Method for semi-short-cut nitrification of matured landfill leachate

Abstract

The application discloses a semi-short-cut nitrification method for middle-aged and old landfill leachate, which mainly adopts two-stage short-cut nitrification reactors to generate nitrous nitrogen, and the two-stage short-cut nitrification reactors are combined with aeration sedimentation tanks, the respective suitable process parameters and nitrite oxidation bacteria inhibition modes are controlled, and the strategy of periodically alternating the process sequence of the two-stage short-cut nitrification reactors is adopted, so that the 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] This invention belongs to the field of landfill leachate treatment technology, specifically relating to a semi-short-cut nitrification method for leachate from middle-aged and older landfills. Background Technology

[0002] Sanitary landfill and incineration are the main methods of municipal solid waste treatment, both of which produce leachate, accounting for approximately 10%–20% and 15%–30% of the waste volume, respectively. Landfill leachate is a type of high-ammonia-nitrogen organic wastewater. Currently, my country mainly uses a typical process based on traditional biological denitrification (nitrification to denitrification) using membrane bioreactors + nanofiltration, which suffers from high energy consumption and the need for external carbon sources. The leachate produced by existing landfills is generally from middle-aged landfills (over 5 years old). The water quality of middle-aged landfill leachate typically exhibits the following characteristics: pH 7.8–8.9, COD 1500–5000 mg / L, B / C ratio less than 0.25, ammonia nitrogen 1000–2700 mg / L, and alkalinity 5000–12000 mg / L. It is a high-concentration ammonia-nitrogen wastewater, while the C / N ratio is often below 2, indicating an extreme lack of carbon sources. To ensure that total nitrogen meets the standards, the cost of additional carbon sources is 15-60 yuan per ton, which places a huge burden on local finances and treatment companies.

[0003] Anaerobic ammonium oxidation (ANAO) is highly promising for treating high ammonia nitrogen wastewater due to its advantages such as not requiring external carbon sources and low aeration power consumption. However, the key to stable operation of ANAO lies in efficiently and stably obtaining nitrite nitrogen. Currently, cut-cut nitrification is the main method for providing nitrite nitrogen for ANAO. Essentially, it selectively enriches ammonia-oxidizing bacteria while inhibiting the growth of nitrite-oxidizing bacteria, thereby accumulating nitrite nitrogen. Methods to inhibit the growth of nitrite-oxidizing bacteria include controlling dissolved oxygen, temperature, pH, and sludge age; utilizing free ammonia / free nitrite for inhibition; and intermittent aeration. Controlling dissolved oxygen is the most common method, and utilizing free ammonia / free nitrite is also effective. However, these mainstream inhibition strategies suffer from long-term instability in practical applications. After a period of operation, the nitrite nitrogen content gradually decreases until the performance of cut-cut nitrification deteriorates, making it difficult for the cut-cut nitrification + ANAO process to effectively remove nitrogen. The root cause is that during long-term operation of cut-cut nitrification, new microbial populations that can adapt to the used inhibition strategies gradually become ineffective. Therefore, the basic approach proposed in this invention is to periodically change the effective inhibition method during long-term operation. That is, when one inhibition method shows a decreasing trend in effectiveness, it is replaced by another, preventing new populations of nitrite-oxidizing bacteria that gradually adapt to the current inhibition method from growing and expanding. Simultaneously, the short-cut nitrification process should be simple, novel, and highly practical, thereby achieving a stable production of high-concentration nitrite nitrogen and laying a solid foundation for the efficient and stable operation of anaerobic ammonia oxidation. Summary of the Invention

[0004] The purpose of this invention is to provide a semi-short-cut nitrification method for leachate from medium- and old landfills. This method achieves long-term short-cut nitrification by employing a two-stage short-cut nitrification reactor (combined with an aerated sedimentation tank) with different combinations of nitrite-oxidizing bacteria inhibition modes, and by periodically alternating the process sequence of the two stages. This method is efficient, economical, practical, and stable in operation.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A semi-short-cut nitrification method for leachate from medium- and old landfills includes the following steps: 1) The leachate from medium- and old landfills is pretreated in a denitrification tank to remove most of the biodegradable organic matter (BOD < 80 mg / L) and dilute the ammonia nitrogen concentration to between 400 and 600 mg / L. Then, it is discharged into a primary short-cut nitrification reactor (a combination of an aerated sedimentation tank and a primary short-cut nitrification reactor). The dissolved oxygen (DO) is controlled at 0.02–0.2 mg / L, pH at 7.6–8.2, free ammonia at greater than 3 mg / L, hydraulic retention time at 3–10 h, and the mixed liquor suspended solids concentration at 3000–5000 mg / L. Simultaneously, the sludge-water mixture from the primary short-cut nitrification reactor undergoes solid-liquid separation in the sedimentation zone. The resulting primary short-cut nitrification supernatant, with a nitrite nitrogen concentration of 100–150 mg / L, flows into the secondary short-cut nitrification reactor, while the settled sludge is returned to the primary short-cut nitrification reactor. The primary short-cut nitrification supernatant enters the secondary short-cut nitrification reactor, which also uses an aeration sedimentation tank combined with a secondary short-cut nitrification reactor, for further short-cut nitrification. The dissolved oxygen (DO) is controlled at 0.06–0.5 mg / L, pH at 7.0–7.6, free nitrite at greater than 0.02 mg / L, hydraulic retention time at 3–10 h, and mixed liquor suspended solids concentration at 3000–5000 mg / L. After further short-cut nitrification, the sludge-water mixture from the secondary short-cut nitrification reactor undergoes solid-liquid separation in the sedimentation zone. The resulting secondary short-cut nitrification supernatant has a nitrite nitrogen concentration of 200–300 mg / L and a nitrite nitrogen / ammonia nitrogen ratio of 0.9–1.5, and enters the subsequent anaerobic ammonia oxidation treatment unit. The settled sludge is returned to the secondary short-cut nitrification reactor reaction zone.

[0006] 2) When the nitrate nitrogen concentration in the effluent of the secondary short-cut nitrification reactor is greater than 40 mg / L, or the nitrite nitrogen accumulation rate is less than 85%, the process sequence of the primary and secondary short-cut nitrification reactors shall be interchanged.

[0007] The significant advantages of this invention are: (1) High efficiency. Short-cut nitrification is a process that consumes alkalinity. If a higher degree of short-cut nitrification (above 50%) is required, the concentration of free ammonia in the reactor will be low due to the decrease in both pH and ammonia nitrogen concentration, which will not effectively inhibit nitrite-oxidizing bacteria. Therefore, this invention divides short-cut nitrification into two stages. The effluent from the first stage still retains a high concentration of ammonia nitrogen, that is, the degree of short-cut nitrification is low (about 30%), and the pH is also alkaline (>7.6). Therefore, the free ammonia concentration in the first-stage short-cut nitrification reactor is still maintained at >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 concentration of nitrite nitrogen in the effluent (reactor) can reach 200~300 mg / L, and the pH further decreases to 7.0~7.6. In this way, the free nitrite concentration reaches above 0.02 mg / L, which can effectively inhibit nitrite-oxidizing bacteria. The two-stage short-range nitrification nitrite nitrogen yield of this invention can reach 1.08 kgN / m³. 3 The nitrite nitrogen accumulation rate reaches over 98%. Therefore, the method of this invention can achieve highly efficient short-cut nitrification.

[0008] (2) Long-term stable operation and strong practicality. There are many ways to inhibit nitrite-oxidizing bacteria, but each method has its shortcomings. This leads to a significant decrease in performance or even collapse of short-cut nitrification systems in engineering after a period of operation. The main reason is that under long-term operation, nitrite-oxidizing bacteria can gradually generate new populations that adapt to the used inhibition methods. Therefore, current research suggests that a feasible method is to continuously change the inhibition methods. Based on this problem and related understanding, this method innovatively proposes a process sequence of two-stage short-cut nitrification reactors with alternating cycles (research has found significant differences in the microbial community structure of each reactor, laying the microbiological mechanism foundation for this method). This frequently changes 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 reactors can be considered during the engineering design, making it easy to switch during the operation phase by taking appropriate engineering measures. Therefore, this invention can achieve long-term stable operation of two-stage short-cut nitrification reactors and has strong practicality.

[0009] (3) Economy. The two-stage short-cut nitrification reactors of this invention are both constructed using a combined aeration and sedimentation tank design, resulting in a compact structure and eliminating the need for a sludge return system. Therefore, they offer advantages in terms of low engineering investment and operating costs. Furthermore, compared to full-process nitrification, short-cut nitrification inherently saves energy, and the stable high concentration of nitrite nitrogen and residual ammonia nitrogen provided can achieve efficient and inexpensive biological denitrification through anaerobic ammonia oxidation. Therefore, this invention is economically viable. Attached Figure Description

[0010] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0011] The following is in conjunction with the appendix Figure 1 The process flow of the present invention will be further described below.

[0012] The entire process consists of two short-cut nitrification reactors, both of which are constructed using a combined aeration sedimentation tank. The specific process is as follows: (1) The middle-aged leachate is pretreated by denitrification tank to degrade organic matter and dilute ammonia nitrogen concentration. The effluent (BOD<80mg / L, ammonia nitrogen concentration of 400~600mg / L) flows into the reaction zone of the first-stage short-cut nitrification reactor. The DO is controlled at 0.02~0.2mg / L, pH at 7.6~8.2, free ammonia greater than 3mg / L, hydraulic retention time at 3~10h, and mixed liquor suspended solids concentration at 3000~5000mg / L. A certain degree of short-cut nitrification is carried out, and the mixed liquor is returned to the pre-denitrification tank with a large return ratio (4~9); (2) The mixed liquor is separated into mud and water in the sedimentation zone of the first-stage short-cut nitrification reactor. After separation, the first-stage short-cut nitrification supernatant is obtained with nitrite nitrogen concentration of 100~150mg / L. It flows into the second-stage short-cut nitrification reactor, while the settled sludge flows back to the reaction zone of the first-stage short-cut nitrification reactor; (3) The first-stage short-cut nitrification reactor is further processed by the first-stage short-cut nitrification reactor. The nitrification supernatant enters the reaction zone of the secondary short-cut nitrification reactor to continue short-cut nitrification, controlling DO to 0.06~0.5mg / L, pH to 7.0~7.6, free nitrite to be greater than 0.02mg / L, hydraulic retention time to 3~10h, and mixed liquor suspended solids concentration to 3000~5000mg / L, to further complete short-cut nitrification; (4) the mixed liquor sludge-water separation is carried out in the sedimentation zone of the secondary short-cut nitrification reactor, and the secondary short-cut nitrification supernatant is obtained after separation, with nitrite nitrogen concentration of 200~300mg / L and nitrite nitrogen / ammonia nitrogen ratio of 0.9~1.5, which enters the subsequent anaerobic ammonia oxidation treatment unit, while the settled sludge is returned to the reaction zone of the secondary short-cut nitrification reactor; (5) when the nitrite nitrogen concentration in the effluent of the secondary short-cut nitrification reactor is greater than 40mg / L, or the nitrite nitrogen accumulation rate is less than 85%, the process sequence of the primary and secondary short-cut nitrification reactors is interchanged.

[0013] Example 1 The present invention will be further illustrated below by taking the short-cut nitrification process of a leachate treatment project at a municipal solid waste landfill as an example.

[0014] The aging leachate treatment project of the closed municipal solid waste landfill has a capacity of 160 tons / day, and the water quality is as follows: pH 7.9~8.6, COD between 2000~3500mg / L, B / C ratio less than 0.25, ammonia nitrogen 1100~1900mg / L, and alkalinity 6000~10000mg / L.

[0015] The leachate from the equalization tank is pumped into the denitrification tank, where it is mixed and denitrified with the mixed liquor from the first-stage short-cut nitrification reactor with a high reflux ratio. This process effectively removes biodegradable organic matter and dilutes the ammonia nitrogen concentration, resulting in effluent with BOD < 80 mg / L and ammonia nitrogen concentration around 500 mg / L. This effluent then flows into the reaction zone of the first-stage short-cut nitrification reactor, where DO is controlled at 0.02–0.1 mg / L, pH at 7.8–8.1, free ammonia greater than 5 mg / L, hydraulic retention time at 5 hours, and mixed liquor suspended solids concentration at 4000–500 mg / L. The ammonia nitrogen removal rate is approximately 30%, and the nitrite nitrogen accumulation rate is 90-100%. The resulting short-cut nitrification mixed liquor is returned to the pre-denitrification tank at a large reflux ratio (varying between 4 and 9 to control the ammonia nitrogen concentration required for the influent of the first-stage short-cut nitrification reactor). The mixed liquor is separated into sludge and water in the sedimentation zone of the first-stage short-cut nitrification reactor. The supernatant obtained after separation has a nitrite nitrogen concentration of approximately 140 mg / L and flows into the second-stage short-cut nitrification reactor. The settled sludge flows back to the reaction zone of the first-stage short-cut nitrification reactor under gravity. The effluent from the primary short-cut nitrification reactor flows into the reaction zone of the secondary short-cut nitrification reactor. The dissolved oxygen (DO) is controlled at 0.1–0.3 mg / L, the pH at 7.2–7.6, and the free nitrite concentration at greater than 0.05 mg / L. The hydraulic retention time is 5 hours, and the mixed liquor suspended solids concentration is 4000–5000 mg / L. This results in a further ammonia nitrogen removal rate of approximately 25% and a nitrite nitrogen accumulation rate of 90–99%. In the sedimentation zone of the secondary short-cut nitrification reactor, the mixed liquor undergoes sludge-water separation. The resulting secondary short-cut nitrification supernatant has a nitrite nitrogen concentration of approximately 260 mg / L and a nitrite nitrogen / ammonia nitrogen ratio of 1.0–1.3. This supernatant then enters the subsequent anaerobic ammonia oxidation treatment unit, while the settled sludge flows back to the reaction zone of the secondary short-cut nitrification reactor under gravity. When the nitrate nitrogen concentration in the effluent of the secondary short-cut nitrification reactor exceeds 40 mg / L or the nitrite nitrogen accumulation rate is below 85% during the treatment process, the primary and secondary short-cut nitrification reactors are swapped in sequence to achieve long-term, efficient and stable operation of the short-cut nitrification treatment process.

[0016] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for semi-short-cut nitrification of matured landfill leachate, characterized by, Includes the following steps: 1) The leachate from the middle-aged and old landfills, after denitrification to remove most of the biodegradable organic matter and dilute the ammonia nitrogen concentration, is discharged into the primary short-cut nitrification reactor. The primary short-cut nitrification mixture obtained after short-cut nitrification is returned to the pre-denitrification tank at a high reflux ratio. At the same time, the primary short-cut nitrification mixture enters the sedimentation zone for solid-liquid separation. The primary short-cut nitrification supernatant obtained after separation enters the secondary short-cut nitrification reactor, while the settled sludge flows back to the reaction zone of the primary short-cut nitrification reactor. The primary short-cut nitrification supernatant continues to undergo short-cut nitrification in the secondary short-cut nitrification reactor, and solid-liquid separation is carried out in the sedimentation zone. The secondary short-cut nitrification supernatant obtained after separation enters the subsequent anaerobic ammonia oxidation treatment unit, while the settled sludge is discharged back to the reaction zone of the secondary short-cut nitrification reactor. 2) Whenever the nitrate nitrogen concentration in the effluent of the secondary short-cut nitrification reactor is greater than 40 mg / L, or the nitrite nitrogen accumulation rate is less than 85%, the process sequence of the primary and secondary short-cut nitrification reactors shall be interchanged. In step 1), both the primary and secondary short-cut nitrification reactors are constructed using a combined aeration sedimentation tank design. In step 1), the free ammonia in the primary short-path nitrification reactor is greater than 3 mg / L; the free nitrite in the secondary short-path nitrification reactor is greater than 0.02 mg / L.

2. The method according to claim 1, wherein the method is characterized by: In step 1), the ammonia nitrogen concentration in the leachate from the middle-aged landfill, which has undergone denitrification to remove most of the biodegradable organic matter and dilute the ammonia nitrogen concentration, is diluted to between 400 and 600 mg / L and the BOD is less than 80 mg / L.

3. The method according to claim 1, wherein the method is characterized by: In step 1), the DO in the primary short-cut nitrification reactor is 0.02~0.2 mg / L and the pH is 7.6~8.2; the DO in the secondary short-cut nitrification reactor is 0.06~0.5 mg / L and the pH is 7.0~7.

6.

4. The method according to claim 1, wherein the method is characterized by: In step 1), the combined hydraulic retention time of the primary and secondary short-cut nitrification reactors is 6-20 hours.

5. The method according to claim 1, wherein the method is characterized by: In step 1), the concentration of suspended solids in the mixed liquor of the primary and secondary short-path nitrification reactors is 3000~5000 mg / L.

6. The method according to claim 1, wherein the method is characterized by: In step 1), the nitrite nitrogen concentration in the effluent of the secondary short-cut nitrification reactor is 200~300 mg / L, and the nitrite nitrogen / ammonia nitrogen ratio is 0.9~1.

5.

7. The method according to claim 1, wherein the method is characterized by: The recirculation ratio of the primary short-cut nitrification mixed liquor to the pre-denitrification tank is 4~9.

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