Method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate

Abstract

The present application belongs to the technical field of wastewater treatment, and relates to a method for simultaneously removing ammonia nitrogen and organic pollutants in landfill leachate. In view of the technical problem that the existing technology has poor removal effect on high-concentration ammonia nitrogen and organic pollutants in landfill leachate, limits the subsequent biochemical treatment effect, and easily causes a huge impact on the biochemical treatment system, the present application provides a method for simultaneously removing ammonia nitrogen and organic pollutants in landfill leachate, which comprises the following steps: performing a struvite crystallization reaction on the landfill leachate; performing solid-liquid separation after gravity sedimentation to obtain upper liquid and crystals; adjusting the pH value of the upper liquid to 2.0-3.0, adding struvite and H2O2, the struvite addition amount is 2 g / L-20 g / L, V(H2O2) / m(struvite) is 0.25 mL / g-5 mL / g, performing a photocatalytic reaction at constant temperature to obtain a photocatalytic reaction liquid, and filtering to obtain the photocatalytic reaction liquid. The method can greatly remove ammonia nitrogen and organic pollutants in the landfill leachate before the landfill leachate enters the biochemical treatment, improve the biodegradability of the landfill leachate, reduce the impact load of the biochemical treatment, and simplify the whole process flow.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically, it relates to a method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate. Background Technology

[0002] In recent years, the amount of municipal solid waste generated in my country has increased dramatically, with over 80% of it ultimately disposed of through sanitary landfills. However, during the landfill process, factors such as the decomposition of organic pollutants in the waste, rainwater infiltration, and the waste's own water content easily generate secondary pollutants, leachate. The most prominent characteristics of leachate are high ammonia nitrogen, high levels of organic pollutants, and high color. It also contains a large number of pathogenic microorganisms, posing a significant threat to the quality of soil, surface water, and groundwater. Therefore, the safe and harmless treatment and disposal of leachate is of paramount importance. While traditional biological wastewater treatment processes are technically mature, biological systems struggle to withstand long-term loads of high ammonia nitrogen and high organic pollutants, resulting in inconsistent effluent quality and even system collapse. If high concentrations of ammonia nitrogen and organic pollutants are significantly removed from the leachate before it enters the biological treatment system, stable effluent quality can be guaranteed.

[0003] Chinese invention patent application publication number CN118388089A, filed on June 18, 2024, entitled "A Full-Scale Treatment Process for Landfill Leachate Based on Fenton Treatment," discloses a treatment process including: firstly, ammonia stripping of the landfill leachate, followed by pumping it into an iron-carbon Fenton tank for Fenton reaction. These two steps remove some ammonia nitrogen and organic pollutants. The leachate is then subjected to biological treatment via anaerobic baffle-biological contact-aerated biological methods. The effluent from this biological treatment undergoes another Fenton reaction to further remove organic pollutants. Coagulants (PAC and PAM) are then added for coagulation and sedimentation. Finally, the coagulated and sedimented leachate is introduced into an electrolytic cell for further treatment. While this method can safely and harmlessly treat landfill leachate, some drawbacks cannot be ignored. Firstly, the leachate pH is below 10, resulting in low ammonia stripping efficiency. Secondly, this method involves two Fenton reactions, producing a significant amount of iron sludge that is difficult to dispose of. Thirdly, the effluent from the biological treatment still requires coagulation, sedimentation, and electrolysis, making the process complex, difficult to debug, requiring large quantities of chemicals, and incurring high operation and maintenance costs. Ultimately, the biological treatment effluent under this method still requires Fenton reactions, coagulation, sedimentation, and electrolysis to further remove ammonia nitrogen and organic pollutants. In essence, the limited effectiveness of upstream ammonia stripping and Fenton reactions in removing ammonia nitrogen and organic pollutants limits the overall effectiveness of the biological treatment.

[0004] Therefore, finding an efficient pretreatment method to remove high concentrations of ammonia nitrogen and organic pollutants from landfill leachate is of great significance for the treatment of landfill leachate. Summary of the Invention

[0005] 1. The problem to be solved

[0006] To address the technical problems of poor removal efficiency of high-concentration ammonia nitrogen and organic pollutants in landfill leachate by existing technologies, which limits the effectiveness of subsequent biological treatment and easily impacts the biological treatment system, this application provides a method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate. This method combines struvite crystallization and photocatalytic oxidation to remove ammonia nitrogen and organic pollutants from landfill leachate. By significantly removing ammonia nitrogen and organic pollutants before the landfill leachate enters the biological treatment process, its biodegradability is improved, which can reduce the impact load on the biological treatment process, simplify the entire process flow, and eliminate the need for deep treatment.

[0007] 2. Technical Solution

[0008] To achieve the above objectives, the provided technical solution is as follows:

[0009] A method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate includes the following steps:

[0010] Landfill leachate was subjected to struvite crystallization reaction to obtain landfill leachate containing crystals;

[0011] The landfill leachate containing crystals was subjected to gravity sedimentation and solid-liquid separation to obtain the supernatant liquid and crystals.

[0012] The pH of the upper liquid is adjusted to 2.0-3.0, and Schiele mineral and H2O2 are added. The amount of Schiele mineral added is 2g / L-20g / L, and V(H2O2) / m(Schiele mineral) is 0.25mL / g-5mL / g. The photocatalytic reaction is carried out at a constant temperature to obtain a photocatalytic reaction solution. The photocatalytic reaction solution is filtered to obtain a liquid that removes ammonia nitrogen and organic pollutants.

[0013] Preferably, the amount of Schiele mineral added is 12 g / L to 16 g / L.

[0014] Preferably, the V(H2O2) / m (Schätschlite) is 1.0 mL / g to 2.5 mL / g.

[0015] Preferably, the gravity settling time is 30 minutes.

[0016] Furthermore, in the struvite crystallization reaction, phosphate is added first, and after it dissolves, a magnesium source is added; the phosphate is one or more of disodium hydrogen phosphate, sodium dihydrogen phosphate, and / or sodium phosphate and their hydrates; the magnesium source is one or more of magnesium chloride, magnesium oxide, and / or magnesium sulfate and their hydrates.

[0017] Furthermore, the phosphate is Na2HPO4·12H2O, and the magnesium source is MgCl2·6H2O.

[0018] Further, the amount of Na2HPO4·12H2O and MgCl2·6H2O added is determined based on the nitrogen content in the landfill leachate; the molar ratio of nitrogen, phosphorus, and magnesium is X∶Y∶Z, where X=Y=1, 0 <Z≤1.25。

[0019] Preferably, X∶Y∶Z=1∶1∶1.

[0020] Furthermore, the struvite crystallization reaction is carried out in a shaker at a speed of 150 r / min to 180 r / min for a time of 30 min to 60 min.

[0021] Preferably, the shaking table rotates at a speed of 180 r / min for 30 min.

[0022] Furthermore, the light source used in the photocatalytic reaction is ultraviolet light, and the intensity of the ultraviolet light is 300W to 500W.

[0023] Preferably, the intensity of the ultraviolet light is 500W.

[0024] Furthermore, the constant temperature is 25℃~35℃; the time is 2h~3h.

[0025] Preferably, the constant temperature is 35°C.

[0026] Furthermore, the initial pH value of the landfill leachate is 7.5 to 11.0, the initial ammonia nitrogen concentration is 750 mg / L to 800 mg / L, the initial COD concentration is 10000 mg / L to 12000 mg / L, the initial TOC concentration is 400 mg / L to 500 mg / L, and the color is 50 times.

[0027] Preferably, the initial pH of the landfill leachate is 9.0.

[0028] Preferably, the pH of the landfill leachate is adjusted using HCl solution and / or NaOH solution.

[0029] Further, the initial pH value is adjusted to 7.5–11.0 using a 1M HCl solution and / or a NaOH solution.

[0030] Furthermore, in the filtration step, Schiele minerals are recovered.

[0031] 3. Beneficial effects

[0032] Compared with existing known technologies, the technical solution provided by this invention has the following beneficial effects:

[0033] This invention discloses a method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate. Through a struvite crystallization reaction, it significantly recovers ammonia nitrogen from the leachate. The resulting struvite crystals are rich in nutrients such as nitrogen (N), phosphorus (P), and trace element magnesium (Mg), making them a high-quality raw material for producing slow-release multi-element compound slow-release fertilizer. This method enhances soil fertility and avoids the waste of nitrogen resources. Organic pollutants in the leachate are degraded by a photocatalytic oxidation reaction between Scheringer's mineral and H₂O₂ under ultraviolet light. Compared to the traditional Fenton reaction for removing organic pollutants, this method does not produce large amounts of ferric hydroxide sludge, and the recovered Scheringer's mineral can still participate in the reaction as a photocatalyst, reducing the cost of chemical reagents. After combined treatment with struvite crystallization and photocatalytic oxidation, the landfill leachate achieved an ammonia nitrogen removal rate of 87.0%, a TOC removal rate of 83.2%, and a COD removal rate of 50.2%. This significantly removed ammonia nitrogen and organic pollutants and improved color. The large molecular organic pollutants in the leachate were degraded into small molecular organic pollutants, greatly reducing the burden of subsequent conventional biochemical treatment, simplifying the existing process flow, and avoiding costly deep treatment steps. Attached Figure Description

[0034] Figure 1 The effect of initial pH on the removal of ammonia nitrogen (a) and the mass of precipitate generated by struvite crystallization in landfill leachate when the molar ratio of nitrogen, phosphorus and magnesium is 1:1:1;

[0035] Figure 2 SEM images of precipitates formed after landfill leachate treatment by struvite crystallization under different initial pH conditions with a nitrogen, phosphorus and magnesium molar ratio of 1:1:1.

[0036] Figure 3 The effect of Schiele mineral addition on color, TOC and COD in photocatalytic degradation of landfill leachate when V(H2O2) / m(Schiele mineral) = 1.5 mL / g;

[0037] Figure 4 The effect of V(H2O2) / m(Schätländer mineral) on color, TOC and COD in landfill leachate when the addition amount of Schätländer mineral is 12 g / L;

[0038] Figure 5 The removal rates of ammonia nitrogen, COD, and TOC after combined treatment of raw landfill leachate and leachate diluted 1.5 times and 3 times;

[0039] Figure 6 SEM images of the Shih mineral after different numbers of uses (a: 1 time, b: 2 times, c: 3 times, d: 4 times);

[0040] Figure 7 Fourier transform infrared spectra of Scheres minerals after different numbers of uses. Detailed Implementation

[0041] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments.

[0042] Example 1

[0043] The method for efficiently removing ammonia nitrogen from landfill leachate in this embodiment includes the following steps:

[0044] Measure 50 mL of landfill leachate into a 100 mL Erlenmeyer flask. Adjust the initial pH of the landfill leachate to 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5 and 11 respectively using 1 M HCl solution and 1 M NaOH solution. According to the molar ratio of nitrogen, phosphorus and magnesium of 1:1:1, first add Na2HPO4·12H2O. After it is completely dissolved, add MgCl2·6H2O. Place it in a shaker at 180 r / min for struvite crystallization reaction for 30 min to obtain landfill leachate containing crystals.

[0045] The leachate containing crystals was subjected to gravity sedimentation for 30 minutes to obtain the upper liquid and the bottom crystals. The upper liquid was decanted, and the bottom crystals were dried in an oven at 45°C to obtain struvite crystals, i.e., precipitate.

[0046] In this embodiment, as pH increases, such as Figure 1 As shown, the precipitate mass first increased and then stabilized, while the ammonia nitrogen removal rate first increased and then decreased. The pH corresponding to the trend change points was 9.0, at which point the precipitate mass reached above 11 g / L, and the ammonia nitrogen removal rate was 88.1%. Figure 2 The SEM images show that as the pH increases from 7.5 to 9.0, the content of irregular prismatic prisms in the precipitate gradually decreases, and the precipitate morphology gradually approaches that of hollow rhombohedrons. Further increasing the pH of the reaction system leads to the precipitate becoming predominantly prismatic, with a decrease in surface smoothness. When pH = 11.0, the precipitate surface is rough, dominated by rhombohedrons composed of needle-like substances, while struvite crystals exhibit a smooth rhombohedron microstructure. Therefore, the SEM image at pH = 9 most closely resembles the microstructure of struvite crystals.

[0047] Example 2

[0048] The method for efficiently removing organic pollutants from landfill leachate in this embodiment includes the following steps:

[0049] Measure 25 mL of landfill leachate into several 50 mL quartz reaction tubes, and adjust the initial pH of the leachate to 2.5 with 1 M H2SO4 solution;

[0050] Add 0, 2, 4, 8, 12, 16, and 20 g / L of Schiele mineral respectively, and then add H2O2. The amount of H2O2 added is V(H2O2) / m(Schiele mineral) = 1.5 mL / g. After mixing, place the mixture in a photocatalytic reactor and react at a constant temperature of 25°C for 2.5 h under 500W ultraviolet light to obtain the photocatalytic reaction solution.

[0051] The photocatalytic reaction solution was filtered, and the removal rates of color, TOC, and COD in the filtrate were measured.

[0052] In this embodiment, when V(H2O2) / m(Schätländer mineral) = 1.5 mL / g, the heterogeneous Fenton reaction of Schätländer mineral and H2O2 exhibits a certain photocatalytic degradation effect on pollutants in landfill leachate. For example... Figure 2 As shown, with the increase of Scheele mineral loading, the removal rates of color, TOC and COD of landfill leachate all showed a gradual upward trend, and basically reached a stable state at 12 g / L, with removal rates of 88.9%, 70.4% and 37.2%, respectively.

[0053] Example 3

[0054] The method for efficiently removing organic pollutants from landfill leachate in this embodiment includes the following steps:

[0055] Measure 25 mL of landfill leachate into several 50 mL quartz reaction tubes, and adjust the initial pH of the leachate to 2.5 with 1 M H2SO4 solution;

[0056] First, add 12 g / L of Schiele mineral, then add H2O2 at V(H2O2) / m(Schiele mineral) of 0.25, 0.5, 1.0, 2.0, 3.0 and 5.0 mL / g respectively. After mixing, place it in a photocatalytic reactor and react at 25℃ for 2.5 h under 500W ultraviolet light to obtain the photocatalytic reaction solution.

[0057] The photocatalytic reaction solution was filtered, and the removal rates of color, TOC, and COD in the filtrate were measured.

[0058] In this embodiment, when the amount of Schiele mineral added is 12 g / L, the amount of H2O2 added has varying degrees of influence on the removal rates of landfill leachate color, TOC, and COD. For example... Figure 3As shown, when V(H2O2) / m(Schätländer mineral) < 2.0, the removal rates of color, TOC, and COD increased from 70.0%, 59.0%, and 30.5% when V(H2O2) / m(Schätländer mineral) = 0.25 to 96.0%, 79.6%, and 44.9% when V(H2O2) / m(Schätländer mineral) = 2, respectively. When V(H2O2) / m(Schätländer mineral) > 2.0, the changes in color and TOC removal rates were smaller. This is because when V(H2O2) / m(Schätländer mineral) is too high, the Schätländer mineral is relatively in a supersaturated state, and the excess H2O2 will react with the previously generated ·OH to prevent the ·OH from further degrading the pollutants.

[0059] Example 4

[0060] The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate in this embodiment includes the following steps:

[0061] S1. Take 50 mL of landfill leachate into a 100 mL conical flask, adjust the initial pH of the leachate to 9.0 with HCl and NaOH solutions, add Na2HPO4·12H2O first according to the molar ratio of nitrogen, phosphorus and magnesium of 1:1:1, and after it is completely dissolved, add MgCl2·6H2O, and place it in a shaker at 180 r / min for struvite crystallization reaction for 30 min to obtain landfill leachate containing crystals;

[0062] S2. Gravity sedimentation of landfill leachate containing crystals for 30 minutes to obtain upper liquid and bottom crystals. Decant the upper liquid and dry the bottom crystals in a 45℃ oven to obtain struvite crystals, i.e., precipitate.

[0063] S3. Pour the upper liquid portion decanted from S2 into a 50mL quartz tube, adjust the pH to 2.5 with 1M H2SO4 solution, add Scheringer mineral and H2O2 sequentially according to the addition amount of Scheringer mineral is 16g / L and V(H2O2) / m(Scheringer mineral) = 2.0mL / g, and then place it in a photocatalytic reactor and react at a constant temperature of 25℃ for 3.5h under 500W ultraviolet light to obtain the photocatalytic reaction solution;

[0064] S4. Filter the photocatalytic reaction solution. The filtrate is the effluent from the pretreatment stage. Measure the removal rates of ammonia nitrogen, color, TOC, and COD in the filtrate.

[0065] Because the pH of landfill leachate is 8.5, which is close to the optimal pH of 9.0 for the struvite crystallization method, and the photocatalytic oxidation method requires a lower pH (pH 2.0-3.0), this application uses the struvite crystallization method first, and then the photocatalytic oxidation method, which avoids adjusting the pH back and forth and saves on reagent costs.

[0066] In this embodiment, after the original landfill leachate was treated by a combination of struvite crystallization and photocatalytic oxidation, the color was 3 times higher, the TP removal rate was 97.8%, and the effluent concentration was 0.002 mg / L, meeting the emission requirements of the "Standard for Pollution Control of Municipal Solid Waste Landfills" (GB16889-2008); the ammonia nitrogen removal rate was 87.0%, and the effluent concentration was 100.9 mg / L; the COD removal rate was 50.2%, and the effluent concentration was 5590 mg / L; the TOC removal rate was 83.2%, and the effluent concentration was 84.72 mg / L, while 11.5 g / L of struvite crystals were generated. In the leachate, macromolecular organic pollutants were degraded into smaller molecular organic pollutants. Before and after photocatalysis, the percentage of organic pollutants with a molecular weight greater than 25,000 Da decreased from 38.7% to 29.5%, the percentage of organic pollutants with a molecular weight greater than 3,500 Da and less than 25,000 Da increased from 29.8% to 48.6%, and the percentage of organic pollutants with a molecular weight less than 3,500 Da decreased from 31.5% to 21.9%. Because the photocatalytic oxidation process was carried out under strongly acidic conditions and ultraviolet light irradiation, no microbial communities were detected in the effluent.

[0067] The recovered Schiele minerals can be reused multiple times. After four reuses, a 40% TOC removal rate is still achieved in the leachate treated with struvite crystallization. The recovered Schiele minerals show no significant changes in morphology or structure (e.g., Figure 6 , Figure 7 As shown in the figure, it still has high-efficiency photocatalytic performance and can be reused, thereby saving treatment costs; it can also be used to treat the effluent multiple times to further reduce the content of organic pollutants and obtain more ideal water quality.

[0068] Example 5

[0069] The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate in this embodiment is basically the same as in Embodiment 4, except that the landfill leachate is diluted 1.5 times.

[0070] In this embodiment, the landfill leachate diluted 1.5 times is treated by a combination of struvite crystallization and photocatalytic oxidation, as follows: Figure 5 As shown, the ammonia nitrogen removal rate was 84.1%, the COD removal rate was 56.0%, the TOC removal rate was 83.6%, and the color was 3 times higher.

[0071] Example 6

[0072] The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate in this embodiment is basically the same as in Embodiment 4, except that the landfill leachate is diluted 3.0 times.

[0073] In this embodiment, the landfill leachate diluted 3.0 times is treated by a combination of struvite crystallization and photocatalytic oxidation, as follows: Figure 5As shown, the ammonia nitrogen removal rate was 81.0%, the COD removal rate was 59.6%, the TOC removal rate was 84.9%, and the color was 2 times.

[0074] This application provides a method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate. First, a significant amount of ammonia nitrogen is recovered from the leachate through a struvite crystallization reaction. The resulting struvite crystals are rich in nutrients such as N and P, as well as the trace element Mg, and can serve as a high-quality raw material for producing slow-release multi-element compound slow-release fertilizer, thus improving soil fertility and avoiding the waste of nitrogen resources. Next, the organic pollutants in the leachate are degraded by a photocatalytic oxidation reaction between Scheringer's mineral and H₂O₂ under ultraviolet light. Compared to the traditional Fenton reaction for removing organic pollutants, this method does not produce large amounts of ferric hydroxide sludge, and the recovered Scheringer's mineral can still participate in the reaction as a photocatalyst, reducing the cost of reagents. After combined treatment by struvite crystallization and photocatalytic oxidation, the leachate significantly removes ammonia nitrogen and organic pollutants and improves color. Large-molecule organic pollutants in the leachate are degraded into smaller-molecule organic pollutants, greatly reducing the burden of subsequent conventional biochemical treatment, simplifying existing processes, and avoiding costly deep treatment stages.

[0075] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate, characterized in that: Includes the following steps: Landfill leachate was subjected to struvite crystallization reaction to obtain landfill leachate containing crystals; The landfill leachate containing crystals was subjected to gravity sedimentation and solid-liquid separation to obtain the supernatant liquid and crystals. The pH of the upper liquid is adjusted to 2.0~3.0, and Schiele mineral and H2O2 are added. The amount of Schiele mineral added is 2g / L~20 g / L, and V(H2O2) / m(Schiele mineral) is 0.25 mL / g~5 mL / g. The photocatalytic reaction is carried out at a constant temperature to obtain a photocatalytic reaction solution. The photocatalytic reaction solution is filtered to obtain a liquid that removes ammonia nitrogen and organic pollutants. In the struvite crystallization reaction, phosphate is added first, and after it dissolves, a magnesium source is added; the phosphate is Na2HPO4·12H2O, and the magnesium source is MgCl2·6H2O. The amount of Na2HPO4·12H2O and MgCl2·6H2O added is determined according to the nitrogen content in the landfill leachate; the molar ratio of nitrogen, phosphorus and magnesium is X∶Y∶Z=1∶1∶1.

2. The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate according to claim 1, characterized in that: The struvite crystallization reaction is carried out in a shaking table at a speed of 150 r / min to 200 r / min for 30 min to 60 min.

3. The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate according to claim 1, characterized in that: The photocatalytic reaction uses ultraviolet light as its light source, and the intensity of the ultraviolet light is 300 W to 500 W.

4. The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate according to claim 1, characterized in that: The constant temperature is 25 ℃~35 ℃; the time is 2 h~3 h.

5. The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate according to any one of claims 1-4, characterized in that: The initial pH of the landfill leachate is 7.5~11.0, the initial ammonia nitrogen concentration is 750 mg / L~800 mg / L, the initial COD concentration is 10000 mg / L~12000 mg / L, the initial TOC concentration is 400 mg / L~500 mg / L, and the color is 50 times.

6. The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate according to claim 5, characterized in that: Adjust the initial pH value to 7.5–11.0 using a 1 M HCl solution and / or a NaOH solution.

7. The method for simultaneously removing ammonia nitrogen and organic pollutants from landfill leachate according to claim 5, characterized in that: In the filtration step, Schiele minerals are recovered.

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