A slow-release carbon source material for biological denitrification, its preparation method and application

Abstract

This invention provides a slow-release carbon source material for biological denitrification, its preparation method, and its application. The slow-release carbon source material comprises a hydrogel framework and a carbon source carried by the hydrogel framework; wherein the carbon source comprises alkalized sugarcane bagasse and sodium acetate; the hydrogel framework comprises a porous structure formed by polyvinyl alcohol and sodium alginate; relative to 1 part by weight of alkalized sugarcane bagasse, the amount of sodium acetate is 0.5-2 parts by weight, and the amount of hydrogel framework is 1.5-2.5 parts by weight; the specific surface area of ​​the slow-release carbon source material is 5-25 m² / g. 2 / g; The slow-release carbon source material in this invention has excellent slow-release effect and good stability, and can maintain a high carbon source release level. It also has a high nitrogen removal rate when used for biological denitrification treatment of wastewater, especially wastewater with a low carbon-to-nitrogen ratio.

Description

Technical Field

[0001] This invention relates to the field of slow-release carbon source materials, and particularly to a slow-release carbon source material for biological denitrification, its preparation method, and its application. Background Technology

[0002] With the continuous development of society and the economy, my country is paying increasing attention to water environmental safety and imposing increasingly stringent standards on wastewater discharge. However, nitrogenous pollutants from industrial production, agricultural nitrogen fertilizers, and domestic wastewater are constantly being discharged into water bodies, increasing the total nitrogen content in wastewater and causing serious nitrogen pollution problems, including excessive nitrogen levels and low C / N ratio wastewater. Domestic wastewater in my country is mainly characterized by a low carbon-to-nitrogen ratio, and the lack of carbon sources leads to incomplete denitrification, thus reducing the denitrification effect and resulting in high nitrogen concentrations in the effluent. Currently, biological denitrification technology is widely used in wastewater treatment. In the biological denitrification process, denitrification is the key step, and sufficient organic carbon sources are essential for ensuring biological phosphorus and nitrogen removal from wastewater.

[0003] For wastewater with low C / N ratios and insufficient carbon sources, adding external carbon sources is the most widely used method. Currently, there are three main types of external carbon sources: liquid-phase, gas-phase, and solid-phase. Among traditional carbon sources, represented by low-molecular-weight organic matter, theoretically, the smaller the carbon source molecule, the easier it is for denitrifying bacteria to utilize, and the higher the nitrogen removal efficiency. However, the dosage is difficult to control and often requires complex control devices and continuous monitoring, thus increasing operating costs. Natural cellulose materials have advantages such as low price, low cost, easy availability, no secondary pollution, and no biotoxicity. However, these carbon sources are greatly affected by temperature and also face problems such as unstable carbon source release and clogging of the packing layer. Artificially synthesized biodegradable polymers are stable solid slow-release carbon sources, but they require trace elements for growth, and the high cost of synthetic materials limits their application.

[0004] In summary, given the current trend of low C / N ratios in domestic sewage, there is an urgent need to develop a composite slow-release carbon source material that is stable in carbon release, has a long carbon release cycle, is inexpensive, has good denitrification effect, and is biodegradable to achieve resource recycling. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a slow-release carbon source material for biological denitrification, its preparation method, and its application. The slow-release carbon source material of this invention has a good slow-release effect and a stable structure, which allows the carbon source release rate to remain at a high level for a long period of time, effectively extending the carbon release cycle. When used for biological denitrification treatment of wastewater, especially wastewater with a low carbon-to-nitrogen ratio, the slow-release carbon source material has an excellent denitrification effect, with not only a high nitrogen removal rate but also a significant increase in the total nitrogen removal.

[0006] The objective of this invention is mainly achieved through the following technical solutions.

[0007] In a first aspect, the present invention provides a slow-release carbon source material for biological denitrification, the slow-release carbon source material comprising a hydrogel framework and a carbon source carried by the hydrogel framework.

[0008] The carbon source includes sugarcane bagasse and sodium acetate that have undergone alkalization treatment.

[0009] The hydrogel framework comprises a porous structure formed from polyvinyl alcohol and sodium alginate.

[0010] The amount of sodium acetate is 0.5 to 2 parts by weight relative to 1 part by weight of alkalized sugarcane bagasse, and the amount of hydrogel skeleton is 1.5 to 4 parts by weight.

[0011] The specific surface area of ​​the slow-release carbon source material is 5-25 m². 2 / g.

[0012] Preferably, the porosity of the slow-release carbon source material is 20% to 80%, more preferably 40% to 80%.

[0013] Preferably, the porosity of the hydrogel skeleton is 30% to 90%, and more preferably 50% to 90%.

[0014] Preferably, the sugarcane bagasse treated with alkalization has a particle size of 0.1 mm to 0.5 mm, more preferably 0.1 mm to 0.3 mm.

[0015] Preferably, the alkalized bagasse comprises 16-20 wt% lignin, 28-35 wt% cellulose, and 15-20 wt% hemicellulose.

[0016] Preferably, the specific surface area of ​​the slow-release carbon source material is 6–22 m². 2 / g, preferably 8-20m 2 / g.

[0017] Preferably, relative to 1 part by weight of alkalized sugarcane bagasse, the amount of sodium acetate is 0.7 to 1.5 parts by weight, and the amount of hydrogel skeleton is 1.6 to 2.2 parts by weight.

[0018] Preferably, the weight ratio of the polyvinyl alcohol to the sodium alginate is 7 to 10:1.

[0019] In a second aspect, the present invention provides a method for preparing the slow-release carbon source material described in the first aspect, the method comprising the following steps:

[0020] Step (1): The sugarcane bagasse raw material is alkalized, dried and crushed to obtain alkalized sugarcane bagasse.

[0021] Step (2): Add 30-50 parts by weight of polyvinyl alcohol and 3-8 parts by weight of sodium alginate to 400-600 parts by volume of water and stir to obtain the hydrogel precursor.

[0022] Step (3): Mix 10-40 parts by weight of the alkalized bagasse obtained in step (1) and 10-35 parts by weight of sodium acetate with 30-75 parts by weight of the hydrogel precursor obtained in step (2) and shape them to obtain a slow-release carbon source material precursor. Then, the slow-release carbon source material precursor is cross-linked and cured under the action of a cross-linking agent.

[0023] Preferably, the sugarcane bagasse raw material comprises 18-22 wt% lignin, 40-50 wt% cellulose, 25-30 wt% hemicellulose and 1.5-3 wt% sugar.

[0024] Preferably, in step (1), the alkalization treatment is carried out in an alkaline solution, the alkaline solution being selected from at least one of sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution and ammonia water; preferably, the concentration of the alkaline solution is 1-5 wt%; and / or, relative to 20-50 g of bagasse raw material, the amount of the alkaline solution used is 300-500 ml.

[0025] Preferably, in step (1), the conditions for alkalization treatment include: a temperature of 20 to 30°C and a time of 20 to 24 hours.

[0026] Preferably, in step (1), before drying, the alkalized bagasse is washed until the pH is 6.8 to 7.2.

[0027] Preferably, in step (2), the stirring conditions include: a temperature of 80-95°C and a time of 1-3 hours.

[0028] Preferably, the stirring speed in step (2) is 130-150 rpm; the stirring frequency is once every 15-25 minutes; and the stirring time is 10-20 minutes per stirring.

[0029] Preferably, in step (3), the molding conditions include: a temperature of -15 to -25°C and a time of 10 to 15 hours.

[0030] Preferably, in step (3), the slow-release carbon source material precursor is impregnated into a crosslinking agent solution for crosslinking curing, wherein the crosslinking agent solution is a saturated boric acid solution containing 3-5 wt% CaCl2.

[0031] Preferably, the cross-linking curing conditions include: a temperature of 3-5°C and a time of 20-24 hours.

[0032] Thirdly, the present invention provides the application of the slow-release carbon source material described in the first aspect or the slow-release carbon source material prepared by the preparation method described in the second aspect in the field of wastewater treatment.

[0033] This invention has the following advantages:

[0034] (1) The slow-release carbon source material can give full play to the advantages of sugarcane bagasse and sodium acetate treated with alkalization as carbon sources. The two, together with the hydrogel skeleton, effectively improve the carbon source slow-release effect of the slow-release carbon source material, which is particularly suitable for biological denitrification treatment of wastewater with low carbon-nitrogen ratio.

[0035] (2) The slow-release carbon source material is used in the biological denitrification treatment process of low C / N ratio wastewater, which overcomes the difficulty of reduced microbial metabolic activity due to insufficient carbon source in the treatment of low C / N wastewater and enhances the denitrification efficiency in the denitrification process.

[0036] (3) The slow-release carbon source material of the present invention has stable carbon source release and a long release cycle;

[0037] (4) This invention realizes the resource utilization of agricultural waste (sugarcane bagasse). Attached Figure Description

[0038] Figure 1 The images are scanning electron microscope (SEM) images of the sustained-release carbon source materials. (A) to (C) are SEM images of the sustained-release carbon source materials M1, D1, and D2 prepared in Example 1, Comparative Example 1, and Comparative Example 2 before carbon source release, respectively; (a) to (c) are SEM images of the sustained-release carbon source materials M1, D1, and D2 prepared in Example 1, Comparative Example 1, and Comparative Example 2 after carbon source release, respectively.

[0039] Figure 2 The images show the elemental scans and energy dispersive spectroscopy (EDS) spectra of the slow-release carbon source materials. (A)–(C) are surface carbon elemental scans of the slow-release carbon source materials M1, D1, and D2 before carbon source release; (a)–(c) are surface nitrogen elemental scans of the slow-release carbon source materials M1, D1, and D2 before carbon source release; and (D)–(E) are EDS spectra of the slow-release carbon source materials M1, D1, and D2 before carbon source release.

[0040] Figure 3 The pseudo-second-order fitting curves of COD curves for the carbon release process of slow-release carbon source materials M1, D1 and D2 in clear water;

[0041] Figure 4 The graphs show the nitrogen removal rates during the biological denitrification process of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 10.

[0042] Figure 5 The following are influent COD curves for biological denitrification processes in Examples 1, 1, 2, and 10:

[0043] Figure 6 The COD curves of the effluent during the biological denitrification process of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 10 are shown. Detailed Implementation

[0044] The preferred embodiments of the invention will now be described in detail with reference to the accompanying drawings, which form part of the invention and, together with the embodiments thereof, serve to illustrate the principles of the invention.

[0045] The inventors of this invention discovered that by mixing alkalized sugarcane bagasse with sodium acetate and a hydrogel precursor to prepare a slow-release carbon source material, the carbon release rate of the slow-release carbon source material was stabilized, and the carbon release cycle was extended. Analysis suggests that the alkalized sugarcane bagasse in this invention contains a porous structure suitable for the adsorption and formation of biofilms by microorganisms, especially denitrifying bacteria. The hydrogel framework in this invention also possesses a specific porous structure, wrinkles, and grooves. After the alkalized sugarcane bagasse and the hydrogel framework are cross-linked and solidified in a specific composition ratio, a structure is formed in which the carbon source (alkalized sugarcane bagasse and sodium acetate) carried by the hydrogel framework is formed, further improving the slow-release effect and carbon release cycle.

[0046] Based on the above research, in a first aspect, the present invention provides a slow-release carbon source material for biological denitrification, the slow-release carbon source material comprising a hydrogel framework and a carbon source carried by the hydrogel framework;

[0047] The carbon source includes sugarcane bagasse and sodium acetate that have undergone alkalization treatment;

[0048] The hydrogel framework comprises a porous structure formed of polyvinyl alcohol and sodium alginate;

[0049] The amount of sodium acetate is 0.5 to 2 parts by weight relative to 1 part by weight of alkalized sugarcane bagasse, and the amount of hydrogel skeleton is 1.5 to 4 parts by weight.

[0050] The specific surface area of ​​the slow-release carbon source material is 5-25 m². 2 / g.

[0051] In this invention, the term "carbon release cycle" refers to the time from the start of releasing carbon source material into the water body (nitrogen-containing wastewater) to the point where the carbon source is released quickly and the carbon-nitrogen molar ratio rises to above 2.5 in a short period of time until the carbon-nitrogen molar ratio in the water body falls below 2.5 due to biological denitrification.

[0052] In this invention, before the carbon source is released, the slow-release carbon source material has a wrinkled, grooved and / or porous structure, which is conducive to the attachment and growth of microorganisms, especially denitrifying bacteria. As the carbon source is gradually released until it is completely released and only the hydrogel skeleton remains, the pores of the slow-release carbon source material gradually increase and enlarge. More and more denitrifying bacteria attach to it to form a uniform biofilm. When used for wastewater treatment, the biological denitrification capacity can be kept at a high level.

[0053] In a preferred embodiment of the present invention, the porosity of the slow-release carbon source material is 20%–80%, preferably 40%–80%; and / or, the porosity of the hydrogel framework is 30%–90%, preferably 50%–90%. The slow-release carbon source material and the hydrogel framework having this preferred porosity can further improve the biological denitrification capacity.

[0054] In this invention, the porosity of the slow-release carbon source material is detected before the carbon source is released, and the porosity of the hydrogel framework is detected after the slow-release carbon source material releases carbon in flowing water for 240 hours. This invention does not impose any special limitations on the porosity detection method; conventional detection methods used in the art, such as the Biosorption Spectrometry (BET) method, can be employed.

[0055] In a preferred embodiment of the present invention, the sugarcane bagasse treated with alkalization has a particle size of 0.1 mm to 0.5 mm, preferably 0.1 mm to 0.3 mm. Using sugarcane bagasse treated with alkalization with this preferred particle size allows the carbon source to be distributed more evenly in the hydrogel framework, and makes the slow-release carbon source material more likely to adsorb microorganisms, especially denitrifying bacteria, to form a biofilm, thereby improving the denitrification effect.

[0056] In this invention, the alkalized bagasse is obtained by alkalizing bagasse raw material. The bagasse raw material refers to the residue left after sugarcane is extracted, and its main components are cellulose, hemicellulose and lignin, with a small amount of disaccharides and monosaccharides remaining, as well as a certain amount of protein, fat, ash and other impurities.

[0057] Studies have found that bagasse has insufficient carbon supply capacity and cannot continuously provide a carbon source, making it unsuitable as a carbon source for denitrification. However, after alkalization treatment, bagasse is combined with sodium acetate as a carbon source, and then mixed with specific amounts of polyvinyl alcohol and sodium alginate to prepare a slow-release carbon source material with a hydrogel framework carrying the carbon source (alkalized bagasse and sodium acetate). This material not only exhibits excellent slow-release carbon source effects but also effectively promotes biological denitrification. Analysis suggests that alkalized bagasse is mainly composed of specific amounts of cellulose, hemicellulose, and lignin. The hydrogel formed with polyvinyl alcohol and sodium alginate, after cross-linking and solidification, produces a material with a unique wrinkled and grooved surface structure and porous structure. This structure is more conducive to the attachment of microorganisms, especially denitrifying bacteria, to form a biofilm, thus improving denitrification. Furthermore, the wrinkled, grooved, and / or porous structure further regulates the slow-release rate and amount of carbon source, ensuring a consistently high carbon-to-nitrogen ratio in the water and extending the carbon release cycle of the slow-release carbon source material.

[0058] In a preferred embodiment of the present invention, the alkalized bagasse comprises 16-20 wt% lignin, 28-35 wt% cellulose, and 15-20 wt% hemicellulose, preferably 17-19 wt% lignin, 30-33 wt% cellulose, and 16-18 wt% hemicellulose. Using alkalized bagasse with this preferred composition as a carbon source to prepare a slow-release carbon source material further optimizes the structure of the slow-release carbon source material, resulting in not only a better slow-release effect and a longer carbon release cycle, but also a higher utilization rate.

[0059] In this invention, the sugarcane bagasse treated with alkali also contains impurities such as protein, fat, and ash.

[0060] In this invention, the component contents of both the bagasse raw material and the alkalized bagasse are dry weight contents.

[0061] In a preferred embodiment of the present invention, the mass transfer coefficient of the carbon source in the slow-release carbon source material is 5–30 mg·(h·g·L), preferably 7–30 mg·(h·g·L). When the slow-release carbon source material of the present invention possesses this preferred mass transfer coefficient, the synergistic effect of the wrinkles, grooves, and porosity on the surface of the slow-release carbon source material results in an unexpected situation when used in biological denitrification processes: the amount of nitrogen removed initially decreases slowly and then increases. Analysis suggests that the release rate of the carbon source from the slow-release carbon source material gradually decreases over time. However, due to the numerous wrinkles, grooves, and more uniform pores on the surface of the slow-release carbon source material, more denitrifying bacteria can be adsorbed and attached. During the release process, the carbon source can be utilized more efficiently by the attached denitrifying bacteria. Although there is a decrease in the amount of nitrogen removed in the initial stage, the increase in the amount and area of ​​attached denitrifying bacteria compensates for the decrease in the amount of nitrogen removed due to the decrease in the carbon source release rate.

[0062] In a preferred embodiment of the present invention, the specific surface area of ​​the slow-release carbon source material is 6–22 m². 2 / g, preferably 8-20m 2 / g. Slow-release carbon source materials with this preferred specific surface area can control the slow-release rate of carbon source within a more reasonable range, maintain and stabilize a higher carbon-nitrogen ratio suitable for denitrification for a longer period of time, and further take into account the effective utilization of carbon source by microorganisms attached to the surface of slow-release carbon source materials and microorganisms in the water, thereby improving the denitrification rate and denitrification amount.

[0063] In this invention, the specific surface area can be detected by conventional methods in the art, such as the method in GB / T19587-2017.

[0064] The present invention does not have any special requirements on the shape of the slow-release carbon source material, and any shape known in the art can be used, such as sphere, cube, cuboid, cylinder, polygonal, triangular pyramid, preferably sphere and / or cube.

[0065] In a preferred embodiment of the present invention, the amount of sodium acetate is 0.7–1.5 parts by weight, and the amount of hydrogel framework is 1.6–2.2 parts by weight, relative to 1 part by weight of alkalized sugarcane bagasse. Within this preferred component content range, the slow-release carbon source material has a superior slow-release effect, and can further improve the denitrification effect when used for biological denitrification.

[0066] In a preferred embodiment of the present invention, the weight ratio of polyvinyl alcohol to sodium alginate in the hydrogel framework is 7–10:1, preferably 7–9:1. The hydrogel framework with this preferred ratio has a more stable structure, and the slow-release carbon source material can maintain a good slow-release effect during biological denitrification, resulting in a high level of biological denitrification.

[0067] The inventors of this invention discovered that sugarcane bagasse, due to its high lignin content and residual disaccharides and monosaccharides, exhibits a high initial carbon release rate and quantity in water bodies, followed by a rapid decrease in the later stages. This results in significant fluctuations in the carbon release rate throughout the entire carbon release cycle, which is detrimental to denitrification and can easily lead to secondary pollution due to excessively high initial carbon release. However, after alkalization treatment, the combination of alkalized sugarcane bagasse and sodium acetate, along with a specific amount of hydrogel precursor, produces a slow-release carbon source material with excellent carbon source slow-release effects. This not only effectively extends the carbon release cycle but also significantly improves the denitrification effect on wastewater.

[0068] In a second aspect, the present invention provides a method for preparing the slow-release carbon source material described in the first aspect, the method comprising the following steps:

[0069] Step (1): The sugarcane bagasse raw material is alkalized, dried and crushed to obtain alkalized sugarcane bagasse;

[0070] Step (2): Add 30-50 parts by weight of polyvinyl alcohol and 3-8 parts by weight of sodium alginate to 400-600 parts by volume of water and stir to obtain the hydrogel precursor;

[0071] Step (3): Mix 10-40 parts by weight of the alkalized bagasse obtained in step (1) and 10-35 parts by weight of sodium acetate with 30-75 parts by weight of the hydrogel precursor obtained in step (2) and shape them to obtain a slow-release carbon source material precursor. Then, the slow-release carbon source material precursor is cross-linked and cured under the action of a cross-linking agent.

[0072] In this invention, the main components of the sugarcane bagasse raw material are cellulose, hemicellulose, and lignin, with a small amount of residual sugar, and also contain a certain amount of protein, fat, ash, and other impurities. Preferably, the sugarcane bagasse raw material comprises 18-22 wt% lignin, 40-50 wt% cellulose, 25-30 wt% hemicellulose, and 1.5-3 wt% sugar, and more preferably comprises 18-20 wt% lignin, 40-48 wt% cellulose, 25-28 wt% hemicellulose, and 1.5-3 wt% sugar. Using sugarcane bagasse raw material with this preferred composition through alkalization treatment, the alkalized sugarcane bagasse, when used in conjunction with a hydrogel framework, can more effectively leverage the synergistic effect of the two in spatial structure, further improving the slow-release effect of the carbon source and being more beneficial for denitrification treatment of water bodies. Furthermore, the sugars contained in the sugarcane bagasse raw material are mainly disaccharides (such as sucrose) and monosaccharides.

[0073] In a preferred embodiment of the present invention, the alkalization treatment is carried out in an alkaline solution, wherein the alkaline solution is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution and ammonia water; more preferably sodium hydroxide solution; and / or, the concentration of the alkaline solution is 1-5 wt% (which can be any value among 1.3 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, and 5 wt%, or any value between any two adjacent values), and preferably 1-3 wt%; and / or, relative to 20-50 g of bagasse raw material, the amount of the alkaline solution used is 300-500 ml, preferably 350-450 ml; and / or, in step (1), the conditions for the alkalization treatment include: a temperature of 20-30°C, preferably 23-27°C; and a time of 20-24 h. By employing this preferred alkalization treatment method, the pore structure of the alkalized bagasse can be further optimized. On the one hand, the carbon source release rate of the alkalized bagasse is more stable. On the other hand, the alkalized bagasse has better adsorption performance for microorganisms, especially denitrifying bacteria. In synergy with the hydrogel framework, it can exert a better carbon source slow release effect and a biofilm formation effect on microorganisms, especially denitrifying bacteria, thus forming a more uniform biofilm and providing denitrification effect.

[0074] In a preferred embodiment of the present invention, in step (1), before drying, the alkalized sugarcane bagasse is washed until the pH is 6.8-7.2. Since a washing step is performed after alkalization, the sugarcane bagasse obtained after alkalization basically does not contain disaccharides and monosaccharides, which can be ignored.

[0075] In a preferred embodiment of the present invention, in step (2), 35-45 parts by weight of polyvinyl alcohol and 4-6 parts by weight of sodium alginate are added to 450-550 parts by volume of water and stirred to obtain a hydrogel precursor. The hydrogel precursor prepared using this preferred ratio, after cross-linking and curing, forms a hydrogel framework that can more uniformly coat the alkalized bagasse and sodium acetate, resulting in a larger and more uniform carbon release area. Furthermore, it is more conducive to leveraging the synergistic carbon release and biofilm formation effects of the alkalized bagasse and the hydrogel framework, thereby improving the denitrification effect.

[0076] In a preferred embodiment of the present invention, the stirring conditions in step (2) include: a temperature of 80–95°C and a time of 1–3 h; and / or, the stirring speed in step (2) is 130–150 rpm, preferably 135–145 rpm; the stirring frequency is once every 15–25 min, preferably once every 18–25 min; and the stirring time is 10–20 min / time, preferably 15–20 min / time. These preferred stirring conditions result in a more uniform pore structure and more wrinkles and grooves in the slow-release carbon source material, further improving the adsorption effect of the slow-release carbon source material on denitrifying bacteria and the slow-release effect of the carbon source, thereby improving the biological denitrification effect.

[0077] In a preferred embodiment of the present invention, in step (3), 20-30 parts by weight of the alkalized sugarcane bagasse obtained in step (1) and 20-30 parts by weight of sodium acetate are mixed with 32-66 parts by weight of the hydrogel precursor obtained in step (2) and shaped to obtain a slow-release carbon source material precursor, and then the slow-release carbon source material precursor is cross-linked and cured under the action of a cross-linking agent.

[0078] In a preferred embodiment of the present invention, the molding conditions in step (3) include: a temperature of -15 to -25°C and a time of 10 to 15 hours.

[0079] In a preferred embodiment of the present invention, step (3) involves cross-linking and curing a slow-release carbon source material precursor by impregnating it in a cross-linking agent solution, wherein the cross-linking agent solution is a saturated boric acid solution containing 3–5 wt% CaCl2; and / or, the cross-linking and curing conditions include a temperature of 3–5°C and a time of 20–24 h. These preferred cross-linking and curing conditions are more conducive to improving the slow-release effect and structural stability of the slow-release carbon source material.

[0080] In this invention, the weight of the hydrogel framework is based on the hydrogel precursor.

[0081] Thirdly, the present invention provides the application of the slow-release carbon source material described in the first aspect or the slow-release carbon source material prepared by the preparation method described in the second aspect in the field of wastewater treatment.

[0082] The following detailed description of preferred embodiments of the present invention illustrates the principles of the invention and is not intended to limit the scope of the invention.

[0083] Cycle (denitrification cycle): The entire process of wastewater influent, biological denitrification, settling and effluent discharge constitutes one denitrification cycle;

[0084] Surface structure of the slow-release carbon source material: Detected and analyzed using a scanning electron microscope (Hitachi Regulus 8100).

[0085] Energy dispersive spectroscopy (EDS), surface carbon (C) element distribution, and surface nitrogen (N) element distribution of the slow-release carbon source material were analyzed using EDS and SEM. The EDS unit was a Thermo Kalpha, and the SEM unit was a Hitachi Regulus 8100.

[0086] Specific surface area: tested and analyzed according to the method of GB / T 19587-2017;

[0087] Porosity: determined using the gas adsorption method (BET method);

[0088] COD in water: The method in the standard HJ / T 399-200, which uses alkaline potassium persulfate digestion and ultraviolet spectrophotometry, was used for detection.

[0089] Nitrogen removal rate: The method was determined according to the method in the rapid digestion spectrophotometric method of potassium dichromate (HJ 636-2012).

[0090] Total nitrogen removal: When the carbon-nitrogen ratio in the water is below 2.5, the nitrogen removal experiment is stopped. At this time, the total nitrogen removal is calculated as follows: (Total nitrogen in the water before nitrogen removal - Total nitrogen in the water after nitrogen removal) ÷ ​​Total nitrogen in the water before nitrogen removal × 100%.

[0091] Sugarcane bagasse raw material: cellulose content 45wt%, hemicellulose content 27wt%, lignin content 20wt%, sugar content 2wt%, and the remainder includes impurities such as protein, fat, and ash;

[0092] Corn stalks: 40wt% cellulose, 25wt% hemicellulose, 20wt% lignin, 1wt% sugar, with the remainder including impurities such as protein, fat, and ash.

[0093] Preparation Example 1

[0094] I. Preparation of slow-release carbon source materials:

[0095] Step (1): Mix 40 parts by weight of sugarcane bagasse raw material dried to constant weight with 400 parts by volume of sodium hydroxide with a concentration of 1.5 wt% and carry out alkalization treatment (alkalization temperature is 25℃, time is 24h).

[0096] After the sugarcane bagasse raw material is alkalized, it is washed with water until the pH of the washing solution reaches 7, and then dried at 60°C to constant weight. After being crushed and sieved, alkalized sugarcane bagasse with a particle size distribution of 0.2 mm is obtained (cellulose content 32wt%, hemicellulose content 17wt%, lignin content 18wt%, and the balance being protein, fat, ash, etc.).

[0097] Step (2): Add 40 parts by weight of polyvinyl alcohol and 5 parts by weight of sodium alginate to 500 parts by volume of ultrapure water, stir at 95°C at a speed of 140 rpm, stir once every 20 min for 15 min each time, and the hydrogel precursor is obtained after 2 h.

[0098] Step (3): Mix 25 parts by weight of alkalized sugarcane bagasse and 25 parts by weight of sodium acetate with 50 parts by weight of the hydrogel precursor prepared in step (2), and then pour into a 1cm... 3 The material was molded in a cubic mold at -20℃ for 12 hours and then demolded. The molded slow-release carbon source material precursor was then immersed in a saturated boric acid solution containing 4% CaCl2 for cross-linking and curing (the cross-linking and curing temperature was 4℃ and the cross-linking and curing time was 24 hours).

[0099] After crosslinking and curing, residual crosslinking agent was rinsed off the surface with ultrapure water, and then dried at 60°C until the material reached constant weight, yielding the slow-release carbon source material M1. Scanning electron microscopy analysis revealed the surface structure of the slow-release carbon source material M1 as follows: Figure 1 The energy spectrum of the slow-release carbon source material M1, as analyzed by EDS and SEM scanning, is shown below. Figure 2 As shown in (D), the C element distribution on the surface is as follows: Figure 2 As shown in (A), the distribution of element N is as follows: Figure 2 As shown in (a);

[0100] The results of measuring the specific surface area of ​​M1, the porosity of M1 before carbon release, and the porosity (porosity of the hydrogel skeleton) of M1 after carbon release are shown in Table 4.

[0101] Preparation Example 2

[0102] I. Preparation of slow-release carbon source materials:

[0103] Step (1) Mix 35 parts by weight of sugarcane bagasse raw material dried to constant weight with 450 parts by volume of sodium hydroxide with a concentration of 1 wt% and carry out alkalization treatment (alkalization temperature is 20℃ and time is 20h).

[0104] After the sugarcane bagasse raw material is alkalized, it is washed with water until the pH of the washing solution reaches 7, and then dried at 60°C to constant weight. After being crushed and sieved, alkalized sugarcane bagasse with a particle size distribution of 0.1 mm is obtained (cellulose content 35wt%, hemicellulose content 20wt%, lignin content 20wt%, and the balance being protein, fat, ash, etc.).

[0105] Step (2) Add 36 parts by weight of polyvinyl alcohol and 4 parts by weight of sodium alginate to 550 parts by volume of ultrapure water, stir at 95°C at a speed of 130 rpm, stir once every 20 min for 10 min each time, and the hydrogel precursor is obtained after 2 h.

[0106] Step (3) Mix 20 parts by weight of alkalized sugarcane bagasse and 30 parts by weight of sodium acetate with 32 parts by weight of the hydrogel precursor prepared in step (2), and then pour into a 1 cm... 3 The material was molded in a cubic mold at -20℃ for 12 hours and then demolded. The molded slow-release carbon source material precursor was then immersed in a saturated boric acid solution containing 4% CaCl2 for cross-linking and curing (the cross-linking and curing temperature was 4℃ and the cross-linking and curing time was 24 hours).

[0107] After cross-linking and curing, the surface residual cross-linking agent is rinsed with ultrapure water, and then dried at 60°C until the material reaches constant weight to obtain slow-release carbon source material M2.

[0108] The results of the determination of the specific surface area of ​​M2, the porosity of M2 before carbon release, and the porosity (porosity of the hydrogel skeleton) of M2 after carbon release are shown in Table 4.

[0109] Preparation Example 3

[0110] I. Preparation of slow-release carbon source materials:

[0111] Step (1) Mix 45 parts by weight of sugarcane bagasse raw material dried to constant weight with 350 parts by volume of sodium hydroxide with a concentration of 2wt% and carry out alkalization treatment (alkalization temperature is 20℃ and time is 20h).

[0112] After the sugarcane bagasse raw material is alkalized, it is washed with water until the pH of the washing solution reaches 7, and then dried at 60°C to constant weight. After being crushed and sieved, alkalized sugarcane bagasse with a particle size distribution of 0.3 mm is obtained (cellulose content 30wt%, hemicellulose content 16wt%, lignin content 17wt%, and the balance being protein, fat, ash, etc.).

[0113] Step (2) Add 42 parts by weight of polyvinyl alcohol and 6 parts by weight of sodium alginate to 450 parts by volume of ultrapure water, stir at 95°C, and stir at a speed of 150 rpm. The stirring frequency is once every 20 min, and the stirring time is 20 min / time. After 2 hours, the hydrogel precursor is prepared.

[0114] Step (3) Mix 30 parts by weight of alkalized sugarcane bagasse and 20 parts by weight of sodium acetate with 66 parts by weight of the hydrogel precursor prepared in step (2), and then pour into a 1 cm... 3 The material was molded in a cubic mold at -20℃ for 12 hours and then demolded. The molded slow-release carbon source material precursor was then immersed in a saturated boric acid solution containing 4% CaCl2 for cross-linking and curing (the cross-linking and curing temperature was 4℃ and the cross-linking and curing time was 24 hours).

[0115] After cross-linking and curing, the surface residual cross-linking agent is rinsed with ultrapure water, and then dried at 60°C until the material reaches constant weight to obtain slow-release carbon source material M3.

[0116] The results of measuring the specific surface area of ​​M3, the porosity of M3 before carbon release, and the porosity (porosity of the hydrogel skeleton) of M3 after carbon release are shown in Table 4.

[0117] Preparation Example 4

[0118] The slow-release carbon source material was prepared according to the method in Example 1, except that...

[0119] I. Preparation of slow-release carbon source materials:

[0120] Step (1) Mix 40 parts by weight of sugarcane bagasse raw material dried to constant weight with 400 parts by volume of sodium hydroxide with a concentration of 1.5 wt% and carry out alkalization treatment (alkalization temperature is 25℃ and time is 24h).

[0121] After the sugarcane bagasse raw material is alkalized, it is washed with water until the pH of the washing solution reaches 7, and then dried at 60°C to constant weight. After being crushed and sieved, alkalized sugarcane bagasse with a particle size distribution of 0.2 mm is obtained.

[0122] Step (2) Add 40 parts by weight of polyvinyl alcohol and 5 parts by weight of sodium alginate to 500 parts by volume of ultrapure water, stir at 78°C at a speed of 120 rpm, stir once every 30 min for 10 min each time, and the hydrogel precursor is obtained after 2 h.

[0123] Step (3) Mix 25 parts by weight of alkalized sugarcane bagasse and 25 parts by weight of sodium acetate with 50 parts by weight of the hydrogel precursor prepared in step (2), and then pour into a 1 cm... 3The material was demolded and formed in a cubic mold at -20℃ for 12 hours. Then, the formed slow-release carbon source material precursor was immersed in a saturated boric acid solution containing 4% CaCl2 for cross-linking and curing (the cross-linking and curing temperature was 10℃ and the cross-linking and curing time was 30 hours).

[0124] After crosslinking and curing, the surface residual crosslinking agent is rinsed with ultrapure water, and then dried at 60°C until the material reaches constant weight, thus obtaining the slow-release carbon source material M4.

[0125] The results of measuring the specific surface area of ​​M4, the porosity of M4 before carbon release, and the porosity (porosity of the hydrogel skeleton) of M4 after carbon release are shown in Table 4.

[0126] Preparation Example 5

[0127] The slow-release carbon source material was prepared according to the method in Example 1, with the following difference:

[0128] I. Preparation of slow-release carbon source materials:

[0129] Step (1) Mix 40 parts by weight of sugarcane bagasse raw material dried to constant weight with 400 parts by volume of sodium hydroxide with a concentration of 1 wt% and carry out alkalization treatment (alkalization temperature is 25℃, time is 12h).

[0130] After the sugarcane bagasse raw material is alkalized, it is washed with water until the pH of the washing solution reaches 7, and then dried at 60°C to constant weight. After being crushed and sieved, alkalized sugarcane bagasse with a particle size distribution of 0.2 mm is obtained (cellulose content 40 wt%, hemicellulose content 25 wt%, lignin content 19 wt%, and the balance being protein, fat, ash, etc.).

[0131] M5, a slow-release carbon source material, was obtained.

[0132] The results of the determination of the specific surface area of ​​M5, the porosity of M5 before carbon release, and the porosity (porosity of the hydrogel skeleton) of M5 after carbon release are shown in Table 4.

[0133] Preparation Example 6

[0134] The slow-release carbon source material was prepared according to the method of Example 1, except that the sugarcane bagasse treated with alkalization had a particle size of 0.8 mm.

[0135] M6, a slow-release carbon source material, was obtained.

[0136] The results of measuring the specific surface area, porosity of M6 before carbon release, and porosity (hydrogel skeleton porosity) of M6 after carbon release are shown in Table 4.

[0137] Preparation Example 7

[0138] The slow-release carbon source material and biological denitrification experiment were prepared according to the method in Example 1, except that sugarcane bagasse was replaced with an equal amount of sodium acetate.

[0139] The slow-release carbon source material D1 was obtained.

[0140] Scanning electron microscopy analysis revealed the following surface structure of the slow-release carbon source material D1: Figure 1 The energy spectrum of the slow-release carbon source material D1, as analyzed by EDS and SEM, is shown below. Figure 2 As shown in (E), the C element distribution on the surface is as follows: Figure 2 As shown in (B), the distribution of element N is as follows: Figure 2 As shown in (b);

[0141] The results of the determination of the specific surface area of ​​D1, the porosity of D1 before carbon release, and the porosity (porosity of hydrogel skeleton) of D1 after carbon release are shown in Table 4.

[0142] Preparation Example 8

[0143] The slow-release carbon source material and biological denitrification experiment were prepared according to the method in Example 1, except that sodium acetate was replaced with an equal amount of alkalized sugarcane bagasse.

[0144] The slow-release carbon source material D2 was obtained.

[0145] Scanning electron microscopy analysis revealed the surface structure of the slow-release carbon source material D2 as follows: Figure 1 The energy dispersive spectroscopy (EDS) spectrum of the slow-release carbon source material D2, as analyzed by EDS and SEM, is shown below. Figure 2 As shown in (F), the C element distribution on the surface is as follows. Figure 2 As shown in (C), the distribution of element N is as follows: Figure 2 As shown in (c);

[0146] The results of the determination of the specific surface area of ​​D2, the porosity of D2 before carbon release, and the porosity (porosity of hydrogel skeleton) of D2 after carbon release are shown in Table 4.

[0147] Preparation Example 9

[0148] The slow-release carbon source material was prepared according to the method in Example 1, except that...

[0149] I. Preparation of slow-release carbon source materials:

[0150] Step (1) Mix 40 parts by weight of sugarcane bagasse raw material dried to constant weight with 400 parts by volume of sodium hydroxide with a concentration of 1.5 wt% and carry out alkalization treatment (alkalization temperature is 25℃ and time is 24h).

[0151] After the sugarcane bagasse raw material is alkalized, it is washed with water until the pH of the washing solution reaches 7, and then dried at 60°C to constant weight. After being crushed and sieved, alkalized sugarcane bagasse with a particle size distribution of 0.2 mm is obtained.

[0152] Step (2) Add 22 parts by weight of polyvinyl alcohol and 2 parts by weight of sodium alginate to 500 parts by volume of ultrapure water, stir at 95°C, and stir at a speed of 120 rpm. The stirring frequency is once every 30 min, and the stirring time is 30 min / time. After 2 hours, the hydrogel precursor is prepared.

[0153] Step (3) Mix 42 parts by weight of alkalized sugarcane bagasse and 8 parts by weight of sodium acetate with 50 parts by weight of the hydrogel precursor prepared in step (2), and then pour into a 1 cm... 3 The material was molded in a cubic mold at -20℃ for 12 hours and then demolded. The molded slow-release carbon source material precursor was then immersed in a saturated boric acid solution containing 4% CaCl2 for cross-linking and curing (the cross-linking and curing temperature was 4℃ and the cross-linking and curing time was 24 hours).

[0154] After crosslinking and curing, the surface residual crosslinking agent is rinsed with ultrapure water, and then dried at 60°C until the material reaches constant weight to obtain slow-release carbon source material D3.

[0155] The results of the determination of the specific surface area of ​​D3, the porosity of D3 before carbon release, and the porosity (porosity of hydrogel skeleton) of D3 after carbon release are shown in Table 4.

[0156] Preparation Example 10

[0157] The slow-release carbon source material was prepared according to the method of Example 1, except that the sugarcane bagasse raw material was replaced with an equal amount of corn stalks.

[0158] The slow-release carbon source material D4 was obtained.

[0159] The results of the determination of the specific surface area of ​​D4, the porosity of D4 before carbon release, and the porosity (porosity of hydrogel skeleton) of D4 after carbon release are shown in Table 4.

[0160] Preparation Example 11

[0161] The slow-release carbon source material was prepared according to the method of Example 1, except that the sugarcane bagasse raw material was replaced with an equal amount of corn stalks, and the sodium acetate was replaced with an equal amount of corn stalks.

[0162] The slow-release carbon source material D5 was obtained.

[0163] The results of the determination of the specific surface area of ​​D5, the porosity of D5 before carbon release, and the porosity (porosity of hydrogel skeleton) of D5 after carbon release are shown in Table 4.

[0164] Preparation Example 12

[0165] The slow-release carbon source material was prepared according to the method of Example 1, except that sodium acetate was replaced with an equal amount of glucose.

[0166] The slow-release carbon source material D6 was obtained.

[0167] The results of the determination of the specific surface area of ​​D6, the porosity of D6 before carbon release, and the porosity (porosity of hydrogel skeleton) of D6 after carbon release are shown in Table 4.

[0168] Preparation Example 13

[0169] The slow-release carbon source material was prepared according to the method of Example 1, except that sodium acetate was replaced with an equal amount of starch.

[0170] The slow-release carbon source material D7 was obtained.

[0171] The results of the determination of the specific surface area of ​​D7, the porosity of D7 before carbon release, and the porosity (porosity of hydrogel skeleton) of D7 after carbon release are shown in Table 4.

[0172] Preparation Example 14

[0173] The slow-release carbon source material was prepared according to the method of Example 1, except that in step (3), 25 parts by weight of alkalized sugarcane bagasse and 5 parts by weight of sodium acetate were mixed with 70 parts by weight of the hydrogel precursor prepared in step (2).

[0174] The slow-release carbon source material D8 was obtained.

[0175] The results of the determination of the specific surface area of ​​D8, the porosity of D8 before carbon release, and the porosity (porosity of hydrogel skeleton) of D8 after carbon release are shown in Table 4.

[0176] Preparation Example 15

[0177] The slow-release carbon source material was prepared according to the method in Example 1, except that the bagasse raw material was not carbonized, but directly dried to constant weight at 60°C, and then crushed and sieved to obtain bagasse raw material with a particle size distribution of 0.2 mm.

[0178] The slow-release carbon source material D9 was obtained.

[0179] The results of the determination of the specific surface area of ​​D9, the porosity of D9 before carbon release, and the porosity (porosity of hydrogel skeleton) of D9 after carbon release are shown in Table 4.

[0180] Preparation Example 16

[0181] Preparation of acclimatized sludge:

[0182] The sludge to be acclimated was taken from the anoxic section of the A2O biological tank in the sewage treatment plant, with an MLSS of 7500 mg / L.

[0183] Step (S01) At a temperature of 30℃ and a dissolved oxygen content of 0.3 mg / mL, the sludge to be acclimated and the acclimation water (composition shown in Tables 1 and 2) are mixed at a volume ratio of 1:4 (MLSS after mixing is 7700 mg / L), stirred for 8 hours and then allowed to stand, and then the supernatant is removed.

[0184] Step (S02) Continue to add acclimatization water to the sludge after removing the supernatant, and repeat step (S01);

[0185] Step (S03) is repeated until the TN removal rate of the supernatant is 90%, the acclimation is completed, and acclimated sludge is obtained.

[0186] Example 1

[0187] Conduct biological denitrification experiments using the following methods.

[0188] Step (S1) Filling with slow-release carbon source material: The slow-release carbon source material M1 is loaded into porous hollow suspended spheres (8 cm in diameter and 3 mm in surface pore size) with a filling rate of 85% (i.e., occupying 85% of the volume of the porous hollow suspended spheres). Then, the porous hollow suspended spheres filled with slow-release carbon source material M1 are filled into the bioreactor and mixed with the acclimated sludge of Preparation Example 16 in the bioreactor. The filling amount of the slow-release carbon source material is 30 g / L of the bioreactor.

[0189] Step (S2) Influent: Wastewater with a C / N ratio of 2.5:1 is introduced into the bioreactor and contacted with the mixture formed by the slow-release carbon source material and sludge (the ratio of acclimated sludge to influent wastewater is 280 mg: 1 L).

[0190] After the influent in step (S3) is completed, the wastewater is subjected to denitrification under denitrification conditions (oxygen content of 0.3 mg / mL, temperature of 30℃, pH value of 7.2, hydraulic retention time of 7h, stirring speed of 140 rpm) to obtain denitrified water, and then the obtained denitrified water is allowed to stand for 1h.

[0191] Step (S4) Effluent: The denitrified water that has been allowed to stand in step (S3) is discharged from the bioreactor;

[0192] The sum of the inlet and outlet times is 1 hour.

[0193] The influent COD, effluent COD, and nitrogen removal rate were measured for each denitrification cycle, and the results are as follows: Figures 4-6 As shown in Table 4, the total amount of nitrogen removed and the carbon release cycle are shown in Table 4.

[0194] Examples 2-6

[0195] Biological denitrification experiments were conducted according to the method in Example 1, except that the slow-release carbon source material M1 was replaced with equal amounts of slow-release carbon source materials M2, M3, M4, M5 and M6, respectively.

[0196] The influent COD, effluent COD, and nitrogen removal rate were measured for each denitrification cycle. The total amount of denitrification and carbon release cycle are shown in Table 4.

[0197] Comparative Example 1

[0198] Biological denitrification experiments were conducted according to the method in Example 1, except that the slow-release carbon source material M1 was replaced with an equal amount of slow-release carbon source material D1.

[0199] The influent COD, effluent COD, and nitrogen removal rate were measured for each denitrification cycle, and the results are as follows: Figure 4-6 As shown in Table 4, the total amount of nitrogen removed and the carbon release cycle are shown in Table 4.

[0200] Comparative Example 2

[0201] Biological denitrification experiments were conducted according to the method in Example 1, except that the slow-release carbon source material M1 was replaced with an equal amount of slow-release carbon source material D2.

[0202] The influent COD, effluent COD, and nitrogen removal rate were measured for each denitrification cycle, and the results are as follows: Figure 4-6 As shown in Table 4, the total amount of nitrogen removed and the carbon release cycle are shown in Table 4.

[0203] Comparative Examples 3-9

[0204] Biological denitrification experiments were conducted according to the method in Example 1, except that the slow-release carbon source material M1 was replaced with an equal amount of slow-release carbon source materials D3-D9.

[0205] The influent COD, effluent COD, and nitrogen removal rate were measured for each denitrification cycle. The total amount of denitrification and carbon release cycle are shown in Table 4.

[0206] Comparative Example 10

[0207] Blank group experiment.

[0208] Biological denitrification experiments were conducted according to the method in Example 1, except that no slow-release carbon source material was added.

[0209] The influent COD, effluent COD, and nitrogen removal rate were measured for each denitrification cycle, and the results are as follows: Figure 4-6 As shown.

[0210] Test Example 1

[0211] Carbon release experiments were conducted on slow-release carbon source materials M1-M6 and D1-D9 using water:

[0212] Weigh 5g of each of the above-mentioned slow-release carbon source materials and add them to their respective 500ml Erlenmeyer flasks. Then add 500ml of distilled water to each flask, seal the mouth of the flask with a rubber stopper, and place the Erlenmeyer flask on a 30℃ constant temperature shaker and shake for 7 days at a speed of 150rpm.

[0213] Leachate samples were taken at 0, 1, 2, 4, 8, 12, 24, 36, 48, 72, 96, 120, 144, and 168 hours. The water in the conical flask was completely replaced after each sampling. The COD change over time during carbon release was simulated using a second-order kinetic equation. The kinetic characteristics of carbon release from the slow-release carbon source materials M1-M6 and D1-D9 were recorded.

[0214] The pseudo-second-order dynamic equation is expressed as follows:

[0215]

[0216] c—COD concentration of the solution during carbon release by a unit mass of slow-release carbon source material, mg / (g·L);

[0217] c m —The saturated COD concentration released per unit mass of slow-release carbon source material in solution, mg / (g·L);

[0218] K—mass transfer coefficient, mg / (h·g·L), represents the carbon release resistance. The larger K is, the smaller the resistance to the carbon release process and the easier it is to release organic carbon.

[0219] t 1 / 2 —The time, h, t, taken for the released COD to reach half of the saturation concentration. 1 / 2 The smaller the concentration, the shorter the time required to reach half of the saturation concentration, and the faster the carbon release rate.

[0220] The pseudo-second-order kinetic equations for the slow-release carbon source materials M1, D1, and D2 are shown in Table 3, and the fitting curves are shown in Table 4. Figure 3 .

[0221] Table 1: Acclimation Water Preparation Formula

[0222]

[0223] Table 2: Formulation of Trace Element Solution

[0224]

[0225]

[0226] Table 3

[0227]

[0228] Table 4

[0229]

[0230]

[0231] from Figure 1 As shown in (A) to (C), before denitrification, the surfaces of all three carbon sources exhibit numerous wrinkles and grooves, and possess porous structures, which are conducive to microbial attachment. Compared to Comparative Examples 1 and 2, the surface of M1 in Example 1 has denser wrinkles and grooves, and more and more uniform pores; from Figure 1 As shown in (a) to (c), after denitrification, the pore structure on the surface of M1 further increases, while the pores on the surface of D1 are less; the wrinkles on the surface of D2 increase. This indicates that when sodium acetate and bagasse are used together as carbon sources, M1 can form a denser pore structure after the carbon source is released, which is more conducive to the attachment and growth of microorganisms.

[0232] from Figure 2 From (A) to (C), it can be seen that the carbon element distribution of M1, D1, and D2 is relatively uniform, which is conducive to the growth of denitrifying bacteria attached to the surface. The uneven distribution may be due to the presence of surface wrinkles and grooves. Figure 2 As shown in (a) to (c), the N element in M1, D1, and D2 is uniformly distributed and present in low amounts, having little impact on TN detection during the experiment. Overall, this indicates that the carbon source is uniformly embedded and effectively utilized during the fabrication of the slow-release carbon source material. Figure 2 As shown in (D) to (F), the C content on the surface of the slow-release carbon source material is higher than the N content.

[0233] from Figure 3 It can be seen that when the pseudo-second-order kinetic equation is used to fit the carbon release process of the slow-release carbon source material, R 2All values ​​were above 0.97, therefore the carbon release process of each slow-release carbon source material followed a pseudo-second-order kinetic equation. The corresponding kinetic equations and parameter calculations are shown in Table 2. As can be seen from Table 2, the K value of M1 is less than D1 and greater than D2. To a certain extent, this can alleviate the problem of rapid release rate caused by the easy solubility of sodium acetate in water when it is used alone as an encapsulated carbon source, and can reduce the impact of excessive initial carbon release on water quality. At the same time, it can alleviate the shortcomings of large carbon release resistance and slow carbon release when sugarcane bagasse is used alone as a carbon source. Moreover, compared to D1, the mass transfer coefficient K of M1 decreased by 25.2%, but the Cm of M1 decreased by only 12.6% compared to D1. This indicates that the sustained-release carbon source material prepared by combining sodium acetate and alkalized bagasse as carbon sources with the hydrogel framework is not a simple superposition of the carbon release effects when sodium acetate and bagasse are used as carbon sources alone. Instead, it combines the advantages of both to achieve the effect of reducing the carbon source release rate but releasing a large amount of carbon source during the carbon release cycle.

[0234] from Figures 4-6 It can be seen that in the first denitrification cycle, the nitrogen removal rate of Example 1 was slightly lower than that of Comparative Example 1. However, in the second and early stages of the third denitrification cycle, the nitrogen removal rate of Example 1 rebounded and was higher than that of Comparative Example 1. Analysis suggests that in the first denitrification cycle, because the denitrifying bacteria had just begun to attach to the surface of the slow-release carbon source material M1, the amount attached was small, and the carbon release from M1 was less than that from D1 in the initial stage. Therefore, Comparative Example 1 had a higher nitrogen removal rate. However, because M1 has more wrinkles, grooves, and pores on its surface, more denitrifying bacteria were adsorbed on the surface over time. Furthermore, the carbon source release rate of M1 was not significantly different from that of D1, allowing more denitrifying bacteria on the M1 surface to more quickly receive the released carbon source, thus improving the nitrogen removal rate. From the third denitrification cycle onwards, due to the synergistic effect of M1's higher adsorption capacity for denitrifying bacteria and higher carbon source release rate, the nitrogen removal rate of Example 1 was higher than that of Comparative Example 1 and remained at a high level.

[0235] Compared to Example 4, where the preparation conditions for the slow-release carbon source material were not within the preferred range, Example 1, prepared under the following conditions: stirring at 95°C at a speed of 140 rpm; stirring frequency of once every 20 minutes for 15 minutes per stirring cycle; and crosslinking curing temperature of 4°C for 24 hours, produced a slow-release carbon source material M1 with a porosity of 58%, a hydrogel framework porosity of 71%, and a specific surface area of ​​15.8 m². 2 / g, used for biological denitrification of wastewater, can achieve a total denitrification rate of 95% and a carbon release cycle of up to 215h.

[0236] Compared to Example 5, where the alkalization treatment conditions for sugarcane bagasse raw material were not within the preferred range, Example 1 used a 1.5wt% sodium hydroxide solution to alkalize the sugarcane bagasse at 25°C for 24 hours. The resulting alkalized sugarcane bagasse was used to prepare slow-release carbon source material M1 for biological denitrification of wastewater, which can effectively improve the total amount of denitrification and the carbon release cycle.

[0237] Compared to Example 6, which used alkalized bagasse with a particle size of 0.8 mm, Example 1 used alkalized bagasse with a particle size of 0.2 mm to prepare slow-release carbon source material M1, which has higher porosity and specific surface area, effectively improving the total amount of denitrification and carbon release cycle.

[0238] Compared to Comparative Example 1, which used sodium acetate alone to prepare a slow-release carbon source material, and Comparative Example 2, which used alkalized sugarcane bagasse alone to prepare a slow-release carbon source material, the slow-release carbon source material M1 prepared in Example 1 using a combination of sodium acetate and alkalized sugarcane bagasse exhibits higher porosity and specific surface area, effectively improving the total amount of nitrogen removed and the carbon release cycle. Analysis suggests that although sodium acetate in D1 initially releases at a rapid rate and releases a large amount of carbon, the lack of alkalized sugarcane bagasse results in excessively low porosity and specific surface area. This is detrimental to microbial adsorption and biofilm formation, leading to low surface area and amount of microbial attachment, which in turn hinders microbial metabolic growth and ultimately results in poor nitrogen removal. Furthermore, the rapid initial release coupled with insufficient carbon release capacity in the later stages leads to a short carbon release cycle. Although the D2 prepared in Comparative Example 2 has a high specific surface area due to the numerous wrinkles on the material surface, the sugarcane bagasse treated with alkalization releases carbon too slowly, resulting in a low amount of carbon released. This leads to a poor effect in improving the carbon-nitrogen ratio, resulting in a short carbon release cycle and a low total amount of denitrification.

[0239] Compared to Comparative Example 3, which uses alkalized bagasse and sodium acetate in a weight ratio of approximately 1:0.2, the slow-release carbon source material M1 prepared by compounding alkalized bagasse and sodium acetate in a weight ratio of 1:1 in Example 1 has a larger porosity and specific surface area, effectively improving the total amount of denitrification and the carbon release cycle.

[0240] Compared to Comparative Example 4, which used a mixture of corn stalk residue and sodium acetate, and Comparative Example 5, which used corn stalk residue alone, the slow-release carbon source material M1 prepared by Example 1 using alkalized sugarcane bagasse and sodium acetate has a higher total nitrogen removal volume and carbon release cycle for biological denitrification treatment of wastewater.

[0241] Compared to Comparative Example 6, which used glucose and alkalized bagasse, and Comparative Example 7, which used starch and alkalized bagasse, the slow-release carbon source material M1 prepared by Example 1 using alkalized bagasse and sodium acetate for biological denitrification of wastewater has a higher total nitrogen removal.

[0242] Compared to Comparative Example 8, which used 25 parts by weight of alkalized sugarcane bagasse, 5 parts by weight of sodium acetate, and 70 parts by weight of hydrogel precursor to prepare a slow-release carbon source material, Example 1, which used 25 parts by weight of alkalized sugarcane bagasse, 25 parts by weight of sodium acetate, and 50 parts by weight of hydrogel precursor to prepare a slow-release carbon source material M1 for biological denitrification of wastewater, showed a higher total nitrogen removal volume and carbon release cycle. Analysis suggests that Example 1, with its superior raw material ratio, not only provides a more suitable porosity and specific surface area for the formation of a more uniform biofilm by adsorbing microorganisms, but also ensures that the carbon source release is maintained within a more suitable range, while simultaneously achieving a longer carbon release cycle and a more stable carbon-to-nitrogen ratio environment, thus comprehensively improving the denitrification effect.

[0243] Compared to Comparative Example 9, which used a mixture of sugarcane bagasse and sodium acetate to prepare a slow-release carbon source material, Example 1, which used alkalized sugarcane bagasse and sodium acetate, produced a slow-release carbon source material with superior porosity and specific surface area, as well as a longer carbon release cycle, effectively increasing the total amount of nitrogen removed. Analysis suggests that Comparative Example 9, using sugarcane bagasse, contained small amounts of sugar (such as disaccharides and monosaccharides), resulting in a higher initial carbon release but a poor sustained carbon release capacity. Furthermore, the structure of the sugarcane bagasse and the hydrogel framework did not synergize, leading to poor biofilm formation, uneven microbial biofilm uniformity, and a small biofilm area, further reducing the nitrogen removal effect.

[0244] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A slow-release carbon source material for biological denitrification, characterized by, The slow-release carbon source material comprises a hydrogel framework and a carbon source carried by the hydrogel framework; The carbon source is composed of alkali-treated bagasse and sodium acetate; The hydrogel framework comprises a porous structure formed by polyvinyl alcohol and sodium alginate; The amount of sodium acetate is 0.5-2 parts by weight relative to 1 part by weight of alkali-treated bagasse, and the amount of hydrogel framework is 1.5-4 parts by weight; The specific surface area of the slow-release carbon source material is 5-25 m 2 / g; The porosity of the slow-release carbon source material is 20%-80%; The porosity of the hydrogel framework is 30%-90%; The particle size of the alkali-treated bagasse is 0.1 mm-0.5 mm.

2. The slow-release carbon source material according to claim 1, characterized by, The porosity of the slow-release carbon source material is 40%-80%; And / or, the porosity of the hydrogel framework is 50%-90%; And / or, the particle size of the alkali-treated bagasse is 0.1 mm-0.3 mm; And / or, the composition of the alkali-treated bagasse comprises 16-20 wt% lignin, 28-35 wt% cellulose, and 15-20 wt% hemicellulose; And / or, the specific surface area of the slow-release carbon source material is 6-22 m² / g.

3. The slow-release carbon source material according to claim 2, characterized by, The specific surface area of the slow-release carbon source material is 8-20 m² / g.

4. The slow-release carbon source material according to any one of claims 1 to 3, characterized by, The amount of sodium acetate is 0.7-1.5 parts by weight relative to 1 part by weight of alkali-treated bagasse, and the amount of hydrogel framework is 1.6-2.2 parts by weight.

5. The slow-release carbon source material according to any one of claims 1 to 3, characterized by, The weight ratio of polyvinyl alcohol to sodium alginate is 7-10:

1.

6. The method of producing the slow-release carbon source material according to any one of claims 1 to 5, characterized by, The preparation method comprises the following steps: Step (1): alkali treatment of bagasse raw material, drying and crushing to obtain alkali-treated bagasse; Step (2): adding 30-50 parts by weight of polyvinyl alcohol and 3-8 parts by weight of sodium alginate to 400-600 parts by volume of water and stirring to prepare a hydrogel precursor; Step (3): mixing 10-40 parts by weight of alkali-treated bagasse obtained in step (1) and 10-35 parts by weight of sodium acetate with 30-75 parts by weight of hydrogel precursor obtained in step (2) to form a slow-release carbon source material precursor, and cross-linking and curing the slow-release carbon source material precursor under the action of a cross-linking agent.

7. The production method according to claim 6, characterized by, The composition of the bagasse raw material comprises 18-22 wt% lignin, 40-50 wt% cellulose, 25-30 wt% hemicellulose, and 1.5-3 wt% sugar.

8. The production method according to claim 6 or 7, characterized by, In step (1), the alkali treatment is carried out in an alkali solution selected from at least one of sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution, and ammonia water; and / or, the amount of alkali solution is 300-500 ml relative to 20-50 g of bagasse raw material; And / or, in step (1), the alkali treatment conditions include a temperature of 20-30 ℃ and a time of 20-24 h; And / or, in step (1), the alkali-treated bagasse is washed to a pH of 6.8-7.2 before drying.

9. The production method according to claim 8, characterized by, The concentration of the alkali solution is 1-5 wt%.

10. The production method according to any one of claims 6, 7 and 9, characterized by, In step (2), the stirring conditions include a temperature of 80-95 ℃ and a time of 1-3 h; And / or, the stirring speed in step (2) is 130-150 rpm; the stirring frequency is 1 time / 15-25 min, and the stirring time is 10-20 min / time; And / or, in step (3), the forming conditions include: temperature is -15 to -25 ℃, and time is 10-15 h.

11. The production method according to any one of claims 6, 7 and 9, characterized by, In step (3), the cross-linking and curing is carried out by immersing the slow-release carbon source material precursor into a cross-linking agent solution, which is a saturated boric acid solution containing 3-5 wt% CaCl2; And / or, the cross-linking and curing conditions include: temperature is 3-5 ℃, and time is 20-24 h.

12. The slow-release carbon source material of any one of claims 1-5 or the slow-release carbon source material prepared by the preparation method of any one of claims 6-11 is applied in the field of wastewater biological denitrification treatment.

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