Denitrification method of waste disposal site

Abstract

To provide a denitrification method of a waste disposal site for effectively utilizing a disposal field and conducting denitrification.SOLUTION: There is provided a denitrification method of a waste disposal site in which: leachate which is leached from a waste sedimentary layer 3 is caught; the caught leachate is sent to wastewater treatment means 7 having an aeration tank 11 via a drain pipe; nitrate nitrogen-containing water 12 is formed by nitrification reaction in the aeration tank 11; the nitrate nitrogen-containing water 12 is sprayed over the waste sedimentary layer 3; hydrogen derived from organic substances included in the waste sedimentary layer 3 is reacted with nitrate nitrogen to form nitrogen; and nitrogen is discharged to the atmospheric air from the waste sedimentary layer 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a denitrification method for a waste disposal site, which performs denitrification treatment using the disposal site. [Background technology]

[0002] Traditionally, at waste disposal sites, leachate that seeps out from waste piles where dumped waste is piled up has been managed based on pH, BOD (biochemical oxygen demand), COD (chemical oxygen demand), TN (total nitrogen), etc.

[0003] Currently, in Japan's controlled waste disposal sites, incineration ash and fly ash from incinerated waste are often dumped, and it is known that the incineration ash often causes the soil to become highly alkaline.

[0004] On the other hand, there are some disposal sites where unincinerated combustible waste and animal and plant residues are brought in, and at these sites, the BOD, COD and TN of the leachate are higher than at disposal sites that mainly use incineration ash, making treatment of these substances a challenge.

[0005] Leachate from such landfills can be collected from the landfill and the sludge is condensed and settled in a condensation and settling tank, and then aeration treatment (aerobic decomposition of organic matter through biological treatment) is carried out in an aeration tank. This can reduce the BOD and COD concentrations of the treated water, but in order to treat the nitrogen, denitrification equipment and large amounts of dilution water are required.

[0006] On the other hand, methods for treating nitrogen include a method in which water collected from a disposal site is oxygen-enriched and this oxygen-enriched water is then sprayed back into the disposal site to convert the nitrogen present in the disposal site into nitrate form, and then denitrification is performed under semi-aerobic conditions (see Patent Document 1), and a method in which the air supply and water level to a semi-aerobic landfill site are controlled to nitrify ammoniacal nitrogen using nitrifying bacteria (facultative aerobes) in the aerobic region, and denitrification is performed by denitrifying bacteria (facultative anaerobes) in the anaerobic region (see Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-021310 A [Patent Document 2] JP 2004-351242 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, the denitrification reaction requires organic matter and nitrate nitrogen. Although there is sufficient nitrogen within the disposal site, most of it exists in the form of ammonia, and in the absence of nitrate nitrogen, the denitrification reaction does not proceed even under anaerobic conditions. On the other hand, in the treated water, although the nitrification reaction proceeds through aeration and sufficient nitrate nitrogen is produced, the denitrification reaction does not proceed due to a lack of organic matter.

[0009] In view of the above-mentioned problems, the present invention has been made with an object of providing a method for denitrification at a waste disposal site, which makes effective use of the disposal site and performs denitrification. [Means for solving the problem]

[0010] The feature of the invention described in claim 1 for solving the above-mentioned conventional problems is that in a denitrification method for a waste disposal site having a waste sedimentary layer on which waste containing organic matter is accumulated, leachate leached from the waste sedimentary layer is collected, and the collected leachate is sent through a drainage pipe to a wastewater treatment means having an aeration tank, in which a nitrification reaction is carried out to produce nitrate nitrogen-containing water containing nitrate nitrogen, the nitrate nitrogen-containing water is sprayed on the waste sedimentary layer under semi-aerobic or anaerobic conditions, the nitrate nitrogen is reacted with hydrogen derived from the organic matter contained in the waste sedimentary layer to produce nitrogen, and the nitrogen is released from the waste sedimentary layer into the atmosphere.

[0011] Furthermore, the feature of the invention described in claim 2 is that, in addition to the configuration of claim 1, when the nitrate nitrogen-containing water is sprayed onto the waste deposition layer, an opening / closing valve provided in the drainage pipe is closed to retain the leachate in the waste deposition layer.

[0012] The invention as set forth in claim 3 is characterized in that, in addition to the configuration as set forth in claim 2, the opening and closing of the on-off valve is repeated at predetermined time intervals.

[0013] The invention as set forth in claim 4 is characterized in that, in addition to the configuration of claim 2 or 3, the waste sedimentary layer is divided into a plurality of sections, and the on-off valve is opened and closed for each of the sections. Effect of the Invention

[0014] The denitrification method for waste disposal sites according to the present invention, by being provided with the configuration described in claim 1, effectively utilizes the disposal site as a denitrification facility and performs denitrification within the disposal site, eliminating the need for denitrification equipment or large amounts of dilution water at the wastewater treatment facility. In addition, by spraying nitrate nitrogen-containing water, organic matter and nitrogen content are washed out of the waste, which is expected to lead to early stabilization of the disposal site.

[0015] In addition, in the present invention, by providing the configuration described in claim 2, the water level in the disposal tank can be controlled by flooding, thereby making it possible to control the anaerobic and denitrifying conditions.

[0016] Furthermore, in the present invention, by providing the configuration described in claim 3, the formation of an anaerobic region by flooding and the discharge of leachate can be periodically repeated, thereby efficiently promoting denitrification treatment.

[0017] Furthermore, in the present invention, by providing the configuration described in claim 4, it is possible to carry out denitrification treatment while performing management adapted to the conditions of each section. [Brief description of the drawings]

[0018] [Figure 1] 1 is a block diagram showing an outline of an embodiment of a denitrification method for a waste disposal site according to the present invention. [Diagram 2] FIG. 2 is a block diagram showing an example of details of the wastewater treatment means in FIG. 1. [Diagram 3] FIG. 1(a) is a schematic cross-sectional view for explaining the denitrification reaction in a waste sediment layer according to the present invention, and FIG. 1(b) is a view showing the state in which leachate is flooded in the waste sediment layer. [Figure 4] FIG. 2 is a block diagram showing an outline of another embodiment of the above. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Next, an embodiment of the denitrification method for a waste disposal site according to the present invention will be described based on the examples shown in Figures 1 to 4. In the figures, reference numeral 1 denotes a disposal site.

[0020] The disposal site 1 has a storage space 2 partitioned by impermeable walls, and waste is poured onto the bottom impermeable layer within the storage space 2 to form a waste deposit layer 3.

[0021] It is desirable that this disposal site 1 is configured, for example, as a closed disposal site in which the storage space 2 is covered with a covering facility such as a roof, or as a portable closed disposal site as shown in Figure 4, in which the storage space 2 is divided into several sections and a covering facility 4 such as a roof is moved in sequence to promote stabilization for each section A, B, C. The disposal site 1 may also be an open disposal site in which water is not normally sprayed on the waste deposition layer 3.

[0022] In addition, in this disposal site 1, water is sprayed from above onto the waste pile 3, and a water collection pipe (not shown) is installed in the lower part of the storage space 2 to collect leachate that seeps out from the waste pile 3 and send it to wastewater treatment means 6 through a drainage pipe 5. The reference numeral 7 in the figure denotes an opening and closing valve.

[0023] As shown in FIG. 2, the wastewater treatment means 6 includes a flow rate adjustment tank 10 for adjusting the flow rate of the leachate flowing in from the drain pipe 5, a first condensation and settling tank 11 for condensing and settling sludge from the leachate sent from the flow rate adjustment tank 10, an aeration tank 13 for aerating the leachate from which the sludge has been condensed and settling in the first condensation and settling tank 11 and subjecting it to a nitrification reaction to produce nitrate-nitrogen-containing water 12 containing nitrate nitrogen, a second condensation and settling tank 14 for condensing and settling the remaining sludge from the nitrate-nitrogen-containing water 12, and a storage tank 15 for storing the nitrate-nitrogen-containing water 12. The nitrate-nitrogen-containing water 12 stored in the storage tank 15 is circulated through the storage space 2 and sprayed onto the waste sedimentation layer 3 from above.

[0024] The flow rate adjustment tank 10 comprises a sand settling tank section 10a separated by an overflow wall, and first and second flow rate adjustment tank sections 10b and 10c. Leachate is poured into the sand settling tank section 10a from the drainage pipe 5, and sand settles and is separated in the sand settling tank section 10a, overflowing into the first flow rate adjustment tank section 10b and then into the second flow rate adjustment tank section 10c.

[0025] In the second flow rate adjustment tank section 10c, the leachate that has overflowed from the first flow rate adjustment tank section 10b is agitated by air sent from an agitation blower 16, and then returned to the first flow rate adjustment tank section 10b.

[0026] In the first flow rate control tank section 10b, a scale dispersant and a dewatering aid are added to the leachate that has flowed in from the sand settling tank section 10a and the second flow rate control tank section 10c, and the leachate is agitated by air sent in from the agitation blower 16. The agitated leachate is then sent to the first condensation and sedimentation tank 11 while the flow rate is adjusted by the pump 17.

[0027] The first condensation settling tank 11 includes a first condensation settling tank main body 11a disposed in the center, a first mixing tank section 11b and a first condensation tank section 11c disposed upstream of the first condensation settling tank main body 11a, and a neutralization tank section 11d and a bypass tank section 11e disposed downstream of the first condensation settling tank main body 11a.

[0028] The leachate sent from the flow rate control tank 10 first flows into the first mixing tank section 11b, where admixtures such as aluminum sulfate and caustic soda are added and stirred, and then sent to the first condensation tank section 11c, where a condensation aid is added and stirred.

[0029] Next, the leachate is sent from the first condensation tank section 11c to the first condensation settling tank main body 11a, and the condensed sludge in the first condensation settling tank main body 11a settles to the bottom and is scraped up and transported to the sludge treatment equipment 19. In the figure, reference numeral 20 denotes a scraping device that scrapes up the sludge that has settled to the bottom, and reference numeral 21 denotes a pump that transports the sludge to the sludge treatment equipment 19.

[0030] Then, the supernatant of the leachate from which sludge has settled in the first condensation and sedimentation tank body 11a flows into the first neutralization tank section 11d, where a neutralizing agent such as sulfuric acid is added and stirred, and then the supernatant overflows into the bypass tank section 11e and is sent from the bypass tank section 11e to the aeration tank 13.

[0031] The aeration tank 13 comprises a temperature rising tank section 13a disposed downstream and an aeration tank main body 13b disposed across an overflow wall from the temperature rising tank section 13a, and the leachate after sludge settling flows from the first condensation and sedimentation tank 10 into the temperature rising tank section 13a, where it is heated to a predetermined temperature, then overflows into the aeration tank main body 13b, where it is aerated by air sent from an aeration blower 22. Reference numeral 24 in the figure denotes a heating device that heats the water in the temperature rising tank section 13a.

[0032] At that time, the leachate flowing into the aeration tank 13 has separated sludge, has little organic matter, and contains ammonia nitrogen. A nitrification reaction occurs under aerobic conditions caused by aeration, producing nitrate nitrogen-containing water 12 containing nitrate nitrogen, as shown below.

[0033] Nitrification reaction (under aerobic conditions) 2NH4 + +O2→2NO2 - +2H2+4H + 2NO2 - +O2→2NO3 -

[0034] The generated nitrate nitrogen-containing water 12 is sent from the aeration tank 13 to a second condensation and settling tank 14.

[0035] The second condensation settling tank 14 includes a second mixing tank section 14b and a second condensation tank section 14c, both of which are disposed upstream of the second condensation settling tank main body 14a. The nitrate nitrogen-containing water 12 generated in the aeration tank 13 flows into the second mixing tank section 14b, where admixtures such as aluminum sulfate and caustic soda are added and stirred, and the water is then sent to the second condensation tank section 14c, where a condensation aid is added and stirred.

[0036] Next, the nitrate nitrogen-containing water 12 is sent from the second condensation tank section 14c to the second condensation and settling tank main body 14a, where the condensed sludge residue settles to the bottom, and only the supernatant of the nitrate nitrogen-containing water 12 overflows into the storage tank 15.

[0037] The sludge residue that has settled to the bottom of the second condensation and settling tank body 14a is pumped up by a pump 24 and transported to the sludge treatment facility 19.

[0038] A pump 25 is installed in the storage tank 15 to pump up the stored nitrate nitrogen-containing water 12, and the pumped nitrate nitrogen-containing water 12 is transported through a water supply pipe 26 onto the waste pile 3 of the disposal site 1 and sprayed thereon.

[0039] In addition, any nitrate nitrogen-containing water 12 that exceeds the amount required for sprinkling is discharged after being diluted with dilution water, but since most of the nitrate nitrogen-containing water 12 is circulated to the waste sediment layer 3 for sprinkling, only a small amount of dilution water is required.

[0040] When the nitrate nitrogen-containing water 12 is sprayed, as shown in Figure 3(a), since there is an abundance of organic matter in the waste pile 3 which is under anaerobic or semi-anaerobic conditions, a denitrification reaction proceeds as shown below, and hydrogen derived from the organic matter contained in the waste pile 3 reacts with the nitrate nitrogen to generate nitrogen, which is then released from the waste pile 3 into the atmosphere.

[0041] Denitrification reaction (anaerobic conditions) 2NO2 - +3H2→N2+2OH - +2H2O 2NO3 - +5H2→N2+2OH - +4H2O

[0042] Furthermore, even when the on-off valve 7 provided on the drainage pipe 5 is open, the waste sediment layer 3 is in semi-aerobic and partially anaerobic conditions, and sufficient denitrification reactions are expected to occur. However, as shown in Figure 3(b), by closing the on-off valve 7 provided on the drainage pipe 5 and leaving the leachate 27 in the waste sediment layer 3, the lower part of the waste sediment layer 3 can be made to be in anaerobic conditions reliably, and the denitrification reaction can be promoted.

[0043] The on-off valve 7 may be repeatedly opened and closed at predetermined time intervals. For example, the on-off valve 7 may be closed before water spraying, kept closed for a certain time after water spraying, i.e., for the time required for the denitrification reaction, and then opened after the predetermined time has elapsed. This operation may be repeated.

[0044] In addition, by spraying the nitrate nitrogen-containing water 12, organic matter and ammonia nitrogen are washed out of the waste pile 3, promoting early stabilization of the disposal site 1, and the resulting leachate is sent to the wastewater treatment means 6.

[0045] Then, the leachate seeping out from the waste sedimentary layer 3 is sent to the wastewater treatment means 6, and the nitrate nitrogen-containing water 12 produced in the wastewater treatment means 6 is circulated as water sprayed on the waste sedimentary layer 3, repeating this cycle.

[0046] The denitrification method of the landfill 1 configured in this manner recirculates the nitrate nitrogen-containing water 12 produced in the process of treating the leachate that seeped from the waste sediment layer 3, and sprinkles it instead of conventional rainwater or tap water, thereby making it possible to effectively utilize the landfill 1 itself and carry out denitrification treatment efficiently without the need for large-scale denitrification equipment or large amounts of dilution water.

[0047] In addition, in the denitrification method for this disposal site 1, by spraying nitrate nitrogen-containing water 12, organic matter and ammonia nitrogen are washed out of the waste deposit layer 3, thereby promoting early stabilization of the disposal site 1.

[0048] Furthermore, as shown in Figure 4, when the storage space 2 is divided into several sections and the on-off valve 7 is opened and closed for each section, the anaerobic and denitrification reactions can be controlled by managing the water retention condition (water level) and water quality for each section.

[0049] For example, when the waste deposit layer 3 in section B is covered with a covering facility 4 such as a roof and waste dumping work is carried out in the covering facility 4, since there is no rainfall, nitrate nitrogen-containing water 12 generated in the wastewater treatment means 6 is sprayed onto the waste deposit layer 3 to promote washing out and microbial decomposition as well as to advance denitrification.

[0050] On the other hand, in the case of section C, where the waste input and intermediate soil cover 30 have been completed and the waste pile layer 3 is in an open state, washing out and microbial decomposition can be expected due to rainfall, but denitrification does not proceed because the nitrogen is mainly ammonia nitrogen. Therefore, normally, the on-off valve 7 is opened and the leachate is sent to the wastewater treatment means 6, which generates nitrate nitrogen-containing water 12. The reference numeral 30 in the figure denotes the soil cover.

[0051] In addition, in the section C, it is possible to promote denitrification by sprinkling the nitrate nitrogen-containing water 12 generated by the wastewater treatment means 6 during periods of low rainfall, etc.

[0052] Furthermore, in the case of section A, when section BC is in the process of being filled or has been filled or intermediate soil covering has been completed before landfilling, the on-off valve 7 of section A can be closed to store rainwater, and the stored water can be used as dilution water or sprinkling water in the wastewater treatment means 6.

[0053] Furthermore, the BOD, COD, nitrogen, temperature, gas concentration, generation amount, etc. of the leachate from each compartment are monitored at any time, and depending on the stabilization status, nitrate nitrogen-containing water 12 generated by the wastewater treatment means 6 is sprayed on compartments that require stabilization or compartments where denitrification is progressing efficiently.

[0054] In the above embodiment, the nitrate nitrogen-containing water 12 is circulated to the storage space 2 (waste sedimentation layer 3) by a pump, but the nitrate nitrogen-containing water 12 may be collected together with sludge by a vacuum truck or the like from the upstream part of the second condensation and settling tank 14 of the wastewater treatment means 6, and the collected water may be transported to a disposal site and sprinkled there. In this case, the load of the additionally required extraction, dewatering and disposal of sludge can be reduced. [Explanation of symbols]

[0055] 1. Disposal Site 2. Storage space 3 Waste pile 4. Covering facility 5 Drain pipe 6 Wastewater treatment methods 7. On-off valve 10 Flow rate adjustment tank 11 First condensation and settling tank 12 Nitrate-containing water 13 Aeration tank 14 Second condensation and settling tank 15 Reservoir 16 Agitation blower 17 Pump 18 Mixer 19 Sludge treatment facility 20. Scraping device 21 Pump 22 Aeration blower 23 Heating device 24 Pump 25 Pump 26 Water pipe

Claims

1. A method for denitrification at a waste disposal site having a waste sediment layer in which waste containing organic matter is accumulated, comprising the steps of: A denitrification method for a waste disposal site, comprising the steps of: collecting leachate that has seeped out from the waste sediment layer; sending the collected leachate through a drainage pipe to a wastewater treatment means having an aeration tank; causing a nitrification reaction in the aeration tank to produce nitrate nitrogen-containing water containing nitrate nitrogen; spraying the nitrate nitrogen-containing water onto the waste sediment layer under semi-aerobic or anaerobic conditions; reacting the nitrate nitrogen with hydrogen derived from organic matter contained in the waste sediment layer to produce nitrogen; and releasing the nitrogen from the waste sediment layer into the atmosphere.

2. 2. A method for denitrification at a waste disposal site according to claim 1, wherein when said nitrate nitrogen-containing water is sprayed onto said waste sedimentary layer, an on-off valve provided in said drainage pipe is closed to cause said leachate to remain in said waste sedimentary layer.

3. 3. A method for denitrification at a waste disposal site according to claim 2, wherein the opening and closing of the on-off valve is repeated at predetermined time intervals.

4. 4. A method for denitrification at a waste disposal site according to claim 2 or 3, wherein the waste sedimentary layer is divided into a plurality of sections, and the on-off valve is opened and closed for each of the sections.

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