A modified ceramsite filler based on iron-sulfur autotrophic denitrification, its preparation method and application

Abstract

This invention discloses a modified ceramsite packing material based on iron-sulfur autotrophic denitrification, its preparation method, and its application, belonging to the field of wastewater treatment technology. The modified ceramsite packing material based on iron-sulfur autotrophic denitrification of this invention is ceramsite loaded with modifiers; the modifiers include iron powder, pyrite powder, and biochar; the mass ratio of iron powder, pyrite powder, and biochar is 3:6:1; the mass ratio of modifiers to ceramsite is 1.5:1. This invention, by jointly modifying ordinary ceramsite with iron powder (zero-valent iron), pyrite powder, and biochar, significantly improves the denitrification effect of biological filters on low C / N wastewater. Under typical experimental conditions, the denitrification rate of biological filters containing modified ceramsite packing material for low C / N ratio wastewater is more than 90% higher than that of ordinary ceramsite biological filters. Furthermore, the modified ceramsite packing material prepared by this invention can significantly improve the phosphorus removal effect of biological filters on low C / N ratio wastewater.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a modified ceramsite packing material based on iron-sulfur autotrophic denitrification, its preparation method, and its application. Background Technology

[0002] Nitrogenous pollutants are currently one of the major aquatic environmental and ecological problems. The main sources of nitrogen pollution include non-point source pollution from nitrogen fertilizer application and point source pollution from domestic sewage and industrial nitrogen-containing wastewater discharge. Among these, the discharge of low-carbon-nitrogen ratio effluent from urban secondary wastewater treatment plants is a significant source of nitrogen and phosphorus pollution. Large amounts of nitrogen- and phosphorus-containing wastewater treatment plant effluent discharged into water bodies can cause eutrophication, leading to algal blooms or red tides, causing aquatic organism mortality and damaging biodiversity. Furthermore, nitrate pollution in water bodies can also harm human health, potentially inducing methemoglobinemia and sclerotherapy.

[0003] Currently, various treatment methods exist for low C / N ratio wastewater, mainly categorized into physicochemical and biological methods. Physicochemical methods include membrane separation (electrodialysis, reverse osmosis), ion exchange, chemical oxidation, and coagulation sedimentation, but these methods have drawbacks such as high operating costs, difficulty in maintenance, and susceptibility to secondary pollution. Biological methods, including traditional heterotrophic and autotrophic denitrification technologies, are the primary means of wastewater denitrification. However, in traditional heterotrophic denitrification, the growth and metabolism of heterotrophic denitrifying bacteria depend on organic carbon, making it unsuitable for treating low C / N ratio effluent from secondary wastewater treatment plants. Furthermore, adding an external organic carbon source not only leads to high operating costs but also generates secondary pollution. In today's pursuit of low-carbon technologies, autotrophic denitrification technology, which does not require an external carbon source, plays an increasingly important role in water pollution control. Autotrophic denitrification technology refers to the utilization of inorganic carbon (CO2, HCO3) by autotrophic denitrifying bacteria. - CO3 2- As a carbon source, inorganic compounds (S, S) 2- Fe, Fe 2+ Fe 3+ (e.g., H2) as electron donors, and (e.g., NO3) as electron acceptors. - -N or NO2 - The biological denitrification process, which reduces nitrogen oxides (NOx) to nitrogen (N2), requires no external carbon source and has advantages such as low sludge production and minimal secondary pollution. Autotrophic denitrification technologies include sulfur-based autotrophic denitrification, iron-based autotrophic denitrification, anaerobic ammonium oxidation, and hydrogen-based autotrophic denitrification. Sulfur-based autotrophic denitrification produces acid, while iron-based, hydrogen-based, and anaerobic ammonium oxidation consume acid. Therefore, single-stage autotrophic denitrification can lead to significant pH fluctuations during the reaction, affecting the denitrification efficiency of autotrophic bacteria and resulting in poor effluent quality. Furthermore, studies have shown that SO4 is produced during sulfur oxidation. 2- The amount of NO3- The reduction of -N is positively correlated, indicating that sulfur-based autotrophy will produce secondary pollution. Summary of the Invention

[0004] The purpose of this invention is to provide a modified ceramsite filler based on iron-sulfur autotrophic denitrification, its preparation method, and its application, so as to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention is: a modified ceramsite packing material based on iron-sulfur autotrophic denitrification, wherein the modified ceramsite packing material is ceramsite loaded with modifiers;

[0007] The components of the modified material include iron powder, pyrite powder, and biochar;

[0008] The mass ratio of iron powder, pyrite powder and biochar is 3:6:1;

[0009] The mass ratio of the modifier to the ceramsite is 1.5:1.

[0010] The second technical solution of the present invention: a method for preparing the above-mentioned modified ceramsite filler, comprising the following steps:

[0011] Iron powder, pyrite powder, biochar and cement (binder) are mixed evenly to obtain a modifier. The modifier is then attached to ceramsite and cured to obtain the modified ceramsite filler.

[0012] Furthermore, the curing time is 10 to 12 days; the particle size of the modified ceramsite filler is 5 to 8 mm; and the amount of cement used is 20% of the total mass of iron powder, pyrite powder, and biochar.

[0013] The third technical solution of the present invention: an application of the above-mentioned modified ceramsite filler in wastewater treatment.

[0014] Furthermore, the wastewater is nitrogen- and phosphorus-containing wastewater.

[0015] The fourth technical solution of the present invention: a biological filter for removing nitrogen and phosphorus from wastewater, using the above-mentioned modified ceramsite packing as the main layer.

[0016] Furthermore, the biological filter is provided with a main body layer and a filter layer;

[0017] Wastewater first passes through the main body layer, and then through the filter layer;

[0018] The thickness ratio of the main layer to the filter layer is 3:2;

[0019] The filter layer is composed of limestone and biochar in a mass ratio of 9:1.

[0020] Furthermore, the particle size of both the limestone and biochar is 3-5 mm.

[0021] Limestone, used as a filter media, can adjust the pH value of the effluent; biochar, used as an auxiliary material, can enhance the biological oxidation effect.

[0022] The present invention discloses the following technical effects:

[0023] (1) The modified ceramsite packing material of the present invention can significantly improve the nitrogen and phosphorus removal effect of biological filters on wastewater with low C / N ratio (normal carbon-nitrogen ratio is 10-20, and C / N ratio is less than 5, which belongs to low carbon-nitrogen ratio).

[0024] (2) This invention improves the denitrification effect of biological filters on low C / N wastewater by modifying ordinary ceramsite with iron powder (zero-valent iron), pyrite powder and biochar. Under typical experimental conditions, the denitrification rate of biological filters containing modified ceramsite filler for low C / N ratio wastewater is more than 90% higher than that of ordinary ceramsite biological filters (Table 2). This is mainly because the divalent iron and sulfur contained in zero-valent iron and pyrite powder exist on the surface of modified ceramsite, which can produce a synergistic effect of iron and sulfur autotrophic denitrification. The presence of biochar is conducive to the enrichment and growth of iron and sulfur autotrophic bacteria, thereby further enhancing the synergistic effect of iron and sulfur autotrophic denitrification. This invention represents a major improvement over the existing denitrification technology of ceramsite biological filters and has significant technological progress. It is of great significance for the biological denitrification of low C / N ratio wastewater.

[0025] (3) This invention significantly improves the phosphorus removal efficiency of biological filters for low C / N ratio wastewater by using modified ceramsite filler prepared from iron powder (zero-valent iron), pyrite powder, and biochar. Under typical experimental conditions, the phosphorus removal rate of biological filters containing modified ceramsite filler for low C / N ratio wastewater is more than 15% higher than that of ordinary ceramsite biological filters (Table 3). This is mainly because both biological and chemical phosphorus removal occur simultaneously on the surface of the modified ceramsite filler. Iron and sulfur are elements for microbial growth, which is beneficial to the growth of iron- and sulfur-autotrophic bacteria, while biochar has the function of enriching microorganisms. The coupling of the three can promote biological phosphorus removal. Chemical phosphorus removal mainly relies on the reaction and precipitation of iron ions and their hydroxides with phosphate ions. At the same time, the iron-carbon micro-electrolysis can promote autotrophic denitrification to generate iron ions, thereby improving the phosphorus removal efficiency. Attached Figure Description

[0026] 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.

[0027] Figure 1This is a schematic diagram of the structure of the biological filter used in Example 1;

[0028] Figure 2 The nitrogen removal efficiency of biological filters;

[0029] Figure 3 This demonstrates the phosphorus removal efficiency of a biological filter. Detailed Implementation

[0030] 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.

[0031] 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. Every smaller range between any stated value or intermediate value within a stated range, and 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The main component of the pyrite powder used in this invention is FeS2, with a FeS2 content of 99 wt.%. The pyrite powder also contains small amounts of elements such as cobalt, nickel, and selenium, and has a NaCl-type crystal structure.

[0036] The silicate cement used in this invention is PO 42.5 ordinary silicate cement; the particle size of iron powder is ≤75μm; the particle size of pyrite powder is ≤1mm; and the particle size of biochar is ≤150μm.

[0037] Example 1

[0038] A method for preparing modified ceramsite packing based on iron-sulfur autotrophic denitrification:

[0039] (1) Mix iron powder, pyrite powder and biochar in a mass ratio of 3:6:1, and then add silicate cement (the amount of silicate cement is 20% of the total mass of iron powder, pyrite powder and biochar) and mix evenly to obtain the modified material.

[0040] (2) Add a certain amount of ordinary spherical ceramsite (carrier) with a diameter of 4-6 mm to the coating machine, start the coating machine, and spray water evenly during machine operation to moisten the surface of the carrier. Then add the modifier (the mass ratio of the modifier to the ordinary spherical ceramsite is 1.5:1), spray an appropriate amount of water to make the modifier adhere to the ceramsite. After the modifier is evenly adhered to the surface of the ceramsite (aggregates into moist spherical particles), it is naturally cured at room temperature (25℃) for 11 days to obtain modified ceramsite filler (EF-D) with a particle size of 5-8 mm.

[0041] Comparative Example 1

[0042] Same as Example 1, except that the raw materials for preparing the modified compound do not contain pyrite powder, and step (1) is as follows:

[0043] Iron powder and biochar were mixed in a mass ratio of 9:1, and then silicate cement (the amount of silicate cement was 20% of the total mass of iron powder and biochar) was added and mixed evenly to obtain the modified material.

[0044] The modified ceramsite filler prepared according to this comparative example is designated as EF-B, with a particle size of 5–8 mm.

[0045] Comparative Example 2

[0046] Same as Example 1, except that step (1) is as follows: mix iron powder, pyrite powder and biochar in a mass ratio of 9:9:1, and then mix with silicate cement (the amount of silicate cement is 20% of the total mass of iron powder, pyrite powder and biochar) until uniformly mixed to obtain the modified material.

[0047] The modified ceramsite filler prepared according to this comparative example is designated as EF-C, with a particle size of 5–8 mm.

[0048] Example of effect 1

[0049] (1) Construction of biological filter:

[0050] The inlets at the bottom of the four acrylic columns (EF-A, EF-B, EF-C, and EF-D) are connected in series to a water tank equipped with a peristaltic pump (which controls the continuous flow of water). The acrylic columns contain a water distribution layer, a main body layer, and a filter layer. The upper part of the acrylic columns has a sampling port and an overflow port. The sampling port is located above the filter layer, and the overflow port is located above the sampling port.

[0051] The filter layers of the plexiglass columns EF-A, EF-B, EF-C and EF-D are composed of limestone (particle size 3-5 mm) and biochar (particle size 3-5 mm) in a mass ratio of 9:1.

[0052] The water distribution layers of the plexiglass columns EF-A, EF-B, EF-C and EF-D are filled with gravel with a particle size of 8-10 mm, and a perforated water distribution pipe (perforated pipe) is installed in the middle of the water distribution layer.

[0053] The main layer of the EF-A acrylic column is filled with ordinary spherical ceramic particles with a diameter of 4 to 6 mm;

[0054] The main layer of the plexiglass column EF-B is filled with the modified ceramic filler EF-B prepared in Comparative Example 1;

[0055] The main layer of the plexiglass column EF-C is filled with the modified ceramic filler EF-C prepared in Comparative Example 2;

[0056] The main layer of the plexiglass column EF-D is filled with the modified ceramsite filler EF-D prepared in Example 1.

[0057] The dimensions of the acrylic column are: H (height) = 320mm, d (diameter) = 40mm; the height of the water distribution layer is 40mm, and a perforated (2mm diameter) water distribution pipe is used to evenly distribute water at the top of the water distribution layer; the height of the main layer is 120mm; and the height of the filter layer is 80mm.

[0058] See the structural diagram of the biological filter. Figure 1 .

[0059] (2) Determine experimental conditions and methods

[0060] The flow rate of each plexiglass column in the experimental setup was set to 710 μL / min, and the hydraulic retention time was 5.9 h (the influent was simulated wastewater). Before the formal operation of the experiment, a rapid biofilm formation method was used for a two-month microbial acclimation and biofilm formation process (sludge from the aeration tank of a wastewater treatment plant was inoculated into the main body layer and the filter layer for microbial acclimation and biofilm formation, with a sludge concentration of approximately 3000 mg / L). Effluent parameters were measured daily, and the first stage of the experiment was conducted after the effluent quality stabilized. The experimental water was simulated wastewater prepared with glucose (nutrients), ammonium chloride, sodium nitrate, sodium nitrite, potassium dihydrogen phosphate, and trace elements necessary for microbial growth. This process was continued for 2–3 days. When the effluent stabilized and reached the initial effluent quality concentration of the first stage (ammonia nitrogen and total nitrogen removal rates both reached approximately 30%), the acclimation and biofilm formation were considered successful.

[0061] The main water quality parameters of the influent (simulated wastewater) are shown in Table 1.

[0062] In stages I and II, glucose is added as a carbon source, and the C / N ratio is controlled at approximately 4:1. In stages III to V, the C / N ratio is approximately 1:2. Intermittent aeration is only performed on the influent in stages II and III, with an influent DO of 6.5–8.0 mg·L⁻¹. -1 No aeration was performed during the remaining stages, and the influent DO was 4.2–5.6 mg·L⁻¹. -1 The water temperature (inlet water temperature) for stages I to IV is 20±1.7℃, and the water temperature (inlet water temperature) for stage V is 15.3±2.2℃. The inlet pH is 7.13±0.43, and the outlet pH is 7.37±0.56.

[0063] Table 1. Average values ​​(mg·L⁻¹) of main water quality parameters of influent (simulated wastewater) at each stage -1 )

[0064] stage <![CDATA[NH4 + -N]]> <![CDATA[NO3 - -N]]> <![CDATA[NO2 - -N]]> TN TP Ⅰ 22.93 － － 22.93 0.81 Ⅱ 25.82 － － 25.82 0.81 Ⅲ 25.86 － － 25.86 0.79 Ⅳ － 14.41 － 14.41 － Ⅴ － 2.08 5.13 7.21 －

[0065] Water samples were collected daily from the sampling port, filtered through a 0.45μm filter membrane, and then the water quality analysis indicators were measured. NH4 + -N: Nano-reagent spectrophotometry; NO3 - -N: Ultraviolet spectrophotometry; NO2 - -N: (1-Naphthyl)-ethylenediamine spectrophotometry; PO4 3- Ammonium molybdate spectrophotometric method. Water temperature, dissolved oxygen (DO), and pH were measured using a portable dissolver (JPB-607). Total inorganic nitrogen (TN) content was obtained by summing the various forms of nitrogen.

[0066] (3) Effect of nitrogen and phosphorus removal

[0067] 1) NH4 + -N removal effect

[0068] The ammonia nitrogen removal performance of each biological filter is shown in the table below. Figure 2 Figure (a) and Table 2.

[0069] In the first stage, the ammonia nitrogen removal rate of each reactor was low, with an average removal rate of around 30%. The main reason was that the content of nitrifying bacteria was low at the beginning of reactor operation. Another reason was that the dissolved oxygen concentration in the water was low, which inhibited nitrification.

[0070] In Phase II, the ammonia nitrogen removal efficiency of each reactor improved. The average ammonia nitrogen removal rates of reactors EF-A, EF-B, EF-C, and EF-D were 43.63%, 63.13%, 36.77%, and 37.73%, respectively.

[0071] In Phase III, under the simulated tailwater with a low carbon-to-nitrogen ratio, the ammonia nitrogen concentration in the effluent from the four reactors did not change significantly compared to the previous phase.

[0072] The ammonia nitrogen removal efficiency in EF-B was significantly better than the other three reactor groups, which may be partly due to the adsorption effect of biochar; the addition of zero-valent iron (iron powder) to improve the nitrification efficiency in the aerobic stage is likely the main reason. In EF-C and EF-D, the addition of pyrite altered the dominant microorganisms, which may have created ecological competition with nitrifying bacteria, affecting the activity of nitrifying bacteria and the efficiency of nitrification.

[0073] Table 2 Nitrogen removal rate (%)

[0074]

[0075] In Phase III, under the simulated tailwater with a low carbon-to-nitrogen ratio, the ammonia nitrogen concentration in the effluent from the four reactors did not change significantly compared to the previous phase.

[0076] 2) NO X - -N removal effect

[0077] from Figure 2 As shown in Figure (b), in Stage I, the nitrate nitrogen concentrations in all four reactors were below the detectable range because the ammonia nitrogen removal rates in all four reactors were low, resulting in low cumulative nitrate nitrogen content (not shown in Figure (b)). In Stage II, the ammonia nitrogen removal rates in all reactors improved, leading to an increase in the concentration of nitrate nitrogen, an intermediate product generated during the conversion. Nitrate nitrogen accumulation occurred in reactors EF-A and EF-B, while reactors EF-C and EF-D remained below the detectable nitrate nitrogen concentration. Compared to EF-A, EF-B had a lower nitrate concentration in the effluent, indicating that the combined application of iron powder and biochar enhanced biological denitrification.

[0078] In stage III, a large accumulation of nitrate nitrogen (4.41 mg·L⁻¹) was found in the EF-A reactor. -1The reason is that in the EF-A reactor, denitrification is inhibited due to the lack of a carbon source, leading to a large accumulation of nitrate nitrogen. Compared with the EF-A reactor, the effluent nitrate nitrogen concentration in the EF-B reactor is lower (0.70 mg·L⁻¹). -1 The combined application of iron powder and biochar can enhance the nitrate removal efficiency of low C / N effluent. The effluent concentrations of both EF-C and EF-D are 0.30 mg·L⁻¹. -1 Compared to EF-B, it shows an improvement because pyrite can participate in autotrophic denitrification and synergistically enhance denitrification performance with iron powder and biochar.

[0079] In stage IV, the nitrate nitrogen removal rates of each reactor were 7.68%, 57.98%, 95.64%, and 98.45%, respectively. Reactor EF-B showed better performance compared to reactor EF-A because biochar could provide a carbon source to some extent; furthermore, zero-valent iron (iron powder) could promote nitrate nitrogen removal. Compared to EF-B, EF-C and EF-D showed removal rates increased by 37.66% and 40.47%, respectively, further demonstrating the synergistic effect of pyrite, iron powder, and biochar in enhancing denitrification.

[0080] In stage V, the influent nitrate nitrogen mainly comes from the oxidation of added sodium nitrite. The nitrate nitrogen removal rate in EF-A showed no significant change. Compared to the previous stage, the removal rates in EF-B, EF-C, and EF-D decreased by 29.65%, 65.51%, and 21.62%, respectively, due to NO3... - The removal rate of -N decreases with decreasing temperature, while EF-D is relatively less affected by temperature (this may be related to its chemical nitrate removal mechanism).

[0081] from Figure 2 As can be seen in Figure (c), NO2 - The changes in nitrite (N) concentration in the effluent. In the first four stages, nitrite nitrogen in the water is an intermediate product of nitrification and denitrification, and the nitrite nitrogen content in the effluent of the four reactors is low with no significant difference. In stage V, sodium nitrite is actively added to the influent, and the removal rates of the four reactors are 7.04%, 27.99%, 28.33%, and 60.72%, respectively; reactor EF-D is significantly better than the other three reactors. EF-C and EF-D occur based on pyrite autotrophic denitrification, while biochar releases carbon sources to promote autotrophic denitrification, forming a synergistic effect of heterotrophic autotrophic denitrification. Compared with EF-B, EF-D shows that the addition of pyrite can significantly improve the nitrite removal rate.

[0082] 3) TN removal effect

[0083] from Figure 2As shown in Figure (d), in stages I to III, the denitrification performance of EF-B is superior to the other three reactors because EF-B has better nitrification performance. The denitrification effects of EF-C and EF-D are not significant, mainly due to their poor nitrification performance. In stage IV, the TN removal rate of EF-B (57.81%) is significantly higher than that of EF-A (7.40%). This is because zero-valent iron (iron powder) can remove nitrate nitrogen through chemical reactions, while biochar provides a carbon source to synergistically remove nitrate nitrogen through iron autotrophic denitrification. EF-C (TN removal rate of 95.04%) is 37.23% higher than EF-B, while EF-D (TN removal rate of 98.04%) is 3.00% higher than EF-C. This is because the addition of pyrite enhances the autotrophic denitrification of sulfur bacteria. In stage V, due to the decrease in temperature, the TN removal rates of all reactors decrease to varying degrees, but reactor EF-D still shows a high TN removal rate (65.42%). The denitrification effect of the modified ceramsite packing in EF-D is significantly better than the existing research results on denitrification by single pyrite and denitrification by combined zero-valent iron and pyrite (FeS2), indicating that the denitrification effect of the coupling of zero-valent iron, pyrite and biochar is better.

[0084] 4) Phosphorus removal efficiency

[0085] Depend on Figure 3 As shown in Table 3, in Stage I, the EF-C reactor achieved the highest TP removal rate of 56.79%. In Stage II, the TP removal rates of all reactors increased to varying degrees, reaching 69.12%, 79.85%, 74.77%, and 86.02%, respectively. In reactors EF-B, EF-C, and EF-D, iron ions could combine with phosphate ions to form precipitates and remove phosphate; the adsorption of iron hydroxide precipitates also promoted further phosphorus removal. Furthermore, the adsorption effect of biochar in the transition layer and the formation of Ca5(OH)(PO4)2 from limestone and phosphate also contributed to the removal. 3- 5. Precipitation also played a certain role in phosphorus removal. In stage III, the TP removal efficiency of each reactor decreased. This was partly due to the lack of carbon source inhibiting the biological activity of polyphosphate-accumulating bacteria, and partly due to the accumulation of nitrate nitrogen in the water inhibiting phosphorus release under anaerobic conditions. The EF-D reactor was least affected, indicating that adding pyrite helps in the phosphorus removal problem of low-carbon wastewater.

[0086] Table 3 Phosphorus removal rate (%)

[0087] stage EF-A EF-B EF-C EF-D Ⅰ 50.50 44.64 56.79 43.42 Ⅱ 69.12 79.85 74.77 86.02 Ⅲ 54.04 55.14 51.68 69.03

[0088] 4) Phosphorus removal efficiency

[0089] (4) Analysis of the mechanism of enhanced nitrogen and phosphorus removal

[0090] 1) Denitrification mechanism

[0091] The nitrate nitrogen removal of this invention mainly achieves its effect through three mechanisms: traditional denitrification, iron autotrophic denitrification based on zero-valent iron and pyrite, and sulfur autotrophic denitrification. Traditional denitrifying bacteria are anaerobic heterotrophic bacteria, whose nitrate nitrogen conversion is strictly dependent on carbon sources. At low C / N ratios, denitrification is not conducive to nitrogen removal. This invention, however, by inoculating aerobic denitrifying bacteria, synergistically promotes both nitrification and denitrification, thereby improving nitrate nitrogen removal efficiency. Furthermore, the modified ceramsite packing used in this invention contains biochar. The organic matter released by the biochar provides a carbon source for microorganisms, which to some extent compensates for the inhibition of denitrification under low C / N ratios (insufficient carbon sources). The enrichment effect of biochar also promotes the distribution of denitrifying bacterial communities, thus accelerating the denitrification process. The added zero-valent iron (iron powder) can enhance the relative abundance of denitrifying bacteria in the iron-based biological system, improving denitrification efficiency and reducing organic carbon consumption.

[0092] In the iron-carbon microelectrolysis system, iron and biochar serve as electrode materials, forming numerous micro-cells, which then generate Fe(II) and [H] during the reaction. These are highly active and can decompose most organic pollutants, and the high [H] production rate also promotes the metabolism of autotrophic denitrifying bacteria.

[0093] Anode: Fe-2e - →Fe 2+ (1)

[0094] Cathode: O2 + 4H + +4e - →2O · +4[H]→2H2O (2)

[0095] Autotrophic denitrification based on pyrite can be represented by equations (3) and (4);

[0096]

[0097]

[0098] Fe(0) removes NO3 - The -N process involves both chemical and biological reactions. The chemical reaction produces NO3. - -N is converted to NH4 + -N (Equations (5), (6)), the biological reaction uses H2 produced by Fe(0) corrosion under anaerobic conditions as an electron donor, NO3 - -N is the electron acceptor to generate N2 (Equations (7), (8)). On the one hand, Fe(0) can react with Fe produced by FeS2-driven denitrification. 3+ The reaction increases Fe 2+The concentration of Fe(III) (Equation (9)) is used to achieve the Fe(III) / Fe(II) cycle; on the other hand, the Fe in the modified ceramsite filler is... 2+ It provides more electrons for denitrification; increasing iron ions can accelerate the electron transfer rate of autotrophic denitrification, thereby improving denitrification performance.

[0099]

[0100] Fe 0 +2H₂O→H₂+Fe 2+ +2OH - (7)

[0101]

[0102] Fe 0 +2Fe 3+ →3Fe 2+ (9)

[0103] In summary, the traditional denitrification process, iron autotrophic denitrification, sulfur autotrophic denitrification, and the enrichment effect of biochar on microorganisms in this invention synergistically enhance the denitrification effect on wastewater with a low C / N ratio, thereby improving the denitrification performance of the system.

[0104] 2) Phosphorus removal mechanism

[0105] The phosphorus removal pathway of the biological filter in this invention involves both chemical and biological phosphorus removal. Biological phosphorus removal is primarily based on the Enhanced Biological Phosphorus Removal (EBPR) theory. Polyphosphate-accumulating bacteria release and absorb phosphorus under alternating anaerobic and aerobic conditions, converting it into intracellular polyphosphates. Phosphorus removal is achieved by removing phosphorus-rich sludge. The modified ceramsite packing used in this invention contains iron, an essential element for microbial growth. Iron is a crucial component of cytochromes in biological oxidation enzyme systems, playing an electron transfer role in biological oxidation and promoting bacterial reproduction and enzyme secretion, thus enhancing microbial growth and phosphorus removal. Chemical phosphorus removal utilizes both the adsorption of phosphorus by the limestone filter layer and the significant role of iron ions and their hydroxides. Furthermore, biochar adsorption also contributes to phosphorus removal. The added pyrite acts as an electron donor for sulfur autotrophic denitrification, promoting iron ion generation through iron-carbon micro-electrolysis and thereby improving phosphorus removal efficiency.

[0106]

[0107] 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 biological filter for removing nitrogen and phosphorus from wastewater, characterized in that, The biological filter is provided with a main body layer and a filter layer; Wastewater first passes through the main body layer, and then through the filter layer; The filter layer is composed of limestone and biochar; The C / N ratio of the wastewater is less than 5; The main body layer is a modified ceramsite filler based on iron-sulfur autotrophic denitrification; The modified ceramsite filler is ceramsite loaded with modifiers; The components of the modified material include iron powder, pyrite powder, and biochar; The mass ratio of iron powder, pyrite powder and biochar is 3:6:1; The mass ratio of the modifier to the ceramsite is 1.5:1; The preparation steps of the modified ceramsite filler include: Iron powder, pyrite powder, biochar and cement are mixed evenly to obtain a modifier. The modifier is then attached to ceramsite and cured to obtain the modified ceramsite filler.

2. The biological filter according to claim 1, characterized in that, The curing time is 10 to 12 days; the particle size of the modified ceramsite filler is 5 to 8 mm; and the amount of cement used is 20% of the total mass of iron powder, pyrite powder, and biochar.

3. The biological filter according to claim 1, characterized in that, The thickness ratio of the main layer to the filter layer is 3:

2.

4. The biological filter according to claim 1, characterized in that, The mass ratio of limestone to biochar is 9:

1.

5. The biological filter according to claim 1, characterized in that, The limestone and biochar both have a particle size of 3–5 mm.

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