
105
106
165
8
14
41
24
1 Total
/"* 1 i
Color iMkaiini}
!
38
4
12
24
5
0
4
27
30
11
50
8
10
14
30
4 26
50 J 15
11
12
74
48
92
80
54
10
17
51
13
71
17
34
27
it
41
Total
;!arr!r>ess
13
40
83
71
127
100'
84
12
17
110
16
86
17
69
43
5
71
Xagncs-
IUTTI as
4
13
25
15
34
10
13
2
6
33
3
16
4
24
7
1
17
MgC03 TREATMENT ALUM TREATKENT j
Total
Mkalinity
38
29'
40
33
36
37
30
39
55
32
44
32
33
34
38
40
40
Total [ Total
Hardness JAlknlinity
3b
53
47
56
68
57
54
39
55
83
44
50
33
66
53
42
68
16
24
71
51
93
86
52
16
18
59
13
73
21
56
29
9
40
Total j
Hardness 1
18 *
54 !
87 i
82
136
112
91
23
23
121
22 5
97 jj
30 f
95 i
55 5
15 I
76 |
(a) Requested to be deleted from publication
(b) Tennessee "iver used for source of rav vater
(c) Chatt.ihoochee- River used for source of rav water
-------
Solubility of Magnesium Hydroxide
The solubility of magnesium hydroxide has been determined by many
investigators, In this study it was increasingly 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 increase in solubility. In the jar tests the time allowed for
equilibrium was usually only one hour. In plant use, four to six hpurs
are normally allowed for precipitation which should decrease the
magnesium solubility. 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 sufficient 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 solubility product, K . This
value was found to be 1.66 x lO"-^ with a standard error of the estimate
equal to 1.27,
The solubility relationship found is shown in Figure 6, where the mag-
nesium 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 satis-
factory treatment. The solubility relationship developed allows calcu-
lation of the amount of magnesium carbonate which must be fed to pre-
cipitate 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 CCL 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" MgC03'3H20 to be added.
In addition three alternative conditions are considered:
Case I. Lime recovery is practiced, providing CC^ at no cost and
90% lime at $.006/lb.
43
-------
100-
10-
I
tO 20
Tern PL » 29* C
EMptrlmcnlol K.,-1.66 XIO'10
Th*or*tleal K^ • 2.9 X KT"
• • • Exp«rl»«ntol Oat*rntl*atlon
1060
11.00
PH
11.40
FIG. 6 SOLUBILITY OF Mg(OH)2 (AS MgC05 • 3H20) AS A
FUNCTION OF pH FOR 23 NATURAL WATERS
-------
Case II. Lime is purchased at $,01/lb but CC>2 is available at no
cost from a source within or near the water plant.
Case III, Lime is purchased at $,01/lb and CC^ generated at a cost
of $.01/lb.
A cost of $.05/lb was assumed for the MgCO^'SHjO,
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 inde-
pendent of the total carbonate present in the water. In Figure 7, the
cost to raise the pH from 10.5 to the desired pH is shown for the three
cases considered. Figure 7 also includes the cost of C02 to stabilize
the water back to pH 10,5. The MgCOo'Sl^O cost curve was developed from
the solubility relationship curve. It was assumed that MgCO^-Sl^O left
in solution represented a cost, i.e. make-up coagulant. Summing the
magnesium carbonate cost and the lime and C02 costs for the three cases,
a total cost curve is shown in Figure 8. The optimum pH values and
costs can then be determined as:
Case I pH = 11,35
Cost = $9.57
Case II pH = 11.15
Cost = $10,85
Case III pH = 11.00
Cost = $12.45
To this cost, the cost to raise the pH to 10.5 and stabilize the water
back to approximately 9.0 must be added. These costs are related to
the total alkalinity of the water and are shown in Figure 9 assuming
the C02 in the water is negligible. Summing the costs in Figures 8
and 9 produces the working curve shown in Figure 10. An additional cost
must be added for the lime required to precipitate magnesium hydroxide
and for CC^ used in the recovery process. The costs are shown in Figure
11 and are a function of the amount of MgCOo'SI^O precipitated. Figures
10 and 11 therefore, represent the two basic working curves for calcu-
lating treatment chemical costs.
The total cost found must be reduced by an amount dependent upon the
magnesium present in the raw water, as this will reduce the MgCOo'SI^O
make-up. If the coagulation pH results in greater than 100% recovery
of MgCO,'3H20 this value will exceed the cost allocated to the MgCOn'SI^O
remaining in solution as shown in Figure 7. Therefore, before treatment
cost estimates are made for a water, using Figure 6, the pH of saturation
is determined. When the optimum pH values, determined in Figure 8, are
higher than the pH for 100% recovery, the treatment costs are calculated
using Figure 8, 9 and 11. The application of these curves will be illus-
trated using three waters which represent all conditions which might be
encountered.
45
-------
M.OO'
IZ.OO-
IOOO-
aoo-
19
2
eoo-
4.00-
2.00-
IO.S
- S0.05/*
o-CoO, COi - |O.OI/*
o-CoO - 80 Ol/*
«-CoO-
IO.T
It.S
FIG. 7 PARTIAL TREATMENT COSTS IN $/M.G. FOR CoO, C02
AND MgCOs AS A FUNCTION OF COAGULATION pH
-------
MOO
aoo
12.00
IIJOO
MuOO
900
tJOO-
mjplmu* coet - g 12.45
optimum pM - ILOO
minimum co«t - JIO.85
optimum pH - tt.19
• - C«0 * COt -Ol/*
- C«0-.CM/*
o-C«0-.OO«/*
mlnlmuM cett - |9.97
H - 11.39
KX90
10.70
10.90 11.10
pH
11.30
11.SO
FIG. 8 TREATMENT COST IN «/M.G. AS A FUNCTION OF COAGULATION pH
-------
12.00-
KJ.OO-
aoo-
-p-
oo
o
o
4.00-
200-
20 4O 60 80 100 120 140
ALKALINITY (Mg/1 o* CoCO,)
160
ISO
ZOO
FIG. 9 TREATMENT COST IN $/M. G. FOR CoO AND C02 TO
RAISE THE RAW WATER pH TO 10.5 AND REDUCE
THE pH BACK TO pH 9.0 FOR STABILIZATION
-------
vo
20.00-
iaoo
t&OO
O
o
14.00
12.00-
IOOO
2O
30
4O SO 60 70
ALKALINITY (mfl/l at CoCOj)
80 90
100
FIG. 10 TREATMENT COST IN I/M.G. AS A FUNCTION
OF THE RAW WATER TOTAL ALKALINITY
-------
5OO-
ZJOO-
ui
o
o
Z
ix>o-
10 20
MgCOj NEEDED (wifl/l)
90
4O
FIG. 11 TREATMENT COST IN $/M.G. AS A FUNCTION
OF THE AMOUNT OF MgC05 PRECIPITATED
-------
Water A ^ Atlanta? Georgia
Total alkalinity = 11 mg/1
Magnesium (as MgCO-j'SH^O) =5,5 mg/1
Precipitated MgC03«3H20 required (from jar test data) ^ 32 mg/1
This water had a small amount of magnesium present in the raw water.
Figure 6 was checked to see that the magnesium recovery was not greater
than 100% for the three cases of treatment. The pH value which would
represent 100% recovery was greater than 11,6 so the two basic working
curves can be used for all cases for this water, From Figures 10 and
11 the costs were calculated as:
Case I Case II Case III
Figure 10
(for a total alkalinity of 11 mg/1) $10.10 $11.60 $15.38
Figure 11
(for 32 mg/1 MgCOj $ 1.02 $1.60 $2.60
$11.12 $13,20 $18.00
Credit for magnesium in raw water at
$.05/lb for MgC03-3H20 $-2.29 $-2.29 $-2.29
$ 8.73 $10.91 $15.69
Water B - Baltimore, Maryland
Total alkalinity = 12 mg/1
Magnesium as MgCOySK^O = 18 mg/1
Precipitated magnesium carbonate required = 21 mg/1
Figure 6 shows that the pH for 100% recovery is 11.30, which is less
than 11.35 used in Case I. Therefore for Case I, an optimum pH of 11.30
will be used. Cases II and III, pH 11,15 and 11.00, would each provide
less than 100% recovery so Figures 10 and 11 are used.
Case I
Cost to raise pH from 10.5 to 11.3 from
Figure 7 $ 2.32
Cost to raise pH to 10,5 for an alkalinity of
12 using Figure 9 $ .50
Cost to precipitate 21 mg/1 MgCO,'3H20 from
Figure 11 $ .61
$ 3,43
51
-------
Case II Case III
figure 10 (for a total alkalinity of 12 mg/1 $11,65 "$15.45" '
Figure 11 (for 21 mg/1 MgC03) $ 1.10 $ 1.70
$12,75 $17.15
Credit magnesium present in water $-7 50 $-7.50
$ 5,25 $ 9.65
Water C ^ Washington, D, C.
Total alkalinity = 41 mg/1
Magnesium as MgC03*3H20 present =23,5 mg/1
Precipitated MgC03'3H20 required = 24 mg/1
From Figure 6, the pH for 100% recovery is 10,95. All cases will use
this as the pH of coagulation as any pH higher will give greater than
100% recovery,
Case I Case II Case III
Figure 7 (cost to raise pH to 10,95) $1.30 $2.20 $4.40
Figure 9 (for a total alkalinity of
41 mg/1) $ .75 $1.25 $1.98
Figure 11 (for 24 mg/1 MgCOO $ .80 $1.30 $2.50
$2.85 $4.75 $8.88
This method of determining costs and optimum pH for coagulation is based
on the following assumptions:
1) A specific amount of precipitated Mg(OH)2 is required for satisfactory
treatment and can be determined by jar testing.
2) The "pooled" magnesium solubility relationship will estimate the
actual magnesium solubility in practice. As discussed previously,
this is a very conservative estimate and no doubt greater recovery
efficiencies will be obtained, allowing a lower optimum operating
pH and subsequent cost savings.
3) All relationships are based on the costs shown. If costs are
different, the operating pH for the minimum cost will be different.
4) A maximum of 100% recovery of the required MgC03'3H20 dosage. It
is possible that a stable market for MgC03'3H20 will develop which
might make it economically attractive to recover greater than
100% of the required MgC03'3H20 dosage.
5) Magnesium present in the raw water is an asset and decreases
treatment costs.
52
-------
No credits are given for the savings in chlorine, The costs for the
seventeen natural waters studied are calculated and given in Table 11,
The present treatment costs shown in this table are for use of only
lime and alum and were determined either from laboratory evaluation or
annual reports supplied by the cities, A recent survey of treat-
ment costs in Alabama^! was used in cost estimation for the cities in
that state. Daily water production was taken from the 1962 Public Health
Service Survey'^ where present production was not known,
Electrophoretic Mobility as a Measure of Coagulation Efficiency
The degree to which electrophoretic mobility describes treatment
efficiency determines its value as an analytical tool in the coagulation
process. A linear regression analysis between particle mobility during
coagulation and settled color or turbidity gave an evaluation of this
relationship for twelve of the natural waters. Table 12 summarizes the
results. In every case, mobility showed a highly significant linear
correlation with color reduction, Five of the twelve waters indicated
a highly significant linear correlation between mobility and settled
turbidity, while two waters were significantly correlated. Figure 12
illustrates the relationship between coagulation particle mobility and
settled color for Jackson, Mississippi water. Figure 13 illustrates a
high degree of correlation between coagulation particle mobility and
settled turbidity for Lanett, Alabama water.
The effect of activated silica on the mobility-turbidity relationship
is illustrated for the Cleveland water, A significant relationship
existed between particle mobility and residual turbidity for seven
coagulation experiments using alum as the flocculant aid. When the five
experiments using activated silica as the flocculant aid are included,
almost no correlation exists. This effect was noticeable for all jar
tests using activated silica. Increased dosages improved the treatment
efficiency without reducing the particle mobility.
Charge reversal did not result in a restabilization of the colloidal
color nor turbidity as would be expected for alum or ferric sulfate
treatment. In Figure 13, turbidity removal increased as the mobility
became more positive. In the normal pH range of coagulation with alum,
the predominant hydrolysis species is Al(OH)o which is relatively
uncharged.93 For coagulation with magnesium carbonate, positively
charged magnesium hydroxide will predominate at high coagulant dosages.
A possible "sweeping effect" of the color or turbidity by the excessive
amount of magnesium hydroxide produced could explain the good turbidity
removals at highly positive mobilities.
Prediction of the Required Coagulant Dose
Each of the waters required some minimum amount of magnesium hydroxide
floe for satisfactory treatment. The amount of MgCO 'SKUO fed as a
coagulant is relatively unimportant since only that portion precipitated
as Mg(OH)2 is effective in coagulation. Considering the magnesium
53
-------
Ln
-P-
TABLE 11
ECONOMIC COMPARISON OF TREATMENT METHODS FOR 17 NATURAL WATERS
CITY
Atlanta, 3a.
Baltimore, >!d .
Birmingham, Ala.
(a)
Cleveland, Ohio
Detroit, Mich.
Huntsville, Ala.
Jackson, Xiss.
Lanett, Ala.
Louisville, Ky.
Montgomery, Al.1. .
Nashville, Tenn.
Opelika, Ala.
Philadelphia, Pa,
/tichmond, Va.
Tuscaloosa, Ala.
"'ashincton. D. C.
(h)
Avg. Daily
yroci'jction
A<
v- -g/ ' )
32
21
15
22
34
30
22
35
30
33
40
20
10
24
30
10
24
Cost in S/M.G. for M.gCO-, Treatment and Coagulation
pH for Minimum Cost
Cas-- 1 (ci)
C"st
3.73
3.43
2.65
3.50
3.75
3-15
2.80
9. 39
7.59
2.27
9.70
3.80
8.75
2.60
7.37
10.20
2.85
PH
J1.35
11.30
10.55
11.10
10.50
10.50
10.80
11.35
11.35
10.50
11.35
1J .00
11.35
10.95
11.35
11.35
10,50
Case 2 (e)
Cost
10.91
5.25
4.45
5.82
6.30
5.28
4.70
12.12
10.96
3.85
12.23
6.35
10.70
4.35
8.85
12.00
4.75
pH
11.15
11.15
10.55
11.10
10.50
10.50
10.80
11.15
11.15
10.50
11.15
11.00
11.15
10.95
11.15
11.15
10.50
Case 3 (f)
Cost
15.69
9.65
7.12
10.33
9.45
8.30
8.30
17.05
14.64
6.85
18.23
10.30
14.75
C.50
14.43
16.10
8.88
pH
11.00
11.00
10.55
11.00
10.50
10.50
10.80
11.00
10.50
11.00
11.00
11.00
11.00
10.95
11.00
11.00
10.50
(g)
Present
Treatment
Costs
5.94
6.08
12.26
6.25
5.70
6.40
15.00
13.50
5.00
6.12
11.22
5.58
6.30
7.40
11.08
5.70
8.39
(a) Requested to be deleted from publication
(b) From 1960 PH~ Survey uhero present production not known
(c) Precipitated XgCO, as Mg(OH)2
(d) Lime recovery, CaO @ 512.00/ton
(e) C02 source available, CaO @ $20.00/ton
(0 CO- & S.Ol/lb., CaO & $20.00/ton
(g) Based on annual report supplied by city or laboratory evaluation using alum.
and alum.
Cost includes only lime
-------
TABLE 12
RELATIONSHIP BETWEEN ELECTROPHORETIC MOBILITIES AND
SETTLED COLOR OR TURBIDITY FOR 12 NATURAL WATERS.
City
Richmond
Montgomery
Atlanta
Jackson
Tuscaloosa
Loriett
Richmond
Montgomery
Clevelanda
Cleveland
Atlanta
Jackson
Birmingham
Philadelphia
Washington, D.C.
Lonett
Huntsville
Opelika
Tuscaloosa
Independent
Variable
Color
Color
Color
Color
Color
Color
Turbidity
Turbidity
Turbidity
Turbidity
Turbidity
Tumidity
Turbidity
Turbidity
Turbid ity
Turbidity
Turbidity
Turbidity
Turbidity
Observa-
tion
8
33
8
11
10
12
8
33
7
12
8
11
12
8
12
12
6
6
10
Correlation
Coefficient
.811**
.811**
.914**
.965**
.929**
.720**
.919**
.757**
.844v.
.299
.458
.822**
.308
. 824*
.498
. 852**
.148
.919**
.628
Standard
Deviation
2.61
5.72
3.57
3.23
2.40
4.70
1.61
4.87
3.18
5.24
7.62
2.36
5.11
1.18
2.19
1.13
3.59
2.67
1.23
aincludes data using activated silica
*denotes significant correlation (a= .05)
**denotes high significant correlation («= .01)
55
-------
30-
25-
: 20-
Ln
Ul
_>
Ul
in
15-
10-
3-
-.10 -.20 -.30 -.40 -.50 -.60 -.70
MOBILITY (p/kM. ptr V/cm.)
-.SO
-.90
-I.OO
FIG. 12 SETTLED COLOR AS A FUNCTION OF PARTICLE MOBILITY
DURING COAGULATION , JACKSON MISSISSIPPI WATER
-------
I2JO
IO.O
4JO-I
20'
+.80 +.60
+.40 +.20
MOBILITY
0 -.20
per V/cm)
-.40
-.60 -.80
FIG. 13 SETTLED TURBIDITY AS A FUNCTION OF
COAGULATION MOBILITY - LANETT WATER
-------
present in the raw water, the magnesium added for coagulation, and the
magnesium in solution after coagulation? the magnesium precipitated as
Mg(OR)2 can be calculated. The lowest amount of Mg(OH)2 to give satis-
factory treatment was determined for each of the seventeen waters.
The required Mg(OH)2 dosage to treat a water must relate to the chemical
or physical properties of the water, A stepwise linear regression
analysis was made on the data shown in Table 13. The required Mg(OH)
as MgCO '3H20 was regressed as function of a water*s color, turbidity,
total alkalinity, and total hardness. Again a BMD02R library computer
program ^ was used for the analysis, The resulting equation was:
Minimum magnesium dosage (as mg/1 of MgCO., •3H.?0) =
8.33 -f ,03 (turbidity) + .46 (organic color) -
.03 (total alkalinity) + .14 (total hardness).
The independent variables explained 67.6 percent of variations of the
dependent variable, the minimum magnesium dosage, with a standard error
of the estimate of 7.1. The variables were added in the order of greatest
reduction of the regression sums of squares, i.e., turbidity explained
more of the variation of the dependent variable than did hardness. This
equation has regression coefficients almost identical to those found for
the synthetic waters. While turbidity was significant in explaining
relationships, organic color determines the required coagulant dosage.
The average color for the seventeen waters studied was only 18. Had it
been higher, possibly more statistical significance would have resulted,
as was the case for the synthetic waters.
It is interesting to note that neither the base exchange capacity nor the
level of turbidity present influenced the coagulant dose to any great
extent. Montmorillonite clay, emathlite clay, and natural turbidity
each gave similar predictive equations. One hundred JCU of turbidity
would require only 2 to 3 mg/1 of precipitated MgCOo'SH^O for coagulation.
Charge reversal did not occur in coagulating emathlite or montmorillonite
turbidity. In several synthetic water experiments using kaolinite clay
turbidity, a very low, base-exchange capacity clay, charge reversal was
common. Possibly charge reversal in natural water coagulation is re-
lated to the base exchange capacity of the turbidity present, which could
then be a measure of the type of clay present.
Coagulant Recovery
As previously noted, magnesium is separated from softening plant sludge
at Dayton by carbonation. The raw water at Dayton is a very clear,
hard, ground water with no turbidity or organic color present. Coagu-
lation of turbid waters containing organic color would be a different
situation. Turbidity and organic color become highly concentrated in
the sludge and would be expected to influence magnesium recovery. Ten
experiments, four with natural and six with synthetic waters, evaluated
these effects. The results of five of these experiments are shown in
58
-------
TABLE :13
AMOUNT OF MAGNESIUM PRECIPITATED AS RELATED TO PHYSICAL AND
CHEMICAL CHARACTERISTICS FOR 17 NATURAL WATERS
Mg Required Turbidity Color Alkalinity Hardness
(mg/1 as MgC03,3H.20) (j, c. ) (:Pt.Co.) (mg/1) (mg/1)
40.
30
10
15
22
10
25
24
30
35
35
25
24
32
21
20
22
165
105
4
10
13
14
106
50
24
7.5
6
2.5
41
104
2
7.5
15
50
30
26
12
4
10
11
15
30
27
5
0
14
38
4
8
24
13
17
4
74
54
17
51
41
27
10
92
80
34
11
12
71
48
16
17
5
83
84
17
110
71
43
12
127
100
69
13
40
86
71
59
-------
Tables 14 through 18, Figure 14, a plot of the values shown in Table
16, graphically demonstrates the 'relationship between Kg"*"*", €3++ and
color as carbonation proceeds.
Table 19 summarizes the results of the recovery experiments. These
experiments show that nearly 100% recovery of magnesium from the sludge
was possible. Several experiments indicated greater than 100% recovery
of magnesium from the sludge. A combination of analytical error and
release of magnesium by the montmorillonite clay on carbonation no doubt
accounted for this error. The release of color on carbonation would
not be a problem in coagulating waters with an average color of 100 or
less. More highly colored waters would require either llwasting" of a
portion of the recovered coagulant or a more elaborate recovery process.
In every case the carbonated sludge filtrate was free from turbidity,
indicating that release of turbidity would not be a problem. The amount
of calcium, as calcium carbonate, released by the sludge on carbonation
ranged from 35 mg/1 to a high of 200 mg/1. Assuming that the sludge
volume was equal to 1% of the total flow, the high value would represent
an increase of only 2 mg/1 total hardness. The rate of carbonation and
the amount of turbidity in the raw water did not appear to effect the
solubilization of Mg(OH)_ or the release of color and calcium. Color
release was closely related to magnesium solubilization, generally
reaching a maximum when about 90% of the magnesium had been recovered.
An interesting aspect of the sludge recovery experiments was the fact
that considerably less magnesium was found in solution after coagulation
in the 36 liter vessel than in the 1 liter jar tests. The magnesium
values found for these studies, at the indicated pH values, are shown
in Table 20.
TABLE 20
MAGNESIUM SOLUBILITY AS A FUNCTION OF pH
FOR COAGULANT RECOVERY STUDIES
1.63 9.4 11.25
0.50 3.3 11.30
0.60 3.4 11.25
0.30 1.7 11.35
0.80 4.5 11.20
1.32 7.5 11.45
0.32 1.8 11.30
0.11 0.6 11,30
0.65 3.8 11.30
60
-------
TABLE 14
CARBONATION OF SLUDGE PRODUCED FROM THE COAGULATION OF
36 LITERS OF SYNTHETIC WATER CONTAINING. 200 mg/1
OF ORGANIC COLOR AiND 50 mg/1 TURBIDITY
Time (Min.)
1.5
3.0
5.0
10.0
15,0
20.0
30.0
45.0
60.0
Mg^dng/l)
12
16
14
36
63
105
190
260
270
Ca++ (rag/1)
18
23
30
28
27
34
40
50
40
Color
76
138
140
410
440
720
920
1040
1020
1460 ml of sludge made up to 2 liters with distilled water.
61
-------
TABLE 15
CARBONATION OF SLUDGE PRODUCED FROM THE COAGULATION
OF 36 LITERS OF SYNTHETIC WATER CONTAINING 2QO mg/1
ORGANIC COLOR AND 15 mg/1 TURBIDITY
Time (Min.) Ms"(mg/1) Casing/I)
5
10
15
20
30
45
60
75
90
100
110
18
25
52
86
130
184
212
218
248
255
265
24
30
18
28
54
30
34
37
48
48
85
100
205
370
480
760
820
1080
1180
1180
1020
1360 ml of sludge made up to 2 liters with distilled water.
62
-------
TABLE 16
CARBONATION OF SLUDGE PRODUCED FROM TOE COAGULATION OF 36
LITERS OF SYNTHETIC WATER CONTAINING 50 mg/1
ORGANIC COLOR AND 15 mg/1 TURBIDITY
Time (min.) pH Mg (mg/1) Ca^Cmg/l) Organic Color
(Rt.Co, units)
5
10
15
20
25
30
45
8.35
7.75
7.35
7.00
6.85
6.70
17
26
32
40
45
48
52
22
25
25
30
40
50
65
100
138
165
146
214
130
146
1300 ml"sludge made up to 2 1 with distilled water before
carbohation.
63,
-------
TABLE 17
CARBONATION OF SLUDGE PRODUCED FROM THF COAGUIATION
OF 36 LITERS OF SYNTHETIC WATER CONTAINING 15 nig/1
ORGANIC COLOR AND 15 mg/1 TURBIDITY
Color
Time (Min,
5
10
15
20
25
40
1375 ml
) PH
9.20
7.20
6.85
6.60
6.60
6.50
of sludg
Mg (mg/
6
16
26
25
27
30
e made u
1) Ca (mgy
25
29
54
66
94
108
p to 2 liter
'!) (Pt.C.o, units)
12
15
32
50
30
32
volume.
TABLE 18
CARBONATION OF SLUDGE PRODUCED FROM THE COAGULATION
OF 36 LITERS OF NATURAL WATER CONTAINING
200 mg/'l OF ORGANIC COLOR AND 50 mg/1 ADDED
MONTMORILLONITE CLAY TURBIDITY
, ,
Time (Min.) .pH Mg (mg/1)
Color
(rag/1) (pt.Co. units)
5
10
15
20
30
40
--
--
9.35
8.90
7.20
6.85
13
35
54
76
112
119
33
28
32
31
46
48
40
165
240
360
410
545
Total sludge volume 2820 ml.
experiment.
1410 ml made up to 2 1 for this
64
-------
60-
30 •
40-
30-
20-
IO-
240
200
40
o-Mo.** by Atomic Absorption
o-Co** by Atomic Abvorptlon
A-Color (uncorrtctcd for pH)
60
•50
•40
•30
•20
•10
\O
20 30
TIME fmln.)
40
FIG. 14 MAGNESIUM RECOVERY BY CARBONATION
-------
TABLE .19
COAGULANT RECOVERY STUDIES
Water
Montgomery
Montgomery
Atlanta
Austin Cary Forest
Synthetic
Synthetic
Synthetic
Synthetic
Synthetic
Synthetic
Color
(Pt.Co.
units)
50
50
38
200
15
50
200
200
50
15
Tur-
bidity
(J.Q. )
165
165
104
50
50
50
50
15
15
15
MgCOo.
3H20
Adaed
(Grams)
0.15
0.45
1.26
2.80
0.53
1..40
2.88
2.88
0.72
0.36
MgCOo.
3H20J
in Sludge
(Grams)
0.07
0.25
1.15
2.70
0.38
1.41
3.00
3.00
0.59
0.34
Percent
Color
Released
11.0
4,5
4.2
25.0
6.1
18.0
28.0
16.0
9.0
25.0
% MgC03
Recovered
From
Sludge
45
54
92
96
73
100
106
103
83
95
-------
This could have been due to a mass action effect increasing the MgCOH),,
precipitation rate, However the longer time allowed fox settling^ from
3 to 12 hbutSj, is a more likely explanation, Both effects would be
present in actual plant conditions tending to make the economic evaluationf
based on higher magnesium solubility, more conservative,
Limited studies of sludge filterability showed that the carbonated sludge
was considerably easier to filter than the uncarbonated sludge, Treat-
ment of the carbonated sludge with 1,5 mg/1 of anionic polymer increased
the filterability while higher dosages tended to have a negative effect^
Approximately 1 g/1 of CaCOo greatly improved filterability producing a
dry, friable cake, Indicati-ons are that only sludges produced in treat-
ing very soft waters will present any problem in dewatering. Addition
of an inert material, such as CaCO,,, or the use of polymers may be
necessary for these waters. The CaCO-j precipitated in stabilization
may be adequate for this purpose,
Coagulation With Recovered Magnesium
Table 21 demonstrates the effectiveness of recovered magnesium. Three
levels of magnesium carbonate were used to determine the effectiveness
of twice-recovered magnesium bicarbonate in solution. This magnesium
had been used twice in previous experiments. The resulting settled
color, turbidity, stabilized chemical characteristics of water so
treated were almost identical with those of water treated with fresh
material. The reused magnesium bicarbonate was that recovered from
treating a highly colored water, thus representing the most unfavorable
conditions.
Application of the Process
The use of this new coagulation process in large water treatment plants
allows the recovery and reuse of both the lime and the magnesium carbonate
with carbon dioxide supplied from the recalcination of the lime.
The majority of the more than 4000 water plants in the United States
however, will not find it economically attractive to recover lime. Since
the COo produced in recalcination greatly reduces the treatment cost, it
would be advantageous to locate an inexpensive source near the plant.
In many cases such a source exists in the form of diesel or natural gas
engine exhaust, stack gases from incinerators or power plants, or some
other industrial source. As noted in Table 11, the difference in treat-
ment costs between Cases II and III is due entirely to the purchase of CO,.,.
A flow diagram of the unit operations involved is shown in Figure 15.
The sludge from the settling basin, containing MgCOH)-, CaCO,, turbidity,
color, etc., is pumped to the carbonation tank. Carbon dioxide is
introduced with rapid mixing for a detention time of approximately one
hour. The magnesium is completely solubilized as MgCHCO^)- or MgCO-,
while the CaCOo, turbidity, etc. remain as solids. Vacuum filtration
separates the solids so that the liquid phase, containing the magnesium,
67
-------
CTv
00
TABLE 21
EVALUATION OF TWICE RECYCLED MAGNESIUM IN -COAGULATION OF SYNTHETIC WATER
Jar
No.
*1
*2
*3
4
5
6
Dosage in ppir
CO
00 O
"2: O
40
50
60
40
50
60
CM
« rc
0 O
^^
130
142
153
112
117
122
g
3
5!
.5
.5
.5
.5
.5
•5
PH
11.15
11.15
11.10
11.15
11.00
11.15
u
o
r-l
O
C_>
36
34
33
34
41
30
>,
.u
•H
T3
•r^
,0
)-l
D
...H J
4
8
5
6
8
12
>>
u
•H
tH
•H
,0
O
zz
-.62.
-.61
-.71
-.62
-.70
-.67
Alkalinity
SB
O
.82
60
50
68
46
70
CO
O
CJ
96
92
84
100
100
76
f>
o
u
£C
0
0
0
0
•0
0
o
u
^ Si
<$ a*
U
in
9.0
8.7
Vj
o
r-H
O
O
20
18
Alkalinity
CO
o
o
6
0
m
o
u
44
49
Hardness
C
41
47
NC
0
0
T
41
47
B
3 o
•H O
o> w
C O
oo
w w
S CO
4
>
6
j
Characteristics of raw water
Alkalinity as CaC03 25
Total Hardness as CaC03 2_5_
?H
Organic Color .... 110_
Turbidity 60_
Comments
*Twice recovered solution of Mg(HC03)2 used as
coagulant
Type Clay Montmorlllonite
-------
ON
\o
FILTER BACK WASH
RAW WATER
R.M.
TUX-
SETTLING BASIS
:HEMICAi.
F"o n
L— ' «
SLUDGE
< I
-[
. - I
._.co2 i
'—I V.F. I—I PLOT.
TUMIDITY
FIG. 15 FLOW DIAGRAM FOR TURBIDITY REMOVAL
PLANT USING MgC03 AND LIME RECALCINING
-------
can be recycled for reuse. If lime is not recovered, this filter cake
represents a plant waste which could be handled easily and disposed of
as land fill or it might find application in agricultural use as a pH
stabilizer for soil. Carbon dioxide, from either a source available
near the plant or by generation, is supplied to the carbonation and
stabilization units.
The dashed lines in Figure 15 show the additional unit operations
necessary for lime recovery, The filter cake is slurried and the clay
turbidity, color, etc. floated off in a small flotation cell. This
process, which has been shown to be successful at a very minimal cost,
purifies the calcium carbonate before recovery. The small volume of
float, which can easily be dewatered and disposed of as land fill,
represents the only waste product from the entire process. The relatively
pure calcium carbonate is then dewatered by centrifugation, and burned
in a lime kiln producing calcium oxide and carbon dioxide. The calcium
oxide is then slaked and reused while the carbon dioxide is used for
stabilization of the water and carbonation of the sludge as shown in the
flow diagram.
Sludge thickening before carbonation could prove to be desirable. For
most waters, the sludge before carbonation will rarely exceed 1% solids,
suspended in water containing 70-80 mg/1 of hydroxide alkalinity.
Thickening the sludge to 3% solids would allow recycling of the clear,
highly alkaline supernatant which would have a volume equal to 2/3 of
the total sludge flow. This would reduce the required lime dosage and
also reduce the amount of carbon dioxide required for sludge carbonation
as well as the size of the carbonation basin. These advantages must be
weighed against the capital cost and operational problems resulting from
the additional unit required.
Plants reusing lime must carbonate sludge on a continuous basis. For a
one hour carbonation detention time, a fifty million gallon per day
plant would require only an 11,000 gallon carbonation basin, assuming
the sludge volume is 0.5% of the total flow. A five million gallon per
day plant, recovering magnesium on a batch basis, would require a
25,000 gallon basin for the same conditions. In addition, at least a
25,000 gallon storage tank for the magnesium carbonate solution would
be necessary. Sludge thickening prior to carbonation would reduce the
size of both tanks.
Where lime recovery is not practiced, plants treating a moderately turbid
water could vacuum filter the carbonated sludge on an intermittent basis.
All of the carbonated sludge could be recycled until the solids reached
an undesirable level. Removal of the solids by vacuum filtration would
allow the cycle to continue. The increased solids concentration could
possibly increase the coagulation and settling efficiency, particularly
for waters very low in turbidity.
70
-------
Photographic Comparison, of the Formation of Floes Produced With
Magnesium Carbonate and With Alum
In all of the coagulation studies, the magnesium carbonate floes formed
more rapidly and were generally larger in size and more dense than the
alum floes. Photographs taken during coagulation of organic color with
alum in one jar and with MgCO^ in the other allow comparison of both the
rate of floe formation and the physical characteristics of the two floes
formed. The raw water which was coagulated contained 250 mg/1 of organic
color with an adjusted alkalinity- and hardness of 30 mg/1. The dosage
of alum required for good coagulation was established as 85 mg/1. The
optimum dosage of MgC03 was 140 mg/lf hydrolyzed with 160 mg/1 of hydrated
lime, A dosage of 0,5 mg/1 of potato starch was used as a flocculant
with the magnesium carbonate treatment. Five minutes of rapid mixing,
fifteen minutes of slow mixing, and twenty minutes' settling was provided
as in previous jar tests.
Figure 16 shows the water betore addition ot coagulants and live minutes
after the coagulants were added. Figure 17 shows the floe formed seven
minutes after coagulant addition.
71
-------
Before coagulant addition
Five minutes after coagulant addition
FIG. 16 PHOTOGRAPHIX COMPARISON OF Mg003 AMD ALUM FLOG DURING
RAPID MIXING IN THE REMDVAL OF ORGANIC OOLOR
72
-------
FTC. 1? PHDTOGRAPHIC ODMPARISON OF Mg003 AND ALUM FLOG DURING FLOCCULATION IN THE
REMDVAL OF ORGANIC OOLOR
-------
FIG. 18 PHOTOGRAPHIC COMPARISON OP THE RATE OF SETTLING FOR Mg003 AND ALUM FLOGS FORMED
IN THE REMDVAL OF ORGANIC COLOR
-------
A
v «y • •
NT
.
FIG. 19 MAGNESIUM CARBON FLOG (MAGNESIUM HYDROXIDE DARK
WITH ABSORBED COLOR AND CALCIUM CARBONATE
CRYSTALS) MAGNIFIED 200 TIMES
•» i
FIG. 20 PHOTO-MICROGRAPH OF ALUM FLOG MAGNIFIED 100 TIMES
75
-------
a-
PIG. 21 PHD TO-MICROGRAPH OP ALUM FLOG MAGNIFIED 200 TIMES
-------
SECTION VII, ACKNOWLEDGEMENTS
Acknowledgement is extended to the following personnel of the City of
Gainesville, Florida whose advice and assistance was most helpful in
carrying out this study;
John R, Kelly, Director of Public Utilities
Charles H, Oakley, Director of Finance
H, E, Wbrsham, Controller
R, P» Vogh, Sup^t, Water and Waste Water
Linda Warrington, Account Clerk
Acknowledgement is also extended to the Department of Environmental
Engineering, University of Florida, for making available laboratory
space and all needed facilities for carrying out this study, and for
the helpful advice and assistance of the following:
Dr. E, E. Pyatt, Department Chairman
Dr. Wt H. Morgan, Assistant Chairman
Dr, J. E, Singley, Professor of Water Chemistry
Roger Yorton, Graduate Student
Roy Burke, Graduate Student
Jeanne Dorsey, Secretary,
Acknowledgement is extended to Mr. Edmond P. Lomasney, Project Officer,
for his cooperative direction and many helpful suggestions.
77
-------
SECTION VIII. REFERENCES
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*
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79
-------
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SO
-------
28. Berg, Gerald, R. B. Dean, and D. 'R. Dahling. "Removal
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-81
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41, Herz, W. and Muhs, G. "Uber das Gleichgewicht Mg(OH)?
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41 (1904). Z *
42. Kohlrausch, F. and Rose, F. "Die Loshlichkeit einiger
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43. Loyen, J. M. "Chemishes Gleich guvicht in Ammonia
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44. Larson, T. E., Lane, R. W. and Neff, C. H. "Stabiliza-
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83
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84
-------
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85
-------
SECTION IX. APPENDIX
87
-------
TABLE 22
COAGULATION OF ATLANTA, GEORGIA WATER WITH MgC03 AND ALUM
Jar
No.
1
2
3
4
5
6
Dosage in ppm
ro
W> O
s o
20
30
40
40
CX!
/ — \
03 S
C_> O
91
97
103
118
E
D
f— 1
<
.5
.5
.5
.5
10
13
PH
11.15
11.15
11.15
11.25
7.50
7.48
1-4
O
^
0
o
24
20
15
2
9
8
furbidity
23.0
Mobility
-.45
14.oL.34
4.6
1.0
6.C
3.C
0
+ .41
Alkalinity
:r
o
64
76
68
92 '
0
0
oo
O
0
60
64
76
60
0
0
CO
0
0
0
0
0
0
10
8
0
u
J3 X
S) C^
u
to
9.0
9.0
9.0
t-i
o
r-i
O
u
11
Alkalinity
fl
O
0
0
0
0
ro
O
0
45
38
16
Hardness
C
45
38
16
NC
0
0
2
T
45
38
18
Magnesium
as CaCO-j
16
10
oo
00
Characteristics of raw water
Alkalinity as CaC03
Total Hardness as CaCO-j
PH
Organic Color ....
Turbidity
Type Clay
Magnesium as CaCOj
11
13
Comments
Raw water mobility -1.24
7.65
38
104
Natural
-------
TABLE 23
MgC03 AND ALUM COAGULATION OF BALTIMORE, MARYLAND WATER
Jar
No.
1
2
3
4
5
'*
Dosage in ppm
CO
bOO
S O
—
15
20
.25
cv
x-\
^s
95
105
105
107
s
3
r-t
<
2
1.5
.5
.5
8
3D
pH
11.15
11.15
11.15
11.15
6.00
6.00
v<
o
r-{
O
u
Turbidity
2.1
3.5
2.5
2.1
1.3
0.6
Mobility
-.57
-.47
-.33
0
Alkalinity
M
O
74
70
64
56
P
CO
O
O
48
60
56
60
0
f>
o
o
PC
0
0
0
0
10
0
u
JD 32
nj a.
4J
CO
9.0
9.0
9.0
»J
o
•H
O
o
Alkalinity
CO
o
o
0
0
-
n
o
CJ
•x.
54
40
24
Hardness
C
54
40
24
NC
32
29
30
T
86
69
54
Magnesium
as CaC03
10
16
00
vO
Characteristics of raw water
; •
Alkalinity as -CaC03
Total Hardness as CaC03
pH.
Organic Color ....
Turbidity
Type Clay
Magnesium as .CaCO-
Comments
12
40
6.00
Natural
13
-------
TABLE 24
LIME AND ALUM COAGULATION OF BIRMINGHAM, ALABAMA WATER
Jar
No.
1
2
3
4
5
6
Dosage in ppir
tN!
x~-\
« re
o o
s— '
90
130
140
150
e
3
i— 1
<
.5
.5
15
20
vO
cfl CT>
33 rH
.5
pH
10.70
11.15
11.18
11.25
7.50
7.45
M
O
•H
O
O
8
7
8
8
8
6
Turbidity
15
4.5
5.5
4.6
1.0
0
Mobility
-.55
-.58
-.58
0
Alkalinity
5C
O
45
72
80
81
0
0
f>
O
U
70
48
48
62
0
0
ro
O
c_>
T"
0
0
0
0
$2
60
o
u
,0 W
CO B.
4-1
to
9.0
9.0
8.8
M
0
rH
O
CJ>
3
3
7
Alkalinity
n
O
0
2
0
8
ro
O
O
32
37
52
63
Hardness
C
39
52
71
NC
5
9
16
T
44
61
.87
§ rt
•H O
to c_>
0) CO
C U
oo
cd w
2 to
14
18
25
VD
O
Characteristics of raw water
Alkalinity as CaC03 74
Total Hardness as CaCC^ 83
pH. . 7.60
Comments
Raw water mobility -.77
Organic Color ....
Turbidity
Type Clay
Magnesium as CaCO-
12
10
Natural
25
-------
TABLE 25
MgC03, LIME, AND ALUM COAGULATION OF CHATTANOOGA, TENNESSEE WATER
Jar
No.
1
2
3
4
5
6
Dosage in ppm
CO
00 O
"Z, 0
15
20
25
CM
.*~s
H> 33
CJ O
v^
120
116
125
128
e
<— i
_.SL_
.5
.5
.5
.5
15
20
pH
11.15
11.10
11,15
11.15
7.30
7.25
M
o
1-1
o
u
19
15
15
11
11
8
Turbidity
15
10
10
7
3.0
1.8
Mobility
-.81
-.42
0
K38
Alkalinity
*-r<
0
86
64
86
82
0
0
(O
O
U
56
60
68
72
0
0
CO
O
u
0
0
0
0
40
38
o
4J
.0 ad
CO O.
iJ
w
9.0
9.0
9.0
9.0
^
o
r~\
O
o
6
6
4
7.0
Alkalinity
CO
o
o
0
0
0
0
CO
8
•x.
42
38
44
51
Hardness
C
42
38
44
51
NC
20
18
22
31
T
62
56
66
82
Magnesium
as CaC03
11
13
16
15
Characteristics of raw water
Alkalinity as CaC03
48
Total Hardness as CaCO-j
71
Comments
Mobility of raw water -1.07
pH
Organic Color . . .
Turbidity
Type Clay . . . . .
Magnesium as CaCOg
7.85
24
15
Natural
15
-------
TABLE 26
COAGULATION OF CLEVELAND, OHIO WATER WITH LIME AND ALUM
Jar
No.
1
2
3
4
5
6
Dosage in ppm
CM
^s
rt 33
CJ> O
^-^
90
90
160
180
M
•rl tsl
W O.
1!
2.0
4.0
a
3
iH
<
.5
8
10
PH
10.35
10.35
11.20
11.35
7.90
7.80
vj
o
tH
O
O
2
2
2
2
2
2
Turbidity
4.8
3.3
6.0
2.7
4.0
2.6
Mobility
-1.10
-i.o;
0
+ .57
Alkalinity
32
O
14
14
76
88
0
0
n
O
o
44
50
28
28
0
0
f>
0
o
i-r*
0
0
0
0
as
86
0
U
& re
03 CU
ij
in
9.0
9.0
9.0
9.0
9.0
M
O
••H
0
O
1
1_
Alkalinity
<*•»
0
o
0
0
0
0
0
c->
O
O
X
39
47
38
36
98
Hardness
C
39
47
38
36
98
NC
31
32
32
32
38
T
70
79
70
70
136
e
3 <^
•H O
w o
-------
TABLE 27
COAGULATION OF DETROIT, MICHIGAN WATER BY
PRECIPITATION OF MAGNESIUM PRESENT BY LIME ADDITION
Jar
No.
1
2
3
4
i
i '
5
6
Dosage in ppm
c^3
CO Dll
O O
75
40
120
120
150
z
rH
.5
15
ii
•H CM
in o
II
4.0
1.0
3.0
pH
10.70
10.50
11.10
11.10
11.20
7.60
V-i
o
rH
O
o
Turbidity
3.5
5.5
9-0
6.0
5.0
2.0
Mobility
-.34
-.53
-.46
Alkalinity
X
o
14
2
50
74
0
o
u
38
56
28
24
0
ro
0
o
0
0
0
0
74
o
.u
,0 J£
CO O*
ij
an
9.0
9.0
9.0
9.0
u
o
o
Alkalinity
o
0
0
0
0
CO
o
o
42
37
35
86
Hardness
C
42
37
35
86
NC
31
20
17
26
T
73
57
52
112
Magnesium
as CaC03
20
9
30
100
Characteristics of raw water
Alkalinity as CaC03 §0_
Total Hardness as CaCO-j
pH
Organic Color ....
Turbidity
Type Clay
Magnesium as CaCOo
Comments
7.90
2.5
Natural
30
-------
VD
TABLE 28
COAGULATION OF HUNTSVILLE, ALABAMA WATER WITH MgC03 AND WITH
ALUM
Jar
No.
1
2
3
*4
Dosage in ppn|
ro
000
S f-5
0
15
20
20
5 J20
6 j 30
Cs
rt pi
o o
0
120
£
r-t
^
7
.5
125 I .5
f
125
110
115
.5
.5
.5
pH
7.5
11.15
11.15
14
O
o
o
5.0
3.0
1.0
11.155 3.0
10.95J 1.0
11.05
1.0
Turbidity
3.0
3.8
2.5
6.4
JD.O
10.0
Mobility
-.48
-.37
0
-.56
•K48
0
Alkalinity
a
o
0
88
92
86
54
62
o
0
48
60
64
44
. 44
o
o
w
50
0
0
0
.0
0
o
.JO X
CO P«
u
9.0
9.0
V)
o
«-i
o
o
Alkalinity
cT
6
2
0
re
52
28
Hardness
c |NC
58
30
33
24
1
1
|
T
91
54
Magnesium
as CaCOj
20
14
Calcium
as CaC03
71
40
| j i
31 1 1
24 I
!
Characteristics of raw v;ater
Alkalinity as CaC03 54_
Total Hardness as CaCO-j 84
Cosssnts
*Hal95 at .5 mg/1
7.5
Organic Color .
Turbidity . . .
Type Clay . . .
13
Natural
-------
TABLE 29
MgC03 AND ALUM COAGULATION OF JACKSON, MISSISSIPPI WATER
Jar
No.
1
2
3
4
5
. 6
Dosage in ppm
CO
bOO
£ 0
20
30
40
50
r-i
s~\
nj js
O 0
V^
90
95
113
119
e
rH
^
•t-1
0
0
0
0
.9
8
o
jj
.0 SB
to o.
ij
V)
9.0
9.0
M
0
iH
O
e>
5
8
Alkalinity
CO
o
o
2
0
o
o
u
te
38
16
Hardness
C
39
16
NC
0
7
T
39
23
Magnesium
as CaC03
11
VO-.
Characteristics of raw water
Alkalinity as CaC03 10
Comments
12
7.55
27
Total Hardness as CaC03
pK
Organic Color ....
Turbidity- 7.4
Typ« Clay ....... Natural
Magnesium as CaCO, 2
-------
TABLE 30
MgC03 AND ALUM COAGULATION OF LANETT, ALABAMA WATER
Jar
!No.
1
2
3
4
5
6
Dosage in ppm
CO
OOO
s o
30
35
40
35
CN
s~^
« w
o o
**^t
105
108
110
125
e
3
i-H
<
.5
.5
.5
.5
10
15
PH
11.15
11.15
11.15
11.25
7.10
7.00
K
0
iH
O
0
30
13
11
13
13
11
Turbidity
5.0
3.0
2.0
2.4
3.6
3.6
Mobility
-.32
•K.37
•K47
+ .34
Alkalinity
K
0
94
87
0
0
n
O
c_>
60
54
0
0
en
O
O
22
0
0
.7
5
o
4J
.C K
tO O.
JJ
V3
9.0
9.0
9.0
j-i
o
r-l
0
o
4
5.0
5.0
Alkalinity
n
O
o
0
2
2
ro
0
o
X
53
16
12
Hardness
C
53
18
14
NC
8
5
9
T
61
23
25
Magnesium
as CaCO-j
14
13
Characteristics^ of raw water
Alkalinity as CaC03 17
Total Hardness as CaCO^ 17
PH 7.55
Organic Color .... 30
Turbidity 105 ___
Type Clay Natural
Comments
-------
TABLE 3Z
LIME AND ALUM COAGULATION OF LOUISVILLE, KENTUCKY WATER
Jar
No.
1
2
3
4
5
6
Dosage in ppm
0>l
td /*~s
0 35
O
*^r
60
120
100
140
e
3
t-i
<
.5
.5
10
15
ii
vH e>j
CO O
II
2.0
2.0
PH
10.75
11.20
10.90
11.25
7.35
7.30
i*
o
r-i
o
o
3
3
10
4
6
4
Turbidity
14.5
8.0
7.8
4.5
1.8
1.4
Mobility
•K38
4-. 73
Alkalinity
35
0
34
92
42
80
0
0
ro
O
U
60
60
60
56
0
0
CO
0
o
32
0
0
0
0
50
48
0
u
.0 35
(0 (X
u
w
1
9.0
9.0
9.0
>j
0
rH
0
O
5
•4
5
Alkalinity
ro
O
<_>
0
0
0
CO
O
U
32
28
59
Hardness
C
32
28
59
NC
61
55
62
T
83
81
121
Magnesium
as CaCO-j
17
12
\o
-J
Characteristics of raw wat_er
Alkalinity as CaC03 51
Total Hardness as CaCp3 110
PH 7.50
Organic Color .... 11
Turbidity 106
Type Clay Natural
Magnesium as CaCOj 33
Comments
Mobility of raw water -.98
-------
TABLE 32
MgC03, LIME, AND ALUM COAGULATION OF NASHVILLE, TENNESSEE WATER
Jar
No.
1
2
3
4
5
6
Dosage in ppm
P")
00 O
H o
10
15
CM
x-N
(0 22
0 0
v^s
110
150
116
120
E
iH
<
.5
.5
LO
12
pH
10.95
11.20
11.00
11.00
7.55
7.50
vj
o
t-{
o
(_>
8
7
8
8
8
7
turbidity
5.4
2.8
6.0
4.6
2.6
1.6
Mobility
-.63
-.60
-.67
-.57
. Alkalinity
pr!
O
43
98
48
56
0
0
(*•>
O
O
54
58
44
44
0
0
CO
o
O
SB
0
0
0
0
6,6
65
o
4_>
.
.0 E
RJ a
u
CO
9.0
9.0
9.0
9.0
i-i
o
i-i
o
u
8
4
6
8
Alkalinity
CO
O
O
2
0
4
12
rn
o
o
40
38
33
61
Hardness
C
42
38
37
73
NC
16
20
15
24
T
58
58
52
97
Magnesium
as CaCOo
15
12
19
Stabalized
Turbidity
0.3
0
.so
CD
Characteristics of raw water
Alkalinity as CaCO-j 71
Total Hardness as CaCO-j 86
pH. 7.60
Organic Color .... 8
Turbidity 7 .5
Type Clay Natural
Magnesium as CaCO^ 17
Comments
-------
TABLE 33'
MgC03 AND ALUM COAGULATION OF OPELIKA, ALABAMA WATER
Jar
No.
1
2
3.
4
5
6
Dosage in pptr
PO
60 O
S "
5
10
20
25
C-J
X~N
« s
u o
N—X
90
92
106
109
s
fH
<
.5
.5
0
.5
7
LO
pH
10.95
11.10
11.10
11.15
6.90
6.80
t-i
0
«H
O
0
7
1
2
3
7
4
[Turbidity
13
16
12. f
3.4
1.0
0
Mobility
-.81
-.68
-.49
+ .43
Alkalinity
*i"«
o
66
72
0
CO
0
0
32
32
0
CO
0
y
0
0
14
o
tj
n) "E.
u
C/5
9.0
9.0
u
o
^i
0
o
Alkalinity
fo
o
o
3
CO
O
CJ
18
Hardness
C
21
NC
9
T
30
Magnesium
as CaCO-j
10
Characteristics of raw water
Alkalinity as CaC03 17
Total Hardness as CaCO^ 17
pH 6.95
Organic Color .... 10
Turbidity 14
Type Clay Natural
Comments
-------
TABLE 34
LIME, MgC03, AND ALUM COAGULATION OF PHILADELPHIA, PENNSYLVANIA WATER
Jar
No.
1
2
3
*4
5
6
Dosage in ppm
CO
oo o
£ 0
10
CN]
X-N
-------
TABLE ..35
COAGULATION OF RICHMOND, VIRGINIA WATER WITH MgC03 AND ALUM
Jar
No.
1
2
3
4
5
6
Dosage in ppw
f>
60 O
s o
20
25
30
40
CNJ
x-x
-i
o
T-H
O
O
5
5
12
8
Alkalinity
CO
o
o
0
0
0
0
ro
0
U
Z
40
38
29
31
Hardness
C
40
38
29
31
NC
15
15
24
24
T
55
53
53
55
3 CO
•H O
tn o
a) n)
C 0
60
r; w
S «tf
15
17
Characteristics of raw water
Alkalinity as CaC03 _
Total Hardness as
pH
Comments
27
43
Organic Color ....
Turbidity ......
Type Clay ..... •.
Magnesium as CaCOo
30
24
Natural
-------
10
TABLE 36
MgC03 AND ALUM COAGULATION OF TUSCALOOSA, ALABAMA WATER
Jar
No.
1
2
3
4
5
6
Dosage in ppm
CO
w> o
S o
15
20
20
25
—
—
CN'
x-x
to a
o o
V— '
83
86
97
100
1
2
B
D
•H
O
*
0
.3
0
u
jz a
CO C.
4->
W
9.0
9.0
S-l
o
r-1
0
CJ>
Alkalinity
CO
O
c_>
2
3
ro
O
O
a:
38
6
Hardness
C
40
9
NC
2
6
T
42
15
Magnesium
as CaC03
12
4.0
Characteristics of raw water
Alkalinity as CaC03
Total Hardness as CaC03 5.0
pH 6.3
Organic Color .... 26
Turbidity 4
Type Clay '. Natural
Comments
-------
TABLE 37-
MgC03, LIME, AND ALUM COAGULATION OF WASHINGTON, D.C. WATER
Jar
No.
*1
*2
3
4
5
6
Dosage in ppm
CO
00 O
•Z. o
10
15
20
OJ
s~\
rt re
u o
^^x
120
127
130
117
(=
3
,-!
-i
o
i-H
O
<_>
12
8
7
11
10
6
Turbidity
3.0
2.2
2.0
2.6
3.0
1.5
Mobility
0
K49
K41
+ .72
Alkalinity
a
o
76
78
72
56 '
0
0
n
0
c_>
48
48
54
64
0
0
CO
O
CJ
«-r-
0
0
0
0
37
33
o
u
JD a:
CO CL
4-1
in
9.0
8.4
u
o
t-H
0
u
5
7
Alkalinity
f>
0
o
4
0
CO
O
u
3=
44
40
Hardness
C
48
40
NC
27
36
T
75
76
Magnesium
as CaC03
18
17
o
Characteristics of raw water
Alkalinity as CaCO-j
Total Hardness as
PH
Organic Color ..
Turbidity
Type Clay
Magnesium as CaCOo
Comments
41
71
7.50
15
Mobility of raw water -.96
*.5 mg/I Hal96
50
Natural
17
-------
TABLE 38
CALCULATED POTENTIAL PRODUCTION OF MfeCOo.SHoO BY
20 AMERICAN CITIES, 1968° *
City
Indianapolis
Des Moines
Kansas City, Mo.
Kansas City, Kan.
Flint, Mich.
Lansing, Mich.
Minneapolis
St. Paul
St. Louis
Omaha
Cincinnati
Columbus
Oklahoma City
Fort Wayne , Ind .
Dayton, Ohio
San Diego
St. Louis Co. W.C.
Austin, Tex.
New Orleans
Wichita, Kan.
M.g. Water
treated
daily
80
30
98
32
v36
X23
70
46
190
68
112
38
*15
X25
x70
X50
60
X35
X120
35
MB++ in
untreated
water, ppm
22
33
18
21
25
33
13
14
14
23
10
.28
X31
20
33
29
17
19
11
14
Amount
removed
ppm
18
29.
14
17
21
23
9
10
10
19
6
.24
"27
16
24
25
13
15
7
10
Annual
production
of MgCOo.
3H20 tons
12,500
7,200
11,800
4,500
6,400
4,500
5,000
3,800
16,400
11,000
5,800
7,900
3,300
3,300
14,500
10,400
6,800
4,500
7,200
3,000
1-49 , 800
Annual gross
revenue at
2c per Ib.
$ 500,000
288,000
472,000
180,000
256,000
180,000
200,000
152,000
656,000
440,000
232,000
316,000
132,000
132,000
680,000
416,000
136,000
180,000
288,000
120,000
$5,956,000
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TABLE 3'gr (Continued)
Comments
196711968
Morse plant 54 mgd Mg+tl5 - 4 ~ 11 11 x"54 = 594
Dublin plant 38 mgd MgT"^28 - 4 = 24 38 x 24 = 912
Both plants 92 mgd Mg 20 -.3 =12 92x12=1104
Preferred method would probably recover at Dublin only, and calculated on
this basis.
'Oklahoma City has three treatment plants
Lake Overholzer - 6 mgd Mg,, = 29
Lake Hefner -15 mgd MgjT = 31
Lake Draper -18 mgd Mg = 4
So calculations based on recovery at Hefner plant only.
St. Louis County Water Co. has four plants, 3 deriving water from the Missouri
River, one from the Minimac River.
Calculation based on largest plant only.
xExtrapolated from 1962 data.
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TABLE 39
CALCULATIONS OF POTENTIAL
CONSUMPTION OF MgC03,3^0 BY WATER TREATMENT PLANTS
IN THE UNITED STATES-
460 Plants Serving 55,757.215 People Use Alum
70 Plants Serving 11,282.820 People Use Iron Salts
530 Plants Serving 67,040.035 People Use Al or Fe
(67 x 106) people x (55 x 103) gal, yr. = 3.7 x 1012 gal/yr.
3.700,000,000,000 gal. = 3,700,000 mg/yr,
25 ppm MgC03 . 3H20 = 200 Ibs/mg.
15% make- up = 30 Ibs/mg,
3,700,000 x 30 = 111,000,000 Ibs.
Ill ,000,000 Ibs.
= 55,000 tons/yr.
2000
3400 filtration plants below 4 mgd (25,000 people)
25% Treat 3 mgd = 2600 nigd
2570 Treat 2 mgd = 1700 mgd
50% Treat 1 mgd = 1700 mgd
Total 670W mgd
6,000 rogd x 20 Ibs/mg x 365 days = 43,800,000 Ibs.
43,800,000 Ibs.
= 22,000 tons/yr.
2000
Total of all plants 77,000 tons/yr, 1963 basis
Corrected for 1971 production - 102,000 tons/yr.
*From 1964 USPHS summary of municipal water facilities in
Communities of 25,000 or more.
106
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1
Access/on Number
w
5
r. Subject Field & Group
05D
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
Department of Public Utilities, City of Gainsville, P.O. Box 490,
Gainsville, Florida
r;<;e
Magnesium Carbonate, A Recycled Coagulant for Water Treatment
] Q Authors)
Dr. A. P. Black
Dr. C. G. Thompson
16
21
Project Designation
EPA Grant Project 12120 ESW
6/71
Note
22
Citation
23
Descriptors (Starred First)
Water Purification, Coagulation, Chemical Precipitation, Sludge Treatment,
Industrial Wastes.
25
identifiers (Starred First)
27
Abstract
An entirely new system of water treatment has been developed. It is a unique
combination of softening and conventional coagulation, and may be used for all
types of waters, surface or ground, hard or soft. Magnesium carbonate is used as
the coagulant and lime is added to precipitate gelatinous MgCOH)-, which is as
effective as alum for the removal of both turbidity and organic color. The floes
formed are larger and heavier than alum floe, since they are "loaded" with CaCO^.
The sludge, composed of a slurry of CaCOo, Mg(OH)2 and clay is carbonated with
C02 and the Mg(HO)2 selectively and completely dissolved as the bicarbonate. The
carbonated .slurry is filtered and the filtrate recycled to the point of addition
of chemicals to the raw water and reprecipitated with lime thus recovering both
the coagulant and the sludge water. In small plants, the filter cake of CaGO,
can be used as land fill. In larger plants, it is slurried in a flotation cell
and the clay separated and used as land fill. The purified CaCO~ is filtered and
the cake passes to a multiple hearth furnace or Kiln and calcined to high quality
lime. Chemical treatment costs are substantially reduced for most waters and the
quality of the treated water is superior to that treated with alum.
This report was submitted in fulfillment of Water Quality Research Grant Project
12120 ESW with the Environmental Protection Agency.
Abstractor
C. G. Thompson
Institution
Department of Public Utilities
SENO WITH COPY OP DOCUMENT. TO: WATER RESOURCES SCIENTIFIC 1NFORMAT tOWCENT ER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 20240
* CPO: 1070-369*930
WR:IO2 (REV JULY 1969)
WRSIC
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