Apparatus and method for removing calcium from leachate, and leachate treatment system

Abstract

To provide an apparatus and a method for removing calcium from leachate and a leachate treatment system.SOLUTION: An apparatus for removing calcium from a leachate includes: means for maintaining the leachate in a neutral to alkaline range during a calcium removal step; and means for supplying gas containing CO2 to the leachate. Also provided is a method for removing calcium from a leachate, the method including the steps of maintaining the leachate in a neutral to alkaline range during the calcium removal step, and supplying gas containing CO2 to the leachate.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for removing calcium from leachate from a final waste disposal site, and a leachate treatment system, and in particular to an apparatus and method for removing calcium from leachate using a gas containing carbon dioxide (CO2). [Background technology]

[0002] Much of the waste landfilled at final disposal sites contains calcium. As a result, calcium elutes from the landfilled waste, and the resulting leachate causes problems such as calcium scale forming on the pipes and equipment in leachate treatment facilities.

[0003] To avoid such problems, calcium is removed from the leachate. For example, Non-Patent Document 1 describes removing calcium using an ion exchange resin method. Non-Patent Document 2 discloses various removal methods, and indicates that the alkaline coagulation and precipitation method (lime soda method (sodium carbonate method)) in which sodium carbonate is added is the most commonly used. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Tamura, Noritoshi et al., Calcium Removal Technology Using Ion Exchange Resin, Journal of the Japan Society of Material Cycles and Waste Management, Vol. 26, No. 1, pp. 53-58, 2015 [Non-patent document 2] Yasuo Horii, Current Status and Issues of Advanced Leachate Treatment Technology, Journal of Japan Society of Material Cycles and Waste Management, Vol. 26, No. 1, pp. 35-46, 2015 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the sodium carbonate method, which is currently commonly used, adds more salt to the leachate, which already contains a high concentration of salt, which can lead to high salinity problems.In addition, the cost of the added sodium carbonate is high, which places a burden on the facility in terms of running costs.

[0006] In view of these circumstances, the inventors of the present application have an object to provide an apparatus and method for removing calcium from leachate, as well as a leachate treatment system, that do not use sodium carbonate and that place less strain on the environment. [Means for solving the problem]

[0007] In order to achieve the above object, an apparatus for removing calcium from leachate according to one embodiment of the present invention comprises: means for maintaining the leachate in a neutral to alkaline range during the calcium removal step; a means for supplying a gas containing CO2 to the leachate; The present invention is characterized by comprising:

[0008] In one embodiment of the present invention, the means for maintaining the leachate in a neutral to alkaline range may be carried out before the means for supplying gas is carried out.

[0009] In one embodiment of the present invention, the means for maintaining the leachate in a neutral to alkaline range may be carried out while the means for supplying gas is being carried out.

[0010] Furthermore, in one embodiment of the present invention, the means for maintaining the leachate in a neutral to alkaline range may be carried out after the means for supplying gas is carried out.

[0011] Another embodiment of the present invention relates to a method for removing calcium from a leachate, comprising the steps of: maintaining the leachate in a neutral to alkaline range during the calcium removal step; and a step of supplying a gas containing CO2 to the leachate.

[0012] Furthermore, another embodiment of the present invention relates to a leachate treatment system comprising a plurality of steps including a step of using the calcium removal device and a coagulation and sedimentation step. [Effects of the Invention]

[0013] According to the above aspects, it is possible to provide an apparatus and method for removing calcium from leachate, and a leachate treatment system that do not use sodium carbonate and that place less strain on the environment. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of the leachate treatment process. [Figure 2] FIG. 1 is a schematic diagram of a calcium removal process using the device of the present invention. [Figure 3] FIG. 1 is a schematic diagram of a conventional calcium removal process. [Figure 4] FIG. 10 is a diagram showing calcium ion concentration and gas supply time in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] An apparatus for removing calcium from leachate according to one embodiment of the present invention (hereinafter simply referred to as a "calcium removal apparatus") will be described below. The drawings used in this embodiment are intended to explain the configuration, arrangement of each part, function, action, and effect of the present invention, and are not intended to limit the specific shape, aspect ratio, etc. of the present invention.

[0016] In this specification, "leachate" refers to "retained water, etc. discharged outside of a landfill site" as defined in Section 20 of the Third Definition of Terms in the Guidelines for Final Waste Disposal Site Performance (published in 2000). In other words, it refers to the liquid discharged outside of a landfill site that is the water contained in waste buried at a final waste disposal site and the surface water that has permeated into the landfill site.

[0017] 1. Calcium removal device Fig. 1 shows the process for treating leachate discharged from a final waste disposal site. The calcium removal device of the present invention is used as part of the first coagulation and sedimentation treatment process to remove calcium from the leachate.

[0018] The calcium removal device of the present invention comprises a means for maintaining the leachate in a neutral to alkaline range during the calcium removal step, and a means for supplying a gas containing CO2 to the leachate. The calcium removal step is a step in which calcium ions in the leachate react with the supplied CO2, thereby removing the calcium ions from the leachate.

[0019] The means for maintaining the leachate in a neutral to alkaline range during the calcium removal step (hereinafter simply referred to as "alkalinity maintaining means") may be any means capable of maintaining the acidity of the leachate in a neutral to alkaline range, and may, for example, be a means for adding an alkaline solution such as an aqueous sodium hydroxide solution to the leachate. Furthermore, the alkalinity maintaining means may be equipped with a sensor for measuring the acidity of the leachate in the apparatus.

[0020] Furthermore, as long as the leachate can be maintained in the neutral to alkaline range during the calcium removal step, the alkalinity maintaining means can be used at any time relative to the gas supply step. For example, the acidity of the leachate may be adjusted to a weak alkaline state before the gas supply step. Alternatively, the acidity of the leachate may be adjusted by adding an alkaline solution dropwise during the gas supply step. Furthermore, after the gas supply step, an alkaline solution may be added dropwise to adjust the acidity of the leachate to a weak alkaline state, and calcium removal may then be performed.

[0021] The means for supplying a CO2-containing gas to the leachate (hereinafter simply referred to as the "gas supply means") may be any means for supplying a gas to the leachate, and various aeration means may be used. For example, a bubble contact type physical aeration means in which an air diffuser or air diffuser is installed in the aeration tank, or a mechanical aeration means using an axial flow mixer or agitator may be used. The CO2-containing gas may be injected into the leachate to form fine bubbles.

[0022] Furthermore, the gas supply means may be a combination of multiple means, such as an agitator in addition to an air diffuser. Gas may also be supplied under pressure. In this case, at least a portion of the calcium removal device of the present invention may be equipped with a pressure-resistant vessel. Pressurized gas may also be supplied into the liquid.

[0023] 2. Leachate treatment system One embodiment of the present invention relates to a leachate treatment system that includes multiple steps, including a step using the calcium removal device described above and a coagulation and sedimentation step.

[0024] Furthermore, the process using the calcium removal device of the present invention is installed upstream of the coagulation and sedimentation process in the multiple processes of the leachate treatment system, as shown in Figure 1. Preferably, it is installed upstream of the most upstream coagulation and sedimentation process. By installing the process using the calcium removal device upstream, the calcium ion concentration in the liquid can be reduced, and calcium scale deposition in the downstream piping and on the device can be suppressed.

[0025] Figure 2 is a schematic diagram of a calcium removal process using the calcium removal device of the present invention, which forms part of the leachate treatment system of the present invention. In the calcium removal device of the present invention, an alkaline substance such as sodium hydroxide is added to maintain the solution in a neutral to alkaline range, while a CO2-containing gas is supplied, or an alkaline substance such as sodium hydroxide is added after the CO2-containing gas is supplied to maintain the solution in a neutral to alkaline range, thereby forming carbonates. Subsequently, a coagulant and / or coagulation aid is added to coagulate and precipitate the carbonates, and the precipitate is filtered to remove calcium-containing salts.

[0026] Figure 3 shows a conventional calcium removal process using sodium carbonate. In the conventional method, sodium carbonate is added, resulting in a high salt concentration and a larger amount of precipitate in the coagulation and precipitation process than in the present invention.

[0027] Hereinafter, embodiments of the present invention will be described in detail, including experimental results.

[0028] [First embodiment] In a first embodiment, the alkalinity maintaining device adjusts the acidity of the leaching solution to a weak alkaline level before the gas supply step.

[0029] In the first embodiment, the CO2-containing gas is preferably air. Normally, the CO2 concentration in air is 0.04%, but as long as air is used, the CO2 concentration is not limited to this, and may be air containing a large amount of CO2, such as exhaust gas.

[0030] In the first embodiment, during the calcium removal step, the leachate is maintained in a neutral to alkaline range, preferably weakly alkaline (pH 8 to 11). More preferably, the pH of the leachate is adjusted to 10 or higher before the gas supply means is applied.

[0031] (Calcium removal test 1 using air supply) For Examples 1-1 and 1-2 and Comparative Example 1, calcium removal tests by air supply were carried out as follows.

[0032] Experimental method (1) Leachate A collected from a final disposal site was adjusted to pH 8.0 and pH 10.0 with 1.0 M NaOH aqueous solution, and 1 L of each was poured into a beaker (Examples 1-1 and 1-2). In Comparative Example 1, the pH of the leachate was not adjusted, and 1 L of the leachate was prepared in a beaker. (2) Next, ambient air was supplied to each of the prepared exudates for 15 hours using an aeration pump (Non-noise W600, manufactured by Nippon Dobutsu Yakuhin Co., Ltd.). (3) Samples were taken before and after aeration, and calcium ions were quantified by chelate titration. The results are shown in Table 1. The removal rate was calculated based on the calcium ion concentration in the solution after pH adjustment.

[0033] [Table 1]

[0034] In both cases in Example 1, the calcium ion concentration decreased after aeration, indicating that the CO2 in the air was able to remove calcium from the leachate. In addition, increasing the pH improved the calcium removal rate.

[0035] (Calcium removal test 2 using air supply) Experimental method (1) Leachates B to D collected on different collection days from the final disposal site were adjusted to pH 10 with 1.0 M NaOH aqueous solution, and 1 L of each was poured into a measuring cylinder (Examples 2 to 4). (2) Next, ambient air was supplied to each of the prepared exudates for 15 hours using an aeration pump (Non-noise W600, manufactured by Nippon Dobutsu Yakuhin Co., Ltd.). (3) Samples were taken before and after aeration, and calcium ions were quantified by chelate titration. The results are shown in Table 2. The removal rate was calculated based on the calcium ion concentration in the solution after pH adjustment.

[0036] [Table 2]

[0037] In both cases, the calcium ion concentration decreased after aeration, and when the pH was increased to 10, the calcium in the leachate was also efficiently removed by CO2 in the air.

[0038] [Second embodiment] In a second embodiment, the alkalinity maintaining device drips an alkaline solution during the gas supply step to adjust the acidity of the leachate. In the second embodiment, the CO2-containing gas may be air or exhaust gas containing CO2. It may also be a gas with a concentrated CO2 concentration. The CO2 concentration of the CO2-containing gas may be 4% or more, or 25% or more, or 80% or more, or 90% or more.

[0039] In the second embodiment, the leachate is maintained in a neutral to alkaline range, preferably weakly alkaline (pH 8 to 11), during the calcium removal step. More preferably, the leachate is adjusted to maintain a pH of 8 to 9 during the gas supply step.

[0040] (Calcium removal test 1 using CO2 gas supply) For Examples 5 to 7 and Comparative Examples 2 to 4, calcium removal tests by supplying CO2 gas were carried out as follows.

[0041] Experimental method (1) Leachates A, E, and F collected from a final disposal site on different collection days were adjusted to pH 8.2 with 1.0 M NaOH aqueous solution, and 1 L of each was poured into a beaker (Examples 5 to 7). In Comparative Examples 2 to 4, the pH of the leachate was not adjusted, and 1 L of each was prepared in a beaker. (2) Next, a 10 M NaOH aqueous solution was added to each of the prepared leachates to maintain the pH at 8.0 to 9.0, while CO2 gas (Air Water Inc.: 99.5% by volume) was supplied at a flow rate of 2.0 L / min for 30 minutes (Examples 5 to 7). In Comparative Examples 2 to 4, CO2 gas was supplied at a flow rate of 2.0 L / min for 30 minutes without adjusting the pH of the leachate. (3) Samples were taken before and after the CO2 gas supply, and calcium ions were quantified by chelate titration. The results are shown in Table 3 and Figures 4(a) to 4(c). The removal rate was calculated based on the calcium ion concentration in the solution adjusted to pH 8.2 before the CO2 gas supply.

[0042] [Table 3]

[0043] In Examples 5 to 7, 90% or more of the calcium ions were removed within 5 minutes of the start of CO2 gas supply. On the other hand, in Comparative Examples 2 to 4, in which the pH was not adjusted during CO2 gas supply, the reaction solution became weakly acidic immediately after the start of CO2 gas supply, and almost no calcium ions were removed.

[0044] [Third embodiment] In a third embodiment, the alkalinity maintaining device drips an alkaline solution after the gas supply step to adjust the acidity of the leachate.

[0045] In the third embodiment, the CO2-containing gas may be air or exhaust gas containing CO2. It may also be a gas with a concentrated CO2 concentration. The CO2 concentration of the CO2-containing gas may be 4% or more, or 25% or more, or 80% or more, or 90% or more.

[0046] In the third embodiment, during the calcium removal step, the leachate is maintained in a neutral to alkaline range, preferably at a weak alkaline pH (pH 8 to 11), and more preferably at a pH of 8 to 9.

[0047] (Calcium removal test 2 using CO2 gas supply) For Examples 8 to 10 and Comparative Examples 5 to 7, calcium removal tests by supplying CO2 gas were carried out as follows.

[0048] Experimental method (1) 1 L of each of leachates G, H, and I collected from the final disposal site on different collection days was poured into a beaker (Examples 8 to 10). (2) Next, CO2 gas (Air Water: 99.5% by volume) was supplied to each of the prepared leaching solutions at a flow rate of 2.0 L / min for 1 minute, 3 minutes, and 5 minutes. (3) After gas supply, the pH of the leachate was adjusted to 8.2 with 10 M NaOH aqueous solution. (4) After pH adjustment, an aliquot of the sample was taken, and calcium ions were quantified by chelate titration. The results are shown in Table 4. The calcium removal rate was the removal rate after 5 minutes of aeration, and was calculated based on the calcium ion concentration of the leachate, which was adjusted to pH 8.2 by only adjusting the pH before CO2 gas supply. In Comparative Examples 5 to 7, calcium ions were quantified without adjusting the pH of the leachate after gas supply.

[0049] [Table 4]

[0050] In Examples 8 to 10, 60% or more of the calcium ions were removed after 5 minutes of CO2 gas supply. On the other hand, in Comparative Examples 5 to 7, in which the pH was not adjusted to a weak alkaline level after CO2 gas supply, almost no calcium ions were removed.

[0051] [Fourth embodiment] In a fourth embodiment, the CO2-containing gas comprises CO2 emitted from a waste treatment facility or an industrial plant. The CO2 from the flue gas may be concentrated.

[0052] In this way, by using CO2 contained in exhaust gas from a waste treatment facility to remove calcium from leachate discharged from a final disposal site, it is possible to fix CO2 emitted from the system in a waste treatment system that includes a waste treatment facility and a final disposal site. Furthermore, it is possible to suppress calcium scaling and contribute to the conservation of leachate treatment equipment from final disposal sites.

[0053] Although various embodiments have been described above, the present invention is not limited to these. Other embodiments conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention. Furthermore, one or more of the above-described embodiments may be combined as appropriate.

Claims

1. 1. An apparatus for removing calcium from a leachate, comprising: means for maintaining the leachate in a neutral to alkaline range during the calcium removal step; The leachate is added to CO 2 a means for supplying a gas comprising An apparatus comprising:

2. The device of claim 1 , wherein the leaching solution is maintained at a slightly alkaline pH.

3. The device of claim 2, wherein the leachate is maintained at a pH of 8 to 9.

4. 2. The apparatus of claim 1, wherein the step of maintaining the leachate in a neutral to alkaline range is performed before the step of supplying gas is performed.

5. 5. The apparatus of claim 4, wherein the gas is air, and the leachate is adjusted to a pH of 10 or higher before the gas supplying means is applied.

6. 2. The apparatus of claim 1, wherein the means for maintaining the leachate in a neutral to alkaline range is performed while the means for supplying gas is in operation.

7. The gas is CO 2 7. The device of claim 6, wherein the gas has a concentration of 4% or more.

8. The gas is CO 2 7. The device of claim 6, wherein the gas has a concentration of 25% or more.

9. The gas is CO 2 7. The device according to claim 6, wherein the gas has a concentration of 80% or more.

10. 2. The apparatus of claim 1, wherein the step of maintaining the leachate in a neutral to alkaline range is performed after the step of supplying gas.

11. The gas is CO 2 The device of claim 10, wherein the gas has a concentration of 4% or more.

12. The gas is CO 2 The device of claim 10, wherein the gas has a concentration of 25% or more.

13. The gas is CO 2 The device according to claim 10, wherein the gas has a concentration of 80% or more.

14. The gas is CO emitted from a waste treatment facility. 2 The apparatus of claim 1 , comprising:

15. 1. A method for removing calcium from a leachate, comprising: maintaining the leachate in a neutral to alkaline range during the calcium removal step; The leachate is added to CO 2 10. A method comprising: providing a gas comprising:

16. 16. The method of claim 15, wherein the leachate is maintained at a slightly alkaline pH.

17. 16. The method of claim 15, wherein the step of maintaining the leachate in a neutral to alkaline range is performed before the step of supplying gas.

18. 16. The method of claim 15, wherein the step of maintaining the leachate in a neutral to alkaline range is performed during the step of supplying gas.

19. The gas is CO 2 19. The method of claim 18, wherein the gas has a concentration of 4% or more.

20. 16. The method of claim 15, wherein the step of maintaining the leachate in a neutral to alkaline range is performed after the step of providing gas.

21. The gas is CO 2 21. The method of claim 20, wherein the gas has a concentration of 4% or more.

22. The gas is CO emitted from a waste treatment facility. 2 16. The method of claim 15, comprising:

23. A leachate treatment system comprising a plurality of steps including a step of using the device according to any one of claims 1 to 14 and a coagulation and sedimentation step.

24. 24. The leachate treatment system according to claim 23, wherein the process using the device is installed upstream of the coagulation and sedimentation process in the plurality of processes.

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