A manganese-carbon composite controlled-release material, its preparation method and application

Abstract

The present invention belongs to the field of wastewater treatment. The present invention provides a manganese-carbon composite controlled-release material, a preparation method thereof and an application. The manganese-carbon composite controlled-release material comprises the following components: manganese-rich minerals, natural plant carbon sources, gelling materials, aggregates, additives and foaming agents. The manganese-carbon composite controlled-release material of the present invention can regulate the carbon release and manganese cycle processes by means of the interaction between manganese and carbon, significantly improve the electron transfer and mass transfer efficiency, realize synergistic denitrification, significantly improve the overall denitrification efficiency, and achieve simultaneous denitrification and phosphorus removal and adaptive continuous denitrification. The raw materials required for preparing the manganese-carbon composite controlled-release material are all environmentally friendly and inexpensive, the preparation process is simple, the preparation cost is low, and it can be applied to the fillers in the submerged areas of constructed wetlands, biological filters and bioretention systems, and can be widely applicable to application scenarios such as the advanced treatment of the tail water of sewage treatment plants, the treatment of rural agricultural sewage and the purification of initial rainwater.

Description

Technical Field

[0001] The present invention belongs to the field of wastewater treatment, and particularly relates to a technology for treating wastewater with a low carbon-nitrogen ratio. Background Art

[0002] The water quality of many low-pollution river waters, the treated tail water of sewage treatment plants, urban surface runoff, agricultural runoff (including rural decentralized domestic sewage), etc. can meet the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants", but it is still inferior to the Class V surface water quality standard value. These low-pollution waters have a large quantity and lack biodegradable organic matter, and there is a common problem of a low carbon-nitrogen ratio (C / N < 5.0).

[0003] Most treatment measures adopt the method of directly adding liquid carbon source (LCS) for advanced denitrification. In the short term, this method has low investment and is easy to implement, but in the long term, its process operation cost is high and the environmental benefit is poor, which is mainly reflected in the continuous addition of carbon source, high yield of excess sludge and large carbon emissions, etc. There is an urgent need to find a technology for treating wastewater with a low carbon-nitrogen ratio that is efficient and energy-saving.

[0004] The solid-phase denitrification technology for treating wastewater with a low carbon-nitrogen ratio is mainly developed based on natural solid-phase carbon sources or synthetic carbon sources. The natural solid-phase carbon sources (SCS) that have been studied more currently are mainly inexpensive and easily available agricultural wastes (AW), such as wood chips, straws, rice husks, cottons, corncobs, peanut shells, etc. However, these natural materials generally have the problems of excessive release of dissolved organic matter (DOM) in the initial stage of the reaction, and even rapid release of a large amount of colored dissolved organic matter (CDOM) causing apparent pollution, slow decomposition of lignin and other refractory components in the later stage of the reaction, and insufficient sustainability of denitrification. Moreover, some plant carbon sources will release nutrients such as N and P during the carbon release process, causing secondary pollution. At the same time, the loose surface of natural materials makes them sensitive to changes in external conditions and prone to clogging problems.

[0005] Autotrophic denitrification has more environmental and economic advantages than heterotrophic denitrification: low sludge yield, relatively low cost, no need to add external carbon source, reduction of secondary organic carbon pollution, and the new manganese-driven autotrophic denitrification has become a research hotspot in recent years. Using low-cost manganese as an electron donor to achieve the denitrification process of coupling manganese oxidation with NO2 - -N or NO3 - -N is called NDMO. NDMO is coupled with the manganese ammonia oxidation (Mnammox) process to form a nitrogen transformation process driven by the manganese cycle (Equations 1 - 4). At the same time, the accompanying bio-oxidized manganese (BMO) has a larger specific surface area, a higher redox potential, stronger adsorption ability and higher catalytic activity. High-valent manganese oxides can promote the degradation of refractory organic matter and use its products as denitrification carbon sources, making NO3 -The -N removal rate is further improved. However, using only low-valent manganese as an inorganic electron donor to drive autotrophic denitrification lacks sufficient power, and excessive introduction of low-valent manganese will also cause secondary pollution.

[0006] <![CDATA[3MnO2 + NH4 + + 4H + → 3Mn 2+ + NO2 - + 4H2O]]> (1) <![CDATA[4MnO2 + NH4 + + 6H + → 4Mn 2+ + NO3 - + 5H2O]]> (2) <![CDATA[3MnO2+ 2NH4 + + 4H + → 3Mn 2+ + N2+ 6H2O]]> (3) <![CDATA[2NO3 - + 5Mn 2+ + 4H2O → N2+ 5MnO x + 8H + > (4)

[0007] Currently, the following problems exist in the manganese-rich deep denitrification purification materials: ① Most manganese oxides are poorly soluble substances, and the utilization degree of high-valent manganese by manganese autotrophic denitrifying bacteria is limited. The reaction kinetics rate is slow, so the residence time required in the anaerobic bioreactor usually needs to reach more than 7 days, affecting the overall denitrification efficiency. Therefore, how to improve the biological utilization degree of high-valent manganese through packing modification and shorten the hydraulic residence time is the key technical problem that urgently needs to be solved in the denitrification process based on manganese-rich packing. ② During the use of manganese oxides, crusting problems will occur due to surface passivation, resulting in incomplete manganese cycling and reduced efficiency; how to continuously generate manganese bio-oxides with a larger specific surface area and higher activity in the bioreactor is the key technical problem that urgently needs to be solved to maintain the manganese oxidation-manganese reduction balance, realize manganese cycling, and drive nitrogen conversion for a long time in the bioreactor based on manganese-rich packing.

[0008] Carbon materials are excellent mediators for electron transfer. Adding carbon materials can improve the electron transfer efficiency of the manganese oxidation-reduction process. This type of manganese-carbon composite material is mainly prepared by direct chemical synthesis methods such as high-temperature and high-pressure grafting. For example, Patent Application CN110416530B discloses a flower-like manganese dioxide / carbon composite material, its preparation method and application, and Patent No. CN104392849B discloses a preparation method of a manganese dioxide / carbon composite material, belonging to the field of secondary batteries. Similarly, Patent No. CN115650302B discloses a novel manganese oxide-carbon composite material with a branched structure and its preparation method, in which the manganese oxide colloid prepared by chemical reagents is hermetically heated and in-situ grafted onto the surface of the carbon material to form a composite material. Theoretically, this type of composite material can utilize the carbon component to enhance extracellular electron transfer during the denitrification process and improve the electron utilization rate of denitrifying microorganisms. However, in the process of this type of composite material used to improve battery activity, the selected carbon materials are commercial high-conductivity carbon materials such as activated carbon, carbon nanotubes, graphene, acetylene black ACEF, conductive carbon black Super P, Ketjen black EC-300J, or Cabot black, etc. Their raw material costs are high, and they hardly have the ability to act as a denitrifying carbon source.

[0009] Natural plant carbon sources can be used as the growth substrate of autotrophic denitrifying bacteria and the trigger for nitrogen conversion and metabolism. Coupling heterotrophic denitrification and autotrophic denitrification can achieve deep denitrification treatment of low-carbon-nitrogen ratio wastewater. Patent Application No. CN118702273A discloses MnO x-Slow-release carbon source combined with enhanced deep denitrification filler for low C / N sewage and its preparation method, but the slow-release solid carbon therein is only the sodium hydroxide modification of crushed agricultural waste, and the technical means for enhancing the deep denitrification of low C / N sewage is the simple combination of MnO x and slow-release carbon source. This will cause the following problems: ① Alkali modification mainly controls the initial carbon release rate by partially eliminating dissolved organic matter, but has limited impact on the stability and sustainability of the carbon release process; ② The electron transfer and mass transfer efficiency between manganese filler and carbon filler are insufficient, and manganese reduction, carbon decomposition, heterotrophic and autotrophic denitrification are not unified in time and space, making it difficult to achieve synergistic denitrification; ③ A large amount of H + is produced by the hydrolysis and fermentation of plant carbon source by microorganisms, and manganese autotrophic denitrification is also an acid production process, which makes the pH in the anaerobic bioreactor unstable and reduces the biochemical activity of denitrifying microorganisms. Therefore, similar studies only focus on the denitrification functions of manganese-rich materials and carbon materials respectively, and the great potential of using manganese-carbon composite materials to regulate the carbon release process and manganese cycle process has not been explored, lacking overall consideration of the manganese-carbon composite denitrification process.

[0010] In recent years, some studies have also melt-compounded synthetic carbon sources with manganese oxides. For example, Patent No. CN116239224B discloses an artificial wetland composite material, its preparation method and application, and proposes to compound manganese oxides with the biodegradable solid carbon material polycaprolactone for denitrification in artificial wetlands. However, in the application process, it is found that the dosage of polycaprolactone is large, the price is expensive, the chemical composition is single, and the microbial film formation time is long. Patent No. CN103157435B discloses a preparation method of a microbial-based manganese-carbon composite material, which is prepared by generating secondary manganese oxide by manganese-oxidizing bacteria in a carbon-rich medium (yeast extract, peptone, agar) and then activating it. However, the microbial culture period is long, the yield is low, and the material needs to be activated at high temperature before use, making it difficult to be applied on a large scale. Moreover, such composite materials mainly remove pollutants through physical and chemical actions such as adsorption, and the adsorption capacity is limited.

[0011] Therefore, it is very necessary to develop a manganese-carbon composite controlled-release material with low raw material cost, simple preparation method and sustainability for denitrification of low carbon-nitrogen ratio wastewater. Summary of the Invention

[0012] In order to solve the problems of the existing technology, the present invention provides a manganese-carbon composite controlled-release material, its preparation method and application. The manganese-carbon composite controlled-release material of the present invention optimizes the organic / inorganic electron donor ratio to regulate the release rate, enhances the denitrification efficiency and stability of the system, realizes synchronous denitrification and phosphorus removal and adaptive continuous denitrification, and has excellent denitrification and phosphorus removal performance.

[0013] The object of the present invention is to provide a manganese-carbon composite controlled-release material, which comprises the following components: manganese-rich minerals, natural carbon sources, gelling materials, aggregates, additives and foaming agents.

[0014] The mass ratio of manganese-rich minerals: natural carbon sources: gelling materials: aggregates: additives is 40-100: 4-10: 40-100: 40-60: 20-60.

[0015] The dosage of the foaming agent is 0.015%-0.2% of the sum of the masses of manganese-rich minerals, natural carbon sources, gelling materials, aggregates and additives.

[0016] The mass of the manganese-rich minerals accounts for 20%-35% of the mass of all components, and the mass of the natural carbon sources accounts for 1.5%-5.0% of the mass of all components.

[0017] Among them, the particle size of the natural carbon source is 20-200 mesh, and the particle size of the manganese-rich minerals is 20-200 mesh.

[0018] The manganese-carbon composite controlled-release material of the present invention optimizes the ratio of organic / inorganic electron donors, realizes the regulation of the carbon release rate and the manganese cycle process by means of the interaction between manganese and carbon, enhances the denitrification efficiency and stability of the system; significantly improves the electron transfer and mass transfer efficiency, realizes the synergistic denitrification of manganese reduction, carbon decomposition, heterotrophic and autotrophic denitrification, improves the denitrification efficiency, has more stable carbon release performance and better denitrification effect; the carbon release process has better stability and sustainability, improves the utilization rate of manganese oxides, is easy for microorganisms to attach to the film, and shortens the hydraulic retention time.

[0019] Furthermore, the above natural carbon source is obtained by alkali pretreatment. The pretreatment conditions are as follows: pretreatment is carried out with a sodium hydroxide solution with a concentration of 0.2-0.5M, the solid-liquid ratio of the natural carbon source to the sodium hydroxide solution is 1:5-10, the soaking time is 16-48h, the soaking temperature is 20-40°C, the number of water washing times is ≥3, the drying temperature is 40-60°C, and the drying time is 12-48h. After the natural carbon source is treated with alkali, the crystal structure between lignin and hemicellulose can be broken, and the bioavailability can be improved.

[0020] Preferably, the natural carbon source includes at least one of plant waste and wetland plant residues. The plant waste includes at least one of wheat straw, rice straw, reed and corncob. The wetland plants include at least one of reed, scirpus validus and Spartina alterniflora.

[0021] Preferably, the manganese-rich minerals include at least one of natural manganese sand, pyrolusite, psilomelane and rhodochrosite.

[0022] In the present invention, the cementitious material includes at least one of cement, silicate material, and synthetic resin. The alkalinity generated by cementitious materials such as cement neutralizes the acidity generated during the hydrolysis of natural carbon sources and the autotrophic denitrification process, and the pH stability is high. The aggregate includes at least one of coarse sand, gravel sand, angular gravel, crushed stone, and limestone.

[0023] The additive includes at least one of steel slag, fly ash, attapulgite, gypsum, bentonite, and diatomaceous earth. Steel slag can be used to improve the strength and durability of the composite material, and can also endow the composite material with certain electrical conductivity. At the same time, the steel slag contains Ca 2+ 、Mg 2+ 、Al 3+ ions that can form precipitates with PO4 3- to enhance the phosphorus removal performance of the composite material.

[0024] In addition, components such as cement, gypsum, and fly ash contain a large amount of calcium and magnesium ions, which can effectively adsorb and precipitate phosphorus, and can also neutralize the acidity generated during processes such as hydrolysis and fermentation, enhancing the pH stability of the system.

[0025] Preferably, the foaming agent includes at least one of carbonate inorganic foaming agents, rosin soap foaming agents, animal and plant protein foaming agents, and pulp waste liquor.

[0026] The present invention also aims to provide a preparation method of the above-mentioned manganese-carbon composite controlled-release material, including the following steps:

[0027] (1) Mix the above-mentioned manganese-rich mineral, natural carbon source, cementitious material, aggregate, and additive evenly according to the above ratio to obtain a mixed material;

[0028] (2) Spray a foaming agent dilution with a foaming agent content of 0.05wt%-0.5wt% on the surface of crushed stone particles with a particle size of 2-6 mm, add them to a drum granulator, start the drum granulator, pour the mixed material obtained in step (1) into the drum granulator, and intermittently spray a certain amount of water during the rolling process to obtain manganese-carbon composite particles with a particle size of 3-10 mm. After taking out the manganese-carbon composite particles from the drum granulator, naturally cure them for 3-7 days to obtain an agglomerated and coated manganese-carbon composite controlled-release material.

[0029] Preferably, the mass ratio of the above-mentioned manganese-rich mineral, natural carbon source, cementitious material, aggregate, and additive is 40-100:5-10:50-80:40-60:26-50.

[0030] The present invention also aims to provide another preparation method of a manganese-carbon composite controlled-release material, including the following steps:

[0031] (1) Mix the above-mentioned manganese-rich mineral, natural carbon source, cementitious material, aggregate, and additive evenly according to the ratio to obtain a mixed material;

[0032] (2) Add a foaming agent diluent with a foaming agent content of 0.05 wt% - 0.5 wt% to the mixed material obtained in step (1), stir until it becomes viscous, air-dry for 1 - 3 days, cure at a temperature of 15 - 25 °C for 7 - 15 days. During curing, spray a certain amount of water every 1 - 2 days, and finally obtain the coagulation-cured manganese-carbon composite controlled-release material after mechanical crushing.

[0033] Preferably, the mass ratio of the above-mentioned manganese-rich mineral, natural carbon source, cementitious material, aggregate, and additive is 60 - 80:4 - 10:40 - 60:40 - 60:30 - 60.

[0034] The foaming agent in the present invention needs to be diluted into a foaming agent diluent with a mass fraction of 0.05% - 0.5% before use. By changing the mass fraction of the foaming agent in the preparation process, the pores, specific surface area, and density of the material can be regulated, and thus the carbon release rate can be regulated.

[0035] The specific surface area of the manganese-carbon composite controlled-release material of the present invention is 300 - 400 m 2 / kg.

[0036] Another object of the present invention is that the above-mentioned manganese-carbon composite controlled-release material is applied to the fillers in constructed wetlands, biological filters, and the submerged areas of bioretention systems.

[0037] Another object of the present invention is that the above-mentioned manganese-carbon composite controlled-release material is applied to the treatment of the tail water of sewage treatment plants, rural domestic sewage, farmland non-point source treatment, and the purification of initial rainwater.

[0038] For the manganese-carbon composite controlled-release material of the present invention, appropriate preparation raw material ratios and filling methods are selected according to the water quality and quantity characteristics of the tail water of sewage treatment plants, farmland return water, and initial rainwater, which have pertinence and flexibility. It has excellent nitrogen and phosphorus removal performance as a filler for biological filters in tail water treatment. Compared with the biological filter with inert fillers, the removal rate is increased by more than 70% when the residence time is 1 day.

[0039] The present invention also provides a preparation method of a manganese-carbon controlled-release material composite porous plate. Use P20 or P20 + Ni type steel as the mold. The length of the mold is 160 - 200 cm, the length-width ratio is 5:3 - 16:9, the bottom thickness of the mold is 3 - 5 cm, the edge thickness is 25 - 30 cm, and the edge width is 5 - 10 cm. Cylinders with a diameter of 15 - 25 cm and a height of 8 - 12 cm are evenly arranged in the mold at intervals of 8 - 10 cm. For the above-mentioned manganese-carbon controlled-release material, add water according to a solid-liquid mass ratio of 1.5 - 2:1, stir evenly and then inject it into the mold. The depth of the slurry is 15 - 20 cm. After air-drying and forming, demold to form the manganese-carbon controlled-release material composite porous plate.

[0040] The present invention also provides an application of the above-mentioned manganese-carbon controlled-release material composite porous plate. Anchor piles are pre-constructed in the constructed wetland, with a spacing of 100-115 cm between piles. Openings are provided around the anchor piles, with a depth of 20-23 cm. The manganese-carbon controlled-release material composite porous plate is inserted into the openings of the anchor piles in a mortise-tenon manner to form a functional constructed wetland based on the manganese-carbon controlled-release material.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) In the manganese-carbon composite controlled-release material of the present invention, the manganese component enhances the stability and sustainability of carbon release. The manganese oxides in the manganese-rich minerals have strong oxidizing properties and can oxidize the refractory organic matter in the plant carbon source into small molecular organic matter that is easily utilized by denitrifying microorganisms, improving the effectiveness of the plant-derived carbon source and promoting the degradation and utilization of the residual carbon source in low-pollution water. Manganese ions dissolve out from the composite material, promoting the erosion of the carbon skeleton, which is beneficial for rapid film formation on the composite material in the early stage of the reaction and promoting the release of the carbon source inside the composite material in the later stage of the reaction. The intermediate products (such as proteins) decomposed from the plant carbon source combine with manganese to form manganese oxide-organic matter complexes, which can buffer the process of organic carbon release and improve the stability and sustainability of carbon source release;

[0043] (2) The manganese-carbon coupling in the present invention effectively prevents the failure of the manganese-rich functional material caused by surface passivation. The formation of manganese oxide-organic matter complexes can change the dense morphology of the surface oxide layer, alleviate the surface passivation and crusting problems of the high-valent manganese on the interface during the reaction of the manganese-rich minerals, and improve its solubility and reaction activity;

[0044] (3) The lignin in plant waste is rich in semi-quinone structures and can act as an electron shuttle. The multivalent manganese in the manganese-rich minerals can also mediate electron transfer through redox cycles. Both can improve the utilization of organic carbon sources by microorganisms and the denitrification efficiency. The manganese-rich minerals themselves can drive biological denitrification processes such as manganese ammonia oxidation and nitrate-dependent manganese oxidation, and can also remove ammonia nitrogen through processes such as adsorption and chemical oxidation. Its denitrification path is diverse, the denitrification power is sufficient, and the start-up time is short;

[0045] (4) The manganese-carbon composite material realizes synchronous denitrification and phosphorus removal and adaptive continuous denitrification. In the early stage of operation, the gelling material wrapped around the manganese-carbon delays the release of the internal organic carbon source through physical action, avoiding excessive carbon release and secondary pollution caused by the process of dissimilatory nitrate reduction to ammonium (DNRA), and improving the controllability of the heterotrophic denitrification process. During the use process, the interaction between manganese and carbon buffers the release rate of the organic electron donor and enhances the dissolution of the inorganic electron donor. In the face of different carbon-nitrogen ratio environments, microorganisms adaptively utilize organic / inorganic electron donors to achieve multi-electron donor synergistic denitrification. In the late stage of operation, the refractory components of the natural carbon source can be used as carbon sources or electron shuttles. Under the condition of sufficient carbon source in the wastewater, the composite material mediates the decomposition of the organic carbon source and heterotrophic denitrification as an electron shuttle. Under the condition of a low carbon-nitrogen ratio, microorganisms utilize the chelated manganese-carbon components derived from the composite material as energy and electron donors, and cooperate with the bio-manganese oxides generated by the previous biochemical reactions for denitrification, improving the denitrification efficiency.

[0046] (5) Components such as cement, gypsum, and fly ash in the gelling material and additives contain a large amount of calcium and magnesium ions, which can effectively adsorb and precipitate phosphorus. The alkalinity generated by gelling materials such as cement neutralizes the acidity generated during the hydrolysis of plant carbon sources and autotrophic denitrification processes, with high pH stability.

[0047] (6) The manganese-carbon composite controlled-release material of the present invention has the characteristics of a large specific surface area, controllable density, and easy microbial film formation. It can continuously produce bio-manganese oxides with relatively high activity, maintain the manganese oxidation-manganese reduction balance, realize manganese cycling, and drive nitrogen conversion for a long time, significantly improving the overall efficiency of the denitrification process. While improving the denitrification performance of low-pollution water, it also extends the service life of the material.

[0048] In summary, the manganese-carbon composite controlled-release material of the present invention optimizes the controlled carbon release process and manganese cycling process, realizes the regulation of the carbon release rate and manganese cycling process through the interaction between manganese and carbon, significantly improves the overall denitrification efficiency, realizes synchronous denitrification and phosphorus removal and adaptive continuous denitrification. The raw materials required for preparing the manganese-carbon composite controlled-release material are all environmentally friendly and inexpensive, its preparation process is simple, the preparation cost is low, and the resource utilization of waste fiber materials is realized. It can be widely applied to application scenarios such as the advanced treatment of the tail water of sewage treatment plants, the treatment of rural agricultural sewage, and the purification of initial rainwater. Description of the Drawings

[0049] Figure 1 is the product drawing of the manganese-carbon composite controlled-release material;

[0050] Figure 2 is the denitrification test result of the micro anaerobic bottle;

[0051] Figure 3 is the denitrification performance of the biological filter reaction column;

[0052] Figure 4 Schematic diagram of nitrogen conversion process in constructed wetland based on manganese-carbon composite material;

[0053] Figure 5 Schematic diagram of preparation mold structure of manganese-carbon controlled-release material composite porous plate;

[0054] Figure 6 Installation method of manganese-carbon controlled-release material composite porous plate in constructed wetland. Specific implementation manners

[0055] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0056] The embodiments of the present invention use modified plant waste as a natural carbon source, crushed natural manganese-rich ore as an inorganic electron donor, use cement, limestone, etc. as inorganic binders and pH regulators, and plant fiber and its protein-based slurry as pore-forming agents.

[0057] Plant waste includes wheat straw, rice straw, reed, corn cob, etc., which are crushed and used as carbon-rich substrates. The pretreatment process of plant waste includes: putting the plant waste into a crusher for crushing and sieving, then soaking it in a sodium hydroxide solution, washing it repeatedly with water and drying it, and storing it sealed at room temperature. The purpose is to break the crystal structure between lignin and hemicellulose and improve bioavailability.

[0058] The conditions for pretreatment of plant waste are: crushing particle size of 20-200 mesh, concentration of sodium hydroxide solution of 0.2-0.5 M, solid-liquid ratio of 1:5-10, soaking time of 16-48 h, soaking temperature of 20-40 °C, number of water washing times ≥ 3, drying temperature of 40-60 °C, and drying time of 12-48 h.

[0059] Manganese-rich minerals include manganese sand, rhodochrosite, birnessite, etc., which are crushed and used as manganese-rich substrates. The pretreatment process and conditions of manganese-rich minerals are: putting the purchased manganese-rich mineral materials into a crusher for crushing, with a particle size of 20-200 mesh.

[0060] Aggregates include inert particles such as coarse sand, gravel sand, angular gravel, crushed stone, limestone, etc.

[0061] Cementitious materials include inorganic binders such as cement and fly ash, which are used for granulation bonding.

[0062] Foaming agents include inorganic foaming agents such as carbonates or rosin soaps, organic foaming agents such as animal and plant protein-based foaming agents, and pulp waste liquor, which are used for foaming and pore formation.

[0063] Mix the pretreated plant waste, manganese-rich material and the above components in a certain proportion, and granulate by the drum coating method or the agglomeration-crushing method.

[0064] Prepare the agglomerated coated manganese-carbon composite controlled-release material by the drum granulation method. Specifically, mix the manganese-rich material, plant carbon source powder, cement, aggregates such as gravel sand, additives (fly ash, steel slag, attapulgite, gypsum, etc.) in a mass ratio of 40-100:5-10:50-80:40-60:26-50, stir evenly to obtain a mixed material; spray a foaming agent dilution solution with a foaming agent content of 0.05%-0.5% on the surface of gravel particles with a particle size of 2-6 mm, and add it to a drum granulator; start the granulator containing gravel, slowly pour the mixed material into it, and intermittently spray a certain amount of water during the rolling process to obtain manganese-carbon composite particles with a particle size of 3-10 mm; after taking out the manganese-carbon composite particles from the drum granulator, cure them naturally for 3-7 days to obtain the agglomerated coated manganese-carbon composite material.

[0065] Prepare the coagulation-cured manganese-carbon composite controlled-release material by the cement agglomeration method. Specifically, mix the manganese-rich material, plant carbon source powder, ordinary Portland cement, aggregates such as gravel sand, additives (powder of non-metallic mineral materials such as fly ash, steel slag, gypsum, bentonite and diatomite) in a mass ratio of 60-80:4-10:40-60:40-60:30-60, stir evenly to obtain a mixed solid material; add an aqueous solution with a foaming agent content of 0.05%-0.5% and accounting for 30%-40% of the total mass of the mixed solid material, stir until it is viscous, and air dry for 1-3 days; cure at a temperature of 15-25 °C for 7-15 days, and spray a certain amount of water every 1-2 days during curing. Finally, obtain the coagulation-cured manganese-carbon composite controlled-release material after mechanical crushing.

[0066] Example 1 Preparation of the agglomerated coated manganese-carbon composite controlled-release material

[0067] S1. Mix the crushed natural manganese sand powder, corn cob powder, ordinary Portland cement, coarse sand or gravel sand, steel slag, fly ash, and gypsum in a mass ratio of 40:8:80:40:10:10:10, stir evenly to obtain a mixed material;

[0068] S2. Spray a plant protein-based foaming agent dilution solution with a content of 0.5 wt% on the surface of gravel particles with a particle size of 3-5 mm, and add it to a drum granulator;

[0069] S3. Start the granulator containing gravel, roll at a speed of 20 rpm / min, use an electric sprayer to spray 1 mL of water every 3 seconds, and slowly pour the mixed material into it after each water spraying to obtain manganese-carbon composite particles with a particle size of 3-7 mm;

[0070] S4. After taking out the manganese-carbon composite particles from the drum granulator, cure them naturally for 7 days to obtain the agglomerated and coated manganese-carbon composite controlled-release material MC1, as Figure 1 shown.

[0071] Example 2 Preparation of the agglomerated and coated manganese-carbon composite controlled-release material

[0072] S1. Mix the pulverized natural manganese sand powder, corn cob powder, ordinary Portland cement, coarse sand or gravel sand, steel slag, fly ash, and gypsum in a mass ratio of 60:8:60:40:10:10:10, and stir evenly to obtain a mixed material;

[0073] S2. Spray a dilution of a plant protein-based foaming agent with a content of 0.5 wt% on the surface of gravel particles with a particle size of 3-5 mm, and add them to a drum granulator;

[0074] S3. Start the granulator containing gravel, roll it at a speed of 20 rpm / min, use an electric sprayer to spray 1 mL of water every 3 seconds, and slowly pour the mixed material into it after each water spraying to obtain manganese-carbon composite particles with a particle size of 3-7 mm;

[0075] S4. After taking out the manganese-carbon composite particles from the drum granulator, cure them naturally for 7 days to obtain the agglomerated and coated manganese-carbon composite material MC2, as Figure 1 shown.

[0076] Example 3 Preparation of the coagulated and solidified manganese-carbon composite controlled-release material

[0077] S1. Mix the pulverized natural manganese sand powder, corn cob powder, ordinary Portland cement, coarse sand or gravel sand, steel slag, bentonite, and gypsum in a mass ratio of 80:8:60:60:10:35:5, and stir evenly to obtain a mixed solid material;

[0078] S2. Add an aqueous solution with a plant protein-based foaming agent content of 0.5 wt% and accounting for 35% of the total mass of the mixed solid material, stir until it becomes viscous, and air-dry for 3 days;

[0079] S3. Cure for 7 days at a temperature of 15-25 °C, and spray a certain amount of water every 1-2 days during the curing;

[0080] S4. Finally, obtain the coagulated and solidified manganese-carbon composite material MC3 after mechanical crushing, as Figure 1 shown as MC3.

[0081] Example 4 Preparation of the coagulated and solidified manganese-carbon composite controlled-release material

[0082] S1. Mix the natural manganese sand powder, corncob powder, ordinary Portland cement, coarse sand or gravel sand, steel slag, bentonite or diatomite, and gypsum obtained after crushing according to a mass ratio of 80:4:60:60:10:35:5, and stir evenly to obtain a mixed solid material;

[0083] S2. Add an aqueous solution with a plant protein-based foaming agent content of 0.5 wt% and accounting for 40% of the total mass of the mixed solid material, stir until it becomes viscous, and air-dry for 3 days;

[0084] S3. Cure for 7 days at a temperature of 15 - 25 °C, and spray a certain amount of water every 1 - 2 days during curing;

[0085] S4. Obtain the coagulation and solidification type manganese-carbon composite material MC4 through mechanical crushing, as shown in Figure 1 MC4 shown.

[0086] Application Example 1

[0087] Fill 100 g of the manganese-carbon composite controlled-release materials MC1, MC2, MC3, and MC4 prepared in the above examples into four 250 mL micro anaerobic bottles, and add 200 mL of synthetic wastewater. The NO3 - -N concentration in the synthetic wastewater is about 30 mg / L, and the sludge concentration MLVSS is about 200 mg / L. Let it stand for 3 days to allow microorganisms to form a biofilm, and drain the remaining solution. Re-prepare new synthetic wastewater without activated sludge and with a NO3 - -N concentration of about 30 mg / L and add it to the above four 250 mL micro anaerobic bottles. The hydraulic retention time is 3 days. Take samples to test the NO3 - -N concentration in the effluent. The denitrification test results of the manganese-carbon composite controlled-release materials MC1, MC2, MC3, and MC4 in the micro anaerobic bottles are as shown in Figure 2 shown. It can be seen from Figure 2 that the nitrate nitrogen removal rates of the manganese-carbon composite controlled-release materials MC1, MC2, MC3, and MC4 are all greater than 75%.

[0088] Application Example 2

[0089] Fill the manganese-carbon composite controlled-release materials MC3 and MC4 into a reaction column with a diameter of 10 cm and a height of 50 cm, inoculate activated sludge with an MLVSS of about 300 mg / L, and let it stand for three days to allow microorganisms to form a biofilm. Another blank control group CK is set up, filled with gravel inert fillers of the same particle size.

[0090] Prepare a solution containing NO3 - -N concentration of about 30 mg / L and PO4 3-Synthetic wastewater with a -P concentration of approximately 3.0 mg / L, along with the addition of other macro and trace elements, including 61.0 mg / L of MgCl2·6H2O, 33.2 mg / L of CaCl2, 0.03 mg / L of CuSO4·5H2O, 10.8 mg / L of ZnSO4·7H2O, 0.25 mg / L of NaMoO4·2H2O, 0.025 mg / L of CoCl2·6H2O, and 6.2 mg / L of H3BO3. These macro and trace elements are the main elements of cell components and enzymes and are crucial for the formation of cell structures and the maintenance of enzyme activity. These macro and trace elements are to ensure the normal growth and metabolism of microorganisms, construct and maintain a stable biofilm, and enhance the efficiency and stability of biochemical reactions.

[0091] Domestication and cultivation were carried out for 3 cycles with a hydraulic retention time (HRT) of 3 days. After domestication and cultivation, it entered the operation period with a hydraulic retention time of 2 days, and it continued to operate for 3 cycles. Samples were taken at different time points during each cycle to test the effluent NO3 - -N concentration. The average effluent NO3 - -N concentration is as Figure 3 shown.

[0092] When the hydraulic retention time was 24 h, the nitrate removal rates of MC3 and MC4 were 90.0% and 72.8% respectively; when the hydraulic retention time was 40 h, the nitrate nitrogen removal rates of MC3 and MC4 both reached over 94%, while the removal rate of the control group was almost zero. This indicates that without adding any liquid carbon source, relying on the manganese-carbon composite material can significantly promote the denitrification process and efficiently remove NO3 - -N.

[0093] Application Example 3 Nitrogen transformation process in constructed wetland based on manganese-carbon composite controlled-release material

[0094] The nitrogen transformation process in the constructed wetland based on the manganese-carbon composite controlled-release material of the present invention is as Figure 4 shown. The manganese-carbon composite controlled-release material contains the main active components manganese oxide and plant carbon source. In the aerobic zone of the constructed wetland, ammonia nitrogen can be oxidized by MnO in the composite material or transformed into nitrate nitrogen under the action of nitrifying bacteria. In the anaerobic and anoxic zones of the constructed wetland, the plant carbon source releases a certain amount of dissolved organic matter (DOM), which is degraded into small molecule organic carbon sources under the action of manganese oxide and microorganisms, promoting heterotrophic denitrification; the reduced manganese generated by the reduction of manganese oxide serves as an electron donor for denitrifying bacteria, driving manganese autotrophic denitrification; during the biochemical process, the reduced manganese is re-oxidized to form bio-manganese oxide (BMO). On the one hand, it can serve as an electron acceptor for ammonia oxidation and promote the removal of ammonia nitrogen through chemical catalytic oxidation or manganese ammonia oxidation (Mnammox). On the other hand, it can combine with intermediate organic acids decomposed from the plant carbon source to form MnO x and so on. x- The organic complex, as an electron reserve carrier, prolongs the release time of the electron donor and ensures sustainable denitrification.

[0095] During the use of the manganese-carbon composite controlled-release material of the present invention, the proportion of the organic / inorganic electron donor can be adjusted by adjusting the mass fractions of manganese and carbon in the composite material, so as to further control the denitrification performance of the filler for wastewater under different nitrogen loads and carbon-nitrogen ratios.

[0096] Application Example 4

[0097] The coagulation-cured manganese-carbon composite controlled-release material prepared according to Example 3 or 4 is made into a manganese-carbon controlled-release material composite porous plate and applied to the constructed wetland.

[0098] Use P20 or P20+Ni type steel as the mold. The length of the mold is 160-200 cm, the length-width ratio is 5:3-16:9, the bottom thickness of the mold is 3-5 cm, the edge thickness is 25-30 cm, and the edge width is 5-10 cm. Cylinders with a diameter of 15-25 cm and a height of 8-12 cm are evenly arranged in the mold at intervals of 8-10 cm. During use, add materials according to the component ratio of the coagulation-cured manganese-carbon composite controlled-release material prepared in Example 3 or 4, add water according to the solid-liquid mass ratio of 1.5-2:1, stir evenly and then inject into the mold. The depth of the slurry is 15-20 cm. After air-drying and forming, demold to form a manganese-carbon controlled-release material composite porous plate. The structure of the mold for preparing the manganese-carbon controlled-release material composite porous plate is as Figure 5 shown.

[0099] Anchoring piles are pre-constructed in the constructed wetland. The distance between the piles is 100-115 cm. The periphery of the anchoring piles is open, and the opening depth is 20 cm. During use, insert the prefabricated manganese-carbon controlled-release material composite porous plate into the opening of the anchoring pile in a "mortise and tenon" manner to form a functional constructed wetland based on the manganese-carbon controlled-release material. The installation method of the manganese-carbon controlled-release material composite porous plate in the constructed wetland is as Figure 6 shown. Nitrogen and phosphorus pollutants in the water body are efficiently removed by contacting the manganese-carbon controlled-release material composite porous plate. This constructed wetland can achieve efficient denitrification and phosphorus removal, and the manganese-carbon controlled-release material composite porous plate can be assembled or replaced according to needs. It has the characteristics of low cost, simple installation and convenient maintenance.

[0100] In summary, the raw materials required for preparing the manganese-carbon composite controlled-release material of the present invention are all environmentally friendly and inexpensive. The preparation process is simple, the preparation cost is low, and the resource utilization of waste fiber materials is realized. The manganese-carbon composite controlled-release material of the present invention optimizes the ratio of organic / inorganic electron donors to control the release rate, enhances the denitrification efficiency and stability of the system, significantly improves the electron transfer and mass transfer efficiency, realizes synergistic denitrification, has excellent denitrification and phosphorus removal performance, more stable carbon release performance, and better stability and sustainability for the carbon release process.

[0101] The above embodiments are only for illustrating the present invention and not for limiting the present invention. Those skilled in the relevant technical fields can also make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also fall within the scope of the present invention, which should be defined by each claim.

Claims

1. A manganese-carbon composite controlled-release material for denitrification, characterized in that, It includes the following components: manganese-rich minerals, natural carbon sources, cementitious materials, aggregates, additives, and foaming agents; The mass ratio of the manganese-rich minerals, natural carbon sources, cementitious materials, aggregates, and additives is 40 - 100:4 - 10:40 - 100:40 - 60:20 - 60; The dosage of the foaming agent is 0.015% - 0.2% of the sum of the masses of the manganese-rich minerals, natural carbon sources, aggregates, cementitious materials, and additives; The mass of the manganese-rich minerals accounts for 20% - 35% of the total mass of all components, and the mass of the natural carbon source accounts for 1.5% - 5.0% of the total mass of all components; Among them, the particle size of the natural carbon source is 20 - 200 mesh, and the particle size of the manganese-rich minerals is 20 - 200 mesh; The natural carbon source is obtained through alkali pretreatment. The pretreatment conditions are as follows: pretreatment is carried out using a sodium hydroxide solution with a concentration of 0.2 - 0.5 M. The solid-liquid ratio of the natural carbon source to the sodium hydroxide solution is 1:5 - 10, the soaking time is 16 - 48 h, the soaking temperature is 20 - 40 °C, the number of water washing times is ≥ 3, the drying temperature is 40 - 60 °C, and the drying time is 12 - 48 h; The natural carbon source includes at least one of agricultural waste and wetland plant residues; The manganese-rich minerals include at least one of natural manganese sand, pyrolusite, psilomelane, and rhodochrosite; The cementitious materials include at least one of cement and synthetic resins, the aggregates include at least one of coarse sand, gravel sand, angular gravel, crushed stone, and limestone, and the additives include at least one of steel slag, fly ash, attapulgite, gypsum, bentonite, and diatomite; The specific surface area of the manganese-carbon composite controlled-release material is 300 - 400 m 2 / kg; The preparation method of the manganese-carbon composite controlled-release material is obtained by the first preparation method or the second preparation method. The first preparation method of the manganese-carbon composite controlled-release material includes the following steps: (1) Mix the manganese-rich minerals, natural carbon sources, cementitious materials, aggregates, and additives evenly according to the ratio to obtain a mixed material; (2) Spray a foaming agent dilution solution with a foaming agent content of 0.05 wt% - 0.5 wt% on the surface of crushed stone particles with a particle size of 2 - 6 mm, add them to a drum granulator, start the drum granulator, pour the mixed material obtained in step (1) into it, and intermittently spray water during the rolling process to obtain manganese-carbon composite particles with a particle size of 3 - 10 mm, and naturally cure for 3 - 7 days to obtain an agglomerated and coated manganese-carbon composite controlled-release material; The second preparation method of the manganese-carbon composite controlled-release material includes the following steps: (1) Mix the manganese-rich minerals, natural carbon sources, cementitious materials, aggregates, and additives evenly according to the ratio to obtain a mixed material; (2) Add a foaming agent dilution solution with a foaming agent content of 0.05 wt% - 0.5 wt% to the mixed material obtained in step (1), stir until it becomes viscous, air dry for 1 - 3 days, cure at a temperature of 15 - 25 °C for 7 - 15 days, spray water every 1 - 2 days during curing, and finally obtain a coagulated and solidified manganese-carbon composite controlled-release material after mechanical crushing.

2. The manganese-carbon composite controlled-release material according to claim 1, wherein When the preparation method is the first preparation method, the mass ratio of the manganese-rich minerals, natural carbon sources, cementitious materials, aggregates, and additives is 40 - 100:5 - 10:50 - 80:40 - 60:20 - 50.

3. The manganese-carbon composite controlled release material according to claim 1, characterized in that The preparation method is the second preparation method, and the mass ratio of the manganese-rich mineral, natural carbon source, gelling material, aggregate, and additive is 60-80:4-10:40-60:40-60:30-60.

4. Application of the manganese-carbon composite controlled-release material according to any one of claims 1-3, wherein the manganese-carbon composite controlled-release material is applied to the fillers in the submerged areas of constructed wetlands, biological filters, and bioretention systems, and the purification treatment of the tail water of sewage treatment plants, rural domestic sewage, farmland non-point source pollution, and initial rainwater.

5. A preparation method of a manganese-carbon composite controlled-release material composite porous plate, characterized in that, P20 or P20+Ni steel is used as the mold. The length of the mold is 160-200 cm, the length-width ratio is 5:3-16:9, the bottom thickness of the mold is 3-5 cm, the edge thickness is 25-30 cm, and the edge width is 5-10 cm. Cylinders with a diameter of 15-25 cm and a height of 8-12 cm are evenly arranged in the mold at intervals of 8-10 cm. The components of the manganese-carbon composite controlled-release material are added according to the ratio claimed in claim 3, water is added according to the solid-liquid mass ratio of 1.5-2:1, and after stirring evenly, it is poured into the mold. The depth of the slurry is 15-20 cm. After air drying and forming, it is demolded to form a manganese-carbon composite controlled-release material composite porous plate.

6. Use of a composite porous plate of a manganese-carbon composite controlled-release material prepared by the preparation method according to claim 5, characterized in that, Anchoring piles are pre-constructed in the constructed wetland, and the distance between the piles is 100-115 cm. Openings are provided around the anchoring piles, and the depth of the openings is 20-23 cm. The manganese-carbon composite controlled-release material composite porous plate is tenon-mortised into the openings of the anchoring piles to form a functional constructed wetland based on the manganese-carbon composite controlled-release material.

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