JPH06190250A - Washing method for membrane module - Google Patents

Abstract

PURPOSE:To efficiently wash a membrane module while suppressing intrusion of a detergent into the filtrate side of this module by applying a pressure by gas below the valve point of a separating membrane from the filtrate side and simultaneously adding the detergent to an original liquid side. CONSTITUTION:The filtrate side is filled with gas when the membrane is pressurized by the gas from its filtrate side. The pores are, however, filled with the gas as well if this pressure exceeds the valve point pressure (the valve point pressure varies with the pressure under which air bubbles appear on the secondary side of the sufficiently wetted filter when an air pressure is applied to this filter and the surface tension of the liquid for wetting) and, therefore, the pressure to be applied on the membrane must be lower than the valve point pressure. The valve point value at the time of using water is a reference in the case of the filter original water and detergent of a water system. The membrane surface is chemically washed by filling the original liquid side with a washing chemical in this state. The liquid chemical is penetrated into the pores by a diffusion phenomenon. The membrane module is reproduced by resting the membrane for a specified period of time in this state.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel chemical cleaning method for membrane modules.

[0002]

2. Description of the Related Art As separation membranes used in membrane modules, reverse osmosis membranes, ultrafiltration membranes, microfiltration membranes and the like are used depending on the difference in pore size, and the membrane morphology is flat membrane, tubular membrane, hollow fiber membrane. Etc. are used properly according to the purpose. All of these membranes can be cleaned with chemicals, and are regenerated by cleaning when the surface of the membrane is clogged.

[0003] The selection of chemicals is determined by the chemical resistance of the membrane material and the module member, but typical examples include caustic soda, hydrochloric acid, sodium hypochlorite, and surfactants. . As a cleaning method, an outside system immersion cleaning method in which a module is taken out of a can body and immersed in a chemical tank, an in-system cleaning method in which the inside of the can body is completely filled with a chemical, and the like are mainly performed.

[0004]

However, when the membrane module is cleaned by these methods, the following problems occur. Of course, after the chemical cleaning, the chemical used must be washed away, but when the chemical reaches the filtrate side of the membrane, a large amount of cleaning liquid (water or buffer etc.) is required.

In the case of the immersion cleaning outside the system, a large amount of chemicals is required, and the operation for attaching and detaching the module is complicated. Further, when a specific member (for example, a resin fixing portion in the hollow fiber membrane module) is weak against the chemical, the chemical to be used is specified by the chemical resistance of the member.

An object of the present invention is to provide a method for cleaning a membrane module, which can efficiently clean the minimum necessary area to be cleaned with a minimum required amount of chemical when cleaning the membrane module with chemicals. It is in.

[0007]

The gist of the present invention is to apply a gas pressure below the bubble point of the separation membrane from the filtrate side when cleaning the membrane module for filtering liquid with chemicals,
A method for cleaning a hollow fiber membrane module is characterized in that a cleaning agent is added to the raw solution side at the same time.

In most cases, the substance that clogs the membrane is trapped on the membrane surface (the undiluted side of the membrane) and in the pores of the membrane, and hardly exists on the filtrate side. Therefore, if the membrane surface and the inside of the pores can be sufficiently washed, the membrane can be washed and regenerated.

When gas is applied from the filtrate side of the membrane,
The filtrate side is filled with gas. However, if the pressure exceeds the bubble point pressure (the pressure at which bubbles appear on the secondary side when air pressure is applied to a sufficiently wet filter; the bubble point pressure varies depending on the interfacial tension of the liquid to be wetted), the inside of the pores also. Since it is filled with gas, the applied pressure must be lower than the bubble point pressure. In the case of water-based filtered raw water and cleaning agents, the bubble point value when water is used is the standard.

In this state, the membrane surface can be chemically washed by filling the stock solution side with a washing chemical. Further, the drug solution penetrates into the pores due to the diffusion phenomenon. The membrane module is regenerated by leaving a certain time in this state.

The types of chemicals used for chemical cleaning include, for example, hydrochloric acid, caustic soda, hydrogen peroxide, sodium hypochlorite,
Examples thereof include surfactants and enzymes.

[0012]

The present invention will be described in detail with reference to the following examples. Example 1 Twenty polyethylene porous hollow fiber membranes (EHF270T manufactured by Mitsubishi Rayon Co., Ltd., inner diameter 270μ, outer diameter 380μ, pore diameter 0.1μ) were bundled and the ends were fixed with urethane resin, and an effective filtration area of 12 cm ² was obtained. A module was produced. The initial water permeability of this module was measured, and then the Escherichia coli culture solution (106 cfu / ml) was filtered to close the module. After measuring the water permeability of the module, a pressure of 1.5 kg / cm ² of gas was applied from the filtrate side, and 1% by weight of a caustic soda aqueous solution was charged into the raw water side in that state. After leaving it overnight, it was thoroughly washed with water, and the water permeability was measured again. The immersion temperature was room temperature. The results are shown in Table 1.

Comparative Example 1 The same module as in Example 1 was used and treated in the same manner as in Example 1 except that the step of applying a gas pressure of 1.5 kg / cm ² from the filtrate side was omitted. The results are shown in Table 1.

[0014]

[Table 1]

As described above, there is no difference in the water permeability recovery state after chemical washing between the example and the comparative example, and the module can be sufficiently washed by the method of the present invention.

[0016]

By using the membrane module cleaning method of the present invention, it is possible to suppress the mixing of the cleaning agent into the filtrate side of the module as much as possible without lowering the cleaning efficiency as compared with the conventional method.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masumi Kobayashi 4-chome, Sunadabashi, Higashi-ku, Nagoya, Aichi Prefecture 60-1 Mitsubishi Rayon Co., Ltd. Product Development Laboratory

Claims (1)

[Claims] 1. A hollow fiber membrane characterized in that, when a membrane module for filtering a liquid is chemically washed, pressure from a filtrate side by a gas below a bubble point of a separation membrane is applied, and at the same time, a detergent is added to a stock solution side. How to clean the module.