CN1785846B - Leachate treatment method using ventilated landfill - Google Patents

Abstract

The method for treating leachate by using a ventilated landfill layer relates to a leachate treatment method for municipal solid waste landfill, which is achieved by circulating and recharging the leachate in a special ventilated landfill unit in the landfill, The special unit is intermittently forced to ventilate, so that the landfill layer of the unit forms a sequentially alternating aerobic, anoxic, and anaerobic environmental conditions, which promotes the formation of aerobic, facultative, and anaerobic mixed microbial flora in the layer. It performs aerobic, facultative and anaerobic metabolic removal of oxygen-consuming organic matter in leachate; at the same time, aerobic nitrifying bacteria and facultative denitrifying bacteria remove ammonia nitrogen in leachate through nitrification/denitrification . The advantages of the present invention are: in the same landfill layer, the aerobic organic matter and ammonia nitrogen in the leachate are simultaneously purified by recycling and recharging, and the COD of the treated water is less than 1g/L, and the ammonia nitrogen is less than 0.005g/L, effectively reducing the amount of leachate The cost of pollution control. The present invention is suitable for implementation in newly built and existing landfills.

Description

Leachate treatment method using ventilated landfill

technical field

The invention relates to a leachate treatment method for landfill of municipal domestic garbage. the

Background technique

Landfill is the most widely used domestic waste disposal technology, and leachate is the main secondary pollutant produced during its treatment. These domestic waste landfill leachates are mainly oxygen-consuming organic matter and ammonia nitrogen. The traditional treatment method is: after the domestic waste landfill leachate is collected, it is treated outside the landfill pile ('Landfill leachate treatment.' Keenan J.D., R.L. Steiner, and A.A. Fungaroli. Journal of the Water Pollution Control Federation56, 27-33 , 1984), but the processing cost is high. Bioreactor landfill (Bioreactor landfill) technology has developed the above method. It uses the landfill as a bioreactor and purifies the leachate through the circulation of the leachate in the landfill ('Landfill bioreactor: historical perspective , fundamental principles, and new horizons in design and operations'. Pohland, F.G., 1995. In Landfill Bioreactor Design and Operation Sem.Proc., EPA/600/R-95/146, 9-24), but due to the usual landfill The metabolic environment is anaerobic, so this method can only purify oxygen-consuming organic matter, but not ammonia nitrogen. Price et al. (‘Nitrogen management in bioreactor landfills’ Price, G.A., M.A.Barlaz, and G.R.Hater, 2003. Waste Management23, 675-688.) biologically nitrify the leachate outside the landfill first, and then nitrate nitrogen The leachate is recirculated and refilled into the landfill pile, and the leachate denitrification of nitrate nitrogen into nitrogen gas is denitrified by using the anoxic condition in the landfill pile. However, this method still needs the traditional biological nitrification outside the landfill pile. The device completes the denitrification treatment of ammonia nitrogen in the leachate, which complicates the leachate circulation and recharge treatment technology. the

Contents of the invention

The object of the present invention is to provide a leachate treatment method with a simple process. The method of the present invention can simultaneously treat two main pollutants in the leachate: oxygen-consuming organic matter and ammonia nitrogen. the

In order to achieve the above object, the present invention uses the principle of biological denitrification to remove ammonia nitrogen in the leachate, and the principle includes the oxidation of ammonia nitrogen by nitrifying and nitrifying bacteria under aerobic conditions, and the nitrate and nitrous state produced by the oxidation of ammonia nitrogen Nitrogen is reduced to nitrogen by denitrifying bacteria in two basic steps under anoxic conditions. And these two steps must be completed under different oxygen environment (aerobic and anoxic or anaerobic) conditions, therefore, the basic technical problem that the present invention solves is to form alternate aerobic and anoxic (or anaerobic) in the landfill pile body Anaerobic) environment meets the needs of biological denitrification. The technical key to forming an aerobic and anoxic alternate environment is the ventilation method and ventilation control conditions in the landfill. Because the ventilation of the landfill pile has certain technical complexity (increasing facilities and investment), considering the technical economy, it is necessary to control the ventilation within a certain range in the landfill, thus, the technical scheme of the present invention is as follows:

The first step is to set up a dedicated landfill unit in the landfill: the landfill unit is equipped with the same anti-seepage layer as the rest of the landfill, and a leachate collection layer that is hydraulically independent from the rest of the landfill and leachate storage tanks. the

The second step is to set up forced ventilation facilities in the dedicated landfill unit: the forced ventilation facilities are composed of a ventilation pipe network laid on the leachate collection layer of the unit, and a blower for supplying air to the ventilation pipe network. the

The third step is to bury domestic garbage in the special unit: the depth of garbage landfill in the unit should be less than 6m, generally 3-6m. In order to avoid the impact of organic matter and ammonia nitrogen released during the biodegradation process of domestic waste on the leachate treatment process, the landfilled waste in this unit should preferably be buried in other parts of the landfill or other landfills for 3 years Above, basically stable garbage after biodegradation. the

If in practical application, it is impossible to obtain garbage that meets the above requirements, or it is not suitable to use such garbage due to the high cost of collection and transportation, it can also be directly filled with fresh domestic garbage, but the filled garbage needs to be treated with accelerated degradation and stabilization. The specific operation method is: 1) Collect the leachate discharged from the unit to the independent storage tank of the unit; 2) The leachate in the independent storage tank, calculated according to the cross section of the unit, has a water load of 30L/m ² · d, 2 cycles per day, half of the water volume each time, is transported to the water distribution pipe network of the unit by the leachate recharge pump (see the fourth step below), and circulates in the unit; Carry out 2 times of forced ventilation, the volume of each ventilation is 4~6m ³ /m ² according to the cross-section of the unit, and the time of each ventilation is not more than 1 hour; 4) Accelerate the degradation and stabilization operation until the leachate water quality in the independent storage tank At the same time, stop when COD is less than 3000mg/L and ammonia nitrogen is less than 300mg/L.

The fourth step is to set up the leachate circulation backfill water distribution layer on the landfill garbage layer: on the landfill garbage surface that has been landfilled and leveled, lay the leachate circulation backfill cloth composed of main pipes and branch pipes The water pipe network and the main pipe of the water distribution pipe network are connected to the leachate recharge pump to provide the conditions for water supply to the pipe network. The gaps between the pipe networks should be filled with graded gravel and leveled. the

The fifth step is to cover the unit with airtightness: synthetic geomembrane is used for airtight coverage, and the covered synthetic geomembrane is welded to the synthetic geomembrane of the anti-seepage layer of this unit to achieve airtight coverage, but the covering The synthetic geomembrane is left with a gas collection pipe interface to organize the discharge of the gas (generated gas) generated by biodegradation in the unit. Cover the synthetic geomembrane with cover soil for protection. the

The sixth step is the control of the generated gas in the unit: after the unit is covered, each gas collecting pipe interface is connected with the gas collecting main pipe. The elevation of the exhaust should be higher than the surrounding ground by more than 10m. A methane gas detector and a gas burner are arranged in the main pipe. The detector continuously monitors the methane volume ratio of the gas entering the main pipe. If the methane volume fraction in the gas is greater than 15%, it will output a signal to the controller, and the controller will automatically ignite the burner to burn the methane in the gas, so that the exhaust gas will not Will cause an explosion. If the volume fraction of methane in the gas is less than 15%, there is no need to start the burner, and the natural dilution of the atmosphere after the gas is discharged can control the risk of explosion. the

The seventh step, leachate treatment operation: the special unit that has completed the above steps has the ability to process leachate and purify organic matter and ammonia nitrogen in it. The specific treatment operations are: 1) Water distribution, which is drawn from the general storage tank of the landfill site The leachate, twice a day, is transported to the water distribution pipe network of the unit with a water volume load of 10-20L/m ² ·d based on the cross section of the unit each time; 2) Ventilation, twice a day, each time at the The cross-section of the unit is 4~6m ³ /m ² for forced ventilation of the unit. This operation makes aerobic, facultative and anaerobic biological metabolic activities exist in the garbage layer at the same time, and the aerobic organic matter, ammonia nitrogen and organic nitrogen in the recharge leachate can be effectively removed.

The outstanding effects of the present invention are as follows:

1. The present invention utilizes the recharge method to simultaneously purify two types of main macro-pollutants in the leachate: oxygen-consuming organic matter (COD) and ammonia nitrogen (COD of treated effluent is less than 1g/L, ammonia nitrogen is less than 0.005g/L). the

2. By optimizing the ventilation mode of the landfill layer, a sequential change of aerobic, anoxic, and anaerobic environmental conditions is formed in the landfill layer. This environmental condition is related to the flow delay of the recharge leachate in the layer. The combination of features enables the present invention to perform nitrification and denitrification of ammonia nitrogen in the same landfill layer to realize a complete denitrification process. the

3. The ventilation volume of the landfill layer for treating leachate is effectively controlled, which is compatible with the ventilation conditions of the landfill layer under the existing landfill process conditions, and no special modification of the existing landfill process is required, reducing the implementation cost. get under control. the

4. The leachate produced by the entire landfill is treated with a special landfill unit, which avoids the construction of ventilation facilities for the entire landfill, which not only reduces the implementation cost, but also improves the feasibility of technical implementation. the

Description of drawings

Fig. 1 is process schematic diagram of the present invention

Fig. 2 is the sectional structure schematic diagram of ventilated landfill layer of the present invention

The labels in the accompanying drawings are explained as follows:

1—base soil layer of landfill; 2—groundwater drainage layer; 3—U-shaped water seal; 4—clay layer under anti-seepage membrane; 5—HDPE anti-seepage membrane; 6—protective layer of anti-seepage membrane; 7—seepage Filtrate drainage layer; 8—ventilation air distribution layer; 9—garbage layer; 10—recharge water distribution layer; 11—covering and sealing layer; 12—leachate recharge pump; 13—generated gas collection pipe; 14—ventilation supervisor ; 15—blower. the

Detailed ways

The invention is implemented in newly built and existing landfills respectively. the

Example 1

The implementation method in the new landfill is as follows:

The first step is to select the first landfill unit in the landfill area as a special ventilated leachate treatment unit. The effective landfill depth of this unit should be greater than 3m, but not greater than 6m; The daily average value (V _max ) of the year in which the maximum amount of leachate is expected to be produced in the burial site is determined, and the relationship between the two is V _max /S=0.02～0.04.

When the planar area of the dedicated leachate treatment unit is less than 4000m ² , there is no need for division within the unit. If the total area is greater than 4000m ² , the unit needs to be divided into divisions, but the area of each division should not be less than 2000m ² . The meaning of zoning is: different zones are separated by earth dams covered with waterproof cushioning materials, leachate in each zone is collected and recharged independently, and ventilation and gas collection piping systems should also be independent of each other.

Preparatory procedures for the construction of special leachate treatment units: firstly, the reservoir area of the newly built landfill should be cleaned, bottom leveled and side slope repaired according to the routine construction of sanitary landfills. Then, build the landfill leachate storage tank, which should be divided into two hydraulically independent parts, which are respectively used as the general storage area of the landfill and the storage area of the leachate treatment unit. The capacity of the storage area of the leachate treatment unit is not less than 3 times of the above V _max , and the capacity of the total storage area is determined according to the design method of the conventional sanitary landfill, and the construction of the special leachate treatment unit can be carried out.

The second step is the construction of a special leachate treatment unit: see the cross-sectional structure of the ventilated landfill layer in Figure 2. Firstly, a groundwater drainage layer 2 is set at the bottom of the proposed unit according to the construction requirements of the sanitary landfill, and a groundwater drainage pipe is set in the drainage layer 2, which is connected to the surface runoff drainage system of the landfill. Then set the clay layer 4 under the anti-seepage membrane on the groundwater drainage layer 2 to ensure that the synthetic membrane (usually made of high-density polyethylene HDPE) laid on it has a reasonable hydraulic gradient, and at the same time, it should meet the requirements of other HDPE membrane construction specifications . Thereafter, the HDPE anti-seepage membrane 5 is laid according to the specifications, and then the anti-seepage membrane protective layer 6 (clay or geotextile) is set on the membrane, and the leachate drainage layer 7 (usually river pebbles or gravels) is laid on the protective layer 6. ), and the leachate drainage pipe is buried in the layer. The above construction steps and their parameter requirements can be implemented with reference to the current sanitary landfill construction standards, while the following construction steps are determined by the functional requirements of this special landfill treatment unit. the

1. Connect the leachate drainage main pipe to the leachate treatment unit storage area in the landfill leachate storage tank through a U-shaped water seal 3 of not less than 500 mm. the

2. Lay a ventilation air distribution layer 8 on the leachate drainage layer 7. The ventilation air distribution layer 8 is composed of a ventilation pipe network and filled gravels that cover and protect it. The ventilation pipe network includes main pipes and branch pipes, and the ventilation main pipe 14 provided in each unit partition is connected with the centrifugal blower 15, and the output air pressure of the blower is not less than 2500Pa under the air supply flow rate. The main pipe and the branch pipe in the unit are connected orthogonally, and the distance between the pipes is 5-10m. In the half circle, holes are evenly distributed with an opening rate of 5-10% and a hole diameter of 5-20mm. In the second half circle, only a single row of holes with a diameter of 10-20mm is opened at the bottom at an interval of 500mm. The diameter of gravel covering the ventilation pipe network is 5-20mm. 20mm grading, covering thickness to ensure at least 10cm of gravel layer protection above the top of the pipe with the largest diameter. the

The third step is to fill in garbage to protect the ventilation system. When the thickness of the filled garbage is less than 2m, the garbage is only leveled once with the bulldozer without rolling; -Three passes of rolling to control uneven settlement, but steel wheel compactors should not be used for compaction. The other links of the garbage operation are similar to the conventional sanitary landfill, and the landfill stops when the thickness of the garbage layer specified by this unit is reached, so as to form the garbage layer 9 . the

The fourth step is to lay the back irrigation water distribution layer 10 . After leveling the surface of the garbage layer 9, first lay a layer of 200mm-thick construction sand with a medium-coarse particle size (1-4mm), and then lay a water distribution pipe network on the sand layer. The pipe network consists of main pipes and branch pipes. Composition, each unit partition is provided with a main pipe to connect with the leachate recharge pump 12 located in the general storage area of the landfill to supply water to the pipe network. The main pipe and the branch pipe are connected orthogonally, and the distance between the pipes is 5-10m. The main pipe is not perforated, and the branch pipe is perforated for refilling and water distribution. The hole opening scheme is: no holes are opened in the first half of the circle, and holes with a diameter of 5-15mm are evenly distributed in the second half of the circle with an opening rate of 8%. The bottom of the water distribution pipe network is directly placed on the garbage layer, and the gap between the pipes is covered with gravel with a particle size of 6-30mm. The covering thickness ensures that the top of the pipe with the largest diameter is protected by a layer of gravel at least 10cm above. the

The fifth step is unit covering, gas conduction and gas treatment. Firstly, cover the unit partitions that have completed the laying of the recharge water distribution layer 10 and cover the sealing layer 11, from bottom to top: the lowest layer of 400g/m ² geotextile, on which is a 1mm thick low-density polyethylene (LDPE) film, and then The top is 200g/m ² geotextile, then 0.3m thick compacted clay, and the top is 0.1m thick gravel aquifer (10-30mm particle size gradation). For the situation where landfill still needs to be carried out above the unit, conventional landfill operations can be carried out above the aquifer. On top of that, farming (nutrient) soil covering and vegetation reclamation should be carried out according to the construction requirements of the final covering layer of the sanitary landfill. The gas guide system matched with the covering and sealing layer 11 is mainly composed of vertically arranged unit air guiding pipes and subsequent gas treatment devices. The unit air guiding pipes are evenly distributed in a square grid (tube spacing 20-30m) on the unit covering and sealing layer 11 The upper and lower ends are inserted into the crushed stone cover layer of the refilling water distribution layer 10 for about 10cm. The pipe is made of HDPE with a diameter of 10-20cm. The intersection of the pipe and the LDPE film is sealed by welding. The length of the air guide pipe is related to whether landfill is carried out on the unit coverage surface. If the landfill continues, each vertical unit air guide pipe should be connected with the horizontal air guide collection branch pipe in the aforementioned compacted clay layer, and the branch pipe leads to the filling After the layer is buried, it is connected with the main gas pipe, and finally connected to the gas treatment device; if the landfill is not continued, the vertical air pipes extend upward to the final covering surface, and then connect with the horizontal gas branch pipes and main pipes. The gas is directed to a gas processing unit.

The sixth step, gas treatment: the gas treatment device is a vertical exhaust tube with a diameter of 0.5-1m, and the height difference between the top of the tube and the installed ground is ≥10m; the gas in the air duct is introduced at the bottom of the tube by the air compressor through the gas combustion nozzle In the barrel, a gas concentration monitoring point is set in front of the combustion nozzle to monitor the methane concentration in the gas online. When the methane volume concentration is less than 15%, the gas will be discharged directly; The fuel burner ignites the gas, burns it and then discharges it. After the construction of the special leachate recharge treatment unit, landfill, covering and installation of gas guide and treatment devices, the accelerated stabilization operation of fresh garbage in the unit should be carried out. the

Accelerated stabilization operation of fresh waste in the unit: refill the leachate twice a day from the storage area of the leachate treatment unit to the unit, and the refill water load is 10-20L/m ² each time; Forced ventilation, each ventilation volume is 4-6m ³ /(m ² unit horizontal cross-sectional area), but each ventilation time does not exceed 1 hour; When the COD of the leachate discharged from the unit is less than 3000mg/L, and the ammonia nitrogen is less than 300mg/L, it means that the garbage in the unit has been basically stabilized, and the unit can enter the normal leachate treatment stage, which is used to treat the leachate produced by other parts of the landfill .

The seventh step, normal leachate treatment operation: 2 times a day from the leachate general storage area to this unit, according to the water load of 10-20L/m ² each time, refill the leachate; at the same time 2 times a day, each time In no more than 1 hour, 4-6m ³ /m ² of air is introduced into the unit. After treatment, the leachate discharged from the unit passes through the storage area of the treatment unit, and is directly discharged into the urban sewage pipe network, or is further treated by physical and chemical methods and then discharged into the surface water body.

Example 2

Implementation methods in established landfills:

Firstly, the storage pool should be separated or rebuilt to form a general storage area and a processing unit storage area with a capacity that meets the requirements (specifically the same as in Embodiment 1). Then, build a special-purpose ventilation treatment unit. If the unit is arranged in an area that has not yet been landfilled in the site, its construction method is consistent with Embodiment 1 in the aforementioned new landfill. After excavating old garbage that has been buried for more than 3 years, it will be refilled into this unit, so that the garbage in this unit does not need to be accelerated and stabilized, but can be directly used to treat the leachate generated in the site; if the unit must be installed in the site In addition to laying a layer of graded gravel (5-15mm) with a thickness of 0.1m on the garbage layer, instead of the aforementioned groundwater drainage layer 2, and at the same time fill in the unit Except the rubbish that has been buried for more than 3 years, all the others are the same as the implementation mode in the new landfill, i.e. embodiment 1.

Claims (4)

1. Utilize the method for ventilated landfill to carry out leachate treatment, it is characterized in that: The first step is to set up a special landfill unit in the landfill: the landfill unit is equipped with an anti-seepage layer, a leachate collection layer, and a leachate storage tank; the leachate collection layer, the leachate storage tank and the landfill The hydraulic power of other parts of the field is independent of each other; The second step is to set up forced ventilation facilities in the dedicated landfill unit: the forced ventilation facilities are composed of a ventilation pipe network laid on the leachate collection layer of the unit, and a blower for supplying air to the ventilation pipe network; The third step is to bury domestic garbage in the special unit: the depth of the garbage in the unit is 3-6m; the garbage buried in this unit has been buried in other parts of the landfill or other landfills for more than 3 years , after biodegradation is basically stable, or filled with fresh domestic waste, then accelerate the degradation and stabilization treatment; The fourth step is to set up the leachate circulation backfill water distribution layer on the landfill garbage layer: on the landfill garbage surface that has been landfilled and leveled, lay the leachate circulation backfill cloth composed of main pipes and branch pipes The water pipe network and the main pipe of the water distribution pipe network are connected to the leachate recharge pump to provide the conditions for water supply to the pipe network. The gaps between the pipe networks should be filled with graded gravel and leveled; The fifth step is to perform airtight covering on the unit: synthetic geomembrane is used for airtight covering, and after the covering is completed, the covered synthetic geomembrane is welded and connected with the synthetic geomembrane of the anti-seepage layer of the unit; the covered synthetic geomembrane There is a gas collecting pipe interface on the top to export the gas generated by biodegradation in the unit; the covered synthetic geomembrane is covered with soil for protection; The sixth step is the control of the gas generated in the unit: after the unit is covered, each gas collecting pipe interface is connected with the gas collecting main pipe. The elevation of the gas place should be higher than the surrounding ground by more than 10m. A methane gas detector and a gas burner are installed in the main pipe. The detector continuously monitors the methane volume fraction of the gas entering the main pipe: the methane volume fraction in the gas is greater than 15%, that is, the output signal To the controller, the controller automatically ignites the burner to burn the methane in the gas, so that the exhaust gas will not cause an explosion; if the volume fraction of methane in the gas is less than 15%, there is no need to start the burner, and it will be naturally diluted by the atmosphere after the gas is discharged its explosion hazard can be controlled; The seventh step, leachate treatment operation: the special unit that has completed the above steps has the ability to process leachate and purify organic matter and ammonia nitrogen in it. The specific treatment operations are: 1) Water distribution, which is drawn from the general storage tank of the landfill site The leachate, twice a day, is transported to the water distribution pipe network of the unit with a water volume load of 10-20L/m ² ·d based on the cross section of the unit each time; 2) Ventilation, twice a day, each time at the The cross-section of the unit is 4~6m ³ /m ² for forced ventilation of the unit. 2. The method for leachate treatment using ventilated landfill layer according to claim 1, characterized in that: in the second step, when the special landfill unit is equipped with forced ventilation facilities, the gas distribution pipe network is arranged in the seepage area. Above the filtrate drainage layer (7), it is composed of dry pipes with no holes and branch pipes with holes on the wall: the branch pipes are arranged in parallel, the distance between the pipes is 5-10m, and the wall opening ratio of the upper half of the branch pipes is 5-10%. , the aperture is 5-20mm, and in the second half of the cycle, only a single row of holes with an aperture of 10-20mm is opened at the bottom interval of 500mm; the ventilation main pipe (14) provided in each unit partition is connected with the blower (15), and the blower outputs air under the air flow rate. The wind pressure is not less than 2500Pa, and at the same time, when the main leachate drainage pipe of this unit is connected to the corresponding leachate storage tank, it must pass through the water seal layer with a height of more than 500mm. 3. the method for utilizing ventilated landfill layer to carry out leachate treatment according to claim 1, is characterized in that: the accelerated degradation stabilization of the fresh rubbish of described the 3rd step: earlier the leachate that this unit discharges is collected to The independent storage tank of the unit; then, the leachate in the independent storage tank, calculated according to the cross section of the unit, has a water volume load of 30L/m ² ·d, which is divided into 2 cycles every day, half of the water volume each time, and is recharged by the leachate The pump is sent to the water distribution pipe network of the unit and circulated in the unit; at the same time as the leachate is circulated, the unit is forced to ventilate twice a day, and the volume of each ventilation is 4~6m ³ /m ² according to the cross section of the unit. The time is 0.5 to 1 hour; the accelerated degradation stabilization operation is terminated when the leachate water quality in the independent storage tank reaches COD less than 3000mg/L and ammonia nitrogen less than 300mg/L at the same time. 4. The method for leachate treatment using ventilated landfill layer according to claim 1, characterized in that: the recharging water distribution layer in the fourth step is composed of water distribution pipe network and filler for protection pipe network, and the distribution The water pipe network includes main water distribution pipes without openings and water distribution branch pipes with openings on the wall. The pipe network is arranged horizontally; the branch pipes are arranged in parallel with a distance of 5-10m. 8% opening rate, evenly distributed holes with a diameter of 5-15mm, the bottom of the water distribution pipe network is directly set on the garbage layer, the gap between the pipes is filled with graded gravel with a particle size of 6-30mm, and the covering thickness ensures the largest diameter The top of the pipe is protected by a layer of crushed rock of at least 10cm.

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