Treatment method for treated water, decomposition device for chelating agent-derived substances, and purification treatment system

Abstract

To provide a method for treating water to be treated that is capable of decomposing at least a part of each of a chelating agent containing a dithiocarbamic acid structure, a COD component derived from the chelating agent, and a nitrogen component derived from the chelating agent contained in the treated water.SOLUTION: The present invention provides a method for treating treated water Wb that includes a chelating agent containing a dithiocarbamate structure and chloride ions, the method including a decomposition process in which, while passing the water Wb to be treated through an intermediate chamber 16 of a reaction tank 10 having an anode chamber 12, a cathode chamber 14 and the intermediate chamber 16, provided between the anode chamber 12 and the cathode chamber 14. voltage is applied between the anode chamber 12 and the cathode chamber 14 to decompose at least a part of each of the chelating agent, COD components derived from the chelating agent, and nitrogen components derived from the chelating agent in the treated water Wb.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for treating treated water, a decomposing device for chelating agent-derived substances, and a purification treatment system.

Background Art

[0002] In Japan, where the land area is small and it is extremely difficult to secure final disposal sites, after volume reduction, detoxification, and resource recovery by introducing intermediate treatment such as incineration, the residues are landfilled. As a result, incineration residues now account for about 80% of the waste that is finally disposed of in general waste. Among incineration residues, fly ash is a specially managed general waste, and after insolubilization treatment mainly using an organic chelating agent to prevent elution of Pb etc., it is landfilled.

[0003] When rainwater etc. penetrates into the layer of landfilled waste, leachate (permeated water) in which various organic and inorganic substances derived from the waste and its treatment agent elute is generated. In order to remove these eluted components, the leachate is purified in a purification treatment system and then discharged into public waters such as rivers (Patent Document 1). FIG. 4 shows an example of a general leachate purification treatment system. Thus, in a leachate purification treatment system, usually, after calcium removal (Ca removal), biological treatment, coagulation sedimentation treatment, sand filtration treatment, activated carbon treatment etc. are performed, and COD, BOD, nitrogen components etc. in the leachate are removed.

[0004] However, when fly ash treated with a chelating agent is landfilled, residual chelating agent, COD components and nitrogen components derived from the chelating agent elute into the leachate. Since these are hardly decomposable, it has been confirmed that they cause treatment inhibition or nitrification inhibition in the leachate purification treatment process, and are an obstacle to proper leachate purification treatment.

[0005] As organic chelating agents (heavy metal scavengers) for fly ash, chelating agents containing a dithiocarbamic acid structure, such as dithiocarbamic acid-based chelating agents (alkylamine-based dithiocarbamic acid compounds) and piperazine-based chelating agents (piperazine-based dithiocarbamic acid compounds), are widely used. Experimentally, it has been confirmed that these residual chelates can be decomposed by ozone treatment or an accelerated oxidation method (Non-Patent Document 1). Also, it has been confirmed that chelating agents can be separated by adsorption with activated carbon or the reverse osmosis membrane method (Reverse Osmosis Membrane Method, hereinafter RO) (Non-Patent Documents 2 and 3), but decomposition is difficult.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the decomposition of residual chelates by ozone treatment or advanced oxidation processes, it was difficult to decompose the COD components and nitrogen components derived from the chelating agent. In addition, in the adsorption using activated carbon or the reverse osmosis membrane method, it was necessary to further treat the separated chelating agent after separation.

[0009] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for treating treated water that can decompose at least a part of each of a chelating agent containing a dithiocarbamic acid structure, a COD component derived from the chelating agent, and a nitrogen component derived from the chelating agent (hereinafter sometimes referred to as "chelating agent-derived substances") contained in the treated water. Another object of the present invention is to provide a decomposition apparatus for chelating agent-derived substances that can decompose chelating agent-derived substances contained in the treated water. Furthermore, an object of the present invention is to provide a purification treatment system that can purify leachate and / or surplus water containing chelating agent-derived substances.

Means for Solving the Problems

[0010] As a result of intensive studies to solve the above problems, the present inventor has found that the following invention meets the above object, and has reached the present invention. That is, the present invention relates to the following inventions.

[0011] <1> A method for treating treated water containing a chelating agent containing a dithiocarbamic acid structure and chloride ions, comprising an electrolysis step of passing the treated water through an electric current to decompose at least a part of each of the chelating agent, the COD component derived from the chelating agent, and the nitrogen component derived from the chelating agent in the treated water to obtain treated water. <2> The method for treating treated water according to <1>, wherein the chelating agent, the COD component derived from the chelating agent, and the nitrogen component derived from the chelating agent in the treated water are each decomposed by 50% or more. <3> The decomposition step is a step of passing the water to be treated through the flow path of a reaction tank having an anode part, a cathode part, and a flow path that is in contact with the anode part and the cathode part and is not partitioned by an ion exchange membrane, and applying a voltage between the anode part and the cathode part to perform decomposition. The method for treating water to be treated according to <1> or <2> above. <4> The concentration of the chelating agent in the water to be treated subjected to the decomposition step is 50 to 500 ppm, and the concentration of the chloride ions is 0.5 to 3% by mass. The method for treating water to be treated according to any one of <1> to <3> above. <5> The water to be treated is leachate discharged from a final disposal site for waste and / or surplus water discharged from a sea disposal site. The method for treating water to be treated according to any one of <1> to <4> above. <6> Before the decomposition step, there is a calcium removal step of removing calcium ions in the leachate and adjusting a low-concentration calcium solution with a calcium concentration of 100 ppm or less. The method for treating water to be treated according to any one of <1> to <5> above.

[0012] <7> A decomposition device for a chelating agent-derived substance that decomposes at least a part of each of a chelating agent containing a dithiocarbamic acid structure in the water to be treated, a COD component derived from the chelating agent, and a nitrogen component derived from the chelating agent. The decomposition device includes a reaction tank having an anode part, a cathode part, and a flow path in contact with the anode part and the cathode part through which the water to be treated flows, and a power source that applies a voltage between the anode part and the cathode part. <8> The decomposition device for a chelating agent-derived substance according to <7>, wherein the flow path is not partitioned by an ion exchange membrane.

[0013] <9> A purification treatment system for leachate discharged from a final disposal site of waste and / or surplus water discharged from a sea disposal site, comprising a raw water tank for storing the leachate and / or the surplus water, calcium removal equipment for removing calcium ions in the leachate and / or the surplus water and adjusting a low-concentration calcium solution with a calcium concentration of 100 ppm or less, a chelating agent containing a dithiocarbamic acid structure in the low-concentration calcium solution, and a decomposing device for the chelating agent-derived substance according to <7> or <8> for decomposing at least a part of each of the COD component derived from the chelating agent and the nitrogen component derived from the chelating agent.

Effect of the Invention

[0014] According to the present invention, there is provided a method for treating treated water capable of decomposing at least a part of each of a chelating agent containing a dithiocarbamic acid structure, a COD component derived from the chelating agent, and a nitrogen component derived from the chelating agent contained in the treated water. Further, there is provided a decomposing device for chelating agent-derived substances capable of decomposing at least a part of each of a chelating agent containing a dithiocarbamic acid structure, a COD component derived from the chelating agent, and a nitrogen component derived from the chelating agent contained in the treated water. Furthermore, there is provided a purification treatment system capable of purifying leachate and / or surplus water containing these chelating agent-derived substances.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

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[0016] The following is a detailed description of the embodiments of the present invention, but the following description of the constituent elements is one example (representative example) of the embodiment of the present invention, and the present invention is not limited to the following content as long as the gist of the present invention is not changed. Note that in this specification, when the expression "~" is used, it is used as an expression including the numerical value or physical property value before and after it.

[0017] <Treatment method for untreated water> The present invention relates to a method for treating water to be treated that contains a chelating agent having a dithiocarbamic acid structure and chloride ions, the method comprising a decomposition step of passing an electric current through the water to be treated to decompose at least a portion of the chelating agent in the water to be treated, the COD components derived from the chelating agent, and the nitrogen components derived from the chelating agent, thereby obtaining treated water (hereinafter, sometimes referred to as the "treatment method of the present invention").

[0018] As described above, organic chelating agents such as piperazine-based chelating agents and dithiocarbamine-based chelating agents are known as difficult-to-decompose organic substances. The present inventors have discovered that by passing electricity through the water to be treated that contains such organic chelating agents, the organic chelating agents can be efficiently decomposed, and furthermore, the COD components derived from the organic chelating agents and the nitrogen components derived from the organic chelating agents can also be decomposed. The organic chelating agents and the COD components and nitrogen components derived from the chelating agents are decomposed by N 2 Or CO 2It is presumed that it has been gasified and removed in gases such as

[0019] By adopting a treatment method such as the present invention, in addition to a chelating agent containing a dithiocarbamic acid structure, COD components and nitrogen components can be efficiently decomposed. Note that COD means Chemical Oxygen Demand, and the COD component means the component measured in COD analysis. Also, the nitrogen component means the component measured in total nitrogen (T-N) analysis.

[0020] (Water to be treated) The water to be treated processed by the treatment method of the present invention is an aqueous solution containing a chelating agent containing a dithiocarbamic acid structure and chloride ions, and examples include leachate (leachate water) from the final disposal site of waste (inland disposal site or sea surface disposal site), surplus water at the sea surface disposal site, wastewater from factories, etc.

[0021] The chelating agent containing a dithiocarbamic acid structure is a compound containing a structure represented by "N-(C=S)-S". Such a compound can be obtained by reacting an amine or piperazine with carbon disulfide, and as chelating agents, there are alkali metal salts, alkaline earth metal salts, ammonium salts of aliphatic amine-based dithiocarbamic acids; alkali metal salts, alkaline earth metal salts, ammonium salts of aromatic amine-based dithiocarbamic acids; alkali metal salts, alkaline earth metal salts, ammonium salts of polyamine-based dithiocarbamic acids; alkali metal salts, alkaline earth metal salts, ammonium salts of polyamine-based dithiocarbamic acids; alkali metal salts, alkaline earth metal salts, ammonium salts of piperazine-based dithiocarbamic acids, etc. These compounds may be contained singly or in combination of two or more.

[0022] For example, as the chelating agent, a compound represented by the following formula (1) can be mentioned. The compound represented by formula (1) is a chelating agent that reacts with a divalent metal ion to form a chelate complex, and is sometimes referred to as a dithiocarbamic acid-based chelating agent (DTC-based chelating agent).

[0023]

Chem.

[0024] In formula (1), R 1 , R 2 each independently represents an alkyl group, and M represents an alkali metal or ammonium. The alkyl group represented by R 1 , R 2 includes linear, branched or cyclic alkyl groups having 1 to 5 carbon atoms such as methyl group, ethyl group, n-propyl group, i-propyl group, etc. Examples of the alkali metal represented by M include sodium and potassium.

[0025] Specific examples of the chelating agent represented by formula (1) include, as dithiocarbamic acid-based chelating agents, potassium-diethylamine-N-carbodithioate, sodium-diethylamine-N-carbodithioate, and the like.

[0026] In addition, examples of the chelating agent include a compound represented by the following formula (2). The compound represented by formula (2) is a chelating agent that reacts with a divalent metal ion to form a chelate complex, and is sometimes referred to as a piperazine-based chelating agent (PIP-based chelating agent).

[0027]

Chem.

[0028] In formula (2), M represents an alkali metal or ammonium. Examples of the alkali metal represented by M include sodium and potassium.

[0029] Specific examples of the chelating agent represented by formula (2) include, as piperazine-based chelating agents, dipotassium-piperazine-1,4-dicarbodithioate, disodium-piperazine-1,4-dicarbodithioate, and the like.

[0030] In the decomposition process, since electricity is passed through the water to be treated, the concentration of chloride ions in the water to be treated is preferably 0.5 mass% or more (5000 ppm or more). Therefore, when the concentration of chloride ions in the water to be treated is less than 0.5 mass%, it is preferable that the water to be treated is adjusted to a chloride ion concentration of 0.5 mass% or more and then supplied to the decomposition process. The upper limit of the chloride ion concentration to be adjusted is appropriately set in consideration of salt precipitation and the like, but it is more preferable that the water to be treated is adjusted to a chloride ion concentration of 0.5 to 3 mass% and then supplied to the decomposition process. Generally, NaCl is used to adjust the chloride ion concentration. The chloride ion concentration may be adjusted in terms of salt concentration.

[0031] When the concentration of chloride ions in the water to be treated is 0.5 mass% or more, it can be directly supplied to the decomposition process. On the other hand, if the chloride ion concentration is too high, there is a risk of salt precipitation during the treatment. Therefore, the chloride ion concentration of the water to be treated when subjected to the decomposition process is preferably 0.5 to 3 mass%. Therefore, when the chloride ion concentration of the water to be treated exceeds 3 mass%, it is preferable that the water to be treated is adjusted to a chloride ion concentration of 0.5 to 3 mass% and then supplied to the decomposition process.

[0032] Examples of the water to be treated with a chloride ion concentration of 0.5 mass% or more include leachate at the final disposal site and surplus water at the sea disposal site. As described above, fly ash accounts for a large proportion as the waste to be landfilled at the final disposal site. Also, at the sea disposal site, it is exposed to seawater. Therefore, leachate and surplus water contain high concentrations of chloride ions, sodium ions, potassium ions, calcium ions, and the like.

[0033] The concentration of the chelating agent in the water to be treated subjected to the decomposition process is not particularly limited and may be, for example, 1000 ppm or less, 800 ppm or less, etc. However, if the concentration of the chelating agent is too high, the decomposition rate of the chelating agent tends to decrease. Therefore, it is preferable to adjust the concentration of the chelating agent to 500 ppm or less and supply it to the decomposition process, and it is more preferable to adjust it to lower concentrations in the order of 300 ppm or less, 250 ppm or less, and 200 ppm or less and supply it to the decomposition process. Also, when the concentration of the chelating agent is too low, the decomposition rate of the chelating agent also tends to decrease. Therefore, the concentration of the chelating agent is preferably 50 ppm or more, and more preferably 100 ppm or more.

[0034] For example, although it also depends on the amount of chelating agent added to fly ash in an incineration facility, generally, infiltration water and surplus water contain 10 - 500 ppm of the chelating agent. When treating these, they may be directly subjected to the decomposition process, or the concentration of the chelating agent may be appropriately adjusted and then subjected to the decomposition process.

[0035] (Decomposition device) First, a decomposition device for a chelating agent-derived substance (hereinafter, may be simply referred to as a "decomposition device") capable of performing the decomposition process of the treatment method of the present invention will be described. The decomposition device for the chelating agent-derived substance includes a reaction tank and a power source. The reaction tank has an anode part, a cathode part, and a flow path in contact with the anode part and the cathode part through which the water to be treated flows. Also, the power source applies a voltage between the anode part and the cathode part and energizes the water to be treated flowing through the flow path.

[0036] Figure 1 is a schematic diagram showing an example of a decomposition device for a chelating agent-derived substance. The decomposition device 100 shown in Figure 1 includes a reaction tank 10 for energizing the water to be treated Wb, a power source 20 for applying a voltage, an electrode liquid storage tank 30, and electrode liquid circulation means 32.

[0037] (Reaction tank) The reaction tank 10 has an anode chamber 12 as an anode part, a cathode chamber 14 as a cathode part, and an intermediate chamber 16 provided between the anode chamber 12 and the cathode chamber 14 as a flow path. That is, the reaction tank 10 is an example of a reaction tank in which the inside of the flow path is not partitioned by an ion exchange membrane (diaphragm), and is a three-chamber type reaction tank composed of the anode chamber 12, the cathode chamber 14, and the intermediate chamber 16.

[0038] (Anode chamber) The anode chamber 12 is a part where the anode 12A is disposed, partitioned from the intermediate chamber 16 by a partition plate 12B, and has a supply port 12i and a discharge port 12o. The supply port 12i is communicated with the outlet 30o of the electrode liquid storage tank 30 via a circulation pipe 40, and the discharge port 12o is communicated with the supply port 14i via the circulation pipe 40. When treating the water to be treated Wb, the electrode liquid S in the electrode liquid storage tank 30 is supplied from the supply port 12i. For the anode 12A, a titanium-platinum electrode or the like can be used. The partition plate 12B is an insulating member having an opening 12b penetrating in the thickness direction, and the end of the opening 12b on the anode chamber 12 side is covered by the anode 12A.

[0039] (Cathode chamber) The cathode chamber 14 is a part where the cathode 14A is disposed, partitioned from the intermediate chamber 16 by a partition plate 14B, and has a supply port 14i and a discharge port 14o. The supply port 14i is communicated with the discharge port 12o via a circulation pipe 40, and the discharge port 14o is communicated with the inlet 30i of the electrode liquid storage tank 30 via the circulation pipe 40. When treating the water to be treated Wb, the electrode liquid S discharged from the discharge port 12o is supplied from the supply port 14i. For the cathode 14A, a titanium-platinum electrode or the like can be used. The partition plate 14B is an insulating member having an opening 14b penetrating in the thickness direction. The opening 14b faces the opening 12b, and the end on the cathode chamber 14 side is covered by the cathode 14A.

[0040] (Intermediate chamber) The intermediate chamber 16 is the portion between the partition plate 12B on the anode chamber 12 side and the partition plate 14B on the cathode chamber 14 side, and has a supply port 16i and a discharge port 16o. The width of the intermediate chamber 16 (the distance between the anode 12A and the cathode 14A) is about 0.5 to 1 cm. The water to be treated Wb is supplied from the supply port 16i and is energized when passing through the region in contact with the electrodes in the intermediate chamber 16 (the region sandwiched between the opening 12b and the opening 14b), so that the piperazine-based chelating agent and / or dithiocarbamic acid-based chelating agent contained in the water to be treated Wb, and the COD components and nitrogen components derived therefrom are decomposed. The treated water Wa is discharged from the discharge port 16o.

[0041] (Electrode liquid storage tank, electrode liquid circulation means) The electrode liquid storage tank 30 is a tank for storing the electrode liquid S supplied to the anode chamber 12 and the cathode chamber 14, and is connected to the anode chamber 12 and the cathode chamber 14 via a circulation pipe 40. An electrode liquid circulation means 32 (for example, a pump) is provided in the middle of the circulation pipe 40. The electrode liquid storage tank 30, the anode chamber 12, the cathode chamber 14, the circulation pipe 40, and the electrode liquid circulation means 32 form a circulation path in which the electrode liquid S in the electrode liquid storage tank 30 passes through the anode chamber 12 and then through the cathode chamber 14 and returns to the electrode liquid storage tank 30. When treating the water to be treated Wb, the electrode liquid S is circulated by the electrode liquid circulation means 32.

[0042] In addition, the reaction tank 10 and the electrode liquid storage tank 30 may have a gas discharge port for discharging the gas generated by the decomposition of the chelating agent and the COD and nitrogen components derived therefrom.

[0043] (Power supply 20) The power supply 20 is a means for applying a voltage between the anode 12A and the cathode 14A. The power supply 20 may be a constant current power supply or a constant voltage power supply. In addition, it is equipped with an ammeter and a voltmeter, and the voltage may be adjusted appropriately.

[0044] Note that the decomposing device for the chelating agent-derived substance only needs to be configured to prevent short circuits, and is not limited to the decomposing device 100. For example, a configuration in which the anode chamber and the intermediate chamber are partitioned by an ion exchange membrane, and the cathode chamber and the intermediate chamber are partitioned by an ion exchange membrane may be used. As the reaction tank, a reaction tank used in the field of electrolysis, such as a three-chamber electrolytic cell, may be used. Further, a configuration without a partition may be used.

[0045] (Decomposition step) Next, the decomposition step of the treatment method of the present invention will be described by taking the case where the decomposition device 100 is used as an example.

[0046] In the decomposition step, while applying a voltage between the anode chamber 12 (anode part) and the cathode chamber 14 (cathode part), the water to be treated Wb is passed through the intermediate chamber 16 (a flow path that is in contact with the anode part and the cathode part and is not partitioned by an ion exchange membrane) to decompose the chelating agent-derived substance (that is, the chelating agent, the COD derived from the chelating agent, and the nitrogen component derived from the chelating agent) in the water to be treated Wb.

[0047] Specifically, the electrode liquid S is circulated between the electrode liquid storage tank 30, the anode chamber 12, and the cathode chamber 14 by the electrode liquid circulation means 32. While applying a voltage between the anode 12A and the cathode 14A from the power source 20, the water to be treated Wb is supplied from the supply port 16i, so that the chelating agent-derived substance in the water to be treated Wb in the intermediate chamber 16 is decomposed. As the electrode liquid S, an aqueous sodium sulfate solution, an aqueous sodium hydroxide solution, or the like can be used, and an aqueous sodium sulfate solution is preferred.

[0048] The energization conditions are appropriately set according to the configuration of the decomposition device. The voltage can be 1.0 to 25.0 V, 5.0 to 20.0 V, 9.0 to 15.0 V, etc. The current value can be 1.0 to 10 A, 2.0 to 8.0 A, 3.0 to 5.0 A, etc. The current density can be 0.02 to 0.2 A / cm 2 or 0.04 to 0.15 A / cm 2 , 0.08 to 0.1 A / cm 2 etc., and can be 0.04 A / cm 2 or more or 0.08 A / cm2 The above is preferable. The treatment time (the residence time in the region where electricity flows between the anode and the cathode) can be 30 to 60 minutes, or 40 to 50 minutes.

[0049] Among them, the concentration of the chelating agent in the water to be treated is adjusted to 50 to 500 ppm, the concentration of chloride ions is adjusted to 0.5 to 3% by mass, an aqueous sodium sulfate solution is used as the electrode solution, and the current density is 0.04 A / cm 2 It is preferable to perform the decomposition step under the above conditions.

[0050] In the decomposition step of the treatment method of the present invention, a decomposition rate of the chelating agent of 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100%, etc. can be achieved. The decomposition rate (removal rate) of the chelating agent can be obtained by "(mass of chelating agent in the water to be treated - mass of chelating agent in the treated water) / mass of chelating agent in the water to be treated × 100 (%)". By this decomposition step, for example, the concentration of the chelating agent in the treated water when measured by the copper ratio turbidimetry can be reduced to 10 ppm or less, 5 ppm or less, 1 ppm or less, or below the detection limit.

[0051] Also, in the decomposition step of the treatment method of the present invention, the COD component in the water to be treated can be removed, and a decomposition rate of COD in the decomposition step of 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100%, etc. can be achieved. The COD decomposition rate (removal rate) can be obtained by "(COD in the water to be treated - COD in the treated water) / COD in the water to be treated × 100 (%)". Note that COD can be measured by the potassium permanganate method based on the factory wastewater test method of JIS K 0102 (2019).

[0052] In addition, in the decomposition step of the treatment method of the present invention, the TOC components in the water to be treated can be removed, and TOC removal rates of 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100%, etc. in the decomposition step can be achieved. The TOC decomposition rate (removal rate) can be obtained by "(TOC in the water to be treated - TOC in the treated water) / TOC in the water to be treated × 100 (%)". Note that TOC means Total Organic Carbon, and the TOC component means the component measured in TOC analysis. TOC can be measured by combustion oxidation - infrared TOC analysis method based on the factory wastewater test method of JIS K 0102 (2019).

[0053] In addition, in the decomposition step of the treatment method of the present invention, the nitrogen components in the water to be treated can be removed, and nitrogen removal rates of 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100%, etc. in the decomposition step can be achieved. The nitrogen decomposition rate (removal rate) can be obtained by "(total nitrogen in the water to be treated - total nitrogen in the treated water) / total nitrogen in the water to be treated × 100 (%)". Note that total nitrogen (T-N) can be measured by ultraviolet absorption photometry based on the factory wastewater test method of JIS K 0102 (2019).

[0054] (Purification treatment system) Next, as an example of a purification treatment system using the treatment method of the present invention, with reference to FIGS. 2 and 3, a method and a purification treatment system for purifying leachate (leachate water) will be described. FIG. 2 is an example of a schematic diagram of a purification treatment system for leachate, and FIG. 3 is an example of a flowchart of a method for purifying leachate. The purification treatment of leachate using the treatment method of the present invention includes a raw water tank 110 for storing leachate water W1 (leachate) shown in FIG. 2, a calcium removal facility 120 for removing calcium ions in the leachate water W1 and adjusting a low-concentration calcium solution W2 with a calcium concentration of 100 ppm or less, and a decomposition device 100 for treating the low-concentration calcium solution W2. It can be carried out by a leachate purification treatment system 200.

[0055] First, the leachate W1 leached from the waste landfill site is stored in the raw water tank 110. The raw water tank 110 is a facility that stores the leachate W1 while supplying a part of the leachate W1 to the calcium removal facility 120. By controlling the discharge amount of the leachate W1 from the raw water tank 110, the flow rate of the leachate W1 supplied to the calcium removal facility 120 is controlled.

[0056] The leachate W1 contains inorganic salts such as chloride ions and calcium ions caused by fly ash, and a chelating agent containing a dithiocarbamic acid structure. Inorganic salts such as high-concentration calcium ions cause scaling in pipes and equipment. Therefore, in order to prevent scaling, the leachate W1 is supplied to the calcium removal facility 120, and in the calcium removal facility 120, a calcium removal step S1 (see Fig. 3) for removing calcium ions from the leachate W1 and adjusting a low-concentration calcium solution W2 with a calcium concentration of 100 ppm or less is performed.

[0057] The calcium removal facility 120 is a facility that removes calcium in the leachate W1 supplied from the raw water tank 110 and adjusts the low-concentration calcium solution W2. As the calcium removal facility 120, a facility used in the field of leachate treatment can be used.

[0058] The low-concentration calcium solution W2 adjusted by the calcium removal facility 120 is supplied to the decomposition device 100. The configuration of the decomposition device 100 is as described above, and by the decomposition device 100, a decomposition step S2 (see Fig. 3) for decomposing the chelating agent-derived substance in the low-concentration calcium solution W2 is performed. The treated water W3 treated by the decomposition device 100 has the COD, BOD, and nitrogen components removed.

[0059] Also, as described above, the water to be treated supplied to the decomposition device 100 preferably has a chloride ion concentration of 0.5% or more. This is because, in order to pass an electric current through the water to be treated, the water to be treated needs to be an electrolyte solution. Therefore, when the chloride ion concentration of the leachate or surplus water, which is the water to be treated, is diluted by precipitation or the like and becomes less than 0.5% by mass, it tends to cause an electric current conduction inhibition. Therefore, when the chloride ion concentration of the low-concentration calcium solution W2 becomes 0.5% by mass or less, it is preferable to add NaCl to adjust the chloride ion concentration to 0.5% by mass or more. When the chloride ion concentration of the low-concentration calcium solution W2 is 0.5% by mass or more, the low-concentration calcium solution W2 is directly supplied to the next device.

[0060] Therefore, in FIG. 2, the decomposition device 100 is provided next to the calcium removal facility 120, but the purification treatment system according to the present invention is not limited to this. For example, a concentration control device may be provided to monitor and control the concentration so that the chloride ion concentration of the low-concentration calcium solution W2 becomes 0.5% by mass or more. For example, a concentration adjustment facility may be provided next to the low-concentration calcium removal facility 120 to monitor the chloride ion concentration and the concentration of the chelating agent of the low-concentration calcium solution W2 and adjust the concentration, and the decomposition device 100 may be provided next to the concentration adjustment facility.

[0061] As described above, in the purification treatment system for leachate of the present invention, the biological treatment process (BOD oxidation, nitrification, denitrification, re-aeration), sedimentation and aggregation, and activated carbon treatment can be omitted. In addition, it can also be applied to the treatment of surplus water at the sea disposal site. By omitting the proper treatment and the biological treatment process, it becomes unnecessary to perform biological sludge domestication, and economic treatment such as reduction of biological treatment construction costs and reduction of maintenance personnel becomes possible. In addition, the electric power used for electrolysis is smaller than the electric power of blowers, pumps, etc. used for biological treatment, and the environmental load can also be reduced.

Example

[0062] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless the gist thereof is changed.

[0063] <Reagent> Chelating agents used were piperazine-based chelating agents (PIP-based chelating agents, manufactured by Kurita Water Industries, Ltd., product number S814) and dithiocarbamate-based chelating agents (DTC-based chelating agents, manufactured by Kurita Water Industries, Ltd., product number S803). The brine was prepared by dissolving commercially available table salt. Composition analysis was performed based on the factory wastewater test method of JIS K 0102 (2019). Table 1 shows the composition analysis results of the PIP-based chelating agent, Table 2 shows the composition analysis results of the DTC-based chelating agent, and Table 3 shows the composition analysis results of the commercially available table salt.

[0064]

Table 1

[0065]

Table 2

[0066]

Table 3

[0067] (Experimental apparatus) The experimental apparatus used was one in which the ion exchange membrane was removed from an electrodialysis membrane experimental apparatus (Asiraizer EX3B manufactured by Astom Co., Ltd.), and a processed rubber plate with an opening formed to penetrate in the thickness direction was installed so as to be in contact with the anode and the cathode respectively (see Fig. 5). Titanium-platinum electrodes were used for the electrode plates (anode and cathode). The processed rubber plate was prepared by cutting out the central part of a commercially available rectangular natural rubber plate (thickness 5 mm) into a rectangular shape of 6.1 cm × 9 cm. The energization area was 55 cm 2 , the width of the reaction chamber was 1 cm, and the reaction area where energization was performed was 55 cm 3 . Fig. 6 shows a schematic diagram of the experimental apparatus.

[0068] (Chelate decomposition experiment) As the experimental sample, 800 mL of raw water was used. This was placed in the raw water tank, and while passing the liquid, the current value was fixed at 1.1 A, and electrolysis experiments were conducted for 45 minutes under the condition that the voltage was varied to 9.0 V, 12.0 V, and 15.0 V. The electrode solution used was 5% NaSO 4 was used.

[0069] (Analysis of treated water) The concentrations of chelating agents, COD, TOC, and T-N in the water to be treated and the treated water after decomposition treatment were measured. The concentration of the chelating agent (residual chelating agent) was calculated by the copper turbidimetry method, and the decomposition rate of each was determined. COD was calculated by the potassium permanganate method. TOC was calculated by the combustion oxidation-infrared TOC analysis method using a total organic carbon meter (TOC-V) manufactured by Shimadzu Corporation. T-N was calculated by the ultraviolet absorption photometry method using an ultraviolet-visible spectrophotometer (V-650) manufactured by JASCO Corporation.

[0070] Table 4 shows the measurement results of the concentration of the chelating agent (residual chelating agent), COD, T-N, and TOC in the treated water. As shown in Table 4, the residual chelating agent was ND (below the detection limit) in all cases. For COD, TOC, and T-N, the decomposition rate increased with the increase in voltage, and at 15 V, it was 85% or more for COD and TOC, and 75% or more for T-N.

[0071]

Table 4

[0072] <Experimental Example 2> Electrolysis experiments were conducted in the same manner as in Example 1, except that the current value was fixed at 2.2 A and the condition of varying the voltage to 9.0 V, 12.0 V, and 15.0 V was changed from the condition of fixing the current value at 1.1 A and varying the voltage to 9.0 V, 12.0 V, and 15.0 V.

[0073] Table 5 shows the measurement results of the concentration of the chelating agent (residual chelating agent), COD, T-N, and TOC in the treated water. As shown in Table 5, the residual chelating agent was ND in all cases. For COD, TOC, and T-N, the decomposition rate increased with the increase in the current value, showing a high decomposition rate of 85.9% - 97.9%.

[0074]

Table 5

[0075] <Experimental Example 3> An electrolysis experiment was conducted in the same manner as in Example 1, except that the condition of fixing the current value at 1.1 A and varying the voltage from 9.0 V, 12.0 V, and 15.0 V was changed to the condition of fixing the current value at 4.4 A and varying the voltage from 9.0 V, 12.0 V, and 15.0 V.

[0076] Table 6 shows the measurement results of the concentration of the chelating agent (residual chelating agent), COD, T-N, and TOC in the treated water. As shown in Table 6, the residual chelating agent was ND in all cases, and the decomposition rate of COD, TOC, and T-N was 100% in all cases.

[0077]

Table 6

[0078] <Experimental Example 4> An electrolysis experiment was conducted in the same manner as in Example 1, except that the condition of fixing the current value at 1.1 A and varying the voltage from 9.0 V, 12.0 V, and 15.0 V was changed to the condition of fixing the voltage at 9.0 V and varying the current value from 1.1 A, 2.2 A, and 4.4 A.

[0079] Table 7 shows the measurement results of the concentration of the chelating agent (residual chelating agent), COD, T-N, and TOC in the treated water. As shown in Table 7, the residual chelating agent was ND in all cases. COD was decomposed by 93.4% at 2.2 A and 100% at 4.4 A. TOC was decomposed by 90.4% at 2.2 A and 100% at 4.4 A. T-N was decomposed by 85.9% at 2.2 A and 100% at 4.4 A.

[0080]

Table 7

[0081] <Experimental Example 5> An electrolysis experiment was conducted in the same manner as in Example 1, except that the condition of fixing the current value at 1.1 A and varying the voltage from 9.0 V, 12.0 V, 15.0 V was changed to the condition of fixing the voltage at 12.0 V and varying the current value from 1.1 A, 2.2 A, 4.4 A.

[0082] Table 8 shows the measurement results of the concentration of the chelating agent (residual chelating agent), COD, T-N, and TOC in the treated water. As shown in Table 8, the residual chelating agent was ND in all cases. COD was decomposed by 96.7% at 2.2 A and 100% at 4.4 A. TOC was decomposed by 94.0% at 2.2 A and 100% at 4.4 A. T-N was decomposed by 94.9% at 2.2 A and 100% at 4.4 A.

[0083]

Table 8

[0084] <Experimental Example 6> An electrolysis experiment was conducted in the same manner as in Example 1, except that the condition of fixing the current value at 1.1 A and varying the voltage from 9.0 V, 12.0 V, 15.0 V was changed to the condition of fixing the voltage at 15.0 V and varying the current value from 1.1 A, 2.2 A, 4.4 A.

[0085] Table 9 shows the measurement results for the concentration of the chelating agent in the treated water (residual chelating agent), COD, TN, and TOC. As shown in Table 9, the residual chelating agent was ND in all cases. COD was decomposed at 97.9% at 2.2A and 100% at 4.4A. TOC was decomposed at 96.4% at 2.2A and 100% at 4.4A. TN was decomposed at 97.4% at 2.2A and 100% at 4.4A.

[0086] [Table 9]

[0087] <Experimental Example 7> The concentration of the PIP chelating agent was set to 200 mg / L, and it was dissolved in pure water to prepare 800 mL of test solution, and an electrolysis experiment was performed. Table 10 shows the electrolysis conditions and the experimental results. The lower limit of quantification of the chelating agent concentration was 10 mg / L.

[0088] [Table 10]

[0089] (Analysis of generated gas) In the electrolysis experiment, gas was generated from the electrode chamber. The electrode chamber was sealed and the generated gas was collected in an airbag, and N (nitrogen atom) and C (carbon atom) were analyzed, and their respective balances were calculated.

[0090] The amount of gas collected by the air bag was 28 mL. This gas was introduced into the gas washing bottle from the supply port A, passed through the washing liquid, and gas (B) was collected from the outlet B. As shown in FIG. 7, the gas washing bottle contained 0.5 mass % H 2 O 2 Two stages were placed with 40 mL of the aqueous solution, and the third stage was placed with 0.1% by mass Ca(OH) 2 A gas washing bottle containing 100 mL of aqueous solution was used.

[0091] 0.5% by mass H after gas passage2 O 2 The aqueous solutions (cleaning solutions from the first and second gas washing bottles) were collected from both stages and analyzed by ion chromatography. 3 The concentration is 6×10 -3 mg / L,NO 2 The concentration is 2.1 x 10 -4 mg / L.

[0092] Ca(OH) after passing gas 2 The aqueous solution (the washing liquid from the third gas washing bottle) was collected, filtered, and the weight of the precipitate was measured. As a result, the weight of the precipitate was 53 mg. Ca(OH) 2 The predicted composition of the gas recovered by the cleaning solution is CO 2 It is inferred that...

[0093] The amount of gas (B) was 9 mL. The gas that passed through the gas washing bottle was analyzed with a gas detector tube, and the result was N 2 5mL, H 2 The volume of the gas was 4 mL. Therefore, the predicted gas composition is H 2 , N 2 , CO 2 It is inferred that...

[0094] The overall balance was calculated based on the above experimental results. All units were converted to moles for comparison.

[0095] The results of the N balance calculation are shown in Table 11. The mass balance between input and recovery was 97.8% (4.4×10 -4 mol÷4.5×10 -4 Therefore, with regard to nitrogen, most of the input N was gasified and N 2 It is collected as gas and NO X Some of it was broken down, but the amount is presumably very small.

[0096] [Table 11]

[0097] The calculation results of the balance of C are shown in Table 12. The mass balance of input and recovery was 96.3% (5.3×10 -4 mol÷5.5×10 -4 mol = 96.3%).

[0098]

Table 12

[0099] From the above results, it is inferred that the PIP-based chelating agent was electrolyzed, and the N and C components were converted into nitrogen and carbon dioxide and removed as gases (the COD component and the nitrogen component were decomposed).

[0100] <Example 8> (Experimental apparatus) The experimental apparatus used an electrodialysis membrane experimental apparatus (Asiraizer EX3B manufactured by Asahi Kasei Corporation). While supplying the water to be treated to the desalination chamber and the concentration chamber, an electric current was applied to conduct an electrolysis experiment. The water to be treated was prepared by using a PIP-based chelating agent or a DTC-based chelating agent, with chelate concentrations of 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 500 ppm, 750 ppm, and 1000 ppm, and chloride ion concentrations of 0 mass%, 1 mass%, and 2 mass%. The experimental conditions were a current value of 4.4 A, a voltage of 9 - 15 V, and an electrode solution of Na 2 SO 4 , and room temperature (20°C).

[0101] The chelating agent concentration in the treated water (the sum of the chelating agent concentration in the desalinated liquid and the chelating agent concentration in the concentrated liquid) was measured, and the decomposition rate of the chelating agent was calculated. Fig. 8 shows a plot of the relationship between the concentration of the PIP-based chelating agent in each water to be treated before treatment and the decomposition rate of the chelating agent by the decomposition treatment. Fig. 9 shows a plot of the relationship between the concentration of the DTC-based chelating agent in each water to be treated before treatment and the decomposition rate of the chelating agent by the decomposition treatment. As a result, for the PIP-based chelating agent, a decomposition rate of 100% of the chelating agent was obtained when the concentration of the chelating agent in the water to be treated was 150 ppm and the chloride ion concentration was 2% by mass. For the DTC-based chelating agent, a decomposition rate of 98% of the chelating agent was obtained when the concentration of the chelating agent in the water to be treated was 150 ppm and the chloride ion concentration was 2% by mass.

[0102] <Example 9>: Pb redissolution confirmation experiment Since both the PIP-based chelating agent and the DTC-based chelating agent bound to Pb may be redissolved by electrolysis, a Pb redissolution confirmation experiment was conducted. Since the PIP-based chelating agent and the DTC-based chelating agent show similar tendencies, an elution experiment was conducted using the PIP-based chelating agent as an example. As a result of conducting an elution test with 50 g of fly ash and 500 mL of solution, when 1.6% of the PIP-based chelating agent was added to 50 g of fly ash, the Pb was 0 mg / L. On the other hand, when no PIP-based chelating agent was added, the Pb concentration in 50 g of fly ash was 32 mg / L. Therefore, the total amount of Pb was 16 mg (500 mL × 32 mg / L = 16 mg), and the required amount of the PIP-based chelating agent at this time was 800 mg (50 g × 1.6% = 0.8 g = 800 mg). Thus, the required amount of the PIP-based chelating agent per 1 mg of Pb was set to 50 mg.

[0103] Regarding the experimental conditions, a 1 L solution with a Pb concentration of 10 mg / L was prepared using a Pb standard solution, and 500 mg, which is the required amount of the PIP-based chelating agent, was added to the solution. Further, a commercially available salt was added to the solution to adjust the chloride ion concentration to 1% by mass to obtain the water to be treated. Using the adjusted water to be treated, an electrolysis experiment was conducted in the same manner as in Example 8. As a result, Pb was not detected in either the desalinated liquid or the concentrated liquid after electrolysis.

Industrial applicability

[0104] The present invention is useful in the field of waste liquid treatment such as leachate treatment in a final disposal site.

Explanation of reference numerals

[0105] 10 Reaction tank 12 Anode chamber 12A Anode 12B, 14B Partition plate 12b, 14b Opening 14 Cathode chamber 14A Cathode 16 Intermediate chamber 12i, 14i, 16i Inlet 12o, 14o, 16o Outlet 20 Power supply 30 Electrolyte storage tank 30i Inlet 30o Outlet 32 Electrolyte circulation means 40 Circulation pipe 100 Decomposition device 110 Raw water tank 120 Calcium removal facility 200 Purification treatment system for leachate S Electrolyte W1 Leachate W2 Low-concentration calcium solution W3, Wa Treated water Wb Water to be treated

Claims

1. A method for treating water to be treated containing a chelating agent having a dithiocarbamic acid structure and chloride ions, comprising: a decomposition step of passing the water to be treated through an electric current to decompose at least a part of each of the chelating agent, the COD component derived from the chelating agent, and the nitrogen component derived from the chelating agent in the water to be treated to obtain treated water.

2. The method for treating water to be treated according to claim 1, wherein the chelating agent, the COD component derived from the chelating agent, and the nitrogen component derived from the chelating agent in the water to be treated are each decomposed by 50% or more.

3. The decomposition step is a step of passing the water to be treated through the flow path of a reaction tank having an anode part, a cathode part, and a flow path that is in contact with the anode part and the cathode part and is not partitioned by an ion exchange membrane, and applying a voltage between the anode part and the cathode part to perform decomposition. The method for treating water to be treated according to claim 1 or 2.

4. The method for treating water to be treated according to claim 1 or 2, wherein the concentration of the chelating agent in the water to be treated subjected to the decomposition step is 50 to 500 ppm, and the concentration of the chloride ions is 0.5 to 3% by mass.

5. The method for treating water to be treated according to claim 1 or 2, wherein the water to be treated is leachate discharged from a final waste disposal site and / or surplus water discharged from a sea disposal site.

6. Before the decomposition step, a calcium removal step of removing calcium ions in the water to be treated and adjusting a low-concentration calcium solution having a calcium concentration of 100 ppm or less is provided. The method for treating water to be treated according to claim 5.

7. A purification treatment system for leachate discharged from a final waste disposal site and / or surplus water discharged from a sea disposal site, comprising: a raw water tank for storing the leachate and / or the surplus water; calcium removal equipment for removing calcium ions in the leachate and / or the surplus water and adjusting a low-concentration calcium solution having a calcium concentration of 100 ppm or less; a decomposition device for a chelating agent-derived substance that decomposes at least a part of each of a chelating agent having a dithiocarbamic acid structure, a COD component derived from the chelating agent, and a nitrogen component derived from the chelating agent in the low-concentration calcium solution. The decomposition device for the chelating agent-derived substance is A reaction tank having an anode portion, a cathode portion, and a flow path in contact with the anode portion and the cathode portion through which the low-concentration calcium solution flows. A purification treatment system comprising a power source for applying a voltage between the anode portion and the cathode portion. **Claim 8** The purification treatment system according to claim 7, wherein the flow path is not partitioned by an ion exchange membrane.

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