Title of Invention

WATER TREATMENT SYSTEM

Abstract A water treatment system having a biological treatment step (a secondary treatment step) and a membrane separation step (a tertiary treatment step), wherein a portion of the raw water to be treated and/or a portion of the primarily treated water in the pretreatment step are biologically treated and supplied into a reaction tank in the membrane separation step as the main channel system, while the remainder the raw water to be treated and/or the remainder of the primarily treated water in the pretreatment step are added together with a flocculating agent to the reaction tank in the membrane separation step, and then the membrane separation is conducted in the membrane separation step.
Full Text - 1 -
Description
WATER TREATMENT SYSTEM
Technical Field
[0001]
The present invention relates to a water treatment
system and to a technique for carrying out an advanced
treatment on wastewater using a membrane separation
apparatus.
Background Art
[0002]
A conventional water treatment technique of this kind
is described in, for example, Japanese Patent Laid-Open
No. 2004-840. The technique will be described with
reference to FIG. 6.
[0003]
Sludge and excrement 41 from water treatment tanks
are guided to an aeration tank 42, where a biological
treatment is carried out on the sludge and excrement 41
using microorganisms. The biologically treated water is
fed via a biological treatment tank 43 to a first
membrane separation apparatus 44, which separates the
sludge and excrement into concentrated sludge 4 5 and
membrane separated water 46.
[0004]
The concentrated sludge 45 is partly returned to the
aeration tank 42 and the biological treatment tank 43 as
sludge to be returned. The rest of concentrated sludge is
continuously or intermittently fed to a dehydrator 47. On
the other hand, the membrane separated water 46 is mixed
with a flocculation agent in a mixture tank 48. The
mixture is then guided to a flocculation tank 49, in
which flocs are formed. The resulting water is then

- 2 -
guided to a flocculation membrane raw water tank 5 0 and
then to a second membrane separation apparatus 51. In the
second membrane separation apparatus 51, the water is
separated into flocculated concentrated sludge 52 and
membrane separated water 53 with a flocculation system.
[0005]
The membrane separated water 53 with a flocculation
system is guided out of the system, and the flocculated
concentrated sludge 52 is partly returned to the
flocculation membrane raw water tank 50, with the
remaining sludge continuously supplied to the dehydrator
47 as sludge slurry together with the rest of
concentrated sludge 45. The dehydrated sludge 55 is
guided out of the system, and a dehydrated separated
liquid 56 separated from the sludge is continuously
returned to the biological treatment water tank 43.
[0006]
Another conventional technique is disclosed in
Japanese Patent Laid-Open No. 2003-236584. The technique
will be described with reference to FIG. 7.
[0007]
A sewage treatment apparatus 3 0 comprises a
pretreatment facility 31, a first flocculation separation
facility 32, a biological treatment facility 33, a second
flocculation separation facility 34, an oxidization
facility 35, an adsorption facility 36, a
demineralization facility 37, a drying facility 38, and
an effluent facility 39.
[0008]
The pretreatment facility 31 carries out a
pretreatment such as adjustment and homogenization of the
amount and quality of sewage. The first flocculation
separation facility 32 carries out a flocculation
precipitation separation treatment and is located
downstream of and adjacent to the pretreatment facility

- 3 -
31. The biological treatment facility 33 carries out a
biological treatment and is located downstream of and
adjacent to the first flocculation separation facility 32
The second flocculation separation facility 34 carries
out a flocculation membrane separation treatment and is
located downstream of and adjacent to the biological
treatment facility 33.
[0009]
The oxidization facility 35 carries out an advanced
oxidization treatment and is located downstream of and
adjacent to the second flocculation separation facility
34. The adsorption facility 36 carries out a suction
treatment and is located downstream of and adjacent to
the oxidization facility 35. The demineralization
facility 37 carries out a demineralization treatment and
is located downstream of and adjacent to the adsorption
facility 36.
[0010]
The drying facility 38 takes out solid salt and is
located downstream of and adjacent to the
demineralization facility 37. The effluent facility 39
releases the final treated water to a public water area
and is located downstream of and adjacent to the
demineralization facility 37.
Disclosure of the Invention
[0011]
As described above, in Japanese Patent Laid-Open No.
2004-840, the biologically treated water biologically
treated in the aeration tank 42 is subjected to membrane
separation at multiple levels by the first membrane
separation apparatus 44 and the second membrane
separation apparatus 51. In particular, in the second
membrane separation apparatus 51, the flocculation agent
is used together for flocculation membrane separation.

- 4 -
[0012]
Japanese Patent Laid-Open No. 2003-236584 achieves an
advanced treatment by carrying out the flocculation,
precipitation, and separation treatment in the first
flocculation separation facility 32, the biological
treatment in the biological treatment facility 33, and
the membrane filtration separation treatment with a
flocculation agent in the second flocculation separation
facility 34.
[0013]
However, the BOD concentration of the biologically
treated water is not constant but varies depending on the
BOD concentration of raw water that has not been
biologically treated. Thus, when an advanced treatment is
carried out in a reaction tank with a membrane separation
apparatus placed therein, using a flocculation agent
together, the following problems may occur.
[0014]
The low BOD concentration (for example, less than 2 0
mg/L) of the biologically treated water reduces the
amount of sludge generated in the reaction tank (the
amount of microorganisms) and thus the concentration of
organic substances in the reaction tank decreases. Thus,
even with the addition of the flocculation agent, smaller
sludge flocs are formed in the reaction tank, and said
sludge flocs are likely to be dispersed easily, so that
the amount of flocculation agent might be increased.
[0015]
An environment with a lower inflowing BOD
concentration causes the exhaustion of extracellular
substrates of the microorganisms in the reaction tank.
The microorganisms thus start to use intracellular carbon
sources (endogenous substrates), causing the self-
degradation of microorganisms contained in the sludge
flocs, which are thus dispersed in the form of fragments.

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Thus, the dispersed very small fragments of the sludge
and microorganisms self-degrade into small solid
substance of the microorganisms. This makes a membrane
surface in the membrane separation apparatus likely to be
occluded.
[0016]
When a submerged membrane separation tank with a
flocculation system is used for the advanced treatment, a
certain range of sludge concentration is suitable for
operation. This sludge concentration range is required to
ensure sufficient treatment performance or to form sludge
flocs of a preferred size. However, a low inflowing BOD
concentration requires a long time to reach the sludge
concentration suitable for operation or makes it
difficult to reach that concentration.
[0017]
The present invention solves the above problems. An
object of the present invention is to provide a water
treatment system using a membrane separation apparatus to
treat biologically treated water, the system making it
possible to inhibit fouling of membrane surfaces and to
reduce the amount of flocculation agent used.
[0018]
To solve the problems described above, the present
invention provides a water treatment system in which raw
water to be treated flowing into the system flows into a
reaction tank for a membrane separation process via a
biological treatment process and in which in the membrane
separation process, a flocculation agent is used together
to carry out a membrane separation treatment, the system
comprising a raw water supply unit that supplies the
treatment target raw water to the reaction tank and a
flocculation agent addition unit that adds the
flocculation agent to the reaction tank.
[0019]

- 6 -
With the above configuration, when an activated
sludge method with a membrane separation is applied to an
advanced treatment, if the BOD concentration of the water
flowing into the reaction tank for the membrane
separation process is low (for example, less than 20
mg/L), resulting in a very small amount of generated
sludge, the raw water supply unit supplies the reaction
tank with an appropriate amount of treatment target raw
water not subjected to the biological treatment process.
Further, the flocculation agent addition unit adds the
flocculation agent to the reaction tank.
[0020]
The addition of the treatment target raw water
increases the amount of organic components and SS to
adjustably make the nature of the membrane separation
target liquid in the reaction tank suitable for floc
formation. The flocculation agent is then used to
flocculate the organic components (dissoluble substances)
and SS (solid substances) to form sludge flocs of a
sufficient size.
[0021]
By thus adjustably setting the concentration of the
sludge in the reaction tank at a suitable value for floc
formation to increase the diameter of sludge flocs, it is
possible to reduce the fouling of membrane surfaces and
to improve a filtration property. This makes it possible
to suitably treat the treated water in the biological
treatment process and to reduce the amount of added
flocculation agent.
[0022]
A desirable flocculation agent is an organic polymer
flocculation agent which is unlikely to be degraded under
disturbance conditions and which is unlikely to
biological decomposition.
[0023]

- 7 -
The flocculation agent may be independently added to
the reaction tank or may be mixed with the treatment
target raw water and then supplied to the reaction tank
together with the treatment target raw water. The
flocculation agent is added to the water, with the ratio
of the amount of added flocculation agent to the amount
of introduced treatment target raw water, set at a given
value.
[0024]
The ratio of the amount of added flocculation agent
to the amount of sludge generated in the reaction tank or
the amount of reduction in sludge needs to be set at a
given value (the amount of flocculation agent per sludge
concentration). This addition ratio enables the amount of
added flocculation agent to be optimized. Alternatively,
the amount of flocculation agent contained in excess
sludge discharged from the reaction tank may be measured,
and the shortage of the flocculation agent may be
determined from the measurement on the basis of the rule
of thumb. In this case, the determined shortage could be
the amount of flocculation agent to be replenished.
[0025]
This allows the flocculation agent to be added more
easily than the conventional technique, that is, the
technique of measuring the dissoluble COD concentration
in the reaction tank, the COD concentration of outflowing
water flowing out of the reaction tank, and turbidity and
adding the flocculation agent so as to adjust these
measurements to appropriate values. The membrane
separation treatment during the membrane separation
process may be carried out by immersing the membrane
separation unit in the reaction tank or placing the
membrane separation unit outside the reaction tank.
[0026]

- 8 -
The present invention provides a water treatment
system in which raw water to be treated flowing into the
system is sequentially subjected to a pretreatment
process and a biological treatment process and then flows
into a reaction tank for a membrane separation process
and in which in the membrane separation process, a
flocculation agent is used in combination to carry out a
membrane separation treatment, the system comprising a
treated water supply unit that supplies the treated water
in the pretreatment process to the reaction tank and a
flocculation agent addition unit that adds the
flocculation agent to the reaction tank.
[0027]
With the above configuration, when an activated
sludge method with a membrane separation is applied to an
advanced treatment, if the BOD concentration of the water
flowing into the reaction tank for the membrane
separation process is low (for example, less than 20
mg/L), resulting in a very small amount of generated
sludge, the treated water supply unit supplies the
reaction tank with an appropriate amount of treated water
in the pretreatment process not subjected to the
biological treatment process. Further, the flocculation
agent addition unit adds the flocculation agent to the
water.
[0028]
The addition of the treated water in the pretreatment
process increases the amount of organic components and
SSs to adjustably make the nature of the membrane
separation target liquid in the reaction tank suitable
for floc formation. The flocculation agent is then used
to flocculate the organic components (dissoluble
substances) and SSs (solid substances) to form sludge
flocs of a sufficient size.
[0029]

- 9 -
By thus adjustably setting the concentration of the
sludge in the reaction tank at a suitable value for floc
formation to increase the diameter of sludge flocs, it is
possible to reduce the fouling of membrane surfaces and
to improve the filtration property. This makes it
possible to suitably treat the treated water in the
biological treatment process and to reduce the amount of
added flocculation agent.
[0030]
The flocculation agent may be independently added to
the reaction tank or may be mixed with the treated water
in the pretreatment process and then supplied to the
reaction tank together with the treated water. The
flocculation agent is added to the water, with the ratio
of the amount of added flocculation agent to the amount
of introduced treated water, set at a given value.
[0031]
The ratio of the amount of added flocculation agent
to the amount of sludge generated in the reaction tank or
the amount of reduction in sludge needs to be set at a
given value (the amount of flocculation agent per sludge
concentration). This addition ratio enables the amount of
added flocculation agent to be optimized. Alternatively,
the amount of flocculation agent contained in excess
sludge discharged from the reaction tank may be measured,
and the shortage of the flocculation agent may be
determined from the measurement on the basis of the rule
of thumb. In this case, the determined shortage could be
the amount of flocculation agent to be replenished.
[0032]
In the water treatment system in accordance with the
present invention, the pretreatment process comprises a
solid-liquid separation treatment process or a
dissolution treatment process.
[0033]

- 10 -
In the above configuration, the solid-liquid
separation treatment process may use a screen or a method
such as precipitation separation, filtration separation,
or flocculation separation using a flocculation agent is
applicable. The dissolution treatment process cruses
excrement residues and physico-chemically dissolves SSs.
[0034]
The water treatment system in accordance with the
present invention has, between the biological treatment
process and the membrane separation process, a
precipitation treatment unit that carries out a
precipitation treatment on outflowing water in a
biological treatment tank constituting the biological
treatment process and supplies separated water to the
reaction tank for the membrane separation process, and a
mixture supply unit that directly supplies the outflowing
water in the biological treatment tank to the reaction
tank for the membrane separation process without passing
the outflowing water through the precipitation treatment
unit.
[0035]
With the above configuration, the separated water
having passed through the precipitation treatment unit is
introduced into the reaction tank for the membrane
separation process and the reaction tank is supplied with
an appropriate amount of outflowing water in the
biological treatment tank which has not passed through
the precipitation treatment unit. This allows the
concentration of the sludge in the reaction tank to be
adjusted to control the amount of added flocculation
agent. In this case, the reaction tank may be supplied
only with the separated water having passed through the
precipitation treatment unit.
[0036]

- 11 -
The present invention provides a water treatment
system comprising a submerged membrane separation
apparatus in the reaction tank for the membrane
separation process, the submerged membrane separation
apparatus comprising a membrane separation unit, an air
diffuser located below the membrane separation unit, and
a control unit that controls the amount of aeration in
the air diffuser, the control unit controlling the amount
of aeration in the air diffuser using as a control
indicator at least one of a trans-membrane pressure in
the membrane separation unit, the amount of load flowing
into the reaction tank, the level of the water in the
reaction tank, and the amount of membrane permeation
liquid flowing out through the membrane separation unit.
[0037]
Thus, according to the present invention, when in the
membrane separation process, the membrane separation
treatment is carried out on the outflowing water from the
biological treatment tank constituting the biological
treatment process, the treatment target raw water or the
treated water in the pretreatment process is supplied
together with the flocculation agent. This makes it
possible to inhibit the fouling of membrane surfaces in
the membrane separation unit to reduce the amount of
flocculation agent used.
Brief Description of the Drawings
[0038]
FIG. 1 is a flow sheet showing a water treatment
system in accordance with Embodiment 1 of the present
invention;
FIG. 2 is a schematic diagram showing a submerged
membrane separation tank with a flocculation system in
accordance with Embodiment 1;

- 12 -
FIG. 3 is a flow sheet showing a water treatment
system in accordance with Embodiment 2 of the present
invention;
FIG. 4 is a flow sheet showing a water treatment
system in accordance with Embodiment 3 of the present
invention;
FIG. 5 is a graph showing the relationship between
MLSS and negative pressure increase acceleration;
FIG. 6 is a flow sheet showing a conventional water
treatment system, and
FIG. 7 is a block diagram showing the conventional
water treatment system.
Best Mode for Carrying Out the Invention
[0039]
Embodiments of the present invention will be
described below with reference to the drawings.
[0040]
Embodiment 1
In FIGS. 1 and 2, a water treatment system has a
primary treatment process comprising a first
precipitation tank 2 for a pretreatment process, a
secondary treatment process comprising a biological
treatment tank 3 for a biological treatment process and a
precipitation tank 4 for a precipitation treatment unit,
and a tertiary treatment process comprising a submerged
membrane separation tank 5 with a flocculation system for
a membrane separation process.
[0041]
The first precipitation tank 2 carries out a solid-
liquid separation treatment on treatment target raw water
1 flowing into the system. The biological treatment tank
3 biologically treats primarily treated water flowing out
of the first precipitation tank 2. The precipitation tank
4 carries out a solid-liquid separation treatment on

- 13 -
outflowing water flowing out of the biological treatment
tank 3 . The submerged membrane separation tank 5 with a
flocculation system biologically treats separated water
that is secondarily treated water flowing out of the
precipitation tank 4.
[0042]
Although Embodiment 1 has the precipitation tank 4,
outflowing water from the biological treatment tank 3 may
be supplied directly to the submerged membrane separation
tank 5 with a flocculation system for a biological
treatment. The submerged membrane separation tank 5 with
a flocculation system has a submerged membrane separation
apparatus 7 immersed in a reaction tank 6. However, a
membrane separation apparatus may be located outside the
reaction tank 6. The water treatment system in accordance
with Embodiment 1 is basically continuously operated but
may be operated so as to carry out a batch treatment in
each of the tanks.
[0043]
The water treatment system has a main channel line 8
that sequentially connects the first precipitation tank 2,
the biological treatment tank 3, the precipitation tank 4,
and the submerged membrane separation tank 5 with a
flocculation system. Besides the main channel 8, the
system has a primarily treated water supply line 9
constituting a treated water supply unit that supplies
primarily treated water to the reaction tank 6 and a
mixture supply line 10 that supplies outflowing water
from the biological treatment tank 3 directly to the
reaction tank 6 without passing the water through the
precipitation tank 4.
[0044]
The submerged membrane separation tank 5 with a
flocculation system has a flocculation agent supply line
11 constituting flocculation agent addition unit for

- 14 -
supplying a flocculation agent to the reaction tank 6.
The flocculation agent supply line 11 can be provided
being connected to the middle of a raw water supply line
9.
[0045]
Although not disclosed in the drawings, the
biological treatment tank 3 has an aeration apparatus.
Each of the main channel 8, the primarily treated water
supply line 9, and the mixture supply line 10
appropriately has a pump and a valve apparatus.
[0046]
The submerged membrane separation apparatus 7
comprises a plurality of plate-like membrane cartridges
21 and an air diffuser 22 that ejects a membrane surface
cleaning gas from the bottom thereof being located inside
a case 23. A blower 24 is located outside the tank to
supply air to the air diffuser 22. Each of the membrane
cartridges 21 is in communication with a permeation water
guide-out pipe 25 via a water collection pipe (not shown)
[0047]
The submerged membrane separation apparatus 7 aerates
an activated sludge mixture in the tank using air ejected
by the air diffuser 22 and allows aeration air to act on
the membrane surface of the membrane cartridges 21 as
membrane surface cleaning air.
[0048]
In the aerating state, the submerged membrane
separation apparatus 7 allows a suction pump 2 6 to apply
driving pressure to the membrane cartridges 21, which
thus filters the activated sludge mixture in the tank.
The permeation water having permeated through the
membrane cartridges 21 is guided out of the tank through
the permeation water guide-out pipe 25 as treated water.
The membrane cartridge 21 can be used for gravity

- 15 -
filtration using a water head in the tank as driving
pressure.
[0049]
The aerated air ejected from the air diffuser 22
causes a rising flow of the mixture in the tank. The
rising flow comprising bubbles of the aerated air and the
mixture in the tank washes the membrane surfaces of the
membrane cartridges 21. This inhibits a separation
function from being degraded to prevent malfunctioning.
[0050]
In Embodiment 1, the pretreatment process comprises
the first precipitation tank 2. However, the technique
for the pretreatment may be appropriately selected in
accordance with the nature of the treatment target raw
water 1. For example, when the treatment target raw water
1 contains large excrement residues, a screen is used to
separate the residues into solids and liquids. Removal of
the large excrement residues prevents fouling in the
membrane cartridges 21 and air diffuser 22 in the
submerged membrane separation apparatus 7.
[0051]
If the excessively high BOD concentration of the
treatment target raw water 1 adversely affects the
concentration of biologically persistent substances and
COD concentration in the treated water in the submerged
membrane separation apparatus 7, then precipitation
separation, filtration separation, flocculation
separation, or the like is carried out to reduce the BOD
concentration of the primarily treated water flowing into
the biological treatment process. This inhibits an
increase in the concentration of MLSS in the reaction
tank 6.
[0052]
If the excessively low BOD concentration of the
treatment target raw water 1 prevents the concentration

- 16 -
of MLSS in the reaction tank 6 from increasing to a
sufficient value, then for example, the biologically
persistent substances are made easily degradable by
crushing excrement residues by a physical technique,
carrying out a chemical reaction-like dissolution
treatment using chemicals, or causing oxidation using
chemicals. This allows an increase in the BOD
concentration of the primarily treated water flowing into
the biological treatment process and promote an increase
in the concentration of MLSS in the reaction tank 6.
[0053]
As shown in FIG. 2, in the submerged membrane tank 5
with a flocculation system, the reaction tank 6 has a
water gauge 12, and the main channel 8, the primarily
treated water supply line 9, and the mixture supply line
10, each connecting to the reaction tank 6, have
respective flow meters 13, 14, 15. The permeation water
guide-out pipe 25 has a flow meter 16 and a pressure
gauge 17. A control apparatus 18 controls the operation
of the blower 24 and suction pump 26 on the basis of
measurements from the flow meters 13, 14, 15, 16 and the
pressure gauge 17.
[0054]
Embodiment 1 has the primarily treated water supply
line 9. However, as shown in FIG. 3, in Embodiment 2 of
the present invention, a raw water supply line 18 may be
provided which serves as a raw water supply unit that
supplies the treatment target raw water 1 to the reaction
tank 6. As shown in FIG. 4, as Embodiment 3, the raw
water supply line 18 may be connected to the primarily
treated water supply line 9 so as to selectively supply
the primarily treated water or the treatment target raw
water 1 or their mixture to the reaction tank 6.
[0055]

- 17 -
The effects of the configuration in accordance with
Embodiment 1 will be described below. The basic effects
of Embodiments 2 and 3 are the same as those of
Embodiment 1 and will not be described below.
[0056]
The treatment target raw water 1 flowing into the
system is treated by sequentially passing through the
first precipitation tank 2, the biological treatment tank
3, and the submerged membrane separation tank 5 with a
flocculation system.
[0057]
When the secondarily treated water in the secondary
treatment process is treated in the submerged membrane
separation tank 5 with a flocculation system, the reduced
BOD concentration (for example, less than 20 mg/L) in the
reaction tank 6 significantly reduces the amount of
sludge generated in the reaction tank 6.
[0058]
In this case, an appropriate amount of primarily
treated water is supplied from the primarily treated
water supply line 9 to the reaction tank 6 in the
submerged membrane separation tank 5 with a flocculation
system. Here, in Embodiment 2, an appropriate amount of
treatment target raw water 1 is supplied through the raw
water supply line 18. In Embodiment 3, at least either of
the primarily treated water or the treatment target raw
water 1 is supplied.
[0059]
The supply of the primarily treated water (or the
treatment target raw water 1) adjusts the BOD
concentration of the water flowing into the reaction tank
6 to increase the amount of sludge generated in the
reaction tank 6. Further, an appropriate amount of
flocculation agent is added to the water through the
flocculation agent supply line 11.

- 18 -
[0060]
To adjust the concentration of the sludge in the
reaction tank 6, an appropriate amount of outflowing
water from the biological treatment tank 3 may be
supplied directly to the reaction tank 6 through the
mixture supply line 10 without passing the water through
the precipitation tank 4. The amount of the flocculation
agent to be added can be inhibited by this adjustment of
the sludge concentration. In this case, all the
secondarily treated water to be introduced into the
reaction tank 6 may be used as outflowing water from the
biological treatment tank 3 which does not flow through
the precipitation tank 4.
[0061]
As described above, the primarily treated water and
the flocculation agent are added to the target water to
increase the amount of organic components and SSs in the
reaction tank 6. The nature of the mixture (membrane
separation target liquid) in the reaction tank 6 is
adjusted so that the concentration of the sludge is
suitable for floc formation. The flocculation agent is
further used to flocculate the organic components
(dissoluble substances) and SSs (solid substances) to
form sludge flocs of a sufficiently large size.
[0062]
By thus adjustably making the concentration of the
sludge in the reaction tank 6 suitable for floc formation
to increase the diameter of sludge flocs, it is possible
to reduce the fouling of the membrane surfaces and to
improve the filtration property. This enables the treated
water in the biological treatment process to be suitably
treated, allowing a reduction in the amount of added
flocculation agent.
[0063]

- 19 -
In the above configuration, the flocculation agent is
independently added to the reaction tank 6. However, the
flocculation agent may be added to the treatment target
raw water 1 in the raw water supply line 9. In this case,
the flocculation agent is added to the water, with the
ratio of the amount of added flocculation agent to the
amount of introduced treatment target raw water 1, set at
a given value. The treatment target raw water 1 premixed
with the flocculation agent is thus supplied to the
reaction tank 6.
[0064]
The amount of added flocculation agent can be
optimized by setting the ratio of the amount of added
flocculation agent to the amount of generated sludge or
the amount of reduction in sludge at the given value (the
amount of flocculation agent per sludge concentration).
Alternatively, the amount of flocculation agent contained
in excess sludge discharged from the reaction tank 6 may
be measured, and the shortage of the flocculation agent
may be determined from the measurement on the basis of
the rule of thumb. In this case, the determined shortage
could be the amount of flocculation agent to be
replenished. The amount of added flocculation agent is
determined as follows.
If the concentration of the sludge in the reaction
tank 6 increases:
That is, if the amount of sludge increases owing to
the BOD derived from the primarily treated water or the
concentration of the solids, SSs, contained in the
secondarily treated water, the amount E(mg/d) of
flocculation agent added per day is determined in
accordance with:
E = C x D.
Here, it is assumed that the flocculation agent is
present adhering to the sludge flocs and that the

- 20 -
concentration A(mg/L) of the flocculation agent in the
reaction tank 6 is proportional to the concentration
B(mg/L) of the sludge. Then, the concentration C = A/B of
the flocculation agent per sludge concentration is
determined. Then, the amount E(mg/d) of flocculation
agent added per day is determined on the basis of the
amount D(mg/d) of increase in the amount of sludge in the
reaction tank 6 per day.
[0065]
In the case where the concentration of the sludge in
the reaction tank 6 decreases:
That is, if almost all of the secondarily treated
water introduced into the reaction tank 6 has passed
through the biological treatment tank 3 and the
precipitation tank 4 and the amount of the sludge in the
reaction tank 6 decreases owing to self-degradation and
decreases as extraction of excess sludge, the amount
(mg/d) of flocculation agent added per day is determined
in accordance with the following equation.
Amount of added flocculation agent = sludge amount
decrease rate = sludge concentration decrease rate x
reaction tank capacity
Here, the sludge amount decrease rate in the reaction
tank 6 = MLSS decrease rate - MLSS increase rate.
Dividing both sides of the above equation by the capacity
of the reaction tank 6 results in sludge concentration
decrease rate = MLSS concentration decrease rate - MLSS
concentration increase rate.
[0066]
The above technique allows the flocculation agent to
be added to the water more easily than the conventional
technique of measuring the dissoluble COD concentration
in the reaction tank 6, the COD concentration and
turbidity of outflowing water flowing out of the reaction

- 21 -
tank 6, and adding the flocculation agent so that these
measurements reach respective appropriate values.
[0067]
To carry out stirring in the reaction tank 6, either
mechanical or pneumatic measures may be adopted. However,
the present embodiment uses aeration carried out by the
air diffuser 22 in the submerged membrane separation tank
5 with a flocculation system.
[0068]
FIG. 5 shows the relationship between negative
pressure increase rate (kPa/d) and MLSS concentration
(mg/L) in the case where the submerged membrane
separation apparatus 7 in the submerged membrane
separation tank 5 with a flocculation system is operated
in accordance with a suction filtration scheme. The more
a value for the negative increase rate is, the more
likely the membrane gets fouled.
[0069]
The figure clearly indicates that a reduced MLSS
concentration increases the negative pressure increase
rate to make the membrane of the plate-like membrane
cartridge 21 more likely to get dirty. The clogging of
the membrane can be inhibited by adding the primarily
treated water and the flocculation agent to increase the
MLSS concentration.
[0070]
A description will be given with reference to Table 1.
[0071]
[Table 1]

Assumed sludge
throughput m3/d 100
Raw water quality Secondarily treated
water quality
BOD mg/L 200
T-N mg/L 40
Steady state operation

- 22 -
Reaction tank HRT Hr 2
Reaction tank capacity m3 8.33
Yield coefficient 0.75
Killing coefficient 1/d 0.1
Apparent yield 0.4
coefficient
Assumed MLSS in Mg/L 8000
reaction tank
BOD removal speed kg/kgMLSS/d 0.12
(20oC)
Case 1 Reduction in flocculation agent in steady state operation (only BOD
regulation)
No raw sewage Raw sewage
introduced
BOD removal speed in kg/d 8 8
reaction tank
Allowable amount of m3/d 42
raw sewage to be
introduced
Amount of introduced m3/d 0 20
raw sewage
MLSS increase rate g/d 750 3600
MLSS decrease rate g/d 6700 6700
Flocculation agent g/d 5950 3100
addition requirement
Flocculation agent 2850
reduction amount
Flocculation agent % 48
reduction rate
Case 2 Reduction in flocculation agent in steady state operation (T-N regulated,
at most 10 mgN/L)
BOD removal speed in Kg/d 8 8
reaction tank
Allowable amount of m3/d 42
raw sewage to be
introduced
Amount of introduced m3/d 0 6.25
raw sewage
MLSS increase rate g/d 800 1600
MLSS decrease rate g/d 6700 6700
Flocculation agent g/d 5950 5100
addition requirement
Flocculation agent 800

- 23 -
reduction amount
Flocculation agent % 14
reduction rate
Case 3 Reduction in flocculation agent in steady state operation (T-N regulated,
at most 10 mgN/L)
Secondarily treated water supplied without passing the : outflowing water
through precipitation tank
BOD removal speed in kg/d 8 8
reaction tank
Allowable amount of m3/d 42
raw sewage to be
Introduced
Amount of introduced m3/d 0 6.25
raw sewage
MLSS increase rate g/d 800 1600
MLSS decrease rate g/d 6700 6700
MLSS addition speed g/d 4200 4200
with secondarily
treated water
Flocculation agent g/d 1700 900
addition requirement
Flocculation agent 800
reduction amount
Flocculation agent % 47
reduction rate
[0072]
Case 1
This shows the case where the secondarily treated
water quality was subjected only to BOD regulation, and
2 0 m3/d of raw sewage (primarily treated water) was added
to the tank; this amount accounts for about 50% of the
amount of sewage that can be introduced. The flocculation
agent addition requirement was 5,950 g/d when no raw
sewage (primarily treated water) was introduced. However,
introduction of raw sewage reduced the flocculation agent
addition requirement to 3,100 g/d. The flocculation agent
addition requirement was reduced by 2,850 g/d, that is,
by 48%.
[0073]
Case 2

- 24 -
The secondarily treated water quality was subjected
to BOD and T-N regulations. The amount of introduced raw
sewage (primarily treated water) was smaller than that in
Case 1; 6.25 m3/d of raw sewage was added to the tank.
The flocculation agent addition requirement was 5,900 g/d
when no raw sewage was introduced. However, introduction
of raw sewage reduced the flocculation agent addition
requirement to 5,100 g/d. The flocculation agent addition
requirement was reduced by 800 g/d, that is, by 14%.
[0074]
Case 3
The secondarily treated water quality was subjected
to BOD and T-N regulations, 6.25 m3/d of raw sewage
(primarily treated water) was added to the tank, and an
appropriate amount of outflowing water from the
biological treatment tank 3 was supplied directly to the
reaction tank 6 for an advanced treatment process through
the mixture supply line 10 without passing the outflowing
water through the precipitation tank 4 . When no raw
sewage was introduced and outflowing water from the
biological treatment tank 3 was introduced without
passing the outflowing water through the precipitation
tank 4, the flocculation agent addition requirement was
1,700 g/d. However, the flocculation agent addition
requirement was reduced to 900 g/d by introducing both
raw sewage and outflowing water from the biological
treatment tank 3 not having passed through the
precipitation tank 4. The flocculation agent addition
requirement was reduced by 800 g/d, that is, by 47%.
[0075]
The quality of the treatment target raw water 1 is
not constant but varies. With variation in water quality,
the increase in the amount of sludge in the reaction tank
6 varies. An increase in the amount of sludge leads to
increase in the amount of flocculation agent used. Thus,

- 25 -
to sufficiently exert the flocculation agent reduction
effect in accordance with the present invention, it is
necessary to control the increase in the amount of sludge
to within an appropriate range in spite of a variation in
water quality.
[0076]
The increase in the amount of sludge can be
controlled by varying conditions for mixing the primarily
treated water 1 or treatment target raw water 1 with the
secondarily treated water, taking into account the
quality of the treatment target raw water 1 and the
quality of the secondarily treated water in the
biological treatment tank 3. However, this is an advanced
control that requires much experience.
[0077]
Further, when the submerged membrane separation
apparatus 7 is operated under a load condition where the
concentration of MLSS in the reaction tank 6 is low as in
the present invention, a variation in the quality of the
treatment target raw water 1 sensitively affects the
filtration of the mixture in the reaction tank 6. Thus,
the amount of generated sludge needs to be controlled in
real time depending on the water quality. However, since
it is difficult to quickly analyze water quality, real
time control is substantially impossible.
[0078]
For example, if plural types of soft drinks are
manufactured on the same line and industrial wastewater
is biologically treated, a change in the types of
manufactured products significantly varies the quality of
the industrial wastewater. This varies the BOD load on
the biological treatment tank 3. However, several days
are required to have biologically treated activated
sludge adapted to a variation in environment.
Consequently, much experience is required to stabilize

- 26 -
the quality of the secondarily treated water in a short
period of time, that is, the inflowing BOD in the
reaction tank 6.
[0079]
Further, in the case where biological treatment
efficiency is improved, the BOD concentration of the
secondarily treated water decreases to allow the
stabilization to be achieved by adjusting the mixture
rate of the primarily treated water. However, with
reduced biological treatment efficiency, the BOD
concentration of the secondarily treated water increases
to reduce the amount of water. In this state, to keep the
quality and quantity of the permeation water in the
submerged membrane separation tank 5 with a flocculation
system at respective target values, it is necessary to
increase the amount of flocculation agent used.
[0080]
An explanation will be given of the adverse effect of
a variation in the quality of the treatment target raw
water 1 on the filtration of the mixture in the tank.
With a common biological treatment method, when the
relationship between the biomass X(mg/L) in the tank and
inflowing BOD C(mg/L) and tank residence time T (day) is
such that 0.01 treated water is high but active sludge proliferates
inappropriately. Furthermore, when C/TX > 0.1, the
biological treatment is difficult, degrading the quality
of treated water.
[0081]
Also in the present invention, a significant
variation in the quality of the treatment target raw
water 1 significantly varies the quality of the
secondarily treated water in the biological treatment
tank 3. That is shown in Table 2 and Table 3.
[0082]

- 27 -
[Table 2]
Raw water Biologically-
treated water Inflowing water
into reaction
tank
Mixture ratio (raw
water:biologically
treated water) 1:10
BOD (mg/L) small 50 3 7
BOD (mg/L) standard 150 20 32
BOD(mg/L) large 500 150 182
[0083]
[Table 3]
Inflowing BOD C (mg/L) 7 32 182
Tank residence time T(day) 0.25 0.25 0 .25
Tank biomass X(mg/L) 7000 7000 7000
BOD load C/TX 0. 004 0.02 0.1
[0084]
As shown in Table 2, when the BOD of the raw water
(treatment target raw water 1) is as low as 50 (mg/L),
the BOD of the biologically treated water (secondarily-
treated water) is 3 (mg/L) and the BOD of the inflowing
water to the reaction tank, obtained by mixing the raw
water with the biologically treated water in the ratio of
1:10, is 7 (mg/L). When the BOD of the raw water
(treatment target raw water 1) is standard, that is, 150
(mg/L), the BOD of the biologically treated water
(secondarily treated water) is 2 0 (mg/L) and the BOD of
the inflowing water to the reaction tank, obtained by
mixing the raw water with the biologically treated water
in the ratio of 1:10, is 32 (mg/L). When the BOD of the
raw water (treatment target raw water 1) is as high as
500 (mg/L), the BOD of the biologically treated water
(the secondarily treated water in the biological
treatment tank 3) is 150 (mg/L) and the BOD of the
inflowing water to the reaction tank, obtained by mixing

- 28 -
the raw water with the biologically treated water in the
ratio of 1:10, is 182 (mg/L).
[0085]
As shown in Table 3, provided that the tank residence
time T is 0.25 (day) and the tank biomass X is 7,000
(mg/L), the BOD load C/TX is 0.004 when the inflowing BOD
C of the inflowing water is 7 (mg/L), 0.02 when the
inflowing BOD C of the inflowing water is 32 (mg/L), and
0.1 when the inflowing BOD C of the inflowing water is
182 (mg/L).
[0086]
Accordingly, although the BOD load C/TX is 0.02 and
the water quality is thus stable during a normal
operation in which the inflowing BOD C is 32 (mg/L), a
significant variation in the quality of the treatment
target raw water 1 increases the BOD load C/TX to 0.1 to
promote the proliferation of sludge. Microorganisms thus
produce sub-metabolites (biopolymers) to make the
filtration of the mixture in the tank unsuitable for
membrane separation.
[0087]
Thus, the control apparatus 18 controls the amount of
aeration of the air diffuser 22 using as a control
indicator at least one of the trans-membrane pressure
acting on the membrane cartridge 21, the amount of loads
flowing into the reaction tank 6, the level of the water
in the reaction tank 6, and the amount of outflow of
membrane permeation liquid.
[0088]
The trans-membrane pressure is measured using the
pressure gauge 17. The inflow amount of loads flowing
into the reaction tank 6 refers to the amount of water
flowing into the reaction tank 6 through the main channel
8, the primarily treated water supply line 9, and the
mixture supply line 10. The inflow amount is measured

- 29 -
using the flow meters 13, 14, 15. The level of the water
in the reaction tank 6 is measured using the water gauge
12. The outflow amount of the membrane permeation liquid
is measured using the flow meter 16.
Control method 1
The trans-membrane pressure is an indicator
indirectly indicating the fouling state of the membrane
surface in the membrane separation apparatus. An increase
in trans-membrane pressure tends to clog the membrane
surface. Thus, when the pressure gauge 17 shows an
increase in trans-membrane pressure, the operation of the
blower 24 is controlled to increase the amount of
aeration of the air diffuser 22.
[0089]
[Table 4]
Trans-membrane pressure (kPa) Aeration amount rate (%)
Minimum trans-membrane pressure 100
Minimum trans-membrane pressure
+ 5 kPa 150
Minimum trans-membrane pressure
+10 kPa 200
[0090]
For example, as shown in Table 4, it is assumed that
the aeration amount corresponding to the minimum trans-
membrane pressure preset to be a design value be 100%. If
trans-membrane pressure increases by 5 kPa from the
minimum value, an aeration amount is set to 150%. If
trans-membrane pressure increases by 10 kPa from the
minimum value, an aeration amount is set to 2 0 0%. Table 5
shows that the increase in aeration amount contributes to
reducing the fouling state of the membrane surface.
[0091]
[Table 5]
Aeration amount increase Effect
Instantaneous flux Aeration amount Trans-membrane
pressure increase

- 30 -
rate
(m/d) (L/min/sheet) (kPa/d)
2.2 12 0.6
2.2 16 0.12
[0092]
Table 5 shows that, an increase in aeration amount
reduced the trans-membrane pressure increase rate from
0.6 to 0.12 and that the instantaneous flux can be kept
at 2.2.
Control method 2
Increased flux and the increased operation rate of
the membrane separation apparatus cause the fouling of
the membrane surface to progress faster. Thus, the amount
of liquid having permeated the membrane cartridge 21 is
measured using the flow meter 16. The amount of water
flowing into the reaction tank 6 is measured using the
flow meters 13, 14, 15. Alternatively, the level of the
water in the reaction tank 6 is measured using the water
gauge 12.
[0093]
[Table 6]
Instantaneous
flux Inflow discharge
amount Water level in
reaction tank Aeration
amount
rate
(m/d) (m3/min) (m) (%)
Design flux Design flow rate
x1 Reference water level 100
Design flux x2 Design flow rate
x2 Reference water level
+ 0 . 5m 150
Design flux x2 . 5 Design flow rate
x2 . 5 Reference water level
+ 1. 0m 200
[0094]
Table 6 shows flux as the instantaneous flux and the
amount of water flowing into the reaction tank 6 as the
inflow discharge amount. As shown in Table 6, it is
assumed that the aeration amount corresponding to the

- 31 -
design flux, the design flow rate, and the reference
water level in the reaction tank, which are preset as
design values, is 100%. When the inflow discharge amount
(the inflowing water amount measured using the flow
meters 13, 14, 15) doubles the design flow rate, the
operation of the suction pump 26 is controlled so as to
double the instantaneous flux and the operation of the
blower 24 is controlled so as to set the aeration amount
to be 150%.
[0095]
When the inflow discharge amount (the inflowing water
amount measured using the flow meters 13, 14, 15) is 2.5
times as large as the design flow rate, the operation of
the suction pump 26 is controlled so as to increase the
instantaneous flux by a factor of 2.5 and the operation
of the blower 24 is controlled so as to set the aeration
amount to be 2 0 0%.
[0096]
An increase or decrease in inflow discharge amount
can be sensed on the basis of the level of the water in
the reaction tank 6. Thus, when the water level measured
using the water gauge 12 is 0.5 m higher than the
reference water level, the operation of the suction pump
26 is controlled so as to double the instantaneous flux
and the operation of the blower 24 is controlled so as to
set the aeration amount to be 150%.
[0097]
When the water level measured using the water gauge
12 is 1.0 m higher than the reference water level, the
operation of the suction pump 26 is controlled so as to
increase the instantaneous flux by a factor of 2.5 and
the operation of the blower 24 is controlled so as to set
the aeration amount to be 2 00%.
[0098]

- 32 -
The aeration amount can also be controlled by a
combination of the trans-membrane pressure measured using
the pressure gauge 17, the inflow amount measured using
the flow meters 13, 14, 15, and the water level measured
using the water gauge 12.

- 33 -
CLAIMS
1. A water treatment system in which raw water to be
treated flowing into the system flows into a reaction
tank for a membrane separation process via a biological
treatment process and in which in the membrane separation
process, a flocculation agent is used together to carry
out a membrane separation treatment, the system
comprising a raw water supply unit that supplies the
treatment target raw water to the reaction tank and a
flocculation agent addition unit that adds the
flocculation agent to the reaction tank.
2 . A water treatment system in which raw water to be
treated flowing into the system is sequentially subjected
to a pretreatment process and a biological treatment
process and then flows into a reaction tank for a
membrane separation process and in which in the membrane
separation process, a flocculation agent is used together
to carry out a membrane separation treatment, the system
comprising a treated water supply unit that supplies the
treated water from the pretreatment process to the
reaction tank and a flocculation agent addition unit that
adds the flocculation agent to the reaction tank.
3. The water treatment system according to claim 2,
wherein the pretreatment process comprises a solid-liquid
separation treatment process or a dissolution treatment
process.
4. The water treatment system according to claim 1,
wherein the system has, between the biological treatment
process and the membrane separation process, a
precipitation treatment unit that carries out a
precipitation treatment on out-flowing water from a
biological treatment tank constituting the biological
treatment process and supplies separated water to the
reaction tank for the membrane separation process, and a

- 34 -
mixture supply unit that supplies the outflowing water
from the biological treatment tank to the reaction tank
for the membrane separation process without passing the
outflowing water through the precipitation treatment unit.
5. The water treatment system according to claim 2,
wherein the system has, between the biological treatment
process and the membrane separation process, a
precipitation treatment unit that carries out a
precipitation treatment on outflowing water from a
biological treatment tank constituting the biological
treatment process and supplies separated water to the
reaction tank for the membrane separation process, and a
mixture supply unit that supplies the outflowing water
from the biological treatment tank to the reaction tank
for the membrane separation process without passing the
outflowing water through the precipitation treatment unit.
6. The water treatment system according to claim 1,
comprising a submerged membrane separation apparatus in
the reaction tank for the membrane separation process,
the submerged membrane separation apparatus comprising a
membrane separation unit, an air diffuser located below
the membrane separation unit, and a control unit that
controls the amount of aeration in the air diffuser, the
control unit controlling the amount of aeration in the
air diffuser using as a control indicator at least one of
a trans-membrane pressure in the membrane separation unit,
the amount of load flowing into the reaction tank, the
level of the water in the reaction tank, and the amount
of membrane permeation liquid flowing out through the
membrane separation unit.
7. The water treatment system according to claim 2,
comprising a submerged membrane separation apparatus in
the reaction tank for the membrane separation process,
the submerged membrane separation apparatus comprising a
membrane separation unit, an air diffuser located below

- 35 -
the membrane separation unit, and a control unit that
controls the amount of aeration in the air diffuser, the
control unit controlling the amount of aeration in the
air diffuser using as a control indicator at least one of
a trans-membrane pressure in the membrane separation unit,
the amount of load flowing into the reaction tank, the
level of the water in the reaction tank, and the amount
of membrane permeation liquid flowing out through the
membrane separation unit.

A water treatment system having a biological
treatment step (a secondary treatment step) and a
membrane separation step (a tertiary treatment step),
wherein a portion of the raw water to be treated and/or a
portion of the primarily treated water in the
pretreatment step are biologically treated and supplied
into a reaction tank in the membrane separation step as
the main channel system, while the remainder the raw
water to be treated and/or the remainder of the primarily
treated water in the pretreatment step are added together
with a flocculating agent to the reaction tank in the
membrane separation step, and then the membrane
separation is conducted in the membrane separation step.

Documents:

02972-kolnp-2007-abstract.pdf

02972-kolnp-2007-claims.pdf

02972-kolnp-2007-correspondence others 1.1.pdf

02972-kolnp-2007-correspondence others 1.2.pdf

02972-kolnp-2007-correspondence others 1.3.pdf

02972-kolnp-2007-correspondence others 1.4.pdf

02972-kolnp-2007-correspondence others-1.5.pdf

02972-kolnp-2007-correspondence others.pdf

02972-kolnp-2007-description complete.pdf

02972-kolnp-2007-drawings.pdf

02972-kolnp-2007-form 1.pdf

02972-kolnp-2007-form 18.pdf

02972-kolnp-2007-form 2.pdf

02972-kolnp-2007-form 3.pdf

02972-kolnp-2007-gpa.pdf

02972-kolnp-2007-international publication.pdf

02972-kolnp-2007-international search report.pdf

02972-kolnp-2007-priority document.pdf

02972-kolnp-2007-translated copy of priority document.pdf

2972-KOLNP-2007-(01-10-2012)-FORM-27.pdf

2972-KOLNP-2007-(18-11-2011)-FORM-27.pdf

2972-KOLNP-2007-PETITION UNDER RULE 137.pdf

2972KOLNP-2007-ABSTRACT 1.1.pdf

2972KOLNP-2007-AMANDED CLAIMS.pdf

2972KOLNP-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

2972KOLNP-2007-FORM 2 1.1.pdf

2972KOLNP-2007-FORM 3 1.1.pdf

2972KOLNP-2007-OTHERS 1.1.pdf

abstract-02972-kolnp-2007.jpg


Patent Number 247626
Indian Patent Application Number 2972/KOLNP/2007
PG Journal Number 17/2011
Publication Date 29-Apr-2011
Grant Date 28-Apr-2011
Date of Filing 14-Aug-2007
Name of Patentee KUBOTA CORPORATION
Applicant Address 2-47, SHIKITSU-HIGASHI 1-CHOME, NANIWA-KU OSAKA-SHI, OSAKA
Inventors:
# Inventor's Name Inventor's Address
1 KAZUHISA NISHIMORI C/O KUBOTA CORPORATION, 1-1, HAMA 1-CHOME, AMAGASAKI-SHI, HYOGO 661-8567
2 TAICHI UESAKA C/O KUBOTA CORPORATION, 1-1, HAMA 1-CHOME, AMAGASAKI-SHI, HYOGO 661-8567
3 TATSUYA UEJIMA C/O KUBOTA CORPORATION, 1-1, HAMA 1-CHOME, AMAGASAKI-SHI, HYOGO 661-8567
4 HIDETOSHI MASUTANI C/O KUBOTA MEMBRANE CO., LTD., 2-35, JINMU-CHO, YAO-SHI, OSAKA 581-0067
5 SHIGETO MIUMA C/O KUBOTA MEMBRANE CO., LTD., 2-35, JINMU-CHO, YAO-SHI, OSAKA 581-0067
6 KIYOSHI IZUMI C/O KUBOTA CORPORATION, 1-1, HAMA 1-CHOME, AMAGASAKI-SHI, HYOGO 661-8567
PCT International Classification Number C02F 9/00, C02F 1/44
PCT International Application Number PCT/JP2006/303549
PCT International Filing date 2006-02-27
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2005-052174 2005-02-28 Japan