Half short-cut nitrification method for middle-aged and old-aged landfill leachate

Abstract

The invention discloses a half short-cut nitrification method for middle-aged and aged landfill leachate, which mainly adopts two stages of short-cut nitrification reactors to generate nitrite nitrogen, the two stages of short-cut nitrification reactors are both aeration sedimentation tank combined construction types, and the nitrite nitrogen is generated by controlling respective proper process parameters and nitrite oxidizing bacteria inhibition modes. And meanwhile, a strategy of periodically alternating a two-stage short-cut nitrification reactor process sequence is adopted, so that the purpose of long-term stable operation of short-cut nitrification is achieved. The method is efficient, economical, stable in operation and high in practicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of landfill leachate treatment, and particularly relates to a semi-shortcut nitrification method for middle-aged and old landfill leachate. Background Art

[0002] Sanitary landfill and incineration are the main treatment methods for municipal solid waste, both of which will produce leachate, with yields of about 10% - 20% and 15% - 30% of the waste volume respectively. Landfill leachate is a type of high-ammonia-nitrogen organic wastewater. At present, the typical process of membrane bioreactor + nanofiltration based on traditional biological nitrogen removal (nitrification - denitrification) is mainly adopted in China, which has the disadvantages of high energy consumption and the need for external carbon sources. The leachate generated by existing landfills is basically in the middle-aged and old stage (landfill age greater than 5 years). The water quality of middle-aged and old landfill leachate generally shows the following characteristics: pH value is 7.8 - 8.9, COD is 1500 - 5000 mg / L, B / C ratio is less than 0.25, ammonia nitrogen is 1000 - 2700 mg / L, alkalinity is 5000 - 12000 mg / L. It is a high-concentration ammonia-nitrogen wastewater, while the C / N ratio is often lower than 2, that is, the carbon source is extremely lacking. In order to ensure the compliance of total nitrogen, the cost of external carbon source required reaches 15 - 60 yuan per ton, bringing a huge burden to local finances and treatment enterprises.

[0003] Anaerobic ammonium oxidation has great application prospects in the treatment of high-ammonia-nitrogen wastewater due to its advantages such as no need for external carbon source and aeration power consumption. However, how to obtain nitrite nitrogen efficiently and stably is the key to the stable operation of anaerobic ammonium oxidation. At present, shortcut nitrification is the main method to provide nitrite nitrogen for anaerobic ammonium oxidation. Its essence is to selectively enrich ammonia-oxidizing bacteria and inhibit the growth of nitrite-oxidizing bacteria, so as to achieve the accumulation of nitrite nitrogen. The means to inhibit the growth of nitrite-oxidizing bacteria include regulating low dissolved oxygen, temperature, pH and sludge age, inhibiting with free ammonia / free nitrous acid, and intermittent aeration mode, etc. Among them, controlling low dissolved oxygen is the most commonly used method, and using free ammonia / free nitrous acid is also an effective method. However, these mainstream inhibition strategies have the problem of not being able to be long-term and stable in practical applications. After running for a period of time, the content of nitrite nitrogen generated will gradually decrease until the shortcut nitrification performance deteriorates, making it difficult for the shortcut nitrification + anaerobic ammonium oxidation process to play the nitrogen removal role normally. In essence, it is because new microbial populations that can adapt to the used inhibition strategies will appear during the long-term operation of shortcut nitrification and gradually become ineffective. Therefore, the basic idea of the present invention to solve the problem is to periodically switch effective inhibition methods during the long-term operation, that is, when a certain inhibition method shows a trend of decreasing efficiency, switch to another method alternately, so that the new population of nitrite-oxidizing bacteria that gradually adapts to the current inhibition method has no chance to grow and expand. At the same time, the shortcut nitrification process should be simple, novel and highly practical, so as to stably produce high-concentration nitrite nitrogen and lay a solid foundation for the efficient and stable operation of anaerobic ammonium oxidation. Summary of the Invention

[0004] The object of the present invention is to provide a semi-shortcut nitrification method for middle-aged and old landfill leachate, which realizes long-term shortcut nitrification by making two-stage shortcut nitrification reactors with an integrated aeration and sedimentation tank type in different inhibition modes of nitrite-oxidizing bacteria combinations and periodically alternating the process sequences of the two-stage shortcut nitrification reactors. This method is efficient, economical, highly practical and operates stably.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A semi-shortcut nitrification method for middle-aged and old landfill leachate, which comprises the following steps: 1) Pretreat the middle-aged and old landfill leachate in a denitrification tank to remove most of the biodegradable organic matter (BOD < 80 mg / L), and after diluting the ammonia nitrogen concentration to be between 400 and 600 mg / L, discharge it into a first-stage shortcut nitrification reactor with an integrated aeration and sedimentation tank type, control the DO to be 0.02 - 0.2 mg / L, the pH to be 7.6 - 8.2, the free ammonia to be greater than 3 mg / L, the hydraulic retention time to be 3 - 10 h, and the mixed liquor suspended solid concentration to be 3000 - 5000 mg / L; meanwhile, perform solid-liquid separation on the mud-water mixture of the first-stage shortcut nitrification reactor in the sedimentation area, and after separation, obtain the supernatant of the first-stage shortcut nitrification with a nitrite nitrogen concentration of 100 - 150 mg / L, which flows into the second-stage shortcut nitrification reactor, while the sedimented sludge flows back to the reaction area of the first-stage shortcut nitrification reactor; after the supernatant of the first-stage shortcut nitrification enters the second-stage shortcut nitrification reactor with the same integrated aeration and sedimentation tank type, continue to perform shortcut nitrification, control the DO to be 0.06 - 0.5 mg / L, the pH to be 7.0 - 7.6, the free nitrous acid to be greater than 0.02 mg / L, the hydraulic retention time to be 3 - 10 h, and the mixed liquor suspended solid concentration to be 3000 - 5000 mg / L; perform solid-liquid separation on the mud-water mixture of the second-stage shortcut nitrification reactor after further shortcut nitrification in the sedimentation area, and after separation, obtain the supernatant of the second-stage shortcut nitrification with a nitrite nitrogen concentration of 200 - 300 mg / L and a nitrite nitrogen / ammonia nitrogen ratio of 0.9 - 1.5, which enters the subsequent anaerobic ammonium oxidation treatment unit, while the sedimented sludge flows back to the reaction area of the second-stage shortcut nitrification reactor.

[0006] 2) When the nitrate nitrogen concentration in the effluent of the second-stage shortcut nitrification reactor is greater than 40 mg / L, or the nitrite nitrogen accumulation rate is lower than 85%, exchange the process sequences of the first-stage and second-stage shortcut nitrification reactors.

[0007] The remarkable advantages of the present invention are as follows: (1) High efficiency. Short-cut nitrification is a process that consumes alkalinity. If a relatively high degree (above 50%) of short-cut nitrification is required, due to the dual decline of pH and ammonia nitrogen concentration, the free ammonia concentration in the final reactor will be relatively low, which cannot effectively inhibit nitrite oxidizing bacteria. Therefore, in the present invention, short-cut nitrification is divided into two stages. In the effluent of the first stage, there is still a relatively high concentration of ammonia nitrogen, that is, the degree of short-cut nitrification is relatively low (about 30%), and the pH is also alkaline (>7.6). Therefore, the free ammonia concentration in the first-stage short-cut nitrification reactor still remains >3 mg / L, which can effectively inhibit nitrite oxidizing bacteria. The second-stage short-cut nitrification reactor continues to convert ammonia nitrogen into nitrite nitrogen. The nitrite nitrogen concentration in the effluent (reactor) can reach 200-300 mg / L, and the pH further drops to 7.0-7.6. In this way, the free nitrous acid concentration reaches above 0.02 mg / L, which can effectively inhibit nitrite oxidizing bacteria. The nitrite nitrogen production rate of the two-stage short-cut nitrification of the present invention can reach 1.08 kgN / m 3 .d, and the nitrite nitrogen accumulation rate reaches more than 98%. Therefore, the method of the present invention can achieve high-efficiency short-cut nitrification.

[0008] (2) Long-term stable operation and strong practicability. There are many ways to inhibit nitrite oxidizing bacteria, but each method has its deficiencies, which makes the performance of the short-cut nitrification system in engineering significantly decrease or collapse after running for a period of time. The main reason is that under long-term operation, nitrite oxidizing bacteria can gradually generate new populations adapted to the used inhibition methods. Therefore, the currently considered feasible method is to continuously change the inhibition methods. Based on this problem and related understandings, this method innovatively proposes the process sequence of a periodic alternating two-stage short-cut nitrification reactor (it is found that the microbial community structures are significantly different, laying a microbiological mechanism foundation for this method), so as to frequently change the inhibition methods and habitats of nitrite oxidizing bacteria, making it difficult for them to generate new populations. In engineering, the process sequence of the two-stage short-cut nitrification reactor can be considered in the engineering design to be interchanged, and thus it is easy to switch in the operation stage by taking appropriate engineering measures. Therefore, the present invention can realize the long-term stable operation of the two-stage short-cut nitrification reactor and has strong practicability.

[0009] (3) Economy. Both two-stage short-cut nitrification reactors of the present invention adopt the combined form of an aeration sedimentation tank, which has a compact structure and can save a set of sludge return equipment. Therefore, it has the advantages of low engineering investment and operation cost. In addition, compared with complete nitrification, short-cut nitrification inherently saves energy, and the stable high-concentration nitrite nitrogen and the remaining ammonia nitrogen provided can achieve high-efficiency and low-cost biological nitrogen removal through anaerobic ammonium oxidation. Therefore, the present invention has good economy. Description of the Drawings

[0010] Figure 1 is the process flow chart of the present invention. Detailed Embodiments

[0011] The following will further describe the process flow of the present invention in conjunction with the attached drawings Figure 1 。

[0012] The entire technological process consists of two - stage shortcut nitrification reactors that both adopt the combined form of aeration sedimentation tanks. The specific process is as follows: (1) The medium - aged landfill leachate is pretreated in a denitrification tank to degrade organic matter and dilute the ammonia - nitrogen concentration, and then the effluent (BOD < 80mg / L, ammonia - nitrogen concentration is 400 - 600mg / L) flows into the reaction zone of the first - stage shortcut nitrification reactor. Control DO to be 0.02 - 0.2mg / L, pH to be 7.6 - 8.2, free ammonia to be greater than 3mg / L, hydraulic retention time to be 3 - 10h, and the mixed - liquor suspended - solid concentration to be 3000 - 5000mg / L for a certain degree of shortcut nitrification, and the mixed liquor is refluxed to the pre - placed denitrification tank at a large reflux ratio (4 - 9); (2) The mixed liquor in the sedimentation zone of the first - stage shortcut nitrification reactor is separated into mud and water. After separation, the supernatant of the first - stage shortcut nitrification is obtained, with a nitrite - nitrogen concentration of 100 - 150mg / L, which flows into the second - stage shortcut nitrification reactor, while the sedimented sludge flows back to the reaction zone of the first - stage shortcut nitrification reactor; (3) The supernatant of the first - stage shortcut nitrification enters the reaction zone of the second - stage shortcut nitrification reactor to continue shortcut nitrification. Control DO to be 0.06 - 0.5mg / L, pH to be 7.0 - 7.6, free nitrous acid to be greater than 0.02mg / L, hydraulic retention time to be 3 - 10h, and the mixed - liquor suspended - solid concentration to be 3000 - 5000mg / L to further complete shortcut nitrification; (4) The mixed liquor in the sedimentation zone of the second - stage shortcut nitrification reactor is separated into mud and water. After separation, the supernatant of the second - stage shortcut nitrification is obtained, with a nitrite - nitrogen concentration of 200 - 300mg / L and a nitrite - nitrogen / ammonia - nitrogen ratio of 0.9 - 1.5, which enters the subsequent anaerobic ammonium oxidation treatment unit, while the sedimented sludge is refluxed to the reaction zone of the second - stage shortcut nitrification reactor; (5) When the nitrate - nitrogen concentration in the effluent of the second - stage shortcut nitrification reactor is greater than 40mg / L, or the nitrite - nitrogen accumulation rate is lower than 85%, the process sequences of the first - stage and second - stage shortcut nitrification reactors are interchanged.

[0013] Example 1 Taking the shortcut nitrification treatment link of a domestic waste landfill leachate treatment project as an example, the present invention will be further described below.

[0014] The scale of the treatment project for the aged leachate of the closed domestic waste landfill is 160 tons per day, and the water quality is as follows: pH is 7.9 - 8.6, COD is between 2000 - 3500mg / L, B / C ratio is less than 0.25, ammonia - nitrogen is 1100 - 1900mg / L, and alkalinity is 6000 - 10000mg / L.

[0015] The leachate in the regulating tank is pumped and lifted into the denitrification tank, where it is mixed and denitrified with the mixed liquor of the first-stage shortcut nitrification reactor with a large reflux ratio, so as to fully remove the biodegradable organic matter and dilute the ammonia nitrogen concentration. The effluent has a BOD < 80 mg / L and an ammonia nitrogen concentration of about 500 mg / L, and then flows into the reaction zone of the first-stage shortcut nitrification reactor. The DO is controlled at 0.02 - 0.1 mg / L, the pH is 7.8 - 8.1, the free ammonia is greater than 5 mg / L, the hydraulic retention time is 5 h, and the mixed liquor suspended solid concentration is 4000 - 5000 mg / L. The ammonia nitrogen removal rate is about 30%, and the nitrite nitrogen accumulation rate is 90 - 100%. The formed shortcut nitrification mixed liquor is refluxed to the pre-positioned denitrification tank at a large reflux ratio (varying between 4 and 9 to control the ammonia nitrogen concentration required for the inlet water of the first-stage shortcut nitrification reactor); the mixed liquor in the sedimentation zone of the first-stage shortcut nitrification reactor is separated into mud and water, and the supernatant of the first-stage shortcut nitrification is obtained after separation. The nitrite nitrogen concentration is about 140 mg / L and flows into the second-stage shortcut nitrification reactor, while the sedimented sludge flows back to the reaction zone of the first-stage shortcut nitrification reactor under the action of gravity. The supernatant effluent of the first-stage shortcut nitrification reactor flows into the reaction zone of the second-stage shortcut nitrification reactor. The DO is controlled at 0.1 - 0.3 mg / L, the pH is 7.2 - 7.6, the free nitrous acid is greater than 0.05 mg / L, the hydraulic retention time is 5 h, and the mixed liquor suspended solid concentration is 4000 - 5000 mg / L. The further ammonia nitrogen removal rate is about 25%, and the nitrite nitrogen accumulation rate is 90 - 99%; the mixed liquor in the sedimentation zone of the second-stage shortcut nitrification reactor is separated into mud and water, and the supernatant of the second-stage shortcut nitrification is obtained after separation. The nitrite nitrogen concentration reaches about 260 mg / L, and the nitrite nitrogen / ammonia nitrogen ratio is 1.0 - 1.3, and then it enters the subsequent anaerobic ammonium oxidation treatment unit, while the sedimented sludge flows back to the reaction zone of the second-stage shortcut nitrification reactor under the action of gravity. When the nitrate nitrogen concentration in the effluent of the second-stage shortcut nitrification reactor is greater than 40 mg / L or the nitrite nitrogen accumulation rate is lower than 85% during the treatment operation process, the first-stage and second-stage shortcut nitrification reactors are interchanged in the front and back order to achieve the long-term efficient and stable operation of the shortcut nitrification treatment link.

[0016] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate, characterized in that, It includes the following steps: 1) Discharge the middle-aged and old landfill leachate that has undergone denitrification treatment to remove most of the biodegradable organic matter and dilute the ammonia nitrogen concentration into the first-stage shortcut nitrification reactor. The first-stage shortcut nitrification mixed liquor obtained through shortcut nitrification is refluxed to the pre-denitrification tank at a large reflux ratio; meanwhile, the first-stage shortcut nitrification mixed liquor enters the sedimentation area for solid-liquid separation. After separation, the first-stage shortcut nitrification supernatant enters the second-stage shortcut nitrification reactor, while the sediment sludge flows back to the reaction area of the first-stage shortcut nitrification reactor; the first-stage shortcut nitrification supernatant continues to undergo shortcut nitrification in the second-stage shortcut nitrification reactor and undergoes solid-liquid separation in the sedimentation area. After separation, the second-stage shortcut nitrification supernatant enters the subsequent anaerobic ammonium oxidation treatment unit, while the sediment sludge is discharged back to the reaction area of the second-stage shortcut nitrification reactor.

2. The semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: In step 1), both the first-stage and second-stage shortcut nitrification reactors adopt the combined form of an aeration sedimentation tank.

3. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: In step 1), the ammonia nitrogen concentration in the middle-aged and old landfill leachate that has undergone denitrification treatment to remove most of the biodegradable organic matter and dilute the ammonia nitrogen concentration and is discharged into the first-stage shortcut nitrification reactor is diluted to between 400 and 600 mg / L, and the biodegradable organic matter BOD is less than 80 mg / L.

4. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: In step 1), the DO of the first-stage shortcut nitrification reactor is 0.02 - 0.2 mg / L, and the pH is 7.6 - 8.2; the DO of the second-stage shortcut nitrification reactor is 0.06 - 0.5 mg / L, and the pH is 7.0 - 7.

6.

5. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: In step 1), the total hydraulic retention time of the first-stage and second-stage shortcut nitrification reactors is 6 - 20 h.

6. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: In step 1), the free ammonia in the first-stage shortcut nitrification reactor is greater than 3 mg / L; the free nitrous acid in the second-stage shortcut nitrification reactor is greater than 0.02 mg / L.

7. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: In step 1), the mixed liquor suspended solid concentration of both the first-stage and second-stage shortcut nitrification reactors is 3000 - 5000 mg / L.

8. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: In step 1), the nitrite nitrogen concentration in the effluent of the second-stage shortcut nitrification reactor is 200 - 300 mg / L, and the nitrite nitrogen / ammonia nitrogen ratio is 0.9 - 1.

5.

9. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: In step 1), whenever the nitrate nitrogen concentration in the effluent of the second-stage shortcut nitrification reactor is greater than 40 mg / L, or the nitrite nitrogen accumulation rate is lower than 85%, the process sequence of the first-stage and second-stage shortcut nitrification reactors is interchanged.

10. A semi-shortcut nitrification method for middle-aged and elderly landfill leachate according to claim 1, characterized in that: The reflux ratio of the first-stage shortcut nitrification mixed liquor refluxed to the pre-denitrification tank is 4 - 9.

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