JPS5930443B2 - Membrane separation method - Google Patents

Description

Detailed Description of the Invention The present invention provides a method for separating, concentrating, or diffusing liquids containing various organic or inorganic substances by using a membrane such as a permeable membrane. The present invention relates to a useful method that can easily prevent contaminants from directly depositing or adhering to the surface of a permeable membrane such as a porous membrane, an ultrafiltration membrane, or a reverse osmosis membrane, and can perform effective membrane separation treatment.

Recently, methods using ultrafiltration membranes or reverse osmosis membranes have been attracting attention as a method for fractionating or concentrating components dissolved or suspended in a liquid.

In this method, suspended solids and dissolved organic and inorganic components contained in the liquid are concentrated on the high-pressure side of the membrane to obtain an extremely pure permeate on the permeate side (low-pressure side) of the membrane. It can also be used to separate and concentrate nonionizable organic substances, which is impossible with electrodialysis, which is a desalting method that uses the same membrane.
Fractionation, separation, and concentration of proteins in the fermentation industry and food industry,
It is widely used for lactose concentration, sugar concentration, amino acid concentration, desalination of underground brine, treatment of heavy metal wastewater, treatment of sewage plant wastewater, etc., and has great potential for use as a means of closed systems.

Although the membrane is used in a wide range of fields as described above, the most important problem with this method is membrane contamination.

In other words, in this method, since concentration progresses on the membrane surface, components in the liquid naturally precipitate on the membrane surface, and suspended matter that is already present in the liquid also adheres, causing a decrease in the amount of liquid permeating through the membrane. This will not only lead to a decline in quality but also place a heavy burden on maintenance management.

Conventionally, countermeasures have been to perform precise pretreatment of the liquid to be treated to remove suspended substances, and even if they are not suspended substances, colloidal organic substances and S
Methods have been devised to remove iO2 or to increase the flow rate of the liquid flowing over the membrane surface to prevent concentration polarization at the membrane surface.

However, depending on the quality of the feed liquid, contaminants may adhere to the membrane surface even after thorough pretreatment, especially in protein concentration processes, sugar concentration processes, sewage treatment processes, and industrial wastewater treatment processes. This is almost inevitable when applying the filtration method or reverse osmosis method.

In addition, the pore 5
A microporous membrane of about micron to 0.1 micron can be used, but naturally this membrane also suffers from membrane surface contamination.

This type of membrane includes inorganic ones such as metal, ceramic, and carbon, and organic ones such as empty cellulose, acetyl cellulose, polyester, and acrylonitrile.

For this reason, the conventional membrane contaminant removal force method uses a high fluid flow rate to prevent precipitation or adhesion due to concentration polarization on the membrane surface. In addition, there are problems such as an increase in pump capacity.Also, there is a method of narrowing the gap between membrane surfaces and applying shear force by fluid to the membrane surface to remove contaminants, but in this case, the equipment is very complicated. becomes.

In addition, physical methods such as chemical cleaning using chemicals, flush cleaning using water jets, and physical cleaning using air or sponge bodies have also been proposed in case of contamination.
Each has advantages and disadvantages, and there are still many issues that need to be resolved before they can be put into practical use, such as countermeasures against damage to the membrane, rationalization of the cleaning system, disposal of cleaning chemicals, and the relationship between heating and membrane properties to increase cleaning efficiency.

The present invention provides a useful processing power method that can effectively remove membrane surface contaminants even during operation, accurately prevent permeable membrane surface contamination, and fully utilize membrane functions for a long period of time. The object of the present invention is to provide a method for efficiently removing membrane surface contaminants and recovering membrane function.

Further, the method of the present invention is to provide a membrane treatment method that protects the permeable membrane without damaging it, enables stable membrane treatment, and is extremely simple and economical in terms of maintenance management, mainly removing membrane contaminants.

The present invention relates to a permeable membrane treatment in which a liquid to be treated is separated by a permeable membrane into a permeate liquid and a residual liquid on the ventral side (hereinafter referred to as a concentrated liquid) such as a concentrated liquid, a separated liquid, and a diffused liquid using pressure as a driving force for separation. The method is characterized in that a thin layer of fine powder is formed on the surface of the permeable membrane to be used, and then the liquid to be treated is passed through the membrane for treatment.

As the fine powder used in the present invention, organic, inorganic, charged or uncharged fine powder of several μ or less can be used, such as natural natural materials such as bentonite, kaolin, acid clay, diatomaceous earth, etc. Natural minerals such as clay minerals, feldspar, quartz, and silica sand, artificial minerals such as artificial zeolites and metal oxides and hydroxides such as aluminum, magnesium, and iron, and microorganisms such as resins, proteins, and polymer electrolytic substances. Examples include powders.

In addition, in order to form a thin layer of these fine powders on the permeable membrane surface, in order to form it on the high-pressure system side, it is suspended in a separate liquid and passed through the membrane surface. You can also choose to mix it into a liquid to form a thin layer.

In this way, by forming a thin layer of fine powder on the permeable membrane surface in advance and then passing the liquid to be treated, direct precipitation and adhesion of contaminants on the permeable membrane surface is prevented. Since contaminants are deposited on the surface of the thin layer, such contaminants are very easily removed and do not damage the permeable membrane.

In other words, contamination on a thin layer can be removed by physical cleaning such as water flushing, air-water flushing, foam ball cleaning, or by cleaning, peeling, and penetration using chemicals such as surfactants, acids, alkalis, and chelating agents. It can be removed extremely easily along with the thin layer by peeling and cleaning using this phenomenon.

In this way, when a certain amount of contaminants have adhered to the thin layer, it is periodically washed off separately, or when the thin layer is made of a substance whose leaching is promoted by heat, the liquid to be treated is heated and passed through. It may be liquefied or separately leached with hot water, etc., and then a thin layer of fine powder is again formed as described above.

Furthermore, the thin layer peeled off as described above can be separated by membrane separation.
It can also be recovered by separation means such as sedimentation, flotation, filtration, and centrifugation and reused for forming a thin layer.

For this reuse, it is convenient to mix it into the liquid to be treated or mix it into a separate dedicated liquid and use it in a suspended state.

Furthermore, to show a specific example of the present invention, the NaCl removal rate is 90%.
pressure of 30 kg f/cr? t, at a temperature of 25°C,
A solution in which kaolin of about 0.2 to 5 μm was suspended at about 1200 ppm was passed through the module at 70 crrL/S for 15 minutes, and the kaolin suspension remaining in the module was removed.
As the liquid to be treated, secondary treated water of sewage filtered through a sand filter was passed under the same pressure and temperature conditions as above.

The properties of this liquid to be treated are as follows: turbidity 1°, BODl 7■/7
．． C0D22~/12. The pH was 6, 6725°C.

In addition, the concentration rate of the permeable membrane is about 4 times the volume ratio, and the average amount of liquid permeated through the membrane is 5407 / m 2 after about 24 hours of treatment.
It was a day.

Then, one cycle is 24 hours, and the permeable membrane is flushed with gas and water at a rate of 2 kgf/cr? After 10 minutes at r, the amount of permeate through the membrane was safely recovered.
Immediately thereafter, a kaolin suspension was passed through the tube under the same conditions as above, and then the same liquid to be treated was passed through the tube again, and the same results as described above were obtained.

I performed these operations once every 24 hours, but
Equal membrane permeate volumes were obtained.

The formation of a thin layer of kaolin was determined by a slight decrease in the amount of water permeating through the membrane and/or a slight decrease in the removal rate by mixing NaCl into the kaolin suspension.

As described above, in the present invention, a thin layer of fine powder is formed on the permeable membrane surface in the membrane separation operation, and then the liquid to be treated is passed through the membrane. It effectively prevents contamination, removes contaminants very easily along with the thin layer, and regenerates the thin layer easily, allowing the membrane to function satisfactorily for a long period of time without impairing the properties and performance of the permeable membrane. In addition, fine powders whose charge changes depending on the liquid properties, such as clay minerals and polymer electrolytic substances, can also be used, and depending on the charge of the charged substance in the liquid to be treated, they can be effectively adsorbed. In addition to simple physical adsorption of contaminants, electrochemical adsorption is also possible, and the operation is simple and stable.
It significantly improves work efficiency, makes it easy to ensure proper operation, and allows you to obtain a large amount of high-quality treated water at a low cost.
There are also benefits such as being able to perform economical processing without putting a burden on maintenance management.

Claims (1)

[Claims] 1. In a process such as separating, concentrating, or diffusing a liquid to be treated containing at least one of an organic substance or an inorganic substance, the liquid to be treated is permeated using pressure as a driving force for separation. A membrane treatment characterized by forming a thin layer of fine powder on the surface of the permeable membrane and then passing the liquid to be treated through the membrane when separating the permeated liquid and the concentrated liquid using the membrane. Method. 2. The membrane processing method according to claim 1, wherein the fine powder is mixed into the liquid to be treated and a thin layer of the fine powder is deposited on the surface of the permeable membrane. 3. The membrane treatment method according to claim 1 or 2, wherein the thin layer of fine powder deposited on the permeable membrane is once peeled off and then the membrane is subjected to a liquid passage treatment by forming a thin layer of fine powder again. 4. The membrane processing method according to claim 2 or 3, characterized in that the thin layer of fine powder is peeled off and collected. 5. Claim 3, wherein the liquid to be treated is heated and passed through the liquid, and after the thin layer is leached, a thin layer is formed again.
The membrane treatment method according to item 1 or 4.