Leachate treatment system and leachate treatment method

Abstract

To provide an exudation water treatment system and an exudation water treatment method that enable smooth treatment without adding a chemical such as sodium carbonate that reacts with calcium in exudation water treatment.SOLUTION: In order to solve the above problems, an exudation water treatment system having a reaction tank that adjusts a Langelier index of exudation water to 1.5 or less, and an exudation water treatment method using the system are provided. According to the system and the method, by adjusting the Langelier index of the exudation water within a specific range, calcium precipitation (scale formation) in the exudation water is suppressed, it is possible to smoothly treat the exudation water by taking measures against scale without generating and removing calcium compounds by adding the chemical that reacts with calcium (such as sodium carbonate) in exudation water treatment, and it is possible to significantly reduce running costs in the exudation water treatment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a leachate treatment system and a leachate treatment method. [Background technology]

[0002] Leachate generated from waste landfill sites often contains various chemical substances (salts, organic matter, heavy metals, etc.) resulting from the waste itself and additives added during the waste treatment process, and must be properly treated before being discharged into public waters. It is known that the calcium contained in the leachate adheres to the equipment as scale, which can cause problems in that it impedes the safe operation of the treatment system. For this reason, measures against calcium-based scale are being considered for the treatment of leachate.

[0003] For example, Patent Document 1 describes a method in which sodium carbonate is added to the leachate, the precipitated calcium carbonate is separated, and then the pH is adjusted to prevent the precipitated calcium from redissolving and remove the calcium from the leachate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-16341 A Summary of the Invention [Problem to be solved by the invention]

[0005] As described in Patent Document 1, it is known that a chemical such as sodium carbonate is added to the leachate to remove calcium by precipitating / settling as calcium carbonate, thereby taking measures against scale formation. However, in order to precipitate the calcium in the leachate as calcium carbonate, it is necessary to add an equivalent amount of sodium carbonate to the calcium. Therefore, the higher the calcium concentration in the leachate, the more sodium carbonate is required, which increases the cost of the chemicals, and there is also the problem that the cost of treating the precipitates formed by adding the chemicals is also high.

[0006] Therefore, an object of the present invention is to provide a leachate treatment system and a leachate treatment method that enable smooth treatment without adding chemicals that react with calcium, such as sodium carbonate. [Means for solving the problem]

[0007] As a result of extensive research into the above-mentioned problems, the present inventors have discovered that by adjusting the Langelier index, which is known as an index of water corrosivity, when treating leachate, it is possible to take measures against scale and enable smooth treatment without adding chemicals that react with calcium, such as sodium carbonate. That is, the present invention relates to the following leachate treatment system and leachate treatment method.

[0008] In order to solve the above problems, the leachate treatment system of the present invention is a leachate treatment system that treats leachate, and is characterized by having a reaction tank that adjusts the Langelier index of the leachate to 1.5 or less. According to this leachate treatment system, by adjusting the Langelier index of the leachate within a specific range, calcium precipitation (scaling) in the leachate is suppressed, and the leachate can be treated smoothly without removing calcium ions in the leachate. In other words, it is possible to take measures against scaling without generating and removing calcium compounds by adding chemicals that react with calcium (sodium carbonate, etc.), and it is possible to significantly reduce the running costs of leachate treatment.

[0009] Furthermore, one embodiment of the leachate treatment system of the present invention is characterized in that it is equipped with a pH adjustment means for adjusting the pH of the leachate, and the pH adjustment means adjusts the pH in the reaction tank to be greater than 6.0. According to this feature, by providing a means for adjusting the pH, which has a large contribution to the Langelier index, it becomes easy to adjust the Langelier index so that it falls within an appropriate numerical range. In addition, by adjusting the pH to be greater than 6.0, it is possible to prevent the Langelier index from becoming a large negative value, and to maintain a state that allows both scale countermeasures and corrosion tendency suppression, and it is also possible to reduce the cost associated with pH adjustment.

[0010] In addition, one embodiment of the leachate treatment system of the present invention is characterized in that the leachate contains calcium and suspended solids, and a coagulation and sedimentation tank is provided downstream of the reaction tank. According to this feature, unlike conventional leachate treatment in which calcium compounds (calcium carbonate) are precipitated by adding chemicals that react with calcium, there is no need to perform coagulation and precipitation treatment for calcium compounds. Therefore, in addition to eliminating the need to add chemicals that react with calcium, it is also possible to reduce the amount of coagulant added. This has the effect of making it possible to smoothly carry out scale countermeasures and coagulation and precipitation treatment in leachate treatment without incurring running costs.

[0011] One embodiment of the leachate treatment system of the present invention is characterized in that it is provided with a biological treatment tank downstream of the reaction tank or the coagulation and sedimentation tank. According to this feature, unlike conventional leachate treatment in which calcium compounds (calcium carbonate) are precipitated by adding chemicals that react with calcium, it is possible to smoothly treat the leachate for release into public water bodies without removing calcium and after taking measures against scale. In particular, since it is no longer necessary to add chemicals that react with calcium and to carry out treatment related to calcium compounds, it is possible to achieve an effect of significantly reducing running costs compared to conventional leachate treatment.

[0012] In addition, the leachate treatment method of the present invention for solving the above problems is a leachate treatment method for treating leachate, and is characterized in that it includes a Langelier index adjustment step for adjusting the Langelier index of the leachate to 1.5 or less. According to this leachate treatment method, by adjusting the Langelier index of the leachate within a specific range, conditions are created in which calcium precipitation (scaling) in the leachate is suppressed, and the leachate can be treated smoothly without removing calcium ions in the leachate. In other words, it is possible to take measures against scaling without generating and removing calcium compounds by adding chemicals that react with calcium (sodium carbonate, etc.) in the leachate treatment, and it is possible to significantly reduce the running costs of the leachate treatment. Effect of the Invention

[0013] According to the present invention, it is possible to provide a leachate treatment system and a leachate treatment method that enable smooth treatment without adding chemicals that react with calcium, such as sodium carbonate. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a leachate treatment system according to a first embodiment of the present invention. [Diagram 2] 1 is a graph showing an example of the calculation results of the Langelier index for standard leachate. [Diagram 3] 2 is a graph showing an example of the results of adjusting the Langelier index of standard leachate using the leachate treatment system according to the first embodiment of the present invention. [Figure 4] 1 is a graph showing an example of the results of adjusting the Langelier index of standard leachate using another aspect of the leachate treatment system according to the first embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram showing the configuration of a leachate treatment system according to a second embodiment of the present invention. [Figure 6] FIG. 11 is a schematic diagram showing the configuration of a leachate treatment system according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A preferred embodiment of the present invention will be described below with reference to the drawings. The leachate treatment method of the present invention is replaced with the following description of the configuration and operation of the leachate treatment system. The present invention is not limited to this embodiment.

[0016] The leachate treatment system of the present invention is intended to be used for treating leachate from a final waste landfill site. Here, the "leachate" in the present invention refers to water derived from waste buried in a final waste landfill site, or rainwater that falls in a final waste landfill site and passes through the waste layer, and particularly refers to water that contains calcium (calcium ions), which is a cause of scale. Leachate to be treated in the present invention has a calcium concentration of 1 mg / L or more. This makes it possible to fully exert the effect of the present invention, which is to suppress the impact of scale generation on leachate treatment. Other components contained in the leachate are not particularly limited, but examples thereof include suspended solids (hereinafter referred to as "SS"), heavy metals, and the like. As described below, one embodiment of the leachate treatment system of the present invention is particularly useful in treating leachate containing calcium and SS.

[0017] [First embodiment] FIG. 1 is a schematic diagram showing the configuration of a leachate treatment system according to a first embodiment of the present invention. The leachate treatment system 1A of this embodiment treats leachate W, and as shown in Fig. 1, includes a reaction tank 2 and a Langelier index adjustment means 3 for adjusting the Langelier index in the reaction tank 2. It also includes a line L1 for supplying leachate W to the reaction tank 2 and a line L2 for discharging leachate W1 with its Langelier index adjusted from the reaction tank 2. In Fig. 1, the arrows indicate the flow of water.

[0018] The reaction tank 2 is a tank for storing the leachate W and for adjusting the Langelier index of the leachate W to be within a specific range. The reaction tank 2 is also equipped with a Langelier index adjustment means 3 for adjusting the Langelier index of the leachate W. As shown in Fig. 1, the leachate W is supplied into the reaction tank 2 via a line L1. The reaction tank 2 is not particularly limited as long as it can store the leachate W and can adjust the Langelier index by the Langelier index adjustment means 3. Although one tank is shown as the reaction tank 2 in Fig. 1, a combination of multiple tanks may be used.

[0019] The Langelier index is an index used as an indicator of the corrosiveness of water, and is a numerical value that indicates the tendency of calcium carbonate to precipitate (form a film) in water. Note that the more positive the Langelier index is, the more likely calcium carbonate will precipitate, whereas when the Langelier index is negative, calcium carbonate will not precipitate, and the more the absolute value of the index is, the more corrosive the water is.

[0020] As shown in the following formula 1, the Langelier Index (LI) is calculated from the difference between the actual pH of water and the pH when calcium carbonate in the water is in an equilibrium state where it is neither dissolved nor precipitated (theoretical pH: hereinafter referred to as "pHs"), and is affected by the water temperature (T (unit: °C)).

number

[0021] The pHs is calculated according to the following formula 2.

number

number

[0022] The calculation of the Langelier index based on the above formulas 1 to 3 will be explained below using a specific example. Here, the calculation of the Langelier index will be explained by taking as an example a leachate having general properties of being highly alkaline and containing a certain amount of calcium ions (hereinafter referred to as "standard leachate").

[0023] Fig. 2 is a graph showing the calculation results of the Langelier index for the standard leachate. More specifically, Fig. 2 is a graph showing the contribution of each parameter to the Langelier index for the standard leachate. The properties of the standard leachate in Figure 2 are pH 11.0, calcium ion concentration 1,500 mg / L (= 74.8 meq / L), total alkali content 63 mg / L (= 1.3 meq / L), evaporation residue concentration 14,600 mg / L, and water temperature 20°C. As shown in Fig. 2, the Langelier index of the standard leachate taken as an example is 3.83 as a result of calculations made using Equations 1 to 3 based on the parameters of the standard leachate. Note that the inventors have confirmed that this Langelier index causes scale formation during leachate treatment.

[0024] On the other hand, in the reaction tank 2 in this embodiment, the Langelier index is adjusted to be within a specific range. More specifically, it is preferable to adjust the Langelier index of the leachate W in the reaction tank 2 to 1.5 or less. This makes it possible to create conditions that suppress calcium precipitation (scale generation) in the leachate W, and to smoothly treat the leachate W without removing calcium ions in the leachate W. In other words, scale prevention can be performed without generating and removing calcium compounds by adding chemicals that react with calcium (sodium carbonate, etc.) in the leachate treatment, and it becomes possible to significantly reduce the running costs in the leachate treatment.

[0025] Furthermore, the upper limit of the Langelier index of the leachate W in the reaction tank 2 is more preferably 1.0 or less, and even more preferably 0.5 or less, which can further enhance the effect of suppressing scale generation. On the other hand, since a negative value of the Langelier index increases the tendency of water to corrode, it is preferable to set the lower limit of the Langelier index of the leachate W in the reaction tank 2 to -1.0 or more. This makes it possible to prevent corrosion of the leachate treatment system 1A. In particular, by setting the Langelier index close to 0, it is possible to suppress both the formation of scale and the tendency to corrode.

[0026] The Langelier index adjustment means 3 is for carrying out a Langelier index adjustment step of adjusting the Langelier index of the leachate W in the reaction tank 2. Here, the parameters of the Langelier index are pH value, calcium ion concentration, total alkali concentration, evaporation residue concentration, and water temperature, as shown in Equations 1 to 3. In addition, as shown in Fig. 2, the pH value of water has a particularly large contribution to the Langelier index. For this reason, the Langelier index adjustment means 3 in this embodiment may be provided with various means for adjusting parameters relating to the Langelier index based on the above formulas 1 to 3.

[0027] An example of the Langelier index adjustment means 3 in this embodiment is to provide a means for adjusting the pH value of water, which is a parameter that has a high contribution to the Langelier index. That is, a pH adjustment means 30 for adjusting the pH value of the leachate W in the reaction tank 2 is provided.

[0028] The pH adjusting means 30 is not particularly limited as long as it can adjust the pH value of the leachate W. 1, an example of the pH adjustment means 30 is an aeration device 31 that uses air and is provided in the reaction tank 2. The aeration device 31 may also function as an agitation means in the reaction tank 2.

[0029] By performing air aeration using the aeration device 31, components contained in the air (particularly carbon dioxide) dissolve in the leachate W. At this time, the carbon dioxide dissolved in the leachate W becomes acidic. As described above, the leachate W is mainly highly alkaline, and a neutralization reaction occurs due to the dissolution of carbon dioxide, causing the pH of the leachate W to decrease. This makes it possible to adjust the pH value of the leachate W. The range of pH adjustment by the aeration device 31 depends on the solubility of carbon dioxide in the leachate W, and the pH of the leachate W is in the range of approximately 7 to 9.

[0030] Furthermore, when adjusting the pH by the aeration device 31, a control means for adjusting the amount of aeration by the aeration device 31 may be provided. In this case, it is preferable to provide a pH meter (pH sensor) in the reaction tank 2 and control the amount of aeration while monitoring the pH. This makes it easy to adjust the pH value of the leachate W so as to satisfy a predetermined Langelier index.

[0031] Fig. 3 is a graph showing the results of adjustment of the Langelier index by adjusting the pH of the standard leachate shown in Fig. 2 using the aeration device 31. More specifically, Fig. 3 is a graph showing the contribution of each parameter to the Langelier index in the leachate that has been pH adjusted. As shown in Fig. 3, when the pH value of the standard leachate (leachate W) is set to 8.0 by the aeration device 31, the Langelier index falls to 0.83. The inventors have confirmed that this Langelier index suppresses scale generation during leachate treatment. This makes it possible to suppress calcium precipitation (scale generation) in the leachate treatment system 1A without using chemicals that react with calcium, and to smoothly treat the leachate.

[0032] As another example of the pH adjusting means 30, as shown in FIG. 1, a pH adjusting agent adding section 32 for adding a pH adjusting agent to the reaction tank 2 may be provided. The pH adjuster adding unit 32 is not particularly limited in terms of its specific structure as long as it can add a pH adjuster to the reaction tank 2. For example, it may include a storage tank 32a for storing the pH adjuster and a pipe 32b for adding the pH adjuster from the storage tank 32a to the reaction tank 2. Note that the pipe 32b is preferably provided with an addition amount adjustment mechanism such as a valve for adjusting the amount of pH adjuster added.

[0033] The pH adjuster is not particularly limited as long as it can adjust the pH of the leachate W. The leachate W is mainly highly alkaline, and in order to adjust the Langelier index to a predetermined range, it is necessary to lower the pH of the leachate W. For this reason, it is preferable to use an acid as the pH adjuster in this embodiment, but an alkali may be used depending on the properties of the leachate W. In the present embodiment, an example of the pH adjuster is an inorganic acid, taking into consideration the effect on leachate treatment and ease of availability and handling. More specifically, sulfuric acid is used.

[0034] Fig. 4 is a graph showing the results of adjustment of the Langelier index by performing pH adjustment using the pH adjuster adding unit 32 on the standard leachate shown in Fig. 2. More specifically, Fig. 4 is a graph showing the contribution of each parameter to the Langelier index in the leachate that has been pH adjusted. As shown in Fig. 4, an inorganic acid (sulfuric acid) is added as a pH adjuster by the pH adjuster adding unit 32, and the pH value of the standard leachate (leachate W) is set to 7.1. At this time, the total alkali concentration value also changes (0.4 meq / L (= 22 mg / L)) due to the addition of the inorganic acid, and the Langelier index falls to -0.52. The inventors have confirmed that this Langelier index suppresses scale formation during leachate treatment. This makes it possible to suppress calcium precipitation (scale formation) in the leachate treatment system 1A without using chemicals that react with calcium, and to smoothly treat the leachate.

[0035] When the pH adjusting means 30 includes a pH adjuster adding section 32 and adjusts the pH of the leachate W with a pH adjuster, it becomes easy to make the pH of the leachate W more acidic. However, as described above, making the pH of the leachate W more acidic causes the Langelier index to become a large negative value, which is not preferable from the viewpoint of corrosion tendency. In addition, using more pH adjuster than necessary is not preferable from the viewpoint of running costs. Therefore, in the pH adjustment by the pH adjusting means 30, the pH of the leachate W is preferably adjusted to be greater than 6.0. More preferably, the pH of the leachate W is adjusted to be 7.0 or greater.

[0036] 1 shows the pH adjustment means 30 provided with an aeration device 31 and a pH adjuster adding section 32, but the present invention is not limited to this and may be any means capable of performing the necessary pH adjustment. For example, the leachate treatment system 1A may be provided with either the aeration device 31 or the pH adjuster adding section 32. This allows the structure of the leachate treatment system 1A to be simplified and allows the running costs to be reduced.

[0037] The Langelier index adjusting means 3 in this embodiment is not limited to providing a means for adjusting pH. For example, a water temperature adjusting means for adjusting the water temperature in the reaction tank 2, or a calcium concentration adjusting means that does not involve the addition of a chemical that reacts with calcium to produce a precipitate, may be provided. More specifically, a cooling device for lowering the water temperature in the reaction tank 2, or a means for introducing dilution water into the reaction tank 2 may be provided.

[0038] Furthermore, as one of the Langelier index adjustment means 3, a measuring device for acquiring values ​​related to each parameter for calculating the Langelier index may be provided. For example, in addition to the above-mentioned pH meter (pH sensor), a thermometer, a calcium concentration meter, etc. may be included. In this case, the timing of measurement by each measuring device is not particularly limited, and in addition to constant (real-time) measurement, measurement may be performed periodically or at any timing. In this case, the measurements using each measuring device may be performed inside the reaction tank 2, or may be performed on a sample of a portion of the leachate W in the reaction tank 2.

[0039] In the reaction tank 2, the leachate W1 adjusted to a predetermined Langelier index is discharged outside the system via a line L2. In addition, if the leachate W1 does not contain components related to the effluent standards (organic substances, heavy metals, etc.) and meets the water quality requirements for discharge into public waters, it can be discharged directly into public waters via line L2.

[0040] In this embodiment, the leachate treatment system 1A adjusts the Langelier index of the leachate W to within a specific range, thereby creating conditions in which calcium precipitation (scale formation) in the leachate W is suppressed, and it is possible to smoothly treat the leachate W without removing calcium ions in the leachate W. In addition, in this embodiment, the leachate treatment system 1A is sufficient if the Langelier index of the leachate W in the reaction tank 2 is within a specific range, resulting in a state in which calcium precipitation is suppressed, and it is not an essential requirement to calculate the Langelier index during treatment in the leachate treatment system 1A.

[0041] [Second embodiment] FIG. 5 is a schematic diagram showing the configuration of a leachate treatment system according to a second embodiment of the present invention. As shown in Fig. 5, the leachate treatment system 1B of the second embodiment is provided with a coagulation and sedimentation tank 4 downstream of the reaction tank 2 in the first embodiment. The reaction tank 2 and the coagulation and sedimentation tank 4 are connected by a line L3, and the leachate W1 with an adjusted Langelier index is supplied from the reaction tank 2 to the coagulation and sedimentation tank 4 via the line L3. The coagulation and sedimentation tank 4 further includes a line L4 and a line L5 for discharging the separated solids S and liquid (treated water W2) out of the system, respectively. Note that a description of the same configuration as in the first embodiment will be omitted.

[0042] When leachate W contains calcium and SS, it cannot be discharged into public waters while still containing SS. In addition, as described below, when biological treatment is applied as one of the leachate treatment methods, it is known that SS is an inhibitor of the biological treatment. Therefore, in order to smoothly treat the leachate, it is necessary to suppress the precipitation of calcium in the leachate W and to separate the SS.

[0043] Here, in the leachate treatment system 1B in this embodiment, the reaction tank 2 and the coagulation sedimentation tank 4 are separately provided, and the reaction tank 2 is disposed upstream of the coagulation sedimentation tank 4. This makes it possible to perform the treatment related to the Langelier index adjustment of the leachate W in advance and independently, and the coagulation sedimentation treatment is performed on the leachate W1 in which calcium precipitation is suppressed. Therefore, unlike the conventional leachate treatment in which calcium compounds (calcium carbonate) are precipitated by adding a chemical that reacts with calcium, in the coagulation sedimentation tank 4 in this embodiment, there is no need to perform the coagulation sedimentation treatment related to calcium compounds, and only the coagulation sedimentation treatment of SS is performed. Therefore, in addition to eliminating the need to add a chemical that reacts with calcium, it is also possible to reduce the amount of coagulant added. This makes it possible to smoothly proceed with scale countermeasures and SS treatment in the leachate treatment without incurring running costs.

[0044] The leachate W to be treated by the leachate treatment system 1B according to this embodiment has a calcium concentration of 1 mg / L or more and a SS concentration of 100 mg / L or more, which allows the effect of the leachate treatment system 1B according to this embodiment to be fully exhibited.

[0045] The coagulation sedimentation tank 4 in this embodiment is not particularly limited as long as it can perform coagulation sedimentation treatment for SS in the leachate W1. For example, the coagulation sedimentation tank 4 may be provided with a coagulant addition unit that adds a coagulant, or a stirring unit that stirs and mixes the coagulant and the leachate W1. The coagulant addition unit may be provided in the reaction tank 2, and adjustment of the Langelier index and mixing of the coagulant may be performed in the reaction tank 2 at the same time.

[0046] The flocculant added in the coagulation settling tank 4 is not particularly limited. The flocculant used in this embodiment may be either an inorganic flocculant or a polymer flocculant, and may be used in combination with an inorganic flocculant depending on the components and flocculation state in the leachate W1. For example, inorganic flocculants include polyferric sulfate, ferric chloride, polysilica iron, aluminum sulfate, polyaluminum chloride, etc., and polymer flocculants include cationic polymer flocculants such as polyaminoalkyl methacrylate, polyethyleneimine, halogenated polydiallylammonium, chitosan, and urea-formalin resin, anionic polymer flocculants such as sodium polyacrylate, polyacrylamide partial hydrolysate, partially sulfomethylated polyacrylamide, and poly(2-acrylamide)-2-methylpropane sulfate, nonionic polymer flocculants such as polyacrylamide and polyethylene oxide, and amphoteric polymer flocculants such as a copolymer of acrylamide, aminoalkyl methacrylate, and sodium acrylate. It is preferable to use at least an inorganic flocculant because it is possible to maintain a good flocculation state.

[0047] The solid fraction S and liquid fraction (treated water W2) separated in the coagulation and settling tank 4 are discharged to the outside of the system via line L4 and line L5, respectively.

[0048] At this time, the solid content S is mainly derived from SS, and it is preferable to further treat it as necessary. More specifically, the solid content S is supplied to a dehydration facility via a line L4. The dehydration facility may be equipped with one or more devices related to the dehydration treatment of the solid content S, and examples of such devices include a concentration tank, a storage tank, a chemical introduction device, a dehydrator, etc. As described above, the leachate treatment system 1B in this embodiment performs treatment without precipitating calcium in the leachate W. Therefore, compared to conventional leachate treatment in which calcium compounds are precipitated by adding a chemical that reacts with calcium, it is possible to reduce the amount of solids S precipitated and discharged in the coagulation sedimentation tank 4. This reduces the amount of solids S supplied to the dehydration equipment, which has the effect of reducing the treatment costs associated with the dehydration.

[0049] On the other hand, the liquid portion (treated water W2) contains components other than SS (calcium and other components) that were contained in the leachate W1. Therefore, if the treated water W2 does not contain components related to the effluent standards (organic substances, heavy metals, etc.) and meets the water quality requirements for discharge into public waters, it can be discharged directly into public waters via line L5.

[0050] [Third embodiment] FIG. 6 is a schematic diagram showing the configuration of a leachate treatment system according to a third embodiment of the present invention. As shown in Fig. 6, the leachate treatment system 1C of the third embodiment is provided with a biological treatment tank 5 downstream of the coagulation and sedimentation tank 4 of the second embodiment. The coagulation and sedimentation tank 4 and the biological treatment tank 5 are connected by a line L6, and the liquid (treated water W2) separated in the coagulation and sedimentation tank 4 is supplied to the biological treatment tank 5 via the line L6. The biological treatment tank 5 is further provided with a line L7 for discharging the biologically treated treated water W3 to the outside of the system. Note that explanations of the same configurations as those of the second embodiment will be omitted.

[0051] If the leachate W contains nitrogen-containing compounds and organic matter that are subject to discharge standards in addition to calcium and SS, the treated water W2 cannot be discharged directly into public waters because it cannot be treated entirely by coagulation and sedimentation alone. Therefore, in addition to the coagulation and sedimentation treatment, it is necessary to apply a further treatment method to treat the treated water W2 to a water quality suitable for discharge into public waters.

[0052] Here, the leachate treatment system 1C in this embodiment is provided with a biological treatment tank 5 downstream of the reaction tank 2 and the coagulation and sedimentation tank 4. As a result, after adjusting the Langelier index, biological treatment is carried out on the treated water W2 that has been subjected to the coagulation and sedimentation treatment. Therefore, unlike conventional leachate treatment in which calcium compounds (calcium carbonate) are precipitated by adding chemicals that react with calcium, this method makes it possible to smoothly carry out the entire leachate treatment without removing calcium and after taking measures against scale. In particular, since it is no longer necessary to add chemicals that react with calcium and to carry out treatment related to calcium compounds, it is possible to significantly reduce running costs compared to conventional leachate treatment. In addition, by providing a biological treatment tank 5 downstream of the coagulation and sedimentation tank 4, biological treatment can be performed on treated water W2 from which SS, which is an inhibiting factor in biological treatment, has been removed in advance, allowing for smoother treatment progress without reducing the treatment efficiency of the entire leachate treatment.

[0053] The biological treatment tank 5 in this embodiment is not particularly limited as long as it can treat nitrogen-containing compounds and organic matter in the leachate W (treated water W2). For example, a nitrification tank to which activated sludge containing nitrifying bacteria is added, and a denitrification tank to which activated sludge containing denitrifying bacteria is added, etc. are included. The nitrification tank oxidizes ammonia nitrogen to oxidized nitrogen by nitrifying bacteria in an oxidizing (aerobic) atmosphere. The denitrification tank reduces oxidized nitrogen to nitrogen gas by denitrifying bacteria in a reducing (anaerobic) atmosphere. These biological treatment tanks 5 may be used alone or in combination of multiple tanks.

[0054] If the amount of SS in the leachate W to be treated is less than 100 mg / L and no SS separation treatment is required, the coagulation and sedimentation tank 4 in Fig. 6 may be omitted and a biological treatment tank 5 may be connected downstream of the reaction tank 2. This makes it possible to simplify the configuration of the leachate treatment system 1C.

[0055] After treatment in the biological treatment tank 5, the treated water W3 is discharged outside the system via line L7. If the treated water W3 does not contain components related to the effluent standards (heavy metals, etc.) and meets the water quality requirements for discharge into public water areas, it can be discharged directly into public water areas via line L7.

[0056] On the other hand, when the treated water W3 does not meet the water quality requirement for discharge into a public water area, an advanced treatment facility for treating the treated water W3 may be further provided downstream of the biological treatment tank 5 in this embodiment. The advanced treatment facility may include one or more devices for treating substances that cannot be completely treated by the coagulation and sedimentation treatment in the coagulation and sedimentation tank 4 or the biological treatment in the biological treatment tank 5. Examples of such devices include a filtration device, an activated carbon adsorption tower, a chelating adsorption tower for capturing heavy metals, an ozone treatment device, an acidic coagulation and sedimentation treatment tank, etc.

[0057] In this case, a part of the treated water discharged from the advanced treatment facility may be used as a pH adjuster. For example, the pH of the treated water in the acidic coagulation sedimentation treatment tank is about 4 to 5. Therefore, as the Langelier index adjustment means 3 in this embodiment, instead of the pH adjuster addition section 32, a line for supplying a part of the treated water from the advanced treatment facility (acidic coagulation sedimentation treatment tank) to the reaction tank 2 in this embodiment may be provided. This makes it possible to further reduce the running cost of the leachate treatment system 1C.

[0058] The above-mentioned embodiment shows an example of a leachate treatment system and a leachate treatment method using this system. The leachate treatment system and the leachate treatment method according to the present invention are not limited to the above-mentioned embodiment, and the leachate treatment system and the leachate treatment method according to the above-mentioned embodiment may be modified within the scope of the gist of the claims.

[0059] For example, as the leachate treatment system and leachate treatment method of the present invention, a configuration (reaction tank 2 and Langelier index adjustment means 3) related to the leachate treatment system of this embodiment may be provided for an existing leachate treatment system that adds chemicals such as sodium carbonate, and the operation (leachate treatment method) related to the existing leachate treatment system and the leachate treatment system of this embodiment may be configured to be able to be switched as needed. This makes it possible to both recover calcium carbonate, etc. from the calcium contained in the leachate and remove the calcium contained in the leachate, and to allow the leachate to be discharged without removing the calcium contained in the leachate. In other words, it becomes possible to select a more appropriate treatment system and treatment method in consideration of the running costs related to the use of chemicals and the treatment efficiency for making the water quality dischargeable, depending on the properties of the leachate (concentration of calcium contained, types of components contained other than calcium, etc.). [Industrial Applicability]

[0060] The leachate treatment system and the leachate treatment method of the present invention can be used for treating leachate, and are particularly suitable for treating leachate that requires measures against scale, such as leachate that contains calcium. [Explanation of symbols]

[0061] Reference Signs List 1A, 1B, 1C... leachate treatment system, 2... reaction tank, 3... Langelier index adjustment means, 30... pH adjustment means, 31... aeration device, 32... pH adjuster addition section, 32a... storage tank, 32b... piping, 4... coagulation and settling tank, 5... biological treatment tank, L1 to L7... lines, S... solids, W... leachate, W1... leachate with Langelier index adjusted, W2, W3... treated water

Claims

1. A leachate treatment system for treating leachate, comprising: A reaction tank for adjusting the Langelier index of the leachate to 1.5 or less, A leachate treatment system, characterized in that the reaction tank is installed upstream of a coagulation sedimentation tank or a biological treatment tank.

2. A pH adjusting means for adjusting the pH of the leachate is provided, 2. The leachate treatment system according to claim 1, wherein the pH adjusting means adjusts the pH in the reaction tank to be greater than 6.

0.

3. The leachate treatment system according to claim 1 or 2, characterized in that the leachate contains calcium and suspended solids.

4. A leachate treatment method for treating leachate, comprising the steps of: A Langelier index adjustment step is provided for adjusting the Langelier index of the leachate to 1.5 or less, A leachate treatment method, characterized in that the Langelier index adjustment step is provided prior to a coagulation and sedimentation step or a biological treatment step of the leachate.

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