A solid slow-release carbon source and its preparation and application

Abstract

The present invention discloses a solid slow-release carbon source and its preparation and application. The method includes: adding octadecyl acrylate to a polyvinyl alcohol solution, heating and stirring at 95 °C, adding a carbon source and fully mixing and reacting; slowly dropping tetraethyl orthosilicate into the mixture through a peristaltic pump; removing bubbles by ultrasonic treatment, pouring into a mold and naturally cooling to room temperature, freezing and forming at -20 °C, naturally thawing at room temperature, and repeating the above freezing-thawing operation, demolding and putting it into a saturated boric acid solution containing CaCl2 for chemical cross-linking at 4 °C; washing with ultrapure water, drying to constant weight at 60 °C and then storing in a sealed manner to isolate oxygen. The present invention solves the problems in the prior art of high carbon release rate, poor slow-release effect, and inability to control the COD concentration in water bodies. The carbon release rate can be stabilized at 0.22 mg / (g·h), and it is used for denitrification and nitrogen removal in water bodies mainly containing nitrate nitrogen, which is not only efficient and stable, but also can better control the COD concentration of the effluent.

Description

Technical Field

[0001] The present invention relates to a slow-release carbon source for denitrification and nitrogen removal, and particularly to a solid slow-release carbon source and its preparation and application. Background Art

[0002] The total control indicators of the water environment include COD, TP, and ammonia nitrogen. Most sewage treatment facilities discharge the ammonia nitrogen in the wastewater after oxidizing it into nitrate. In the non-point source pollution brought by surface runoff, due to the long surface runoff confluence time and shallow water depth, the ammonia nitrogen in farmland wastewater or domestic sewage is basically oxidized into nitrate. Whether it is the tail water of sewage treatment facilities or the non-point source pollution runoff will eventually enter rivers and lakes, and the large amount of nitrate nitrogen contained therein will still cause obvious harm to the river and lake ecosystem. Therefore, carrying out research on denitrification of high-nitrate-nitrogen water bodies and laying a foundation for including nitrate nitrogen or total nitrogen in the total control indicators is of great significance for thoroughly improving the water environment quality.

[0003] Since the oxidation of ammonia nitrogen in water usually occurs after the oxidation of COD, the COD concentration in water bodies with high nitrate nitrogen concentration is usually extremely low. The existing nitrate nitrogen removal technologies mainly include short-cut denitrification technologies that do not require external carbon sources and denitrification technologies that require external carbon sources. Among them, technologies such as short-cut denitrification technologies and simultaneous denitrification technologies that do not require external carbon sources are not mature enough, and the implementation conditions are harsh. Therefore, the current mainstream technology still adopts the denitrification technology with external liquid carbon sources. Since solid slow-release carbon sources can not only save carbon source dosing equipment but also improve the denitrification effect by serving as a microbial attachment carrier at the same time, in recent years, there has been a research boom on replacing liquid carbon sources with solid slow-release carbon sources for denitrification and nitrogen removal. The preparation of solid slow-release carbon sources includes two methods: pyrolysis and chemical cross-linking. The solid slow-release carbon source obtained by pyrolysis is basically in the form of biochar, with high mechanical strength but complex preparation conditions, large fluctuations in yield, and low utilization efficiency. The current main research direction is to prepare solid slow-release carbon sources by chemically cross-linking natural organic matter or organic synthetic materials. The solid slow-release carbon source that can be applied in engineering is required to have high mechanical strength, low carbon release rate, stable carbon release rate, good denitrification effect, and no secondary pollution.

[0004] The existing literature 1 (patent number: CN118005196A) proposes a straw resource-based slow-release carbon source material with high mechanical strength. This invention uses perforated acrylic balls as the carbon source carrier. Although the denitrification effect is good, there is a problem of serious COD exceeding the standard. Literature 2 (patent number: CN118125612A) discloses a denitrifying biological carrier based on iron agents, modified activated carbon, polycaprolactone, sodium dodecyl sulfate, and hydrogel binders, where the modified activated carbon is 3-chloro-2-hydroxypropyltrimethylammonium chloride-modified activated carbon, as well as its preparation method, but it cannot guarantee the COD concentration in the effluent. Literature 3 (patent number: CN118255461A) relates to a preparation method of a hydrogel-coated slow-release carbon source. The material is entirely prepared from natural polysaccharide materials, encapsulating various sizes of molecular sugars and high-molecular carbon sources, and is entirely biodegradable, but the carbon release rate is high, and the carbon source is basically released within 24 hours, and the slow-release effect is not ideal enough. Summary of the Invention

[0005] The purpose of the present invention is to provide a solid slow-release carbon source and its preparation and application, which solves the problems of high carbon release rate, poor slow-release effect, and inability to control the COD concentration in the prior art. The carbon release rate can be stabilized at 0.22 mg / (g·h), and it is used for denitrifying and removing nitrogen from water bodies mainly containing nitrate nitrogen, which is not only highly efficient and stable but also can better control the COD concentration in the effluent to avoid secondary pollution.

[0006] To achieve the above purpose, the present invention first provides a preparation method of a solid slow-release carbon source, which includes:

[0007] (1) Add octadecyl acrylate to the polyvinyl alcohol solution, place it at 95°C and heat with stirring, add the carbon source and mix well to react to obtain a mixed solution. The carbon source is corn starch or acetate starch.

[0008] (2) Slowly drip tetraethyl orthosilicate into the mixed solution through a peristaltic pump.

[0009] (3) Remove bubbles by ultrasonic treatment. Pour the solution after ultrasonic bubble removal into a mold and let it cool naturally to room temperature, freeze-mold at -20°C, thaw naturally at room temperature, and repeat the above freezing-thawing operation to obtain the formed material; demold and place it in a saturated boric acid solution containing CaCl2 for chemical cross-linking at 4°C.

[0010] (4) Wash the cross-linked material with ultrapure water, dry it at 60°C to constant weight, and then store it in a sealed and oxygen-isolated manner to obtain the solid slow-release carbon source.

[0011] Preferably, in step (1), the mass ratio of polyvinyl alcohol to octadecyl acrylate in the polyvinyl alcohol solution is (5 - 20):1, and the molar ratio of polyvinyl alcohol to carbon source in the polyvinyl alcohol solution is (1 - 5):(1 - 5). Polyvinyl alcohol is a water-soluble polymer with excellent mechanical properties. It is safe and non-toxic under certain conditions and only produces carbon dioxide and water after decomposition, causing no pollution to the environment. It is an ideal material for modifying carbon sources. However, carbon sources such as starch and the hydroxyl groups in polyvinyl alcohol molecules are hydrophilic, which can cause the structure of the slow-release carbon source to be unstable. By modifying the hydroxyl groups, the stability of the material structure can be improved, and the slow-release rate of the carbon source can be controlled. Octadecyl acrylate has unique colloidal properties and high stability, which can improve the physical properties of polyvinyl alcohol. After blending the two, a network-like carrier is formed, and the carbon source is connected by chemical bonds to form a slow-release carbon source. Under hydrolysis or microbial decomposition, the chemical bonds break, achieving the purpose of carbon slow-release. The mass ratio of the two mixtures affects the stability of the carrier structure and the pore size.

[0012] Preferably, in step (2), the volume-mass ratio of tetraethyl orthosilicate to the carbon source is (5 - 15) mL:10 g, and the slow dropping rate of tetraethyl orthosilicate is 10 mL / 3.5 h. When the volume-mass ratio of tetraethyl orthosilicate to the carbon source is (5 - 15) mL:10 g, the prepared slow-release carbon source has a complete coating, a stable structure, good slow-release effect, and good mechanical properties.

[0013] Preferably, in step (3), the time for freeze-forming is 24 h; the time for chemical cross-linking is 24 h. The size of the mold is 1 cm 3 , the concentration of CaCl2 in the saturated boric acid solution containing CaCl2 is 1 - 10%; the number of times of repeated freeze-thaw operations is 3 times.

[0014] More preferably, the concentration of CaCl2 in the saturated boric acid solution containing CaCl2 is 3%. Polyvinyl alcohol undergoes chemical cross-linking with boric acid to form a network structure, and octadecyl acrylate also forms a network structure through Ca 2+ affinity. The two network structures interpenetrate and wrap around the surface of the carbon source, reducing the hydrophilicity of the slow-release carbon source and further improving the structural stability.

[0015] Preferably, in step (4), the drying time is 24 h.

[0016] The present invention provides a solid slow-release carbon source prepared by the preparation method as described.

[0017] Preferably, the carbon release rate of the solid slow-release carbon source is 0.22 mg / (g·h).

[0018] The present invention provides an application of the solid slow-release carbon source as described in denitrification.

[0019] Preferably, the application includes denitrification of water bodies containing nitrate nitrogen pollution.

[0020] A solid slow-release carbon source, its preparation method and application according to the present invention solve the problems of high carbon release rate, poor slow-release effect and inability to control COD concentration in the prior art, and have the following advantages:

[0021] 1. The solid carbon release rate prepared by the present invention can be stabilized at 0.22 mg / (g·h). By calculating the amount of carbon source released, it can be efficiently utilized by microorganisms for denitrification.

[0022] 2. Compared with the existing inventions, the solid slow-release carbon source of the present invention is used for denitrification of water bodies mainly containing nitrate nitrogen, which is not only efficient and stable, but also can better control the COD concentration of the effluent to avoid secondary pollution. Description of the Drawings

[0023] Figure 1 It is a comparison chart of the COD effluent concentration when YX-3 in Example 4 and CX-3 in Example 1 of the present invention are used for denitrification.

[0024] Figure 2 It is a comparison chart of the nitrate nitrogen removal rate when YX-3 in Example 4 and CX-3 in Example 1 of the present invention are used for denitrification. Detailed Embodiments

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] In the following embodiments, unless otherwise specified, the chemicals used are all of analytical grade and purchased from Chengdu Kelong Chemical Co., Ltd. The instruments and equipment used are shown in Table 1.

[0027] Table 1 List of Instruments and Equipment

[0028]

[0029] Example 1

[0030] A preparation method of a solid slow-release carbon source, the method comprising:

[0031] (1) Prepare a 10% polyvinyl alcohol (PVA) solution. Add octadecyl acrylate (SA) to the PVA solution and place it in a 95°C collecting heat type constant temperature heating magnetic stirrer for heating and stirring for 2 h. Then add acetate starch and mix well for a reaction for 2 h to obtain a mixed solution. The mass ratio of PVA to octadecyl acrylate in the PVA solution is 4:5, and the mass ratio of PVA in the PVA solution to starch in the acetate starch is 1:5.

[0032] (2) Slowly drip tetraethyl orthosilicate into the mixed solution through a peristaltic pump (drip rate: 10 mL / 3.5 h). The mass ratio of starch in the acetate starch to tetraethyl orthosilicate is 1:1.

[0033] (3) Remove bubbles by ultrasonic treatment. Pour the solution after ultrasonic bubble removal into a 1 cm 3 cube mold and let it cool naturally to room temperature. Freeze it at -20°C for 24 h to form a shape, then thaw it naturally at room temperature for 2 h, and repeat the above freezing-thawing operation 2 times. Subsequently, demold the formed material and quickly put it into a saturated boric acid solution containing 3% CaCl2, and carry out chemical cross-linking at 4°C for 24 h;

[0034] (4) Wash the material after cross-linking 5 times with ultrapure water to remove the excessive chemical cross-linking agent on the surface. Dry it in a 60°C constant temperature oven for 24 h until it reaches a constant weight, and then store it in a sealed and oxygen-isolated manner to obtain a solid slow-release carbon source, denoted as CX-3.

[0035] Example 2

[0036] A preparation method of a solid slow-release carbon source is basically the same as that of the example, except that: in step (1), the acetate starch is adjusted to corn starch, step (2) is not carried out, and the repeated freezing-thawing process is not carried out in step (3); through the same operations as in Example 1, the obtained solid slow-release carbon source is denoted as YS-NT.

[0037] Example 3

[0038] A preparation method of a solid slow-release carbon source is basically the same as that of the example, except that: in step (1), the acetate starch is adjusted to corn starch, and the repeated freezing-thawing process is not carried out in step (3); through the same operations as in Example 1, the obtained solid slow-release carbon source is denoted as YS-T.

[0039] Example 4

[0040] A preparation method of a solid slow-release carbon source is basically the same as that of the example, except that: in step (1), the acetate starch is adjusted to corn starch; through the same operations as in Example 1, the obtained solid slow-release carbon source is denoted as YS-3.

[0041] Comparative Example 1

[0042] The preparation method of a solid slow-release carbon source is basically the same as the embodiment, except that: in step (1), there is no acetate starch (no carbon source is added); through the same operation as in Example 1, the obtained carbon source is denoted as the carbon source without added carbon source.

[0043] Experimental Example 1 verifies the carbon release and compressive strength performance of the solid slow-release carbon sources prepared in Examples 1 to 4

[0044] 1. Carbon release

[0045] The carbon release process of the solid slow-release carbon sources prepared in Examples 1 to 4 can be divided into a rapid release period, a stable period, and an end period. The carbon release process mainly focuses on the stable period, that is, the carbon release rate during the stable period of the solid slow-release carbon source can be stably and preferably at a low level. The higher the compressive strength of the solid slow-release carbon source, the better. The carbon release rate was used to investigate the carbon release performance of the slow-release carbon source by the method of static carbon release in clear water. The specific test method was as follows: Weigh 10 g of the slow-release carbon source into a blue-mouth bottle, inject 500 mL of distilled water and seal it with a lid. At 25 °C, samples were taken at certain intervals (0, 2, 4, 6, 8, and 10 h) and the distilled water was replaced. Subsequently, the distilled water was replaced every 24 h, and the COD concentration in the water sample was measured. The first-order kinetic equation and the second-order kinetic equation were used to describe the change of COD with time during the carbon release process, and the carbon release rate of the slow-release carbon source was calculated and judged. The specific results are shown in Table 2.

[0046] Table 2 Comparison of carbon release rates of YS-NT in Example 2 and YS-T in Example 3

[0047]

[0048] As can be seen from Table 2, the carbon release rate of YS-T in Example 3 is lower and the carbon release effect is better.

[0049] 2. Compressive strength

[0050] The test method for compressive strength was as follows: Randomly take 30 complete sample materials, regardless of size and mass. Use a digital display push-pull force gauge to vertically press each material until the value on the push-pull force gauge is recorded when it produces irreversible deformation or breaks. The average value represents its compressive ability. The higher the compressive strength of the solid slow-release carbon source, the better. The specific results are shown in Table 3.

[0051] Table 3 Comparison of compressive strengths of YS-NT in Example 2 and YS-T in Example 3

[0052]

[0053] As can be seen from Table 3, the compressive strength of YS-T in Example 3 is higher and the stability is good.

[0054] Experimental Example 2 verifies the application of the solid slow-release carbon sources prepared in Examples 1 to 4 in denitrification and nitrogen removal

[0055] When the types of carbon sources selected can be efficiently utilized by denitrifying bacteria, they can be efficiently utilized during denitrification and nitrogen removal, avoiding the release into the water body where they cannot be utilized in time and causing secondary pollution of COD. The present invention will conduct denitrification and nitrogen removal applications on the carbon source-free of Comparative Example 1, the carbon source YX-3 of Example 4, and the carbon source CX-3 of Example 1. The specific method is as follows:

[0056] (1) Calculate the flow rate Q1 of the solid slow-release carbon source required for denitrification and nitrogen removal according to the amount of the water body to be treated and the nitrate content therein;

[0057] (2) Calculate the amount Q2 of the solid slow-release carbon source based on the microbial utilization rate of 75% of the released carbon source during the denitrification and nitrogen removal process;

[0058] (3) Calculate the dosage M of the solid slow-release carbon source according to the carbon release rate of 0.22 mg / (g·h);

[0059] (4) Add the solid slow-release carbon source with a mass of M to a suitable container, and then add the water body to be treated for nitrogen removal and let it stand for 24 h.

[0060] As Figure 1 shown, the comparison chart of the effluent COD concentration when YX-3 of Example 4 and CX-3 of Example 1 of the present invention are used for denitrification and nitrogen removal. Among them, YX-3 is Example 4, CX-3 is Example 1, and the effluent without added carbon source is Comparative Example 1. From Figure 1 it can be seen that the effluent COD concentration in the denitrification experiment system adding CX-3 in Example 1 basically remains at about 20 mg / L; the denitrification experiment system adding YX-3 in Example 4 stabilizes at 20-50 mg / L after 10 days of the experiment. Thus, it can be seen that the carbon release stability of the slow-release carbon source of the present invention is good.

[0061] As Figure 2 shown, the comparison chart of the nitrate nitrogen removal rate when YX-3 of Example 4 and CX-3 of Example 1 of the present invention are used for denitrification and nitrogen removal. Among them, YX-3 is Example 4, CX-3 is Example 1, and the one without added carbon source is Comparative Example 1. From Figure 2 it can be seen that the two slow-release carbon sources of Example 4 and Example 1 of the present invention both contribute to microbial denitrification and nitrogen removal, and the nitrate nitrogen removal effect of CX-3 in Example 1 is better than that of YX-3 in Example 4.

[0062] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and substitutions of the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a solid slow-release carbon source, characterized in that: The method includes: (1) adding octadecyl acrylate to a polyvinyl alcohol solution, heating and stirring at 95° C., adding a carbon source and mixing and reacting to obtain a mixed solution; the carbon source is corn starch or acetate starch; and the mass ratio of polyvinyl alcohol to octadecyl acrylate in the polyvinyl alcohol solution is 4:5; (2) slowly adding ethyl orthosilicate to the mixed solution by a peristaltic pump; (3) ultrasonic degassing, pouring the solution after ultrasonic degassing into a mold and naturally cooling it to room temperature, freezing it at -20°C, thawing it naturally at room temperature, and repeating the above freezing-thawing operation to obtain a molded material; demolding and placing it in a saturated boric acid solution containing CaCl2, and chemically cross-linking it at 4°C; (4) The cross-linked material was washed with ultrapure water, dried at 60° C. to constant weight, and then sealed and oxygen-proofed for storage to obtain a solid slow-release carbon source.

2. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of polyvinyl alcohol to carbon source in the polyvinyl alcohol solution is (1-5):(1-5).

3. The preparation method according to claim 1, characterized in that: In step (2), the volume mass ratio of the tetraethyl orthosilicate to the carbon source is (5-15) mL:10 g, and the slow dripping speed of the tetraethyl orthosilicate is 10 mL / 3.5 h.

4. The preparation method according to claim 1, characterized in that: In step (3), the size of the mold is 1 cm 3 The concentration of CaCl2 in the saturated boric acid solution containing CaCl2 is 3%; the number of freeze-thaw operations is 3 times.

5. The preparation method according to claim 1, characterized in that: In step (3), the freezing molding time is 24 hours; the chemical cross-linking time is 24 hours.

6. The preparation method according to claim 1, characterized in that: In step (4), the drying time is 24 hours.

7. A solid slow-release carbon source prepared by the preparation method according to any one of claims 1 to 6.

8. The solid slow-release carbon source according to claim 7, characterized in that: The carbon release rate of the solid slow-release carbon source reaches 0.22 mg / (g·h).

9. Use of the solid slow-release carbon source as claimed in claim 7 in denitrification.

10. The use according to claim 9, characterized in that: The application includes denitrification of water bodies contaminated with nitrate nitrogen.

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