Preparation method of slow-release carbon source and application of slow-release carbon source in treatment of low-carbon-nitrogen-ratio wastewater

Abstract

The invention discloses a preparation method of a slow-release carbon source and application of the slow-release carbon source in treatment of low-carbon-nitrogen-ratio wastewater. The preparation method comprises the following steps: S1, taking a waste straw material, poly (butylene succinate), polyvinyl alcohol, sodium alginate and deionized water for later use; s2, mixing the waste straw material with the poly (butylene succinate) to obtain a mixed solid; mixing polyvinyl alcohol, sodium alginate and deionized water to obtain a mixed solution; s3, adding the mixed solid into the mixed solution, uniformly mixing, injecting into a mold, freezing, demolding, soaking, cleaning and drying to obtain a slow-release carbon source; the prepared slow-release carbon source is applied to low-carbon-nitrogen-ratio wastewater treatment, the carbon source can be slowly released, the denitrification process can be promoted in the wastewater treatment process, and the slow-release carbon source is an environment-friendly technology for improving the wastewater treatment efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and specifically to a preparation method of a slow-release carbon source and its application in treating wastewater with a low carbon-to-nitrogen ratio. Background Art

[0002] With the growth of the global population and the continuous development of agricultural production, the output of agricultural waste has increased year by year. These wastes, including straws, fruit husks, roots and rhizomes, etc., will cause environmental pollution and resource waste when not properly treated. In recent years, recognizing the potential value of agricultural waste, more and more researchers have begun to focus on its resource utilization. Converting agricultural waste into a slow-release carbon source provides new impetus for sustainable agricultural development.

[0003] Agricultural waste is the general term for the organic substances generated and discarded during the harvesting, production and processing of agricultural crops. China is a large agricultural country, but at the same time it is also the country with the largest output of agricultural waste in the world. In recent years, with the continuous growth of the population, the demand for agricultural crops has also increased day by day, and the waste generated by agricultural production is immeasurable. However, since most farmers dispose of agricultural waste at will in their production and life, burning or abandoning the vast majority of agricultural waste in place has caused serious resource waste and made the overall resource utilization level of China's agricultural waste very low. This has not only become a key issue for rural environmental protection, but also posed a huge hidden danger to China's environmental pollution. How to effectively utilize agricultural waste under the background of sustainable development, reduce pollution and damage to the ecological environment has become a key issue for China's development.

[0004] During the treatment of wastewater with a low carbon-to-nitrogen ratio, the amount of carbon source becomes the main limiting factor affecting the total nitrogen removal efficiency. Adding an external carbon source is a common means to improve the total nitrogen removal efficiency. The carbon source materials for slow release include natural carbon source materials (such as straws, rice husks, wood chips, etc.) and biodegradable polymers (such as polylactic acid, polyvinyl alcohol, polybutylene succinate, etc.). Although using natural carbon source materials is inexpensive, their denitrification effect is not good and the denitrification load is relatively low. Using polymers as carbon sources can achieve an ideal denitrification effect, but their cost is relatively high. Mixing the two in a certain proportion to make a synthetic carbon source can solve the problems of price and denitrification effect. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a preparation method of a slow-release carbon source and its application in treating wastewater with a low carbon-to-nitrogen ratio.

[0006] A preparation method of a slow-release carbon source includes the following steps:

[0007] S1. Prepare waste straw material, polybutylene succinate, polyvinyl alcohol, sodium alginate, and deionized water in the ratio of 8 - 12 g : 0.1 - 4 g : 8 g : 1 g : 100 ml; among them, the waste straw material is one of wheat straw, reed straw, corn straw, sesame straw, and soybean straw;

[0008] S2. First, mix the waste straw material with the polybutylene succinate to obtain a mixed solid; among them, the polybutylene succinate is in powder form; then mix the polyvinyl alcohol, sodium alginate, and deionized water, and heat and stir at a temperature of 95 - 100 °C for 60 - 120 min, and then cool to obtain a mixed solution;

[0009] S3. Add the mixed solid to the mixed solution and mix evenly, then inject it into a mold and freeze at a temperature of -18 - -16 °C for 11 - 14 h, demold, soak, and wash after freezing, and then dry at 60 - 70 °C to obtain a slow-release carbon source.

[0010] Note: The above method combines agricultural waste straw, straw with the biodegradable polymer material polybutylene succinate and polyvinyl alcohol to prepare a slow-release carbon source for treating low carbon-nitrogen ratio wastewater, realizing the resource utilization of agricultural waste, and also having the advantages of low cost, stable carbon source release, and convenient use. Compared with other slow-release carbon sources in the prior art, it helps to improve the denitrification efficiency of wastewater treatment.

[0011] Further, in some implementation modes, the waste straw material is wheat straw after acid soaking treatment, and the acid soaking treatment is: soaking wheat straw with a 2% sulfuric acid solution by mass, heating in a water bath at 100 °C for 15 - 25 min, and then drying completely at a temperature of 60 - 70 °C;

[0012] In some implementation modes, the waste straw material is wheat straw after alkali soaking treatment, and the alkali soaking treatment is: soaking with 2% NaOH by mass, heating in a water bath at 100 °C for 15 - 25 min, and then drying completely at a temperature of 60 - 70 °C.

[0013] Note: The above acid or alkali soaking treatment of wheat straw can effectively remove lignin and hemicellulose in the straw, enhance the enzymatic hydrolysis efficiency and biodegradability of the straw, thereby improving the performance and application effect of the slow-release carbon source.

[0014] Further, in some other implementation modes, the waste straw material in S1 is obtained through enzyme treatment, and the method of enzyme treatment includes:

[0015] S1-1. First, take dry waste straw, crush it, and sieve it to obtain straw particles with a particle size of 0.45 - 1 mm;

[0016] S1-2. Then, add a mixed enzyme preparation accounting for 1 - 2% of the mass of the straw particles to the straw particles. The mixed enzyme preparation includes ligninase and cellulase with an equal number of active units;

[0017] S1-3. Subsequently, carry out the reaction in a constant temperature shaker. The reaction temperature is 45 - 55 °C, the reaction time is 20 - 24 h, and the shaker rotation speed is 150 - 200 rpm;

[0018] S1-4. Through centrifugation or filtration, obtain solid residues, wash the solid residues to neutral, and then dry them to constant weight at 60 - 80 °C to obtain waste straw materials.

[0019] Note: Through enzyme treatment, the lignin and cellulose structures in the straw are effectively damaged, increasing its hydrophilicity and reactivity to improve its binding ability with PBS and PVA - SA. Furthermore, it is convenient to form a slow - release carbon source with waste crops as the core base, polyvinyl alcohol - sodium alginate as the skeleton, and the polymer material polybutylene succinate as the supplementary carbon source, and optimize its structure, especially showing better effects in the treatment process of low - carbon - nitrogen - ratio wastewater.

[0020] Furthermore, the stirring speed of the heating and stirring in S2 is 100 - 120 rpm.

[0021] Note: The above - mentioned stirring speed is relatively preferred. Beyond this range, it may lead to non - uniform and unreasonable distribution of the formed structure.

[0022] Furthermore, the mold is a block - shaped mold.

[0023] Note: Compared with other mold shapes, the block - shaped mold has the advantages of simple operation, easy process control, stable structure, long service life, etc. It can release carbon source slowly and stably for a long time, strengthen the denitrification process, can release carbon source slowly and stably for a long time, meet the carbon source requirements of microorganisms, strengthen the denitrification process, help improve the utilization rate of carbon source, and promote the wastewater treatment effect.

[0024] Furthermore, the preparation method of the powdery polybutylene succinate in S2 includes: First, place granular polybutylene succinate in N,N - dimethylacetamide liquid according to the ratio of 4 - 8 g:200 ml, dissolve it at a temperature of 70 - 80 °C for 1 h. After the solution cools, carry out suction filtration to obtain a solid, and then grind it.

[0025] Description: Through the above method, powdery polybutylene succinate can be prepared. The powdery PBS is easier to mix with other materials, improving the processing performance and application performance of the materials and expanding its application scope in the fields such as wastewater treatment.

[0026] Further, the method of mixing the waste straw material with the polybutylene succinate to obtain a mixed solid in S2 is as follows: Mix the waste straw material with the powdery polybutylene succinate evenly in a high-speed mixer for 10 - 15 minutes to obtain a mixture. Then, add the mixture to deionized water at a ratio of 2 g : 1 - 2 ml and perform spray drying through a spray drying tower. Control the droplet size to be 50 - 100 microns and spray dry until the deionized water completely evaporates to obtain the mixed solid.

[0027] Description: By fully mixing the waste straw material with the powdery polybutylene succinate in a high-speed mixer and then using spray drying technology to prepare the mixed solid, it has the advantages of uniform mixing, high production efficiency, and good product quality. During the spray drying process, the precise control of the droplet size helps to obtain materials with uniform particle size and stable performance, meeting the requirements of the slow-release carbon source for the release rate and stability, providing an efficient and reliable carbon source material for wastewater treatment and facilitating the formation of the subsequent slow-release carbon source structure.

[0028] Further, the solution for soaking in S3 is a cross-linking agent boric acid - calcium chloride solution. The cross-linking agent boric acid - calcium chloride solution is an aqueous solution with a mass fraction of both CaCl2 and H3BO4 being 4%, and the soaking time is 20 - 26 hours.

[0029] Description: The soaking in the above solution enhances the cross-linking degree of the material, making it have a better slow-release effect; it can improve the slow-release performance of the material and enhance its mechanical strength and stability.

[0030] The present invention provides an application of a slow-release carbon source prepared by the above method in treating low carbon-nitrogen ratio wastewater.

[0031] Description: The slow-release carbon source obtained by the present invention has significant advantages in treating low carbon-nitrogen ratio wastewater, can effectively improve the sewage treatment efficiency, reduce the operating cost, and improve the water quality.

[0032] Furthermore, the low C / N ratio wastewater includes domestic sewage, industrial wastewater, and agricultural polluted water, and the C / N ratio of the low C / N ratio wastewater is 1.0 - 8.5; the method for applying the slow-release carbon source to treat low C / N ratio wastewater is as follows: adding the slow-release carbon source at a ratio of 200 mg / L in the denitrifying biological filter of the low C / N ratio wastewater, controlling the water temperature at 20 - 30 °C, the pH value at 7 - 8, the hydraulic retention time at 4 - 6 h, controlling the dissolved oxygen in the low C / N ratio wastewater at 1 - 3 mg / L through intermittent aeration, and regularly monitoring the nitrogen concentration in the low C / N ratio wastewater until the treatment is completed.

[0033] Explanation: The above application method constructs an optimal active environment for denitrifying bacteria groups, significantly improving the nitrogen removal efficiency; the continuous and stable carbon supply characteristic of the slow-release carbon source avoids the instantaneous release problem of traditional carbon sources, reducing both carbon source waste and preventing secondary pollution; combined with intermittent aeration and regular monitoring, dynamic regulation of the treatment process is achieved, ensuring that the total nitrogen in the effluent meets the standards stably, and it is applicable to the large-scale treatment requirements of high-load, low C / N ratio (i.e., the C / N ratio ranges from 1.0 to 8.5) wastewater.

[0034] The beneficial effects of the present invention are as follows:

[0035] The method of the present invention combines agricultural waste straw, straw with biodegradable polymer materials polybutylene succinate and polyvinyl alcohol to prepare a slow-release carbon source for treating low C / N ratio wastewater. Compared with the single waste straw carbon source, it solves problems such as difficult control of the dosing amount or excessive initial release amount. This carbon source has a large and stable carbon release amount, good carbon release performance, and the carbon source block can provide a good living space for microorganisms, facilitating the denitrification process and improving the nitrogen removal efficiency; it realizes the resource utilization of agricultural waste, and also has the advantages of low cost, stable carbon source release, and convenient use. Compared with other slow-release carbon sources in the prior art, it helps to improve the nitrogen removal efficiency of wastewater treatment. The preparation method of the present invention is simple and efficient, the performance of the slow-release carbon source is stable, the cost is lower compared with polymer synthetic carbon sources, on the other hand, it improves the utilization rate of waste crops, and is more energy-saving and environmentally friendly. Description of the Drawings

[0036] Figure 1 is the crushed waste crops in Example 1 of the present invention;

[0037] Figure 2 is the polymer material PBS in Example 1 of the present invention;

[0038] Figure 3 is the framework material of the present carbon source in Example 1 of the present invention;

[0039] Figure 4 is the synthetic slow-release carbon source uniformly mixed in Example 1 of the present invention;

[0040] Figure 5 In Example 1 of the present invention, the slow-release carbon source was immersed in a solution of 4% calcium chloride and boric acid;

[0041] Figure 6 In Example 1 of the present invention, a slow-release carbon source was synthesized;

[0042] Figure 7 It is a graph of the COD release amount of the straw carbon source in Example 5 of the present invention;

[0043] Figure 8 It is the COD release amount of the pretreated straw carbon source in Example 3 of the present invention;

[0044] Figure 9 It is the COD release amount of the carbon source with different synthesis ratios of two kinds of straws in Example 2 of the present invention. Detailed implementation manner

[0045] To further elaborate on the methods adopted and the effects achieved by the present invention, the technical solutions of the present invention will be clearly and completely described below in combination with experiments.

[0046] Example 1: A preparation method of a slow-release carbon source, comprising the following steps:

[0047] As Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 shown, S1. According to the ratio of 10g: 2g: 8g: 1g: 100ml, take waste straw material, polybutylene succinate, polyvinyl alcohol, sodium alginate, and deionized water for use; wherein, the waste straw material is wheat straw;

[0048] The waste straw material is obtained by enzyme treatment, and the method of the enzyme treatment includes:

[0049] S1-1. First, take the dry waste straw material, crush and sieve it to obtain straw particles with a particle size of 0.45 - 1 mm;

[0050] S1-2. Then, add a mixed enzyme preparation accounting for 1.5% of the mass of the straw particles to the straw particles. The mixed enzyme preparation includes lignin enzyme and cellulase, and the active unit numbers of the lignin enzyme and the cellulase are equal;

[0051] S1-3. Subsequently, carry out the reaction in a constant temperature shaker. The reaction temperature is 50 °C, the reaction time is 22 h, and the shaker rotation speed is 180 rpm;

[0052] S1-4. Obtain solid residues by centrifugation or filtration, wash the solid residues to neutral, and then dry them to constant weight at 70 °C to obtain waste straw material;

[0053] S2. First, mix the waste straw material with the polybutylene succinate to obtain a mixed solid. Among them, the polybutylene succinate is in powder form. Then, mix polyvinyl alcohol, sodium alginate, and deionized water, heat and stir at 98 °C for 90 min, and then cool to obtain a mixed solution. The stirring speed of the heating and stirring in S2 is 110 rpm.

[0054] The preparation method of the powdered polybutylene succinate in S2 includes: First, place the granular polybutylene succinate in N,N-dimethylacetamide liquid according to the ratio of 6 g:200 ml, dissolve at 75 °C for 1 h. After the solution cools, perform suction filtration to obtain a solid, and then grind it until the particle size of the polybutylene succinate is 10 - 200 μm.

[0055] The method of mixing the waste straw material with the polybutylene succinate to obtain a mixed solid in S2 is: Mix the waste straw material with the powdered polybutylene succinate evenly in a high-speed mixer for 13 min to obtain a mixed material. Then, add the mixed material to deionized water according to the ratio of 2 g:1.5 ml, and perform spray drying through a spray drying tower. Control the droplet size at 50 - 100 microns, and spray dry until the deionized water completely volatilizes to obtain a mixed solid.

[0056] As Figure 5 、 Figure 6 shown, S3. Add the mixed solid to the mixed solution and mix evenly, then inject it into a mold and freeze at -17 °C for 12 h. After freezing, demold, soak, and wash, and then dry at 65 °C to obtain a slow-release carbon source. The mold is a block mold. The soaking solution is a cross-linking agent boric acid-calcium chloride solution, and the cross-linking agent boric acid-calcium chloride solution is an aqueous solution containing 4% by mass of both CaCl2 and H3BO4, and the soaking time is 24 h.

[0057] Example 2: The difference between this example and Example 1 is that the raw material component ratios are different. Reserve waste straw material, polybutylene succinate, polyvinyl alcohol, sodium alginate, and deionized water according to the ratio of 8 g:4 g:8 g:1 g:100 ml.

[0058] Example 3: The difference between this example and Example 1 is that the raw material component ratios are different. Reserve waste straw material, polybutylene succinate, polyvinyl alcohol, sodium alginate, and deionized water according to the ratio of 12 g:0.1 g:8 g:1 g:100 ml.

[0059] Example 4: The difference between this example and Example 1 is that the waste straw material is reed straw.

[0060] Example 5: The difference between this example and Example 1 is that the waste straw material is corn straw.

[0061] Example 6: The difference between this example and Example 1 is that the waste straw material is sesame straw.

[0062] Example 7: The difference between this example and Example 1 is that the waste straw material is soybean straw.

[0063] Example 8: The difference between this example and Example 1 is that in S1, the parameters of the enzyme treatment are different.

[0064] S1-1: First, take the dry waste straw, crush and sieve it to obtain straw particles with a particle size of 0.45 - 1 mm.

[0065] S1-2: Then, add a mixed enzyme preparation accounting for 1% of the mass of the straw particles to the straw particles.

[0066] S1-3: Subsequently, carry out the reaction in a constant temperature shaker. The reaction temperature is 45 °C, the reaction time is 24 h, and the shaker rotation speed is 150 rpm.

[0067] S1-4: Through centrifugation or filtration, obtain solid residues. Wash the solid residues to neutral, and then dry them to a constant weight at 60 °C to obtain the waste straw material.

[0068] Example 9: The difference between this example and Example 1 is that in S1, the parameters of the enzyme treatment are different.

[0069] S1-1: First, take the dry waste straw, crush and sieve it to obtain straw particles with a particle size of 0.45 - 1 mm.

[0070] S1-2: Then, add a mixed enzyme preparation accounting for 2% of the mass of the straw particles to the straw particles.

[0071] S1-3: Subsequently, carry out the reaction in a constant temperature shaker. The reaction temperature is 55 °C, the reaction time is 20 h, and the shaker rotation speed is 200 rpm.

[0072] S1-4: Through centrifugation or filtration, obtain solid residues. Wash the solid residues to neutral, and then dry them to a constant weight at 80 °C to obtain the waste straw material.

[0073] Example 10: The difference between this example and Example 1 is that the heating parameters in S2 are different. At a temperature of 95 °C, heat and stir for 60 min, and then cool to obtain a mixed solution. The stirring speed of the heat and stir is 120 rpm.

[0074] Example 11: The difference between this example and Example 1 is that the heating parameters in S2 are different. At a temperature of 100 °C, heat and stir for 120 min, and then cool to obtain a mixed solution. The stirring speed of the heat and stir is 100 rpm.

[0075] Example 12: The difference between this example and Example 1 is that the preparation parameters of the powdery polybutylene succinate are different. According to the ratio of 8 g: 200 ml, first place the granular polybutylene succinate in N,N-dimethylacetamide liquid, dissolve it at a temperature of 70 °C for 1 h. After the solution cools, perform suction filtration to obtain a solid, and then grind it.

[0076] Example 13: The difference between this example and Example 1 is that the preparation parameters of the powdery polybutylene succinate are different. According to the ratio of 4 g: 200 ml, first place the granular polybutylene succinate in N,N-dimethylacetamide liquid, dissolve it at a temperature of 80 °C for 1 h. After the solution cools, perform suction filtration to obtain a solid, and then grind it.

[0077] Example 14: The difference between this example and Example 1 is that the freezing parameters are different. Freeze at a temperature of -18 °C for 11 h.

[0078] Example 15: The difference between this example and Example 1 is that the freezing parameters are different. Freeze at a temperature of -16 °C for 14 h.

[0079] Example 16: The difference between this example and Example 1 is that the drying temperature in S3 is different. Dry at 60 °C.

[0080] Example 17: The difference between this example and Example 1 is that the drying temperature in S3 is different. Dry at 70 °C.

[0081] Example 18: The difference between this example and Example 1 is that the soaking time in S3 is 20 h.

[0082] Example 19: The difference between this example and Example 1 is that the soaking time in S3 is 26 h.

[0083] Example 20: The difference between this example and Example 1 is that the waste straw material is wheat straw after acid soaking treatment. The acid soaking treatment is as follows: Soak wheat straw with a 2% sulfuric acid solution by mass, heat it in a water bath at 100 °C for 20 min, and then dry it completely at a temperature of 65 °C.

[0084] Example 21: The difference between this example and Example 21 is that the acid soaking treatment is as follows: wheat straw is soaked with a 2% sulfuric acid solution by mass, heated in a water bath at 100 °C for 15 min, and then dried completely at 70 °C.

[0085] Example 22: The difference between this example and Example 21 is that the acid soaking treatment is as follows: wheat straw is soaked with a 2% sulfuric acid solution by mass, heated in a water bath at 100 °C for 25 min, and then dried completely at 60 °C.

[0086] Example 23: The difference between this example and Example 1 is that the waste straw material is wheat straw after alkali soaking treatment, and the alkali soaking treatment is as follows: soaked with 2% NaOH by mass, heated in a water bath at 100 °C for 20 min, and then dried completely at 65 °C.

[0087] Example 24: The difference between this example and Example 1 is that the alkali soaking treatment is as follows: soaked with 2% NaOH by mass, heated in a water bath at 100 °C for 15 min, and then dried completely at 70 °C.

[0088] Example 25: The difference between this example and Example 1 is that the alkali soaking treatment is as follows: soaked with 2% NaOH by mass, heated in a water bath at 100 °C for 25 min, and then dried completely at 60 °C.

[0089] I. Explore the slow-release effect and stability of the slow-release carbon source obtained from different straws as raw materials, acid-base treatment, waste crops, and the synthesis ratio of polymer carbon sources;

[0090] Experimental Example 1: The slow-release carbon source materials prepared in Example 1, Example 4, Example 5, Example 6, and Example 7 were subjected to static carbon release in the laboratory to study the differences in the carbon release performance of the slow-release carbon sources prepared from five kinds of straws.

[0091] The experimental process is as follows: Take three pieces of each of the five straw slow-release carbon sources and weigh them. The weights are 5.0301 g, 5.2688 g, 5.3 g, 4.4213 g, and 4.2728 g respectively. Place them in five 250 ml beakers, add 200 ml of ultrapure water, take water every day and measure the COD released by the material. After taking water every day, change the water completely. The experimental period is set to 25 days. The specific carbon release amount is shown in Figure 7 ; from Figure 7It can be seen that the first three days are the rapid release period, and the 4th - 25th days are the stable release period. The cumulative COD release amount of wheat straw is the largest, that of reed straw and corn straw is in the middle, and the release amounts of sesame straw and soybean straw are the lowest. Therefore, wheat straw, reed straw, and corn straw with larger release amounts are selected for the next experimental exploration, that is, to explore the effect of acid - base pretreatment on the material.

[0092] Experimental Example 2: In order to explore the effect of acid - base soaking treatment of straw on the material, three kinds of straws with good carbon release effects in Experimental Example 1, namely wheat straw, reed straw, and corn straw, are selected as raw materials, and acid - base pretreatment is carried out on them respectively. The three kinds of straws after acid - base pretreatment are synthesized into slow - release carbon sources again, and static carbon release experiments are carried out. The experimental process is as follows: Take three pieces of each of the 6 slow - release carbon sources of wheat, reed, and corn straws after acid - base treatment and weigh them. The weights are 6.8122g, 5.3474g, 5.2201g, 8.1604g, 6.4911g, and 7.6494g respectively. Place them in six 250 - ml beakers, add 200 ml of ultrapure water, take water every day and measure the COD released by the material. After taking water every day, change the water completely. The experimental period is set to 25 days. The specific carbon release amount is shown in Figure 8 . From Figure 8 It can be seen that in terms of COD release amount, the alkali treatment effect of wheat straw and corn straw is better than the acid treatment effect; the total release amount of reed straw after acid treatment is slightly higher than that after alkali treatment, but the alkali treatment effect has better slow - release property. After 25 - day static carbon release of the alkali - treated composite carbon source of wheat straw, the material structure is loose and not conducive to use. Therefore, the alkali - treated reed straw and corn straw are selected for the next experimental exploration, that is, to explore the synthesis ratio of waste crops and polymer carbon sources.

[0093] Experimental Example 3: In order to explore the synthesis ratio of waste crops and polymer carbon sources, two kinds of straws with good carbon release effects in Experimental Example 2, namely reed and corn alkali - treated straws, are used. Three ratios are set for synthesizing slow - release carbon sources, and the ratios of PVA﹕SA﹕straw﹕PBS are 8﹕1﹕8:4, 8﹕1﹕10:2, and 8﹕1﹕12:0.1 respectively. The experimental process is as follows: Take three pieces of each of the slow - release carbon sources with different ratios and weigh them. The weights are 6.926g, 7.2136g, 5.0765g, 5.869g, 5.2585g, and 5.0996g respectively. Place them in six 250 - ml beakers, add 200 ml of ultrapure water, take water every day and measure the COD released by the material. After taking water every day, change the water completely. The experimental period is set to 25 days. The specific carbon release amount is shown in Figure 9 . From Figure 9 It can be seen that no matter what kind of composite slow - release carbon source, the higher the addition ratio of natural materials, the higher the COD release amount of the corresponding carbon source.

[0094] II. Explore the treatment effect of the slow-release carbon source obtained in the embodiments of the present invention on low-carbon-nitrogen ratio wastewater;

[0095] Experimental Example 4: The slow-release carbon source was applied to the treatment process of low-carbon-nitrogen ratio wastewater. The low-carbon-nitrogen ratio wastewater includes domestic sewage, industrial wastewater, and agricultural polluted water with a carbon-nitrogen ratio of 1.0 - 8.5. Specifically, the low-carbon-nitrogen ratio wastewater in this experimental example is domestic sewage. The method of applying the slow-release carbon source to the treatment process of low-carbon-nitrogen ratio wastewater includes: adding the slow-release carbon source at a ratio of 200 mg / L in the denitrifying biological filter of the low-carbon-nitrogen ratio wastewater, controlling the water temperature at 25 °C, the pH value at 7, the residence time at 5 h, controlling the dissolved oxygen in the low-carbon-nitrogen ratio wastewater at 2 mg / L through intermittent aeration, and regularly monitoring the nitrogen concentration in the low-carbon-nitrogen ratio wastewater until the treatment is completed (regular monitoring is carried out once every 24 h).

[0096] Experimental Example 5: The difference between this embodiment and Experimental Example 4 is that the parameters for applying the slow-release carbon source to the treatment process of low-carbon-nitrogen ratio wastewater are different. The slow-release carbon source is added at a ratio of 200 mg / L in the denitrifying biological filter of the low-carbon-nitrogen ratio wastewater, controlling the water temperature at 25 °C, the pH value at 7, the residence time at 6 h, controlling the dissolved oxygen in the low-carbon-nitrogen ratio wastewater at 3 mg / L through intermittent aeration, and regularly monitoring the nitrogen concentration in the low-carbon-nitrogen ratio wastewater until the treatment is completed.

[0097] Experimental Example 6: The difference between this embodiment and Experimental Example 4 is that the parameters for applying the slow-release carbon source to the treatment process of low-carbon-nitrogen ratio wastewater are different. The slow-release carbon source is added at a ratio of 200 mg / L in the denitrifying biological filter of the low-carbon-nitrogen ratio wastewater, controlling the water temperature at 25 °C, the pH value at 7, the residence time at 4 h, controlling the dissolved oxygen in the low-carbon-nitrogen ratio wastewater at 1 mg / L through intermittent aeration, and regularly monitoring the nitrogen concentration in the low-carbon-nitrogen ratio wastewater until the treatment is completed.

[0098] Experimental Example 7: The difference between this embodiment and Experimental Example 4 is that the low-carbon-nitrogen ratio wastewater in this experimental example is industrial wastewater.

[0099] Experimental Example 8: The difference between this embodiment and Experimental Example 4 is that the low-carbon-nitrogen ratio wastewater in this experimental example is agricultural polluted water.

[0100] The slow-release carbon source obtained in Example 1 was treated according to Experimental Example 4, Experimental Example 5, and Experimental Example 6 for 10 days to obtain the degradation rate of total nitrogen in the wastewater;

[0101] Comparative Example 1: The slow-release carbon source obtained by the method with the patent publication number CN115594300B was treated according to Experimental Example 4 for 10 days to obtain the degradation rate of total nitrogen in the wastewater;

[0102] Comparative Example 2: Different from Example 1, the steps of enzymatic treatment and acid-base treatment of straw were not carried out. After direct crushing, the slow-release carbon source prepared in Example 1 was used for Treatment 10d in Experimental Example 4 to obtain the degradation rate of total nitrogen in the wastewater;

[0103] Comparative Example 3: Different from Example 1, the form of polybutylene succinate was granular with a particle size of 1-3 mm. The obtained slow-release carbon source was used for Treatment 10d in Experimental Example 4 to obtain the degradation rate of total nitrogen in the wastewater;

[0104] Comparative Example 4: Different from Example 1, the soaking step in S3 was not carried out, and it was directly washed and then used; the obtained slow-release carbon source was used for Treatment 10d in Experimental Example 4 to obtain the degradation rate of total nitrogen in the wastewater;

[0105] The total nitrogen degradation rate results of the above Example 1 and Comparative Examples 1-4 were compared, as shown in Table 1;

[0106] Table 1 Experimental results of total nitrogen degradation rate after wastewater treatment under different treatment methods

[0107]

[0108]

[0109] As can be seen from Table 1, by comparing Example 1 with Comparative Example 1, it can be seen that the degradation rate of total nitrogen in the wastewater after treatment in Example 1 using the method in Experimental Example 4 is relatively high. This may be because the structural framework of the slow-release carbon source in Example 1 is more optimized, and the effect of continuously supplying the carbon source is better. In Example 1, the carbon source is slowly released to maintain the microbial activity, improve its growth environment, and promote the formation of biofilm, thereby stably and efficiently promoting the denitrification process and achieving wastewater denitrification.

[0110] By comparing Example 1 with Comparative Example 2, it can be seen that compared with the untreated straw in Comparative Example 2, the slow-release carbon source obtained after enzymatic treatment of straw in Example 1 has a better treatment effect on wastewater. This may be because enzymatic treatment can effectively destroy the lignin and cellulose structures in straw, increase its hydrophilicity and reactivity, improve its binding ability with PBS and PVA-SA, and optimize its structure, especially in the treatment of low carbon-nitrogen ratio wastewater.

[0111] By comparing Example 1 with Comparative Example 3, it can be found that the form of polybutylene succinate in Example 1 is more optimized. This may be because powdered PBS is more easily mixed with other materials, improving the processing performance and application performance of the materials, and expanding its application scope in the fields of wastewater treatment and others.

[0112] Comparing Example 1 with Comparative Example 4, it can be seen that the soaking step in Example 1 can enhance the crosslinking degree of the material, making it have a better sustained-release effect; it can improve the sustained-release performance of the material and enhance its mechanical strength and stability. Comparing Experimental Example 4, Experimental Example 5 and Experimental Example 6, it can be seen that the wastewater treatment parameters of Experimental Example 4 are relatively preferable.

Claims

1. A method for preparing a slow-release carbon source, characterized in that, It includes the following steps: S1. Take waste straw material, polybutylene succinate, polyvinyl alcohol, sodium alginate, and deionized water for standby according to the ratio of 8 - 12 g: 0.1 - 4 g: 8 g: 1 g: 100 ml; wherein, the waste straw material is one of wheat straw, reed straw, corn straw, sesame straw, and soybean straw; S2. First, mix the waste straw material with the polybutylene succinate to obtain a mixed solid; wherein, the polybutylene succinate is in powder form; then mix the polyvinyl alcohol, sodium alginate, and deionized water, and heat and stir at a temperature of 95 - 100 °C for 60 - 120 min, and then cool to obtain a mixed solution; S3. Add the mixed solid to the mixed solution and mix evenly, then inject it into a mold and freeze at a temperature of -18 - -16 °C for 11 - 14 h, demold, soak, and wash after freezing, and then dry at 60 - 70 °C to obtain a slow-release carbon source.

2. The method according to claim 1, characterized in that, The waste straw material in S1 is wheat straw after acid soaking treatment, and the acid soaking treatment is: soak the wheat straw with a 2% sulfuric acid solution by mass, heat it in a water bath at 100 °C for 15 - 25 min, and then dry it completely at a temperature of 60 - 70 °C.

3. The method according to claim 1, wherein The waste straw material in S1 is wheat straw after alkali soaking treatment, and the alkali soaking treatment is: soak the wheat straw with a 2% sodium hydroxide solution by mass, heat it in a water bath at 100 °C for 15 - 25 min, and then dry it completely at a temperature of 60 - 70 °C.

4. The method according to claim 1, wherein The stirring speed of the heating and stirring in S2 is 100 - 120 rpm.

5. The method according to claim 1, characterized in that, The preparation method of the powdered polybutylene succinate in S2 includes: according to the ratio of 4 - 8 g: 200 ml, first place the granular polybutylene succinate in N,N-dimethylacetamide liquid, dissolve it at a temperature of 70 - 80 °C for 1 h, after the solution cools, perform suction filtration to obtain a solid, and then grind it.

6. The method according to claim 1, characterized in that, The method of mixing the waste straw material with the polybutylene succinate in S2 to obtain a mixed solid is: mix the waste straw material with the powdered polybutylene succinate evenly in a high-speed mixer for 10 - 15 min to obtain a mixture, then add the mixture to deionized water according to the ratio of 2 g: 1 - 2 ml, and perform spray drying through a spray drying tower, control the droplet size to be 50 - 100 microns, and spray dry until the deionized water evaporates completely to obtain a mixed solid.

7. The method according to claim 1, wherein The solution for soaking in S3 is a crosslinking agent boric acid - calcium chloride solution, and the crosslinking agent boric acid - calcium chloride solution is an aqueous solution with a mass fraction of 4% for both CaCl2 and H3BO4, and the soaking time is 20 - 26 h.

8. Application of the slow-release carbon source prepared by the method according to any one of claims 1 - 7 in treating low carbon-nitrogen ratio wastewater.

9. The application according to claim 8, wherein The low carbon-nitrogen ratio wastewater includes domestic sewage, industrial wastewater, and agricultural polluted water, and the carbon-nitrogen ratio of the low carbon-nitrogen ratio wastewater is 1.0 - 8.5; The method of applying the slow-release carbon source to treat wastewater with a low carbon-nitrogen ratio is as follows: Add the slow-release carbon source at a ratio of 200 mg / L in the denitrifying biological filter for wastewater with a low carbon-nitrogen ratio, control the water temperature at 20 - 30 °C, the pH value at 7 - 8, the hydraulic retention time at 4 - 6 h, control the dissolved oxygen in the wastewater with a low carbon-nitrogen ratio at 1 - 3 mg / L by intermittent aeration, and regularly monitor the nitrogen concentration in the wastewater with a low carbon-nitrogen ratio until the treatment is completed.

Images