JPS60114304A - Method for washing membrane - Google Patents

Abstract

PURPOSE:To remove the contaminants regardless of the kind of a membrane, and to maintain and recover the performance of the membrane by bringing the surface of the membrane into contact with an acid and then with a liquid contg. hydrazine. CONSTITUTION:The surface of a contaminated membrane is brought into contact with an acid to remove a part of the contaminants. An organic acid having a chelating and a reducing action such as oxalic, citric, and tartaric acids are preferably used as said acid. The concn. of the acid is suitably regulated to 0.05-3%, and the pH to 2-4. The membrane is then washed with a liquid contg. hydrazine, and the most of the contaminants which are not removed by the acid washing is removed. The concn., in this case, is preferably regulated to 0.01-1% and the pH to 7.5-10. A surfactant can be preferably added to the acid and/or the liquid contg. hydrazine, and used at 0.001-0.5% concn.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cleaning a contaminated membrane surface of a membrane separation device, and particularly to a method for maintaining and restoring the amount of water permeated through a membrane.

Separation technology using polymer membranes has been put into practical use for applications such as concentration of waste products from vegetables and fruits, purification in the sugar and starch industries, and various wastewater treatment applications.

However, the various solutions used in these applications contain components such as proteins, carbohydrates, lipids, and salts, and during membrane separation, these components adhere to and accumulate on the membrane surface, impairing the permeation performance of the membrane. significantly decreased. For this reason, efficiently removing such membrane contaminants has become a major issue in the actual use of membrane separation devices.

There are two main types of membrane cleaning methods for removing membrane contaminants: physical methods and chemical methods. Physical methods include hot water, pulsation, and mixed air/water cleaning methods, but these methods are complex in terms of equipment and operation, and often do not provide sufficient cleaning.

For this reason, chemical cleaning methods using various cleaning agents are generally practiced. As cleaning agents, surfactants, acids, alkalis, oxidizing/reducing agents, chelating agents, enzymes, etc. are used, and these are used alone or in combination. However, the recovery of membrane performance cannot be said to be sufficient. Therefore, in order to maintain the amount of water permeated through the membrane, cleaning frequency must be increased, resulting in a shortened membrane life. On the other hand, there is a method of cleaning the membrane surface using a cleaning agent in stages.

For example, there is a method (Japanese Patent Publication No. 52-20038) in which the membrane surface is brought into contact with an acid and then an alkaline solution.
Unless the pH of the alkaline solution is raised, the recovery of membrane performance will be insufficient, and membrane deterioration due to high alkalinity is likely to occur.
The types of membranes that can be used are also limited.

An object of the present invention is to provide a membrane cleaning method that can sufficiently remove membrane contaminants and reliably maintain and restore membrane performance, regardless of the type of membrane to be cleaned.

The present invention is a method for cleaning a contaminated membrane surface of a membrane separation device, which is characterized in that the membrane surface is brought into contact with an acid and then brought into contact with a hydrazine-containing liquid.

First, in the present invention, acid is brought into contact with the contaminated membrane surface to remove a portion of the contaminants. As the acid, an organic acid having a chelating effect or a reducing effect is preferable, and oxalic acid, citric acid, tartaric acid, etc. are preferable.

The acid concentration is determined as appropriate depending on the type of acid, contaminant components, etc., but it is usually 0.05 to 3%.

The pH is preferably 2-4.

After cleaning with the above acid, cleaning is performed with a hydrazine-containing liquid. By washing with this hydrazine-containing liquid,
Most of the contaminants that could not be removed by acid cleaning are removed. The hydrazine concentration may normally be 0.01 to 1%. The pH is preferably 6.5 to 12, particularly pH 7.5 to 12.
10 is preferred.

Although the object of the present invention can be achieved by the acid cleaning and hydrazine-containing liquid cleaning described above, it is preferable to add a surfactant to the acid and/or hydrazine-containing liquid. Any anionic, cationic, nonionic, or amphoteric monomer can be used as the surfactant, and specific examples include sodium alkylbenzene sulfonate, sodium higher alcohol sulfate, sodium alkyl sulfate, sodium alkyl sulfonate, and alkyl sulfosuccinic acid. soda,
Sodium alkylnaphthalene sulfonate formalin condensate, sodium alkylnaphthalene sulfonate, sulfonated heterocyclic compound, fatty acid-amino acid condensate; polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether, polyethylene glycol fatty acid ether, Polyoxyethylene fatty acid amide ether, polyhydric alcohol fatty acid ester, polyoxyethylene polyhydric alcohol fatty acid ester; alkylpyridinium hydrochloride, alkyltrimethylammonium halide, polyoxyethylene alkylamine, polyoxyethylene dodecylamine; betaine type, imidacilline type, Examples include sulfone type and alanine type amphoteric surfactants. These surfactants may be added at a concentration of 0.001 to 0.5%, preferably 0.2 to 0.4%.

The method of the present invention can be applied to cleaning reverse osmosis membranes, ultrafiltration membranes, electrolytic diaphragms, etc., and the components include cellulose acetate, polyacrylonitrile, polychloride-5=vinyl, polysulfol, polyamide, polyethylene, and polypropylene membranes. It can be widely applied to cleaning etc.

According to the present invention, membrane contaminants mainly composed of organic matter, which are difficult to remove without using a highly alkali or oxidizing agent, can be efficiently removed, and the membrane is less likely to deteriorate and can be applied to a wide range of membranes.

Hereinafter, the effects of the present invention will be specifically illustrated by examples.

Example 1 Kitchen wastewater that has passed through a 70 mesh screen is treated with H2SO
, After adjusting the pH to 5.5 to 6.5, the pressure was 2°ky/cr.
& Cellulose acetate membrane (NTR-1530 manufactured by Nitto Denko Corporation) at a water flow rate of 107/min and a water temperature of 24 to 29°C.
; Standard permeated water amount was 1.1 ze/pi.D). The module is a tube type with a diameter of 500 mm and a diameter of 11.5 mm. It was operated for 1,000 hours while periodically flushing with water and cleaning with a cleaning agent using a surfactant. As a result, the amount of permeated water was 1.1 ze/ze・D, but it was 0.25 d
/Ba・D Ma 6- decreased.

This contaminated film is soaked in cleaning agent for 4 hours (in the case of two-stage cleaning, two
time).

In order to see the effect of cleaning, the amount of permeated water after cleaning was measured. The results are shown in Table 1 along with the cleaning agent used. The amount of permeated water shown in Table-1 is 2000 rv/l for UF permeated water.
Dissolve NaCl and pH 5.5-6 with H2SO.
．． The solution adjusted to 5 was heated to a pressure of 20 kp/d1 water
/min, the value after passing water for 30 minutes at a water temperature of approximately 25°C.

(The following is a blank space) 7- From the results in Table 1, it can be seen that in Cases 1 and 5 according to the present invention, the membrane performance was sufficiently recovered.

Example 2 A 4% solution of commercially available skim milk was heated to a pressure of 4 ky/cd.
.

Water was passed through a polysulfone-based membrane (NTU-3020 manufactured by Nitto Denko Corporation; standard permeated water rate 5.1 m/m-D) for 20 hours at a water flow rate of 101/min and a water temperature of 15 to 20°C. The module is a two-person tube type with dimensions of 500m x φ11.5m. As a result of water flow, the amount of permeated water was 5.1 pi/I-D
However, it decreased to 3.06-/pi·D.

This contaminated film is soaked in cleaning agent for 4 hours (in the case of two-stage cleaning, two
time).

Table 2 shows the cleaning agents used and the amount of permeated water.

The amount of permeated water shown in Table 2 is UF permeated water at a pressure of 4ky.
/'s The value is after passing water for 30 minutes at a water flow rate of 101/min and a water temperature of approximately 25°C.

It can also be seen from the results in Table 2 that in Case 7 according to the present invention, the membrane performance was sufficiently recovered.

11- −31=

Claims (1)

[Scope of Claims] 1. A membrane cleaning method for cleaning a contaminated membrane surface of a membrane separation device, which comprises bringing the membrane surface into contact with an acid and then contacting the membrane surface with a hydrazine-containing liquid. 26. The method according to claim 1, wherein the acid is an organic acid. 3. The method according to claim 1 or 2, wherein the acid and/or hydrazine-containing liquid contains a surfactant.