A method for enhancing autotrophic denitrification by pyrite photoelectric effect

Abstract

The application discloses a pyrite photoelectric effect-based autotrophic denitrification method, which comprises the following steps: S1, inoculating pretreated activated sludge into a nitrate solution and performing aeration treatment to obtain a mud-water mixture; S2, adding pretreated pyrite into the mud-water mixture obtained in the step S1, and culturing microbial flora under the irradiation of visible light in the range of 400-500 nm; and S3, standing the mixed solution obtained in the step S2, removing supernatant, and introducing nitrogen-containing wastewater into the mixed solution, and removing inorganic nitrogen in the nitrogen-containing wastewater through a chemical oxidation-reduction reaction and microbial action under the irradiation of visible light. The photoelectric effect of the pyrite and the synergistic effect of the pyrite and the microorganism can effectively improve the solubility and electron supply capacity of the pyrite in an anaerobic environment, thereby significantly improving the autotrophic denitrification rate of the pyrite and realizing efficient denitrification.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method for enhancing autotrophic denitrification based on the photoelectric effect of pyrite. Background Technology

[0002] With rapid industrialization and urbanization, eutrophication and nitrogen pollution in water bodies are becoming increasingly serious problems. Nitrogen pollution mainly originates from agricultural emissions (such as fertilizers and pesticides), industrial wastewater, and domestic sewage. These nitrogen pollutants, once in water bodies, cause eutrophication, leading to excessive algal growth, damaging aquatic ecosystems, and endangering aquatic life and human health. Therefore, researching and developing efficient nitrogen removal technologies is of significant environmental and social importance. Currently, commonly used nitrogen removal methods include physical, chemical, and biological methods. Physical methods, such as air stripping and adsorption, are simple and easy to operate, but are inefficient and costly. Chemical methods, such as chemical precipitation and redox methods, can quickly remove nitrogen pollutants, but are prone to secondary pollution and consume large amounts of chemicals. Biological methods are currently the most widely used nitrogen removal methods, mainly including heterotrophic denitrification and autotrophic denitrification. Heterotrophic denitrification requires an external organic carbon source, resulting in high operating costs and potential sludge bulking. In autotrophic denitrification, autotrophic denitrifying bacteria utilize inorganic matter as an energy and carbon source, offering advantages such as cost savings and environmental friendliness.

[0003] In autotrophic denitrification methods, pyrite (FeS2), as a common sulfide mineral, has shown great application potential. Pyrite is not only abundant in nature and inexpensive, but also has good environmental compatibility. Pyrite autotrophic denitrification utilizes pyrite as an electron donor, and through the metabolic activities of microorganisms, reduces nitrates and nitrites to nitrogen gas, achieving denitrification. Pyrite can undergo oxidative dissolution in the presence or absence of microorganisms, producing ferrous ions and sulfates, which are then utilized by autotrophic denitrifying bacteria to remove nitrates. However, pyrite dissolves slowly under anaerobic conditions, resulting in low bioavailability and a relatively slow autotrophic denitrification reaction rate, requiring a long reaction time to achieve the desired denitrification effect.

[0004] Therefore, those skilled in the art are dedicated to developing an environmentally friendly and efficient denitrification method based on pyrite (FeS2). Summary of the Invention

[0005] Pyrite exhibits a photoelectric effect under illumination, meaning that light excites electrons in the pyrite, causing them to transition to the conduction band and become free electrons. Currently, there is relatively little research on the synergistic application of the pyrite photoelectric effect with microbial autotrophic denitrification for nitrogen removal.

[0006] The inventors of this application have discovered that the photoelectric effect of pyrite plays an important role in autotrophic denitrification. Under illumination, pyrite (FeS2) absorbs photons and generates photogenerated electrons (electrons). - ) and photocavities (h + Light-hole (h) + Photogenerated electrons possess strong oxidizing properties, capable of oxidizing water to generate hydroxyl radicals (·OH). These radicals have high oxidizing power, capable of oxidizing organic matter, decomposing it into smaller organic molecules, which are then utilized by denitrifying bacteria, thereby reducing nitrate nitrogen. Photogenerated electrons can enhance the dissolution of pyrite under anaerobic conditions, promoting microbial utilization, and can also be directly captured by nitrates for chemical denitrification; secondly, photons can promote the growth of photosynthetic bacteria, while photogenerated electrons can serve as an energy source for some non-photosynthetic microorganisms, promoting their growth and metabolism; furthermore, photogenerated electrons can reduce Fe(III) in solutions or microbial extracellular polymeric substances (EPS), reducing iron crust formation in microorganisms, promoting iron conversion, and enhancing iron cycling.

[0007] Based on this, this application develops a denitrification method that fully utilizes the photoelectric effect of pyrite to enhance its solubility in anaerobic environments, increase the electron supply rate, and promote microbial metabolism, thereby achieving efficient denitrification. This method overcomes the problems of low bioavailability of pyrite and slow autotrophic denitrification rate under anaerobic conditions.

[0008] Specifically, this application provides a method for enhancing autotrophic denitrification nitrogen removal based on the photoelectric effect of pyrite, including:

[0009] S1. The pretreated activated sludge is inoculated into a nitrate nitrogen solution and aerated to obtain a sludge-water mixture.

[0010] S2. Add pretreated pyrite to the mud-water mixture obtained in step S1, and cultivate the microbial community under visible light irradiation in the range of 400-500 nm.

[0011] S3. Let the mixed solution obtained in step S2 stand, remove the supernatant, and pass nitrogen-containing wastewater into it. Under visible light irradiation, inorganic nitrogen in the nitrogen-containing wastewater is removed through chemical oxidation-reduction reaction in conjunction with microbial action.

[0012] Preferably, in step S1, the nitrate solution contains NO3. - The concentration c of -N is determined by the following formula:

[0013]

[0014] r: Denitrification rate

[0015] k: Maximum denitrification rate

[0016] c: Substrate NO3 - -N concentration

[0017] k d : The half-saturation constant of the denitrification process.

[0018] Preferably, the nitrate solution in step S1 contains 5-100 mg / L NO3. - -N.

[0019] Preferably, the aeration treatment in step S1 is N2 aeration treatment, and the dissolved oxygen (DO) of the mud-water mixture is <0.5 mg / L.

[0020] Preferably, the pretreatment of pyrite in step S2 includes: crushing pyrite to a particle size of 3-5 mm, and removing the oxide film on the surface by water washing and acid washing.

[0021] Preferably, in step S2, the amount of pyrite added is 5-20 g / L, and / or the light intensity irradiated on the surface of the pyrite is 5-30 mW / cm². 2 .

[0022] Preferably, the microbial community culture in step S2 is carried out in a closed anaerobic environment with the temperature maintained at 25-35℃.

[0023] Preferably, the visible light irradiation conditions in step S3 are achieved through one or more of the following methods: LED light source, solar light source, and fiber optic transmission light source.

[0024] Preferably, in step S3, when the ratio of organic carbon to inorganic nitrogen (C / N) in the nitrogen-containing wastewater is <2.5, one or more of the following carbon sources are added: acetic acid, methanol, glucose and glycerol.

[0025] Preferably, the method for treating nitrogen-containing wastewater adopts a continuous or intermittent water influent method, with a hydraulic retention time (HRT) ≥ 12h.

[0026] The technical solution of this application achieves the following technical effects:

[0027] 1. This application utilizes the photoelectric effect of pyrite and its synergistic effect with microorganisms to effectively enhance the solubility and electron supply capacity of pyrite under anaerobic conditions, thereby significantly increasing its autotrophic denitrification rate and achieving efficient nitrogen removal.

[0028] 2. Pyrite is a mineral that is widely found in nature. It is inexpensive to obtain and does not require the addition of expensive chemical reagents, which greatly reduces processing costs.

[0029] 3. This method avoids the secondary pollution problems that may be caused by the use of a large number of chemical reagents in traditional chemical denitrification methods. It uses natural pyrite and microbial metabolism, making the process green and environmentally friendly.

[0030] The following will further explain the concept, specific structure and technical effects of this application in conjunction with the accompanying drawings, so as to fully understand the purpose, features and effects of this application. Attached Figure Description

[0031] Figure 1 This is a model diagram of the autotrophic denitrification process in this application.

[0032] Figure 2 This is the ultraviolet-visible diffuse reflectance spectrum of pyrite.

[0033] Figure 3 This refers to the restricted width of the pyrite zone.

[0034] Figure 4 The photocurrent response curve for pyrite is shown.

[0035] Figure 5 This is a schematic diagram illustrating the principle of enhanced autotrophic denitrification based on the photoelectric effect of pyrite.

[0036] Figure 6 The graph shows the change in nitrate nitrogen concentration over time in nitrogen-containing wastewater of Examples 1 and Comparative Examples 1-3.

[0037] Figure 7 The graph shows the specific denitrification rates of nitrogen-containing wastewater with different C / N ratios in Example 2. Detailed Implementation

[0038] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0039] Some exemplary embodiments of this application have been described for illustrative purposes. It should be understood that this application may be implemented in other ways not specifically shown in the accompanying drawings.

[0040] The method for enhanced autotrophic denitrification based on the photoelectric effect of pyrite disclosed in this application includes the following steps:

[0041] S1. The pretreated activated sludge is inoculated into a nitrate nitrogen solution and aerated to obtain a sludge-water mixture.

[0042] S2. Add pretreated pyrite to the mud-water mixture obtained in step S1, and cultivate the microbial community under visible light irradiation in the range of 400-500 nm.

[0043] S3. Let the mixed solution obtained in step S2 stand, remove the supernatant, and pass nitrogen-containing wastewater into it. Under visible light irradiation, inorganic nitrogen in the nitrogen-containing wastewater is removed through chemical oxidation-reduction reaction in conjunction with microbial action.

[0044] The activated sludge in step S1 is taken from the secondary sedimentation tank of a wastewater treatment plant. The activated sludge in the secondary sedimentation tank comes from the aeration tank and mainly consists of aerobic heterotrophic microorganisms. Heterotrophic bacteria and saprophytic fungi are primarily responsible for purification, with bacteria, especially cocci, playing the most crucial role. Well-functioning activated sludge is characterized by flocs composed of cocci with filamentous bacteria as the framework. The pretreatment of this activated sludge refers to washing it to remove nitrogenous pollutants; specifically, it is washed using a 0.9% sodium chloride aqueous solution.

[0045] The nitrate solution in step S1 refers to the solution containing nitrate nitrogen (NO3). - The nitrate solution (NO3-N) can be prepared by the user. Specifically, in this application, the nitrate solution can be prepared using tap water, and the nitrate solution contains NO3-. - The concentration c of -N is obtained through, for example... Figure 1 The model shown and the following formulas determine:

[0046]

[0047] r: Denitrification rate;

[0048] k: Maximum denitrification rate;

[0049] c: Substrate (NO3) - -N) concentration;

[0050] k d : The half-saturation constant of the denitrification process.

[0051] r(mg / (g·h)) 0 2.5 3.0 4.5 5.1 5.5 5.0 c(mg / L) 40 50 60 70 80 90 100 r(mg / (g·h)) 5.5 5.4 5.4 5.8 4.9 5.2 5.3

[0052] exist Figure 1 In the model shown, the reaction rate increases with the substrate (NO3). - The concentration of NO3- increases with increasing N-N concentration until it reaches a maximum value, and then tends to plateau. However, in this application, the applicant found that in actual biological reactions, when the substrate (NO3-) concentration increases, the concentration of NO3- increases with increasing N-N concentration until it reaches a maximum value, and then tends to plateau. - When the NO3- concentration is too high (above 100 mg / L), substrate inhibition occurs, i.e., excessive NO3- concentration leads to substrate inhibition. - -N concentration can actually inhibit the reaction rate, thus reducing the denitrification rate. This is due to several reasons:

[0053] 1. Osmotic pressure effect

[0054] High concentrations of nitrates increase the osmotic pressure of wastewater, which puts stress on the cell membranes of microorganisms. To maintain osmotic balance inside and outside their cells, microorganisms need to consume more energy to regulate the intracellular osmotic pressure, which affects their normal metabolic activities and growth rate.

[0055] 2. Toxic effects

[0056] Although nitrates themselves are relatively non-toxic, their reduction product, nitrite (NO2), is harmful. - Nitrates are highly toxic. The presence of high concentrations of nitrates increases the risk of nitrite accumulation. Nitrites have a direct toxic effect on microbial cells, inhibiting their enzyme systems and interfering with their normal metabolic processes.

[0057] 3. Changes in the structure of the microbial community

[0058] High concentrations of nitrates can alter the structure of the microbial community. Some microorganisms with low tolerance to high nitrate environments may be suppressed or eliminated, while more tolerant microorganisms may become dominant. This change can lead to decreased system stability and inconsistent treatment results.

[0059] Considering the above-mentioned reasons, in step S1 of this application, the nitrate nitrogen in the nitrate nitrogen solution (NO3) - The concentration of (-N) is preferably 5-100 mg / L.

[0060] The aeration treatment in step S1 is N2 aeration treatment, which ultimately makes the dissolved oxygen (DO) of the mud-water mixture < 0.5 mg / L, so as to create an anaerobic environment that is conducive to the domestication and cultivation of autotrophic denitrifying microorganisms.

[0061] The pyrite in step S2 is natural pyrite. Pretreatment of pyrite mainly includes crushing and washing steps. In the crushing step, excessively large pyrite particles lead to the following defects: ① Small surface area: Large particles have a relatively small surface area, limiting the active surface area available for contact with microorganisms, which is detrimental to microbial metabolism and electron transfer; ② Reduced photoelectric effect: Light penetration depth of larger particles is limited, failing to fully excite internal electrons, thus reducing the photoelectric effect of pyrite. Excessively small pyrite particles also have the following defects: ① Loss problem: Excessively small particles are easily lost with the liquid flow in the mixture and cannot be effectively retained in the reactor, affecting the denitrification effect; ② Particle aggregation: Small particles easily aggregate into clumps, reducing the contact area with microorganisms and potentially hindering the uniform distribution of light; ③ Increased processing difficulty: Excessively small particles increase the difficulty of subsequent solid-liquid separation, which is detrimental to operation and maintenance. Therefore, this application preferably crushes the pyrite to a particle size of 3-5 mm. The washing step mainly removes the oxide film on the surface of the pyrite, which can be carried out by water washing and acid washing (1%-5% HCl).

[0062] Figure 2 The ultraviolet-visible diffuse reflectance spectrum of pyrite is shown. It can be seen that pyrite exhibits photoreactions under ultraviolet, visible, and even infrared light irradiation, and that pyrite has the strongest light absorption ability in the wavelength range of 400-500 nm. Therefore, in step S2, the visible light source wavelength range is selected as 400-500 nm, and the intensity of the irradiation on the pyrite surface is 5-30 mW / cm². 2 Under this irradiation intensity, the photogenerated electron production and microbial activity of pyrite reached an optimal balance. Too low a light intensity would not effectively excite electrons in pyrite, leading to a decrease in the reaction rate; too high a light intensity might inhibit microorganisms and affect their metabolic activities. Figure 3 The band gap of pyrite is shown to be 1.84 eV. According to... Figure 4 The photocurrent response curve of pyrite shows that pyrite can generate photogenerated electrons under visible light irradiation, and this photoelectric effect is repeatable.

[0063] In step S2, the dosage of pyrite is 5-20 g / L. Dosage below this amount will result in insufficient electron supply, a reduced reaction rate, low nitrate reduction efficiency, and unsatisfactory denitrification. Dosage above this amount will have the following drawbacks:

[0064] 1. Inhibitory effect: Excessive pyrite can inhibit certain microorganisms.

[0065] Fe 2+ and S 2- Toxicity: Pyrite releases Fe during dissolution. 2+ and S 2- Although these ions are beneficial to the denitrification process within a suitable range, excessive Fe... 2+ and S 2- It can have a toxic effect on microorganisms, inhibiting their growth and metabolic activities.

[0066] 2. Accumulation of oxidation products: Excess pyrite will produce a large amount of oxidation products, such as sulfate (SO4), during light exposure and chemical reactions. 2- These oxidation products, at high concentrations, can affect the growth environment of microorganisms, leading to metabolic imbalances.

[0067] 3. Formation of an acidic environment: The oxidation and dissolution process of pyrite releases H₂. + Ions lower the pH of the reaction system, creating an acidic environment that affects the activity and metabolic efficiency of microorganisms.

[0068] In step S2, the 400-500nm visible light irradiation condition can be achieved by a corresponding LED light source or by other light sources, as long as the light source can provide 400-500nm visible light.

[0069] In step S2, the microbial community is cultivated, mainly by domesticating and cultivating autotrophic denitrifying microorganisms to achieve maximum enrichment, which will facilitate the denitrification treatment of nitrogen-containing wastewater in the later stage. The cultivation conditions are a closed anaerobic environment with the temperature maintained at 25-35℃.

[0070] This application describes the growth of microorganisms under limited resource conditions using the Logisi equation.

[0071]

[0072] N(t): The number of microorganisms at time t

[0073] N max The maximum number of microorganisms that the environment can support.

[0074] N0: Initial number of microorganisms

[0075] r: Maximum specific growth rate

[0076] t: time

[0077] Lag Phase

[0078] When microorganisms first enter a new environment, they need time to adapt to the new conditions, including nutrients, temperature, and pH. While the number of microorganisms doesn't change significantly, they are undergoing metabolic preparation internally.

[0079] Log phase

[0080] Microorganisms adapted to the environment and began to reproduce rapidly, with their numbers increasing exponentially.

[0081] Stationary Phase

[0082] Due to the depletion of nutrients or the accumulation of metabolic products, the growth rate of microorganisms decreases, reaching a dynamic equilibrium. The total number of microorganisms remains at a relatively stable level.

[0083] Death Phase

[0084] Nutrients are further depleted, metabolic products accumulate to harmful levels, the rate of microbial death exceeds the rate of reproduction, and the total number decreases.

[0085] In this application, during the acclimatization process, the microbial community needs a certain amount of time to adjust its metabolic pathways to adapt to the new environmental conditions and substrate in order to better utilize pyrite as an electron donor and adapt to light conditions. During this period, the microorganisms will gradually enhance their ability to utilize pyrite and the photoelectric effect. Within 2-3 days of acclimatization, the activity and reaction rate of the microorganisms can reach a high level while maintaining the stability of the system. Therefore, in step S2, the cultivation time for the microbial community is 2-3 days.

[0086] After the microbial community cultivation is complete, step S3 is performed. The mixed solution is allowed to stand, and the supernatant is removed to obtain the cultured activated sludge. At this point, nitrogenous wastewater is passed into the cultured activated sludge. Under visible light irradiation, inorganic nitrogen in the nitrogenous wastewater is removed through chemical oxidation-reduction reactions in conjunction with the microbial action. Step S3 is preferably carried out in an anaerobic environment (DO < 0.5 mg / L), specifically, it can be achieved through aeration, such as nitrogen aeration.

[0087] In treating nitrogen-containing wastewater, the mass ratio of nitrogen-containing wastewater to cultured activated sludge should be adjusted between 4:1 and 100:1. Specifically, when the nitrogen content is high: the mass ratio of nitrogen-containing wastewater to activated sludge can be set lower, for example, 4:1. This ensures sufficient sludge volume to treat high concentrations of nitrogen pollutants. When the nitrogen content is low: the mass ratio of nitrogen-containing wastewater to activated sludge can be set higher, for example, up to 100:1. In this case, the sludge volume is relatively small, but sufficient to treat low concentrations of nitrogen pollutants. This is achieved by adjusting the nitrate nitrogen (NO3) content in the wastewater. - By appropriately adjusting the ratio of nitrogen-containing wastewater to cultured activated sludge and the treatment time according to the required nitrogen concentration, it can be ensured that the wastewater meets the discharge standards.

[0088] Furthermore, nitrogen-containing wastewater can be treated using either continuous or intermittent influent methods, the specific choice depending on the actual process requirements. The hydraulic retention time (HRT) should be at least 12 hours to ensure sufficient treatment time. Depending on the actual required nitrate nitrogen concentration in the effluent, longer HRTs, such as 18 hours, 24 hours, or 36 hours, can be set to ensure optimal treatment results.

[0089] This application utilizes the photoelectric effect of pyrite and its synergistic effect with microorganisms to effectively enhance the solubility and electron supply capacity of pyrite under anaerobic conditions, thereby significantly increasing its autotrophic denitrification rate and achieving efficient nitrogen removal. Under illumination, pyrite (FeS2) absorbs photons and generates photogenerated electrons (electrons). - ) and photocavities (h + Light-hole (h) +Photogenerated electrons possess strong oxidizing properties, capable of oxidizing water to generate hydroxyl radicals (·OH). These radicals have high oxidizing power, oxidizing organic matter and breaking it down into smaller organic molecules, which are then utilized by denitrifying bacteria, thereby reducing nitrate nitrogen. Photogenerated electrons can enhance the dissolution of pyrite under anaerobic conditions, promoting microbial utilization, and can also be directly captured by nitrates for chemical denitrification. Secondly, photons can promote the growth of photosynthetic bacteria, while photogenerated electrons can serve as an energy source for some non-photosynthetic microorganisms, promoting their growth and metabolism. Furthermore, photogenerated electrons can reduce Fe(III) in solutions or microbial extracellular polymeric substances (EPS), reducing iron crust formation in microorganisms, promoting iron conversion, and enhancing iron cycling. (Reference) Figure 5 The specific work process is as follows:

[0090] a. Generation of photogenerated electrons and holes

[0091] When pyrite (FeS2) is irradiated with visible light (especially 400-500 nm), the photon energy is sufficient to excite electrons in the pyrite to transition to the conduction band, forming photogenerated electrons (e electrons). - ) and holes (h + ).

[0092] FeS2+hv→FeS2(e - +h + )

[0093] b. Utilization of photogenerated electrons

[0094] Photogenerated electrons can act as electron donors in the denitrification process, converting nitrates (NO3) into electrons. - It is reduced to nitrogen gas (N2).

[0095]

[0096] c. Utilization of optical holes

[0097] Light hole (h) + It has strong oxidizing properties and can oxidize water to generate hydroxyl radicals (·OH). These radicals have high oxidizing power and can oxidize organic matter, decomposing it into smaller organic molecules, which are then utilized by denitrifying bacteria to reduce nitrate nitrogen.

[0098] H2O+h + →·OH+H +

[0099] {CH2O} n (Large organic molecules) + ·OH → {CH₂O} (Small organic molecules)

[0100]

[0101] d. Dissolution and electron supply of pyrite

[0102] Under light conditions, the dissolution rate of pyrite increases, releasing more Fe. 2+ and SO4 2- Autotrophic denitrifying bacteria utilize the dissolved products of pyrite for metabolic activities, reducing nitrates to nitrogen gas, thus achieving denitrification.

[0103] 2FeS2+6NO3 - +4H₂O→4SO₄ 2- +2Fe(OH)3+3N2+2H +

[0104] e. Promotion of growth and metabolism of non-photosynthetic microorganisms

[0105] Photons can promote the growth of photosynthetic bacteria, while photogenerated electrons can serve as an energy source for some non-photosynthetic microorganisms, promoting their growth and metabolism.

[0106] f. Promotion of iron cycling

[0107] Photogenerated electrons can reduce Fe(III) in solutions or microbial EPS, reduce iron crust formation in microorganisms, promote iron conversion, and enhance iron cycling.

[0108] Fe 3+ +e - →Fe 2+

[0109] The visible light irradiation conditions in step S3 are achieved through one or more of the following methods: LED light source, solar light source, and fiber optic transmission light source.

[0110] Regarding LED light sources, 400-500nm LEDs are preferred due to their advantages such as high efficiency and energy saving (LEDs have high photoelectric conversion efficiency and low energy consumption), long lifespan (reducing replacement frequency and maintenance costs), and high flexibility (light intensity and wavelength can be adjusted as needed to adapt to different experimental and application requirements). However, they also have higher initial costs (the initial investment for LEDs is higher than that for traditional light sources) and heat dissipation issues (high-intensity LEDs require a good heat dissipation system to prevent overheating from affecting the lifespan and efficiency of the light source). Although the initial investment for LEDs is high, their long-term operating costs are low, they are highly feasible, and they are highly flexible and adjustable, making them suitable for both laboratory and practical applications.

[0111] Regarding solar light sources (natural light), they have advantages such as low cost (using natural light sources, almost no operating costs) and environmental friendliness (completely green and environmentally friendly, requiring no electricity and causing no pollution). However, they are easily affected by the weather (the intensity and duration of light are greatly affected by weather and seasonal changes, making them unstable) and difficult to control (it is difficult to control the intensity and duration of light, making them unsuitable for experiments requiring precise control). Solar light sources are suitable for open environments and projects with low light requirements, but not for experiments that require a stable light source.

[0112] Regarding fiber optic transmission light sources, 400-500nm is preferred. It has advantages such as directional transmission (fiber optics can directionally transmit the light source to a specific location, improving light utilization efficiency) and flexible arrangement (fiber optics can be flexibly arranged according to needs to adapt to complex experimental setups). However, its installation is complex (fiber optic transmission systems are complex to install and require precise installation and maintenance) and its cost is high (fiber optics and related equipment are expensive, resulting in a large initial investment). Fiber optic transmission light sources are suitable for high-precision experiments and applications with specific requirements, but are not suitable for projects with large areas and cost constraints.

[0113] The advantages and disadvantages of each light source are listed above, and you can choose according to your actual situation.

[0114] The requirement for an organic carbon to inorganic nitrogen ratio (C / N) of 5-10:1 in wastewater is typically applied to heterotrophic denitrifying bacteria, as these bacteria require organic carbon sources as electron donors and energy for the denitrification process. While this application primarily concerns autotrophic denitrification, and although autotrophic denitrifying bacteria do not require organic carbon sources, the organic carbon to inorganic nitrogen ratio remains a crucial factor affecting nitrogen removal efficiency. The applicant found that when the organic carbon to inorganic nitrogen ratio (C / N) < 2.5:1, the denitrification rate is slow, necessitating the addition of organic carbon sources to achieve a C / N ratio ≥ 2.5:1, preferably around 3. The specific reasons are as follows:

[0115] 1. Microbial balance in the composite system

[0116] In many wastewater treatment systems, heterotrophic and autotrophic denitrifying bacteria often coexist. This combined system can leverage the strengths of both types of bacteria to improve overall nitrogen removal efficiency. An appropriate C / N ratio ensures the activity of the heterotrophic bacteria, thereby achieving better nitrogen removal through the combined denitrification process.

[0117] 2. Facilitates the growth of microorganisms

[0118] Although autotrophic denitrifying bacteria primarily rely on inorganic carbon sources, the presence of organic carbon sources in actual systems can have a positive impact on the overall microbial community. For example, organic carbon sources can promote the growth of certain helper microorganisms, which can indirectly promote the activity and metabolism of autotrophic denitrifying bacteria.

[0119] 3. System stability and efficiency

[0120] In some complex wastewater treatment systems, the presence of organic carbon sources can help stabilize the microbial community and prevent a decline in treatment efficiency due to fluctuations or insufficiency of inorganic carbon sources. A reasonable C / N ratio helps maintain stable system operation and efficient nitrogen removal.

[0121] 4. Supplement to the denitrification process

[0122] In some cases, although autotrophic denitrification is the primary method of operation, a certain amount of organic carbon source still needs to be supplemented to cope with high or fluctuating nitrogen loads. This ensures that the system can maintain high nitrogen removal efficiency under different operating conditions.

[0123] Organic carbon sources can be selected from one or more conventional organic carbon sources such as acetic acid, methanol, glucose, and glycerol. Acetic acid is readily utilized by microorganisms and can rapidly increase the C / N ratio; methanol is widely used in denitrification processes and is relatively inexpensive; glucose can be rapidly metabolized by microorganisms, increasing their activity; and glycerol, as a highly efficient carbon source, can improve the denitrification rate.

[0124] Example 1: Treatment of Nitrogen-Containing Wastewater (Prepared Wastewater)

[0125] Step 1: Crush the natural pyrite to 5mm and wash away the oxide film on the surface with water and 1% HCl;

[0126] Step 2: Use a 0.9% sodium chloride aqueous solution to wash the activated sludge from the secondary sedimentation tank of the wastewater treatment plant to remove nitrogen pollutants.

[0127] Step 3: Inoculate the activated sludge obtained in Step 2 into a nitrile nitrogen solution (containing 50 mg / L NO3). - In the N2 treatment, a mud-water mixture with DO less than 0.5 mg / L was obtained;

[0128] Step 4: Add the pyrite obtained in Step 1 to the mud-water mixture obtained in Step 3. Under visible light irradiation in the range of 400-500 nm, cultivate the microbial community in a closed anaerobic environment at a temperature maintained at 35℃ for 3 days. The intensity of the irradiation on the pyrite surface is 18.84 mW / cm². 2 The dosage of pyrite is 20 g / L;

[0129] Step 5: Let the mixed solution from Step 4 stand, remove the supernatant, and then dispose of the nitrogen-containing wastewater (laboratory preparation, containing 50 mg / L NO3) under anaerobic conditions (DO < 0.5 mg / L). --N, C / N=2.8) is introduced into the mixture through intermittent water intake for mixing and reaction. LED light strips are added, and nitrogen in the water is removed through chemical oxidation-reduction reaction in conjunction with the action of microorganisms.

[0130] Comparative Example 1 is similar to Example 1, except that pyrite was not added and there was no visible light irradiation.

[0131] Step 1: Use a 0.9% sodium chloride aqueous solution to wash the activated sludge from the secondary sedimentation tank of the wastewater treatment plant to remove nitrogen pollutants contained therein;

[0132] Step 2: Inoculate the activated sludge obtained in Step 1 into a nitrile nitrogen solution (containing 50 mg / L NO3). - The mud-water mixture with DO less than 0.5 mg / L was obtained by exposing it to N2 in the -N) solution. The microbial community was then acclimatized and cultured in a closed anaerobic environment at a temperature of 35℃ for 3 days.

[0133] Step 3: Let the mixture from Step 2 stand, remove the supernatant, and then dispose of the nitrogen-containing wastewater (laboratory preparation, containing 50 mg / L NO3) under anaerobic conditions (DO < 0.5 mg / L). - -N, C / N=2.8) is introduced into it intermittently to mix and react in order to remove nitrogen from nitrogen-containing wastewater.

[0134] Comparative Example 2 is similar to Example 1, except that pyrite was not added.

[0135] Step 1: Use a 0.9% sodium chloride aqueous solution to wash the activated sludge from the secondary sedimentation tank of the wastewater treatment plant to remove nitrogen pollutants contained therein;

[0136] Step 2: Inoculate the activated sludge obtained in Step 2 into a nitrile nitrogen solution (containing 50 mg / L NO3). - In the N2 treatment, a mud-water mixture with DO less than 0.5 mg / L was obtained;

[0137] Step 3: Under visible light irradiation in the range of 400-500nm, the microbial community in the mud-water mixture obtained in Step 2 is domesticated and cultured in a closed anaerobic environment at a temperature of 35℃ for 3 days.

[0138] Step 4: Let the mixed solution from Step 3 stand, remove the supernatant, and then dispose of the nitrogen-containing wastewater (laboratory preparation, containing 50 mg / L NO3) under anaerobic conditions (DO < 0.5 mg / L). - -N, C / N=2.8) is introduced into the mixture through intermittent water intake for mixing and reaction, and LED light strips are added to remove nitrogen from the nitrogen-containing wastewater.

[0139] Comparative Example 3 is similar to Example 1, except that it was not irradiated with visible light.

[0140] Step 1: Crush the natural pyrite to 5mm and wash away the oxide film on the surface with water and 1% HCl;

[0141] Step 2: Use a 0.9% sodium chloride aqueous solution to wash the activated sludge from the secondary sedimentation tank of the wastewater treatment plant to remove nitrogen pollutants contained therein;

[0142] Step 3: Inoculate the activated sludge obtained in Step 2 into a nitrile nitrogen solution (containing 50 mg / L NO3). - In the N2 treatment, a mud-water mixture with DO less than 0.5 mg / L was obtained;

[0143] Step 4: Add the pyrite obtained in Step 1 to the mud-water mixture obtained in Step 3, and acclimate and cultivate the microbial community in a closed anaerobic environment at a temperature of 35℃ for 3 days, wherein the amount of pyrite added is 20g / L.

[0144] Step 5: Let the mixed solution from Step 4 stand, remove the supernatant, and then dispose of the nitrogen-containing wastewater (laboratory preparation, containing 50 mg / L NO3) under anaerobic conditions (DO < 0.5 mg / L). - -N, C / N=2.8) is introduced into it intermittently to mix and react in order to remove nitrogen from nitrogen-containing wastewater.

[0145] Figure 6 The changes in nitrate nitrogen concentration over time in nitrogen-containing wastewater of Examples 1 and Comparative Examples 1-3 are shown. It can be seen that the biological denitrification effect of microorganisms is better under visible light irradiation. This is because light promotes the growth of photosynthetic denitrifying bacteria in the microbial community, thereby further promoting the reduction of nitrate nitrogen. After the addition of pyrite, the removal rate of nitrate nitrogen and total nitrogen is faster, and is higher under light conditions than under no light conditions. This is because pyrite dissolves slowly in an anaerobic environment and is difficult for microorganisms to utilize. However, under light conditions, the photoelectric effect of pyrite promotes its dissolution and electron supply, further improving the denitrification effect.

[0146] Example 2: The effect of the ratio of organic carbon to inorganic nitrogen (C / N) in nitrogen-containing wastewater on water treatment

[0147] The procedure of Example 1 was repeated, except that in step 5, nitrogen-containing wastewater with different C / N ratios (C / N = 0, 0.5, 1.5, 2.5, 4, 6, 8, 10) was selected for treatment, with a hydraulic retention time of 15 hours. The treatment results are as follows: Figure 7As shown in the figure, the specific denitrification rate of nitrogen-containing wastewater with different C / N values ​​is displayed. It can be seen from the figure that when C / N < 2.5, the specific denitrification rate increases rapidly with the increase of C / N value; when C / N ≥ 2.5, the specific denitrification rate increases relatively slowly with the increase of C / N value.

[0148] Example 3: Treatment of Nitrogen-Containing Wastewater (Actual Wastewater)

[0149] This embodiment describes the treatment of wastewater in a real-world scenario. The treatment process is similar to that in Embodiment 1. The treatment results for each nitrogen-containing wastewater are shown in the table below.

[0150] Table 1 - Results of the treatment of the first nitrogen-containing wastewater

[0151] <![CDATA[NO3 - -N]]> 98.6 mg / L 3.9 mg / L

[0152] Wherein, C / N = 3.5:1; hydraulic residence time 24h.

[0153] Table 2 - Results of the second nitrogen-containing wastewater treatment

[0154] <![CDATA[NO3 - -N]]> 56.9 mg / L 2.2 mg / L

[0155] Wherein, C / N = 3:1; hydraulic residence time 18h

[0156] Table 3 - Results of the treatment of nitrogen-containing wastewater

[0157] <![CDATA[NO3 - -N]]> 18.6 mg / L 0.6 mg / L

[0158] Wherein, C / N = 2.5:1; hydraulic residence time 12h.

[0159] Table 4 - Results of Nitrogen-Containing Wastewater Treatment

[0160] <![CDATA[NO3 - -N]]> 80.3 mg / L 3.1 mg / L

[0161] The C / N ratio was 2:1; the hydraulic retention time was 24 hours, during which an appropriate amount of acetic acid was added to bring the C / N ratio to 3:1.

[0162] Table 5 - Results of the fifth nitrogen-containing wastewater treatment

[0163] <![CDATA[NO3 - -N]]> 46.1 mg / L 1.6 mg / L

[0164] The C / N ratio was 1.5:1; the hydraulic retention time was 18 hours, during which time an appropriate amount of glycerol was added to bring the C / N ratio to 2.8:1.

[0165] Table 6 - Results of the treatment of nitrogen-containing wastewater (Sixth category)

[0166] <![CDATA[NO3 - -N]]> 15.4 mg / L 0.5 mg / L

[0167] The C / N ratio was 0.9:1; the hydraulic retention time was 12 hours, during which an appropriate amount of glucose was added to bring the C / N ratio to 2.5:1.

[0168] The above results demonstrate that the pyrite photoelectric effect-enhanced autotrophic denitrification method proposed in this application can rapidly achieve NO3 reduction. - -N was removed, and the removal rate exceeded 96%.

[0169] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A method for enhancing autotrophic denitrification nitrogen removal based on the photoelectric effect of pyrite, characterized in that, include: S1. Pretreated activated sludge is inoculated into a nitrile nitrogen solution and aerated with N2 to obtain a sludge-water mixture. The nitrile nitrogen solution contains 5-100 mg / L NO3. - -N, the dissolved oxygen (DO) of the mud-water mixture is <0.5 mg / L; S2. Add pretreated pyrite to the mud-water mixture obtained in step S1, and cultivate the microbial community under visible light irradiation in the range of 400-500nm in a closed anaerobic environment with the temperature maintained at 25-35℃. The amount of pyrite added is 5-20 g / L. S3. Let the mixed solution obtained in step S2 stand, remove the supernatant, and pass nitrogen-containing wastewater into it. Under visible light irradiation, inorganic nitrogen in the nitrogen-containing wastewater is removed through chemical oxidation-reduction reaction in conjunction with microbial action.

2. The method for enhanced autotrophic denitrification based on the photoelectric effect of pyrite as described in claim 1, characterized in that, NO3 in the nitrate solution in step S1 - The concentration c of -N is determined by the following formula: r: Denitrification rate k: Maximum denitrification rate c: Substrate NO3 - -N concentration k d : The half-saturation constant of the denitrification process.

3. The method for enhanced autotrophic denitrification based on the photoelectric effect of pyrite as described in claim 1, characterized in that, The pretreatment of pyrite in step S2 includes: crushing pyrite to a particle size of 3-5 mm, and removing the oxide film on the surface by water washing and acid washing.

4. The method for enhanced autotrophic denitrification based on the photoelectric effect of pyrite as described in claim 1, characterized in that, The light intensity irradiated onto the pyrite surface in step S2 is 5-30 mW / cm. 2 .

5. The method for enhanced autotrophic denitrification based on the photoelectric effect of pyrite as described in claim 1, characterized in that, The visible light irradiation conditions in step S3 are achieved through one or more of the following methods: LED light source, solar light source, and fiber optic transmission light source.

6. The method for enhanced autotrophic denitrification based on the photoelectric effect of pyrite as described in claim 1, characterized in that, In step S3, when the ratio of organic carbon to inorganic nitrogen in the nitrogen-containing wastewater (C / N) is less than 2.5, one or more of the following organic carbon sources are added: acetic acid, methanol, glucose, and glycerol.

7. The method for enhanced autotrophic denitrification based on the photoelectric effect of pyrite as described in claim 6, characterized in that, The nitrogen-containing wastewater is fed continuously or intermittently, with a hydraulic retention time (HRT) ≥ 12 h.

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