JP2023167782A - Method and apparatus for treating wastewater containing organic chelating agent and heavy metals - Google Patents

Abstract

To provide a method for removing heavy metals that is applicable to wastewater containing heavy metals and chelating agents with biological treatment inhibitory effects.SOLUTION: There is provided a method for treating wastewater containing organic chelating agents and heavy metals, in which (1) a Fenton reagent containing hydrogen peroxide and ferrous chloride at a molar equivalent ratio of Fe/H2O2 of 0.10 to 0.26 is added to the wastewater, (2) a calcium source is added so that Ca is at a molar equivalent ratio of 0.15 to 0.45 times or more with respect to Fe in the Fenton reagent, (3) the wastewater to which the Fenton reagent and calcium source are added is treated at a pH of 9.0 to 10.5 or less, and (4) an amphoteric polymer flocculant is added to the wastewater after aeration treatment, and solid-liquid separation is performed under alkaline conditions of pH between 9.0 and 10.5.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method and apparatus for treating wastewater containing an organic chelating agent and heavy metals.

Plating processes are essential when manufacturing products such as semiconductors, electronic components, medical equipment, bio-equipment, and decorative items. The waste liquid discharged from the plating process contains various harmful substances and organic substances including heavy metals. As a treatment for heavy metals in waste liquid, it is common to insolubilize the heavy metals under alkaline conditions and perform a coagulation-precipitation treatment. However, in wastewater that contains chelating agents in addition to heavy metals, the heavy metals are combined with the chelating agent, so the heavy metals cannot be insolubilized, and heavy metals cannot be removed by coagulation and precipitation under alkaline conditions. I can't.

As a method for treating waste liquid containing a chelating agent, Japanese Patent Laid-Open No. 2007-125482 (Patent Document 1) discloses that, before coagulation and precipitation treatment in which a calcium compound is added to form an insolubilized substance, a chelating agent is extracted from raw water by microorganisms. A method has been proposed to decompose the organic components derived from the plant. However, if the heavy metals and chelating agents contained in the waste liquid have a biological inhibitory effect, biological treatment before coagulation and sedimentation treatment is not effective.

Fenton treatment using a Fenton reagent is known as a treatment for decomposing contaminants that cannot be removed by biological treatment or flocculation treatment. Fenton's reagent is a reagent with strong oxidizing power that is made by adding ferrous salt to hydrogen peroxide solution. Generally, Fenton's reagent is added to wastewater containing difficult-to-biodegradable organic substances under acidic conditions to generate hydroxyl radicals and decompose the organic substances. JP-A No. 2007-130518 (Patent Document 2) states that the conditions for general Fenton treatment are pH 2 to 4, H ₂ O ₂ [mg/L]/TOC of treated water [mg/L] = 3 to 4. 6. It is stated that Fe [mg/L]/TOC of treated water [mg/L] = 3.5 to 7.

This publication discloses the use of the Fenton method to remove fluorine and/or phosphorus from wastewater containing a chelating agent. By providing a step of Fenton treatment in the presence of ferrous ions and hydrogen peroxide before acting with a calcium compound to form an insolubilized product, the formation of calcium chelate is prevented and the interaction with fluorine and/or phosphorus is prevented. Calcium compounds can be formed, but the chemical costs are high because a large amount of ferrous ions are required, and a large amount of iron (III) hydroxide sludge is generated due to the added ferrous salts, so the chemical costs are high. A method is described in which ferrous ions are generated by irradiating light while bringing ferric ions or ferric salts into contact with a photocatalyst in order to reduce the amount of sludge and prevent the generation of a large amount of sludge. The publication states that the pH during Fenton treatment should be 2 to 4, the pH when adding calcium salt should be 3 to 12, and that an aluminum-based inorganic flocculant should be added to the water to be treated after the calcium compound reaction. It is described that the pH is adjusted to 5 to 8.5. In order to prevent the addition of a large amount of ferrous salt and the generation of a large amount of sludge, it is necessary to irradiate the photocatalyst with light while bringing it into contact with the photocatalyst, which complicates the processing equipment. Furthermore, a large amount of calcium salt is required to insolubilize fluorine and/or phosphorus. The use of large amounts of calcium salts increases the risk of calcium scale development.

The method for treating wastewater containing heavy metals, chelating agents, and phosphorus includes the Fenton treatment process in which ferrous iron is added to the wastewater and Fenton treatment is performed in the presence of hydrogen peroxide, and the Fenton treatment process involves adding sodium hydroxide to the Fenton-treated water. The process includes an aeration process in which peroxide is removed by adding water peroxide, and a solid-liquid separation process in which a polymer flocculant is added after the aeration treatment to adjust the pH and cause the flocculation to separate solid and liquid. After separation, it is processed in separate processing equipment. To remove phosphorus, it is necessary to add large amounts of ferrous iron, which increases sludge production. In order to reduce the amount of ferrous salt added, it is necessary to remove phosphorus in advance, which requires separate processing equipment. When adding a polymer flocculant to flocculate, it is possible to treat phosphorus using the ferrous salt used in Fenton treatment if the pH is set to 4.5 to 5.0, but on the alkaline side Heavy metals remain that need to be disposed of. Although heavy metals can be removed by adjusting the pH to 9.0 to 10.0, phosphorus remains. In either case, separate processing equipment is required to remove residual phosphorus or heavy metals. Therefore, conventional processing equipment requires additional processing equipment, making the overall equipment larger and more complex.

Japanese Patent Application Publication No. 2007-125482 Japanese Patent Application Publication No. 2007-130518

In the etching process and electroless nickel plating process necessary for manufacturing semiconductors, wiring boards, electronic components, etc., wastewater containing heavy metals such as copper and nickel and phosphorus is generated. In addition, wastewater containing chelating agents is generated in other processes, and factory wastewater contains heavy metals, phosphorus, and chelating agents. In order to remove heavy metals from such wastewater, it was found that if a chelating agent for flocculation treatment, which is different from the chelating agent contained in the wastewater, was added, a large amount of chelating agent would be required, and phosphorus could not be removed. . In the case of wastewater containing a cation chelating agent, heavy metals are separated by adding calcium salts or magnesium salts that bind more selectively to the cation chelating agent than to heavy metals that form complexes with the cation chelating agent. It can be made insoluble. However, heavy metals that form a complex with a strong chelating agent will not be replaced by the heavy metal even if calcium salts or magnesium salts are added, and the heavy metal will remain complexed with the chelating agent and will not separate. Therefore, it was found that insolubilization could not be achieved. Furthermore, even if substitution is possible, large amounts of calcium and magnesium salts are required, resulting in scaling problems.

In order to treat the chelating agent, we investigated a method of biological treatment before the coagulation and sedimentation treatment proposed in Patent Document 1, but it is difficult to treat wastewater or persistent organic matter that contains copper and chelating agents, which have a biological inhibitory effect. It was found that this cannot be applied to wastewater containing

When Fenton treatment was investigated to treat the chelating agent, it was confirmed that heavy metals could be insolubilized and that heavy metals could be removed by coagulation and precipitation treatment under alkaline conditions. However, it was found that in order to remove phosphorus, coagulation and precipitation treatment under acidic conditions was necessary, and a large amount of iron reagent needed to be used.

An object of the present invention is to provide a method for removing heavy metals that can be applied to wastewater containing heavy metals and chelating agents that inhibit biological treatment.

Another object of the present invention is to provide a method for removing heavy metals from wastewater containing heavy metals and a chelating agent, which can suppress the formation of calcium scale.

Furthermore, the present invention aims to provide a method for removing heavy metals from wastewater containing heavy metals and chelating agents, which is capable of removing phosphorus.

Another object of the present invention is to provide a method for removing heavy metals from wastewater containing heavy metals and chelating agents, which can reduce the amount of reagents used, the amount of sludge generated, and the volume of sludge.

Furthermore, it is an object of the present invention to provide a downsized processing device that can remove heavy metals and phosphorus in the same process.

As a result of intensive research to solve the above problems, the present inventor decomposed the organic chelating agent by using Fenton's reagent, separated the heavy metals bound to the organic chelating agent, and made the heavy metals insolubilized. They found that the remaining chelating agent can be treated by adding and binding calcium ions, and have completed the present invention.

According to the present invention, a processing method and a processing apparatus according to the following aspects are provided.
[1] A method for treating wastewater containing an organic chelating agent and heavy metals, comprising:
(1) Adding a Fenton reagent containing hydrogen peroxide and ferrous salt at a Fe/H ₂ O ₂ molar equivalent ratio of 0.10 or more and less than 0.26 to the wastewater,
(2) Adding a calcium source so that the molar equivalent ratio of Ca to Fe in the Fenton reagent is 0.15 times or more and 0.45 times or less,
(3) aerating the wastewater to which the Fenton reagent and calcium source have been added under alkaline conditions with a pH of 9.0 or more and 10.5 or less;
(4) A method for treating wastewater, which comprises adding an amphoteric polymer flocculant to wastewater after aeration treatment, and performing solid-liquid separation under alkaline conditions with a pH of 9.0 or more and 10.5 or less.
[2] The method for treating wastewater according to [1] above, wherein the heavy metals include one or more selected from nickel, copper, lead, zinc, manganese, and cadmium.
[3] The method for treating wastewater according to [1] or [2] above, wherein the wastewater further contains phosphorus.
[4] A treatment device for wastewater containing an organic chelating agent and heavy metals,
Fenton reagent addition means for adding a Fenton reagent containing hydrogen peroxide and ferrous salt at a molar equivalent ratio of Fe/H ₂ O ₂ of 0.10 or more and less than 0.26 to the wastewater;
A calcium source addition means for adding a calcium source so that the molar equivalent ratio of Ca to Fe in the Fenton reagent is 0.15 times or more and 0.45 times or less;
a Fenton treatment tank for treating wastewater to which at least Fenton reagent has been added; and an aeration treatment tank for aerating the wastewater after Fenton treatment under alkaline conditions with a pH of 9.0 or more and 10.5 or less;
an amphoteric polymer flocculant addition means for adding an amphoteric polymer flocculant to wastewater after aeration treatment;
a solid-liquid separator that separates wastewater containing insolubilized heavy metals after coagulation treatment into solid-liquid under alkaline conditions with a pH of 9.0 or more and 10.5 or less;
A wastewater treatment device characterized by comprising:

The wastewater treatment method of the present invention can also be applied to wastewater containing a chelating agent and heavy metals that have a bioinhibitory effect, and can remove heavy metals from the wastewater.

By regulating the amount of calcium added to the iron added as the Fenton reagent, the formation of calcium scale can be suppressed. Further, since the Fenton treatment is performed at a pH of 4.0 or lower, the production of calcium carbonate can be suppressed by adding calcium to the Fenton treatment solution in which few carbonate ions remain.

By setting the pH at the time of solid-liquid separation to an alkaline condition of 9.0 or more and 10.5 or less, the phosphorus removal effect due to the combination of ferric ions and phosphorus ions after Fenton treatment can be maintained. . Furthermore, by adding a calcium source in addition to the Fenton reagent, calcium phosphate is formed, making it possible to remove phosphorus with high efficiency. Furthermore, when a chelating agent that tends to form a complex with calcium remains in the Fenton treatment solution, adding calcium has the effect of forming a calcium complex, that is, masking the chelating agent with calcium.

Furthermore, the amount of iron added as a Fenton reagent can be reduced, the amount of sludge generated can be reduced, and the volume of sludge can be reduced.

According to the treatment method of the present invention, the chelating agent, heavy metals, and phosphorus can be treated in the same process, so the equipment configuration can be minimized.

FIG. 2 is an explanatory diagram showing a processing flow for explaining the processing method of the present invention. FIG. 1 is a schematic explanatory diagram showing the device configuration of a processing device of the present invention. FIG. 2 is an explanatory diagram showing a processing flow of only Fenton processing used in Comparative Examples 1 and 2. A graph showing the relationship between Ca/Fe and the concentration (residual) of Cu, Ni, and P in the treated water in Examples 1 to 3.

Preferred embodiment

Hereinafter, the present invention will be described in further detail with reference to the accompanying drawings, but the present invention is not limited thereto.

The method for treating wastewater containing an organic chelating agent and heavy metals of the present invention includes:
(1) Adding a Fenton reagent containing hydrogen peroxide and ferrous salt at a Fe/H ₂ O ₂ molar equivalent ratio of 0.11 to 0.19 to the wastewater,
(2) Adding a calcium source so that the molar equivalent ratio of Ca to Fe in the Fenton reagent is 0.15 times or more and 0.45 times or less,
(3) aerating the wastewater to which the Fenton reagent and calcium source have been added under alkaline conditions with a pH of 9.0 or more and 10.5 or less;
(4) It is characterized by adding an amphoteric polymer flocculant to the wastewater after the aeration treatment, and performing solid-liquid separation under alkaline conditions with a pH of 9.0 or more and 10.5 or less.

FIG. 1 shows a processing flow of the present invention. A Fenton reagent is added to the wastewater to perform Fenton treatment, a calcium source is added and then aeration treatment is performed, and then an amphoteric polymer flocculant is added to cause flocculation, followed by solid-liquid separation.

The Fenton treatment utilizes the Fenton reaction, in which hydrogen peroxide (H ₂ O ₂ ) is decomposed by metal ions such as ferrous ions (Fe ²⁺ ) into hydroxy radicals (HO・) and hydroxy ions (OH ⁻ ). This is a method of oxidizing organic substances using radicals (HO.).

In the treatment method of the present invention, by reacting wastewater containing an organic chelating agent and heavy metals with Fenton's reagent, hydroxyl radicals (HO) generated by the Fenton reaction oxidize and decompose the organic chelating agent to remove heavy metals. By reducing or eliminating the chelating effect on metals, heavy metals are dissociated and made insoluble. Hydroxy radicals (HO.) change an organic chelating agent into a form that easily forms a complex with calcium, and then add a calcium source to form a calcium complex, thereby dissociating and insolubilizing heavy metals. By adding a calcium source after the Fenton treatment, calcium ions (Ca ²⁺ ) combine with phosphorus in the wastewater to form calcium salts such as hydroxyapatite (HAP), making the phosphorus insoluble. Next, by adding a polymer flocculant, the insolubilized heavy metals and phosphorus are flocculated, solid-liquid separated, and removed from the wastewater.

Fenton's reagent contains hydrogen peroxide and a ferrous salt at a Fe/H ₂ O ₂ molar equivalent ratio of 0.10 or more, preferably more than 0.10, more preferably 0.11 or more and less than 0.26, preferably It is contained at 0.19 or less, more preferably at 0.13 or less. When the molar equivalent ratio of Fe/H ₂ O ₂ is within this range, heavy metals and phosphorus can be successfully removed from wastewater containing an organic chelating agent, and an increase in the amount of sludge generated can also be prevented. Examples of the ferrous salt include ferrous chloride and ferrous sulfate, with ferrous chloride being preferably used. The molar equivalent ratio of hydrogen peroxide to COD _Cr contained in the waste water is desirably 0.50 times or more and 1.5 times or less, preferably 1.0 times or more and 1.5 times or less. Within this range, heavy metals and organic substances can be removed from wastewater containing an organic chelating agent.

Since the Fenton reaction occurs at a pH of 4.0 or lower, it is desirable to adjust the pH of the wastewater to which the Fenton reagent has been added to 1.5 to 4.0, preferably 2.5 to 3.0.

Generally, the reaction time between Fenton's reagent and waste water needs to be long, but in the treatment according to the present invention, the same effect was obtained with 30 minutes or 60 minutes, so the reaction time is preferably 30 minutes or more. It is desirable that the duration be 30 minutes or more and 60 minutes or less.

In addition to Fenton's reagent, add a calcium source. The amount of calcium source added is such that calcium (Ca) is 0.09 times or more and 0.45 times or less, preferably 0.13 times or more and 0.45 times or less, more preferably 0.13 times or more and 0.45 times or less, relative to iron (Fe) in the Fenton reagent. It is desirable that the amount provides a molar equivalent ratio of 0.18 times or more and 0.45 times or less.

It is preferable that the amount of iron added and the amount of calcium source added are in a ratio that allows heavy metals to be insolubilized and removed. When the amount of calcium added to iron in the Fenton reagent is Ca/Fe=0.09 or more and 0.45 or less in molar equivalent ratio, copper and nickel in the waste water can be removed. When the molar equivalent ratio of Ca/Fe is 0.18 or more and 0.45 or less, copper, nickel, and phosphorus in the waste water can be efficiently removed.

In addition, if the Fe concentration ratio is unilaterally high, the formation of calcium salt (HAP) or iron salt (FePO ₄ ) in the subsequent aeration process will be inhibited, and the Ca concentration ratio will be unilaterally high. If it is high, calcium scale will occur. Therefore, Ca is 50 mg/L or more and 300 mg/L or less, preferably 100 mg/L or more and 250 mg/L or less, more preferably 150 mg/L or more and 200 mg/L or less, and Fe is 400 mg/L or more and 900 mg/L or less, preferably 500 mg/L. It is preferable to add in a range of from 600 mg/L to 850 mg/L, more preferably from 600 mg/L to 850 mg/L. The greater the amount of Fe added, the higher the effectiveness of removing copper, nickel, and _phosphorus from wastewater. It is desirable to use a small amount.

Calcium sources include calcium hydroxide and calcium chloride. In particular, calcium hydroxide, which is inexpensive and easily available, can be preferably used.

Next, the wastewater to which the Fenton reagent and calcium source have been added is aerated under alkaline conditions with a pH of 9 or more and 10.5 or less. By aeration under alkaline conditions of pH 9.0 or more and 10.5 or less, residual hydrogen peroxide is removed and calcium salt (HAP) is formed. Since hydrogen peroxide inhibits coagulation, it is necessary to remove it before the coagulation/solid-liquid separation step. pH adjustment can be performed by adding a pH adjuster such as sodium hydroxide. Note that it is sufficient that calcium is present in the waste water during the aeration treatment, and the calcium source may be added in either the Fenton treatment step or the aeration treatment step.

The aeration treatment time is not particularly limited as long as hydrogen peroxide is removed and calcium compounds are formed, but it is preferably 30 minutes or more and 60 minutes or less. If the aeration treatment time becomes longer, HAP adhesion (scale) will occur in the aeration tank, so the aeration treatment time is preferably 50 minutes or less, more preferably 40 minutes or less.

Next, an amphoteric polymer flocculant is added to the aerated wastewater to flocculate the insolubilized heavy metals and phosphorus, followed by solid-liquid separation under alkaline conditions with a pH of 9.0 to 10.5. By performing the solid-liquid separation process under the same alkaline conditions as the aeration process, with a pH of 9.0 to 10.5, in addition to the insolubilization of phosphorus due to the formation of hydroxyapatite (HAP) and _FePO4 in the aeration process, By using this method, heavy metals can be precipitated while being insolubilized, and phosphorus and heavy metals can be simultaneously removed by solid-liquid separation. Note that the reaction in which iron added as a Fenton reagent turns into ferric ions and insolubilizes phosphorus as _FePO4 is said to occur in an acidic region, but in the present invention, it can be carried out even under alkaline conditions of pH 9.0 to 10.5. It has been confirmed through experiments that it can be insolubilized as _FePO4 . In addition, in water treatment, anionic polymer flocculants are generally used when flocculating under alkaline conditions, but in the present invention, by using an amphoteric polymer flocculant, the flocculating properties can be improved even under alkaline conditions. It has been confirmed through experiments that flocs with excellent solid-liquid separation properties are formed. For solid-liquid separation, natural sedimentation using a settling tank can be preferably used.

The amphoteric polymer flocculant is a copolymer of cationic monomer units, anionic monomer units, and nonionic monomer units. Amphoteric polymer flocculants have a neutralizing effect on suspended particles (cations) and entanglement with polymer chains (high molecular weight), and this entanglement is reinforced by electrostatic attraction due to the charges of anions and cations (cations and anions). can. Examples of amphoteric polymer flocculants that are particularly effective in the present invention include at least one of dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate (both are preferably quaternized methyl chloride), acrylamide, and acrylic acid. Preferred examples include polymers.

FIG. 2 shows a schematic configuration of an apparatus for treating wastewater containing an organic chelating agent and heavy metals according to the present invention. The treatment apparatus of the present invention includes a Fenton reagent addition means 12 for adding a Fenton reagent containing hydrogen peroxide and ferrous salt at a Fe/H ₂ O ₂ molar equivalent ratio of 0.10 to 0.13 to the wastewater. , a calcium source addition means 22 for adding a calcium source so that the molar equivalent ratio of Ca to Fe in the Fenton reagent is 0.15 times or more and 0.45 times or less, and wastewater to which at least Fenton's reagent has been added. an aeration treatment tank 20 that aerates the wastewater after the Fenton treatment under alkaline conditions with a pH of 9 or more and 10.5 or less, and an amphoteric polymer flocculant is added to the wastewater after the aeration treatment. and a solid-liquid separator 30 for separating solid-liquid wastewater containing insolubilized heavy metals after coagulation treatment under alkaline conditions of pH 9 or more and 10.5 or less. shall be.

If the calcium source addition means 22 can add a calcium source to the wastewater after the Fenton treatment and before the aeration treatment, the calcium source addition means 22 can be added to the Fenton treatment tank 10, the aeration treatment tank 20, or the piping 14 that conveys wastewater from the Fenton treatment tank to the aeration treatment tank. It is sufficient if it is provided so that a calcium source can be added. Preferably, it is provided so as to be added to the aeration treatment tank 20.

The solid-liquid separation device 30 may be any device that can perform solid-liquid separation by natural sedimentation, such as a settling tank. The amphoteric polymer flocculant addition means 32 only needs to be capable of adding an amphoteric polymer flocculant to the wastewater to be subjected to solid-liquid separation, and may be connected to the piping 24 that sends the wastewater from the aeration treatment tank 20 to the solid-liquid separator 30 or the solid-liquid It is sufficient if the separation device 30 is provided so that the amphoteric polymer flocculant can be added thereto. Preferably, it is provided so as to be added to the solid-liquid separator 30.

The treatment device of the present invention insolubilizes heavy metals in a Fenton treatment tank, then insolubilizes phosphorus in an aeration treatment tank, and sediments the insolubilized heavy metals and phosphorus in a flocculation/solid-liquid separation tank to perform solid-liquid separation. Since no additional processing equipment is required, the equipment configuration is simple.

[Fe/H ₂ O ₂ ratio of Fenton reagent]
In order to determine the appropriate range of the Fe/H ₂ O ₂ ratio in the Fenton reagent, the ratio of hydrogen peroxide to Fe during Fenton treatment was changed as shown in Table 1 without adding a calcium source. Copper (S-Cu) and nickel (S-Ni) in the resulting treated water are added to wastewater and aerated, and then a polyacrylic acid ester-based amphoteric polymer flocculant is added to perform flocculation and solid-liquid separation. , calcium (S-Ca) was analyzed by high-frequency inductively coupled plasma optical emission spectroscopy (ICP). Further, total phosphorus (STP) was measured by potassium peroxodisulfate decomposition method.

As the wastewater to be treated, wastewater containing 58.2 mg/L of Ni, 11.4 mg/L of Cu, 94.0 mg/L of total phosphorus (TP), and a chelating agent was used.
The amount of hydrogen peroxide in the Fenton reagent was 4100 mg/L, and ferrous sulfate heptahydrate was used as the Fe source.

The pH during Fenton treatment was 2.5, the Fenton treatment time was 60 minutes, and the pH during aggregation and solid-liquid separation was 9.0. To adjust the pH during coagulation and solid-liquid separation, sodium hydroxide and sulfuric acid were used as pH adjusters. The treatment test conditions and results are shown in Table 1.

From Table 1, it can be seen that when the Fe/H ₂ O ₂ ratio in the Fenton reagent is 0.10 or more, the removal effect of Cu and Ni is significantly improved, and as the ratio becomes higher, the removal effect of Cu, Ni, and P is improved. I understand. No. 6 and no. 7, the removal effect of Cu and Ni is the same when the Fe/H ₂ O ₂ ratio is 0.19 and 0.26, and the removal effect of P is better when the Fe/H ₂ O ₂ ratio is 0.26. However, sludge generation is observed. Therefore, by setting the Fe/H ₂ O ₂ ratio in the Fenton reagent to 0.10 or more and less than 0.26, preferably 0.19 or less, sludge generation can be suppressed and heavy metals and It was confirmed that phosphorus could be removed.

[Fe/H ₂ O ₂ ratio of Fenton reagent and amount of calcium source added]
During the Fenton treatment, the ratio of hydrogen peroxide to Fe and the amount of calcium hydroxide added were changed as shown in Table 2, and the mixture was added to the wastewater to be treated and aerated, and then a polyacrylate-based amphoteric polymer flocculant was added. Copper (S-Cu), nickel (S-Ni), and calcium (S-Ca) in the resulting treated water were analyzed using high-frequency inductively coupled plasma emission spectroscopy (ICP). analyzed. Further, total phosphorus (STP) was measured by potassium peroxodisulfate decomposition method.

As the wastewater to be treated, wastewater containing 62.1 mg/L of Ni, 11.7 mg/L of Cu, 94.0 mg/L of total phosphorus (TP), and a chelating agent was used.
The amount of hydrogen peroxide in the Fenton reagent was 4100 mg/L, and ferrous chloride tetrahydrate was used as the Fe source.

The pH during Fenton treatment was 2.5, the Fenton treatment time was 60 minutes, and the pH during aggregation and solid-liquid separation was 9.0. To adjust the pH during coagulation and solid-liquid separation, sodium hydroxide and sulfuric acid were used as pH adjusters. The treatment test conditions and results are shown in Table 2.

It can be seen that by performing the treatment of the present invention, copper, nickel, and phosphorus in the wastewater to be treated can be removed. Both Fe/H ₂ O ₂ ratios in the Fenton reagent of 0.10 and 0.13 are effective in removing copper, nickel, and phosphorus, but No. 2 does not contain calcium hydroxide. 11 and no. 14, it can be seen that when the Fe/H ₂ O ₂ ratio is increased from 0.1 to 0.13, the removal effect of phosphorus is the same, but the removal effect of copper and nickel is significantly improved. . No. adding calcium hydroxide. 12 and no. 16 comparisons and no. 13 and no. 17 shows that increasing the Fe/H ₂ O ₂ ratio from 0.1 to 0.13 significantly improves the nickel and phosphorus removal effect. No. 16 and no. The copper content in No. 17 is less than 0.1 mg/L, and the copper content in No. 17 is less than 0.1 mg/L. When compared with No. 14, it can be seen that there is a remarkable removal effect. No. 2 with the same Fe/H ₂ O ₂ ratio. 11～No. 13 comparisons and no. From the comparison of Nos. 14 to 17, it can be seen that the removal effect of copper, nickel, and phosphorus is significantly improved when the amount of calcium hydroxide added is 200 mg/L and 300 mg/L, compared to when it is 100 mg/L or less. From the above results, it was confirmed that when the Fe/H ₂ O ₂ ratio in the Fenton reagent was 0.10 or more and 0.13 or less, there was a particularly good effect of removing heavy metals and phosphorus.

[Examples 1 to 3 and Comparative Examples 1 to 2]
According to the treatment method of the present invention (Examples 1 to 3) shown in Figure 1 and the treatment method (Comparative Examples 1 to 2) shown in Figure 3, the amount of chemical injection was changed as shown in Table 3, and the wastewater to be treated was treated. Then, copper (S-Cu) and nickel (S-Ni) in the treated water were analyzed by ICP, and the total amount of sludge (vol%) and amount of sludge generated (g/L) were measured. Total phosphorus (STP) was measured by potassium peroxodisulfate decomposition method.

As the wastewater to be treated, wastewater containing 62.1 mg/L of Ni, 11.7 mg/L of Cu, 94.0 mg/L of total phosphorus (TP), and a chelating agent was used.
In Examples 1 to 3 and Comparative Example 1, Fenton's reagent (Fe/H ₂ O ₂ =0.13) containing 3000 mg/L of FeCl _{2.4H 2} O and 4100 mg/L of H ₂ O ₂ was used, and Comparative Example 2 Here, Fenton's reagent (Fe/H ₂ O ₂ =0.24) containing 8200 mg/L of FeSO ₄ .7H ₂ O and 4100 mg/L of H ₂ O ₂ was used.

In both Examples and Comparative Examples, 2000 mg/L of NaOH was added as a pH adjuster in the aeration treatment step and aeration was performed, and in the coagulation and solid-liquid separation steps, the pH was adjusted to 9.0 and natural sedimentation was performed. The treatment test conditions and test results are shown in Table 3. In addition, in Table 3, Fe/H ₂ O ₂ and Ca/Fe each indicate a molar equivalent ratio.

[Comparative example 1]
Only the Fenton treatment shown in FIG. 3 was performed. In the Fenton treatment step, Fenton reagent containing 3000 mg/L of FeCl ₂ 4H ₂ O and 4100 mg/L of H ₂ O ₂ was added to the wastewater, and in the aeration treatment step, 2000 mg/L of NaOH was added and aerated, and polyacrylic acid An ester amphoteric polymer flocculant was added, and the flocculation/solid-liquid separation process was carried out by natural sedimentation at pH 9.0. S-T-P of the treated water is 24.1 mg/L, S-Cu is 1.7 mg/L, S-Ni is 9.4 mg/L, sludge is 34.3 vol%, and the amount of sludge generated is 1.6 g/L. It was L. There was a lot of sludge and the cohesion was not stable.

[Comparative example 2]
The process was carried out in the same manner as in Comparative Example 1, except that 8200 mg/L of FeSO ₄ .7H ₂ O was added as a Fenton reagent and 3300 mg/L of NaOH was added in the aeration process. The residual amount of S-T-P in the treated water was 2.0 mg/L, S-Cu was less than 0.1 mg/L, and S-Ni was 0.2 mg/L, and the removal effect was recognized. However, the amount of sludge was 55.0 vol%, and the amount of sludge generated was significantly increased to 3.2 g/L. It was found that in order to insolubilize and remove all Cu, Ni, and P without adding calcium hydroxide, the amount of Fe added must be 1650 mg/L or more.

[Example 1]
100 mg/L of Ca(OH) ₂ was added in the aeration step of FIG. 1 so that the molar equivalent ratio Ca/Fe to Fe added as a Fenton reagent was 0.09. The pH of the wastewater from the aeration process was adjusted to 9.0, an amphoteric polymer flocculant was added, and solid-liquid separation was performed by natural sedimentation while maintaining the pH at 9.0. The S-T-P of the treated water is 15.1 mg/L, the S-Cu is 1.4 mg/L, and the S-Ni is 8.4 mg/L, and the residual amounts of Cu, Ni, and P are lower than in Comparative Example 1. It can be seen that the removal of heavy metals and phosphorus has been improved. In particular, the phosphorus removal rate was improved by about 9.6 points compared to Comparative Example 1. It was found that in the treatment method of the present invention, Cu, Ni, and P can be insolubilized and removed at 848 mg/L, which is about half of the iron addition amount of 1650 mg/L in Comparative Example 2.

[Example 2]
The process was carried out in the same manner as in Example 1, except that 200 mg/L of Ca(OH) ₂ was added in the aeration step of FIG. 1 so that the molar equivalent ratio of Ca to Fe added as the Fenton reagent, Ca/Fe, was 0.18. did. The S-T-P of the treated water was 4.3 mg/L, the S-Cu was less than 0.1 mg/L, and the S-Ni was 0.3 mg/L. It can be seen that the removal of heavy metals and phosphorus is greatly improved. In particular, the phosphorus removal rate was improved by about 21 points compared to Comparative Example 1.

[Example 3]
Processing was carried out in the same manner as in Example 1, except that 300 mg/L of Ca(OH) ₂ was added in the aeration step of FIG. 1 so that the molar equivalent ratio Ca/Fe to Fe added as the Fenton reagent was 0.27. did. S-T-P of the treated water is 2.0 mg/L, S-Cu is less than 0.1 mg/L, S-Ni is less than 0.9 mg/L, and Cu, Ni and P are lower than in Comparative Example 1. It can be seen that the residual amount is significantly reduced, and the removal of heavy metals and phosphorus is greatly improved. In particular, the phosphorus removal rate was improved by about 21 points compared to Comparative Example 1. The sludge was 25.0 vol% and the amount of sludge generated was 1.9 g/L, which was an improvement of 30 points in sludge and 40.6 points in the amount of sludge generated compared to Comparative Example 2, and the volume was significantly reduced. I understand that. Furthermore, the sludge was improved by 9.3 points compared to Comparative Example 1 in which the amount of iron added was the same, indicating that the cohesiveness was stabilized.

FIG. 4 shows the relationship between the Ca/Fe molar equivalent ratio and the residual amounts of Cu, Ni, and P in the treated water in Examples 1 to 3. From FIG. 4, in order to reduce all of Cu, Ni and P, it is necessary to make the Ca/Fe molar equivalent ratio 0.9 or more, and when the Ca/Fe molar equivalent ratio is 0.18, Ni and P It can be seen that 90% or more of Cu is removed when the Ca/Fe molar equivalent ratio is 0.27 or more.

Claims (4)

A method for treating wastewater containing an organic chelating agent and heavy metals, the method comprising:
(1) Adding a Fenton reagent containing hydrogen peroxide and ferrous salt at a Fe/H ₂ O ₂ molar equivalent ratio of 0.10 or more and less than 0.26 to the wastewater,
(2) Adding a calcium source so that the molar equivalent ratio of Ca to Fe in the Fenton reagent is 0.15 times or more and 0.45 times or less,
(3) aerating the wastewater to which the Fenton reagent and calcium source have been added under alkaline conditions with a pH of 9.0 or more and 10.5 or less;
(4) A method for treating wastewater, which comprises adding an amphoteric polymer flocculant to wastewater after aeration treatment, and performing solid-liquid separation under alkaline conditions with a pH of 9.0 or more and 10.5 or less. The method for treating wastewater according to claim 1, wherein the heavy metals include one or more selected from nickel, copper, lead, zinc, manganese, and cadmium. The wastewater treatment method according to claim 1 or 2, wherein the wastewater further contains phosphorus. A treatment device for wastewater containing an organic chelating agent and heavy metals,
Fenton reagent addition means for adding a Fenton reagent containing hydrogen peroxide and ferrous salt at a molar equivalent ratio of Fe/H ₂ O ₂ of 0.10 or more and less than 0.26 to the wastewater;
A calcium source addition means for adding a calcium source so that the molar equivalent ratio of Ca to Fe in the Fenton reagent is 0.15 times or more and 0.45 times or less;
a Fenton treatment tank that performs a Fenton treatment on wastewater to which at least a Fenton reagent has been added;
an aeration treatment tank for aerating wastewater after Fenton treatment under alkaline conditions with a pH of 9.0 or more and 10.5 or less;
an amphoteric polymer flocculant addition means for adding an amphoteric polymer flocculant to wastewater after aeration treatment;
a solid-liquid separator that separates wastewater containing insolubilized heavy metals after coagulation treatment into solid-liquid under alkaline conditions with a pH of 9.0 or more and 10.5 or less;
A wastewater treatment device characterized by comprising: