Waste disposal method

Abstract

To rapidly and safely progress the stabilization of waste in a waste disposal method for depositing an intermediate soil covering layer and a waste layer.SOLUTION: When it is desired to sufficiently supply water to the waste-layer 10A to 10E, it is preferable to use crushed stone (low water-holding capacity material) having a low water-holding capacity and a particle diameter of 2. 5mm or more for the intermediate soil-cover layer 20A to 20D. When the wastes (water-phobic wastes) to which water is not preferably supplied during stabilization are contained in the wastes layers 10A to 10E because harmful gas may be generated by moisture, silica sand (high water-holding capacity material) having a high water-holding capacity and a particle diameter of 0. 6mm or less is preferably used as the intermediate soil cover layers 20A to 20D.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a waste disposal method in which waste is buried underground and stabilized. [Background technology]

[0002] At controlled disposal sites, which are the final disposal sites for waste designated by the government, waste is stored in layers in landfill pits built underground and made harmless (stabilized). In this process, rainwater and other water that seeps into the landfill pits plays an important role, but because this water contains harmful substances, the water that passes through the waste layers is collected and treated at a purification facility before being released. Meanwhile, the stored waste is stabilized (made harmless).

[0003] Patent Document 1 describes the structure of a waste disposal site that performs such treatment. Here, a waterproof sheet is placed on the inner surface of a landfill pit formed in the ground to prevent moisture from leaking to the outside, and multiple layers of waste (waste layers) are piled up inside the landfill pit. However, a cover soil layer (intermediate cover soil layer) is placed on top of each individual waste layer, and each waste layer is piled up with this cover soil layer separating the waste layers, and then a cover soil is placed on top. This makes it possible to safely store and stabilize a large amount of waste in a single landfill pit. Soil that makes up the ground is generally used as the cover soil layer (intermediate cover soil layer).

[0004] In the technology described in Patent Document 2, a water supply pipe for supplying water and an air supply pipe for supplying air are provided in this structure, thereby promoting the stabilization of waste. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-032195 [Patent Document 2] Japanese Patent Application Publication No. 11-216441 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above technology, the moisture that passes through the waste layer contributes to the stabilization of the waste, but most of this moisture is supplied to the waste layer through the intermediate soil cover layer above it. Therefore, when soil is used as the intermediate soil cover layer as in the past, sufficient moisture is not supplied to the waste layer below, which can slow the progress of stabilization.

[0007] On the other hand, some materials that make up waste may emit harmful gases if they are exposed to moisture, such as gypsum board. In this case, it is not desirable to supply a large amount of water to the waste layer.

[0008] The present invention has been made in view of the above circumstances, and aims to rapidly and safely proceed with the stabilization of waste in a waste disposal method in which an intermediate cover soil layer and a waste layer are piled up. [Means for solving the problem]

[0009] The waste disposal method of the present invention is a waste disposal method that stabilizes waste by using a waste disposal site that has a configuration in which layered waste layers containing waste are stacked and stored in a landfill pit formed underground with intermediate cover layers between them, and water is supplied from above and drained from the bottom.As a material for constituting the intermediate cover layer, if the waste that constitutes the waste layer directly below the intermediate cover layer is hydrophilic waste to which it is preferable to supply water for stabilization, a low water retention material with low water retention capacity is used, and if the waste that constitutes the waste layer directly below the intermediate cover layer is hydrophobic waste to which it is not preferable to supply water for stabilization, a high water retention material with higher water retention capacity than the low water retention material is used. The low water retention material may be crushed stone having a particle size of 2.5 mm or more. The high water retention material may be silica sand having a particle size of 0.6 mm or less. A drainage channel that penetrates the waste layer vertically and is buried in the material that constitutes the intermediate cover soil layer that is vertically adjacent to the waste layer may be provided locally in the waste layer in a plan view. [Effects of the Invention]

[0010] According to the present invention, in a waste disposal method in which an intermediate cover soil layer and a waste layer are piled up, stabilization of waste can be progressed quickly and safely. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing the structure of a waste disposal site used in a waste disposal method according to an embodiment of the present invention. [Figure 2] FIG. 1 is a cross-sectional view showing the configuration of an experimental device used to investigate the effects of using low water retention material and high water retention material in the intermediate soil cover layer. [Figure 3] This shows the results of measuring the ratio of the drainage volume in the layered area to the drainage volume in the drained area when low water retention material (a) and high water retention material (b) are used as the intermediate cover soil layer. [Figure 4] FIG. 1 is a diagram showing a schematic diagram of water flow in the intermediate soil cover layer when a low water retention material (a) and a high water retention material (b) are used in the intermediate soil cover layer. [Figure 5] FIG. 10 is a cross-sectional view showing an example of a configuration in which a drainage channel is provided in the waste layer. DETAILED DESCRIPTION OF THE INVENTION

[0012] Next, embodiments of the present invention will be described in detail with reference to the drawings.

[0013] FIG. 1 shows a vertical cross-sectional view of a waste disposal site 1 used in the waste disposal method of this embodiment. In this structure, a landfill pit G0 formed in the ground G has a waterproof sheet 90 provided on the inner surface thereof. Inside, waste layers 10A-10E are stacked with intermediate soil cover layers 20A-20D interposed therebetween, with soil cover layer 20E provided on the top. A drain 40 is provided at the bottom, which allows moisture that has passed through this layered structure to be removed to the outside and treated in a treatment device (not shown) that removes hazardous substances, etc. Moisture supplied to this structure can be rainwater, etc., but moisture supply pipes and air supply pipes may also be provided as appropriate, as in the technology described in Patent Document 2.

[0014] The structure in Figure 1 is similar to that of a conventional waste disposal site. However, whereas in conventional technology the intermediate cover layer was simply the soil that made up the ground G, in this waste disposal site 1, each intermediate cover layer is determined so that the waste can be appropriately treated according to the waste layer directly below it.

[0015] This point will be explained below. Figure 2 shows the structure used in the experiment to investigate the state of moisture permeation in such a layered structure of intermediate soil cover layer and waste layer. In this structure, the state of moisture permeation from the upper side to the lower side in a structure provided with a layered structure of drainage layer 120 corresponding to the intermediate soil cover layer and waste layer 110 was investigated.

[0016] In Figure 2, in the experimental tank 100, in a horizontal region (stacking region) on the left side of the figure with a width L1 (= 45 cm), waste layers 110 are stacked so that a drainage layer 120 with a thickness T2 (= 5 cm) exists on top of three waste layers 110 with a thickness T1 (= 10 cm). On the other hand, in a region (drainage region) on the right side of the figure with a width L2 (= 5 cm), no waste layers 110 exist, and only a drainage layer 120 with a vertical thickness of 45 cm exists. Drains 140A and 140B are provided at the bottom of the stacking region and the bottom of the drainage region, respectively. In addition, a partition plate 150 is provided at the boundary between the stacking region and the drainage region at the bottom.

[0017] Water was uniformly supplied from above this structure as shown by the arrows, to simulate rainfall, and the amount of water discharged from drains 140A and 140B was measured. In addition, moisture sensors were appropriately installed in each waste layer 110 in the stacking region and in the drainage layer 120 at a height corresponding to the waste layer 110 in the drainage region in Figure 2, and it was confirmed that water actually passed through them.

[0018] Here, the moisture discharged from drain 140A can be considered to be moisture that has passed through the stacked structure of three drainage layers 120 (thickness T2) and three waste layers 110 (thickness T1) in the stacked region. On the other hand, the moisture discharged from drain 140B can be considered to be the sum of moisture that has passed directly vertically through the 45 cm thick drainage layer 120 and moisture that has flowed laterally from the stacked region to the drainage region. In other words, the moisture discharged from drain 140A includes a component that has passed vertically through waste layer 110, while the latter does not include a component that has passed vertically through waste layer 110. In the waste disposal site 1 of Figure 1, the component that has passed vertically through waste layer 110 is particularly important.

[0019] Here, incineration bottom ash was used as the waste layer 110 for the experiment. In contrast, two types of materials were used to construct the drainage layer 120 for evaluation. One was coarse-grained crushed stone (grain size 2.5 mm), and the other was fine-grained silica sand (grain size 0.6 mm). Here, the particle size is specified in accordance with JIS A5001-2008. The crushed stone is a material with a larger grain size than incineration bottom ash and has high water permeability (low water retention), while the silica sand is a material with a smaller grain size than incineration bottom ash and has low water permeability (high water retention).

[0020] In the above configuration, the amount of drainage from drain 140A (amount of drainage from the stacked area Q1) and the amount of drainage from drain 140B (amount of drainage from the drainage area Q2) were measured according to the amount of water added from above. Figure 3 shows the ratio of Q1 / Q2 to the total amount of drainage (amount of added water = Q1 + Q2) when crushed stone was used as the drainage layer 120 (a) and when silica sand was used (b).

[0021] As shown here, Q1 / Q2≦1, and the larger Q1 (closer to Q2) is, the more water has permeated the waste layer 110 in the vertical direction, meaning that more water has been supplied to the waste layer 110. In this regard, when large-grained crushed stone is used (FIG. 3(a)), Q1 / Q2 is uniformly 95% or more within the measurement range, and when crushed stone is used, a uniform amount of water is supplied to the waste layer 110.

[0022] On the other hand, when silica sand with a small particle size is used (Figure 3(b)), the Q1 / Q2 value is uniformly low, at around 70%. Furthermore, Q1 / Q2 decreases as the total amount of wastewater increases. This means that when silica sand is used, it becomes difficult for water to be supplied to the waste layer 110, and even if the amount of water supplied is increased, the rate at which the increased amount of water flows through the waste layer 110 decreases.

[0023] In Fig. 2, the typical water flow in the stacked area in this case is shown by dotted arrows A (horizontal) and B (vertical). Fig. 4 is a diagram showing the flow of water in the channels in the drainage layer 120 between the waste layers 110 in Fig. 2 when the crushed stone (a) and silica sand (b) are used for the drainage layer 120, and the thickness of the horizontal arrow corresponds to the flow rate.

[0024] Here, we first focus on the horizontal flow (dotted arrow A) in Figure 2. In both cases (a) where crushed stone is used and (b) where silica sand is used, this flow occurs near the boundary between the drainage layer 120 and the upper waste layer 110.

[0025] In the case of using crushed stone (a), the particle size is large and the voids are large, so the flow rate of flow A is large on the left side of the figure, but the component flowing downward (arrow B in Figure 2) also becomes large. Therefore, this horizontally flowing water flow becomes smaller as it moves toward the right side (the drainage area side). Therefore, the contribution of flow B in Figure 1 becomes larger. In other words, the drainage layer 120 made of crushed stone has a low water retention capacity, and instead, water is easily supplied to the waste layer 110.

[0026] In the case of using silica sand (b), the flow rate of the flow indicated by arrow A is small due to the small particle size and small voids. At this time, the component flowing downward (arrow B in FIG. 2) is also blocked, and this flow is also blocked by the lower waste layer 110. For this reason, the flow indicated by arrow B in FIG. 1 becomes particularly small, and both become small. Furthermore, some components of the flow indicated by arrow B are blocked by the lower waste layer 110, and these components end up flowing horizontally, increasing the contribution of the flow indicated by arrow A in FIG. 2. Alternatively, since silica sand has high water retention, in this case the water retention capacity of the drainage layer 12 is high, and it is difficult for water to be supplied to the waste layer 110.

[0027] That is, when crushed stone with low water retention capacity is used (FIG. 4(a)), the proportion of the flow indicated by arrow B flowing vertically through the drainage layer 120 is large, and moisture is easily supplied to the waste layer 110. On the other hand, when silica sand with high water retention capacity is used (FIG. 4(b)), the proportion of the flow indicated by arrow A flowing horizontally through the drainage layer 120 is large, and moisture is not easily supplied to the waste layer 110.

[0028] In Figure 1, if it is desired to supply sufficient moisture to waste layers 10A-10E, it is effective to increase the flow of arrow B. Based on the above results, in this case, it is preferable to use crushed stone (low-water-retention material) with a particle size of 2.5 mm or more, which has low water-retention capacity, for the intermediate cover soil layers 20A-20D. Examples of waste (water-loving waste) to which it is particularly preferable to supply water during detoxification include incineration bottom ash, as used here, as well as incineration fly ash, non-combustible crushed waste, sludge, etc. When treating these wastes, it is possible to infiltrate a large amount of moisture into the waste layers composed of these wastes, thereby stabilizing the waste in each waste layer.

[0029] On the other hand, if the waste layers 10A-10E contain waste materials (water-phobic waste) for which it is undesirable to add water during stabilization due to the risk of generating harmful gases from moisture, such as gypsum board, it is undesirable to allow a large amount of moisture to penetrate into the waste layers 10A-10E. In this case, increasing the flow of A is effective, and based on the above results, it is preferable to use silica sand (high-water-retention material) with a particle size of 0.6 mm or less, which has high water-retention capacity, as the intermediate soil cover layers 20A-20D. Note that soil used in conventional intermediate soil cover layers may also be used as such a high-water-retention material, as long as it has moisture permeability (water-retention capacity) equivalent to that of the silica sand.

[0030] That is, depending on the contents of the waste layer, either a low water retention material or a high water retention material can be selected and used as the intermediate soil cover layer. The soil cover layer 30 can also be made of the same material as the intermediate soil cover layer.

[0031] 1, the contents of waste layers 10A to 10E do not have to be the same; for example, waste layer 10A can be incineration bottom ash, and the waste layer 10B above it can be gypsum board. In such cases, the material of the intermediate soil layer can be set to suit the waste layer immediately below it. For example, in this case, intermediate soil layer 20A above waste layer 10A can be crushed stone, and intermediate soil layer 20B above waste layer 10B can be silica sand.

[0032] Figure 2 shows the structure used in the above experiment, in which a drainage area with width L2 was provided at the end to transport moisture vertically without passing through the waste layer. In the above waste disposal site, especially when the total number of waste layers and intermediate cover soil layers is large, the amount of moisture supplied to the lower waste layer may be limited if the moisture is supplied only through the upper waste layer and intermediate cover soil layer. For this reason, an area where the waste layer is partially removed, corresponding to the drainage area in Figure 2, can be appropriately provided as a moisture supply path, especially for the lower waste layer. This allows moisture to be efficiently supplied to the lower waste layer as well.

[0033] Figure 5 shows two types of structures similar to that of Figure 1, in which a region (drainage channel 50) that allows water to flow vertically is provided by partially removing the waste layer in the horizontal plane. The structure of Figure 5(a) is substantially similar to the structure of Figure 2 used in the experiment. Here, intermediate soil cover layers 20B-20D are provided between waste layers 10B-10E, but an area where waste layers 10B-10C have been partially removed is provided at the right end of the figure, so a long drainage channel 50 is provided on the right side along the vertical direction, similar to the drainage region in Figure 2. In this case, the drainage channel 50 is a laminated structure of the materials that make up the intermediate soil cover layers 20B-20D and the soil cover layer 20E.

[0034] In the structure shown in Figure 5(b), drainage channels 50, which are areas where waste layers 10B-10C have been partially removed, are provided at different positions in adjacent upper and lower waste layers. In this case, for example, in the intermediate cover soil layer 20C, water can flow horizontally between the drainage channel 50 in the upper waste layer 10D and the drainage channel 50 in the lower waste layer 10C, and this water can be efficiently supplied to the lower intermediate cover soil layer 20B and waste layer 10B. Therefore, this configuration is particularly effective when, for example, the lower waste layer 10B is made of hydrophilic waste, the intermediate cover soil layer 20B is made of a low-water-retention material, and the upper waste layer 10C is made of hydrophobic waste.

[0035] In Figure 5, the intermediate soil cover layer is shown as an integrated unit, but as mentioned above, the waste constituting the waste layer and the material constituting the intermediate soil cover layer (soil cover layer) may be different for each layer. Even in such cases, providing a drainage channel as described above is effective, particularly when water-loving waste and low-water-retention materials are used in the lower layer. Conversely, when water-phobic waste and high-water-retention materials are used in the lower layer, not providing such a drainage channel 50 can limit the supply of water to the waste layer.

[0036] In the structure of Figure 5(b), the drainage channel formed in the waste layer is buried with the material that makes up the intermediate soil cover (soil cover layer), which can be the same material as either the intermediate soil cover (soil cover layer) above or the intermediate soil cover layer below this waste layer. However, in the structure of Figure 1, because the intermediate soil cover (soil cover layer) above it is placed after each waste layer is installed, it is particularly easy to bury the drainage channel with the same material as the upper intermediate soil cover layer.

[0037] The present invention has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in terms of the combination of the respective components, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0038] 1. Waste disposal site 10A~10E, 110 Waste layer 20A~20D Intermediate soil cover layer 20E Soil cover layer 40, 140A, 140B Drain 50 Drainage Channel 90 Waterproof sheet 100 Experimental tank 120 Drainage layer 150 Divider G Ground G0 Landfill Pit

Claims

1. A waste disposal method for stabilizing waste using a waste disposal site having a configuration in which layered waste layers containing waste are stacked and stored in a landfill pit formed underground with intermediate soil covering layers interposed therebetween, and water is supplied from above while water is drained from the bottom, comprising: As a material constituting the intermediate soil cover layer, When the waste constituting the waste layer immediately below the intermediate soil layer is a hydrophilic waste for which it is preferable to supply moisture for stabilization, a low water retention material is used, A waste disposal method characterized by using a high-water-retention material with higher water-retention capacity than the low-water-retention material when the waste constituting the waste layer directly below the intermediate cover soil layer is water-phobic waste for which it is undesirable to supply water for stabilization.

2. 2. A waste disposal method according to claim 1, wherein the low water retention material is crushed stone having a particle size of 2.5 mm or more.

3. 3. A waste disposal method according to claim 1, wherein the high water retention material is silica sand having a particle size of 0.6 mm or less.

4. A waste disposal method as described in claim 1 or 2, characterized in that a drainage channel is locally provided in the waste layer in a plan view, the drainage channel being buried in the material constituting the intermediate cover layer that penetrates the waste layer vertically and is vertically adjacent to the waste layer.

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