Pyrite autotrophic denitrification system and process for sewage treatment

Abstract

The invention relates to a pyrite autotrophic denitrification system and process for sewage treatment, and the system comprises a denitrification tank and an electrochemical system capable of applying an electric field into the denitrification tank; a composite filler layer is laid in the denitrification tank, and the composite filler layer comprises a porous filter material modified by pyrite and ferric iron chelate; the porous filter material can slowly release ferric iron chelate; autotrophic denitrification microorganisms are inoculated in the composite filler layer; after nitrogen-containing wastewater is introduced into the denitrification tank, the electrochemical system can intermittently provide an external electric field for the denitrification tank, so that the oxidation-reduction potential in the denitrification tank is kept at + 200 to + 250 mV in a staged manner; the external electric field can drive the pyrite to be dissolved; meanwhile, the slow-released ferric iron chelate can promote the dissolution of the pyrite. The method has the beneficial effect that nitrate and nitrite in the low-carbon-nitrogen-ratio wastewater are efficiently and stably removed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, and in particular to a pyrite autotrophic denitrification system and process for sewage treatment. BACKGROUND

[0002] The pyrite autotrophic denitrification technology has attracted much attention in the field of low-carbon-nitrogen-ratio nitrogen-containing wastewater treatment in recent years due to its unique advantage of not requiring external organic carbon source. The technology uses natural pyrite (FeS2) as an electron donor, and reduces nitrate (NO3 - ) to nitrogen (N2) by autotrophic denitrification microorganisms, and has the advantages of low operating cost, low sludge yield, and environmental friendliness.

[0003] However, the engineering application of the process is always subject to a core bottleneck: the extremely slow rate of pyrite electron release. Due to the dense structure and strong chemical inertness of pyrite, it is difficult to release sufficient reducing substances (such as Fe 2+ , S 0 , S2O3 2- , etc.) under normal reaction conditions, resulting in insufficient supply of electron donors and severely limiting the metabolic activity of autotrophic denitrifying bacteria and the denitrification rate. Although some research has attempted to improve system performance by means of microbial domestication, filler modification, or reactor configuration optimization, none of these strategies has fundamentally broken through the key limiting factor of slow pyrite dissolution kinetics, making it difficult to efficiently release and utilize the huge denitrification potential contained in pyrite. SUMMARY

[0004] (I) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a pyrite autotrophic denitrification system and process for sewage treatment, which solves the technical problem of insufficient supply of electron donors in the existing pyrite autotrophic denitrification process for sewage treatment, which limits the metabolic activity of autotrophic denitrifying bacteria and the denitrification rate.

[0006] (II) Technical solutions

[0007] In order to achieve the above-mentioned purposes, the main technical solutions adopted by the present application include:

[0008] In a first aspect, the present application provides a pyrite autotrophic denitrification system for sewage treatment, comprising a denitrification tank and an electrochemical system capable of applying an electric field to the denitrification tank;

[0009] The denitrification tank is paved with a composite filler layer, and the composite filler layer comprises pyrite and trivalent iron chelate modified porous filter material; the porous filter material can slowly release trivalent iron chelate;

[0010] The autotrophic denitrification microorganism is inoculated in the composite filler layer;

[0011] When the nitrogen-containing wastewater is introduced into the denitrification tank, the electrochemical system can intermittently provide an external electric field to the denitrification tank, so that the redox potential in the denitrification tank is kept at +200 to +250 mV.

[0012] The external electric field can drive the dissolution of the pyrite, and the slowly released ferric iron chelate can promote the dissolution of the pyrite.

[0013] As a preferred embodiment of the present application, the ferric iron chelate in the pyrite autotrophic denitrification system for wastewater treatment is ferric citrate.

[0014] As a preferred embodiment of the present application, the porous filter material in the pyrite autotrophic denitrification system for wastewater treatment is at least one selected from the group consisting of ceramsite, zeolite, volcanic rock, activated carbon and biochar.

[0015] As a preferred embodiment of the present application, the volume ratio of pyrite to ferric iron chelate modified porous filter material in the composite filler layer in the pyrite autotrophic denitrification system for wastewater treatment is 1:1-6:1.

[0016] The particle size of the composite filler layer is 3-10 mm.

[0017] As a preferred embodiment of the present application, the pyrite autotrophic denitrification system for wastewater treatment,

[0018] The electrochemical system comprises a power supply, and an anode and a cathode electrically connected to the power supply.

[0019] The anode is in a columnar shape, and the anode is vertically inserted into the composite filler layer.

[0020] The cathode is in a sheet shape, and is arranged on the inner wall of the denitrification tank.

[0021] The distance between the anode and the cathode is ≥10 cm.

[0022] As a preferred embodiment of the present application, the pyrite autotrophic denitrification system for wastewater treatment,

[0023] The filling height of the composite filler layer is 0.6-1 m.

[0024] The distance between the lower end of the anode and the bottom wall of the denitrification tank is 10-15 cm, the height of the upper end of the anode protruding out of the composite filler layer is 10-20 cm, and the upper end of the anode is electrically connected to the positive electrode of the power supply.

[0025] As a preferred embodiment of the present application, the pyrite autotrophic denitrification system for sewage treatment, the anode is a graphite rod or a titanium-based ruthenium iridium coating electrode.

[0026] The cathode is a copper mesh or a carbon felt.

[0027] As a preferred embodiment of the present application, the pyrite autotrophic denitrification system for sewage treatment, the power supply is a pulse power supply system, and the output voltage is 0.5-3V.

[0028] The cathode is arranged at the bottom of the denitrification tank.

[0029] A supporting layer is arranged between the composite filler layer and the cathode, and the supporting layer is used for supporting the composite filler layer.

[0030] In the second aspect, the embodiments of the present application provide a pyrite autotrophic denitrification process for sewage treatment, and the pyrite autotrophic denitrification system for sewage treatment comprises the following steps:

[0031] S1, introducing the nitrogen-containing wastewater into the denitrification tank paved with the composite filler layer, inoculating the autotrophic denitrification microorganism after domestication in the composite filler layer, and making the nitrogen-containing wastewater fully contact with the composite filler layer and the autotrophic denitrification microorganism;

[0032] S2, applying an intermittent external electric field to the wastewater in the denitrification tank through the electrochemical system, and the application frequency of the intermittent external electric field is 4-6 times per day, and each time is 5-10 min;

[0033] S3, the nitrate nitrogen in the sewage is reduced to nitrogen by the autotrophic denitrification microorganism under the action of the electron donor generated by the dissolution of the pyrite.

[0034] As a preferred embodiment of the present application, the pyrite autotrophic denitrification process for sewage treatment, when the ferric ion chelate is ferric citrate, the preparation process of the porous filter material modified by the ferric ion chelate is as follows:

[0035] The dry porous filter material is mixed and immersed with the ferric citrate solution with a concentration of 2-5% w according to a volume ratio of 1:1-4:1, the ferric citrate solution is adsorbed into the pore structure of the porous filter material, and then the mixture is sealed and placed at room temperature for 4-12 h, and then dried at 40-60℃ for 6-12 h.

[0036] (Three) beneficial effects

[0037] The beneficial effects of this invention are as follows: This invention provides a pyrite autotrophic denitrification system and process for wastewater treatment. The filter bed of the autotrophic denitrification system is filled with a composite packing layer of porous filter media modified with pyrite and ferric chelate. Furthermore, an intermittently applied external electric field maintains the system's redox potential (ORP) at +200 to +250 mV. Under these ORP conditions, on the one hand, the redox potential directly drives the dissolution of pyrite; on the other hand, ferric citrate adheres to the porous filter media and can slowly dissolve, releasing ferric citrate complexes. These ferric citrate complexes continuously promote the indirect oxidation process of pyrite, thereby accelerating the dissolution of pyrite and releasing electron donors (Fe2+). 2+ S 2- (etc.). Simultaneously, the ferric citrate complex is reduced to the ferrous citrate complex, and the Fe in the ferrous citrate complex... 2+ Under the influence of an electric field and nitric acid and nitrite, it is regenerated into Fe. 3+ (Iron citrate complex), Fe 3+ This further accelerates the dissolution of pyrite and releases electron donors, thereby forming a highly efficient iron-catalyzed cycle that greatly enhances the rate of pyrite autotrophic denitrification.

[0038] An intermittent external electric field is applied. When the external electric field is applied, it provides the redox potential. When the external electric field is removed, it promotes the further reduction of N2O accumulated during the application of the external electric field, thereby ensuring denitrification efficiency.

[0039] Compared to existing technologies, this invention fundamentally overcomes the kinetic limitations of pyrite dissolution through the synergistic effect of physicochemical and electrochemical catalysis, thereby significantly increasing the autotrophic denitrification rate. This invention achieves NO3- oxidation via an electrochemical-biological coupling pathway. - The conversion to N2 enables efficient and stable removal of nitrates and nitrites from wastewater with a low carbon-to-nitrogen ratio.

[0040] The anode extends 10-20 cm above the composite packing layer. While the main reaction area of ​​the anode is the portion submerged in the packing, keeping the upper end exposed ensures that current is evenly distributed throughout the entire anode column from the top, preventing localized short circuits or current concentration caused by packing buildup. Simultaneously, controlling the effective reaction length (i.e., the anode length within the packing) concentrates the electric field distribution more effectively in the denitrification core region. The anode's extension above the composite packing layer also facilitates the dissipation of bubbles generated during the hydrogen evolution reaction, maintaining a good conductive interface. Furthermore, the extended anode facilitates electrical connections and maintenance, preventing mechanical damage to connection points caused by packing compaction.

[0041] The cathode uses copper mesh or carbon felt to avoid hydrogen evolution reaction, promote the reduction reaction of nitrate and nitrite in the solution, and improve denitrification efficiency.

[0042] The cathode can be arranged annularly along the inner wall of the denitrification tank or placed below the supporting layer at the bottom of the denitrification tank, and the wire connected with the power supply of the cathode is led out from the side wall or the bottom of the denitrification tank to avoid being washed by water flow.

[0043] The pyrite autotrophic denitrification system for sewage treatment has the advantages of simple structure, convenient operation, easy industrial application, and good economic and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 FIG. 1 is a schematic diagram of the pyrite autotrophic denitrification system for sewage treatment in Example 1 of the present application.

[0045] BRIEF DESCRIPTION OF DRAWINGS

[0046] 1, composite filler layer; 2, anode; 3, supporting layer; 4, cathode; 5, wire, 6, power supply; 7, denitrification tank. DETAILED DESCRIPTION

[0047] In order to better explain the present application, the following will be described in detail in combination with the drawings and specific embodiments.

[0048] In order to better understand the above technical solutions, the exemplary embodiments of the present application will be described in more detail below with reference to the drawings. Although the exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a clearer, more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0049] Example 1

[0050] This embodiment provides a pyrite autotrophic denitrification system for sewage treatment, as shown in FIG. 1. Figure 1 The autotrophic denitrification system includes a denitrification tank 7, which has a size of Φ0.6x1m and is internally filled with a composite filler layer 1 of pyrite / ferrocitrate modified ceramsite filter material with a particle size of 3-5mm. The volume ratio of pyrite to ferrocitrate modified ceramsite filter material is 4:1, and the filling height is 0.6m.

[0051] The anode 2 of the electrochemical system is an inert anode graphite rod with a size of Φ0.02x0.7m. The anode is inserted into the composite filler layer, and the bottom of the anode 4 is at least 10cm above the cathode. The cathode is carbon felt with a size of Φ58cm, which is laid flat at the bottom of the supporting layer 3. The anode 2 and the cathode 4 are connected to the positive and negative electrodes of the power supply 6 (constant potential voltage) respectively through the wire 5, and the voltage is set to 1.5V. The supporting layer 3 is used to support the composite filler layer 1.

[0052] The autotrophic denitrification microorganism is inoculated into the denitrification tank, and then the autotrophic denitrification microorganism is gradually acclimated to adapt to the nitrogen-containing wastewater to be treated. After the autotrophic denitrification microorganism is successfully acclimated, the simulated wastewater containing nitrate nitrogen with a concentration of 50 mg / L is introduced into the denitrification tank at a flow rate of 0.12 m 3 / h. The nitrogen-containing wastewater is fully contacted with the pyrite / citric acid iron modified porous filter material and the autotrophic denitrification microorganism in the denitrification tank. The electrochemical system is started, and under the driving of the applied voltage, the pyrite oxidation in the anode region is directly promoted. The electrons flow to the cathode through the wire, and the cathode electric field enriches NO3 - in the wastewater, thereby improving the reduction efficiency of nitrate nitrogen.

[0053] In the above examples, the inoculation and acclimation of the autotrophic denitrification microorganism refer to the prior art.

[0054] The output voltage of the external power supply is adjusted to control the redox potential in the denitrification tank to be maintained at 220-250 mV. The redox potential provides a suitable growth and metabolism environment for the autotrophic denitrification microorganism, significantly improves the denitrification rate, and greatly improves the treatment efficiency.

[0055] The redox potential and the concentration of nitrate nitrogen in the denitrification tank are monitored every day, and the concentration of nitrate nitrogen in the effluent of the denitrification tank is stably maintained below 30 mg / L.

[0056] In the above examples, the other parts not described in detail in the pyrite autotrophic denitrification system do not involve the innovation of the present application, and please refer to the prior art.

[0057] Example 2

[0058] The pyrite autotrophic denitrification process for wastewater treatment is provided in this example, and the pyrite autotrophic denitrification system in Example 1 is used.

[0059] The tail water containing nitrate nitrogen with a concentration of 15 mg / L from a wastewater treatment plant is introduced into the denitrification tank at a flow rate of 0.24 m 3 / h, and the original cell system is started.

[0060] The redox potential and the water quality indicators in the denitrification tank are monitored in real time, the electrode spacing and the external load are adjusted, and the redox potential is stably maintained at 230-250 mV. The redox potential and the concentration of nitrate nitrogen in the denitrification tank are monitored every day, and the concentration of nitrate nitrogen in the effluent of the denitrification tank is reduced to below 5 mg / L.

[0061] Example 3

[0062] The pyrite autotrophic denitrification process for wastewater treatment is provided in this example, and the pyrite autotrophic denitrification system in Example 1 is used.

[0063] The tail water of the sewage treatment plant containing nitrate nitrogen with a concentration of 15 mg / L was introduced into the denitrification tank at a flow rate of 0.2 m 3 / h, and the original battery system was started;

[0064] By adjusting the output voltage of the external power supply, the redox potential in the denitrification tank was maintained at 200-230 mV; the rest was the same;

[0065] The redox potential and the concentration of nitrate nitrogen in the denitrification tank were monitored every day, and the concentration of nitrate nitrogen in the effluent of the denitrification tank was reduced to below 5 mg / L.

[0066] Example 4

[0067] The preparation method of the ferric iron chelate modified porous filter material used in Example 1 is as follows: the dried ceramic filter material and the ferric citrate solution (2%wt) are mixed at a volume ratio of 4:1; the ceramic filter material is immersed until there is no obvious liquid volume on the surface of the ceramic filter material, then the wet porous filter material loaded with ferric citrate is sealed in a container and placed at room temperature for 4h; then the porous filter material loaded with ferric citrate is placed in an oven and dried at a low temperature (40°C) for 12h until completely dry, thereby obtaining the ferric iron chelate modified porous filter material product.

[0068] Example 5

[0069] The preparation method of the ferric iron chelate modified porous filter material used in Example 3 is as follows: the dried zeolite filter material and the ferric citrate solution (5%wt) are mixed at a volume ratio of 1:1; the zeolite filter material is immersed until there is no obvious liquid volume on the surface of the zeolite filter material, then the wet porous filter material loaded with ferric citrate is sealed in a container and placed at room temperature for 12h; then the porous filter material loaded with ferric citrate is placed in an oven and dried at a low temperature (60°C) for 6h until completely dry, thereby obtaining the ferric iron chelate modified porous filter material product.

[0070] Comparative Example 1

[0071] This comparative example provides a pyrite autotrophic denitrification system for sewage treatment, which is different from Example 1 in that the electrochemical system is not started.

[0072] The rest of the steps are the same, and the concentration of nitrate nitrogen in the effluent of the denitrification tank of this comparative example is reduced to below 40 mg / L.

[0073] Comparative Example 2

[0074] This comparative example provides a pyrite autotrophic denitrification process for sewage treatment, which is different from Example 2 in that the electrochemical system is not started.

[0075] The remaining steps are the same, and the nitrate nitrogen concentration of the effluent of the denitrification tank of the comparative example is reduced to below 10 mg / L.

[0076] Comparative Example 3

[0077] The comparative example provides a pyrite autotrophic denitrification process for sewage treatment, which is different from Example 2 in that the ferrocitrate modified ceramic filter material in the composite filler layer is replaced by pyrite / ceramic filter material.

[0078] The remaining steps are the same, and the nitrate nitrogen concentration of the effluent of the denitrification tank of the comparative example is reduced to below 9 mg / L.

[0079] Based on the above examples and comparative examples, the following analysis is made:

[0080] Comparing Example 1 with Comparative Example 1, it can be seen that the applied electric field can directly drive the dissolution of pyrite and release electron donors (Fe 2+ , S 2- , etc.), which improves the rate and efficiency of the biological denitrification process and is suitable for engineering applications.

[0081] Comparing Example 2 with Comparative Examples 2 and 3, it can be seen that the separately applied electric field and the separately used ferrocitrate modified ceramic filter material have poor treatment effects on sewage, and the combination of the two can have a better synergistic effect, such as the nitrate nitrogen concentration in the wastewater of Example 2 being reduced to below 5 mg / L.

[0082] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A pyrite autotrophic denitrification system for wastewater treatment, characterized in that, Includes a denitrification tank and an electrochemical system capable of applying an electric field to the denitrification tank; The denitrification tank is lined with a composite packing layer, which includes porous filter media modified with pyrite and ferric chelate; the porous filter media can slowly release ferric chelate. The composite packing layer is inoculated with autotrophic denitrifying microorganisms; When nitrogen-containing wastewater is introduced into the denitrification tank, the electrochemical system can intermittently provide an external electric field to the denitrification tank so that the redox potential in the denitrification tank is maintained at +200 to +250 mV in stages. The applied electric field can drive the dissolution of the pyrite; at the same time, the slowly released trivalent iron chelate can promote the dissolution of the pyrite.

2. The pyrite autotrophic denitrification system for wastewater treatment as described in claim 1, characterized in that, The ferric chelate is ferric citrate.

3. The pyrite autotrophic denitrification system for wastewater treatment as described in claim 2 or 3, characterized in that, The porous filter media is selected from at least one of ceramsite, zeolite, volcanic rock, activated carbon, and biochar.

4. The pyrite autotrophic denitrification system for wastewater treatment as described in claim 1, characterized in that, The volume ratio of pyrite to trivalent iron chelate-modified porous filter media in the composite packing layer is 1:1 to 6:1; The particle size of the composite filler layer is 3-10 mm.

5. The pyrite autotrophic denitrification system for wastewater treatment as described in claim 1, characterized in that, The electrochemical system includes a power source, and an anode and a cathode electrically connected to the power source; The anode is columnar and is vertically inserted into the composite filler layer; The cathode is plate-shaped and is disposed on the inner wall of the denitrification tank; The distance between the anode and the cathode is ≥10cm.

6. The pyrite autotrophic denitrification system for wastewater treatment as described in claim 5, characterized in that, The filling height of the composite filler layer is 0.6-1m; The lower end of the anode is 10-15cm away from the bottom wall of the denitrification tank, the upper end of the anode extends 10-20cm beyond the composite packing layer, and the upper end of the anode is electrically connected to the positive terminal of the power supply.

7. The pyrite autotrophic denitrification system for wastewater treatment as described in claim 5, characterized in that, The anode is a graphite rod or a titanium-based ruthenium-iridium coated electrode; The cathode is a copper mesh or a carbon felt.

8. The pyrite autotrophic denitrification system for wastewater treatment as described in claim 6, characterized in that, The power supply is a pulse power supply system with an output voltage of 0.5-3V; The cathode is disposed at the bottom of the denitrification tank; A support layer is provided between the composite filler layer and the cathode, and the support layer is used to support the composite filler layer.

9. A pyrite autotrophic denitrification process for wastewater treatment, characterized in that, The pyrite autotrophic denitrification system for wastewater treatment according to any one of claims 1 to 8 includes the following steps: S1. Nitrogenous wastewater is introduced into a denitrification tank with a composite packing layer, and the composite packing layer is inoculated with acclimatized autotrophic denitrifying microorganisms, so that the nitrogenous wastewater is in full contact with the composite packing layer and the autotrophic denitrifying microorganisms. S2. An intermittent external electric field is applied to the wastewater in the denitrification tank through an electrochemical system. The frequency of the intermittent external electric field application is 4-6 times a day, each time for 5-10 minutes. S3. Nitrate nitrogen in wastewater is reduced to nitrogen gas by autotrophic denitrifying microorganisms using electron donors generated from the dissolution of pyrite.

10. The pyrite autotrophic denitrification process for wastewater treatment as described in claim 9, characterized in that, When the ferric chelate is selected as ferric citrate, the preparation process of the porous filter material modified with the ferric chelate is as follows: The dried porous filter material is mixed with a 2-5% w ferric citrate solution at a volume ratio of 1:1-4:1 and impregnated to allow the ferric citrate solution to be adsorbed into the pore structure of the porous filter material. The mixture is then placed at room temperature and sealed for 4-12 hours, and then dried at 40-60℃ for 6-12 hours.

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