JPS5820319B2 - Water treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating water, and more particularly to a method for removing trace amounts of iron from water using a polyvinyl alcohol (hereinafter referred to as PVA) hollow fiber membrane.

Regarding industrial water and water used for food production, the influence of trace amounts of iron contained in water has long been considered a problem.

For example, in boiler water used as industrial water, the iron contained in the water adheres to pipes as scale, reducing heat transfer efficiency and causing the pipes to become clogged.

Furthermore, iron in the water used to produce foods such as sake and miso makes the color of the product cloudy or discolored, so it is desirable to remove it as much as possible.

The standard for sake brewing water is iron: 0. O2 ppm or less.

For conventional iron removal, methods of filtering with various P materials, such as sand, anthracite, firing furnace materials, etc., have been used.
A filtration treatment using a polyacrylonitrile-based synthetic polymer hollow fiber membrane has been proposed.

However, in conventional filtration using p-material, the pores are relatively coarse and the fractionation property is not sharp.
Iron removal efficiency is still not sufficient.

In addition, the equipment is large and maintenance is complicated, so there is a lot of room for industrial improvement.

On the other hand, the method using a polyacrylonitrile hollow fiber membrane has the advantages of using a hollow fiber membrane, namely, miniaturization of the device,
It is expected to simplify maintenance and improve filtration performance by improving the micropore structure.

However, when carrying out membrane filtration, it is important to regenerate the membrane to remove fine iron particles adhering to the surface micropores of the membrane, but polyacrylonitrile hollow fiber membranes do not have sufficient acid resistance. Regeneration treatment with an acid solution, which is effective for removing iron particles, cannot be performed sufficiently, so it has not yet been widely used.

As a result of intensive research into this pressing problem, the present inventors discovered that iron removal treatment from water can be carried out extremely efficiently by using a PVA-based hollow fiber membrane, which the present applicant has already partially put into practical use. He completed his invention.

That is, the present invention involves filtering raw water containing a trace amount of iron through a PVA-based hollow fiber membrane having a micropore structure of 0.01 to 0.5μ, with or without oxidation treatment, and
This water treatment method is characterized by regenerating hollow fiber membranes using an acid solution.

The water treated by the method of the present invention contains ferrous ions (Fe+2) and/or ferric compounds as iron content, and contains an amount of several tens of microns or less.

Of course, it is possible to treat raw water containing a larger amount of iron and other particulate components, but in order to efficiently perform treatment with hollow fiber membranes, it is necessary to pre-treat the raw water with various F materials or pre-treatment. It is advantageous to process and bring it to the level mentioned above.

The raw water is treated with a hollow fiber membrane with or without oxidation treatment.

The oxidation treatment converts ferrous ions into ferric compounds, making them water-insoluble and making them easier to remove by filtration.

Oxidation treatment can be omitted in raw water with extremely low ferrous ions.

The oxidation treatment can be carried out using any known method, taking into consideration that it will not have an adverse effect on the use of the water.

For example, a chlorine injection method, an air oxidation method, etc. are used.

In the case of the chlorine injection method, filtration treatment using a PVA-based hollow fiber membrane having excellent chemical resistance can be performed immediately after the oxidation treatment by this method.

In the case of the air oxidation method, it is more efficient to carry out air oxidation in a system in which an appropriate oxidation catalyst is present in addition to a simple aeration method.

Furthermore, it has been found that Mn ions often coexist with iron ions in raw water, and that the method of the present invention can also insolubilize and remove Mn ions.

Combined amount of PVA system forming the hollow fiber membrane used in the present invention Polymerization degree 500-3500, saponification degree 85-100 mol%
PVA and an ethylene-vinyl alcohol copolymer copolymerized with 10 to 50 mol% of ethylene.

In addition, copolymers of vinylpyrrolidone, vinyl chloride, methyl methacrylate, acrylonitrile, itaconic acid esters, etc. (including block copolymers and graft copolymers), as well as formaldehyde, glyoxal, glucuraldehyde, PVA dialdehyde, etc. Contains partially acetalized derivatives such as

It is important that the PVA-based polymer described above not only provides a hollow fiber membrane with excellent water permeability, but also has excellent acid resistance and alkali resistance.

These PVA-based polymers were prepared using a 30% caustic soda solution, 2
It is completely stable against a 0% sulfuric acid aqueous solution and a 15% hydrochloric acid aqueous solution at room temperature, and can be washed multiple times using a strong solution without any loss in membrane performance.

In addition, partially acetalized derivatives of polyvinyl alcohol homopolymers have heat resistance up to around 120°C, making it possible to perform chemical cleaning under even harsher conditions.
This is extremely advantageous for cleaning and reusing the membrane.

Furthermore, the membrane can be thermally sterilized, making it easy to provide a sterile membrane.

On the other hand, other materials such as cellulose acetate, polyacrylonitrile, polyamide, etc. cannot withstand the above-mentioned acidic or alkaline solutions at all, and cleaning with chemical solutions is almost impossible.

Therefore, these conventional membranes can only be backwashed with filtrate or air, or mechanically cleaned with a cleaning body such as a sponge ball. It is impossible to completely remove it.

In addition, the PVA-based polymer mentioned above has a pore size of 0.005μ to 1
．． Porous hollow fiber membranes with pores of 0μ can be easily produced.

In order to remove iron, which is the objective of the present invention, it is necessary to have a fine pore structure that can cut long-lasting and soluble iron compound fine particles, and the effective pore size is 0.01 to 0.5μ.
That's about it.

Of course, a smaller pore diameter will result in better larval release properties, but the water permeability per unit membrane area will tend to be lower, so the above range is suitable for practical use.

The PVA-based hollow fiber membrane used in the present invention is, for example,
-123385 and 53-31580.

That is, about 100 parts by weight of polyethylene glycol is added to 1 part by weight of polyvinyl alcohol,
A water solution groove with a polyvinyl alcohol concentration of about 15% was adjusted, and the spinning stock solution was passed through an annular nozzle to form NaOH/N.
It is spun into a coagulation bath of about a 2804-=077240 g/l to form a hollow fiber.

Then glutaraldehyde/H2SO4/Na25O4
= 3/30/2009/L treatment bath for 5 hours at 70°C for cross-linking treatment, and further hot water treatment at 93°C for 3 hours, followed by washing with water and air drying.

Further, an ethylene-vinyl alcohol copolymer having an ethylene content of 32 mol% is dissolved in dimethyl sulfoxide to prepare a solution having a concentration of 20% by weight.

20% by weight of dimethyl sulfoxide, which was cooled to 5°C.
Spun in a coagulation bath of an aqueous solution, then immersed in anhydrous acetone at 40° C. for 30 minutes, taken out from the acetone, left in the same acetone vapor for 3 minutes, and then air-dried.

Other solvents such as methanol, inpropatol, dimethylformamide, etc. can also be used.

In order to obtain the desired pore size in these hollow fiber membranes, for example, in the case of polyvinyl alcohol-based materials, by appropriately changing the molecular weight of polyethylene glycol used, the amount added, coagulation conditions, etc. In the case of vinyl alcohol copolymer materials, it is possible to freely control the thickness from 0.01 to about 0.5μ by changing the solvent and coagulation bath temperature.

The fine pores may be uniformly present, or may have a gradient from finer to coarser in the range of 0.01 to 0.5 microns, or vice versa, from the surface to the inside.

In addition, the hollow fibers used in the present invention have an outer diameter of 0.3 to 3 mvt, preferably 0.8 to 2 mvt from the viewpoint of pressure loss, and the thinner the membrane thickness, the better the permeability, but the strength and pressure resistance From the viewpoint of properties, the thickness is preferably 0.1 to 0.2 mm.

In the present invention, when the above-mentioned PVA-based hollow fiber membrane becomes clogged, it can be washed with acid.

The limiting concentration is about 20% sulfuric acid and 15% hydrochloric acid at room temperature, and by washing with a concentration of about 1 to 2%, iron compounds and other organic substances such as microorganisms are completely dissolved or decomposed and removed. can do.

Hollow fiber membranes made of other materials cannot withstand such chemical cleaning.

In addition to this chemical cleaning, it is of course possible to perform backwashing with filtrate or air, or other mechanical cleaning, if necessary.

In order to remove iron from water according to the present invention, the above-mentioned hollow fiber membranes are arranged in an appropriate length, preferably 50 to 150, and at least 10 or more, usually about 1000 to 5000, are bundled. , housed in water treatment equipment.

The processing device can be of various known structures, such as one in which both ends of the hollow fiber are fixed to the container with adhesive and an open end is provided, or one in which only one end of the hollow fiber is fixed to the container and the other end is fixed to the container. can be used in a free state with one end free structure in which only the hollow part of the hollow fiber is sealed with an adhesive.

The raw water is subjected to p-supertreatment using a device such as that described above, preferably under pressure.

According to the present invention, water-insoluble iron compounds can be efficiently removed from water for various uses, and the treated water can be used as is or after water-soluble iron ions are removed using an ion exchange resin.

The present invention will be explained below with reference to Examples.

Example 1 Water containing 118 ppb of iron as intermediate water used in a boiler was filtered through a PVA hollow fiber membrane (micropore diameter of about 0.02 μ) that cuts 95% of 0.05 μ diameter particles.

As the water flow rate increases, the hollow fiber surface turns brown,
It was confirmed that iron removal was sufficient.

The iron content in the permeated water was analyzed and found to be 8 ppb, and the removal rate was 93.2%.

When the hollow fibers were immersed in a 1% aqueous hydrochloric acid solution for 1 hour at room temperature, the hollow fibers were completely colored and could be reused smoothly after washing with water.

Example 2 Kurashiki city tap water for use in sake brewing was treated with a PVA hollow fiber membrane (A membrane) that cuts 95% of 0.05μ diameter particles and 0.05μ diameter particles.
When treated with a PVA hollow fiber membrane (micropore size approximately 0.01μ2B membrane) that cuts 0.02μ diameter particles by 95%, the iron and manganese removal results shown in the following table were obtained.

All the membranes used were soaked in 0.5% hydrochloric acid aqueous solution at 50%
It was possible to completely regenerate it by immersing it at ℃ for 10 minutes and washing it with water.

Claims (1)

[Claims] 1 Raw water containing a trace amount of iron is subjected to oxidation treatment or without oxidation treatment through a polyvinyl alcohol hollow fiber membrane having a micropore structure of 0.01 to 0.5μ, and the polyvinyl alcohol hollow fiber membrane is A water treatment method characterized by regenerating water using an acid solution.