JPH09248556A - Method for removing arsenic in water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove arsenic in a raw water of city water source by mixing a hypochlorite with the water to be treated to allow arsenic in the water to be treated with the hypochlorite and passing through a fine chipped adsorbent selected from a group composed of Fe2 O3 , Fe3 O4 and Fe3 O5 . SOLUTION: The water to be treated and the hypochlorite are mixed in a stirring mixer 9 by making the water to be treated to flow-in from a flow-in port 7 of a reaction vessel 3 and the hypochlorite to flow-in from a storage vessel 2 through a supply port 6 to allow arsenic in the water to be treated to react, with the hypochlorite to produce the reaction product. Next, the water to be treated is made to flow-in to a flow-in port 4a of a filtration vessel 4 through a pipe line 10 from a flow-out port 8 of the reaction vessel 3 and is passed through the fine chipped adsorbent layer 12 selected from the group composed of the magnetized Fe2 O3 , Fe3 O5 and through a filter 11 and is made to flow-out to the outside of the device from a flow-out port 4d. As a result, arsenic in the raw water of the city water source is removed at a low cost.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to water, particularly river water, lake water, used as drinking water such as tap water source or well water.
The present invention relates to a method and an apparatus for removing a trace amount of arsenic or an arsenic compound contained in natural water such as groundwater (in the claims and the following description, these are collectively referred to as "arsenic").

[0002]

2. Description of the Related Art Although a small amount of arsenic may be contained in water, since arsenic is harmful, the permissible concentration of arsenic in tap water is 0.01 mg / l according to the water quality standard according to the Water Supply Act.
It is prescribed as follows. Therefore, if the concentration of arsenic in tap water exceeds this standard, it must be removed at the water treatment plant to reduce its concentration below the standard value.

As a method of removing arsenic in water, conventionally known is a method of adsorbing and removing arsenic in wastewater from a factory with alumina.

[0004]

The conventional method for adsorbing and removing arsenic with alumina is costly and is applicable when treating a relatively small amount of water, but it is a purified water for treating a large amount of raw tap water. It is economically unsuitable for use in places.

The present invention has been made in view of the above circumstances, and it is possible to economically implement arsenic in water used as drinking water such as raw water (untreated water) as a tap water source or well water. It is an object of the present invention to provide a method and an apparatus that can be removed at a cost.

[0006]

Means for Solving the Problems In the course of conducting experiments and research to achieve the above object, the present inventor was selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite. Chlorinated hypochlorite is added to the water to be treated and mixed to react arsenic in water with hypochlorite, and the reaction product is converted from Fe ₂ O ₃ , Fe ₃ O ₄ and Fe ₃ O ₅ Surprisingly, it was discovered that when passed through a strip-like or powdery adsorbent selected from the group, the reaction product was significantly adsorbed by the adsorbent and removed from the water to be treated. Then, the present invention has been reached.

That is, the apparatus for removing arsenic in water according to the invention of claim 1 for achieving the object of the present invention is selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite. A storage tank for storing the prepared hypochlorite, a hypochlorite supply unit connected to the storage tank and supplied with the hypochlorite from the storage tank, and water to be treated containing arsenic An inflow part, an outflow part of the water to be treated, and a reaction tank comprising a mixing means for mixing the hypochlorite and the water to be treated to react arsenic and hypochlorite in the water to be treated,
And a filter tank filled with an adsorbent in the form of flakes or powders selected from the group consisting of Fe ₂ O ₃ , Fe ₃ O ₄ and Fe ₃ O ₅ and connected to the outlet of the reaction tank. Is characterized by.

An apparatus for removing arsenic in water according to a second aspect is characterized in that, in addition to the above configuration, a magnet for magnetizing the adsorbent is further provided.

The apparatus for removing arsenic in water according to claim 3 stores hypochlorite selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite. A storage tank, a hypochlorite supply unit connected to the storage tank and supplied with hypochlorite from the storage tank, an inflow section of the treated water containing arsenic, and an outflow section of the treated water And a mixing means for mixing hypochlorite and water to be treated to react arsenic in the water to be treated with hypochlorite, Fe ₂ O ₃ , Fe ₃ O ₄ and Fe ₃ O
Means for charging a strip-shaped or powdery adsorbent selected from the group consisting of ₅ into the reaction tank and mixing with the water to be treated are provided.

A method for removing arsenic in water according to the invention of claim 4 is a hypochlorite selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite. Is added to natural water to react arsenic in natural water with hypochlorite to form a reaction product, and the reaction product is Fe ₂ O ₃ , Fe ₃ O ₄ and Fe.
It is characterized in that it is adsorbed by a strip-like or powdery adsorbent selected from the group consisting of ₃ O ₅ .

In the present specification, "natural water" means water which is untreated or in the process of being used as a source of drinking water such as river water, lake water, tap water such as groundwater or well water source, All purified water treatment including chlorination is completed and does not include tap water supplied as usable water.

[0012]

[Function] Hypochlorite such as sodium hypochlorite has been used as an oxidizing agent and a bleaching agent in the past, and it may be added as a sterilizing and disinfecting agent instead of chlorine in water purification plants. And the reaction product of hypochlorite is Fe ₂ O
It has not been known at all that it is remarkably adsorbed by an adsorbent composed of ₃ , Fe ₃ O ₄ or Fe ₃ O ₅ , and arsenic is removed in facilities that treat natural water as a tap water source, such as water purification plants. There is no example where such a method has been used for.

The present invention provides an inexpensive hypochlorite such as sodium hypochlorite and an inexpensive adsorbent such as Fe ₂ O ₃ which have been used in the same manner as chlorine for sterilizing and disinfecting raw water for tap water. The concentration of arsenic in a large amount of raw water or well water can be reduced to a desired value such as a standard value based on the Water Supply Act only by using it, and it is possible to economically implement arsenic in water at water purification plants. It can be removed at cost, and its social contribution is extremely large.

According to the first aspect of the present invention, the hypochlorite supplied from the storage tank into the reaction tank is mixed with the water to be treated which has flowed into the reaction tank, and the arsenic and hypothiae in the water to be treated are mixed. A reaction product with the chlorate is formed. This reaction product is adsorbed by an adsorbent selected from the group consisting of Fe ₂ O ₃ , Fe ₃ O ₄ , and Fe ₃ O ₅ in the filtration tank, so that the concentration of arsenic in the water to be treated is changed to the standard value concentration. Etc. can be reduced to a desired value.

According to the second aspect of the invention, since the adsorbent is magnetized by the magnet, the arsenic adsorption efficiency is further improved.

According to the third aspect of the invention, the hypochlorite supplied from the storage tank into the reaction tank is mixed with the water to be treated which has flowed into the reaction tank, and the arsenic and hypothiae in the water to be treated are mixed. A reaction product with the chlorate is formed. This reaction product is fed into the reaction tank and mixed with the water to be treated Fe ₂ O ₃ , Fe ₃
Adsorbed by an adsorbent selected from the group consisting of O ₄ and Fe ₃ O ₅ .

According to the fourth aspect of the invention, it is possible to remove arsenic in natural water used as drinking water such as raw water from a tap water source or well water at an economically feasible low cost.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic sectional view showing an embodiment of the present invention. The arsenic removal device 1 includes a hypochlorite storage tank 2, a reaction tank 3, and a filtration tank 4.

The hypochlorite storage tank 2 stores an aqueous solution of sodium hypochlorite.

The reaction tank 3 is cylindrical and has a lid 3a and a bottom 3
b, a lid 3a is provided with a supply port 6 to which sodium hypochlorite is supplied from the storage tank 2 through a pipe 5 and an inlet 7 of the water to be treated, and a bottom portion to be treated. A water outlet 8 is formed. The shaft 9a of the rotary stirring mixer 9 is inserted through the opening 3c at the center of the lid portion 3a, and the stirring mixer 9 is rotationally driven by a motor (not shown).
The stirring mixer 9 forms a mixing means for mixing sodium hypochlorite and the water to be treated.

The filtration tank 4 is cylindrical and has a treated water inlet 4c on the lid 4a and a treated water outlet 4d on the bottom 4b. The outflow port 8 of the reaction tank 3 communicates with the untreated water inflow port 4c of the filtration tank 4 via a pipe 10. A filter plate 11 such as a non-woven fabric filter is arranged and fixed in the upper and lower parts of the filtration tank 4, and the space between these filter plates 11 is filled with strip-shaped magnetite (Fe ₃ O ₄ ) as an adsorbent. The adsorbent layer 12 is formed by being deposited.

Further, annular magnets 13 and 14 are placed on the filter plates 11 and 11, and the adsorbent layer 12 is magnetized by the lines of magnetic force. Each ring magnet 1
3, 14 are positioned so that their respective positions coincide with each other in the vertical direction, and the annular magnets 13 and 14 have their magnetic lines of force aligned with each other, in particular, in the opposite direction to the flow of water, Moreover, the magnetic lines of force are arranged so as to follow the flow of water.

Due to the arrangement of the annular magnets 13 and 14, the respective magnetic lines of force of the annular magnets 13 and 14 are coupled to each other and reinforce each other, and in particular, upward, that is, along the flow of water and in the opposite direction, it is uniform and strong. A magnetic field is formed to strongly magnetize the adsorbent layer 12 made of magnetite.

Next, the operation of this device will be described. The water to be treated flows in from the inflow port 7 of the reaction tank 3, while sodium hypochlorite from the storage tank 2 flows in from the supply port 6. Sodium hypochlorite is mixed with the water to be treated by the stirring mixer 9, and arsenic in the water to be treated reacts with sodium hypochlorite to produce a reaction product.

Next, the water to be treated flows from the outlet 8 of the reaction tank 3 into the inlet 4a of the filtration tank 4 through the pipe 10, and the adsorbent layer 12 made of magnetized Fe ₃ O ₄ through the filter 11. Through the outlet 4d to flow out of the apparatus. During this period, most of the reaction product of arsenic and sodium hypochlorite is adsorbed by the adsorbent in the adsorbent layer 12, resulting in the filtration tank 4
The concentration of arsenic in the water to be treated flowing out of the outlet 4d is reduced to a desired value (for example, 0.01 mg / l).

FIG. 2 is a schematic sectional view showing another embodiment of the present invention. In this embodiment, the device 21 comprises a hypochlorite storage tank 22, a reaction tank 23, and an adsorbent storage tank 24.

The hypochlorite storage tank 2 stores an aqueous solution of sodium hypochlorite. Also, the adsorbent storage tank 24
Stores powdery Fe ₂ O ₃ .

The reaction tank 23 is in the shape of a rectangular cylinder and has a lid portion 23a and a bottom portion 23b. The lid portion 23a is supplied with sodium hypochlorite from the storage tank 22 through a pipe 25, and a cover port. An inflow port 27 of treated water and a supply port 29 to which the adsorbent is supplied from the adsorbent storage tank 24 through a pipe 28 are formed. Further, the bottom portion 23b has an outlet 3 for the water to be treated.
0 is formed. Further, the opening 23c at the center of the lid 23a
The shaft 31a of the rotary stirring mixer 31 is inserted through the rotary stirring mixer 31, and the stirring mixer 31 is rotationally driven by a motor (not shown). The stirring mixer 31 forms a mixing means for mixing the hypochlorite and the water to be treated, and also serves as a means for mixing the adsorbent with the water to be treated.

Reference numeral 32 is a rectangular filter plate made of a nonwoven fabric filter or the like, and a caster 33 is attached to the lower side thereof. The filter mesh of the filter plate 32 is set to a value that does not allow the powdery adsorbent to pass through. The lower part of one side of the reaction tank 23 is connected to the reaction tank 2 by a hinge 34.
It is formed as an opening / closing window portion 35 hinged to the wall portion 23d of the third member so as to be openable / closable, and can be opened / closed by a handle 35a. Therefore, it is possible to open the opening / closing window 35 and take out the filter plate 32 to the outside.

Next, the operation of the device 21 will be described. The water to be treated flows from the inlet 27 of the reaction tank 23, while the sodium hypochlorite from the storage tank 22 flows from the supply port 26. Further, Fe ₂ O ₃ powder from the storage tank 24 is continuously or intermittently charged as an adsorbent from the supply port 29. Stir mixer 31 for sodium hypochlorite
By which the arsenic in the water to be treated reacts with sodium hypochlorite to produce a reaction product.

On the other hand, the adsorbent charged into the reaction vessel 23 through the supply port 29 is also mixed with the water to be treated with stirring to adsorb most of the reaction product of arsenic and sodium hypochlorite in the water to be treated. As a result, the concentration of arsenic in the water to be treated flowing out from the outlet 30 of the reaction tank is reduced to a desired value.

When the adsorption capacity of the reaction product by the adsorbent reaches a saturated state or when the adsorption capacity decreases, the operation of the apparatus is stopped and all the water to be treated in the reaction tank 23 is discharged from the outlet 30. The adsorbent is deposited on the filter plate 32. Next, the opening / closing window 35 is opened, the filter plate 32 is taken out to remove the adsorbent, the filter plate 32 is returned to the reaction tank 23, the opening / closing window 35 is closed, and the operation of the apparatus is restarted.

Although the agitation mixers 9 and 31 are used as the mixing means in each of the above-mentioned devices, the mixing means is not limited to this, and other methods such as rotationally driving the reaction tank may be used.

In the apparatus shown in FIG. 1, the adsorbent in the filtration tank 4 is magnetized by the annular magnets 13 and 14, but other magnets may be used as the magnet. Alternatively, the reaction product may be magnetized by an adsorbent that is not magnetized without using a magnet. However, as a result of the experiment, the magnetized adsorbent has a better adsorption effect of the reaction product than the same non-magnetized adsorbent, and therefore, the removal of arsenic can be performed quickly, and a larger amount of treated water can be obtained within the same time. Can be processed.

Next, one experimental example of the present invention will be described.
1 liter of well water containing 100 ppb As (III) was added to the reaction vessel, 0.1 mM sodium hypochlorite was added thereto, and then a predetermined amount of Fe ₂ O ₃ powder was added as an adsorbent for 15 minutes. It was filtered with a shaken back paper (No. 2). For comparison, sodium hypochlorite was not added and only Fe ₂ O ₃ powder was added and the same treatment as above was performed. The arsenic concentration of the filtered water was measured by hydride generation ICP emission spectrometry. The limit of quantification by this measuring method was 1 ppb. The results of arsenic concentration measurement are shown in Table 1.

[0036]

[Table 1]

From the above results, it is understood that arsenic cannot be completely removed when sodium hypochlorite is not added, but arsenic can be almost completely removed when the reaction is carried out with sodium hypochlorite. .

Further, an arsenic removal experiment was conducted under the same conditions as above except that powdered Fe ₃ O ₄ was used as the adsorbent instead of Fe ₂ O ₃ . Table 2 shows the results.

[0039]

[Table 2]

In an experiment using Fe ₃ O ₄ as an adsorbent, Fe ₃ O ₄ has a larger particle size than Fe ₂ O _{3 and} therefore has a smaller total adsorption surface area, and Fe ₃ O ₄ has a smaller particle size than Fe ₂ O _3. Since it is heavy and sinks heavily at the bottom of the container, the adsorption efficiency is F
It was inferior to e ₂ O _{3 and} the removal rate of arsenic was inferior. However, even when Fe ₃ O ₄ is used as an adsorbent,
It is clear that the arsenic removal rate is better when sodium hypochlorite is added than when it is not added. When Fe ₃ O ₄ is used in the embodiment shown in FIG. 1 and especially when magnetizing Fe ₃ O ₄ , the arsenic removal rate is not particularly inferior to that of Fe ₂ O ₃ , but rather excellent. There is also.

[0041]

As described above, according to the invention described in claim 1, the hypochlorite supplied from the storage tank into the reaction tank is mixed with the water to be treated flowing into the reaction tank, A reaction product of arsenic and hypochlorite is produced in the water to be treated. This reaction product is Fe ₂ O ₃ , Fe ₃ O ₄ , Fe in the filtration tank.
By being adsorbed by an adsorbent selected from the group consisting of ₃ O _5, the concentration of arsenic in the water to be treated can be reduced to a desired value such as a reference value concentration.

According to the second aspect of the invention, since the adsorbent is magnetized by the magnet, the arsenic adsorption efficiency is further improved.

According to the third aspect of the present invention, the hypochlorite supplied from the storage tank into the reaction tank is mixed with the water to be treated which has flowed into the reaction tank, and the arsenic and hypothiae in the water to be treated are mixed. A reaction product with the chlorate is formed. This reaction product is fed into the reaction tank and mixed with the water to be treated Fe ₂ O ₃ , Fe ₃
Adsorbed by an adsorbent selected from the group consisting of O ₄ and Fe ₃ O ₅ .

According to the fourth aspect of the invention, it is possible to remove arsenic in natural water used as drinking water such as raw water from a tap water source or well water at a low cost which is economically feasible.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of the present invention.

FIG. 2 is a sectional view schematically showing another embodiment of the present invention.

[Explanation of symbols]

 2,22 Hypochlorite storage tank 3,23 Reaction tank 4 Filtration tank 12 Adsorbent layer 13,14 Magnet 24 Adsorbent storage tank

Claims (4)

[Claims] 1. A storage tank for storing a hypochlorite selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite, and a storage tank connected to the storage tank. The hypochlorite supply part to which the hypochlorite is supplied from, the inflow part of the treated water containing arsenic, the outflow part of the treated water, the hypochlorite and the treated water. A reaction vessel equipped with a mixing means for mixing arsenic in the water to be treated with hypochlorite, and a strip selected from the group consisting of Fe ₂ O ₃ , Fe ₃ O ₄ and Fe ₃ O _5. An apparatus for removing arsenic in water, comprising: a filter tank filled with a particulate or powdery adsorbent and connected to the outlet of the reaction tank. 2. The apparatus of claim 1, further comprising a magnet that magnetizes the adsorbent. 3. A storage tank for storing a hypochlorite selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite, and a storage tank connected to the storage tank. The hypochlorite supply part to which the hypochlorite is supplied from, the inflow part of the treated water containing arsenic, the outflow part of the treated water, the hypochlorite and the treated water. A reaction vessel equipped with a mixing means for mixing arsenic in the water to be treated with hypochlorite, and a strip selected from the group consisting of Fe ₂ O ₃ , Fe ₃ O ₄ and Fe ₃ O _5. An apparatus for removing arsenic in water, comprising means for charging an adsorbent in the form of powder or powder into the reaction tank and mixing with the water to be treated. 4. Arsenic and hypochlorous acid in natural water are obtained by adding hypochlorite selected from the group consisting of sodium hypochlorite, potassium hypochlorite and calcium hypochlorite to natural water. The reaction product is formed by reacting with a salt, and the reaction product is mixed with Fe ₂ O ₃ , Fe ₃ O ₄ and Fe ₃ O ₅
A method for removing arsenic in water, which comprises adsorbing to a strip-like or powder-like adsorbent selected from the group consisting of.