Kitchen waste fermentation slow-release composite carbon source and preparation method thereof

Abstract

This invention relates to a slow-release composite carbon source for kitchen waste fermentation and its preparation method, belonging to the field of environmental engineering technology. The composite carbon source has a microcapsule structure, comprising, from the inside out, an inner layer, a middle layer, and an outer layer: the inner layer is a modified biochar framework loaded with redox mediators, containing a hierarchical porous biochar framework. The surface of the hierarchical porous biochar framework contains oxygen-containing functional groups, and quinone mediators are loaded on its surface and within its pores; the middle layer is a semi-solid carbon source wetting layer, which is a semi-solid gel buffer layer containing a lignocellulose framework and short-chain volatile fatty acids, prepared by concentrating the anaerobic co-fermentation broth of kitchen waste and agricultural straw; the outer layer is a semi-permeable polymer cross-linked barrier layer, which wraps around the outer surface of the middle layer. This invention can improve the carbon source loading and slow-release stability, realize the synergistic resource utilization of multi-source solid waste such as agricultural straw and kitchen waste, and enhance the denitrification efficiency under antibiotic stress.

Description

Technical Field

[0001] This invention relates to the field of environmental engineering technology, and in particular to a slow-release composite carbon source for kitchen waste fermentation and its preparation method. Background Technology

[0002] Biological denitrification is the core process for nitrate nitrogen removal in urban wastewater treatment and the treatment of livestock and poultry wastewater. Existing wastewater treatment systems generally suffer from a low carbon-to-nitrogen ratio, requiring external carbon sources to ensure the smooth operation of the denitrification process. Traditional liquid carbon sources (sodium acetate, methanol) are prone to leakage, have large supply fluctuations, and cannot provide stable carbon supply, resulting in low overall utilization rates. Meanwhile, livestock and poultry wastewater often contains combined pollution from nitrates and tetracyclines; antibiotics can damage the cell membranes of denitrifying bacteria and inhibit denitrification enzyme activity, easily leading to the failure of the denitrification process.

[0003] Existing slow-release carbon sources are mostly simple passive physical encapsulation structures, which cannot achieve controllable release of carbon sources according to the actual operating status of wastewater biochemical systems, resulting in insufficient carbon release stability. Single kitchen waste fermentation liquid has technical bottlenecks such as easy putrefaction, low carbon source loading rate, and easy leakage. At the same time, in response to the problem of decreased denitrification efficiency under antibiotic stress, existing carbon sources lack effective means of enhanced regulation, making it difficult to achieve simultaneous and efficient removal of nitrates and antibiotics. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the background technology by proposing a slow-release composite carbon source for kitchen waste fermentation that can improve carbon source loading and slow-release stability, realize the synergistic resource utilization of multi-source solid waste such as agricultural straw and kitchen waste, and enhance the denitrification efficiency under antibiotic stress.

[0005] The technical solution of this invention: A slow-release composite carbon source for kitchen waste fermentation, wherein the composite carbon source has a microcapsule structure, comprising, from the inside out, an inner layer, a middle layer, and an outer layer: The inner layer is a modified biochar framework loaded with redox mediators, which includes a hierarchical porous biochar framework. The surface of the hierarchical porous biochar framework contains oxygen-containing functional groups, and its surface and pores are loaded with quinone mediators. The middle layer is a semi-solid carbon source impregnation layer that covers the outer side of the inner layer. The middle layer is a semi-solid gel buffer layer containing a lignocellulose skeleton and short-chain volatile fatty acids. The semi-solid gel buffer layer is made by concentrating the anaerobic co-fermentation liquid of kitchen waste and agricultural straw. The outer layer is a semi-permeable polymer cross-linked barrier layer that wraps around the outer surface of the middle layer. The outer layer is composed of an interpenetrating polymer network formed by cross-linking and curing sodium alginate, polyvinyl alcohol, and chitosan with divalent metal ions.

[0006] Furthermore, the raw materials for preparing the hierarchical porous biochar framework are selected from wheat straw or peanut shells; the quinone mediator is anthraquinone-2,6-disulfonate (AQDS); and the main components of the short-chain volatile fatty acids are acetic acid and propionic acid.

[0007] Furthermore, the chitosan doped in the interpenetrating polymer network is a microbial degradable material, distributed in the semi-permeable polymer cross-linked barrier layer as a biological enzymatic degradation site; the chitosan in the interpenetrating polymer network constitutes a microbial enzymatic degradation site, which can be degraded by enzymes secreted by the sewage biochemical system and the attached biofilm community in the external environment, thus assisting in the controllable release of carbon source.

[0008] Furthermore, the raw material components forming the interpenetrating polymer network of the outer layer, by mass fraction, include: 1%-3% sodium alginate, 2%-5% polyvinyl alcohol, and 0.5%-1% chitosan; the divalent metal ion is Ca. 2+ .

[0009] A method for preparing a slow-release composite carbon source from kitchen waste fermentation includes the following steps: S1. Inner layer preparation: Biochar is prepared by pyrolysis of agricultural waste selected from wheat straw or peanut shells. After activation by acid and alkali treatment, it is immersed in a solution containing quinone mediator for loading and then dried to obtain the inner layer. S2, Middle layer construction: Collect the co-fermentation broth, and after coarse filtration to retain the fine lignocellulose skeleton, concentrate it under reduced pressure to prepare a semi-solid slurry; place the inner layer obtained in step S1 into the semi-solid slurry, impregnate it under vacuum negative pressure, and after the vacuum is released, obtain the carrier core covered with the middle layer. S3. Outer layer coating and curing: Prepare a mixture containing sodium alginate, polyvinyl alcohol and chitosan, and adjust the pH of the mixture to be slightly acidic; disperse the carrier obtained in step S2 in the mixture, and then drop it into a crosslinking bath containing divalent metal ions adjusted to the same slightly acidic pH value, and crosslink and cure at a constant temperature to obtain the slow-release composite carbon source for kitchen waste fermentation.

[0010] Further, in step S1, the concentration of the quinone mediator in the solution is 1-3 mmol / L; the loading is carried out by isothermal oscillation at 25℃-40℃ for 12-24 hours.

[0011] Further, in step S2, the mass ratio of kitchen waste to agricultural straw is 4:1; the solid content of the semi-solid slurry is controlled at 15%; the vacuum negative pressure condition is -0.08MPa to -0.1MPa, and the soaking time is 2-4 hours.

[0012] Further, in step S3, the pH value of the mixture and the pH value of the crosslinking bath containing divalent metal ions are both adjusted and controlled within the range of 4.0-4.5 by acetic acid; the crosslinking bath containing divalent metal ions is a calcium chloride solution with a mass concentration of 2%-4%; the temperature for constant temperature crosslinking and curing is 25°C, and the time is 4-12 hours.

[0013] Compared with the prior art, the present invention has the following beneficial technical effects: 1. This invention constructs a three-layer microcapsule structure of "core-middle layer-shell". The outer layer achieves stable and slow release of carbon source through the physical spatial steric hindrance and pore diffusion restriction of the polymer network. At the same time, the bio-responsive release of carbon source is achieved through the microbial enzymatic degradation characteristics of chitosan. This avoids the problems of rapid loss and large supply fluctuations of traditional liquid carbon sources, greatly extends the carbon release cycle, and improves the comprehensive utilization rate of carbon source.

[0014] 2. The inner layer of this invention accelerates electron transfer based on the redox mediator effect of AQDS, which can effectively improve the extracellular electron transfer efficiency of denitrifying microorganisms and alleviate the inhibitory effect of antibiotics on the activity of denitrifying bacteria; at the same time, the multi-level porous biochar framework can adsorb antibiotics in water, reduce their toxic impact on functional microorganisms, thereby achieving simultaneous and efficient removal of nitrates and antibiotics.

[0015] 3. The middle layer of this invention uses anaerobic co-fermentation liquid of kitchen waste and agricultural straw as the core raw material. The retained lignocellulose skeleton can form a stable gel buffer structure, increase the carbon source loading, and solve the problems of easy leakage, easy spoilage and low loading rate of pure liquid fermentation liquid. At the same time, it realizes the synergistic resource utilization of multi-source solid waste such as agricultural straw and kitchen waste, and reduces the carbon source preparation cost. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a system flowchart of an embodiment of the present invention. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0020] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it an embodiment that is mutually exclusive, either alone or selectively, with other embodiments.

[0021] Preparation of co-fermentation broth After being crushed, kitchen waste was mixed with wheat straw at a mass ratio of 4:1, and the solid content was adjusted to 8%. Anaerobic sludge was then inoculated and anaerobic fermented at a constant temperature of 35℃ for 10 days. During the fermentation process, the pH was maintained at 6.5-7.0 to obtain the coupled fermentation stock solution.

[0022] Example 1 like Figure 1 As shown, the present invention proposes a method for preparing a slow-release composite carbon source for kitchen waste fermentation, comprising the following steps: S1. Inner layer preparation: Wheat straw was washed, crushed, and pyrolyzed at 500℃ for 2 hours under limited oxygen to prepare biochar; it was then activated with 1 mol / L hydrochloric acid and sodium hydroxide in sequence, washed until neutral, and dried; the activated biochar was immersed in a solution containing 2 mmol / L AQDS, and loaded with constant temperature shaking at 30℃ for 18 hours, and then freeze-dried to obtain a modified biochar framework loaded with redox mediator; S2, Middle Layer Construction: The coupled fermentation broth prepared above is coarsely filtered through a 100-mesh sieve to retain the fine lignocellulose skeleton, and concentrated under reduced pressure to a solid content of 15% to prepare a semi-solid slurry; the inner layer prepared in S1 is placed in the semi-solid slurry and impregnated under a vacuum of -0.09MPa for 3 hours. After the vacuum is released, a core with a semi-solid carbon source impregnation layer is obtained. S3. Outer layer coating and curing: Prepare a mixture containing 2% sodium alginate, 3% polyvinyl alcohol and 0.5% chitosan, and precisely adjust the pH to 4.2 with acetic acid; disperse the carrier prepared in S2 in the above mixture, and then drop it into a calcium chloride crosslinking bath with pH=4.2 and a mass concentration of 3%; crosslink and cure at 25°C for 8 hours; filter out, wash and freeze dry to obtain the finished composite carbon source.

[0023] Example 2 The slow-release composite carbon source for kitchen waste fermentation and its preparation method proposed in this embodiment are identical to those in Example 1, except for the following steps: In the preparation of the inner layer of S1, peanut shells were used as raw materials for biochar preparation, and the biochar was pyrolyzed at 400℃ with limited oxygen for 2 hours; the AQDS solution concentration was 1 mmol / L, and the isothermal shaking loading time was 12 hours. In the S3 outer layer coating and curing process, the mixture formula is 1% sodium alginate, 2% polyvinyl alcohol, and 0.5% chitosan. The pH value of both the mixture and the crosslinking bath is controlled at 4.0, the calcium chloride solution mass concentration is 2%, and the crosslinking curing time is 4 hours.

[0024] Example 3 The slow-release composite carbon source for kitchen waste fermentation and its preparation method proposed in this embodiment are identical to those in Example 1, except for the following steps: In the preparation of the inner layer of S1, wheat straw was used as the raw material for biochar preparation, and oxygen-limited pyrolysis was performed at 600℃ for 2 hours; the concentration of AQDS solution was 3 mmol / L, and the isothermal shaking loading time was 24 hours. In the S3 outer layer coating and curing process, the mixture formula is 3% sodium alginate, 5% polyvinyl alcohol, and 1% chitosan. The pH value of both the mixture and the crosslinking bath is controlled at 4.5, the calcium chloride solution mass concentration is 4%, and the crosslinking curing time is 12 hours.

[0025] Comparative Example 1 The carbon source preparation method in this comparative example is the same as that in Example 1, except for the following steps: The inner layer is not loaded with AQDS, and the outer layer mixture does not contain chitosan, but only 2% sodium alginate and 3% polyvinyl alcohol.

[0026] Comparative Example 2 This comparative example uses a traditional liquid sodium acetate carbon source and is compared with the finished product of Example 1 in a parallel control experiment with the same COD equivalent.

[0027] Performance verification test 1. Verification of the simultaneous removal effect of pollutants under antibiotic stress Setting up simulated wastewater influent NO3 - -N=50mg / L, tetracycline (TC)=10mg / L, equal amounts of carbon source materials from Examples 1-3 and Comparative Example 1 were added respectively, and the mixture was run continuously for 7 days. The pollutant removal rate was then tested, and the results are as follows: Comparative Example 1: On day 7, the nitrate removal rate was 17.8%, and the tetracycline removal rate was 22.3%; Example 1: On day 7, the nitrate removal rate was 89.5%, and the tetracycline removal rate was 84.9%. Example 2: On day 7, the nitrate removal rate was 81.2%, and the tetracycline removal rate was 76.5%. Example 3: On day 7, the nitrate removal rate was 87.6%, and the tetracycline removal rate was 85.1%.

[0028] Experimental results show that the composite carbon source prepared in this invention can maintain stable and efficient denitrification and antibiotic degradation effects under high concentrations of tetracycline stress. Compared with Comparative Example 1, which suffered system performance collapse in the later stages of operation due to the lack of electron shuttles and sustained-release mechanisms (denitrification rate of only 17.8% on day 7), Examples 1-3 not only achieved extremely high final removal rates but also showed no significant performance degradation during the 7-day operation period. This is attributed to the effective mitigation of antibiotic toxicity inhibition by the inner AQDS mediator and the long-term stable release of the carbon source brought about by the outer polymer network combined with the chitosan degradation characteristics.

[0029] Furthermore, a comparison of different parameter groups revealed that: in Example 2, due to the thinner cross-linked shell and faster carbon source release, the denitrification rate slightly decreased on day 7 (81.2%); while in Example 3, thanks to the abundant pores resulting from the higher pyrolysis temperature and the high concentration of AQDS loading, the removal rate of tetracycline reached the highest (85.1%). The parameter ratio in Example 1 achieved the optimal balance between slow carbon source release and denitrification / detoxification.

[0030] 2. Assessment of carbon release cycle and carbon source utilization rate In a standard continuous flow denitrification biological treatment tank, equivalent amounts of the finished product from Example 1 and the conventional liquid sodium acetate carbon source from Comparative Example 2 were added respectively to test the effective life cycle and comprehensive utilization rate of the carbon sources. The results are as follows: Comparative Example 2 (Traditional liquid sodium acetate carbon source): The effective carbon release cycle is only 3 days, a large amount of carbon source is lost with the effluent, and the overall carbon source utilization rate is only 36.5%; Example 1: The effective carbon release cycle was extended to 18 days, and the overall carbon source utilization rate reached 92.1%.

[0031] Experimental results show that the present invention, through a three-layer structure design, combined with the diffusion restriction effect of the polymer network and the carbon locking effect of the semi-solid carbon source wetting layer, significantly extends the carbon release cycle of the carbon source and significantly improves the comprehensive utilization rate of the carbon source.

[0032] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A slow-release composite carbon source for kitchen waste fermentation, characterized in that: The composite carbon source has a microcapsule structure, consisting of an inner layer, a middle layer, and an outer layer from the inside out: The inner layer is a modified biochar framework loaded with redox mediators, which includes a hierarchical porous biochar framework. The surface of the hierarchical porous biochar framework contains oxygen-containing functional groups, and its surface and pores are loaded with quinone mediators. The middle layer is a semi-solid carbon source impregnation layer that covers the outer side of the inner layer. The middle layer is a semi-solid gel buffer layer containing a lignocellulose skeleton and short-chain volatile fatty acids. The semi-solid gel buffer layer is made by concentrating the anaerobic co-fermentation liquid of kitchen waste and agricultural straw (hereinafter referred to as co-fermentation liquid). The outer layer is a semi-permeable polymer cross-linked barrier layer that wraps around the outer surface of the middle layer. The outer layer is composed of an interpenetrating polymer network formed by cross-linking and curing sodium alginate, polyvinyl alcohol, and chitosan with divalent metal ions.

2. The slow-release composite carbon source for kitchen waste fermentation according to claim 1, characterized in that, The raw materials for preparing the hierarchical porous biochar framework are selected from wheat straw or peanut shells; The quinone mediator is anthraquinone-2,6-disulfonate (AQDS). The main components of the short-chain volatile fatty acids are acetic acid and propionic acid.

3. The slow-release composite carbon source for kitchen waste fermentation according to claim 2, characterized in that, The chitosan doped in the interpenetrating polymer network is a microbially degradable material, distributed in the semi-permeable polymer cross-linked barrier layer as a bio-enzymatic degradation site.

4. The slow-release composite carbon source for kitchen waste fermentation according to claim 3, characterized in that, The raw material components for forming the interpenetrating polymer network of the outer layer comprise, by mass fraction: 1%-3% of sodium alginate, 2%-5% of polyvinyl alcohol, 0.5%-1% of chitosan; the divalent metal ion is Ca 2+ .

5. A method for preparing a slow-release composite carbon source for kitchen waste fermentation, based on the slow-release composite carbon source for kitchen waste fermentation according to claim 1, characterized in that, The method includes the following steps: S1. Inner layer preparation: Biochar is prepared by pyrolysis of agricultural waste selected from wheat straw or peanut shells. After activation by acid and alkali treatment, it is immersed in a solution containing quinone mediator for loading and then dried to obtain the inner layer. S2, Middle layer construction: Collect the co-fermentation broth, and after coarse filtration to retain the fine lignocellulose skeleton, concentrate it under reduced pressure to prepare a semi-solid slurry; place the inner layer obtained in step S1 into the semi-solid slurry, impregnate it under vacuum negative pressure, and after the vacuum is released, obtain the carrier core covered with the middle layer. S3. Outer layer coating and curing: Prepare a mixture containing sodium alginate, polyvinyl alcohol and chitosan, and adjust the pH of the mixture to be slightly acidic; disperse the carrier obtained in step S2 in the mixture, and then drop it into a crosslinking bath containing divalent metal ions adjusted to the same slightly acidic pH value, and crosslink and cure at a constant temperature to obtain the slow-release composite carbon source for kitchen waste fermentation.

6. The method for preparing a slow-release composite carbon source for kitchen waste fermentation according to claim 5, characterized in that, In step S1, the concentration of quinone mediator in the solution is 1-3 mmol / L; the loading is carried out by isothermal oscillation at 25℃-40℃ for 12-24 hours.

7. The method for preparing a slow-release composite carbon source for kitchen waste fermentation according to claim 6, characterized in that, In step S2, the mass ratio of kitchen waste to agricultural straw is 4:1; the solid content of the semi-solid slurry is controlled at 15%; the vacuum negative pressure condition is -0.08MPa to -0.1MPa, and the soaking time is 2-4 hours.

8. The method for preparing a slow-release composite carbon source for kitchen waste fermentation according to claim 7, characterized in that, In step S3: The pH value of the mixture and the pH value of the crosslinking bath containing divalent metal ions are both adjusted and controlled within the range of 4.0-4.5 by acetic acid; the crosslinking bath containing divalent metal ions is a calcium chloride solution with a mass concentration of 2%-4%; the temperature for constant temperature crosslinking and curing is 25°C, and the time is 4-12 hours.

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