Technical Field
The present invention relates to a water treatment
process and a water treatment system for reproducing water to
be treated containing Ca ions (Ca2+), sulfate ions (SO4
2-), and
5 carbonate ions.
Background Art
It is known that industrial waste water, saline water,
and sewage contain large amounts of ions. In addition, in a
10 cooling tower, heat is exchanged between a high-temperature
exhaust gas discharged from the boiler, etc., and cooling
water. As a result of this heat exchange, some of the cooling
water turns into steam, and, accordingly, ions in the cooling
water are concentrated. Therefore, the cooling water
15 discharged from the cooling tower (blowdown water) has
increased concentrations of ions.
Water containing a large amount of ions is subjected to
a demineralization treatment and then discharged into the
environment. As devices that perform the demineralization
20 treatment, a reverse osmosis membrane device, a
nanofiltration membrane device, an ion-exchange equipment,
and the like are known.
Among ions contained in the water mentioned above,
monovalent cations such as Na+, K+, and NH4
+ and anions such as
Cl- and NO3
- 25 are highly soluble in water. On the other hand ,
divalent metal ions such as Ca2+ and anions such as SO4
2- and
CO3
2- are scale-forming components. Salts of scale-forming
components have low solubility in water, and thus they tend
to be deposited as scales. In particular, the saline water,
30 industrial waste water, and blowdown water from a cooling
tower mentioned above contain large amounts of Ca2+, SO4
2-, and
carbonate ions (CO3
2-, HCO3
-). An example of the property is
as follows: pH: 8, Na ions: 20 mg/L, K ions: 5 mg/L, Ca ions:
50 mg/L, Mg ions: 15 mg/L, HCO3 ions: 200 mg/L, Cl ions: 200
3
mg/L, SO4 ions: 120 mg/L, PO4 ions: 5 mg/L. Among these, the
concentrations of Ca ions, Mg ions, SO4 ions, and HCO3 ions
are high, and as a result of their reaction, scales (CaSO4,
CaCO3, etc.) are formed. When scales are produced in the
device that performs a demineralization 5 treatment, the
treatment capacity is reduced. Therefore, it is required to
perform a demineralization treatment without allowing for the
production of scales.
Here, examples of plants using a water-cooling-type
10 cooling tower are plants equipped with power generation
facilities (power generation facilities include those for
business purposes for electric power selling and those for
industrial purposes for in-house electricity use, and the
power generation is thermal power generation, geothermal
15 power generation, etc.), plants equipped with power
generation facilities and cooling facilities, etc. In
addition, plants include ordinary chemical plants, steel
plants, mining plants, oil field plants, gas field plants,
mechanical plants, etc.
20 As a process for removing Ca ions, a lime soda process
is known. According to the lime soda process, sodium
carbonate is added to water to be treated, and Ca ions in the
water to be treated are deposited/precipitated as calcium
carbonate and thereby removed from the water.
25 Patent Literature 1 discloses a waste water treatment
device including a combination of a chemical softening
device, an ion-exchange equipment, a reverse osmosis membrane
device, and the like using the lime soda process.
30 Citation List
Patent Literature
PTL 1 U.S. Pat. No. 7815804
Summary of Invention
Technical Problem
4
The lime soda process requires the addition of sodium
carbonate for the treatment, and thus the treatment cost is
high. In the lime soda process, when 1 mol of Ca ions are
precipitated as calcium carbonate, 2 mol of Na+ is produced.
Meanwhile, in the case where SO4
2- is contained 5 in water to be
treated, it is not removed by the lime soda process. That is,
in the lime soda process, water after the treatment contains
an increased number of moles of ions.
Also in the case where Ca ions are removed using an ion10
exchange equipment, the treatment of 1 mol of Ca ions results
in the production of 2 mol of Na+, and water the after
treatment contains an increased number of moles of ions.
According to the system of Patent Literature 1, water
that has been treated by the lime soda process and in an ion15
exchange equipment is further treated in a reverse osmosis
membrane device to remove ion components. Accordingly, the
system of Patent Literature 1 has a problem in that because
of the increased number of moles of ions; the osmotic
pressure in the reverse osmosis membrane device is high,
20 resulting in an increased treatment load. In addition, with
the device of Patent Literature 1, SO4
2- is not removed but
remains in the treated water, and it has been difficult to
obtain high water recovery.
In addition, the waste water treatment device of Patent
25 Literature 1 requires a large amount of chemicals for the
reproduction of the ion-exchange equipment, and thus there
has also been the problem of high treatment cost.
An object of the present invention is to provide a water
treatment process and a water treatment system, which are
30 capable of reproducing water containing salts with high water
recovery.
Solution to Problem
A first aspect of the present invention is a water
5
treatment process including: a scale inhibitor supplying step
of supplying a calcium scale inhibitor which is a scale
inhibitor for inhibiting the deposition of a scale containing
calcium to water to be treated containing Ca ions, SO4 ions,
and carbonate ions; a demineralizing step 5 of separating the
water to be treated into concentrated water in which the Ca
ions, the SO4 ions, and the carbonate ions are concentrated
and treated water after the scale inhibitor supplying step; a
crystallizing step of supplying seed crystals of gypsum to
10 the concentrated water so that gypsum is crystallized from
the concentrated water; a pH measuring step of measuring the
pH of the concentrated water in the crystallizing step; and a
supplied amount controlling step of reducing the amount of
the seed crystals of the gypsum to be supplied when the
15 measured pH falls within a pH range in which a scale
inhibiting function of the calcium scale inhibitor is
reduced, and increasing the amount of the seed crystals of
the gypsum to be supplied when the measured pH is beyond the
pH range.
20 A second aspect of the present invention is a water
treatment system, including: a scale inhibitor supplying
section that supplies a calcium scale inhibitor which is a
scale inhibitor for inhibiting the deposition of a scale
containing calcium to water to be treated containing Ca ions,
25 SO4 ions, and carbonate ions; a demineralizing section that is
positioned on a downstream side of the scale inhibitor
supplying section and separates the water to be treated into
concentrated water in which the Ca ions, the SO4 ions, and the
carbonate ions are concentrated and treated water; a
30 crystallizing section which is positioned on a downstream
side of the demineralizing section and which includes a
crystallizing tank that crystallizes gypsum from the
concentrated water and a seed crystal supplying section that
supplies seed crystals of gypsum to the crystallizing tank; a
6
pH measuring section that measures the pH of the concentrated
water in the crystallizing tank; and a controlling section
that reduces the amount of the seed crystals of the gypsum to
be supplied when the pH measured in the pH measuring section
falls within a pH range in which a scale inhibition 5 function
of the calcium scale inhibitor is reduced, and increases the
amount of the seed crystals of the gypsum to be supplied when
the pH measured in the pH measuring section is beyond the pH
range.
10 According to the first aspect and the second aspect,
owing to the effects of the calcium scale inhibitor, the
production of scales in the demineralizing section and the
demineralizing step can be inhibited. In addition, seed
crystals of gypsum are added to the concentrated water in the
15 crystallizing section and the crystallizing step, whereby
gypsum can be crystallized and separated from the water to be
treated even when a scale inhibitor is present. As a result,
the water to be treated containing Ca ions and SO4 ions can be
treated with high water recovery, and the operation cost can
20 be reduced. Further, this is also advantageous in that highpurity
gypsum can be recovered. Since seed crystals of gypsum
are effectively provided, the amount of seed crystals used
can be reduced.
A third aspect of the present invention is a water
25 treatment process including: a first scale inhibitor
supplying step of supplying a calcium scale inhibitor which
is a scale inhibitor for inhibiting the deposition of a scale
containing calcium to water to be treated containing Ca ions,
SO4 ions, carbonate ions and silica; a first pH adjusting step
30 of adjusting the water to be treated to a pH at which the
silica is soluble in the water to be treated; a first
demineralizing step of separating the water to be treated
into first concentrated water in which the Ca ions, the SO4
ions, the carbonate ions and the silica are concentrated and
7
treated water after the first scale inhibitor supplying step
and the first pH adjusting step; a first crystallizing step
of supplying seed crystals of gypsum to the first
concentrated water so that gypsum is crystallized from the
first concentrated water; a first pH 5 measuring step of
measuring the pH of the first concentrated water in the first
crystallizing step; and a first supplied amount controlling
step of reducing the amount of the seed crystals of the
gypsum to be supplied when the measured pH falls within a pH
10 range in which a scale inhibiting function of the calcium
scale inhibitor is reduced, and increasing the amount of the
seed crystals of the gypsum to be supplied when the measured
pH is beyond the pH range.
A fourth aspect of the present invention is a water
15 treatment system including: a first scale inhibitor supplying
section that supplies a calcium scale inhibitor which is a
scale inhibitor for inhibiting the deposition of a scale
containing calcium to water to be treated containing Ca ions,
SO4 ions, carbonate ions and silica; a first pH adjusting
20 section that supplies a pH adjuster to the water to be
treated to adjust the pH of the water to be treated to such a
value that the silica is soluble in the water to be treated;
a first demineralizing section that is positioned on a
downstream side of the first scale inhibitor supplying
25 section and the first pH adjusting section and separates the
water to be treated into first concentrated water in which
the Ca ions, the SO4 ions, the carbonate ions and the silica
are concentrated and treated water; a first crystallizing
section which is positioned on a downstream side of the first
30 demineralizing section and which includes a first
crystallizing tank that crystallizes gypsum from the first
concentrated water and a first seed crystal supplying section
that supplies seed crystals of gypsum to the first
crystallizing tank; a first pH measuring section that
8
measures the pH of the first concentrated water in the first
crystallizing tank; and a first controlling section that
reduces the amount of the seed crystals of the gypsum to be
supplied when the pH measured in the first pH measuring
section falls within a pH range in which 5 a scale inhibition
function of the calcium scale inhibitor is reduced, and
increases the amount of the seed crystals of the gypsum to be
supplied when the pH measured in the first pH measuring
section is beyond the pH range.
10 According to the third aspect and the fourth aspect, a
calcium scale inhibitor is added, and also the water to be
treated is adjusted to a pH at which silica is soluble,
followed by a water treatment. Accordingly, the production of
scales in the first demineralizing section and the first
15 demineralizing step can be inhibited. In addition, by adding
seed crystals of gypsum to the first concentrated water in
the first crystallizing section and the first crystallizing
step, even when a scale inhibitor is present, gypsum can be
crystallized and separated from the water to be treated. As a
20 result, while inhibiting the production of scales, the water
to be treated containing Ca ions, SO4 ions, carbonate ions,
and silica can be treated with high water recovery. In
addition, the amount of chemicals required for the treatment
and the power required for the operation can be reduced, and
25 also maintenance is facilitated. Accordingly, the operation
cost can be reduced.
A fifth aspect of the present invention is a water
treatment process, including: a second scale inhibitor
supplying step of supplying a calcium scale inhibitor which
30 is a scale inhibitor for inhibiting the deposition of a scale
containing calcium and a silica scale inhibitor which is a
scale inhibitor for inhibiting the deposition of silica to
water to be treated containing Ca ions, SO4 ions, carbonate
ions and silica; a second demineralizing step of separating
9
the water to be treated into second concentrated water in
which the Ca ions, the SO4 ions, the carbonate ions and the
silica are concentrated and treated water after the second
scale inhibitor supplying step; a second crystallizing step
of supplying seed crystals of gypsum 5 to the second
concentrated water so that gypsum is crystallized from the
second concentrated water; a second pH measuring step of
measuring the pH of the second concentrated water in the
second crystallizing step; and a second supplied amount
10 controlling step of reducing the amount of the seed crystals
of the gypsum to be supplied when the measured pH falls
within a pH range in which a scale inhibiting function of the
calcium scale inhibitor is reduced, and increasing the amount
of the seed crystals of the gypsum to be supplied when the
15 measured pH is beyond the pH range.
A sixth aspect of the present invention is a water
treatment system, including: a second scale inhibitor
supplying section that supplies a calcium scale inhibitor
which is a scale inhibitor for inhibiting the deposition of a
20 scale containing calcium and a silica scale inhibitor which
is a scale inhibitor for inhibiting the deposition of silica
to water to be treated containing Ca ions, SO4 ions, carbonate
ions and silica; a second demineralizing section that is
positioned on a downstream side of the second scale inhibitor
25 supplying section and separates the water to be treated into
second concentrated water in which the Ca ions, the SO4 ions,
the carbonate ions and the silica are concentrated and
treated water; a second crystallizing section which is
positioned on a downstream side of the second demineralizing
30 section and which includes a second crystallizing tank that
crystallizes gypsum from the second concentrated water and a
second seed crystal supplying section that supplies seed
crystals of gypsum to the second crystallizing tank; a second
pH measuring section that measures the pH of the second
10
concentrated water in the second crystallizing tank; and a
second controlling section that reduces the amount of the
seed crystals of the gypsum to be supplied when the pH
measured in the second pH measuring section falls within a pH
range in which a scale inhibition function 5 of the calcium
scale inhibitor is reduced, and increases the amount of the
seed crystals of the gypsum to be supplied when the pH
measured in the second pH measuring section is beyond the pH
range.
10 In the fifth aspect and the sixth aspect, owing to the
effects of the calcium scale inhibitor and the silica scale
inhibitor, the production of scales in the second
demineralizing section and the second demineralizing step can
be inhibited. In addition, by adding seed crystals of gypsum
15 to the first concentrated water in the first crystallizing
section and the first crystallizing step, even when a scale
inhibitor is present, gypsum can be crystallized and
separated from the water to be treated. As a result, the
water to be treated containing Ca ions, SO4 ions, and silica
20 can be treated with high water recovery, and the operation
cost can be reduced. Further, this is also advantageous in
that high-purity gypsum can be recovered.
In the present invention, the water treatment processes
of the third aspect and the fifth aspect and the water
25 treatment systems of the fourth aspect and the sixth aspect
can be combined in the flow direction of the water to be
treated to perform a water treatment.
In the above aspect, it is preferable that the water
treatment process includes: a second pH measuring step of
30 measuring the pH of the second concentrated water in the
second crystallizing step; and a second supplied amount
controlling step of reducing the amount of the seed crystals
of the gypsum to be supplied when the measured pH falls
within a pH range in which a scale inhibition function of the
11
calcium scale inhibitor is reduced, and increasing the amount
of the seed crystals of the gypsum to be supplied when the
measured pH is beyond the pH range.
In this case, it is preferable that the gypsum separated
in the first separating step is used as seed 5 crystals of the
gypsum. It is preferable that the gypsum separated in the
second separating step is used as seed crystals of the
gypsum.
In addition, it is preferable that the water treatment
10 process includes a first concentration measuring step of
measuring at least one of the concentration of the Ca ions
and the concentration of sulfate ions in the first
concentrated water after the first crystallizing step,
wherein the first supplied amount controlling step is
15 intended to control the amount of the seed crystals of the
gypsum to be supplied according to at least one of the
concentration of the Ca ions and the concentration of sulfate
ions measured in the first concentration measuring step. It
is preferable that the water treatment process includes a
20 second concentration measuring step of measuring at least one
of the concentration of the Ca ions and the concentration of
sulfate ions in the second concentrated water after the
second crystallizing step, wherein the second supplied amount
controlling step is intended to control the amount of the
25 seed crystals to be supplied according to at least one of the
concentration of the Ca ions and the concentration of sulfate
ions measured in the second concentration measuring step.
In the above aspect, it is preferable that the water
treatment system includes: a second pH measuring section that
30 measures the pH of the second concentrated water in the
second crystallizing tank; and a second controlling section
that reduces the amount of the seed crystals of the gypsum to
be supplied when the pH measured in the second pH measuring
section falls within a pH range in which a scale inhibition
12
function of the calcium scale inhibitor is reduced, and
increases the amount of the seed crystals of the gypsum to be
supplied when the pH measured in the second pH measuring
section is beyond the pH range.
In this case, it is preferable that the 5 gypsum separated
in the first separating section is used as seed crystals of
the gypsum. It is preferable that the gypsum separated in the
second separating section is used as seed crystals of the
gypsum.
10 It is preferable that the water treatment system
includes, on a downstream side of the first crystallizing
section, a first concentration measuring section that
measures at least one of the concentration of the Ca ions and
the concentration of sulfate ions in the first concentrated
15 water, wherein the first controlling section is intended to
control the amount of the seed crystals of the gypsum to be
supplied according to at least one of the concentration of
the Ca ions and the concentration of sulfate ions measured in
the first concentration measuring section. It is preferable
20 that the water treatment system includes, on a downstream
side of the second crystallizing section, a second
concentration measuring section that measures at least one of
the concentration of the Ca ions and the concentration of
sulfate ions in the second concentrated water, wherein the
25 second controlling section is intended to control the amount
of the seed crystals of the gypsum to be supplied according
to at least one of the concentration of the Ca ions and the
concentration of sulfate ions measured in the second
concentration measuring section.
30 According to the above aspect, seed crystals of gypsum
are efficiently supplied, and thus the amount of seed
crystals of gypsum to be used can be reduced.
In the above aspect, it is preferable that a third pH
adjusting step of adjusting the second concentrated water to
13
a pH at which calcium carbonate is soluble, wherein in the
second crystallizing step, the gypsum separated in the first
separating step is supplied into the second concentrated
water after the adjustment of the pH in the third pH
5 adjusting step.
In the above aspect, it is preferable that wherein the
second pH adjusting section adjusts the second concentrated
water to a pH at which calcium carbonate is soluble, and
supplies the gypsum separated in the first separating section
10 to the second crystallizing section.
According to the above aspect, high-purity gypsum can be
recovered in the course of water treatment.
Advantageous Effects of Invention
According to the water treatment system and the water
15 treatment process of the present invention, while inhibiting
the production of scales such as calcium carbonate during the
treatment, Ca2+ and SO4
2- can be removed as gypsum from the
water to be treated. Accordingly, the water recovery can be
further improved.
20 Water treated by the present invention has a
significantly reduced number of moles of ions on the
downstream side. Therefore, the power of the demineralizing
section located downstream can be significantly reduced.
Further, the present invention is also advantageous in
25 that high-purity gypsum can be crystallized and recovered.
Brief Description of Drawings
Fig. 1 is a schematic diagram of a water treatment
system according to the first reference embodiment.
Fig. 2 shows simulation results for the pH dependency of
30 the amount of gypsum deposited.
Fig. 3 shows simulation results for the pH dependency of
the amount of calcium carbonate deposited.
Fig. 4 is a graph showing the pH dependency of the
14
amount of silica dissolved.
Fig. 5 shows the results of gypsum deposition
experiments performed using simulated water in which gypsum
is supersaturated with changing the pH of the simulated
5 water.
Fig. 6 shows the results of gypsum deposition
experiments performed using simulated water in which gypsum
is supersaturated with changing the concentration of seed
crystals.
10 Fig. 7 is a microphotograph of gypsum crystallized under
Condition 5.
Fig. 8 is a microphotograph of gypsum crystallized under
Condition 3.
Fig. 9 is a schematic diagram of a water treatment
15 system according to a second reference embodiment.
Fig. 10 is a schematic diagram of a water treatment
system according to a first example of a third reference
embodiment.
Fig. 11 is a schematic diagram of a water treatment
20 system according to a second example of the third reference
embodiment.
Fig. 12 is a schematic diagram of a water treatment
system according to a fourth reference embodiment.
Fig. 13 is a schematic diagram explaining a water
25 treatment system according to a fifth reference embodiment.
Fig. 14 is a schematic diagram explaining a water
treatment system according to a first embodiment.
Fig. 15 is a schematic diagram explaining a water
treatment system according to a seond embodiment.
30 Fig. 16 is a schematic diagram explaining a water
treatment system according to a third embodiment.
Fig. 17 is a schematic diagram explaining a water
treatment system according to a sixth reference embodiment.
15
Description of Embodiments
Water that is an object to be treated in the present
invention (water to be treated) contains Ca2+, SO4
2-, carbonate
ions, and silica. Specifically, the water to be treated (raw
water) is saline water, sewage, industrial 5 waste water,
blowdown water from a cooling tower, or the like. The water
to be treated may also contain metal ions, such as Mg ions.
First Reference Embodiment
Fig. 1 is a schematic diagram of a water treatment
10 system according to the first reference embodiment of the
present invention. The water treatment system 1 of Fig. 1 is
configured such that two water treatment sections are
connected in the flow direction of the water to be treated.
In the water treatment system 1 of this reference embodiment,
15 depending on the properties of the water to be treated, the
number of water treatment sections may be one, and it is also
possible that three or more water treatment sections are
connected.
Each water treatment section includes, from the upstream
20 side of the water to be treated, a first demineralizing
section 10 (10a, 10b) and a first crystallizing section 20
(20a, 20b). The concentration sides of the first
demineralizing sections 10a and 10b are connected to the
first crystallizing sections 20a and 20b, respectively. The
25 water treatment section includes a first scale inhibitor
supplying section 30 (30a, 30b) and a first pH adjusting
section 40 (40a, 40b) in the flow path on the upstream side
of each first demineralizing section 10 (10a, 10b).
The first scale inhibitor supplying section 30 (30a,
30 30b) is made up of a tank 31 (31a, 31b), a valve V1 (V1a,
V1b), and a control section 32 (32a, 32b). The control
sections 32a and 32b are connected to the valves V1a and V1b,
respectively. The tanks 31a and 31b have stored therein a
16
scale inhibitor.
The scale inhibitor used in this reference embodiment
serves to inhibit the deposition of scales containing calcium
in the water to be treated. It will be hereinafter referred
to as “calcium 5 scale inhibitor”.
The calcium scale inhibitor suppresses the crystal
nucleation of gypsum or calcium carbonate in the water to be
treated. At the same time, the calcium scale inhibitor
adheres to the surface of crystal nucleus of gypsum or
10 calcium carbonate contained in the water to be treated (seed
crystals, small-diameter scales deposited due to the
exceeding of the saturation concentration, etc.), and
functions to suppress the crystal growth of gypsum or calcium
carbonate. Alternatively, there is another type of calcium
15 scale inhibitor, which has the function of dispersing
particles in the water to be treated (inhibiting
aggregation), such as deposited crystals.
Examples of calcium scale inhibitors include phosphonicacid-
based scale inhibitors, polycarboxylic-acid-based scale
20 inhibitors, and mixtures thereof. A specific example is
FLOCON260 (trade name, manufactured by BWA).
In the case where Mg ions are contained in the water to
be treated, a scale inhibitor that inhibits the deposition of
scales containing magnesium (e.g., magnesium hydroxide) in
25 the water to be treated can be used. It will be hereinafter
referred to as “magnesium scale inhibitor”.
Examples of magnesium scale inhibitors include
polycarboxylic-acid-based scale inhibitors, etc. A specific
example is FLOCON 295N (trade name, manufactured by BWA).
30 Although Fig. 1 shows only one first scale inhibitor
supplying section 30a/30b in each position, in the case where
two or more kinds of scale inhibitors are loaded, it is
preferable that two or more first scale inhibitor supplying
sections are installed. In this case, the scale inhibitors
17
are sorted according to kind and stored in the respective
tanks.
The first pH adjusting section 40 (40a, 40b) is made up
of a tank 41 (41a, 41b), a valve V2 (V2a, V2b), a control
section 42 (42a, 42b), and a pH meter 43 5 (43a, 43b). The
tanks 41a and 41b have stored therein an alkali as a pH
adjuster. The alkali is calcium hydroxide or sodium
hydroxide, for example. Calcium hydroxide is particularly
preferable because Ca ions are recovered as gypsum in the
10 below-mentioned crystallizing step, and thus the amount of
ions that reach the demineralizing section on the downstream
side is reduced. The control sections 42a and 42b are
connected to the valves V2a and V2b and the pH meters 43a and
43b, respectively.
15 In Fig. 1, the first demineralizing sections 10a and 10b
are reverse osmosis membrane devices. In addition, the first
demineralizing sections 10a and 10b may also be
electrodialyzers (ED), electro dialysis reversal devices
(EDR), electro de-ionization devices (EDI), ion-exchange
20 equipments (IEx), capacitive de-ionization devices (CDI),
nanofilters (NF), evaporators, etc.
Here, in a nanofilter (NF), an electrodialyzer (ED), an
electro dialysis reversal device (EDR), an electro deionization
device (EDI), and a capacitive de-ionization
device (CDI), scale components (divalent ions, Ca2+, Mg2+25 ,
etc.) are selectively removed, while monovalent ions such as
Na+ and Cl- permeate. The use of these demineralizers
suppresses an increase in the ion concentration of ions that
serve as scale components in concentrated water. Accordingly,
30 the water recovery can be improved, and also energy saving
(e.g., the reduction of pump power, etc.) can be achieved.
In addition, in the case where the water to be treated
is blowdown water from a cooling tower, the reclaimed water
does not have to be pure water, and what is necessary is that
18
scale components (divalent ions, Ca2+, Mg2+, etc.) are removed.
Accordingly, it is advantageous to use a nanofilter (NF),
etc.
Although only one first demineralizing section 10a/10b
is shown in Fig. 1, the system may also 5 be configured such
that two or more demineralizers are connected in parallel or
in series in the flow direction of the water to be treated.
The first crystallizing section 20 (20a, 20b) is made up
of a first crystallizing tank 21 (21a, 21b) and a first seed
10 crystal supplying section 22 (22a, 22b). The first seed
crystal supplying sections 22a and 22b are connected to the
first crystallizing tanks 21a and 21b, respectively. The
first seed crystal supplying sections 22a and 22b have a seed
crystal tank 23 (23a, 23b), a valve V3 (V3a, V3b), and a
15 control section 24 (24a, 24b). The control sections 24a and
24b are connected to the valves V3a and V3b, respectively.
The seed crystal tanks 23a and 23b store gypsum particles as
seed crystals.
In the water treatment system 1 of Fig. 1, a first
20 precipitating section 50 (50a, 50b) may be installed on the
downstream side of each of the first crystallizing sections
20a and 20b. The first precipitating sections 50a and 50b
each include a first precipitating tank 51 (51a, 51b) and a
first filtration device 52 (52a, 52b).
25 The water treatment system 1 includes a downstream side
demineralizing section 60 on the downstream side of the water
to be treated of the first crystallizing section 20b located
on the most downstream.
In Fig. 1, the downstream side demineralizing section 60
30 is a reverse osmosis membrane device. The downstream side
demineralizing section 60 may also be an electrodialyzer
(ED), an electro dialysis reversal device (EDR), an electro
de-ionization device (EDI), an ion-exchange equipment, a
capacitive de-ionization device (CDI), a nanofilter (NF), an
19
evaporator, etc.
In the water treatment system 1, a precipitating tank 71
and a filtration device 72 are installed as a first upstream
side precipitating section 70 on the upstream side of the
first scale inhibitor supplying section 30a 5 and the first pH
adjusting section 40a which are located on the most upstream
of the water to be treated. The precipitating tank 71 and the
filtration device 72 have the same configuration as the first
precipitating tank 51 and the first filtration device 52 of
10 the first precipitating section 50.
In particular, in the case where Mg ions are contained
in the water to be treated, the first upstream side
precipitating section can be configured such that two or more
precipitating tanks 71 are connected in series in the flow
15 direction of the water to be treated.
In the water treatment system 1 shown in Fig. 1, a first
deaerating section 73 may be provided on the upstream side of
the first upstream side precipitating section 70.
Specifically, the first deaerating section 73 is a deaeration
20 tower equipped with a filler for removing carbon dioxide or
is a separation membrane. On the upstream side of the water
to be treated of the first deaerating section 73, a pH
adjusting section (not shown) that adjusts the water to be
treated to a pH at which carbonate ions are present in the
25 form of CO2 may be installed.
The first deaerating section 73 may also be installed on
the downstream side of the water to be treated of the first
upstream side precipitating section 70 and on the upstream
side of the first scale inhibitor supplying section 30a and
30 the first pH adjusting section 40a.
It is also possible that a deaerating section having the
same configuration as the first deaerating section 73 is
installed in the flow path between the first demineralizing
section 10 and the first crystallizing section 20, in the
20
flow path between the first crystallizing section 20 and the
first precipitating section 50, and on the downstream side of
the first precipitating section 50 and in the flow path
between it and the first demineralizing section 10b or the
downstream side demineralizing 5 section 60.
In the case where the concentration of Ca ions in the
water to be treated is high, an ion-exchange equipment (not
shown) may be installed on the downstream of the filtration
device 72 and on the upstream of the first scale inhibitor
10 supplying section 30a and the first pH adjusting section 40a
which are located on the most upstream. The ion-exchange
equipment may be an ion-exchange resin column or an ionexchange
membrane device, for example.
When gypsum in the water to be treated flowing into the
15 first demineralizing section 10a is already supersaturated,
because ions are further concentrated in the first
demineralizing section 10a, the resulting gypsum
concentration is even higher. In this case, the loading of a
large amount of calcium scale inhibitor is required. Further,
20 the concentration of gypsum may become too high for the
calcium scale inhibitor to exert its effect, resulting in the
production of scales in the first demineralizing section 10a.
Thus, in the case where gypsum in the raw water (water
to be treated) is supersaturated, it is possible that an
25 upstream side crystallizing section (not shown) having the
same configuration as the first crystallizing tanks 21a and
21b are provided on the upstream of the first scale inhibitor
supplying section 30a and the first pH adjusting section 40a
on the most upstream, so that the concentration of gypsum is
30 reduced, and then the water to be treated is fed to the first
demineralizing section 10a.
A process for treating water to be treated using the
water treatment system 1 of the first reference embodiment
will be described hereinafter.
21
First, the deposition behaviors of gypsum, silica, and
calcium carbonate in water will be explained. Fig. 2 shows
simulation results for the pH dependency of the amount of
gypsum deposited. Fig. 3 shows simulation results for the pH
dependency of the amount of calcium carbonate 5 deposited. In
the figures, the abscissa is pH, and the ordinate is the
amount of gypsum or calcium carbonate deposited (mol). Using
a simulation software manufactured by OLI, the simulation was
performed under the conditions where 0.1 mol/L of each solid
10 component was mixed with water, and H2SO4 and Ca(OH)2 were
added as an acid and an alkali, respectively.
Fig. 4 is a graph showing the pH dependency of the
amount of silica dissolved (source: Fig. 4 of U.S. Pat. No.
7815804). In the figure, the abscissa is pH, and the ordinate
15 is the amount of silica dissolved (mg/L).
From Fig. 2, it can be understood that gypsum deposition
has no pH dependency, and deposition is possible over the
entire pH range. However, when a calcium scale inhibitor is
added, in a high-pH region, gypsum is present in the state of
20 being dissolved in water. From Fig. 3, calcium carbonate is
deposited when the pH is more than 5. From Fig. 4, silica
tends to dissolve in water when the pH is 10 or more.

In the case where the water to be treated is industrial
25 waste water, etc., before the water to be treated flows into
the first upstream side precipitating section 70, a step of
removing oils, floating particles, and the like from the
water to be treated and a step of removing organic substances
by a biological treatment or a chemical oxidation treatment
30 are performed.

In the water treatment system 1 of Fig. 1, the water to
be treated before flowing into the first deaerating section
73 is adjusted to a low pH. Carbonic acid in the water to be
22
treated is in the following equilibrium depending on the pH
of the water to be treated.
Chemical Formula 1
In the case where the pH is as low as 5 6.5 or less, it is
mainly present as HCO3
- and CO2 in the water to be treated.
The water to be treated containing CO2 flows into the
first deaerating section 73. CO2 is removed from the water to
be treated in the first deaerating section 73. When the water
10 to be treated has been previously adjusted to a pH at which
carbonate ions are present as CO2, carbon dioxide can be
efficiently removed.
The water to be treated, whose carbonate ion
concentration has been reduced in the first deaerating step,
15 is fed to the first upstream side precipitating section 70.

In the first upstream side precipitating section 70,
some of Ca ions and carbonate ions are previously removed
from the water to be treated as calcium carbonate.
20 In the case where metal ions other than Ca ions are
contained in the water to be treated, in the first upstream
side precipitating section 70, some of the metal ions are
previously removed from the water to be treated as a metal
compound having low solubility in water. This metal compound
25 is mainly a metal hydroxide, but may also include a
carbonate.
In the precipitating tank 71, Ca(OH)2 and an anionic
polymer (manufactured by Mitsubishi Heavy Industries
Mechatronics Systems, Ltd., trade name: Hishifloc H305) are
30 loaded to the water to be treated, and the pH in the
precipitating tank 71 is controlled to 4 or more and 12 or
23
less, and preferably 8.5 or more and 12 or less.
As shown in Fig. 3, the solubility of calcium carbonate
is low in this pH range. When calcium carbonate is
supersaturated, calcium carbonate is deposited and
precipitated at the bottom of the precipitating 5 tank 71.
The solubility of a metal compound depends on pH. A more
acidic pH leads to a higher solubility of metal ions in
water. For many metal compounds, the solubility is low in the
above pH range. In the above pH range, a metal compound
10 having low solubility in water aggregates in the
precipitating tank 71, resulting in precipitation at the
bottom of the precipitating tank 71.
The precipitated calcium carbonate and metal compound
are discharged from the bottom of the precipitating tank 71.
15 Mg ions form salts that are poorly soluble in water, and
thus are components that tend to be deposited as scales.
Mg(OH)2 is deposited at pH 10 or more.
In the case where the water to be treated containing Mg
ions is treated by the water treatment system 1 of this
20 reference embodiment, the pH of the water to be treated in
the precipitating tank 71 is adjusted to a pH at which a
magnesium compound (mainly magnesium hydroxide) is deposited.
Specifically, the pH of the water to be treated is adjusted
to 10 or more, preferably 10.5 or more, and more preferably
25 11 or more. Accordingly, a magnesium compound is deposited
from the water to be treated, precipitated at the bottom of
the precipitating tank 71, and removed. As a result, some of
Mg ions in the water to be treated are removed, resulting in
a decrease in the concentration of Mg ions in the water to be
30 treated.
In the above case, it is preferable that the water to be
treated after being discharged from the first upstream side
precipitating section 70 is adjusted to a pH at which the
above magnesium compound is soluble. Specifically, the pH is
24
adjusted to less than 10. Accordingly, the formation of
scales in devices and steps on the downstream side,
particularly the first demineralizing section 10a and the
first demineralizing step, can be inhibited.
In the case where two or more stages 5 of precipitating
tanks 71 are provided, Mg ions in the water to be treated can
be reliably removed, and the concentration of Mg ions in the
water to be treated fed to the downstream side can be
reduced.
10 The supernatant in the precipitating tank 71, which is
the water to be treated, is discharged from the precipitating
tank 71. FeCl3 is added to the discharged water to be
treated, and solids in the supernatant, such as calcium
carbonate and a metal compound, aggregate with Fe(OH)3.
15 The water to be treated is fed to the filtration device
72. The solids aggregated with Fe(OH)3 are removed through
the filtration device 72.
In the case where the first deaerating step is performed
after the first upstream side precipitating step, the pH of
20 the water to be treated is adjusted to a pH at which
carbonate ions can be present as CO2, specifically 6.5 or
less.
Incidentally, depending on the properties of the water
to be treated, the first deaerating step and the first
25 upstream side precipitating step may be omitted.
In the case where an ion-exchange equipment is
installed, Ca ions in the water to be treated are removed by
the ion-exchange equipment. In the case where Mg ions are
contained in the water to be treated, the Mg ions are also
30 removed by the ion-exchange equipment.
In the case where gypsum in the raw water is
supersaturated, seed crystals of gypsum are loaded to the
water to be treated in the upstream side crystallizing
section installed immediately after the filtration device 72,
25
and gypsum is crystallized, thereby reducing the
concentration of gypsum in the water to be treated. The water
to be treated having a reduced concentration of gypsum is fed
to the first demineralizing section 10a.

The control section 32a of the first scale inhibitor
supplying section 30a opens the valve V1a and supplies a
predetermined amount of calcium scale inhibitor to the water
to be treated from the tank 31a. The control section 32a
10 adjusts the opening of the valve V1a so that the
concentration of the calcium scale inhibitor is a
predetermined value set according to the properties of the
water to be treated.
In the case where Mg ions are contained in the water to
15 be treated, a magnesium scale inhibitor is supplied to the
water to be treated in the first scale inhibitor supplying
step in the same manner as above. In this case, the calcium
scale inhibitor and the magnesium scale inhibitor are stored
in the tank of each of two or more first scale inhibitor
20 supplying sections, and each control section adjusts the
amounts of calcium scale inhibitor and magnesium scale
inhibitor to be supplied.

The control section 42a of the first pH adjusting
25 section 40a controls the pH of the water to be treated at the
entrance of the first demineralizing section 10a to such a
value that silica is soluble in the water to be treated.
Specifically, the pH of the water to be treated fed to the
first demineralizing section 10a is adjusted to 10 or more,
30 preferably 10.5 or more, and more preferably 11 or more.
The pH meter 43a measures the pH of the water to be
treated at the entrance of the first demineralizing section
10a. The control section 42a adjusts the opening of the valve
V2a so that the value measured by the pH meter 43a is a
26
predetermined pH control value, and allows an alkali to be
loaded to the water to be treated from the tank 41a.

In the first demineralizing section 10a, the pH-adjusted
water to be treated is treated. In the case 5 where the first
demineralizing section 10a is a reverse osmosis membrane
device, the water that has passed through the reverse osmotic
membrane is recovered as treated water. Ions and scale
inhibitors contained in the water to be treated cannot pass
10 through the reverse osmosis membrane. Therefore, on the nonpermeate
side of the reverse osmosis membrane, there is
concentrated water having a high concentration of ions. Also
in the case where other demineralizers, such as a capacitive
de-ionization device, are used, for example, the water to be
15 treated is separated into treated water and concentrated
water having a high concentration of ions (first concentrated
water).
As shown in Fig. 4, as a result of the first
demineralizing step, silica is contained in the first
20 concentrated water in the state of being dissolved in the
water to be treated. Even in the case where gypsum and
calcium carbonate in the first concentrated water are
concentrated to the saturation concentration or higher, the
production of scales is suppressed by the calcium scale
25 inhibitor.
In the case where Mg ions are contained in the water to
be treated, the concentration of Mg ions contained in the
first concentrated water increases as a result of the first
demineralizing step. However, the production of scales
30 containing magnesium is suppressed by the magnesium scale
inhibitor.
The first concentrated water is fed toward the first
crystallizing section 20a.

27
The first concentrated water discharged from the first
demineralizing section 10a is stored in the first
crystallizing tank 21a of the first crystallizing section
20a. The control section 24a of the first seed crystal
supplying section 22a opens the valve 5 V3a and adds seed
crystals of gypsum to the first concentrated water in the
first crystallizing tank 21a from the tank 23a.
The pH of the first concentrated water from the first
demineralizing section 10a is 10 or more. As mentioned above,
10 gypsum is in the state of being dissolved in water in a highpH
region where a calcium scale inhibitor is present.
However, when seed crystals are sufficiently present, even
when a scale inhibitor is present, gypsum is crystallized
using the seed crystals as nuclei. In the water treatment
15 system 1 of Fig. 1, the crystal-grown gypsum having a large
diameter (e.g., having a particle diameter of 10 μm or more,
more preferably 20 μm or more) is precipitated at the bottom
of the first crystallizing tank 21a. The precipitated gypsum
is discharged from the bottom of the first crystallizing tank
20 21a.
Meanwhile, when the pH 10 is or more, silica is present
in the state of being dissolved in the first concentrated
water in the first crystallizing tank 21a. Even in the case
where the concentration of silica in the first concentrated
25 water exceeds the saturation solubility, because seed
crystals of silica are not present, silica is deposited as
floating matters in a colloidal form or the like and unlikely
to be precipitated.
With reference to Fig. 3, calcium carbonate tends to be
30 deposited at pH 10 or more. However, because the calcium
scale inhibitor has been added, the deposition of calcium
carbonate is suppressed in the first crystallizing tank 21a.
In addition, in the case where the first upstream side
precipitating section or the first deaerating section is
28
provided, the concentration of calcium carbonate has been
previously reduced. As a result, in the first crystallizing
tank 21a, calcium carbonate is unlikely to be crystallized
using the seed crystals of gypsum as nuclei.
Incidentally, although gypsum 5 is crystallized
independent of pH when seed crystals of gypsum are present,
the crystallization rate increases with a decrease in pH.
Fig. 5 shows the result of gypsum deposition experiments
with changing the pH of simulated water in the case where a
10 scale inhibitor (FLOCON260) is added to simulated water
(containing Ca2+, SO4
2-, Na+, and Cl-) in which gypsum is
supersaturated. The experimental conditions are as follows:
The degree of gypsum supersaturation in simulated water
(25°C): 460%,
15 The amount of scale inhibitor to be added: 2.1 mg/L,
pH: 6.5 (Condition 1), 5.5 (Condition 2), 4.0 (Condition
3), 3.0 (Condition 4),
The amount of seed crystals to be added: 0 g/L.
Two hours and 6 hours immediately after the pH
20 adjustment, the concentration of Ca in the simulated water
treated under each condition was measured using an atomic
absorption spectrometer (manufactured by Shimadzu
Corporation, AA-7000), and the degree of supersaturation was
calculated. The results are shown in Fig. 5. In the figure,
25 the ordinate is the degree of supersaturation (%).
With reference to Fig. 5, even under conditions where
seed crystals are absent, the crystallization rate increases
with a decrease in pH. From this, it can be understood that
in the case where seed crystals are present, gypsum is
30 crystallized even under Condition 1 (pH 6.5), and the
relation of the crystallization rate is such that the
crystallization rate increases with a decrease in pH as shown
in Fig. 5.
In the case where carbonate ions are contained in the
29
water to be treated, under low-pH conditions, carbonate ions
are removed from the water to be treated as CO2 as in chemical
formula (1). In addition, as can be understood from Fig. 3,
in the case where the pH is low, calcium carbonate is in a
5 dissolved state.
From these results, when the first crystallizing step is
performed under low-pH conditions, because of the low content
of calcium carbonate and silica, high-purity gypsum is
crystallized and recovered from the bottom of the first
10 crystallizing tank 21a. In the case where the first
crystallizing step is performed at low pH, a third pH
adjusting section (not shown) that supplies an acid as a pH
adjuster is installed in the first crystallizing tank 21a or
in the flow path between the first demineralizing section 10a
15 and the first crystallizing tank 21a. The pH adjusting
section has the same configuration as the below-mentioned
second pH adjusting section.
Meanwhile, in order to change the pH in the course of
water treatment, it is necessary to supply a large amount of
20 chemicals (acid or alkali). The use of an acid or an alkali
leads to an increase in the amount of ions transferred to the
downstream side of the first crystallizing section 20a, and
this causes an increase in the power of demineralizing
sections on the downstream side (in Fig. 1, the first
25 demineralizing section 10b or the downstream side
demineralizing section 60). In terms of operation cost, it is
more advantageous that the pH is not changed between the
first demineralizing step and the first crystallizing step.
The gypsum crystallization rate depends on the loading
30 of seed crystals. Fig. 6 shows the results of gypsum
deposition experiments with changing the amount of seed
crystals to be added in the case where a calcium scale
inhibitor (FLOCON260) is added to simulated water. The
experimental conditions were the same as in Fig. 5 except
30
that the pH was 4.0, and that gypsum (CaSO4-2H2O) was added as
seed crystals in the following amounts:
The amount of seed crystals to be added: 0 g/L
(Condition 3), 3 g/L (Condition 5), 6 g/L (Condition 6), 3
5 g/L (Condition 7).
Under Conditions 5 and 6, seed crystals and sulfuric
acid for pH adjustment were added to the simulated water
having added thereto a scale inhibitor. Under Condition 7,
seed crystals pre-immersed in the above scale inhibitor were
10 added to the simulated water having added thereto a scale
inhibitor, and sulfuric acid was added for pH adjustment.
Two hours immediately after the pH adjustment, the
concentration of Ca in the simulated water treated under each
condition was measured by the same technique as in Fig. 5. In
15 Fig. 6, the ordinate is the degree of supersaturation (%).
From the results of Fig. 6, it can be understood that
although the degree of supersaturation was 215% under
Condition 3 where seed crystals are not added, the degree of
supersaturation decreases to 199% (Condition 5) and 176%
20 (Condition 6) with an increase in the concentration of seed
crystals, leading to an increase in the gypsum deposition
rate. Also under high-pH conditions, similarly, the gypsum
deposition rate tends to increase with an increase in the
loading of seed crystals. Condition 5 and Condition 7 are the
25 same test conditions, except for whether the used seed
crystals are not immersed or immersed in a scale inhibitor.
Also under Condition 7 where seed crystals have a scale
inhibitor previously adhering thereto, the degree of
supersaturation is 199%, and it has been confirmed that
30 gypsum is deposited at the same level as under Condition 5.
That is, the results under Condition 5 and 7 show that
independent of the immersion time of seed crystals in a
calcium scale inhibitor, when the pH is reduced to 4.0, the
function of the scale inhibitor is reduced.
31
Figs. 7 and 8 each show a microphotograph of gypsum
resulting from crystallization. Fig. 7 shows results under
Condition 5 (seed crystals added), and Fig. 8 shows results
under Condition 3 (no seed crystals added). Under Condition
5, gypsum having a larger size was deposited 5 than under
Condition 3. Generally, the water content decreases with an
increase in the size of deposited gypsum. A low water content
leads to high-purity gypsum. When the average particle
diameter is 10 μm or more, preferably 20 μm or more, the
10 resulting gypsum has a sufficiently reduced water content.
The “average particle diameter” in the present invention is a
particle diameter measured by the method specified in JIS Z
8825 (laser diffractometry).

15 The supernatant (first concentrated water) in the first
crystallizing section 20a is fed to the first precipitating
section 50a. In the first precipitating section 50a, Ca(OH)2
and an anionic polymer (Hishifloc H305) are loaded to the
first concentrated water after the crystallizing step, and
20 the pH in the first precipitating tank 51a is controlled to 4
or more and 12 or less, and preferably 8.5 or more and 12 or
less. In the first precipitating tank 51a, calcium carbonate
and a metal compound are precipitated and removed from the
first concentrated water. The precipitated calcium carbonate
25 and metal compound having low solubility in water are
discharged from the bottom of the first precipitating tank
51a.
The water to be treated, which is the supernatant in the
first precipitating tank 51a, is discharged from the first
30 precipitating tank 51a. FeCl3 is added to the discharged
water to be treated, and solids in the water to be treated,
such as calcium carbonate and a metal compound, aggregate
with Fe(OH)3.
The water to be treated is fed to the first filtration
32
device 52a. The solids aggregated with Fe(OH)3 are removed
through the first filtration device 52a.
Silica in the supernatant in the first crystallizing
section 20a may be removed from the first concentrated water
in the first precipitating step, or may 5 also be fed to the
downstream side without being removed.
Whether silica is removed in the first precipitating
step is determined according to the properties of the water
to be treated or the first concentrated water.
10 In the case where silica is not removed, the first
precipitating step is performed without supplying seed
crystals of silica and a precipitant for silica to the first
precipitating tank 51a. In this case, silica is separated
from the treated water in demineralizing sections located on
15 the downstream side (the first demineralizing section 10b and
the downstream side demineralizing section 60).
In the case where silica is removed, at least one of
seed crystals of silica and a precipitant for silica is
supplied into the first concentrated water in the first
20 precipitating section 50a from a supply section (not shown).
The seed crystals of silica are a silica gel, for example,
and the precipitant for silica is MgSO4 or Na aluminate
(Na[Al(OH)4]), for example. In the case where silica is
removed, it is preferable that the first concentrated water
25 in the first precipitating tank 51a is adjusted to pH 8 or
more and 10 or less. In the case where seed crystals of
silica are used, silica is crystallized using the seed
crystals as nuclei. In the case where MgSO4 is used as a
precipitant for silica, magnesium silicate is deposited. The
30 crystallized silica or the crystallized magnesium silicate is
precipitated at the bottom of the first precipitating tank
51a and discharged from the bottom of the first precipitating
tank 51a.
In the case where Mg ions are contained in the water to
33
be treated, Mg ions react with silica in the first
concentrated water in the first precipitating step, resulting
in precipitation. The steps for silica/Mg ion removal vary
depending on the balance between the content of Mg ions and
the content of silica in the first concentrated 5 water in the
first precipitating tank 51a.
In the case where the first concentrated water in the
first precipitating step has a lower concentration of Mg ions
relative to the silica content, Mg ions are consumed by
10 precipitation with silica. In order to remove an excess of
silica that is not consumed by precipitation with Mg ions, a
precipitant for silica (MgSO4) is supplied. With respect to
the amount of precipitant for silica to be supplied,
according to the content of silica and the content of Mg ions
15 in the first precipitating step, the precipitant is supplied
in such an amount that the excess of silica is consumed.
In the case where the first concentrated water in the
first precipitating step has a higher concentration of Mg
ions relative to the silica content, Mg ions remain as a
20 result of the precipitation of Mg ions and silica. When the
first concentrated water having a high concentration of
residual Mg ions is discharged from the first precipitating
tank 51a, scales containing Mg may be deposited in
demineralizing sections of subsequent stages (the first
25 demineralizing section 10b in Fig. 1; in the case of the
first precipitating section on the most downstream, the
downstream side demineralizing section 60).
Thus, the first concentrated water in the first
precipitating tank 51a is adjusted to such a value that a
30 magnesium compound (mainly magnesium hydroxide) can be
deposited. Accordingly, a magnesium compound is precipitated
in the first precipitating tank 51a, thereby reducing the
concentration of Mg ions in the first concentrated water in
the first precipitating tank 51a. Further, after the first
34
precipitating step, the first concentrated water discharged
from the first precipitating tank 51a is adjusted to a pH at
which the magnesium compound is soluble, specifically to a pH
of less than 10. Accordingly, the deposition of scales
containing Mg in a demineralizing section 5 can be suppressed.
In the case where the treatment is performed in several
stages, the first concentrated water that has passed through
the first filtration device 52a of the first water treatment
section of the previous stage flows into the water treatment
10 section of the subsequent stage as water to be treated. In
the water treatment section of the subsequent stage, the
steps from the first scale inhibitor supplying step to the
first precipitating step mentioned above are performed.

15 The concentrated water (first concentrated water) that
has passed through the first precipitating section 50b
located on the most downstream of the water to be treated is
fed to the downstream side demineralizing section 60. The
water that has passed through the downstream side
20 demineralizing section 60 is recovered as treated water. The
concentrated water in the downstream side demineralizing
section 60 is discharged out of the system. The installation
of the downstream side demineralizing section 60 makes it
possible to further recover treated water from water that has
25 been treated in a water treatment section. Accordingly, the
water recovery is improved.
In the water treatment system 1 of this reference
embodiment, ions are concentrated in the first demineralizing
section 10. However, gypsum, calcium carbonate, silica, etc.,
30 have been removed in the first crystallizing section, the
first precipitating section, etc. Accordingly, the water
flowing into the downstream side demineralizing section 60
has a smaller number of moles of ions than before the
treatment. Accordingly, the osmotic pressure is low in the
35
first demineralizing section 10b or the downstream side
demineralizing section 60 located downstream, and the
required power is reduced.
An evaporator (not shown in Fig. 1) may be installed on
the downstream on the concentrated-5 water side of the
downstream side demineralizing section 60. In the evaporator,
water is evaporated from the concentrated water, and ions
contained in the concentrated water are deposited as a solid
and recovered as a solid. Because water is recovered on the
10 upstream side of the evaporator, and the amount of
concentrated water significantly decreases, the evaporator
can be reduced in size, and the energy required for
evaporation can be reduced.
Second reference Embodiment
15 Fig. 9 is a schematic diagram of a water treatment
system of the second reference embodiment of the present
invention. In Fig. 9, the same configurations as in the first
reference embodiment are indicated with the same reference
numerals. In the water treatment system 100 of the second
20 reference embodiment, a first separating section 180 (180a,
180b) is installed on the downstream side of the first
crystallizing sections 20a and 20b. The water treatment
system 100 of Fig. 9 is configured such that two water
treatment sections are connected in the flow direction of the
25 water to be treated. In the water treatment system 100 of
this reference embodiment, depending on the properties of the
water to be treated, the number of water treatment sections
may be one, and it is also possible that three or more water
treatment sections are connected.
30 In Fig. 9, the first separating section 180 (180a, 180b)
includes a classifier 181 (181a, 181b) and a dehydrator 182
(182a, 182b). The classifiers 181a and 181b are liquid
cyclones, for example. The dehydrators 182a and 182b are belt
36
filters, for example.
Although the first separating section 180 has only one
classifier installed in Fig. 9, it is also possible that two
or more classifiers are connected in series in the flow
direction of the water 5 to be treated.
In the water treatment system 100 of the second
reference embodiment, the water to be treated is treated
through the same steps as in the first reference embodiment,
except that the first separating step is performed
10 immediately after the first crystallizing step.

First concentrated water in the first crystallizing
tanks 21a and 21b is transferred to the first separating
sections 180a and 180b. The first concentrated water
15 transferred here is water containing solid matters deposited
in the first crystallizing tanks 21a and 21b.
The first concentrated water discharged from the first
crystallizing tanks 21a and 21b contains gypsum having
various particle diameters, as well as calcium carbonate and
20 silica deposited due to the exceeding of the saturation
concentration. Because the deposition of calcium carbonate
and silica has taken place in the absence of seed crystals,
they have small diameters or are floating matters in a
colloidal form.
25 When the first concentrated water flows into the
classifiers 181a and 181b, gypsum having a predetermined
size, for example, gypsum having an average particle diameter
of 10 μm or more, sediments at the bottom of the classifiers
181a and 181b, and gypsum having a small particle diameter,
30 calcium carbonate, and silica remain in the supernatant. The
gypsum sedimented at the bottom of the classifiers 181a and
181b is further dehydrated by the dehydrators 182a and 182b
and recovered. The supernatant containing gypsum having a
small particle diameter, calcium carbonate, and silica is fed
37
to the first precipitating sections 50a and 50b.
In this reference embodiment, seed crystals are added to
cause crystallization. Therefore, gypsum having an average
particle diameter of 10 μm or more is mainly deposited, and
the proportion of gypsum having a small 5 diameter is low.
Through the first separating step, gypsum having a low water
content and containing no impurities (i.e., high-purity
gypsum) can be separated and recovered with high recovery.
Some of the gypsum recovered in the first separating
10 sections 180a and 180b may be circulated through the seed
crystal tanks 23a and 23b as seed crystals.
First Example of Third Reference Embodiment
Water that is an object to be treated in the present
invention (water to be treated) contains Ca2+, SO4
2-, and
15 carbonate ions. Specifically, the water to be treated (raw
water) is saline water, sewage, industrial waste water,
blowdown water from a cooling tower, or the like. The water
to be treated may also contain metal ions, such as Mg ions.
Fig. 10 is a schematic diagram of a water treatment
20 system of the first example of the third reference embodiment
of the present invention. The water treatment system 201 of
Fig. 10 is configured such that two water treatment sections
are connected in the flow direction of the water to be
treated. Depending on the properties of the water to be
25 treated, the number of water treatment sections may be one,
and it is also possible that three or more water treatment
sections are connected.
In the water treatment system 201 of the first example
of the third reference embodiment, each water treatment
30 section includes, from the upstream side of the water to be
treated, a second demineralizing section 210 (210a, 210b) and
a second crystallizing section 220 (220a, 220b). The
concentration sides of the second demineralizing sections
38
210a and 210b are connected to the second crystallizing
sections 220a and 220b, respectively. The water treatment
section includes a second scale inhibitor supplying section
230 (230a, 230b) in the flow path on the upstream side of
each second demineralizing section 5 210 (210a, 210b).
The second scale inhibitor supplying sections 230a and
230b are each made up of a tank 231 (231a, 231b), a valve V4
(V4a, V4b), and a control section 232 (232a, 232b). The
control sections 232a and 232b are connected to the valves
10 V4a and V4b, respectively. The tanks 231a and 231b of the
second scale inhibitor supplying sections 230a and 230b store
a scale inhibitor.
The scale inhibitor used in the first example of this
reference embodiment serves to inhibit the deposition of
15 scales containing calcium in the water to be treated. It will
be hereinafter referred to as “calcium scale inhibitor”.
The calcium scale inhibitor suppresses the crystal
nucleation of gypsum or calcium carbonate in the water to be
treated. At the same time, it adheres to the surface of
20 crystal nucleus of gypsum or calcium carbonate contained in
the water to be treated (seed crystals, small-diameter scales
deposited due to the exceeding of the saturation
concentration, etc.), and functions to suppress the crystal
growth of gypsum or calcium carbonate. Alternatively, there
25 is another type of calcium scale inhibitor, which has the
function of dispersing particles in the water to be treated
(inhibiting aggregation), such as deposited crystals.
Examples of calcium scale inhibitors include phosphonicacid-
based scale inhibitors, polycarboxylic-acid-based scale
30 inhibitors, and mixtures thereof. A specific example is
FLOCON260 (trade name, manufactured by BWA).
Fig. 10 shows tanks 231a and 231b. The tanks 231a and
231b store a calcium scale inhibitor.
In Fig. 10, the second demineralizing sections 210a and
39
210b are reverse osmosis membrane devices. In addition, the
second demineralizing sections 210a and 210b may also be
electrodialyzers (ED), electro dialysis reversal devices
(EDR), electro de-ionization devices (EDI), ion exchangers
(IEx), capacitive de-ionization devices 5 (CDI), nanofilters
(NF), evaporators, etc.
Here, in a nanofilter (NF), an electrodialyzer (ED), an
electro dialysis reversal device (EDR), an electro deionization
device (EDI), and a capacitive de-ionization
device (CDl), scale components (divalent ions, Ca2+, Mg2+10 ,
etc.) are selectively removed, while monovalent ions such as
Na+ and Cl- permeate. The use of these demineralizers
suppresses an increase in the ion concentration of ions that
serve as scale components in concentrated water. Accordingly,
15 the water recovery can be improved, and also energy saving
(e.g., the reduction of pump power, etc.) can be achieved.
In addition, in the case where the water to be treated
is blowdown water from a cooling tower, the reclaimed water
does not have to be pure water, and what is necessary is that
scale components (divalent ions, Ca2+, Mg2+20 , etc.) are removed.
Accordingly, it is advantageous to use a nanofilter (NF),
etc.
Although only one second demineralizing section
210a/210b is shown in Fig. 10, the system may also be
25 configured such that two or more demineralizers are connected
in parallel or in series in the flow direction of the water
to be treated.
The second crystallizing section 220 (220a, 220b) is
made up of a second crystallizing tank 221 (221a, 221b) and a
30 second seed crystal supplying section 222 (222a, 222b). The
second seed crystal supplying sections 222a and 222b are
connected to the second crystallizing tanks 221a and 221b,
respectively. The second seed crystal supplying sections 222a
and 222b have a seed crystal tank 223 (223a, 223b), a valve
40
V5 (V5a, V5b), and a control section 224 (224a, 224b). The
control sections 224a and 224b are connected to the valves
V5a and V5b, respectively. The seed crystal tanks 223a and
223b store gypsum particles as seed crystals.
In the water treatment system 201 of 5 Fig. 10, a second
precipitating section 250 (250a, 250b) may be installed on
the downstream side of the second crystallizing sections 220a
and 220b. The second precipitating sections 250a and 250b
each include a second precipitating tank 251 (251a, 251b) and
10 a second filtration device 252 (252a, 252b).
The water treatment system 201 includes a downstream
side demineralizing section 60 on the downstream side of the
water to be treated of the second crystallizing section 220b
located on the most downstream.
15 In Fig. 10, the downstream side demineralizing section
60 is a reverse osmosis membrane device. The downstream side
demineralizing section 60 may also be an electrodialyzer
(ED), an electro dialysis reversal device (EDR), an electro
de-ionization device (EDI), an ion exchanger, a capacitive
20 de-ionization device (CDI), a nanofilter (NF), an evaporator,
etc.
An evaporator (not shown in Fig. 10) may be installed on
the downstream on the concentrated-water side of the
downstream side demineralizing section 60. In the evaporator,
25 water is evaporated from the concentrated water, and ions
contained in the concentrated water are deposited as a solid
and recovered as a solid. Because water is recovered on the
upstream side of the evaporator, and the amount of
concentrated water significantly decreases, the evaporator
30 can be reduced in size, and the energy required for
evaporation can be reduced.
In the water treatment system 201 of the first example
of the third reference embodiment, a second pH adjusting
section 240 (240a, 240b) may be installed between the second
41
demineralizing section 210 and the second crystallizing
section 220. The second pH adjusting section 240 is made up
of a tank 241 (241a, 241b), a valve V6 (V6a, V6b), a pH meter
243 (243a, 243b), and a control section 242 (242a, 242b). The
tank 241 has stored therein an acid as a 5 pH adjuster. The
acid used may be hydrochloric acid, sulfuric acid, nitric
acid, or the like, for example. Sulfuric acid is particularly
preferable because SO4
2- is removed as gypsum in the
crystallizing step, and thus the amount of ions that reach
10 the demineralizing section on the downstream side can be
reduced. The control section 242 is connected to the valve V6
and the pH meter 243. The pH meter 243 may be installed in
the flow path between the second demineralizing section 210
and the second crystallizing section 220 as shown in Fig. 10,
15 or may also be installed in the second crystallizing tank
221.
In the water treatment system 201, a precipitating tank
271 and a filtration device 272 are installed as a second
upstream side precipitating section 270 on the upstream side
20 of the second scale inhibitor supplying section 230a located
on the most upstream of the water to be treated. The second
upstream side precipitating section 270 has the same
configuration as the first precipitating tank 251 and the
first filtration device 252 of the first precipitating
25 section 250.
In particular, in the case where Mg ions are contained
in the water to be treated, the second upstream side
precipitating section 270 can be configured such that two or
more precipitating tanks 271 are connected in series in the
30 flow direction of the water to be treated.
In the water treatment system 201, a second deaerating
section 273 may be provided on the upstream side of the
second upstream side precipitating section 270 as shown in
Fig. 10. Specifically, the second deaerating section 273 is a
42
deaeration tower equipped with a filler for removing carbon
dioxide or is a separation membrane. On the upstream side of
the water to be treated of the second deaerating section 273,
a pH adjusting section (not shown) that adjusts the water to
be treated to a pH at which carbonate ions 5 are present in the
form of CO2 may be installed.
The second deaerating section 273 may be installed on
the downstream side of the water to be treated of the second
upstream side precipitating section 270 and on the upstream
10 side of the second scale inhibitor supplying section 230a.
It is also possible that a deaerating section having the
same configuration as the second deaerating section 273 is
installed in the flow path between the second demineralizing
section 210 and the second crystallizing section 220, in the
15 flow path between the second crystallizing section 220 and
the second precipitating section 250, and on the downstream
side of the second precipitating section 250 and in the flow
path between it and the second demineralizing section 210b or
the downstream side demineralizing section 60.
20 In the case where the concentration of Ca ions in the
water to be treated is high, an ion exchanger (not shown) may
be installed on the downstream of the filtration device 272
and on the upstream of the second scale inhibitor supplying
section 230a located on the most upstream. The ion exchanger
25 may be an ion-exchange resin column or an ion-exchange
membrane device, for example.
When gypsum in the water to be treated flowing into the
second demineralizing section 210a is already supersaturated,
because ions are further concentrated in the second
30 demineralizing section 210a, the resulting gypsum
concentration is even higher. In this case, the loading of a
large amount of calcium scale inhibitor is required. Further,
the concentration of gypsum may become too high for the
calcium scale inhibitor to exert its effect, resulting in the
43
production of scales in the second demineralizing section
210a.
Thus, in the case where gypsum in the raw water (water
to be treated) is supersaturated, it is possible that an
upstream side crystallizing section (not 5 shown) having the
same configuration as the second crystallizing sections 221a
and 221b is provided on the upstream of the second scale
inhibitor supplying section 230a on the most upstream, so
that the concentration of gypsum is reduced, and then the
10 water to be treated is fed to the second demineralizing
section 210a.
In the first example of this reference embodiment, a
second separating section 280 (280a, 280b) is installed on
the downstream side of the second crystallizing section 220
15 as shown in Fig. 10. The second separating section 280 has
the same configuration as the first separating section 180
and includes a classifier 281 (281a, 281b) and a dehydrator
282 (282a, 282b). The classifiers 281a and 281b are liquid
cyclones, for example. The dehydrators 282a and 282b are belt
20 filters, for example.
Although the second separating section 280 has only one
classifier installed in Fig. 10, it is also possible that two
or more classifiers are connected in series in the flow
direction of the water to be treated.
25 A process for treating water to be treated using the
water treatment system 201 of the first example of the third
reference embodiment will be described hereinafter.
First, the deposition behaviors of gypsum and calcium
carbonate in water will be explained. Fig. 2 shows simulation
30 results for the pH dependency of the amount of gypsum
deposited. Fig. 3 shows simulation results for the pH
dependency of the amount of calcium carbonate deposited. In
the figures, the abscissa is pH, and the ordinate is the
amount of gypsum or calcium carbonate deposited (mol). Using
44
a simulation software manufactured by OLI, the simulation was
performed under the conditions where 0.1 mol/L of each solid
component was mixed with water, and H2SO4 and Ca(OH)2 were
added as an acid and an alkali, respectively.
From Fig. 2, it can be understood that 5 gypsum deposition
has no pH dependency, and deposition is possible over the
entire pH range. However, when a calcium scale inhibitor is
added, in a high-pH region, gypsum is present in the state of
being dissolved in water. From Fig. 3, calcium carbonate is
10 deposited when the pH is more than 5.

In the case where the water to be treated is industrial
waste water, etc., before the water to be treated flows into
the second upstream side precipitating section 270, a step of
15 removing oils, floating particles, and the like from the
water to be treated and a step of removing organic substances
by a biological treatment or a chemical oxidation treatment
are performed.

20 In the water treatment system 201 of Fig. 10, the water
to be treated before flowing into the second deaerating
section 273 is adjusted to a low pH. Carbonic acid in the
water to be treated is in the following equilibrium depending
on the pH of the water to be treated.
25 [Chemical Formula 2]
In the case where the pH is as low as 6.5 or less, it is
mainly present as HCO3
- and CO2 in the water to be treated.
The water to be treated containing CO2 flows into the
30 second deaerating section 273. CO2 is removed from the water
to be treated in the second deaerating section 273. When the
45
water to be treated has been previously adjusted to a pH at
which carbonate ions are present as CO2, carbon dioxide can be
efficiently removed.
The water to be treated, whose carbonate ion
concentration has been reduced in the second 5 deaerating step,
is fed to the second upstream side precipitating section 270.

In the second upstream side precipitating section 270,
Ca ions and carbonate ions are previously roughly removed
10 from the water to be treated as calcium carbonate. In the
case where metal ions other than Ca ions are contained in the
water to be treated, in the second upstream side
precipitating section 270, the metal ions are previously
roughly removed from the water to be treated as a metal
15 compound having low solubility in water. This metal compound
is mainly a metal hydroxide, but may also include a
carbonate.
In the precipitating tank 271, Ca(OH)2 and an anionic
polymer (manufactured by Mitsubishi Heavy Industries
20 Mechatronics Systems, Ltd., trade name: Hishifloc H305) are
loaded to the water to be treated, and the pH in the
precipitating tank 271 is controlled to 4 or more and 12 or
less, and preferably 8.5 or more and 12 or less.
As shown in Fig. 3, the solubility of calcium carbonate
25 is low in this pH range. When calcium carbonate is
supersaturated, calcium carbonate is deposited and
precipitated at the bottom of the precipitating tank 271.
The solubility of a metal compound depends on pH. A more
acidic pH leads to a higher solubility of metal ions in
30 water. For many metal compounds, the solubility is low in the
above pH range. In the above pH range, a metal compound
having low solubility in water aggregates in the
precipitating tank 271, resulting in precipitation at the
bottom of the precipitating tank 271.
46
The precipitated calcium carbonate and metal compound
are discharged from the bottom of the precipitating tank 271.
Mg ions form salts that are poorly soluble in water, and
thus are components that tend to be deposited as scales.
Mg(OH)2 is deposited 5 at pH 10 or more.
In the case where the water to be treated containing Mg
ions is treated by the water treatment system 201 of the
first example of this reference embodiment, the pH of the
water to be treated is adjusted to a pH at which a magnesium
10 compound (mainly magnesium hydroxide) is deposited in the
second upstream side precipitating section 270. Specifically,
the pH of the water to be treated is adjusted to 10 or more,
preferably 10.5 or more, and more preferably 11 or more.
Accordingly, a magnesium compound is deposited from the water
15 to be treated, precipitated at the bottom of the
precipitating tank 271, and removed. As a result, Mg ions in
the water to be treated are roughly removed, resulting in a
decrease in the concentration of Mg ions in the water to be
treated.
20 In the above case, it is preferable that the water to be
treated after being discharged from the second upstream side
precipitating section 270 is adjusted to a pH at which the
above magnesium compound is soluble. Specifically, the pH is
adjusted to less than 10. Accordingly, the formation of
25 scales in devices and steps on the downstream side,
particularly the second demineralizing section 210 and the
second demineralizing step, can be inhibited.
In the case where two or more stages of precipitating
tanks 271 are provided, Mg ions in the water to be treated
30 can be reliably removed, and the concentration of Mg ions in
the water to be treated fed to the downstream side can be
reduced.
The supernatant in the precipitating tank 271, which is
the water to be treated, is discharged from the precipitating
47
tank 271. FeCl3 is added to the discharged water to be
treated, and solids in the supernatant, such as calcium
carbonate and a metal compound, aggregate with Fe(OH)3.
The water to be treated is fed to the filtration device
272. The solids aggregated with Fe(OH)3 are 5 removed through
the filtration device 272.
In the case where the second deaerating step is
performed after the second upstream side precipitating step,
the pH of the water to be treated is adjusted to a pH at
10 which carbonate ions can be present as CO2, specifically 6.5
or less.
Depending on the properties of the water to be treated,
the second deaerating step and the second upstream side
precipitating step may be omitted.
15 In the water treatment system 201 of the first example
of the third reference embodiment, in the case where an ionexchange
membrane device is installed, Ca ions in the water
to be treated are removed by the ion exchanger. In the case
where Mg ions are contained in the water to be treated, the
20 Mg ions are also removed by the ion exchanger.
In the case where gypsum in the raw water is
supersaturated, seed crystals of gypsum are loaded to the
water to be treated in the upstream side crystallizing
section installed immediately after the filtration device
25 272, and gypsum is crystallized, thereby reducing the
concentration of gypsum in the water to be treated. The water
to be treated having a reduced concentration of gypsum is fed
to the second demineralizing section 210a.

30 The control section 232a of the second scale inhibitor
supplying section 230a opens the valve V4a and supplies a
predetermined amount of calcium scale inhibitor to the water
to be treated from the tank 231a. The control section 232a
adjusts the opening of the valve V4a so that the
48
concentration of the calcium scale inhibitor is a
predetermined value set according to the properties of the
water to be treated.
In the case where Mg ions are contained in the water to
be treated, a magnesium scale inhibitor 5 is supplied to the
water to be treated in the second scale inhibitor supplying
step in the same manner as above. In this case, the calcium
scale inhibitor and the magnesium scale inhibitor are stored
in the tank of each of two or more second scale inhibitor
10 supplying sections, and each control section adjusts the
amounts of calcium scale inhibitor and magnesium scale
inhibitor to be supplied.
In the water treatment system 201 of the first example
of the third reference embodiment, the pH adjustment of the
15 water to be treated immediately before flowing into the
second demineralizing section 210 is optionally performed.
For example, in the configuration of Fig. 10, as a
result of the addition of FeCl3, the water to be treated is
adjusted to about pH 5 or 6 and then flows into the second
20 demineralizing section 210a. As shown in Fig. 3, the
solubility of calcium carbonate in water is high when the pH
of the water to be treated is 6.5 or less. In addition, as in
formula (1), in the above pH range, carbonic acid is present
mainly in the form of HCO3
- and CO2 in water. The water to be
25 treated flowing into the second demineralizing section 210a
has a reduced concentration of calcium carbonate. In such a
case, it is not necessary to adjust the pH immediately before
the second demineralizing section 210a.
Incidentally, in the case where the pH of the water to
30 be treated, which is to be treated in the second
demineralizing step, is adjusted, it is possible that a pH
adjusting section having the same configuration as the second
pH adjusting section is installed on the upstream of the
second demineralizing section 210a, and the pH-adjusted water
49
to be treated is fed to the second demineralizing section
210a.

In the second demineralizing section 210a, the water to
be treated containing the scale inhibitors is 5 treated. In the
case where the second demineralizing section 210a is a
reverse osmosis membrane device, the water that has passed
through the reverse osmotic membrane is recovered as treated
water. Ions and scale inhibitors contained in the water to be
10 treated cannot pass through the reverse osmosis membrane.
Therefore, on the non-permeate side of the reverse osmosis
membrane, there is concentrated water having a high
concentration of ions (second concentrated water).
Even in the case where gypsum and calcium carbonate in
15 the second concentrated water are concentrated to the
saturation concentration or higher as a result of the
treatment in the second demineralizing section 210a, the
production of scales is suppressed by the calcium scale
inhibitor.
20 In the case where Mg ions are contained in the water to
be treated, the concentration of Mg ions contained in the
second concentrated water increases as a result of the second
demineralizing step. However, the production of scales
containing magnesium is suppressed by the magnesium scale
25 inhibitor.
Also in the case where other demineralizers, such as a
capacitive de-ionization device, are used, for example, the
water to be treated is separated into treated water and
concentrated water having a high concentration of ions
30 (second concentrated water). The second concentrated water is
fed toward the second crystallizing section 220a.

In the first example of this reference embodiment, the
pH of the water to be treated (second concentrated water) may
50
be adjusted by the second pH adjusting section 240a between
the second demineralizing section 210a and the second
crystallizing section 220a.
The second pH adjusting section 240a controls the pH of
the second concentrated water to such 5 a value that the
function of the calcium scale inhibitor is reduced and gypsum
in the second concentrated water can be deposited. The pH
meter 243a measures the pH of the second concentrated water.
The control section 242a adjusts the opening of the valve V6a
10 so that the value measured by the pH meter 243a is a
predetermined pH control value.

The second concentrated water discharged from the second
demineralizing section 210a is stored in the second
15 crystallizing tank 221a of the second crystallizing section
220a. The control section 224a of the second seed crystal
supplying section 222a opens the valve V5a and adds seed
crystals of gypsum from the seed crystal tank 223a to the
second concentrated water in the second crystallizing tank
20 221a.
The pH of the second concentrated water from the second
demineralizing section 210a is 10 or more. As mentioned
above, gypsum is in the state of being dissolved in water in
a high-pH region where a calcium scale inhibitor is present.
25 However, when seed crystals are sufficiently present, even
when a scale inhibitor is present, gypsum is crystallized
using the seed crystals as nuclei. In the water treatment
system 201 of Fig. 10, the crystal-grown gypsum having a
large diameter (e.g., having a particle diameter of 10 μm or
30 more, more preferably 20 μm or more) is precipitated at the
bottom of the second crystallizing tank 221a. The
precipitated gypsum is discharged from the bottom of the
second crystallizing tank 221a.
51
With reference to Fig. 3, calcium carbonate tends to be
deposited at pH 10 or more. However, because the calcium
scale inhibitor has been added, the deposition of calcium
carbonate is suppressed in the second crystallizing tank
221a. In addition, in the case where the second 5 upstream side
precipitating section or the second deaerating section is
provided, the concentration of calcium carbonate has been
previously reduced. As a result, in the second crystallizing
tank 221a, calcium carbonate is unlikely to be crystallized
10 using the seed crystals of gypsum as nuclei.
Incidentally, although gypsum is crystallized
independent of pH when seed crystals of gypsum are present,
the crystallization rate increases with a decrease in pH.
Fig. 5 shows the result of gypsum deposition experiments
15 with changing the pH of simulated water in the case where a
scale inhibitor (FLOCON260) is added to simulated water
(containing Ca2+, SO4
2-, Na+, and Cl-) in which gypsum is
supersaturated. The experimental conditions are as follows:
The degree of gypsum supersaturation in simulated water
20 (25°C): 460%,
The amount of scale inhibitor to be added: 2.1 mg/L,
pH: 6.5 (Condition 1), 5.5 (Condition 2), 4.0 (Condition
3), 3.0 (Condition 4),
The amount of seed crystals to be added: 0 g/L.
25 Two hours and 6 hours immediately after the pH
adjustment, the concentration of Ca in the simulated water
treated under each condition was measured using an atomic
absorption spectrometer (manufactured by Shimadzu
Corporation, AA-7000), and the degree of supersaturation was
30 calculated. The results are shown in Fig. 5. In the figure,
the ordinate is the degree of supersaturation (%).
With reference to Fig. 5, even under conditions where
seed crystals are absent, the crystallization rate increases
with a decrease in pH. From this, it can be understood that
52
in the case where seed crystals are present, gypsum is
crystallized even under Condition 1 (pH 6.5), and the
relation of the crystallization rate is such that the
crystallization rate increases with a decrease in pH as shown
5 in Fig. 5.
In the case where carbonate ions are contained in the
water to be treated, under low-pH conditions, carbonate ions
are removed from the water to be treated as CO2 as in chemical
formula (1). In addition, as can be understood from Fig. 3,
10 in the case where the pH is low, calcium carbonate is in a
dissolved state.
From these results, when the second crystallizing step
is performed under low-pH conditions, because of the low
content of calcium carbonate, high-purity gypsum is
15 crystallized and recovered from the bottom of the second
crystallizing tank 221a. In the case where the second
crystallizing step is performed at low pH, a third pH
adjusting section (not shown) that supplies an acid as a pH
adjuster is installed in the second crystallizing tank 221a
20 or in the flow path between the second demineralizing section
210a and the second crystallizing tank 221a. The pH adjusting
section has the same configuration as the second pH adjusting
section.
Meanwhile, in order to change the pH in the course of
25 water treatment, it is necessary to supply a large amount of
chemicals (acid or alkali). The use of an acid or an alkali
leads to an increase in the amount of ions transferred to the
downstream side of the second crystallizing section 220a, and
this causes an increase in the power of demineralizing
30 sections on the downstream side (in Fig. 10, the second
demineralizing section 210b or the downstream side
demineralizing section 60). In terms of operation cost, it is
more advantageous that the pH is not changed between the
second demineralizing step and the second crystallizing step.
53
The gypsum crystallization rate depends on the loading
of seed crystals.
Fig. 6 shows the results of gypsum deposition
experiments with changing the amount of seed crystals to be
added in the case where a calcium scale inhibitor 5 (FLOCON260)
is added to simulated water. The experimental conditions were
the same as in Fig. 5, except that the pH was 4.0, and that
gypsum (CaSO4·2H2O) was added as seed crystals in the
following amounts.
10 The amount of seed crystals to be added: 0 g/L
(Condition 3), 3 g/L (Condition 5), 6 g/L (Condition 6), 3
g/L (Condition 7).
Under Conditions 5 and 6, seed crystals and sulfuric
acid for pH adjustment were added to the simulated water
15 having added thereto a scale inhibitor. Under Condition 7,
seed crystals pre-immersed in the above scale inhibitor were
added to the simulated water having added thereto a scale
inhibitor, and sulfuric acid was added for pH adjustment.
Two hours immediately after the pH adjustment, the
20 concentration of Ca in the simulated water treated under each
condition was measured by the same technique as in Fig. 5. In
Fig. 6, the ordinate is the degree of supersaturation (%).
From the results of Fig. 6, it can be understood that
although the degree of supersaturation was 215% under
25 Condition 3 where seed crystals are not added, the degree of
supersaturation decreases to 199% (Condition 5) and 176%
(Condition 6) with an increase in the concentration of seed
crystals, leading to an increase in the gypsum deposition
rate. Also under high-pH conditions, similarly, the gypsum
30 deposition rate tends to increase with an increase in the
loading of seed crystals.
Condition 5 and Condition 7 are the same test
conditions, except for whether the used seed crystals are not
immersed or immersed in a scale inhibitor. Also under
54
Condition 7 where seed crystals have a scale inhibitor
previously adhering thereto, the degree of supersaturation is
199%, and it has been confirmed that gypsum is deposited at
the same level as under Condition 5. That is, the results
under Condition 5 and 7 show that 5 independent of the
immersion time of seed crystals in a calcium scale inhibitor,
when the pH is reduced to 4.0, the function of the scale
inhibitor is reduced.
Figs. 7 and 8 each show a microphotograph of gypsum
10 resulting from crystallization. Fig. 7 shows results under
Condition 5 (seed crystals added), and Fig. 8 shows results
under Condition 3 (no seed crystals added). Under Condition
5, gypsum having a larger size was deposited than under
Condition 3. Generally, the water content decreases with an
15 increase in the size of deposited gypsum. A low water content
leads to high-purity gypsum. When the average particle
diameter is 10 μm or more, preferably 20 μm or more, the
resulting gypsum has a sufficiently reduced water content.
The “average particle diameter” in the present invention is a
20 particle diameter measured by the method specified in JIS Z
8825 (laser diffractometry).
In Fig. 6, as a comparison with Condition 5 (pH 4.0),
under Condition 7 (pH 4.0), seed crystals pre-immersed in the
above calcium scale inhibitor were added to simulated water
25 having added thereto a calcium scale inhibitor, and sulfuric
acid was added for pH adjustment. Condition 5 and Condition 7
are otherwise the same, and gypsum deposition experiments
were performed under such conditions. Two hours after the pH
adjustment, the concentration of Ca in the simulated water
30 was measured by the same technique as in Fig. 3.
As a result, as shown in Fig. 6, the degree of
supersaturation was 199% or less both under Condition 5 and
Condition 7. From this, it can be said that independent of
the immersion time of seed crystals in a calcium scale
55
inhibitor, when the pH is reduced to 4.0, the function of the
calcium scale inhibitor is reduced.
In consideration of the effects of the calcium scale
inhibitor, the pH of the second concentrated water is
adjusted in the second pH adjusting step 5 to 6.0 or less,
preferably 5.5 or less, and more preferably 4.0 or less. In
particular, when the second concentrated water is adjusted to
pH 4.0 or less, the function of the calcium scale inhibitor
can be significantly reduced. By adjusting the pH of the
10 second concentrated water to such a value that the scale
inhibition function of the calcium scale inhibitor is
reduced, crystallization in the second crystallizing section
220a is promoted. According to the kind of scale inhibitor,
the pH range in the second pH adjusting step is suitably
15 determined.
With reference to Fig. 3, calcium carbonate dissolves in
water at pH 6.0 or less.
From the above, high-purity gypsum can be recovered in
the second crystallizing tank 221a of the second water
20 treatment section.

The second concentrated water in the second
crystallizing tanks 221a and 221b is transferred to the
second separating sections 280a and 280b. The second
25 concentrated water transferred here is water containing solid
matters deposited in the second crystallizing tanks 221a and
221b.
The second concentrated water discharged from the second
crystallizing tanks 221a and 221b contains gypsum having
30 various particle diameters deposited by crystallization, as
well as calcium carbonate deposited due to the exceeding of
the saturation concentration. Because the deposition of
calcium carbonate has taken place in the absence of seed
crystals, they have small diameters or are floating matters
56
in a colloidal form.
When the second concentrated water flows into the
classifiers 281a and 281b, gypsum having a predetermined
size, for example, gypsum having an average particle diameter
of 10 μm or more, sediments at the bottom 5 of the classifiers
281a and 281b, and gypsum having a small particle diameter,
calcium carbonate, and silica remain in the supernatant. The
gypsum sedimented at the bottom of the classifiers 281a and
281b is further dehydrated by the dehydrators 282a and 282b
10 and recovered. The supernatant containing gypsum having a
small particle diameter, calcium carbonate, and silica is fed
to the second precipitating sections 250a and 250b.
In the first example of this reference embodiment, seed
crystals are added to cause crystallization. Therefore,
15 gypsum having an average particle diameter of 10 μm or more
is mainly deposited, and the proportion of gypsum having a
small diameter is low. Through the second separating step,
gypsum having a low water content and containing no
impurities (i.e., high-purity gypsum) can be separated and
20 recovered with high recovery.
Some of the gypsum recovered in the second separating
sections 280a and 280b may be circulated through the seed
crystal tanks 223a and 223b as seed crystals.
In the case where the second separating section 280a is
25 not installed, gypsum precipitated at the bottom of the
second crystallizing tank 221a of the second crystallizing
section 220a is discharged from the second crystallizing tank
221a. The supernatant in the second crystallizing tank 221a
is fed to the second precipitating section 250a.
30
The supernatant (second concentrated water) in the
second crystallizing section 220a or the supernatant (second
concentrated water) discharged from the second separating
57
section 280a is fed to the second precipitating section 250a.
In the second precipitating section 250a, Ca(OH)2 and an
anionic polymer (Hishifloc H305) are loaded to the second
concentrated water after the crystallizing step, and the pH
in the second precipitating tank 251a is 5 controlled to 4 or
more and 12 or less, and preferably 8.5 or more and 12 or
less. In the second precipitating tank 251a, calcium
carbonate and a metal compound are precipitated and removed
from the second concentrated water. The precipitated calcium
10 carbonate and metal compound having low solubility in water
are discharged from the bottom of the second precipitating
tank 251a.
The water to be treated, which is the supernatant in the
second precipitating tank 251a, is discharged from the second
15 precipitating tank 251a. FeCl3 is added to the discharged
water to be treated, and solids in the water to be treated,
such as calcium carbonate and a metal compound, aggregate
with Fe(OH)3.
The water to be treated is fed to the second filtration
20 device 252a. The solids aggregated with Fe(OH)3 are removed
through the second filtration device 252a.
In the case where the treatment is performed in several
stages as shown in Fig. 10, the second concentrated water
that has passed through the second filtration device 252a of
25 the second water treatment section of the previous stage
flows into the water treatment section of the subsequent
stage as water to be treated. In the water treatment section
of the subsequent stage, the steps from the second scale
inhibitor supplying step to the second precipitating step
30 mentioned above are performed.

The second concentrated water that has passed through
the second precipitating section 250b located on the most
downstream of the water to be treated is treated in the
58
downstream side demineralizing section 60. The water that has
passed through the downstream side demineralizing section 60
is recovered as treated water. The concentrated water in the
downstream side demineralizing section 60 is discharged out
of the system. The installation of the 5 downstream side
demineralizing section 60 makes it possible to further
recover treated water from water that has been treated in a
water treatment section. Accordingly, the water recovery is
improved.
10 Also in the first example of this reference embodiment,
an evaporator (not shown) may be installed on the downstream
on the concentrated-water side of the downstream side
demineralizing section 60.
In the first example of the third reference embodiment,
15 in the case where the second concentrated water is adjusted
in the second pH adjusting step to a pH at which the function
of the calcium scale inhibitor is reduced, as a third pH
adjusting step, the pH of the second concentrated water may
be adjusted after the second crystallizing step in order for
20 the calcium scale inhibitor to exert its function.
Specifically, the pH is preferably adjusted to 4.0 or more,
preferably 5.5 or more, and more preferably 6.0 or more. The
third pH adjusting step is performed after the second
crystallizing step and before the second demineralizing step,
25 or after the second crystallizing step and before the
downstream side demineralizing step.
In the water treatment system 201 of the first example
this reference embodiment, ions are concentrated in the
second demineralizing section 210a. However, gypsum, calcium
30 carbonate, etc., have been removed in the second
crystallizing section 220a, the second precipitating section
250a, etc. Accordingly, the water flowing into the second
demineralizing section 210b or the downstream side
demineralizing section 60 has a smaller number of moles of
59
ions than before the treatment. Accordingly, the osmotic
pressure is low in the second demineralizing section 210b or
the downstream side demineralizing section 60 located
downstream, and the required power is reduced.
In the water treatment system 201 of 5 the first example
of this reference embodiment, in order to perform the third
pH adjusting step, a third pH adjusting section (not shown in
Fig. 10) having the same configuration as the second pH
adjusting section is installed between the second
10 crystallizing section and the second demineralizing section
immediately thereafter (in Fig. 10, between the second
crystallizing section 220a and the second demineralizing
sections 210b, particularly the second precipitating section
250a and the second demineralizing section 210b). In
15 addition, a third pH adjusting section (not shown in Fig. 10)
having the same configuration as the second pH adjusting
section is installed between the second precipitating section
250b and the downstream side demineralizing section 60 on the
most downstream. Accordingly, even in the case where the
20 second concentrated water is treated in the downstream side
demineralizing step, and the concentration of Ca ions is high
on the concentrated-water side, the formation of scales can
be suppressed by the function of the calcium scale inhibitor.
By using the water treatment system 201 of the first
25 example of the third reference embodiment, water to be
treated containing ions can be treated with high water
recovery.
In particular, in the first example of the third
reference embodiment, gypsum is mainly deposited in the
30 second crystallizing section 220. Accordingly, the gypsum
recovery in the second crystallizing section 220 is high, and
the number of moles of ions fed to the downstream side is
further reduced. In addition, the purity of the gypsum
recovered in the second crystallizing section 220 can be
60
increased.
Second Example of Third Reference Embodiment
Fig. 11 is a schematic diagram of a water treatment
system of the second example of the 5 third reference
embodiment of the present invention. The water treatment
system 200 of Fig. 11 is configured such that two water
treatment sections are connected in the flow direction of the
water to be treated. Depending on the properties of the water
10 to be treated, the number of water treatment sections may be
one, and it is also possible that three or more water
treatment sections are connected.
In the water treatment system 200 of the second example
of the third reference embodiment, each water treatment
15 section includes, from the upstream side of the water to be
treated, a second demineralizing section 210 (210a, 210b) and
a second crystallizing section 220 (220a, 220b). The
concentration sides of the second demineralizing sections
210a and 210b are connected to the second crystallizing
20 sections 220a and 220b, respectively. The water treatment
section includes a second scale inhibitor supplying section
230 (230a, 230b) in the flow path on the upstream side of
each second demineralizing section 210 (210a, 210b).
The second scale inhibitor supplying sections 230a and
25 230b are each made up of a tank 231 (231a, 231b), a valve V4
(V4a, V4b), and a control section 232 (232a, 232b). The
control sections 232a and 232b are connected to the valves
V4a and V4b, respectively. The tanks 231a and 231b of the
second scale inhibitor supplying sections 230a and 230b have
30 stored therein a scale inhibitor.
Scale inhibitors used in the second example of the third
reference embodiment are the calcium scale inhibitor
described in the first reference embodiment and a scale
inhibitor that inhibits the deposition of silica as scales in
61
the water to be treated (referred to as “silica scale
inhibitor”). Examples of silica scale inhibitors include
phosphonic-acid-based scale inhibitors, polycarboxylic-acidbased
scale inhibitors, and mixtures thereof. A specific
example is FLOCON260 (trade name, manufactured 5 by BWA).
Fig. 11 shows two tanks 231a. For example, a calcium
scale inhibitor is stored in one tank 231a, and a silica
scale inhibitor is stored in the other tank 231a.
In Fig. 11, the second demineralizing section 210 is a
10 reverse osmosis membrane device. In addition, the second
demineralizing section 210 may also be an electrodialyzer
(ED), an electro dialysis reversal device (EDR), an electro
de-ionization device (EDI), an ion-exchange equipment, a
capacitive de-ionization device (CDI), a nanofilters (NF), an
15 evaporator, etc.
Although only one second demineralizing section 210 is
shown in Fig. 11, the system may also be configured such that
two or more demineralizers are connected in parallel or in
series in the flow direction of the water to be treated.
20 The second crystallizing section 220 (220a, 220b) is
made up of a second crystallizing tank 221 (221a, 221b) and a
second seed crystal supplying section 222 (222a, 222b). The
second seed crystal supplying section 222 is connected to the
second crystallizing tank 221. The second seed crystal
25 supplying section 222 has a seed crystal tank 223 (223a,
223b), a valve V5 (V5a, V5b), and a control section 224
(224a, 224b). The control section 224 is connected to the
valve V5. The seed crystal tank 223 stores gypsum particles
as seed crystals.
30 In the water treatment system 200 of the second example
of the third reference embodiment, a second pH adjusting
section 240 (240a, 240b) may be installed between the second
demineralizing section 210 and the second crystallizing
section 220. The second pH adjusting section 240 is made up
62
of a tank 241 (241a, 241b), a valve V6 (V6a, V6b), a pH meter
243 (243a, 243b), and a control section 242 (242a, 242b). The
tank 241 has stored therein an acid as a pH adjuster. The
acid used may be hydrochloric acid, sulfuric acid, nitric
acid, or the like, for example. Sulfuric acid 5 is particularly
preferable because SO4
2- is removed as gypsum in the
crystallizing step, and thus the amount of ions that reach
the demineralizing section on the downstream side can be
reduced. The control section 242 is connected to the valve V6
10 and the pH meter 243. The pH meter 243 may be installed in
the flow path between the second demineralizing section 210
and the second crystallizing section 220 as shown in Fig. 11,
or may also be installed in the second crystallizing tank
221.
15 In the water treatment system 200, a precipitating tank
271 and a filtration device 272 are installed as a second
upstream side precipitating section 270 on the upstream side
of the second scale inhibitor supplying section 230a located
on the most upstream of the water to be treated. The second
20 upstream side precipitating section 270 has the same
configuration as the first upstream side precipitating
section 70. As in the first reference embodiment, two or more
stages of precipitating tanks 271 may be connected in series
in the flow direction of the water to be treated.
25 In the water treatment system 200, a second deaerating
section 273 may be provided on the upstream side of the
second upstream side precipitating section 270 as shown in
Fig. 11. The second deaerating section 273 has the same
configuration as the first deaerating section 73 of the first
30 reference embodiment.
The second deaerating section 273 may be installed on
the downstream side of the water to be treated of the second
upstream side precipitating section 270 and on the upstream
side of the second scale inhibitor supplying section 230a.
63
It is also possible that a deaerating section having the
same configuration as the second deaerating section 273 is
installed in the flow path between the second demineralizing
section 210a and the second crystallizing section 220a, in
the flow path between the second crystallizing 5 section 220
and the second precipitating section 250, and on the
downstream side of the second precipitating section 250 and
in the flow path between it and the second demineralizing
section 210b or the downstream side demineralizing section
10 60.
As in the first reference embodiment, an ion-exchange
equipment (not shown) may be installed on the downstream of
the filtration device 272 and on the upstream of the second
scale inhibitor supplying section 230a located on the most
15 upstream. In addition, depending on the concentration of
gypsum in the water to be treated, an upstream side
crystallizing section (not shown) having the same
configuration as the second crystallizing section may be
installed on the upstream of the second scale inhibitor
20 supplying section 230a on the most upstream.
In the second example of this reference embodiment, a
second separating section 280 (280a, 280b) may be installed
on the downstream side of the second crystallizing section
220 as shown in Fig. 11. The second separating section 280
25 has the same configuration as the first separating section
180 and includes a classifier 281 (281a, 281b) and a
dehydrator 282 (282a, 282b).
In the water treatment system 200 of Fig. 11, a second
precipitating section 250 (250a, 250b) may be installed on
30 the downstream side of the second crystallizing section 220.
The second precipitating section 250 has the same
configuration as the first precipitating section 50 and
includes a second precipitating tank 251 (251a, 251b) and a
second filtration device 252 (252a, 252b).
64
The water treatment system 200 includes a downstream
side demineralizing section 60 on the downstream side of the
water to be treated of the first water treatment section. An
evaporator (not shown in Fig. 11) may be installed on the
downstream on the concentrated-water side 5 of the downstream
side demineralizing section 60.
A process for treating water to be treated using the
water treatment system 200 of the second example of the third
reference embodiment will be described hereinafter.
10
The water to be treated is subjected to the pretreatment
described in the first reference embodiment.

In the same manner as in the first deaerating step
15 described in the first reference embodiment, CO2 in the water
to be treated is removed in the second deaerating section
273, whereby the concentration of carbonate ions in the water
to be treated is reduced.

20 In the second upstream side precipitating section 270,
some of Ca ions and carbonate ions are previously removed
from the water to be treated as calcium carbonate. In the
case where metal ions other than Ca ions are contained in the
water to be treated, in the second upstream side
25 precipitating section 270, some of a metal compound having
low solubility in water is previously removed from the water
to be treated.
The second upstream side precipitating step is performed
in the same manner as in the first upstream side
30 precipitating step.
In the case where water to be treated containing Mg ions
is treated in the water treatment system 200 of the second
example of this reference embodiment, as in the first
reference embodiment, the water to be treated is adjusted to
65
a pH at which a magnesium compound is deposited in the second
upstream side precipitating section 270, and some of Mg ions
in the water to be treated are removed. Subsequently, it is
preferable that the water to be treated is adjusted to a pH
at which the magnesium compound is soluble 5 on the downstream
side of the second upstream side precipitating section 270.
Specifically, the pH is adjusted to less than 10.
Accordingly, the formation of scales in devices and steps on
the downstream side, particularly the second demineralizing
10 section 210 and the second demineralizing step, can be
inhibited.
In the case where the second deaerating step is
performed after the second upstream side precipitating step,
the pH of the water to be treated is adjusted to a pH at
15 which carbonate ions can be present as CO2, specifically 6.5
or less.
Depending on the properties of the water to be treated,
the second deaerating step and the second upstream side
precipitating step may be omitted.
20 In the case where an ion-exchange membrane device is
installed, in the water treatment system 200 of the second
example of the third reference embodiment, Ca ions and Mg
ions in the water to be treated are removed by the ionexchange
membrane device.
25 In the case where an upstream side crystallizing section
is installed, the concentration of gypsum in the water to be
treated is reduced in the upstream side crystallizing section
through the same steps as in the first reference embodiment.

30 The control section 232a of the second scale inhibitor
supplying section 230a opens the valve V4a and supplies a
predetermined amount of calcium scale inhibitor to the water
to be treated from the tank 231a. The control section 232b of
the second scale inhibitor supplying section 230b opens the
66
valve V4b and supplies a predetermined amount of silica scale
inhibitor to the water to be treated from the tank 231b. The
control section 232a and the control section 232b adjust the
valve opening of the valve V4a and the valve V4b,
respectively, so that the concentrations of 5 the calcium scale
inhibitor and the silica scale inhibitor are

CLAIMS
1. A water treatment process comprising:
a scale inhibitor supplying step of supplying a
calcium scale inhibitor which is a scale inhibitor for
inhibiting the deposition of a scale 5 containing calcium
to water to be treated containing Ca ions, SO4 ions, and
carbonate ions;
a demineralizing step of separating the water to be
treated into concentrated water in which the Ca ions, the
10 SO4 ions, and the carbonate ions are concentrated and
treated water after the scale inhibitor supplying step;
a crystallizing step of supplying seed crystals of
gypsum to the concentrated water so that gypsum is
crystallized from the concentrated water;
15 a pH measuring step of measuring the pH of the
concentrated water in the crystallizing step; and
a supplied amount controlling step of reducing the
amount of the seed crystals of the gypsum to be supplied
when the measured pH falls within a pH range in which a
20 scale inhibiting function of the calcium scale inhibitor
is reduced, and increasing the amount of the seed
crystals of the gypsum to be supplied when the measured
pH is beyond the pH range.
2. The water treatment process according to claim 1,
25 comprising a separating step of separating the gypsum
from the concentrated water after the crystallizing step,
wherein the gypsum separated in the separating step is
used as seed crystals of the gypsum.
3. The water treatment process according to claim 1 or 2,
30 comprising a concentration measuring step of measuring at
least one of the concentration of the Ca ions and the
concentration of sulfate ions in the concentrated water
92
after the crystallizing step,
wherein the supplied amount controlling step is
intended to control the amount of the seed crystals of
the gypsum to be supplied according to at least one of
the concentration of the Ca ions and the 5 concentration of
sulfate ions measured in the concentration measuring
step.
4. A water treatment system, comprising:
10 a scale inhibitor supplying section that supplies a
calcium scale inhibitor which is a scale inhibitor for
inhibiting the deposition of a scale containing calcium
to water to be treated containing Ca ions, SO4 ions, and
carbonate ions;
15 a demineralizing section that is positioned on a
downstream side of the scale inhibitor supplying section
and separates the water to be treated into concentrated
water in which the Ca ions, the SO4 ions, and the
carbonate ions are concentrated and treated water;
20 a crystallizing section which is positioned on a
downstream side of the demineralizing section and which
includes a crystallizing tank that crystallizes gypsum
from the concentrated water and a seed crystal supplying
section that supplies seed crystals of gypsum to the
25 crystallizing tank;
a pH measuring section that measures the pH of the
concentrated water in the crystallizing tank; and
a controlling section that reduces the amount of
the seed crystals of the gypsum to be supplied when the
30 pH measured in the pH measuring section falls within a pH
range in which a scale inhibition function of the calcium
scale inhibitor is reduced, and increases the amount of
the seed crystals of the gypsum to be supplied when the
pH measured in the pH measuring section is beyond the pH
93
range.
5. The water treatment system according to claim 4,
comprising, on a downstream side of the crystallizing
section, a separating section that separates the gypsum
from the concentrated water, wherein 5 the separating
section separates the gypsum having a predetermined size,
followed by recovery.
6. The water treatment system according to claim 4 or 5,
comprising, on a downstream side of the crystallizing
10 section, a concentration measuring section that measures
at least one of the concentration of the Ca ions and the
concentration of sulfate ions in the concentrated water,
wherein the controlling section is intended to
control the amount of the seed crystals of the gypsum to
15 be supplied according to at least one of the
concentration of the Ca ions and the concentration of
sulfate ions measured in the concentration measuring
section.
20 7. A water treatment process comprising:
a first scale inhibitor supplying step of supplying
a calcium scale inhibitor which is a scale inhibitor for
inhibiting the deposition of a scale containing calcium
to water to be treated containing Ca ions, SO4 ions,
25 carbonate ions and silica;
a first pH adjusting step of adjusting the water to
be treated to a pH at which the silica is soluble in the
water to be treated;
a first demineralizing step of separating the water
30 to be treated into first concentrated water in which the
Ca ions, the SO4 ions, the carbonate ions and the silica
are concentrated and treated water after the first scale
94
inhibitor supplying step and the first pH adjusting step;
a first crystallizing step of supplying seed
crystals of gypsum to the first concentrated water so
that gypsum is crystallized from the first concentrated
5 water;
a first pH measuring step of measuring the pH of
the first concentrated water in the first crystallizing
step; and
a first supplied amount controlling step of
10 reducing the amount of the seed crystals of the gypsum to
be supplied when the measured pH falls within a pH range
in which a scale inhibiting function of the calcium scale
inhibitor is reduced, and increasing the amount of the
seed crystals of the gypsum to be supplied when the
15 measured pH is beyond the pH range.
8. The water treatment process according to claim 7,
comprising, after the first crystallizing step:
a second scale inhibitor supplying step of
20 supplying the calcium scale inhibitor and a silica scale
inhibitor which is a scale inhibitor for inhibiting the
deposition of the silica to the water to be treated;
a second demineralizing step of separating the
water to be treated into second concentrated water in
25 which the Ca ions, the SO4 ions, the carbonate ions and
the silica are concentrated and treated water after the
second scale inhibitor supplying step; and
a second crystallizing step of supplying seed
crystals of gypsum to the second concentrated water so
30 that gypsum is crystallized from the second concentrated
water.
9. The water treatment process according to claim 7,
comprising a first separating step of separating the
gypsum from the first concentrated water after the first
95
crystallizing step, wherein the gypsum separated in the
first separating step is used as seed crystals of the
gypsum.
10. The water treatment process according 5 to claim 7 or 9,
comprising a first concentration measuring step of
measuring at least one of the concentration of the Ca
ions and the concentration of sulfate ions in the first
concentrated water after the first crystallizing step,
10 wherein the first supplied amount controlling step
is intended to control the amount of the seed crystals of
the gypsum to be supplied according to at least one of
the concentration of the Ca ions and the concentration of
sulfate ions measured in the first concentration
15 measuring step.
11. The water treatment process according to claim 8,
comprising:
a second pH measuring step of measuring the pH of
20 the second concentrated water in the second crystallizing
step; and
a second supplied amount controlling step of
reducing the amount of the seed crystals of the gypsum to
be supplied when the measured pH falls within a pH range
25 in which a scale inhibition function of the calcium scale
inhibitor is reduced, and increasing the amount of the
seed crystals of the gypsum to be supplied when the
measured pH is beyond the pH range.
30 12. The water treatment process according to claim 11,
comprising a second separating step of separating the
gypsum from the second concentrated water after the
second crystallizing step, wherein the gypsum separated
in the second separating step is used as seed crystals of
96
the gypsum.
13. The water treatment process according to claim 11 or 12,
comprising a second concentration measuring step of
measuring at least one of the concentration 5 of the Ca
ions and the concentration of sulfate ions in the second
concentrated water after the second crystallizing step,
wherein the second supplied amount controlling step
is intended to control the amount of the seed crystals to
10 be supplied according to at least one of the
concentration of the Ca ions and the concentration of
sulfate ions measured in the second concentration
measuring step.
15 14. The water treatment process according to claim 8,
comprising a third pH adjusting step of adjusting the
second concentrated water to a pH at which calcium
carbonate is soluble,
wherein in the second crystallizing step, the
20 gypsum separated in the first separating step is supplied
into the second concentrated water after the adjustment
of the pH in the third pH adjusting step.
15. A water treatment process, comprising:
25 a second scale inhibitor supplying step of
supplying a calcium scale inhibitor which is a scale
inhibitor for inhibiting the deposition of a scale
containing calcium and a silica scale inhibitor which is
a scale inhibitor for inhibiting the deposition of silica
30 to water to be treated containing Ca ions, SO4 ions,
carbonate ions and silica;
a second demineralizing step of separating the
water to be treated into second concentrated water in
which the Ca ions, the SO4 ions, the carbonate ions and
97
the silica are concentrated and treated water after the
second scale inhibitor supplying step;
a second crystallizing step of supplying seed
crystals of gypsum to the second concentrated water so
that gypsum is crystallized from the second 5 concentrated
water;
a second pH measuring step of measuring the pH of
the second concentrated water in the second crystallizing
step; and
10 a second supplied amount controlling step of
reducing the amount of the seed crystals of the gypsum to
be supplied when the measured pH falls within a pH range
in which a scale inhibiting function of the calcium scale
inhibitor is reduced, and increasing the amount of the
15 seed crystals of the gypsum to be supplied when the
measured pH is beyond the pH range.
16. The water treatment process according to claim 15,
comprising, after the second crystallizing step:
20 a first scale inhibitor supplying step of supplying
the calcium scale inhibitor to the water to be treated;
a first pH adjusting step of adjusting the water to
be treated to a pH at which the silica is soluble in the
water to be treated;
25 a first demineralizing step of separating the water
to be treated into first concentrated water in which the
Ca ions, the SO4 ions, the carbonate ions and the silica
are concentrated and treated water after the first scale
inhibitor supplying step and the first pH adjusting step;
30 and
a first crystallizing step of supplying seed
crystals of gypsum to the first concentrated water so
that gypsum is crystallized from the first concentrated
water.
98
17. The water treatment process according to 1. A water treatment process comprising 15,
comprising a second separating step of separating the
gypsum from the second concentrated water after the
second crystallizing step, wherein the gypsum separated
in the second separating step is used as 5 seed crystals of
the gypsum.
18. The water treatment process according to claim 15 or 17,
comprising a second concentration measuring step of
10 measuring at least one of the concentration of the Ca
ions and the concentration of sulfate ions in the second
concentrated water after the second crystallizing step,
wherein the second supplied amount controlling step
is intended to control the amount of the seed crystals of
15 the gypsum to be supplied according to at least one of
the concentration of the Ca ions and the concentration of
sulfate ions measured in the second concentration
measuring step.
20 19. The water treatment process according to claim 16,
comprising:
a first pH measuring step of measuring the pH of
the first concentrated water in the first crystallizing
step; and
25 a first supplied amount controlling step of
reducing the amount of the seed crystals of the gypsum to
be supplied when the measured pH falls within a pH range
in which a scale inhibition function of the calcium scale
inhibitor is reduced, and increasing the amount of the
30 seed crystals of the gypsum to be supplied when the
measured pH is beyond the pH range.
20. The water treatment process according to claim 19,
comprising a first separating step of separating the
99
gypsum from the first concentrated water after the first
crystallizing step, wherein the gypsum separated in the
first separating step is used as seed crystals of the
gypsum.
5
21. The water treatment process according to claim 19 or 20,
comprising a first concentration measuring step of
measuring at least one of the concentration of the Ca
ions and the concentration of sulfate ions in the first
10 concentrated water after the first crystallizing step,
wherein the first supplied amount controlling step
is intended to control the amount of the seed crystals of
the gypsum to be supplied according to at least one of
the concentration of the Ca ions and the concentration of
15 sulfate ions measured in the first concentration
measuring step.
22. The water treatment process according to claim 20,
comprising a third pH adjusting step of adjusting the
20 second concentrated water to a pH at which calcium
carbonate is soluble,
wherein in the second crystallizing step, the
gypsum separated in the first separating step is supplied
into the second concentrated water after the adjustment
25 of the pH in the third pH adjusting step.
23. A water treatment system comprising:
a first scale inhibitor supplying section that
supplies a calcium scale inhibitor which is a scale
30 inhibitor for inhibiting the deposition of a scale
containing calcium to water to be treated containing Ca
ions, SO4 ions, carbonate ions and silica;
a first pH adjusting section that supplies a pH
adjuster to the water to be treated to adjust the pH of
100
the water to be treated to such a value that the silica
is soluble in the water to be treated;
a first demineralizing section that is positioned
on a downstream side of the first scale inhibitor
supplying section and the first pH adjusting 5 section and
separates the water to be treated into first concentrated
water in which the Ca ions, the SO4 ions, the carbonate
ions and the silica are concentrated and treated water;
a first crystallizing section which is positioned
10 on a downstream side of the first demineralizing section
and which includes a first crystallizing tank that
crystallizes gypsum from the first concentrated water and
a first seed crystal supplying section that supplies seed
crystals of gypsum to the first crystallizing tank;
15 a first pH measuring section that measures the pH
of the first concentrated water in the first
crystallizing tank; and
a first controlling section that reduces the amount
of the seed crystals of the gypsum to be supplied when
20 the pH measured in the first pH measuring section falls
within a pH range in which a scale inhibition function of
the calcium scale inhibitor is reduced, and increases the
amount of the seed crystals of the gypsum to be supplied
when the pH measured in the first pH measuring section is
25 beyond the pH range.
24. The water treatment system according to claim 23,
comprising, on a downstream side of the first
crystallizing section with respect to the water to be
30 treated:
a second scale inhibitor supplying section that
supplies the calcium scale inhibitor and a silica scale
inhibitor which is a scale inhibitor for inhibiting the
deposition of silica to the water to be treated;
101
a second demineralizing section that is positioned
on a downstream side of the second scale inhibitor
supplying section and separates the water to be treated
into second concentrated water in which the Ca ions, the
SO4 ions, the carbonate ions 5 and the silica are
concentrated and treated water; and
a second crystallizing section which is positioned
on a downstream side of the second demineralizing section
and which includes a second crystallizing tank and
10 crystallizes gypsum from the second concentrated water
and a second seed crystal supplying section that supplies
seed crystals of gypsum to the second crystallizing tank.
25. The water treatment system according to claim 23,
15 comprising, on a downstream side of the first
crystallizing section, a first separating section that
separates the gypsum from the first concentrated water,
wherein the gypsum separated in the first separating
section is used as seed crystals of the gypsum.
20
26. The water treatment system according to claim 23 or 25,
comprising, on a downstream side of the first
crystallizing section, a first concentration measuring
section that measures at least one of the concentration
25 of the Ca ions and the concentration of sulfate ions in
the first concentrated water,
wherein the first controlling section is intended
to control the amount of the seed crystals of the gypsum
to be supplied according to at least one of the
30 concentration of the Ca ions and the concentration of
sulfate ions measured in the first concentration
measuring section.
27. The water treatment system according to claim 24,
102
comprising:
a second pH measuring section that measures the pH
of the second concentrated water in the second
crystallizing tank; and
a second controlling section 5 that reduces the
amount of the seed crystals of the gypsum to be supplied
when the pH measured in the second pH measuring section
falls within a pH range in which a scale inhibition
function of the calcium scale inhibitor is reduced, and
10 increases the amount of the seed crystals of the gypsum
to be supplied when the pH measured in the second pH
measuring section is beyond the pH range.
28. The water treatment system according to claim 27,
15 comprising, on a downstream side of the second
crystallizing section, a second separating section that
separates the gypsum from the second concentrated water,
wherein the gypsum separated in the second separating
section is used as seed crystals of the gypsum.
20
29. The water treatment system according to claim 27 or 28,
comprising, on a downstream side of the second
crystallizing section, a second concentration measuring
section that measures at least one of the concentration
25 of the Ca ions and the concentration of sulfate ions in
the second concentrated water,
wherein the second controlling section is intended
to control the amount of the seed crystals of the gypsum
to be supplied according to at least one of the
30 concentration of the Ca ions and the concentration of
sulfate ions measured in the second concentration
measuring section.
30. The water treatment system according to claim 25, wherein
103
the second pH adjusting section adjusts the second
concentrated water to a pH at which calcium carbonate is
soluble, and supplies the gypsum separated in the first
separating section to the second crystallizing section.
5
31. A water treatment system, comprising:
a second scale inhibitor supplying section that
supplies a calcium scale inhibitor which is a scale
inhibitor for inhibiting the deposition of a scale
10 containing calcium and a silica scale inhibitor which is
a scale inhibitor for inhibiting the deposition of silica
to water to be treated containing Ca ions, SO4 ions,
carbonate ions and silica;
a second demineralizing section that is positioned
15 on a downstream side of the second scale inhibitor
supplying section and separates the water to be treated
into second concentrated water in which the Ca ions, the
SO4 ions, the carbonate ions and the silica are
concentrated and treated water;
20 a second crystallizing section which is positioned
on a downstream side of the second demineralizing section
and which includes a second crystallizing tank that
crystallizes gypsum from the second concentrated water
and a second seed crystal supplying section that supplies
25 seed crystals of gypsum to the second crystallizing tank;
a second pH measuring section that measures the pH
of the second concentrated water in the second
crystallizing tank; and
a second controlling section that reduces the
30 amount of the seed crystals of the gypsum to be supplied
when the pH measured in the second pH measuring section
falls within a pH range in which a scale inhibition
function of the calcium scale inhibitor is reduced, and
increases the amount of the seed crystals of the gypsum
104
to be supplied when the pH measured in the second pH
measuring section is beyond the pH range.
32. The water treatment system according to claim 31,
comprising, on a downstream side 5 of the water to be
treated in the second crystallizing section:
a first scale inhibitor supplying section that
supplies the calcium scale inhibitor to the water to be
treated;
10 a first pH adjusting section that supplies a pH
adjuster to the water to be treated to adjust the pH of
the water to be treated to such a value that the silica
is soluble in the water to be treated;
a first demineralizing section that is positioned
15 on a downstream side of the first scale inhibitor
supplying section and the first pH adjusting section and
separates the water to be treated into first concentrated
water in which the Ca ions, the SO4 ions, the carbonate
ions and the silica are concentrated and treated water;
20 and
a first crystallizing section which is positioned
on a downstream side of the first demineralizing section
and which includes a first crystallizing tank that
crystallizes gypsum from the first concentrated water and
25 a first seed crystal supplying section that supplies seed
crystals of gypsum to the first crystallizing tank.
33. The water treatment system according to claim 31,
comprising, on a downstream side of the second
30 crystallizing section, a second separating section that
separates the gypsum from the second concentrated water,
wherein the gypsum separated in the second separating
section is used as seed crystals of the gypsum.
105
34. The water treatment system according to claim 31 or 33,
comprising, on a downstream side of the second
crystallizing section, a second concentration measuring
section that measures at least one of the concentration
of the Ca ions and the concentration 5 of sulfate ions in
the second concentrated water,
wherein the second controlling section is intended
to control the amount of the seed crystals of the gypsum
to be supplied according to at least one of the
10 concentration of the Ca ions and the concentration of
sulfate ions measured in the second concentration
measuring section.
35. The water treatment system according to claim 32,
15 comprising:
a first pH measuring section that measures the pH
of the first concentrated water in the first
crystallizing tank; and
a first controlling section that reduces the amount
20 of the seed crystals of the gypsum to be supplied when
the pH measured in the first pH measuring section falls
within a pH range in which a scale inhibition function of
the calcium scale inhibitor is reduced, and increases the
amount of the seed crystals of the gypsum to be supplied
25 when the pH measured in the first pH measuring section is
beyond the pH range.
36. The water treatment system according to claim 35,
comprising, on a downstream side of the first
30 crystallizing section, a first separating section that
separates the gypsum from the first concentrated water,
wherein the gypsum separated in the first separating
section is used as seed crystals of the gypsum.
37. The water treatment system according to claim 35 or 36,
comprising, on a downstream side of the first
crystallizing section, a first concentration measuring
section that measures at least one of the concentration
5 of the Ca ions and the concentration of sulfate ions in
the first concentrated water,
wherein the first controlling section is intended
to control the amount of the seed crystals of the gypsum
to be supplied according to at least one of the
10 concentration of the Ca ions and the concentration of
sulfate ions measured in the first concentration
measuring section.
38. The water treatment system according to claim 36, wherein
15 the second pH adjusting section adjusts the second
concentrated water to a pH at which calcium carbonate is
soluble, and supplies the gypsum separated in the first
separating section to the second crystallizing section.