Slow-release carbon source material for biological denitrification as well as preparation method and application of slow-release carbon source material

Abstract

The invention provides a slow-release carbon source material for biological denitrification as well as a preparation method and application of the slow-release carbon source material. The slow-release carbon source material comprises a hydrogel skeleton and a carbon source carried by the hydrogel skeleton, wherein the carbon source comprises bagasse subjected to alkalization treatment and sodium acetate; the hydrogel skeleton comprises a porous structure formed by polyvinyl alcohol and sodium alginate; relative to 1 part by weight of alkalized bagasse, the amount of the sodium acetate is 0.5-2 parts by weight, and the amount of the hydrogel skeleton is 1.5-2.5 parts by weight; the specific surface area of the slow-release carbon source material is 5-25m < 2 > / g; the slow-release carbon source material disclosed by the invention has an excellent carbon source slow-release effect and good stability, can be continuously kept at a relatively high carbon source release level, and has a relatively high nitrogen removal rate when being used for biological nitrogen removal treatment of wastewater, especially wastewater with a low carbon-nitrogen ratio.

Description

Technical Field

[0001] The present invention relates to the field of slow-release carbon source materials, and particularly to a slow-release carbon source material for biological denitrification, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous development of social economy, China has paid more and more attention to the water environment safety issue, and the sewage discharge standards have become increasingly strict. However, nitrogen-containing pollutants generated by industrial production, agricultural nitrogen fertilizers, and residents' lives are continuously discharged into water bodies, increasing the total nitrogen content of sewage, causing serious water body nitrogen pollution problems, exceeding the nitrogen standard, and generating low C / N ratio sewage. Domestic sewage in China mainly shows the characteristics of low carbon-nitrogen ratio. The lack of carbon source leads to incomplete denitrification, thereby reducing the denitrification effect and resulting in a higher nitrogen concentration in the effluent. At present, biological denitrification technology is widely used in wastewater treatment. In the process of biological denitrification, the denitrification link is the key step of denitrification, and sufficient organic carbon source is a necessary condition to ensure biological phosphorus and nitrogen removal from sewage.

[0003] In view of the lack of carbon source in low C / N ratio sewage, adding external carbon source is the most widely used method. At present, the externally added carbon sources mainly include liquid-phase carbon source, gas-phase carbon source, and solid-phase carbon source. Among the traditional carbon sources represented by low-molecular-weight organic substances, theoretically, the smaller the carbon source molecule, the easier it is for denitrifying bacteria to utilize, and the higher the denitrification efficiency. However, the dosing amount is difficult to control, and complex control devices and continuous monitoring processes are often required, thereby increasing the operating cost. Natural cellulose substances have the advantages of low price, low cost, easy availability, no secondary pollution, and no biological toxicity. However, such carbon sources are greatly affected by temperature, and problems such as unstable carbon source release and clogging of the packing layer will also occur. Artificial synthetic degradable polymers are stable as solid slow-release carbon sources, but they require trace elements to meet growth, and the synthetic materials are expensive, which limits their application.

[0004] In summary, in view of the current trend of low C / N in domestic sewage, there is an urgent need to develop a composite slow-release carbon source material with stable carbon release, long carbon release period, low price, good denitrification effect, and biodegradability to achieve resource recycling. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention provides a slow-release carbon source material for biological denitrification, a preparation method thereof, and an application thereof. The slow-release carbon source material of the present invention has a good carbon source slow-release effect and a stable structure, so that the carbon source release rate is maintained at a relatively high level for a long time, effectively extending the carbon release period; the slow-release carbon source material is used for biological denitrification treatment of wastewater, especially low carbon-nitrogen ratio wastewater, and has excellent denitrification effect, not only high nitrogen removal rate, but also a significant increase in the total amount of nitrogen removed.

[0006] The object of the present 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, and the slow-release carbon source material includes a hydrogel skeleton and a carbon source carried by the hydrogel skeleton.

[0008] Wherein, the carbon source includes alkalized bagasse and sodium acetate.

[0009] The hydrogel skeleton includes a porous structure formed by polyvinyl alcohol and sodium alginate.

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

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

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

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

[0014] Preferably, the particle size of the alkalized bagasse is 0.1 mm to 0.5 mm, preferably 0.1 mm to 0.3 mm.

[0015] Preferably, the composition of the alkalized bagasse contains 16 to 20 wt% of lignin, 28 to 35 wt% of cellulose, and 15 to 20 wt% of hemicellulose.

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

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

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

[0019] In a second aspect, the present invention provides a preparation method of the slow-release carbon source material described in the first aspect, and the preparation method includes the following steps:

[0020] Step (1): Alkalize the bagasse raw material, and after drying and pulverizing, obtain alkalized bagasse.

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

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

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

[0024] Preferably, in step (1), the alkalization treatment is carried out in an alkaline solution, and the alkaline solution is 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 the bagasse raw material, the dosage of the alkaline solution is 300 - 500 ml.

[0025] Preferably, in step (1), the conditions of the alkalization treatment include: temperature is 20 - 30 °C, and time is 20 - 24 h.

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

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

[0028] Preferably, in step (2), the stirring speed is 130 - 150 rpm; the stirring frequency is 1 time per 15 - 25 min, and the stirring time is 10 - 20 min per time.

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

[0030] Preferably, in step (3), the crosslinking and curing is carried out by immersing the precursor of the slow-release carbon source material into a crosslinking agent solution, and the crosslinking agent solution is a saturated boric acid solution containing 3 - 5 wt% CaCl2.

[0031] Preferably, the conditions of the crosslinking and curing include: temperature is 3 - 5 °C, and time is 20 - 24 h.

[0032] In a third aspect, the present invention provides an 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] The present invention has the following advantages:

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

[0035] (2) When the slow-release carbon source material is used in the biological denitrification treatment process of wastewater with a low carbon-nitrogen ratio, it overcomes the difficulty of reduced microbial metabolic activity due to insufficient carbon source in low C / N sewage treatment, and strengthens 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 period;

[0037] (4) The present invention realizes the resource utilization of agricultural waste (bagasse). Description of the Drawings

[0038] Figure 1 It is a scanning electron microscope image of the slow-release carbon source material. Among them, (A) to (C) are the scanning electron microscope images of the slow-release carbon source materials M1, D1, and D2 prepared in Example 1, Comparative Example 1, and Comparative Example 2 before carbon source release; (a) to (c) are the scanning electron microscope images of the slow-release carbon source materials M1, D1, and D2 prepared in Example 1, Comparative Example 1, and Comparative Example 2 after carbon source release;

[0039] Figure 2 It is an elemental scanning image and an energy spectrum diagram of the slow-release carbon source material. Among them, (A) to (C) are the surface C element scanning images of the slow-release carbon source materials M1, D1, and D2 before carbon source release; (a) to (c) are the surface N element scanning images of the slow-release carbon source materials M1, D1, and D2 before carbon source release; (D) to (E) are the energy spectrum diagrams of the slow-release carbon source materials M1, D1, and D2 before carbon source release;

[0040] Figure 3 It is the quasi-second-order fitting curve of the COD curve graph of the carbon source release process of the slow-release carbon source materials M1, D1, and D2 in clear water;

[0041] Figure 4 It is the nitrogen removal rate curve graph in the biological denitrification processes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 10;

[0042] Figure 5 It is the influent COD curve graph in the biological denitrification processes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 10;

[0043] Figure 6 It is the effluent COD curve graph during the biological denitrification processes of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 10. Detailed implementation manners

[0044] The following combines the accompanying drawings to specifically describe the preferred embodiments of the present invention. Among them, the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to explain the principle of the present invention.

[0045] The inventors of the present invention have found through research that after preparing a slow-release carbon source material by mixing the combination of alkalized bagasse and sodium acetate with a hydrogel precursor, the carbon release rate of the slow-release carbon source material is stabilized and the carbon release period is extended. It is analyzed that in the present invention, the alkalized bagasse contains a pore structure suitable for microorganisms, especially denitrifying bacteria, to adsorb and form a biofilm, and the hydrogel skeleton in the present invention also has a specific pore structure, folds, and grooves. After the alkalized bagasse and the hydrogel skeleton are crosslinked and solidified in a specific composition ratio, a structure of the carbon source carried by the hydrogel skeleton (alkalized bagasse and sodium acetate) is formed, further improving the carbon source slow-release effect and the carbon release period.

[0046] Based on the above research, on the one hand, the present invention provides a slow-release carbon source material for biological denitrification, and the slow-release carbon source material includes a hydrogel skeleton and a carbon source carried by the hydrogel skeleton;

[0047] Among them, the carbon source includes alkalized bagasse and sodium acetate;

[0048] The hydrogel skeleton includes a porous structure formed by polyvinyl alcohol and sodium alginate;

[0049] Relative to 1 part by weight of alkalized bagasse, the amount of sodium acetate is 0.5 - 2 parts by weight, and the amount of the hydrogel skeleton is 1.5 - 4 parts by weight;

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

[0051] In the present invention, the term "carbon release period" refers to the time from when the slow-release carbon source material is put into water (nitrogen-containing wastewater) to release the carbon source (at this time, the carbon source is released relatively fast, and the carbon-nitrogen molar ratio rises above 2.5 in a short time) to when the carbon-nitrogen molar ratio in the water is lower than 2.5 due to biological denitrification.

[0052] In the present invention, before the release of the carbon source, the slow-release carbon source material has a wrinkled, grooved and / or porous structure, which is beneficial to the attachment and growth of microorganisms, especially denitrifying bacteria. As the carbon source is gradually released until the hydrogel skeleton remains after complete release, the pores of the slow-release carbon source material gradually increase in number and size, and more and more denitrifying bacteria attach to it to form a uniform biofilm. When used for wastewater treatment, the biological nitrogen removal ability can be maintained at a relatively high level all the time.

[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 skeleton is 30% - 90%, preferably 50% - 90%. The slow-release carbon source material and the hydrogel skeleton having such preferred porosities can further improve the biological nitrogen removal ability.

[0054] In the present invention, the porosity of the slow-release carbon source material is detected before the release of the carbon source, and the porosity of the hydrogel skeleton is detected after the slow-release carbon source material releases carbon in flowing clean water for 240 h. There is no special limitation on the detection method of the porosity in the present invention, and conventional detection methods in the art can be used, such as the gas adsorption method (BET method).

[0055] In a preferred embodiment of the present invention, the particle size of the alkalized bagasse is 0.1 mm - 0.5 mm, preferably 0.1 mm - 0.3 mm; using the alkalized bagasse with such a preferred particle size can make the carbon source more evenly distributed in the hydrogel skeleton, and make the slow-release carbon source material more likely to adsorb microorganisms, especially denitrifying bacteria, to form a biofilm, thereby improving the nitrogen removal effect.

[0056] In the present invention, the alkalized bagasse is obtained by alkalizing bagasse raw materials. The bagasse raw materials refer to the residues remaining after sugarcane is squeezed for sugar, and the main components are cellulose, hemicellulose and lignin, with a small amount of disaccharides and monosaccharides remaining, and also including a certain amount of impurities such as protein, fat and ash.

[0057] It has been found through research that the sugarcane bagasse raw material has insufficient carbon supply sustainability and cannot continuously provide a carbon source, so it is not suitable as a carbon source for denitrification. However, after the sugarcane bagasse raw material is alkalized and used in combination with sodium acetate as a carbon source, and is mixed with specific amounts of polyvinyl alcohol and sodium alginate, the prepared slow-release carbon source material with a hydrogel skeleton carrying the carbon source (alkalized sugarcane bagasse and sodium acetate) not only exhibits excellent carbon source slow-release effects, but also effectively promotes biological denitrification. It is analyzed that the alkalized sugarcane bagasse mainly consists of specific contents of cellulose, hemicellulose and lignin. The material surface formed by the hydrogel formed with polyvinyl alcohol and sodium alginate through cross-linking and curing has special folds and groove structures, and there are pore structures, which are more conducive to the attachment of microorganisms, especially denitrifying bacteria, to form biofilms, improving denitrification. Moreover, the existing fold, groove structure and / or pore structure further regulate the slow-release rate and slow-release amount of the carbon source, not only keeping the carbon-nitrogen ratio in the water at a relatively high level all the time, but also extending the carbon release period of the slow-release carbon source material.

[0058] In a preferred embodiment of the present invention, the components of the alkalized sugarcane bagasse include 16-20 wt% of lignin, 28-35 wt% of cellulose and 15-20 wt% of hemicellulose, preferably 17-19 wt% of lignin, 30-33 wt% of cellulose and 16-18 wt% of hemicellulose. Using the alkalized sugarcane bagasse with this preferred component composition as a carbon source to prepare the slow-release carbon source material can further optimize the structure of the slow-release carbon source material. Not only does it have good carbon source slow-release effects and a long carbon release period, but also the utilization rate of the alkalized sugarcane bagasse is higher.

[0059] In the present invention, the alkalized sugarcane bagasse also contains impurities such as protein, fat and ash.

[0060] In the present invention, the component contents of the sugarcane bagasse raw material and the alkalized sugarcane bagasse are both 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 has this preferred mass transfer coefficient and acts synergistically with the wrinkles, grooves and porosity on the surface of the slow-release carbon source material, an unexpected situation occurs when the slow-release carbon source material of the present invention is used in the biological denitrification process, that is, the denitrification amount first slowly decreases and then increases at the initial stage of biological denitrification. It is considered through analysis that the release rate of the carbon source of the slow-release carbon source material will gradually decrease with time. However, due to the relatively large number of wrinkles and grooves on the surface of the slow-release carbon source material and more and more uniform pores, more denitrifying bacteria can be adsorbed and attached. During the release process of the carbon source, it can be more efficiently utilized by the attached denitrifying bacteria. Although the denitrification amount will have a downward process in the initial stage, with the increase in the amount of attached denitrifying bacteria and the attached area, it makes up for the decrease in the denitrification amount caused by 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 m 2 / g, preferably 8-20 m 2 / g. The slow-release carbon source material with this preferred specific surface area can control the slow-release rate of the carbon source within a more reasonable range, maintain and stabilize the relatively high carbon-nitrogen ratio required for denitrification for a longer time, and further take into account the effective utilization of the carbon source by the microorganisms attached to the surface of the slow-release carbon source material and the microorganisms in the water body, improving the denitrification rate and denitrification amount.

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

[0064] The present invention has no special requirements for the shape of the slow-release carbon source material, and any known shape in the art can be adopted, such as spherical, cubic, cuboid, cylindrical, polyhedral, triangular pyramid, preferably spherical and / or cube-shaped.

[0065] In a preferred embodiment of the present invention, relative to 1 part by weight of alkalized bagasse, the dosage of sodium acetate is 0.7-1.5 parts by weight, and the dosage of the hydrogel skeleton is 1.6-2.2 parts by weight. Within the range of this preferred component content ratio, the slow-release carbon source material has a more excellent 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 skeleton is 7 to 10:1, preferably 7 to 9:1. The hydrogel skeleton with this preferred ratio has a more stable structure. During the process of using the slow-release carbon source material for biological denitrification, it can continuously maintain a good slow-release effect, so that the biological denitrification amount is at a relatively high level.

[0067] The inventors of the present invention have found through research that due to the high content of lignin and residual disaccharides and monosaccharides in the bagasse raw material, the carbon release rate and carbon release amount of the bagasse raw material are high in the early stage in water, but decrease rapidly in the later stage, resulting in large fluctuations in the carbon release rate during the entire carbon release cycle, which is not conducive to denitrification, and there is also a problem of secondary pollution easily caused by excessive carbon release amount in the early stage. However, after the bagasse raw material is alkalized, the combination of the alkalized bagasse and sodium acetate and the slow-release carbon source material prepared with a specific dosage of the hydrogel precursor have a good carbon source slow-release effect, which can not only effectively extend the carbon release cycle, but also effectively improve the denitrification effect on sewage.

[0068] In a second aspect, the present invention provides a preparation method of the slow-release carbon source material described in the first aspect, and the preparation method includes the following steps:

[0069] Step (1): Alkalize the bagasse raw material, and after drying and pulverizing, obtain the alkalized bagasse;

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

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

[0072] In the present invention, the main components of the bagasse raw material are cellulose, hemicellulose and lignin, with a small amount of sugar remaining, and also containing a certain amount of impurities such as protein, fat and ash. Preferably, the components of the bagasse raw material include 18-22 wt% of lignin, 40-50 wt% of cellulose, 25-30 wt% of hemicellulose and 1.5-3 wt% of sugar, more preferably including 18-20 wt% of lignin, 40-48 wt% of cellulose, 25-28 wt% of hemicellulose and 1.5-3 wt% of sugar. Using the bagasse raw material with the preferred components for alkalization treatment and then using the alkalized bagasse in combination with the hydrogel skeleton can more effectively exert the synergistic effect of the two in the spatial structure, further improve the slow-release effect of the carbon source, and be more conducive to the denitrification treatment of the water body. Further, the sugar contained in the bagasse raw material is mainly disaccharide (such as sucrose) and monosaccharide.

[0073] In a preferred embodiment of the present invention, the alkalization treatment is carried out in an alkali solution, and the alkali 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 alkali 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 the bagasse raw material, the dosage of the alkali solution is 300-500 ml, preferably 350-450 ml; and / or, in step (1), the conditions of the alkalization treatment include: the temperature is 20-30 °C, preferably 23-27 °C; the time is 20-24 h. Using this preferred alkalization treatment method can further optimize the pore structure of the obtained alkalized bagasse. On the one hand, the carbon source release rate of the obtained alkalized bagasse is more stable, and on the other hand, the obtained alkalized bagasse has better performance in adsorbing microorganisms, especially denitrifying bacteria. Acting synergistically with the hydrogel skeleton, it can synergistically exert a more excellent carbon source slow-release effect and a film-forming effect on microorganisms, especially denitrifying bacteria, to form a more uniform biofilm, thereby improving the denitrification effect.

[0074] In a preferred embodiment of the present invention, in step (1), before the drying, the alkalized bagasse is washed to a pH of 6.8-7.2. Since the washing step is carried out after the alkalization treatment, the alkalized bagasse obtained basically does not contain disaccharide and monosaccharide and can be ignored.

[0075] In a preferred embodiment of the present invention, in step (2), 35 to 45 parts by weight of polyvinyl alcohol and 4 to 6 parts by weight of sodium alginate are added to 450 to 550 parts by volume of water and stirred to prepare a hydrogel precursor. The hydrogel skeleton formed by crosslinking and curing the hydrogel precursor prepared with this preferred ratio can more uniformly coat the alkalized bagasse and sodium acetate, resulting in a larger and more uniform carbon release area, and is more conducive to exerting the synergistic carbon release and film-forming effects of the alkalized bagasse and the hydrogel skeleton, thereby improving the denitrification effect.

[0076] In a preferred embodiment of the present invention, in step (2), the conditions of the stirring include: the temperature is 80 to 95 °C, and the time is 1 to 3 h; and / or, the stirring speed in step (2) is 130 to 150 rpm, preferably 135 to 145 rpm; the stirring frequency is 1 time per 15 to 25 min, preferably 1 time per 18 to 25 min; the stirring time is 10 to 20 min per time, preferably 15 to 20 min per time. Using this preferred stirring condition makes the slow-release carbon source material have a more uniform pore structure and more wrinkles and grooves, 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 to 30 parts by weight of the alkalized bagasse obtained in step (1) and 20 to 30 parts by weight of sodium acetate are mixed and formed with 32 to 66 parts by weight of the hydrogel precursor obtained in step (2) to obtain a slow-release carbon source material precursor, and then the slow-release carbon source material precursor is crosslinked and cured under the action of a crosslinking agent.

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

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

[0080] In the present invention, the weight of the hydrogel skeleton is based on the hydrogel precursor.

[0081] In the third aspect, 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] Next, the preferred embodiments of the present invention will be specifically described to illustrate the principle of the present invention, rather than to limit the scope of the present invention.

[0083] Cycle (denitrification cycle): The whole process of wastewater completing influent, biological denitrification, static settlement, and effluent is one denitrification cycle;

[0084] Surface structure of the slow-release carbon source material: It is detected and analyzed by using a scanning electron microscope (model Hitachi Regulus8100);

[0085] Energy spectrum diagram, surface C element distribution, and surface N element distribution of the slow-release carbon source material: They are analyzed by using EDS (energy dispersive spectrometer) and SEM (scanning electron microscope); The model of EDS is Thermo Kalpha, and the model of SEM is HitachiRegulus8100;

[0086] Specific surface area: It is detected and analyzed by using the method of GB / T 19587-2017;

[0087] Porosity: The gas adsorption method (BET method) is adopted;

[0088] COD in water: It is detected by referring to the method in the standard of alkaline potassium persulfate digestion ultraviolet spectrophotometry HJ / T 399-200;

[0089] Nitrogen removal rate: It is detected by referring to the method in the standard of potassium dichromate rapid digestion spectrophotometry HJ 636-2012;

[0090] Total denitrification amount: When the carbon-nitrogen ratio in the water body is lower than 2.5, the denitrification experiment is stopped. At this time, the total denitrification amount = (total nitrogen amount in water before denitrification - total nitrogen amount in water after denitrification) ÷ total nitrogen amount in water before denitrification × 100%.

[0091] Bagasse raw material: Cellulose content is 45wt%, hemicellulose content is 27wt%, lignin content is 20wt%, sugar content is 2wt%, and the balance also includes impurities such as protein, fat, and ash;

[0092] Corn stalk: Cellulose content is 40wt%, hemicellulose content is 25wt%, lignin content is 20wt%, sugar content is 1wt%, and the balance also includes impurities such as protein, fat, and ash.

[0093] Preparation Example 1

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

[0095] Step (1): Mix 40 parts by weight of bagasse raw material dried to constant weight with 400 parts by volume of sodium hydroxide with a concentration of 1.5wt% for alkalization treatment (the alkalization temperature is 25°C and the time is 24h);

[0096] After the alkalization treatment of the bagasse raw material is completed, it is washed with water until the pH of the washing liquid reaches 7, and then dried to a constant weight at 60 °C. After being crushed and sieved, alkalized bagasse with a particle size distribution of 0.2 mm is obtained (cellulose content 32 wt%, hemicellulose content 17 wt%, lignin content 18 wt%, and the balance is 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 a temperature of 95 °C, and the stirring speed is 140 rpm; the stirring frequency is 1 time / 20 min, and the stirring time is 15 min / time. After 2 h, a hydrogel precursor is prepared;

[0098] Step (3): Mix 25 parts by weight of the alkalized 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 it into a 1 cm 3 cubic mold. After 12 h at -20 °C, demold and form, and then immerse the formed slow-release carbon source material precursor in a saturated boric acid solution containing 4% CaCl2 for cross-linking and curing (the cross-linking and curing temperature is 4 °C, and the cross-linking and curing time is 24 h);

[0099] After the cross-linking and curing is completed, rinse the surface residual cross-linking agent with ultrapure water, and then dry it to a constant weight at 60 °C to obtain the slow-release carbon source material M1; through scanning electron microscope analysis, the surface structure of the slow-release carbon source material M1 is as Figure 1 ; through EDS and SEM scanning analysis, the energy spectrum diagram of the slow-release carbon source material M1 is as Figure 2 (D) shown, and the C element distribution on the surface is as Figure 2 (A) shown, and the N element distribution is as Figure 2 (a) shown;

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

[0101] Preparation Example 2

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

[0103] Step (1) Mix 35 parts by weight of the bagasse raw material dried to a constant weight with 450 parts by volume of 1 wt% sodium hydroxide for alkalization treatment (the alkalization temperature is 20 °C and the time is 20 h);

[0104] After the alkalization treatment of the bagasse raw material is completed, it is washed with water until the pH of the washing liquid reaches 7, then dried to a constant weight at 60 °C, pulverized and sieved to obtain alkalized bagasse with a particle size distribution of 0.1 mm (cellulose content 35 wt%, hemicellulose content 20 wt%, lignin content 20 wt%, and the balance being proteins, fats, 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 a temperature of 95 °C, and the stirring speed is 130 rpm; the stirring frequency is 1 time / 20 min, and the stirring time is 10 min / time. After 2 h, a hydrogel precursor is prepared;

[0106] Step (3): Mix 20 parts by weight of the alkalized bagasse, 30 parts by weight of sodium acetate and 32 parts by weight of the hydrogel precursor prepared in step (2), and then pour it into a 1 cm 3 cubic mold. After 12 h at -20 °C, demold and form, and then immerse the formed slow-release carbon source material precursor in a saturated boric acid solution containing 4% CaCl2 for crosslinking and curing (the crosslinking and curing temperature is 4 °C, and the crosslinking and curing time is 24 h);

[0107] After the crosslinking and curing are completed, rinse the surface residual crosslinking agent with ultrapure water, and then dry it to a constant weight at 60 °C to obtain the slow-release carbon source material M2;

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

[0109] Preparation Example 3

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

[0111] Step (1): Mix 45 parts by weight of the bagasse raw material dried to a constant weight with 350 parts by volume of sodium hydroxide solution with a concentration of 2 wt%, and carry out alkalization treatment (the alkalization temperature is 20 °C, and the time is 20 h);

[0112] After the alkalization treatment of the bagasse raw material is completed, it is washed with water until the pH of the washing liquid reaches 7, then dried to a constant weight at 60 °C, pulverized and sieved to obtain alkalized bagasse with a particle size distribution of 0.3 mm (cellulose content 30 wt%, hemicellulose content 16 wt%, lignin content 17 wt%, and the balance being proteins, fats, 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 a temperature of 95 °C, with a stirring speed of 150 rpm; the stirring frequency is 1 time / 20 min, and the stirring time is 20 min / time. After 2 h, a hydrogel precursor is prepared.

[0114] Step (3): Mix 30 parts by weight of alkalized bagasse and 20 parts by weight of sodium acetate with 66 parts by weight of the hydrogel precursor prepared in step (2), then pour it into a 1 cm 3 cubic mold. After 12 h at -20 °C, demold and form. Then immerse the formed slow-release carbon source material precursor in a saturated boric acid solution containing 4% CaCl2 for crosslinking and curing (the crosslinking and curing temperature is 4 °C, and the crosslinking and curing time is 24 h);

[0115] After crosslinking and curing is completed, rinse the surface residual crosslinking agent with ultrapure water, and then dry it at 60 °C until the material reaches a constant weight to obtain the slow-release carbon source material M3;

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

[0117] Preparation Example 4

[0118] Prepare the slow-release carbon source material according to the method of Example 1, except that

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

[0120] Step (1): Mix 40 parts by weight of bagasse raw material dried to a constant weight with 400 parts by volume of 1.5 wt% sodium hydroxide for alkalization treatment (the alkalization temperature is 25 °C, and the time is 24 h);

[0121] After the alkalization treatment of the bagasse raw material is completed, wash it with water until the pH of the washing liquid reaches 7, then dry it to a constant weight at 60 °C, pulverize and sieve it to obtain alkalized bagasse with a particle size distribution of 0.2 mm;

[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 a temperature of 78 °C, with a stirring speed of 120 rpm; the stirring frequency is 1 time / 30 min, and the stirring time is 10 min / time. After 2 h, a hydrogel precursor is prepared.

[0123] Step (3): Mix 25 parts by weight of alkalized bagasse and 25 parts by weight of sodium acetate with 50 parts by weight of the hydrogel precursor prepared in step (2), then pour it into a 1 cm 3Inside the cubic mold, demolding and forming are carried out after 12 h at -20°C, and then the formed slow-release carbon source material precursor is immersed in a saturated boric acid solution containing 4% CaCl2 for crosslinking and curing (the temperature of crosslinking and curing is 10°C, and the time of crosslinking and curing is 30 h);

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

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

[0126] Preparation Example 5

[0127] The slow-release carbon source material is prepared according to the method of Example 1, except that:

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

[0129] Step (1) Mix 40 parts by weight of sugarcane bagasse raw material dried to a constant weight with 400 parts by volume of 1 wt% sodium hydroxide for alkalization treatment (the temperature of alkalization is 25°C, and the time is 12 h);

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

[0131] The slow-release carbon source material M5 is obtained.

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

[0133] Preparation Example 6

[0134] The slow-release carbon source material is prepared according to the method of Example 1, except that the particle size of the alkalized sugarcane bagasse is 0.8 mm.

[0135] The slow-release carbon source material M6 is obtained.

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

[0137] Preparation Example 7

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

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

[0140] After scanning electron microscope analysis, the surface structure of the slow-release carbon source material D1 is as Figure 1 , after EDS and SEM analysis, the energy spectrum diagram of the slow-release carbon source material D1 is as Figure 2 (E) shown, and the C element distribution on the surface is as Figure 2 (B) shown, and the N element distribution is as Figure 2 (b) shown;

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

[0142] Preparation Example 8

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

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

[0145] After scanning electron microscope analysis, the surface structure of the slow-release carbon source material D2 is as Figure 1 ; after EDS and SEM analysis, the energy spectrum diagram of the slow-release carbon source material D2 is as Figure 2 (F) shown, and the C element distribution on the surface is as Figure 2 (C) shown, and the N element distribution is as Figure 2 (c) shown;

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

[0147] Preparation Example 9

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

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

[0150] Step (1) Mix 40 parts by weight of the 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 (the alkalization temperature is 25 °C and the time is 24 h);

[0151] After the alkalization treatment of the bagasse raw material is completed, it is washed with water until the pH of the washing liquid reaches 7, and then dried to constant weight at 60 °C, pulverized and sieved to obtain alkalized bagasse with a particle size distribution of 0.2 mm.

[0152] In step (2), 22 parts by weight of polyvinyl alcohol and 2 parts by weight of sodium alginate were added to 500 parts by volume of ultrapure water, stirred at a temperature of 95 °C, and the stirring speed was 120 rpm; the stirring frequency was 1 time / 30 min, and the stirring time was 30 min / time. After 2 h, a hydrogel precursor was prepared.

[0153] In step (3), 42 parts by weight of alkalized bagasse and 8 parts by weight of sodium acetate were mixed with 50 parts by weight of the hydrogel precursor prepared in step (2), and then poured into a 1 cm 3 cubic mold. After 12 h at -20 °C, demolding was carried out, and then the formed slow-release carbon source material precursor was immersed in a saturated boric acid solution containing 4% CaCl2 for crosslinking and curing (the crosslinking and curing temperature was 4 °C, and the crosslinking and curing time was 24 h);

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

[0155] The measurement results of the specific surface area of D3, the porosity of D3 before carbon release, and the porosity of D3 after carbon release (hydrogel skeleton porosity) 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 bagasse raw material was replaced with an equal amount of corn stalks.

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

[0159] The measurement results of the specific surface area of D4, the porosity of D4 before carbon release, and the porosity of D4 after carbon release (hydrogel skeleton porosity) 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 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 measurement results of the specific surface area of D5, the porosity of D5 before carbon release, and the porosity of D5 after carbon release (hydrogel skeleton porosity) 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 the sodium acetate was replaced with an equal amount of glucose.

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

[0167] The measurement results of the specific surface area of D6, the porosity of D6 before carbon release, and the porosity of D6 after carbon release (the porosity of the hydrogel skeleton) 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 measurement results of the specific surface area of D7, the porosity of D7 before carbon release, and the porosity of D7 after carbon release (the porosity of the hydrogel skeleton) 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 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 measurement results of the specific surface area of D8, the porosity of D8 before carbon release, and the porosity of D8 after carbon release (the porosity of the hydrogel skeleton) are shown in Table 4.

[0176] Preparation Example 15

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

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

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

[0180] Preparation Example 16

[0181] Preparation of acclimated sludge:

[0182] The acclimated sludge was taken from the anoxic section of the A2O biological pool in Wastewater Treatment Plant A, and the MLSS was 7500 mg / L.

[0183] Step (S01) Under the conditions of a temperature of 30°C and a dissolved oxygen content of 0.3 mg / mL, mix the sludge to be acclimated with the acclimation influent water (the composition is shown in Tables 1 and 2) at a volume ratio of 1:4 (the MLSS after mixing is 7700 mg / L), stir for 8 h and then let it stand, and then remove the supernatant;

[0184] Step (S02) Continue to add the acclimation influent water to the sludge from which the supernatant has been removed, and repeat Step (S01);

[0185] Step (S03) Repeat Step (S02) until the TN removal rate of the supernatant is 90%, and the acclimation is completed to obtain the acclimated sludge.

[0186] Example 1

[0187] Conduct the biological denitrification experiment according to the following method.

[0188] Step (S1) Fill the slow-release carbon source material: Load the slow-release carbon source material M1 into the porous hollow suspension balls (with a diameter of 8 cm and a pore diameter on the surface of 3 mm), and the filling rate is 85% (that is, occupying 85% of the volume of the porous hollow suspension balls), and then fill the porous hollow suspension balls loaded with the slow-release carbon source material M1 in the bioreactor and mix with the acclimated sludge in 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) Inlet water: Pass the wastewater with a C / N ratio of 2.5:1 into the bioreactor and contact with the mixture formed by the slow-release carbon source material and the sludge (the ratio of the acclimated sludge to the incoming sewage is 280 mg:1 L);

[0190] Step (S3) After the inlet water is completed, carry out the denitrification reaction treatment on the wastewater under the denitrification conditions (oxygen content is 0.3 mg / mL, temperature is 30°C, pH value is 7.2, hydraulic retention time is 7 h, and stirring speed is 140 rpm) to obtain the denitrified water, and then let the obtained denitrified water stand for 1 h;

[0191] Step (S4) Outlet water: Drain the denitrified water after standing in Step (S3) from the bioreactor;

[0192] Among them, the sum of the inlet water time and the outlet water time is 1 h.

[0193] Measure the inlet COD, outlet COD and nitrogen removal rate of each denitrification cycle, and the measurement results are respectively as Figures 4 - 6 shown, and the total denitrification amount and carbon release cycle are shown in Table 4.

[0194] Examples 2 - 6

[0195] The biological denitrification experiment was carried out according to the method of Example 1, except that the slow-release carbon source material M1 was replaced with an equal amount of slow-release carbon source materials M2, M3, M4, M5, and M6, respectively.

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

[0197] Comparative Example 1

[0198] The biological denitrification experiment was carried out according to the method of 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 of each denitrification cycle were measured, and the measurement results are respectively as Figures 4 - 6 shown, and the total denitrification amount and carbon release cycle are shown in Table 4.

[0200] Comparative Example 2

[0201] The biological denitrification experiment was carried out according to the method of 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 of each denitrification cycle were measured, and the measurement results are respectively as Figures 4 - 6 shown, and the total denitrification amount and carbon release cycle are shown in Table 4.

[0203] Comparative Examples 3-9

[0204] The biological denitrification experiment was carried out according to the method of 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, respectively.

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

[0206] Comparative Example 10

[0207] Blank group experiment.

[0208] The biological denitrification experiment was carried out according to the method of Example 1, except that no slow-release carbon source material was added.

[0209] The influent COD, effluent COD, and nitrogen removal rate of each denitrification cycle were measured, and the measurement results are respectively as Figures 4 - 6 shown.

[0210] Test Example 1

[0211] The carbon release experiments in clear water were carried out on the slow-release carbon source materials M1-M6 and D1-D9, respectively:

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

[0213] Take samples of the leachate at 0, 1, 2, 4, 8, 12, 24, 36, 48, 72, 96, 120, 144, and 168 h respectively. After each sampling, thoroughly change the water in the conical flask. Use the second-order kinetic equation to simulate the change law of COD with time during the carbon release process, and record the kinetic characteristics of carbon release of the slow-release carbon source materials M1-M6 and D1-D9 respectively.

[0214] The expression of the pseudo-second-order kinetic equation is:

[0215]

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

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

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

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

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

[0221] Table 1: Formulation of domesticated influent

[0222]

[0223] Table 2: Formulation of trace element solution

[0224]

[0225]

[0226] Table 3

[0227]

[0228] Table 4

[0229]

[0230]

[0231] From Figure 1 It can be seen from (A) to (C) that before denitrification, there are many wrinkles and grooves on the surfaces of all three carbon sources, and there are pore structures, which are beneficial to the attachment of microorganisms. Compared with Comparative Example 1 and Comparative Example 2, the wrinkles and grooves on the surface of M1 in Example 1 are denser, and the pores are more and more uniform; From Figure 1 It can be seen from (a) to (c) that after denitrification, the pore structure on the surface of M1 increases further, and the pores on the surface of D1 are fewer; the wrinkles on the surface of D2 increase; it shows that when sodium acetate and bagasse are used as carbon sources together for M1, a denser pore structure can be formed after the release of the carbon source, which is more beneficial to the attachment and growth of microorganisms.

[0232] From Figure 2 It can be seen from (A) to (C) that the C element distribution of M1, D1 and D2 is relatively uniform, which is beneficial to the growth of denitrifying bacteria attached to the surface. Some uneven places may be due to the existence of surface wrinkles and grooves; From Figure 2 It can be seen from (a) to (c) that the N element distribution of M1, D1 and D2 is uniform and the content is small, which has little impact on the TN detection in the experiment. The above generally shows that during the production process of the slow-release carbon source material, the carbon source is evenly embedded and distributed, and the carbon source is reasonable and effective; From Figure 2 It can be seen from (D) to (F) that the C element content on the surface of the slow-release carbon source material is higher than the N element content.

[0233] From Figure 3 It can be seen that when the quasi-second-order kinetic equation is used to fit the carbon release process of the slow-release carbon source material, R 2All are above 0.97. Therefore, the carbon release processes of all slow-release carbon source materials follow the pseudo-second-order kinetic equation. The corresponding kinetic equation and parameter calculations are shown in Table 2. As can be seen from Table 2, the K value of M1 is less than that of D1 and greater than that of D2. To a certain extent, it can alleviate the problem of rapid release rate caused by the easy solubility of sodium acetate when used alone as an embedded carbon source, and can reduce the impact on water quality caused by excessive initial carbon release. At the same time, it can alleviate the deficiency of large carbon release resistance and slow carbon release when using bagasse alone as a carbon source. Moreover, compared with D1, the mass transfer coefficient K of M1 is reduced by 25.2% compared with the mass transfer coefficient K of D1, but the Cm of M1 is only reduced by 12.6% compared with the Cm of D1. This shows that the slow-release carbon source material prepared by combining sodium acetate and alkalized bagasse as carbon sources with the hydrogel skeleton does not simply superimpose the carbon release effects of sodium acetate and bagasse when used alone as carbon sources, but combines the advantages of both well, achieving the effect of reducing the slow-release rate of the carbon source while having a relatively large total amount of carbon source released during the carbon release cycle.

[0234] From Figures 4 - 6 it can be seen that in the first denitrification cycle, compared with Comparative Example 1, the nitrogen removal rate of Example 1 is slightly lower. However, in the second denitrification cycle and the early stage of the third denitrification cycle, the nitrogen removal rate of Example 1 rebounds and is higher than that of Comparative Example 1. It is analyzed that in the first denitrification cycle, since denitrifying bacteria have just started to attach to the surface of the slow-release carbon source material M1 and the attachment amount is small, and the carbon release amount of M1 is less than that of D1 in the initial stage. Therefore, the situation of high nitrogen removal rate in Comparative Example 1 occurs. However, due to the relatively more wrinkles, grooves and pores on the surface of M1, with the passage of time, relatively more denitrifying bacteria are adsorbed on the surface, and the carbon source release rate of M1 is not significantly different from that of D1, enabling more denitrifying bacteria on the surface of M1 to receive the released carbon source more quickly, thus increasing the nitrogen removal rate. Starting from the third denitrification cycle, due to the synergistic effect of the high ability of M1 to adsorb denitrifying bacteria and the high carbon source release rate, the nitrogen removal rate of Example 1 is higher than that of Comparative Example 1 and remains at a relatively high level.

[0235] Compared with Example 4 where the preparation conditions of the slow-release carbon source material are not within the preferred range, Example 1 uses a stirring temperature of 95 °C, a stirring speed of 140 rpm, a stirring frequency of 1 time / 20 min, a stirring time of 15 min / time, and a crosslinking and curing temperature of 4 °C and a crosslinking and curing time of 24 h. The prepared slow-release carbon source material M1 has a porosity of 58% and a porosity of the hydrogel skeleton of 71%, and a specific surface area of 15.8 m 2 / g. When used for biological denitrification of wastewater, the total denitrification amount can reach 95%, and the carbon release cycle can reach 215 h.

[0236] Compared with Example 5 where the alkalization treatment conditions of the bagasse raw material are not within the preferred range, in Example 1, the bagasse was alkalized with a 1.5 wt% sodium hydroxide solution at 25°C for 24 h, and the alkalized bagasse obtained was used to prepare the slow-release carbon source material M1 for biological nitrogen removal from wastewater, which can effectively increase the total nitrogen removal amount and the carbon release period.

[0237] Compared with Example 6 where the particle size of the alkalized bagasse is 0.8 mm, the slow-release carbon source material M1 prepared from the alkalized bagasse with a particle size of 0.2 mm in Example 1 has a higher porosity and specific surface area, effectively increasing the total nitrogen removal amount and the carbon release period.

[0238] Compared with Comparative Example 1 where sodium acetate is used alone to prepare the slow-release carbon source material and Comparative Example 2 where only alkalized bagasse is used to prepare the slow-release carbon source material, the slow-release carbon source material M1 prepared by compounding sodium acetate and alkalized bagasse in Example 1 has a higher porosity and specific surface area, effectively increasing the total nitrogen removal amount and the carbon release period. It is analyzed that although the initial release rate of sodium acetate in D1 is fast and the carbon release amount is large, due to the lack of compounding with alkalized bagasse, the porosity and specific surface area of D1 are too low, which is not conducive to the adsorption and biofilm formation of microorganisms, and also results in a low attachment area and amount of microorganisms on the material surface, which is not conducive to the metabolic growth of microorganisms, ultimately leading to poor nitrogen removal effect; moreover, due to the fast release in the early stage and insufficient carbon release capacity in the later stage, the carbon release period is short. Although D2 prepared in Comparative Example 2 has a relatively high specific surface area due to more wrinkles on the material surface, due to the too slow carbon release rate of the alkalized bagasse, the carbon release amount is low, resulting in a poor effect of increasing the carbon-nitrogen ratio, and overall leading to a short carbon release period and a low total nitrogen removal amount.

[0239] Compared with Comparative Example 3 where the weight ratio of alkalized bagasse to sodium acetate is about 1:0.2, the slow-release carbon source material M1 prepared by compounding alkalized bagasse and sodium acetate at a weight ratio of 1:1 in Example 1 has a larger porosity and specific surface area, effectively increasing the total nitrogen removal amount and the carbon release period.

[0240] Compared with Comparative Example 4 using the compound of corn stalk residue and sodium acetate and Comparative Example 5 using only corn stalk residue, the slow-release carbon source material M1 prepared by compounding alkalized bagasse and sodium acetate in Example 1 for biological nitrogen removal treatment of wastewater has a higher total nitrogen removal amount and a longer carbon release period.

[0241] Compared with Comparative Example 6 using the compound of glucose and alkalized bagasse and Comparative Example 7 using the compound of starch and alkalized bagasse, the slow-release carbon source material M1 prepared by compounding alkalized bagasse and sodium acetate in Example 1 for biological nitrogen removal treatment of wastewater has a higher total nitrogen removal amount.

[0242] Compared with Comparative Example 8 of the slow-release carbon source material prepared using 25 parts by weight of alkalized bagasse, 5 parts by weight of sodium acetate, and 70 parts by weight of the hydrogel precursor, the slow-release carbon source material M1 prepared using 25 parts by weight of alkalized bagasse, 25 parts by weight of sodium acetate, and 50 parts by weight of the hydrogel precursor in Example 1 has a higher total denitrification amount and a longer carbon release period when used for biological denitrification treatment of wastewater. It is analyzed that Example 1 adopts a more preferred raw material dosage ratio, which not only has a porosity and specific surface area that are more suitable for adsorbing microorganisms to form a more uniform biofilm, but also ensures that the carbon source release amount is maintained within a more suitable range, while taking into account a longer carbon release period and a more stable carbon-nitrogen ratio environment, comprehensively improving the denitrification effect.

[0243] Compared with Comparative Example 9 of the slow-release carbon source material prepared by compounding bagasse raw materials and sodium acetate, in Example 1, alkalized bagasse and sodium acetate are compounded, and the prepared slow-release carbon source material has more excellent porosity and specific surface area, and also has a longer carbon release period, effectively increasing the total denitrification amount. It is analyzed that Comparative Example 9 uses bagasse raw materials, which contain a small amount of sugars (such as disaccharides and monosaccharides). Although the initial carbon release amount is relatively high, the continuous carbon release ability is poor; moreover, due to the fact that the structures of the bagasse raw materials and the hydrogel skeleton cannot play a synergistic role, the film-forming ability is poor, the uniformity of the formed microbial film is poor, and the film area is small, further reducing the denitrification effect.

[0244] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention as stipulated, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A slow-release carbon source material for biological denitrification, characterized in that: The slow-release carbon source material comprises a hydrogel skeleton and a carbon source carried by the hydrogel skeleton; Wherein, the carbon source includes alkalized bagasse and sodium acetate; The hydrogel skeleton comprises a porous structure formed by polyvinyl alcohol and sodium alginate; Relative to 1 part by weight of alkalized bagasse, the amount of sodium acetate is 0.5 to 2 parts by weight, and the amount of the hydrogel skeleton is 1.5 to 4 parts by weight; The specific surface area of ​​the slow-release carbon source material is 5 to 25 m 2 / g.

2. The slow-release carbon source material according to claim 1, characterized in that: The porosity of the slow-release carbon source material is 20% to 80%, preferably 40% to 80%; and / or, the porosity of the hydrogel skeleton is 30% to 90%, preferably 50% to 90%; And / or, the particle size of the alkalized bagasse is 0.1 mm to 0.5 mm, preferably 0.1 mm to 0.3 mm; And / or, the composition of the alkalized bagasse comprises 16-20wt% lignin, 28-35wt% cellulose and 15-20wt% hemicellulose; And / or, the specific surface area of ​​the slow-release carbon source material is 6 to 22 m 2 / g, preferably 8 to 20 m 2 / g.

3. The slow-release carbon source material according to claim 1 or 2, characterized in that: Relative to 1 weight part of alkalized bagasse, the amount of sodium acetate used is 0.7 to 1.5 weight parts, and the amount of the hydrogel skeleton used is 1.6 to 2.2 weight parts.

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

1.

5. The method for preparing the slow-release carbon source material according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: Step (1): alkalizing the bagasse raw material, drying and crushing it to obtain alkalized bagasse; Step (2): adding 30 to 50 parts by weight of polyvinyl alcohol and 3 to 8 parts by weight of sodium alginate to 400 to 600 parts by volume of water and stirring to prepare a hydrogel precursor; Step (3): 10 to 40 parts by weight of the alkalized bagasse obtained in step (1) and 10 to 35 parts by weight of sodium acetate are mixed and molded with 30-75 parts by weight of the hydrogel precursor obtained in step (2) to obtain a slow-release carbon source material precursor, and the slow-release carbon source material precursor is cross-linked and cured under the action of a cross-linking agent.

6. The preparation method according to claim 5, characterized in that: The components of the bagasse raw material include 18-22 wt% of lignin, 40-50 wt% of cellulose, 25-30 wt% of hemicellulose and 1.5-3 wt% of sugar.

7. The preparation method according to claim 5 or 6, characterized in that: In step (1), the alkalization treatment is carried out in an alkaline solution, and the alkaline solution is selected from at least one of a sodium hydroxide solution, a potassium hydroxide solution, a lithium hydroxide solution and aqueous ammonia; preferably, the concentration of the alkaline solution is 1 to 5 wt%; and / or, relative to 20 to 50 g of bagasse raw material, the amount of the alkaline solution is 300 to 500 ml; And / or, in step (1), the conditions of the alkalization treatment include: temperature of 20 to 30° C., time of 20 to 24 h; And / or, in step (1), before drying, the alkalized bagasse is washed to a pH of 6.8 to 7.

2.

8. The preparation method according to any one of claims 5 to 7, characterized in that: In step (2), the stirring conditions include: temperature of 80 to 95° C. and time of 1 to 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 molding conditions include: temperature of -15 to -25°C and time of 10 to 15 hours.

9. The preparation method according to any one of claims 5 to 8, characterized in that: In step (3), the slow-release carbon source material precursor is immersed in a cross-linking agent solution for cross-linking and curing, 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 to 5° C. and a time of 20 to 24 hours.

10. Use of the slow-release carbon source material according to any one of claims 1 to 4 or the slow-release carbon source material prepared by the preparation method according to any one of claims 5 to 9 in the field of wastewater treatment.

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