JPH08126824A - Washing of filter membrane - Google Patents

Abstract

PURPOSE: To provide a washing method by which a filter membrane having high treating capacity is used for a long time, by effectively washing the stained filter membrane. CONSTITUTION: When washing a stained filter membrane, after first foreign matter stuck on the membrane is washed off with water, the filter membrane is subjected to a washing treatment in which drying treatment and chemical treatment are combined. In this washing treatment, it is preferable that, first, the chemical treatment is carried out and next the drying treatment is performed. The filter membrane is preferably the one whose surface is hydrophilic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a filtration membrane, and more particularly, a method for cleaning a filtration membrane used in a membrane separation activated sludge method in which organic waste water is treated with activated sludge and then treated water is obtained by membrane separation. Regarding the method.

[0002]

2. Description of the Related Art Membrane separation processes have hitherto been used in the field of high-level treatment, but recently they are often used in the field of secondary treatment such as substitution of a settling tank in the activated sludge method. It's coming. With the expansion of the field of use, the stock solution for membrane separation is becoming more contaminated. Further, in order to reduce the power required for membrane separation, a method of directly immersing the membrane main body in a filtration stock solution and performing filtration has been performed. The membrane separation step is usually operated by a method called cross-flow filtration, and filtration is performed while always cleaning the membrane surface by ensuring a sufficient membrane surface flow velocity. However, even in this state, minute solids that do not pass through the membrane inside the membrane,
The clogging of the colloidal substance, etc. reduces the filtration capacity. Chemical cleaning is performed to remove the contaminants inside the membrane and restore the filtration capacity.
Solutions of sodium hypochlorite, sodium hydroxide, chlorine dioxide, sodium salts of ethylenediaminetetraacetate, hydrochloric acid, citric acid, etc. are used. However, as the degree of contamination of the target undiluted solution increases, the degree of contamination of the filtration membrane also increases, so the recovery rate due to chemical cleaning decreases, the frequency of cleaning the filtration membrane increases, and the life of the filtration membrane increases. It's getting shorter.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned prior art, and it is a method for cleaning a filter membrane which can be used for a long period of time by effectively cleaning the contaminated filter membrane. The challenge is to provide.

[0004]

In order to solve the above-mentioned problems, in the present invention, when cleaning a contaminated filter membrane, first, foreign substances attached to the membrane are washed off with water, and then the filter membrane is dried. And a chemical solution treatment are combined to carry out a washing treatment. In the filtration membrane cleaning method, the combination of the chemical treatment and the drying treatment is optional, and the chemical treatment may be performed after the completion of the drying treatment, but the drying treatment is performed as the final step after the completion of the chemical treatment after the cleaning. It is advantageous for storing the membrane. As described above, according to the present invention, the membrane that has been required to be washed due to the progress of contamination is washed with water to remove foreign substances such as sludge and dust, and then subjected to chemical cleaning treatment and drying treatment.

As a method for the drying treatment, an ordinary drying method such as a method of performing natural drying by leaving it in the air or a method of drying in a temperature-controlled dryer may be adopted. The difference in drying method is only the difference in time and energy required.
The chemical cleaning process is performed by immersing the contaminated film in the chemical. The chemicals used are not particularly limited, but considering the safety of the chemicals, the ease of post-treatment, the cost, etc., it is preferable to use a surfactant such as an alkylbenzene sulfonate or an alpha sulfo fatty acid salt. . Of course, conventionally used chemicals such as alkali can also be used. In addition, it is very effective to raise the temperature of the chemical liquid and treat it at a high temperature. The membrane used in the present invention is a membrane using a known material such as polyethylene or vinyl chloride and having microfiltration / ultrafiltration properties, and it is desirable that the surface of the membrane be hydrophilized. The application field is not particularly limited, but the membrane used in the step of separating activated sludge after treating organic wastewater with activated sludge is suitable for the present method.

[0006]

The present invention is a method for cleaning a filtration membrane, characterized in that the filtration membrane is washed by combining a conventional chemical washing with a drying step. By incorporating a drying process, it becomes possible to effectively recover the filtration performance of the membrane by washing with a chemical that is low in concentration and safe for the human body. Although future research is expected to elucidate the principle of cleaning the filtration membrane by the drying process, it is presumed that the cleaning effect will be improved by contracting and peeling the adhered contaminants by drying.

[0007]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited thereto. Example 1 A test was carried out by cleaning including the drying treatment according to the present invention and, as a comparative example, cleaning using only conventional chemical cleaning. As the filtration membrane, a polyethylene hollow fiber membrane whose surface was processed to be hydrophilic was used. The hollow fiber membrane was immersed in a sewage activated sludge treatment aeration tank, and a negative pressure was applied to the inside of the membrane by suction to take out the treated water. The membrane used in the activated sludge separation process is the membrane used for about one year. The drying treatment was natural drying, and after standing for 6 hours, chemical treatment was performed with a detergent mainly containing sodium alkylbenzenesulfonate (trade name "Attack"). Table 1 shows the results.

[0008]

[Table 1] In Table 1, the recovery rate of filtration pressure was calculated from the following formula. Recovery rate = (filtration pressure of contaminated membrane-filtration pressure after washing) /
(Filtration pressure of contaminated membrane-Filtration pressure of new membrane) The recovery rate was 60% in the conventional method, but according to the present invention, the recovery rate was 83%. According to the present invention, it is possible to effectively clean a contaminated film by using a safer chemical than conventional alkalis, acids, chlorine and the like.

Example 2 A repeated cleaning test was conducted on a hollow fiber membrane used in a membrane separation activated sludge method for sewage. The washing operation is to wash the contaminated membrane with water to remove the deposits, and then add 0.1% of surfactant.
It was immersed in an aqueous solution for 2 hours, washed, and naturally dried for 2 days. Fig. 1 shows the change in filtration pressure when washing and continuous filtration are repeated.
Shown in By repeating the washing according to the present invention,
The filtration could be continued stably for a long period of time.

[0010]

The method of cleaning a filtration membrane according to the present invention can effectively recover the contamination of the filtration membrane, and the filtration membrane can be used for a long period of time. According to the present invention, since safe chemicals can be used for effective cleaning, maintenance of the filtration membrane can be performed easily and economically.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between repeated washing operation and filtration pressure according to the present invention.

Claims (4)

[Claims] 1. When cleaning a contaminated filtration membrane,
First, a method for washing a filtration membrane, which comprises washing away foreign matter attached to the membrane with water, and then subjecting the filtration membrane to a washing treatment by combining a drying treatment and a chemical treatment. 2. The filtration membrane cleaning method according to claim 1, wherein the cleaning treatment is performed by first performing a chemical treatment and then performing a drying treatment. 3. The method of cleaning a filtration membrane according to claim 1, wherein the surface of the filtration membrane is hydrophilic. 4. The method for cleaning a filtration membrane according to claim 1, 2 or 3, wherein the contaminated filtration membrane is obtained by filtering an activated sludge mixed solution.