Preparation method, product and application of aquatic plant-based iron-carbon micro-electrolysis filler

Abstract

The present application relates to sewage treatment technical field, especially to a kind of aquatic plant-based iron-carbon micro-electrolysis filler preparation method, product and application.The aquatic plant-based iron-carbon micro-electrolysis filler preparation method includes the following steps: step 1, after washing and air-drying aquatic plant, cut section, dry, crush, obtain aquatic plant powder;Pyrolysis is carried out to aquatic plant powder, and biochar is obtained;Step 2, mix uniformly reduced iron powder, the biochar, kaolin, ammonium bicarbonate and quartz sand, and granulation is added to water, and iron-carbon microspheres are obtained;After drying iron-carbon microspheres, cooling, calcination is then obtained aquatic plant-based iron-carbon micro-electrolysis filler.The iron-carbon micro-electrolysis filler prepared by the method of the present application has a porous structure, a rich content of functional groups, and better electron transfer capacity, which can significantly improve the adsorption performance of nitrogen and phosphorus pollutants.The raw materials of the present application are easy to obtain, and the preparation method is simple, low in cost, low in energy consumption and significantly improves the efficiency of nitrogen and phosphorus removal.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a method for preparing, a product of, and the application of an aquatic plant-based iron-carbon micro-electrolysis packing material. Background Technology

[0002] Secondary effluent from wastewater treatment plants is a significant source of nitrogen and phosphorus emissions, accounting for 48% of nitrogen and phosphorus emissions from surface water bodies.

[0003] Secondary effluent from wastewater treatment plants typically exhibits low organic matter content, poor biodegradability, and a low carbon-to-nitrogen ratio, making it a typical example of low-carbon-to-nitrogen, low-pollution water and a key focus and challenge for advanced nitrogen removal. Iron-carbon microelectrolysis is an advanced redox technology based on galvanic cell reactions, utilizing iron (Fe²⁺)... 0 It forms micro-galvanic cells with carbon (C) in solution, and efficiently removes nitrogen and phosphorus through multiple processes such as electrochemical corrosion, adsorption, flocculation, and redox.

[0004] In recent years, iron-carbon micro-electrolysis has shown excellent performance in industrial wastewater treatment (such as electroplating, pharmaceutical, and dyeing wastewater), but its application in secondary effluent from wastewater treatment plants still faces significant challenges: such as material passivation, Fe... 0 A dense passivation layer (such as Fe2O3) easily forms on the surface, leading to a rapid decrease in reactivity. To address this issue, researchers have recently improved the performance of iron-carbon microelectrolysis through the optimization of carbon materials.

[0005] Existing technologies typically use high-temperature calcined activated carbon as the raw material for iron-carbon micro-electrolysis fillers, which is costly, energy-intensive, and prone to passivation and deactivation. Therefore, there is an urgent need to provide a method for preparing biochar using a medium-low temperature calcination method as the carbon material for iron-carbon micro-electrolysis fillers, in order to slow down the caking and passivation of iron-carbon micro-electrolysis fillers and improve the nitrogen and phosphorus removal performance of secondary effluent from wastewater treatment plants. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing an aquatic plant-based iron-carbon micro-electrolysis packing material, a product thereof, and its application in improving the nitrogen and phosphorus removal efficiency of secondary effluent from wastewater treatment plants. The method of the present invention uses low-temperature calcination of aquatic plant biomass to prepare porous biochar rich in functional groups, and uses the biochar as a carbon material to prepare the iron-carbon micro-electrolysis packing material, thereby improving the problems of low electron transfer efficiency and poor nitrogen and phosphorus removal performance of traditional iron-carbon micro-electrolysis packing materials.

[0007] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing an aquatic plant-based iron-carbon micro-electrolysis filler, comprising the following steps: Step 1: Wash and air-dry the aquatic plants, then cut them into sections, dry them further, and pulverize them to obtain aquatic plant powder; pyrolyze the aquatic plant powder to obtain biochar. Step 2: Mix reduced iron powder, biochar, kaolin, ammonium bicarbonate and quartz sand, add water and granulate to obtain iron-carbon microspheres; dry the iron-carbon microspheres and cool them, then calcine them to obtain the aquatic plant-based iron-carbon microelectrolysis filler.

[0008] The second technical solution of the present invention is an aquatic plant-based iron-carbon micro-electrolysis filler prepared by the above preparation method.

[0009] The third technical solution of this invention is the application of the above-mentioned aquatic plant-based iron-carbon micro-electrolysis packing material in the denitrification and phosphorus removal of secondary effluent from sewage treatment plants.

[0010] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing iron-carbon micro-electrolysis packing material and improving the nitrogen and phosphorus removal performance of secondary effluent from wastewater treatment plants. It utilizes aquatic plants as raw materials to produce biochar and iron-carbon micro-electrolysis packing material, providing a reference for the resource utilization of aquatic plant biomass. The iron-carbon micro-electrolysis packing material prepared in this invention has a porous structure, abundant functional groups, and better electron transport capacity, significantly improving the adsorption performance for nitrogen and phosphorus pollutants. Compared with existing technologies, the aquatic plant-based iron-carbon micro-electrolysis packing material described in this invention uses readily available raw materials, has a simple preparation method, low cost, low energy consumption, and significantly enhances nitrogen and phosphorus removal efficiency. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 The graph shows the adsorption kinetics of nitrate nitrogen by the iron-carbon micro-electrolysis packing material in Example 1. Figure 2 The graph shows the adsorption kinetics of ammonia nitrogen by the iron-carbon micro-electrolysis packing material in Example 1. Figure 3 The diagram shows the adsorption kinetics of total phosphorus by the iron-carbon micro-electrolysis packing material in Example 1. Detailed Implementation

[0013] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0014] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0015] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0016] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0017] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0018] Unless otherwise specified, "room temperature" in this invention refers to 15-30°C.

[0019] Aquatic plant waste (such as reeds, cattails, and water hyacinths) provides an ideal raw material for the preparation of high-performance biochar due to its unique microstructure and abundant oxygen-containing functional groups. Studies have shown that aquatic plant biochar has a higher ion exchange capacity and metal loading capacity than wood-based biochar, which can improve the nitrogen and phosphorus adsorption performance of iron-carbon micro-electrolysis packing materials. This provides a new approach for developing aquatic plant-based iron-carbon micro-electrolysis packing materials. This invention uses biochar prepared from aquatic plant biomass through low-temperature calcination as the carbon material for iron-carbon micro-electrolysis packing materials. Utilizing the mesoporous structure and abundant functional groups of biochar, electron transfer capacity is improved, the caking and passivation of the iron-carbon micro-electrolysis packing material is slowed down, and the nitrogen and phosphorus removal performance of secondary effluent from wastewater treatment plants is enhanced.

[0020] The first aspect of this invention provides a method for preparing an aquatic plant-based iron-carbon microelectrolysis filler, comprising the following steps: Step 1: Wash and air-dry the aquatic plants, then cut them into sections, dry them further, and pulverize them to obtain aquatic plant powder; pyrolyze the aquatic plant powder to obtain biochar. Step 2: Mix reduced iron powder, biochar, kaolin, ammonium bicarbonate and quartz sand, add water and granulate to obtain iron-carbon microspheres; dry the iron-carbon microspheres and cool them, then calcine them to obtain the aquatic plant-based iron-carbon microelectrolysis filler.

[0021] In a preferred embodiment of the present invention, the aquatic plant includes at least one of reeds, calamus, cattails, and canna lilies. In this invention, aquatic plants such as calamus, cattails, and canna lilies can achieve similar technical effects to reeds, thus fulfilling the purpose of the invention.

[0022] In a preferred embodiment of the present invention, in step 1, the drying temperature is 105°C and the time is 8 hours; the pulverization specifically refers to pulverizing to 100 mesh.

[0023] In a preferred embodiment of the present invention, in step 1, the pyrolysis conditions are set as follows: under an inert atmosphere (nitrogen atmosphere), the temperature is increased to 500°C at a rate of 10°C / min and held for 1 hour.

[0024] In a preferred embodiment of the present invention, in step 2, the particle size of the reduced iron powder is 60-320 mesh. Optionally, the particle size of the reduced iron powder can be 60 mesh, 150 mesh, 320 mesh, or any value between the two aforementioned values.

[0025] In a preferred embodiment of the present invention, the mass ratio of the reduced iron powder, the biochar, the kaolin, the ammonium bicarbonate and the quartz sand is 1:2:5:1:1.

[0026] The present invention does not impose any particular limitation on the amount of water used in step 2. The amount of water is sufficient to knead the reduced iron powder, the biochar, the kaolin, the ammonium bicarbonate and the quartz sand into a dough.

[0027] In a preferred embodiment of the present invention, the drying conditions in step 2 are set as follows: drying at 120°C for 2 hours; cooling to room temperature. If the material is not cooled and then directly calcined after drying, the stability of the prepared material will be reduced, and it will easily crumble during use.

[0028] In a preferred embodiment of the present invention, in step 2, the calcination conditions are set as follows: calcination at 400°C for 1-2 hours.

[0029] A second aspect of the present invention provides an aquatic plant-based iron-carbon microelectrolysis filler prepared by the above-described preparation method.

[0030] A third aspect of this invention provides the application of the aforementioned aquatic plant-based iron-carbon micro-electrolysis packing material in the denitrification and phosphorus removal of secondary effluent from wastewater treatment plants. The aquatic plant-based iron-carbon micro-electrolysis packing material of this invention can improve the denitrification and phosphorus removal efficiency of secondary effluent from wastewater treatment plants.

[0031] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0032] The reduced iron powder used in the embodiments of this invention was purchased from Aladdin Biochemical Technology Co., Ltd.

[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1 Step 1, Preparation of aquatic plant-based biochar: Reeds were collected in constructed wetland systems during their mature stage as a raw material for biochar preparation. After being washed with deionized water and air-dried naturally, the reed residues were cut into 2-5 cm lengths and dried in an oven at 105℃ for 8 hours. After being crushed, they were passed through a 100-mesh sieve for later use. A quartz boat containing 250 g of reed powder was placed in a tube furnace, and nitrogen gas was introduced into the furnace at a flow rate of 0.45 L / min to allow pyrolysis under a nitrogen atmosphere. The pyrolysis temperature was set to 500 °C and maintained at that temperature for 1 hour, with the heating rate controlled at 10 °C / min. After cooling to room temperature, powdered reed-based biochar was obtained.

[0035] Step 2, Preparation of iron-carbon micro-electrolysis filler: Reduced iron powder (320 mesh), reed-based biochar, kaolin, ammonium bicarbonate, and quartz sand (particle size 0.5-2 mm…) were thoroughly mixed in a mass ratio of 1:2:5:1:1 until homogeneous. An appropriate amount of ultrapure water was added to facilitate subsequent granulation. After further mixing, 5 g of the homogeneous material was weighed and kneaded into spheres with a particle size of approximately 2 cm (i.e., iron-carbon microspheres). The iron-carbon microspheres were first dried in a 120℃ oven for 2 hours, then cooled to room temperature and placed in a tube furnace for calcination at 400℃. The temperature was maintained at 400℃ for 1 hour, and after natural cooling, the microspheres were removed to obtain the aquatic plant-based iron-carbon microelectrolysis filler.

[0036] The effectiveness of the aquatic plant-based iron-carbon micro-electrolysis filler prepared in Example 1 was verified, as follows: Preparation of simulated wastewater treatment plant effluent: In the laboratory, using tap water as the raw water, potassium nitrate, ammonium chloride, and potassium dihydrogen phosphate were added to prepare simulated secondary effluent from a wastewater treatment plant. The concentrations of nitrate nitrogen, ammonia nitrogen, and total phosphorus in the prepared solution were 10.22±1.82 mg / L, 5.14±2.15 mg / L, and 0.56±0.12 mg / L, respectively.

[0037] Using a 250mL glass bottle as a reactor, 200mL of the simulated secondary effluent from a wastewater treatment plant was added. Four experimental groups were set up: iron filings group (5g of iron filings added), biochar group (5g of reed biochar added), iron-biochar mixture group (5g of a simple mixture of iron powder and biochar added, with a mass ratio of 1:1), and iron-carbon micro-electrolysis packing group (5g of the iron-carbon micro-electrolysis packing prepared in step 2 of Example 1 added). Each experimental group was set up in triplicate. The uniformly mixed material was placed in a porous nylon mesh bag, placed in the reactor, and placed in a constant temperature shaker (25℃, 150 rpm). Samples were taken at preset time points (0 min, 10 min, 30 min, 1 h, 4 h, 8 h). After sampling, the concentrations of nitrate nitrogen, ammonia nitrogen, and total phosphorus were measured. The results are as follows: Figure 1 The graph shows the adsorption kinetics of nitrate nitrogen by the iron-carbon micro-electrolysis packing material in Example 1; as shown. Figure 1 As shown, the iron-carbon micro-electrolysis packing group exhibited the highest adsorption capacity, reaching 1.24 mg / g, which is 20.67 times, 2.82 times, and 1.90 times higher than the iron filings group (0.06 mg / g), the biochar group (0.44 mg / g), and the iron-biochar mixture group (0.65 mg / g), respectively, demonstrating its superior performance in nitrate and nitrogen adsorption. This indicates that the porous structure and high specific surface area of ​​the iron-carbon micro-electrolysis packing may provide more active adsorption sites, and the micro-electrolysis may further promote the chemical reduction of nitrate and nitrogen, thereby improving the adsorption efficiency.

[0038] Figure 2 The graph shows the adsorption kinetics of ammonia nitrogen by the iron-carbon micro-electrolysis packing material in Example 1. Figure 2 The adsorption kinetics of ammonia nitrogen by different materials are shown, and the adsorption kinetic curves of each material can be fitted by a pseudo-first-order kinetic model. For example... Figure 2As shown, the adsorption capacity of the iron-carbon micro-electrolysis packing group was 0.65 mg / g, significantly better than other materials (iron filings group: adsorption capacity 0.05 mg / g; biochar group: adsorption capacity 0.25 mg / g; iron-biochar mixture group: adsorption capacity 0.38 mg / g). The data shows that the adsorption capacity of the iron-carbon micro-electrolysis packing group was 13 times that of iron filings, 2.6 times that of biochar, and 1.71 times that of the iron-biochar mixture. This indicates that the iron-carbon micro-electrolysis packing group has a higher adsorption capacity for ammonia nitrogen. The high specific surface area and porous structure of the iron-carbon micro-electrolysis packing group provide more adsorption sites. In contrast, iron filings, due to their easily passivated surface, form an oxide layer that hinders further adsorption of ammonia nitrogen, resulting in poor adsorption performance. Although biochar has a high specific surface area and functional groups, its adsorption rate and capacity are limited due to a lack of sufficient active sites. The iron-biochar mixture combines the advantages of iron filings and biochar, improving adsorption efficiency, but its adsorption performance is still inferior to that of the iron-carbon micro-electrolysis packing group. Iron-carbon micro-electrolysis fillers not only have a large specific surface area, but may also generate more Fe due to micro-electrolysis. 2+ This increases the likelihood of chemical precipitation and adsorption of ammonia nitrogen. Furthermore, the porous structure of the microspheres may enhance the diffusion of ammonia nitrogen within the pores, thereby increasing the adsorption rate and capacity.

[0039] Figure 3 The diagram shows the adsorption kinetics of total phosphorus by the iron-carbon micro-electrolysis packing material in Example 1. Figure 3 The adsorption kinetics of total phosphorus by four materials—iron filings, biochar, iron-biochar mixture, and iron-carbon microelectrolysis filler—were demonstrated. The adsorption processes of all materials conformed to a pseudo-first-order kinetic model. Figure 3 As shown, the iron-carbon micro-electrolysis packing group exhibits the best adsorption characteristics, with an adsorption capacity of 0.08 mg / g and an adsorption rate constant of 1.92 h⁻¹. -1 The specific surface area of ​​the carbon micro-electrolysis filler is significantly higher than that of other materials. This is due to the high specific surface area and rapid adsorption kinetics of the carbon micro-electrolysis filler, which promotes the production of Fe during the micro-electrolysis process. 2+ It reacts with phosphate to form Fe3(PO4)2 precipitate. Furthermore, the porous structure and high porosity of the microspheres significantly enhance the adsorption rate and capacity. Rapid adsorption depends on the iron-carbon microspheres. In contrast, iron filings exhibit the lowest adsorption performance, with an adsorption capacity and rate constant of only 0.02 mg / g and 1.07 h⁻¹, respectively. -1 This is mainly because a passivation layer easily forms on the surface of iron filings, hindering the continuous adsorption process. The adsorption capacity of biochar is 0.04 mg / g, and the adsorption rate constant is 1.31 h⁻¹. -1 The adsorption capacity and rate constant of the iron-biochar hybrid material were 0.05 mg / g and 1.66 h, respectively. -1 It shows a synergistic effect between iron filings and biochar, but it is still not as good as iron-carbon micro-electrolysis filler.

[0040] Comparative Example 1 The difference from Example 1 is that the calcination temperature in step 2 is set to 300°C, while the other steps and parameters are the same as in Example 1.

[0041] The aquatic plant-based iron-carbon microelectrolysis packing material prepared in this comparative example was subjected to the same performance verification as in Example 1. The results showed that the packing material prepared in this comparative example had an adsorption capacity of 0.95 mg / g for nitrate nitrogen, an adsorption capacity of 0.51 mg / g for ammonia nitrogen, an adsorption capacity of 0.06 mg / g for total phosphorus, and an adsorption rate constant of 1.68 h for total phosphorus. -1 Compared to Example 1, the filler obtained by calcination at a lower temperature had insufficiently developed porous structure, and the bonding strength and conductive network between iron and carbon particles may not have reached their optimal levels, resulting in lower adsorption performance and reactivity than in Example 1. This confirms that 400℃ is an optimized calcination temperature in this preparation method, which can effectively balance the retention of biochar functional groups, the solidification of the binder (kaolin), and the formation of the overall filler structure, thereby obtaining the best comprehensive nitrogen and phosphorus removal performance.

[0042] Comparative Example 2 The difference from Example 1 is that step 1 is omitted; in step 2, the reed-based biochar is replaced with an equal mass of commercially available coal-based activated carbon (particle size 100-200 mesh); the remaining steps and parameters are the same as in Example 1.

[0043] The iron-carbon micro-electrolysis packing material prepared in this comparative example was subjected to the same performance verification as in Example 1. The results showed that the packing material prepared in this comparative example had an adsorption capacity of 0.78 mg / g for nitrate nitrogen, an adsorption capacity of 0.38 mg / g for ammonia nitrogen, an adsorption capacity of 0.04 mg / g for total phosphorus, and an adsorption rate constant of 1.45 h for total phosphorus. -1 Compared to Example 1, the packing material prepared using commercial activated carbon exhibits significantly lower performance across all indicators. Analysis suggests that while commercial activated carbon (especially coal-based activated carbon) may have a higher specific surface area, the variety and abundance of its surface functional groups (particularly oxygen-containing functional groups) are generally inferior to biochar prepared by the pyrolysis of aquatic plants such as reeds at 500°C. The aquatic plant biochar described in this invention possesses a richer mesoporous structure and more surface active sites, enabling more effective iron loading, promoting electron transfer, and mitigating the passivation of iron-carbon packing materials. Furthermore, using commercial activated carbon contradicts the original intention of this invention: "reducing raw material costs through the resource utilization of waste." This comparative example further confirms that using biochar prepared from specific aquatic plants as a carbon source is indispensable for obtaining high-performance, low-cost iron-carbon micro-electrolysis packing materials.

[0044] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing an aquatic plant-based iron-carbon microelectrolysis filler, characterized in that, Includes the following steps: Step 1: Wash and air-dry the aquatic plants, then cut them into sections, dry them further, and pulverize them to obtain aquatic plant powder; pyrolyze the aquatic plant powder to obtain biochar. Step 2: Mix reduced iron powder, biochar, kaolin, ammonium bicarbonate and quartz sand, add water and granulate to obtain iron-carbon microspheres; dry the iron-carbon microspheres and cool them, then calcine them to obtain the aquatic plant-based iron-carbon microelectrolysis filler.

2. The preparation method according to claim 1, characterized in that, The aquatic plants include at least one of reeds, calamus, cattails, and canna lilies.

3. The preparation method according to claim 1, characterized in that, In step 1, the drying temperature is 105℃ and the time is 8-16 h; the pulverization specifically refers to pulverizing to 100 mesh.

4. The preparation method according to claim 1, characterized in that, In step 1, the pyrolysis conditions are set as follows: under an inert atmosphere, the temperature is increased to 500°C at a rate of 10°C / min and held for 1 hour.

5. The preparation method according to claim 1, characterized in that, In step 2, the particle size of the reduced iron powder is 60-320 mesh.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the reduced iron powder, biochar, kaolin, ammonium bicarbonate, and quartz sand is 1:2:5:1:

1.

7. The preparation method according to claim 1, characterized in that, In step 2, the drying conditions are set as follows: dry at 120℃ for 2 hours; then cool to room temperature.

8. The preparation method according to claim 1, characterized in that, In step 2, the calcination conditions are set as follows: calcination at 400℃ for 1-2 hours.

9. An aquatic plant-based iron-carbon microelectrolysis filler prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the aquatic plant-based iron-carbon micro-electrolysis packing material as described in claim 9 in the denitrification and phosphorus removal of secondary effluent from wastewater treatment plants.

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