DESCRIPTION
TITLE OF THE INVENTION:
FRESH WATER PRODUCTION PROCESS
5
TECHNICAL FIELD
[0001]
The present invention relates to a fresh water production method using a
semipermeable membrane unit for the purpose of producing fresh water from a plurality
10 of kinds of raw water such as a combination of seawater with river water, industrial
wastewater, sewage wastewater or treated water thereof.
BACKGROUND ART
[0002]
15 With water-environment deterioration which is recently becoming serious, a
water treatment technology becomes important as before and a separation membraneutilizing
technology has been very widely applied.
[0003]
Separation membranes for use in water treatment are roughly classified into
20 a microfiltration membrane that achieves separation with fme pores of the order of
submicrometer, an ultrafiltration membrane with smaller ones, a nanofiltration
membrane capable of nano-order separation, and a reverse osmosis membrane capable
of subnano-order separation. Of these, a nanofiltration membrane having small fine
pores and a reverse osmosis membrane are called semipermeable membranes and are
25 classified as membranes through which water permeates but a solute does not permeate.
In particular, the reverse osmosis membrane is especially widely applied as a
technology capable of obtaining fresh water, which is suitable for drinking water, from
seawater or brackish water.
[0004]
Although fresh water production by means of a semipermeable membrane
5 using seawater as raw water is energetically superior to an evaporation process, the
production uses a high-pressure process resulting from high osmotic pressure of
seawater, so that high energy is required as compared with a clean water production
process using river water as raw water. Recently, there has been proposed a system in
which osmotic pressure is lowered by mixing seawater with water having lower salt
10 concentration than that of seawater, such as river water, industrial wastewater, or
sewage wastewater for diluting the seawater to decrease an energy cost (see Patent
Document 1 ). Moreover, there are cases where concentrated drainage discharged by a
process where industrial wastewater or sewage wastewater is subjected to purification
treatment, recycled with a semipermeable membrane, and reused is used as diluting
15 water (see Patent Documents 2 to 6).
[0005]
Generally, in the case where river water, industrial wastewater, or sewage
wastewater is subjected to semipermeable membrane treatment, the water is fed to a
semipermeable membrane after removing suspended substances by pre-treatment but,
20 BOD (Biological Oxygen Demand) components, COD (Chemical Oxygen Demand)
components, and organic substance components such as polymeric polysaccharides and
chlorophyll, and microorganism components are not efficiently removed by the pretreatment
in many cases. Accordingly, in a system in which diluted seawater obtained
by mixing with river water, industrial wastewater, sewage wastewater, or concentrated
25 drainage thereof containing much organic substance components and microorganism
components is subjected to semipermeable membrane treatment, as compared with
seawater, it has become a problem that microorganisms are prone to proliferate on the
surface of the semipermeable membrane and the performance of the semipermeable
membrane decreases through the generation ofbiofouling.
[0006]
5 Furthermore, the organic substance components and microorganism
components in the river water, industrial wastewater, and sewage wastewater to be used
as diluting water vary depending on rainfalls and seasons when the water is river water,
vary depending on time zones and seasons when the water is sewage wastewater, vary
depending on production quantities, production processes, and the like when the water
10 is industrial wastewater, so that it has also become a problem that fouling of the
semipermeable membrane becomes remarkable when seawater mixed with diluting
water collected during a period when much organic substance components and
microorganism components are present. In particular, in the case where semipermeable
membrane-concentrate derived from river water, industrial wastewater, and sewage
15 wastewater is used as diluting water, the organic substance components and
20
microorganism components are concentrated and the fouling of the semipermeable
membrane that separates the diluted seawater into permeate and concentrate becomes
more remarkable, so that the case has been problematic.
[0007]
Moreover, in the semipermeable membrane treatment of the river water,
industrial wastewater, and sewage wastewater, in order to prevent the proliferation of
microorganisms on the semipermeable membrane surface, when a bactericide is added
intermittently or continuously during operation as described in Non-Patent Documents 1
and 2, flushing washing in which the semipermeable membrane surface is periodically
25 washed with a water flow is performed as described in Patent Document 7, or
backwashing in which the semipermeable membrane surface is washed by allowing a
washing liquid to flow in a direction opposite to the direction of a raw water inflow at
water production is . performed as described in Patent Document 8, the fouling
containing the organic substance components and microorganism components exfoliates
from the semipermeable membrane surface into the semipermeable membrane-
5 concentrate and the fouling of the semipermeable membrane that separates the diluted
seawater into the permeate and the concentrate becomes more remarkable, so that the
cases have been seriously problematic.
BACKGROUND ART DOCUMENT
I 0 PATENT DOCUMENT
[0008]
Patent Document 1: W02011/114967
Patent Document 2: JP-A-2010-207805
Patent Document 3: JP-A-2012-16695
15 Patent Document 4: JP-A-2012-16696
Patent Document 5: JP-A-2010-149100
Patent Document 6: JP~A-2010-149123
Patent Document 7: Japanese Patent No. 4472050
Patent Document 8: JP-A-2012-139614
20 NON-PATENT DOCUMENT
[0009]
Non-Patent Document 1: Takuhei Kimura et al., "Innovative Biofouling
Prevention on Seawater Desalination Reverse Osmosis Membrane," Proceedings of
IDA World Congress, BAH01-048 (2001).
Non-Patent Document 2: Katariina Majamaa et al., "Field Trial to Optimize
the Use ofDBNPA in WRU Application," Proceedings ofiDA World Congress, DB09-
076 (2009).
5 SUMMARY OF THE INVENTION
PROBLEMS THAT THE INVENTION IS TO SOLVE
[0010]
An object of the present invention is, in the fresh water production method
using a semipermeable membrane unit for the purpose of producing fresh water from a
10 plurality of kinds of raw water such as a combination of seawater with river water,
industrial wastewater, sewage wastewater or treated water thereof, to efficiently prevent
a semipermeable membrane from fouling due to organic substances and/or
microorganisms contained in the river water, industrial wastewater, sewage wastewater
or treated water thereof for diluting the seawater.
15
MEANS FOR SOLVING THE PROBLEMS
[0011]
In order to solve the problems described above, the present invention has
the following constitutions (1) to (16).
20 (1) A method for producing fresh water in which water to be treated A is
treated in a first semipermeable membrane unit to produce fresh water, first concentrate
Ac generated during the treatment in the first semipermeable membrane unit is mixed
with water to be treated B having a solute concentration higher than that of the frrst
concentrate Ac, and the mixed water is treated in a second semipermeable membrane
25 unit to produce fresh water,
the method including:
5
an organic substance/microorganism removal line in which the first
concentrate Ac is allowed to pass through an organic substance/microorganism removal
unit to reduce organic substance concentration or microorganism concentration of the
first concentrate Ac and is mixed with the water to be treated B; and
a bypass line in which the first concentrate Ac is mixed with the water to be
treated B without via the organic substance/microorganism removal unit,
in which a flow volume of the first concentrate Ac to the organic
substance/microorganism removal unit is controlled according to at least one of: the
organic substance concentration or microorganism concentration in the first concentrate
10 Ac on an upstream side of the organic substance/microorganism removal unit; and a
change in a differential pressure between an inflow side and a non-permeation side of
the first semipermeable membrane unit, the differential pressure being calculated by
15
subtracting a pressure of the first concentrate Ac from a pressure of feed water of the
first semipermeable membrane unit.
(2) The method for producing fresh water according to ( 1 ), in which the flow
volume of the first concentrate Acto the organic substance/microorganism removal unit
is controlled according to the change in the differential pressure when the change in the
differential pressure between the inflow side and the non-permeation side of the first
semipermeable membrane unit exceeds a predetermined value, and the flow volume of
20 the first concentrate Ac to the organic substance/microorganism removal unit is
controlled according to the organic substance concentration or microorganism
concentration in the first concentrate Ac when the change in the differential pressure
between the inflow side and the non-permeation side of the first semipermeable
membrane unit is lower than or equal to the predetermined value.
(3) The method for producing fresh water according to (1) or (2), in which the
water to be treated A is treated in a pre-treatment unit before the treatment in the first
semipermeable membrane unit.
(4) The method for producing fresh water according to (3), in which a
5 treatment process that constitutes . the organic substance/microorganism removal unit
includes at least one treatment process different from a treatment process that
constitutes the pre-treatment unit for the water to be treated A.
( 5) The method for producing fresh water according to any one of (1) to ( 4 ), in
which a fine bubble generation unit capable of generating fme bubbles by reducing a
10 pressure of the first concentrate Ac is provided on the upstream side of the organic
substance/microorganism removal unit, and fme bubbles are generated in the first
concentrate Ac.
( 6) The method for producing fresh water according to any one of ( 1) to ( 5), in
which the organic substance/microorganism removal unit is a pressure filtration unit for
15 performing separation utilizing a water pressure ofthe first concentrate Ac.
(7) The method for producing fresh water according to any one of (1) to ( 6), in
which a filtration material whose material is the same as that of a filtration material of
the second semipermeable membrane unit is used as a filtration material of the organic
substance/microorganism removal unit.
20 (8) The method for producing fresh water according to any one of (1) to (7), in
which treated drainage from the organic substance/microorganism removal unit is
mixed with concentrate from the second semipermeable membrane unit, followed by
being discharged from the system.
(9) A method for producing fresh water in which water to be treated A is mixed
25 with water to be treated B having a solute concentration higher than that of the water to
be treated A and the mixed water is treated m a semipermeable membrane unit to
produce fresh water,
the method including:
an organic substance/microorganism removal line in which the water to be
5 treated A is allowed to pass through an organic substance/microorganism removal unit
to reduce organic substance concentration or microorganism concentration of the water
to be treated A and is mixed with the water to be treated B; and
a bypass line in which the water to be treated A is mixed with the water to
be treated B without via the organic substance/microorganism removal unit,
10 in which a flow volume of the water to be treated A to the organic
substance/microorganism removal unit is controlled according to the organic substance
concentration or microorganism concentration of the water to be treated A on an
upstream side of the organic substance/microorganism removal unit.
(10) The method for producing fresh water according to (9), in which the water
15 to be treated A is treated in a pre-treatment unit before mixed with the water to be
treated B.
(11) The method for producing fresh water according to (1 0), in which a
treatment process that constitutes the organic substance/microorganism removal unit
includes at least one treatment process different from a treatment process that
20 constitutes the pre-treatment unit for the water to be treated A.
(12) The method for producing fresh water according to any one of (9) to (11),
in which a filtration material whose material is the same as that of a filtration material
of the semipermeable membrane unit is used as a filtration material of the organic
substance/microorganism removal unit.
25 (13) The method for producing fresh water according to any one of (9) to (12),
in which treated drainage from the organic substance/microorganism removal unit is
mixed with concentrate from the semipermeable membrane unit, followed by being
discharged from the system.
(14) The method for producing fresh water according to any one of (l) to (13),
in which the organic substance concentration or microorganism concentration includes
5 at least one selected from the group consisting of total organic carbon concentration
(TOC), assimilative organic carbon (AOC), dissolved organic carbon concentration
(DOC), chemical oxygen demand (COD), biological oxygen demand (BOD), ultraviolet
absorbance (UV), transparent extracellular polymer particle (TEP), adenosine
triphosphate (A TP), bacteria count, and chlorophyll.
10 (15) The method for producing fresh water according to any one of (1) to (14),
in which the organic substance/microorganism removal unit includes at least one
selected from the group consisting of floatation separation, sedimentation separation,
lagoon process, sand filtration, microfiltration, ultrafiltration, nanofiltration,
flocculation treatment, oxidation treatment, and adsorption treatment.
15 ( 16) The method for producing fresh water according to any one of ( 1) to ( 15),
in which the organic substance/microorganism removal unit is also used as a pretreatment
unit for the water to be treated B.
ADVANTAGE OF THE INVENTION
20 [0012]
According to the fresh water production apparatus of the invention, at the
time of producing fresh water from a plurality of kinds of raw water such as a
combination of seawater with river water, industrial wastewater, sewage wastewater or
treated water thereof, it becomes possible to prevent a semipermeable membrane for
25 treating mixed water from fouling due to organic substances and/or microorganisms
contained in the river water, industrial wastewater, sewage wastewater or treated water
thereof
BRIEF DESCRIPTION OF THE DRAWINGS
5 [0013]
[Fig. 1] Fig. 1 is a flow chart showing one example of an embodiment of
the method for producing fresh water according to the invention.
[Fig. 2] Fig. 2 is a flow chart showing one example of another embodiment
ofthe method for producing fresh water according to the invention.
10 [Fig. 3] Fig. 3 is a flow chart showing one example of still another
embodiment of the method for producing fresh water according to the invention.
[Fig. 4] Fig. 4 is a flow chart showing one example of further another
embodiment of the method for producing fresh water according to the invention.
[Fig. 5] Fig. 5 is a flow chart showing one example of still another
15 embodiment of the method for producing fresh water according to the invention.
[Fig. 6] Fig. 6 is a flow chart showing one example of further another
embodiment of the method for producing fresh water according to the invention.
[Fig. 7] Fig. 7 is a flow chart showing one example of still another
embodiment of the method for producing fresh water according to the invention.
20 [Fig. 8] Fig. 8 is a flow chart showing one example of further another
embodiment of the method for producing fresh water according to the invention.
MODE FOR CARRYING OUT THE INVENTION
[00 14]
5
The embodiments of the present invention will be explained below with
reference to the drawings but the invention should not be construed as being limited to
the following embodiments shown in the drawings.
[00 15]
Fig. 1 is a flow chart showing one example of an embodiment of the
method for producing :fresh water according to the invention. Water to be treated A is
stored in a water-to-be-treated-A tank 1 and thereafter is fed to a first pre-treatment unit
3 by means of a water-to-be-treated-A feed pump 2. After subjected to pre-treatment
such as suspended substance removal, the water is temporarily stored in a first prel
0 treated water tank 4 and then is treated in a first semipermeable membrane unit 6 by
means of a first booster pump 5. In the first semipermeable membrane unit 6, the
semipermeable membrane-treated water resulting from the pre-treatment ofthe water to
be treated A is separated into a permeated component (permeate) and a non-permeated
component (concentrate), and the permeate (hereinafter sometimes referred to as "first
15 permeate Ap") is stored as fresh water in a first permeate tank 7. On the other hand, the
concentrate (hereinafter referred to as "first concentrate Ac") discharged from the first
semipermeable membrane unit 6 is temporarily stored in a first concentrate tank 9
having a water quality sensor 8a.
[0016]
20 In the method for producing fresh water of the invention, the flow volume
of the first concentrate Ac to an organic substance/microorganism removal unit 12 is
controlled according to a detected value on the water quality sensor 8a. As means for
controlling the flow volume of the first concentrate Ac, a first concentrate feed valve
lOa and a second concentrate feed valve 1 Ob may be exemplified. By adjusting
25 opening/closing degrees of the first concentrate feed valve 1 Oa and the second
concentrate feed valve 1 Ob, the flow volume of the first concentrate Ac flowing through
the organic substance/microorganism removal unit 12 by means of a first concentrate
pump 1 1 and the flow volume thereof flowing through a bypass line 13 that bypasses
the organic substance/microorganism removal unit 12 are controlled. The whole
volume of the first concentrate Ac may flow through the bypass line 13 or may be
5 allowed to pass through the organic substance/microorganism removal unit 12 and
treated therein. In the invention, the flow volumes of the first concentrate Ac to the
organic substance/microorganism removal unit 12 and the bypass line 13 are controlled
according to the detected value on the water quality sensor 8a and/or a change in the
differential pressure between the inflow side and the non-permeation side of the first
1 0 semipermeable membrane unit 6 determined by means of a pressure sensor 21 to be
mentioned later.
[00 17]
The first concentrate Ac passing through the organic
substance/microorganism removal unit 12 and the first concentrate Ac passing through
15 the bypass line 13 join on the downstream side of the organic substance/microorganism
removal unit 12 and are temporarily stored in a mixed water tank 14 for mixing with
water to be treated B.
[00 18]
Incidentally, the water to be treated B is stored in a water-to-be-treated-B
20 tank 15 and thereafter is fed to a second pre-treatment unit 1 7 by means of a water-tobe-
treated-B feed pump 16. After subjected to pre-treatment such as suspended
substance removal, the water is fed to the mixed water tank 14. The mixed water
including the first concentrate Ac and the water to be treated B in the mixed water tank
14 was pressurized by a second booster pump 18 and then is treated in a second
25 semipermeable membrane unit 19, and the permeate (hereinafter sometimes referred to
as "second permeate Bp") from the second semipermeable membrane unit 19 is stored
in a second permeate tank 20. Incidentally, the permeate in the first permeate tank 7
and the permeate in the second permeate tank 20 are used after pH, Langelier's index,
bactericide concentration, and mineral concentration are appropriately adjusted as
needed.
5 [0019]
The water to be treated A and water to be treated B which are objects to be
treated in the method for producing fresh water of the invention are not particularly
limited as long as they are different in the concentration of a solute that influences
osmotic pressure. For example, seawater and concentrated seawater which have high
10 concentration, and river water, ground water, sewage wastewater, industrial wastewater
and treated water thereof having lower concentration than that of seawater can be used.
As the treated water, filtrate and concentrate are exemplified. As exemplified in Fig. 1,
when the first concentrate Ac obtained by treating the water to be treated A in the
semipermeable membrane unit is used as diluting water, concentrated drainage that is
15 usually discharged from the system can be effectively utilized, so that the case is
effective. On the other hand, as exemplified in Fig. 2 and Fig. 3, when the water to be
treated A (e.g., sewage wastewater) having low concentration without treating in the
semipermeable membrane unit is used as diluting water for the water to be treated B
(e.g., seawater) having high concentration, diluted seawater can be easily prepared with
20 suppressing capital investment, so that the case is preferred. As for specific methods for
controlling the flow volume in Fig. 2 and Fig. 3, in the example of Fig. 2, the water to
be treated A is treated in the first pre-treatment unit 3 and, based on the detected value
ofthe resulting pre-treated water on the water quality sensor 8a, the water is fed to the
mixed water tank 14 via the organic substance/microorganism removal unit 12 and/or
25 the bypass line 13 and can be mixed with the water to be treated B. Moreover, in the
example of Fig. 3, the water quality of the water to be treated A is detected on the water
quality sensor 8c and, based on the resulting detected value, the water is fed to the
mixed water tank 14 via the organic substance/microorganism removal unit 12 and/or
the bypass line 13 and can be mixed with the water to be treated B. In both cases,
according to the detected value on the water quality sensor Sa equipped with the water-
5 to-be-treated-A tank l or the detected value on the water quality sensor 8b equipped
with the first pre-treated water tank 4, the flow volume of the water to be treated A or
the pretreated water of the water to be treated A to the organic substance/microorganism
removal unit can be controlled. In Fig. 2 and Fig. 3, the explanation of symbols and
signs common to those in Fig. l are omitted.
10 [0020]
The pre-treatment unit 3 may be anyone as long as it is a process capable of
treating suspending substances and organic substances. For example, floatation
separation, sedimentation separation, lagoon process, sand ftltration, microftltration,
ultraftltration, nanoftltration, flocculation treatment, oxidation treatment, adsorption
15 treatment, and the like can be mentioned and a plurality of the treatment processes may
be combined in series.
[0021]
The semipermeable membrane unit 6 can be selected from a nanoftltration
membrane having small ftne pores, reverse osmosis membrane, and the like.
20 [0022]
The organic substance/microorganism removal unit 12 may be anyone as
long as it is a treatment process capable ofreducing organic substance components and
microorganism components including microorganisms and metabolites thereof, and byproducts,
which are objective substances to be removed. For example, floatation
25 separation, sedimentation separation, lagoon process, sand ftltration, microfiltration,
ultraftltration, nanoftltration, flocculation treatment, oxidation treatment, adsorption
treatment, and the like can be mentioned. In the organic substance/microorganism
removal unit 12, a plurality of the treatment processes may be combined in series or a
plurality of the treatment processes may be combined in parallel and the treatment
processes may be switched according to the detected values on the water quality sensors
5 8a, 8b, and 8c.
[0023]
The objective substances to be removed by the organic
substance/microorganism removal unit 12 includes microorganisms and metabolites
thereof and by-products, and, as organic substance concentration or microorganism
10 concentration thereof, it is preferred to measure a water quality index that is usually
used in the water treatment field. The measurement of the organic substance
concentration or microorganism concentration is not particularly limited but, as for the
organic substance concentration, TOC (total organic carbon concentration), AOC
(assimilative organic carbon), DOC (dissolved organic carbon concentration), COD
15 (chemical oxygen demand), BOD (biological oxygen demand), and the like are
common. As for the microorganism concentration, TEP (transparent extracellular
polymer particle), bacteria count, ATP (adenosine triphosphate), chlorophyll, and the
like can be applied.
The water quality sensor 8a, 8b, or 8c may be anyone as long as it can
20 measure the organic substance concentration or microorganism concentration
mentioned above. Also, the water quality sensor 8a, 8b, or 8c may be a measuring
instrument for manual measurement or a measuring instrument capable of on-line
measurement but, from the standpoint of capability of instantaneously coping with a
change in water quality of the water to be treated A and the first concentrate Ac, the
25 water quality sensor 8a, 8b, or 8c is preferably a measuring instrument for on-line
measurement.
[0024]
Moreover, as means for controlling the flow volume to the organic
substance/microorganism removal unit 12, for example, various valves and three-way
valves which are capable of adjusting flow rate can be exemplified. For example, in the
5 case where the water quality sensor 8a, 8b, or 8c is a TOC meter, the opening/closing
degrees of the first concentrate feed valve 1 Oa and the second concentrate feed valve
1 Ob can be adjusted so that the flow volume to the bypass line 13 is increased in the
case where TOC of the frrst concentrate Ac is less than 5 mg/1 and the flow volume to
the organic substance/microorganism removal unit 12 is increased in the case where
10 TOC thereof is 5 mg/1 or more. In Fig. 1, the flow volume ofthe first concentrate Ac is
15
controlled by adjusting the opening/closing degrees of the first concentrate feed valve
lOa and the second concentrate feed valve lOb but the whole volume may be switched
using a three-way valve as the first concentrate feed valve.
[0025]
In addition, there is a concern that the biofouling generated inside the first
semipermeable membrane unit 6 may be exfoliated as a fouling containing organic
substance components and microorganism components from the semipermeable
membrane surface through excessive proliferation on the semipermeable membrane
surface and/or stress caused by a change in water temperature or water quality, may be
20 dispersed into the first concentrate Ac, and may contaminate the downstream second
semipermeable membrane unit 19. Also, there is a concern that the fouling may be
exfoliated by the addition of a bactericide or the washing of the membrane surface, may
cause deterioration of water quality ofthe first concentrate Ac, and may contaminate the
downstream second semipermeable membrane unit 19. In this case, by the removal
25 (exfoliation) of the biofouling substance, a differential pressure (flow path pressure
loss), which is calculated by subtracting the pressure of the concentrate obtained
without permeation through the first semipermeable membrane unit 6 (pressure on the
non-permeation side) from the pressure of feed water of the first semipermeable
membrane unit 6 (pressure on the feed side), on the non-permeation side in the first
semipermeable membrane unit 6 decreases. Namely, a change in water quality of the
5 first concentrate Ac can be estimated from the change in the differential pressure
between the inflow side and the non-permeation side of the first semipermeable
membrane unit 6. Therefore, according to the change in the differential pressure
between the inflow side and the non-permeation side of the first semipermeable
membrane unit 6, the opening/closing degrees of the first concentrate feed valve 1 Oa
10 and the second concentrate feed valve 1 Ob are adjusted, whereby the flow volume of the
first concentrate Ac to the organic substance/microorganism removal unit 12 can be
controlled.
[0026]
The differential pressure between the inflow side and the non-permeation
15 side of the first semipermeable membrane unit 6 can be measured by disposing a
pressure sensor 21 for detecting the pressure of the first feed water Af and the pressure
of the first concentrate Ac to show the differential pressure on the non-permeation side
(flow path pressure loss), as shown in Fig. 4. Incidentally, in the method for producing
fresh water using a semipermeable membrane, the differential pressure between the
20 inflow side and the non-permeation side ofthe first semipermeable membrane unit is an
important parameter for monitoring the degree of biofouling formation and a pressure
sensor for detecting the differential pressure between the inflow side and the nonpermeation
side of a semipermeable membrane unit is frequently installed on a fresh
water production apparatus using a semipermeable membrane. Therefore, by
25 controlling the opening/closing degrees of the first concentrate feed valve 1 Oa and the
second concentrate feed valve 1 Ob according to the change in the differential pressure
between the inflow side and the non-permeation side of the first semipermeable
membrane unit, the water quality sensor 8a for monitoring the change in water quality
of the first concentrate Ac can be omitted and an equipment cost can be suppressed, so
that the case is preferred.
5 [0027]
As for the change in the differential pressure between the inflow side and
the non-permeation side of the first semipermeable membrane unit 6, for example, in
the case where the differential pressure decreases by 10 kPa or more, namely, in the
case where a biofJlm on the semipermeable membrane surface is exfoliated, it is
10 preferred to increase the flow volume to the organic substance/microorganism removal
unit 12 and, in the case where the differential pressure decreases by 20 kPa or more, it is
more preferred to further increase the flow volume to the organic
substance/microorganism removal unit 12 or to allow the whole amount of the first
concentrate Ac to pass through the organic substance/microorganism removal unit 12.
15 Moreover, for example, in the case where a bactericide is added to the water to be
treated of the first semipermeable membrane unit 6, even in the case where an decrease
in the differential pressure between the inflow side and the non-permeation side ofthe
first semipermeable membrane unit 6 is low as compared with a non-addition system, it
is possible to adjust the opening/closing degrees ofthe first concentrate feed valve lOa
20 and the second concentrate feed valve 1 Ob so as to increase the flow volume to the
organic substance/microorganism removal unit 12.
[0028]
In the method for producing fresh water ofthe invention, the flow volume
ofthe first concentrate Ac to the organic substance/microorganism removal unit 12 can
25 be controlled according to the detected value on the water quality sensor 8a as shown in
Fig. 1, the flow volume of the first concentrate Ac to the organic
substance/microorganism removal unit 12 can be controlled according to the change in
the differential pressure between the inflow side and the non-permeation side ofthe first
semipermeable membrane unit 6, the differential pressure being calculated by
subtracting the pressure of the first concentrate Ac from the pressure of the first feed
5 water Af of the semipermeable membrane unit 6 as shown in Fig. 4, or the flow volume
ofthe first concentrate Acto the organic substance/microorganism removal unit 12 can
be controlled according to the detected value on the water quality sensor 8a and the
change in the differential pressure between the inflow side and the non-permeation side
ofthe first semipermeable membrane unit 6 as shown in Fig. 5.
10 [0029]
In the method for producing fresh water shown in Fig. 5, the flow volume
of the first concentrate Ac to the organic substance/microorganism removal unit 12 can
be controlled according to both of the detected values on the water quality sensor and
the pressure sensor. The water quality sensor 8a and the pressure sensor 21 can be used
15 at the same time. On this occasion, the flow volume to the organic
substance/microorganism removal unit can be controlled according to the change in the
differential pressure between the inflow side and the non-permeation side of the first
semipermeable membrane unit detected on the pressure sensor 21 in a preferential
manner. For example, the flow volume of the first concentrate Ac to the organic
20 substance/microorganism removal unit can be controlled according to the detected value
on the water quality sensor 8a when the change in the differential pressure is less than
10 kPa and according to the detected value on the pressure sensor wlien the change in
the differential pressure is 10 kPa or more.
[0030]
25 Incidentally, since the organic substances and microorganisms in the first
concentrate Ac also include the organic substances and microorganisms not sufficiently
removed in the first pre-treatment unit 3, the organic substance/microorganism removal
unit 12 preferably includes at least one treatment process which is different from the
first pre-treatment unit 3. For example, in the case where the first pre-treatment unit 3
is so lid-liquid separation such as sand filtration, micro filtration or ultrafiltration, the
5 organic substances and microorganisms that have not been able to be removed by the
solid-liquid separation may be decomposed and removed by performing oxidation
treatment such as ozone or biological treatment in the organic substance/microorganism
removal unit 12 or the organic substances and microorganisms may be removed by
adding a flocculant or an adsorbent. For example, as shown in Fig. 1, by disposing a
10 flocculant tank or adsorbent tank 22a and a flocculant addition pump or adsorbent
addition pump 23a on the upstream side of the organic substance/microorganism
removal unit 12, a flocculant or adsorbent is added to the first concentrate Ac and thus
the organic substances and microorganisms can be decomposed and removed.
[0031]
15 Furthermore, from the standpoint of reduction of an equipment cost of the
organic substance/microorganism removal unit 12, the second pre-treatment unit 17 for
treating the water to be treated B is preferably used also as the organic
substance/microorganism removal unit as shown in Fig. 6. In Fig. 6, the water to be
treated A is stored in the water-to-be-treated-A tank 1, and then is fed to the first pre-
20 treatment unit 3 by means ofthe water-to-be-treated-A feed pump 2. After subjected to
pre-treatment, the water is temporarily stored in the first pre-treated water tank 4 and
subsequently treated in the first semipermeable membrane unit 6 by means of the first
booster pump 5. In the first semipermeable membrane unit 6, the permeate Ap ofthe
semipermeable membrane is stored as fresh water in the first fresh water tank 7. On the
25 other hand, the first concentrate Ac discharged from the first semipermeable membrane
unit 6 flows to a pipeline having a water quality sensor 8. In the example of Fig. 7, the
first concentrate tank and the first concentrate pump are not disposed, and by the
pressure ofthe first concentrate Ac, the opening/closing degrees ofthe first concentrate
feed valve 1 Oa and the second concentrate feed valve 1 Ob are adjusted according to the
detected value on the water quality sensor 8 and the water is fed to the second pre-
5 treatment unit 17 or the mixed water tank 14 for mixing with the water to be treated B.
Here, by disposing a flocculant tank or adsorbent tank 22b and a flocculant addition
pump or adsorbent addition pump 23b on the upstream side ofthe second pre-treatment
unit 17, a flocculant or adsorbent is added to the first concentrate Ac and thus the
organic substances and microorganisms can be decomposed and removed. Moreover,
10 the water to be treated B is stored in the water-to-be-treated-B tank 15 and then is fed to
the second pre-treatment unit 17 by means of the water-to-be-treated-B feed pump 16.
After subjected to pre-treatment together with at least a part of the aforementioned first
concentrate Ac, the mixed water is fed to the mixed water tank 14. After the mixed
water containing the first concentrate Ac and the water to be treated B in the mixed
15 water tank 14 is pressurized by means of the second booster pump 18, the mixed water
is treated in the second semipermeable membrane unit 19 and permeate (second
permeate Bp) from the second semipermeable membrane unit 19 is stored in the second
permeate tank 20.
[0032]
20 In the method for producing fresh water of the invention, the organic
substance/microorganism removal unit is preferably a treatment unit including at least
one selected from the group consisting of floatation separation, sedimentation
separation, lagoon process, sand filtration, microftltration, ultrafiltration, nanofiltration,
flocculation treatment, oxidation treatment, and adsorption treatment. Of these, the
25 floatation separation is suitable in the case where much light oil components and
surfactants are present and pressure floatation separation is effective in which fme
bubbles such as microbubbles or nanobubbles are introduced under pressure. The fine
bubbles may be generated by blowing compressed air therein or may be generated by
rapid pressure reduction of pressurized water. Furthermore, in the case where a huge
land area can be secured, the lagoon process in which aerobic treatment is performed at
5 an upper part and anaerobic treatment is performed at a lower part at the same time is
preferable because the organic substances and microorganisms in the first concentrate
Ac can be reduced without power. In the lagoon process, the water is preferably
retained for about 5 to 30 days usually in a reserving pond having a depth of 1.2 to 2.5
m.
10 [0033]
In the case ofthe sand filtration, it is possible to apply gravity type filtration
that is a type of natural flowing-down and also it is possible to apply pressurized type
filtration in which sand is filled into a pressure tank. As for the sand for filling, it is
possible to apply sand composed of single component but it is possible to increase
15 filtration efficiency by combining anthracite, silica sand, garnet, pumice, and/or the like.
Moreover, the first concentrate Ac may be allowed to pass through a permeable layer to
reduce the organic substance concentration or microorganism concentration of the first
concentrate Ac utilizing purification/decomposition functions of anaerobic and aerobic
useful microorganisms including photosynthetic bacteria, yeast fungi, lactic acid
20 bacteria, filamentous bacteria, actinomycetes, and the like and thereafter, one
accumulated in an underground aquifer may be used as diluting water.
[0034]
The microfiltration membrane and the ultrafiltration membrane are not
particularly limited and one having any shape, such as a flat sheet membrane, a hollow
25 fiber membrane, a tubular membrane, or a pleat-shaped one can be appropriately used.
The material of the membrane is also not particularly limited and polyacrylonitrile,
polyphenylene sulfone, polyphenylene sulfide sulfone, poly(vinylidene fluoride),
polypropylene, polyethylene, po lysu lfone, po lytetrafluoroethylene, poly( viny I a leo ho 1),
cellulose acetate, polyamides, polyesters, polyimides, vinyl polymers, and inorganic
materials such as ceramics can be used. Moreover, as for filtration methods, it is
5 possible to apply both of a pressure filtration method in which feed water is pressurized
and filtered and a suction filtration method in which filtration is performed by sucking
the permeation side. Furthermore, it is also possible to apply a pressure floatation
filtration that uses pressure floatation and sand filtration in combination or a
submerged-type membrane filtration unit. Particularly, in the case of the suction
I 0 filtration method, it is also preferred to apply a so-called flocculation membrane
filtration or a membrane bioreactor (MBR) in which a microfiltration membrane or an
ultrafiltration membrane is submerged in a flocculation sedimentation tank or a
biological treatment tank to perform filtration.
[0035]
15 As for the semipermeable membranes such as nanofiltration membranes
and reverse osmosis membranes, as materials for the membranes, polymer materials
such as cellulose acetate-based polymers, polyamides, polyesters, polyimides, and vinyl
polymers can be used. Moreover, the membrane structure thereof may be either of an
asymmetric membrane having a dense layer in at least one surface of the membrane and
20 having micropores, the pore diameter ofwhich gradually becomes larger from the dense
layer toward an inner part of the membrane or toward the other surface or a composite
membrane having an exceedingly thin functional layer formed on the dense layer ofthe
asymmetric membrane and made of another material. However, in view of protecting
the second semipermeable membrane unit 19 from a component easily adsorbable to the
25 semipermeable membrane, the filtration material of the organic
..
substance/microorganism removal unit is preferably the same material as the filtration
material ofthe second semipermeable membrane unit.
[0036]
The flocculation treatment that constitutes the organic
5 substance/microorganism removal unit is a treatment for flocculating the organic
substances and microorganisms in water by adding a flocculant and making solid-liquid
separation efficient. In this case, the first concentrate Ac subjected to the flocculation
treatment can be converted into feed water suitable for allowing to pass through the
second semipermeable membrane unit by performing sand filtration or performing
10 micro filtration or ultrafiltration after precipitation using an inclined plate or the like.
Flocculants are roughly classified into inorganic flocculants and organic polymer
flocculants and examples of the inorganic flocculants include aluminum-based
flocculants such as aluminum sulfate (sulfate band) and polyaluminum chloride (PACl)
and iron-based flocculants such as ferric chloride and polyferric sulfate. In addition,
15 examples of the organic polymer flocculants include cationic polymer flocculants such
as aminoalkyl (meth)acrylate quaternary salt (co)polymers, anionic polymer flocculants
such as acrylamide/sodium acrylate copolymer, and nonionic polymer flocculants such
as polyacrylamide. These flocculants may be used singly or may be used as a
flocculation aid in combination with an inorganic flocculant. Moreover, since the
20 generation of sludge can be suppressed when an organic polymer flocculant is used
rather than an inorganic flocculant, an inorganic flocculant and an organic polymer
flocculant are preferably used in combination rather than the inorganic flocculant is
used singly. Moreover, in the flocculation, since the effects are remarkably varied by
pH of the water to be treated, it is preferred to adjust the pH to an appropriate range
25 using an alkali such as sodium hydroxide, lime, or sodium bicarbonate or an acid such
as hydrochloric acid or sulfuric acid.
[0037]
As the oxidation treatment, biological treatment, ozone and ultraviolet ray
or gamma ray irradiation, fluorine or hydrogen peroxide addition, catalytic treatment,
and the like may be mentioned and it is also possible to apply accelerated oxidation
5 treatment in which at least two of them are used in combination. In consideration of
influences on the environment, ozone or ultraviolet ray irradiation, hydrogen peroxide
addition, and catalytic treatment are preferred. As the catalyst, there may be mentioned
catalysts of iron, copper and manganese which can enhance oxidizing power in
combination with ozone or hydrogen peroxide, metal oxides having a so-called
10 photocatalytic function, e.g., titanium oxide, and the like. The accelerated oxidation
treatment is referred to as AOP (=Advance Oxidance Process) and is a method in which
a hydroxy radical having large oxidizing power is generated in water by using ozone,
ultraviolet rays, hydrogen peroxide, a catalyst (photocatalyst or the like), and the like in
combination to decompose organic substances. Furthermore, the accelerated oxidation
15 treatment is characterized in that secondary wastes are not generated and deodorization,
decoloration, sterilization, and the like can be achieved as effects of the treatment, in
addition to the decomposition of the organic substances. As the combination for the
accelerated oxidation treatment, a combination capable of generating much more
hydroxy radical contributing to oxidative decomposition is preferred and a combination
20 of hydrogen peroxide and ultraviolet rays, ozone and hydrogen peroxide, or ozone and
ultraviolet rays is more preferred. In the case where three of ozone, ultraviolet rays and
hydrogen peroxide are combined, the oxidative decomposition can be more efficiently
performed, so that the case is preferred.
[0038]
25 The adsorption treatment is a treatment in which relatively small organic
substances having a molecular weight of several hundreds or less in water are adsorbed
on a solid surface by adding an adsorbent. As the adsorbent, active carbon, ionexchange
resins, zeolites, and the like may be mentioned and, from the standpoint of
relatively easy handling, powdery active carbon is preferably used. In the case where
the adsorbent has a granular shape, it is configured so that it is filled into a column and
5 water is allowed to pass through the column. In the case where the adsorbent has a
powdery shape, it is appropriate to use it through the addition to the first concentrate Ac
directly in combination with solid-liquid separation such as sedimentation separation or
membrane filtration. Moreover, an adsorbent filter coated with an adsorbent such as
active carbon or ion-exchange resin may be used.
10 [0039]
Incidentally, in the case of low-salt-concentration water such as river water,
industrial wastewater or sewage wastewater, a semipermeable membrane such as a
reverse osmosis membrane for low pressure or a nanofiltration membrane is applied as
the semipermeable membrane unit 6. However, owing to low osmotic pressure, high
15 recovery operation is possible and, as a result, the amount of the first concentrate Ac
decreases. Therefore, even when an energy recovering unit is installed on a
downstream side to which the concentrate from the semipermeable membrane unit is
discharged, recoverable energy is little and cost performance of the energy recovering
unit decreases, so that the installation is not economical in many cases. For the reason,
20 in the semipermeable membrane unit 6 for treating low-salt-concentration water, the
water is frequently discharged from the system without recovering energy.
Consequently, as exemplified in Fig. 7, when, as an organic substance/microorganism
removal unit for reducing the organic substance concentration or microorganism
concentration of the first concentrate Ac, a pressure filtration unit 12a capable of
25 performing filtration under concentrate pressure is directly connected to the first
semipermeable membrane unit 6, the organic substance concentration or microorganism
concentration can be reduced without power, so that the case is preferred. As for the
pressure filtration unit 12a, there can be used a cartridge filter, a disk filter,
microfiltration, ultrafiltration, sand filtration, biological carrier filtration, nano filter,
sand filtration, a precoat filter, an adsorbent filter coated with active carbon or ion-
5 exchange resin, and the like.
[0040]
Moreover, in the case where low-salt-concentration water such as river
water, industrial wastewater or sewage wastewater is subjected to semipermeable
membrane treatment, the first concentrate Ac maintains a concentrate pressure of about
I 0 0.8 to 1.5 MPa. Therefore, it is preferred to provide a fine bubble generation unit 24
capable of rapidly reducing the pressure of the first concentrate Ac to generate fine
bubbles in the first concentrate Ac. By generating fine bubbles in the concentrate of the
first semipermeable membrane unit 6 by means of the fme bubble generation unit 24,
energy required for a blower, a compressor, or the like for generating fine bubbles can
15 be reduced in the case where the organic substance/microorganism removal unit is
pressure floatation separation or biological treatment and thus the case is preferred. In
addition, the separation into permeate and concentrate can be achieved while washing
the membrane surface with fme bubbles in the case where the organic
substance/microorganism removal unit is a membrane separation unit that adopts a cross
20 flow method and thus the case is preferable. As the fine bubble generation unit 24
capable of rapidly reducing the pressure of the first concentrate Ac, for example, an
aspirator or the like can be exemplified. The position to which the fme bubble
generation unit 24 is disposed may be any position as long as it is a pipeline to which
the pressure of the concentrate is applied. However, as exemplified in Fig. 7, in the
25 case where the first concentrate Ac is separated in the organic substance/microorganism
removal unit (pressure filtration unit 12a) utilizing the concentrate pressure thereof, it is
necessary to generate the fine bubbles with maintaining a balance with the energy
necessary for separation.
[0041]
In the invention, since physical washing drainage containing much organic
5 substances and microorganisms and concentrated drainage of the membrane separation
unit that adopts a cross flow method are discharged from the organic
substance/microorganism removal unit, as exemplified in Fig. 8, when treated drainage
such as washing drainage and concentrated drainage 25 from the pressure filtration unit
12a is mixed with concentrate Be ofthe second semipermeable membrane unit 19 and
1 0 then discharged from the system through a discharging line 26, the washing drainage
and concentrated drainage containing much organic substances and microorganism from
the organic substance/microorganism removal unit can be diluted and also the
concentrate Be having high concentration ofthe second semipermeable membrane unit
19 can be also diluted, so that the invention is friendly to the environment and
15 preferable.
[0042]
While the invention has been described in detail and with reference to
specific embodiments thereof, it will be apparent to one skilled in the art that various
changes and modifications can be made therein without departing from the spirit and
20 scope thereof The present application is based on Japanese Patent Application No.
2013-059548 filed on March 22, 2013, and the contents are incorporated herein by
reference.
INDUSTRIAL APPLICABILITY
25 [0043]
The present invention provides a method for producing fresh water using a
semipermeable membrane unit and a fresh water production method to produce fresh
water from a plurality of kinds of raw water such as a combination of seawater with
river water, ground water or treated sewage wastewater, more specifically, a method for
5 producing fresh water to efficiently prevent a semipermeable membrane from fouling
due to organic substances or microorganisms contained in concentrated drainage.
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
[0044]
10 1: Water-to-be-treated-A tank
2: Water-to-be-treated-A feed pump
3: First pre-treatment unit
4: First pre-treated water tank
5: First booster pump
15 6: First semipermeable membrane unit
7: First permeate tank
8, 8a, 8b, 8c: Water quality sensor
9: First concentrate tank
1 Oa: First concentrate feed valve
20 1 Ob: Second concentrate feed valve
11: First concentrate pump
12: Organic substance/microorganism removal unit
12a: Pressure filtration unit
13: Bypass line
25 14: Mixed water tank
15: Water-to-be-treated-B tank
16: Water-to-be-treated-B feed pump
17: Second pre-treatment unit
18: Second booster pump
19: Second semipermeable membrane unit
5 20: Second permeate tank
21: Pressure sensor
22a, 22b: Flocculant tank or adsorbent tank
23a, 23b: Flocculant addition pump or adsorbent addition pump
24: Fine bubble generation unit
10 25: Organic substance/microorganism removal unit washing drainage line or
concentrated drainage line
26: Discharging line

CLAIMS
[Claim 1]
A method for producing fresh water in which water to be treated A is
treated in a first semipermeable membrane unit to produce fresh water, first concentrate
5 Ac generated during the treatment in the first semipermeable membrane unit is mixed
with water to be treated B having a solute concentration higher than that of the frrst
concentrate Ac, and the mixed water is treated in a second semipermeable membrane
unit to produce fresh water,
the method comprising:
10 an organic substance/microorganism removal line in which the first
concentrate Ac is allowed to pass through an organic substance/microorganism removal
unit to reduce organic substance concentration or microorganism concentration of the
first concentrate Ac and is mixed with the water to be treated B; and
a bypass line in which the first concentrate Ac is mixed with the water to be
15 treated B without via the organic substance/microorganism removal unit,
wherein a flow volume of the frrst concentrate Ac to the organic
substance/microorganism removal unit is controlled according to at least one of: the
organic substance concentration or microorganism concentration in the first concentrate
Ac on an upstream side of the organic substance/microorganism removal unit; and a
20 change in a differential pressure between an inflow side and a non-permeation side of
the first semipermeable membrane unit, the differential pressure being calculated by
subtracting a pressure of the first concentrate Ac from a pressure of feed water of the
frrst semipermeable membrane unit.
[Claim 2]
25 The method for producing fresh water according to claim 1, wherein the
flow volume of the first concentrate Ac to the organic substance/microorganism
removal unit is controlled according to the change in the differential pressure when the
change in the differential pressure between the inflow side and the non-permeation side
of the first semipermeable membrane unit exceeds a predetermined value, and the flow
volume of the first concentrate Acto the organic substance/microorganism removal unit
5 is controlled according to the organic substance concentration or microorganism
concentration in the first concentrate Ac when the change in the differential pressure
between the inflow side and the non-permeation side of the first semipermeable
membrane unit is lower than or equal to the predetermined value ..
[Claim 3]
10 The method for producing fresh water according to claim 1 or 2, wherein
the water to be treated A is treated in a pre-treatment unit before the treatment in the
first semipermeable membrane unit.
[Claim 4]
The method for producing fresh water according to claim 3, wherein a
15 treatment process that constitutes the organic substance/microorganism removal unit
comprises at least one treatment process different from a treatment process that
constitutes the pre-treatment unit for the water to be treated A.
[Claim 5]
The method for producing fresh water according to any one of claims 1 to
20 4, wherein a fine bubble generation unit capable of generating fine bubbles by reducing
a pressure of the first concentrate Ac is provided on the upstream side of the organic
substance/microorganism removal unit, and fme bubbles are generated in the first
concentrate Ac.
[Claim 6]
The method for producing fresh water according to any one of claims 1 to
5, wherein the organic substance/microorganism removal unit is a pressure filtration
unit for performing separation utilizing a water pressure ofthe first concentrate Ac.
[Claim 7]
5 The method for producing fresh water according to any one of claims 1 to
6, wherein a filtration material whose material is the same as that of a filtration material
of the second semipermeable membrane unit is used as a filtration material of the
organic substance/microorganism removal unit.
[Claim 8]
10 The method for producing fresh water according to any one of claims 1 to
7, wherein treated drainage from the organic substance/microorganism removal unit is
mixed with concentrate from the second semipermeable membrane unit, followed by
being discharged from the system.
[Claim 9]
15 A method for producing fresh water in which water to be treated A is mixed
with water to be treated B having a solute concentration higher than that of the water to
be treated A and the mixed water is treated in a semipermeable membrane unit to
produce fresh water,
the method comprising:
20 an organic substance/microorganism removal line in which the water to be
treated A is allowed to pass through an organic substance/microorganism removal unit
to reduce organic substance concentration or microorganism concentration of the water
to be treated A and is mixed with the water to be treated B; and
a bypass line in which the water to be treated A is mixed with the water to
25 be treated B without via the organic substance/microorganism removal unit,
wherein a flow volume of the water to be treated A to the organic
substance/microorganism removal unit is controlled according to the organic substance
concentration or microorganism concentration of the water to be treated A on an
upstream side of the organic substance/microorganism removal unit.
5 [Claim 10]
10
15
20
25
The method for producing fresh water according to claim 9, wherein the
water to be treated A is treated in a pre-treatment unit before mixed with the water to be
treated B.
[Claim 11]
The method for producing fresh water according to claim 10, wherein a
treatment process that constitutes the organic substance/microorganism removal unit
comprises at least one treatment process different from a treatment process that
constitutes the pre-treatment unit for the water to be treated A
[Claim 12]
The method for producing fresh water according to any one of claims 9 to
11, wherein a filtration material whose material is the same as that of a filtration
material of the semipermeable membrane unit is used as a filtration material of the
organic substance/microorganism removal unit.
[Claim 13]
The method for producing fresh water according to any one of claims 9 to
12, wherein treated drainage from the organic substance/microorganism removal unit is
mixed with concentrate from the semipermeable membrane unit, followed by being
discharged from the system.
[Claim 14]
The method for producing fresh water according to any one of claims 1 to
13, wherein the organic substance concentration or microorganism concentration
includes at least one selected from the group consisting of total organic carbon
concentration (TOC), assimilative organic carbon (AOC), dissolved organic carbon
concentration (DOC), chemical oxygen demand (COD), biological oxygen demand
(BOD), ultraviolet absorbance (UV), transparent extracellular polymer particle (TEP),
5 adenosine triphosphate (ATP), bacteria count, and chlorophyll.
[Claim 15]
The method for producing fresh water according to any one of claims 1 to
14, wherein the organic substance/microorganism removal unit includes at least one
selected from the group consisting of floatation separation, sedimentation separation,
10 lagoon process, sand filtration, microfiltration, ultrafiltration, nanofiltration,
flocculation treatment, oxidation treatment, and adsorption treatment.
[Claim 16]
The method for producing fresh water according to any one of claims 1 to
15, wherein the organic substance/microorganism removal unit is also used as a pre-
15 treatment unit for the water to be treated B.