A vinasse-based slow-release material, a preparation method and applications thereof

Abstract

The present application relates to the technical field of groundwater pollution remediation, and in particular to a distiller's grains-based slow-release material, a preparation method and application. The method uses distiller's grains material as a carbon source, chitosan and gelatin as carriers, and prepares the distiller's grains-based slow-release material through emulsification and cross-linking. The method uses natural biomass distiller's grains as a slow-release carbon source, chitosan and gelatin as carrier materials, and synthesizes a new slow-release material with environmental friendliness, low cost, adjustable morphology and slow-release performance through emulsification and cross-linking, to provide a carbon source and an electron donor required by functional microorganisms and enhance the activity of the functional microorganisms. The material has the advantages of low cost and good effect, can effectively implement in-situ remediation of groundwater pollution, and on the premise of realizing economic environmental protection, high efficiency, stability and no secondary pollution, can strengthen the in-situ functional microorganism remediation effect.

Description

Technical Field

[0001] This invention relates to the field of groundwater pollution remediation technology, and more specifically, to a distillers' grains-based slow-release material, its preparation method, and its application. Background Technology

[0002] Halogenated organic compounds are commonly used in chemical production as organic solvents, metal surface cleaners, pesticides, and intermediates in pesticide synthesis. They easily enter groundwater environments, leading to serious groundwater halogenated hydrocarbon pollution. Halogenated hydrocarbons are denser than water and poorly soluble in water, belonging to the heavy non-aqueous phase liquid (DNAPL) category. They have low viscosity, tend to accumulate at the bottom of aquifers, and are difficult to remove. Furthermore, halogenated hydrocarbons are toxic and carcinogenic, posing a serious threat to human health and the ecological environment.

[0003] Currently, in-situ bioremediation is considered a feasible and relatively efficient remediation technology for low- to medium-concentration organohalogenated hydrocarbon pollution. Compared to physical and chemical methods, it has advantages such as low cost, environmental friendliness, and strong sustainability. In-situ bioremediation technology delivers nutrients such as carbon sources and electron donors into the groundwater environment to stimulate the growth and metabolism of organohalogenated respiring bacteria, thereby promoting the dehalogenation reaction of halogenated hydrocarbons. However, in practical applications, this technology suffers from problems such as tailing, rebound, and the need for repeated chemical additions.

[0004] To address these issues, slow-release carbon source materials have emerged as a new development direction. These materials, through slow fermentation, produce volatile fatty acids such as acetic acid and propionic acid, as well as hydrogen gas. This provides carbon sources and electron donors for organohalogenating respiratory bacteria, enabling them to maintain long-term biological activity and achieve the mineralization and degradation of halogenated organic compounds, avoiding the tailing and rebound phenomena present in remediation processes. Furthermore, the elimination of the need for repeated addition of carbon sources and electron donors significantly reduces economic costs.

[0005] Currently, a variety of slow-release carbon source materials have been developed, mainly including emulsified vegetable oil, polycaprolactone, and commercial slow-release carbon sources (EVO, EOS, etc.). However, these materials still have insurmountable drawbacks, such as high cost, uncontrollable material morphology, size and slow-release performance, and complex preparation procedures.

[0006] For example, patent CN 115650449 A provides a composite nutrient material for adsorbing and degrading anthracene and pyrene in groundwater. This composite nutrient material uses wheat straw as a slow-release carbon source and KH2PO4, CaCl2, etc. as nutrient matrices. It can efficiently adsorb anthracene and pyrene in groundwater, while activating degrading bacteria in the groundwater to improve their degradation efficiency, thereby achieving the purpose of efficiently removing anthracene and pyrene from groundwater. However, this technology does not use a carrier material, the slow-release period is short and unstable, and it cannot meet the requirements for the long-term slow-release effect of the agent. At the same time, the active ingredients contain a variety of ionic salts, which can easily affect the groundwater environment and cause secondary pollution and changes to the groundwater environment in practical applications.

[0007] For example, patent CN 118005196 A discloses a slow-release carbon source with straw as its core, which effectively utilizes agricultural waste. The synthesized slow-release carbon source exhibits superior carbon release performance, stable slow-release properties, and low cost, reducing the cost of adding carbon sources in wastewater treatment. The addition of graphene during the preparation process increases the material's impact resistance; simultaneously, the material is encapsulated with acrylic spheres, thereby improving its mechanical strength. However, this technology involves cumbersome synthesis steps, the size of the slow-release material cannot be controlled, and the carrier material content is high and non-degradable. The high carrier material content increases the cost of the slow-release material and weakens the main role of the effective components.

[0008] These drawbacks lead to poor in-situ bioremediation results, high costs, and may even cause secondary pollution, severely restricting the promotion and use of in-situ bioremediation. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a distillers' grains-based slow-release material, its preparation method and application, so as to solve the problems of poor material repair effect, high cost, uncontrollable material morphology, size and slow-release performance and complex preparation process in the prior art.

[0010] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0011] This invention provides a method for preparing a distillery lees-based sustained-release material, which uses distillery lees as a carbon source and chitosan and gelatin as carriers, and prepares the distillery lees-based sustained-release material through emulsification and cross-linking.

[0012] Based on the above technical solution, the present invention can be further improved as follows.

[0013] Furthermore, the mass ratio of the chitosan, the gelatin, and the distiller's grains is 1.5:0.5:2.

[0014] Furthermore, the lees material is lees solid particles, and the particle size of the lees solid particles is 1 to 999 micrometers.

[0015] Furthermore, the following steps are included:

[0016] S1. The pretreated lees are ball-milled to obtain the lees solid particles;

[0017] S2. An aqueous solution is prepared using the aforementioned solid particles of distiller's grains, chitosan, and gelatin, and an oil-phase solution is prepared using Span80 and soybean oil.

[0018] S3. The aqueous phase solution is added dropwise to the oil phase solution for emulsification to obtain an emulsion solution. A crosslinking agent is then added to the emulsion solution for crosslinking to obtain a mixed solution.

[0019] S4. Perform solid-phase washing and centrifugation on the mixed solution. After the solid and liquid phases in the mixed solution are separated, obtain the solid phase, and dry it to obtain the distillers grains-based slow-release material.

[0020] Further, in step S2, the aqueous solution is prepared by mixing the chitosan, the gelatin, and the solid particles of distiller's grains in an aqueous acetic acid solution, mixing and stirring at 38°C to 42°C to obtain the aqueous solution.

[0021] Furthermore, the volume percentage of acetic acid in the acetic acid aqueous solution is 2%.

[0022] Furthermore, in step S2, the preparation process of the oil phase solution is as follows: the span80 is dispersed in soybean oil and stirred at 38℃~42℃ to obtain the oil phase solution.

[0023] Furthermore, the mass percentage of Span80 in the oil phase solution is 6 wt.%.

[0024] Further, in step S3, the volume ratio of the aqueous phase solution to the oil phase solution is 1:3.5 to 4.5; after emulsification, the mixture is stirred at 38°C to 42°C to obtain the emulsion solution.

[0025] Furthermore, in step S3, the crosslinking agent is a glutaraldehyde solution, wherein the volume percentage of glutaraldehyde in the glutaraldehyde solution is 45% to 55%; and the crosslinking temperature is 38°C to 42°C.

[0026] The present invention also provides a distillers' grains-based slow-release material, which is prepared by the method described above.

[0027] Such as the application of distillers grains-based slow-release materials in in-situ bioremediation methods for groundwater.

[0028] The present invention also provides a method for in-situ bioremediation of groundwater, which uses the distillers grains-based slow-release material described above for in-situ bioremediation of groundwater.

[0029] Furthermore, the groundwater contains halogenated organic compounds.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) The preparation method of the distillers' grains-based sustained-release material of the present invention uses natural biomass distillers' grains as a sustained-release carbon source, and chitosan and gelatin as carrier materials. The new sustained-release material with environmental friendliness, low cost and controllable morphology and sustained-release performance is synthesized by emulsification crosslinking method, which provides carbon source and electron donor required by functional microorganisms and enhances the activity of functional microorganisms.

[0032] (2) The preparation method of the distillers' grains-based slow-release material of the present invention has the advantages of simple preparation process, high efficiency and low cost;

[0033] (3) The slow-release material based on lees of the present invention uses lees as a fermentation substrate, which can provide carbon source and electron donor for microorganisms, enhance the microbial reduction and dehalogenation performance, and lees is agricultural waste, which is low in cost, easy to obtain, and environmentally friendly, and can realize the secondary utilization of agricultural waste.

[0034] (4) In the distillers' grains-based slow-release material of the present invention, chitosan and gelatin are used as carrier materials, and due to their charge characteristics, electrostatic cross-linking can be achieved;

[0035] (5) The groundwater in-situ bioremediation method of the present invention uses the distillers grains-based slow-release material of the present invention to effectively remediate groundwater pollution in situ. Under the premise of achieving economic and environmental protection, high efficiency and stability and without causing secondary pollution, the in-situ functional microbial remediation effect is enhanced. Attached Figure Description

[0036] Figure 1 This is a schematic flowchart of the preparation method of the distillers' grains-based sustained-release material of the present invention;

[0037] Figure 2 In the preparation method of the distillers' grains-based slow-release material of the present invention, in Example 1, the cumulative TOC of different biomass was measured. Figure 2 In the middle, 'a' represents a corn cob. Figure 2 In the middle, b represents straw. Figure 2 In the middle, 'c' represents distiller's grains;

[0038] Figure 3 The preparation method of the distillers' grains-based slow-release material of the present invention is illustrated in Example 1, which shows the acid production diagram of different biomass fermentation processes. Figure 3 In the middle, 'a' represents a corn cob. Figure 3 In the middle, b represents straw. Figure 3 In the middle, 'c' represents distiller's grains;

[0039] Figure 4 In Example 2, the preparation method of the distillers' grains-based slow-release material of the present invention is shown in the figure of acid production during short-term fermentation of distillers' grains after different treatments. Figure 4In the middle, 'a' represents distiller's grains. Figure 4 In the middle, b is distiller's grains - 1% NaOH. Figure 4 c represents distiller's grains - 3% NaOH. Figure 4 In the middle, d represents distiller's grains - 5% NaOH;

[0040] Figure 5 In Example 2, the distillers' grains underwent long-term fermentation and acid production, as described in the preparation method of the slow-release material based on lees of the present invention. Figure 5 In the middle, 'a' represents distiller's grains. Figure 5 In the middle, b is distiller's grains - 1% NaOH. Figure 5 c represents distiller's grains - 3% NaOH. Figure 5 In the middle, d represents distiller's grains - 5% NaOH;

[0041] Figure 6 In Example 3, for the preparation method of the distillers' grains-based sustained-release material of the present invention, morphology images of CS-GL@DG prepared with different mass ratios of chitosan, gelatin, and distillers' grains are shown below: Figure 6 The mass ratio of a in the mixture is 1.5:0.5:1. Figure 6 The mass ratio of b in the mixture is 1.5:0.5:2. Figure 6 The mass ratio of c in the mixture is 1.5:0.5:3. Figure 6 The mass ratio of d in the middle is 1.5:0.5:4;

[0042] Figure 7 In Example 3, for the preparation method of the distillers' grains-based sustained-release material of the present invention, morphology images of CS-GL@DG prepared using different crosslinking times are shown below: Figure 7 The crosslinking time of α is 1 hour. Figure 7 The crosslinking time of b is 2 hours. Figure 7 The cross-linking time of c is 3 hours. Figure 7 The crosslinking time of d is 4 hours;

[0043] Figure 8 In Example 4, a bar graph showing the acid production of the distillers' grains-based slow-release material during fermentation is provided as part of the preparation method of the distillers' grains-based slow-release material of the present invention.

[0044] Figure 9 This is a schematic diagram illustrating the release mechanism of the distillers' grains-based sustained-release material CS-GL@DG during use. Figure 9 Figure 'a' is a schematic diagram of the microstructure of the first-stage sustained-release material. Figure 9 Figure b is a schematic diagram of the microstructure of the sustained-release material in the second stage. Figure 9 The diagram in C is a schematic diagram of the microstructure of the sustained-release material in the third stage. Detailed Implementation

[0045] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0046] The method for preparing the distillers' lees-based sustained-release material of the present invention uses distillers' lees as a carbon source and chitosan and gelatin as carriers to prepare the distillers' lees-based sustained-release material through emulsification and cross-linking.

[0047] The present invention discloses a method for preparing a distillers' grains-based slow-release material. Distillers' grains serve as a fermentation substrate, providing carbon and electron donors for microorganisms, enhancing their reductive dehalogenation performance. Furthermore, distillers' grains are agricultural waste, making them low-cost, readily available, and environmentally friendly, enabling the secondary utilization of agricultural waste. Chitosan and gelatin are used as carrier materials; due to their charge properties, electrostatic cross-linking is achieved. Simultaneously, glutaraldehyde, a cross-linking agent, is introduced to initiate an amine-aldehyde condensation reaction. The morphology and slow-release properties of the material are controlled by adjusting the proportions of chitosan and gelatin and the cross-linking time, thereby extending the release period.

[0048] Specifically, the distiller's grains (DG) of this invention are the residues left after brewing rice, wheat, sorghum, etc. As an agricultural waste, they are widely available and inexpensive. Distiller's grains are rich in crude fiber, alcohols, and starch, and are easily degraded and utilized by microorganisms. Fermentation produces volatile fatty acids such as acetic acid and propionic acid, as well as hydrogen gas, which can provide carbon and electron donors for organic halogenated respiratory bacteria.

[0049] Chitosan (CS) is a positively charged natural alkaline polysaccharide obtained by deacetylation of chitin. It is rich in amino and hydroxyl groups, has excellent biocompatibility and biodegradability, and can bind to negatively charged polyelectrolytes, making it widely used as a drug carrier.

[0050] Gelatin (GL) is a macromolecular hydrophilic colloid, a product of partial hydrolysis of collagen. It possesses many excellent physical, chemical, and biological properties, making it a superior material for preparing microspheres. Electrostatic crosslinking occurs through the electrostatic attraction between the anionic groups of gelatin and the cationic groups of chitosan. Simultaneously, hydrogen bonds between the hydroxyl or amino groups in chitosan and gelatin further promote crosslinking between molecular chains.

[0051] Emulsification crosslinking is a method that uses drugs and natural polymers as the aqueous phase and emulsifies them with an oil phase containing an emulsifier. Under stirring, the surface tension of the polymer solution itself is used to form spherical droplets, forming a stable water-in-oil emulsion. A chemical crosslinking agent needs to be added to cause amine-aldehyde condensation or alcohol-aldehyde condensation reactions to obtain powdered microspheres.

[0052] Preferably, the mass ratio of chitosan, gelatin and distiller's grains is 1.5:0.5:2; the slow-release material prepared using this mass ratio can achieve good coating of distiller's grains by chitosan and gelatin.

[0053] Preferably, the lees material of the present invention is lees solid particles with a particle size of 1 to 999 micrometers.

[0054] Further preferably, the solid particles of the distiller's grains of the present invention are microspheres with a particle size in the micrometer range. Microspheres refer to a particulate dispersion system formed by dispersing or adsorbing drugs within a polymer matrix. Many carrier materials can be used to prepare microspheres, mainly divided into natural polymer microspheres (such as starch microspheres, albumin microspheres, gelatin microspheres, chitosan microspheres, etc.) and synthetic polymer microspheres (such as polylactic acid microspheres). Their release rate is affected by multiple factors such as microsphere particle size, loading method, and carrier content.

[0055] The method of the present invention includes the following steps:

[0056] S1. The pretreated lees are ball-milled to obtain solid lees particles.

[0057] Preferably, the pretreatment method is to dry and crush the lees, pass them through a 100-mesh sieve, and then ball mill them to obtain micron-sized powder particles. This pretreatment method increases the specific surface area of ​​the material by reducing the particle size of the reactants and destroying their internal structure.

[0058] S2. An aqueous phase solution was prepared using distillers' grains, chitosan, and gelatin, and an oil phase solution was prepared using Span80 and soybean oil.

[0059] Preferably, the aqueous solution is prepared by mixing chitosan, gelatin, and solid particles of distiller's grains in an aqueous acetic acid solution, mixing and stirring at 38°C to 42°C to obtain the aqueous solution.

[0060] Specifically, the solution was sonicated for 10 minutes at 40°C to ensure uniform dispersion, and then magnetically stirred at 600 rpm for 2 hours at 40°C to obtain an aqueous solution.

[0061] Preferably, the volume percentage of acetic acid in the aqueous acetic acid solution is 2%.

[0062] Preferably, the preparation process of the oil phase solution is as follows: Span80 is dispersed in soybean oil and stirred at 38℃~42℃ to obtain the oil phase solution.

[0063] Specifically, an oil phase solution was obtained by magnetic stirring at 600 rpm for 30 minutes at 40°C.

[0064] Preferably, the mass percentage of Span80 in the oil phase solution is 6 wt.%.

[0065] S3. The aqueous solution is added dropwise to the oil phase solution for emulsification to obtain an emulsion solution. Then, a crosslinking agent is added to the emulsion solution for crosslinking to obtain a mixed solution.

[0066] Preferably, the volume ratio of the aqueous phase solution to the oil phase solution is 1:3.5 to 4.5; after emulsification, the solution is stirred at 38°C to 42°C to obtain an emulsion solution.

[0067] Preferably, the crosslinking agent is a glutaraldehyde solution, wherein the volume percentage of glutaraldehyde in the glutaraldehyde solution is 45% to 55%; and the crosslinking temperature is 38°C to 42°C.

[0068] The morphology and sustained-release properties of the material are controlled by introducing glutaraldehyde as a crosslinking agent to carry out an amine-aldehyde condensation reaction. The proportion of chitosan and gelatin and the crosslinking time are used to extend the release period.

[0069] Specifically, an emulsion solution with a volume ratio of 1:4 was formed by magnetic stirring at 600 rpm at 40°C. 2.5 mL of glutaraldehyde (50%) was slowly added to the emulsion solution, and cross-linking was carried out at 40°C while magnetic stirring at 600 rpm. The mixture was then centrifuged at 3500 r / min for 5 min.

[0070] S4. Perform solid-phase cleaning and centrifugation on the mixed solution. After the solid and liquid phases in the mixed solution are separated, obtain the solid phase, and dry it to obtain the distillers' grains-based slow-release material.

[0071] Specifically, the solid phase was repeatedly washed with isopropanol and centrifuged until the supernatant was clear. Finally, the obtained solid was dried at 40°C for 24 hours to obtain the final distillers' grains-based sustained-release microspheres, named CS-GL@DG.

[0072] In one embodiment of the present invention, the preparation steps of the distillers' grains-based sustained-release material are as follows: Figure 1 As shown.

[0073] The distillers' grains-based sustained-release material of the present invention is prepared by the method described above; the material has the advantages of being environmentally friendly, low-cost, and having adjustable morphology and sustained-release performance.

[0074] The distillers grains-based slow-release material of the present invention can be applied in in-situ bioremediation of groundwater to provide carbon and electron donors for functional microorganisms, enhance their activity, and strengthen the in-situ functional microbial remediation effect while achieving economic, environmentally friendly, efficient, stable, and non-polluting results.

[0075] The present invention discloses a method for in-situ bioremediation of groundwater, which utilizes a distillers' grains-based slow-release material to perform in-situ bioremediation of groundwater. This distillers' grains-based slow-release material can effectively treat groundwater containing halogenated organic compounds.

[0076] The present invention will be specifically described below through specific embodiments:

[0077] Example 1: Screening of different carbon source materials

[0078] Leaching experiments can reflect the dissolution state of the selected natural biomass carbon source. Different natural biomass carbon sources have different release cycles and release rates.

[0079] This embodiment screens carbon sources based on the analysis of the release cycle and release rate of the selected biomass carbon sources.

[0080] Specifically, this embodiment conducted leaching tests on three biomass carbon source materials: corn cob, straw, and distiller's grains. The test procedure was as follows: 2g of powdered biomass (corn cob, straw, and distiller's grains) was weighed and added to a serum bottle, and 80mL of deionized water was added to suspend the biomass in the water. The bottle was then sealed and placed in a constant temperature shaking incubator at a shaking rate of 100rpm and a temperature of 25℃. The leaching time gradients for agricultural waste were set to 0, 1, 2, 4, 6, 8, and 10 days, respectively. Samples were taken according to the time gradients, and the TOC content was tested after filtering the samples.

[0081] The fermentation experiment mainly measures the content of volatile organic fatty acids (acetic acid, propionic acid, and butyric acid) produced by the fermentation of different biomass.

[0082] This embodiment conducted fermentation experiments on three biomass carbon source materials: corn cob, straw, and distiller's grains. The experimental procedure was as follows: 2g of powdered biomass (corn cob, straw, and distiller's grains) was weighed and added to a serum bottle, along with 75mL of buffer solution and 5mL of activated sludge for anaerobic culture in the dark (simulating a groundwater environment). Samples were periodically taken from the bottles, filtered, and the volatile organic fatty acid content of the samples was tested.

[0083] The results and analysis of the above experiment are as follows:

[0084] The accumulation of organic carbon and the carbon release rate of three biomass carbon sources—corn cob, straw, and distiller's grains—over a certain period of time are as follows: Figure 2 As shown. According to Figure 2It can be seen that, compared with natural biomass such as straw and corn cobs, distillers' grains have a higher initial TOC content, which is beneficial for meeting the large demand for carbon sources from the microorganisms in the initial dehalogenation process. Corn cobs and straw have low initial TOC content, but the release rate is faster in the later stages, resulting in a larger total accumulated TOC. As a secondary fermentation product, distillers' grains have a low release rate in the later stages and a lower accumulated TOC content, but their cost is relatively lower than that of corn cobs and straw. The final accumulated TOC is not much different from that of corn cobs, and the excessive release of biomass in the later stages may lead to organic pollution.

[0085] The acid production performance of three biomass fermentation methods, namely corn cob, straw, and distiller's grains, is as follows: Figure 3 As shown, butyric acid is butyric acid, propionic acid is propionic acid, and acetic acid is acetic acid. According to... Figure 3 It can be seen that corn cobs produce the highest acid yield and have a longer acid production cycle, but the fatty acid content decreases after day 25, and the initial start-up is slow, resulting in unstable acid production. Straw produces a relatively high acid yield, but its acid production cycle is shorter, starting to decline after 12 days, and the acid yield fluctuates significantly. Compared to common corn cobs and straw, distillers' grains produce a lower initial acid yield, but a longer cycle, with smaller fluctuations and greater stability. Initial fermentation starts quickly and shows a steady upward trend, providing a stable carbon source for the organisms. Furthermore, distillers' grains are widely available and cheaper, offering a potential solution to waste pollution by utilizing them as a biomass carbon source.

[0086] Therefore, based on the experimental results of this embodiment, by selecting distiller's grains as a biomass carbon source and optimizing its bioavailability, in-situ bioremediation can be carried out.

[0087] Example 2: Fermentation Experiment with Distillers' Grains and Different Concentrations of Alkali Treatment

[0088] Alkali treatment can effectively disrupt the bonding structure between lignin, hemicellulose, and cellulose, causing cellulose to swell and become exposed, increasing enzyme accessibility and facilitating biomass hydrolysis and fermentation.

[0089] To explore the optimal pretreatment method for distiller's grains, this example measured the content of volatile organic fatty acids (acetic acid, propionic acid, and butyric acid) produced by the fermentation of distiller's grains and distiller's grains treated with different concentrations of alkali (1% NaOH, 3% NaOH, and 5% NaOH).

[0090] The specific experimental procedure in this embodiment is as follows: 5g of powdered biomass (both untreated and alkali-treated distiller's grains at different concentrations) was weighed and added to a serum bottle, along with 75mL of buffer solution and 5mL of activated sludge for anaerobic incubation in the dark (simulating a groundwater environment). Samples were periodically taken from the bottle, filtered, and the volatile organic fatty acid content of the samples was tested.

[0091] The test results in this embodiment are divided into short-term and long-term. The short-term test results are as follows: Figure 4 As shown, the long-term test results are as follows: Figure 5 As shown.

[0092] according to Figure 4 It can be seen that within 10 days, alkali treatment with 3% NaOH was more conducive to the fermentation of organic matter, resulting in an increase in both the amount and rate of acid production during the initial fermentation of the lees, thus accelerating the fermentation start-up. However, the amount and rate of acid production decreased with alkali treatment with 5% NaOH. This analysis suggests that while higher concentrations of alkali treatment improve the bioavailability of organic matter, they also remove some organic matter, leading to a decrease in the amount and rate of acid production. Therefore, it is impossible to determine whether alkali treatment improves the bioavailability of organic matter in lees within a short fermentation cycle; further analysis of the long-term fermentation acid production performance of lees and different concentrations of alkali treatment is needed.

[0093] according to Figure 5 It can be seen from long-term fermentation experiments that the initial acid production rate of the distiller's grains increased after alkali treatment, and the acid accumulation in the first 20 days was also higher than that of the original distiller's grains. After 20 days, the acid accumulation of the alkali-washed distiller's grains decreased significantly, entering the next stage of fermentation—the methanogenesis stage. In contrast, the acid accumulation of the untreated distiller's grains continued to increase gradually until 50 days. Therefore, alkali washing significantly shortened the fermentation cycle. Analysis shows that although alkali treatment improved the bioavailability of the distiller's grains, it shortened the hydrogen and acid production stages and accelerated the fermentation process. At the same time, alkali washing also dissolved and removed some hemicellulose and organic matter. In addition, alkali washing increased the processing cost. Therefore, the original distiller's grains were ultimately chosen as the biomass carbon source.

[0094] Example 3: Morphological observation of sustained-release materials

[0095] To evaluate the effect of the proportion of chitosan and gelatin on the morphology and structure of the sustained-release material, this embodiment uses an electron microscope to examine the microstructure of the sustained-release material with different mass ratios.

[0096] An appropriate amount of gelatin can provide sufficient cross-linking sites, while excessive gelatin may lead to over-cross-linking, affecting the material's flexibility and mechanical properties. A chitosan to gelatin mass ratio of 1.5:0.5 ensures a moderate cross-linking density. At this ratio, the mixture of chitosan and gelatin can form a more uniform and stable emulsion. The cationic nature of chitosan can reduce the repulsive forces between emulsion droplets, while the film-forming properties of gelatin can form a stable emulsion interface. Therefore, a chitosan to gelatin mass ratio of 1.5:0.5 was chosen for subsequent research.

[0097] In this embodiment, the experimental groups were prepared with chitosan:gelatin:distillers' grains in mass ratios of 1.5:0.5:1, 1.5:0.5:2, 1.5:0.5:3, and 1.5:0.5:4.

[0098] The experimental procedure in this embodiment is as follows: CS-GL@DG prepared according to the above different proportions is placed in deionized water, the suspended CS-GL@DG is placed on a glass slide, and the morphological characteristics are observed under an optical microscope.

[0099] The experimental results of this embodiment are as follows: Figure 6 As shown. According to Figure 6 It can be seen that the morphology and structure of the material changed significantly when the ratio of chitosan, gelatin, and distiller's grains was changed. As the proportion of the carrier material increased, the content of distiller's grains encapsulated within it decreased slightly, and the size of the sustained-release material decreased accordingly. This indicates that this method can synthesize sustained-release materials with different sizes, achieving controlled release of the carbon source. In this material, when the ratio of chitosan, gelatin, and distiller's grains was 1.5:0.5:2, the distiller's grains were encapsulated in microspheres with better uniformity. Therefore, CS-GL@DG with a chitosan, gelatin, and distiller's grains ratio of 1.5:0.5:2 was selected for subsequent release performance studies.

[0100] To evaluate the effect of crosslinking time on the morphology and structure of the sustained-release material, this embodiment uses electron microscopy to examine the microstructure of the sustained-release material with different crosslinking times.

[0101] The CS-GL@DG with a chitosan, gelatin and distiller's grains ratio of 1.5:0.5:2 was selected for research. The experimental groups in this embodiment were crosslinking times of 1, 2, 3 and 4 hours.

[0102] The experimental procedure in this embodiment is as follows: CS-GL@DG with different crosslinking times as described above is placed in deionized water, the suspended CS-GL@DG is placed on a glass slide, and the morphological characteristics are observed under an optical microscope.

[0103] The experimental results of this embodiment are as follows: Figure 7 As shown. According to Figure 7 It can be seen that the morphology of the material changes significantly with changing the crosslinking time. With increasing crosslinking time, the morphology of the sustained-release material becomes more uniform and stable, and the encapsulation efficiency is higher, indicating that this method can synthesize sustained-release materials with different encapsulation efficiencies, achieving controlled release of the carbon source. In this material, when the crosslinking time is 4 hours, the distiller's grains are encapsulated in microspheres with better uniformity; therefore, CS-GL@DG with a crosslinking time of 4 hours was selected for subsequent release performance studies.

[0104] Example 4: Test of the sustained-release performance of the sustained-release material

[0105] To evaluate the acid release behavior of the CS-GL@DG fermentation material prepared in this invention, the sustained-release performance of the sustained-release material was tested in this embodiment.

[0106] The specific preparation method of the sustained-release material in this embodiment is as follows:

[0107] (1) After drying and crushing the lees, pass them through a 100-mesh sieve and ball mill them to obtain micron-sized powder particles. Use the ball-milled lees as a carbon source for encapsulation to prepare sustained-release microspheres.

[0108] (2) Chitosan, gelatin, and distiller's grains were mixed and added to an acetic acid solution. The mixture was sonicated at 40°C for 10 minutes to ensure uniform dispersion. Then, the mixture was magnetically stirred at 600 rpm at 40°C for 2 hours to obtain an aqueous solution. Span80 was dispersed in soybean oil, and the mixture was magnetically stirred at 600 rpm at 40°C for 30 minutes to obtain an oil solution.

[0109] In this embodiment, the mass ratio of chitosan, gelatin, and distiller's grains is 1.5:0.5:2.

[0110] In the aqueous acetic acid solution, the volume ratio of acetic acid is 2%, and the concentration of Span80 in the oil phase solution is 6 wt.%.

[0111] (3) The aqueous solution was added dropwise to the oil phase solution for emulsification. The mixture was magnetically stirred at 600 rpm at 40°C to form a 1:4 volume ratio emulsion. 2.5 mL of glutaraldehyde (50%) was slowly added to the emulsion, and cross-linking was performed at 40°C while simultaneously stirring magnetically at 600 rpm. The mixture was centrifuged at 3500 r / min for 5 min. The solid phase was repeatedly washed with isopropanol and centrifuged until the supernatant was clear. Finally, the obtained solid was dried at 40°C for 24 hours to obtain the final distillers' grains-based sustained-release microspheres CS-GL@DG.

[0112] The sustained-release performance of the obtained CS-GL@DG was tested. The test process was as follows:

[0113] Add 2g of CS-GL@DG to a serum bottle, along with 75mL of buffer solution and 5mL of activated sludge, and incubate anaerobically in the dark (simulating a groundwater environment). Periodically sample from the bottle, filter the samples, and test the volatile organic fatty acid content to identify the types and amounts of fatty acids produced during fermentation and assess the bioavailability of the material. Observe the morphology of the material under an optical microscope at 0, 10, and 30 days.

[0114] The sustained-release performance test of CS-GL@DG is as follows: Figure 8 As shown. According to Figure 8 It can be seen that within 30 days, compared to the original fermentation of distiller's grains, the acid production ( Figure 4In step c), the fermentation acid production rate of CS-GL@DG decreased, while the amount of acid produced steadily increased, with a higher proportion of acetic acid, prolonging the hydrogen and acid production stage. This indicates that the prepared slow-release material can provide a sustainable carbon source for microorganisms, improving the bioremediation effect. Therefore, it can be inferred that changing the proportion of the carrier material can control the morphology and size of the slow-release material, thereby achieving the controlled release of the slow-release carbon source.

[0115] Through experiments in the above embodiments, distiller's grains were selected as the preferred biomass carbon source, and it was verified that distiller's grains treated without alkali treatment were more effective.

[0116] Furthermore, it was verified that using chitosan and gelatin as carrier materials, and synthesizing sustained-release microspheres via emulsification cross-linking, encapsulating distiller's grains within the microsphere structure, can extend the carbon source release cycle. By limiting the mass ratio, the morphology and size of the sustained-release material can be effectively controlled, thereby achieving the controllable release of the sustained-release carbon source.

[0117] Regarding the acid release mechanism of CS-GL@DG fermentation, such as Figure 9 As shown, the fermentation and acid release of CS-GL@DG can be divided into three stages: In the first stage, the macromolecules in the lees on the surface of the slow-release material hydrolyze and ferment to produce acid, releasing nutrients; in the second stage, the slow-release material swells, the material pores become larger, water and fermenting acid-producing bacteria enter the interior, and the lees slowly ferment to produce acid and release nutrients; in the third stage, the intermolecular breaking between gelatin and chitosan disperses the network structure, and rapid fermentation produces acid.

[0118] According to the above mechanism, the sustained-release material begins to swell after 10 days, and after 30 days, some of the material can be observed to rupture due to swelling, resulting in structural damage and the release of a large amount of nutrients.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a distillers' grains-based sustained-release material, characterized in that, The distillers' lees-based sustained-release material was prepared by emulsification and cross-linking using distillers' lees as a carbon source and chitosan and gelatin as carriers.

2. The method for preparing a distillers' grains-based slow-release material according to claim 1, characterized in that, The mass ratio of the chitosan, the gelatin and the distiller's grains is 1.5:0.5:1 to 4.

3. The method for preparing a distillers' grains-based slow-release material according to claim 1 or 2, characterized in that, The lees material is solid lees particles with a particle size of 1 to 999 micrometers.

4. The method for preparing a distillers' grains-based slow-release material according to claim 3, characterized in that, Includes the following steps: S1. The pretreated lees are ball-milled to obtain the lees solid particles; S2. An aqueous solution is prepared using the aforementioned solid particles of distiller's grains, chitosan, and gelatin, and an oil-phase solution is prepared using Span80 and an oil-based solvent. S3. The aqueous solution is added dropwise to the oil phase solution for emulsification to obtain an emulsion solution. A crosslinking agent is then added to the emulsion solution for crosslinking to obtain a mixed solution. S4. Perform solid-phase washing and centrifugation on the mixed solution. After the solid and liquid phases in the mixed solution are separated, obtain the solid phase, and dry it to obtain the distillers grains-based slow-release material.

5. The method for preparing a distillers' grains-based slow-release material according to claim 4, characterized in that, In step S2, the aqueous solution is prepared by mixing the chitosan, gelatin, and distillers' grains in an aqueous acetic acid solution, mixing and stirring at 38°C to 42°C to obtain the aqueous solution.

6. The method for preparing a distillers' grains-based slow-release material according to claim 5, characterized in that, The acetic acid aqueous solution contains 2% acetic acid by volume.

7. The method for preparing a distillers' grains-based slow-release material according to claim 4, characterized in that, In step S2, the preparation process of the oil phase solution is as follows: the span80 is dispersed in the oily solvent and stirred at 38℃~42℃ to obtain the oil phase solution.

8. The method for preparing a distillers' grains-based slow-release material according to claim 7, characterized in that, The oil phase solution contains 6 wt.% of Span80 by mass.

9. The method for preparing a distillers' grains-based slow-release material according to claim 4, characterized in that, In step S2, the oily solvent is soybean oil, liquid paraffin, peanut oil, or an alkane solvent.

10. The method for preparing a distillers' grains-based sustained-release material according to claim 4, characterized in that, In step S3, the volume ratio of the aqueous phase solution to the oil phase solution is 1:3.5 to 4.5; after emulsification, the mixture is stirred at 38°C to 42°C to obtain the emulsion solution.

11. The method for preparing a distillers' grains-based sustained-release material according to claim 4, characterized in that, In step S3, the crosslinking agent is a glutaraldehyde solution, and the volume percentage of glutaraldehyde in the glutaraldehyde solution is 45% to 55%; the crosslinking temperature is 38°C to 42°C.

12. A distillers' grains-based slow-release material, characterized in that, It is prepared by the method described in any one of claims 1 to 11.

13. The application of the distillers grains-based slow-release material as described in claim 12 in the in-situ bioremediation method for groundwater.

14. A method for in-situ bioremediation of groundwater, characterized in that, In-situ bioremediation of groundwater was carried out using the distillers grains-based slow-release material as described in claim 12.

15. A method for in-situ bioremediation of groundwater according to claim 14, characterized in that, The groundwater contains halogenated organic compounds.

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