JP4804097B2 - Continuous operation method of water purification system - Google Patents

Description

  The present invention relates to a continuous operation method of a water purification system.

  Water purification systems applying membrane separation technology are attracting attention as a new technology that replaces the conventional method of coagulation-precipitation-sand filtration-chlorine sterilization process. For example, cross-flow as a water purification system using separation membranes Filtration has been widely attempted. Cross-flow filtration means that the raw water is supplied to one membrane surface of the separation membrane (raw water supply side separation membrane surface) and the permeated water that has permeated through the separation membrane is used as the other membrane surface of the separation membrane (permeated water side separation membrane surface). The filtration method has the effect of stripping off turbid substances contained in the raw water adhering to the separation membrane surface by flowing raw water parallel to the separation membrane surface of the raw water supply side when collecting from the membrane. Say. However, even with cross-flow filtration, turbid substances contained in the raw water are laminated on the surface of the separation membrane as the filtration time elapses, resulting in clogging of the separation membrane.

  Since this clogging causes interruption of the operation of the water purification system, in order to eliminate or prevent this clogging, back pressure washing (hereinafter referred to as “back washing”) is generally performed, and the separation membrane is used. In order to enable long-term use, methods for changing the backwash frequency, backwash time, and the like based on various changes such as raw water turbidity, permeate water amount, permeate water pressure, and the like have been proposed.

  For example, as backwashing in crossflow filtration, periodic backwashing depending on the raw water turbidity is described in the Journal of Water Supply Association (Vol. 61, No. 11, 19-26, 1992), and Japanese Patent Application Laid-Open No. 4-247226. The gazette discloses a method of changing the backwashing conditions of the membrane when the filtration rate tends to decrease due to fluctuations in water quality and filtration rate. JP-A-5-317660 discloses backwashing according to fluctuations in raw water turbidity. A method is disclosed that can adjust the frequency, eliminate the risk of closing the separation membrane, and increase the water recovery rate.

  In these methods, when turbid substances adhere to the raw water side separation membrane surface, the raw water pressure on the raw water supply side rises due to clogging. Used to remove turbid substances. Accordingly, a high pressure is always applied to the separation membrane, which may shorten the useful life of the separation membrane. Moreover, the high pressure load extends not only to the separation membrane but also to the pump used.

For this reason, there is a demand for the development of a backwashing method that can improve backwashing efficiency, ease the conditions for using expensive separation membrane modules, and can easily cope with various water purification systems. Patent Document 1 discloses that a filtration process is paused immediately before or immediately after backwashing, and that backwashing water containing a bactericide is used, and Patent Document 2 discloses a backwashing process, hypochlorous acid. A method of cleaning a filtration membrane having an acid salt injection immersion step and a sulfuric acid injection immersion step and having an immersion cleaning time of 10 to 60 minutes is disclosed.
JP-A-8-197053 Japanese Patent Laid-Open No. 2005-87887

  The invention of Patent Document 1 describes that the pause process immediately after backwashing is 1 to 10 hours, but the number of pause processes is described to be once every 30 hours in Example 2. Only.

  Since the invention of Patent Document 2 is a method of using sulfuric acid so that the hypochlorite concentration is as high as 100 to 500 mg / L and the pH is 2 to 4, it contains a high concentration of hypochlorite and sulfuric acid. There is a problem of wastewater treatment.

  In the backwash process, when introducing immersion cleaning in which a filtration membrane is immersed in a chemical solution, the treatment conditions in the immersion cleaning can be specified in a narrow range, so that the filtration membrane can be prevented from being damaged, and the filtration capability can be dramatically improved. It is an object of the present invention to provide a continuous operation method of a water purification system that can be recovered to a high level.

As a means for solving the problems, the present invention
It has a filtration process of filtering raw water using a hollow fiber type filtration membrane module and a backwashing process of backwashing the filtration membrane module, and in the backwashing process, immersion washing is performed by immersing the filtration membrane in a chemical solution. A continuous operation method of a water purification system,
Provided is an operation method of a water purification system that operates so that immersion cycle coefficients k ₁ and k ₂ obtained from Equation (1) and Equation (2) are 0.7 <k ₁ <4.0 and 1.5 <k ₂ <5.0. .

N = k ₁ t (k ₁ = N / t) (1)
N = k ₂ / t (k ₂ = Nt) (2)
[Wherein, N is an immersion cycle (times / day), t is an immersion time (hr), and k ₁ and k ₂ are immersion cycle coefficients. ]

  According to the operation method of the present invention, since the cleaning effect by backwashing is high, the high water permeability of the filtration membrane module can be maintained over a long period of time.

1 and 2, the operation method of the water purification system of the present invention will be described. FIG. 1 is a flow diagram of the water purification system, and FIG. 2 is an explanatory diagram of immersion cycle coefficients k ₁ and k ₂ .

  During the filtration operation, the valve 10 is opened, the permeated water automatic valve 13 is opened, the washing water discharge automatic valve 14 and the backwashing automatic valve 19 are closed, and the raw water is fed by the raw water supply pump 11 into a hollow fiber membrane membrane module. 12 is filtered and the generated permeate is stored in the permeate tank 17. The raw water that does not pass through the filtration membrane module 12 is sent to the filtration membrane module 12 again via the circulation path 16 and the raw water supply pump 11.

  As the raw water, for example, natural water such as ground water, rain water, river water and lake water can be used. As a membrane material of the filtration membrane of the hollow fiber membrane membrane module 12, hydrophilic polymer materials such as cellulose acetate, polyacrylonitrile polymer, polyvinyl alcohol and the like can be used, and the backwash effect of the present invention is particularly remarkable. Cellulose acetate is preferred.

  If the filtration process is continued, the filtration membrane is clogged and the filtration capacity decreases, so a backwash process is provided.In the present invention, the chemical solution immersion cleaning is performed in which the filtration membrane is immersed in the chemical solution in the backwash process. I do. In such a backwashing process, it is preferable to carry out treatment for one cycle or two cycles or more, with backwashing of the filter membrane (previous backwashing), chemical solution immersion cleaning and backwashing (backstage backwashing) as one cycle.

  In the pre-stage backwash, the raw water supply pump 11 is stopped, the backwash automatic valve 19 and the medicine automatic valve 25 are opened, the backwash water supply pump 18 and the medicine supply pump 22 are operated, and the disinfectant ( Backwash water (sodium hypochlorite or the like) added to the permeate of the permeate tank 17 is preferably 3-16 m / day, more preferably 3 to 16 m / day, more preferably tap water. Backwashing is performed at a flux of 6 to 12 m / day, preferably for 60 to 180 seconds, more preferably for 60 to 120 seconds.

  In the subsequent chemical liquid immersion cleaning, the backwash water supply pump 18 and the medicine supply pump 22 are stopped while the raw water supply pump 11 is stopped, the backwash automatic valve 19 and the medicine automatic valve 25 are closed, and permeated water is generated and reversed. Stop washing together.

  Next, in the subsequent backwashing, the backwashing automatic valve 19 is opened and the backwashing operation is performed by the backwashing water supply pump 18. The backwash condition is preferably a flux of 3 to 16 m / day, more preferably a flux of 6 to 12 m / day, preferably 60 to 180 seconds, more preferably 60 to 120 seconds. Even in the latter backwashing, the medicine automatic valve 25 may be opened and the sterilizing agent may be included in the backwashing water by the medicine supply pump 22.

The chemical liquid immersion cleaning is performed so that the immersion cycle coefficient k ₁ obtained from the formulas (1) and (2) is in the range of 0.7 <k ₁ <4.0 and the immersion cycle coefficient k ₂ is in the range of 1.5 <k ₂ <5.0. .

N = k ₁ t (k ₁ = N / t) (1)
N = k ₂ / t (k ₂ = Nt) (2)
[Wherein, N is an immersion cycle (times / day), t is an immersion time (hr), and k ₁ and k ₂ are immersion cycle coefficients].

The immersion cycle coefficient k ₁ obtained from the equation (1) is indicated by two straight lines in FIG. 2, and the immersion cycle coefficient k ₂ obtained from the equation (2) is indicated by two curves in FIG. It is what Therefore, the range surrounded by the two straight lines and the two curves is the range indicated by the immersion cycle coefficients k ₁ and k ₂ .

The immersion cycle coefficient k ₁ is preferably 0.8 <k ₁ <3.5, more preferably 1 <k ₁ <2.5, and the immersion cycle coefficient k ₂ is preferably 1.5 <k ₂ < 4.5, more preferably 1.5 <k ₂ <4.

Thus, by dipping cycle coefficients k ₁ and k ₂ is a chemical immersion cleaning to a predetermined range, and relieve pressure during backwashing, it is possible to shorten the backwashing time, load on the filtration membrane reduces The film life can be extended.

The injection amount of the chemical solution in the immersion process is preferably controlled so that the drug concentration in the permeated water at the permeate outlet of the filtration membrane module 12 is 3 to 100 mg / L, preferably 5 to 60 mg / L. By chemical immersion immersion cleaning so that the immersion cycle coefficients k ₁ and k ₂ are within a predetermined range, the chemical concentration can be lowered as compared with the invention of Patent Document 2, and there is no need to use a strong acid such as sulfuric acid. .

Example 1
Using a water purification system including the hollow fiber membrane module shown in FIG. 1, a filtration operation by cross-flow filtration of river water was performed. A cellulose acetate membrane (effective membrane area: 100 m ² , membrane inner diameter: 0.8 mm, outer diameter: 1.3 mm, fractional molecular weight: 150,000) is used as the hollow fiber membrane module. A filtration operation was performed.

First, the raw water was fed to the filtration membrane module 12 from the upper and lower ends of the module by the raw water supply pump 11, and the whole amount was filtered. The filtration operation was constant flow filtration, the flow rate was 15 m ³ / hr, and the filtration time was 58 minutes. After completion of the filtration process, the process shifted to a backwash process.

  In the backwashing process, two cycles were provided per day (t = 1, N = 2), with the first backwashing, the chemical solution immersion washing, and the second backwashing as one cycle. Note that backwash water containing sodium hypochlorite having an effective chlorine concentration of 10 mg / L was used at the time of backwashing in the previous stage.

In the pre-back washing, the washing water discharge automatic valve 14 and the back washing automatic valve 19 are opened to operate the back washing water supply pump 18, and the permeated water from the permeate tank 17 is used as the back washing water to the filtration membrane module 12 for 1 minute. It was supplied at a flow rate of 45 m ³ / hr. At this time, the backwash water used was sodium hypochlorite injected so that the effective chlorine concentration was 5 mg / L. Then, chemical | medical solution immersion washing was performed on the conditions shown in Table 1, and back | latter stage backwashing was performed on the same conditions as front | latter stage backwashing.

  The series of operations described above were performed periodically using an automatic valve, and as a result of measuring the change over time in the transmembrane pressure difference, stable operation continued for 100 days without increasing the transmembrane pressure difference.

Example 2
Cleaning was performed under the same operating conditions as in Example 1 except that the same hollow fiber membrane module as in Example 1 was used and chemical solution immersion cleaning was performed under the conditions shown in Table 1. Even under these operating conditions, stable operation could be continued for 100 days.

Example 3
Cleaning was performed under the same operating conditions as in Example 1 except that the same hollow fiber membrane module as in Example 1 was used and chemical solution immersion cleaning was performed under the conditions shown in Table 1. Even under these operating conditions, stable operation could be continued for 100 days.

Comparative Example 1
Cleaning was performed under the same operating conditions as in Example 1 except that the same hollow fiber membrane module as in Example 1 was used and chemical solution immersion cleaning was performed under the conditions shown in Table 1. Under these operating conditions, the transmembrane pressure increased after 40 days.

Comparative Example 2
Cleaning was performed under the same operating conditions as in Example 1 except that the same hollow fiber membrane module as in Example 1 was used and chemical solution immersion cleaning was performed under the conditions shown in Table 1. Under these operating conditions, the transmembrane pressure difference increased after 48 days.

Comparative Example 3
Cleaning was performed under the same operating conditions as in Example 1 except that the same hollow fiber membrane module as in Example 1 was used and chemical solution immersion cleaning was performed under the conditions shown in Table 1. Under these operating conditions, the transmembrane pressure increased after 40 days.

Comparative Example 4
Cleaning was performed under the same operating conditions as in Example 1 except that the same hollow fiber membrane module as in Example 1 was used and chemical solution immersion cleaning was performed under the conditions shown in Table 1. Under these operating conditions, the transmembrane pressure increased after 40 days.

表１及び図３における実施例１〜３と比較例１〜４の膜間差圧が上昇するまでの日数の対比から明らかなとおり、本発明の運転方法を適用することにより、濾過運転の継続による濾過膜の目詰まりが解消された結果、ファウリングが防止され、長期間、膜間差圧の上昇がなかった（即ち、高い透水性能を長期にわたり維持することができた）。このような結果は、薬液浸漬洗浄の条件を特定することにより、その後の逆洗（後段逆洗）によって効果的に汚染物質が剥離され、洗浄効果が上がったものと考えられる。

As is apparent from the comparison of the number of days until the transmembrane pressure difference of Examples 1 to 3 and Comparative Examples 1 to 4 in Table 1 and FIG. 3 is increased, the filtration operation is continued by applying the operation method of the present invention. As a result of the clogging of the filtration membrane due to the fouling, fouling was prevented, and there was no increase in the transmembrane pressure difference for a long time (that is, high water permeability performance could be maintained for a long time). From such a result, it is considered that by specifying the conditions of the chemical solution immersion cleaning, the contaminants were effectively peeled off by the subsequent backwashing (the subsequent backwashing), and the cleaning effect was improved.

The flow chart of a water purification system. Illustration of immersion cycles coefficients k ₁ and k _2. Explanatory drawing of the filtration driving | running state after washing | cleaning in an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 23 Check valve 11, 18 Pump 12 Hollow fiber membrane module 13 Permeated water automatic valve 14 Concentrated water discharge automatic valve 17 Permeated water tank 19 Backwash automatic valve 21 Drug tank 22 Drug injection pump 24 Drug injection route 25 Drug injection automatic valve

Claims (4)

It has a filtration process of filtering raw water using a hollow fiber type filtration membrane module and a backwashing process of backwashing the filtration membrane module. In the backwashing process, the filtration membrane is sodium hypochlorite as a chemical solution. Water of natural water that is immersed in an aqueous solution (however, the injection amount of the chemical solution in the immersion process is controlled so that the concentration of the drug in the permeated water at the permeate outlet of the filtration membrane module is 3 to 60 mg / L). A continuous operation method of a purification system,
The membrane material of the filtration membrane module is cellulose acetate,
An operation method of the water purification system that operates so that the immersion cycle coefficients k ₁ and k ₂ obtained from the expressions (1) and (2) are 0.7 <k ₁ <4.0 and 1.5 <k ₂ <5.0.
N = k ₁ t (k ₁ = N / t) (1)
N = k ₂ / t (k ₂ = Nt) (2)
[Wherein, N represents an immersion cycle (times / day), t represents one immersion time (hr), and k ₁ and k ₂ represent immersion cycle coefficients. ] Immersion cycle coefficient k ₁ Is 0.8 <k ₁ <3.5, immersion cycle coefficient k ₂ 1.5 <k ₂ The continuous operation method of the water purification system according to claim 1, wherein <4.5. Immersion cycle coefficient k ₁ Is 1 <k ₁ <2.5, immersion cycle coefficient k ₂ 1.5 <k ₂ The continuous operation method of the water purification system according to claim 1, wherein <4. The continuous operation of the water purification system according to any one of claims 1 to 3, wherein in the backwashing process, the backwashing of the filtration membrane, the chemical liquid immersion cleaning and the backwashing are performed as one cycle, and the treatment is performed for one cycle or more. Method.

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