JP7283088B2 - Water treatment method and water treatment equipment - Google Patents

Description

The present invention relates to a water treatment method and a water treatment apparatus.

The Fenton reaction is a reaction in which ferrous ions are reacted with hydrogen peroxide to generate hydroxyl radicals. Hydroxy radicals have a strong oxidizing power, and are expected to be applied to various fields such as sterilization, decomposition of harmful substances and persistent pollutants, etc., by utilizing the strong oxidizing power.

The ferrous ions used in the Fenton reaction are oxidized as the reaction progresses to become ferric ions. Some of the ferric ions are known to be partially reduced to ferrous ions in the presence of hydrogen peroxide. However, this reduction reaction is known to be very slow compared to the Fenton reaction. Therefore, there is a problem that the decomposability of oxidizable substances is reduced due to the decrease in the concentration of ferrous ions supplied to the Fenton reaction.

In Patent Document 1, in addition to the Fenton reaction, it is proposed to irradiate ultraviolet light (λ=254 nm) with a low wavelength to decompose the oxidizable substance using the ultraviolet light's ability to decompose the oxidizable substance.

Japanese Patent Application Laid-Open No. 2003-285083

However, if the oxidizable substance is directly decomposed by short-wave ultraviolet rays, the ultraviolet irradiation apparatus is expensive, the electricity bill is high, and the treatment cost is high. Furthermore, there is a problem that special measures are required due to the low wavelength.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a water treatment method for decomposing oxidizable substances by enhancing decomposition by the Fenton reaction, and a water treatment apparatus using the same.

That is, the present invention has the following aspects.
[1] A mixed solution (A) containing water to be treated containing an oxidizable substance, ferrous ions, hydrogen peroxide, and an iron reduction catalyst is irradiated with light to decompose the oxidizable substance. A water treatment method having an oxidation step (A2).
[2] The water treatment method according to [1], wherein the mixture (A) contains a complex-forming substance, and the complex-forming substance is a substance that forms a complex with the ferrous ion.
[3] The water treatment method according to [1] or [2], wherein the mixed solution (A) contains ferric ions.
[4] The mixture (A) according to any one of [1] to [3], wherein the mixed solution (A) contains a complex-forming substance, and the complex-forming substance is a substance that forms a complex with the ferric ion. water treatment method.
[5] The water treatment method according to any one of [1] to [4], wherein in the oxidation step (A2), the light has a wavelength of 380 nm or more.
[6] Any one of [1] to [5], wherein in the oxidation step (A2), the concentration of the iron reduction catalyst is 100 to 10000 mass ppm with respect to the total mass of the mixed solution (A). The water treatment method according to the item.
[7] A mixed solution (B) containing water to be treated containing an oxidizable substance, ferrous ions, hydrogen peroxide, and a complex-forming substance is irradiated with light to decompose the oxidizable substance. A water treatment method having an oxidation step (B2).
[8] In the presence of a mixed solution (A) containing water to be treated containing an oxidizable substance, ferrous ions, hydrogen peroxide, and an iron reduction catalyst, the Fenton reaction is performed under light irradiation, A water treatment system comprising a reactor for decomposing oxidizable substances.

ADVANTAGE OF THE INVENTION According to this invention, the water-treatment method which raises the decomposition|disassembly by a Fenton reaction and decomposes an oxidizable substance, and a water-treatment apparatus using the same can be provided.

It is a mimetic diagram showing a schematic structure of water treatment equipment 1. 4 is a graph showing the resolution of oxides in Example 1 and Comparative Examples 1 and 2. FIG. 10 is a graph showing the resolution of oxides in Example 2 and Comparative Example 3. FIG. 10 is a graph showing the resolution of oxides in Example 3 and Comparative Example 4. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in all the drawings below, the dimensions and ratios of the constituent elements are appropriately changed in order to make the drawings easier to see.

[Water treatment equipment]
The structure of the water treatment apparatus 1 used for the water treatment method of this embodiment will be described. FIG. 1 is a diagram showing a schematic configuration of a water treatment device 1 of this embodiment. As shown in FIG. 1 , the water treatment apparatus 1 includes a reaction tank 11 , an insolubilization tank 21 , an adjustment tank 41 and a storage tank 61 .

The water treatment apparatus 1 includes a first pH adjusting means 14 , an iron reagent adding means 15 , a hydrogen peroxide adding means 16 , a catalyst adding means 17 and a light irradiation means 18 in the reaction tank 11 .

The water treatment apparatus 1 includes a second pH adjusting means 24 in the insolubilization tank 21 . A concentrator 22 is provided in the insolubilization tank 21 .

The water treatment apparatus 1 is provided with suspension return means 32 between the insolubilization tank 21 and the reaction tank 11 .

The water treatment device 1 includes a separation device 42 between the adjustment tank 41 and the storage tank 61 .

(Water to be treated)
In the water treatment by the water treatment apparatus 1, water to be treated containing oxidizable substances is oxidized using the Fenton reaction. Examples of oxidizable substances include organic substances that are difficult to decompose by biological treatment, and inorganic substances such as phosphorous acid and hypophosphorous acid.

Examples of the organic substances include organic solvents such as 1,4-dioxane and humic substances. A humic substance is a fraction obtained by extracting soil with an alkali such as sodium hydroxide, or an extract obtained by extracting soil with natural water. It refers to the fraction eluted from the adsorbed substance with a dilute alkaline aqueous solution.
Phosphorous acid and hypophosphorous acid are contained in industrial wastewater from plating plants.

The water to be treated may contain a complex-forming substance. As used herein, the term “complex-forming substance” means a substance that forms a complex with ferrous ions (Fe ²⁺ ) and/or ferric ions (Fe ³⁺ ). In the present invention, ferric ions are generally produced by oxidation of ferrous ions. Ferrous ions are produced by reduction of ferric ions. Complex-forming substances include aldehydes, cyanide compounds, amine compounds, chlorides, carboxylic acid compounds, and the like. Among them, aldehydes, cyanide compounds, amine compounds and chlorides are preferred.
As used herein, "aldehyde" means a compound having an aldehyde group in the molecule. Aldehydes include formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, vinylaldehyde, and glyoxal.
As used herein, "cyanide" means a compound having "CN" in the molecule. Examples of the cyanide include cyanides such as potassium cyanide and sodium cyanide; nitriles such as acetonitrile and acrylonitrile;
As used herein, the term "amine compound" means a compound having one or more primary to tertiary amino groups in the molecule. Amine compounds include primary amine compounds, secondary amine compounds, tertiary amine compounds, salts thereof, and the like.
As used herein, "chloride" means a compound having "Cl" in the molecule. Chlorides include inorganic chlorides such as potassium chloride and sodium chloride; organic chlorides such as chloroform and dichloromethane;
As used herein, the term "carboxylic acid compound" means a compound having a carboxy group or a functional group derived from a carboxy group in its molecule. Examples of carboxylic acid compounds include organic acids such as oxalic acid, formic acid, acetic acid, citric acid, propionic acid, butyric acid, isobutyric acid, and acrylic acid; and organic acid esters such as ethyl propionate.

The oxidizable substance is more likely to be decomposed if the water to be treated does not contain the complex-forming substance. However, according to the present invention, the oxidizable substance can be decomposed even if the water to be treated contains the complex-forming substance.
When the water to be treated contains a complex-forming substance, its concentration is preferably 20000 mg/L or less, more preferably 10000 mg/L or less, and even more preferably 5000 mg/L or less, relative to the total mass of the water to be treated. Also, it is preferably 1 mg/L or more, more preferably 10 mg/L or more, and even more preferably 100 mg/L or more.
When the concentration of the complex-forming substance is equal to or higher than the above lower limit, the complex structure formed by the ferrous ion and/or ferric ion and the complex-forming substance is destroyed by light irradiation to form a complex. easy to prevent.
When the concentration of the complex-forming substance is equal to or less than the above upper limit, the formation of the complex is easily suppressed, and the Fenton reaction is easily prevented from progressing.

(Reaction tank)
In the reaction tank 11, oxidizable substances contained in the water to be treated are oxidized by the Fenton reaction in the presence of ferrous ions (Fe ²⁺ ) and hydrogen peroxide under light irradiation.
When an iron reduction catalyst is used, ferric ions (Fe ³⁺ ) produced by the Fenton reaction are reduced to ferrous ions by the iron reduction catalyst under light irradiation.
When the water to be treated contains a complex-forming substance, the complex structure formed by the ferrous ions and/or ferric ions and the complex-forming substance is destroyed by irradiation with light to remove ferrous iron. Release ions and/or ferric ions.

A first channel 12 and a second channel 13 are connected to the reaction tank 11 . The first flow path 12 is for flowing (supplying) water to be treated containing oxidizable substances into the reaction tank 11 . The second flow path 13 allows the reaction liquid discharged from the reaction tank 11 to flow into (supply) the insolubilization tank 21 .

In the water treatment apparatus 1 shown in FIG. 1, the method of supplying the reaction solution from the reaction tank 11 to the insolubilization tank 21 is not particularly limited. liquid may be supplied.

In addition, in the water treatment apparatus 1 shown in FIG. 1, although the example provided with the one reaction tank 11 was shown, the several reaction tank 11 may be arrange|positioned in series. In that case, the time required for the Fenton reaction can be lengthened, so that hydrogen peroxide can be sufficiently consumed by the Fenton reaction.

In addition, when a plurality of reaction tanks 11 are arranged, the method of transferring the liquid from the first reaction tank to the second reaction tank is not particularly limited, and the liquid may be sent using a pump, or using an overflow. Liquid may be sent.

(Means for adding iron reagent)
The iron reagent adding means 15 adds an iron reagent into the reaction tank 11 .

The iron reagent is not particularly limited as long as it dissolves in water to generate ferrous ions, but ferrous salts or ferrous oxides are preferred. Of these, iron sulfate or iron chloride is preferable because it does not need to be controlled according to wastewater standards and has excellent solubility. Further, iron sulfate is more preferable because of its high versatility and low corrosiveness.

Moreover, when using an iron-reducing catalyst, the iron-reducing catalyst reduces ferric ions to regenerate ferrous ions, so a ferric compound can also be used as the iron reagent.

The iron reagent may be added to the reaction vessel 11 in a solid state, or may be added to the reaction vessel 11 in a liquid state such as an aqueous solution of the iron reagent.

The concentration of ferrous ions is appropriately determined according to the type of wastewater.

(Means for adding hydrogen peroxide)
The hydrogen peroxide adding means 16 adds hydrogen peroxide into the reaction tank 11 .

In the reaction tank 11, ferrous ions react with hydrogen peroxide to generate hydroxyl radicals. When the oxidizable substance contained in the water to be treated is an organic matter, the generated hydroxy radicals oxidatively decompose the organic matter. Inorganic substances such as phosphorous acid and hypophosphorous acid are oxidized by hydroxyl radicals, respectively, and phosphorous acid becomes orthophosphoric acid, and hypophosphorous acid becomes phosphorous acid and orthophosphoric acid.

On the other hand, in the reaction tank 11, ferrous ions are oxidized by the action of hydrogen peroxide to become ferric ions.

When a plurality of reaction tanks 11 are arranged, the reaction tank 11 to which hydrogen peroxide is added from the hydrogen peroxide adding means 16 is preferably a tank other than the most downstream reaction tank 11 . The more upstream the reaction tank 11 to which hydrogen peroxide is added, the longer the time required for the Fenton reaction, so that the hydrogen peroxide can be sufficiently consumed in the Fenton reaction. Therefore, leakage of unreacted hydrogen peroxide into the insolubilization tank 21 and the adjustment tank 41 downstream of the reaction tank 11 can be suppressed. In addition, it is possible to suppress an increase in the chemical oxygen demand in the treated water due to unreacted hydrogen peroxide.

(First pH adjusting means)
The first pH adjusting means 14 adjusts the pH in the reaction tank 11 by adding acid or alkali into the reaction tank 11 according to the pH in the tank.

The inside of the reaction tank 11 is adjusted to a pH range in which the iron reagent can be dissolved in water to generate ferrous ions and hydroxyl radicals. In this embodiment, the pH in the reaction tank 11 is preferably adjusted within the range of 1.0 to 4.0. When the pH in the reaction tank 11 is 1.0 or more and 4.0 or less, the solubility of the iron reagent in water can be maintained satisfactorily. Moreover, when using an iron-reducing catalyst, the contact efficiency between the ferric ion and the iron-reducing catalyst can be enhanced. The pH in the reaction tank 11 is more preferably 2.0 or more and 3.0 or less, and further preferably 2.5 or more and 3.0 or less.

Moreover, it is preferable to install a measuring device (not shown) for measuring the pH in the reaction tank 11 .

Examples of the acid include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, and organic acids such as oxalic acid, citric acid, formic acid and acetic acid. Among them, sulfuric acid or hydrochloric acid is preferable, and sulfuric acid is more preferable because it hardly captures the hydroxyl radicals generated by the Fenton reaction. These acids may be used individually by 1 type, and may use 2 or more types together.

Examples of alkali types include sodium hydroxide, sodium carbonate, calcium hydroxide, and magnesium hydroxide. Among them, sodium hydroxide is preferred because it is highly versatile and does not react with the substance produced by the Fenton reaction.
These alkalis may be used individually by 1 type, and may use 2 or more types together.

(Catalyst adding means)
The catalyst adding means 17 adds an iron reduction catalyst into the reaction vessel 11 .

Any iron reduction catalyst may be used as long as it does not substantially hinder the Fenton reaction and promotes the reaction in which ferric ions are reduced to regenerate ferrous ions. Examples of iron reduction catalysts include activated carbon, zeolite, resin, and quartz sand. Among them, activated carbon is more preferable from the viewpoint of catalyst efficiency and treatment of waste catalyst.

The concentration of the iron reduction catalyst is preferably 100 to 10000 mass ppm, more preferably 500 to 5000 mass ppm, relative to the total mass of the mixture.
When the concentration of the iron reduction catalyst is at least the above lower limit, the efficiency of the reduction reaction of ferric ions generated in the Fenton reaction can be easily increased.
When the concentration of the iron reduction catalyst is equal to or less than the above upper limit, it becomes easier to reduce the amount of waste catalyst.
Here, the "mixed liquid" includes water to be treated containing oxidizable substances, ferrous ions, and hydrogen peroxide.
Furthermore, the liquid mixture may contain a complex-forming substance and/or an iron-reducing catalyst.

The shape of the iron reduction catalyst is preferably powdery from the viewpoint of catalytic efficiency. Further, the average particle size of the primary particles of the iron reduction catalyst is preferably 0.05 μm to 100 μm because the catalyst can be easily recovered. In addition, in this specification, an average particle diameter can be measured by the method of a laser diffraction method.

(Light irradiation means)
The light irradiating means 18 irradiates the inside of the reaction vessel with light.
The wavelength of light is preferably 300 nm or longer, more preferably 350 nm or longer, and even more preferably 380 nm or longer. Also, the wavelength of the light is preferably 650 nm or less, more preferably 540 nm or less.
When the wavelength of light is at least the above lower limit, the electricity consumption for light irradiation can be reduced.
When the wavelength of light is equal to or less than the above upper limit, the reduction reaction of ferric ions is likely to be promoted, and the complex is easily broken to release ferrous ions.

The intensity of light is preferably 100-5000 W/m ² , more preferably 500-5000 W/m ² .
When the light intensity is equal to or higher than the above lower limit, the electricity consumption for light irradiation can be reduced.
When the light intensity is equal to or less than the above upper limit, the reduction reaction of ferric ions is likely to be promoted, and the complex is easily broken to release ferrous ions.

(Insolubilization tank)
The insolubilization tank 21 insolubilizes the ferrous ions and the ferric ions generated by the Fenton reaction to remove them from the reaction solution, thereby generating ferrous compounds and ferric compounds.

In this embodiment, ferrous ions and ferric ions are insolubilized as iron compounds such as iron oxide, iron hydroxide or iron chloride.

(Second pH adjusting means)
The second pH adjusting means 24 adjusts the pH in the insolubilization tank 21 by adding an alkali into the insolubilization tank 21 according to the pH in the tank. The inside of the insolubilization tank 21 is adjusted to a pH range capable of insolubilizing ferrous ions and ferric ions. The pH in the insolubilization tank 21 is preferably adjusted within the range of 6.0 or more and 10.0 or less. The pH in the insolubilization tank 21 is more preferably 7.0 or more and 9.0 or less, more preferably 7.5 or more and 8.5 or less, and particularly preferably 7.8 or more and 8.3 or less.

In addition, it is preferable to install a measuring device (not shown) for measuring the pH in the insolubilization tank 21 .

Examples of the type of alkali to be added include those similar to the alkali that can be added by the first pH adjusting means 14 .

If the oxidizable substance contained in the water to be treated is an inorganic substance such as phosphorous acid or hypophosphorous acid, adding calcium hydroxide as an alkali causes the phosphorous acid and calcium hydroxide in the reaction solution to react. A precipitate forms. Therefore, in the concentrating device 22, which will be described later, the sediment containing phosphorous acid and the treated water can be precipitated and separated. Also, orthophosphoric acid in the reaction solution reacts with ferric ions to form a precipitate. Therefore, the sediment containing orthophosphoric acid and the treated water can be sedimented and separated in the concentrator 22, which will be described later.

(Concentrator)
The concentration device 22 obtains a concentrated suspension of sludge containing the iron compound, the iron reduction catalyst and the complex from the suspension in which the ferrous compound, the ferric compound, the iron reduction catalyst and the complex are suspended. It is. The concentrator 22 employs a dead end filtration system using the first membrane module 23 . By using the first membrane module 23, even when the suspension contains a high concentration of sludge, it can be separated with high separation performance. In the present embodiment, a concentration method using a dead end filtration method is adopted, but a cross flow filtration method may be adopted.

The first membrane module 23 comprises a filtration membrane such as a microfiltration membrane or an ultrafiltration membrane. Microfiltration membranes include hollow fiber membranes, flat membranes, tubular membranes, and monolithic membranes. Ultrafiltration membranes include hollow fiber membranes, flat membranes and tubular membranes. Among them, hollow fiber membranes are preferably used because of their high volume filling factor.

When a hollow fiber membrane is used for the first membrane module 23, the material thereof includes cellulose, polyolefin, polysulfone, polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), and the like. Among them, polyvinylidene difluoride (PVDF) and polytetrafluoroethylene (PTFE) are preferable as the material for the hollow fiber membrane because of their chemical resistance and resistance to pH changes.

When a monolithic membrane is used for the first membrane module 23, it is preferable to use a ceramic membrane.

The average pore size of micropores formed in the microfiltration membrane or ultrafiltration membrane is preferably 0.01 μm to 1.0 μm, more preferably 0.05 μm to 0.45 μm. When the average pore diameter of the fine pores is at least the lower limit, the pressure required for solid-liquid separation can be kept sufficiently low. On the other hand, if the average pore diameter of the fine pores is equal to or less than the upper limit, it is possible to suppress leakage of sludge containing iron compounds, iron reduction catalysts, and complexes into the treated water.

In the present embodiment, the ratio of the mass concentration of the iron reduction catalyst to the total amount of the suspension when the mass concentration of the iron reduction catalyst to the total amount of the reaction solution is used as a reference (hereinafter, this may be referred to as "concentration ratio"). It is preferable to concentrate so that the concentration is about 4 to 20 times. If the concentration ratio is 4 times or more, the amount of acid used for adjusting the pH in the reaction tank 11 can be reduced when the suspension is returned to the reaction tank 11 by the suspension return means 32, which will be described later. Further, if the concentration ratio is 20 times or less, it becomes easy to thicken the sludge using the thickener 22 and return the suspension using the suspension returning means 32 .

A third channel 31 is connected to the first membrane module 23 . The third flow path 31 discharges the treated water that has passed through the microfiltration membranes or ultrafiltration membranes of the first membrane module 23 from the concentrator 22 and allows it to flow into the adjustment tank 41 . A pump 31 a is installed in the third flow path 31 . Thereby, the treated water can be discharged from the insolubilization tank 21 .

Moreover, it is preferable that the third flow path 31 is provided with a measuring device for measuring the total iron concentration in the treated water. If the measuring device determines that the total iron concentration in the treated water exceeds 0.04 ppm, the pH in the insolubilization tank 21, or the solid-liquid separation in the first membrane module 23, or both are appropriate. We will respond appropriately so that

In addition, the concentrator 22 may be provided with an aeration means for cleaning the membrane surface arranged below the first membrane module 23 . A well-known thing can be used as the aeration means.

Furthermore, the concentrator 22 may use other separation means in addition to the first membrane module 23 . Other separation means include, for example, sand filtration, pressure flotation separation, centrifugation, belt press, sedimentation in a sedimentation basin, and the like.

(Suspension returning means)
The suspension return means 32 returns at least part of the suspension in which the sludge is concentrated from the insolubilization tank 21 to the reaction tank 11 . Suspension return means 32 comprise a fifth channel 33 . The fifth flow path 33 discharges at least part of the suspension from the insolubilization tank 21 and flows (supplies) it into the reaction tank 11 .
A pump 33 a is installed in the fifth flow path 33 . Thereby, at least part of the suspension in the insolubilization tank 21 can be returned from the insolubilization tank 21 to the reaction tank 11 .

When a plurality of reaction tanks 11 are arranged, the reaction tank 11 to which at least part of the suspension is returned from the insolubilization tank 21 is preferably a tank other than the most downstream reaction tank 11 . The farther upstream the reaction tank 11 that returns at least a part of the suspension is, the more the ferric compound in the suspension dissolves into ferric ions, which are further reduced to ferrous ions before the Fenton reaction. can be used for a longer cycle of becoming ferric ions and being reduced to ferrous ions. Therefore, ferric compounds in the recirculated suspension can be effectively reused in the Fenton reaction.

(Adjustment tank)
The adjustment tank 41 stores the treated water supplied from the insolubilization tank 21 through the third channel 31 .

A seventh flow path 55 is connected to the adjustment tank 41 . The seventh flow path 55 is for discharging the treated water stored in the adjustment tank 41 and allowing it to flow into the separator 42 . A pump 55a and an adjustment valve 55b are installed in the seventh flow path 55 . This allows the treated water to be discharged from the adjustment tank 41 . Note that the adjustment valve 55b may be omitted.

The separation device 42 membrane-separates the treated water separated in the concentration step into oxidizable substances contained in the treated water and permeated water. The separation device 42 employs a cross-flow filtration system using the second membrane module 43 . By adopting the cross-flow filtration method, deposition of oxidizable substances on the membrane surface can be suppressed, and the filtration flux can be maintained.

The second membrane module 43 comprises a nanofiltration membrane or a reverse osmosis membrane. When a nanofiltration membrane is used for the second membrane module 43, its material includes polyethylene, polyamide including aromatic polyamide and crosslinked polyamide, aliphatic amine condensation polymer, heterocyclic polymer, polyvinyl alcohol, Examples include cellulose acetate-based polymers.

When a reverse osmosis membrane is used for the second membrane module 43, its material includes polyamide, polysulfone, cellulose acetate, etc., and aromatic polyamide or polyamide containing crosslinked aromatic polyamide is preferable.

A fourth flow path 51 is connected to the second membrane module 43 . The fourth flow path 51 is for discharging the permeated water that has passed through the nanofiltration membrane or the reverse osmosis membrane of the second membrane module 43 from the separation device 42 and allowing it to flow into the storage tank 61 . By applying pressure to the filtration surface side (upstream side) of the second membrane module 43 with the pump 55a described above, the permeated water is discharged from the adjustment tank 41 and is separated by the separation device 42. . The flow rate can be adjusted by adjusting the output of the pump 55a.

(reservoir tank)
The storage tank 61 stores the permeated water supplied from the separator 42 through the fourth channel 51 . The permeated water stored in the storage tank 61 is diluted with industrial water or the like and discharged into a river or the like.

When an iron reduction catalyst is used, ferric compounds that have conventionally been discarded can be reused in water treatment using the Fenton reaction. Therefore, the amount of iron reagent added from the iron reagent adding means 15 can be reduced, and the generation of sludge derived from ferric compounds can be reduced. In particular, when an iron reduction catalyst is used, the oxidation reaction of the oxidizable substance and the reduction reaction of ferric ions generated by the Fenton reaction are carried out in one reaction vessel 11 equipped with light irradiation means. Thereby, the water treatment apparatus 1 can be made more compact. In addition, since the concentration of ferrous ions supplied to the Fenton reaction increases due to the reduction of ferric ions, the reaction efficiency of the oxidative decomposition reaction of the oxidizable substance can be further enhanced.

Further, when the water to be treated contains a complex-forming substance, the complex structure formed by the ferrous ion and/or ferric ion and the complex-forming substance can be destroyed by irradiating with light. Monoferric ions and/or ferric ions can be liberated. Therefore, the amount of iron reagent added from the iron reagent adding means 15 can be reduced, and the generation of sludge derived from the complex can be reduced. Further, when the water to be treated contains a complex-forming substance, the oxidation reaction of the oxidizable substance and the destruction of the complex structure are performed in one reaction tank 11 equipped with light irradiation means. Thereby, the water treatment apparatus 1 can be made more compact. In addition, since the concentration of ferrous ions supplied to the Fenton reaction increases due to the destruction of the complex structure, the reaction efficiency of the oxidative decomposition reaction of the oxidizable substance can be further enhanced.

[Water treatment method]
In the water treatment method of the first embodiment of the present invention, the pH adjustment step (A1), the oxidation step (A2), the insolubilization step (A3), the concentration step (A4), the separation step (A5), and a suspension return step (A6).

A water treatment method using the water treatment apparatus 1 shown in FIG. 1 will be described. In the water treatment method of the present embodiment, first, the pH of the water to be treated containing oxidizable substances is adjusted to 1.0 or more and 4.0 or less in the reaction tank 11 (pH adjustment step (A1)).
Subsequently, in the presence of an iron compound, hydrogen peroxide, and an iron reduction catalyst, the Fenton reaction is performed while irradiating with light to oxidize the oxidizable substance. The ferric ions generated by the Fenton reaction are reduced to ferrous ions by light irradiation in the presence of an iron reduction catalyst (oxidation step (A2)).

Next, in the insolubilization tank 21, the pH of the reaction solution obtained in the oxidation step (A2) is adjusted to 6.0 or more and 10.0 or less, and ferrous ions and ferric ions generated by the Fenton reaction are insolubilized. to produce a ferrous compound and a ferric compound (insolubilization step (A3)).
Furthermore, the suspension in which the ferrous compound, the ferric compound and the iron reduction catalyst are suspended is solid-liquid separated into sludge containing the iron compound and the iron reduction catalyst and treated water by the concentrator 22, and the sludge is A concentrated suspension is obtained (concentration step (A4)).

Next, the treated water separated in the concentration step (A4) is stored in the adjustment tank 41 . Then, the treated water is discharged from the adjustment tank 41 to the separation device 42 and is subjected to membrane separation by the separation device 42 (separation step (A5)). In the separation step (A5), the treated water is separated into oxidizable substances contained in the treated water and permeated water.
Furthermore, in the storage tank 61, the permeated water separated in the separation step (A5) is stored.

In the suspension return means 32, the suspension concentrated in the concentration step (A4) is returned from the insolubilization tank 21 to the reaction tank 11 (suspension return step (A6)).
The ferric compound in the suspension returned to the reaction tank 11 dissolves in the reaction tank 11 to become ferric ions, which are reduced to ferrous ions by an iron reduction catalyst and light irradiation (reduction step (A7)).

In the water treatment method of the first embodiment of the present invention, the oxidation reaction of oxidizable substances and the reduction reaction of ferric ions generated by the Fenton reaction are carried out in one-pot while irradiating with light. Therefore, the amount of iron reagent added from the iron reagent adding means 15 can be reduced, and the generation of sludge derived from ferric compounds can be reduced. In addition, since the concentration of ferrous ions supplied to the Fenton reaction increases due to the reduction of ferric ions, the reaction efficiency of the oxidative decomposition reaction of the oxidizable substance can be further enhanced.

In the water treatment method of the second embodiment of the present invention, the pH adjustment step (B1), the oxidation step (B2), the insolubilization step (B3), the concentration step (B4), the separation step (B5), and a suspension return step (B6).

A water treatment method using the water treatment apparatus 1 shown in FIG. 1 will be described. In the water treatment method of the present embodiment, first, the pH of the water to be treated containing the oxidizable substance and the complex-forming substance is adjusted to 1.0 or more and 4.0 or less in the reaction tank 11 (pH adjustment step (B1 )).
Subsequently, the Fenton reaction is performed in the presence of an iron compound and hydrogen peroxide while irradiating with light to oxidize the oxidizable substance (oxidation step (B2)).
The insolubilization step (B3), the concentration step (B4), the separation step (B5), and the suspension return step (B6) are the above-described insolubilization step (A3), concentration step (A4), separation step (A5), and It can be carried out in the same manner as the suspension return step (A6).

In the water treatment method of the second embodiment of the present invention, the oxidation reaction of the oxidizable substance and the liberation of ferrous ions by breaking the complex are carried out in one-pot while irradiating with light. Therefore, the amount of iron reagent added from the iron reagent adding means 15 can be reduced, and the generation of sludge derived from the complex can be reduced. Moreover, since the concentration of ferrous ions supplied to the Fenton reaction increases due to the destruction of the complex, the reaction efficiency of the oxidative decomposition reaction of the oxidizable substance can be further enhanced.

In addition, the water treatment apparatus and the water treatment method of this invention are not limited to embodiment mentioned above. For example, the water treatment apparatus 1 may further have complex-forming substance concentration measuring means (not shown). The complex-forming substance concentration measuring means is for measuring the concentration of the complex-forming substance contained in the water to be treated supplied to the reaction tank 11 . Moreover, when the iron reduction catalyst is not used, the catalyst adding means may be omitted in the water treatment device 1 .
Furthermore, in the water treatment device 1, the insolubilization tank 21, the adjustment tank 41, the separator 42, and the storage tank 61 may be omitted.
In the water treatment method of the first embodiment of the present invention, since ferric ions are reduced and reused as ferrous ions in the reaction tank 11, sludge derived from ferric compounds is generated less. . Therefore, the insolubilization tank 21, the adjustment tank 41, the separation device 42, and the storage tank 61 can be omitted.
In addition, in the water treatment method of the second embodiment of the present invention, the complex is destroyed in the reaction tank 11 to liberate ferrous ions, so that the generation of sludge derived from the complex is small. Therefore, the insolubilization tank 21, the adjustment tank 41, the separation device 42, and the storage tank 61 can be omitted.

Further, for example, in the above embodiment, the sludge concentration method using the concentration device 22 does not necessarily have to be a method using the first membrane module 23 . For example, sand filtration, pressurized flotation separation, centrifugation, belt press, sedimentation in a sedimentation pond, and the like described above may be used.

Furthermore, although an example in which the concentrating device 22 is provided inside the insolubilization tank 21 has been shown, the concentrating device 22 may not be provided inside the insolubilization tank 21 . In that case, another tank may be arranged between the insolubilization tank 21 and the adjustment tank 41, and the concentrator 22 may be provided in this tank.

When the concentrator 22 is not provided in the insolubilization tank 21, the configuration of the first membrane module 23 may be the configuration shown below. For example, a filtration membrane (microfiltration or ultrafiltration) is secured in a housing such that the primary and secondary sides of the filtration membrane are isolated. Then, the primary side of the filtration membrane in the housing communicates with a storage tank in which a suspension containing sludge and treated water containing an iron compound, an iron reduction catalyst, and a complex is stored through a circulation flow path, and two of the filtration membranes The secondary side may be connected with a suction pump.

The water treatment method in the first embodiment of the present invention has a pH adjustment step (A1), but if the water to be treated has a pH that can be used for the Fenton reaction, the pH adjustment step is not performed. good.
Also, the insolubilization step (A3), the concentration step (A4), the separation step (A5), and the suspension return step (A6) may not be performed. In the oxidation step (A2), since ferric ions are reduced and reused as ferrous ions, sludge derived from ferric compounds is less generated. Therefore, it is not necessary to perform the insolubilization step (A3), the concentration step (A4), the separation step (A5), and the suspension return step (A6).

The water treatment method in the second embodiment of the present invention has a pH adjustment step (B1), but if the water to be treated has a pH that can be used for the Fenton reaction, the pH adjustment step may be omitted. good.
Also, the insolubilization step (B3), the concentration step (B4), the separation step (B5), and the suspension return step (B6) may not be performed. In the oxidation step (B2), the ferrous ions are liberated from the complex structure formed by the ferrous ions and the complex-forming substance, so that the generation of sludge derived from the complex is reduced. Therefore, the insolubilization step (B3), the concentration step (B4), the separation step (B5), and the suspension return step (B6) do not need to be performed.

EXAMPLES The present invention will be described in detail below with reference to Examples, but the present invention is not limited by the following description. In addition, the structure common to the water treatment apparatus shown in FIG. 1 is demonstrated using the same name.
In addition, the following materials were used as each reagent.
_Iron reagent: iron (II) sulfate heptahydrate ( _FeSO4.7H2O )
Iron reduction catalyst: activated carbon (DiaFellow CT, manufactured by Mitsubishi Chemical Aqua Solutions Co., Ltd.)
Propionaldehyde (Fujifilm Wako Pure Chemical Industries, Ltd.)

[Example 1]
A water treatment apparatus was prepared in which a reaction tank was provided with a first pH adjusting means, an iron reagent adding means, a hydrogen peroxide adding means, a catalyst adding means, and a light irradiation means.
Orange II was added to pure water so as to have a concentration of 30 mg/L to prepare water to be treated.
The water to be treated was placed in a reaction tank, and the pH was adjusted to 3.0 with sulfuric acid.
Subsequently, hydrogen peroxide was added to the reaction tank so that the concentration of hydrogen peroxide with respect to the total volume of the water to be treated was 500 mg/L.
Further, the iron reagent was added to the reaction tank so that the concentration of the iron reagent with respect to the total volume of the water to be treated was 5 mg/L (1 mg/L in terms of ferrous ion).
Furthermore, an iron reduction catalyst was added to the reaction tank so that the concentration of the iron reduction catalyst with respect to the total weight of the water to be treated was 100 mass ppm.
The water to be treated thus obtained was irradiated with light having a wavelength of 380 nm and an intensity of 1600 W/m ² , and the concentration (mg/L) of Orange II in the water to be treated was measured every 5 minutes from the start of light irradiation. The obtained results are shown in Table 1 and FIG.
The concentration of Orange II was measured by an absorptiometric method.

[Comparative Example 1]
Water treatment was carried out in the same manner as in Example 1 except that no light was irradiated, and the concentration (mg/L) of Orange II in the treated water was measured every 5 minutes after the addition of the iron reduction catalyst. The obtained results are shown in Table 1 and FIG.

[Comparative Example 2]
Water treatment was carried out in the same manner as in Example 1 except that no iron reduction catalyst was added, and the concentration (mg/L) of Orange II in the treated water was measured every 5 minutes from the start of light irradiation. The obtained results are shown in Table 1 and FIG.

In Example 1, Orange II in the water to be treated was almost completely oxidatively decomposed 20 minutes after the start of light irradiation.
In Comparative Example 1 in which light was not irradiated, it took about 40 minutes until Orange II in the water to be treated was almost completely oxidatively decomposed.
In Comparative Example 2 in which no iron reduction catalyst was added, it took about 40 minutes until Orange II in the water to be treated was almost completely oxidatively decomposed.

[Example 2]
A water treatment apparatus was prepared in which a reaction tank was provided with a first pH adjusting means, an iron reagent adding means, a hydrogen peroxide adding means, and a light irradiation means.
Orange II was added to pure water to a concentration of 200 mg/L, and propionaldehyde was added to a concentration of 800 mg/L to prepare water to be treated.
The water to be treated was placed in a reaction tank, and the pH was adjusted to 3.0 with sulfuric acid.
Subsequently, hydrogen peroxide was added to the reaction tank so that the concentration of hydrogen peroxide with respect to the total volume of the water to be treated was 500 mg/L.
Further, the iron reagent was added to the reaction tank so that the concentration of the iron reagent with respect to the total volume of the water to be treated was 5 mg/L (3 mg/L in terms of ferrous ion).
The water to be treated thus obtained was irradiated with light having a wavelength of 380 nm and an intensity of 1600 W/m ² , and the concentration (mg/L) of Orange II in the water to be treated was measured every 5 minutes from the start of light irradiation. The obtained results are shown in Table 2 and FIG.
The concentration of Orange II was measured by an absorptiometric method.

[Comparative Example 3]
Water treatment was carried out in the same manner as in Example 2, except that light was not irradiated, and the concentration (mg/L) of Orange II in the water to be treated was measured every 5 minutes after the addition of the iron reagent. The obtained results are shown in Table 2 and FIG.

In Example 2, about half of Orange II in the water to be treated was oxidatively decomposed 40 minutes after the start of light irradiation.
In Comparative Example 3, in which light was not irradiated, Orange II in the water to be treated was hardly oxidatively decomposed even after 40 minutes from the start of light irradiation.

[Example 3]
A water treatment apparatus was prepared in which a reaction tank was provided with a first pH adjusting means, an iron reagent adding means, a hydrogen peroxide adding means, a catalyst adding means, and a light irradiation means.
Orange II was added to pure water to a concentration of 200 mg/L, and propionaldehyde was added to a concentration of 800 mg/L to prepare water to be treated.
The water to be treated was placed in a reaction tank, and the pH was adjusted to 3.0 with sulfuric acid.
Subsequently, hydrogen peroxide was added to the reaction tank so that the concentration of hydrogen peroxide with respect to the total volume of the water to be treated was 500 mg/L.
Further, the iron reagent was added to the reaction tank so that the concentration of the iron reagent with respect to the total volume of the water to be treated was 5 mg/L (3 mg/L in terms of ferrous ion).
Furthermore, an iron reduction catalyst was added to the reaction tank so that the concentration of the iron reduction catalyst with respect to the total weight of the water to be treated was 100 mass ppm.
The water to be treated thus obtained was irradiated with light having a wavelength of 380 nm and an intensity of 1600 W/m ² , and the concentration (mg/L) of Orange II in the water to be treated was measured every 5 minutes from the start of light irradiation. The obtained results are shown in Table 3 and FIG.
The concentration of Orange II was measured by an absorptiometric method.

[Comparative Example 4]
Water treatment was carried out in the same manner as in Example 3, except that light was not irradiated, and the concentration (mg/L) of Orange II in the treated water was measured every 5 minutes after the addition of the iron reduction catalyst. The obtained results are shown in Table 3 and FIG.

In Example 3, more than half of Orange II in the water to be treated was oxidatively decomposed 40 minutes after the start of light irradiation.
In Comparative Example 4 in which light was not irradiated, about half of Orange II in the water to be treated was oxidatively decomposed after 40 minutes from the start of light irradiation, but oxidative decomposition was slower than in Example 3. .

DESCRIPTION OF SYMBOLS 1... Water treatment apparatus, 11... Reaction tank, 14... First pH adjustment means, 17... Catalyst addition means, 18... Light irradiation means, 21... Insolubilization tank, 22... Concentration apparatus, 24... Second pH adjustment means, 32 ...suspension return means, 42...separation device

Claims (7)

A mixture containing water to be treated containing an oxidizable substance, ferrous ions, hydrogen peroxide, an iron reduction catalyst, and a complex-forming substance , adjusted to a pH range of 1.0 or more and 4.0 or less A water treatment method comprising an oxidation step (A2) of irradiating the liquid (A) with light to decompose the oxidizable substance,
A water treatment method, wherein the iron reduction catalyst is activated carbon. The water treatment method according to claim 1, wherein the complex-forming substance is a substance that forms a complex with the ferrous ion. The water treatment method according to claim 1 or 2, wherein the mixed solution (A) contains ferric ions. The water treatment method according to claim 3, wherein the complex-forming substance is a substance that forms a complex with the ferric ion. The water treatment method according to any one of claims 1 to 4, wherein the wavelength of the light irradiated in the oxidation step (A2) is 380 nm or more. The water according to any one of claims 1 to 5, wherein in the oxidation step (A2), the concentration of the iron reduction catalyst is 100 to 10000 mass ppm with respect to the total mass of the mixed liquid (A). Processing method. A mixture containing water to be treated containing an oxidizable substance, ferrous ions, hydrogen peroxide, an iron reduction catalyst, and a complex-forming substance , adjusted to a pH range of 1.0 or more and 4.0 or less A water treatment apparatus comprising a reaction tank for decomposing the oxidizable substance by performing a Fenton reaction under light irradiation in the presence of the liquid (A),
A water treatment device, wherein the iron reduction catalyst is activated carbon.

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