JP4384741B2 - Cleaning agent and cleaning method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cleaning agent containing percarbonate and a cleaning method.
[0002]
[Prior art]
Conventionally, separation membranes have been used for various purposes, and concentration and separation by filtration have been performed. For example, it has been used for the production of aseptic water, drinking water, high-purity water, purification of air, concentration and addition of gas, and the like. In recent years, ultrafiltration membranes and microfiltration membranes have been used for direct filtration of river water in water purification plants, filtration of industrial tap water, filtration of pool water, secondary and tertiary treatment in sewage treatment plants, solid-liquid separation in septic tanks, It is used for highly polluted water treatment applications such as solid-liquid separation of ss (suspended suspended solids) in industrial wastewater.
[0003]
However, in these applications, the membrane surface becomes clogged as the operation such as filtration continues, and there arises a problem that the filtration differential pressure increases. Such an increase in the filtration differential pressure will eventually increase to the extent that it is difficult to secure the treatment liquid. Therefore, by removing this clogging substance, the increased differential pressure is lowered again. It is necessary to continue driving.
[0004]
The clogging on the film surface is roughly classified into two. One is the deposition of solids such as fine particles on the film surface. On the other hand, the film surface can be cleaned, that is, the deposit on the film surface can be removed by cross-flow filtration or scrubbing cleaning with a gas-liquid mixed flow. The other is fouling derived from adsorption to a film material, such as organic substances and minute inorganic compounds. This fouling cannot be easily removed by physical means such as scrubbing, and chemical cleaning with a chemical solution or the like is required.
[0005]
Various cleaning agents are used in chemical cleaning of membranes. When fouling of an inorganic compound typified by a metal salt or the like occurs, cleaning is performed by immersing or passing the film in an acid aqueous solution. In addition, when organic fouling occurs, some can be removed with acid or alkali, but a method often used is an aqueous solution of hypochlorite as a cleaning agent. The active chlorine in the cleaning agent oxidizes and decomposes organic substances from the film surface.
[0006]
[Problems to be solved by the invention]
However, after cleaning with a cleaning agent containing hypochlorite, if the used cleaning liquid is discharged directly into sewage, etc., chlorine in hypochlorite can react with organic substances to generate trihalomethane, etc., which is difficult to decompose. There is sex. In waterworks, trihalomethane produced by the reaction between hypochlorite and organic substances introduced for the purpose of sterilization is a problem, but in the cleaning of membranes as described above, particularly high concentrations of hypochlorite are used. Similar problems may occur in the conventional detergents to be contained.
[0007]
On the other hand, a method is also conceivable in which the spent liquid containing hypochlorite is discharged after the membrane is washed and then discharged after some treatment so as not to affect the environment. However, when a large amount of high-concentration liquid is processed, large costs and complicated operations are required. Therefore, the conventional detergent containing hypochlorite is not preferable in that it may adversely affect the environment and the post-treatment of the used liquid is complicated.
[0008]
The present invention has been made to solve the above problems, and an object thereof is to provide a separation membrane cleaning agent that can be handled safely without using hypochlorite, and a separation membrane cleaning method using the cleaning agent. .
[0009]
[Means for Solving the Problems]
The present inventor conducted extensive research to solve the above problems, and found that when a detergent containing percarbonate is used, the separation membrane can be washed without adversely affecting the environment, leading to the present invention. It was.
[0010]
The separation membrane cleaner of the present invention is characterized by containing peroxomonocarbonate . Moreover, the separation membrane cleaning agent of the present invention are further Dressings containing divalent iron salt with percarbonate. Furthermore, the cleaning agent of the present invention may further contain at least one of an oxidizing agent other than hypochlorite and hydrogen peroxide, a surfactant, a chelating agent, and a pH adjusting agent.
[0011]
The separation membrane cleaning method of the present invention is characterized in that the separation membrane is brought into contact with a solution comprising the above-described cleaning agent. A hollow fiber membrane is suitable as the separation membrane to be washed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. The separation membrane cleaning agent of the present invention is characterized by containing a percarbonate. Here, the percarbonate is peroxocarbonate, and there are peroxomonocarbonate and peroxodicarbonate. In the present invention, peroxomonocarbonate is mainly used. Percarbonate is present in the form of adduct of hydrogen peroxide to carbonate. Examples of percarbonate include alkali metal salts or alkaline earth metal salts such as sodium salt, potassium salt, lithium salt, calcium salt, magnesium salt, and beryllium salt, but it is commercially available as sodium percarbonate. It is what has been. In a preferred embodiment of the cleaning agent of the present invention, a sodium salt represented by the following chemical formula is dissolved in water and used.
Na ₂ CO ₃ .1.5H ₂ O ₂
[0013]
When this compound is dissolved, the organic substance adhering to the film surface is oxidatively decomposed by the hydrogen peroxide component in the compound, and the clogging substance can be removed from the film surface. The washing solution after washing is safe without generating harmful substances even if it is discharged as it is. In the cleaning agent of the present invention, the percarbonate is preferably contained in the cleaning solution in the range of 0.1 wt% to 10 wt%, more preferably 1 wt% to 5 wt%.
[0014]
In addition, the separation membrane cleaning agent of the present invention contains a divalent iron salt in order to further enhance the cleaning properties with percarbonate. As a result, a so-called Fenton reaction represented by the following reaction formula occurs between hydrogen peroxide adducted in the percarbonate and divalent iron ions, and OH radicals are generated.
^{_{H 2 O 2 + Fe 2+ →}} · OH + OH - + Fe 3+
[0015]
This OH radical has very high oxidation reactivity such as hydrogen abstraction with respect to the organic matter, and promotes oxidative decomposition of the organic matter. The divalent iron salt used here may be supplied by any salt and can be contained in the cleaning agent of the present invention in the form of chloride, sulfate, nitrate or the like. Preferably, the divalent iron ion is in the range of 1 × 10 ⁻⁹ to 1 × 10 ⁻¹ (mol / l), more preferably 1 × 10 ⁻⁷ to 1 × 10 ^{−1 in} the cleaning solution of the present invention. It should be in the range of (mol / l).
[0016]
In the cleaning agent of this invention, you may include what accelerates | stimulates washing | cleaning other than percarbonate. Examples include surfactants, chelating agents, and acids and alkalis that adjust pH. More specifically, a surfactant such as sodium dodecyl sulfonate and a pH adjuster such as phosphate can be used. In using the separation membrane cleaning agent of the present invention, the cleaning agent having the above composition is completely dissolved in water.
[0017]
The cleaning method of the present invention is characterized in that a separation membrane to be cleaned is brought into contact with a solution comprising the above-described cleaning agent.
[0018]
The separation membrane washed by the method of the present invention may basically have various forms and materials, and is not particularly limited. Examples of the form of the membrane include a flat membrane and a tubular membrane. Furthermore, the cleaning method of the present invention can be applied even if these membranes are fixed in a casing or a housing and modularized. Moreover, in terms of increasing the membrane area per unit volume, hollow fiber membrane types are widely used for various separations. Of course, the cleaning method of the present invention is also applied to cleaning this type of separation membrane. Is possible.
[0019]
On the other hand, the material of the membrane is not particularly limited, but examples include polyolefin, polysulfone, polyacrylonitrile, polyester, polycarbonate, nylon, polyvinyl alcohol, cellulose, silicon, fluoropolymer, and ceramic.
[0020]
In the cleaning method of the present invention, the contact method of the separation membrane to be cleaned and the cleaning agent is not particularly limited as long as the separation membrane to be cleaned and the cleaning agent are in sufficient contact with each other. It is preferable to use a liquid. Here, “immersion” means that the inside and the outside of the separation membrane are completely immersed in a solution made of a cleaning agent. On the other hand, the term “liquid passing” refers to passing a cleaning solution through a separation membrane in the same manner as in normal separation. When contacting the cleaning solution with the separation membrane, a physical cleaning method such as scrubbing cleaning by air bubbling or ultrasonic cleaning may be combined.
[0021]
Various conditions during washing, such as washing temperature and washing time, depend on the degree of clogging of the separation membrane to be washed, the nature of the clogging substance, the concentration of percarbonate in the washing liquid (detergency), etc. Those skilled in the art may determine appropriately.
[0022]
【Example】
The present invention will be described in detail with reference to examples.
[0023]
Example 1
Using a membrane filter made of cellulose mixed ester with a pore size of 0.22 μm (GSWP type, diameter 47 mm, manufactured by Nihon Millipore) as a flat membrane type filtration membrane, first, 5000 ppm yeast suspension water is filtered to clog the membrane. Then, this clogged membrane was washed by immersing it in a 1% aqueous sodium percarbonate solution at room temperature for 6 hours.
[0024]
In each stage, the flow rate of the above membrane filter at a transmembrane pressure difference of 0.1 Mpa was as follows:
Before clogging: 24.6 mL / min · cm ² ;
After filtration of the yeast suspension: 7.77 mL / min · cm ² ;
After washing: 17.2 mL / min · cm ² .
[0025]
(Example 2)
In this example, a hollow fiber type filtration membrane was used. The filtration membrane was prepared as follows. Polyethylene was melt-spun to obtain a hollow fiber membrane (outer diameter 410 μm, inner diameter 270 μm) having a pore diameter of 0.1 μm. The hollow fiber membrane was hydrophilized by coating the membrane surface with an ethylene-vinyl alcohol copolymer. 16 hollow fiber membranes were folded in a U shape, and fixed with resin while maintaining the open state of the end portion to obtain a hollow fiber membrane module. The hollow fiber membrane module was clogged by filtering 5000 ppm yeast suspension. The clogged membrane was washed by immersing it in a 1% aqueous sodium percarbonate solution at room temperature for 6 hours or 24 hours.
[0026]
In each stage, the flow rate of the above membrane filter at a transmembrane pressure difference of 0.1 Mpa was as follows:
Before clogging: 4.15 mL / min · cm ² ;
After filtration of the yeast suspension: 0.85 mL / min · cm ² ;
After washing for 6 hours: 1.96 mL / min · cm ² ;
After washing for 24 hours: 2.41 mL / min · cm ² .
[0027]
(Example 3)
A hollow fiber membrane module similar to that used in Example 2 was prepared, and the membrane was clogged by filtering 5000 ppm yeast suspension water into the hollow fiber membrane module. The clogged film was cleaned by immersing it in a cleaning solution consisting of 1% sodium percarbonate and 500 ppm of iron (II) chloride (FeCl 2 .nH 2 O) at room temperature for 6 hours or 24 hours.
[0028]
In each stage, the flow rate of the above membrane filter at a transmembrane pressure difference of 0.1 Mpa was as follows:
Before clogging: 4.39 mL / min · cm ² ;
After filtration of the yeast suspension: 0.77 mL / min · cm ² ;
After washing for 6 hours: 2.35 mL / min · cm ² ;
After washing for 24 hours: 3.78 mL / min · cm ² .
[0029]
【The invention's effect】
Since the separation membrane cleaning agent of the present invention uses percarbonate, there is no adverse environmental impact due to generation of trihalomethane or the like even if it is discharged into sewage, rivers, etc. after use. In addition, when the cleaning agent of the present invention contains a divalent iron salt, a radical reaction caused by OH radicals generated by iron ions causes decomposition of substances deposited on and adhered to the film, particularly organic substances. Cleaning efficiency is improved. Furthermore, according to the cleaning method of the present invention, it is possible to safely clean the membrane and restore the function of the separation membrane without generating harmful substances such as trihalomethane due to the cleaning agent.

Claims (3)

  A separation membrane cleaning agent comprising a percarbonate and a divalent iron salt.   The separation membrane cleaning agent according to claim 1, further comprising at least one of an oxidizing agent other than hypochlorite and hydrogen peroxide, a surfactant, a chelating agent, and a pH adjusting agent. . A separation membrane cleaning method comprising contacting a separation membrane to be cleaned with a solution comprising the cleaning agent according to any one of claims 1 to 2 .