Dual-reservoir composite slow-release carbon source, preparation method and application thereof

Abstract

The application discloses a double-library composite slow-release carbon source and a preparation method and application thereof, and belongs to the technical field of water treatment and biological denitrification. The double-library composite slow-release carbon source comprises first modified rice husks, second modified rice husks, modified biochar, a calcium-containing component, ferroferric oxide and an additive; the first modified rice husks are prepared from first rice husks through first alkali-oxidation composite modification and first water pre-extraction; the second modified rice husks are prepared from second rice husks through second alkali-oxidation composite modification and second water pre-extraction; the first modified rice husks have a faster organic carbon release speed than the second modified rice husks; and the modified biochar comprises biochar loaded with rice husk homologous easily soluble organic carbon. The application constructs a fast-release carbon library and a slow-release carbon library by using rice husks with different modification degrees, loads the easily soluble organic carbon in the water pre-extraction solution of the rice husks on the biochar, and compounding the calcium-containing component, the ferroferric oxide and the additive, so that the fast-release and slow-release carbon are provided in cooperation, and the coordination of water treatment denitrification starting and long-term operation is improved.

Description

Technical Field

[0001] This invention relates to the field of water treatment and biological denitrification technology. Specifically, this invention relates to a dual-source composite slow-release carbon source, its preparation method, and its application. Background Technology

[0002] With increasingly stringent wastewater discharge standards, the requirements for total nitrogen discharge from wastewater treatment plants are becoming more and more stringent. In biological denitrification processes, heterotrophic denitrifying microorganisms require organic matter as electron donors to reduce nitrate and nitrite nitrogen to nitrogen gas. For low C / N ratio water bodies such as wastewater treatment plant effluent, some industrial wastewater, polluted surface water, and nitrate-contaminated groundwater, the denitrification process is easily limited by insufficient bioavailable organic carbon sources, resulting in low nitrate nitrogen removal rates and difficulty in consistently meeting effluent total nitrogen standards.

[0003] Currently, liquid carbon sources such as methanol, sodium acetate, and glucose are commonly used in engineering to improve denitrification efficiency. Although liquid carbon sources are easily utilized by microorganisms, their dosage needs to be adjusted in real time according to the influent water quality and quantity. Insufficient dosage will lead to incomplete denitrification, while excessive dosage can easily cause an increase in effluent chemical oxygen demand, an increase in excess sludge production, and an increase in operating costs, as well as the risk of secondary pollution.

[0004] To reduce the operational burden caused by continuous addition of liquid carbon sources, natural plant materials and biodegradable polymers are used to prepare solid slow-release carbon sources. Among them, agricultural wastes such as rice husks, corn cobs, and straw have advantages such as wide availability, low cost, and biodegradability. However, uncontrolled natural plant materials often suffer from problems such as dense lignocellulose structure, insufficient surface hydrophilicity, concentrated release of readily soluble organic matter in the initial stage, insufficient effective carbon source in the later stage, low mechanical strength, and easy floating or disintegration.

[0005] Chemical modification can disrupt the dense structure of plant materials, thereby increasing their organic carbon release capacity. However, when all plant materials are subjected to the same and strong modification conditions, the initial carbon release rate can be too rapid, leading to an increase in the chemical oxygen demand (COD) of the effluent. Conversely, milder modification conditions may result in insufficient carbon supply and slow biofilm formation during reactor start-up. Therefore, using plant materials with a single degree of modification makes it difficult to simultaneously meet the requirements of rapid carbon supply during reactor start-up and continuous carbon supply in the later stages.

[0006] In addition, cleaning or pre-extracting modified plant materials can remove some soluble organic matter that is prone to causing an initial burst of organic carbon. However, the organic carbon contained in the pre-extract is usually discharged with the waste liquid, which not only causes carbon source loss, but also increases the treatment burden of the pre-extract waste liquid.

[0007] Therefore, it is still necessary to develop a composite slow-release carbon source particle that can reduce the initial burst release of organic carbon, recover and utilize organic carbon in the pre-extract, and simultaneously meet the carbon supply needs during the denitrification start-up phase and the middle and later stages. Summary of the Invention

[0008] This invention is based on the inventor's discovery and understanding of the following facts and problems: the rapid release of organic carbon in the initial stage of natural biomass slow-release carbon source materials, insufficient carbon supply in the middle and later stages, the lack of utilization of organic carbon in the pre-extraction solution, and the limited carbon supply capacity of ordinary biochar itself.

[0009] Although ordinary biochar has a large specific surface area and abundant pore structure, which can provide attachment sites for denitrifying microorganisms, the amount of usable organic carbon that biochar itself can release is limited, and it cannot independently undertake the long-term carbon supply function for denitrification.

[0010] Composite slow-release carbon source particles are mostly produced by direct blending and granulation, without directional allocation of organic carbon with different release characteristics in plant materials.

[0011] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a dual-library composite slow-release carbon source, its preparation method, and its application. A fast-release carbon library and a slow-release carbon library are constructed using rice husks with different degrees of modification. Biochar is used to recover homologous, readily soluble organic carbon from the pre-extracted water solution of the rice husks. A calcium-containing component, iron tetroxide, and additives are combined to reduce the risk of initial burst release of organic carbon, achieving synergistic carbon supply from both fast and slow release. This solution functions as both a carbon source and a biofilm carrier, enabling the recovery and utilization of pre-extracted organic carbon. It exhibits good mechanical strength and water resistance, improving the coordination between denitrification start-up and long-term operation.

[0012] This invention provides a dual-source composite slow-release carbon source, comprising: a first modified rice husk, a second modified rice husk, modified biochar, a calcium-containing component, iron tetroxide, and additives. The first modified rice husk is obtained by first alkali-oxidation composite modification treatment and first water pre-extraction treatment of rice husk; The second modified rice husk is obtained by subjecting the second rice husk to a second alkali-oxidation composite modification treatment and a second water pre-extraction treatment; The organic carbon release rate of the first modified rice husk is faster than that of the second modified rice husk. The modified biochar includes biochar loaded with readily soluble organic carbon from rice husks.

[0013] In some embodiments, the carbon release time of the second modified rice husk is longer than that of the first modified rice husk. And / or, the particle size of the first modified rice husk is 0.4~0.8 mm; And / or, the particle size of the second modified rice husk is 0.4~0.8 mm; And / or, the mass ratio of the first modified rice husk to the second modified rice husk is 2~4:6~8.

[0014] In some embodiments, the rice husk-based readily soluble organic carbon in the modified biochar originates from the water pre-extract generated during the preparation of the first modified rice husk and / or the second modified rice husk. And / or, the modified biochar has a particle size of 0.3~0.6 mm; And / or, the total volume ratio of the first modified rice husk and the second modified rice husk to the volume ratio of the modified biochar is 1~3:1.

[0015] In some embodiments, the calcium-containing component includes calcium chloride; And / or, based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the calcium-containing component is 1.0% to 1.5%; And / or, the particle size of the iron oxide is 0.25-0.35 mm; And / or, based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the iron oxide is 0.5%~1.0%; And / or, the additives include bridging powders and adhesives.

[0016] In some embodiments, the adhesive includes sodium carboxymethyl cellulose; And / or, the bridging powder includes at least one of corn flour, wood flour, starch, and fine plant fiber powder; And / or, the bridging powder has a particle size of 0.6-0.9 mm; And / or, based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the bridging powder is 1.0% to 3.0%.

[0017] In some embodiments, the shape of the dual-source composite slow-release carbon source includes at least one of spherical, ellipsoidal, or columnar shapes; And / or, the equivalent diameter of the dual-source composite slow-release carbon source is 14-20 mm; And / or, the moisture content of the dual-source composite slow-release carbon source is 12%~18%.

[0018] This invention provides a method for preparing a dual-source composite sustained-release carbon source, comprising the following steps: (1) The first rice husk is soaked in a first composite modification solution containing alkali and oxidizing reagent for the first alkali-oxidation composite modification treatment. After the modification is completed, it is washed until neutral. Then it is soaked in water for the first water pre-extraction treatment to obtain the first water pre-extraction solution and the first modified rice husk. (2) The second rice husk is soaked in a second composite modification solution containing alkali and oxidizing reagent for a second alkali-oxidation composite modification treatment. After the modification is completed, it is washed until neutral. Then it is soaked in water for a second water pre-extraction treatment to obtain a second water pre-extraction solution and a second modified rice husk. (3) Modified biochar is obtained by adsorbing the homologous soluble organic carbon of rice husk in the first water pre-extract and / or the second water pre-extract. (4) The first modified rice husk, the second modified rice husk, modified biochar, calcium-containing components, iron tetroxide, additives and water are mixed evenly to obtain a wet mixture; then the wet mixture is pressed into shape and dried to obtain a dual-source composite slow-release carbon source.

[0019] In some embodiments, in step (1), the particle size of the first rice husk is 0.4~0.8 mm; And / or, the base includes at least one of calcium hydroxide, sodium hydroxide, and potassium hydroxide; And / or, the oxidizing agent includes sodium hypochlorite; And / or, the solvent of the first composite modified solution includes water; And / or, in the first composite modified solution, the mass percentage concentration of the alkali is 8%~12%; And / or, in the first composite modified solution, the mass percentage concentration of the oxidizing agent is 4%~6%; And / or, the temperature of the first alkali-oxidation composite modification treatment is 40~80℃; And / or, the first alkali-oxidation composite modification treatment time is 6~24 hours; And / or, in the first water pre-extraction treatment, the solid-liquid volume ratio of rice husk to water after the first alkali-oxidation composite modification is 0.8~1.2:30; And / or, the temperature of the first water pre-extraction treatment is 20~30℃; And / or, the first water pre-extraction treatment time is 2 to 6 hours.

[0020] In some embodiments, in step (2), the particle size of the second rice husk is 0.4~0.8 mm; And / or, the base includes at least one of calcium hydroxide, sodium hydroxide, and potassium hydroxide; And / or, the oxidizing agent includes sodium hypochlorite; And / or, the solvent of the second composite modified solution includes water; And / or, in the second composite modified solution, the mass percentage concentration of the alkali is 4%~8%; And / or, in the second composite modified solution, the mass percentage concentration of the oxidizing agent is 2%~4%; And / or, the temperature of the second alkali-oxidation composite modification treatment is 40~80℃; And / or, the second alkali-oxidation composite modification treatment time is 6~24 hours; And / or, in the second water pre-extraction treatment, the solid-liquid volume ratio of rice husk to water after the second alkali-oxidation composite modification is 0.8~1.2:30; And / or, the temperature of the second water pre-extraction treatment is 20~30℃; And / or, the second water pre-extraction treatment time is 2 to 6 hours.

[0021] In some embodiments, the first alkali-oxidation composite modification treatment satisfies at least one of the following conditions (A) to (D) relative to the second alkali-oxidation composite modification treatment: (A) The first composite modified solution has a high alkali concentration; (B) The concentration of the oxidizing agent in the first composite modified solution is relatively high; (C) The temperature of the first alkali-oxidation composite modification treatment is relatively high; (D) The first alkali-oxidation composite modification treatment takes a long time.

[0022] In some embodiments, in step (3), the adsorption temperature is 20~30℃; And / or, in step (3), oscillation is performed during the adsorption process; And / or, in step (3), the adsorption time is 6 to 12 hours; And / or, in step (3), the ratio of the mass of the biochar to the total volume of the first water pre-extract and / or the second water pre-extract is 1~1.2g:0.5~30mL; And / or, the first water pre-extraction treatment and the second water pre-extraction treatment are carried out in the same water system to obtain a mixed water pre-extraction solution. In step (3), biochar is used to adsorb the rice husk homologous soluble organic carbon in the mixed water pre-extraction solution to obtain modified biochar. And / or, in step (4), the pressing pressure is 1.0~1.5MPa; And / or, in step (4), the holding time for pressing is 30 to 60 seconds.

[0023] This invention provides an application of a dual-source composite slow-release carbon source or a dual-source composite slow-release carbon source prepared by the method described in this invention, for use in water treatment.

[0024] In some embodiments, it is used for denitrification of water bodies; And / or, the dual-source composite slow-release carbon source is used in a denitrification reactor as a slow-release carbon source and biofilm carrier for denitrifying microorganisms to remove nitrate nitrogen from water. And / or, in the initial stage of water treatment operation, the modified biochar in the dual-pool composite slow-release carbon source desorbs at least part of the homologous soluble organic carbon from rice husk, and together with the first modified rice husk, provides the organic carbon required for denitrification startup. And / or, in the later stages of water treatment operation, the second modified rice husk continuously releases organic carbon to sustain the denitrification process.

[0025] This invention provides a denitrification system, comprising: the dual-source composite slow-release carbon source described in this invention or the dual-source composite slow-release carbon source prepared by the preparation method described in this invention.

[0026] According to the dual-library composite slow-release carbon source provided by this invention, rice husks are divided into two parts. A fast-release carbon library and a slow-release carbon library are constructed using first and second modified rice husks with different degrees of modification. These are then subjected to alkali-oxidation composite modification treatments of varying intensities to form a fast-release carbon library responsible for carbon supply during the initial stage and a slow-release carbon library responsible for continuous carbon supply in the later stages. Simultaneously, the modified rice husks undergo water pre-extraction to transfer some readily soluble organic carbon that could easily cause an initial burst release of organic carbon to the water pre-extraction solution. Then, biochar is used to adsorb and recover homologous readily soluble organic carbon from the rice husk pre-extraction solution. The biochar loaded with homologous readily soluble organic carbon is then reintroduced into the composite slow-release carbon source particles, thereby achieving the directional migration, recovery, and redistribution of readily soluble organic carbon from the rice husks. Simultaneously, the compound contains calcium-containing components, iron oxide, bridging powder, and adhesives. These components work synergistically to reduce the risk of initial organic carbon burst release, achieving a synergistic supply of carbon through both rapid and slow release. It functions as both a carbon source and a biofilm carrier, enabling the recovery and utilization of pre-extracted organic carbon and improving the coordination between the start-up and long-term operation of denitrification in water treatment. The dual-liquidity composite slow-release carbon source particles of this invention are suitable for water treatment, specifically for deep denitrification of wastewater effluent, remediation of low C / N ratio surface water, treatment of groundwater nitrate pollution, and denitrification treatment of other low C / N ratio water bodies.

[0027] Dual-liquid composite slow-release carbon source particles of the present invention: (i) Constructing fast-release and slow-release carbon libraries using rice husks with different modification strengths Rice husk particles were divided into a first rice husk component and a second rice husk component, and each component was subjected to alkali-oxidation composite modification treatment with different intensities. The modification intensity of the first rice husk component was higher than that of the second rice husk component, and the difference in modification intensity was adjusted by at least one of the following: alkali reagent concentration, oxidizing reagent concentration, modification temperature, and modification time.

[0028] After undergoing strong alkali-oxidation composite modification, the dense surface structure of the first rice husk component is significantly disrupted, resulting in a relatively high degree of pore opening and hydrophilicity, and a relatively fast organic carbon release rate. It is mainly used for carbon supply during the reactor start-up phase, forming a fast-release carbon pool.

[0029] After relatively mild alkali-oxidation composite modification, the second rice husk component retains more of the dense structure of lignocellulose, and the organic carbon release rate is relatively low but the duration is long. It is mainly used for stable carbon supply in the middle and later stages of the reactor, forming a slow-release carbon pool.

[0030] (ii) Using water pre-soaking extraction to regulate the initial organic carbon release of modified rice husks After the first and second rice husks undergo alkali-oxidation composite modification treatment and are washed to neutral, they are not directly mixed with other materials for granulation. Instead, they are pre-extracted with water, either separately or together. Pre-extraction allows some of the soluble organic matter (soluble organic carbon) in the alkali-oxidation composite modified rice husks, which is prone to concentrated release in the initial stage of material addition, to enter the water pre-extraction solution. After solid-liquid separation, the first modified rice husk, the second modified rice husk, and the water pre-extraction solution containing soluble organic carbon from the rice husks are obtained, respectively. Pre-extraction treatment reduces the risk of organic carbon release peaks after the modified rice husks are directly added to water bodies.

[0031] (III) Recovery of homologous soluble organic carbon from pre-leached water solution using biochar Biochar particles are contacted with a first aqueous pre-extract of first modified rice husk, a second aqueous pre-extract of second modified rice husk, or a mixture of the two (mixed extract or mixture), so that at least part of the rice husk soluble organic carbon in the aqueous pre-extract is adsorbed and loaded onto the surface and pores of the biochar particles, thus obtaining biochar particles loaded with homologous soluble organic carbon, i.e., modified biochar.

[0032] The term "homogeneous soluble organic carbon" in this invention refers to soluble organic carbon derived from the same batch or type of rice husks used to prepare the composite slow-release carbon source particles of this invention, and separated from the modified rice husks through water pre-extraction.

[0033] The aqueous pre-extract is not directly discharged as waste liquid, but is used for organic carbon loading of biochar particles, allowing the soluble organic carbon pre-separated from the modified rice husk to return to the composite slow-release carbon source particles. This reduces the organic pollution load of the aqueous pre-extract and avoids the waste of usable organic carbon.

[0034] (iv) Constructing a synergistic carbon supply system between rice husk fast and slow carbon pools and biochar adsorption-desorption carbon pools. This invention forms at least three mutually compatible carbon-donating components: The first modified rice husk particles form a fast-release carbon pool, which is used to supply carbon during the reactor start-up phase and the initial stage of operation. The second modified rice husk particles form a slow-release carbon pool for continuous carbon supply during the later stages of operation. Modified biochar particles form an adsorption-desorption regulating carbon pool, which replenishes the carbon source demand during the start-up phase and the middle stage of operation through the gradual desorption of homologous soluble organic carbon on the surface and in the pores of biochar.

[0035] Through the synergistic effect between the aforementioned carbon pools, soluble organic carbon is no longer directly released into water bodies in large quantities from modified rice husks. Instead, it is first separated by water pre-extraction, then recovered and loaded by biochar, and finally gradually released during the operation of the composite slow-release carbon source particles, thus realizing the directional migration, recovery, and redistribution of carbon sources between rice husks and biochar.

[0036] (v) Add calcium-containing components, iron oxide particles and bridging powder to the composite slow-release carbon source particles. During the wet mixing process, calcium chloride dissolves and forms a calcium-containing component, which is distributed within the composite slow-release carbon source particles. Calcium ions can participate in the formation of the internal bonding structure of the particles and are beneficial for microbial attachment and extracellular polymer formation.

[0037] Ferric oxide particles are distributed inside the composite slow-release carbon source particles, which can serve as an iron-based functional medium, providing an iron-based interface for the biofilm attachment area and facilitating interfacial electron transfer during the denitrification process.

[0038] Bridging powder fills part of the gaps between pre-impregnated modified rice husk particles and modified biochar particles, improving the effective bonding area between different particles and the stability of compression molding.

[0039] (vi) Compared with related technologies, the present invention has the following beneficial effects: (1) Reduce the risk of initial organic carbon burst release. By pre-extracting the alkali-oxidation composite modified rice husk into water, some of the easily soluble organic carbon that is prone to cause concentrated release of initial organic carbon is pre-entered into the water pre-extract, reducing the risk of a high COD peak after direct addition of granules.

[0040] (2) Realize the recycling of organic carbon from pre-leaching. Biochar is used to adsorb homologous soluble organic carbon in the water pre-leaching solution, and the loaded biochar is added back to the composite particles, so that the organic carbon in the pre-leaching solution can be returned to the denitrification material, avoiding carbon source waste and reducing the treatment burden of pre-leaching waste liquid.

[0041] (3) Achieve synergistic carbon supply of rapid and slow release. By modifying rice husks with alkali-oxidation composites of different intensities, a rapid-release carbon library that undertakes the carbon supply function in the initiation stage and a slow-release carbon library that undertakes the continuous carbon supply function in the middle and late stages can be formed. The carbon source release process can be regulated without the need to use high-cost synthetic polymer carbon sources such as PHB, PHA or PCL.

[0042] (4) Improve the coordination between reactor start-up and long-term operation. Modified biochar and first modified rice husk can provide readily available organic carbon during the water treatment start-up stage, while second modified rice husk can continuously supply carbon during the middle and later stages of water treatment operation, thereby alleviating the contradiction between insufficient carbon source during the start-up stage and carbon supply decay after long-term operation.

[0043] (5) It has the functions of both carbon source and biofilm carrier. In addition to being used to recover homologous soluble organic carbon, biochar can also provide attachment sites for denitrifying microorganisms by utilizing its pore structure and specific surface area, thereby increasing the microbial load inside and on the surface of the composite particles.

[0044] (6) Good mechanical strength and water resistance. The sodium carboxymethyl cellulose binder network, bridging powder and calcium-containing components work together to improve the molding stability and wet mechanical strength of the composite particles, reducing the risk of rapid disintegration of the particles during long-term operation in water.

[0045] (7) Low raw material cost. The main raw materials are rice husks, biochar and plant-derived bridging powder, which can realize the resource utilization of agricultural waste and reduce the preparation cost of solid slow-release carbon source materials.

[0046] (8) The preparation process is simple. The entire preparation process mainly includes alkali-oxidation composite modification, water pre-extraction, biochar adsorption loading, wet mixing, pressing and molding and low temperature drying. No high temperature melt extrusion equipment is required, which is convenient for large-scale production. Attached Figure Description

[0047] Figure 1 It is the total organic carbon release rate of different biomass carbon sources.

[0048] Figure 2 It is the total nitrogen release rate of different biomass carbon sources.

[0049] Figure 3 It is the C / N ratio released by different biomass carbon sources.

[0050] Figure 4 It involves screening methods for modifying biomass raw materials.

[0051] Figure 5 It refers to the wear resistance of materials prepared using different adhesives.

[0052] Figure 6 It refers to the stability of materials prepared using different bridging powders.

[0053] Figure 7 The modified biochar after adsorbing the pre-extracted water solution responded to the dual-source composite slow-release carbon source. (A) Biochar adsorbed organic carbon in the pre-extracted solution; (B) Comparison of the release rates of the dual-source composite slow-release carbon source and the carbon source from rice husk.

[0054] Figure 8 This is a long-term carbon source release stability test of a dual-library composite slow-release carbon source.

[0055] Figure 9 This is a comparison of the denitrification performance of different materials. Detailed Implementation

[0056] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0057] An embodiment of the present invention provides a dual-source composite slow-release carbon source comprising: a first modified rice husk, a second modified rice husk, modified biochar, a calcium-containing component, iron tetroxide, and additives. The first modified rice husk is obtained by first alkali-oxidation composite modification treatment and first water pre-extraction treatment of rice husk; The second modified rice husk is obtained by subjecting the second rice husk to a second alkali-oxidation composite modification treatment and a second water pre-extraction treatment; The organic carbon release rate of the first modified rice husk is faster than that of the second modified rice husk. The modified biochar includes biochar loaded with readily soluble organic carbon from rice husk (also known as biochar loaded with readily soluble organic carbon from rice husk).

[0058] The dual-library composite slow-release carbon source of this invention constructs a fast-release carbon library and a slow-release carbon library using first and second modified rice husks with different degrees of modification. It utilizes biochar to recover homologous, easily soluble organic carbon from the pre-extracted rice husk, and combines it with calcium-containing components, iron tetroxide, and additives. The components work synergistically to reduce the risk of initial organic carbon burst release, achieving synergistic carbon supply from both fast and slow release. It functions as both a carbon source and a biofilm carrier, enabling the recovery and utilization of pre-extracted organic carbon. It also exhibits good mechanical strength and water resistance, improving the coordination between denitrification start-up and long-term operation.

[0059] In some embodiments, the organic carbon release rate of the first modified rice husk is faster than that of the second modified rice husk. Optionally, the carbon release time of the second modified rice husk is longer than that of the first modified rice husk. Optionally, the first modified rice husk constitutes a fast-release carbon library, and the second modified rice husk constitutes a slow-release carbon library.

[0060] In some embodiments, the first modified rice husk is obtained by first alkali-oxidation composite modification treatment and first water pre-extraction treatment of the first rice husk; optionally, the first water pre-extraction treatment yields a first water pre-extraction solution and the first modified rice husk; at least some of the readily soluble organic carbon is separated by the first water pre-extraction treatment. Optionally, the second modified rice husk is obtained by second alkali-oxidation composite modification treatment and second water pre-extraction treatment of the second rice husk; Optionally, the second water pre-extraction treatment yields a second water pre-extraction solution and a second modified rice husk; at least some of the readily soluble organic carbon is separated by second water pre-extraction. The first rice husk mentioned above may be the same as or different from the second rice husk; This invention does not impose any special restrictions on the source of the first rice husk and the second rice husk; Optionally, the first or second alkali-oxidation composite modification treatment respectively includes soaking the first or second rice husk in a first or second composite modification solution containing alkali and oxidizing agent. Optionally, the alkali includes at least one of calcium hydroxide, sodium hydroxide, and potassium hydroxide; the oxidizing agent includes sodium hypochlorite; and the solvent of the composite modified solution includes water. Optionally, in the first composite modified solution, the mass percentage concentration of the alkali is 8%~12%; in the first composite modified solution, the mass percentage concentration of the oxidizing agent is 4%~6%; the temperature of the first alkali-oxidation composite modification treatment is 40~80℃; and the time of the first alkali-oxidation composite modification treatment is 6~24 hours. Optionally, in the second composite modification solution, the mass percentage concentration of the alkali is 4%~8%; in the second composite modification solution, the mass percentage concentration of the oxidizing agent is 2%~4%; the temperature of the second alkali-oxidation composite modification treatment is 40~80℃; and the time of the second alkali-oxidation composite modification treatment is 6~24 hours. Optionally, the intensity of the alkali-oxidation composite modification treatment experienced by the first modified rice husk is higher than the intensity of the alkali-oxidation composite modification treatment experienced by the second modified rice husk.

[0061] In this embodiment of the invention, the first modified rice husk and the second modified rice husk are respectively obtained by treating rice husk with alkali-oxidation composite modification of different intensities, followed by water pre-extraction and separation of at least some soluble organic carbon.

[0062] In this embodiment of the invention, rice husk raw material is divided into two parts and treated with different intensities of alkali-oxidation composite conditions to construct fast-release and slow-release components. The first rice husk component undergoes stronger modification conditions to give it a higher degree of pore openness and hydrophilicity, enabling it to release usable organic carbon more quickly in the early stages of operation, providing a carbon source for the initiation of denitrifying microorganisms and biofilm formation. The second rice husk component undergoes milder modification conditions to retain more dense lignocellulose structure, giving it a lower initial carbon release rate and a longer sustained carbon release period, mainly undertaking the function of stable carbon supply in the middle and later stages. The two types of rice husks with different degrees of modification are co-granulated, achieving a synergistic fast-release and slow-release carbon supply without using expensive synthetic polymer carbon sources such as PHB, PHA, or PCL.

[0063] In this embodiment of the invention, rice husks modified by alkali / oxidation and washed to neutrality are subjected to short-term water pre-extraction. This transfers readily soluble organic carbon, which is prone to causing an initial COD burst release, into the pre-extraction solution. Solid-liquid separation is then used to obtain pre-extracted modified rice husks and a pre-extraction solution containing readily soluble organic carbon from the rice husks. Subsequently, biochar is used to adsorb the readily soluble organic carbon in the pre-extraction solution, resulting in biochar loaded with homologous readily soluble organic carbon. This biochar is then recombined with the modified rice husks and granulated. Through this process, readily soluble organic carbon, which is normally prone to rapid loss, is directionally transferred from the rice husks to the pores and surface of the biochar and redistributed within the composite, thus forming a carbon pool composed of modified rice husks and modified biochar. The modified biochar regulates the carbon source supply during the start-up and mid-operation stages through adsorption-desorption, thereby reducing the risk of an initial organic carbon burst release, avoiding waste of pre-extracted organic carbon, and compensating for the insufficient carbon supply capacity of ordinary biochar.

[0064] In some embodiments, the mass ratio of the first modified rice husk to the second modified rice husk is 2~4:6~8, specifically, 2~4 (e.g., 2, 2.5, 3, 3.5, 4):6~8 (e.g., 6, 6.5, 7, 7.5, 8); the first modified rice husk mainly serves as a fast-release carbon pool, and the second modified rice husk mainly serves as a slow-release carbon pool; optionally, the first modified rice husk accounts for 20%~40% of the total mass of the two types of rice husks (first modified rice husk and second modified rice husk), specifically, for example, 20%, 25%, 30%, 35%, 40%, and the second modified rice husk accounts for 60%~80% of the total mass of the two types of rice husks (first modified rice husk and second modified rice husk), specifically, for example, 60%, 65%, 70%, 75%, 80%.

[0065] In this embodiment of the invention, the first modified rice husk particles and the second modified rice husk particles are added together to the composite slow-release carbon source particles, so that the composite slow-release carbon source particles have both the carbon supply capacity in the start-up stage and the continuous carbon supply capacity in the middle and later stages. By adjusting the ratio of the two, preferably, the mass ratio of the first modified rice husk and the second modified rice husk is 2~4:6~8, which is conducive to further realizing the synergistic carbon supply of fast-release and slow-release and improving the coordination of long-term operation.

[0066] In some embodiments, the particle size of the first modified rice husk is 0.4 to 0.8 mm, specifically, for example, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm; and the particle size of the second modified rice husk is 0.4 to 0.8 mm, specifically, for example, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm.

[0067] In some embodiments, the modified biochar includes biochar loaded with readily soluble organic carbon derived from rice husks. Optionally, in the biochar loaded with rice husk-derived soluble organic carbon, the soluble organic carbon is loaded on the surface and in the pores of the biochar; the present invention does not have any special restrictions on the type and source of biochar, which can be obtained by purchase; Optionally, the rice husk-based readily soluble organic carbon in the modified biochar originates from the water pre-extract generated during the preparation of the first modified rice husk and / or the second modified rice husk. For example, it may originate from a mixture of the water pre-extract generated during the preparation of the first modified rice husk and the second modified rice husk. Optionally, the biochar loaded with readily soluble organic carbon from rice husk is prepared by adsorbing readily soluble organic carbon from rice husk in the water pre-extract generated during the preparation of the first modified rice husk and / or the second modified rice husk; alternatively, the biochar particles are brought into contact with the water pre-extract, and at least part of the readily soluble organic carbon from rice husk in the water pre-extract is adsorbed through the surface and pores of the biochar particles, and modified biochar particles are obtained after solid-liquid separation.

[0068] In this embodiment of the invention, the modified biochar is prepared by adsorbing at least a portion of the soluble organic carbon in the water pre-extraction solution containing soluble organic carbon in rice husk produced during the water pre-extraction process of rice husk preparation. This allows at least a portion of the soluble organic carbon pre-separated from the modified rice husk to be transferred and loaded onto the surface and pores of the biochar.

[0069] In some embodiments, the modified biochar has a particle size of 0.3 to 0.6 millimeters (mm), specifically, for example, 0.3 mm, 0.4 mm, 0.5 mm, and 0.6 mm.

[0070] In this embodiment of the invention, the modified biochar has a particle size of 0.3~0.6 mm, which is beneficial for the biochar to fully contact with the first modified rice husk water pre-extract, the second modified rice husk water pre-extract, or a mixture of the two, so as to utilize the surface and pores of the biochar to adsorb the easily soluble organic carbon of rice husk in the pre-extract.

[0071] In some embodiments, the total volume ratio of the first modified rice husk and the second modified rice husk to the volume ratio of the modified biochar is 1 to 3:1, specifically, for example, 1:1, 2:1, 3:1, preferably 2:1.

[0072] In this embodiment of the invention, it is beneficial to further realize the synergistic carbon supply of fast-release and slow-release carbon and improve the coordination of long-term operation.

[0073] In some embodiments, the calcium-containing component includes calcium chloride; or, the dual-source composite sustained-release carbon source includes a calcium-containing component, the raw material of which includes calcium chloride; or, calcium chloride is dissolved in the wet mixing process (the process of mixing each component with water) during the preparation of the dual-source composite sustained-release carbon source and serves as the calcium-containing component. Optionally, based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar (100%), the mass addition of the calcium-containing component (or calcium chloride) is 1.0% to 1.5%, specifically, for example, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, preferably 1.5%.

[0074] In this embodiment of the invention, the slow-release carbon source includes a calcium-containing component introduced by calcium chloride. Calcium ions can participate in the formation of internal bonding structures and are beneficial for microbial attachment and extracellular polymer formation.

[0075] In some embodiments, the particle size of the iron oxide is 0.25-0.35 mm, specifically, for example, 0.25 mm, 0.3 mm, 0.35 mm; based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the iron oxide is 0.5% to 1.0%, specifically, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, preferably 1.0%.

[0076] In this embodiment of the invention, iron(III) oxide is distributed inside the composite slow-release carbon source, which can serve as an iron-based functional medium, providing an iron-based interface for the biofilm attachment area and facilitating interfacial electron transfer during the denitrification process.

[0077] In some embodiments, the additive includes bridging powder and adhesive.

[0078] In some embodiments, the adhesive includes sodium carboxymethyl cellulose. The present invention does not impose special restrictions on the parameters and source of sodium carboxymethyl cellulose, which can be obtained through purchase. The components of the dual-source composite slow-release carbon are bonded together by sodium carboxymethyl cellulose to form the dual-source composite slow-release carbon. Sodium carboxymethyl cellulose is distributed between adjacent modified rice husks and modified biochar, with at least a portion of the sodium carboxymethyl cellulose covering at least a portion of the outer surface of the dual-source composite slow-release carbon. The amount of adhesive used is sufficient to form a stable, non-dispersed, non-fluid state after the wet-mixed material is added to the adhesive aqueous solution. For example, in some embodiments, based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the adhesive is 1.2% to 1.8%, specifically, for example, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, and 1.8%.

[0079] In this embodiment of the invention, the first modified rice husk, the second modified rice husk, and the modified biochar are bonded together by sodium carboxymethyl cellulose to form a composite. Calcium-containing components, iron oxide, and bridging powder are distributed internally, while the sodium carboxymethyl cellulose bonding network is distributed between adjacent modified rice husks and modified biochar, and at least partially covers the outer surface of the slow-release carbon source.

[0080] In some embodiments, the bridging powder includes at least one of corn flour, wood flour, starch, and fine plant fiber powder; the present invention does not have special restrictions on the source of the bridging powder, which can be purchased; the particle size of the bridging powder is 0.6-0.9 mm, specifically, for example, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm; based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the bridging powder is 1.0% to 3.0%, specifically, for example, 1.0%, 1.5%, 1.6%, 2.0%, 2.5%, 3.0%, preferably 1.6%; the bridging powder fills at least a portion of the gaps between the modified rice husk and the modified biochar.

[0081] In this embodiment of the invention, bridging powder is filled in part of the gap between modified rice husk and modified biochar to improve the effective bonding area between different particles and the stability of compression molding.

[0082] In some embodiments, the present invention does not impose any particular limitation on the shape of the dual-source composite slow-release carbon source. For example, the shape may include at least one of spherical, ellipsoidal, or columnar shapes; optionally, the columnar shape includes short columnar shapes; the equivalent diameter of the dual-source composite slow-release carbon source is 14 to 20 millimeters (mm), specifically, for example, 14 mm, 15 mm, 18 mm, 20 mm; the water content (mass percentage of water) of the dual-source composite slow-release carbon source is 12% to 18%, specifically, for example, 12%, 14%, 16%, 18%.

[0083] A method for preparing a dual-liquidity composite sustained-release carbon source according to an embodiment of the present invention includes the following steps: (1) The first rice husk is soaked in a first composite modification solution containing alkali and oxidizing reagent for the first alkali-oxidation composite modification treatment. After the modification is completed, it is washed until neutral. Then it is soaked in water for the first water pre-extraction treatment to obtain the first water pre-extraction solution and the first modified rice husk. Optionally, solid-liquid separation is performed after the first water pre-extraction treatment. (2) The second rice husk is soaked in a second composite modification solution containing alkali and oxidizing reagent for a second alkali-oxidation composite modification treatment. After the modification is completed, it is washed until neutral. Then it is soaked in water for a second water pre-extraction treatment to obtain a second water pre-extraction solution and a second modified rice husk. Optionally, solid-liquid separation is performed after the second water pre-extraction treatment. (3) Biochar is used to adsorb the homologous soluble organic carbon of rice husk in the first water pre-extract and / or the second water pre-extract to obtain modified biochar; optionally, solid-liquid separation is performed after adsorption to obtain modified biochar. (4) The first modified rice husk, the second modified rice husk, modified biochar, calcium-containing components, iron tetroxide, additives and water are mixed evenly to obtain a wet mixture; then the wet mixture is pressed into shape and dried to obtain a dual-source composite slow-release carbon source.

[0084] In some embodiments, in step (1), the present invention does not have a special limitation on the source of the first rice husk; the particle size of the first rice husk is 0.4~0.8 mm, specifically, for example, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm; the rice husk is crushed and sieved into rice husks with a particle size of 0.4~0.8 mm to obtain the first rice husk; optionally, the rice husk is crushed and sieved into rice husks with a particle size of 0.4~0.8 mm, and the rice husk is divided into the first rice husk and the second rice husk; optionally, the washed and dried rice husk is crushed.

[0085] In some embodiments, in step (1), the first rice husk is soaked in a first composite modification solution containing alkali and oxidizing agent to perform a first alkali-oxidation composite modification treatment, and after modification, it is washed until neutral. Optionally, the alkali includes at least one of calcium hydroxide, sodium hydroxide, and potassium hydroxide; in the first composite modified solution, the mass percentage concentration of the alkali is 8% to 12%, specifically, for example, 8%, 9%, 10%, 11%, or 12%. Optionally, the oxidizing agent includes sodium hypochlorite; in the first composite modified solution, the mass percentage concentration of the oxidizing agent is 4% to 6%, specifically, for example, 4%, 4.5%, 5%, 5.5%, 6%. Optionally, the solvent of the first composite modified solution includes water, and optionally, deionized water; In a specific embodiment, the mass fraction of the alkali in the first composite modified solution is 10%, and the mass fraction of the oxidizing agent is 5%. Optionally, the temperature of the first alkali-oxidation composite modification treatment is 40~80℃, specifically, for example, 40℃, 50℃, 60℃, 70℃, 80℃; the time of the first alkali-oxidation composite modification treatment is 6~24 hours (h), specifically, for example, 6h, 12h, 18h, 24h. Optionally, after modification, the material is washed with water until it is nearly neutral.

[0086] In this embodiment of the invention, the first rice husk component is subjected to strong modification conditions, which gives it a higher degree of pore opening and hydrophilicity, enabling it to release usable organic carbon more quickly in the early stage of operation, providing a carbon source for the initiation of denitrifying microorganisms and the formation of biofilm.

[0087] In some embodiments, in step (1), the rice is then soaked in water for a first water pre-extraction treatment to obtain a first water pre-extraction solution and a first modified rice husk. Optionally, the first water pre-extract contains readily soluble organic carbon derived from rice husks; Optionally, in the first water pre-extraction treatment, the solid-liquid volume ratio of the rice husk and water after the first alkali-oxidation composite modification is 0.8~1.2:30, specifically, for example, 0.8:30, 0.9:30, 1.0:30, 1.1:30, 1.2:30; Optionally, the temperature of the first water pre-extraction treatment is 20~30℃, specifically, for example, 20℃, 22℃, 25℃, 28℃, 30℃; the time of the first water pre-extraction treatment is 2~6 hours (h), specifically, for example, 2h, 3h, 4h, 5h, 6h; optionally, the first water pre-extraction treatment is subjected to shaking. Optionally, after the first water pre-extraction treatment, solid-liquid separation is performed to obtain the first water pre-extraction solution and the first modified rice husk.

[0088] In this embodiment of the invention, rice husks that have been modified by alkali / oxidation and washed to neutrality are subjected to short-term water pre-extraction, so that at least some of the easily soluble organic carbon that is prone to causing an initial COD burst release is transferred to the water pre-extraction solution. Modified rice husks and water pre-extraction solutions containing easily soluble organic carbon from rice husks are obtained by solid-liquid separation.

[0089] In some embodiments, in step (2), the present invention does not have a special limitation on the source of the second rice husk; the particle size of the second rice husk is 0.4~0.8 mm; specifically, for example, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm; the rice husk is crushed and sieved into rice husks with a particle size of 0.4~0.8 mm to obtain the second rice husk; optionally, the rice husk is crushed and sieved into rice husks with a particle size of 0.4~0.8 mm, and the rice husk is divided into the first rice husk and the second rice husk; optionally, the washed and dried rice husk is crushed.

[0090] In some embodiments, in step (2), the second rice husk is soaked in a second composite modification solution containing alkali and oxidizing agent to perform a second alkali-oxidation composite modification treatment, and then washed until neutral after modification; Optionally, the alkali includes at least one of calcium hydroxide, sodium hydroxide, and potassium hydroxide; in the second composite modified solution, the mass percentage concentration of the alkali is 4% to 8%, specifically, for example, 4%, 5%, 6%, 7%, 8%. Optionally, the oxidizing agent includes sodium hypochlorite; in the second composite modified solution, the mass percentage concentration of the oxidizing agent is 2% to 4%, specifically, for example, 2%, 2.5%, 3%, 3.5%, 4%. Optionally, the solvent of the second composite modified solution includes water, and optionally, deionized water; Optionally, the temperature of the second alkali-oxidation composite modification treatment is 40~80℃, specifically, for example, 40℃, 50℃, 60℃, 70℃, 80℃; the time of the second alkali-oxidation composite modification treatment is 6~24 hours (h), specifically, for example, 6h, 12h, 18h, 24h; Optionally, after modification, the material is washed with water until it is nearly neutral.

[0091] In this embodiment of the invention, the second rice husk component is modified under milder conditions to retain more dense lignocellulose structure, giving it a lower initial carbon release rate and a longer continuous carbon release period, and mainly undertaking the function of stable carbon supply in the middle and later stages.

[0092] In some embodiments, in step (2), the rice is then soaked in water for a second water pre-extraction treatment to obtain a second water pre-extraction solution and a second modified rice husk. Optionally, the second water pre-extract contains readily soluble organic carbon derived from rice husks; Optionally, in the second water pre-extraction treatment, the solid-liquid volume ratio of the rice husk after the second alkali-oxidation composite modification to water is 0.8~1.2:30, specifically, for example, 0.8:30, 0.9:30, 1.0:30, 1.1:30, 1.2:30; Optionally, the temperature of the second water pre-extraction treatment is 20~30℃, specifically, for example, 20℃, 22℃, 25℃, 28℃, 30℃; the time of the second water pre-extraction treatment is 2~6 hours (h), specifically, for example, 2h, 3h, 4h, 5h, 6h; optionally, the second water pre-extraction treatment is agitated. Optionally, after the second water pre-extraction treatment, solid-liquid separation is performed to obtain the second water pre-extraction solution and the second modified rice husk.

[0093] In some embodiments, the first alkali-oxidation composite modification treatment satisfies at least one of the following conditions (A) to (D) relative to the second alkali-oxidation composite modification treatment: (A) The first composite modified solution has a higher alkali concentration; that is, the first composite modified solution has a higher alkali concentration than the second composite modified solution. (B) The concentration of the oxidizing agent in the first composite modified solution is higher; that is, the concentration of the oxidizing agent in the first composite modified solution is higher than the concentration of the oxidizing agent in the second composite modified solution. (C) The temperature of the first alkali-oxidation composite modification treatment is higher; that is, the temperature of the first alkali-oxidation composite modification treatment is higher than the temperature of the second alkali-oxidation composite modification treatment. (D) The first alkali-oxidation composite modification treatment takes a longer time; that is, the first alkali-oxidation composite modification treatment takes a longer time than the second alkali-oxidation composite modification treatment.

[0094] Optionally, the rice husk after the first alkali-oxidation composite modification treatment has a higher degree of pore opening and organic carbon release rate than the rice husk after the second alkali-oxidation composite modification treatment; compared with the rice husk after the first alkali-oxidation composite modification treatment, the rice husk after the second alkali-oxidation composite modification treatment retains a relatively larger amount of dense lignocellulose structure.

[0095] In this embodiment of the invention, the modification intensity of the first alkali-oxidation composite modification treatment experienced by the first rice husk component is higher than the modification intensity of the second alkali-oxidation composite modification treatment experienced by the second rice husk component. The difference in modification intensity can be achieved by increasing at least one of the following methods: increasing the concentration of the alkali reagent in the first alkali-oxidation composite modification treatment, increasing the concentration of the oxidizing agent sodium hypochlorite, increasing the modification treatment temperature, or extending the modification treatment time. This results in the rice husk after the first alkali-oxidation composite modification treatment having a higher organic carbon release rate than the rice husk after the second alkali-oxidation composite modification treatment, and the rice husk after the second alkali-oxidation composite modification treatment having a longer continuous carbon release time than the rice husk after the first alkali-oxidation composite modification treatment.

[0096] In some embodiments, the first water pre-extraction treatment and the second water pre-extraction treatment include water pre-extraction of rice husks after the first alkali-oxidation composite modification treatment and rice husks after the second alkali-oxidation composite modification treatment, respectively or together, so that at least part of the easily soluble organic carbon that is prone to cause the initial concentrated release of organic carbon enters the water pre-extraction solution. After solid-liquid separation, the first modified rice husk, the second modified rice husk, and the first water pre-extraction solution and / or the second water pre-extraction solution containing the easily soluble organic carbon of rice husk are obtained. Optionally, the first water pre-extraction treatment and the second water pre-extraction treatment are carried out in the same water system to obtain a mixed water pre-extraction solution. In this case, in step (3), biochar is used to adsorb the rice husk homologous soluble organic carbon in the mixed water pre-extraction solution to obtain modified biochar. Optionally, solid-liquid separation is performed after adsorption.

[0097] In this embodiment of the invention, water is used to pre-extract rice husks after the first alkali-oxidation composite modification treatment and the second alkali-oxidation composite modification treatment for a short time, so that at least part of the easily soluble organic carbon that is likely to be released in the early stage of operation enters the aqueous phase.

[0098] In some embodiments, in step (3), biochar is used to adsorb rice husk homologous soluble organic carbon in the first water pre-extract and / or the second water pre-extract to obtain modified biochar; Alternatively, the present invention does not impose any special restrictions on the source of biochar; Optionally, the biochar has a particle size of 0.3 to 0.6 millimeters (mm), specifically, for example, 0.3 mm, 0.4 mm, 0.5 mm, or 0.6 mm; Optionally, biochar is used to adsorb the first water pre-extract, the second water pre-extract, or a mixture of the two. Optionally, the adsorption temperature is 20~30℃, specifically, for example, 20℃, 22℃, 25℃, 28℃, 30℃; the adsorption process involves oscillation, optionally, the oscillation speed is 150~200 rpm; the adsorption time is 6~12 hours (h), specifically, for example, 6h, 8h, 10h, 12h; Optionally, the ratio (solid-liquid ratio) of the mass of the biochar to the total volume of the first aqueous pre-extract and / or the second aqueous pre-extract (or the mass of the biochar to the volume of the mixed aqueous pre-extract) is 1~1.2g : 0.5~30mL, specifically, 1~1.2g (e.g., 1.0g, 1.1g, 1.2g) : 0.5~30mL (e.g., 0.5mL, 1mL, 5mL, 10mL, 20mL, 30mL). Optionally, after adsorption is completed, solid-liquid separation is performed to obtain modified biochar; alternatively, the modified biochar obtained by solid-liquid separation is used directly in step (4), or it is used in step (4) after being dried (at low temperature).

[0099] In this embodiment of the invention, biochar is contacted with a pre-extracting aqueous solution. At least a portion of the readily soluble organic carbon from the rice husk in the pre-extracting solution is adsorbed through the surface and pores of the biochar. After solid-liquid separation, biochar loaded with homologous readily soluble organic carbon is obtained. The pre-extracting aqueous solution is not discharged as waste liquid but is used for organic carbon loading of the biochar, allowing the readily soluble organic carbon pre-separated from the modified rice husk to return to the composite slow-release carbon source. Vibration adsorption allows the biochar to rapidly adsorb organic carbon, while during operation, it remains in a static state, allowing for the slow release of organic carbon.

[0100] In some embodiments, in step (4), the first modified rice husk, the second modified rice husk, modified biochar, calcium-containing components, iron tetroxide, additives and water are mixed evenly to obtain a wet-mixed material. Optionally, in step (4), sodium carboxymethyl cellulose and water are first prepared into a sodium carboxymethyl cellulose solution; sodium carboxymethyl cellulose is first added to water to prepare a sodium carboxymethyl cellulose solution with a mass fraction of 2% to 3% (e.g., 2%, 2.5%, 2.6%, 3%), optionally using deionized water; and stirred at 60 to 80°C until uniformly dissolved, for example, by magnetic stirring. Optionally, sodium carboxymethyl cellulose and water are first prepared into a sodium carboxymethyl cellulose solution; then, the first modified rice husk, the second modified rice husk, and the modified biochar are mixed, and bridging powder, calcium chloride, and iron oxide are added and stirred until uniform to obtain a mixture; the sodium carboxymethyl cellulose solution is added to the mixture and stirred to form a wet mixture; optionally, the amount of sodium carboxymethyl cellulose used is sufficient to form a stable, non-dispersed, non-fluid state in the wet mixture after adding the sodium carboxymethyl cellulose aqueous solution.

[0101] In this embodiment of the invention, sodium carboxymethyl cellulose solution is added to a solid mixture and stirred continuously to make sodium carboxymethyl cellulose evenly distributed between the first modified rice husk, the second modified rice husk, and the modified biochar, forming a wet mixture that can be pressed and molded and does not contain obvious free water.

[0102] In some embodiments, in step (4), the wet mixed material is then pressed into shape and dried to obtain a dual-source composite slow-release carbon source; Optionally, the wet mixture is filled into a mold and pressed into shape, the mold including a spherical, ellipsoidal or short cylindrical mold; Optionally, the pressing pressure is 1.0~1.5MPa, specifically, for example, 1.0MPa, 1.1MPa, 1.2MPa, 1.3MPa, 1.4MPa, 1.5MPa; the pressing holding time is 30~60 seconds (s), specifically, for example, 30s, 40s, 50s, 60s; Optionally, drying can be carried out at 50~65℃ (e.g., 50℃, 55℃, 60℃, 65℃) for 12~20 hours (e.g., 12h, 15h, 18h, 20h). Optionally, the moisture content after drying is 12%~18%, resulting in a dual-source composite slow-release carbon source.

[0103] The application of a dual-source composite slow-release carbon source according to an embodiment of the present invention, or a dual-source composite slow-release carbon source prepared by the preparation method described in the embodiments of the present invention, is for water treatment.

[0104] In some embodiments, it is used for denitrification of water bodies; specifically, it is used for deep denitrification of wastewater treatment plant effluent, remediation of low C / N ratio surface water, treatment of groundwater nitrate pollution, or denitrification treatment of other low C / N ratio water bodies.

[0105] In some embodiments, the dual-source composite slow-release carbon source is used in a denitrification reactor as a slow-release carbon source and biofilm carrier for denitrifying microorganisms to remove nitrate nitrogen from the water. Optionally, the dual-source composite slow-release carbon is added to or filled into the denitrification reactor; Optionally, in the initial stage of water treatment operation, the modified biochar in the dual-pool composite slow-release carbon source desorbs at least part of the homologous soluble organic carbon from rice husk, and together with the first modified rice husk, provides the organic carbon required for denitrification startup. Optionally, as the operating time increases (e.g., in the later stages of water treatment operation), the second modified rice husk continues to release organic carbon to sustain the denitrification process.

[0106] A denitrification system according to an embodiment of the present invention includes: the dual-source composite slow-release carbon source described in the embodiment of the present invention or the dual-source composite slow-release carbon source prepared by the preparation method described in the embodiment of the present invention.

[0107] In some embodiments, the reactor body is also included, and the dual-source composite slow-release carbon source is filled inside the reactor body.

[0108] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0109] Experimental Example 1: Different Biomass Carbon Sources Experimental Methods: Canna indica, Thalia dealbata, rice husks, corn cobs, peanut shells, rice straw, and wheat straw biomass raw materials were cleaned and dried to constant weight in a 60℃ oven. After pulverization, the particles were sieved to a diameter of 0.4–0.8 mm for later use. 1.0 g of each biomass particle was weighed and placed in a 250 mL Erlenmeyer flask. 150 mL of deionized water was added, and the flask was continuously shaken and incubated at 25±1℃ and 150 rpm. Samples were taken at set times to determine the total organic carbon (TOC) and total nitrogen (TN) concentrations. TOC was measured using a total organic carbon analyzer, and TN was measured using alkaline potassium persulfate digestion-ultraviolet spectrophotometry. Three replicates were set for each treatment, and the average value was taken.

[0110] Figure 1 The total organic carbon release rate is the total organic carbon release rate of different biomass carbon sources. Among the biomass sources that can release organic carbon stably and efficiently, corn cobs and rice husks have the highest TOC concentration and can release organic carbon stably and efficiently.

[0111] Figure 2 The total nitrogen release rate of different biomass carbon sources was investigated. Among the above-mentioned different biomass sources, corn cob had the highest nitrogen release rate and was not suitable as a biomass feedstock for nitrogen removal.

[0112] Figure 3 It is the C / N ratio released by different biomass carbon sources. Figure 1 and Figure 2 The higher the C / N ratio, the more organic carbon and nitrogen are released, which is more conducive to denitrification. Rice husks have a C / N ratio higher than 8, which has the best performance, followed by canna lilies and tamarisk.

[0113] Experimental Example 2: Different Modification Methods Rice husks were crushed and sieved to obtain particles of 0.4–0.8 mm, and divided into 7 groups: rice husks (unmodified control group), hydrochloric acid treatment group, sodium hypochlorite treatment group, sodium hydroxide treatment group, sodium hydroxide + hot water bath treatment group, hydrogen peroxide treatment group, and sodium hydroxide + sodium hypochlorite combined treatment group.

[0114] The specific conditions for modification in each group are as follows: (1) Rice husk (unmodified control group): No treatment was performed.

[0115] (2) Hydrochloric acid treatment group: Rice husks were treated with a 5% hydrochloric acid solution at 60℃ for 12 h; (3) Sodium hypochlorite treatment group: Rice husks were treated with a 5% sodium hypochlorite solution at 60℃ for 12 h; (4) Sodium hydroxide treatment group: Rice husks were treated with a 10% sodium hydroxide solution at 60℃ for 12 h; (5) Sodium hydroxide + hot water bath treatment group: Rice husks were treated with a 10% sodium hydroxide solution and heated in an 80℃ water bath for 12 h; (6) Hydrogen peroxide treatment group: Rice husks were treated with a 5% hydrogen peroxide solution at 60℃ for 12 h; (7) Sodium hydroxide + sodium hypochlorite combined treatment group: Rice husks were treated at 60°C for 12 h with a mixed solution containing 10% sodium hydroxide and 5% sodium hypochlorite by mass. After modification, the rice husks were washed with deionized water until neutral and dried at 60℃. 1 g of each of the above groups of rice husks was placed in a 250 mL Erlenmeyer flask, 150 mL of deionized water was added, and the mixture was continuously shaken and cultured at 25±1℃ and 150 rpm. The total organic carbon (TOC) concentration of the water samples was periodically measured.

[0116] Figure 4 This involves screening methods for modifying biomass feedstocks. (By...) Figure 4 It can be seen that, compared with the unmodified control group, all treatment groups can increase the TOC release rate. Among them, sodium hydroxide and sodium hypochlorite can both promote the TOC release rate of rice husk to a certain extent, and the promoting effect is most obvious under the combined condition of sodium hydroxide and sodium hypochlorite.

[0117] Experimental Example 3: Different Adhesives A method for preparing a dual-source composite sustained-release carbon source includes the following steps: (1) The rice husks were crushed and sieved (0.4~0.8 mm) and divided into two portions, namely the first rice husk particles and the second rice husk particles. The first rice husk particles were subjected to the first alkali-oxidation composite modification treatment with a first composite modification solution containing 10% NaOH and 5% NaClO (60℃, 12 h). After the modification was completed, the rice husks were washed with water until neutral. Then, the washed rice husks after the first alkali-oxidation composite modification were soaked in water at a volume ratio of 1:30 to water and pre-extracted by shaking at 25℃ for 6 hours. The solid and liquid were separated to obtain the first water pre-extract and the first modified rice husk particles.

[0118] (2) The second rice husk particles were subjected to a second alkali-oxidation composite modification treatment (60℃, 12 h) using a second composite modification solution containing 5% NaOH and 2.5% NaClO by mass. After modification, the particles were washed with water until neutral. Then, the washed second alkali-oxidation composite modified rice husks were soaked in water at a volume ratio of 1:30 to water and pre-extracted at 25℃ for 6 hours. Solid-liquid separation was performed to obtain the second water pre-extract and the second modified rice husk particles.

[0119] (3) Combine the first aqueous pre-extract and the second aqueous pre-extract to obtain a mixture of the first aqueous pre-extract and the second aqueous pre-extract. Select biochar particles with a particle size of 0.3~0.6 mm and soak them in the mixture of the first aqueous pre-extract and the second aqueous pre-extract. The solid-liquid ratio of the biochar particles to the pre-extract mixture is 1:10 (g / mL). Shake and adsorb at 25℃ for 12 hours. After the adsorption is completed, the solid and liquid are separated to obtain modified biochar particles.

[0120] (4) Mix the first modified rice husk particles and the second modified rice husk particles at a mass ratio of 3:7, and then add the modified biochar particles so that the total volume ratio of the two types of modified rice husk particles to the volume ratio of the modified biochar particles is 2:1. Based on the total dry mass of the first modified rice husk particles, the second modified rice husk particles and the modified biochar, add 1.5% calcium chloride and 0.8% iron(III) oxide, stir and mix evenly to obtain a solid mixture. A 2.6% (w / w) aqueous solution of a candidate adhesive was added to the above solid mixture, namely CMC, polyvinyl alcohol, chitosan, or starch-PVA (starch to PVA mass ratio 7:3). The mixture was stirred continuously to form a wet mixture until a stable, non-dispersed, non-fluid state was formed. The mixture was then pressed into shape (1.5 MPa, 30 s) and dried at 65°C for 12 h to obtain dual-capacitor composite slow-release carbon source particles containing different adhesives. The mass addition of the adhesive was 1.5% based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar.

[0121] The wear residue rate was determined by wet oscillation abrasion method: 10 g of the above-mentioned test particles were placed in a 250 mL Erlenmeyer flask, and 200 mL of deionized water was added. The flask was oscillated continuously for 24 h at 25℃ and 150 rpm. The particles were then removed, dried to constant weight, and the remaining mass was weighed. The wear residue rate was calculated based on the dry weight of the particles after oscillation.

[0122] Figure 5 This refers to the wear resistance of materials prepared using different adhesives. Overall, CMC showed the highest wear residue rate, indicating that CMC has the best bonding strength and the strongest water resistance.

[0123] Experimental Example 4: Different Bridging Powders The preparation method is the same as that of the dual-source composite slow-release carbon source in Example 3. The difference is that in step (4), 1.6% of corn flour, wood flour, rice husk powder or starch is added as bridging powder to the solid mixture based on the total dry mass of the first modified rice husk particles, the second modified rice husk particles and the modified biochar. A control group without bridging powder is also set up. Each group is added with 2.6% sodium carboxymethyl cellulose solution as adhesive. After mixing evenly, the mixture is pressed into shape and dried at 65°C for 12 hours to obtain the dual-source composite slow-release carbon source.

[0124] Take 10 g of the above-mentioned test particles and place them in a 250 mL Erlenmeyer flask. Add 200 mL of deionized water and shake continuously for 24 h at 25℃ and 150 rpm. Take out the particles, dry them to constant weight, weigh the remaining mass, and calculate the wear residue rate based on the dry weight of the particles after shaking.

[0125] Figure 6 The stability of materials prepared using different bridging powders was tested. Bridging powders are used to fill the gaps between modified rice husk and modified biochar particles, enhancing adhesion and solving the problems of difficult molding and easy disintegration. Experiment 4 tested four types of bridging powders, with wear residue rates of 94.7% (without bridging powder), 96.8% (corn flour), 95.3% (wood flour), 94% (rice husk powder), and 95.5% (starch), with corn flour showing the best effect. Bridging powders fill part of the gaps between modified rice husk and modified biochar particles, increasing the effective bonding area between different particles and improving molding stability.

[0126] Experimental Example 5 The dual-source composite slow-release carbon source used in Example 4 is a dual-source composite slow-release carbon source with corn flour as the bridging powder.

[0127] (A) TOC adsorption of biochar: Biochar was mixed with the first water pre-extract and the second water pre-extract at a solid-liquid ratio of 1:10 (g / mL), and continuously shaken at 25±1℃ and 150 rpm. The TOC concentration was measured at 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 16, 20 and 24 h.

[0128] (B) Comparison of dual-source composite slow-release carbon and biomass carbon: 3.5 g of each of the dual-source composite slow-release carbon particles and the untreated biomass carbon (0.4–0.8 mm rice husk particles) were placed in 250 mL Erlenmeyer flasks, 150 mL of deionized water was added, and the flasks were allowed to stand at 25±1℃. Total organic carbon (TOC) concentrations were measured periodically. Three parallel samples were set up for each treatment, and the average value was taken. After 37 days of continuous operation, the cumulative release curve was plotted based on the measured TOC values ​​at each sampling point and the cumulative release rate was calculated using the cumulative release rate calculation formula.

[0129] Figure 7 It is the response of modified biochar particles after adsorbing water pre-extract to the dual-source composite slow-release carbon. Figure 7 In Figure (A), biochar clearly adsorbed the organic carbon in the water pre-extract, and the concentration of TOC in the solution decreased from 317.5 mg / L to 64.2 mg / L. Figure 7 In Figure (B), the dual-source composite slow-release carbon source particles of this invention contain modified biochar that adsorbs TOC from the water pre-extract, and the carbon source release rate is compared with that of untreated biomass carbon source (rice husk). The untreated biomass carbon source showed a faster release rate initially, followed by a slower release rate later. The dual-source composite slow-release carbon source particles, however, exhibited a more stable release rate, thus preventing the release of large amounts of organic carbon in the early stages. Both achieved similar TOC release levels of 199.46 mg / L and 191.48 mg / L, respectively, at 37 days.

[0130] Experimental Example 6: Long-term carbon source release stability Using the dual-source composite slow-release carbon material from Example 5, a static release test of the dual-source composite slow-release carbon material was conducted in a 200ml conical flask. The reaction conditions were: reaction volume 150ml, material loading 10g, running cycle 100d, sealing with sealing film to prevent water evaporation and external contamination, pH 7, no added microorganisms, operating temperature 25±1℃. After multiple samplings, the water will gradually be depleted, and the reaction system needs to be replenished with water periodically. The test was conducted in six phases.

[0131] Figure 8 This is a long-term carbon source release stability test of the dual-liquid composite slow-release carbon source. It can be seen that TOC maintains efficient and stable carbon source release even after a long release period of 100 days, demonstrating the long-term stability of the dual-liquid composite slow-release carbon source material of this invention, unlike other biomass materials that fail later due to rapid release. The first phase showed the fastest release rate, at 26.6 mg / (L·d) of TOC, while the fourth phase showed the slowest, at 14.4 mg / (L·d).

[0132] Experimental Example 7: Denitrification Performance Compared with the dual-source composite slow-release carbon source granular material in Experimental Example 5 of this invention, the material that does not contain calcium chloride and iron oxide (hereinafter referred to as the slow-release material without calcium chloride and iron oxide), corn cob, PHBV (polyhydroxybutyrate valerate), PHA (polyhydroxyalkanoate), and gravel are filled into five sets of conical flasks of the same capacity. The flasks were run continuously for 26 days under the conditions of nitrate nitrogen concentration in the influent water of 15 mg / L and temperature of 25±1℃, and samples were taken and measured every 2 days.

[0133] Figure 9 This study compares the denitrification performance of different materials. The results show that the average nitrate nitrogen removal rate of the dual-liquid composite slow-release carbon source particles of this invention is 85.8%, which is higher than that of the same material without calcium chloride and iron oxide (81.7%), corn cob (61.5%), and gravel (12.4%), and similar to that of PHBV (polyhydroxybutyrate valerate) (87.7%) and PHA (polyhydroxyalkanoate) (86.3%). The dual-liquid composite slow-release carbon source particles of this invention have a short start-up period after inoculation, similar to other chemical reagent carbon sources, which is about 10 days. After 10 days, the denitrification rate significantly increases. Considering the denitrification efficiency, start-up speed, and raw material cost, the dual-liquid composite slow-release carbon source particles of this invention have the potential to replace synthetic polymer slow-release carbon sources.

[0134] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0135] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A dual-source composite slow-release carbon source, characterized in that, include: First modified rice husk, second modified rice husk, modified biochar, calcium-containing components, iron tetroxide, and additives; The first modified rice husk is obtained by first alkali-oxidation composite modification treatment and first water pre-extraction treatment of rice husk; The second modified rice husk is obtained by subjecting the second rice husk to a second alkali-oxidation composite modification treatment and a second water pre-extraction treatment; The organic carbon release rate of the first modified rice husk is faster than that of the second modified rice husk. The modified biochar includes biochar loaded with readily soluble organic carbon from rice husks.

2. The dual-liquidity composite slow-release carbon source according to claim 1, characterized in that, The carbon release time of the second modified rice husk is longer than that of the first modified rice husk. And / or, the particle size of the first modified rice husk is 0.4~0.8 mm; And / or, the particle size of the second modified rice husk is 0.4~0.8 mm; And / or, the mass ratio of the first modified rice husk to the second modified rice husk is 2~4:6~8.

3. The dual-liquidity composite slow-release carbon source according to claim 1, characterized in that, The rice husk-based readily soluble organic carbon in the modified biochar is derived from the water pre-extract produced during the preparation of the first modified rice husk and / or the second modified rice husk. And / or, the modified biochar has a particle size of 0.3~0.6 mm; And / or, the total volume ratio of the first modified rice husk and the second modified rice husk to the volume ratio of the modified biochar is 1~3:

1.

4. The dual-liquidity composite slow-release carbon source according to claim 1, characterized in that, The calcium-containing component includes calcium chloride; And / or, based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the calcium-containing component is 1.0% to 1.5%; And / or, the particle size of the iron oxide is 0.25-0.35 mm; And / or, based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the iron oxide is 0.5%~1.0%; And / or, the additives include bridging powders and adhesives.

5. The dual-source composite slow-release carbon source according to claim 4, characterized in that, The adhesive includes sodium carboxymethyl cellulose; And / or, the bridging powder includes at least one of corn flour, wood flour, starch, and fine plant fiber powder; And / or, the bridging powder has a particle size of 0.6-0.9 mm; And / or, based on the total dry mass of the first modified rice husk, the second modified rice husk, and the modified biochar, the mass addition amount of the bridging powder is 1.0% to 3.0%.

6. The dual-liquidity composite slow-release carbon source according to claim 1, characterized in that, The shape of the dual-source composite slow-release carbon source includes at least one of spherical, ellipsoidal, or columnar shapes; And / or, the equivalent diameter of the dual-source composite slow-release carbon source is 14-20 mm; And / or, the moisture content of the dual-source composite slow-release carbon source is 12%~18%.

7. A method for preparing a dual-source composite sustained-release carbon source according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) The first rice husk is soaked in a first composite modification solution containing alkali and oxidizing reagent for the first alkali-oxidation composite modification treatment. After the modification is completed, it is washed until neutral. Then it is soaked in water for the first water pre-extraction treatment to obtain the first water pre-extraction solution and the first modified rice husk. (2) The second rice husk is soaked in a second composite modification solution containing alkali and oxidizing reagent for a second alkali-oxidation composite modification treatment. After the modification is completed, it is washed until neutral. Then it is soaked in water for a second water pre-extraction treatment to obtain a second water pre-extraction solution and a second modified rice husk. (3) Modified biochar is obtained by adsorbing the homologous soluble organic carbon of rice husk in the first water pre-extract and / or the second water pre-extract. (4) The first modified rice husk, the second modified rice husk, modified biochar, calcium-containing components, iron tetroxide, additives and water are mixed evenly to obtain a wet mixture; then the wet mixture is pressed into shape and dried to obtain a dual-source composite slow-release carbon source.

8. The method for preparing a dual-source composite sustained-release carbon source according to claim 7, characterized in that, In step (1), the particle size of the first rice husk is 0.4~0.8 mm; And / or, the base includes at least one of calcium hydroxide, sodium hydroxide, and potassium hydroxide; And / or, the oxidizing agent includes sodium hypochlorite; And / or, the solvent of the first composite modified solution includes water; And / or, in the first composite modified solution, the mass percentage concentration of the alkali is 8%~12%; And / or, in the first composite modified solution, the mass percentage concentration of the oxidizing agent is 4%~6%; And / or, the temperature of the first alkali-oxidation composite modification treatment is 40~80℃; And / or, the first alkali-oxidation composite modification treatment time is 6~24 hours; And / or, in the first water pre-extraction treatment, the solid-liquid volume ratio of rice husk to water after the first alkali-oxidation composite modification is 0.8~1.2:30; And / or, the temperature of the first water pre-extraction treatment is 20~30℃; And / or, the first water pre-extraction treatment time is 2 to 6 hours.

9. The method for preparing a dual-source composite sustained-release carbon source according to claim 7, characterized in that, In step (2), the particle size of the second rice husk is 0.4~0.8 mm; And / or, the base includes at least one of calcium hydroxide, sodium hydroxide, and potassium hydroxide; And / or, the oxidizing agent includes sodium hypochlorite; And / or, the solvent of the second composite modified solution includes water; And / or, in the second composite modified solution, the mass percentage concentration of the alkali is 4%~8%; And / or, in the second composite modified solution, the mass percentage concentration of the oxidizing agent is 2%~4%; And / or, the temperature of the second alkali-oxidation composite modification treatment is 40~80℃; And / or, the second alkali-oxidation composite modification treatment time is 6~24 hours; And / or, in the second water pre-extraction treatment, the solid-liquid volume ratio of rice husk to water after the second alkali-oxidation composite modification is 0.8~1.2:30; And / or, the temperature of the second water pre-extraction treatment is 20~30℃; And / or, the second water pre-extraction treatment time is 2 to 6 hours.

10. The method for preparing a dual-source composite sustained-release carbon source according to claim 7, characterized in that, The first alkali-oxidation composite modification treatment satisfies at least one of the following conditions (A) to (D) relative to the second alkali-oxidation composite modification treatment: (A) The first composite modified solution has a high alkali concentration; (B) The concentration of the oxidizing agent in the first composite modified solution is relatively high; (C) The temperature of the first alkali-oxidation composite modification treatment is relatively high; (D) The first alkali-oxidation composite modification treatment takes a long time.

11. The method for preparing a dual-source composite sustained-release carbon source according to claim 7, characterized in that, In step (3), the adsorption temperature is 20~30℃; And / or, in step (3), oscillation is performed during the adsorption process; And / or, in step (3), the adsorption time is 6 to 12 hours; And / or, in step (3), the ratio of the mass of the biochar to the total volume of the first water pre-extract and / or the second water pre-extract is 1~1.2g:0.5~30mL; And / or, the first water pre-extraction treatment and the second water pre-extraction treatment are carried out in the same water system to obtain a mixed water pre-extraction solution. In step (3), biochar is used to adsorb the rice husk homologous soluble organic carbon in the mixed water pre-extraction solution to obtain modified biochar. And / or, in step (4), the pressing pressure is 1.0~1.5MPa; And / or, in step (4), the holding time for pressing is 30 to 60 seconds.

12. The application of a dual-source composite sustained-release carbon source according to any one of claims 1 to 6 or a dual-source composite sustained-release carbon source prepared by any one of claims 7 to 11, characterized in that, Used for water treatment.

13. The application according to claim 12, characterized in that, Used for nitrogen removal in water bodies; And / or, the dual-source composite slow-release carbon source is used in a denitrification reactor as a slow-release carbon source and biofilm carrier for denitrifying microorganisms to remove nitrate nitrogen from water. And / or, in the initial stage of water treatment operation, the modified biochar in the dual-pool composite slow-release carbon source desorbs at least part of the homologous soluble organic carbon from rice husk, and together with the first modified rice husk, provides the organic carbon required for denitrification startup. And / or, in the later stages of water treatment operation, the second modified rice husk continuously releases organic carbon to sustain the denitrification process.

14. A denitrification system, characterized in that, include: The dual-source composite sustained-release carbon source according to any one of claims 1 to 6 or the dual-source composite sustained-release carbon source prepared by any one of claims 7 to 11.

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