An acid-buffering capping material for enhancing degradation in a landfill and preparation and use thereof

Abstract

The application discloses an acid buffer coating material for reinforcing landfill degradation and a preparation method and application thereof, and is mainly made of the following materials: 70-85 parts of municipal solid waste incinerator slag, 5-10 parts of clay and 10-25 parts of quicklime. After the materials are mixed, water is added, and then the mixture is subjected to phased stirring and immersion for 20-25 hours, and then is dried until the water content is less than 5%, and then is sent to a crusher for crushing, and the particle size of the crushed product is controlled to be 2-5 mm. The acid buffer coating material is modified, has strong acid buffer capacity, and has stable acid buffer effect; can significantly increase the production of landfill gas, reduce harmful gas components in the landfill gas; can significantly reduce the concentration of pollutants in the landfill leachate, reduce the cost of subsequent disposal; and can greatly shorten the stabilization time of the landfill waste. The municipal solid waste incinerator slag is mainly used as a raw material, the use of soil resources is reduced, and the resource utilization of the municipal solid waste incinerator slag is realized.

Description

Technical Field

[0001] This application relates to the field of sanitary landfill technology, and in particular to an acid buffer covering material for enhancing landfill degradation, its preparation and application. Background Technology

[0002] The main methods for treating and disposing of municipal solid waste include sanitary landfill, composting, incineration, and pyrolysis. Landfills require a large amount of land resources. According to the regulations for the operation and management of sanitary landfills, waste should be covered after reaching a certain thickness and after each day's filling to prevent the scattering of lightweight waste, the breeding of mosquitoes and flies, the spread of odors, and to reduce infiltration from rainfall or other water sources. Currently, clay is commonly used as the covering layer, with a thickness of 20 centimeters or more. In the landfill space, the soil layer used to cover the waste occupies a large amount of space, reaching 10-20%. Taking a landfill designed for a 15-year lifespan as an example, its operation period is equivalent to 1.5-3 years of soil covering. Calculated based on the construction of 100 sanitary landfills of the same scale, 10-20 of them are occupied and wasted by soil layers. Although some landfills are currently trying to use plastic geomembranes to replace the traditional soil covering layer, the cost is relatively high, and the effect on enhancing waste degradation is not obvious.

[0003] Invention application CN201010213155.5 discloses a soilless waste covering material, mainly composed of cement, fiber, and a polymer binder. The polymer binder is prepared from materials such as dispersible latex powder, resin powder, chloroprene latex, styrene-butadiene latex, and nitrile latex. In application, the soilless waste covering material is mixed with water in a certain proportion, and then the slurry is evenly sprayed onto the landfill to form a closed covering surface. This method can reduce the operation time of covering with soil and alleviate the labor intensity of operators, effectively control the spread of germs from birds foraging, and has certain flame-retardant properties. However, the cost is high, and the material is not environmentally friendly. Invention application CN201510229012.6 discloses an environmentally friendly and efficient municipal solid waste covering agent and its preparation method. The municipal solid waste covering agent is mainly composed of bentonite, sodium carbonate, calcium carbonate, and alkaline protease. This covering layer can remove organic pollutants and inhibit their migration in the environment through adsorption and exchange. However, the material has a high preparation cost and limited effectiveness in enhancing the degradation of landfill waste. Summary of the Invention

[0004] This application provides an acid buffering material for enhancing landfill degradation, its preparation and application. It uses diatomaceous earth, clay and quicklime to modify municipal solid waste incinerator slag, thereby realizing the resource utilization of municipal solid waste incinerator slag while improving the acid buffering capacity of the acid buffering material, which can replace clay to reduce the use of soil resources.

[0005] An acid buffer coating material for enhancing landfill degradation is made from the following raw materials by weight percentage: 70-85% municipal solid waste incinerator slag, 5-10% quicklime, 5-10% clay, and 5-10% diatomaceous earth.

[0006] Optionally, the particle size of the acid buffer coating material is 2 to 5 mm.

[0007] The specific surface area of ​​the municipal solid waste incineration ash is 1.18 m². 2 The apparent relative density is 2.73, and the hydrophilicity coefficient is 0.75. The acid buffer coating material modified according to this invention has a specific surface area of ​​2.3–2.5 m² / g. 2 / g, with an apparent relative density of 2.9–3 and a hydrophilicity coefficient of 0.78–0.8.

[0008] Optionally, it is made from the following raw materials by weight percentage: 75-80% municipal solid waste incinerator slag, 8-10% quicklime, 5-6% clay, and 5-10% diatomaceous earth.

[0009] Furthermore, in one scheme, the municipal solid waste incinerator slag comprises 80%, quicklime 10%, clay 5%, and diatomaceous earth 5%; in another scheme, the municipal solid waste incinerator slag comprises 75%, quicklime 10%, clay 5%, and diatomaceous earth 10%.

[0010] This application also provides a method for preparing an acid buffer coating material for enhancing landfill degradation, comprising:

[0011] By weight percentage, 70-85% municipal solid waste incinerator slag, 5-10% quicklime, 5-10% clay, and 5-10% diatomaceous earth are initially mixed to obtain a mixed material. Water is added at a weight ratio of 1:0.8-1.2 with the mixed material, and the mixture is stirred and soaked for 20-25 hours in stages. Then, it is dried in a drying oven at 180℃-220℃ until the moisture content is less than 5%. Then, it is sent to a crusher for crushing, and the particle size of the crushed material is controlled at 2-5mm.

[0012] Optionally, after mixing the raw materials, add water at a weight ratio of 1:1 with the mixed materials, stir in stages and soak for 24 hours, and then dry in a drying oven at 200°C.

[0013] This application also provides the application of the acid buffer coating material as described above in landfills, wherein the acid buffer coating material is filled as a coating on the top surface and / or the middle of the landfill waste.

[0014] Optionally, when the height of the landfill is 1 to 2 meters, the acid buffer coating material is evenly sprinkled onto the surface of the landfill as a coating layer, and the coating thickness is controlled between 5 and 30 cm.

[0015] Optionally, the waste is municipal waste.

[0016] Compared with the prior art, this application has at least one of the following beneficial effects:

[0017] (1) The amount of acid buffer coating material used is reduced by one-third to one-quarter, which can save a huge amount of space and create greater economic and social benefits.

[0018] (2) The coating material is friendly, which reduces the amount of clay used and enables the resource utilization of slag from municipal solid waste incineration; the modified acid buffer coating material has strong acid buffering capacity and stable acid buffering effect.

[0019] (3) It can significantly increase the production of landfill gas and reduce the harmful gas components in landfill gas;

[0020] (4) It can significantly reduce the concentration of pollutants in landfill leachate and reduce the cost of subsequent treatment;

[0021] (5) It can significantly shorten the stabilization time of landfill waste;

[0022] (6) It mainly uses municipal solid waste incineration slag as raw material, which reduces the use of soil resources and realizes the resource utilization of municipal solid waste incineration slag. Attached Figure Description

[0023] Figure 1 This is a graph showing the changes in the waste settling rate of each landfill column in Example 1;

[0024] Figure 2 This is a diagram showing the biodegradability (BDM) of solid waste in each landfill column in Example 1;

[0025] Figure 3 This is a graph showing the changes in CODcr concentration in the leachate of each landfill column during the landfill cycle in Example 1;

[0026] Figure 4 This is a graph showing the change in methane concentration in landfill gas during the landfill cycle for each landfill column in Example 1. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0029] Example 1

[0030] Under laboratory conditions, simulated landfill columns were constructed to evaluate the performance of a novel acid-buffered cover material for enhancing landfill waste degradation. Four simulated experimental columns were set up, each with a diameter of φ2.5m x 3m and an effective column volume of 14m³. 3 .

[0031] Three different covering materials were prepared before the waste was dumped:

[0032] Material 1: Ordinary clay.

[0033] Material 2: Municipal Solid Waste Incineration Ash: Ash from a municipal solid waste incinerator in Zhejiang Province was collected. Scanning electron microscopy (SEM) observation of the ash particles revealed significant differences in particle diameter and varied shapes, including spherical, rod-shaped, needle-shaped, flaky, and cotton-like forms. The structure was asymmetrical but possessed a rich porous structure. The specific surface area was measured to be 1.18 m². 2 The apparent relative density is 2.73, and the hydrophilicity coefficient is 0.75. The main components are alumina, magnesium oxide, silicon dioxide, and calcium, sodium, and potassium salts. Municipal solid waste incinerator slag is dried, crushed, and sieved; the sieved material with a particle size of 10–20 mm is used as the coating material.

[0034] Material 3: Modified municipal solid waste incinerator slag, i.e., the acid buffer material of this invention, is prepared by:

[0035] The following ingredients are mixed in a mass ratio: municipal solid waste incinerator slag (80%, from the same source as the second type of coating material), quicklime (10%), clay (5%), and diatomaceous earth (5%). After initial mixing, water is added at a 1:1 weight ratio. The mixture is stirred intermittently and soaked for 24 hours (i.e., intermittent stirring during the soaking process). Then, it is dried in a 200℃ drying oven until the moisture content is less than 5%. Finally, it is sent to a crusher for crushing, with the particle size controlled at 2-5 mm.

[0036] Scanning electron microscopy revealed that the modified acid buffer material had relatively uniform particle diameter, primarily spherical, and possessed a rich porous structure. The specific surface area was measured to be 2.38 m². 2 / g, with an apparent relative density of 2.99 and a hydrophilicity coefficient of 0.79.

[0037] Waste is prepared manually:

[0038] The main components of the waste are vegetable scraps, plant leaves and roots, stones, and plastic bags. Before landfilling, large pieces of waste are shredded or crushed (less than 5cm in diameter), mixed evenly, and then loaded. The effective waste loading capacity is 9.5 tons, and anaerobic landfilling is used throughout. Before loading, a 60mm thick layer of gravel is laid at the bottom of each landfill column, followed by a layer of wire mesh. During the degradation process, leachate is produced and seeps into the gravel layer. The leachate is then collected and reinjected into the upper part of the landfill column via a collection device.

[0039] After the waste is filled, No. 1 landfill column is not covered with a waste cover layer; No. 2 landfill column is covered with a 20cm thick layer of clay (material commonly used in landfills, i.e., Material 1); No. 3 landfill column is covered with a 20cm thick layer of municipal solid waste incineration slag (Material 2); and No. 4 landfill column is covered with a 20cm thick layer of acid buffer material (Material 3). The recharge ratio for each landfill column is 15%. Each landfill column is equipped with two solid sampling holes, located 0.5m and 2m from the bottom of the main landfill area, respectively, with an inner diameter of 12cm. The outer ends are sealed with epoxy resin baffles and fixed with bolts. The baffles are immediately sealed after sampling.

[0040] The landfill experiment lasted 200 days, during which the settling rate of the landfill column, the biodegradability of solid waste, changes in pollutant concentrations in the leachate, and the methane content in the landfill gas were measured. The results are as follows:

[0041] After municipal solid waste enters the landfill, organic matter continuously degrades and transforms into inorganic matter under the action of microorganisms, thus continuously increasing the settling rate. The changes in the settling rate of waste in each landfill column during the experimental period are shown below. Figure 1As shown in the figure, the settling rate of each landfill column was relatively fast in the first 10 days, and then slowed down. The trends of the settling rate changes in the experimental group and the control group were basically the same, but there were still significant differences in the rate. On day 100, the settling rate of landfill column 1 was 53%, and the settling rate of landfill column 2 was 56%, indicating that the use of clay cladding material can improve the degradation rate of waste. Landfill columns 3 and 4 both used municipal solid waste incineration ash as cladding material, but on day 100, the settling rates of landfill columns 3 and 4 were 57% and 61%, respectively, indicating that modified incineration ash has a greater advantage in enhancing the degradation of landfill waste.

[0042] Household waste has a complex composition, containing both readily biodegradable and recalcitrant substances. The degree of biodegradability (BDM) is typically used to measure the extent of biodegradability in waste components. Figure 2 The biodegradability (BDM) of solid waste in each landfill column is shown. Both the experimental and control groups showed a rapid decline in BDM. After 60 days, the rate of change in BDM decreased in each landfill column. Overall, the BDM of landfill column 1 < 2 < 3 < 4. Landfill column 4 showed the highest BDM, indicating that the novel acid-buffered coating material developed in this application can enhance the degradation of landfill waste, and the modified municipal solid waste incinerator slag can achieve better degradation results.

[0043] During the landfill degradation process, waste will generate a certain amount of leachate. Figure 3 The changes in CODcr concentration in leachate from each landfill column during the landfill cycle are shown. The CODcr concentration in the leachate of the experimental and control groups showed a similar trend during the experiment: a slight increase in the early stages followed by a rapid decrease. Initially, the leachate production in each experimental group was low, but the CODcr concentration was high, approximately 28,000–29,000 mg / L. On day 20 of the experiment, the CODcr concentration in landfill column 1 was 33,123 mg / L, in column 2 it was 32,190 mg / L, and in columns 3 and 4 it was 31,241 mg / L and 28,564 mg / L, respectively. After 150 days of the landfill experiment, the CODcr concentration in landfill column 1 was 10765 mg / L, in column 2 it was 9967 mg / L, and in columns 3 and 4 it was 8732 mg / L and 5433 mg / L, respectively. This indicates that the use of modified municipal solid waste incinerator slag coating material significantly reduced the concentration of pollutants in the leachate, thereby reducing the economic cost of subsequent leachate treatment.

[0044] Landfill gas is generated during the landfilling process, and its main components include carbon dioxide, methane, and hydrogen sulfide. Among these, the higher the methane content, the better the quality of the landfill gas, and the more conducive it is to the resource utilization of landfill gas. Figure 4 The graph shows the changes in methane content in landfill gas for each landfill column during the landfill cycle. As can be seen from the graph, during the same landfill period, column 1 (without a waste cover layer) produced the lowest methane concentration in the landfill gas, while column 4 (with a novel acid-buffered coating material) had the highest methane concentration. For example, on day 100 of the landfill experiment, the methane concentration in column 1 was 35%, in column 2 it was 40%, in column 3 it was 45%, and in column 4 it was 52%. Column 4, due to the use of modified municipal solid waste incinerator slag as the coating material, increased the absorption of acidic impurity gases, significantly increasing the methane concentration in the landfill gas, which is beneficial for the resource utilization of landfill gas.

[0045] Example 2

[0046] A pilot-scale experimental study was conducted at a corner of a landfill. The area where the landfill is located has a warm and humid climate year-round, with an average annual temperature of 17.5℃, 1000 hours of sunshine, and an average annual precipitation of 922 mm. The average number of rainy days per year is 175, with uneven rainfall distribution, concentrated mainly from June to September. The relative humidity is 60%–90%, and the annual evaporation is 620–1001 mm, mainly influenced by temperature and humidity.

[0047] The field test consisted of three landfill units. During landfilling, a 20cm layer of clay was laid at the bottom of each unit as a substrate, followed by an HDPE membrane, gravel layer, geotextile, and leachate collection pipes. Each landfill unit was equipped with two aeration pipes. The pilot-scale test used municipal solid waste, primarily composed of food scraps, plastic bags, branches and leaves, bricks, soil, and glass. The waste had a moisture content of 35%, a biodegradability of 42%, a total carbon content of 20%, and an organic matter content of 45%.

[0048] During the unit landfilling process, the net content of the waste is first weighed and recorded, and then mechanically leveled and compacted. The height of the waste filling in each landfill unit is 3 meters. After filling, each landfill unit is then covered with a layer: the first landfill unit uses clay (material one in Example 1) as the layer, with a layer thickness of 30 cm; the second landfill unit uses municipal solid waste incineration slag (material two in Example 1) as the layer, with a layer thickness of 30 cm; the third uses self-made modified municipal solid waste incineration slag as the layer, with a layer thickness of 15 cm. Among them, the self-made modified municipal solid waste incineration slag is the same as material three in Example 1, except that the content of municipal solid waste incineration slag and diatomaceous earth is different. In this example, by mass ratio, the composition is municipal solid waste incineration slag (75%), quicklime (10%), clay (5%), and diatomaceous earth (10%).

[0049] Starting from day 10, each landfill unit began refilling with leachate every ten days. Two solid sampling sections were set up in each landfill unit, 1m and 2m from the bottom of the main landfill area, respectively. The effects of different cover materials on the degradation of landfill waste were investigated from three aspects: solid waste, leachate, and landfill gas. Table 1 lists the experimental results on day 50.

[0050] Table 1. Results of the landfill experiment on day 50.

[0051]

[0052] Settlement rate directly reflects the degradation effect of waste; a higher settlement rate indicates a faster degradation rate and the most ideal landfill effect. After 50 days of biodegradation, the settlement rate of landfill unit 1 was 33%, landfill unit 2 was 37%, and column landfill unit 3 was 42%. Experimental results show that the novel acid-buffered cladding material can accelerate the degradation of landfill waste. On day 50, at a sampling section at a height of 1m (distance from the bottom of the landfill unit), the biodegradation rate of each landfill unit was: landfill unit 1 < landfill unit 2 < landfill unit 3. A similar pattern was observed at a sampling section at a height of 2m, indicating that the acid-buffered cladding material developed in this invention significantly promotes the biodegradation of landfill waste compared to traditional clay cladding materials; its effect in promoting landfill waste degradation is also superior to unmodified municipal solid waste incinerator slag.

[0053] High-throughput sequencing was used to determine the diversity and distribution characteristics of the microbial community structure in landfills. Sampling was conducted at the same landfill depth. The Simpson index results were: Landfill Unit 1 > Landfill Unit 2 > Landfill Unit 3; the Shannon index results were: Landfill Unit 1 < Landfill Unit 2 < Landfill Unit 3. This indicates that the newly developed covering material (Landfill Unit 3) exhibits greater bacterial community diversity than unmodified municipal solid waste incinerator slag and traditional clay covering materials (Landfill Units 2 and 1). Bacterial community diversity decreased with increasing landfill depth.

[0054] The leachate parameters also reflect that the acid-buffered coating material developed in this application is superior to unmodified municipal solid waste incinerator slag and traditional clay coating materials. On day 50, the pH of the leachate from landfill unit 3 reached 7.5, indicating that the acid-buffered coating material can significantly improve acid inhibition during the anaerobic degradation process of waste and promote methane gas production. The CODcr and ammonia nitrogen concentrations in the leachate from landfill unit 3 were also significantly lower than those in landfill units 2 and 1, demonstrating that the acid-buffered coating of this invention can significantly reduce the concentration levels of pollutants in the leachate.

[0055] The landfill gas indicators also confirmed that the performance of the novel acid-buffered coating material is significantly superior to that of municipal solid waste incineration slag and traditional clay coating materials. On day 50, the gas production rate in landfill zone 3 was significantly faster than that in landfill zone 2, and more than twice that of landfill zone 1, indicating that the acid-buffered coating material developed in this invention can enhance the anaerobic degradation process of landfill waste. Furthermore, the methane content in the landfill gas from landfill zone 3 was significantly higher than that in landfill zones 2 and 1, while the concentration of the harmful gas hydrogen sulfide was lower than that in landfill zones 2 and 1. This indicates that the acid-buffered coating material can effectively absorb the acidic gases generated during landfilling, increase the methane concentration, reduce the cost of subsequent landfill gas purification, and facilitate the resource utilization of landfill gas.

[0056] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. The application of acid-buffered coating materials in landfills, characterized in that, An acid buffer coating material is filled on the top surface and / or in the middle of the landfill waste as a coating layer. When the height of the landfill is 1-2m, the acid buffer coating material is evenly sprinkled on the surface of the waste pile as a coating layer. The thickness of a single coating layer is controlled between 5-30cm. The waste pile is municipal waste. The buffer coating material is made from the following raw materials by weight percentage: 70-85% municipal solid waste incinerator slag, 5-10% quicklime, 5-10% clay, and 5-10% diatomaceous earth; the preparation of the buffer coating material includes: The raw materials are initially mixed to obtain a mixed material. Water is added at a weight ratio of 1:0.8~1.2 to the mixed material. The mixture is stirred in stages and soaked for 20~25 hours. Then it is dried in a drying oven at 180℃~220℃ until the moisture content is less than 5%. Then it is sent to a crusher for crushing. The particle size of the crushed material is controlled at 2~5mm. The specific surface area of ​​the buffer coating material is 2.3~2.5m². 2 / g, with an apparent relative density of 2.9~3 and a hydrophilicity coefficient of 0.78~0.

8.

2. The application according to claim 1, characterized in that, It is made from the following raw materials by weight percentage: 75-80% municipal solid waste incineration slag, 8-10% quicklime, 5-6% clay and 5-10% diatomaceous earth.

3. The application according to claim 1, characterized in that, After mixing the raw materials, add water at a weight ratio of 1:1 with the mixed materials, stir in stages and soak for 24 hours, and then dry in a drying oven at 200℃.

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