JP2010104920A - Method for operating reverse osmosis membrane separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a long-term stable operation by suppressing a deterioration of membrane surface permeation flux in an RO separator where desalination and/or organic matter removal is performed. <P>SOLUTION: The method for operating a reverse osmosis membrane separator provided in a multistage where a reverse osmosis membrane separating means for performing the desalination and/or organic matter removal is performed is provided, wherein flushing is performed on a first reverse osmosis separating means (vessels 21-24) only by opening a valve V<SB>A</SB>, flushing drainage is discharged outside the separator through pipes 41-44, 45, and 49, the valve V<SB>A</SB>may be closed during flushing, the valves V<SB>A</SB>, V<SB>C</SB>may be opened, and flushing frequency may be controlled based on a differential pressure (P<SB>1</SB>-P<SB>2</SB>). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for operating a reverse osmosis membrane separation device (RO device), and in particular, suppresses an increase in operating pressure and / or a decrease in membrane surface permeation flux of an RO device that performs desalting and / or organic matter removal, The present invention relates to an operation method of an RO device that enables long-term stable operation.

  RO devices are used in a wide range of fields such as fresh water production processes, food / pharmaceutical water production processes, and wastewater recovery processes. In particular, in recent years, the number of cases where RO devices are used in the wastewater recovery process is increasing for the purpose of reducing the cost of wastewater for use and reducing the environmental load.

  Usually, the RO device has an arrangement called a Christmas tree as shown in FIG. 4 for the purpose of increasing the water recovery rate for the supplied water. That is, in FIG. 4, a first RO vessel group in which four RO vessels (RO body) 1A, 1B, 1C, 1D incorporating RO elements are arranged in parallel (the RO vessel group is also referred to as a “bank”). 1 and a second RO bank 2 in which two RO vessels 2A and 2B are arranged in parallel constitute a Christmas tree type multi-stage RO device.

  The water to be treated, that is, the supply water (RO feed water) of the RO device first flows into the first bank 1 and is separated into permeated water and concentrated water. Subsequently, the concentrated water in the first bank 1 flows into the second bank 2 and is again separated into permeated water and concentrated water. The permeated water of the first bank 1 and the permeated water of the second bank 2 merge and are transferred to the subsequent processing step. On the other hand, the concentrated water in the second bank 2 is discharged out of the system or transferred to a wastewater treatment facility or the like. Usually, the Christmas tree structure in the RO device is often composed of two or three banks, depending on the required water recovery rate.

  Such an RO device can be used as an irrigation process, particularly an irrigation process or an effluent treatment process with insufficient removal of turbidity in the treated water, especially a wastewater recovery process with a relatively high concentration of organic components in the treated water. In the case of use, the membrane surface is blocked due to the inflow of turbidity, microbial organic gel, etc. into the RO device, and the operating pressure and the permeate flow rate in the RO device, especially the first bank, increase. There is a problem that cleaning has to be carried out, and this problem tends to become particularly prominent in recent years.

  In JP 2007-125526 A, in a method of operating a reverse osmosis membrane separation device having reverse osmosis membrane separation means arranged in series in two stages, an alkali is added to adjust the pH to 9.5 to 13 Water is used as flushing water. First, flushing water is supplied only to the first-stage reverse osmosis membrane separation means for flushing, and then flushing water is supplied in series to the first-stage reverse osmosis membrane separation means and the second-stage reverse osmosis membrane separation means. A method of flushing the latter reverse osmosis membrane separation means is also described.

However, since this method flushes all the reverse osmosis membrane separation means, it takes time to switch the flow path, and the configuration of the flow path switching means becomes complicated. Furthermore, there is a possibility that the obstruction in the first bank is sent to the second and third banks by flushing.
JP 2007-125526 A

  An object of the present invention is to solve the above-mentioned conventional problems, and to provide a method of operating an RO apparatus that can suppress a decrease in membrane surface permeation flux by simple flushing and enables long-term stable operation.

  The operation method of the reverse osmosis membrane separation device according to claim 1 is an operation method of the reverse osmosis membrane separation device having reverse osmosis membrane separation means installed in multiple stages in series. In the operation method of the reverse osmosis membrane separation apparatus having a flushing process for flushing, in the flushing process, only the first-stage reverse osmosis membrane separation means is flushed, and the flushing waste water is discharged outside the reverse osmosis membrane separation apparatus. It is a feature.

  The operation method of the reverse osmosis membrane separation device according to claim 2 is the method of claim 1, wherein the concentrated water outlet of the first-stage reverse osmosis membrane separation means and the treated water inlet of the second-stage reverse osmosis membrane separation means are provided. The flushing drainage channel branches off from the connecting channel, and in the permeated water sampling process, the entire amount of concentrated water from the first-stage reverse osmosis membrane separation means is used as the second-stage reverse osmosis membrane separation means. In the supply and flushing step, the entire amount or almost the entire amount of concentrated water from the first-stage reverse osmosis membrane separation means is maintained while continuing to introduce the treated water into the first-stage reverse osmosis membrane separation means. It discharges out of the reverse osmosis membrane separation device from the flushing drainage channel.

  The operation method of the reverse osmosis membrane separation device according to claim 3 is the operation method according to claim 2, wherein in the flushing step, the entire amount of flushing drainage from the first stage reverse osmosis membrane separation means is discharged out of the reverse osmosis membrane separation device. It is characterized by doing.

  The operation method of the reverse osmosis membrane separation apparatus according to claim 4 is the operation method according to any one of claims 1 to 3, wherein the flushing step is performed at a frequency of 1 to 30 times / day and once for a flushing time of 5 to 500 seconds. It is characterized by doing.

  The operation method of the reverse osmosis membrane separation apparatus according to claim 5 is the method according to any one of claims 1 to 3, wherein the detection means detects a differential pressure between the first-stage treated water inlet and the concentrated water outlet, The control means controls such that the frequency of the flushing process is increased as the differential pressure increases.

  According to the present invention, a simple flushing in which only the first-stage reverse osmosis membrane separation means is temporarily flushed during operation of the RO device can suppress a decrease in membrane surface permeation flux, and can be stable over a long period of time. It becomes possible to drive.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a method for operating an RO apparatus of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment of a method for operating an RO apparatus according to the present invention.

  In the RO apparatus shown in FIG. 1, four RO vessels 21 to 24 are arranged in parallel to form a first bank (a group of vessels), and three RO vessels 51 to 53 form a second stage. This is a three-stage Christmas tree RO apparatus in which the second bank is configured and the third bank of the third stage is configured by two RO vessels 81 and 82.

  Each RO vessel 21-24, 51-53, 81, 82 has one or more RO elements built therein.

  In addition to the normal RO membrane, a membrane whose surface is modified with a surface treatment agent may be used as the RO membrane. Examples of the surface treatment agent include polyalkylene glycol having a molecular weight of 2000 to 10,000 or a derivative thereof. Examples of the derivatives include polyalkylene glycols having an ionic group, an ether, or an ester-bonded alkyl group. Examples of the ionic group include a sulfo group, a carboxyl group, and an amino group, and the alkyl group preferably has 1 to 20 carbon atoms. Further, cationic and anionic polymers having a molecular weight of 100,000 or more can also be mentioned.

  It is also effective to perform the treatment multiple times by changing the type of the surface treatment agent. As the order of treatment, for example, after treatment with a cationic polymer, treatment with an anionic polymer stabilizes the adsorption layer, and the anionic group on the surface strengthens anion repulsion, and anionic Adsorption of substances can be suppressed.

  As the RO membrane, a surface treated with an oxidizing agent may be used. For example, a hydrogen peroxide-treated RO membrane disclosed in Japanese Patent No. 3807395 can be given.

In FIG. 1, treated water (raw water) flows from a raw water pipe 10 having a pressure gauge P ₁ into branch raw water pipes 11, 12, 13, and 14. The permeated water from the vessels 21 to 24 is taken out from the system (outside the apparatus) through the permeated water pipes 31, 32, 33, and 34 through the collective permeated water pipe 30.

Concentrated water from each of the vessels 21 to 24 is collected from the concentrated water pipes 41, 42, 43, and 44 into the concentrated concentrated water pipe 45, and then passes through the valve _VA to be connected to the second through the branch pipes 46, 47, and 48. It is supplied to the vessels 51, 52, 53 of the bank.

_A flushing drain pipe 49 is branched from the upstream side of the valve _VA of the concentrated water pipe 45. With a pressure gauge P ₂ is provided in the pipe 49, the valve V _B for performing discharge and drainage stop flushing wastewater downstream is provided than that.

  The permeated water from the vessels 51 to 54 is taken out of the system from the permeated water pipes 61, 62, 63 through the collective permeated water pipes 64, 30.

Concentrated water from each of the vessels 51 to 53 is collected from the concentrated water pipes 71, 72, 73 to the collective concentrated water pipe 74 and then supplied to the vessels 81, 82 of the third bank via the branch pipes 75, 76. .
Incidentally, the pressure gauge P ₃ are provided on the concentrated water pipe 74.

  The permeated water from the vessels 81 and 82 is taken out of the system from the permeated water pipes 91 and 92 through the aggregate permeated water pipes 93 and 30.

Concentrated water from the vessel 81 passes a set concentrated water pipe 103 and the valve _{V C} from the concentrated water pipe 101, and is discharged out of the system. Incidentally, the pressure gauge P ₄ is provided on the upstream side of the valve V _C of the concentrated water pipe 103.

In RO apparatus of Figure 1, during normal operation of the (water sampling operation), the valve V _B is closed, the V _A open, the valve V _C is the degree of opening of a predetermined water recovery, water supply pump ( (Not shown) is operated, and the water to be treated is pressurized and supplied from the pipe 10 to the RO vessels 21 to 24 of the first bank via the pipes 11 to 14, and the permeated water is supplied to the outside of the system via the pipes 31 to 34 and 30. To discharge. On the other hand, the concentrated water is introduced into the RO vessels 51 to 53 of the second bank through the pipes 41 to 48, and the permeate is discharged out of the system through the pipes 61 to 64. The concentrated water from the RO banks 51 to 53 in the second bank is introduced into the RO vessels 81 and 82 in the third bank through the pipes 71 to 76, and the permeate is discharged out of the system through the pipes 91 to 93. The concentrated water is discharged from the third bank to the outside through the pipe 103.
The concentrated water is discharged or sent to a wastewater treatment device at the subsequent stage. The permeated water is further fed to a subsequent processing device.
After such normal operation is performed for a predetermined time, flushing is performed as follows.

First, while operating the water supply pump as in normal operation, open the valve V _B. At this time, the valve _VA may be closed or may remain open. By the valve V _B opened, RO vessel (if the valve V _A closed) the total amount of flowing water in 21 to 24 or most of the first bank (when left the valve V _A open), the Without passing through the RO membrane, it is discharged out of the system through the pipes 41 to 44, 49.

  By this operation, a large amount of water flows at a high flow rate along the membrane surfaces of the RO vessels 21 to 24 of the first bank, thereby cleaning each membrane surface.

As described above, after making flushing only the first bank, when the valve V _A is closed back to open, and the valves V _B is closed, resume normal operation.

  In the present invention, the frequency of flushing is not particularly limited and is appropriately determined according to the quality of the water to be treated, the RO treatment conditions, and the like, but is usually 5 to 500 seconds per time at a rate of once every 1 to 30 days. It is preferable to carry out to the extent.

  In FIG. 1, a Christmas tree in which four RO vessels are arranged in parallel in the first bank, three RO vessels are provided in the second bank, and two RO vessels are provided in the third bank. Although the RO device to which the present invention is applied is not limited to the one shown in FIG. 2, the number of vessels in each bank is arbitrary and the number of banks is two or more. is there. Not only a Christmas tree type RO device but also one RO vessel of each stage may be connected in multiple stages.

  In the case of a Christmas tree type RO device, the number of banks and the number of vessels are not particularly limited, but the number of banks is usually two or three. However, it goes without saying that a multi-stage configuration of four or more stages may be used. Further, the number of RO vessels in each bank is appropriately set according to the amount of treated water and the processing capacity of the RO vessel, but in general, the number is larger on the upstream side and smaller on the downstream side. Normally, in the case of two stages, the number of vessels in the first bank: the number of vessels in the second bank = 2: 1 is set. In the case of three stages, the number of vessels in the first bank: second bank The number of vessels is often set at a ratio of the number of vessels: the number of vessels in the third bank = 4: 2: 1. The number of vessels in the final stage may be one.

In any case, as described above, each RO vessel has a built-in RO element, and one vessel contains one or more RO elements. Also, at least, the concentrated water pipe from the bank of the last stage provided throttle valve or opening adjustable valve V _C is adapted to adjust the operating pressure according to the RO vessel of all banks.

The on-off valve and throttle valve are preferably automatic valves, but may be manual valves. FIG. 2 shows that the valves V _A and V _B are automatic valves, and the opening and closing thereof are automatically controlled by the control device 110 based on the pressure difference between the pressure gauges P ₁ and P ₂ , thereby automatically performing the normal flushing process. It is something that is done inside.

  In this case, it is preferable to increase the frequency of flushing as the membrane permeation differential pressure increases. However, the time for one flushing may be increased. The other structure of FIG. 2 is the same as that of FIG. 1, and the same code | symbol has shown the same part.

  In the case of a multi-stage RO device such as a Christmas tree type RO device, particularly when an ultra-low pressure RO membrane is used, turbidity removal is insufficient, or water to be treated that does not use a microbial inhibitor is treated. Since the RO membrane contamination of the first-stage bank (or vessel) becomes significant, as described above, the permeated water amount can be kept high for a long period only by flushing only the first-stage bank (vessel group). Can do.

In the present invention, the valve _VA may be left open during the flushing of the first bank, so the valve _VA may be omitted.

  In the present invention, a RO membrane whose surface is modified with a polymer (for example, polyethylene glycol) or treated with an oxidizing agent may be used.

  The operation method of the RO device of the present invention is such that the TOC concentration is 0.5 mg / L or more, for example, 0.5 to 20 mg / L, such as treated water or effluent recovery process with SDI of insufficient turbidity removal of 3 or more. This is effective when the water to be treated or the water to be treated having a viable count of 5000 CFU / mL or more is used as RO water supply. In addition, although TOC is a dissolved component, when a polymer such as a biological metabolite is included, it may be concentrated on the membrane surface or may be gelled by binding with a cation. It has been found that the flow path may be blocked by adhering to the liquid.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
In the following Examples and Comparative Examples, raw water of the quality shown in Table 1 was used.

Examples 1 and 2 and Comparative Examples 1 and 2
When water sampling, the valve _{V A} opens, the valve _{V B} closed, the valve _{V C} half open, RO apparatus according to the raw water in Figure 1 (film Kurita Water Industries Ltd. K-RO-A2032. Vessel 1 was supplied at ^{30 m} 3 / h into four per, the concentrated water flow rate was set to ^{10 m} 3 / h, the recovery rate of 75%.

In Examples 1 and 2, flushing was performed by opening and closing V _A , V _B , and V _C at a frequency of once / day for 60 seconds per time as shown in Table 2. In Comparative Example 1, no flushing was performed. In Comparative Example 2, 60 seconds per once with a frequency of once / day, was fully open valve _{V C.}

Example 3
As shown in FIG. ₂ , the detected values of the pressure gauges P ₁ and P ₂ are input to the control device 110, and the valve V _B is opened for 60 seconds according to the differential pressure (P ₁ -P ₂ ), and the valve Flushing for closing _VA for 60 seconds was performed at the following frequency.

1 time / day when P ₁ -P ₂ is less than 0.15
When P ₁ -P ₂ is 0.15 to 0.20, 2 times / day
3 times / day when P ₁ -P ₂ is 0.20 to 0.25
4 times / day when P ₁ -P ₂ exceeds 0.25
The material of the film and the film area of each vessel are the same as in Examples 1 and 2 and Comparative Examples 1 and 2.

Tables 3 and 4 show the detected values of the pressure gauges P _{1 to} P ₄ immediately after the start of operation of Examples 1 to 3 and Comparative Examples 1 and 2 and after one month. In Tables 3 and 4 and Tables 5 and 7 described later, the unit of conductivity is mS / m.

In Comparative Example 1 in which flushing is not performed, the pressure of the pressure gauge 1 is increased and the pressure of the pressure gauge 4 is decreased. In Comparative Example 2 in which V _C is opened, this tendency is small, but the pressure rise of the pressure gauge 1 and the pressure drop of other pressure gauges are also remarkable. In the present invention (Examples 1, 2 and 3) in which V _B is opened, the pressure rise of the pressure gauge 1 and the pressure drop of other pressure gauges were suppressed. In Example 3 in which the opening / closing of the valve is controlled according to the pressure, this effect is most significant.

Example 4, Comparative Example 3
As the membrane, except that the above-mentioned K-RO-A2032 was subjected to a water treatment at 0.75 MPa for 30 minutes with a 2 ppm polyethylene glycol aqueous solution (average molecular weight 3000) and modified with polyethylene glycol, respectively. Water was passed under the same conditions as in Example 3 and Comparative Example 1. Table 5 shows the detected values of the pressure gauges P _{1 to} P ₄ immediately after the start of operation and after one month.

  As shown in Table 5, the initial pressure immediately after the start of operation is high because the resistance of the membrane is increased by the modification treatment. However, in both Example 4 and Comparative Example 3, the pressure increase after one month was suppressed compared to Example 3 and Comparative Example 1, and in Example 4, the pressure increase was remarkably suppressed.

Example 5
The raw water shown in Table 6 was supplied to the RO apparatus shown in FIG. ³ at 28 m ³ / h, the concentrated water flow rate was 12 m ³ / h, and the recovery rate was 70%.

  The RO apparatus of FIG. 3 is composed of two banks, a first bank and a second bank. The first bank is provided with eight RO vessels 21-24, 24a-24d in parallel, and pipes 11-14, 14a- The raw water is supplied by 14d, the permeated water is taken out by the pipes 31 to 34 and 34a to 34d, and the concentrated water is sent to the pipe 45 through the pipes 41 to 44 and 44a to 44d.

  The second bank is provided with four RO vessels 52 to 53, 53A in parallel, the concentrated water from the piping 45 is supplied to the respective vessels 51 to 53A by branch piping 46 to 48, 4a, and the permeated water is supplied to the piping 61 to 63. 63a, and the concentrated water is sent out to the pipe 74 through the pipes 71 to 73 and 73a and taken out of the system.

  Other configurations are the same as those in FIG. 1, and the same reference numerals indicate the same parts.

  As the membrane, NTR-759HR manufactured by Nitto Denko Corporation was immersed in 1% hydrogen peroxide solution for 24 hours.

Flushing was carried out by the open only 60 seconds per once only valve V _B at a frequency of once / hr. Table 7 shows the detected values of pressure gauges P _{1 to} P ₄ immediately after the start of operation and after one month has elapsed.

Comparative Example 4
In Example 5, the same film as Example 5 was used except that the film was not subjected to hydrogen peroxide solution and flushing was not performed. Table 7 shows the detected values of pressure gauges P _{1 to} P ₄ immediately after the start of operation and after one month has elapsed.

Comparative Example 5
Example 5 was the same as Example 5 except that flushing was not performed. Table 7 shows the detected values of pressure gauges P _{1 to} P ₄ immediately after the start of operation and after one month has elapsed.

As Table 7, the pressure rise in the pressure gauge P ₁ after one month has elapsed as compared with Comparative Examples 4 and 5 In Example 5 is remarkably suppressed, is maintained at a value lower P ₂ and P _3.

It is a systematic diagram which shows embodiment of the operating method of RO apparatus of this invention. It is a systematic diagram which shows embodiment of the operating method of RO apparatus of this invention. It is a systematic diagram which shows embodiment of the operating method of RO apparatus of this invention. It is a systematic diagram which shows the structure of a general Christmas tree type RO apparatus.

Explanation of symbols

1 First bank (first RO vessel group)
2 Second bank (second RO vessel group)
21-24, 51-53, 81, 82 RO vessel

Claims (5)

A method of operating a reverse osmosis membrane separation device having reverse osmosis membrane separation means installed in multiple stages in series,
In a method of operating a reverse osmosis membrane separation apparatus having a flushing step of temporarily flushing the reverse osmosis membrane separation means,
In the flushing step, only the first-stage reverse osmosis membrane separation means is flushed, and the flushing waste water is discharged out of the reverse osmosis membrane separation device. In claim 1,
A flushing drainage channel is branched from a channel connecting the concentrated water outlet of the first-stage reverse osmosis membrane separation means and the treated water inlet of the second-stage reverse osmosis membrane separation means,
In the permeated water sampling process, the entire amount of concentrated water from the first-stage reverse osmosis membrane separation means is supplied to the second-stage reverse osmosis membrane separation means,
In the flushing step, the entire amount or almost all of the concentrated water from the first-stage reverse osmosis membrane separation means is continuously discharged into the first-stage reverse osmosis membrane separation means while the treated water is continuously introduced into the first-stage reverse osmosis membrane separation means. A method for operating a reverse osmosis membrane separation device, wherein the reverse osmosis membrane separation device is discharged from a flow path to the outside of the reverse osmosis membrane separation device.   3. The operation method of a reverse osmosis membrane separation device according to claim 2, wherein in the flushing step, the entire amount of flushing waste water from the first stage reverse osmosis membrane separation means is discharged out of the reverse osmosis membrane separation device. .   The method of operating a reverse osmosis membrane separation device according to any one of claims 1 to 3, wherein the flushing step is performed at a frequency of 1 to 30 times / day in a single flushing time of 5 to 500 seconds. .   4. The method according to claim 1, wherein the detection means detects a differential pressure between the first-stage treated water inlet and the concentrated water outlet, and the frequency of the flushing process is increased as the differential pressure increases. And a control means for controlling the reverse osmosis membrane separation device.

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