JP7545874B2 - Water purification method and water purification system - Google Patents

Description

The present invention relates to a water purification method and a water purification system for filtering raw water to obtain purified water.

In order to increase the recovery rate of purified water, for example, as shown in FIG. 10, this type of water purification system has a raw water tank 202 for storing raw water 201, a first-stage membrane filtration device 204 that filters the raw water 201 in the raw water tank 202 to obtain purified water 203, a purified water tank 205 for storing the purified water 203, a backwash wastewater receiving tank 207 for storing backwash wastewater 206 discharged from the first-stage membrane filtration device 204 when the first-stage membrane filtration device 204 is backwashed with the purified water 203 in the purified water tank 205, and a second-stage membrane filtration device 208 that filters the backwash wastewater 206 in the backwash wastewater receiving tank 207 to obtain purified water 203.

The second-stage membrane filtration device 208 is immersed in the backwash drainage 206 in the backwash drainage receiving tank 207. The purified water 203 obtained by the first-stage membrane filtration device 204 is stored in the purified water tank 205 and distributed from the purified water tank 205 to the water distribution area. The purified water 203 obtained by the second-stage membrane filtration device 208 is taken out from the purified water recovery pipe 209 and recovered in the purified water tank 205.

According to this, raw water 201 is introduced from raw water tank 202 through raw water supply piping 211 into first-stage membrane filtration device 204, and purified water 203 obtained by filtering in first-stage membrane filtration device 204 is stored in purified water tank 205 through purified water extraction piping 212.

The purified water 203 is then back-flowed through the first-stage membrane filtration device 204 at regular intervals to perform backwashing, and the backwash wastewater 206 discharged from the first-stage membrane filtration device 204 during this process is supplied to the backwash wastewater receiving tank 207 via the backwash wastewater feed pipe 213. The purified water 203 obtained by filtering the backwash wastewater 206 in the backwash wastewater receiving tank 207 with the second-stage membrane filtration device 208 is collected in fixed amounts in the purified water tank 205 via the purified water recovery pipe 209.

In this way, by obtaining purified water 203 from the backwash wastewater 206 discharged from the first-stage membrane filtration device 204, the recovery rate of the purified water volume relative to the raw water volume is improved.

The above-mentioned water purification system is described, for example, in Patent Document 1 below.

JP2006-272218A

However, in the above conventional system, the purified water 203 is back-flowed into the first-stage membrane filtration device 204 at predetermined time intervals to perform backwashing. For example, if the turbidity of the raw water 201 increases suddenly, the first-stage membrane filtration device 204 will become clogged in a short time, so it is necessary to shorten the time interval between backwashes and increase the frequency (number of times) of backwashing. However, as the frequency of backwashing increases, the amount of backwash wastewater 206 supplied from the first-stage membrane filtration device 204 to the backwash wastewater receiving tank 207 also increases, causing a sudden decrease in the amount of purified water in the purified water tank 205, which may result in a decrease in the amount of purified water 203 distributed from the purified water tank 205 to the water distribution area.

The present invention aims to provide a water purification method and system that can stably distribute a constant amount of purified water to a distribution area even if the frequency of backwashing varies depending on the quality of the raw water, etc.

In order to achieve the above object, the first invention includes a first filtration step of filtering raw water with a first filtration device to obtain first purified water;
A first backwashing step of backwashing the first filtration device using the first purified water;
A water purification method comprising: a second filtration step of filtering the backwash wastewater discharged from the first filtration device in the first backwash step in a second filtration device to obtain second purified water;
The time interval from the first backwash step to the next first backwash step is defined as a backwash cycle.
The water balance is calculated by subtracting the amount of the first purified water consumed in the first backwashing process from the total purified water amount obtained by adding the amount of the first purified water obtained in the first filtration process and the amount of the second purified water obtained in the second filtration process.
The length of the backwash cycle is adjusted according to the quality of the raw water or the filtration resistance of the first filtration device.
The amount of second purified water obtained from the second filtration device per unit time is adjusted so that the average value of the water balance per unit time in each backwash cycle is constant.

According to this, in the second filtration process, the backwash wastewater discharged from the first filtration device in the first backwash process is filtered in the second filtration device to obtain second purified water, improving the recovery rate of the purified water volume relative to the raw water volume.

In addition, even if the frequency of performing the first backwash process changes depending on factors such as the quality of the raw water, the average water balance per unit time in each backwash cycle remains constant, allowing a constant amount of purified water to be stably distributed to the distribution area.

The water purification method according to the second aspect of the present invention is characterized in that the amount of first purified water obtained per unit time during the filtration operation of the first filtration device is kept constant in the first filtration step.
In the water purification method according to the third aspect of the present invention, the first filtration device is a casing-type membrane filtration device in which a filtration membrane is housed in a closed space formed in a casing,
The second filtration device is an immersion-type membrane filtration device in which a filtration membrane is housed in an open space formed within a housing, and the housing and the filtration membrane are immersed in the backwash wastewater stored in a drainage tank.

In the water purification method according to the fourth aspect of the present invention, the first filtration device and the second filtration device each have a ceramic filtration membrane.

The water purification method in the fifth aspect of the present invention includes a manganese removal step of removing manganese from the first purified water obtained in the first filtration step using a manganese removal device;
and a second backwashing step of backwashing the manganese removal device using the first purified water that has been subjected to the manganese removal step .
In the second filtration process, the backwash wastewater discharged from the first filtration device in the first backwash process and the backwash wastewater discharged from the manganese removal device in the second backwash process are filtered in the second filtration device to obtain second purified water.

This allows for an improved recovery rate of purified water relative to the amount of raw water, and allows the manganese in the first purified water to be removed by the manganese removal device.

In the water purification method according to the sixth aspect of the present invention, in the first filtration step, raw water in which a flocculant has been added to form flocs is filtered in a first filtration device.

The seventh invention is a water purification system for performing the water purification method according to any one of the first to sixth inventions,
a first filtration device for filtering raw water to obtain first purified water;
a purified water storage section for storing the first purified water;
a second filtration device that obtains second purified water by filtering backwash wastewater discharged from the first filtration device when the first filtration device is backwashed with the first purified water in the purified water storage section;
A control unit,
The control unit adjusts the length of the backwash cycle in accordance with the water quality of the raw water or the filtration resistance of the first filtration device, and controls operation by adjusting the amount of second purified water obtained from the second filtration device per unit time so that the average value of the water balance per unit time in each backwash cycle is constant.

As described above, according to the present invention, even if the frequency of performing the first backwash process changes depending on the quality of the raw water, etc., the average value of the water balance per unit time in each backwash cycle is kept constant, so a constant amount of purified water can be stably distributed to the distribution area.

FIG. 2 is a diagram of the water purification system according to the first embodiment of the present invention, showing the flow of water during the first and second filtration steps. FIG. 4 is a cross-sectional view of a first filtration device provided in the water purification system of the first embodiment. FIG. 2 is a perspective view of a membrane element of a first filtration device provided in the water purification system of the first embodiment. FIG. 4 is a cross-sectional view of a second filtration device provided in the water purification system of the first embodiment. FIG. 1 is a diagram of the water purification system, showing the water flow during the first backwash process. 1 is a graph showing the operating time of the water purification system and the amount of purified water per hour in each process. FIG. 11 is a diagram of a water purification system according to a second embodiment of the present invention, showing the flow of water during the first and second filtration steps and the manganese removal step. FIG. 1 is a diagram of the water purification system, showing the water flow during the first backwash process. FIG. 1 is a diagram of the water purification system, showing the water flow during the second backwash process. FIG. 1 is a diagram of a conventional water purification system.

The following describes an embodiment of the present invention with reference to the drawings.

(First embodiment)
In the first embodiment, as shown in FIG. 1, 1 is a water purification system that filters raw water 2 to obtain purified water 3. The water purification system 1 includes a raw water storage section 8 that stores raw water 2, a first filtration device 10 that filters the raw water 2 in the raw water storage section 8 to obtain a first purified water 9, a purified water reservoir 11 (an example of a purified water storage section) that stores the first purified water 9, a pressurizing tank 16 that extracts a part of the first purified water 9 in the purified water reservoir 11 and pressurizes it, a drainage tank 13 that stores backwash drainage 12 discharged from the first filtration device 10 when the first filtration device 10 is backwashed using the first purified water 9 in the purified water reservoir 11, a second filtration device 15 that filters the backwash drainage 12 in the drainage tank 13 to obtain a second purified water 14, and a control section (not shown). The purified water 3 stored in the purified water reservoir 11 is a mixture of the first purified water 9 and the second purified water 14.

The raw water storage section 8 has a receiving well 19 and a mixing basin 20. The mixing basin 20 is equipped with a flocculant addition section 22 that adds a flocculant 21 to the raw water 2, and a stirring device 23 that stirs the raw water 2 with the flocculant 21 added. The raw water 2 is supplied to the receiving well 19 from the outside, and flows from the receiving well 19 into the mixing basin 20. By adding the flocculant 21 to the raw water 2 in the mixing basin 20 and stirring it, a large number of flocs are generated in the raw water 2.

As shown in Figures 2 and 3, the first filtration device 10 is a casing-stored membrane filtration device in which a membrane element 28 (an example of a filtration membrane) is stored in a closed space 27 formed in a casing 26, and filters the entire amount of the supplied raw water 2. The membrane element 28 is made of a plurality of ceramic molded bodies 29 having a substantially rectangular parallelepiped shape, and is formed by bonding the porous ceramic molded bodies 29 together via a bonding material layer 30. A plurality of through-flow passages 31 are formed in the membrane element 28, penetrating between both end faces 32, 33. The inner surface side of the through-flow passages 31 forms the primary side, and the outer surface side of the membrane element 28 forms the secondary side.

The membrane element 28 has multiple slits 34. The slits 34 extend in the axial direction of the through-flow passage 31 and are groove-shaped openings on the side surface 35 of the membrane element 28, with both ends of the slits 34 closing near the end faces 32, 33 of the membrane element 28.

The casing 26 has an upper primary side chamber 37 formed at the top and a lower primary side chamber 38 formed at the bottom. The upper end of the membrane element 28 is exposed in the upper primary side chamber 37, and the lower end of the membrane element 28 is exposed in the lower primary side chamber 38, and the through flow passage 31 is connected to the upper primary side chamber 37 and the lower primary side chamber 38.

The lower primary side chamber 38 has a raw water inlet 39, and the upper primary side chamber 37 has a pressurized air inlet 40. The casing 26 also has a purified water outlet 41, which is connected to the space surrounding the secondary side of the membrane element 28.

As shown in FIG. 4, the second filtration device 15 is an immersed membrane filtration device in which multiple tubular membrane elements 45 are housed in an open space 44 formed in a housing 43, and the housing 43 and membrane elements 45 are immersed in the backwash wastewater 12 stored in a wastewater tank 13.

The housing 43 has a rectangular cross section with openings at the top and bottom, forming an open space 44 inside.

Each membrane element 45 is made by forming a filtration membrane 47 on the surface of a ceramic porous tubular support 46, and is arranged with its axis (length) aligned horizontally and in parallel at a specified interval. In addition, below the membrane element 45, an air diffuser 48 capable of adjusting the amount of air diffused is provided. A blower 49 is connected to the air diffuser 48.

As shown in FIG. 1, a raw water supply line 51 is connected between the mixing basin 20 and the raw water inlet 39 of the first filtration device 10, and a raw water supply pump 52 and a first valve 53 are provided in the raw water supply line 51.

A purified water pipe 55 is connected between the purified water outlet 41 of the first filtration device 10 and the purified water reservoir 11, and a second valve 56 is provided in the purified water pipe 55.

A purified water extraction pipeline 57 is connected between the purified water reservoir 11 and the pressurized tank 16, and a purified water extraction pump 58 and a third valve 59 are provided in the purified water extraction pipeline 57.

One end of a first backwash pipe 60 that supplies the first purified water 9 in the pressurized tank 16 to the first filtration device 10 as backwash water is connected to the pressurized tank 16, and the other end of the first backwash pipe 60 is connected midway through the purified water pipe 55. A fourth valve 61 is provided in the first backwash pipe 60.

In addition, pressurized air 63 (compressed air) is supplied from an external compressor and stored in the pressurized tank 16. A pressurized air supply line 64 is connected between the pressurized tank 16 and the pressurized air inlet 40 of the first filtration device 10, and a fifth valve 65 is provided in the pressurized air supply line 64.

In addition, a backwash drainage feed pipe 67 that sends the backwash drainage 12 discharged from the raw water inlet 39 of the first filtration device 10 to the drainage tank 13 branches off from the raw water supply pipe 51 and is connected to the drainage tank 13. A sixth valve 68 is provided in the backwash drainage feed pipe 67.

A purified water recovery pipe 70 is connected between the second filtration device 15 and the purified water reservoir 11 to recover the second purified water 14 obtained by permeating the backwash wastewater 12 in the wastewater tank 13 from the outside to the inside of the membrane element 45 of the second filtration device 15 into the purified water reservoir 11. The purified water recovery pipe 70 is provided with a purified water recovery pump 71 and a seventh valve 72.

One end of a second backwash pipe 74 is connected to the purified water reservoir 11, and supplies the first purified water 9 in the purified water reservoir 11 to the second filtration device 15 as backwash water. The other end of the second backwash pipe 74 is connected to the purified water recovery pipe 70. The second backwash pipe 74 is provided with a second backwash pump 75 and an eighth valve 76.

A water distribution pipeline 78 is connected to the purified water reservoir 11, which distributes the first purified water 9 in the purified water reservoir 11 to the water distribution area.

The water purification method using the water purification system 1 described above is described below.

The water purification process includes a first filtration process A, a first backwash process B, and a second filtration process C.

First, the first filtration process A is a process in which raw water 2 is filtered by the first filtration device 10 to obtain first purified water 9. That is, as shown in FIG. 1, by opening the first valve 53 and the second valve 56 while keeping the fourth to sixth valves 61, 65, and 68 closed, the raw water 2 in the mixing basin 20 is supplied from the raw water supply pipe 51 to the raw water inlet 39 of the first filtration device 10, and is filtered while flowing through the through passage 31 of the membrane element 28 of the first filtration device 10 from the primary side to the secondary side, to obtain the first purified water 9.

The first purified water 9 obtained in this manner is discharged from the purified water outlet 41, passes through the purified water pipeline 55, and is stored in the purified water reservoir 11.

Next, the first backwashing process B is a process of backwashing the first filtration device 10 with the first purified water 9 after the first filtration process A has been performed for a predetermined time. That is, the first valve 53 and the second valve 56 are closed, and the third valve 59, the fourth valve 61, and the sixth valve 68 are opened. As a result, as shown in FIG. 5, a part of the first purified water 9 in the purified water reservoir 11 is supplied to the pressurized tank 16 through the purified water extraction pipe 57. The first purified water 9 in the pressurized tank 16 is pressurized with the pressurized air 63 and supplied to the purified water outlet 41 of the first filtration device 10 through the first backwashing pipe 60 and the purified water pipe 55, and the membrane element 28 is backwashed by flowing the through passage 31 of the membrane element 28 from the secondary side to the primary side.

As described above, the first purified water 9 that has flowed back through the membrane element 28 is discharged from the raw water inlet 39 as backwash wastewater 12 and is supplied to the wastewater tank 13 through the backwash wastewater feed pipe 67.

Furthermore, by opening the fifth valve 65 immediately before the end of the first backwash process B while backwashing the membrane element 28 with the first purified water 9 as described above, the pressurized air 63 in the pressurized tank 16 is supplied to the upper primary side chamber 37 from the pressurized air inlet 40 of the first filtration device 10 through the pressurized air supply pipe 64, and the backwash wastewater 12 remaining in the casing 26 is reliably discharged together with the pressurized air 63 from the raw water inlet 39 to the backwash wastewater feed pipe 67.

Next, the second filtration process C is a process in which the backwash wastewater 12 discharged from the first filtration device 10 in the first backwash process B is filtered by the second filtration device 15 to obtain the second purified water 14. That is, the fourth to sixth valves 61, 65, and 68 are closed, and the seventh valve 72 is opened. As a result, as shown in FIG. 1, the backwash wastewater 12 in the drainage tank 13 is filtered as it flows through the membrane element 45 of the second filtration device 15 from the outside (primary side) to the inside (secondary side), and the second purified water 14 is obtained.

The second purified water 14 obtained in this manner is collected in the purified water reservoir 11 through the purified water collection pipe 70 from the second filtration device 15.

When the second filtration process C is performed, the first filtration process A or the first backwash process B is also performed in parallel. As shown in FIG. 4, an upward flow is generated by diffusing air from the air diffuser 48, and the backwash wastewater 12 in the wastewater tank 13 circulates inside and outside the housing 43. The upward flow becomes a crossflow against the membrane element 45, cleaning the filtration membrane 47 on the surface of the membrane element 45.

In addition, by carrying out the second filtration process C, the turbid matter in the backwash wastewater 12 in the wastewater tank 13 is concentrated, and is appropriately discharged outside the wastewater tank 13 as concentrated sludge.

FIG. 6 is a graph showing the relationship between the operation time [hr] of the water purification system 1 and the amount of purified water 9, 14 per hour [m ³ /hr] in each of the above processes A to C.

In each bar graph G1, the shaded portion G1a indicates the amount of first purified water 9 supplied from the first filtration device 10 to the purified water reservoir 11 in the first filtration process A. The dotted portion G1b indicates the amount of first purified water 9 supplied from the purified water reservoir 11 to the first filtration device 10 via the pressurized tank 16 in the first backwash process B. Furthermore, the white portion G1c indicates the amount of second purified water 14 recovered from the second filtration device 15 to the purified water reservoir 11 in the second filtration process C.

The backwash cycle shown in the graph of FIG. 6 corresponds to the time interval from the first backwash step B to the next first backwash step B. Here, the control unit adjusts the length of the backwash cycle according to the water quality of the raw water 2, for example the turbidity of the raw water 2, and controls the operation of the second filtration device 15. For example, a threshold value is set for the turbidity, and if the measured turbidity of the raw water 2 is equal to or lower than the threshold value, it is determined to be normal water quality as shown in FIG. 6, and the backwash cycle is set to 3 hours. If the measured turbidity of the raw water 2 exceeds the threshold value, it is determined to be high turbidity water quality, and the backwash cycle is shortened to 1 hour.

In bar graph G1 of Figure 6, the raw water 2 is of normal quality from the start of operation until 15 hours have passed, so the backwash cycle is set to 3 hours and the first backwash process B is carried out every 3 hours.

Here, only the first filtration step A is carried out for three hours from the start of operation, and 16 m ³ of first purified water 9 is supplied from the first filtration device 10 to the purified water reservoir 11 per hour.

Then, from the fourth hour onwards, the first filtration process A, the first backwash process B and the second filtration process C are carried out. The time required for the first backwash process B is several minutes, which is set to be significantly shorter than the time required for the first filtration process A and the second filtration process C.

At the fourth hour, in the first filtration process A, 16 [ ^m3 /hour] of the first purified water 9 is supplied from the first filtration device 10 to the purified water reservoir 11 as shown in the shaded area G1a, in the first backwash process B, 0.9 [ ^m3 /hour] of the first purified water 9 is supplied from the purified water reservoir 11 to the first filtration device 10 for backwashing as shown in the dotted area G1b, and in the second filtration process C, 0.3 [ ^m3 /hour] of the second purified water 14 is recovered from the second filtration device 15 to the purified water reservoir 11 as shown in the white area G1c.

Thereafter, at the fifth hour, the first filtration process A and the second filtration process C are carried out. In the first filtration process A, 16 ^m3 /hour of the first purified water 9 is supplied from the first filtration device 10 to the purified water reservoir 11, as shown in the shaded area G1a, and in the second filtration process C, 0.3 ^m3 /hour of the second purified water 14 is recovered from the second filtration device 15 to the purified water reservoir 11, as shown in the white area G1c.

Then, in the sixth hour, the first filtration process A and the second filtration process C are carried out in the same manner as in the fifth hour above.

Then, in the seventh hour, the first filtration process A, the first backwash process B, and the second filtration process C are carried out in the same manner as in the fourth hour above.

In this case, if the water balance is the total purified water amount obtained by adding up the amount of first purified water 9 obtained in the first filtration process A and the amount of second purified water 14 obtained in the second filtration process C minus the amount of first purified water 9 consumed in the first backwash process B, the average hourly water balance during the backwash cycle at normal water quality (i.e., the three hours from the fourth hour to the sixth hour) is as follows:
Amount of first purified water 9 obtained in the first filtration process A from the 4th hour to the 6th hour (see the shaded area G1a of the bar graph G1): 16 ^m3 x 3 = 48 ^m3
Amount of second purified water 14 obtained in the second filtration process C from the 4th hour to the 6th hour (see the white portion G1c of the bar graph G1): 0.3 ^m3 x 3 = 0.9 ^m3
Amount of first purified water 9 consumed in the first backwash process B from the 4th hour to the 6th hour (see the dotted portion G1b of the bar graph G1): 0.9 ^m3
●Water balance from the 4th hour to the 6th hour: ^48m3 + 0.9m3 ^{- 0.9m3} = ^48m3
●Average hourly water balance from the 4th to the 6th hour: 48 ^m3 ÷ 3 hours = 16 ^m3 /hour Similarly, the control unit controls the operation of the second filtration device 15 so that the average hourly water balance for each backwash cycle (3 hours) under normal water quality, i.e., the average hourly water balance from the 7th to the 9th hour, the average hourly water balance from the 10th to the 12th hour, and the average hourly water balance from the 13th to the 15th hour, are each 16 [ ^m3 /hour].

If the water quality of raw water 2 changes from normal quality to high turbidity 15 hours after the start of operation, the backwash cycle is shortened to 1 hour, and the first backwash process B is carried out every hour from the 16th hour to the 21st hour.

In this case, the average hourly water balance during the backwash cycle (i.e., the 16th hour) is as follows:
Amount of first purified water 9 obtained in the first filtration process A at the 16th hour (see the shaded area G1a of the bar graph G1): ¹⁶ m3
Amount of the second purified water 14 obtained in the second filtration process C at the 16th hour (see the white portion G1c of the bar graph G1): 0.9 ^m3
Amount of first purified water 9 consumed in the first backwashing process B at the 16th hour (see dotted portion G1b of bar graph G1): 0.9 ^m3
●Water balance at the 16th hour: 16m ³ + 0.9m ³ - 0.9m ³ = 16m ³
●Average hourly water balance at the 16th hour: 16 ^m3 ÷ 1 hour = 16 ^m3 /hour Similarly, the control unit controls the operation of the second filtration device 15 so that the average hourly water balance for each backwash cycle (1 hour) during high turbidity water quality, i.e., the average hourly water balance from the 17th hour to the 21st hour, is also 16 [ ^m3 /hour].

Then, when the water quality of the raw water 2 returns from high turbidity to normal quality after 21 hours have elapsed since the start of operation, the backwash cycle is returned from 1 hour to 3 hours, and the control unit controls the operation of the second filtration device 15 so that from the 22nd hour onwards, the average hourly water balance for each backwash cycle (3 hours) when the water quality was normal is 16 ^m3 /hour, similar to the 4th to 15th hours described above.

According to the water purification method described above, in the second filtration step C, the backwash wastewater 12 discharged from the first filtration device 10 in the first backwash step B is filtered in the second filtration device 15 to obtain the second purified water 14, improving the recovery rate of the amount of purified water 3 relative to the amount of raw water 2.

Furthermore, even if the frequency of performing the first backwash process B changes depending on the water quality of the raw water 2, the average value of the water balance per unit time in each backwash cycle is kept constant, so that a constant amount of purified water 3 can be stably distributed from the distribution pipeline 78 to the distribution area.
Second Embodiment
7 , the water purification system 1 is provided with a manganese removal device 100 for removing soluble manganese contained in the first purified water 9 obtained in the first filtration step A. The manganese removal device 100 has a filter medium 102 built in a container 101. The container 101 is provided with a purified water inlet 103 into which the first purified water 9 before manganese removal flows in, a purified water outlet 104 from which the first purified water 9 after manganese removal is discharged, and a backwash wastewater outlet 105 from which the backwash wastewater 12 is discharged.

An upstream purified water pipe 55a is connected between the purified water outlet 41 of the first filtration device 10 and the purified water inlet 103 of the manganese removal device 100, and a ninth valve 107 is provided in the upstream purified water pipe 55a.

A downstream purified water pipe 55b is connected between the purified water outlet 104 of the manganese removal device 100 and the purified water reservoir 11.

The first backwash pipe 60 has one end connected to the pressurized tank 16 and the other end connected midway through the upstream purified water pipe 55a.

One end of a backwash pipe 108 for the manganese removal device is connected to the purified water extraction pipe 57, which supplies the first purified water 9 in the purified water reservoir 11 to the manganese removal device 100 as backwash water, and the other end of the backwash pipe 108 for the manganese removal device is connected midway through the downstream purified water pipe 55b. A tenth valve 109 is provided in the backwash pipe 108 for the manganese removal device.

In addition, a backwash drainage feed pipe 110 for the manganese removal device, which sends the backwash drainage 12 discharged from the backwash drainage outlet 105 of the manganese removal device 100 to the drainage tank 13, is connected between the backwash drainage outlet 105 and the drainage tank 13. An eleventh valve 111 is provided in the backwash drainage feed pipe 110 for the manganese removal device.

The water purification method using the water purification system 1 is described below.

The water purification method includes a first filtration process A, a manganese removal process D, a first backwash process B, a second backwash process E, and a second filtration process C.

First, the first filtration process A is a process in which raw water 2 is filtered by the first filtration device 10 to obtain first purified water 9. That is, the fourth to sixth valves 61, 65, 68, the tenth valve 109, and the eleventh valve 111 are closed, and the first valve 53, the second valve 56, and the ninth valve 107 are opened. As a result, as shown in FIG. 7, raw water 2 in the mixing basin 20 is supplied from the raw water supply pipe 51 to the raw water inlet 39 of the first filtration device 10, and is filtered while flowing through the through passage 31 of the membrane element 28 of the first filtration device 10 from the primary side to the secondary side, to obtain the first purified water 9.

The manganese removal process D is a process in which manganese is removed from the first purified water 9 obtained in the first filtration process A by the manganese removal device 100. That is, the first purified water 9 obtained in the first filtration device 10 by the first filtration process A is discharged from the purified water outlet 41 of the first filtration device 10, passes through the upstream purified water pipe 55a, and is supplied to the manganese removal device 100 from the purified water inlet 103, where it passes through the filter media 102, thereby removing the manganese from the first purified water 9.

The first purified water 9 then flows from the purified water outlet 104 of the manganese removal device 100 through the downstream purified water pipe 55b and is stored in the purified water reservoir 11.

The first filtration process A and the manganese removal process D are carried out simultaneously in parallel.

Next, the first backwashing process B is a process of backwashing the first filtration device 10 with the first purified water 9 after the manganese removal process D. That is, the first valve 53, the second valve 56, and the ninth valve 107 are closed, and the third valve 59, the fourth valve 61, and the sixth valve 68 are opened. As a result, as shown in FIG. 8, a part of the first purified water 9 in the purified water reservoir 11 is supplied to the pressurized tank 16 through the purified water extraction pipe 57. The first purified water 9 in the pressurized tank 16 is pressurized by the pressurized air 63 and supplied to the purified water outlet 41 of the first filtration device 10 through the first backwashing pipe 60 and the upstream purified water pipe 55a, and the membrane element 28 is backwashed by flowing the through passage 31 of the membrane element 28 from the secondary side to the primary side.

As described above, the first purified water 9 that has flowed back through the membrane element 28 is discharged from the raw water inlet 39 as backwash wastewater 12 and is supplied to the wastewater tank 13 through the backwash wastewater feed pipe 67.

Furthermore, by opening the fifth valve 65 immediately before the end of the first backwash process B while backwashing the membrane element 28 with the first purified water 9 as described above, the pressurized air 63 in the pressurized tank 16 is supplied to the upper primary side chamber 37 from the pressurized air inlet 40 of the first filtration device 10 through the pressurized air supply pipe 64, and the backwash wastewater 12 remaining in the casing 26 is reliably discharged together with the pressurized air 63 from the raw water inlet 39 to the backwash wastewater feed pipe 67.

Next, the second backwashing process E is a process of backwashing the manganese removal device 100 with the first purified water 9 after the first backwashing process B. That is, the third to sixth valves 59, 61, 65, and 68 are closed, and the tenth valve 109 and the eleventh valve 111 are opened. As a result, as shown in FIG. 9, a portion of the first purified water 9 in the purified water reservoir 11 passes from the purified water extraction pipe 57 through the manganese removal device backwashing pipe 108 and the downstream purified water pipe 55b, and is supplied from the purified water outlet 104 of the manganese removal device 100 into the container 101, and the filter media 102 is backwashed by flowing it back from the secondary side to the primary side.

The first purified water 9 that has flowed back through the filter media 102 as described above is discharged from the backwash drainage outlet 105 to the outside of the manganese removal device 100 as backwash drainage 12, and is supplied to the drainage tank 13 through the backwash drainage feed pipe 110 for the manganese removal device.

Next, the second filtration process C is a process in which the backwash wastewater 12 discharged from the first filtration device 10 in the first backwash process B and the backwash wastewater 12 discharged from the manganese removal device 100 in the second backwash process E are filtered in the second filtration device 15 to obtain the second purified water 14. That is, the fourth to sixth valves 61, 65, 68, the tenth valve 109, and the eleventh valve 111 are closed, and the seventh valve 72 is opened. As a result, as shown in FIG. 7, the backwash wastewater 12 in the drainage tank 13 is filtered as it flows from the outside (primary side) to the inside (secondary side) of the membrane element 45 of the second filtration device 15, and the second purified water 14 is obtained.

The second purified water 14 obtained in this manner is collected in the purified water reservoir 11 through the purified water collection pipe 70 from the second filtration device 15.

When the second filtration process C is being carried out as described above, the first valve 53, the second valve 56, and the ninth valve 107 are opened, and the first filtration process A and the manganese removal process D are also being carried out in parallel at the same time.

As described above, the relationship between the operating time [hr] of the water purification system 1 equipped with the manganese removal device 100 and the amount of purified water 9, 14 per hour [m ³ /hr] in each of the above processes A to E is similar to that shown in the graph in Fig. 6. In this case, in the bar graph G1, the shaded area G1a indicates the amount of first purified water 9 supplied to the purified water reservoir 11 from the first filtration device 10 via the manganese removal device 100 in the first filtration process A and the manganese removal process D.

The dotted portion G1b indicates the total amount of the first purified water 9 supplied from the purified water reservoir 11 to the first filtration device 10 via the pressurized tank 16 in the first backwash process B and the amount of the first purified water 9 supplied from the purified water reservoir 11 to the manganese removal device 100 in the second backwash process E.

Furthermore, the white portion G1c indicates the amount of second purified water 14 recovered from the second filtration device 15 to the purified water reservoir 11 in the second filtration process C.

According to this, similarly to the first embodiment described above, in the second embodiment, the control unit controls the operation of the second filtration device 15 so that the average value of the water balance per hour in the backwash cycle (3 hours) when the water quality is normal and the average value of the water balance per hour in the backwash cycle (1 hour) when the water quality is high are 16 [ ^m3 /hour]. Therefore, even if the frequency of performing the first and second backwash processes B and E changes depending on the water quality of the raw water 2, the average value of the water balance per unit time in each backwash cycle is kept constant, so that a constant amount of purified water 3 can be stably distributed from the distribution pipeline 78 to the distribution area.

In each of the above embodiments, the values for water volume, operating time, backwash cycle, etc. shown in the graph in Figure 6 are merely examples and are not limited to these values.

In each of the above embodiments, if the measured turbidity of the raw water 2 is below a threshold, it is determined that the water quality is normal and the backwash cycle is set to 3 hours, and if it exceeds the threshold, it is determined that the water quality is high turbidity and the backwash cycle is shortened to 1 hour, but an index other than turbidity may be used. For example, the filtration resistance (intermembrane pressure difference, etc.) of the first filtration device 10 may be measured, and if the measured filtration resistance is below a threshold, it is determined that the water quality is normal and the backwash cycle is set to 3 hours, and if it exceeds the threshold, it is determined that the water quality is high turbidity and the backwash cycle is shortened to 1 hour.

In each of the above embodiments, the opening and closing of each valve 53, 56, 59, 61, 65, 68, 72, 76, 107, 109, 111 and the operation of each pump 52, 58, 71, 75 in each of the processes A to E may be automatically controlled by a control unit or may be operated manually.

In each of the above embodiments, the backwash cycle is set to a discontinuous value consisting of two steps of 1 hour and 3 hours, but it may be set to a discontinuous value consisting of three or more steps. Also, depending on the water quality of the raw water 2, the backwash cycle may be set to change to a linear or curved continuous value rather than the discontinuous value as described above.

In addition, in each of the above embodiments, the water balance does not show the amount of first purified water 9 consumed in the process of backwashing the second filtration device 15. Here, in the process of backwashing the second filtration device 15, the first purified water 9 in the purified water reservoir 11 is supplied as backwash water from the secondary side to the primary side of the second filtration device 15 through the second backwash pipe 74. Such a backwashing process of the second filtration device 15 is carried out at predetermined time intervals, but the first purified water 9 consumed is only about 1 to 5% of the total amount of treated water obtained in the second filtration process C of the second filtration device 15, and compared to the amount of the first purified water 9, the impact on the water balance is considered to be negligible. Therefore, in each of the above embodiments, for ease of explanation and understanding, the net amount of treated water obtained by subtracting the first purified water 9 consumed in the backwashing process of the second filtration device 15 from the treated water obtained in the second filtration process C of the second filtration device 15 is described as the amount of second purified water 14, and the description of the first purified water 9 consumed in the backwashing process of the second filtration device 15 is omitted.

1 Water purification system 2 Raw water 8 Raw water storage section 9 First purified water 10 First filtration device 11 Purified water reservoir (purified water storage section)
12 Backwash drainage 13 Drainage tank 14 Second purified water 15 Second filtration device 21 Coagulant 26 Casing 27 Closed space 28 Membrane element (filtration membrane)
43 Housing 44 Open space 47 Filtration membrane 100 Manganese removal device A First filtration step B First backwashing step C Second filtration step D Manganese removal step E Second backwashing step

Claims (7)

A first filtration step of filtering raw water with a first filtration device to obtain first purified water;
A first backwashing step of backwashing the first filtration device using the first purified water;
A water purification method comprising: a second filtration step of filtering the backwash wastewater discharged from the first filtration device in the first backwash step in a second filtration device to obtain second purified water;
The time interval from the first backwash step to the next first backwash step is defined as a backwash cycle.
The water balance is calculated by subtracting the amount of the first purified water consumed in the first backwashing process from the total purified water amount obtained by adding the amount of the first purified water obtained in the first filtration process and the amount of the second purified water obtained in the second filtration process.
The length of the backwash cycle is adjusted according to the quality of the raw water or the filtration resistance of the first filtration device.
A water purification method characterized by operating the system by adjusting the amount of second purified water obtained from the second filtration device per unit time so that the average value of the water balance per unit time in each backwash cycle is constant. 2. The water purification method according to claim 1, wherein in the first filtration step, the amount of the first purified water obtained per unit time during the filtration operation of the first filtration device is kept constant. The first filtration device is a casing-type membrane filtration device in which a filtration membrane is housed in a closed space formed in a casing,
The water purification method according to claim 1 or 2, characterized in that the second filtration device is an immersed type membrane filtration device in which a filtration membrane is stored in an open space formed in a housing, and the housing and the filtration membrane are immersed in the backwash wastewater stored in the drainage tank . 4. The water purification method according to claim 3, wherein the first filtration device and the second filtration device each have a filtration membrane made of ceramics . a manganese removal step of removing manganese from the first purified water obtained in the first filtration step using a manganese removal device;
and a second backwashing step of backwashing the manganese removal device using the first purified water that has been subjected to the manganese removal step.
The water purification method according to any one of claims 1 to 4, characterized in that in the second filtration step, the backwash wastewater discharged from the first filtration device in the first backwash step and the backwash wastewater discharged from the manganese removal device in the second backwash step are filtered in the second filtration device to obtain second purified water . 6. The water purification method according to claim 1, wherein in the first filtration step, raw water in which a flocculating agent has been added to form flocs is filtered by the first filtration device . A water purification system for performing the water purification method according to any one of claims 1 to 6,
a first filtration device for filtering raw water to obtain first purified water;
a purified water storage section for storing the first purified water;
a second filtration device that obtains second purified water by filtering backwash wastewater discharged from the first filtration device when the first filtration device is backwashed with the first purified water in the purified water storage section;
A control unit,
The control unit controls operation of the water purification system by adjusting the length of the backwash cycle in accordance with the quality of the raw water or the filtration resistance of the first filtration device, and by adjusting the amount of second purified water obtained from the second filtration device per unit time so that the average value of the water balance per unit time in each backwash cycle is constant.

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