CN108529735B

CN108529735B - Water treatment method and water treatment apparatus

Info

Publication number: CN108529735B
Application number: CN201810175249.4A
Authority: CN
Inventors: 安保贵永; 皆川正和
Original assignee: Mitsubishi Chemical Water Solutions Co ltd
Current assignee: Wilsey Co
Priority date: 2017-03-03
Filing date: 2018-03-02
Publication date: 2021-07-23
Anticipated expiration: 2038-03-02
Also published as: CN108529735A

Abstract

A water treatment method capable of efficiently performing water treatment. The method for treating wastewater containing oxidizable pollutants comprises the following steps: (i) a reaction step of obtaining a reaction solution by an oxidation treatment in which ferrous ions and hydrogen peroxide are added to wastewater satisfying the following condition a so as to satisfy the following condition B to oxidize oxidizable contaminants in the wastewater, and a reduction treatment in which ferric ions generated by the oxidation treatment are reduced to ferrous ions in the presence of an iron reduction catalyst; (ii) an insolubilization step of adjusting the pH of the reaction solution to 6 to 10 to insolubilize ferrous ions and ferric ions in the reaction solution to obtain a suspension in which a ferrous compound and a ferric compound are suspended; (iii) a concentration step of separating the treated water from the suspension to obtain a concentrated suspension in which the sludge containing the ferric iron compound is concentrated; the pH value of the wastewater A is more than 1 and less than 4, and the ratio of B to R₁Is 1.9 to 100 inclusive.

Description

Water treatment method and water treatment apparatus

Technical Field

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

Background

The Fenton (Fenton) reaction is a reaction in which hydrogen peroxide reacts with ferrous ions to generate hydroxyl radicals. The hydroxyl radical has strong oxidizing power, and is expected to be applied to various fields such as sterilization, decomposition of harmful substances and difficultly decomposed pollutants by utilizing the strong oxidizing power.

The ferrous ions used in the fenton reaction are oxidized to become ferric ions as the reaction proceeds. For example, when wastewater containing oxidizable contaminants is treated by fenton reaction, sludge containing trivalent iron compounds is a waste, and the cost of treatment is high.

It is known that a part of ferric ions generated in the fenton reaction is 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. In contrast, a method is known in which an iron reduction catalyst that promotes the reduction reaction is added to simultaneously perform the fenton reaction and the reduction reaction. Examples of such a catalyst include an iron reduction catalyst in which activated carbon is added (patent documents 1 and 2).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 56-48290

Patent document 2: japanese patent No. 5215578

Disclosure of Invention

Problems to be solved by the invention

The methods described in patent documents 1 and 2 may have low treatment efficiency.

Accordingly, an object of one embodiment of the present invention is to provide a water treatment apparatus capable of effectively performing water treatment in water treatment using fenton reaction accompanied by reduction reaction of ferric ions, and a water treatment method using the same.

Technical scheme for solving problems

The present inventors have conducted intensive studies in order to solve the above problems, and as a result, have found that hydrogen peroxide is one of the main factors for deactivating the iron reduction catalyst. Further, a ratio R calculated by the following formula was found₁The present inventors have completed the present invention by carrying out the fenton reaction under conditions of 1.9 to 100 inclusive to suppress the deactivation of the iron reduction catalyst.

R₁＝A₁/B₁

A₁Indicates the mass concentration of the iron reduction catalyst relative to the total amount of the reaction solutionDegree (unit: mg/L).

B₁Represents the mass concentration (unit: mg/L) of hydrogen peroxide calculated by dividing the total mass (unit: mg) of hydrogen peroxide added to the wastewater in a set time by the amount (unit: L) of wastewater treated in the step (i) in a set time.

That is, the present invention has the following aspects.

[1] A water treatment method for wastewater containing oxidizable pollutants, comprising the following steps (i) to (iii):

(i) a reaction step of performing an oxidation treatment of adding ferrous ions and hydrogen peroxide to the wastewater satisfying the following condition (a) so as to satisfy the following condition (B) to oxidize the oxidizable pollutant in the wastewater, and a reduction treatment of reducing ferric ions generated by the oxidation treatment to ferrous ions in the presence of an iron reduction catalyst to obtain a reaction solution;

(ii) an insolubilization step of adjusting the pH of the reaction solution to 6 or more and 10 or less to insolubilize ferrous ions and ferric ions in the reaction solution to obtain a suspension in which a ferrous compound and a ferric compound are suspended;

(iii) a concentration step of separating treated water from the suspension to obtain a concentrated suspension in which sludge containing a ferric compound is concentrated;

(A) the pH value of the wastewater is more than 1 and less than 4

(B) The ratio R calculated according to the following formula₁Is 1.9 or more and 100 or less,

R₁＝A₁/B₁

wherein A is₁Represents the mass concentration (unit: mg/L) of the iron reduction catalyst relative to the total amount of the reaction solution,

B₁(ii) represents the mass concentration (unit: mg/L) of the hydrogen peroxide by dividing the total mass (unit: mg) of the hydrogen peroxide added to the wastewater in the set time by the step (i)) The amount of the wastewater treated in a set time (unit: l) is calculated.

[2] The water treatment method according to [1], which comprises a suspension refluxing step of refluxing either or both of at least a part of the suspension and at least a part of the concentrated suspension to the step (i).

[3] The water treatment method according to [1] or [2], which comprises a magnetic separation step of separating paramagnetic substances contained in either one or both of the suspension and the concentrated suspension by magnetism.

[4] The water treatment method according to any one of [1] to [3], wherein the iron reduction catalyst is at least one selected from the group consisting of activated carbon and zeolite.

[5] The water treatment method according to any one of [1] to [4], wherein in the step (i), the pH of the wastewater is adjusted to 1 or more and 4 or less using an acid.

[6] The water treatment method according to any one of [1] to [5], wherein a ferrous salt or a ferrous oxide is added in the step (i).

[7] The water treatment method according to any one of [1] to [6], wherein in the step (iii), the concentrated suspension is obtained using a filtration membrane.

[8] The water treatment method according to any one of [1] to [7], which comprises a separation step of separating the treated water into the oxidizable pollutant and filtered water contained in the treated water by using a nanofiltration membrane or a reverse osmosis membrane.

[9] A water treatment device comprising the following (1) to (3):

(1) a reaction tank in which a ratio R calculated according to the following formula is present₂Oxidizing an oxidizable pollutant contained in wastewater by a Fenton reaction under a condition of 1.9 to 100 inclusive, and reducing ferric ions generated by the Fenton reaction to ferrous ions by an iron reduction catalyst to obtain a reaction solution,

R₂＝A₂/B₂

wherein A is₂Represents the mass concentration (unit: mg/L) of the iron reduction catalyst relative to the total amount of the reaction solution in the reaction tank,

B₂represents a mass concentration (unit: mg/L) of the hydrogen peroxide calculated by dividing a total mass (unit: mg) of the hydrogen peroxide added to the wastewater within the set time by an amount (unit: L) of the wastewater flowing into the reaction tank within the set time;

(2) an insolubilization tank in which ferrous ions and ferric ions contained in the reaction solution are insolubilized to produce a ferrous compound and a ferric compound, thereby obtaining a suspension in which the ferrous compound and the ferric compound are suspended;

(3) and a concentration device for separating the treated water from the suspension to obtain a concentrated suspension in which the sludge containing the ferric iron compound is concentrated.

[10] The water treatment apparatus according to [9], which comprises a suspension returning mechanism for returning either one or both of at least a part of the suspension and at least a part of the concentrated suspension to the reaction tank.

[11] The water treatment apparatus according to [9] or [10], which comprises a magnetic separation device for magnetically separating paramagnetic substances contained in either one or both of the suspension and the concentrated suspension.

[12] The water treatment apparatus according to [10] or [11], comprising:

a catalyst concentration measuring section that measures at least one of a mass concentration of the iron reduction catalyst relative to a total amount of the suspension and a mass concentration of the iron reduction catalyst relative to a total amount of the concentrated suspension;

a control section that controls the ratio R₂1.9 or more and 100 or less;

wherein the control unit determines the flow rate of either or both of at least a part of the refluxed suspension and at least a part of the concentrated suspension and the amount of the iron reduction catalyst to be added, and determines the amount of the hydrogen peroxide to be added at the same time, based on the measurement result of the catalyst concentration measuring unit.

[13] The water treatment apparatus according to any one of [9] to [12], comprising a catalyst addition mechanism that adds the iron reduction catalyst to the reaction tank.

[14] The water treatment apparatus according to any one of [9] to [13], comprising:

a first pH adjusting device for adjusting the pH of the wastewater by supplying an acid or a base to the reaction tank;

and a second pH adjusting device for adjusting the pH of the reaction solution by supplying an alkali to the insolubilization tank.

[15] The water treatment apparatus according to [14], wherein the acid is sulfuric acid or hydrochloric acid.

[16] The water treatment apparatus according to any one of [9] to [15], wherein the concentration device has a filter membrane, and the suspension is obtained using the filter membrane.

[17] The water treatment apparatus according to any one of [9] to [16], wherein the concentration device is provided in the insolubilization tank.

[18] The water treatment apparatus according to any one of [9] to [17], which comprises a separation apparatus having a nanofiltration membrane or a reverse osmosis membrane, wherein the treated water is separated into the oxidizable pollutant and filtered water contained in the treated water by using the nanofiltration membrane or the reverse osmosis membrane.

[1] A water treatment method comprising the following steps (i) to (v):

(i) an oxidation step of adjusting the pH value of wastewater containing oxidizable pollutants to 1.0 or more and 4.0 or less at a ratio R calculated according to the following formula₁Performing a Fenton reaction under conditions of 2.0 to 100 inclusive to oxidize the oxidizable contaminant,

R₁＝A₁/B₁

wherein A is₁Represents the oxidation stepThe mass concentration (unit: mg/L) of the iron reduction catalyst obtained in (1) above with respect to the total amount of the reaction solution,

B₁represents the mass concentration (unit: mg/L) of hydrogen peroxide relative to the total amount of the wastewater fed in the oxidation step;

(ii) an insolubilization step of adjusting the pH of the reaction solution to 6.0 or more and 10.0 or less to insolubilize ferrous ions and ferric ions generated by the Fenton reaction to generate a ferrous compound and a ferric compound;

(iii) a concentration step of separating a suspension in which the ferrous compound and the ferric compound are suspended into sludge containing the ferric compound and treated water to obtain the suspension in which the sludge is concentrated;

(iv) a suspension reflux step of refluxing at least a part of the suspension to the oxidation step;

(v) a reduction step of reducing the ferric ions to the ferrous ions by an iron reduction catalyst.

[2] The water treatment method according to [1], wherein the iron reduction catalyst is at least one selected from activated carbon and zeolite.

[3] The method for treating water according to [1] or [2], wherein in the oxidation step, the pH of the wastewater is adjusted to 1.0 or more and 4.0 or less using an acid.

[4] The water treatment method according to any one of [1] to [3], wherein a ferrous salt or a ferrous oxide is added in the oxidation step.

[5] The water treatment method according to any one of [1] to [4], wherein the suspension is obtained using a filter membrane in the concentration step.

[6] The water treatment method according to any one of [1] to [5], which comprises a separation step of separating the treated water into the oxidizable pollutant and filtered water contained in the treated water by using a nanofiltration membrane or a reverse osmosis membrane.

[7] A water treatment device comprising the following (1) to (4):

(1) a reaction tank in which a ratio R calculated according to the following formula is present₂Oxidizing an oxidizable pollutant contained in wastewater by a Fenton reaction under a condition of 2.0 to 100 inclusive, and reducing ferric ions generated by the Fenton reaction to ferrous ions by an iron reduction catalyst to obtain a reaction solution,

R₂＝A₂/B₂

wherein A is₂Represents the mass concentration (unit: mg/L) of the iron reduction catalyst in the reaction vessel relative to the total amount of the reaction solution,

B₂represents the mass concentration (unit: mg/L) of hydrogen peroxide relative to the total amount of the wastewater flowing into the reaction tank;

(2) an insolubilization tank in which the ferrous ions and the ferric ions contained in the reaction solution supplied from the reaction tank are insolubilized to produce a ferrous compound and a ferric compound.

(3) And a concentration device for separating a suspension in which the ferrous compound and the ferric compound are suspended into sludge containing the ferric compound and treated water to obtain the suspension in which the sludge is concentrated.

(4) And a suspension reflux mechanism for refluxing at least a part of the suspension to the reaction tank.

[8] The water treatment apparatus according to [7], comprising:

a catalyst concentration measuring unit that measures the mass concentration of the iron reduction catalyst relative to the total amount of the suspension;

a control section that controls the ratio R₂Is not less than 2.0 and not more than 100,

wherein the control unit determines the flow rate of the suspension to be refluxed and the addition amount of the confirmed iron reduction catalyst based on the measurement result of the catalyst concentration measuring unit, and determines the addition amount of the hydrogen peroxide at the same time.

[9] The water treatment apparatus according to [7] or [8], which comprises a catalyst adding mechanism for adding the iron reduction catalyst to the reaction tank.

[10] The water treatment apparatus according to any one of [7] to [9], comprising:

[11] The water treatment apparatus according to [10], wherein the acid is sulfuric acid or hydrochloric acid.

[12] The water treatment apparatus according to any one of [7] to [11], wherein the concentration device has a filter membrane, and the suspension is obtained using the filter membrane.

[13] The water treatment apparatus according to any one of [7] to [12], wherein the concentration device is provided in the insolubilization tank.

[14] The water treatment apparatus according to any one of [7] to [13], which comprises a separation apparatus having a nanofiltration membrane or a reverse osmosis membrane, wherein the treated water is separated into the oxidizable pollutant and filtered water contained in the treated water by using the nanofiltration membrane or the reverse osmosis membrane.

[1] A water treatment method comprising the following steps (i) to (vi):

(i) an oxidation step of oxidizing oxidizable contaminants contained in the wastewater by a Fenton reaction under acidic conditions;

(ii) an insolubilization step of adjusting the pH of the reaction solution obtained in the oxidation step to 6.0 or more and 10.0 or less to insolubilize iron including ferrous ions and ferric ions generated by the fenton reaction to generate a ferrous compound and a ferric compound;

(iii) a concentration step of separating a suspension in which the ferrous compound and the ferric compound are suspended into sludge containing the ferric compound and treated water to obtain a concentrated suspension in which the sludge is concentrated;

(iv) a suspension reflux step of refluxing at least a part of the concentrated suspension to the oxidation step;

(v) a reduction step of reducing the ferric ions to the ferrous ions by an iron reduction catalyst;

(vi) a magnetic separation step of separating paramagnetic substances contained in either one or both of the suspension and the concentrated suspension by magnetism.

[3] The method for treating water according to [1] or [2], wherein in the oxidation step, an acid is used under acidic conditions.

[4] The method for treating water according to any one of [1] to [3], wherein at least one selected from a ferrous salt and a ferrous oxide is added in the oxidation step.

[5] The water treatment method according to any one of [1] to [4], wherein the concentration step uses a filter membrane to obtain the concentrated suspension.

[7] A water treatment device comprising the following (1) to (4):

(1) a reaction tank in which oxidizable pollutants contained in wastewater are oxidized by a fenton reaction, and ferric ions generated by the fenton reaction are reduced to ferrous ions by the iron reduction catalyst;

(2) an insolubilization tank in which the ferrous ions and the ferric ions contained in the reaction solution supplied from the reaction tank are insolubilized to produce a ferrous compound and a ferric compound;

(3) a concentration device for separating a suspension in which the ferrous compound and the ferric compound are suspended into sludge containing the ferric compound and treated water in the tank to obtain a concentrated suspension in which the sludge is concentrated;

(4) a suspension reflux mechanism for refluxing at least a part of the concentrated suspension to the reaction tank;

(5) and a magnetic separation device for magnetically separating paramagnetic substances contained in either or both of the suspension and the concentrated suspension.

[8] The water treatment apparatus according to [7], wherein the reaction tank is provided with an addition mechanism for adding at least one selected from a ferrous salt, a ferrous oxide, a ferric salt and a ferric oxide.

[9] The water treatment apparatus according to [8], which comprises a catalyst concentration measuring unit for measuring a mass concentration of the iron reduction catalyst with respect to a total amount of the reaction solution, and wherein the iron reduction catalyst is added and at least one selected from the group is added based on a measurement result of the catalyst concentration measuring unit.

[10] The water treatment apparatus according to any one of [7] to [9], comprising a catalyst addition mechanism that adds the iron reduction catalyst to the reaction tank.

[11] The water treatment apparatus according to any one of [7] to [10], comprising:

[12] The water treatment apparatus according to [11], wherein the acid is sulfuric acid or hydrochloric acid.

[13] The water treatment apparatus according to any one of [7] to [12], wherein the concentration device has a filter membrane, and the concentrated suspension is obtained using the filter membrane.

[14] The water treatment apparatus according to any one of [7] to [13], wherein the concentration device is provided in the insolubilization tank.

[15] The water treatment apparatus according to any one of [7] to [14], wherein the magnetic separation device is provided in at least one selected from the group consisting of the reaction tank, the insolubilization tank, and the suspension reflux mechanism.

[16] The water treatment apparatus according to any one of [7] to [15], which comprises a separation apparatus having a nanofiltration membrane or a reverse osmosis membrane, wherein the treated water is separated into the oxidizable pollutant and filtered water contained in the treated water by using the nanofiltration membrane or the reverse osmosis membrane.

Effects of the invention

According to one embodiment of the present invention, a water treatment apparatus and a water treatment method using the same, which can effectively perform water treatment, are provided in the water treatment using the fenton reaction accompanied by the reduction reaction of ferric ions.

Drawings

Fig. 1 is a schematic configuration diagram showing a water treatment apparatus 1.

Fig. 2 is a schematic configuration diagram showing the water treatment apparatus 2.

Description of the reference numerals

1 … water treatment device, 11 … reaction tank, 14, 24 … pH adjusting device, 15 … iron reagent adding mechanism, 17 … catalyst adding mechanism, 19A … hydrogen peroxide concentration measuring part, 18, 19B … catalyst concentration measuring part, 19C … control part, 21 … insolubilization tank, 22 … concentrating device, 32 … suspension reflux mechanism, 34 … magnetic separating device, 42 … separating device

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. In all the drawings described below, the dimensions, proportions, and the like of the respective constituent elements are appropriately changed in order to facilitate understanding of the drawings.

< first embodiment >

[ Water treatment apparatus ]

The structure of the water treatment apparatus 1 used in the water treatment method of the present embodiment will be described. Fig. 1 is a schematic configuration diagram showing a water treatment apparatus 1 according to the present 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, in a reaction tank 11: a pH adjusting device 14, an iron reagent adding mechanism 15, a hydrogen peroxide adding mechanism 16, a catalyst adding mechanism 17, and a hydrogen peroxide concentration measuring unit 19A.

The water treatment apparatus 1 includes, in an insolubilization tank 21: the catalyst concentration measuring unit 19B, pH adjusts the device 24. Further, a concentration device 22 is provided in the insolubilization tank 21.

In the present specification, the pH adjusting device 14 corresponds to a first pH adjusting device in the claims. Further, the pH adjusting device 24 corresponds to a second pH adjusting device in the claims.

The water treatment apparatus 1 includes a control unit 19C.

The water treatment apparatus 1 further includes a suspension reflux mechanism 32 between the insolubilization tank 21 and the reaction tank 11.

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

(waste water)

In the water treatment by the water treatment apparatus 1, wastewater containing oxidizable pollutants is oxidized by fenton reaction. Examples of oxidizable contaminants include: organic substances which are difficult to decompose by biological treatment, or inorganic substances such as phosphorous acid and hypophosphorous acid.

Examples of the organic substances include: organic solvents such as 1, 4-dioxane, humus, etc. The humus is a fraction obtained by extracting soil with an alkali such as sodium hydroxide or an extract obtained by extracting soil with natural water, adsorbing the fraction to an XAD resin (a copolymer of styrene or acrylic acid and divinylbenzene), and eluting the adsorbed material with a dilute aqueous alkali solution.

The waste water from plating plants contains phosphorous acid and hypophosphorous acid.

(reaction tank)

In the reaction tank 11, oxidizable contaminants contained in the wastewater are oxidized by Fenton's reaction, and at the same time, the oxidizable contaminants are reduced by an iron reduction catalystFerric ions generated by Fenton reaction are reduced into ferrous ions. The reaction tank 11 is filled with at least ferrous ion (Fe)²⁺) An iron reagent, hydrogen peroxide and an iron reduction catalyst.

The first flow path 12 and the second flow path 13 are connected to the reaction tank 11. The first flow path 12 allows wastewater containing oxidizable contaminants to flow (supply) into the reaction tank 11. In the water treatment apparatus 1 of the present embodiment, the wastewater may be continuously fed into the reaction tank 11 or may be intermittently fed into the reaction tank 11. In addition, a measuring instrument capable of measuring the flow rate and flow velocity of the waste water may be provided in the first flow path 12. The second flow path 13 allows the reaction solution discharged from the reaction tank 11 to flow (supply) into the insolubilization tank 21.

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

In the water treatment apparatus 1 shown in fig. 1, one reaction tank 11 is provided, and a plurality of reaction tanks 11 may be arranged in series. In this case, since the time required for the fenton reaction can be extended, hydrogen peroxide can be sufficiently consumed in the fenton reaction.

When a plurality of reaction vessels 11 are arranged, the method of transferring from the first reaction vessel to the second reaction vessel is not particularly limited, and the transfer may be performed by a pump or by overflow.

In the present specification, the reaction vessel in the claims is composed of a first reaction vessel and a second reaction vessel.

(iron reagent adding mechanism)

The iron reagent adding means 15 is a means for adding an iron reagent into the reaction tank 11.

The iron reagent is not particularly limited as long as it is soluble in water and can generate ferrous ions, and a ferrous salt or a ferrous oxide is preferable. Among them, iron sulfate or iron chloride is preferable because it is not necessary to control the treatment according to the wastewater standards and the solubility is excellent. In addition, iron sulfate is more preferable because of high versatility and low corrosiveness.

In the present embodiment, since ferric ions are reduced by an iron reduction catalyst and ferrous ions are regenerated, a ferric compound can be used as the iron reagent.

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

(Hydrogen peroxide adding mechanism)

The hydrogen peroxide adding mechanism 16 is a mechanism for adding hydrogen peroxide into the reaction tank 11.

In the reaction tank 11, the ferrous ions react with hydrogen peroxide to generate hydroxyl radicals. When the oxidizable pollutant contained in the wastewater is an organic substance, the organic substance is oxidized and decomposed by the generated hydroxyl radicals. In the case of inorganic substances such as phosphorous acid and hypophosphorous acid, the oxidation of phosphorous acid to orthophosphoric acid and the oxidation of hypophosphorous acid to phosphorous acid or orthophosphoric acid are carried out by hydroxyl radical oxidation.

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

In the present embodiment, hydrogen peroxide can be used not only for the fenton reaction but also for the reduction reaction of ferric ions generated by the fenton reaction. Therefore, the amount of hydrogen peroxide added by the hydrogen peroxide adding mechanism 16 is preferably larger than the theoretical value used in the fenton reaction.

When a plurality of reaction vessels 11 are arranged, the reaction vessel 11 to which hydrogen peroxide is added from the hydrogen peroxide addition mechanism 16 is preferably a vessel other than the most downstream reaction vessel 11. The time required for the fenton reaction can be further extended as the reaction tank 11 to which hydrogen peroxide is added is located upstream, and thus hydrogen peroxide can be sufficiently consumed in the fenton reaction. This can suppress leakage of unreacted hydrogen peroxide in the insolubilization tank 21 and the adjustment tank 41 downstream of the reaction tank 11. Further, an increase in chemical oxygen demand in the treated water caused by unreacted hydrogen peroxide can be suppressed.

(first pH adjusting device)

The pH adjusting device 14 is a device for adjusting the pH in the reaction tank 11 by adding an acid or an alkali to the reaction tank 11 in accordance with the pH value in the tank.

The reaction tank 11 is adjusted to a pH range in which the iron reagent is dissolved in water to generate ferrous ions and hydroxyl radicals. In the present embodiment, the pH in the reaction tank 11 can be adjusted to a range of 1.0 to 4.0. If the pH in the reaction tank 11 is 1.0 or more and 4.0 or less, the contact efficiency between the ferric ions and the iron reduction catalyst can be improved while the solubility of the iron reagent in water is maintained well. The pH in the reaction tank 11 is preferably 2.0 or more and 3.0 or less, and more preferably 2.5 or more and 3.0 or less.

It is preferable that the reaction tank 11 is provided with a measuring instrument (not shown) for measuring the pH in the tank.

The kind of acid may be exemplified by: inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc.; organic acids such as oxalic acid, citric acid, formic acid, and acetic acid. Among these, sulfuric acid and hydrochloric acid are preferable, and sulfuric acid is more preferable because it is difficult to capture a hydroxyl radical generated in the fenton reaction. These acids may be used alone or in combination of two or more.

The kind of the base may be exemplified by: sodium hydroxide, sodium carbonate, calcium hydroxide, magnesium hydroxide, and the like. Among them, sodium hydroxide is preferable because of its high versatility and non-reactivity with substances produced in the fenton reaction.

These bases may be used alone or in combination of two or more.

(catalyst adding mechanism)

The catalyst adding means 17 is a means for adding an iron reduction catalyst into the reaction tank 11.

The iron reduction catalyst may be any catalyst that promotes a reaction in which ferric ions are reduced by hydrogen peroxide and ferrous ions are regenerated, while substantially not inhibiting the fenton reaction. The iron reduction catalyst is preferably selected from at least one of activated carbon and zeolite, more preferably activated carbon, from the viewpoint of catalyst efficiency and treatment of the spent catalyst.

Conventionally, in water treatment utilizing Fenton reaction accompanied by reduction reaction of ferric ionAs the fenton reaction proceeds and the iron reduction catalyst is deactivated, the efficiency of the fenton reaction may be low. The present inventors have conducted intensive studies in order to solve the above problems, and as a result, have found that hydrogen peroxide is one of the main factors for deactivating the iron reduction catalyst. Further, a ratio R calculated by the following formula was found₂The fenton reaction is performed under a condition of 1.9 to 100 inclusive, and deactivation of the iron reduction catalyst can be suppressed.

R₂＝A₂/B₂

A₂The mass concentration (unit: mg/L) of the iron reduction catalyst relative to the total amount of the reaction solution in the reaction tank 11 is shown.

B₂Represents the mass concentration (unit: mg/L) of hydrogen peroxide, which is calculated by dividing the total mass (unit: mg) of hydrogen peroxide added to the wastewater in a set time by the amount (unit: L) of the wastewater flowing into the reaction tank 11 in a set time. Note that the two setting times are the same in length.

That is, it was found that the mass concentration of the iron reduction catalyst relative to the total amount of the reaction liquid in the reaction tank 11 was adjusted to the ratio R calculated according to the above formula₂Is 1.9 to 100 inclusive, and can suppress deactivation of the iron reduction catalyst.

As an embodiment, the above-mentioned A₂Is the mass concentration of the iron reduction catalyst added to the reaction tank 11 relative to the total amount of the reaction solution stored in the reaction tank 11. Estimation of the above A in the Fenton reaction₂No change occurred.

When the wastewater continuously flows into the reaction tank 11, the mass concentration of the hydrogen peroxide decreases unless the hydrogen peroxide is allowed to flow into the reaction tank 11. If the mass concentration of hydrogen peroxide is decreased, the target fenton reaction or the ferric ion reduction reaction may be difficult to proceed. Therefore, in the water treatment apparatus 1 of the present embodiment, the mass concentration of hydrogen peroxide at each set time is confirmed so that the mass concentration of hydrogen peroxide does not become too low.

In the water treatment apparatus 1 of the present embodiment, the set time is set in accordance with the capacity of the reaction tank 11 and the flow rate of wastewater. In the water treatment apparatus 1 of the present embodiment, the set time is, for example, 10 minutes.

When the wastewater intermittently flows into the reaction tank 11, the above-mentioned B₂The mass concentration of the hydrogen peroxide added to the reaction tank 11 may be set to the total amount of the wastewater flowing into the reaction tank 11.

If the ratio R is calculated according to the above formula₂When the amount is 1.9 or more, the deactivation of the iron reduction catalyst can be sufficiently suppressed. Therefore, if the ratio R is₂When the amount is 1.9 or more, the effect of promoting the reduction reaction of the ferric ion can be sufficiently obtained. The ratio R₂The higher the content, the more the deactivation of the iron reduction catalyst can be suppressed, and if it exceeds 100, the mass concentration of hydrogen peroxide becomes relatively low, and thus the target fenton reaction or the ferric ion reduction reaction may be difficult to proceed. In contrast, if the ratio R is₂When the amount is 100 or less, the amount of the iron reduction catalyst to be used can be reduced, and the cost required for the iron reduction catalyst can be reduced.

The above ratio R is set in order to increase the treatment efficiency in the water treatment method of the present embodiment and to reduce the cost for using the iron reduction catalyst₂Preferably 1.9 or more and 80 or less, more preferably 2.5 or more and 40 or less, further preferably 2.7 or more and 30 or less, and particularly preferably 3.0 or more and 15 or less.

The mass concentration of the iron-reducing catalyst relative to the total amount of the reaction solution is preferably 50000mg/L or less. The decomposition reaction of hydrogen peroxide by the iron-reducing catalyst can be suppressed by adjusting the mass concentration of the iron-reducing catalyst to 50000mg/L or less. Further, the sludge containing the iron compound in which iron ions are insolubilized by using the later-described concentration apparatus can be easily concentrated. Further, when the obtained concentrated suspension is returned to the reaction tank 11 by the suspension returning mechanism 32, the amount of the acid used for pH adjustment in the reaction tank 11 can be suppressed.

The shape of the iron reduction catalyst is preferably a powder from the viewpoint of catalyst efficiency. Further, since the catalyst is easily recovered, the particle size of the iron reduction catalyst is preferably 0.05 μm to 100 μm.

(Hydrogen peroxide concentration measuring part)

The hydrogen peroxide concentration measuring unit 19A is a measuring unit that measures the mass concentration of hydrogen peroxide with respect to the total amount of the reaction solution.

The method for measuring the mass concentration of hydrogen peroxide with respect to the total amount of the reaction solution includes the following methods: the reaction solution in the reaction tank 11 was sampled, and hydrogen peroxide in the sampled reaction solution was developed with potassium iodide and measured with an absorption spectrophotometer (for example, product name "Digital Pack Test" by Kyowa chemical Co., Ltd.). In addition, another method is a method of measuring the relative refractive index of the sampled reaction solution with a refractometer and calculating the mass concentration of hydrogen peroxide from the relative refractive index. In addition, there is a method of measuring the density of the sampled reaction solution with a densitometer and calculating the mass concentration of hydrogen peroxide from the density. Further, a method of measuring the mass concentration of hydrogen peroxide by an oxygen electrode method is also included.

In this embodiment, the hydrogen peroxide concentration measuring unit 19A may not be provided.

(insolubilization tank)

The insolubilization tank 21 is a tank for removing ferrous ions and ferric ions generated by fenton reaction from the reaction solution to insolubilize them to generate ferrous compounds and ferric compounds.

In the present embodiment, the "suspension" refers to a liquid produced by an insolubilization treatment in the insolubilization tank 21. The "suspension" in the present embodiment includes (a) treated water in which oxidizable contaminants are removed or reduced from wastewater of a treatment target, (b) a ferrous compound, (c) a ferric compound, and (d) sludge. In the present embodiment, the "suspension" is a "concentrated suspension" because the concentration device 22 is provided in the insolubilization tank 21. Thus, the insolubilization tank 21 of the present embodiment contains a "concentrated suspension".

In the present embodiment, the "concentrated suspension" refers to a liquid produced by the concentration process in the concentration device 22 of the insolubilization tank 21. The "concentrated suspension" in the present embodiment is a concentrated product of (b) a ferrous compound, (c) a ferric compound, and (d) sludge obtained by removing (a) treated water from the "suspension".

In the present embodiment, the ferrous ion and the ferric ion are not dissolved as iron compounds such as iron oxide, iron oxide in water, or iron chloride.

(second pH adjusting device)

The pH adjusting device 24 is a device for adjusting the pH in the insolubilization tank 21 by adding an alkali to the tank 21 in accordance with the pH value in the tank. The pH range in the insolubilization tank 21 can be adjusted so that ferrous ions and ferric ions are insolubilized. The pH in the insolubilization tank 21 is adjusted to be in the range of 6.0 to 10.0. The pH in the insolubilization tank 21 is preferably 7.0 or more and 9.0 or less, more preferably 7.5 or more and 8.5 or less, and still more preferably 7.8 or more and 8.3 or less.

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

Examples of the type of the base to be added include the same bases as those that can be added by the pH adjusting device 14.

When the oxidizable pollutant contained in the wastewater is an inorganic substance such as phosphorous acid or hypophosphorous acid, if calcium hydroxide is added as an alkali, the phosphorous acid in the reaction solution reacts with the calcium hydroxide to form a precipitate. Therefore, the precipitate containing phosphorous acid and the treated water can be separated by precipitation in the concentrating device 22 described later. In addition, orthophosphoric acid in the reaction solution reacts with ferric ions to form a precipitate. Therefore, the precipitate can be separated into the orthophosphoric acid-containing precipitate and the treated water in the concentrating device 22 described later.

Concentration device

The concentration device 22 is a device for solid-liquid separating a suspension in which a ferrous compound and a ferric compound are suspended into sludge containing an iron compound and an iron reduction catalyst and treated water to obtain a concentrated suspension in which the sludge is concentrated. The concentration device 22 employs a total 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, the separation can be performed with a high separation capacity.

The first membrane module 23 includes a filtration membrane such as a microfiltration membrane or an ultrafiltration membrane. Examples of the microfiltration membrane include a monolithic membrane. Examples of ultrafiltration membranes include: hollow fiber membranes, flat membranes, tubular membranes. Among them, a hollow fiber membrane is preferably used because of its high volume filling rate.

When the hollow fiber membrane is used as the first membrane module 23, the following materials may be used: cellulose, polyolefin, polysulfone, polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), and the like. Among them, the hollow fiber membrane is preferably polyvinylidene fluoride (PVDF) or Polytetrafluoroethylene (PTFE) in view of chemical resistance and strong pH change resistance.

When an integrated membrane is used as the first membrane module 23, a ceramic membrane is preferably used.

The average pore diameter of the micropores formed in the microfiltration membrane or ultrafiltration membrane is preferably 0.01 to 1.0. mu.m, more preferably 0.05 to 0.45. mu.m. If the average pore diameter of the micropores is not less than the lower limit, the pressure required for solid-liquid separation can be suppressed sufficiently. On the other hand, if the average pore diameter of the micropores is not more than the upper limit value, the sludge containing the iron compound and the iron reduction catalyst can be inhibited from leaking 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 concentrated suspension (hereinafter, sometimes referred to as "concentration ratio") is preferably concentrated to about 4 to 20 times when the mass concentration of the iron reduction catalyst to the total amount of the reaction solution is used as a standard. When the concentration ratio is 4 or more, the amount of the acid used for pH adjustment in the reaction tank 11 can be suppressed when the concentrated suspension is refluxed to the reaction tank 11 by a suspension refluxing mechanism 32 described later. Further, if the concentration ratio is 20 times or less, the concentration of the sludge by the concentration device 22 and the reflux of the concentrated suspension by the suspension reflux mechanism 32 are facilitated.

The third flow path 31 is connected to the first membrane module 23. The third flow path 31 is a flow path through which the treated water filtered by the microfiltration membrane or ultrafiltration membrane of the first membrane module 23 is discharged through the concentration device 22 and flows into the adjustment tank 41. The third flow path 31 is provided with a pump 31 a. Thereby, the treated water can be discharged from the insolubilization tank 21.

Further, it is preferable that a measuring device for measuring the total iron concentration in the treated water is provided in the third flow path 31. If it is judged by this measuring apparatus that the total iron concentration in the treated water is higher than 0.04ppm, appropriate measures are taken to optimize the pH value in the insolubilization tank 21, the solid-liquid separation in the first membrane module 23, or both.

The concentration device 22 may further include an aeration mechanism for cleaning the membrane surface disposed below the first membrane module 23. The aeration means may be any known means.

Further, the concentration device 22 may be combined with a separation mechanism other than the first membrane module 23. Other separating mechanisms may be mentioned, for example: sand filtration, pressurized flotation separation, centrifugal separation, belt filter press, sedimentation in sedimentation tank, etc.

(means for refluxing suspension)

The suspension reflux mechanism 32 is a mechanism for refluxing at least a part of the concentrated suspension obtained by concentrating the sludge from the insolubilization tank 21 to the reaction tank 11. The suspension refluxing mechanism 32 includes a fifth channel 33. The fifth channel 33 is a channel for discharging (supplying) at least a part of the concentrated suspension from the insolubilization tank 21 to the reaction tank 11.

The fifth flow path 33 is provided with a pump 33 a. This makes it possible to return at least a part of the concentrated suspension in the insolubilization tank 21 from the insolubilization tank 21 to the reaction tank 11.

When a plurality of reaction vessels 11 are arranged, it is preferable that the reaction vessel 11 in which at least a part of the concentrated suspension is returned from the insolubilization vessel 21 is a vessel other than the most downstream reaction vessel 11. The more upstream the reaction tank 11, which returns at least a part of the concentrated suspension, the more the trivalent iron compound in the concentrated suspension can be dissolved into trivalent iron ions, and the more the time from the reduction into ferrous ions to the fenton reaction can be extended. This allows the ferric iron compound in the refluxed concentrated suspension to be effectively reused in the fenton reaction.

In the present embodiment, the waste ferric iron compound can be reused in the water treatment by fenton reaction. Therefore, in addition to reducing the cost required for the treatment of the ferric iron compound, the amount of the iron reagent added by the iron reagent adding mechanism 15 can be reduced.

(catalyst concentration measuring part)

The catalyst concentration measuring unit 19B is a measuring unit for measuring the mass concentration of the iron reduction catalyst with respect to the total amount of the concentrated suspension. In the present embodiment, the concentration ratio can be determined from the mass concentration of the iron reduction catalyst relative to the total amount of the reaction solution and the measurement result of the catalyst concentration measuring unit 19B.

The method for measuring the mass concentration of the iron reduction catalyst with respect to the total amount of the concentrated suspension includes the following methods: the concentrated suspension in the insolubilization tank 21 was sampled, and the calculation was performed based on the amount of the concentrated suspension sampled and the mass of the residue obtained by drying the concentrated suspension. In addition, another method is a method of measuring the amount of scattered light when a sampled concentrated suspension is irradiated with light to measure the mass concentration of the iron reduction catalyst. The catalyst concentration measuring unit 19B is a device capable of performing such a measuring method.

In the present embodiment, the catalyst concentration measuring unit 19B is provided in the insolubilization tank 21, and may be provided in the suspension reflux mechanism 32.

(control section)

The controller 19C controls the hydrogen peroxide adding means 16 and the catalyst adding means 17 so that the ratio R is calculated according to the following equation₂A control unit of 1.9 to 100 inclusive.

R₂＝A₂/B₂

B₂Represents the mass concentration (unit: mg/L) of hydrogen peroxide calculated by dividing the total mass (unit: mg) of hydrogen peroxide added to the wastewater within a set time by the amount of the wastewater flowing into the reaction tank 11 within a set time.

The controller 19C is connected to at least the hydrogen peroxide addition mechanism 16 and the catalyst addition mechanism 17. The controller 19C determines the flow rate of the refluxed concentrated suspension and the addition amount of the iron reduction catalyst based on the measurement result of the catalyst concentration measuring unit 19B, and determines the concentration of hydrogen peroxide to be added and the flow rate of hydrogen peroxide (the addition amount of hydrogen peroxide) at the same time. Then, a predetermined amount of iron reduction catalyst is added to the reaction tank 11 by the catalyst adding means 17. Further, a predetermined amount of hydrogen peroxide is added to the reaction tank 11 by the hydrogen peroxide adding means 16.

When a plurality of reaction vessels 11 are arranged, the controller 19C controls the hydrogen peroxide addition mechanism 16 and the catalyst addition mechanism 17 in the uppermost reaction vessel 11 so that the ratio R calculated according to the above formula₂Is 1.9 or more and 100 or less.

(adjustment tank)

The adjustment tank 41 is a tank for storing the treated water supplied from the insolubilization tank 21 through the third flow path 31.

The seventh flow path 55 is connected to the adjustment tank 41. The seventh flow path 55 is a flow path through which the treated water stored in the adjustment tank 41 is discharged and flows into the separation device 42. The seventh flow path 55 is provided with a pump 55a and an adjusting valve 55 b. This allows the treated water to be discharged from the adjustment tank 41. Note that the regulating valve 55b may be omitted.

The separation device 42 is a device for separating the water membrane of the treatment water separated in the concentration step into oxidizable contaminants and filtered water contained in the treatment water. The separation apparatus 42 employs a cross-flow filtration system using the second membrane module 43. By adopting the cross-flow filtration method, the accumulation of oxidizable contaminants on the membrane surface can be suppressed, and the filtration flux can be maintained.

The second membrane module 43 includes a nanofiltration membrane or a reverse osmosis membrane. When a nanofiltration membrane is used for the second membrane module 43, the following materials may be used: polyethylene, polyamides containing aromatic polyamides or crosslinked polyamides, aliphatic amine polycondensates, heterocyclic polymers, polyvinyl alcohols, cellulose acetate polymers, and the like.

When a reverse osmosis membrane is used as the second membrane module 43, examples of the material include: polyamide, polysulfone, cellulose acetate and the like, and preferably polyamide containing aromatic polyamide or crosslinked aromatic polyamide.

The fourth flow path 51 is connected to the second membrane module 43. The fourth flow path 51 is a flow path through which filtered water that has passed through the nanofiltration membrane or reverse osmosis membrane of the second membrane module 43 is discharged from the separation device 42 and flows into the storage tank 61. By applying pressure to the filtration surface side (upstream side) of the second membrane module 43 by the pump 55a, the filtered water can be discharged from the adjustment tank 41, and membrane separation can be performed by the separation device 42. The adjustment of the flow rate can be performed by the output adjustment of the pump 55 a.

(storage tank)

The retention tank 61 is a tank that retains the filtered water supplied from the separation device 42 through the fourth flow path 51. The filtered water stored in the storage tank 61 may be diluted with industrial water or the like and discharged to a river or the like.

According to the water treatment apparatus 1 having the above-described configuration, in the water treatment using the fenton reaction accompanied by the reduction reaction of the ferric ion, the deactivation of the iron reduction catalyst used in the reduction reaction is suppressed, and the fenton reaction efficiency is excellent. That is, according to the water treatment apparatus 1, water treatment can be performed efficiently.

[ Water treatment method ]

The water treatment method of the present embodiment includes: an oxidation step (oxidation treatment), an insolubilization step, a concentration step, a separation step, a suspension reflux step, and a reduction step (reduction treatment).

In the present specification, the oxidation step and the reduction step correspond to the "reaction step" in the claims.

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, the pH of the wastewater containing oxidizable contaminants is first adjusted to 1.0 or more and 4.0 or less in the reaction tank 11. While in the ratio R calculated according to the following formula₁The fenton reaction is performed under the condition of 1.9 to 100 inclusive, and the oxidizable pollutant is oxidized (oxidation step).

R₁＝A₁/B₁

A₁The mass concentration of the iron-reducing catalyst relative to the total amount of the reaction solution (unit: mg/L) is shown.

B₁Represents the mass concentration (unit: mg/L) of hydrogen peroxide, which is calculated by dividing the total mass (unit: mg) of hydrogen peroxide added to wastewater within a set time by the amount (unit: L) of the wastewater treated within a set time in the oxidation step.

Next, in the insolubilization tank 21, the pH of the reaction solution obtained in the oxidation step is adjusted to 6.0 or more and 10.0 or less, and ferrous ions and ferric ions generated by fenton reaction are insolubilized to generate a ferrous compound and a ferric compound (insolubilization step).

Further, the suspension in which the ferrous compound and the ferric compound are suspended is subjected to solid-liquid separation by the concentration device 22 into sludge containing the ferric compound and the iron reduction catalyst and treated water, to obtain a concentrated suspension in which the sludge is concentrated (concentration step).

Next, the treated water separated in the concentration step is stored in the adjustment tank 41. The treated water is then flowed out of the conditioning tank 41 to the separator 42, and is subjected to membrane separation by the separator 42 (separation step). In the separation step, the treated water is separated into oxidizable contaminants and filtered water contained in the treated water. Further, the filtered water separated in the separation step is stored in the storage tank 61.

The suspension reflux mechanism 32 is configured to reflux the concentrated suspension concentrated in the concentration step from the insolubilization tank 21 to the reaction tank 11 (suspension reflux step). Further, the control unit 19C determines the flow rate of the refluxed suspension and the addition amount of the iron reduction catalyst based on the measurement result of the catalyst concentration measuring unit 19B, and determines the addition amount of hydrogen peroxide at the same time. Then, a predetermined amount of iron reduction catalyst is added to the reaction tank 11 by the catalyst adding means 17. Further, a predetermined amount of hydrogen peroxide is added to the reaction tank 11 by the hydrogen peroxide adding means 16.

The ferric iron compound in the suspension refluxed into the reaction tank 11 is dissolved as ferric ions in the reaction tank 11, and is reduced to ferrous ions by hydrogen peroxide and an iron reduction catalyst (reduction step).

According to the water treatment method having the above method, in the water treatment using the fenton reaction accompanied by the reduction reaction of the trivalent iron ion, the deactivation of the iron reduction catalyst used for the reduction reaction is suppressed, and the fenton reaction efficiency is excellent. That is, according to the water treatment method of the present embodiment, water treatment can be performed efficiently.

< second embodiment >

[ Water treatment apparatus ]

The structure of the water treatment apparatus 2 used in the water treatment method of the present embodiment will be described. Fig. 2 is a schematic configuration diagram of the water treatment apparatus 2 according to the present embodiment. As shown in fig. 2, the water treatment apparatus 2 has a structure partially similar to that of the water treatment apparatus 1 of the first embodiment. Thus, in the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

The water treatment apparatus 2 includes, in the reaction tank 11: a pH adjusting device 14, an iron reagent adding mechanism 15, a hydrogen peroxide adding mechanism 16, a catalyst adding mechanism 17, and a catalyst concentration measuring unit 18.

The water treatment apparatus 2 includes a suspension reflux mechanism 32 between the insolubilization tank 21 and the reaction tank 11. The suspension recirculation mechanism 32 is provided with a magnetic separator 34.

(catalyst concentration measuring part)

The catalyst concentration measuring unit 18 is a measuring unit that measures the mass concentration of the iron reduction catalyst with respect to the total amount of the reaction solution in the reaction tank 11. In the present embodiment, the iron reduction catalyst is added so that the mass concentration of the iron reduction catalyst with respect to the total amount of the reaction solution becomes a predetermined concentration, based on the measurement result of the catalyst concentration measuring unit 18. At the same time, an iron reagent is added so that the mass concentration ratio of the iron reduction catalyst and the iron reagent reaches a predetermined value. The predetermined concentration of the iron reduction catalyst means the concentration of the iron reduction catalyst required in the reduction reaction of the trivalent iron ions using the hydrogen peroxide in an amount corresponding to the target treated water quality. Further, the predetermined value of the mass concentration ratio of the iron reduction catalyst and the iron reagent means the mass concentration ratio of the iron reduction catalyst and the iron reagent capable of undergoing the reduction reaction of ferric ions.

The method for measuring the mass concentration of the iron reduction catalyst in the reaction tank 11 with respect to the total amount of the reaction solution includes the following methods: the reaction solution in the reaction tank 11 was sampled, and the mass of the residue obtained by sampling the reaction solution and drying the reaction solution was calculated. In addition, another method is a method of measuring scattered light of light transmitted through a reaction solution to be sampled. The catalyst concentration measuring unit 18 is a device capable of performing such a measuring method.

When a plurality of reaction vessels 11 are arranged, the catalyst concentration measuring unit 18 measures the mass concentration of the iron reduction catalyst in the most upstream reaction vessel 11.

(means for refluxing suspension)

The suspension reflux mechanism 32 is a mechanism for refluxing at least a part of the concentrated suspension obtained by concentrating the sludge from the insolubilization tank 21 to the reaction tank 11 through the magnetic separation device 34.

Magnetic separator

The magnetic separator 34 is a device for separating paramagnetic substances contained in the concentrated suspension from the concentrated suspension by using magnetism.

Conventionally, in the water treatment using the fenton reaction accompanied by the reduction reaction of the trivalent iron ion, the iron reduction catalyst is deactivated with the progress of the fenton reaction, and the efficiency of the fenton reaction may be lowered. In order to solve this problem, a method of recovering the iron reduction catalyst is employed in order to add a new iron reduction catalyst to the reaction tank. However, in the conventional water treatment, only the active iron reduction catalyst is recovered, and there is no method for efficiently recovering the deactivated iron reduction catalyst.

On the other hand, the present inventors have conducted intensive studies in order to solve the above problems, and as a result, have found that poorly soluble iron oxide crystals are formed on the surface of the iron reduction catalyst as the fenton reaction proceeds. The present inventors speculate that the iron reduction catalyst is deactivated because reaction sites on the surface of the iron reduction catalyst are lost due to the formation of poorly soluble iron oxide crystals.

In addition, iron oxide crystals were found, the main component of which contained ferroferric oxide or gamma-ferric oxide, or both. Further, it has been found that, since ferriferrous oxide and gamma-ferric oxide exhibit paramagnetism, the deactivated iron reduction catalyst can be efficiently taken out of the reaction system by utilizing magnetism.

The magnetic separation device 34 may employ a known magnetic separation device. Examples of the mechanism for generating magnetism include: a permanent magnet, an electromagnet or a superconducting magnet, and particularly a superconducting magnet is preferable because it can generate a strong magnetic field. The paramagnetic substances separated by the magnetic separation means 34 can be taken out from the magnetic separation means 34 to the outside by reducing the magnetic field strength of the magnetic separation means 34. In the case of a magnetic separator using an electromagnet or a superconducting magnet, the magnetic field strength can be reduced by reducing the power supply. The magnetic separation device 34 may also be provided with a known recovery device capable of recovering the paramagnetic substance separated by the magnetic separation device 34.

The magnetic separator 34 includes a sixth flow path 39. The sixth flow path 39 is a flow path for allowing (supplying) the concentrated suspension from which the paramagnetic substance is separated to flow into the reaction tank 11.

The magnetic separation device 34 may be installed in any cycle of the reaction tank 11 and the insolubilization tank 21. In the present embodiment, an example in which the magnetic separator 34 is provided in the suspension reflux mechanism 32 is shown, but the present invention is not limited thereto. The magnetic separator 34 may be provided in at least one selected from the reaction tank 11, the insolubilization tank 21 and the suspension reflux mechanism 32.

Since there is little concern about corrosion and the mass concentration of the iron reduction catalyst with respect to the total amount of the reaction solution can be easily controlled, it is preferably provided in the insolubilization tank 21 or the suspension reflux mechanism 32.

Further, as in the present embodiment, an intermediate tank (not shown) may be provided in the circulation of the reaction tank 11 and the insolubilization tank 21, and the magnetic separation device 34 may be provided in the intermediate tank.

According to the water treatment apparatus 2 having the above-described configuration, in the water treatment utilizing the fenton reaction accompanied by the reduction reaction of the ferric ion, the deactivated iron reduction catalyst can be efficiently taken out of the reaction system. That is, according to the water treatment apparatus 2, water treatment can be performed efficiently.

[ Water treatment method ]

The water treatment method of the present embodiment is the same as the water treatment method of the first embodiment in a part of the steps. The water treatment method of the present embodiment is different from the water treatment method of the first embodiment in that it includes a magnetic separation step.

In the magnetic separation step of the present embodiment, in the suspension reflux step, the paramagnetic substance contained in the concentrated suspension is separated from the concentrated suspension by magnetism using the magnetic separation device 34 provided in the suspension reflux mechanism 32.

According to the water treatment method having the above method, in the water treatment utilizing the fenton reaction accompanied by the reduction reaction of the ferric ion, the deactivated iron reduction catalyst can be efficiently taken out of the reaction system. That is, according to the water treatment method of the present embodiment, water treatment can be performed efficiently.

The water treatment apparatus and the water treatment method according to the present embodiment are not limited to the above-described embodiments. For example, in the water treatment apparatus 1 or the water treatment apparatus 2, the separation step may be omitted in which the adjustment tank 41 and the separation device 42 are not performed. In this case, the treated water passing through the concentration device 22 may be directly stored in the storage tank 61.

For example, in the above embodiment, the sludge concentration method using the concentration device 22 is not necessarily a method using the first membrane module 23. For example, the sand filtration, the pressure flotation separation, the centrifugal separation, the belt filter press, the sedimentation in the sedimentation tank, and the like can be used.

Further, the example in which the concentration device 22 is provided in the insolubilization tank 21 is shown, and the concentration device 22 may not be provided in the insolubilization tank 21. In this case, another tank may be disposed between the insolubilization tank 21 and the adjustment tank 41, and the concentration device 22 may be provided in this tank. At this time, "suspension" is present in the insolubilization tank 21 and "concentrated suspension" is present in the tank provided with the concentration device 22. The magnetic separator 34 of the present embodiment magnetically separates paramagnetic substances contained in either or both of the suspension and the concentrated suspension.

When the concentration device 22 is not installed in the insolubilization tank 21, the first membrane module 23 may have the following structure. For example, the membrane casing is fixed with a filter membrane (microfiltration or ultrafiltration) at an upstream side and a downstream side thereof. The upstream side of the filter membrane in the membrane housing is connected to a storage tank storing a suspension containing sludge containing an iron compound and an iron reduction catalyst and treated water through a circulation flow path, and the downstream side of the filter membrane may be connected to a suction pump.

The water treatment apparatus 1 or the water treatment apparatus 2 may omit the suspension refluxing step performed by the suspension refluxing mechanism 32.

The reaction tank 11 according to the first embodiment may be provided with the catalyst concentration measuring unit 18 according to the second embodiment. In this case, the controller 19C can determine the flow rate of the returned concentrated suspension and the amount of addition of the iron reduction catalyst based on the measurement results of the catalyst concentration measuring unit 18 and the catalyst concentration measuring unit 19B, and can determine the concentration of the hydrogen peroxide to be added and the flow rate of the hydrogen peroxide (the amount of addition of the hydrogen peroxide) at the same time. Thus, the controller 19C easily controls the hydrogen peroxide adding mechanism 16 and the catalyst adding mechanism 17 so that the ratio R is calculated according to the following equation₂Is 1.9 or more and 100 or less.

R₂＝A₂/B₂

A₂The mass concentration (unit: mg/L) of the iron reduction catalyst in the reaction vessel 11 relative to the total amount of the reaction mixture is shown.

B₂Represents the mass concentration (unit: mg/L) of hydrogen peroxide, which is calculated by dividing the total mass (unit: mg) of hydrogen peroxide added to the wastewater within a set time by the amount (unit: L) of the wastewater flowing into the reaction tank 11 within a set time.

In such a management ratio R₂In the water treatment apparatus within the above range, deactivation of the iron reduction catalyst can be suppressed. This water treatment apparatus can effectively perform water treatment.

The suspension recirculation mechanism 32 according to the first embodiment may include the magnetic separator 34 according to the second embodiment. This is considered to be one of the causes of the low efficiency of the fenton reaction, because the deactivated iron reduction catalyst can be efficiently separated and reduced from the reaction tank 11. This water treatment apparatus can effectively perform water treatment.

The water treatment apparatus 2 according to the second embodiment may include the controller 19C according to the first embodiment. In this case, the controller 19C can confirm the amount of the iron reduction catalyst added and the concentration of the hydrogen peroxide added and the flow rate of the hydrogen peroxide (the amount of hydrogen peroxide added) based on the measurement result of the catalyst concentration measuring unit 18. Then, a predetermined amount of iron reduction catalyst is added to the reaction tank 11 by the catalyst adding means 17. Further, a predetermined amount of hydrogen peroxide is added to the reaction tank 11 by the hydrogen peroxide adding means 16.

The reaction tank 11 of the second embodiment may be provided with the hydrogen peroxide concentration measuring unit 19A of the first embodiment. The insolubilization tank 21 according to the second embodiment may be provided with a catalyst concentration measuring unit 19B according to the first embodiment. This enables hydrogen peroxide to react with the iron reduction catalyst at a more appropriate ratio.

Examples

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following. The same configuration as that of the water treatment apparatus 1 shown in fig. 1 will be described with the same names.

[ calculation of the removal Rate of Total organic carbon ]

The removal rate of total organic carbon (hereinafter, sometimes referred to as "total organic carbon" as "TOC") is one of the indicators representing the activity of the iron reduction catalyst, and it is considered that the higher the removal rate of TOC, the higher the activity of the iron reduction catalyst. The TOC removal rates of the examples and comparative examples were calculated from the TOC concentration in the raw water (wastewater model) and the TOC concentration in the treated water according to the formula (S1).

[ number 1]

The TOC concentration in the treated water was measured by a combustion method total organic carbon analyzer (model "TOC-300V", manufactured by Mitsubishi chemical ANALYTECH, K.K.) in accordance with JIS K0102 "22. organic carbon (TOC)".

< evaluation of lifetime of iron reduction catalyst >

The water treatment of raw water was repeated every day using the water treatment apparatuses of examples and comparative examples, and treated water was sampled every day. The time until the TOC removal rate of the obtained treated water was less than 50% (hereinafter, sometimes referred to as "deactivation time") was calculated. The longer this time, the more the deactivation of the iron reduction catalyst is suppressed, and the longer the life of the iron reduction catalyst is considered.

The following materials were used for each reagent.

Iron reagent: iron (II) sulfate heptahydrate (FeSO)₄·7H₂O)

Iron reduction catalyst: activated carbon (DiaFellow CT, manufactured by Mitsubishi chemical Water solution Co., Ltd.)

[ example 1]

A water treatment device having the following structure was produced: a first reaction tank, a second reaction tank connected in series with the first reaction tank, and an insolubilization tank provided with a concentration device. In this example, the reaction tank in the claims is composed of a first reaction tank and a second reaction tank. Further, dimethyl sulfoxide (DMSO) was added to pure water to 200mg/L (total organic carbon content: 65mg/L), and the mixture was dissolved to prepare a solution as a wastewater model. It was confirmed that DMSO was not substantially removed by adsorption on activated carbon. The wastewater model is treated by the prepared water treatment device.

In the following examples, the amount of the mixed liquid in which the hydrogen peroxide and the iron reduction catalyst are mixed, the amount of the reaction liquid after the mixed liquid is reacted, the amount of the acid or alkali used for pH adjustment of the waste water model, and the amount of the iron reagent are the same. Thus, the amount of the mixed solution was used as the amount of the reaction solution in the calculation of each mass concentration.

An ultrafiltration membrane (manufactured by Mitsubishi-yang hydrolysis solution Co., Ltd., nominal pore diameter of 0.05 μm) was used as the membrane provided with the first membrane module.

First, raw water flows (is supplied) into the first reaction tank, and overflows to be supplied to the second reaction tank and the insolubilization tank in this order. The residence time in which the flow rate of the concentrated suspension refluxed from the insolubilization tank by the suspension reflux mechanism was not taken into consideration was set to 4 hours in the first reaction tank, 1 hour in the second reaction tank, and 1 hour in the insolubilization tank. Further, the pH value in the first reaction tank was adjusted to 2.9 with sulfuric acid. On the other hand, the pH in the insolubilization tank was adjusted to 8.0 with sodium hydroxide.

Hydrogen peroxide was added to the first reaction tank so that the mass concentration of hydrogen peroxide relative to the total amount of raw water became 600 mg/L.

Further, an iron reagent was added to the first reaction vessel and the second reaction vessel so that the concentration of the mass of the iron reagent to the total amount of the reaction solution in the first reaction vessel and the second reaction vessel became 1200mg/L (240 mg/L in terms of ferrous ions).

Further, an iron reduction catalyst was added to either or both of the first reaction tank and the second reaction tank so that the mass concentration of the iron reduction catalyst relative to the total amount of the reaction liquid in the first reaction tank and the second reaction tank became 2000 mg/L.

In example 1, the ratio R was calculated by the following formula₂Is 3.3 (A)₂＝2000mg/L、B₂＝600mg/L)。

R₂＝A₂/B₂

A₂The mass concentration of the iron reduction catalyst in the reaction vessel relative to the total amount of the reaction mixture (unit: mg/L) is shown.

B₂Represents the mass concentration (unit: mg/L) of hydrogen peroxide, which is calculated by dividing the total mass (unit: mg) of hydrogen peroxide added to the wastewater in a set time by the amount (unit: L) of the wastewater flowing into the reaction tank in a set time (10 minutes).

Further, an iron reagent was added to the insolubilization tank so that the mass concentration of the iron reagent with respect to the total amount of the concentrated suspension in the insolubilization tank became 12000mg/L (2400 mg/L in terms of ferrous ions). Further, an iron reduction catalyst was added to the insolubilization tank so that the mass concentration of the iron reduction catalyst with respect to the total amount of the concentrated suspension in the insolubilization tank became 20000 mg/L. Then, the sludge containing the ferric iron compound and the iron reduction catalyst was returned from the insolubilization tank to the first reaction tank so that the mass concentration of the iron reduction catalyst with respect to the total amount of the reaction solution in the first reaction tank and the second reaction tank was maintained at 2000 mg/L.

The wastewater model was subjected to water treatment using the water treatment apparatus having the above-described structure, with the result that the time until the TOC removal rate in the treated water was less than 50% was 15 days.

[ example 2]

The iron reagent was added to the first reaction vessel and the second reaction vessel so that the mass concentration of the iron reagent relative to the total amount of the reaction solution in the first reaction vessel and the second reaction vessel became 600mg/L (120 mg/L in terms of ferrous ions).

In example 2, the ratio R calculated according to the above formula₂Is 3.3 (A)₂＝2000mg/L、B₂＝600mg/L)。

Further, an iron reagent was added to the insolubilization tank so that the mass concentration of the iron reagent with respect to the total amount of the concentrated suspension in the insolubilization tank became 6000mg/L (1200 mg/L in terms of ferrous ions). The same operation as in example 1 was carried out except for the above-mentioned operation.

The wastewater model was subjected to water treatment using the water treatment apparatus having the above-described structure, with the result that the time until the TOC removal rate in the treated water was less than 50% was 8 days.

[ example 3]

The iron reagent was added to the first reaction vessel and the second reaction vessel so that the mass concentration of the iron reagent was 4500mg/L (900 mg/L in terms of ferrous ions) relative to the total amount of the reaction solution in the first reaction vessel and the second reaction vessel. Further, an iron reduction catalyst was added to either or both of the first reaction tank and the second reaction tank so that the mass concentration of the iron reduction catalyst relative to the total amount of the reaction liquid in the first reaction tank and the second reaction tank became 1500 mg/L.

In example 3, the ratio R calculated according to the above formula₂Is 2.5 (A)₂＝1500mg/L、B₂＝600mg/L)。

Further, an iron reagent was added to the insolubilization tank so that the mass concentration of the iron reagent relative to the total amount of the concentrated suspension in the insolubilization tank became 45000mg/L (9000 mg/L in terms of ferrous ions). Further, an iron reduction catalyst was added to the insolubilization tank so that the mass concentration of the iron reduction catalyst with respect to the total amount of the concentrated suspension in the insolubilization tank became 15000 mg/L. The same operation as in example 1 was carried out except for the above-mentioned operation.

The wastewater model was subjected to water treatment using the water treatment apparatus having the above-described structure, with the result that the time until the TOC removal rate in the treated water was less than 50% was 13 days.

[ example 4]

The iron reagent was added to the first reaction vessel and the second reaction vessel so that the mass concentration of the iron reagent relative to the total amount of the reaction solution in the first reaction vessel and the second reaction vessel became 720mg/L (144 mg/L in terms of ferrous ions).

In example 4, the ratio R was calculated according to the above formula₂Is 2.0 (A)₂＝1200mg/L、B₂＝600mg/L)。

Further, an iron reagent was added to the insolubilization tank so that the mass concentration of the iron reagent was 7200mg/L (1440 mg/L in terms of ferrous ions) based on the total amount of the concentrated suspension in the insolubilization tank. The same operation as in example 1 was carried out except for the above-mentioned operation.

Comparative example 1

The iron reagent was added to the first reaction vessel and the second reaction vessel so that the mass concentration of the iron reagent relative to the total amount of the reaction solution in the first reaction vessel and the second reaction vessel became 600mg/L (120 mg/L in terms of ferrous ions). Further, an iron reduction catalyst is added to either or both of the first reaction tank and the second reaction tank so that the mass concentration of the iron reduction catalyst with respect to the total amount of the reaction liquid in the first reaction tank and the second reaction tank becomes 1000 mg/L.

In comparative example 1, the ratio R calculated according to the above formula₂Is 1.7 (A)₂＝1000mg/L、B₂＝600mg/L)。

Further, an iron reagent was added to the insolubilization tank so that the mass concentration of the iron reagent with respect to the total amount of the suspension in the insolubilization tank became 6000mg/L (1200 mg/L in terms of ferrous ions). Further, an iron reduction catalyst was added to the insolubilization tank so that the mass concentration of the iron reduction catalyst relative to the total amount of the suspension in the insolubilization tank became 10000 mg/L. The same operation as in example 1 was carried out except for the above-mentioned operation.

The wastewater model was subjected to water treatment using the water treatment apparatus having the above-described structure, with the result that the time until the TOC removal rate in the treated water was less than 50% was 2 days.

Comparative example 2

An iron reduction catalyst is added to either or both of the first reaction tank and the second reaction tank so that the mass concentration of the iron reduction catalyst relative to the total amount of the reaction liquid in the first reaction tank and the second reaction tank is 1000 mg/L.

In comparative example 2, the ratio R was calculated according to the above formula₂Is 1.7 (A)₂＝1000mg/L、B₂＝600mg/L)。

Adding an iron reduction catalyst into the insolubilization tank so that the mass concentration of the iron reduction catalyst relative to the total suspension in the insolubilization tank reaches 10000 mg/L. The same operation as in example 1 was carried out except for the above-mentioned operation.

The results of examples and comparative examples are shown in table 1.

[ Table 1]

As shown in Table 1, the ratio R calculated according to the above formula₂In examples 1 to 4 in which R is 1.9 or more and 100 or less, the ratio to R is₂The deactivation time was prolonged in comparative example 1, which was less than 1.9, as compared with comparative example 2. That is, in examples 1 to 4 to which one embodiment of the present invention was applied, deactivation of the iron reduction catalyst was suppressed, and the fenton reaction efficiency was excellent.

Also, from the results of example 1 and example 2, and the above ratio R₂Is 1.9 or more and 100 or less, it is considered that the deactivation time is prolonged by increasing the mass concentration of the iron reagent with respect to the total amount of the reaction solution. That is, in example 1, the deactivation of the iron reduction catalyst was more suppressed than in example 2, and the fenton reaction efficiency was more excellent.

The above results show that the present invention has utility.

Claims

1. A water treatment method for wastewater containing oxidizable pollutants, comprising the following steps (i) to (iii):

(iii) a concentration step of separating treated water from the suspension to obtain a concentrated suspension in which sludge containing a ferrous compound and a ferric compound is concentrated;

(A) the pH value of the wastewater is more than 1 and less than 4

R₁＝A₁/B₁

wherein A is₁The mass concentration of the iron reduction catalyst relative to the total amount of the reaction solution is expressed in mg/L,

B₁(ii) represents the mass concentration of the hydrogen peroxide calculated by dividing the total mass of the hydrogen peroxide added to the wastewater in a set time by the amount of the wastewater treated in the set time in step (i), wherein the mass concentration of the hydrogen peroxide is in mg/L, the amount of the wastewater is in L, and the total mass of the hydrogen peroxide is in mg.

2. The water treatment method according to claim 1, comprising a suspension refluxing step of refluxing either or both of at least a part of the suspension and at least a part of the concentrated suspension to the step (i).

3. The water treatment method according to claim 1 or 2, comprising a magnetic separation step of separating paramagnetic substances contained in either one or both of the suspension and the concentrated suspension by magnetism.

4. The water treatment method according to claim 1 or 2, wherein the iron reduction catalyst is at least one selected from the group consisting of activated carbon and zeolite.

5. The method of water treatment according to claim 1 or 2, wherein in the step (i), the pH of the wastewater is adjusted to 1 or more and 4 or less using an acid.

6. The method for treating water according to claim 1 or 2, wherein a ferrous salt or a ferrous oxide is added in the step (i).

7. The water treatment method according to claim 1 or 2, wherein in the step (iii), the concentrated suspension is obtained using a filter membrane.

8. The water treatment method according to claim 1 or 2, comprising a separation step of separating the treated water into the oxidizable pollutant and filtered water contained in the treated water by using a nanofiltration membrane or a reverse osmosis membrane.

9. A water treatment device comprising the following (1) to (3):

R₂＝A₂/B₂

wherein A is₂Represents the mass concentration of the iron reduction catalyst relative to the total amount of the reaction solution in the reaction tank, and the unit thereof is mg/L,

B₂represents a mass concentration of hydrogen peroxide calculated by dividing a total mass of hydrogen peroxide added to the wastewater in a set time by an amount of the wastewater flowing into the reaction tank in a set time, the mass concentration of hydrogen peroxide being in mg/L, the amount of the wastewater being in L, the total mass of hydrogen peroxide being in mg;

(3) and a concentration device for separating the treated water from the suspension to obtain a concentrated suspension in which the sludge containing the ferrous compound and the ferric compound is concentrated.

10. The water treatment apparatus according to claim 9, further comprising a suspension returning mechanism for returning either one or both of at least a part of the suspension and at least a part of the concentrated suspension to the reaction tank.

11. The water treatment apparatus according to claim 9 or 10, further comprising a magnetic separation device for magnetically separating paramagnetic substances contained in either one or both of the suspension and the concentrated suspension.

12. The water treatment apparatus according to claim 10 or 11, comprising:

a control section that controls the ratio R₂1.9 or more and 100 or less;

13. The water treatment apparatus according to claim 9 or 10, further comprising a catalyst adding means for adding the iron reduction catalyst to the reaction tank.

14. The water treatment apparatus according to claim 9 or 10, comprising:

15. The water treatment apparatus of claim 14, wherein the acid is sulfuric acid or hydrochloric acid.

16. The water treatment apparatus according to claim 9 or 10, wherein the concentration apparatus has a filter membrane, and the concentrated suspension is obtained using the filter membrane.

17. The water treatment apparatus according to claim 9 or 10, wherein the concentration device is provided in the insolubilization tank.

18. The water treatment apparatus according to claim 9 or 10, further comprising a separation device having a nanofiltration membrane or a reverse osmosis membrane, wherein the treated water is separated into the oxidizable pollutant and filtered water contained in the treated water by using the nanofiltration membrane or the reverse osmosis membrane.