JP4255110B2 - Permeable membrane cleaner for water treatment and cleaning method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a membrane cleaning agent, and more particularly to a membrane cleaning agent and a cleaning method used for chemical cleaning of a permeable membrane for water treatment.
[0002]
[Prior art]
[Patent Document 1]
In recent years, processes using separation membranes are rapidly spreading in water purification and sewage treatment. In particular, in water purification, microfiltration membranes and ultrafiltration membranes are used as alternative processes for coagulating sedimentation sand filtration, and in sewage treatment, biological treatment is actively applied to solid-liquid separation.
In any membrane filtration device, if the treatment is continued for a certain period of time, organic contamination or inorganic matter contained in the raw water gradually adheres to the membrane surface or membrane pores, and the water permeability of the membrane decreases. When membrane contamination progresses and the water permeability of the membrane reaches a practical level or lower, chemical cleaning is performed to restore the water permeability of the membrane.
Generally, when washing organic pollutants, sodium hypochlorite or sodium hydroxide is used.
For contamination with inorganic substances such as iron and manganese, washing is performed with an organic acid such as oxalic acid and citric acid, an inorganic acid such as hydrochloric acid, sulfuric acid, and nitric acid, or a mixture thereof.
[0003]
As described above, acid cleaning is performed for cleaning a film contaminated with a metal oxide such as iron or manganese. However, inorganic acids such as hydrochloric acid and sulfuric acid have problems such as being ineffective at low concentrations, requiring heating, and increasing the cleaning time. In addition, the use at a high concentration increases the effect to some extent, but there are problems such as its own strong irritating odor and adverse effects on the film material.
Organic acids such as oxalic acid and citric acid are more effective for cleaning than inorganic acids, but oxalic acid is particularly toxic to the human body and is particularly resistant to water purification treatment. Although citric acid is not toxic, it has less cleaning effect than oxalic acid and has problems such as use at a high concentration of several percent or more, necessity of heating, and prolonged cleaning time.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a cleaning agent and a cleaning method for a water treatment permeable membrane that has a strong cleaning effect and does not adversely affect the membrane and the human body.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, a membrane cleaning agent used for cleaning a permeable membrane for water treatment, which is selected from the group consisting of L-cysteine hydrochloride, hydrates thereof and derivatives thereof The film cleaning agent is characterized by containing at least one kind.
Moreover, in this invention, it is set as the film | membrane washing | cleaning method used for washing | cleaning the permeation | transmission film | membrane for water treatments although the said film | membrane cleaning agent was contaminated with the inorganic substance.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present inventor has conducted extensive research and is a membrane cleaning agent used for membrane cleaning, including at least one selected from the group consisting of L-cysteine hydrochloride, its hydrate, and derivatives thereof. The present inventors have found that the film can be easily cleaned by using a film cleaner, and have reached the present invention.
For example, manganese is a typical inorganic contaminant that adheres to the film. The film adheres in the form of manganese dioxide, and washing and removing from the film means that it is decomposed and converted into divalent manganese ions and dissolved in water. This reaction is expressed as follows.
MnO ₂ + 4H ⁺ + 4e ⁻ → Mn ²⁺ + 2H ₂ O
As can be seen from the above equation, hydrogen ions and electrons are required to convert manganese dioxide into manganese ions, and in order to proceed the reaction quickly, the pH of the cleaning solution is set to the acidic side and the reducing atmosphere is changed. Need to make.
[0007]
L-cysteine hydrochloride is a hydrochloride of L-cysteine, which is a sulfur-containing amino acid exhibiting a specific reducing property, and since it is a hydrochloride, the aqueous solution thereof is an acidic solution. Therefore, L-cysteine hydrochloride alone functions as a reducing agent exhibiting hydrochloric acid acidity, and thus is a good cleaning agent for cleaning metal oxides such as manganese. Moreover, since it is a powdery hydrochloride, there is no off-flavor and it is easier to handle than inorganic acids.
Since L-cysteine hydrochloride monohydrate, which is a hydrate of L-cysteine hydrochloride, is used as a food additive and is easily available, it is preferably used in the present invention. Other compounds and derivatives containing cysteine may be used. For example, D-cysteine hydrochloride monohydrate, DL-cysteine hydrochloride monohydrate, L-cysteine methyl ester hydrochloride and the like.
[0008]
The cleaning agent of the present invention can be used for cleaning inorganic substances containing metal oxides such as iron and manganese, and is preferable for cleaning a membrane for water purification treatment from the viewpoint of chemical safety. Various conditions at the time of cleaning, for example, the concentration of the drug, the cleaning temperature, the cleaning time, etc. may be appropriately determined by the operator according to the contamination state of the film to be cleaned. % Range is preferred. This is because at a concentration of 0.02% or less, the effect of the drug is low because the concentration is low, and even when the concentration is greater than 0.2% by weight, the improvement of the effect is reduced.
In the cleaning liquid containing the film cleaning agent of the present invention, each cleaning liquid may contain other substances that promote cleaning.
The present invention is not limited to the type of permeable membrane, but examples include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. Moreover, filter bodies and filtration support bodies, such as a nonwoven fabric used for dynamic filtration, and a woven fabric, may be sufficient. Moreover, it is not limited to the form and shape of a membrane, For example, a flat membrane, a hollow fiber membrane, a tubular membrane, and a spiral membrane may be sufficient.
[0009]
The material of the membrane is not limited, and examples include polyolefin, polysulfone, polyacrylonitrile, polyvinyl alcohol, cellulose-based, fluorine-based polymer, ceramic and the like.
The present invention may add other physical cleaning methods during contact between the membrane and the cleaning liquid. For example, ultrasonic cleaning and cleaning with a sponge are included. Air bubbling may be used, but the gas used is preferably an inert gas that does not react with a cleaning agent such as nitrogen, argon, or helium.
[0010]
【Example】
Hereinafter, the present invention will be specifically described by way of examples.
Example 1
The hollow fiber membrane module (nominal pore size: 0.1 μm, material: polyethylene) used for the actual water purification treatment was washed with chemicals using the underground water as raw water. The form of the membrane filtration apparatus is a tank immersion type suction filtration system, and air scrubbing washing is used for physical washing. The chemical cleaning was performed by off-line cleaning performed by removing the membrane module from the membrane filtration device. The removed membrane module was washed with a tap water stream and then subjected to chemical cleaning. Since the film before washing was colored brown, obviously contaminants such as iron and manganese were attached.
For washing, 0.1 wt% L-cysteine hydrochloride monohydrate was used, the washing time was 60 minutes, and the washing temperature was 20 ° C.
The fresh water permeation performance after washing was as follows.
Water permeability of membrane (m / day / m-Aq at 20 ° C)
Before use 1.50
Before washing 1.05
After washing 1.49
[0011]
Example 2
The contaminated membrane of Example 1 was washed with 0.025 wt% L-cysteine hydrochloride monohydrate, with a washing time of 60 minutes and a washing temperature of 20 ° C. The fresh water permeation performance after washing was as follows.
Water permeability of membrane (m / day / m-Aq at 20 ° C)
Before use 1.50
Before washing 1.05
After washing 1.48
[0012]
Comparative Example 1
The contaminated film of Example 1 was washed with 1 wt% citric acid at a washing temperature of 20 ° C. for a washing time of 60 minutes. The fresh water permeation performance after washing was as follows.
Water permeability of membrane (m / day / m-Aq at 20 ° C)
Before use 1.50
Before washing 1.05
After washing 1.05
[0013]
Comparative Example 2
The contaminated film of Example 1 was washed using 10% by weight citric acid at a washing temperature of 20 ° C. for a washing time of 60 minutes. The fresh water permeation performance after washing was as follows.
Water permeability of membrane (m / day / m-Aq at 20 ° C)
Before use 1.50
Before washing 1.05
After washing 1.15
[0014]
【The invention's effect】
By using a membrane cleaning agent containing at least one selected from the group consisting of L-cysteine hydrochloride, hydrates thereof and derivatives thereof, cleaning of membranes clogged with metal oxides such as iron and manganese has been conventionally performed. It can be cleaned more effectively than organic acids that have been used. In particular, the membrane used for water purification can be cleaned more safely.

Claims (2)

A membrane cleaning agent used for cleaning a permeable membrane for water treatment, comprising at least one selected from the group consisting of L-cysteine hydrochloride, hydrates thereof and derivatives thereof Agent. A membrane cleaning method comprising: cleaning a water treatment permeable membrane contaminated with an inorganic substance using the membrane cleaning agent according to claim 1.