Iron-carbon micro-electrolysis-based denitrification biological filler, and preparation method and application thereof

Abstract

This invention discloses a denitrification biological packing material based on iron-carbon micro-electrolysis, its preparation method, and its application, belonging to the field of wastewater treatment technology. The invention involves mixing iron powder and activated carbon powder, adding a binder to bind them together into iron-carbon particles; then adding sulfur powder and stirring at the melting point of sulfur to ensure a tight and uniform bond between the sulfur and the iron-carbon particles. After adding the binder, granulation and cooling yield a spherical composite packing material with a microscopic structure of sulfur molecules coating elemental iron and activated carbon. The packing material and related autotrophic bacteria are added to the nitrate wastewater to be treated, forming a coupled denitrification system. This invention introduces an iron-carbon micro-electrolysis reaction, enabling faster and better integrated coupling of anaerobic ammonia oxidation and sulfur autotrophic denitrification, which not only improves the system's denitrification efficiency but also enhances its buffering capacity.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and in particular relates to a denitrification biological packing material based on iron-carbon micro-electrolysis, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid pace of urbanization and industrialization, water environment problems have become increasingly prominent, and eutrophication caused by excessive nitrogen and phosphorus in water bodies has become increasingly serious, urgently requiring the emergence of new denitrification processes. Sulfate autotrophic denitrification, using sulfur sources (such as elemental sulfur) as electron donors, has advantages such as a short process flow, no need for organic carbon sources, and low investment and operating costs, and has been the subject of numerous research precedents both domestically and internationally. Under the action of sulfur autotrophic denitrifying bacteria, nitrate, acting as an electron acceptor, is preferentially reduced to nitrite and accumulated; this process is called sulfur autotrophic short-cut denitrification. This accumulated nitrite can then participate in anaerobic ammonia oxidation as a substrate, after which nitrite is reduced to nitrogen gas by sulfur, as shown in the following reaction formula:

[0003] (1),

[0004] (2).

[0005] Anaerobic ammonium oxidation (ANAMMOX), an autotrophic denitrification reaction using ammonia as an inorganic electron donor for nitrite denitrification, has become a research hotspot in the field of biological denitrification in recent years due to its ability to significantly reduce the energy consumption of aerobic ammonium oxidation. Its reaction formula is as follows:

[0006] (3);

[0007] However, the Anammox process suffers from long reactor start-up time, low cell yield, inhibition by high-concentration matrix, and influent NH4. + / NO2 - The imbalance and high sensitivity to external environmental factors limit its application in practical engineering. However, iron-carbon micro-electrolysis technology is an electrochemical water purification technology with broad application prospects in nitrogen removal, often combined with other nitrogen removal technologies to treat nitrogen in various wastewaters. It not only maintains system pH stability, but the generated iron ions also promote cell growth and shorten reactor start-up time. Its reaction formula is:

[0008] (4),

[0009] (5).

[0010] Currently, the coupling of the above technologies has been widely reported in the field of wastewater treatment. For example, CN 115650426 A discloses a high-efficiency denitrification process based on micro-electrolysis waste iron sludge-based filling material. This process uses micro-electrolysis waste iron sludge as raw material to manufacture TF and TN materials, providing the iron sources required by the Feammox reaction zone and the NDFO reaction zone, respectively. The effluent from the Feammox reaction zone is the influent from the NDFO reaction zone. By coupling the Feammox reaction and the NDFO reaction, and through two biological denitrification processes, high-efficiency denitrification treatment of ammonia nitrogen-containing wastewater is achieved. The ammonia nitrogen, total nitrogen, and COD of the final effluent all meet the Class IV water standard limits in the Surface Water Environmental Quality Standard (GB3838-2002). At the same time, it also realizes the recycling and reuse of solid waste resources, turning waste iron sludge, agricultural and forestry waste, and other solid waste resources generated by iron-carbon micro-electrolysis into valuable resources and avoiding secondary pollution to the environment. However, because it uses waste iron sludge as the material, the removal rate of pollutants such as ammonia nitrogen is relatively slow and the load is low. CN 115490322B discloses a method for simultaneous nitrogen and phosphorus removal via biological denitrification based on carbon-coated nano-zero-valent iron materials. This method involves adding nano-zero-valent iron materials and mixed liquor volatile suspended solids (MLVSS) to wastewater after nitrogen deoxygenation. Under anaerobic conditions, carbon and nano-zero-valent iron act as electron donors in the autotrophic denitrification system, synergistically removing nitrogen and phosphorus from the wastewater. This overcomes the bottleneck of simultaneous phosphorus removal inhibiting iron reactivity and biological denitrification efficiency. However, the nano-zero-valent iron materials involved in this technology are not only highly reactive and easily oxidized, but also costly, resulting in less than ideal practical applications.

[0011] In summary, packing materials made primarily of elemental sulfur and iron-carbon particles not only exhibit good removal efficiency for pollutants such as ammonia nitrogen but also have low cost, making them ideal for practical applications. Furthermore, in systems formed using this packing material, sulfur autotrophic denitrification, iron-carbon microelectrolysis, and Anammox require similar environmental conditions, and the substrates and products can complement each other well. Combining these processes can not only achieve simultaneous removal of multiple nitrogen-containing compounds and improve the system's denitrification efficiency but also enhance its buffering capacity. However, no research has yet been reported on the coupling of these three reactions. Summary of the Invention

[0012] This invention provides a denitrification biological packing material based on iron-carbon microelectrolysis, its preparation method, and its application. It solves the problems existing in the biological denitrification technology of the prior art, realizes the simultaneous removal of multiple nitrogen-containing compounds, improves the denitrification efficiency of the system, and also makes the system have a stronger buffering capacity.

[0013] To achieve the above objectives, the present invention adopts the following technical solution:

[0014] A denitrification biological packing material based on iron-carbon microelectrolysis, wherein the packing material is a 3-5mm spherical composite packing material formed by sulfur powder coating elemental iron-activated carbon;

[0015] The mass ratio of elemental iron to activated carbon in the composite filler is 2-4:1; the mass ratio of sulfur powder to iron-carbon powder is 10-15:1.

[0016] The preparation method of the above-mentioned denitrification biological packing includes the following steps:

[0017] Iron powder (Fe) 0 ) and activated carbon powder (AC) are combined in a mass ratio of 2~4:1, and an appropriate amount of polylactic acid solution is added as a binder to bind them together into tiny particles with a diameter of about 0.1 mm; then an appropriate amount of sulfur powder is added so that sulfur reacts with iron and carbon (Fe) 0 The mass ratio of sulfur to iron and carbon (AC) is 10~15:1. At the melting point of sulfur (115℃±2℃), the mixture is stirred at 480r / min for 5-10min to ensure that sulfur and iron and carbon particles are tightly and uniformly combined. After adding polylactic acid solution as an adhesive, the mixture is granulated and cooled to obtain spherical composite fillers with a diameter of 3~5mm.

[0018] The above-mentioned denitrification biological packing is used for autotrophic biological denitrification. The biological packing and anaerobic sludge are added to the nitrate nitrogen wastewater to be treated to form a coupled denitrification system. The following reactions occur during the denitrification process: (1) Sulfur autotrophic denitrification: The elemental sulfur in the packing is consumed, and the nitrate nitrogen is converted into nitrogen gas, accompanied by a small amount of NO2. - Accumulation of -N, and exposure of iron and carbon (Fe) 0 -AC) particles; (2) exposed Fe 0 -AC undergoes a micro-electrolysis reaction in wastewater, generating highly reducing hydrogen atoms on the AC surface, which partially reduce the adjacent adsorbed nitrates to NH4. + -N; (3) Anaerobic ammonia oxidizing bacteria in anaerobic sludge will convert the NO2 produced in the above two steps into NO2. - -N, NH4 + -N is reduced to N2, and the small amount of nitrate nitrogen produced can be consumed by the first two reactions, allowing the entire system to be organically combined.

[0019] The above reaction is operated at a temperature of 25~35 ℃; the pH of the wastewater is controlled within the range of 6~9; and the hydraulic retention time (HRT) in the reactor is 2~8h.

[0020] Beneficial effects: This invention provides a denitrification biological filler based on iron-carbon microelectrolysis, its preparation method, and its application. Compared with existing technologies, it has the following advantages:

[0021] 1. The iron and carbon in the biological packing material of this invention enable anammox and sulfur autotrophic denitrification (S...0 AD) has achieved faster and better integrated coupling, breaking through the limitations of only S 0 When AD is coupled with Anammox, the bottleneck of microbial activity and biological denitrification efficiency is overcome, increasing the denitrification load of the original coupled system by about 20%, which not only improves the denitrification efficiency of the system, but also makes it more buffered.

[0022] 2. The addition of iron to the coupling system formed by the packing material of this invention is beneficial to the growth of microorganisms, improves the activity of microorganisms, and also improves the pH stability of the system;

[0023] 3. The introduced iron-carbon micro-electrolysis makes S 0 The coupling system of AD and Anammox does not require the addition of NH4. + -N, NO2 - -N reduces reaction costs and also reduces SO4 in the system. 2- The reduced production greatly avoids secondary pollution of the water body;

[0024] 4. The method of the present invention operates under mild conditions, can be carried out at normal pressure, requires no specific conditions, can be widely applied in practice, and does not generate any toxic or harmful substances, making it safe and harmless to the environment. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the internal structure of the sulfur-iron-carbon composite filler in an embodiment of the present invention;

[0026] Figure 2 This invention relates to the influent and effluent of bioreactors R1, R2, and R3 at each stage in the embodiments of the present invention. Schematic diagram of concentration change;

[0027] Figure 3 The following describes the bioreactors R1, R2, and R3 in each stage of the embodiments of the present invention. A diagram illustrating the removal efficiency;

[0028] Figure 4 This is a schematic diagram showing the pH changes of bioreactors R1, R2, and R3 at each stage in an embodiment of the present invention. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0030] Example 1

[0031] A sulfur-coated elemental iron-activated carbon (Fe 0 The composite filler (-AC) is prepared by the following method: elemental iron powder (Fe) is added... 0) and activated carbon powder (AC) are combined in a 3:1 mass ratio, and an appropriate amount of adhesive is added to bind them together into tiny particles with a diameter of about 0.1 mm; then an appropriate amount of sulfur powder is added so that sulfur reacts with iron and carbon (Fe) 0 The mass ratio of sulfur powder to carbon (AC) is 15:1. At the melting point of sulfur (115°C), the mixture is stirred at high speed for 5 minutes to partially melt the sulfur powder and allow it to adhere to the small iron-carbon particles. After adding a binder, the mixture is granulated using a disc mill to obtain spherical composite fillers with a diameter of 3-5 mm. The internal structure is as follows: Figure 1 As shown, sulfur powder coating of elemental iron-activated carbon forms a dense and uniform structure.

[0032] The newly manufactured composite packing material was used to treat the wastewater. It was filled into the biological filter reactor, with a working volume of 0.5L (diameter of 4cm and height of 40cm).

[0033] Comparative Example 1

[0034] This comparative example prepares a filler whose main component is elemental sulfur by the following method: An appropriate amount of sulfur powder is added, and the mixture is stirred at high speed for 5 minutes at the melting point of sulfur, i.e., 115°C, until the sulfur powder partially melts and adheres to each other to form small particles. After adding a binder, the particles are granulated using a disc mill to obtain spherical composite fillers with a diameter of 3-5 mm. The method is basically the same as in Example 1, except that elemental iron-activated carbon (Fe) is not added in this comparative example. 0 -AC).

[0035] The newly manufactured composite packing material was used to treat the wastewater. It was filled into the biological filter reactor, with a working volume of 0.5L (diameter of 4cm and height of 40cm).

[0036] Comparative Example 2

[0037] This comparative example prepares activated carbon with elemental iron as its main component (Fe). 0 The filler (-AC) is prepared by the following method: elemental iron powder (Fe...) 0 The composite filler is made by combining activated carbon powder (AC) in a mass ratio of 3:1, adding an appropriate amount of binder, and then granulating it using a disc mill to obtain spherical composite fillers with a diameter of 3-5 mm. The method is basically the same as that in Example 1, except that elemental sulfur powder is not added in this comparative example.

[0038] The biofilter reactor formed by filling with the packing material in Example 1 is designated as R1, the biofilter reactor formed by mixing and filling the packing materials of Comparative Example 1 and Comparative Example 2 at a mass ratio of 15:1 is designated as R2, and the biofilter reactor formed by filling with the packing material in Comparative Example 1 is designated as R3. The working volume is 0.5L (diameter is 4cm and height is 40cm). Under the same other conditions, a continuous flow experiment was conducted to verify its denitrification effect.

[0039] The reactors were inoculated with 5 g / L of sulfur-autotrophic bacteria sediment and 1 g / L of anaerobic ammonia-oxidizing bacteria sediment, respectively, and the operating temperature was 28℃. The pH of the simulated wastewater was controlled at 8, and the hydraulic retention time (HRT) in the reactors was 4 h. The synthetic wastewater, after deoxygenation, entered the reactors for denitrification.

[0040] The specific operating steps of the experiment are as follows:

[0041] (1) Before the denitrification filter is put into operation, the biofilter needs to be treated with biofilm formation. Denitrifying bacteria solution is inoculated into the three biofilters and the biofilm formation solution is replaced every 4 days. After 3 cycles, the water quality indicators (culture medium utilization) are monitored daily. When the water quality indicators are stable for 3 consecutive cycles and the culture medium utilization is good, the biofilm formation is considered successful.

[0042] (2) After the biofilm is attached to the biological filter, simulated wastewater is prepared using laboratory tap water. Potassium nitrate (KNO3) is used as the only nitrogen source. The nitrogen load is increased in increments of 20 mg / L. The specific influent water quality at each stage is shown in Table 1. Water samples are taken from the effluent tank once a day and each water quality indicator is tested.

[0043] Table 1. Water quality of influent at each stage of the experiments in the examples and comparative examples.

[0044]

[0045] Figure 2-4 The graphs show the denitrification performance of reactors R1, R2, and R3 on simulated wastewater. It can be observed that reactor R3, without the addition of iron and carbon, exhibits poor denitrification performance. In contrast, reactors R1 and R2, with the addition of iron and carbon, not only demonstrate better denitrification performance but also exhibit better pH stability. Specifically, reactor R1 achieves approximately 15% higher nitrate removal than R2, and its pH level shows better shock resistance, generally remaining above 7.0.

[0046] In the first stage (1–21 days), with an HRT of 4 h, R1 achieved approximately 100% (20 ppm) complete removal of nitrate nitrogen, and the pH of the reaction system remained relatively stable. From the second to the fourth stage (22–84 days), as the reactor load increased in stages, the removal capacity of nitrate nitrogen in all three reactors also increased, but their removal efficiency continuously decreased. Moreover, the pH of the system decreased very rapidly with the increasing nitrogen load. Overall, throughout the entire reaction process, R1 showed the best removal effect for nitrate nitrogen, and the system was the most stable.

[0047] In summary, the sulfur-iron-carbon composite packing material produced by this invention is not only simple to manufacture, but also promotes autotrophic denitrification and improves the nitrate nitrogen treatment effect of the reactor.

[0048] The above are merely preferred embodiments of the present invention, which will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that for those skilled in the art, any modifications and improvements made without departing from the concept of the present invention are protected by the present invention.

Claims

1. A method for preparing a denitrification biological filler based on iron-carbon microelectrolysis, characterized in that, The process includes the following steps: mixing iron powder and activated carbon powder at a mass ratio of 2-4:1, adding an adhesive to bind them together into iron-carbon particles; then adding sulfur powder, wherein the mass ratio of sulfur powder to iron-carbon is 10-15:1, and stirring at high speed at the melting point of sulfur (115℃±2℃) to ensure that the sulfur and iron-carbon particles are tightly and uniformly combined; after adding the adhesive, granulation and cooling are performed to obtain a spherical composite filler of sulfur powder coated with elemental iron-activated carbon.

2. The method for preparing the denitrification biological packing material based on iron-carbon microelectrolysis according to claim 1, characterized in that, The iron-carbon particles are tiny particles with a diameter of 0.1 mm.

3. The method for preparing the denitrification biological packing material based on iron-carbon microelectrolysis according to claim 1, characterized in that, After adding sulfur powder, stir for 5-10 minutes.

4. The denitrification biological packing material based on iron-carbon microelectrolysis prepared by the method according to any one of claims 1-3, characterized in that, The filler is a spherical composite filler with a diameter of 3-5 mm formed by sulfur powder coating elemental iron and activated carbon.

5. The denitrification biological packing material based on iron-carbon microelectrolysis according to claim 4, characterized in that, The filler has a microstructure of sulfur molecules coating elemental iron-activated carbon.

6. The application of the denitrification biological packing material based on iron-carbon microelectrolysis as described in any one of claims 4-5, characterized in that, The biological packing material is used for autotrophic biological denitrification. The biological packing material and anaerobic sludge are added to the nitrate nitrogen wastewater to be treated to form a coupled denitrification system.

7. The application of the denitrification biological packing material based on iron-carbon microelectrolysis according to claim 6, characterized in that, The coupled denitrification system undergoes the following reactions during the denitrification process: (1) Sulfur autotrophic denitrification: consuming elemental sulfur in the packing material, converting nitrate nitrogen into nitrogen gas, and accompanied by a small amount of NO2. - Accumulation of -N, and exposure of iron and carbon (Fe) 0 -AC) particles; (2) exposed Fe 0 -AC undergoes a micro-electrolysis reaction in wastewater, generating highly reducing hydrogen atoms on the AC surface, which partially reduce the adjacent adsorbed nitrates to NH4. + -N; (3) Anaerobic ammonia oxidizing bacteria in anaerobic sludge will convert the NO2 produced in the above two steps into NO2. - -N, NH4 + -N is reduced to N2, and the small amount of nitrate nitrogen produced is consumed by the first two reactions, allowing the entire system to be organically combined.

8. The application of the denitrification biological packing material based on iron-carbon microelectrolysis according to claim 6 or 7, characterized in that, The system operates at a temperature of 25-35 ℃; the pH of the wastewater is controlled within the range of 6-9; and the hydraulic retention time in the reactor is 2-8 h.

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