Method for inhibiting toxic and harmful gas in leachate pool of urban garbage dump

Abstract

The invention relates to a method for inhibiting toxic and harmful gas in a leachate pool of an urban garbage dump. The method comprises the steps of three-dimensional closed system construction, precise spraying adsorption system configuration and flexible operation and maintenance of an auxiliary system. According to the invention, gas diffusion is blocked through the three-dimensional sealing cover, and a high-pressure micro-mist spraying technology is combined, so that micron-sized adsorbent mist is in full contact with harmful gas, the adsorbent has high-efficiency adsorption capacity on multi-component gases such as hydrogen sulfide and carbon monoxide, the concentration of the harmful gas in a sealed space is greatly reduced, and the removal efficiency can reach 90% or above; the selected composite adsorbent takes modified zeolite as a core component, harmless treatment or recycling can be performed after adsorption saturation, and no new pollutants are generated; meanwhile, the closed system avoids direct contact between the adsorbent and the external environment, and overcomes the defects that in the prior art, the treatment efficiency of poisonous and harmful gas in the percolate pool of the urban garbage dump is low, the poisonous and harmful gas is easy to diffuse, and secondary pollution is possibly generated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental protection, in particular to a method for inhibiting toxic and harmful gases in a leachate tank of a municipal garbage dump. BACKGROUND

[0002] With the acceleration of urbanization, the amount of municipal solid waste is increasing year by year. The leachate tank of the garbage dump is a key area in the waste treatment process. Due to the anaerobic decomposition of garbage and other reactions, hydrogen sulfide, carbon monoxide, methyl mercaptan, dimethyl sulfide, ammonia and other toxic and harmful gases will be continuously released. These gases not only have a strong irritating odor, causing serious health threats to the respiratory system and nervous system of garbage dump workers, but also spread to the surrounding residential areas, causing discomfort to residents, polluting the atmospheric environment and disrupting the surrounding ecological balance.

[0003] For example, Chinese patent 202010551003.X discloses a wastewater microbial deodorization method and its application. The application of the wastewater microbial deodorization method has the advantages of improving the deodorization effect to some extent and low cost. For example, Chinese patent 201911133554.8 discloses a harmful gas treatment method in the fracturing flowback process. An air outlet is provided for the flowback of fracturing fluid to the upper fracturing pipe column passage during the fracturing flowback process. The gas-liquid separation mechanism is used to separate the harmful gas in the fracturing fluid. The air outlet is used to discharge the harmful gas into the exploited reservoir.

[0004] However, the existing treatment methods for toxic and harmful gases in the leachate tank mostly use single ventilation and exhaust or simple chemical agent spraying. Ventilation and exhaust can only transfer the gas to the external environment and cannot fundamentally eliminate harmful gases, but can expand the pollution range. Simple chemical agent spraying has the problems of uneven distribution of the agent and insufficient contact with harmful gases, resulting in low gas removal efficiency, and some agents may cause secondary pollution. Therefore, the practicality and environmental protection need to be improved. Therefore, there is an urgent need for a method that can achieve efficient adsorption of harmful gases, avoid diffusion and is easy to operate, to solve the problems of the prior art. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a method for inhibiting toxic and harmful gases in a leachate tank of a municipal garbage dump. It is suitable for various municipal solid waste landfill leachate treatment scenarios and can effectively control the emission and diffusion of hydrogen sulfide, carbon monoxide, methyl mercaptan, dimethyl sulfide, ammonia and other toxic and harmful gases around the leachate tank, ensuring the health of workers and the safety of the surrounding ecological environment. Through the design of three-dimensional closure, precise spraying adsorption and flexible operation and maintenance, efficient control of harmful gases is achieved, overcoming the defects of low treatment efficiency, easy diffusion and possible secondary pollution of toxic and harmful gases in the leachate tank of the municipal garbage dump in the prior art.

[0006] To achieve the above object, the present application provides the following technical solution: a method for inhibiting toxic and harmful gases in a leachate tank of a municipal landfill, comprising three coordinated steps of three-dimensional closed system construction, precise spray adsorption system configuration, and flexible operation and maintenance auxiliary system operation: (1) Three-dimensional closed system construction: according to the planar size of the leachate tank (5-50 meters long, 3-20 meters wide), a three-dimensional closed cover of color steel material is built, the horizontal projection area of which completely matches the land occupation area of the leachate tank, the edge of which seamlessly fits the top of the tank wall (gap ≤0.5mm), and the gap is sealed with silicone sealant (Shore hardness 40-50HA, tensile strength ≥1.5MPa) all around; the color steel cover is 2-2.5 meters high, ensuring that the corresponding closed space volume of a single cubic meter of leachate tank is ≥0.3 cubic meters, the gas contact time is ≥3 seconds, and the adsorbent fine mist loss rate is ≤5%; (2) Precise spray adsorption system configuration: the UPVC pipeline (DN25-DN50) in the color steel cover connects the spray assembly, the adsorbent supply unit, and the main system to form a closed loop; the spray assembly atomizes the adsorbent solution by high-pressure mist technology, the fine mist contacts with harmful gases such as hydrogen sulfide and carbon monoxide, and the gases are fixed by physical and chemical adsorption; the adsorbent supply unit provides stable concentration adsorbent solution, and the main system provides power and intelligent control; (3) Flexible operation and maintenance auxiliary system operation: 304 stainless steel sliding rails (thickness 5-8mm, width 20-30mm) are installed on the top of the tank wall on both sides of the color steel cover, and the sliding rails are detachably fixed with the spray main pipeline (DN32-DN40) through sliding seats; the pipeline can be pulled out to ≥1 meter outside the cover along the sliding rail for easy maintenance; the pipeline can be removed and stored in winter (≤5℃) to avoid damage to the equipment due to freezing of the solution.

[0007] Further, the color steel cover is a double-layer color steel sandwich panel, the outer layer and the inner layer are both hot-dip galvanized color steel plates (galvanized layer ≥80g / m 2 , base material thickness 0.3-0.5mm), and the middle is filled with polyurethane thermal insulation core material (density ≥35kg / m 3 , thermal conductivity ≤0.024W / (m・K)); the sandwich panel is 50-75mm thick, the wind load resistance is ≥0.5kN / m 2 , the snow load resistance is ≥0.3kN / m 2 , the service life in the landfill environment is ≥5 years, and there is no obvious aging under ultraviolet radiation for ≥3 years.

[0008] Further, the spray assembly comprises quick-connection 304 stainless steel spray heads (containing chromium ≥ 18%, containing nickel ≥ 8%), main pipes, branch pipes and quick-connection joints; the water inlet of the spray head is G1 / 4-G1 / 2 internal thread, and the quick-connection joint is connected with the branch pipe through a butyl rubber O-ring seal; the spray heads are symmetrically arranged on both sides in the cover, and one is additionally arranged every 4 meters along the length direction (5-8 on one side), with a spacing of 2 meters and an installation height of 1 meter (from the liquid surface), and the waste rate of the adsorbent is ≤ 3%.

[0009] Further, the spray head is a high-pressure centrifugal structure, and 5-30 μm fine mist is sprayed: 5-10 μm accounts for 30%-40%, 10-20 μm accounts for 40%-50%, and 20-30 μm accounts for 10%-20%; the fine mist suspension time is ≥ 5 seconds, the loss rate is ≤ 2%, the static wind range is 3-4 meters, the mist droplet concentration deviation in a closed space is ≤ 10%, and there is no spray dead angle.

[0010] Further, the adsorbent supply unit comprises a storage tank, a stirring device, a concentration sensor and a replenishment pump; the adsorbent is a modified zeolite composite adsorbent: natural zeolite (80-120 mesh) is soaked in 10%-15% hydrochloric acid at 60-80°C for 2-3 hours, then stirred and adsorbed in 5%-8% ferric chloride at 40-50°C for 1-2 hours, dried at 105-110°C for 2-3 hours, and then mixed with activated carbon powder (100-150 mesh, iodine adsorption value ≥ 1000 mg / g) at 8:2; the adsorbent has a hydrogen sulfide capacity ≥ 15 mg / g, a carbon monoxide capacity ≥ 8 mg / g, a methyl mercaptan capacity ≥ 5 mg / g, a dimethyl sulfide capacity ≥ 3 mg / g and an ammonia capacity ≥ 10 mg / g; the adsorbent is mixed with water at 1:20-1:30 (stirring speed 150-200 r / min, time 10-15 minutes), monitored by a concentration sensor (accuracy ± 0.1%), and when the concentration is lower than 1:30, a replenishment pump (0.5-1 L / min) automatically replenishes.

[0011] Further, the main system comprises a plunger type high-pressure pump (cast iron material, ceramic plunger, pressure 0.8-1.2 MPa, flow rate 50-100 L / min), a polyethylene liquid tank (thickness 8-12 mm, impact resistance ≥ 20 kJ / m²), a PLC control system, a 50-100 mesh 304 stainless steel basket filter and a pressure sensor (0-2 MPa, accuracy ± 0.02 MPa); the filter filters impurities to prevent blockage, and the system automatically alarms and stops when the pressure exceeds the range.

[0012] Further, the control system takes Siemens S7-200 SMARTPLC as the core, is equipped with 7-10 inch touch screen and 50 meters 433MHz remote controller; has three modes: timing control (interval 40 minutes-1.5 hours, time length 10-20 minutes, adjust according to gas concentration), manual control (debugging emergency use), remote controller control (safe area operation); can self-diagnose water pump overload and other faults, and shows fault code when stopping.

[0013] Further, the slide rail contains C type 304 stainless steel body (slot width 25-35mm, slot depth 15-20mm), sliding clamping base, limiting block and flexible PVC dust cover (0.5-1mm); the body is fixed on the concrete pool wall above C30 through M8-M10 expansion bolts (buried depth ≥50mm), the length is consistent with the cover and each end extends 1-1.5 meters; the clamping base is internally provided with polytetrafluoroethylene sliding block (friction coefficient ≤0.04), and the sliding resistance is ≤50N; the dust cover is elastically connected with the clamping base to prevent impurities from entering.

[0014] Further, the liquid tank volume is designed as 500-1500L according to the effective volume (length x width x effective water depth 1-3 meters) of the leachate tank (formula: volume=effective volume x 20-effective volume x 50), so that 3-5 days of continuous operation (8-12 hours of spraying per day) is met; the liquid tank is provided with a liquid level sensor (0-1500mm, accuracy ±1mm), and an alarm is given when the liquid level is lower than 10% of the volume; the top is provided with a 150-200mm filling port with a 100 mesh filter screen, and the bottom is provided with a 50-80mm ball valve blowdown port (blowdown every 15-30 days).

[0015] Compared with the prior art, the technical scheme of the present application has the following beneficial effects: 1、The present application blocks the diffusion of gas by the three-dimensional closed cover, and combines the high-pressure micro-fog spraying technology, so that the micron-level adsorbent fine mist and harmful gas are in full contact, the adsorbent has high adsorption capacity for multi-component gases such as hydrogen sulfide and carbon monoxide, the concentration of harmful gas in the closed space is greatly reduced, and the removal efficiency can reach more than 90%, which is much higher than that of the existing simple spraying method. 2、The composite adsorbent selected in the present application takes modified zeolite as the core component, can be harmlessly treated or regenerated after adsorption saturation, and will not produce new pollutants; at the same time, the closed system avoids direct contact of the adsorbent with the external environment, prevents the adsorbent from polluting the surrounding soil and water, and has excellent environmental protection performance. 3、The host system of the present application has multiple control modes, can realize automatic operation, and reduces manual intervention; the remote controller control and the slide rail auxiliary maintenance design enable the workers to complete the operation and maintenance without entering the closed area or dangerous environment, and significantly improve the operation safety. 4、The design of the color steel cover and the spraying system can be adjusted according to the actual size of the leachate tank, and the adaptability is strong; the color steel material, the stainless steel nozzle, the high-pressure nylon pipe and the like selected for the equipment are all conventional and low-cost materials, the main system structure is simple, the maintenance cost is low in the later period, and the application in various municipal garbage sites is easy. BRIEF DESCRIPTION OF DRAWINGS

[0016] Fig. 1 A method for inhibiting toxic and harmful gases in a leachate tank of a municipal garbage site according to the present application is shown in the flowchart; Fig. 2 A whole schematic diagram of the equipment according to the present application is shown in the flowchart; Fig. 3 A horizontal arrangement schematic diagram of the nozzle according to the present application is shown in the flowchart. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0018] Please refer to Figs. 1-3 A method for inhibiting toxic and harmful gases in a leachate tank of a municipal garbage site according to the present application is shown in the flowchart; Three-dimensional closed system construction A three-dimensional closed cover made of color steel is built above the leachate tank of the municipal garbage site to form a closed space and block the diffusion path of the toxic and harmful gases to the external environment. The height of the color steel cover is set to 2-2.5 meters. This height design can not only reserve sufficient gas residence space above the leachate tank to ensure that the gas and the adsorbent are in full contact in the subsequent spraying and adsorption process, but also avoid the increase of adsorbent loss and the increase of equipment installation and maintenance difficulty caused by the over-high closed space. The color steel cover needs to be precisely fitted with the edge of the leachate tank, and the joint is sealed with sealant to prevent gas leakage from the gap. At the same time, the color steel cover is made of corrosion-resistant and anti-aging color steel material to adapt to the humid and corrosive environment of the garbage site and prolong the service life of the closed system.

[0019] Precise spraying and adsorption system configuration 1. Selection and arrangement of spraying assembly Spray head: Choose fast-connection stainless steel spray head, which has good corrosion resistance to avoid corrosion and damage of the spray head by the adsorbent. Install spray heads symmetrically on both sides of the color steel cover, 5 on each side, with a distance of 2 meters and an installation height of 1 meter. This arrangement can form a spraying effect on both sides to ensure that the spraying range covers the entire closed space above the leachate tank without any dead angle. Spray parameter control: Use high-pressure micro-spray technology to provide high pressure through the host system to make the spray head spray micron-level fine mist with a diameter of 5-30 μm. The fine mist with this particle size has a large specific surface area and can form a semi-floating cage state in the closed space, greatly increasing the contact area and contact time with toxic and harmful gases and improving the adsorption efficiency. At the same time, the static wind range of the fine mist is controlled within 3-4 meters, combined with the distance and installation height of the spray head, to achieve uniform distribution of the mist droplets in the closed space. 2. Adsorbent selection and supply Adsorbent formula: Choose a special hydrogen sulfide and carbon monoxide composite adsorbent, which uses modified zeolite as the core component. The zeolite is modified by a special process to enhance its adsorption active sites for hydrogen sulfide and carbon monoxide. It also has a certain adsorption capacity for other toxic and harmful gases such as methyl mercaptan, dimethyl sulfide, and ammonia, achieving simultaneous removal of multiple components. Adsorbent supply: The adsorbent is stored in the liquid tank of the host system, and the adsorbent solution is delivered to the spray pipeline by a high-pressure water pump, and then sprayed into the closed space through the spray head after atomization, fully contacting and reacting with toxic and harmful gases to fix the gases on the surface of the adsorbent, thereby reducing the concentration of toxic and harmful gases in the closed space. 3. Host system design Composition structure: The host system consists of a high-pressure water pump, a liquid tank, a control system, and a filter. The high-pressure water pump provides stable high-pressure power for spraying to ensure that the mist droplet size and range meet the design requirements. The liquid tank is used to store the adsorbent solution, and its volume is designed according to the size of the leachate tank and the spraying frequency to meet the continuous operation requirements. The filter is installed in the adsorbent solution delivery pipeline to filter impurities in the solution, prevent clogging of the spray head, and ensure stable operation of the spraying system. Control mode: The control system has three modes: timing control, manual control, and remote control. Timing control can preset the spraying time interval and single spraying time according to the generation law of toxic and harmful gases in the leachate tank to achieve automatic operation. Manual control can be used when the gas concentration suddenly rises or during equipment debugging for flexible operation by workers. Remote control allows workers to control the spraying system from a safe location away from the enclosed area, further ensuring the safety of workers. Flexible operation and maintenance auxiliary system design A sliding rail is installed inside the color steel cover, the sliding rail is fixedly connected with the spray pipeline, and the extension direction of the sliding rail is consistent with the length direction of the color steel cover. When it is necessary to maintain and overhaul the spray pipeline and the spray head, the spray pipeline can be pulled out along the sliding rail to the outside of the color steel cover, without the need for workers to operate in the enclosed space, thereby reducing the maintenance difficulty and safety risk; in a low-temperature environment in winter, the amount of toxic and harmful gases generated in the leachate tank is reduced, and the low temperature may cause the adsorbent solution to freeze, affecting the operation of the spraying system, at this time, the spray pipeline can be pulled out along the sliding rail for disassembly and storage, avoiding damage to the equipment due to low temperature, and reducing unnecessary energy consumption in winter.

[0020] Example 1: Small leachate tank (50-100 tons of garbage per day for garbage dump) 1.1 Applicable scenario For a small leachate tank in a county-level city garbage dump, the tank body size is 20 meters long x 10 meters wide x 3 meters deep. The routine monitoring shows that the initial concentration of harmful gases on the tank surface is: hydrogen sulfide 80 ppm, carbon monoxide 50 ppm, methyl mercaptan 0.8 ppm, ammonia 30 ppm, and there is no fixed heating facility. The lowest environmental temperature in winter is-5℃. 1.2 System construction and operation steps (1) Three-dimensional closed system construction Material selection: double-layer color steel sandwich panel (outer layer 0.3mm hot-dip galvanized color steel plate + inner layer 0.2mm stainless steel plate, filled with 50mm thick polyurethane insulation cotton in the middle) is selected, which takes into account corrosion resistance and thermal insulation performance to avoid condensation on the inner wall of the closed cover in winter; Installation process: first pour 30cm wide C30 concrete coping (pre-bury M10 expansion bolts) on the edge of the leachate tank, fix the color steel cover steel frame (50x50mm square steel, spacing 2 meters) to the coping through expansion bolts, then splice the color steel sandwich panel, fill the panel joint with weather-resistant silicone sealant (model: Dow Corning 791), and finally open 1 access door (size 1.2m x 2m with observation window) at each end of the cover body, and install a three-component EPDM sealing strip at the contact between the door and the frame; Size control: the internal clearance size of the color steel cover is 20.2 meters long x 10.2 meters wide x 2 meters high, ensuring that the tank body is completely covered, and leaving a 10cm edge for sealing. (2) Precise spraying adsorption system configuration Spraying assembly installation: On the steel frame on both sides inside the color steel cover, DN32 stainless steel spraying main pipe is fixed through U-shaped clamps, and the main pipe is 1 meter away from the tank surface in height; Along the main pipe, install 1 quick-connection type stainless steel spray head (model: SS-1 / 4J, caliber 0.5mm) every 2 meters, a total of 5 on each side, the spray heads on both sides are arranged in a symmetrical and opposite spraying layout, and the spray head spraying angle is adjusted to 45° to ensure that the mist covers the tank surface without dead angles; Adsorbent configuration: Mix the modified zeolite composite adsorbent (100 mesh) and tap water at a mass ratio of 1:20, stir in a 500 L plastic stirring tank at a speed of 150 r / min for 15 minutes, and then filter (100 mesh screen) after standing for 5 minutes to remove undissolved impurities; Inject the filtered adsorbent solution into the main system tank (volume 500 L, with liquid level meter and heating rod), set the heating rod temperature to 5°C to prevent freezing of the solution in winter; Main system debugging: Adjust the pressure of the high-pressure water pump (model: 3WZ-40) to 0.8 MPa, monitor the pipeline flow rate through the flow meter to ensure that the single nozzle flow rate is stable at 1.2 L / h; Set the control system (PLC model: Siemens S7-200 SMART) to a timing mode: spray interval 1 hour, single spray duration 10 minutes, and simultaneously start the "low liquid level protection" function (automatic shutdown and alarm when the tank liquid level is below 10%). (3) Installation of flexible operation and maintenance auxiliary system Parallelly lay two 304 stainless steel slides (model: C-type groove, groove width 25 mm, length 22 meters) on the steel frames on both sides of the color steel cover, with one end of the slide extending 1 meter outside the maintenance door; Connect the spray main pipe with the slide using buckles, and the main pipe can slide along the slide with a sliding resistance ≤30 N, facilitating pulling out for maintenance; Install a limit block at the end of the slide to prevent the main pipe from sliding out of the slide, and apply lithium-based lubricating grease (model: Great Wall 7019) on the surface of the slide to reduce jamming in winter at low temperatures. 1.3 Verification of operation effect Short-term effect (running for 72 hours): Use a portable gas detector (model: RAESystems PGM-7340) to sample at 5 monitoring points (corners + center) inside the cover, with an average concentration of hydrogen sulfide 6 ppm, carbon monoxide 4 ppm, methyl mercaptan 0.05 ppm, and ammonia 5 ppm, with removal rates of 92.5%, 92%, 93.75%, and 83.3%, respectively; Long-term effect (continuous operation for 1 month): Inspect one nozzle every week, and no blockage is found; the adsorbent solution is supplemented every 5 days, with a single supplement of about 300 L; During the winter low-temperature period (-5°C), the liquid tank heating rod works normally, the solution does not freeze, and the spray system runs stably without recorded failure shutdown. Example 2: Medium-sized leachate tank (suitable for 100-300 ton garbage dump per day) 2.1 Applicable scenarios For the medium-sized leachate pond in the prefecture-level city landfill, the size of the pond body is 30 meters long x 15 meters wide x 4 meters deep, and the initial concentration of harmful gases on the pond surface is high: hydrogen sulfide 100 ppm, carbon monoxide 60 ppm, methyl mercaptan 1.2 ppm, dimethyl sulfide 0.5 ppm, and there are residential areas within 500 meters of the landfill, with strict odor control requirements (must meet the GB14554-93 "Odor Pollutant Emission Standard" factory boundary secondary standard). 2.2 System optimization and operation points (1) Upgrade of three-dimensional closed system The height of the color steel cover is increased to 2.5 meters, increasing the closed space volume (from 303 cubic meters to 1136.25 cubic meters), and prolonging the gas residence time; Install 2 axial flow fans (model: T35-11, air volume 5000m 3 / h, with rain cover) on the top of the cover, the fan is linked with the control system, when the gas concentration in the cover exceeds the set threshold (hydrogen sulfide 10 ppm), it will automatically start and discharge the adsorbed gas to a 15-meter-high exhaust pipe (to avoid affecting the surrounding residents). (2) Strengthen the spray system Spray component adjustment: increase to 2 main pipes (DN32) on each side, arranged parallel along the length of the cover, with a spacing of 1.5 meters, and install 8 nozzles (spacing 2 meters) on each main pipe, a total of 32 nozzles on both sides, ensuring that the droplet density is increased to 200 ml / m³; Adsorbent formula optimization: based on the original modified zeolite composite adsorbent, add 0.5% calcium hydroxide powder (analytical pure), to enhance the neutralization ability of acidic gases (hydrogen sulfide, methyl mercaptan), and adjust the adsorbent solution concentration to 1:15 (adsorbent: water); Main system expansion: increase the liquid tank volume to 1000L, replace the high-pressure water pump with model 3WZ-60 (pressure 1.0MPa, flow 60L / h), and install a Y-type filter (filtering precision 80 mesh) at the water pump inlet to prevent impurities from entering the pump body. (3) Running parameter setting The control system uses "concentration linkage control": install 4 gas sensors (monitoring hydrogen sulfide, carbon monoxide, ammonia, and methyl mercaptan) in the cover, when the concentration of any gas exceeds the threshold (hydrogen sulfide 8 ppm, carbon monoxide 5 ppm, methyl mercaptan 0.1 ppm, ammonia 8 ppm), automatically start the spray, the spray duration is adjusted according to the concentration difference (difference > 20 ppm, spray for 20 minutes, difference 5-20 ppm, spray for 15 minutes, difference < 5 ppm, spray for 10 minutes); Take samples at the outlet of the exhaust pipe every day to ensure that the discharged gas meets the GB14554-93 standard (hydrogen sulfide ≤0.06mg / m 3 , ammonia ≤1.5mg / m3 , a malodor value of < 20). 2.3 Application effect After continuous operation for 2 months, the average concentration of harmful gases in the cover was stabilized at: hydrogen sulfide 5 ppm, carbon monoxide 3.5 ppm, methyl mercaptan 0.03 ppm, and dimethyl sulfide 0.02 ppm. The gas concentration at the outlet of the exhaust cylinder met the plant boundary standards, and there were no odor complaints from the surrounding residential areas. The saturation period of the adsorbent was about 30 days (judged by monitoring the change in gas concentration after spraying), and after the saturated adsorbent solution was precipitated (left standing for 24 hours), the supernatant could be recycled (supplemented with new adsorbent to a concentration of 1:15), and the precipitate was sent to a landfill for collaborative disposal without secondary pollution. Example 3: Large-scale leachate tank (suitable for landfills with more than 300 tons of garbage per day) 3.1 Applicable scenarios A large-scale leachate conditioning tank in a landfill in a provincial capital city had a tank size of 50 meters long x 25 meters wide x 5 meters deep. The tank surface was temporarily covered with a floating cover membrane (HDPE membrane), but a large amount of harmful gases still accumulated under the membrane, with initial concentrations of: hydrogen sulfide 120 ppm, carbon monoxide 80 ppm, and ammonia 50 ppm. In addition, there was a leachate treatment station around the tank, which needed to avoid corrosion of the equipment by the gases. 3.2 Customized design of the system (1) Three-dimensional closed system The "steel frame + membrane structure" combination was used: the steel frame was 100 x 100 mm square steel (spacing 3 meters), the top was covered with PVDF membrane (thickness 0.8 mm, tensile strength ≥ 30 MPa), and the membrane material had a light transmittance of 30% to avoid the growth of microorganisms caused by internal darkness. Liftable roller shutters (height 1-2 meters) were installed on both sides of the membrane structure. In summer, the roller shutters were opened for ventilation and heat dissipation, and in winter, they were closed for insulation. The contact between the roller shutter and the steel frame was sealed with neoprene rubber. The cover body was designed to be 3 meters high, and 4 gas convection channels (diameter 500 mm with air valves) were installed inside to ensure uniform gas distribution and avoid excessive local concentration. (2) Spraying and adsorption system The "main pipe + branch pipe" hierarchical layout was used: 2 DN50 main pipes were installed at the top of the cover (3 meters from the tank surface), each main pipe was connected to 5 DN32 branch pipes, the branch pipe spacing was 5 meters, and 10 nozzles (spacing 1 meter) were installed on each branch pipe, for a total of 100 nozzles, ensuring that the mist coverage density reached 300 ml / m³. The adsorbent was a modified zeolite-activated carbon composite adsorbent (mass ratio 7:3, particle size 80 mesh), and the solution concentration was adjusted to 1:12 to enhance the adsorption capacity for high-concentration gases. The host system adopts a dual-pump standby design (2 high-pressure water pumps, model: CR45-10, one for use and one for standby). When the main pump fails, the standby pump automatically starts to ensure continuous operation of the system. (3) Operation and maintenance auxiliary system Four slide rails (length 55 meters, extending 2 meters to the maintenance area) are laid on both sides of the cover. Each slide rail corresponds to a set of spray branch pipes. The branch pipes are connected to the slide rails through electric trolleys (load capacity 50 kg, speed 0.5 m / s). The movement of the trolleys can be controlled by a remote controller to quickly withdraw the branch pipes for maintenance. An adsorbent automatic dispensing device (including a powder hopper, a stirring tank, and a metering pump) is arranged beside the liquid tank. The device can automatically supplement the adsorbent according to the liquid level signal, reducing manual operation. 3.3 Operation effect and economic analysis Treatment efficiency: After one week of system operation, the concentration of harmful gases under the membrane was reduced to 8 ppm of hydrogen sulfide, 6 ppm of carbon monoxide, and 10 ppm of ammonia. The removal rates were 93.3%, 92.5%, and 80%, respectively. The corrosion rate of the leachate treatment station equipment was reduced by 60% compared to before. Economic efficiency: The monthly consumption of adsorbent is about 1.2 tons (single price 2000 yuan / ton), the electricity cost is about 800 yuan (water pump power 7.5 kW, daily average operation time 12 hours), the labor maintenance cost is about 1000 yuan, and the total monthly operation cost is about 4200 yuan, which is 47.5% lower than the traditional chemical agent spraying (monthly cost about 8000 yuan). Example 4: Special conditions - high-salt leachate pond (applicable to coastal landfill sites) 4.1 Special requirements The leachate pond of a certain coastal landfill site receives part of the industrial waste, and the salt content of the leachate reaches 5% (mainly sodium chloride), resulting in a small amount of hydrogen chloride (initial concentration 5 ppm) in the harmful gases on the pond surface. Ordinary stainless steel equipment is easily corroded, and the material selection needs to be optimized accordingly. 4.2 Key adjustment measures Spray assembly: Replace the stainless steel nozzle and main pipe with 316L stainless steel material (molybdenum content 2-3%, resistant to chloride ion corrosion), and use PTFE sealing pads for pipe connection to avoid salt mist corrosion. Adsorbent: Add 1% sodium carbonate powder to the composite adsorbent to neutralize the hydrogen chloride gas and prevent it from reacting with the adsorbent to generate corrosive substances. Enclosed cover: Replace the inner layer plate with glass steel material (thickness 5 mm, resin content ≥65%), and coat the surface with vinyl ester anti-corrosion coating to enhance the salt mist resistance. 4.3 Verification results After 3 months of continuous operation, the spray system had no corrosion and leakage, the inner layer plate of the enclosed cover had no blistering and falling off, and the hydrogen chloride in the cover was reduced to 1 ppm.

[0021] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting; it is not intended to exclude myriad other embodiments of the present application that other inventors can develop based on the same general inventive concepts embodied by the described embodiments. That is, although the present application is described in terms of particular embodiments and implementations, it is to be understood that the terminology used is for the purpose of descriptive clarity and that it is intended to be limited only by the words recited in the appended claims. It is to be understood that the terms "including", "comprising", "consisting" and variations thereof do not preclude the addition of further integers to the claimed combination of integers. It is to be understood that the terms "including", "comprising", "consisting" and variations thereof encompass the various features of the embodiments described herein, and are not restricted to the use of only the most preferred embodiments. It is further to be understood that the use of relational terms such as first and second, and the like, do not denote a physical or logical order or relationship among the various elements, but are used simply for distinguishing between various elements for clarity. It is to be understood that the terms "comprising", "including", and "having" and variations thereof are intended to be equivalent and open-ended, and include the various embodiments of the present application as recited in the claims. It is to be understood that the terms "including", "comprising", "consisting" and variations thereof encompass the various features of the embodiments described herein, and are not restricted to the use of only the most preferred embodiments. It is further to be understood that the use of relational terms such as first and second, and the like, do not denote a physical or logical order or relationship among the various elements, but are used simply for distinguishing between various elements for clarity. It is to be understood that the terms "comprising", "including", and "having" and variations thereof are intended to be equivalent and open-ended, and include the various embodiments of the present application as recited in the claims.

[0022] While the embodiments of the application have been shown and described herein, it is understood that modifications, substitutions, changes, and alterations can be made by those skilled in the art without departing from the spirit of the present application, which is defined by the appended claims and their equivalents.

Claims

1. A method for suppressing toxic and harmful gases in leachate ponds of urban landfills, characterized in that, It includes three collaborative steps: constructing a three-dimensional closed system, configuring a precision spray adsorption system, and facilitating flexible operation and maintenance to support system operation. (1) Construction of a three-dimensional closed system: Based on the plan dimensions of the leachate tank, a three-dimensional closed cover made of color steel is constructed. Its horizontal projected area is completely matched with the area occupied by the leachate tank. The edges are seamlessly attached to the top of the tank wall, and the gaps are sealed with silicone sealant around the circumference. The height of the color steel cover is 2-2.5 meters to ensure that the closed space volume corresponding to a single cubic meter of leachate tank is ≥0.3 cubic meters, the gas contact time is ≥3 seconds, and the adsorbent fine mist loss rate is ≤5%. (2) Configuration of precision spray adsorption system: The spray assembly, adsorbent supply unit and main system are connected by UPVC pipes inside the color steel cover to form a closed loop; the spray assembly atomizes the adsorbent solution with high pressure micro-mist technology, and the fine mist comes into contact with harmful gases such as hydrogen sulfide and carbon monoxide, and fixes the gas through physical and chemical adsorption; the adsorbent supply unit provides a stable concentration of adsorbent solution, and the main system provides power and intelligent control; (3) Flexible operation and maintenance auxiliary system operation: 304 stainless steel slide rails are installed on the top of the pool walls on both sides of the color steel cover. The slide rails are equipped with sliding brackets and can be detachably fixed to the main spray pipeline. The pipeline can be pushed along the slide rail to be pulled out to ≥1 meter outside the cover for easy maintenance. The pipeline can be disassembled and stored in winter to avoid the solution freezing and damaging the equipment.

2. The method for suppressing toxic and harmful gases in leachate ponds of urban landfills according to claim 1, characterized in that, The color steel cover is a double-layer color steel sandwich panel, with both the outer and inner layers being hot-dip galvanized color steel sheets, and the middle layer filled with polyurethane insulation material; the sandwich panel thickness is 50-75mm, and the wind load resistance is ≥0.5kN / m. 2 Snow load resistance ≥ 0.3 kN / m 2 It has a service life of ≥5 years in a landfill environment and shows no obvious aging under ultraviolet radiation for ≥3 years.

3. The method for suppressing toxic and harmful gases in leachate ponds of urban landfills according to claim 1, characterized in that, The spray assembly includes quick-connect 304 stainless steel spray heads, main pipeline, branch pipelines, and quick-connect fittings; the spray head inlet has a G1 / 4-G1 / 2 internal thread and is connected to the branch pipeline through a quick-connect fitting sealed with a nitrile rubber O-ring; the spray heads are symmetrically arranged on both sides inside the hood, with one additional spray head every 4 meters along the length, spaced 2 meters apart, and installed at a height of 1 meter (from the liquid surface), with an adsorbent waste rate of ≤3%.

4. A method for suppressing toxic and harmful gases in leachate ponds of urban landfills according to claim 1, characterized in that, The spray head is a high-pressure centrifugal structure that sprays out a fine mist of 5-30μm: 5-10μm accounts for 30%-40%, 10-20μm accounts for 40%-50%, and 20-30μm accounts for 10%-20%; the fine mist suspension time is ≥5 seconds, the loss rate is ≤2%, the range in still wind is 3-4 meters, the droplet concentration deviation in a closed space is ≤10%, and there are no spray dead zones.

5. A method for suppressing toxic and harmful gases in leachate ponds of urban landfills according to claim 1, characterized in that, The adsorbent supply unit includes a storage tank, a stirring device, a concentration sensor, and a feed pump. The adsorbent is a modified zeolite composite adsorbent: natural zeolite is soaked in 10%-15% hydrochloric acid at 60-80℃ for 2-3 hours, then stirred and adsorbed with 5%-8% ferric chloride at 40-50℃ for 1-2 hours, dried at 105-110℃ for 2-3 hours, and then mixed with activated carbon powder at a ratio of 8:

2. The adsorbent has a capacity for hydrogen sulfide ≥15mg / g, carbon monoxide ≥8mg / g, methanethiol ≥5mg / g, dimethyl sulfide ≥3mg / g, and ammonia ≥10mg / g. The adsorbent is mixed with water at a ratio of 1:20-1:30, and the concentration sensor monitors the mixture. When the ratio is lower than 1:30, the feed pump automatically replenishes the adsorbent.

6. A method for suppressing toxic and harmful gases in leachate ponds of urban landfills according to claim 1, characterized in that, The main system includes a plunger-type high-pressure pump, a polyethylene liquid tank, a PLC control system, a 50-100 mesh 304 stainless steel basket filter, and a pressure sensor; the filter removes impurities to prevent clogging, and the system automatically alarms and shuts down when the pressure exceeds the range.

7. A method for suppressing toxic and harmful gases in leachate ponds of urban landfills according to claim 1, characterized in that, The control system is based on a Siemens S7-200SMART PLC, equipped with a 7-10 inch touch screen and a 433MHz remote control with a range of 50 meters; it has three modes: timed control, manual control, and remote control control; it can self-diagnose faults such as water pump overload, and display fault codes when the machine stops.

8. A method for suppressing toxic and harmful gases in leachate ponds of urban landfills according to claim 1, characterized in that, The slide rail includes a C-type 304 stainless steel body, a sliding bracket, a limiting block, and a flexible PVC dust cover. The body is fixed to the concrete pool wall of C30 or above by M8-M10 expansion bolts, with the length consistent with the cover and extending 1-1.5 meters at each end. The bracket has a built-in polytetrafluoroethylene slider with a sliding resistance of ≤50N. The dust cover is elastically connected to the bracket to prevent impurities from entering.

9. A method for suppressing toxic and harmful gases in leachate ponds of urban landfills according to claim 1, characterized in that, The liquid tank is designed with a volume of 500-1500L based on the effective volume of the leachate tank, which can meet the requirements of 3-5 days of continuous operation. The liquid tank is equipped with a liquid level sensor, which will alarm when the volume is below 10%. There is a 150-200mm feeding port with a 100-mesh filter at the top and a 50-80mm ball valve drain port at the bottom.

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