JP2011067716A - Water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method in which a membrane module is cleaned with a small amount of a surfactant aqueous solution of high concentration to keep high filtration performance thereof. <P>SOLUTION: A filtration system includes an original water tank 1, a pre-filter 2, the membrane module 3, and a filtrate tank 4, wherein a closed-system circulation line comprising a second feed line 11b, a third feed line 11c, the membrane module 3, a first return line 13a, and a second return line 13b is formed. A small amount of the surfactant aqueous solution is injected from an injection port 40 and circulated through the circulation line to clean a separation membrane in the membrane module 3 circularly. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a water treatment method applicable to filtration treatment of washing wastewater such as vegetables and river water.

  When filtering wastewater or the like with a membrane module, the membrane is washed with a chemical solution such as sodium hypochlorite in order to recover the filtration performance that has deteriorated due to the continuation of filtration. However, sodium hypochlorite often cannot be cleaned. For example, when the film is contaminated with fats and oils, performance is not recovered only with sodium hypochlorite.

  Therefore, in such a case, cleaning with a surfactant is desired. However, surfactants are organic and have COD and BOD loads, and if there is a large amount of washing wastewater, it is often difficult to treat wastewater.

  Further, after the chemical solution cleaning, the membrane module is washed with water in order to remove the remaining chemical solution. Since the surfactant easily adheres to the film and it is difficult to completely remove the chemical solution, a large amount of rinsing water is required, resulting in time and a large amount of drainage. For this reason, an efficient method for cleaning a film that can use a surfactant is desired.

  The invention of Patent Document 1 describes a method of performing reverse pressure cleaning with raw water after immersion cleaning in which a surfactant module is filled in a membrane module.

  The invention of Patent Document 2 describes a method for back-pressure washing of a separation membrane with washing water containing polylysine, and the invention of Patent Document 3 describes that the separation membrane is back-pressure washed with washing water containing a cypress plant extract component. How to do is described.

JP 2007-181773 A JP-A-8-309164 JP-A-9-52027

  When the chemical solution is washed to restore the filtration performance of the membrane module, a large amount of water is required because the washing is performed with the washing water in which the chemical is added to the filtered water or tap water, and the treatment of the washing waste water becomes a heavy burden.

  An object of the present invention is to provide a water treatment method capable of maintaining high filtration performance by washing a membrane module with a small amount and a high concentration surfactant aqueous solution.

As a means for solving the problems, the present invention
A water treatment method using a filtration treatment system,
The filtration processing system includes at least a raw water tank, a membrane module, and a filtrate water tank, the raw water tank and the raw water inlet of the membrane module are connected by a feed line, and the filtrate outlet and the filtrate water tank of the membrane module are connected to the filtrate water line. The concentrated water outlet of the membrane module and the feed line are connected at the return line,
The water treatment method has a filtration step and a washing step,
The washing step is a step of dissolving a surfactant in water to obtain a surfactant aqueous solution, and a step of bringing the surfactant aqueous solution into contact with the filtration membrane in the membrane module for washing.
The contact cleaning process between the surfactant aqueous solution and the filtration membrane in the membrane module forms a closed system circulation line that includes the membrane module and does not contain the raw water tank and the filtrate water tank in part of the feed line and the return line. Then, a water treatment method is provided, which is a step of circulating and washing by directly injecting an aqueous detergent solution into the circulation line.

  The water treatment method of the present invention can maintain high filtration performance for a long time by applying circulation cleaning with a small amount of a surfactant aqueous solution. In addition, since the cleaning is performed with a small amount of the surfactant aqueous solution, the processing load of the cleaning waste water is reduced.

It is the schematic of the filtration processing system used with the water treatment method of this invention.

<Filtration processing system>
The filtration system used in the water treatment method of the present invention will be described. The filtration processing system shown in FIG. 1 includes a raw water tank 1, a prefilter 2, a membrane module 3, and a filtered water tank 4. In addition, when the stain | pollution | contamination of raw | natural water is small, the prefilter 2 does not need to be installed.

  The raw water tank 1 and the pre-filter 2 are connected by a first feed line 11a, and an open / close valve 21 and a raw water pump 5 are installed.

  Between the pre-filter 2 and the raw water inlet 3a of the membrane module 3, a second feed line 11b (a line from the pre-filter 2 to the open / close valve 23) and a third feed line 11c (a line from the open / close valve 23 to the raw water inlet 3a) Connected with.

  In the second feed line 11b, an opening / closing valve 22, a circulation pump 6, and an opening / closing valve 23 are installed in this order from the prefilter 2 side.

  The third feed line 11c is connected to a drainage line 17 for backwashing drainage in which an open / close valve 24 is installed.

  A filtrate water line 12 connects between the filtrate outlet 3 b of the membrane module 3 and the water storage tank 4. Open / close valves 25 and 26 are installed in the filtrate water line 12.

  A back pressure washing line 14 connects between the bottom of the water storage tank 4 and the open / close valves 25 and 26 of the filtrate water line 12. In the back pressure cleaning line 14, an opening / closing valve 30, a back pressure cleaning pump 7, and an opening / closing valve 31 are installed in order from the side closer to the water storage tank 4.

  Between the concentrated water outlet 3c of the membrane module 3, the open / close valve 22 of the second feed line 11b and the circulation pump 6, a first return line 13a (a line from the concentrated water outlet 3c to the open / close valve 27) and a second return line 13b. (Lines from the open / close valve 27 to the second feed line 11b).

  An opening / closing valve 32 is installed in the second return line 13b, and an inlet 40 for an aqueous surfactant solution is provided at a desired position. The injection port 40 for the surfactant aqueous solution can be installed in the first feed line 11b, the third feed line 11c, and the first return line 13a, or can be installed in two or more locations.

  Connected to the first return line 13a are a concentrated water drain line 15 having an open / close valve 28 and a circulating wash water drain line 16 having an open / close valve 29.

  The membrane module 3 is a known one. For example, as shown in the drawing, a separation membrane is accommodated in a module case having three liquid inlets / outlets 3a, 3b, 3c.

  The separation membrane may be made of either a hydrophobic material or a hydrophilic material, but the recovery effect of the filtration performance when the filtration performance recovery method of the present invention is applied is particularly applied to a separation membrane made of a hydrophobic material. Sometimes it becomes prominent.

  Examples of the hydrophobic material include polysulfone resins, polyether sulfone resins, polyvinylidene fluoride resins, polyacrylonitrile resins, polyimide resins, polyaramid resins, polypropylene resins, polyethylene resins, and the like. Examples of the hydrophilic material include cellulose materials such as cellulose acetate, cellulose propionate, cellulose butyrate, regenerated cellulose, and a mixture thereof. Moreover, polyvinyl alcohol etc. can also be used.

  The separation membrane may be any of a hollow fiber membrane, a tubular membrane, a spiral membrane, a microfiltration membrane, a flat membrane, etc., but from the viewpoint of circulating the treated water as washing water for plants containing vegetables and / or fruits, A hollow fiber membrane having a high purification capacity is preferred.

  When using a hollow fiber membrane, for example, an inner diameter of 0.3 to 3.0 mm (preferably 0.5 to 1.0 mm), an outer diameter of 0.4 to 5.0 mm (preferably 0.7 to 1.7 mm). Thus, an ultrafiltration membrane having a molecular weight cut-off of 3,000 or more (preferably 100,000 or more) is preferable.

  The hollow fiber membrane can be used as one bundle or two or more bundles of hollow fiber membranes in which necessary numbers are bundled according to the amount of raw water and the concentration of turbid components in the raw water.

<Water treatment method using filtration system>
Next, a water treatment method using the filtration treatment system will be described. The water treatment method has a filtration step and a washing step.

[Filtration process]
In the filtration process, the raw water pump 5 is operated, and raw water is sent from the raw water tank 1 to the membrane module 3 through the first feed line 11a, the second feed line 11b, and the third feed line 13c. In this process, a large foreign matter is removed by the pre-filter 2. In the filtration step, each open / close valve is opened and closed as follows.

(Open / close valve to be opened)
All open / close valves from the raw water tank 1 to the membrane module 3 Open / close valves 25 and 26 of the filtrate water line 12
(Open / close valve to be closed)
Open / close valve 27 of the first return line 13a
Open / close valve 32 of the second return line 13b
Open / close valve 24 of the drainage line 17 for backwashing drainage
Open / close valve 28 of concentrated water drainage line 15
Open / close valve 29 for the drain line 16 of the circulating cleaning water
Open / close valves 30 and 31 of the back pressure washing line 14

  The filtrate filtered by the membrane module 3 is sent to the filtrate tank 4 through the filtrate line 12 and stored. Note that the concentrated water in the membrane module 3 is drained by opening the open / close valve 28 of the concentrated water drain line 15 according to the state of implementation of the filtration operation.

The filtration operation conditions (water transmission rate etc.) when using a hollow fiber membrane (ultrafiltration membrane) as a separation membrane in the membrane module 3 can be appropriately set according to the amount of raw water and the concentration of turbid components in the raw water. For example, the filtration operation is performed for 10 to 1500 minutes at a water permeability of 0.5 to 5.0 m / day.
[Washing process]

  In the course of the filtration operation, when the filtration performance (determined by the water transmission rate or the like) is reduced, or by periodically cleaning the separation membrane in the membrane module 3, the filtration performance of the separation membrane is maintained at a high level. be able to. In the cleaning step, it is preferable to apply a cleaning method that combines the circulation cleaning described below and back pressure cleaning.

  First, each open / close valve is opened and closed as follows to form a closed circulation line that includes the membrane module 3 and does not include the raw water tank 1, the pre-filter 2, and the filtrate water tank 4. At this time, raw water or the like is present in the membrane module 3, the second feed line 11b, and the third feed line 11c in the circulation line.

(Open / close valve to be opened)
Open / close valve 23 of the second feed line 11b
Open / close valve 27 of the first return line 13a
Open / close valve 32 of the second return line 13b
(Open / close valve to be closed)
Open / close valve 22 of the second feed line 11b
Open / close valve 24 of the drainage line 17 of the backwash water
Open / close valve 25 of filtrate water line 12
Open / close valve 28 of concentrated water drainage line 15
Open / close valve 29 for the drain line 16 of the circulating cleaning water

  After the circulation line is formed by operating the on-off valve in this manner, the surfactant aqueous solution is injected from the surfactant aqueous solution inlet 40.

  Then, the separation membrane in the membrane module 3 is washed by operating the circulation pump 6 to circulate the surfactant aqueous solution in the circulation line. The waste water after the circulation washing is drained from the drain line 16 of the circulation washing water by opening the opening / closing valve 29.

As surfactant,
Fatty acid salt, rosin acid salt, alkyl sulfate salt, alkyl benzene sulfonate salt, alkyl diphenyl ether sulfonate salt, polyoxyethylene alkyl ether sulfate salt, sulfosuccinic acid diester salt, α-olefin sulfate salt, α-olefin sulfonate salt, etc. Anionic surfactants;
Cationic surfactants such as mono- or dialkylamines or polyoxyethylene adducts thereof, mono- or di-long-chain alkyl quaternary ammonium salts;
Polyoxyethylene fatty acid esters, sucrose fatty acid esters, sorbitan fatty acid esters, polyoxysorbitan fatty acid esters, glycerin fatty acid esters, propylene glycol fatty acid esters, polyoxyethylene fatty acid esters, and other ester-type nonionic surfactants (among these, Sucrose fatty acid esters, sorbitan fatty acid esters, glycerin fatty acid esters, which are preferably recognized as food additives), other alkyl glucosides, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene propylene block copolymers, amines Nonionic surfactants such as oxides;
One type or a combination of two or more types selected from amphoteric surfactants such as carbobetaine, sulfobetaine, and hydroxysulfobetaine can be given.

  In the present invention, a surfactant alone can be used, but a detergent containing a surfactant can also be used. Detergents include SC series (trade names SC-1000, SC-MAGIC PAN, etc.) manufactured by Infinity Co., Ltd., trade names Artan vegetable and fruit products manufactured by Altan Co., Ltd. (containing only sucrose fatty acid ester as a surfactant) ), Trade name Ultra Zeal 53 (containing an anionic surfactant and a nonionic surfactant as a surfactant) manufactured by Ecolab Co., Ltd., and the like.

  The amount of the cleaning agent in the membrane device is the sum of the hold amount (retention amount) on the membrane module raw water side filled with the detergent and the hold amount (retention amount) on the raw water side circulation line. If this amount is large, it takes time for rinsing after chemical cleaning. In the present invention, since the detergent is put only in the necessary portion on the raw water side, rinsing can be efficiently performed.

The total amount of detergent, that is, the hold amount on the membrane module raw water side and the hold amount on the raw water side circulation line is preferably 0.3 to 2.0 L with respect to 1 m ² of the effective membrane area of the membrane in the membrane module. 0.5 to 1.5 L is more preferable, and 0.5 to 1.0 L is more preferable.

  The circulation cleaning time is preferably 0.5 to 24 hours, more preferably 1 to 4 hours, and further preferably 1.5 to 2.5 hours.

  As for the pressure at the time of circulation cleaning, the pressure at the raw water inlet 3a of the membrane module 3 is preferably 0.01 to 0.1 MPa, and more preferably 0.01 to 0.06 MPa.

  After circulating cleaning, back pressure cleaning is performed to clean and remove the surfactant remaining in the circulating line. When back pressure cleaning is performed, each open / close valve is opened and closed as follows.

(Open / close valve to be opened)
Open / close valve 25 of filtrate water line 12
Open / close valves 30 and 31 of the back pressure washing line 14
Open / close valve 24 of the drainage line 17 of the backwash water
(Open / close valve to be closed)
Open / close valve 26 of the filtrate water line 12
Open / close valve 23 of the second feed line 11b

  In the reverse pressure washing, the back pressure washing pump 7 is operated, and the filtrate in the filtrate tank 4 is pressed from the filtrate outlet 3b side of the membrane module 3 to the raw water inlet 3a side for washing. The waste water after washing is drained from the line 17.

  Thereafter, the on-off valve is opened and closed as described above, and the filtration operation, circulation cleaning, and back pressure cleaning are repeated.

  The water treatment method of the present invention is a water treatment method for treating washing wastewater from a plant containing vegetables and / or fruits and reusing the obtained treated water as washing water for the plants containing vegetables and / or fruits. Suitable as

  The water treatment method of the present invention is also suitable as a water treatment method for filtering natural water taken from natural water systems such as rivers and lakes and using it as drinking water or industrial water.

  Furthermore, the water treatment method of the present invention maintains high safety when reusing treated water by using an ester-type nonionic surfactant that can be used as a food additive as a surfactant used for washing. Can do.

Example 1
The following onion wash water was filtered by the filtration system shown in FIG.

  Onion washing water: About 150 to 250 g of commercially available onions were cut with a kitchen knife so as to have a cross section of about 5 cm in diameter, and then 20 peeled surfaces were prepared. This was submerged in about 40 L of tap water, and the water was stirred and washed for 5 minutes to obtain washing water.

  Pre-filter 2: Strainer with a filtration accuracy of 20μm

Membrane module 3: A bundle of 40 cellulose acetate hollow fiber membranes (FUC1582; manufactured by Daisen Membrane Systems Co., Ltd.) is placed in a transparent vinyl chloride resin case with an outer diameter of 26 mm and an inner diameter of 20 mm. A membrane module 3 (effective membrane area 0.026 m ² ) was prepared by bonding and integrating both ends of the membrane.

  Each line is made of a tube, and the inner diameter is 4 mm, which is the same for all lines.

[Filtration process]
With the on-off valve operated as described above, the entire amount was filtered at a pressure of 0.1 MPa at the raw water inlet 3a of the membrane module 3. After 2 hours from the start of the operation, the filtration operation was stopped when the water permeation rate at the filtrate water outlet 3b was reduced to about 60%.

[Circulating washing process and back pressure washing process]
Next, in the state where the open / close valve was operated as described above to form a circulation line, a high concentration chemical aqueous solution was injected from the injection port 40 and circulated and washed for 2 hours. At this time, the total of the hold amount on the membrane module raw water side and the hold amount on the raw water side circulation line was about 20 ml. That is, the amount of the surfactant solution per 1 m ^{2 of} membrane area was about 0.8 L. As the surfactant aqueous solution, SC-Magic pan manufactured by Infiniti was used.

  After completion of the circulation cleaning, backwashing was performed for 2 minutes at 0.1 MPa using filtered water. Thereafter, when the filtration operation was restarted in the same manner, the water permeability of Surfactant 1 recovered to almost 100%. Then, when rinsing with tap water for 1 hour, the TOC in the rinse water became 2 mg / L.

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Pre filter 3 Membrane module 4 Water storage tank 5 Raw water pump 6 Circulation pump 7 Back pressure washing pump 21-32 Open / close valve

Claims (5)

A water treatment method using a filtration treatment system,
The filtration processing system includes at least a raw water tank, a membrane module, and a filtrate water tank, the raw water tank and the raw water inlet of the membrane module are connected by a feed line, and the filtrate outlet and the filtrate water tank of the membrane module are connected to the filtrate water line. The concentrated water outlet of the membrane module and the feed line are connected at the return line,
The water treatment method has a filtration step and a washing step,
The washing step is a step of dissolving a surfactant in water to obtain a surfactant aqueous solution, and a step of bringing the surfactant aqueous solution into contact with the filtration membrane in the membrane module for washing.
The contact cleaning process between the surfactant aqueous solution and the filtration membrane in the membrane module forms a closed system circulation line that includes the membrane module and does not contain the raw water tank and the filtrate water tank in part of the feed line and the return line. Then, a water treatment method, which is a step of circulating and washing by directly injecting an aqueous detergent solution into the circulation line. The amount of the surfactant aqueous solution to be washed (the total of the hold amount on the membrane module raw water side and the hold amount on the raw water side circulation line) is 0.3 to ^{2 with} respect to 1 m ² of the effective membrane area of the membrane in the membrane module. The water treatment method according to claim 1, which is 0 L.   The water treatment method according to claim 1 or 2, wherein, in the washing step, reverse pressure washing using filtered water is performed after circulation washing.   The said water treatment method is for treating the washing waste_water | drain of the plant containing vegetables and / or fruits, and reusing the obtained treated water as the washing water of the plants containing the said vegetables and / or fruits. Item 4. The water treatment method according to any one of Items 1 to 3.   The water treatment method according to claim 1, wherein the water treatment method is for filtering natural water.

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