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

Abstract

The application discloses a preparation method of slow-release carbon source and application of the slow-release carbon source in treatment of low carbon-nitrogen ratio wastewater, and the preparation method comprises the following steps: S1, taking abandoned straw material, polybutylene succinate, polyvinyl alcohol, sodium alginate and deionized water for standby; S2, mixing the abandoned straw material with the polybutylene succinate to obtain a mixed solid; mixing the polyvinyl alcohol, the sodium alginate and the deionized water to obtain a mixed solution; S3, uniformly mixing the mixed solid into the mixed solution, then pouring into a mold for freezing treatment, demolding, soaking, cleaning and drying to obtain the slow-release carbon source; the slow-release carbon source prepared by the application can slowly release carbon source, and is helpful to promoting the denitrification process in the wastewater treatment process, and is used for improving the wastewater treatment efficiency and is an environmental protection technology.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method for preparing a slow-release carbon source and its application in treating wastewater with a low carbon-to-nitrogen ratio. Background Technology

[0002] With global population growth and the continuous development of agricultural production, the output of agricultural waste is increasing year by year. This waste, including straw, fruit shells, and roots, can cause environmental pollution and resource waste if 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. Transforming agricultural waste into a slow-release carbon source provides new impetus for sustainable agricultural development.

[0003] Agricultural waste is a general term for organic matter generated and discarded during the harvesting, production, and processing of agricultural crops. my country is a major agricultural country, but it is also the world's largest producer of agricultural waste. In recent years, with the continuous growth of the population, the demand for crops has increased significantly, resulting in incalculable amounts of waste generated from agricultural production. However, because most farmers dispose of agricultural waste haphazardly in their production and daily lives, burning or discarding the vast majority of it on-site, serious resource waste has resulted in a very low overall resource utilization rate for agricultural waste in my country. This has not only become a key issue for rural environmental protection but also poses a significant threat to my country's environmental pollution. How to effectively utilize agricultural waste and reduce pollution and ecological damage within the context of sustainable development has become a crucial issue for my country's development.

[0004] In the treatment of low C / N ratio wastewater, the amount of carbon source becomes the main limiting factor affecting total nitrogen removal efficiency. Adding an external carbon source is a common method to improve total nitrogen removal efficiency. Carbon-releasing materials include natural carbon-releasing materials (straw, rice husks, sawdust, etc.) and biodegradable polymers (polylactic acid, polyvinyl alcohol, polybutylene succinate, etc.). While natural carbon-releasing materials are inexpensive, their denitrification effect is poor, and their denitrification load is low. Using polymers as carbon sources can achieve a more ideal denitrification effect, but their cost is relatively high. Mixing the two in a certain proportion to create a synthetic carbon source can solve the problems of price and denitrification effect. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing a slow-release carbon source and its application in treating wastewater with a low carbon-to-nitrogen ratio.

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

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

[0008] S2. First, the waste straw material is mixed with the polybutylene succinate to obtain a mixed solid; wherein the polybutylene succinate is in powder form; then, polyvinyl alcohol, sodium alginate and deionized water are mixed and heated and stirred at a temperature of 95-100°C for 60-120 minutes, and then cooled to obtain a mixed liquid.

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

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

[0011] Furthermore, in some implementations, the waste straw material is wheat straw that has undergone acid soaking treatment. The acid soaking treatment is as follows: soaking the wheat straw in a 2% sulfuric acid solution, heating it in a water bath at 100°C for 15-25 minutes, and then drying it completely at a temperature of 60-70°C.

[0012] In some implementations, the waste straw material is wheat straw that has undergone alkali soaking treatment. The alkali soaking treatment is as follows: soaking with 2% NaOH by mass, heating in a water bath at 100°C for 15-25 minutes, and then drying completely at a temperature of 60-70°C.

[0013] Note: The above-mentioned acid or alkali soaking treatment of wheat straw can effectively remove lignin and hemicellulose from 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] Furthermore, in some other implementations, the waste straw material in S1 is obtained through enzymatic treatment, the enzymatic treatment method including:

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

[0016] S1-2. Then, add 1-2% of a mixed enzyme preparation by mass of the straw particles to the straw particles. The mixed enzyme preparation includes ligninase and cellulase in equal amounts of active units.

[0017] S1-3, The reaction is then carried out in a constant temperature shaker at a temperature of 45-55℃ for 20-24 hours and a shaking speed of 150-200 rpm.

[0018] S1-4. Obtain solid residue by centrifugation or filtration, wash the solid residue until neutral, and then dry it at 60-80°C to constant weight to obtain waste straw material.

[0019] Explanation: Enzymatic treatment effectively disrupts the lignin and cellulose structures in straw, increasing its hydrophilicity and reactivity. This enhances its binding capacity with PBS and PVA-SA, facilitating the formation of a slow-release carbon source with waste crop residues as the core, polyvinyl alcohol-sodium alginate as the framework, and polybutylene succinate as a supplementary carbon source. This optimizes the structure of the carbon source, making it particularly effective in treating wastewater with a low carbon-to-nitrogen ratio.

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

[0021] Note: The stirring speed mentioned above is preferred. Exceeding this range may result in uneven structure morphology and unreasonable distribution.

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

[0023] Note: Compared to other mold shapes, block-shaped mold blocks have advantages such as simple operation, easy process control, stable structure, and long service life. They can release carbon sources slowly and stably over a long period of time, enhance the denitrification process, meet the carbon source requirements of microorganisms, enhance the denitrification process, help improve the utilization rate of carbon sources, and promote the wastewater treatment effect.

[0024] Furthermore, the preparation method of the powdered polybutylene succinate described in S2 includes: placing the granular polybutylene succinate in N,N-dimethylacetamide liquid at a ratio of 4-8g:200ml, dissolving it at a temperature of 70-80℃ for 1 hour, and after the solution is cooled, filtering to obtain a solid, and then grinding it.

[0025] Note: The above method can prepare powdered polybutylene succinate (PBS). Powdered PBS is easier to mix with other materials, which improves the processing and application performance of the material and expands its application range in wastewater treatment and other fields.

[0026] Further, the method described in S2 for mixing the waste straw with the polybutylene succinate to obtain a mixed solid is as follows: the waste straw and powdered polybutylene succinate are mixed evenly in a high-speed mixer for 10-15 minutes to obtain a mixture. Then, the mixture is added to deionized water at a ratio of 2g:1-2ml, and spray-dried in a spray drying tower with the droplet size controlled at 50-100 micrometers until the deionized water is completely evaporated to obtain a mixed solid.

[0027] Description: By thoroughly mixing waste straw with powdered polybutylene succinate in a high-speed mixer and then using spray drying technology to prepare a mixed solid, the method has the advantages of uniform mixing, high production efficiency, and good product quality. During the spray drying process, precise control of droplet size helps to obtain materials with uniform particle size and stable performance, which meets the requirements of slow-release carbon source for release rate and stability. This provides efficient and reliable carbon source material for wastewater treatment and also helps to form the subsequent slow-release carbon source structure.

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

[0029] Note: Soaking in the above solution enhances the cross-linking degree of the material, giving it a better sustained-release effect; it can improve the sustained-release performance of the material and enhance its mechanical strength and stability.

[0030] This invention provides an application of the slow-release carbon source prepared by the above method in the treatment of wastewater with a low carbon-to-nitrogen ratio.

[0031] Note: The slow-release carbon source obtained by this invention has significant advantages in the treatment of wastewater with low carbon-to-nitrogen ratio, and can effectively improve wastewater treatment efficiency, reduce operating costs, and improve water quality.

[0032] Further, the low C / N ratio wastewater includes domestic sewage, industrial wastewater, and agricultural pollutant, and the C / N ratio of the low C / N ratio wastewater is 1.0 to 8.5. The method of applying the slow-release carbon source to treat the low C / N ratio wastewater is as follows: a slow-release carbon source is added at a ratio of 200 mg / L to the denitrification biological filter of the low C / N ratio wastewater, and the water temperature is controlled at 20 to 30°C, the pH value is controlled at 7 to 8, the hydraulic retention time is controlled at 4 to 6 hours, the dissolved oxygen in the low C / N ratio wastewater is controlled at 1 to 3 mg / L by intermittent aeration, and the nitrogen concentration in the low C / N ratio wastewater is monitored regularly until the treatment is completed.

[0033] Note: The above application method constructs the optimal active environment for denitrifying bacteria, significantly improving nitrogen removal efficiency; the continuous and stable carbon supply characteristics of the slow-release carbon source avoid the instantaneous release problem of traditional carbon sources, reducing carbon source waste and preventing secondary pollution; combined with intermittent aeration and regular monitoring, dynamic control of the treatment process is achieved, ensuring that the total nitrogen in the effluent consistently meets the standards, and is suitable for the large-scale treatment needs of high-load, low C / N ratio (i.e., carbon-nitrogen ratio range of 1.0 to 8.5) wastewater.

[0034] The beneficial effects of this invention are:

[0035] This invention utilizes agricultural waste straw, combined with biodegradable polymers such as polybutylene succinate and polyvinyl alcohol, to prepare a slow-release carbon source for treating wastewater with a low carbon-to-nitrogen ratio. Compared to carbon sources made solely from waste straw, this method solves problems such as difficulty in controlling the dosage or excessive initial release. The carbon source exhibits a large and stable carbon release capacity and good performance. Furthermore, the carbon source blocks provide a favorable living space for microorganisms, promoting denitrification and improving nitrogen removal efficiency. It achieves resource utilization of agricultural waste and offers advantages such as low cost, stable carbon source release, and ease of use. Compared to other existing slow-release carbon sources, it helps improve nitrogen removal efficiency in wastewater treatment. The preparation method of this invention is simple and efficient, the slow-release carbon source has stable performance, and it is less expensive than synthetic polymer carbon sources. Moreover, it improves the utilization rate of waste agricultural products, making it more energy-efficient and environmentally friendly. Attached Figure Description

[0036] Figure 1 It is the waste agricultural product after being crushed in Embodiment 1 of the present invention;

[0037] Figure 2 It is PBS, the polymer material of Example 1 of this invention;

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

[0039] Figure 4 It is a uniformly mixed synthetic slow-release carbon source of the present invention, as described in Example 1 of this invention;

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

[0041] Figure 6 This is the slow-release carbon source synthesized in Example 1 of the present invention;

[0042] Figure 7 This is a graph showing the COD release of five different straw carbon sources according to embodiments of the present invention;

[0043] Figure 8 These are the COD release amounts of the three pretreated straw carbon sources in the embodiments of the present invention;

[0044] Figure 9 The COD release amounts of two different carbon source carbon sources with varying synthesis ratios in embodiments of the present invention are shown. Detailed Implementation

[0045] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

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

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

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

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

[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 ligninase and cellulase, and the number of active units of the ligninase and cellulase are equal.

[0051] S1-3, The reaction was then carried out in a constant temperature shaker at a temperature of 50°C for 22 hours and a shaking speed of 180 rpm.

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

[0053] S2. First, the waste straw material is mixed with the polybutylene succinate to obtain a mixed solid; wherein the polybutylene succinate is in powder form; then, polyvinyl alcohol, sodium alginate and deionized water are mixed and heated and stirred at 98°C for 90 minutes, and then cooled to obtain a mixed liquid; the stirring speed of heating and stirring in S2 is 110 rpm.

[0054] The preparation method of the powdered polybutylene succinate described in S2 includes: placing the granular polybutylene succinate in N,N-dimethylacetamide liquid at a ratio of 6g:200ml and dissolving it at 75℃ for 1h. After the solution is cooled, it is filtered to obtain a solid, which is then ground until the particle size of the polybutylene succinate is 10-200μm.

[0055] The method described in S2 for mixing the waste straw with the polybutylene succinate to obtain a mixed solid is as follows: the waste straw and powdered polybutylene succinate are mixed evenly in a high-speed mixer for 13 minutes to obtain a mixture. Then, the mixture is added to deionized water at a ratio of 2g:1.5ml and spray-dried in a spray drying tower with the droplet size controlled at 50-100 micrometers until the deionized water is completely evaporated to obtain a mixed solid.

[0056] like Figure 5 , Figure 6 As shown, in step S3, the mixed solid is added to the mixed liquid and mixed evenly, then poured into a mold and frozen at -17°C for 12 hours. After freezing, the mixture is demolded, soaked, and washed, and then dried at 65°C to obtain a slow-release carbon source. The mold is a block mold. The soaking solution is a crosslinking agent boric acid-calcium chloride solution, which is an aqueous solution containing 4% CaCl2 and 4% H3BO4 by mass, and the soaking time is 24 hours.

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

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

[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: This example differs from Example 1 in that the enzyme treatment parameters are different in S1.

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

[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, The reaction was then carried out in a constant temperature shaker at a temperature of 45°C for 24 hours and a shaking speed of 150 rpm.

[0067] S1-4. Obtain solid residue by centrifugation or filtration, wash the solid residue until neutral, and then dry it at 60°C to constant weight to obtain waste straw material.

[0068] Example 9: This example differs from Example 1 in that the enzyme treatment parameters are different in S1.

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

[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, The reaction was then carried out in a constant temperature shaker at a temperature of 55°C for 20 hours and a shaking speed of 200 rpm.

[0072] S1-4. Obtain solid residue by centrifugation or filtration, wash the solid residue until neutral, and then dry it at 80°C to constant weight to obtain waste straw material.

[0073] Example 10: This example differs from Example 1 in that the heating parameters in S2 are different. The mixture is heated and stirred at 95°C for 60 minutes, and then cooled to obtain a mixture. The stirring speed of the heating and stirring is 120 rpm.

[0074] Example 11: This example differs from Example 1 in that the heating parameters in S2 are different. The mixture is heated and stirred for 120 minutes at a temperature of 100°C and then cooled to obtain a mixture. The stirring speed of the heating and stirring is 100 rpm.

[0075] Example 12: This example differs from Example 1 in that the preparation parameters of the powdered polybutylene succinate are different. According to the ratio of 8g:200ml, the granular polybutylene succinate is first placed in N,N-dimethylacetamide liquid and dissolved at 70°C for 1 hour. After the solution is cooled, it is filtered to obtain a solid, which is then ground.

[0076] Example 13: The difference between this example and Example 1 is that the preparation parameters of the powdered polybutylene succinate are different. According to the ratio of 4g:200ml, the granular polybutylene succinate is first placed in N,N-dimethylacetamide liquid and dissolved at 80°C for 1 hour. After the solution is cooled, it is filtered to obtain a solid, which is then ground.

[0077] Example 14: This example differs from Example 1 in that the freezing parameters are different; the freezing temperature is -18°C for 11 hours.

[0078] Example 15: This example differs from Example 1 in that the freezing parameters are different; the freezing temperature is -16°C for 14 hours.

[0079] Example 16: This example differs from Example 1 in that the drying temperature in S3 is different; it is dried at 60°C.

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

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

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

[0083] Example 20: The difference between this example and Example 1 is that the waste straw material is wheat straw that has been treated with acid soaking. The acid soaking treatment is as follows: the wheat straw is soaked in a 2% sulfuric acid solution, heated in a water bath at 100°C for 20 minutes, and then dried completely at 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 in a 2% sulfuric acid solution, heated in a water bath at 100°C for 15 minutes, 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 in a 2% sulfuric acid solution, heated in a water bath at 100°C for 25 minutes, 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 that has been treated with alkali. The alkali soaking treatment is as follows: soaking with 2% NaOH by mass, heating in a water bath at 100°C for 20 minutes, and then drying completely at 65°C.

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

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

[0089] I. To investigate the slow-release effect and stability of slow-release carbon sources obtained by using different straw as raw materials, acid and alkali treatment, waste agricultural crops and high molecular weight carbon sources in different synthesis ratios;

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

[0091] The experimental procedure was as follows: Three pieces of each of the five types of slow-release carbon sources from straw were taken and weighed. The weights were 5.0301g, 5.2688g, 5.3g, 4.4213g, and 4.2728g, respectively. Each piece was placed in one of five 250ml beakers, and 200ml of ultrapure water was added. Water was collected daily, and the COD released by the materials was measured. The water was completely replaced after each collection. The experimental period was set at 25 days. For specific carbon release amounts, see [link to relevant documentation]. Figure 7 ;Depend on Figure 7It can be seen that the first three days are the rapid release period, and days 4-25 are the stable release period. Wheat straw has the highest cumulative COD release, followed by reed straw and corn straw, while sesame straw and soybean straw have the lowest release. Therefore, wheat straw, reed straw, and corn straw, which have the highest release rates, were selected for the next experimental investigation, namely, to explore the effect of acid-base pretreatment on the material's performance.

[0092] Experiment Example 2: To investigate the effect of acid-alkali soaking on the carbon release of straw, three types of straw with good carbon release performance from Experiment Example 1—wheat straw, reed straw, and corn straw—were selected as raw materials and subjected them to acid-alkali pretreatment. Slow-release carbon sources were then synthesized from the pretreated straws, and static carbon release experiments were conducted. The experimental procedure was as follows: Three pieces of each of the six slow-release carbon sources (wheat, reed, and corn straw) after acid-alkali treatment were taken and weighed. The weights were 6.8122g, 5.3474g, 5.2201g, 8.1604g, 6.4911g, and 7.6494g, respectively. These were placed in six 250ml beakers, and 200ml of ultrapure water was added. Water was collected daily, and the COD released by the materials was measured. The water was completely replaced after each collection. The experimental period was set at 25 days. Specific carbon release amounts are detailed in [link to relevant documentation]. Figure 8 .Depend on Figure 8 It can be concluded that, in terms of COD release, alkali treatment of wheat straw and corn straw is more effective than acid treatment; the total COD release of reed straw after acid treatment is slightly higher than that after alkali treatment, but alkali treatment is more slow-release. After 25 days of static carbon release, the composite carbon source of wheat straw treated with alkali exhibits a loose material structure, which is not conducive to use. Therefore, alkali-treated reed straw and corn straw will be selected for further experimental research, namely, to investigate the ratio of waste agricultural products to polymeric carbon sources.

[0093] Experiment Example 3: To investigate the synthesis ratio of waste agricultural crops and polymeric carbon sources, two types of straw with good carbon release effects from Experiment Example 2, namely reed straw and corn straw treated with alkali, were used. Three ratios were set for synthesizing slow-release carbon sources: PVA:SA:straw:PBS ratios of 8:1:8:4, 8:1:10:2, and 8:1:12:0.1. The experimental procedure was as follows: Three pieces of each slow-release carbon source were taken and weighed, with weights of 6.926g, 7.2136g, 5.0765g, 5.869g, 5.2585g, and 5.0996g, respectively. They were placed in six 250ml beakers, and 200ml of ultrapure water was added. Water was collected daily, and the COD released by the materials was measured. The water was completely replaced after each collection. The experimental period was set at 25 days. For specific carbon release amounts, see [link to relevant documentation]. Figure 9 .Depend on Figure 9 It can be seen that, regardless of the type of composite slow-release carbon source, the higher the proportion of natural materials added, the higher the COD release of the corresponding carbon source.

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

[0095] Example 4: Applying a slow-release carbon source to the treatment of low C / N ratio wastewater. The low C / N ratio wastewater includes domestic sewage, industrial wastewater, and agricultural pollutant with a C / N ratio of 1.0 to 8.5. Specifically, in this example, the low C / N ratio wastewater is domestic sewage. The method for applying a slow-release carbon source to the treatment of low C / N ratio wastewater includes: adding a slow-release carbon source at a ratio of 200 mg / L to the denitrification biological filter of the low C / N ratio wastewater, controlling the water temperature at 25℃, the pH value at 7, and the retention time at 5 h, controlling the dissolved oxygen in the low C / N ratio wastewater at 2 mg / L through intermittent aeration, and periodically monitoring the nitrogen concentration in the low C / N ratio wastewater until the treatment is completed (periodic monitoring is every 24 hours).

[0096] Example 5: This example differs from Example 4 in that the parameters for applying the slow-release carbon source to the treatment process of low C / N ratio wastewater are different. In the denitrification biological filter of low C / N ratio wastewater, the slow-release carbon source is added at a ratio of 200 mg / L, and the water temperature is controlled at 25℃, the pH value at 7, and the retention time at 6h. The dissolved oxygen in the low C / N ratio wastewater is controlled at 3 mg / L through intermittent aeration, and the nitrogen concentration in the low C / N ratio wastewater is monitored regularly until the treatment is completed.

[0097] Example 6: This example differs from Example 4 in that the parameters for applying the slow-release carbon source to the treatment process of low C / N ratio wastewater are different. In the denitrification biological filter of low C / N ratio wastewater, the slow-release carbon source is added at a ratio of 200 mg / L, and the water temperature is controlled at 25℃, the pH value at 7, and the retention time at 4h. The dissolved oxygen in the low C / N ratio wastewater is controlled at 1 mg / L through intermittent aeration, and the nitrogen concentration in the low C / N ratio wastewater is monitored regularly until the treatment is completed.

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

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

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

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

[0102] Comparative Example 2: Unlike Example 1, the straw was not subjected to enzyme treatment or acid / alkali treatment. Instead, it was directly crushed and treated with the slow-release carbon source prepared in Example 1 for 10 days to obtain the degradation rate of total nitrogen in the wastewater.

[0103] Comparative Example 3: The difference from Example 1 is that the polybutylene succinate is in the form of particles with a particle size of 1-3 mm. The obtained slow-release carbon source was treated with the experimental example 4 for 10 days to obtain the degradation rate of total nitrogen in the wastewater.

[0104] Comparative Example 4: Unlike Example 1, the soaking step in S3 was not performed; the sample was directly washed and used. The obtained slow-release carbon source was used to treat Example 4 for 10 days to obtain the degradation rate of total nitrogen in the wastewater.

[0105] The total nitrogen degradation rate results of Example 1 and Comparative Examples 1 to 4 above 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, comparing Example 1 and Comparative Example 1, it can be seen that the total nitrogen degradation rate in the wastewater treated by the method of Experimental Example 4 in Example 1 is higher. 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 carbon source is better. In Example 1, the slow release of carbon source maintains the activity of microorganisms, improves their growth environment, and promotes biofilm formation, thereby stably and efficiently promoting the denitrification process and realizing the denitrification of wastewater.

[0110] Comparing Example 1 and Comparative Example 2, it can be seen that, compared with the case of no pretreatment of straw in Comparative Example 2, the slow-release carbon source obtained after enzyme treatment of straw in Example 1 has a better treatment effect on wastewater. This may be because enzyme treatment can effectively destroy the lignin and cellulose structure in straw, increase its hydrophilicity and reactivity, thereby improving its binding ability with PBS and PVA-SA and making its structure more optimized, especially for the treatment of wastewater with low carbon-to-nitrogen ratio.

[0111] Comparing Example 1 and Comparative Example 3, it can be found that the morphology of polybutylene succinate in Example 1 is more preferred. This may be because powdered PBS is easier to mix with other materials, which improves the processing performance and application performance of the material and expands its application range in wastewater treatment and other fields.

[0112] Comparing Example 1 and Comparative Example 4, it can be seen that the soaking step in Example 1 can enhance the cross-linking degree of the material, giving it a better sustained-release effect; it can improve the sustained-release performance of the material and enhance its mechanical strength and stability. Comparing Experimental Examples 4, 5, and 6, it can be seen that the wastewater treatment parameters in Experimental Example 4 are more optimized.

Claims

1. A method for preparing a slow-release carbon source, characterized in that, Includes the following steps: S1. Take waste straw, polybutylene succinate, polyvinyl alcohol, sodium alginate, and deionized water in the ratio of 8~12g:0.1~4g:8g:1g:100ml for later use; wherein, the waste straw is one of wheat straw, reed straw, corn straw, sesame straw, and soybean straw. The waste straw material is obtained through enzyme treatment, and the enzyme treatment method includes: S1-1. First, take dry waste straw, crush it, and sieve it to obtain straw microparticles with a particle size of 0.45~1mm. S1-2. Then, add 1-2% of a mixed enzyme preparation by mass of the straw particles to the straw particles. The mixed enzyme preparation includes ligninase and cellulase in equal quantities of active units. S1-3, The reaction is then carried out in a constant temperature shaker at a temperature of 45-55℃ for 20-24 hours and a shaking speed of 150-200 rpm. S1-4. Obtain solid residue by centrifugation or filtration, wash the solid residue until neutral, and then dry it at 60~80℃ to constant weight to obtain waste straw material; S2. First, the waste straw material is mixed with the polybutylene succinate to obtain a mixed solid; wherein the polybutylene succinate is in powder form; then, polyvinyl alcohol, sodium alginate and deionized water are mixed and heated and stirred at a temperature of 95~100℃ for 60~120 minutes, and then cooled to obtain a mixed liquid. The method for mixing the waste straw with the polybutylene succinate to obtain a mixed solid is as follows: the waste straw and powdered polybutylene succinate are mixed evenly in a high-speed mixer for 10-15 minutes to obtain a mixture. Then, the mixture is added to deionized water at a ratio of 2g:1-2ml, and spray-dried in a spray drying tower with the droplet size controlled at 50-100 micrometers until the deionized water is completely evaporated to obtain a mixed solid. S3. Add the mixed solid to the mixed liquid and mix evenly. Then pour it into a mold and freeze it at a temperature of -18~-16℃ for 11~14h. After freezing, demold, soak, and wash, and then dry at 60~70℃ to obtain a slow-release carbon source. The waste straw material mentioned in S1 is wheat straw that has undergone acid soaking treatment. The acid soaking treatment is as follows: soaking the wheat straw in a 2% sulfuric acid solution, heating it in a water bath at 100°C for 15-25 minutes, and then drying it completely at a temperature of 60-70°C. The waste straw material mentioned in S1 is wheat straw that has undergone alkali soaking treatment. The alkali soaking treatment is as follows: the wheat straw is soaked in a 2% sodium hydroxide solution, heated in a water bath at 100°C for 15-25 minutes, and then dried completely at a temperature of 60-70°C.

2. The method as described in claim 1, characterized in that, The stirring speed for heating and stirring in S2 is 100~120 rpm.

3. The method as described in claim 1, characterized in that, The preparation method of the powdered polybutylene succinate described in S2 includes: placing the granular polybutylene succinate in N,N-dimethylacetamide liquid at a ratio of 4~8g:200ml, dissolving it at a temperature of 70~80℃ for 1h, and after the solution is cooled, filtering to obtain the solid, and then grinding it.

4. The method as described in claim 1, characterized in that, The soaking solution described in S3 is a cross-linking agent boric acid-calcium chloride solution, which is an aqueous solution with a mass fraction of 4% for both CaCl2 and H3BO3, and the soaking time is 20~26h.

5. The application of the slow-release carbon source prepared by the method according to any one of claims 1 to 4 in the treatment of wastewater with a low carbon-to-nitrogen ratio.

6. The application as described in claim 5, characterized in that, The low carbon-to-nitrogen ratio wastewater includes domestic sewage, industrial wastewater, and agricultural pollutant water, and the carbon-to-nitrogen ratio of the low carbon-to-nitrogen ratio wastewater is 1.0 to 8.

5. The method for applying the slow-release carbon source to treat low C / N ratio wastewater is as follows: add the slow-release carbon source at a ratio of 200 mg / L to the denitrification biological filter of the low C / N ratio wastewater, control the water temperature at 20~30℃, the pH value at 7~8, and the hydraulic retention time at 4~6h, control the dissolved oxygen in the low C / N ratio wastewater at 1~3 mg / L through intermittent aeration, and regularly monitor the nitrogen concentration in the low C / N ratio wastewater until the treatment is completed.

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